. 7 September 1981 57 3 it "c152 T $5“ [Myla- PULLMAN SO A z Distribution, Importance, ariabilitv S1 Management The Texas Agricultural Experiment Station, Neville P. Clarke, Director, College Station, Texas in cooperation with United States Department of Agriculture, Agricultural Research Service and Soil Conservation Service Contents AUTHORS Paul W. Unger, soil scientist, USDA, ARS, Conservation and Production Research Laboratory, Bushland. Fred B. Pringle, soil scientist, USDA, Soil Conservation Service, Amarillo. Summary i Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l Area occupied by Pullman soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l History of the Pullman series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Physiography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Uses and importance of Pullman soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Typical site for Pullman soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Present water management systems . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Objectives of the study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Experimental Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8. Site selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Sampling sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Sampling techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Sample preparation and analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Results and Dicussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l0 Profile descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . lO Particle size distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l3 Organic matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l5 Bulk density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l5 Water retention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Water infiltration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l6 Implications for Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Plant available water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l7 Water application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Water infiltration variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Crop sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Tillage and cropping practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l9 Ranching and livestock production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2O Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 G fi Cover photo: The picture on the cover shows wheat being harvested on Pullman clay loam. The landform is typical of the expansive areas of this soil 0n the Texas High Plains (USDA —— Soil Conservation Service photo SUMMARY Pullman soils are the most extensive arable soils in Texas, covering 3.8 million acres. The area of Pullman soils in Texas is bounded by the New Mexico-Texas state line 0n the west, the Canadian River 0n the north, and the caprock escarpment at the High Plains-Rolling Plains boundary on the east. A catena of loamy soils extending from F arwell to near Lubbock forms the southwest boundary. Pullman soils occupy about 75 percent of the land in this area. The remaining area is composed of soils mainly associated with playa lakes that are found throughout the area.‘ About 56 percent of the Pullman soil area is cropland, 4O percent is rangeland, and the remainder is in roads, towns, and other non-agricultural uses. Irrigation is used on 53 percent of the cropland area. Major crops are wheat, grain sorghum, cotton, and corn. To determine the variability of soil characteristics, Pullman soils were sampled at seven widely separated locations. 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; 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 profile above the calcic horizon was greater in the northern province than in the central province, which in turn was greater than in the southwestern province. Depth to the calcic horizon ranged from 4O to 59 inches. In general, the profiles had less sand and more silt and clay in the northern province than in the central and southwestern provinces. Associated with the higher silt and clay contents were higher mean water retention values, which, along with the deeper profiles, resulted in greater capacity to store plant available water in profiles in the northern province. Total water infiltration and infiltration rates at 1O minutes generally were higher in the sandier southwestern province than in the northern province. Total infiltration at 2O hours ranged from 4.12 to 4.90 inches, except at Site 7 in the southwestern province where it was only 3.18 inches. This low total infiltration in 2O hours resulted from low infiltration rates for the period from l to 2O hours after applying water. Based on the results of the various measurements, indications are that about 24 hours of water application is needed to fill the profile with water in the southwestern province. The profile has capacity for greater storage in the northern province, but from 8 to 25 more hours would be needed to store each extra inch of water. Applying irrigation water for more than 24 hours is not practical because tailwater runoff losses become excessive. Also, crops such as grain sorghum do not use water from below about 4 feet in Pullman soil. Therefore, unless deeper-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 deeper-rooted crop can result in more efficient use of water by extracting some of the deeply-stored water, provided the soil throughout the profile contains adequate water for root growth. Because of declining supplies of water for irrigation, water conservation has received considerable attention 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 applica- ble to Pullman soils. These practices conserve water by reducing runoff, increasing infiltration, or reducing evaporation. Crop yields have been in- creased where these practices were used on Pullman soils. Practices for conserving irrigation water include improved water application techniques, tailwater recovery systems, and no-tillage farming. l nuuw somuuw urscona nun: noun mncm nouns nnmuu man»: mrru cusou on nntnll “m...” - DALI. Wm” m. 4;}; i I m: i 1 l I 5'" WING! I mscoc mu. 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' l . | . 4T._ __T_.l' ;__._l_l1,_, . \ ‘ : l '~ l k ‘kwm i unborn "W" mu N \‘- ,)b_._'-L!_-—L use zoo \/ sun ,/ . __--n ‘ ‘ ‘ l L“? l! IIIDALCO L.‘ APPROXIMATE SCALE ' MILES \ n a..,,_..l.__ TABLE 1. BASE COMPILED FROM USGS NATIONAL ATLAS, 1'70 EDlTlON Figure I. Counties of Texas in which Pullman soils have been mapped are within the heavy-lined area. CLASSIFICATION OF SOILS MENTIONED IN THE TEXT AND FIGURES Series Acuff Amarillo Berda Bippus Drake Estacado Houston Black Lipan Lofton Mansker Mobeetie Olton Potter Pullman RandaH Richfield Sherm Classification mixed, thermic Aridic Paleustolls mixed, thermic Aridic Paleustalfs mixed, thermic Aridic Ustochrepts mixed, thermic Cumulic Haplustolls Fine-loamy, mixed (calcareous), thermic Typic Ustorthents Fine-loamy, mixed, thermic Calciorthidic Paleustolls Fine, montmorillonitic, thermic Udic Pellusterts Fine, montmorillonitic, thermic Entic Pellusterts Fine, mixed, thermic Vertic Argiustolls Fine-loamy, carbonatic, thermic Calciorthidic Paleustolls Coarse-loamy, mixed, thermic Aridic Ustochrepts Fine, mixed, thermic Aridic Paleustolls Loamy, carbonatic, thermic, shallow Ustollic Calciorthids Fine, mixed, thermic Torrertic Paleustolls Fine, montmorillonitic, thermic Udic Pellusterts Fine, montmorillonitic, mesic Aridic Argiustolls Fine, mixed, mesic Torrertic Paleustolls Fine-loamy, Fine-loamy, Fine-loamy, Fine-loamy, T‘ Pullman Soils: Distribution, Importance, Variability, and Management Paul W. Unger and Fred B. Pringle INTRODUCTION o K L A H O M A AFEH OCCUPTGd by Pullman SOllS DALLAM lSHERMAN lHANSFORD luclllllnrr lurscoma Pullman soilsl occupy parts of 21 l ‘Shallow Tl‘ E X A $ lOKWIylOH l F°""l' counties in the High Plains of Texas l l l l (Fig. 1, 2). The portions of diilerent l l l l "*"'“"“°H "so counties occupied by Pullman soil _______D1"E'_I_=______l ______ __l ______ __l_ ______ __l ____ __Mi'__ HARTLEY lMQORE Soumay lHUTCHlNSON lROBKRTS ‘HEMPHILKL (Table 2). The area of Pullman soils l comm, I o slIfllwll l l °imulan is bounded by the New Mexico- I l SanlOfd I l Texas state line on the West, the Chanmnoe l l zlillllllls l M-eel-e l caprock escarpment at the Canadian Rililfll """"""" "'ll>'6lTllT"_""'l¢KIl§BlT"*J"l'e F“ “" " lTllTli"”"“ River on the north, and the caprock l N 0 r t h e r n p rlo V I n c a l Slenymm l a PalZDLaEIUIS l whlaow, escarpment at the High Plains- l ' M“ l l Rolling Plains boundary on the east. O l l 1 ‘eelleeele l l l A catena of loamy soils extending _ ,l__/___:(_g_lj___ ____'_"<_>___l____ _ ____Milf"'_'_l____illi_uloila frmn Farwen to near Lubbock fonns o o rsul/llll z‘ lawman lARMSTROGfGUUP lONLEY lCOLLINGSWORIH the southwest boundary of Pullman >-é l/ \-” ’ \ l‘— ~ o Cjmyo I C ‘e n t r a I p rlo V I n C 0 soils. Within this roughly triangular l l l °°'°'°“"“" l = area, Pullman soils occupy about 75 Lu l\__“_@"3£>'_<*_==_ \ I l l Himwo l Wmwungud percent of the land surface. 2 "ll?ll“__"“l¢llsllle""\{“‘lgllglznelalm ‘lie? “"'l_"l'ill'l__M;f_;j1"l6llTeTlEs's" The area of Pullman soils ranges ""0 3' \ \ l l l from about 100° 30’ to 103° O3’ West g OBOVIHD I e \\\<>I~'-a l "'“"""“°l | longitude and from about 33° 31' to I 5 \\ I °”""""' l T M l Climbs l 35° 45' north latitude. Elevation of Lu Game“ l l \ l U“ O l . u Y We" l the surface of Pullman soils ranges z “my o lLAMazEgar-lli llrml’ "l;°T“T_____ lwmm ~13 from 21l)()11t3,(l00 to 4,200 feel above l l l _ l l l mean sea level. The area is in a l '5“°"" l gawcemlwl \\ I ‘Macao, l f°°“°°“ l subhumid to semiarid climatic zone l Lllllelleslimnsl I pcmb I l olluyrladal l l where average annual precipitation ______ __I ______ __ 215g; ._____U_g_l___? ____l___3gel_-nll_s_l>~_~qgl ______ _1, ranges froln abOut 17 inches at the cocllml o lHOCKLEY Anlofl’, lluaaoqll- lcaosav l lclllns lémgellla GIOW l western edge to about 23 inches at 3 q u t h w “3"'§"l Qll’ n p r o v lh g g ldalou. ' n - ‘W; l l U Gull“? l the eastern edge. Some higher pre- l Levcnlsgd l °L“b"°"‘l "lwml °l""“'"‘ l l l cipitation values are presented in _ l Roupestrlco l Slamm- l l 08pm l l Teble s, eel lhey were ebleleee el le.el~-~l-l;;.:—~~~,--l;.l. ————— ~ llezez; "l cities that are riot on Pullman soils I M°°°°" l lm“ I Jlllloml l l and that afg at lgwgr elgvatigng °l"°'"$ l Brownllcldq l lahoh" l evlll luimlmmt Q l ‘QI W"! 