Distribution Importance, Variability, and Management The Texas Agricultural Experiment Station Edward A. Hiler, Director College Station, Texas in cooperation with United States Department of Agriculture Agricultural Research Service Soil Conservation Service Contents Introduction .............................................................................................................................................................................. .. 1 Area Occupied by Acuff Soils ...................................................................................................................................... ..1 v Objectives of the Study .................................................................................................................................................. ..1 History of the Acuff Series ............................................................................................................................................ ..4 Physiography .................................................................................................................................................................. ..5 Uses and Importance of Acuff Soils ............................................................................................................................ ..7 Typical Site for Acuff Soils ............................................................................................................................................ ..7 Present Water Management Systems .......................................................................................................................... .. 8 Experimental Procedure ......................................................................................................................................................... .. 9 Site Selection ................................................................................................................................................................... ..9 Sampling Techniques ..................................................................................................................................................... ..9 Sample Preparation and Analyses ............................................................................................................................... ..9 Results and Discussion .......................................................................................................................................................... .. 10 Profile Descriptions ...................................................................................................................................................... ..10 ~ Particle Size Distribution ............................................................................................................................................. .. 16 Bulk Density .................................................................................................................................................................. .. 16 Organic Matter .............................................................................................................................................................. .. 20 pH ................................................................................................................................................................................... ..20 Calcium Carbonate (CaCOa) Equivalent ................................................................................................................... .. 20 Water Retention ............................................................................................................................................................ .. 20 Water Infiltration .......................................................................................................................................................... ..21 Implications for Management .............................................................................................................................................. ..23 Plant-available Water (PAW) ..................................................................................................................................... ..23 Water Application ........................................................................................................................................................ ..24 Water Infiltration Variation ........................................................................................................................................ ..25 Crop Sequences ............................................................................................................................................................ .. 26 Tillage and Cropping Practices .................................................................................................................................. ..26 Ranching and Livestock Production ......................................................................................................................... ..28 CV Summary ................................................................................................................................................................................. .. 29 Literature Cited ...................................................................................................................................................................... ..31 Paul W. Unger, Fred B. Pringle, and Dan A. Blackstock, Soil Scientists, USDA, Agricultural Research Service, Bushland, Texas 79012; USDA, Soil Conservation Service, Amarillo, Texas 79121; and USDA, Soil Conservation Service, Lubbock, Texas 79414. Editor, Tom Sneed Cover design, Roxy Pike Typesetting, Cherie LeBlanc Department of Agricultural Communications Texas A&M University System Cover photographs: F urrow dikes retain both irrigation and rain water on the land. Dryland grain sorghum Benefits from residues ‘\/' from the previous irrigated winter wheat crop managed on the soil surface by no-tillage methods. i Q Acuff Soils — Distribution, Importance, Variability, and Managementl UERARy SEP 2 9 1993 Paul W. Unger, Fred B. Pringle, and Dan A. Blackstock y Introduction Area Occupied by Acuff Soils Acuff soils’ occupy parts of 22 counties in the Southern High Plains of Texas and parts of three counties in eastern New Mexico (Figures 1, 2). The portions of different coun- ties occupied by Acuff soil range from about 0.1 to 37 percent (Table 2). The area of Acuff soils is bounded by the area of Pullman soils on the north and east, the Edwards Plateau escarpment on the south, the Cap- rock escarpment at the High Plains- Rolling