U.S. GEOlOGICAl SURVEY CIRCULAR 1017 

Sources and use 

for agriculture 
Cover art by Marty Simmons and Marilyn Billone 
Essential Elements and 

Soil Amendments for Plants: 

Sources and Use for 

Agri culture 

By R. C. Severson and Hansford T. Shacklette 

Geologic and incidental sources of elements essential 

for plant growth, and amendments used to improve 

physical properties of soils 

U.S. GEOLOGICAL SURVEY CIRCULAR 1017 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U. S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1988 

Free on application to 

Books and Open-File Reports Section, 

U.S. Geological Survey, 

Box 25425, Building 81 0, 

Federal Center, 

Denver, CO 80225 

Library of Congress Cataloging in Publication Data 

Severson, R. C. (Ronald Charles), 1945-

Essential elements and soil amendments for plants. 

(U.S. Geological Survey circular; 1017) 

"Geologic and incidental sources of elements essential for plant growth, and 

amendments used to improve physical properties of soils." 

Supt. of Docs. no.: I 19.4/2:1017 

1. Crops and soils. 2. Crops-Nutrition. 3. Soil 

chemistry. 4. Geochemistry. 5. Fertilizers. 6. Soil amendments. I. Shacklette, Hansford T. II. Title. Ill. Series. 

S596.7.S48 1988 631.8 88-600362 
CONTENTS 

Introductory statement 1 

Chemical elements essential for plants 2 

Introduction 2 

Major essential elements (macronutrients) 2 

Nitrogen 2 

Phosphorus 4 

Potassium 7 

Sulfur 11 

Calcium 14 

Magnesium 17 

Minor essential elements (micronutrients) 20 

Boron 20 

Chlorine 22 

Copper 24 

Iron 27 

Manganese 29 

Molybdenum 32 

Zinc 34 

Use of soil amendments to improve the physical properties of soil 36 

Introduction 36 

Mineral materials 37 

Clays 37 

Zeolites 38 

Volcanic materials 38 

Sand 39 

Organic materials 39 

Peat 39 

Humates 40 

Miscellaneous materials 40 

Fly ash 40 

Use to improve soil physical properties 41 

Use to improve soil chemical properties 41 

Other materials 41 

References cited 41 

Selected references 42 

Appendixes 

1. Suggested terminology for soil amendments 44 

2. Conversion factors used for English and metric units 45 

3. Common plant names used in this report, with corresponding scientific 

names 45 

4. Glossary of selected terms used in this report 46 

Contents Ill 

Essential Elements and 

Soil Amendments for Plants: 

Sources and Use for Agriculture 

By R. C. Severson and Hansford T. Shacklette 

INTRODUCTORY STATEMENT 

The material in this report was derived from 

published sources, from unpublished data in our files, or 

from our experiences as soil scientist and botanist. We 

thought that a complete citation list for all data was both 

cumbersome and unnecessary in an outline of this type; 

therefore, only those references that represent large data 

sets are included in the text and are listed under 

"References Cited." The references we consulted 

frequently for facts and figures, but did not cite in the 

text, are listed under "Selected References." The 

selected references also include some compilations of 

information that we did not rely on heavily because they 

are tangential to the focus of this report but may be of 

value to the reader. We accept full responsibility for the 

discussions of plant nutrients or toxicants as being within 

our fields of competence. On the other hand, statements 

or inferences of nutritional and toxic effects of elements 

on man or domestic animals are taken directly from 

statements of animal nutritionists and are so identified by 

reference citations. 

There are inconsistences in the order of expressing 

units of area and weight in the data given in this report. 

Agricultural reports prepared as practical guides tend to 

use the English system of weights and measures, rather 

than the metric system that is used most commonly in 

research reports. It is difficult for most American 

farmers to think in terms of "kilograms per hectare" 

rather than "bushels per acre" when considering crop 

yields; conversely, it is just as difficult for most scientists 

to visualize a bushel of corn weighing 60 pounds, or a 

bushel of oats weighing 34 pounds, to name but two of 

the vagaries in bushel weights. We have tried to first give 

the units in which the measurements were made as 

Publication approved by the Director, U.S. Geological Survey, March 23, 

1988. 

reported, followed by a conversion to the alternative 

system. We have also included metric-English conversion 

factors as Appendix 2. 

Information in this report, for each element and 

amendment is arranged as follows: 

ELEMENT 

OCCURRENCE IN NATURAL MATERIALS 

ABUNDANCE IN SELECTED ROCKS 

ABUNDANCEIN"NATURAL"UNAMENDED 

SOILS 

MINERALS 

ORGANICS 

ABUNDANCE IN SOILS 

ABUNDANCE IN PLANTS 

SOURCES FOR FERTILIZERS 

GEOLOGIC OR OTHER PRINCIPAL 

SOURCES 

INCIDENTAL GEOLOGIC OR OTHER 

SOURCES 

ATMOSPHERIC 

IRRIGATION WATER 

MINERAL 

ORGANIC 

REACTIONS WITH SOIL CONSTITUENTS 

FORMS USED BY PLANTS 

FUNCTIONS IN PLANT METABOLISM 

EXTENT OF USE 

LOSSES FROM SOILS 

LEACHING 

EROSION 

CROP REMOVAL 

OTHER (VOLATILIZATION) 

BALANCE SHEET 

ADDITIONS 

LOSSES 

SOILS WHERE DEFICIENCIES ARE MOST 

COMMON 

Introductory Statement 1 
Information for all major and minor elements is 

presented using a similar outline where possible. 

An example of the outline format for amendments 

is illustrated as follows: 

AMENDMENT 

SOURCES 

MODE OF ACTION 

EXTENT OF USE 

POTENTIAL FOR USE 

We have also included a glossary of terms 

(Appendix 4) containing terms commonly used in soil 

science, botany, and agriculture, which will enable the 

reader to conveniently find the definition of an unfamiliar 

term. 

We acknowledge with gratitude the assistance 

given by our colleagues in the U.S. Geological Survey in 

preparing this outline. 

CHEMICAL ELEMENTS 

ESSENTIAL FOR PLANTS 

Introduction 

The background information provided on major 

and minor elements essential for plant growth may be 

useful in considering the application of geologic 

materials and processes to increase production and yield 

of food plants. This background information is not 

intended to be a detailed treatment of any aspect of 

fertilizer production or use, nor is it intended to include 

all materials and reactions involved in plant responses. 

Neither is it a guide to agricultural practices. Forms of 

fertilizers used and rates of application that are given 

only are examples selected to provide a general concept 

of kinds and quantities of fertilizers currently being 

utilized in the United States and other countries where 

agricultural technology is highly developed. 

The manner in which the different elements are 

discussed is not entirely uniform but has been modified 

as we thought appropriate for the several classes of 

materials. For example, estimates of the annual 

production and use of the major nutritive elements and 

balance sheet estimates are available, and therefore 

could be given; whereas, estimates of the amounts of 

some minor elements used probably have not been made. 

Some elements used in fertilizers have a direct source in 

geologic materials, others are derived as byproducts of 

ore processing and other industrial operations or are 

manufactured from materials that are only indirectly 

related to geologic deposits. Our discussions reflect these 

differences. 

Major Essential Elements 

(Macronutrients) 

NITROGEN-(N) 

OCCURRENCE IN NATURAL MATERIALS 

ABUNDANCE IN SELECTED ROCKS 

From Turekian and Wedepohl (1961), in parts 

·per million (ppm) 

Ultrabasic, 6 

Basaltic, 20 

Granitic 

High calcium, 20 

Low calcium, 20 

Syenites, 30 

ABUNDANCEIN"NATURAL"UNAMENDED 

SOILS 

MINERALS 

There is no appreciable quantity of N in soil 

minerals. 

ORGANICS 

Most of the N in soils is held in decaying 

(hum us) and living organic matter. 

"Representative" analysis of organic matter in 

soils: Humid regions, 80,000 lb/acre-furrowslice (89,600 kg!ha-furrow-slice) or 4%. Arid 

regions, 65,000 lb/acre-furrow-slice (72,800 

kg!ha-furrow-slice) or 3.25%. Range ordinarily 

expected, 0.40--10%. 

The N content of soils is almost entirely of 

atmospheric origin, most having been fiXed as 

oxides or other compounds by nodule bacteria 

and by nonsymbiotic bacteria and algae. In 

uncultivated soils, the N content reaches 

equilibrium at a level ranging from about 6,600 

lb/acre/40 in. depth (7,392 kg/ha/101.6 em 

depth) in southern sandy s<>ils to about 200,000 

lb/acre/40 in. depth (224,000 kg/ha/101.6 em 

depth) in northern peats in which the N is 

largely unavailable to plants. Total N in soils is 

a negative exponential function of 

temperature-for every 18°F (10°C) fall in 

mean temperature, the N content increases 2-3 

times because of the higher ratio of organic 

matter formation to decomposition. 

ABUNDANCE IN SOILS 

"Representative" analysis of agricultural soils (as 

N2), 4,000 lb/acre-furrow-slice (2,000,000 lb) or 

4,480 kg!ha-furrow-slice (weighing 908,000 kg). 

In the U.S., N is highest in Brunizem or BoraH 

soils of the prairie region of the Central States and 

declines eastward and westward in other soil 

groups. Some representative estimates (lb/acre/40 

in. depth) follow: 

2 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Nitrogen -Continued 

ABUNDANCE IN "NATURAL"-Continued 

Boralls (Brunizem) ........................................ 16,000 

(17,920 kglha/101.6 em depth), 3.2%. 

Ultisols (Red and Yellow Podzolic) .............. 4,000 

(4,480 kglha/101.6 em depth), 0.8%. 

Inceptisols or Mollisols (Brown Forest) ....... 6,700 

(7,504 kglha/101.6 em depth), 1.3%. 

Ustols (Chestnut) ........................................... 10,000 

(11,200 kglha/101.6 em depth), 2.0%. 

ABUNDANCE IN PLANTS 

The N content of some crop plants is illustrated by 

the following examples: 

Alfalfa hay, yield 4 tons/acre (9 metric tons/ha)-

190 lb/acre (213 kg/ha) N. 

Cabbage, yield 15 tons/acre (33.3 metric tons/ 

ha)-105 lb/acre (118 kg/ha) N. 

Corn grain, yield 130 bu/acre (113 hl/ha)-120 

lb/acre (134 kglha) N. 

Oats grain, yield 50 bu/acre (43.5 hllha)-35 

lb/acre (39 kg/ha) N. 

Potato tubers, yield 200 bu/acre (174 hl/ha)-45 

lb/acre (50 kg/ha) N. 

Sugar beet roots, yield 15 tons/acre (33.6 metric 

tons/ha)- 78 lb/acre (87 kglha) N. 

Wheat grains, yield 60 bu/acre (52 hl/ha)-70 

lb/acre (78 kg/ha) N. 

SOURCES FOR FERTILIZER 

GEOLOGIC OR OTHER PRINCIPAL 

SOURCES 

Chilean nitrate (96 +% NaN03 ). Insignificant 

amounts now used in the U.S. 

Coal. Coking coal contains approximately 1-2% 

N. In coking, ammonia is driven off and reacted 

with sulfuric acid to produce ammonium sulfate. 

Yielding about 13 lb ammonium sulfate per ton of 

coal (6.5 kg/metric ton). 

Cynamide process. Uses CaC03, plus coke as a 

source ofN. 

Synthetic ammonia. Presently the most important 

N fertilizer. N + H heated with a catalyst 

(osmium + iron) forms ammonia. Methane is 

used as a source of H; the source of N is coke, 

ammonia oxidation from nitric acid production, 

or fractional distillation of liquid air. 

INCIDENTAL GEOLOGIC OR OTHER 

SOURCES 

ATMOSPHERIC 

Lightning discharges. Form oxides of N that are 

washed out of the atmosphere and deposited on 

the soil, adding N at the rate of 5-7 lb/acre/yr 

(5.6--7.8 kg/ha/yr). 

Nitrogen -Continued 

INCIDENTAL GEOLOGIC-Continued 

Industrial and vehicular emissions. Contain 

oxides of N that eventually are deposited on the 

soil. No estimates of amounts deposited or 

benefit to plants are available. 

ORGANIC 

Guano. Contains up to 13% N. The richest 

deposits have been exhausted. 

Animal manures. Contain 0.60-1.0% N, or 

approximately 10 lb/ton (5 kg/metric ton). Used 

at a declining rate in modern agriculture due to 

cost of hauling and spreading, compared to 

high-test synthetic N fertilizers. 

Green manures (high-N vegetation that is 

plowed under). Contains various amounts ofN, 

but its use is declining in large-scale 

agriculture. 

Sewage sludge. Contains 5-6% N. A limited, 

but useful, source if cost of application and 

presence of toxic elements do not preclude its 

use. 

Miscellaneous organic residues. A wide variety 

of materials have limited, often local, use 

depending on availability and cost, including 

animal tankage (5-10% N), dried blood 

(6--14% N), fish scrap (6--10% N), cottonseed 

meal (5-7% N), tobacco stems (1-2% N), etc. 

REACTIONS WITH SOIL CONSTITUENTS 

Soil micro-organisms are the principal soil 

constituents involved in N reactions through their 

functions in the N cycle. Certain bacteria (Rhizobium sp.) that live in root nodules of legumes and 

certain other plants are able to utilize 

atmospheric N to build organic N compounds that 

are absorbed by higher plants. Some nonsymbiotic bacteria and algae in soil can perform the same 

function. When these organic materials undergo 

bacterial decomposition, the proteins are 

converted to amino acids that yield ammonium 

compounds by enzymatic hydrolysis brought 

about by soil bacteria, fungi,and ascomycetes. The 

ammonium ions can be absorbed by 

micro-organisms and higher plants and are also 

subject to oxidation by the nitrite and nitrate 

bacteria-the process of nitrification. These 

bacteria obtain energy from the process and the 

nitrates are a byproduct. The process also releases 

hydrogen ions, tending to lower the soil pH. 

Nitrates are the most important form of N in the 

growth of the higher plants. But under certain soil 

Nitrogen 3 
Nitrogen -Continued 

REACTIONS WITH SOIL-Continued 

conditions, particularly if poorly drained, nitrites 

and nitrates are reduced, liberating gaseous N 

which escapes into the atmosphere. 

FORMS USED BY PLANTS 

Nitrate (N03-1

) ions, ammonium(~+ 1

) ions, 

urea (NH2CONH2), water-soluble amino acids, 

and nucleic acid. 

FUNCTIONS IN PLANT METABOLISM 

An essential constituent of all living matter 

because it is part of the protein molecule. Many 

of the proteins are enzymes, others are nucleoproteins that are present in the chromosomes. 

The latter proteins serve as catalysts and as 

directors of metabolism. N is also an integral 

part of the chlorophyll molecule. The supply of 

N is related to carbohydrate utilization. If N 

supply in the tissues is low, carbohydrates 

accumulate; when the N supply becomes 

adequate, proteins are formed from the 

carbohydrates, more protoplasm is formed, and 

growth occurs. Therefore, the N and 

carbohydrate balance is critical in obtaining the 

plant product that is wanted-if succulent, 

rapid-growth plant tissues are wanted (as in 

salad vegetables), high N is maintained; if 

starch or sugar storage is wanted after sufficient 

growth has occurred (as in fruits, grains, roots, 

tubers), a lower N supply is desired for proper 

maturation of the produce. 

EXTENT OF USE 

Worldwide, 60 million metric tons (66.1 million 

English tons) of chemically-fJXed nitrogen are 

used per year. Nitrogen fertilizers are used in 

all significant agricultural production because 

N is a factor for increasing plant growth on 

almost all soils. Application rates range widely, 

depending on type of crop, season, climate, 

nature of the soil, and so on. An example of 

nitrogen fertilizers applied in a "standard" 

rotation in relation to crops grown follows: 

Corn crop, following 

Legumes, or heavy manuring, 50--75 lb/ 

acre (56-84 kg!ha) N. 

Soybeans, small grain, or 1 year of corn, 

100--120 lb/acre (112-134 kg!ha) N. 

Corn following corn, continuously 

100--150 lb/acre (112-168 kg!ha) N. 

LOSSES FROM SOIL 

Main losses are from leaching, crop removal, 

decay processes, and denitrification. A general 

estimate follows: 

Removed in crops, 60 lb/acre/yr ( 67.2 

kglha!yr). 

Nitrogen -Continued 

FORMS USED BY PLANTS-Continued 

Leaching and volatilization, 70 lb/acre/yr 

(78.4 kg!ha/yr). 

BALANCE SHEET 

A generalized sample of the estimated balance 

follows (no N fertilizers added): 

ADDITIONS (lb/acre/yr) 

Rainfall........................................................ 7 

(7 .8 kg!ha!yr) 

Symbiotic bacteria...................................... 80 

(89.6 kg!ha/yr) 

Nonsymbiotic organisms........................... -25 

(28 kg!ha/yr) _ 

Total .................................................... 112 

(125 kg!ha!yr) 

LOSSES (lb/acre/yr) 

Crop removal (corn, 65 bu/acre 

(56.5 hl!ha) ............................................ 60 

( 67.2 kg!ha) 

Leaching, erosion, and 

volatilization........................................... 150 

(168 kg!ha) _ 

Total ........................................... 210 

(235kg!ha) 

Net Loss- 98 lb/acre/yr (110 kg!ha/yr) 

SOILS WHERE DEFICIENCIES ARE MOST 

COMMON 

Soils of tropical and subtropical regions (rapid 

decomposition of organic matter). 

Arid soils (minimal plant growth and biological 

activity). 

Sandy soils (rapid leaching of N). 

PHOSPHORUS-(P) 

OCCURRENCE IN NATURAL MATERIALS 

ABUNDANCE IN SELECTED ROCKS 

From Connor, Shacklette, and others (1975), in 

percent 

Granite, Precambrian; Missouri................ 0.04 

Rhyolite, Precambrian; Missouri .............. .03 

Sandstone 

Sauk sequence; Western United States. .14 

Roubidoux Formation; Missouri............ .01 

Pope Megagroup; Kentucky ..................... 03 

Pennsylvanian; Kentucky ......... .......... ...... .03 

Pennsylvanian; Missouri.......................... .07 

Shale 

Sauk sequence; Western United States. .08 

Lower Mississippian; Kentucky ............... 03 

Upper Mississippian; Kentucky.............. .04 

Mississippian; Missouri............................ .05 

Pennsylvanian; Kentucky ......... .......... ...... .05 

Pennsylvanian; Missouri .......... .......... ...... .07 

4 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Phosphorus-Continued 

ABUNDANCE IN SELECfED-Continued 

Limestone and dolomite 

Sauk sequence; Western United States. .06 

Sauk sequence; Missouri ......................... .01 

Upper Ordovician; Kentucky.................. .11 

Tippecanoe sequence; Missouri ......... < .013 

Lower Mississippian; Kentucky ........ ...... .02 

Upper Missippippian; Kentucky............. .01 

Mississippian; Missouri............................ .04 

Pennsylvanian; Kentucky ......................... .09 

Pennsylvanian; Missouri .......................... .07 

ABUNDANCE IN "NATURAL" UNAMENDED 

SOILS 

MINERALS 

The native phosphorus in soils originated 

largely from the disintegration and 

decomposition of rocks containing apatite, 

Calo(P04)6(F, Cl, OH)2. It occurs as finely 

divided fluorapatite, hydroxyapatite, or chlorapatite, as iron or aluminum phosphates, in 

combination with the clay fraction, and in other 

combinations. 

ORGANICS 

In natural ecosystems, P in an available form is 

largely held in a closed biological cycle as 

follows: Stable P compounds in plants and 

animals -+ soluble P compounds produced by 

decomposition -+ absorption of the soluble P 

compounds by plants --+ stable P compounds in 

plants and animals. Amounts lost from this 

cycle are relatively minor and are replaced by P 

from weathering of the soil minerals. In agroecosystems, the return of crop residues and 

animal manures can replace some of the P that 

was removed from the soil by plants. 

ABUNDANCE IN SOILS 

"Representative" analysis of agricultural soils (as 

P20 5 ), 3,000 lb/acre-furrow-slice (2,000,000 lb or 

908,000 kg of soil) (3,600 kglha-furrow-slice ). 

In 1,140 samples (10 from each Missouri county) 

of the surface horizon of agricultural soils, 

0.065%, range < 0.01-0.61%. 

Average, all U.S. soils, 420 ppm (840 lb/acrefurrow-slice; 940 kglha-furrow-slice ). 

Average, Eastern U.S. soils, 324 ppm (648 

lb/acre-furrow-slice; 726 kglha-furrow-slice ). 

Average, Western U.S. soils, 448 ppm (896 

lb/acre-furrow-slice; 1,104 kglha-furrow-slice). 

Distribution of abundances in U.S. surficial 

materials was given by Shacklette and Boerngen 

Phosphorus-Continued 

ABUNDANCE IN SOILS-Continued 

(1984). Concentrations in many cultivated and 

uncultivated U.S. soils are given by Connor, 

Shacklette, and others (1975). 

ABUNDANCE IN PLANTS 

P tends to be concentrated in the reproductive 

parts of plants (seeds, grain, fruits) or in other 

parts that are rich in protein. Examples of the P 

content of vegetables follow (geometric mean 

percent of ash weight): 

Lima bean seeds, central Georgia, 6. 7 

Soybean seeds, unglaciated prairie, Missouri, 

10 

Corn grains, Missouri floodplains, 22 

Sweet pepper fruits, Wisconsin, 1.9 

Cabbage leaves, northern Georgia, 1.2 

Onion bulbs, Wisconsin, 3.7 

Potato tubers, Wisconsin, 2.2 

P concentration in woody tissue of trees and 

shrubs, as in herbaceous stems, tends to be low, as 

illustrated by the following examples (geometric 

mean percent of ash weight): 

Black gum stems, northern Georgia, 1.2 

Pignut hickory stems, Kentucky, 0.76 

Red maple stems, central Georgia, 1.4 

White oak stems, Missouri, 1.1 

Examples of P concentrations in forage, hay, and 

browse plants (geometric mean percent in ash): 

Johnson grass, Missouri floodplain, 3.5 

Big bluestem grass, Missouri glaciated prairie, 

2.1 

Kentucky bluegrass, Eastern U.S., 1.5 

Western wheatgrass, Western U.S., 0.28 

Alfalfa, Western U.S., 1.07 

Mesquite, Southwestern U.S., 1.1 

SOURCES FOR FERTILIZERS 

GEOLOGIC OR OTHER PRINCIPAL 

SOURCES 

Phosphate rock. The principal phosphate 

compound in all commercially important deposits 

is apatite, in which the phosphate is not readily 

available to plants. The phosphate rock is 

generally acidulated near its source to produce 

various forms of soluble phosphates; these acid 

phosphates constitute the common commercial P 

fertilizers. 

INCIDENTAL GEOLOGIC OR OTHER 

SOURCES 

MINERAL (Industrial) 

Basic slag (see p. 15), (CaO)s·P20s·Si02 

(15-20% P20 5 ) 

Bone black, Ca3(P04 )2 (32-35% P20s) 

Steamed bonemeal, Ca3(P04 )2 (23-30% P20s) 

Phosphorus 5 
Phosphorus-Continued 

INCIDENTAL GEOLOGIC-Continued 

ORGANICS 

Guano, 9% P. No longer an appreciable 

fraction of total P fertilizers used. 

Sewage sludge, 2-3% P20s. 

Animal tankage, 5-18% P20s. 

Fish scrap, 5-8% P20s. 

Bonemeal, 17-30% P20s. 

REACTIONS WITH SOIL CONSTITUENTS 

In acid mineral soils, the H2P04 ions react with 

soluble AI, Fe, and Mn ions, forming hydroxyphosphates which are relatively insoluble and not 

readily available to plants. The H2P04 ions may 

also react with insoluble hydroxides of these 

elements, forming insoluble compounds. In 

alkaline soils, phosphate is precipitated by Ca 

compounds, in most cases from CaC03; the 

available P will react with both the Ca ion and its 

carbonate, forming relatively insoluble 

compounds. These compounds may be converted 

to even more insoluble compounds, such as oxy-, 

carbonate-, or even fluorapatite. This type of 

reaction may occur on heavily limed soils and is 

especially serious in Western U.S. soils because of 

the widespread presence of excess CaC03. P may 

also become fixed by silicate clays and rendered 

relatively unavailable to plants. 

P, in the organic compounds phytin and nucleic 

acid, can be utilized by plants as long as the 

compounds remain soluble. In acid soils, Fe and 

AI phytates are formed; in alkaline soils, Ca 

phytates; all are relatively insoluble. Nucleic acids 

are strongly adsorbed on clays, particularly montmorillonite, causing low P availability, especially 

in acid soils. 

As a general rule, minimum fiXation, therefore 

greater availability to plants, occurs if the soil pH 

is maintained at pH 6-7. 

