Salt Management Guide forLandscape Irrigation with Recycled Waterin Coastal Southern California
A Comprehensive Literature Review
Kenneth Tanji,1 Stephen Grattan,2 Catherine Grieve,3 Ali Harivandi,4 Larry
Rollins,5 David Shaw,6 Bahman Sheikh,7 and Lin Wu8
1

Professor emeritus in hydrology and water quality aspects of irrigation and drainage,
Department of Land, Air, and Water Resources, University of California–Davis

2

University of California Cooperative Extension specialist in plant-water relations, Departmentof Land, Air, and Water Resources, University of California–Davis3

Research leader/supervisory plant physiologist specializing in salt tolerance of plants, U.S.
Department of Agriculture—Agricultural Research Service, U.S. Salinity Laboratory,
Riverside, California

4

University of California Cooperative Extension environmental horticulture advisor in turfgrass,soils, and water, Alameda County, California

5Technical writer specializing in hydrology and geology, Davis, California

6

University of California Cooperative Extension advisor in landscape, turfgrass, and Christmas
tree industry, San Diego County, California

7

Water reuse specialist, independent consultant, San Francisco, California

8

Professor emeritus in environmental horticulture, salt tolerance of native and landscape plants,
Department of Environmental Horticulture, University of California–Davis
Assisted by
Pat Suyama, editor, Davis, California,
andMichele Tobias, graduate research assistant, University of California–DavisContents
Page
Acknowledgments............................................................................................................... iii
Extended Executive Summary.................................................................................................
..............................................................................................................ES­1
Chapter I.

Introduction ............................................................................................. I­1

Chapter II.

Present Status: Potential Benefits of Irrigating Landscapeswith Recycled Water, Current Use of Recycled Water,
and Regulations........................................................................................II­1

Chapter III.

Water Quality Guidelines for Recycled Water Use
for Landscape Irrigation ..........................................................................III­1

Chapter IV.

Salinity Control in the Root Zone and Deep Percolationof Salts from the Root Zone into Groundwater Basins ............................ IV­1
Appendix. Hydrosalinity Model 1 ........................................................ HM­1
Appendix. Hydrosalinity Model 2 ........................................................ HM­2
Appendix. Hydrosalinity Model 3 ........................................................ HM­3
Appendix. Hydrosalinity Model 4 ........................................................ HM­4

Chapter V.

Tolerance by Landscape Plants ofSalinity and of Specific Ions.....................................................................V­1

Chapter VI.

Selecting Plants for Coastal Southern
California Landscapes ........................................................................... VI­1

Chapter VII.

Irrigation Systems for Recycled Water ................................................. VII­1

Chapter VIII.

Estimating Water Needs and Scheduling Irrigation
for Landscapes .....................................................................................VIII­1

Chapter IX.

Soil­Related Problems............................................................................ IX­1

Chapter X.

Diagnosing and Solving General and Plant­Specific
Problems ..................................................................................................X­1

Appendix.

Acronyms and Abbreviations ...............................................................AA­1

Appendix.

Conversion Factors ............................................................................... CT­1

Appendix.

Glossary ............................................................................................... GL­1

Subject Index.............................................................................................................. SI­1ii

Acknowledgments

The WateReuse Foundation provided substantial funds to support the development of thisreport and the complementing interactive CD on salt management, i.e., the Salinity
Management Guide. Eight other organizations also provided funds: the Bureau of
Reclamation, the California Department of Water Resources, the National Water
Research Institute (NWRI), the Southern California Salinity Coalition, the Central Basin
Municipal Water District, the City of Cerritos, the Los Angeles Department of Water andPower, and the West Basin Municipal Water District. Jeff Mosher of the WateReuse
Foundation served as overall project manager at the beginning. Later, after Jeff assumed
a position at NWRI, Joshua Dickinson became overall project manager. Jennifer Benderof the Central Basin Municipal Water District served as the day-to-day project manager.
Kenneth Tanji of the University of California–Davis is the principal investigator (PI). Dr.
Tanji formed an eight-person project team consisting of six co-PIs and a documentation
specialist to address the project objectives.

A Project Advisory Committee, assembled by the WateReuse Foundation, reviewed thereport’s contents. The members of the advisory committee were Michelle Chapman,
USBR; Victoria Cross, Los Angeles Department of Water and Power; Hoover Ng, Water
Replenishment District of Southern California; Dennis Pittenger, University ofCalifornia–Riverside; and Ken Tate, City of Cerritos. Dr. Tanji was also assisted by apanel of peer reviewers as well. The members of the peer review panel who reviewed one
or more chapters included Takashi Asano, Hossein Ashktorab, Robert Bastian, Sharon
Benes, Harvey Collins, Larry Costello, James Crook, David Hills, Mike Huck, Stephen
Kaffka, Seiichi Miyamoto, Lorance Oki, Robert Perry, Warren Roberts, and Lawrence
Schwankl.

iii

Extended Executive Summary
Salt Management Guide for Recycled Waters
Used for Irrigation of Landscapes in Coastal Southern California

A comprehensive review of the scientific literature has been conducted to consolidate in
one document the factors that affect the use of recycled waters for irrigating landscapes in
California’s south coastal region, where potable water is becoming increasingly scarce. Althoughmany opportunities exist for using recycled waters in urban areas and the California Recycled
Water Task Force encourages such use, some landscape professionals are reluctant to use
recycled water out of concerns that the water may be excessively saline and harmful to landscapeplants.
This document presents a Salinity Management Guide for the irrigation of landscapeswith recycled water, including guidelines on evaluating water quality, controlling salinity in theroot zone, discovering the tolerance of plants to salinity and salinity-related effects, anddiagnosing and solving problems that might be encountered in the irrigation of turfgrasses, trees,
shrubs, and ground covers. It also includes related aspects of landscape irrigation, including
California’s Water Recycling Criteria, selecting plants, choosing and using irrigation systems,
calculating the water needed by the plants, and mitigating problems with the soil.

Title 22 Regulations and Present Use of Recycled Waters for Landscape Irrigation
California’s Water Code states that using a potable source of water when nonpotablewater could be safely used instead is a wasteful or unreasonable use of water. The state’s recycledwater regulations are contained in Title 22, Code of Regulations on Water Recycling Criteria.
These regulations require tertiary treatment and disinfection of recycled waters used to irrigate
parks and playgrounds, school yards, residential landscapes, and golf courses with unrestricted
access. This level of treatment, which is aimed at protecting public and ecological health, exceeds
the level of treatment of most potable water supplies and meets the level of treatment required formost wastewaters discharged to waters of the state. The regulations require that recycled waterused to irrigate cemeteries, freeway landscapes, golf courses with restricted access, ornamental
nurseries, and sod farms receive somewhat less treatment, i.e., secondary treatment anddisinfection levels of 2.2 to 23 median counts of total coliform bacteria per 100 mL of water.

ES-1

Of the current 533,000 acre-ft of recycled waters used in California, about 21% is used toirrigate landscapes, mostly turfgrasses in golf courses and lawns. Opportunities to further use
recycled waters exist; i.e., recycled waters could be used to irrigate golf courses, lawns, trees,
shrubs, ground covers, vines, ornamental plants, and flowers of other landscapes now being
irrigated with potable waters.

Significant Constituents in Water Used to Irrigate
Most recycled waters do not inherently contain excessively high levels of salinity, eventhough they typically contain about 140 to 400 more milligrams of salts per liter than do the
potable waters from which they originated. The salinity of waters may affect plants due toosmotic effects; i.e., plants must expend more energy to extract water from the soil when thatwater is more saline, and plants may suffer slowed growth, damaged leaves, and death in theseverest cases. Plants have a wide range of tolerance of salinity, and many could be irrigated withrecycled waters.
If communities use sodium chloride-based water softeners, the recycled water originatingfrom such communities may contain elevated numbers of sodium and chloride ions. Moreover,use of cleaning agents, such as detergents, may elevate concentrations of boron in recycledwaters. Plants differ in their sensitivity to sodium and chloride ions and boron. Sensitive plants
typically exhibit damaged leaves and, in severer cases, defoliation and death. Excessive levels of
sodium may also cause an imbalance in the mineral nutrition of plants, such as a deficiency of
calcium.
Another significant constituent in recycled waters is nitrogen in the form of dissolved
ammonia or ammonium ions and nitrates. The concentration levels of these forms of nitrogen are
dependent on the wastewater treatment processes used. Ammonia or ammonium ions in recycledwaters are eventually oxidized into nitrate ions in the soil. Other forms of nitrogen, such asorganic nitrogen and nitrite, occur in smaller concentrations. Nitrogen in recycled water used toirrigate can pose problems if the nitrates not taken up by plants leach below their roots andcontribute to the contamination of underlying groundwater basins. Such leaching of nitrates may
be minimized if the amount of nitrogen in recycled water is taken into account in fertilizer
applications and if less nitrogen-containing fertilizer is consequently applied.
The combined effects of salinity and sodicity of irrigation water can affect the soil’s
permeability, reducing water infiltration rates and soil permeability. Sodicity is usually evaluatedby its ratio of sodium to calcium plus magnesium, known as the sodium adsorption ratio (SAR),
and salinity is typically assessed by electrical conductivity (EC). A moderate SAR and a low levelES-2

of EC may result in reduced permeability in some types of soil. The detrimental effects of amoderate SAR on a soil’s permeability may be partially overcome by a moderate level of EC.
The treatment processes for recycled waters involve the use of additives that elevate the SAR,
such as sodium hypochlorite, frequently used to disinfect, and bicarbonate and carbonate from thelime, used to neutralize the water’s pH. Another parameter of sodicity is the residual sodium
carbonate (RSC), which is the sum of bicarbonate and carbonate ions minus the sum of calcium
and magnesium ions. It can be used to evaluate the detrimental effects of sodicity, which cancause the dispersal of organic matter and clays in the soil, resulting in dark unsightly matting on
the turf of golf courses and slower water infiltration into turf soils.
Some communities blend several sources of water for potable purposes, such as imported
water from the Colorado River Aqueduct and the California Aqueduct with local surface and well
waters. These sources contain differing salinities. For example, the Colorado River water contains
about 750 mg of total dissolved solids (TDS)/L, the California Aqueduct water contains about
450 mg of TDS/L, and well water contains as little as 200 mg of TDS/L from granitic watershed
and alluvium. Blending practices tend to change, according to the demand for water and theavailability of source waters. As a result, water salinity and sodicity may change seasonally withchanges in blending. This situation causes the quality of recycled water to fluctuate. Landscapeirrigators need to keep abreast of these changes in water quality, so as to manage irrigation
appropriately. This caution is particularly important when plants in the landscape are sensitive tosalinity and sodicity and when the concentrations of nitrogen are high.

Selecting Plants for Coastal Southern California
Plants vary in their requirement for sunlight, water, and nutrients, as well as in theirsusceptibility to adverse environmental conditions. Although many plants can tolerate a wide
range of conditions, others have distinct preferences for particular climates and soils and do not
thrive elsewhere. The natural distribution of plants is determined by the interaction of manyenvironmental factors, including the intensity and duration of sunlight; the temperature; theproperties of the soil; the availability of plant nutrients; the amount of rainfall; the amount andquality of irrigation water; any wind, floods, or fires; and biotic interactions, such as competingwith other plants for space and sunlight, being consumed by plant-eating animals, and being
exposed to disease-causing microbes.
Plant ecologists have combined environmental and climatological data to delineate plant
environment zones or regions. One can determine from this information the type of plants thatwill thrive in these zones. We have reviewed several comprehensive guides for selecting shrubs,

ES-3

trees, and ground covers, including Perry’s 1981 book, Trees and Shrubs for Dry California
Landscapes, a comprehensive general-purpose guide that lists 360 species of plants, emphasizing
species that survive with limited water. Part I of his book, titled “Regional Plant Environments,”
describes nine plant environments and includes a detailed guide for selecting plants. Part II, titled“Planting Guidelines,” covers appropriate planting concepts within the constraints of function,
aesthetics, costs, resources, and maintenance requirements. Perry also wrote a 1992 book,“Landscape Plants for Western Regions,” which builds on his 1981 book and includes sections on“Issues and Goals,” “Regional Characteristics,” “Estimating Water Needs of Landscapes,” andlastly, “Plant Palettes,” for selecting plants that can be combined to achieve visual and aesthetic
character, along with cultural compatibility.
The Sunset Western Garden Book, which is available in more than four editions, isperhaps the best-known and most widely available guide to selecting plants. As with Perry’s 1992
book, this book includes a system of climatological zones depicted on maps. A major portion of
the book is a plant encyclopedia that describes several thousand species of plants used forlandscapes in the western United States. Labadie’s 1978 book, Native California Plants, which
evolved from his years of teaching at Merritt College in Oakland, CA, covers 101 species ofplants that are native to California. A number of brief lists of plants for particular situations, suchas plants that do well in partial shade and plants that tolerate wind, is appended to the book.
Lenz and Courley’s 1981 book, California Native Trees and Shrubs, also presents a mapillustrated system of climatological zones. Based on the authors’ 50 years of horticulturalexperience at the Rancho Santa Ana Botanic Garden, the book focuses on trees and shrubs forsouthern California. It contains a comprehensive glossary and a cross-index of the common andscientific names of plants. Lenz also published a book in 1956, Native Plants in California, aspart of a series of papers published by the Rancho Santa Ana Botanic Garden. In that book, henames 102 species of native flora suitable for use by landscape professionals.
After Perry and others, we have listed 57 ground covers appropriate for coastal southern
California, identifying them as native or not and the regions where they flourish, i.e., in the
coastal margin, intermediate valleys, coastal foothills, inland valleys, or inland foothills. This
document includes a map of these regions as well as tables identifying well over 300 shrubs andtrees of various heights, including 56 shrubs up to 5 ft tall, 85 shrubs up to 10 ft tall, 96 shrubs
from 10 to 18 ft tall, 60 trees up to 25 ft tall, 49 trees up to 40 ft tall, and 45 trees that are 40 ft ortaller.
Ground covers listed include Little Sur manzanita (Arctostaphylos edmundsii), bearberry(Arctostaphylos uva ursi), coast sagebrush (Artemisia pynocephala), maritime ceanothus

ES-4(Ceanothus maritimus), common buckwheat (Eriogonum fasciculatum), juniper (Juniperus spp.),annual lupine (Lupinus nanus), and creeping sage (Salvia sonomensis). Small shrubs listed
include Monterey manzanita (Arctostaphylos hookeri), hollyleaf ceanothus (Ceanothus
purpureus), golden yarrow (Eriophyllum confertiflorum), tree lupine (Lupinus arboreus),
Mexican sage brush (Salvia leucantha), evergreen currant (Ribes viburnifolium), and purple sage
(Salvia leucophylla). Medium-sized shrubs include star acacia (Acacia verticillata), quail bush
(Artiplex lentiformis), coyote brush (Baccaris pilularis consanguinea), carmel ceanothus(Ceanothus griseus), bush lantana (Lantana camara), Oregon grape (Mahonia aquifolium),
redberry (Rhamnus croceus), rosemary (Rosmarinus officinalis), and cape honeysuckle(Tecomaria capensis). Large shrubs include Catalina ironwood (Lyonothanmus spp.), California
buckeye (Aesculus californica), western redbud (Cercis occidentalis), white escallonia(Escallonia bifida), Italian jasmine (Jasminum humile), cape pittosporum (Pittosporum
viridiflorum), and elderberry (Sambucus spp.). Small trees include common manzanita(Arctostaphylos manzanita), palo verde (Cercidium spp.), crape myrtle (Lagerstroemia indica),
tree mallow (Lavatera assurgentiflora), scrub oak (Quercus dumosa), and Italian buckthorn(Rhamnus alaternus). Medium-sized trees include peppermint tree (Agonis flexuosa), weeping
bottlebrush (Callistemon viminalis), cypress (Cupressus spp.), walnut (Juglans spp.), Chinese
pistache (Pistacia chinensis), live canyon oak (Quercus chysolepis), and holly oak (Quercus ilex).
And large trees include madrone (Arbutus menziesii), coast live oak (Quercus agrifolia), aleppo
pine (Pinus halepensis), Monterey pine (Pinus radiata), blue oak (Quercus douglassii), valleyoak (Quercus lobata), and Leyland cypress (Cupressocyparis leylandii).
Other guides to plants are located on the website of the Rancho Santa Ana Botanic
Garden in Claremont, CA, which includes a “California Classics Plant Palette,” and the websiteof the San Diego Chapter of the California Native Plant Society, which lists “Easy-to-Grow
California Native Plants for San Diego County” and “12 Most Wanted Native Shrubs That
Succeed in a Garden Without Your Really Trying.”
We have listed 12 cool-season turfgrasses and 6 warm-season turfgrasses suitable for
California. Cool-season grasses include Kentucky bluegrass (Poa pratensis), tall fescue (Festuca
arundinacea), weeping alkaligrass (Puccinellia distans), and red fescue (Festuca rubra). Warmseason grasses include seashore paspalum (Paspalum vaginatum), zoysiagrass (Zoysia spp.),kikuyugrass (Pennisetum clandestinum), and St. Augustine grass (Stenotaphrum secundatum).
These turfgrasses provide a landscaping base for athletic fields, golf course, parks, playgrounds,
home lawns, office parks, and cemeteries. Turfgrasses also play an important role in conserving
soil and controlling pollution in places such as flood control basins, greenbelts, freeways, andES-5

street medians. Temperature, moisture, and sunlight are the most important climatic factors
affecting the performance of turfgrass. Warm-season grasses usually lose their greenness and go
dormant in the winter, if the average temperature drops below 50 to 60 oF. Cool-season grasses do
not lose their greenness, unless the average temperature drops below 32 oF for an extended
period. It should be noted that grasses vary in their greenness from bright green Kentucky
bluegrass (Poa pratensis) to apple-green annual ryegrass (Lolium multiflorum) or grayish-green
bermudagrass (Cynodon dactylon).
We have listed 35 California-native plants cited by the Rancho Santa Ana Botanical
Gardens for oak woodland landscapes, 34 California-native plants for riparian woodland
landscapes, and 40 California-native plants for scrubland landscapes. Native plants associatedwith oak woodland landscapes include the trees California buckeye (Aesculus californica), coast
live oak (Quercus agrifolia), and mesa oak (Quercus engelmannii); the shrubs California
coffeeberry (Rhamnus californica and cultivars), redberry (Rhamnus croceus), toyon(Heteromeles arbutifolia), sunset manzanita (Arctostaphylos “Sunset”), and bush anemone(Carpenteria californica); the ground covers prostrate coyote bush (Baccaris pilularis var.
pilularis), Carmel creeper (Ceanothus griseus var. horizontalis), creeping snowberry(Symphoricarpus mollis), and island alumroot (Heuchera maxima); and the perennials narrowleaf milkweed (Aschlepias fascicularis), coyote mint (Monardella villosa), California buttercup(Ranunculus californica), and meadow rose (Thalictrum fendleri spp. polycarpum). Native plants
associated with riparian woodland landscapes include the trees white alder (Alnus rhombifolia),
western sycamore (Platanus racemosa), Fremont cottonwood (Populus fremontii), California bay(Umbellularia californica), and valley oak (Quercus lobata); the shrubs western redbud (Cercis
occidentalis), creek dogwood (Cornus sericea), mock orange (Philadelphus lewisii), California
rose (Rosa californica), and interior rose (Rosa woodsii var. ultramontana); the ground covers
Edmunds manzanita (Arctostaphylos edmundsii), compact Oregon grape (Mahonia aquifolium“compacta”), creeping barberry (Mahonia repens), and evergreen currant (Ribes viburnifolium);the perennials showy milkweed (Asclepias speciosa), coral bells (Heuchera spp. and cultivars),deer grass (Muhlenbergia rigens), giant chain fern (Woodwardia fimbriata), and Pacific Coast iris
(Iris douglasina and cultivars); and the vine Roger’s Red California grape (Vitis californica“Roger’s Red”). Native plants associated with scrubland landscapes include the tree elderberry(Sambucus mexicana); the shrubs black sage (Salvia mellifera), California buckwheat(Eriogonum fasciculatum), chaparral whitethorn ceanothus (Ceanothus leucodermis), andbigberry manzanita (Arctostaphylos glauca); the ground covers Edmunds manzanita(Arctostaphylos edmundsii), prostrate California buckwheat (Eriogonum fasciculatum cvs.),

ES-6

Matilija poppy (Romneya coulteri), and Haye’s iva (Iva hayesiana); the perennials narrow-leaf
milkweed (Asclepias fascicularis), California fuchsia (Zauschneria spp. and cultivars), Canyon
Prince wild ryegrass (Leymus condensatus “Canyon Prince”), and Wayne Roderick’s daisy(Erigeron “Wayne Roderick”), and the vine Anacapa Pink morning glory (Calystegia
macrostegia “Anacapa Pink”).
From Labadie, we have excerpted 100 native plants recommended for California
landscapes categorized according to the type of plant (ground cover, shrub, or tree) and thedimensions of the plant’s height and spread, as well as notes relating to the environmental
conditions under which they thrive, such as soils of various permeability and other properties; theamount of sun and shade; and tolerance of drought, extremes in temperature, and sprinkler
irrigation with saline water. Recommended drought-tolerant native plants include the trees blueoak (Quercus douglasii), interior live oak (Quercus wislinzeni), and Catalina mountain mahogany(Cercocarpus betuloides var. traskiae); the shrubs chamise (Adenostoma fasciculatum), summer
holly (Comarostaphylis diversiloba), California buckwheat (Eriogonum fasciculatum), andCalifornia holly grape (Mahonia pinnata); and the ground covers Carmel creeper (Ceanothus
griseus var. horizontalis) and dwarf coyote bush (Baccharis pilularis). Native plants that requiredeep, well-drained soils include the trees California buckeye (Aesculus californica), coast
redwood (Sequoia sempervirens), Monterey pine (Pinus radiata), and torrey pine (Pinus
torreyana); the shrubs southern fremontia (Fremontiadendron mexicanum), redberry (Rhamnus
croceus), purple sage (Salvia leucophylla), and rhododendron (Rhododendron macrophyllum),and the ground covers hollyleaf ceanothus (Ceanothus purpureus), island bush snapdragon(Galvensia speciosa), and Santa Barbara ceanothus (Ceanothus impressus). Native plants thatthrive in full sun include the trees western hemlock (Tsuga heterophylla), fern-leaf Catalina
ironwood (Lyonothamnus floribundus), torrey pine (Pinus torreyana), Catalina cherry (Prunus
lyonii), and California black oak (Quercus kelloggii); and the shrubs California holly grape(Mahonia pinnata), Santa Cruz Island buckwheat (Eriogonum arborescens), laurel sumac(Malosma laurina), and Nevin’s barberry (Mahonia nevinii). Native plants that require shade andmoist soils include the trees California bay (Umbellaria californica) and Pacific dogwood(Cornus nuttallii); the shrubs evergreen currant (Ribes viburnifolium), western azalea(Rhododendron occidentale), bush anemone (Carpenteria californica), and ocean spray(Holodiscus discolor); and the ground covers snowberry (Symphoricarpos albus), giant chain fern
(Woodwardia fimbriata), western sword fern (Polystichum munitum), and wild ginger (Asarum
caudatum). Native plants that do best in coastal areas include the trees tanbark oak (Lithocarpus
densiflora), Lawson cypress (Chamaecyparis lawsoniana), Catalina ironwood (Lyonothamnus

ES-7floribundus), and Pacific wax myrtle (Myrica californica); and the shrubs laurel sumac (Malosma
laurina) and salal (Gaultheria shallon). Native plants that tolerate sprinkler irrigation by saline
water include the tree Bishop pine (Pinus muricata) and the ground covers Point Reyes creeper(Ceanothus gloriosus) and Monterey manzanita (Arctostaphylos hookeri).
We have also summarized notes about selecting plants for certain types of landscapes,
including a general landscape design guide, turf and trees for golf courses, turf for playing fields
and parks, and plants for medians and street sides.

Tolerance by Plants of Salinity and Boron
An extensive review of the scientific literature was conducted to prepare a list oflandscape plants appropriate for the south coastal region of California, as well as lists oflandscape plants according to their tolerances of salinity and boron. Many earlier studies on thesalt tolerances of plants were conducted in solution cultures or soil pots that were surface
irrigated, i.e., via the soil. However, much landscape irrigation is conducted via sprinklers, whichwets and exposes leaves to salts in the irrigation water. Fortunately, recent studies regarding thesalt tolerances of plants have involved evaluating the response of plants to salts in both sprinkler
irrigation and irrigation via the soil.
A book by Perry (1981) of California State University–Pomona identifies 36 salt-tolerant
trees and shrubs grown in south coastal California, including 25 rated for their tolerance of salts
when sprinkler irrigated, 19 rated for their tolerance of salts when irrigated via the soil, and 8
rated for their tolerance of both sprinkler irrigation and irrigation via the soil. Salt-tolerant trees
include the beefwood (Casuarinas spp.), desert gum (Eucalyptus rudis), and coral gum(Eucalyptus torquata) varieties of eucalyptus and the torrey (Pinus torreyana), and aleppo (Pinus
halepensis) varieties of pine. Salt-tolerant shrubs include bird of paradise bush (Caesalpina
gilliesii), Italian jasmine (Jasminum humile), sandhill sage (Artemesia pycnocephala),
pittosporum (Pittosporum crassifolium), and Little Sur manzanita (Arctostaphylos edmundsii).
A study at the University of California–Davis by Wu et al. (2001) and Wu and Gao(2005) evaluated the salt tolerances of landscape plants irrigated by sprinklers versus the salt
tolerances of landscape plants when irrigated via the soil. Three waters of varying qualities wereused: a potable well water with an EC of 0.6 decisiemens (dS)/m, water with an EC of 0.9 dS/m
to which 500 mg of sodium chloride/L was added to the well water, and water with an EC of 2.1
dS/m to which 1,500 mg of sodium chloride/L was added to the well water. The well waters towhich sodium chloride was added resembled typical recycled water in the San Francisco Bay
region. Sprinkler-irrigated plants were categorized as highly tolerant, tolerant, moderately

ES-8

tolerant, or sensitive, depending on the degree of symptoms of salt-related stress that developed in
the leaves. Soil-irrigated plants were categorized as highly tolerant, tolerant, moderate, or
sensitive, depending on the level of soil salinity tolerated. Those plants tolerant of saline spray
were found to be equally tolerant of soil salinity, and those plants sensitive to saline spray were
found to be also sensitive to soil salinity.
Wu and his team of researchers tested the salt tolerances of a total of 87 trees, 67 shrubs,
and 59 ground covers and vines with both sprinkler and soil irrigation. Salt-sensitive trees
included red maple (Acer rubrum), Chinese hackberry (Celtis sinensis), cornelian cherry (Cornusmas), ginkgo (Ginkgo biloba), jacaranda (Jacaranda mimosifolia), crape myrtle (Lagerstoemia
indica), southern magnolia (Magnolia grandifolia), Chinese pistache (Pistacia chinensis), laureloak (Quercus laurifolia), and coast redwood (Sequoia sempervirens). Salt-sensitive shrubs
included abelia (Abelia grandiflora), shrimp plant (Justicia brandegeana), camellia (Camelia
japonica), croton (Codiaeum variegatum), poinsettia (Euphorbia pulcherrima), coral plant(Jatropha multifida), California holly grape (Mahonia pinnata), heavenly bamboo (Nandina
domestica), photonia (Photinia fraseri), and roses (Rosa sp.). Salt-sensitive ground covers andvines included carpet bugle (Ajuga repens), lady fern (Athyrium filix-femina), caladium(Caladium sp.), peperomia (Peperomia obtusifolia), verbena (Verbena sp.), coral vine (Antigonon
leptopus), bleeding heart vine (Clerodendrum thomsoniae), and violet trumpet vine (Clytostoma
callistegioides).
We have categorized 17 species of turfgrass as sensitive, moderately sensitive,
moderately tolerant, or tolerant based upon their responses to soil salinity. Sensitive species
include annual bluegrass (Poa annua), colonial bentgrass (Agrostis tenuis), hard fescue (Festuca
langifolia), rough bluegrass (Poa trivialis), and Kentucky bluegrass (Poa pratensis), while
moderately sensitive species include annual ryegrass (Lolium multiflorum), buffalograss (Buchloe
dactyloides) and creeping bentgrass (Agrostis palustris). Moderately tolerant species include
zoysiagrasses (Zoysia spp.), perennial ryegrass (Lolium perenne), and tall fescue (Festuca
arundinacea), and tolerant species include bermudagrass (Cynodon spp.), St. Augustine grass(Stenotaphrum secundatum) and seashore paspalum (Paspalum vaginatum).
We have compiled in this document a list of the salt tolerances of 97 species of flowers
from various sources in the scientific literature, much of it by researchers at the U.S. Salinity
Laboratory, Riverside, CA. Very sensitive species include Peruvian lily (Alsthoemeria hybrids),
anthurium (Anthurium andreanum), rex begonia (Begonia Rex-cultorum), cosmos (Cosmos
bipinnatus), orchid (Cymbidium spp.), poinsettia Barbara Ecke (Euphorbia pulcherrima“Barbara Ecke”), fuchsia (Fuchsia hybrida), amaryllis (Hippeastrum hybridum), and bird of

ES-9paradise (Strelitzia reginae). Sensitive species include begonia (Begonia bunchii), ornamental
cabbage (Brassica oleracea), camellia (Camellia japonica), cyclamen (Cyclamen persicum),poinsettia Redsails (Euphorbia pulcherrima “redsails”), golden marguerite (Euryops pectinatus),
gladiola (Gladiolus spp.), hibiscus (Hibiscus rosa-sinensis), impatiens (Impatiens × hawkeri),geranium (Pelargonium × hortorum), rose (Rosa × hybrida), and pansy (Viola × wittrockiana).
Moderately sensitive species include ageratum (Ageratum houstonianum), snapdragon(Antirrhinum majus), dusty miller (Artemesia stelleran), China aster (Callistephus chinensis),coreopsis (Coreopsis grandiflora), jade plant (Crassula ovata), pinks (Dianthus barbatus),
gerbera daisy (Gerbera jamesonii), globe amaranth (Gompherena globosa), giant turf lilly(Ophiopogon jaburan), azalea (Rhododendron hybrids), lisianthus (Eustoma grandiforum), andzinnia (Zinnia elegans).
We have also compiled a list of 42 ornamental plants according to their tolerances ofboron, after Mass (1984). Extremely sensitive ornamental plants include Oregon grape (Mahonia
aquifolium), photinia (Photinia × fraseri), xylosma (Xylosma congestum), wax-leaf privet(Ligustrum japonicum), Japanese pittosporum (Pittosporum tobira), Chinese holly (Ilex cornuta),
juniper (Juniperus chinensis), and American elm (Ulmus americana). Sensitive ornamental plants
include zinnia (Zinnia elegans), pansy (Viola adorata), violet (Viola tricolor), larkspur(Delphinium spp.), glossy abelia (Abelia × grandiflora), rosemary (Rosmarius officinalis),oriental arborvitae (Platycladus orientalis), and geranium (Pelargonium × hortorum). Moderately
sensitive plants include gladiola (Gladiolus spp.), poinsettia (Euphorbia pulcherrieues), China
aster (Callistephus chinensis), gardenia (Gardenia spp.), southern yew (Podocarpus
macrophyllus), bush cherry (Syzgium paniculatum), and blue dracaena (Cordyline indivisa).
The book Abiotic Disorders of Landscape Plants by Costello et al. (2003) provides useful
guidelines for assessing the salt tolerance of a plant and diagnosing plant-related problems. The
authors list the salinity tolerances and boron tolerances of 610 landscape plants in several tables
for shrubs, trees, palms, ground covers, vines, herbaceous plants, and turfgrasses. This list is
useful for comparing species and for discovering the salt or boron tolerance of a particular species
already chosen for or planted in a landscape.
Other useful tables in Costello et al. (2003) provide information on common fertilizers
and their relative salinities, such as the salt content of commercially available organic soil
amendments including animal manures, peat, and redwood compost. Yet another table in thebook provides guidance for readers who need to interpret chemical data resulting from laboratory
tests of soil, water, and plant tissue.

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Clearly, some landscape plants are sensitive to salinity and boron. However, there exists awide array of trees, shrubs, turfgrasses, ground covers, vines, flowers, and ornamental plants that
could be irrigated with recycled waters containing moderate salinities and moderateconcentrations of sodium, chloride, and boron. Many are listed in this document.

Water Quality Guidelines
The quality of recycled waters may have measurable or observable effects, some ofwhich are adverse, on plants, soils, and irrigation systems.
The assessment and management of irrigation are much more established for agricultural
irrigation than for landscape irrigation, except for the irrigation of turf. Thus, a significant portionof this literature review explored the applicability of the management of agricultural irrigation to
the management of landscape irrigation in terms of evaluating water quality, diagnosing
problems, and implementing management practices. The primary difference between the two isthat the management of agricultural irrigation is aimed at maximizing yield, whereas the
management of landscape irrigation is focused on maintaining the aesthetic quality andappearance of the landscape.
We recommend the Water Quality Guidelines advanced by the United Nations’ Food andAgriculture Organization (FAO) (Ayers and Westcot, 1985). These guidelines for using recycledwater to irrigate croplands and landscapes are used worldwide. A Committee of Consultants fromthe Agricultural Experiment Station of University of California initially proposed these guidelines
after extensive consultation with the U.S. Salinity Laboratory. The FAO then adopted andextended the guidelines.
The FAO guidelines consist of a matrix in which specific irrigation-related problems arealigned vertically and degrees of restriction on use are aligned horizontally. The problems include
salinity, infiltration or soil permeability, specific ion toxicity, and miscellaneous effects. Eachproblem is then associated with particular constituents of water quality, such as salinity by the EC
and the TDS; infiltration by the SAR and the EC; specific ion toxicity by the concentrations ofsoluble sodium, chloride, and boron; and miscellaneous effects by nitrogen in the form ofammonia and nitrate, bicarbonate, and the pH. The degrees of restriction on use are categorized
into none, slight to moderate, and severe, with numeric values or ranges of numeric values foreach parameter identified in cited problems. Though these three categories are somewhat
arbitrary since there are no clear-cut specific boundaries to distinguish the categories and since

ES-11changes occur gradually, the numeric guidelines were based on the collective opinions of soil,
plant, and water scientists with extensive research and practical experience.
When one uses the FAO’s water quality guidelines, there are a number of caveats andassumptions regarding yield potential, conditions at the site, methods and timing of irrigation, andthe uptake of water by crops. The guidelines cover a wide range of conditions encountered inirrigated agriculture and should be used as an initial evaluation and modified with local expertiseas needed. In particular, the guidelines are not plant specific and may be too restrictive for somesalt-tolerant species of plants and perhaps not restrictive enough for some sensitive species.
These guidelines were applied to four representative compositions of recycled waters in
California. These waters had levels of EC ranging from 1.0 to 1.6 dS/m, SAR ranging from 3.4 to
4.9, <0 to 1.7 meq of RSC/L, 157 to 185 mg of sodium/L, 188 to 226 mg of chloride/L, 0.4 to 0.6
mg of boron/L, 0.2 to 31.3 mg of ammonium/L expressed as nitrogen, and 0.8 to 13.9 mg ofnitrate/L expressed as nitrogen. All of these waters tended to rank in the “slight to moderate
restriction on use” categories, with some exceptions. These exceptions were that three waters fellin the “no restriction on use” category with regard to RSC and boron hazards and that one of themfell in the “severe restriction on use” category due to its elevated concentrations of nitrogen and
an RSC value of moderate concern.
Certain management practices can help decrease the moderate to severe restrictions onuse. One such practice is to take into account the nitrogen in recycled water and reduce theamount of nitrogen-containing fertilizer applied. Another is to inject an acid or add a calciumcontaining amendment to water with a high RSC to prevent organic matter and clays in the soil
from dispersing and water from poorly infiltrating. Yet another practice is to replace sensitiveplants that may be detrimentally affected by salinity or concentrations of specific ions with moretolerant plants. It is our considered opinion that the FAO water quality guidelines tend to be on
the conservative side. This view was confirmed by a case study of irrigation of turfgrasses withrecycled waters.

Salinity Control in the Root Zone
The soil is the medium from which plants extract water and essential mineral nutrients. It
also supports the roots of plants. Salts tend to accumulate in the root zone of actively transpiring
plants, as water is lost to the atmosphere through transpiration from plants and evaporation fromthe soil, leaving behind the dissolved mineral salts in the soil water. These dissolved mineral salts
have an osmotic effect: as salts increase in the soil, plants must expend greater energy to draw
water from the soil. Also, some ions of these salts, such as sodium and chloride, as well as boron,

ES-12

may accumulate to concentrations in the soil that are high enough to harm plants. Maintaining asalt balance in the root zone is critical for satisfactory plant performance in a semiarid climate
with insufficient rainfall for leaching salts from the root zone. In surface-irrigated soils with
unimpeded drainage, salts leach from the upper root zone and accumulate in the lower root zone.
Fortunately, most landscape plants are more densely rooted at and near the surface of thesoil, where the soil tends to be least saline. Plants extract soil water from the more saline deeper
root zone only when the soil water that is available in the less saline portions at and near thesurface becomes limited. The extent to which salts accumulate in the lower root zone is regulatedby the leaching fraction (LF), the ratio of the depth of drainage water to the depth of irrigationwater. The depth of drainage water is the irrigation water minus the water lost to the atmospherefrom transpiration by plants and evaporation from the soil. In freely draining soils, acomparatively small depth of drainage may be sufficient to maintain a salt balance in the rootzone. An LF of 0.15 to 0.2 is usually adequate to maintain a salt balance for most agricultural
crops irrigated with typically saline water. This LF also should be applicable to landscape plants
with a similar range of salt tolerances.
Using the FAO approach of computing the accumulation of salts in quartile root zones,i.e., four increments of depth, the principles and applications of steady-state LF were addressedby considering the pattern in which roots extract water, as well as the irrigation water’s LF and
EC. The EC of the drainage water past the root zone may be estimated from the ratio of the EC of
the irrigation water to the LF. Computations can be facilitated with an Excel model that is basedon the assumption that salts are a conservative parameter; i.e., salts are not chemically reactive,
such as in mineral precipitation, mineral dissolution, and cation exchange. This model is in an
appendix. Also considered were the impact of rainfall on the leaching of salts, any mixed
qualities of supply waters, and reclamation leaching with use of a mixing cell Excel model that
includes the initial salinity of the soil. This model is also in an appendix.
More complex aspects of root zone salinity were addressed, including a chemical
equilibrium model (WATSUIT) and its use in assessing the accumulation of salts in quartile rootzones. WATSUIT was also used to assess the precipitation of calcite and gypsum as a function of
the LF for Colorado River water. Based on these data, a simplified reactive salt accumulation
model was developed that incorporated prescribed increments of soil depth (typically more thanfour) and their initial concentrations of soil salinity into the mixing cell model. This Excel modelis also in an appendix.
Shaw et al. (1995) conducted a case study on the composition of drainage from the rootzone from plots of turfgrass irrigated with potable and recycled waters. These plots were locatedES-13

at the Whispering Palms site on the sandy soils of the San Dieguito River’s flood plains in San
Diego County. Turfgrasses involved in this experiment included cool-season grasses, namely, tallfescue (Festuca arundinacea) and a Kentucky bluegrass (Poa pratensis)-perennial ryegrass(Lolium perenne) mixture, and warm-season grasses, namely, bermudagrass (Cynodon dactylon)
and kikuyugrass (Pennisetum clandestinum). Irrigation was scheduled according to the water
budget method and with the use of real-time data about local weather. Water infiltrated into thesoil from irrigation and rainfall is lost to the atmosphere via transpiration by plants andevaporation from the soil, which is collectively referred to as evapotranspiration (ET). In the
study conducted by Shaw et al., the ET of the grasses in inches per day approximately equaled 0.6
× the reference ET (ETo) for warm-season grasses and 0.8 × ETo for cool-season grasses. Rainfall
from January 1993 through November 1994 was 25.1 in. The cool-season grasses received 105
in. of irrigation, while the warm-season grasses received 84 in. of irrigation. The calculated ET
for cool-season grasses was 74.5 in. and for warm-season grasses was 54.1 in. Irrigation waterplus rainfall minus ET equaled the drainage out of the root zone, which averaged 56 in. for coolseason grasses and 54 in. for warm-season grasses. The LF for cool-season grasses was 0.42. The
LF for warm-season grasses was 0.50.
The potable water in the case study had an EC of 1 dS/m, a SAR of 2.7, 0.15 mg/L ofboron, 0.2 mg/L of nitrate expressed as nitrogen, and 0.07 mg/L of ammonium expressed as
nitrogen. The recycled water in the case study had an EC of 1.4 dS/m, a SAR of 4.8, 0.5 mg ofboron/L, 11.2 mg of nitrate/L expressed as nitrogen, and 0.2 mg of ammonium/L expressed as
nitrogen. Shaw and his colleagues analyzed samples of soil from the root zone, i.e., 0–24 in.
below the surface, and samples of soil from below the root zone, i.e., 24–36 in. below the surface.
The EC of the extract from a saturated soil paste (ECe) of root-zone samples ranged from 2.7 to
3.3 dS/m, and the ECe of samples from below the root zone ranged from 1.7 to 2.5 dS/m. The ECe
was only two to three times greater than the EC of irrigation waters because of comparatively
high LFs. The plots of turfgrass all received 544 lbs. per acre of nitrogen-containing fertilizer.
The nitrogen in the recycled water used to irrigate was equivalent to 225 lbs. per acre. However,
nitrate concentrations in the root zone for all treatments were low, ranging from 0.4 to 3.2 mg/L
expressed as nitrogen, indicating that the grasses extracted much nitrogen. Turfgrasses are known
to be heavy feeders of nitrogen and are often described as luxury consumers of nitrogen.
Based on the aforementioned data, the mass loading and emission of nitrogen and TDS
were estimated. The plots irrigated with potable water had a mass loading of 548 lbs. of nitrogen
per acre. The recycled-water treatments had a mass loading of 769 lbs. of nitrogen per acre. The
mass emission of nitrogen from bermudagrass irrigated with potable water was 47 lbs. per acre

ES-14

and from kikuyugrass irrigated with potable water was 59 lbs. per acre. The mass emission rate of
TDS from bermudagrass irrigated with recycled water was 84 lbs. per acre and from kikuyugrass
irrigated with recycled water was 59 lbs. per acre. These rates of mass emission amounted to theleaching of 8 to 13% of the nitrogen from water and fertilizers. The plots irrigated with potablewater had an average mass TDS loading of 5.7 tons per acre, while the plots irrigated withrecycled water averaged 9.2 tons per acre. The mass emission rate of TDS from bermudagrass
irrigated with potable water was 8.8 tons per acre (or 150% drained) and for kikuyugrass irrigatedwith potable water was 7.3 tons per acre (or 125% drained). The mass emission rate of TDS frombermudagrass irrigated with recycled water was 7.2 tons per acre (or 77% drained) and fromkikuyugrass irrigated with recycled water was 8.8 tons per acre (or 94% drained). The percentage
of salts that drained ranged from 77 to 125%. This range is acceptable, considering that several
sinks and sources of salts within the root zone were not considered in this mass balance, with only
mass inputs and mass outputs calculated. Though the 150% salt leaching appears to beunacceptable, it should be noted that the initial ECe of the soil for bermudagrass irrigated withpotable water was 1.7 dS/m, which is higher than the initial ECe of all the others, which ranged
from 1.1 to 1.2 dS/m.
This case study demonstrated that recycled water can be beneficially used to irrigate
established turfgrasses, thus conserving potable waters. Relatively few problems were noted.
Shaw et al. (1995) had initial concerns about the EC, the SAR, the nitrate, and the boron in therecycled water, but they caused no significant problems. However, Shaw et al. (1995) state thatthe reliability of the recycled water’s quality is a key. Any significant changes in quality should
be noted and appropriate management practices taken to avoid problems.
In contrast to the situation with established turfgrasses, there can be some concerns whenusing recycled water to establish new turf stands by vegetative parts or seed. Depending upon soil
and water salinity levels, newly seeded turf may demonstrate reduced germination percentages,
poor seedling vigor, and an overall lower establishment and maturation rate. Cool-season
varieties overseeded into established warm-season turf show similar problems that are generally
associated with higher total salinity and sodium concentrations of the recycled waters. Sod,springs, and stolons can also be affected, showing slower root development and stacking of roots
into the soil. Higher seeding, springing, and stolonizing rates and planning for a longer
establishment must be considered when using waters of moderate salinities for irrigation of
turfgrasses. Another, more effective approach is to irrigate with nonsaline water until turfgrassstand is well established.

ES-15

Irrigation Systems and Water Requirements of Landscape Plants
An irrigation system’s major function is to provide water to plants in a manner suitablefor fostering their growth and performance in the landscape. The system should be able to meetthe landscape’s peak demands for water, apply enough water to leach salts through thelandscape’s root zone, and perhaps be useful in meeting other needs, such as the control of frost.
The system should be appropriately and effectively designed, installed, built, operated, andmaintained. The major components for successful irrigation include design, installation andconstruction, operation, and maintenance. A well-designed system contains appropriate irrigationand drainage components for the plants, includes specific construction details and maintenancerequirements, meets regulatory guidelines, and includes a water budget and an irrigation schedule
to establish the landscape, as well as sustain it.
The components of an irrigation system typically include the following: a pump whenneeded; a main line and laterals; a flow meter; flow control and pressure-regulating valves; filters
when needed; parts that apply the water, such as sprinkler heads, bubblers, drip emitters, or drip
tapes; and a timer to regulate the time and duration of irrigation. The parts of a system that
distribute and apply recycled water—the pipelines, pumps, valves, sprinkler heads, bubblers,
etc.—are all colored purple to clearly distinguish them from parts of systems that distribute andapply potable water. If secondary effluent is used or recycled water that was held in storage ponds
before application is used, then a filtration system is needed. If acids or other amendments are
injected into the irrigation system, the system’s components must be selected or modified totolerate these amendments.
Sprinkler irrigation is the most common method of irrigating with recycled water. The
sprinkler heads may consist of a spray head that delivers water in all directions simultaneously or
may consist of a rotating or impact stream head that directs water over a wider radius than sprayheads do. The sprinkler heads may be those that pop up when operating, or they may be attached
to a riser. Drip irrigation may be placed on a surface, as with a surface drip system, or be placed
below the surface, as with a buried or subsurface drip system.
When one is irrigating landscapes, the differing water needs of the mix of plants in thespecific landscape must be kept in mind. For example, in a landscape consisting of both trees andturf, the trees may need to be irrigated separately with bubblers and drip irrigation because theirwater requirements differ from those of turfgrasses.
The installation and construction phase of an irrigation system includes not only
installing the system but coordinating other activities, such as grading the land, preparing the soil,
selecting plants, and installing lighting and signage. Operating the irrigation system consists of

ES-16

determining the landscape’s water budget and scheduling its irrigation. Maintenance is essential
for an efficiently operating system. Proper cultural treatment of plants and other components of
the landscape not only improves the landscape’s appearance and value but can also affect the useof water in the landscape.
The ET of crop plants has been widely investigated and known, but such is not the casewith the ET of landscape plants, except for that of turfgrasses. In agriculture, the ET of crops(ETc) is estimated by a number of methods. Weather-based estimates of ET are obtained bymultiplying the reference ET (ETo) by the crop coefficient (Kc). The monthly Kc for cool-season
and warm-season turfgrasses in California is available in this document. The Kc for establishedtrees and shrubs is also available in this document. The daily ET may be estimated and compiled
as weekly, monthly, or seasonal ET by using data from the California Irrigation Management
Information System (CIMIS), a network of over 120 stations strategically placed throughout thestate providing hourly and daily ETo that is electronically based on the amount of sunlight, thetemperature, the relative humidity, wind speed, etc. A few water agencies have installed their own
weather stations. Some irrigators may use historic ETo values instead of real-time data.
Estimating coefficients for other types of plants for landscapes, especially heterogeneous
mix of plants, is more difficult than for turfgrasses. Research-based data regarding the water
needed by plants in landscapes with a mix of plants are limited. Plant species with differing needs
for water exist, and those needs are influenced by their location in the landscape and theirinteraction with the surrounding environment. This complexity severely limits the ability toaccurately estimate water needs using the ETo-Kc approach. Despite these limitations, several
approaches for estimating water needed by a landscape have been proposed.
One popular method, the Water Use Classification of Landscape Species (WUCOLS)(University of California Cooperative Extension and California Department of Water Resources,
2000), introduces a landscape coefficient (KL) adjusted to take into account for differences inlandscape species (Ks), plant density (Kd), and microclimate (Kms). Though this method takes into
account factors that affect the KL, quantitative data are not readily available, and thus ETo × KL
produces a rough initial estimate of ET that will need to be adjusted after the initial estimates are
obtained. Procedural guidelines to assign numerical values for Ks, Kd, and Kms for high,moderate, low, and very low values for landscape coefficient factors are outlined in WUCOLS
III. Since California’s climate varies substantially, hundreds of plant species are evaluated for six
regions (climatic zones). It is expected that, after extensive application and testing, the WUCOLS
approach will become more reliable.

ES-17

With many recycled waters, irrigating beyond what is needed for ET is typically required
for leaching salts. The irrigation system’s uniformity of application is another important factor for
adding water beyond what is needed for ET. The irrigation system’s uniformity of distribution
should be considered in the total water applied, too. It should be noted, though, that runoff fromareas irrigated with recycled water is prohibited.
Uniform distribution of applied water is extremely important for root zone salinity
management in golf and sports turf. Achieving a uniform application will maintain a uniform
wetting front when one is leaching salts through the soil profile and prevents the development ofexcessively wet or dry area associated with poor root distribution. In golf or sports turf situations,this precaution not only impacts aesthetics but also safety implications (e.g., firm footing) andcustomer satisfaction by providing a dry playing surface.
Scheduling irrigation involves calculating when and how much to irrigate. When toirrigate is determined by one of several methods, including the flexible or soil water depletion
method, the fixed calendar method, or the soil moisture sensor method. How much to irrigate isdetermined by estimates of the plant’s ET, the irrigation system’s rate of application, and thesystem’s uniformity of distribution. A number of water calculators are available to schedule
irrigation, including some from local water districts and other local agencies. A properly designed
and well-managed irrigation system will provide optimal amounts of water to landscape plants,
except perhaps when a mixture of species needs to be irrigated.

Soil Problems and Management Options
As previously discussed, the quality of recycled water may affect plants and soils.
Specifically, salinity of water and specific ions in water may affect plants and the soil’s
permeability. There are other aspects of particular note when irrigating a landscape with recycledwater.
One such aspect is the salinity of the soil, denoted by the EC of an extract of saturated
soil paste (ECe) that may affect the growth of plants, and the sodicity of the soil, indicated by theexchangeable sodium percentage (ESP) or SAR. Soils are considered nonsaline if the ECe is lessthan 4 dS/m, the ESP is less than 15%, and the pHs (pH of the saturated soil paste) is less than
8.5. Saline soils have an ECe of more than 4 dS/m, an ESP of less than 15%, and pHs of less than
8.5. Sodic soils have an ECe of less than 4 dS/m, an ESP of greater than 15%, and pHs of morethan 8.5. Saline-sodic soils have an ECe of more than 4 dS/m, an ESP of more than 15%, and pHsof less than 8.5.

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Measuring the salinity of water in terms of the EC or TDS is quite straightforward, but
measuring the salinity of soil is more challenging due to its dynamic nature. The salinity of soilchanges over time, with irrigation and rainfall replenishing water in the soil and evaporation andtranspiration depleting it. Moreover, dissolved mineral salts are highly mobile in the soil due totheir transport by the flow of water. Thus, the roots of plants are exposed to temporal and spatialchanges in soil salinity. Such changes pose a challenge in measuring soil salinity. Methods formeasuring soil salinity include sampling the soil and analyzing the ECe in a laboratory; measuring
the salinity of soil water in terms of its electrical conductivity, i.e., the ECsw, with the use ofdevices such as an EM-38 electromagnetic probe or a time domain reflectrometry (TDR) probe;
and using ceramic suction probes to collect soil water from moist soils and then measuring the EC
as ECsw.
As pointed out earlier, soil salinity may be controlled by the LF. When the plant’s
threshold salt tolerance is known, the average salinity of the root zone may be regulated with theleaching requirement (LR), which includes enough water to meet the plant’s ET and to leach salts
yet remain within the plant’s threshold salt tolerance. As previously discussed with well-drained
sprinkler-irrigated soils, the root zone at the surface is where salts are leached and the lower rootzone is where salts accumulate. Fortunately, most plants have the densest roots in the upper rootzone nearest the surface, where it is least saline, and the sparsest roots in the lower root zone,
where it is most saline. Drip irrigation results in a different pattern of salt distribution. The wetted
zone of drip-irrigated soils is somewhat ellipsoidal in shape, with salts tending to accumulate in
the outer edges of the wetted perimeter. After prolonged drip irrigation, salts may accumulate
between drip emitters to levels that are detrimental to plants and may need to be leached with theuse of sprinkler irrigation. Heavy rainfall on salinized drip-irrigated soils will redistribute the salts
vertically and horizontally, affecting salt-sensitive plants. To prevent such redistribution of salts
by reducing the lateral flow of salts, operation of drip irrigation is recommended during rainfall.
A high ESP and SAR in the soil will adversely affect the structure of the soil, especiallyat the surface, causing aggregates of soil to break down and clays and organic matter in the soil todisperse. This process, in turn, reduces the rate at which water infiltrates the soil. Excess ESP iscommonly ameliorated by adding calcium amendments, such as gypsum (CaSO4·2H2O), to thesoil or into the irrigation water. As acids react with soil calcite (CaCO3) to produce soluble
calcium, sometimes acids, such as sulfuric acid, and acid-forming amendments, such as elemental
sulfur, are used to reduce ESP. Slow water infiltration may also be caused by surface crusting insome soils, which results from the beating action of raindrops and the spray of water fromES-19

sprinklers, or from the compaction of soil from vehicular and foot traffic, especially in a clayey,
moist soil.
Maintaining adequate plant nutrition is important to keep plants healthy and attractive.
Plants need 17 essential mineral nutrients. Three of these—carbon, hydrogen, and oxygen—are
readily available from the atmosphere and water. Another three—nitrogen, potassium, andphosphorus—are known as primary nutrients because plants need them in large amounts. Three
more—calcium, magnesium, and sulfur—are secondary nutrients and required by plants in lesser
amounts. The remaining eight elements are required in trace amounts and are known as
micronutrients. They are zinc, iron, manganese, copper, boron, molybdenum, chlorine, andnickel.
When these nutrients become less available to plants, visible symptoms of deficiency areoften noted. Symptoms include discolored leaves, spotted leaves, dead leaf margins, and injured
buds. It should be noted that some symptoms of deficiency may look like symptoms of anotherdeficiency. For example, symptoms of a deficiency of manganese closely resemble symptoms ofa deficiency of iron or symptoms of damage from the pre-emergence application of herbicides.
The location of symptoms on the plant can be very useful in diagnosing deficiencies. For
example, symptoms of deficiencies of the three most commonly limited nutrients—nitrogen,phosphorus, and potassium—become noticeable on older leaves first, while symptoms of
deficiencies of sulfur, iron, and zinc first become apparent on newly emerging leaves andsymptoms of deficiencies of boron and calcium manifest early on as dead buds or the dieback ofgrowing tips.
Landscapes contain a wide range of plant species, and therefore, it is not surprising thatmineral nutrient requirements can vary widely as well. For instance, turfgrasses require a large
amount of nitrogen, while many species of flowers require higher proportions of phosphorus andpotassium. Inorganic and organic fertilizers can be added to nutrient-deficient soils.
The grading of land in landscapes may result in the loss of topsoils, if topsoils are
removed with cut portions, leaving behind infertile soil, or if infertile soils are used as fill soils,e.g., if infertile fill soil from a construction site is used to convert a landfill to a golf course.
These infertile-soil landscapes established on sandy and gravelly soils, as in river floodplains or
stream channels, typically require more fertilization.

Diagnosing and Solving Problems
The last chapter of this document covers the diagnosis of problems and suggested
management solutions. The chapter focuses on salinity-related problems encountered in

ES-20

landscapes, but since such problems should not be viewed in complete isolation, it also includes
other landscape problems. A problem encountered in landscapes may have multiple abiotic andbiotic causes; thus, accurately diagnosing and appropriately solving a problem may bechallenging. Sources of abiotic stress that may cause or contribute to the injury or disease of aplant include salinity, deficiencies and excesses of minerals, extremes of moisture andtemperature, wind, air pollutants, and drift of herbicide. Sources of biotic stress that may cause orcontribute to the injury or disease of a plant include insects, mammals and birds, bacteria, fungi,
nematodes, and viruses. These problems need to be addressed in a timely and comprehensive
manner to avoid high maintenance costs and sustain the quality of landscapes. This last chapter,
drawing upon information from previous chapters, summarizes irrigation and drainage problems
and the abiotic factors that cause problems for plants.
We consider such problems related to irrigation and drainage as plants suffering fromwater stress, which could be caused by insufficient irrigation and may be solved by increasing theduration and/or rate of irrigation enough to satisfy the plant’s ET; the presence of dry or wet
areas, which could be caused by poor uniformity of irrigation and may be solved by changing
the spacing of lateral lines and sprinkler heads or nozzles to improve the uniformity of irrigation;
excessive ponding, which could be caused by water with a high SAR and a low EC and may besolved by adding gypsum to the soil; waterlogging, which could be caused by compacted soil andmay be solved by reducing foot and machinery traffic; and runoff, which could be caused by theslow infiltration of water through the soil and may be solved by decreasing the rate and/or
duration of irrigation.
We also consider such problems involving turfgrasses and lawns as localized dry and wet
spots, which could be caused by compacted soil at the surface and may be solved by core-aerating
the soil; spotty bare spots with salt crust, which could be caused by an excessively saline soil andmay be solved by conducting localized leaching to remove salts; bare spots with dispersed
organic matter, which could be caused by an excess of RSC in the water and may be solved byinjecting acids into the source water; uniform abnormal yellowing of leaves, which could becaused by a deficiency of nitrogen and may be solved by applying nitrogen-containing fertilizers
and improving drainage; unusual yellowing of younger leaves, which could be caused by a
deficiency of iron and may be solved by applying iron chelate or other iron-containing fertilizers;
the dark green discoloration of older leaves, which could be caused by a deficiency of phosphorus
and may be solved by applying appropriately broadcasted phosphorus-containing fertilizers; andleaf rolling, which could be caused by a deficiency of potassium and may be solved by

ES-21

broadcasting potassium-containing fertilizer and incorporating it into the ground as much as
possible.
We furthermore consider such problems involving trees and shrubs as atypicallyyellowed and prematurely dropping leaves, which could be caused by excessive irrigation and/or
poor drainage and may be solved by decreasing irrigation and improving drainage and aeration;
abnormally light green and short needles on conifers, which could be caused by a deficiency ofnitrogen and may be solved by applying a nitrogen-containing fertilizer or improving the
restricted growth of roots; the bronzing of lower leaves with purple or brown spots, which could
be caused by a deficiency of phosphorus and may be solved by applying a phosphorus-containing
fertilizer and checking for damages from the use of herbicide; deadened tips of needles in
conifers, which could be caused by a deficiency of potassium and may be solved by applying a
potassium-containing fertilizer; uncharacteristically yellowish and undersized new leaves withgreen veins, which could be caused by a deficiency of iron and may be solved by adding acidic
amendments or iron chelates to lower the soil’s pH; discolored leaves, which could be caused bysunburn or scalding and may be solved by selecting more sun-tolerant plants; trees appearing
stressed by lack of water, with dropping leaves and injured bark and trunk, which could be theresult of wind damage and may be solved by selecting wind-tolerant plants and providing windbreaks; and unusually yellowish to brown leaves or needles, which could be caused by air
pollution and may be solved by selecting more ozone-tolerant plants.
The appendices, in addition to the Excel models, contain a glossary, acronyms andabbreviations used in this report, and conversion factors for SI (Système International) and non-SI
units, chemical units and other useful conversions, a table for field capacity and available soil
moisture as a function of soil texture, and a subject index.
This Salt Management Guide will be heavily cited and attached in the forthcominginteractive CD, the Salt Management Guide for Landscape Professionals.

ES-22

Chapter I. Introduction
K. Tanji and B. Sheikh
California will need to improve its efficiency of water use, both in the agricultural andurban sectors, to meet its water needs by 2030. This exigency is indicated by the most recent
water plan of the state (California Department of Water Resources, 2004). The plan further
suggests that California water providers will find it advantageous to recycle more water than they
currently do. Recycled water produced from wastewater already treated to a fairly high level,
typically tertiary (secondary treatment, filtration, and disinfection), can be used in many
nonpotable applications and, therefore, can help reduce the overall demand for fresh water.
Currently, California’s agricultural, industrial, and urban sectors use a total of about
530,000 acre-ft of recycled municipal wastewater per year. About 46% is used to irrigate
agricultural crops. About 21% is used for landscape irrigation and about 14% for groundwater
recharge. The rest—19%—goes to various uses, such as cooling water for oil refineries andpower plants and flushing toilets and urinals, as well as to environmental enhancements, such as
supplying water for wetlands and ponds, including reflecting ponds. In urban areas, recycledwater often is used to irrigate golf courses, commercial and residential landscapes, plant nurseries,
parks and greenbelts, school yards and playing fields, and highway medians and margins.
According to a recent survey, 409 parks or playgrounds and 295 schools’ grounds in California
are irrigated with recycled water (Crook, 2005).
By the year 2030, it is estimated that an additional 1.2 million acre-ft of recycled water
will be available annually. That water, if used, could free up enough fresh water to meet thehousehold water needs of 30 to 50% of the 17 million additional people who will live in
California in 2030 (California Department of Water Resources, 2004). The expanded use ofrecycled water for landscape irrigation is of especially high priority in south coastal California(the Los Angeles-to-San Diego corridor) in order to help alleviate current and future shortfalls of
potable water.
Recycled water is used for many nonpotable uses in California at the present time.
Though many additional opportunities for using recycled water in California’s urban areas exist
and though such use is encouraged by the state (California Recycled Water Task Force, 2003),
some landscape irrigators are reluctant to use recycled water. Some do not fully understand thatrecycled water can be safe and suitable for irrigating landscapes. Some believe that recycledwater may be excessively saline and therefore harmful to landscape plants.

I-1

To help foster a broader acceptance of recycled water, the Central Basin Municipal Water
District, the WateReuse Foundation, the California Department of Water Resources, and several
other institutions recently teamed up to begin informing the public and members of the landscapeindustry about the utility of recycled water. Part of that program involves developing aninteractive, CD-based salt management guide for landscape professionals. Another part of the
program involves outreach—developing and publishing an educational brochure. A third part
involves researching the state of knowledge and publishing a literature review summarizing what
is known at present regarding the factors that control the need for salt management when one is
irrigating a landscape with recycled water. This document comprises the literature review
component of the program. It should be noted that, although there are several indirect potablereuse projects involving groundwater recharge, this review does not address potable reuse orpotential health-related groundwater contamination resulting from irrigation with recycled water.
It also does not cover the public health aspects of using recycled water, as the authors do not haveexpertise on this topic. And, except in passing, this review does not address the effect of irrigatinglandscape plants with recycled water on the regional salinity of underlying groundwater basins,
since regional salt balance in southern California is a complex topic that will require additional
research, including three-dimensional modeling coupling unsaturated and saturated zones fortransport of water and salts in site-specific hydrogeologic formations.

References
California Department of Water Resources. 2004. The California Water Plan. California
Department of Water Resources, Sacramento, CA.
California Recycled Water Task Force. 2003. Final Report: Water Recycling 2030.
Recommendations of the California Recycled Water Task Force, June 2003. California
Department of Water Resources, Sacramento, CA.
Crook, J. 2005. Irrigation of Parks, Playgrounds, and Schoolyards with Reclaimed Water: Extent
and Safety. WateReuse Foundation, Alexandria, VA.

I-2

Chapter II. Present Status: Potential Benefits of Irrigating Landscapeswith Recycled Water, Current Use of Recycled Water, and Regulations
K. Tanji and B. Sheikh

II.A. Potential Benefits of Using Recycled Water
II.B. Current Uses of Recycled Water
II.C. California’s Relevant Regulations
II.D. References

This chapter summarizes the potential benefits of using recycled water, given theincreasing scarcity of potable water, as well as the current uses of recycled water for irrigatinglandscapes in California. The chapter also summarizes the state’s regulations governing use ofrecycled water.

II.A. Potential Benefits of Using Recycled Water
Substituting recycled water for valuable and scarce potable water often serves to augmentsupplies of fresh water. Communities and water purveyors also may benefit in other ways, too. As
mentioned in several publications (California Department of Water Resources, 2004; California
Recycled Water Task Force, 2003; Sheikh et al., 1998; WateReuse Foundation, 2003), thebenefits of using recycled water include the following:·

When uncertainties exist with a supply of traditional (potable) water, the use of recycledwater for such nonpotable applications as landscape irrigation can help reduce thedemand on a water system, thereby increasing the supply of available water andimproving the reliability of its supply.

·

Augmenting a water system with recycled water can, in some situations, decrease thediversion of fresh waters from sensitive ecosystems.

·

Recycling treated wastewater reduces the discharge of effluent to sensitive environments
and protects the quality of surface water and groundwater. Furthermore, recycled water
may be used to enhance and create wetlands and riparian habitats.

II­1

·

Using recycled water may reduce the costs of wastewater treatment and disposal. It may
also provide other economic benefits to dischargers and, indirectly, to businesses and the
public.

·In communities that recycle water, water purveyors may be able to “bank” a portion of
their imported water during average and above­average water years or to reserve some of
the imported water for use during dry years.

·

The use of recycled water, obtained from a local source, often partially offsets the need toimport water. That strategy, in turn, reduces the need for pumping and other energy­
consumptive activities associated with importing water.

II.B. Current Uses of Recycled Water
0B

Recycled water has been used in California since the late 1800s (California Department of
Water Resources, 2004). Guidelines and regulations directed at public health protection withregard to water reuse have been in effect since the early 1900s. Use of recycled water has
increased during the past several decades, as water agencies strove to meet shortfalls in supplies
of potable water caused by drought or population growth and concurrent increases in the demand
for water. Currently, with California’s population continuing to increase by approximately
500,000 people per year and with additional new supplies of water virtually nonexistent orincreasingly expensive to develop, recycled water could be considered the fastest­growing supplyof water available (California Department of Water Resources, 2003).
The Office of Water Recycling at the California State Water Resources Control Board
recently surveyed water users to determine the amount of municipal wastewater being recycled
and the types of recycled water use (California State Water Resources Control Board Office ofWater Recycling, 2002). The survey determined that, as of 2002, approximately 525,000 acre­ftof wastewater was being reclaimed and recycled in California each year. At that time the survey
was conducted, 48.5% of the total amount of recycled water used in the state was used for
agricultural irrigation, 21.1% for landscape irrigation, 9.3% for groundwater recharge, 7.8% forrecreational impoundments, 4.9% for seawater barriers, and 11.1% for other uses. Note that thesefigures refer to direct and intentional use and exclude indirect or incidental reuse such as thedisposal of treated wastewater effluent into rivers and streams and subsequent diversion of theriver water by downstream water users.
According to data compiled by the Office of Water Recycling in 2003 (Table II.B.1), theproportion of total recycled water used for landscape irrigation in southern California ranges

II­2Table II.B.1. Use of Recycled Water in Selected Service Areas in California (from California State Water
Resources Control Board Office of Water Recycling, 2002).
PurposeAmt. of water used in:a

Los Angeles
regionSanta Ana
regionSan Diego region

San Francisco Bay
regionAgricultural irrigation

3,752 acre­ft/year or
2%

30,795 acre­ft/year
or 37%

5,033 acre­ft/year or
16%

8,318 acre­ft/year
or 28%

Landscape irrigation

26,229 acre­ft/year
or 17%

28,135 acre­ft/year
or 34%

24,191 acre­ft/year
or 78%

10,114 acre­ft/year
or 34%

Groundwater
recharge

46,247acre­ft/year or30%

0 acre­ft/year

286 acre­ft/year
or 1%

0 acre­ft/year

Seawater barrier

10,651acre­ft/year or
7%

15,000 acre­ft/year
or 18%

0 acre­ft/year

0 acre­ft/year

Other uses

65,437 acre­ft/year
or 43%

97,20 acre­ft/year or
12%

1,445 acre­ft/year or
5%

11,087 acre­ft/year
or 38%

Total recycled water

152,316 acre­ft/year

83,650 acre­ft/year

30,955 acre­ft/year

29,519 acre­ft/yearaCurrently, greater than 0%.

from 17% for the Los Angeles region to 78% for the San Diego region. From these figures, it isevident that opportunities exist to further use recycled waters to irrigate landscapes.

II.C. California’s Relevant Regulations
California’s regulations governing the use of recycled water are known as Water Recycling
Criteria and are found in Title 22, Division 4, Chapter 3, of the California Administrative Codeand are often simply referred to as Title 22, Code of Regulations on Water Recycling Criteria(California Department of Health Services, 2001). According to Section 13550 of the California
Code, using a potable source of water—for example, to irrigate cemeteries, golf courses,
landscaped areas along highways, greenbelts, and parks and playgrounds—is a wasteful or
unreasonable use of water if reclaimed water is available that meets certain conditions (State
Water Resources Control Board, 2000). These conditions include the following (Crook andSurampalli, 1996):·

The source of recycled water is of adequate quality for the proposed uses andavailable for such uses.

·

The recycled water may be furnished for these uses at a reasonable cost comparable
to, or less than, the cost of potable water.

·

After concurrence with the California Department of Health Services, the use ofrecycled water from the proposed sources will not be detrimental to public health.

II­3Secondary treatment of wastewater includes removal of biodegradable organic matter insolution or suspension and suspended solids (Tchobanoglous et al., 2003). Typically,
conventional secondary treatment also includes disinfection.

Tertiary treatment of wastewaters includes removal of residual suspended solids after
secondary treatment by usually membranes, granular medium filtration or micro­screen.
Disinfection is also a part of tertiary treatment (Tchobanoglous et al., 2003).

·

The proposed uses of recycled water will not adversely affect downstream waterrights, will not degrade water quality, and is determined to be not injurious to plants,
fish, and other wildlife.

Before recycled water can be used to irrigate a landscape, the water must be treated tocertain secondary and tertiary levels (Table II.C.1). All recycled water used for landscapeirrigation must be disinfected. Water that has not been disinfected is deemed unacceptable for any
type of landscape irrigation. For irrigation of cemeteries, freeway margins, sod farms, and othersuch places where public contact with irrigation water is unlikely, the requirements for treating
recycled water are less stringent than those for irrigation with recycled water of public use lands
that have unrestricted access, such as golf courses, parks, and playgrounds. Undisinfected,
secondarily treated recycled water is acceptable for ornamental nursery stock and sod farms,
provided no irrigation with recycled water occurs for a period of 14 days prior to harvesting,retail sale, or access by the general public.
As pointed out by Levine and Asano (2004), new or advanced types of treatment
processes eventually may be necessary to respond to chemicals that newly emerge and become
introduced into municipal wastewater—for example, residues from pharmaceuticals and personalcare products. However, these newly emerging chemicals appear not to have an adverse effect onlandscape plants. Levine and Asano further assert that recycling treated wastewater isincreasingly becoming a necessity. Especially in arid and densely populated areas, such as theLos Angeles basin, where freshwater resources are becoming scarce, recycling wastewater andprioritizing its reuse are essential activities if water supplies are to be truly sustainable in the
future.

II­4

Table II.C.1. Allowed Uses of Recycled Water for Irrigating Landscapes in California (from WateReuse
Foundation, 2003).

aDisinfectedasecondary­2.2
recycled water
Allowed

Status of:Disinfectedasecondary­23
recycled water
AllowedUndisinfected
secondary recycled
water
Not allowed

Landscape for
irrigation
Cemeteries

Disinfected tertiary
recycled water
AllowedFreeway landscaping

AllowedAllowedAllowedNot allowed

Golf courses withrestricted access

AllowedAllowedAllowedNot allowed

Golf courses withunrestricted access

AllowedNot allowed

Not allowed

Not allowed

Ornamental
nurseries and sod
farms
Parks andplaygrounds

AllowedAllowedAllowedNot allowed

AllowedNot allowed

Not allowed

Not allowed

Residential
landscaping

AllowedNot allowed

Not allowed

not allowed

School yards

AllowedNot allowed

Not allowed

Not allowed

Refers to 7­day median counts of total coliform bacteria per 100 mL of water.

II­5

II.D. References
California Department of Health Services. 2001. California Health Laws Related to Recycled
Water—June 2001 Update, p. 51–57. California Department of Health Services, Sacramento, CA.
California Department of Water Resources. 2003. Recycled Municipal Water, Section 14,
Chapter 5, Resource Management Strategies. In California Water Plan Update 2003, vol. I.
California Department of Water Resources, Sacramento, CA.
California Department of Water Resources. 2004. The California Water Plan, vol. 2. Resource
Management Strategies. Bulletin 160, 2004 Draft. California Department of Water Resources,
Sacramento, CA.
California Recycled Water Task Force. 2003. Final Report: Water Recycling 2030.
Recommendations of the California Recycled Water Task Force, June 2003. California
Department of Water Resources, Sacramento, CA.
California State Water Resources Control Board Office of Water Recycling. 2002. Survey of
Recycled Water Use in California. California State Water Resources Control Board Office ofWater Recycling, Sacramento, CA.
Crook, J., and R. Y. Surampalli. 1996. Water reclamation and reuse criteria in the U.S. Wat. Sci.
Technol. 33:451–462.
Levine, A. D., and T. Asano. 2004. Recovering sustainable water from wastewater. Environ. Sci.
Technol. 38:202A–208A.
Sheikh, B., E. Rosenblum, S. Kasower, and E. Hartling. 1998. Accounting for all the benefits ofwater recycling. In Proceedings, Water Reuse ’98.
State of California. 2000. Porter­Cologne Water Quality Control Act. California Administrative
Code, Division 7. State Water Resources Control Board, Sacramento, CA.
State of California. 1978. Wastewater reclamation criteria, p. 1557–1609. California
Administrative Code. Title 22, Division 4. California Department of Health Services, Berkeley,CA.
Tchobanoglous, G., F. L. Burton, and H. D. Stensil. 2003. Wastewater Engineering, Treatment,
and Reuse, 4th ed. McGraw­Hill, New York, NY.
WateReuse Foundation. 2003. Recycled Water Uses Allowed in California. Personalcommunication.

II­6

Chapter III. Water Quality Guidelines for Recycled Water
Use for Landscape Irrigation
K. Tanji, S. Grattan, D. Shaw, and B. Sheikh

III.A. Water Quality Constituents of Concern in Irrigation Water
III.A.1. Salinity or Osmotic Effects
III.A.2. Specific Ion Toxicity
III.A.3. Sodicity and Soil Permeability
III.A.4. Other Constituents of Concern
III.B. Water Quality Guidelines
III.B.1. Early Water Quality Guidelines
III.B.2. Current Guidelines
III.B.3. Caveats and Assumptions for Using Current Guidelines
III.C. Quality of Recycled Waters
III.C.1. Representative Composition of Recycled Waters
III.C.2. Evaluation of Representative Recycled Waters Using FAO Guidelines
III.D. A Case Study: Use of Potable and Recycled Waters on Turfgrasses at Whispering Palms
Site
III.E. References

Most recycled waters do not inherently contain excessively high levels of salinity, though
they typically carry about 150 to 400 mg of salts/L more than does the potable water from which
they originated. Given a supply of potable water of low to moderate salinity, the recycled water
resulting from it would still be quite suitable as irrigation water for all practical purposes, undermost conditions.
Evaluating the suitability of waters for irrigation requires a broad understanding of water
quality characteristics and interactions with plant, soil, and irrigation management systems. This
chapter identifies key water quality parameters and describes how they are interpreted forsuitability or to serve as water quality guidelines.
Since water quality assessment and management in irrigated agriculture are much moreestablished than in landscape irrigation except for turf irrigation, a significant portion of thischapter involves what is applicable to irrigated crop production that is also applicable to irrigatedIII­1

landscape management in terms of evaluating water quality, diagnosing problems, and choosing
management strategies. It should be noted, however, that a major difference in evaluating thesuitability of waters for irrigating agricultural crops and waters for irrigating landscape plants isthat the former is based on harvested crop yield, while the latter is based on aesthetic quality or
appearance.
Discussions of the quality of irrigation water in the agronomic literature, which refer towater that is not recycled, are equally applicable to recycled water, as discussed in the following
section. The principal book references on this topic include Ayers and Westcot (1985),
Pettygrove and Asano (1986), and Tanji (1990).

III.A. Water Quality Constituents of Concern in Irrigation Water
Recycled water contains dissolved mineral salts, nutrients, and residues of chemicals
used in the treatment and disinfection of the recycled water. Though all water supplies containdissolved mineral salts, the dissolved­mineral content of recycled waters primarily depends on thequality of the source water supply and the incidental addition of a small amount of salts—
typically from about 100 to 400 mg/L—stemming from the water’s use for municipal andindustrial purposes. A larger amount of salts will accrue if water softeners containing sodium
chloride (NaCl) are used extensively in the community that contributes wastewater flowing to thewastewater treatment plant. Nutrients contained in recycled water include ammonia, ammonium
ions, nitrates, and phosphorus. The concentrations of these nutrients will vary depending on theextent of wastewater treatment provided.
The principal constituents of concern with regard to the quality of recycled water for
irrigation are the following: salinity, which contributes to osmotic effects that affect theavailability of soil water to plants; specific ions toxic to sensitive plants—for example, sodium,
chloride, and boron; and the combined effects of sodicity and salinity, which affect the rate at
which water infiltrates the soil surface and the permeability of the soil profile. Other constituentsof concern include nitrogen, bicarbonates, residual chlorine, and constituents that may
cumulatively clog the small orifices of sprinkler irrigation systems. It should be noted that thoseparameters of water quality that affect human health, such as pathogenic bacteria, protozoa, andviruses, and those that affect the environment, such as dissolved oxygen and oxygen­demandingorganics, are not addressed in this document.

III­2

III.A.1. Salinity or Osmotic Effects
The salinity of water affects plants due to osmotic effects: plants must expend moreenergy to extract soil water from saline soil solutions than from nonsaline soil solutions. A widelyused indicator of the salinity hazard posed by waters to plants is electrical conductivity (EC,
specific conductance), a lumped salinity parameter. Water salinity can be readily measured as EC
having units of decisiemens per meter (dS/m), equivalent to millimhos per centimeter(mmhos/cm), and millisiemens per centimeter (mS/cm) in more saline waters and microsiemens
per centimeter (mS/cm), equivalent to micromhos per centimeter (μmhos/cm) in less saline
waters. EC is a readily obtained measure of how easily electric current is conducted by charged
ions present in the water. Waters contain positively charged ions—major cations such as Na+,
Ca2+, Mg2+, K+, NH4+, and H+—and negatively charged ions—major anions such as Cl−, HCO32−,
CO32­, SO42−, and NO3−. The higher the salt content, the greater is the EC. Since water is anelectrolyte and since electrical neutrality prevails in nature, the milliequivalent­per­liter (meq/L,
based on equivalent combining weight) concentration of cations is balanced by the meq/Lconcentration of anions. EC is the lumped salinity parameter that is preferred for use with waterused to irrigate plants because EC can be readily related to osmotic pressure (OP in atmospheres= EC in dS/m ´ 0.36), affecting the availability of soil water to plants.
Another lumped salinity parameter for waters is total dissolved solids (TDS, sometimes
referred to as dissolved residues). Obtained labor intensively in a laboratory, TDS is a parameterof capacity expressed in mass per unit volume: milligrams per liter (mg/L) or parts per million(ppm) on a volume basis for fresh waters and recycled waters and gallons per liter (g/L) or parts
per thousand (ppt) on a volume basis for saline waters, such as seawater. The conversion of EC to
TDS varies, depending on the composition of cations and anions and the overall concentration ofdissolved salts. For example, a salt solution dominated by Na+ and Cl− ions has a higher EC thando Na+ and SO42− ions (or Na+ and HCO3− ions) of equal meq/L concentration, because a Cl− ion
conducts more electricity than do SO42− and HCO3− ions. Nevertheless, TDS in mg/L may be
estimated from EC in dS/m by multiplying EC by a rule­of­thumb factor of 640 (a factor of 735
appears to fit better for waters of mixed composition such as Colorado River water). For ECs
greater than about 5 dS/m, a conversion factor of 800 is suggested to convert EC into TDS.
A third salt concentration unit is tons of salt per acre­foot (ac­ft) of water, which can be
estimated from TDS (tons salt/ac­ft = TDS in mg/L ´ 0.00136) or from EC (tons salt/ac­ft = EC
in dS/m ´ 0.87; sometimes, a factor of 1.00 is used instead of 0.87).