Plains boundary on the southeast, and a catena of sandy soils extending from Stanton, Texas, to Clovis, New Mexico, on the west. Within this roughly crescent-shaped area, Acuff soils occupy about 21 percent of the land surface. The area of Acuff soils ranges from about 101°10min. to 103°5O min. west longitude and from about 32°1 0 min. to 35°40 min. north latitude Eleva- tion of the surface ranges from about 2,500 to 4,200 feet above mean sea level. The area is in a subhumid to semiarid climatic zone where aver- age annual precipitation ranges from about 16 inches at the western edge to about 21 inches at the eastern edge (Table 3). Also listed in Table 3 are the average length and dates of the frost-freeperiod,average daily maxi- mum and minimum temperatures, and average precipitation in coun- ties in which Acuff soils are found. Acuff soils occupy about 1.1 2 mil- . lion acres of land (Table 2) and are among the most extensive arable soils in Texas. Acuff soils also oc- cupy a small area of New Mexico. Other major arable soils in Texas are ‘Contribution from the USDA, Agricultural Research Service, P.O. Drawer 1 0, Bushland, Texas 79012, and the USDA, Soil Conserva- tion Service, Amarillo, Texas 79121, and Lubbock, Texas 79414. ‘See Table 1 for classification of soils men- tioned in this report. Pullman with 3.8 million acres, Amarillo with 2.75 million acres, and Houston Black with 1.5 million acres. Objectives of the Study Most research information re- garding Acuff soils was obtained at the Texas A&M Research and Exten- AS1111‘? UNIVERSITY sion Center at Lubbock, Texas, and at the Agricultural Research Service Laboratory at Big Spring, Texas. Most research applicable to Acuff soils was conducted in conjunction with, or as a component of, projects involving the Amarillo series. In other instances, measurements were made in order to augment other re- Figure l. The approximate major area of Acuff soils is delineated by the solid line. Approximate locations of sampling sites are indicated by numbered dots. 1 l" DIVIS r 01;: — KIIIIM UMISIMII NNIHIIHHPJZIUI I {Q HIICIMSN IOIIIIS WIHMI I I mum I I cm 1 uusrnorrc 0mm =~~-*~""‘ I "$5M gun MIMI!!! e ‘WIN, mum norm com! Q '_1 tom "c" neuron cnosuv olmus KM mo! ‘ "“°' ‘i IIINIX xun stourwut msxru ' - 5cm" HSIII IONS “"6" IlTCHll sviifiic IIIWSYII ___I E CHI!!!" SCH l KIWI _____. m“ SIIIHII I! VIA. VHO! 1 m . , \ Figure 2. Counties of Texas and New Mexico in which Acuff soils have been mapped extensively are within the heavy-lined area. Table 1. Classification oi soils mentioned in the text and figures. Series Classification Acult Fine-loamy, mixed, thermic Aridic Paleustolls Amarillo Fine-loamy, mixed, thermic Aridic Paleustalls Arvana Fine-loamy, mixed, thermic Petrocalcic Paleustalls Berda Fine-loamy, mixed, thermic Aridic Ustochrepts Bippus Fine-loamy, mixed, thermic Cumulic Hapluslolls Drake Fine-loamy, mixed (calcareous), thermic Typic Ustonhents Estacado Fine-loamy, mixed, thermic Calcionhldic Paleustolls Houston Black Fine, monlmorillinitic, thermic Udic Pellusterts Lazbuddie Fine, monlmorillinitic, thermic Entic Pellusterls Lipan Fine, montmorillinitic, thermic Entic Pellustens Lollon Fine, mixed, thermic Verlic Arglustolls Mansker Fine-loamy, carbonatic, thermic Calciorthidic Paleustolls Mobeetie Coarse-loamy, mixed, thermic Aridic Ustochrepts Olton Fine, mixed, thermic Aridic Paleuslolls Pep Fine-loamy, mixed, thermic Aridic Calciustolls Portales Fine-loamy, mixed, thermic Aridic Calciustolls Posey I Fine-loamy, carbonalic, thermic Calcionhidic Paleustolls Potter Loamy, carbonatic, thermic, shallow Ustollic Calcionhids Pullman Fine, mixed, thermic Torrertic Paleustolls Randall Fine, mixed, thermic Udic Pellustens Richlield Fine, montmorillinitlc, mesic Aridic Argiuslolls Sherm Fine, mixed, mesic Torrertic Paleustolls Table 2. Areas occupied by Acull soils. Mapping Portion Total unit oi series Total Irrigated Other County, State Slope area county area cropland cropland Rangeland land " (%) (acres) (%) (acres)‘ (acres) (acres) (acres) (acres? Bailey, Texas 0-1 5890 1 .1 7580 5340 1 1 10 490 60 1-2 1690 0 3 - 1020 20 Borden, Texas 0-1 21380 3 7 44760 1000 12610 220 1-3 23380 4.0 3510 100 19640 230 Briscoe, Texas 0-1 3510 0.6 9310 3160 1600 ' 300 50 1-3 5800 1 0 1570 1000 70 Castro, Texas . 0-1 9450 1 6 22000 8040 820 100 1-3 11790 2 0 8370 6890 3300 120 3-5 760 0.1 - - 760 - Cochran, Texas 0-1 1 800 0.4 2390 1 320 930 460 20 1-2 590 0 1 1140 390 _ 10 Curry, New Mexico 0-2 157650 17 6 171500 119350 47740 37300 1000 2-5 13850 1 5 5540 1940 8180 130 Dawson, Texas 0-1 31060 5 4 32090 23300 9000 7460 300 1-3 1030 0 2 100 450 50 Donley, Texas 1-0 1970 0 3 14770 1600 1000 320 50 1-3 8400 1 4 5460 2000 2840 100 3-5 4400 0 7 1100 500 3240 60 Garza, Texas 0-1 11150 1 9 14830 8290 1050 2760 100 1-3 3680 0 6 2050 60 1610 20 Hale, Texas 0-1 3710 0 6 13890 3470 2250 220 20 1-3 10180 1 6 8590 6450 1490 100 Hockley, Texas 0-1 85450 14 7 92390 66790 29140 16860 1800 1-3 6940 1 .2 5900 1020 1020 20 Howard, Texas 0-1 27910 4.8 35990 18140 3650 9470 300 1-3 8080 1 4 3230 650 4800 50 Lamb, Texas 0-1 30580 4 7 42160 29120 27760 620 840 1-3 11580 1.8 11100 10950 250 230 Lea, New Mexico 0-1 3870 0.1 3870 400 3440 30 Lubbock, Texas 0-1 111010 19 3 124030 100700 67860 4760 5550 1-3 13020 2 3 11670 5250 1200 150 Lynn, Texas 0-1 169940 29 7 211600 133360 66320 34580 2000 1-3 41660 7 3 31230 9020 10130 300 Martin, Texas 0-1 10440 3 2 18440 11300 2260 7040 100 Oldham, Texas 0-1 6760 0 7 42950 5750 2500 960 50 1-3 28210 2 9 21160 8000 6850 200 3-5 7980 0 8 2800 800 ' 5140 40 Parmer, Texas 0-1 63300 11 2 93100 58450 55210 2950 1900 1-3 29800 5 3 20500 14070 8410 890 Potter, Texas 0-1 1230 0 2 58690 1100 600 110 20 1-3 34560 5 9 20700 7300 13360 500 3-5 22900 3.9 8000 800 14450 450 Randall, Texas 0-1 3060 0.5 5570 2600 1300 400 60 1-3 2510 0.4 1500 500 960 50 Roberts, Texas 0-1 6520 1.1 9330 4900 2400 1560 60 - 1-3 2810 0 5 - - - - - Roosevelt, New Mexico 0-1 31030 2 0 42050 18600 11200 12130 300 1-3 11020 0.7 4400 1760 6510 110 Terry, Texas 0-1 6010 1 .1 6460 2360 530 3530 1 20 1-3 450 0.1 30 280 10 Swisher, Texas 1-3 620 0.1 620 1 10 410 10 Total 1120370 1 120370 819750 425860 278840 18970 ‘Includes total area lorall slopes and condition. Totals for the different slopes and conditions may not equal the total for the series because of rounding values to the nearest 10 acres. ‘includes land in reads, towns, and other non-agricultural uses. search projects. These soils cover extensive areas of the High Plains of Texas and New Mexico and vary considerably in profile properties across the area. One property that varies widely is depth to the calcic horizon. Because profile depth strongly influences plant rooting depth and thus the effective