UNIVERSITY OF CALIFORNIA

COLLEGE OF AGRICULTURE

AGRICULTURAL EXPERIMENT STATION

BERKELEY, CALIFORNIA

Water Requirements of Cotton on

Sandy Loam Soils in Southern

San Joaquin Valley

S. H. BECKETT AND CARROLL F. DUNSHEE

BULLETIN 537

August, 1932

UNIVERSITY OF CALIFORNIA PRINTING OFFICE BERKELEY, CALIFORNIA

CONTENTS

PAGE

Introduction 3

General description of the area 4

Soil types of the area 5

Water supply 6

Climate 6

Definition of terms 7

Location of experimental plots and methods of procedure 8

Size of plots 9

Irrigation and measurement of water 10

Preparation of seed bed and seeding 11

Soil sampling and computation 11

Preliminary observations, season of 1926 12

Conclusions from preliminary observations 13

Field-plot investigations during 1927, 1928, 1929, and 1930 13

Results of soil-moisture observations 15

Seasonal use of water by cotton 26

Growth and yield 28

Effect of irrigation on size of plants 28

Effect of irrigation on flowering 29

Effect of irrigation on shedding and number of bolls 31

Effect of irrigation on length of fiber and lint index 32

Effect of irrigation on yields 33

Use of water and yields of cotton grown in tanks 33

Purpose of experiment 33

Description of tanks and equipment 35

Irrigation treatments 36

Procedure 37

Use of water by cotton grown in tanks 37

Flowering records and yields of cotton grown in tanks 43

Conclusions.... 44

WATER REQUIREMENTS OF COTTON ON SANDY

LOAM SOILS IN SOUTHERN

SAN JOAQUIN VALLEY1

S. H. BECKETT2 and CARROLL F. DUNSHEE3 INTRODUCTION

Cotton has been produced on a commercial scale in the San Joaquin Valley of California since 1918, when 1,100 acres of cotton was reported. In 1930, 270,000 acres was harvested; and cotton is now one of the major crops in the Valley.

Throughout the cotton-producing area of San Joaquin Valley, production depends almost entirely upon irrigation; and, because of wide variation in the soil types upon which the crop is grown, the irrigation problem is complex. Methods and practices of irrigation adapted to one locality may not necessarily apply to another locality where a different soil type predominates.

This bulletin presents the results of a five-year study dealing principally with the irrigation requirements of cotton grown on the sandy loam soils of the Delano series, and with the effects of soil- moisture deficiency on growth and yields.

The investigations described covered the years 1926 to 1930, inclu- sive, and were conducted at the United States Cotton Field Station at Shafter, California.4

i Received for publication May 10, 1932.

2 Professor of Irrigation Investigations and Practice and Irrigation Engineer in the Experiment Station.

s Assistant Crop Irrigationist in the Experiment Station ; resigned June 30, 1929.

4 During the first three and one-half years, the field work on which this report is based was in charge of Carroll F. Dunshee, who, with the senior author, organized the work and carried the responsibility of planning the experiments and successfully conducting them through that period. In 1929 and 1930 the field work was conducted by L. C. Schultz, Assistant Crop Irrigationist in the Experiment Station. The senior author has been associated with the study in an advisory capacity from the begin- ning. During 1926, 1927, and 1928, valuable advice and assistance in planning and carrying out the field and laboratory work were received from W. B. Camp, then Agronomist and Superintendent of the Cotton Field Station at Shafter. His successors, Fred W. Herbert and J. E. Hite, continued the splendid cooperation during the last two years of the investigations. John W. Carter, Assistant Scientific Aid; W. E. Clark, Junior Agronomist; and Joe F. Schuh, Assistant Scientific Aid, all of the Cotton Field Station, gave material help in the detailed field work of the experiments.

University of California — Experiment Station

GENERAL DESCRIPTION OF THE AREA

Cotton growing in the San Joaquin Valley is confined principally to the six most southerly counties (Kern, Tulare, Kings, Madera, Fresno, and Merced), with a limited area in Stanislaus and San Joaquin counties. Of the 270,000 acres harvested in California in 1930, 88 per cent was in the San Joaquin Valley. However, the cotton acreage in California is less than 1 per cent of the total for the United States.