III­3

A fourth salt concentration unit less frequently used in irrigation practice is total soluble
cations or total soluble anions in meq/L. Analytical chemists check their water analyses in meq/Lby balancing the sum of cations and anions. If there is a substantial imbalance, they reanalyze thewater. Total soluble cations (or total soluble anions) in meq/L may be obtained by multiplying EC
in dS/m by 10.
The accumulation patterns of salt in irrigated soils depends on the irrigation systems used
and the amount of water applied that exceeds crop water demands (Figure III.A). When water isuniformly applied across the irrigated land, as in sprinkler and border irrigation, the surface soil
depths become the zone of salt leaching and the bottom soil depths become the zone of salt
accumulation. The extent of salt accumulated in the bottom of the root zone depends on theleaching fraction (LF, namely, the ratio of drainage out of the root zone to infiltrated water). The
higher the LF, the less salt is accumulated in the soil. When water is applied by furrow irrigation,
salts increase with soil depth in the bottom of the furrow while the beds of the furrow tend toaccumulate salts. When water is applied by drip irrigation, salts tend to accumulate concentricallyaround the wetted perimeter of the zone irrigated.
Soils may contain soluble minerals that, when chemically weathered, contribute to theoverall salinity in the soil solution. Soil minerals such as calcite (CaCO3) and feldspars (sodic­,
calcic­, and potassium silicates) have low solubilities and contribute relatively little to soil
salinity, while minerals such as gypsum (CaSO4∙2H2O) have higher solubilities and may
contribute significant concentrations of Ca and SO4 ions. The solubility of gypsum in pure water
is about 2,600 mg/L and much higher in the presence of Na+ and Mg2+ ions (Tanji, 2002). Other
more highly soluble evaporite minerals, such as sodium chloride, sodium sulfate, and magnesium
sulfate, are sometimes present in strongly salt­affected soils. These highly soluble salts are readilyleached by rainfall and irrigation into deeper zones, sometimes beyond the root zones.
The salinity parameter of interest on plant performance is EC to assess osmotic effects.
Osmotic effects on plants are reflected by stunted growth, chlorosis, and wilting in some casesand death in the most severe cases. Plants vary in their tolerance to salts (osmotic effects) as
indicated in Chapter V of this document. Salt tolerant plants expend less metabolic energy toadjust to a saline environment than do more salt­sensitive plants (Lauchli and Epstein, 1990).

III­4

Figure III.A.1. Typical salt accumulation patterns in soils irrigated by sprinklers or surface flooding, border checkirrigation, furrow irrigation, and drip irrigation (Ayers and Westcot, 1985).

III­5

III.A.2. Specific Ion Toxicity
Some plants may be sensitive to specific ions such as Na+, Cl-, and B, the last usually inthe form of undissociated boric acid or H3BO3 at pH in the neutral range. These negative impacts
are collectively known as specific ion toxicity (Chapter V). As pointed out above, the use ofwater softeners increases the concentration of Na+ and Cl- ions in recycled waters. Also, a few
communities use potassium chloride (KCl) instead of sodium chloride (NaCl) in their watersofteners, increasing the concentration of Cl- ions in the recycled water. Use of boron­containing
household cleansers may elevate concentrations of boron in recycled waters. The symptoms ofspecific ion toxicity include chlorosis and necrosis on marginal edges of leaves, necrotic spots onleaves, interveinal chlorosis on leaves, damage to growing tips, and death in the severer cases.
Though some specific ions, particularly boron and chloride, are essential to plant growth in low
concentrations, the range in concentration between essential and toxic is narrow in sensitiveplants. Plants also vary in their tolerance to specific ions (Chapter V). Woody plants (e.g., trees
and shrubs) tend to be more severely affected by specific ions than do annual plants, since
specific ions may be translocated and accumulated over time in roots, trunks, leaves, and growing
tips. Annual plants may suffer from specific ion toxicity if the water contains elevatedconcentrations of such ions and accumulates to a sufficient degree during the shorter growing
period of the plants. Toxicity to specific ions, especially Cl- and Na+, can also occur in annuals
and perennials from direct absorption through the leaves when wetted by sprinkler systems.
Visual diagnosis of foliar damage due to specific ions may be compounded by osmotic
effects (salinity). As waters increase in salinity, specific ions also tend to increase inconcentration, especially Na+ and Cl- ions. Thus, osmotic effects and specific ion toxicity
frequently cannot always be clearly differentiated. In such cases, chemical analyses of leaf tissues
for specific ions and salinity may more accurately reveal the cause(s) of plant damage or poor
performance.

III.A.3. Sodicity and Soil Permeability
Excess Na+ in waters may impact mineral nutrition in plants, causing Na­induced calcium
deficiency and specific ion toxicity and affecting soil permeability and rates of water infiltration.
Accumulation of excess adsorbed Na (exchangeable Na) on the soil exchange complex(negatively charged sites on soil colloids and organic matter) causes soil colloids and organic
matter to disperse, resulting in the destruction of soil structure, particularly the larger pores, andreduced permeability of soil to water and gases. Dispersion of soil organic matter produces a
black mucky mat on moist soil surfaces; such soils are referred to as black alkali soil.

III­6

Exchangeable Na on the soil exchange complex is most frequently appraised with the sodium
adsorption ratio (SAR) of the soil solution, since the analytical method for determining
exchangeable sodium is time­consuming. SAR is defined as the ratio (Na+)/(Ca2++Mg2+)0.5 whenunits are in millimoles per liter or as (Na+)/[(Ca2++Mg2+)/2]0.5 when units are in meq/L. Thus,
SAR has units of (millimoles/liter)0.5 or (meq/L)0.5.
SARadj (or adjusted SAR) is sometimes used to account for the tendency of calcium todecrease in the soil solution due to the precipitation of calcite. The theoretical computation of
SARadj is based on the Langelier saturation index (Langelier, 1936), which is used widely in thewater industry. A much simpler method of calculating SARadj is based on tabular values of
expected Ca2+ concentration from a matrix of ratio of HCO3- to Ca2+ and EC of the water(technically referred to as adj RNa by Ayers and Westcot, 1985). This expected Ca2+ concentration
replaces Ca2+ in the denominator of the SAR expression. Ayers and Westcot (1985) calculated
SAR and SARadj for 250 water samples from throughout the world and noted that SAR was
within ±10% of SARadj for most waters. In waters with more of a tendency to form carbonate
minerals, SARadj may be markedly higher than SAR. This may be the case for some but not for all
recycled waters with elevated HCO3- concentrations as a result of chemicals used in wastewater
treatment processes. Ayers and Westcot (1985) now recommend taking SARadj ´ 0.5 as a morecorrect representation of SAR adjusted for the effects of calcite precipitation in irrigated soils.
The rate of water infiltration into soils and soil hydraulic conductivity are affected by theinteraction between the SAR and the EC of the water. Moderate to high SAR (sodicity) may
cause soil colloids to disperse and result in reduced infiltration rates. A relatively high EC(salinity or electrolyte concentration) may cause soil colloids to coagulate, resulting in increased
infiltration rates. An illustrative interaction of SAR and EC is shown in Figure III.A.2 (after
Henderson, 1955). The impact of electrolyte concentration (EC) on hydraulic conductivity ofColumbia silt loam is shown by the curve labeled SAR­0. Note that reduced hydraulicconductivity of this soil may be partially overcome by increasing water salinity for waters oflower SARs.
Another view of the SAR­EC relationship (Figure III.A.3) is widely used to evaluate theeffects of sodicity and salinity on rates of water infiltration in medium­ to fine­textured soils(Ayers and Westcot, 1985). Note that the SAR poses the most hazard to soil permeability at low
ECs and that this hazard may be partially overcome by increasing EC. Experience in California
water recycling practice indicates that nearly all such recycled waters fall within the safe zone ofthis graph—that is, no reduction in infiltration rate occurs (B. Sheikh, personal communication).

III­7

Satd. hyd. cond., in/hr .

Soil hydraulic conductivity as a function of watersalinity and sodicity
5
4
SAR­0

3

SAR­5
2

SAR­10

1
0
0

2

4

6

Water EC, dS/m
Figure III.A.2. The interaction of salinity and sodicity on the saturated hydraulic conductivity of Columbia silt
loam (after Henderson, 1955).

35

Severe Reductionin Infiltration

30

Sodium Adsorption Ratio

Slight to Moderate
Reduction in Infiltration

25

20

15

10

No Reduction in Infiltration

5

0
0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

EC of Irrigation Water (dS/m)
Figure III.A.3. A diagram to evaluate the effects of SAR and EC of waters on water infiltration rates in medium­ tofine­textured soils (after Ayers and Westcot, 1985).

III­8

A second parameter of sodicity widely used before the advent of SAR is residual sodium
carbonate (RSC), which is equal to (HCO32- + CO32-) – (Ca2+ + Mg2+) in meq/L (Eaton, 1950). A
positive difference between carbonate alkalinity and hardness would result in residual carbonates.
When combined with Na+, these carbonates disperse soil organic matter, forming a black residue
known as black alkali on the surface of soils. RSC exceeding 1.25 meq/L may cause increasingproblems with sodicity.

III.A.4. Other Constituents of Concern
Irrigation waters, especially recycled waters, may contain a number of other constituentsof concern. They include nitrogen (nitrates and ammonium), bicarbonates, residual chlorine, andconstituents that might plug the small orifices of irrigation systems, such as drip irrigation
emitters.

NitrogenSome natural waters, especially groundwaters, may contain appreciable concentrations of
nitrates from geochemical origins. Other ground­ and surface waters may have an accumulationof nitrates leached from excessive land applications of chemical fertilizers, animal manures anddairy wastewaters, biosolids, and other products of wastewater origin. Untreated municipal
wastewaters contain organic nitrogen and some NH3. The organic nitrogen is oxidized inwastewater treatment into NH3 (and NH4+) and is further oxidized into NO2- and NO3-. The
oxidation of NH4+ by microbes results in the production of protons (H+), and hence the acidified
water is typically neutralized by chemicals such as lime. Thus, Title 22 recycled waters typicallycontain from 15 to about 50 mg of N of NO3- and NH4+ ions/L, which is equivalent to 41 to 136
lbs. of N per ac­ft of water applied (lbs./ac­ft = mg/L ´ 2.72). These sources of nitrogen, if nottaken into account when fertilizing the plants with nitrogen, may cause excessive vegetative
growth, lodging, delayed or reduced flower bloom, and the leaching of excess N beyond the root
zone, possibly contaminating groundwater.

Phosphorus
Unlike the discharge of phosphorus­containing effluents into surface water, the land
application of phosphorus from recycled waters is of little concern, given its low solubility, use
by plants, and lack of mobility in the soil column. On the other hand, phosphorus is sometimes
the limiting nutrient for algal productivity in surface water. Therefore, the discharge ofIII­9phosphorus­containing effluents into surface waters may result in proliferic algal growth. Ponds,
lakes, and reservoirs holding recycled water may present algal management problems.

Carbonates
Carbonate ions (HCO3- and CO32-) are not found at elevated concentrations in waters andsoil solutions since carbonate minerals have very low solubility product constants. In fact, theprecipitation of carbonate minerals during evapoconcentration of soil water reduces theaccumulation of soluble salts in soils. However, the deposition of carbonates from overhead
sprinklers on fruits, such as table grapes, apples, and pears, and on flowering plants lowers themarket quality of the fruits and flowers. The deposition of carbonates may also lead to plugging
of irrigation systems.
The precipitation of carbonates of calcium and magnesium is of concern in constructedroot zones used on golf greens and sports fields in arid climates when they are irrigated withwater unusually high in alkalinity (carbonates) and hardness (calcium and magnesium). Suchcarbonate precipitation may lead to plugging of pores in sands because sands have less surface
area than do clays. Consequently, it would be advisable to ensure that carbonate ions are notexcessive in the recycled water.

Residual Chlorine
Molecular chlorine (Cl2) and its related chlorine compounds—sodium hypochlorite(NaOCl), calcium hypochlorite (Ca[OCl]2), and chlorine dioxide (ClO2) —are used, usually as a
final step in the treatment process. Hydrolysis of chlorine compounds forms hypochlorous acid
(HOCl), which ionizes into hypochlorite ion (OCl-) (Metcalf and Eddy, 2003). The combined
concentration of molecular chlorine, hypochlorous acid, and hypochlorite ion is known as freeavailable chlorine, which is a very good disinfection agent. However, free available chlorine
reacts rapidly with ammonia and other organic nitrogen usually present in wastewaters, forming
combined available chlorine, which is not as effective as free chlorine in disinfecting water.
Unless the ammonia and organic nitrogen in wastewaters have not been oxidized to nitrate by thetreatment processes, the primary disinfection agent in chlorinated recycled water will be
combined chlorine.
Excessive levels of free residual chlorine in recycled waters that have been oxidized to
the nitrate form—more than 5 mg/L—may result in root and foliar damage to sprinkler­irrigatedplants, since free chlorine is a strong oxidizing agent. However, as pointed out above, mostIII­10Table III.A.1. Plugging potential of irrigation water used in drip irrigation systems (Nakayama, 1982).
Degree of potential restrictions on use
Type of problem
Physical: suspended solids, mg/L
Chemical: pH
TDS, mg/L

LittleSlight to moderate

Severe< 50

50–100

>100

<7

7–8

>8

<500

500–2,000>2,000Manganese, mg/L

<0.1

0.1–1.5>1.5

Iron, mg/L

<0.1

0.1–1.5>1.5

Hydrogen sulfide, mg/L

<0.5

0.5–2.0>2.0

10,000–50,000>50,000

Biological: bacterial population<10,000(maximum number/mL)

recycled waters contain little if any free residual chlorine, most of which if present will dissipate
fairly quickly upon exposure to the atmosphere.
Because of stricter trihalomethane (THM) standards, there has been some changeover inthe use of chlorine to chloramine for disinfection of potable waters. However, chloraminecompounds have been identified as corrosive to certain metals and degrade rubber and someplastic elastomers in earlier irrigation equipment (AWWA Research Foundation, 1993). Most
irrigation equipment is now manufactured with components resistant to chloramine degradation,but occasionally an older irrigation system that has been retrofitted to recycled water may
demonstrate problems. Fortunately, PVC (polyvinyl chloride) and CPVC (chlorinated polyvinyl
chloride) compounds typically used to manufacture irrigation pipe, fittings, and lake liners appear
to be resistant to chloramine degradation.

Clogging Constituents
Recycled waters contain physical, chemical, and biological constituents that might
cumulatively clog small orifices in sprinkler irrigation systems, such as drip emitters (Nakayama,1982). Physical constituents include suspended solids, mainly sand fractions. Chemical
constituents include those that form precipitates, such as calcium carbonate, iron and manganesehydroxides, and hydrogen sulfides. Biological constituents may result from microbial activities,
such as the production of hydroxides and sulfides from microbially mediated redox reactions.

III­11

Table III.B.1. Water quality classification proposed by Wilcox and Magistad, U.S. Salinity Laboratory in 1943
(Wilcox, 1948).
Quality characteristic
Class IClass IIClass III
Excellent to good
Good to injurious
Injurious tounsatisfactoryEC, dS/m<1
1–­3>3
Boron, mg/L

<0.5

0.5–2.0>2.0

Chloride, mg/L

<178

178–355>355

Sodium, % of cations

<60

60–75

>75

Table III.A.1 summarizes the plugging potentials of certain levels of these three types of
constituents in water applied in drip irrigation systems (Nakayama, 1982). Constituents in mostrecycled waters, especially waters receiving Title 22 tertiary treatment, pose little potential
restriction on use for virtually all of these parameters. A possible exception is TDS, which may
pose slight to moderate potential restriction on use.

III.B. Water Quality Guidelines
For nearly a century, chemical constituents in water used to irrigate have been known tohave some potential effect on soils and crops. A concerted effort to classify waters according totheir suitability for irrigating crops and landscape plants has been made in the past 60 years or so.
This section summarizes some earlier guidelines regarding water quality and then focuses oncurrent guidelines.

III.B.1. Early Water Quality Guidelines
The U.S. Salinity Laboratory in 1943 suggested one of the earliest water quality
classification schemes for irrigated agriculture (Wilcox, 1948). It involved four quality
characteristics and three classes (Table III.B.1), including salinity (EC), specific ion toxicity(boron or chloride), and sodicity (Na%). Since then, H. Chapman of University of California–
Riverside, L. D. Doneen of University of California–Davis, F. Eaton of the U.S. Department ofAgriculture, H. Dregne and H. J. Maker of New Mexico State University, and J. P. Thorne andW. P. Thorne of Utah State University have advanced several more classification systems (Lunt,
1963).
In 1954, the U.S. Salinity Laboratory published Agricultural Handbook No. 60 (Richards,
1954), which became regarded worldwide as the definitive book on diagnosing and improving
saline and alkali soils. Included in the handbook was a diagram for classifying irrigation water(Figure III.B.1) with regard to salinity hazard (EC) and sodium hazard (SAR), each with fourlevels of hazard for a total of 16 classes.

III­12

Figure III.B.1. Diagram for the classification of irrigation waters (Richards, 1954).

III­13

Low­salinity C1 waters—those with an EC of less than 0.25 dS/m—can be used toirrigate most crops on most soils with little likelihood that soil salinity will pose a problem.
Moderate­salinity C2 waters—those with an EC of 0.25 to 0.75 dS/m—can be used for irrigation
without special salinity control practices, if a moderate amount of leaching occurs or moderately
salt­tolerant plants are grown. High­salinity C3 waters—those with an EC of 0.75 to 2.25 dS/m—
can be used to irrigate only plants with good salt tolerance on soils without restricted internal
drainage and possibly with special salt management measures required. Very­high­salinity C4waters—those with an EC of more than 2.25 dS/m—are ordinarily unsuitable for irrigation but
may be used to irrigate highly salt­tolerant crops and under such special circumstances as
extensive leaching. Handbook 60 contained tables on fruit, vegetable, forage, and field crops withlow, moderate, and high salt tolerances.
The sodium hazard was evaluated primarily on physical properties of soils as affected byaccumulation of exchangeable sodium on the cation exchange sites and secondarily on specificion toxicity of Na+. The accumulation of exchangeable sodium is related to the SAR, a soil waterparameter discussed above. Unlike salinity hazard, the classification of sodium hazards has anegative slope on the SAR­versus­EC matrix. Low­sodium­hazard S1 waters can be used toirrigate almost all soils with little danger of accumulating harmful levels of exchangeable Na but
not when such Na+­sensitive crops as stone fruits and avocados are involved, since such crops
may accumulate injurious concentrations of Na+. Medium­sodium­hazard S2 waters may be used
for irrigation of coarse­textured or organic soils with good permeability. Irrigating with thesewaters will present an appreciable hazard in fine­textured soils with high cation exchange
capacity, especially under low LFs. If gypsum is present in the soil, the sodium hazard will be
reduced, since Ca2+ dissolved from gypsum will reduce levels of exchangeable Na. Use of high­sodium­hazard S3 waters for irrigation may result in harmful levels of exchangeable Na in mostsoils and will require special soil management, such as good drainage, high leaching, andadditions of organic matter. Gypsiferous soils may not develop harmful levels of exchangeable
Na with this type of water. Chemical amendments may need to be used to lower exchangeable
Na. Very­high­sodium­hazard S4 waters are generally unsuitable for irrigation.
Though the U.S. Salinity Laboratory system for classifying irrigation water with regard to
EC and SAR (Figure III.B.1) was broadly accepted and applied, some noted that the diagonallines appeared to have the wrong slope for the permeability of fine­ to medium­textured soils. A
water with low sodium hazard and low salinity hazard infiltrates slowly over the long term, whilea water with low sodium hazard and medium to high salinity infiltrates at an acceptable rate (see,e.g., Figure III.A.2). SAR can cause soil colloids, especially clay minerals such as smectites, toIII­14

disperse, resulting in a poor rate of water intake, while EC coagulates soil colloids, promoting agood rate of water intake, so that the adverse effects of SAR are partially overcome by higher
salinity (Figure III.A.3). Currently, Figure III.A.3 is used to appraise the combined EC­SAR
effects on the permeability of soil, while Figure III.B.1 is used to assess the hazards of
exchangeable sodium on plants and soils.
Agricultural Handbook No. 60 also included a system for classifying permissible limitsof boron in waters (Table III.B.2) suggested by Scofield (1936). Boron, an essential element forplants at very low concentrations, is injurious to plants at slightly above essential concentrations.
Citrus, stone fruits, and beans are particularly sensitive to boron. (Refer to Chapter V for a listingof boron­sensitive plants.)
Handbook 60 additionally contained a system for classifying RSC (Table III.B.3)
advanced by Eaton (1950). This parameter is used by many water­testing soil and horticulturallaboratories. Waters having an RSC of 1.25 to 2.5 may be used to irrigate if Ca­producing
amendments, as well as good soil and water management practices, are also used.
In the early 1960s, a number of disagreements arose over the use of various classification
systems. In 1963, the University of California Water Resources Center convened a workshop to
evaluate various systems for classifying agricultural water (Lunt, 1963), where a consensus wasreached on recommendations for a new classification system (Table III.B.4). It excluded
consideration of the aforementioned SAR­EC relationship for soil permeability (Figure III.A.2).
Table III.B.2. Permissible limits of boron for several classes of irrigation waters (after Scofield, 1936).
Concn of boron in irrigation water (mg of boron/L) for:Boron classSensitive crops

Semitolerant crops

Tolerant crops

1

<0.33

<0.67

<1.00

2

0.33–0.67

0.67–1.33

1.00–2.00

30.67–1.00

1.33–2.00

2.00–3.00

4

1.00–1.25

2.00–2.50

3.00–3.75

5

>1.25

>2.50

>3.75

Table III.B.3. Suitability of waters for irrigation based on RSC (after Eaton, 1950).
RSC in meq/L

Suitability<1.25

Probably safe

1.25–2.5

Marginal quality for irrigation>2.5

Not suitable for irrigationIII­15

In the mid­ to late 1960s, nitrate contamination of groundwaters was increasingly
detected. This phenomenon was of concern to public health, as some of those waters served assources of drinking water. One investigation conducted in the Upper Santa Ana River Basin(Ayers and Branson, 1973) identified excess fertilizers, animal manure, dairy wastewaters, andmunicipal and industrial wastewaters as the major sources of nitrate in groundwaters. The safe
disposal and wise use of nitrogen­containing wastes and their salt content became a concern. The
California Regional Water Quality Control Boards requested reevaluations of land treatment andrecycling of animal wastes and dairy wastewaters. In 1973, a University of California Committeeof Consultants convened to reevaluate and revise water quality guidelines for producing crops(Ayers and Branson, 1975). The revised guidelines (Table III.B.5) were streamlined to categorize
certain levels of constituents in irrigation water as presenting either “no problems,” “increasingproblems,” or “severe problems.” The electrolyte effect on the permeability of soil, specific ion
toxicity differentiated by root absorption versus foliar absorption, the significance of NH4+ andNO3- in waters, and the deposit of carbonates on plants were all considered in these guidelines.
Table III.B.4. Recommended water classification system, UC Water Resources Center (Lunt, 1963).
Salinity hazard

Low

MediumHigh

Very highEC, dS/m<0.75

0.75–1.50

1.50–3.00

3Sodium hazard

Low

MediumHigh

Very high

<3

3­5

5­8

>8

Boron hazard

Safe for sensitive
crops

Sensitive crops
will show injury

Semitolerant
crops will show
injuryTolerant crops
will show injury

Hazardous
for nearly
all crops

Boron, mg/L

<0.5

0.5–1.0

1.0–2.0

2.0–4.0>4.0

Chloride hazard

Safe for sensitive
crops

Sensitive crops
will show injury

Medium tolerant
crops will show
injuryModerately
tolerant crops willshow injury

Chloride, mg/L

<71

71–142

142–284>284

RSC hazard

Probably low

Intermediate

Probably high

RSC, meq/L<0

0–1.25>1.25

SAR, (mM/L)

0.5

III­16

Table III.B.5. Guidelines for the interpretation of quality of water for irrigation (Ayers and Branson, 1975).
Water quality guidelines

Problem and related
constituent in irrigationwater

No problem

Increasingproblems

Severe problems

Salinity, ECw in dS/m

<0.75

0.75–3.0>3.0

Permeability, ECw in dS/m

>0.5

<0.5

<0.2

Adjusted SAR

<6

6–9

>9

Specific ion toxicity
From root absorption:
Sodium, adjusted
SAR
Chloride, mg/L

<3

>3

<142

142–355>355

Boron, mg/L

<0.5

0.5–2.0

2.0–10.0

Sodium, mg/L

<69

>69

Chloride, mg/L

<106

>106

NH4­N + NO3­N, mg/L

<5

5–30

>30

HCO3, mg/L (only withoverhead sprinklers)<90

90–520>520

From foliar absorption(sprinklers):

MiscellaneouspHnormal range: 6.5–8.4

III.B.2. Current Guidelines
Ayers and Westcot (1976)1 developed the most widely used water quality
guidelines for irrigation (Table III.B.6). Given in detail in Irrigation and Drainage Paper 29 of
the Food and Agriculture Organization (FAO), these guidelines were based on the 1975
University of California Committee of Consultants Guidelines with some revisions.1 The FAO
guidelines included recommended maximum concentrations of trace elements in irrigation waters(Table 111.B.7), much of which was based on accumulation of trace elements in soils under long­term normal irrigation and potential uptake of trace elements by plants (Pratt, 1972).
Later, Ayers and Tanji (1981) recommended that the FAO guidelines could also be used
for irrigating crops with wastewater. A few years later, Ayers and Westcot (1985) revised the
FAO guidelines. These guidelines were further adapted in a guidance manual on irrigation withreclaimed municipal wastewater (Pettygrove and Asano, 1986). Currently, the FAO guidelines
are applied internationally in irrigated agriculture and nationally in the use of recycled water toirrigate crops and landscapes.
1

Robert Ayers, a UC Extension Water Specialist and coauthor of the 1975 UC Committee of Consultants’
Water Quality Guidelines (Ayers and Branson, 1975), took a sabbatical leave at the FAO in Rome. There
he worked with soil scientist Dennis Westcot of FAO, who currently is a private consultant after service
with the California Central Valley Regional Water Quality Control Board, to adapt and expand on the UC
Committee of Consultants Water Quality Guidelines.

III­17

Table III.B.6. Guidelines for interpretation of water quality for irrigation (Ayers and Westcot, 1985).
Degree of restriction on use
Potential irrigatedproblem

Units
None

Slight tomoderate

SevereSalinity (affects cropwater availability)
ECw

dS/m

<0.7

TDS

mg/L

<450

0.7–3.0
450–
2,000

>3.0
>2,000Infiltration(affects infiltration rateof water into the soil)a

SAR = 0­3, and ECw =(meq/L)

0.5a

>0.7

0.7–0.2<0.2

SAR = 3­6, and ECw =>1.2

1.2–0.3<0.3

SAR = 6­12, and ECw =>1.9

1.9–0.5<0.5

SAR = 12­20, and ECw =>2.9

2.9–1.3<1.3

SAR = 20­40, and ECw =>5.0

5.0–2.9

<2.9

<3

3­9

>9

Specific ion toxicity(affects sensitive
crops)
Sodium (Na)0.5

Surface irrigation, SAR(meq/L)

+

mg/L

69

>69

mg/L

<142

142–355

mg/L

<106

>106

mg/L

<0.7

0.7–3.0

Nitrogen, NO3­N

mg/L

<5

5–30

>30

Bicarbonate (HCO3)

mg/L

92

92–518

>518

1–5

>5

Sprinkler irrigation, Na
Chloride (Cl)­

Surface irrigation, Cl­

Sprinkler irrigation, Cl
Boron (B)

>355
>3.0

Trace elements(see Table IV.C.5)
Miscellaneous effects(affects susceptible crops)

No problems expected with normal pH range ofpH

6.5–8.4
aResidual chlorine(overhead sprinkling only)
a

mg/L

<1

Added by Pettygrove and Asano (1986). For clogging, see Table III.A.1.

III.B.3 Caveats and Assumptions for Using Current Guidelines
The FAO Water Quality Guidelines were developed based on the collective opinions ofseveral soil, plant, and water scientists with extensive research and practical experience. With
these guidelines, a wide range of conditions encountered in irrigated agriculture is covered, andwater quality is evaluated in terms of the “degree of restriction on use”; i.e., as water quality isIII­18degraded, it requires higher management skills to safely use that water. These guidelines should
be used as a first approximation for considering the suitability of water for irrigation and thenmodified for local conditions as needed. Not plant specific, they may be too restrictive for somemore tolerant plants and perhaps not restrictive enough for some more sensitive plants.
The guidelines are based on the following assumptions:
Yield Potential
No restrictions on use indicate full production capability without the use of special
management practices. Restrictions on use indicate that the choice of crop may be limited or thatspecial management practices are required to attain full production capability. This situation may
not be as predominant a concern in the case of landscape plants, as their visual appearance ismore important than is harvested yield or biomass.

Table III.B.7. Recommended maximum concentrations of trace elements in irrigation waters that might limit crop
production due to toxicity and/or limit the utilization of the produce (adapted from National Academy of Sciences
and National Academy of Engineering [1972] and Pratt [1972]).
Element

Recommended maximum concn (mg/L)

Al (aluminum)

5.0

As (arsenic)

0.10

Be (beryllium)

0.10

Cd (cadmium)0.01

Co (cobalt)

0.05

Cr (chromium)

0.10

Cu (copper)

0.20

F (fluoride)

1.0

Fe (iron)

5.0

Li (lithium)

2.5

Mn (manganese)

0.20

Mo (molybdenum)

0.01

Ni (nickel)

0.20

Pb (lead)

5.0

Se (selenium)

0.02

Sn (tin)

N/A

Ti (titanium)

N/A

W (tungsten)

N/A

V (vanadium)

0.10

Zn (zinc)2.0

III­19Site Conditions
Soil texture ranges from sandy loam to clay loam with good internal drainage andshallow water table controllable to within 2 m of land surface. The climate is semiarid to arid
with low rainfall. Rainfall does not contribute much to meeting crop water demand or to meetingthe leaching requirement of crops. The guidelines are too restrictive when rainfall is high during
the growing season..

Methods and Timing of Irrigation
Normal surface or sprinkler irrigation methods are used. Water is applied when available
soil water depletion is less than 50% before the next irrigation. LF, the ratio of root zone drainage
to infiltrated irrigation water, is 0.15 or greater. These guidelines are too restrictive for drip
irrigation or for daily to frequent irrigations.

Water Uptake by Crops
The root water extraction pattern is about 40–30–20–10% of crop reference
evapotranspiration (ETo) from surface root zone quartile to bottom quartile. Each irrigation event
results in leaching of salts in the upper root zone and accumulation of salts in the bottom rootzone. The average root zone salinity in soil water (ECsw) is estimated to be about three times
greater than in the applied water (ECw), and the average root zone salinity of the soil saturation
extract (ECe) is estimated to be about 1.5 times ECw. These relationships are based on a steady­state LF of 15 to 20% (or 0.15 to 0.20).

Restriction on Use
The three categories of restrictions on use, which are somewhat arbitrary due to the lackof a clear­cut specific boundary and the gradual occurrence of changes, are based on studies,observations, and experiences in the field. A change of 10 to 20% above or below a numericguidance value may have little significance for crop yield if other guidance values have norestrictions or less restriction. Moreover, the management skill of the water user could alter the
degree of restrictions. For instance, an ECw of 0.85 dS/m may not necessarily pose a restriction on
use if the LF exceeds 15%, because there will be only a small accumulation of salts in the rootzone. However, if the water SAR is 9, there may be slight to moderate problems in water intake
rates that might be corrected with water or soil amendments containing Ca2+. Moreover,sprinkler­applied water with a SAR of 9 could severely damage Na+­sensitive plants, such asstone fruits.

III­20

The FAO guidelines, though accepted worldwide in irrigated agriculture and widely usedsince 1976, should be considered part of an initial effort to evaluate the suitability of waters forlandscape irrigation. As landscape professionals gain experience in the use of recycled waters toirrigate landscape plants, they may need to consider additional constraints or modifications inaddition to potential plugging (Table III.A.1) and RSC (Table III.B.3).

III.C. Quality of Recycled Waters
Generally speaking, if a source water is of acceptable quality to irrigate landscape plants,
the recycled water will likewise be of acceptable quality for irrigating landscape plants, since
recycled water usually accrues small amounts of dissolved minerals—from 150 to 400 mg of
TDS/L (Asano et al., 1985). There are, however, some exceptions:First, as discussed above, if a significant number of water softeners utilizing sodium
chloride are used in the community served by the wastewater treatment plant, there may besignificant accumulation of Na+ and Cl- ions in the recycled water. This accumulation might posea specific ion toxicity hazard to sensitive plants, as well as adversely affect soil water infiltration,
especially when highly trafficked turf is being irrigated.
Second, recycled waters often contain 15 to 40 mg of nitrogen/L as organic­N, NH4­N,
and NO3­N (Asano et al., 1985). Since each milligram of N per L equals 2.72 lbs. of N per ac­ftof water, this source of N needs to be taken into account when considering the plant’s need for N.
Third, recycled waters are neutralized with bases such as lime or soda ash, because theoxidation of NH4­N to NO3­N produces acidity, substantially raising the RSC of the water.
Fourth, recycled waters may contain sufficiently high concentrations of boron to injureboron­sensitive plants.
Fifth, some recycled waters may contain constituents that tend to plug parts of sprinkler
irrigation systems, such as the small orifices in drip emitters.

III.C.1. Representative Composition of Recycled Waters
Data were compiled on the composition of Title 22 recycled waters used to irrigate
landscapes and agricultural crops at four different sites (Table III.C.1) in three different studies(Sheikh et al., 1990; Shaw et al., 1995; and West Basin Municipal Water District, 2004). The datareported are mean or median values for samples of water obtained at regular intervals: residual
chlorine and turbidity were monitored continuously, the pH and EC were monitored daily, SS(suspended solids) were monitored weekly, dissolved minerals were monitored monthly, andIII­21a

Table III.C.1. Representative composition of recycled waters compiled from various sources.

Description

pH

Torrey Pines,
San Diego County,
1992–94(mean and sd, n =31)
Shaw et al., 1995

7.2

Location and values
Whispering
WBWRF,
Palms,
Los Angeles
San Diego
County,County,2001–03
1993–94(mean n = 36)(mean and sd, n =WBMWD, 200430)
Shaw et al., 1995
7.3
7.0

MC,
Monterey County
1980–85,(median, n = 91)
Sheikh et al., 1990

7.2

EC, dS/m

1.55 ± 0.23

1.41 ± 0.13

1.03

1.26

TDS, mg/L

989 ± 58

900 ± 83

671

778

Na, mg/L

179 ± 17185 ± 12157

166

Ca, mg/L

80 ± 1963 ± 1147

52

Mg, mg/L

34 ± 826 ± 520

21

K, mg/L

14 ± 217 ± 417

15

Cl, mg/L

226 ± 67

198 ± 52

188

221

SO4, mg/L

92 ± 2185 ± 13

110

107

HCO3, mg/L

90 ± 59

161 ± 32

159

97

148

264

261

159

4.2 ± 1.0

4.8 ± 1.0

3.4

4.9

Alk., mg/L as CaCO3
0.5

SAR, meq/L

0.5

Adj. SAR, meq/L

4.5

5.3

4.5

5.1

RSC, meq/L

<0.0

<0.0

1.7

<0.0

B, mg/L

0.4 ± 0.1

0.5 ± 0.07

0.6

0.4

NH3, mg/L as N

0.24 ± 0.26

0.18 ± 0.23

31.3

1.2

NO3, mg/L as N

13.9 ± 5.7

11.7 ± 6.2

0.83

8.0

NO2, mg/L as N

0.23

Total P, mg/L

(6.2)

TSS, mg/L

6.0

Turbidity, JTU

2.2

Residual Cl2, mg/L

5.6

Sulfide, mg/L(<0.1)

Iron, mg/L

(0.43)2.7

a

WBWRF = West Basin Water Recycling Facility;
MC = including MWRSA = Monterey Wastewater Reclamation Study for Agriculture;

ammonia and nitrate were monitored quarterly. Standard deviations are reported whereappropriate.
The recycled water reported for Torrey Pines Golf Course initially originated from theMission Valley Aquaculture Treatment Plant (later originated from the Whispering Palms Water
Pollution Control Facility) and irrigated the Torrey Pines Golf Course in La Jolla. The recycledwater reported for Whispering Palms originated from the Whispering Palms Water Pollution
Control Facility and irrigated plots of experimental turf in the San Dieguito River basin near thevillage of Fairbanks Ranch, a site targeted to receive recycled water in the future and located in aIII­22

floodplain representative of many San Diego County golf courses. Recycled water reported for
the West Basin Water Recycling Facility irrigated landscapes at Toyota Motor Sales USA, theHome Depot National Training Center, Goodyear, golf courses such as Victoria Golf Course in
Carson, and other landscaped sites. The recycled water reported for Monterey County in a
Monterey Wastewater Reclamation Study for Agriculture at Castroville was a demonstration
study of recycled water used to irrigate crops of artichokes, broccoli, cauliflower, lettuce, andcelery. It is also representative of recycled waters used on golf courses in Monterey County.
As pointed out above, the amount of dissolved minerals in recycled water primarily
depends on the quality of the source water, plus the small increase of additional salts, as well as
nutrients, from water usage.

III.C.2. Evaluation of Representative Recycled Waters Using FAO Guidelines
The FAO Water Quality Guidelines (Ayers and Westcot, 1985), though based on workwith irrigated agricultural crops, are generally applicable to landscape plants (Ayers and Tanji,1981). However, the FAO guidelines for sodicity may not be applicable for all landscape plants.
That is, sodicity is more of an issue in landscape than in agricultural lands since landscape plants,
such as turf, are permanent, eliminating the tillage conducted between the growing seasons ofmost irrigated crops to improve soil tilth and control weeds. Nevertheless, the four representative
recycled waters discussed above could be evaluated by using the FAO guidelines and their threeclassifications regarding the extent of restrictions on the use of waters: no restrictions, slight tomoderate restrictions, and severe restrictions (Table III.C.2).
The recycled water from the West Basin Water Recycling Facility in Los Angeles County
falls into two categories of severe restriction on use: excess residual chlorine and excess N. It is
expected that the 5.6 mg of residual chlorine/L in this recycled water will tend to be dissipatedwithin the distribution system and to be rapidly dissipated at the time of its application. The
excess N is more problematic if normal fertilization rates are practiced with this water. The 32.4
mg of N/Lin this recycled water contains about 88 lbs. of N/ac­ft. About 352 lbs. of N would beapplied for a seasonal water application rate of 4 ac­ft/acre, a level of application that fulfills theN requirement of most plants. Therefore, commercial N fertilizer would not be needed when one
is irrigating with this recycled water. Furthermore, some N is expected to be leached beyond theroot zone because plants do not consume 100% of the applied N as either applied fertilizer or as
N dissolved in water.
Slight to moderate restrictions on use are expected for each of the four recycled waters
discussed above, depending on the species of plants, the types of soil, and the practice of waterIII­23

Table III.C.2. Evaluation of representative recycled waters based on the FAO Water Quality Guidelines(TP = Torrey Pines, WP = Whispering Palms, WRF = WBWRF, MRS = MWRSA).
Potential problem
Degree of restriction on use
None

Slight tomoderate

Severe0.7–3.0>3.0

1. Affects availability of soil water to plants
ECw, dS/m<0.7

Recycled waters

WRF, MC, WP, TP

2. Affects soil hydraulic conductivity
SAR = 3­6, and ECw indS/m =
Recycled waters>1.2

1.2–0.3

MC, TP, WP

WRF

<0.3

3. Dispersion of soil organic matter and reduced water intake rates
RSC, meq/L
Recycled waters<1.25

1.25–2.5

TP, WP, MC

WRF

>2.5

4. Specific ion toxicity hazard of Na for surface irrigation
0.5

SAR, meq/L

<3

3­9

Recycled waters>9

WRF, TP, MC, WP

5. Specific ion toxicity hazard of Na for sprinkler irrigation
Na, mg/L

69>69

Recycled waters

WRF, MC, TP, EL

6. Specific ion toxicity hazard of Cl for surface irrigation
Cl, mg/L<142

142–355

Recycled waters>355

WRF, MC, TP, WP

7. Specific ion toxicity hazard of Cl for sprinkler irrigation
Cl, mg/L

<106

>106

Recycled waters

WRF, MC, TP, WP

8. Specific ion toxicity hazard of boron
B, mg/L
Recycled waters<0.7

0.7–3.0>3.0

TP, MC, WRF, WP

9. Excess nitrogen for susceptible plants
NH3 + NO3, mg/L as N

<5

Recycled waters

5–30

>30

MC, TP, WP

WRF

>518

10. Carbonate deposition on foliage, flowers, and fruit
HCO3 + CO3, mg/L

92

92–518Recycled waters

TPMC, WRF, WP

<1

1–5

11. Potential toxicity of chlorine residual
Chlorine residual foroverhead sprinklers, mg/L
Recycled waters

>5
WRF*

management, among other considerations. First, the ECw of these waters ranges from 1.0 to 1.6
dS/m and may be too salty for the more salt­sensitive plants while having little or no osmotic
effects on the more salt­tolerant plants (refer to Chapter V for salt tolerance ratings). One solution
would be to replace salt­sensitive plants with more salt­tolerant plants. Second, the combined
effects of ECw and SAR of the recycled water from the West Basin Water Recycling Facility may

III­24

reduce permeability for some types of soils, especially those with silt loam texture and that are
dominated by smectite clay minerals, which swell upon wetting and shrink upon drying. Third,
the recycled water from the West Basin Water Recycling Facility has an RSC of 1.7 mg/L andmay disperse soil organic matter and reduce water infiltration, as noted at the Victoria Golf
Course in Carson, Calif., where acids are being injected into the water line to ameliorate theproblem. Fourth, all four waters are judged to have slight to moderate restrictions on use becauseof the Na+ and Cl- specific ion hazard when irrigated by both sprinkler and surface irrigation
methods. A solution to this problem is that plants sensitive to Na+ and Cl- could be replaced bymore tolerant ones. The recycled waters discussed above (Monterey Wastewater Reclamation
Study for Agriculture, Torrey Pines, and Whispering Palms) have from 9 to 14 mg of total N/Land thus may have slight to moderate restrictions on use.
Landscape plants are generally more sensitive to boron than are agricultural crop plants,
and the numerical limits presented in Table III.B.5 (Ayers and Branson, 1975) may be more
appropriate: i.e., no restrictions, less than 0.5 mg of B/L; slight to moderate restrictions, 0.5 to 2.0
mg/L; and severe restrictions, 2 to 10 mg/L. If the Ayers and Branson (1975) limits are applied,
water produced by the West Basin Water Recycling Facility will fall in the slight to moderate
restriction in use for landscape irrigation.
In summary, certain characteristics of recycled waters require attention when the waters
are used to irrigate landscape plants. Such characteristics include total N, EC, SAR, RSC, B, Na+,and Cl- ions. Therefore, wastewater reclamation facilities should ideally be designed andoperated so that these constituents in the water produced do not pose a hazard or restrictions on
use on landscape irrigation. However, for reclamation facilities that have multiple customers withvarious end users, it may not be cost effective to install multiple plant modifications to meet
specific user requirements.

III.D. A Case Study: Use of Potable and Recycled Waters on
Turfgrasses at Whispering Palms Site
Of some concern is the chemical composition of the leachates that result from deep
percolation of irrigation drainage into groundwater basins and the load of salts and nitrates thatleach from the root zone of landscapes irrigated with recycled waters, especially when theunderlying groundwater serves as a source of drinking water. Observed data on the quality of rootzone drainage in landscape irrigation are unfortunately scarce. Leachate composition is difficult
to predict because of the numerous processes that affect the composition and amount (load) ofleachates produced. These processes include the following:III­25·

loss of pure water to the atmosphere from evapotranspiration (ETo), with salts
remaining in the soil solution·

leaching from irrigation and rainfall·

net mineral precipitation from evapoconcentration and mineral dissolution from thechemical weathering of soil minerals·

uptake by plants of such ions as NH4+, NO3-, Na+, K+, Cl-, etc.

·

cation exchange between solution cations and exchangeable cations on the soil
exchange complex, e.g., solution Na replacing exchangeable Ca·transformations such as oxidation of NH4®NO2®NO3, mineralization of organic
N®NH4, and denitrification of NO3®NO2®N2O®N2·adsorption of solution ions onto surfaces of iron and aluminum oxides of soil clays,e.g., boron.
A simplified approach for estimating the leaching of salinity from root zones into thevadose zone, the unsaturated zone above the water table of groundwater basins, is presented in
Chapter IV. A case study on observed leaching of salt and nitrates comparing potable andrecycled water irrigation on turfgrasses follows.
Shaw et al. (1995) conducted extensive studies in San Diego County of the use ofrecycled waters to irrigate landscapes. Of particular interest is the field trial using potable andrecycled water from the Whispering Palm facility to irrigate plots of turfgrass—an ideal site inthat many San Diego County golf courses are similarly located in river basin floodplains and thatthe drainage of these floodplain soils allows leaching to eliminate the accumulation of salts due toirrigation with moderately saline waters. The soils at this site are identified as Grangeville finesandy loam and Tujunga sand.
As noted in Table III.D.1, the recycled water used in this study contained concentrationsof constituents greater than those found in the associated potable water. Chemical analyses forboth waters range quite widely due to changes in blending of imported waters: Colorado Riverthrough the Colorado River Aqueduct and northern California water from the California
Aqueduct were blended with local surface and well waters in San Diego County. The EC, SAR,
and NO3­N of the recycled water are of particular concern from a water quality perspective (Shawet al., 1995).

III­26

Table III.D.1. The mean and range (parentheses) of water quality of potable and recycled waters used in the
Whispering Palms turfgrass study (Shaw et al., 1995).
Property measured
Potable water
Recycled waterpHEC, dS/m
TDS, mg/L
0.5(6.8–8.0)(6.8–7.7)

0.98 (0.77–1.09)

1.41 (1.24–1.63)

630 (493–685)

900 (736–1043)

SAR, mM/L

2.7 (2.2–3.1)

4.8 (4.0–5.5)

Na, mg/L

105 (85–116)

185 (147–212)

Cl, mg/L

117 (75–190)

198 (82–269)

Boron, mg/L

0.15 (0.08–0.23)

0.50 (0.28–0.67)

NO3­N, mg/L

0.19 (0.05–0.51)

11.2 (2.5–23.7)

NH4­N, mg/L

0.07 (0.04–0.26)

0.18 (0.01–0.66)

Table III.D.2. Irrigation data for turfgrass from Whispering Palms study (Shaw et al., 1995).
Property measured
Cool­season turf
Warm­season turf
CIMIS ETo, in.

90.7

90.7

Calcd. ETc, in.

74.5

54.1

Rainfall, in.

25.1

25.1

PotableRecycled

PotableRecycled

Irrigation, in.

103.4

106.7

78.3

88.7

Total applied water, in.

128.5

131.8

103.4

113.8

Drainage, in.

54

57.3

49.3

59.7

LF,
Drainage/total applied water

0.42

0.42

0.48

0.52

The turfgrasses selected for this study included two warm­season varieties, common
bermudagrass (Cynodon dactylon) and kikuyugrass (Pennisetum clandestinum), and two cool­seasonvarieties,

tall

fescue (Festuca

arundinacea)

andKentuckybluegrass(Poa

pratensis)/perennial ryegrass (Lolium moltiflorum) mixture, all grasses commonly planted in San
Diego County golf courses, parks, and landscapes. Kikuyugrass, not a commonly recommended
turfgrass, has become the dominant species in many parks and golf courses due to its adaptability
and invasiveness. Warm­season turfgrasses have a higher tolerance of drought and salinity,
requiring about 25% less water than do cool­season turfgrasses and achieving peak growth andappearance during the summer. These grasses become dormant in the winter, unlike cool­season
grasses, which grow most and are at their aesthetic best in the fall through spring. Consequently,
warm­season grasses are being used more often and are overseeded with ryegrass while dormant
in the winter to maintain an acceptable appearance.
The experimental design at Whispering Palms involved plots of cool­season and warm­
season turfgrasses, randomly assigned, with each having three replicates of irrigation water(potable and recycled waters) and three replicates of turfgrass species. Each plot was 20 ft by 20

III­27

ft for water treatment, with each subdivided into two subplots that were 20 ft by 10 ft for cool­and warm­season grasses, for a total of 12 plots with 24 subplots. Irrigation scheduling
Table III.D.3. Soil saturation extract analyses within and below the turfgrass root zone in Whispering Palms study(Shaw et al., 1995).
Within root zone
Below root zone
0–24­in. depths
ECe

Grass
species

LF

Irrigation type

Bermudagrass

0.48

Bermudagrass

0.52

Kikuyugrass
Kikuyugrass

SAR
0.5

24–36­in. depths
NO3­N

ECe

SAR
0.5

NO3­N

dS/m

mM/L

Mg/L

dS/m

mM/L

Mg/L

Potable water

3.3

5.8

0.2

2.5

3.8

2.1

Recycled water

3.0

5.6

1.0

2.2

5.0

3.1

0.48

Potable water

2.7

8.2

0.8

1.7

5.6

3.2

0.52

Recycled water

3.7

10.4

0.4

1.9

6.5

2.2

was conducted by the water budget method and involved real­time data about local weather fromthe California Irrigation Management Information System (CIMIS) weather station. The durationof irrigation was proportionally adjusted to the changes in reference ETo. Turfgrass ETo (ETc) in
inches per day was assumed as approximately equal to 0.6 ´ ETo for warm­season grasses and 0.8´ ETo for cool­season grasses.
Table III.D.2 presents the irrigation data. The cool­season grasses received an average of
105 in. of irrigation, and warm­season grasses received an average of 84 in. The total water
applied, irrigation plus rainfall, for cool­season grasses averaged 130 in. and for warm­season
grasses averaged 109 in. from January 1993 through November 1994. The calculated turf ETo forcool­season grasses was 74.5 in. and for warm­season grasses was 54.1 in. The difference
between total applied water and ETo is the drainage out of the root zone, which averaged 56 in.
for cool­season grasses and 54 in. for warm­season grasses. The LF, the ratio of drainage to total
applied water, averaged 0.42 for cool­season grasses and 0.50 for warm­season grasses.
Shaw et al. (1995) determined dissolved mineral constituents within the root zone andbelow the root zone of the turfgrasses. This database, along with the irrigation data, may be used
to estimate mass emission of nitrates and salts from the root zone into the vadose zone, theunsaturated zone above the groundwater table. Table III.D.3 presents soil data on EC, SAR, andNO3­N determined in the extracts of saturated soil pastes (a standard method of analyzing soil
samples [Richards, 1954]). The results show that, with a moderate LF of about 0.5, the EC ofextracts of soil paste in both recycled and potable water was comparatively low within the rootzone and below, even though the recycled water had an EC of 1.4 dS/m. These soil salinity values
are within the acceptable limits of salt tolerance for these turfgrasses. The FAO guidelines
indicate that a water of 1.4 dS/m may have slight to moderate restriction on use. The guideline isbased on an LF of 0.15 to 0.20 and is not plant specific. With an LF higher than 0.2, theIII­28

restriction on use may be lessened. At Whispering Palms, the LFs ranged from 0.4 to 0.5, except
during the rainy season, when LFs were about 0.7.
The results also show that NO3­N within the root zone and below for both potable andrecycled water treatments was low, although the recycled water had an NO3­N concentration of
11.2 mg/L. This finding indicates that turfgrasses are heavy feeders of N and can effectively
recover N from fertilizer and irrigation water. Clearly, N in the recycled water should beconsidered for meeting part of the N requirement of grasses. Shaw et al. (1995) believe that
excessive nitrate­N leaching losses can be avoided by adjusting fertilizer N applications andlowering the LF. The FAO guidelines suggest that Whispering Palms recycled water would haveslight to moderate constraints in use based on the total N content of the water.
Table III.D.4. Estimated mass loading of nitrates and salts from the root zone into the vadose zone at the
Whispering Palms study (after Shaw et al., 1995).
Loading value

Bermudagrass
Potablewater
544

Bermudagrass
Recycled water

Kikuyugrass
Potable water

Kikuyugrass
Recycled water

544

544

544

N content in water
lbs./acre

4

225

4

225

Total N applied
lbs./acre

548

769

548

769

NO3­N in drainage
mg/L

2.1

3.1

3.2

2.2

LF

0.48

0.52

0.48

0.52

N in drainage
lbs./acre

47

84

72

59

N drained
%

8.6

10.9

13.1

7.7

TDS in applied water
mg/L

630

900

630

900

TDS in applied water
tons/acre

5.59

9.05

5.86

9.32

TDS in drainage
mg/L

1,412

1,062

1,180

1,294

TDS in drainage
tons/acre

8.78

7.19

7.33

8.76

TDS drained
%

150

a

77

125

94

Applied N fertilizer
lbs./acreaInitial soil salinity (ECe) was 1.7 dS/m compared to 1.1 to 1.2 dS/m for the others.

III­29

The SARs for the plots of kikuyugrass irrigated with both potable and recycled waters
were slightly greater than the SARs for the plots of bermudagrass. Shaw et al. (1995) had someconcerns about loss of permeability and reduction in infiltration rates, but these were notobserved during the 23 months of the study. The sustainability of soil permeability over a longer
period has not been ascertained. Contrary to the FAO guidelines, the SAR and EC of the recycledwater in this study did not result in slight restrictions on use. If Figure III.A.3 is used as a guide,
the Whispering Palms recycled water falls within the no­reduction­in­permeability category. Itshould be noted that heavy foot and mower traffic on golf courses with fine­textured (clayey)soils sometimes leads to problems with water penetration.
Table III.D.4 presents the estimated mass loadings of nitrates and salts into the vadosezone based on volume of drainage past the root zone (Table III.D.2) and concentrations of nitrates
and salts found below the root zone (Table III.D.3). With regard to nitrates, the total N load
applied to the grasses was 548 lbs. per acre for the potable water application and 769 lbs. per acre
for the recycled water application. Applied N fertilizer was a major source, along with N in therecycled water. The N load discharged with the percolating water below the root zone was only 8
to 13% of the total N applied. This finding confirms that turfgrasses are heavy feeders of N. It
should be noted that clippings from mowed grasses remain on site and contribute to organic
matter in the soil, a small portion of which becomes bioavailable upon mineralization. In contrast,
the mass emission of salts differed from nitrates. The load of salts applied with irrigation water
ranged from 5.6 to 9.3 tons per acre. The salt concentration below the root zone ranged from
1,060 to 1,410 mg/L or a discharge load ranging from 7.2 to 8.8 tons/acre. Unlike N, most of theapplied salts—77 to 125%— were leached out of the root zone. The calculated deviations from
100% are considered acceptable for salt leaching due to the complex chemical reactivity of salts.
The bermudagrass irrigated with potable water was an exception with a 150% salt leaching. A
plausible reason for this is that the initial soil salinity in the plots of bermudagrass irrigated withpotable water had an ECe of 1.4 dS/m, while other plots had an initial soil ECe of 1.1 to 1.2 dS/m.
Shaw et al. (1995) monitored the aesthetic quality of the turfgrasses throughout the study,
using a standard turf­scoring procedure that involves a scale from 1, which equals dead turf, to 9,
which equals perfect color, texture, density, absence of pests, and overall quality. Both the cool­season and warm­season turfgrasses scored an average of about 6.5, indicating acceptable quality.
Turfgrasses are known to be relatively tolerant of Na+, Cl-, and B but are not well
documented in the literature. They are mowed at heights ranging from 1.5 to 3.0 in. for cool­season grasses and less than 1.0 in. for warm­season grasses. For both cool­season and warm­
season turfgrasses, the concentrations of Na+ in the soil extracts ranged from about 115 to 345

III­30mg/L and the concentrations of Cl- ranged from about 106 to 320 mg/L. Concentrations of B
ranged from about 0.25 to 0.6 mg/L in the extract of saturated soil pastes. Salts accumulating in
the leaf tips are removed during mowing, and consequently leaf tip burns from salts, Na+, Cl-, orB are not typically observed. However, there is some concern that leaving mulched mowedclippings on site can cause Na+, Cl-, and B to return to the soil, resulting in long­term increases ofthese constituents in the soil. The FAO guidelines for these specific ions indicate slight tomoderate restrictions on use of the recycled water for Na+ and Cl- and none for B.
This study demonstrated that recycled water can be beneficially used to irrigate
turfgrasses, thus conserving potable waters. Relatively few problems were observed in this 23­
month study. Shaw et al. (1995) further state that reliability of the quality of recycled waters isimportant. Any significant changes should be reported to the user of recycled water or to aprofessional landscape advisor, so that appropriate agronomic and water management options canbe taken to avoid problems. Variations in the quality of recycled water, the types of soil,
management practices, patterns of use, climate and expected quality of turfgrass should be notedwhen evaluating the benefits of using recycled water to irrigate golf courses. This case study
demonstrated that the FAO Water Quality Guidelines are a useful guide that is perhaps somewhat
conservative for the irrigation of turfgrasses. Nitrate leaching losses at this study’s site were kept
to a minimum, while salts were extensively leached out.

III.E. References
Asano, T., R. G. Smith, and G. Tchobanoglous. 1985. Municipal wastewater: treatment andreclaimed characteristics, p. 2­1–2­24. In G. S. Pettygrove and T. Asano (ed.), Irrigation with
Reclaimed Municipal Wastewater: a Guidance Manual. Lewis Publishers.
AWWA Research Foundation. 1993. Chloramine effects on distribution system materials. Projectno. 508). AWWA.
Ayers, R. S., and R. L. Branson (ed.). 1973. Nitrates in the Upper Santa Ana River basin in
relation to groundwater pollution. Agric. Experiment Station Bull. 861:1–60.
Ayers, R. S., and R. L. Branson. 1975. Water quality. Guidelines for interpretation of water
quality for agriculture. University of California Cooperative Extension report. University ofCalifornia.
Ayers, R. S., and D. W. Westcot. 1976. Water quality for agriculture. FAO irrigation anddrainage paper 29. Food and Agriculture Organization of the United Nations, Rome, Italy.
Ayers, R. S., and D. W. Westcot. 1985. Water quality for agriculture. FAO irrigation anddrainage paper 29, rev. 1. Food and Agriculture Organization of the United Nations, Rome, Italy.

III­31Ayers, R. S., and K. K. Tanji. 1981. Agronomic aspects of crop irrigation with wastewaters, p.
578–586. Proceedings of the Specialty Conference, Water Forum ’81, vol. I. American Society of
Civil Engineers, San Francisco, CA.
Eaton, F. M. 1950. Significance of carbonates in irrigation waters. Soil Sci. 69:123–133.
Langelier, W. F. 1936. The analytical control of anticorrosion water treatment. J.—Am. Water
Works Assoc. 34:1667–1684.
Lauchli, A., and E. Epstein. 1990. Plant responses to saline and sodic conditions, p. 113–137. In
K. K. Tanji (ed.), Agricultural Salinity Assessment and Management. ASCE manual no. 71.
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Lunt, O. R. (ed.). 1963. Proceedings, Agricultural Water Quality Research Conference.
University of California Water Resources Center.
Metcalf and Eddy. 2003. Wastewater Engineering Treatment and Reuse, 4th. ed. McGraw­Hill,
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Nakayama, F. S. 1982. Water analysis and treatment techniques to control emitter plugging, p.
97–112. In Proceedings of the Irrigation Association Exposition Conference.
National Academy of Sciences and National Academy of Engineering. 1972. Water quality
criteria. U.S. Environmental Protection Agency report no. EPA­R373­033.
Pettygrove, G. S., and T. Asano (ed.). 1986. Irrigation with Reclaimed Municipal Wastewater: a
Guidance Manual, p. 1­1–15­20, Appendices A–H. Lewis Publishers.
Pratt, P. F. 1972. Quality criteria for trace elements in irrigation waters. California Agricultural
Experiment Station.
Richards, L. D. (ed.). 1954. Diagnosis and Improvement of Saline and Alkali Soils. USDA
agricultural handbook no. 60. U.S. Department of Agriculture, Washington, DC.
Scofield, C. S. 1936. The salinity of irrigation water, p. 275–287, illustrations. Smithsonian
Institution Annual Report 1935. U.S. Government Printing Office, Washington, DC.
Shaw, D. A., A. C. Chang, V. A. Gibeault, M. McMaster, J. D. Oster, D. R. Pittenger, M. V.
Yates, and P. F. Zellam. 1995. Agronomic study of the use of reclaimed water for irrigation of
turfgrass and landscape plant materials. Phase II final report to Metropolitan Wastewater
Department. University of California Cooperative Extension, San Diego, Calif.
Sheikh, B., R. P. Cort, W. R. Kirkpatrick, R. S. Jaques, and T. Asano. 1990. Monterey
wastewater reclamation study for agriculture. Res. J. Wat. Pollut. Control Federation 2:216–226.
Tanji, K. K. (ed.). 1990. Agricultural salinity assessment and management. American Society of
Civil Engineers manual no. 71. American Society of Civil Engineers.
Tanji, K. K. 2002. Salinity in the soil environment, p. 21–51. In A. Lauchli and U. Luttge (ed.),Salinity: Environment—Plants—Molecules. Kluwer Academic Publishers, Dordrecht, The
Netherlands.

III­32

West Basin Municipal Water District. 2004. West Basin water recycling requirement, C.I. No.
7453. 2003 annual monitoring report summary, table 4, Title 22 reclaimed water monitoring.
West Basin Municipal Water District.
Wilcox, L. V. 1948. The quality of water for irrigation. U.S. Department of Agriculture technicalbulletin no. 962. U.S. Department of Agriculture, Washington, DC.

III­33

Chapter IV. Salinity Control in the Root Zone and Deep Percolation of
Salts from the Root Zone into Groundwater Basins
K. Tanji, S. Grattan, and B. Sheikh
IV.A. Root Zone Salinity
IV.A.1. LF and LR—Root Zone as a Whole
IV.A.2. LF and Profile Salt Distribution
IV.A.3. Soil Salinity as Affected by Irrigation and Rainfall
IV.A.4. Reclamation Leaching
IV.A.5. Pore Volume Reclamation Leaching
IV.B. More Complex Treatment of Soil Salinity
IV.B.1. Chemical Reactivity of Salts in Water in the Soil
IV.B.2. Equilibrium Chemical Model—WATSUIT
IV.B.3. Application of WATSUIT to Quartile Root Zone Salt Accumulation
IV.B.4. Application of Reactive Mixing Cell Model for Salt Accumulation and Leaching
IV.C. Concerns about Salt Loading into Regional Groundwater Basins
IV.D. Summary
IV.E. References
Since soil salinity reduces the availability of soil water to plants due to osmotic effects(Chapter III), salts in the root zone should be kept below the maximum level tolerated by plants
for optimal plant performance (Chapter V). When salinity in the root zone exceeds this level,
plants experience osmotic stress and their growth is adversely affected. In low­rainfall regions,
irrigating plants causes soluble salts to accumulate in the root zone, as most of the salts in theirrigation water remain in the soil after more or less pure water is lost to the atmosphere via
evaporation and transpiration (Chapter V). Excessive levels of salinity do not accumulate in theroot zone if sufficient leaching occurs: i.e., if rainfall and/or irrigation exceeds the water holding
capacity in the root zone and if soil water drains past the root zone, carrying salts with it.
Irrigation and drainage water management can play a significant role in keeping soil salinity
below the maximum level tolerated by plants. In this chapter, the principles of water and soil
salinity management, as well as their practical application, are covered. Included in the
appendices are a number of Excel­based hydrosalinity models that can be used to perform someof the calculations that follow. A specific model will be used when appropriate.

IV­1

IV.A. Root Zone Salinity
IV.A.1. LF and LR—Root Zone as a Whole
Leaching fraction (LF) is defined as the steady state (long­term) ratio of the depth ofdrainage water (Ddw) that drains past the root zone to the depth of irrigation water (Diw) that
infiltrates the root zone. The ratio of Ddw to Diw was formerly defined as the leaching requirement(LR) by the U.S. Salinity Laboratory (Richards, 1954) but presently is known as LF (LR will bedefined later),

LF =Diw - Det Ddw
=
Diw
Diw

(IV­1)In the absence of rainfall, the depth of drainage water is the difference between Diw andDet, depth of evapotranspiration (ET). Det, which is equivalent to ETc as defined in Chapter VIII,
is defined in this chapter by

Det = Deto* Kc(IV­2)

where Deto is the depth of reference ET or ETo (obtained, e.g., from a nearby CIMIS weather
station) and Kc is the crop coefficient.
The FAO Water Quality Guidelines (Ayers and Westcot, 1985) assumed an LF of 15 to
20%, and if Det can be estimated with Equation IV­2, the amount of water needed for irrigation,
Diw, can be obtained by rearranging Equation IV­1,

Di w =

Det(1 - LF )(IV­3)

In some quarters, distribution uniformity of water application (DU) is considered in
Equation IV­3 as

Diw =

Det
(1 - LF ) * DU

(IV­4)

IV­2

The DU with a well­managed irrigation system ranges from 0.70 to 0.95 (Tanji and
Hanson, 1990). Correcting for DU will lead to large values of Diw if the irrigation systems are notmaintained and operated to achieve high DU, resulting in excessive leaching in much of theirrigated land and root pathogens, such as Phytophtera. In some quarters, the DU is ignored inestimating depth of irrigation. Though a small portion of the irrigated land may be underirrigatedwhile ignoring the DU and plant performance may be adversely affected in that portion, ignoring
the DU is acceptable with respect to water conservation in irrigated agriculture. If, however, ahigh, uniform quality of appearance is desired, as in turfgrass and lawns, then the DU may beconsidered.
Illustrative example IV­1
What is the annual depth of irrigation required for a cool­season turfgrass (such as Kentucky
bluegrass) with annual ETo of 50.6 in. in Los Angeles and annual crop coefficient Kc of 0.80,
while assuming an LF of 0.20?

Det = Deto * Kc = 50.6 in. * 0.80 = 40.5 in.

Diw =

Det
40.5 inches== 50.6 inches
1 - LF
1 - 0.20

Handbook No. 60 (Richards, 1954) points out that salinity is inversely proportional to water in its
LR expression, i.e.,

LF =Ddw EC iw=
Diw EC dw(IV­5)ECiw
LF(IV­6)

Thus, ECdw isEC dw =The ET process evapoconcentrates soil water as more or less pure water is lost to the atmospherethrough transpiration and evaporation, resulting in an increased concentration of salt in the root
zone.

IV­3

Illustrative example IV­2
What is the EC of the water draining past the root zone if the irrigation water has an EC of 1.5
dS/m and if LF is 0.20?

EC dw =

EC iw 1.5 dS / m== 7.5 dS / m
LF
0.20

The steady­state salinity in the drainage water (ECdw) is 7.5 dS/m, and considering the root zone
as a whole, the EC of the soil water (ECsw) in the root zone is somewhere between ECiw in the soil
surface and ECdw in the bottom of the root zone. If a simple average between these two is
assumed, the average root zone salinity is 4.5 dS/m [(1.5 +7.5 dS/m)/2)]. This EC of 4.5 dS/m
represents the average root zone ECsw at field capacity (FC) soil moisture. FC refers to the soil
water status after adequate irrigation and when drainage stops or reduces to a low rate. Since salt
tolerance threshold values for plants are expressed as ECe, the EC of the extract from a saturated
soil paste, ECsw, needs to be converted to ECe. The conversion factor used is 0.5, assuming thatsoil saturation percentage (SP) is twice the soil water content at FC for most soil types. Thus, theaverage root zone ECe for this example is 2.25 dS/m (4.5 dS/m * 0.5) for an LF of 0.2 and ECiwof 1.5 dS/m.

LR is a plant­specific parameter. It is a prescribed value of leaching, so that root zone
salinity does not exceed the threshold salinity tolerance of the plant in question. This plant­
specific LR is defined as

LR =

EC iw
5 * EC a - ECiw

(IV­7)

where ECa is the plant­specific threshold soil salinity, above which yields decrease in the case ofcrops and above which performance is reduced in the case of landscape plants, and the factor “5”is an empirically derived factor to account for distribution of salts by soil depth (Rhoades, 1974).
Threshold salinity values for plants are reported in Chapter V.

IV­4

Illustrative example IV­3
What is the LR for Kentucky bluegrass that has a threshold salinity value ECa of 3.0 dS/m and isirrigated with water ECiw of 1.5 dS/m?

LR =

ECiw
1.5dS / m=
= 0.115 * EC a - EC iw (5 * 3.0 dS / m ) - 1.5dS / m(IV­8)The depth of annual applied water, Diw, to satisfy the LR of this plant is

Diw =

Det
40.5 inches== 45.5 inches
1 - LR
1 - 0.11(IV­9)

meaning that 5 in. of water in excess of Det will satisfy the LR.

Root zone
quartiles

Appliedwater
LF0, EC0

Wq1

Wq2

0.4 ET
LF1, EC1
0.3 ET
LF2, EC2

Wq3

Wq4

0.2 ET
LF3, EC3
0.1 ET
LF4, EC4

Figure IV.A.1. Crop root zone subdivided into quartiles with specified root water extraction pattern to calculate
for quartile LF and EC (after Ayers and Westcot, 1985).

IV­5

IV.A.2. LF and Profile Salt Distribution
The distribution of salts in the root zone as affected by root water extraction patterns, Diw,
Det, LFs, and ECiw, will now be examined. Figure IV.A.1 divides the root zone into quartiles (fourlayers) and assumes that most crop plants extract soil water to meet their seasonal ET with a 40–
30–20–10% water extraction pattern (Wq) in the root zone quartiles (Ayers and Westcot, 1985).
Based on the previously outlined ET evapoconcentration approach, the LF, the resulting EC at thebottom of each quartile, and the distribution of salts in the root zone can be estimated.

Illustrative example IV­4
What is the long­term salt distribution in the root zone of a cool­season grass uniformly sprinkler
irrigated with 52.4 in. of water/year (Diw) at proper intervals to meet the water needs of the grass,with water of 1.5 dS/m (ECiw) and ET of 41.9 in./year (Det), assuming that the root water
extraction pattern is 40–30–20–10% of ET (Wq)? Use Hydrosalinity Model 1 in the appendices.
Table IV.A.1 gives the illustrative computation. First, the LF of each root zone quartile(LFq) is calculated with Eq. IV­10 (given in Table IV.A.1), and then the EC of the soil waterleaving the root zone quartile (ECq) is calculated with Eq. IV­6 (given in Table IV.A.1). As wateris extracted in the root zone quartile, the LF decreases and the EC of the water draining from thequartile increases. The overall root zone LF is 0.20, and ECdw is 7.50 dS/m. Within the root zone
quartile, the EC of the soil water (ECsw) is assumed to be the average between water entering thequartile and water leaving the quartile; e.g., ECsw in the fourth quartile is the average between
5.34 (EC3) and 7.50 dS/m (EC4) or 6.42 dS/m. The average root zone ECsw for the soil profile asa whole is 3.99 dS/m [(1.5+2.21+3.41+5.34+7.5 dS/m)/5].
Figure IV.A.2 is a plot of the calculated values in Table IV.A.1 as the ECsw­1 curve with aroot water extraction pattern of 40–30–20–10% of crop ET in the root zone quartiles. This cool­season grass is assumed to have a rooting depth of 12 in., and thus each quartile is of 3­in.
increments. Curve ECsw­2 is for the same case, except the extraction pattern is 60–25–10–5% of
ET. Because the extraction in the first root zone quartile is higher (60 versus 40%), the ECsw inthe bottom of the quartile is slightly higher in ECsw­2 than in ECsw­1. But the ECdw (bottom of the
fourth quartile) is the same because the overall LF is the same.

IV­6

Table IV.A.1. LF and EC by root zone quartiles for surface irrigation.
Root­
zone
quartile

LFq =0,
surface

Diw - åWq Det( Eq IV - 10)Diw

52.4 - (0)41.9 52.4in
=
= 1.0
52.4
52.4in52.4 - (0.4)41.9 35.6in
LF1 === 0.6852.4
52.4in
LF0 =

1st

2nd

ECiw
( Eq IV - 6)
LFq

1.5dS / m
= 1.5dS / m
1.0
1.5dS / m
EC1 == 2.21dS / m
0.68
EC0 =

LF2 =

52.4 - (0.7)41.9 23.1in== 0.4452.4
52.4inEC2 =1.5dS / m
= 3.41dS / m
0.44

LF3 =

52.4 - (0.9)41.9 14.7in== 0.2852.4
52.4inEC3 =1.5dS / m
= 5.34 dS / m
0.28

LF4 =

52.4 - (1.0)41.9 10.5in== 0.2052.4
52.4inEC4 =1.5dS / m
= 7.50 dS / m
0.20

3rd

4th,
bottomECq =Root zone salinity with differing root water extraction
pattern8ECsw, dS/m

765

ECsw­14ECsw­2

3
2
1
0
0

2

4

6

8

10

12

14

Soil depth, inches
Figure IV.A.2. Calculated distribution of salinity in the root zone of a cool­season grass. Extraction pattern for
ECsw­1 is 40–30–20–10% and for ECsw­2, 60­25­10­5%.

IV­7Figure IV.A.3 contains a plot of salt profiles in which only the LF varies for a cool­season grass that has an annual ET of 41.9 in., is irrigated with water EC of 1.5 dS/m, and has aroot water extraction pattern of 60–25–10–5% of ET. This plot clearly shows that root zone
salinity is highly regulated by the LF, assuming there is no impediment to root zone drainage.
The threshold salinity of plants is given as average root zone salinity in the extract ofsaturated soil paste or ECe in dS/m. The data plotted in Figure IV.A.3 are in terms of ECsw, andthe conversion to ECe is made by multiplying ECsw by 0.5. The average root zone ECsw values for
LFs of 0.05, 0.10, 0.20, and 0.30 are 10.62, 6.64, 4.25, and 3.27 dS/m, respectively, which, whenconverted to average ECe, would be 5.32, 3.34, 2.12, and 1.64 dS/m, respectively. If the thresholdsalinity of a cool­season grass is assumed to be ECe of 3 dS/m, then using an ECiw of 1.5 dS/mwill require an LF slightly greater than 0.10—an LF of 0.11 to be exact (see Equation IV­8).

Salinity distribution with LF varied
35

ECsw, dS/m

30
25
LF=0.05
20

LF=0.1015

LF=0.20
LF=0.30

10
5
0
0

2

4

6

8

10

12

14

Soil depth, inches
Figure IV.A.3. Salinity profile for a cool­season grass irrigated with ECiw of 1.5 dS/m, ET of 41.9 in./year, and root
water extraction pattern of 60–25–10–5% of ET.

IV.A.3. Soil Salinity as Affected by Irrigation and Rainfall
Up to now, the effects of rainfall on root zone salinity and leaching were ignored. The
equations on water and salts extended for annual rainfall include one from Richards, 1954:

LF=
iw + rw(D + D ) - D
D
iw
rw
et =
dw
D +D
D +D
iw
rw
iw
rw

IV­8

(IV­11)

where Drw denotes depth of annual effective rainfall (infiltrated into the soil). The effective
annual rainfall is about 50% of annual rainfall for a typical amount of rainfall, ground cover, andtopographical slope on irrigated lands of California. In

ECiw+ rw =( D * EC ) + ( D * EC )
iw
iw
rw
rw
(D + D )iw
rw(IV­12)ECrw refers to EC of rainwater and ECiw+rw is the volume­weighted average EC of the mixed
supply water. These same equations may apply for a second source of supply water other than
rainwater, such as a blend of two irrigation waters of differing water salinities. A more precise
treatment can be realized if monthly to weekly values are used instead of seasonal data inequations IV­11 and IV­12.

Illustrative example IV­5
What is the long­term distribution of salts in the root zone of a cool­season grass, assuming thesame conditions as in Example IV­4 but with an effective annual rainfall of 8 in. and an EC ofrainwater of 0.01 dS/m? Use Hydrosalinity Model 2 in the appendices.
Table IV.A.4 shows that computations similar to those used in Table IV.A.1 are
employed to solve this problem. The EC of mixed supply water is

ECiw+ rw =( D * EC ) + ( D * EC ) (1.5 * 52.4) + (0.1 * 8.0)
iw
iw
rw
rw =
= 1.31 dS / m(D + D )52.4 + 8.0
iw
rw

Figure IV.A.4 plots the salt accumulation pattern computed in Table IV.A.2 and iscompared to that calculated in Table IV.A.1. The average root zone salinity (ECsw) is 4.0 dS/mwith irrigation water and 2.68 dS/m with irrigation water plus rainfall. The salt accumulation isless, as rainwater EC is very low. The LF is greater (0.31 versus 0.20), since 8.0 in. of effective
rainwater is added to the 52.4 in. of irrigation. Therefore, effective rainfall should be taken into
account when it is a significant fraction of the infiltrated water and salt accumulation is ofconcern. In California, since most rainfall occurs during the winter and most irrigation occurs inthe summer, the aforementioned calculations may differ slightly from actual calculations. Winterrains will leach the salts accumulated in the previous summer and fall months. These rains may
serve as reclamation leaching, if there is sufficient rainfall.

IV­9

Table IV.A.2. LF and EC by root zone quartiles for mixed supply irrigation waters.

LFiw + rw =( Diw + Drw ) - SWq Det( Diw + Drw )( Eq IV - 13)

EC q =

EC iw+ rw
LFiw + rw( Eq IV - 14)

LF0 =(52.4 + 8.0) - 0( 41.9) 60.4in== 1.0(52.4 + 8.0)
60.4inEC0 =1.31= 1.31 dS / m
1. 0

LF1 =

(52.4 + 8.0) - 0.4( 41.9) 43.6in== 0.72(52.4 + 8.0)
60.4inEC1 =1.31= 1.82 dS / m
0.72

LF2 =

(52.4 + 8.0) - 0.7( 41.9) 31.1in== 0.51(52.4 + 8.0)
60.4inEC2 =1.31= 2.57 dS / m
0.51

LF3 =

(52.4 + 8.0) - 0.9( 41.9) 22.7in== 0.38(52.4 + 8.0)
60.4inEC0 =1.31= 3.45 dS / m
0.38

LF4 =

(52.4 + 8.0) - 1.0(41.9) 18.5in== 0.31(52.4 + 8.0)
60.4inEC0 =1.31= 4.26 dS / m
0.31

ECsw, dS/m

Salt accumulation from irrigation water and irrigation water andrainfall
8
7
6
5
4
3
2
1
0

ECiw+rw
ECiw

0

2

4

6

8

10

12

14

Soil depth, inches
Figure IV.A.4. Comparison of salt accumulation patterns with 52.4 in. of EC iw of 1.5 dS/m and 52.4 of EC iw of 1.5
and 8.0 in. of ECrw (effective rainfall) of 0.01 dS/m.

IV.A.4. Reclamation Leaching
Leaching as a means of salt control in the root zone may take place with each irrigation
event or after a crop is harvested and before the next planting. Reclamation salt leaching may bedescribed by a simple mixing cell transport model (Tanji et al., 1967), in which

ECq, j = 0.5 * ( ECq, j - 1 + ECq - 1, j )(IV­15)where q is the space­related increment, such as root zone quartiles or a specified increment in thedepth of the soil, and j is the time­related increment or leaching event number. Equation IV­15

IV­10

states that the concentration of salt in a particular depth of soil and at a particular time is theaverage of the concentration of salt in that particular depth from a previous time (resident salt)
and the concentration of salt entering from a depth above at that particular time (invading salt).

Illustrative example IV­6
Given an initial soil salinity in 6­in. depth increments of a 48­in. clay loam soil profile with ECsw
of 10, 12, 18, 12, 6, 4, 4, and 4 dS/m, calculate the degree of reclamation leaching with water
having an ECiw of 1.5 dS/m.
Figure IV.A.5 gives the results of using Equation IV­15 with an initial salinity given as
curve j­1. If the soil texture is clay loam, it would have a field capacity of about 4 in. of water/ft
of soil or in this case 2 in. per 6­in. soil depth. This 2­in. depth of water is the increment ofreclamation leaching water applied. After leaching with one increment of ECiw of 1.5 dS/m, thesalt profile is given by curve “j,” two increments of leaching water by curve “j+1,” and so forth.
The salt bulge in the 18­in. soil depth is slowly displaced downward with each increment ofreclamation leaching. The average ECsw for the initial salt profile for each increment ofreclamation leaching is 8.75 (j­1), 8.35 (j), 7.82 (j+1), 7.14 (j+2), 6.37 (j+3), 5.57 (j+4), 4.80(j+5), and 4.10 dS/m (j+6). This model is applicable to leaching by rainwater or any other ECiw
water. Use Hydrosalinity Model 3 in the appendices.

Reclamation salt leachingECsw, dS/m

20
15
10
5
0
0

20

40

60

j­1
j
j+1
j+2
j+3
J+4
j+5
j+6

Soil depth, inches
Figure IV.A.5. Results of reclamation leaching for initial salt profile given by curve j­1 with ECiw of 1.5 dS/m. The
salt bulge at the 18­in. soil depth is displaced downward with each leaching water increment j, equivalent to a 2­
in. depth of reclamation water.

