Water Use by Saltcedar 

as Measured by the 

Water Budget Method 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 491-E 

Water Use by Saltcedar 

as Measured by the 

Water Budget Method 

By T. E. A. van Hylckama 

STUDIES OF EVAPOTRANSPIRATION 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 491-E 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1974 
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress Cataloging in Publication Data 

Van Hylckama, T. E. A. 

Water use by saltcedar as measured by the water budget method. 

(Studies of evapotranspiration) (Geological Survey Professional Paper 491-E) 

Supt. of Docs. No.: I 1916:491-E 

Bibliography: p. 

1. Tamarix pentandra. 2. Evapotranspiration. I. Title. II. Series. III. Series: United States Geological Survey Professional 

Paper 491-E. 

QE75.P9 no. 491-E [QK495.T35] 557.3'08s [551.5'72] 74-17416 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402- Price $1.30 (paper cover) 

Stock Number 2401-02563 
CONTENTS 

Page Page 

Abstract ................................................ . E1 Water use, large tanks.-Continued 

Background of the Buckeye Project ....................... . 1964: Floods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E 11 

Reduction of water loss .............................. . 1965: Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

Water use by saltcedar .............................. . 1 1966: Density of stand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

Measurement of water loss ........................... . 2 1967: Finale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

Evapotranspirometers .................................... . 2 Soil moisture and soil-moisture fluctuations . . . . . . . . . . . . . . . . 16 

Definition .......................................... . 2 Method of measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

Oasis effect ......................................... . 2 Ambient air temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

The Buckeye test site .................................... . 3 Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

Location ............................................ . 3 Chloride content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

Test environment ................................... . 3 Vegetation growth and development . . . . . . . . . . . . . . . . . . . . . . . 19 

Climate ........................................ . 3 Transpiration rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Floods .......................................... . 4 Water use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Cicadas ........................................ . 4 Sunlight, salinity, stand density . . . . . . . . . . . . . . . . . . . . . . . 19 

Tank Construction .................................. . 5 Plant variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

Instrumentation ..................................... . 7 Water use, small tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

Floatless control system .......................... . 7 Harmonic analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

Adverse conditions .............................. . 8 Oasis tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

Water level ..................................... . 9 Bare-soil tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Soil moisture and temperature ................... . 9 Water table fluctuations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

Vegetation .......................................... . 9 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 

Tank planting .................................. . 9 Varying factors of water use . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 

Transpiration volume ............................ . 9 Methods of evaluating water use . . . . . . . . . . . . . . . . . . . . . . 29 

Water use, large tanks ................................... . 10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

1961-63: Depth to water ............................. . 10 Appendix: Analysis of variance with multiple classification . . 30 

ILLUSTRATIONS 

Page 

FIGURE 1. Photograph showing saltcedar freely exposed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E3 

2. Photograph showing saltcedar as part of a thicket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

3. Map showing l9cation of the Buckeye test site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

4-8. Photographs showing: 

4. Frost damage on saltcedar twigs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

5. Two scenes of results of typical floods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

6. Cicada egress holes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

7. Saltcedar twigs damaged by cicada egg laying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

8. An evapotranspirometer newly planted to saltcedar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

9. Diagram showing location of tanks and instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

10. Photograph of instrumentation for the water budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

11. Schematic cross section of an evapotranspirometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

12. Graph showing soil moisture by volume in the six large tanks on a typical summer day in 1965 . . . . . . . . . . . . . . . . . . . . . 13 

13. Bar graph of total water use during 1965 in six evapotranspirometers showing the effect of depth to water and flushing of 

saline ground water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

14. Photographs comparing plant growth for evapotranspirometers 7 and 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

15. Photographs of three of the six evapotranspirometers after treatment of vegetation in March 1966 . . . . . . . . . . . . . . . . . . . 15 

16. Graph showing accumulated water use in six evapotranspirometers during 1966 showing the effects of density of stand and 

salinity of artifically maintained ground water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

17. Graph showing accumulated water use in tanks 1 to 6 between April 1 and September 1, 1967 . . . . . . . . . . . . . . . . . . . . . . 16 

18. Calibration curve of soil moisture measurements by the neutron method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

19-22. Graphs showing: 

19. Soil moisture variation with depth in one tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

20. Apparent fluctuations in soil moisture during a three-day period in one evapotranspirometer . . . . . . . . . . . . . . . 18 

21. Effect of chloride concentrations on the counting ratios of a neutron logger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

22. Soil moisture in tank 4 in May of 1963, 1965, 1966, and 1967 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

III 
IV CONTENTS 

Page 

FIGURE 23. Photographs of two- to three-month-old branches of saltcedar from the Buckeye Project site along the Gila River in Arizona E21 

24. Photograph of the small-tank area at the Buckeye Project, March 1963 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

25. Recording chart of tank 7 showing frequency of filling during a week in May 1967 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

26-35. Graphs showing: 

26. Water use in evapotranspirometers 7, planted to saltcedar, and 11, bare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

27. First and second harmonics of the analyses of average hourly water use in evapotranspirometers 7 and 11 . . . . . . . 22 

28. Second harmonics of water-use fluctuations of bare-soil tank 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

29. Water use in tanks 7 and 8, planted to saltcedar, surrounded by bare soil (oasis tanks) . . . . . . . . . . . . . . . . . . . 24 

30. Water levels in evapotranspirometer 9 and inverted barometric pressure................................... 25 

31. Water levels in evapotranspirometer 1 and barometric pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

32. Water levels in evapotranspirometer 2 and barometric pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

33. Average water levels, average barometric pressures, and average observed and computed water use in tank 6, 

planted to saltcedar, for June 30-July 4, 1966 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 

34. Yearly water use (1961-1963) versus depth to ground water in six evapotranspirometers at the Buckeye Project 28 

35. Total water use per year in six evapotranspirometers versus specific conductance of the saturation extract of the 

soil samples taken from the root zones in July or August of each year............................... 28 

TABLES 

TABLE 1. Page 

Meteorological data for project site near Buckeye, Ariz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E6 

2. Dates of flooding of the Waterman Wash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

3. Results of surveys of saltcedar, taken in the fall of each year, in the evapotranspirometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

4. Monthly water use in evapotranspirometers, excluding rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

5. Yearly water use in evapotranspirometers, excluding rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

6. Quality of ground water in evapotranspirometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

7. Water use, excluding rainfall, in evapotranspirometers during 1965 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

8. Analysis of project water and better-quality water from a new well south of the project site . . . . . . . . . . . . . . . . . . . . . . . . . 15 

9. Water use in six evapotranspirometers between April 1 and September 1, 1966 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

10. Water use in six evapotranspirometers between April 1 and September 1, 1967 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

11. Change in soil moisture content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

12. Increase in twig length of saltcedar inside and outside evapotranspirometers between April 5 and June 22, 1966 . . . . . . 20 

13. Mean and amplitudes of the harmonic analysis of water use in tanks 7 and 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

14. Water use in oasis tanks_ 7 and 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

15. Evaporation from bare soils in tanks 10 and 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

16. Monthly evaporation, excluding rainfall, from ground water in bare-soil tanks at Imperial Camp and near Buckeye, Ariz 26 

17. Summary by years of water use in and treatment of six evapotranspirometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 
STUDIES OF EVAPOTRANSPIRATION 

WATER USE BY SAL TCEDAR 

AS MEASURED BY THE WATER BUDGET METHOD 

By T. E. A. van HYLCKAMA 

ABSTRACT 

Water use by saltcedar (Tamarix pentandra) was studied from 1961 

through 1967 near Buckeye, Ariz. The test site, in ·the flood 

plain of the Gila River, was surrounded by a kilometer-wide dense strip 

of saltcedar thickets. Areas to the north and south of the strip were 

mainlJ desert and a few cotton fields. The test site growing season lasts 

8 to 9 months, the humidity is low, winds are strong, summer 

temperatures at the site often reach 50°C, and evapotranspiration 

rates are a.mong the highest in the United States. 

Evapotranspiration rates and quantities were observed in six plasticlined evapotranspirometers (tanks) with 81-m2 (square-meter) surfaces. 

Analyses were made on the effects of depth to ground water in the 

tanks, of salinity of soil moisture, and of vegetation density. Rates of 

water use from bare and vegetated soil were observed in five smaller 

tanks (36m2 each). 

When the depth to ground water, or water table, was 1.5 m (meters) 

the average water use was about 215 cm/yr (centimeters per year); 

when the water table was 2.1 m, the use diminished to about 150 cm/yr; 

and when the water table was 2.7 m, the yearly water use was less than 

100 em/yr. 

Water use varies greatly with salinity of the soil moisture. Salinity 

may be expressed in terms of specific conductance of the saturation extract (ECs) in mmho/cm (millimhos per centimeter) at 25°C. In tanks 

which measured ECs=20, the water use was 70 percent; in tanks which 

measured ECs=30, the water use was only half that in tanks with an 

ECs=lO. 

When the vegetation was cut twice a year from an original average 

height of 3 m. to a height of about 50 em the water use decreased to 

about half that in tanks where the vegetation was not cut. However, 

when the vegetation was thinned to 50 percent of the original density 

the water use diminished by only 10 percent. 

The maximum yearly water use (311 em) was measured in 1~65 in a 

tank with a high water table, a dense vegetation, and an ECs less than 

10. Although in half of the 36 cases (6 tanksX6 years) the yearly ~ater 

use was 150 em or less, there were 11 tank-years with a water use of 200 

em and more-when the table was high, the salinity was comparatively 

low, and the stand density was medium to high. 

The daily fluctuations in water use from bare soil showed that in 

summer the evaporation at midday diminishes because of the formation of a vapor barrier; but, evaporation continues from the soil underneath a dense vegetation. 

Atmospheric pressure fluctuations which affect the water level in the 

plastic-lined tanks must be considered when such levels are used to 

determine water consumption quantitatively. 

BACKGROUND OF THE BUCKEYE PROJECT 

REDUCTION OF WATER LOSS 

The increasing population of the arid and semiarid 

regions of the southwestern United States and the accompanying need for more water has continually focused 

the attention of hydrologists and water managers on 

ways and means to salvage water when and wherever 

possible. 

Current studies reflect efforts to conserve water by: 

reducing water loss from lakes and ponds (and even 

plants) by covering the surfaces with chemicals that 

reduce evaporation; determining the most economical 

methods of irrigation; eradicating plant growth along 

arroyos and rivers; condensing moisture in the air to induce precipitation; and desalting saline water for industrial, domestic, and agricultural use. The 

southwestern United States and many other parts of the 

world will be able to support their present and future 

populations only if some or all of such studies eventually 

make more water available. 

This paper discusses reduction of water loss by converting saltcedar jungles, vegetation which uses a lot of 

water, into less thirsty pasturelands or bare soil. 

WATER USE BY SALTCEDAR 

The Latin name for saltcedar (Tamarix pentandra), 1 

and the often used name "tamarisk", were derived from 

the name of a river in the Pyrenees. Maybe this led to the 

belief that saltcedar was imported into this country by 

early colonists from the Mediterranean regions. Later 

studies (Horton, 1964) raise doubt on this supposition. 

(There is, for instance, evidence that in 1823 sal tcedar 

was imported simply as a garden plant, at least in New 

York.) Whatever happened, saltcedar was introduced 

and started to spread. No attention was paid to this until 

construction of reservoirs and excessive use of ground 

l Dr. B. R. Baum (1967), botanist at the Hebrew University, ,Jerusalem. discovered that T. 

pentandra Pallas might be the wrong name forT. chinensis or T. ramosissima. However, ,J. S. 

Horton (written commun ... June 1971 I is of the opinion that most and perhaps all of the fivestamen tamarisk in North America are in either the T. pentandra or the T. !Wllica group of 

genotypes. 

El 
E2 STUDIES OF EVAPOTRANSPIRATION 

water began in many places to lower the water table ' most accurate data, provided the physical surroundings 

along rivers. As a result, the native vegetation died, and are properly maintained and controlled. This paper dissaltcedar, with its deep rooting system and salt exuda- cusses the water budget and presents data on water use 

tion, was left in sole command of the water-depleted as measured in evapotranspirometers. 

areas. During the 1920's people began to realize that the This project was established as a joint effort by the 

plant might well be using copious amounts of ground Geological Survey and the Bureau of Reclamation. The 

water. Thus began the studies on saltcedar and many author gratefully acknowledges the generous assistance 

other phreatophytes. given by the Bureau and its personnel, especially by CurAlthough saltcedar has some value for the control of tis W. Bowser. Also the assistance and advice of other insoil erosion and for wildlife habitat, these beneficial dividuals too numerous to mention is acknowledged with 

features are offset by its lavish use of water. The gratitude. 

sometimes remarkably deep rooting system developed 

by this species enables it to use ground water from 

depths as great as 10 m (meters) or more (30ft (feet) or 

more) below the land surface, a feat equaled only by a 

few other species, usually known by the generic name of 

phreatophytes or "well plants" (Meinzer, 1927). Because 

of this deep rooting capacity, saltcedar may have free 

access to water and, therefore, may consume by 

evapotranspiration as much or more water than the 

amount that would (other things being equal) evaporate 

from a lake surface. For instance, the U.S. Bureau of 

Reclamation (1964) estimates that along the Colorado 

River 67,000 hectares (167,000 acres) of saltcedar and 

other water-loving plants2 consume as much as 700 

million m3 (cubic meters) (568,000 acre-ft) of water per 

year. It is, therefore, not surprising that eradication of 

saltcedar has been undertaken over vast areas of the 

Southwest. 

MEASUREMENT OF WATER LOSS 

Water use by vegetation or evaporation losses from 

bare soil can be measured in several ways. There is a 

great demand for techniques that use portable or 

semiportable instrumentation with which one can 

measure the evapotranspiration indirectly. The advantages are obvious: the hardware can be moved from place 

to place, and, once proper correlation between direct and 

indirect methods is established, information can be obtained in a comparatively short time. Such methods 

have been successfully tested over open water (U.S. 

Geological Survey, 1954; Harbeck and others, 1958) and 

over low vegetation (Rider, 1956; Tanner, 1960) but rarely over such high stands as saltcedars. The Buckeye 

Project was equipped with instruments to observe the 

radiation balance as well as to collect data on mass 

transfer. These instruments and their functions will be 

explained and the' data will be presented in another 

report in this series. 

The most direct method of measuring water use is the 

water-budget method, in which an account is kept of the 

amounts of water applied to, and lost from, a particular 

container, area, or type of surface. Such a method is expensive and time consuming but generally gives the 

~Some of these water-loving plants sharing saltcedar's notoriety have been extensively 

studied by McDonald and Hughes (1968). 

EV APOTRANSPIROMETERS 

DEFINITION 

According to the "Glossary of Meteorology" (Huschke, 

1959), evapotranspirometers are instruments which · 

measure the rate of evapotranspiration, the loss of water 

from the soil both by evaporation and by transpiration 

from plants growing on that soil. Evapotransirometers 

consist of a vegetated soil tank designed so that all water 

added to the tank and all water remaining after 

evapotranspiration can be measured. Some are quite 

simple, such as oil drums filled with soil and inserted 

into the ground. Others are large elaborate structures attached to recorders which indicate gains and losses of 

weight due to gains and losses of moisture. Some have 

perforated bottoms and the water seeping through can 

be tapped off, weighed and chemically analyzed; they 

are called lysimeters, a word derived from the Greek 

"A.v uav" which means "to dissolve". Whereas a 

lysimeter can nearly always be used as an 

evapotranspirometer, the reverse is not true. 

The size of evapotranspirometers is partly determined 

by the type of vegetation to be studied. Obviously, a 

small container might suffice for grasses, but instruments like those built in the Netherlands, which 

have an area of 625m2 (square meters) (6, 725 ft 2 (square 

feet)) and are 5 or more meters deep ( 15 ft and over), 

may be needed for studying trees. The larger the size, the 

more difficult it becomes to detect malfunctioning such 

as leakage (Penman and Schofield, 1941) and to accurately maintain ground water at intended levels. 

OASIS EFFECT 

It is difficult to imitate natural conditions inside and 

outside the lysimeters or evapotranspirometers. Often 

the failure to maintain a representative test environment 

has resulted in grossly overestimated amounts of water 

used by similar plants in a natural environment 

(Mather, 1954). Figures 1 and 2 for example illustrate 

variations of plant density. The first photograph shows a 

saltcedar plant standing alone with the fronds (as the 

terminal branches with their scalelike leaves are called) 

all green down to the ground. Such plants have a large 

active surface and therefore are capable of transpiring 

more water than plants shown in figure 2. Owing to in-
WATER USE BY SALTCEDARAS MEASURED BY THE WATER BUDGET METHOD E3 

FIGURE 2.-Saltcedar as part of a thicket. Rod is a standard stadia type {feet and tenthl:) of feet). 

tolerance to shade and possibly to lack of moisture, these 

plants have shed many of their fronds. Each plant has 

much less active surface and consequently can transpire 

less, other things being equal, than a single plant standing as if in an oasis. 

Clearly, if the use of water by a single plant such as 

shown in figure 1 is measured, it is not warranted to apply 

results on a per-plant basis to an acre, much less to 

thousands of acres of dense growth. To dispel the oasis 

effect, an evapotranspirometer must be surrounded by a 

buffer zone planted with the same vegetation as that of 

the tank, and all other conditions should be as similar as 

possible to those of the instrument. The size of such a 

buffer zone depends on climatic conditions. 

Thornthwaite and Mather (1955) point out: "In a moist 

climate such as Ireland a square 50 meters on a side 

should be sufficient, but in the desert probably a square 

400 meters on a side would not be too large. " In semiarid 

climates, however, the riparian vegetation is subject to 

some oasis effects anyway, especially when winds blow 

normal rather than parallel to the stream. The actual 

size of the buffer zone becomes relatively insignificant 

compared with the requirements that the vegetation is of 

equal height and density and that the surrounding soil is 

kept as moist as the soil in the tanks. 

