8-1513 March 13 jhermjolls Distribution Importance ariability & Management The Texas Agricultural Experiment Station, Neville P. Clarke, Director, College Station, Texas in cooperation with United States Department oi Agriculture, Agricultural Research Service and Soil Conservation Service Contents Page Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Area occupied by Sherm soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..l Objectives of the study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..2 History of the Sherm series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Physiography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 Uses and importance of Sherm soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Typical site for Sherm soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..7 Present water management systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..8 Experimental Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..9 Site selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 Sampling sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 Sampling techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 ' Sample preparation and analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..10 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 Profile descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 Particle size distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..16 Bulk density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..19 Organic matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20 pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Calcium carbonate (CaCOs) equivalent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..20 Water retention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..21 Water infiltration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21 Implications for management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..24 Plant-available water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..24 Water application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..25 Water infiltration variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..27 Crop sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27 Tillage and cropping practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28 Ranching and livestock production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 AUTHORS Paul W. Unger, soil scientist, USDA, ARS, Conservation and Production Research Laboratory, Bushland, Texas 79012. Fred B. Pringle, soil scientist, USDA, Soil Conservation Service, Amarillo, Texas 79101. Cover photos-Some of the uses of Sherm soils are irrigated and dryland grain crops and cattle finishing. (USDA- Soil Conservation Service photo). SHERM SOILS-DISTRIBUTION, IMPORTANCE, VARIABILITY, AND MANAGEMENT‘ Paul W. Unger and Fred B. Pringle INTRODUCTION Area Occupied by Sherm Soils Sherm soilsz occupy parts of eight counties in the northern High Plains of Texas and parts of two counties in the Oklahoma Panhandle (Figures 1, 2). The portions of different counties occupied by Sherm soil range from about 0.4 to 51 percent (Table 2). The area of Sherm soils ranges from about 101° 30' to 103° 30' west longitude and from about 35° 40' to 36° 40' north latitude. This area is bounded by the breaks above the North Canadian River on the north, the caprock escarpment at the Cana- dian River on the south, the caprock escarpment at the High Plains- Rolling Plains boundary on the east, and a catena of loamy soils extending from Kerrick to Channing on the west. Within the area of occurrence, Sherm soils occupy about 75 percent of the land surface. Elevation ranges from about 2,800 to 4,200 ft above mean sea level. The area is in a subhumid to semiarid climatic zone where average annual precipitation ranges from about 16 inches at the western edge to about 22 inches at the eastern edge (Table 3). Also listed in Table 3 are the average length and dates of the frost-free period, average daily maximum and minimum temperatures, and average annual precipitation in counties where “Sherm soils occur. ‘Contribution from USDA, Agricultural Research Service, P.O. Drawer 10, Bushland, Texas 79012, and USDA, Soil Conservation . ‘Service, Amarillo, Texas 79101. ZSee Table 1 for classification of soils men- tioned in this report. Sherm soils occupy about 1.3 million acres in Texas (Table 2) and are among the most extensive arable soils in the state. Sherm soils also oc- cupy a small area of Oklahoma. Other major arable soils in Texas are Pullman with 3.8 million acres and Amarillo with 2.5 million acres in the southern High Plains, and Houston Black with 1.5 million acres in the Blacklands area. Soil taxonomy was implemented for use in the National Cooperative Soil Survey in -the mid-1960’s. A few of the published soil surveys on the Texas High Plains were completed before the advent of this system. But most were conducted while the soil classification system was in its in- fancy. Since then, soil taxonomy has undergone many refinements. Because of this and the accumulation 5""! "F"! l"- Ifinln 541cm“? Figure 1. Counties of Oklahoma and Texas in which Sherm soils have been mapped are Within the heavy-lined area. TABLE 1. CLASSIFICATION OF SOILS MENTIONED IN THE TEXT AND FIGURES fine, mixed, mesic family of Torrer- Series Classification Amarillo Fine-loamy, mixed, thermic Aridic Paleustalfs Berthoud Fine-loamy, mixed, mesic Aridic Ustochrepts Conlen Fine-loamy,icarbonatic, mesic Calciorthidic Paleustolls Dumas Fine-loamy, mixed, mesic Aridic Paleustolls Gruver Fine, mixed, mesic Aridic Paleustolls Houston Black Fine, montmorillonitic, thermic Udic Pellustersts Humbarger Fine-loamy, mixed, mesic Cumulic Haplustolls Likes Mixed, thermic Typic Ustipsamments Ness Fine, montmorillonitic, mesic Udic Pellusterts Plack Loamy, mixed, mesic, shallow Petroclacic Calciustolls Pullman Fine, mixed, thermic Torrertic Paleustolls Richfield Fine, montmorillonitic, mesic Aridic Argiustolls Sherm Fine, mixed, mesic Torrertic Paleustolls Sunray Fine-loamy, mixed, mesic Calciorthidic Paleustolls Ulysses Fine-silty, mixed, mesic Aridic Haplustolls tic Paleustolls. The soil was formed from fine-textured sediments of the High Plains eolian (wind-deposited) mantle under a dense cover of short grasses (Figure 3). The Sherm series was established in 1970 during the soil survey of Sherman County, Texas (SCS, 1975b). It was named after Sherman County in the northern Texas Panhandle. Before 1970, Sherm soils were included in other series, main- ly the Pullman and Richfield series.“ The process of inventorying and classifying soils on the High Plains of additional laboratory and field data, the central concept of some soil series has changed. Accordingly, all soils included in the Sherm series do not conform to the current classifica- was also determined. tion criteria. However, each sample site in this report is representative of the Sherm soil in its geographic locale. These soils met the criteria in force at the time individual county soil surveys were in progress. Objectives of the Study Most research information regard- ing Sherm soils was obtained at the North Plains Research Field at Etter. Information obtained on Pullman soils at the Conservation and Pro- duction Research Laboratory at Bushland is also considered general- ly applicable to Sherm soils because the two soils are similar in many respects. The information is general- ly considered reliable and has been widely used as the basis for manag- ing Sherm soils. These soils cover ex- tensive areas of the High Plains of Texas and Oklahoma and vary con- siderably in profile properties across the region. One propertythat varies i widely is depth to buried soil horizons and to the calcic horizon. Because profile depth strongly in- fluences plant rooting depth and thus the effective depth for storing water, a knowledge of profile depth along with a characterization of other profile properties is important for improved water and crop management on Sherm soil. The ob- jective of this study was to determine the variation in depth, bulk density, texture, organic matter content, pH, calcium carbonate equivalent, and 2 .' u x ‘ - h ‘ r ‘ ' "a. 4» .....» Figu dots. water retention of the different horizons of Sherm soil as affected by location in the region. Water in- filtration at the different locations History of the Sherm Series The Sherm series is classified by soil taxonomists as a member of th v ' f. y“. .'--/,,,; r"; ; - .. gwm._ area She The approximate Ioca tions of the sa began with the publication of the Reconnaissance Soil Survey of the Panhandle Region of Texas in 1910. In this survey, Sherm soils were called Amarillo silty clay loam. The Amarillo series was established in this survey and included soils rang- ing from sands to clays. As soil surveys and investigations continued, differences in the physical and chemical properties of . "xii .5 ' ,,_ . I’ . '~ ,2,» - , ’ I ' 1 II,‘ ' ' 9. -.,‘;.¢ ' "~ 1f. 5 ’ " w m soi s is delineated by the solid line. m plin g sites are indicated by the numbered M \-z TABLE 2. AREAS OCCUPIED BY SHEFIM SOILS Mapping Portion Total County, unit of series Total Irrigated , state Slope area county area‘ cropland cropland Rangeland Other land2 % acres % acres Beaver, Oklahoma 0-1 6,913 0.6 6,910 6,365 2,169 200 345 Dallam, Texas 0-1 32,800 3.5 32,800 23,944 13,887 7,216 1,640 Hansford, Texas 0-1 277,118 47.7 293,900 274,427 210,436 15,582 3,981 0-1 16,553 2.8 0-1, erod. 322 <0.1 Hartley, Texas 0-1 71,100 7.5 71,100 58,620 50,609 9,028 3,452 Hutchinson, Texas 0-1 101,690 17.4 106,010 96,777 76,071 7,185 2,048 1-3 4,320 0.7 Lipscomb, Texas 0-1 7,850 1.3 9,320 8,620 3,730 325 375 1-3 1,470 0.3 Moore, Texas 0-1 266,578 45.6 276,540 223,208 189,828 42,527 10,805 1-3 9,960 1.7 Ochiltree, Texas 0-1 283,431 48.8 291,790 275,501 109,110 12,892 3,397 1-3 8,357 1.4 Sherman, Texas 0-1 182,565 31.0 182,570 161,428 135,104 16,531 4,611 Texas, Oklahoma 0-1 4,166 0.4 4,170 4,145 1,488 — 25 Total 1,275,200 1 ,133,035 792,432 1 11,486 30,679 ‘Includes total area for all slopes and conditions. Totals for the different slopes and conditions may not equal the total for series because of rounding values to the nearest 10 acres. 2|ncludes land in roads, towns, and other non-agricultural uses. TABLE 3. ELEVATION AND CLIMATIC FACTORS IN COUNTIES HAVING SHERM SOILS Avg daily temp Avg Avg annual lake Avg growing annual County, state, station Elev evaporation season Max Min precip‘ i l g period °F in Beaver, Oklahoma, Beaver 2,5602 62 198 Apr 5-Oct 20 72.4 39.6 17.00 Dallam, Texas, Dalhart 3,989 60 178 Apr 23-Oct 18 70.7 40.5 16.25 Hansford, Texas, Spearman 3,250 63 184 Apr 20-Oct 22 71.3 40.8 21.26 Hartley, Texas, Dalhart 3,989 60 178 Apr 23-Oct 18 70.7 40.5 16.25 Hutchinson, Texas, Borger 3,1402 65 187 Apr 20-Oct 24 73.4 45.5 20.70 Lipscomb, Texas, Follett 2,7802 66 202 Apr 10-Oct 29 70.4 43.3 21.57 Moore, Texas, Dumas 3,500 64 185 Apr 20-Oct 22 71.0 41.8 18.95 Ochiltree, Texas, Perryton 2,930 64 191 Apr 18-Oct 26 72.0 42.0 21.13 Sherman, Texas, Stratford 3,699 62 182 Apr 23-Oct 22 70.9 39.9 16.55 Texas, Oklahoma, Goodwell 3,300 64 191 Apr 17-Oct 25 70.5 39.8 17.00 ‘Avera e values for monthl maximum and minimum tem eratures and reci itation are available in most ublished soil surve s. P Y 2Recording station not located in Sherm series area of occurrence. soils were noted. This led to the recognition of other soil series. Further investigations led to the establishment of the Pullman series, which was first recognized in the Soil Survey of Potter County published in 1929. Sherm soils were included in the Pullman series at that time. In 1970, the Sherm series was established for those soils north of the Canadian River that had previously been classified as Pullman. The Sherm series has a mean annual soil temperature of less than 59°F at a 20-inch depth. For Pullman soils, the mean temperature is greater than 59°F. Physiography The topography consists of near- ly level to gently sloping, smooth, treeless plains (Figure 4). Surfaces are plane to convex and slopes range from O to 3 percent, but are mainly O to 2 percent. These broad plains are interrupted by a few creeks and by the numerous playas, or shallow lakes, containing other soils. Except where pitted by playas or disected by creeks, the surface is remarkably smooth. The playas range from a few square yards to several square miles in surface area, and from a few inches to more than 5O ft deep. The average grade of the High Plains is about 1O ft/mi to the southwest. Runoff follows a poorly defined pat- tern. Water flows mainly into the playas, from which there is no definite outlet. The water collected in playas is lost mainly by evapora- tion, but some of it is used for irrigation. Other soils associated with the Sherm series in its area of occurrence include Conlen, Dumas, Gruver, Ness, Richfield, Sunray, and Ulysses (Figures 5, 6, 7, 8, and 9). Conlen and Sunray are calcareous, loamy soils on low convex ridges, on sideslopes around playas, and along 3 X‘. ‘p .1‘ .. " * ,~ y, ~f x o~ a‘ g, Figure 3. Dense c0 draws. Dumas and Cruver soils are on smooth plains and are similar in appearance to Sherm. But the Bt horizons of these soils are somewhat redder, have loamy textures, and are more permeable. Ness soils are dark gray and have clay textures throughout. They are on playa bot- toms. Richfield soils are on nearly level to gently sloping smooth plains along the margins of the area. They are similar in appearance to the Sherm series, but the Bt horizon has a loamy texture and is more permeable. Ulysses soils are calcareous, have silty clay loam tex- tures, and are more permeable than Sherm soils. They are on convex knolls or oval-shaped hills that rise above the broad smooth plains. There are differences in the mor- phological properties of the Sherm series that are related to geographic location. There differences affect soil water storage capacity, which in turn affects water management on these soils. The varying mor- phological features are depth to a strong calcic horizon (> 3O percent calcium carbonate—CaCOs), depth to a layer of strongly contrasting material, soil texture, and permeability . An analysis of soil survey field notes for seven counties and addi- tional profile observations revealed that depth to a strong calcic horizon ranges from 4O inches to more than 93 inches. Observations by soil and plant scientists indicate that calcic horizons containing more than 3O percent lime inhibit root develop- ment in most crops. Based on 4 vr of grses Sherm soil. igure 4. Sr1rr1g d 1' f f) hwing the typical topography of the Sherm soil region (USDA-Soil Conservation Service photo). laboratory determinations using a simple volume calcimeter, the average CaCOs content in the Btk horizon of Sherm soils is about 5O percent. To present a clearer understand- ing of these soils as they relate to geographic location, it is convenient to divide the large area into three soil provinces (Figure 2). The western province includes the eastern por- tions of Dallam and Hartley Coun- ties and the northwestern corner of Moore County. Also included is that portion of Sherman County north- west of Coldwater Creek and the area occupied by Sherm soils in Texas County, Oklahoma. Slopes are nearly level to gently undulating (Figure 6). Surfaces are smooth and slightly convex. In the western pro- vince, Sherm soils are intermingled with areas of Conlen, Dumas, Cruver, Ness, and Sunray soils. Sherm soils make up about 4O per- cent of the total area, Cruver soils make up 26 percent, and Dumas soils 14 percent. Conlen, Ness, and Sunray soils make up the remaining 2O percent. Conlen and Sunray soils are on low convex ridges and sideslopes around playas. Ness soils are on playa bottoms. Dumas and Cruver soils occupy the same general landscape as Sherm, although their surfaces are more convex. Buried profiles with contrasting textures are common below depths of 24 to 4O inches. Because of these discon- tinuities, the depth to a strong calcic horizon is quite variable. It ranges from less than 4O inches to more than 72 inches deep. In addition, the CaCOs content is erratic, ranging from about 2O to 5O percent. The central province extends from near the Texas-Oklahoma state line southwest to the caprock escarpment at the Canadian River, and is bounded on the east roughly by Palo Duro Creek and South Palo Duro Creek. It includes parts of Hansford, Hutchinson, Moore, and Sherman Counties. Slopes are nearly level to gently sloping, and surfaces are plane to slightly convex (Figure 7). Sherm soils comprise about 85 per- cent of the total area. The remainder is mainly Dumas, Gruver, Ness, and Sunray soils. Dumas and Cruver soils are on smooth plains with slightly convex surfaces. Ness soils are on playa bottoms, and Sunray soils are on sideslopes around playas and along draws. Readily discern- able buried soil profiles are noticeably absent in this province, and consequently, the soil above a strong calcic horizon is more uniform in depth. The depth to a strong calcic horizon ranges from 48 to 6O inches, but is commonly about 55 inches. Calcium carbonate content ranges from about 4O percent to more than 6O percent and averages about 53 percent. The eastern province covers an area east of Palo Duro Creek and north of the caprock escarpment at the Canadian River. It is bounded on the north by the breaks into the North Canadian River and on the east by the caprock escarpment that separates the High Plains from the Rolling Plains. Included are parts of Hansford, Hutchinson, Lipscomb, Berthoud {Richfieldk | h '“' ' , z u . ‘ n55 on Mantle iq in H!