l1 {'51, 4/5 Ewfii“ TEXAS AGRICULTURAL EXPERIMLQQQ A. B. CONNER, DIRECTOR, College Station, Texas BULLETIN NO. 655 AUGUST 151$ (Q90 ‘r s WATER CONSERVATION IN GREAT PLAINS WHEAT PRODUCTION H. H. FINNELL Division 0f Agronomy in covopefation with Soil Conservation Service U. S. Depélrtment 0f Agriculture AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS GIBB GILCHRIST, President E02-844-4M-L180 [Blank Page in Original Bulletin] Farmers’ experience in 901 cases of winter wheat production in the high p, ' s of Texas and adjacent areas shows that seasonal conditions and In moisture accumulations preparatory to sowing in the fall may I e as a dependable forecast of production possibilities. Favorable July I» all was a big factor in preparing a good soil condition for high yields l i a large subsoil moisture store on hand at sowing time in the fall tributed greatly to the size of grain yields the following year. ‘Where contour tillage and level terracing were used to retain surface "of water favorable sowing conditions more frequently occurred and a a risk of crop failure and wind erosion damage was reduced. evertheless, water conservation alone is not enough to make the best é of current soil and water resources available in the winter wheat " of the Texas high plains. The amount and distribution of seasonal - all naturally vary so much that a definite program of flexibility in m use off summer fallowing, tillage methods, and the rotation of diversi- crops becomes a physical necessity. The combined objectives of wind ‘on control and efiicient production emphasize the importance and prac- bility of using soil moisture and crop residues as guides to tillage ods and cropping plans. CONTENTS Page Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5 History of the Ideas Explored in these Studies . . . . . . . . . . . . . . . . . . . . . . . . 5 Sources of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 6 Analysis of the Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 7 Soil Texture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 9 ‘ Fall Soil Moisture Store . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 9 July Rainfall Previous, to Wheat Sowing . . . . . . . . . . . . . . . . . . . . . . . .. 12 Spring Rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 14 Wind Erosion Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15 Date of Seeding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 16 Fall and Winter Grazing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 16 Water Conservation Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 17 Wheat Pasturage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 18 Factors Affecting Soil Moisture Accumulation . . . . . . . . . . . . . . . . . . . . . .. 18 a Analysis of the Wheat Yield Increase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 20 Crop Management in Relation to Water Conservation Practices . . . . . . . . . 21 Practical Problems in Wheat Growing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Character of Rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Disposition of Rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 24 Soil Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .L . . . . . . . . . .. 27 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 i Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 31 TER CONSERVATION IN SOUTHERN GREAT PLAINS WHEAT PRODUCTION LBy H. H. Finnell, Research Specialist, Soil Conservation Service i Amarillo, Texas a e problem of efficiently utilizing the soil and water resources of the them Great Plains for winter wheat production is one that has occupied ithought of farmers and students almost from the beginning of agri- j--= l development in the high plains. .; onomists, farmers, and millers have debated the merits of different ‘l; varieties. The appearance of insects and diseases has given the crop try many starts and alarms. The waxing and waning of fads in farm 'nery have gradually increased the labor efficiency of wheat producing ods and equipment. The crop-management problems interjected by the inties “of economic depression and war demands have beclouded the e. But most formidable of all seemed the dark clouds of dust that rolled the Plains during the “dirty thirties” when protracted drouth made g-erosion control more difiicult than usual. Through this period men’s V,’ es and their soil resources suffered but also much has been learned g should be turned to use. ; is becoming more and more evident, as our knowledge of semi-arid Vlture increases, that the element of gambling in Southern High u wheat production is being injected because of the farmers’ disregard portant advance conditions of soil and moisture rather than by the ' s of unknown variables. A ' l} essential productive conditions accrue, exist, and are measurable ‘us to sowing time and adequate substitutes for them cannot be an-- kted later during the crop-growing season with any reasonable degree g bability. _1 the light of these facts, the efficiency of wheat production is capable _ough practical improvement to completely eliminate erosion hazards 4w» by injudicious sowing, to save the waste of seed and labor on ifitable production possibilities, and at the same time, to afford highly ble crop diversification opportunities wherein forage and grain feed may be successfully produced on soil and water resources that would ~ be Wasted in producing weeds and wheat failures under a system ight wheat farming. I ‘HISTORY OFATHE IDEAS EXPLORED IN THESE STUDIES study of the relatio-ns between initial soil moisture stores and result- heat yields was first reported in the Southern Great Plains by Call lialstead in 1915. ( 1) Continued observations were reported by Finnell .Plains about 100 miles wide and 250 miles long, stretching in a northeast- 6 BULLETIN NO. 655, TEXAS AGRICULTURAL EXPERIMENT STATION in 1929 ('7, 8, 9), by Halstead and Coles in 1930 (17), by Henny in 1932 (18), by Finnell in 1933 (10). Studies of the functions of level-terraces in water conservation and crop production were started by Dickson and Finnell at about the same time in Texas and Oklahoma. Yield increases of sorghum due to terracing were first reported by Finnell (9) in 1929. Yield increases of cotton d-ue to terracing for water conservation were first reported by Conner, Dickson, and Scoates in 1930 (2) and of wheat by Finnell (11) in 1930. Further reports were made by Finnell in 1931 (12) and 1934 (16), by Daniel in 1935 (3), by Daniel and Finnell in 1939 (4), and by Dickson, Langley and Fisher in 1940 (5). - Information along both these lines produced by the experiment stations of Kansas, Oklahoma, and Texas was made the basis of water and crop management phases of the conservation program developed and demon- strated by the Soil Conservation Service in the Southern Great Plains region from 1934 to 1942. (The field records of these demonstrations carried out under average farm conditions form the body of data analyzed in this study.) The lessons of practical application learned in the demon- stration projects have since been used by Agricultural Adjustment Ad- ministration and in the framing of programs and plans of work adopted by soil conservation districts in the Southern High Plains area. SOURCES OF DATA The field records of the soil conservation demonstration project areas of the Southern Great Plains afford a mass of information revealing some of the behavior of water conservation practices in relation to soil, climatic, and cultural variations as they afiect wheat production. The farm results studied represent, roughly, an area of Southern Great southwesterly direction from southwestern Kansas across northwestern Oklahoma and Texas into eastern New Mexico. The records are complete on 901 farms taken during the years 1938 and 1939. Although the records cover only a period of two years, the variation in seasonal conditions sampled is greatly augmented by the distribution of the farms among 11 separate demonstration areas in addition to the local variations recorded within areas by a network of rain gages. For example, the July rainfall varied from 1 to 5 inches and the August to October period rainfall varied from 2 to 12 inches. The yields of whea ranged from 0 to 34 bushels. These variations are characteristic of singl location records extending over periods of 10 to 2O years. Top-soil texture was determined by a detailed soil survey of each int dividual field and was translated into numerical terms by devising a scal of 1 to '7 as an index of textures ranging from clay loam to loamy fin sandyFrom the same detailed survey information about soil depth, slopes and erosion conditions was obtained. WATER CONSERVATION IN GREAT PLAINS WHEAT PRODUCTION 7 iThe rainfall records during the preparatory and crop growing seasons ire kept by