THE BUCKEYE TEST SITE 

LOCATION 

The test site is located in the southeast corner of section 11, R. 3 E. and T. 1 S. of the Gila and Salt river base 

line and meridian (33°21' N. and 112c3f W.), as indicated in figure 3, and its elevation is about 260 m (855 

ft) above mean sea level. The area was inspected in the 

fall of 1958 by members of the U.S. Geological Survey 

and the U.S. Bureau of Reclamation. At that time, most 

of sections 11 and 12 as well as the land furthur up and 

downstream along the Gila River presented a nearly 

homogeneous stand of very dense saltcedar. For this 

reason, and because electric power lines were near, the 

site was considered ideal for the phreatophyte studies. 

The low-flow channel of the Gila River was remote 

enough to eliminate danger of flooding; but as the map 

(fig. 3) shows, the low-flow channel of the Waterman 

Wash curves very closely around the project site and 

minor flooding could be expected. 

TEST ENVIRONMENT 

CLIMATE 

In general, the climate at the project site is typical of 

that of the Sonoran Desert, but it differs in detail considerably from the average climate. As mentioned 

before, the area lies in the flood plain of the Gila River. 

Fire km (kilometers) (3 mi (miles)) to the south are the 

Buckeye Hills which rise to 270 m (900 ft) above the 

valley floor; 16 km (10 mi) to the north are the White 

Tank Mountains, rising slowly at first and then steeply 

to 600 m (2,000 ft); and to the east the Sierra Estrella 

towers 1,100 m (3,600 ft) above the project site. Daytime 

temperatures can be very high, indeed, compared with 

those observed at standard weather installations outside 

the area. But, as a result of the surrounding mountains, 

there is considerable cold-air drainage on quiet nights, 
E4 STUDIES OF EVAPOTRANSPIRATION 

T. 1 S. 

0 

0 

R. 3 W. 

LOWER RIVER ROAD 

2000 4000 FEET 

c.:: 

~ ..... 

c.:: 

Cl 

<::) 

1 KILOMETER "\ 

~ 

8 

FIGURE 3.-Location of the Buckeye test site. 

and, even during the summer, nights are often cool. 

Freezing in the dawn hours of the early spring 

sometimes damaged young fronds, as shown in figure 4. 

However, it is not likely that the frost affected 

evapotranspiration because the plants quickly outgrew 

the damage. 

The dense vegetation and large irrigated areas north 

and south of the Gila River can create relatively high 

humidities. Table 1 presents monthly data on total 

precipitation, mean maximum and mean minimum 

temperatures and relative humidities, average wind 

speed, and average daily solar radiation. At first it was 

planned to install a U. S. Weather Bureau class A 

evaporation pan, but the dusty winds in the area 

together with dead leaves and other trash falling from 

surrounding saltcedars would make pan data practically 

worthless. 

FLOODS 

When the project site was chosen there was some 

concern about the frequency of flooding of the Waterman 

Wash. Based on information obtained here, it was 

decided that floodings were so rare that the risk of 

damage to the site would be small. However, during the 

F JGURF. 4.-Frosl damage on saltcedar twigs . 

second half of 1959 the project site was inundated nine 

times. When flood conditions such as shown in figure 5 

again occurred repeatedly during 1960, it became 

necessary to construct levees capable of preventing small 

floods from upsetting the records. 

All floodings between July 1959 and September 1967 

and the times that levees had to be s~rengthened or 

repaired are listed in table 2. 

On November 2, 1963, a severe storm with hail stones 

as large as 2.5 em (centimeters) (about 1 in. (inch)) in 

diameter hit the project site. One pyrheliometer was 

smashed and anemometer cups were so severely dented 

that five sets had to be replaced. 

The Gila River flooded a few times, usually only making access roads north of the project site impassable. 

But, in December, 1965, the Salt River Project was 

forced to release water from behind Roosevelt and other 

dams, and the usually dry bed of the Gila became a 

"mile-wide" river; however, water reached just the 

northern row of evapotranspirometers, causing some 

gullying which was easily repaired. 

CICADAS 

During the latter half of May and the beginning of 

June each year, thousands of cicadas crawled out of the 

ground (fig. 6) and invaded the saltcedar stands. 

Damage was done by the females who laid eggs on the 

young branches after making an incision in the bark for 

each egg. This often resulted in girdling of the branches; 

the parts above the girdling died as shown in figure 7. 

However, regrowth from the plant underneath the 
WATER USE BY SALTCEDAR AS MEASURED BY THE WATER BUDGET METHOD E5 

J· 

t 

I ·' 

F IGURE 5.-Two results of typical floods. Top: December 1959; tank 5 in foreground has not 

been planted yet. Bott:)m: September 1966, mud deposited on and in one of the recorders; 

high water mark about 9~ em (3.5 ft) above ground level. 

girdled areas was so vigorous that the cicada damage 

could not possibly have affected water use significantly. 

TANK CONSTRUCTION 

In May 1959 construction started on the first of six 

tanks, 9X9 m (30X30 ft) in surface and about 4.25 m (14 

ft) deep. To reduce cost and construction time, large 

s heets of plastic were u s ed to line the 

evapotranspirometers, as suggested by Robinson and 

Bowser (1959). Robinson (1970) has described the construction and the plumbing in detaiL It is necessary to 

mention here only that since the tanks were dug without 

shoring and the soil was fairly dry even at great depths it 

FIGURE 6.- Cicada egress holes; pencil is 15 em (6 in.) long. 

FIGURE 7 .- Saltcedar twigs damaged by cicada egg laying. 

was not surprising that cave-ins occurred. As a result, the 

sides of the tanks were not straight walls, as suggested in 

figure 5 of Robinson's paper. The surface, too, deviated 

somewhat from the intended 9 X 9 m. 

After each tank was finished, it was planted to 

saltcedar. Vigorously growing bushes were selected from 

the surrounding stands and carefully dug up. Branches 

and roots were pruned to about 60 em (2ft). Twenty-five 

crown cuttings were planted in each tank, and when 

the last one was finished in October 1959, the surroundings of the tanks were similarly planted. Figure 8 

shows a newly planted tank. 

In 1962, five small tanks were constructed north of the 

existing ones as shown in figure 9. These new tanks were 

6 meters square (20X20 ft) and only a little more 

than 2 m (6ft) deep. They were lined with heavy butyl 

rubber instead of plastic. Tanks 7 and 8 were planted to 

saltcedar in February, 1963, but the others were kept 
E6 STUDIES OF EVAPOTRANSPIRATION 

TABLE 1.-Meteorological data for project site near Buckeye, Ariz. 

Mean temperature Relative humidity Wind speed Solar 

Precipitation \"C! (• F) (percent) at 4 meters radiation 

Month (in.) (em) (em/sec) (mph) Langleys/day 

Max Min Max Min Max Min 

1961 

Jan 0.43 1.1 21.2 4.7 70.1 40.5 98.5 38.7 121 2.7 282 

Feb ... ... .. 0.00 0.0 23.9 -0.9 75.1 30.3 82.7 23.1 421 

Mar . . ... . .. 0.24 0.6 27.5 2.2 81.5 35.9 68.5 21.0 130 2.9 514 

Apr . . . . . . . . 0.00 0.0 31.9 4.2 89.5 39.6 46.0 17.0 103 2.3 682 

May 0.00 0.0 38.6 9.3 101.5 48.7 59.5 19.5 80 1.8 717 

June . ... . .. 0.00 0.0 44.4 14.5 111.9 58.1 83.4 23.8 94 2.1 698 

July .... .... 0.67 1.7 44.5 22.3 112.1 72.1 87.0 26.0 121 2.7 648 

Aug ... ..... 0.55 1.4 42.7 22.3 108.9 72.1 86.0 25.2 125 2.8 567 

Sept 0.08 0.2 39.2 15.2 102.5 59.4 84.5 24.4 119 2.6 529 

Oct ........ 0.20 0.5 33.1 6.9 91.5 44.5 74.0 22.0 139 3.1 429 

Nov .. . ..... 0.00 0.0 23.8 1.1 74.8 33.9 87.0 26.0 89 2.0 305 

Dec ..... . .. 1.65 4.2 18.8 -0.8 65.9 30.5 96.0 33.6 80 1.8 259 

Total or mean 3.82 9.7 32.5 8.4 90.4 47.1 79.4 25.0 109 2.4 504 

1962 

Jan .. . ..... 1.61 4.1 19.7 -1.2 67.4 29.8 93.6 28.0 85 1.9 307 

Feb .. . . . ... 0.75 1.9 23.2 3.1 73.7 37.5 92.0 30.0 119 2.6 369 

Mar .. .. .... 0.63 1.6 24.8 0.5 76.6 32.9 81.0 23.3 119 2.6 505 

Apr ... . .. .. 0.00 0.0 34.7 6.4 94.4 43.6 78.0 22.6 139 3.1 630 

May 0.00 0.0 36.0 8.3 96.8 47.0 60.4 21.6 94 2.1 696 

June . .... . . 0.20 0.5 42.3 12.4 108.1 54.4 67.5 21.0 67 1.5 654 

July ........ 0.24 0.6 45.1 19.1 113.1 66.3 51.5 18.0 134 3.0 679 

Aug ... . .. . . 0.08 0.2 46.1 19.4 114.9 66.9 62.1 18.4 148 3.3 623 

Sept 1.50 3.8 41.3 17.4 106.4 63.3 82.6 30.3 94 2.1 488 

Oct ..... . .. 0.00 0.0 35.3 7.5 95.6 45.5 84.7 21.6 67 1.5 450 

Nov ........ 0.16 0.4 28.4 3.3 83.1 38.0 83.7 25.6 76 1.7 321 

Dec . . .. .. .. 0.35 0.9 22.6 0.3 72.7 32.6 87.0 28.7 268 

Total or mean 5.52 14.0 33.3 8.0 91.9 46.5 77.0 24.1 104 2.3 499 

1963 

Jan 0.16 0.4 19.3 -3.7 66.7 25.3 85.2 23.9 314 

Feb . . . ... .. 0.32 0.8 28.3 3.4 82.9 38.2 82.1 22.6 403 

Mar ..... . .. 0.28 0.7 27.4 1.6 81.3 34.8 77.7 20.4 530 

Apr . .. . .... 0.00 0.0 30.8 3.8 87.5 38.8 83.4 16.4 628 

May 0.00 0.0 39.8 11.9 103.6 53.4 50.3 16.2 680 

June ....... 0.00 0.0 40.8 12.3 105.4 54.2 53.4 19.8 732 

July ........ 0.00 0.0 45.9 22.1 114.6 71.7 58.5 24.9 656 

Aug .... . .. . 2.60 6.6 41.9 22.0 107.4 71.6 81.3 25.4 558 

Sept 0.04 0.1 41.7 18.4 107.0 65.2 76.9 22.3 124 2.8 532 

Oct ... . . .. . 0.91 2.3 36.6 11.6 97.9 52.8 83.2 23.9 105 2.3 435 

Nov ....... . 0.87 2.2 26.8 5.2 80.3 41.4 90.0 28.0 153 3.4 437 

Dec . .... . .. 22.8 -3.7 73.1 25.4 87.7 21.8 319 

Total or mean 5.18 13.1 33.5 8.7 92.3 47.7 74.1 22.1 127 2.8 519 

1964 

Jan . . .. . ... 0.28 0.7 19.4 -4.4 67.3 24.1 76.7 23.1 290 

Feb . ...... . 0.08 0.2 22.4 -4.3 72.3 24.3 65.4 19.1 407 

Mar . . . . . .. . 0.87 2.2 24.4 1.5 76.0 34.7 79.4 19.6 521 

Apr .. . ..... 0.00 0.0 32.0 5.9 89.6 42.7 66.5 21.0 598 

May 0.00 0.0 36.8 9.6 98.2 49.2 53.4 17.3 152 3.4 683 

June ....... 0.00 0.0 41.3 14.6 106.4 58.3 53.8 21.4 120 2.7 685 

July .... . .. . 0.87 2.2 44.5 22.6 112.1 72.5 63.0 22.6 129 2.9 632 

Aug . . . .. . .. 2.60 6.6 41.2 21.6 106.1 70.8 84.0 26.7 129 2.9 517 

Sept 1.54 3.9 36.1 16.7 97.0 62.1 85.9 24.2 118 2.6 478 

Oct ........ 0.35 0.9 33.6 10.6 92.5 51.1 83.0 22.2 80 1.8 409 

Nov .... . .. . 0.43 1.1 22.1 0.5 71.8 32.9 90.3 26.1 320 

Dec . .. . .... 0.71 1.8 20.2 -0.7 68.4 30.7 85.9 30.3 245 

Total or mean 7.73 19.6 31.2 7.8 88.1 46.1 73.9 22.8 121 2.7 482 
WATER USE BY SALTCEDARAS MEASURED BY THE WATER BUDGET METHOD 

Table I.- Meteorological data for project site near Buckeye, Ariz- Continued 

Month 

1965 

Precipitation 

(in.) (em) 

Jan 1.65 4.2 

Feb .. .. .. .. 1.54 3.9 

Mar .. . . . . . . 0.79 2.0 

Apr . . . . . . . . 1.54 3.9 

May 0.43 1.1 

June . . . . . . . 0.08 0.2 

July . . . . . . . . 0.35 0.9 

Aug .. .. . . .. 0.08 0.2 

Sept 0.35 0.9 

Oct .. .. . .. . 0.00 0.0 

Nov . . . . . . . . 0.67 1.7 

Dec .. .. .. .. 3.78 9.6 

Total or mean 10.83 28.6 

1966 

Jan ....... . Feb ....... . Mar . ... . . . . Apr . .. . . . . . May 

June .. . . . . . July ... . ... . Aug ....... . Sept 

Oct ... . ... . Nov . . . ... . . 

Dec . .. .... . 

0.55 

1.54 

0.16 

0.00 

trace 

0.00 

0.83 

0.51 

4.49 

0.28 

0.43 

0.00 

1.4 

3.9 

0.4 

0.0 

trace 

0.0 

2.1 

1.3 

11.4 

0.7 

1.1 

0.0 

Total or mean 8.79 22. 3 

1967 

Jan 0.24 0.6 

Feb .. .. .. .. 0.00 0.0 

Mar . . . . . . . . 0.24 0.6 

Apr . . . . . . . . 0.20 0.5 

May 0.00 0.0 

June . . . . . . . 0.16 0.4 

July . . . . . . . . 0.24 0.6 

Aug .. .. .. .. 0.20 0.5 

Total or mean 1.28 3.2 

Mean temperature 

('C) ('F) 

Max Min Max Min 

19.0 1.3 66.2 34.4 

21.2 -0.6 70.2 31.0 

23.1 2.0 73.6 35.6 

28.6 6.1 83.5 42.9 

34.1 7.6 93.4 45.6 

37.4 9.7 99.4 49.4 

42.3 20.3 108.2 68.5 

41.7 18.8 107.1 65.8 

40.9 12.6 105.7 54.6 

35.2 7.1 95.3 44.7 

26.6 3.8 79.8 38.8 

19.9 2.9 67.8 37.2 

30.8 7.6 87.5 45.7 

17.8 

18.3 

27.1 

32.2 

38.1 

41.6 

43.3 

39.6 

37.8 

31.2 

26.7 

21.2 

-2.3 64.1 

-1.1 64.9 

3.9 80.8 

5.4 89.9 

10.8 100.6 

14.3 106.8 

20.8 109.9 

22.2 103.2 

16.6 100.0 

8.1 88.1 

4.0 80.0 

-2.3 70.1 

27.8 

30.1 

39.0 

41.8 

51.4 

57.7 

69.5 

72.0 

61.8 

46.6 

39.2 

27.8 

31.2 8.4 88.2 47.1 

20.1 -3.7 68.1 25.3 

24.8 -2.0 76.6 28.4 

28.4 2.8 83.7 37.1 

27.4 3.4 81.4 38.1 

34.8 7.9 94.6 46.2 

39.6 14.2 103.3 57.5 

44.9 22.9 112.9 73.3 

43.1 23.3 109.5 74.0 

32.9 8.6 91.2 47.5 

Relative humidity 

(percent) 

Max Min 

91.5 28.4 

88.6 23.4 

86.4 22.7 

85.1 19.6 

71.5 18.1 

59.5 18.4 

66.1 21.1 

70.4 20.7 

78.3 21.5 

71.8 22.0 

83.2 29.2 

96.5 46.7 

79.1 24.3 

97.5 

97.6 

92.7 

81.5 

76.8 

71.7 

80.1 

83.8 

89.2 

93.8 

93.4 

86.9 

31.6 

28.3 

21.0 

29.9 

24.4 

23.9 

28.0 

24.8 

26.1 

23.7 

25.5 

27.6 

87.1 25.4 

79.6 23.2 

63.6 20.7 

74.4 24.5 

85.1 21.5 

72.4 21.7 

74.1 24.4 

89.5 27.5 

72.6 25.1 

76.4 23.6 

Wind speed Solar 

at 4 meters radiation 

(em/sec) (mph) Langleys/day 

156 3.5 

163 3.6 

162 3.6 

190 4.2 

220 4.9 

162 3.6 

171 3.8 

181 4.0 

149 3.3 

150 3.4 

113 2.5 

117 2.6 

161 3.6 

151 

170 

258 

172 

139 

166 

186 

131 

3.4 

3.8 

5.8 

3.8 

3.1 

3.7 

4.2 

2.9 

172 3.8 

281 6.3 

168 3.8 

164 3.7 

156 3.5 

187 4.2 

191 4.3 

267 

367 

433 

518 

592 

639 

577 

582 

465 

432 

260 

194 

444 

253 

360 

440 

575 

649 

677 

576 

527 

457 

378 

270 

255 

451 

285 

437 

512 

636 

696 

513 

E7 

TABLE 2.-Dates of flooding of the Waterman Wash 

Year Dates 1 Total 

1959 .. . J uly 18, 30; Aug. 2, 6, 11; Oct. 29; Dec. /3, 25, 3/ ' 9 

bare. Tank 11, however, was surrounded by a triple 

hedge of saltcedar about 3 m (10ft) wide . The purpose 

was to determine whether an "oasis-in-reverse" situation 

would have any effect on evaporation from bare soil. 1960 ... Mar. I; J uly 30; Aug. /0, 22. Levees built in November. 4 

1961 ... July 3, 23; Aug. 18, 20, 23; Sept. 13 . . 6 

1962 ... Jan. 24; Feb. 21 ; Aug. 19; Sept. 22. Levees strengthened in October . 