IV­11

IV.A.5. Pore Volume Reclamation Leaching
Reclamation leaching of constructed root zones established on modern sports fields andgolf greens with soil mixes and sand do not often behave in a manner similar to that of nativesoils. The constructed root zones often incorporate high­sand­content soil mixes of prescribed
depths, typically 12 to 14 in., layered profiles designed to perch the water table, and/or confinedroot zones with impermeable barriers that use a combination of subsurface irrigation/drainage
systems. Moreover, common turfgrass management practices such as light and frequent sandtopdressing result in an accumulation of high­sand­content root zones over a native soil baselacking subsurface drainage. The low­cation­exchange­capacity, high­sand­content root zone
mixtures result in a more rapid development of salt accumulation and stress symptoms than isfound in native clay and loam soil profiles and therefore require more frequent leaching events.
Thus, adaptation and modification of leaching protocols become necessary.
Carrow et al. (2000) utilize a leaching method based upon pore volume (PV), the total
pore space (Rhoades and Loveday, 1990), in the constructed root zone. Table IV.A.1 presents theestimated reclamation needs based on soil texture.

Table IV.A.1. Estimated reclamation leaching needs based on soil texture.
Soil texture

PV in %

No. of in. of waterper 12­in. soil to fill
to PV

Sand (>95% sand content)

35

4.2

Loamy sand

38

4.56

Sandy loam

42

5.05

Clays

50

6

Soil texture

PV equivalent ofwater required toleach 70% of totalasalts

Sand (>95% sand content)

0.7

Sandy loam

1.00–1.25

Loams

1.50–2.50

b
b

b
Clays
2.50–4.00
PV equivalent values are adjusted by Carrow, Huck, and Duncan based on experience.
b
Use higher values for 2:1 lattice shrink swell cracking clays and lower values for 1:1 noncracking clays.
a

IV­12

Illustrative example IV­7
What is the depth of water needed to leach salts on a high­sand (>95% sand) golf course or sports
field to a depth of 16 in. overlying a subsurface drainage tile lines? This example was contributed
by Mike Huck (personal communication).

A sandy soil texture has a PV of 35%, requiring a 4.20­in. depth of water per 12­in. soil depth tofill its PV. Thus, for a 16­in. reconstructed soil depth, 5.60 in. of water (4.20 in. of water ´ 16
in./12 in.) would be required. For these high­sand greens, a PV equivalent of 0.70 is used toachieve approximately 70% leaching of soluble salts. Therefore, 3.90 in. of water (5.60 in. ofwater ´ 0.70) applied would leach 70% of the salts across the 16­ in. soil depth.

IV.B. More Complex Treatment of Soil Salinity
In previous sections of this chapter, it has been assumed that salinity in the water is aconservative parameter; i.e., it does not chemically react. Strictly speaking, dissolved mineralsalts in waters are chemically reactive. For example, they participate in mineral dissolution,
precipitation reactions, and cation exchange reactions. This section describes some common
water chemical processes that affect salinity and the use of chemical equilibrium computermodels to appraise more quantitatively the chemical reactivity of waters.

IV.B.1. Chemical Reactivity of Salts in Waters in the Soil
The major chemical reactions occurring in the soil that affect salinity are the dissolution
and precipitation of such minerals as calcite (CaCO3) and gypsum (CaSO4∙2H2O) and theexchange of cations—Na, Ca, Mg, NH4, and K—between those soluble forms in the soil solution
and those forms adsorbed onto the soil exchange complex, which consists of negatively charged
clay minerals and soil organic matter.
Figure IV.B.1 depicts this chemistry of soil solutions (Tanji, 1990). Note that interactive
chemical reactions involve particular chemical ion species. For example, the dissolution of
gypsum (CaSO4∙2H2O) produces free calcium ions (Ca2+) and free sulfate ions (SO42−). The free
Ca ion may replace exchangeable magnesium ion on the soil exchange complex, and SO4 ions
may form the neutrally charged MgSO4 ion pair and monovalently charged NaSO4− ion pair. As
cation exchange and ion pair reactions occur, they raise the solubility of gypsum to a level higher
than that of the solubility of gypsum in distilled water. Because of this complexity and theinteractive nature of such soil chemical reactions, chemical equilibrium models are used toevaluate chemical speciation and the equilibrium chemistry of waters and soil solutions.

IV­13

Figure IV.B.1. Interactive chemical reactions in soil water systems (Tanji, 1990). The solution phase consists of+−completely dissociated ions such as Na as well as incompletely dissociated ion (ion pairs) such as NaSO4 .

IV.B.2. Equilibrium Chemical Models—WATSUIT
The Water Suitability Determination Model (WATSUIT) by Rhoades and Dell’Osso(1976) will be used first to evaluate equilibrium water chemistry in this section and then toevaluate root zone salt accumulation in the next section.
To illustrate the complex nature of interactive chemistry in soils, changes in waterchemistry resulting from the evapoconcentration of Colorado River water will be examined, using
WATSUIT. Evapoconcentration of waters in this computer model is evaluated by applying the
LF; i.e., an LF of 1.0 will have no evaporation, while an LF of 0.1 means the original volume ofwater has been evapoconcentrated 10­fold. As a first approximation, the concentration of salt isincreased 10­fold.
Table IV.B.1 presents the results of evapoconcentrating Colorado River water from 1­ to
20­fold. The column titled “River water” gives the initial concentration in milliequivalents perliter (meq/L) (WATSUIT uses combining chemical concentration units or meq/L), while
concentration in milligrams per liter (mg/L) is given in parentheses. The data for an LF of 1.0 are
the computed chemical equilibrium concentration with no evapoconcentration. Note that
Colorado River water is saturated with respect to calcite (CaCO3) and that this mineral
precipitates out of the water under equilibrium

IV­14

Table IV.B.1. Simulation results from WATSUIT on the chemistry of Colorado River water subjected to various
LFs with a fixed CO2 pressure of 0.01 atm (simulation runs by Tanji, 1999).

ConcnaRiver watera
meq/L
Evapoconcn. factor(ECF)
ECw ´ ECF,c dS/m
Calcd. EC, dS/m
Ca
Mg
Na
K
Na + K
Cl
CO3
HCO3
SO4
MgCO3
CaCO3b

1.27
6.95 (139)3.63 (44)3.35 (77)0.22 (9)3.57 (86)1.03 (37)3.73 (228)9.31 (447)

LF = 1.0

LF = 0.4

LF = 0.3

LF = 0.2

1.0

2.5

3.3

5.0

10.0

20.0

1.03

2.58

3.40

5.15

10.3

20.6

1.03
5.01
3.63

2.48
14.93
9.08

3.12
17.56
12.10

4.44
22.81
18.15

7.15
25.66
36.30

12.15
23.42
72.64

3.57
1.11
0.44
1.36
9.31

8.93
2.77
0.42
6.46
23.28

11.90
3.70
0.43
6.40
31.08

17.85
5.55
0.43
6.29
46.55

35.70
11.10
0.45
7.03
79.07

71.10
22.20
0.52
8.97
135.74

1.94
(97)

2.44
(122)

5.61
(280)

11.94
(597)

8.04

7.09

7.02

7.00

29.81
(1,490)14.03(1,207)7.03

65.11(3,256)50.47(4,340)
7.05

CaSO4∙2H2Ob
pH

LF = 0.1 LF = 0.05

a

All chemical concentrations are in meq/L; except those in parentheses are in mg/L.
The calcite levels and gypsum concentrations given in mg/L may be converted to pounds per acre­foot with a conversion
factor of 2.72.
cECw, evapoconcentration factor assumes salts are not reactive, i.e., no mineral precipitation.
bconditions at an LF of 1.0. As the river water is increasingly evapoconcentrated, calcite
precipitates in increasing amounts and the chemical speciation also changes. Calcite has a small
solubility product constant of 10-9 and thus is a very insoluble mineral. In contrast, gypsum has asolubility product constant of 10-5 and is a more soluble mineral than calcite. Therefore, gypsum
does not precipitate out until about an LF of 0.1, about a 10­fold evapoconcentration of initial
Ca2+ and SO42- ions.
Table IV.B.1 contains data regarding the chemical reactivity of Colorado River water.
Assuming salts are not reactive, the difference between the WATSUIT calculated EC and the EC´ ECF (initial ECiw ´ evapoconcentration factor) is due to mineral precipitation. The precipitationof calcite and gypsum with evapoconcentration may be viewed positively because they would
decrease salt accumulation in irrigated soils as seen in the next section.

IV.B.3. Application of WATSUIT to Quartile Root Zone Salt Accumulation
Figure IV.B.2 contains ECsw curves in the root zone quartiles when irrigation with
Colorado River water at an LF of 0.2 occurs. The curve labeled “EC, nonreactive” assumes thatsalts in this river water act conservatively as discussed in Chapter IV.B.2, while the curve labeledIV­15

“reactive” is predicted by WATSUIT, which considers reactive water chemistry. Reduced salt
accumulation in the reactive case is caused by the deposition of calcite and gypsum as irrigationwater is increasingly evapoconcentrated by root water extraction. The concentrations of calcite
forming in the root zone quartiles are plotted in meq/L, a range of values equivalent to about 100
to 600 ppm (mg/L = meq/L ´ mg/meq = meq/L ´ 50.04 mg/meq). The LF for the first to fourth
quartiles in this case is 0.68, 0.44, 0.28, and 0.20. The average ECsw for the nonreactive case is3.38 dS/m and for the reactive case is 2.34 dS/m. If one accounts for the natural chemistry of thewater and appropriate chemical reactions, the effective salinity in this Colorado River water isreduced by about 30%.
Figure IV.B.3 plots salt accumulation from the use of Colorado River water at LFs that
range from 0.05 to 0.40 (5 to 40% of infiltrated water) as calculated by WATSUIT. The average
ECsw values for LFs of 0.4, 0.3, 0.2, 0.1 and 0.05 are 1.77, 2.03, 2.34, 3.38, and 4.66 dS/m,
respectively. If the threshold salinity of the plants is known, the LFs can be managed to keep soil
salinity at a tolerable level during the use of Colorado River water.

ECsw, dS/m, and CaCO3,
meq/L

Comparison of rootzone salinity withreactive and nonreactive models
14
12
10
nonreactive

8

watsuit6

meq/LCaC03

4
2
0
0

2

4

6

Root zone quartiles
Figure IV.B.2. Comparison of root zone salt accumulation from irrigation with Colorado River water at an LF of
0.2, assuming on the one hand that salts in the water behave conservatively (nonreactive) and on the other handthat they are chemically reactive as predicted by WATSUIT. Also plotted is the concentration of calcite
precipitating as its solubility product constant is exceeded. The deposition of calcite reduces salt accumulationin the root zone quartiles.

IV­16

Root zone salt accumulation with LF varied
14

ECsw , d S/m

12
LF 0.410

LF 0.38

LF 0.2

6

LF 0.1

4

LF 0.05

2
0
0

1

2

3

4

5

Root zone quartiles
Figure IV.B.3. Salt accumulation from irrigation with Colorado River water at various LFs as predicted by
WATSUIT.

IV.B.3. Application of Reactive Mixing Cell Model for Salt Accumulation andLeaching
The reclamation leaching mixing cell model (IV.A.4) can be extended to consider more
flexible and dynamic vadose zone conditions (Tanji, 2000) by

EC q, j = 0.5 * ( EC q, j -1 + ( ECq - 1, j/ LF ))q(IV­16)In this model, there is no constraint on the number of increments of soil depth to be considered(such as quartile root zone), and each increment will be of specified length (inches or feet).
ECq,j−1 is the initial concentration of soil salinity in each soil depth, and accumulated salt may benonuniformly distributed in the soil profile. The evapoconcentrating effect of root water
extraction in each depth increment is considered by LFq. If there is no root water extraction at thatsoil depth, LFq assumes a value of unity (1.00) and salt transport can be calculated below therooting depth.

IV­17

Traditional root­water extraction patterns are typically given in root zone quartiles (fourdepths) in the rooting soil depth. They could be subdivided further into any number of depths,
such as eight depth increments instead of four. When water infiltrates the soil surface, the ECq−1,jin Equation IV­16 is the salinity of the applied water of a given source or the salinity of multiple
sources of water, which is the volume­weighted average ECiw, as in Equation IV­12. This model
is applicable to reclamation leaching, too, should one assume LFq is unity and reduce EquationIV­16 to IV­15.
Equation IV­16 may be further extended to consider the chemical reactivity of waters.
Given the mineral precipitation data of Colorado River water in Table IV.B.1, the reduction inaccumulated salts and EC as a function of LF can be estimated. Table IV.B.2 contains calcite andgypsum precipitation data from Table IV.B.1. The precipitation of these minerals will reduce theresulting EC upon evapoconcentration of Colorado River water. For instance, the EC of the water
subjected to an LF of 0.1, assuming no chemical reactions, is 10.3 dS/m. The estimated reductionin EC from mineral precipitation is 3.67 dS/m for an LF of 0.1, and the resulting EC after
chemical reaction is 6.63 dS/m. The reduction in ECs is quite substantial at smaller LFs.
Figure IV.B.4 plots the reduction in EC in Colorado River water due to mineral
precipitation at various LFs. A curve fitting this plot yields ECsw = -0.0265/LF2, which is theninserted into Equation IV­16 to account for chemical reactivity of Colorado River water as

ECq, j = 0.5 * (ECq, j -1 + [(ECq - 1, j
0.0265
)-(
)]
LFq
LF 2

(IV­17)

Table IV.B.2. Mineral precipitation with evapoconcentration of Colorado River water and estimates of reduction of
accumulated salt concentration. The ECiw of water is 1.03 dS/m.

Calcite precipitation, mg/L(row 1)Gypsum precipitation, mg/L(row 2)Sum of precipitation, mg/L(row 3 = 1 + 2)a

LF = 1.0

LF = 0.4

LF = 0.3

LF = 0.1

LF =
0.05

97

122

280

1,490

3,256

1,207

4,340

97

122

280

2,697

7,596

Estimated EC reduction
from precipitation, dS/m(row 4 = 3/735)a

0.132

0.166

0.381

3.669

10.335

Nonreactive
evapoconcentration, dS/m(row 5 = ECiw/LF)

1.03

2.575

3.433

10.3

20.6

Reactive
evapoconcentration,
dS/m (row 6 = 5−4)

0.898

2.409

3.052

6.631

10.265

Reader should assume that 735 mg/L equals 1 dS/m.

IV­18

Reduction in ECsw due to mineral deposition
0
0

0.2

0.4

0.6

0.8

1

1.2

ECsw, dS/m.

­2
­4
­6
­8
­10
­12
Leaching fraction
Figure IV.B.4. Reduction in EC due to mineral precipitation with evapoconcentration (decreasing LF) of Colorado
2
River water. Best curve fitting gives EC= -0.0256/LF .

Salt accumulation from irrigation with ECiw of 1.5 dS/mand LF of 0.20

ECsw, dS/m.

12
10
0 in

8

10.5 in6

21.0 in4

52.4 in

2
0
0

5

10

15

20

25

30

35

Soil depth, inches
Figure IV.B.5. Salt accumulation in soil irrigated with water of EC 1.5 dS/m having an initial soil salinity given by“0 in” (0 in. of irrigation). Crop ET is 41.9 in,, and total irrigation is 52.4 in., resulting in an LF of 0.20. The rooting
depth is 21 in., with a water extraction pattern of 30–30–15–10–5–5–5%.

IV­19

Illustrative example IV­8
What is the degree of salt accumulation in a 30­in. soil profile in which a cool­season grass isgrown with a water EC of 1.5 dS/m? The crop ET is 41.9 in., and total irrigation is 52.4 in.,resulting in an LF of 0.20. The rooting depth is 21 in. with root water extraction pattern of 30–30–
15–10–5–5–5% of ET. The initial soil salinity values in 3­in. depth increments are 1.5, 2.5, 3.0,
3.5, 4.6, 5.9, 7.4, 9.7, 8.7, and 5.9 dS/m. Use Hydrosalinity Model 4 in the appendices.
Figure IV.B.5 contains the initial soil salinity (ECsw) given by the curve labeled “0 in.”
The hydrosalinity model calculates salt distribution after each 5.24­in. irrigation in this particular
problem. After 10.5 in. of irrigation, the salt bulge below the root zone has been displaced. By 21
in. of irrigation, the salt profile is approaching the final salt profile that one finds after 52.4 in. of
irrigation.

IV.C. Concerns about Salt Loading into Regional Groundwater Basins
The Southern California Salinity Coalition is concerned about regional salt balance in
California’s south coastal region. There is also a Water Replenishment District that is concernedwith salt loading into its groundwater basins. This admittedly complex problem will be addressedin this section only relative to the use of recycled water for irrigating landscapes.
Water from irrigation and rainfall not used by plants that infiltrates past the root zone are
known as deep percolation. This deep percolation carries salt into the groundwater basin. Suchtransport of salt into a groundwater basin may or may not be of crucial significance. It is a matterof concern where irrigation occurs above an unconfined aquifer with a relatively shallow watertable. This phenomenon is less the case where salt from a farm or from landscaped fields deeply
percolates into a salt sink that is used on a limited basis or where the aquifer is confined below a
deep aquiclude and there is little seepage across this barrier.
Whatever the site­specific circumstances, it is necessary to address the ability of saltleaching below the root zone to eventually accumulate in the subsoil or in the aquifer underlying
it. The length of time it takes for the accumulation of salt in groundwater basins to reach serious
levels depends on a number of factors, including natural and artificial recharge to the aquifer,amount of rainfall, extraction of water with wells, interflow to adjoining aquifers, and the effectsof such local hydrogeophysical characteristics as vertical faults.
Consequently, deep percolation of salts into regional groundwater basins cannot be
straightforwardly determined to always or never be a problem. Under certain conditions,however, it can become a significant problem if not mitigated.

IV­20

Depending on the flow path and depth to the water table in an unconfined aquifer, deep
percolation through the vadose zone may take from months to decades to reach the surface of thesaturated zone. The extent of deep percolation may be estimated as the difference between
infiltrated water and ET. Deep percolation is usually estimated as the LF, a decimal fraction of
the ratio of deep percolation and infiltrated water, where deep percolation is the difference
between infiltrated water and ET losses. The amount of deep percolation in landscape irrigation
may vary widely. Intensively irrigated turf and lawns with shallow rooting systems may have an
LF that ranges from 0.4 to 0.6. Less intensively irrigated landscape covered by deep­rooted trees
and shrubs may have an LF ranging from 0.1 to 0.4. When recycled water is used instead of
potable water to irrigate a landscape, the LFs are expected to be about the same or slightly higher.
A case study presented in Chapter III compared the extents of nitrate and salt leaching for potablewater irrigation and recycled water irrigation of turfgrasses.
Assuming that salts are nonreactive in the root zone, under steady­state conditions, themass of salts present in deep percolation from the root zone would be the same as that introducedby irrigation and rainfall. Due to the concentrating effects of ET, however, the concentration ofsalt in deep percolation is greater. The degree of evapoconcentration may be approximated fromthe product of salt concentration in the applied water and the reciprocal of LF, i.e., 1/LF (Tanji,
2002). For instance, if the EC of the water (ECw) is 1 dS/m, the EC of deep percolation from theroot zone for an LF of 0.6 is 1.7 dS/m (1 dS/m ´ 1/0.6), for an LF of 0.4 is 2.5 dS/m, and for an
LF of 0.2 is 5 dS/m (see previous sections of this chapter for further details on soil salinity). If thesalts are also assumed to be nonreactive in the vadose zone beneath the root zone, the EC of thewater reaching the water table would remain the same as that of the root zone deep percolation.
But typically, there is a net accrual of dissolved mineral salts in deeply percolating water throughthe vadose zone and rarely a net deposit of salts (Tanji et al., 1967).
Salt mass, which is the product of salt concentration and volume of water, may beobtained by converting EC in dS/m to total dissolved solids (TDS) in mg/L and surface depth ofwater into volume per unit area irrigated. For instance, salt concentration is obtained by a factor
of 634 mg of TDS/L per dS of EC/m (sometimes a factor of 735 is used), so that an EC of 1 dS/m
contains 634 mg/L. The concentration of salts in deep percolation per acre­foot (ac­ft) of water(Cdp) will be the product of salt concentration (634 mg of TDS/L) and the factor 0.00126 ton ofsalt per ac­ft of water per mg of TDS/L or 634 ´ 0.00126 or 0.8 ton of salt per ac­ft. The surface
depth of deep percolation (Ddp) is obtained from the product of LF and infiltrated irrigation water(Diw). If seasonal Diw is assumed to be 5 ft and LF to be 0.4, the Ddp is 0.4 ´ 5 ft or 2 ft and thevolume of deep percolation per unit area (Vdp) irrigated will be 2 ac­ft/acre. Finally, the massIV­21

loading of salts in deep percolation (Mdp) is the product of salt concentration (Cdp) and volume perunit area (Vdp). For this example, if Cdp is 0.8 tons per ac­ft and Vdp is 2 ac­ft/ac, the seasonal Mdp
is 0.8 ton salt per ac­ft 2 ac­ft/ac of irrigated land or 1.6 tons per acre.
When landscapes previously irrigated with potable waters are irrigated with recycledwaters, the concentration and mass of salt in deep percolation may be slightly higher because of
the residual accrual of dissolved mineral salts in recycled water. The concentration of such salts
in domestic recycled waters is typically 150 to 400 mg/L higher than in potable water for an EC
increase of about 0.2 to 0.6 dS/m (Asano et al., 1985). Hence, the mass loading of salts into thegroundwater basin from irrigating with recycled water is slightly greater than the mass loading ofsalts from irrigation with potable waters. And salt loading into the groundwater basin would
increase even more if previously unirrigated land is irrigated. The increase in mass loading isbased on the assumption that the salts in irrigation water do not react with the minerals in thestrata through which they percolate.
Assuming that all of the salts arriving in irrigation water will ultimately reach theunconfined groundwater aquifer and that complete blending with the aquifer waters occurs, it ispossible to compute the equilibrium concentration increase for salts (or any specific constituent)
after decades of time during which irrigation with recycled water continues at a constant rate. An
Excel­based program was developed for an unconfined aquifer in Santa Clara Valley (B. Sheikh,personal communication), in which characteristics of the aquifer, rainfall, and a range of
irrigation acreages were entered to determine the ultimate impact on groundwater quality. This
program, for the most conservative scenario, calculates the acreages that can be irrigated for eachgiven recycled water quality without adverse impact.
The quality of deep percolation water from the root zone may, in fact, differ from that of
the applied water if salts are reactive, for instance, due to net mineral precipitation or net mineraldissolution. Applied water is evapoconcentrated in the soil solution as more or less pure water islost to the atmosphere during ET and the salts in the water remain in the soil solution, where they
concentrate during the drying phase of irrigation. The solubility product constants of sparingly
soluble salts may be exceeded, and mineral precipitation may take place. The minerals that
predominantly precipitate in irrigated soils are calcium carbonate (CaCO3) and gypsum(CaSO4∙2H2O). Other minerals that might precipitate include magnesium carbonate, calcium
phosphate minerals, and silicate minerals. During the wetting phase of irrigation, the more soluble
soil minerals present, such as gypsum and calcic feldspars, may dissolve. Reducing the LF
generally reduces the mass of salts in deep percolation because of mineral precipitation (Rhoades
et al., 1974). Within the flow path of deep percolation into the vadose and saturated zones, theIV­22

quality of the groundwater may be subject to change, depending on the chemistry of thesubstratum materials (Tanji et al., 1967). Assessment of mass loading of reactive salts will requirea geochemical model coupled to a transport simulation model (Tanji, 2002).
In summary, the mass loading of salts into the groundwater basin from irrigatinglandscapes with recycled water is expected to be somewhat different from that when irrigatingwith potable water. Depending on whether salts are reactive in the flow path due to mineral
precipitation (a salt sink) or mineral dissolution (a salt source), the mass loading of salts could beless when mineral precipitation dominates and greater when mineral dissolution dominates. Thus,
it would be imprudent to predict the combined net effect of salt loading and precipitation or
dissolution on the groundwater for all situations without precise site­specific knowledge of
geochemistry and recycled water characteristics. Currently, the Santa Clara Valley Water District,in collaboration with the California Department of Water Resources and the University ofCalifornia–Davis, is conducting a field study to determine the actual impacts of irrigation withrecycled water on soil water chemistry as leachate moves beyond the root zone toward an
unconfined water table (Ashktorab, 2005). The results of that study are expected to become
available in 2007.

IV.D. Summary
Salts tend to build up in the root zone of actively transpiring plants because more or lesspure water is lost to the atmosphere through evaporation and transpiration while dissolved
mineral salts in the irrigation water remain in the soil solution. One principal means of controllingroot zone salinity is by LF, which is defined as the ratio of water draining past the root zone andthe applied water. For most waters and most plants, an LF of 0.15 to 0.20 is more than adequate
to keep soil salinity at less than harmful levels (Ayers and Westcot, 1985).
This chapter covered the principles and applications of LF. The FAO approach ofcomputing salt accumulation in quartile root zone by considering the root­water extraction
pattern, the LF, and the EC of applied water was covered in detail. The impacts of rainfall on saltleaching and/or mixed­quality supply waters as well as reclamation salt leaching were also
considered. Simple Excel­based hydrosalinity models were used to demonstrate these concepts
and practices. These models assume salinity to be a conservative parameter, i.e., not a chemicallyreactive parameter. This assumption on salinity may be appropriate for conditions of high LFs(i.e., >0.3) and/or for waters that do not tend to form calcite and gypsum upon
evapoconcentration.

IV­23

More complex aspects of root zone salinity were addressed, including a chemical
equilibrium model (WATSUIT) and its use in quartile root zone salt accumulation. WATSUIT
was also used to assess precipitation of calcite and gypsum as a function of LF for Colorado
River water. This data was used to develop a simplified reactive salt accumulation model, which
was incorporated into a mixing cell model, an Excel­based model applicable to more than quartile
root zone salt accumulation.

IV.E. References
Asano, T., R. G. Smith, and G. Tchobanoglous. 1985. Municipal wastewater: treatment andreclaimed characteristics, p. 2­1–2­26. In G. S. Pettygrove and T. Asano (ed.), Irrigation with
Reclaimed Municipal Wastewater: a Guidance Manual. Lewis Publishers.
Ashktorab, H. 2005. Personal communication, July 27, 2005.
Ayers, R. S., and D. W. Westcot. 1985. Water quality for agriculture. FAO irrigation anddrainage paper 29, rev. 1. Food and Agriculture Organization of the United Nations, Rome, Italy.
Carrow, R. N., M. Huck, and R. R. Duncan. 2000. Leaching for salinity management of turfgrasssites. USGA Green Section Rec. 38:15–24.
Rhoades, J. D. 1974. Drainage for salinity control, p. 433–468. In J. van Schilfgaarde (ed.),Drainage for Agriculture. Agronomy monograph no. 17. American Society of Agronomy,
Madison, WI.
Rhoades, J. D., J. D. Oster, R. D. Ingavalson, J. M. Tucker, and M. Clark. 1974. Minimizing thesalt burdens of irrigation drainage waters. J. Environ. Qual. 3:311–316.
Rhoades, J. D., and G. P. Dell’Osso. 1976. Water Suitability Determination Model (WATSUIT).
Revised by W. J. Alves, 1989. U.S. Salinity Laboratory.
Rhoades, J. D., and J. Loveday. 1990. Salinity in irrigated agriculture, p. 1091–1142. In B. A.
Stewart and D. R. Nielsen (ed.), Irrigation of Agricultural Crops. Agronomy monograph no. 30.
American Society of Agronomy, Madison, WI.
Richards, L. D. (ed.). 1954. Diagnosis and Improvement of Saline and Alkali Soils. USDA
agricultural handbook no. 60. U.S. Department of Agriculture, Washington, DC.
Tanji, K. K. (ed.). 1990. Agricultural salinity assessment and management. American Society of
Civil Engineers manual no. 71.
Tanji, K. K. 2000. Hydrosalinity model for non­cracking soils. Coachella Valley Water District.
Tanji, K. K. 2002. Salinity in the soil environment, p. 21–51. In A. Lauchli and U. Luttge (ed.),Salinity: Environment—Plants—Molecules. Kluwer Academic Publishers, Dordrecht, The
Netherlands.

IV­24

Tanji, K. K., L. D. Doneen, and J. L. Paul. 1967. Quality of percolating waters. III. The quality ofwater percolating through stratified substrata, as predicted by computer analyses. Hilgardia
38:319–347.
Tanji, K. K., and B. R. Hanson. 1990. Drainage and return flows in relation to irrigation
management, p. 1057–1088. In B. A. Stewart and D. R. Nielsen (ed.), Irrigation of Agricultural
Crops. Agronomy monograph no. 30. American Society of Agronomy, Madison, WI.

IV­25

Appendices: Hydrosalinity Excel Models
Hydrosalinity Excel Model 1. LF and ECsw in root zone quartile FAO model.
Hydrosalinity Excel Model 2. LF and ECsw in root zone quartile FAO model with
mixed supply water, e.g., rainwater and irrigation water.
Hydrosalinity Excel Model 3. Reclamation leaching—mixing cell model of a salt­
affected soil profile.
Hydrosalinity Excel Model 4. Reactive salt accumulation—mixing cell model for
irrigated soil profiles.

IV­26

Appendix: Hydrosalinity Model 1
Hydrosalinity Model 1 for Illustrative Example IV-4.
Example IV-4:
What is the long-term salt distribution in the root zone of a cool-season grass uniformily sprinkler
irrigated with 52.4 in./yr (Diw) at proper intervals to meet the grass's water needs with water of 1.5
dS/m (ECiw) and ET of 41.9 in./yr (Det), while assuming that the root water extraction pattern is 40–30–
20–10% of ET?
Computational model Eq. IV-10
LFq = (Diw - ΣWqDet)/(Diw)

Computational model Eq. IV-6
ECq = ECiw/LFq

Computational model Eq. IV-2
Det = Deto * Kc

Depth of rooting of cool-season grasses
Annual bluegrass = 0.08–0.33 ft
Kentucky bluegrass = 0.5–1.5 ft
Perennial ryegrass = 0.5–1.5 ft
Tall fescue = 1.5–3.0 ft
Mo.
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Avg.
Total

Kc

ETo (in.) ET (in.)
0.61
2.2
1.342
0.64
2.6
1.664
0.75
3.7
2.775
1.04
4.7
4.888
0.95
5.5
5.225
0.88
5.9
5.192
0.94
6.1
5.734
0.86
6.1
5.246
0.74
5.3
3.922
0.75
3.9
2.925
0.69
2.6
1.794
0.6
2
1.2
0.7875 4.216667 3.49225
41.907

Computations (codings are embedded)
Quartile
LF
ECsw
ECe
0
1
1.5
0.75
1 0.680153 2.205387 1.102694
2 0.440267 3.407022 1.703511
3 0.280344 5.350579 2.675289
4 0.200382 7.485714 3.742857
Avg.
3.98974 1.99487

LF = Leaching fraction
q = Quartile soil depth interval
LFq = Calculated LF in quartile depth
Diw = Depth of irrigation water
Wq = Root water extraction patternDet = Depth of evapotranspiration
ECq = Calculated EC in quartile depth
ECiw = EC of irrigation water
Deto = Depth of reference ET (ETo)Kc = Crop coefficient

Root zone divided into 4 soil depth
increments (quartile)

Input data
Diw
Det
Wq0
Wq1
Wq2
Wq3
Wq4
ECiw

52.4
41.9
0
0.4
0.3
0.2
0.1
1.5

NOTE: Any changes made in the input data
will cause new values to be calculated forcomputations and plottings.

ECsw = EC in soil water at field capacity
ECe = EC in extract of saturated soil paste

HM1-1

EC, dS/m

Calculated root zone salinity with ECiw of 1.5 dS/mand LF of 0.2
8
7
6
5
4
3
2
1
0

ECsw
ECe

0

1

2
3
Quartile root zone

HM1-2

4

5

Appendix: Hydrosalinity Model 2

Hydrosalinity Model 2 for Illustrative Example IV-5
Example IV-5:
What is the long-term distribution of salts in the root zone of a cool-season grass, assuming thesame conditions as for Illustrative Example IV-4 but with an effective annual rainfall of 8 in. andan EC of rainwater of 0.01 dS/m?
Illustrative Example IV-4:
What is the long-term salt distribution in the root zone of a cool-season grass uniformily sprinkler
irrigated with 52.4 in./yr (Diw) at proper intervals to meet the grass's water needs with water of 1.5
dS/m (ECiw) and ET of 41.9 in./yr (Det) and assuming that the root water extraction pattern is 40–30–
20–10% of ET?
Computational model: Eq. IV-13
LFiw+rw = ((Diw + Drw) -ΣWq*Det)/(Diw + Drw)

Co
putat o a model:
ode Eq.
q IV-14
Computational
ECq = ECiw+rw/LFiw+rw

Computational model: Eq. IV-2
Det = Deto * Kc

LFiw+rw = LF of combined irrigation andrain waters
Diw = Depth of irrigation water
Drw = Depth of rainwater
Wq = Root water extraction patternDet
et = Depth
ept o
of e
evapotranspiration
apot a sp at o
ECq = Calculated EC in quartile depth q
ECiw = EC of irrigation water
ECrw = EC of rainwater
ECiw+rw = Average EC of mixture ofirrigation and rain water
Kc = Crop coefficient
Deto = Depth of Eto

Computational model: Eq. IV-12
ECiw+rw = (Diw*ECiw + Drw*ECrw) / (Diw + Drw)

Depth of rooting of cool-season grasses
Annual bluegrass = 0.08–0.33 ft
Kentucky bluegrass = 0.5–1.5 ft
Perennial ryegrass = 0.5–1.5 ft
Tall fescue = 1.5–3.0 ft
Mo.
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct

Kc
0.61
0.64
0.75
1.04
0.95
0.88
0.94
0.86
0.74
0.75

ETo (in)ET (in)
2.2
1.342
2.6
1.664
3.7
2.775
4.7
4.888
5.5
5.225
5.9
5.192
6.1
5.734
6.1
5.246
5.3
3.922
3.9
2.925

Root zone divided into 4 soil depth
increments (quartile)

Input data
Diw
Det
Wq0
Wq1
Wq2
Wq3
Wq4
ECiw
Drw
ECrw

HM2-1

52.4
41.9
0
0.4
0.3
0.2
0.1
1.5
8
0.1

Nov
Dec
Avg.
Total

0.69
2.6
0.6
2
0.7875 4.216667

1.794
1.2
3.4922541.907

ECiw+rw

1.31

NOTE: Any changes made in the input data
will cause new values to be calculated forcomputations and plottings.

Computations (codings are embedded)
IV-5
IV-5
IV-4
IV-4
Quartile
LF
ECsw
ECe
ECsw
ECe
0
1
1.31
0.655
1.5
0.75
1 0.722517 1.813107 0.906554
2.21
1.105
2 0.514404 2.546637 1.273318
3.41
1.705
3 0.375662 3.487175 1.743587
5.34
2.67
4 0.306291 4.276973 2.138486
7.5
3.75
Avg.
2.686778 1.343389
3.992
1.996
ECsw = EC in soil water at field capacity
ECe = EC in extract of saturated soil pasteEC, dS/m

Calculated soil salinity for Case IV-5 (ECiw+rw of 1.31
dS/m and LF of 0.31) and Case IV-4 (ECiw of 1.5 dS/mand LF of 0.2)
8
7
6
5
4
3
2
1
0

IV-5 ECsw
IV-4 ECsw

024Root zone quartiles

HM2-2

6

Appendix: Hydrosalinity Model 3

Hydrosalinity Model 3 for Illustrative Example IV-5
Example IV-5:
A clay loam soil profile is salt affected and requires reclamation leaching. The
ECiw of the water available for reclamation is 1.5 dS/m, and the EC of soil water (ECsw) in thesoil profile in 6-in. depth increments is 10, 12, 18, 12, 6, 4, 4, and 4 dS/m. What will be thesalinity in this profile if about 1 ft. of reclamation leaching is applied?
Computational model: Eq. IV-15 (mixing cell transport model)
ECq,j = 0.5 * (ECq,j-1 + EC q-1,,j)EC = EC of soil waterq = Specified space (soil depth) increment in inches
j = Time increment or leaching event number
Eq. IV-15 states that the salt concentration in a particular soil depth q and a particulartime j is the average of salt concentration from a previous time (resident salt) and salt
concentration entering from a soil depth above (q-1) at that particular time (invading salt).
Calculated EC is ECsw or EC at field capacity soil moisture.
Soil texture
Sand
Loamy sand
Sandy loam
Loamy sandSilt loam
Sandy clay loam
Sandy clay
Clay loam
Silty clay loam
Silty clay
Clay

Field capacity
In. of water per ft of soil
1.2
1.9
2.5
3.2
3.6
3.5
3.4
3.8
4.3
4.8
4.8

Initial values
Soil depth ECsw (dS/m)
0–6 in.
10
6–12 in.
12
12–18 in.
18
18–24 in.
12
24–30 in.
6
30–36 in.
4
36–42 in.
4
42–48 in.
4
ECiw

Assume that this clay loam soil has a field
capacity of 4 in. of water per ft of soil or
2 in. of water per 6 in. of soil.
The depth of water applied will be in 2-in.
increments for this case.

NOTE: Any changes made in the input data will automaticallycause new values to be calculated in the computations below andthe plot.

1.5 dS/m

HM3-1

Computations:
Soil depth j - 1 (0 in.) j (2 in.)j + 1 (4 in.) j + 2 (6 in.) j + 3 (8 in.) j + 4 (10 in.) j + 5 (12 in.) j + 6 (14 in.)
6
10
5.75
3.625
2.56252.03125 1.765625 1.6328125 1.5664063
12
12
8.875
6.25
4.40625
3.21875 2.4921875
2.0625 1.8144531
18
18
13.4375
9.84375
7.125 5.171875 3.8320313 2.9472656 2.3808594
24
12 12.71875 11.28125 9.203125
7.1875 5.5097656 4.2285156 3.3046875
30
6 9.359375 10.320313 9.7617188 8.4746094 6.9921875 5.6103516 4.4575195
36
4 6.6796875
8.5 9.1308594 8.8027344 7.8974609 6.7539063 5.6057129
42
4 5.3398438 6.9199219 8.0253906 8.4140625 8.1557617 7.454834 6.5302734
48
4 4.6699219 5.7949219 6.9101563 7.6621094 7.9089355 7.6818848 7.1060791
Avg.
8.75 8.3537598 7.8168945 7.140625 6.3703613 5.5692444 4.7965088 4.0957489

Ecswm dS/m

Reclamation leaching with ECiw of 1.5 dS/m of a saline soil
with 2-in. leaching increments
20
18
16
14
12
10
8
6
4
2
0

j - 1 (0 in.)j (2 in.)j + 1 (4 in.)j + 2 (6 in.)j + 3 (8 in.)j + 4 (10 in.)j + 5 (12 in.)

0

20

40
Soil depth, in.

HM3-2

60

j + 6 (14 in.)

Appendix: Hydrosalinity Model 4
Hydrosalinity Model 4 for Illustrative Example IV-6
Example IV-6:
What is the degree of salt accumulation in a 30-in. soil profile in which a cool-season grass isgrown with a water EC of 1.5 dS/m? Assume that salts in the applied water are reactive using thechemical reactivity function for Colorado River water. The crop ET is 41.9 in., and total irrigation
is 52.4 in., resulting in an LF of 0.20. The rooting depth is 21 in., with a root water extraction
pattern of 30–30–15–10–5–5–5% of ET. The initial soil salinity in 3-in. soil depth increments is 1.5,
2.5, 3.0, 3.5, 4.6, 5.9, 7.4, 9.7, 8.7, and 5.9 dS/m.
Computational model Eq. IV-17
ECq,j = 0.5*(ECq,j-1+((ECq-1,,j/LFq)-(0.0265/LF^2))
Eq IV-15
ECq,j = 0.5*(ECq, j-1 + ECq-1,j)Chemical reactivity function for Colorado River water
ECsw = -0.0265/LF^2
Eq. IV-10
LFq = (Diw - ΣWqDet)/(Diw)
Eq. IV-6
ECq = ECiw/LFq
Eq. IV-2

Eq. IV-17 is a combination of Eqs. IV-15,
IV-10, IV-6, IV-2, and a salt reactivity
function to account for mineral precipitationfrom evapoconcentration of soil water due toET.
EC = EC of soil waterq = Specified soil depth increment
j = Time increment
LFq = LF in qth depth increment
Diw = Depth of irrigation water
Wq = Root water extraction
extraction patternpattern
Det = Depth of evapotranspiration
ECq = EC of soil water in qth increment
Deto = Depth of ETo
Kc = Crop coefficient

Det = Deto * Kc

Depth of rooting of cool-season grasses
Annual bluegrass = 0.08–0.33 ft
Kentucky bluegrass = 0.5–1.5 ft
Perennial ryegrass = 0.5–1.5 ft
Tall fescue = 1.5–3.0 ft
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Avg.
Total

Kc

ETo (in.) ET (in.)
0.61
2.2
1.342
0.64
2.6
1.664
0.75
3.7
2.775
1.04
4.7
4.888
0.95
5.5
5.225
0.88
5.9
5.192
0.94
6.1
5.734
0.86
6.1
5.246
0.74
5.3
3.922
0.75
3.9
2.925
0.69
2.6
1.794
0.6
2
1.2
0.7875 4.216667 3.49225
41.907

HM4-1

Input data
Diw
Det
ECiw
Wq0
Wq1
Wq2
Wq3
Wq4
Wq5
Wq6
Wq7
Wq8
Wq9
Wq10

52.4
41.9
1.5
0
0.3
0.3
0.15
0.1
0.05
0.05
0.05
0
0
0

ECsw1
ECsw2
ECsw3
ECsw4
ECsw5
ECsw6
ECsw7
ECsw8
ECsw9
ECsw10

1.5
2.5
3
3.5
4.6
5.9
7.4
9.7
9.7
5.9

NOTE: Any changes made in the input data
will cause new values to be calculated forcomputations.
Computations
Depth
LFq
0
1
3 0.760115
6 0.520229
9 0.400286
12 0.320324
15 0.280344
18 0.240363
21 0.200382
24 0.200382
27 0.200382
30 0.200382
j =0
0 in.

Depth
3
6
9
12
15
18
21
24
27
30
Avg.

j=1
j=2
j=3
j=4
j=5
j=6
j=7
5.24 in.
10.48 in. 15.72 in. 20.96 in. 26.2 in.
31.44 in. 36.68 in.
1.5 1.713761 1.820641 1.874081 1.900801 1.914161 1.920841 1.924181
2.5 2.642714 2.714072 2.74975 2.76759 2.776509 2.780969 2.783199
3 3.290965 3.436448 3.509189 3.545559 3.563745 3.572837 3.577384
3.5 3.962244 4.193366 4.308926 4.366707 4.395597 4.410042 4.417265
4.6 4.806698 4.910047 4.961722 4.987559 5.000478 5.006937 5.010167
5.9 5.840945 5.811417 5.796653 5.789271 5.78558 5.783735 5.782812
7.4 7.112868 6.969302 6.897519 6.861627 6.843681 6.834709 6.830222
9.7 8.262868 7.544302 7.185019 7.005377 6.915556 6.870646 6.848191
9.7 8.262868 7.544302 7.185019 7.005377 6.915556 6.870646 6.848191
5.9 6.362868 6.594302 6.710019 6.767877 6.796806 6.811271 6.818503
5.37 5.22588 5.15382 5.11779 5.099775 5.090767 5.086263 5.084011

HM4-2

j=8
j=9
j = 10Depth
41.92 in. 47.16 in. 52.4 in.
3 1.925851 1.926686 1.927104
6 2.784314 2.784871 2.784871
9 3.579657 3.580793 3.580793
12 4.420876 4.422682 4.422682
15 5.011781 5.012589 5.012589
18 5.782351 5.78212 5.78212
21 6.827979 6.826857 6.826857
24 6.836963 6.831349 6.831349
27 6.836963 6.831349 6.831349
30 6.82212 6.823928 6.823928
Avg.
5.082886 5.082323 5.082364

Depth

0 in.
3
6
9
12
15
18
21
24
27
30

1.5
2.5
3
3.5
4.6
5.9
7.4
9.7
9.7
59
5.9

10.48 in. 20.96 in. 52.4 in.
1.82
1.9
1.93
2.71
2.77
2.78
3.44
3.55
3.58
4.19
4.37
4.42
4.91
4.99
5.01
5.81
5.79
5.78
7
6.86
6.83
7.54
7.01
6.83
7.54
7.01
6.83
66
6.6
6 77
6.77
6 82
6.82

Ecsw, dS/m

Salt accumulation from irrigation with ECiw of
1.5 dS/m, LF of 0.2, and salt reactive function for
Colorado River water
12
10
8
6
4
2
0

0 in.
10.48 in.
20.96 in.

0

10

20
Soil depth, in.

30

HM4-3

40

52.4 in.

Chapter V. Tolerance by Landscape Plants ofSalinity and of Specific Ions
C. Grieve, L. Wu, L. Rollins, and A. Harivandi
V.A. General Information Regarding Salt Tolerance
V.A.1. Defining Plant Salt Tolerance
V.A.2.Response of a Plant to Salinity
V.A.3.Symptoms of Salt­Related Stress
V.B. Salt Tolerance of Trees, Shrubs, and Ground Covers
V.B.1.Findings from Recent Research
V.B.2.Other Sources of Information
V.C. Salt Tolerance of Floricultural Plants
V.D. Salt Tolerance of Turfgrasses
V.E. Salt Tolerance of Native Plants
V.F. Sensitivity of Plants to Specific Ions
V.F.1.Sensitivity of Trees, Shrubs, Ground Covers, and Floricultural Plants
V.F.2.Sensitivity of Turfgrasses
V.G. Effects of Environment and Management
V.H. Gallery
V.I. References

In many communities where recycled water is available, the salinity of the recycled water
is somewhat higher than the salinity of municipal drinking water. Therefore, in using recycledwater to irrigate golf courses, parks, and other landscapes, it may be beneficial to include salt­
tolerant plants, as much as possible, in a landscape’s design. The information in this chapter isprovided in the hope that it will help park designers, landscapers, maintenance personnel, andothers who work with plants to specify, install, and nurture trees, shrubs, ground covers,
floricultural plants, and turfgrasses that can thrive when irrigated with recycled water.
Quite a few landscape plants can withstand small or moderate amounts of salt; many arelisted in this chapter. Because native Californian plants are favored for park design by the cities
of Los Angeles and San Diego and by a number of other communities and individuals in the state,
we have included salt tolerance information for native plants to the extent that it is available.

V­1

The responses of plants to salts are manifested in two ways. The osmotic effect produced
by total salinity decreases the soil water potential, which causes water in the soil to become lessavailable to plants. And when specific constituents (ions) of salts are present in highconcentrations, they can disrupt the plant’s mineral nutrient status, sometimes becoming toxic. At
times, concentrations of ions such as sodium (Na+), chloride (Cl−), and boron (B) in soil or
irrigation water, or both, can prove to be a major constraint in choosing plants or in deciding
where to position plants within a landscape. We describe some of the effects of these salt ions onplants and the concentrations at which the ions can become a problem. In addition, we outline a
number of management practices that can be used to minimize salt injury to plants.
When one is preparing for landscape irrigation with recycled water, environmental
quality is an important consideration, especially when the landscape is situated within an urban
area. To use the lists of plants in this chapter successfully, information regarding water quality,
irrigation management, physical and chemical properties of the soil, and any unfavorable
environmental conditions should be obtained and thoroughly reviewed.
In addition to choosing plant species that are sufficiently salt tolerant, the landscapeprofessional must select species that adapt well to local climates. California has many different
climatic zones ranging from cool, relatively dry, temperate regions in the inland valleys and highmountains to extremely dry, hot deserts to humid, foggy zones along the coast. Since informationon the adaptation of plants to climate is readily available elsewhere, we will not further cover the
topic in this chapter.

V.A. General Information Regarding Salt Tolerance
V.A.1. Defining Plant Salt Tolerance
The salt tolerance of a plant is often defined as the plant’s inherent ability to withstandthe effects of high salts in the root zone or on its leaves without significant adverse effects. The
actual salt tolerance of a plant will vary, depending on the growth stage at which salinization is
initiated and the final level of salinity to which the plant is subjected (Lunin et al., 1963). Anotherreason for variation is that the genes that determine a plant’s salt tolerance function in
combination with other genes, some of which influence both quantitative traits andenvironmentally influenced traits, such as salt tolerance (Shannon, 1997).
A crop’s salt tolerance can be described as a complex function of its yield decline in
response to salinity. The yield response curve is typically valid for a range of concentrations ofsalts and is sigmoidal in shape. Mathematical descriptions of these relationships have provenuseful for crop simulation modeling (van Genuchten and Hoffman, 1984). However, because cropV­2

survival rates tend to be very low at high salinities, the validity of the bottom part of the yield
response curve is often in doubt. Maas and Hoffman (1977) proposed a two­piece linear model
described by two parameters: the threshold (electrical conductivity of the extract of a saturated
soil paste [ECe] at which significant yield reduction begins), and the slope (percentage of
expected yield decline per unit increase in salinity above the threshold value). In landscape plants,
aesthetic quality of the plants is more important than yield of crop plants. Nevertheless, theconcept of salt tolerance is of value for landscape plants.

V.A.2. Response of a Plant to Salinity
Lauchli and Epstein (1990) conclude that salinity is stressful for many plants because of
two concurrent processes: the osmotic effect and specific­ion effects described earlier. The
authors examine the various mechanisms by which plants respond to osmotic effects and to theeffects of specific ions. They point out that a plant typically responds to the osmotic effects ofsalinity by absorbing salt from the medium and by synthesizing organic solutes internally so as tomake the water potential gradient more favorable for water uptake.
To evaluate what is known about the responses of plants to salinity, Lauchli and Epstein
review and then summarize results from a number of studies on the topic. They describe how
plants respond during the two successive stages of growth—development and vegetative growth.
They conclude the following:·

It is not possible to establish a distinct dividing line between saline stress, on the one
hand, and lack of stress, on the other. Instead, a continuum exists between the two.

·

The sensitivity of a plant to salinity changes during the development of the plant.

·

The integration of responses in the whole plant is critical for the health and survivalof a plant under saline conditions.

·

Highly salt­tolerant plants (halophytes) tend to absorb salt ions from the medium andsequester them in the vacuoles of cells. Such plants also manufacture organic solutes
to balance the osmotic changes that occur in the cell cytoplasm.

·

Salt­sensitive plants, referred to as nonhalophytes or glycophytes, tend to exclude
sodium and chloride from their shoots and, especially, from their leaves.
Consequently, when subjected to salinity, glycophytes must rely more extensively on
the synthesis of organic solutes than do halophytes.

·

The presence of calcium at elevated concentrations sometimes can help to mitigate
the adverse effects of salinity.
V­3

The initial and primary effect of salinity, especially at low to moderate concentrations ofsalt, results from osmotic effects (Munns and Termaat, 1986). Maturity may be delayed oradvanced, depending on the species. For example, salt­related stress in wheat accelerates its
development and causes early maturity, whereas salt­related stress in rice causes the plants tomature more slowly. The magnitude of a plant’s response to salinity depends not only on thespecies but also on the interactive effects of environmental factors such as relative humidity,
temperature, radiation, and air pollution (Shannon et al., 1994).
Depending on the composition of the irrigation water, ion toxicities or nutritional
deficiencies may also arise. These result from a preponderance of a certain specific ion or fromcompetitive effects among cations or anions (Grattan and Grieve, 1999). The osmotic effects ofsalinity contribute to a reduced rate of growth and to changes in the color of leaves. They also canlead to morphological changes such as smaller leaves or shorter stature or, frequently, to fewer
leaves and nodes. Ionic effects generally manifest as damaged leaves or formative plant tissue oras symptoms typical of nutritional disorders. Thus, high concentrations of sodium or chloride ions
may accumulate in leaves or in portions of leaves and result in the “scorch” or “firing” of leaves,
whereas symptoms of nutritional deficiency are often similar to those that occur in the absence ofsalinity.
Environmental stresses can cause physiological and morphological disruptions in root
tissues. Salinity, for example, decreases the integrity and increases the permeability of cell
membranes and ultimately results in reduced growth and yield. Such changes may also increase aplant’s susceptibility to invasion by pathogens. Chrysanthemum, a relatively salt­tolerant floral
species, showed a definite predisposition to infection by Phytophthora cryptogea when it wasaffected by salinity. MacDonald (1982) reported a strong positive relationship between the degreeof salt stress and the severity of this root rot.

V.A.3 Symptoms of Salt­Related Stress
The typical observable symptom of a plant injured by salt­related stress is leaf chlorosis(a scorched­like appearance). It is detrimental physically and aesthetically to plants. If subjected
to severe salt­related stress, the whole leaf blade may become chlorotic and die. Under moderatesalt­related stress, symptoms are similar among salt­sensitive species of plants, although thesymptoms on the leaves have a slightly different pattern of distribution.
Species assessed to be “highly tolerant” are unlikely to develop any symptoms of salt­
related stress when irrigated with recycled water, even during the dry and warm summer season.
Such species include the tree known as Mexican pinon pine (Pinus cembriodes), the shrub known
V­4

as oleander (Nerium oleander), the ground cover red apple iceplant (Aptenia cordifornia), and thegrass known as alkali sacaton (Sporobolus airoides). All of these species can tolerate salt spray
containing over 1,000 mg of sodium chloride/L, and all are tolerant of soil with a salinity of 10
decisiemens/m (dS/m), or even greater. These plants require only routine management practices.
Plants assessed to be “tolerant” are generally able to tolerate spray with water (i.e.,wetted foliage from sprinkler irrigation) that contains concentrations of salt equivalent to thosefound in most recycled waters and generally do not develop apparent symptoms of salt­related
stress if the salinity of the soil remains below an ECe of 6 dS/m. However, when the foliage of atolerant plant is exposed to concentrations of salt exceeding 200 mg of sodium/L and 300 mg ofchloride/L, symptoms of salt­related stress begin to appear.
Species determined to be “moderately tolerant” can tolerate spray with water containing
the concentrations of salts found in most recycled waters. Under such conditions, their aesthetic
quality generally remains acceptable, though they may develop symptoms of salt­related stressnear the end of the growing season, by which time leaves may have accumulated considerable salt
or the salinity of the soil may have exceeded the permissible level. In areas where wet seasons
recur cyclically and frequently, moderately tolerant plants will likely do very well through mostof the year, even if irrigation is discontinued during the wet seasons.
Plants deemed “sensitive” may develop symptoms of salt­related stress under a spray ofwater containing a concentration of sodium that reaches or exceeds 200 mg/L and a concentrationof chloride that reaches or exceeds 400 mg/L, especially if the weather is warm and dry. One suchspecies is liquidambar (Liquidambar styraciflua). Typical symptoms of salt­related and boron­
related stresses for plant species are shown in plates 1 and 2 (Gallery), respectively. Plants
sensitive to salt spray from sprinkler irrigation tend also to be sensitive to salinity in the soil. For
example, roses may develop severe symptoms of salt­related stress if the salinity in the soil
reaches or exceeds 3 dS/m. Research with agronomic plants (Benes et al., 1996) has shown that,for some crops, postwashing (finishing an irrigation, then giving a brief, freshwater rinse) cangreatly reduce foliar injury from sprinkling.

V.B. Salt Tolerance of Trees, Shrubs, and Ground Covers
V.B.1. Findings from Recent Research
Based on a recent series of experiments, Wu and Dodge (2005) compiled salt tolerance
information for over 200 species of trees and palms, shrubs, and ground covers. Reproduced here
as Tables V.B.1.1, V.B.1.2, and V.B.1.3, the lists work fairly well as a plant selection guide fordecision­makers in the field of landscape management.
V­5

These lists were developed by a team of University of California–Davis researchers who
used sprinkler and drip irrigation systems and waters with salinities near the upper level found in
most recycled waters. The field trials were aimed at differentiating the salt tolerance of landscapeplants based on the aesthetic effects of salinity, rather than yield reduction as would be done withagronomic crops (Wu et al., 2001). The response of the plants to saline stress was evaluatedvisually or measured by using image analysis technology (Lumis et al., 1973; Wu et al., 2001;
Wu and Guo, 2005).
The researchers reviewed the relatively scant literature to date on the relationshipbetween the tolerance by plants of salinity in the water applied to leaves, as compared totolerance of salinity in the water applied to roots. In one study, these two characteristics were
found to have evolved independently between different ecotypes for a species of creeping
bentgrass, Agrostis stolonifera L., in a seacoast environment (Ashraf et al., 1986). In anotherstudy that involved salt­tolerant creeping fescue cultivars (Festuca rubra L.), the characteristicsof leaf wettability were found to be responsible for tolerance of salt spray (Humphreys, 1986).
There appears to exist a positive relationship between the salt tolerance by many landscape plants
for saline spray and their tolerance of salinity in the root zone (Wu et al., 2001). In some cases,
the tolerance for salts entering the plant via its roots was found to be three to four times higher
than the tolerance for salts entering the plant through leaves (Wu et al., 2001). Exceptions werecertain fruit trees grafted onto rootstocks of different species. Their tolerance of salt spray andtolerance of soil salinity may be unrelated.
Based on the results of their field trials, which were conducted in the summer months,
and information found in the literature, the researchers estimated the salt tolerances of over 200
species of plants for landscapes (Tables V.B.1.1, V.B.1.2, and V.B.1.3).
Although five or six descriptors have been used to categorize the salt tolerance of crop
species (Maas and Grattan, 1999), that number was deemed unnecessarily high for differentiating
salt tolerance in landscape plants because landscapes often include plants with a wide range ofsalt tolerance. Instead, these researchers categorized plants using four descriptors for the plants’ability to tolerate salts in irrigation water: highly tolerant, tolerant, moderately tolerant, or
sensitive. They concluded that ranking based on the visual quality of the plants was a practical
approach.

V­6

aTable V.B.1.1.Tolerance by selected landscape tree species of salt spray and of soil salinity.
Botanical nameCommon name

Tolerance ofbsalt spray

Tolerance of soilcsalinity

Acer rubrum L.

Red maple

Sensitive

Sensitive

Acer pseudoplatanus L.

Sycamore maple

Sensitive

Sensitive

Albizia julibrissin Durazz.

Silk tree

Sensitive

Sensitive

Araucaria heterophylla (Salisb.)

Norfolk Island pine

Highly tolerant

Tolerant

Averrhoa carambola L.

Carambola, starfruit

Moderate

Moderate

Bauhinia purpurea L.

Orchid tree

Sensitive

Moderate

Callistemon citrinus Curtis.

Lemon bottlebrushTolerant

Moderate

Carya illinoinensis Koch.

Pecan

Moderate

Moderate

Cedrus deodara D. Don

Deodar cedar

Moderate

Moderate

Celtis sinensis Pers.

Chinese hackberry

Sensitive

Sensitive

Citrus limon L.

Lemon

Sensitive

Sensitive

Citrus paradisi Macf.

Grapefruit

Sensitive

Sensitive

Citrus reticulata Blanco.

Tangerine

Sensitive

Sensitive

Citrus sinensis Osbeck.

OrangeSensitive

Sensitive

Coccoloba uvifera L.

Sea grape

Highly tolerant

Tolerant

Cornus mas L.

Cornelian cherry

Sensitive

Sensitive

Cotoneaster microphyllus Lindl.

Rockspray or little­leaf cotoneaster

Tolerant

Moderate

Cupressus sempervirens L.

Italian cypress

Moderate

Moderate

Diospyros digyna L.

Black sapote

Moderate

Moderate

Diospyros virginiana L.

American persimmon

Sensitive

Sensitive

Eriobotrya japonica Lindl.

LoquatModerate

Moderate

Euryops pectinatus

Golden marguerite

Sensitive

Sensitive

Ficus carica L.

Edible fig

Tolerant

Tolerant

Forsythia intermedia Zabel

Forsythia

Tolerant

Tolerant

Fraxinus oxycarpa Bieb. Ex Willd.

Raywood ash

Moderate

Moderate

Gingko biloba L.

GingkoSensitive

Sensitive

Grevillea robusta Cunn.

Silk oakHighly tolerant

Tolerant

Jacaranda mimosifolia D. Don.

Jacaranda

Sensitive

Sensitive

Juniperus silicicola Bail.

Southern red cedar

Highly tolerant

Tolerant

Juniperus virginiana L.

Skyrocket juniper

Highly tolerant

Tolerant

Koelreuteria paniculata Laxm.

Golden rain tree

Moderate

Moderate

Lagerstroemia indica L.

Crape myrtle

Sensitive

Sensitive

Ligustrum japonicum Thunb.

Japanese privet

Moderate

Moderate

Liquidambar styraciflua L.

SweetgumSensitive

Sensitive

Litchi chinensis Sonn.

LycheeSensitive

Sensitive

Malus sylvestris Mill.

Crabapple

Sensitive

Sensitive

Mangifera indica L.

Mango

Sensitive

Sensitive

Mangnolia grandiflora L.

Southern magnolia

Sensitive

Sensitive

Manilkara zapota

Sapodilla

Tolerant

Tolerant

Musa acuminata Colla.

BananaSensitive

Sensitive

Olea europaea L.

Olive

Sensitive

Sensitive

Parthenium argentatum Gray.

GuayuleHighly tolerantHighly tolerant

Persea americana Mill.

AvocadoModerate

Moderate

Pinus cembroides Zucc.

Mexican stone pine

Highly tolerant

TolerantV­7

Pinus clausa Vasey

Sand pine

Highly tolerant

Tolerant

Pinus elliotti Engelm.

Florida slash pine

Moderate

Moderate

Pinus halepensis Mill.

Aleppo pine

Moderate

Moderate

Pinus thunbergii Parl.

Japanese black pine

Moderate

Moderate

Pistachia chinensis Bunge.

Chinese pistache

Sensitive

Sensitive

Platycladus orientalis Franco

Oriental arborvitae

Moderate

Moderate

Plumaria spp. L.

Frangipani

Tolerant

Tolerant

Plumbago auriculata Lam.

Cape plumbago

Tolerant

Moderate

Prunus armeniaca L.

Apricot

Sensitive

Sensitive

Prunus caroliniana Ait.

Carolina laurel cherry

Moderate

Sensitive

Prunus dulcis D. A. Webb.

AlmondSensitive

Sensitive

Prunus persica Batsch

Peach

Sensitive

Sensitive

Prunus spinosa L.

Blackthorn

Tolerant

Moderate

Psidium guajava L.

Guava

Sensitive

Sensitive

Punica granatum L.

Pomegranate

Moderate

Moderate

Pyrus communis L.

Pear

Sensitive

Sensitive

Pyrus spinosa Forssk.

Almond­leaved pear

Moderate

Moderate

Quercus agrifolia Nee

Coast live oak

Tolerant

Tolerant

Quercus laurifolia Michux

Laurel oak

Sensitive

Sensitive

Quercus suber L.

Cork oakModerate

Moderate

Quercus virginiana Mill.

Live oakHighly tolerant

Tolerant

Sapium sebiferum Roxb.

Chinese tallow tree

Highly tolerant

Tolerant

Schefflera actinophylla Harms

Schefflera, umbrella tree

Moderate

Moderate

Sensitive

Sensitive

Moderate

Moderate

Sequoia sempervirens Endl.
Sequoia sempervirens Endl.

Coast redwood
Var. Aptos Blue
Coast redwood
Var. Los Altos

Syzgium jambos Alston

Rose apple

Sensitive

Sensitive

Ulmus parvifolia Drake

Drake elm

Moderate

Moderate

Ulmus parvifolia Jacq.

Chinese elm

Moderate

Moderate

Butia capitata Becc.

Pindo palm

Tolerant

Tolerant

Chamaerops humilis L.

European fan palm

Tolerant

Tolerant

Phoenix canariensis Chabaud.

Canary Island date

Moderate

Moderate

Phoenix dactylifera L.

Date palmetto

Tolerant

Tolerant

Sabal palmetto Lodd.

Cabbage palmetto

Tolerant

Tolerant

Serenoa repens Small

Saw palm

Tolerant

Tolerant

Washingtonia robusta Wendl.

Washingtonia palm

Tolerant

Tolerant

Chrysalidocarpus lutescens Wendl.

Areca palm

Moderate

Moderate

Caryota mitis Lour.

Fishtail palm

Moderate

Moderate

Rhapis excelsa Henry

Lady palm

Moderate

Moderate

Acoelorrhaphe wrightii Becc.

Paurotis palm

Moderate

Moderate

Phoenix roebelinii O’Brien.

Pygmy date palm

Moderate

Moderate

Phoenix reclinata Jacq.

Senegal date palm

Moderate

Moderate

Syagrus romanzoffiana L.

Queen palm

Moderate

Moderate

Nolina recurvata Hemsle

Ponytail palm (not a true palm)

Moderate

Moderate

Palm

V­8

a

Data in the table adapted from Wu and Dodge, 2005 (in press).

b

Tolerances of salt spray are defined by the degree of salt stress symptoms developed in the leaves of the plants
and the salt concentrations in the irrigation water as follows:
Highly tolerant: No apparent salt stress symptoms may be observed when the plants are irrigated with water−1−1
that contains 600 mg of sodium L and 900 mg of chloride L and has an ECiw of 2.1 dS/m.

cTolerant:

No apparent salt stress symptoms may be observed when the plants are irrigated with water−1−1
containing 200 mg of sodium L and 400 mg of chloride L .

Moderate:

Less than 10% of symptoms develop when the plants are irrigated with water containing 200−1−1
mg of sodium L and 400 mg of chloride L and having an ECiw of 0.9 dS/m.

Sensitive:

More than 20% of the leaves may develop symptoms when the plants are irrigated with water−1−1
containing 200 mg of sodium L and 400 mg of chloride L and having an ECiw of 0.6 dS/m.

The definitions of soil salinity tolerance are as follows:−1

Highly tolerant: Permissible soil ECe greater than 6 dS m ,−1Tolerant:

Permissible soil ECe greater then 4 and less than 6 dS m ,Moderate:

Permissible soil ECe greater than 2 and less than 4 dS m , andSensitive:−1−1

Permissible soil ECe less than 2 dS m .

V­9

a

Table V.B.1.2. Tolerance by landscape shrub species of salt spray and of soil salinity.

Botanical nameCommon name

Tolerancebof salt spray

Tolerance ofcsoil salinity

Abelia grandiflora Rehd.
Acacia redolens Maslin.
Acalypha wilkesiana Muell.

“Edward Goucher” Abelia
Prostrate acacia
Copper leaf

Sensitive
Tolerant
Sensitive

Sensitive
Tolerant
Sensitive

Agave americana L.

Century plant

Highly tolerant

Tolerant

Arctostaphylos densiflora M.S.Bac

Vine hill manzanita

Tolerant

Tolerant

Bambusa sp. Schreb.
Buddleja davidii Franch.

BambooButterfly bushModerate
Sensitive

Moderate
Sensitive

Buxus microphylla Mull. Arg.

Japanese boxwood

Tolerant

Moderate

Calliandra haematocephala Hassk.
Callistemon rigidus R. Br.
Camellia japonica L.
Cannax generalis Bailey.
Carica papaya L.

Powder puff tree
Bottlebrush
Camellia
Canna lily
PapayaSensitive
Moderate
Sensitive
Moderate
Moderate

Sensitive
Moderate
Sensitive
Moderate
Moderate

Carissa macrocarpa A. DC.

Natal plum

Highly tolerant

Tolerant

Ceanothus thyrsiflorus Esch.

Blue blossom

Tolerant

Moderate

Cestrum aurantiacum Lindl.
Codiaeum variegatum Blume.
Cornus mas L.
Cotoneaster congestus Baker
Cotoneaster microphylla Lindl.
Dracaena deremensis Engler.

Orange cestrum
CrotonCornelian cherry
Pyrenees cotoneaster
Rockspray cotoneaster
Dracaena

Moderate
Sensitive
Sensitive
Sensitive
Moderate
Moderate

Moderate
Sensitive
Sensitive
Sensitive
Sensitive
Moderate

Elaeugnus pungens Thunb.

Silverthorn, silverberryHighly tolerant

Tolerant

Escallonia rubra Pers.

Escallonia

Tolerant

Moderate

Eugenia unifora L.

Surinam cherry

Sensitive

Sensitive

Euphorbia milii Ch. Des Moulins

Crown of thorns

Highly tolerantHighly tolerant

Euphorbia pulcherrima Willd.

Poinsetta

Sensitive

Sensitive

Euryops pectinatus L.

Golden shrub daisy

Tolerant

Moderate

Forsythia intermedia Zabel

Hybrid forsythia

Moderate

Moderate

Gamolepis chrysanthemoides DC.

African bush daisy

Highly tolerant

Tolerant

Gardenia augusta Merrill
Heliconia sp.

Cape jasmine, gardenia
Heliconia
Rose of China, garden
hibiscus

Moderate
Moderate

Moderate
Moderate

Moderate

Moderate

Hydrangea macrophylla Ser.

Hydrangea

Tolerant

Moderate

Ilex cornuta Burford

Chinese holly

Moderate

Moderate

Ilex vomitoria Ait.

Yaupon holly

Tolerant

Tolerant

Ilex vomitoria Nana

Dwarf Yaupon holly

Highly tolerant

Tolerant

Ixora coccinea L.
Jasminum polyanthum Franch.
Jatropha multifida L.
Justicia brandegeana Wassh.

Ixora
JasmineCoral plant
Shrimp plant

Sensitive
Moderate
Sensitive
Sensitive

Sensitive
Moderate
Moderate
Sensitive

Lantana camara L.

Lantana

Highly tolerant

Tolerant

Mahonia aquifolium Nutt.
Mahonia pinnata Fedde
Murraya paniculata L.

Oregon grape
California holly grape
Orange jessamine

Sensitive
Sensitive
Sensitive

Sensitive
Sensitive
Sensitive

Myrica cerifera L.

Wax myrtle

Highly tolerant

Tolerant

Myrtus communis L.

True myrtle

Tolerant

Tolerant

Nandina domestica Thunb.

Heavenly bamboo

Sensitive

Sensitive

Hibiscus rosa L.

V­10

Nerium oleander L.

OleanderHighly tolerant

Tolerant

Opuntia sp. Miller

Opuntia cactus

Moderate

Tolerant

Parthenium argentatum Gray.

GuayuleHighly tolerantHighly tolerant

Sensitive

Sensitive

Sensitive
Sensitive

Sensitive
Sensitive

Photinia glabra Maxim.
Photinia fraseri DressPentas, Egyptian star­clusterJapanese Photinia
Photinia

Pittosporum tobra Aiton

Mock orange

Highly tolerant

Tolerant

Plumbago auriculata am.

Cape plumbago

Tolerant

Tolerant

Podocarpus macrophyllus D. Don
Pyracantha coccinea Roem.

Yew pine
Red firethorn

Sensitive
Moderate

Sensitive
Moderate

Raphiolepis indica Lindl.

Indian hawthorn

Highly tolerant

Tolerant

Rosa sp. L.
Russelia equisetiformis Schlecht &Cham.
Sambucus callicarpa Greene
Schefflera arboricola L.
Strelitzia reginae Bankses Dryander
Viburnum odoratissimum Ker.
Viburnum suspensum Lindl.

Rose

Sensitive

Sensitive

Firecracker plantModerate

Moderate

Coast red elderberry
Dwarf Shefflera
Bird of paradise
Sweet Viburnum
Sandankwa Viburnum

Tolerant
Moderate
Moderate
Moderate
Moderate

Moderate
Moderate
Moderate
Moderate
Moderate

Yucca aloifolia L.

Spanish bayonet

Highly tolerantHighly tolerant

Pentas lanceolata DeflersaData in the table adapted from Wu and Dodge, 2005 (in press).

b

Tolerances of salt spray are defined by the degree of salt stress symptoms developed in the leaves of the plants
and the salt concentrations in the irrigation water as follows:
Highly tolerant: No apparent salt stress symptoms may be observed when the plants are irrigated with water−1−1
containing 600 mg of sodium L and 900 mg of chloride L and having an ECiw of 2.1 dS/m.

cTolerant:

No apparent salt stress symptoms may be observed when the plants are irrigated with water−1−1
containing 200 mg of sodium L and 400 mg of chloride L .

Moderate:

Less than 10% symptoms may be observed when the plants are irrigated with water−1−1
containing 200 mg of sodium L and 400 mg of chloride L and having an ECiw of 0.9 dS/m.

Sensitive:

More than 20% of the leaves may develop symptoms when the plants are irrigated with water−1−1
containing 200 mg of sodium L and 400 mg of chloride L and having an ECiw of 0.6 dS/m.

The definitions of soil salinity tolerance are−1

Highly tolerant: Permissible soil ECe greater than 6 dS m ,−1Tolerant:

Permissible soil ECe greater then 4 and less than 6 dS m ,Moderate:

Permissible soil ECe greater than 2 and less than 4 dS m , andSensitive:−1−1

Permissible soil ECe less than 2 dS m .

V­11

a

Table V.B.1.3. Tolerance by various landscape ground covers and vine species of salt spray and of soil salinity.

Botanical nameCommon name

Tolerance ofbsalt spray

Tolerance of soilcsalinity

Adiantum sp. L.
Ajuga repens

Maidenhair fern
Carpet bugle

Moderate
Sensitive

Moderate
Sensitive

Aloe vera Burm. f.

Aloe

Highly tolerant

Tolerant

Alternanthera ficoidea R. Br.
Aptenia cordifolia N. E. Br.
Arctostaphylos densiflora “Lynne” M. S.
Back.
Athyrium filix­femina Rith.
Bromeliaceae sp. L.
Caladium sp. Vent.

JoyweedRed apple iceplantModerate
Tolerant

Moderate
Tolerant

Lynne’s vine hill manzanita

Moderate

Moderate

Lady fern
Bromeliads
Caladium

Sensitive
Moderate
Sensitive

Sensitive
Moderate
Sensitive

Carissa macrocarpa A. DC.

Natal plum

Highly tolerant

Tolerant

Carpobrotus edulis L. Bolus.

Hottentot fig

Highly tolerant

Tolerant

Catharanthus roseus G. Donf.
Chlorophytum comosum Jacq.
Cuphea hyssopifolia Kunth.
Cyperus alternifolius L.

Periwinkle
Spider plant
False heather
Umbrella sedge

Tolerant
Moderate
Moderate
Moderate

Moderate
Moderate
Tolerant
Moderate

Delosperma “Alba” N. E.

White iceplant

Highly tolerantHighly tolerant

Dietes spp. Salisb. ex Klatt.

African Iris

Moderate

Moderate

Drosanthemum hispidum Schwantes.

Rosea iceplant

Highly tolerantHighly tolerant

Ficus pumila L.

Creeping fig

Highly tolerant

Tolerant

Hemerocallis sp. L.

Daylily

Moderate

Moderate

Malephora crocea Schwantes.

Iceplant

Highly tolerantHighly tolerant

Juniperus chinensis L.
Juniperus conferta Parl.

Chinese juniper
Shore juniper

Moderate
Tolerant

Moderate
Tolerant

Juniperus horizontalis Moench.

Creeping juniper

Highly tolerant

Tolerant

Juniperus procumbens Siebild ex Endl.
Kalanchoe sp. Adans.

Japanese garden juniper
Kalanchoe

Moderate
Moderate

Moderate
Moderate

Lampranthus productus N. E. Br.

Purple iceplant

Highly tolerantHighly tolerant

Liriope muscari L. H. Bail.
Iris hexagona Walter

Lilyturf (Liriope)
Iris

Moderate
Moderate

Moderate
Moderate

Nephrolepis exaltata Schott.

Sword fern

Highly tolerant

Tolerant

Peperomia obtusifolia Dietr.
Portulaca grandiflora Hook.
Rosmarinus officinalis L.
Salvia farinacea Benth.

Peperomia
Purslane (rose moss)
Rosemary
Mealycup sage

Sensitive
Moderate
Moderate
Sensitive

Sensitive
Sensitive
Moderate
Sensitive

Tigridia pavonia Ker Gawler

Tiger flower

Tolerant

Moderate

Tradescantia pallida Hunt.

Purple queen

Highly tolerant

Tolerant

Tulbaghia violacea Harvey
Verbena sp. L.

Society garlic
Verbena

Moderate
Sensitive

Moderate
Sensitive

Zamia integrifolia L. f.

Coontie

Highly tolerant

Tolerant

Vine
Allamanda cathartica L.
Allamanda blanchetii A. DC.
Antigonon leptopus Hookery

Allamanda
Purple Allamanda
Coral Vine

Tolerant
Moderate
Sensitive

Tolerant
Moderate
Moderate

Bougainvillea glabra Choisy

Bougainvillea

Highly tolerant

Tolerant

Campsis radicans Seem.
Clerodendrum thomsoniae Balf. f.
Clytostoma callistegioides Miers ex Bur.
Cyperus altenifolius L.

Trumpet creeper
Bleeding heart vine
Violet trumpet vine
Umbrella sedge

Sensitive
Sensitive
Sensitive
Moderate

Sensitive
Sensitive
Sensitive
ModerateV­12

Epipremnum sp. Schott.

PothosModerate

Moderate

Ficus pumila L.

Creeping fig

Highly tolerant

Tolerant

Hedera canariensis Willd.

Algerian ivy

Highly tolerant

Tolerant

Hedera helix L.
Hylocereus undatus Britton & Rose

English ivy
Night blooming cereus

Moderate
Moderate

Moderate
Moderate

Ipomoea pescaprae R. Br.

Railroad vine

Highly tolerant

Tolerant

Ipomoea stolonifera Gmel.

Seafoam morning glory

Highly tolerant

Tolerant

Philodendron williamsii Hook.
Passiflora incanata L.
Salvia farinacea Benth.
Tecomaria capensis Spach.
Trachelospermum jasminoides Lem.

Philodendron
Passion flower
Mealycup sedge
Cape honeysuckle
Star jasmine

Moderate
Sensitive
Sensitive
Tolerant
Tolerant

Moderate
Sensitive
Sensitive
Tolerant
TolerantaData in the table adapted from Wu and Dodge, 2005 (in press).

b

Tolerances of salt spray are defined by the degree of salt stress symptoms developed in the leaves of the plants
and the salt concentrations in the irrigation water as follows:
Highly tolerant: No apparent salt stress symptoms may be observed when the plants are irrigated with water−1−1
containing 600 mg of sodium L and 900 mg of chloride L and having an ECiw of 2.1 dS/m.

cTolerant:

No apparent salt stress symptoms may be observed when the plants are irrigated with water−1−1
containing 200 mg of sodium L and 400 mg of chloride L .

Moderate:

Less than 10% symptoms may be observed when the plants are irrigated with water−1−1
containing 200 mg of sodium L and 400 mg of chloride L and having an ECiw of 0.9 dS/m.

Sensitive:

More than 20% of the leaves may develop symptoms when the plants are irrigated with water−1−1
containing 200 mg of sodium L and 400 mg of chloride L and having an ECiw of 0.6 dS/m.

The definitions of soil salinity tolerance are−1

Highly tolerant: Permissible soil ECe greater than 6 dS m ,−1Tolerant:

Permissible soil ECe greater then 4 and less than 6 dS m ,Moderate:

Permissible soil ECe greater than 2 and less than 4 dS m , andSensitive:−1−1

Permissible soil ECe less than 2 dS m .