TABLE 1 Area of Cropped Lands and Area of Cotton Harvested in 1930 in Each of the Counties in the Cotton-Producing Areas of California, with the Average Yields per Acre and the Gross Production in Bales

District or county	Area of cropped land*	Area of cotton harvested in 1930\|	Average yield of cotton fiber per acre in 1930t	Gross production in 1930t
	acres 316,900 201,600 458,300 83,300 236,300 138,000 675,300	acres 63,400 51,300 47,000 26,800 21,600 25,200 2,900 238,200	pounds 484 602 479 450 354 532 217 495	bales (500 pounds) 64 , 090
Kern County	64,585
	47,066
	25,200
	15,962
Kings County	28,012
	1,316

	2,109,700	246,231

Palo Verde Valley	32,300 16,000	15,900 1,500	286 392 295	9,517
	1,229

		17,400	10,746

Imperial Valley	424,100 5,100	8,600 5,800	125 375 225	2,239
Bard area	4,541

	429,200	14,400	6,780

		270,000	468	263,757

* Land classification by State Engineer, 1929.

t Report of California Cooperative Crop Reporting Service, 1930.

Table 1 shows the areas of cropped land and the areas of cotton harvested in the cotton-producing counties or districts in California in 1930, the average cotton yields per acre, and the gross production in bales.

Figure 1 shows the general location of the principal cotton- producing areas in the San Joaquin Valley.

Bul. 537] Water Requirements of Cotton on Sandy Soils 5

Soil Types of the Area. — Throughout the cotton-producing areas of the San Joaquin Valley a wide variation in soil type is found, ranging from the light sandy loams and fine sandy loams of the Hanford, Delano, Fresno, and San Joaquin series to the extremely heavy clay adobes of the Stockton and Panoche series. Although

Fig. 1. — Location of the principal cotton-producing areas in the San Joaquin Valley, 1930. Each dot represents 1,000 acres.

information is not available for an accurate estimate of the cotton acreage on each of the soil types, a general survey of the area, indi- cates that production on the sandier types amounts to at least 75 per cent of the total. In the Bakersfielcl, McFarland, Wasco, and Hanford areas, the Hanford and Delano fine sandy loams and sandy loams

6 University of California — Experiment Station

are the most prominent. In the Madera and Fresno areas, the sandy loams and loams of the San Joaquin, Madera, Fresno, and Hanford series are the most common.

The heavier soil types upon which cotton is extensively grown are found in the lands bordering the Buena Vista and Tulare lake beds and in the area extending along the west side of the central part of the valley. In the Buena Vista and Tulare lake areas, the heavy soils are principally the loams, clay loams, and clays of the Tulare and Pond series. On the west side of the valley, including the Tran- quillity, Firebaugh, and Dos Palos areas, the heavy types include the Stockton and Fresno loams and clay loams, the Merced clays, and the very heavy Stockton and Panoche clay adobes.

Water Supply. — The water supply for the cotton area of the San Joaquin Valley is obtained by gravity and by pumping. The principal gravity supplies come from the Kern, Kaweah, Kings, San Joaquin, and Merced rivers.

The principal pumped areas are found bordering Buena Vista and Tulare lakes in Kern and Kings counties; in the vicinity of Arvin, Shafter, McFarland, Wasco, and Delano in Kern County; in the Tulare and Tipton areas of Tulare County; and above the gravity canals on the west side of the valley in Fresno and Merced counties. Numerous pumping plants are also found in the areas generally covered by the gravity supplies. In practically all of the main pumped areas, the underground water level has been decidedly lowered from year to year.

Climate. — The climate is characterized by dry, hot summers and limited rainfall, practically all occurring between harvest and plant- ing. The lower and flatter parts of the valley are most frequently visited by frosts, the usual frost period extending through, the months of December, January, and February. The highest and lowest temperatures recorded in the cotton area of the San Joaquin Valley are 118° and 13° Fahrenheit. Temperatures of 105° to 110° F are not unusual.