‘ ¢ \. ‘avg s l ‘I __ L. ‘l. . 'H_ ' | ‘ t~ , 0 u ._ ---., ‘D 0h . -»--=-=-.--~ -- =. .__~ o0 - ~ "I 0 ,- a - ._';_-_~-'_,, . ._-;.- ' ‘s_'.';--‘--:.‘_.' _',' .-_ .'_- _ / _ _. _ "__.- -"P,_.‘~ " ' _'..:;-';._~-;T.-_-._-,‘,'_..\. ._ ._'- °. j. ._-l_'_ I ___> ;--\ ___ i \\- _‘ __ _'.~_-,§.*_-p', ;_ ' _'.'._ _. ' .. . . ' .' ' 0_¢.o,:¢ "u: ‘I " .' f: ' a - ' o ¢.I:~::-" "3': . .' ‘n :'.a."- _,.-'_'..-- .._~-. :-..'.‘._.':¢.,Q,:': ‘I / . , ‘I 3- qx-j-x...‘ ":1- '..-' . o- --' . J r- \ ' '5'" '. ' -'--. - a - 0 0.. .,__ - u...‘ ..'I' ..', .._. ‘ .._:____ . I 0 g oil’! .I.‘°n'o ._. I 1:‘. _ _ ‘I.', u ':'.¢ ‘y. ~.' ‘Iz’. 0°. '0 "_,'..'. g 0-. . :\'\ _ . ‘?_Z \ ‘ . -.»__ C _.'\°. °‘I‘.: \ 0' ".' ~0-__..-~ .' ,-.*,_:~¢._.\_'7¢ _.._,_,~..,._-§.¢'_,..\_.__ . -_._ 4f‘: ‘, _ r ...._,.---'_': _:.-_ _ _ a . | ' " '- '-.' .. ".-_ ‘ ' .'_.-.."'."_'-" . \Triossic ,- \ \ \ i"? -- 1"":;' "" ' ~_ _ _ _ \ \\ \ \ \ \ \ \ g\ ‘I\ \\\\\ \ - . _ ‘ . . . . ’ . . - . ~ ' _ \\ \\.\\\.\\‘Q.\\\\\ \_\\\ ~\\‘ \\.\_ \ ‘ '" \ _ \ . a I ‘I ' v 3-’, '- . | ... \ \ 1 - Q a . - - ¢ - . - ¢ Q ¢ - - - Q -_-__._._._.____...>, \ __.___._n, *...-..-.-.:-.?:-.-_:'.-.r.:'.::".:r.:".tttr.t1T:'t.1't:'.-:T'9E’['r.'.* "-17.7327. :7. Permian .-.-'.t‘.".'.".."t-~. .—.-.:-J - 1 _ I Alluvnuml/ Figure 5. Major soils and underlying formations in the area occupied by Sherm soils. Reddi sh Brown Si I ty Dark Brown Clay LQam Silty Clay \_\ \\\\\\‘ 4 ‘I s \\\,““ '0 ‘b ’ “wkhil - ‘ 0 \\\\ '32’ I \\\\\ ‘I’ “i. Soft Cal iche . s .-. {I i. ' ~=-.-_.,:_; -. ‘$.11; w} n“. " n_ U} ‘ "'2'?!" ' ' ¢ n , ' o u , \ Figure 6. Soil pattern in the Western province. Dark Brown Si lty Clay Soft Caliche Ogallala Outwash Figure 7. Soil pattern in the central province. Reddish Brown Silty Dark Brown Silty Clay C'ay Loam Soft Cal iche Figure 8. Soil pattern in the southern part of the eastern province. 6 K V-H-lfl/ g?’ /f// {Q41 ~"/' u: ‘ u / >>> \\\“\\\";o" ' f‘: . 0°!‘ ’ .' ‘i <11» '4'» o . ' ,_ .- _-_. ; v__ c"r'l; ‘ . f 1 ‘_ ° ':I_\'.-.'*,'.-..;.- ‘ ~. - . .._-°, w’ 99371616 Outwash . ..°.‘ .'.I’\I t! \ '.. Qt “.0, ’ I .° ".-'."'.°.-~.~.-‘. ". b.>5'°." "u_._ yo": a ‘Q. :,'-.°. ‘a’ ' l- I", . "o.‘ a . .8‘ o: G u: I‘ . - I ° s‘ Figure 9. Soil pattern in the northern part of the eastern province. and Ochiltree Counties in Texas and Beaver County in Oklahoma. Slopes are nearly level to gently sloping and surfaces are plane to slightly convex (Figures 8 and 9). Sherm soils cover about 9O percent of the total area and Ness soils about 5 percent. Bichfield soils are on nearly level to gently sloping margins of the plains. Ulysses soils are on gently sloping knolls that rise above the broad, smooth plains. Readily observable buried profiles are common below a depth of 3O to 4O inches. Because of this lithologic discontinuity, the depth to a strong calcic horizon ranges from 65 inches to more than 93 inches. Uses and Importance of Sherm Soils Sherm soils are used primarily for agriculture, with about 89 percent of their area being used for crop pro- duction and about 9 percent for rangeland. The remaining area is in roads, towns, and other non- agricultural uses. Of the cropland area of Sherm soil, about 7O percent is irrigated and 3O percent is dryland The area of irrigated Sherm soil represents about 1O per- cent of all irrigated land in Texas. Wheat (Triticum aestioum L.), grain sorghum [Sorghum bicolor L. (Moench)], and corn (Zea mays L.) were the major field crops produced on Sherm soils in 1982 (Texas Dept. Agric. , 1982). Other crops grown on smaller areas of Sherm soils were oats (Avena satioa L.), barley (Hordeum oulgare L.), sugar beet (Beta oulgaris L.), soybean (Glycine max L.), forage sorghum (Sorghum sp.), alfalfa (Medicago satioa L.), sunflower (Helianthus annuus L.), and vegetables. Because Sherm soils are in a subhumid to semiarid region, yields of dryland crops are relatively low. Irrigation from the O gallala Aquifer greatly increases yields, but the water supply is limited and being depleted. Also, the cost of energy for pumping water has greatly increased in recent years. Surface water for ir- rigation is negligible. Therefore, it is essential that the water be used as ef- ficiently as possible to enhance economic returns from crop produc- tion and to delay the inevitable return to dryland crop production as long as possible. When dryland farming replaces irrigated farming, even if only on the Sherm soils, a significant amount of the total pro- duction of some crops in Texas will be lost. Typical Site for Sherm Soils Sherm soils developed in a relatively cool, subhumid to semiarid climate from medium- to fine- textured sediments largely or entirely of eolian origin. They occupy exten- sive smooth areas that are nearly level to gently sloping. Surface slopes range from O to 3 percent, with most of the 1 to 3 percent slopes being toward the playas or shallow basins. The typical native vegetation on Sherm soils was shortgrasses, prin- cipally blue grama (Bouteloua gracilis) and buffalograss (BuchIoe dactyloides). Profiles of Sherm soil, shown in Figures 10, 11, and 12, are from Dallam, Moore, and Ochiltree Counties, respectively. The surface layer of a typical Sherm soil is a brown to dark brown silty clay loam, but the texture may range from clay loam to silty clay loam. The thickness of the surface layer usually ranges from 6 to 8 in- ches, where there is a clear boundary to a dark brown to dark grayish- brown clay or silty clay with blocky structure (Figures 10, 11, and 12). The soil may contain buried horizons of older soils at 3 to 5 ft below the surface. Theu buried horizons usually have a clay loam texture. 7 1Tb‘? uPPer boundary of the calcic orizon, where present, is clear and WaYY- AlthOlIgh depth to the calcic horizon is often considered to be the effective depth of the Sherm soil for Crop production, winter wheat and especially sunflower apparently use kvlvater from deep in the calcic orizon, based on observations and measurements on a similar S01] (Pullman Clay loam) at Bushland, Texas Jones, Bushland, Texas, unpublished data; Unger, 1978a). Present Water Management Systems Based on data from the North pPlains Research Field at Etter (per- Eonal communication, Cecil Regier, httef, TeXas) and values published in tr e Soil Survey of Moore County, 6X35 (SCS, 197521), the Sherm soil at Etter has a total water storage capacity of about 17.1 and 24,7 inches to 4- and 6-foot profile depths, respectively. Of the total Water stQrage Capacity, about 8.7 and 12.3 lIlCl1€S are available for use by plants. The remainder (8.4 and 12.4 inches to 4- and 6-foot depths JQJDQLJJJgQ p) 1;, ,1. ,1 g ,, Qé ,, g [Z4 fffékfiéSd f5 47 5173541551? (Tépfffi respectively) is held at tensions (energy levels) against which plants cannot extract the water. Because of limited and erratic precipitation during the growing season, it is desirable to have the soil profile filled to capacity with water at planting time, especially for dryland crops. When the soil is filled to capacity at planting, crops usual- ly experience less water stress during the growing season than when the soil contains a limited amount of water. Crop yields usually are higher when water stress is not severe dur- ing the growing season. Although irrigation can provide water to crops, soil water content at planting is still important because any water stored from precipitation reduces the amount required from irrigation. When water storage from precipitation is low, a preplant or emergence irrigation is often used to increase the soil water content. Because the Sherm soil is slowly permeable, relatively long periods of water application are required to add large amounts of water to the soil. With furrow irrigation (Figure 13), which is the most common method, considerable tailwater é Sherm soil profile in Dal-lam Cunty, Texas. Major uits are in feet (USDA-Soil Conservation Service photo). Texas. Units are in cm \b un ty, ’ Figure 11. Sherm soil profile in Moore Co 8 (x10 '1) and feet. runoff is usually permitted so that adequate water is stored at the lower end of the field. Unless effective tailwater recovery systems (Figure 14) are used, tailwater runoff reduces the efficiency of water use. In recent years, many center-pivot sprinkler systems (Figure 15) have been installed on Sherm soil. These systems, when properly designed and operated, reduce runoff amount compared to furrow irrigation but require considerably more energy in- put than furrow irrigation. “With all farming systems on both dryland and irrigated land, a knowledge of the water-holding capacity of the soil profile (Figure 16) is important for effective water management. EXPERIMENTAL PROCEDURE Site Selection To obtain samples that would represent a near-complete range in the expected variation in soil proper- ties, sites were selected at 11 widely separated locations across the region. The sampling sites were in Dallam, Hansford, Hartley, Moore, Ochiltree, and Sherman Counties in the Texas Panhandle, and in Beaver and Texas Counties in the Oklahoma Panhandle. Although the locations were widely separated, samples were not obtained near the edges of the region to avoid zones of transition to other soils. Likewise, locations of transition to other soils within the region were avoided. The sampling was restricted to “typical” Sherm soil sites for the particular location. o >_ - _ Figure 12. Sherm soil profi] in Ochiltree (Cyoun exa Units are in feet (USDA -So1'I Conservation Service photo). Sampling Sites The ll sampling sites are in- dicated on Figure 2. Brief descrip- tions of the locations are given with the profile descriptions in the Results and Discussion section. All sites were in irrigated fields on nearly level uplands of the High Plains. Sites l, 2, 4, 5, and 11 were in the western province; Sites 3, 6, 7 in the central province; and Sites 8, 9, and 10 in the eastern province. Figure . Taildwter recvry pit and Iake pump to recycle Water t0 cropland. (USDA- Soil Conservation Service photo). Sampling Techniques At each sampling site, loose soil of the plow layer, usually to the depth of the Ap horizon, was removed before obtaining core samples with a hydrualically-operated, pickup- mounted core sampler. The inside diameter of the cutting tip was 1.625 inches. The first two cores at each site were used for profile description. Other cores were then taken and separated into depth segments based on the thickness of the different horizons. Three or more cores were obtained to provide adequate material from each depth for deter- mining water retention. The core segments were immediately dipped in a liquified saran solution, which made the cores rigid after drying. After the saran had dried, the in- dividual segments were wrapped in plastic bags for transport to the laboratory. Two additional cores were obtained and sectioned by horizons to obtain samples for bulk density determination. Two samples of the surface layer of soil were also collected in bags at each site. At a different time, three water infiltra- tion determinations were made at each site with recorder-equipped, constant head, double-ring in- filtrometers. These double-rings are seated into the most restrictive sub- surface layer, and 1.5-inch head of water is maintained for the duration of the test. Water surfaces are covered to prevent evaporation. Placement of individual in- filtrometers is determined after ex- amining the field to reflect tillage zone conditions at the time of testing. 1O Texas. >- "‘ 4 g; f o 2 < a u 3 < Z u o Q o__ 2 E o O .- ..: a 1 O O U. ‘F \ n01’ AVAILABLE T0 PLANTS ==: m; o >- g. k0 a ma O: mg’ i h: ;>-: >3 >7‘! >- < c z z: z‘ zz‘ < J‘ °(< (( (<( ( ;__ 4 ..< (O -‘Q O 5O __...cO 4Q m-JQ 4 v-o U! ILUI “J ll“; J JJU-J U; t‘); U S O I L T E X T U R E Figure 16. Typical Wa ter-holdin g capacities of soils with different textures (adapted from USDA, 1955). Sample Preparation and Analyses The core samples used for water retention measurements were cut in- to sections about 0.75 inch long and reinforced with cellophane tape before making the measurements at -1/s and -15 bars matric potential. The measurements were made with pressure plate equipment using four sections from each depth at each potential. Bulk density was determined by drying the cores at 105°C, then weighing them. Soil from these cores was retained and ground to pass a 2-mm sieve. Subsamples of this sieved soil were then used to deter- mine organic matter content by the Walkley-Black method (Jackson, 1958), pH (1:1 soilzwater ratio), and particle size distribution (mechanical analyses) by the hydrometer method (Day, 1965). The sand from the par- ticle size distribution analyses was subsequently sieved to determine the size distribution of the sand in the samples. Samples of surface soil were air- dried, ground, and passed through a 2-mm sieve. Subsamples of surface soil were used to determine water retention, particle size distribution, organic matter content, and pH by the methods described above. The relationships among various Ap, Btl, and Bt2 horizons, total pro- file characteristics, total water in- filtration in 1O min and 20 hr, and infiltration rates at these times were investigated by multiple linear regression analyses. The horizon and profile characteristics investigated were thickness; sand, silt, clay, and organic matter content; and bulk density. For the Ap, Btl, and Bt2 horizons, actual values were used. For the entire profile, weighted mean values were calculated from values for the different horizons, resulting in one value for each variable of the profile at each site. 5.1 Sprinkler-irrigation“system near Besides the partial regression coeffi- cients and the coefficient of correla- tion (R), standardized partial regres- 'on coefficients and t-values were also calculated (Ezekiel and Fox, 1959; Steel and Torrie, 1960). Based on the standardized coefficients, the independent variables were ranked numerically in order of their relative importance for influencing total in- filtration or infiltration rates. All in- dependent variables were used in the initial analysis for each set of data. In subsequent analyses, the lowest- ranking variable was excluded, which resulted in the last analysis be- ing a simple linear regression analysis. RESULTS AND DISCUSSION Profile Descriptions This section describes the profiles at the 11 sites and their locations. The profile descriptions are based on examination and determinations made in the field immediately after extracting the cores. Although data in subsequent sections are based mainly on horizons above the calcic horizon, the calcic horizon is in- cluded in the profile descriptions. The descriptions are: Site N0. 