1963 ... Aug. 6, 22, 26, 30; Sept. 18; Oct. 25; Nov. 7 ....... .... . 

1964 . . . J an . 23; Mar. 2; July 24, 31; Aug. 4, 12, 13, 26; Sept. 13; 14; Oct. 17; Dec. 19. 

Levees repaired in November . . . ........... . . . ..... 12 

1965 ... Feb. 7; Mar. 11 ; July 18, 29; Sept. 4, 18; Nov. 23; Dec. 23 8 

1966 ... May 8; July 24; Aug. 9, 11; Sept. 16' . . . . . . . . . . . . . . . . . . . . . . . . .. .. .. 5 

1967 ... J uly 11; Sept. 43 • . . • • • • . • • • • • • • • . • • • . • • • • • • • • • • . • • • • • • . . • . • • • • .. • '2 

Total 

1

Dates on which the evapotranspirometer site was partly or totally inundated 

are italicized. 2

Mter July 1 only. 3

These were very large floods, of more than 3,000 m3/sec (10,000 cfs). 

' Before Sept. 5 only. 

... 57 

INSTRUMENTATION 

FLOA TLESS CONTROL SYSTEM 

The water level m the tanks was regulated by a 

floatless control system in which a valve automatically 

opened as soon as the water level fell below the lowest of 

two electrical contact points. Water then entered the 

tank until the level reached the upper contact point, 

which was about 5 mm (millimeters) (0.2 in.) above the 

lower point. A pen on an event recorder indicated the 

time and duration that the valve was open, and the 
E8 STUDIES OF EVAPOTRANSPIRATION 

FiGURE 8.- Man standing on surface of an evapotranspirometer newly planted to saltcedar; 

original vegetation in the background. 

r--------- - ---------------------------, I I 

I I 

I o I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

0 

Bare soil 

L----------------------------- ------ 0 0 0 

0 

0 50 100 FEET 

I I 'I I I I I I 

0 10 20 30 METERS 

N 

1 FIGURE 9.-Location of tanks and instruments. Tanks 1- 6 are inside a dense stand of saltcedar; 

tanks 7- 11 in an open area, 7 and 8 planted to saltcedar; tanks 9,10 and 11 are bare but 11 is 

surrounded by a hedge of saltcedar. P, R, and W, solid dots, are instrument masts. Circles 

indicate locations of access tubes for determining soil moisture outside the tanks. Tanks 1, 2, 

3, 4, and 6 were constructed in May and June of 1959, tank 5 in October, 1959, and tanks 

7- 11 in November and December of 1962. 

quantity of water (to the nearest tenth of a gallon) that 

entered the tank could be read from a standard water 

meter. Routinely, the meters were read every morning 

from Monday through Friday, and frequently, on Saturdays and Sundays. Occasionally (quite often in 1966 and 

1967) readings were taken at 2-hour intervals for periods 

of 72 hours or more. Figure 10 shows the instrumentation at 

one of the tanks. One pen on the recorder, a, indicates 

the temperature of the water; the other pen marks the 

time that the magnetic valve b is open and water via 

FIGUHElO.~Instrumentation for the water budget: a, on/off and water temperature recorder; b, 

magnetic valve; c, water meter; d, valve-control mechanism. 

meter centers the tank. The switching mechanism, d, 

opens and closes valve b. 

Figure 11 is a schematic cross section of a tank, showing contact points of the electrode rods at the water table 

and other features. 

ADVERSE COND ITIONS 

It is not surprising that the rigors of the climate often 

adversely affected the contol system. Temperatures as 

high as 50°C (122°F) combined with high humidity were 

not infrequent. Dust storms interfered with the electrical 

.--- _5'1 Recorder~ Well Stand Electrodes for 

= p1pe water-level point 

control Water level - r--

Rods 

(/) 

a: Water table w Float tw Contact 

~ : points 

' I I I I <t ; II ; I I 

I I I I 

I I II 

~ I I II 

I I II 

L....J II 

v __________ _I'~.!_o_.!:~~_p_pe -, 

9 METERS 

F'ICURE ll.- Schematic cross section of an evapotranspirometer. Access tubes for soil moisture 

determination, tensionmeters and thermocouples not shown . (Instruments and plumbing 

not to scale.) 
WATER USE BY SALTCEDAR AS MEASURED BY THE WATER BUDGET METHOD E9 

contacts. During the colder seasons, frost damage occurred in the plumbing, even though heat bands were installed to protect the pipes from bursting. The well water 

often contained a large amount of sand, and, owing to 

the comparatively high content of dissolved solids, the 

metal pipes and aluminum tubes and rods corroded, easily. 

As a result, valves stuck, water meters did not turn, 

and contacts failed. Various quantities of water which 

entered the tanks were sometimes unaccounted for, but 

the amount of water was always in excess of that used 

during such periods through evapotranspiration alone. 

The method which was devised to correct for these undesirable effects is discussed in the following section. 

WATER LEVEL 

In order to have a certain amount of control on 

malfunctioning which might escape attention, 11/z-in. 

(about 4-cm) well points were installed about 3 m (9 ft) 

from the stand pipe (fig. 11). Depth to water in the well 

points was measured whenever the water meters were 

read. Corrections for apparent excessive use could 

reasonably be made by plotting the actual water-level 

fluctuations and assuming a 40-percent porosity of the 

subsoil in the tanks. Effects of unintentional flooding 

were also corrected sometimes by pumping water out of 

the tanks until the intended depth to water table was 

reached again. 

Similar corrective measures were taken each time one 

or more of the evapotranspirometers was inundated by 

flooding of the Waterman Wash. In 1964 flooding occurred so frequently (see table 2) that only water-use 

data for short periods of controlled conditions could be 

considered reliable. · 

SOIL MOISTURE AND TEMPERATURE 

The tanks were equipped with aluminum access tubes, 

each with 2-in. (about 5-cm) outside diameters and 1%-

in. (about 4.5-cm) inside diameters, for measuring soil 

moisture by the neutron scattering method. (These 

tubes are not shown in fig. 11.) 

Most of the tanks had 8-inch (about 20-cm) plastic 

pipes which extended down to the water table. At times, 

water-level recorders were placed on these pipes. 

Batteries and tensiometers were installed in a few tanks 

in 1963 and in all tanks in 1965. The batteries made it 

possible to estimate moisture stress in the soil at 

different levels and also to estimate directions of soilmoisture flow towards or away from the land surface. 

Tanks 1 and 6 were equipped with heat-flow plates to 

determine the incoming and outgoing sensible heat; also, 

several sets of thermocouples were installed inside and 

outside these and other tanks to measure soil 

temperature at two or more levels. Finally, most of the 

tanks were equipped with a small rain gage to measure 

throughfall. 

VEGETATION 

TANK PLANTING 

Usually, phreatophytic vegetation along streambeds 

or around reservoirs and lakes is mapped by a set of standard survey procedures (Horton and others, 1964). These 

methods are very useful and effective in providing data 

which can be subjected to statistical and other analyses; 

they are unsatisfactory, however, for a small area such as 

an evapotranspirometer. The standard methods are not 

sensitive enough to elicit the possibly small differences 

that may exist between two tanks. In this experiment, 

the size of the tanks allowed detailed observation of the 

vegetation to be made conveniently by the procedures 

described below. 

The surface of each tank was divided into twenty-five 

squares. Each square supposedly contained: one 

originally planted crown cutting, growth resulting from 

the sprouting of pieces of stem and root (buried during 

the construction of the tanks), and growth from seeds 

that were blown or washed in after construction. 

Growths of the latter two types sometimes reached the 

top of the vegetation, especially in the few areas where 

the crown cuttings did not succeed in dominating the 

surroundings. The leaf area completely shading the 

ground was estimated by percentage of each square, and 

the area of the canopy for each bush or clump was 

similarly estimated and then converted into square 

meters. 

TRANSPIRATION VOLUME 

It has often been assumed that consumptive water use 

by phreatophytes is more or less related to the volume of 

transpiring foliage. A method was therefore sought that 

would give a measure of volume of transpiring foliage. 

The total volume of the vegetation taken as the product 

of the area of the canopy times the average height, 

sometimes corrected for crown depth, has been used as a 

parameter (Gatewood and others, 1950). 

This method has, at least for saltcedar, a decided disadvantage. The plants are considered to be a set of 

cylinders, and as a result, the actual transpiring volume 

is greatly over-estimated. Nonetheless, such data can be 

used to compare one area with another. A more natural 

geometric configuration is obtained, however, if one 

assumes the transpiring volume of the bush to be the upper half of an oblate spheroidal shell. In the tanks at the 

Buckeye Project, such a shell is about 50 em (about 20 

in.) thick. The horizontal radius is that of the mean 

radius of the more-or-less circular area shading the 

ground, and the vertical radius is about one-third of the 

total height of clump or bush. The volume of half an 

oblate spheroid is (27r/3) a2b in which a is the longer, in 

this case horizontal, radius, and b is the vertical or shorter 

·radius. The volume of the shell is then (27r/3) a 2 b-(27r/3) 

[(a-50)2(b-50)], and represents a transpiring volume 
E10 STUDIES OF EVAPOTRANSPIRATION 

based on a more realistic shape than that of cylinders. 

Volumes for 1965 computed by the method of Gatewood 

and others (1950) were between 150 and 250 percent 

larger than those obtained by the spheroidal shell 

method. 

The average height, the mean coverage in percent of 

the total area, and the total transpiring volume of the 

canopy are shown in table 3 for each tank surveyed in the 

fall of the years 1962-66. As can be seen, equilibrium 

seemed to have been reached by 1964. It appears that 

although there were differences in rate of growth (to be 

discussed later), these differences were offset in each 

tank by the dying of parts that were no longer exposed to 

sufficient sunlight. In addition to being a phreatophyte, 

saltcedar is obviously a heliophyte. 

TABLE 3.-Results of surveys of saltcedar, taken in the fall of each year, 

in the evapotranspirometers 

Mean Mean Total 

Date of height cover spheroidal 

survey (m)t density volume 

(percent) (m3) 

Tank 1 

1962 ...................... 2.40 80 74.0 

1963 ...................... 2.70 90 90.8 

1964 ...................... 3.15 100 98.7 

1965 ...................... 3.30 100 100.8 

1966 ...................... 3.25 99 99.5 

Tank 2 

1962 ...................... 2.50 80 81.2 

1963 ...................... 2.90 80 88.3 

1964 ...................... 2.90 90 96.4 

1965 ...................... 3.25 100 98.7 

1966 ...................... 3.30 95 96.9 

Tank 3 

1962 ...................... 2.40 80 78.4 

1963 ...................... 2.75 80 92.4 

1964 ...................... 3.00 100 110.3 

1965 ...................... 3.15 95 108.2 

1966 ...................... 3.05 100 113.1 

Tank 4 

1962 ...................... 2.30 75 75.4 

1963 ...................... 2.80 90 94.3 

1964 ...................... 3.05 105 104.8 

1965 ...................... 3.20 100 110.5 

1966 ...................... 3.15 105 112.8 

Tank 5 

1962 ...................... 2.50 70 82.3 

1963 ...................... 2.95 80 90.2 

1964 ...................... 3.20 100 107.6 

1965 ...................... 3.15 100 108.0 

1966 ...................... 3.15 100 111.0 

Tank 6 

1962 ...................... 2.40 75 79.7 

1963 ...................... 2.80 75 93.8 

1964 ...................... 3.00 105 101.2 

1965 ...................... 3.00 95 105.2 

1966 ...................... 3.10 100 100.5 

'To nearest 5 em. 

Finally, table 3 shows that there are considerable 

differences between the observed variables in the tanks 

(actually more than 10 percent), but they are not 

statistically significant. No attempt, therefore, has been 

made to relate water use to these variables. Moreover, 

the relationship between transpiring volume and water 

use, for example, is not so simple as is often assumed. 

This will be discussed under "Vegetation Growth and 

Development''. 

WATER USE, LARGE TANKS 

1961-63: DEPTH TO WATER 

During 1961, 1962, and 1963, the water levels in tanks 

3 and 5 were maintained at 1.5 m (5 ft) below the land 

surface; in tanks 4 and 1, at 2.1 m (7ft); and in tanks 2 

and 6, at 2.7 m (9ft). The water use by months is given 

in table 4. These 3 years are tabulated separately 

because the treatment did not change during this time; 

after 1964, some of the tanks were flushed to reduce the 

salinity of the ground water, and in 1966 other changes 

were made as explained below. 

Table 5 summarizes the total use per tank per 

year for 1961, 1962, and 1963 and includes the results of 

an analysis of variance (Fisher, 1944; Fisher and Yates, 

1943). (See "Appendix: Analysis of Variance" for explanation of least significant difference.) The analysis of 

variance, as can be seen from the table, shows a significant effect of interaction between years and depth to 

water. The table gives an F-value which is significant at 

the 1-percent level for effects of depth to water. Although 

some tanks show an increase in water use between 1961 

and 1963, such increases are not statistically significant 

and are completely overshadowed by the depth-to-water 

effect. Data from tanks 2 and 6 show a gradual decrease 

in water use probably due to an increase in salinity of the 

ground water. 

Unfortunately only a few measurements of specific 

conductance were made prior to 1963, but it may be 

assumed that the conductance in all the tanks was the 

same. Table 6 shows that the conductance of the ground 

water in tanks 2 and 6 had increased much more than in 

the other tanks. The low water use in tanks 2 and 6 may 

have been caused by high salinity of the ground water 

rather than depth to ground water. The difference, 

however, in water use between tanks 3 and 5, with a 

water table depth at 1.5 m (5 ft), and 1 and 4, with a 

water table depth at 2.1 m (7ft), must have been caused 

by the deeper water table in tanks 1 and 4 because the 

specific conductance of the ground water in all four was 

practically the same. Further evidence of the effect of 

salinity of soil moisture will be discussed in "1965: 

Salinity. " 
WATER USE BY SAL TCEDAR AS MEASURED BY THE WATER BUDGET METHOD 

TABLE 4.-Monthly water use in evapotranspirometers by saltcedar, excluding rainfall 

Tank No .... 

Depth to 

water (ern). . . 

Date 

1961 

Crn 

Jan . . . . . . . . 2.0 

Feb . . . . . . . . 3.6 

Mar........ 5.6 

Apr . . . . . . . . 16.8 

May . . . . . . . 26.0 

June . . . . . . . 33.4 

July........ 37.3 

Aug........ 30.6 

Sept . . . . . . . 22.5 

Oct . . . . . . . . 12.4 

Nov........ 5.8 

Dec . . . . . . . . 2.9 

Total 198.9 

1962 

Jan . . . . . . . . 1.7 

Feb . . . . . . . . 2.6 

Mar........ 5.4 

Apr . . . . . . . . 23.3 

May . . . . . . . 40.0 

June . . . . . . . 42.3 

July . . . . . . 24.3 

Aug........ 22.0 

Sept . . . . . . . 20.6 

Oct . . . . . . . . 16.0 

Nov........ 14.3 

Dec . . . . . . . . 5.8 

Total 218.3 

1963 

Jan . . . . . . . . 0.8 

Feb . . . . . . . . 3.5 

Mar........ 5.0 

Apr . . . . . . . . 16.4 

May . .. . .. . 37.3 

June . . . . . . . 42.5 

July........ 41.8 

Aug . . . . . . . . 24.4 

Sept . . . . . . . 27.3 

Oct . . . .. . .. 19.1 

Nov........ 7.5 

Dec . . . . . . . . 0.9 

Total 226.5 

150 

ln. 

0."79 

1.42 

2.20 

6.61 

10.23 

13.15 

14.68 

12.05 

8.86 

4.88 

2.28 

1.14 

78.29 

0.67 

1.02 

2.12 

9.17 

15.75 

16.65 

9.57 

8.66 

8.11 

6.30 

5.63 

2.28 

85.93 

0.31 

1.38 

1.97 

6.46 

14.68 

16.73 

16.46 

9.61 

10.75 

7.52 

2.95 

0.35 

89.17 

Crn 

2.1 

4.1 

6.0 

16.4 

22.8 

27.3 

39.5 

33.9 

21·.5 

10.2 

9.4 

6.3 

199.5 

2.9 

2.6 

4.1 

22.0 

40.4 

45.0 

25.6 

22.4 

20.7 

17.9 

14.2 

3.9 

221.7 

3.7 

4.2 

5.7 

16.8 

36.8 

43.2 

36.5 

23.9 

25.3 

20.8 

10.6 

1.2 

228.7 

150 

ln. 

0.83 

1.61 

2.36 

6.46 

8.98 

10.75 

15.55 

13.35 

8.46 

4.01 

3.70 

2.48 

78.54 

1.14 

1.02 

1.61 

8.66 

15.90 

17.71 

10.08 

8.82 

8.15 

7.05 

5.59 

1.53 

87.26 

1.46 

1.65 

2.24 

6.61 

14.49 

17.01 

14.37 

9.41 

9.96 

8.19 

4.17 

0.47 

90.03 

4 

210 

Crn ln. 