FORMS USED BY PLANTS 

Plants absorb most of their P as the primary 

orthophosphate ion, H2P04 ·l but smaller 

amounts of the secondary orthophosphate ion, 

HP04 ·

2

, are also absorbed. In addition, pyrophos-· 

phates and metaphosphates may possibly be 

absorbed by plant roots. Certain soluble organic 

phosphates, such as nucleic acid and phytin, are 

also absorbed, but because of their instability in 

the presence of an active microbial population, 

their importance as P sources for higher plants is 

limited. 

FUNCTIONS IN PLANT METABOLISM 

Phosphate or phosphoryl radicals in plant cells 

are transported to an acceptor group by a 

Phosphorus-Continued 

FORMS USED BY PLANTS-Continued 

transfer reaction called phosphorylation; the 

activity of a compound is increased, and the 

number of chemical reactions possible in the 

plant system is enormously increased. 

Therefore, the P compounds are necessary for 

photosynthesis, interconversion of carbohydrates, glycolysis, amino-acid metabolism, fat 

metabolism, sulfur metabolism, biological 

oxidations, and many other life processes. 

EXTENT OF USE 

Worldwide estimate, more than 10 million 

metric tons (11.02 million English tons) per 

year applied as fertilizer. After nitrogen, the 

most common element for increasing 

agricultural production. 

Example of annual application rate, lb/acre (as 

P20s): 

Small grain, 40-80 ( 44.8-89.6 kg!ha) 

Vegetable crops, 60-120 (67.2-134.4 kg!ha) 

Alfalfa, 160-320 (179.2-353.4 kg!ha) 

Much larger amounts are often used for 

certain crops. 

Large amounts, 1-5 tons/acres (2.2-11.2 

metric tons!ha) of raw rock phosphate 

(12-35% total P) may be used to build a 

reserve of slowly available P. 

LOSSES FROM SOILS 

LEACHING 

Only minor amounts are lost by leaching, as 

the P in soils is mostly in relatively insoluble 

compounds. Principal losses follow: 

EROSION 

P is found chiefly in the finest particles of the 

soil, which are most easily carried away from 

the surface by running water and by wind. 

Examples of erosion losses (lb/acre/yr) 

follow: 

Continuous corn (clean cultivation), 18 

(20.2 kg/ha/yr ). 

Continuous wheat, 9.4 (10.5 kg!ha!yr). 

Continuous bluegrass, 0.2 (0.22 kg!ha!yr). 

CROP REMOVAL 

Pis concentrated in seeds (about 75% of the 

total Pin the plant). When the seeds (grain) 

are sold, therefore, about 75% of the P that 

the plants obtained from the soil is lost from 

the farm. For example, a ton (0.9 metric ton) 

6 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Phosphorus-Continued 

FORMS USED BY PLANTS-Continued 

of wheat contains about Sib (3.6 kg) P. If this 

grain is fed to meat animals on the farm, 

about 30% of the P in the grain is absorbed 

by the animal, about 20% is lost in handling 

the manure, leaving about 50% that can be 

returned to the soil in manure. This return 

contrasts with the 20% that can be returned 

to the soil in straw or stover if the grain is 

sold from the farm. These methods of soil P 

removal are illustrated by the following 

statement of Thorne (1930): "Seven 1,000-

bushel [190,680 kg] carloads of corn or oats, 

or five such carloads of wheat, carry away as 

much phosphorus as is found in the plowed 

surface of an average acre of land, even 

though the stover and straw are 

conscientiously returned to the land * * *. Six 

carloads of fat cattle, or 14 carloads of fat 

hogs, may contain phosphorus equivalent to 

that contained in the surface 6 inches [15.2 

em] of an acre, and the milk from a dairy of 

130 average cows will carry off this quantity 

of phosphorus every year." 

BALANCE SHEET 

A generalized example of the estimated P 

balance (lb/acre/yr) follows: 

ADDITIONS 

Fertilizers (minimal application)............ 1.9 

(2.12 kg!ha/yr) 

Animal manure and bedding.................. 1.5 

(1.7 kg!ha/yr) 

Seeds sown.................................................. .2 

(0.22 kglha/yr) 

Roots and unharvested parts................... .9 

(1.0 kglha/yr) 

Total ............................................... 4.5 

(5.04 kglha/yr) 

LOSSES 

Harvested crops....................................... 3.8 

(4.3 kglha/yr) 

Grazing...................................................... .2 

(0.24 kg!ha/yr) 

Erosion (cropland only)......................... 10.6 

(11.8 kglha/yr) 

Total loss .................................... 14.6 

(16.4 kg!ha/yr) 

Net loss, 10.1 (11.4 kglha/yr) 

(Note that in high-production farming, 

phosphate fertilizers are applied at a high 

rate, often resulting in a net gain of total P in 

the soil.) 

Phosphorus-Continued 

SOILS WHERE DEFICIENCIES ARE MOST 

COMMON 

Soils derived from parent material that is low in P. 

Highly weathered and eroded soils. 

Soils with a long history of heavy cropping. 

Calcareous and acid soils (low availability of P). 

Peat and muck soils (low availability of P). 

POTASSIUM-(K) 

OCCURRENCE IN NATURAL MATERIALS 

ABUNDANCE IN SELECTED ROCKS 

From Connor, Shacklette, and others (1975), in 

percent: 

Granite, Precambrian; Missouri.............. 4.30 

Rhyolite, Precambrian; Missouri ............ 4.89 

Sandstone 

Sauk sequence; Western U.S............... 1.12 

Roubidoux Formation; Missouri......... .14 

Pope Megagroup; Kentucky................ .55 

Pennsylvanian; Kentucky ........ :............. 1.12 

Pennsylvanian; Missouri....................... 1.08 

Shale 

Sauk sequence; Western U.S............... 5.94 

Lower Mississippian; Kentucky........... 1.98 

Upper Mississippian; Kentucky........... 2.41 

Mississippian; Missouri........................ 2.92 

Pennsylvanian; Kentucky...................... 2.53 

Pennsylvanian; Missouri ....................... 2.83 

Limestone and dolomite 

Sauk sequence; Western U.S............... .73 

Sauk sequence; Missouri...................... .44 

Upper Ordovician; Kentucky............... .48 

Tippecanoe sequence; Missouri .......... .24 

Lower Mississippian; Kentucky........... .54 

Upper Missippippian; Kentucky.......... .34 

Pennsylvanian; Kentucky...................... .84 

Pennsylvanian; Missouri ....................... .24 

ABUNDANCEIN"NATURAL"UNAMENDED 

SOILS 

MINERALS 

Feldspars ( sanidine, orthoclase, microcline ), 

muscovite H2KA13 (Si04 ) 3, biotite 

(H,K)2 (Mg,Fe)2Al2 (Si04 ) 3, and illite. K is also 

held as an adsorbed cation on some other 

minerals. 

Potassium 7 
Potassium -Continued 

ABUNDANCE IN "NATURAL" -Continued 

ORGANICS 

K constitutes 25% or more of plant ash, being 

exceeded as an element in plants only by the 

silica content in ash of silica-accumulating 

plants. In natural ecosystems, most of the total 

K is in unavailable compounds in the soil-the 

lesser soluble amounts are held in a loose cycle 

as follows: Kin soil solution -.Kin plants (in 

the ionic form, or as charged particles on 

colloidal surfaces, not part of a specific 

compound) -. K in animals (most is secreted in 

urine) -. soluble K compounds in the soil 

solution from animal excretions and 

decomposition of plants and animals. The K in 

the soil solution that is lost by the slight 

leaching and erosion is replaced through 

extraction of K by plant roots from primary 

minerals and from the K fixed on clay 

structures. In agroecosystems, the return of 

plant residues and manures replaces some of 

the K that was removed from the soil by 

cropping. 

ABUNDANCE IN SOILS 

"Representative" analysis of agricultural soils: 

Humid region soils, 1.70% or 34,000 lb/acrefurrow-slice ( 48,000 kg!ha-furrow-slice) 

(2,000,000 lb, or 908,000 kg); arid region soils, 

2% or 40,000 lb/acre-furrow-slice ( 44,800 kg!hafurrow-slice ). 

Ranges ordinarily expected, 0.17-3.30%. 

In 1,140 samples (10 from each Missouri county) 

of the surface horizon of agricultural soils, 1.4%, 

range 0.33-3.7%. 

Average, all U.S. soils, 1.2% 

Average, Eastern U.S. soils, 0.74% 

Average, Western U.S. soils, 1.7% 

Distribution of concentrations in U.S. surficial 

materials mapped in USGS Professional Paper 

1270. Concentrations in a wide variety of 

cultivated and uncultivated U.S. soils were given 

by Connor, Shacklette, and others (1975). 

ABUNDANCE IN PLANTS 

Examples of the K concentration in vegetables 

and crop plants (geometric mean percent in ash) 

follow: 

Lima bean seeds, central Georgia, 35 

Soybean seeds, unglaciated prairie, Missouri, 39 

Potassium -Continued 

ABUNDANCE IN PLANTS-Continued 

Corn grains, Missouri floodplain, 29 

Snap bean pods (fruit), central Georgia, 33 

Cabbage leaves, northern Georgia, 18 

K concentrations in stems and leaves of woody 

plants tend to be about half that in seeds and fruits 

of crop plants; moreover, leaves usually have 

higher levels than do stems. Examples (geometric 

mean percent in ash) follow: 

Black gum stems, central Georgia, 11 

Black gum leaves, central Georgia, 16 

Red maple stems, central Georgia, 11 

Red maple leaves, central Georgia, 12 

White oak stems, Missouri, 5.1 

Examples of K concentrations in forage, hay, and 

browse plants (geometric mean percent in ash) 

follow: 

Johnson grass, Missouri floodplain, 16.0 

Big bluestem, Missouri glaciated prairie, 16.0 

Western wheatgrass, Western U.S., 11.9 

Alfalfa, Western U.S., 17.8 

Mesquite, Southwestern U.S., 10.8 

Concentrations of Kin a wide variety of cultivated 

and native plants were given by Connor, Shacklette, and others (1975). 

A large number of species (mostly trees and 

shrubs) that were sampled at 910 widely 

distributed localities in the U.S. averaged 13% K 

in ash. 

SOURCES FOR FERTILIZERS 

GEOLOGIC OR OTHER PRINCIPAL 

SOURCES 

Sylvite, KCl, 52.3% K. 

Langbeinite, KC1·2MgS04, 18.8% K. 

Sylvinite, KCl·NaCl mixture. 

Carnallite, KCl·MgCh·6H20, 14.1% K. 

Kainite, MgS04KC1·3H20, 15.7% K. Niter, KN03, 

38.6% K. 

Poly halite, K2S04MgS04 ·2CaS04 ·2H20, 

13.5% K. 

8 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Potassium -Continued 

INCIDENTAL GEOLOGIC OR OTHER 

SOURCES 

MINERAL 

Glauconite, 5% as K20. 

Sea water, 1.6 million tons mi3 (2.87 million 

metric tons/km3). Research on use of this source 

has made little progress, although Norwegian 

workers have reported some success. 

Lake brines. Searles Lake, California, brines are 

reported to contain 4.7% K as KCI. 

ORGANIC 

Seaweed, kelp, 30% in ash as K20. Tobacco 

byproducts, 6-10% in ash as K20. Water 

hyacinth (an aquatic weed), 4% in ash. Wood 

ashes, 6%. 

REACTION WITH SOIL CONSTITUENTS 

The total amount of K in soils generally is high 

compared to the content of N and P, but most 

exists in the unavailable form. When K as an 

available (soluble) salt is applied to soils, the 

extent of fiXation as insoluble compounds is 

almost always directly proportional to the content 

of colloidal matter in the soil, being greatest in 

clays and clay loams and least in sands and sandy 

loams. For this reason, smaller amounts can be 

applied to sandy soils to satisfactorily increase 

crop yield than are necessary for the same effect 

on clay soils, but at the same time leaching losses 

are greatest in the sandy soils. The latter soils 

should have the fertilizer applied at a time when 

the crop plants can absorb it immediately to 

prevent excessive loss through leaching. In 

"heavier" soils it is possible to build a K reservethe fixed K can move slowly (become soluble) at a 

rate determined by the nature of the colloidal 

complex. Applications of lime increase K fiXation 

in some soils. This effect may be desirable on 

sandy soils in that leaching losses are reduced. In 

other soils, K deficiency for plants may be caused 

by excess calcium carbonate. Of the total K in 

soils, 90-98% is estimated to be relatively 

unavailable, being contained mostly in the feldspars and micas which are quite resistant to 

weathering. They are thought to supply relatively 

small quantities of K during a single growing 

season, but their accumulative contribution from 

year to year to the total available soil K is of 

considerable importance. For this reason, the idea 

that each pound of K removed by plants or 

Potassium -Continued 

REACTIONS WITH SOIL-Continued 

through leaching must be returned in fertilizers 

may not always be correct. 

FORMS USED BY PLANTS 

K is absorbed by plants as the ion K+ 1

• 

Compounds which provide the K in a readily 

available form are KN03, &P04, KCl, K2S04, 

and K2C03. 

FUNCTIONS IN PLANT METABOLISM 

K apparently does not form an integral part of 

such plant components as protoplasm, fats, and 

cellulose; its function appears to be catalytic in 

nature. Still, it is essential to many physiological 

functions in plants, including carbohydrate 

metabolism and breakdown and translocation 

of starch, nitrogen metabolism and synthesis of 

protein, regulation of the activities of various 

essential mineral elements, neutralization of 

physiologically important organic acids, 

activation of various enzymes, growth of 

meristematic tissue, and adjustment of stomatal 

movement and water relations. 

An important effect of K deficiency relates to 

its function in protein synthesis. This deficiency 

may result in a buildup of amide N and a 

reduced conversion to protein. This results 

further in an accumulation of nonprotein N, 

which is easily deaminated in the rumen of 

sheep and other ruminants. The rapid release 

of large amount of NH3 in the rumen may be 

very injurious to the animal (Tisdale and Nelson, 1967, p. 83-84). 

Sodium can replace K as a nutrient in certain 

plants. For example, Na can replace 80% of the 

K requirement of sugar beets, but almost none 

of the K requirement of potatoes. 

EXTENT OF USE 

Estimated worldwide use, 15 million metric 

tons/yr (16.5 million English tons/yr) as 

manufactured fertilizers. In modern 

agriculture, high yields promoted by the 

increased use of N and P have greatly increased 

the draft on soil K which, coupled with the 

considerable l~aching loss of K, has increased 

the demand for K to the point that its usage in 

commercial fertilizers now exceeds that of 

nitrogen and rivals that of phosphorus. 

An example of recommended K applications to 

soils low in K for a typical crop rotation (lbs/ 

acre) follow: 

Broadcast before first plowdown, 208 (233 

kg!ha) 

Potassium 9 
Potassium -Continued 

FORMS USED BY PLANTS-Continued 

Corn, first year, 0 

Corn, second year, 20 (22.4 kg/ha) 

Soybeans,O 

Wheat, 17 (19 kg/ha) 

Examples of annual application rate as K2 0 

(lb/acre) follow: 

Potatoes (North Carolina), 80-100 

(89.6-112 kg/ha). 

Cotton (Southeastern U.S.), 175-200 

(196-224 kg/ha). 

Alfalfa, corn, cereals, 160 (179 kg/ha). 

LOSSES FROM SOILS 

LEACHING 

Losses by leaching are dependent on fiXation 

of soluble K in the soil. Fixed K slowly 

becomes soluble. In sandy soils, K may move 

down to the ground water; while in clay or silt 

soils, the movement is largely restricted to 

the upper 4-6 inches (10.2-15.2 em) of soil. 

Silty clay loam, Ithaca, N.Y., lb/acre/yr (10-yr 

averages) 

Bare soil, 87 (97.4 kg/ha/yr) 

Rotated cropland, 69 (77.3 kg/ha/yr) 

Continuous grass, 75 (kg/ha/yr) 

EROSION 

Because most of the available K is in the 

upper soil horizons, erosion of surface soil 

can cause severe K deficiencies for crops. 

However, most of the total K in soils is in the 

lower horizons, so erosional loss of total K is 

not as great as that of total N and P. An 

example of K losses by erosion (lb/acre/yr) in 

Missouri follows: 

Continuous corn cultivation, 605 ( 677.6 

kg/ha/yr) 

Rotation; corn, wheat, clover, 214 (239.7 

kg/ha/yr) 

CROP REMOVAL 

The amount of K lost from this cause is, 

under many conditions, the greatest loss. 

Because K is not combined in organic 

compounds but moves freely through plant 

tissues, there is no limit fiXed by metabolic 

requirements on the amounts absorbed. 

Consequently, if the soil solution contains 

abundant K, plants may absorb much more K 

than is necessary for its catalytic functionsthe so-called luxury consumption of K. This 

excessive use of K can significantly increase 

the amount of K lost from the soil by crop 

removal. Amounts of K lost by crop removal 

(lb/acre/yr) follow: 

Potassium -Continued 

FORMS USED BY PLANTS-Continued 

Corn, yield 100 bu/acre (87.hl!ha), 25 (28 

kg/ha/yr). 

Wheat, yield 50 bu/acre (44 hl!ha), 12 

(13.4 kg/ha!yr). 

Alfalfa, yield 10 tons/acre (22.4 metric 

tons/ha), 100 (112 kg/ha/yr). 

Beets, yield 12¥2 tons/acre (10.9 metric 

tons/ha), 125 (140 kg/ha!yr). 

The following examples illustrate the loss of 

K by plant removal at a larger scale: 

Ecuador exports 1 million metric tons 

(0.44 million English tons) of bananas 

annually, containing 4,600,000 kg 

(10,143,000 lb) K. Hawaii exports 

2,000,000 kg ( 4,410,000 lb) of K annually 

in its pineapple crop. 

BALANCE SHEET 

ADDITIONS 

Except for the addition of small amounts of 

K by weathering of soil minerals, there is no 

addition of K by natural processes. 

LOSSES 

The loss or gain in K under the widely 

ranging cultivation practices, crops grown, 

and soil types cannot be easily generalized. 

However, the following estimate may suggest 

the magnitude of this loss (crop residues left 

in the field; loss in lb/acre/yr): 

Wheat, yield 50 bu/acre....................... 12 

( 43.5 hl!ha) (13.4 kg/ha!yr) 

Leaching................................................. 58 

(64.9 kg/ha!yr) 

Erosion.................................................. 200 

(224 kg/ha/yr) 

Total Loss................................. 270 

(302.3 kg/ha/yr) 

The total loss represents the approximate 

amount that must be added annually under 

the above conditions if fertility is to be 

maintained. Even if leaching and erosion are 

eliminated from the losses and all crop 

residue is left on the field, for every ton (0.9 

metric ton) of wheat produced and shipped 

from the farm, about 8 lb (3.6 kg) of the 

available soil K is lost. If corn is grown and 

fed to meat animals (wheat is not commonly 

a livestock feed), the manure (especially the 

urine) is returned to the soil, and the animals 

sold from the farm, for every ton (0.9 metric 

ton) of corn produced, probably only about 

2-3 lb (0.9-1.4 kg) of available K leaves the 

farm. 

10 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Potassium -Continued 

SOILS WHERE DEFICIENCIES ARE MOST 

COMMON 

Light sandy soils which are easily leached (low 

total amount). 

Organic soils such as peat and muck (low 

availability). 

Soils that have been heavily cropped, leached, and 

eroded. 

Highly leached soils of tropical regions are 

universally low in available K. 

SULFUR-(S) 

OCCURRENCE IN NATURAL MATERIALS 

ABUNDANCE IN SELECTED ROCKS 

From Turekian and Wedepohl (1961), in parts 

per million (ppm) 

"Igneous" rocks, 300 

Sedimentary rocks 

Shales, 2,400 

Sandstones, 240 

Carbonates, 1,200 

From E. R. Cressman (oral commun., 1974), in 

percent 

Phosphatic limestone, Ordovician; Kentucky 

16 samples, average 0.44; range 0.15-0.60 

9 samples, average 0.23; range 0.15-0.89 

ABUNDANCE IN "NATURAL" UNAMENDED 

SOILS 

MINERALS 

Sulfates of Ca, Mg, N, and K. These soil 

minerals are most abundant in arid regions. 

ORGANICS 

Much of the S of humid-region soils is in the 

organic form. S occurs in tissue of all plants as 

organic S (a component of the protein 

molecule), the amount ranging widely as a 

genetic trait at the species or family level. In 

addition, plants commonly contain readily 

mobile sulfate sulfur in the vascular system in 

amounts, for many species, greatly in excess of 

metabolic requirements and which are 

controlled by the concentration of S in the soil. 

The sulfur in plant roots is a normal component 

of soil chemistry, and eventually is recycled into 

new living plants, or leaves the system through 

leaching, erosion, or volatilization through 

bacterial action. 

ABUNDANCE IN SOILS 

"Representative" analysis, agricultural soils, in 

lb/acre-furrow-slice (2,000,000 lb; 908,000 kg)-

Humid regions, 800 (896 kg!ha-furrow-slice); arid 

regions, 1,600 (1,792 kg!ha-furrow-slice). Range 

Potassium -Continued 

ABUNDANCE IN SOILS-Continued 

, in percentages that may be ordinarily expected, 

0.01-0.20%. 

ABUNDANCE IN PLANTS 

The S in plant tissues occurs in two formssulfate S and organicS. The following examples of 

concentrations are for total S (percent, dry weight 

basis): 

Corn grains, 0.24 

Wheat grains, 0.18 

Barley grains, 0.14 

Rice grains, 0.124-0.128 

Alfalfa hay, 0.41 

Clover hay, 0.25 

Soybean hay, 0.23 

S is known to be concentrated in many species of 

the mustard family (cabbage, cauliflower, 

mustard, turnip, and radish, for example), but 

quantitative data are not available. 

SOURCES FOR FERTILIZERS 

GEOLOGIC OR OTHER PRINCIPAL 

SOURCES 

Elemental S 

Pyrite, FeS2 

Other sulfide minerals (as refining byproducts) 

Gypsum, CaS04 ·2H20 

Fossil fuels (removed in refining petroleum and 

natural gas; removed from stack emissions in 

pollution control) 

INCIDENTAL GEOLOGIC OR OTHER 

SOURCES 

ATMOSPHERIC 

Atmospheric S, derived from industrial 

emissions, ocean spray, and as H2S and S02 

from swamps and marshes, can be absorbed 

directly by plants, or indirectly from soil if 

washed out of the air by precipitation as H2S03 • 

Plants can absorb 25-35% of their S 

requirement directly from the air. The total 

atmospheric S added to soil is largely controlled 

by distance from sources of industrial 

emissions, and ranges from 1-10 lb/acre/yr 

(1.12-11.2 kg!ha/yr). Atmospheric S, as S02, 

also enters the soil by direct gaseous diffusion. 

Grey and Jenson (1972) reported that in the 

Salt Lake City, Utah, area bacteriogenic S 

released by anaerobes from mud may rival 

industrial S emissions as a source of 

atmospheric S compounds. Buckman and 

Brady (1969, p. 463-464) wrote, "The 

recognition that clean air is a laudable goal will 

necessitate finding alternative means of 

supplying sulfur for plant growth." 

Sulfur 11 
Sulfur-Continued 

INCIDENTAL GEOLOGIC-Continued 

ORGANIC 

Plant residues 

The return of plant residue to the soil 

constitutes a significant addition of S that is 

readily available to plants. The amount 

returned varies greatly among residues from 

different plants, and no quantitative data are 

available. 

Animal manures 

A useful source of S, among other major 

nutrient elements, the S content ranges 

widely according to kinds of animals, manure 

storage, and application practices. General 

estimates of the amounts of S in different 

manures follow (kg/metric ton, fresh 

material): 

Dairy cattle, 0.5 (1.2 lb/English ton) 

Fattening cattle, 0.85 (2.07 lb!English ton) 

Hogs, 1.35 (3.28lb!English ton) 

Horses, 0.7 (1.7 lb/English ton) 

Sheep, 0.9 (2.2 lb/English ton) 

Sewage sludge 

Sewage contains significant amounts of S, but 

because of the obnoxious odor of H2S that is 

liberated if applied raw to fields, storage and 

drying are used to reduce the S content 

through bacterial action. Quantitative data 

on S in finished sewage sludge are not 

available. 

REACTIONS WITH SOIL CONSTITUENTS 

Sulfate is the end product of all S fertilizers added 

to soils. In arid region soils, it forms sparingly 

soluble salts with some cations present. In humid 

regions, sulfate is commonly leached from the 

upper soil horizons and either accumulates in 

lower horizons or is leached from the soil. Factors 

enhancing adsorption of sulfate on .soil 

constituents are large amounts of clay, especially 

kaolin; presence of hydrous Fe and AI oxides; low 

soil pH; high sulfate concentration; impe(:led 

movement of soil solution to increase period of 

contact; presence of weakly held anions such as 

nitrate and chloride; and occurrence of cations 

that enhance sulfate adsorption. Liming and 

phosphate fertilization both reduce sulfate 

adsorption. Adsorbed sulfate has lower 

availability than soluble sulfate but is an 

important source for some plants and helps 

conserve S fertilizers and native soil S by reducing 

leaching losses. 