V.B.2. Other Sources of Information
Literature regarding the response of plants to salinity has accumulated so rapidly over theyears that a comprehensive bibliography is needed to help search for key references. Fortunately,
L. E. Francois and E. V. Maas of the U.S. Salinity Laboratory assembled such a bibliography in
1978. It contains 2,350 literature citations from 1900 to 1977, including citations for papers that
describe the effects of salt and boron on whole plants. Key phrases for each citation include plantname, experimental materials and methods, treatments and variables evaluated, and results or dataobtained. The bibliography has four sections, one listing common plant names, another listing
botanical names, another describing treatments, and yet another organized by results.
An updated version of this bibliography that currently includes over 6,200 literature
citationsexistsonthe

Salinity

Laboratory’s

websiteV­13

atwww.ars.usda.gov/Services

/docs.htm?docid=8908. It is available to everyone, with no password needed to access it, as of2006.
Researchers at the Salinity Laboratory have written a number of key papers over theyears. In one of the earliest papers, “Salt Tolerance of Ornamental Shrubs and Ground Covers”(Bernstein, Francois, and Clark, 1972), the authors describe their experiments on 25 species ofplants salinized with sodium chloride and calcium chloride. They discovered that overall salt
tolerance does not correlate well with tolerance to injury by chloride or sodium (specific ions).
They also concluded that survival of a plant under highly saline conditions is not necessarily agood indicator of overall salt tolerance. The paper includes several tables and one illustrationcomparing the salt tolerances of various shrubs and ground covers.
Another key reference by Salinity Laboratory researchers is “Salt Tolerance ofOrnamental Shrubs, Trees, and Iceplant” (Francois and Clark, 1978). As with the earlier study,
the researchers artificially salinized plants with combination of sodium chloride and calcium
chloride salts in the water or soil. They evaluated 10 species of shrubs, 2 species of trees, and 4
species of iceplant. Tolerant varieties were reported to include Texas sage (Leucophyllum
frutescens), brush cherry (Syzygium paniculatum), Aleppo pine (Pinus halepensis), croceum
iceplant (Hymenocyclus croceus), purple iceplant (Lampranthus productus), rosea iceplant(Drosanthemum hispidum), and white iceplant (Delosperma alba). Those species were affected
little, if at all, by soil with salinities as high as an ECe (electrical conductivity of the saturated soil
paste extract) of 7 dS/m. Sensitive species included glossy abelia (Abelia grandiflora), photinia(Photinia fraseri), Oregon grape holly (Mahonia aquifolium), and Pyrenees cotoneaster(Cotoneaster congestus). Each of those was severely damaged, or killed, when the ECe measured
4 dS/m. Another important finding by these researchers was that leaves typically were injured
only at levels of salinity that suppressed growth by 50% or more.
Another pertinent reference by Salinity Laboratory researchers is “Salt Tolerance ofPlants” (Maas, 1986). In that journal article, Maas examined the salt tolerance of both crops andornamental plants, including the criteria for establishing salt tolerance, the factors that influence
the salt tolerance of plants, and the relative salt tolerances for herbaceous crops, woody crops, andornamentals in a series of five tables. Maas pointed out that susceptibility to foliar injury varies
considerably among species and depends more on leaf characteristics and the rate of absorption ofwater than on tolerance of soil salinity. Maas examined the effects of chloride, sodium, and boron
on both crops and ornamental plants and provided several tables listing sensitivities of plants tochloride, sodium, and boron.

V­14

The Salinity Laboratory’s parent organization, the U.S. Department of Agriculture,published a series of leaflets known as Home and Garden Bulletins during the 1960s and 1970s.
One of those, the leaflet titled “Reducing Salt Injury to Ornamental Shrubs in the West” (Homeand Garden Bulletin No. 95), describes how salinity affects plants, outlines how to diagnose salt
injury, and presents a few strategies for coping with salinity (Bernstein, 1964). This leaflet isavailable at certain libraries: visit www.worldcatlibraries.org on the Internet, click on “Try asearch,” and enter the leaflet’s author and title. The mentioned leaflet has been superseded byanother one in the series, “Salt Injury to Ornamental Shrubs and Ground Covers” (Francois,1980), which includes a table showing the relative tolerances of 41 different trees, shrubs, andground covers. A PDF of this leaflet can be downloaded from the Internet atwww.agnic.msu.edu/hgpubs/modus/morefile/hg231_80.pdf. Though both leaflets were written in
earlier decades, they contain pertinent general information.
Bernstein (1980) examined the effects of salinity on fruit trees, such as apple, plum,
prune, apricot, and almond, which are occasionally used in landscapes. He relates that the relative
importance of osmotic effects and specific ion effects on inhibiting plant growth varies widely,depending on the species. He further states that the yields of some species of fruit tree are
relatively unaffected by elevated levels of chloride and sodium ions, even when the leaves areseverely injured. However, the yields of certain other species of fruit trees are greatly affected byinjuries related to chloride or sodium toxicity. Bernstein outlines several other conclusions, too.
First, most fruit trees used as crops are salt sensitive. Second, if the salt tolerance for a particular
type of fruit tree tends to vary, it is mainly because different varieties or rootstocks absorb toxic
ions at different rates. Third, although salinity generally impairs the quality of fruit, in certain
cases it can be beneficial to the fruit quality. Fourth, for sprinkler­irrigated trees, uptake ofchloride or sodium by wetted leaves can cause severe leaf burn. And fifth, irrigating infrequently,
which is often recommended for ornamental trees and shrubs, can accentuate the effect of salinity
on fruit trees.
The book Abiotic Disorders of Landscape Plants: a Diagnostic Guide (Costello et al.,2003) provides useful guidelines for assessing the salt tolerance of a plant and diagnosing plant­
related problems. The authors list the salinity tolerances and boron tolerances of 610 landscapeplants in a table in that book. Entries are listed within categories (shrub, tree, palm, ground cover,vine, herbaceous plant, and turfgrass) and are sorted alphabetically by botanical or scientificname. The list is useful for comparing species and for discovering the salt tolerance or boron
tolerance of a particular plant already chosen for a landscape. The authors also provide a table ofthe same plants sorted according to salt tolerance, as well as a table sorted according to boron
V­15

tolerance, with each entry appearing in one of three columns: high, moderate, or low tolerance.
These tables are helpful when one is seeking a particular plant to satisfy a known salt tolerance orboron tolerance.
Abiotic Disorders of Landscape Plants: a Diagnostic Guide provides several other usefultypes of information. One table in the book lists 12 different common fertilizers and the relative
salinity of each. Another table in the book displays the salt content of seven kinds ofcommercially available organic soil amendments, including, for example, chicken manure, steer
manure, peat, and redwood compost. Another of the book’s tables provides guidance for readers
who need to interpret chemical data resulting from laboratory tests of soil, water, or plant tissue.
Yet another table in the book lists the methodology and criteria used in evaluating the salinity andboron tolerance data for another of the book’s tables. Still another table provides a summary ofsalt­related problems.
Equally useful, if not more so, is information in Chapters 1, 4, 5, and 6 of theaforementioned book on a structured process for diagnosing plant problems caused by salinity orother abiotic agents. Chapter 6 illustrates the process by outlining six case studies.
Salt tolerances for 18 species of eucalyptus—often used in California’s landscapes due totheir adaptability to the climate, their ability to tolerate little to no irrigation, their relative lack ofnatural pests, and their fairly high rate of growth—are included in the aforementioned book on
abiotic disorders of landscape plants (Costello et al., 2003). A list of 60 species of eucalyptus,
plus numerous species of casuarina, acacia, and other Australian shrubs and small trees, appears
in an appendix of a book published by the UN Food and Agriculture Organization (Tanji andKielen, 2002). The list of salt­tolerant plants originated from the Australia Department ofAgriculture’s farm­revegetation project as part of its sustainable rural development program in
1998.
Many books have been published over the years to help people choose landscape trees,
shrubs, and ground covers for California’s cool, marine coastal climates and its dry, warm inland
climates. Many focus on water­conserving plants because minimizing water usage continues to be
one of California’s perennial challenges. Very few of the available books contain information
about choosing salt­tolerant plants for those same California climate zones. One book that does,by Perry (1981), provides not only a list of plants tolerant of saline soils but also a list of thosethat do well in the presence of salt spray. Table V.B.2.1 in this chapter, excerpted and adaptedfrom the lists in Perry’s book, displays the relative salt tolerance of 36 species of shrubs and treesthat are well adapted to the climatic zones of the Los Angeles and San Diego areas.

V­16

A number of websites contain helpful information. Currently, the following relevant links
are active:·

www.edis.ifas.ufl.edu/EP012

At this site of the University of Florida’s Institute ofFood and Agricultural Sciences, there are two fairly extensive tables that list the salt
tolerances of a number of trees, shrubs, ground covers, vines, and grasses
recommended by the institute for landscapes in northern Florida and for southern
portions of the state. Many species listed are popular elsewhere in the United States,
including California.

·

www.denverwater.org At this website of Denver Water, Colorado’s largest water
utility, click on the side heading “Recycled Water” and then click on the hyperlink“Effects of Recycled Water on Trees and Shrubs” that subsequently emerges on themain window for a number of tips for keeping trees and shrubs healthy when one is
irrigating them with recycled water.

·www.sanjoseca.gov/sbwr/Landscape/GuidePlantList.htm This section of the website
for the city of San Jose, Calif., has a list of locally available plants for landscapes
found to be compatible with irrigation by local recycled water. The list includes 47
species of trees, 29 species of shrubs, 10 species of ground covers, 3 species of vines,
7 species of perennials, and 13 species of native grasses. The vast majority are
relatively common varieties that are popular for landscapes elsewhere in California.

In light of the ever­changing and ephemeral nature of websites and their links, theaforementioned may or may not continue to be active. In any case, a search engine can be used to
discover alternate relevant links.

V.C. Salt Tolerance of Floricultural Species
Beginning over 50 years ago, researchers at the University of California–Los Angeles,
the U.S. Salinity Laboratory in Riverside, and the Metropolitan Water District in La Verneevaluated the salt tolerance of many agronomic and horticultural species. Their legacy—salt
tolerance ratings assigned to a number of species and the recommendations for soil, plant andirrigation management practices—is still valid and pertinent today. It should be noted, however,that some varieties and cultivars of major crops have changed and that in some cases there can besignificant varietal differences in salt tolerance. This finding is particularly true with perennial
crops where rootstock, as well as scion, varieties have changed over the years.

V­17

The work of earlier researchers indicated that waters containing 500 parts per million(ppm, or mg/L) of total dissolved solids (TDS) are likely to reduce the growth or cause leaf burnonly for the most salt­sensitive plants or for plants grown either in poorly suited soil, along withunfavorable temperature, sunlight, or humidity or with inappropriate irrigation management
practices (Pearson, 1949).
They determined that waters containing 800 to 1,000 ppm of TDS also may be usedwithout risk, provided that the kinds of salts contributing to salinity (e.g., sodium, chloride, andsulfate) are considered. Most types of fuchsia (Fuchsia spp.), camellia (Camellia spp.), andrhizomatous begonia (Begonia spp.), for example, grow well in waters of 800 ppm of TDS if
sulfate is the principal anion. Yet the same water can cause problems for certain varieties ofazaleas and for the Rex begonia. These earlier researchers also found that saline waters
dominated by chloride may cause unsightly leaf burn, particularly with sprinkler irrigation.
In the late 1940s, researchers found that calcium­dominated saline waters seemed lessdetrimental to the growth of plants than did waters containing high concentrations of sodium.
Their work suggested that plants may be adversely affected by interactions or imbalances of ions,either in the plant, in the water, or in the soil (Hayward and Wadleigh, 1949). For example, levelsof calcium that meet the nutritional requirements of plants not subjected to sodium­based salinity
may be inadequate for plants that are exposed to high levels of sodium (Hayward and Bernstein,1958). Water in the soil that is dominated by sodium not only reduces the availability of calcium
but also reduces the mobility and transport of calcium to actively growing tissues. Salinity­
induced nutritional disorders may result from the effects of sodium­dominated salinity on nutrient
availability, as well as on the uptake, transport, and partitioning of competitive ions within theplant.
In the 1940s and 1950s, researchers examined the effects of specific ions such as boron,
chloride, and bicarbonate in soils and irrigation waters on the health of floral species. Azaleas(Rhododendron spp.), for example, were found to be relatively sensitive to nutritional imbalances,and even with only slightly saline conditions, calcium deficiency was induced by bicarbonate in
the irrigation water (Lunt et al., 1956). Researchers reported that floral species typically respondto salinity by growing less: the length and weight of flowering stems were reduced, or flowers
were fewer or smaller. Boron, however, was less detrimental than salinity to the number, size,
length, and width of flowering stems of azalea and gardenia (Gardenia spp.; Lunt et al., 1957),
carnation (Dianthus caryophyllus; Lunt et al., 1956), China aster (Callistephus chinensis; Kohl etal., 1957), gladioli (Gladiolus spp.; Kofranek et al., 1957), and poinsettia (Euphorbia
pulcherrima; Kofranek et al., 1956). Once the boron tolerance limits for the species wereV­18

exceeded, injury was characterized by interveinal chlorosis, marginal leaf scorch, and finally, leaf
abscission. Refer to Table V.C.1 for boron tolerance limits of selected floral species.
Some researchers in the 1960s and later conducted salt tolerance trials in which they useda single salt, generally sodium chloride, as the salinizing agent. Other researchers, however, haverecommended using saline water with sodium/(sodium + calcium) ratio, i.e., Na+/(Na+ + Ca2+), in
the range of 0.1 to 0.7 in experimental studies, as this recommendation better reflects the ion
ratios in irrigation water or in the water in the soil for most horticultural crops (Pearson, 1949;
Bernstein, 1975). The uncharacteristic salinizing composition of the former may induce ion
imbalances that contribute to calcium­related physiological disorders in certain crops (Shear,
1975; Sonneveld, 1988). Furthermore, the use of single­salt solutions in salt tolerance
experiments may result in misleading and erroneous interpretations of a plant’s response tosalinity.
Grattan and Grieve (1999) examined the relationship between a horticultural crop’s
mineral nutrients and its salinity tolerance. They reviewed the literature that pertains to salinity
and mineral nutrition, particularly nitrogen, phosphorus, potassium, calcium, magnesium, sulfur,
and boron, and briefly examined the potential interactions between certain micronutrients—
copper, iron, manganese, molybdenum, and zinc—and salinity. They concluded that a
multiplicity of salinity­nutrient interactions occur simultaneously for many types of plants andthat whether those interactions ultimately affect the plant as measured by yield, quality, size or
elongation, etc. depends on the levels of salinity, the composition of salts, the species, thenutrients, and a host of other environmental factors.
Even under nonsaline conditions, significant economic losses have been linked toinadequate calcium nutrition of horticultural crops. A number of factors can influence the amountof plant­available calcium, including the total supply of calcium, the nature of the counter­ions,the pH of the substrate, and the ratio of calcium to other cations in the irrigation water (Grattan
and Grieve, 1999). Calcium­related disorders may even occur in plants grown on substrates
where the calcium concentration appears to be adequate (Pearson, 1949; Bernstein, 1975).
Symptoms indicating nutritional deficiency are generally caused by differences in calcium
partitioning to the growing regions of the plant. All parts—leaves, stems, flowers, and fruits—
actively compete for the pool of available calcium, and each part independently influences the
movement of calcium. Organs that transpire more actively are likely to have the highest
concentrations of calcium.
In agricultural crop plants that consist of large heads enveloped by outer leaves, such as
cabbage and lettuce, excessive transpiration by the outer leaves diverts calcium from the rapidlyV­19

growing embryonic plant tissue (Bangerth, 1979). A deficiency of calcium manifests as internal
browning in the younger tissues of cabbage and lettuce and as “blackheart” in celery. Calcium
deficiency may also occur in reproductive tissues and cause decreases in quality such as “blossom
end rot” of tomato, melon, and pepper; “soft nose” of mango and avocado; and cracking and“bitter pit” of apple. Artichokes grown under arid, but nonsaline, conditions can exhibit calcium
deficiency, with injury appearing as necrosis of inner bracts (Francois, 1995).
Horticultural crops that are susceptible to calcium­related disorders without salinity
become even more so under saline conditions. As the concentration of salt in the root zone
increases, the plant’s requirement for calcium also increases (Bernstein, 1975). At the same time,
the uptake of calcium from the substrate may be depressed because of ion interactions, chemical
precipitation, and increases in ionic strength (Grattan and Grieve, 1999). When these susceptible
crops are also challenged by salinity, their market quality can decline significantly.
Very little information is available on the differential partitioning of calcium and any
resulting patterns of injury in floricultural species. Certain varieties of Asiatic hybrid lilies are
susceptible to calcium­related disorders, whereas others are immune. Injury on “Star Gazer,”“Acapulco,” and “Muscadet” manifests as necrosis of the upper leaves (Chang et al., 2004) andon “Pirate,” as white­gray cross bands on the leaves, as well as tip burn (Berghoef, 1986). The
varieties “Alliance” and “Helvetia” appear to be resistant to the disorder (Chang et al., 2004).
Poinsettia (Euphorbia pulcherrima) also exhibits variety­dependent susceptibility to calcium
deficiency, with injury usually appearing as marginal necrosis of the bracts. Wissemeier (1993)
demonstrated that “Angelika” and “Supjibi” were sensitive. In contrast, injuries do not appear tooccur in the varieties “Diva Starlight” and “Lilo.”
The effect of salinity on the sensitivity of floral crops to calcium­related disorders has notbeen widely explored. One study, however, was conducted with poinsettia, a moderately salt­
tolerant crop (Cox, 1991; Dole and Wilkins, 1999). No visible symptoms associated with excess
fertilizer salinity were observed in “Red Sails” poinsettia (Cox, 2001) or “V−14 Glory” poinsettia(Ku and Hershey, 1991), although measurements of EC revealed that salinity levels in the rootzone exceeded the satisfactory range for the crop (Hartmann et al., 1988).
Other information on the salt tolerance of floral species results from studies of the
responses of plants to chloride­dominated saline irrigation waters. Such water typically contains
both sodium chloride and calcium chloride. A few researchers evaluated the salt tolerance offloral crops by using irrigation waters prepared to simulate recycled or saline waters typical of a
specific location or site. Dutch growers often use solutions with compositions of salts adjusted tothe average found in surface waters in the western Netherlands (Bik, 1980; Sonneveld, 1988).
V­20

Saline waters (EC = 2.5 to 4.5 dS/m) from local wells in Israel continue to be used successfully
for growing floral species on over 700 ha throughout the Negev Desert (Shillo et al., 2002).
Arnold and fellow researchers (2003) demonstrated that recycled runoff from a plant nursery andwater from a constructed wetland were suitable for irrigating certain bedding plants and flowers.
Recent floriculture research at the U.S. Salinity Laboratory involved the use of artificial waters
specially prepared to mimic three waters used for irrigation in California: the sodium­ and sulfate­dominated drainage effluents from the San Joaquin Valley, various concentrations of Colorado
River water, and groundwaters affected by seawater intrusion along the California coast (Grieve
et al., 2005; Carter et al., 2005; and Grieve et al., 2006).
An important caveat to bear in mind is that research on the salt tolerance of floricultural
species continues to be largely devoted to providing information useful for helping commercial
floricultural growers maintain the productivity, quality, and profitability of their plants. The
standards of quality for plants in landscapes are far less stringent. For example, because exposureof a plant to salinity generally decreases the length of the stems and the number of florets—twomajor determinants of quality in commercial flowers—growers of floricultural crops are likely to
use the highest quality of water available to maximize the plant’s height and number of blooms.
However, a slightly shorter flowering plant with somewhat fewer florets would be aesthetically
acceptable for use in a landscape—as long as its overall health remains uncompromised, its stems
are robust, its leaves and flowers remain true to color, and its flowers and leaves sustain novisible salt injury. Take the specific example of two species of statice grown to be sold as
flowers, Limonium perezii and L. sinuatum, which complete their life cycles in water saltier thanseawater (Aronson, 1989). To discover if either could produce marketable cut flowers at lower
salinities, both species were grown under irrigation with waters ranging from 2 to 30 dS/m
(Grieve et al., 2005). Both species of statice flowered and set seed in all treatments, but theirheight decreased consistently and significantly as salinity increased, with plants receiving themost saline treatment growing only one­third as tall as those irrigated with nonsaline waters.
However, even under severe salt­related stress, both produced healthy plants with attractive
foliage and colorful flowers on sturdy, albeit short, stems. The salt tolerance of both species foruse as marketable cut flowers is rated as “low” based on stem length (Farnham et al., 1985), but
for use in a landscape, they would fall in the “very tolerant” category.
It should also be noted that the effects of salinity on floral crops are not always adverse.
Salt­related stress can beneficially affect the yield, quality, and disease resistance of a plant. In
some instances, the uptake and accumulation of salinizing ions stimulates growth. Cabrera (2001)
and Cabrera and Perdomo (2003) observed a positive correlation between relatively high leaf­
V­21

chloride concentrations (0.45%) and dry weight for container­grown rose (“Bridal Pink” on Rosa
manetti rootstock). Yield and quality were unaffected. Salinity imposed early in the life cycle ofsome cut­flower species tends to limit vegetative growth with favorable results. Salinity­induced
reduction in the length of leaf­supporting stems may be beneficial in chrysanthemum, where tallcultivars are treated with growth regulators to keep the plants compact and short. While plantheight is often reduced by moderate salinity, the length of time to maturity and the size ofdeveloping floral buds generally remain unaffected by stress (Lieth and Burger, 1989).
Application of salinity after some optimal period of vegetative growth tends to enhance
reproductive growth and often improves quality. Shillo and coresearchers (2003) reported thatsalinity imposed on Eustoma grandiflorum during its final stages of vegetative growth resulted insignificant increases in the number of flowers and in stem weight and diameter. Another benefitof salt treatment was the production of more compact flower clusters, the compactness of which
prevents developing buds from drooping. Similar positive effects have been noted with carnation.
Salt­related stress during its early reproductive growth resulted in shorter, more robust flower­
bearing stalks with larger developing buds (Baas et al., 1995).
Some of the significant varietal differences in salt tolerance reported for cut­flower crops(Table V.C.2) may be due to differences in climate, nutrition, composition of the salinizing
medium, and the duration of exposure to salinity. These differences become very important inselecting plants for landscapes irrigated with recycled waters.
In trials conducted under nearly identical cultural conditions, Sonneveld andcoresearchers (1987, 1999) reported that the carnation cultivar “Beauty” was significantly moretolerant of soil salinity than were either “Scania” or “Nora Barlo.” In the same study, the hybridlilies “Star Gazer” and “Connecticut King” both produced lighter­weight flowers when thesalinity in the soil extract exceeded 1.2 dS/m. Also, the lilies produced 9.6 and 4.6% fewer
flowers, respectively, with each unit increase in salinity. Additional information regarding
varietal differences in salt tolerance for selected cut flowers is included in Table V.C.3.
The parameters used to assess the salt tolerance of cut flowers need to be considered toaccurately assign a tolerance category to a species. Generally, flower quality is less sensitive tosalinity than is vegetative growth. For example, once the threshold of “Fabiola” gerbera (Gerbera
jamesonii) is exceeded, yield based on the number of flower­bearing stalks per plant declines
17% for each unit increase in salinity, but the diameter of the flowers is relatively insensitive,
declining only 3% per unit increase. Likewise, the number and weight of flowering stalks in
Anthurium spathes are more affected by salinity than are the diameter of its flowers. The salt
tolerance of the poinsettia variety “Barbara Ecke Supreme” is higher when the rating is based onV­22

the diameter of bracts rather than on injury to leaves and an increase in abscissions—the droppingof flowers, fruits, or leaves from the plant (Kofranek et al., 1956).
Salt tolerance ratings of some flower crops as shown in Table V.C.1 are derived fromdata collected from closely related plants of horticultural and agronomic value. Data regarding thesalt tolerance of ornamental Brassica species such as kale and cabbage are virtually nonexistent,
but it would be reasonable to assume that their salt tolerance would not vary sharply from that of
the same leafy vegetables grown under agronomic conditions. Similarly, the Carthamus tinctorius
varieties of safflower used as cut flowers and bedding plants will likely fall into the same salt
tolerance category as the well­known seed oil­producing variety. The commercially important
pistachio tree (Pistacia vera) and its close relatives are also relatively tolerant of both salt andexcess boron stresses (Ferguson et al., 2002). P. atlantica and P terebinthus are attractive
ornamentals, potentially useful for salt­affected sites.
Table V.C.1. Boron tolerance limits for cut flowers.
SpeciesSensitivity to boron
Sensitive

Moderately sensitive

Moderately tolerant3

Threshold (g/m )Reference

Botanical nameCommon name

Delphium sp.

Larkspur

0.5–1.0

Eaton, 1944

Pelargonium x hortorum

Geranium

0.5–1.0

Kofranek et al., 1958

Viola odorata

Violet0.5–1.0

Eaton, 1944

Viola tricolor

Pansy

0.5–1.0

Eaton, 1944

Zinnia elegans

Zinnia

0.5–1.0

Eaton, 1944

Calendula officinalis

Marigold

1.0–2.0

Francois and Clark, 1979

Callistephus officinalis

China aster

1.0–2.0

Kohl et al., 1957

Euphorbia pulcherrima

Poinsettia

1.0–2.0

Gardenia sp.

Gardenia

1.0–2.0

Gladiolus sp.

Gladiola

1.0–2.0

Dianthus carophyllus

Carnation

2.0–4.0

Lunt et al., 1956

Lathyrus odoratus

Sweet pea

2.0–4.0

Eaton, 1944

V­23

Kofranek et al., 1956
Lunt et al., 1957
Kofranek et al., 1957

Table V.C.2. Salt tolerance of selected landscape flower crops.
aBotanical nameCommon nameSalt tolerance

Agapanthus orientalis

Lily of the Nile

Sensitive

Skimina, 1980

Ageratum
houstonianum

Ageratum

Moderately sensitive

Devitt and Morris, 1987

Alstroemeria hybrids

Inca lily, Peruvian lily

Very sensitive

Sonneveld, 1988

Amaranthus
hypochondriacus

Pygmy torch

Tolerant

Aronson, 1989

Amaranthus tricolor

Love­lies­bleeding

Tolerantb

Aronson, 1989

Anthurium andreanum

Anthurium

Very sensitive

Sonneveld and Voogt, 1983

Antirrhinum majus

Snapdragon

Moderately sensitive

Artemesia stelleran

Dusty Miller

Moderately sensitive

Glattstein, 1989

Begonia bunchii

Begonia

Sensitive

Pearson, 1949

Begonia Rex­cultorumRex begonia

Very sensitive

Pearson, 1949

Begonia ricinifolia

Begonia

Sensitive

Pearson, 1949

Bouvardia longiflora

Bouvardia

Moderately sensitive

Sonneveld et al., 1999b

Maas and Grattan, 1999b

Reference(s)cCarter et al., 2005

Brassica oleracea

Ornamental cabbage

Sensitive

Brassica oleracea

Ornamental kale

Sensitive

Shannon et al., 2000

Calendula officinalis

Pot marigold

Moderately tolerant

Chaparzadeh et al., 2003

Callistephus chinensis

China aster

Moderately sensitive

Kohl et al., 1957

Moderately tolerant

Sonneveld et al., 1999

Calocephalus brownii

Cushion bushModerately sensitive

Costello et al., 2003

Camellia japonica

Camellia

Sensitive

Pearson, 1949

Carathamus tinctorius

Safflower

Moderately tolerantBeke and Volkmer, 1994

Catharanthus roseus

Vinca

Sensitive

Arnold et al., 2003; Huang andCox, 1988

Celosia argenta cristata

Crested coxcomb

Moderately sensitive

Devitt and Morris, 1987

Celosia argenta cristata

Chief celosia

Tolerant

Carter et al., 2005

Cereus peruviana

Apple cactus

Moderately sensitive

Costello et al., 2003

Chlorophytum
comosum

St. Bernard’s lily

Tolerant

Zurayk et al., 1993

Chrysanthemum
morifolium

Mum

Moderately tolerant

Kofranek et al., 1953; Pearson,
1949

Clematis orientalis

Clematis

Very tolerant

Krupenikov, 1946

Coleus blumei

ColeusTolerant

Zurayk et al., 1993

Codiaeum punctatus

CrotonModerately tolerant

Farnham et al., 1985

Consolida ambigua

LarkspurSensitive

Arnold et al., 2003

Cosmos bipinnatus

CosmosVery sensitiveb

Devitt and Morris, 1987cCoreopsis grandifloraCoreopsis

Moderately sensitive

Glattstein, 1989

Crassula ovata

Jade plantModerately sensitive

Skimina, 1980

Cyclamen persicum

CyclamenSensitive

Bik, 1980

Cymbidium spp.

OrchidVery sensitivede Kreij and van den Berg, 1990

Dianthus barbatus

Pinks

Moderately sensitive

Monk and Peterson, 1961

Dianthus caryophyllus

Carnation

Moderately tolerant

Baas et al., 1995

Dianthus chinensis

Carnation

Moderately tolerant

Devitt and Morris, 1987

Eschscholzia californica

California poppy

Moderately tolerant

Glattstein, 1989

Euphorbia pulcherrima

Poinsettia “Red Sails”

Sensitive

Cox, 1991

Euphorbia pulcherrima

Poinsettia“Barbara Ecke”

Very sensitive

Kofranek et al., 1956

c

V­24

Euryops pectinatus

Golden marguerite

Sensitive

Wu et al., 1999

Eustoma grandiforum

Lisianthus

Moderately sensitive

Shillo et al., 2002

Felicia amelloides

Felicia

Sensitive

Farnham et al., 1985; Skimina,
1980

Fuchsia hybrida

Fuchsia

Very sensitive

Pearson, 1949

Gardenia augusta

Gardenia

Sensitive

Lunt et al., 1957

Gazania aurantiacum

Gazania

Moderately tolerant

Costello et al., 2003

Gerbera jamesonii

Gerbera daisy

Moderately sensitive

Sonneveld and Voogt, 1983; Baaset al., 1995; Savvas et al., 2002

Gazania spp.

Treasure flower

Very tolerant

Perry, 1989

Gladiolus spp.

Gladiola

Sensitive

Kofranek et al., 1957

Gomphrena globosa

Globe amaranthModerately sensitive

Gyposphila paniculata

Baby’s breath

Moderately tolerant

Shillo et al., 2002

Helianthus annuus

Sunflower

Moderately tolerant

Ashraf and O’Leary, 1995

Helianthus debilis

Cucumber leaf

Very tolerant

Costello et al., 2003

Hibiscus rosa­sinensis

Hibiscus

Sensitive

Bernstein et al., 1972

Hippeastrum hybridum

Amaryllis

Very sensitive

Shillo et al., 2002; Sonneveld andVoogt, 1983

Hymenocallis keyensis

Spiderlily

Moderately tolerant

Costello et al., 2003

Impatiens ´ hawkeri

Impatiens

Sensitive

Todd and Reed, 1988

Kalanchoe spp.

Kalanchoe

Moderately tolerant

Costello et al., 2003

Kochia childsii

KochiaTolerant

Monk and Peterson, 1961

Lathyrus japonica

Sweet pea

Moderately tolerant

Costello et al., 2003

Lilium spp.

Asiatic hybrid lily

Sensitive

Sonneveld, 1988

Lilium spp.

Oriental hybrid lily

Sensitive

Sonneveld and Voogt, 1983

Limonium spp.

Japanese Limonium

Very tolerant

Shillo et al., 2002

Limonium latifolium

Sea lavender

Very tolerant

Aronson, 1989

Limonium perezii

Statice

Sensitive

Farnham et al., 1985

Very tolerant

Grieve et al., 2005; Carter et al.,2005cKang and van Iersel, 2002

Limonium sinuatum

Statice

Very tolerant

Grieve et al., 2005; Carter et al.,2005

Lobularia maritima

Sweet Alyssum

Moderately tolerant

Monk and Peterson, 1961

Matthiola incana

Stock

Very tolerant

Lunt et al., 1964; Wigdor et al.,
1958

Narcissus tazetta

Paperwhite
Narcissus

Sensitive

Arnold et al., 2003

Oenthera speciosa

Mexican evening
primrose

Moderately tolerant

Costello et al., 2003

Ophiopogon jaburan

Giant turf lily

Moderately sensitive

Skimina, 1980

Ornithogalum arabicum

Arabian star flower

Very sensitive

Shillo et al., 2002

Pelargonium ´ hortorum

Geranium

Sensitive

Kofranek et al., 1958

Pelargonium
domesticum

Geranium

Tolerant

Zurayk et al., 1993

Pelargonium peltatum

Ivy geranium

Moderately tolerant

Costello et al., 2003

Petunia hybrida

Petunia

Tolerant

Devitt and Morris, 1987

Portulaca grandiflora

Moss rose

Very tolerant

Devitt and Morris, 1987

Phalaenopsis hybrid

OrchidVery sensitive

Wang, 1998

Protea obtusifolia

ProteaModerately tolerant

Rodrigues­Perez et al., 2000

Rhododendron hybrids

AzaleaModerately sensitive

Cabrera, 2003

V­25

Rhododendron obtusum

AzaleaSensitive

Pearson, 1949; Lunt et al., 1957

Rosa ´ hybrida

Rose

Sensitive

Cabrera and Perdomo, 2003;
Fernández Falcón et al., 1986

Stapelia gigantea

Starfish flower

Moderately tolerant

Costello et al., 2003

Strelitzia reginae

Bird of paradise

Very sensitive

Farnham et al., 1985

Tagetes erecta

MarigoldModerately tolerantWest et al., 1980

Tagetes patula

MarigoldModerately tolerant

Devitt and Morris, 1987

Trachelium caeruleum

Blue throatwort

Sensitive

Shillo et al., 2002c

Tropaeolum majus

Nasturtium

Moderately sensitive

Glattstein, 1989

Vinca major

Periwinkle

Moderately tolerant

Costello et al., 2003

Vinca minor

MyrtleSensitive

Farnham et al., 1985

Viola ´ wittrockiana

Pansy

Sensitive

Arnold et al., 2003

Zinnia elegans

ZinniaModerately sensitive

Devitt and Morris, 1987a

Criteria for assigning salt tolerance: not more than 50% reduction in growth, no visually observable foliar−1burn, and maximum permissible ECe (dS m ) as follows:<2,

very sensitive;

2–3,

sensitive;

3–4,

moderately sensitive;

4–5,

moderately tolerant;

5–6,

tolerant; and>6,very tolerant.

bcBased on salt tolerance classification of related agronomic or horticultural species or variety.

Only qualitative data are available.

V­26

Table V.C.3.

Varietal differences in salt tolerance for selected cut­flower crops.

Common name

Variety

Carnation

AdefieChrysanthemum

Threshold ECe(dS m−1)

Slope (%)

Reference

1.1

2.1

Sonneveld et al.,
1999

Beauty4.3

3.9

Sonneveld et al.,1999

Princess white

5.0—

Devitt and Morris,
1987

Scania1.2

6.9

Sonneveld andVoogt,1987

Nora Barlo

1.2

5.5

Sonneveld andVoogt,1987

Indianapolis white

2.4—

Rutland,1972

Spider

>0.8

6.8

Sonneveld andVoogt, 1987

Horim

>0.8

12.1

Sonneveld andVoogt, 1987

a

Maghi

>8.0

—

Rahi and Datta, 2000

Basantika>8.0—

Rahi and Datta, 2000

Bronze Kramer

6.0

9.0

Kofranek et al., 1953

Albatross

2.0—

Lunt et al., 1962

Beauty1.5

9.8

Sonneveld et al.,1999

Mandarine

<0.6

5.1

Fabiola

<0.6

BaccaraaGerberaRosebSonneveld andVoogt, 1983

6.5bSonneveld andVoogt, 1983

1.0

10

Yaron et al., 1969

Grenoble

2.1

20

Bernstein et al., 1972

Forever yours

1.8—

Hughes and Hanan,
1978

Sonia

1.0

10

Zeroni and Gale,
1989

Europa2.1

5.3

Sonneveld etal.,1999

Madelon

4.8

2.0

Baas and Berg, 1999

Kardinal

2.2

20

Wahome et al., 2000d—Cabrera, 2001

Bridal pink

c

5.4

a

Plants grown from cuttings subjected to mutagenesis by gamma irradiation resulted in more salt­tolerant
genotypes.
b
Based on weight of peduncle.
cRecirculating irrigation system.
d
EC of leachate.

V­27

V.D. Salt Tolerance of Turfgrasses
The quality of a turfgrass stand is the net result of inherent genetic characteristics of theparticular species being grown and the interactions of climate, pests, and the soil. In arid andsemiarid regions where rainfall is insufficient to leach salt out of the root zone, excessive amounts
of soluble salts may accumulate in the root zone. This phenomenon can impose limits on the
production or the management of quality turf (Carrow and Duncan, 1998; Marcum, 2006).
Salinity­related stress on turfgrasses is also a serious problem near the seacoast, both because theconcentration of salt in the air typically is higher than that found inland and because shallow
water tables may be unusually saline.
Wherever salinization of soils occurs, it is a continuous process resulting from various
combinations of these factors: insufficient rainfall, inadequate irrigation, poor drainage, irrigation
with water of poor quality, and the upward movement of salts from saline shallow groundwater.
As a general rule, if the amount of water applied to the soil (irrigation plus naturalprecipitation)exceeds

evapotranspiration,

salt

moves

downward.

Conversely,

ifevapotranspiration exceeds the amount of water applied, salt movement is upward. In the latter
case, salt drawn to the soil surface gradually accumulates to levels toxic to turfgrasses.
Depending on the salinity tolerance of the turfgrass grown, full stands of grass cansometimes be established at low or moderate levels of soil salinity. Turfgrass growth in highly
saline soils, however, is restricted (Carrow and Duncan, 1998).
The symptoms of salinity­related stress in turfgrasses are likely to vary somewhat,
because existing salt can result in osmotic stress (physiological drought), nutritional imbalances,
toxicity, or a combination of these maladies. In general, however, the following symptoms areassociated with turfgrass grown under saline conditions:·

Turf is likely to appear blue­green or light bright­green in color during the early stagesof salt stress. This coloration is followed by irregular shoot growth.

·

Necrotic spots may develop on leaves if toxicity from a specific ion (such as boron)
occurs.

·As salinity­related stress increases, the shoots increasingly wilt and become
progressively darker green.

·

Higher levels of salinity cause burning of the tips of leaves, with the burn eventuallyextending downward toward the entire leaf surface. At this level, shoot growth isgreatly reduced and turfgrass is stunted. As salinity­related stress increases, leaves
generally become finer textured and the growth of roots is stunted, often resulting inV­28

shallow roots. If corrective steps are not taken, the growth of grass will be minimal, thedensity of shoots will decrease, and individual plants will die, thinning the stand. The
extent of salt uptake and its consequent effects on the growth of turf are directly related
to the concentration of salt in the soil water. Growth of most turfgrasses is not
significantly affected by salt levels below an ECe of 2 dS/m. In soils with salt levels of
more than 2 dS/m, the growth of most turfgrasses is gradually restricted. Some notable
exceptions, however, would include bermudagrass and seashore paspalum, which cantolerate soil salinities greater than an ECe of 10 dS/m. Due to pronounced differencesamong turfgrass species and cultivars in their tolerance to both individual salt ions andtotal salinity, each turfgrass must be individually evaluated with regard to a specific
type of soil salinity.

·

Higher levels of salinity cause burning of the tips of leaves, with the burn eventuallyextending downward toward the entire leaf surface. At this level, shoot growth isgreatly reduced and turfgrass is stunted. As salinity­related stress increases, leaves
generally become finer textured and the growth of roots is stunted, often resulting inshallow roots. If corrective steps are not taken, the growth of grass will be minimal, thedensity of shoots will decrease, and individual plants will die, thinning the stand.

Due to many interacting factors, the “absolute” salinity tolerance of a turfgrass species cannot
be determined. However, different turfgrasses can be compared, with relative salt tolerance given
in terms of the acceptable salt content of the soil root zone, expressed as the ECe of soil water
extract. Table V.D.1 (Harivandi et al., 1992; Marcum, 1990; Marcum, 1999) is a general guide to
the salt tolerance of turfgrass species (substantial differences in salt tolerance exist amongcultivars within species) and shows, for example, that Kentucky bluegrass (Poa pratensis)
tolerates soil salinity at ECe levels up to 3 dS m−1. As the table indicates, soils with an ECe below
3 dS m−1 are considered satisfactory for growing most turfgrasses. Soils with an ECe above 10 dS
m−1 successfully support only highly salt­tolerant turfgrass species. Salt tolerances of warm­
season and cool­season turfgrass cultivars, given in terms of both top growth and root growth,
have been summarized by Carrow and Duncan (1998).
Much work has been done in screening existing cultivars or ecotypes for salinity
tolerance, including these turfgrass species: Agrostis stolonifera (Marcum, 2001), Buchloe
dactyloides (Wu and Lin, 1994), Cynodon spp. (Dudeck et al., 1983; Francois, 1988; andMarcum, 1999), Distichlis spicata (Marcum et al., 2005), Festuca spp. (Horst and Beadle, 1984;
and Leskys et al., 1999), Lolium perenne (Rose­Frincker and Wipff, 2001), Paspalum vaginatum(Dudeck and Peacock, 1985; Marcum and Murdoch, 1990; and Lee et al., 2004a; 2004b), PoaV­29

pratensis (Qian et al., 2001; Qian and Suplick, 2001; and Rose­Fricker and Wipff, 2001),
Puccinellia spp. (Harivandi et al., 1982, 1983), Stenotaphrum secundatum (Dudeck et al., 1993),
and Zoysia spp. (Marcum et al., 1998; and Qian et al., 2000). Such work is important and needs tobe updated at regular intervals, in order to keep up with the rapid introduction of new cultivars.
The turfgrass industry is expanding rapidly at the same time that pressures from thedomestic, agricultural and ecological sectors are placing increasing demands on freshwater
resources. Allocation of high­quality waters to high­priority uses has resulted in the transition oflandscape sites, parklands, and golf courses to the use of recycled waters. From a survey of golfcourse superintendents who currently use recycled water for irrigation in the southwestern UnitedStates, Devitt et al. (2004) concluded that golf course personnel, while not opposing the switch toreuse water, found that significant changes in turfgrass management practices were required tominimize negative impacts of recycled water.
a

Table V.D.1. California turfgrass species tolerate various levels of soil salinity.
Sensitive−1

Moderately
sensitive−1

Moderately
tolerant

Tolerant−1−1(<3 dS m )(3 to 6 dS m )(6 to 10 dS m )(>10 dS m )Annualbluegrassess (Poaannua)

Annual ryegrass(Lolium
moltiflorum)

Course­leaf
zoysiagrasses(Japonica type)

Alkaligrass(Puccinellia spp.)

Colonial bentgrass(Agrostis tenuis)

Buffalograss(Buchloe
dactyloides)

Perennial
ryegrass (Lolium
perenne)

Bermudagrasses(Cynodon spp.)

Hard fescue(Festuca
longifolia)

Creeping
bentgrass(Agrostispalustris)

Tall fescue(Festuca
arundinacea)

Fineleafzoysiagrasses(Matrella type)Kentuckybluegrass (Poapratensis)

Slender, creeping
red, andChewings fescues(Festuca rubra)

Rough bluegrass(Poa trivialis)

Saltgrass(Distichlis spp.)
Seashore
paspalum(Paspalum
vaginatum)
St. Augustine
grass(Stenotaphurm
secundatum)aGrasses listed here are grouped by their tolerance of soil salinity (expressed as the ECe of soil paste extract).

V.E. Salt Tolerance of Native Plants
Much information has been published, both in books and on the Internet, to describe
California’s native plants. However, few sources of information are available regarding the saltV­30

tolerances of such plants. Southwestern Landscaping with Native Plants (Phillips, 1987) provides
relative salt tolerances (as well as other horticultural information) for numerous trees, shrubs, andground covers that are native to southeastern California, Nevada, Arizona, New Mexico, southern
Colorado, southern Utah, and western Texas (see Table V.E.1.1). We have excerpted from thatbook and then consolidated and edited relevant data for those species of plants reported to benatives of California. The result is Table V.E.1.2, which lists 21 different varieties of shrubs,
trees, and ground covers that may be useful for landscape projects in southern California. It is
important, however, that the plants featured in this table are arid land varieties; therefore, some
may not be particularly well suited for landscapes in Los Angeles or San Diego or elsewhere
along the southern California coastal plain. Cross­checking these entries against other sources ofhorticultural information is recommended.
In the absence of published quantitative data from controlled experiments or field trials
involving the salinity of native plants, qualitative salt tolerance information may prove useful.
The key is to collect such information with care and to test the information thoroughly forsoundness. One method for qualitatively estimating the salt tolerance of a plant is to infer that if
the plant originated in an area where saline soils are common, then that plant may do well in othersaline environments. Such reasoning is not without risk, however, because many otherenvironmental factors are important during the establishment and growth of a plant and because
one or more of those factors may not match between the plant’s native origin and the desired site.
For example, the microclimate where a plant originally thrived in the wild may not match that of
the intended landscape even though the salinity of the soil and perhaps various other factors may
be similar.
Another strategy that might work well is to choose several different desirable native
species for your landscaping project and then attempt to research those or similar plants in
Costello et al. (2003) or other references that list salt tolerance data for “conventional”
ornamental plants. It may be that one or more of the California native plants for which
information is sought have already become a somewhat popular plant and that their salt tolerance
is listed in one of the aforementioned sources.

V­31

a

Table V.E.1.1. Salt tolerance of selected California native trees, shrubs, and ground covers.

aBotanical nameCommon nametype

Native range

Salt
tolerance

Artemesia tridentata

Bigleaf sage

Shrub

Dakotas, Rockies, Sierra
Nevada, and Cascades;
predominant in Great BasinregionLow tomoderate

Atriplex canescens

Fourwing saltbush(Chamiso)

Shrub

New Mexico north to South
Dakota and west to California

Excellent

Baccharis emoryii

Broom Baccharis

Shrub

Texas, New Mexico, Arizona,
California, Nevada, Utah,
Colorado

Good

Baccharis pilularis

Dwarf coyotebush

Ground cover

California coast—Sonoma toMonterey counties

Undocumented;
coastal native origin
suggests tolerance
fair or better

Berberis repens

Creeping Mahonia

Ground cover

Texas, New Mexico, Arizona,
California; north to Nebraska
and British Columbia

Very poor

Bouteloua gracilisBlue Grama

Ground cover

Wisconsin to Alberta, Canada;
Missouri, Texas, southern
California, New Mexico

Fair

Ceratoides lanata

Winterfat

Shrub

Canada south to Mexico, Rocky
Mountains west to Pacific Coast

Fair

Chamaebatieria
millefolium

Fernbush

Shrub

Idaho south to New Mexico,
Arizona, California

Fair

Chilopsis linearis

Desert willow(Flor de Mimbres)

Tree

Central Texas west to
California, northern Mexico

Very good

Chrysothamnus
nauseosus

Chamisa(Rabbitbrush)

Shrub

Western Canada south toCalifornia, Texas, northern
MexicoModerate

Cowania mexicana

Cliffrose

Shrub

Southern Colorado west to
southeastern California, Mexico

Fair

Elaeagnus angustifolia“King Red”

Russian olive

Tree

Southern Europe andsouthwestern Asia. Naturalized
in western U.S.

Excellent

Fallugia paradoxa

Apache plume

Shrub

Texas west to California;
Colorado to Mexico

Fair

Fraxinus species

Ash

Tree

Texas to California, Colorado
and Utah south to Mexico

Fair to poor

Gaillardia species

Blanketflower

Ground cover

Throughout North America

Good
Fair to poor

Linum lewisii

Blue flax

Ground cover

Alaska east to Saskatchewan
and south to Kansas, Texas,
New Mexico, Arizona, California

Penstemon ambiguus

Bush penstemon

Ground coverKansas, Colorado, Utah, Texas
west to California

Fair

Populus tremuloides

Quaking aspen

Tree

Alaska east to Labrador, south
to Virginia; Rocky Mountains
south to New Mexico andArizona

Poor

Populus fremontii andsubspecies

Cottonwood

Tree

Nevada, Southwestern Utah,northern California, Arizona,
New Mexico

Fair

Rhus microphylla

Littleleaf sumac(Lemita)

Shrub

Washington to Missouri,
California east to Texas

Fair

Rhus trilobata

Threeleaf sumac(Lemita)

Shrub

Washington to Missouri,
California east to Texas

Poor tomoderate

Adapted from Phillips (1987).

V­32

a

Table V.E.1.2. Salt­tolerant trees and shrubs for coastal southern California.
Tolerant of
Botanical nameCommon name
Type of plantsaltwater spray?

Tolerant ofsaline soil?

Acacia longifolia

Sydney golden wattle

Shrub

Yes

No

Acacia melanoxylon

Blackwood acacia

Shrub

Yes

No

Albizia lophantha

Plume Albizia

Tree

Yes

No

Arctostaphylos edmundsii

Little Sur manzanita

Shrub

Yes

No

Artemisia pycnocephala

Sandhill sage

Shrub

No

Yes

Atriplex species

Saltbush

Shrub

Yes

Yes

Baccharis pilularis

Dwarf chaparral broom

Shrub

Yes

No

Caesalpinia gilliesii

Bird of paradise bush

Shrub or small
tree

Yes

No

Callistemon species

Bottlebrush

Shrub or small
tree

Yes

Yes

Casuarina species

Beefwood

Tree

No

Yes

Elaeagnus angustifolia

Russian olive

Small tree

No

Yes

Elaeagnus pungens

Silverberry

Shrub

Yes

No

Encelia californica

California Encelia

Shrub

Yes

No

Eriogonum giganteum

St. Catherine’s lace

Shrub

Yes

No

Eucalyptus camaldulensis

Red gum

Tree

No

Yes

Eucalyptus rudis

Desert gum

Tree

No

Yes

Eucalyptus torquata

Coral gum

Tree

Yes

Yes

Hakea suaveolens

Sweet Hakea

Shrub

Yes

No

Jasminum humile

Italian jasmine

Shrub

Yes

No

Lavatera assurgentiflora

Tree mallow

Shrub

Yes

Yes

Leptospermum laevigatum

Australian tea tree

Small tree

Yes

No

Melaleuca nesophila

Pink Melaleuca

Tree or large
shrub

Yes

Yes

Melaleuca styphelioides

Black tea tree

Tree

Yes

No

Metrosideros tomentosus

New Zealand Christmas
treeTree or large
shrub

Yes

Yes

Myoporum laetum

Myoporum

Shrub or tree

No

Yes

Nerium oleander

Oleander

Shrub

No

Yes

Pinus halepensis

Aleppo pine

Tree

No

Yes

Pinus pinea

Italian stone pine

Tree

Yes

No

Pinus torreyana

Torrey pine

Tree

Yes

No

Pittosporum crassifolium

Pittosporum

Shrub

Yes

Yes

Pittosporum phillyraeoides

Willow Pittosporum

Shrub

Yes

Yes

Prunus lyonii

Catalina cherry

Shrub or tree

Yes

No

Rhus integrifolia

Lemonade berry

Shrub

Yes

No

Schinus terebinthifolius

Brazilian pepper

Tree

No

Yes

Tamarix species

Tamarisk

Tree

No

Yes

Zizyphus jujuba

Chinese jujube

Small tree

No

Yes

a

All these plants survive well in the climate zones of the Los Angeles and San Diego areas. After Perry, 1981.

V­33

V.F. Sensitivity of Plants to Specific Ions
A plant can be salt tolerant yet still be sensitive to and potentially damaged by specificions. The ions responsible for most of the damage are chloride, sodium ion, and boron. In theparagraphs that follow, some of the effects of chloride, sodium ion, and boron are described.

V.F.1 Sensitivity of Trees, Shrubs, Ground Covers, and Floricultural Species
At the early stages, symptoms of salinity and specific ion toxicities in plants are often
difficult to distinguish from each other. Foliage may be off­color green with yellowing of the tips
or margins of leaves. These observed symptoms, however, are of little diagnostic value unlessaccompanied by chemical analysis for specific ions in the tissue.

Chloride Ion
The element chlorine is an essential micronutrient for plants. Its common ionic form ofchlorine is chloride (Cl−). Woody species appear to be more susceptible to chloride toxicity thanare herbaceous crops. Tolerances of woody species vary among varieties or rootstocks and areassociated with the plant’s ability to restrict the accumulation of chloride in the shoot andparticularly in the leaves. Tolerances may be significantly improved by selecting varieties orrootstocks that prevent accumulation of chloride.
Moderate chloride toxicity in stone fruit trees may cause reduced vigor and no othervisible symptoms. More severe toxicity often results in bleached or bronzed leaves and inscorched margins on leaves. In citrus, bronzing from chloride toxicity is difficult to distinguishfrom the orange mottling caused by boron toxicity. Proper selection of rootstock helps to avoid
the effects of chloride toxicity.

Sodium
Sodium is not considered an essential nutrient for most plants, yet it does aid the growthof plants at concentrations below the salt tolerance threshold. In water, sodium exists as sodium
ions (Na+). Above the salt tolerance threshold, the sodium ion can have both direct and indirect
detrimental effects on plants. Direct effects caused by the accumulation of toxic levels of sodium
ions are generally limited to woody species. Symptoms of injury do not usually appear
immediately after saline water is applied. Initially, the sodium ion is retained in the roots andbasal sections of the trunk. After several years, as sapwood is converted to heartwood, storedsodium ion is released and transported to the leaves, causing the burning of leaves andabscission—the separation of flowers, fruits, or leaves from plants at a special separation layer.

V­34

Indirect detrimental effects of sodium ions include nutritional imbalances and impairmentof the soil’s physical condition. The presence of sufficient calcium both in the plant and in theroot environment is essential to prevent the accumulation of sodium ions to levels that are
injurious to the plant (Maas, 1986). Symptoms of sodium­induced calcium deficiency are weakstems, chlorosis and necrosis of leaves, and leaves distorted by failure to unroll.

Boron
Boron (B) is an essential micronutrient for plants. For most crops, the optimal
concentration of plant­available boron falls within a very narrow range and various criteria havebeen proposed to define those levels necessary for adequate boron nutrition and yet low enoughto avoid toxicity that results in injury and reduced yield (Maas, 1986; and Grieve and Poss, 2000).
Boron deficiency is more widespread than boron toxicity, particularly in humid climates. In
contrast, boron toxicity is more of a concern in arid environments, where salinity problems also
exist (Grattan and Grieve, 1999). As with salt tolerance, the tolerance of a plant to boron varies,
depending on the climate, the soil’s conditions, and the variety of the plant.
Many of the existing data about boron tolerance were obtained from experiments
conducted during 1930 to 1934 by Eaton (1944). These experiments provided threshold tolerance
limits for more than 40 different crops. While useful, Eaton’s data cannot be reliably correlated tothe corresponding growth of most crops (Maas and Grattan, 1999). Bingham et al. (1985)
demonstrated that the response of plants to excess boron can be described by a two­piece linear
response model. Threshold and slope parameters for such a model have been estimated for alimited number of crops.
Francois and Clark (1979) examined the response of 25 species of ornamental shrub tobeing irrigated with waters containing either high or low concentrations of boron, 7.5 or 2.5
mg/L, respectively. Boron tolerance was based on reduced growth and deterioration of the plant’s
appearance overall (Table V.F.1.1). The salt tolerance of these species had been established in an
earlier study (Bernstein et al., 1972), and no correlation was found between the boron tolerancesand salinity tolerances of the species tested. Maas (1984) also studied the boron tolerance limits
for a variety of ornamental plants (Table V.F.1.2).

Symptoms of Boron Toxicity
As boron in the root environment increases, characteristic visible symptoms become
evident and often sharp boundaries distinctly separate the symptomatic and the unaffected green
tissues. Leaves exhibit scorched and necrotic margins, finally dropping prematurely.
Chlorosis followed by necrosis first appears at the end of the veins of leaves. In parallel­veined leaves, such as in grasses and lilies, the necrosis is found at the tips of leaves where theV­35veins end. A similar pattern is found in lanceolate leaves, such as those of stock and carnation,
where the principal vein terminates at the tip. In such species as geranium, where veins are moreradially distributed, boron toxicity appears as an injured zone all around the margin. In leaves
with a well­developed network of veins and with many veins ending in areas between principalside veins, such as the leaves of gerbera, aster, and most citrus species, symptoms first develop as
interveinal yellow or red spots. As injury progresses, chlorosis spreads to the margins (Oertli andKohl, 1961).
Ranges of boron concentrations in healthy, chlorotic, and necrotic plant tissues are shownin Table V.F.1.3. Necrosis of leaves may be expected when concentrations of boron in planttissue reach 1,500 to 2,000 ppm on a dry weight basis. Differences in the time necessary for theplants to show symptoms of boron toxicity are apparently not caused by differences in tissue
tolerance but, instead, are a function of the rate at which boron accumulates (Oertli and Kohl,
1961).
Other symptoms of boron toxicity commonly observed in plants in landscapes include
terminal dieback of twigs, necrotic spots on leaves, abnormal forms and textures in leaves, andcracking bark. Necrosis associated with boron is often black and sometimes red such as in
eucalyptus, and for most species it is more severe on the older foliage (Chapman, 1966).
Characteristic symptoms of boron toxicity in stone fruit trees include reduced bud formation, poor
fruit set, and malformed, very poorly flavored fruit (Johnson, 1996). In citrus trees, symptoms
often progress from chlorosis and mottling of the leaf tips to the formation of tan, resinous
blisters on the underside of leaves (Wutscher and Smith, 1996).

V.F.2 Sensitivity of Turfgrasses
In addition to overall deleterious effects of salinity, several ions comprising the totalsalinity may have a direct toxic effect on turfgrasses. The most important of those ions are
sodium, chloride, and boron.

SodiumThe roots of a turfgrass plant absorb sodium and transport it to the leaves, where it canaccumulate and cause injury. The leaf symptoms of sodium toxicity resemble those of salt burn.
Because salts can be absorbed directly by leaves, irrigation water with a high level of sodium
salts can be particularly toxic if applied to turfgrass leaves via overhead sprinklers. Sodium
toxicity is often of greater concern with plants other than turfgrasses, primarily because theaccumulated sodium in turfgrass is removed each time the grass is mowed. Of the grasses grownon golf courses, annual bluegrass and bentgrass are the most susceptible to sodium phytotoxicity.
V­36

Chloride
Besides contributing to the total concentration of soluble salt in irrigation water, chloride
may be directly toxic to plants grown on a golf course, park, or other landscape site. Althoughchloride is not particularly toxic to turfgrasses, many trees, shrubs, and ground covers are quitesensitive to it.
Chloride is absorbed by the roots of plants and translocated to leaves, where it
accumulates. In sensitive plants, this accumulation leads to necrosis: scorched margins of leaves
in minor cases and death of the leaves and abscission in severe cases. Similar symptoms may
occur on sensitive plants if high­chloride water is applied via overhead sprinklers, since chloride
can be absorbed by wetted leaves as well as by roots. As long as they are mowed regularly,
turfgrasses tolerate all but extremely high levels of chloride.

Boron
Boron is an essential micronutrient for the growth of plants, though it is required in verysmall amounts. Even at concentrations as low as 1 to 2 mg/L in the saturation extract of soil, it isharmful to most ornamental plants and capable of causing leaf burn. The most obvious symptoms
appear as a dark necrosis on the margins of older leaves. Turfgrasses generally tolerate boron
better than do most other plants grown in a landscape—even though they are more sensitive toboron toxicity than to either sodium or chloride toxicity. Most turfgrasses may be grown in soils
with levels of boron as high as 5 mg/L.

V­37

a

Table V.F.1.1. Boron injury to leaves and growth reduction in 25 species of shrub.
SpeciesSensitivity
Concn ofObserved
Commonb
Botanical nameboron
to boron
responsename
Natal plum

Carissa grandiflora(E.H. Mey.) A. DC.
cv. Tuttlei)

Indianhawthorn

Raphiolepis indica (l.)
Lindl. cv.
Enchantress

Chinesehibiscus

Hibiscus rosa­sinesis
L.

Tolerant

Low

No injury

0High

No injury

0Low

No injury

0High

No injury

0Low

No injury

0

Slight prematureleaf drop
No injury
Narrow (1–2 mm)
marginal
chlorosis;
slight tip burn

High
OleanderNerium oleander L.

Low
High

Japaneseboxwood

Buxus microphylla
Siebold and Zucc.
var. japonica (Mull.
Arg.)

Low

No injury
General marginalchlorosis withnecrotic older
leavesSlight marginalcoloration similar
to HB
Marginal
anthocyanin
coloration (5 mmfrom leaf tip)
progressed
inward insemicircle pattern
toward midrib;
marginal and tip
necrosisdeveloped asleaves matured

High

Bottlebrush

Callistemon citrinus(Curtis) Stapf

Low

High

Cenisa

Leucophylum
frutescens (Berland.)
I.M. Johnst. cv.
CompactumLow

No injury
Older leaves
droppedprematurely
Tip burn, 5–7 cm(1973); 10–13 cm(1975)
Tip burn, 7–10
cm (1973); 18–22
cm (1975)
Slightanthocyanin
spotting on oldest
leavesHigh

Blue dracaena

Cordyline indivisa (G.
Forst) Steud.

Low

High

Brush cherry

Syzgium paniculatum
Gaertn.

Growthreduction
(%)

Low

V­38

0
21
24

0

0

0

0

15

24

0

0

0

Sensitivity
to boronSpeciesCommonnameBotanical nameConcn ofbboron

Moderateanthocyanin
spotting; oldest
leaves dropped
prematurely;
generalappearance
chlorotic
Slight tip burnwith narrow
chlorotic band
between burn andremainder of leaf
Moderate tosevere tip burn (1cm) with narrow
chlorotic area like
LB; leaves onlower 3/4 of plant
exhibited burn
Slight chlorosis tonecrosis on tips ofolder leaves
Severe necrosisof older leaves;
only outer
perimeter of plant
was still green
Tip necrosis ofolder leaves
Tip necrosis of allleavesBronzing and tip
burn on older
leavesBronzing of allleaves; slight leaf
drop
Tip and marginalleaf burn onintermediate andolder leaves;
some hastenedleaf drop
Moderate tosevere leaf burnon all leaves;
severe leaf drop
Moderate tip burnon older leaves
Severe tip burn allleaves, except
perimeter of newleaves; center
leaves of plant
deadSome marginal
burn andinterveinal
chlorosis

High

Semitolera
ntSouthern yew

Podocarpus
macrophyllus(Thunb.) D. Don var.
Maki Endl

Low

High

Orientalarbivitae

Platycladus orientalis(L.) Franco

Low

High

Rosemary

Rosemarius
officinalis C

Low
High

Glossy abelia

Abelia X grandiflora(Andre) Rehd.

Low

High

Yellow sage

Lantana camara L.

Low

High

Sensitive

Juniper

Juniperus chinensis
L. cv. Armstrongii

Low

High

Chinese holly

Ilex cornuta Lindl.
and Paxt. cv.
Burfordii

Observed
response

Low

V­39

Growthreduction
(%)

11

0

8

27

30

20
51
56

70

14

82

20

47

17

Sensitivity
to boronSpeciesCommonnameBotanical nameConcn ofbboron

Tip and marginal
burn on allleaves; prematureleaf drop
Margin burn andtip burn distal halfolder leaves;
premature leaf
drop
Premature leaf
drop all leaves,
except very
youngest; young
leaves chlorotic
with moderate tosevere marginal
and tip burn;
small rosettes
young leaves atbranch tips

High

Japanesepittosporum

Pittosporum tobira

Low

High

Spindle tree

Euonymus japonica
Thunb. cv.
Grandiflora

Slight tip burn;
slight leaf drop

Low

Severe chlorosis
and tip burn allleaves; severeleaf drop
Slight tip burn 1styear; moderateleaf drop,
moderate tip, andmarginal burn1974 and 1975
Severe leaf drop;
all leaves showed
severe tip andmarginal burn;
youngest leaves
also chlorotic
No apparent
injury symptoms,
except reduced
growthTerminal 1/2 to
2/3 of branches
dead; necrotic
spotting older
leaves; nearlycompletely
defoliatedMarginal and tip
burn intermediateand older leaves;
moderate leaf
drop
Severe tip andmarginal burn allleaves, except
very youngest

High

Pineapple
guava

Feijoa sellowiana O.
Berg

Low

High

Wax­leaf privet

Ligustrum japonicum
Thunb.

LowHigh

Laurustinus

Viburnum tinus L. cv.
RobustumObserved
response

Low

High

V­40

Growthreduction
(%)
88

50

50

4

100

13

35

17

100

0

100

Sensitivity
to boronSpeciesCommonname
Thornyelaeagnus

Botanical nameElaegnus pungens
Tnunb. cv. Fruitlandii

Concn ofbboron

Older leaves
interveinal andmarginal chlorosis
on distal half ofleaf
Severe chlorosis
with marginal
necrosis; severeleaf drop nearly
all, but youngest,
leaves; remaining
leaveshypnonastic
Older leaves
anthocynanin
mottling and tip
burn; more
severe by mid­summer; severeleaf drop older
leavesMany branches
dead;
anthocyanin
mottling andsevere tip burn allleaves; nearlycomplete leaf
drop
Marginal and tip
burn older leaves
Severe leaf burn;
severe leaf drop;
stem tips dead;
death mid­1974
Tip necrosis
young leaves;
severe leaf drop
older leaves
Severe leaf drop,
except very
youngest; severeburn older andintermediateleaves; tip burnyoung leaves;
barely survived
1st year (1973).

Low

High

Xylosma

Xylosma congestum(Lout.) Merrill

Low

High

Photinia

Photinia X Fraseri
Dress

Low

High

Oregon grape

Mahonia aquifolium(Pursh) Nutt.

Observed
response

Low

High

Growthreduction
(%)

11

70

23

100

0

100

50

100

a

Excerpted from Francois and Clark (1979).

b

Boron concentrations were 2.5 mg/L (low) and 7.5 mg/L (high). Control plants were treated with 0.5 mg of boron/L.

V­41

a

Table V.F.1.2. Boron tolerance limits for ornamentals.
bSpeciesSensitivity toboron
Common nameVery sensitive

Sensitive

Moderately sensitive

Moderately tolerant

TolerantabBotanical nameThreshold (g/m3)

Oregon grape

Mahonia aquifolium<0.5

Photinia

Photinia X Fraseri<0.5Xylosma

Xylosma congestum<0.5

Thorny elaeagnus

Elaegnus pungens<0.5

Laurustinus

Viburnum tinus<0.5

Wax­leaf privet

Ligustrum japonicum<0.5

Pineapple guava

Feijoa sellowiana<0.5

Spindle tree

Euonymus japonica<0.5Japanese pittosporum

Pittosporum tobira<0.5

Chinese holly

Ilex cornuta<0.5

Juniper

Juniperus chinensis<0.5

Yellow sage

Lantana camara<0.5

American elm

Ulmas americana<0.5

ZinniaZinnia elegans

0.5–1.0

Pansy

Viola tricolor

0.5–1.0

VioletV. adorata

0.5–1.0

LarkspurDelphinium sp.

0.5–1.0

Glossy abelia

Abelia X grandiflora

0.5–1.0

Rosemary

Rosemarius officinalis

0.5–1.0

Oriental arbivitae

Platycladus orientalis

0.5–1.0

Geranium

Pelargonium X
hortorum

0.5–1.0

Gladiolus

Gladiolus sp.

1.0–2.0

Marigold

Calendula officinalis

1.0–2.0

Poinsettia

Euphorbia pulcherrima

1.0–2.0

China aster

Callistephus chinensis

1.0–2.0

Gardenia

Gardenia sp.

1.0–2.0

Southern yew

Podocarpus
macrophyllus

1.0–2.0

Brush cherry

Syzgium paniculatum

1.0–2.0

Blue dracaena

Cordyline indivisa

1.0–2.0

Cenisa

Leucophylum
frutescens

1.0–2.0

Bottlebrush

Callistemon citrinus

2.0–4.0

California poppy

Eschscholzia californica

2.0–4.0

Japanese boxwood

Buxus microphylla

2.0–4.0

OleanderNerium oleander L.

2.0–4.0

Chinese hibiscus:

Hibiscus rosa­sinesis

2.0–4.0

Sweet pea

Larkyrus odorarus

2.0–4.0

Carnation

Dianthus caryophyllus

2.0–4.0

Indian hawthorn

Raphiolepis indica

6.0–8.0

Natal plum

Carissa grandiflora

6.0–8.0

Oxalis

Oxalis bouiei

6.0–8.0

After Maas, 1984.
Species listed in order of increasing tolerance, based on appearance as well as growth.

V­42

Table V.F.1.3. Boron concentration in green, chlorotic, and necrotic leaves of landscape speciesaand time necessary to produce necrosis.
Days
until
necrosis

Type

SpeciesOrnamentals

Botanical nameBegonia sp.

Common nameBegonia

In green leaves
290–380

In chlorotic
leaves—In necrotic
leaves1,560–2,830

20

Callistephus chinensis

China aster

600–1,000

1,090–1,280

1,100–1,620

4

Chrysanthemum
morifoliumMum

270–330

370–570

3,080–3,700

12Dianthus caryphyllus

Carnation

60–6801,630–2,200

1,510–5,770

57

Fuchsia sp.

Fuchsia

640–860

100–1,190

5,050–8,280

22

Gerbera sp.

Gerbera daisy

410–5101,880–2,510

2,210–2,500

14Gladiolus sp.

Gladiola

200–1,850—

2,050–3,480

12

Hedera canariensis

Algerian ivy

80–4501,210–1,480

1,540–2,120

49

Hibiscus rosasinensis

Hibiscus

140–200

200–260—

52

Hydrangea sp.

Hydrangea

600–950—

3,510–3,590

20

Kalanchoe spp.

Kalanchoe

220–990—770–2,030

12

Matthiola incana

Stock90–340—1,840–4,800

12Pelargonium X
hortorum

Geranium

550–780—

1,800–3,090

7Rhododendron
hybrids

Azalea680–1140—

1,120–3,900

77

Rosa sp.

Rose

600–810—3,780–5,170

20

Tagetes patula

Marigold

540–820

1,180–1,260

2,100–3,580

12

Cynodon dactylon

Bermudagrass

40–700—1,380–5,770

16

Festua sp.

Alta fescue

50–760—1,510–8,200

8Lolium perenne

Perennial
ryegrass

100–290810

950–2,690

8

1,860–6,800

12Grassesa

Boron concn (ppm)

Poa annuaBluegrass
40–960—After Oertli and Kohl (1961). Concentration of boron in external solution was 10 mg/L.

V.G. Effects of Environment and Management
Such factors as weather, the soil’s texture, structure, and fertility, management practices,and the interactions between the plants and these factors affect the response of any given species
to salts.
Various aspects of weather, including temperature, radiation, humidity, and wind speed,
affect the plant’s transpiration rate and, therefore, its accumulation of salt and its salt tolerance.
Most plants in landscapes can tolerate greater salt­related stress when the weather is cool andhumid than when it is dry and warm. Plants may consequently sustain good aesthetic quality inthe winter and spring, but when the weather becomes dry and warm in the summer or windy,
severe foliar injury may suddenly occur due to increased rates of transpiration and increased saltV­43

accumulation in their leaves. This is especially true for salt­sensitive species. Moderately tolerant
plants often develop salt injury later—in the fall, for example—when the accumulation of salt intheir leaves surpasses threshold levels. For moderately salt­sensitive and salt­sensitive plants, thesoil’s salinity and irrigation practices need to be closely monitored and well managed.
Any adverse soil conditions inevitably reduce the overall health of plants, causing theplants to become more vulnerable to salt­related stress. Soil with poor structure or impermeable
layers can restrict the growth of roots and the distribution of water and salt in the soil. Flooded or
poorly drained soils have poor aeration and in some situations can foster the development of ashallow water table. Less fertile, nutrient­deficient soil can reduce the salt tolerance of plants.
The salinity of soil in the field is seldom constant and may indeed be highly variable (seeChapters III and IV). Concentrations of salt near the soil’s surface can be nearly equal to that of
the irrigation water and many times greater at the bottom of the root zone. If a saline water table
exists within 1 m of the surface, and if leaching fractions are low, salts may be transported
upward by capillary flow, in which case the highest concentrations of salt will tend to be found at
the surface. The salinity of soil also increases between irrigations, due to the transpiration ofwater withdrawn by the roots and evaporation of water in moist soil surfaces. Water is lost in thevapor form to the atmosphere in both transpiration and evaporation, and soluble salts remain in
the soil solution. The growth of plants closely responds to changes in salt concentrations in theroot zone because this is where most water absorption is occurring. Modifying the soil’s physicalcondition and improving management practices can reduce the salt accumulation in the root zone
and therefore better sustain plants.
The method of irrigation—drip, surface application, or sprinklers—will influence how
landscape plants respond to irrigation water of a given salinity. In California, sprinkler irrigation
is preferred for most landscapes because it requires less maintenance and is less vulnerable todamage than drip irrigation. Plants irrigated by sprinkling, however, are subject to injury not only
from salts in the soil but also from salt absorbed directly through the wetted leaves. Managementof the sprinkler irrigation of plants in landscapes can affect the degree of injury to leaves causedby salt deposition. Wherever possible, irrigation should be infrequent and heavy, rather thanfrequent and light. Slowly rotating sprinklers that allow drying between cycles should be avoided.
It is best to sprinkler irrigate at night or in the early morning, avoiding hot, dry, and windy days.
Extra management will be needed to irrigate salt­sensitive and moderately salt­tolerant
species of plants with recycled water, if salt concentrations in the recycled water exceed thetolerance levels of the species. Such species are particularly vulnerable in the early stages ofgrowth. For example, the young leaves and buds of salt­sensitive and moderately salt­tolerantV­44

trees are more vulnerable to being sprayed with saline water than are mature leaves. Once thetrees grow above the height of the spray, there is less need for this type of sprinkler management,
though branches at lower levels may still be exposed to the spray of water and develop symptomsof salt­related stress. In irrigation of salt­sensitive shrubs and ground covers, switching to drip
irrigation can help prevent the water from coming into contact with the foliage. However, withdrip irrigation, the salinity of the soil needs to be monitored (Chapter IX). When one is designinga new landscape or upgrading an older one, much advantage can be gained by grouping plants ofsimilar salt tolerance in the same area. Each such area can then be irrigated accordingly.
Recommendations advanced by researchers for growing ornamental plants and cut
flowers with moderately saline waters include the following:· Water more heavily and less often.
· Keep the soil as moist as possible without retarding the plant’s growth or creating
disease problems.

· Use soil containing considerable organic matter.
· Select varieties most tolerant of the type of water being used.
· Apply slow­release fertilizers as needed to meet the plant’s nutritional requirements,
since leaching to control the salinity of the soil may reduce its fertility.

· Confirm suspected salt­related injury to a plant before beginning to correct it, as thecauses may be unrelated to salinity. For instance, stunting of growth may result fromdrought, and leaf burn may be caused by drought or toxic amounts of boron.

· Judge the suitability of a particular water for irrigation not only by considering its saltcontent but also by evaluating the manner in which the water is applied, as well as thetype of soil to which it will be applied.

V.H. Gallery
Two color plates accompany the text of this chapter. Plate 1 consists of two pages
displaying 14 color photos of salt­damaged plants and leaves. The species and genera illustrated
include the following: liquidambar (Liquidambar styraciflua), bottlebrush (Callistemon spp.),bougainvillea(Bougainvillea

glabra),cotoneaster(Cotoneasterspp.),

crape

myrtle(Lagerstroemia indica), eucalyptus (Eucalyptus spp.), hibiscus (Hibiscus spp.), orchid tree
(Bauchinia purpura), and xylosma (Xylosma spp.). Plate 2 consists of a single page displaying
images of a boron­damaged liquidambar tree.

V­45

Plate 1. Salt­damaged plants and leaves.

V­46

V­47

Plate 2. Boron­damaged eucalyptus tree.

V­48

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Chapter VI. Selecting Plants for Coastal
Southern California Landscapes
L. Rollins and A. Harivandi

VI.A. Selection Based on Zones
VI.B. Guides for Selecting Trees, Shrubs, and Ground Covers
VI.C. Guide for Selecting Turfgrasses
VI.D. Guides Available via the Internet
VI.E. Guides about Native Plant Communities
V.I.F. Selecting Plants for Certain Types of Landscapes
VI.F.1. General Guidelines
VI.F.2. Selecting Plants for Golf Courses
VI.F.3. Selecting Plants for Playing Fields
VI.F.4. Selecting Plants for Parks
VI.F.5. Selecting Plants for Medians and Sides of Streets
VI.G. Using Guides Cited
VI.H. References
In this chapter, numerous plant selection guides are described, with a particular focus on
guides that pertain to the Los Angeles and San Diego areas, portions of which are served bypipelines conveying recycled water that could be used for landscape irrigation.
The goal is to provide information helpful in choosing plants for relatively large
landscapes, such as regional parks, golf courses, city parks, cemeteries, and highway medians.
Most of the information is equally relevant for selecting plants for smaller landscapes, such asneighborhood parks or street­side plantings.
Some of the plant species mentioned in this chapter may be less than ideal for sites
irrigated with water of moderate or high salinity. For projects that rely on such water, the site
designer should screen candidate species by reading about them thoroughly here and in Chapter V(and in the references cited in both chapters), afterward choosing only those species that are
relatively salt tolerant. Likewise, some of the plants listed here may be appropriate only for well­drained soil. Others may be considered weeds or invasive species in certain circumstances. Careful
screening of candidate species is, once again, the best way to ensure a proper match between plantand environment.

VI­1

V.I.A. Selection Based on Zones
A plant responds to many different environmental factors, including the following:·

Intensity and daily duration of sunlight·

Quantity of rainfall and of irrigation water·

Quality of available water·

Amount and type of nutrients available·

Temperature·

Physical and chemical properties of the soil·

Physical disturbances, such as wind, flooding, or fire·

Biotic interactions, such as competition by other plants for space or for sunlight,
grazing by plant­eating animals, and diseases caused by various microbes.

These various factors, when examined together, can be used to help define a series ofgeographical and climatological zones or regions for California. This is the approach taken by theauthors of some of the more comprehensive plant selection guides described in the following
section. The idea is that, by looking at a plant environment map and finding out what zone pertains
to a desired project area, one can more reliably determine which species of plants will survive andprosper in the area.

VI.B. Guides for Selecting Trees, Shrubs, and Ground Covers
Seven books are described below, each of which contains information that is helpful whenselecting trees, shrubs, and ground covers. Three of the books cover both native and nonnative
species. The other four are specifically about species native to California.

Trees and Shrubs for Dry California Landscapes (Perry, 1981)
This book is a comprehensive guide to plants for California landscapes, with an emphasison species that survive with limited water. The book includes lists of plants that tolerate certain
problematic situations in landscapes, such as saline spray and alkaline soil. It also includes detailed
descriptions, accompanied by photographs, of 360 different species. Some of the species are native
to California. Others are natives of other areas in the world that have Mediterranean­like climates
similar to California’s: central Chile, South Africa, parts of southern Australia, and, of course, thecountries bordering the Mediterranean Sea.

VI­2

Perry reviews the plants in light of their suitability for specific environments. He thenrelates that choosing plants for a landscape is specialized work and that the plant selection tables
and descriptions of plants he provides should be interpreted with caution. He recommends cross­checking against the lists and information of others.
Perry’s book contains four main sections. In the first part, “Regional Plant Environments,”
he describes nine macroenvironment zones, shown in Figure VI­1. He also includes a detailed plantselection guide consisting of seven lists: ground covers, small shrubs, medium shrubs, large shrubs,
small trees, medium trees, and large trees. Each list contains information about the compatibility of
the relevant plants with each of the aforementioned zones.

Figure VI­1. Map of plant environments for coastal southern California (after Perry, 1981).

VI­3

Because Perry’s lists represent an invaluable source of information unavailable elsewhereand because his book is now out of print, we have, with his permission, reproduced the lists in thisdocument as Tables VI­1 through VI­7. These tables, when used with the plant environment map,
are a highly useful tool for selecting plants during the design of a landscape. The tables and map
can be best used in the following stepwise fashion:(1) Using the map, select the appropriate zone or zones for the area of interest.
(2) Using the tables, choose plants that seem to fit the project.
(3) Cross­check with other relevant guides, such as the Sunset Western Garden Book
(2001) to make sure that the selected plants truly are optimal for the project’s local
microclimate.
(4) Gather details about the selected plants from other books and, if possible, fromlandscape designers or horticultural experts familiar with the area where the project islocated.
In the second part of Perry’s book, titled “Planting Guidelines,” he points out that any
landscape project consists of various site­specific conditions and design criteria. The goal, he says,
is to establish an appropriate planting concept within the constraints of function, aesthetics, costs,
resources, and required maintenance. Several different criteria for design are addressed by thevarious guidelines provided, including the following: planting from seed, planting on slopes,
planting for fire safety, and using species native to California. For each such guideline, Perry lists
a number of plants that satisfy the stated criterion. For example, in the guideline for fire­safe
landscapes, he defines four zones in the landscape and describes how to use those zones to protect
a project’s buildings from adjacent fire­prone natural vegetation, such as chaparral.
In the third part of the book, titled “Plant Lists for Landscape Situations,” Perry lists
plants that can tolerate certain problematic situations that may be encountered in a landscape, suchas oak root fungus, alkaline soil, saline spray, and invasive plants.
The fourth, final, and most comprehensive part of Perry’s book, titled “Plant
Compendium,” consists of text and photographs of 360 different species that have proven useful or
popular for California landscapes.