1.5 0.59 

3.6 1.42 

2.8 1.10 

7.7 3.03 

14.9 5.86 

21.6 8.50 

27.8 10.94 

21.1 8.31 

18.5 7.28 

12.3 4.84 

7.9 3.11 

1.4 0.55 

141.1 55.53 

0.8 0.31 

1.1 0.43 

2.5 0.98 

11.2 4.41 

25.9 10.20 

33.1 13.03 

16.7 6.57 

12.7 5.00 

11.7 4.61 

10.5 4.13 

7.3 2.87 

3.5_ 1.38 

137.0 53.92 

1.0 

1.4 

2.1 

7.9 

24.9 

36.2 

28.2 

16.4 

17.9 

14.5 

6.1 

2.9 

159.5 

0.39 

0.55 

0.82 

3.11 

9.80 

14.25 

11.10 

6.46 

7.05 

5.71 

2.40 

1.14 

62.78 

210 

Crn In. 

1.2 0.47 

1.8 0.71 

5.0 1.97 

8.2 3.22 

21.6 8.50 

27.1 10.67 

30.3 11.93 

17.8 7.01 

16.8 6.61 

11.0 4.33 

3.7 1.46 

0.9 0.35 

145.4 57.23 

0.0 0.00 

1.1 0.43 

2.5 0.98 

12.0 4.72 

29.5 11.57 

34.2 13.46 

17.2 6.77 

15.3 6.02 

12.7 5.00 

11.4 4.49 

9.9 3.90 

4.5 1.77 

150.3 59.11 

1.0 

1.2 

2.7 

9.8 

27.4 

35.8 

32.3 

16.3 

17.9 

11.5 

5.0 

2.4 

163.3 

0.39 

0.47 

1.06 

3.86 

10.79 

14.09 

12.71 

6.42 

7.05 

4.53 

1.97 

0.94 

64.28 

Crn 

0.4 

1.8 

3.8 

6.3 

16.2 

18.1 

27.2 

19.3 

8.7 

2.9 

0.0 

0.0 

104.7 

0.0 

1.1 

3.4 

9.0 

19.1 

20.5 

10.6 

7.8 

7.9 

7.4 

4.7 

2.3 

93.8 

0.0 

0.9 

2.6 

5.3 

13.5 

16.9 

13.6 

8.6 

9.5 

9.1 

4.1 

2.4 

86.5 

270 

ln. 

0.16 

0.71 

1.50 

2.48 

6.38 

7.12 

10.71 

7.60 

3.42 

1.14 

0.00 

0.00 

41.22 

0.00 

0.43 

1.34 

3.54 

7.52 

8.07 

4.17 

3.07 

3.11 

2.91 

1.85 

0.90 

36.91 

0.00 

0.35 

1.02 

2.09 

5.31 

6.65 

5.35 

3.38 

3.74 

3.58 

1.61 

0.94 

34.02 

Cm 

0.4 

1.8 

1.4 

7.6 

15.8 

21.2 

27.2 

21.3 

6.8 

4.5 

0.0 

0.0 

108.0 

0.0 

1.1 

3.4 

9.0 

15.2 

21.7 

10.1 

8.2 

8.8 

8.1 

5.8 

2.8 

94.2 

0.8 

1.8 

2.7 

6.1 

14.8 

16.9 

12.7 

7.6 

10.3 

10.8 

5.5 

2.4 

92.4 

270 

In. 

0.16 

0.71 

0.55 

2.99 

6.22 

8.35 

10.71 

8.38 

2.68 

1.77 

0.00 

0.00 

42.52 

0.00 

0.43 

1.34 

3.54 

5.98 

8.54 

3.98 

3.23 

3.46 

3.19 

2.28 

1.10 

37.07 

0.31 

0.71 

1.06 

2.40 

5.83 

6.65 

5.00 

2.99 

4.05 

4.25 

2.16 

0.94 

36.35 

Ell 

1964: FLOODS 

0 bviously something had to be done to improve the 

quality of the ground water, and 1n January and 

February of 1964 all tanks were flushed. Therefore, the 

water-level controls were disconnected and water was 

forced through the stand pipe and the laterals at the bottom of the tank, thus driving water from the bottom to 

the top of the tank. Specific conductance (mmho em -

1 at 

25°C) of the effluent was measured daily, and 

backwashing was continued for 5 to 10 days until the 

conductance was about equal to that of the well water. 

This treatment had two secondary effects which were 

foreseen but about which little could be done. First, the 

water content of the soil above the ground-water level 

was greatly increased, and it was expected that it would 

take considerable time before the water content in the 

soil would return to the 1963 levels, even though excess 

water was pumped out. The second effect, a result of the 

frequent flooding prior to the building of the levees, was 

that additional soil had been dumped on the 

evapotranspirometer site, and in many places the soil 

was higher than the plastic lining. As long as the top 
E12 STUDIES OF EVAPOTRANSPIRATION 

TABLE 5.-Yearly water use in evapotranspirometers, exluding rainfall tanks saturated with large quantities of freshwater. The 

Depth to Mean ground water .. m .. 1.5 2.1 2.7 of .. ft .. 5 7 9 all 

Tank No ..... 4 tanks 

1961: 

Cm ...... 198.9 199.5 141.1 145.4 104.7 108.0 149.6 In ........ 78.29 78.54 55.53 57.23 41.22 42.52 58.89 1962: 

Cm ...... 218.3 221.7 137.0 150.3 93.8 94.2 152.6 In ........ 85.93 87.26 53.92 59.11 36.91 37.07 60.03 1963: 

Cm ...... 226.5 228.7 159.5 163.3 86.5 92.4 159.5 In ........ 89.17 90.03 62.78 64.28 34.02 36.35 62.77 

Mean of 

3 years: 

Cm ...... 213.6 216.6 145.9 153.0 95.0 98.2 153.9 

In ........ 83.36 85.28 57.41 60.21 37.40 38.65 60.38 

Analysis of variance 

Source of Sum of Degrees of Mean FI 

variance squares freedom square 

Years ......... 308.91 2 154.5 9.6 

Depth to water 42,660.78 2 21,330.4 **1,324.9 

Interaction ..... 1,282.81 4 320.7 *19.9 

Error .......... 144.79 9 16.1 ......... 

Total .... 44,397.29 17 ......... 

1

F values: significant differences indicated by • at 5-percent level, ** at !-percent level. 

Least significant difference at !-percent level is 25.0 em. 

TABLE 6.-Quality of ground water in evapotranspirometers 

[In 1960 only three tanks were sampled; in 1963 all tanks were sampled but in three tanks 

samples were taken from two locations: a) where water enters the tanks, and b) where the 

ground water is more or less stagnant and less diluted with incoming water. Agency making 

analysis: U.S. Geological Sur'-'¥ Qualitv of Water Laboratory, Albuquerque, N.Mex.] 

Specific conductance ~oJlUin plus potassium Chlorine (mmho cm· 1 at 25°C) (mg/1) (mg/1) 

Tank 

No. May 11, May 6, 1963 May 11, May 6, 1963 May May 6, 1963 11, 1960 b 1960 b 1960 b 

1 ....... 7.2 ....... 1,190 2,140 2 ....... 5.9 7.4 12.6 730 1,120 1,820 1,580 1,950 3,980 

3 ....... 7.3 ....... 1,130 1,990 4 ....... 7.6 ....... 1,200 2,110 5 ....... 6.5 7.4 7.0 750 1,130 1,190 1,710 1,960 1,960 6 ....... 6.2 7.7 31.0 740 1,150 5,180 1,640 2,040 10,800 

layers of the soil were dry, this did not matter. However, 

when tops of the tanks and also the surroundings were 

saturated, root growth from trees inside the tanks could 

be expected to reach over the tank boundaries. Also, 

roots from surrounding trees might penetrate the tanks. 

In March 1964, trenches were dug to the plastic lining 

wherever necessary to prevent the roots from 

overreaching. 

As expected, water use increased enormously in 1964, 

not only due to the lowering of the salinity but also 

because of the high evaporation rate from the soil surfaces of the saturated tanks. In addition, the area suffered three floods (see table 2) which not only partially 

refilled the trenches, but also kept the topsoils of the 

water-use data for short periods could be used for comparison between tanks and for correlation studies with 

climatological phenomena. However, the monthly and 

yearly totals were so· heavily influenced by these 

catastrophes that any attempt to compensate for them 

was thought to be futile and would result in completely 

unreliable data. For these reasons, data from 1964 are 

not tabulated in this report. 

1965: SALINITY 

After a sturdy dike was built in November 1964 to 

keep the Waterman Wash floods out of the study area, 

attention was once more focused on the water use by 

saltcedar. As was pointed out, by the end of 1963 it 

became apparent that the decrease in water use in tanks 

2 and 6 might have been due to deterioration of the 

ground-water quality in those tanks. The vigorous 

growth and the tremendous increase in water use following the flushing in 1964 provided more evidence. 

To make comparisons, one of each of the pairs of tanks 

with equal depth to water was flushed and the other was 

not. In 1964, when the flushing was finished, the excess 

water was simply pumped out until the water level had 

reached the original depth; whereas in 1965 the water 

table was lowered as far as the pump could draw it down. 

The soil moisture was then allowed to drain and the tank 

was again pumped out. This was repeated until no more 

water collected in the stand pipe. This procedure 

reduced the soil moisture above the capillary fringe, and 

the water content became more comparable with that in 

the untreated tanks. After this drying process, ground 

water was allowed to rise to its intended level. 

Effectiveness of this treatment is shown in figure 12, 

where the percentages of soil moisture are plotted 

against depth for each of the six tanks. While the higher 

moisture content resulting from a higher water table is 

quite evident, there is no significant difference of 

moisture content between flushed and unflushed tanks. 

It seems, therefore, reasonable to assume that the 

differences in water use so clearly shown in table 7 are 

due to differences in salinity and depth to ground water 

and do not result from differences in soil moisture above 

the capillary fringe. Figure 13 summarizes the data from 

table 7 (third section). It is obvious that the differences 

between flushed and unflushed tanks significantly 

overshadow the influence of depth to ground water on 

the rate of water use. 

Another study provided corroborative material. As 

mentioned previously, two of the small tanks were 

planted to saltcedar in 1963. About the same time, a cotton farmer to the south of the project area drilled a new 

well in the vicinity of the Waterman Wash. Results of 

the chemical analysis of samples from this well water 

and of the project water are presented in table 8. Clearly, 
WATER USE BY SALTCEDAR AS MEASURED BY THE WATER BUDGET METHOD E13 

(/) 0 .5 

a: 

UJ 

rUJ 

::;;; 

z 1.0 

UJ 

u 

<( 

lL 

a: 1.5 

:::l 

(/) 

s: 

0 

~ 2.0 co 

I 

rc.. 

UJ 

0 2.5 

Water. levels bel ow land surfaces 

\ 

Numbers are tank numbers \ \ 

3and5: 1.5m(5ft) 

1 and 4: 2.1 m (7ft) 

2and6: 2 .7m(9ft) 

2, 3, 4 flushed to reduce the -......_, 

salinity of the ground ......._ 

w ater 

1, 5, 6 not treated 

·0L_--~ __ _l ____ L_ __ ~--~----3L----L---~--~--~50 

MOISTURE, IN PERCENT BY VOLUME 

FIGURE 12.-Soil moisture by volume in the six large tanks on a typical summer day in 196.1. 

(/) 

a: TANK NUMBER ' UJ 

r- "'"' UJ 4 , 1 2,6 .,.- ::;;; f- E XP LANATIOf 

i= r- I Least z a: UJ <( -I significant 

u UJ difference 

z >- 200 I- DFiushed - a: Jan. ,1965 ·w 

~c.. I Not :::l flushed 100 I- •····· a: [J±! Means UJ •: .. r-

<( . ,. s: 0 2.1 2.7 Means LO'""";t'-: 

~"'"' DEPTH TO GROUND WATER, I N METt:RS 

FiGURE 13.-Total water use during 1965 in six evapotranspirometers (tanks) showing the effect 

of depth to water and flushing of saline ground water. The bar denotes the least significant 

difference at the 5 percent level. Tanks 3, 4, and 2 were flushed in January 1965. The three 

columns to the right show the mean water use as a function of depth to ground water. 

water from the farmer's well is of far better quality than 

the water obtained at the project site. A (3,750-l (liter)) 

(1,000-gal (gallon)) container was installed near tank 7 

so that water from the new well could be stored and 

delivered either to tank 7 or to tank 8 or both. From June 

1963 through March 1964, tank 7 was provided with 

water from the new well while tank 8 was fed with project 

water. 

Figure 14 shows that during this time, the saltcedar 

grew much more vigorously in tank 7 than in tank 8. It is 

not surprising that water use was also higher in tank 7. 

During the period mentioned, tank 7 used 264 em (104 

in.) in contrast to 170 em (67 in.) for tank 8. It should be 

FIGURE 14.-Evapotranspirometer 7, top, received better quality water between June 1963 and 

February 1964 (when photograph was taken). The plants in tank 8, bottom, grew on project 

water. 

noted that the vegetation in these two tanks stood 

isolated, and actual water use obviously cannot be compared with that of the other tanks. Nonetheless, because 

such isolated clumps do occur in nature, some further 

results are discussed under "Water Use, Small Tanks." 

1966: DENSITY OF STAND 

Gatewood and others (1950) developed a method to 

compute estimated water use based on the assumption 

that water loss is directly proportional to the volume of 

green vegetative material growing on the area. The 

method implies that the denser the vegetation, the more 

voluminous is the water loss. Although objections 
E14 STUDIES OF EVAPOTRANSPIRATION 

TABLE 7.- Water use, excluding rainfall, in evapotranspirometers during 1965 

Tank No. 

Depth to 

water . . .m. 1.5 1.5 2.1 2.1 2.7 2.7 

ft . 5 5 7 7 9 9 

Flushed . Yes No Yes No Yes No 

Month Cm In. Cm In. Cm ln. Cm ln. Cm ln. Crn In. 

Jan . .... ..... . 0 0 0 0 0 0 0 0 0 0 0 0 

Feb ...... . . . . . 1.0 .39 .4 .16 .4 .16 0 0 0 0 0 0 

Mar ... .. .. .... 9.6 3.78 4.4 1.73 4.1 1.61 2.7 1.06 0 0 2.7 1.06 

Apr .. . . . . . .... 27.1 10.67 16.8 6.61 21.3 8.39 6.9 2.72 18.9 7.44 3.7 1.46 

May .. .. ...... 52.1 20.51 32.0 12.60 48.0 18.90 27.3 10.75 43.0 16.93 16.4 6.46 

June . . ...... .. 63.6 25 .04 42.9 16.89 60.7 23.90 36.8 14.49 52.6 20.71 21.2 8.35 

July .. . . ....... 45.8 18.03 33.0 12.99 37.1 14.61 28.6 11.26 34.1 13.43 16.2 6.38 

Aug . . . . .. ..... 37.5 14.76 30.6 12.05 29.9 11.77 20.2 7.95 29.2 11.50 14.4 5.67 

Sept ...... .. .. 30.5 12.01 26.8 10.55 24.9 9.80 18.6 7.32 24.2 9.53 12.4 4.88 

Oct 00 ••• •••• • • 27.4 10.79 25.1 9.88 21.7 8.54 17.7 6.97 24.4 9.61 10.6 4.17 

Nov . .. . . .. ... . 15.0 5.91 12.6 4.96 10.4 4.09 7.8 3.07 9.7 3.82 5.8 2.28 

Dec .. . . . . . .... 1.3 .51 1.1 .43 1.4 .55 .9 .35 1.7 .67 2.1 .83 

Total . .. . 310.8 122.36 225.8 88.90 259.8 102.28 167.5 65.94 238.0 93.70 105.6 41.57 

Mean of 

tanks Nos 3 and 5 4 and I 2 and 6 3, 4, and 2 5, I, and 6 

Depth to 

water (m) 1.5 2.1 2.7 Flushed Not flushed 

Month Cm ln. Crn In. Crn . In. Cm In. Cm ln. 

Jan ··· ·· ·· · · .. 0 0 0 0 0 0 0 0 0 0 

Feb . .. . . ...... .7 .28 .2 .08 0 0 .5 .20 .2 .08 

Mar .. . ... . .. . . 7.0 2.76 3.4 1.34 1.4 .55 4.6 1.81 3.3 1.30 

Apr ....... . ... 22.0 8.66 14.1 5.55 11.3 4.45 22.4 8.82 9.1 3.58 

May .... ...... 42.0 16.54 37.6 14.80 29.7 11.69 47.7 18.78 25.2 9.92 

June ..... . . . .. 53.3 20.98 48.7 19.17 36.9 14.53 59.0 23.23 33.6 13.23 

July .......... . 39.4 15.51 32.9 12.96 25.1 9.88 39.0 15.35 25.9 10.20 

Aug . .. . .. . . . . . 34.0 13.39 25.1 9.88 21.8 8.58 32.2 12.68 21.8 8.58 

Sept . .. . .. .... 28.7 11.30 21.7 8.54 18.3 7.20 26.5 10.43 19.3 7.60 

Oct ... . . .... .. 26.2 10.31 19.7 7.76 17.5 6.89 24.5 9.65 17.8 7.01 

Nov ... . ... ... . 13.8 5.43 9.1 3.58 7.7 3.03 11.7 4.61 8.7 3.43 

Dec ... . . . ... .. 1.2 .47 1.1 .43 1.9 .75 1.4 .55 1.4 .55 

Total .. . . 268.3 105.63 213.7 84.13 171.8 67.64 269.6 106.14 166.3 65.47 

Depth to water (rn ) 1.5 2.1 2.7 Mean Analysis of variance 1 

Source of Sum of Degrees of Mean 'F Flushing Crn ln. Cm In. Crn In. Crn ln. variance squares freedom square 

Flushed .. .... 310.8 122.36 259.8 102.28 238.0 93.70 269.6 106.11 Depth to water 9,366.86 2 4,683.43 14.38 

Not f1ushed ... 225.8 88.90 167.5 65.94 105.6 41.57 166.3 65.47 Flushed vs. not flushed . . . 15,985.68 1 15,985.68 *49.08 

Mean . . 268.3 105.63 213.7 84.11 171.8 67.64 Error . ... . ... . . 651.35 2 325.68 

Total .... 26,003.89 5 . . . . . . . . . 