0 of the Rolling Plains. Also listed in l l l l A’ l l l Table 3 are the average length and fff'_*'fgY__l_ ______ ___l____._O-_9(,_,,_,,£,,_l_ ______ __l_ _______ __l _______ __I_ Hates of the frost-free period, aver- age daily maximum and minimum ‘See Table 1 for classification of soils men- Fig. 2. The approximate area of Pullman soils is represented by the part of the map within the tioned in this report. solid line. The approximate sampling sites are indicated by the numbered dots. TABLE 2. AREAS OCCUPIED BY PULLMAN SOILS Total Series Portion of series Total lrrigated Other County Slope area county area“ cropland cropland Rangeland land‘! _ % Acres % Acres Armstrong 0-1 167,850 28.8 208,670 73,650 16,550 128,750 6,260 1-3 39,470 6.8 1-3, eroded 1,350 0.2 Briscoe 0-1 163,000 28.6 175,420 55,330 19,170 114,830 5,260 1-3 12,420 2.2 Carson 0-1 251,000 43.7 302,090 159,520 100,540 133,510 9,060 1-3 37,000 6.4 1-3, eroded 14,090 2.4 Castro 0-1 233,240 41 .4 256,580 175,000 167,330 73,880 7,700 1-3 23,340 4.1 Crosby 0-1 137,260 23.5 143,600 92,740 17,110 46,550 4,310'\ 1-3 6,340 1.1 Deaf Smith 0-1 534,820 55.4 601,070 257,780 172,280 325,260 18,030 1-3 55,050 5.7 1-3, eroded 740 0.1 0-1, Pullman- Ulysis complex 7,5003 0.8 1-3, Pullman- Ulysis complex 2,9703 0.5 Dickens 0-1 25,920 4.4 29,340 4,390 600 24,070’ 880 1-3 3,430 0.6 Donley 0-1 12,290 2.1 13,150 11,840 4,730 1,180 140 1-3 860 0.1 Floyd 0-1 422,300 66.4 446,150 259,630 165,990 173,130 13,380 1-3 23,850 3.7 Gray 0-1 153,570 25.5 172,700 98,300 21,540 69,220 5,180 1-3 19,130 3.1 Hale 0-1 333,590 53 .2 344,040 331,910 227,560 1,810 10,320 1-3 10,450 1.7 Hemphill 0-1 620 0.1 620 440 0 160 20 Lubbock 0-1 51,980 9.1 51,980 18,880 4,030 31,540 1,560 Motley 0-1 4,540 0.7 4,540 3,180 2,630 1,220 140 Oldham 0-1 115,750 12.2 129,140 63,470 12,420 61,800 3,870 1-3 13,390 1.4 Parmer 0-1 69,380 12.6 72,760 55,620 50,910 14,960 2,180 1-3 3,380 0.6 Potter 0-1 50,620 8.6 62,620 31 ,470 8,660 18,620 12,520 1-3 12,000 2.0 Randall 0-1 284,500 48.3 352,750 168,450 53,350 168,700 15,600 1-3 54,850 9.3 1-3, eroded 3,260 0.6 0-1, moderately shallow 8,340 1.4 1-3, moderately shallow 1,800 0.3 Roberts 0-1 25,090 4.4 25,0904 17,560 8,780 7,110 420 Swisher 0-1 379,710 66.2 413,440 278,830 93,740 122,210 12,400 1-3 33,730 5.9 Wheeler 0-1 350 0.1 350 290 0 50 10 Total 3,791,980 2,158,280 1,147,920 1,518,560 129,240 g llncludes 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 , l. the nearest 10 acres. zlncludes land in roads, towns, and other non-agricultural uses. 3Values shown are for the estimated area of complex that is Pullman —- 40% for 0-1 slope, 60% for 1-3% slope. ‘Includes some Sherm soil. 2 temperatures, and average annual recipitation in counties in which gPullman soils are found. Pullman soils occupy about 3.8 million acres of land (Table 2). Pull- man soils are the most extensive ar- able soils in Texas. Other major ar- able soils in Texas are Amarillo with 2.5 million acres, Houston Black with 1.5 million acres, and Sherm with 1.3 million acres. There are also about 11,000 acres of Sherm soils in Oklahoma. History of the Pullman Series The Pullman series is classified by soil scientists as a member of the fine, mixed, thermic family of Tor- rertic Paleustolls. The soil de- veloped from fine-textured sedi- ments of the High Plains eolian (wind deposited) mantle under a dense cover of short grasses (Fig. 3). The Pullman series was estab- lished in the Soil Survey of Potter County, Texas, in 1929. It was named after Pullman Switch, a rail- road siding which is east of Amarillo. Before 1929, Pullman soils were in- cluded in other series, mainly the Amarillo and Richfield series. The process of cataloging and classifying soils on the High Plains began with the publication of the Reconnais- sance Soil Survey of the Panhandle Region of Texas in 1910. In this sur- vey, Pullman soils were called Amarillo silty clay loam. The Amaril- lo series was established in this sur- vey and included soils ranging from sands to clays. As soil surveys and investigations continued, differences in the physi- cal and chemical properties of soils were noted. This led to the recogni- tion of other soil series. Early soil surveys of Dickens, Lubbock, and Wheeler counties included these soils in the Richfield series. Further investigations led to the establish- ment of the Pullman series. In the 1929 Soil Survey of Potter County and the 1930 Soil Survey of Randall County, three phases of Pullman soils were recognized. These were Pullman silty clay loam, Pullman silty clay loam (bench phase), and Pullman clay loam. Ad- ditional studies of landscapes, closer examination of soil properties, and refinements in series criteria result- ed in narrowing the limits of the Pullman series. In subsequent soil surveys on the High Plains, the Lof- ton series replaced the bench phase of Pullman soils. Lofton soils have properties similar to those of Pull- man, but receive additional mois- ture from runoff and have grayish a Fig. 3. Blue grama grass, the major native grass 0n Pullman soils. TABLE 3. ELEVATION AND CLIMATIC FACTORS IN THE COUNTIES HAVING PULLMAN SOILS Avg. daily temp.l Avg. lake Avg. County City Elev. Evap. Avg. growing season Max. Min. precip.‘ ft. in. clays period °F °F in. Armstrong Claude 3,400 69 198 Apr. 10-Oct. 25 72.0 44.5 23.24 Briscoe Silverton 3,280 69 214 Apr. 6-Nov. 6 71.7 42.6 20.77 Carson Panhandle 3,450 62 197 Apr. 17-Oct. 31 -- -- 22.00 Castro Dimmitt 3,855 -- 193 Apr. 16-Oct. 26 72.4 41.2 17.50 Crosby Crosbyton 3,105 -- 206 Apr. 10-Nov. 2 74.5 45.5 21.42 Deaf Smith Hereford 3,810 67 185 Apr. 20-Oct. 22 72.1 42.3 18.04 Dickens Spur 2,3602 69 217 Apr. 4-Nov. 7 78.1 46.9 20.43 Donley Clarendon 2,7003 68 206 Apr. 9-Nov. 1 73.6 44.3 21.51 Floyd Floydada 3,180 69 213 Apr. 7-Nov. 6 74.2 2 44.9 18.75 Cray Pampa 3,230 65 195 Apr. 15-Oct. 27 70.4 44.0 20.13 Hale Plainview 3,370 69 210 Apr. 10-Nov. 6 73.9 44.3 19.01 Hemphill Canadian 2,3352 64 204 Apr. 9-Oct. 30 72.9 45.1 20.50 Lubbock Lubbock 3,150 69 211 Apr. 7-Nov. 4 72.9 47.1 18.41 Motley Matador 2,2802 68 218 Apr. 3-Nov. 7 75.7 48.4 20.22 Oldham Vega 4,000 -- --- ---- 70.5 41.0 17.75 Parmer Flriona 4,010 -- 183 Apr. 20-Oct. 20 71.3 42.1 17.50 Potter Arnarillo 3,650 68 191 Apr. 20-Oct. 28 70.8 43.9 20.28 Randall Canyon 3,577 66 200 Apr. 15-Nov. 1 73.8 43.2 19.53 Roberts Miami 2,8002 -- ---- 71.6 42.8 20.66 Tulia 3,500 68 205 Apr. 10-Nov. 1 72.9 42.6 17.24 Shamrock 2,3452 69 20s Apr. 7-Nov. 1 74.5 46.2 23.17 ‘Average monthly maximum and minimum temperatures and precipitation are available in the soil surveys for most counties. 2Be|ow Caprock escarpment. 3 . . . Lower than elevation at which Pullman SOllS are commonly found. colors throughout the profile. The Clton series was established to ac- commodate those soils that had pre- viously been classified as Pullman clay loam. They were slightly more red, had lighter textures, and were more permeable. In 1970, the Sherm series was es- tablished 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 nearly level to gently sloping, smooth treeless plains (Fig. 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 only by the numerous playas, or shallow lakes, containing other soils. Except where pitted by playas, the surface is remarkably smooth. The playas range from a few square yards to several square miles in surface area, and from a few in- ches to more than 5O feet in depth. The average grade of the High Plains is about 1O feet per mile to the southeast. Runoff follows a poorly defined pattern. Water flows mainly into the playas, from which there is no definite outlet. The water collect- ed in playas is lost mainly by evapo- ration, but some of it is used for irrigation. Other soils associated with Pull- man are Acuff, Drake, Estacado, Li- pan, Lofton, Mansker, Olton, and Randall (Fig. 5, 6, 7, and 8). Drake soils are on recent eolian dunes that occupy the eastern rim of some play- as throughout the central and south- ern parts of the area. These dunes are absent in the northern area. Es- tacado and Mansker soils are on sideslopes around playas and along draws. Lipan and Lofton soils are on low benches around playa bottoms. Acuff and Olton soils are on smooth plains that have slightly convex sur- faces. These soils are intermingled with Pullman along the southwest boundary of the area. Randall soils are on playa bottoms. There are differences in the mor- phological properties of the Pullman series that are related to geographic location. These differences affect soil water storage capacity, which in turn directly affects water management on these soils. The morphological properties are depth to the calcic horizon, texture, and permeability. F ig." 4. Aerial view of the topography of the land occupied by Pullman soils. The circular area near the center is a playa, 0r shallow lake, which contains other soils (USDA — Soil Conservation Service photo). 4 An analysis of soil survey field notes for 17 counties and additional‘? profile observations revealed tha depth to the calcic horizon ranges from 3O to more than 72 inches. Observations by soil and plant scien- tists indicate that calcic horizons containing at least 3O percent calcite inhibit root development of most crops. Based on field determinations using a simple volume calcimeter, the average calcium carbonate con- tent of the Btca horizon of Pullman soils is about 5O percent. To present a clearer understand- ing of these soils as they relate to geographical location, it is conve- nient to divide this large area into three soil provinces (Fig. 2). The northern province includes the High Plains portions of Carson, Donley, Gray, Hemphill, Oldham, Potter, Roberts, and Wheeler Counties and the northern portions of Armstrong, Deaf Smith, and Randall Counties. In the northern province, depth to a strong calcic horizon (>30 percent CaCO3) ranges from 55 to more than 72 inches. The central province extends southeastward from western Deaf Smith County to western Briscoe County. It includes all or parts of Armstrong, Briscoe, Castro, Deaf Smith, Randall, and Swisher Coun- ties. The southern boundary of this province roughly follows Terra Blan- ca and Tule Creeks. The depth to a strong calcic horizon ranges from 45 to 55 inches. The southwest province of Pull- man soils is the area south of Terra Blanca and Tule Creeks. Included are parts of Briscoe, Castro, Crosby, Deaf Smith, Dickens, Floyd, Hale, Lubbock, Motley, Parmer, and Swisher Counties. The depth to a strong calcic horizon ranges from 3O to 48 inches, but is mainly from 33 to 45 inches. Along the southwestern boundary, Pullman soils are closely associated with Acuff and Olton soils (Fig. 8). While similar to Pullman soils in appearance, the Bt horizons of these soils are somewhat redder, have loamy textures, and are more permeable. Acuff and Clton soils oc- cupy the same general landscape as Pullman soils, although their sur- faces are slightly more convex. r \ t‘ Mobeefie » ‘i '1!“ \ I l‘ f ‘f / \“\\\\\ bk‘ / l l l I \ _- \ Pullman / (I Eslocodo l \ ..;-_ - ,‘-- .,-... -_ _._.._._-.._,_,_ .. .'- |._ .-, __..-o--u-_ ‘luau. v‘. '2 - "-.-'_\ '- e ' I I ol '.~'~.' .__° ‘m’; F.1-f_:'0gon .'- -.'~; 3-. - _'-__ _ ___ f ('--.'. _.‘._:-~»,v'_ ‘L. "'.' ._o . . _._ ' '-'.' I ___v , nu N... .-- '¢ ‘- - I L a» .-__. ____.._._..._____..._____-_4 iTITZTLTUT- Permian ----,--__---J / AlIuvium-J Fig. 5. Major soils and underlying formations in the area occupied by Pullman soils. Rondufl — Soft Coliche. l l‘ l Pullman i-n-n-inii-t-mq- 4-’ qr \\\ 1?; [l %—~\ . . ,/"\ Hugh Plums ,’ Estocodo | I] \\ Eolion Mantle \ / \ “ \\ -- , \ \ ‘C \ \ \ \\ ‘ => ~~ \\ gm» Lofton "<< \ /- ' l . ._ o - ’ \ \ ‘\ \\\\ :\\\ r”'\\ 4*‘ V \ f ‘E l o. "'-\ u ?\-“ ’ -'; ,_'-. .‘ \‘ \ \ l <<»’~‘\“~ 51 /,L../9‘\>? \\\ \ 6‘ Y \ P? gill-kg rig/x “_.Z__ 1? / / / Q . o 6 . . o; ’-._'.__\_o. \\\ \\\ \_ 66s ‘ ' ‘ gt‘ Z1“ “ /" ’ ” a "°. Q ' z‘ '.' o £359 ’.-“'.' :\ \\\\;r \ < u IRODdOII: $73: f; ~_ 5’ _;°°"_-;,I-- j sil -_‘-_'.'_‘..'-_"_.° h‘ \ \-‘:“ z S \7:,jJ_)/___:___ _ _ c. 3.’),- -°..‘_._ ’ .: :62... ~30 a. '25- 0 0O ‘TY’: 0"‘ '13.‘: O ' b ' ‘f '_ 0 9-3.. w?‘ . ... _._‘-'-\.',_\"~‘ ‘O -¢‘:_ :_~'.:' -';:-. °-, i, .-_;.'-? xr- 1.’, -' 51-91 v‘ .‘-_.- Ru‘ ' ¢._’l.‘-’ ,\ - i‘ i. 2x10 ‘$45’: ' ~'-:<.>.-- <> :-.°.- "- 1°»: ' Ogullcla Outwash Fig. 6. Soil pattern in the northern province. High Plains Eolion Mantle Soft Culiche ¢\0( \'.