Sulfur-Continued 

FORMS USED BY PLANTS 

Sulfate sulfur is probably the only form absorbed 

by plant roots. Some compounds in which the S is 

readily available to plants are K2S04, CaS04, 

Na2S04, and FeS04. 

FUNCTIONS IN PLANT METABOLISM 

Synthesis of the amino acids cystine, cysteine, 

and methionine, which are essential 

components of protein. 

Necessary for chlorophyll formation, although 

not a component. 

Activation of certain proteolytic enzymes such 

as papainases. 

Synthesis of certain vitamins (biotin and thiamin or vitamin B1), glutathione, and of 

coenzyme A. 

Formation of the glucoside oils found in onions, 

garlic, and so on. 

Formation of disulfide linkages associated with 

the structure of protoplasm. 

Formation of ferredoxin, which has an 

important role in all photosynthetic processes. 

Formation of ferredoxin-like compound 

involved in N fiXation by nodule and free-living 

bacteria. 

EXTENT OF USE 

Worldwide production (1969), 29 million 

metric tons (32 million English tons) annually; 

of this total18 million metric tons (19.8 English 

tons) are from elemental S, and 11 million 

metric tons (12.1 English tons) are from 

pyrites. About one-half of this total is used in 

producing P fertilizers, ammonium sulfate, or 

for direct fertilizer application asS. 

Areas of S deficiency are increasing in the U.S. 

as well as in certain other countries. S 

deficiency for different crops has been reported 

in soils from 16 of the 50 U.S. States. This 

increasing deficiency has been brought about 

by the increased use of practically S-free 

fertilizers, higher crop yields, increased use of 

low-sulfur fuels and the emphasis on control of 

industrial emissions, by the decreased use of S 

as an insecticide and fungicide and by the 

decreased levels of soil organic matter. 

12 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Sulfur-Continued 

FORMS USED BY PLANTS-Continued 

Because known S-deficient soils are distributed 

widely throughout the world and the methods 

used to correct the deficiency differ greatly, a 

"representative" value of S applications to soils 

as a fertilizer is difficult to estimate. In applying 

S directly to soils (that is, not as a component of 

N, P, or K fertilizers), either elemental S or 

gypsum is used, depending on relative cost. An 

example of application rates and yield response 

follows: 

Alfalfa grown on S-deficient soil, California 

Treatment 

None 

200 lb/acre (244 kglha) 

gypsum 

400 lb/acre (448 kglha) 

gypsum 

Yield 

(lb/acre/cutting) 

550 (616 kglha) 

1,600 (1,792 

kglha) 

2,200 (2,464 

kglha) 

The addition of S to "normal" soils can increase 

the S content of the crops, but the response is 

not uniform among species. An example 

follows: 

Alfalfa grown on "normal" soil, Kentucky 

Treatment TotalS (% dry weight) 

in crop 

None 0.36 

100 lb/acre (112 kglha) S .44 

200 lb/acre (224 kglha) S .48 

LOSSES FROM SOILS 

LEACHING 

Sulfate sulfur moves readily in the soil 

solution, and its loss through leaching is 

governed largely by physical, not chemical, 

properties of the soil, and by the organic 

content. For this reason, the losses range 

widely in different soils. An example follows: 

Silty clay loam, Ithaca, N.Y., 10-15-yr 

averages, no runoff loss allowed (lb/ 

acre/yr) 

Bare soil, 53 (59 .4 kg!ha/yr) 

Standard crop rotation, 43 ( 48.2 

kg!ha!yr) 

Continuous grass, 44 (49.3 kg!ha/yr) 

EROSION 

Erosional losses can be severe, especially in 

clay soils where high S concentrations may 

occur in the surface layer. An example from 

Missouri experiments on soil subject to 

moderate erosion follows (lb/acre/yr): 

Sulfur-Continued 

FORMS USED BY PLANTS-Continued 

Continuous corn (field bare between 

crops), 17 (19 kglha!yr) 

Standard crop rotation, 6 ( 6.6 kg!ha/yr) 

CROP REMOVAL 

The loss of S from soil by crop removal is 

similar to that of P. The approximate amount 

of S removed by certain crops (kg!ha/yr) 

follows: 

Corn, yield 200 bu/acre (174 hl!ha), 49 ( 43.7 

lb/acre/yr) 

Wheat, yield 80 bu/acre (70 hl!ha), 25 

(22.3lb/acre!yr) 

Rice, yield 145 bu/acre (126 hl!ha), 20 (17.8 

lb/acre/yr) 

Alfalfa, yield 6 tons/acre (13.4 metric 

tons/ha), 34 (30.3 lb/acre/yr) 

Soybeans, yield 50 bu/acre (43.5 hl!ha), 

11 (9.8 lb/acre!yr) 

Sugar beets, yield 30 tons/acre (67 metric 

tons/ha), 55 (49lb/acre/yr) 

Cabbage, yield 20 tons/acre ( 45 metric 

tons/ha), 41 (36.5 lb/acre/yr) 

Potatoes, yield 400 bu/acre (348 hl!ha), 

30 (26.7 lb/acre/yr) 

OTHER (VOLATILIZATION) 

Sulfur compounds in the soil resemble N 

compounds in that both can be lost by 

conversion to gaseous compounds through 

the action of bacteria. In highly organic soils 

under relatively severe anaerobic conditions, 

such as in swamps and bogs, much of the 

organic S compounds and the free sulfate 

sulfur is converted to H2S and lost from the 

soil. Estimates of this loss are not available. 

BALANCE SHEET 

The retention of sulfate sulfur in different soil 

types and the addition of S to soils from the 

atmosphere and in fertilizers range widely; 

moreover, the amount of S removed by crops 

varies greatly among species. Therefore, only a 

generalized balance can be estimated, as 

illustrated by the following example based on 

field experiments in Missouri (lb/acre/yr): 

ADDITIONS 

Atmospheric source..................................... 5 

(5.6 kg!ha/yr) 

Fertilizers and manures .............................. 0 

Total Gain ........................................ 5 

(5.6 kg!ha/yr) 

Sulfur 13 
Sulfur-Continued 

FORMS USED BY PLANTS-Continued 

LOSSES 

Crop removal (average, standard 

rotation)......................................................... 15 

(16.8 kglhalyr) 

Leaching.................................................... 43 

( 48.2 kglha!yr) 

Erosion...................................................... 6 

(6.7 kglha!yr) 

Total Loss..................................... 64 

(56.7 kglha!yr) 

Net Loss, 59 (51.1 kglha!yr) 

If the above example is used, except that corn 

is grown continuously, the S lost through 

erosion increases to 17 (19 kg!ha!yr), the 

leaching loss increases to 53 (59.4 kglha/yr), 

and crop removal increases to 49 (54.8 

kg!ha!yr), making a total of 119 lb/acre/yr 

(133 kg!ha!yr) lost. Unless S fertilizers are 

added, and if the amount gained from the 

atmosphere remains 5 lb/acre/yr (5.6 

kglha/yr), the net loss is 114lb/acrelyr (127.4 

kglha/yr) .With different management 

practices, including sulfur application, the 

loss of S may be greatly reduced, or a gain in 

total S may be achieved, if leaching, erosion, 

and volatilization losses are not excessive. 

SOILS WHERE DEFICIENCIES ARE MOST 

COMMON 

Soils deficient in primary S minerals. 

Sandy soils of warm temperate to tropical regions 

(excessive leaching). 

Soils low in organic matter (poor S retention). 

Soils of areas distant from industrial pollution. 

Soils that have been heavily cropped with highsulfur plants. 

CALCIUM-(Ca) 

OCCURRENCE IN NATURAL MATERIALS 

ABUNDANCE IN SELECTED ROCKS 

From Connor, Shacklette, and others (1975), in 

percent 

Granite, Precambrian; Missouri................ 0.53 

Rhyolite, Precambrian; Missouri............... .41 

Sandstone 

Sauk sequence; Western U.S................. .99 

Pennsylvanian; Kentucky ............... ......... .28 

Calcium -Continued 

ABUNDANCE IN SELECTED-Continued 

Shale 

Sauk sequence; Western U.S ................. 2.8 

Lower Mississippian; Kentucky ............. 4.9 

Upper Mississippian; Kentucky ............. 3.1 

Pennsylvanian; Kentucky ........................ .29 

Pennsylvanian; Missouri ......................... 2.9 

Limestone and dolomite 

Sauk sequence; Western U.S ................ 20 

Sauk sequence; Missouri ....................... 22 

Upper Ordovician; Kentucky................ 29 

Tippecanoe sequence; Missouri ........... 32 

Lower Mississippian; Kentucky ............ 25 

Upper Missippippian; Kentucky........... 33 

Mississippian; Missouri .......................... 32 

Pennsylvanian; Kentucky ....................... 25 

Pennsylvanian; Missouri ........................ 31 

ABUNDANCE IN "NATURAL" UNAMENDED 

SOILS 

MINERALS 

Calcite, dolomite, gypsum, apatite, calcium 

feldspars, amphiboles, and many other lessimportant minerals. Much of the Ca present in 

soils is held on the surfaces of the colloids as 

adsorbed cations. These cations are easily 

released to the soil solution by exchanging with 

other cations. 

ORGANICS 

The concentration of Ca in plant tissues ranges 

widely among taxonomic groups, grasses and 

leaves of deciduous trees usually having high 

levels; whereas, the leaves of coniferous trees 

are low in Ca. This Ca is released to the soil 

solution when the organic material decays and 

is cycled from soil to plant to soil in a loosely 

held cycle. 

ABUNDANCE IN SOILS 

"Representative" analysis of agricultural soils (as 

Ca): Humid region soils, 0.40% or 8,000 lb/acrefurrow-slice (8,960 kglha-furrow-slice) of 

2,000,000 lbs (908,000 kg); arid region soils, 

1.0%or 20,000 lb/acre-furrow-slice (22,400 kglhafurrow-slice ). Ranges ordinarily expected: 

0.07-3.6%. 

In 1,140 samples (10 from each Missouri 

county) of the surface horizon of agricultural 

soils, 0.41 %, range < 0.07-5.6%. 

Average, all U.S. soils, 2.4%. Average, 

Eastern U.S. soils, 0.54%. Average, Western 

U.S. soils, 3.24%. 

14 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Calcium-Continued 

ABUNDANCE IN SOILS-Continued 

Distribution of concentrations in U.S. surficial 

materials was given by Shacklette and Boerngen (1984). Concentrations in many cultivated 

and uncultivated U.S. soils were given by Connor, Shacklette, and others (1975). 

ABUNDANCE IN PLANTS 

Examples of the Ca concentration in vegetables 

and crop plants (geometric mean percent in ash) 

follow: 

Lima bean seeds, central Georgia, 3 

Soybean seeds, unglaciated prairie, Missouri, 

6.2 

Corn grains, Missouri floodplain, 0.30 

Snap bean pods (fruit), central Georgia, 5.3 

Cabbage leaves, northern Georgia, 16 

Ca concentrations in stems and leaves of woody 

plants tend to be 2-3 times the concentration in 

seeds and fruits of crop plants. Examples 

(geometric mean percent in ash) follow: 

Black gum stems, central Georgia, 25 

Black gum leaves, central Georgia, 17 

Red maple stems, central Georgia, 24 

Red maple leaves, central Georgia, 17 

White oak stems, Missouri, 33 

Shortleaf pine, stems and leaves, Missouri, 13 

Examples of Ca concentrations in forage, hay, and 

browse plants (geometric mean percent in ash) 

follow: 

Johnson grass, Missouri floodplain, 6.1 

Big bluestem grass, Missouri glaciated prairie, 

5 

Western wheatgrass, Western U.S., 4.4 

Alfalfa, Western U.S., 21 

Mesquite, Southwestern U.S., 28 

Concentrations of Ca in a wide variety of cultivate 

and native plants were given by Connor, Shacklette, and others (1975). 

A large number of species (mostly trees and 

shrubs) that were sampled at 910 widely 

distributed localities in the U.S. averaged 12% in 

ash. 

SOURCES FOR FERTILIZERS 

GEOLOGIC OR OTHER PRINCIPAL 

SOURCES 

Limestone, dolomite, and gypsum. Generally, a 

dolomitic limestone is preferred for agricultural 

use in that essential magnesium is supplied at the 

same time. For most soils there should be at least 

one-third as much Mg as Ca in the lime applied in 

order to proportionately meet the outgo of the 

two constituents. If additional Ca is required as a 

plant nutrient in some alkali soils, gypsum is a 

satisfactory source of the element. 

Calcium -Continued 

INCIDENTAL GEOLOGIC OR OTHER 

SOURCES 

MINERAL 

Marl. A soft, unconsolidated deposit of calcium 

carbonate. It occurs in usable quantities in 

many of the Eastern States and is easily mined. 

Its value as liming material depends on its 

having low levels of incorporated clay. Marls 

are almost always low in magnesium. 

Blast-furnace slag. A byproduct of pig iron 

manufacture. In th~~ reduction of iron, the 

calcium carbonate loses its carbon dioxide, then 

the calcium oxide unites with the molten silica 

to form calcium silicate. This material is just as 

effective as limestone in crop production, if 

application rates are increased to counteract its 

lower Ca content. 

Basic slag. A byproduct of the open-hearth 

process of making steel from pig iron. The 

impurities in the iro1n, including P and Si, are 

fluxed with lime and slagged off. The pulverized 

material is used primarily for its P content, but 

it also has a neutralizing value in soils equal to 

65-80% of that of calcium oxide. 

Electric-furnace slag. Results from the electric 

furnace reduction of phosphate rock in the 

preparation of elemental P. The slag is formed 

when the silica and calcium oxide fuse to form 

calcium silicate. It has a low (0.9-2.3%) 

phosphate content, s<~lls at a low price, and has 

a neutralizing value in soils equal to 65-80 

percent of that of calcium oxide. 

Mine tailings. If largely composed of limestone 

and dolomite, is som<:times used as agricultural 

lime. Its content of certain toxic metals may 

preclude its use as a fertilizer. 

ORGANIC 

Shell deposits. In some coastal areas, large 

deposits of oyster or other shells occur and are 

used as a Ca source in industry and agriculture. 

REACTIONS WITH SOIL CONSTITUENTS 

The major importance of Ca as a soil amendment 

is its use to raise the pH of soils, rather than in 

correcting deficiencies as a plant nutrient. For 

optimum crop productivity, Ca must be the 

dominant base in the. exchange complex. Its 

Calcium 15 
Calcium-Continued 

REACTIONS WITH SOIL-Continued 

widespread use in large amounts relates largely to 

maintaining this exchange relationship. In acid 

soils, Ca and other bases are replaced by 

hydrogen and aluminum ions. This acidity may 

increase solubility of B, Mn, AI, Cu, Ni, and 

certain other elements to toxic concentrations, 

convert P to the less soluble Fe and AI 

compounds, and cause Mo deficiency. Acidity 

also promotes breakdown of montmorillonitic 

clay minerals into kaolinitic forms.that have lower 

exchange capacity. Below pH 5.5, the rate of N 

fixation by micro-organisms begins to decrease, 

leading to N deficiency. In alkali soils and many 

saline soils, Na concentration increases at the 

expense of Ca. Increased Na leads to higher soil 

pH, resulting in depressed solubility and 

availability of Ca, P, Mn, Zn, B, and Fe. Structural 

deterioration of soil follows because of the 

dispersing effect of Na, which adversely affects 

water movement, permeability, and aeration of 

soils. Toxic amounts of Na may be absorbed by 

plants. Therefore, Ca is used as a soil amendment 

in both acid and alkaline soils. A major effect of 

Ca is on soil structure, in that it promotes 

flocculation of clay particles, therefore improving 

soil tilth. Ca is the principal element used to 

correct soil toxicity problems. 

FORMS USED BY PLANTS 

Is absorbed by plant roots as the ion Ca + 2 from 

the soil solution. This ion enters the soil solution 

from compounds such as Ca(N03 ) 2 , CaS04 , 

CaC12 , CaH4 (P04 ) 2 , Ca(HC03 h, and others. It 

may also be absorbed by roots by the process of 

contact exchange. 

FUNCTIONS IN PLANT METABOLISM 

Ca functions in plants largely in the 

development of tissue structure and cell 

elongation. Calcium is deposited in the middle 

lamella of tissues, possibly as calcium pectate 

and is thought to be the "cementing" material 

that holds plant cells together. Ca is also 

believed to function in protein synthesis and is 

active in certain enzyme systems. Ca is 

considered to be an immobile element in plants, 

that is, it generally cannot move from older 

tissues to supply the Ca requirement of younger 

tissues. The amount of Ca in plant tissues is 

largely genetically controlled; the concentration 

in the soil solution exerts very little effect on 

this amount. Most soils contain sufficient Ca for 

the metabolic requirements of plants; Ca 

deficiencies of plants are rarely seen in the field. 

Calcium-Continued 

FORMS USED BY PLANTS-Continued 

EXTENT OF USE 

Annually, 26 million tons (23.6 million metric 

tons) of Ca as limestone are applied to soils in 

the U.S. This exceeds the tonnage of any other 

soil amendment used in this country, and 

contrasts to the 4.5 million tons ( 4.08 million 

metric tons) N, 3.4 million tons (3.08 million 

metric tons) P2 0 5 , and 2.7 million tons (2.44 

mi11ion metric tons) K2 0 that are used 

annually. Soil scientists estimate that 80 million 

tons (72.6 million metric tons) of limestone 

should be used in this country for maximum 

crop production, especially in view of the high 

levels of N that are being used, which increase 

the demand for Ca by the crops. A general 

estimate suggests that 500-600 lb/acre/yr 

(560-672 kg!ha!yr) may be required to meet 

the Ca loss from cropped soils in humid 

regions. Natural soils of humid regions 

generally are deficient in Ca for maximum crop 

production; whereas, arid soils commonly have 

sufficient Ca but its availability to plants may be 

reduced by excessive Na. "Typical" application 

rates for Ca (as limestone) range from 4-16 

tons/acre ( 4.48-9.69 metric tons/ha) broadcast 

on the soil surface then incorporated into the 

plow layer. Frequency of application depends 

on quantity applied, fineness of the material, 

and degree of pH correction necessary. As an 

example, in the North-central States, 2 tons of 

ground limestone per acre ( 4.48 metric tons/ 

ha) will usually replace the Ca loss from soil 

for a period of 10-20 years. Farther south, a 

greater annual supply must generally be 

provided. 

LOSSES FROM SOILS 

LEACHING 

Leaching loss of Ca is much greater than loss 

in crop removal. An example of this loss 

follows: 

Silty clay loam, Ithaca, N.Y., lb/acre/yr 

Bare soil, 398 (445.8 kg/ha!yr) 

Rotated cropland, 230 (257.6 kg!ha!yr) 

Continuous grass, 260 (291.2 kg!ha!yr) 

EROSION 

Loss of Ca by erosion, even on a 4% slope, 

may exceed the removal of Ca by crop plants. 

These losses are controlled by 

meteorological factors, soil structure, 

amount of Ca present, and vegetative cover, 

therefore ranging widely in amount. An 

example of Ca losses (lb/acre/yr) in Missouri 

experiments follows: 

16 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Calcium-Continued 

FORMS USED BY PLANTS-Continued 

Corn, grown continuously, 220 (246.4 

kgtha/yr) 

Rotation; corn, wheat, clover, 85 (95.2 

kglha!yr) 

CROP REMOVAL 

The amount of Ca in plant tissues differs 

greatly among plant species and among plant 

organs. Ca is generally low in seeds and 

grains (soybean seeds, 5.6% in ash; corn 

grains, 0.3% in ash) and tubers and roots 

(potato, 0.8% in ash; beet roots, 1.8% in 

ash), but higher in leaves and stems (cabbage 

leaves, 16% in ash; tree leaves and stems, 

15-30% in ash). The "average" Ca removal 

by a standard crop rotation is estimated to be 

35 lb/acre/yr {39.2 kg!ha!yr). However, 

continuous monoculture where a crop 

containing high calcium is grown on a field 

year after year will result in much greater Ca 

loss by crop removal. 

BALANCE SHEET 

ADDITIONS 

There are no natural means of consequence 

for replacing a total loss from the soil, 

although in special circumstances, some Ca 

may be added by windblown dust or carried 

in irrigation water. The management 

practices that can reduce this loss are the 

return of plant residues and animal manures 

to the soil, the use of fertilizers that contain 

calcium, and the application of lime to the 

soil. 

LOSSES 

An example of total Ca losses in cropland 

(lb/acre/yr), corn grown continuously, no 

crop rotation, based on Missouri and New 

York experiments, follows: 

Erosion ......... ........... .......................... 220 

(246.4 kg!ha/yr) 

Leaching loss .......... .......... ................ 398 

( 445.8 kg!ha/yr) 

Crop removal..................................... 35 

(39.2 kg!ha/yr) 

Total Loss............................... 653 

(731.4 kg!ha!yr) 

SOILS WHERE DEFICIENCIES ARE MOST 

COMMON 

Acid soils (calcium saturation of the exchange 

complex less than 25%). 

Sandy soils, particularly where rainfall is over 30 

in./yr (low supply, excessive leaching). 

Calcium-Continued 

SOILS WHERE DEFICIENCIES-Continued 

Soils derived from serpentine (low total supply). 

Strongly acid peat soils (low supply, low 

availability). 

Soils in which the dominant clay is montmorillonitic rather than kaolinitic (low availability). 

Alkali or sodic soils where exchangeable Na and 

pH are high (low availability; excess of N a over 

Ca). 

MAGNESIUM-(Mg) 

OCCURRENCE IN NATURAL MATERIALS 

ABUNDANCE IN SELECTED ROCKS 

From Connor, Shacklette, and others (1975), in 

percent 

Granite, Precambrian; Missouri ................ 0.13 

Rhyolite, Precambrian; Missouri............... .10 

Sandstone 

Sauk sequence; Western U.S................. .33 

Pope Megagroup; Kentucky................... .29 

Pennsylvanian; Kentucky .... ........... ......... .20 

Pennsylvanian; Missouri ......................... .56 

Shale 

Sauk sequence; Western U.S ................. 1.3 

Lower Mississippian; Kentucky ............. 1.3 

Upper Mississippian; Kentucky ............. 1.1 

Mississippian; Missouri........................... 2.4 

Pennsylvanian; Kentucky ........................ .73 

Pennsylvanian; Missouri ......................... .99 

Limestone and dolomite 

Sauk sequence; Missouri ....................... 11 

Ordovician; Kentucky.............................. 2.3 

Upper Ordovician; Kentucky................. 3.2 

Tippecanoe sequence; Missouri ... ......... 4.3 

Lower Mississippian; Kentucky ............. 2.2 

Upper Missippippian; Kentucky............ 1.6 

Mississippian; Missouri........................... 2.3 

Pennsylvanian; Kentucky ........................ 1.2 

Pennsylvanian; Missouri ......................... 1.5 

ABUNDANCEIN"NATURAL"UNAMENDED 

SOILS 

MINERALS 

Dolomite, serpentine, olivine, micas, and 

others. Mg is also held on clay in an 

exchangeable form. 

ORGANICS 

Mg in ash of plants ranges from about 0.14 to 

> 10%; therefore, the organic constituents of 

soil provide a ready source of this element that 

is held in a loose soil-plant-soil cycle. The Mg 

that is solubilized from soil minerals by 

Magnesium 17 
Magnesium -Continued 

ABUNDANCE IN "NATURAL" -Continued 

weathering may be held on soil organic matter 

in an exchangeable form and is available for 

plant use. 

ABUNDANCE IN SOILS 

"Representative" analysis of agricultural soils: 

Humid region soils, 0.30% or 6,000 

lb/acre-furrow-slice ( 6. 720 kg!ha-furrow-slice) 

weighing 2,000,000 lb (908,000 kg); arid region 

soils, 0.60% or 12,000 lb/acre-furrow-slice 

(13,440 kg!ha-furrow-slice ). Range ordinarily 

expected, 0.12-1.50%. 

In 1,140 samples (10 from each Missouri 

county) of the surface horizon of agricultural 

soils, 0.28%, range 0.05-2.8%. 

Average, all U.S. soils, 0.92%. 

Average, Eastern U.S. soils, 0.48%. 

Average, Western U.S. soils, 1.01%. 

Distribution of concentrations in U.S. surficial 

materials was given by Shacklette and Boerngen 

(1984). Concentrations in many cultivated and 

uncultivated U.S. soils was given by Connor, 

Shacklette, and others (1975). 

ABUNDANCE IN PLANTS 

Mg levels tend to be slightly higher in seeds and 

grains than in the vegetative parts of plants. 