1

The analysis of variance indicates that no interaction between depth to water and flushing could be taken into account because of lack of replication 

F value: ~indicates significant difference at the 5-percent level. 

against this method have been cited (Coleman, 1953), 

Horton, Robinson, and McDonald (1964) stated, "No 

better method is yet known." 

The Buckeye Project provided opportunity to shed 

some qualitative light on the relationship between density of stand and water use. It is, after all, reasonable to 

assume that in fairly open stands wind can penetrate 

deeper into the vegetation, and, at least on favorable occasions, the wind may take away moisture, thus allowing 

"space" for additional evaporation and transpiration. 

For this reason the following experiment was conducted 

in 1966. 

After tanks 2, 3, and 4 had again been flushed, the 

water level in all tanks was brought to 2.1 m (7ft) and in 
WATER USE BY SALTCEDAR AS MEASURED BY THE WATER BUDGET METHOD E15 

TABLE B.-Analysis of project water and better-quality water from a 

new well south of the project site. 

(Agency making analysis: U.S . Geological Survey Quality of Water Laboratory, Albuquerque, 

N. Mex., May 1963. Data in mg/l except when otherwise designated] 

Analysis factors 

Residue at 180°C .. .... . . . . . .. . 

Hardness as CaC03 • • • .... .•••• 

Percent Na ............ ... . .. . Sodium adsorption ratio 

pH ...................... .... . Specific conductance 

(mmho em·' at 25° C) ...... . . 

Si02 ... . . .. . .... ............ . Ca ...... . .. .... . . ........... . Mg .. ... ........... ... .... ... . Na+K ................ .... .. . HC03 ....................... . 

so,··········· ······· ········ Cl ...... .. .. .. ..... ... . ..... . F .......... ........... .. . ... . 

NO, .. ... . .. ... ... . . . . ... ... . 

Project water 

4,760 

1,490 

63 

13 

6.8 

7.57 

31 

396 

122 

1,150 

405 

836 

1,980 

1.3 

1.0 

Better 

quality water 

2,2150 

650 

63 

8.8 

7.3 

3.64 

32 

182 

48 

515 

234 

256 

915 

2.5 

17 

March of 1966 the vegetation in tanks 1 and 4 was thinned 

out to approximately 50 percent of the original density. 

This was accomplished by simply cutting half of the 

branches in. each clump, taking the diameter of the 

branches into consideration. All vegetation in tanks 3 

and 5 was shorn off at knee height. Figure 15 illustrates 

the general appearance of three of the six tanks, and 

figure 16 shows the combined results of the two 

treatments. 

As expected, the tanks that had been flushed (2, 3, 

and 4) used more water than those that were not treated. 

The water use in the shorn tanks was much less than in 

the vegetated tanks, but within two months, use increased sharply with regrowth of the vegetation. The 

shorn stumps, still having their root systems, sprouted 

very fast, especially in tank 3. In mid-July tanks 3 and 5 

were again shorn and water use dropped for the second 

time. 

(f) 

a: 

w 

.... 

w 

2 

.... 

z 

w 

u 

~ 

50 

Vegetation in tanks 

3 and 5 cut during 

March and July 

4 and 1 thinned 

2 and 6 control 

F M A M 

5 

A s 0 N 0 

MONTH 

FIGURE 16.-Accumulated water use in six evapotranspirometers (numbers shown at right on 

curves) during 1966 showing the effects of density of stand and salinity of artificially main· 

tained ground water. Dashed curves represent tanks flushed in Jan. 1966; solid curves represent tanks not flushed. Numbers in parentheses give the specific conductance (mmho cm-1 

at 25°C) of the soil moisture extract in the ro(Jt zones as determined from samples taken in 

August. 

Figure 16 also shows the comparatively small 

difference between the quantity of the water used by the 

thinned-out vegetation and that used in the control 

tanks. Of course, the vegetation in the thinned-out tanks 

did not remain at the original 50 percent density. 

Nonetheless, even in September the thinned-out stands 

were still much more open than the controls. The 

numbers in parentheses in figure 16 are the specific conductances of the soil moisture saturation extract taken 

in August and explain the differences in water use due to 

salinity. Conductance in tank 3 remains much lower 

than in tanks 2 and 4, probably because much less water 

FIGU"E 15.-Three of the six evapotranspirometers after treatment of vegetation in March 1966. Tank 3 (left), all vegetation above knee height removed; 

tank 1 (center) thinned out 50 percent of its original density; tank 2 (right), no treatment. 
E16 STUDIES OF EVAPOTRANSPIRATION 

was used and, therefore, much less salt could accumulate in that tank. 

Table 9 presents the water use data for the period of 

most vigorous growth. It can be seen that thinning did 

not produce significant increases in water use but 

flushing resulted in great differences between shorn, 

thinned-out, and control tanks. 

TABLE 9.- Water use in six evapotranspirometers between Aprill and 

September 1, 1966 

[Least significant difference between values at the 5-percent level is 48.7 ern (19.17 in.)] 

Vegetation Tank Flushed Tank Nol Flushed Mean 

treatment No. Cm In. No. Cm In. Cm In. 

Shorn 3 108.0 42.52 5 35.6 14.01 71.8 28.27 

Thinned . . ... 4 180.4 71.02 1 85.3 33.58 132.9 52.30 

Control . . . ... 2 206.2 81.18 6 101.4 35.92 153.8 60.55 

Mean .. . . 164.9 64.92 74.1 29.17 

1967: FINALE 

No further manipulation of the tanks, either in terms 

of flushing or cutting and thinning, took place in 1967. 

The vegetation was allowed to grow and the inevitable 

salt accumulation took place, as will be shown. Table 10 

presents the total water use during 1967. A comparison 

with table 9 shows that an equalizing effect has taken 

place. The analysis of variance gives a least significant 

difference larger than all of the differences in water use. 

As during 1966, all six tanks had the water level at the 

same depth and there remained only slight differences in 

salinity due to previous flushings and possibly due to 

slight differences in density of stand. 

TABLE 10.-Water use in six evapotranspirometers between April1 and 

September 1, 1967 

[Least significant difference between values at the 5-percent level is 36.0 em (14.17 in.)] 

Not 

Vegetation Tank Flushed in Tank flushed in treatment No. 1965 and 1966 No. 1965 and 1966 Mean of 1966 Cm In. Cm In. Cm ln. 

Shorn 3 96.0 37.80 5 60.4 23.78 78.2 30.79 

Thinned ..... 4 112.6 44.33 1 76.2 30.00 94.4 37.17 

Control ...... 2 109.3 43.03 6 93.8 36.93 101.6 39.98 

Mean ... . 106.0 41.73 ... 76.8 30.24 . ... . . .. . 

As will be shown later, growth and development of the 

vegetation in the thinned or shorn tanks was much 

greater than in the control tanks, and this accounts for a 

distinct trend to equalization of the stands. In figure 17, 

the accumulated water-use data for the six tanks are 

plotted, but only for the growing season up to September 

when the project was terminated. Conductances (ECs) 

(f) 

~ 120.-------,--------,-------.--------,-------, w 

1-

w 

:2 

1-

z 

w 

u 

z 

w 

(f) 

::> 

~ 

w 

1-

<( 

s: 

0 

w 

1-

<( 

_J 

::> 

:2 

::> 

u 

u 

<( 

80 

APR IL MAY JUNE 

1967 

JULY AUGUST 

FIGURE 17.- Accumulated water use in tanks 1 to 6 between April 1 and September 1, 1967. 

Dashed curves represent tanks flushed in .Jan. 1966; solid curves represent tanks not flushed. 

See figure 16 for tank treatments. Tank numbers indicated on curves; numbers in 

parentheses indicate conductance of soil moisture in August 1967 (mmho cm· 1 at 25°C). 

observed in August 1967 are shown in parentheses. Comparison with the data of figure 16 shows that salinity increased very fast, especially in the tanks that used the 

greatest amount of water in 1966 and 1967. The rapid increase of water use in tanks 3 and 5 (shorn twice in 1966) 

is also worthy of notice. 

The last flood of the project history occurred on 

September 4, which made it virtually impossible to work 

in the project area during the rest of the month. In October dismantling of the equipment began, and in 

November some of the tanks were partially excavated to 

determine the condition of the linings. It appeared that 

the plastic and the rubber had endured well, except 

that occasionally small holes made by gophers or mice 

were encountered in the top 30 em (12 in.). However, 

since these holes were well above the water table and in 

the dry region of the soil blocks, effects on water use were 

suspected to be negligible. 

Below the level of the water table a fine network of 

roots clung to the outside of the plastic lining. The insides of the tanks below and slightly above the water 

table were considerably cooler than the dry soil at the 

same level outside the plastic. Even though the soil outside the tank was very dry at these depths there was 

enough vapor to condense on the lining. Thus, roots coming in contact with this water developed into the fine 

network. 

SOIL MOISTURE AND SOIL-MOISTURE 

FLUCTUATIONS 

METHOD OF MEASUREMENT 

In reports on water use by vegetation in lysimeters or 

evapotranspirometers, the increase or decrease of water 
WATER USE BY SALTCEDAR AS MEASURED BY THEW ATER BUDGET METHOD E17 

during a period is often taken into account (for instance, 

Gatewood and others, 1950). If from one month to the 

next, there is a rise in the water table, the increase in 

content is subtracted from the amount of water 

measured in the tank, and the actual water use by the 

vegetation is obtained. The water levels in the project 

tanks varied little, usually less than 1.5 em (0.05 ft) from 

one month to the next, and there was not a discernible 

seasonal fluctuation. This is not surprising in view of the 

mechanism by which the water levels were controlled. 

(The daily fluctuations, to be discussed later, have no 

measurable effect on the monthly water use.) 

It was surprising that at times soil moisture contents 

above the water level varied considerably. Fairly large 

differences in water content from month to month occurred or, 8S explained below, seemed to have occurred 

in some of the tanks. It appears, however, that these 

changes may have been due to causes other than water 

use or lack of use by the vegetation, since the increases 

and decreases were not consistent. Table 11 shows examples of changes in soil moisture content expressed as 

centimeter depth of water and as the percentages of 

measured water use during the indicated period. For instance, from May 16 to June 24, 1963, there is an increase 

in water content of 4.5 percent in tank 4, but in tanks 1, 

2, and 6, a decrease is measured. From May 3 to June 13, 

1966, there is a decrease in tanks 2 and 3 whereas there is 

an increase in tanks 1 and 4. 

TABLE 11.-Change in soil moisture content 

[..l =change expressed as centimeter depth of water, and percent= change expressed as percentage of measured use of water during indicated periods; minus symbol indicates a decrease] 

Tank No .... 

..l Percent ..l Percent ..l Percent ..l Percent ..l Percent ..l Percent 

1963 

May 16-June 24 ... ... -1.0 2.2 -2.8 13.5 No data. 1.9 4.5 No data . -0.8 3.8 

1965 

July 21- Aug 20 1.4 4.3 1.4 3.3 5.2 9.4 0.9 2.0 0.4 1.1 2.6 7.0 

1966 

May 3-June 13 2.5 9.1 -3.9 5.4 -2.2 7.3 0.7 1.1 3.9 1

50.0 14.0 1

48.0 

1

This increase resulted when a sprinkler hose burst between tanks 5 and 6 in early June. 

These soil-moisture measurements were made by the 

neutron scattering method with instruments calibrated 

at the project (Task Force, 1964). Figure 18 shows the instrument calibration data. The correlation coefficient is, 

as the figure shows, highly significant, yet a considerable 

scattering i~ possible. A good example of what can 

happen is given in figure 19 where a few soil-moisture 

measurements by the neutron scattering method are 

plotted against depth. 

Soil-moisture readings obtained in August and October of 1963 were 3-5 percent higher than readings taken 

in May and June, but the greatest differences were in 

readings about 0.5 m (1.6 ft) above and below the water 

f--

z 

::l 

0 

u 60 

0 

a: 

<( 

0 

z 

<( 

f--

~ 40 _J 

<( 

:J 

f--

u 

<( 

II 20 

0 

~ a: 

10 20 30 40 50 

MOISTURE CONTENT MEASURED, IN PERCENT BY VOLUME 

FIGURE lB.-Calibration curve of soil moisture measurements by the neutron method; individual readings indicated by dots. The correlation coefficient (r) is 0.911 and is highly 

significant. 

w 

u 

<( 

lL 

a: 1.5 ::l 

(f) 

August and October 

1963 

I 

May and June------1 

1963 '-

~----Ground-water level 

' ' ' " 

I 

I 

' 

l 

\ 

\ 

\ 

\ 

10 20 30 40 

SOIL MOISTURE, IN PERCENT BY VOLUME 

FIGURE 19.-Soil moisture in one tank showing the typically small variations. 

50 

table, where the soil is saturated and such large 

variations are not likely to occur. 

AMBIENT AIR TEMPERATllRE 

During two of the special observation series undertaken in 1966, soil-moisture readings were taken at 3- to 

4-hour intervals over a period of 3 days. Data for one 

tank are plotted in figure 20. While the water-level fluctuations are negligible, there seems at first sight to be a 

considerable fluctuation in soil moisture, but these flue-
E18 STUDIES OF EVAPOTRANSPIRATION 

----=--: ___ J 

44~--------------------------------------------~ 

~l~ 19: I I I I I I I I l 0600 N 1800 0600 N 1800 0600 N 1800 M 

AUG 1966 3 4 5 

LOCAL SOLAR TIME 

FIGURE 20.-Apparent fluctuations in soil moisture during a 3-day period in one 

evapotranspirometer; true solar time, N=1200 and M=2400. Variations may be due to 

temperature sensitivity of the counting apparatus, the probe and the standard. Numbers at 

the left end of curves indicate depth of sampling, in centimeters, below soil surface. 

tuations are inconsistent. For instance, on August 3 soil 

moisture at all levels decreased between 1030 and 1600 

hours, but between the same times on the next day the 

moisture increased. Temperature of the ambient air near 

neutron loggers can have a profound influence on the 

readings (Task Force, 1964), and this probably accounts 

for the apparent anomalies. Usually though, soilmoisture readings were taken in the early mornings and 

the effect of temperature differences could safely be ignored. 

SALINITY 

Another source of possible misreadings was the salinity of the soil moisture. It is known (Benz and others, 

1965) that a high chloride content of the soil can affect 

the readings because chloride atoms are capable of absorbing neutrons. The result is that, with increasing 

chloride content, the count ratio goes down. In order to 

measure this, several batches of rock salt and water were 

mixed and neutron readings were taken at different concentrations. The batches were then analyzed for chloride 

content. In figure 21, counting ratios of the neutron 

logger are plotted against the chloride contents of the 

II 

0 

I-

<! 

a: 

·---. -........... 

102 103 104 105 

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER 

FIGURE 21.-Effect of chloride concentrations on the counting ratios of a neutron logger. 

batches and also against chloride contents of the project water and of the town-of-Buckeye water. The counting rates diminished very little between nearly pure 

water and that containing 2,000 mg/1 (milligrams per 

liter) chloride. 

CHLORIDE CONTENT 

The maximum chloride content determined in the 

saturation extracts at the project site was 11,000 mg/l. 

According to the curve of figure 21, this would bring a 

count down by about 0.2 on the ratio scale, equivalent to 

about 2 percent of soil moisture by volume. Obviously, 

such high chloride contents may affect the readings 

significantly. On the other hand, the chloride content in 

the saturation extracts was rarely more than 7,000 mg/l. 

Nonetheless, one could expect higher meter readings for 

a given moisture content. An example is given in figure 

22. Moisture contents of the saturated soil between 25 

em above and 50 em below the water table are plotted 

against depth below the land surface. When the salinity 

was high (ECs=30 mmho) as in May of 1963 and 1967, 

rn 0 a: 

w 

Iw 

~ 

z 

-

w· 

u 

<! 

u. 

a: 2.1 ::J 

rn 

0 

z 

<! 

...J 

~ 

0 

...J 

w 

Cll 

I 

Ia., 

w 

0 

Tank 4 flushed in 

1965 and 1966 

1963 and 1967 

1965 and 1966 

30 40 50 

SOIL MOISTURE CONTENT, IN PERCENT BY VOLUME 

FIGURE 22.-Soil moisture near the water table in tank 4 in May of 1963, 1965, 1966 and 1967. 
WATER USE BY SALTCEDAR AS MEASURED BY THE WATER BUDGET METHOD E19 

neutron logger readings were lower than in May of 1965 

and 1966, when flushing had reduced the salinity to 

about 10 mmho or less. 

VEGETATION GROWTH AND DEVELOPMENT 

TRANSPIRATION RATE 

In many studies of the use of water by plants it is 

assumed that the transpiration rate is controlled only by 

the ambient conditions at the test site. For this to be true 

at all, it must further be assumed that the vegetation is 

of uniform height and forms a closed stand completely 

shading the ground (Penman, 1955). When this happens 

and water is freely available to the plant, the amount of 

water transpired per unit time is said to be the potential 

transpiration (Thornthwaite, 1948; Penman, 1948). 

The vegetation on evapotranspirometers 1 through 6 

blended with the surrounding vegetation, creating an 

evenly growing homogeneous stand of saltcedar. Since 

the water in the tanks is near the surface, the plants can 

draw on it freely and one might expect transpiration to 

take place at the potential rate. 

The controversy on the subject of the effect of soil 

moisture availability on water use is still raging. Some 

maintain that transpiration continues at a potential rate 

so long as the moisture content in the root zone is above 

the wilting percentage, while others say that a decrease 

in soil moisture necessitates a decrease in water use. An 

intermediate position is taken by Penman ( 1955), who 

considers that limited supplies can come from the soil 

below the root zone. A good survey is given by Chang 

(1968). 