depth for storing water, a knowledge of profile depth along withacharacter- ization of other profile properties is important for improved water and crop management on Acuff soils. The 3 objective of this study was to deter- mine the variation in depth, bulk density, texture, organic matter con- tent, pH, calcium carbonate equiva- lent, and water retention of the dif- ferent horizons of Acuff soils as af- fected by location in the region. Table 3. Elevation and climatic factors in counties having Acull soils. Avg annual Average Avg daily Avg lake growing season temp‘ annual County, state,station Elev evaporation Max Min precip‘ it in d period °F in Bailey, Texas, Muleshoe 4,000 69 181 Apr 23 - Oct 22 73.7 41.0 17.44 Borden, Texas, Gail 2,500’ 69 214 Apr 6 - Nov 6 77.1 51.1 17.37 Briscoe, Texas, Silverton 3,280 69 214 Apr 6 - Nov 6 71.7 p 42.6 20.77 Castro, Texas, Dimmitt 3,855 - 193 Apr 16 - Oct 26 72.4 41.2 17.50 Curry, New Mexico, Clovis 4,280 - 195 Apr 16 - Oct 28 72.4 41.2 18.19 Dawson, Texas, Lamesa 2,975 69 208 Apr 8 - Nov 2 72.1 43.2 18.61 Donley, Texas, Clarendon 2,700 68 206 Apr 9 - Nov 1 73.6 44.3 21.51 Garza, Texas, Post 2,500’ 71 216 Apr 5 - Nov 7 75.1 50.2 18.82 Hale, Texas, Plainview 3,370 69 211 Apr 10 - Nov 6 73.9 44.3 19.01 Hockley, Texas, Levelland 3,500 70 205 Apr 13 - Nov 3 75.7 45.3 17.64 Howard, Texas, Big Spring 2,400 84 219 Apr 3 - Nov 8 76.5 49.3 18.65 Lamb, Texas, Littlefield 3,556 70 201 Apr 14 - Nov 1 75.9 45.6 18.91 Lubbock, Texas, Lubbock 3,250 69 211 Apr 7 - Nov 4 73.9 44.3 18.30 Lynn, Texas, Lubbock 3,250 69 211 Apr 7- Nov 4 73.9 44.3 18.30 Oldham, Texas, Vega 4,000 68 185 Apr 26 - Oct 21 70.5 41.0 17.75 Parmer, Texas, Friona 4,101 68 183 Apr 20 - Oct 20 71.3 42.1 17.50 Potter, Texas, Amarillo 3,650 68 198 Apr 20 - Oct 28 70.8 43.9 20.28 Randall, Texas, Canyon 3,577 68 200 Apr 15 - Nov 1 73.8 43.2 19.53 Roberts, Texas, Miami 2,875’ 69 194 Apr 20 - Oct 24 71.6 42.8 20.66 Roosevelt, New Mexico, Portales 4,350 72 183 Apr 20 - Oct 20 74.0 42.0 16.94 Swisher, Texas, Tulia 3,500 68 205 Apr 10 - Nov 1 72.9 42.6 17.24 Terry, Texas, Lamesa 2,975 69 208 Apr 8 - Nov 2 73.9 44.3 15.95 ‘Average values ior monthly and maximum and minimum temperatures and precipitation are available in most published soil surveys. ‘Recording station not located in Acuii series area oi occurrence. Water infiltration at the different lo- . cations was also determined. History of the Acuff Series The Acuff series was established in the Soil Survey of Hale County, Texas, in 1969 (SCS, 1974). It was named after the town of Acuff in Lubbock County on the Southern High Plains. Before 1969, Acuff soils wereincluded in other series, mainly the Amarillo and Richfield series. The process of inventorying and clas- sifying soils on the High Plains be- gan with the publication of the Re- connaissance Soil Survey of the Pan- handle Region of Texas in 1910. In this survey, Acuff soils were called Amarillo loam. The Amarillo series was established in this survey 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 of the Texas High Plains included these soils in both the Amarillo and Richfield series. Further investigations plus the implementation of soil taxonomy resulted in refinements to series cri- teria. The Acuff series was estab- lished for those soils of the Southern High Plains that have dark colored loamy surfaces and reddish brown subsoils with clay contents less than 35 percent, and a mean annual soil temperature greater than 59°F at a 20-inch depth. The soil was formed from fine-textured sediments of the High Plains eolian (wind deposited) mantle under a dense cover of short grasses (Figure 3). Figure 3. Dense cover of short grasses once covered Acuff soils. \ Physiography The topography consists of nearly level to gently sloping, smooth tree- less plains (Figure 4). Surfaces are plane to convex and slopes range from 0 to 3 percent, but are mainly O to 2 percent. These broad plains are interrupted only by the numerous playas (or shallow lakes) and a few major drainageways containing other soils. Except where pitted by playas, the surface is normally re- markably smooth. The playas range from less than one acre to several square miles in surface area, and from a few inches to more than 5O feet in depth. The average grade of the High Plains is about 10 feet per mile to the southeast. Runoff fol- lows a poorly defined drainage pat- tern. Water flows mainly into the playas, from which there is no defi- nite outlet. The water collected in playasislost rnainlyby evaporation, but some does infiltrate and some is pumped from the lakes for irriga- tion. Other soils associated with the Acuff series in the landscape include Amarillo, Drake, Estacado, Lazbuddie (T, tentative), Lofton, Mansker, Olton, Pep (T), Posey, Pull- man, and Randall (Figures 5, 6, and 7). Amarillo soils have light colored, fine sandy loam surfaces. They are found on the same general land- scape, and in close association, with Acuff. Estacado, Mansker, Pep, and Posey are calcareous, loamy soils on low convex ridges, on sideslopes around playas, and along draws. Pullman and Olton soils are on smooth plains and are similar to, Acuff in appearance. However, the Bt horizons of these soils are dark brown, have clay or clay loam tex- tures, and are less permeable than Acuff. Randall soils, which are dark gray and have clay textures through- out, are on playa bottoms. Drake soils are calcareous, have clay loam textures, and are more permeable. They are on convex knolls or cres- cent-shaped dunes along the eastern rims of playas. Lazbuddie and Lofton soils are on bottoms of smaller playas and on benches of larger pla- yas. Lofton soils have dark colored, loamy surfaces and grayish-brown- clayey subsoils. Lazbuddie soils are QFigure 4. This cropland shows the typical topography of the Acuff soil region. clayey throughout with a dark gray surface layer and light gray subsoils. There are differences in the mor- phological properties of the Acuff series that are related to geographic location. These differences affect soil water storage capacity, which, in turn, affects water management on these soils. The morphological features are: depth to strong calcic horizon (>30% CaCOs), depth to layer of strongly contrasting mate- rial, soil texture, and permeability. An analysis of soil survey field notes for 1O counties and additional profile observations revealed that depth to a strong calcic horizon ranges from 34 to more than 54 inches. Observations by soil and plant scientists indicate that calcic horizons containing at least 3O per- cent lime (CaCOs) inhibit root devel- opment of most crops. Based on laboratory determinations using a simple volume calcimeter, the aver- age CaCO3 content in the Btk hori- zon of Acuff soils