Examples of Mg concentrations in vegetables and 

crop plants (geometric mean percent in ash) 

follow: 

Lima bean seeds, central Georgia, 3.4 

Soybean seeds, unglaciated prairie, Missouri, 

3.2 

Corn grains, Missouri floodplain, 6.2 

Snap bean pods (fruit), central Georgia, 3.6 

Cabbage leaves, northern Georgia, 2.7 

The Mg content of stems and leaves of woody 

plants are about equal. Examples (geometric 

mean percent in ash) follow: 

Black gum stems, central Georgia, 5.7 

Black gum leaves, central Georgia, 5.9 

Red maple stems, central Georgia, 2.5 

Red maple leaves, central Georgia, 2.3 

White oak stems, Kentucky, 2.0 

Shortleaf pine stems and leaves, Missouri, 3.5 

Examples of Mg concentrations in forage, hay, 

and browse plants (geometric mean percent in 

ash) follow: 

Johnson grass, Missouri floodplain, 2.9 

Big bluestem grass, Missouri glaciated prairie, 

1.5 

Western wheatgrass, Western U.S., 1.1 

Alfalfa, Western U.S., 2.8 

Mesquite, Southwestern U.S., 2.9 

Magnesium -Continued 

ABUNDANCE IN PLANTS-Continued 

The Mg content of a large number of cultivated 

and native plant species was given by Connor, 

Shacklette, and others (1975). 

SOURCES FOR FERTILIZERS 

GEOLOGIC OR OTHER PRINCIPAL 

SOURCES 

The most widely used material for general 

application is dolomite or dolomitic limestone. If 

Mg is to be added to mixed fertilizers, potassium 

magnesium sulfate (K2S04 , MgS04 ; 18% K, 11% 

Mg, 18% S) is often used. Magnesium sulfate 

alone may be used, and also magnesia which is 

made by calcining magnesite or brucite to give 

magnesium oxide. 

INCIDENTAL GEOLOGIC OR OTHER 

SOURCES 

MINERALS 

Asbestos tailings 

Basic slag, 3.4% Mg 

Well brines and sea water. These materials are 

treated with calcium hydroxide and heated to 

produce MgO (55% Mg). 

ORGANICS 

Animal manures, 1.6-5.8 lb!English ton 

(0.66-2.38 kg metric tons) Mg. 

Sewage sludge, 6-16 kg/metric ton of solids 

(14.6-38.9 lb/English ton) Mg. 

REACTIONS WITH SOIL CONSTITUENTS 

If solubilized from soil minerals by weathering, 

Mg may be held on clay or organic matter in an 

exchangeable form. If calcitic limestone is applied 

to the soil, some of the exchangeable Mg will be 

replaced by Ca, and the Mg may be leached from 

the soil. Plant deficiencies of Mg may result if the 

Ca:Mg ratio is too wide-about 7:1 is the best 

ratio in most soils. High levels of available soil K 

generally reduce Mg uptake by plants, especially 

in low-Mg soils. This interaction results from an 

excessively wide ratio of exchangeable K to 

exchangeable Mg, and soils having this ratio may 

produce pastures (especially grass) that are 

extremely low in Mg (grasses having < 0.2% Mg 

in dry weight). Animals grazing this grass may 

develop a nutritional disease called hypomagnesanemia or grass tetany (Mortvedt and Cunningham, 1971, p. 425). The use of soluble Mg 

fertilizers, such as MgS04 , has been reported to 

reduce Zn deficiency symptoms in some crop 

plants, but the chemical interactions are not well 

understood. 

FORMS USED BY PLANTS 

Mg is absorbed by plants as the ion Mg + 2 from 

the soil solution. It may possibly also be absorbed 

18 Essential Elements and Soli Amendments for Plants: Sources and Use for Agriculture 
Magnesium -Continued 

FORMS USED BY PLANTS-Continued 

by the mechanism of contact exchange. Some 

compounds in which the Mg is readily available to 

plants are MgO, MgS04, MgCh, and 

Mg(HC03)4. 

FUNCTIONS IN PLANT METABOLISM 

Mg is the only mineral constituent of the 

chlorophyll molecule and is essential for the 

process of photosynthesis with about 10% of 

the Mg in leaves in the chlorophyll. Mg is 

required for activation of enzymes that function 

in carbohydrate metabolism and is involved in 

the citric acid cycle of cell respiration. Mg 

catalyzes numerous phosphorylation reactions 

related to N metabolism in plants and also 

functions in the synthesis of oils. 

EXTENT OF USE 

Because Mg is not widely applied as a pure 

compound, but as a constituent of liming 

materials in dolomitic limestone, data are not 

available as to annual amount used. The 

amounts lost from soils in agricultural 

operations are usually replaced by liming that is 

aimed principally at correcting soil acidity. For 

this reason, the material used in liming soil 

should contain at least one-third as much Mg as 

Ca in order to proportionately replenish the 

loss of these two elements. 

For certain crops in some areas, Mg 

deficiencies are severe and may be corrected by 

direct application of Mg compounds to the soil 

or directly to plants in a foliar spray. Examples 

of Mg applications follow: 

Applied to soil 

Apple trees, 400 lb/acre (448 kg!ha) 

magnesium sulfate corrected deficiency in 

2-3 years. 

Potatoes, 60-100 lb/acre (67-112 hl!ha) 

magnesium sulfate, or 2~30 lb/acre 

(33.6-44.8 kg!ha) magnesium oxide. 

Soybeans, 3~0 lb/acre (33.6-44.8 kg!ha) 

magnesium oxide. 

Cauliflower, 300 lb/acre (336 kg!ha) 

magnesium oxide. 

Foliar spray 

Apple trees with severe deficiency, 8 sprays 

using 20 lb (2.4 kg) magnesium sulfate per 

100 gallons (378.41) of water, applied at 1- to 

2-week intervals. 

Orange trees, 10 lb (1.2 kg) magnesium 

nitrate per 100 gallons (378.4 1) of water. 

One report stated that a spray with a 2% 

suspension in water of finely ground burnt 

dolomite corrected the Mg deficiency. 

Magnesium -Continued 

FORMS USED BY PLANTS-Continued 

LOSSES FROM SOILS 

LEACHING 

Loss of Mg by leaching is roughly the same as 

the loss by crop removal but is markedly 

affected by factors, such as fertilization 

levels, cropping patterns, and soil texture and 

drainage. An example of leaching loss 

follows: 

Representative humid-region loam cropped 

to a standard rotation, 20 lb/acre/yr (22.4 

kg!ha!yr). 

EROSION 

Loss of Mg by erosion, even on a 4% slope, 

may exceed the removal of Mg by crop 

plants. The control of Mg erosional losses is 

essentially the same as that for Ca losses. An 

example of Mg losses by erosion (lb/acre/yr) 

in Missouri experiments follows: 

Corn, grown continuously, 87 (97.4 

kg!ha/yr) 

Rotation; corn, wheat, clover, 29 (32.4 

kg!ha/yr) 

CROP REMOVAL 

Plant species and varieties differ both in their 

Mg req~irement and in their Mg 

concentration in tissues. Mg concentrations 

also tend to differ in the several plant organs. 

Mg in seeds and grains tend to range from 

2.5-5% in ash, but corn grains have a range 

of greater values, about 6-13%. Ash of stems 

and leaves from both herbaceous and woody 

plants ranges from 3-7% Mg, with 

exceptional values of 10 percent or greater. 

Losses by crop removal in a standard rotation 

of corn, wheat, and legumes are estimated to 

be about 25 lb/acre/yr (28 kg!ha/yr). 

BALANCE SHEET 

ADDITIONS 

There is no important natural process for 

replacing soil losses, although under special 

conditions some Mg may be added by 

windblown dust or in irrigation water. Loss 

can be corrected by return of plant residues 

and animal manures to the soil, use of Mgcontaining fertilizers, and application of 

dolomitic limestone. 

LOSSES 

An estimate of total Mg losses (lb/acre/yr) in 

a standard rotation silt loam soil, humid 

region, follows: 

Magnesium 19 
Magnesium-Continued 

FORMS USED BY PLANTS-Continued 

Erosion................................................... 29 

(32.4 kglha/yr) 

Leaching loss......................................... 20 

(22.4 kglha/yr) 

Crop removal......................................... 25 

(28.0 kglha/yr) 

Total I..oss.................................. 74 

(82.8 kglha/yr) 

Some soils of arid regions have an excess of 

Mg, therefore loss from the soil may be 

beneficial. For example, in a heavy clay soil in 

the Napa Valley, California, more than 90% 

of the cation exchange capacity was saturated 

with Mg, which rendered the soil almost 

completely unproductive. 

SOILS WHERE DEFICIENCIES ARE MOST 

COMMON 

Acid, sandy soils receiving moderate to high 

rainfall. 

Imperfectly drained clay soils. 

Peat and muck soils. 

Minor Essential Elements 

(Micronutrients) 

BORON-(B) 

OCCURRENCE IN NATURAL MATERIALS 

ABUNDANCE IN SELECTED ROCKS 

From Connor, Shacklette, and others (1975), in 

parts per million (ppm) 

Granite, Precambrian; Missouri.............. < 20 

Rhyolite, Precambrian; Missouri............. < 20 

Arkose, Fountain Formation; Colorado.. 6.7 

Sandstone 

Roubidoux Formation; Missouri.............. 20.7 

Pope Megagroup; Kentucky ...................... 19.8 

Pennsylvanian; Kentucky ........................... 22.0 

Pennsylvanian; Missouri............................. 43.2 

Shale 

Sauk sequence; Western U.S ................ 60.2 

!..ower Mississippian; Kentucky............ 79.2 

Upper Mississippian; Kentucky ............ 74.8 

Mississippian; Missouri.......................... 70.4 

Pennsylvanian; Kentucky ....................... 58.8 

Pennsylvanian; Missouri........................ 73.4 

Black shale, Devonian and Mississippian; 

Kentucky ................................................... 112.0 

Limestone and dolomite 

Upper Ordovician; Kentucky................ 34.1 

Tippecanoe sequence; Missouri ........... < 20 

!..ower Mississippian; Kentucky ............ 31.9 

Upper Missippippian; Kentucky........... <50 

Boron-Continued 

ABUNDANCE IN SELECTED-Continued 

Mississippian; Missouri........................ < 20 

Pennsylvanian; Kentucky ....................... <50 

Pennsylvanian; Missouri ...................... < 20 

ABUNDANCE IN "NATURAL" UNAMENDED 

SOILS 

MINERALS 

Tourmalines (borosilicates, about 10% B) are 

the main B-containing minerals, and are very 

slowly soluble. Precipitated Al(OH)3 adsorbs 

large amounts of B; liming of acid soils 

increases adsorption due to increase in amount 

of exchangeable AI. 

ORGANICS 

Most of the available soil B is held by the 

organic fraction, where it is retained until the 

organic matter decomposes; then B is released, 

taken up by plants, held in clay lattices, or lost 

by leaching. 

ABUNDANCE IN SOILS 

"Representative" analysis of agricultural soils, 50 

ppm (100 lb/acre-furrow-slice; 112 kglha-furrowslice), range 50-150 ppm. 

In 1,140 samples (10 from each Missouri county) 

of the surface horizon of agricultural soils, 33 

ppm; range < 20-700 ppm. 

Average, all U.S. soils, 34 ppm 

Average, Eastern U.S. soils, 38 ppm. 

Average, Western U.S. soils, 28 ppm. 

Distribution of concentrations in U.S. surficial 

materials was given by Shacklette and Boerngen 

(1984). Concentrations in many cultivated and 

uncultivated U.S. soils were given by Connor, 

Shacklette, and others (1975). 

ABUNDANCE IN PLANTS 

The concentrations are strongly genetically 

controlled and range widely among different plant 

families and species. There is also a wide range 

among different plant organs. Soil concentrations 

of available B also influence plant contents. For a 

particular species of plant, differences between 

deficient levels and toxic levels in soils commonly 

are very small. Much higher concentrations of B 

occur in plant than in animal tissues. 

Most dicotyledonous plants (broad leafed, as in 

common herbs and trees) have higher B 

requirement than do monocotyledonous plants 

(narrow leafed, as in grasses). Perennial crop 

plants, such as alfalfa, clover, fruit and nut trees, 

tend to suffer B deficiencies more commonly than 

do annual crop plants. Members of the mustard 

family (cabbage, cauliflower, and turnip, for 

20 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Boron-Continued 

ABUNDANCE IN PLANTS-Continued 

example) have both a high B requirement and a 

high B tolerance; whereas, cereal crops have a low 

requirement and low tolerance. 

Legumes (beans, peas, and peanuts, for example) 

generally are richest in B (25-50 ppm, dry weight 

basis), followed by fruits and vegetables (5-20 

ppm), with cereal grains and hays the poorest 

(1-5 ppm). Concentrations found in 895 samples 

of a wide variety of plants from throughout the 

U.S. (mostly trees and shrubs) averaged 314 ppm 

in ash, and ranged from <30-2,000 ppm. 

Concentrations of B in many vegetables and 

native plants of the U.S. are given by Connor, 

Shacklette, and others (1975). 

SOURCES FOR FERTILIZERS 

GEOLOGIC OR OTHER PRINCIPAL 

SOURCES 

Borax, Na2B407·10H20, 16.6% B. Soluble in 

water; is absorbed rapidly by plants, and readily 

leached from soils. The most widely used form in 

fertilizers. 

Colemanite, Ca2B60n·5H20, 50.95% B203. 

Considerably less soluble than borax, therefore 

superior as a soil fertilizer, particularly on light, 

sandy soils. Supplies of this mineral in the U.S. 

have been largely depleted. 

Kernite, Na2B401·4H20, 51.0% B203. In the 

U.S. the B mineral mined in the largest quantities. 

It is unusual in that crystallization of a water 

solution of the ore mineral yields 1.59 times as 

much of the desired product, borax. 

Howlite, Ca2SiBs09(0H)s, 44.6% B203. Slowly 

soluble, therefore a desirable B fertilizer material. 

Borosilicate glass (frits), 3-6% B. Made by fusion 

of B compounds with glass, it extends the period 

of availability of B in soils and is becoming widely 

used. Rate of B release to the soil solution can be 

regulated to meet the needs of a particular crop 

by controlling the particle size of the frits. 

INCIDENTAL GEOLOGIC OR OTHER 

SOURCES 

IRRIGATION WATER 

If the B content of irrigation water is 0.16-0.20 

ppm or more and 1 acre-foot (1,233.6 m

3

) is 

used, B deficiency is unlikely. If the B content is 

Boron-Continued 

INCIDENTAL GEOLOGIC-Continued 

greater than 0.75 ppm, some sensitive plants 

(citrus trees, among others) will show toxicity 

symptoms. 

MINERAL 

Chilean sodium nitrat.e. Use of this fertilizer in 

the U.S. is insignificant at the present time. 

Boron has been reported as an atmospheric 

contaminant of soils, having originated in soot 

from the burning of coal for domestic use. 

Samples of this soot contained 555-650 ppm 

water-soluble B. 

ORGANIC 

Sewage sludge commonly contains 

considerable B; however, estimates of amounts 

are not available. Night soil (human excrement) 

in Paris, France, contained an average B 

content of 23.3 ppm in dry matter. At the 

application rate used on horticultural crops, 

100 metric tons/ha/yr ( 44.6 English tons/ 

acre/yr), night soil supplied 1.4 kg/ha!yr (1.2 

lb/acre/yr) B, the equivalent of a 12-kg (26.4lb) 

borax application. 

Animal manures are only slightly less rich in B; 

the "average" concentration was reported as 

20.2 ppm in dry matter, with a range of 4.5-52 

ppm. 

REACTIONS WITH SOIL CONSTITUENTS 

Reactions include sorption of B as borate ions 

(H3B04 "

2

) or as molecular H3B03, precipitation 

of insoluble B with alumina and silica, and entry 

of B into clay mineral lattices which increases 

markedly with increasing pH. This latter reaction 

is rapid and reversible, and reactivity is in a 

decreasing order with illite, kaolinite, and montmorillonite. B is readily bound to the organic 

fraction of soils. 

Applications of K fertilizers aggravate B 

deficiencies in some crop plants. Increased Ca 

concentrations decrease B toxicity at high B levels 

in soils and increase B deficiency symptoms at low 

B levels in soil. 

FORMS USED BY PLANTS 

Probably absorbed as boric acid, H3B03, from the 

soil solution in acid soils; in basic soils possibly 

largely absorbed by contact exchange at root 

surface. 

FUNCTIONS IN PLANT METABOLISM 

Required for the processes of cell 

differentiation and maturation and for 

optimum rate of water absorption. The 

Boron 21 
Boron-Continued 

FORMS USED BY PLANTS-Continued 

reactions involved are not known but possibly 

are enzyme related. B is thought to prevent 

excessive polymerization of sugars at sites of 

sugar synthesis, and therefore to aid in sugar 

translocation. Deficiencies of B lead to 

breakdown of meristematic tissues and 

parenchyma and to poor development of 

vascular tissue. 

EXTENT OF USE 

The estimated amount of B (expressed on an 

elemental basis) sold for fertilizer in the U.S. in 

fiscal1969 was 2,250 metric tons (2,480 English 

tons). 

The range between soil deficiency and toxicity 

for many plants is narrow. The very small 

amounts usually applied per acre require it to 

be added to other fertilizers, inert "filler" 

material, ·or water in order to permit even 

distribution on the soil. 

Application rates range widely among different 

soils and crops. The rates of 0.25-3 kg/ha/yr 

(0.22-2.7 lb/acre/yr) are generally 

recommended if deficiency symptoms appear in 

a crop, the lower rate for the more sensitive 

crops, such as com, and the higher rates for 

B-tolerant crops, such as alfalfa. Foliar 

applications as a spray of 15--60 g (0.5-2.1 

ounces) of B per tree are generally 

recommended for correcting deficiencies of 

fruit and nut crops. Repeated applications of B 

fertilizers over a long time may result in B 

toxicity in soils for B-sensitive species. 

SOILS WHERE DEFICIENCIES ARE MOST 

COMMON 

Soils naturally low in B, such as those derived 

from acid igneous rocks or from freshwater 

sedimentary deposits. 

Naturally acid soils where much of the original B 

content has been removed by leaching. 

Light-textured, sandy soils (excessive leaching). 

Acid peat and muck soils. 

Alkali soils, especially those containing free lime. 

Irrigated soils where B content of water is low, 

and where salt or carbonate deposition has 

occurred. 

Boron -Continued 

SOILS WHERE DEFICIENCIES-Continued 

Soils low in organic matter. 

Regions in the U.S. in which the soils are 

particularly low in B are the Atlantic and Gulf 

coasts from Maine to Texas, the North-central 

States, California, and the Pacific Northwest. 

CHLORINE-(CI) 

OCCURRENCE IN NATURAL MATERIALS 

ABUNDANCE IN SELECTED ROCKS 

From Turekian and Wedepohl (1961), in parts 

per million (ppm) 

Igneous 

Ultrabasic, 85 

Basaltic, 60 

Granitic 

High calcium, 130 

Low calcium, 200 

Sedimentary 

Shales, 180 

Sandstones, 10 

Carbonates, 150 

ABUNDANCE IN "NATURAL" UNAMENDED 

SOILS 

MINERALS 

The Cl ion is highly soluble in water, therefore 

readily dissociates from most compounds and 

enters the soil solution. It is not adsorbed on 

soil colloids. The common source of Cl in 

natural soils is halite (NaCl), but it occurs as 

crystals only in very dry soils. Cl may 

accumulate in humid area soils solutions where 

drainage is impeded. 

ORGANICS 

Because of the high solubility of Cl, it is rapidly 

leached from the nonliving organic matter of 

soils. Therefore, soil humus is not an important 

reservoir of soil Cl. 

ABUNDANCE IN SOILS 

"Representative" analysis of agricultural soils, 50 

ppm (100 lb/acre-furrow-slice, or 112 

kg/ha-furrow-slice; range, 10-1,000 ppm. One 

measurement of the yearly average Cl in a 

productive agricultural soil was reported as 8,519 

kg/ha-furrow-slice depth (9,550 lb/acre-furrowslice). 

ABUNDANCE IN PLANTS 

A general estimate of the Cl content of plants is 

0.025% in dry tissue, or expressed another way, 

one pound of Cl in each 4,000 pounds (2.2 

kg/1,000 kg) of dry matter produced. Cl 

accumulates in plant tissue with age, and young 

22 Essential Elements and Soli Amendments for Plants: Sources and Use for Agriculture 
Chlorine-Continued 

ABUNDANCE IN PLANTS-Continued 

leaves can contain less than optimum amounts 

while older leaves on the plant may have already 

accumulated a toxic excess. One measurement of 

seasonal accumulation in leaf stalks of grape was 

reported as follows (percent, dry weight basis): 

October 25, 0.62 

December 20, 1.37 

February 15, 2.11 

The Cl content ranges widely among both species 

and organs of plants. For example, with stone 

fruits (like peaches, plums, and cherries), one 

investigator found Cl concentrations in roots and 

leaves to be about the same, followed by 

concentrations in bark, with the wood having 

about one-tenth as much as in the leaves. Some 

examples of the "normal" concentration in crop 

plants follow (percent, in dry matter): 

Barley, stems and leaves, 4.20-4.40 

Bean, leaves, 2.69-5.65 

Carrot, roots, 1.07 

Corn, leaves, 2.11 

Potato, stems and leaves, 0.83 

Onion, bulbs, 0.25 

Date palm fruit, 0.16-0.69. 

A comparison of the Cl in soils and in plant stems 

and leaves in one experiment in Wisconsin 

follows: 

Soils, 0-6-in. (0-15.2 em) depth, 34 lb/acre 

furrow-slice (38 kg!ha-furrow-slice) 

Plants, 30 lb/acre (33.5 kg!ha) 

A study in California determined the yearly 

average Cl in soils and plants as follows (kg!hafurrow-slice ): 

Soils, 8,519 (9,550 lb/acre-furrow-slice) 

Soil bacteria, 1,589 (1,781lb/acre-furrow-slice) 

Vascular (higher) plants, 1,918 (2,150 lb/acrefurrow-slice) 

SOURCES FOR FERTILIZERS 

GEOLOGIC OR OTHER PRINCIPAL 

SOURCES 

Production of Cl primarily for direct application 

(as a salt) to correct Cl deficiencies of soils is of 

little importance. The Cl supplied by natural 

processes, in addition to the Cl in fertilizers, 

generally meet the needs of crop plants. However, 

common salt (NaCI) or potassium chloride (KCI) 

is used on soils that have a natural Cl deficiency, 

and of course halite and sylvite deposits and 

brines constitute the geologic sources. 

Chlorine-Continued 

INCIDENTAL GEOLOGIC OR OTHER 

SOURCES 

ATMOSPHERIC 

The Cl brought down in rainfall largely 

originates from sea water; therefore, the annual 

rate of deposition on soil is related to distance 

from the sea and prevailing wind direction. The 

salt is injected into the atmosphere as particles 

0.1-1 micrometer or larger from oceans by the 

bursting of air bubbles as they reach the 

surface. In areas near the sea, deposits of 100 

lb/acre/yr (112 kglha!yr) or more are common. 

Measurements made at Geneva, New York, 

and at Madison, Wisconsin, indicated an annual 

deposit of 16 lb/acre (167.9 kg!ha). Some 

reports suggest that Cl is added to soil from 

industrial emissions, but supporting data are 

not available. 

IRRIGATION WATER 

The most common problem is with excess, 

rather than inadequate, amounts for crop 

production. Irrigation water containing 500 

ppm Cl as NaCI is immediately injurious to 

Cl-sensitive plants, such as avocado, and longtime use of this water may lead to excesses in 

soils for many crops. One extremely resistant 

crop plant to Cl, asparagus, seldom is injured by 

Cl concentrations in soils, and is an important 

crop plant in some coastal salt marshes, 

particularly in Taiwan. 

ORGANIC 

Cl released by plant decomposition is quickly 

absorbed by nearby living plants. If none is 

present, the Cl generally is soon lost from the 

soil by leaching. 

REACTIONS WITH SOIL CONSTITUENTS 

Cl accumulation in soils is reduced if 

concentrations of either nitrate or sulfate ions are 

increased. The addition of superphosphate 

fertilizers was found in one study to have 

synergistic effect on Cl uptake. Excess soil Cl 

depresses the absorption by plants of nitrates and 

sulfates. Some experiments indicated that leaves 

accumulate higher Cl if calcium chloride is 

substituted for sodium chloride. If the calcium ion 

is the dominant cation in the plant root, the 

negative potential is low and more Cl ions 

accumulate than if sodium is the dominant cation. 

The addition of Cl increases silicon absorption by 

plants from Si-deficient solutions. 

Chlorine 23 
Chlorine-Continued 

FORMS USED BY PLANTS 

Cl is absorbed from the soil solution as the Cf1 ion, 

or directly by leaves from atmospheric NaCl 

deposits on the leaves. 

FUNCTIONS IN PLANT METABOLISM 

Cl was only recently classified as an essential 

element for plants, although it is used in larger 

quantities by crop plants than any other micronutrient except iron. Little is known of its 

metabolic function other than that it is required 

for growth and development. Recent research 

indicates that Cl functions in the photosynthetic 

reactions of chloroplasts in the electron-flow 

mechanism of cyclic phosphorylation. Older 

literature reported that Cl was necessary for 

carbohydrate translocation, but recent 

experiments cast some doubt on this function. 