Table 2 gives a comparison of temperatures and rainfall, and table 3 shows the general frost data at different points in the valley, both being taken from the annual summaries of the United States Weather Bureau.

Bul. 537] Water Requirements of Cotton on Sandy Soils

TABLE 2

Annual Temperatures and Precipitation at Various Centers of the Cotton-Producing- Areas of the San Joaquin Valley*

	Length of record	Temperature 1	Seasonal rainfall
Locality	Maximum	Minimum	Mean	Maximum	Minimum	Average
Bakersfield Tulare	years 33 40 41 50 44 23 39	°F 118 114 115 116 111 113 110	°F 13 18 17 16 15 14 20	°F 64.6 62.4 63 0 62.2 63.8 61.6	inches 9 30 13.70 19.45 22 08 19.04 12.51 14.41	inches 2.77 3.07 4.96 3.20 3.58 5.57 3.24	inches 5 71 8 12
	9 82
Merced	11.17
	10.55
	8 77
Los Banos	8.52

* U. S. Dept. Agr. Summary of climatological data for the United States. Section 14. — Central California.

TABLE 3

Dates of Killing Frosts and Length of Growing Season at Different Localities in the San Joaquin Valley*

Locality	Length of record	Average date of last killing frost in spring	Average date of first killing frost in autumn	Average length of growing season	Latest date of killing frost in spring	Earliest date of killing frost in autumn
Bakersfield Tulare	years 21 12 26 25 14 24 16	February 22 March 13 February 14 March 1 February 1 March 7 January 16	November 25 November 18 November 19 November 20 December 5 November 13 December 6	days 276 250 288 264 307 251 324	April 1 April 11 April 13 April 29 March 1 May 26 February 18	October 21 October 20
Fresno	October 31
Merced	October 27
Modesto	November 11
	October 19

* U. S. Dept. Agr. California.

Summary of climatological data for the United States. Section 14.— Central

DEFINITION OF TERMS

In presenting the results of these investigations, reference is fre- quently made to a number of terms used in irrigation practice. The most common of these are here denned :

Moisture percentage: the weight of water contained in a volume of soil, divided by the oven-dry weight of the soil and multiplied by 100. It is a comparison between the weight of water in a soil and the oven-dry weight of that soil.

Apparent specific gravity: the oven-dry weight of a volume of undisturbed soil divided by the weight of an equal volume of water.

Moisture equivalent : the amount of water retained in a soil against a centrifugal force 1,000 times gravity. It is expressed as a per-

8 University of California — Experiment Station

centage of the oven-dry weight of the soil, and is a laboratory method of estimating the amount of water contained in the wetted portion of a soil.

Field capacity: the amount of water held in a soil against the force of gravity under unrestricted drainage. It is the moisture condition found in the wetted portion of the soil after an irrigation or rain and after removal of the free water by drainage.

Permanent wilting percentage:5 the moisture percentage in the soil at which plants wilt and do not recover unless water is added to the soil. It is expressed in percentage of moisture based on the oven-dry weight of soil.

Temporary wilting percentage: the moisture percentage in the soil at which the leaves of the plant lose their turgidity for short periods of time, but revive without the application of water.

Efficiency of irrigation: the percentage of the water applied to the land that is accounted for in soil-moisture increase in the soil mass occupied by the principal rooting system of the plant.

Redaction of moisture percentages to acre-inches of water: in reducing moisture percentages to equivalent losses in acre-inches per

acre, the formula D = is used, where P represents the moisture

percentage, v the apparent specific gravity of the soil (often referred to as the volume weight), d the depth of soil in inches, and D the equivalent depth of water in acre-inches per acre.