is about 45 per- cent. To present a clearer understand- ing of these soils as they relate to geographic location, it is convenient to divide the large area into two soil provinces (Figure 2). The northern province includes those areas of Acuff soils in Castro, Parmer, and Swisher Counties as well as the northern one-third of Lamb County. Also included is that portion of Hale County north of the sand hills and the area of Acuff soils in Curry County, New Mexico. Slopes are nearly level to gently sloping (Fig- ure 6). Surfaces are smooth and slightly convex. In the northern prov- ince, Acuff soils are intermingled with areas of Estacado, Lazbuddie, Mansker, Olton, Pep, Posey, Pull- man, and Randall soils. Of the total area, Acuff soils make up approxi- mately 40 percent, Pullman 2O per- cent, and Olton 20 percent. Estacado, Lazbuddie, Mansker, Pep, Posey, and Randall soils make up the re- maining 2O percent. Ol ton and Pull- man soils occupy the same general landscape as Acuff, although their surfaces are smoother. Clay content in the upper 20 inches of the Acuff subsoil is commonly about 32 per- cent. Acuff soils in the northern province closely associated with Playa Soils Berda an ‘Mantle’ . Q's-say | . _ -o ‘.5, .-.-..'.-.~ 1'..~-'-- - . : -- "v ~I.._..o '1'." ‘J5 . Acufi‘ \\\ /--"""'"'__7""‘-~\ a/ _. -"" r ,\\ —' __ __ _l 1/ \ /‘<\ \ \ , ’ \\ "I \ I ’ “ Estacado (" -' Maggie-i ~ ~ \ \ \ \\ ' . §* l \ ‘ . \ .._-1- —’4~\ ~ \\ / \ \‘\;‘\) k I ’ \ \ “ \ .. “s P‘? ‘ Lofton _ ‘Y \ If ’ f». \\\\\q>- m’ '31,‘ ,7\>; \r /\ / k ,1? \ \ \ \ \ f - ,1’ f! " \ -; \ .\ as» t ~:=~..>~"“ .~ Llpafl / 8. .- l .-='---a \ §\ n)’ “\ Q‘ \' ' .' l/f’ ’ ’ ' " -' 0.153‘ . \ 9 x \ \ I r 4" ‘f4 i I ~ >> t ‘*\ ~ '" 11-4, 1+ - ~ . K ‘ ~ - I ,4"; 6) x‘; ’ v _._-- r L0. - !'/ ‘I. g 5.3x 25.1% _,._._7“Randallf’ ‘ _ iiifigra ‘-, “*"“-*°-": ~"",i5£€p' 4: 4mn "m" ' ‘ -~ . ewz/ a t - "-- f; I.~.=i°» _ w... . i , . . alwfls; "°, fofzé: 42:1'lli.;§;pozy.f'hzk;f‘ __ _ . -' ‘ _ v0 ‘ _ '1 l / _ Dark Gray and Gray Clays Soft Callche Figure 6. Soil pattern in the northern province is shown. Olton and Pullman soils have clay contents of the upper subsoil that average about 35 percent. The depth to a strong calcic horizon averages about 49 inches. The CaCOa content of this layer averages about 5O per- cent and ranges from 35 to 56 per- cent. The southern province extends from near the sand hills of Bailey, Lamb, and Hale Counties south to the Edwards Plateau. It includes parts of Bailey, Borden, Crosby, Dawson, Garza, Hale, Hockley, Howard, Lamb, Lubbock, Lynn, and Terry Counties. Also included are Acuff soils in Lea and Roosevelt Counties in New Mexico. The south- western boundary extends along Lost Draw in Hockley and Terry Fleddish Brown Clay loam _. High Plains Eolian Mantle unconsolidated Calcareous Sands, Silts and Clays Counties and along Sulphur Springs Draw in Dawson and Howard Coun- ties. It is bounded on the east by the Caprock escarpment. Slopes are nearly level to gently undulating, and surfaces are plane to slightly convex (Figure 7). Acuff soils com- prise about 25 percent of the total area. The remainder is mainly Ama- rillo, Arvana, Drake, Mansker, Pep, \ High Plains __ Eolian Mantle Unconsolidated / Calcareous I / Sands, Silts and Clays Figure 7. Soil pattern in the southern province is shown. Portales, and Randall soils. Ama- rillo and Arvana soils are on smooth plains with slightly convex surfaces. Mansker, Pep, and Portales soils are on sideslopes around playas and along draws. Randall soils are on playa bottoms. Acuff soils in native rangeland vegetation have surface textures of loam, sandy clay loam, or clay loam, and organic matter contents greater than 1 percent. Farm management practices commonly used on culti- vated fields have modified these characteristics in many areas mapped as Acuff soils. Cotton, a low residue producing plant, has been the dominant crop in this prov- ince for over 40 years. In many cases, it has been grown with little or no rotation with high residue crops. As a result, the surface texture of many Acuff pedons in this province gener- ally reflect the influence of winnow- ing of silt and clay by wind erosion. Also, surface layer organic matter (has been reduced from an original "(content of greater than 1 percent to less than 1 percent. Acuff soils in the southern province generally have higher sand contents and lower silt and clay contents. This is especially true of the surface layer. Clay con- tents of the upper subsoil range from 24 to 31 percent and average 28 per- cent. The subsoils of some pedons exhibit evidence of profile modifica- tion by deep plowing for wind ero- sion control. The depth to a strong calcic horizon ranges from 34 to 54 inches, but is commonly about 43 inches. Calcium carbonate content ranges from about 35 to more than 55 percent and averages about 42 percent. Uses and Importance of Acuff Soils Acuff soils are used primarily for crop production (about 73%) and rangeland (about 25%). The remain- ing area is in roads, towns, and non- agricultural uses. Of the cropland area, about 52 percent is irrigated and 48 percent is dryland (Table 2). The area of irrigated Acuff soil rep- resents about 7 percent of all irri- gated land in Texas. Cotton (Gossypium hirsutum L.), grain sor- ghum [Sorghum bicolor (L.) Moench], corn (Zea mays L.), and wheat (Triticum aes tivum L.) were the major field crops produced on Acuff soils in 1988 (Texas Dept. Agric., 1988). Other crops grown on smaller areas were oats (Avena sativa L.), barley (Hordeum vulgare L.), sugar beet (Beta vulgaris L.), soybean (Glycine max L.), forage sorghum (Sorghum spp.), alfalfa (Medicagosativa L.), sunflower (Helianthus annuus L.), and veg- etables. Because Acuff soils are located in a subhumid to semiarid region, yields of dryland crops are relatively low. Irrigation from the Ogallala Aquifer greatly increases yield s, but the water supply is limited and be- ing depleted. Also, the cost of en- 7 "x -f/-v'-..