cooperative observers under the technical supervision of ject engineers using standard rain gages located from 2 to 4 miles I within the demonstration areas. Regular daily and monthly records i precipitation were available from all the demonstration areas. The est rain gage record was applied to most fields; however, where a _- was located half-way between two gages, or in a three-gage triangle, ‘ or more records were averaged if the rainfall at adjacent points _ 'ed greatly. _ e water conservation practice and age of terraces were recorded by jject technicians. Three degrees of water conservation practice were "5 ized and differentiated by the amounts of surface water capable f-being retained by the structures used. ‘.4 .. e time of seeding, the rate of seeding, and the fallow period previous Seeding were observed and recorded by project technicians at the ap- riate seasons of the year. The wheat yields were determined by fject technicians in collaboration with the cooperators on the basis of Qels of grain per sowed acre. On most of the projects, these were cal- _‘ted to .1 bushel but, in some cases, the nearest even bushel was rded. 4» depth of soil moisture penetration at seeding time in the fall was » ined for each separate field by project technicians using a soil a or tube and recorded in inches from the surface. The amount of and winter grazing utilized was recorded by project technicians in ration with the farmers and was calculated to the nearest .1 cow- ‘Uh per acre. a ANALYSIS OF THE DATA first step in the study consisted of determining which factors showed ' ificant relation to wheat yield in order that these might be analyzed ition to water conservation practice. ' ificant increases of wheat yield resulted from each of the following: jitial soil moisture stores, (2) July rainfall previous to sowing, (3) terracing and contour farming, and (4) favorable spring rainfall, significant decreases resulted from (5) soil erosion damage, (6) ed seeding, and (7) fall and winter grazing. e additional information has been obtained from studies of various 'sions of the group. It may be briefly noted that the unfavorable 10f land slope appears to have been off-set lyy the effects of terracing ntour farming; that summer fallowing, as practiced on the average _ farm, proved to be much less effective than experiments would lead i: expect; that variations in the May rainfall, which is popularly I ed to cover a very critical period in the crop year, is of little or no _, nce separate and apart from the rainfall of the January to May ; and that the August to October rainfall operates almost entirely v 8 BULLETIN NO. 655, TEXAS AGRICULTURAL EXPERIMENT STATION through its contribution to the storage of a subsoil moisture supply f0 later use. A good estimate of probable yield can be made, using only factors whic» are known and measurable previous to sowing time or which can be rea sonably anticipated previous to sowing time. If no grazing is anticipat no delay in sowing, and no part of the area is susceptible to wind-erosior damage, the following formula may be used: Multiply the number of inches of July rainfall by 2%; divide th number of inches of depth of soil moisture penetration at wheat sow ing time by 3; add these two values together, and substract 6%. The number obtained will be the average expected yield per acre ' bushels of Wheat,_and the chances are 2 to 1 that this average will r within 5 bushels of the actual yield harvested. Since the efficient use of soil and moisture resources constitutes the oth half of conservation, it is always important to take advantage of favorab seasonal conditions to increase production just as it is important to avo a waste of seed and labor when conditions are so unfavorable as t0 predi an almost sure failure or unprofitable yield. Table 1. Wheat Yields Averaged According to Significant Variables Observed in the South » Great Plains, 1938-1939 - \ Mean Yield Significance Methods 0r Condition Number Bushels Wheat Differences", Fields Per Sowed Acre Between Me Fall Soil Moisture Penetration: O—~12 inches . . . . . . , . . . . . . . . . . . . . . . . . . . . 128 1.37 13~24 inches . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 3.07 ** 25—36 inches . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 8.49 37 plus inches . . . . . . . . . . . . . . . . . . . . . .. 175 12 60 Previous July Rainfall: .50—1.50 inches . . . . . . . . . . . . . . . . . . . . . . . 276 4.57 1.51—2.50 inches . . . . . . . . . . . . . . . . . . . . . .. 495 6.01 ** 2.51—3.50 inches . . . . . . . . . . . . . . . . . . . . . . . 85 10.19 3.51 plus inches . . . . . . . . . . . . . . . . . . . . . . . .. 45 17.42 Portion of Field Affected by Erosion: 0— 407 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 836 6.79 . 50—— 80% . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 51 3.90 ** 90—100% . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 .57 - Not Grazed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588 5.65 Fall and Winter Grazed . . . . . . . . . . . . . . . . . . . . . 313 8.17 ** September Seeding . . . . . . . . . . . . . . . . . . . . . . . . . . . 739 6.87 October to December Seeding . . . . . . . . . . . . . . . . . 162 4.96 ** January to May Rainfall: 2— 3 inches . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 1.62 4-— 5 inches . . . . . . . . . . . . . . . . . . . . . . . . . . .. 405 7.32 6— 7 inches . . . . . . . . . . . . . . . . . . . . . . . . . . .. 248 8.48 ** 8— 9 inches . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 11.35 10 plus inches . . . . . . . . . . . . . . . . . . . . . . . .. 12 17.42 Without Water Holding Structures. .. . . . . . . . . . . 386 5.11 Level Terraced or Contour Farmed . . . . . . . . . . . . 146 6.31 ** Level Terraced and Contour Farmed . . . . . . . . . . . 369 8.10 WATER CONSERVATION 1N GREAT PLA-INS WHEAT PRODUCTION 9 Tle 1. Wheat Yields Averaged According to Significant Variables Observed in the Southern .‘ Great Plains, l936-1939—Continued _ Mean Yield Significance of Methods or Condition Number Bushels Wheat Differences F1elds Per Sowed Acre Between Means _ t_After Wheat: _Without Water Holding Structures. .. . . . . . . 216 4.42 TTVLevel Terraced 0r Contour Farmed . . . . . . . . . 74 5 . 69 ** _jLevel Terraced and Contour Farmed . . . . . . . 150 7.31 “t After Sorghums: fWithouLWater Holding Structures . . . . . . . . . 84 5.64 j Level Terraced 0r Contour Farmed . . . . . . . . . 37 6.35 Level Terraced and Contour Farmed . . . . . . . 72 7.36 W: [After Summer Fallow: ‘rWithout Water Holding Structures. .. . . . . . . 86 6.35 r vel Terraced or Contour Farmed . . . . . . . . . 35 7.60 ** vel Terraced and Contour Farmed . . . . . . . 14 9.26 t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440 5.62 ‘Sorghum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 6.42 ** i ummer Fallow . . . . . . . . . . . . . . . . . . . . . . . . . . 268 .11 ut Water Holding Structures: ter Wheat . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 4.42 ter Sorghums . . . . . . . . . . . . . . . . . . . . . . . . . 84 5.64 * ~" ter Summer Fallow . . . . . . . . . . . . . . . . . . . . 86 6.35 * ‘Terraced or Contour Farmed: ‘f ter Wheat . . . . . . . . . . . . . . . . . . . . . . . . . . .. 74 5.69. ter Sorghums . . . . . . . . . . . . . . . . . . . . . . . . . 37 6.35 ' er Summer Fallow . . . . . . . . . . . . . . . . . . .. 35 7.60 Terraced and Contour Farmed: er Wheat . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 7.31 ter Sorghums . . . . . . . . . . . . . . . . . . . . . . . . . . 72 7.36 * f er Summer Fallow . . . . . . . . . . . . . . . . . . . . . 