Cotton Irrigation In the Lower Rio Grancle Valley TEXAS A&M UNIVERSITY" Texas Agricultural Experiment Station R. E. Patterson, Director, College Station, Texas In cooperation with the U. S. Department of Agriculture Contents Summary _________________________________________________________________ __ 2 Introduction .............................................................. __ 3 Definition of Terms .................................................. __ 3 Climate ............................. ..................................... ._ 3 Location and Soils .................................................... __ 4 Willacy Series ................................................. __ 4 Hidalgo Series .................................................. .. 4 Laredo Series .......................................... ....... -. 4 Harlingen Series .............................................. .- 4 Discussion ot-Yield Data ......................................... -_ 4 Moisture Level-Spacing-Planting Date Studies on Willacy Series ............................. .. 4 Moisture Level Studies on Hidalgo Series ....... 6 Moisture Level Studies on Laredo Series .......... _. 7 Moisture Level-Spacing Studies on Harlingen Seriesc ................................... -. 7 Discussion of Water Requirements of Cotton ............ J0 Water Requirement of Cotton on Willacy ........ ..'l0 Water Requirement of Cotton on Harlingen .... ..'ll Irrigation Schedules ..................... ..l ......................... ..'l2 Irrigation Schedules for Cotton Grown on Willacy Loam .............................................. ..'|3 Low Water Supply—-One Irrigation ........ ..'|3 Adequate Water Supply—- ‘ Three Irrigations .................................. ..'|3 Irrigation Schedule—-Harlingen Clay Soil ................ ..'l5 Literature Cited ................. .................................... .-'l 5 Summary Irrigation spacing experiments for cotton ind the water requirement of cotton is dependent up Q type which determines the rooting characterist i cotton plant. Moisture use on the Harlingen cl stricted mainly to the surface 2 feet of soil beca 99 percent of the roots were found to be in the s t of soil. Eighty percent of the roots of the co growing in Willacy loam soil were found to be l 2 feet of soil. However, moisture use on the occurred at lower soil depths because some root ment was found to occur at 3 to 5 feet. Because root growth on Harlingen clay, cotton grown on similar soils must be irrigated more frequently grown on soils of the Willacy or Hidalgo series. Maximum demand for moisture by cotton s during the early flowering stage and continued of the bolls were mature. Additions of water t f gation or rainfall during this critical water de i (during and immediately after bloom stage) in v ton yields. Proper timing of irrigation to coincide i“ of maximum use and demand can reduce wa ~ produce higher yields. ‘ Irrigation schedules for cotton have been p i Willacy loam and Harlingen clay soils. Satisfa” have been produced with a preplanting irrigat"; irrigation about 3O days after appearance of 1 on the Willacy loam soil, but this schedule must i for a given farm situation. Satisfactory yields duced on Harlingen clay when the cotton plantsf gated at approximately 15-day intervals during ing and fruiting period. * Close spacing of cotton (3 to 6 plants per f - é yields when a high level of soil moisture was i’ TTON ACCOUNTS for 40 to 50 percent 0f the p, farm cash income in the Lower Rio Grande alley. As cotton is important to the economy f: the area, research has been conducted at the vwer Rio Grande Valley Experiment Station ‘nce 1949 to find answers to some of the prob- of soil and water management in cotton toduction and to find ways of making more ‘lficient use of the limited supply of irrigation ater. A Studies to determine the influence of mois- 1 re levels, plant spacings and date of planting the yields and quality of cotton on coarse u medium-textured soils were conducted in 149-50 and 1955-57. Results of these studies ere reported previously (3, 4, 5, 7, 8). , Additional research was conducted on the redo clay loam and Willacy loam in 1958 and 59, respectively, and on the Harlingen clay om 1960-62 (9). Research was conducted on idalgo sandy clay loam in 1961-62. Objectives of the investigations were: g 1. To determine the effects of moisture ‘vels, plant spacings and date of planting on v eld, growth and fiber characteristics of cotton. 2. To determine the water requirements of tton as influenced by treatment and stage of nt growth. 3. To determine the best water management actices for the production of acceptable and /or onomical yields of cotton with only a limited pply of irrigation water. The purpose of this publication is to sum- _j rize the results of the studies and to propose 1 gation schedules for coarse and medium-tex- red soils such as the Willacy and Hidalgo soil riesl and fine-textured soils such as the Harlin- 1- c ay. Definition of Terms Available soil moisture refers to the water tained in the soil between the limits of field ipacity and the permanent wilting percentage. lis the moisture available to plants. _ Field capacity is the quantity of water re- v ned in the soil after gravitatio-nal water drains espectively, associate soil physicist, associate agrono- ist, superintendent, Lower Rio Grande Valley Research nd Extension Center (Field Station No. 15), Weslaco, exas; research soil scientist, Soil and Water Conserva- 1'» Research Division, Agricultural Research Service, . S. Department of Agriculture; and head, Department v Soil and Crops Sciences, College Station, Texas. Cotton Irrigation in Lower Rio Grande Valley C. J. Gerard, C. A. Bnrleson, W. R. Cowley, L. N. Namken and M. E. Bloodworth* following an irrigation or heavy rain (1 to 3 days after an irrigation or rain). Permanent wilting percentage refers to the soil moisture remaining in the soil after the plants have withdrawn all they can and wilt permanently. ' Moisture percentage refers to the moisture in the soil based on the weight of the ovendry soil. Ovendry soil refers to a soil that has been heated at 110° C. for 24 hours. Transpiration refers to the water absorbed by the crop or plants and evaporated from plant surfaces. Evaporation refers to the moisture loss from a fallow or barren soil. Evapotranspiration refers to the total mois- ture used in evaporation and transpiration. Climate The Lower Rio Grande Valley includes Cameron, Hidalgo, Willacy and Starr Countie-s and is located at the southern tip of Texas. The climate is subtropical. Weather records for 