LOCATION OF EXPERIMENTAL PLOTS AND METHODS OF PROCEDURE

In starting the investigation reported herein, it was decided that more information of value could be obtained by an intensive study of the effects of variable irrigation treatments given to plots of limited areas than by less complete studies in commercial fields. The advantages of the smaller field plots are that they may be selected for uniformity in depth and type of soil; that they may be more evenly leveled ; that water may be more evenly applied to them than to larger areas ; and, finally, that they permit a more accurate record of seasonal soil-moisture conditions and fluctuations.

The work was centered at the United States Cotton Field Station at Shafter in Kern County because of the splendid facilities offered

5 Veihmeyer, F. J., and A. H. Hendrickson. Essentials of irrigation and culti- vation of orchards. California Agr. Ext. C'ir. 50:1-24. 1930.

Bul. 537] Water Requirements of Cotton on Sandy Soils

i)

there. This station, located about 20 miles northwest of Bakersfield, is in one of the principal cotton-producing' areas of the southern San Joaquin Valley.

The soil where the experimental plots were located is classed as a Delano sandy loam, typical of much of the plains area northwest and southeast of Bakersfield. Cotton is one of the principal crops produced in the area occupied by this soil type.

Delano sandy loam is grayish-brown and gritty, contains some mica, and is fairly uniform in texture to a depth of 5 feet. Below 5 feet is a layer of coarse sand of varying thickness. This type, though low in organic matter, is very fertile and easily cultivated, and takes water readily. Table 4 gives the principal characteristics of this soil as found at the Cotton Field Station.

TABLE 4

Characteristics of Delano Sandy Loams at United States Cotton Field Station on Which Plot Experiments Were Conducted

Depth of soil	Apparent specific gravity	Moisture equivalent	Observed field capacity	Permanent wilting percentage	Water-holding capacity between permanent wilting percentage and field capacity
	1.42 1.50 1.53 1.55 1.51 1.47 1.50	per cent 10.11 8.78 10.36 10.52 9.08 5.85 10 10	per cent 11.00	per cent 3.50	acre-inches per acre-foot of soil

Third foot

Fifth foot

Average for first 5 feet	1.35

Irrigation water is obtained by pumping from two wells, one 12 inches and the other 14 inches in diameter. The pumps discharge into an earthen reservoir of about 1 acre-foot capacity. Distribution from this reservoir is made through a concrete-pipe system equipped with necessary gates and valves for constant-flow regulation.

Throughout the five years of the experiment, irrigation water was obtainable on demand and in any desired quantity.

Size of Plots.— During 1926, plots 40 feet wide and 300 feet long were used, each containing 9 rows of cotton spaced 48 inches apart. Beginning in 1927, however, the size of all plots was reduced to 16 by 90 feet, and the number of replications increased to nine for each of the major treatments. Four rows 48 inches apart were seeded in each plot, and the cotton was chopped to the same number of plants

10

University of California — Experiment Station

in each row, with as nearly as possible an equal spacing of 12 inches between plants. In chopping, special care was taken to leave only normal plants. Soil samples, and all counts, measurements, and yield data were taken each year (including 1926) from the two middle rows of the plots, the outside rows being left as guards.

Fig. 2. — A field ditch and rectangular weirs used in delivering and measuring water to cotton plots.

Irrigation and Measurement of Water. — Water was delivered to each of the plots either directly from the concrete pipe line or from temporary field ditches. This arrangement permitted uniform application of any desired depth of water to the plots.

All water applied to the plots was measured through 1-foot rec- tangular weirs, installed in the field ditches extending along the upper

Bul. 537] Water Requirements of Cotton on Sandy Soils 11

end of each tier of plots. Weir measurements of the flow were made at 5-minute intervals during" the irrigation of each plot. Figure 2 shows a field ditch with weirs used in delivering and measuring water to the plots.

In each irrigation, including that given before planting, sufficient water was added to bring the soil in each plot to its full field capacity, to a depth of at least 5 feet.

Preparation of Seed Bed and Seeding. — Recognized good practices were used in preparing the seed bed and in seeding. Each year selected seed of the Acala variety was used, and a standard width of planting of 48 inches between rows was maintained. All plots were irrigated by flooding; and, while the plants were small, each irriga- tion was followed by a cultivation. As the season advanced, the size of the plants necessitated discontinuance of cultivation.