VI­4

a

Table VI–1. Plant selection guide for coastal southern California: ground covers (after Perry, 1981).
Botanical nameCommon nameNative?
(3 = yes)

CoastalmarginIntermediate
valleys

Coastalfoothills

•

•

•

•

•

3

•

•

•

•

•

3

•

+

•

+

+

3

•

+

•

+

+

3

•

+

•

+

•

Acacia redolens
Achillea millefolium

Yarrow

Arctostaphylos densiflora‘James West’
Arctostaphylos edmundsii

Little Sur manzanita

Arctostaphylos hookeri
Arctostaphylos uva ursi

Bearberry

InlandvalleysInlandfoothills

3

•

+

•

+

•

Arctostaphylos“Emerald Carpet”

3

•

+

•

+

•

Arctostaphylos “Indian Hill”

3

•

+

•

+

+

•

+

•

+

+

•

+

•

+

•

Arctostaphylos “Sea Spray”
Arctostaphylos“Winter Glow”

3

Artemisia caucasica

Silver spreader

•

•

•

•

•

Artemisia pyncocephala

Coast sagebrush

•

•

•

+

+

•

•

•

•

+

•

•

•

•

•

3

Atriplex glauca
Atriplex semibaccata

Australian sagebrush

Baccharis pilularis

Prostrate coyote brush

3

•

•

•

+

+

Ceanothus gloriosus

Point Reyes
ceanothus

3

•

+

•

+

+

Ceanothus gloriosus
porrectus

3

•

+

•

+

+

Ceanothus gloriosus
exaltatus “Emily Brown”

3

•

+

•

+

+

3

•

+

•

+

+

3

•

•

•

+

+

3

•

+

•

+

+

Ceanothus griseus
horizontalis

Carmel creeper

Ceanothus griseus
horizontalis “Yankee Point”
Ceanothus maritimus

Maritime ceanothus

Centaurea cineraria

Dusty Miller

•

•

•

•

•

Cistus salviifolius

Sageleaf rockrose

•

+

•

+

+

Coprosma kirkii

Creeping Coprosma

•

•

•

+

+

Cotoneaster buxifolius

Bright beadcotoneaster

•

•

•

•

•

•

•

•

•

•

Cotoneaster congestus
Eriogonum crocatum

Saffron buckwheat

3

•

+

•

+

+

Eriogonum fasciculatum

Common buckwheat

3

•

•

•

•

•

Gazania species

Gazania

•

•

•

•

+

Grevillea lanigera

Woolly grevillea

•

•

•

•

+

•

•

•

•

+

•

•

•

•

+

•

•

•

•

•

•

•

•

+

+

•

•

•

•

•

Grevillea “Noelli”
Grevillea rosmarinifolia

Rosemary grevillea

Helianthemum species

SunroseHypericum calycinum

Aaron’s beard

Juniperus species

Juniper

Lantana montevidensis

Trailing lantana

•

•

•

•

+

Lippia canescens

Lippia

•

•

•

•

+

Lobularia maritima

Sweet alyssum

•

•

•

•

•

Lupinus nanus

Annual lupine

•

•

•

•

3

3

VI­5

Mahonia repens

Creeping mahonia

Myoporum debile

•

+

•

+

+

•

•

•

+

+

Myoporum parvifolium

Creeping boobialla

•

•

•

•

+

Osteospermum species

African daisy

•

•

•

•

+

Pyracantha species

Firethorn

•

•

•

•

•

Ribes viburnifolium

Evergreen currant

•

+

•

+

+

Rosmarinus officinalis“Prostratus”

Prostrate rosemary

•

•

•

•

•

Salvia sonomensis

Creeping sage

•

+

•

+

•

Santolina chamaecyparissus

Lavender cotton

•

•

•

•

+

•

•

•

•

+

•

•

•

•

+

•

•

•

•

•

3

3

Santolina virens
Trifolium frageriferum
O’Connor’s

O’Connor’s legumeZauschneria californica

California fuchsiaa3

Most of the information in the table above is from the book Trees and Shrubs for Dry California Landscapes (Perry, 1981).
Used with permission. •, plant is well suited to this type of landscape; +, plant will do well in this type of landscape if
exposure and soil conditions are optimal.

VI­6

a

Table VI–2. Plant selection guide for coastal southern California: small shrubs, 3–5 ft (after Perry, 1981).
Botanical nameCommon nameAchillea millefolium

Yarrow

Arctostaphylos densiflora“James West”

Native?
(3 = yes)

CoastalmarginIntermediate
valleys

Coastalfoothills

InlandvalleysInlandfoothills

3

•

•

•

•

•

3

•

•

+

+

+

Arctostaphylos hookeri

Monterey manzanita

3

•

+

•

+

+

Arctostaphylos pumila

Sandmat manzanita

3

•

•

•

+

+

3

•

•

•

+

+

+

•

3

•

•

•

•

•

Arctostaphylos“Green Sphere”
Argemone species

Prickly poppy

Artemisia californica

California sagebrush

Calliandra californica

•

•

•

•

•

•

•

3

Calliandra eriophylla

False mesquite

3

Cassia species

Senna

3

Ceanothus purpureus

Hollyleaf ceanothus

Ceanothus rigidus“Snowball”
Ceanothus “Blue Cushion”

•

•

•

•

+

•

•

•

•

+

3

•

•

•

+

+

3

•

•

•

+

+

Cistus species

Rockrose

•

•

•

•

+

Convolvulus cneorum

Bush morning glory

•

•

•

•

+

Cotoneaster buxifolius

Bright beadcotoneaster

•

•

•

•

•

•

•

•

•

•

•

•

•

+

Cotoneaster congestus
Encelia californica

California encelia

3

Encelia farinosa

Desert encelia

3

•

•

•

•

Eriogonum arborescens

Santa Cruz buckwheat

3

•

•

•

+

+

Eriogonum cinerium

Ashyleaf buckwheat

3

•

•

•

+

+

Eriogonum crocatum

Saffron buckwheat

3

•

•

•

+

Eriogonum fasciculatum

Common buckwheat

3

•

•

•

•

•

Eriogonum giganteum

St. Catherine’s lace

3

•

•

•

•

•

Eriogonum latifolium
rubescens

Red buckwheat

3

•

•

•

•

+

Eriogonum parvifolium

Seacliff buckwheat

3

•

+

•

+

+

Eriophyllum confertiflorum

Golden yarrow

3

•

•

•

•

•

Eriophyllum staechadifolium

Lizard tail

3

•

•

•

•

•

•

+

+

•

•

•

•

•

•

•

•

•

•

•

•

•

•
•

Hypericum beanii
Juniperus species

Juniper

Lavandula species

LavenderLeptodactylon californicum

Prickly phylox

Leucophyllum frutescens“Compactum”

Texas ranger

•

•

•

•

Limonium perezii

Sea lavender

•

•

•

+

Lotus scoparius

Deerweed

+

•

•

•

•

Lupinus albifrons

Silver lupine

3

•

•

•

•

+

Lupinus arboreus

Tree lupine

3

•

•

•

•

•

Lupinus chamissonis

Dune lupine

3

•

•

•

+

+

Mahonia repens

Creeping mahonia

•

•

•

+

+

Mimulus species

Monkey flower

•

•

•

+

+

Osteospermum species

African daisy

•

•

•

+

+

3

3

3

VI­7

Pennisetum setaceum

Fountain grass

•

•

•

•

•

Penstemon centranthifolius

Scarlet bugler

3

+

•

•

•

•

Penstemon heterophyllus

Blue penstemon

3

+

•

•

•

•

Penstemon spectabilis

Showy penstemon

3

+

•

•

•

•

Pittosporum tobira“Wheeleri”

Wheeler’s dwarf
pittosporum

•

•

•

•

•

Pyracantha species

Firethorn

•

•

•

•

•

Ribes speciosum

Fuchsia­flowering
gooseberry

3

•

•

•

+

+

Ribes viburnifolium

Evergreen currant

3

•

+

•

+

+

Rosmarinus officinalis“Prostratus”

Prostrate rosemary

•

•

•

•

•

Salvia clevelandii

Cleveland sage

•

+

•

•

•

Salvia leucantha

Mexican bush sage

•

•

•

•

•

Salvia leucophylla

Coastal purple sage

•

•

•

•

Salvia mellifera

Black sage

3

•

•

•

•

•

•

•

•

•

Woolly blue curls

3

•

+

•

+

•

3

3

Santolina species
Trichostema lanatuma•

Most of the information in the table above is from the book Trees and Shrubs for Dry California Landscapes (Perry, 1981).
Used with permission. •, Plant is well suited to this type of landscape; +, plant will do well in this type of landscape if
exposure and soil conditions are optimal.

VI­8

a

Table VI–3. Plant selection guide for coastal southern California: medium shrubs, 5–10 ft (after Perry, 1981).
Botanical nameCommon nameNative?
CoastalIntermediate
CoastalInlandvalleysfoothills
valleys(3 = yes) margin
Acacia cultriformis

Knife acacia

Acacia redolens

Inlandfoothills

•

•

•

•

•

•

•

•

•

•

Acacia verticillata

Star acacia

•

•

•

•

+

Arbutus unedo “Compacta”

Dwarf strawberry tree

•

•

•

•

+

•

+

•

+

+

•

•

•

+

+

Arctostaphylos densiflora‘Harmony’

3

Arctostaphylos franciscana
Arctostaphylos glandulosa

Eastwood manzanita

3

Arctostaphylos stanfordiana

Stanford manzanita

3

Artemisia tridentata

Big Basin sagebrush3

Atriplex canescens

Four­wing saltbush

3

Atriplex lentiformis

Quail bush3

Atriplex lentiformis breweri

Brewer lenscale

3

Atriplex nummularia

•
•

•

•

•

+

+

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

Baccharis pilularis
consanguinea

Coyote brush

Baccharis viminea

Mulefat

•

•

•

•

•

Bougainvillea species

Bougainvillea

•

•

•

+

+

Caesalpinia species

Bird of paradise bush

•

•

•

•

Calliandra tweedii

Trinidad flame bush

•

•

•

•

•

Callistemon citrinus

Lemon bottlebrush

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

3

Callistemon pallidus••

Callistemon rigidus

Stiff bottlebrushCassia species

Senna

3

•

•

•

•

+

Ceanothus griseus

Carmel ceanothus

3

•

•

•

+

+

Ceanothus “Concha”

3

•

•

•

+

+

Ceanothus “Joyce Coulter”

3

•

•

•

+

+

Ceanothus “Julia Phelps”

3

•

•

•

+

+

Ceanothus “Mountain Haze”

3

•

•

•

+

+

Ceanothus “Sierra Blue”

3

•

•

•

+

+

Cercocarpus ledifolius

Curl­leaf mountainmahogany

Chamelaucium uncinatum

Geraldton waxflower

•

•

•

•

+

Cistus corbariensis

White rockrose

•

+

•

+

+

Cistus purpureus

Orchid rockrose

•

•

•

+

+

Cotoneaster lacteus

Red clusterberry

•

•

•

•

+

Cytisus species

Broom

Dendromecon harfordii

Island bush poppy

3

•

•

•

+

+

Dendromecon rigida

Bush poppy

3

•

•

•

•

•

Dodonea viscosa

Hopseed bush

•

•

•

•

•

Echium fastuosum

Pride of Madeira

•

•

+

+

+

Elaeagnus pungens

Silverberry

•

•

•

•

•

•

•

•

+

+

•

•

•

•

•

•

•

•

•

•

•

•

•

Escallonia exoniensis
Eucalyptus macrocarpa•

3

Desert malee

Eucalyptus rhodantha
Feijoa sellowiana

Pineapple guava

•

VI­9

Garrya species

Silktassel

Grevillea lanigera•

3

Grevillea “Aromas”
Woolly grevillea

Grevillea “Noelli”

•

•

•

•

•

•

•

•

•

•

+

•

•

•

•

•

Grevillea rosmarinifolia

Rosemary grevillea

•

•

•

•

•

Grevillea thelemanniana

Hummingbird bush

•

•

•

•

+

Isomeris arborea

Bladderpod

•

•

•

•

+

Jasminus humile

Italian jasmine

•

•

•

+

+

Juniperus species

Juniper

•

•

•

•

•

Lantana camara

Bush lantana

•

•

•

+

•

Laurus nobilis

Sweet bay

•

•

•

•

•

Leptospermum scoparium

New Zealand tea tree

•

•

•

+

+

Leucophyllum frutuscens

Texas ranger

•

•

•

•

•

Lupinus albifrons

Silver lupine

3

•

•

•

•

+

Lupinus arboreus

Tree lupine

3

•

•

•

•

•

3

•

•

•

+

+

3

•

•

•

+

+

•

•

•

+

+

Mahonia amplectans
Mahonia aquifolium

Oregon grape

3

3

Mahonia “Golden
Abundance”
Mahonia nevinii

Nevin mahonia

3

Mahonia pinnata

California holly grape

3

Nerium oleander
Penstemon antirrhinoides

•

•

•

•

•

•

•

+

+

Oleander

+

•

•

•

•

Yellow penstemon

•

•

•

•

•

•

•

•

+

+

Photinia fraserii
Pittosporum tobira

Tobira

•

•

•

•

•

Pyracantha species

Firethorn

•

•

•

•

•

Rhamnus californica

California coffeeberry

3

•

•

•

•

•

Rhamnus crocea

Redberry

3

•

•

•

•

Ribes aureumGolden currant

3

•

•

•

+

Ribes sanguineum

Red flowering
gooseberry

3

•

•

•

+

+

3

•

•

•

+

+

3

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

Ribes sanguineum“Glutinosum”
Romneya coulteri

Matilija poppy

Rosmarinus officinalis

Rosemary

Salvia apiana

White sage

3

Simmondsia chinensis

Jojoba3

Spartium junceum

Spanish broom

Tecomaria capensis

Cape honeysuckle

Viguiera species•
3

Xylosma congestum“Compacta”
a

+
•

•

•

•

•

•

+

•

•

•

•

•

•

•
•

•

Most of the information in the table above is from the book Trees and Shrubs for Dry California Landscapes (Perry, 1981).
Used with permission. •, plant is well suited to this type of landscape; +, plant will do well in this type of landscape if
exposure and soil conditions are optimal.

VI­10

a

Table VI–4. Plant selection guide for coastal southern California: large shrubs, 10–18 ft (after Perry, 1981).
Botanical nameCommon nameNative?
CoastalIntermediate
CoastalInlandvalleysfoothills
valleys(3 = yes) margin

Inlandfoothills

Acacia baileyana

Bailey acacia

•

•

•

•

•

A. baileyana “Purpurea”

Purple­leaf acacia

•

•

•

•

•

Acacia cultriformis

Knife acacia

•

•

•

•

•

•

•

•

•

•

Acacia cyclopis
Acacia dealbata

Silver wattle

•

•

•

•

•

Acacia decurrens

Green wattle

•

•

•

•

•

Acacia farnesiana

Sweet acacia

Acacia greggii

Catclaw acacia

Acacia longifolia

Sydney golden wattle

•

•

•

•

+

Acacia pendula

Weeping acacia

•

•

•

+

+

Acacia podalyriifolia

Pearl acacia

•

•

•

•

+

Acacia pycnantha

Golden wattle

•

•

•

+

+

Acacia saligna

Willow acacia

•

•

•

+

+

Adenostoma sparsifolium

Red shanks

3•

Aesculus californica

California buckeye

3

•

+

•

Agonis flexuosa

Peppermint tree

Arbutus menziesii

MadroneArbutus unedo

Strawberry tree

Arctostaphylos glauca

Bigberry manzanita

3

Arctostaphylos manzanita

Common manzanita

3

Baccharis viminea

Mulefat

•

•

•

•

•

Bougainvillea species

Bougainvillea

•

•

•

+

+

Calliandra tweedii

Trinidad flame bush

•

•

•

•

Callistemon citrinus

Lemon bottlebrush

•

•

•

•

•

Callistemon viminalis

Weeping bottlebrush

•

•

•

•

+

Ceanothus arboreus

Felt­leaf ceanothus

3

•

+

•

+

+

Ceanothus crassifolius

Hoary­leaf ceanothus

3

•

+

•

Ceanothus cyaneus

San Diego ceanothus

3

•

+

•

+

Ceanothus griseus

Carmel ceanothus

3

•

+

•

+

+

Ceanothus impressus

Santa Barbara
ceanothus

3

•

+

•

+

+

Ceanothus “Frosty Blue”

3

•

+

•

+

+

Ceanothus “Ray Hartman”

3

•

+

•

+

+

3

•

+

•

+

+

•

•

•

•

+

Ceanothus “Sierra Blue”

•
•

3

•

•

3
•

•

•

•

+

+

+

+

+

•

•

+
•

+

+

Ceratonia siliqua

Carob tree

Cercidium species

Palo verde

3

+

+

+

•

+

Cercis occidentalisWestern redbud

3

+

+

+

+

+

Cercocarpus species

Mountain mahogany

3

Comarostaphylis diversifolia

Summer holly

3

Cotoneaster lacteus

Red clusterberry

Dalea spinosa

Smoke tree

3

Dendromecon harfordii

Island bush poppy

3

Dodonea viscosa
Elaeagnus pungens
Eriobotrya deflexa

•

•

+

+

•

+

+

•

•

•

•

+

•

•

•

•

+

+

+

Hopseed bush

•

•

•

•

•

Silverberry

•

•

•

•

+

Bronze loquat

+

•

•

•

•

VI­11

Botanical nameCommon name

Eriobotrya japonica

Native?
(3 = yes)

CoastalmarginIntermediate
valleys

Coastalfoothills

InlandvalleysInlandfoothills

Loquat

+

•

•

•

+

Escallonia bifida

White escallonia

•

•

•

+

+

Eucalyptus erythrocorys

Red cap gum

•

•

•

+

+

Eucalyptus lehmannii

Bushy yate

•

•

•

+

+

Eucalyptus macrocarpa

Desert malee

+

•

•

•

•

Eucalyptus niphophila

Snow gum

+

•

•

•

+

Feijoa sellowiana

Pineapple guava

Fremontodendron species

Flannel bush

Grevillea banksii
Hakea laurina

•

•

•

•

•

+

+

•

+

•

Crimson coneflower

•

•

•

+

+

Sea urchin

•

•

•

+

+

Hakea suaveolens

Sweet hakea

•

•

•

+

+

Heteromeles arbutifolia

Toyon

+

+

•

+

•

Jasminus humile

Italian jasmine

•

•

•

+

+

Juniperus species

Juniper

•

•

•

•

•

Laurus nobilis

Sweet bay

•

•

•

•

•

Lavatera assurgentiflora

Tree mallow

•

+

•

+

+

Leptospermum laevigatum

Australian tea tree

•

•

•

+

+

Leptospermum scoparium

New Zealand tea tree

•

•

•

+

+

Lithocarpus densiflorus

Tanbark oak

3

Lyonothamnus species

Catalina ironwood

3

•

+

•

3

•

•

•

•

•

•

•

•

+

+

•

•

•

•

+
+

Mahonia higginsae
Melaleuca armillaris

3

3

3

3

Drooping melaleuca

Melaleuca elliptica

+

+
+

+

Melaleuca nesophila

Pink melaleuca

•

•

•

+

Metrosideros excelsus

New Zealand
Christmas tree

•

•

•

+

•

•

•

+

+

Oleander

+

•

•

•

•

•

•

•

+

+

•

•

+

•

Myoporum laetum
Nerium oleander
Photinia fraserii
Photinia serrulata

Chinese photinia

Pistacia vera

Pistachio nut•

Pittosporum crassifolium

•

•

•

•

+

+

Pittosporum phillyraeoides

Willow pittosporum

•

•

•

+

+

Pittosporum rhombifolium

Queensland
pittosporum

•

•

•

•

+

Pittosporum undulatum

Victorian box

•

•

•

+

+

Pittosporum viridiflorium

Cape pittosporum

•

•

•

+

+

Plumbago auriculata

Cape plumbago

•

•

•

•

+

Prunus species

Prunus

•

•

•

+

+

Psidium guajava

Guava

•

•

•

•

•

Psidium littorale

Strawberry guava

•

•

•

+

+

Punica granatum

Pomegranate

+

•

•

•

+

Pyracantha species

Firethorn

•

•

•

•

•

Quercus chrysolepis

Canyon live oak

+

•

+

•

Quercus domosa

Scrub oakRhamnus alaternus

Italian buckthorn

3

3

•
•

VI­12

•

•

•
•

•

Botanical nameCommon nameNative?
(3 = yes)

CoastalmarginIntermediate
valleys

Coastalfoothills

Rhamnus californica

California coffeeberry

3

•

•

•

•

+

Rhus integrifolia

Lemonade coffeeberry

3

•

+

•

+

+

Rhus laurina

Laurel sumac

•

•

•

Rhus ovata

Sugar bush

•

•

•

•

•

Sambucus species

Elderberry

•

•

•

•

+

Schinus molle

California pepper

•

•

•

•

•

Schinus terebinthifolius

Brazilian pepper tree

•

•

•

•

+

Tecomaria capensis

Cape honeysuckle

•

•

•

+

+

Xylosma congestum

Shiny xylosma

•

•

•

•

+

a

3

Inlandvalleys+

Most of the information in the table above is from the book Trees and Shrubs for Dry California Landscapes (Perry, 1981).
Used with permission. •, plant is well suited to this type of landscape; +, plant will do well in this type of landscape if
exposure and soil conditions are optimal.

VI­13

Inlandfoothills

aTable VI–5. Plant selection guide for southern California: small trees, 15–25 ft (after Perry).
Botanical nameCommon name

Acacia cyanophylla

Blue­leaf wattle

Acacia greggii

Catclaw acacia

Acacia longifolia

CoastalmarginIntermediate
valleys

Coastalfoothills•••

Sydney golden wattle

•

•

•

Acacia pendula

Weeping acacia••

Acacia podalyriifolia

Pearl acacia••

Aesculus californica

California buckeye

Agonis flexuosa

Peppermint tree•

Arbutus unedo

Strawberry tree•

Arctostaphylos manzanita

Common manzanita

Callistemon citrinus

Lemon bottlebrush

•

•

•

•

Callistemon rigidus

Stiff bottlebrush

•

•

•

•

Callistemon viminalis

Weeping bottlebrush

•

•

•

+

Ceanothus arboreus

Felt­leaf ceanothus

•

+

•

+

+

Ceanothus “Ray Hartman”

Native?
(3 = yes)

Inlandfoothills

+

+

+

+

•

+

•

+

+

•

•

+

•

+

•

•

•

+

+

•

•

•

+

3

3

+

3

3

Inlandvalleys

+
•

3

•

+

•

+

+

Cercidium species

Palo verde

3

+

+

+

•

+

Cercis occidentalisWestern redbud

3

+

+

+

+

+

Cercocarpus betuloides

Mountain mahogany

3

Comarostaphylis diversifolia

Summer holly

3

+

+

Dalea spinosa

Smoke tree

3

Elaeagnus angustifolia

Russian olive

Eriobotrya deflexa

Bronze loquat

+

•

•

•

•

Eriobotrya japonica

Loquat

+

•

•

•

+

Escallonia bifida

White escallonia

•

•

•

+

+

Eucalyptus erythrocorys

Red cap gum

•

•

•

+

+

Eucalyptus lehmannii

Bushy yate

•

•

•

•

+

Eucalyptus niphophila

Snow gum

•

•

•

+

Eucalyptus torquata

Coral gum

•

•

+

+

Feijoa sellowiana

Pineapple guava

Fremontodendron species

Flannel bush

Geijera parviflora
Hakea laurina
Heteromeles arbutifolia

Toyon

Koelreuteria paniculata

Golden rain tree

Lagerstroemia indica

Crape myrtle

Laurus nobilis

Sweet bay

Lavatera assurgentiflora

Tree mallow

Leptospermum laevigatum

Australian tea tree

Lyonothamnus species

Catalina ironwood

Melaleuca armillaris

Drooping melaleuca

•
+

+

•

•

•

•

•

•

•

+

•

•

•

•

•

+

+

•

+

•

Australian willow

•

•

•

•

+

Sea urchin

•

•

•

+

+

+

+

•

+

•

•

•

+

+

•

•

3

3

•

3

3

Melaleuca elliptica

•

•

•

•

•

•

+

•

+

+

•

•

•

+

+

•

+

•

+

+

•

•

•

+

+

•

•

•

•

+

Melaleuca nesophila

Pink melaleuca

•

•

•

+

+

Metrosideros excelsus

New Zealand
Christmas tree

•

•

•

+

Nerium oleander

Oleander

+

•

•

•

•

Parkinsonia aculeata

Jerusalem thorn

+

+

3

VI­14

+

Botanical nameCommon nameNative?
(3 = yes)

Photinia fraserii

CoastalmarginIntermediate
valleys

Coastalfoothills•

InlandvalleysInlandfoothills

•

•

+

+

Photinia serrulata

Chinese photinia

•

•

+

•

Pistacia vera

Pistachio nut•

Pittosporum crassifolium

•

•

•

•

+

+

Pittosporum phillyraeoides

Willow pittosporum

•

•

•

+

+

Pittosporum rhombifolium

Queensland
pittosporum

•

•

•

•

+

Pittosporum viridiflorium

Cape pittosporum

•

•

•

+

+

Prunus species

Prunus

•

•

•

+

+

Psidium littorale

Strawberry guava

•

•

•

+

+

Punica granatum

Pomegranate

+

•

•

•

+

Quercus domosa

Scrub oakRhamnus alaternus

Italian buckthorn

Rhus integrifolia

Lemonade coffeeberry

Rhus lancea

African sumac

Rhus ovata

Sugar bush

Sambucus species

Elderberry

Schinus terebinthifolius

Brazilian pepper tree

a

3

•

•

•

•

•

•

+

•

+

•

+

+

•

•

•

•

+

3

•

•

•

•

•

3

•

•

•

•

•

•

•

•

•

+

3

Most of the information in the table above is from the book Trees and Shrubs for Dry California Landscapes (Perry, 1981).
Used with permission. •, plant is well suited to this type of landscape;+, plant will do well in this type of landscape if
exposure and soil conditions are optimal.

VI­15

a

Table VI–6. Plant selection guide for coastal southern California: medium trees, 25–40 ft (after Perry, 1981).
Botanical nameCommon name

Acacia baileyana

Native?
(3 = yes)

CoastalmarginIntermediate
valleys

Coastalfoothills

Bailey acacia

•

•

•

•

Acacia decurrens

Green wattle

•

•

•

•

•

Acacia podalyriifolia

Pearl acacia

•

•

•

•

+

Agonis flexuosa

Peppermint tree

•

•

•

+

+

Ailanthus altissima

Tree­of­heaven

•

•

•

•

•

Albizia julibrissin

Silk tree

•

+

•

•

Arbutus menziesii

Madrone++Arbutus unedo

Strawberry tree•+

Brachychiton acerifolius

Flame tree

Brachychiton populneus

Bottle tree

•

•

•

+

Callistemon viminalis

Weeping bottlebrush

•

•

•

•

+

Casuarina stricta

Beefwood

•

•

+

+

+

Ceratonia siliqua

Carob tree

•

•

•

•

+

Cercidium floridum

Blue palo verde•+

Cupressocyparis leylandii

Leyland cypress

Cupressus species

Cypress

Dalea spinosa

Smoke tree

Elaeagnus angustifolia

Russian olive•

Eucalyptus niphophila

Snow gum•

Eucalyptus pulverulenta

Silver mountain gum•

Eucalyptus rudis

Desert gum+

Eucalyptus sideroxylon

Red ironbark

Geijera parviflora

Australian willow

Juglans species

WalnutKoelreuteria paniculata

Golden rain tree••

Laurus nobilis

Sweet bay••

Lithocarpus densiflorus

Tanbark oak

3

Lyonothamnus species

Catalina ironwood

3

•

+

•

+

+

Melaleuca linariifolia

Flaxleaf paperbark

•

•

•

•

+

Melaleuca quinquenervia

Cajeput tree

•

•

•

•

+

Melaleuca styphelioides

Black tea tree

•

•

•

•

+

•

•

•

+

+

Olea europaea

Olive

+

•

•

•

•

Parkinsonia aculeata

Jerusalem thorn

Pistacia chinensis

Chinese pistache

Pittosporum undulatum

Victorian box

Prunus caroliniana

Carolina laurel cherry

Prunus lyonii

Catalina cherry3

Quercus chrysolepis

Live canyon oak

3

Quercus ilex

Holly oak•Quercus suber

Cork oak+•Robinia pseudoacacia

Black locust

•

•

•

•

•

Sambucus species

Elderberry

•

•

•

•

+

Schinus polygamus

Peruvian pepper tree

+

•

•

+

Schinus terebinthifolius

Brazilian pepper tree

•

•

•

+

3
•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

+

•

•

+

•

•

•

+

•

+

•

•

•

•

•

•

•

•

•

•

•

+

•

•

•

+

•

+

•

•

3

VI­16

•
+

+

+

•

+

•

+

•

+

•

•

•

+

+

•

•

•

+

+

•

•

•

•

•

+

•

+

•

•

•

•

•

3

3

•

•

3

Myoporum laetum

Inlandfoothills•

33Inlandvalleys••Botanical nameCommon nameTamarix aphylla

Athel tree

Tristania conferta

Brisbane box

Zelkova serrata

Sawleaf zelkova

Zizyphus jujuba

Chinese jujubeaNative?
(3 = yes)

CoastalmarginIntermediate
valleys

Coastalfoothills

•
•

•

•

•
•

+

•

InlandvalleysInlandfoothills

•

+

+

+

•

+

•

+

Most of the information in the table above is from the book Trees and Shrubs for Dry California Landscapes (Perry, 1981).
Used with permission. •, plant is well suited to this type of landscape; +, plant will do well in this type of landscape if
exposure and soil conditions are optimal.

VI­17

a

Table VI–7. Plant selection guide for coastal southern California: large trees, 40 ft or taller (after Perry, 1981).
Botanical nameCommon name

Acacia decurrens

Native?
(3 = yes)

CoastalmarginIntermediate
valleys

Coastalfoothills

Green wattle

•

•

•

•

•

Acacia d. dealbata

Silver wattle

•

•

•

•

•

Acacia melanoxylon

Blackwood acacia

•

•

•

•

•

Ailanthus altissima

Tree­of­heaven

•

•

•

•

•

Arbutus menziesii

Madrone+++Brachychiton acerifolius

Flame tree

Casuarina cunninghamiana

Australian pine

•

•

+

•

+

Casuarina equisetifolia

Horsetail tree

•

•

+

•

+

Cedrus atlantica

Atlas cedar

•

•

•

•

+

Cedrus deodara

Deodar cedar

+

•

•

•

+

Ceratonia siliqua

Carob tree

•

•

•

•

+

Cupressocyparis leylandii

Leyland cypress

•

•

•

•

•

Cupressus species

Cypress

•

•

•

•

•

Eucalyptus camaldulensis

Red gum

•

•

•

•

•

3
•

3

Eucalyptus catophylla

InlandvalleysInlandfoothills

•

+

•

•

•

+

Eucalyptus cladocalyx

Sugar gum

•

•

•

+

+

Eucalyptus globulus“Compacta”

Dwarf blue gum

+

•

•

•

+

Eucalyptus leucoxylon

White ironbark

•

•

•

•

•

Eucalyptus polyanthemos

Silver dollar gum

•

•

•

•

•

Eucalyptus rudis

Desert gum

+

•

+

•

•

Eucalyptus sideroxylon

Red ironbark

•

•

•

•

•

Eucalyptus viminalis

Manna gum

•

•

•

•

•

Grevillea robusta

Silk oak

•

•

•

•

+

Lithocarpus densiflorus

Tanbark oak

3

Lyonothamnus species

Catalina ironwood

3

•

+

•

+

+

Pinus canariensis

Canary Island pine

•

•

•

•

•

Pinus coulteri

Coulter pine

Pinus halepensis

Aleppo pine

•

•

•

•

•

Pinus pinea

Italian stone pine

•

•

•

•

+

Pinus radiata

Monterey pine

3

•

+

•

+

+

Pinus sabiniana

Digger pine

3

Pinus torreyana

Torrey pine

3

•

•

•

+

+

Pistacia chinensis

Chinese pistache

•

+

•

+

Quercus agrifolia

Coast live oak

3

•

•

•

•

•

Quercus chrysolepsis

Live canyon oak

3

+

•

+

•

Quercus douglasii

Blue oak3

Quercus engelmannii

Mesa oak3

Quercus ilex

Holly oakQuercus lobata

Valley oak

Quercus suber

Cork oak

+

•

+

•

Robinia pseudoacacia

Black locust

•

•

•

•

•

Schinus molle

California pepper

•

•

•

•

•

Schinus polygamus

Peruvian pepper tree

+

•

•

+

Tamarix aphylla

Athel tree

•

•

•

+

+

+

•

3

+

+
•

+

•

•

•

+

•

•

•

•

•

+

+

3

VI­18

+
+

Botanical nameCommon name

Zelkova serrata

Sawleaf zelkova

Native?
(3 = yes)aCoastalmarginIntermediate
valleys

Coastalfoothills•+•

Inlandvalleys•

Most of the information in the table above is from the book Trees and Shrubs for Dry California Landscapes (Perry, 1981).
•,plant is well suited to this type of landscape; +, plant will do well in this type of landscape if exposure and soil conditions are
optimal.

VI­19

Inlandfoothills+

Sunset Western Garden Book (7th ed., 2001)
One of the best­known and most widely available plant selection guides, this book, like
Perry’s, is based on a system of climatological zones and related maps. Some horticulturists havestated that the climate zone maps in the Sunset book are more refined and more thorough than any
in the other planting references available. Indeed, Sunset is seen as a leader in pointing out that
understanding climate conditions is a key prerequisite for the successful selection and growing ofplants.
The first part of the book includes maps and descriptions of the climatological zones.
Cities and towns in coastal southern California can be found in the map for the San Diego area orin the map for the Los Angeles region. Next in the book is a relatively brief section listing plants
for specific landscaping situations—for example, plants for seacoast gardens, shady areas, dry
areas, and windy areas. The third and main part of the book consists of an encyclopedia describing
several thousand species of plants used for landscapes throughout the western United States.
Unfortunately, the text within the book’s encyclopedia section describes the tolerance ranges ofplants for various climate zones. Using those ranges often leads to the selection and use of plants
well beyond the climate conditions for which the plants are well suited. Some workers suggest that
Sunset should place more emphasis on the preference ranges of plants, in addition to reporting thetolerance ranges. Using this book to select plants involves first consulting the appropriate zone map
and the lists of plants for specific landscape situations and then consulting the encyclopedia.

Native Plants for Use in the California Landscape (Labadie, 1978)
In this book, author Emile Labadie draws upon his many years of experience as an
instructor of ornamental horticulture at a California college to describe 101 species of California
native plants. At the front of the book is a key for identifying trees, shrubs, and ground covers. At
the back of the book are lists of plants that tolerate particular situations, such as full sun, partial
shade, considerable shade, hot and dry weather, and wind, as well as lists of plants that serve a
special function, such as providing a visual screen or hedge, a barrier, erosion control, or shade.
Table VI­8 is a summary of some information from this book. The notes regarding planting
conditions may prove particularly useful.

VI­20

a

Table VI–8. Native plants recommended by Labadie (1978) for California landscapes.
Botanical nameCommon nameType

Spread(ft)

Height(ft)

Arctostaphylos edmundsii

Notes

Little Sur manzanita

Ground cover

8+

0.5–2

Sun or partial shade; tolerates
salt spray

Arctostaphylos hookeri

Hooker manzanita, Monterey
manzanita

Ground cover

6–8

0.5–3

Sun or shade; tolerates salt
spray, drought

Arctostaphylos uva­ursi

bearberry, kinnikinnick,creeping manzanita

Ground cover

Up to
15

6–12

Best in sandy soil; drought­
tolerant

Artemisia pycnocephala

Coast sagebrush

Ground cover

Up to 2

1.5–2.5

Best where temperature ismoderate; drought­tolerant; short­
lived

Asarum caudatum

Wild ginger

Ground cover

Wide

0.8

Best in shade in rich, moist soil;
needs pure water for irrigation

Baccharis pilularis

Dwarf coyote bush

Ground cover

2–10

0.5–1

Tolerates moisture as well as
drought; tolerates moderately
saline, somewhat alkali soil

Ceanothus gloriosus

Point Reyes creeper

Ground cover5+

0.5–1.5

Tolerates wind, salt spray

Ceanothus griseus
var. horizontalis

Carmel creeper

Ground cover

5–15

3–5

Needs little water

Ceanothus impressus

Santa Barbara ceanothus

Ground cover

8–10

3–5

Best in well­drained soil

Ceanothus purpureus

Hollyleaf ceanothus

Ground cover

5–6

2–4

Best in well­drained soil

Equisetum hyemale

Horsetail, common scouring­rush

Ground cover

Wide

2–4

Moist, shaded areas from sea
level to 8,500 ft

Galvezia speciosa

Island bush snapdragon

Ground cover

3–5

7–8

Moist, well­drained soil; may
tolerate moderately saline,
somewhat alkali soil

Polystichum munitum

Western sword fern

Ground cover

2–4

2–4

Needs moist, rich soil, partial
shade; needs pure water for
irrigation

Satureja douglasii

Yerba buena

Ground cover

3+

0.5

Best in moist, rich soil, sun orpartial shade; needs pure water
for irrigation

Symphoricarpos albus

Snowberry

Ground cover

Wide

2–6

Best in well­drained soil, shade;
valuable food plant for wildlife

Woodwardia fimbriata

Giant chain fern

Ground cover9+

Up to 9

Moist, well­drained soil, partial
shade

Zauschneria californica

California fuchsia,
hummingbird fuchsia

Ground cover

1.5

1.5–3

Well­drained soil, sun

Washingtonia filifera

California fan palm

Palm

8–20

20–80

Moist, well­drained soil, sun;
tolerates drought and saline,
alkaline soil; only palm native to
Calif.; not good for sites right on
the coast

Adenostoma fasciculatum

Chamise, greasewood

Shrub

5

2–10

Best in hot, dry areas; flammable

Arctostaphylos densiflora

Vine Hill manzanita, Sonoma
manzanita

Shrub

4–6

1.5–6

Tolerant of dry soil; sun or partial
shade

Atriplex lentiformis var.
breweri

Brewer saltbush

Shrub

6–10

6–10

Tolerates salt spray, alkaline soil

Calycanthus occidentalis

Spicebush, sweet shrub

Shrub

4–12

4–12

Best in moist soil

Carpenteria californica

Bush anemone

Shrub

4–6

6–15

Best in partial shade

8–20

Anywhere except desert
Drought­tolerant

Cercis occidentalisWestern redbud

Shrub

Up to
16

Comarostaphylis diversifolia

Summer holly

Shrub

4–8

6–18

Eriogonum arborescens

Santa Cruz Island
buckwheat

Shrub

3.5–4

Up to 3.5

Eriogonum fasciculatum

California buckwheat

Shrub

3–4

2–3

VI­21

Good for rocky slopes, full sun;
tolerates wind
Good for dry slopes

Botanical nameCommon nameType

Spread(ft)

Height(ft)

Notes

Eriogonum giganteum

St. Catherine’s lace

Shrub

4–6

3–6

Drought­tolerant

Fragaria chiloensis

Sand strawberry

Shrub

Wide

0.5–1

Needs fertile, well­drained soil;
may tolerate moderately saline,
somewhat alkali soil

Fremontodendron
californicum

Common flannel bush,
leatherwood, Fremontia

Shrub

8–15

6–18

For hot, dry locations

Gaultheria shallon

Salal

Shrub

Wide

1.5–6

Best in moist soil in partial shade;
native to coastal redwood region;
needs pure water for irrigation

Holodiscus discolor

Cream bush, ocean spray

Shrub

10–12

3–20

Moist slopes, canyons; sun orpartial shade; needs pure water
for irrigation

Mahonia aquifolium

Oregon grape

Shrub

1–6

1–6

Best in partial shade, in well­drained soil

Mahonia nervosa

Longleaf mahonia

Shrub

Up to 20.8–2Best in moist soil in partial shade

Mahonia nevinii

Nevins barberry

Shrub

3–10

3–10

Best in sun; tolerates any soil,
little or much water

Mahonia pinnata

California holly grape

Shrub

5+

2.5+

Tolerates heat, drought; full sun

Physocarpus capitatus

Ninebark

Shrub

6–8

6–8

Partial shade, moist soil

Rhamnus californica

California coffeeberry

Shrub

4–8

4–18

Drought­tolerant; prefers sun,rocky or heavy soil

Rhamnus crocea

Redberry, buckthorn

Shrub

5–8

5

Adaptable, but needs gooddrainage

Rhododendron
macrophyllum

Rhododendron, California
rose bay

Shrub

4–10

4–10

Needs moist, rich, well­drained
soil, part shade; foliage toxic tolivestock; needs pure water for
irrigation

Rhododendron occidentale

Western azalea

Shrub

6–10

6–10

Needs moist, rich, well­drained
soil, part shade; foliage toxic tolivestock

Rhus integrifolia

Lemonade berry

Shrub

3–10

3–10

Best near the coast; may toleratemoderately saline, somewhat
alkali soil

Rhus laurina

Laurel sumac

Shrub

5–7

5–7

Best on sunny, dry slopes below
3,000 ft, coastal; may toleratemoderately saline, somewhat
alkali soil

Rhus ovata

Sugar bush, sugar sumac

Shrub

2.5–10

3–10Best on dry slopes below 2,500 ft

Ribes sanguineum var.
glutinosum

Pink winter currant, red­
flowering currant

Shrub

5–12

5–12

Best in moist soil in partial shade;
needs pure water for irrigation

Ribes speciosum

Fuchsia­flowering
gooseberry

Shrub

3–6

3–10

Moist, well­drained soil, partial
shade

Ribes viburnifolium

Evergreen currant

Shrub

12

3–6

Best in partial shade; drought­
tolerant

Romneya coulteri

Matilija poppy, coulter poppy

Shrub

Wide

3–8

Best in sun in well­drained soil;
invasive

Rubus parviflorus

Thimble berry

Shrub

3–5

4–6

Likes open woods and canyon
areas; needs pure water for
irrigation

Salvia leucophylla

Purple sage

Shrub

5+

5+

Best in dry, well­drained soil,
sun; tolerates heat

Vaccinium ovatum

California huckleberry

Shrub

3–5

2–8

Best in well­drained acidic soil,
part shade; needs pure water for
irrigation

Acer circinatum

Vine maple

Shrub orsmall tree

25–35

5–35

Best in moist, rich soil, partial
shade; tolerates heat, cold;
needs pure water for irrigation

VI­22

Botanical nameCommon name

Amelanchier alnifolia

Western serviceberry

Fremontodendron
mexicanumType

Spread(ft)

Height(ft)

Notes

Shrub orsmall tree

6–8

4–15

Best in dry, rocky soil, sun

Southern Fremontia

Shrub orsmall tree

8–15

8–20

Best in dry, well­drained soil

Garrya elliptica

Coast silktassel

Shrub orsmall tree

8–10

4–30

Likes partial shade, coastal
conditions

Abies bracteata

Santa Lucia fir, bristlecone fir

Tree

15­20

30­100Best in dry, rocky, acidic soil,
sun, cool climate

Abies concolor

White fir, silver fir

Tree

40–60

60–100Best in deep, rich, moist loam incold areas; tolerates coarse, dry
soilAbies magnifica

Red fir, silver tip

Tree

30–60

60–200Deep, well­drained soil, sun; highaltitudeAcer macrophyllum

Bigleaf maple

Tree

30–50

30–95

Deep, rich, moist soil; sun orpartial shade

Acer negundo var.
californicum

California box elder

Tree

50+

20–40

Tolerates various soils; box elder
bug is a pest

Aesculus californica

California buckeye,
horsechestnut

Tree

30–60

15–40

Best in moist, well­drained loam;
coastalAlnus oregona

Red alder, Oregon alder,western alder

Tree

20–30

100–130

Best in deep, well­drained loamwith ample water; roots fix
nitrogen; needs pure water for
irrigation

Alnus rhombifolia

White alder

Tree

Up to
40

40–100Best in moist soil

Arbutus menziesii

Pacific madrone

Tree

15–75

Up to 80

Best in warm, moist areas, yettolerates wide climate range;
prefers rocky or sandy soil

Calocedrus decurrens

Incense cedar

Tree

Up to
50

50–150Tolerates extreme heat and cold

Cercocarpus betuloides var.
traskiae

Catalina mountainmahogany, Catalina hard­
tack

Tree

15+

up to 25

Best on dry slopes or in washes

Cercocarpus ledifolius

Curl­leaf mountainmahogany, desert mountainmahogany

Tree

15+

up to 30

Native to southern Calif. deserts
and mountains

Chamaecyparis lawsoniana

Lawson cypress, Port Orford
cedar

Tree

30–50

75–200Best in cool, coastal areas

Cornus nuttallii

Pacific dogwood

Tree

Up to
20

30–50

Best in partial shade, with somemoisture; needs pure water for
irrigation

Corylus cornuta var.
californica

Hazelnut, filbert

Tree

5–12

5–12

Moist slopes, partial shade

Cupressus macrocarpa

Monterey cypress

Tree

up to 75

20–75

Coastal areas; wind­tolerant

Dendromecon harfordii

Island tree poppy

Tree

2–20

2–20

Best in well­drained soil, full sun

Heteromeles arbutifolia

Toyon, Christmas berry,
California holly

Tree

5–20

6–25

Best in dry soil, up to 3,500 ft
elev.

Juglans hindsii

California black walnut

Tree

20–50

30–70

Best near streams in moist,
sandy or gravelly soil; tolerates
wind, heat

Lithocarpus densiflora

Tanbark oak, tan oak

Tree

Up to
50

50–150Best in coastal areas, not forinterior valleys

Lyonothamnus floribundus
var. asplenifolius

Fern­leaf Catalina ironwood

Tree

15–40

25–50

Best in coastal areas in full sun;
doesn’t tolerate extreme heat or
cold

Myrica californica

Pacific wax myrtle

Tree

15–20

10–35

Best in coastal areas

VI­23

Botanical nameCommon nameType

Spread(ft)

Height(ft)

Notes

Pinus contorta

Shore pine, beach pine

Tree

15–30

15–30

Best in sandy, moist soils

Pinus coulteri

Coulter pine

Tree

20–40

40–80

For warm, dry slopes; tolerates
heat, wind

Pinus muricata

Bishop pine

Tree

20–40

45–75

Coastal areas; tolerates salty air
and wind

Pinus ponderosa

Ponderosa pine, western
yellow pine

Tree

30–40

50–200Best in dry, sandy soil; needssome moisture

Pinus radiata

Monterey Pine

Tree

30–50

40–80

Well­drained, sandy soil, sun;
tolerates heat, cold, wind, salt
spray

Pinus sabiniana

Digger pine

Tree

25–30

40–80

Best in hot, dry inland valleys andfoothills

Pinus torreyana

Torrey pine, Soledad pine

Tree

25–30

20–60

Dry, well­drained soil, sun;
moderate temp.; may toleratemoderately saline, somewhat
alkali soil

Platanus racemosaWestern sycamore

Tree

50–70

40–90

Deep, rich, moist soil;
anthracnose a problem

Prunus ilicifolia

Hollyleaf cherry

Tree

10–25

10–25

Best in well­drained soil, sun;
long­lived

Prunus lyonii

Catalina cherry

Tree

15–30

15–45

Best in relatively dry soil, sun orpartial shade

Pseudotsuga menziesii

Douglas fir

Tree

30–60

70–250Best in humid area with well­drained soil, sun or partial shade

Quercus agrifolia

Coast live oakTree

60–10030–75

Needs well­drained soil

Quercus chrysolepis

Maul oak, canyon oak

Tree

Up to
100

25–100Best in moist soil on slopes
below 6,500 ft

Quercus douglasii

Blue oak

Tree

25–50

up to 50

Best in dry, well­drained soil, sun

Quercus kelloggii

California black bak

Tree

25–30

30–80

Dry, gravelly soil, sun

Quercus lobata

Valley oak, California white
oak

Tree

70+

70+

Deep soil, sun; tolerates heat

Quercus wislizenii

Interior live oak

Tree

75+

30–75

Tolerates poor, dry soil; best insun

Sambucus caerulea

Blue elderberry

Tree

15–30

15–30

Best in moist, well­drained soil;
bark is toxic

Sequoia sempervirens

Coast redwood

Tree

20–40

100–300

Best in deep, moist, rich, well­drained soil, sun

Sequoiadendron giganteum

Giant sequoia

Tree

75–100

150–250

Deep, rich, well­drained soil, sun;
not for areas without winter snow

Thuja plicata

Giant arborvitae, western red
cedar

Tree

35–60

up to 200

Best in rich, moist, well­drained
soil; tolerates extreme heat andcold

Tsuga heterophylla

Western hemlock, coast
hemlock, Alaska pine

Tree

20

125–160

Moist, sandy soil, sun; needs
pure water for irrigation

Umbellularia californica

California bay, California
laurel, Oregon myrtle

Tree

30–100

20–100Best in fertile, moist, deep, well­drained soil; sun or partial shadea

All plants listed are California natives. Information excerpted from text in Labadie (1978). Some notes in the rightmost column

were provided by reviewers of this literature review.

VI­24

California Native Trees and Shrubs (Lenz and Dourley, 1981)
This book is based on a system of climatological zones and maps similar to those in Perry(1981). The book’s subtitle, For Garden and Environmental Use in Southern California andAdjacent Areas, makes clear the authors’ focus. Basing their book on 50 years of horticultural datafrom Rancho Santa Ana Botanic Garden, Lenz and Dourley begin by describing the climate andgeological environment of southern California. The authors then describe the seven zones in theirclimatological system. This description is followed by a brief excursion into the realm of native­
plant ecology, in which they describe the dominant plant communities of the southern California
wildlands: valley grassland, coastal sage scrub, chaparral, creosote bush scrub, Joshua tree
woodland, pinion juniper woodland, yellow pine forest, and desert oasis. Key species of each
community are outlined in some detail. Next in the book is a chapter that contains detailed
descriptions of 361 species of trees and shrubs native to California, including line drawings andphotographs for many of them. In subsequent chapters, Lenz and Dourley report on nonnativeplants, the survivability of plants without horticultural care, and the development of superior
cultivars. At the back of the book, they provide a table listing all species described in the book andthe zones for which those species are well suited. Also provided are a relatively comprehensive
glossary and a cross­index between common names and scientific names of plants. The book is
best used either as an encyclopedic reference or as a map­based guide to selecting plants.

California Native Plants for the Garden (Bornstein, Fross, and O’Brien , 2005)
This recent book covers some of the same ground as Lenz (1956), Lenz and Dourley(1981), and Labadie (1978). Chapter 1 reviews briefly the efforts of those gardeners, nurseryworkers, landscape designers, and others who sought during the past century to promote the use ofnative plants in California gardens. Chapter 2 describes the major California plant communities:
chaparral, coastal scrub, grassland, woodland, forest, desert scrub, desert woodland, and the highmountain (alpine) regions. Chapter 3 outlines the basics of designing a garden featuring
California’s native flora: site analysis, selection of a design theme, planning, plant selection, andplacement of plants. Chapter 4 describes the best ways to care for native plants. It covers such
topics as site preparation, soil management, acquisition of seeds and plants, planting, watering,fertilizing, mulching, pruning, and managing pests and weeds. Next in the book is a fairly lengthy
section (176 of the book’s 259 pages) titled “Plant Profiles.” Here is where the authors describe indetail (and depict with photos) approximately 200 key plants. Along the way they also describe
briefly some 300 other native plants. The key plants are ones deemed to be reliable performers that
also have high aesthetic value, are readily available, and are resistant to insects and other pests. A

VI­25

final, but no less important, section provides 30 plant selection lists intended to help a gardenerchoose appropriate plants for a variety of specific site conditions or particular plant characteristics.
The site conditions include, for example, moist habitats, seashore conditions, and meadows. The
plant characteristics include aromatic foliage, fast growth, slow growth, and fall color.
The chief value of this book, when compared to others mentioned here, is that it features
plants widely available now and that it advocates using native species not just as drought­tolerant
species (a common use in former years) but also as the featured plants in a variety of morefavorable sites.

Landscape Plants for Western Regions (Perry, 1992)
This book builds on the body of information provided in Perry’s earlier (1981) book. As he
explains, “Since the completion of Trees and Shrubs for Dry California Landscapes in 1980, I
have pursued the study of landscape plants with renewed interest and rigor ... I wanted to have somuch information on plants that I could answer any question regarding their needs and tolerancesand could give the best advice on the ecological guidelines that influence our use of them. So, I
collected better reference materials, made more field observations, and started to travel to otherparts of the world in an effort to see some of our ornamental plants growing in their naturalenvironments.”
In the book’s first section, “Issues and Goals,” Perry shares his thoughts regarding thechanging nature of landscaping and society’s need to keep redefining its landscaping goals andknowledge. Many of the ideas address environmental issues and encourage pursuing the goal ofsustainability as part of the process of designing a landscape.
In his book’s second section, “Regional Characteristics,” Perry defines and depicts on a
map a number of landscape regions. He also provides maps outlining intensities of rainfall and thenumbers of days of frost per year. They are followed by detailed descriptions and photographs ofthe various landscape regions—regions that are similar to the ones defined in his earlier book andin Lenz and Dourley’s book.
In the third section, “Plants and Environment,” Perry introduces a number of ecologicalconcepts helpful when planning and designing landscapes. He also provides illustrative
photographs.
The fourth section, “Estimating Water Needs of Landscape Plants,” contains an extensive
table of 475 trees, shrubs, vines, ground covers, perennials, and succulents, with the water needs ofVI­26

each species indicated for each of the landscape regions described in the book’s second section.
This is a good place to start when beginning the plant­selecting phase of designing a landscape.
In the fifth section, “Design Checklists,” Perry provides an extensive table listing therelevant height, width, flowering season, flower color, and value to wildlife habitat of each species.
The table is also another source of information to refer to early in the process of designing alandscape. Perry continues the section by presenting a number of “plant palettes”—groupings ofplants that are compatible both aesthetically and in terms of horticultural requirements. The
western native palettes include a coast live oak category, a Monterey pine category, and a Westernsycamore category. The Mediterranean palette includes olive tree, holly oak, and sweet bay
categories. The groupings of Australian species include the sugar gum, the river red gum, thepeppermint tree, and the shoestring acacia categories. Other groupings are for Asian species, suchas crape myrtle and related plants, and South African species, such as fortnight lily. Also in thisfifth section is a list of plants that can help “fix” nitrogen from the air, enhancing the nitrogencontent of the plant litter and soil, and a number of planting guidelines aimed at helping to restore
native plants or wildlife habitat.
In his book’s sixth and final section, “Plant Compendium,” Perry describes in detail 475
species of plants. Each description includes a clear, well­composed color photograph of therelevant plant.

Native Plants for California Gardens (Lenz, 1956)
Published in 1956 by Rancho Santa Ana Botanic Garden, Claremont, Calif., this book ispart of a series of papers devoted to botany and the horticulture of California plants. According toLenz’s foreword, he attempted to select those species of native flora that can be recommended togardeners and landscape designers. Lenz describes briefly California’s various plant communities
and early botanical collections. He also provides useful tips for propagating and handling nativeplants, including germinating seeds, transplanting, rooting, grafting, and preventing disease. The
remaining 131 pages of this 166­page book are a detailed compendium of 102 species of plants
native to California. Sharp, clear black­and­white illustrative photographs are provided.

VI.C. Guide for Selecting Turfgrasses
Turfgrasses often are valuable components of the environments where people live, work,and play. They can be used to provide an essential base for sports and leisure activities in suchsettings as baseball fields, football and soccer fields, golf courses, and school grounds. They alsoVI­27

prove useful in soothing landscapes in such places as office parks, cemeteries, and home gardens.
Yet turf also is seen by some as problematic, for it sometimes contributes to a net loss of oxygen in
the atmosphere and often requires considerable water, the conservation of which is a main reason
for switching to recycled water in the first place. Also, turfgrass may require the application offertilizer or other chemical treatments, which may in some instances, foster the contamination ofsoil or other non­point source pollution problems. The key to avoiding all these potential problems
is to use turf only where necessary and to choose a variety of turf that best fits the intended
application.
Selecting a turfgrass involves considering a number of factors, including the intended useof the turf, the desired appearance, and the degree of required maintenance. The choice of aturfgrass is also dictated by geography, the soil and biotic conditions under which grass will begrown, and the climate, particularly temperature, rainfall, and the amount of sunlight. Table VI­9lists all species commonly grown in California, divided into warm­ and cool­season species. Warm­season grasses grow predominantly in southern California, in the Central Valley, and along the
Pacific coast as far north as San Francisco. Cool­season grasses are grown throughout California,
except in the state’s deserts and southernmost regions.
Warm­season turfgrasses usually lose their greenness and go dormant in winter if theaverage temperature drops below 50 to 60 ˚F. Some may die if exposed to subfreezing
temperatures for extended periods. Cool­season turfgrasses do not ordinarily lose their greenness
unless the average air temperature drops below 32 ˚F for an extended period. They regain theirgreenness as soon as temperatures rise above freezing and are not usually damaged by subfreezing
temperatures. It should be noted that grasses vary in the hue and intensity of their color, from thebright green of Kentucky bluegrass (Poa pratensis) to the grayish green of common bermudagrass(Cynodon spp.).
The following information applies to the turfgrasses listed in Table VI­9 when suchgrasses are grown in California:

Bentgrasses (Agrostis spp.)
Though they tolerate close mowing and can provide lawns of good quality, bentgrasses require
more maintenance than other lawn grasses and extra effort to ward off disease during the summer.

·

The colonial variety of bentgrass (Agrostis tenuis) may spread very slowly by shortrhizomes and, less often, short stolons. Its layer of thatch extends above and below the soil.

VI­28

This variety is adapted to the northern coastal climate and does not form a dense turf in otherareas.

·The highland variety (Agrostis spp. cv. “Highland”) is adapted to valley climates and willsurvive extensive droughts. It forms solid patches of grass that turn a frosty blue frommorning dew during cool seasons. It may form both short rhizomes and stolons.

·

The creeping variety (Agrostis palustris) is used for specialized turf, such as golf, bowling
and tennis greens. The skill and expense required to maintain it usually preclude its use forhome lawns. This variety spreads by stolons to form a mat or layer of thatch above the soil.

Bluegrasses (Poa spp.)
Three distinct bluegrasses are grown in California.

·

The annual variety of bluegrass (Poa annua), considered a weed, is well adapted to the cool,moist conditions of California’s Pacific coast from Los Angeles to the Oregon border. It is
the predominant species on golf greens, bowling greens, and croquet courts. It also quickly
invades the dead and worn areas of a significant number of overused sports fields and parks,
as it is very well suited to the coastal climate and is a prolific producer of seeds. This variety
often successfully invades golf and bowling greens because it tolerates very close mowing.
Shallow­rooted and drought intolerant, this turfgrass is a short­lived perennial in cool, moist
climates and persists as an annual in sites with hot, dry summers.

·

Kentucky bluegrass (P. pratensis) is the standard of quality among turfgrasses in areas
where it is well adapted. In areas of marginal adaptation, it suffers from diseases, invasion
by weeds, and stress related to high temperatures. Each variety of Kentucky bluegrass has
characteristic virtues and faults, with none adapted to hot valley climates. Blending equal
portions of several seed varieties usually leads to optimal results. For example, a seed
mixture of Kentucky bluegrass and perennial ryegrass is more resistant to disease than isbluegrass alone.

·

Roughstalk bluegrass (P. trivialis) is a short­lived perennial that is well adapted to moist,
shady sites. Due to its superior performance during winter and after close mowing, it iscommonly used to overseed dormant bermudagrass on golf putting greens.

Fescue (Festuca spp.)
These grasses, which vary considerably by species, are appropriate for a range of purposes.

VI­29

·

Hard and red fescues (Festuca longifolia and F. rubra) are recognizable by their fine texture
and, thus, are also known as “fine­leaf” fescues. They do not prosper in hot climates, except
in shady, dry situations, and they do not tolerate being closely mowed or excessively
fertilized. Their color, texture, and pattern of growth make them excellent companion grasses
for Kentucky bluegrass, as long as these moderately drought­tolerant grasses are grown inmoderately shady exposures or dry soil. Fine fescues seldom exceed 8 in. (20 cm) in height,
except when in flower, and thus can be useful where a low­maintenance lawn is desired, suchas at a summer cabin at cool mountain elevations where a single mowing will remove theseed heads. They can also be used for controlling hillside erosion in urban areas, such as
unmowed ground covers along roadsides, and for golf course roughs, parks, and cemeteries.

·

Tall fescue (F. arundinacea), when densely sown, produces a moderately coarse­textured
lawn that is trouble free and uniform in appearance. In a mix with other cool­season grasses,
individual tall fescue plants appear as coarse weeds. New selections, known as turf­type anddwarf­type tall fescues, are finer textured and shorter than older selections. Bare or wornspots within tall fescue stands must be reseeded, as these grasses do not produce runners.
Tall fescues are quite tolerant of drought and heat and require the least maintenance of allcool­season grasses in California.

Ryegrass (Lolium spp.)
Two distinct ryegrass species are commonly planted in California.

·

Annual ryegrass (Lolium multiflorum), quite coarse textured, is used only to overseed
dormant bermudagrass or to provide a temporary annual cover.

·

Perennial ryegrass (L. perenne), a strong performer in coastal fog belts and adequate
elsewhere, is often used in seed mixtures with Kentucky bluegrass. It germinates quickly andprovides a rapid turf cover and so is also used to overseed winter­dormant Bermuda grasslawns. It has no rhizomes or stolons, so bare or worn areas should be reseeded.

Weeping alkaligrass (Puccinellia distans)
This grass is only marginally adapted to the cool central and northern coast, as well as to mountainregions. Its only use is in areas with severe soil or water salinity problems since it does not produce
an attractive, durable lawn. Because weeping alkaligrass tolerates low mowing, it may provide an
acceptable alternative for winter overseeding of bermudagrass on salt­affected golf greens.

VI­30Bermudagrass (Cynodon dactylon)
This grass is well adapted to the warm regions of California. Spreading both by rhizomes andstolons, it can be a troublesome invader of other areas in a landscape. Short mowing helps produce
a neat, restrained turf. Bermudagrass does not tolerate shade and turns brown with continued low
temperatures. Hybrid bermudagrasses are propagated vegetatively and require a high level ofmanagement. If ordinary management is available, common bermudagrass is preferable.
Bermudagrasses are highly drought and salt tolerant.

Seashore paspalum (Paspalum vaginatum)This grass grows well near the ocean, where it is subjected to saltwater. It has excellent toleranceof salinity.

St. Augustine grass (Stenotaphrum secundatum)This grass is a coarse­textured, subtropical grass with excellent tolerance of shade, drought, andsalinity.

Kikuyugrass (Pennisetum clandestinum)This grass is a weedy grass grown in coastal and some inland areas of California. This native ofhigh­altitude equatorial Africa thrives in climates with moderate, even temperatures. Sometimes
mistaken for St. Augustine grass, kikuyugrass forms vigorous stolons and has slightly flattened,hairy leaf sheaths and blades with files of hairs. It tolerates low fertility, drought, and frequent
close mowing.

Zoysiagrass (Zoysia spp.)

This grass is well adapted only in the warmest areas of California. It is a high­quality, erect turfthat forms a dense carpet that may be difficult to mow evenly. Zoysia tolerates moderate shade,though it is slow to become established, even in full sun. The nursery trade uses Zoysia tenuifolia,
known as mascarengrass or Japanese temple grass, as a ground cover. A fine­leafed, dwarf plantthat requires no mowing, this grass slowly yet strongly invades nearby plants. Zoysia japonica,
known as Japanese lawn grass, is very drought tolerant and the primary zoysia species used as
turfgrass in California. The Meyer variety resembles tall fescue in color and texture. El Toro, avariety patented by the University of California, covers faster and is coarser and shorter than otherzoysias.

VI­31

Table VI­9. California turfgrasses.
Names for cool­season grasses
Common nameScientific nameaBentgrass (colonial)

Agrostis tenuis Sibth.

Bentgrass (creeping)

Agrostis palustris Huds.

Bentgrass (highland)

Agrostis spp. cv. “Highland”

Bluegrass (annual)Poa annua L.

Bluegrass (Kentucky)

Poa pratensis L.

Bluegrass (roughstalk)Poa trivialis L.

Fescue (hard)

Festuca longifolia Thuill.

Fescue (red)Festuca rubra L.

Fescue (tall)

Festuca arundinacea Schreb.

Ryegrass (Annual)

Lolium multiflorum Lam.

Ryegrass (perennial)

Lolium perenne L.

Weeping alkaligrass

Puccinellia distans (L.) Parl.

aaNames for warm­season grassesb

Bermudagrass (Common)

Cynodon dactylon (L.) Pers.

Bermudagrass (“Hybrid”)

Cynodon dactylon (L.) Pers.

Kikuyugrass

Pennisetum clandestinum Hochst.

Seashore paspalum

Paspalum vaginatum O. Swartz

St. Augustine grass

Stenotaphrum secundatum (Walt.) Kuntze

Zoysiagrass

Zoysia spp.

abThis species is not well­adapted for hot summers.
bConsidered by some to be a weed.

VI.D. Guides Available via the Internet
Many guides for selecting plants for landscapes are available on the Internet. They tend tobe narrower in focus than the books cited previously in this chapter. Some useful ones are found on
the websites of the Rancho Santa Ana Botanic Garden and the San Diego chapter of the California
Native Plant Society. Both sites contain numerous links to many other useful sites.

Rancho Santa Ana Botanic Garden (www.rsabg.org)
The website of Rancho Santa Ana Botanic Garden, Claremont, Calif., hosts a number of
useful Web pages and downloadable documents. One of the latter is the California Classics Plant
Palette, a 10­page brochure. This document lists the most reliable, garden­worthy, and widely
available native plants for southern California gardens and public landscapes. Plants are groupedby ecological community. These include oak woodlands, riparian woodlands, scrubland andVI­32chaparral, Mojave Desert, and Colorado Desert. Excerpts from the oak woodland, riparian
woodland, and scrubland and chaparral lists are presented here as Tables VI­10, VI­11, and VI­12.
All of these groupings are helpful when designing a landscape that includes or consists entirely ofplants native to California.
aTable VI–10. “Classic” California native plants for oak woodland landscapes.
Type of plant

Botanical nameCommon name

Trees

Aesculus californica

California buckeye

Quercus agrifolia

Coast live oak

Quercus engelmannii

Mesa oak

Arctostaphylos bakeri “Louis
Edmunds”

Louis Edmunds manzanita

Arctostaphylos “Howard McMinn”

Howard McMinn manzanita

Arctostaphylos “Sunset”

Sunset manzanita

Carpenteria californica

Bush anemone

Ceanothus “Concha”

Concha Ceanothus

Ceanothus “Ray Hartman”

Ray Hartman Ceanothus

Ceanothus “Wheeler Canyon”

Wheeler Canyon Ceanothus

Galvesia speciosa

Island snapdragon

Heteromeles arbutifolia

Toyon

Mahonia (Berberis) “Golden
Abundance”

Golden abundance barberry

Prunus ilicifolia

Holly­leaf cherry

Rhamnus californica and cultivars

California coffeeberry

Rhamnus crocea

Redberry

Ribes malvaceum

Chaparral currant

Ribes speciosum

Fuschia­flowered gooseberry

Symphoricarpos albus var. laevigatus“Tilden Park”

Tilden Park snowberry

Arctostaphylos edmundsii

Edmunds manzanita

Baccharis pilularis var. pilularis

Prostrate coyote brush

Ceanothus griseus var. horizontalis

Carmel creeper

Ceanothus “Joyce Coulter”

Joyce Coulter ceanothus

Mahonia (Berberis) repens

Creeping barberry

Ribes viburnifolium

Catalina perfume currant

Symphoricarpos mollis

Creeping snowberry

Achillea millefolium

Yarrow

Asclepias fascicularis

Narrow­leaf milkweed

Heuchera maxima

Island alumroot

Fragaria chiloensis

Beach strawberry

Monardella villosa

Coyote mint

Ranunculus californica

California buttercup

Salvia spathacea

Hummingbird sage

Sisyrinchium bellumBlue­eyed grass

Thalictrum fendleri subsp.
polycarpum

Meadow rose

ShrubsGround covers

Perennials

VI­33

Notes

May tolerate moderately alkaline,
somewhat saline soil

May tolerate moderately alkaline,
somewhat saline soil

Likes shadea

The first three columns in this table were excerpted from the California Classics Plant Palette (Rancho Santa Ana Botanical
Garden, 2005). The notes in the fourth (rightmost) column were provided by a reviewer of this literature review. Unless noted
otherwise, all the species in this table are likely to be unsuccessful unless the water with which they are irrigated is relatively
low in dissolved salts and alkali.

VI­34

a

Table VI–11. “Classic” California native plants for riparian woodland landscapes.
Type of plant
Trees

ShrubsGround covers

Perennials

Vine

Botanical nameCommon name

Notes

Alnus rhombifolia

White alder

A mistletoe magnet

Platanus racemosaWestern sycamore

Populus fremontii

Fremont cottonwood

Quercus lobata

Valley oak

Umbellularia californica

California bay

Calycanthus occidentalis

Spice bush

Carpenteria californica

Bush anemone

Cercis occidentalisWestern redbud

Cornus sericea

Creek dogwood

Lavatera assurgentiflora

Malva rosa

Lavatera “Purísima”

Purísima mallow

Mahonia (Berberis) “Golden
Abundance”

Golden abundance barberry

Philadelphus lewisii

Mock orange

Ribes speciosum

Fuschia­flowered gooseberry

Rosa californica

California rose

Rosa nutkana var. nutkana

Nootka rose

Rosa woodsii var. ultramontana

Interior rose

Ceanothus griseus var. horizontalis
and cultivars

Carmel creeper

Iva hayesiana

Hayes iva

Arctostaphylos edmundsii

Edmunds manzanita

Baccharis pilularis var. pilularis

Prostrate coyote brush

Mahonia (Berberis) aquifolium“Compacta”

Compact Oregon grape

Mahonia (Berberis) repens

Creeping barberry

Ribes viburnifolium

Evergreen currant

Aquilegia formosa

Western columbine

Asclepias speciosa

Showy milkweed

Achillea millefolium

Yarrow

Heuchera species and cultivars

Coral bells

Iris douglasiana and cultivars

Pacific coast iris

Juncus patens

Wire grass

Muhlenbergia rigens

Deer grass

Thalictrum fendleri subsp.
polycarpum

Meadow rue

Woodwardia fimbriata

Giant chain fern

Vitus californica “Roger’s Red”

Roger’s red California grapea

A mistletoe magnet

May tolerate moderately alkaline,
somewhat saline soil

Tolerates soil that’s moderately
alkaline and somewhat saline
Tolerates soil that’s moderately
alkaline and somewhat saline

May tolerate moderately alkaline,
somewhat saline soil

The first three columns in this table were excerpted from the California Classics Plant Palette (Rancho Santa Ana Botanical
Garden, 2005). The notes in the fourth (rightmost) column were provided by a reviewer of this literature review. Unless noted
otherwise, all the species in this table are likely to be unsuccessful unless the water with which they are irrigated is relatively
low in total dissolved solids.

VI­35

a

Table VI–12. “Classic” California native plants for scrubland landscapes.
Type of plant

Botanical nameCommon nameTree

Sambucus mexicana

Elderberry

Arctostaphylos bakeri “Louis Edmunds”

Louis Edmunds manzanita

Arctostaphylos glauca

Bigberry manzanita

Artemisia californica “Montara”

Montara California sagebrush

Ceanothus “Concha”

Concha ceanothus

Ceanothus leucodermis

Chaparral whitethorn ceanothus

Ceanothus “Sierra Blue”

Sierra blue ceanothus

Cercocarpus betuloides

Mountain mahogany

Dendromecon harfordii

Island bush poppy

Encelia californica

California sunflower

Encelia farinosa

Incienso

Eriogonum fasciculatum

California buckwheat

Eriogonum giganteumSaint Catherine’s lace

Heteromeles arbutifolia

Toyon

Isomeris arborea

Bladderpod

Mahonia (Berberis) nevinii

Nevin’s barberry

Rhus ovata

Sugar bush

Salvia apiana

White sage

Salvia clevelandii and cultivars

Cleveland sage

Salvia leucophylla

Purple sage

Salvia mellifera

Black sage

Yucca whipplei

Our Lord’s candle

Arctostaphylos hookeri

Hooker manzanita

Arctostaphylos edmundsii

Edmunds manzanita

Artemisia californica “Canyon Gray”

Prostrate California sagebrush

Eriogonum fasciculatum cultivars

Prostrate California buckwheat

Iva hayesiana

Hayes iva

Romneya coulteri

Matilija poppy

Salvia “Bee’s Bliss”

Bee’s bliss sage

Salvia “Dara’s Choice”

Dara’s choice sage

Salvia mellifera “Terra Seca”

Prostate black sage

Artemisia pycnocephala “David’s Choice”

David’s choice sandhill sage

Asclepias fascicularis

Narrow­leaf milkweed

Erigeron “Wayne Roderick”

Wayne Roderick’s daisy

Eriogonum crocatum

Sulphur buckwheat

Eriogonum grande var. rubescens

Red buckwheat

Leymus condensatus “Canyon Prince”

Canyon Prince wild ryegrass

Mimulus (Diplacus) species and cultivars

Shrubby monkeyflower

Zauschneria (Epilobium) species andcultivars

California fuschia

Calystegia macrostegia “Anacapa Pink”

Anacapa Pink morning glory

ShrubsGround covers

Notes

May tolerate moderately alkaline,
somewhat saline soil

Tolerates soil that’s moderately
alkaline and somewhat saline

May tolerate moderately alkaline,
somewhat saline soil

and bank plants

Perennials

VineaTolerates soil that’s moderately
alkaline and somewhat saline

The first three columns in this table were excerpted from the California Classics Plant Palette (Rancho Santa Ana Botanical
Garden, 2005). The notes in the fourth (rightmost) column were provided by a reviewer of this literature review.

VI­36

San Diego Chapter of the California Native Plant Society (www.cnpssd.org)
The website of the San Diego chapter of the California Native Plant Society includes anumber of brief documents that can be useful when designing a landscape. One, titled “Easy­to­Grow California Native Plants for San Diego County,” is a 16­page article that describes 20
species widely appreciated by gardeners. The native ranges and tips for cultivation are provided foreach species.
Also on the website is a reprint of a brief 1972 article from the San Diego Natural History
Museum, informatively titled “The Twelve Most Wanted Native Shrubs That Succeed in a Garden
without Your Really Trying.” The growth pattern, leaf color, watering needs, and type of flower
and fruit are described for each species. The 12 species described are Hooker’s manzanita(Arctostaphylos hookeri), quail brush (Atriplex lentiformus breweri), dwarf coyote bush
(Baccharis pilularis), Oregon grape, also known as holly grape (Berberis aquifolium), Carmel
creeper (Ceanothus griseus horizontalis), St. Catherine’s lace (Eriogonum giganteum), toyon,
also known as California holly (Heteromeles arbutifolia), hollyleaf cherry (Prunus ilicifolia),
lemonade berry (Rhus integrifolia), sugar bush (Rhus ovata), evergreen currant or Catalina
currant (Ribes viburnifolium), and chaparral yucca (Yucca whipplei).
Yet another useful document at this website is a single­page, three­part layout that relates
the water tolerances of certain native plants and includes a brief list of native plants that are goodsubstitutes for nonnatives, such as eucalyptus.

California Invasive Plant Council (www.cal­ipc.org)
The website of the California Invasive Plant Council provides a variety of information
about plants that are invading California. The subpage titled “Don’t Plant a Pest” (www.cal­
ipc.org/landscaping/dpp/index.php) provides a handy map that makes it easy to list invasive
species for any particular region of California and to list native species that are desirable
alternatives to the invasive ones.

VI.E Guides about Native Plant Communities
Numerous scientific papers, reports, and symposium proceedings have been published in
the past several decades as part of an attempt on the part of botanists, ecologists, andhorticulturists to agree on definitions and concepts related to plant habitats and communities. A
useful summary of some concepts and ideas regarding plant communities is provided in the book
Plant Communities of Southern California (Latting, 1976). It includes papers describing bothVI­37

modern­day plant communities and past (paleontological) plant communities of southern
California. Information is provided about the types of vegetation in the San Gabriel, Santa Ana,
San Jacinto, and San Bernardino mountains, as well as about the vegetation and plant communities
of southern California deserts.
A more recent contribution is the document “A Manual of California Vegetation”(California Native Plant Society, 2000). This document is more botanically inclined than mostlandscape designers need, but it is relevant for the landscape design process for any large park
project that includes native plant communities.

VI.F. Selecting Plants for Certain Types of Landscapes
A city park typically contains a variety of functional elements. It may include, forexample, trees and shrubs around its perimeter as visual screens to block the view of nearbybuildings. The park might also include meadow­like areas or playing fields covered in turfgrass.
And it might include smaller garden areas, each of which might have a particular design theme. A
site that is primarily a playing field, on the other hand, might be nearly all turfgrass, with few trees,
shrubs, or other ornamental design elements. Golf courses and highway medians have yet otherdesign requirements. The following sections provide a variety of notes that may be useful when
designing these types of landscapes and selecting appropriate species of plants.

VI.F.1. General Guidelines
Quite a few different books about landscape design are available. One book that is
appropriate and useful for both professionals and for part­time designers charged with designing or
redesigning a site is Landscape Design Guide, Volume 1: Soft Landscapes, by Adrian Lisney and
Ken Fieldhouse, 1990. In it, the authors outline the basic principles of designing with plants andprovide practical information about selecting and caring for plants. They emphasize that no twosites are identical and that conducting a thorough visual and physical survey is therefore essential
before beginning design work. To achieve the best results, the authors note, the designer draws
inspiration from the character of the site: existing trees and buildings, plus the open spaces between
those trees and buildings. They also note that principles such as unity and simplicity can help tocreate effective and practical solutions to the design equation and provide continuity throughout adesign scheme.

VI­38

Chapters 1 through 4 of the book provide a conceptual basis by describing the design
process and horticultural and ecological concepts, such as plant communities and climaticconditions. Chapters 5 through 16 provide the specifics of designing with plants, including theparticular advantages of trees, shrubs and hedges, climbers, ground cover, grasses, herbaceous
plants and bulbs, and woodlands.

VI.F.2. Selecting Plants for Golf Courses
Of greatest importance at golf courses is the turfgrass itself. Yet trees and shrubs make thecourse a beautiful or desirable place to play, so they, too, are critical to a well­designed, enjoyable
environment. A comprehensive, site­based plan is essential if the resulting links are to provide avariety of challenges to professional players and amateurs alike.

Trees
On nearly every golf course hole, trees help to define the course and provide a backdrop
against which a ball in flight is more easily seen. They also provide a valuable wind buffer and, on
hot days, much­welcomed shade.
Fream (2001) outlines many of the issues that must be explored and addressed to place
trees at a course properly and to ensure the trees remain healthy for many years. First, he notes
that, before a course is built, a number of decisions must be made regarding clearing of the site. He
points out that a more natural and harmonious design will result if the position, size, health, andappearance of existing trees are made part of the design process. He also says, “If you’re going tosave it, save it.” By that he means to take care to protect all trees from potential damage while thecourse is being built. Traffic within the drip line of a tree is to be avoided at all costs, he notes.
Regrading the soil within the drip line must also be avoided, as any such changes can, for many
species, cause a slow but sure death. Fream also describes the issues of fertilizing, watering, andthinning trees.
Coate (2004) also notes that trees are an important, but often overlooked, component of agolf course. He notes that trees and turf are usually incompatible, because the trees typically do
best with infrequent, deep irrigation, whereas turf performs best with frequent, relatively shallow
irrigation. He suggests resolving this dilemma by selecting and planting, where possible, species oftrees that tolerate the conditions inherent in the turf environment. Tupelo (Nyssa sylvatica), swamp
myrtle (Tristanopsis laurina), and bald cypress (Taxodium distichum) all can grow in areas withVI­39

consistent surface water nearby. Western sycamore (Platanus racemosa) also is well adapted tocreek side conditions or spring­fed sites.
Coate (2004) mentions a number of difficult planting environments for trees at golfcourses. One is the marine coastline, where salt spray often is potentially a problem. Landfills areanother, because the soil in such places often is overly compact and, in some cases, contains
methane gas. Coates includes a list of 81 species recommended for golf courses. Extensive data arepresented for each type of tree, including such parameters as the width of the canopy, preferences
regarding amount of sun and shade, requirements regarding drainage and irrigation, tolerance ofwind and heat, rate of growth, and expected useful life span.
Sharon Lilly, in her 1999 book Golf Course Tree Management, describes in some detail
how trees grow. Their growth process is a necessary topic of study, she says, in order to develop
sound judgment for choosing and maintaining trees. Lilly examines the same trees­versus­turf
dilemma pointed out by Coate (2004) but discusses it in greater detail, devoting an entire chapter toit. She notes that trees and turf tend to be mutually exclusive in nature. As she says, “For the mostpart, you won’t see many trees growing in the prairies or grasslands, and grass is not common on
the forest floor.” The problem is that a forest or stand of trees produces too much shade for grass
to grow, she explains. In open land, the roots of grasses dominate because they are more aggressive
than are the roots of trees; they colonize bare expanses of soil faster and establish a dense rootsystem more quickly.
Lilly (1999) describes a number of tree­turf interactions, including competition between
the roots of trees and the roots of grass for the same space just below the soil’s surface and for
infiltrating water. Another conflict, she notes, is exemplified by the many problems that can occur
when trees shade grass. A third form of interaction is the phenomenon called allelopathy: inhibitionof a plant’s growth by another plant that produces chemicals such as terpenes, phenols, organic
acids, tannins, steroids, or other compounds. Such chemicals may be leached from the roots into
the soil, or volatilized into the air, or exuded from other parts of plants. She points out that speciesof pine, plane tree, maple, hackberry, eucalyptus, and sumac have all been shown to be capable ofallelopathy.
Other issues involving trees on golf courses that Lilly (1999) examines include managing
the shade created by trees, controlling roots, fertilizing, controlling debris dropped by trees,
protecting turf when the trees are pruned, monitoring the health of plants, planning for andselecting trees, practicing irrigation and drainage, and protecting trees during construction.