48 years at the Weslaco station show an aver- age annual precipitation of 23 inches. However, the annual precipitation varies considerably from year to year. The highest recorded annual pre- cipitation during this period was 40.4 inches in 1941; the lowest recorded was 7.8 inches in 1956. Variations in rainfall throughout the growing season emphasize the importance of irrigation to the agricultural economy of the area. The average monthly rainfall over a period of years indicates that the highest amount oc- curs from April through October. These aver- age monthly rainfall data vary from 1 inch in February to about 4 inches in September. The average relative humidity is approxi- mately 75 percent. Open-pan evaporation is ap- proximately 0.15 inch per day (55 inches per year). However, the average daily evaporation loss varies from approximately 0.08 inch per day in January and December to 0.25 inch per day in July and August. Wind velocity is ex- tremely variable, but the average is 4 miles per hour. Prevailing wind direction is from the southeast. A 48-year record at the Weslaco station shows an average maximum temperature of 84.5° F. and an average minimum temperature of 63.3° F. A 25-year period shows an average annual growing season of 330 days, with the average 3 g, 200- K 35 lo 3K Z 2 ‘l’. 5 a ‘Noni-irrigated ‘Low oisture Medium Moisture Figure l. Yield of lint cotton as influenced by four moisture levels and three plant spacings on Willacy fine sandy loam, 1949. date of the first killing frost 0n December 20, and the average date of the last killing frost on January 25. Climatic conditions favor the planting of cotton from February 1 to March 31. Pink boll- worm infestations make it necessary for the farmers to harvest and destroy green cotton stalks each year before September 1 to aid in the control of this pest. Such factors allow a growing period of 120 to 180 days for the cotton crop. Location and Soils Willacy Series (8) Irrigation experiments were conducted on the Lower Rio Grande Valley Research and Ex- tension Center (Field Station No. 15), two miles east of Weslaco, in Hidalgo County. The sta- tion is centrally located in the irrigated area of the Lower Rio Grande Valley. The experiments were conducted on Willacy fine sandy loam and loam soils. The Willacy series is a deep, coarse to medium-textured, moderately permeable soil. The subsoil has a depth of more than 10 feet in places and usually is "classed as a sandy clay loam or clay loam. Moderate to good drainage and a deep sandy clay loam subsoil enables this soil to hold a good reserve of soil moisture. The top 5 feet of this soil will hold 9 to 11 inches of available soil moisture. The organic matter content of the surface 6 inches varies from 1 to 1.5 percent. Hidalgo Series Irrigation studies designed to study the internal moisture stress within plants were con- ducted on Hidalgo sandy clay loam during 1961- TABLE 1. MOISTURE LEVELS USED AND PER- CENTAGES OF MOISTURE AT WHICH IRRIGATION WATER WAS APPLIED TO COTTON ON WILLACY FINE SANDY LOAM SOIL Percentage Percentage of soil M ' t _ moisture at maximum féielre vfmgfsillirrlgle allowable stress 1949 1950 High 75 15.4 13.3 Medium 50 12.8 11.2 Low 25 10.1 9.1 4 62 on the Agricultural Research Servif 5 miles north of Weslaco, Texas. resemble the Willacy soils except the I series are calcareous on the surface; soils are not calcareous to a depth of t‘ 18 inches. The drainage, water-holding ; and organic matter content are similarj Willacy series. . § Laredo Series l An irrigation-fertility experiment ducted in 1958 a few miles southeast of i Texas about 1/4 mile from the Rio Gr The clay loam surface was underlain The sand usually was found at 2 to 3i; also was found at depths of from 1 to r this particular location. Some of the; this location might be classified as a; of Laredo and Cameron soils. Laredo, surface drainage but excellent inte age; Cameron has slow surface drail slow internal drainage. The top 5 fe soil will hold 8 to 14 inches of available i ture. The organic matter of the surfaceii varies from 1.5 to 2 percent. Harlingen Series Irrigation-spacing experiments were conducted about a mile northeast? a reso, Texas. This soil is a clay to a d0, < least 5 feet. The clay mineral is if q montmorillonite. The Harlingen claygi i high swelling and shrinkage, severe cra t dry and very poor surface and internal This soil is highly calcareous ‘and tains over 2 percent organic matter. 5 feet of soil will hold about 7 to 8 available moisture} l Discussion of Yield D Moisture Level-Spacing-Planting Date A on Willacy Series The influence of moisture le j studies in 1949-50 are indicated in and 2 (5). Description of treatmentsi; in Table 1; the amounts of Water Q the different treatments and amount; supplied by rainfall are indicated Cotton yields were significantly in s] irrigation in 1949 but not in 1950., fall after blooming caused an incre‘ yields of cotton on the nonirrigatedé moisture treatments in 1950. Cotton thinned to 6-inch spacin. duced higher yields than cotton spa 18 inches apart when a high level of was maintained, Figures 1 and 2. ‘Field capacity was approximately equivff atmosphere percentage as determined 0n sample in the laboratory. zProcedures used in conducting experiment information of these studies are described in: cultural Experiment Station Bulletin 916 (8 7- ' "ls ABLE 2. AMOUNTS OF WATER APPLIED, EFFEC- TIVE RAINFALL, AND NUMBER OF IRRI- GATIONS ON MOISTURE LEVEL AND PLANT SPACING EXPERIMENT IN 1949 AND 1950 ON WILLACY FINE SANDY LOAM SOIL g Number of irrigations Total I oisture Before During Water Rainfall» Walfler ‘a eat- bloom bloom applied, Inches aPPhed’ i ents stage stage inches Inches f 1949 j g1. 1 4 17.0 3.6 20.6 edium 0 3. 