TEXAS AGRICULTURAL EXPERIMENT STATION R. D. LEWIS, Director, College Station, Texas um 767 LJBRPJQY fluQa/JZ r953 A. & M. COLLEGE 0F TEXAS Conservation and Utilization 0t Soil Moisture v in cooperation with the UNITED STATES DEPARTMENT OF AGRICULTURE The TEXAS AGRICULTURAL AND MECHANICAL CCLLEGE SYSTEM GIBB GILCHRIST. Chancellor THE FRONT COVER PICTURE Aerial photo of the Spur station 12 hours after a highly a rential rain of 2.54 inches on June 19, 1946. ’ <- Farmstead which does not show. (2) Ten-acre cotton field with rows up and down the slope. Note accumulation of runoff at lower end of field. ‘ (3) Ten-acre field with contour rows and closed level terr Note uniform distribution of Water over field. ‘ (4) Field area that received runoff water from a 300-) water-shed. i (5) Shows location of highway culvert that drains water station land. l (6) Water from land with a slope of 1 to 2 percent b terraces and later spread over field area 8. ' (7) Land with 0.5 percent slope that did not get wet bee: of heavy runoff. ' (8) The syrup-pan terrace system made maximum use flood waters from a 1,200-acre watershed. i (9) Land devoted to production of wheat and sorghums. t slope varies from 1 to 3 percent. (10) Experimental grazing pastures. (11) Mesquite control studies, including grazing trials cleared and uncleared pastures. 1 ACKNOWLEDGMENTS The authors wish to make acknowledgment to the late Dickson, formerly superintendent of Substation No. 7, folj» development and supervision of the early phases of researe moisture conservation; to B. C. Langley, former agronomist, his valuable assistance and suggestions; and to W. F. T former agronomist, and P. T. Marion, associate animal husband w; who have assisted with certain phases of the studies. ‘ Acknowledgment also is made of support received from; Soil Conservation Service, U. S. Department of Agricultur certain phases of this study from 1936 through 1945. DIGEST Y onservation and utilization of moisture is 0f major importance heavy soils of the Rolling Plains since water is the principal é g factor affecting crop production. Research by the Texas ‘f tural Experiment Station, Substation No. 7 near Spur, f ed in this bulletin, shows that the amount and character f g all, soil type, plant residues, slope of land, tillage and rvation practices are the factors that largely govern the " t of water that is stored in the soil for plant use. jlontouring and terracing to prevent runoff and erosion have f,» icantly increased the amount of available moisture in the d the yield of cotton from it. The use of flood waters, crop pies and tillage offer additional means of increasing the ‘=1 of water that is stored for plant use. eseasonal rainfall from November 1 to June 1 and seasonal 4 from June 1 to October 31 provide general information , ' moisture content of the soil for an area. Measurement of p ount of water stored in the soil, or the depth of moisture .8 tion, gives a reliable index of soil moisture which may be by the farmer on his individual farm. a e close relationship between the amount of availablemoisture in the soil at planting time and the yield of cotton indicates " high moisture content in the soil is followed by a high yield low content by a low yield. Thus, the amount or depth of re may be used as a guide to probable cotton yields on the I- soils of the region. The knowledge of likely crop prospects ‘Yon moisture stored in the soil offers a means of adjusting J g plans and farming operations to make the best use of ble moisture. ese findings show that every effort should be made to use f- ation practices that will bring about a greater storage of ‘ life in the soil to help stabilize crop production and to reduce rds of farming in a 20-inch rainfall belt. CONTENTS The Front Cover Picture ..................................................................................... "T" Acknowledgments .............................................................................................. .. Digest ...................................................... -- A Introduction .............................................................. -- Description of the Area .............................................................................. .- Method of Study ............................................................................................ .- Soil Moisture Accumulation .................................................. .3 .................. .- Amount and Character of Rainfall .................................................. .. Soil Types ........ .. Evaporation .............................................. .. Crops and Slope .................................................................................... .. Conservation Practices .......................................................................... .. Utilization of Soil Moisture ...... .. Effect of Available Moisture at Planting Time on the Yield of Cotton ......................................... .. Relation of Depth of Soil Moisture at Planting Time to the Yield of Cotton ...................................................................................... .. Effect of Preseasonal Rainfall on the Yield of Cotton .......................... .. i Effect of Summer Rainfall on the Yield of Cotton ................................. Effect of Conservation Practices on Cotton Production, f Runoff and Soil Moisture ...................................................................... .. Value and Use of Soil Moisture Information ............................................. Summary .......................................................................................................... .. Literature Cited ................................................................................................ .. Conservation and Utilization of Soil Moisture B. E. Fisher and Earl Burnett* i PRODUCTION on the Rolling Plains of West Texas is ed largely by the amount of Water that is available for 51 growth. Soil fertility is seldom a factor in crop production H heavier soils that occupy much of the area. The sandy of the area are usually lower in fertility and occasionally nd to soil fertility practices when rainfall is above normal ‘, ) '1 yn most years, rainfall is adequate for the production of crops atic distribution, with torrential rains followed by long dry is, make it desirable to conserve a maximum amount of for crop use. The soils generally are relatively porous, deep i: ve ample Water holding capacity to store large amounts of j I for plant use if steps are taken to prevent heavy runoff ‘to reduce evaporation. The use of conservation practices, y r planting in combination with closed level terraces, diverting spreading of flood Water and other related practices has icantly increased the depth of moisture penetration and the ;t of Water stored in the soil. This additional accumulation isture has materially increased the yields of crops and reduced gzards of farming. i.» .jor emphasis in this bulletin is placed on factors that ince the accumulation and utilization of soil moisture. Results gyears of research at Substation No. 7 on moisture conservation ported. Early Work on runoff and water conservation on filling Plains was published by Conner, Dickson and Scoates ind Dickson, Langley and Fisher (3). These findings are y applicable to some 14 million acres of heavy soils on the l Plains and indirectly to heavy soils in other regions Where moisture limits crop production. ,ater conservation research at Spur includes factors that Wnce the accumulation of soil moisture by reduction of runoff ivaporation, the utilization of soil moisture by crops, the inship between available moisture in the soil at planting time he yield of cotton, the effect of preseasonal and seasonal ‘_l on the yield of cotton and the effect of conservation _ es on cotton production, runoff and available soil moisture. i’ ively, superintendent and assistant agronomist, Substation No. 7, Texas ltural Experiment Station, Spur, Texas. u» rs in parentheses refer to literature cited. p-ai—ioaionix + oaum Susana»; umsroao Own-TRUE ha?“ B 2 A HARTLEY . MOORE HUTCHINSOH ROB€R€ HCHQHILL QgQp-(QM pQfTcQ CARSON bRlV JIHCELCR 011M’ smfu RANDALL coumoswonnv §‘ I I 7 _ _l 1 I PARHER casrao isunsncn iscbc uAu. (NILDRPBS; l d ! O l JNQQOENAN | BAuJIY LANG “M: LQYKE _ ‘ .W'\.B»\RuER . ~ a ' ' othe 1-~~~~ . * I k . 0 | cuw s ' ‘ ? mi i‘ ’-i.i | ' , v Q9, KRLNCR cocumm wocuu WBPQ“ | "~'\¢~5 “W0 mm! m“ i " Os u? _1-- ,?_ p .1- -—-o-r—'—"' a i JQ!‘ u . .@ VOAKUM "rcmzv KEN? 5T0“ “ML! “hnzLL Tnnoflnoatm I " L- ikjoi _- .._- __ -—---—r-—'-”""'"’- I-o-m ‘ I - 9M0 PW F|§HER "SHAKIKFORD Y‘.PHLNS , ! ._ _. '._._.. ...__.__.-_ { hip-i .11; a-ipoin n-nu—~ ' ,- ' ANDR[W5 "HTCNELL won ‘TAYLOR ‘emu-m £°*°“"“° !£R~‘”yf. i _ _ /\ F a o l " > ‘ D~r-~/\k \ / \ , __ __. _-!.._..__. _... _-J -——~ ~ uonmwf- \_ °' “i KTOR M-Ogkub flxAfibtOLa-l STERL RU'\NEL5 ‘iLiaAN BROwu-\ |_ rwnfi \ ' a N _/ f REAGAN —->-'-j ‘é L / \. r (ONCHQ \R\ON . I _ o; c u *~ “ W ‘ 51m Sl-BA -{m ‘ ' ---'.