147 9 .26 ~ _ly significant differences between means. fun _cant differences between means. ._ » significant differences between means. Table 1, the wheat yields are classified according to variations in of the factors found to have a statistically significant relation to ‘i The column showing the number of fields indicates the frequency hich different conditions occurred within the group of farms studied. v bols in the last column of the table indicate whether the differ- between mean yields are great enough to be significant or not. Soil Texture lugh the variations in soil texture do not show up as an important affecting wheat yield in any of the subgroups, the fact sandier f soil prevailed Where wheat followed sorghum in the rotation, a ~ subdivision apart from all the others and helps to explain the In divergence of moisture relations to soil and crop. It is a com- _.observed fact that the sandier soils are less subject to extreme 20f drouth or wet weather. With equal slopes, they are less urgently l‘ of water holding structures and, for the same physical reasons, k'ted with being able to make more effective use of rainfall oc- 10 BULLETIN NO. 655, TEXAS AGRICULTURAL EXPERIMENT STATION curring during the preparatory and crop growing season. The soils wére noticeably sandier in texture in that group where wheat was sowed in sorghum stubble than in the group where wheat followed summer fallow. This observation reflects the popular conception that sandy soils are best suited to diversified farming and that summer fallowing is most effective on hard lands. It should also be pointed out that under farm conditions wheat does not follow sorghum nearly as often as it does wheat or summer fallow. Ex- ceptional conditions such as a thin stand of sorghum or effective late summer and early fall rainfall are usually necessary to suggest this rather difficult crop sequence. It is recognized that the 193 cases of wheat sowing in sorghum stubble recorded in this study do not represent the average conditions found on sorghum land at wheat sowing time. However, when favorable conditions do exist in sorghum fields, the value of taking advantage of them for wheat production should not be ignored. Fall Soil Moisture Store Measuring the depth of moisture penetration is not an exactly accurate method of determining the store of available moisture in the soil. How- ever, the simplicity and ease of making this determination more than compensates for small errors. It is a method which can be used just as readily by the average farmer as by any technician. When wheat yields were classified according to depth of fall soil moisture penetration, the extremes ranged from an average of 1.37 bushels, where moisture penetration was 12 inches or less, to 12.60 bushels, where pene- tration was above 36 inches. (See Table 1 and Figure 1.) Almost sure failure was indicated by an initial moisture supply of less than 24 inches penetration, and a penetration of more than 36 inches was necessary to insure a profitable yield within reasonable limits. Only 13 failures occurred out of 175 sowings, or less than 7-‘z%, where an adequate initial soil mois- ture supply was on hand at sowing time. With 12 inches or less of initial soil moisture penetration, 85 failures occurred out of 128 sowings, and only 7.0% yielded 6 bushels per acre or better. ' As a single criterion upon which to base cropping plans, this factor of stored moisture supply is the most dependable. However, much more ac- curate forecasts can be made by also taking other advance conditions into consideration. - The effect on wheat yield of soil moisture supply at sowing time was highly significant under all conditions studied. Its greatest relative im- portance, in comparison with other factors, was shown where wheat followed wheat. Variations in soil moisture store were less effective where wheat followed sorghum. In this case, its relative weight was exceeded by that of the previous July rainfall. It was approximately of equal im- portance under all other conditions. WATER CONSERVATION IN GREAT PLAINS WHEAT PRODUCTION 11 e greater importance of initial moisturelsupply when wheat follows it cannot be explained by differences in the amount of available --- was 22 inches, compared to 27 on sorghum stubble land. The soil wetted, per inch of summer and early fall rainfall, was 3.00 inches re wheat followed wheat, and 3.28 inches where Wheat followed “hum on sandier types of soil. g ere the group was subdivided according to crop sequence, it was ’ a» that the July rainfall also contributed more to the fall soil moisture‘ _‘ - where wheat followed fallow or wheat, than where a sorghum crop pied the land until wheat sowing time. radical difference existed in the seasonal progress of soil moisture fthe two types of crop succession. Land being prepared for sorghum itinued to increase in moisture content beyond the month of June, when hum planting was usually done, and was ordinarily well supplied with Figure I. RELATION 0F INITIAL SOIL MOISTURE TO WINTER WHEAT YIELD IN THE SOUTHERN GREAT PLAINS. AVERAGE YIELD ' eusuzrs PER _ ACRE "0 F=l42.25 , . o-I2 l3-24 25 3s INCHES DEPTH sou. MOISTURE PENETRATION AT sowme TIME ‘Hndicates number of fields averaged in each group. F = Variance Ratio, sture during the month of July; whereas land bearing a wheat crop roached midsummer with a continuing decline in soil moisture content, f‘ 'ng its most completely exhausted condition at harvest time, about ‘first of July. From midsummer on until wheat sowing time in the fall, ' land bearing a sorghum crop continued to be cleanly cultivated, but soil moisture supply was used up at least as fast as it was replenished I current rainfall. Under thick stands of sorghum it was used up r. I f I years of deficient summer rainfall an initially adequate soil moisture e would be seriously depleted under a growing sorghum crop. Hence, fture involved. The average depth of penetration on wheat stubble 12 BULLETIN NO. 655, TEXAS AGRICULTURAL EXPERIMENT STATION the subsoil moisture supply at wheat sowing time is governed in about the same degree by the August to October rainfall on summer cropped land as on stubble or fallow land. The major essential difference involved is that the summer rainfall operates to build up a soil moisture store in stubble land while it operates to maintain a soil moisture store in summer cropped land. Based on the simple averages, the effect of initial (stored soil moisture supplies was to increase the wheat yield .31 bushels per inch of moist soil, but when the effect of other related factors was eliminated by calculation, one inch of moistened soil was equal to .26 bushels of wheat per acre. July Rainfall Previous to Wheat Sowing The amount of July rainfall previous to sowing is highly significant to wheat yields harvested 11 months later. This relationship was first pointed out in_the territory represented by this study in a 10-year observa- tion made on 60 wheat crops at Goodwell, Oklahoma (1924-1933) (10). July rainfall exerted a strong effect on yield independent of its contribu- tion to the initial soil moisture stores. l When the 901 wheat yields in this study were classified according to the previous July rainfall, the extremes ranged from an average 4.57 bushels per acre, after a 1 inch July rainfall, to 17.42 bushels after a 4 inch July rainfall. (See Table 1 and Figure 2.) Under all the conditions studied, this factor was positively related to wheat yield in a highly significant degree. July rainfall operated practically without regard to the presence or absence of water conservation structures. However, there was a marked difference in the relative weight of its effect during different years in a crop rotation. On land where wheat followed sorghum, the July rainfall was of greater i weight than any other factor. It was slightly less important where wheat followed wheat, and decidedly less important where summer fallowing i was practiced in preparation for wheat. The most important effect of July rainfall upon the succeeding wheat crop seemed to be related to fertility conditions. l From the standpoint of preparation for fall sowing, ample July rainfall afforded an opportunity for early plowing or listing, the sprouting of volunteer wheat, killing of Weeds, and the partial incorporation of straw and stubble residues in the soil during the Warm part of the year. In the presence of ample moisture the rapid decay of incorporated organic matter was started. Although it is desirable to leave as much unrotted trash on the surface as possible, in order to prevent severe nitrate de- pressions in the top-soil and to provide a protective ground covqr against wind erosion, at the same time a certain amount of incorporation of trash is unavoidable. From a study of the progress of soil nitrate formation '2 after various crops and under various field conditions in the High Plains area (13), it appears that the recovery of a normal nitrate supply occurred WATER CONSERVATION _IN GREAT PLAINS WHEAT PRODUCTION 13 uch sooner during the following crop season on early plowed land and t this was a distinct advantage to the oncoming wheat crop. Although heat might even suffer from an excess of available nitrogen in the soil sowing time, it requires a progressive increase reaching a maximum v ' g the growing period the following spring. Ample July rainfall sets e stage to accomplish this. A p The advantages to soil preparation of a favorable July rainfall accounts A a large part, if not most, of the favorable relationship between the Figure 2. RELATION OF PREVIOUS JULY RAINFALL TO WINTER WHEAT YIELD IN THE SOUTHERN GREAT PLAINS. ' AVERAGE YIELD - BUSHELS PER _ ACRE ‘l5 F= 60.|5 2:45, " * .50-I.5O l.5I-2.5O 2.51-3.50 3.5l+ INCHES OF JULY RAINFALL PREVIOUS TO SOWING *lndicotes number of fields averaged in each group. F=Vorionce Ratio. 