Where the condition of the cotton plant, as indicated by change in color of the foliage or wilting, was used as a basis for determining the time to irrigate, reliance was placed on the judgment of qualified authorities of the Cotton Field Station.

Soil Sampling and Computation. — Soil samples were taken on each plot to a depth of 5 feet before and after every irrigation, and a record was made of the quantity of water applied each time. Frequent measurements were also made of the average depth of moisture pene- tration when different depths of water were applied, and of the variation in depth of penetration through the length of the border checks.

All soil samples were taken with the improved soil tube.6 In obtaining the soil samples, the top 3 inches of soil was removed, and the samples were taken from definitely established sampling points at 1-foot intervals, to a depth of 5 feet, Standard methods were used in weighing and drying the soil samples and in computation of mois- ture percentages. Soil samples were taken at the beginning and end of the season as well as before and after each irrigation. From the moisture percentages thus obtained, the amounts of water in acre- inches per acre from each foot of soil were computed by using the

Pvd previously discussed formula D = 1 ; the total loss was then

reduced to equivalent losses for 30-day periods, The method of cal- culation may perhaps be made clearer by showing the detailed steps in a particular case. To obtain the average rate of loss for treatment

6 Veihmeyer, F. J. An improved soil sampling tube. Soil Science 27:147- 152. 1929.

12

University of California — Experiment Station

1, plot 23, from July 6 to July 14, for example, the average moisture content for each foot of depth on July 6 and July 14 is obtained from table 5, and the percentage loss and equivalent loss in acre-inches per acre calculated as shown in the accompanying table. The average rate of loss per 30 days can then be calculated from the total equiva- lent loss in acre-inches per acre from July 6 to July 14 (8 days) :

2.56X30 Q_n

= 9.60 acre-inches per acre.

o

These losses were next plotted, and a consumptive use-of-water curve for the season was obtained. The average consumptive use of water for each month was then taken directly from the curve.

	First foot	Second foot	Third foot	Fourth foot	Fifth foot	Total
Average moisture content, July 6, per	10 2 5.4 4.8 1.50 0.86	9.6 5.8 3.8 1 50 0.68	10 7 7.8 2.9 1.50 0.52	11.9 9.2 2.7 1 50 0.48	10 4 10 3 0.1 1 50 0.02
Average moisture content, July 14, per
Loss, July 6 to July 14, per cent

Equivalent loss, acre-inches per acre*....	2.56

* Calculated for each foot by the formula D acre-inch per acre.

Pvd . ., -. ., ++u. .,. 4.8x1.50x12 — — ; for the first foot this would be — —

0.86

PRELIMINARY OBSERVATIONS, SEASON OF 1926

The season of 1926 was spent in studying the effects of a limited number of treatments on plots at the Cotton Field Station, and in observing the results of different irrigation practices on commercial fields in the southern San Joaquin Valley.

Early in April, four border plots were set aside for these pre- liminary studies, and the following irrigation treatments were outlined :

Treatment A (duplicate plots) : To be irrigated when the plants showed by their change from a light green to a dark bluish-green color that they were nearing the wilting stage. This treatment was expected to produce normal growth and yields.

Treatment B (single plot) : To be irrigated when the plants showed definite indications of wilt at 4 p.m.

Treatment C (single plot) : To be irrigated when the plants showed definite indications of wilt at 9 a.m. This is a more severe treatment than treatment B.

Buii. 537] Water Requirements of Cotton on Sandy Soils 13

At different times during" the season, counts were made of the shedding of the squares and of the number of bolls set on twelve representative plants under the 4 p.m. and 9 a.m. wilt treatments. At the end of the season, comparative yield records were obtained from these two plots.

Conclusions from Preliminary Observations. — All the growers interviewed, as well as those interested in investigational work in cotton production, believed proper irrigation to be one of the most important factors affecting the yield and the quality of the product. The field observations and plot studies in 1926 led to the following conclusions :

1. Cotton is sensitive to soil-moisture fluctuations; one of the causes of excessive shedding of the squares is unfavorable soil-moisture conditions.