-—--l---I—1‘i '_' __'-'-_ _-1 u an: (Ragnar? n ecuLc-nwfifl “£'*ARD ' ' Figure 1. The Rolling Plains of Texas. _7__ DESCRIPTION OF THE AREA Rolling Plains occupy approximately 30 million acres in "est Texas and Central Oklahoma, Figure 1. The elevation from 1,000 feet on the east to over 2,500 feet on the West. lly, the area is rolling but there are numerous areas of level, undulating or only gently rolling topography. Rough, land occurs frequently along the main Water courses and ‘ly devoted to grazing and livestock production. The er land is used principally for the production of cultivated t Average monthly and annual evaporation, wind movement, and mean, mean maximum, mean minimum temperatures and rainfall at the Spur station, 1911-52‘ {Jamf Feb. [Man] Apr.‘ MayI June] July| Aug.|Sept.I Oct. N0v.IDec.| Total or ||l||1|| Ilaveraze 2.44 2.99 5.11 6.30 7.19 8.66 8.84 8.16 6.04 4.78 3.30 2.48 66.35 4684 5038 6118 6211 5863 5249 4331 3837 3932 4021 4426 4471 58,181 41.5 45.9 52.5 61.9 70.0 78.6 81.6 80.9 73.3 63.3 51.2 43.0 62.0 56.6 61.4 69.1 77.8 84.6 93.1 95.9 95.6 87.5 78.3 66.6 57.5 77.0 26.5 30.4 35.8 46.0 55.3 64.1 67.3 66.1 59.2 48.3 35.9 28.5 47.0 .56 .79 .86 1.85 2.87 2.55 2.00 2.47 2.82 2.33 .85 .89 20.85 “n records are for 1916-52. Wind movement records are for 1917-52. f station No. 7 of the Texas Agricultural Experiment Station 1 lies near the western edge of the Rolling Plains. The i‘ rainfall at the station from 1911 to 1952 was 20.85 inches ‘losely similar to that of 16 other Weather reporting stations jthroughout the Rolling Plains. ,_ area has extremes of rainfall, temperature, evaporation l d movement, Tables 1 and 2. Long periods Without .- rainfall are common. The rains are often heavy and l, and produce much runoff. p important feature of the rainfall distribution pattern is Asummer depression which usually extends from June 15 1 st 15. This depression coincides With a period of high ftures Which cause heavy moisture losses by evaporation e soil at a time when plants are making rapid growth and large amounts of Water. During this critical period, crops , te rapidly unless there is ample Water stored in the soil ‘gh effective rainfall occurs. annual evaporation from a free Water surface was slightly 1 inches, with extremes of 81 inches in 1934 and 52 inches p The highest evaporation occurs during June, July and when high temperatures and hot Winds prevail and the t‘ humidity of the air is low. It is common to have 40 or ys during the summer when the maximum temperature ” 100° F. The absolute maximum temperature recorded at May, and is lowest in August and September. The preva direction of the Wind is from the south from March to Oc ’ and from the north from November to February. The av frost-free season of 216 days extends from April 2 to Novem. which is long enough for the normal maturing of commonly- crops. brown or brown to very dark brown in color. The red to red brown soils are found on the more sloping areas, While? associated brown to very dark brown soils occupy the flatter - ' The principal series of the red to reddish-brown soils are Vernon, Weymouth and Tillman. The surface texture of _, soils ranges from sand to clay. The subsoils are highly calca 1 and often have a zone of calcium carbonate at varying Soil productivity ranges from moderate to low, varying with H of soil and moisture conditions. " Table 2. Monthly and annual rainfall, Spur, 1911-52 i Year I Jan. I Feb. IMarch I April I May I June I July I Aug. I Sept. I Oct. I Nov. I Dec. I 7 1911 .16 4.61 .15 1.78 1.15 .56 4.97 1.69 1.34 1.03 .39 2.89 1912 .00 1.15 1.02 1.99 .53 3.14 .53 1.66 2.04 1.87 .00 .60 1913 .04 .41 1.23 .77 .44 4.35 .70 .07 5.72 2.94 3.64 1.89 -; 1914 .09 .19 .33 1.99 10.58 1.28 4.70 5.89 1.41 5.23 .87 1.57 . 1915 .40 2.10 3.20 7.64 2.31 4.08 .78 1.48 7.65 5.17 .00 1.05 1916 .00 .00 .43 2.35 1.31 2.36 .56 4.01 1.12 2.63 .82 .00 1917 .22 .51 .00 1.27 1.71 .14 2.17 1.58 4.12 .12 .07 .00 ' 1918 .00 .64 .30 .62 2.44 1.97 .44 1.42 .92 2.60 .20 1.37 1919 .28 .21 3.56 3.78 4.37 2.03 2.60 2.44 4.26 7.48 .80 .00 1920 1.31 .00 .16 .99 6.91 3.36 .75 8.34 2.20 2.49 1.11 .38 ~ 1921 .30 1.08 .66 .00 .91 4.45 .00 .09 4.08 .00 .00 .05 1922 .31 .00 .76 5.57 5.18 1.77 .25 1.60 1.00 1.06 1.80 .03 I 1923 .05 .85 1.01 3.89 1.14 4.95 .26 1.40 1.57 6.58 2.36 .87 ' 1924 .00 .09 1.88 .81 1.98 .65 2.01 .87 2.00 .80 .00 .00 I 1925 .34 .16 .19 4.77 2.75 1.74 3.43 7.37 3.66 .73 .22 .24 1 1926 .67 .04 1.62 4.18 3.17 2.14 7.37 7.04 3.50 5.13 .52 2.70 = 1927 1.10 .26 1.06 .40 .66 4.56 1.47 .78 4.22 1.19 .00 .42 . 1928 .24 .96 .36 .20 4.33 1.60 5.15 3.97 .05 1.37 1.43 .33 1929 .27 .21 1.49 .02 2.80 1.23 1.17 .33 3.74 3.07 .40 .03 5 1930 .86 T .43 1.66 1.54 1.28 .05 2.05 .89 6.53 .75 2.56 '- 1931 .79 1.62 .33 2.18 1.22 1.29 1.80 1.14 .00 2.53 2.42 1.14 ' 1932 1.71 2.39 T 1.91 1.43 3.38 2.67 5.55 4.24 .58 .09 3.75 . 1933 .19 1.47 .00 .15 2.86 .00 2.51 3.32 3.17 .35 1.12 .45 1934 .12 .21 2.20 1.16 2.50 .07 .11 1.18 2.52 .87 1.93 .01 1935 .01 .61 .98 .71 4.54 6.93 .99 1.05 3.62 2.22 1.50 .62 “ " 1936 1.11 T .22 2.49 2.79 1.43 2.85 .11 11.13 1.41 .48 .45 1937 .38 T 2.05 .86 2.92 1.31 .68 6.93 2.18 2.47 .09 .41 1938 1.14 3.31 .82 .89 2.89 5.16 3.30 .21 .09 1.33 .78 .04 1939 1.98 .25 .52 .29 2.07 1.80 .44 1.85 .00 2.62 .60 .64 ,1 1940 .16 1.14 .00 1.79 1.17 1.06 .07 3.24 .41 1.34 3.16 .04 . 1941 .88 1.64 2.04 4.17 6.94 4.12 2.94 1.46 9.90 7.90 .21 .67 . 1942 .06 .33 .31 3.67 1.63 3.44 1.60 3.40 3.88 2.82 .17 1.79 i 1943 .10 .00 .32 1.14 2.81 2.95 5.36 .00 2.37 .31 .80 1.64 ; 1944 1.77 1.78 .12 .89 2.49 2.50 2.51 2.34 1.18 1.07 1.95 2.72 ' 1945 .89 1.04 .34 .58 .08 3.30 4.29 1.78 4.27 2.12 .69 .21 1946 1.05 .19 .36 1.40 1.57 3.33 .05 3.71 2.48 2.78 .32 1.68 .. 1947 .60 .00 1.51 1.27 6.43 2.01 .00 .28 .15 .65 2.14 2.03 I, 1948 .18 2.28 .15 .57 2.00 4.78 1.30 .89 .07 1.58 .45 .08 1949 2.50 .43 1.78 1.62 5.28 4.63 2.45 4.06 2.71 2.64 .00 1.08 I 1950 .35 .38 .01 1.94 4.92 3.16 3.91 .90 6.23 .00 .04 .02 ‘ 1951 .27 .35 2.19 .81 3.01 2.88 2.30 5.82 1.29 2.29 .03 .00 z 1952 .70 .21 .23 3.33 1.36 .06 2.81 .46 1.22 .00 1.25 .86 * Mean .56 .79 .86 1.85 2.87 2.55 2.00 2.47 2.82 2.33 .85 .89 I __9_ vilene, Roscoe and Spur are the principal series of the brown ,~.~ dark brown soils. These soils are generally heavier than i» soils since they occupy the flatter areas and have poorer i; drainage. They are less subject to wind erosion than ociated red soils and are usually more fertile, but tend to f thy. ye heavier soil types generally have good water-holding y and are deep enough for adequate moisture storage. Most shallow soils are not in cultivation except Where they occur f. iation with the deep soils. The sandier types often produce yields with average rainfall because losses from runoff and ' tion are much lower than on the heavy soils. The most 3*‘- soil for crop production on the Rolling Plains is one with -. loam surface texture underlain by a sandy clay subsoil. ifjof this type can take up Water readily to prevent runoff, a ample water-holding capacity to carry crops through the if mer depression. tton is the principal cultivated crop grown on the Rolling '1‘ Wheat is grown extensively, especially in the northern part. ms are well adapted and are grown extensively but largely ond choice to cotton, depending on the type of farming, l, e and economic conditions. Crops of minor or local are oats, barley, rye, alfalfa, castor beans and peanuts. ‘Vmately 70 percent of the land is in native grass and is V, devoted to the production of cattle. METHOD OF STUDY e effect of slope, crops, tillage and character of rainfall on {and erosion was determined on small plots on Tillman clay QMeasurements of soil moisture, runoff and yield were made field plots on Abilene clay loam with 0.5 to 2 percent “The conservation practices used on land planted continuously p n included rows with the slope, contoured rows and dyed rows supplemented with closed level terraces. There replication of these practices on field areas from 1927 to ee replications of each practice from 1930 to 1945 and lication from 1946 to 1952. In addition, four field areas Hrraces that had variable grades and different vertical were included in the study from 1930 to 1946. ,1 moisture determinations were made at monthly intervals pril 20 to October 20 on the experimental areas of the ' The samples for moisture determinations were taken pjfoot layers of soil. The sampling depth was 3 feet from 1936, 5 feet from 1937 to 1939 and 6 feet from 1940 to 1952. ’ e all of the moisture present in the soil can not be utilized ts, only that portion that is available for plant growth is Hf» The available moisture was determined by the following _1()__ procedure: Total moisture percentage is determined by 3 drying. This percentage is converted to inches by use of‘ m W formula I I where I is the inches of water in one foo »~ 5.196 soil; m is the percentage (expressed as a decimal) of soil mois r and W is the weight (pounds) per cubic foot of oven-dry soil. ‘ quantity 5.196 is the weight (pounds) of a square foot of wf 1 inch deep and at a density of 62.35 pounds per cubic ; (density of water at 60 degrees F.) (11). The lowest point to which crops normally reduce the moi, in the soil, designated as the minimum point of exhaustion, determined for each foot-section of soil by averaging the moi content at times during the growing season when it was ce p that the supply of available moisture was exhausted and the» was suffering for water. The difference between the moisture present in each foot of soil and the minimum poi, exhaustion represents the amount of available moisture present’ SOIL MOISTURE ACCUMULATION Conservation practices that increase the amount and dep penetration of moisture make better use of the soil as a st‘ place for Water and offer excellent opportunities for incr crop yields and reducing evaporation, runoff and erosion. I'_ Rolling Plains it is seldom that the soil is wet to a depth of which includes the root zone of most cultivated crops. Some f’ that have been studied at Spur which influence the accumu of moisture in the soil include the amount and character of rail’ soil type, crops, plant residues, slope of land, tillage and conser practices. 