Penman points out that the evidence cited one way or 

another is often irrelevant because it deals wit growth 

rate rather than water use, and growth rate may decline 

before there is a decline in the rate of water use. It is 

often assumed that for maximum growth it is necessary 

for the plant to maintain a maximum rate of transpiration. It does not seem that this "axiom", as Penman calls 

it, has ever been proved, certainly not as a general rule. 

But what about the opposite: Does a plant having optimum access to water ever stop growing at the maximum rate permitted by weather conditions; and if the 

plant for any reason (other than weather or water conditions) stops growing at the maximum or optimum rate, 

does that coincide with a decline in water use? . 

In the spring and early summer of several years, young 

shoots inside and outside the evapotranspirometers were 

tagged and the increase in their lengths was measured at 

intervals varying from 5 to 10 days. In some years, the 

number of side shoots developing was also counted. If 

either the growth rate, as expressed by the increase in 

length, or the development, as expressed by the number 

of side shoots, would correlate with a change in rate of 

water use, one could conclude that plants begin to use 

less water when they stop growing or developing, even if 

at the same time the environmental conditions would indicate a higher potential water use. 

WATER USE 

Studies undertaken in 1961 and 1962 suggested a 

relationship between growth and water use (van 

Hylckama, 1963). In the quoted article, the salinity of 

the ground water in the tanks was considered to be of no 

influence on the growth or development rate, or on water 

use. The data quite clearly showed that a decrease in 

growth and development paralleled a diminishing use of 

water, even though this water seemed to be freely 

available. These results were, qualitatively at least, 

similar to those reported by Arkley (1963), who 

specifically excluded evaporation and only studied the 

relationships between plant growth and transpiration, a 

distinction not made by van Hylckama. However, the 

latter compared water use during periods when 

differences in water use could assuredly be assigned to 

differences in transpiration only. 

SUNLIGHT, SALINITY, STAND DENSITY 

Between April and June 1966, 10 trees inside each 

tank were again marked with numbered labels, and 10 

controls were chosen outside the tanks, 5 trees on dry 

land and 5 on ground in the vicinity of the tanks (where 

sprinklers were used). 

The results of the 1966 observations are tabulated in 

table 12 where the total increase in length for each twig 

during the observation period is listed. There exist very 

large variations among individuals, but differences 

between treatments are nonetheless very convincing. In 

tank 3, with soil moisture of low conductance, the mean 

daily increase in twig lengths was no less than 25 mm, 

and on individual branches increases of more than 50 

mm/day were observed. The combined effect of better 

water, a well-developed root system, and full sunlight 

resulted in this fantastic growth. 

In tanks where the vegetation was thinned out, the 

combined effects of water low in dissolved solids and of 

light are also discernible. Where the salinity of the water 

was high, as in tank 1, the growth was hardly faster than 

in tank 6, which also was not flushed, but which had a 

density of stand twice that of tank 1. It is also worthy of 

note that on irrigated lands outside the tanks no 

detrimental salt accumulation took place and growth 

rate equaled that in a flushed-out tank with full density 

of stand, such as tank 2. 

Evidently, at least some of the results reported for 

1961 and 1962 may have been affected by an increase in 

salinity during 1962. 

It is obvious from the foregoing discussion that effects 

of exposure to light and of quality of soil moisture or 

ground water may mask any correlation that might exist 
E20 STUDIES OF EVAPOTRANSPIRATION 

TABLE 12.-Increase in twig length of saltcedar inside and outside 

evapotranspirometers between April 5 and June 22, 1966. 

Treatment ... None Thinned Shorn 'Controls 

Tank No .... A B 

Flushed ..... 

Twig length .. 

(mm) 

Mean .. 

Yes 

387 

524 

534 

463 

343 

430 

428 

445 

555 

533 

464 

No Yes 

108 741 

282 810 

300 508 

151 475 

182 626 

97 765 

332 743 

226 989 

325 863 

590 1,396 

259 792 

No Yes No 

325 1,998 943 76 

253 1,742 945 123 

282 2,410 902 68 

236 1,800 1,246 69 

431 1,865 575 145 

148 1,785 833 185 

255 2,396 553 178 

432 2,522 738 49 

403 1,345 620 120 

123 1,805 647 240 

289 1,967 800 125 

Mean per day. 5.9 3.3 10.1 3.7 25.2 10.2 1.6 

Analysis of variance 

Density of 

Source of 

variance 

stand .................... Salinity of 

ground water ............. Interaction ................. Error ...................... 

Total ................ 

Sum of 

squares 

158,217.47 

60,318.64 

22,559.65 

29,829.25 

270,925.01 

Degrees of 

freedom 

Mean 

square 

4 39,554.37 

1 60,318.64 

4 5,639.91 

70 432.31 

79 ......... 

597 

594 

270 

553 

264 

586 

774 

212 

374 

253 

448 

5.7 

**91.50 

**139.53 

**13.05 

... .. ... 

'Controls outside tanks: A, on nonirrigated area; B, on sprinkler-irrigated grounds. 2

F value: significant differences indicated by ** at the !-percent level; least significant 

difference at !-percent level is 174 mm. 

between water use and growth rate of the vegetation. 

Neither do the present data allow for a growth rate versus salinity analysis, although there is a clear tendency 

toward less growth as salinity increases. (see 

"Discussion"). 

PLANT VARIATIONS 

It was mentioned that a large variation exists among 

individual plants, at least along the Gila River near the 

project site. Figure 23 shows an example. Here are four 

branches taken from four plants of equal height and 

volume and of equal exposure. Such variations may be 

genetic or they may be due to chemical characteristics of 

soil moisture. In the first case we would have genotypes 

and, therefore, real subspecies or variations; in the second case the variations are phenotypical. Added to the 

illustrated differences, there are also plants with 

various shades of green foliage and flower colors which 

vary from near-white to pink to deep red. All this might 

well be the cause of what Douglas (1967) calls "confusion 

among saltcedars." 

WATER USE, SMALL TANKS 

The original plan required that the vegetation from 

the large tanks (1 through 6) would be removed after sufficient data on water use had been gathered. Observations would then continue on the water loss from bare 

soil. It was feared, however, that this would delay completion of the study by at least 2 years. Moreover, it would 

have been impossible to remove the roots without 

destroying the plastic lining of the tanks. Therefore, the 

U.S. Bureau of Reclamation in 1962 installed the five 

smaller tanks previously mentioned in "The Buckeye 

Test Site." Figure 24 presents a view of the small-tank 

area shortly after construction. The vegetation was not 

surrounded by an equal stand as was that in the large 

tanks. The water use, therefore, cannot be compared 

with that of tanks 1 through 6 because of possible oasis 

effects as discussed in "Evapotranspirometers." A synopsis of water use in the small tanks is presented at the 

end of this chapter. 

HARMONIC ANALYSIS 

During the summer of 1963, when saltcedar became 

established in tanks 7 and 8, detailed observations were 

made on the water use (van Hylckama, 1966). The water 

was maintained at a nearly constant level of 1.20 m (4ft) 

below the surface in the manner discussed in 

"Instrumentation." When the tanks filled frequently, it 

was possible to compute the water use by 1- or 2-hour 

periods. Figure 25 shows a 1-week record of fillings in 

tank 7. It can be seen that during the day this tank filled 

more frequently than during the night. For computing 

short time rates it was necessary to assume that equal 

quantities of water were used per tank for each filling 

period; however, this did not actually happen because 

the rate of inflow was influenced by the pressure in the 

storage reservoir that delivered water to the 

evapotranspirometers. It was also necessary to assume a 

constant rate of water use between one filling and the 

next. With these assumptions, 2-hour points were obtained, centered on the uneven hour, and expressed as 

liters per hour for 5-day periods. A curve was drawn 

through these sets of points; thus, irregularities were 

smoothed out and one set of diurnal fluctuations could 

be compared with another. The data from the curves 

formed the basis for harmonic analyses. 

For those not familiar with this method the following 

discussion may be useful. If we plot, for example, daily 

mean temperatures from moderate climates for each day 

of a year, a curve is obtained that reaches a maximum in 

summer and a minimum in winter. Such a curve, 

however, will rarely be smooth because of small day-today differences. 

Mathematical analysis of periodic fluctuations makes 

it possible to separate a complicated curve into two or 
WATER USE BY SALTCEDAR AS MF JURED BY THE WATER BUDGET METHOD E21 

----·-· -~_j· 

F IGURE 23.- Two- t.o three-month-old branches of saltcedar from the- Buckeye Project site along the Gila River in Arizona showing the large variability in appearance of the species Tamarix that 

grows in this area. 

more simple ones having a variety of amplitudes and 

frequencies. We may have a simple wave, peaking once 

a day, a second wave with two peaks per day, and a third 

wave peaking every 6 hours, or four times a day, and so 

on. These waves are called harmonics and the difference 

between the maximum and the mean values is called 

amplitude. In the present study Fourier series were 

employed using a method described by Brooks and 

Carruthers (1953). Analysis showed that nearly always 

95 percent or more of the daily variations could be attributed to the first and second harmonics. Additional 

harmonics seemed to be due to random noise, such as 

irregularity of fillings, fluctuations in water level (see 

"Soil Moisture and Soil Moisture Fluctuations" ), and 

other variables. 

How well two harmonics describe the observations is 

illustrated in figure 26. The top curves in each graph present the average hourly fluctuations for tank 7 during 
E22 STUDIES OF EVAPOTRANSPIRATION 

FIGURE; 24.-Small·tank area at the Buckeye Project, March 1963. The new plants in tanks 7 

and 8 are visible in the background, as is the better-quality-water reservoir (arrows) near 

tank 7. The man stands near tank 10. 

._, J7--f& 

b ~~ 

/ 

- I.. 

~~CL.LJCL';;t . 

FIGURa 25.- Recording chart of tank 7 showing frequency of filling durmg a week in May 1967. 

Each "tick" indicates time that water entered the tank. (Actual diameter of chart is 19 em.) 

two 5-day periods. This tank was planted to saltcedar 

and both the increase in foliage and a higher radiation 

input resulted in a larger amplitude during June 25-30 

than during June 9-13. The curves for tank 11 show less 

water use because the tank was kept bare. 

Figure 27 shows the first and second harmonics for the 

separate curves of figure 26, and also gives two more sets 

of average hourly fluctuations for later periods. 

In figure 27, a first harmonic represents the rate of 

water use due to the daily fluctuations of radiation and 

A 

0:: 10 ::> 

0 

I 11 0:: 

w 

"- 0 (/) 

0:: 

w 40 r 

..J 

z 

w' 

(/) 

::> 

0:: 

w 

r 

<( 

~ 

0900 1300 1700 2100 0100 0500 

LOCAL SOLAR TIME 

FIGURE 26.- Water use in evapotranspirometers 7, planted to saltcedar, and 11, bare. A, 

average hourly fluctuations for June 9-13; B, average hourly fluctuations for June 25- 30. 

Heavy solid line represents measured water use for a mean of five days; light solid line, harmonic analysis using three harmonics; dashed line, harmonic analysis using two harmonics. 

~50r---------------------~ r----------------------.+7 

z c 

.40 w 

(/) 

::>30 

D 

05~~~==~_L __ L_~ 9 13 17 21 1 5 5 9 13 17 21 

LOCAL SOLAR TIME 

+6 

+5 

+4 

+3 

+2 

m 

FlGURE 27 .-First (solid line) and second (dashed line) harmonics of the analyses of average 

hourly water use for the periods June 9-13, A, June 25-29, B, July 3- 7, C, and July 9-13, 

D, 1963, in evapotranspirometers 7, planted to saltcedar, and 11, bare. Second harmonics are 

plotted around a common mean (m). 

temperature. There is only one maximum, shortly after 

noon, and one minimum, after midnight. The second 

harmonic has two peaks and two lows; it appears that 

this represents the rate of evaporation from the soil. 

Toward the middle of the day the top soil dries out and 
WATER USE BY SALTCEDAR AS MEASURED BY THE WATER BUDGET METHOD E23 

the vapor shield prevents further evaporation. When the 

soil cools off condensation occurs and the soil moisture at 

the surface is again in contact with the ground water. 

The capillary rise can follow the demand for water due to 

radiation, air temperature, winds, and so on. At night, of 

course, the evaporation from the soil diminishes just as 

does the transpiration. 

Note that the second harmonics are drawn on an 

enlarged scale (the same for both tanks) and centered 

around a common mean. The similarity of the second 

harmonics is quite striking, although there is an apparent phase shift of about 2 hours in the harmonics of 

figures 27B and 27C. Whether this is due to the technique of averaging the values, or to the effects of shading, 

or to noise, cannot be determined with certainty. There 

appears to be no mathematical method by which the 

significance of differences in phase angles can be determined. It seems safe to conclude that the differences are 

probably not significant. 

Figure 27 D shows that the second harmonic for tank 7 

virtually disappeared while the one of tank 11 remained 

as before. These curves were drawn from data taken in 

July 1963. At that time tank 7 was well overgrown, the 

soil was shaded, and the second harmonic accounts for 

only 1 percent of the total variation. In tank 11, however, 

35 percent of the variation is due to fluctuations of the 

second harmonic. 

Table 13 summarizes the means and amplitudes for 

the two tanks during the periods discussed above, and it 

also gives data from analyses of observations made in 

1966 and 1967. Some anomalies in this table beg for an 

explanation. The water use in tank 7 during the first part 

of 1966 seems to have been about equal to that of comparable periods in previous years, but use decreased 

after July 1966. The last time tank 7 was flushed was in 

the early spring of 1965, and it is quite likely that the salt 

build-up resulted in the decrease in water use in the late 

summer of 1966. 

By contrast, the mean use in tank 11 was considerably 

higher in 1966 than in 1963. Tank 11 was flooded by the 

Gila River in 1965 (see "Test Environment") and the 

water level did not fall to its proper level until the beginning of April. The soil-moisture content above the water 

table remained much higher throughout 1966 than it was 

in 1963. (A similar phenomenon was discussed in "1964: 

Floods.")~ 

Statistics on the second harmonic (table 13) show the 

effect of a dry layer of top soil on the rate of evaporation 

from bare soil, except early in the year (May 1966 and 

1967). The drying effects become visible in June, remain 

so throughout the summer, but diminish in September. 

Figure 28 enables us to compare the second harmonics 

for the observation periods of 1966 and 1967 and shows 

the remarkable regularity with which the wetting and 

drying of the top soil controls the evaporation rates. 

TABLE 13.-Mean and amplitudes of the harmonic analysis of water use 

in tanks 7 and 11 (l/hr) 

[Numbers in parentheses are percentages of effect of amplitude on total variance (minus sign 

= less than 1 percent). Tank 7 was planted to saltcedar and tank 11 was bare soil] 

Starting 

date of 

5-day period 

1963 

June9 ....... 

July9 ······· 

Aug.12 ...... 

Sept.23 ..... 

1964 

Aug.lO ...... 

1966 

May4 ....... 

June 2 ....... 

July6 ....... 

Aug. 3 ....... 

Sept. 7 ...... 

1967 

May 10 ...... 

- +2 z 

<( 

w 

~a: 

w:J 

I 0+1 I-I 

~a: 

0~ a:(/) 

U.a: 

CIJW 

Zlo- _...J 

1-z 

~- -1 

> 

w 

0 

Mean 

Tank 7 Tank 11 

14.7 

28.0 

28.2 

27.6 

25.6 

14.8 

19.6 

27.8 

17.3 

18.6 

18.3 

5.1 

3.4 

4.0 

4.8 

4.0 

6.0 

9.0 

7.4 

6.5 

7.3 

Amplitudes 

First harmonic Second harmonic 

Tank 7 Tank 11 Tank 7 Tank 11 

5.2 2.3 1.0 0.9 

(95) (87) (3) (12) 

15.4 1.6 0.1 1.3 

(99) (56) (1) (35) 

10.6 4.1 1.2 2.0 

(98) (76) (1) (19) 

15.2 2.3 

(98) (2) 

10.3 0.6 1.0 0.5 

(98) (50) (1) (39) 

5.6 2.1 0.9 0.4 

(89) (86) (2) (4) 

7.0 1.9 1.7 1.7 

(86) (48) (5) (39) 

10.2 2.2 0.3 2.3 

(91) (41) (-) (44) 

5.5 2.6 0.3 2.9 

(89) (37) (-) (47) 

11.7 2.0 1.9 1.5 

(89) (52) (2) (30) 

13.8 3.1 0.4 0.2 

(91) (90) (-) (1) 

3 5 7 9 11 13 15 17 19 21 23 3 5 

LOCAL SOLAR TIME 

FIGURE 28.-Second harmonics of water-use fluctuations of bare-soil tank 11, computed from 

hourly means of 5-day periods. -

OASIS TANKS 

Monthly water-use data from oasis tanks 7 and 8 are 

given in table 14, and the results are graphically 

presented in figure 29. During 1963, tank 7, supplied 
E24 STUDIES OF EVAPOTRANSPIRATION 

80 

R 

I f f- Tank 7: On better quality watero---o---<>; on project water ---

z 

0 Tank 8: On better quality water o-----<>----<>; on project water •--------e 

~ 

0 

0 

a: 0 

w ...J 

Q_ 6 IJ_ 

Ul 40 I a: Ul 

w <{ 

f- .... s w 2! ~ Ill 

j: 3: 

z "0 

CD w ~ 

u -~ 

OL-~~~~_L_L_L~~~L-~~~_L_L_L~~~L_L_LJ~_L_L_L~~~L_~~~_L_L_L_L~~L-L-~~~_L~ 

JJASONDJFMAMJJASONDJFMAMJJASONDJFMAMJJASONDJFMAMJJAS 

1963 1964 1965 1966 1967 

FIGURE 29.-Water use in tanks 7 and 8, planted to saltcedar, surrounded by bare soil (oasis tanks.) 