Bromine, at somewhat higher concentrations 

than Cl, can substitute for Cl, at least in part. 

Plant species differ in their resistance to Cl 

deficiencies in the soil solution. Plants that 

suffer the least, such as corn, beans, and 

squash, are those that are able to make more 

efficient use of atmospheric Cl. 

Increase of Cl in the soil solution, up to a 

certain point, increases the osmotic 

concentration of plant cell sap. This elevated 

osmotic pressure may influence the absorption 

of other elements from the soil solution. 

EXTENT OF USE 

Chlorine salts, except KCI, are not widely used 

as fertilizers; additions of Cl from the 

atmosphere are believed to be adequate to 

meet crop needs in almost all localities. 

Commercial fertilizers commonly supply 

additional amounts of Cl to crop plants, 

especially the K fertilizers. Cl deficiency in crop 

plants is marked by fairly well-defined 

morphological symptoms. If these symptoms 

appear, the general recommendation is to apply 

20 lb/acre (22.4 kg!ha) Cl in fertilizer mixtures 

(often as KCI). 

SOILS WHERE DEFICIENCIES ARE MOST 

COMMON 

Soils at locations far inland from the sea. 

Coarse-textured soils (sands, sandy loams) where 

rapid leaching occurs. 

Soils that are heavily cropped with high-Cl plants. 

Soils left bare of vegetation (no cover crop) for 

part of every year. 

Soils low in organic matter. 

COPPER-(Cu) 

OCCURRENCE IN NATURAL MATERIALS 

ABUNDANCE IN SELECTED ROCKS 

From Connor, Shacklette, and others (1975), in 

parts per million (ppm) 

Granite, Precambrian; Missouri ................ 2.6 

Rhyolite, Precambrian; Missouri............... 2.1 

Arkose, Fountain Formation; Colorado... 8.9 

Sandstone 

Sauk sequence; Western U.S................. 8.0 

Roubidoux Formation; Missouri........... 1.6 

Pope Megagroup; Kentucky................... 9.2 

Pennsylvanian; Kentucky ........................ 8.5 

Pennsylvanian; Missouri ........................ 12.6 

Shale 

Sauk sequence; Western U.S............... 23.1 

Lower Mississippian; Kentucky........... 16.8 

Upper Mississippian; Kentucky........... 19.2 

Mississippian; Missouri......................... 20.8 

Black shale 

Devonian and Mississippian; Kentucky 143 

Limestone and dolomite 

Sauk sequence; Western U.S................. 6.4 

Sauk sequence; Missouri ........................ 3.0 

Upper Ordovician; Kentucky................. 6.1 

Tippecanoe sequence; Missouri ............ 1.8 

Lower Mississippian; Kentucky............. 4.8 

Upper Missippippian; Kentucky............ 3.1 

Mississippian; Missouri........................... 1.0 

Pennsylvanian; Kentucky .... .................... 3.8 

Pennsylvanian; Missouri ......................... 4.6 

ABUNDANCE IN "NATURAL" UNAMENDED 

SOILS 

Copper in soils occurs principally as the Cu + 2 ion 

absorbed by clay minerals and in the organic 

matter where it is very tightly held. Smaller 

amounts of neutral insoluble salts, water-soluble 

compounds, and copper minerals may also be 

present. 

ABUNDANCE IN SOILS 

"Representative" analysis of agricultural soils, 50 

ppm; range, 5-150 ppm. 

In 1,140 samples (10 from each Missouri county), 

of the surface horizon of agricultural soils, 14 

ppm; range, 5-150 ppm. 

Average, all U.S. soils, 25 ppm. 

Average, Eastern U.S. soils, 21 ppm. 

Average, Western U.S. soils, 26 ppm. 

24 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Copper-Continued 

ABUNDANCE IN SOILS-Continued 

Distribution of concentrations in U.S. surficial 

materials was given by Shacklette and Boerngen 

(1984). Concentrations in many cultivated and 

uncultivated U.S. soils were given by Connor, 

Shacklette, and others (1975). 

ABUNDANCE IN PLANTS 

The concentrations of Cu are controlled by the 

genetic characteristics of the species, by the plant 

organ that is sampled, and by the amount of 

available Cu in the soil. A wide variety of species 

that were sampled at 910 widely distributed 

localities in the U.S. averaged 124 ppm Cu in ash, 

with a range of 5-1,000 ppm. 

The Cu content (ppm in ash) of some crop plants 

follow (Connor, Shacklette, and others, 1975; 

Shacklette, Sauer, and Miesch, 1970): 

Corn grains, Missouri, 30-220 

Soybean seeds, Missouri, 100-300 

Beans, snap (pods), Georgia, 30-300 

Cabbage leaves, Georgia, 10-300 

Tomato fruits, Georgia, 30-500 

Carrot roots, Wisconsin, 20-120 

Potato tubers, Wisconsin, 40-150 

Examples of Cu concentrations in forage, hay, and 

browse plants (geometric mean ppm in ash) 

follow: 

Johnson grass, Missouri floodplain, 107 

Bluegrass, Eastern U.S., 107 

Western wheatgrass, Western U.S., 50 

Alfalfa, Western U.S., 94 

Mesquite, Southwestern U.S., 105 

The wide range in Cu given above, even within a 

species of crop plant, is notable. This range may 

be related to differences in availability of soil Cu, 

to climatological factors, or even to genetic 

differences within a species (varietal). The Cudeficiency symptoms of crops have been welldefined and provide reliable guides to the 

necessity for Cu fertilization. Tissue analysis, in 

many species, indicate the Cu status of the plant. 

Examples of the levels of Cu (ppm, dry tissue) in 

crop plants that indicate Cu deficiency follow: 

Apple leaves, 1-4 

Orange leaves, 1-10 

Red clover leaves and stems, < 5 

Coffee leaves, 3 

Currant leaves, 2-4 

Grape leaves, 1-5.4 

Oats leaves and stems, 2 

Peach leaves, 0.134>.39 

Pear leaves, 3.2-6.7 

Wheat grains, 1.5 

Copper-Continued 

ABUNDANCE IN PLANTS-Continued 

Concentrations of Cu in a wide variety of 

cultivated and native plants were given by Connor, 

Shacklette, and others (1975). 

SOURCES FOR FERTILIZER 

GEOLOGIC OR OTHER PRINCIPAL 

SOURCES 

The Cu material commonly used as fertilizer, 

copper sulfate (CuS04 ·SH20; 25.5% Cu, 12.8% 

S), is manufactured from metallic Cu that is in the 

trade, so this fertilizer does not have a direct 

geologic source. Other Cu fertilizers, including 

CuO, Cu(OH)2, and Cu chelates are sometimes 

used. 

INCIDENTAL GEOLOGIC OR OTHER 

SOURCES 

ATMOSPHERIC 

Direct evidence of atmospheric Cu being 

utilized by crop plants is not available. 

However, Spanish moss, an epiphyte that is 

totally dependent on airborne elements, was 

found to contain an average of 150 ppm Cu in 

ash (an amount within the "normal" range of 

crop plants); furthermore, concentrations 

showed positive correlation with distance from 

sources of atmospheric Cu pollution. It seems 

likely that crop plants utilize some airborne Cu 

if in an area of heavy pollution. 

IRRIGATION WATER 

Most irrigation waters carry too little Cu to be 

of significance in correcting Cu deficiencies, 

and the alkalinizing effect of irrigation waters 

on soils may reduce copper availability and 

bring on deficiencies. 

ORGANIC 

Farm manures, general range, 0.01-0.03 

lbs/ton (0.005-0.015 kg/metric ton), wet weight 

basis. 

Fresh animal manures, average, 15.6 ppm (dry 

weight basis). 

Sewage sludge, Chicago, 0.45 kg/metric ton (0.9 

lb/English ton), dry weight basis. 

Plant refuse returned to the soil replaces some 

the Cu that was removed from the soil by the 

crop. 

The use of Cu-containing sprays as fungicides, 

especially Bordeaux mixture (copper sulfate 

and lime), has greatly increased the Cu content 

of old orchard soils to as much as 300 ppm. 

Copper 25 
Copper-Continued 

INCIDENTAL GEOLOGIC-Continued 

These sprays have largely been replaced by 

organic fungicides. 

REACTIONS WITH SOIL CONSTITUENTS 

Cu availability is strongly controlled by soil pH. At 

low pH, Cu may reach toxic levels, but as the pH 

rises, the availability declines to a satisfactory 

nutritional level at about pH 7; above this pH 

value, availability greatly declines to the point of 

deficiency for plants. Throughout these changes, 

total Cu in the soil can remain at approximately 

the same level. Cu retention in soils increases as 

organic matter increases because of Cu-humus 

complexing. In some soils the Cu is retained so 

tightly that it is not available to plants; in others, 

plants can absorb Cu from these complexes. As 

the organic N or S content of organic soils (in one 

example, peat) increased, the number of stable 

Cu-organic complexes was found to increase. 

High AI concentrations in soil solutions are 

thought to decrease Cu uptake by plants. Some 

experiments have shown that maximum growth of 

certain crop plants is controlled more by the 

Cu:Fe ratio than by the amounts of either element 

separately, and that the best ratio was 2.5:3.0. It is 

certain that excessive amounts of Cu depress the 

activity of Fe, and this may lead to Fe-deficiency 

symptoms in plants. High rates of N fertilizer can 

cause Cu deficiencies both by increasing the 

degree of organic complexing, and by removal of 

more Cu in crop plants because of the higher 

yields promoted by N. High Cu levels in soils 

diminish the ability of plants to utilize P. 

FORMS USED BY PLANTS 

Cu is absorbed from the soil solution as Cu + 2 

ions, or through the leaves as a Cu salt on organic 

complexes, such as EDTA. If the soil is well 

aerated, ions of higher valence tend to 

predominate. If drainage is poor, reductions may 

occur and the low-valence forms will be present. 

FUNCTIONS IN PLANT METABOLISM 

Cu is the activato~ of several enzymes, including 

tyrosinase, laccase, and ascorbic acid oxidase. It 

probably is one of the metals involved in the 

light reaction of photosynthesis-one obvious 

Cu-deficiency symptom is chlorosis. Secondary 

influences of Cu on plant metabolism have not 

been satisfactorily explained. 

EXTENT OF USE 

The amount of Cu (expressed on an elemental 

basis) sold for fertilizer in the U.S. in 1969-70 

was 772 metric tons (851 English tons). 

Cu fertilizers can be applied directly to soil, or 

can be sprayed on plant leaves. Copper sulfate 

Copper-Continued 

FORMS USED BY PLANTS-Continued 

is commonly used for both methods of 

application. Copper ammonium phosphate is 

likewise used, is slowly available in soils, and is 

only slightly soluble in water but can be 

suspended in water and sprayed. Cu salts are 

also produced in frits, which makes the Cu 

slowly available, therefore is absorbed by plants 

over a period of time rather than entering into 

insoluble forms on clays or in organic 

complexes. Cu may also be chelated, and in this 

form it is soluble but only slightly ionizes, so it 

does not readily go to unavailable forms in the 

soil. 

Most Cu-deficient soils respond readily to Cu 

fertilization. On mineral soils, one application 

of 5-25lb/acre (5.6-28 kg!ha) copper sulfate is 

usually sufficient for pastures and field crops. 

Organic soils may require the addition of 

50-200 lb/acre (56-224 kg!ha) of copper 

sulfate for vegetable and field crops. On muck 

soils in Michigan, an initial application of 100 

lb/acre (112 kg!ha) copper sulfate is 

recommended, followed by annual applications 

of lesser amounts until a total of 250 lb/acre 

(2780 kg!ha) has been applied. This treatment 

provides adequate Cu for many years. 

The Cu applied to most soils is not subject to 

leaching, being tightly held in clays and organic 

matter. The amount removed in crops is 

extremely small compared to the amounts used 

as fertilizers-for example, with citrus fruits 

about 30 years of heavy cropping are required 

to remove 1 lb/acre (1.12 kg!ha) from the soil 

by harvesting the fruit. 

Some general rates of copper sulfate 

applications follow: 

Apple, Yz lb (0.22 kg) per tree to soil, or a 

0.05% foliar spray. 

Cereal crops, 2¥2-10 lb/acre (2.8-11.2 kg!ha). 

Hay crops, 25 lb/acre (28 kg!ha). 

Corn and cowpeas, 30 lb/acre (33.5 kg!ha) on 

raw peat soils. 

Pasture plants, 5 lb/acre (5.6 kg!ha). 

SOILS WHERE DEFICIENCIES ARE MOST 

COMMON 

Peat and muck soils (unavailable). 

Alkaline and calcareous soils (unavailable). 

Leached sandy soils (excessive removal). 

26 Essential Elements and Soli Amendments for Plants: Sources and Use for Agriculture 
Copper-Continued 

SOILS WHERE DEFICIENCIES-Continued 

Old corrals and feedlots (excessive N). 

Soils heavily fertilized with N. 

Regions of the U.S. where Cu deficiencies have 

been reported to occur in a few to many crop 

plants are the Atlantic Coastal Plain, the Great 

Lakes region, California, and parts of the Pacific 

Northwest. 

IRON-(Fe) 

OCCURRENCE IN NATURAL MATERIALS 

ABUNDANCE IN SELECTED ROCKS 

From Connor, Shacklette, and others (1975), in 

parts per million (ppm) 

Granite, Precambrian; Missouri................ 1.9 

Rhyolite, Precambrian; Missouri ............... 1.9 

Arkose, Fountain Formation; Colorado... .9 

Sandstone 

Roubidoux Formation; Missouri.......... .17 

Pope Megagroup; Kentucky.................. 1.3 

Pennsylvanian; Kentucky ....................... 2.0 

Pennsylvanian; Missouri ........................ 2.3 

Shale 

Lower Mississippian; Kentucky ............ 4.2 

Upper Mississippian; Kentucky............ 4.6 

Mississippian; Missouri.......................... 2.0 

Pennsylvanian; Kentucky....................... 5.4 

Pennsylvanian; Missouri ........................ 4.1 

Black shale 

Devonian and Mississippian; Kentucky. 3.6 

Limestone and dolomite 

Sauk sequence; Western U.S................ 1.1 

Sauk sequence; Missouri ....................... .23 

Upper Ordovician; Kentucky................ 1.1 

Tippecanoe sequence; Missouri ........... .17 

Lower Mississippian; Kentucky............ . 7 5 

Upper Missippippian; Kentucky........... .55 

Mississippian; Missouri.......................... .34 

Pennsylvanian; Kentucky ....................... 2.4 

Pennsylvanian; Missouri ........................ 1.4 

ABUNDANCE IN "NATURAL" UNAMENDED 

SOILS 

Most of the Fe occurs in primary minerals, clays, 

oxides, and hydroxides. Both Fe+ 2 and Fe+ 3 

forms are found in minerals, although the Fe+ 3 

form predominates in all well-drained soils. 

Transformations occur with changes in the 0 2 

supply in soils. Amounts of extractable Fe+ 2 and 

Fe+ 3 forms of Fe are very sensitive to changes in 

Copper-Continued 

ABUNDANCE IN "NATURAL" -Continued 

the redox potential of the soil due to 

submergence. The Fe+ 3 ions predominate at 

potentials > 200 mv, while the amount of Fe+ 2 

increases rapidly at potentials below this value. 

ABUNDANCE IN SOILS 

"Representative" analysis of agricultural soils, 

2.5%; range, 0.5-5%. 

In 1,140 samples (10 from each Missouri county), 

of the surface horizon of agricultural soils, 2.1 %; 

range, 0.5-5.4%. 

Average, all U.S. soils, 2.5%. 

Average, Eastern U.S. soils, 2.5%. 

Average, Western U.S. soils, 2.4%. 

Distribution of concentrations in U.S. surficial 

materials was given by Shacklette and Boerngen 

(1984). Concentrations in many cultivated and 

uncultivated U.S. soils were given by Connor, 

Shacklette, and others (1975). 

ABUNDANCE IN PLANTS 

Total Fe content of soils is of little usefulness in 

predicting soil deficiency for plants. Most soils are 

abundantly supplied with Fe, but only a small part 

of it exists in a form that can be absorbed by 

plants. There is a strong genetic control on iron 

absorption that varies greatly among plant 

species. Fe tends to be concentrated in seeds and 

grains, and to a lesser extent in fruits, rather than 

in leaves, stems, or roots. Examples of Fe contents 

of vegetables (geometric mean percent of ash 

weight) follow: 

Lima bean seeds, central Georgia, 0.11 

Soybean seeds, unglaciated prairie, Missouri, 

0.13 

Corn grains, Missouri floodplains, 0.17 

Sweet pepper fruits, Wisconsin, 0.16 

Cabbage leaves, central Georgia, 0.071 

Onion bulbs, Wisconsin, 0.094 

Potato tubers, Wisconsin, 0.16 

There is a strong tendency for perennial plants, 

especially trees and shrubs, to accumulate more 

Iron 27 
Iron-Continued 

ABUNDANCE IN PLANTS-Continued 

Fe than do the annual field crops, as illustrated by 

the following analyses (geometric mean percent 

of ash weight): 

Red maple leaves, northern Georgia, 0.28 

Red maple stems, northern Georgia, 0.14 

Willow oak stems, Missouri floodplain, 0.25 

Red cedar Guniper) stems and leaves, glaciated 

prairie, Missouri, 0.72 

Shortleaf pine stems and leaves, Missouri, 0.52 

Examples of concentrations in forage, hay, and 

browse plants (geometric mean percent in ash) 

follow: 

Johnson grass, Missouri floodplain, 0.19 

Big bluestem grass, Missouri glaciated prairie, 

0.24 

Kentucky bluegrass, Eastern U.S., 0.19 

Western wheatgrass, Western U.S., 0.48 

Alfalfa, Western U.S., 0.19 

Mesquite, Southwestern U.S., 0.36 

Concentrations of Fe in a wide variety of 

cultivated and native plants were given by Connor, 

Shacklette, and others (1975). 

SOURCES FOR FERTILIZERS 

GEOLOGIC OR OTHER PRINCIPAL 

SOURCES 

There is seldom an absolute deficiency of Fe in 

agricultural soils, only a deficiency in available 

amounts. This deficiency commonly is corrected 

by the application of iron sulfate (FeS04 ·7H20). 

This compound is not very efficient if applied to 

soils because it rapidly oxidizes in the soil to ferric 

ion, Fe+ 3

, a form of low availability to plants. If 

applied as a foliar spray, the effectiveness is 

greatly increased; therefore, only small amounts 

are required to correct deficiencies. However, 

there is very little residual effect of foliar sprays, 

so repeated applications may be necessary, at 

least from crop to crop. 

Iron sulfate can be injected as dry salt into trunks 

and limbs of fruit trees, or painted on cut surfaces 

that result from tree pruning. These treatments 

are very effective, but care is necessary to avoid 

toxic concentrations in the tissues. 

Iron chelates are the next most widely used Fe 

fertilizer, and contain from 6-12% Fe. Several 

chelating agents are used, and the chelated Fe is 

water soluble but non-ionizing, therefore, 

remaining in an available form in the soil. A 

comparison of chelated iron and iron sulfate 

Iron-Continued 

GEOLOGIC OR OTHER-Continued 

applications illustrates the economy in using the 

higher priced (per pound) chelate: 

To correct the Fe-deficiency symptoms of citrus 

trees in Florida by soil applications, 2,500 Ib 

(1,135 kg) of ferrous sulfate per tree or 10-50 g 

(0.35-1.75 oz.) of a chelated Fe compound per 

tree was required. 

Fritted ferrous iron is satisfactory for use on acid 

soils where slow release is wanted, but it is not for 

use on alkaline or calcareous soils. 

INCIDENTAL GEOLOGIC OR OTHER 

SOURCES 

Because availability, not total amount, of Fe is 

related to deficiency problems, natural or byproduct materials (although commonly containing 

considerable Fe) cannot contribute materially to 

correcting Fe deficiencies. Fe compounds carried 

in by wind, rain, or irrigation water contain Fe 

largely in the ferric state, which is already 

abundant in deficient soils, but is largely 

unavailable to the plants. 

REACTIONS WITH SOIL CONSTITUENTS 

The importance of oxidation-reduction reactions 

in changing the ionized state of Fe was discussed 

earlier. The conversion of soil P to an available 

form is largely dependent on reduction of Fe+ 3 

compounds and accounts for the high levels of P 

usually found in submerged soils. The solubility of 

Fe is also related to pH, being much greater in 

acid than in alkaline soils. The stability of Fe 

chelates in soil is also related to pH. Above pH 

7.0, FeEDTA is unstable, and Ca is substituted 

for Fe. Then, the released Fe reacts with the soil 

to form insoluble products. 

With competition from Zn, less Fe is complexed 

with chelates. Translocation of Fe from roots to 

leaves of certain crop plants is reduced if HC03 -I 

ions are in the nutrient solution; this reaction is 

not completely understood. Reaction of Fe with 

Mo, as occurs in lateritic soils ( oxisol), prevents 

leaching of Mo. In acid soils, Fe reacts with P 

fertilizers to form complex products which are 

relatively insoluble. High Mn concentrations in 

plants may induce Fe deficiency. 

FORMS USED BY PLANTS 

Although ferric iron may be absorbed by plants, 

the metabolically active form is ferrous (Fe+ 2

). 

Fe can be absorbed from iron sulfate or Fe 

chelates applied as a spray to leaves. 

FUNCTIONS IN PLANT METABOLISM 

Fe acts as an electron carrier in enzyme systems 

which bring about oxidation-reduction 

reactions in plants that are necessary for plant 

28 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Iron-Continued 

FORMS USED BY PLANTS-Continued 

development and reproduction. Fe is essential 

in chlorophyll formation, although not a 

constituent of chlorophyll, and also is essential 

for the synthesis of proteins contained in the 

chloroplasts. The principal symptom of Fe 

deficiency is chlorosis-the lack of chlorophyll 

in tissues that normally are green. 

EXTENT OF USE 

The amount of Fe (expressed on an elemental 

basis) sold for fertilizer in the U.S. in 1969-70 

was 3,259 metric tons (3,591 English tons). 

Adequate amounts of Fe in an available form 

usually are present in acid soils. Fe deficiencies 

in alkaline soils theoretically could be corrected 

by acidifying the soils, thereby making adequate 

amounts of Fe available to plants, but the cost 

would be prohibitive for field crops. For 

example, 10 tons (9.07 metric tons) of sulfuric 

acid per acre-foot (1,233.6 m3

) of soil would be 

required for each percent of calcium carbonate 

present. Soil acidification is practical only for 

some horticultural plants of high unit value. The 

problem in Fe fertilization is in applying and 

keeping the Fe in an available state until it is 

absorbed by plants. For this reason, soluble Fe 

salts are used mostly in foliar or injection, 

rather than in soil, applications. Fe chelates 

may be applied to both soils and leaves. 

Examples of application rates and methods 

follow: 

Fe chelates, soil application 

Vegetables and flowers, 1 oz/100 ft of row 

(9.3 g!m). 

Shrubs and small trees,¥4-2 oz/tree (0.11-

0.45 kg/tree). 

Large trees, Y..-1 lb/tree (0.11-0.45 

kg/tree). 

Potted plants, Y..-1 teaspoonful. 

Lawns, 1 oz/100 fe (100 g!m2

). 

Citrus trees, 10-20 g/tree (0.35-0.70 

oz/tree). 

Fe chelates, spray application 

Flax, 8 lb/100 gallons (9.5 g/100 1) water 

Fe salts, injection 

Citrus, ferric citrate placed in holes in 

trees, or ferrous sulfate, 50-100 g/1-2 

gallons (13-26 g/11-22 1) water, injected 

into tree trunks and limbs at 50-100 psi 

(3.44-6.89 bars). 

Apple, ferric phosphate placed in holes 

bored into trunks. 

Iron -Continued 

FORMS USED BY PLANTS-Continued 

Fe salts, soil application 

Rice, broadcast applications of 50-1,000 

lb/acre (560-1,120 kg!ha) ferric sulfate 

before planting. 

Fe salts, spray application 

Sorghum, 4% ferrous sulfate, applied at 

the rate of 30 gallons/acre (2841/ha). 

Magnetite (Fe+ 2

Fe2 + 3 04) 

In an experiment with Fe-deficient citrus 

trees, soil applications of finely powdered 

magnetite were found to be an excellent 

source of Fe, even in an alkaline nutrient 

solution. Rates of application not given. 

SOILS WHERE DEFICIENCIES ARE MOST 

COMMON 

Calcareous soils. 

Poorly drained soils. 

Manganiferous soils. 

Areas of Fe deficiency in soils for specific crops 

are widespread in the U.S., but most occur in the 

western states where soils tend to be on the 

alkaline side of neutral. 