1 Amount and Character of Rainfall The annual rainfall at Spur for the 43-year period, 1911 to?‘ was 20.85 inches. Large fluctuations have occurred in the w‘? Menage 1 n92 2| 22232123252121329303432 33 343s 3631 36 3340“ 424344454641ll_ Figure 2. Distribution of annual rainfall at Spur, 1911-52. 2 O :4_ 5— _11__ l, varying from 11.09 inches in 1924 to 42.87 inches in 1941, ‘l 2. Above normal rainfall has not always favored good crops; ,r has below normal rainfall always indicated poor crops. lto excellent crops have been produced in the dry years of @1924, 1927, 1931 and 1947 with the benefit of timely rainfall "foisture stored in the soil during the previous season. otal rainfall during the season gives a general picture of e conditions but it is not a reliable index to the amount of that may be available for plant use. Long time studies that 61 percent of the annual rainfall produces runoff, from .57 to 10.66 inches with an average of 3.55 inches per i-iTable 3. This alone represents a loss of 17 percent of the A, rainfall. In addition, another 2.74 inches, or 13 percent p, rainfall, is lost as small, ineffective showers. If some lion is not made to control or prevent runoff losses, the amount tive rainfall is reduced from 17.82 to 14.27 inches. Losses “evaporation and weed growth still further reduce the amount i all that eventually becomes stored moisture for use in crop tion. e character of rainfall—whether torrential, moderate or intensity—greatly influences runoff and thus the amount Fter that accumulates in the soil for plant use, but the ‘nship is not always clearly evident. Such factors as total Amount of annual rainfall lost as runoff and ineffective showers, Spur, 1926-52 a Annual Runoff, Ineffective Effective rainfall inchesl showers? rainfall“ 38.08 7.13 3.51 27.44 3“ 16.12 .57 6.59 8.96 j, 19.99 3.19 5.47 11.33 ~ 14.76 3.46 3.59 7.71 18.60 2.78 2.63 13.19 16.46 .77 3.76 11.93 27.70 3.13 1.48 23.09 1 15.59 2.28 2.37 10.94 “V; 12.88 2.17 1.69 9.02 23.78 5.21 1.87 16.70 24.47 4.69 2.80 16.98 20.28 3.30 2.99 13.99 19.96 3.16 2.23 14.57 13.06 1.44 3.70 7.92 13.58 2.84 2.64 8.10 42.87 10.66 2.89 29.32 23.10 4.46 2.02 16.62 17.80 3.45 2.68 11.67 21.32 1.66 2.89 16.77 19.59 4.79 3.36 11.44 18.92 3.63 1.91 13.39 17.07 2.17 1.27 13.63 14.33 2.58 1.12 " 10.63 29.18 8.01 1.88 19.29 21.86 5.22 1.75 14.89 21.24 2.02 2.92 16.30 12.49 1.08 1.98 9.43 , 555.08 95.85 73.97 385.25 , 20.56 3.55 2.74 14.27 l total rainfall 17.27 13.33 69.41 p m land with 2 percent slope in continuous cotton without conservation practices. t ry designation for rains of less than .25 inch. fall less runoff and ineffective showers. _12_ amount of rainfall, physical condition of the soil, crop gr‘ moisture content of the soil and other factors tend to influ the amount of runoff. Table 4 shows that of the annual rai of 12.68 inches that produced runoff, 5.92 inches were torren 1.82 inches moderate and 4.93 inches fell as gentle or slow The greatest opportunities for storing water in the soil ' preventing floods and erosion are closely associated with _ periods of 2 inches or more. Thirty-five percent of the a ii rainfall from 1912 to 1952 occurred in rain periods of 2 , or more. Most of these 2-inch rain periods occur in Septe“ and October, Figure 3. Conservation of water from these h__ rain periods benefits the current crop and stores water in th" for future use. i‘ The distribution of rainfall during the year and the am of available water in the soil to a depth of 3 feet on cotton from April 20 to October 20 are shown in Figure 4. Mo rainfall is usually low, less than an inch, during the winter, it increases with a peak in May and September. The mid-su depression of rainfall extends from June 15 to August 15 crops normally require the most water. Figure 4 shows that soil moisture accumulates over a p of about 8 months, beginning about October 1 and reaching a5, on May 20. It is then depleted by crops during June, July, A, and September. From May 20 to August 20, the growth of _ requires more water than normally can be expected from ra‘ Table 4. Intensity of rainfall at Spur in relation to runoff, 1926 A‘ N.o_ Aggwglilof Character of rain, inches‘ Year ragga?“ producing l’ runoff g rilrlllzafei, Torrential Medium Slow 1926 14 25.30 8.78 6.97 9.55 1927 l0 10.92 5.80 1.45 3.67 1928 17 12.60 8.47 2.71 1.42 1929 10 10.17 6.01 .90 3.26 1930 9 12.46 5.58 .21 6.67 1931 l0 8.00 4.17 2.39 1.44 1932 12 19.65 5.27 2.29 12.09 1933 9 9.65 4.65 1.05 3.95 1934 5 5.35 3.21 .82 1.32 1935 10 13.42 7.06 2.18 4.18 1936 11 14.34 7.82 1.34 5.18 1937 6 12.63 5.41 2.23 4.99 1938 9 12.59 6.78 1.57 4.24 1939 6 7.20 3.30 1.38 2.52 1940 5 5.71 2.66 .28 2.77 1941 12 34.46 16.90 3.06 14.50 1942 12 18.22 8.25 2.18 7.79 1943 5 10.34 6.70 1.35 2.29 1944 7 6.65 3.74 .93 1.98 1945 5 10.42 4.18 .60 5.64 1946 4 9.74 3.75 3.23 2.76 1947 4 9.10 1.84 1.00 6.24 Average 8.72 12.68 5 92 1.82 4.93 Percent total rainfa producing run-off 46.69 14.35 38.88 lTorrentiab-intensity of more than .75 inch per hour. Medium—intensity between .40 and .75 inch per hour. S1ow—intensity of less than .40 inch per hour. __13_ ifklon. Feb. Mar. Apr. May Jun. Jul, Aug. Sep. Oct. Nov. Dec. igure 3. Distribution of monthly rainfall that has occurred in rain f: of over 2 inches, 1911-52. soil moisture has accumulated prior to planting, it serves as e t0 be used by the plants to supplement rainfall. 41 the event little or no soil moisture has accumulated prior nting, the crop will be entirely dependent on above normal ely distribution of rainfall. The heaviest use of water by f‘ occurs during the mid-summer depression of rainfall. Only ‘in the 22-year period has the summer rainfall been ample pduce good crops without an adequate moisture reserve in ‘il at planting time. Rainfall \ V ," ‘ "s1 ' \v/ o1 IHOISlUIG 1 1 1 1 1 1 1 1 1 1 1 Feb. Ma: Apr May June July Auq Sep. Oct. Nov. Dec 20 2O 2O 2O 2O 2O 2O 2O 2O 2O 2O Y: re 4. Average rainfall and average available soil moisture in the 3 feet, by monthly periods, 1930-52. _14_ Soil Types The amount of moisture that can be stored in the soil? plant use is largely dependent on the texture, structure and d of the soil. The heavy clay and clay 10am soils that predom'_ on the Rolling Plains have a high water holding capacity ancf retain from 8 to 12 inches or more of available water in the zone of crops. These soils are fertile but usually are drouthy: to the relatively slow rate of infiltration and to moderate to losses of rainfall as runoff and evaporation. Conservation praci that tend to overcome the low rate of infiltration by reta runoff increase the amount and depth of penetration of mo’ and increase the storage of moisture in the soil. The sandy or light soils that are usually underlain by a w‘ sandy clay subsoil are highly prized for crop production i; Table 5. Total inches of percolate from lysimeters at Spur, summary Size Total Depth of soil and manure in lysimeter 5 of rain, rainfall, 2 inches I 4 inches I 8 inches i “ch” “ch” Sand I Clay [Manure I Sand I Clay IManure ISand I Clay I 0 to .50 25.18 .82 .65 2.17 .60 .37 1.77 .44 .08 I .51 t0 1.00 22.00 6.97 2.71 12.82 1.76 .53 12.61 .41 .10 1.01 to 2.00 25.42 11.68 9.10 17.94 7.81 4.52 17.54 3.33 1.78 2.01 t0 3.00 16.75 11.05 8.98 14.15 8.50 6.46 13.37 5.61 2.94 - 3.01 8: over 18.31 12.77 10.91 15.91 10.70 _ 9.31 15.87 8.89 8.01 1 Total 107.66 43.29 32.35 62.99 29.37 21.19 61.16 18.68 12.91 l % 12.00 ~ 40.20 30.00 58.50 27.30 19.60 56.80 17.40 4D O I Q O I N O I O‘! O I ——-manure fine sandy loom- per cent rainfall percolating below 4 inch depth 8 I 40- 30- -—cloy loom 20- l0- o O lo .5 2 to 3 .5 to | _ I 1o 2 Size of romfell, inches Figure 5. Effect of size of rainfall on percent of rainfall pe A through 4-inch layers of three materials. :# __15__ i» These soils are usually not as fertile as the heavy clay but since they absorb water readily runoff is not