__ r \ Estaca_q’g_ , I 77- ’ ergy for pumping water has greatly increased in recent years. Surface water for irrigation is negligible. It is, therefore, essential that water be used as efficiently as possible so eco- nomic crop production can be main- tained and the eventual return to mostly dryland crop production can be delayed as long as possible. When dryland farming replaces irrigated farming, even if only on the Acuff soils, a significant amount of the to- tal production of some crops in Texas will be lost. Typical Site for Acuff Soils Acuff soils developed in a rela- tively cool, subhumid to semiarid climate from medium-textured sedi- ments largely or entirely of eolian origin. They occupy smooth areas that are nearly level to gently slop- ing. Surface slopes range from 0 to about 5 percent toward the playas or shallow basins. Although largely cultivated, the typical vegetation on Acuff soils was short-grasses, prin- cipally blue grama (Bouteloua gracilis) and buffalo grass (Buchloe dactyloides). Profiles of Acuff soil, shown in Figures 8, 9, and 10, are from Castro, Lubbock, and Lynn Counties, respectively. The surface layer of a typical Acuff soil is a brown to dark brown loam, but the texture may be a sandy clay loam, loam, or clay loam. The or- ganic matter content is greater than 1 percent. The thickness of the sur- Figure 8. An Acuff soil profile from Castro County. face layer usually ranges from 6 to 8 inches. A clear boundary is visable where the surface layer meets the brown, reddish brown, or dark red- dish brown sandy clay loam or clay loam with moderate blocky struc- ture. The soil may contain buried horizons of older soils at 3 to 5 feet below the surface. The buried hori- zons usually have a loam or clay loam texture. The upper boundary of the calcic layer is clear and wavy. Although depth to the calcic layer is often considered to be the effective depth of the soil for crop production purposes, winter wheat and espe- cially sunflower apparently use wa- ter from well into the calcic layer, based on observations and measure- ments on a similar soil (Pullman clay loam) at Bushland, Texas (O. R. Jones, Bushland, Texas, unpublished data; Unger, 1978a). Present Water Management Systems Based on data from the Research Centers at Lubbock and Halfway and values published in the Soil Sur- veys of Hale and Lubbock Counties, Texas (SCS, 1974, 1979), the Acuff soil at these locations has a total water storage capacity of about 10.1 and 13.4 inches to 3- and 4-foot pro- file depths, respectively. Of the total water storage capacity, about 5.4 and 7.2 inches are available for use by plants. The remainder (4.7 and 6.2 inches to 3- and 4-foot depths, re- spectively) is held at greater ten- sions (energy levels) than plants can overcome. Because of limited and erratic pre- J cipitation during the growing sea- i son, it is desirable to have the soil filled to capacity with water at plant- ing, especially for dryland crops. When the soil is filled to capacity at planting, crops usually experience less water stress during the growing season than when the soil contains a limited amountof water. Crop yields usually are higher when water stress is not severe during the growing season. Although irrigation can provide water to crops, soil water content at planting is still important because any water stored from precipitation reduces the amount required from irrigation. When water storage from precipitation is low, a preplant or emergence irrigation is often used to increase the soil water content. Be- cause Acuff soils are moderately permeable, relatively short periods of water application must be used to avoid deep drainage losses. With furrow irrigation (Figure 11), con- siderable tailwater runoff is usually permitted so that adequate water is stored at the lower end of the field. Unless an effective tailwater recov- ery system (Figure 12) or a surge irrigation system (Figure 13) is used, tailwater runoff reduces the effi- ciency of water use. Surge systems pulse irrigation water down the fur- rows, which reduces deep drainage losses and increases the uniformity of water applied throughout the length of the furrow. In recent years, many center-pivot sprinkler systems (Figure 14) have been installed on Acuff soils. These systems, when properly designed and operated, reduce runoff com- pared to furrow irrigation, but re- quire considerably more energy in- put than furrow systems. With all ‘d!’ l-"igure 9. An Acuff soil profile from Lubbock County. farming systems on both dryland and irrigated land, a knowledge of the water-holding capacity of the soil profile (Figure 15) is important for effective water management. Experimental Procedure Site Selection To obtain samples that would rep- resent a near-complete range in the expected variation in soil proper- ties, sites were selected at 12 widely separated locations across the region. The sampling sites were in Bailey, Castro, Dawson, Hale, Hockley, Howard, Lamb, Lubbock, Lynn, and Parmer Counties in Texas and in Curry County, New Mexico. Al- though the locations were widely separated, samples were not ob- tained near the edges of the region to avoid zones of transition to other soils. Likewise, locations of transi- tion to other soils within the region were avoided. The sampling was restricted to areas identified as Acuff soils in the particular region. The 12 sampling sites are indicated on Fig- ure 2. Brief descriptions of the loca- tions are given with the profile de- scriptions in the Results and Discus- 9 sion Section. Sites 1, 2, 3, 5, and 6 are in irrigated fields. Sites 4, 7, 8, 9,10, 11, and 12 are in dryland fields. All sites are on nearly level uplands of the High Plains. Sites 1, 2, 3, and 5 are in the Northern Province; and Sites 4, 6, 7, 8, 9,10,11, and 12 are in the Southern 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 two cores at each location were used for profile de- scription. Other cores were taken and separated into depth segments based on thickness of the different horizons. Three or more cores were obtained to provide adequate amounts of material from each depth for determining water retention. The core segments were immediately dipped in a liquified saran solution, which made the cores rigid after dry- ing. After the saran had dried, the individual segments were wrapped in plastic bags for transport to the laboratory. Two additional cores were obtained and sectioned by ho- rizons to provide samples for bulk density and particle size determina- tion. Two samples from the surface layer of soil were also collected at each site. At a different time, three water infiltration determinations were made at each site using re- corder-equipped, constant-head, double-ring infiltrometers. The two rings were seated into the most re- strictive subsurface layer, and a 1.5- inch head of water was maintained for the duration of the test. Water surfaces were covered to prevent evaporation. Placement of indi- vidual infiltrometers was deter- mined after examining the field to determine tillage zone conditions at the time of testing. Sample Preparation and Analyses The core samples used for water retention measurements were cut into sections about 0.75 inch long and reinforced with cellophane tape before making the measurements at -15 bars matric potential. The mea- Figure 10. An Acuff soil profile from Lynn County. surements were made with pressure plate equipment using four sections from each depth. Bulk density was determined by drying the cores at 105°C, then weighing