1 Soil Type: Sherm clay loam Location: Hartley County, Texas; in a cultivated field 1,300 ft east of unpaved county road, 1.7 mi northwest and 0.25 mi west of the intersection of U.S. Highway 385 and Farm Road 998 in Hartley. Pedon Description: Sample No. S81TX205-1-(1-6) Ap—0 to 6 inches; brown (7.5YR 4/2) clay loam, dark brown (7.5YR 3/2) moist; weak, medium granular and subangular blocky structure; slightly hard, friable; many fine and medium roots; few fine pores; mildly alkaline; abrupt smooth boundary. Btl—6 to 18 inches; brown (7.5YR 4/2) clay, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; few small stress surfaces in lower part; extremely hard, extreme- ly firm; common fine roots; few very fine pores; thin con- tinuous clay films; few vertical cracks; mildly alkaline; gradual smooth boundary. Bt2—18 to 28 inches; brown (7.5YR 5/2) clay loam, brown (7.5YR 4/2) moist; moderate medium blocky structure; very hard, very firm; few fine roots; few very fine pores; thin con- tinuous clay films; few small vertical cracks; few threads and films of calcium car- bonate; calcareous; mildly alkaline; gradual smooth boundary. Bt3-—28 to 36 inches; brown (7.5YR 5/4) clay loam, brown (7.5YR 4/4) moist; weak coarse prismatic structure, parting to moderate medium blocky; very hard, very firm; few fine roots; common fine pores; thin con- tinuous clay films; few threads and films of calcium car- bonate; calcareous; mildly alkaline; gradual smooth boundary. Bt4—36 to 60 inches; yellowish red (5YR 5/6) clay loam, yellowish red (5YR 4/6) moist; weak coarse prismatic struc- ture, parting to moderate medium blocky; hard, firm; few very fine roots; common fine pores; few patchy clay films; few threads and films of calcium carbonate; calcareous; mildly alkaline; clear wavy boundary. Btk—60 to 72 inches; pink (5YR 8/4) clay loam, pink (5YR 7/4) moist; moderate medium subangular blocky structure; hard, friable; common fine pores; about 45 percent of the soil mass consists of soft masses and concretions of calcium car- bonate; calcareous; moderate- ly alkaline. Site N0. 2 Soil Type: Sherm clay loam Location: Dallam County, Texas; in a cultivated field 300 ft north of irrigation well, 0.5 mi east and 1.5 mi north of Farm Road 297, and 18.3 mi east of its intersection with U.S. Highway 385 in Dalhart. Pedon Description: Sample No. S81TX111-1-(1-7) Ap—0 to 7 inches; brown (7.5YR 4/2) clay loam, dark brown (7.5YB 3/2) moist; weak medium granular and subangular blocky structure; hard, friable; many fine roots; few fine pores; dense plow pan is present in lower 2 inches; mildly alkaline; clear smooth boundary. Bt1—7 to 17 inches; brown (7.5YR 4/2) clay loam, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; extremely hard, ex- tremely firm; common fine roots; few very fine pores; thin continuous clay films; few ver- tical cracks; mildly alkaline; gradual smooth boundary. Bt2—17~ to 26 inches; brown (7.5YR 5/4) clay loam, brown (7.5YR 4/4) moist; moderate medium blocky structure; very hard, very firm; common fine roots; few fine pores; thin con- tinuous clay films; few threads and films of calcium car- bonate; calcareous; mildly alkaline; gradual smooth boundary. Bt3—26 to 38 inches; brown (7.5YR 5/4) clay loam, brown (7.5YR 4/4) moist; moderate medium blocky structure; slightly hard, friable; few fine roots; common fine pores; thin continuous clay film; common threads and films of calcium carbonate; calcareous; mildly alkaline; clear smooth boundary. Ab—38 to 48 inches; brown (7.5YB 5/2) clay loam, brown (7.5YR 4/2) moist; moderate medium subangular blocky structure; slightly hard, friable; few fine roots; com- mon fine pores; calcareous; mildly alkaline; gradual smooth boundary. Btb1—48 to 60 inches; reddish brown (5YR 5/4) clay loam, reddish brown (5YR 4/4) moist; weak coarse prismatic structure, parting to moderate medium blocky; hard, firm; few fine roots in upper part; common pores; thin con- tinuous clay films; calcareous; mildly alkaline; gradual smooth boundary. Btb2—60 to 74 inches; 11 yellowish red (5YR 5/6) clay loam, yellowish red (5YR 4/6) moist; weak coarse prismatic structure, parting to moderate medium blocky; hard, firm; common fine pores; thin con- tinuous clay films; calcareous; moderately alkaline. Site N0. 3 Soil Type: Sherm silty clay loam Location: Moore County, Texas; in a cultivated field 800 ft east of un- paved county road, 0.9 mi north of Farm Road 281, 1.3 mi east of its intersection with U.S. Highway 287 in Etter. Pedon Description: Sample No. S8lTX34l-1-(1-5) A Ap—O to 6 inches, brown (7.5YR 4/2) silty clay loam, dark brown (7.5YR 3/2) moist; weak fine granular and medium subangular blocky structure; slightly hard, friable; many fine and medium roots; common pores; moderately alkaline; clear smooth boundary. Bt1—6 to 19 inches, dark brown (7.5YR 4/2) silty clay, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; few wedge-shaped peds; few small stress surfaces; extremely hard, extremely firm; many fine roots; few very fine pores; thin continuous clay films; few vertical cracks; mildly alkaline; gradual smooth boundary. Bt2—19 to 34 inches, brown (7.5YR 5/4) silty clay loam, brown (7.5YR 4/4) moist; moderate medium blocky structure; very hard, very firm; few small stress surfaces; com- mon fine roots; few very fine pores; thin continuous clay films; few threads and films of calcium carbonate; calcareous; mildly alkaline; gradual smooth boundary. Bt3-—34 to 54 inches; reddish brown (5YR 5/4) clay loam, reddish brown (5YR 4/4) moist; moderate medium blocky structure; very hard, very firm; few fine roots; few fine pores; common patchy clay films; few threads, films, and small concretions of calcium carbonate; calcareous; 12 mildly alkaline; clear smooth boundary. Btk—54 to 72 inches, pink (7.5YR 8/4) silty clay loam, pink (7.5YR 7/4) moist; weak coarse platy and moderate medium blocky structure; very hard, friable; few fine pores; about 55 percent of the soil mass consists of soft masses and concretions of calcium car- bonate; calcareous; moderate- ly alkaline. Site N0. 4 Soil Type: Sherm clay Location: Texas County, Oklahoma; in a cultivated field, 300 ft east of State Highway 136 and 2.05 mi south of its intersection with U.S. Highway 54 in Cuymon. Pedon Description: Sample No. S810K70-1-(1-5) Ap—O to 6 inches; dark grayish brown (l0YR 4/2) clay, very dark grayish brown (IOYR 3/ 2) moist; weak fine granular and subangular blocky structure; hard, friable; many roots and incorporated residue; mod- erately alkaline; clear smooth boundary. Bt1—6 to 2O inches; dark grayish brown (IOYR 4/ 2) clay loam, very dark grayish brown (10YR 3/2) moist; moderate medium blocky structure; ex- tremely hard, extremely firm; few small stress surfaces; com- mon fine roots; few fine pores; thin continuous clay films; few vertical cracks; moderately alkaline; gradual smooth boundary. Bt2—2O to 38 inches; brown (10YR 5/3) clay loam, brown (l0YR 4/3) moist; moderate medium blocky structure; very hard, very firm; common fine roots; few fine pores; common clay films; few small concre- tions of calcium carbonate that are hard and pitted; calcareous; moderately alkaline; gradual smooth boundary. Btb1—38 to 63 inches; brown (10YR 5/3) silty clay loam, brown (IOYR 4/ 3) moist; weak coarse prismatic structure, parting to moderate medium blocky; hard, firm; few fine roots; few fine pores; few patchy clay films; few fine black concretions; few threads, films, and small concretions of calcium carbonate; calcareous; moderately alkaline; gradual smooth boundary. Btb2—63 to 72 inches; grayish brown (IOYR 5/2) silty clay loam, dark} grayish brown (IOYB 4/ 2) moist; weak coarse prismatic structure, parting to moderate medium blocky; slightly hard, friable; common fine pores; few threads and films of calcium carbonate; calcareous; moderately al- kaline. Site N0. 5 Soil Type: Sherm clay loam Location: Sherman County, Texas; in a cultivated field 300 ft west of Farm Road 2104, 2.0 mi south of U.S. Highway 54, 3.0 mi southwest of its intersection with U.S. Highway 287 in Stratford. Pedon Description: Sample No. S8lTX421-l-(1-6) Ap-—0 to 6 inches; brown (7.5YR 4/2) clay loam, dark brown (7.5YR 3/2) moist; weak fine granular and subangular blocky structure; hard, friable; many roots; dense plowpan is present in lower 2 inches; mildly alkaline; clear smooth boundary. Bt1—6 to 17 inches; brown (7.5YR 4/2) clay loam, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; extremely hard, ex- tremely firm; common fine roots; few fine pores; thin con- tinuous clay films; few small vertical cracks; mildly alkaline; gradual smooth boundary. Bt2-—l7 to 27 inches; brown (7.5YR 5/4) clay loam, brown (7.5YR 4/4) moist; moderate medium blocky structure; very hard, very firm; common fine roots; thin continuous clay films; few threads and films of calcium carbonate; calcareous; moderately alkaline; gradual smooth boundary. Bt3—27 to 36 inches; brown (7.5YR 5/4) clay loam, brown (7.5YR 4/4) moist; weak coarse prismatic structure, parting to moderate medium blocky; hard, firm; few fine roots; common fine pores; few patchy clay films; few threads, films and small concretions of calcium carbonate; calcareous; moderately alkaline; clear smooth boundary. Bt4—36 t0 44 inches; reddish brown (5YR 5/4) clay loam, reddish brown (5YR 4/4) moist; weak coarse prismatic structure, parting to moderate medium blocky; very hard, very firm; few fine roots; few fine pores; common patchy clay films; few threads, films, and small concretions of calcium carbonate; calcareous; moderately alkaline; gradual smooth boundary. Btk—44 to 72 inches; pink (7.5YR 8/4) clay, pink (7.5YR 7/4) moist; weak coarse platy structure, parting to moderate medium blocky; very hard, firm; common fine pores; about 20 percent of the soil mass consists of soft masses and weakly cemented concretions of calcium carbonate; calcareous; moderately al- kaline. Site N0. 6 Soil Type: Sherm silty clay loam Location: Moore County, Texas; in a cultivated field 200 ft east of private road, 1.05 mi north of paved county road, 1.0 mi west of Farm Road 1060 at a point 4.0 mi north of its intersection with State Highway 152, 16.0 mi east of Dumas. Pedon Description: Sample No. S81TX341-2-(1-5) Ap—O to 7 inches; dark reddish gray (5YR 4/ 2) silty clay loam, dark reddish brown (5YB 3/ 2) moist; weak fine granular and subangular blocky structure; boundary. Bt2—l9 to 35 inches; reddish brown (5YR 4/4) clay, reddish brown (5YR 3/4) moist; moderate medium blocky structure; few small stress sur- faces; extremely hard, ex- tremely firm; few fine roots; few fine pores; thin continuous clay films; calcareous; moderately alkaline; gradual smooth boundary. Bt3—35 to 58 inches; brown (7.5YR 5/4) silty clay, brown (7.5YR 4/4) moist; moderate medium blocky structure; very hard, very firm; few fine roots; few fine pores; thin continuous clay films; few threads and films of calcium carbonate; calcareous; moderately alkaline; clear wavy boundary. Btk—58 to 74 inches; pink (7.5YR 8/4) silty clay loam, pink (7 .5YR 7/4) moist; weak coarse platy structure, parting to moderate medium blocky; very hard, friable; very few fine roots in upper 2 inches; about 5O percent of the soil mass consists of weakly cemented concretions of calcium carbonate; calcareous; moderately alkaline. Site N0. 7 Soil Type: Sherm silty clay Location: Hansford County, Texas; in a cultivated field, 2,500 ft west of State Highway 136, 8.7 mi north of Gruver. Pedon Description: Sample No. S82TX195-1-(1-6) Ap—O to 6 inches; dark brown (7.5YR 4/2) silty clay, dark brown (7.5YR 3/2) moist; weak fine granular and moderate medium subangular blocky structure; hard, friable; smooth boundary. Bt2—18 to 26 inches; brown (lOYR 5/3) silty clay, brown (IOYR 4/3) moist; moderate medium blocky structure; few small stress surfaces; very hard, firm; few fine roots; few fine pores; thin continuous clay films; calcareous; moderately alkaline; gradual smooth boundary. Bt3—26 to 39 inches; brown (7.5YR 5/4) silty clay loam, brown (7.5YR 4/4) moist; weak coarse prismatic struc- ture, parting to moderate medium subangular blocky structure; hard, firm; few fine roots; fewvery fine pores; few patchy‘clay films; common threads and films of calcium carbonate; calcareous; mod- erately alkaline; gradual smooth boundary. Bt4—39 to 53 inches; brown (7.5YR 5/4) silty clay, brown (7.5YR 4/4) moist; weak coarse prismatic structure, parting to moderate medium subangular blocky; few fine roots; few very fine pores; few patchy clay films; few threads and films of calcium carbonate; calcareous; moderately alkaline; clear smooth boundary. Btk—53 to 76 inches; pink (7.5YR 8/4) silty clay loam, pink (7.5YR 7/4) moist; weak coarse platy structure, parting to moderate medium blocky structure; very hard, friable; common fine pores; about 45 percent of the soil mass consists of soft masses and concretions hard, friable; many roots; moderately alkaline; clear smooth boundary. Bt1——7 to 19 inches; dark red- dish brown (5YR 3/2) silty clay, dark reddish brown (5YR 2/2) moist; ‘moderate medium blocky structure; few small stress surfaces; extremely hard, extremely firm; common fine roots; few fine pores; thin con- tinuous clay films; few vertical cracks; calcareous; moderate- ly alkaline; gradual smooth common roots; common pores; dense plowpan present in lower part; mildly alkaline; clear smooth boundary. Btl—6 to 18 inches; dark brown (7.5YR 4/2) silty clay, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; few wedge-shaped peds; few small stress surfaces; extremely hard, very firm; common fine roots; few fine pores; thin continuous clay films; mildly alkaline; gradual of calcium carbonate; calcareous; moderately alkaline. Site N0. 