1 ‘hr ‘y rainfall and the succeeding wheat yield. The apparent reason why factor is of measurably less importance on summer fallowed ground f l at its most important functions have already been largely taken care ‘here fallowing operations are carried out previous to July. ' this connection, it will also be noted that the relation of July rainfall lie accumulation of soil moisture stores was not affected by difi’erent Opes of water conservation practice. It contributed to the fall soil ture store in cases where a crop did not occupy‘ the land during July, here wheat followed Wheat or summer fallow, but a heavy July rain- licontributed only to the current growth of sorghum when that crop present. From the simple averages, it would appear that each inch uly rainfall accounted for 4.28 bushels of grain per’ acre, but when calculated effect of other factors was eliminated it was 2.62 bushels o llnlCh. 14 BULLETIN N0. 655, TEXAS AGRICULTURAL EXPERIMENT STATION Spring Rainfall Third in importance among the factors affecting wheat yield was the spring rainfall. The idea that the rainfall during the month of May pro- vides a turning point between success and failure of the crop was tested and disproved. Although the May rainfall averaging 1.71 inches, in this group of 901 farms, fluctuated rather violently, the analysis showed that variation in May rainfall was not statistically significant in its effect on wheat yield independent of the January to May period of rainfall. After the effects of summer rainfall and soil moisture store had been accounted for, the spring period, January to May, inclusive, constituted the next most important moisture segment contributing to wheat yield. The effect of these three portions of contributing moisture supply, ex- pressed as per cent of the total influence determining yield was 15.2% for the fall soil moisture store, 10.6% for the July rainfall, and 8.1% for the January to May rainfall. When the wheat yields were classified according to spring rainfall (Janu- ary to May, inclusive), the average yields ranged from 1.62 bushels per Figure 3. RELATION OF JANUARY THROUGH MAY RAINFALL TO WINTER VI/HEAT YIELD IN THE SOUTHERN GREAT PLAINS. ' AVERAGE YIELD ' BUSHELS PER . ACRE 'I5 - F= 49.56 -IO -5 2-3 4-5 6-7 8-9 IO + INCHES OF JANUARY THROUGH MAY RAINFALL ON THE CROP flndicotes number of fields averaged in each group. F= Variance RaIio. acre under 2-3 inches of rainfall to 17.42 bushels when it exceeded 10 inches. (See Table 1 and Figure 3.) About 7 inches of spring rainfall were needed to make a profitable yield of wheat, initial supplies being average, but indications were that a spring deficiency could be partially WATER CONSERVATION IN GREAT PLAINS WHEAT PRODUCTION 15 l overcome by ample supplies of soil moisture carried over from the previous year. The relative importance of spring rainfall, as could be reasonably ex- pected, decreased with the intensity of water conservation practices. It was 13.4% without water holding structures, 10.3% with partial water conservation practice in effect, and 6.7% with complete water conserva- l tion consisting of terracing and contour farming. This relationship shows very clearly that the prevention of loss by runoff during the preparatory period, as Well as during the crop growing season, relieves the Wheat crop very substantially from the unfavorable effects of variation in the amount _ and distribution of the spring rainfall. There was little difference in the importance of spring rainfall where _wheat followed wheat or summer fallow, but it Was markedly less im- portant on the sandier soils of sorghum land. As calculated from the simple averages, 1 inch of spring rainfall accounted for 1.97 bushels of h wheat per acre, but when the effect of other factors was eliminated it was really about half this amount, or .94 bushels. Wind Erosion Damage Of the 118,413 acres covered by 901 wheat records, 10.1% was subject i to wind erosion during the wheat year. The subgroup most affected was a that in which summer fallowing was practiced with 13% of the area sub- ject to wind erosion, while the least affected area was that in which wheat . followed sorghum, with 7.6% of the area affected by wind erosion. Wind erosion was a significant factor in reducing wheat yield in all the subdivisions of study but one. In spite of the fact that erosion damage was less frequent on sorghum stubble, its relative effect was very high ~ when control was lost, representing 6.1% of the total determining in- .fluence. It was lowest where wheat followed Wheat, representing 4.8%. Involved as elements in this factor were the previous damages to the p‘ soil by erosion which made it more susceptible to the recurrence of blow- citing, and the loss of vegetative cover exposing portions of the current i i crop to direct wind damage. Although the frequency of high wind erosion damage was not great in - p this group, (see Table 1 and Figure 4) it is apparent that yields were very drastically diminished where a large proportion of the area of a ‘ T‘ field was subject to erosion. The reduction in yield indicated by simple averages was .83 bushels for each 10% of the field area affected by soil blowing. Calculated apart l-from inter-related factors it was .52 bushels per acre. r i? Worthy of note is the fact that fields which had suffered most from ljffwind erosion damages were selected first by farmers to be terraced and f5contour farmed. However, after 5 years of operations during which much 16 BULLETIN NO. 655, TEXAS AGRICULTURAL EXPERIMENT STATION undamaged land also was terraced and many of the appearances of former damages were obliterated by successful cropping, the indices of erosion were not far apart in the treated and untreated subdivisions. Date of Seeding The delay of wheat seeding after September resulted in a significant decrease in yield. However, the weight of this factor was not sufficiently great to be noticeable in all subdivisions. Apparently, the delay of sowing was more serious where wheat was placed 0n summer fallowed land than in any other place in the rotation. This would naturally be expected to have a relation to the clean condition of the soil. However, the effect of delayed sowing after summer fallowing is highly significant, independent of susceptibility to wind erosion. Delayed sowing was also a significant Figure 4. RELATION OF WIND EROSION CONDITIONS TO WINTER WHEAT YIELD IN THE SOUTHERN GREAT PLAINS. AVERAGE YIELD BUSHELS PER ACRE F = 9.05 _. M 0-40 50'8O 90-I0O PERCENT OF FIELD AREA AFFECTED BY WIND EROSION *lndicotes number of fields averaged in each group. F = Variance Ratio. factor on lands where water conservation practices were used, probably due to an apparent tendency to put ofl’ the sowing of terraced and con- tour farmed land until the latter part of the season. The losses resulting from delayed sowing, however, were great enough to warrant all possible care in carrying out timely operations. From simple averages, each 10 days’ delay after September 15 appeared to reduce the yield .32 bushels per acre, but the real eifect was a reduction of .44 bushels. Fall and Winter Grazing Winter wheat is almost universally grazed with cattle or sheep in the area represented, when summer and fall moisture conditions are favorable to early sowing‘ and rapid fall growth. Three hundred and thirteen fields which were grazed yielded an average of 8.17 bushels compared to 5.65 bushels harvested from those not grazed. These averages, as shown in Table 1, appear to associate fall and winter grazing with high grain yield. i 1 i I I I I WATER CONSERVATION IN GREAT PLAINS WHEAT PRODUCTION 17 gwever, when the real eflect of grazing utilizations was calculated, it A found that an average of .46 cow month per acre reduced the yield E lr acre 9%; bushels of grain. The contrary indications 0f the simple average 'ulted from the inclusion in the ungrazed group of a large number of which were a failure from the start having been sowed under such f3 avorable conditions that no grazing capacity was produced, although izing may have been desired. Water Conservation Practices . The intensity of water conservation methods practiced showed a highly Vificant favorable relation to wheat yield, particularly ‘where wheat llowed wheat or summer fallow. When wheat yields were classified ac- Erding to water conservation treatment, fields without structures averaged j‘ 1 bushels per acre, terraced alone or contour farmed alone, 6.31 bushels, y terraced and contour farmed together, 8.10 bushels. (See Table 1 Figure 5.) This is an average gain of 2.99 bushels of wheat per acre Fig.5. RELATION OF WATER CONSERVATION - PRACTICE TO WINTER WHEAT YIELD IN = THE SOUTHERN GREAT PLAINS. AVERAGE YIELD BUSHELS PER F=|z2| ACRE NONE TERRACED OP TERRAGED 8 OONTOURED CONTOURED INTENSITY OF WATER CONSERVATION PRACTICE *lndicates number of fields averaged in each group. F = Variance Ratio. to a complete water conservation program. The relative weight of ter conservation practice was