TABLE 14.-Water use in oasis tanks 7 and 8 

Year. . . . . . 1963 1964 1965 

Tank No.... 8 

Month Cm In. Cm In. Cm In. Cm In. Cm In. Cm In. 

Jan ........ 7.9 3.11 1.6 0.63 2.8 1.10 0.8 0.31 

Feb ........ 7.9 3.11 1.6 0.63 (') (') (1) (') 

Mar ........ 6.2 2.44 0.7 0.27 9.8 3.85 4.3 1.69 

Apr ........ (') (') (") (l) 23.8 9.37 18.0 7.09 

May ....... (') (") (') (') 48.1 18.94 45.0 17.72 47.6 18.74 40.5 15.94 June ....... 36.0 14.17 28.4 11.18 68.8 27.09 73.1 28.78 57.5 22.64 42.8 16.85 

July ........ 54.4 21.42 47.4 18.66 63.8 25.12 66.9 26.34 49.2 19.37 43.8 17.24 

Aug ........ 41.1 16.18 25.0 9.84 (') (') (5) (') 50.1 19.72 47.0 18.50 

Sept ....... 50.5 19.88 31.2 12.28 (") (6) (6) (6) 37.8 14.88 35.4 13.94 

Oct ........ 32.8 12.91 21.6 8.50 (6) (6) (6) (6) 33.7 13.27 30.00 11.81 Nov ........ 20.0 7.87 8.1 3.19 16.5 6.49 12.5 4.92 15.2 5.98 9.8 3.85 

Dec ........ 12.6 4.96 4.8 1.89 6.7 2.74 2.9 1.14 (') (') (') (') 

Year . . . . . . . 1966 1967 'Not connected 

'Ground water in tanks 

Tank No .... flushed out with project 

water. -------------------1 1Tank was fed better 

Cm In. Cm In. Cm In. Cm In. quality water (see analysis 

-------------------lin table 8). 

0

_

5 0 20 'Tank was fed project 

3

_

5 1

:

38 water (see analysis in table Jan ........ (') (') 

Feb . . . . . . . . (") (') 

Mar ........ 1.3 0.51 

Apr ........ 16.1 6.34 

May ....... 35.1 13.82 

.June ....... 41.1 16.18 

July ........ 42.4 16.69 

Aug ........ 18.3 7.20 

Sept ....... (') (') 

Oct ........ 16.2 3.38 

Nov ........ 10.7 4.21 

Dec ........ 4.5 1.77 

(') (') 

(') (') 

8.1 3.19 

27.1 10.67 

52.4 20.63 

54.2 21.34 

47.3 18.62 

38.2 15.04 (5) (') 

15.3 6.02 

11.4 4.48 

3.9 1.53 

0.5 0.20 

0.9 0.35 

4.1 1.61 

15.8 6.22 

36.4 14.33 

42.0 16.53 

39.1 15.39 

28.9 11.38 

3.2 1 26 8). 

16.2 6:38 ;~~ot:ta 35·

3 13·

90 'Gila River floods 43.2 17.01 

40.5 15.94 

31.3 12.32 

with better quality water, used more water than did tank 

8 on project water. 

Mter the water qualities of the two tanks were 

switched in 1964 tank 8 began to use more water than 

did tank 7, but the differences were comparatively small. 

In 1965, tank 8 remained on better quality water, and 

was not flushed whereas tank 7 remained on project 

water but was flushed. Tank 7 measured higher water 

use than tank 8; although tank 8 was using better water, 

the salt accumulation resulted in a lower use. In 1966 

tank 8 was flushed and fed project water, while tank 7 

was not flushed but was switched to better water. Clearly, flushing increased the rate of water use significantly 

more than the feeding of better quality water without 

flushing. After the flood of September 1966, both tanks 

were fed project water and the differences in water use 

disappeared, as can be seen by the data of 1967. 

BARE-SOIL TANKS 

Bare-soil tank 9 was used for a variety of purposes, 

making it impossible to derive meaningful data on 

monthly water use. At times the water supply to this 

tank was shut off and the rate of change in the declining 

water table was used in connection with energy budget 

analysis. For the same purpose, the tank was shaded occasionally to study the different effects of drying of the 

top soil on the rate of water loss. Some of the results are 

discussed under "Water Table Fluctuations"; other 

results will be discussed in a paper dealing with the 

energy budget and mass-transfer methods for determining evapotranspiration. 

Data from tanks 10 and 11 are summarized in table 15 . 

Here, as in the vegetated tanks 1 through 6, the effect of 

change in water level on water losses is quite apparent. 

Compare, for instance, the data for tank 10 with those of 

tank 11 between June 1964 and December 1965. Before 

June 1964 the water level in both tanks was the same and 

tank 10 seemed to use more water, which might be due to 

the fact that tank 10 did not have the protective belt 

which surrounded tank 11. However, in 1966, tank 11 

used more water than tank 10. It is possible that the 

previous high water level in tank 10 resulted in a considerable salt accumulation in the top layers of the tank 

which, in turn, may have affected the monthly water 

use. It is interesting to compare the water use recorded 

for these tanks with data published earlier on water use 

in similar tanks near Yuma, Ariz. (McDonald and 
WATER USE BY SALTCEDAR AS MEASURED BY THEW ATER BUDGET METHOD E25 

TABLE 15.-Euaporation from bare soil in tanks 10 and 11 

Tank 10 Tank 11 

Date Nominal Nominal 

depth Water use depth Water use 

to water to water 

Cm Ft Cm In. Cm Ft Cm In. 

1963 

July ........... 125 4.1 (I) (1) 125 4.1 5.2 2.05 

Aug ........... 125 4.1 2

2.1 20.82 125 4.1 2

3.6 21.42 

Sept .......... 125 4.1 9.5 3.74 125 4.1 6.0 2.36 

Oct •• 0 ••••••• 0 

125 4.1 25.8 22.28 125 4.1 2

4.5 21.77 

Nov ........... 125 4.1 3.5 1.38 125 4.1 2.1 0.82 

1964 

Jan 00 ••••••••• 125 4.1 2.2 0.87 125 4.1 1.4 0.55 

Feb ........... 125 4.1 2.9 1.14 125 4.1 1.9 0.75 

Mar ........... 125 4.1 3.7 1.45 125 4.1 2.3 0.90 

Apr ........... 125 4.1 4.2 1.65 125 4.1 3.7 1.46 

May .......... 125 4.1 (3) (3) 125 4.1 4.3 1.69 

June ••••••••• 0 100 3.3 10.0 3.94 125 4.1 7.5 2.95 

July ........... 100 3.3 29.4 23.70 125 4.1 27.3 22.87 

Aug ........... 100 3.3 29.0 23.54 125 4.1 25.3 22.08 

Sept .......... 100 3.3 25.7 22.24 125 4.1 24.2 21.65 

Oct •••••••••• 0 100 3.3 5.7 2.24 125 4.1 4.4 1.73 

Nov ........... 100 3.3 5.1 2.12 125 4.1 (1) (1) 

Dec ........... 100 3.3 4.2 1.65 125 4.1 (1) (1) 

1965 

Apr ........... 100 3.3 27.4 22.91 125 4.1 25.6 2

2.20 

May .......... 100 3.3 11.6 4.56 125 4.1 9.6 3.78 

June ••••••••• 0 100 3.3 12.1 4.76 125 4.1 10.5 4.13 

July ........... 100 3.3 11.4 4.49 125 4.1 8.0 3.15 

Aug ........... 100 3.3 12.5 4.92 125 4.1 10.3 4.06 

Sept .......... 100 3.3 9.4 3.70 125 4.1 6.0 2.36 

Oct ••••••••• 0 0 100 3.3 6.0 2.36 125 4.1 5.1 2.01 

Nov ........... 100 3.3 4.7 1.85 125 4.1 3.4 1.34 

Dec ........... 100 3.3 (1) (1) 125 4.1 1.4 0.55 

1966 

Apr ........... 150 4.9 (1) (1) 150 4.9 5.2 2.05 

May ••••••••• 0 150 4.9 2.6 1.02 150 4.9 n.d. n.d. 

June ·········· 150 4.9 4.0 1.57 150 4.9 6.3 2.48 

July ........... 150 4.9 23.3 21.30 150 4.9 25.0 21.98 

Aug ........... 100 4.9 24.7 21.85 150 4.9 2

6.2 22.44 

1967 

Apr ........... 100 3.3 2.2 0.87 100 3.3 (4) (4) 

May ·········· 100 3.3 5.4 2.12 100 3.3 (4) (4) 

June .......... 100 3.3 7.3 2.87 100 3.3 (4) (4) 

July ........... 100 3.3 10.0 3.94 100 3.3 (4) (4) 

Aug ........... 100 3.3 12.2 4.80 100 3.3 (4) (4) 

'Insufficient data to compute monthly use. 

'Water use affected by rainfall. 

'Chane of water level. 

of the differences in water use might be explained by the 

differences in the soil. McDonald and Hughes (1968) present sieve analysis of the soils in the bare tanks at 

Imperial Camp. The percentage of particles less than 

0.02 mm for the three Yuma tanks are 14, 8, and 6. The 

average percentage of particles for the soil in the bare 

tanks at the Buckeye Project is 28 for the top em and 25 

for the top 50 em, with respectively 6.5 and 5.8 percent 

clay (particles less than 0.002 mm). Obviously, the soil at 

the Buckeye site is much finer and, although this may 

slow down the upward movement of water, it also accounts for finer capillaries and assures a more continuous supply of water for evaporation. 

WATER TABLE FLUCTUATIONS 

White (1932) and also Gatewood and others (1950) 

describe how one can make an estimate of 

evapotranspiration by analyzing the diurnal fluctuations 

of the water table. The fluctuations are partly caused by 

evaporation from the soil, but they are mainly caused by 

a pumping action as plants draw water from the water 

table or from the soil moisture above it. For this to be 

true, there should be a fall in water level during the day 

and a rise during the night. Although the phenomenon 

has been observed under natural conditions, the fluctuations of the water table in the evapotranspirometers 

showed the opposite: a rise during the day and a decline 

during the night. 

A typical example of fluctuation in water table for a 

bare tank with the water controls shut off is given in 

figure 30. There is a gradual decline in the water table, 

but contrary to what is expected, there is a rise in the 

water table in the afternoon. Afternoon rises, however, 

coincide with lowering of the barometric pressure. To 

make the comparison easier to follow, the barometer 

readings have been reversed and the scale adjusted. The 

distance between "low" and "high" represents 5-cm 

water pressure and is 40 percent of the distance between 

1.50 and 1.55 on the left scale. This percentage is called 'Data suspect, excessive use probably due to leaks. , the barometric efficiency (Ferris, 1959). 

Hughes, 1968) and in the Humboldt River Valley m 

Nevada (Robinson, 1970). 

The Humboldt River Valley report mentions water use 

by year but does not give data on temperatures and 

radiation. The growing season is undoubtedly shorter, 

radiation is less, and monthly temperatures are lower 

than those in either Yuma or Buckeye. It is therefore not 

surprising that the use is much less than that reported 

for the Yuma area. 

A comparison of the weather data in Yuma and 

Buckeye shows clearly that the situations are quite 

similar, yet the water use near Buckeye is very much 

higher. Table 16 allows comparison of the water use in 

three tanks near Yuma with the use in two tanks near 

Buckeye during the later part of 1963 and for 1964. Some · 

Figure 31 shows a similar situation for a tank planted 

to saltcedar. The plants were dormant and the average 

FIGURE 30.-Water levels in evapotranspirometer 9 and inverted barometric pressure. No 

vegetation; water controls off; June 10-14, 1964. 
E26 STUDIES OF EVAPOTRANSPIRATION 

TABLE 16.-Monthly evaporation, excluding rainfall, from ground water in bare-soil tanks at Imperial 

Camp and near Buckeye, Ariz. 

Tank No .... 

Nominal 

depth 

to water 

BS1 

in 1963 ... em, ft... 60 1.9 

Month Cm In. 

July..... 4.1 1.61 

Aug . . . . . 22.4 20.94 

Sept ... . Oct .... . Nov .... . 

Nominal 

depth 

to water in 1964 ... em, ft. 65 2.1 

Month Cm In. 

.Jan ..... 2.6 1.04 

Feb ..... 2.4 0.94 

Mar ..... 3.1 1.23 

Apr ..... 4.0 1.57 

May 5.9 2.31 

June .... 9.2 3.62 

July ..... 7.0 2.74 

Aug ..... 6.0 2.37 

Sept 5.2 2.05 

Oct ..... 5.1 2.01 

Imperial Camp' 

BS2 

90 3.0 

Cm In. 

2.7 1.05 

21.3 20.45 

21.1 20.42 

2.2 0.87 

90 3.0 

Cm In. 

1.7 0.67 

1.0 0.43 

1.1 0.44 

2.2 0.88 

3.0 1.17 

3.0 1.19 

2.4 0.96 20.2 20.07 

1.4 0.56 

0.7 0.27 

'Adapted from McDonald and Hughes (1968, table 6). 2Water use affected by rainfall. 3Depth to ground water was 100 em (3.3 ft) after May 1964. 4Change in water level. 

FIGURE 31.-Water levels in evapotranspirometer 1 and barometric pressure. Tank planted to 

saltcedar but plants leafless and dormant; January 31-February 5, 1967. 

water level remained stationary, but the fluctuations 

followed the barometric ups and downs as before. The efficiency is again about 40 percent. 

On vegetated tanks where saltcedar is transpiring, the 

barometric fluctuations and those of the water level are 

out of phase as shown in figure 32. The little wiggles were 

produced by the water-stage recorder in response to filling and -occur at exactly the same time that the recorders 

BS3 

105 3.5 

Cm In. 

1.6 0.65 

20.4 20.18 

1.1 0.42 

120 4.0 

Cm In. 

0.4 0.17 

0.4 0.17 

0.1 0.04 

0.1 0.04 

1.1 0.44 

0.7 0.28 

1.5 0.61 2

0.7 20.27 

2.6 1.01 

0.8 0.32 

26 

Buckeye 

10 

125 4.1 125 

Cm In. Cm 

5.2 22.1 20.82 23.6 

9.5 3.74 6.0 

25.8 22.28 24.5 

3.5 1.38 2.1 

1253 4.P 125 

Cm In. Cm 

2.2 0.87 1.4 

2.9 1.14 1.9 

3.7 1.45 2.3 

4.2 1.65 3.7 

(4) (4) 4.3 

10.0 3.94 7.5 

29.4 23.70 27.3 29.0 23.54 2

5.3 25.7 2

2.24 24.2 

5.7 2.24 4.4 

,., 

I ' 

' I 

Pressure 

'\ /'\ 

\ I \ \./ 

\/ 

11 

4.1 

In. 

2.05 21.42 

2.36 21.77 

0.82 

4.1 

In. 

0.55 

0.75 

0.90 

1.46 

1.69 

2.9!) 

22.87 22.08 21.65 

1.73 

27 28 29 

MAY 1966 

30 31 

FIGURE 32.-Water levels in evapotranspirometer 2 and barometric pressure. Tank planted to 

saltcedar; May 26-31, 1966. 

indicate filling by the system illustrated in figure 25. Obviously the water level in the control pipes which contain 

the contact points (see "Instrumentation") did not respond to the atmospheric fluctuations. The water-level 

control pipes probably had a finer screen than the 

recorder pipes; also, the control pipes were installed 

shortly after the tanks had been constructed and a considerable amount of clogging could be expected. The 
WATER USE BY SALTCEDAR AS MEASURED BY THEW ATER BUDGET METHOD E27 

reaction to falling and rising water levels in the control 

pipes was therefore sluggish compared to that in the 

water-level recorder tubes which were installed in 1964. 

It is now possible to construct a hypothetical water 

level by adjusting the actual one for the atmospheric 

pressure changes, assuming a 40 percent barometric efficiency throughout. Under high atmospheric-pressure 

conditions the water level would have been shallower 

had the pressure been lowered to the mean pressure; under low atmospheric-pressure conditions the water level 

would have been deeper if the atmospheric pressure were 

increased to the mean. Figure 33 shows the results of 

such a manipulation of data for a 5-day average of the 

changes in evapotranspirometer 6. The line representing 

the adjusted water level and the points showing observed 

hourly rates of water use are clearly in phase. 

FIGURE 33.-Average water levels, average barometric pressures, and average observed and 

computed water use in tank 6, planted to saltcedar, for June 30-July 4, 1966. 

The picture gets more complicated when there appear 

to be effects of salinity of the soil moisture. When the 

conductivity of soil moisture is low the plants seem to 

use that water first, and the ground-water levels are not 

affected until 2 to 4 hours after the transpiration has 

started. The result is a phase shift between the waterlevel curve adjusted for barometric effects and the curve 

drawn through measured points (van Hylckama, 1968). 

It is clear that diurnal atmospheric-pressure effects 

can be masked, and yet they may have influenced the 

water level in transpiration wells. Also it is possible that 

there was selective water uptake by the vegetation; 

without that the analysis of transpiration-well data 

could lead to wrong estimates, if not of the daily amount 

of water transpired, at least of the time of consumption. 

DISCUSSION 

In the foregoing pages two things seem to stand out 

rather clearly: (1) water use by saltcedar varies 

with many factors, and (2) plastic-lined 

evapotranspirometers may be capricious instruments 

yielding data that should be considered with caution. 

Both statements, while true, are not very useful and 

should be reinforced with some further analytical 

studies. 