8.5 3.6 12.1 ‘W 0 2 5.5 3.6 9.1 on- rigated 0 0 0 3.6 3.6 1950 " 'gh 2 3 16.4 10.9 27.3 edium 1 3 13.6 10.9 24.5 "w 0 2 7.5 10.9 18.4 zon- 0 0 0 10.9 10.9 I ‘gated The influence of soil moisture treatments i planting dates on yields was evaluated from 55 through 1957 and is indicated in Figure i (8). Descriptions of treatments are indicated p Table 3; the amount of water applied to dif- é ent treatments and rainfall for 1955-57 are dicated in Table 4. Cotton yields were gen- ally increased by irrigation during the bloom- and fruiting period, especially in 1955-56 cause the cotton was grown under relatively conditions. The yield of cotton grown on tment D, planted on March 15, 1956, was . because it failed to receive one scheduled 'gation late in the season. Cotton grown on atment E, which received a preplanting irri- tion and an irrigation 30 to 4O days after ‘a st bloom, averaged over 2 bales per acre dur- 1955-57. This practice produced high yields i} made efficient use of water which is often ited. 1 Yield differences between planting dates 1955-56 were insignificant. However, yields March-planted cotton in 1957 were» higher in February-planted cotton. t; Some factors which may favor delaying on planting until March 1 to 15 are: ) cotton planted in late March requires less ter than cotton planted in early February; ) March-planted cotton may be exposed to -= cold, damp weather which often reduces i200 w ~ . em’ 6,600 ' 1,00 . l. 0 l 2. ‘Yield of lint cotton as influenced by four moisture levels three plant spacings on Willacy fine scmdy loom soil, ‘I950. E Irrigated throughout growth and yield; (3) results seem to indicate that March-planted cotton produces as n1uch or more cotton than February-planted cotton; and (4) planting cotton in March will often reduce» production cost, notably in fewer irrigations. The need for reseeding March-planted cotton probably is less frequent than for February- TABLE 3. IRRIGATION TREATMENTS FOR COTTON GROWN ON WILLACY LOAM SOIL, 1955- 57, 1959 AND LAREDO CLAY LOAM, 1958 Years in Percentage which of soil specific moisture treatments at maximum were allowable evaluated stress‘ Mdsmre a level treatments A Irrigated when the average available moisture content of the top 2 feet of soil reached 65 percent at any time before bloom stage. Cut off irrigation water after blooms appeared. B Irrigated when the average available moisture content of the top 2 feet of soil reached 35 percent before bloom stage. Cut off irrigation water after blooms ap- peared. 1955-59 16.4 Early season 1955-57 12.8 Early season C Irrigated when the 1955-59 12.8 average available Early season moisture content of the to top 2 feet of soil reached 16.4 35 percent before late season bloom stage. From bloom stage until most of the bottom bolls were mature and open, irrigated when the average available moisture content of the top 2 feet of soil reached 65 percent. D Irrigated when the 1955-59 12.8 average available ‘ Early season moisture content of the to top 2 feet of soil reached 16.4 35 percent until the late $688011 bottom bolls were hard ' and firm. From this boll maturity stage un- til approximately three- fourths of the bolls were mature, irrigated when the average avail- able moisture content of the top 2 feet of soil reached 65 percent. 1955-59 11.0 the season when the All season average available mois- ture content of the top 2 feet of soil reached 20 percent. F No irrigation after pre- 1957 planting irrigation. ‘Average soil moisture percentage in top 2 feet of soil, which was used as the moisture control zone. 5 TABLE 4. AMOUNTS OF WATER APPLIED TO DIF- FERENT MOISTURE LEVEL TREAT- MENTS AND AMOUNTS OF RAINFALL DURING THE COTTON SEASON ON WIL- LACY LOAM SOIL, 1955-57 Average Inches 0f Water number Feb. 15 March 15 0f {"1- Treat‘ planting date planting date gatwns ments for each 1955 1956 1957 1955 1956 1957 treat- ment A 6.0 8.1 10.4 6.2 6.1 5.0 2 B 4.7 5.0 6.0 3.0 4.2 5.6 1 C 21.6 21.1 23.3 16.2 17.3 2.4.0 4 D 22.4 15.5 17.8 14.6 10.7 17.6 3 E 6.9 7.7 7.4 7.0 5.7 7.8 1 F 0.0 0.0 0 Total rainfall 3.5 4.3 13.5 3.3 4.0 9.6 planted cotton. However, February-planted cot- ton matures 7 to 10 days earlier, which usually makes the problem of boll weevil and bollworm control less serious than with the March-planted cotton. Cotton planted in February, on the average, can be harvested completely before the possible occurrence of tropical storms and heavy rains late in August, thus reducing the likeli- hood of field losses and poor grades. The influence of irrigation treatments A, C, D and E3 on cotton yields and moisture use was evaluated in 1959 as shown in Table 5. The amount of water applied, number of irrigations for each treatment and rainfall also are indi- cated in Table 5. Yields were significantly in- fluenced by treatments. Cotton on treatment E, which received two irrigations after first blooms produced the highest yields. Cotton on treatment A which received three irrigations before first blooms produced the lowest yields. Insect infestation late in the season and boll rot were probably responsible for the difference in yields between treatments C, D and E. Cotton quality varied slightly with mois- ture treatments and planting dates, but irriga- tion generally decreased strength and increased fiber length (8). Lint percent and boll size were greater in the February-planted cotton “Treatments described in Table 3. TABLE 5. YIELD AND MOISTURE USE BY COTTON ON WILLACY LOAM IN 1959 15 rather than on February 15. Appli t Lint Cotton Pounds per to a a» 5 o o 8 8 o § 8 . t.- _ Inertia B l’ llllllllllilllllllllllll m lllllllllllllllllll t, IIIIIIIIIIIIIIIIIIIIIII 5.; Treatments Figure 3. Effect of soil moisture levels and planting“: cotton yields on Willacy loom soil, 1955-57. than in the March-planted cotton pletion of harvesting usually was dela proximately 7 to 10 days by planting water during fruiting (treatments C, D‘ delayed maturity. Moisture Level Studies on Hidalgo Se? Irrigation treatments based on the; turgidity4 of the cotton leaves on Hidalf clay loam were investigated during 1961 treatment descriptions are listed in the yield and moisture use data are in Table 7. Treatments based on relati dity did not have any influence on 1961, but they significantly influenced 1962. Differential responses in 1961; probably caused by climatic factors. Relative turgidity of the cotton plan,‘ on treatment B fell below 70 percent i? times in 1961. Timely rainfall and mif transpiration conditions caused no gr, ences to occur in plant moisture stre the treatments in 1961. It is important, that 4.8 inches of rain fell on the p first bloom until 40 days after first 1961. I The yield data in 1962 sharply with the 1961 data. Marked differenc, ‘Relative turgidity (RT) = %¥_:_%$. FW z fresh weight of cotton leaves; TW 3; ually lost by evaporation and not us i plants. ' Moisture level C was the most 1.; treatment with respect to pounds of duced per inch of water; treatment least efficient. High moisture level t1‘ delayed maturity and decreased lint p}? A summary of cotton yields in '1‘ fluenced by moisture treatments, is 1f in Table 12. Cotton yields ranged fromag mately 725 pounds of lint cotton per treatment B to about 500 pounds H ment A. Factors such as climate, crop tem (continuous cotton) and use of poo water probably contributed to poor low yields in 1962. Cotton planted on; and 26 and on April 11 for the purpose; ating the influence of moisture levels q, spacings