greater on summer fallowed land than wheat followed wheat in the rotation, although yield increases made lsummer fallowing were no greater with water holding structures than >L out them. 5 e effect of water holding structures calculated separately from their tribution to the initial soil moisture supply was to- increase the yield bushels per acre. This represents the effect of water conservation p’ g parts of the year other than the summer and early fall preparatory 7' through October rainfall moistened the soil an average depth of inches. Under terraces and contour tillage, on 369 fields, the penetra- fod. On 386 fields without water holding structures, each inch of the A 1s BULLETIN NO. 655, TEXAS AGRICULTURAL EXPERIMENT STATION tion was 22.2% greater, reaching an average of 3.68 inches deep per inch of rainfall during the preparatory period. The increased initial moisture supply represented by 4.37 inches of addi- tional penetration due to structures caused a gain of 1.14 bushels of wheat per acre to be added to the 1.36 bushels per acre growing season results of Water conservation practices. This specifically identified yield increase totaling 2.50 bushels per acre accounted for nearly all of the 2.99 bushel "increase associated with water holding structures. An opportunity to investigate the efiect of the age of terraces, as an index to the effectiveness of maintenance being given them by the farmers, y occurred in the subgroup of 369 farms where terracing and contour farm- ing were practiced together. In this group the age of terraces did not ' significantly affect the yield of grain, indicating they were being main- tained in an effective condition. However, the maximum age of any ter- » races was 5 years, while the average age of all those studied was slightly under 2 years. The hazards of failure of terrace systems due to excessive rainfall is not as great in the Southern Great Plains wheat belt as in many a other areas, and the methods of upkeep are relatively simple. WHEAT PASTURAGE . Since occasionally a very profitable part of the wheat production is harvested in the form of fall and Winter pasturage, a study was made of the relations of soil, erosion, seasonal, and cultural practice conditions affecting wheat pasture production. The only measure of pasture production available was the actual amount of grazing utilized by the farmers. This may be accepted as a rough measure. Considering that it is the general practice to pasture wheat in this area when the wheat pasture is good, it may be reasonable assumed that the majority of fields affording a profitable opportunity for pasturing were used and it is certain that none was used upon which no forage was available. The statistics showed that pasturage depended mainly upon favorable summer and early fall rainfall and early seeding of the crop. The accumu- tion of a subsoil moisture supply was unimportant, which would indicate that the fall growth used for grazing draws mainly from the current rain- . "fall and top-soil moisture supply if given the opportunity by early seeding. Land slope, erosion damage, the rate of seeding, and summer fallowing » did not affect the amount of grazing afforded. FACTORS AFFECTING SOIL MOISTURE ACCUMULATION Since the accumulated supply of sub-soil moisture at sowing time has i proved to be the single dominant factor influencing, grain yields to a greater extent than any other one condition known to arise previous to _ or during the crop growing season, a further study was made to determine what conditions contribute to the building up of a soil moisture supply. »WATER CONSERVATION IN GREAT PLAINS WHEAT PRODUCTION 19" ed in the order of their relative importance, they are: the August l g ber rainfall, the July rainfall except after sorghum, the water con- gtion practice, the length of fallow preparatory period, and the coarse- igof soil texture. Factors which did not generally affect the accumula- jof a soil moisture store significantly were: the July rainfall, the soil ‘n damage, the land slope, and depth of fertile soil section. u 2. Fall Soil Moisture Accumulations According to Preparatory Season Rainfall and. ' Capacity of Water Holding Structures in the Southern Great Plains, 1938-1939 Mean Depth Number Inches Fall Significance of Method or Condition Fields Soil Moisture Differences Penetration Between Means. f to October Rainfall: 3 inches . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 14.85 ** 5 inches . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 25.62 7 inches . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354 27.55 - 9iinches . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 34.60 ‘1 » l0 plus inches . . . . . . . . . . . . . . . . . . . . . . . . 48 36.67 f t Water Holding Structures . . . . . . . . . . . . . 386 23.42 Terraced or Contour Farmed . . . . . . . . . . . . . 146 25.89 ** Terraced and Contour Farmed . . . . . . . . . . . 369 27.79 ‘lily significant differences between means. ‘e fact that the beneficial effects of summer fallowing and of the late 4| and early fall rainfall operated to benefit the wheat crop almost ‘ively through the mechanism of soil moisture storage was very Lly brought out. The effects of terracing and contour tillage were E- between increasing the advance store of soil moisture and in- f the efficiency of utilization of the current rainfall coming during prop gro-wing period. ' m Table 2, the 2 inch class under August to October rainfall showed depth of moisture penetration of 14.85 inches. Where the rainfall i» 10 inches, the penetration was 36.67 inches, a difference of 21.82: i‘ ~ penetration due to an 8 inch rainfall increase. This is equivalent :1 73 inches of moistened soil per inch of rainfall, or approximately of the precipitation becoming soil stored water available for plant- ‘ Table 3 are compiled the July to October rainfall and moisture pene- y means for fields in which wheat followed wheat subdivided accord- gto water conservation practices. this particular crop sequence subdivision, the soil reaches harvest exhausted of available moisture and must depend on the rainfall that ‘ws maturity of the crop to build up a new supply. This comes, rough- §~ ring the period July to October, inclusive. Hence, the moisture pene- on measured in the fall can practically all be credited to the rainfall i?‘ intervening period. p 20 BULLETIN NO. 655, TEXAS AGRICULTURAL EXPERIMENT STATION Table 3. Soil Storage of Rainfall Between Harvest and Seeding of Winter Wheat, Southern Great Plains, 1938-1939 Mean Depth Penetration Per Cent Number Mean July Soil Per Inch Rainfall Field Conditions Fields to October Moisture Rainfall, Becoming _ Rainfall Penetration Inches Soil Stored Water Without water holding structures . . . . . . . . . . 216 7.28 20.52 2.82 23.42 'With level terraces and contour farming. . . . 150 7.03 23.83 3.39 28.24 In all calculations, a rough factor of 1 inch of available soil stored "moisture per foot of soil was used to convert the penetration measure- ment to available water terms. Numerous determinations within the range of soil types that prevail in this study show that to be fractionally under the actual. Therefore, such estimates may be taken to be slightly con- servative. Determinations by soil "moisture sampling from heavy silt loam soil at the Panhandle Experiment Station at Goodwell, Oklahoma, 1926-1929, (7) showed that 20.7% of the entire yearly rainfall became soil stored water on unterraced land and that 25.2% was saved on terraced land. (See Figure 7.) An average of the terraced and unterraced land at Good- well, 22.95%, roughly agrees with the field observations in soil conserva- tion demonstrations of which 492 were unterraced and 409 were terraced, averaging 22.8092. ANALYSIS OF THE WHEAT YIELD INCREASE The data of 146 fields level terraced or contour farmed where 106 of these were contour farmed, while 40 were terraced but farmed without regard to slope, reveals an average yield increase of 1.20 bushels per acre. The combined use of terracing and contour farming yielded an increase of 2.99 bushels per acre. Of this 2.15 bushels of the yield increase were ‘due to the terracing and .84 bushels were due to the contour farming. -Contour farming ‘provides, during a large part of the preparatory period, as much Water holding capacity as terracing only when listing is em- ployed, but after drilling the seed only the drill marks are likely to remain for contour effect. Hence, under wheat production the effect of contour cultivation does not cover the same length of time during the crop year as the efiect of terraces and, in fact, is considerably less effective than the same method employed with row cultivated crops, where lister and row cultivation maintains a contour effect through both preparatory and growing periods. In calculating the grain yield increase from the simple averages, (Table 1 and Figure 6) terracing and contour farming practiced jointly increased the yield 2.99 bushels of which 1.35 bushels resulted from the increase of | l WATER CONSERVATION IN GREAT PLAINS WHEAT PRODUCTION 21 "Q moisture stored before the crop was seeded, leaving 1.64 bushels of I rease to be accounted for by moisture saving while the crop occupied land. Assuming that all of the contour farming effect took place -; the preparatory period, the difference between 1.35 bushels ac- Figure s. souRcEs OF WATER CONSERVATION YIELD INCREASE AND PERIOD OF EFFECTIVENESS ‘I 1‘ L64 BUSHELS Y|ELD |NCREA$E EFFECTED IN 32.! % 0F 2J5 BU$HEL$ GROWING SEASON Dug TQ -‘—-—4L—— I TERRACING L35 BUSHELS IN ""|0-0°/<> PREPARATORY ’ PERIOD .84 BUSHELS ous TO CONTOURING .4° ON LAND AVERAGE YIELD WITHOUT 5.