2. The average yield of cotton in the upper San Joaquin Valley was reduced by an amount estimated at from 10 to 15 per cent because of improper irrigation in the latter part of the season.

3. Poor preparation of land for irrigation very often accounts for the ' ' spotted ' ' condition of growth and yields.

4. Where the water is limited, there is a tendency to serve too large an acreage with the supply at hand.

The Delano sandy loams at the Shafter Station have a field capa- city of about 11 per cent and a temporary wilting percentage of from 4.0 to 4.5 per cent. Permanent wilting occurred at 3.5 per cent.

With the soil at the permanent wilting percentage, 1.35 acre-inches of water per acre was required to bring 1 foot depth of soil to its field capacity.

A definite difference was shown in shedding, number of bolls, and yields in the plots irrigated when the plants wilted at 4 p.m. and at 9 a.m. The 4 p.m. -wilt plots had 11.3 per cent less shedding, produced 13.7 per cent more bolls, and yielded 15 per cent more cotton.

FIELD-PLOT INVESTIGATIONS DURING 1927, 1928, 1929,

AND 1930

After the preliminary observations of 1926, the investigations were limited to field plots and to tanks located at the Cotton Field Station at Shafter. The tank layout and the procedure and results obtained are discussed in a later section of this bulletin.

From 1927 to 1930 the method of measuring the amounts of water applied to the plots, the preparation of the seed bed, the selection of seed, and the seeding, were substantially the same as during 1926.

14 University of California — Experiment Station

In each of the four years the following irrigation treatments were given :

Treatment 1 : Irrigated when the average moisture content of the top 5 feet of soil reached approximately 7 per cent. This is about halfway between field capacity and the permanent wilting percentage. It was anticipated that if the average moisture content were main- tained above this figure, readily available moisture would be present in the entire soil depth throughout the season, and that at no time during the season would the plants show indications of approaching the wilting stage.

Treatment 2: Irrigated when the plants wilted at 4 p.m. Mid- afternoon wilt shows a lack of available moisture in the soil ; a change in color of the foliage from a light green to a dark bluish-green indicates that the plants are approaching wilting.

Treatment 3 : Irrigated when the plants wilted at 9 a.m. Early- morning wilt was considered to indicate definite distress in the plant resulting from a lack of soil moisture.

Treatment 4: Irrigated as in treatment 1 until midseason (about July 20), after which water was not applied until the plants wilted at 9 a.m. It was anticipated that in this treatment an abundance of soil moisture would be available during the first half of the season, with a definite deficiency during the last half.

Treatment 5 : Irrigated during the first half of the season (until about July 20) when the plants wilted at 9 a.m., as in treatment 3, after which it was irrigated as in treatment 1. Treatment 5 thus provided for a deficiency in available moisture during the first half of the season and no deficiency during the second half.

Treatment 1a : In this treatment, introduced during the 1930 season, water was added when the plants changed from a light green to a dark bluish-green color. This change in color usually occurs several days in advance of wilting and is the first indication given by the plant of soil-moisture shortage. The total depth of water applied during the season was intermediate between the amounts applied in treatments 1 and 2.

Treatment Iaa: This, the second new treatment added in 1930, was planned as an intermediate treatment between 1 and 1a, with the water applied when the moisture content of the soil, to a depth of 5 feet, had reached an average of 5.5 to 6.0 per cent.

Figure 3 shows the general arrangement of the plots with the plot number and irrigation treatment. Substantially this same arrange-

Bul. 537] Water Requirements of Cotton on Sandy Soils

15

ment was followed during 1927, 1928, 1929, and 1930. This arrange- ment provided for nine replications of treatments 1 and 2, eight of treatment 3, and five of treatments 4 and 5. In 1930 five new plots were added to take care of treatment 1a, and four for treatment Iaa.