on yields failed to emerge factory stand. However, the stand V‘ April 11 planting was used to study ence of moisture level on yields. Co under treatments A, C and D were n cantly different. Because treatments B and C p l-{l proximately the same yields duringlfi treatment C was changed in 1962 the importance of irrigation at bl" Treatment B was irrigated when the appeared; treatment C was irrigated‘ after the appearance of first blooms cotton under treatment C may have e-nced by high intensity rains Whi the first irrigation in 1962. Howeve ference in yield between treatments? was probably due to the delay in i _ ivbloom stage, suggesting that it is important to initiate irrigation soon after the appearance 10f the first blooms. Observations indicate that early application of water to small cotton on this soil often delays the growth of the plants and subsequently low- ers yields. This is probably a function of soil temperatures. Low night temperatures in the spring and summer were probably responsible ifor marked reduction in yields and retarded growth of cotton plants in the Lower Rio Grande Valley in 1962. Treatment A was higher in yield in 1962 than in previous years because of heavy rains (5.8 inches) from June 23-26. A High moisture level treatments increased boll size, decreased lint percentage, decreased the pounds of cotton produced per inch of water and delayed maturity in 1962. Cotton fiber length was increased but fiber strength was de- "reased by the application of water during the Fruiting period. V Plants grown under a low level of moisture Qwere about 20 inches tall; plants under a high level of moisture were about 30 to 36 inches ~ll. Cotton grown on moisture treatment D " as only slightly taller than cotton grown on * reatment A. Closely spaced cotton produced significantly figher yields, as indicated in Table 11, especially 1 nder treatments B and C. It seemed to mature arlier on treatments A, B, C and D in 1960 ind A, C and D in 1961 but delayed maturity ‘in he case of treatment B in 1961. It produced ‘ smaller boll, Table 11, greater total tonnage .1 plant material and smaller plants, which g ad a tendency to lodge in 1960 but not in 1961.“ _ 1 his may have been due to a difference in variety. 61 ON HARLINGEN CLAY‘ TABLE 12.. SUMMARY OF DATA FOR COTTON IRRI- GATION EXPERIMENT CONDUCTED IN 1962 ON HARLINGEN CLAY SOIL‘ Average P Irrigation yleld of 0:319:11 Bells Percent treatments pounds per inch per lint of lint f t r pound per acre’ 0 wa e A 500 37 99 35.8 B 725 31 96 33.4 C 555 27 98 34.0 D 520 36 97 35.5 L.S.D. (0.05) = 75 pounds per acre. L.S.D. (0.01) = 110 pounds per acre. ‘Average of four replications. 2These yield values were corrected to eliminate skips in the row. Cotton grown under moisture level treat- ments B and D did not defoliate as well as under other treatments possibly because of moisture stress of plants at time of application. How- ever, closely spaced cotton did not defoliate as Well probably because the lower leaves of the cotton plant did not receive adequate concentra- tion of defoliant. This was also probably true of moisture level treatment B which produced high plant tonnage. However, the defoliation response of cotton grown on moisture level treat- ment D was probably due to moisture stress of plants or physiological stage of plant growth. Inadequate coverage of the row middles by cotton plants in treatment D resulted in a high weed population late in the season. Modifica- tion of the soil moisture regime causes tremendous changes in the plant growth which would in- fluence the management of the cotton crop. ‘ABLE 11. SUMMARY OF DATA FOR COTTON IRRIGATION-SPACING EXPERIMENT CONDUCTED IN 1960- Average Pounds » . t. Plant yield pound of of cotton per B°us 2 Percent lint gating): spacing lint per acre inch of water Per pound a treatment 1960 1961 1960 1961 1960 1961 1960 1961 A 1 322 342 34 31 106 104 36.6 38.4 . A 2 330 334 34 30 93 102 36.0 37.3 A 3 314 349 32 31 92 89 36.5 37.2 verage 325 341 33 31 97 98 36.3 37.6 § B 1 898 1093 41 44 82 90 35.6 36.3 if B 2 861 1067 39 43 78 85 36.0 36.5 1 B 3 824 977 38 39 77 82 36.2 36.1 ‘verage 860 1045 39 42 79 86 36.0 36.3 { C 1 1037 1127 48 51 82 91 36.9 36.3 ~ C 2 936 1083 44 49 77 85 36.5 36.9 , C 3 919 996 43 45 76 83 37.4 36.8 ‘verage 963 1068 45 49 78 86 36.9 36.3 i D 1 = 729 772 37 39 ss 94 36.3 37.2 D 2 704 794 36 40 82 85 36.3 37.0 r D ‘ 3 749 752 38 38 81 85 36.5 36.8 verage 727 772 37 39 84 88 36.3 37.0 X oisture level L.S.D. (0.05) _ inear component of spacing significant at (0.05). ll size at time of first picking. ioisture level L.S.D. (0.01) = 109 (1960), 72 (1961) pounds of lint cotton per acre. — 72 (1960), 47 (1961) pounds of lint cotton per acre. Discussion of Water Requirements of Cotton Angus (2) referred t0 the water use by crops as an energy-controlled process which is modified by plant, soil and atmospheric factors. In discussing the role 0f atmospheric factors in the physics of evaporation, it was indicated that the physical requirements to cause water to vaporize are a source of heat (solar energy) and diffusion of the water vapor from greater to lower concentrations. In plants the diffusion is from the surface of the plant leaves (greater concentration) to the turbulent atmosphere (lesser concentration). Water requirement of cotton, as used in this, publication, will refer to the amount of water needed to produce a satisfactory yield of cotton.’ The discussion will not include con- veyance losses from the source to the farm or field. It is impossible to give the water require- ment of cotton for every farm or field in the Valley because this is dependent upon many factors. However, it is important that the grower understand some of the factors which contribute to the water requirement of cotton. Such an under- standing should place the grower in a better position to make more efficient use of his soil and water resources. ‘A satisfactory yield will refer to 1.5 to 2.0 bales per acre. TABLE 13. AVERAGE DAILY EVAPOTRANSPIRA- TION RATES IN INCHES BY COTTON AS INFLUENCED BY MOISTURE LEVEL TREATMENTS AND PLANTING DATES ON WILLACY LOAM, 1955-57 February 15 — Planting date‘ March April May June July Treatment Feb. A 0.05 0.07 0.13 0.25 0.10 0.11 Average irrigation dates — April 18 and May 6 B 0.04 0.08 0.09 0.21 0.11 0.08 Average irrigation date — May 10 C 0.04 0.07 0.08 0.22 0.48 0.36 Average irrigation dates -— May 10, June 2, 16 and 27 D 0.04 0.07 0.08 0.11 0.48 0.32 Average irrigation dates — June 1, 18 and 26 0.04 0.09 0.08 0.06 0.20 0.20 Average irrigation date -— June 10 F‘ 0.05 0.11 0.10 0.09 0.12 0.12 March 