8 Soil Type: Sherm silty clay loam Location: Hansford County, Texas; in a cultivated field 3,200 ft east of a paved county road, 3.6 mi south of State Highway 15, at a point 1.3 mi northeast of its junc- tion with U.S. Highway 207 in Spearman. Pedon Description: Sample No. S82TX195-2-(1-6) Ap-—0 to 6 inches; dark brown (7.5YR 4/2) silty clay loam, dark brown (7.5YR 3/ 2) moist; 13 14 weak granular and moderate medium subangular blocky structure; hard, friable; many fine roots; common fine pores; mildly alkaline; clear smooth boundary. Btl—6 to 2O inches; dark brown (7.5YR 4/2) silty clay loam, dark brown (7.5YR 3/ 2) moist; moderate medium blocky structure; extremely hard, very firm; common fine roots; few very fine pores; thin continuous clay films; few small stress surfaces; moderate- ly alkaline; gradual smooth boundary. Bt2—2O to 37 inches; brown (lOYR 5/3) silty clay loam, brown (lOYR 4/3) moist; moderate medium blocky structure; extremely hard, very firm; few fine roots; few very fine pores; thin continuous clay films; few small stress surfaces; calcareous; moderately alkaline; clear smooth boundary. Ab—37 to 5O inches; brown (7.5YR 5/4) silty clay loam, brown (7.5YR 4/4) moist; moderate medium subangular blocky structure; very hard, firm; few fine roots; few very fine pores; few threads, films, and small concretions of calcium carbonate; calcareous; moderately alkaline; clear smooth boundary. Btb1—5O to 6O inches, reddish yellow (5YR 6/6) silty clay loam, yellowish red (5YR 5/6) moist; weak coarse prismatic structure, parting to moderate medium blocky structure; hard, friable; few fine roots; few patchy clay films; common very fine pores; common threads and films of calcium carbonate; calcareous; moderately alkaline; gradual smooth boundary. Btb2—6O to 93 inches; reddish yellow (5YR 6/8) silty clay loam, yellowish red (5YR 5/8) moist; weak coarse prismatic structure, parting to moderate medium blocky; hard, friable; few fine roots to 76 inches; few patchy clay films; common very fine pores; common threads, films, and small con- cretions of calcium carbonate; calcareous; moderately al- kaline. Site N0. 9 Soil Type: Sherm silty clay loam Location: Beaver County, Oklahoma; in a cultivated field 500 ft north of unpaved county road, 11.8 mi east of U.S. Highway 83 at a point 0.25 mi north of the Texas-Oklahoma state line. Pedon Description: Sample No. S810K4-l-(l-6) Ap—O to 7 inches; dark brown (7.5YB 4/2) silty clay loam, dark brown (7.5YR 3/ 2) moist; weak fine granular and subangular blocky structure; hard, friable; many fine and medium roots; mildly alkaline; clear smooth boundary. Bt1—7 to l9 inches; brown (7.5YR 4/2) silty clay, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; few small stress sur- faces; extremely hard, ex- tremely firm; many fine roots; a few fine pores; thin con- tinuous clay films; few vertical cracks; mildly alkaline; gradual smooth boundary. Bt2—19 to 36 inches; brown (lOYR 5/3) silty clay, brown (lOYR 4/3) moist; moderate medium blocky structure; few small stress surfaces; extreme- ly hard, extremely firm; few fine roots; few fine pores; few threads and films of calcium carbonate; calcareous; mildly alkaline; clear smooth boundary. Ab—36 to 43 inches; brown (lOYR 4/3) silty clay loam, dark brown (lOYR 3/3) moist; moderate medium subangular blocky structure; hard, friable; few fine roots; common fine pores; few threads, films and weakly cemented concretions of calcium carbonate; calcareous; mildly alkaline; gradual smooth boundary. Btbl—43 to 59 inches; brown (7.5YR 5/4) silty clay loam, brown (7.5YR 4/4) moist; moderate medium subangular blocky structure; hard, firm; few fine roots; common fine pores; few patchy clay films; calcareous; mildly alkaline; gradual smooth boundary. Btb2—59 to 72 inches; brown (7.5YR 5/4) silty clay loam, brown (7.5YR 4/4) moist; moderate medium subangular blocky structure; hard, firm; common patchy clay films; few fine pores; mildly alkaline. Site N0. 1O a Soil Type: Sherm silty clay loam Location: Ochiltree County, Texas; in a cultivated field 100 ft south of unpaved county road, 2.2 mi west of U.S. Highway 83 at a point 5.6 mi south of its intersec- tion with State Highway 15 in Perryton. Pedon Description: Sample No. S82TX357-1-(1-6) Ap—O to 8 inches; dark brown (7.5YR 4/2) silty clay loam, dark brown (7.5YR 3/ 2) moist; weak fine granular and subangular blocky structure; hard, friable; many fine roots and incorporated residue; mildly alkaline; clear smooth boundary. Bt1—8 to 24 inches; brown (7.5YR 4/2) silty clay, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; few small stress sur- faces; extremely hard, ex- tremely firm; common fine roots; few fine pores; thin con- tinuous clay films; few vertical cracks; mildly alkaline; gradual smooth boundary. Bt2—24 to 38 inches; brown (7.5YR 5/2) silty clay, brown (7.5YR 4/2) moist; moderate medium blocky structure; few small stress surfaces; extreme- ly hard, extremely firm; few fine roots; few fine pores; thin continuous clay films; few ver- tical cracks; mildly alkaline; clear smooth boundary. Ab—38 to 51 inches; brown (lOYR 5/3) silty clay, brown (IOYR 4/3) moist; moderate medium subangular blocky structure; hard, firm; few fine roots; few fine pores; few threads and films of calcium carbonate; calcareous; mildly alkaline; gradual smooth boundary. Btbl—5l to 63 inches; yellowish brown (IOYR 5/4) silty clay 10am, dark yellowish brown (l0YR 4/4) moist; weak coarse prismatic structure, par- ting t0 moderate medium blocky; very hard, firm; few fine roots; few fine pores; com- mon patchy clay films; calcareous; mildly alkaline; gradual smooth boundary. Btb2—63 to 76 inches; brown (7.5YR 5/4) silty clay loam, brown (7.5YR 4/4) moist; weak coarse prismatic struc- ture, parting to moderate medium blocky; very hard, firm; occasional very fine roots; few fine pores; common patchy clay films; calcareous; mildly alkaline. Site N0. 11 Soil Type: Sherm clay loam Location: Dallam County, Texas; in a cultivated field, 1,000 ft south of Farm Road 695, 21 mi east of U.S. Highway 54, at a point 5.2 mi northeast of its intersection with U.S. Highway 385 in Dalhart. Pedon Description: Sample No. S84TX111-1-(1-5) Ap—0 to 7 inches; reddish brown (5YR 4/3) clay loam, dark reddish brown (5YR 3/ 3) moist; weak fine granular and subangular blocky structure; hard, friable; many roots; mildly alkaline; clear smooth boundary. Btl—7 to 20 inches; reddish brown (5YR 4/3) clay 10am, dark reddish brown (5YR 3/3) moist; moderate medium blocky structure; few small stress surfaces; extremely hard, extremely firm; common fine roots; few fine pores; thin con- tinuous clay films; few vertical cracks; calcareous; mildly alkaline; gradual smooth boundary. Bt2——20 to 32 inches; reddish brown (5YR 5/3) clay loam, reddish brown (5YR 4/3) moist; moderate medium blocky structure; few small stress surfaces; extremely hard, extremely firm; few fine roots; few fine pores; thin continuous clay films; calcareous; mildly alkaline; gradual smooth boundary. Bt3—32 to 47 inches; yellowish red (5YR 5/ 6) silty clay loam, yellowish red (5YR 4/6) moist; moderate medium blocky structure; very hard, very firm; few fine roots; few fine pores; thin continuous clay films; few threads and films of calcium carbonate; calcareous; mildly alkaline; clear wavy boundary. Btk—47 to 80 inches; pink (5YR 7/4) silty clay loam, light red- dish brown (5YR 6/4) moist; weak coarse platy structure, parting to moderate medium blocky; very hard, friable; very few fine roots in upper 2 in- ches; about 50 percent of the soil mass consists of weakly cemented concretions of calcium carbonate; calcareous; moderately alkaline. Based on the field descriptions, profiles at the various sites differed mainly in thickness, color, and tex- ture of the different horizons; depth to the calcic horizon or to a buried horizon; and presence or absence of buried horizons. Table 4 indicates which profiles are present at the dif- ferent sites. The Ap horizon is 6 to 7 inches thick at all sites except at Site 10, where it was 8 inches thick. Color is brown at Sites l, 2, 3, and 5; dark grayish brown at Site 4; dark reddish gray at Site 6; reddish brown at Site 11; and dark brown at Sites 7, 8, 9, and 10. Surface textures are clay loam at Sites 1, 2, 5; and 11; silty clay at Site 7; silty clay loam at Sites 3, 6, 8, 9, and 10; and clay at Site 4. This horizon represents mainly the plow layer. The differences in thickness and local differences in tex- ture possibly resulted from mixing the upper layers in plowing. The Btl horizon is mainly 12 to 14 inches thick. But its thickness is 10 inches at Site 2, 11 inches at Site 5, and 16 inches at Site 10. Texture is primarily silty clay but is clay at Site 1; clay loam at Sites 2, 4, 5, and 11; and silty clay loan at Site 8. Colors are mainly brown, but range to dark grayish brown at Site 4; dark reddish gray at Site 6; dark brown at Sites 3, 7, and 8; and dark reddish brown at Site 11. The Bt2 horizon is commonly 14 to 17 inches thick, but thickness varies from 8 inches at Site 7 to 18 inches at Site 4. Texture is clay loam at Sites 1, 2, 4, 5, and 11; silty clay loam at Site 3 and 8; clay at Site 6; and silty clay at Sites 7, 9, and 10. Color is brown except at Sites 6 and 11, where it is reddish brown. The Bt3 horizon is present at Sites 1, 2, 3, 5, 6, 7, and 11. Thickness is commonly 12 to 20 inches but is 8 inches at Site 1, 9 inches at Site 5, and 23 inches at Site 6. Texture is mainly clay loam but is silty clay loam at Site 7 and 11 and silty clay at Site 6. Color is commonly brown but is yellowish red at Site 11 and reddish brown at Site 3. The Bt4 horizon is present at Sites 1, 5, and 7. Thickness is commonly 8 to 14 inches but is 24 inches at Site 1. Texture is dominantly clay loam. Color is brown at Site 7, reddish brown at Site 5, and yellowish red at Site 1. Buried profiles, or horizons, are present at depths of 36 to 39 inches in Sites 2, 4, 8, 9, and 10. These layers have readily discernable features in the form of colors, tex- tures, or structure that combine to exhibit sharp contrast with overlying horizons. The sand and silt fractions TABLE 4. HORIZONS IDENTIFIED IN SHEFIM SOIL PROFILES AT THE VARIOUS SAMPLING SITES Site County, state Ap Bt1 Bt2 Bt3 Bt4 Ab Btb1 Btb2 Btk 1 Hartley, Texas X X X X X X 2 Dallam, Texas X X X X X X X 3 Moore, Texas X X X X X 4 Texas, Oklahoma X X X X X 5 Sherman, Texas X X X X X X 6 Moore, Texas X X X X X 7 Hansford, Texas X X X X X X 8 Hansford, Texas X X X X X X 9 Beaver, Oklahoma X X X X X X 10 Ochiltree, Texas X X X X X X 11 Dallam, Texas X X X X X 15 of buried profiles are reddish yellow. Colors of the sand and silt fractions in the upper horizons are light gray or light brownish gray. A clear boundary commonly is present be- tween buried horizons and overlying layers. In sites where an Ab horizon is not readily observable, the boun- dary between a Btbl and the over- lying horizon is usually gradual. The Btb horizons are commonly brown, reddish brown, or yellowish red, but colors range to dark yellowish brown and dark grayish brown at Sites 4 and 10, respective- ly. Textures are clay loam at Site 2 and silty clay loam at Sites 4, 8, 9, and 10. Btk horizons are present in Sites 1, 3, 5, 6, 7, and 11. Thickness ranges from 12 inches to more than 28 inches. Color is primarily pink, but is light reddish brown at Site 11. Texture is clay loam at Site 1 and silty clay loam at Sites 3, 6, 7, and 11. Calcium carbonate content com- monly is 45 to 55 percent by volume but is 22 percent at Site 5. Other than horizon thickness, col- or, and texture, most profile condi- tions that were determined by the field descriptions were similar for all sites for the Ap, Btl, and Bt2 horizons. The slight differences among sites should have no major in- fluence on soil and crop manage- ment practices, except that the dense plowpan present in the Ap horizon at Sites 2, 5, and 7 could adversely affect water infiltration and plant root growth. Below the Bt2 horizon, conditions were more variable because some profiles contained buried horizons. Also, depth to a calcic horizon varied greatly among sites, ranging mostly from 53 to 60 inches when present. However, at Site 5, the calcic horizon was present at a 44-inch depth while no calcic horizon was found at a depth of 72 to 76 inches at Sites 2, 4, 9, and 10, or at 93 inches at Site 8. Particle Size Distribution Results of the particle size distribution analyses are included in Table 5. The weighted mean for sand content was highest at Sites 1, 2, 5, and 11; intermediate at Sites 3 and 4; and lowest at Sites 6, 7, 8, 9, and 10. The mean sand content, in general, decreased from west to east across the region. The size distribu- tion of the sand fraction varied for samples from the different sites as determined by the percent retained on standard sieves (Table 6). No samples contained a high amount of TABLE 5. CHARACTERISTICS OF THE SHERM SOIL AT THE STUDY SITES coarse sand, but the amount of fine and very fine sand in the samples, in general, incrased from west to east across the region. The distribution of sand within the profiles was variable and erratic, especially at Sites 1 through 5 and Site 11. At some of these sites (Sites 1 and 5), maximum sand content was at the surface, but some deeper horizons had similar sand contents. At other sites, maximum sand con- tents were in deeper horizons (Sites 2, 3, 4, and 11). At Sites 6 through 10, sand contents tended to increase with depth, but some intermediate horizons had lower sand contents than either the Ap or the deep horizons (Sites 7, 9, and 10). The weighted mean for silt con- tent was lowest at Sites 1, 2, 5, and 11; intermediate at Sites 3, 4, and 6; and highest at Sites 7, 8, 9, and 10. These trends are opposite those for sand content. Silt content was also variable in the profiles, and no horizon had the highest or lowest silt content in all cases. The weighted mean for clay con- tent varied less among sites than sand and silt contents, ranging from a low of 32.7 percent at Site 2 to a high of 43.8 percent at Site 6. Clay content usually was highest in the Btl and- or Bt2 horizons, except at Site 4, Site, county, Water content state, and CaCoa at bars potential Sample no. Hor Depth Sand Silt Clay Texture O.M. pH B.D. equiv -1/32 -15 Plant-availwaler Adjusted to 60-in in l °/o q/cma % % by volume _"/o__ _in_/in_ in/flr depth“ Site 1—Har1ley, Texas S81TX205-1-1 Ap 0-6 35.2 33.2 31.6 Clay loam 1.45 7.75 1.26‘ - 29.5 19.2 10.3 0.103 0.62 -2 Bt1 6-18 23.6 32.8 43.6 Clay 0.93 7.65 1.53 - 37.9 22.8 15.1 0.151 1.81 -3 Bt2 18-28 20.5 39.8 39.7 Clay loam 0.63 7.60 1.62 - 34.4 20.6 13.8 0.138 1.38 -4 B13 28-36 26.7 37.9 35.4 Clay loam 0.39 7.60 1.63 - 30.1 19.9 10.2 0.102 0.82 -5 Bt4 36-60 35.8 30.5 33.7 Clay loam 0.23 7.50 1.51 - 27.1 17.4 9.7 0.097 2.33 -6 Btk 60-72 29.9 40.9 29.2 Clay loam 0.25 7.90 1.46 45.25 — — - - - Weighted mean‘ 29.5 33.7 36.7 — 0.58 7.59 1.52 — 31.1 19.5 11.6 0.116 — Profile total-in - — - - - - - - - - - - 6.96 6.96 Site 2—Da||am, Texas S81TX111-1-1 Ap 0-7 36.0 32.4 31.6 Clay loam 1.75 7.70 1.26‘ - 31.1 20.2 10.9 0.109 0.76 -2 Bt1 7-17 32.8 29.3 37.9 Clay loam 0.84 7.60 1.58 — 33.8 18.6 15.2 0.152 1.52 -3 Bt2 17-26 43.9 25.4 30.7 Clay loam 0.39 7.60 1.55 — 26.0 16.9 9.1 0.091 0.82 -4 B13 26-38 46.0 27.6 26.4 Clay loam 0.36 7.50 1.49 — 22.2 17.6 4.6 0.046 0.55 -5 Ab 38-48 22.0 45.6 32.4 Clay loam 0.45 7.70 1.51 — 27.2 19.3 7.9 0.079 0.79 -6 Btb1 48-60 33.0 32.1 34.9 Clay loam 0.34 7.70 1.64 — 29.6 19.0 10.6 0.106 1.27 -7 Btb2 60-74 40.3 24.9 34.8 Clay‘ loam 0.23 7.90 1.69 — — - - — — Weighted mean 36.6 30.7 32.7 — 0.54 7.68 1.55 — 28.0 18.5 9.5 0.095 - Profile total-in — — - - - - - - - - - 5.71 5.71 16 TABLE 5. CONTINUED Site, county, Water content state, and CaCoa at bars potential Sample no. Hor Depth Sand Silt Clay Texture O.M. pH B.D. equiv -1/32 -15 Plant-avail water Adjusted to 60-in in l % q/cm“ °/o % by volume _°A__ lily i@r degth“ Site 3—Moore, Texas S81TX341-1-1 Ap 0-6 16.8 47.2 36.0 Silty clay loam 2.17 7.90 1.26‘ - 36.4 24.3 12.1 0.121 0.73 -2 Bt1 6-19 12.0 41.3 46.7 Silty clay 1.13 7.80 1.41 — 40.2 22.4 17.8 0.178 2.31 -3 Bt2 19-34 13.9 48.0 38.1 Silty clay loam 0.56 7.80 1.51 — 31.9 20.5 11.4 0.114 1.71 -4 Bt3 34-54 26.5 41.2 32.3 Clay loam 0.30 7.70 1.58 — 27.0 21.5 5.5 0.055 1.10 -5 Btk 54-72 18.2 56.2 25.1 Silty clay ' loam 0.24 7.90 1 .38 58.48 — — - — - Weighted mean 18.4 43.8 37.8 — 0.80 7.77 1.48 — 32.6 21.8 10.8 0.108 — Profile total-in — — — — — — — — — — — — 5.85 618 Site 4—Texas, Oklahoma S810K70-1-1 Ap 0-6 22.9 36.7 40.4 Clay 