‘l. . o .030). . f / \\\\ I/EQQCO / do. Ogallola Outwash Fig. 7. Soil pattern in the central province. High Plains Eolion Mantle Pullman Ogollolu Outwush Fig. 8. Soil pattern in the southwest province. Uses and Importance of Pullman Soils Pullman soils are used primarily for agriculture with about 56 percent of their area being used for crop production. Almost 4O percent of the area of Pullman soils is in rangeland. The remaining area is in roads, towns, and other non-agricultural uses. Of the cropland area of Pull- man soil, about 53 percent is irri- gated and 47 percent is dryland (Table 2). The area of irrigated Pull- man soil represents about 13 percent of all irrigated land in Texas. Of the total acreage devoted to wheat (Triticum aestivum L.), cotton (Cos- sypium hirsutum L.), grain sorghum [Sorghum hicolor L. (Moench)], and corn (Zea mays L.) in Texas, about 11, 9, 7, and 11 percent, respective- ly, were produced on Pullman soils in 1977 (Texas Dept. Agric., 1977). Other major crops grown on smaller areas of Pullman soils are sugar beets (Beta vulgaris L.), soybeans (Glycine max L.), forage sorghum (Sorghum sp.), alfalfa (Medicago sativa L.), sunflower (Helianthus annuus L.), and vegetables. Because Pullman soils are located in a subhumid to semiarid region, yields of dryland crops on Pullman soils are relatively low. Irrigation from the Ogallala Aquifer greatly in- creases 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 irrigation is negligible. It is, therefore, essential that the water be used as efficiently as possible so that economic crop production can be maintained and the eventual return to dryland crop production can be delayed as long as possible. When dryland farming re- jplaces irrigated farming, even if only on the Pullman soils, a significant amount of the total production of some crops in Texas will be lost. Typical Site for Pullman Soils Pullman soils developed in a rela- tively cool, subhumid to semiarid climate from medium- to fine- ‘textured sediments largely or entire- l y of eolian origin. They occupy ex- tensive smooth areas that are nearly level to gently sloping. Surface slopes range from O to about 3 per- Fig. 9. Surface conditions and soil profile at a typical site of Pullman soil. The site is at the USDA Conservation and Production Research Laboratory, Bushland, Texas (USDA — Soil C onserva- tion Service photo). cent toward the playas or shallow basins. Although largely cultivated, the typical native vegetation on Pull- man soils was short-grasses, princi- pally blue grama (Bouteloua gracilis) and buffalograss (Buchloe dacty- loides). The surface conditions and profile at a typical site of Pullman soil are shown in Fig. 9 andFig. 10, respectively. The profile shown is at the Conservation and Production Research Laboratory at Bushland. It is near the site used by Taylor et al. (1963) for their study of Pullman soil and also near Site 3 (Fig. 2) of this study. The surface horizon of a typical Pullman soil is a brown to dark brown silty clay loam, but the tex- ture may range from loam to clay loam. The thickness of the surface horizon usually ranges from 4 to 7 inches, at which depth there is a rather abrupt boundary to a dark brown to dark grayish-brown clay with blocky structure (Fig. 10). The soil may contain buried horizons of older soils at 3 to 5 feet below the surface. The buried horizons usually have a clay loam texture. At the site used by Taylor et al. (1963), a caliche or calcic horizon occurred at a depth of 53 inches. Based on other samples taken at the Laboratory, depth to the calcic horizon ranges from 5 to 6 feet on O to 1 percent slopes and from 2 to 4 feet on 1 to 3 percent slopes. As shown in Fig. 10, the upper boundary of the calcic horizon is clear and wavy. Although depth to the calcic horizon is often considered to be the effective depth of the Pull- man soil for crop production pur- poses, winter wheat and especially x .3 >Iu> ‘ Fig. 10. A ypical Pullman soil profile. Profile shown is at the USDA Conservation and Pro- duction Research Laboratory, Bushland, Tex- as (USDA — Soil Conservation Service photo sunflower use water from well into the calcic horizon. Sunflower roots have been found at a 9-foot depth in Pullman soil (O. R. Jones, Bushland, Texas, unpublished data) and have extracted soil water to about a 10- foot depth (Unger, 1978a). Present Water Management Systems When filled to capacity, Pullman soil at Bushland holds about 17.0 inches of total water and about 7.7 inches of plant available water to a 4- foot depth, and about 24.6 and 10.5 inches to a 6-foot depth (Taylor et al., 1963). Because of erratic precipi- tation during the growing season, it is desirable to have the soil profile filled to capacity with water at plant- ing of dryland crops. However, the soil is rarely filled to capacity to a 4- or 6-foot depth, even when a fallow period of up to 16 months precedes winter wheat (Unger, 1972). In some newly developed cropping systems involving surface residue mainte- nance, the soil has been filled to near-capacity during a fallow period of only 1O or 11 months (Unger, 1978b; Unger and Wiese, 1979). These systems involved a rotation of winter wheat and grain sorghum. When the soil is filled to capacity with water at planting time, crops usually experience less severe water stress during the growing season than when the soil contains a limited amount of water. When stress is re- duced, crop yields usually are higher. 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, preplant or emergence irrigation is often used to increase the soil water content. Be- cause the Pullman soil is very slowly permeable, Yrelatively long periods of water application are required to add large amounts of water to the soil. With furrow irrigation (Fig. 11), which is the most common method, considerable tailwater runoff is usu- ally permitted so that adequate wa- ter is stored at the lower end of the field. Unless effective tailwater re- 8 Fig. 11. Furrow irrigation 0f cotton 0n Pullman Conservation Service photo). covery systems are used, tailwater runoff reduces the efficiency of wa- ter use. In recent years, numerous sprin- kler systems have been installed on Pullman soils. These systems, when properly designed and operated, eliminate the runoff problem, but require considerably more energy input than furrow irrigation. With all farming systems on both dryland and irrigated land, a knowledge of the water holding capacity of the soil profile is important for effective wa- ter management. Objectives of the Study Most published research informa- tion regarding Pullman soils was ob- tained at the Conservation and Pro- duction Research Laboratory at Bushland. Much of it is based on descriptions and analyses performed on samples obtained at the typical site at the Laboratory (Taylor et al., 1963; Coover et al., 1953). The infor- mation is generally considered reli- able and has been widely used as the basis for managing Pullman soils. These soils, however, cover exten- sive areas of the High Plains of Texas and are known to vary considerably in profile properties across the re- gion. One property that varies wide- ly across the region is depth to the calcic horizon. Because profile depth soil in Swisher County, Texas (USDA — Soil strongly influences plant rooting depth and thus the effective depth for storing water, a knowledge of profile depth along with a characteri- zation of other profile properties is important for improved water and crop management on Pullman soil. The objective of this study was to determine the variation in depth, bulk density, texture, organic matter content, pH, and water retention of the different horizons of Pullman soil as affected by location in the region. EXPERIMENTAL PROCEDURE Site Selection To obtain samples that would re- present a near-complete range in the expected variation in soil properties, sites were selected at seven widely separated locations across the re- gion. The sampling sites were in Armstrong, Carson, Castro, Deaf Smith, Floyd, Randall, and Swisher Counties. Although the locations were widely separated, samples were not obtained at the extreme edges of the region so that zones of transition to other soils were avoid- ed. Likewise, locations of transition to other soils within the region were avoided. The sampling was restrict- ed to typical Pullman soil sites for the particular location in the region. F“ Tl Sampling Sites The seven sampling sites indi- cated in Fig. 2 are numbered in the order in which the samples were obtained. Site identifications, sam- pling dates, and locations are given in Table 4. All sites had a nearly level upland High Plains physio- graphic description. All sites were in cultivated fields that were irrigated, except for Site 3, which was dryland. Sites 1 and 3 were in the northern province, Sites 2 and 6 in the central province, and Sites 4, 5, and 7 in the southwest province. Sampling Techniques At each sampling site, loose soil of the plow layer, usually to the depth of the Ap horizon, was removed be- fore obtaining core samples with a hydraulically-operated, pickup- mounted core sampler. The inside diameter of the cutting tip was 1.625 inches. The first core at each site was used for profile description. Subse- quent cores were then taken and separated into depth segments based on the thickness of the differ- ent horizons. Two or more cores were obtained to provide adequate material from each depth for making water retention determinations. Im- mediately after separating the cores by depths in the field, the segments were dipped in a liquified saran solu- tion to provide rigidity to the cores. After the saran had dried, the indi- vidual segments were wrapped in newspaper for transport to the labo- ratory. Two additional cores were obtained and sectioned by horizons for obtaining samples for bulk densi- ty determination. In addition to the core samples, two samples of the surface horizon of soil were collected in bags at each site. At a different time, water infiltration was deter- mined at each site by the double- ring infiltrometer method. Sample Preparation and Analyses The core samples to be used for water retention“ measurements were cut into sections about 0.75 inch long and further reinforced with cel- ‘lophane tape before making the measurements at — Vs and — 15 bars matric potential. The measurements were made with pressure plate equipment using four sections from TABLE 4. each depth at each potential. Some core soil from each depth was ground to pass a 2-mm sieve and then used to determine the wilting points by the sunflower method. To determine bulk density, the cores were dried at 105°C, then weighed. Soil from these cores was retained and ground to pass a 2-mm sieve. Subsamples of this sieved soil were then used to determine parti- cle size distribution by the hydrome- ter method (Day, 1965), organic matter content by the Walkley-Black method (Iackson, 1958), and pH (1:1 soilzwater ratio). Samples of surface soil were air- dried, ground, and passed through a 2-mm sieve. Subsamples of surface soil were used for determining water retention, particle size distribution, organic matter content, and pH by the methods described above. The relationships among various B21t horizon and total profile char- acteristics and total water infiltration in 1O minutes and 20 hours and infil- tration rates at these times were in- vestigated by multiple linear regres- sion analyses. Horizon and profile variables were thickness; sand, silt, clay, and organic matter content; and bulk density. For the B21t hori- zon, actuallvalues were used. For the entire profile, weighted mean values were calculated from values for the different horizons, thus re- sulting in one value for each variable of the profile at each site. Besides the partial regression coefficients SITE IDENTIFICATION, SAMPLING DATE, AND LOCATION Site SCS no. ident. no. Date sampled County and location description 1 S79TX-065-1 March 6, 1979 2 S79TX-O11-1 March 6, 1979 3 S79TX-381-3 March 7, 1979 4 S79TX-437-1 March 8, 1979 5 S79TX-O69-1 6 S79TX-117-1 7 S79TX-153-1 April 18, 1979 March 19, 1979 March 19, 1979 Carson County, Texas; in a cultivated field 1000 feet west and 1300 feet north of the intersection of State Highway 207 and Farm Road 293, 0.5 mile north of Panhandle. Armstrong County, Texas; in a cul- tivated field 200 feet south of Farm Road 285, 5.5 miles west of its intersec- tion with State Highway 207, 25 miles south of Claude. Randall County, Texas; in a cultivated field 520 feet east of paved county road, 2.0 miles west and 0.6 mile south of the intersection of Interstate High- way 40 and Farm Road 2381 in Bush- land. Swisher County, Texas; in a cultivated field 150 feet south of county road, 1.1 miles west of Farm Road 2301, at a point 2.0 miles