15 — Planting date‘ A 0.04 0.06 0.20 0.16 0.12 Average irrigation dates — May 7 and 25 - B 0.06 0.06 0.14 0.17 0.09 Average irrigation date — May 20 C 0.05 0.06 0.16 0.42 0.36 Average irrigation dates — May 21, June 8, 18 and July 3 D 0.04 0.04 0.12 0.27 0.35 Average irrigation dates — June 10, 30 and July 7 E 0.05 0.05 0.09 0.19 0.23 Average irrigation date — June 25 2 0.08 0.08 0.08 0.17 0.07 Average evaporation from open pan‘ 0.13 0.17 0.18 0.20 0.23 0.27 ‘Average dates of first blooms for February and March- planted cotton were May 3 and 19, respectively. ‘One-year average (1957). Other treatments show aver- ages for 1955-57 . ‘From Class A standard weather bureau type. l0 In the discussion of research datak water requirement of cotton, recommey to growers will be separated into a d', of: (1) Willacy and related coarse and ». textured soils and (2) Harlingen clay so' search findings on Hidalgo and Lare have indicated that cotton grown on th I responded similarly to cotton grown on l. soil. However, cotton grown on‘ Lar would be expected to vary considerabi location to location because of soil var‘ Water Requirement of Cotton on Wil The approximate daily evapotra sf, rates by cotton plants as influenced throughout the growing season, planti and moisture levels, are shown in T’ These data are the average evapotra z; with the exception of treatment F, f’ grown in 1955-57. The average daily f tion from an open pan for the v1? periods is also shown in Table 13. E fj tion caused a marked increase in evapor- tion because the applied water is held? tension by the soil and more easily -" “pumped” from the soil by plants. q '_ the growing plants must exert to remo, ture from the soil increases as the soil moisture decreases. Therefore, a i in available moisture causes a corres" crease in evapotranspiration. Treatment A received an average; irrigations, treatment B only one treatments A and B were irrigated befoyl ing, treatment C received an average. irrigations and treatment D received a1; of three irrigations. Treatments C a irrigated when soil moisture stress q early in the season and when soil moist i,‘ was low late in the season. Treatm ceived one irrigation late in the seas" ment F received no irrigation water. y transpiration data indicated that maxi‘ and demand for soil moisture by cot begin just before or during bloom stage? tinue until most of the bolls are mature; The importance of available mois ing the first 40 days after appearan; first blooms was evaluated by determ correlation between maximum increase»; of cotton due to irrigation and rainf this stage of plant growth. The m crease in yield due to irrigation could ated only in 1949, 1950, 19578, 1961 because a nonirrigated treatment was.‘ in the experiments in these years a other years. The correlation coeffici" -0.917) indicated a high inverse re” between rainfall during these 40 days f mum increase in yield due to irrigati" 4. The relationship between total n] ing the cotton season and maximum,‘ due to irrigation was not nearly as if “Cotton planted in February and March was n‘ 1957. 4OO ' '>}=_4s.s4x- :-384.6 300 R=—O.9l7 ZOO IOO Pounds ‘of lint cotton per acre I I O 1 1 J O 2 4 6 8 Roinfol I- inches llgfigure 4. Relationship between maximum increase in yield due irrigation on Willacy and Hidalgo type soils and rainfall cluring the first 4O clays after appearance of first bloom. 20.762). On the Willacy and Hidalgo soil, the otton plant should receive water during the 'riod of 30 to 40 days after first blooms appear, A satisfactory yields are to be made? This ould help explain the satisfactory yield re- ponse obtained from one irrigation 30 to 40 ays after first bloom during 1955-57, and the lck of response due to irrigation during cer- in years when timely rains occurred during this critical moisture demand period. This does lot mean that in certain years and locations actors such as insect infestation, high water Able and other climatic factors are not import- lnt and do not influence the response of cotton irrigation. However, the relationship between .55.»: during this growth stage and maximum a a crease in yield is amazingly high, particularly "ince years, soil type, locations and planting date {I ust have contributed somewhat to the observed ‘eld responses. p Typical root development and distribution ‘y cotton plants under different moisture levels in Willacy loam soil are reported in Table 14. pil cores for root distribution studies were ob- kined with a Kelley soil sampling machine (10). ighty percent or more of the cotton roots were § the top 2 feet of soil, regardless of the mois- re level imposed. Cotton on treatments A and , which grew under high moisture levels during l‘ early part of the season and were permitted to» “dry out” during fruiting stages, seemed to velop shallower root systems. The most ex- nsive root system occurred in treatment E g d was followed by treatments D and C. Studies on Willacy loam soil in 1959 by emiya et at. 5(1), indicated that the pattern soil moisture depletion by cotton was a func- in of the pattern of active root development i; Well as of the relative wetness or dryness l the soil. It was apparent during the early ages of growth that most of the moisture de- tisfactory yields for this area would be 11/2 to 2 bales ~ r acre. pletion occurred in the upper 2 feet of the pro- file. As the plant continued to grow and as a deeper root system became established, suc- cessively greater amounts of moisture were uti- lized by the plants from the third and fourth feet. However, the moisture data. indicated that significant amounts of water were not removed from the fourth foot until the moisture in the third foot was under a suction of approx- imately 1 bar, which in this case was when 45 percent of the available water was depleted. When this occurred, moisture in the first and second feet of the profile was under a suction of approximately 3 to 1.5 bars, which repre- sented depletions of 9O and 60 percent, respec- tively. As soil moisture depletion continued and as the moisture suction in the first 3 feet be- came greater, more water was removed from the fourth and fifth feet. During the critical period, which began about the first week in June, cotton in treatments A, D and E showed a relative decline in growth. An examination of the soil moisture data showed that this growth decline during this critical stage was during a time when the soil was allowed to become rela- tively dry. Consequently, the plants extracted much of their water from depths below the third foot. This occurred in spite of the fact that moisture suction