|| BUSHELS WATER PER ACRE CONSERVATION STRUCTURES I I funted for through summer moisture accumulations in the soil and .84 shels due to contouring, leaves .51 bushels creditable to the service of aces during the summer, the balance of 1.64 bushels of yield increase due to the operation of terraces during the fall, Winter, and spring “VI growing seasons. is: OP MANAGEMENT‘ IN RELATION TO WATER CONSERVATION PRACTICES g - Divided into three groups according to the intensity of water conserva- practice used, there were 386 farms without water holding structures, with a partial program consisting of contour ifarming alone or level aces tilled without regard to slopes, and 369 with a complete program i‘ contour farmed level terraces. The crop succession and relative acreages of the main land uses for giese groups are indicated in Table 4. ‘The type of farming represented in this study is clearly defined as wheat I ' ing With from 66 to 70% of the cultivated acreage seeded to wheat. isThe amount of summer fallowing increased with the intensity of water nservation practices used. This might indicate that farmers most pro- essive in adopting terracing and contour farming were those also making most use of summer fallowing. 22 BULLETIN NO. 655, TEXAS AGRICULTURAL EXPERIMENT STATION Of particular interest is the middle group in which farmers seemed disposed t0 undertake surface water control and conservation tentatively by going part Way only. Compared to those who ignored conservation needs, they increased both the sorghum and summer fallow acreage while de- creasing wheat acreage accordingly. Those who adopted a complete water conservation program decreased their Wheat acreages even more, but kept sorghums about the same and devoted practically all of the acreage re- leased from Wheat to summer fallow. There appears to be a definite tendency for operators to couple careful crop management with conservative Water management. Since summer fallowing is a much older practice in the Southern Great Plains wheat area than terracing and contour farming, it might be assumed that those who have already progressed in developing the use of summer fallow more readily and more completely adopted the newer Water conservation prac- tices. Table 4. Crop Sequence and Acreage Distribution of Crops Associated With Different Intensities of Water Conservation Practice, Southern Great Plains, 1938-1939 % Wheat Distribution of Culti- Number Average Acreage vated Acreage Re- . Previous Fields Size of Following quired to Approx. Group of Farms Crop of Field, Designated Maintain Successions . Wheat Acres Crop iii- Crop % Acreages Without Water Wheat 216 125 58.79 Wheat . . . . . . . 70.59 Holding Structures Sorghum 84 93 17.10 Sorghum. . . . . 11 .76 Fallow 86 129 24.11 Fallow . . . . . . . 17.65 With Level Terraces or Wheat 74 '127 53.33 Wheat. . . . . . . 68.18 Contour Farming Sorghum 35 144 18.07 Sorghum. . . . . 13.64 Fallow 37 86 28.60 Fallow . . . . . .. 18.18 With Level Terraces Wheat 150 182 49.67 Wheat . . . . . .. 66.67 ‘ and Contour Farming Sorghum 147 132 15.23 Sorghum. . . . . 11.11 Fallow 72 116 35.09 Fallow . . . . . . . 22.22 In this connection, it is also interesting to note that according to the longest rainfall record in the Texas Panhandle, at Spearman, Where an unbroken series of observations extends over 64 years, only 26, or 40% of the years received 7 inches of rainfall or more during the January to May period. According to- this study, 7 inches of spring rainfall are needed to produce a profitable Wheat yield without regard to carried over moisture. This observation also checks with the short term records of actual wheat production on the Goodwell, Oklahoma station (14) where it was con- cluded that 4 better-than-average yields might be expected out of 10 years due to favorable seasons, but that 3 additional uncertain yields might be turned into profitable yields by the use of water conservation practices. _ With the average expectancy of effective periods of spring rainfall being 40%, the importance of water conservation practices and summer fallowing in good farm management becomes apparent. According to ex- WATER CONSERVATION IN GREAT PLAINS WHEAT PRODUCTION 23 » periment station records, there would be expected also about 3 years out of 10 when the opportunity to secure advance storage of soil water and the spring rainfall would fail simultaneously. In those bad years the most ‘profitable thing the farmer could do would be to avoid the waste of seed and labor in the fall and determine the next use of the land by the timing of the soil moisture accumulation. PRACTICAL PROBLEMS IN WHEAT GROWING A common sense appraisal of the weather records of the southern Great Plains confirms the prevalent supposition that rainfall is not dependable in this region. Other than the circumstances that winter follows summer with a reasonable degree of regularity, the principal condition that can be relied upon in the semi-arid High Plains is an unsystematic variation in the amount and distribution of the seasonal rainfall. However, the con- clusion that is frequently drawn from this fact, that farming is imprac- tical under such rainfall conditions, may be subject to considerable ques- tioning. There is no record of dependable rainfall periods upon which to base systematic crop planning. However, it has been proved by farmers’ ex- perience that worth-while productive potentialities exist in the soil and moisture resourcesof the area. The task of working out the most practical way of efliciently utilizing , these resources seems to require first of all a willingness to abandon some of the traditional ideas about crop rotation. The proposition is not that the needs of soil fertility can be ignored, but that both production and ‘f ifertility maintenance should be accomplished in a manner more con- f. sistently in harmony with natural conditions. i; Exploration to find a dependable basis for planning the crop manage- i. ment in the wheat land area of the southern High Plains has consisted first of identifying the factors that limit results and, second, measuring Q3, their relative importance and analyzing their behavior under various type \__ conditions. The object of such studies was to find what may be actually counted on in lieu of the uncertain seasonal expectations.‘ A few reliable, ', although not constant, conditions have been identified. ' Quantities of available moisture already stored in the soil root zone may ‘be counted on for future use. Surface crop residue already present in the . field may be counted on for futureuse. Well maintained level terraces may be counted on as ready to prevent undue waste from excessive rains fwhenever they may come. CHARACTER OF RAINFALL p, As an approach to the methods of using this information in crop man- Iagement, there should first be examined the nature of the water supply, spits normal disposition, and the capacity of the storage facilities. i Rainfall can be divided, roughly, into three classes. __ A representative rainfall record in the High Plains area (15), shows that light showers too small to penetrate the surface mulch were equally \ 24 BULLETIN ONO. 655, TEXAS AGRICULTURAL EXPERIMENT STATION distributed throughout the year and that this type of rainfall constituted 31.1% of the total annual rainfall. The main effect of light showers is a temporary one on atmospheric conditions. No additions were made to the available‘ subsoil moisture supply by light showers, and the surface mois- ture thus produced was soon evaporated. Moderate rains, one-half to one inch, may be classified as effective in . adding to the soil moisture store without runoff or undue loss by evapora- tion. This type of rainfall constituted 55.3% of the total annual rainfall and 87% of it came in the April to October period. Rains classified as effective supplied the surface and subsoil moisture upon which crops I largely subsisted. That portion of effective rains penetrating below the surface soil mulch, into