south of its intersection with Farm Road 145 in Claytonville. Castro County, Texas; in a cultivated field, 900 feet west of Farm Road 168, at a point 1.5 miles south of its intersec- tion with State Highway 86 in Nazareth. Deaf Smith County, Texas; in a cul- tivated field 2500 feet east of Farm Road 1057, 0.5 mile north of its intersection with Farm Road 1058, 6.0 miles west of Hereford. Floyd County, Texas; in a cultivated field, 100 feet west of a county road, 0.5 mile north of U.S. Highway 70, 2.0 miles east of its intersection with State Highway 207 in Floydada. and the coefficient of correlation standardized partial regression coef- ficients and t-values were also cal- culated (Ezekial and Fox, 1959; Steel and Torrie, 1960). Based on the standardized coefficients, the in- dependent variables were ranked numerically in order of their relative importance for influencing total infil- tration or infiltration rates. All inde- pendent variables were used in the initial analysis for each set of data. In subsequent analyses, the lowest ranking variable was excluded until the last analysis, which was a simple linear regression analysis. RESULTS AND DISCUSSION Profile Descriptions In this section, the profiles at the seven sites are described in detail by horizons. These descriptions are based on examination and determi- nations made in the field immediate- ly after extracting the cores. Al- though data in subsequent sections are based mainly on horizons above the calcic horizon, the calcic horizon is included in the profile descrip- tions. The descriptions are: Site l, Carson County, Sample No. S79TX-O65-l-(l-5) Ap—O to 6 inches; brown (7.5YR 4/2) silty clay loam, dark brown (7.5YR 3/2) moist; weak fine and medium granu- lar structure; hard, friable; few fine roots; few fine pores; neutral; abrupt smooth boundary. B2lt—6 to l4 inches; dark brown (7.5YR 4/2) silty clay, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; few wedge shaped peds; extremely hard, very firm; few fine roots on ped faces; few fine pores; thin continuous clay films; few vertical cracks; neutral; gradual smooth boundary. B22t—14 to 26 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 slickensides 2 to 4 inches across; extremely 10 hard, very firm; few fine roots; few fine pores; thin continuous clay films; few threads and films of calcium carbonate; calcareous; mildly alkaline; gradual smooth boundary. B23t—26 to 39 inches; reddish brown (5YR 5/3) silty clay, reddish brown (5YR 4/3) moist; moderate medium blocky structure; few slicken- sides 2 to 4 inches across; ex- tremely hard, very firm; few pores; thin clay films on ped faces; few threads and films of calcium carbonate; calcare- ous; mildly alkaline; gradual smooth boundary. B24t—39 to 59 inches; yellow- ish red (5YR 5/6) silty clay, yellowish red (5YR 4/6) moist; moderate medium subangu- lar blocky structure; few small pressure faces; very hard, firm; few fine pores; few patchy clay films; com- mon threads and films of cal- cium carbonate; calcareous; mildly alkaline; clear smooth boundary. B25tca——59 to 80 inches; pink (7.5YR 8/4) clay loam, pink (7.5YR 7/4) moist; moderate medium subangular blocky structure; very hard, friable; few fine pores; about 45 per- cent of the soil mass consists of soft masses and concretions of calcium carbonate; calcare- ous; moderately alkaline. Site 2, Armstrong County, Sample No. S79TX-Oll-l-(l-5) Ap—O to 6 inches; brown (7.5YR 4/2) clay loam, dark brown (7.5YR 3/2) moist; weak fine and medium granu- lar structure; hard, friable; few fine roots; few fine pores; mildly alkaline; abrupt smooth boundary. B2lt—6 to 13 inches; dark brown (7.5YR\Q2) clay, dark brown (7.5YR‘3/2) moist; moderate medium blocky structure; few wedge shaped peds; extremely hard, very firm; few fine roots on ped faces; few fine pores; thin continuous clay films; com- mon vertical cracks; mildly alkaline; gradual smoot boundary. B22t—l3 to 21 inches; dark brown (7.5YR 4/2) clay, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; few wedge shaped peds; few slickensides 2 to 4 inches across; extremely hard, very firm; few fine roots; few fine pores; thin continuous clay films; few threads and films of calcium 1 carbonate; calcareous; mildly 6* alkaline; gradual smooth boundary. B23t——2l to 35 inches; reddish brown (5YR 5/4) clay, reddish brown (5YR 4/4) moist; moderate medium blocky structure; few slickensides 2 to 4 inches across; extremely hard, very firm; few pores; thin clay films on ped faces; few threads and films of cal- cium carbonate; calcareous; mildly alkaline; gradual smooth boundary. B24t—35 to 5O inches; yellow- ish red (5YR 5/6) clay, yellow- ish red (5YR 4/6) moist; moderate medium subangu- lar blocky structure; few small pressure faces; very hard, firm; few fine pores; few patchy clay films; com- mon threads and films of cal- cium carbonate; calcareous; mildly alkaline; clear smooth boundary. B25tca—5O to 7O inches; red- dish yellow (5YR 7/6) clay loam, reddish yellow (5YR 6/6) moist; moderate medium subangular blocky structure; very hard, friable; few fine pores; about 35 percent of the soil mass consists of soft mas- ses and concretions of cal- cium carbonate; calcareous; moderately alkaline. Site 3, Randall County, Sample No. S79TX-381-3-(l-5) Ap—O to 6 inches; brown (7.5YR 4/2) silty clay loam ~f dark brown (7.5YR 3/2) moist; weak fine and medium granu- lar structure; hard, friable; few fine roots; few fine pores; ‘AS neutral; abrupt smooth boundary. B21t—6 t0 16 inches; dark brown (7.5YR 4/2) clay, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; few wedge shaped peds; extremely hard, very firm; few fine roots 0n ped faces; few fine pores; thin continuous clay films; few vertical cracks; neutral; gradual smooth boundary. ous; moderately alkaline; gradual smooth boundary. B26tca—8O to 92 inches; red- dish yellow (5YR 7/6) clay loam, reddish yellow (5YR 6/6) moist; moderate medium subangular blocky structure; very hard, firm; few fine pores; few patchy clay films; about 2O percent of the soil mass consists of soft masses and concretions of calcium carbonate; calcareous; mildly alkaline; gradual smooth boundary. B24t—42 to 48 inches; light brown (7.5YR 6/4) clay, brown (7.5YR 5/4) moist; moderate medium subangu- lar blocky structure; few small pressure faces; very hard, firm; few fine pores; few patchy clay films; com- mon threads and films of cal- cium carbonate; calcareous; moderately alkaline; clear smooth boundary. B25tca—48 to 6O inches; pink (7.5YR 8/4) clay loam, pink (7.5YR 7/4) moist; moderate B22t—l6 to 29 inches; dark moderately alkahne' brown (7.5YR 4/2) silty clay, dark brown (7.5YR 3/2) moist; moderate medium blocky Site 4, Swisher County, Sample No. S79TX-437-l-(l-5) Ap—() to 6 inches; brown structure; few wedge shaped peds; few slickensides 2 to 4 inches across; extremely hard, very firm; few fine roots; few fine pores; thin continuous clay films; few threads and films of calcium carbonate; calcareous; neu- tral; gradual smooth bound- ary. B23t—29 to 44 inches; reddish brown (5YR 5/4) silty clay, reddish brown (5YR 4/4) moist; moderate medium blocky structure; few slicken- sides 2 to 4 inches across; ex- tremely hard, very firm; few pores; thin clay films on ped faces; few threads and films of calcium carbonate; calcare- ous; mildly alkaline; gradual smooth boundary. B24t——44 to 58 inches; yellow- ish red (5YR 5/6) clay, yellow- ish red (5YR 4/6) moist; moderate medium subangu- lar blocky structure; few small pressure faces; very hard, firm; few fine pores; few patchy clay films; com- mon threads and films of cal- cium carbonate; calcareous; mildly alkaline; clear smooth boundary. B25tca—58 ;.to 80 inches; pink (7.5YR 8/4) clay loam, pink (7.5YR 7/4) moist; moderate medium subangular blocky structure; veryghard, friable; few fine pores; about 5O per- cent of the soil mass consists of soft masses and concretions of calcium carbonate; calcare- (7.5YR 4/2) clay loam, dark brown (7.5YR 3/2) moist; weak fine and medium granu- lar structure; hard, friable; few fine roots; few fine pores; neutral; abrupt smooth boundary. B2lt——6 to 17 inches; dark brown (7.5YR 4/2) clay, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; few wedge shaped peds; extremely hard, very firm; few fine roots on ped faces; few fine pores; thin continuous clay films; few vertical cracks; mildly al- kaline; gradual smooth boundary. B22t——I7 to 3O inches; dark brown (7.5YR 4/2) clay, dark brown (7.5YB 3/2) moist; moderate medium blocky structure; few wedge shaped peds; few slickensides 2 to 4 inches across; extremely hard, very firm; few fine roots; few fine pores; thin continuous clay films; few threads and films of calcium carbonate; calcareous; mildly alkaline; gradual smooth boundary. B23t—3O to 42 inches; reddish brown (7.5YR 5/4) clay loam, brown (7.5YR 4/4) moist; moderate medium blocky structure; few slickensides 2 to 4 inches across; extremely hard, very firm; few pores; thin clay films on ped faces; few threads and films of cal- cium carbonate; calcareous; medium subangular blocky structure; very hard, friable; few fine pores; about 60 per- cent of the soil mass consists of soft masses and concretions of calcium carbonate; calcare- ous; moderately alkaline. Site 5, Castro County, Sample No. S79TX-O69-1-(l-5) Ap——() to 6 inches; brown (7.5YR 4/2) clay loam, dark brown (7.5YR 3/2) moist; weak fine and medium granu- lar structure; hard, friable; few fine roots; few fine pores; neutral; abrupt smooth boundary. B2lt—6 to 13 inches; dark brown (7.5YR 4/2) clay loam, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; few wedge shaped peds; extremely hard, very firm; few fine roots on ped faces; few fine pores; thin continuous clay films; few vertical cracks; neutral; gradual smooth boundary. B22t—l3 to 2O inches; dark brown (7.5YR 4/2) clay loam, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; few wedge shaped peds; few slickensides 2 to 4 inches across; extremely hard, very firm; few fine roots; few fine pores; thin continuous clay films; few threads and films of calcium carbonate; calcareous; mildly alkaline; gradual smooth boundary. 11 B23t——20 t0 32 inches; reddish brown (5YR 5/3) clay, reddish brown (5YR 4/3) moist; moderate medium blocky structure; few slickensides 2 t0 4 inches across; extremely hard, very firm; few pores; thin clay films 0n ped faces; few threads and films 0f cal- cium carbonate; calcareous; mildly alkaline; gradual smooth boundary. B24t—32 to 4O inches; reddish brown (5YR 5/4) clay, reddish brown (5YR 4/4) moist; moderate medium subangu- lar blocky structure; few i small pressure faces; very hard, firm; few fine pores; few patchy clay films; com- mon threads and films of cal- cium carbonate; calcareous; mildly alkaline; clear smooth boundary. B25tca—4O to 65 inches; red- dish yellow (SYR 7/6) clay loam, reddish yellow (5YR 6/6) moist; moderate medium subangular blocky structure; very hard, firm; few fine pores; about 3O percent of the soil mass consists of soft mas- ses and concretions of cal- cium carbonate; calcareous; moderately alkaline. Site 6, Deaf Smith County, Sample No. S79TX—ll7-l-(l-4) Ap—O to 6 inches; brown (7.5YR 4/2) clay loam, dark brown (7.5YR 3/2) moist; weak fine and medium granu- structure; few wedge shaped peds; few slickensides 2 to 4 inches across; extremely hard, very firm; few fine roots; few fine pores; thin continuous clay films; few threads and films of calcium carbonate; calcareous; mildly alkaline; gradual smooth boundary. B23t—28 to 38 inches; reddish brown (5YR 5/4) clay, reddish brown (5YR 4/4) moist; moderate medium blocky structure; few slickensides 2 to 4 inches across; extremely hard, very firm; few pores; thin clay films on ped faces; few threads and films of cal- cium carbonate; calcareous; mildly alkaline; gradual smooth boundary. B24t—38 to 52 inches; reddish yellow (5YR 7/6) clay, reddish yellow (5YR 6/6) moist; moderate medium subangu- lar blocky