Turf
VI­40

In his comprehensive, 643­page book Turf Management for Golf Courses, James B. Beardof Texas A & M University describes how to choose and plant turfgrasses and how to keep turf
healthy afterward (Beard, 1982). Chapters in which the turf­related aspects of the different parts ofa typical golf course are described are named, appropriately enough, “The Putting Green,” “TheTee,” “The Fairway,” “The Rough,” and “The Bunker.”
Beard notes that, for tees in such warm­climate regions as southern California,
bermudagrass (Cynodon dactylon) is most favored. He notes that Tifway and Tifgreen, twocultivars of bermudagrass, perform very well and that common seeded bermudagrass is also usedwidely with good results. In portions of southern California where air quality is less than pristine, aspecial smog­tolerant variety known as Santa Ana has proven effective, he adds.
For the fairways of golf courses in southern California, bermudagrass is preferred, thoughperennial ryegrass is sometimes used instead or in addition. Popular varieties of bermudagrass arecommon bermudagrass, Santa Ana, and Tifway. According to Beard, the putting greens of mostgolf courses situated along the Pacific coast consist of bentgrass (Agrostis spp.) rather than of
bermudagrass. For the roughs along the fairways, golf courses in southern California typically use
common bermudagrass (Cynodon dactylon), Kentucky bluegrass (Poa pratensis), or perennial
ryegrass (Lolium perenne).
Elsewhere in his book, Beard describes irrigation systems for turf. Yet another section of
his book covers typical turf pests, such as nematodes, weeds, viruses and other microbes, androdents.

VI.F.3. Selecting Plants for Playing Fields
As with golf courses, the primary park element in a playing field or school yard is the turf.
In this case, the turf is chosen for its durability and ease of drainage. Soccer fields and baseballfields both must withstand tremendous amounts of foot traffic and, therefore, must be covered withvery durable grass.
Trees, shrubs, ground covers, and ornamental plants at a playing field or school yard
provide the border landscaping or fringe buffer zones for the main playing areas. The types ofplants appropriate for this depend greatly on the microclimate and on the park designer’s theme orarchitectural concept.
Establishing and Maintaining the Natural Turf Athletic Field, a 56­page booklet by
Stephen Cockerham, Victor Gibeault, and Deborah Silva (2004), provides a variety of guidelines
for designing and maintaining athletic fields. They note that those athletic fields that are wellVI­41

designed, well constructed, and well maintained are most likely to provide optimal safety,
playability, aesthetics, and durability.
The authors explore different choices for root zone media. As they put it, “What’s under
the turfgrass is very important.” They note that the typical turf is underlain by a mixture of 80 to
100% of sand of various sizes, up to 8% silt, up to 2% clay, and soil amendments such as peat andweathered sawdust.
They also note that, besides looking good, turfgrasses for athletic fields must tolerate foottraffic, must recover from injury, and must provide high playability. Tolerance of sports traffic—
the scuffing, compaction, and tearing of grass by shoes, particularly cleated shoes—requires
turfgrasses that have considerable lignin and cellulose in the shoot and hardened or sclerified plant
cells, providing strength and rigidity. Such characteristics typically are found in perennial ryegrass,tall fescue, and bermudagrass. Tolerance of foot traffic and recovery from foot­traffic­related
damage are also higher in species of turfgrass that produce rhizomes, stolens, or tillers, or all three.
The authors note that Kentucky bluegrass has tillers and rhizomes; perennial ryegrass and tallfescue have tillers; kikuyugrass has tillers and stolens; and bermudagrass and zoysiagrass have all
three.
The method of planting and maintenance practices are important for all turfgrasses. The
authors provide a number of suggestions in these areas.

VI.F.4. Selecting Plants for Parks
Aside from turf, it is difficult to identify the primary plant typically used in a municipal
park in southern California. That difficulty arises because the purposes and designs of parks vary
so widely. Whether constructing a new park or upgrading an old one, perhaps the best guideline tobear in mind is that, ideally, the park’s design should exhibit unity and simplicity (Lisney and
Fieldhouse, 1988). Also, it is essential that any desired species of plants be checked thoroughly
against reference materials to ensure that they will survive in the expected microclimate(s) that willbe created by the project.

VI.F.5. Selecting Plants for Medians and Sides of StreetsVI­42

Street­tree programs for residential neighborhoods help to define the types of trees that are
beneficial along automotive rights of way. The ideal tree has a canopy shaped somewhat like an
inverted cone; the branches go outward as they go upward. The tree develops a tapered profile as it
matures, with most of its branchlets up high, not down low. The area near the base of the tree isrelatively clear, helping to ensure that the view along the street remains unobstructed (Grey, 1996).

VI.G. Using Guides Cited
In selecting plants for nearly any landscape, the best place to begin is one of Perry’s
books. The 1981 book is the simpler of the two, and the tables presented here will get you started.
The 1992 book is more comprehensive, though it may require a greater investment of time to be
used effectively.
The next step is to consult the Sunset Western Garden Book and any other guides thatseem relevant. If a landscape is intended to consist partially or totally of plants native to California,
refer in particular to the book by Labadie and to the one by Lenz and Dourley.
For a golf course, a playing field, or highway median, consult the references citedpreviously.
Copies of all aforementioned books are available in numerous libraries throughout
southern California. To find a library near you that has the book or books you are looking for, visit
www.worldcatlibraries.org on the Internet, click on “Try a Search,” and enter the book’s title,
author, or ISBN (tip: the Yahoo search function within Worldcat appears to work more reliably
than do the other search options).

VI.H. References
Beard, J. B. 1982. Turf Management for Golf Courses. Burgess Publishing Co., Minneapolis,
MN.
Bornstein, C., D. Fross, and B. O’Brien. 2005. California Native Plants for the Garden. Cachuma
Press, Los Olivos, CA.
California Native Plant Society. Recommended List for Landscaping with Native Plants in the
Santa Monica Mountains. Available online at www.lacnps.org/pubs.html (cited Aug 26, 2005).
Coate, B. D. 2005. Trees suitable for golf courses in northern California. Western Arborist 31:31–
39.
Cockerham, S. T., V. A. Gibeault, and D. B. Silva. 2004. Establishing and Maintaining the
Natural Turf Athletic Field. Agriculture and Natural Resources Communication Services,
University of California, Oakland, CA.

VI­43

Fream, R. W. Keep Trees On Course. Available online at
mag.com/mag/grounds_maintenance_keep_trees_course/ (cited Sep 2, 2005).

www.grounds­

Labadie, E. L. 1978. Native Plants for Use in the California Landscape. Sierra City Press, Sierra
City, CA.
Latting, J. (ed.). 1976. Plant Communities of Southern California. Symposium Proceedings.
California Native Plant Society, Berkeley, CA.
Lenz, L. W. 1956. Native Plants for California Gardens. Abbey Garden Press, Pasadena, CA.
Lenz, L. W., and J. Dourley. 1981. California Native Trees and Shrubs for Garden andEnvironmental Use in Southern California and Adjacent Areas. Rancho Santa Ana Botanical
Garden, Claremont, CA.
Lilly, S. 1999. Golf Course Tree Management. Ann Arbor Press, Chelsea, MI.
Lisney, A., and K. Fieldhouse. 1990. Landscape Design Guide, vol. 1. Soft Landscape. Gower
Publishing Co., Hants, England.
Perry, B. 1992. Landscape Plants for Western Regions. Land Design Publishing, Claremont, CA.
Perry, B. 1981. Trees and Shrubs for Dry California Landscapes. Land Design Publishing, San
Dimas, CA.
Rancho Santa Ana Botanic Garden. California Classics Plant Palette. Available online atwww.rsabg.org/content/view/120/112/ (cited Aug 26, 2005).
Sunset Books and Sunset Magazine Editors. 2001. Sunset Western Garden Book, 7th ed. Sunset
Publishing Corp., Menlo Park, CA.

VI­44

Chapter VII. Irrigation Systems for Recycled Water
D. Shaw, S. Grattan, and A. Harivandi

VII.A. Function of the Irrigation System
VII.B. Performance of the Irrigation System
VII.C. Major Phases of Successful Irrigation
VII.C.1. Design, Layout, and Staking
VII.C.2. Installation and Construction
VII.C.3. Operation
VII.C.4. Maintenance
VII.D. Types of Irrigation Systems for Distributing Recycled Water to Landscapes
VII.D.1. Rotor Sprinklers
VII.D.2. Fixed Spray Sprinklers
VII.D.3. Sprinkler Distribution Profiles and Matched PRs
VII.D.4. Drip Irrigation
VII.E. Components of Irrigation Systems
VII.E.1. Backflow Devices and Point of Connection
VII.E.2. Filters
VII.E.3. Pressure Regulators
VII.E.4. Quick Couplers and Hose Bibs
VII.E.5. Components of Recycled Water Systems
VII.E.6. Injection Systems
VII.F. Retrofit of Potable Systems to Recycled Water Systems
VII.F.1.Cross­Connection Testing
VII.G. References

This chapter summarizes literature relevant to the types of irrigation systems used to deliver
recycled water to turf and landscape plants. The literature consists of many trade magazine articles on
irrigation systems and their maintenance and use for distributing recycled water, as well as a few
irrigation manuals considered to be peer reviewed that were developed by the University of California(Shaw and Pittenger, 2005) and California Polytechnic State University–San Luis Obispo (Irrigation
Association, 2004). Information on irrigation systems is also available in manufacturers’ catalogs, whichcontain product specifications and describe intended uses for virtually any landscape application.
Publications on irrigation design, including books with theories and formulas used in the process ofdesigning an irrigation system as well as computer­aided design (CAD) programs, contain informationVII­1

used by landscape architects and irrigation designers to determine flow and precipitation rates (PRs), pipe
sizes, and equipment specifications in designing an irrigation system. Planning codes and regulations,which are developed and published by municipalities and water districts, set standards for the needed
equipment, design of irrigation systems, and specifications for installation. These regulations are relevant
to all irrigation systems, regardless of the type of water used. With the increase in use of recycled water,
the regulations have been expanded to include systems that use recycled water. The response frommanufacturers has included a full line of components for use specifically in irrigation systems to deliver
recycled water.
Recycled water purveyors, water­reuse organizations and associations, and the Irrigation
Association have also published guidelines about irrigation systems that deliver recycled water and about
retrofitting existing irrigation systems to deliver recycled water (American Water Works Association,
1997; Terry, 1994; and San Diego County Water Authority, 1999).
Articles in such trade magazines as Grounds Maintenance and various manufacturers’ data sheets
cover topics from the design of irrigation systems to their installation, operation, and maintenance. They
are intended for landscape designers, irrigators, and maintenance personnel (Vinchesi, 2000; andZupancic, 1999).
Peer­reviewed scientific literature pertinent to components of irrigation systems is limited.
However, there are a number of published papers regarding the use of subsurface drip systems, theuniformity of irrigation with various nozzles and sprinklers, and materials for valves and other hardware(Greene et al., 1994; and Suarez­Rey et al., 2000).
Clearly, there is a wide and varied array of information available on landscape irrigation systems
and hardware relevant to irrigation with recycled, as well as potable, water. This chapter will focus on
basic requirements for all irrigation systems, while expanding on needs and strategies for systems
delivering recycled water.
What is the function of an irrigation system?
• The irrigation system delivers water to the plants in a way suitable for
fostering the growth and performance of the landscape. The system shouldhave the capacity to meet the landscape’s peak water demands.
• The system should have the ability to apply enough water to leach salts
through the root zone.
• The system may also be used to control frost or to provide other culturalneeds.

VII­2

What is a hydrozone?
Plants and their irrigation systems are organized into areas known ashydrozones according to water­related factors, such as water need,
exposure to sun or shade, and salinity tolerance. Multiple valves andsystem control allow for different types of systems, such as spray anddrip, to be independently operated as part of a larger irrigation system toapply the correct amount of water to each hydrozone.

VII.A. Function of the Irrigation System
The irrigation systems used in almost all irrigated landscapes in California provide several
functions. The major function is to provide water to plants during spring, summer, and fall because little
to no rainfall occurs during these seasons. Irrigation systems also are used during the winter in dry years,
when rainfall is inadequate to meet landscape water demands.
As emphasized in Chapter VIII of this document, irrigation systems provide water to meet theevapotranspiration (ET) needs of plants, which is a major component contributing to the health andaesthetic value of turfgrass and the landscape. However, this objective becomes complex because
different species of plants have different water needs, different growth patterns, and different rooting
characteristics (Meyer and Camenga, 1985; Shaw and Pittenger, 2005; and Vinchesi, 2000). Moreover,planted areas can be irregular in size and shape due to property boundaries, buildings, and hardscape andmay have differences in slope, exposure to sun and shade, and exposure to wind. Usually, different
irrigation systems or separate valves are used to factor in and accommodate these differences. Hence,different irrigation systems are used for turfgrass and ground covers; for shrubs and trees; for areas withdifferent watering requirements in terms of timing, amount, or both; and for certain situations that warrant
their use, including irregularly shaped areas, median strips, and plants in containers. These areas where
the irrigation system must be matched to the particular plant materials, microclimate, or other specificneed are called hydrozones.
Since all irrigation water contains some salts, irrigation systems must have the capability for
applying enough water to effectively leach salts from the root zone. Recycled water usually contains from
140 to 400 parts per million (ppm) more salts than does potable water (Chapter III of this document), so
an irrigation system’s leaching ability becomes more important. Where drainage is limited, precise
management to leach salts while preventing water logging must be practiced.
A landscape’s irrigation system can also be used to fulfill the landscape’s cultural needs otherthan watering, such as providing frost control, cooling the landscape, and applying fertilizer.
VII­3

VII.B. Performance of the Irrigation System
An irrigation system’s performance is usually measured in terms of its irrigation efficiency, its
distribution uniformity (DU), its PR, and the integrity of its components (Shaw and Pittenger, 2005).
These criteria are used to evaluate each valve and associated distribution system within an overall
irrigation system. The most important considerations with regard to performance are the irrigation
efficiency and/or DU and the PR, which together with an assessment of the plant material involved,
provide the information necessary for irrigation scheduling.
A system’s irrigation efficiency equals the ratio of the amount of water used beneficially divided
by the total amount applied. This value is less than 100% because, in order to irrigate all plants
adequately, some plants are overwatered. In the overwatered areas, water is lost to runoff or deep
percolation or both. While the total water applied is determined easily from a water meter reading or
water bill, the beneficial use is often determined from an estimate of the landscape ET because runoff anddeep percolation are very difficult to measure. Irrigation efficiency can be assessed on an irrigation eventor a monthly or even yearly basis. It is not uncommon to have a significant range in values because
efficiency is a function of both equipment and management. Only through deficit or underirrigation canefficiency reach 100%.
DU is a measure of how evenly water is delivered to the landscape. This performance measure isrelated more to system hardware than to management. In the field, DU is easily assessed from datacollected in a catch can test. It is the average of measurements of water applied to the low quarter (25% of
the area receiving the least water) divided by the overall average. Systems with high DU are usuallyeasier to manage. With such a system, the irrigator can easily determine when to irrigate based on soil
moisture or the condition of plants. In other words, if all areas receive about the same amount of water,
there will be less variability in the landscape’s moisture level and health. Less variability speeds thedecision­making process for the irrigation manager. In addition, through improvements in uniformity
alone, water waste can be reduced and the quality of the landscape increased. Leaching salts delivered in
the recycled water is also much easier with high DU since a more uniform wetting front can be
maintained throughout the soil profile. High DU helps prevent drier areas of coverage from not receiving
their intended leaching fraction and becoming salinized as well as wetter areas from becoming saturated
and resulting in runoff or deep percolation.
Runoff can be caused by high rates of water application (PR), poor DU, broken components,
and/or mismanagement. The PR of an irrigation system is expressed in number of inches per hour and canrange from 0.1 to greater than 3.0. Lower rates are helpful in reducing runoff by matching the PR to thesoil infiltration rate. Alternatively, the cycling on and off of systems has been successful in allowing
adequate water penetration while reducing runoff. The elimination of runoff is mandated by mostVII­4

recycled water regulations and by water quality regulations in most localities (San Diego County Water
Authority, 1999).
The performance characteristics of the irrigation system are influenced by the design process andinstallation of the system. Often the PR and DU are specified in the landscape irrigation system design.
However, field verification of PR and DU is necessary to provide for accurate irrigation scheduling. The
performance of each valve and distribution system cannot be assumed to be similar without testing orverification in the field.
The performance of an irrigation system also depends on the integrity of the system’s
components. Components of poor quality, those installed incorrectly, and those inadequately protectedfrom breakage, vandalism, or other damage will ensure a poorly performing system. Repairs take timeand expense and can leave the landscape in need of water. A well­performing irrigation system is criticalfor aesthetically pleasing and functional landscapes. To achieve and maintain good performance,
irrigation systems need to be properly designed, installed, operated, and maintained.

VII.C. Major Phases of Successful Irrigation
For successful landscape irrigation, four major phases must be addressed and coordinated: thedesign, construction and installation, operation, and maintenance phases.

VII.C.1. Design, Layout, and Staking
The design phase of an irrigation system encompasses the conception and artistic application oflandscape components, the necessary engineering and planning, and the specification of materials. This
process includes selecting plants that are tolerant of the soil and water conditions at the site. It also
includes developing hydrozones and appropriate irrigation and drainage systems for the plants, as well as
specifying construction details, irrigation schedules, and maintenance requirements for the landscape. The
designer must also meet regulatory guidelines, including plumbing codes, local and state ordinances,permits, and any regulations required by the recycled water purveyor, and submit plans to be approved by
local regulators. The designer also determines the water budgets and irrigation schedules to use during thelandscape’s establishment and as the landscape matures.

VII.C.2. Installation and Construction
The installation and construction phase includes installing the irrigation system, as well as
coordinating with other construction operations, such as land grading, preparing the soil, and installing
hardscape, plants, lighting, signage, and other components of the landscape. Proper layout and staking of
the system are critical so similar sprinklers are installed at uniform spacing distances to maintain uniform
PRs and high DU and maximize potential irrigation efficiency within each hydrozone. Often substitutionsand variations from the design can occur during construction. The irrigation designer should approveVII­5

changes and substitutions related to the irrigation design to maintain optimum efficiency of the final
product. Plans that depict the landscape “as built,” including any changes in design, are of tremendous
value to operation and maintenance personnel.

VII.C.3. Operation
The operation phase of an irrigation system involves managing the landscape’s irrigation
scheduling and water budgeting. As mentioned in Chapter VIII of this document, this requirement varies
according to locations in the landscape and time of the year.

VII.C.4. MaintenanceDuring the maintenance phase, activities that maintain and maximize the effectiveness of theirrigation system are conducted. The proper cultural treatment of plants and other components of thelandscape not only improve the landscape’s appearance and value but can also affect the use of water inthe landscape. Maintenance personnel also play an important role by either sustaining the integrity of thesystem as designed by replacing failed sprinklers or nozzles with “like” equipment of the same PR or
making intelligent and sound modifications to the system as the landscape matures. Proper maintenancealso includes precise pruning, fertilization, and other cultural practices to promote the most efficient use
of water for the aesthetic need of the landscape.
Maintenance personnel may need to diagnose problems affecting system flow and pressure. In
general, if the entire system is affected, the point of connection and main filter and pressure regulator
should be checked. In areas undergoing new development, the purveyor’s water pressure and flow may be
reduced due to new service activity or other reasons. Pressure and flow will also drop if too many valves
are operated simultaneously or if modifications are made, such as adding sprinklers or increasing nozzle
size, that change the system’s hydraulics. If pressure losses occur in one valve station or along one lateralline, the valve may be faulty or there may be a broken or constricted pipe. Clogging of lines or individual
devices can also be caused by flow back into the system. For example, dirt or contaminants can enter pop­
up sprinkler nozzles placed below grade when the valve is turned off.
Strategic planning, coordination, and competency among all phases—design, installation,
operation, and maintenance—are important for sustaining the health and aesthetic appearance of turfgrass
and all landscape plants. For example, the landscape architect and irrigation designer—often one and thesame—must select trees and shrubs that are suitable to the site and purpose and then design an irrigation
system that will supply water to them without saturating their root crown areas. Sometimes a temporary
system is installed to keep root balls moist, while the plants are becoming established. The designer may
also specify a drainage system to handle excess water or storm water.
In the construction and installation phase, the contractor must achieve a functional landscapefrom the plans. This task includes following plans for selecting and installing pipes and otherVII­6components. It also includes properly locating selected plants and planting them at the proper depths. If
trees are planted too deeply, water will pond near the root crown and create conditions favorable to
Phytophthora species and other “water mold” fungi (Chapter X of this document). These diseases candevastate a landscape very rapidly. In addition, the plants cannot be placed where they will deflect theapplication of water, such as directly in front of a sprinkler. Hence, installing the irrigation system must
be well coordinated with installing plants.
The operator must follow and refine irrigation schedules that allow for adequate irrigation, while
avoiding runoff or oversaturation of the root crowns. Continuing with the aforementioned example, theoperator may overirrigate or underirrigate or may continue to use the temporary irrigation system
specified for wetting the root balls while the plants become established and consequently overirrigate theplant’s crown area. Either of these actions would also tend to result in diseases and a poorly performing
landscape.
The process of applying water to trees and shrubs demonstrates the amount of coordination andthe level of competency needed among the design, installation, operation, and maintenance phases oflandscape irrigation.

What constitutes a good irrigation system for distributing recycled water?
•

The system selected should be compatible with the landscape being irrigated.
It should be well designed and constructed and easily repaired andmaintained.

•

The irrigation system and its components are easily identified as conveying
recycled water.

•

The system must be completely independent of potable water systems. Most water
purveyors require separation of buried pipes and cross­connection testing to verify
the integrity of the recycled water system.

Table VII­1. Performance characteristics of sprinkler systems.
Radius of throwType
PR (in/h)(ft)

DU (%)

Geared rotor

20–1000.1–1.570–80

Impact rotor

30–1500.1–1.5

60–70

Fixed spray

3–15

1.0–2.5

40–80

VII­7

VII.D. Types of Irrigation Systems for Distributing Recycled Water toLandscapes
Irrigation systems for landscapes consist of sprinkler, drip, and bubbler systems (Irrigation
Association, 2004). Within the category of sprinkler systems, there are gear­driven or impact­driven rotor
sprinkler heads, which are commonly used for large areas of turf or ground cover, and fixed spray heads,
which are commonly used for irrigating shrubs, flower beds, and small or irregularly shaped areas.
Sprinklers can be individually valved or connected to a lateral line governed by one valve (Meyer and
Camenga, 1985; Rainbird Corporation, 2005; Smith et al., 1985; and Terry, 1994). The irrigation of golfcourses and other large areas of turf may involve the use of rotors, where a valve is integrated into large
rotor heads, i.e., a valve in head design (Balogh and Walker, 1992).
The PR of any irrigation system will depend on the spacing and flow rate of the sprinklers used.
Flow rate will depend on the size of the nozzle’s orifices and the water pressure (Irrigation Association,2004).

VII.D.1. Rotor Sprinklers
Geared rotor sprinklers usually have an arrangement of gears that moves water through one tothree nozzles in a predetermined arc. Impact rotors usually have one or two nozzles that rotate by theaction of a reciprocating spoon that interrupts the water stream (Irrigation Association, 2004).

VII.D.2. Fixed Spray Sprinklers
Fixed spray sprinklers usually have no moving parts. The water is directed through orifices in a
fixed pattern of spray over the irrigated area. However, some have adjustable arcs and adjustable flow
rates.

VII.D.3. Sprinkler Distribution Profiles and Matched PRs
The irrigation industry has made many improvements in sprinkler design to facilitate the uniform
distribution of water to the irrigated area. Most sprinkler manufacturers publish specifications, which
include water distribution profiles—graphically, the amount of water distributed versus distance from thenozzle—for different nozzle sizes and water pressures. This information is used during the design phaseto specify sprinkler spacing and operating pressure to achieve precise, uniform application of water to theirrigated area. This information is used to design systems with what are known as matched PRs. The
Center for Irrigation Technology at California State University–Fresno provides testing and data for many
available products.
Matched PR is the practice of matching the rate of sprinkler flow with the area or arc covered.
This objective can be achieved in two ways: sprinklers with different patterns or arcs (360°, 180°, or 90°
VII­8

or full, half, or quarter) should use differently sized nozzles (for differing gallons per minute [gpm]) tocompensate for the different size of area being covered if they are operated together on the same valve.
Alternatively, the same nozzles can be used in both full­circle and part­circle sprinklers if they are on
separate valves. In this case, the run time is adjusted; e.g., full circle heads are operated twice as long as
half­circle heads, etc., to achieve matched PRs and higher uniformity (Irrigation Association, 2004).
Fixed spray heads are also being produced with matched PRs (Rainbird Corporation, 2005),
which allow a more even distribution of water with heads with different arcs. Also, new technology, suchas small rotor heads that replace fixed spray nozzles, is available.

VII.D.4. Drip Irrigation
Drip systems, both aboveground drip systems and subsurface drip systems, are also used to
distribute recycled water. These systems distribute the water through many small orifices or emitters at
rates of 0.5 to 5.0 gal/h. They are commonly used to irrigate areas with trees and shrubs where it is notnecessary to wet the entire root zone of the plants. Filtration is more important in drip systems due to thesmallness of the emitters’ orifices. In addition, injection systems are commonly used with drip systems to
inject sanitizing agents, such as chlorine, or acids to eliminate emitter­clogging biotic growth andcarbonate deposits. Injection systems can also be used to apply fertilizer or other materials through theirrigation system.
Suarez­Rey et al. (2000) make a strong argument for specifying the use of subsurface drip
irrigation for areas of turfgrass, as well as for other areas of the landscape. Use of these systems avoids
exposing maintenance personnel to recycled water and enables irrigation at any time or day. Also, runoff
potential is reduced, and water does not contact the leaves of plants. This benefit would be particularly
important if plants are sensitive to foliar absorption of sodium or chloride. On the other hand, increased
maintenance is often necessary and subsurface turf irrigation designs can become complex, if not
impractical on sites with significant land contours and elevation changes. Subsurface turf irrigation is best
suited to relatively flat or uniformly sloped turf areas such as athletic fields and residential lawns.

VII­9Advantages and disadvantages of drip irrigation systems
Advantages

Disadvantages• Precise placement of water• Relatively more maintenance• Retention of foliage’s dryness• Difficulty of access to buried system• Fewer time­of­day restrictions• Limited access in thorny plants• Use of nearby water fountains• Compensation of pressure for topography• Attainability of high irrigation application efficiencies

VII.E. Components of Irrigation Systems
Irrigation systems vary tremendously, depending on the size and complexity of the landscapeirrigated, the type or types of systems used, the amount of sophistication in the systems’ design, and thenumber of control and monitoring options used (American Water Works Association, 1997; HunterIndustries, 2004; and Rainbird Corporation, 2005). For example, a simple system may require only abackflow prevention device, a controller, several valves, and a distribution system. A complex system
may be controlled by a computer; be capable of sensing and metering flow; incorporate sensors
monitoring soil moisture or other relevant aspects; and consist of rotor, spray, and drip distribution
systems. Depending on its complexity, an irrigation system may include backflow prevention devices,flow meters, pressure regulators, master and station valves, check valves, valve and equipment
enclosures, pipe and fittings, emission devices (sprinklers, emitters, etc.), quick couplers, pumps,
reservoirs, and flush­out valves. Control systems may vary in the degree of sophistication and cost andmay include sensing devices to determine flow rates or soil moisture, operate injection systems, or
operate backwash systems for filters. While irrigation systems for delivering recycled water contain manyof the same components as systems delivering potable water, the components of the system using
recycled water are usually colored purple or have signs, so that they are easily recognizable as conveying
recycled water (Chapter II).

VII.E.1. Backflow Devices and Point of Connection
Water purveyors require that irrigation systems have backflow devices to prevent water fromreturning to and possibly contaminating their distribution system. While most potable water purveyors
require a reduced pressure backflow device at the point of connection with the purveyor’s system,
recycled water purveyors usually only require a check valve or one­way gate valve to prevent backflow.
If a lake or water feature is used to store recycled water, the delivery should have an air gap to prevent
backflow.

VII­10In addition to the backflow prevention device, a meter, filter, booster pump and/or pressure
regulator may be present at the point of connection.

How to Eliminate Runoff from Landscape Irrigation
Design and use an irrigation system with a PR that is lower than or equal tothe infiltration rate of the soil.
Operate the irrigation system in cycles or “cycle and soak” periods tomaximize water penetration into the soil.
Use antisiphon valves and check valves within an irrigation system toeliminate low head drainage caused by the landscape’s changes in elevation.
Immediately repair leaks and broken components. Flow sensors and control
systems can readily identify lines with excessive flow due to broken
components and shut the valve off. Inline components are available that
restrict or close orifices with excessive flow.
Provide cultural needs to maximize water distribution to the landscape, suchas minor grading, aeration of turf areas, application of mulch, and/or
application of wetting agents or gypsum.

VII.E.2. Filters
To maintain the integrity of irrigation systems, filters are used to trap particulates, algae, andother contaminants from entering the systems (Chapter III). Contaminants can lodge in pipes and fittingsand valves and emission devices and restrict water flow. If flow is reduced, the system will not perform
up to its design potential. If flow is changed significantly, the engineered hydraulics of the system will becompromised, resulting in nonuniform distribution of water. In severe cases, the landscape will receive
inadequate water or the affected lines and devices, such as drip emitters, may be permanently damaged.
Generally, if water is properly filtered, clogging of valves, screens, and emission devices is minimized.
The filters to use depend on the quality of the recycled water, the amount used, the type of
irrigation system used, and cost (Smith et al., 1985). For large systems, sand or medium filters are used.
Often, an automatic reverse flushing system is used with media filters, especially if the recycled watercontains high suspended solids. The flushing system may be actuated by a timer or by pressure sensors.
Screen or disk filters are useful in systems where the water quality is relatively good and less cleaning isnecessary. The degree of filtration necessary depends on the size of the orifices in the system’s
components. For example, a drip system will require a finer filtration than does a typical sprinkler system.
The filter selected should be properly matched to the system’s components for both the system’s flow andthe size of particles involved. Finer filtration may seem advantageous, but if the filter is too small or
filtration too fine, frequent cleaning may be necessary. For systems with different types of distributionVII­11systems, one filter may be used for the mainline service and additional filters used for drip or
microirrigation systems. These filters are finer and may be inline or Y­type screen filters.
Filter maintenance is important to sustain the integrity and performance of the irrigation system.
Although self­cleaning filter systems are also available, maintenance personnel need to know where thefiltration devices are and when they need to be cleaned. Mainline filters and inline screen filters may bequite obvious. However, most backflow prevention devices, pressure regulators, and sprinkler heads all
contain a screen or basket type of filter. In addition, it is not uncommon to find screened washers or
gaskets placed inline or at hose connections. A system flow sensor or pressure gauges placed before andafter the filter will show reduced flow or significant pressure drop through the filter, indicating thatcleaning is necessary.

VII.E.3. Pressure Regulators
Pressure regulators are used to adjust the water pressure at the point of connection to the levelspecified during the design phase. While excessive pressure can cause components of the system to burst
and destroy rubber and plastic parts, low pressure can cause reduced flow and uneven distribution ofwater along lateral lines. The most common signs of excessive pressure are the overatomization of water
droplets, excessive drift, and loss of the sprinkler distribution profile. The irrigation designer determines
the pressure and flow needed at each sprinkler head, determines the pipe size required by calculating thefriction loss in the pipe, and accounts for differences in pressure caused by changes in topographicalelevation.
There are several types of pressure regulators: positive shutoff; regulating valves; inline
regulators; and diaphragms or flow constrictors within the sprinkler, emitter, or other emission device.
Positive shutoff regulators are usually adjustable and maintain the set pressure regardless of the flow rate.
These can be located at the point of connection to district lines and may be integrated with a backflow
prevention device. In general, these regulators are positioned before valve manifolds. Regulating valves
that incorporate an adjustable pressure regulation device within the valve are available from most major
irrigation manufacturers.
Inline regulators are usually inexpensive and preset for desired pressure within a range of flow,e.g., 20 lbs./sq. in. (psi) at 1 to 5 gpm. These are often used in drip systems or in lateral lines where
topography is a concern or at individual sprinkler heads to reduce lateral pressures to the sprinkler andprevent atomization. Manufacturers have incorporated nozzle screens or flow constrictors within sprinkler
heads that adjust the pressure within sprinklers. Pressure­compensating drip emitters contain a flexible
diaphragm to maintain the same flow over a range of pressures.
There are many different valves available for virtually any application in irrigation systems. They
include ball valves and gate valves for manually closing flow and solenoid valves for automaticallycontrolled systems. Most designers will specify “dirty water” or “contamination­proof” valves forVII­12

irrigation with recycled water. These valves have self­cleaning screens (internal “scrubbers” that clean
screens inside the valves), scouring systems that operate when the water is flowing to keep particulates
from accumulating, or filtered pilot flow, i.e., flow that actuates the diaphragm.

VII.E.4. Quick Couplers and Hose Bibs
Quick couplers allow fast connection of a hose line to the recycled water lines to facilitate
syringing of dry areas in the landscape. Quick couplers specifically designed for use with recycled water
systems are now available. These devices do not allow connection between potable and recycled systems.

VII.E.5. Components of Recycled Water Systems
Irrigation manufacturers have incorporated various materials into diaphragms, seals, and otherflexible components of valves and sprinklers used for recycled water in order to prolong the life of thesecomponents. These improvements have helped to address the effects of scaling and corrosion fromsalinity, pH, chlorine, and other constituents present in recycled water. Valve diaphragms can be fabricreinforced and made of more resistant rubber. The industry standard for rubber used in seals and valves
has been Buna­N rubber. It is being replaced by ethyelene propylene diene monomer, because of its
resistance to corrosion and chlorine and chloramine (a by­product that forms in recycled water whenchlorine and ammonia combine). Manufacturers are also experimenting with polyester materials suitable
for recycled water.

VII.E.6.Injection Systems
Injection systems are used to inject fertilizers, wetting agents, acids, gypsum, sanitizing agents,and other materials into and through an irrigation system (Schwankl and Prichard, 2001; and Burt et al.,1998). Injection equipment, materials, and best management practices are addressed in Chemigation in
Tree and Vine Micro­Irrigation Systems (Schwankl and Prichard, 2001) and Fertigation (Burt et al.,1998) and are applicable to systems delivering recycled water to landscapes. Schwankl and Prichard
discuss batch tank systems, venture injection systems, and positive displacement pump systems and theirrelative cost. Schematics are provided for incorporating an injection system into the irrigation system,
including the proper placement of valves, check valves, and filter screens for the various systems.
In addition, best management practices are suggested to achieve a uniform distribution of theinjected material. With proper design, installation, and management, a microirrigation system can apply
water very uniformly throughout a hydrozone. Application of chemicals through the irrigation system canalso be very uniform if an appropriate injector is selected, the correct amount of material is injected, andthe material is injected for the correct length of time. If the injection time is too short, orifices nearest the
injection point receive the most injected material. Injection practices must also be compatible withirrigation scheduling in order to keep the injected material, e.g., fertilizer, from running off or percolatingVII­13

below the root zone. Best management practices involve determining the length of time required for the
injected material to travel to the emitter farthest away hydraulically from the injection point. Once thesystem is fully pressurized, inject the chemical over a period at least as long as the travel time. Once
injection is stopped, continue running the system for a period at least as long as the travel time to thefurthest emitter. Schwankl and Prichard also discuss selection of materials and use of chlorine forsanitizing drip or microirrigation systems.

VII.F. Retrofit of Potable Systems to Recycled Water Systems
Retrofitting an existing irrigation system for use with recycled water involves assessing the site,
the condition of the landscape, and the condition of the irrigation system. Components of the system areevaluated for wear and effectiveness at providing water to the landscape without significant runoff.
Potential cross­connections, any water supply or existing pipelines nearby, the locations of hose bibs andquick couplers, and the locations of water fountains or other features that should not be in contact withrecycled water all need to be identified. Components of the irrigation system need to be visibly
distinguishable as parts of a system that delivers recycled water. This goal can be achieved by purchasing
new components, e.g., sprinklers, etc., by installing purple recycled water caps or tags onto existing
equipment, or by painting components.

VII.F.1. Cross­Connection TestingOnce the recycled irrigation system is installed or a system is retrofitted to use recycled water, across­connection test is performed to verify the independence of recycled and potable water systems.
These tests, usually performed by the health department or the water purveyor, involve shutting off eachsystem while the other is charged. Pressure or flow recorders are connected to the system mainlines todetermine if there are any connections between the two. This requirement is especially important inretrofitted systems, where numerous modifications to the system may have occurred over time. Also,
during the cross­connection testing, the recycled water system is inspected for leaks, overspray tononlandscape areas, and contact with drinking fountains or other potable water components.

VII­14

VII.G. References
American Water Works Association. 1997. Guidelines for the On­Site Retrofit of Facilities Using
Disinfected Tertiary Recycled Water. American Water Works Association.
Balogh, J. C., and W. J. Walker (ed.). 1992. Golf Course Management and Construction: Environmental
Issues. Lewis Publishers.
Burt, C., K. O’Connor, and T. Ruehr. 1998. Fertigation. California State Polytechnic University, San
Luis Obispo.
Greene, A. K., P. J. Vergano, B. K. Few, and J. C. Serafini. 1994. Effect of ozonated water sanitization on
gasket materials used in fluid food processing. J. Food Eng. 21:439–446.
Hunter Industries. 2004. Hunter Industries 2004–2005 Product Catalog. Hunter Industries, San Marcos,
CA.
Irrigation Association. 2004. Certified Landscape Irrigation Auditor Training Manual. Irrigation
Association, Falls Church, VA.
Meyer, J. L., and B. C. Camenga. 1985. In V. A. Gibeault and S. T. Cockerham (ed.), Irrigation Systems
for Water Conservation in Turfgrass Water Conservation. Division of Agriculture and Natural Resources
publication 21405. University of California.
Rainbird Corporation. 2005. Rainbird Landscape Irrigation Products 2005–2006 Catalog. Rainbird
Corp., Glendora, CA.
San Diego County Water Authority. 1999. Recycled Water Site Supervisor Training Manual. San Diego
County Water Authority, San Diego, CA.
Schwankl, L., and T. Prichard. 2001. Chemigation in Tree and Vine Micro­Irrigation Systems. Division ofAgriculture and Natural Resources publication 21599. University of California.
Shaw, D. A., and D. R. Pittenger. 2005. Landscape irrigation system evaluation and management.
University of California Cooperative Extension, San Diego.
Smith, R. G., J. L. Meyer, G. L. Dickey, and B. R. Hanson. 1985. Irrigation system design. In G. S.
Pettygrove and T. Asano (ed.), Irrigation with Reclaimed Municipal Wastewater—a Guidance Manual.
Lewis Publishers.
Suarez­Rey, E., C. Y. Choi, P. M. Waller, and D. M. Kopec. 2000. Comparison of subsurface drip andsprinkler irrigation for Bermuda grass turf in Arizona. Trans. ASAE 43:631–640.
Terry, A. 1994. Design of Delivery Systems for Wastewater Irrigation in Wastewater Reuse for Golf
Course Irrigation. Lewis Publishers.
Vinchesi, B. E. 2000. Irrigation 101. Grounds Maintenance 35:2.
Zupancic, J. 1999. Reclaimed water: challenges of irrigation use. Grounds Maintenance 34:3.

VII­15

Chapter VIII. Estimating Water Needs and Scheduling Irrigation forLandscapes
S. Grattan, D. Shaw, B. Sheikh, and A. Harivandi

VIII.A. Estimating the Water Needs of Plants
VIII.A.1. Evaporation and Transpiration
VIII.A.2. Determining ET
VIII.A.3. ETo and CIMIS
VIII.A.4. Kc
VIII.A.5. Modeling Coefficients for Landscape Plants after Kc
VIII.A.6. Coefficients for Turfgrasses
VIII.A.7. Coefficients for Other Types of Landscape Plants
VIII.B. Scheduling Irrigation
VIII. B.1. Duration of Irrigation
VIII.B.2. Frequency of Irrigation
VIII.B.3. Using the Flexible Method
VIII.B.4. Using the Calendar Method
VIII.B.5. Using Soil Moisture Sensors
VIII.B.6. Components of Efficient Irrigation Scheduling Programs
VIII.C. Conserving Water by Irrigating with Recycled Water
VIII.D. References
Proper irrigation management ensures that plants in landscapes receive adequate waterto grow well and sustain aesthetic appeal. This task involves applying the correct amount ofwater at the right time as efficiently as possible. The focus of this chapter is on determining thewater needs of plants in landscapes and scheduling their irrigation. Refer to Chapter VII for
information regarding how to irrigate efficiently and uniformly with various types of irrigation
systems.
Most methods developed over the past several decades for estimating the water needsof plants in California’s landscapes are modeled after those used for estimating the water needsof agricultural crops, which is where most of the research has been conducted. These methods
estimate the water need of a crop by using historical water use records or by using atmosphericdata, such as statistics for humidity, solar radiation, temperature, and wind speed.

VIII­1

It should be noted that the goal in irrigating landscape plants differs from the goal in
irrigating crops. In landscapes, the goal is to maximize the intended utility or, by implication,
usually to sustain healthy, attractive plants and sometimes also to control erosion or fire
hazards. In agriculture, the goal is to optimize profitability or, by implication, to maximize thecrops’ growth and yield. Regardless of these differing goals, it is important to accurately
estimate the amount of water needed by plants in a landscape to improve the landscape’s
quality while at the same time conserving water and ultimately reducing costs (Costello et al.,2000).

V.III.A. Estimating the Water Needs of Plants
Considerable research has been conducted over the past century regarding how toestimate the amount of water needed by agricultural crops. In the most widely accepted method
to date, which is described by Allen and others in a paper prepared for the UN Food andAgriculture Organization (1998), the water needs of crops are referred to as crop
evapotranspiration (ETc). This concept includes both evaporation, the physical process bywhich water vaporizes from the soil at the surface, and transpiration, the movement of waterfrom inside the crop’s leaf to the atmosphere.
Though water is likewise transpired by landscape plants and evaporated from the soil inwhich they grow, adopting this method to estimate the water needs of landscape plants involves
taking into account the wider range of variables in landscapes, such as types of plants, groundcovers, mulches, shading, and structures.

VIII.A.1. Evaporation and Transpiration
Most evaporation from the soil occurs in its top 6 in. When the surface of the soil dries
out, the rate of evaporation diminishes rapidly, even though the soil beneath the surface remains
moist. Water evaporates more rapidly from wet, fine­textured, or compact soils than it doesfrom wet, coarse­textured, sandy, or loose soil. Bark and other mulches applied to the soil
surface reduce evaporation.
Transpiration in a plant is important for cooling it and for transporting nutrients fromthe soil (American Society of Plant Biologists, 2005). Over 99% of the water absorbed by theroots of most mature plants is transpired to the atmosphere. Most of this water is transpired
through the plant’s stomata, pores with openings controlled by guard cells, all located on thesurface of the plant’s leaves. When guard cells expand with water, the stomatal pores open andwater is transpired. At the same time, the carbon dioxide needed for photosynthesis enters.

VIII­2

When the guard cells contract, the stomatal pores close, reducing transpiration and conserving
water within the plant.
The shape, location, density, and opening and closing of stomata vary according to
species. Most species open their stomata during the day and close them at night. This process
allows the plant to cool and carbon dioxide to enter the leaf for photosynthesis. If the plants
undergo stress, such as when the soil becomes completely dry, some plants will close theirstomata in the middle of the afternoon as a means of conserving water. Others, such as many
succulent species in the family Crassulaceae, close their stomata during the day and open themat night. Their special type of sugar metabolism allows carbon dioxide to enter the leaf at nightand be fixed into an organic acid—a feature that makes these types of plants more water
efficient.

VIII.A.2. Determining ET
The processes of evaporation and transpiration combine to become evapotranspiration(ET), a term synonymous with the water use of plants.
In agricultural water management, an ETc is measured indirectly by using a reference
grass. In this method, ETc is related to the use of water by a healthy, unstressed cool­season
grass uniformly cut to a height of 4 to 6 in. (Allen et al., 1998). The use of water by thisunstressed reference grass is referred to as reference evapotranspiration (ETo). As the reference
grass’s ET increases, so in direct proportion does the crop’s consumptive use. ETc can becalculated as

ETc = ETo * Kc

(VIII­1)

where Kc is defined as the crop coefficient(s), a factor that simply adjusts the ETo to ETc andvaries according to the type and maturity of the plant, the extent to which the plant covers thesoil at the surface, and water management.
A plant’s use of water is affected by the amount of sunlight, the temperature andhumidity of the air, and the speed of the wind (Doorenbos and Pruitt, 1984). Increases in theamount of sunlight, the temperature, and wind speed raise the ET. An increase in humidity
reduces the ET.
Four primary factors contribute to differences in the ET of a crop and the ET of areference grass (Allen et al., 1998). One is the height and roughness of the canopy, which

VIII­3

influences the amount of aerodynamic resistance. Taller, rougher canopies lose more water
under the same conditions than do shorter, smoother canopies. A second factor is the reflective
power of the surfaces of the crop and the soil at the surface. The higher the reflective power, theless the total energy enters the crop and soil and thus the lower the ET. A third factor is theresistance of canopies, which depends on the architecture of the plants and leaves, the densityof leaves and stomata, and the opening and closing of stomata. A fourth factor is the extent towhich evaporation from the soil at the surface contributes to the overall ET. Dry surfaces andthose heavily shaded by taller nearby plants or buildings lose considerably less water thansurfaces that are exposed to the sun and frequently wetted. All four of these factors integrate
and are reflected in the resulting Kc.
The Kc implies that the crop in question is nonstressed—adequately watered, free frompests and diseases, etc.—and this factor usually varies between 0.3 and 1.2, depending on thetype of crop, the architecture of the canopy, and the extent to which it covers the ground, thelocation, and management practices (Allen et al., 1998).

VIII.A.3. ETo and CIMISOver the years, several formulas for estimating ETo have been developed (Doorenbos
and Pruitt, 1984). Some more effectively predicted the ETo along coastal environments. Others
were better suited for predicting the ETo of hotter, drier inland areas. The Penman–Monteith
formula has recently been recommended as the standard method for defining and calculating
ETo (Allen et al. 1998). This formula has proved to be reasonably accurate at estimating ETo ina variety of climates throughout the world. The method requires the use of real­time data
including solar radiation, temperature, humidity, and speed of the wind. To learn more about
this method and the parameters used with this method, refer to the paper of Allen et al. (1998)
or visit www.fao.org/docrep/X0490E/X0490E00.htm on the Internet.
California has developed a statewide, computer­based network of weather stations thatgenerates daily ET values. Known as the California Irrigation Management Information System(CIMIS), this statewide network of nearly 120 weather stations provides daily and hourly
estimates of ETo. The weather stations collect data on the key meteorological parameters used
to calculate ETo, which include the amount of solar radiation, the temperature, the humidity,
and the speed of the wind, as well as data regarding rainfall. These ETo values are referred to as“real­time” ETo estimates and differ from those where historical averages are provided. These
weather stations (refer to photograph VIII­1) were developed by the University of California
under a grant from the California State Department of Water Resources and are now owned,

VIII­4

Photo VIII­1. A typical CIMIS weather station used to collect and transmit meteorological data used to calculate
ETo.

operated, and maintained by the Department of Water Resources. These computer­based
weather stations estimate ETo by using the modified Penman method, a method that differs
slightly from the Penman–Monteith formula. CIMIS weather stations and their ETo estimatesprovide irrigation managers, growers, and irrigation districts with valuable information for real­time irrigation scheduling. This information is available at the CIMIS website atwwwcimis.water.ca.gov/cimis/welcome.jsp.
The ETo estimates of the CIMIS, usually reported as a depth of water per unit of time,such as inches per month or millimeters per day, can vary dramatically over time and atdifferent locations. In a given year, particular variation occurs during the spring and fallmonths, when the weather changes dramatically from day to day. Such variation is shown in
Figure VIII­1, which illustrates real­time ETo values in two California locations: Davis, which
is located inland in the Sacramento valley, and San Luis Obispo, which is located in the south­
central part of the state along the coast.

VIII­5

DavisSan Luis Obispo­1

Penman­Monteith ETo (mm day )

12
10
8
6
4
2

Figure VIII­1. Variations of real­time ETo values in two different locations in California.

Historical values are used instead of real­time estimates to adjust for the high variationthat occurs during transition months in a particular year. When this adjustment is done for thesame locations, it can easily be seen that the maximal use of water occurs in both locations
between May and September, when the days are long and the amount of solar radiation isgreatest (Figure VIII­2). During the summer months, the ETo in the inland areas is substantiallyhigher than the ETo in cooler, more humid coastal areas. In the winter months, the reverse istrue, with the ETo in inland areas less than the ETo of coastal areas, since the inland areas
receive more fog and less sun than do the coastal areas.
The historical ETo values are particularly useful for planning the allocation of water,
for designing an irrigation system, and for estimating the water needed by a plant, using
generalized irrigation schedules. Though the water needed by a plant can be estimated withreasonable accuracy by using historical ETo data, it is important to recognize that these figures
are averages for 30 and 40 years and that actual daily data can vary significantly from a 30­ or
40­year average (Shaw and Pittenger, 2005). For example, a historical ETo value for a day in

VIII­626­Dec26­Nov

27­Oct27­Sep

28­Aug29­Jul29­Jun30­May30­Apr

31­Mar1­Mar

31­Jan1­Jan0DavisSan Luis Obispo

8
7

5
4

ET

o

(mm d

­1

)

6

3
2

27­Dec27­Nov

28­Oct28­Sep

29­Aug30­Jul30­Jun31­May

1­May

1­Apr

2­Mar

31­Jan

0

1­Jan

1

Figure VIII­2. Historical average ETo values in two different locations in California.

February in Oceanside is 0.09 in., but the actual ETo was 0.04 in. on February 14, 1992, andsoared fivefold to 0.20 in. on February 23, 1992. In such instances, the “real­time” ETo fromCIMIS weather stations would provide a much more accurate estimate for operating anirrigation system than would the use of historical ETo values.

VIII.A.4. Kc
In agriculture, Kc have been developed for a number of crops (Allen et al., 1998). They
were developed to estimate the water needed by a crop when the crop is not subjected to stress.
Kc are usually presented in relation to the time of the year rather than as a stage ofdevelopmental growth, even though the latter system provides less error (Grattan et al., 1998).
They have been developed for annual crops, as well as for perennial crops (Figure VIII­3). The
Kc for annual crops and deciduous orchards earlier in the growing season, when the crop covers
less than 20% of the soil at the surface, depends on management practices, such as how often
the soil is wetted. This finding occurs because most of the ETc comes from evaporation fromthe soil. Generally, the Kc is low during the early season, unless the soil is frequently wetted.
Later, when the crop covers more than 70% of the soil at the surface, most of the ETc is due totranspiration and the type of crop determines the Kc. Unlike for annual and deciduous crops, the
VIII­7

Kc of evergreen species is relatively constant over the year. For a complete list of the Kc fornumerous agricultural crops, as well as methods for adjusting the Kc to account for off­season
values, irrigation frequency, and plants grown in suboptimal conditions, refer to Allen et al.
(1998).

VIII.A.5. Modeling Coefficients for Landscape Plants after Kc
A plant’s overall architecture, size, and location in the landscape, as well as the climate,
are the primary factors that affect ET. For example, when grown under the same conditions,
bluegrass uses more water than does juniper or ivy. More water would have to be applied tobluegrass and juniper growing in the desert region of Palm Springs than to the same plants
growing on the coast in Long Beach due to the higher ETo of the hotter, drier Palm Springs
climate (refer to Figure VIII­1).
The amount of water needed by a plant varies according to species and its location in
the landscape. Most plants for landscapes, such as turfgrass, ground covers, shrubs, and trees,
need less water than does the standard reference grass ETo (Shaw and Pittenger, 2005). For
example, since actively growing bermudagrass (Cynodon dactylon) needs about 60% of thewater estimated as ETo, if information from a CIMIS weather station indicates that the ETo for a
day was 0.20 in., then bermudagrass would need 0.12 in. of water a day.
As previously noted, Kc for agricultural crops were developed to estimate the water neededby a crop when the crop is not subjected to stress. Coefficients for landscapes may not need tobe this stringent. It is perfectly acceptable, if not encouraged in many instances, to induce
stress, particularly with drought­tolerant plants, as a way to control excessive vegetative
growth, thereby minimizing the need for maintenance (Costello et al., 2000). The extent towhich this practice can be done without fatal consequences to the plant remains unclear. Whenirrigating with recycled water, which may be somewhat more saline than potable water, andparticularly when other conditions facilitate the accumulation of salts in the root zone, suchstrategies may be unwise and caution is advised.

VIII.A.6. Coefficients for Turfgrasses
Since lawns, sports fields, golf courses, and other such places with turfgrass consist
mostly of turfgrass and since the ET of turfgrass closely reflects the ETo of the reference grass(Shaw and Pittenger, 2005), the use of water by such landscapes can be more confidently
estimated than can the use of water in more heterogeneous types of landscapes. Turfgrasscoefficients have

VIII­8a

Table VIII­1. Kc for cool­season and warm­season turfgrasses in California (from Shaw and Zellman, 2005).
Cool­season cropbcoefficientWarm­season crop coefficient

January

0.61

0.55

February

0.64

0.54

March

0.75

0.76

April

1.04

0.72

May

0.95

0.79

June

0.88

0.68

July

0.94

0.71

August0.86

0.71

September

0.74

0.62

October

0.75

0.54

November

0.69

0.58

December

0.6

0.55

0.8

0.6

Month

Annual avg.
aSee Meyer et al. (1985).

bSpecies include tall fescue, ryegrass, bentgrass, and Kentucky bluegrass.

ccSpecies include bermudagrass, zoysiagrass, and St. Augustine grass.

.been developed to estimate the water needed by common speciesof turfgrass to perform

optimally (Table VIII­1). Though annual Kc averages are commonly used to schedule irrigation,
it is important that monthly values generate irrigation schedules that more precisely match theneeds of turfgrass (Shaw and Pittenger, 2005).

VIII.A.7. Coefficients for Other Types of Landscape Plants
Arriving at the coefficients for other types of plants for landscapes is not as simple asarriving at coefficients for turfgrass. Research­based data regarding the water needed by plants
in landscapes with a heterogeneous variety are limited. Hundreds of species with differingneeds for water exist, and those needs are influenced by their location in the landscape and theirinteraction with the surrounding environment. This complexity severely limits the ability toaccurately estimate water needs by using the ETo­Kc approach. Estimating the water needed by
species in a heterogeneous landscape is even more difficult (Costello et al., 2000; and Shaw and
Zellman, 2005).
Despite these limitations, several approaches for estimating water needed by a landscapehave been proposed. One popular method, the Water Use Classification of Landscape Species(WUCOLS), introduces a landscape coefficient adjusted with the use of inputs that take into
account differences in microclimates, densities, and species (Costello et al., 2000; or visit

VIII­9

Evergreen

Almond Orchard

Grain Corn

Bare Soil

1.20

Crop Coefficient (Kc)

1.00

0.80

0.60

0.40

0.20

27­Dec27­Nov

28­Oct28­Sep

29­Aug30­Jul30­Jun31­May

1­May

1­Apr

2­Mar

31­Jan

1­Jan

0.00

Figure VIII­3. Typical Kc and their variation over the year for four different types of crops (courtesy of R. L.
Snyder, UC–Davis).

www.owue.water.ca.gov/docs/wucols00.pdf). In this approach, the landscape coefficient, KL, isused rather than Kc, and KL is calculated as

KL = Ks * Kd * Kmc(VIII­2)

where Ks is a species coefficient, Kd is the plant density coefficient, and Kmc is a coefficient that
accounts for the microclimate. Refer to Costello et al. (2000) for detailed information about thewater needed by various plants within landscapes and the qualitative approaches for adjusting
estimates to take into account the mixtures of types of plants, the density of plants, and othersite­specific conditions. Though this method takes into account factors that affect the KL, eachindividual coefficient adds an additional level of uncertainty, resulting in an uncertain KL. Thismethod produces rough, initial estimates of ET that will probably need to be adjusted after firstestimates are used.
A simple and somewhat qualitative approach in adjusting the Kc may be suitable to take
into account differences related to aspect, shade, microclimate, densities of plants, stress, and

VIII­10

Table VIII­2. Initial Kc values or irrigation amount required (as percent ETo) for selected landscape groundacovers and shrubs to provide acceptable landscape performance after establishment.
Scientific nameCommon name
Initial Kc
Arbutus unedo“Compacta”

Compact strawberry tree

18–36

Arctostaphylos uva­ursi“Pacific mist”

Bearberry

18–36

Artemisia “Powis Castle”

Wormwood

0–36

Baccharis pilularis “Twinpeaks”

Twin Peaks coyote bush20

Calliandra
haematocephala

Pink powder puff

18–36

Cassia artemisioides

Feathery cassia

0–36

Cistus x purpureus

Orchid spot rock rose

0–36

Correa alba “Ivory Bells”

White Australian correa

18–36

Drosanthemum hispidum

Pink iceplant

20

Echium fastuosum

Pride of Madeira

0–36

Escallonia x exoniensis“Fradessii”

Frades escallonia

18–36

Galvezia speciosa

Bush snapdragon

0–36

Gazania rigens var.
leucolaena“Yellow Cascade” trailing gazania

50–80

Grevillea “Noelii”

Noel grevillea

0–36

Hedera helix“Needlepoint”

Needlepoint English ivy

20–30

Heteromeles arbutifolia

Toyon

0–36

Hibiscus rosa­sinensis

Rose of China

40–60

Lantana montevidensis

Trailing lantana

18–36

Leptospermum scoparium

New Zealand tea tree

18–36

Leucophyllum frutescens“Green Cloud” Texas ranger

0–36

Ligustrum japonicum“Texanum”

Texas privet

40–60

Myoporum “Pacificum”

Prostrate myoporum

0–36

Otatea acuminata

Mexican bamboo

18–36

Phormium tenax

New Zealand flax

18–36

Pittosporum tobira

Mock orange

18–36

Potentillatabernaemontanii

Spring cinquefoil

70–80

b,d

b,c

b

b

b,c

b

b

VIII­11

b,c

b

a
b

c

Scientific nameCommon name

Initial Kc

Prunus caroliniana

Carolina laurel cherry

0–36

Pyracantha koidzumii“Santa Cruz” firethorn

0–36

Rhaphiolepis indica

Indian hawthorn

18–36

Teucrium chamaedrys

Germander

18–36

Vinca major

Periwinkle; myrtle

30–40

Westringia
rosamarinaformis

Rosemary bush

18–36

Xylosma congestum

Shiny xylosma

18–36

b

b

See Pittenger et al. (1990), Pittenger et al. (2001), Shaw and Pittenger (2004), and Staats and Klett (1995).
Acceptable landscape performance with no summer irrigation shown only on the immediate coast. Inland plantings
may require summer irrigation up to the maximum amount listed.

Species typically provides unacceptable landscape performance in summer and fall months regardless of irrigation
amount.

dRequires renovation every 3 years to maintain acceptable performance.

frequency of irrigation. The standard or “initial” Kc can be adjusted according to the site’sconditions and the desired amount of water­related stress. For example, the Kc may need to be
adjusted downward for plants partially shaded by a building or taller nearby trees. Or the Kc
may need to be adjusted higher when plants are irrigated with more­saline water or exposed toexcessive wind or heat from a nearby street or parking lot. The degree of adjustment issomewhat arbitrary since a heterogeneous group of plants with different needs for water,
tolerances to salinity, and microclimates makes rigid numerical adjustments to the K c
impractical. Nevertheless, such adjustments need to be made to the initial Kc either upward or
downward, depending on the outcome of the first adjustment.
The range of Kc provided in Table VIII­2, which has been developed by University ofCalifornia scientists based on research and field experiences, is a sound starting point (Shawand Zellman, 2005). The higher Kc is relevant for maintaining actively growing plants in goodaesthetic condition, such as the turf in a sports field. Lower Kc apply to keeping plants alive
under minimal irrigation, such as during periods of restricted water use, and do not maximize
aesthetic quality. The Kc typically chosen by irrigation managers falls somewhere in the middleof the range of values listed in Table VIII­2. When one is irrigating with relatively more­saline
water, using the higher­end Kc or possibly even a higher value is likely to be advisable.
For species with unknown needs for water, it is currently recommended to set initialirrigation schedules at 50% ETo for established nonturf plants for landscapes (Shaw and
Zellman, 1995). Subsequently adjusting the Kc is the easiest way to handle differences in

VIII­12aspect, shade, microclimate, densities of plants, stress, frequency of irrigation, and water
quality. Costello et al. (2000) provide a table listing hundreds of plants and their relative needs
for water, i.e., high, moderate, or low. Though no quantitative values are provided, referring tothis table is a useful first step.

VIII.B. Scheduling Irrigation
Scheduling irrigation involves determining how long and how often to irrigate. It canbe done by hand or by computer.
To develop a schedule for irrigating a landscape, it is critical to first estimate the water
needed by the landscape based on the type of plant, the ETo, and the Kc selected in Table VIII­
2. The landscape’s ET is estimated from both the ETo—either historical or “real­time” fromweather stations—and the Kc.

Example VIII­1
What is the water needed by a cool­season turfgrass, such as Kentucky bluegrass, in
Los Angeles in July with a monthly ETo of 6.2 in.? Assume that the Kc is 0.80 and does notchange during the year.

ETc = ETo * Kc = 6.2 in. * 0.80 = 5.0 in. for July
VIII.B.1. Duration of Irrigation
Using either a hand­held calculator or such scheduling software as TURFIMP on acomputer, the duration of irrigation can be calculated on a daily, weekly, or monthly basis withthe use of the following information:
1) The irrigation system’s application rate (AR) in inches/hour.

2) The irrigation system’s distribution uniformity (DU), which has been described in
Chapter VII and is an estimate of how uniformly water is applied. The DU will accountfor the losses due to nonuniformity of irrigation. Irrigation efficiency (IE) accounts forlosses due to uniformity, runoff, and deep percolation. If runoff is minimal and theaverage depth of water applied to the low quarter is equal to the landscape’s use ofwater, then the DU is a viable estimate of IE.
3) Historical or real­time ETo.

VIII­13

4) Initial or adjusted Kc.
With a hand­held calculator or scheduling software on a computer, the aforementioned
information is used in the following formula to calculate how long each irrigation should last:

ETo in./day * Kc * 60 min/h
Run time (minutes) = ______________________________
AR in./h * DU

(VIII­3)

The duration of irrigations for successive days can be determined by adding daily run
times or using the cumulative ETo value. The weekly duration of irrigations can be determinedby multiplying the average daily ETo by 7.

Example VIII­2
What is the daily run time for irrigating shrubs in a landscape in the southern coastal
area with a Kc of 0.50, a daily ETo of 0.18 inches, and a water application rate (AR) of 0.75
in./h? Assume that the irrigation system’s DU is 80% (0.80).

0.18 in./day * 0.50 * 60
Daily run time = __________________________ = 9.0 min/day
0.75 in./h * 0.80

(VIII­4)

This particular example above works best for sprinkler irrigation. Under drip irrigation,
the system run time will be based on the number of emitters and emitter discharge rates (gallons
per hour) for the area being irrigated. Usually there are numerous plant types, plant sizes, andemitter discharge rates on a particular station. In these instances, it is best to have flow meters
installed. In example VI­2, the amount of water that needs to be added each day during thistime of year is 0.11 in. (ETo * Kc/0.8). For an acre of landscape, the meter would have to run forabout 400 ft3 (about 3,000 gal).

VIII.B.2. Frequency of Irrigation
Since the approximate amount of water that a plant needs can be calculated on a daily
basis, that amount of water theoretically could be applied daily, but applying small amounts ofwater on a daily basis is an inefficient and unsound practice in most cases (Hanson et al., 1994).

VIII­14

A more practical and effective method is to wait for a period of time—usually several days—
and then to apply the accumulated amount.
The following should be considered in determining how often to irrigate:
Factors that necessitate frequent irrigation are as follows:·

Plants that use water at a high rate·

Plants with shallow roots·

Sandy soils with little capacity for retaining water·High probability of runoff due to sloping land or compacted soil·

Poor rate of infiltration due to compacted or clay soils.

Factors that allow for infrequent irrigation are as follows:·

Low rates of ET·

Additional water from rain, dew, or fog·

Plants with deep roots and dense roots·

Plants that are drought tolerant·

No problems with runoff·

A site able to maintain acceptable quality or use with infrequent irrigation·

More­saline waters used to irrigate, requiring deep watering with a higher leaching
fraction.

Observations in the field including appearance of plants, the depth of their roots, thepenetration of water into the soil, the type of soil, and the estimated available water­holding
capacity will help in determining how often to irrigate. Often, a field estimate of the amount ofwater in the soil or the amount of visible water­related stress being sustained by the plants isused to decide when to irrigate and ET data are used to determine how long to irrigate or withhow much water. If conditions at the site limit the rate of infiltration, the length of time thatelapses before runoff occurs will determine the longest possible run time at that site. Multiple
cycles should be programmed if additional run time is needed for water to infiltrate to a desired
depth in the soil.
Three common methods for deciding when to irrigate include the flexible method, which isbased on an estimate of the allowable depletion of moisture from the root zone; the fixed­day
calendar method, which accommodates weekly cultivational practices and weekly activities
involving use of the site; and soil moisture sensors. Many irrigation controllers provide

VIII­15

programming functions for all three methods, using a 7­ or 14­day calendar, features for skipping aday, and sensor inputs. Each method is acceptable, as long as the proper amount of water is applied
and runoff is minimized.

VIII.B.3. Using the Flexible Method
With the flexible method, the duration of each irrigation remains the same and thefrequency of irrigation varies during the year according to an estimate of the allowable
depletion of moisture from the soil and the daily use of water by plants.
The amount of water in the soil available to the plant depends on the type of soil andthe depth of the roots of the plant in question. Tables exist that provide estimates of available
water for soils of various textures (Goldhamer and Snyder, 1989). Coarse­textured soils—sands
to sandy loams—typically have 0.5 to 1.25 in. of available water/ft of soil. Medium­textured
soils—fine­sandy loams to silt loams—generally have 1.0 to 2.0 in. of available water per ft.
Fine­textured soils—clay loams to clays—have 1.5 to 3.0 in. of available water per ft. The total
available water is the available water multiplied by the effective root depth. For example, aplant with an effective root depth of 2 ft grown in a soil with 1.5 in. of available water/ft has 3
in. of total available water.
It should be noted that all of what is termed total available water is not all readily
available to the plant. Its roots can readily extract water when the soil is relatively wet, but thisprocess becomes progressively more difficult as the soil dries. Consequently, instead ofscheduling a irrigation after the total water is extracted, it is recommended that an allowable
depletion of the total available water in the soil be selected to prevent potentially fatal stress tothe plant. This allowable depletion can vary between 20 and 70%. An allowable depletion of 20
to 30% may be appropriate for more drought­sensitive plants. More drought­tolerant plants may
be able to handle an allowable depletion of 70%. If the lesser allowable depletion is selected,
more frequent irrigations will obviously be required.
The frequency of irrigation is determined by summing up the values for daily use ofwater by plants (ETo ´ Kc), until the total water use equals the desired depletion of water in thesoil (Figure VIII­4). The effect of rainfall and fog, which may contribute to moisture in the soil,
can be assessed only by observation in the field.

VIII­16

Figure VIII­4. Soil water depletion (flexible) method.

VIII.B.4. Using the Calendar Method
With the calendar method, the frequency of irrigation is fixed to specific days of the weekthat generally accommodate the site’s activities. Since the water needs of plants vary according
to the time of year and evaporative demand, the run time per irrigation will vary during theyear. The calendar method involves taking the following steps: First, determine the number ofminutes of run time per week. Second, determine the number of irrigation days per week.
Third, calculate the run time per day:minutes per week
Run time per day = __________________
irrigation days per week

(VIII­5)

If runoff occurs during this run time, then the run time will need to be divided into more cyclesof irrigation. If the soil permits a high rate of application, then only one cycle per day is needed.

VIII.B.5. Using Soil Moisture Sensors
Soil moisture sensors are sometimes used in landscapes to determine when to startirrigating and, in some cases, when to stop irrigating. It is very important that these sensors be

VIII­17

located in the active root zone and that they be properly calibrated for the specific conditions of
the site’s soil. Sensors should be read and recorded in a routine and timely way. When one isusing soil moisture sensors, uniformity of irrigation remains an important factor andinformation about ET plays a limited role in water management, but irrigation may bescheduled based on data about historical ETo and sensors can be used to shut down theirrigation system when water is not needed.

VIII.B.6. Components of Efficient Irrigation Scheduling Programs
As with all irrigation practices, the plant’s observed response, measurements of the
moisture in the soil, and the irrigation manager’s judgment will help to verify theappropriateness of the irrigation schedule. Modifying the Kc or analyzing data about theirrigation system’s performance and subsequently recalculating the run times will be needed tofine­tune the schedule.
A high­quality, efficient system for irrigating a landscape is the product of good design,high­quality hardware, professional installation, and timely maintenance. Each component
depends on the others for success. The failure of any one component may result in the entire
system’s demise. An efficient program for irrigating a landscape combines a high­quality
irrigation system with knowledgeable people performing proper scheduling and monitoring.

VIII.C. Conserving Water by Irrigating with Recycled Water
Irrigating a landscape with recycled water instead of with water that has never beenpreviously used constitutes a major water­conserving measure. Such a conservation­oriented
water management policy does not necessarily involve an irrigation water of lesser quality. Not
all recycled water is of poor quality, and not all potable water is necessarily of low salinity. If
the recycled water used to irrigate has a higher salt content than did the water used before, thencare should be taken when simultaneously adopting deficit irrigation, as the combination could
create excessive accumulation of salinity in the root zone, which could adversely affectsensitive plants. Under most circumstances, however, irrigating with recycled water may not
involve the need for any special management practices above and beyond those needed for
irrigating with high­quality potable water. It depends on the recycled water’s source. Recycledwater from municipalities with potable water of low salinity would be superior to that derived
from communities with potable water of a higher salt content.

VIII­18

VIII.D. References
Allen, R. G., L. S. Pereira, D. Raes, and M. Smith. 1998. Crop evapotranspiration—guidelines
for computing crop water requirements. FAO irrigation and drainage paper 56. Food andAgriculture Organization of the United Nations, Rome, Italy. Also available online at
http://www.fao.org/docrep/X0490E/X0490E00.htm.
American Society of Plant Biologists. 2005. Available online at http://www.aspb.org/education/
lab_photosyn.cfm.
Costello, L. R., N. P Matheny, J. R. Clark, and K. S. Jones. 2000. A guide to estimating
irrigation water needs of landscape plantings in California: the landscape coefficient method
WCUOLS III. University of California and Department of Water Resources joint publication.
Also available online at http://www.owue.water.ca.gov/docs/wucols00.pdf.
Doorenbos, J., and W. O. Pruitt. 1984. Guidelines for predicting crop water requirements. FAO
irrigation and drainage paper 24. Food and Agriculture Organization of the United Nations.
Rome, Italy.
Goldhamer, D. A., and R. L. Snyder. 1989. Irrigation scheduling: a guide for efficient on­farm
water management. University of California Division of Agriculture and Natural Resources
publication no. 21454.
Grattan, S. R., W. Bowers, A. Dong, R. L. Snyder, J. J. Carroll, and W. George. 1998. New
crop coefficients estimate water use of vegetables, row crops. Calif. Agric. 52:16–21.
Hanson, B., L. Schwankl, S. Grattan, and T. Prichard. 1994. Drip irrigation for row crops.
University of California Irrigation Program. University of California–Davis, Davis.
Meyer, J. L., et al. 1985. Irrigation of turfgrass below replacement of evapotranspiration as ameans of water conservation: determining Kc of turfgrasses, p. 357–364. In F. Lemaire (ed.),Proceedings of the 5th International Turfgrass Research Conference. INRA Publications,Versailles, France.
Meyer, J. L., and V. A. Gibeault. 1986. Turfgrass performance under reduced irrigation. Calif.
Agric. 40:19–20.
Pittenger, D. R., D. R. Hodel, and D. A. Shaw. 1990. Relative water requirements of six
groundcover species. HortScience 25:1085. (Abstract.).
Pittenger, D. R., D. A. Shaw, D. R. Hodel, and D. B. Holt. 2001. Responses of landscapegroundcovers to minimum irrigation. J. Environ. Hortic. 19:78–84.
Shaw, D. A., and D. R. Pittenger. 2005. Landscape irrigation system evaluation andmanagement. University of California Cooperative Extension, San Diego.
Shaw, D. A., and D. R. Pittenger. 2004. Performance of landscape ornamentals given irrigation
treatments based on reference evapotranspiration. In Proceedings of 4th International
Symposium on Irrigation of Horticultural Crops.

VIII­19

Staats, D., and J. E. Klett. 1995. Water conservation potential and quality of non­turf
groundcovers versus Kentucky bluegrass under increasing levels of drought stress. J. Environ.
Hortic. 13:181–185.

VIII­20

Chapter IX. Soil­Related Problems
K. Tanji, B. Sheikh, and S. Grattan

IX.A. Saline Soils
IX.B. Sodic Soils
IX.C. Slowly Permeable Soils
IX.C.1.Causes
IX.C.2. Solutions
IX.D. Infertile Soils
IX.D.1. Essential Plant Nutrients
IX.D.2. Symptoms of Deficiencies
IX.D.3. Nutrients Required by Landscape Plants
IX.D.4. Soil Analysis
IX.D.5. Plant Analysis
IX.D.6. Nutrients in Recycled Water
IX.E. Other Soil­Related Problems
IX.F. References
The soil is the medium supporting the growth of plants. It is here where the roots draw
water and absorb essential nutrients. Consequently, any soil­related problem will markedly affectthe health and viability of plants. Problems involving soils include excessively saline soils,
excessively sodic soils, insufficiently fertile soils, those that are less penetrable to water, thosethat contain toxic amounts of trace elements, and those that are steeply sloped—a condition that
contributes to the runoff of irrigation water and the erosion of soil.

IX.A. Saline Soils
In soils with an excessive amount of salinity, i.e., greater than an electrical conductivityof extract of soil paste (ECe) of 4 dS/m (Table IX.A.1), the availability of water in the soil toplants is reduced by osmotic effects. Saline soils are typically dominated by Na, Mg, Cl, and SO4ions, which typically form highly soluble salts and consequently accumulate to highconcentrations. Their pattern is in contrast with that of Ca, HCO3, and CO3 ions, which form lesssoluble salts and thus less readily accumulate soluble salts (Chapter IV). Symptoms of excessive
salinity to plants include wilting and other signs of stress induced by

IX­1

a

Table IX.A.1. Classification of salt­affected soils and distinguishing properties (after Richards, 1954).
ECe
ESP
Class
pHs
dS/m
%

a

Nonsaline

<4

<15

<8.5

Saline

>4

<15

<8.5

Sodic

<4

>15

>8.5

Saline­sodic

>4

>15

<8.5

ECe = EC of extract of saturated soil paste;

ESP = (exchangeable Na/CEC) ´ 100, with both Na and CEC in number of milliequivalents/100 g of soil;
CEC = cation exchange capacity (negatively charged sites) in number of milliequivalents/100 g of soil; andpHs = pH of saturated soil paste.

insufficient water, as well as stunted growth, and, in severe cases, damaged leaves and death(Chapter V).
Soils become salinized either through nature, which is known as primary salinization, or
via human activity, known as secondary salinization. The primary natural source of salinity insoils is the geochemical weathering of rocks, sediments, and soil minerals, which produces
dissolved mineral salts. Elevated salinity is naturally present in soils derived from saline marine
sedimentary rocks. Some soils in coastal zones are saline due to seawater intrusion or being
sprayed by seawater. Salinity in soils introduced by human (anthropogenic) activity includes salts
from applied irrigation water, from such amendments to soil and water as gypsum and sulfuric
acid, from animal manures, and from biosolids.
Though measuring salinity in waters is straightforward and though the result is expressed
as EC or total dissolved salts (TDS), measuring the salinity of a soil presents more of a challenge
due to the dynamic changes that occur within a soil over time and space. The concentration ofdissolved mineral salts generally does not change in direct proportion to changes in soil watercontents because of mineral solubility, cation exchange, and ion association (Paul et al., 1966).
Soil water content undergoes cyclical wetting and drying. Soil water content is replenished byirrigation and rainfall and depleted by evapotranspiration. Moreover, dissolved mineral salts arehighly mobile in the soil due to chemical diffusion (ion diffusion) and to convective anddispersive transport by soil water flow. Therefore, plant roots are exposed to dynamic temporaland spatial changes in soil salinity, and these changes pose a challenge in measuring soil salinity.
Methods to measure the salinity of a soil include (1) collecting samples of the soil andmeasuring the ECe, (2) collecting water in the soil in situ with ceramic suction cups when the soil
is moist and measuring soil salinity (ECsw), and (3) using the time domain reflectometry device(TDR) or electromagnetic devices (EM­38 probe) to remotely sense ECsw in situ.

IX­2

Figure IX.A.1 illustrates the dynamic changes in a lysimeter with soil depth of 120 cm, inwhich a crop of alfalfa was grown. It specifically depicts changes in the salinity of soil in two
depths and in the water potential of the soil in one depth (Rhoades, 1972). Note that the ECsw at a
depth of 40 cm is less than the ECsw at a depth of 80 cm in this lysimeter. This result occurs
because salts are leached at the surface and tend to accumulate in the lower depths. The ECsw wasmeasured with salinity sensors embedded in the soil column. Irrigation water was applied when
the water pressure in the soil at a depth of 60 cm reached about 0.5 bars as measured withtensiometers. When irrigation water was applied, the ECsw abruptly decreased and then slowly
increased, as plants extracted water in the soil, with salts remaining residually. The time­
integrated ECsw at a depth of 40 cm was 7.4 and 12.4 dS/m at a depth of 80 cm. Roots of theplants were consequently exposed to various amounts of water and salinity in the soil over timeand space. The alfalfa example is given because the authors did not find a similar data set for
turfgrasses.

Figure IX.A.1. Dynamic changes in soil salinity in two soil depths and soil water potential in one soil depth as
influenced by irrigation and evapotranspiration of alfalfa grown in a lysimeter (after Rhoades, 1972).

IX­3

The salinity of a soil depends on the salinity of the water that irrigates it and the leaching
fraction (LF) provided with each irrigation event or seasonally (Chapters III and IV). It is
assumed that the soil profile is permeable: i.e., no restrictions on drainage. The seasonal LF isdefined as

LF =Diw - Det Ddw
=
Diw
Diw

(IX­1)

where Diw denotes the depth to which irrigation water has infiltrated, Det denotes the depth ofplant ET, and Ddw the depth of drainage water leaching past the root zone. The distribution ofsalts in the soil varies according to the pattern of root water extraction and the depth of rooting(Chapter IV). If the rainfall that infiltrates the soil contributes substantially to meet the plant’s ET
requirements, fewer salts accumulate in the root zone than with irrigation alone, since rainwatercontains a very low level of salts—approximately from 5 to 20 ppm of TDS.
A root zone’s average salinity may be sustained within a plant’s known threshold fortolerating salt (Chapter V) with the leaching requirement (LR). The seasonal LR is defined as

LR =

EC iw
5 * EC a - ECiw

(IX­2)

where ECa is the plant­specific threshold soil salinity, above which plant performance is impairedand “5” is an empirical factor to account for the distribution of salt in the soil (Rhoades, 1972).
The way in which salt is eventually distributed in irrigated soils depends greatly on thetype of irrigation system and the extent of leaching. Figure IX.A.2 illustrates the wetting patterns
with several methods of surface and subsurface irrigation (FAO, 1997). Salts tend to accumulate
in the wetted perimeter of soils. Figure IX.A.3 illustrates the gravimetric soil moisture contents
around two surface drippers in a strawberry field and the pattern of soil salinity (Hanson andBendixson, 2004).

IX­4

Figure IX.A.2. Wetting patterns for surface drip, subsurface drip, microspray, and bubbler irrigation application
systems (from FAO, 1997) .

IX­5Figure IX.A.3. Moisture and salinity distribution patterns for two surface drippers (from Hanson and Bendixson,
2004).