which air freely circulates, may be used currently by present vegetation or held over for future use at the Will of the farmer. Heavy rains in which more than one inch fell in 24 hours usually sup- I plied more than could be absorbed by the soil or evaporated, thus causing surface runoff. All such rains are of maximum effectiveness up to the point at which runoff begins. Precipitation above this point was classified as excessive. It amounted to 13.5% of the total annual rainfall and 92% of it came during the 6 months of May to October. DISPOSITION OF RAINFALL If these characteristics of High Plains rainfall be kept in mind, the disposition of the moisture supply on wheat land can be much more readily understood and manipulated favorably. The disposition of a rainfall of the type just described was determined at Goodwell, Oklahoma (3) by periodic soil moisture determinations over a period of four years, supplemented and verified by artificial rain studies on typical wheat land. The normal disposition concluded from these studies was 65.8% loss by evaporation, 13.5% loss by runoff, and 20.7% storage in the subsoil. The total evaporation item was increased to 68.5% of the moisture supply by normal‘ tillage operations which temporarily, from time to time, deepened the zone of surface air circulation. As a result of necessary tillage to prepare the seedbed and control weed competition, the amount, 20.7%, of the rainfall available for plant growth was reduced to 18.0%. No loss of moisture was observed by percolation beyond the root zone depth of 6 feet. However, a risk of such loss might be incurred as a result of following a fixed summer fallow schedule into the second of two con- secutive wet years. The possibilities of increasing the moisture using efficiency by methods of runoff prevention evidently are not large as measured in inches of water, but are quite important as measured in percentage of the net. amounts of moisture normally available to crops. For example, under an 18 inch average rainfall, only about 3.58 inches became available to plant. use and the prevention of 2.33 inches of possible runoff waste by terracing allowed .80 inches of the impounded water to soak in, thereby raising the-_ available supply approximately 22%. Likewise, relatively small effects of physical factors influencing the rate l of infiltration and the rate of evaporation at the soil surface and acting f: to reduce even slightly a Waste totalling 68.5% of the potential supply f‘ would be capable of greatly increasing the efficiency of water utilization. Of interest in this connection are mulches and tillage practices (6). Although land improvements in the form of terrace or other permanent f, Figure 7. AVERAGE CHARACTER OF HIGH PLAINS RAINFALL AND THE EFFECT OF WATER CONSERVATION PRACTICE ON ITS DISPOSITION % 25.; 5/. I35 °/o &/ TYPE WITHOUT AND WITH RAINFALL WATER CONSERVATION PRACTICES 1.16m Run-on" men-terms ?i1§1i- _ curses sueson. EXCESSIVE G LOST BY EVAPORATION ‘s. It measures developed in practical application, there will undoubtedly be ctices of tillage and crop residue management Woven into productive lethods that are as potentially effective in increasing moisture supply by l bing evaporation waste as terracing and contour cultivation are in bing runoff Waste. Methods designed to accomplish these results are ‘ted and rapidly developed. 'WATER CONSERVATION IN GREAT PLAINS WHEAT PRODUCTION 2s" lrface water control structures are the easiest and most positive type. .; consistent with erosion control needs and are being Widely investif 26 BULLETIN NO. 655, TEXAS AGRICULTURAL EXPERIMENT STATION Fig. 8. Contour tillage supported by level terraces retaining surface water for increased crop production and the continuity of vegetative cover. One way to stay in business in the high plains. Fig. 9. A needless waste of much needed water from land with ample subsoil storage capacity. One way to go broke in the high plains. WATER CONSERVATION IN GREAT PLAINS WHEAT PRODUCTION 2': SOIL PREPARATION The conditions most vital to safe and efficient wheat production are: (1) the soil moisture accumulation to provide ample top-soil moisture for prompt germination of the seed which should exceed a penetration of 36 inches in order to carry the crop Well through the period of rainfall un- certainty. in the spring; (2) enough erosion resistant crop residue left on the surface of the field to prevent soil movement during the late Winter and early spring blow season, and (3) such remaining organic matter as may be incidentally worked into the top-soil during preparatory tillage l. 11. One method of stubble land plowing designed to leave the trash on the surface. 28 BULLETIN NO. 655, TEXAS AGRICULTURAL EXPERIMENT STATION incorporated not later than midsummer in the presence of moisture and high temperature, in order to insure prompt decomposition resulting in a favorable initial nitrate depression followed by a rapid increase of nitrate formation timed to reach a maximum during the spring growing period of the crop. Some facts that must be dealt with in an effort to prepare a favorable condition are: ( 1) a considerable quantity of effective rainfall is required to supply the initial moisture needed; (2) the time which must pass before the required amount of moisture is stored up may vary from 3 to 15 months; and (3) as time passes, the surface trash left over from the pre- vious crop begins to wear out. Perhaps the most clear cut starting point in preparation for wheat seed- ing would be at the harvest of the previous wheat crop. Starting the dis- cussion of soil preparation here need not commit one to continuous culture of wheat, though wheat may often follow wheat in a diversified rotation. Whether such a crop succession is practical or not depends on particular conditions. At harvest time, the soil is ordinarily completely exhausted of available moisture to a depth of 4 or 5 feet. The straw and stubble of the harvested crop occupy the land. If harvest time rains or a thin stand of wheat have permitted weeds to start in the stubble, immediate one-way disking would be justified. But if the harvest time has been dry, it is best to let the stubble stand re- gardless of the amount of crop residue present. Volunteer wheat will not sprout until it rains, neither will the weeds. If the weather then continues so dry that weeds do not start after harvest, it is best to let the stubble stand on through the fall and winter. There will not be a favorable prospect for fall seeding anyway, and all the ground cover possible will be needed to prevent wind erosion. If adequate rains come during the month of July, contour listing is the best preparation that can be given, working down the trashy ridges with disk cultivations as later rains bring on the weeds and volunteer wheat. If the July rains do not wet the soil deep enough for listing, yet the weeds start, the one-way disk or any one of a variety of subtillage machines best fit the field needs. If the stubble is light, the subtillage method would be best, leaving as much trash on the surface as possible. If no effective rains come in July but moisture is received in August, flat methods of tillage are preferable to listing. A portion of the residue re- maining at the surface will be ample for wind erosion prevention if the stubble is heavy. Hence, the partial incorporation of the straw and stubble is desirable. The general principle may be followed that the later in the summer the effective rains come, the flatter and shallower should be the tillage operations. Last minute preparation where the weeds are disked down immediately ahead of the drill produces the poorest results of any method of prepara- tion. WATER CONSERVATION IN GREAT PLAINS WHEAT PRODUCTION 29 Being guided by the July rainfall in the timing and kind of preparation, u one may accomplish simultaneously the best use of available moisture, of available crop residues, and of nitrate formation to supply the maximum needs of the oncoming crop. If early preparation cannot be done and a promising supply of soil moisture cannot be stored up, it is better to omit the seeding altogether or confine it to that part of the field where the better conditions exist. Emergency tillage operations or the planting of cover crops, if needed to prevent erosion, can be carried out more easily and with less waste of the scant available moisture if none is wasted on a wheat failure. Of course, if the trash from the last crop is plentiful, emergency tillage or a cover crop will not be needed. The trashy surface soil will take care of itself against erosion while awaiting rainfall, and will aid in more eflicient moisture utilization, but it must not be allowed to become weedy. If a stubble field comes through the winter dry and insufficient spring rainfall is received to stock