in the third foot was less than 2 bars and only 65 percent of the avail- able moisture had been depleted. Although moisture below the third foot was at a suction of less than 0.8 bar, cotton plants were unable to extract sufficient moisture to maintain opti- mum growth. Cotton plants may extract mois- ture from depths below their primary root zone (0 to 3 feet) but may not be able to extract an amount sufficient to maintain optimum growth during the critical period, even at relatively low suction values. Water Requirement of Cotton on Harlingen The amount of water applied, number of irrigations and water use data for 1960-62 are indicated in Table 15. Moisture level treatments had a marked influence on evapotranspiration. Water loss caused by evapotranspiration was high during the blooming and fruiting period of the cotton plants under low moisture stress conditions. Evapotranspiration was high be- TABLE 14. EFFECT OF SOIL MOISTURE DIFFER- ENTIALS ON ROOT DEVELOPMENT AND DISTRIBUTION BY COTTON PLANTS ON WILLACY LOAM SOIL Soil Percentage of total roots by treatments‘ depth, feet‘ A B C D E 0-1 67.2 74.0 57.5 58.0 53.6 1-2 19.3 18.3 25.5 24.1 27.0 2-3 6.7 4.9 6.6 9.5 11.6 3-4 4.8 2.8 6.2 5.9 4.9 4-5 2.0 A 0.0 4.0 2.5 2.9 ‘Treatments described in Table 3. ll A 5 I’ x '6 ' "T":P_:_:-\--—L. 5' s \ . v“ ‘o\ I E \\ \\ 4 u) 4 " \\ \\ m \ '+ I \ \ _ . 2 PPT. PPT. \ \—X 3 “’ \ [Ll \\ ' n: 3 r \\~~- ___g 3 sou. MOISTURE TREATMENT A 1* g | FT. mcnemsnrs |_|Q 5 , PPT. .1 - FIRST BLOOM a Z ' U) l A l l L l L l l l l_ C 5 Igx /’”“*~\_ q, [i/ g *~ §f>§x~ ----T\V._Jo y p5 ' K ,\ I’ l l?) 4 T\A \ /~ -~ _ \ //~ \A/\\.'/L_ '\¥ I g sou. MOISTURE TREATMENT B i | FT. INCREMENTS \\\ g; |.s 1.2 oso |.|o r 5 PPT PPT. PPT. PPT. \ E FIRsQ/atoou \ __| / 8 2 ~ A A 2.9a" 2.52" 3.25" 3.50 2.23" L l l 1 l l l l L I L 2o so no 2o 3o l0 2b so |o 2o 3o |o APR. MAY JUNE JULY Figure i5. Seasonal soil moisture changes for a 5-foot profile as influenced by soil moisture treatments A and B and cotton plant spacing treatments on Harlingen clay, ‘I960. Dates and amounts of rainfall indicated by ppt. Irrigation dates and amount under symbol. cause the soil moisture is easily available to plants at low moisture- stress, potential evapo- transpiration is high in the Lower Rio Grande Valley and quantities of evaporative surfaces are high when the cotton plants are relatively large. During this period, the evapotranspira- tion data often showed losses which ranged be- tween 0.2 and 0.4 inch per day after an irrigation. Typical soil moisture-use curves for differ- ent soil depths and for treatments A and B are indicated in Figure 5. Moisture use throughout the season was restricted largely to the top 2 feet of soil. This may have been caused by plant root distribution in the Harlingen clay. Ninety to 99 percent of the roots were found to be in the first foot of soil as indicated in Table 1.6. With the exception of treatment A, reduc- tion in soil moisture from the third foot was not noticeable until late in the season. Loss of water at lower depths under treatment A occurred after cessation of plant growth; mois- ture loss probably was caused by soil evapora- tion. Moisture use at different soil depths under treatments C and D was similar to moisture use under treatment B with greater moisture depletion in the top 2 feet of soil before irriga- tion. The amounts of water in the soil under soil moisture treatments A and B and spacing treat- 12 tended to use the available soil moisture-T ments during the growing season are inf in Figure 6. ~ I 1 Cotton plants grown under close rapidly. However, differences were rel, small and varied somewhat with locati; moisture-level treatment. Irrzgatzon Schedules"; From the yield and evapotranspiratio; as influenced by plant spacings, planting; and moisture regimes, it is possible to efo j irrigation schedules for the Lower Rio g Valley. Such schedules must be mod' local farmers to suit their particular water conditions. Some of the factors} will influence the irrigation schedule are-i. of soil, available water-holding capacity amount and quality of available water for‘? tion, soil depth, plant spacing, presence o? table or restricting layers in the soil, lity, cropping history, infiltration ratél and length of the irrigation run and in" festation during‘ the growing season. worth (6) has discussed the influences of these factors on the proper irrigation The exact influence of the individual f . the irrigation schedule is not known, but =s A edge of them will help to formulate a mor gent irrigation schedule for a specific g situation. The county agricultural agentE . Conservation Service technician can 1191?,- "Much of these data were obtained from Bulletin? w?‘ TABLE 15. SUMMARY OF RAIN AND 11m WATER APPLIED TO MOISTUR TREATMENTS ON HARLING FROM 1960-62 » To , wat , use; Mois- - A Irri- Number S011 . . tum of irri- moisture gatmn Ran“ treab gations‘ depletioni water fan ments — — — — — — Inches — - 1960 A 0 6.8 0.0 2.9 B 5 4.6 14.4 2.9 C 5 3.6 15.0 2.9 D 3 4.2 12.4 2.9 1961 H_ 11 0 4.6 01> 115 gs 1; 5 21. 16;; as ,5 C 4 3.3 12.2 6.5 I) 3 1.9 11-5 (15 <3 1962 3; 1A 13 215 (L0 81. ‘i€ 1; 5 1.6 131; 81. ;; C 4 +0.2 12.6 8.1 1) 3 %—1.2 7&5 s;1 14;; ‘$2 ‘A preplanting irrigation was applied to all j The numbers of irrigations refer to the irri plied after first blooms. zRefers to the difference in the soil moisture (l defoliation from the initial soil moisture at »_;_f leaf stage of plant growth. Ii?- 3In 1962-, a high intensity rain from June sidered equivalent to one irrigation (5.75 inche I‘? _~ ulate an irrigation schedule by identifying the a soil and furnishing information on its available . Water-holding capacity (11, 12). Infiltration rate of the soil, slope of the irrigated field and the length of run will influ- ence the amount of water which can be applied ,1 efficiently to the soil during any one irrigation. Land leveling is usually necessary in the Valley a if efficient application and distribution of water i is to be obtained. The farmer is often not able alto distribute the water to the field uniformly because of these factors. Inefficient applica- tion and distribution of water may result in a reduction in yield caused by lack in uniformity in growth and yield of the cotton plants. ‘Irrigation Schedules for Cotton Grown on Willacy Loam Irrigation schedules are outlined for what “usually is considered a “low” supply and an , “adequate” supply of irrigation water. The pro- posed schedules are made with the» following as- sumptions: that the soil is deep (5 feet or a more) with no water table or restricting zones and will