1.87 7.90 1.26‘ — 38.1 26.1 12.0 ~ 0.120 0.72 -2 Bt1 6-20 28.6 32.6 38.8 Clay loam 1.07 7.90 1.50 — 34.9 25.1 9.8 0.098 1.37 -3 Bt2 20-38 22.3 39.0 38.7 Clay loam 0.56 7.90 1.60 — 33.1 24.5 8.6 0.086 1.55 -4 Btb1 38-63 17.1 44.6 38.3 Silty clay loam 0.38 7.90 1.58 - 31.7 23.5 8.2 0.082 2.05 -5 Btb2 63-72 16.2 47.4 36.4 Silty clay loam 0.34 7.90 1 .60 — — — — — — Weighted mean 21.0 40.6 38.4 — 0.68 7.90 1.55 — 33.4 24.4 9.0 0.090 — Profile total-in — — — — -— — — — — — — — 5.69 5.44 Site 5—Sherman, Texas S81TX421-1-1 Ap 0-6 34.4 32.4 33.2 Clay loam 1.70 7.60 1.26‘ — 32.0 21.0 11.0 0.110 0.66 -2 Bt1 6-17 23.8 40.0 36.2 Clay loam 0.86 7.80 1.48 — 31.8 20.9 10.9 0.109 1.20 -3 Bt2 17-27 22.9 37.3 39.8 Clay loam 0.46 7.90 1.56 — 33.1 24.3 8.8 0.088 0.88 -4 Bt3 27-36 34.8 31.6 33.6 Clay loam 0.32 7.90 1.57 — 27.9 19.6 8.3 0.083 0.75 -5 B14 36-44 33.1 31.4 35.5 Clay loam 0.32 7.90 1.47 — 28.5 16.0 12.5 0.125 1.00 -6 Btk 44-72 26.8 33.2 40.0 Clay 0.16 8.00 1.57 21.63 — — — - — Weighted mean 29.0 35.1 36.0 — 0.68 7.83 1.48 — 30.7 20.5 10.2 0.102 - Profile total-in - — — - — - — — — — — — 4.49 6.49 Site 6—Moore, Texas S81TX341~2-1 Ap 0-7 10.5 52.7 36.8 Silty clay loam 1.94 7.90 1.26‘ — 40.7 28.2 12.5 0.125 0.88 -2 Bt1 7-19 9.9 46.6 43.5 Silty clay 1.06 8.00 1.54 — 33.1 24.3 9.4 0.094 1.13 -3 Bt2 19-35 14.0 38.1 47.9 Clay 0.67 8.00 1.62 — 40.5 24.6 15.9 0.159 2.54 -4 Bt3 35-58 13.5 41.8 44.7 Silty clay 0.35 8.00 1.38 — 34.5 22.2 12.3 0.123 2.46 -5 Btk 58-74 16.8 47.5 35.7 Silty clay loam 0.33 7.90 1.75 54.17 — — - — - Weighted mean 12.6 43.6 43.8 — 0.78 7.99 1.46 — 36.7 24.0 12.7 0.127 - Profile total-in — — — — — — - — — — — — 7.01 7.26 Site 7-Hansford, Texas S82TX195-1-1 Ap 0-6 8.3 50.1 41.6 Silty clay 2.14 7.70 1.26‘ - 40.3 27.7 12.6 0.126 0.76 -2 Bt1 6-18 5.6 51.2 43.2 Silty clay 0.97 7.80 1.44 - 37.1 24.5 12.6 0.126 1.51 -3 Bt2 18-26 5.8 53.9 40.3 Silty clay 0.61 7.90 1.53 — 33.9 22.8 11.1 0.111 0.89 -4 Bt3 26-39 9.3 51.9 38.8 Silty clay loam 0.54 7.90 1.39 - 31.3 21.7 9.6 0.096 1.25 -5 Bt4 g 39-53 13.1 44.1 42.8 Silty clay 0.33 8.00 1.44 — 33.6 15.3 18.3 0.183 2.56 -e Btk sa-ve 17.1 48.6 34.3 Silty clay ‘ loam 0.22 8.00 1 .77 45.25 - — — — — Weighted mean 8.8 49.8 41.4 — 0.77 7.88 1.42 — 34.6 21.5 13.1 0.131 — Profile total-in — - — — — — — — - - - — 6.97 8.25 (continued on next page) 17 TABLE 5. CONTINUED Site, county, Water content state, and CaCoa at bars Qtential Sample no. Hor Depth Sand Silt Clay Texture O.M. pH B.D. equiv -1/32 -15 Plant-avail water Adjusted to 60-in in _°/9_ °/o q/cm“ % °/o by volume % in/in l@r depth“ Site 8—Hanslord, Texas S82TX195-2-1 Ap 0-6 8.8 54.6 36.6 Silty clay ~ loam 2.85 7.80 1.26‘ — 40.2 26.9 13.3 0.133 0.80 -2 Bt1 6-20 8.2 52.2 39.6 Silty clay loam 1.22 7.90 1.47 — 36.0 25.6 10.4 0.104 1.46 -3 Bt2 20-37 8.5 51.9 39.6 Silty clay loam 0.80 7.90 1.59 — 34.9 23.9 11.0 0.110 1.87 -4 Ab 37-50 19.0 44.1 36.9 Silty clay loam 0.53 7.90 1.59 - 31.6 19.2 12.4 0.124 1.61 -5 Btb1 50-60 19.7 45.8 34.5 Silty clay loam 0.28 7.80 1.35 — 26.5 15.7 10.8 0.108 1.08 -6 Btb2 60-93 18.6 47.9 33.5 Silty clay loam 0.27 7.80 1.24 — — - — - - Weighted mean 14.7 49.0 36.3 — 0.71 7.84 1.40 — 33.6 22.2 11.4 0.114 - Profile total-in - — - - - — — — — - — - 6.82 6.82 Site 9—Beaver, Oklahoma S81OK4-1-1 Ap o-7 11.9 56.5 31.6 Silty clay loam 2.33 7.70 1.26‘ — 34.0 22.1 11.9 0.119 0.83 -2 Bt1 7-19 9.6 47.2 43.2 Silty clay 1.20 7.80 1.43 — 38.2 24.9 13.3 0.133 1.60 -3 Bt2 19-36 7.7 49.1 43.2 Silty clay 0.65 7.80 1.54 — 36.3 24.6 11.7 0.117 1.99 -4 Ab 3643 8.4 53.2 38.4 Silty clay loam 0.55 7.70 1.42 — 31.3 22.0 9.3 0.093 0.65 -5 Btb1 4359 8.9 52.1 39.0 Silty clay loam 0.58 7.50 1.26 — 30.5 19.3 11.2 0.112 1.79 -6 Btb2 59-72 13.1 46.9 40.0 Silty clay 0.48 7.30 1.14 — — — — — — Weighted mean 9.5 50.2 40.1 - 0.85 7.62 1.35 — 34.2 22.6 11.6 0.116 - Profile total-in - - — — — — - — - — — — 6.86 7.04 Site 10—Ochiltr‘ee, Texas S82TX357-1-1 Ap 0-8 9.3 61.0 29.7 Silty clay loam 3.03 7.50 1.26‘ — 36.1 23.1 13.0 0.130 1.04 -2 Bt1 8-24 6.3 50.2 43.5 Silty clay 1.41 7.50 1.51 - 40.1 26.1 14.0 0.140 2.24 -3 Bt2 24-38 4.9 51.5 43.6 Silty clay 0.89 7.70 1.62 - 38.5 26.9 11.6 0.116 1.62 -4 Ab 38-51 4.1 53.7 42.2 Silty clay 0.85 7.70 1.41 - 35.5 21.0 14.5 0.145 1.89 -5 Btb1 51-63 6.9 55.6 37.5 Silty clay loam 0.68 7.70 1.44 — 31.5 21.3 10.2 0.102 1.22 -6 Btb2 63-76 10.4 51.5 38.1 Silty clay loam 0.57 7.70 1.39 — t — — — — — Weighted mean 6.8 53.3 40.0 — 1.13 7.64 1.46 - 36.6 23.9 12.7 0.127 - Profile total-in — — — — — — — — — — — — 8.01 7.70 Site 11—DalIam, Texas S84TX111-1-1 Ap 0-7 37.3 31.9 30.8 Clay loam 1.61 6.80 1.26‘ - 29.8 19.7 10.1 0.101 0.71 -2 Bt1 7-20 35.4 26.8 37.8 Clay loam 0.70 7.40 1.49 — 32.2 22.2 10.0 0.100 1.30 -3 Bt2 20-32 38.5 22.7 38.8 Clay loam 0.31 7.60 1.45 - 30.7 20.4 10.3 0.103 1.24 -4 B13 32-47 52.2 13.2 34.6 Silty clay loam 0.19 7.80 1.60 — 28.3 23.0 4.7 0.407 0.71 -5 Btk 47-80 51.1 14.5 34.4 Silty clay loam 0.14 8.10 1.62 49.52 — — — — — Weighted mean 41.8 22.1 36.0 — 0.63 7.83 1.48 - 30.2 21.6 8.6 0.086 — Profile total-in — - — - — - - — — — — — 3.96 4.57 ‘Bulk density of the Ap horizon was estimated from values obtained from other studies because this horizon was the loosened tillage layer and core sampling was not possible when the samples were obtained. ZWater contents at the -1/3-bar matric potential were calculated by Equation 1, Table 7, of Unger (1975). “Adjusted to 60-inch depth for all horizons by adding or subtracting plant-available water based on water retention of the horizon above or the horizon occurring at the 60-inch depth. ‘The calcic horizon, when present, was not included in the weighted mean calculations. For water content, weighted means were calculated only to the depth to which data are presented. 18 Y TABLE 6. SAND CONTENT AND SIZE DISTRIBUTION OF THE SAND IN SHERM SOIL Percent of sand retained on standard sieves with openings of (mm) Site, county, Total 0.850 0.425 0.250 0.150 0.106 0.053 & state Hor Depth sand (#20) (#40) (#60) (#100) (#140) (#270) in % % Site 1— Ap O-6 35.2 0.2 5.5 20.4 18.3 23.5 32.1 Hartley, Texas Bt1 6-18 23.6 0.6 6.7 24.2 16.1 21.2 31.2 Bt2 18-28 20.5 2.4 7.2 22.6 14.9 19.5 33.4 Bt3 28-36 26.7 1.0 6.2 24.1 17.5 20.6 30.6 Bt4 36-60 35.8 0.4 4.8 23.1 18.3 22.2 31.2 Btk 60-72 29.9 2.8 5.9 21.7 17.4 22.0 30.2 Weighted mean‘ 31.3 0.8 5.8 23.1 17.2 21.5 31.6 Site 2— Ap 0-7 36.0 0.1 5.4 24.4 17.6 20.7 31.8 Dallam, Texas Bt1 7-17 32.8 0.1 5.4 22.9 17.9 21.8 31.9 Bt2 17-26 43.9 0.3 5.9 27.1 19.1 20.0 27.6 Bt3 26-38 46.0 0.2 10.0 33.5 17.3 16.9 22.1 Ab 38-48 22.0 1.1 7.1 22.5 15.6 19.4 34.3 Btb1 48-60 33.0 0.5 6.8 23.9 15.7 17.0 36.1 Btb2 60-74 40.3 0.3 8.4 31.3 19.4 19.9 20.7 Weighted mean 36.6 0.4 7.2 27.0 17.5 19.2 28.7 Site 3— Ap 0-6 16.8 0.0 1.9 10.7 14.9 24.3 48.2 Moore, Texas Bt1 6-19 12.0 0.2 2.1 11.1 14.1 22.2 50.3 Bt2 19-34 13.9 2.1 3.2 10.4 14.7 23.2 46.4 Bt3 34-54 26.5 0.9 1.8 9.5 16.1 25.9 45.8 Btk 54-72 18.2 1.7 2.3 11.8 17.4 27.5 39.3 Weighted mean 18.4 1.0 2.3 10.3 15.1 24.1 47.3 Site 4— Ap 0-6 22.9 0.1 5.7 18.6 14.2 23.5 37.9 Texas, Oklahoma Bt1 6-20 28.6 0.3 5.0 14.1 10.3 16.2 54.1 Bt2 20-38 22.3 0.6 5.7 15.2 10.8 15.7 52.0 Btb1 38-63 17.1 1.5 5.3 13.2 10.2 14.6 55.2 Btb2 63-72 16.2 1.0 4.8 11.7 9.3 13.4 59.8 Weighted mean 21.0 0.9 5.3 14.1 10.6 15.8 53.3 Site 5- Ap 0-6 34.4 0.4 2.4 13.2 20.7 27.7 35.6 Sherman, Texas Bt1 6-17 23.8 0.4 3.0 11.5 16.5 23.5 45.1 Bt2 17-27 22.9 7.2 6.4 10.3 14.0 23.3 38.8 Bt3 27-36 34.8 5.6 7.5 12.1 15.9 23.8 35.1 Bt4 36-44 33.1 2.1 4.7 13.1 20.5 29.2 30.4 Btk 44-72 26.8 1.0 3.0 11.4 19.3 28.9 36.4 Weighted mean 29.0 3.3 4.9 11.9 17.1 25.1 37.1 Site 6- Ap 0-7 10.5 0.7 1.8 4.0 6.1 17.4 70.0 Moore, Texas Bt1 7-19 9.9 0.0 2.0 5.2 8.1 22.2 62.5 Bt2 19-35 14.0 1.7 2.8 5.6 8.5 22.7 58.7 Bt3 35-58 13.5 2.5 2.9 5.8 8.9 23.4 56.5 Btk 58-74 16.8 2.3 3.1 6.4 9.7 25.7 52.8 Weighted mean 12.6 1.6 2.5 5.3 8.1 21.8 60.6 Site 7— Ap 0-6 8.3 0.0 4.7 8.7 7.7 17.4 61.5 Hansford, Texas Bt1 6-18 5.6 0.7 3.5 6.2 5.2 13.6 70.8 Bt2 18-26 5.8 2.7 6.2 7.9 6.7 14.4 62.1 Bt3 26-39 9.3 3.0 7.9 9.2 7.6 15.6 56.7 Bt4 39-53 13.1 1.6 8.4 10.3 7.7 15.1 56.9 Btk 53-76 17.1 2.5 6.6 10.2 9.5 19.8 51.4 Weighted mean 8.8 1.7 6.4 8.6 7.0 15.0 61.3 Site 8- _ Ap 0-6 8.8 0.0 2.0 4.1 4.3 17.5 72.1 Hansford, Texas i_ Bt1 6-20 8.2 1.1 1.8 2.6 2.5 15.6 76.4 Bt2 20-37 8.5 1.5 2.5 3.8 3.5 17.6 71.1 Ab 37-50 19.0 2.2 2.4 3.4 3.9 20.5 67.6 Btb1 50-60 19.7 1.8 2.5 3.5 3.7 20.1 68.4 Btb2 60-93 18.6 1.2 2.0 3.3 3.3 20.1 70.1 Weighted mean 14.7 1.4 2.2 3.4 3.4 18.9 70.8 (continued on next page) where it was highest in the Ap horizon. Clay content usually was lowest in the Ap horizon, except that it was lowest in the Bt3 at Site 2; Btb2 at Sites 4 and 8; and Btk at Sites 3, 6, and 7. Bulk Density Bulk density of the Ap horizon (plow layer) was not determined because this horizon was loosened by tillage and remained loose at the time of sampling. Other studies, however, have shown that the bulk density of this horizon is highly variable, depending on type and recency of tillage. For this study, a bulk density of 1.26 g/cm“ was assumed for the Ap horizon at all sites (Table 5). This value is the average for the Ap horizon in studies by Taylor et al. (1963), Unger (1969, 1972), and Unger et al. (1973) on Pullman clay loam, which is a similar soil. The assumed value is provided for calculating the available water content of this horizon in a subsequent section. Bulk density of the Btl horizon ranged from 1.41 g/cm“ at Site 3 to 1.58 g/cm3 at Site 2. Densities usually were highest in the Bt2 or Bt3 horizons except at Site 2, where it was highest in the Btb2 horizon (1.69 g/cmi‘), and at Sites 6, 7, and 11 where it was highest in the Btk horizon. Some unusually low bulk densities at horizons other than the Ap were 1.38 g/cm“ in the Bt3 at Site 6; 1.39 g/cm“ in the Bt3 at Site 7; 1.35 and 1.24 g/cms in the Btb1 and Btb2, respectively, at Site 8; 1.26 and 1.14 g/cm“ in the Btb1 and Btb2, respectively, at Site 9; and 1.39 g/cm3 in the Btb2 at Site 10. The low bulk densities in the lower part of the profile suggest that root growth would not be impeded by soil density in these horizons if roots could readily penetrate the horizons above. Bulk densities at the different sites are not high enough to prevent root penetration if the soil water content is adequately high, but some reduc- tion in root penetration may occur. Resistance to root penetration is in- fluenced by soil strength, which is a function of soil bulk density and water content (Taylor and Gardner, 1963). In their study with Amarillo 19 TABLE 6. CONTINUED Percent ot sand retained on standard sieves with openings of (mm) Site, county, Total 0.850 0.425 0.250 0.150 0.106 0.053 8t state Hor Depth sand (#20) (#40) (#60) (#100) (#140) (#270) in °/o °/o Site 9- Ap 0-7 11.9 0.2 1.7 2.5 2.4 9.9 83.3 Beaver, Oklahoma Bt1 7-19 9.6 0.6 1.9 1.7 1.7 8.2 85.9 Bt2 19-36 7.7 3.4 2.9 1.8 1.6 5.6 84.7 Ab 36-43 8.4 4.8 3.5 1.8 1.5 4.8 83.6 Btb1 43-59 8.9 1.7 1.9 1.7 1.8 9.7 83.2 Btb2 59-72 13.1 0.6 1.4 2.0 2.2 12.7 81.1 Weighted mean 9.5 1.9 2.2 1.9 1.8 8.6 83.7 Site 10- Ap 0-8 9.3 0.0 2.4 2.7 2.7 11.9 80.3 Ochiltree, Texas Bt1 8-24 6.3 1.2 1.9 2.0 2.0 10.1 82.8 Bt2 24-38 4.9 2.3 2.9 2.5 2.5 9.3 80.5 Ab 38-51 4.1 8.4 5.7 4.4 2.7 8.3 70.5 Btb1 51-63 6.9 3.9 2.8 2.1 2.2 14.0 75.0 Btb2 63-76 10.4 1.1 1.7 2.2 2.8 16.9 75.3 Weighted mean 6.8 2.9 2.9 2.6 2.5 11.6 77.5 Site 11— Ap 0-7 37.3 0.2 6.1 24.2 17.8 20.2 31.5 Dallam, Texas Bt1 7-20 35.4 0.3 4.0 18.0 18.4 27.0 32.3 Bt2 20-32 38.5 0.9 4.9 22.2 21.1 24.6 26.3 Bt3 32-47 52.2 0.2 5.4 23.8 21.6 25.1 23.9 Btk 47-80 51.1 0.1 5.5 23.4 21.5 25.0 24.5 Weighted mean 37.1 0.5 5.0 21.8 20.0 24.8 28.0 ‘Calic horizons, where present, were not included in calculating the weighted means. fine sandy loam, Taylor and Gard- ner (-1963) showed that some roots penetrated the soil at a bulk density of 1.75 g/cm“ if the soil matric potential was - % bar or higher. For bulk densities equal to or less than 1.65 g/cm“, some root penetration occurred when the matric potential was 3% bar or higher. Resistance to root penetration at similar soil matric potentials and bulk densities may be different in Sherm soils than in Amarillo soils. And the bulk den- sities measured by core samples may be considerably different than those determined on individual soil clods. With core sampling, the bulk densi- ty represents an average density of the sampled volume, which includes the soil and the shrinkage cracks that develop as the soil dries. For in- dividual clods, shrinkage cracks are not included in the sample volume. The density of the clods, therefore, may be considerably higher than those obtained by core sampling and may be high enough to prevent root penetration in some horizons of the soil. 2O Organic Matter Soil organic matter content was highest in the Ap horizon at all sites and usually decreased progressively with soil depth (Table 5). An excep- tion was at Site 2, where the Ab horizon had a higher organic matter content than the Bt2 and Bt3 horizons above it. For the Ap horizon, the organic matter content was lowest at Site 1 (1.45 percent) and next lowest at Site 11 (1.61 per- cent). These sites also had high sand contents in the Ap horizon. High organic matter contents (2.14 to 3.03 percent) were found in the Ap horizon at Sites 7 to 10, all of which had 5O percent or more silt in the Ap horizon. Based on weighted means for the entire profile, organic mat- ter contents ranged from 0.54 per- cent at Site 2 to 1.13 percent at Site 10. A significant positive relationship between soil organic matter and silt content was previously established for Texas soils (Unger, 1975). pH Soil pH (Table 5) varied relative- ly little (s 0.30 pH unit) throughout the profiles at most sites. Exceptions were at Site 2, where the range was 0.40 unit, and at Site 9, where the range was 0.50 unit. In general, there were no consistent trends related to soil depth except at Sites 5, 6, 7, 10, and 11, where pH in- creased with soil depth. The lowest weighted mean pH (7.59) occurred at Site 1. The highest (8.10) and lowest (7.30) pH for a horizon was at Site 11. The soil was mildly to moderate- ly alkaline in all cases (see profile descriptions), which corresponds with pH values of more than 7.0. Although alkaline, the pH is not high enough to suggest that field crops usually grown would be adversely affected. But plants sensitive to alkaline conditions may be affected and, therefore, may require special treatments for good growth. Calcium Carbonate (CaCO3) Equivalent The CaCOa equivalent, which refers to the neutralizing power of the soil material, was determined for calcic horizons in the soil profiles. The CaCOs equivalents ranged from 21.6 percent at Site 5 to 58.5 percent at Site 3. But even soil with such CaCOs equivalents is con- sidered low grade in value for lim- ing purposes (Lawton and Kurtz, 1957). Water Retention Cores were not obtained from the Ap horizon because this horizon was the loosened tillage layer. Therefore, water contents at -1/s and -15 bars matric potentials for this horizon (Table 5) were calculated by equa- tions developed by Unger (1975). The equations are based on the soil bulk density, organic matter con- tent, and clay content of the horizon. The water contents at - l/a-bar matric potential for other horizons were also calculated by the equation of Unger (1975) because values determined for this study were generally lower than expected or previously determined values for this soil. The calculated values should be valid because the correlation coefficients obtained when developing the equations were significant at the 0.1 percent level (Unger, 1975). For other than the Ap horizon, determined values are given for water contents at -15 bars matric potential. The