IX­6

With drip irrigation, the wetted zone is somewhat ellipsoidal in shape and salts
accumulate in the outer wetted edges, as shown in Figure IX.A.3. Though the LF principle does
not apply directly to this wetted zone, a greater application of drip irrigation will result in theaccumulation of salt farther away from the roots of the plant. After drip irrigating with saline
waters for a prolonged period in agricultural crops, it is common to carry out reclamationleaching by using the sprinkler irrigation method to leach soil salts before the planting of the next
crop. Such a practice could be adopted for annual landscape plants. Heavy rainfall on drip­
irrigated soil with a high accumulation of salt will redistribute the salts vertically and laterally.
Since this redistribution of salts may adversely affect salt­sensitive plants, it is suggested that drip
irrigation be conducted during rainfall to reduce the influx of salts into the root zone.

IX.B. Sodic Soils
Sodic soils contain excessive levels of exchangeable (adsorbed) Na, causing suchunfavorable physical conditions in the soil as a reduced rate of water infiltration (Chapter III).
High exchangeable sodium percentage (ESP) and soil pH result in the dispersion of clays andorganic matter in the soil. High ESP may be toxic to sensitive plants (USSL, 1954). Sodic soils
have a pH greater than 8.5 due to the presence of sodium in the form of Na2CO3 or NaOH.
The genesis of sodic soils is more complex than that of saline soils. Some sodic soils may
be formed by leaching of saline soils rich in Na, resulting in excess ESP. Other sodic soils may
result from the chemical weathering of igneous rocks, forming NaHCO3 under nonsalineconditions and being subjected to evapoconcentration from transpiration of plants andevaporation from bare soils. Another pathway of sodicity involves the biological formation of
Na2CO3 by the reduction of sulfate to sulfide ions in wetland environments (Whittig and Janitsky,1963).
In sodic soils, the ratio of exchangeable Na to cation exchange capacity (CEC) multipliedby 100—the ESP—exceeds 15% (Table IX.A.1). Analytical determination of ESP involves
extraction of exchangeable and soluble Na, as well as the determination of CEC. Since
determining the ESP requires a lengthy and complex process, a proxy sodicity parameter known
as the sodium adsorption ratio (SAR) is commonly used. The SAR is calculated from the soluble
Na, Ca, and Mg in the extract of soil saturated paste. It is defined as

IX­7

SAR =Na +[Ca + + + Mg + + ]0.5

with all ionic concentrations in mmoles/liter(IX­3)

Figure IX.B.1. Nomograph for determining the SAR value of a saturation extract and for estimating thecorresponding ESP value of a soil at equilibrium with the extract (Richards, 1954).

IX­8

or SAR =Na +[0.5 * (Ca + + + Mg + + )]0.5

with all ionic concentrations in number ofmilliequivalents/liter(IX­4)The SAR in the soil solution may be empirically related to the ESP on the soil exchange complex
by a nomogram (Figure IX.B.1) found in Richards (1954) or calculated from

ESP =100(-0.0126 + 0.01475 * SAR)
1 + (-0.0126 + 0.01475 * SAR)

(IX­5)A high ESP or SAR adversely affects a soil’s structure, especially at the surface. It resultsin the breakdown of soil aggregates and the dispersion of clays and organic matter, reducing rates
of water intake. S. Miyamoto (personal communication) has found that the ESP in turf irrigatedwith saline­sodic waters is affected by LF as much as by the SAR of the irrigation water. This
discussion of sodic soils is considered more fully in the next section.
The dispersion of clays and organic matter is also affected by salt (electrolyte)
concentration. The combined effects of EC and SAR in the water on the permeability of soil arecommonly evaluated with the approach shown in Figure IX.B.2.

Another water sodicity parameter that was frequently used in the past is residual sodium
carbonate (RSC). It is defined as

RSC = (HCO3 + CO3) – (Ca + Mg) in number of milliequivalents/liter(IX­6)

When the RSC exceeds 1.25 meq/L, clays and organic matter in the soil may disperse, resulting
in reduced permeability (Richards, 1954). Although the use of RSC is somewhat dated, many
testing laboratories for soils and horticulture still use this parameter and find it to be a usefulsodicity parameter.

IX­9Excessive levels of sodicity are commonly ameliorated by adding Ca amendments into
the soil’s surface or to the water used to irrigate. This topic will be further discussed in the next
section.
Figure IX.B.3 shows the SAR­EC combinations for a number of sources of recycledwater, as reported by some of California’s major water recycling agencies (B. Sheikh, personalcommunication). As can be seen, many of these waters fall within the zone of no reduction in

Figure IX.B.2. An approach for evaluating the combined effects of water salinity and sodicity on soil permeability(from Ayers and Westcot, 1985).

the infiltration rate, several waters in the zone of slight to moderate reduction in the infiltration
rate, and no water in the zone of severe reduction in the rate at which water infiltrates theirrigated soil. Some agencies whose recycled water reduces the rate slightly to moderately havebegun to add gypsum, so that irrigating with the amended water does not cause infiltration
problems. For example, Carmel Area Wastewater District, which provides recycled water to
IX­10seven Pebble Beach golf courses, is planning to desalinate its recycled water enough to meetcertain criteria for concentrations of TDS. Ironically, meeting these criteria may cause therecycled water to move from the no­impact zone to a slight reduction in the irrigated soil’s rate of
infiltration, unless gypsum continues to be added.

IX­11

Figure IX.B.3. EC­SAR combinations of major sources of recycled water in California (from personalcommunication by B. Sheikh with personnel at the respective agencies featured in the graphic).

0

1

2

3

4

5

6

7

8

S O D IU M A D S O R P T IO N R A T IO ( S A R ) O F
IR R IG A T IO N W A T E R

9

0

0.2

0.4

0.8

Irvine

1

1.2

1.4

Las Virgenes MWD

LACSD Pomona

Daly City­­post­gypsum amendment

Marin County

LACSD Saugus
Torrey Pines

1.6

LACSD Valencia

Monterey (MRWPCA)LACSD Los Coyotes

San Diego
San Jose SBWR

LACSD SJC E

WBMWD El Segundo

LACSD Whittier Narrows

Daly City

Redwood City

1.8

Pebble Beach­Carmel

East Lake GC

No Reduction In Infiltration Rate

ELECTRICAL CONDUCTIVITY OF IRRIGATION WATER, (dS/M)

0.6

Coachella Valley

Chino Hills

San Francisco

Slight to Moderate Reduction in
Infiltration Rate
LACSD Long Beach

Pebble Beach­­post­desalination

Severe Reduction
In Infiltration Rate

S a n ta R o s a

10IMPACT OF SALTS IN CALIFORNIA RECYCLED WATER ON INFILTRATION RATE OF IRRIGATED SOILSLA C SD SJC W

IX­12

2

IX.C. Slowly Permeable Soils
If a soil is slowly penetrated by water, that low penetration rate may be caused byconditions at the surface that slow the intake of water, as well as by the sluggish movement ofwater below the surface. Symptoms include plants stunted by lack of water, soil dryness evenafter prolonged irrigation, excessive ponding and/or runoff during irrigation and rainfall, poorly
aerated soil, increased incidence of root diseases, excessive wilting of plants during hot summer
months, and the need to irrigate for an excessively long time, which, in turn, can prevent orinterfere with other cultural practices such as weeding, fertilization, etc. (Oster et al., 1984). In
landscapes, prolonged wetness from the prolonged need to irrigate may also interfere with themowing of turf and with the public use of the landscapes.

IX.C.1. Causes
Solving the problem of slow soil penetration by water depends on its cause. It could be
the quality of the water used to irrigate, coupled with the types of clays in the soil. A water with
an EC exceeding about 0.5 dS/m will tend to promote the aggregation of particles of soil. A farless saline water, e.g., one with an EC of less than 0.2 dS/m, will tend to disperse them. If a soil isdominated by kaolinite and illite clays, which do not swell, the soil’s particles will tend toaggregate. If the soil is dominated instead by smectite clays, which swell, the soil’s particles willtend to swell, separate, and disperse.
A second cause could be that crusting of the soil is impeding the water intake rate. The
two kinds of crusts that cause water to penetrate a soil poorly are structural crusts anddepositional crusts (Oster et al., 1984). Structural crusts are formed when drops of rain and waterfrom sprinklers wet and beat the soil, collapsing its structure. When the soil dries, the thin crustthat forms decreases the number and size of larger water­conducting pores. Depositional crusts
are formed when sediment­laden water infiltrates the soil, leaving a residual layer of sediment on
the soil’s surface that is usually thicker than structural crusts.
A third cause could be that sodicity, which is reported as SAR, is impeding water
infiltration. This potentiality was discussed previously in IX.B.2. Note that the criteria forsodicity developed for agricultural soils may not be directly applicable to soils in heavily
trafficked landscapes, particularly those that are moist and clay rich, as they can becomecompacted.
This discussion brings up a fourth cause: compaction of the soil by the traffic ofmachines and humans, especially when the soil is moist. The applied force of such traffic

IX­13

rearranges particles of soil, increasing its dense bulk and decreasing its number of larger water­
conducting pores.
A fifth cause could be that stratification of the soil below the surface is impeding water
movement in the soil profile. Possible strata may include clay pan, cemented hardpan, andbedrock. A clay pan is formed when the soil’s clays are leached into the subsoil, accumulating at
depths of 12 to 24 in. A hardpan is a layer of subsoil strongly cemented with silica and calcium
carbonate. Dropping a sample of the pan into a bucket of water helps to distinguish a clay pan
from a hardpan: if it softens and falls apart, it is a clay pan; if it does not, it is a cemented
hardpan.
A sixth cause of slowly permeable soil is abrupt textural stratifications in alluvial soils.
Such stratifications can prevent the uniform flow of water in the soil. Clay layers can restrict the
movement of water and cause a perched water table and poor aeration. Sandy layers can cause thesame problems as clay layers, since overlying layers of soil must become saturated with water
before water will flow into the sandy layers.

IX.C.2. Solutions
Management options can be divided into solutions for such problems as crusting andcompaction. They may be addressed at the soil’s surface with the addition of chemical
amendments, the addition of organic matter and/or tillage; solutions for subsurface problems, andremedies that involve a change in irrigation systems. The following solutions have proveneffective over decades of agricultural practice with natural sources of water and should work justas effectively with recycled water. These amendments may not be as effective for recycled waters
having an EC of 1.5 to 3.5 dS/m as used in the landscapes of the southwestern United States(Miyamoto, 1998). Mechanical means of improving soil permeability tend to give better results
than do chemical amendments in the Southwest.

GypsumA chemical amendment—mainly either calcium or an acid­producing amendment thatyields calcium—can improve both the soil and the quality of water used to irrigate. Gypsum(CaSO4.2H2O), a relatively inexpensive and easily applied soil and water amendment, is widelyused. The calcium released from gypsum reduces the SAR of the water and soil. It enhances thestable aggregation of soil and increases the concentration salt in water with low salinity, which
would otherwise poorly penetrate soil. Gypsum is applied to the soil at a rate of 1 to 4 tons peracre by being spread on the soil’s surface and is then tilled into the soil. It is applied to water witha device that dissolves gypsum into a slurry and injects it into water. Doing so increases the
IX­14

concentration of calcium by 2 to 4 meq/L (40 to 80 mg/L). Sometimes phosphogypsum, a by­
product in the manufacture of phosphorus fertilizer, is used instead of gypsum with equally goodresults.

Acidification
Such acid­forming amendments as sulfur, sulfur dioxide gas, lime sulfur, sulfuric acid,ammonium polysulfide, and ammonium thiosulfate may also be used. These amendments
produce hydrogen ions, which dissolve the soil’s calcium carbonate, releasing soluble calcium
ions. A conversion table outlining the number of tons equivalent to pure gypsum or elemental
sulfur is available (California Fertilizer Association, 1998), as is a conversion table with thenumber of pounds required per acre­foot of water to obtain 1 meq of calcium/L or that required
per acre to replace 1 meq/100 g of exchangeable sodium in the top 6 in. of soil (Oster et al.,1984).

Soil Conditioners
Soil conditioners consisting of synthetic organic polymers are used to bind smaller aggregates ofsoil into larger ones. Polyacrylamide (PAM) applied at a rate of 30 lbs. per acre in the irrigationwater improves water intakes. PAM is also used to reduce sediment load in tailwater (runoffs)
from furrow irrigated fields.

Organic Matter
Such organic matter as residues of crops, cover crops, manure, and biosolids generated from thetreatment of municipal wastewater, when added to soil, improves the rate at which water
infiltrates that soil. Polysaccharides in the organic matter appear to bind particles of soil,
promoting their aggregation and maintaining the structure of the soil.

IX.D. Infertile Soils
IX.D.1. Essential Plant Nutrients
Maintenance of adequate plant nutrition is important in landscape settings to keep plants
healthy and attractive. Plants require 17 nutrients to metabolize or to complete their life cycle.
These 17, known as essential nutrients, are extracted by plants from the air, the water, and thesoil. Three of them—carbon (C), hydrogen (H), and oxygen (O)—are readily available from theatmosphere and water (California Plant Health Association, 2002). Another three—nitrogen (N),phosphorus (P), and potassium (K)—are known as primary nutrients and are the most commonly
deficient. Plants need the secondary plant nutrients of calcium (Ca), magnesium (Mg), and sulfur(S) in the same amounts as N, P, and K. These secondary nutrients are less frequently deficient,IX­15

particularly in California’s soils. The remaining eight nutrients are required in small amounts.
Referred to as micronutrients, they consist of zinc (Zn), iron (Fe), manganese (Mn), copper (Cu),boron (B), molybdenum (Mo), chlorine (Cl), and nickel (Ni). The roots and some leaves of plants
take up these nutrients in the form of ions and in the form of simple molecules, excluding larger
molecules, including nearly all organic molecules (Epstein and Bloom, 2004).

IX.D.2. Symptoms of Deficiencies
When plants are lacking in these 17 essential nutrients, they exhibit such visuallyapparent symptoms as discolored leaves, spotting, marginal leaf necrosis, and injured buds andleaves (Table IX.D.1.). Some symptoms may resemble another deficiency or disorder. For
instance, symptoms of a deficiency in Mn closely resemble those of a deficiency in Fe, as well as
symptoms of damage sustained from applying herbicides to the soil before weeds have emerged(Costello et al., 2003).
A symptom’s location on the plant can be useful in figuring out the nutrients that arelacking. For example, deficiencies of the three most frequently limiting elements—i.e., N, P, and
K—and deficiencies of magnesium and Mo first become noticeable on older leaves. Deficiencies
in S, Fe, Mn, Zn, and Cu first become noticeable in young, newly emerging leaves. Deficiencies
in B and Ca manifest themselves as dead buds and as the dieback of growing tips. It is important
to corroborate the particular nutrient deficiency deemed to be the culprit by collecting andanalyzing samples of leaf tissue and soil. The symptoms of some deficiencies in nutrients may
appear similar to symptoms stemming from other causes, such as toxicity from boron or chloride
or injury from ozone in the air.

IX.D.3. Nutrients Required by Landscape Plants
The nutrients required by plants in landscapes vary as widely as the number of types ofplants found in landscapes. For example, turfgrasses require a large amount of N to promote
vegetative growth, whereas many flowering plants require higher proportions of P and K. A
proper balance of nutrients is desired for optimal plant performance. Inorganic and organic formsof fertilizer are available for nutrient­deficient soils. The rates and times to apply fertilizers may
be obtained from local landscape horticulturists and testing laboratories. Excess fertilization with
one nutrient can induce the deficiency of another nutrient. For instance, a heavy application of P
may induce deficiencies in Fe, Zn, and Cu (Merhaut, 2001).

IX­16

IX.D.4. Soil Analysis
Results from collecting samples of soil from the landscape and subjecting them toanalysis in the laboratory can be used to determine the kinds and amounts of fertilizer that need tobe added by indicating the existence of mineral deficiencies.
Coarse­textured (sandy) soils with relatively little soil organic matter are typically lessfertile and require regular fertilization. Heavily graded landscapes without topsoil may also be
nutrient deficient. The availability of nutrients varies with the pH of the soil.
The primary and secondary plant nutrients are generally readily available when the soil
has a pH of 6 to 8. An exception is P, which is less available when its pH is alkaline due tocomplexation with calcium (California Plant Health Association, 2002). Fe, Mn, Zn, and Cu arealso less available when the soil has an alkaline pH. Often deficiencies in micronutrients can becorrected by adjusting the pH of the soil.
Soil tests can be conducted at any time, but the best time is early spring. Such timing
allows for corrective measures if analyses indicate that a nutrient deficiency may be likely tooccur before the plant begins to grow. Though scant information exists regarding the fertility ofsoil required for specific ornamental plants, local extension advisors in ornamental horticulture
can help interpret the results of tests.

IX­17

Table IX.D.1. Symptoms of deficiency in plants (after California Plant Health Association, 2002; Costello et al.,
2003; and Merhaut, 2001).
Nutrient
Typical symptoms indicating deficiency of nutrient in plants
NitrogenOverall decrease in vigor in all plants, chlorosis (yellowing) especially in citrus and conifers, necrosis(death) of tips and margins of leaves, delayed blooming of flowering plants, uniform yellowing andsenescence of older leaves to chlorotic canopy, stunted plants in severe cases

Phosphorus

Slow growth and stunted growth, purplish discoloration on older leaves of some plants, fewer flowers inflowering plants

Potassium

Slow growth, tip and marginal chlorosis, necrosis of older leaves, weak stem and stalks, dieback of tips of
new growth, yellowish and reddish brown conifer leaves

Calcium

Death of growing tips, abnormal dark green appearance of foliage, premature shedding of blossoms andbuds, leaf necrosis, death of meristem

Magnesium

Interveinal chlorosis of older leaves, curling of leaves upwards along margins, marginal yellowing,
yellowing of palm leaves with midrib green, necrotic older leaves

SulfurRetarded growth, small and spindly plants, light green to yellowish young leaves, necrotic leaf tips

Zinc

Mottled, interveinal chlorosis, rosetting of terminal leaves, decreased stem growth, reduced fruit bud
formation, stunted and chlorotic conifer needles, leaf drop

Iron

Interveinal chlorosis of young leaves, chlorosis of young leaves with green spots, twig dieback, stunted
and chlorotic new conifer needles, caused by high­pH calcareous soils

Manganese

Interveinal chlorosis of young leaves with green bands along veins, gradual pale green leaf coloration,
withered and scorched older leaves, frizzletop in palms

CopperStunted growth, dieback of terminal shoots in trees, wilting and eventual death of leaf tips, young leaves
turn white in monocots

Boron

Death of terminal growth, thickened, curled, wilted and chlorotic leaves, reduced flowering, cracked roots

Molybdenum

Yellow spotting of citrus, marginal scorching, undergoing of chlorosis by older then younger leaves,rolling/cupping of leaves

Chlorine

Spotting of older leaves first, delayed maturity

NickelChlorosis of young leaves, death of the meristem

IX.D.5. Plant Analysis
Collecting and analyzing samples of leaf tissue are often recommended in conjunction
with collecting and analyzing samples of soil. This requirement is particularly critical for many
species of trees and other woody plants with deep root systems. In these instances, it is difficult tosample the soil that fully represents the active root system where the plants absorb nutrients.
Also, analyzing leaf tissue helps to more accurately gauge the amount of nutrient actuallyavailable to the plant. Again, it is recommended that local advisors in ornamental horticulture be
consulted to interpret results from analyses.

IX.D.6. Nutrients in Recycled Water
Many recycled waters contain significant concentrations of nitrates and/or ammonia. A
concentration of 20­mg/L nitrate as N contains 54.4 lbs. of N (20 mg/L ´ 2.72) in an acre­ft ofwater. A seasonal irrigation of 4 acre­ft/acre equals an application rate of about 218 lbs. ofN/acre. Hence, the amount of nitrogen in recycled waters used to irrigate should be considered in

IX­18

fertilizing with N. Based on the assumption that NH3­N will be eventually oxidized to NO3­N, theconversion factor of NH3­N to NO3­N is 0.82. Plants can also take up NH3­N usually in the formof NH4 ions. In most analyses of water, the N species are reported as number of milligrams of N
per liter (e.g., NH3 as number of milligrams of N per liter) and so conversions are not needed if
the total amount of N is of interest.
Another nutrient present in recycled waters is phosphorus (P), which occurs as inorganic(mainly as Ortho­PO4) and organic species. Frequently, the total amount of P is reported. Unlike
NH4 and NO3, inorganic phosphorus is immobile in soils because it is held tightly by particles ofsoil. Organic P may be mineralized by microbes similar to the mineralization of organic N but atmuch lower concentrations.

IX.E. Other Soil­Related Problems
Boron
Boron is an essential nutrient required especially at the early stages of the plant’s growth. At
slightly higher concentrations—more than about 0.3 mg/L in the irrigation water—boron can betoxic to boron­sensitive plants, especially ornamentals (Chapter V). Boron­tolerant plants may
not be harmed at 2.0 mg/L or less. Boron is adsorbed by the oxide surfaces of particles of soil andis not readily leached and may accumulate to toxic levels in the root zone. Most recycled water in
California contains less than 0.5 mg of boron/L. In rare cases, where the soil parent material
contains boron minerals or hot springs contribute water to a wastewater treatment plant, higher
concentrations may be observed. In such situations, control at the source would be the best
remedy, as boron is not removed in wastewater treatment short of reverse osmosis.

IX. F. References
Ayers, R. S., and D. W. Westcot. 1985. Water quality for agriculture. FAO irrigation anddrainage paper 29, rev. 1. Food and Agriculture Organization of the United Nations, Rome, Italy.
California Fertilizer Association. 1998. Western Fertilizer Handbook, 2nd horticulture ed.
Interstate Publishers.
California Plant Health Association. 2002. Western Fertilizer Handbook, 9th ed. Interstate
Publishers.
Costello, L. R., E. J. Perry, N. P. Matheny, J. M. Henry, and P. M. Geisel. 2003. Abiotic
Disorders of Landscape Plants: a Diagnostic Guide. Division of Agriculture and Natural
Resources, University of California, Oakland.

IX­19

Epstein, E., and A. J. Bloom. 2004. Mineral Nutrition of Plants: Principles and Perspectives, 2nded. Sinauer Associates, Cambridge, MA.
Food and Agriculture Organization. 1997. Criteria and options for appropriate irrigation methods.
Small­Scale Irrigation for Arid Lands. FAO Development Series 2. Food and Agriculture
Organization of the United Nations, Rome, Italy.
Hanson, B., and W. Bendixson. 2004. Drip irrigation evaluated in Santa Maria strawberries.
Calif. Agric. 58:48–53.
Merhaut, D. J. 2001. Fertility management in the landscape, p. 10–13. Proceedings, University ofCalifornia–Riverside Turfgrass and Landscape Management Field Day.
Miyamoto, S. Personal communication.
Miyamoto, S. 1998. Use of acids and acidulates on alkali soils and water, p. 217–256. In A.
Wallace and R. E. Terry (ed.), Handbook of Soil Conditioners. Marcel Dekker, New York, NY.
Oster, J. D., M. J. Singer, A. Fulton, W. Richardson, and T. Prichard. 1984. Water Penetration
Problems in California Soils. Diagnoses and Solutions. Kearney Foundation of Soil Science,
Division of Agriculture and Natural Resources, University of California.
Paul, J. L., K. K. Tanji, and W. D. Anderson. 1966. Estimating soil and saturation extract
composition by a computer method. Soil Sci. Soc. Am. Proc. 30:15–17.
Rhoades, J. D. 1972. Water quality for irrigation. Soil Sci. 113:277–286.
Richards, L. D. (ed.), 1954. Diagnosis and Improvement of Saline and Alkali Soils. USDA
agricultural handbook no. 60. U.S. Department of Agriculture, Washington, DC.
Tanji, K. K. (ed.). 1990. Agricultural salinity assessment and management. American Society of
Civil Engineers manual no. 71. American Society of Civil Engineers.
Whittig, L. D., and P. Janitsky. 1963. Mechanisms of formation of Na2CO3 in soils.
Manifestations of biological conversions. J. Soil Sci. 14:322–333.

IX­20

Chapter X. Diagnosing and Solving Generaland Plant­Specific Problems
K. Tanji, A. Harivandi, L. Wu, C. Grieve, B. Sheikh, S. Grattan, and D. Shaw
X.A. Challenges of Accurate Diagnosis
X.B. Diagnostic Checklist and Strategy
X.C. General Symptoms, Diagnoses, and Potential Solutions
X.D. Problems with Turfgrasses and Lawns
X.E. Problems with Trees and Shrubs
X.F. References

Salinity­related problems encountered in irrigating landscapes with recycled water should
not be viewed in complete isolation, since associated causes may be contributing to these
problems. The quality of recycled waters used to irrigate landscapes may have broader impacts on
the plants, soils, and irrigation system (Chapter III). It can affect the performance of plants due tosalinity (osmotic) and the toxic effects of specific ions (Chapter V). It can affect the salinity,
sodicity, and permeability of the soil (Chapters IV and IX). It can also lead to small orifices in
irrigation systems such as drip emitters and sprinkler heads becoming clogged with suspended
matter and precipitated chemicals (Chapters III and VII).
This chapter gives an overview of diagnosing and solving problems that may arise whenirrigating plants in landscapes with recycled water, drawing upon the contents of previous
chapters of this literature review.

X.A. Challenges of Accurate Diagnosis
Costello et al. (2003) presents a highly informative approach to accurately diagnosing
abiotic disorders of plants in landscapes and solving those problems. Dreistadt et al. (2004)
presents a companion publication on appraising biotic problems—pests and diseases—of trees
and shrubs. In this chapter, the primary focus will be on abiotic problems.
Some problems such as stunted growth, moderate to severe foliar injury, waterlogging
and standing water, and plugging of drip systems are visually obvious. Other problems, such as
inadequate plant performance caused by insufficient irrigation or an imbalance in mineral
nutrition, are subtler and less easily discerned. A problem may be due to multiple causes,X­ 1

rendering accurate diagnosis more challenging (Costello et al. 2003). In any case, problems need
to be addressed punctually and comprehensively to avoid high maintenance costs and sustain thequality of landscapes.
Accurately diagnosing problems depends on the following (Harris, 1983):·

observing subtle differences from the norm in the appearance of the plants or of thesurrounding environment·

becoming well informed about the relevant plants, soil, climate, growing practices,pests, diseases, and their interactions·

obtaining accurate information about the recent history of affected plants, the site, theclimate, and growing practices·

using a few simple tools to diagnose the problems·

analyzing the results from testing samples of plant tissue, soil, and water to diagnose
certain problems.

A familiarity with what constitutes normal in the appearance and growth of plants and in
the environmental setting is essential for accurately diagnosing problems. Inexperienced
observers may think they have encountered a serious problem, when the supposed symptom may
merely be a plant’s normal feature, a seasonal change in its appearance, or the sign of a
nonparasitic agent (Harris, 1983). Recognizing the appearance of healthy plants at different stagesof growth and during different seasons is important to differentiate disorders from the norm. Achange in the color of leaves may indicate nutrient deficiency or waterlogging. However, theleaves of some plants may normally change color. For example, the leaves of maturing conifers
may change from green to yellow to brown before they drop and the new leaves of Chinesephotinia (Photinia serrulata) may be copper or reddish before turning green with maturity.
Certain nonnative plants chosen for a landscape based on aesthetic appeal may be grownat the limit of their tolerance to the prevailing climate, soil, and water and require special growing
practices to promote good performance. Several types of plants grown at the same site may havediffering water and other requirements, unlike monoculture systems found in agriculture. Plants
may be mechanically injured by high winds and infestations of insects, chemically injured by thedrift of herbicide or excessive salt, and thermally injured by low temperature. Table X.A.1
includes abiotic and biotic causes of injury or disease to plants (Harris, 1983).

X­ 2

Table X.A.1. Abiotic and biotic causes of injury and disease in plants (after Harris, 1983)
Causes of injury
Causes of disease
Abiotic

BioticAbiotic

Biotic

Salt

Insects

Mineral deficiencies
and excesses

Bacteria

Air pollutants

Mammals

Salt

Fungi

Herbicides

Birds

Air pollutants

Nematodes

Moisture extremes

Moisture extremes

Viruses

Temperature extremesPesticides

Higher plants

Wind

Radiation

Snow and ice
Lightning
Radiation

The conditions of a landscape’s site can significantly affect its vitality. If a site is locatednear buildings, then the soil is likely to be compacted and suffer from poor drainage. Such a site
will need to be prepared before planting to promote the healthy growth of plants subsequently
placed there. If a landscape has been graded to a moderate to severe extent, then topsoil will havebeen removed, which could lead to poor soil fertility, inadequate rooting depth due to shallow
soil, and poor drainage. If a landscape has been established on a landfill with infertile fill soils
obtained from construction sites, then the site needs to be adequately covered with topsoil of goodquality to minimize problems with poor soil fertility. The soil should be sufficiently deep tominimize the upward movement of toxic gases from the buried landfill into the root zone ofplants. If a landscape is established on a steep slope, then the soil there may be highly eroded byrainfall and irrigation without the establishment of ground cover or without the mulching of soil
to prevent such erosion and promote adequate infiltration of water into the soil.

X.B. Diagnostic Checklist and Strategy
Harris (1983) provides a detailed diagnostic checklist for diagnosing problems with trees
and woody shrubs by assessing conditions at the site—soils, plant species, cultural practices,
weather, air quality, pests, and diseases—to ascertain the following: the number of plants
affected; the species affected; the existence of a pattern related to space, if any; the occurrence ofdepressions, if any, indicating problems with frost and drainage; the amount of moisture in thesoil; any unusual color to the soil; any unusual odor emanating from the soil; and, if there is one,any recent occurrence that might account for it, such as construction, paving, excavation, or soil
filling and the location of gas, water, sewer, and septic fields. Harris (1983) delves into further
detail about examining the various affected parts of trees and woody shrubs, such as leaves,X­ 3shoots, dormant twigs, the trunk, the main branches, and the roots. He also recommends certain
tools and equipment useful for diagnosis and explains how to collect samples of plants and soils
to verify or disconfirm on­site diagnosis.
Costello et al. (2003) also outlines a similar step­by­step strategy for diagnosing
problems with not only trees and woody shrubs but with other plants as well. They point out thata systematic approach provides a thorough, accurate diagnosis that could lead to corrective
actions that are specific to the problem. The diagnostic steps that they recommend are as follows:

1. Identify the injured plant or plants. Determining the genus, the species, and, if
appropriate, the cultivar is an essential first step. Such determination will provide anunderstanding of the plant’s origin, characteristics of its growth, and its growing
requirements. Identifying the plant’s family may provide further useful information. If
you are unable to identify the plant, ask a colleague. Or submit a sample of the plant to a
local botanical garden, arboretum, nursery, or University of California Cooperative
Extension office for identification. If you inaccurately identify a plant, you may
misdiagnose a problem. What appears to be a disorder may be normal for the particularplant. Once the plant is accurately identified, refer to horticultural manuals for
information regarding the specific plant’s cultural requirements.

2. Identify symptoms. After examining the plant’s injured part or parts, list all symptoms as
thoroughly and accurately as possible. Look for discoloration, distortion, signs ofchlorosis and necrosis, and abnormal size and development. For a description of common
symptoms, see Tables X.C.1, X.C.2, and X.C.3 of this chapter.

3. Inspect the whole plant. If symptoms of injury are uniformly evident throughout, thecause is often found in the root zone, though there are some exceptions, such as
anthracnose on leaves of London plane (Platanus ´ acerifolia). If symptoms are limited
to certain areas, the cause is likely linked to the injured part or parts of the plant. Checkfor signs of delayed growth such as no new leaves or flowers; signs of infestation by
insects such as droppings or cast skins; and signs of disease, such as foaming caused bybacteria.

4. Inspect the site. Search for conditions that may be contributing to injury. Evaluate thesoil’s physical and chemical properties, which may require a laboratory analysis ofX­ 4samples. Try to identify all of the factors that may have contributed to the identified
symptoms. Check the terrain for slopes; the soil for its drainage, textural layers, andcompacted zones; irrigation of the area and its scheduling; the existence of wet or dry
areas; exposure to wind, heat, and cold; limitations to the development of plants imposedby the infrastructure or nearby buildings, walkways, and such; and adjacent vegetationthat could be contributing to injury by shading or by competing for water and minerals.

5. Look for patterns. Are symptoms evident throughout the plant, scattered, on one side
only, or on old or young foliage? Is one plant affected, or are many? Is one species
affected or several? Lack of soil oxygen due to overwatering, for example, is likely toaffect all of the species in a landscape, whereas diseases are more likely to affect a single
species or only species within one family. Do the symptoms form a pattern in thelandscape that correlate to topography? Frost, for instance, may more adversely affectplants in low areas of the landscape where cold air accumulates.

6. Investigate the history of the landscape’s management: contact a person knowledgeable
about the site and its plants. Collect as much information as possible. Find out if any
records of the landscape’s installation and maintenance exist. Bear in mind that available
information may not be comprehensive or, in some cases, such as when negligencecontributed to injury, inaccurate. Obtain, if possible, such details as the following: thedate when the site was planted; the size or age of the plants at the outset; any occurrenceof previous problems and any similarity to current problems; the irrigation, fertilization,soil amendment, mulching, pruning, and pest management practices of the site; the site’ssource of water; the existence of any previous analyses of water quality; the use, if any,of plant growth regulators or other chemicals; the occurrence of construction in the area,
if any; the use of deicing salts on adjacent walkways or roadways, if any; and any otherchanges that may affect the plants in the landscape.

7. Integrate all collected information. Once information about the plant and site has beengathered, thoroughly and comprehensively identify possible causes of the problem. Zeroin on the most likely causes, listing reasons that support each diagnosis.
8. Test for likely causes. To arrive at an accurate diagnosis, samples of soil, water or tissue
from the plant may need to be obtained and submitted to a horticultural or agricultural

X­ 5Table X.C.1. Problem description, diagnosis, and potential solution: general aspects (after California Plant Health
Association, 2002; Harivandi et al., 1992; and Costello et al., 2003).
Symptom or condition

Diagnosis

Potential solution

Plants showing signs of water stress,e.g., wilting

Insufficient irrigation

Increase duration and/or rate ofirrigation to satisfy plantevapotranspiration

Excessive soil salinity

Increase leaching fraction to leach out
excessive soil salts

Excessive water salinity

Replace plants with more salt­tolerant
ones, blend with less saline water

Plants sensitive to specific ionsReplace plants with more­tolerant
plants, change from sprinkler to drip
irrigation to prevent foliar wetting,reposition sprinkler heads to avoid
spraying foliage

Herbicide damage

Reduce and/or eliminate applicationsof herbicides and minimize drift

High air temperature

Replace plants with more heat­
tolerant plants

Excessive exposure to sunlight

Replace shade­loving plants withmore sunlight­tolerant plants

Poor uniformity of water application
system

Improve uniformity with change inspacing of lateral lines and sprinkler
heads, adjustments in water pressure

Variability in soil texture and water
holding capacity

Adjust sprinklers and nozzle heads,
install separate lines

High sodium adsorption ratio and low
electrical conductivity

Add Ca source like gypsum to water
and/or soil to increase soil
permeability

High residual sodium carbonate(RSC)

Inject acid into irrigation water or add
gypsum to soil to reduce RSC

Soil compaction

Reduce machine traffic and tillage
when soils are moist, use soil aerators

Soil stratification

Deep tillage to break up stratified
layersSlow water penetration

Decrease irrigation application rate
and/or duration

Runoff on steep slopes

Improve infiltration rates with dense
vegetation such as ground cover andmulching

Sediments

Install sand filtration system for drip
irrigation

Water chemistry (carbonate
deposition)

Inject acids into water supply line to
reduce calcium carbonate deposits

Microbial slimes and iron precipitates

Inject biocides into water supply line tosuppress microbial growth

Plants suffering foliar injury/damage

Presence of dry or wet areas

Excessive ponding, waterlogging

Excessive soil runoff

Plugging of drip emitters and low
volume sprinklers

laboratory for analysis. This task is particularly essential if nutrient deficiencies, specificion toxicities, salts, or pH­related problems are suspected. With results in hand, create alist of likely causes. If an abiotic disorder is suspected, refer to such sources as Costello etal. (2003). If a disorder caused by an organism, such as an insect, fungus, or bacterium, issuspected, refer to such sources as Dreistadt et al. (2004). Check to see if the descriptionof the problem in the reference corroborates your tentative diagnosis. If not, then the listX­ 6

of most likely causes will need to be reevaluated, perhaps with the help of specialists.
According to Costello (2003), hallmarks of a good diagnostician include an educational
background in plant biology and horticulture, field experience for a better understandingof the conditions of the site and growing practices, and experience with use of diagnostic
techniques. Bear in mind that multiple causes may be involved. Or entirely new problems
may arise that occurs more commonly with biotic disorders than with abiotic disorders.
Some disorders cannot be remedied, which though unfortunate from a management
perspective, at least precludes unnecessary, inappropriate, or ineffective actions.

X.C. General Symptoms, Diagnoses, and Potential Solutions
Table X.C.1 contains a summary of plant symptoms or other problems, diagnoses, andpotential solutions generally applicable to plants in landscapes. Common plant symptoms cited
include plants suffering water stress and foliar injury. Other related irrigation problems include
the presence of wet or dry spots, excessive ponding and waterlogging, excessive soil runoff, andplugging of drip emitters and low­volume sprinklers. Potential solutions are suggested for eachproblem. The information can be used in conjunction with the diagnostic steps recommended by
Costello et al. (2003) and Harris (1983). The module in the compact disk on “Solve a Problem
Related to Plants, Water or Soil” contains numerous images accompanied with a text on
symptoms, diagnosis, and recommended solutions.

X.D. Problems with Turfgrasses and Lawns
By far the largest amount of recycled water used in California’s south coast region goesto irrigate golf courses, sport fields and lawns in playgrounds, school yards, greenbelts, andindustrial parks. Table X.C.2 contains a summary of problems with turfgrasses and lawns, as wellas their potential causes and solutions. The first group of problems cited is related to salinity andto irrigation and drainage. The second group of problems cited is related to the mineral nutritionof turfgrasses and lawns.

X.E. Problems with Trees and Shrubs
After turfgrasses and lawns, trees on golf fairways, in playgrounds, school yards,
industrial parks, and roadways are the biggest recipients of recycled irrigation water. Trees andwoody shrubs in landscapes adjacent to buildings, roadways, walkways, greenbelts, and the like
are

also

X­ 7

Table X.C.2. Problem description, diagnosis and potential solution: turfgrasses and lawns (after Beard, 2002;
Merhaut, 2001; Harivandi, 2002; and Harivandi et al., 1992).
Symptom or condition

Diagnosis

Potential solution

Tip burning, bluish­green leaves

Excess salinity in water and/or soil

Increase leaching fraction and/or
replace with more salt­tolerant turf,
blend with less saline water

Extensive vegetative desiccation

Insufficient irrigation

Increase duration and/or rate of water
application

Localized dry and wet spots

Nonuniform irrigation patterns

Improve uniformity of application

Surface soil compaction

Carry out soil core aeration, addorganic matter such as compost

Subsoil impermeable layers

Improve drainage with installation of
subsurface drainage

Water­repellent sand­based turf

Add wetting agents and clay colloids
like zeolites

Difficulties in seed germination andearly seedling growth

Excessive salinity in water and/or soils

Select and plant more salt­tolerant
turf, blend saline water with less saline
water or conduct reclamation leaching
before seeding

Spotty bare spots with salt crust

Excessive salinity in soils

Conduct localized leaching to removesalts

Spotty bare spots with no salt crust

Excessive sodicity in soils

Add calcium amendments like gypsum
to soil and/or water

Bare spots with dispersed organic
matterExcessive RSC in water

Inject acids to source water, add
calcium amendment to soil or water

Uniform yellowing and senescence ofolder leaves

Nitrogen deficiency

Apply N fertilizers, improve drainage,
aerate to relieve compaction

Uniform chlorosis of younger andolder leaves, leaf tips necrotic, stunted
growthSulfur deficiency

Rare but resembles N deficiency
symptoms. Apply S­containing
fertilizer.

Yellowing of younger leaves and newleaves white or necrotic in severe
cases

Iron deficiency

Add acid­forming materials tocalcareous soils, apply iron chelate orother iron fertilizers

Dark green discoloration of older
leavesPhosphorus deficiency

Apply P fertilizer appropriately
broadcasting or by injection into watersupply; P will tend to precipitate incalcareous soils and high­bicarbonate
watersDrooping of leaves, chlorosis, and leaf
rolling

Potassium deficiency

Broadcast K fertilizer, incorporate inground as much as possible

New leaves chlorotic, deformed, andstunted or necrotic

Calcium deficiency

Rare in alkaline and neutral soils

Interveinal chlorosis of older leaves or
necrosis of older leaves

Magnesium deficiency

Rare in alkaline and neutral soils

irrigated with recycled waters. Presented in Table X.C.3 is a summary of problems with trees andwoody shrubs, as well as their potential causes and solutions. The first group of problems cited isrelated to salinity, specific ions, and irrigation and drainage. The second group of problems citedis related to the mineral nutrition of trees and woody shrubs.

X­ 8Table X.C.3. Problem description, diagnosis and potential solution: trees and shrubs (after Costello et al., 2003;
Dreistadt et al., 2004; Harris, 1983; and Harris et al., 2004).
Symptom or condition

Diagnosis

Stunted growth, chlorosis, leaf tip
burn, marginal burn, defoliation, death

Excess salinity in soil and/or water

Stunted growth, chlorosis, necrosis,
black salt crust on soil surface, water
ponding
Stunted growth, chlorosis, necrosis,
white salt crust on soil surface

Excess sodicity in soil and/or water
Excess salts and sodicity

Stunted growth, necrosis of leaf tips
and margins, bronzing, leaf drop

Excess chloride in water and/or soil

Yellowing of leaf tip, necrosis of leaf
margins and between veins

Excess boron in water and/or soil

Mottled and interveinal chlorosis
leaves, burning of growing tips

Excess sodium in water and/or soil

Yellowing foliage and leaf drop,
damage to buds, limbs and shoots,
root crown diseases
Excessive growth and succulent
tissue, dark green foliar margins

Potential solution
Leach soil, increase leaching fraction,
select more salt­tolerant plants,
correct drainage problem, blend withless saline water
Add gypsum, acid or acid­forming
materials to soil or water, and leach
Leach salts, add gypsum, acid, oracid­forming materials
Leach or increase leaching fraction,correct drainage problem, reduce
foliar wetting, select more chloride­
tolerant plants
Avoid foliar wetting, leach soil, selectboron­tolerant plants
Avoid foliar wetting, leach soils, plant
more sodium­tolerant plants, injectacid into water, apply gypsum to soil

Excess irrigation and/or poor drainage

Decrease irrigation, improve drainage
and aeration

Excess N fertilization

Decrease N fertilization
Apply N fertilizer; nutrient deficiency inwoody plants is usually not caused by
deficiency of soil nutrients except forcontainer plants. Sometimes N
deficiency confused with symptoms
caused by restricted root growth
Add P fertilizer. P deficiency in woody
plants is normally rare; symptoms may
look like herbicide damage
Apply K fertilizer, K deficiency is rareamong conifers and broadleaf species
but occurs in palms and fruit and nut
trees; P deficiency may resemble leaf
spot damage from sucking insects andcertain pre­emergence herbicides
Noted especially in acid­loving plants
grown in calcareous soils; reduce thesoil pH with acidic amendments; apply
iron chelate and improve drainage andaeration

Uniform yellowing of leaves, lightgreen coloring, yellowish and shortneedles in conifers

Nitrogen deficiency

Bronzing of lower leaves with purple
or brown spots, dieback of needles in
conifers

Phosphorus deficiency

Leaf spotting and sparse leaf growth,older leaves yellow, marginal necrosis
along leaflets, necrosis at needle tips
in conifers

Potassium deficiency

New foliage yellowish and undersizedwith green veins, causes curling andburning in palms, stunted andchlorotic needle tips in conifers

Iron and/or manganese deficiency

Uniformly yellow and stunted new
growth may turn purplish and die,small leaves, branches and needles
extremely stunted, and die back ofterminals in conifers

Zinc deficiency

Apply zinc chelates or zinc sulfate;
may be confused with systemic
herbicide (glyphosate) damage

Yellowing of leaves, premature leaf
drop, wilting, stunted growth

Poor aeration or soil aeration deficit

Improve drainage, reduce excess
irrigation, conduct appropriate site
preparation before planting

Low­temperature injury

Select more cold­tolerant trees andshrubs. Protect sensitive plants during
periods of low temperature

Sunburn or scalding damage

Select more tolerant plants, shadeplants, irrigate adequately

Wind damage

Select wind­tolerant species, provide
windbreaks

Air pollution injury

Select trees more tolerant to ozone,
sulfur dioxide, etc.

Dieback of youngest foliage, damage
to lower leaves and canopy dieback,dieback of limbs. Rapid onset of foliar
symptoms
Leaf discoloration and necrosis,
damage to bark and trunk
Trees appears to be under water
deficit, leaf necrosis and leaf drop,
tattering of leaves, fewer leaves onwindward side
Leaves or needles turn yellow tobrown, foliage dieback, stippling or
specking of leaves

X­ 9X.F. References
Beard, J. B. 2002. Turf Management for Golf Courses, 2nd ed. Ann Arbor Press, Chelsea, MI.
California Plant Health Association. 2002. Western Fertilizer Handbook, 9th ed. Interstate
Publishers.
Costello, L. R., E. J. Perry, N. P. Matheny, J. M. Henry, and P. M. Geisel. 2003. Abiotic
Disorders of Landscape Plants: a Diagnostic Guide. Division of Agriculture and Natural
Resources, University of California, Oakland.
Dreistadt, S. H., J. K. Clark, and M. J. Flint. 2004. Pests of Landscape Trees and Shrubs: an
Integrated Pest Management Guide, 2nd ed. Agriculture and Natural Resources publication.
University of California.
Harivandi, M. A. 2002. Turfgrass traffic and compaction: problems and solutions. Agriculture
and Natural Resources publication no. 8080. Division of Agriculture and Natural Resources,
University of California.
Harivandi, A., J. D. Butler, and L. Wu. 1992. Salinity and turfgrass culture, p. 207–229. In D. V.
Waddington, R. N. Carrow, and R. C. Shearman (ed.), Turfgrass. Agronomy monograph no. 32.
American Society of Agronomy, Madison, WI.
Harris, R. W. 1983. Arboriculture: Care of Trees, Shrubs, and Vines in the Landscape. Prentice
Hall, Englewood Cliffs, NJ.
Harris, R. W., J. R. Clark, and N. P. Matheny. 2004. Arboriculture: Integrated Management Of
Landscape Trees, Shrubs and Vines, 4th ed. Prentice Hall, Englewood Cliffs, NJ.
Merhaut, D. J. 2001. Fertility management in the landscape, p. 10–13. Proceedings, University ofCalifornia–Riverside Turfgrass and Landscape Management Field Day.

X­ 10

Appendix. Acronyms and Abbreviationsac = Acreac­ft = Acre­feet
AR = Application rate
B = Boron
Ca = Calcium
CaCO3 = Calcium carbonate
CaSO4•2H2O = Gypsum
CIMIS = California Irrigation Management Information System
Cl = Chloride
Cl2 = Molecular chlorine
CO3 = Carbonate
Cu = Copper
Ddw = Surface depth of drainage water
Det = Surface depth of evapotranspiration
Deto = Surface depth of reference evapotranspiration
Diw = Surface depth of irrigation water
DS = Dissolved solids (same as TDS)
dS/m = Decisiemens per meter
DU = Distribution uniformity
EC = Electrical conductivity, specific conductance
ECa = Plant­specific threshold soil salinity in electrical conductivity
ECdw = Electrical conductivity of drainage water
ECe = Electrical conductivity of extract of saturated soil paste
ECiw = Electrical conductivity of irrigation water
ECrw = Electrical conductivity of rainwater
ECsw = Electrical conductivity of soil water at field capacity soil moisture
ECw = Electrical conductivity of water
ECF = Evapoconcentration factor
ESP = Exchangeable sodium percentage of soil cation exchange capacity
ET = Evapotranspiration
ETc = Crop (plant) evapotranspirationAA­1

ETo = Reference evapotranspiration
FAO = Food and Agriculture Organization of the United Nations
Fe = Iron
HCO3 = Bicarbonate
IE = Irrigation efficiency
K = Potassium
Kc = Crop coefficient
Kd = Plant density coefficient
KL = Landscape coefficient
Kmc = Plant microclimate coefficient
Ks = Species coefficient
LF = Leaching fraction
LR = Leaching requirement
meq/L = Milliequivalents per liter
Mg = Magnesium
mg/L = Milligrams per liter
mmol/L = Millimoles per liter
Mn = Manganese
mS/cm = Millisiemens per centimeter
N = Nitrogen
Na = Sodium
NH3 = Ammonia
NH4 = Ammonium
NO3 = Nitrate
P = Phosphorus
PAM = Polyacrylamide
pHs = pH of saturated soil paste
PO4 = Phosphate
ppb = Parts per billion
ppm = Parts per million
RSC = Residual sodium carbonate
S = Sulfur
SAR = Sodium adsorption ratioAA­2

SARadj = Adjusted sodium adsorption ratio
SO4 = Sulfate
TDS = Total dissolved solids
WATSUIT = Water Suitability Determination Model
Zn = Zinc

AA­3

Appendix. Conversion Factors
Table of conversion factors for SI and non­SI units
To convert Column 1
into Column 2,
multiply by

Column 1
SI unit

2.47

Lengthkilometer, km
meter, mmillimeter, mm
centimeter, cm
Area
hectare, ha

247

sq. kilometer, km2

0.621
3.28
0.00394
0.394

2Column 2
Non­SI unit

To convert Column 2
into Column 1,
multiply by

mile, mifoot, ftinch, in.
inch, in.

1.609
0.305
25.4
2.54

acre, ac0.405

acre, ac0.00405

acre, ac

4,047

sq. foot, ft2

0.09290.000247

sq. meter, m

10.76

sq. meter, m2
Volume0.00973

cubic meter, m3acre­inch, ac­in.

102.8

0.00081

cubic meter, m3acre­foot, ac­ft

1,234

0.81
0.265

cubic kilometer, km3
liter, L
Massgram, gkilogram, kg
kilogram, kg
ton, tYield
kg/hatonne/hatonne/haRatemillions of acre­feet, maf
gallon, gal

1.234
3.785

pound, lb.
ton (U.S.), tonpound, lb.
ton (U.S.), ton

454
907
0.454
0.907

pounds per acre, lb/ac
pounds per acre, lb/ac
U.S. tons per acre, ton/ac

1.12
0.001120.00220.0011
2.205
1.102
0.893
893

264 ´ 10−6
0.107
2.24
9.9
10

m3/dayL/ham/s
Pressure
megapascal, MPa
megapascal, MPa

0.02090.000145
0.00987

pascal, Pa
pascal, Pa
kilopascal, kPa

millions of gallons per day,mgd
gallons per acre, gal/ac
miles per hour, mi/h

3,785
9.35
0.447

atmosphere, atm
bar

0.101
0.1

pounds per sq. foot, lb./ft
pounds per sq. inch, psi
atmosphere, atm

CT­1

2

47.9
6,900
101.3

To convert Column
1
into Column 2,
multiply by

Column 1
SI unitColumn 2
Non­SI unit

To convert Column
2
into Column 1,
multiply by

10
1
0.001
1

Electrical conductivity
siemen/m, S/mdecisiemen/m, dS/m
decisiemen/m, dS/m
millisiemen/cm, mS/cm
Water measurement

millimho/cm, mmho/cm
millimho/cm, mmho/cm
micromho/cm, umho/cm
micromho/cm, umho/cm

0.1
1
1,000
1

0.00973m3

ac­in.

102.8

0.00981

3

m /h

cfs

101.9

35.59

m3/s

cfs

0.028

4.4
8.11

3

m /h
ha­m

gal/min
ac­ft

0.227
0.12330.0008197.28
0.0821

m3
ha­m
ha­cm

ac­ft
ac­in
ac­ft

1234
0.010312.33

0.000328

m3/ha

ac­ft/ac

3,047

3.279
0.264

m3/m2
L/min
Concentration
centimole/kg
g/kg
mg/kg
mg/L
μg/kg
μg/L
g/L
g/L

ac­ft/ac
gpm

0.305
3.788

meq/100 g%
ppm (weight basis)ppm (volume basis)ppb (weight basis)ppb (volume basis)oz/gallb./gal

1
10
1
1
1
1
7.489
119.8

1
0.1
1
1
1
1
0.13350.00835

CT­2

Table for Chemical Conversion Units
To convert Column
1
into Column 2,
multiply by
0.04990.08230.04350.02560.01640.033
0.02820.02080.01610.0554

To convert Column
1
into Column 2,
multiply by
0.025
0.0411
0.04350.02560.01640.01670.02820.01040.01610.0554

Column 1
Milligrams/liter

Column 2
Milliequivalents/liter

mg/L Ca
mg/L Mg
mg/L Na
mg/L K
mg/L HCO3
mg/L CO3
mg/L Cl
mg/L SO4
mg/L NO3
mg/L NH4

meq/L Cameq/L Mg
meq/L Na
meq/L K
meq/L HCO3
meq/L CO3
meq/L Cl
meq/L SO4
meq/L NO3
meq/L NH4

Column 1
Milligrams/liter

Column 2
Millimoles/liter

mg/L Ca
mg/L Mg
mg/L Na
mg/L K
mg/L HCO3
mg/L CO3
mg/L Cl
mg/L SO4
mg/L NO3
mg/L NH4

mmol/L Ca
mmol/L Mg
mmol/L Na
mmol/L K
mmol/L HCO3
mmol/L CO3
mmol/L Cl
mmol/L SO4
mmol/L NO3
mmol/L NH4CT­3

To convert Column
2
into Column 1,
multiply by
20.04
12.15
22.99
39.1
61.02
30
35.45
48.03
62
18.04

To convert Column
2
into Column 1,
multiply by
40.08
24.31
22.99
39.1
61.02
60
35.45
97.06
62.01
18.04

Other Useful Conversions
mg/L TDS = EC dS/m ´ 640
mg/L TDS = EC dS/m ´ 735 (preferred for Colorado River water)
mg/L TDS = EC dS/m ´ 800 (for saline waters)
lbs/ac­ft TDS = mg/L TDS ´ 2.72
tons/ac­ft TDS = mg/L TDS ´ 0.00136
atm osmotic pressure = EC dS/m ´ 0.36
1 ac = 43,560 sq. ft
1 mi = 5,280 ft
1 ac­ft soil = 4 million lbs. (approx.)
1 ton/ac = 20.8 g/sq. ft
1 g/sq. ft = 96 lbs./ac
1 lb./ac = 0.0104 g/sq. ft
1 cu. ft = 7.48 gals
1 gal = 8.345 lbs.
1 cfs = 448.8 gpm
1 cfs/24 h = 1.98 ac­ft
1 mgd = 3.07 ac­ft/24 h
1 mgd = 1.547 cu ft/s
1 mgd = 694.4 gpm
1 ac­ft = 325,851 gals
1 atm = 14.7 psi
1 psi = 14.22 kg/sq. cm
1 bar = 14.5 psi
1 bar = 1,023 cm of waterCT­4

Table for Soil Water

Soil texture

Sand
Loamy sand
Sandy loam
Loam
Silt loam
Sandy clay loam
Sandy clay
Clay loam
Silty clay loam
Silty clay
Clay

Field capacity or
water holding
capacity(inches of water per ft
of soil)
1.2
1.9
2.5
3.2
3.6
3.5
3.4
3.8
4.3
4.8
4.8

Available soil
moisture(inches of water per ft
of soil)
0.7
1.1
1.4
1.8
1.8
1.3
1.6
1.7
1.9
2.4
2.2

CT­5

Appendix. Glossary
Abiotic. Pertaining to processes that involve physical or chemical mechanisms not influenced byliving organisms; nonliving.
Abiotic disorder. A disease caused by factors other than a pathogen such as adverse nevironmental
conditions or inappropriate cultural practices.
Abscission. The dropping off of a leaf, fruit, or flower.
Acid soil. Soil for which the pH is less than 7.0.
Acidic. Having a high concentration of hydrogen ions; pH less than 7.0.
Acre­foot. Amount of water that would cover 1 acre to a depth of 1 ft; equivalent to 43,560 cu. ft or
325,851 gal (1 acre­ft of water is considered enough water to meet the needs of two families of four
for a year).
Action level. The level of a contaminant in drinking water that is considered not to pose a significant
health risk to people ingesting that water on a daily basis. Action levels (ALs) are health­based
advisory levels established by DHS for chemicals in drinking water that lack maximum contaminantlevels (MCLs).
Activated sludge process. A treatment process that removes (by biological assimilation anddecomposition) organic matter from wastewater by using a biological floc in an aerobic environment.
Adsorption. The combination of physical and chemical processes by which atoms, molecules, or ionsbind to the surfaces of solids.
Adsorption complex. Collection of various organic and inorganic substances in soil that are capableof adsorbing ions and molecules.
Advanced wastewater treatment. Additional treatment provided to remove suspended and dissolved
substances after conventional secondary treatment. Often this term is used to mean additional
treatment after tertiary filtration and disinfection treatment for the purpose of further removing
contaminants of public health or other water quality concern. This process may include membrane
filtration and advanced oxidation.
Aerobic. Occurring in the presence of molecular oxygen, as in certain chemical or biochemical
processes (for example, aerobic respiration).
Aggregation. The process whereby primary soil particles (sand, silt, and clay) are bound together,usually by natural forces and substances derived from root exudates and microbial activity.
Agricultural drainage. (1) The process of directing excess water away from root zones by natural or
artificial means, such as by using a system of drains placed below ground surface level; also calledsubsurface drainage. (2) The water drained away from irrigated farmland.
Agronomy. The theory and practice of crop production and soil management.

GL­1Alkali soil. Soil in which sodium is the primary cation and is present in large enough quantities toadversely affect plant growth; a soil with a pH of 8.5 or higher and with exchangeable sodium
percentage greater than 15%; now called sodic soil.
Alkaline. Having a high concentration of hydroxyl ions (OH–); pH greater than 7.0.
Alkaline soil. Soil for which the pH exceeds 7.
Alkalinity. The capacity of water to neutralize acids, a property resulting from the presence ofcarbonates, bicarbonates, hydroxides, and occasionally of borates, silicates, and phosphates.
Expressed in milligrams of equivalent calcium carbonate per liter.
Allowable depletion. That part of soil water stored in the plant root zone managed for use by plants,
usually expressed as equivalent depth of water in inches (acre­inches per acre, or inches).
Amendment. Any material such as gypsum, fertilizer, and soil conditioners added to water and soils
to improve soil properties.
Ammonia. A form of nitrogen gas, highly soluble in water and extremely toxic to aquatic organisms.
At alkaline pH values, ammonia exists as ammonium ion in waters.
Ammonium. An inorganic ion formed from the microbial oxidation of organic nitrogen. This cation
may be adsorbed to soil exchange complex.
Anaerobic. Occurring in the absence of molecular oxygen, as in certain biochemical processes.
Angiosperm. A plant that produces seeds inside an enlarged ovary, which at maturity is called a fruit(synonymous with the term flowering plant.)
Anions. Negatively charged ions such as chloride, sulfate, bicarbonate, carbonate, and nitrate.
Annual. A plant that germinates, flowers, fruits, and dies within a year.
Anoxia. The condition of being without oxygen or of receiving a reduced supply of oxygen (e.g.,
tissues within a plant).
Anoxic environment. An environment without oxygen.
Apical meristem. The tissues at the tip of roots and shoots where cells divide, giving rise to new
growth.
Application efficiency (Ea). The ratio of the average depth of irrigation water infiltrated and stored in
the root zone to the average depth of irrigation water applied, expressed as a percentage.
Application rate. Rate that water is applied to a given area. Usually expressed in units of depth pertime such as inches per hour.
Aquifer. A geologic formation that holds and yields useable amounts of water. Aquifers can beclassified as confined or unconfined.

GL­2

Arid. A term describing a climate or region in which precipitation is so deficient in quantity or occurs
so infrequently that intensive agricultural production is not possible without irrigation.
Artificial recharge. (1) The addition of surface water to a groundwater reservoir by human activity,
such as putting surface water into a spreading basin. (2) The designed (as per human activities as
opposed to the natural or incidental) replenishment of groundwater storage from surface watersupplies such as irrigation or induced infiltration from streams or wells.
Available soil water. (See available water capacity.)
Available water. The portion of water in a soil that can be readily absorbed by plant roots.
Considered by most workers to be that water held in the soil against a pressure of up to approximately
15 bars.
Available water capacity (AWC). The portion of soil water that can be readily absorbed by plantroots of most crops, expressed in millimeters of water per millimeter of soil (inches per inch, inches
per foot, or total inches) for a specific soil depth. It is the amount of water stored in the soil between
field capacity (FC) and permanent wilting point (WP). It is typically adjusted for salinity (electricalconductivity) and rock fragment content. Also called available water holding capacity (AWHC) or
available soil water.
Average annual precipitation. The long­term or historic arithmetic mean of annual precipitation(rain, snow, and dew) received by an area.
Average daily use rate. Calculated or measured water used by plants in 1 day throughevapotranspiration, expressed as an equivalent depth in millimeters per day (inches per day).
Backflow. (1) The backing up of water through a conduit or channel in the direction opposite tonormal flow. (2) The undesirable flow of water from a plumbing system back into the community
potable water supply. (3) A reverse flow condition created by a difference in water pressures thatcauses water to flow back into the distribution pipes of a drinking water supply from any source otherthan the intended one. Backflow prevention assemblies prevent contamination and are required bycity and state laws. Also referred to as back siphonage.
Bacteria (singular: bacterium). (1) Microscopic one­celled organisms, which live everywhere andperform a variety of functions. While decomposing organic matter in water, bacteria can greatly
reduce the amount of oxygen in the water. They also can make water unsafe to drink. (2) Microscopic
unicellular organisms, typically spherical, rodlike, or spiral and threadlike in shape, often clumped
into colonies. Some bacteria cause disease, while others perform an essential role in nature in therecycling of materials, for example, decomposing organic matter into a form available for reuse byplants. Some forms of bacteria are used to stabilize organic wastes in wastewater treatment plants, oilspills, or other pollutants. Disease­causing forms of bacteria are termed “pathogenic.”
Bacterium (plural: bacteria). A microscopic, single­celled organism that does not produce
chlorophyll. Most bacteria obtain nitrogen and energy from organic matter. Some bacteria cause plant
and animal diseases.
Bare­root plant. A plant grown in the open ground and then lifted, without soil around its roots, forreplanting elsewhere.

GL­3

Basic intake rate. Rate at which water percolates into soil after infiltration has decreased to a low
and nearly constant value.
Beneficial use (of water). A use of water resulting in appreciable gain or benefit to the user,
consistent with state law, which varies from one state to another. In California, beneficial uses ofwaters of the state that may be protected against quality degradation include, but are not necessarily
limited to, “domestic, municipal, agricultural and industrial supply; power generation; recreation;
aesthetic enjoyment; navigation; and preservation and enhancement of fish, wildlife, and otheraquatic resources or preserves.” (Water Code, Section 13050(f)).
Best management practices (BMP). (1) A generally accepted practice for some aspect of natural
resources management to protect or achieve the best use of the resources, such as water conservation
measures, drainage management measures, or erosion control measures. Typically incorporates
conservation criteria. (2) A set of field activities that provide the most effective means for reducing
pollution from a nonpoint source.
Biochemical oxygen demand (BOD). (1) A measure of the quantity of dissolved oxygen, in
milligrams per liter, necessary for the decomposition of organic matter by microorganisms, such asbacteria. (2) A measure of the amount of oxygen removed from aquatic environments by aerobic
microorganisms for their metabolic requirements. Measurement of BOD is used to determine thelevel of organic pollution of a stream or lake. The greater the BOD, the greater the degree of waterpollution. Also referred to as biological oxygen demand.
Biodegradation. The metabolic breakdown of materials into simpler components by livingorganisms. A more specific form of biotransformation.
Biofouling. The gradual accumulation of waterborne organisms (as bacteria and protozoa) on thesurfaces of engineering structures in water that contributes to corrosion of the structures and to adecrease in the efficiency of moving parts. Biofouling contributes also to the clogging of membranes
and filters.
Biogas. Methane gas produced during the anaerobic decomposition of the remains of plants or animal
wastes by bacteria.
Biological oxidation. Decomposition of complex organic materials by microorganisms. Occurs in theself­purification of water bodies and in activated sludge wastewater treatment processes.
Biological wastewater treatment. The use of bacteria to degrade and decompose organic materials
in wastewater.
Biosolids. A nutrient­rich organic material that is a by­product or waste resulting from the treatmentof wastewater. Biosolids contain nitrogen and phosphorus along with other supplementary nutrientsin smaller doses, such as potassium, sulfur, magnesium, calcium, copper, and zinc. Soil that is lacking
in these substances can be reclaimed with biosolid use. The application of biosolids to land improves
soil properties and plant productivity and reduces dependence on inorganic fertilizers. The terms
biosolids, sludge, and wastewater sludge can be used interchangeably.
Biotic. Pertaining to living organisms; alive.

GL­4Black alkali soil. A soil with a pH of 8.5 or higher or with an exchangeable sodium percentage
greater than 15%. Dissolved organic matter may be deposited on the soil surface as soil water
evaporates (now known as sodic soil).
Blackwater. Water that contains animal, human, or food wastes; wastewater from toilet, latrine, andagua privy flushing and sinks used for food preparation. Compare to graywater.
Blade. The flat, expanded portion of a leaf or petal.
Blending. The mixing or combination of one water source with another, typically a finished source ofwater with raw water to reuse water while still satisfying water quality standards, for example, mixingof product water from a desalting plant with conventional water to obtain a desired dissolved­solid
content or mixing brine effluents with wastewater treatment plant effluents in order to reduce
evaporation pond size.
BOD. See biochemical oxygen demand (biological oxygen demand).
BOD5. The amount of dissolved oxygen consumed in 5 days by biological processes breaking downorganic matter. This is the common standard of measurement of BOD. Also see biochemical oxygen
demand (BOD).
Brackish water. Water containing dissolved minerals in amounts that exceed normally acceptable
standards for municipal, domestic, and irrigation uses but that are less than the amounts found inseawater. Typically, water containing from 1,000 to 10,000 mg of dissolved solids/L.
Bubbler irrigation. The application of water to flood the soil surface using a small stream orfountain. The discharge rates for point­source bubbler emitters are greater than for drip or subsurface
emitters but are generally less than 225 L/h (1 gpm). A small basin is usually required to contain orcontrol the water.
Bulb. In horticulture, the term “bulb” is used for plants that produce their leaves and flowers directlyfrom an underground storage organ.
Bulk density. The mass of dry soil per unit volume, expressed as grams per cubic centimeter.
Calcareous soil. Soil containing sufficient free CaCO3 to effervesce visibly when treated with cold
0.1 M hydrochloric acid.
Calcium ion. A positively charged inorganic ion that contributes to the hardness of water; forms
calcite (CaCO3) and gypsum (CaSO4∙2H2O).
Carbon filtration. The passage of treated wastewater or domestic water supplies through activatedcharcoal to remove low concentrations of dissolved chemicals.
Cations. Positively charged ions such as calcium, sodium, magnesium, potassium, and hydrogen.
Cation exchange capacity (CEC). The sum of exchangeable cations (usually Ca, Mg, K, Na, Al, andH) that negatively charged soil constituents (clay and organic matter) can adsorb at a specific pH,
usually expressed in centimoles of charge per kilogram of soil (cmolc/kg), millimoles per charge perkilogram (mmolc/kilogram), or milliequivalents per 100 g of soil at neutrality (pH = 7.0) (meq/100 g).

GL­5Centrifugal pump. Pump consisting of rotating vanes (impeller) enclosed in a housing and used to
impart energy to a fluid through centrifugal force.
cfs (cubic feet per second). A unit of measurement of flowing liquid equal to a rate of 1 cu. ft/s pasta given section. A rate of flow equivalent to 448.83 gal/min. Also called second­foot. Also written as
C.F.S. and cfs.
Chaparral. Low­growing, woody vegetation composed of rigidly branched shrubs that have small,
hard leaves and extensive roots. Plant cover is nearly 100%, and leaf area index is twice that of desert
scrub. The shrubs within chaparral typically are 1 to 3 m in height.
Check valve. A type of backflow preventer.
Chelates. Certain organic chemicals known as chelating agents forming ring compounds with a metal
ion like iron such as EDTA (ethylenediaminetetraacetic acid).
Chemical oxygen demand (COD). (1) A measure of the chemically oxidizable material in water,which provides an approximation of the amount of organic and inorganic oxygen reducing materialpresent. The determined value may correlate with biochemical oxygen demand (BOD) or withcarbonaceous organic pollution from wastewater or industrial wastes. Nonbiodegradable andrecalcitrant (slowly degrading) compounds, which are not detected by the test for BOD, are includedin this measurement.
Chemical weathering. The breakdown of rocks and minerals due to the presence of water and othercomponents in the soil solution.
Chemigation. Application of chemicals to plants through an irrigation system by mixing them with
the irrigation water.
Chlorination. The application of chlorine or one of its compounds to water or wastewater, often for
disinfection or oxidation purposes.
Chlorine residual. The concentration of chlorine remaining in water or wastewater at the end of a
specified contact period that will react chemically and biologically. May be present as either
combined or free chlorine or both.
Chlorophyll. The green plant pigments that absorb light energy in the process of photosynthesis.
Chlorosis. Yellowing of green portions of a plant, particularly between the leaves.
Christiansen’s uniformity coefficient. A measure of the uniformity of irrigation water application.
The average depth of irrigation water infiltrated minus the average absolute deviation from this depth,
all divided by the average depth infiltrated.
Clarification. A process or combination of processes where the primary purpose is to reduce theconcentration of suspended matter in a liquid.
Clarifier. A device or tank in which wastewater is held to allow the settling of particulate matter.
Coagulant. (1) An agent that causes a liquid or solid to coagulate. (2) A chemical compound, such as
Alum (aluminum sulfate), used to produce coagulation.
GL­6

Coagulation. The process of destabilization and initial aggregation of colloidal and finely divided
suspended matter by the addition of a floc­forming chemical (coagulant) or by biological processes.
Coliform (bacteria). (1) A group of bacteria (Colon bacilli) predominantly inhabiting the intestinesof humans or animals but also found in soil. While typically harmless themselves, coliform bacteria
are commonly used as indicators of the possible presence of pathogenic organisms or fecal material.
Generally reported as bacterial colonies per 100 mL of sample.
Coliform count. Number of coliforms present in a sample of water (usually reported per 100 mL).
Coliform index. An index of the bacteriological quality of water, based on a count of the numbers of
coliform bacteria.
Coliforms. Bacteria that colonize the gastrointestinal tracts of mammals and are present in fecal
material, among other sources. Coliforms are used as indicator organisms in testing water for
microbial contamination.
Collector sewers. Pipes used to collect and carry wastewater from individual sources to aninterceptor sewer that will carry it to a treatment facility.
Community. (1) Public at large including, but not limited to, local ethnic groups, political or social or
economic groups, environmental justice advocates, and environmentalists. (2) A group of plants andanimals that often occurs together within a particular habitat. The group can be described by thepresence of one or more characteristic species.
Community water system. Water treatment and conveyance facility that serves at least 25 residents
year­round or has at least 15 water connections.
Compensating emitter. Microirrigation system emitters designed to discharge water at a near­constant rate over a wide range of pressures.
Competition. Occurs when plants vie for available light, water, or nutrients.
Complete fertilizer. A fertilizer containing nitrogen, potassium, and phosphate.
Composite sample. A representative water or wastewater sample made up of individual smaller
samples taken at periodic intervals.
Conifers. Trees that bear cones. Leaves of conifers are usually needle­like or scale­like, with parallelveins, and most conifers are evergreen.
Consumptive use. The total amount of water taken up by vegetation for transpiration or building ofplant tissue, plus the unavoidable evaporation of soil moisture, snow, and intercepted precipitation
associated with vegetal growth. Synonymous with evapotranspiration.
Constituents. Any of the chemical substances found in water. Typically, measurements of such
constituents in sampled drinking water may consist of total dissolved solids (TDS), hardness(concentrations of calcium and magnesium, specifically), sodium, potassium, sulfate, chloride, nitrate,GL­7alkalinity, bicarbonate, carbonate, fluoride, arsenic, iron, manganese, copper, zinc, barium, boron, andsilica.
Contact recreation (water). Recreational activities involving a significant risk of ingestion of water,
including wading by children, swimming, water skiing, diving, and surfing.
Contaminant. (1) In a broad sense, any physical, chemical, biological, or radiological substance ormatter in the environment. (2) In more restricted usage, a substance in water of public health or
welfare concern. Also, an undesirable substance not normally present or an usually high concentrationof a naturally occurring substance in water, soil, or other environmental medium.
Contamination (water). Impairment of the quality of water sources by wastewater, industrial waste,
or other matters to a degree that creates a hazard to public health. Also, the degradation of the naturalquality of water as a result of human activities. There is no implication of any specific limits because
the degree of permissible contamination depends upon the intended end use, or uses, of the water.
Continuous flushing emitter. Microirrigation system emitter designed to continuously permit
passage of large solid particles while operating at a trickle or drip flow, thus reducing filtration
requirements.
Controlled reuse. The use of recycled water under legal and physical control or restraint even though
the recycled water may be comingled with water in a natural water body.
Conventional wastewater treatment. Well­established wastewater treatment processes typicallyconsisting of primary and secondary treatment and excluding advanced or tertiary treatment.
Cool­season turfgrass. Turfgrass species adapted to favorable growth during cool portions of thegrowing season; may become dormant or injured in hot weather.
Cooling water. Water used for cooling purposes by electric generators, steam condensers, large
machinery or products at industrial plants, and nuclear reactors. Water used for cooling purposes canbe fresh, recycled, or saline water and may be used only once or recirculated multiple times.
Crop coefficient (Kc). The ratio of the crop evapotranspiration (ETc) to its reference crop
evapotranspiration (ETo).
Crop evapotranspiration (ETc). The amount of water used by the crop in transpiration and buildingof plant tissue and that evaporated from adjacent soil or intercepted by plant foliage. It is expressed as
depth in millimeters (inches, or as the volume­depth ratio of acre­inches per acre) and can refer todaily, peak, design, monthly, or seasonal quantities. Sometimes referred to as consumptive use (CU).
Crop irrigation requirement. Quantity of water, exclusive of effective precipitation, that is needed
for crop production. It also may include water requirements for germination, frost protection,
prevention of wind erosion, leaching of salts, and plant cooling.
Crop water use. Calculated or measured water used by plants, expressed in millimeters per day(inches per day). Same as ETc except it is expressed as daily use only.
Cross­connection. A physical connection between two water systems, typically between a potablewater system and any source or system of water or other substance that is not approved for drinking

GL­8Crown. The base of an herbaceous perennial, where stem and root meet and from which fresh shoots
and roots arise. Also, the topmost limbs on a tree or shrub.
Cultivar. A garden variety of a plant found in the wild but which does not breed true from seed,instead being maintained in cultivation by vegetative propagation.
Cumulative intake. The depth of water infiltrated into the soil from the time of initial water
application to the specified elapsed time.
Deciduous plant. A plant that sheds all its leaves each year, typically in the autumn.
Deep percolation. Water that moves downward through the soil profile below the root zone andcannot be used by plants.
Deficit irrigation. An irrigation water management alternative where the soil in the plant root zone is
not refilled to field capacity in all or part of the field.
Denitrification. The biological conversion of nitrate or nitrite to gaseous N2 or N2O.
Desalting (or desalination). A process to reduce the salt concentration of seawater or brackish water.
Desert scrub. Scrub (shrub land) that occurs where annual rainfall is less than 25 cm and where apronounced dry season exists every year.
Dew point. The temperature to which a given parcel of air must be cooled at constant pressure and atconstant water vapor content until saturation occurs or the temperature at which saturation vapor
pressure of the parcel is equal to the actual vapor pressure of the contained water vapor.
Digester. In a wastewater treatment plant, a closed tank that decreases the volume of and stabilizes
raw biosolids or sludge by bacterial action.
Digester gas. The gas produced as a result of the microbial decomposition of particulate organic
matter under anaerobic conditions. Methane and hydrogen are major components.
Digestion. The biochemical decomposition of organic matter, resulting in partial gasification,liquefaction, and mineralization of pollutants. In wastewater treatment, the biological decompositionof organic matter in sludge. See digester.
Dilution. The reduction of the concentration of a substance in air or water by mixing with additional
air or water.
Direct reuse. The planned and deliberate use of treated wastewater for some beneficial purpose suchas irrigation, recreation, industry, or potable reuse without first being discharged to a body of water orinto the ground. (See, for comparison, indirect reuse.)
Discharge. (1) The volume of water (or more broadly, the volume of fluid including solid­ anddissolved­phase material) that passes a given point in a given period of time. (2) The flow of waterfrom an opening into another body of water, like the release of treated wastewater from a treatment
plant into a stream or the ocean. The flow of surface water in a stream or the flow of groundwaterGL­9from a spring, ditch, or flowing artesian well. (3) (Hydraulics) The rate of flow, especially fluid flow;
the volume of fluid passing a point per unit time, commonly expressed as cubic feet per second,
millions of gallons per day, gallons per minute, or cubic meters per second.
Discharge permit. A permit issued by the state to discharge effluent into waters of the state.
Discharge point. A location at which effluent is released into a receiving stream or body of water.
Disinfection. The killing of waterborne fecal and pathogenic bacteria and viruses in water orwastewater by chlorination, ozonation, ultraviolet (UV) radiation, or other processes. When one isquantifying the effectiveness of disinfection, a statistical limit must be specified; for example, awastewater effluent might be disinfected such that not more than 200 colonies of fecal coliform
remain per 100 mL of water.
Disinfection by­products (DBPs). (1) Chemicals that are formed when a disinfectant such as
chlorine is added to water that contains organic matter, usually from decaying plant or animal
material. (2) Compounds that form when chlorine combines with naturally occurring or pollution­
derived organic, carbon­based materials, such as the acids from soils or decaying vegetation andbromide (salt). Some of such by­products are suspected to be human carcinogens. One typical suchdisinfection by­product for which the U.S. Environmental Protection Agency (EPA) has establishedmaximum contaminant levels (MCLs) as part of its enforcement of the Safe Drinking Water Act(SDWA) is total trihalomethanes (TTHMs).
Dissolved organic carbon (DOC). A measure of the organic compounds that are dissolved in water.
In the analytical test for DOC, a water sample is first filtered to remove particulate material, and theorganic compounds that pass through the filter are chemically converted to carbon dioxide, which isthen measured to compute the amount of organic material dissolved in the water.
Dissolved oxygen (DO). (1) Concentration of oxygen dissolved in water and readily available to fish
and other aquatic organisms. (2) The amount of free (not chemically combined) oxygen dissolved inwater, wastewater, or other liquid, usually expressed in milligrams per liter, parts per million, or
percentage of saturation. The content of water in equilibrium with air is a function of atmosphericpressure, temperature, and dissolved­solid concentration of the water. The ability of water to retain
oxygen decreases with increasing temperature or dissolved solids, with small temperature changes
having the more significant offset. Photosynthesis and respiration may cause diurnal variations in
dissolved­oxygen concentration in water from some streams. Adequate concentrations of dissolved
oxygen are necessary for the lives of fish and other aquatic organisms and the prevention of offensive
odors. Dissolved­oxygen levels are considered the most important and commonly employedmeasurement of water quality and indicator of a water body’s ability to support desirable aquatic life.
The ideal dissolved­oxygen level for fish is between 7 and 9 mg/L; most fish cannot survive at levels
below 3 mg of dissolved oxygen/L. Secondary and advanced wastewater treatment techniques are
generally designed to ensure adequate dissolved oxygen in waste­receiving waters.
Dissolved solids. (1) Minerals, chemical compounds, and organic matter dissolved in water. They
form the residue that remains after evaporation and drying. Also known as total dissolved solids(TDS). Excessive amounts of dissolved solids make water unfit to drink or use in industrial processes.
Distribution uniformity. Measure of the uniformity of irrigation water distribution over a field.
DO. See dissolved oxygen (DO).