structure; very hard, firm; few fine pores; few patchy clay films; com- mon threads and films of cal- cium carbonate; calcareous; mildly alkaline; clear smooth boundary. B25tca—52 to 7O inches; pink (7.5YR 8/4) clay loam, pink (7.5YR 7/4) moist; moderate medium subangular blocky structure; very hard, friable; few fine pores; about 50 per- cent of the soil mass consists of soft masses and concretions of calcium carbonate; calcare- firm; few fine roots on ped faces; few fine pores; thi continuous clay films; few vertical cracks; neutral; gradual smooth boundary. B22t—l8 to 3O inches; reddish brown (5YR 4/3) clay, dark reddish brown (5YR 3/3) moist; moderate medium blocky structure; few wedge shaped peds; few slickensides 2 to 4 inches across; extreme- ly hard, very firm; few fine roots; few fine pores; thin continuous clay films; few threads and films of calcium carbonate; calcareous; mildly alkaline; gradual smooth boundary. B23t——3() to 48 inches; reddish brown (5YR 5/4) clay, reddish brown (5YR 4/4) moist; moderate edium blocky structure; rew slickensides 2 to 4 inches across; extremely hard, very firm; few pores; thin clay films on ped faces; few threads and films of cal- cium carbonate; calcareous; mildly alkaline; gradual smooth boundary. B24tca—48 to 6O inches; pink (7.5YR 8/4) clay loam, pink (7.5YR 7/4) moist; moderate medium subangular blocky structure; very hard, friable; few fine pores; about 50 per- cent of the soil mass consists of soft masses and concretions of calcium carbonate; calcare- ous; moderately alkaline. X lar structure; hard, friable; few fine roots; few fine pores; neutral; abrupt smooth boundarv. B2lt—6 to l9 inches; dark Based on the field descriptions, profiles at the various sites differed mainly with respect to thickness, color, and texture of the different horizons, and depth to the calcic ous; moderately alkaline. Site 7, Floyd County, Sample No. S79TX-l53-l-(l-4) Ap—O to 7 inches; brown brown (7.5YR 4/2) clay, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; few wedge shaped peds; extremely hard, very firm; few fine roots on ped faces; few fine pores; thin continuous clay films; few vertical cracks; neutral; gradual smooth boundary. B22t—19 to 28 inches; dark brown (7.5YR 4/4) clay, dark brown (7.5YR 3/4) moist; moderate medium blocky (7.5YR 4/2) clay loam, dark brown (7.5YR 3/2) moist; weak fine and medium granu- lar structure; hard, friable; few fine roots; few fine pores; neutral; abrupt smooth boundary. B2lt—7 to 18 inches; dark brown (7.5YR 4/2) clay, dark brown (7.5YR 3/2) moist; moderate medium blocky structure; few wedge shaped peds; extremely hard, very horizon. The Ap horizon was 6 in- ches thick at all sites, except at Site 7 where it was 7 inches thick. The Ap horizon represents mainly the plow layer, and the slight difference in horizon thickness possibly resulted from a difference in plowing depth. The Ap horizon was a brown silty clay loam at Sites l and 3 and a \ brown clay loam at other sites. The thickness of the B2lt horizo Il- was 7 inches at Sites 2 and 5, 8 at Site 1, l0 at Site 3, ll at Sites 4 and 7, and l3 at Site 6. The color was dark brown at all sites, but the tex- fture was silty clay at Site 1, clay loam at Site 5, and clay at the remaining sites. The B22t horizon was 7 inches tmduuSne5JhuSne2AhuSneQ 12 at Sites 1 and 7, and 13 at Sites 3 and 4. The color was dark brown at all sites, except Site 7 where it was reddish brown. The texture was silty clay at Sites 1 and 3, clay loam at Site 5, and clay at Sites 2, 4, 6, and 7. The thickness of the B23t horizon ranged from 1O inches at Site 6 to 18 n inches at Site 7. Other thicknesses were 12 inches at Site 5, 13 at Sites 1 and 4, 14 at Site 2, and 15 at Site 3. The soil was reddish brown at all sites, except at Site 3 where it was yellowish red. The texture was silty clay at Site 1, clay loam at Site 4, and clay at the remaining sites. The B24t horizon was the most variable horizon above the calcic horizon with respect to thickness and color. At Site 7, the B24t hori- zon was the calcic horizon and, therefore, is excluded from further discussion at this point. The thick- ness of the B24t was 6 inches at Site 4, 8 at Site 5, 14 at Sites 3 and 6, 15 at Site 2, and 2O at Site 1. The soil was yellowish red at Sites 1, 2, and 3, light brown at Site 4, reddish brown at Site 5, and reddish yellow at Site 6. The texture was silty clay at Site 1 and clay at the remaining sites. Other than horizon th. ness, col- or, and texture, profile conditions that were determined by the field descriptions were identical for all sites for the horizon being con- sidered, except for the B21t horizon at Site 2, which had “common verti- cal cracks” rather than “few vertical cracks” as was the case at other sites. , Also, the B24t horizon was the calcic horizon at Site 7, as previously men- tioned. The depth to the calcic horizon was greatest at Site 1, where it was 59 inches, and least at Site 5, where it was 4O inches’: Other depths were 58 inches at Site 3, 52 at Site 6, 5O at Site 2, and 48 at Sites 4 and 7. Depth ‘to the calcic horizon for profiles from different sites and thicknesses of the individual horizons comprising the profiles are illustrated in Fig. 12. This figure illustrates that total B21t | B23? 133C) '— __ ’ - , ':_.__-(; a 4Q l U1 .I 59-.., Fig. 12. Profile depths and thicknesses 0f the different horizons for the profiles at the different sites of Pullman soil. depth was not directly related to the thickness of any particular horizon. Although profile depth was greatest at Site 1, only the B24t horizon was thicker at Site 1 than at any other site. All other horizons were thicker at least at one other site than at Site 1. Likewise, profile depth at Site 5 was the least, but only the B22t was thinner at Site 5 than at any other site. All other horizons were as thick or thinner at least at one other site as at Site 5. Site 7, which had the thick- est B23t horizon, had a greater depth to the calcic horizon than Site 5, even though the B24t horizon at Site 7 was the calcic horizon and, therefore, was not included in the profile depth determination. Particle Size Distribution Results of particle size distribu- tion analyses are included in Table 5. At Sites 1, 4, and 7, sand content s highest in the Ap horizon, while (at Sites 2, 3, 5, and 6, sand content was highest in the B23t (Site 6) or B24t horizon. In intermediate hori- zons, sand content usually was lower than in either the Ap or the B23t or B24t horizons. Exceptions were at Site 1, at which sand content re- mained at 12.0 percent for all hori- zons below the Ap, and at Site 5, where sand content was similar in the Ap, B21t, and B22t horizons, lowest in the B23t horizon, and highest in the B24t horizon. The highest sand content of the Ap hori- zon (33.0 percent) occurred at Sites 4 and 7. The lowest (17.0 percent) occurred at Site 3, which was only 1 percent lower than that at Site 1. Silt content of the profile was highest in the Ap horizon at all sites and usually decreased with profile depth. Exceptions were at Site 1, where the B24t horizon contained more silt than intermediate hori- zons, and at Sites 2, 3, and 7, where the B21t horizon contained less silt than lower horizons. The highest silt content (53.0 percent) in the Ap horizon occurred at Site 3 and the lowest (39.0 percent) occurred at Site 7. At all sites, the Ap horizon con- tained less clay than any other hori- zon. The average for the Ap horizon was 31.0 percent. The highest clay content was either in the B21t or the B22t horizon, except at Site 5 where it was highest in the B23t horizon. 13 TABLE 5. CHARACTERISTICS OF PULLMAN SERIES AT STUDY SITES Water content 45* _ at potential of Site and Bulk county Sample no. Hor. Depth Sand Silt Clay Texture O.M. pH density -‘/3 bar -15 bars Plant available water in % % g/cm3 % in/in in/hor Site 1 _ S79TX-065-1-1 Ap 0-6 10.0 49.0 33.0 Silty clay loam 2.52 0.5a 1.2a‘ 20.52 10.73 9.0 0.123 0.74 Carson -2 B21t 6-14 12.0 41.0 47.0 Silty Clay 1.41 6.87 1.48 28.6 18.9 9.7 0.144 1.15 -3 B22t 14-26 12.0 40.2 47.8 Silty clay 0.94 7.31 1.62 25.8 17.9 7.9 0.128 1.54 -4 B23t 26-39 12.0 40.3 47.7 Silty clay 0.84 7.45 1.56 26.1 16.5 9.6 0.150 1.95 -5 B24t 39-59 12.0 42.1 45.9 Silty Clay 0.62 7.57 1.57 24.5 15.0 9.5 0.149 2.98 Weighted mean 12.6 41.9 45.5 --- 1.03 7.30 1.53 26.1 16.8 9.3 0.142 --- Total -- -- -- --- -- -- -- -- —- -- --- 8.36 Site 2 — S79TX-011-1-1 Ap 0-6 24.0 47.0 29.0 Clay loam 2.01 7.43 1.261 24.22 15.43 8.8 0.112 0.67 Armstrong -2 B21t 6-13 18.0 33.0 49.0 Clay 1.42 7.35 1.48 29.7 20.6 9.1 0.134 0.94 -3 B22t 13-21 16.5 35.7 47.8 Clay 1.07 7.54 1.56 26.9 18.8 8.1 0.126 1.01 -4 B23t 21-35 19.3 34.7 46.0 Clay 0.83 7.79 1.62 24.7 16.7 8.0 0.129 1.81 -5 B24t 35-50 25.0 31 5 43.5 Clay 0.53 7.65 1.65 23.7 16.0 7.7 0.127 1.91 Weighted mean 20.9 35.1 43.9 --- 1.00 7.60 1.56 25.4 17.2 8.2 0.127 --- Total -- -- -- --- -- -- -- -- -- -- --- 6.34 Site 3 _ S79TX-381-3-1 Ap 0-6 17.0 53.0 30.0 Silty clay loam 2.06 0.70 1.26‘ 25.02 10.03 9.0 0.113 0.60 Randall -2 B21t 6-16 13.0 38.8 48.2 Clay 1.29 6.77 1.48 28.8 18.5 10.3 0.152 1.52 -3 B22t 16-29 13.0 40.0 47.0 Silty clay 0.95 7.24 1.60 26.7 18.1 8.6 0.138 1.79 -4 B23t 29-44 15.0 40.8 44.2 Silt cla 0.76 7.58 1.58 24.8 15.7 9.1 0.144 2.16 Y Y -5 B24t 44-58 19.3 37.2 43.5 Clay 0.39 7.65 1.65 24.4 16.7 7.7 0.127 1.78 Weighted mean 15.5 40.7 43.9 --- 1.03 7.29 1.55 25.8 17.0 8.8 0.137 --- Total -- -- -- --- -- -- -- -- -- -- --- 7.93 Site 4 — S79TX-437-1-1 Ap 0-6 33.0 37.0 30.0 Clay loam 1.58 7.23 1.261 23.12 14.83 8.3 0.105 0.63 Swisher -2 B21t 6-17 25.8 33.0 41.2 Clay 1.36 7.54 1.48 25.6 17.4 8.3 0.121 1.33 -3 B22t 17-30 27.5 32.4 40.1 Clay 0.79 7.54 1.78 21.9 18.5 3.4 0.061 0.79 -4 B23t 30-42 32.7 29.3 38.0 Clay loam 0.54 7.73 1.44 21.6 15.1 6.5 0.093 1.12 -5 B24t 42-48 32.0 27.5 40.5 Clay 0.37 7.84 1.38 22.9 15.1 7.8 0.107 0.64 Weighted mean 26.9 31.7 38.6 --- 0.90 7.59 1.51 22.9 16.5 6.4 0.094 --- Total -- -- -- --- -- -— -- -- -- -- --- 4.51 Site 5 — S79TX-069-1-1 Ap 0-6 28.0 42.0 30.0 Clay loam 2.25 6.93 1.261 25.72 16.53 9.2 0.117 0.70 Castro -2 B21t 6-13 28.0 38.0 34.0 Clay loam 2.14 7.07 1.24 27.9 15.3 12.6 0.156 1.09 -3 B22t 13-20 28.1 32.9 39.0 Clay loam 1.46 7.14 1.52 24.5 20.5 4.0 0.061 0.43 -4 B23t 20-32 25.0 32.0 43.0 Clay 0.98 7.40 1.60 24.0 17.9 6.1 0.098 1.17 -5 B24t 32-40 31.5 29.0 39.5 Clay 0.80 7.60 1.46 23.8 15.3 8.5 0.124 0.99 Weighted mean 27.8 34.1 38.1 --- 1.42 7.27 1.44 25.0 17.2 7.8 0.110 --- Total -- -- -- --- -- -- -- -- -- --- 4.38 Site 6 — S79TX-117-1-1 Ap 23.0 40.0 37.0 Clay loam 1.59 7.23 1.261 27.12 18.33 8.8 0.112 0.67 Deaf Smith -2 B21t o-19 21.1 35.7 43.2 Clay 1.14 6.95 1.49 25.7 17.5 8.2 0.122 1.59 -3 B22t 19-28 23.0 33.4 43.6 Clay 0.78 7.39 1.58 26.0 17.4 8.6 0.136 1.22 -4 B23t 28-38 27.1 31.8 41.1 Clay 0.47 7.49 1.63 23.3 16.6 6.7 0.109 1.09 -5 B24t 38-52 27.1 31.8 41.1 Clay 0.37 7.49 1.63 23.3 16.6 6.7 0.109 1.53 Weighted mean 24.4 34.0 41.6 --- 0.79 7.31 1.54 24.8 17.2 7.6 0.117 --- Total -- -- -- --- -- -- -- -- -- -- --- 6.10 Site 7 1- S79TX-153-1-1 Ap 0-7 33.0 39.0 28.0 Clay loam 1.37 6.95 1.261 21.12 13.33 7.8 0.099 0.69 Floyd -2 B21t 7-18 29.1 27.9 43.0 Clay 0.88 7.04 1.49 24.8 19.2 5.6 0.084 0.92 -3 B22t 18-30 26.0 30.8 43.2 Clay 0.68 7.47 1.64 22.8 18.0 4.8 0.078 0.94 -4 B23t 30-48 30.0 29.0 41.0 Clay 0.56 7.73 1.64 23.1 16.2 6.9 0.113 2.04 Weighted mean 29.2 30.7 40.1 --- 0.78 7.39 1.55 23.1 16.9 6.2 0.096 --- Total -- -- --- -- -- -- -- -- -- --- 4.59 lLoosened tillage layer. Bulk density estimated from values obtained from earlier studies. zCalculated by Equation 1, Table 7, of Unger (1975). 3Calculated by Equation 2, Table 7, of Unger (1975). Usually, the B24t horizon contained less clay than horizons above it, ex- cept the Ap horizon. Clay content of the Ap horizon was lowest (28.0 per- cent) at Site“ 7 and highest (37.0 per- cent) at Site 6. For all horizons, the highest clay content (49.0 percent) was in the B21t horizon at Site 2. For all sites, the clay content av- eraged 41.5 percent in the B21t horizon and 44.1 percent in the B22t horizon. 