a serious _‘ Since moisture tends to penetrate deeper on these sandy evaporation losses are small and crops often benefit from I. showers. On the heavy clay soils, these small showers are i! effective. Generally, when rainfall is below normal, the soils are usually the most productive and dependable; er, the more fertile clay soils produce the highest yields when p ill is above normal. ince the heavy soils usually occupy flatter slopes and receive _ from steeper surrounding areas, more water is available ese soils than the total rainfall might indicate. The increased a ation of water helps counteract the high evaporation losses. o show the amount of rainfall that might be expected to f ate to various depths in soils of different texture, a series imeters were filled in duplicate with clay loam and fine sandy ito depths of 2, 4 and 8 inches. Four lysimeters were filled well-decayed manure to the same depths as the mineral soil “als. The water that penetrated below the various depths i easured. It was found that 30 percent of the annual rainfall ated the clay loam, 40 percent penetrated the sandy loam and V cent penetrated the manure to a depth of 2 inches, Table 5. ye 5 shows the effect of the amount of rainfall on the percent ‘netrated below a depth of 4 inches of a clay loam soil, fine loam and well-decayed manure. Under field conditions, heavier runoff usually occurs on clay soils, even greater ‘nces in penetration of moisture could be expected between ndy and clay loam soils. The larger amount of rainfall j penetrated through the well-decayed manure strongly sug- jthe possibility of using mulches and crop residues that will . e the amount of moisture penetration on clay soils. H ration he loss of moisture by evaporation from the soil surface tively high. A measure of the combined effect of -high rature, high wind movement and low humidity on evaporation from a free Water surface is shown in Table 1. Moisture p‘ from the soil are much lower since the surface is dry much f time. Nevertheless, on small fallowed areas of Abilene 30am bordered to prevent runoff, over 60 percent of the that fell during a 2-year study at Spur failed to become i» moisture. Similar and even greater losses by evaporation "ithe soil surface have been reported on the High Plains (5) iDuring the hot summer, moisture losses of one-half inch or {may occur from the surface 6 inches of clay soils by ation within a few days after a rain. The moisture stored ‘i a depth of 6 inches, however, is relatively stable and losses evaporation are negligible (3). These data show that losses _15___ due to evaporation may be reduced by increasing the depth, moisture penetration. On sandy loam soils, a given amount rainfall will penetrate to greater depths and losses by evapora will be less than from clay loam soils (8). Farming pract’, that prevent rapid runoff, leave the surface cloddy to permit r6 penetration (6) and maintain a good cover of crop residues on surface (4) aid deeper penetration of moisture and greatly incr c‘ » , the amount of water available for plant growth. 1 Crops and Slope a The crop grown and the slope of the land are additi, A factors that influence runoff and soil moisture accumula Table 6. Effect of crops on runoff and soil loss on land with 2 percent s Spur, 1926-51 ‘ . Average annual Average ann CPOD runoff, inches loss,tons per _ Cotton 3.65 7.2 Grain sorghum 2.76 3.8 Fallow 5.00 15.5 ~55 Buffalo grass .94 .8 A good cover of buffalo grass offers the most effective mea reduce runoff, followed in effectiveness by grain sorghum, co and then fallow, Table 6. The canopy effect, litter and vegeta, residues of grass, sorghum and wheat, when maintained l? near the soil surface, lessen the impact of raindrops, offer resis to movement of water over the surface and reduce losses drying winds (7). These crops use large amounts of w, rapidly over a greater part of the season and leave storage f Table 7. Effect of slope on runoff and s-o-il loss on land in continuous c_ Spur, 1926-51 ' Slope Average annual Average ann, percent runoff, inches loss, tons per, 0 1.99 2.3 a 1 3.71 5.4. 2 3.65 7.2 3 3.88 8. u l‘ d V‘ ‘ha; Figure 6. Relative amounts of water that percolated various dep~ fine sandy loam and clay loam soils following a rain of 2.62 inches. penetration of moisture on the sandy soils helps reduce losses from evapor- soil for more moisture. Cotton, on the other hand, does povide much vegetative residue and uses water more slowly, during July and August. On clean tilled land in cotton and ,5; low-residue crops, including fallow, provision should be ill-to reduce runoff and evaporation to permit the maximum ation of moisture. oil moisture penetration and accumulation generally tend rease as the slope of the land increases. The relative runoff irosion losses from small plots are shown in Table 7. The iof the plots was established by the movement of soil and fults probably do not reflect actual losses that might occur field conditions. The greatest increase in runoff occurred ; the slope was increased from level or zero to 1 percent. n, on the other hand, increased markedly with each increase slope of the plots. vation Practices he effects of the foregoing factors often may be modified iably by the use of conservation practices to increase the _nt of water available for plant use. Research was undertaken ur in 1926 to determine the effect of terracing, contouring ater spreading on soil moisture content, runoff and yield on. The effect of these practices in increasing the depth of p re penetration and accumulation is shown in Table 8. For -year period, 1937-52 the total available water in the upper t of soil on May 20 was increased from 3.06 inches from row farming to 3.33 and 3.72 inches, respectively, by '3 ring and contouring supplemented with closed level terraces. l e years, there was more available moisture on areas with gin the direction of the slope because the limited growth of l_ the previous year resulted in a carryover of moisture. 4n relatively level areas of land, contouring supplemented losed level terraces also greatly reduced or actually prevented Effect of conservation practices on the total available moisture in l‘ the upper 5 feet of soil at Spur on May 20 Available moisture, inches Rows on contour Rows with slope Rows on contour supplemented with closed level terraces 4.64 4.48 5.16 4.82 5.10 5.50 1.23 .66 .76 1.12 1.90 1.45 6.03 6.27 4.88 7.27 6.78 . 7.00 4.53 4.78 5.09 2.18 1.62 2.22 2.13 2.06 2.10 2.17 3.54 4.13 4.10 4.84 5.87 1.85 1.66 2.31 2.35 4.35 4.73 1.07 1.06 3.30 1.50 2.33 2.81 1.97 1.83 2.29 48.96 53.26 59.60 3.06 3.33 3.72 __18_ runoff and markedly increased the yield of cotton. The use runoff water to increase the available moisture in the soil Y materially increased the yield of cotton, wheat, sorghums » native grass. Other conservation practices, such as crop res‘ management and tillage, which help maintain a cloddy surf play an important part in determining the amount of avail water stored in the soil. Exploratory studies with crop residues of sorghum ap, to cotton land over a 2-year period show that the depth of mois. penetration was greatly increased. Application of 20 to ¢ air-dry sorghum litter per acre increased the yield of lint co‘ from 106 to 228 pounds on land with a 0.5 percent slope "i the rows ran in the direction of the slope. On land that ‘I contoured and terraced to prevent runoff, the yield of lint c0, was increased from 331 pounds to 402 pounds per acre by application of litter. On land that has more than 1 percent slope, a combinati contouring with closed level terraces, supplemented with I residue management and desirable tillage practices, will us furnish the best opportunity for increasing the amount of stored in the soil. UTILIZATION OF SOIL MOISTURE The quantity of soil moisture that may be utilized by a c largely determined by the length of its growing season, p and nature of the root system, soil texture and the amount? distribution of rainfall. The native grasses and associated y commonly found on rangelands of the Rolling Plains can " soil moisture throughout the Winter and summer, thus pro a large potential reservoir for moisture. The native grasses long, fibrous root systems that will utilize soil moisture to of 4 to 6 feet or more. Cotton requires a long season for I‘ growth and development, yet, unlike native grass, it mak’ greatest demand for water over a 90-day period from about ’ 20 to September 20 during the blooming and heavy fruiting of growth, Figure 7. Cotton has a root system that will '_ soil moisture to a depth of 3 to 5 feet; under some conditi may remove moisture in the subsoil to depths of 6 feet or -_f The well-developed, deep root system and the indeterminate fr f habit of cotton enable it to withstand considerable drouth and? temperature and still produce good to excellent yields. i Sorghums have fibrous root systems that utilize soil mo" effectively in the upper 2 to 3 feet of soil but do not moisture as deeply as cotton, wheat or native grasses. L moisture