them. Soil from these cores was retained and ground to pass a 2- mm sieve. Subsamples of this sieved soil were then used to determine organic matter content by the Walkley-Black method (Jackson, 1958), pH (1:1 soil:water ratio), and particle size distribution (mechani- cal analysis) by the hydrometer method (Day, 1965). The sand from the particle size distribution analy- ses was subsequently sieved to de- termine the size distribution of the sand fraction. Samples of surface soil were air- dried, ground, and passed through a sieve with 2-mm openings. Subsamples of surface soil were used to determine water retention, par- ticle size distribution, organic mat- ter content, and pH by the methods described above. The relationships among various Ap, Bt1, and Bt2 horizons; total pro- file characteristics; total water infil- tration in 10 minutes and 20 hours; and infiltration rates at these times 1O were investigated by multiple linear regression analyses. The horizon and profile characteristics investi- gated were: thickness; sand, silt, clay, and organic matter content; and bulk density. For the Ap, Bt1, and Bt2 horizons, actual values were used. Besides the partial regression coefficients and the coefficient of determination (R2), standardized partial regression coefficients were determined (Ezekial and Fox, 1959; Steel and Torrie, 1960). Based on the standardized coefficients, the inde- . pendent variables were ranked nu- merically in order of their relative importance for influencing total in- filtration or infiltration rates. All independent variables were used in the initial analysis for each set of data. In subsequent analyses, the lowest-ranking variable was ex- cluded, which resulted in the last analysis being a simple linear re- gression analysis. Results and Discussion Profile Descriptions The profiles at the 12 sites are described in this section. The profile descriptions are based on examina- tion and determinations made in the field immediately after extracting the cores. Although data in subsequent sections are based mainly on hori- zons above the calcic horizon, the calcic horizon is included in the pro- file descriptions. The descriptions are: Site N0. 1 Soil Type: Acuff clay loam Location: Parmer Coun ,Texas; in a cultivated field 70 feet west of unpaved county road, 0.6 mi north and 2.7 mi west of U.S. Highway 60, 0.9 mi northeast of its intersection with Farm Road 292 in Farwell. Pedon description: Sample No. S82TX369-1-(1-5) Ap—0 to 8 inches; brown (7.5YR 4/2) loam, dark brown (7.5YR 3/2) moist; weak medium subangular blocky structure; slightly hard, friable; many fine and medium roots; common fine and medium pores; neu- tral; abrupt smooth boundary. ‘if structure; very hard, very firm; few fine roots; few fine pores; thin continuous clay films; few threads, films, small concre- tions of calcium carbonate; cal- careous; mildly alkaline; clear smooth boundary. Btk—45 to 86 inches; pink (SYR 8/4) clay; pink (SYR 8/4) moist; moderate medium blocky structure; very hard, friable; common fine pores; about 57 percent of the soil con- sists of masses and concretions of calcium carbonate; calcare- ous; moderately alkaline. Site N0. 2 Soil Type: Acuff clay loam Location: Castro County, Texas; in a cultivated field 800 feet west of unpaved county road, 0.9 mi Figure 11. A basic irrigation method in this area is furrow irrigation through gated south 0f Fann Road 303, 1,0 mi pipe. east of Dodd. Pedon description: Sample No. S82TX069-1-(1-5) Ap——0 to 9 inches; reddish brown (SYR 4 / 4) clay loam, dark red- dish brown (5YR 3/4) moist; weak medium subangular blocky structure; slightly hard, friable; many fine and medium roots; common fine and rne- dium pores; neutral; abrupt smooth boundary. Bt1—9 to 19 inches; reddish brown (SYR 4/3) clay loam, dark red- dish brown (5YR 3/3) moist; moderate medium blocky structure; very hard, very firm; common fine roots; few fine pores; thin continuous clay films; neutral; gradual smooth boundary. . Bt2—-19 to 31 inches; reddish brown (SYR 5/4) clay loam, reddish brown (SYR 4/4) moist; moderate medium blocky structure; very hard, very firm; few fine roots; few Figure 12. This tailwater recovery system with a recovery pit and a lake pump recycles water to the cropland. Bt1—8 to 20 inches; brown (7.5YR 4/2) clay loam, dark brown (7.5YR 3/ 2) moist; moderate mediumblocky structure; very hard, very firm; common fine roots; few fine pores; thin con- tinuous clay films; neutral; gradual smooth boundary. \ Bt2--20 to 33 inches; reddish brown (SYR 5 / 4) clay, reddish brown (SYR 4/ 4) moist; mod- erate mediumblocky structure; very hard, very firm; few fine roots; few fine pores; thin con- tinuous clay films; few threads and films of calcium carbon- ate; calcareous; mildly alkaline; gradual smooth boundary. Bt3—33 to 45 inches; yellowish red (SYR 5/ 6) clay loam, yel- lowish red (SYR 4/6) moist; moderate medium blocky 11 fine pores; thin continuous clay films; few threads and films of calcium carbonate; calcareous; mildly alkaline; gradual smooth boundary. Bt3——31 to 46 inches; yellowish red (SYR 5/6) sandy clay loam, yellowish red (SYR 4/ 6) moist; weak medium blocky structure; very hard, firm; few fine roots; few fine pores; thin patchy clay films; few threads, films, and small con- cretions of calcium carbonate; calcareous; mildly alkaline; clear smooth boundary. Btk—46 to 80 inches; pink (SYR 8/4) clay; pink (5YR 8/4) moist; moderate medium blocky structure; very hard, friable; common fine pores; about 55 percentof the soil con- sists of masses and concretions of calcium carbonate; calcare- ous; moderately alkaline. Figure 13. A surge irrigation system is a newer method thatsupplies a more even flow throughout the length of the furrow and reduces tailwater. Figure 14. This sprinkler irrigation system is designed with drop hoses that deliver water directly into the furrow, thus reducing evaporation. Site No. 3 Soil Type: Acuff fine sandy loam Location: Lamb County, Texas; in a cultivated field 1700 feet north of unpaved county road, 5.6 mi west of U.S. Highway 385, 2.0 mi north of U.S. Highway 70 in Springlake. Pedon description: Sample No. S82TX279-1-(1-6) Ap-0 to 8 inches; reddish brown (SYR 5/3) fine sandy loam, reddish brown (SYR 4/3) moist; weak medium sub- 12 angular blocky structure; slightly hard, friable; many fine and medium roots; common fine and medium pores; neu- tral; abrupt smooth boundary. Bt1—8 to 13 inches; reddish brown (5YR 5/ 3) clay loam, reddish brown (SYR 4/3) moist; mod- erate mediumblocky structure; very hard, very firm; common fine roots; few fine pores; thin continuous clay films; neutral; gradual smooth boundary. Bt2—13 to 27 inches; red (2.5YR 5/6) clay loam, red (2.5YR i“ 4/ 6) moist; moderate medium