14 CTThe soil texture of all horizons at all sites, based on the particle size distribution analyses, was identical to that determined at the time of describing the profiles in the field. Organic Matter At all sites, soil organic matter content was highest in the Ap hori- zon and decreased progressively with soil depth (Table 5). In the Ap horizon, organic matter content ranged from 1.37 percent at Site 7 to 2.52 percent at Site 1. In the B21t horizon, organic matter content ranged from 0.88 percent at Site 7 to 2.14 percent at Site 5. Site 5 also had the highest organic matter content in all deeper horizons. Organic mat- ter content was lowest in the B22t" horizon at Site 7, in the B23t horizon at Site 6, and in the B24t horizon at Sites 4 and 6. pH Soil pH generally was lowest in . he Ap horizon and progressively in- creased with depth (Table 5). Excep- tions occurred at Sites 2 and 6 where pH of the B21t horizons was slightly lower than that of the Ap horizon and at Site 2 where pH of the B24t horizon was lower than that of the B23t horizon. Reasons for the differ- ent trends at these sites are not ap- parent. The highest weighted mean pH value (7.60) was found at Site 2, which was only 0.01 higher than at Site 4. The mean pH at the remain- ing sites ranged from 7.27 to 7.39. Bulk Density Bulk density of the Ap horizon was not determined because this horizon, which was the plow layer, was loosened by tillage and re- mained loose at the time of sam- pling. Other studies, however, have shown that the bulk density of this horizon is highly variable, depend- ing on type and recentness of tillage. For this study, a bulk density of 1.26 g/cmg was assumed for the Ap hori- zon at all sites (Table 5). This value is the average for the Ap horizon in studies by Taylor et al. (1963), C ger (1969, 1972), and Unger et (1973). An assumed value is pro- vided for calculating the available water content of this horizon in a subsequent section. Bulk density of the B21t horizon was 1.48 or 1.49 g/cmB at all sites, except at Site 5 where it was 1.24 g/cmg’. The reason for the low value at Site 5 is not clear, but it possibly resulted from loosening of this hori- zon by deep plowing or chiseling. Bulk density usually increased with profile depths below the B21t hori- zon, but there were some excep- tions. At Sites 1 and 4, bulk density I was highest in the B22t horizon. The exceptionally high bulk density of the B22t horizon at Site 4 suggests that soil compaction had occurred, possibly due to tractor or implement traffic. At Site 4, bulk density pro- gressively decreased with depth be- ‘ow the B22t horizon with the value or the B24t horizon being lower than that of all other measured hori- zons at that site. At Site 5, bulk density of the B24t horizon was low- er than that of the B22t or B23t horizon. Bulk densities found at the differ- ent sites are not high enough to pre- vent root penetration, provided the soil water content is adequately high, but some reduction in root penetration may occur. Resistance to penetration of roots is influenced by soil strength, which is a function of soil bulk density and water con- tent (Taylor and Gardner, 1963). In their study with Amarillo fine sandy loam, Taylor and Gardner (1963) showed that some roots penetrated the soil at a bulk density of 1.75 g/cm3, provided the soil matric po- tential was — 1/2 bar or higher. For bulk densities equal to or below 1.65 g/cms, some root penetration oc- curred when the matric potential was — 2/3 bar or higher. Resistance to root penetration at similar soil ma- tric potentials and bulk densities may be different in Pullman soils than in Amarillo soils. Also, the bulk densities measured by core samples may be considerably different than that determined on individual soil peds. With core sampling, the bulk density represents an average densi- ty of the sampled volume, which includes the soil and the shrinkage cracks that develop as the soil dries. For individual peds, shrinkage cracks are not included in the sam- ple volume. The density of the peds, therefore, may be considerably higher than those obtained by core sampling and may be high enough to prevent root penetration. Although ped densities were not measured, high density of peds undoubtedly is responsible for roots growing be- tween rather than through the peds of Pullman soil, which has been ob- served. Water Retention Because cores were not obtained for the Ap horizon, water contents at — 1%; and — 15 bars matric potential for these horizons (Table 5) were calculated by equations developed by Unger (1975). These equations are based on the bulk density, or- ganic matter content, and clay con- tent of soil from the horizon. For the remaining horizons, determined values are given. The calculated values should be valid because the correlation coefficients obtained when developing the data were sig- nificant at the 0.1% level (Unger, 1975). Also, the values are generally close to those for the B21t horizon. Similar results were obtained by Un- ger (1969, 1970). Plant available water per inch of soil for the different horizons was based on plant available water con- tent (—1/3- minus —15-bar value) and bulk density of the horizons (Table 5). Totals for the profile are summations of the values for the in- dividual horizons. The mean water contents are weighted for the thick- nesses of the different horizons. The profile at Site 1 retained 8.36 inches of plant available water, but this was only 0.43 inch more than the amount at Site 3. The profile at Site 1 also had slightly higher mean water retention per inch of soil (Table 5). The differences in total and mean water retention at Sites 1 and 3 probably were not significant and were expected to be slight be- cause the profiles at these sites were similar in depth and other measured characteristics. The two next highest total water retention values were for profiles at Sites 2 and 6 for which the values were 6.34 and 6.10 inches, respec- tively. Again, similar values were expected for these sites because the profiles were similar in depth and most other characteristics. An ex- ception was the organic matter con- tent, which was lower at Site 6. The lower organic matter content prob- ably contributed to the lower water retention. However, the slightly lower clay content may have been a factor also because there is a closer relationship between clay content and water retention than between organic matter content and water retention (Unger, 1975). Total Water retention for the re- maining sites (Sites 4, 5, and 7) dif- fered by 0.21 inch or less (Table 5). The low total Water retention values resulted not only from the low pro- file depths at these sites, but also from the generally lower clay and higher sand contents at these sites. Sand, silt, and clay contents were similar at these sites. However, the profile at Sites 4 and 7 was 8 inches deeper than at Site 5, yet water 15 retention was not greatly affected. The relatively favorable water retention at Site 5 is attributed to the higher mean organic matter con- tent and lower mean bulk density as compared with those at Sites 4 and 7. Total water retention at Site 3 was 1.14 inches lower than a value of 9.07 inches calculated from data re- ported by Taylor et al. (1963) for a nearby location. Such difference could be within the limits of experi- mental error. However, our —1/s- and —15-bar values, which corres- pond to their field capacity and wilt- ing point values, generally were higher than their values. Also, our values were higher than the minimum values often obtained at harvest of dryland crops at the labo- ratory (unpublished data). These findings suggest that plants ex- periencing water stress for relatively long periods may extract soil water to lower levels than those represent- ed by the -15-bar value, which is normally considered to represent the permanent wilting point.‘ Based on 154 samples taken to a 58-inch depth at the laboratory in 1979, soil water content at harvest of dryland wheat, grain sorghum, and s"nflow- er averaged about 3 percentat units lower than the — 15-bar values given in Table 5 for Site 3. Such amount represents an extra 2.7 inches of plant available water at Site 3. This water may not be readily available to plants, but it may help plants sur- vive short-term droughts or allow plants to produce mature seed or grain, which they might not do with- out this extra water. Data from field sampling are not available from the remaining sites to make a similar comparison. However, if similar dif- ferences did occur, the extra amounts of water would range from about 1.5 inches at Site 5 to 2.9 inches at Site 1, with intermediate values for the remaining sites. Water Infiltration The results of water infiltration measurements are shown in Table 6. These data show total water infiltra- tion at 1O minutes and at 20 hours, and infiltration rates at various times from 10 minutes to 2O hours after applying water. Also included in Table 6 are means for the seven sites along with standard deviations from the means. Total infiltration at 1O minutes was highest at Site 7 (1.64 inches) and lowest at Site 1 (0.80 inch). Infiltra- tion at Site 7 was only O. 12 and 0.24 inch higher than at Sites 5 and 6, respectively. These three sites were near the southwestern boundary of the Pullman soil area where the soil, except for Site 4, has more sand in the profile than at other sites. Sand content and infiltration at 1O min- utes were lowest at Site 1. Multiple regression analyses showed that total infiltration and in- filtration rate at 1O minutes were positively related to sand content in the B21t horizon and the weighted mean sand content for the entire profile (Table 7). Other variables in- TABLE 6. AMOUNT AND RATE OF WATER INFILTRATION INTO PULLMAN SOILS cluded in the multiple regression analyses, both for the B21t horizorw and entire profile, were soil depth, silt content, clay content, organic matter content, and bulk density. The levels of significance and rank- ings of the variables with regard to their effect on infiltration are in- cluded in Table 7. Except for the initial analysis with all six indepen- dent variables, only those results are shown for which at least one partial regression coefficient was statisti- cally significant. The infiltration rate at 10 minutes was highest at Sites 5 and 7 and lowest at Site 2. All independent variables included in the analysis for the B21t horizon had a significant effect on infiltration rate at 10 min- utes. For the entire profile, only sand content had a significant effect. Although Site 7 had the highest total infiltration at 1O minutes, it also had the lowest total infiltration at 20 hours (3.18 inches). For the remain- ing sites, total infiltration at 20 hours ranged from 4.12 inches at Site 3 to 4.90 inches at Site 6, a difference of only 0.78 inch (Table 6). Total infil- tration at 2O hours was significantly related (positively) only with silt content in the B21t horizon (Table 7) The low total infiltration at Site 7 resulted from low infiltration rates from 1 to 20 hours after applying water (Table 6). Except for a rate similar to that at Site 5 at 2 hours, rates at Site 7 were the lowest for the 1- to 20-hour period. Based on the multiple regression Total infiltration at Infiltration rate at Site and County 10 min. 20 hr. 10 min. 30 min. 1 hr. 2 hr. 5 hr. 10 hr. 20 hr. in. in./hr. 1 - Carson 0.80 4.71 1.17 0.45 0.36 0.31 0.17 0.17 0.13 2 - Armstrong; 1.16 4.72 0.90 0.43 0.40 0.31 0.29 0.07 0.11 3 - Randall { 1.23 4.12 1.02 0.60 0.68 0.47 0.17 0.11 0.05 4 - Swisher 1.16 4.20 1.44 0.71 0.53 0.33 0.33 0.16 0.09 5 - Castro 1.52 4.51 2.10 0.63 0.37 0.25 0.17 0.13 0.08 6 - Deaf Smith 1.40 4.90 1.44 0.57 0.30 0.43 0.23 0.16 0.10 7 - Floyd 1.64 3.18 2.10 0.67 0.29 0.26 0.14 0.06 0.04 Mean 1.27 4.33 1.45 0.58 0.42 0.34 0.21 0.12 0.09 S. DY’ 0.28 0.58 0.48 0.11 0.14 0.08 0.07 0.04 0.03 ‘S. D. = Standard deviation. 