hold 7 to 10 inches of available mois- ture; that good quality water is available ;11 that the cotton grower follows recommended ‘fertilizer and insect control practices and plants seed of adapted varieties; that the soil profile “ is filled with a preplanting irrigation; and that it the land topography is graded properly. Low Water Supply—One Irrigation p With a limited supply of water, the grower . should plant his cotton in March. Based on Table F17, the cotton grower should irrigate when ap- . Qproximately 7 inches of water have been re- moved from the soil. The irrigation will occur ~ about 30 days after appearance of first blooms, .according to the proposed schedule. p The average rainfall from March 15 to June 21 is approximately 5.80 inches. Some of the rains are light and relatively ineffective. How- ever, rainfall will often reduce the need for irri- igation water from about 7 inches in dry years ito 3 or 4 inches in wet years. Growers may ,wish to delay the application of water to a later Tate when rainfall is relatively high. However, ?‘Good quality Water refers to water containing less than 51,000 ppm of total salt and having a low sodium content. ABLE 16. — wow - rummzo \_ :5 _ -—- e men SPACING \ g ~22 —--— l2 mcu SPACING \ ‘é \\ V‘ 2' soar MOISTURE TREATMENT A \ \ g; s FT. PROFILE \ :> 2O - 5 T T T T 6 l9 _ 1.5 |.2 0.60 |.|0 in PPT. PPT. PPT. PPT. J 3 |3 t FIRST acoom l, \ a l l‘ . . \ ‘\ <,__2 , p \\ L,’ son. MOISTURE TREATMENT e \ .; g 2| _ 5 FT. PROFILE \ ,l \\,- \ 5 l‘ T T T l! \\l \‘\ 5 2o _ 1.50 |.20 0.60 uo l l \ \ 5 PPT. PPT. PP'|'. PPT. I \ ~, 3' ,9 I FlRS/T BLOOM \\ °° -- NON —TH|NNED \\ I8 - ——-- s mcu SPACING A A A A A \ "'"'2 ‘NCH SPACWG 2.0a" 2.52" 3.25“ 3.s0“2.23" I l I I l 1 l l 1 l l 20 3o no 20 a0 |0 20 so :0 20 so no APR. MAY JUNE JULY AUG, Figure 6. Seasonal soil moisture changes by l-toot increments as influenced by cotton and irrigation treatments A and B, on Harlingen clay, ‘I960. Dates and amounts of rainfall indicated by ppt. Irrigation dates and amounts indicated under symbol. many growers, because 0f unlevel land, long runs, insufficient labor and soil type may not be able to apply 6 to 7 inches 0f water to a cotton field without considerable waste, uneven distribution and sometimes damage to the cotton plants. The grower, by keeping a record of rainfall and using the moisture use data in Table 17 as a guide, can determine the best time to use his single postplanting irrigation. Adequate Water Supply—Three irrigations Since the cotton grower who operates under this condition has filled his soil profile with a preplanting irrigation and has three more irri- gations to finish his crop, the time of planting is not as critical as in the former case. Plans for February and March-planted cotton are proposed. PERCENT ROOTS BY WEIGHT AS INFLUENCED BY MOISTURE LEVEL TREATMENT AND SOIL DEPTH ON HARLINGEN CLAY, 1960-61 oil depth, Treatments, 1960 Treatments, 1961 s“ A; B c 1) A B c n — — — — — — — — — — — —— Percent by weight ————————————— 76.4 82.0 81.5 94.0 91.3 91.3 65.3 84.0 2.3.0 15.6 17.5 5.4 7.5 8.2 34.2 14.7 0.5 1.8 0.8 0.3 0.5 0.4 0.5 1.0 0.1 0.5 0.3 0.3 0.2 0.1 0.1 0.2 0.1 0.2 0.3 0.2 0 3 TABLE 17. IRRIGATION SCHEDULE PROPOSED FOR COTTON GROWN ON WILLACY LOAM WITH ONE POSTPLANTING IRRIGATION. COTTON PLANTED ON MARCH 15, 1956 Moisture Use Days Cum“, Rain- Time after use, lative ilfgllés A-B planting‘ inches inléilzs, (B) per day (A) March 15-31 16 0.05 0.80 0.15 0.65 April 1-15 31 0.05 1.55 0.31 1.24 April 15-30 46 0.05 2.30 1.39 0.91 May 1-15 61 0.09 3.65 1.97 1.68 May 15-31‘ 77 0.09 5.08 1.97 3.12 June 1-15 92 0.19 7.94 1.97 5.97 June 15-21 98 0.19 9.08 2.02 7.06‘ June 2-1-30 107 0.19 1.71 1.44 0.27 July 1-15 122 0.23 5.16 1.60 3.56 July 15-31‘ 138 0.23 8.84 1.94 6.90 ‘Cumulative use = daily use x number of days in period plus moisture use in earlier periods. Example for April = (0.05) (15) plus 0.80 :: 1.55 inches. ‘First blooms occurred on May 19. ‘Approximate time to irrigate (June 21 or 22) with 7 inches per acre. ‘Cotton was defoliated on August 2. Tables 18 and 19 illustrate how cumulative mois- ture use can serve as a guide for irrigation under conditions where water is plentiful. February-planted cotton should receive its first irrigation about 30 days after first blooms appear, but the March planting will need its first irrigation about 15 days after first blooms ap- pear. Early-planted cotton should be irrigated when the cumulative water use, minus the rain- fall, equals about 6 inches. However, March- planted cotton should be irrigated when this is equal to or near 5 inches. Daily use of water by cotton, as indicated in Tables 17, 18 and 19, TABLE 18. IRRIGATION SCHEDULE PROPOSED FOR COTTON GROWN ON WILLACY LOAM WITH THREE POSTPLANTING IRRIGA- TIONS. COTTON PLANTED ON FEBRU- ARY 15, 1956 Days ‘122’ 5:21:21; 1:11- Time afte-r inches inches‘ ’ inches A-B Plantmg per day (A) (B) Feb. 15-28 13 0.04 0.52 0.29 0.23 March 1-15 28 0.07 1.57 0.38 1.19 March 15-31 44 0.07 2.69 0.52 2.17 April 1-15 59 0.08 3.89 0.68 3.21 a: 211 221 s: M3 15-31 105 0111 8:50 2134 61123 June 1-13 118 8.48 6.24 0.00 6.243 June 13-15 120 .48 0.96 0.00 0.96 June 15-30 135 0.48 8.16 1.49 6.673 July 1-15 150 0.32 4.80 0.16 4.64 July 15-26‘ 161 0.32 8.32 0.50 7.82 ‘Cumulative use = daily use x number of days in period plus moisture used in earlier periods. ‘First blooms occurred on May 1. ‘Approximate time to irrigate. ‘Cotton was defoliated on July 26. l4 TABLE 19. IRRIGATION SCHEDULE PROPOS 15;. COTTON GROWN ON WILLACY; WITH THREE POSTPLANTING l; '1l‘IONS. COTTON PLANTED ON 5, 1956 . Moisture use _ Ram- Days 1) '1 c 1 - > Tim .11: 1211:. gggg, Dlalltlng inches inches‘ ‘ ‘“ l per day (A) (B) March 15-31 16 0.04 0.64 April 1-15 31 0.04 1.24 April 15-30 46 0.04 1.84 May 1-15 61 0.12 3.64 May 15-31‘ 77 0.12 5.56 June 1-5 82 0.27 6.91 June 5-15 92 0.27 2.70 June 15-30 107 0.27 6.75 July 1-15 122 0.35 5.25 July 15-31‘ 138 0.35 5.25 ‘Cumulative use = daily use x number of days ‘g plus moisture used in earlier periods. ‘First blooms occurred on May 19. “Approximate time to irrigate. ‘Cotton was defoliated on August 2. is related directly to the amount of wa able to the cotton plants. If a farmer for only two irrigations rather than probably would be desirable to delay irrigation until the cumulative water rainfall is about 6.5 to 7 inches as was _ on the February-planted cotton. The irrigation could be applied when the c __ water use minus rainfall is about 6 inch w. Assuming that only two irrigations H‘ able, it probably would be desirable fort to delay his planting date. For Ma cotton, it would be desirable to delay the gations until the cumulative water “T rainfall is equal to 6 inches. The d use in inches per. day would be slightly}, two than for three irrigations. An j of the daily use for the respective 0:; Tables 18 and 19 probably would be j the actual losses and could be used aal; of moisture use. For example, the l‘ for a schedule of two irrigations for J be approximately 0.23 inch per day}? Schedules for four irrigations coul, terned from Table 18 or 19, depending the cotton is planted in February The additional irrigation could, be used A days before the irrigation dates listed?! 