GL­10

DOC. See dissolved organic carbon (DOC).
Domestic sewage. Wastewater and solid waste that are characteristic of the flow from toilets, sinks,
showers, and tubs in a household. Also referred to as domestic waste.
Domestic wastewater facility. Refers to those facilities that receive or dispose of wastewater derived
principally from residential dwellings, business or commercial buildings, institutions, and the like.
May also include some wastewater derived from industrial facilities. Also referred to as municipal
wastewater facility.
Dominant species. The species in a plant community that determine, by virtue of size or abundance,
the characteristics of that community. Sometimes, two species are co­dominant and the community is
so named; for example, oak­ash woodland.
Dormant period. A period of greatly reduced metabolism, during which a plant, or parts of the plant,
are alive but not actively growing.
Drain. Any closed conduit (perforated tubing or tile) or open channel, used for removal of surplus
ground or surface water.
Drainage. Process of removing surface or subsurface water from a soil or area.
Drainage system. Collection of surface and/or subsurface drains, together with structures and pumps,
used to remove surface or ground water.
Drinking water. Water that does not contain objectionable pollution, contamination, minerals, orinfective agents and is considered satisfactory for domestic consumption (drinking). The term is usedsynonymously with potable water and refers to water that meets federal drinking water standards of
the Safe Drinking Water Act (SDWA) (Public Law 93­523) as well as state and local water quality
standards and is considered safe for human consumption. Fresh water that exceeds establishedstandards for chloride content and dissolved­solid limits is often referred to as slightly saline,
brackish, or nonpotable water and is either diluted with fresher water or treated through a desalination
process to meet drinking water standards for public supply.
Drinking water standards. Regulations established by state agencies and the U.S. Environmental
Protection Agency (EPA) for drinking water.
Drinking water supply. Water provided for use in households. The most common sources are
surface supplies (rivers, lakes, and reservoirs) or subsurface supplies (aquifers). The distribution ofwater to households is regulated under the Safe Drinking Water Act (SDWA) of 1974, as amended, as
well as state regulations.
Drip irrigation. (1) A system in which piping is laid out so that each plant is watered individually, at
its roots. Typically, lesser quantities of water are necessary with this method than for furrow or
sprinkler irrigation. (2) A method of microirrigation wherein water is applied to the soil surface as
drops or small streams through emitters. Discharge rates are generally less than 8 L/h (2 gal/h) for
single­outlet emitters and 12 L/h (3 gal/h) per meter for line­source emitters.
Drought. Hydrologic conditions during a defined period when rainfall and runoff are much less than
average.

GL­11Drought­deciduous shrub. A shrub that retains its leaves during the wet season and sheds the leaves
during the dry season to conserve water. Roots of such plants typically are relatively shallow. Leaves
are thin, requiring relatively little energy (from the plant) to be remade.
Dual­distribution piping (or dual plumbing). The plumbing of a facility to provide two sources ofwater in separate piping systems; for example, a water distribution system that uses one set of pipes
for the distribution of potable water and a separate set for the distribution of reclaimed water.
EC. See electrical conductivity.
E. coli (Escherichia coli). A bacterial species that inhabits the intestinal tract of humans and otherwarm­blooded animals. Although it poses no threat to human health, its presence in drinking water
does indicate the potential presence of other, more dangerous bacteria. Also see bacteria.
Ecology. The study of the interrelationships among plants, animals, and their environment.
ecosystem. A group of interdependent plants and animals and their environment.
Effective precipitation. That portion of total precipitation which becomes available for plant growth.
Effluent. Wastewater or other liquid, treated or in its natural state, flowing from a treatment plant orprocess.
Effluent limitation. An amount or concentration of a water pollutant that can be legally discharged
into a water body by a point source, expressed as the maximum daily discharge, the maximum
discharge per amount of product, and/or the concentration limit in the wastewater stream, as a 24­h or
30­day average.
Electrical conductivity (EC). A measure of the ability of the water to transfer an electrical charge.
Used as an indicator for the estimation of salt concentration, measured in decisiemens per meter(dS/m, equivalent to mmhos/cm) or millisiemens per centimeter (mS/cm or micromhos/cm, 10−3dS/m), at 25 °C (77 °F).
ECe = electrical conductivity of saturated soil water extract
ECi, ECiw, ECw = electrical conductivity of irrigation water
ECsw = electrical conductivity of soil water
Emission uniformity. An index of the uniformity of emitter discharge rates throughout amicroirrigation system. Takes account of both variations in emitters and variations in the pressure
under which they operate.
Emitter. A small microirrigation dispensing device designed to dissipate pressure and discharge asmall uniform flow or trickle of water at a constant discharge, which does not vary significantly
because of minor differences in pressure head. Also called a “dripper” or “trickler.”
Endocrine­disrupting compounds (EDCs). Chemicals that can interfere with the normal hormone
function controlling metabolism, growth, and reproduction in humans and animals.
Environment. The combination of all biotic and abiotic elements that surround and influence anorganism.
Environmental water. The water for wetlands, the in­stream flow for a major river (based on thelargest flow specified in an entire reach of that river for maintenance of fish) or, for wild and scenic
GL­12rivers, the amount of water based on unimpaired natural flow. Also referred to as dedicated natural
flows.
Epiphyte. A plant that grows upon another plant for position or support but which does not parasitize
it.
Erosion. The wearing away of the land surface by detachment and transport of soil and rocks throughthe action of water, wind, or other geologic agents.
Evaporation. The physical process by which a liquid is transformed to the gaseous state, which in
irrigation is restricted to the change of water from liquid to vapor.
Evaporation pan. (1) A standard U.S. Weather Bureau Class A pan (48­in. diameter and 10­in.
depth) used to estimate the reference crop evapotranspiration rate. Water levels are measured daily inthe pan to determine the amount of evaporation. (2) A pan or container containing water. Water
evaporated from the device is measured and adjusted by a coefficient to represent estimated cropwater used during the period.
Evapotranspiration. The combination of water transpired from vegetation and evaporated from thesoil and plant surfaces. Synonymous with consumptive use.
Evergreen plant. A plant that remains green during the dormant season and persists for two or moreseasons.
Exchangeable cation. A positively charged ion held on or near the surface of a solid particle by anegative surface charge of a soil or colloid and which may be replaced by other positively charged
ions in the soil solution.
Exchangeable sodium percentage (ESP). The fraction of the cation exchange capacity of a soil
occupied by sodium ions determined as exchangeable sodium (meq/100 g of soil) divided by CEC(meq/100 g of soil) times 100. It is unreliable in soil containing soluble calcium silicate minerals orlarge amounts of gypsum.
Exchange capacity. The total negative charge of the soil exchange complex.
Feedwater. Water input into a desalting or water treatment plant or an industrial water­using facility.
Fertigation. Application of fertilizer materials through the irrigation system.
Field capacity. Amount of water remaining in a soil when the downward water flow due to gravity
becomes negligible. Usually it is assumed that this condition is reached about 2 to 3 days after a full
irrigation or heavy rain.
Filtration. A process in which suspended matter is removed from a liquid through a medium that ispermeable to the liquid but not to the suspended material. The medium may be sand or a human­madefilter. The objective is often to remove particles that contain pathogens.
Fire­type climate. Places in which a combination of low rainfall, high evaporation, frequent wind,and other climatic factors favor the onset of fires, such that the probability is high that wildfire willreoccur on the same hectare of land every 1 to 3 years.

GL­13

Fixation. The process by which available nutrients such as potassium and phosphorus are rendered
unavailable or fixed in the soil.
Flocculate. To aggregate individual small clusters or aggregation of soil particles that creates
structure such as crumbs and clods.
Flowering plants. See angiosperm.
Flow augmentation. The addition of water to a stream especially to meet in­stream flow needs.
Flow rate. Speed at which water moves, usually measured in terms of volume per time period (forexample, liters per minute).
Forb. Any herbaceous plant that is neither a grass nor grass­like.
Fresh water (freshwater). Water that is not brackish or saline and is obtained from rainwater,
surface waters such as lakes and streams, and groundwater.
Gallons per day (gpd). A measure of the rate of flow or the rate of water withdrawal from a well.
Typically used when the rate of flow in cubic feet per second (cfs) is too low to be useful.
Geographic information system (GIS). Computer data base management system for spatiallydistributed attributes.
Giardia lamblia. A flagellate protozoan that causes the severe gastrointestinal illness giardiasis whenit contaminates drinking water.
Grassland. A vegetation type dominated by herbaceous species, including forbs and grasses, andoccupying an area too dry to support trees. Trees may be present, but typically they occur only in
localized areas, such as on rocky ridges where soil is thin, or along waterways.
Gravimetric (oven dry) soil water method. A method of measuring total soil water content bysampling, weighing, and drying to constant weight in an oven at 105 °C. Percent water, usually on thebasis of dry soil weight, is calculated.
Graywater (or gray water, or greywater). Wastewater from a household or small commercial
establishment that does not include water from a toilet, kitchen sink, dishwasher, or water used forwashing diapers.
Ground cover. Plants which, by their natural habit of low, close growth, are suitable for covering the
ground surface and discouraging weeds.
Groundwater. Water occurring in the zone of saturation in an aquifer or soil. Sometimes referred toas “ground water.”
Groundwater basin. A groundwater reservoir, defined by an overlying land surface and theunderlying aquifers that contain water stored in the reservoir. In some cases, the boundaries ofsuccessively deeper aquifers may differ and make it difficult to define the limits of the basin.

GL­14

Groundwater overdraft. The condition of a groundwater basin in which the amount of water
withdrawn by pumping exceeds the amount of water recharging the basin over a period of years
during which water supply conditions approximate average conditions.
Groundwater recharge. The natural or artificial infiltration of surface water or injection of water
into the zone of saturation (i.e., into groundwater aquifer).
Groundwater table. The upper surface of the zone of saturation in an unconfined aquifer.
Growing season. The period, often the frost­free period, during which the climate is such that crops
can be produced. In the case of annual plants, it approximates the time interval between planting andcrop maturity; for perennial crops, it is the period between certain temperature conditions that
establish growth and dormancy. This growing season is sometimes restricted to the period between
killing frosts.
Gymnosperm. A plant that produces seeds exposed to the environment rather than seeds enclosed ina fruit. All conifers are members of this group, as are gingkos and cycads.
Gypsum. A mineral used in the fertilizer industry as a source of calcium and sulfur. Widely used toreclaim sodic soils and improve water infiltration.
Habitat. The natural environment in which a plant or animal lives.
Halophyte. A plant that can tolerate, or even thrive in, saline water or saline soil.
Hardpan. A hardened or cemented soil horizon or layer cemented by iron oxide, silica, or calcium
carbonate.
Hard water. Water with a high concentration of minerals, principally calcium and magnesium ions.
Herb. A seed plant that does not develop woody tissues.
Herbaceous perennials. Perennial plants that die back each winter, shedding leaves and stems andleaving only the plant’s underground organs, such as a bulb, corm, root, or rhizomes. Examples: iris,
gladiolus, onion (Allium).
Herbaceous plant. A plant having the characteristics of an herb.
Herbicide. A pesticide for controlling weeds.
Humus. The well­decomposed, more or less stable portion of the organic matter in soils.
Hybrid. A plant produced by the crossing of two other, genetically distinct plants. Hybrids may be
between varieties (referred to as a varietal hybrid), between species (specific hybrid), or, more rarely,
between genera (generic hybrid). Such plants may show a blending of characteristics from eachparent or may display the characteristics of one parent more than of the other.
Hydraulic conductivity. The rate of water flow in soil per unit gradient of hydraulic head or
potential.

GL­15

Hydrologic cycle. The continuing process by which atmospheric water condenses, falls to the surfaceof the earth in any of various forms of precipitation, runs through the surface or subterranean passages
toward the sea, and again returns to the atmosphere by evaporation from either the sea or land surface.
Hydrozone. Refers to areas where the irrigation system must be matched to the plant material,
microclimate, or other needs like watering requirement and leaching requirement.
Impermeable layer (soil). Layer of soil resistant to penetration by water, air, or roots.
Incidental reuse. Unplanned use of treated wastewater effluent after disposal.
Incidental runoff. Unintended, but perhaps unavoidable, runoff of water from a site where water isused, such as overspray from sprinkler irrigation.
Indigenous. Plants originating in a particular locality, district, or country.
Indirect reuse. The use of reclaimed water indirectly after it has passed through a natural body ofwater after discharge from a wastewater treatment plant.
Infiltration. The downward entry of water through the soil surface into the soil.
Infiltration opportunity time. The time that water inundates the soil surface, with opportunity toinfiltrate.
Infiltration rate. The quantity of water that enters the soil surface in a specified time interval. Often
expressed in volume of water per unit of soil surface area per unit of time.
Inflorescence. The arrangement of fruits on a floral axis.
Influent. Water, wastewater, or other liquid flowing into a reservoir, basin, or treatment plant.
Inorganic fertilizer. Fertilizer manufactured from mineral­based chemicals.
Instantaneous application rate. The maximum rate that a sprinkler application device applies water
to the soil, expressed in millimeters per hour (inches per hour).
Intake characteristic curves. Curves reflecting cumulative water intake versus time for irrigation
systems.
Intake rate. The rate at which irrigation water enters the soil at the surface (see infiltration).
Expressed as millimeters per hour (inches per hour).
Ion. Chemical constituent that has an electrical charge, either positive like sodium or negative likechloride.
Ion exchange. Process in which ions of one mineral are replaced by ions of another mineral. In
water­softening processes, magnesium and calcium ions are replaced by sodium ions.
Iron chlorosis. A yellowing or loss of greenness in leaf tissue, commonly between veins, due to an
insufficient concentration of iron in the plant.

GL­16

Irrigate. To distribute water to land through artificial means, especially to enhance crop production
either where natural water sources are so deficient as to make crop production impossible otherwise
or where it is advantageous to supplement the natural water supply at certain critical stages in thedevelopment of crops.
Irrigation frequency, interval. The time between irrigation events.
Irrigation scheduling. The process of determining when to irrigate and how much water to apply,
based upon measurements or estimates of soil moisture or water used by the plant.
Irrigation set. The area irrigated at one time within a field.
Irrigation set time, irrigation period. The amount of time required to apply a specific amount ofwater during one irrigation to a given area.
Irrigation system. Physical components and configuration used to apply water by irrigation. May
include pumps, pipelines, valves, nozzles, ditches, gates, siphon tubes, turnout structures, land
shaping, furrows, etc.
Irrigation (system) efficiency. The ratio of the volume of irrigation water that is beneficially used to
the volume of irrigation water applied, expressed as a percentage. Beneficial uses include satisfying
the soil water deficit and any leaching requirement to remove salts from the root zone. It is commonlyinterpreted as the volume of water stored in the soil for evapotranspiration compared to the volume ofwater diverted for this purpose but may be defined and used in different ways.
Irrigation water management (IWM). Managing plant, soil, and water resources (precipitation,
applied irrigation water, humidity, etc.) to optimize water use by the crop.
Irrigation water requirement. The calculated amount of water needed to replace soil water used by
the crop (soil water deficit), for leaching undesirable elements through and below the plant root zone,
plus other production needs, less effective precipitation.
Land application. The reuse of reclaimed water or the utilization or disposal of effluents on, above,or into the surface of the ground through spray fields or other methods.
Land capability. Classification of soil units for the purpose of showing their relative suitability forspecific uses without permanent damage, such as crop production with minimum erosion hazard.
Land grading. The operation of shaping the surface of land to predetermined grades. Also
called “land shaping” (see land leveling for a special case).
Land leveling. Process of shaping the land surface to a level surface. A special case of land grading.
Land smoothing. Shaping the land to remove irregular, uneven, mounded, broken, and jaggedsurfaces without using surveying information.
Landscape impoundment. A body of water that is used for aesthetic enjoyment or that otherwise
serves a function not intended to include contact recreation.

GL­17

Langley. A unit of energy per unit area commonly used in radiation measurements that is equal togram calorie per square centimeter.
Laser leveling. Land leveling in which a stationary laser transmitter and a laser receiver on each
earth­moving machine are used for grade control.
Leaching. Refers either to a process by which substances are dissolved into water flowing over a
surface or through a medium or to the movement of salts, nutrients and other solutes down throughthe soil along with percolating rainwater or irrigation water.
Leaching fraction (LF). The ratio of the depth of subsurface drainage water (deep percolation) to thedepth of infiltrated irrigation water.
Leaching requirement (LR): Quantity of irrigation water required for leaching salts through the soil
profile to maintain a soil salinity level in the root zone that gives maximum crop yield or salinity level
below the threshold salinity of plants.
Leaf litter. A layer of rotting leaves that eventually decays to form humus.
Lime. A mineral such as calcium carbonate (ground limestone), calcium hydroxide (hydrated lime),
or calcium oxide (burned lime).
Limited irrigation. Management of irrigation applications to apply less than enough water to satisfy
the soil water deficiency in the entire root zone. Sometimes called “deficit” or “stress irrigation.”Line source. Continuous source of water emitted along a line.
Low elevation spray application (LESA). Irrigation method using a low­pressure spray applicator
designed to operate near the ground, 0.3 to 0.6 m (1.0 to 2.0 ft), from drop tubes, on either a center­
pivot or a lateral­move sprinkler system (see low pressure in canopy).
Low pressure in canopy (LPIC). A system that may or may not include a complete water, soil, andplant management regimen as required in LEPA. Application devices are located in the crop canopy
with drop tubes mounted on low­pressure center pivot and linear­move sprinkler irrigation system(see low elevation spray application).
Lysimeter. An isolated block of soil, usually undisturbed and in situ, for measuring the quantity,
quality, or rate of water movement through or from the soil. A device such as a tank or large barrel
that contains a mass of soil and vegetation similar to that in the immediate vicinity, which is isolatedhydrologically from its surroundings. It is commonly used in research to determine the water use ofvarious crops in field conditions.
Macroclimate. The climate of a large geographical area; for example, the southwestern UnitedStates.
Macroenvironment. That part of a plant’s environment that is determined by the general climate,elevation, and latitude of the region.
Magnesium ion. A positively charged inorganic ion that contributes to the hardness of water.

GL­18

Maintenance. Routine operations necessary to keep a landscape in good order—for example,
pruning, mowing, and weeding.
Management­allowed depletion. The desired soil­water deficit at the time of irrigation.
Manufacturer’s coefficient of variation. A measure of the variability of discharge of a random
sample of a given make, model, and size of microirrigation emitter, as produced by the manufacturer
and before any field operation or aging has taken place; equal to the ratio of the standard deviation of
the discharge of the emitters to the mean discharge of the emitters.
Maximum contaminant level (MCL). The highest drinking water contaminant concentration
allowed under federal and state Safe Drinking Water Act regulations.
Meadow. Grassland that occurs within a climate capable of supporting forest vegetation. Forbs often
dominate, with grasses secondary.
Mediterranean climate. A climate zone similar to that of the Mediterranean rim of southern Europe.
Four other areas worldwide (besides Europe) have such climates: southern Australia, central Chile,
the Cape region of South Africa, and California. All five regions are located between 32 and 40
degrees north or south latitude and occupy the southern or southwestern edges of the continents ofwhich they are part. Other common characteristics include precipitation of 27 to 90 cm per year,
mainly during the winter; minimal frost; and episodic wildfires. Hot, dry summers and cool, wetwinters are the norm. Vegetation in these areas is diverse, ranging from forest (in the wetter locations)
to woodland or scrub (in the dry locations). Plant cover is relatively high, with broad­leaved, woody,
evergreen flowering plants the dominant vegetation type.
Mesoclimate. The climate of a local area, which may differ from that of the region as a whole; forexample, the climate within a river basin or along a coastal strip.
Microclimate. Climate of a small area, such as an isolated hilltop or walled garden or within a groupof plants.
Microenvironment. The part of a plant’s environment that is modified by nearby abiotic or biotic
surfaces and structures. The microenvironment in the vicinity of a plant surrounded by bare soil, forexample, is much greater than the ambient air temperature, because the bare soil absorbs solar
radiation and radiates heat.
Microirrigation. The frequent application of small quantities of water as drops, tiny streams, orminiature spray through emitters or applicators placed along a water delivery line. The micro­
irrigation method encompasses a number of systems or concepts, such as bubbler, drip, trickle, line
source, mist, or spray.
Micronutrients. Nutrients that plants need in small amounts such as boron, copper, zinc, manganese,molybdenum, and nickel.
Milliequivalent (meq). The combining weight of chemicals equal to millimoles divided by theirvalence or charge.

GL­19

Millimolar (mM). A chemical concentration unit that is 1/1,000 of a molar concentration. A molar
concentration is the atomic weight of the element (or formula weight of the molecule or compound)
dissolved in 1 L of water.
Minerals (in water). Soluble inorganic ions in water.
Mist irrigation. A method of microirrigation in which water is applied in very small droplets.
Moisture deficit, soil moisture depletion. The difference between soil water at field capacity and theactual soil water.
Montane. A midelevation mountain zone, above the foothills and below the subalpine zone.
Montane scrub. Scrub that occupies rocky ridges or south­facing mountain slopes. Sometimes thistype of vegetation develops after wildfire has passed through an area; in such cases, trees may
eventually reclaim the site by growing through the scrub and shading it out.
Mulch. Forest bark, compost, leaf mold, well­rotted farmyard manure, or similar organic material,
spread over the soil surface around plants to conserve moisture and inhibit weed growth by restricting
the light. Stones, gravel, and synthetic sheet material can also be used.
Municipal discharge. The discharge of effluent from wastewater treatment plants that receive
wastewater from households, commercial establishment, and industries. Wastewater from combined
sewers carrying both wastewater and collected storm water is included in this category.
Municipal sewage. Wastewater (mostly liquid) originating from a community, which is composed ofdomestic wastewater and possibly commercial and industrial wastewater.
Municipal wastewater. Wastewater derived from domestic, commercial, and industrial sources.
Municipal wastewater facility. A facility that receives and treats wastewater derived principallyfrom residential dwellings, business or commercial buildings, institutions, and the like. May also
include some wastewater derived from industrial facilities. Also referred to as domestic wastewater
facility.
Native plant. A plant indigenous to a specific area.
Natural regeneration. Regrowth of vegetation on an area of disturbed land.
Necrosis. Localized death of living tissues such as plant leaves.
Necrotic. Appearance of dead tissues on leaves.
Needle. A long, slender leaf blade common in pines and some spruce.
Net irrigation. The actual amount of applied irrigation water stored in the soil for plant use or moved
through the soil for leaching salts. Also includes water applied for crop quality and temperature
modification, i.e., controlling frost or cooling plant foliage and fruit. Application losses, such as
evaporation, runoff, and deep percolation, are not included. Generally measured in millimeters(inches) of water depth applied.

GL­20

Net irrigation water requirement. The depth of water, exclusive of effective precipitation, storedsoil moisture, or ground water, that is required for replacing that lost to crop evapotranspiration forcrop production and other related uses. Such uses may include water required for leaching, frost
protection, cooling, and chemigation.
Nitrification. The formation of nitrates and nitrites from ammonia or ammonium compounds in soils
or waters through microbial activity.
Noncontact cooling water. Water used for cooling that does not come into direct contact with any
raw material, product, by­product, or waste.
Noncontact recreation. Recreational pursuits not involving a significant risk of water ingestion,
including fishing, commercial and recreational boating, and limited body contact incidental toshoreline activity.
Nonpoint. Not from a specific location.
Nonpotable reuse. The use of treated wastewater in water supplies that are not intended for drinking
or ingestion, such as certain industrial uses or the irrigation of certain types of farm crops.
Nonpotable water. Water that is not suitable for drinking because it contains pollutants,
contaminants, minerals, or infective agents.
Nonsaline­alkali soil. (See sodic soil.)
Nutrient cycle. The uptake of nutrients by plants and the subsequent use of such nutrients andeventual return of nutrients to the environment.
Nutrients. Mineral elements and ions that are essential for plant growth.
Opportunity time. The time that water inundates the soil surface with opportunity to infiltrate.
Organic chemical. Molecules made up of carbon along with other elements. All living organisms
consist of organic molecules.
Organic fertilizer. Fertilizer derived from living matter; for example, fishmeal or bone meal.
Osmotic hazards. Salinity hazard to plants causing soil water to become less available to plants.
Plants need to expend more energy to extract soil water in saline than in nonsaline soils.
Outfall. The place where a sewer, drain, or stream discharges; the outlet or structure leaving atreatment plant through which reclaimed water or treated effluent is finally discharged to a receiving
water body.
Overdraft. See groundwater overdraft.
Pan coefficient. A factor to relate actual evapotranspiration of a crop to the rate water evaporates
from a free water surface in an evaporation pan. The coefficient usually changes by crop growthstage.

GL­21

Pan evaporation. Evaporation from a class A or similar pan. The U.S. Weather Bureau class A pan isa cylindrical container fabricated of galvanized iron or Monel metal with a depth of 10 in. and adiameter of 48 in. The pan is accurately leveled at a site that is nearly flat and well sodded and free ofobstructions. The pan is filled with water to a depth of 8 in., and periodic measurements are made of
the changes of the water level with the aid of a hook gauge set in the stilling well. When the waterlevel drops to 7 in., the pan is refilled.
Pathogen. A disease­producing agent. Term usually refers to a living organism (i.e., biological).
Generally, any viruses, bacteria, or fungi that cause disease.
Penman­Monteith method. A method for estimating reference crop evapotranspiration (ETo) using
current climatic data including air temperature, relative humidity, wind speed, and solar radiation.
Percolation. The downward movement of water through soil. Also called deep percolation past theroot zone of plants.
Perennials. Plants that live for many years and usually flower repeatedly.
Permanent wilting point. Soil water content below which plants cannot readily obtain water andpermanently wilt. Sometimes called “permanent wilting percentage.”
Photosynthesis. The process by which green plants combine water and carbon dioxide to form
carbohydrates in the presence of sunlight. Chlorophyll is required for the conversion of light energy
into chemical energy.
Phreatophyte. A woody plant that has deep roots permanently in contact with groundwater. Such aplant is well supplied with water throughout the dry season and experiences stress mainly during
winter. (To avoid winter stress, many such plants shed their leaves during the wintertime.)
Planned reuse. The deliberate direct or indirect use of recycled water without relinquishing control
over the water during its delivery.
Plant community. All the plant populations within a given habitat; usually, such populations are
considered to be somewhat interdependent.
Plant succession. A gradual process in which a plant community changes over time at the populationlevel in a particular place.
Pollution. An alteration of the quality of waters of the state by wastes to a degree that unreasonably
affects (1) such waters for beneficial use or (2) facilities that serve such beneficial uses. Pollution may
include contamination.
Population. A group of freely interbreeding individuals belonging to the same species and occupying
the same habitat.
Potable reuse. The use of treated wastewater in water supplies intended for drinking or ingestion.
Usually involves careful treatment of the wastewater with advanced processes, followed by piping of
the resulting water directly to a water treatment plant.

GL­22

Potable water. Water that is drinkable. Specifically, fresh water that generally meets the standards inquality as established in the U.S. Environmental Protection Agency (EPA) Drinking Water Standards
for drinking water throughout the United States. Potable water is considered safe for humanconsumption and is often referred to as drinking water.
Pot­bound. Said of a pot­grown plant whose roots have grown to fill its pot to the extent that further
development is inhibited. Also known as “root­bound.”Prairie. See grassland.
Precipitation intensity. Rate of precipitation, generally expressed in units of depth per time (seerainfall intensity).
Pre­plant irrigation. Irrigation applied prior to seeding. Sometimes called “preirrigation.”
Pressure regulator. It is used to adjust the water pressure at the point of connection to the levelspecified in the irrigation design.
Primary plant nutrients. Nitrogen, phosphorus, and potassium needed in large amounts by plants.
Primary wastewater treatment. The removal of particulate materials from domestic wastewater,
usually done by allowing the solid materials to settle as a result of gravity. Typically, the first major
stage of treatment encountered by domestic wastewater as it enters a treatment facility. The
wastewater is allowed to stand in large tanks, termed clarifiers or primary settling tanks. Primary
treatment plants generally remove 25 to 35% of the biochemical oxygen demand (BOD) and 45 to
65% of the total suspended matter. Also, any process used for the decomposition, stabilization, or
disposal of sludges produced by settling. The water from which solids have been removed is thensubjected to secondary wastewater treatment and possibly tertiary wastewater treatment.
Puddled soils. Dense, massive soil compacted when wet and having no regular soil structure,commonly caused by machine and heavy foot traffic.
Pumping plant or station. A complete installation of one or more pumps together with all necessary
appurtenances such as power units, sumps, screens, valves, motor controls, motor protection devices,fences, and shelters.
Purification (water). Steps taken to eliminate impurities and pollution from water.
Pyranometer. A general name for instruments that measure the combined intensity of incoming
direct solar radiation and diffuse sky radiation.
Radiation. Process by which electromagnetic radiation is propagated through space.
Net radiation is the difference of the downward solar and long­wave radiation flux and upward solar
and long­wave radiation flux passing through a horizontal plane just above the ground surface (Rn).
Rainfall intensity. Rate of rainfall for any given time interval, usually expressed in units of depth pertime.
Raw water. Untreated surface water or groundwater.

GL­23

Reasonable­use rule. A concept of water law in which a landowner is given the right to thereasonable use of water for domestic or similar needs.
Recharge. Process by which water is added to the zone of saturation to replenish an aquifer.
Recharge area. Land area over which water infiltrates and percolates downward to replenish an
aquifer. For unconfined aquifers, the area is essentially the entire land surface overlying the aquifer,and for confined aquifers, the recharge area may be a part of or unrelated to the overlying area.
Reclaimed water or reclaimed wastewater. See recycled water.
Recycled water. Wastewater that is suitable for a beneficial use as a result of treatment. The degreeof treatment provided for recycled water depends on the quality of water needed for the specificbeneficial use and for public health protection and may include effluent from primary wastewater
treatment, secondary wastewater treatment, tertiary wastewater treatment, or advanced treatment.
Formerly known as reclaimed wastewater.
Reference crop evapotranspiration (ETo). Rate at which water, if available, would be removed
from soil and plant surfaces.
Relative humidity. Ratio of the amount of water present in the air to the amount required forsaturation of the air at the same dry bulb temperature and barometric pressure, expressed as apercentage.
Replenishment. The act of replenishing an aquifer, usually through artificial recharge, to offset
excess groundwater pumping.
Repurified water. As this term has been used in California, repurified water means recycled waterthat is used to augment water supplies by discharging advanced treated recycled water into a surface
water reservoir that supplies water directly to a water treatment facility for a water supply system thatserves domestic uses, including human ingestion. Typically, such waters would undergo extensive
tertiary and advanced wastewater treatment, be stored in a reservoir for a specified minimum time(for example, 1 year), be blended with fresh water within the reservoir, then undergo further treatment
and disinfection through a conventional surface water treatment plant before being distributed in the
potable distribution system.
Reservoir (water). A pond, lake, or basin, either natural or artificial, for the storage, regulation, andcontrol of water.
Reuse (water). The additional use of previously used water. As used in this report, it means the useof recycled water (wastewater that has been treated for beneficial use at a wastewater treatment
plant).
Reverse osmosis (RO). A method to remove salts and other constituents from water by forcing water
through membranes.
Rhizome. A prostrate, thickened stem sending out roots and capable of producing leafy shoots andflowering stems from lateral and terminal buds. May also be a food storage organ that can be used topropagate the plant (as in, for example, bearded iris).
Rib. The primary vein of a leaf.
GL­24

Root­balled plant. A plant grown in the open ground and then lifted with a well­defined ball of soil
around the roots, for planting elsewhere. Usually wrapped in netting for protection. (For comparison,see bare­root plant.)
Root zone. (1) Area of a plant that consists of the roots and related woody or nonwoody tissues thatabsorb water, gases, and nutrients from the soil and atmosphere. (2) Depth of soil that plant roots
readily penetrate and in which the predominant root activity occurs. Sometimes spelled “rootzone.”
Saline. Containing soluble salts.
Saline­sodic soil. Soil containing appreciable quantities of soluble salts and sufficient exchangeablesodium to interfere with the growth of most plants. The electrical conductivity of the saturation
extract is greater than 4 dS/m (4 mmhos/cm), and the exchangeable sodium percentage is greater than
15%.
Saline soil. Nonsodic soil containing soluble salts in such quantities that they interfere with thegrowth of most plants. The electrical conductivity of the saturation extract is greater than 4 dS/m, andthe exchangeable sodium percentage is less than 15%.
Salinity. (1) The concentration of dissolved mineral salts in water on a unit volume basis (e.g.,
milligrams per liter) or salts in soil on a unit mass basis (tons/acre). May be harmful or harmless forthe intended use of the water. Salinity may be also expressed in terms of electrical conductivity inmicrosiemens per centimeter for low­salt waters and decisiemens per meter for saline waters. (2)When one is describing salinity influenced by seawater, salinity often refers to the concentration ofchlorides in the water. (3) The relative concentration of salts, usually sodium chloride, in a given
water sample. It is usually expressed in terms of the number of parts per thousand (‰) or parts per
million (ppm) of chloride (Cl). Although the measurement takes into account all of the dissolved
salts, sodium chloride (NaCl) normally constitutes the primary salt being measured. As a reference,the salinity of seawater is approximately 35‰ or 35,000 ppm. (4) Salinity can harm many plants,
causing leaves to scorch and turn yellow and stunting plant growth. Also see total dissolved solids.
Salt tolerance. Tolerance by plants of osmotic stresses that make soil water less available.
Salt water or seawater intrusion. The invasion of a body of fresh water by a body of salt water. Thisphenomenon is usually caused by a hydraulic gradient resulting from a higher water surface elevationor higher water pressure in the salt water zone than in the freshwater zone. It can occur either insurface or groundwater bodies. The term is applied to the flooding of freshwater marshes by seawater,
the migration of seawater up rivers and navigation channels, and the movement of seawater into
freshwater aquifers along coastal regions.
Salts. Commonly found cations and anions in soils contributing to soil salinity. The primary source ofsalts is chemical weathering of earth materials, and secondary sources include dissolved mineral salts
present in waters or added such as fertilizers, amendments, and animal manures.
Sapling. A young tree; usually pertaining to self­seeded trees.
Saturated paste. A mixture of soil and water commonly used for measurements and for obtaining
soil extracts. For all soils except those with high clay content, at saturation a soil paste glistens as it
reflects light, flows slightly when the container is tipped, and slides freely and cleanly from a spatula.

GL­25

Saturated soil extract. The solution extracted by vacuum from soil pastes wetted to its saturation
percentage (about twice field capacity for most soil textures) with distilled water.
Saturated zone. Groundwater­bearing zone in groundwater basins below the vadose zone.
Savanna. Grassland with overtopping trees that are regularly present but whose canopies cover lessthan 30% of the ground. (See also, for comparison, woodland and steppe.)
Sclerophyllous plant. A plant with small, stiff, leathery leaves that is well adapted to hot and dry
climates.
Scorch. “Burning” of leaf margins caused by infection or by unfavorable environmental conditions.
Scrub. Shrub land; any vegetation dominated by shrubs. Typical of regions where the precipitation or
the water storage capacity of the soil is too low to support grassland. Desert scrub and chaparral are
examples.
Secondary wastewater treatment. Treatment (following primary wastewater treatment) involving
the biological process of reducing suspended, colloidal, and dissolved organic matter in effluent fromprimary treatment systems and which generally removes 80 to 95% of the biochemical oxygen
demand (BOD) and suspended matter. Secondary wastewater treatment may be accomplished bybiological or chemical­physical methods. Activated sludge and trickling filters are two of the mostcommon means of secondary treatment. It is accomplished by bringing together waste, bacteria, andoxygen in trickling filters or in the activated sludge process. This treatment removes floating andsettleable solids and about 90% of the oxygen­demanding substances and suspended solids.
Disinfection is usually the final stage of secondary treatment. Also see primary wastewater
treatment and tertiary wastewater treatment.
Senescence. The stage in the life of a plant or plant part when its rate of metabolic activity declines
prior to death.
Set time (irrigation). Elapsed time between the beginning and end of water application to an
irrigation set.
Sewage. The spent water of a community, now usually referred to as wastewater. Sewage has thefurther implication of wastewater containing domestic waste.
Shelter belt. A line or belt of trees or shrubs (or both) planted at a right angle to the direction of theprevailing wind, to provide shelter by reducing wind speed.
Shrub. A woody perennial with several stems arising from, or originating just above, the groundlevel. Some shrubs can live many decades if they are well adapted to their environment and if theenvironment remains relatively consistent.
SI units. An international metric system developed by General Conference on Weights and Measures(CGPM, Conférence Générale des Poids et Mesures). This system provides for an established single
unit that applies for each physical quantity. Units for all other mechanical quantities are derived fromthese basic units. Also called International System of Units.

GL­26

Sodic soil. A nonsaline soil containing sufficient exchangeable sodium to adversely affect crop
production and soil structure. The exchangeable sodium percentage is greater than 15%, and theelectrical conductivity of the saturation extract is less than 4 dS/m.
Sodium adsorption ratio (SAR). The proportion of soluble sodium ions in relation to the soluble
calcium and magnesium ions in the soil water extract or water expressed as (millimoles/liter)0.5 or(milliequivalents/liter)0.5. SAR can be used to predict the exchangeable sodium percentage.
Sodium adsorption ratio, adjusted (SARadj). The sodium adsorption ratio of a water adjusted forthe precipitation or dissolution of Ca2+ and Mg2+ that is expected to occur when a water reacts withalkaline earth carbonates within a soil. Numerically, it is obtained by multiplying the sodium
adsorption ratio by the value (1 + 8.4 − pHc*), where pHc is the theoretical calculation of the pH ofwater in contact with lime and in equilibrium with soil CO2.
Sodium (Na). An alkali metal element having an atomic weight of 22.99 g. Commonly present inwaters, plants, soils, and everyday chemical compounds such as table salt and salt for water softeners.
Excessive sodium is undesirable for plants, soil properties, and human health.
Sodium percentage. Percentage of total cations that is sodium in water or soil solution.
Softened water. Water treated with sodium to replace calcium and magnesium salts in solution. This
process typically does not reduce the water’s total salinity.
Soil. The unconsolidated minerals and material on the immediate surface of the earth that serve as anatural medium for the growth of plants.
Soil horizon. A layer of soil differing from adjacent genetically related layers in physical, chemical,
and biological properties or characteristics.
Soil moisture. (See soil water.)
Soil moisture (available). Water in the root zone that can be extracted by plants. The available soil
moisture is the difference between field capacity and wilting point.
Soil moisture (unavailable). Water in the root zone that is held so firmly by various forces that it
usually cannot be absorbed by plants.
Soil organic matter. Organic fraction of the soil, including plant and animal residues in various
stages of decomposition, cells and tissues of soil organisms, and substances synthesized by the soil
population.
Soil profile. Vertical section of the soil from the surface through all its horizons into the parent
material.
Soil series. The lowest category of U.S. system of soil taxonomy. A conceptualized class of soil
bodies having similar characteristics and arrangement in the soil profile.
Soil structure. The combination or arrangement of primary soil particles, into secondary particles,
units, or peds that make up the soil mass. These secondary units may be, but usually are not, arrangedin the profile in such a manner as to give a distinctive characteristic pattern. The principal types ofsoil structure are platy, prismatic, columnar, blocky, and granular.

GL­27

Soil texture. Classification of soil by the relative proportions of sand, silt, and clay present in the soil.
Soil water. All water stored in the soil (see water holding capacity).
Soil­water characteristic curve. Soil­specific relationship between the soil­water matric potential
and soil­water content.
Soil­water content. The mass or volume of water in a given volume of soil.
Soil­water deficit. Amount of water required to raise the soil­water content of the crop root zone tofield capacity. It is measured in millimeters (inches) of water. Also called soil­water depletion.
Soil­water tension. A measure of the tenacity with which water is retained in the soil. It is the force
per unit area that must be exerted to remove water from the soil and is usually measured in bars or
atmospheres. It is a measure of the effort required by plant roots to extract water from the soil.
Solar radiation (Rs). Radiation from the sun that passes through the atmosphere and reaches the
combined crop and soil surface. The energy is generally in a waveband width of 0.1 to 5 μm. Net Rs is
incoming radiation minus reflected radiation from a surface.
Solute. Dissolved material, typically soluble ions and molecules.
Solvent. Substance in which other substances, or solutes, dissolve.
Species. A subdivision of a genus, consisting of plants that have the same distinctive characteristics
and that have the capacity to interbreed.
Specific ion toxicity. Plant toxicity (phytotoxicity) resulting from excessive levels of specific ions(e.g., boron).
Spray irrigation. The application of water by a small spray or mist to the soil surface, where travel
through the air becomes instrumental in the distribution of water.
Sprinkle irrigation. (See sprinkler irrigation.)
Sprinkler application rate. The rate at which water is applied to a given area by a sprinkler system,
usually expressed as depth (volume per unit area) per unit time, millimeters per hour (inches perhour).
Sprinkler distribution pattern. Water depth­distance relationship measured from a single sprinkler
head.
Sprinkler head. A device for distributing water under pressure.
Sprinkler irrigation. Method of irrigation in which the water is sprayed, or sprinkled, through the air
to the ground surface. Rotor sprinkler heads are gear driven or impact driven; fixed sprinkler heads
have no moving parts and water is directed through orifices and may have adjustable arcs andadjustable flow rates.

GL­28

Sprinkler irrigation systems.
Boom. An elevated, cantilevered sprinkler(s) mounted on a central stand. The sprinkler boom
rotates about a central pivot.
Center pivot. An automated irrigation system consisting of a sprinkler line rotating about apivot point and supported by a number of self­propelled towers. The water is supplied at thepivot point and flows outward through the line supplying the individual outlets.
Corner pivot. An additional span or other equipment attached to the end of a center pivot
irrigation system that allows the overall radius to increase or decrease in relation to the fieldboundaries.
Lateral move. An automated irrigation machine consisting of a sprinkler line supported by anumber of self­propelled towers. The entire unit moves in a generally straight path and irrigatesa basically rectangular area. Sometimes called a “linear move.”
Permanent. Underground piping with risers and sprinklers.
Portable (hand move). Sprinkler system that is moved by uncoupling and picking up the pipes
manually, requiring no special tools.
Side­move sprinkler. A sprinkler system with the supply pipe supported on carriages andtowing small­diameter trailing pipelines, each fitted with several sprinkler heads.
Side­roll sprinkler. The supply pipe is usually mounted on wheels with the pipe as the axle andwhere the system is moved across the field by rotating the pipeline by engine power.
Solid set. System that covers the complete field with pipes and sprinklers in such a manner that
all the field can be irrigated without moving any of the system.
Towed sprinkler. System where lateral lines are mounted on wheels, sleds, or skids and arepulled or towed in a direction approximately parallel to the lateral.
Steppe. Grassland interspersed with shrubs. (See also, for comparison, woodland, savanna.)
Stomata. Pores, usually in a leaf that, allow gaseous exchange with the atmosphere such as water
vapor and oxygen.
Subalpine zone. A high­elevation mountain region located above the montane zone and below thealpine zone. Typically well forested, this zone differs quite a bit from the alpine zone, which isentirely above the treeline.
Subirrigation. Application of irrigation water below the ground surface by raising the water table towithin or near the root zone.
Subshrub. A multibranched and genetically dwarfed shrub whose stems die back partially eachgrowing season. Maximum height of such plants typically is 30 cm or less.
Subsoil. The soil below the topsoil layer; composed largely of mineral particles.

GL­29

Subsurface drain. Subsurface conduits used primarily to remove subsurface water from soil.
Classifications of subsurface drains include pipe drains, tile drains, and blind drains.
Subsurface drip irrigation. Application of water below the soil surface through emitters, with
discharge rates generally in the same range as those of drip irrigation. This method of water
application is different from and not to be confused with subirrigation, where the root zone is
irrigated by water table control.
Succession. The sequence of plant communities that develops between the initial colonization of bareground and the establishment of climax vegetation. As this sequence unfolds, the plants themselvesmodify the physical environment, new species invade, and the numbers of species and their
proportions gradually change.
Succulent. A plant composed largely of succulent tissue, the cells of which are large and containwater­filled vacuoles. Leaves may be permanently absent or seasonally absent; when leaves areabsent, the plant relies on its green stems to conduct photosynthesis.
Sunburn. Injury to bark and cambium caused by a combination of excessive light, heat, andinsufficient moisture.
Surface irrigation. Broad class of irrigation methods in which water is distributed over the soil
surface by gravity flow.
Surface water. Water sources located above the earth’s surface, including rivers, lakes, reservoirs,
and ponds.
Suspended solids (SS). Solids that either float on the surface of, or are in suspension in, water,
wastewater, or other liquid and that can be largely removed by laboratory filtering. Such suspended
solids usually contribute directly to turbidity. Defined in waste management, these are small particles
of solid pollutants that resist separation from the wastewater. Suspended solids (along withbiochemical oxygen demand [BOD]) are a measurement of water quality and an indicator oftreatment plant efficiency.
Tailwater. Water, in a stream or canal, immediately downstream from a structure or excess irrigationwater that reaches the lower end of a field.
Temperate. Moderate, as in climate.
Tensiometer. A device to measure the tension with which water is held in the soil.
Tertiary wastewater treatment. Biological, physical, and chemical treatment processes that follow
secondary wastewater treatment. The most common tertiary wastewater treatment process consistsof flocculation basins, clarifiers, filters, and disinfection processes. The term tertiary wastewater
treatment is also used to include advanced wastewater treatment beyond filters.
Tidal wetland. Coastal meadows subject to flooding by the sea. Plants in such areas must toleratesalinity, mechanical disturbance, and anaerobic conditions. Vegetation usually consists of a single,
low­growing layer of perennial herbs. The soil beneath is crowded with rhizomes and roots. Flora arerather simple, with relatively few species coexisting within a given wetland.

GL­30

Tile drain. Drain constructed by laying drain tile with unsealed joints in the bottom of a trench that isthen refilled. Tile is usually constructed of clay or concrete.
Tilth. The physical condition of the soil in relation to its ability to support plant growth.
Top dressing. Addition of a fertilizer or soil improver to the soil surface or to grass.
Topsoil. Uppermost layers of soil, containing mineral nutrients and organic matter, soil­dwellingorganisms, and plant roots. Topsoil is derived from weathering of subsoil and from the decay anddecomposition of plant and animal remains.
Total coliform. Escherichia coli and similar gram­negative bacteria that are normal inhabitants offecal discharges and soils. The total coliform group is recognized in drinking water standards.
Total coliform bacteria. A particular group of bacteria that is used as an indicator of possible
wastewater pollution. This group includes coliforms that inhabit the intestines of warm­blooded
animals and those that inhabit soils. They are characterized as aerobic or facultative anaerobic, gram­negative, non­spore­forming, rod­shaped bacteria that ferment lactose with gas formation within 48 h
at 35 °C. In the laboratory, these bacteria are defined as all the organisms that produce colonies with agolden­green metallic sheen within 24 h when incubated at 35 °C plus or minus 1 °C on M­Endo
medium (nutrient medium for bacterial growth). Their concentrations are expressed as the number ofcolonies per 100 mL of sample.
Total dissolved solids (TDS). (1) The sum of all dissolved solids in a water or wastewater and an
expression of water salinity in milligrams per liter (parts per million). It is empirically related toelectrical conductivity (EC in decisiemens per meter) multiplied by 640 or 735. The inorganic salts
are measured by filtering a water sample to remove any suspended particulate material, evaporating
the water, and weighing the solids that remain. An important use of the measure involves theexamination of the quality of drinking water. Water that has a high content of inorganic material
frequently has taste problems and/or water hardness problems. As an example, water that contains an
excessive amount of dissolved salt (sodium chloride) is not suitable for drinking. High­TDS solutions
have the capability of changing the chemical nature of water. High TDS concentrations exert various
degrees of osmotic pressure and often become lethal to the biological inhabitants of an aquatic
environment. The common and synonymously used term for TDS is “salt.” Usually expressed inmilligrams per liter.
Total organic carbon (TOC). A measure of organic matter, which contains carbon, in water.
Because many organic (carbon­containing) compounds can be detrimental to human health, themeasurement of TOC is a useful indicator of the quality of recycled water.
Toxicity. The capacity of a chemical compound to produce injury.
Trace elements. Mineral nutrients required in minute amounts for successful plant growth.
Translocation. Transfer of nutrients (or a virus or herbicide) through a plant.
Transpiration. The process by which water in plants is transferred as water vapor to the atmosphere.

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Treated (wastewater) effluent. Water that has received primary, secondary, or advanced treatment
to reduce its pollution or health hazards and is subsequently released from a wastewater facility after
treatment.
Treatment. Any method, technique, or process designed to remove solids and/or pollutants fromwater or wastewater. Also see primary wastewater treatment, secondary wastewater treatment,
and tertiary wastewater treatment.
Treatment plant. A structure built to treat water or wastewater before using the water, discharging
wastewater into the environment, or reusing the treated wastewater (recycled water).
Tree. Perennial woody plant that, in its natural state, has a distinct trunk or main stem and is usuallytaller than a shrub.
Tree canopy. An interwoven mass of branches and leaves above the main stem of a tree.
Trickle irrigation. See drip irrigation.
Turbidity. (1) A measure of the reduction in transparency of water caused by suspended material.
The term “turbid” is applied to waters containing suspended matter that interferes with the passage oflight through the water or in which visual depth is restricted. The turbidity may be caused by a wide
variety of suspended materials, such as clay, silt, finely divided organic and inorganic matter, solublecolored organic compounds, plankton, and other microscopic organisms and similar substances.
Turbidity in water has public health implications due to the possibilities of pathogenic bacteria being
encased in the particles and thus escaping disinfection processes. Turbidity interferes with water
treatment (filtration) and affects aquatic life. Excessive amounts of turbidity also make water
aesthetically objectionable. The degree of the turbidity of water is measured by a turbidimeter. (2)The collective optical properties of a water sample that cause light to be scattered and absorbed rather
than transmitted in straight lines; the higher the intensity of scattered light, the higher the turbidity.
Turbidity is expressed in nephelometric turbidity units (NTU) or Formazin turbidity units (FTU)
depending on the method and equipment used.
Turf. Grass, especially short varieties upon which people may walk.
Turfgrasses. Grasses grown on playgrounds, parklands, sports fields, and golf courses.
Turfing. Establishment of grass area by laying turf onto a prepared bed.
Unavailable soil water. That portion of water in a soil held so tightly by adhesion and other soil
forces that it cannot be absorbed by plants rapidly enough to sustain growth. Soil water at permanent
wilting point.
Understory. A layer of vegetation growing under groups of trees or shrubs.
Uniformity coefficient. A characterization of the aerial distribution of water in a field as the result of
irrigation.
Unplanned reuse. Unplanned use of treated wastewater effluent after disposal. Also called incidental
reuse. Many communities already unintentionally practice such unplanned reuse by withdrawing
water from rivers containing treated wastewater discharged upstream.

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Upstream. From a reference point in the direction toward the source or upper part of a stream;
against the current. In relation to water rights, the term refers to water uses or locations that affectwater quality or quantity of downstream water uses or locations.
Vadose zone. The aerated region including the root zone above the permanent water table ingroundwater basins.
Variegated. A leaf, steam, or flower of more than one color.
Vegetation type. A superset of the plant community, defined by the dominant growth form andhabitat, rather than by the dominant species. Typically, a vegetation type is given a two­part name;
examples include upland conifer forest, desert scrub, and tidal marsh. There are far fewer vegetation
types than communities; North America has between its shores thousands of plant communities but
fewer than a dozen major vegetation types.
Vein. A vascular bundle of a leaf.
Vine. A plant that has a single, weak trunk and must find additional support by twining around orotherwise climbing up and through neighboring shrubs or trees. The woody tissue in the stem of avine typically contains many more voids than regular wood, making it light and requiring relatively
little metabolic energy to build, thus allowing the plant to grow relatively rapidly and attain great
length (and, with sufficient support, great height).
Virus. The smallest (10 to 300 µm in diameter) life form capable of producing infection or diseases
in humans or other larger species. Complex macromolecules that are able to reproduce themselves
only in living cells and are capable of producing infection and diseases.
Warm­season turfgrass. Turfgrass species adapted to favorable growth during warm portions of thegrowing season; may go dormant during the winter.
Wastewater. (1) A combination of liquid and water­carried pollutants from homes, businesses,
industries, or farms; a mixture of water and dissolved or suspended solids. (2) That water for which,because of quality, quantity, or time of occurrence, disposal is more economical than use at the timeand point of its occurrence. Wastewater to one user may be a desirable supply to the same or anotheruser at a different location. Also referred to as domestic wastewater or sewage if it contains domestic
waste.
Wastewater irrigation. Land application of treated wastewater with the primary purpose of
maximizing crop production per unit of water applied; also, land treatment and disposal of wastewaterwhere maximum crop production is a secondary objective.
Wastewater reclamation. The planned reuse of waste water for specific beneficial purposes.
Wastewater treatment. Any of the mechanical or chemical processes used to modify the quality of
waste water in order to make it more compatible or acceptable to humans and the environment.
Wastewater treatment plant (WTP). A treatment plant containing a series of tanks, screens, filters,
and other mechanical, biological, and chemical processes by which pollutants are removed fromwastewater. Less frequently referred to as “waste treatment plant.”

GL­33

Water application efficiency. Ratio of the average depth of water infiltrated and stored in the rootzone to the average depth of water applied.
Water holding capacity. Total amount of water held in a freely drained soil per increment of depth.
It is the amount of water held between field capacity and oven dry moisture level, expressed incentimeters/centimeter, inches/inch, centimeters/meter, inches/foot, or total centimeters (inches) for a
specific soil depth. Sometimes called total water holding capacity (see available water capacity).
Water purveyor. Anyone who sells water to the public, usually the owner of a public water supply
system; a public utility, mutual water company, county water district, or municipality that delivers
water to customers.
Water quality. A term used to describe the chemical, physical, and biological characteristics ofwater, usually in respect to its suitability for a particular purpose, such as beneficial use or discharge
to the environment.
Water quality guidelines. Used to appraise suitability of water for intended purposes such as
irrigation of plants.
Water reclamation. (1) The treatment of water of impaired quality, including brackish water andseawater, to produce a water of suitable quality for the intended use. (2) A term synonymous withwater recycling. (3) The recovery of wastewater for useful purposes through treatment processes andsubsequent return to either a surface or groundwater source. (See also water reuse.)
Water recycling. (1) The process of treating wastewater for beneficial use, storing and distributing
recycled water, and actually using recycled water. (2) The reuse of water through the same series ofprocesses, pipes, or vessels more than once by one user, wherein the effluent from one use is captured
and redirected into the same use or directed to another use within the same facility of the user. This
form of recycling, often without treatment between uses, is common in industrial facilities, such as
cooling towers.
Water reuse. The preferred general term for the practice of reclaiming water from municipal andindustrial wastewater effluents by applying various treatment processes.
Water softener. A pressurized water treatment device in which hard water is passed through a bed of
cation exchange media for the purpose of exchanging calcium and magnesium ions for sodium or
potassium ions, thus producing a softened water that is more desirable for laundering, bathing, anddishwashing.
Water table. A term used to describe the plane below which the soil or porous rock is completely
saturated with water.
Water transfers. Marketing arrangements that can include the permanent sale of a water right by thewater rights holder; a lease of the right to use water from the water rights holder; the sale or lease of acontractual right to water supply.
Water use. Application of a resource such as water to a particular purpose.

GL­34

Beneficial use. Application of a resource to a purpose that produces economic or other benefits,
tangible, or intangible, economic or otherwise, such as employment of water for domestic
supply, irrigation, industrial supply, power generation, or recreation.
Conjunctive irrigation use. That portion of water applied to irrigation that is absorbed by thecrop and used to build plant tissue or transpired, together with that lost from the cropped areaby evaporation.
Consumptive water use. Employment of water in a manner that makes it unavailable for otherapplication because of absorption, evaporation, transpiration, incorporation in manufactured
product, or changes in quality.
Domestic use. Employment of water for the purposes of the home, including drinking, cooking,bathing, laundry, cooling, watering lawns, washing cars, and filling swimming pools.
Multiple use. Management of resources to satisfy two or more function purposes.
Nonbeneficial consumptive irrigation use. The portion of water withdrawn for irrigation that isneither used directly in crop production nor returned to the stream but rather is lost intransmission by evaporation or otherwise.
Nonconsumptive water use. Employment of water in a manner that does not reduce the amountof suitable water available for other purposes, including both on­site uses of the flow.
On­site water use. Employment of water in a manner that does not require diversion or flow ofwater, chiefly recreation uses and retention and temporary storage of excess water to prevent
flood damage downstream.
Water use efficiency. (1) Dry matter or harvested portion of crop produced per unit of water
consumed. (2) Ratio of water beneficially used to the water delivered to the area being irrigated.
Weathering. The physical, chemical, and biological processes that disintegrate the surfaces of rocks.
Wetland. An area that is periodically inundated or saturated by surface or groundwater on an annual
or seasonal basis that displays hydric soils and that typically supports or is capable of supportinghydrophytic vegetation.
Weed. A plant growing where it is not wanted.
Wet feet. Roots repeatedly or continually exposed to water­saturated soil conditions.
Wilt. Loss of rigidity and drooping of plant parts, generally caused by insufficient water in the plant.
Wilting point. (Synonymous with permanent wilting point.)
Woodland. Grassland with overtopping trees whose canopies cover 30 to 60% of the ground. (Seealso, for comparison, savanna and steppe.)
Woody. Plant type that contains secondary xylem.

GL­35

Woody perennials. Plants that accumulate above­ground stem tissue year after year. Depending on
the size and shape of the stems, these plants may be subshrubs, shrubs, vines, or trees.
Xeric. Drought­resistant or desert­type plant.
Xeriscape. Refers to horticulture that emphasizes water conservation using specific landscape design
elements and management practices.
Xerophyte. A plant able to grow in a very dry environment. Such plants often are light in color andmay have small, hard leaves, an epidermis with thick cuticle, and stomata that close early during theday. They may also have succulent tissue.
Xylem. Plant tissue consisting of tracheids, vessels, parenchyma cells, and fibers; wood.
Zero discharge. The goal, in the preamble to the Clean Water Act (CWA), of zero pollutants in water
discharges.

GL­36

Subject Index
AC

abiotic causes of injury and disease in plants, X­
3
Abiotic Disorders of Landscape Plants: a
Diagnostic Guide, V­15
abiotic plant disorders
avoiding high maintenance costs, X­2challenges of accurate diagnosis, X­1 –X­3diagnosing problems, X­3, X­4, X­6, X­
7, X­8, X­9landscape quality, X­2
patterns, X­5potential solutions, X­6, X­7, X­8, X­9
symptoms, X­3, X­6, X­7, X­8, X­9test for likely causes, X­3accumulation patterns of salt in irrigated soils,III­4, III­5acid­forming amendments, IX­14
acidification, IX­14acronyms and abbreviations, AA­1–AA­3
adjusted SAR (SARadj), III­7
Agricultural Handbook No. 60, III­12
air pollutants causing plant injury and disease,X­3, X­9alkalinity, III­10
allowable depletion of the total available water,
VIII­16
ammonia, IX­17

calcite, III­4, IV­15
calcium deficiency in plants, IX­16, X­8
calcium or acid­producing amendment, IX­13
calcium­related disorders, V­19
California
coastal southern California trees andshrubs’ salt tolerance, V­33
map of plant environments for coastal
southern California, VI­3
turfgrasses, VI­32
turfgrasses’ salt tolerance, V­30
California Invasive Plant Council (Cal­IPC), VI­
36
California Irrigation Management Information
System (CIMIS), VIII­4
weather station, III­28, VIII­4, VIII­5
California native plants, VI­27
coastal southern California nativeplants, VI­7–VI­19
guides, VI­36–Vi­37
oak woodland plants, VI­33
recommended by Labadie (1978) for
California landscapes, VI­21–VI­24
riparian woodland plants, VI­34
scrubland plants, VI­35
trees’ salt tolerance, V­32
California Native Plants for the Garden, VI­25
California Native Plant Society, San Diego
Chapter, VI­36
California Native Trees and Shrubs: for Garden
and Environmental Use in Southern California
and Adjacent Areas, VI­25
carbonates, III­10, X­6cemeteries, II­5chemical amendment, IX­13chemical reactivity of waters, IV­13–IV­14
Chemigation in Tree and Vine Micro­Irrigation
Systems, VII­13
chemistry of soil solutions, IV­13
chloramine, III­11
chloride, III­18, V­34, V­37, X­9chloride hazard, III­16
chlorine, III­10
deficiency in plants, IX­16
chlorosis, X­8clay, IX­12
clay layers in soil, IX­13
clay pan, IX­13
climatic zones, V­2clogging constituents, III­11
coastal foothill plants, VI­7–VI­19

B
bark damage, X­9bentgrasses, VI­28
bermudagrass, III­27, III­29, VI­31
bermudagrass potable water, III­29
bermudagrass recycled water, III­29
bicarbonate, III­18
biotic causes of injury and disease in plants, X­3
blending of imported waters, III­26
bluegrasses, VI­28
boron, III­15, III­18, V­35, V­37, IX­17
damage to leaves, photo, V­48
deficiency, IX­16
hazard, III­16
injury to leaves and growth reduction,V­38
possible limits of, III­15
threshold, V­23
tolerance, V­15, V­35, V­37
tolerance limits for cut flowers, V­23
tolerance limits for ornamentals, V­42
toxicity symptoms, V­35
bud damage, X­9SI­1

Establishing and Monitoring the Natural Turf
Athletic Field, VI­40
estimated mass loading of nitrates and salts fromthe root zone, III­29
estimating water needs forplants, VIII­2–VIII­13
species in heterogeneous landscapes,
VIII­9“Estimating Water Needs for Landscape Plants,”VI­26
ethylene propylene diene monomer, VII­13
evapoconcentration, IV­14
evapoconcentration factor (ECF), IV­15
evaporation, VIII­2
from soil surface, VIII­4
evapotranspiration (ET), IV­2, VII­3, VIII­3crop evapotranspiration (ETc), VIII­2
extract of saturated soil paste (ECe), IX­
2historical average reference
evapotranspiration values, VIII­7historical ETo values, VIII­6“real­time” ETo, VIII­4
reference evapotranspiration (ETo),
VIII­4variance of real­time reference
evapotranspiration, VIII­6
exchangeable sodium, III­6, IX­7exchangeable sodium percentage of soil cationexchange capacity (ESP), IX­2
in turf, IX­9coastal margin plants, VI­7–VI­19
Colorado River water, IV­14
mineral precipitation with
evapoconcentration of, IV­18
salt accumulation from irrigating
with, IV­17
compaction, IX­12comprehensive bibliography, V­13
conifersbrown needles, X­9needle dieback, X­9short needles in, X­9yellowing, X­9conversion factors, CT­1–CT­5
conversion of EC to TDS, III­3, CT­4
copper deficiency in plants, IX­16
crop coefficient (Kc), IV­2, VIII­7
landscape plants, VIII­9–VIII­13, VIII­
11, VIII­12
turfgrass, VIII­8, VIII­9D
deep percolation, IV­20
flow path of, IV­23
in landscape irrigation, IV­21
mass loading of salts in, IV­22
defoliation, X­9depositional crusts, IX­12
design checklists, VI­27
discolored leaves, IX­15
dispersion of clays and organic matter, IX­7
distribution of salinity in the root zone, IV­7
distribution uniformity of water application(DU), IV­2, VII­4drainage, poor, X­3drip irrigation, VII­9, IX­7advantages and disadvantages, VII­10
filtration, VII­9
injection system, VII­9
sanitizing agents, VII­9subsurface drip irrigation, VII­9F
fertilizers and relative salinity, V­16
fescue, VI­29
filters for irrigation systems, VII­11–VII­12
automatic reverse flushing system, VII­
11
maintenance, VII­12
sand or medium filters, VII­11
flowering plants and phosphorus and potassium,
IX­15
free available chlorine, III­10
freeway landscaping, II­5

E
early water quality guidelines, III­12–III­17“Easy­to­Grow California Native Plants for San
Diego County,” VI­36
effects of environment and management, V­43–
V­45
effects of SAR and EC of waters on water
filtration rates, III­8electrical conductivity (EC), III­3, X­6
EC­SAR combinations, IX­11
electrolyte concentration, III­7
equilibrium chemical models, IV­14
essential plant nutrients, IX­14–IX­15

G
glycophytes, V­3golf courses
plant selection, VI­38–VI­40
tee, fairway, rough, andbunker, VI­40
trees, VI­38
turf, VI­39
Victoria Golf Course, III­25
with restricted access, II­5

SI­2

with unrestricted access, II­5
guidelines for the interpretation of quality ofwater for irrigation, III­17, III­18
gypsum, III­4, IV­13, IV­15, IX­13

irrigation system, VII­2, VII­3–VII­4
backflow devices and point ofconnection, VII­10components of, VII­10–VII­14
computer controlled, VII­10
design, layout, and staking, VII­5
distributing recycled water, VII­7
distribution uniformity (DU), VII­4
efficiency, VII­4
filters, VII­11–VII­12
functional landscape, VII­7
injection systems, VII­13–VII­14
installation and construction, VII­5
maintenance, VII­6
maintenance personnel, VII­6
operation, VII­6
plugging of drip emitters and low­
volume sprinklers, X­6plumbing codes, VII­5
pressure regulators, VII­12–VII­13
pressure regulators, types of, VII­12
proper cultural treatment of plants, VII­
6
quick couplers and hose bibs, VII­13
regulatory guidelines, VII­5
runoff elimination, VII­11
strategic planning, VII­6
irrigation systems, types of, VII­8–VII­10drip irrigation, VII­9
fixed spray sprinklers, VII­8
recycled water systems, VII­13
rotor sprinklers, VII­8H
halophytes, V­3hardness, III­10
hardpan, IX­13
heavily graded landscapes, IX­16
herbicide damage in plants, X­3, X­6horticultural crops’ mineral nutrients and salinity
tolerance, V­19
Hydrosalinity Model 1, IV­6, HM­1
Hydrosalinity Model 2, IV­9, HM­2
Hydrosalinity Model 3, IV­11, HM­3
Hydrosalinity Model 4, IV­20, HM­4hydrozone, VII­3

I
illustrative examples
example IV­1, IV­3
example IV­2, IV­4
example IV­3, IV­5
example IV­4, IV­6
example IV­5, IV­9
example IV­6, IV­11
example IV­7, IV­13
example IV­8, IV­20
example VIII­1, VIII­13
example VIII­2, VIII­14
infiltration, III­18
injured buds and leaves, IX­15
inland foothill plants, VI­7–VI­19
inland valley plants, VI­7–VI­19
insufficient irrigation, X­6interaction of salinity and sodicity, III­8
interactive chemical reactions in soil water
systems, IV­14
intermediate valley plants, VI­7–VI­19
iron deficiency in plants, IX­16, X­8, X­9iron precipitates in sprinklers, X­6irrigation
application rate (AR), VIII­13
daily run time, VIII­14
duration, VIII­13, VIII­14
excess, X­9frequency, VIII­15, VIII­16
insufficient, X­8nonuniform patterns, X­8scheduling, VIII­13
scheduling software, VIII­13, VIII­14
irrigation, methods of, V­44
calendar method, VIII­17
flexible method, VIII­16, VIII­17

K
Kentucky bluegrass, III­27, III­29
kikuyugrass, III­27, VI­31
kikuyugrass potable water, III­29

Llaboratory tests of soil, water, or plant tissues, V­
16
landfill landscapes, X­3
landscapecoefficients (KL), VIII­9, VIII­10
design, VI­37
management history, X­5plants’ salinity tolerance, V­15
site conditions, X­3
versus crop irrigation, VIII­2
Landscape Plants for Western Regions, VI­26
leachate composition case study, III­25
leachates, III­25
leaching fraction (LF), III­4, IV­2, IX­4leaching requirement (LR), IV­4, IX­4
leaf

SI­3

bronzing, X­9burn, X­9chlorosis, V­4dark green foliar margins, X­9drop, X­9
injury and damage, X­6light green coloring, X­9purple or brown spots, X­9wilting, X­9yellowing, X­9
LF and EC by root zone quartiles, IV­7
for mixed supply irrigation waters, IV­
10lightning­caused injury in plants, X­3limb damage, X­9chlorine, IX­16
copper, IX­16
iron, IX­16, X­8, X­9magnesium, IX­16, X­9manganese, IX­16, X­9molybdenum, IX­16
nickel, IX­16
nitrogen, IX­16, X­8, X­9phosphorus, IX­16, X­8
potassium, IX­16, X­8, X­9sulfur, IX­16, X­8
symptoms, IX­15, IX­16
zinc, IX­16, X­9O
organic matter, IX­14
ornamental nurseries and sod farms, II­5
osmotic effect, V­2

M
major anions, III­3
major cations, III­3
magnesium deficiency in plants, IX­16, X­8manganese deficiency in plants, IX­16, X­9Manual of California Vegetation, A, VI­37
map of plant environments for coastal southern
California, VI­3
marginal leaf necrosis, IX­15
mass loading of salts in deep percolation, IV­22
mechanical means of improving soil
permeability, IX­13
microbial slimes, X­6
microclimate coefficient (Kmc), VIII­10
micronutrients, IX­14
mineral deficiencies and excesses causing
disease in plants, X­3
mineral precipitation, IV­15
modeling coefficients for landscape plants after
crop coefficients, VIII­8
modified Penman method, VIII­5
moisture distribution patterns, IX­6
molybdenum deficiency in plants, IX­16
Monterey Wastewater Reclamation, III­22

P
palms, curling and burning, X­9parks and playgrounds, II­5
Penman–Monteith formula, VIII­5
perennial ryegrass, III­27
pesticide­caused disease in plants, X­3
pH, adjusting soil, IX­16
phosphogypsum, IX­13
phosphorus, III­9, IX­17
deficiency in plants, IX­16, X­8
plantanalyses, IX­17
density coefficient (Kd), VIII­10
identification, X­4
needs
evapotranspiration, VII­3
water, VII­3
palettes, VI­27
profiles, VI­25
Plant Communities of Southern California, VI­
36“Plant Compendium,” VI­4, VI­27“Plant Lists for Landscape Situations,” VI­4
plant selection
by zones, VI­2
certain types of landscapes, VI­37
golf courses, VI­38–VI­40
medians and street­side plantings, VI­41
parks, VI­41
playing fields, VI­40–VI­41
plant selection guides, VI­1, VI­31–VI­41
coastal southern California groundcovers, VI­5–VI­6coastal southern California large shrubs,VI­11–VI­13

N
Native Plants for California Gardens, VI­27
Native Plants for Use in the California
Landscape, VI­20
necrosis, X­9nickel deficiency in plants, IX­16
nitrates, III­9, IX­17
nitrogen, III­9, III­18,
deficiency in plants, IX­16, X­8, X­9drainage, in, III­29
excess, X­9nutrient deficiencies in plants, IX­15
boron, IX­16
calcium, IX­16, X­8SI­4

coastal southern California large trees,VI­18–VI­19
coastal southern California medium
shrubs, VI­9–VI­10
coastal southern California medium
trees, VI­16–VI­17
coastal southern California small
shrubs, VI­7–VI­8coastal southern California small trees,VI­14–VI­15
online, VI­32–VI­36
trees, shrubs, and ground covers, VI­2–
VI­27
using, VI­41, VI­42
plant­specific threshold soil salinity (ECa), IV­4
“Planting Guidelines,” VI­4
plugging potential of irrigation water used indrip irrigation systems, III­11
polyacrylamide (PAM), IX­14
polysaccharides in the organic matter, IX­14
ponding, X­9pore volume reclamation leaching, IV­12–IV­13
potassium deficiency in plants, IX­16, X­8, X­9precipitation rate (PR), VII­4
primary nutrients, IX­14
primary salinization, IX­2
principles of water and soil salinity management,IV­1effects of soil hydraulicconductivity, III­24
excess nitrogen for susceptible
plants, III­24
potential toxicity of chlorine
residual, III­24
specific ion toxicity hazard ofboron, III­24
specific ion toxicity hazard ofchlorine, III­24
specific ion toxicity hazard of
sodium, III­24
irrigating landscapes, for, II­5
nutrients in, IX­17
potential benefits of, II­1–II­2
quality, III­21, X­1
regulations, II­3–II­5
representative composition of, III­21,
III­22
secondary treatment, II­4
tertiary treatment, II­4
Title 22, Code of Regulations on Water
Recycling Criteria, II­3, III­9undisinfected secondary recycled water,II­5
use of, II­1
use of in selected service areas, II­3
Water Recycling Criteria, II­3
“Reducing Salt Injury to Ornamental Shrubs inthe West,” V­15
reference evapotranspiration (ETo), IV­2
reflective power of soil and crop surfaces, VIII­4
regional groundwater basins’ salt­loading
concerns, IV­20
residential landscaping, II­5
residual chlorine, III­10–III­11, III­18
residual sodium carbonate (RSC), III­9, III­15,
III­16, IX­9resistance of canopies, VIII­4
retrofit of potable systems to recycled water
systems, VII­14
cross­connection testing, VII­14
existing systems, VII­14
purple recycled water caps or tags, VII­
14
root crown disease, X­9root water extraction pattern, III­20, IV­6, IV­8
specified root water extraction pattern,IV­5root zone,
constructed, IV­12
salinity, IV­2
controlling, IV­23
salt accumulation, a comparison of, IV­
16
quartiles, IV­6, IV­7, IV­10, IV­16

R
radiation causing injury and disease in plants, X­
3rainfall on drip­irrigated soil, IX­7
Rancho Santa Ana Botanic Garden, VI­32
reclamation leaching, IV­10–IV­11
needs, IV­12
pore volume reclamation leaching, IV­
12–IV­13
recycled water, I­1, III­2
components of, VII­13
current uses of, II­2–II­3
disinfected secondary­2.2 recycledwater, II­5
disinfected secondary­23 recycledwater, II­5
disinfected tertiary recycled water, II­5
evaluation of representative recycledwaters, III­23, III­24
carbonate deposition on
foliage, flowers, and fruit,III­24dispersion of soil organic
matter and reduced water
intake rates, III­24
effects of availability of soil
water to plants, III­24

SI­5

rooting depth, inadequate, X­3ryegrass, VI­30

salt or saline spray, V­5, V­6, V­7, V­
10, V­12“sensitive,” V­5, V­9soil salinity, V­7, V­10, V­12
“tolerant,” V­5, V­9tolerant plants, III­4trees, shrubs, and ground covers, V­5–
V­13
turfgrasses, V­28, V­30
varietal differences, V­17, V­27
“Salt Tolerance of Ornamental Shrubs andGround Covers,” V­14
“Salt Tolerance of Ornamental Shrubs, Trees,and Iceplant,” V­14
“Salt Tolerance of Plants,” V­14
sandy layers of soil, IX­13
school yards, II­5
seashore paspalum, VI­31
seawater intrusion, IX­2
seawater spray, IX­2
secondary nutrients, IX­14
secondary salinization, IX­2
sediments clogging sprinklers, X­6sensitivity of plants to specific ions, V­34–V­43
shoot damage, X­9slowly permeable soils, IX­12causes, IX­12
intake of water, IX­12solutions, IX­13swell, separate, and disperse, IX­12snow and ice injury in plants, X­3sodic soils, IX­7
sodicity, III­6, III­7, IX­12
sodium, III­18, V­34, V­36
sodium adsorption ratio (SAR), III­12, IX­7, X­6
EC­SAR combinations, IX­11
sodium hazard (sodium adsorption ratio, SAR),
III­12, III­14, III­16
soil
aeration, X­9analysis, IX­15
compaction, X­6, X­8
conditioners, IX­14
dry areas, X­6
excess runoff, X­6
excess salinity, X­8, X­9excess sodicity, X­8, X­9high residual sodium carbonate, X­6high SAR and low EC, X­6moisture sensors, VIII­18
permeability, III­6, IX­10poor drainage, X­9poor fertility, X­3slow water penetration, X­6stratification, X­6subsoil impermeable layers, X­8

S
saline soils, IX­1–IX­7
salinity, III­18
distribution patterns, IX­6
excess soil salinity, X­8
excess water salinity, X­6, X­8, X­9measurement methods, IX­2
osmotic effects of, III­3, V­4plant response to, V­3salinity hazard (EC), III­12, III­16
salinity­induced nutritional disorders, V­18
salinity­induced reduction, V­22
salt(s)accumulation at lower depths, IX­3
accumulation from irrigating with
Colorado River water, IV­17
classification of salt­affected soils, IX­2
disease and injury, X­3entering plant through leaves, V­6entering plant through roots, V­6highly soluble, IX­1
leaching at surface, IX­3
less soluble, IX­1
redistribution of, IX­7
sink, IV­23
source, IV­23
specific constituents of, V­2salt accumulation and leaching application ofreactive mixing cell model, IV­17–IV­10
salt­damaged plant leaves, photos, V­45
“Salt Injury to Ornamental Shrubs and GroundCovers,” V­15
salt­related stress, V­21,
symptoms, V­4–V­5
salt tolerance, V­15
California native trees, V­32
California turfgrasses, V­30
coastal southern California trees andshrubs, V­33
defining plant salt tolerance, V­2–V­3
eucalyptus, V­16
field trials, V­6floriculture species, V­17–V­27“highly tolerant,” V­4, V­9horticultural crops, V­19
landscape floral crops, V­23
landscape groundcover and vine
species, V­12, V­16
landscape shrub species, V­10, V­16
landscape tree species, V­7, V­16
“moderately tolerant,” V­5, V­9native plants, V­31–V­33

SI­6

texture variability and water holding
capacity, X­6waterlogging, X­6
wet areas, X­6
soil salinity
as affected by irrigation and rainfall,IV­8
dynamic temporal and spatial changes,
IX­2, IX­3
excess, X­6threshold, IX­4soil surface
black salt crust, X­8, X­9white salt crust, X­8, X­9solubility of waters for irrigation based onresidual sodium carbonate (RSC), III­15
Southwestern Landscaping with Native Plants,V­31
species coefficient (Ks), VIII­10
specific ion toxicity, III­6, III­18, X­6annual plants, III­6
woody plants, III­6
specific ion toxicity hazard ofboron, III­24
chlorine, III­24
sodium, III­24
spotting, IX­15
sprinkler systems, IX­7
distribution profiles and matchedprecipitation rates, VII­8
distribution uniformity, VII­7, X­6
performance characteristics, VII­7
precipitation rate, VII­7
radius of throw, VII­7
water chemistry problems, X­6
St. Augustine grass, VI­31
standard turf­scoring procedure, III­30
steep slopes, X­3, X­6stomatal pores, VIII­2
stratification of the soil, IX­13
structural crusts, IX­12
stunted growth in plants, X­9succulent tissue, excess growth in, X­9sulfur deficiency in plants, IX­16, X­8sunlight, excessive plant exposure, X­6, X­9Sunset Western Garden Book, The, VI­20

in drainage, III­29
toxic gases, X­3transpiration, VIII­2tree and shrub abiotic disorders, X­7, X­9Trees and Shrubs for Dry California
Landscapes, VI­2, VI­26
trunk damage, X­9
Turf Management for Golf Courses, VI­39
turfgrass, III­27
abiotic disorders, X­7, X­8aesthetic quality of, III­30
bare spots, X­8
California turfgrass’s salinity tolerance,V­30
chlorosis, X­8cool­season turfgrass, III­27, VI­28, VI­
32
crop coefficients, VIII­8, VIII­9
deformed leaves, X­8
desiccation, X­8
discoloration, X­8
ion sensitivity, V­36–V­43
leaf rolling, X­8
localized dry or wet spots, X­8necrosis, X­8nitrogen requirement, IX­15
salt tolerance, V­28
seed germination problems, X­8selection, VI­28
selection guide, VI­27–VI­32
tip burning, X­8yellowing, X­8turfgrass, types of,bentgrasses, VI­28
bermudagrass, III­27, III­29, VI­31, III­29
bluegrasses, VI­28
California turfgrasses, VI­32
fescue, VI­29
Kentucky bluegrass, III­27, III­29
kikuyugrass, III­27, VI­31
perennial ryegrass, III­27
ryegrass, VI­30
seashore paspalum, VI­31
St. Augustine grass, VI­31
warm­season turfgrass, III­27, VI­28,
VI­32
weeping alkaligrass, VI­30
zoysiagrass, VI­31“Twelve Most Wanted Native Shrubs That
Succeed in a Garden Without Your Really
Trying, The” VI­36

T
temperature injury and disease in plants, X­3, X­
6, X­9textural stratification, IX­13
threshold ECe, V­27
Torrey Pines, III­22
total available water, VIII­16
total dissolved solids (TDS), III­3

U
University of California Committee ofConsultants, III­16

SI­7

U.S. Salinity Laboratory, V­13

V
Victoria Golf Course, III­25

W
warm­season turfgrass, III­27, VI­28, VI­32
water
excess RSC in, X­8
excess sodicity in, X­9filtration rate, III­7, III­8stress, X­6water quality constituents of concern, III­2
principal constituents of concern, III­2
water quality guidelines, III­12–III­21, III­17
early water quality guidelines, III­12 –III­17
FAO Water Quality Guidelines, III­17,
III­21
caveats and assumptions in theuse of, III­18–III­21
degree of restriction on use,III­18
restriction on use, III­20
water­repellent sand­based turf, X­8
Water Suitability Determination Model(WATSUIT), IV­14
applied to quartile root zone salt
accumulation, IV­15–IV­17
simulated results with the chemistry ofColorado River water, IV­15
Water Use Classification of Landscape Species(WUCOLS), VIII­9weeping alkaligrass, VI­30
West Basin Water Recycling Facility, III­22
wetted foliage, V­5wetting patterns, IX­4, IX­5
Whispering Palms Turfgrass Study, III­22, III­25, III­27
wind injury in plants, X­3, X­9Z
zinc deficiency in plants, IX­16, X­9zoysiagrass, VI­31SI­8