water contents (Table 5) at J/a-bar matric potential are calculated on a volume basis. The -15-bar values on a volume basis were obtained by multiplying the determined values (weight basis) by the soil bulk density. The plant- available water (PAW) contents for the different horizons are the dif- ferences between the J/a-bar and -15-bar values, presented on a percent-by-volume basis. Water con- tents for individual horizons were obtained by multiplying the horizon thickness by the percent PAW. Totals for the profile are summations of the values for individual horizons. Plant-available water contents were determined only for horizons above the calcic horizon or to a depth (horizon change) at or near 60 inches when a calcic horizon was not encountered (Sites 2, 4, 8, 9, and 10). This depth was used because roots of most crops do not penetrate the calcic horizon or extend beyond the 60-inch depth if the calcic horizon is not present. Because of its shallow depth (47 inches), the pro- file at Site 11 had the lowest total PAW storage capacity (3.96 inches). On a weighted mean basis, the storage capacity per inch of soil at Site 11 was also lowest. The highest weighted mean storage capacity per inch of soil was at Site 7. But because of a depth of only 53 inches, total PAW at Site 7 was only 6.97 inches compared with 7.01 and 8.01 inches at Sites 6 and 10, respectively. The last two profiles had greater total water storage capacity because their depths were greater. To obtain a better comparison of water retention-i among profiles, all profiles were adjusted to a 60-inch depth with the assumption that any calcic horizon had a water holding capacity equal to that of the horizon immediately above it. Profile depths greater than 60 inches were disregarded. For profiles adjusted to a 60-inch depth, maximum PAW holding capacity of 8.25 inches occurred at Site 7. The minimum was 4.57 inches at Site 11. Other capacities ranged from 5.44 to 7.70 inches. In general, the higher the sand content, the lower the PAW holding capaci- ty. These results are similar to expec- tations and previous studies (Unger, 1975; Unger and Pringle, 1981). Even though total PAW holding capacities varied from site to site, the results suggest that no major dif- ferences in management are needed to use the soil effectively as a water storage reservoir for crops. First, the values in Table 5 should serve only as a guide because actual amounts of soil water storage and subsequent use by plants are influenced by many factors, and field values seldom cor- respond with laboratory values. Second, crops with well-developed root systems often extract soil water to lower values than the reported -15-bar values. Probably the most important factor with respect to water holding capacity is that the soil be managed so that the storage reservoir is readily refilled with water from precipitation or irriga- tion. This requires that conditions be maintained for effective infiltration of water into the soil. Soil manage- ment is further discussed in a later section. Water Infiltration The results of water infiltration measurements in Table 7 show the amount of water infiltrated at 10 min and at 12 and 20 hrs, and the infiltration rates at times from 10 min to 20 hrs after water application starts. The values presented are the means for one, two, or three deter- minations at each site under varying surface, plow layer, and residue con- ditions. (See remarks, Table 7). Based on individual sets of obser- vations, the amount of water in- filtrated at 10 min was highest at Site 3 (2.04 inches) and lowest at Site 6 (0.38 inch). At 12 hrs, water in- filtrated was highest at Site 6 (12.22 inches) and lowest (1.03 inches) at Site 4. Sites 3 and 6 had the highest (15.66 inches) and lowest (1.41 inches) infiltration, respectively, at 20 hrs. One factor that apparently had a major influence on infiltration was the bulk density of the Ap horizon, which was determined when in- filtration measurements were made (Table 7). At Site 3, where total in- filtration was 15.66 inches at 20 hrs, the bulk density was 1.10 g/cm“. At Site 6, which had the lowest total in- filtration at 20 hrs (1.41 inches), the bulk density was 1.71 g/cm“. Total infiltration at 20 hrs was also low (1.44 inches) at Sites 4 and 7, where the bulk density of the Ap horizon was 1.74 and 1.76 g/cm“, respectively. A close relationship betwen bulk density of the Ap horizon and water infiltration was confirmed by results .of multiple ~regression analyses (Table 8). Total infiltration and in- filtration rate at 10 min and 20 hrs were significantly influenced by bulk density of the Ap horizon, with a ranking of 1 in all cases. Clay and sand contents were also significant- ly related to total infiltration and in- filtration rate at 10 min but not at 20 hrs. Thickness, silt content, and organic matter content of the Ap horizon did not significantly in- fluence infiltration at 10 min or 20 hrs. Characteristics of the Bt1 horizon (other than bulk density determined when infiltration was measured) were not significantly related to total infiltration or infiltration rate, deter- mined by multiple regression analyses (data not shown). But total infiltration and infiltration rate at 10 min were significantly related to organic matter content and bulk density of the Bt2 horizon (Table 8). The effect of silt content was not significant. When silt content was omitted from the analyses, the coef- ficient of correlation for the relation- ship among infiltration, organic matter content, and bulk density was not significant. For the entire profile involving weighted mean values for the different characteristics, neither total infiltration nor infiltration rate at 10 min and at 20 hrs was significantly related to the profile characteristics. For analyses involving only the bulk densities of the Ap and Bt1 horizons as determined when in- filtration was measures, the density of both horizons was significantly 21 TABLE 7. AMOUNT AND RATE OF WATER INFILTRATION AND RELATED DATA FROM SHERM SOILS Soil bulk Cumulative infiltration Infiltration rate density at at Site location, till Bt 10 12 20 10 30 1 2 5 12 20 Remarks &number of observations zone hor min hr hr min min hr hr hr hr hr g/cma in in/hr Site1 Hartley, Texas 3 1.69 1.61 0.75 2.19 2.57 1.80 0.39 0.24 0.18 0.09 0.04 0.04 Tillagepanpresent;no crust; after harvest. 1 1.44 1.52 0.95 4.08 5.76 2.90 0.60 0.30 0.25 0.25 0.20 0.20 Tillage pan fractured by plowing; no crust; preplant. 2 1.62 1.52 1.00 4.34 5.11 2.88 0.85 0.65 0.40 0.25 0.12 0.09 Wheeltrackfurrow;no crust; preplant. Site2v Dallam, Texas 1 1.63 1.43 0.85 3.07 3.43 2.04 0.60 0.25 0.25 0.15 0.06 0.04 Wheeltrackfurrow; no crust; preplant. 2 1.21 1.35 1.47 8.67 10.80 4.32 1.50 0.83 0.70 0.60 0.35 0.27 Unpacked furrow; no crust; preplant. Site3 Moore, Texas 1 1.10 1.54 2.04 6.17 7.20 5.76 1.44 0.90 0.50 0.24 0.15 0.15 Loose surface follow- ing sweep tillage; no crust; preplant. 2 1.10 1.28 1.80 11.90 15.66 6.48 2.56 1.31 1.05 0.74 0.53 0.40 Loose surface follow- ing sweep tillage; no crust; preplant. Site4 Texas, Oklahoma 1 1.70 1.63 1.00 1.70 1.80 2.40 0.72 0.08 0.06 0.02 0.02 0.016 Loose, fluffy surface; tillage pan present at 2-inch depth; no crust; preplant. 2 1.74 1.60 0.60 1.03 1.44 1.26 0.60 0.11 0.07 0.03 0.01 0.008 Loose, fluffy surface; tillage pan present at 2-inch depth; no crust preplant. Site5 Sherman, Texas 1 1.65 1.53 0.84 3.19 3.81 1.80 0.60 0.45 0.25 ‘0.18 0.10 0.08 Wheeltrackfurrow;no crust; after emergence. 2 1.21 1.37 0.96 9.68 12.81 3.30 1.19 0.94 0.90 0.72 0.48 0.35 Unpacked furrow; no tillage pan; no crust; after energence. Site6 Moore, Texas 2 1.10 1.41 1.00 9.77 11.88 4.32 1.60 1.40 1.08 0.74 0.36 0.25 Unpacked furrow; no tillage pan; no crust; before first irrigation. 1 1.71 1.55 0.38 1.25 1.41 0.72 0.16 0.11 0.07 0.05 0.03 0.02 Wheel track furrow; thick crust present. 1 1.57 1.50 1.20 4.08 4.68 2.88 1.08 1.00 0.45 0.16 0.08 0.08 Tillage pan present at 5-inch depth; crust removed; after harvest. 2 1.10 1.43 1.68 12.22 14.11 6.48 3.60 2.52 1.19 0.64 0.33 0.28 Tillage pan disturbed; 22 crust removed; after harvest. TABLE 7. CONTINUED Soil bulk Cumulative infiltration Infiltration rate density at at Site location, till Bt 10 12 20 10 30 1 2 5 12 20 Remarks &number of observations zone hor min hr hr min min hr hr hr hr hr glcm’ in in/hr Site7 Hansford, Texas 1 1.55 1.51 1.00 4.15 5.14 2.88 0.66 0.54 0.36 0.24 0.12 0.12 Unpacked furrow; moist crust present; preplant. 1 1.76 1.56 0.95 1.20 1.44 1.40 0.04 0.04 0.03 0.02 0.02 0.02 Wheel track furrow; moist crust present; preplant. Site8 Hansford, Texas 3 1.64 1.49 1.65 4.19 4.64 2.88 0.96 0.48 0.16 0.09 0.07 0.06 Tillage pan present; wheat stubble, thin crust present; after harvest. 1 1.48 1.53 1.17 6.30 7.53 3.24 1.17 1.06 0.70 0.36 0.16 0.14 Wheatstubbleonsur- face; thin crust pre- sent; after harvest. 2 1.10 1.49 1.78 8.84 10.56 8.22 1.91 1.43 0.81 0.43 0.24 0.22 Tillage pan disturbed; wheat stubble; crust removed; after harvest. Site9 Beaver, Oklahoma 3 1.19 1.37 1.43 10.27 12.75 5.10 2.93 2.04 1.09 0.67 0.31 0.27 Moist,settledsurface; crust removed follow- ing forage sorghum; after harvest. Site 10 Ochiltree, Texas 1 1.52 1.41 1.32 7.27 8.28 5.76 2.02 1.44 0.77 0.43 0.16 0.13 Tillage pan present; wheat stubble; no crust; after harvest. 2 1.66 1.43 1.26 2.91 3.20 2.88 0.42 0.29 0.20 0.13 0.05 0.04 Tillage pan present; wheat stubble; no crust; after harvest. Site11 Dallam, Texas 2 1.65 1.54 0.60 3.24 3.84 1.20 0.50 0.36 0.18 0.12 0.08 0.06 Loose, fluffy surface; tillage pan present; grain sorghum residue on surface. 1 1.41 1.54 0.80 4.80 6.00 1.44 0.60 0.48 0.30 0.25 0.18 0.12 Loose, fluffy surface; moderate tillage pan development. related to total infiltration and in- filtration rate at 2O hrs (Table 9). At 10 min, infiltration was significant- ly related only to the bulk density of the Ap horizon. Lack of effect of most profile con- ditions and major effect of bulk den- sity of the Ap horizon on total water infiltration suggest that management practices that influence the plow layer (Ap horizon) density have a major influence on water infiltration and, consequently, on water storage in the profile. Effects of manage- ment on tillage zone conditions and, subsequently, on bulk density of the Ap and Btl horizon and rate of water infiltration at 2O hrs are shown in Table 10. These results are a sum- mary of the infiltration and related data presented in Table 7. For loose surface soil with residues on the sur- face and the absence of tillage pans or surface crusts, the infiltration rate at 2O hrs ranged from 0.20 to 0.40 inch/hr. Water infiltration rates decreased as soil density increased, surface residues decreased, soil com- paction increased, crusts became evi- dent, and-or tillage pans developed. With severe compaction, for exam- ple, the bulk density of the Ap horizon was 1.73 g/cm“ and the in- 23 TABLE 8. SUMMARY OF MULTIPLE LINEAR REGRESSION ANALYSES ASSOCIATING TOTAL INFILTRATION AND INFILTRATION RATES AT 10 MIN. AND 2O HR. WITH Ap and Bt2 HORIZON CHARACTERISTICS OF SHERM SOIL OBTAINED AT 11 SITES IN TEXAS AND OKLAHOMA. RANKINGS BASED ON STANDARDISED PARTIAL REGRESSION COEFFICIENTS‘ AND LEVELS OF SIGNIFICANCE OF PARTIAL REGRESSION COEFFICIENTS’ BASED ON t-VALUE ARE ALSO SHOWN. Soil horizon and Independent variables“ dependent variable Intercept Sand Silt Clay O.M. BD SE‘ R5 Ap Partial regression coefficients Total infiltration 4.321 -0.0168(2)‘* — -0.0336(3)** — -1.1111(1)*"' 0.265 0.805" in 10 min-in Total infiltration 30.783 — — — — -16.4920(1)** 1.786 0.921“ in 20 hr-in Infiltration rate 18.874 -0.0657(3)** — -0.1309(2)** — -6.4399(1)** 0.834 0.916" in 10 min-in/hr Infiltration rate 0.749 — — — — -0.4165(1)** 5.203 0.899“ at 20 hr-in/hr Bt2 Total infiltration 21.791 — -0.0466(3)NS — 4.6084(1)* -13.6183(2)* 0.215 0.864* in 10 min-in Infiltration rate 86.451 — -0.2169(3)NS — 20.8030 -54.8674(2)* 0.918 0850* in 10 min-in/hr ‘Rankings are shown in parentheses immediately after partial regression coefficients. Rankings in order from 1 (highest) to 3 (lowest). 2Levels of significance of partial regression coefficients are *(0.05), **(0.01), and NS (not significant). These are shown after the rankings. “Independent variables are % sand content, % silt content, % clay content, % organic matter content, and glcm3 bulk density. ‘Standard error of estimate. sCoefficient of correlation. Levels of significance are *(0.05) and **(0.01). filtration rate was only 0.008 to 0.03 inch/hr. The differences in water infiltra- tion rate and amount at the various sites may not be representative of all the fields in the vicinity of the par- ticular sites. The prevailing condi- tions undoubtedly reflect past management on the fields, such as tillage methods, crops grown, and residue management practices. Therefore, farmers should evaluate conditions on their farms and adjust their practices accordingly. For ex- ample, if a plowpan is hindering water infiltration, some type of tillage operation, such as chiseling, deep sweep plowing, or even moldboard plowing, may be re- quired to disrupt the plowpan and improve water infiltration and storage in the soil. IMPLICATIONS FOR MANAGEMENT Plant-Available Water The total amount of PAW re- tained in the soil profile was in- fluenced by depth to the calcic horizon (or horizon change at or 24 near 60 inches) and by the water holding capacity of soil in different horizons. Total amounts ranged from 3.96 inches at Site 11 to 8.01 inches at Site 10 (Table 5). Therefore, a crop could extract about twice as much water from soil at Site 10 as at Site 11, provided both profiles were initially filled to capacity with water and the crop’s roots permeated and extracted water from the entire soil volume to the depth indicated (Table 5). Both con- ditions, however, often are not fulfilled under field conditions at all locations. TABLE 9. SUMMARY OF MULTIPLE LINEAR REGRESSION ANALYSES ASSOCIATING TOTAL INFILTRATION AND INFILTRATION RATES AT 10 MIN AND 20 HR WITH Ap AND Bt1 HORIZON BULK DENSITIES OF SHERM SOILS OBTAINED AT 11 SITES IN TEXAS AND OKLAHOMA. RANKINGS BASED ON STANDARDIZED PARTIAL REGRESSION COEFFICIENTS‘ AND LEVELS OF SIGNIFICANCE OF PARTIAL REGRESSION COEFFICIENTSZ BASED ON t—VALUE ARE ALSO SHOWN. Independent variables“ Dependent variable Intercept BD of Ap BD of Bt1 SE‘ R5 Partial regression coefficients Total infiltration 2.843 -1.1444(1)** — 0.308 0.688“ in 10 min-in Total infiltration 50.901 -12.6183(1)** -17.4180(2)** 1.335 0.959" in 20 hr-in Infiltration rate 13.113 -6.5700(1)** — 1.056 0.847** at 10 min-in/hr Infiltration rate 1.265 -0.3172(2)** -0.4466(2)** 0.043 0.93 ** at 20 hr-in/hr ‘Rankings are shown in parentheses immediately after partial regression coefficients. Rank- ings in order from 1 (highest) to 2 (lowest). zLevels of significance of partial regression coefficients are *(0.05) and * *(0.01). These are shown after the rankings. “Independent variables are g/cm3 bulk density of Ap and Bt1 horizons. ‘Standard error of estimate. sCoefficient of correlation. Level of significance (**) is 0.01. '\ TABLE 10. SUMMARY OF THE EFFECTS OF TILLAGE ZONE CHARACTERISTICS OF SHERM SOILS ON AVERAGE WATER lNFlLTRATlON RATE AT 20 HR. Tillage zone conditions (Tilth) Average in-place bulk AP density Bf Average infiltration rate ' at 2O hr Loose, bulked surface layers with heavy residue on or near soil surface; absence of tillage pans and surface crusts. Loose, bulked surface layers with moderate residue on or near soil surface, and thin, very weak crusts in place. Residual compaction is pre- sent in upper Bt horizon. Settled surface layers with lit- tle residue on or near soil sur- face, and weak crusts in place. Early stages of tillage pan development are evident. Readily discernable compac- tion in the form of wheel track furrows or well-developed tillage pans; with or without loose, bulked surface layers and residue on or near the surface. Readily discernable compac- tion in the form of tillage pans; with or without residue on or near the surface and loosened surfaces. Severe compaction in the form of tillage pans; with or without crusts, residues on or near the surface, and loosened surface layers. 