blocky structure; very hard, very firm; few fine roots; few fine pores; thin continuous clay films; few threads and films of calcium carbonate; calcareous; mildly alkaline; gradual smooth boundary. Bt3—27 to 41 inches; yellowish brown (2.5YR 5 / 4) sandy clay loam, yellowish brown (2.5YR 4/4) moist; weak medium blocky structure; very hard, very firm; few fine roots; few fine pores; thin patchy clay films; few threads, films, and small concretions of calcium carbonate; mildly alkaline; clear smooth boundary. Bt4—41 to 53 inches; light red (2.5YR 6/6) sandy clay loam, red (2.5YR 5/ 6) moist; weak medium blocky structure; hard, firm; few fine roots; few fine pores; thin patchy clay films; few threads, films, and small concretions of calcium carbonate; calcareous; moder- ately alkaline; clear wavy boundary. Btk—53 to 9O inches; pink (SYR 8/4) clay; pink (SYR 8/4) moist; moderate medium blocky structure; very hard, friable; common fine pores; about 41 percent of the soil con- sistsofmassesand concretions of calcium carbonate; calcare- ous; moderately alkaline. Site No. 4 Soil Type: Acuff fine sandy loam Location: Bailey County, Texas; in a cultivated field 700 feet east of unpaved county road, 0.9 mi north and 18.0 mi west of U.S. Highway 214, 13.2 mi south of its WATER-HOLDING CAPACITY (inches/toot of soil depth) >- > a o Q I u 5 i F! ">2 >3 l>>5 >- z “z < a < I < > z 1 22 < 4 :1 o< << (<4 < < _< < O -‘ Q o m0 _4O 4° m-IQ .1 m um w .4 mo, _| .| .1 J04 u; :04 o SOIL TEXTURE Figure 15. Typical water-holding capacities of soils with different textures (adapted from USDA, 1955). intersection with U.S. Highway 84 in Muleshoe. Pedon Description: Sample No. S84TX017-1-(1-5) Ap—0 to 7 inches; reddish gray (SYR 4/2) fine sandy loam, dark reddish gray (SYR 4/ 2) moist; weak medium sub- angular blocky structure; slightly hard, friable; many fine and medium roots; common fine and medium pores; neu- tral; abrupt smooth boundary. Bt1—7 to 20 inches; dark reddish gray (SYR 4/2) fine sandy loam,darkreddishbrown(5YR 3/2) moist; weak coarse pris- matic structure, parting to weak medium blocky struc- ture; hard, friable; common fine roots; few fine pores; thin patchy clay films; neutral; gradual smooth boundary. Bt2——-20 to 32 inches; reddish brown (5YR 5/4) sandy clay loam, reddish brown (5YR 4/ 4) moist; moderate medium blocky structure; very hard, firm; few fine roots; few fine pores; thin patchy clay films; few threads and films of cal- cium carbonate; calcareous; moderately‘ alkaline; gradual smooth boundary. Bt3-—32 to 46 inches; yellowish red (5YR 5/6) sandy clay loam, yellowish red (SYR 4/6) moist; weak medium blocky structure; very hard, finn; few fine roots; few fine pores; thin patchy clay films; few threads, films, and small concretions of calcium carbon- ate; calcareous; moderately al- kaline; clear smooth boundary. Btk—46 to 70 inches; pink (SYR 8/4) clay; pink (5YR 8/4) moist; moderate medium blocky structure; very hard, friable; common fine pores; about 46 percent of the soil con- sists of masses and concretions of calcium carbonate; calcare- ous; moderately alkaline. Site No. 5 Soil Type: Acuff loam Location: Curry County, New Mexico; in a cultivated field 1400 feet east of paved county road, 3.7 mi north of U.S. Highway 60, 3.0 mi east of its intersection with U.S. Highway 7O in Clovis. Pedon description: Sample No. S85NMOO9-l-(1-5) Ap——0 to 8 inches; brown (7.5YR 4/ 2) loam, dark brown (7.5YR 3/2) moist; weak medium subangular blocky structure; slightly hard, friable; many fine and medium roots; com- mon fine and medium pores; neutral; abrupt smooth bound- a . Bt1—-8 to 20 inches; brown (7.5YR 4/ 2) clay loam, dark brown (7.5YR 3/ 2) moist; moderate medium blocky structure; very hard, very firm; common fine roots; few fine pores; thin con- tinuous clay films; neutral; gradual smooth boundary. 13 Bt2—20 to 30 inches; brown (7.5YR 5/4) clay loam, dark brown (7.5YR4 / 4) moist; mod- eratemediumblockystructure; very hard, very firm; few fine roots; few fine pores; thin con- tinuous clay films; few threads and films of calcium carbon- ate; calcareous; slightly alka- line; gradual smooth bound- ary. Bt3—3O to 46 inches; reddish brown (SYR 5/4) clay loam, yellowish brown (SYR 4/4) moist; moderate medium blocky structure; very hard, very firm; few fine roots; few fine pores; thin continuous clay films; few threads, films, small concretions of calcium carbonate; calcareous; mildly alkaline; clear smooth bound- a . Btk—46 to 80 inches; pink (SYR 8/4) clay; pink (SYR 8/4) moist; moderate medium blocky structure; very hard, friable; common fine pores; about 53 percent of the soil con- sists of masses and concretions of calcium carbonate; calcare- ous; moderately alkaline. Site N0. 6 Soil Type: Acuff fine sandy loam Location: Hale County, Texas; in a cultivated field 300 feet south of unpaved county road, 0.2 mi west of Farm Road 179, 1.0 mi north of Farm Road 597, 14.8 mi west of I- 27 in Abernathy. Pedon description: Sample No. S85TX191-1-(1-5) Ap—-0 to 7 inches; reddish brown (5YR 5/3) fine sandy loam, reddish brown (SYR 4/3) moist; weak medium subangular blocky structure; slightly hard, friable; many fine and medium roots; common fine and medium pores; neu- tral; abrupt smooth boundary. Bt1—-7 to 23 inches; reddish gray (SYR 4/ 2) clay loam, dark red- dish brown (SYR 3/ 2) moist; moderate medium blocky structure; very hard, very firm; common fine roots; few fine pores; thin continuous clay films; neutral; gradual smooth boundary. Bt2—23 to 39 inches; reddish brown (SYR 4/4) clay loam, dark reddish brown (SYR 3/4) moist; moderate medium blocky structure; very hard, very firm; few fine roots; few finepores;thincontinuousclay films; few threads and films of calcium carbonate; calcareous; slightly alkaline; gradual smooth boundary. Bt3—39 to 51 inches; red (2.5YR 4/ 6) sandy clay loam, dark red (2.5YR 3/6) moist; weak me- dium blocky structure; very hard, firm; few fine roots; few fine pores; thin patchy clay films; few threads, films, and small concretions of calcium carbonate; calcareous; mildly alkaline; clear smooth bound- a . Btk—51 to 82 inches; reddish yel- low (SYR 7/6) clay loam, red- dish yellow (5YR 6/6) moist; moderate medium blocky structure; very hard, friable; common fine pores; about 35 percent of the soil consists of masses and concretions of cal- cium carbonate; calcareous; moderately alkaline. Site No. 7 Soil Type: Acuff fine sandy loam Location: Lubbock County, Texas; in a cultivated field 600 feet south of Farm Road 597, 15.2 mi west of I-27 in Abernathy. Pedon description: Sample No. S85TX303—1-(1-5) Ap——0 to 8 inches; reddish brown (SYR 4/3) fine sandy loam, dark reddish brown (5YR 3/3) moist; weak medium subangular blocky structure; slightly