the soil with moisture for oats or barley, the farmer has a legitimate choice between a sorghum crop and summer fal- low. The spring preparation would be the same for both. With plenty of crop residues to prevent blowing and no top-soil moisture to start weeds, cultivation may well wait until the rains and weeds start. Here, again, contour listing is a very desirable preparatory operation if done early because it provides for the best possible safeguarding and distribution of any excessive rainfall encountered. When June, the normal planting time for sorghum, comes, a decision can be made between sorghum and summer fallow based on the productive needs of the farm unit. If feed reserves are low, either forage or grain sorghum may be employed regardless of sub-soil moisture if top-soil moisture is adequate to germinate the seed. In case of scant sub-soil moisture, a thin stand should be planted to insure grain maturity. When sub-soil moisture is low in June, summer fallow may be safely and profita- . bly used if sorghum is not needed and crop residue in the top-soil remains l 5 adequate for wind erosion prevention. But, if considerable sub-soil moisture accumulation has occurred, fallow might be wasteful of both moisture and fertility reserves. In this circumstance, a summer feed crop becomes a cover crop in the traditional sense of the word. It may be needed to prevent A a productive accumulation of moisture and soluble plant food from partially going to waste. ' Whenlsummer fallow has been decided upon for want of soil moisture, 7 there will be no risk of plant food losses by leaching. The principal pre- caution indicated by field experience in case of summer fallowed land a is to avoid delayed seeding. September seeding or even slightly earlier is ~.f!.;'also essential if fall and winter pasturage is expected. According to established weather records, unsystematic variation in amount and distribution of rainfall is a normal condition in the Texas i§High Plains. The dependable part of the moisture supply is that which demonstration areas of the Southern Great Plains. Recommendations de- .30 BULLETIN NO. 655, TEXAS AGRICULTURAL EXPERIMENT STATION has already been stored in the sub-soil. Obviously, flexibility of crop rota- tions, of other enterprizes on the farm, of erosion control, and farm finance is essential to the maximum safe use of soil and water resources under these conditions. Additional equipment needed by many wheat farms, to enable safe and efiicient use of soil and water resources, may be listed as follows: row crop machinery, feed storage facilities, livestock, and a soil auger. SUMMARY A study was made of the results of terracing, contour fanning, summer fallowing, and winter grazing under varying soil and seasonal conditions as represented by 901 records of wheat production in 11 soil conservation rived from it apply specifically to the wheat soils of the Panhandle of Texas and immediately adjoining areas. Significant increases of wheat yield resulted from (1) initial soil moisture stores, (2) July rainfall previous to sowing, (3) level terracing and con- tour farming, and (4) favorable spring rainfall, while significant decreases resulted from (5) soil erosion damage, (6) delayed seeding, and (7) fall and winter grazing. Of greatest weight were the factors of (A) initial soil moisture, and (B) previous July rainfall, both of which are measurable in advance of seeding time. Forty-one per cent of the total influence affecting wheat yield is combined in the simple formula for estimating expected yield: .33 (A) + 2.32 (B) — 6.24 I expected bushels wheat yield per acre, where (A) is expressed as depth of penetration in inches and (B) is the July rainfall in inches. The fall soil moisture store was the predominating factor aflecting wheat yield. The fall soil moisture accumulation was derived from the rainfall of the July to October period, excepting where sorghum preceded Wheat. In that case, the fall store was governed by the August to October rainfall. The July rainfall had a highly significant positive relation to Wheat yield under all conditions studied. Besides contributing measurably to the fall store of moisture, the July rainfall greatly affected the fertility con- dition resulting from summer tillage operations. Ample July rainfall was more important on stubble land than on summer fallowed land, although still a highly significant factor on the latter. The spring rainfall, January to May, inclusive, was the third most important division of moisture supply although the relative weight of its influence was but one-third of that exerted by the seasonal and soil mois- ture conditions prevailing during the summer and early fall before seeding time. Minor factors in net effect, but so consistently related as to be highly significant statistically, were the yield depressing efiects of delay of seed- WATER CONSERVATION IN GREAT PLAINS WHEAT PRODUCTION 31'. . H. beyond September, the failure of wind erosion control, and the grazing; f wheat fields during the fall and winter. p The practices of terracing and contour farming gave consistent yieldi ‘creases averaging 2.99 bushels per acre partly due to increasing the soil oisture accumulation during the preparatory period from 3.01 inches in, depth of penetration per inch of rainfall to 3.68 inches, and partly due to» Zthe more efficient utilization of rainfall during the crop growing season. Soil moisture accumulation during the preparatory period accounted for ithe entire favorable effects of summer fallowing and contour farming on wheat yield, but terraces continued to operate favorably accounting for" .64 bushels of the 2.99 bushel yield increase by more efficient use of‘ rainfall during the crop growing season. The 1.35 bushels of yield increase {effected previous to seeding may be broken down with .84 bushel creditable contour farming, and .51 bushel creditable to terraces. The total effect fof terraces, therefore, was to increase the yield 2.15 bushels of wheat per acre with .84 bushel added by contour farming. The total effect of contour rming on wheat yield was less than that expected from the use of this ethod in row crop production, apparently because of the more general e of fiat methods of tillage in wheat growing than in row crop cultiva- The availability of pasturage from fall sown wheat depended mainly m plentiful top-soil moisture supply before and during the grazing season d on early seeding. - LITERATURE CITED . Call, L. E. and Halstead, A. L. 1915. The Relation of Moisture to Yield of Winter Wheat in Western Kansas. Kans. Agr. Exp. Sta. Bul. 206, p. 34. < Conner, A. B., Dickson, R. E., and Scoates, D. 1930. Factors Influencing Runoff and ' Soil Erosion. Tex. Agr. Exp. Sta. Bul. 411, DD. 41-47. Daniel, Harley A. 1935. Calculated Net Income Resulting From Level Terraces on Rich- field Silt Loam Soil and Suggested Lines of Defense Against Wind Erosion. (Okla.) Panhandle Bul. 58, pp. 3-13. —-€——, and Finnell, H. H. 1939. Climatic Conditions and Suggested Cropping‘ Systems for Northwestern Oklahoma. Okla. Agr. Exp. Sta. Circ. 83, pp. 26. _ Dickson, R. E. Langley, B. C., and Fisher, C. E. 1940. Water and Soil Conservation w Experiments at Spur, Texas. Tex. Agr. Exp. Sta. Bul. 587, pp. 67. ‘ Duley, F. L., and Russell, J. C. 1939. The Use of Crop Residues for Soil and Moisture Conservation. Jour. Amer. Soc. Agron. Vol. 31, No. 8, pp. 703-9. - Finnell, H. H. 1929. Utilization of Moisture on Heavy Soils of the Southern Great Plains. Okla. Agr. Exp. Sta. Bul. 190, pp. 24. ———7 . 1929. Initial Soil Moisture and Crop Yield. Okla. Agr. Exp. Sta. Bul. 19 , pp. 7. . 1929. Heavy Plains Soil Moisture Problems. Okla. Agr. Exp. Sta. Bul. 193, pp. 7. i. 1933. Estimation of Wheat Production Possibilities in the Panhandle of Oklahoma. (OklaJ Panhandle Bul. 52, pp. 22-36. j . 1930. Moisture-Saving Efficiency of Level Terraces Under Semi-Arid Con- , ’ ditions. Jour. Amer. Soc. Agron. Vol. 22, No. 6, pp. 522-529. i ~ii< 1931. Terracing Experiments, 1930-31. (Okla) Panhandle Bul. 31, pp. 2-9. ~. 1932. Factors Affecting the Accumulation of Nitrate Nitrogen in High Plains Soils. Okla. Agr. Exp. Sta. Bul. 203, pp. 47. Ti); 11534. Adjustment Problems in Wheat Production. (Okla) Panhandle Bul. y DD- ' - _ -—i———. 1932. Agricultural Significance of Climatic Features at Goodwell, Okla- . homa. (Okla.) Panhandle Bul. 40, pp. 45. ——————. 1934. Results of Level Terracing on Heavy Silt Loam Soil. (Okla.) Pan- handle Bul. 53, pp. 2-12. I ; Halstead, A. L., and Coles, E. H. 1930. A Preliminary Report on the Relation Between F; Yield of Winter Wheat and Moisture in the Soil at Seeding Time. Jour. Agr. Res.,. f Vol. 41, N0. 6, DD. 467-477. Henny, H. J. 1932. Forecasting the Yield of Winter Wheat Seven Months Prior to» ,__'- Harvest. Jour. Farm Econ., Vol. 14, No. 2, pp. 319-330. x