1.15 1.17 1.21 1.29 1 .54 1.61 1.65 1.73 g/cma 1 .32 1 .38 1 .47 1 .54 1.46 1.53 1 .49 1.59 in/hr 0.31-0.40 0.26-0.30 0.20-0.25 0.14-0.15 0.12-0.13 0.08-0.09 0.04-0.06 0.008-0.03 Figre 17. row irrigation through siphon tubes from open ditches. Based on PAW holding capacities (Table 5) and the measured infiltra- tion rates (Table 7), profiles at Sites 2, 3, 5, 6, 8, and 9 could be com- pletely refilled with water (for exam- ple, by irrigation) in less than 12 hrs. But other profiles would not be refilled even at 20 hrs. Under the in- filtration conditions prevailing at 20 hrs, additional time required to refill the profiles would range from about 9 hrs at Site 5 to about 350 hrs at Site 4. In most cases, prolonging the time of irrigation to fill the profile with water is not practical under the prevailing conditions, and the pro- files at some sites normally would not be refilled with water except during prolonged wet periods or oc- casionally with repeated irrigations. Profiles in most cases would contain about 5 inches or more of PAW when irrigated for 20 hrs (or less in some cases) and would, therefore, provide considerable water for plant use, even though some profiles may not be filled to capacity. Root penetration into a soil varies with plant species. Sunflower and wheat roots have grown into and us- ed water from the calcic horizon from Pullman clay loam at Bushland. In contrast, sorghum generally uses water from only the upper 4 ft of the soil, thus not fully using all available water when the depth to the calcic horizon is more than 4 ft (Unger and Pringle, 1981). The Pullman soil is similar to the Sherm soil, especially at sites where a calcic horizon is present, and root penetration probably would be similar on both soils. Therefore, even though there are differences. in water-holding capacity and soil depth at the different sites, the management required (for example, irrigation frequency) to obtain similar yields with a given amount of water may be nearly identical at all sites, at least for crops that do not root deeply. The water application rate, however, may need to be varied because of infiltration rate differences. Crops that root deeply, tolerate stress, and deplete soil water to low levels would probably per- form well on dryland and would re- quire less frequent irrigation (if ir- rigated) than crops that root less deeply, are sensitive to stress, and fail to extract all PAW. Marked dif- 25 ferences in water extraction by sunflower and grain sorghum have occurred on Pullman soil at Bushland. When grown on adjacent fallowed plots, sunflower extracted more water from the soil at all depths than sorghum (Unger and Pringle, 1981). Similar differences would probably occur on Sherm soils. Water Application F urrow irrigation (Figures 13, 17) is widely practiced on Sherm soils, commonly with furrow lengths of one-half mile. Because of the generally low infiltration rates, it is widely believed that deep percola- tion of water is slight on this soil. But infiltration measurements at the various sites (Table 7) suggest that considerable deep percolation may be occurring at some sites, even when settings are only 12 hrs. Con- sequently, irrigation requires a knowledge of amount of water ap- plied and soil water storage capaci- ty to make efficient use of the water. Deep percolation should be avoided. To evaluate irrigation practices, assistance is available through the water conservation districts and the Soil Conservation Service (Figure 18). Where excessive deep percola- tion is a problem under furrow- irrigated conditions, irrigation sets . ~ may need to be shortened. Other Figure, 19. View of a surge irrigation system. alternatives are to use higher flow Figure 18. Equipment used by Water Conservation District and Soil Con- servation Service personnel to evaluate irrigation systems. . w Figure 20. Low pressure center-pivot Figure 21. Low pressure irrigation system on furrow-diked and open-furrow irrigation system. land. Note runoff in open furrows. 26 rates per furrow with shorter irriga- tion sets, smooth furrow bottoms for more rapid water advance, or use the surge-irrigation system (Figure 19) that has been evaluated recently in the region. Further water savings can be achieved by using pipes rather than open ditches to convey the water to the irrigation furrows. On sites where the infiltration rate is low, tailwater runoff may be high from furrow irrigation unless cut- back flow rates are used. Some of the tailwater can be recycled through recovery systems, but building the systems and pumping more water adds to production ‘costs. Pumping costs are higher for sprinkler systems than for furrow ir- rigation because of the extra head re- quired to pressurize the system. But labor requirements for sprinkler systems, such as center-pivot systems, are lower than for furrow- irrigation systems. The water can also be applied with sprinklers at rates comparable to infiltration rates. In an ideally designed sprinkler system, the water should be applied at a rate slightly less than the infiltration rate. This minimizes the potential for water collecting on the surface and, therefore, water losses by runoff. High-pressure sprinkler systems apply water over a relatively large area, minimizing runoff problems. But these systems are energy inten- sive and may result in high evaporative losses of water from the falling droplets or fine spray. Low- pressure sprinklers require less energy but apply water over a smaller area (Figure 20). Evaporative losses of water should be lower, but runoff losses could be higher unless special provisions are made to reduce runoff. Lyle (1979) controlled runoff and used water ef- ficiently with a low-pressure, preci- sion water application system used with furrow dikes (Figure 21). Another possibility would be to add booms with attached nozzles at right angles to the main frame of the sprinkler system, thus applying water to a larger area at the same time. Water Infiltration Variation The data in Table 7 show more than a five fold variation among the observations in total water infiltra- tion at 1O min and even greater dif- ference in infiltration rates at dif- ferent times. This variation seemed to be most closely related to bulk density of the Ap horizons, but total water infiltration and infiltration rates also varied considerably among measurements within some sites. Such variation resulted from local conditions, such as a surface crust, compaction, and possibly soil crack- ing, and suggests that water behavior on a given field near the sampling sites may differ con- siderably from that indicated by the data in Table 7. Where infiltration is much lower than expected, a compacted zone such as a plow pan may have developed in the soil. Deeper than normal plowing or chiseling while the soil is relatively dry is a possible remedy for overcoming infiltration problems associated with compacted soil layers. Another possible remedy is the use of reduced- or no-tillage cropping systems, which minimize soil compaction because of less traf- fic across the field, increase infiltra- tion because of surface protection af- forded by crop residues (Figure 22), and improve soil conditions because Figure 22. Crop residues maintained on the soil surface are conducive to rapid Water infiltration. F i gu re 23 . Grain storage eleva tor. of decaying plant roots (with no- tillage system). Based on the measurements, large variations in in- filtration are possible at all sites on Sherm soil. Where problems are suspected, appropriate corrective measures should be taken to increase infiltration where it is too low or decrease it where deep percolation occurs. Crop Sequences Wheat, grain sorghum, corn, sunflower, sugarbeets, alfalfa, and some vegetable crops, such as potatoes (Solanum tuberosum) and onions (Allium cepa), are adapatable and grown throughout some part or the entire area of Sherm soils. Much of the grain produced in the region is stored in elevators (Figure 23), then transported to area feedlots (Figure 24) or seaports for export to foreign countries. Whether the crops are grown continuously or in rota- tions depends on such factors as crop prices; water availability; fertilizer cost and availability; weed, insect, and disease problems; and the pro- ducers’ preferences. When irrigated crops that do not root deeply are grown continuously, some water 27 Service photo). generally moves beyond the depth of plant rooting and, therefore, reduces water use efficiency for crop produc- tion. Unless a deep-rooted crop is subsequently grown, this water may be lost for crop production unless it eventually reaches the aquifer from which it could be pumped again. Water losses from deep percola- tion can be minimized by growing deep-rooted crops in rotation with shallower-rooted crops. The effec- tiveness of deep-rooted crops for ex- tracting water from deep in the pro- files is enhanced when these crops are‘ grown without irrigation or with a limited amount of irrigation. In either case, adequate water must be available throughout the profile so that roo_t growth is not restricted by a dry zone of soil. With water available to a 6-ft depth of Pullman soil at Bushland, dryland grain sorghum used water mainly to a 3-ft depth and only a slight amount from the fourth foot of soil in some years (Unger and Wiese, 1979). In contrast, wheat on dryland used water to, a G-ft depth (Iohnson and Davis, 1980), sunflower with limited irrigation used water to a lO-ft depth (Unger, 1978a), and alfalfa used water to a 15-ft depth (Mathers et al. , 1975) on Pullman soil when water was available to these depths. Similar responses are expected for these crops on Sherm soils. Tillage and Cropping Practices Concern about the steady decline of the water level in the Ogallala 28 by O.R. ]ones, USDA-ABS). Figure 24. Catt n feedlots consume much of the grain produced on Sherm soilsj (DA-Soiy/Conervatin Figure 25. Conervation bench terraces uniformly itribute collected runoff Water on the leveled bench portion of the terrace system (photo provided x7 Figure 26. Water retained on a furrdW-blocked field following 2 inches of rain (photo provided by O.R. jones, USDA-ABS). enhanced by lack of residue. Z2“ . igure27. The amount of sidue produced dyIand grain sorghum 0n Sherm soil generally is low. Note presence of thick surface crust which is Figure 28. Te amount of residue produce; by dyland Winter Wheat on Sherm soil generally is Io Figure 29 .1 .¢- ‘ '. *4 ' , . I 4 I . I r- 4 " .‘ I‘ u‘ a i. 1 a; ? w; . W rvest of irrigated Win ter Whea t. Aquifer, which supplies water to ir- rigate Sherm soils, and rising energy costs, have caused emphasis on con- servation of irrigation water and in- creased the emphasis on conservation and use of precipitation for crop pro- duction. Studies conducted on Pullman soils, which are very similar to Sherm soils, can aid in understan- ding the effects of conservation prac- tices on Sherm soils. Under dryland conditions, more water from precipitation was con- served and grain yields were higher where stubble mulch tillage was us- ed instead of one-way disk tillage in continuous wheat or wheat-fallow cropping systems (Johnson and Davis, 1972). Other practices that have conserved water and increased crop yields on dryland are conserva- tion bench terraces (Figure 25) and level bench terraces (Jones, 1975; Jones and Hauser, 1975); narrow benches, narrow conservation ben- ches, and large contour furrows (Jones, 1981); and furrow blocking (Clark and Hudspeth, 1976; Clark and Jones, 1981) (Figure 26). These practices retained potential runoff water where it fell or retained it on a portion of the field, thus increas- ing the amount of water available for crop use. Little benefit was ob- tained with respect to reduced evaporation because the residues produced by dryland crops (Figure 27, 28) generally were not adequate to greatly reduce evaporation, even when all residues were maintained on the surface in no-tillage systems (Army et al. , 1961; Wiese and Army, 1958; Wiese et. al., 1960, 1967). In contrast to the lack of response to surface residues for increasing water storage from precipitation in no-tillage systems on dryland, major increases in water storage were ob- tained when residues from irrigated wheat (Figure 29) were managed on the surface with no-tillage systems compared to working residues into soil with tillage (Musick et al. , 1977; Unger et al., 1971; Unger and Wiese, 1979). The additional stored water decreased the amount of ir- rigation water needed for irrigated grain sorghum (Musick et al., 1977) and resulted in good growth (Figure 30) and yields of dryland grain sorghum (Unger and Wiese, 1979). In a controlled-residue-level study, 29 l 30. An excellent dryland grain rm crop 0n land Where residues from evious irrigated Winter Wheat crop naintained 0n the soil surface by no- methods. water storage during fallow and subsequent grain sorghum yields in- creased as surface residues (wheat) increased from 0 t0 about 11,000 lbs per acre (Unger, 1978b). Dryland wheat often yields only about 1,500 to 2,500 lbs of residue per acre at Bushland. In contrast, irrigated wheat often yields 4,000 to 6,000 lbs of residue per acre; amounts of 10,000 or more pounds per acre have been obtained in some years (Unger, 1977; Unger et al., 1971). The residue amounts produced by irrigated wheat are in the range that substantially increased water storage and grain sorghum yields (Unger, 1978b). Therefore, residues from crops, such as irrigated wheat, are a resource that can be managed to increase water use efficiency for crop production on Pullman soil and, by inference, on Sherm soils. The benefits from surface residues result from greater total infiltration and less evaporation of water. Because of their greater water storage capacity, profiles at Sites 1, 6, 7, 8, 9, and 10 may derive greater benefits from surface residues than those at Sites 2, 3, 4, 5, and 11. Soils with less storage capacity are more readily filled with water because less water is required, provided water in- 30 filtration rates are sufficiently high. The greater response to surface residues on Pullman soils at a deep site at Bushland compared with that at a shallower site near Lubbock was verified by Baumhardt (1980), who compared the effects of disk and no- tillage after wheat on water storage during fallow and subsequent growth and yield of grain sorghum. Because rainfall essentially filled the low-capacity profile with water with both tillage methods near Lubbock, sorghum yields were n'ot significantly different because of tillage. At Bushland, where the storage capaci- ty was greater, no-tillage significant- ly increased grain yields of sorghum over yields with disk tillage when the sorghum was not irrigated. With ir- rigation, sorghum yields were similar with both tillage treatments. A benefit from lower evaporation with surface residues is the prolong- ed time that the surface layer re- mains wet enough to beneficially in- fluence seed germination. Whereas rapid decreases in surface soil water content from evaporation may cause poor germination on relatively