at the heading stage is needed to produce satisf‘ yields. ‘ __]_9___ “flcasionally, favorable distribution of rainfall following plant- _o bring about heavy vegetative growth of cotton and sorghum i‘ orly-developed, shallow root systems. If an ample supply [oil moisture is available, cotton and sorghums can withstand “uth and high temperatures which prevail during the latter p, of the season (9). On the other hand, if the available e in the soil is low, cotton and sorghums deteriorate rapidly ‘ e onset of drouth, since the above-ground growth is too to be sustained by the shallow root system and limited 'e moisture supply. Root systems of cotton, buffalo grass, vgand mesquite that have been removed from Abilene clay V ils during seasons when subsoil moisture was well above fare shown in Figures 8, 9 and 10. / -_'PR. MAY JUNE JULY AUG. SEPT OCT gure 7. Seasonal use of soil water by cotton and native grass. x, JTCT OF AVAILABLE MOISTURE AT PLANTING TIME AON THE YIELD OF COTTON (e amount of available water stored in the soil on land usly planted to cotton is normally highest during the ‘* It declines to a low point during the latter part of July “ugust, when high temperatures prevail and cotton plants ffruiting and require large amounts of water to sustain and development. If ample moisture is stored in the soil “ting time, it serves as a reserve for such deep-rooted plants __2()__ Figure 8. Root systems of buffalo grass and Wheat that extend’ depths of over 6 feet when moisture was stored in the subsoil. 1 _._2]___ ‘lsquite seedling. Deep soils offer excellent opportunities to store large ts 0f Water in the soil for plant use. Root system of cotton when the soil was Wet to a de The moisture stored below a depth of 1 foot Figure 10. 6 feet at planting time. as a reservoir for plants during periods of scanty rainfall. __23__. on when summer rainfall is scanty or poorly distributed. ise relationship between the average amount of available gstored in the soil on May 20, normally the optimum time _ ting cotton at Spur, and the average yield of cotton for the p, period, 1930-52, is shown in Figure 11. Cotton was ed by hail in 1932 and the data for that year are omitted. -é e-coflon yield m _ o» Inches of OVOHOMB water | | | | l n l | | | | | | | l a n o 3| 33 34 3 36 37 38 39 40 4| 4 43 4 45 46 47 48 49 50 5| 52 3. ‘=30 ear s u’; e 11. Available moisture. in the second and third foot of soil at J; time and yield of lint cotton, 1930-52. ere were only 2 seasons during the 22-year period when lount of available Water at planting time gave only a fair ‘on of the probable yield of cotton. A combination of early iivegetative growth of cotton followed by extremely high atures in August greatly reduced the expected yield in {The other instance occurred in 1949 when almost ideal tion of summer rainfall in ample amounts provided suffi- oisture to produce an excellent crop of cotton with only ' age amount of available moisture stored in the soil on ‘i? This favorable rainfall condition, combined with only an e amount of moisture in the soil at planting time, occurred ll during the 22-year period. We relation between the amount of available moisture at time and the yield of cotton may be expressed mathe- lly as a correlation coefficient. This relation was determined _24___ for available moisture content 0f the soil to a depth of 3 feet y 1930 to 1952 0n April 20, May 20 and June 20. .The hi correlation coefficient, 0.747, between available moisture and g. of cotton was found for the moisture content of the secon‘ third feet of soil on May 20, Table 9. The relationship be ' available moisture and cotton yield was slightly lower for :1 minations made on June 20 and much lower for those on Ap ; By omitting the moisture content of the first foot of soil, '9 fluctuates greatly due to losses by evaporation and weed { the relationship was improved on all dates. The available mo’ content of soil to a depth of 5 feet on May 20 for the 5 1937-52, did not affect the correlation coefficient when with the moisture content to a depth of 3 feet. ‘ Table 9. Correlation coefficients for available water and yield of at Spur a Date of Depth of sampling the soil detlglzhsitrilzfteion 0 to 3 feet April 20 _ .5651 May 20 .6901 June 20 .6601 1Highly significant. Tables 10 and 11 show the quantity of available r1 the soil on May 20 and the yield of cotton from 1930 t The close association between these two variables is graphically in Figure 11. It is remarkable that such a high =9 of association exists since other factors, such as insect depredw extremes of temperature and rainfall and many other‘ influence the yield of cotton. Figure 12 shows the expect of cotton for varying amounts of moisture stored in the _ planting time. With one-half inch of available moisture f" Table 10. Available soil moisture by field areas in the second andt at planting time (May 20), Spur, 1930-52 ' Available soil moisture, inches 1 | 2 | 3 l 5 I 6 | 7 I 9 l 11 I 12 I 13 I 14 1930 .25 .02 .41 .74 .99 1.62 .25 .25 .43 .64 1931 2.00 1.44 2.11 1.86 1.99 1.89 2.46 1.06 2.30 2.55 1933 2.39 2.10 2.52 1.74 2.06 2.05 2.61 2.29 2.39 2.89 2.29 Year : 1934 .12 .53 .91 .50 .66 .65 1.06 .00 .28 1.07 .81 1935 1.06 .60 1.74 1.58 2.02 2.04 2.61 .80 1.87 1.76 .68 1936 1.60 1.49 1.81 .90 1.63 1.68 1.37 .57 1.76 1.27 .85 1937 2.34 2.64 2.26 2.27 2.36 2.20 2.52 2.01 2.07 2.60 2.16 1938 2.30 2.21 2.04 2.56 2.80 2.31 2.44 2.12 1.45 2.87 1.24 1939 .11 .19 .71 .18 .53 .11 .50 .89 .44 .29 .09 1940 .65 .47 1.09 .22 .05 .57 .68 .60 .93 .55 .39 1941 2.87 3.15 2.89 2.94 2.75 3.21 3.45 2.49 2.69 2.61 2.60 1942 3.04 3.31 3.06 2.85 2.23 2.97 3.17 2.20 2.72 2.41 2.48 1943 2.21 1.82 2.30 1.56 1.10 1.94 2.09 1.43 1.70 2.52 1.35 1944 .69 .77 .58 .96 .30 .75 .37 .39 .61 .31 .61 1945 1.31 1.55 1.67 1.68 1.18 1.16 1.67 1.02 1.27 .82 .98 1946 1.18 .99 1.79 1947 2.25 2.21 3.02 1948 .60 .69 1.05 1949 1.19 .69 2.25 1950 .29 .25 1.31 1951 .48 .24 .38 1952 .64 .51 .69 Total 29.57 27.87 26.10 22.54 22.65 35.29‘ 28.62 18.12 22.91 25.16 16.53 Av 1.34 1.27 1.74 1.50 1. 1 1.60 1.91 1.21 1.53 1.68 1 Ul __25_. Table 11. Yield of cotton on field areas, Spur, 1930-52 Yield of cotton, pounds lint per acre ‘ 1 I 2 I 3 I 5 | 6 | 7 | 9 I 11 | 12 l 13 | 14 | 15 I 16 34 9 37 46 33 104 129 85 87 75 ‘ 202 186 186 190 145 229 242 159 187 199 -' ~ 340 325 371 442 337 441 521 339 426 435 510 459 463 0 0 0 0 0 0 0 0 0 0 / 186 118 127 191 101 270 254 98 191 185 » 92 221 201 ~_u. 50 39 38 43 36 55 51 16 31 39 17 27 39 3.193 186 170 161 150 292 242 98 122 143 125 146 215 .1, 176 147 163 186 163 236 182 150 191 201 150 189 208 2 6 8 15 17 2 0 15 15 27 0 1»; 41 21 40 61 39 52 82 30 51 51 27 57 62 497 442 442 429 451 478 421 388 433 419 341 421 415 ‘331 285 255 306 285 310 260 288 303 274 275 331 288 106 77 125 105 102 162 128 121 123 136 99 114 149 78 61 102 89 96 96 89 85 98 114 73 93 117 58 63 80 71 82 89 76 59 68 79 53 55 84 1:0 11s 117 . m 15o 211 12s 10s 19o 43o 19s s34 , 12s 111 187 159 so 229 a 1s s 4s 13452 2750 2154 2335 2037 4390 2677 1931 2326 2377 1762 2113 2241 157 125 144 156 136 200 178 129 155 158 136 163 172 a and third feet of soil, the average yield per acre has been nds of lint cotton. When there was one inch of, available e in the soil, the yield increased to 89 pounds of lint per q For amounts of 2.00, 3.00 and 4.00 inches of available _,e at planting time, the yields were 187, 330 and 518 _;. of lint per acre, respectively. Each additional amount of lrlgreatly‘ increased the yield of cotton, especially when the -_ I 2 3 4 1M: of available water in the second and third foot of soil on May 2O re 12. Relation between available soil moisture at planting time and v lint cotton, 1930-52. _1 J I _26_. available moisture was above the minimum amount required, normal growth. Y RELATION 0F DEPTH OF son, MOISTURE AT PLANTV TIME T0 THE YIELD OF COTTON a Even though the quantity of available soil moisture at plan time serves as a reliable yardstick of probable cotton produ it is a measure that is difficult to use. Certain basic informal such as field capacity, minimum point of exhaustion and vol Weight of the soil, must be known to determine the amou v available moisture in the soil. For Widespread use by the ~- Table 12. Relation between depth of soil moisture at planting time and _ of cotton, Spur 1930-52 3‘ DePth “f N“ A“ yield Percent of cases when yield was K moisture of lint lbs. feet cam P" W" 0-99 lbs. | 100-199 lbs. | 200-299 n». | 1 64 44 91 8 2 2 37 104 57 41 0 3 53 170 25 49 17 4 56 300 0 29 23 Tota 210 32,534 AV. 155 44 30 ll Q s- 3 _ O U 5 Q D. Q ‘U c200“ :1 O Q *1 ‘C ._l IOO - O l I 2 3 4 Depth of moisture, feel Figure 13. Effect of depth of soil moisture at planting time u on the yield of cotton. ,' ple and easy method of evaluating soil moisture is needed. p unately, the depth of moisture is a good measure of the amount water stored in the soil (2, 6). When Water penetrates a dry , the first foot must be wet to its carrying capacity before water can reach the second foot. The same holds true l movement of Water to