16 ‘i9 TABLE 7. SUMMARY OF MULTIPLE LINEAR REGRESSION ANALYSES ASSOCIATING TOTAL INFILTRATION AND INFILTRATION RATES AT ‘l0 MINUTES AND AT 20 HOURS WITH VARIOUS B21T HORIZON AND PROFILE CHARACTERISTICS OF PULLMAN SOIL OBTAINED AT SEVEN SITES IN TEXAS. RANKINGS BASED ON STANDARDIZED PARTIAL REGRESSION fgOEFFlClENTSl AND LEVELS OF SIGNIFICANCE OF THE PARTIAL REGRESSION COEFFICIENTSZ BASED ON THE T-VALUE ARE ALSO SHOWN Independent variables3 Intercept Depth Sand Silt Clay 0.04. 0o 5E“ R5 Soil zone and dependent variable B21; horizon Partial regression coefficients Total infiltration 7.0050 0.1057(3)" 0.0200(4)* -0.0102(0)015 0.0054(2)" -0.4040(5)* - 7.4075(1)" 3.047 0.999" i" 1° i"i"- 0.2022 0.1054(4)" 0.0441(3)" -- 0.1012(2)" -0.4004(5)" - 7.4022(1)" 3.902 0.999" 2.0023 0.1300(4)" 0.0573(3)" -- 0.1211(1)" -- -0.3914(2)" 0.310 0.900" 0.3274 -- 0.0513(1)* -- 0.0403(2)01s -- -1.3141(3)015 0.172 0.005* -0.1701 -- 0.0429(1)" -- 0.0122(2)01s -- -- 0.109 0.070" 0.4007 -- 0.0372(1)" -- -- -- -- 0.103 0.002" Infiltration iato 30.0352 -0.1155(0)" -0.2201(1)" -0.2107(3)" -0.3399(2)** -2.0051(4)** - 3.0331(5)** 0.0040 0.999" a‘ 1° "ii" 40.9242 -- -0.3392(1)015 -0.3404(3) -0.3930(2)01s -1.5504(4)* -0.2050(5)01s 0.152 0970* 1.0499 -- -0.0439(1)* -0.0205(2)01s __ __ .. 0.244 0.005" Q 0.3172 -- 0.0571(1)" -- -- -- -- 0.245 0.000" Total infiltration -37.0340 0.1470(0)015 0.2502(1)015 0.2095(3)015 0.2970(2)015 2.0021 (4)015 5.7059(5)01s 0.474 0.099015 i" 2° "0"" 0.0592 -- -- 0.1014(1)" -- -- -- 0.420 0.774" Infiltration rate 0.3059 -0.0099(0)015 -0.0140(1)015 -0.0107(4)01s —0.0215(2)01s 0.0927(5)015 0.0001(3)0i5 0.027 0.002015 a‘ 2° "Oil's 0.3205 -- -0.0045(1)* -- -0.0032(2)01s -- -- 0.027 0.097015 0.1499 -- -0.0030(1)* -- " -- -- 0.020 0035* Entire grofile Partial regression coefficients Total infiltration -20.7023 -0.0345(4) 0.1030(1) 0.2534(2) -0.0050(0) -0.3439(5) 7.3430(3) 0.023 0.999015 i" iii "ii"- -20.0507 -0.0204(4) 0.1059(1)" 0.2403(2)" -- -0.2400(5) 7.1450(3)" 0.010 0.999" -21.3300 -0.0171(4)* 0.1073(1)" 0.2310(2)" -- -- 7.2459(3)" 0.045 0.991" -19.0000 -- 0.1920(1)" 0.2210(2)" -- -- 5.0020(3)" 0.045 0.991" 0.4794 -- 0.0353(1)* -- -- -- -- 0.101 0.015* Infiltration rate -20.0203 0.5012(1) 0.4001(2) -0.3220(5) 0.4990(4) 7.4750(3) -19.9440(0) 0.335 0.900015 a1 1° "ii" -9.0945 -- 0.1770(1)* 0.1003(2) -- -- -- 0.209 0.005‘ 0.2043 -- 0.0571(1)* -- -- -- -- 0.325 0.740* Total infiltration 72.3905 -1.0000(1) -0.5790(4) 1.0019(3) -0.4540(5) -19.9230(2) 2.1000(0) 0.700 0.053015 in 20 hours Infiltration iato 3.9947 -0.0144(2) -0.0210(1) ~0.0119(5) 0.0140(0) -0.3504(3) —1.0371 (4) 0.010 0.977015 "i 2° "W" 4.3017 -0.0294(1) -0.0207(2)* 0.0050(5) -- - 0.0130(3) -1.1407(4) 0.014 0.900015 4.3750 -0.0200(2)* -0.0292(1)* -- -- - 0.5425(3)* -1.1015(4)* 0.012 0904* IRankings are shown in parentheses immediately after partial regression coefficients. Rankings in order from 1 (highest) to 6 (lowest). 2Levels of significance of partial regression coefficients are *0.05, *"0.01, and NS (not significant). These are shown after the rankings. 3lndependent variables are: Depth - inches, sand content - %, silt content - %, clay content - %, organic matter content - "/0, and bulk density - g/cm3. 4Standard error of estimate. sCoefficient of correlation. Levels of significance are: "(0.05), “((101), and NS (not significant). analyses, infiltration rate at 2O hours was significantly related (negatively) to sand content in the B2lt horizon and in the entire profile. Other inde- pendent variables of the profile that significantly affected the infiltration rate at 20 hours were depth, organic matter content, and bulk density (Table 7). IMPLICATIONS FOR MANAGEMENT Plant Available Water The total amount of plant available " ater retained in the soil above the “falcic horizon was influenced by depth to the calcic horizon and by the water holding capacity of soil in different horizons. Total amounts ranged from 4.38 inches at Site 5 to 8.36 inches at Site I (Table 5). Therefore, a crop could extract al- most twice as much water from soil at Site 1 as at Site 5, provided both profiles were initially filled to capaci- ty with water and the crop’s root permeated and extracted water from the entire soil volume above the calcic horizon. Both conditions, however, often are not fulfilled un- der field conditions at all locations. Low water infiltration rates limit total irrigation water infiltration to about 5.0 inches in a 24-hour period (Table 6). This amount would fill the profile at Sites 4, 5, and 7, but about 8 to 25 extra hours would be needed to add each extra inch of water to the soil at the remaining sites. Pro- longed irrigation is not practical, and the profile at these sites is filled with water only during long wet periods or occasionally with repeated irriga- tions. Thus, actual available water contents at planting time may be similar at the different sites, even though the potential water holding capacity at those sites differs widely. Root penetration in Pullman soils varies with plant species. Sunflower and wheat roots have grown into and used water from the calcic horizon at Bushland. In contrast, sorghum gen- erally uses water from only the up- per 4 feet of soil at Bushland, thus not fully using all available water because depth to the calcic horizon is more than 4 feet. Therefore, even 17 though there are differences in wa- ter holding capacity and depth t0 calcic horizon at the different sites, the management required (for exam- ple, irrigation frequency) to obtain similar results with a given amount of water may be nearly identical at the sites, at least for crops that do not root deeply. The rate of water application, however, may need to be varied because of differences in infiltration rates.) Crops that root deeply, tolerate stress, and deplete soil water to lower values would re- quire irrigation less often than crops that root less deeply, are sensitive to stress, and fail to extract all the avail- able water. A marked difference in extent of water extraction by sun- flower and grain sorghum at the same depths of Pullman soil was found by W. C. Iohnson (unpublish- ed data, Bushland, Texas). When these crops were grown on adjacent fallowed plots, sunflower depleted the soil water supply more thor- oughly than grain sorghum at all depths. Water Application The low water infiltration rate into Pullman soil allows the use of long irrigation furrows (Fig. 11) with little deep percolation of water. Even when settings are changed only once daily, deep percolation generally is slight. However, unless cutback flow rates are used, tailwater runoff may be high. Some of this water can be recycled through tailwater recovery Fig .' 13. A tail water recovery system showing a reservoir to collect tail water runoff and a pump to return the water to the field ( USDA — Soil Conservation Service photo). 18 systems (Fig. l3), but the extra pumping adds to production costs. Pumping costs also are high for sprinkler systems (Fig. 14) because of the extra head required to pres- surize the system. However, labor requirements for sprinkler systems, such as center-pivot systems, are lower than for furrow-irrigation sys- tems. Also, the water can be applied with sprinklers at rates comparable to infiltration rates. In an ideally de- signed 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, there- fore, water losses by runoff. High-pressure sprinkler systems simultaneously apply water over a relatively large area, thus minimiz- ing runoff problems. These systems, however, are energy intensive 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. Evaporative losses of water should be lower, but runoff losses could be higher unless special provisions are made to re- duce runoff. Lyle (1979) controlled runoff and used water efficiently with a low-pressure, precision- water-application system used in conjunction with furrow dikes (Fig. 15). Booms, with attached nozzles, can be added at right angles to the main frame of the sprinkler system, thus applying water to a larger area at the same time. Service photo). Fig. 14. Irrigating alfalfa in Parmer County, Texas, with a high- pressure, center pivot sprinkler system (USDA — Soil Conservation Water Infiltration Variation Based on the data in Table there was about a two-fold variation i’ among the different sites in total wa- ter infiltration at 1O minutes and in- filtration rates at different times. This variation was significantly re- lated to various horizon and profile characteristics, as previously dis- cussed. However, total water infil- tration and infiltration rates varied considerably also among measure- ments made at some sites. Such vari- ation suggests that localized compac- tion and possibly soil cracking may m, be affecting infiltration and that wa- ter behavior on a given field in the vicinity of our sampling sites may be considerably different from that in- dicated by the data in Table 6. Where infiltration is much lower than expected, a compacted zone such as a plow pan may have de- veloped 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 afforded by crop residues, and im- prove soil conditions because of de- caying plant roots. Excessive infiltra- tion normally is not a problem on Pullman soil. Based on our measure- ments, large variations in infiltration are possible at all sites on Pullman soil. Fig. 15. Experimental low pressure sprinkler being used 0n a furrow- bloclced field (Photo provided by W. M. Lyle, TAES). Crop Sequences Wheat, grain sorghum, corn, cot- ton, sunflower, sugar beets, alfalfa, and some vegetable crops such as potatoes (Solanum tuberosum) and onions (Allium cepa) are adaptable and widely grown throughout some part or the entire area of Pullman soils. Whether the crops are grown continuously or in various rotations 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 generally moves beyond the depth of plant rooting and, therefore, re- duces water use efficiency for crop production. Unless a deep-rooted crop is subsequently grown, this wa- ter may be lost for crop production unless it eventually reaches the aquifer from which it could be pumped again. Water losses due to 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 ‘l either case, however, adequate wa- er must be available throughout the &rofile so that root growth is not ' restricted by a dry zone of soil. With water available to a 6-foot depth of Pullman soil at Bushland, dryland grain sorghum used water mainly to a 3-foot 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 6-foot depth (Johnson and Davis, 1980), sunflow- er with limited irrigation used water to a 10-foot depth (Unger, 1978a), and alfalfa used water to a 15-foot depth (Mathers et al., 1975) of Pull- man soil when water was available to these depths. Tillage and Cropping Practices Concern regarding the steady de- cline of the water level in the Ogalla- la Aquifer, which supplies water for irrigation of Pullman soils, has caused emphasis on conservation of irrigation water and increased the Fig. 17. Water retained on a furrow-blocked field on Pullman soil (Photo provided by O. B. ]ones, USDA-ABS). Fig. 16. Conservation bench terraces on Pullman soil at Bushland, Texas. Note the uniform distribution of runoff water collected on the leveled bench portion of the terrace system. emphasis on conservation and use of precipitation for crop production. Under dryland conditions, smore water from precipitation was con- served and grain yields were higher where stubble mulch tillage rather than one way disk tillage was used 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 (Fig. 16) and level bench terraces (Jones, 1975; Jones and Hauser, 1975); narrow benches, nar- row conservation benches, and large contour furrows (Jones, 1981); and furrow blocking (Clark and Huds- peth, 1976) (Fig. 17). These prac- tices retained potential runoff water 19 where it fell or retained it 0n a por- tion of the field, thus increasing the amount of water available for crop use. Little benefit was obtained with respect to reduced evaporation be- cause the residues produced by dry- land crops generally were not ade- quate to reduce evaporation greatly, even when all residues were main- tained 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 wa- ter storage from precipitation in no- tillage systems on dryland, major in- creases in water storage were ob- tained when residues from irrigated wheat (Fig. 18) were managed on the surface with no-tillage compared with when residues were worked in- to soil with tillage (Musick et al., 1977; Unger et al., 1971; Unger and Wiese, 1979). The extra stored water decreased the amount of irrigation water needed for irrigated grain sor- ghum (Musick et al., 1977) and in- creased the yields of dryland grain sorghum (Unger and Wiese, 1979) (Fig. 19). In a controlled residue- level study, water storage during fal- low and subsequent grain sorghum yields increased as surface residues (wheat) increased from 0 to about 11,0()0 pounds per acre (Unger, 1978b). Dryland wheat often yields only about 1,500 to 2,500 pounds of residue per acre at Bushland. In contrast, irrigated wheat often yields Fig. 18. Irrigated wheat produces large amounts 0f residue that can be managed for soil and water conservation (USDA —— Soil Conservation Service photo). 