smooth bare soil, the slower evaporation on mulched soils may result in favorable germination of crops. Ranching and Livestock Production Ranching and livestock produc- tion are important agricultural enterprises on the High Plains. Native grassland on Sherm soils covers about 110,000 acres, or 9 per- cent of their total land area. Most ranches are cow-calf operations, though stocker steers make up a significant percentage of many herds (Figure 31). Usually, these stocker cattle are placed in nearby feedlots for finishing. On many ranches, the forage pro- duced on rangeland is supplemented by crop stubble (Figure 32) and small grain. In winter, the native forage is often supplemented with protein concentrate. Creep feeding of calves and yearlings to increase market weight is practiced on some ranches. The native vegetation in many parts of the area has been greatly depleted by continued excessive use (Figure 33). Forage production now may be less than half of the original production. Range productivity can be increased by using management practices that are effective for specific kinds of soils and range sites. Where climate and topography are similar, differences in the kind and amount of climax vegetation produced on rangeland are related closely to the kind of soil. Effective management is based on the rela- tionships among soils, vegetation, and water. The typical vegetation and the ex- pected percentage of each species of the composition of the climax plant community on a typical clay loam range site are given in Tabled 11. The potential total annual produc- tion of vegetation in favorable, nor- mal, and unfavorable years is about 2,000, 1,500, and 1,000 or less pounds of dry matter per acre, respectively. In addition to knowing soil pro- perties and the climax plant com- munity, range management requires evaluating the present condition of the range vegetation in relation to its production potential. Range condi- tion on a particular range site is determined by comparing the pre- sent plant community with the climax plant community for the site. The more closely the existing com- munity resembles the climax com- munity, the better the range condi- tion (Figure 34). The objective in range management generally is to control grazing so that plants grow- ing on a site are similar in type and percentage composition to the climax plant community for that site. Such management generally results in the maximum production of vegetation, conservation of water, and control of erosion. But sometimes a range con- dition somewhatbelow the climax meets grazing needs, provides desirable wildlife habitat, and pro- tects soil and water resources. The major management concern on most rangeland is to control graz- ing so that the types and percentages of plants that make up the climax plant community can become re- established. Controlling brush and minimizing soil erosion by wind are also important management con- cerns. Aids to good range manage- ment include adequate fencing so that different tracts can be grazed on % Figure 33. A heavily grazed rangeland site. a rotation basis and strategic posi- tioning of water (Figure 35) and mineral supplement sources so that the livestock will visit different parts of the tracts during their daily quest for forage, water, and minerals (Merrill, 1983). If sound range management based on soil informa- tion and rangeland inventories is ap- plied, the potential is good for in- creasing the productivity of rangelands. SUMMARY With a land area of 1.3 million acres, Sherm soils are among the ma- jor arable soils in Texas. A small area of Sherm soils also occurs in Oklahoma. The area of Sherm soils is bounded by the breaks above the North CanadianlgRiver on the north, the caprock escarpment of the Cana- dian River on the south, the caprock escarpment at the High Plains- Rolling Plains boundary on the east, and a catena of loamy soils extending from Kerrick to near Channing on the west. Sherm soils occupy about 75 percent of the land within this X Figure 34. Cattle 0n a Well-managed rangeland si igure 31. Stocker cattle at a Water source on Sliermsoil. Figure 32. Stubble from if summer crops provds some forage during Win ter months for cattle grazing on adjacent Wheat pastures. .~'\ te on Sherm soil. (USDA-Soil Conservation Service photo). area. The remaining area is com- posed of soils mainly associated with the playa lakes that are found throughout the area. About 89 percent of the Sherm soil area is cropland, 9 percent is rangeland, and the remainder is in roads, towns, and other non- agricultural uses. Irrigation is used on about 7O percent of the cropland area. Major crops are wheat, grain sorghum, and corn. To determine the variability of soil characteristics, Sherm soils were sampled at l1 widely separated loca- tions. The profiles were described in the field at sampling time, and samples were analyzed in the laboratory for sand, silt, and clay content; organic matter content; pH; bulk density; CaCOs equivalent; and water retention. Plant-available water was calculated from horizon thickness, bulk density, and water retention values. Water infiltration was measured at the sampling sites. The thickness of the profiles was highly variable, ranging from a depth of 44 inches to a calcic horizon at Site 5 in Sherman County, Texas, to 93 inches without reaching a calcic horizon at Site 8 in Hansford County, Texas. Depth to the calcic horizon, where present, ranged from about 44 to about 6O inches. In general, the profiles had less sand and more silt and clay in the eastern province than in the central and western provinces. Associated with the higher silt and clay contents were Figure 35. Sratic positioning of we sources plays an important part in effecz utilitza tion of range grasses. 31 TABLE 11. TYPICAL VEGETATION ON SHERM SOILS (CLAY LOAM RANGE SITE) Plant name Percentage of annual Common Scientific production of dry matter Blue grama Bouteloua gracilis 40 Buffalograss Buch/oe dactyloides 25 Sideoats grama Western wheatgrass Vine-mesquite Silver bluestem Tbbosa Other perennial grasses — Perennial forbs — Bouteloua curtipendula Agropyron smithii Panicum obtusum Andropogon saccharoides Hilaria mutica UIUIUIUIUIUIUI higher mean water retention values, which generally resulted in a greater capacity to store plant available water. Total water infiltration and in- filtration rates at 10 min were highly variable and seemed more closely related to bulk density of the Ap horizon at the time of making the infiltration measurements than to any other determined profile characteristic. Total infiltration at 20 hrs ranged from 1.41 inches at Site 6 in Moore County, Texas, to 15.66 inches at Site 3, also in Moore County. The low total infiltration in 20 hrs resulted from low infiltration rates from '1 to 20 hrs after applying water, and probably resulted from past management in the field. Other fields in the vicinity may not have such low infiltration. Various measurements indicated that about 24 or fewer hours of water application would provide the profile with 5 inches of water at most sites; more time would be needed at others. The profile has capacity for greater storage at some sites, but from about 5 to 125 more hours would be needed to storeeach addi- tional inch of water. Applying ir- rigation water for more than 24 hrs is not practical because tailwater runoff losses become excessive. Also, crops such as grain sorghum do not use water from below about 4 ft in Pullman soil, which is a soil similar in many aspects to the Sherm soil. Therefore, unless deep-rooting crops such as sunflower, wheat, or alfalfa are grown, complete filling of the profile with water may not be desirable. When crops such as sorghum fail to use water from deep in the profile, a rotation involving a 32 deeper-rooted crop can result in more efficient use of water by extrac- ting some of the deeply stored water, provided the soil throughout the pro- file contains adequate water for root growth. At some sites, the measurements suggest that deep per- colation of water may be a problem. In such cases, management practices that minimize deep percolation should be adopted. Because of declining supplies of water for irrigation, water conserva- tion has received considerable atten- tion in recent years. Practices that conserve water from rainfall, such as conservation-bench and level-bench terraces, contour furrows, blocked furrows, and the limited- and no- tillage systems, are applicable to Sherm soils. These practices conserve water by reducing runoff, increasing infiltration, or reducing evapora- tion. Crop yields have been increas- ed where these practices were used on Pullman soils and should give similar results on Sherm soils. Prac- tices for conserving irrigation water include improved water application techniques, tailwater recovery systems, and no-tillage farming. REFERENCES Army, T. J.; Wiese, A. F.; Hanks, R. J. 1961. Effect of tillage and chemical weed con- trol practices on soil moisture losses dur- ing the fallow period. Soil Sci. Soc. Am. Proc. 25:410-413. Baumhardt, Roland Louis. 1980. Influence of tillage and irrigation on grain sorghum production. Lubbock, Texas: Texas Tech Univ. Thesis. Clark, R. N.; Hudspeth, E. B. 1976. Runoff control for summer crop production in the Southern Plains. Trans. Am. Soc. Agric. Eng. Paper No. 76-2008. Clark, R. N.; Jones, O. R. 1981. Furrow dams for conserving rainwater in a semiarid climate. Proc. Crop Production with Con- servation in the 80’s. Chicago, Ill. Am. Soc. Agric. Eng.; December 1980: 198-206. Day, Paul R. 1965. Particle fractionation and particle-size analysis. A. Black ed. Methods of Soil Analysis, Part I. Agron. 9:545-567. Ezekiel, Mordecai; Fox, Karl A. 1959. Methods of correlation and regression analysis. 3rd ed. New York: John Wiley & Sons, Inc. Haise, Howard R.; Donnan, William W.; Phelan, John T.; Lawhon, Lester F .; Shockley, Dell G. 1956. The use of cylinder infiltration to determine intake characteristics of irrigated soils. U.S. Dept. Agric., ARS and SCS, ARS-41-7. Available from: U.S. Government Prin- ting Office, Washington, D.C. Jackson, M. L. 1958. Organic matter deter- mination for soils. Soil Chemical Analysis. Englewood Cliffs, N.J.: Prentice-Hall, Inc.: 205-226. Johnson, Wendell C.; Davis, Ronald G. 1972. Research on stubble-mulch farming of winter wheat. U.S. Dept. Agric.-Agric. Res. Serv. Conserv. Res. Rpt. No. 16. 32 p. Available from: U.S. Government Printing Office, Washington, D.C. Johnson, Wendell C.; Davis, Ronald G. 1980. Yield-water relationships of summer- fallowed winter Wheat. U.S. Dept. Agric., Sci. Educ. Admin., Agric. Res. Results ARR-S-5. 43 p. Jones, Ordie R. 1975. Yields and water-use efficiencies of dryland winter wheat and grain sorghum production systems in the Southern High Plains. Soil Sci. Soc. Am. Proc. 39:98-103. 4 Jones, Ordie R. 1981.“ Land forming effects on dryland sorghum production in the Southern Great Plains. Soil Sci. Soc. Am. J. 45:606-611. Jones, O. R.; Hauser, V. L. 1975. Runoff utilization for grain production. Proc. Water Harv. Symp., Phoenix, Ariz., March 1974. U.S. Dept. Agric., Agric. Res. Serv. W-22. p. 277-283. Lawton, K.; Kurtz, L. T. 1957. Alfred Stef- ferud ed. Soil, the 1957 Yearbook of Agriculture. 184-193. U. S. Dept. Agric. U.S. Govt. Printing Office, Washington, D.C. Lyle, William M. 1979. Low energy precision water application system. Proc. Crop Prod. and Util. Symp., Amarillo, Texas, February 1979: F1-5. Mathers, A. C.; Stewart, B. A.; Blair, Betty. 1975. Nitrate-nitrogen removal from soil profiles by alfalfa. J. Environ. Qual. 4z403-405. Merrill, John. 1983. The XXX Ranch: Manag- ing range for ecology and economy. Jack Hayes ed. Using Our Natural Resources, 1983 Yearbook of Agric. Washington, D.C.: U.S. Gov’t Printing Office: 86-95. Musick, J. T.; Wiese, A. F.; Allen, R. R. 1977. Management of bed-furrow ir- rigated soil with limited- and no-tillage systems. Trans. Am. Soc. Agric. Eng. 20:666-672. d SCS (Soil Conservation Service). 1975a. Soil Survey of Moore County, Texas. U.S. Dept. Agric. Available from: U.S. Government Printing Office, Washington, D.C. SCS (Soil Conservation Service). 1975b. Soil Survey of Sherman County, Texas. U.S. Dept. Agric. Available from: U.S. Government Printing Office, Washington, D.C. Steel, Robert G. D.; Torrie, Iames H. 1960. Principles and Procedures of Statistics with Special Reference to the Biological Sciences. New York: McGraw-Hill Book Co. Taylor, Howard M.; Gardner, Herbert R. 1963. Penetration of cotton seedling tap roots as influenced by bulk density, moisture content, and strength of soil. Soil Sci. 96:153-156. Taylor, Howard M.; Van Doren, C. E.; God- frey, Curtis L.; Coover, Iames R. 1963. Soils of the Southwestern Great Plains Field Station. Texas Agric. Exp. Stn. Misc. Pub. No. 669. 14 p. Texas Dept. of Agric. 1982. Texas county statistics. Texas Dept. Agric., Bull. No. 214. Austin, Texas. Unger, Paul W. 1969. Physical properties of Pullman silty clay loam as affected by dryland wheat management practices. Texas Agric. Exp. Stn. Misc. Pub. No. 933. 1O p. Unger, Paul W. 1972. Dryland winter wheat and grain sorghum cropping systems— Northern High Plains of Texas. Texas Agric. Exp. Stn. Bul. No. 1126. 2O p. Unger, Paul W. 1975. Relationships between water retention, texture, density, and organic matter content of West and South Central Texas soils. Texas Agric. Exp. Stn. Misc. Pub. No. 1192C. 2O p. Unger, Paul W. 1977. Tillage effects on winter wheat production where the ir- rigated and dryland crops are alternated. Agron. I. 69:944-950. Unger, Paul W. 1978a. Effect of irrigation frequency and timing on sunflower growth and yield. Proc. 8th Int. Sunflower Conf., Iuly 1978, Minneapolis, Minn.: 117-129. Unger, Paul W. 1978b. Straw-mulch rate ef- fect on soil water storage and sorghum yield. Soil Sci. Soc. Am. I. 42:486-491. Unger, Paul W.; Allen, Ronald R‘; Parker, Iessie I. 1973. Cultural practices for ir- rigated winter wheat production. Soil Sci. Soc. Am. Proc. 30:437-442. Unger, Paul W.; Allen, Ronald R.; Wiese, Allen F. 1971. Tillage and herbicides for surface residue maintenance, weed con- trol, and water conservation. I. Soil Water Conserv. 26:147-150. Unger, Paul W.; Pringle, Fred B. 1981. Pullman soils: Distribution, importance, variability, and management. Texas Agric. Exp. Stn. Bull. No. 1372. 24 p. Unger, Paul W.; Wiese, Allen F. 1979. Managing irrigated winter wheat residues for water storage and subsequent dryland grain sorghum production. Soil Sci. Soc. Am. I. 43:582-588. U.S. Dept. of Agric. 1955. Typical water- holding capacities of different-textured soils. Alfred Stefferud ed. Water, The Yearbook of Agric., 1955: 120. Available from: U.S. Government Printing Office, Washington, D.C. Wiese, A.F.; Army, T.I. 1958. Effect of tillage and chemical weed control prac- tices on soil moisture storage and losses. Agron. I. 50:465-468. Wiese, A. F.; Bond, I. I.; Army, T. I. 1960. Chemical fallow in dryland cropping se- quences. Weeds 8:284-290. Wiese, A. F.; Burnett, Earl; Box, I. E., Ir. 1967. Chemical fallow in dryland crop- ping sequences. Agron. I. 59:175-177. 33 Mention of a trademark or a proprietary product does not constitute a guarantee or a warranty of the product by The Texas Agricultural Experiment Station or the United States Department of Agriculture and does not imply its approval to the exclusion of other products that also may be suitable. All programs and information of The Texas Agricultural Experiment Station and the United States Department of Agriculture are available to everyone without regard to color, race, religion, sex, age, national origin, or handicap. 2M—3-86