the soil layers at lower depths. The nge from a wet to a dry zone of soil usually occurs within y a few inches and can be easily observed. If the soil contains ugh moisture to form a firm ball when pressed between the ers, it may be considered Wet. Analysis of available moisture i: in view of depth of penetration showed that any foot-section the soil that contained more than one-half inch of available ‘ture should be considered Wet. Thus, if the first foot contained ‘ e than one-half inch available moisture and the second foot ‘j; less than one-half inch, the soil was considered to be wet f, 1 foot deep. The same method was used to determine the th of moisture in the second and third foot layers of soil. For 4 fourth foot, the soil was considered wet when the third foot tained more than 1 inch of available water. F The effect of depth of soil moisture at planting time on the ‘ld of cotton is shown in Table 12 and Figure 13. Of a total of l plot-years, there were 64 cases when moisture was only a foot p or less at planting time. The average yield of lint cotton f 44 pounds per acre; in 91 percent of the cases, the yield was p than 100 pounds of cotton. Timely rainfall during the summer 8 percent of the cases resulted in yields of 100 to 200 pounds, '_j~ in only 2 percent of the cases were yields over 200 pounds. '3 yields of over 300 pounds per acre were produced when the l was wet only 1 foot deep at planting time. Under these ditions, there is only 1 chance in 10 that yields of over 100 _ nds of cotton will be produced. ‘f There were 37 cases when the soil was wet 2 feet deep at _:nting time and the average yield was 104 pounds of lint cotton " acre. In 57 percent of the cases, yields were below 100 pounds » in 41 percent of the cases they ranged from 100 to 200 pounds. l y 3 percent of the crops yielded over 300 pounds per acre. h moisture 2 feet deep at planting time, there are only 4 chances t: of 10 that the yields will exceed 100 pounds of cotton per acre. “1 When the soil was Wet 3 feet deep (53 cases), the average ld of lint cotton was 170 pounds per acre. Twenty-five percent ithe crops produced less than 100 pounds of cotton, 49 percent uced yields between 100 and 200 pounds and 26 percent of F yields were over 200 pounds per acre. With 3 feet of moisture §planting time, the chances are 3 to 1 that yields will be over l pounds and 1 to 3 that yields will be above 200 pounds of cotton acre. There is 1 chance in 10 that the yields will be above pounds. yielded over 300 pounds. The odds of producing yields of l. _.28__ When the soil was Wet 4 feet deep at planting time (56 c f the average yield was 300 pounds of lint cotton per acre. ; of the crops produced less than 100 pounds per acre and 71 pe ' produced over 200 pounds. Forty-eight percent of the ' 200 pounds are approximately 3 to 1 with no yields below? pounds. i EFFECT OF PRESEASONAL RAINFALL ON THE YIELD OF COTTON r There is a close relation between preseasonal rainfall v3 yield of cotton. During most seasons, moisture accumulates i soil on land planted to cotton from rainfall received duri 1 winter and spring When no crop is grown on the land. Occasio however, moisture may remain in the soil from late summer fall on land continuously planted to cotton because of heavy ra'__ or as a result of crop failures, poor stands or other reasons. i Table 13 shows the amount of preseasonal moisture an_ yield of lint cotton for the 35-year period, 1914-52. If the g are classified into groups with varying amounts of total ra received during the period November 1 to June 1, a good indi Table 13. Preseasonal rainfall and yield of cotton, Spur, 1914-5, Total rainfall, Ave I Yearl Nov. 1 to June 1, ” inches 1913-14 18.71 15 18.09 17 4.53 18 4.07 19 13.77 . 21 4.44 22 11.87 23 8.77 24 7.99 25 ' 8.21 26 10.14 27 6.70 28 6.51 30 4.92 31 9.43 33 8.51 34 7.76 35 8.79 36 8.73 37 7.14 38 9.55 39 5.93 40 5.50 41 18.87 42 6.88 43 6.33 44 9.49 45 7.60 46 5.47 47 11.81 48 9.35 49 12.14 50 8.68 51 6.69 52 5.86 Average 8.84 1The cotton crops were destroyed by hail in 1916, 1920, 1929 and 1932. Therefore th_ are omitted. * _g9_ yields of cotton is obtained. The average rainfall from y.‘ 1 to June 1 was 8.84 inches. Table 14 shows that when infall was less than 8.00 inches, the average yield of cotton ,4 to be below normal, and when rainfall was above 8.00 inches average yields were produced. Thus, with a total rainfall so 8 inches from November 1 to June 1, the yield was 126 I- of lint cotton per acre. If the rainfall ranged from 8 to 12 f, the average yield increased to 188 pounds, and to 427 is per acre when the rainfall from November 1 to June 1 "ed 12 inches. I ven though there is a close relationship between the amount seasonal rainfall and the yield of cotton, the large number ’r crops produced when rainfall was above normal and several ‘crops when rainfall was below normal, indicate this measure ' ating yields of cotton is not too reliable, even though easily 14. Effect of preseasonal rainfall, November 1 to June 1, on lint cotton yields, Spur, 1914-52 Q Number of cotton crops producing Avefage Yidd v ' of lmt cotton 0-100 lbs. | 100-200 | 200-300 | 300 & over P" a=r¢ 00 7 s 3 1 126 2.00 4 7 1 2 18s over 0 0 0 5 427 _ Such factors as moisture stored in the soil prior to u ber 1, losses of rainfall due to runoff and evaporation from il, especially following small ineffective showers, losses due growth and occasional late growth of cotton, make it ble to determine the actual amount of water in the soil, least the depth of moisture penetration. CT OF SUMMER RAINFALL ON THE YIELD OF COTTON ilnce cotton is planted, the amount and distribution of rainfall f1 the summer is of great concern to the grower. Even k; available soil moisture at planting time greatly influences Teld of cotton, it is not presumed that high yields can be ‘ced without any summer rainfall. If ample amounts of istributed rainfall should occur throughout the growing in, the amount of moisture in the soil at planting time would 1 little or no influence on yields. Rainfall during the summer 'eld of cotton from 1914 through 1952 are shown in Table 15. ‘Iata from 1930 through 1952 show, however, that there is 7 likelihood of producing high yields of cotton when either yble moisture at planting time or summer rainfall, from June ctober 31, is well below the average, Table 16. The highest ge yield, 239 pounds of lint cotton per acre, was produced both the available moisture at planting time and summer ll were above normal. If soil moisture was above normal nting time and the summer rainfall was below normal,’ the Tge yield was 198 pounds of lint cotton. The yield dropped to 142 pounds per acre when soil moisture at planting time was bel normal and was followed by above normal rainfall duringt summer. If both available soil moisture at planting time a‘ summer rainfall were below normal, the yield averaged only pounds of lint cotton per acre. Table 15. Summer rainfall and yield of lint cotton, Spur, 1914-52 Total rainfall, Average yi Yearl June 1 to October 31, of lint co f inches lbs. per r -' 1914 18.51 1915 19.14 1917 10.68 1918 8.13 1919 7.35 422 ~ 1921 8.62 250 ‘ 1922 5.68 158 . 1923 14.76 ' 1924 6.33 159 . 1925 16.93 125 1926 25.18 324 1927 12.22 290 1928 12.14 110 1930 10.80 w 1931 6.76 206 1933 9.35 369 1934 4.75 1935 14.81 191 1936 16.93 1937 13.57 224 1938 10.09 186 1939 6.71 1940 6.12 1941 26.32 472 1942 15.14 309 1943 10.99 115 1944 9.60 1945 15.7 ‘ 1946 12.35 143 Q 1947 3.09 176 ; 1948 8.62 141 * 1949 16.49 386 1950 14.20 141 ‘ 1951 14.58 162 _ 1952 4.55 23 r Average 11.92 188 1The cotton crops were destroyed by hail in 1916, 1920, 1929 and 1932. Therefore, these l’ are omitted. Table 16. Effect of summer rainfall on the yield of lint cotton at Spur, varying amounts of available moisture at planting time Available . moisture at Rainfall, No. planting time June 1 to Oct. 31 cases Above average Above average 55 Above average Below average 50 Below average Above average 35 Below average Below average 70 EFFECT OF CONSERVATION PRACTICES ON COTTON PRODUCTION, RUNOFF AND SOIL MOISTURE I The use of conservation practices to store greater quanti? of water in the soil offers unlimited possibilities to reduce ru' and erosion, increase yields of crops and stabilize farming on _ Rolling Plains. The effect of terracing and contouring on runi available soil moisture, yields of lint cotton and gross return shown in Table 17. Cotton has been grown continuously on ; .5595 H0 02500: HKHHHHH Q0000 dHHHHQRHHQHH .3 Hvomouwmow nHOhUm ..H0HHHHH0HHH0m HHH HHaHH .3 00.2.0500 HHPHOH .100» H23 HG: MGM H0HHHQE H002 HHc H00>H000H mvoHHHH H.250: :0 1.00am» .HH0n we 000m HZHHHH use H2503 HHHH 6HnaHHa>a Ho: 01.500»? 2.3 2H 3H o HE» 3H vmé 5H =H...m~ rHH >N.H EH 00.2 $4 2.9:: 25H 3.2.. H230 22.. 5.3 20.5w SS :55 3.2m 139M. 2.3 0H. 2.. vmfi 0H Hé. H m2 m Hm. H 3.2 $3 34¢ 3N 2... 3.3 mmH 2.. H 2.3. mm 3. H 3.3 S2 2.3 hwH Hm.H 25m mNH mu. H $4» HHH ma. H 03H S2 $2.2 H5» 3.