MANGANESE-(Mn) 

OCCURRENCE IN NATURAL MATERIALS 

ABUNDANCE IN SELECTED ROCKS 

From Connor, Shacklette, and others (1975), in 

parts per million (ppm) 

Granite, Precambrian; Missouri................. 377 

Rhyolite, Precambrian; Missouri ................ 464 

Arkose, Fountain formation; Colorado..... 336 

Sandstone 

Sauk sequence; Western U.S.................. 252 

Roubidoux Formation; Missouri............ 58 

Pope Megagroup; Kentucky.................... 244 

Pennsylvanian; Kentucky ......................... 240 

Pennsylvanian; Missouri .......................... 870 

Shale 

Sauk sequence; Western U.S .................. 546 

Lower Mississippian; Kentucky .............. 219 

Upper Mississippian; Kentucky.............. 195 

Mississippian; Missouri ............................ 175 

Pennsylvanian; Kentucky ......................... 324 

Pennsylvanian; Missouri ................ .......... 208 

Black shale 

Devonian and Mississippian; Kentucky... 80 

Limestone and dolomite 

Sauk sequence; Western U.S .................. 624 

Sauk sequence; Missouri......................... 145 

Upper Ordovician; Kentucky.................. 598 

Tippecanoe sequence; Missouri ............. 165 

Lower Mississippian; Kentucky .............. 256 

Manganese 29 
Manganese-Continued 

ABUNDANCE IN SELECTED-Continued 

Limestone and dolomite-Continued 

Upper Missippippian; Kentucky.......... 196 

Mississippian; Missouri......................... 192 

Pennsylvanian; Kentucky ...................... 1,001 

Pennsylvanian; Missouri ....................... 1,162 

ABUNDANCE IN "NATURAL" UNAMENDED 

SOILS 

The usual forms of Mn that occur in soils are 

various oxides and hydroxides, with pyrolusite, 

hausmannite, and mannite being the most 

common Mn-bearing minerals. Only a small 

fraction of the total Mn is in the reduced divalent 

form that is unavailable to plants. 

ABUNDANCE IN SOILS 

"Representative" analysis of agricultural soils, 

2,500 ppm; range 200-10,000. 

In 1,140 samples (10 from each Missouri county) 

of the surface horizon of agricultural soils, 851 

ppm; range, 15-3,000 ppm. 

Average, all U.S. soils, 560 ppm. 

Average, Eastern U.S. soils, 656 ppm. 

Average, Western U.S. soils, 467 ppm. 

Distribution of concentrations in U.S. surficial 

materials was given by Shacklette and Boerngen 

(1984). Concentrations in many cultivated and 

uncultivated U.S. soils were given by Connor, 

Shacklette, and others (1975). 

ABUNDANCE IN PLANTS 

Total Mn content of soils is of little usefulness in 

predicting soil deficiency for plants. Most soils are 

abundantly supplied with Mn in relation to plant 

requirements, but only a small part of it exists in 

the divalent form available to plants. 

There is a striking difference in the Mn 

concentrations in ash of annual herbaceous 

plants, including field crops, and in the leaves and 

stems of perennial woody plants (trees and 

shrubs). The reason for this difference is not clear 

but may be caused by the deeper root penetration 

and greater age of the trees and shrubs. Examples 

of the relatively low concentrations of Mn in some 

crop plants (geometric mean ppm in ash) follow: 

Lima bean seeds, central Georgia, 320 

Soybean seeds, unglaciated prairie, Missouri, 

310 

Corn grains, unglaciated prairie, Missouri, 320 

Sweet pepper fruits, Wisconsin, 200 

Cabbage leaves, Wisconsin, 220 

Manganese-Continued 

ABUNDANCE IN PLANTS-Continued 

Carrot roots, Wisconsin, 96 

Potato tubers, Wisconsin, 110 

The Mn content of trees is illustrated by the 

examples that follow (geometric mean ppm in 

ash): 

Red maple leaves, northern Georgia, 6, 700 

Red maple stems, northern Georgia, 6,800 

White oak stems, Kentucky, 13,000 

Red cedar Guniper) stems and leaves, glaciated 

prairie, Missouri, 4,800 

Shortleaf pine stems and leaves, Missouri, 

14,000 

Examples of Mn concentrations in forage, hay, 

and browse plants (geometric mean ppm jn ash) 

follow: 

Johnson grass, Missouri floodplain, 553 

Kentucky bluegrass, Eastern U.S., 580 

Western wheatgrass, Western U.S., 530 

Alfalfa, Western U.S., 250 

Mesquite, Southwestern U.S., 383 

Concentrations of Mn in a wide variety of 

cultivated and native plants were given by Connor, 

Shacklette, and others (1975). 

SOURCES FOR FERTILIZERS 

GEOLOGIC OR OTHER PRINCIPAL 

SOURCES 

Manganese sulfate, MnS04 , has long been the 

principal Mn fertilizer, the commercial grade 

containing about 26% Mn and 15% S. A 

manganese ammonium phosphate fertilizer is 

available in both a chelated and a fritted form. A 

more recent product is manganese oxide, which is 

water-insoluble, but is slightly soluble in dilute 

acids. 

INCIDENTAL GEOLOGIC OR OTHER 

SOURCES 

Farm manures vary in Mn content, depending on 

kind of animal, the feed used, and the bedding 

provided the animal. A general range given for 

Mn is 0.01-0.18 lb/ton (4-800 g/mettic ton). At 

the usual application rates for manure, these 

amounts of Mn are inadequate for correcting Mn 

deficiencies. 

The Mn in dry sewage sludge is reported to range 

from 0.2-1.35 kg/metric ton (0.44-3 lb!English 

ton). 

REACTIONS WITH SOIL CONSTITUENTS 

Mn in the soil is considered to exist in three 

valence states: (1) divalent Mn + 2

, which is 

present as an adsorbed cation or is in the soil 

solution; (2) trivalent Mn + 3

, thought to exist as 

the highly reactive oxide Mn20 3 ; and (3) tetrava30 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Manganese-Continued 

REACTIONS WITH SOIL-Continued 

lent Mn + 4

, which exists as the very inert oxide 

Mn02. The form most likely to occur at pH values 

greater than 8.0 is Mn02; the trivalent form 

occurs at pH values near 7, and the divalent form 

at lower pH values. Therefore, acid soils 

commonly have sufficient soluble Mn for plant 

requirements. Only in some very sandy soils in 

regions of high rainfall does Mn occur in amounts 

inadequate to meet plant needs. 

If soluble Mn fertilizers, such as MnS04, are 

applied to alkaline soils, the Mn rapidly turns into 

an insoluble form; this can be reduced or 

prevented by mixing the Mn fertilizer with an 

acid-forming fertilizer, such as superphosphate. 

Finely ground elemental S may be applied at the 

same time as the Mn fertilizer, which will create a 

temporary lowering of pH and permit plants to 

absorb the Mn while it is still soluble. 

Excessive amounts of available Mn may be 

present in extremely acid soils, leading to Mn 

toxicity for many plant species. This condition is 

usually corrected by liming, or by management 

practices, such as draining, which will reduce the 

soil acidity. 

Mn fertilizers may be applied in the fritted form, 

in which the Mn is slowly released to the soil 

solution and can be absorbed by plant roots 

before it is oxidized to insoluble forms. The 

chelated form, MnEDTA, is usually 

unsatisfactory as a fertilizer, as it often reduces 

crop yields. The reason for this is not clear but 

may be related to displacement of the Mn in the 

chelate by other cations, since the stability 

constant of MnEDT A is relatively low. 

Because of the problems associated with soil 

applications, Mn is often applied as a foliar spray 

as MnS04. 

FORMS USED BY PLANTS 

Only the soluble divalent Mn + 2

, or in molecular 

combinations with certain organic complexing 

agents. 

FUNCTIONS IN PLANT METABOLISM 

Mn functions in the activation of numerous 

enzymes concerned with carbohydrate 

metabolism, phosphorylation reactions, and the 

citric acid cycle and with other metals in the 

activation of the enzymes arginase, cysteine 

desulfhydrase, deoxyribonuclease, and yeast 

Manganese-Continued 

FORMS USED BY PLANTS-Continued 

phosphatase. It is thought to be a specific 

activator of the enzymes prolidase and glutamyl 

transferase. It is also thought to function in 

certain photosynthetic processes. 

EXTENT OF USE 

The amount of Mn (expressed on an elemental 

basis) sold for fertilizers in the U.S. in 1969-70 

was 12,155 metric tons (13,395 English tons). 

Many areas of Mn deficiency for various kinds 

of crops have been reported in the U.S. 

However, these deficiencies are not corrected 

by applications of Mn fertilizers alone, but also 

by management practices that increase the 

supply of available Mn in soils that already have 

abundant total Mn. Moreover, the susceptibility 

to Mn deficiency in the soil varies widely among 

different crop plants so it may be more practical 

to grow crops that can tolerate a degree of soil 

deficiency than to change the available supply in 

the soil. 

To . correct Mn deficiencies of soils, a general 

recommendation is to apply 30-60 lb/acre/yr 

(33.6-67 .2 kg!ha/yr) manganese sulfate in the 

"starter" fertilizer. 

When deficiency symptoms in plants have 

developed, it is too late for soil applications to 

be effective in correcting the deficiency. 

However, foliar applications can reduce the 

deficiency symptoms very rapidly. The crops 

are sprayed with 5-10 lb (2.3-4.5 kg) 

manganese sulfate in 100 gallons (378.4 I) 

water per acre (0.41 ha). 

SOILS WHERE DEFICIENCIES ARE MOST 

COMMON 

Thin, peaty soils overlying calcareous subsoils. 

Alluvial soils and marsh soils derived from 

calcareous materials. 

Poorly drained calcareous soils with a high 

content of organic matter. 

Calcareous black sands and reclaimed acid heath 

soils. 

Old black garden soils where manure and lime 

have been applied regularly for many years. Very 

sandy acid mineral soils that are low in native Mn 

content. 

Manganese 31 
MOLYBDENUM-(Mo) 

OCCURRENCE IN NATURAL MATERIALS 

ABUNDANCE IN SELECTED ROCKS 

From Connor, Shacklette, and others {1975), in 

parts per million (ppm) 

Mean 

Granite, Precambrian; Missouri < 3 

Rhyolite, Precambrian; Missouri < 3 

Sandstone 

Sauk sequence; Western U.S. <4 

Pennsylvanian; Missouri ......... < 3 

Shale, Mississippian; Missouri ... < 3 

Black shale 

Devonian and Mississippian; 

Range 

<3-15 

<3-3 

<4-30 

<3-30 

<3-10 

Kentucky ................................... < 22 < 22-290 

Limestone and dolomite 

Upper Ordovician; Kentucky < 7 

Lower Mississippian; 

Kentucky ............................... < 7 

Upper Missippippian; 

Kentucky ............................... < 7 

Mississippian; Missouri ........... < 3 

Pennsylvanian; Kentucky ........ < 7 

Pennsylvanian; Missouri ......... < 3 

<7-15 

<7-30 

<7-20 

< 3-7 

<7-20 

<3-3 

ABUNDANCE IN "NATURAL" UNAMENDED 

SOILS 

MINERALS 

Most of the Mo in soils occurs either within the 

crystal lattice of primary and secondary 

minerals, or as an exchangeable ion. Significant 

amounts of Mo as Mo04 ·

2 react with hydrous 

oxides of Fe and AI in soils. Apparently, molybdenite (molybdenum sulfide) is rare in soils. 

ORGANICS 

Although no references have been found giving 

the Mo content of organic matter in "natural" 

soil, the Mo content of the ash of vegetation 

generally is considerably higher than the 

concentration in rocks or soil. It is reasonable, 

therefore, to assume that the Mo in natural 

plant residues makes a significant contribution 

to the Mo requirement of soil micro-organisms 

and higher plants. 

ABUNDANCE IN SOILS 

"Representative" analysis of agricultural soils: 2 

ppm; range, 0.2-5 ppm. 

In 1,140 samples {10 from each Missouri county) 

of the surface horizon of agricultural soils, Mo 

was found in only 16 samples in concentrations of 

3 ppm (the lower limit of determination of the 

analytical method used) or greater; the values 

ranged from <3-15 ppm. 

Molybdenum-Continued 

ABUNDANCE IN SOILS-Continued 

In 844 samples of B-horizon soil from throughout 

the conterminous U.S., the Mo concentration 

exceeded 3 ppm in only 9% of the samples, and 

ranged from < 3-7 ppm. 

Distribution of concentrations in U.S. surficial 

materials was given by Shacklette and Boerngen 

{1984). Concentrations in many cultivated and 

uncultivated U.S. soils were given by Connor, 

Shacklette, and others {1975). 

ABUNDANCE IN PLANTS 

Mo, as a component of plant ash, tends to be 

concentrated in seeds and grain, rather than in the 

vegetative parts of plants. Herbaceous plants 

generally have greater concentrations in their 

stems and leaves than have trees and shrubs. 

Examples of Mo concentrations (geometric mean 

ppm in ash) in some crop plants follow: 

Lima bean seeds, central Georgia, 9.5 

Soybean seeds, glaciated prairie, Missouri, 17 

Corn grains, Missouri floodplain, 18 

Snap bean pods (fruit), central Georgia, 4.7 

Cabbage leaves, northern Georgia, < 5.0 

Onion bulbs, Wisconsin, 10 

Potato tubers, Wisconsin, 6.6 

Examples of Mo concentrations (geometric mean 

ppm in ash) in stems and leaves of some woody 

plants follow: 

Black gum stems, central Georgia, < 5 

Black gum leaves, central Georgia, < 5 

Buckbush stems, cedar glades, Missouri, 6.5 

(range, < 5-30) 

Black oak stems, Kentucky, 0.76 

Red cedar Guniper ), cedar glades, Missouri, 7.6 

Red cedar Guniper), oak-hickory forest, 

Missouri, 1.3 

Results of Missouri studies suggest that Mo 

concentrations in trees and shrubs are greatest in 

those growing in alkaline soil. 

Examples of Mo concentrations in forage, hay, 

and browse plants (geometric mean percent in 

ash) follow: 

Johnson grass, Missouri floodplain, 6.0 

Western wheatgrass, Western U.S., 7.25 

Kentucky bluegrass, Eastern U.S., 3.3 

Alfalfa, Western U.S., 18 

Mesquite, Southwestern U.S., 12.9 

32 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Molybdenum-Continued 

SOURCES FOR FERTILIZERS 

GEOLOGIC OR OTHER PRINCIPAL 

SOURCES 

Reports indicate that sodium molybdate, 

ammonium molybdate, and even the less soluble 

molybdenum trioxide were about equally effective 

in supplying Mo to plants. Molybdenite (MoS2)is 

not effective as a fertilizer. Western U.S. 

phosphate rock is reported to contain 60 ppm or 

less Mo, while Eastern U.S. phosphate rock 

contains less than 17 ppm. However, the Mo in 

phosphate fertilizers is not effective in 

overcoming Mo deficiencies for certain crops. 

INCIDENTAL GEOLOGIC OR OTHER 

SOURCES 

A general range given for Mo in farm manures is 

0.001-0.011lb/ton ( 4--40 g!metric ton), and if the 

manure is applied to soil at a high rate, it could 

correct deficiencies in some soils. 

Sewage sludge is reported to contain Mo in the 

range of 2-118 ppm, with most analyses in the 

2-10 ppm range. If not containing certain 

undesirable elements in excess, this material 

could be a useful Mo supplement to soils. 

REACTIONS WITH SOIL CONSTITUENTS 

The total amount of Mo in soils is much smaller 

than that of the other plant nutrients, and most of 

it is unavailable to plants. The Mo held in the 

crystal lattice of primary and secondary minerals 

is not available; whereas, the Mo adsorbed on 

clays, in organic matter, and in soluble 

compounds is available. Availability increases 

with soil pH-just the reverse of the reaction of 

most other soil microelements. A pronounced 

lime-Mo interaction has been shown for many 

Mo-deficient soils, and applications of either lime 

or Mo may increase crop yields, or on some soils, 

both lime and Mo are required. The presence of 

oxides of Fe, AI, and Ti increase the adsorption of 

Mo. Heavy applications of sulfate fertilizer 

depress Mo uptake by plants, thought to result 

from competition at the root surface for the 

Mo04 -

2 and S04 -

2 ions, which are of similar size 

and charge. 

FORMS USED BY PLANTS 

Mo is ~robably absorbed by plant roots as the ion 

Mo04 -

2

. Leaves can absorb Mo from Na2Mo04 

spray, but the form of Mo entering the tissues is 

not known. 

Molybdenum -Continued 

FORMS USED BY PLANTS-Continued 

FUNCTIONS IN PLANT METABOLISM 

Mo is essential for N fixation by the nodule 

bacteria of legumes and is also required by nonlegumes for nitrate reduction. Nitrogen foottion, 

assimilation, and reduction may all be involved in 

amino-acid and protein synthesis. A deficiency of 

Mo results in the accumulation of nitrates in plant 

tissue and a lowering of the activity of ascorbic 

acid oxidase. Mo is known to be specific for the 

activation of the enzymes nitrate reductase and 

xanthine oxidase. 

EXTENT OF USE 

The amount of Mo (expressed on elemental basis) 

sold for fertilizer in the U.S. in 1969-70 was 62 

metric tons (68 English tons). 

Mo deficiencies in soils are corrected by the use of 

Mo fertilizers, or since most soils have sufficient 

Mo, the application of lime to increase Mo 

availability may suffice. Mo is required by plants 

in only small amounts, a point of considerable 

importance because an excess in the soil may 

cause plants to accumulate Mo to levels that are 

toxic to grazing animals. An imbalance of Mo and 

Cu in animal metabolism occurs when the forage 

contains more than 5 ppm (dry weight basis) Mo 

(Allaway, 1968). The amount of Mo normally 

present in large seeds may supply sufficient Mo 

for the plants growing from the seed, even on 

Mo-deficient soils. 

Because of the small amount of Mo required to 

correct deficiencies, Mo is usually added to lime 

or fertilizer mixtures for soil application. It may 

also be applied as a seed treatment or as a foliar 

spray. 

Typical soil applications of Mo range from 1-32 

oz/acre (70-2,250 g!ha). A reported effective 

application of Mo as Na2Mo04 was 18-36 g 

Mo/acre (7.3-14.6 g!ha). Dilute solutions of 

N~Mo04 may be applied to seeds before sowing, 

or sprayed on the foliage of crop plants; the 

methods are equally effective. 

SOILS WHERE DEFICIENCIES ARE MOST 

COMMON 

Highly podzolized soils (low total Mo, 

unavailability) 

Extensively weathered soils (formation of 

secondary minerals may fiX Mo strongly) 

Molybdenum 33 
Molybdenum-Continued 

SOILS WHERE DEFICIENCIES-Continued 

Soils having a pH value below 6.0 (low availability 

ofMo) 

Sandy, well-drained soils low in total Mo 

In the U.S., the soils most likely to have Mo 

deficiencies are the acid sandy soils of the Atlantic 

and Gulf States. 

ZINC-(Zn) 

OCCURRENCE IN NATURAL MATERIALS 

ABUNDANCE IN SELECTED ROCKS 

From Connor, Shacklette, and others (1975), in 

parts per million (ppm) 

Granite, Precambrian; Missouri................... 69 

Rhyolite, Precambrian; Missouri .................. 61 

Sandstone 

Sauk sequence; Western U.S ................ <50 

Roubidoux Formation; Missouri ............. 5.7 

Pennsylvanian; Missouri ............................ 53 

Shale 

Mississippian; Missouri.............................. 99 

Pennsylvanian; Missouri ............................ 86 

Limestone and dolomite 

Sauk sequence; Missouri .......................... 7.6 

Tippecanoe sequence; Missouri ............... 13 

Mississippian; Missouri.............................. 21 

Pennsylvanian; Missouri ............................ 32 

ABUNDANCEIN"NATURAL"UNAMENDED 

SOILS 

MINERALS 

Zn occurs in soils in sulfide, oxide, and silicate 

minerals. It is adsorbed by various clay minerals 

and also by the carbonates of Ca and Mg. Zn 

occurs in the soil solution or adsorbed on 

colloids only in the ionic form Zn + 2

• 

ORGANICS 

Organic matter is an important secondary 

source of Zn, in which the element is held as 

complex combinations by the organic colloids. 

Although when thus held Zn is not readily 

available to plants, its release through 

decomposition of organic matter is an 

important fertility factor. 

ABUNDANCE IN SOILS 

"Representative" analysis of agricultural soils: 

100 ppm; range, 10-250 ppm. 

In 1,140 samples (10 from each Missouri county) 

of the surface horizon of agricultural soils, 53 

ppm; range, 18-640 ppm. 

Molybdenum-Continued Zinc-Continued 

ABUNDANCE IN SOILS-Continued 

Average, all U.S. soils, 54 ppm. 

Average, Eastern U.S. soils, 43 ppm. 

Average, Western U.S. soils, 59 ppm. 

Distribution of concentrations in U.S. surficial 

materials was given by Shacklette and Boerngen 

(1984). Concentrations in many cultivated and 

uncultivated U.S. soils were given by Connor, 

Shacklette, and others (1975). 

ABUNDANCE IN PLANTS 

The range in Zn content .in plant tissues is 

extremely wide and is influenced by kind of plant, 

plant organ sampled, and concentration of 

available zinc in the soil. The reported range is 

< 20-10,200 ppm in dry plant material. Zn, as a 

component of plant ash, is commonly 

concentrated in seeds and grains, but 

concentrations equally high can be found in the 

woody parts of some trees and shrubs. Examples 

of Zn concentrations (geometric mean ppm in 

ash) in some crop plants follow: 

Lima bean seeds, central Georgia, 600 

Soybean seeds, glaciated prairie, Missouri, 870 

Corn grains, unglaciated prairie, Missouri, 

1,900 

Snap bean pods (fruit), central Georgia, 530 

Cabbage leaves, Wisconsin, 250 

Carrot roots, Wisconsin, 180 

Onion bulbs, Wisconsin, 330 

Potato tubers, Wisconsin, 280 

Examples of the Zn concentrations (geometric 

mean ppm in ash) in stems and leaves of some 

woody plants follow: 

Black cherry stems, central Georgia, 1,300 

Black cherry leaves, central Georgia, 220 

Buckbush stems, unglaciated prairie, Missouri, 

1,800 

Red cedar Guniper) stems and leaves, cedar 

glades, Missouri, 320 

Black oak stems, Kentucky, 540 

Shortleaf pine, stems and leaves, Missouri, 

1,200 

Sassafras stems, northern Georgia, 1,300 

Sassafras leaves, northern Georgia, 460 

Examples of Zn concentrations in forage, hay, and 

browse plants (geometric mean ppm in ash) 

follow: 

Johnson grass, Missouri floodplain, 518 

Alfalfa, Western U.S., 223 

Mesquite, Southwestern U.S., 440 

34 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Zinc-Continued 

SOURCE FOR FERTILIZERS 

GEOLOGIC OR OTHER PRINCIPAL 

SOURCES 

Zinc sulfate, containing about 36% Zn, has for 

years been a popular fertilizer material. Zinc 

ammonium phosphate is useful in that it is only 

slightly soluble in water, therefore extending the 

availability of Zn over a long period of time when 

applied to soil. The same effect is produced by 

using Zn carried in frits or in various chelates 

such as ZnEDTA. Zinc oxide is anothe; 

important fertilizer. More recently, a zinc-ironammonium sulfate compound has been 

developed by ammoniating spent sulfuric acid 

containing Fe and Zn as impurities. 

INCIDENTAL GEqLOGIC OR OTHER 

SOURCES 

A general Zn range given for farm manures is 

43-247 ppm in dry matter with an average value 

of 96.2 ppm. This Zn content compares favorably 

with that of inorganic Zn fertilizers and, at the 

application rates generally used for manure, 

should supply adequate Zn for crops on most 

soils. 

Dry sewage sludge is reported to contain Zn in the 

range of 0.7-3.95 kg/metric ton (3.3-18.7 lb/English ton). If it does not contain undesirable 

elements in excess, this material is a useful Zn 

supplement to soils. 

Crop residues can return appreciable amounts of 

Zn to soils, but the amounts vary widely 

depending on the kind and condition of the 

residue. 

REACTIONS WITH SOIL CONSTITUENTS 

The plant availability of Zn is conditioned by 

several soil factors: pH, phosphorus level, organic 

matter content, and adsorption by clays. In 

general, the availability of zinc is a function of soil 

acidity-most Zn deficiencies occur with the 

range of pH 6.0-8.0. Zn deficiency on high 

phosphate soils has been observed frequently, but 

the nature of the reactions involved is not known. 

The simple precipitation of zinc phosphate is 

inadequate to explain this phenomenon, even 

though the solubility of Zn decreases at high 

concentrations of the phosphate ion. Zinc 

deficiencies have been observed on soils high in 

organic matter or that have been fertilized with 

animal manures. The fact that this deficiency can 

be corrected by soil sterilization suggests that 

living organisms in the soil immobilize the zinc, 

but the reactions are unknown. Zn deficiencies 

Zinc-Continued 

REACTIONS WITH SOIL-Continued 

are commonly observed on calcareous soils, and 

liming of acid soils may produce the same effect. 