20 4,000 to 6,000 pounds of residue per acre and 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 in- crease water use efficiency for crop production on Pullman soil. The benefits from surface residues result from greater total infiltration and less evaporation of water. Be- cause of the greater water storage capacity of the deeper profiles at Sites 1 and 3 than that of the shal- lower profiles at Sites 4, 5, and 7, response to surface residues at Sites 4, 5, and 7 may be less than at Sites 1 and 3. With shallower profiles, the soil is more readily filled with water to the calcic horizon, especially where initial water infiltration rates are higher, as at Sites 4, 5, and 7. The greater response to surface resi- dues at a deep site (Site 3) as com- pared 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 es- sentially filled the shallow profile with water with both tillage methods near Lubbock, sorghum yields were not significantly different because of tillage. At Bushland (near Site 3), no-tillage significantly increased grain yields of sorghum over yields with disk tillage when the sorghum was not irrigated. With irrigation, sorghum yields were similar with both tillage treatments. A benefit from lower evaporation with surface residues is the pro- longed time that the surface layer remains wet enough to influence seed germination beneficially. Whereas rapid decreases in surface soil water content because of evapo- ration may cause poor germination on relatively smooth bare soils, the slower evaporation on mulched soils may result in favorable germination of crops. Fig. 19. Grain sorghum planted in standing wheat stubble by the no-tillage method (USDA — Soil Conservation Service photo). Ranching and Livestock Production Banching and livestock produc- tion are important agricultural en- terprises on the High Plains. Native grassland on Pullman soils covers about 1.5 million acres, or 40 per- cent of the total land area. Most ranches are cow-calf operations, though stocker steers make up a sig- nificant percentage of many herds (Fig. 20). Usually, these stocker cat- tle are placed in nearby feedlots for finishing. On many ranches, the forage pro- duced on rangeland is supplemented by crop stubble and small grain. In winter, the native forage is often supplemented with protein concen- trate. 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. Much of the acreage that was once open grassland is now covered with brush, weeds, or cactus (Fig. 21). Forage production now may be less than half the original produc- tion. Productivity of range can b increased by using management practices that are effective for specif- ic kinds of soils and range sites. Where climate and topography _ rennial forbs Fig. 20. Cattle on native-grass rangeland on Pullman soil (USDA — Soil Conservation Service photo) . Fig. 21. Rangeland in poor (left of fence) and excellent condition (right) on Pullman soil. Consistent overuse has resulted in more C holla cactus and small mesquite becoming established in the pasture at the left (USDA — Soil Conservation Service photo). TABLE 8. TYPICAL VEGETATION AND POTENTIAL PRODUCTlONl ON A PULLMAN CLAY LOAM RANGE SITE Plant name Common Scientific %2 Blue grama Bouteloua gracilis 40 Buffalograss Buchloe dactyloides 25 Sideoats grama Western wheatgrass Vine-mesquite “A Silver bluestem Tobosa Other perennial grasses Bouteloua curtipendula Agropyron smithii Panicum obtusum Andropogon saccharoides Hilaria mutica U1U1U1U1U1U1U1 ,1’ ‘Potential production of air-dry vegetation is 2,000 pounds/acre in a favorable year, 1,500 in a normal year, and 1,000 in an unfavorable year. ZPercentages refer to the expected proportion of each species in the total annual production on an air- dry basis. 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 in the composition of the climax plant community on a typical clay loam range site are given in Table 8. The potential total annual production of vegetation in ‘favorable, normal, and unfavorable years is shown in the footnote for the table. In addition to knowledge of soil properties and the climax plant com- munity, range management requires an evaluation of the present condi- tion of the range vegetation in rela- tion to its production potential. Range condition on a particular range site is determined by compar- ing the present plant community with the climax plant community for the site. The more closely the exist- ing community resembles the climax community, the better the range condition (Fig. 22). 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 vege- tation, conservation of water, and control of erosion. Sometimes, how- ever, a range condition somewhat below the climax meets grazing needs, provides desirable wildlife habitat, and protects soil and water resources. y 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. If sound range management based on soil information and range- land inventories is applied, the po- tential is good for increasing the pro- ductivity of rangelands. 21 Fig. 22. A range in excellent condition on Pullman soil in Swisher County, Texas. About 95 percent of the vegetation is blue g TEXAS AMI UNIVERSITY , || 1.9535 721.1179 percent buffalograss (USDA — Soil Conservation Service photo). LITERATURE CITED Army, T. J., A. F. Wiese, and R. J. Hanks. 1961. Effect of tillage and chemical weed control practices 0n soil moisture losses during the fallow period. Soil Sci. Soc. Am. Proc. 25:410-413. Baumhardt, Roland Louis. 1980. Influence of tillage and irrigation on grain sorghum pro- duction. Thesis submitted for Master of Science Degree, Texas Tech University, Lubbock, May 1980. Clark, R. N., and E. B. Hudspeth. 1976. Runoff control for summer crop production in the Southern Plains. Trans. Am. Soc. Agric. Eng. Paper No. 76-2008. Coover, James R., C. E. Van Doren, and Charles J. Whitfield. 1953. Some character- istics of the Pullman soils on the Amarillo Experiment Station. Texas Agric. Exp. Stn. MP-97. 11 pg. A Day, Paul R. 1965. Particle fractionation and particle-size analysis. In C. A. Black (ed) Methods of Soil Analysis, Part 1. Agron.. 9:545-567. Ezekiel, Mordecai, and Karl A. Fox. 1959. Methods of correlation and regression analysis, 3rd ed. John Wiley 8t Sons, Inc., New York. 22 Jackson, M. L. 1958. Organic matter determi- nation for soils. p. 205-226. In Soil Chemi- cal Analysis. Prentice-Hall, Englewood Cliffs, New Jersey. Johnson, Wendell C., and Ronald G. Davis. 1972. Research on stubble-mulch farming of winter wheat. U.S. Dept. Agric.—Agric. Res. Serv. Conserv. Res. Rpt. No. 16. U.S. Gov’t Printing Office, Washington, DC. 32 PP- Johnson, Wendell C., and Ronald G. Davis. 1980. Yield-water relationships of summer- fallowed winter wheat. U.S. Dept. Agric., Sci. Educ. Admin., Agric. Res. Results ARR-S-5. 43 pp. 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. Jones, Ordie R. 1981. Land management ef- fects on dryland sorghum production in the Southern Great Plains. Soil Sci. Soc. Am. J. 45:606-611. Jones, O. R., and V. L. Hauser. 1975. Runoff utilization for grain production. Water , $4.. Harv. Symp. Proc., Phoenix, Arizona. U.S. Dept. Agric., Agric. Res. Serv. W-22. pp. 277-283. Lyle, WIlliam M. 1979. Low energy precision water application system. Crop Prod. and Util. Symp. Proc., Amarillo, Texas, Feb- ruary 1979. p. F1-5. Mathers, A. C., B. A. Stewart, and Betty Blair. 1975. Nitrate-nitrogen removal from soil profiles by alfalfa. J. Environ. Qual. 42403-405. Musick, J. T., A. F. Wiese, and R. R. Allen. 1977. Mangement of bed-furrow irrigated soil with limited- and no-tillage systems. Trans. Am. Soc. Agric. Eng. 20:666-672. Steel, Robert G. D., and James H. Torrie. 1960. Principles and Procedures of Statis- tics with Special Reference to the Biological Sciences. McGraw-Hill Book Co., New York. Taylor, Howard M. and Herbert R. Gardner 1963. Penetration of cotton seedling tat’? roots as influenced by bulk density, mois- ture content, and strength of soil. Soil Sci. 96: 153-156. Taylor, Howard M., C. E. Van Doren, Curtis rama grass and about 5 L. Godfrey, and Iames R. Coover. 1963. Soils of the Southwestern Great Plains Field Station. Texas Agric. Exp. Stn. MP- 669. 14 pp. Texas Department of Agriculture. 1977. Texas county statistics. Texas Dept. Agric., Aus- tin, Texas. Unger, Paul W. 1969. Physical properties of Pullman silty clay loam as affected by dry- land wheat management practices. Texas Agric. Exp. Stn. MP-933. 10 pp. Unger, Paul W. 1970. Water relations of a profile-modified slowly permeable soil. Soil Sci. Soc. Am. Proc. 34:492-495. Unger, Paul W. 1972. Dryland winter wheat and grain sorghum cropping systems —— Northern High Plains of Texas. Texas Ag- ric. Exp. Stn. B-1126. 20 pp. Unger, Paul W. 1975. Relationships between water retention, texture, density and or- ganic matter content of west and south central Texas soils. Texas Agric. Exp. Stn. MP-1192C. 2O pp. Unger, Paul W. 1977. Tillage ellects on win- ter wheat production where the irrigated and dryland crops are alternated. Agron. I. 69:944-950. Unger, Paul W. 1978a. EiTect of irrigation frequency and timing on sunflower growth and yield. Proc. 8th Int. Sunflower Conf, Iuly 1978, Minneapolis, Minnesota. pp. 117-129. Unger, Paul W. 1978b. Straw-mulch rate ef- fect on soil water storage yield. Soil Sci. Soc. Am. 42:486-491. Unger, Paul W., Ronald R. Allen, and Iessie I. Parker. 1973. Cultural practices for irri- gated winter wheat production. Soil Sci. Soc. Am. Proc. 30:437-442. Unger, Paul W., Ronald R. Allen, and Allen F. Wiese. 1971. Tillage and herbicides for surface residue maintenance, weed control, and water conservation. I. Soil Water Con- serv. 26:147-150. Unger, Paul W., and Allen F. Wiese. 1979. Managing irrigated winter wheat residues for water storage and subsequent dryland grain sorghum production. Soil Sci. Soc. Am. 43:582-588. Wiese, A. F., and T. I. Army. 1958. Effect of tillage and chemical weed control practices on soil moisture storage and losses. Agron. I. 50.465468. Wiese, A. F., I. I. Bond, and T. I. Army. 1960. Chemical fallow in dryland cropping sequences. Weeds 8:284-290. Wiese, A. F., Earl Burnett, and I. E. Box, Ir. 1967. Chemical fallow in dryland cropping sequences. Agron. I. 59:175-177. 23 “ at 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 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 are available to everyone without regard to race, ethnic origin, religion, sex, or age. 1.5M - 10-81 a ‘W