“ H22 i; 2H H 2Z5 mmH 3. H 3.3 2.2 2.5 S: 2H Sém HNH 3. H 5.2" 2H 3. H 34H 2.2 “Q2. HHN 24.. £50 S: £4" H flew cmH Hufi H 8.2 HE: 20.3 HRH EH NW3 3H wH.H H 21$ wHH mm. H E22 $2 34H mw 3H m mmfiH mm HHWH HHflu wNSH 2. 3H $5 35H 25H 8.3 em 2.. 0 3.3 HZ. 3. mH. HNGH H0 h». mm. NQHN E2 3.3 N3 vm.H c 3.3 2H Hum 16H E22 S. NmJ S." 23H $3 21$ 0H» H.m.u m .35. Hm» H54... 3. £43 m3 S.» Hmé 3.3 25H 2.3 mhv Had H. 3.3 2:. 5H bHéH NW2. u: B.» 3.2 5.3 H§H $5 3 S. 0 $4 Hv m0. mm. 3a HN HQ. mN.N 3.3 25H 3. N HH. c 3. N HH. 3. o». w 3. 3. 0:4: 25H 0W2 0....» Hui o 36H uhH 3." 2a HoJH 2H Hwfi $5 25H H53 2.2.. 2N 3a a 3.3 2H 3H H-md 2.3 02 Héfi wHJH 3.3 25H 2E 3 3H 0 8;. 3 H54 mm.H mod mm 3H 2w.» HHIHHN 02H 5.3 Qua S." = 5.3 3H 3H mm.“ g3 wHH 3. 2.5 3.2 23H 2. é 2.. 0 2. .5 NH. 9H. 2 0o H». 3. mwfiH 35H 3.3 H: m: m was» 3H mud Hm. ~15 3H 01m em. mwZmH 25H 2 a. H .0 2. 2. H 22H 2. w: H H: =5." ~22 5.5 3H 3H e 3.2 N3 8." m... hmdH 3H 11H 3. 0H1: H»? s}: QQH had 0 51H. 3.. “N. u». 2H m 2. 3H 3.3 23H i. é H 0 2. n. H HH.“ 2. <© H Nmfi HFJH mNmH 03H. bHu H m 2.3 HHH ,H 2.» 3.2 S H mm.“ 35H mNmH 5.3 2a H .0 Ham i.» H “H. 3am 3N H w». flHéH $2 HwHHHHHHwou onuHHfiwuomH 03:05 wuHHu-HH nmwHHmHwHww MQH0Hu 00a 03:05 00:05 HmwHMHHHQHH oHHHuu wHoHHH ~m0HH0HHH moHHuHHH m0HH0HHH .0 H > . H HG. . . . . H . JHHHH . . . . . Hu> d H . HHH . . . . . . 0004 .32? H 003202 mMGGH-um PH0< .32? 025305 wmQ-uium 0H0< .33? 025205 $35M H-Nwfimflmm mooHrHHow H0>0H H0330 03% :23 HuOuHHOEOHHHHHH-m 053500 HHc 980M 05.5500 HHo 930M HuHHoHw HHHHB P335 0HHo7H wmHOHHO<~HHH zoHefwmmmzoo @000 Ho 03m.» Him H3300 HHHHH He H0H0H.» Asa H020 0E3 wHHHHHHnHHH Hm 025205 HHom wHHHnHHHgm HmuHHHHH: HHo 25w an m00HH09HHH HH¢HHw>H0wHHo0 uc H00HHHH SH oHHHfiH. M. Figure 14. Cotton crop that produced 441 pounds of lint per acre; land that was contoured and terraced to prevent runoff and erosion. An: cellent “bottom season” of moisture at planting time was largely respo for the high yield of cotton. Over a 26-year period, the average yield has r 188 pounds on land that has been farmed on the contour with closed terraces. field plots since 1927. The erratic nature of the rainfall is refle in extreme variations in runoff, soil moisture and yields of co The practice of contouring reduced runoff from 2.75 inchesl straight-row farming on land with 0.5 percent slope to 1.95 inc and increased the yield of cotton 29 pounds per acre. The incre annual gross returns for contour farming over straight-row far l; _Figure 15. Cotton crop that produced 61 pounds per acre on land. straight rows and “no bottom season of moisture” at the time of plan The average yield over a 26-year period has been 117 pounds of lint per a on land farmed with rows up and down the slope. The average runoff been 2.7 5 inches. = raged $7.14 per acre. Since little or no additional labor was ssary to farm on the contour, the increased return may be "idered clear profit. The use of closed level terraces in 'unction With contouring prevented runoff, increased the yield “cotton 71 pounds per acre over straight-row farming and f eased the moisture content of the soil. In addition to the atrol of runoff and erosion, the annual value of the increased Figure 16. Following a rain of 1.08 inch on June 4, 1937, Where cotton l: 4 inches high. There was no Water lost from the area having contoured ‘s, but the run-off from the area with straight rows Was .70 inch, and the pe on these rows is only 0.5 percent. These pictures Were made Within an r after the rain had stopped falling. _.34___ cotton production was $16.82 per acre from the use of clos_ level terraces and contour farming. The portion of the increas annual return attributed to terracing, $9.68 per acre, far excee the average cost of $5.00 to $8.00 per acre required once eve_ 10 years for building and maintaining terraces. ' The prevention of runoff by the use of closed level terrac largely accounts for the increased cotton production. Reduci the runoff by one acre-inch increased the acre yield of 1i /. approximately 26 pounds with a value of $5.51. The value of o, acre-foot of water saved averaged $66.12. » The average moisture content of the second and third feet ' soil at planting time on closed level terraced areas was 1.60 inch as compared with 1.27 inches on areas with rows in the directi of the slope. Moisture stored in the subsoil is less subject to los by evaporation and weed growth, hence leaving a greater amou of moisture available to deep-rooted crops such as cotton. . value of subsoil moisture is indicated by the fact that ea additional inch of moisture stored in the subsoil at planting ti increased the average yield of lint cotton approximately 107 poun per acre. I On the land that was contoured and terraced to prevent run and erosion, the highest yield of cotton, 534 pounds per acre, produced after 23 years of continuous cotton production. e1 contoured land, relatively high yields also were produced after long period of cotton production. On areas with straight the highest yield, 442 pounds, was produced after 15 years ‘ continuous cotton production. ' The heavy clay loam soils have not responded to applications nitrogen and phosphorus fertilizer, even when moisture conditi‘ have been highly favorable. ‘ VALUE AND USE OF SOIL MOISTURE INFORMATION Since the productivity of heavy soils on the Rolling Plains largely dependent on available moisture stored in the subsoil, ev effort should be made by farmers to conserve most of the rainf! Effective methods include contouring, terracing, Water spreadi management of crop residue, tillage practices and other that reduce runoff, increase depth of moisture penetration . reduce evaporation. The close relation between the amount of available moisture. planting time and the yield of cotton may be used by the far _ as a valuable guide for planning his farming operations. ’ information also serves as a valuable yardstick for business . industry connected with agriculture in the region. Informat on the likelihood of producing poor, fair and good to excell Figure 17. Use of level terraces to spread Water and prevent runoff has big dividends on land with less than 1 percent slope. Above, a station field owing a 5-inch rain. Below, a crop of Early Hegari produced on the land 7 year. _36__ yields of cotton at planting time permits adjustments to be m early enough in the season, according to probable yield and ret y from different crops, to help stabilize farming and business. The grower, business man and others whose economy largely dependent on cotton production, should determine amount of preseasonal rainfall during the winter and early spr'_ This information will serve as a general guide for the area of amount of moisture that likely will be stored in the soil at plan f time, but will vary according to amount of runoff, character rainfall, previous crop, slope, soil type, preparation of the l and other factors. In most instances, extremes of rainfall, eit t above or below normal, will give some indication of crop prosp The grower will necessarily obtain the greatest benefit f soil moisture information by actually determining how deep» soil is wet in his fields. If the soil is wet to a depth of 4 j or more prior to the planting of cotton, the grower has an excell chance to produce good to excellent yields with little likeli l? of failures. Undoubtedly, he should expand his normal co f acreage to take advantage of the favorable moisture conditi Every opportunity should be taken to use good cultural pracm to obtain maximum yields. In some instances, this might J “u I s r . . a Figure 18. Tillage implements that leave the soil cloddy and ma' crop residues near the surface help reduce runoff, aid deep penetrati moisture and reduce evaporation. i 1 the trial of fertilizers, use of special weed control measures, iaration for the control of insects and the use of other practices it might benefit the crop when there is sufficient moisture to _uce high yields. If the soil is Wet to a depth of 3 feet at planting time, the page of cotton may be expanded if the price outlook is favorable. i odds are about 3 to 1 that yields will be greater than 100 nds of lint per acre and 1 to 3 that yields will exceed 200 ds. Every effort should be made to manage the production jotton from the standpoint of cultural practices and insect and ‘ control measures. i In those years when the soil is wet 2 feet deep at planting e, the grower has approximately a 1 to 1 chance of producing 100 pounds of lint cotton per acre. The likelihood of ucing less than 100 pounds is somewhat greater than of ucing over 100 pounds. The grower probably should plant 3' on on the most productive land and, perhaps, reduce his cotton ‘ge, depending on economic conditions and the opportunity to ,'ze other crops that require less labor and which fit into the i: operations. Expenses and outlay of capital should be curtailed ‘ e the prospects of a good cotton crop are relatively poor. Such ps as late planted grain sorghum. soil-building crops and forage hums offer good possibilities of reducing costs of production n moisture conditions are unfavorable. In some instances, 0w during the summer to improve moisture conditions may be ,' able for the fall seeding of wheat, or clean fallow may be u to control badly-infested fields of Johnson grass. The general g. e of farming under these conditions should be one of reducing nditures and utilizing what moisture is available for temporary short-season crops. a When the soil is wet less than 1 foot deep at planting time, odds are about 9 to 1 that the yield of cotton will be less than pounds per acre. There is little likelihood of producing yields ,ve 200 pounds of cotton. Under these conditions, curtailment ‘xpenditures should usually be the goal for all farm operations. y the most suitable areas of land should be planted to cotton lss other crops cannot be produced and utilized profitably. The A of fallow, sorghums, soil-building and grazing crops, or others it can be grown and harvested at low cost, offer the best means oping with the unfavorable moisture conditions. 