Waste check 26	Waste check 13	Tank	Yard
© 87	® 14	' ®	T /
® 88	® 15	©	2
® 89	© 16	©	3
© 30	® 17	©	4
© 31	® * 18	©	5
® 32	, ® * 19	©	6 lt
® 33	© % 20	3 ©	7
® 34	© * 21	®	8
® 35	© * 22	®	9
® 36	® * 23	©	/O
® 37	® & 2*	©	//
® 38	® * 25	©	12

~we/r

fcweir

Fig. 3. — Arrangement of field plots, delivery ditches, and' weirs, 1927, 1928, and 1929. The stars indicate plots in which soil samples were taken. The treat- ments, indicated by the numbers in circles, were as follows: (1) irrigated when moisture content reached about 7 per cent; (2) irrigated when plants wilted at 4 p.m.; (3) irrigated when plants wilted at 9 A.M. ; (4) high moisture content early in season, low last half of season; (5) low moisture content early in season, high last half of season.

Results of Soil-Moisture Observations. — Throughout each of the four seasons, soil samples were taken to a depth of 5 feet before and after each irrigation at four fixed locations in duplicate plots under treatments 1, 2, and 3, and in single plots under treatments 4 and 5, as well as from duplicate plots in treatment 1a during 1930.

The methods of summarizing the data collected are illustrated in tables 5 and 6. Table 5 summarizes the average moisture content of plot 23 at each sampling, with the dates and quantities of irrigation water applied to it during 1927. In table 6 the moisture percentages obtained from plots 19 and 23 (both given treatment 1) have been reduced to acre-inches of water per acre taken by the growing crop from each foot in depth of soil ; similar data were obtained from each of the plots sampled during the four-year period. Soil-moisture deter- minations were made on approximately 3,000 samples each year. Tables 7 to 10 show the rates of use of water in the intervals between irrigations for each treatment during each of the four years, calculated from the moisture percentages found.

16

University of California — Experiment Station

TABLE 5

Average Moisture Content and Dates and Amounts of Irrigation for Treatment 1, Plot 23 ; May 11 to November 1, 1927

Dates of sampling

May 11

June 2

June 6

June 21

June 24

July 2

July 6

July 14

July 18

July 25

July 28

August 9

August 12

August 23

August 27

September 13 September 16 September 29

October 3

November 1*.

Total

Average moisture content of soil

First foot

10

per

cent 8.1 6 2 2 3 6 6 1

10.2 5.4 9.4 5 2

10.9 5.2 9 8 5.4

10 8 5.4

10 7 6.8

11.0

10.7

Second foot

per

cent 8 0 7.7

10 0 8.5

10 8 7.4 9.6 5.8

1 7 4 7 4 3

9.4

5.1 10.1

7.2 10 4

6.7

Third foot

per

cent 9 5 9 3

11.0 98

11 5 9.7

10.7 7.8 9.7 6.4 9.8 5.5 9.8 5.7 7.5 5.2

10.0 7 3

10.8 7.7

Fourth foot

per cent 9.2 10.1 11.3 10 3

11.6

10 0

11 9 9.2 9 2 8.1 9.2 6.7 9.2 6.6 6.6 4.8 5.8 6.7

10.5 8.1

Fifth foot

per cent 9.1 9.2 9 3 9.2 10.4 10.1 10.4 10 3 9.4 9.1 8.7 7.1 7.5

6 2 5.9 4.8 4.3 4.6 8.5

7 1

Dates of irrigation

June 2

June 22

July 4

July 15

July 26

August 9

August 25

September 14 September 30

Amount of irrigation water applied

acre-inches per acre

4

3

4

5

4

38

* 1.35 inches of rain on October 29 and 30.