These effects are explained by the fact that Zn is 

adsorbed on calcium and magnesium carbonates 

in the following decreasing order: Magnesite 

(MgC03), dolomite (CaMg(C03)2 ), and calcite 

(CaC03 ). In magnesite and dolomite, it is thought 

that the Zn is actually adsorbed into the crystal 

surfaces at the sites in the lattice normally 

occupied by Mg atoms. Zn forms many 

compounds of low solubility in soils by 

precipitation as carbonates, hydroxides, and 

phosphates-which reduces the availability to 

plants. Therefore, from the agronomic standpoint, 

Zn is relatively immobile in most soils. 

FORMS USED BY PLANTS 

Zn is absorbed by plant roots as the ion Zn + 2 and 

may also be absorbed as a molecular complex of 

such chelating agents as EDT A. Zinc is also 

capable of entering the plant directly through the 

leaves if applied as a spray of soluble Zn salts or 

complexes. 

FUNCTIONS IN PLANT METABOLISM 

Zinc functions in plants largely as a metal 

activator of enzymes including enolase, yeast 

aldolase, oxalacetic decarboxylase, lecithinase, 

cysteine desulfhydrase, carbonic anhydrase, 

and others. Like many of the other micronutrients, Zn is toxic to plants in any but small 

quantities. Its concentration in the plants in 

relation to the other heavy metals is of greater 

importance than the absolute amounts present. 

EXTENT OF USE 

The amount of Zn (expressed on elemental 

basis) sold for fertilizer in the U.S. in 1969-70 

was 16,444 metric tons (18,084 English tons). 

A general rate given for the application of zinc 

sulfate, a popular fertilizer, is 40-80 Ib/acre 

( 46-90 kg!ha). The variable fiXation and 

movement of zinc in soils and the danger from 

toxicity have been factors which have tended to 

discourage deficiency corrections by soil 

applications. In one experiment it was found 

that mixing 5 Ib (2.27 kg) zinc sulfate and 5 Ib 

(2.27 kg) calcium chloride and applying in small 

piles to sandy Florida soils greatly increased 

zinc uptake by the trees. TheCa appeared to 

prevent Zn fiXation in the soil. 

In general, the preferred method of Zn 

application to correct plant deficiencies is as a 

spray. Some examples of spray applications 

follow: 

Zinc 35 
Zinc-Continued 

FORMS USED BY PLANTS-Continued 

Alfalfa-A 0.5% zinc sulfate sprayed on 

young plants effected marked recovery in 10 

days. 

Apple trees-Dormant sprays of 25-50 lb 

(2.7-5.6 kg) zinc sulfate per 100 gallons 

(378.4 I) water were found effective. 

Red Mexican beans-A 0.3% zinc sulfate 

foliar spray applied to plants 4-6 in. 

(10.2-15.2 em) high. 

Field corn-A foliar spray composed of 0.5% 

zinc sulfate and 0.25% calcium hydroxide 

applied to corn 6 in. (15.2 em) high. 

Zinc fertilizers can be supplied to trees by 

direct injection, as by boring holes and filling 

them with the fertilizer, or by driving zinccoated nails or pieces of galvanized iron into 

the tree, but the amounts of zinc applied and 

its effectiveness are uncertain and difficult to 

measure. 

SOILS WHERE DEFICIENCIES ARE MOST 

COMMON 

Acid, leached, sandy soils where total Zn is low. 

Alkaline soils where Zn availability is decreased. 

Soils derived from granites and gneisses. 

Some organic soils where Zn is tied up in forms 

that are not readily available to plants. 

Soils containing clays with low Si to Mg ratios. In 

these, Zn may be fiXed in forms not readily 

available to plants. 

USE OF SOIL AMENDMENTS 

TO IMPROVE THE 

PHYSICAL PROPERTIES OF SOIL 

Introduction 

Factors influencing plant growth include moisture, 

heat, light, and the chemical and physical nature of the 

substrate (soil). Soil amendments are materials added to 

soils for the purpose of modifying their chemical and 

physical properties. This section deals only with physical 

amendments. 

Alterations of the physical properties of a soil will 

result in responses which cannot be explained in their 

entirety by a consideration of only the physical action that 

was taken. The physical, chemical, biological, and 

microbiological properties of soils are so integrated that 

an alteration of any single factor will affect each of the 

other factors. Some of the effects of various soil 

amendments on the physical properties of soil are given 

in the discussions that follow. The chemical, biological, 

and microbiological implications of the physical changes 

in soils will not be considered. 

Physical soil amendments are employed in 

agricultural practice to create a more favorable 

environment for plant growth and to aid the conservation 

of soil. For plant growth, these amendments improve the 

seed bed to enhance germination and to modify 

characteristics of the root zone in a manner that improves 

growth. For soil conservation, physical amendments 

aggregate the soil particles into stable units so that water 

infiltration will be maximized, and runoff and soil 

dispersion will be minimized. The ultimate goal in using 

these amendments is to match the properties of the soil 

to the physiological requirements of the plant species 

that is to be cultivated. 

In general, the permanent features of the soil 

landscape (texture, slope, ground water, flooding, and 

local climate) are not readily amended, if at all, by the 

simple addition of some agent. To increase the clay 

content of the plow zone of an average soil by 1 percent 

would require the addition of 10 English tons of clay per 

acre (22.4 metric ton/ha). At present, with the prevailing 

economics of agricultural production, this would not be 

economical. Consideration should be given, therefore, to 

those less permanent features that have the potential to 

be economically amended, such as soil structure, soil 

moisture, soil aeration, and soil temperature. 

Resources of the various mineral soil amendments 

in the United States appear to be adequate to meet the 

present demand, which is largely restricted to the 

horticultural industry, and here the demand is relatively 

small. Commercial mechanized agriculture is using 

energy expended by heavy tillage machinery to maintain 

desirable physical properties of soils in place of using 

mineral or other physical amendments. At present, the 

use of "energy" is an economical way to amend soils, 

compared to the cost of mining, transporting, and 

applying mineral soil amendments. 

The mineral soil amendments have not received 

sufficient attention in experimental field trials to 

demonstrate their benefits and justify their use in 

commercial food production. The present trend, in 

general, is to select species, or develop varieties by 

genetic modification that can withstand the more 

unfavorable "permanent" soil conditions rather than to 

modify these conditions to meet the requirements of a 

36 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
particular species. Interest in the use of soil amendments 

should increase as energy sources become more 

expensive, as soil resources become more limiting, as 

expanding populations demand more agricultural 

production from a finite resource (the soil), and as lands 

presently considered marginal for agriculture are 

brought into production. 

In areas of the world where agriculture is more 

"people intensive" than "power intensive," soil 

amendments may play a significant role in increasing 

a~icultural production. In these agricultural areas, the 

sod amendments should have a local geologic source 

because the availability of and cost of transportation is a 

limiting factor in the utilization of these materials. 

In the following discussion, the physical 

amendments are divided into three groups: (1) mineral 

materials, (2) organic materials, and (3) miscellaneous 

materials. 

Mineral Materials 

CLAYS 

SOURCES 

The phyllosilicate (layered or sheet structured 

arrangement of the silicate tetrahedra) clay 

minerals, such as talc, montmorillonite, and bentonite, for example, constitute the groups of clays 

generally used to amend soils. Various clays are 

mined in every State except Rhode Island and 

Alaska (as of 1969). The materials mined include 

fresh and weathered shales and schist, alluvium, and 

loess. The resources are virtually inexhaustiblethey exceed several billion tons. 

MODE OF ACTION 

Size, ion exchange capacity, and surface area are 

properties of layered clay minerals that account for 

their usefulness as soil amendments. Average 

properties of specific clay minerals within the group 

vary considerably; therefore, some clay species are 

more effective as amendments than others. The 

following table gives an indication of the differences 

in properties of a few clay minerals in the group of 

layered clays: 

Exchange 

Clay mineral Diameter, capacity, Surface area, 

mX10-a meq/100 g m1

/100 g 

Montmorillonite 0.01-1.0 80-150 700-800 

Illite .1-2.0 10-40 100-120 

Kaolinite .1-5.0 3-15 5-20 

Vermiculite 100-150 

Clays-Continued 

As an example of the mode of action of clays, the 

incorporation of clay into a sandy soil affects the 

water relationships and the ability of the soil to 

retain fertilizer. The added clay changes the pore 

size distribution within the soil so that a greater 

proportion of the pores available to hold water are 

smaller in diameter; therefore, more energy is 

required to extract the water from the pores. 

This water in smaller pores is not susceptible to 

drainage by gravity, requires a greater amount of 

energy for evaporation, and is available to plants. 

The interactions of the added clay and the existing 

sand and organic residues produce more stable 

structural aggregates which improve the physical 

condition (tilth) of the soil. Improved tilth reduces 

the susceptibility of the soil to wind and water 

erosion, aiding in soil and nutrient conservation. The 

addition of clay also enhances the ability of soils to 

hold nutrients in a form that is available for plant 

growth against the force of water movement which 

tends to leach or flush the nutrients from the soil. 

EXTENT OF USE 

The majority of mined clay minerals are used for 

nonagricultural purposes. The only important use of 

these minerals in plant culture is in the horticultural 

industry, where vermiculite is commonly a 

component of potting soil mixtures, or is used for 

soil improvement of golf greens and other nonagricultural sods. However, vast areas of clay soils are 

used for intensive agricultural crop production. The 

physical problems of the various clay soils are 

managed by different methods which vary with the 

geographical location and the kind of crops 

produced. In southern California where the clay 

soils are used for intensive vegetable production, for 

example, the physical difficulties of cultivation are 

overcome by energy expenditure. The clay clods are 

physically pulverized by large powerful implements 

and formed into a structure suitable for plant 

growth. 

In eastern North Dakota and northwestern 

Minnesota, the clay soils are managed in such a 

manner that the freezing and thawing action during 

fall, winter, and spring accomplish the disintegration 

of clay clods into a form suitable for crop 

production. This example shows that different 

management techniques are employed in different 

environmental settings to overcome the same 

problem of compacted clays and points up the fact 

that farming practices, including the use of 

amendments, must not only be compatible with the 

physical character of the soil but must also consider 

the environmental setting as a whole. 

Clays 37 
Clays -Continued 

POTENTIAL FOR USE 

The utilization of clay as a soil amendment for 

commercial production of food is in the 

experimental stages. Studies have shown that the 

addition of clay to sandy soils does, in fact, 

improve soil physical properties and increase 

yields. As an example, a study in West Bengal 

showed that 20 percent of the yield variance could 

be attributed to increased aggregate stability that 

resulted from the addition of bentonite and 

organic amendments to a sandy soil. However, the 

variance was not proportioned between the clay 

and the organics added; therefore, it is not 

possible from these data to determine the 

individual effect of the clay additive. 

ZEOLITES 

SOURCES 

Zeolites (hydrated aluminosilicates) are tectosilicates; that is, the silicate tetrahedra (Si04 ) are 

arranged in a three-dimensional framework. Zeolites are associated with diverse geologic settings, 

ages, and lithologies, but most commercial 

exploration for bedded zeolites has occurred in old 

lake beds in the Southwestern U.S. Resources in this 

country are conservatively estimated at 10 trillion 

tons. 

MODE OF ACTION 

Particle size, surface area, and ion exchange capacity 

account for the usefulness of zeolites as soil 

amendments. These properties were discussed 

earlier under "Clays." 

EXTENT OF USE 

Zeolites have not been extensively used as soil 

amendments in commercial agriculture but are used 

to a limited extent in soil mixtures for horticultural 

uses. Reports of experiments with zeolites as soil 

amendments are virtually nonexistent in the U.S. 

literature; however, their effects on soil physical 

properties probably are very similar to those of 

clays. 

POTENTIAL FOR USE 

Present U.S. production of zeolites is only a few 

hundred tons per year. The resources available and 

the economics of mining seem favorable for 

potential expansion of the zeolite industry. Basic and 

applied research is needed to determine the actual 

value of zeolites as soil amendments and the 

economics of their utilization in commercial 

agriculture. 

VOLCANIC MATERIALS 

SOURCES 

Volcanic materials include pumice, pumiceite, perlite, obsidian, and scoria. In chemical composition, 

pumice, pumiceite, perlite, and obsidian resemble 

basalt. In the U.S., volcanic materials are confined to 

the Western States, including Alaska and Hawaii, 

being absent from the Central and Eastern States 

except for the pumiceite deposits that occur in 

Kansas, Nebraska, and Oklahoma. Estimates of 

volcanic materials resources in the U.S. are 1-9 

billion tons of mafic materials and 100-150 million 

tons of silicic materials. 

MODE OF ACTION 

The type of alteration of soil physical properties by 

the incorporation of volcanic materials depends 

largely on the particle size of the materials; that is, 

sand-size particles will assume the mode of action of 

sand, and clay-size particles the action of clays. 

Fresh volcanic materials are generally noncrystalline 

(amorphous) and are readily weathered to form 

various clay minerals. 

The addition of these materials to soil would provide 

several micronutrient elements that are used by 

plants, the specific suite of elements varying with the 

composition of the ash. Fresh volcanic ash fallout 

from the Surtsey volcano in Iceland contained 

concentrations of fluorine that were toxic to sheep 

and cattle that grazed plants which grew in the ash. 

It is assumed that leaching will soon dissipate the 

toxic fluorine levels. 

EXTENT OF USE 

Perlite is used to a limited extent in horticultural 

operations as a component of soil mixtures; but we 

have not found references in American literature on 

the use of other volcanic materials as a soil 

amendment. Volcanic materials are used in situ for 

intensive agricultural production in some regions. 

The physical properties of volcanic soils are variable, 

depending largely on the age and composition of the 

volcanic material from which they were formed. For 

example, in some volcanic soils, the 

welding-together of particles may be sufficient to 

inhibit root penetration, however, in others the high 

degree of porosity may prevent adequate retention 

of water for satisfactory plant growth. 

38 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Volcanic Materials -Continued 

POTENTIAL FOR USE 

Weathered volcanic deposits contain a suite of clay 

minerals, for example, vermiculite and bentonite, 

that have potential value as soil amendments. Their 

actual usefulness for improving the physical 

properties of soils has not been adequately 

demonstrated, and this, together with the economics 

of mining and transporting the materials, has not 

promoted their use in commercial food plant 

production. 

SAND 

SOURCES 

Sand is defined as any rock or mineral within a 

specified range of particle sizes (2-0.05 mm, USDA 

system; Y4-11t6 in., ASTM system). Water and ice 

are the principal sorting and transportation agents 

responsible for the commercially important 

deposits, wind-blown sand comprising only a minor 

part of these deposits except on a very local scale. 

These deposits are distributed in all regions of the 

United States, in that river channels, flood plains, 

marine and lake environments, dunes, and glaciated 

terrain are source areas. The volume of potential 

resources is difficult to estimate, and the value is 

governed by complex economic factors. Shortages of 

sand are predicted for local areas in the near future 

because of land use priorities and the economics of 

production and transportation. 

MODE OF ACTION 

Incorporation of sand into a soil results mainly in 

alterations of physical properties of the soil. The 

surface area of sand particles per unit weight or 

volume precludes their usefulness in ion exchange 

reactions and as readily available sources of plant 

nutrients. However, exceptions are noted in sandsize particles of calcite, apatite, sylvite, and other 

soluble minerals. The addition of sand to clay soils 

changes the pore size distribution in the soils and a 

greater proportion of the pores are larger in 

diameter. This change will improve the air-water 

environment for plant roots, especially in soils that 

are seasonally too wet for satisfactory crop 

production. The implication here is that wet soils are 

"cold" during the seed germination time and only 

warm up slowly. 

EXTENT OF USE 

For mined sand, as for clays, nonagricultural uses 

predominate. Some mined sand is used in the 

horticultural industry for inclusion in soil mixtures. 

Extensive areas of sandy soils throughout the U.S. 

Sand-Continued 

are used for crop production and are valued for their 

ease of cultivation. Maintaining adequate moisture 

and nutrient retention are the greatest management 

problems in crop production on these soils. 

POTENTIAL FOR USE 

The use of sand-size materials as soil amendments 

has received very little experimental attention. A 

specific study, in which sand was incorporated into 

the plow zone (0-6 in. depth; 0-15.2 em) of a clay 

soil, demonstrated that the addition of sand 

decreased the amount of organic matter and 

phosphorus, improved tilth, and facilitated 

mechanical harvesting of the crop. The yield 

response varied with the crop grown but tended to 

remain unchanged or was decreased compared to 

the yield of the control crop plots. The potential 

appears to be very slight for the use of sand as an 

amendment to improve soil physical properties in 

large scale agricultural production. These properties 

can be modified equally as well by annual 

incorporation of crop residues as by the application 

of sand; moreover, plant residues generally are less 

expensive to use and at the same time provide plant 

nutrients that are lacking in sand. 

Organic Materials 

PEAT 

SOURCES 

Peat is an all-inclusive term used for geologic 

accumulations of plant material (excluding coal). 

Specific types of peat are recognized by their plant 

origin, degree of decomposition, ash content, and 

water-holding character. Peat deposits are delimited 

by the occurrence of a favorable climate, 

topography, and vegetation for their formation. The 

northeastern quarter of the U.S. (glaciated terrain), 

the Atlantic and Gulf coasts, the western mountains 

and coasts, and Alaska are source areas for various 

types of peat deposits. Potential resources of peat 

vary in magnitude by lOS tons between certain 

States; for example, the potential resources of 

Delaware are estimated to be lOS tons, contrasted 

with 1010 tons in Minnesota. Quantitative 

information is not available to estimate potential 

resources of various quality peats. The U.S. 

production of peat in 1970 was ¥2 million tons. Of 

the total U.S. consumption, approximately 1h was 

imported from Canada and Europe. The potential 

demand for peat in the U.S. is projected to be 

between 1.2 and 2.4 million tons in the year 2000. 

Peat 39 
Peat -Continued 

MODE OF ACTION 

Water-holding capacity, ion exchange capacity, and 

volume-weight ratio are properties of peat materials 

that account for their desirability as soil 

amendments. Each of these properties may vary 

depending on type of peat; for example, waterholding capacity for a highly decomposed peat may 

be 150% of its dry weight, but for Sphagnum peat 

may be 3,000%. Ion exchange capacity of peat 

materials may range from 125 to 400 milliequivalents per 100 g, the exchange capacity increasing 

with the degree of decomposition. Incorporation of 

peat into a mineral soil will markedly improve the 

physical condition of the soil. Applied to sand, it will 

increase water-holding and nutrient-retention 

capacity; in clay, it will increase water infiltration, 

make the soil more friable, and decrease the 

volume-weight ratio, thus enhancing root 

penetration. 

EXTENT OF USE 

The horticultural industry is the greatest user of 

mined peat for plant propagation in the U.S. Mined 

peat has not been used to an appreciable extent as a 

soil amendment in commercial agriculture, but 

agricultural uses of peat lands has been expanding 

because these lands are quite suitable for intensive 

vegetable production, forestry, and as grazing lands. 

Peat lands are especially well suited to crop 

production in northern areas where peat, when 

drained and cultivated, decomposes more slowly 

than in southern regions. 

POTENTIAL FOR USE 

Probably the greatest potential use for peat lands for 

agricultural production is their cultivation in situ. 

Mining, processing, and transportation costs, 

problems of distribution, and the demand for other 

uses of peat are some factors that limit its use as a 

soil amendment in commercial agriculture. Areal 

distribution and the properties of specific peat types 

need to be inventoried in order to realize the 

potential of the vast peat resources of the U.S. 

HUMATES 

SOURCE 

Humates are dissolved or colloidal organic materials 

of plant and animal origin which have accumulated 

by precipitation or flocculation in certain physiochemical aqueous environments. Humate deposits 

have been identified and characterized in Florida 

along the Gulf Coast (Swanson and Palacas, 1965). 

Humates may also occur in coal deposits which have 

undergone weathering; therefore, the sources of 

Humates-Continued 

humates may be present over large geographic 

areas. Estimates of potential reserves of humates 

have not been published. 

MODE OF ACTION 

Humates have a character similar to some of the 

extracts of soil organic matter. In soil organic 

matter, these materials are the products of microbial 

action on organic residues. Mined humates, 

therefore, would serve to form stable soil aggregates 

by actions similar to those of native organic residues 

in soil. Increased aggregation and organic content of 

soils aids water infiltration, reduces dispersion and 

surface crusting, and provides more favorable airwater relations for plant growth. 

EXTENT OF USE 

We do not know of instances where mined humates 

have been used as soil amendments. 

POTENTIAL FOR USE 

Within the framework of economics of production 

and transportation, mined humates may serve as 

suitable soil amendments. They could potentially be 

used as a source for organic carriers in commercial 

fertilizers and would provide the added benefits of 

adding organic matter to soils. 

Miscellaneous Materials 

Many other materials have potential use as soil 

amendments, but they are not discussed here (except fly 

ash) because of their nongeologic nature, their treatment 

elsewhere in this report, the fact that their usage is 

principally nonagricultural (as in construction), or 

because of the limited information that is available. In 

principle, the miscellaneous amendments used to 

improve the physical properties of the soil will generally 

have (depending on their characteristics) the modes of 

action described for the materials already discussed. 

Their specific actions will depend on the particle size, 

surface area, and ion exchange capacity of the material. 

The function of physical amendments is to alter the 

pore-size distribution in the soil and to improve soil 

structure. Other benefits derived from altering the 

physical properties of soils are related to chemical, 

biological, and microbiological soil properties, and are 

not treated here. One material in this group, fly ash, is 

discussed because of the current interest in the use of 

coal as fuel for electrical energy production. 

FLY ASH 

(abstracted from Capp and Spencer, 1970) 

Widespread use of the pulverized fuel burned by 

electric utilities has produced significant amounts of fly 

ash that have found relatively limited use. In the "2¥2 

40 Essential Elements and Soli Amendments for Plants: Sources and Use for Agriculture 
Fly Ash-Continued 

decades" since the end of World War II, an estimated 

300 million tons of fly ash have been produced in the 

United States, of which only about 3% has been utilized. 

The disposal of fly ash costs from $0.25 to $2 per ton, 

which creates an economic incentive to convert it from a 

liability to an asset. 

Although most of the fly ash used has been in 

industrial processes, studies have been made of its value 

as a soil amendment in spoil bank reclamation, turf-soil 

beneficiation, and crop production. Some fly ashes have a 

high pH, a higher content of some macronutrients and 

most micronutrients, and better moisture retention than 

many soils, and may at the same time improve the tilth of 

"heavy" soils. 

Use To Improve Soil Physical 'Properties 

As an amendment of physical properties, fly ash 

increases the water-holding properties of some soils and 

also the availability of this water to plants. In experiments 

that were conducted in West Virginia, fly-ash treated 

soils accumulated a reservoir of moisture from heavy 

spring rains, and this moisture continued to be available 

even during the summer dry period. In contrast, the 

control soils retained little moisture from spring rains; 

and during the dry period, the moisture held was not in 

the available range for plants during several weeks of the 

dry period. These plots were then fertilized with a 

10--10--10 commercial fertilizer (10% N-10% P-10% 

K), 1,000 lb/acre (1,120 kg!ha), then seeded with grass or 

grass-legume mixtures. The fly-ash treated plots yielded 

1.09 tons/acre (3.44 metric tons/ha), while the control 

plots gave no yield because of very poor plant survival 

after germination that resulted from poor physical 

condition of the soil. 

Sintered fly-ash experiments on turf soil showed 

that the treated sods had higher water intake rates and 

total accumulated intake than the control sods. The 

accumulated intake tended to increase with the increase 

in volume percent of sintered fly ash added. Results of 

these field experiments indicated that this amendment is 

potentially valuable as a soil modifier, particularly to 

assist water infiltration on heavily used turf areas. 

However, the high temperature involved in sintering 

appears to inhibit the release of excessive amounts of 

certain micronutrients that could be present. 