7 Even though the probability of producing good to excellent _s of cotton is largely governed by the amount of preseasonal 'sture and subsoil moisture at planting time, with average _1 mer rainfall, there always remains some chance of producing w crops. The adjustment of cotton acreage to the probable d outlook should serve, however, as a valuable guide to make ‘ best use of moisture, equipment, land and other resources. _3g_ SUMMARY Crop production on the heavy soils of the Rolling Plains chiefly governed by the amount of Water available for plant gro, Soil fertility seldom influences crop yields, except on the ligh sandy soils when rainfall and soil moisture are more favorable. Since available moisture limits crop production, major emph js placed on factors that influence the accumulation and utiliza of soil moisture. Results of 27 years of research at Substation No. 7 near S on moisture conservation studies are reported in this bulletin. Q soils on which these studies were made include Abilene, Till t and Weymouth clay loams with slopes ranging from 0.5 " percent. The findings are applicable to 14 million acres of he soils on the Rolling Plains of Texas and indirectly to other a a where moisture limits crop production. " The average annual rainfall for the 42-year period, 1911 ' was 20.85 inches. Extremes of rainfall have ranged from 11 inches in 1924 to 42.87 inches in 1941. Seventy-two percent? the annual rainfall occurs from May 1 to November 1 and. characterized by two peaks, one in May and one in Septem with a depression extending from June 15 to August 15. i Soil moisture accumulation is influenced largely by the amo and character of rainfall, soil type, evaporation, crops, p ' residues, slope of land, tillage and conservation practices. Total rainfall is not a reliable index of the amount of moist available for plant use. Sixty-one percent of the annual rai produced runoff varying from .57 to 10.66 inches, with an ave i loss of 3.55 inches. Another 2.74 inches of the rainfall are 10s small, ineffective showers. For rainfall causing runoff, 5.92 in Were torrential, 1.82 inches Were moderate and 4.93 inches as gentle rain. Thirty-five percent of the annual rainfall f 1912 through 1952 occurred in rain periods of 2 inches or m with the highest percentage of 2-inch rain periods occurring du August, September and October. Conservation of water f. these heavy rain periods reduces runoff and erosion, benefits c and offers excellent opportunities to store Water in the soil future plant use. a The clay loam soils have a high Water-holding capacity y, provide an excellent storage place for moisture if steps are to reduce runoff and evaporation. Moisture losses by evapora from the soil are relatively high but may be reduced by the , of practices that will increase the depth of moisture penetra and reduce losses from the surface. A good cover of buffalo grass provides the most effec means to reduce runoff and erosion. Clean cultivated crops, s as cotton or fallow, require the use of conservation practice; control runoff and erosion. ' _39___ :- " Contouring supplemented with closed level terraces increased the yield of cotton, depth 0f moisture penetration, and the amount yof Water stored in the soil and reduced runoff and erosion. Applications of sorghum residues increased the depth of ‘fmoisture penetration, the amount of available moisture in the soil "and the yield of cotton. The greatest increase from the use of Icrop residues was obtained on land with rows running with the slope. A combination of contouring and terracing supplemented .with crop residue management appears to offer the best means Y‘ or increasing the amount of Water that is stored in the soil. . Native grasses and associated plants utilize soil moisture to epths of 4 to 6 feet throughout much of the year, thus, providing torage space for additional moisture in the soil. Cotton has a weep root system and uses moisture heavily during a 90-day period rom June 20 to September 20. Sorghums have fibrous root ystems that utilize moisture heavily to a depth of 2 to 3 feet at he heading stage of growth. g The close relationship between the amount of available i: oisture stored in the second and third feet of soil at planting ime and the yield of cotton is indicated by a highly significant ’rrelation coefficient of .747. A high moisture content of soil at lanting time is followed by a high yield, and a low content by a low field. Thus, amounts of 1.00, 2.00, 3.00 and 4.00 inches of moisture tored in the soil at planting time, indicate the likelihood of roducing 89, 187, 330 and 518 pounds of lint cotton per acre, espectively. g There also is a close relationship between the amount of ivailable water stored in the soil and the deoth of moisture netration. Cotton produced an average of 44. 104, 170 and 300 unds of lint per acre when the soil was wet 1, 2, 3, and 4 feet ep, respectively, at planting time. . The odds of producing over 100 pounds of lint cotton per acre ere about 1 to 10 when the soil was wet 1 foot deep at planting e, approximately 1 to 1 when the soil was wet 2 feet deep and to 1 when the soil was wet 3 feet deep. The chances for ioducing over 200 pounds of lint cotton per acre were approxi- ately 1 to 48 when the soil was wet less than 2 feet deep at anting time, and 3 to 1 when the soil was wet 4 feet deep. The amount of preseasonal rainfall from November 1 to May 31 ves a general indication of the amount of moisture that is stored 1 the soil at planting time but is less reliable than soil moisture terminations. Rainfall from June 1 to October 31 influences e yields of cotton less than the amount of moisture stored in e soil at planting time. Farming the land on contour supplemented with closed level races significantly increased the yields of cotton and reduced _4()__ runoff and erosion. Contouring alone increased the yield of cotton an average of 29 pounds per acre over straight-row far while contouring with closed level terraces increased the yield; pounds. The annual increased gross returns from farming land of percent slope on the contour with closed level terraces was $16 per acre over land farmed with straight rows. In addition, th was no runoff or erosion on the contoured and terraced land. Since the productivity of the heavy soils on the Rolling Pl p is largely dependent on the amount of moisture stored in the s the use of conservation practices will reduce runoff and erosi increase yields and help stabilize crop production. ’ Knowledge of the moisture stored in the soil provides yardstick for adjusting the acreage of crops and farming operatii to enable the grower to make the best use available of moist and resources. LITERATURE CITED 1. Conner, A. B., R. E. Dickson and D. Scoates. 1930. Factors Influen Runoff and Soil Erosion. Texas Station Bul. 411. i 2. Cole, John S., and O. R. Mathews. 1940. Relation of the Depth to w the Soil is Wet at Seeding Time to- the Yield of Spring Wheat on Great Plains. USDA Cir. 563. i 3. Dickson, R. E., B. C. Langley and C. E. Fisher. 1940. Water andi Conservation Experiments at Spur, Texas. Texas Station Bul. 587. 4. Duley, F. L., and J. C. Russel. 1948. Stubble Mulch Farming to Soil and Water. USDA Farmers Bul. 1997. 5. Finnell, H. H. 1944. Water Conservation in Southern Great Plains ' J Production. Texas Station Bul. 655. 6. Hallsted, A. L., and O. R. Mathews. 1936. Moisture and Winter ' with Suggestions on Abandonment. Kansas Station Bul. 273. a 7. Johnson, Wendell C. 1950. Stubble Mulch Farming on Wheatlands of; Southern High Plains. USDA Cir. 860. 8. Mathews, O. R., and L. A. Brown. 1938. Winter Wheat and Sori Production in the Southern Great Plains Under Limited Rainfall. ‘j Cir. 477. 9. iii and B. F. Barnes. 1940. Dryland Crops at the Dal’ Texas Field Station. USDA Cir. 564. 10. Quinby, J. R., and J. C. Smith. 1950. Effect of Fertilizers on Yield Lint Cotton on Miles Fine Sand at Chillicothe, Texas. Texas S Progress Report 1219. 7 11. Thysell, J. C. 1938. Conservation and Use of Soil Moisture at Ma» N. Dak. USDA Tech, Bul. 617. .