Bul. 537] Water Requirements of Cotton on Sandy Soils

17

TABLE 6

Quantities of Water Used in Intervals Between Irrigations on Treatment 1, Plots 19 and 23; April 10 to November 1, 1927

Interval

Num- ber of days

Soil-moisture loss, acre-inches per acre

First foot

Second foot

Third foot

Fourth foot

Fifth foot

Total

Equivalent

loss in 30

days

Plot

April 10 to May 11

May 11 to June 2

June 6 to June 21

June 24 to July 2

July 6 to July 14

July 18 to July 25

July 28 to August 9

August 12 to August 23

August 27 to September 13

September 16 to September 29 October 3 to November 1

0 25 0 25 0.88 0.90 0 94 0.70 1.06 0.90 0.86 0 70 0.82

0.11 0.11 0.65 0.61 0.79 0.63 0.77 0.68 0.88 0.48 0.68

0.11 0.09 0.18 0.41 0.50 0.70 0.75 0.66 0.74 0.36 0 49

0 09 0.11 0 31 0.20 0.31 0.20 0.61 0 56 0.40 0.27 0.61

0.11 0 14 0 12 0 14 0.38 0 31 0.70 0.23 0.18

0 47

0

2

3.89

3.03

3.06

1.81

3.07

54

0 65 0 95 4 28 8.46 10.95 10.90 9.70 8.26 5.40 4.18 3.18

Plot 23

May 11 to June 2

June 6 to June 21

June 24 to July 2

July 6 to July 14

July 18 to July 25

July 28 to August 9

August 12 to August 23

August 27 to September 13. September 16 to September October 3 to November 1

0 34 0 70 0.81

0.86 0.76 1.03 0 79 0.97 0 70 0.85

0 06 0 27

0 61 0.68 0.79

1 03 0.74 0.77 0.52 0.67

0 04 0.22 0.32 0.52 0.60 0.77 0.74 0 41 0.48 0.56

0 43

0.18	0.02
0.29	0.05
0 48	0 02
0.20	0.05
0.45	0 29
0.47	0.23
0 32	0 20

0 25

0 44 1.39 2.08

2 56 2.40

3 57 2.97 2.67 1.70 2.76

0 60 2.78 7.80 9.60 10 30 8.92 8.10 4.71 3.92 2 86

18

University of California — Experiment Station

table 7

Rates of Use of Water in Intervals Between Irrigations in Treatments 2, 3, 4, and 5; Season of 1927

Interval

Num- ber of days

Acre-inches per acre

Soil- moisture

Equivalent loss in 30 days

Interval

Num- ber of days

Acre-inches per acre

Soil- moisture loss

Equivalent loss in 30 days

Treatment 2

Plot 20

April 10 to May 11 May 11 to June June 9 to July July 13 to July 26 July 28 to Aug. 18 Aug. 20 to Sept. 1 Sept. 3 to Sept. 26 Sept. 29 to Nov. 1

31	0 57
22	0.49
29	3.63
13	3.59
21	4.92
12	2.24
23	3.35
33	2.46

0.55 0.67 3.75 8.28 7.03 5.60 4.37 2.24

Plot 24

May June July July Aug.

11 to June 2 9 to July 8 11 to July 21 23 to Aug. 1 19 to Sept. 3 Sept. 6 to Sept. 27 Oct. 1 to Nov. 1

0.67 3.46 2.16 3.91 1.65 3.53 2.23

0.91 3.58 6.48 6.18 3.30 5.02 2.16

Treatment 3

Plot 21	Plot 25
April 10 to May 11	31	0.61	0.59
May 11 to June 2	22	0.67	0.91	May	11 to June 2	22	0.77	1 05
June 9 to July 15	36	5.13	4.28	June	9 to July 15	36	4.79	4 00
July 18 to Aug. 6	19	4.08	6.44	July	18 to Aug. 6	19	3.45	5 45
Aug. 9 to Aug. 30	21	4.34	6.20	Aug.	9 to Aug. 27	18	3.42	5.60
Sept. 2 to Sept. 27	25	3.24	3.89	Aug.	30 to Sept. 27	28	3.35	3.59
Oct. 1 to Nov. 1	31	2.93	2.84	Oct.	1 to Nov. 1	31	1.84	1.78
Treatment 4, plot 18	Treatment 5, plot 22
April 10 to May 11	31	0.56