18 or 19. The daily use in inches per» four irrigations could be obtained ~ " column listed as treatment C in Table 13 Soils possessing low water-holding J shallow top soil, restricted zones or a table would need more frequent :5 lesser amounts each time. However, I} “0.19 z evapotranspiration rate for one irrig 2' planted cotton). 0.27 : evapotranspiratio three irrigations (March-planted cotton);- 0.27) (1/2) : 0.23 inch per day. a TABLE 20. IRRIGATION SCHEDULE PROPOSED FOR COTTON GROWN ON HARLINGEN CLAY WITH FOUR POSTPLANTING IRRIGA- TIONS. E X A M P L E FOR MARCH 15 PLANTED COTTON‘ a Days Moisture use ' Time aft?’ Daily use, Cumulative ‘ 11131111118 inches per day use, inches -A March 15-31 16 0.05 0.80 April 1-30 46 0.05 2.30 May 1-20 66 0.05 3.302 May 20-June 5 82 0.20 3.20’ June 5-June 20 97 0.20 3.002 I June 20-July 5 112 0.20 3.002 A ‘This example does not include rainfall. ‘Approximate time t0 irrigate. ; transpiration data could be used as a guide in setting up irrigation schedules for such condi- tions. Irrigation Schedule - - Harlingen Clay Soil Because of a high water-holding capacity, these soils remain relatively cold in the spring. The specific heat“ of this soil, mainly because of its high water-holding capacity, is consider- ably higher than the medium and coarse-tex- ‘tured soils. Temperature conditions in the Har- lingen soil generally favor a delay in cotton planting until March. An irrigation schedule I for the Harlingen clay is proposed with similar assumptions as provided for the Willacy loam. Irrigation should begin at or immediately after 1 the appearance of the first blooms. Earlier irri- gation when temperatures are cold or cool often retard plant growth and cause a reduction in yield of cotton. Applications of four irrigations about every 15 days after the appearance of the first blooms will usually produce from 1.5 to 2.0 bale-s of cotton per acre on this soil. Cotton planted on March 15 would bloom about May 20 and should be irrigated on or about May 20, une 5, June 20 and July 5. Soil moisture use ‘by plants growing in this soil is generally re- stricted to the surface 2 feet because the con- entration of plant roots is restricted to the sur- ace foot of soil. Applications of 3 to 3.5 inches .1 water at each irrigation is usually sufficient u replenish the soil moisture in the depleted Specific heat of a substance or material is the ratio , of its thermal capacity to that of water at 15° C. zone. Water use during the blooming and fruit- ing period amounts to approximately 0.2 to 0.3 inch per day. Small rains generally do not supply available water to the plant roots but may help reduce the evapotranspiration rate. Table 20 can be a guide for the proper irrigation of cotton on Harlingen clay soil. - rainfall, the irrigation schedule could be modi- By keeping a record of fied for each specific situation. (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) Literature Cited Amemiya, M., Namken, L. N., and Gerard, C. J. Soil water depletion by irrigated cotton as influ- enced by water regime and stage of plant de- velopment. Agron. J. 55:376-379. 1963. Angus, D. E. Agricultural water use. Advances 1n Agronomy Vol. XI. Edited A. G. Norman, 1959. Biggar, J. W., Bloodworth, M. E. and Burleson, C. A. Effect of irrigation differentials and planting dates on the growth, yield and fiber characteristics of cot- ton in the Lower Rio Grande Valley. Tex. Agri. Expt. Sta. Prog. Rep. No. 1940. 1957. Bloodworth, M. E., Burleson, C. A. and Cowley, W. R. Effect of irrigation differentials and planting dates on the growth, yield and fiber characteristics of cotton in the Lower Rio Grande Valley. Tex. Agri. Expt. Sta. Prog. Rep. No. 1866. 1956. Bloodworth, M. E., Cowley, W. R. and Morris, J. S. Growth and yield of cotton on Willacy loam as af- fected by different irrigation levels. Tex. Agri. Expt. Sta. Prog. Rep. No. 1217. 1950. Bloodworth, M. E. Some principles and practices in the irrigation of Texas soils. Tex. Agri. Expt. Sta. Bul. No. 937. 1959. Gerard, C. J., Burleson, C. A., Biggar, J. W. and Cowley, W. R. Effect of irrigation differentials and planting dates on yields of cotton in the Lower Rio Grande Valley. Tex. Agri. Expt. Sta. Prog. Rep. No. 2016. 1958. Gerard, C. J., Bloodworth, M. E., Burleson, C. A., and Cowley, W. R. Cotton irrigation in the Lower Rio Grande Valley. Tex. Agri. Expt. Sta. Bul. No. 916. 1958. Gerard, C. J . and Namken, L. N. Effect of irrigation differentials and plant spacings on yield of cotton on Harlingen clay in the Lower Rio Grande Valley. Tex. Agri. Expt. Sta. Prog. Rep. No. 2216. 1961. Kelley, O. J., Hardman, J. A., and Jennings, D. S. A soil sampling machine for obtaining two, three, and four-inch diameter cores of undisturbed soil to a depth of six feet. Soil Sci. Soc. Amer. Proc. 12:85-87. 1947. Thurmond, R. V. How to estimate soil moisture by feel. Tex. Agri. Exten. Ser. Leaflet No. 355. Thurmond, R. V. Soil moisture storage. Tex. Agri. Exten. Ser. Leaflet No. 357. 15 i’ um: srmon o us: suesrnlons I I'll‘ FIELD LLSOFITORIES Q GDQFIIITIIIC STATIONS Location oi field research units oi the Texas Agricultural Experiment Station and cooperating agencies ORGANIZATION OPERATION Research results are carried to Texas farmers, ranchmen and homemakers by county agents and specialists of the Texas Agricultural Ex- tension Service $0610? :4 pecan-ck ~96 jomorrow ,5 P09P855 State-wide Research The Texas Agricultural Experiment Stati is the public agricultural research age ' oi the State oi Texas. and is one oi parts oi Texas A6=M University. i IN THE MAIN STATION, with headquarters at College Station, are l3 matter departments, 3 service departments, 3 regulatory services administrative staff. Located out in the major agricultural areas oi 20 substations and 1O field laboratories. In addition, there are 13 co ' stations owned by other agencies. Cooperating agencies include th‘ Forest Service, Game and Fish Commission of Texas, Texas Prison U. 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