VARYING FACTORS OF WATER USE 

First of all, some of the data show that the water use 

by saltcedar can be enormous. Table 17 is a summary of 

all water-use data in rounded numbers, by years. The 

table shows that in 1965, tank 3 used a little more than 

310 em (122 in.) of water. This is nearly equal to the 

highest pan evaporation observed in the Lake Mead 

studies (Harbeck and others, 1958). A similar value was 

obtained by extrapolating data for tank 2 in 1966. Both 

tanks were flushed out in the spring of each year, and 

part of the high water use may be attributed to a high 

soil-moisture content, at least in the early part of the 

year. The next highest user for two consecutive years was 

tank 4 with 260 em (102 in.) in 1965 and, again by extrapolation, 268 em (106 in.) in 1966. This tank also was 

flushed out both years. The other high uses of 200 or 

more centimeters occured from tanks 3 and 5 in the years 

1961, 1962, 1963, and 1965, and are comparable to the 

use rates observed by Gatewood and others (1950). The 

1965 total use from tank 2 was also high (238 em or 94 in.). 

However, in 50 percent of the tanks the water use was 

less than 150 em (59 in.). 

TABLE 17.-Summary by years of water use in and treatment of six 

evapotranspirometers 

Tank No. ··············· 

Depth towater ... m ....... 1.5 1.5 2.1 2.1 2.7 2.7 

Vegetation treatment .... None None None None None None 

Flushed ................ No No No No No No 

1961...cm ............... 199 200 141 145 105 108 

.. .in ................ 78 79 56 57 41 43 

1962 ... cm ............... 218 222 137 150 94 94 

... in ................ 86 87 54 59 37 37 

1963 ... cm ............... 226 229 160 163 86 92 

.. .in ................ 89 90 63 64 34 36 

Depth to water ... m ....... 1.5 1.5 2.1 2.1 2.7 2.7 

Vegetation treatment .... None None None None None None 

Flushed ················ Yes No Yes No Yes No 

1965 ... cm ............... 311 226 260 168 238 106 

.. .in ................ 122 89 102 66 94 42 

Depth to water ... m ....... 2.1 2.1 2.1 2.1 2.1 2.1 

Vegetation treatment .... (1) (') (2) (2) None None 

Flushed ................ Yes No Yes No Yes No 

19663 ••• cm .............. 154 51 268 122 294 145 

... in ................ 61 20 106 48 116 57 

Depth to water ... m ....... 2.1 2.1 2.1 2.1 2.1 2.1 

Vegetation treatment .... None None None None None None 

Flushed ················ No No No No No No 

19673 ••• cm ·············· 137 86 161 109 156 134 

.. .in ................ 54 34 63 43 61 53 

'Cut to 50 em . 

'Thinned 50 percent. 

"Data extrapolated: 100/70Xmeasured use, Mar. through Aug. 

Figure 34, a graph of the data from table 4, clearly 

demonstrates how the water use diminished with in-
E28 STUDIES OF EVAPOTRANSPIRATION 

400~--------.---------~--------~--------~ 

a: 

<( 

w 

>-

a: 300 

w 

a.. 

(/) 

II 

w 

1-

w 

~ 

f: 200 

z 

w 

u 

~ 

w 

(/) 

:::> 

a: 100 

w 

1-

<( 

s: 

' ', 

' ' '? " ' 

0

o 1 00 200 300 400 

DEPTH TO GROUND WATER, IN CENTIMETERS 

FIGURE 34.-Yearly water use (1961-63) versus depth to ground water in six 

evapotranspirometers at the Buckeye Project. 

creasing depth to ground water. The straight line drawn 

by eye through the points leads to two interesting intersections with they- and x-axes. Extrapolation to the 

1 

zero water level would indicate a water use of about 360 

em (142 in.), which just about equals the 1952-53 pan 

evaporation for Boulder Island, mentioned in table 19 of 

the Lake Mead studies (Harbeck and others, 1958). Extrapolation in the other direction leads to the absurdity 

that the saltcedar would stop using water with a water 

-table at 360 em (12 ft) below the land surface. It seems 

altogether reasonable, though, that the water use would 

continued to diminish with a declining water level, but 

more in character with the curved line in figure 34. 

(/) 

a: 

w 

1-

w 

~ 

f: 

za:: 

w <( 

Uw 

z >- 200 

-a: 

- w ~a.. 

:::> 

a: 

w 

1-

<( 

s: 

• 1965 

c. 1966 

10 20 30 40 

SPECIFIC CONDUCTANCE, IN MILLIMHOS 

PER CENTIMETER AT 25°C 

50 

FIGURE 35.-Total water use per year in six evapotranspirometers versus specific conductance 

of the saturation extract of soil samples taken from the root zones in July or August of each 

year. The number 6 refers to an anomalous datum for tank 6 in 1965. 

The section "1966: Density of Stand" refers to the 

practice of using a volume-density correction factor in 

estimating maximum water use by phreatophytes. For 

instance, if the volume density at time of measurement 

was 50 percent, it was assumed that the water use under 

100 percent conditions would be twice as much. Under 

the circumstances of the experiments described in the 

previous sections, this is not necessarily so. Tanks 

deprived of 50 percent of their transpiring surfaces used 

only 10 to 15 percent less water than a control tank. Obviously, one has to consider these possibilities when estimating water use under natural conditions. On one 

hand the investigator knows the amount of water lost 

from 'a 100 percent volume density stand, and he divides 

this amount in half to estimate water use in an area with 

only 50 percent volume density. His estimates of act~al 

water losses will then be too low. On the other hand, If a 

certain water use by a stand of 50 percent volume density is measured, a prediction as to what might happ.en 

when this stand develops to 100 percent volume density 

The effects of salinity of the ground water and soil 

moisture can be illustrated in a similar manner (see fig. 

35). Extrapolating the line to the left leads to an estimated water use of about 360 em (142 in.) for pure 

water, which again checks with the Lake Mead data. Extrapolating to the right end would lead one to expect a 

zero water use at a conductance of about 50 mmho em -l; 

this is in the range of conductance of saturation extracts 

taken from the top soil. At such concentrations no seed, 

not even saltcedar seed, will germinate. Existing vegetation would stop growing too, as implied in "Vegetation 

Growth and Development." 

1 will lead to conclusions which may be grossly 

overestimated. 

The effects of stand density on water use in this study 

cannot be separated completely from the effects of 

salinity, but the interaction could be mathematical~y 

analyzed, as was done in table 9 with results shown In 

figure 16. 

Although a volume density correction factor is no 

longer used in current phreatophyte research (for example, McDonald and Hughes, 1968; Robinson, 1970)? a 

search is still needed for a satisfactory way of expressing 

water use in relation to stand density on a quantitative 

basis. It would be pleasant to be able to estimate water 

use by simply measuring the vegetation (and maybe a 

few other factors, such as climatological and 

meteorological, which will be discussed in another report 

in this series). 

The evapotranspirometers deserve some further discussion. Gatewood and others (1950) quote a list of 

sources of error in performing experiments with plants 
WATER USE BY SALTCEDAR AS MEASURED BY THE WATER BUDGET METHOD E29 

growing in tanks. Most of these deal with improper conditions of plant and soil compared with the natural environment. The number of tanks, their size, and the 

duration of the project eliminated most of these sources 

of error, but others occurred that were not mentioned. 

Of these sources of error, the salinity build-up was 

probably the most serious. High salinity, however, does 

occur under natural conditions, _and, although the situation in the tanks may have been exaggerated compared 

to what happens under natural conditions, this source of 

error actually led to a better understanding of soil-, 

plant-, water-relationships. Also the water-level fluctuations due to variations in atmospheric pressure could 

and would have affected the water use in the tanks if the 

fluctuations had occurred in the water level control 

pipes. Another possible source of error was the choice of 

the location of the experimental site in the flood plain of 

the Waterman Wash. Flooding was part of the natural 

environment of the vegetation, and when levees were 

built the saltcedar that was not sprinkle-irrigated began 

to die during periods of prolonged drought. Flooding as a 

source of error was eliminated by interpolating observed 

water use from periods in which tank sites were not 

adversely affected by floods. 

METHODS OF EVALUATING WATER USE 

Properly built evapotranspirometers should have 

provisions for draining the soil column, but this makes 

them expensive-even more so when they have to be 

large enough for the study of tall vegetation. Whether 

the apparatus used is of the plastic lining type or of more 

sophisticated construction, studies of water use by the 

evapotranspirometer method is time consuming, especially for such vegetation as saltcedar, mesquite, and 

other trees. 

If only a water budget method is used, the results can 

actually be applied only to areas quite similar in ecology. 

Studies to date on the effects of environment (radiation, 

temperature, winds, and so forth) on rate and quantity 

of water use have been encouraging and may eventually 

lead to a better method of evaluating water use by 

phreatophytes. Portable equipment could be set up in 

places where a knowledge of water use is required. 

Observations made during comparatively short periods 

of a few weeks or months would likely yield results which 

could be reliably extrapolated to yearly quantities. As a 

control, the water losses from the soil should be 

measured and the fluctuations of the ground-water levels 

should be observed. It is along these lines that further 

research in water use by phreatophytes (and other plant 

covers) would be desirable and possible. 

REFERENCES 

Arkley, R. Y., 1963, Relationships between plant growth and 

transpiration: Hilgardia, v. 34, p. 559-584. 

Baum, B. R., 1967, Introduced and naturalized tamarisk in the United 

States and Canada (Tamaricaceae): Baileya, v. 15, p. 19-25. 

Benz, L. D., Willis, W. 0., Nielson, D. B., and Sandaval, F. M., 1965, 

Neutron moisture meter calibration for use in saline soils: Agr. 

Eng., v. 46, p. 326-327. 

Brooks, C. E. P., and Carruthers, N., 1953, Handbook of statistical 

methods in meteorology: London, Her Majesty's Stationery Office, 412 p. 

Chang, Jen-Hu, 1968, Climate and agriculture: Chicago, Aldine 

Publishing Co., p. 129-244. 

Colman, E. A., 1953, Vegetation and watershed management: New 

York, Ronald Press, 412 p. 

Douglas, E., 1967, Confusion among the saltcedars: Arizona FarmerRanchman, v. 46, no. 23. 

Ferris, J. G., 1959, Groundwater, chapter 6 of Wisler, C. 0., and 

Brater, E. F., Hydrology: New York, Wiley and Sons, Inc., 408 p. 

Fisher, R. A., 1944, Statistical methods for research workers: London, 

Oliver and Boyd, Ltd., chap. VII, VIII. 

Fisher, R. A., and Yates, F., 1943, Statistical tables: London, Oliver 

and Boyd, Ltd., table V. 

Gatewood, J. S., Robinson, T. W., Colby, B. R., Hem, J.D., Halpenny, 

L. C., 1950, Use of water by bottom land vegetation in lower Safford Valley, Arizona: U.S. Geol. Survey Water-Supply Paper 1103, 

210 p. 

Harbeck, Jr., G. E., Kohler, M. A., Koberg, G. E., and others, 1958, 

Water-loss investigations: Lake Mead studies: U.S. Geol. Survey 

Prof. Paper 298, 100 p., 1 pl. 

Horton, J. S., 1964, Notes on the introduction of deciduous tamarisk: 

U.S. Forest Service Research Note RM-16, p. 1-7. 

Horton, J. S., Robinson, T. W., and McDonald, H. R., 1964, Guide for 

surveying phreatophyte vegetation: U.S.D.A. Forest Service, Agr. 

Handbook No. 266, Washington, D. C., 37 p. 

Huschke, R. E., ed., 1959, Glossary of meteorology: Am. Meteorol. 

Soc., 638 pp. 

Mather, J. R., ed., 1954, The measurement of potential 

evapotranspiration: Johns Hopkins Univ. Pubs. Climatology, VII, 

p. 7-225. 

McDonald, C. C., and Hughes, G. H., 1968, Studies of consumptive use 

of water by phreatophytes and hydrophytes near Yuma, Arizona: 

U.S. Geol. Survey Prof. Paper 486-F, 24 p. 

Meinzer, 0. E., ed., 1927, Plants as indicators of ground water: U.S. 

Geol. Survey Water-Supply Paper 577, 95 p. 

Penman, H. L., 1948, Natural evaporation from open water, bare soil, 

and grass: Royal Soc. [London] Proc. A, v. 193, p. 120-246. 

__ 1955, Evaporation, an introductory survey: Netherland Jour. 

Agr. Sci., v. 4, p. 9-29. 

Penman, H. L., and Schofield, R. K., 1941, Drainage and evaporation 

from fallow soil at Rothamsted: Jour. Agr. Research, v. 31, p. 74-

109. 

Rider, N. E., 1956, Water losses from various land surfaces: Quart. 

Jour. Royal Meteorol. Soc., v. 83, p. 181-193. 

Robinson, T. W., 1970, Evapotranspiration by woody phreatophytes in 

the Humboldt River Valley near Winnemucca, Nevada: U.S. 

Geol. Survey Prof. Paper 491-D, 41 p. 

Robinson, T. W., and Bowser, C. W., 1959, Buckeye Project-water use 

by saltcedar: U.S. Geol. Survey and Bur. of Reclamation open-file 

rept. 

Tanner, C. B., 1960, Energy balance approach to evapotranspiration 

from crops: Soil Sci. Soc. America Proc., v. 24, p. 1-9. 

Task Force on Use of Neutron Meters, Committee on 

Hydrometeorology, 1964, Use of neutron meters in soil moisture 

measurement: Am. Soc. Civil Engineers Proc., Jour. Hydraulics 

Div., v. 90, p. 21-43. 

Thornthwaite, C. W., 1948, An approach toward a rational classification of climates: Geog. Rev., v. 38, p. 54-94. 
E30 STUDIES OF EVAPOTRANSPIRATION 

Thornthwaite, C. W., and Mather, J. R., 1955, The water balance: 

Johns Hopkins Univ. Pubs. Climatology, v. VIII, p. 1-104. 

U.S. Bureau of Reclamation, 1964, Pacific southwest water plan, 

supplemental information report on water salvage projects: Lower 

Colorado River, Arizona-California: Denver, Colo., U.S. Bur. 

Reclamation, 115 p. 

U.S. Geological Survey, 1954·, Water-loss investigations-Lake Hefner 

studies, technical report: U.S. Geol. Survey Prof. Paper 269, 158 p. 

van Hylckama, T. E. A., 1963, Growth, development, and water use by 

saltcedar: Internat. Assoc. Sci. Hydrology, Pub. 62, p. 75-86. 

__ 1966, Evaporation from vegetated and fallow soils: Water 

Resources Research, v. 2, p. 99-103. 

__ 1968, Water level fluctuations in evapotranspirometers: Water 

Resources Research, v. 4, p. 761-768. 

For instance if we have two treatments, differences in 

depth to ground water and flushing versus non flushing, 

we may write: 

Tij =m+di+{ j+eij, (1) 

where m is the overall effect or mean, di is the effect of 

depth to water on water use, fj is the effect of flushing or 

nonflushing, eij is the error, and Tij is the water use 

value in a tank treated with a depth to water value, i, 

and a flushing treatment, j. Applying the method of 

least-squares we can arrive at an equation of the type: 

White, W. (2) N., 1932, A method of estimating ground-water supplies 

based on discharge by plants and evaporation from the soil: U.S. 

Geol. Survey Water-Supply Paper 659-A, 105 p. in which the C's are constants. Thus, one obtains a set of 

actual and theoretical results to which a test of linearity 

APPENDIX: ANALYSIS OF VARIANCE WITH: can be applied. Then, a t-test to the partial regression ~ MUL TIP(E CLASSIFICATION coefficients would show that, for instance in table 5, the 

If an investigator subjects units of his experiments depth to water was the overriding influence on the quanto a variety of treatments it is possible by statistical tities of water used and that the effect of years was only 

analysis (provided the experiment is properly very small. This method, however, is slow and the error 

designed) to separate the effects of each treatment sum of squares is much more quickly computed by a 

from random, or so-called e~ror, effects. If the err~r technique known as the analysis of variance. In the 

effects du.e to u~expected Influe~ces are larg~, It method of least-squares each observation is represented 

becomes u~po.s~Ible to ~raw ~ehable conclusiOns I as the sum of two or more components according to the 

about the significance ~f IntentiOnal treatments. mathematical model; in the analysis of variance the sum 

For example, in this paper units are tanks or saltcedar of such squares of the observation is partitioned accordtwigs, treatments are depth to water, salinity of soil ing to components. This is illustrated in the analyses of 

moisture, and so on. The random or error effects result variance given in tables 5, 7, and 12. The F-test is then 

from possible differences in exposure to wind or sunlight, applied, and the value obtained is compared with those 

from differences in the functioning of the plumbing ap- in an F table. It is customary to mark F's that indicate 

paratus, from mistakes in chemical analysis or significant differences at the 1-percent level with a double 

measurements, and from other differences between asterisk, those at the 5 percent level with a single 

plants or tanks. 1 variation and interaction that has been computed. Thus 

Since there were only six large tanks the number of one has an estimate of those treatments which had 

prescribed treatments was limited to two; otherwise we significant effects on water use and those which did not. 

would have lost too many degrees of freedom and an The final step is to compute the least significant 

analysis of variance would have been impossible. Our difference, which is done by making use of the so-called 

mathematical model thus becomes a relatively simple t-table. The distribution of t is used to test the 

one. We might say that the magnitude of a particular significance of a deviation when its standard error is esobservation is comprised of the following components: timated from the data. Thus, t is the deviation divided 

(1) the value of a mean that all observations in a par- by its estimated standard error. Then the least signifiticular experiment have in common, (2) one or more cant difference is computed by multiplying the apcomponents arising from particular treatments, and (3) propriate t-value by the root of the mean square for 

a component resulting from errors and random effects.

1 

error. This is the yardstick by which we can judge the 

significance of the differences due to treatment. See 1

A lucid discussion is given by Fisher (1944). We must assume here that the reader is familiar 

with such terms as: mean, standard deviation, variance, and degree of freedom. tables 5, 7, 9, 10 and 12. 

f:r US GOVERNMENT PRINTING OFFICE: 1974-677-304/7