Use To Improve Soil Chemical Properties 

Fly ash ordinarily does not contain sufficient 

macronutrient elements to be classified as a fertilizer 

material on ordinary agricultural soils. It is generally low 

in P and contains almost no N. However, it may prove 

Fly Ash-Continued 

useful as a substitute for natural soil for revegetating 

spoil banks and similarly disturbed areas or to improve 

the fertility of very poor soils. Elemental abundances in 

fly ash were reported as follows: 

Element Percent 

Ca...................................... 1.00 

Mg..................................... .36 

K........................................ 1.74 

P......................................... .13 

Co...................................... .01 

Mo..................................... .01 

B....................................... .01 

Mn..................................... .02 

AI....................................... 14.01 

Fe ..................................... 9.94 

Approximate amount, 

lb/ton ash 

20 (10 kg/metric ton) 

6.7 (3.3 kg/metric ton) 

35 ( 17.6 kg/metric ton) 

2. 7 ( 1.3 kg/metric ton) 

.2 (0.1 kg/metric ton) 

.2 (0.1 kg/metric ton) 

.2 (0.1 kg/metric ton) 

.4 (0.2 kg/metric ton) 

283 (142 kg/metric ton) 

200 (100 kg/metric ton) 

The major problem in using some fly ash as a soil 

amendment is the concentrations of certain elements 

at levels that are toxic to plants. In British experiments, 

fly ash was found to contain amounts (15-30 ppm) of 

B that are toxic to some plants. Because removal of the 

B was impractical, plants were tested for resistance to 

this toxicity. White sweet clover grew under the most 

toxic conditions, followed by white clover, red clover, 

and alfalfa. Rye grasses were very tolerant. Food plants 

of the beet and cabbage family were tolerant, and rye 

was the only cereal that was really tolerant. Oats, 

barley, peas, beans, and potatoes were intolerant. 

OTHER MATERIALS 

Some other miscellaneous materials that have been 

used as soil amendments follow: 

Limestone 

Gypsum 

Calcined clay 

Iron alum ("Flotal") 

Animal manure 

Sewage sludge 

Wood residues, including redwood bark 

Osm unda fiber 

Peanut shells and other crop residues 

Green manures 

Ground-up rubber tires 

Manufactured organic amendments ("Krilium," for 

example) 

REFERENCES CITED 

Allaway, W. H., 1968, Agronomic controls over the 

environmental cycling of trace elements: Advances in 

Agronomy, v. 20, p. 235-274. 

References Cited 41 
Buckman, H. 0., and Brady, N. C., 1969, The nature and 

properties of soils (7th ed.): New York, The Macmillan 

Co., 653 p. 

Capp, J. P., and Spencer, J. D., 1970, Fly ash utilization, a 

summary of applications and technology: Information 

Circular 8483, U.S. Bureau of Mines, 72 p. 

Connor, J. J., Shacklettes H. T., and others, 1975, Background 

geochemistry of some rocks, soils, plants, and vegetables 

in the United States: U.S. Geological Sutvey Professional 

Paper 574-F, 168 p. 

Grey, D. C., and Jenson, M. L., 1972, Bacteriogenic sulfur in air 

pollution: Science, v. 177, no. 4054, p. 1099-1100. 

Mortvedt, J. J., and Cunningham, H. G., 1971, Production, 

marketing, and use of other secondary and micronutrient 

fertilizers, in Olson, B. A., editor-in-chief, Fertilizer 

technology and use (2d ed.): Madison, Wisconsin, Soil 

Science Society of America, Inc., 611 p. 

Shacklette, H. T ., and Boemgen, J. G., 1984, Element 

concentrations in soils and other surficial materials ofthe 

conterminous United States: U.S. Geological Survey 

Professional Paper 1270, 105 p. 

Shacklette, H. T., Sauer, H. I., and Miesch, A. T., 1970, 

Geochemical environments and cardiovascular mortality 

rates in Georgia: U.S. Geological Sutvey Professional 

Paper 574-C, 39 p.Swanson, V. E., and Patacas, J. G., 

1965, Humate in coastal sands of northwest Florida: U.S. 

Geological Sutvey Bulletin 1214-B, 29 p. 

Thorne, C. E., 1930, The maintenance of soil fertility: New 

York, Orange Judd Publication Company, Inc., 332 p. 

Tisdale, S. L., and Nelson, W. L., 1967, Soil fertility and 

fertilizers (2d ed.): New York, The Macmillan Co., 694 p. 

Turekian, K. K., and Wedepohl, K. H., 1961, Distribution of the 

elements in some major units of the Earth's crust: 

Geological Society of America Bulletin, v. 72, p. 

175-192. 

SELECTED REFERENCES 

Barth, R. C., Severson, R. C., and Weiler, G., 1987, Boron, in 

Williams, R. D., and Schuman, G. E., (editors), 

Reclaiming mine soils and overburden in the western 

United States; Analytical Parameters and Procedures: 

Ankeny, Iowa, Soil Consetvation Society of America, 

336p. 

Brobst, D. A., and Pratt, W. 0., eds., 1974, U.S. mineral 

resetves: U.S. Geological Sutvey Professional Paper 820, 

722p. 

Chapman, H. D., (ed.), 1966, Diagnostic criteria for plants and 

soils: Riverside, Calif., California University Division of 

Agricultural Science, 793 p. 

Gardner, W. H., 1972, Use of synthetic soil conditioners in the 

1950's and some implications to their further 

development: Ghent, Belgium, Mededelingen Fakulteit 

Landbouwwetenschappen State University, v. 37, no. 3, 

p. 1046-1061. 

Gough, L. P., and Shacklette, H. T., 1979, Element 

concentrates toxic to plants, animals, and man: U.S. 

Geological Sutvey Bulletin 1466, 80 p. 

International Potash Institute, 1970, Role of fertilization in the 

intensification of agricultural production; 9th Congress 

International Potash Institute, Antibes, 1970 report: 

Berne, Switzerland, International Potash Institute, 489 p. 

Kabota-Pendias, Alena, and Pendias, Henryk, 1984, Trace 

elements in soils and plants: Boca Raton, Florida, CRC 

Press, Inc., 315 p. 

Neuman, D. R., Schrack, J. L., and Gough, L. P., 1987, Copper 

and molybdenum, in Williams, R. D., and Schu~an, G. 

E., eds., Reclaiming mine soils and overburden in the 

western United States; Analytical Parameters and 

Procedures: Ankeny, Iowa, Soil Consetvation Society of 

America, 336 p. 

Olson, B. A., editor-in-chief, 1971, Fertilizer technology and 

use (2d ed.): Madison, Wisconsin, Soil Science Society of 

America, Inc., 611 p. 

Raup, D. B., (editor), 1977, Proceedings of the geology and 

food conference, with related U.S. Geological Sutvey 

Projects and a bibliography: U.S. Geological Survey 

Circular 768, 51 p. 

Reeder, J.D., and Sabey, Bums, 1987, Nitrogen, in Williams, R. 

D., and Schuman, G. E., editors, Reclaiming mine soils 

and overburden in the western United States; Analytical 

Parameters and Procedures: Ankeny, Iowa, Soil 

Consetvation Society of America, 336 p. 

Safaya, N. M., McLean, J. E., and Halverson, G. A., 1987, 

Cadmium and zinc, in Williams, R. D., and Schuman, G. 

E., (editors), Reclaiming mine soils and overburden in 

the western United States; Analytical Parameters and 

Procedures: Ankeny, Iowa, Soil Consetvation Society of 

America, 336 p. 

Shacklette, H. T., 1980, Elements in fruits and vegetables from 

areas of commercial production in the conterminous 

United States: U.S. Geological Sutvey Professional 

Paper 1178, 149 p. 

Shacklette, H. T., and Connor, J. J., 1973, Airborne chemical 

elements in Spanish moss: U.S. Geological Sutvey 

Professional Paper 574-E, 46 p. 

Underwood, E. J., 1971, Trace elements in human and animal 

nutrition (3d ed.): New York and London, Academic 

Press, 543 p. 

42 Essential Elements and Soli Amendments for Plants: Sources and Use for Agriculture 
APPENDIXES 1-4 
APPENDIX 1 

Suggested Terminology For Soil Amendments 

The terms additive, admixture, amendment, 

conditioner, fertilizer, and stabilizer have been used to 

describe various types of soil modification. The lack of 

definitive guidelines for use of the terms in describing 

specific soil modification processes aimed at specific uses 

has led to confusion in terminology. Therefore, we 

propose some specific guidelines based on dictionary 

definitions and intended usages of the following terms: 

DICTIONARY DEFINITIONS 

Additive. To be added; of the nature of an 

addition; characterized by addition. 

Admixture. Anything added; an alien element 

or ingredient. 

Amendment. Act of amending, correction, or 

improvement. 

Conditioner. A restrictive, limiting, or modifying 

circumstance or agent. 

Fertilizer. Any material used to enrich the soil 

for crops, especially a commercial 

orchemical manure. 

Stabilizer. Any compound which, when 

included with a material, decreases 

the ability of the material to 

decompose spontaneously. 

The terms additive, admixture, and stabilizer are 

generally used in describing the modification of soil 

properties for engineering purposes. We propose that 

these terms not be used to describe the modification of 

soil properties for agricultural purposes. 

The terms conditioner and amendment have the 

same general connotation. We propose that amendment 

be employed, rather than conditioner, to describe 

materials of geologic origin used in agronomic aspects of 

soil modification. "Conditioner" has been employed 

quite extensively in the agronomic literature for synthetic 

materials used in the modification of soil properties for 

agricultural purposes; therefore, the use of "conditioner" 

for geologic materials may lead to some confusion. 

The remaining terms, amendment and fertilizer, 

should be used in agreement with their intended function 

and prefiXed with descriptive words to further describe 

their mode of action. For example, if limestone is 

incorporated into the soil to specifically supply calcium 

for plant growth, it should be referred to as an inorganic 

fertilizer. If limestone is added to soil primarily to change 

the soil pH, it should be classified as a chemical 

amendment; however, if used primarily to improve soil 

aggregation, it should be termed a physical amendment. 

We suggest, therefore, limiting the employable 

terms to two-fertilizer and amendment. The rationale 

for this usage is to avoid confusion in use or interpretation and to simplify the terminology yet retain integrity of 

terms. The use of modifiers with these terms should 

make their intended meanings more clearly understood. 

44 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
APPENDIX2 

Conversion Factors Used for English and Metric Units 

To convert To convert 

column 1 into Column 1 Column 2 column 2 into 

column 2, column 1, 

multiply by multiply by I Length 

0.394 centimeter, em inch, in. 2.54 

Area 

247.1 kilometer , km acre, acre 0.00405 

2.471 hectare, ha acre, acre 0.405 

Volljlme 

0.0097 3meter, m acre-inch 102.8 

2.838 hectoliter, hi bushel, bu 0.352 

0.0284 liter, I bushel, bu 35.24 

1.057 liter, I quart Qiquid) qt 0.946 

Mass 

1.102 ton (metric) ton (English) 0.9072 

2.295 kilogram, kg pound, lb 0.454 

0.035 gram, g ounce ( avdp) oz 28.35 

Pres$ure 

14.50 bar lb/inch , psi 0.06895 

Yield qr Rate 

0.446 ton (metric )/ha ton (English )/acre 2.240 

2.4299 kg/ton (metric) lb/ton (English) 0.4115 

0.892 kg!ha lb/acre 1.12 

0.892 kg!ha-furrow-slice lb/acre-furrow-slice 1.12 

1.15 hl/ha bu/acre 0.87 

APPENDIX3 

Common Plant Names Used In This Report~ With Corresponding Scientific Names 

Common names, as used in this text, are listed 

alphabetically. Generally, only common names are given 

in the publications consulted in preparing this report. For 

most of these names, there is no doubt as to their proper 

corresponding scientific names, but a few are ambiguous 

as, for example, the citation of "cherry" without 

specifying whether sweet cherry (Prunus avium) or sour 

cherry (Prunus cerasus) was intended. In these cases, 

both scientific names are given. The common names used 

are those generally applied in the United States. 

Alfalfa, Medicago sativa L. 

Apple, Pyrus malus L. 

Asparagus, Asparagus officina/is L. 

Avocado, Persea gratissima Gaertn. f. 

Banana, Musa paradisiaca var. sapientum Kuntze 

Barley, Hordeum vulgare L. 

Bean, Phaseolus vulgaris L. 

Beet, Beta vulgaris L. 

Big bluestem, Andropogon gerardi Vitman 

Black gum, Nyssa sylvatica Marsh 

Bluegrass, Poa pratensis L. 

Buckbush, Symphoricarpos orbiculatus Moench 

Cabbage, Brassica o/eracea var. capitata L. 

Carrot, Daucus carota var. sativa DC. 

Cauliflower, Brassica o/eracea var. botrytis L. 

Cherry, Pnmus cerasus L., Prunus avium L. 

Clover, Trifolium pratense L. 

Corn, Zea mays L. 

Cotton, Gossypium hirsutum L. 

Cowpea, Vigna sinensis Endl. 

Date palm, Phoenix dactylifera L. 

Field corn, Zea mays var. indent at a Bailey 

Flax, Linum usitatissimum L. 

Grape, Vitis lab1Uscana Bailey, Vitis vinifera L. 

Johnson grass, Sorghum halepense (L.) Pers. 

Kelp, various species of marine Brown Algae, 

Phaeophyta. 

Kentucky bluegrass, Poa pratensis L. 

Lima bean, Phaseolus limensis Macf. 

Mesquite, Prosopis juliflora var. glandulosa Cockerell 

Appendix 3 45 
Mustard, Brassica nigra Koch 

Oats, Avena sativa L. 

Onion, Allium cepa L. 

Orange, Citrus sinensis Osbeck 

Pea, Pisum sativum L. 

Peach, Prunus persica Batsch. 

Peanut, Arachis hypogaea L. 

Pear, Pyrus communis L. 

Pignut hickory, Carya cordifonnis (Wang.) K. Koch 

Pineapple,Ananas comosus (L.) Merr. 

Plum, Prunus salicin a Lindl., Prunus domestica L. 

Potato, Solanum tuberosum L. 

Radish, Raphanus sativus L. 

Red cedar, Juniperus virginiana L. 

Red clover, Trifolium pratense L. 

Red maple, Acer rub rum L. 

Red Mexican beans, Phaseolus vulgaris L. 

Rice, Oryza sativa L. 

Rye, Secale cereale L. 

Ryegrass, Lolium perenne L., Lolium multif/orum Lam. 

APPENDIX 4 

Sassafras, Sassafras albidum (Nutt.) Nees 

Seaweed, various marine Brown Algae (Phaeophyta) and 

Red Algae (Rhodophyta) 

Shortleaf pine, Pinus echinata Mill. 

Snap bean, Phaseolus vulgaris L. 

Sorghum, Sorghum vulgare L. (several subspecies) 

Soybean, Glycine max Merr. 

Spanish moss, Tillandsia usneoides L. 

Squash, Cucurbita maxima Ouch., Cucurbita moschata 

Ouch. 

Sugar beet, Beta vulgaris L. 

Sweet pepper, Capsicum frutescens var. grossum Bailey 

Tobacco, Nicotiana tabacum L. 

Tomato, Lycopersicum esculentum Mill. 

Turnip, Brassica napus L. 

Water hyacinth, Eichomia crassipes (Mart.) Solms Western wheatgrass, Agropyron smithii Rydb. 

Wheat, Triticum aestivum L. 

White clover, Trifolium repens L. 

White oak, Quercus alba L. 

White sweet clover, Melilotus alba Oesr. 

Willow oak, Quercus phellos L. 

Glossary of Selected Terms Used in This Report 

Absorption. The active intake and incorporation of 

ions into plant cells from soil by ion exchange, mass 

flow, or contact exchange. 

Acid soil. See pH. 

Acre-foot. The volume of water required to cover 1 

acre (0.405 ha) to a 1-foot (15.2 em) depth (43,560 

cubic feet or 1,233 cubic metres). 

Acre-furrow-slice. The amount of soil material 

contained within 1 acre (0.405 ha) to a depth of 6 

inches (15.2 em), generally considered to weigh 

2,000,000 pounds (908,000 kg). 

Activity. The effective concentration of an ion or 

molecule in solution. 

Adsorption. An accumulation of ions on a solid, 

caused by ion exchange or other reactions. 

Aerobic. A respiration process occurring only in the 

presence of free oxygen. 

Alkaline soil. See pH. 

Anaerobic. A respiration process occurring only in 

the absence of free oxygen. 

Anion. A negatively charged ion. 

Annual plants. Plants which complete their life cycle 

from seed to new seed in 1 year or one season of 

growth, then die. 

Available nutrient. A nutrient which is not fiXed or 

insoluble, but which can be taken up and used for plant 

growth. 

Browse plants. Woody plants (shrubs or low trees) 

whose leaves and young stems are eaten in the field by 

animals. 

Calcined. Having been made powdery by the action 

of heat; fritted. 

Cation. A positively charged ion. 

Chelates. (Name derived from "claw-like") Organic 

substances that act as ligands (see EOTA) with many 

coordination groups. 

Chloroplast. A chlorophyll-containing body within a 

plant cell. 

Chlorosis. A symptom of nutrient imbalance within 

a plant caused by chemical insufficiency or excess or by 

pathogenic organisms, expressed as yellowing of tissue 

that formerly was green. 

Citric acid cycle. Biochemical pathways for the 

synthesis of cell material and for degradation of 

carbohydrates to gain energy. 

Colloid. A material with a particle size larger than 

that of a substance in solution, generally from 0.001 to 

0.1 micrometer in diameter. 

46 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 
Contact exchange. Ion exchange between the 

external membrane of plant roots and soil colloids by 

direct contact. 

Crystal. A solid body with a shape that reflects the 

regular internal arrangement of constituent atoms or 

ions. 

Deficiency. The absence or insufficiency of some 

material necessary for normal growth and function of 

an organism. 

Denitrification. The biochemical reduction of nitrate 

or nitrite to gaseous nitrogen either as molecular 

nitrogen or as an oxide of nitrogen. 

Dissociation. The reversible decomposition of a complex 

substance into simple constituents. 

EDTA. Abbreviation for ethylene-diamine tetracetic 

acid, an organic substance that acts as a ligand (that is, 

can form coordination complexes with metal ions). 

Electron carrier. The cell material (for example, 

cytochrome) or molecules within the cell that are 

responsible for energy transfer. 

Electron flow. As used in this report, a biochemical 

mechanism for transferring energy. 

Enzyme. An organic catalyst produced by living cells. 

Epiphyte. A plant that grows upon another plant, but 

without having physical connections to, or nutritional 

dependence on, the host plant. 

Exchange capacity. The total ionic charge of the 

adsorption complex that is active in the adsorption of 

ions in soil. 

Fly ash. A furnace residue produced when 

pulverized coal is burned in an electric power 

generating or other industrial plant. 

Foliar application. The process of dusting or ' 

spraying plant leaves with fertilizers or pesticides. 

Forage plants. Herbaceous plants eaten by animals 

in the field, in contrast to harvested plants used for 

animal feed. 

Friable. A term pertaining to soil consistency, 

indicating that the soil is easily crumbled. 

Frit. To prepare by heat, to fuse partly; frits, the , 

material so prepared. 

Geometric mean. The nth root of the product of n · 

numbers; the antilog of the sum of the logarithms of n 

numbers divided by n. The geometric mean is useful in 

describing central tendency if the values are lognormally, or approximately log-normally, distributed .. 

This distribution is generally true for minor element 

values for soil and plant materials. 

Heavy soil. A soil with a high resistance to 

mechanical tillage. 

Ion. An electrically charged atom or group of atoms. · 

Ionize. The process of ion formation. 

Lattice. Atoms or ions having ordered geometric 

arrangement within a crystal. 

Leaching. The removal of soluble constituents from 

soil by the action of percolating water. 

Leaf stalk. Petiole; that part of a leaf which connects 

the blade to the stem. 

Light soil. A soil with a low resistance to mechanical 

tillage. 

Lime. Any compound or mixture of compounds in 

which calcium is the principal component; specifically, 

materials of this nature used on agricultural soils. 

Macroelement. An element essential for organisms 

that is required in large amounts; macronutrient; 

major element. 

Microelement. An element essential for organisms 

that is required only in very small amounts; micronutrient; trace element. 

Monoculture. A system of agriculture in which the 

same kind of crop is grown in a field in successive 

years, sometimes expressed as continuous cultivation, 

such as "continuous corn." Contrasts with "crop 

rotation." See "Rotation (crop)." 

Morphological symptoms. Visible indications, 

expressed as changes in the form or shape of plant 

organs, of internal biological changes such as those 

produced by disease or chemical imbalance. 

Muck. An organic soil composed of plant residues 

that are fairly well decomposed and having a relatively 

large content of mineral matter. 

Neutral soil. See pH. 

Nitrification. The biochemical oxidation of 

ammonium to nitrate. 

Osmotic pressure. The pressure developed within a 

cell in which the concentration of dissolved substances 

is greater within, than outside, the cell. 

Osmunda fibers. · Coarse roots and rhizomes of 

certain large ferns, notably Osmunda cinnamomea and 

Osmunda regalis, used as potting media for certain 

plants or as a soil amendment. 

Oxidation-reduction reactions. See Redox Potential. 

Parenchyma. Large thin-walled isodiametric cells of 

plants. 

Parts Per Million (ppm). Weight of a soluble 

substance divided by weight of solution times one 

million. 

Peat. An organic soil composed of plant residues in 

various stages of decomposition, with little or no 

mineral material present. 

Percent. Weight units of a substance per one 

hundred equivalent weight units. 

Perennial plants. Plants which live for several years, 

usually not producing seed the first year. 

pH. A logarithmic scale ranging from 1 to 14, 

commonly used to express the degree of acidity or 

alkalinity. A pH of 1 is strongly acid and a pH of 14 is 

strongly alkaline; whereas, a pH of7 is neutral (neither 

acid nor alkaline). 

Appendix 4 47 
Phosphorylation. The act or process of converting 

into a compound of phosphorus; specifically, the action 

of a group of enzymes in catalyzing reactions involving 

orthophosphate within a cell. 

Plant cell sap. The liquid constituents of plant cells, 

composed of water and various dissolved organic and 

inorganic materials. 

Plant residue. As applied to agriculture, the unharvested parts of crop plants that remain in the field. 

Plant toxicity. The property of having poisonous 

effects on plants. 

Precipitation. As used in this report, the separation 

of a substance from a solution so that the substance is 

in a solid form. 

Primary minerals. The unweathered minerals of 

rock particles in soil, such as feldspars and micas. 

Redox potential. The potential of a material, 

compared to other materials, to release electrons 

(oxidation) or to receive electrons (reduction), 

commonly measured in millivolts and expresed as Eh. 

Rotation (crop). The practice of growing different 

crops in recurring succession on the same plot of land. 

Scientific name. A compound name consisting of a 

genus and a species name written in the Latin language 

that is assigned to each recognized and described kind 

of organism. Variants in species characteristics may be 

designated as subspecies (populations discrete 

spatially), variety (isolated or random variations within 

a population), or cultivar (variations arising in 

cultivation). In formal writing, the name or 

abbreviated name of the author or authors of the 

scientific name follow the last epithet of the organism's 

name. 

Secondary minerals. The weathered products, such 

as clays, of primary minerals. 

Soil aeration. The process in which soil air is 

exchanged for atmospheric air. The volume and 

continuity of pores in the soil determine the aeration 

rate. 

Soil drainage. The mechanism of water removal 

from soil; the relative degree of water retention by 

different soils. 

Soil fixation. The conversion of an available or 

soluble substance in soil to a relatively insoluble or 

unavailable form. 

Soil flocculation. The union of soil particles to form 

loose aggregates. 

Soil horizon. A layer of soil horizontal to the Earth's 

surface having characteristics that distinguish it from 

soil layers both above and below it. 

Soil permeability. The ease with which materials 

penetrate or pass through a bulk mass of soil. 

Soil solution. The aqueous part of the soil consisting 

of soluble materials and ions dissociated from soil 

particles. 

Soil submergence. Refers to a process in which a soil 

is waterlogged for significant periods of time. 

Soil texture. The relative proportions of different 

sized particles in an amount of soil material. 

Soluble. Capable of being dissolved. 

Synergistic. A type of reaction in which two 

substances reinforce the separate effects produced by 

each or which, in combination, produce new effects. 

Tailings. Mineral refuse from ore milling ope~ations, 

usually deposited as small particles from suspension in 

water. 

Tilth. The physical condition of soil as related to its 

ease of tillage, fitness as a seedbed, and its resistance to 

seedling emergence and root penetration. 

Tissue analysis. Analysis of the chemical 

constituents of plant tissue. 

Ton, English. A unit of weight equaling 2,240 

pounds, also referred to as a "long ton." 

Ton, metric. A unit of weight equaling 1,000 

kilograms. 

Translocation. The movement of dissolved materials 

in cell sap from one plant organ or tissue to another, as 

the movement of sugar from leaves to stem. 

Turf. The low dense sod of grassland, comprising the 

above-ground parts and upper roots and rhizomes of 

plants, with attached soil particles. 

Unavailable nutrient. See Soil Fixation. 

Valence. The relative combining capacity of an atom 

or molecule compared to that of the standard 

hydrogen atom. 

Vascular plants. Plants having specialized 

conducting tissue through which water, mineral salts, 

and food move. 

Volatilization. The conversion of a solid or a liquid 

into a gas or vapor. 

Woody plants. Plants that have pronounced 

development of wood (xylem) in their stems; usually 

applied to trees, shrubs, and certain vines. 

48 Essential Elements and Soil Amendments for Plants: Sources and Use for Agriculture 

tf U.S. GOVERNMENT PRINTING OFFICE:1988-573-047/66090