hard, friable; many fine and medium roots; com- mon fine and medium pores; neutral; abrupt smooth boundary. Bt1—8 to 19 inches; dark reddish gray (SYR 4/ 2) sandy clay loam, dark reddish brown (SYR 3/ 2) moist; weak coarse prismatic structure, parting to weak medium blocky struc- ture; very hard, firm; common fine roots; few fine pores; thin patchy clay films; neutral; gradual smooth boundary. Bt2—19 to 30 inches; reddish brown (SYR 4/4) clay loam, dark reddish brown (SYR 3/4) moist; moderate med- ium blocky structure; very hard, very firm; few fine roots; few fine pores; thin continu- ous clay films; few threads and filmsofcalciumcarbonate;cal- careous; mildly alkaline; gradual smooth boundary. Bt3—30 to 39 inches; red (SYR 5/ 6) clay loam, red (5YR 4 / 6) moist; moderate medium blocky structure; very hard, very firm; few fine roots; few fine pores; thin continuous clay films; few threads, films, and small concretions of calcium carbonate; calcareous; mildly alkaline; clear smooth bound- a . Btk—39 to 70 inches; pink (SYR 8/4) clay; pink (5YR 8/4) moist; moderate medium blocky structure; very hard, friable; common fine pores; about 38 percent of the soil con- sists of masses and concretions of calcium carbonate; calcare- ous; moderately alkaline. Site N0. 8 Soil Type: Acuff sandy clay loam Location: Lubbock County, Texas; in a cultivated field 250 feet south of unpaved county road, 1.2 mi east of U.S. Highway 84, 1.4 mi southeast of its intersection with Farm Road 2150 in Slaton. Pedon description: Sample No. S82TX303-1—(1-5) Ap——-0 to 7 inches; reddish brown (SYR 4/4) sandy clay loam, dark reddish brown (SYR 3/ 4) moist; weak medium sub- angular blocky structure; slightly hard, friable; many fine and medium roots; common fine and medium pores; neu- tral; abrupt smooth boundary. Bt1—7 to 18 inches; reddish brown (SYR 4/4) sandy clay loam, dark reddish brown (5YR 3/ 4) moist; weak coarse prismatic structure, parting to weak me- dium blocky structure; very hard, firm; common fine roots; few fine pores; thin patchy clay films; mildly alkaline; gradual smooth boundary. 14 Bt2—18 to 26 inches; yellowish red (5YR 5/8) sandy clay loam, yellowish red (SYR 4/8) moist; weak medium blocky structure; very hard, firm; few fine roots; few fine pores; thin patchy clay films; calcareous; mildly alkaline; gradual smooth boundary. Bt3—-26 to 39 inches; red (5YR 5/ 8) sandy clay loam, red (SYR 4/6) moist; weak medium blocky structure; very hard, firm; few fine roots; few fine pores; thin patchy clay films; A few threads, films, and small concretions of calcium carbon- ate; calcareous; mildly alkaline; clear smooth boundary. Btk—39 to 70 inches; pink (SYR 8/4) clay loam, pink (SYR 8 / 4) moist; moderate medium blocky structure; very hard, friable; common fine pores; about 55 percent of the soil consists of masses and concre- tions of calcium carbonate; cal- careous; moderately alkaline. Site N0. 9 Soil Type: Acuff fine sandy loam Location: Dawson County, Texas; in a cultivated field 150 feet north of unpaved county road, 2.1 mi west of U.S. Highway 87, 6.1 mi north of Ackerly. Pedon description: Sample No. S85TX115-1-(1-5) Ap—O to 7 inches; reddish brown (SYR 4/3) fine sandy loam, dark reddish brown (SYR 3/3) moist; weak medium subangular blocky structure; slightly hard, friable; many fine and medium roots; com- mon fine and medium pores; mildlyalkaline;abruptsmooth boundary. Bt1—7 to 14 inches; reddish brown (5YR 4/3) fine sandy loam, dark reddish brown (SYR 3/ 3) moist; weak coarse prismatic structure, parting to weak rne- dium blocky structure; hard, friable; common fine roots; few fine pores; thin patchy clay films; mildly alkaline; gradual smooth boundary. Bt2—-14 to 23 inches; reddish brown (SYR 4/ 3) sandy clay loam, dark reddish brown H K (5YR 3/3) moist; weak medium blocky structure; very hard, firm; few fine roots; few fine pores; thin patchy clay films; few threads and films of cal- cium carbonate; calcareous; mildly alkaline; gradual smooth boundary. Bt3—23 to 29 inches; reddish brown (5YR 4/4) clay loam, dark reddish brown (5YR 3/4) moist; moderate medium blocky structure; very hard, very firm; few fine roots; few fine pores; thin continuous clay films; few threads, films, and small concretions of calcium carbonate; calcareous; mildly alkaline; gradual smooth boundary. Bt4—29 to 35 inches; yellowish red (5YR 5/6) sandy clay loam, yellowish red (5YR 4 / 6) moist; weak medium blocky structure; few fine roots; few fine pores; thin patchy clay films; few threads, films, and small concretions of calcium carbonate; calcareous; mildly alkaline; clear smooth bound- a . Btk—35 to 60 inches; pink (5YR 8/4) clay, pink (5YR 8/4) moist; moderate medium blocky structure; very hard, friable; common fine pores; about 38 percentof the soil con- sists of masses and concretions of calcium carbonate; calcare- ous; moderately alkaline. Site No. 10 Soil Type: Acuff fine sandy loam Location: Howard County, Texas; in a cultivated field 350 feet west of unpaved county road, 1.0 mi south of U.S. Highway 87, 2.9 mi southeast of Ackerly. Pedon description: Sample No. S83TX227-1-(1-6) Ap——0 to 7 inches; brown (7.5YR 4/2) fine sandy loam, dark brown (7.5YR 3/2) moist; weak medium subangular blocky structure; slightly hard, friable; many fine and medium roots; common fine and me- dium pores; mildly alkaline; abrupt smooth boundary. Bt1—7 to 13 inches; brown (7.5YR 4/2) sandy clay loam, dark brown (7.5YR 3/2) moist; weak coarse prismatic struc- ture, parting to weak medium blocky structure; very hard, firm; common fine roots; few fine pores; thin patchy clay films; mildly alkaline; gradual smooth boundary. Bt2—13 to 18 inches; brown (7.5YR 4/ 2) sandy clay loam, dark brown (7.5YR 3 / 2) moist; weak medium blocky struc- ture; very hard, firm; few fine roots; few fine pores; thin patchy clay films; mildly alka- line; gradual smooth bound- ary. Bt3—18 to 24 inches; reddish brown (5YR 5/ 3) sandy clay loam, reddish brown (5YR 4/3) moist; weak medium blocky structure; very hard, firm; few fine roots; few fine pores; thin patchy clay films; few threads and films of cal- cium carbonate; calcareous; mildly alkaline; clear smooth boundary. Bt4—24 to 35 inches; yellowish red (5YR 5/6) sandy clay loam, yellowish red (5 YR 4/6) moist; weak medium blocky structure; very hard, firm; few fine roots; few fine pores; few patchy clay films; few threads, films, and small concretions of calcium carbon- ate;calcareousmiildlyalkaline; clear smooth boundary. Btk—35 to 72 inches; pink (5YR 8/4) clay, pink (5YR 8/4) moist; moderate medium blocky structure; very hard, friable; common fine pores; about 44 percent of the soil consists of masses and concre- tionsofcalciumcarbonate;cal- careous; moderately alkaline. Site No. 11 Soil Type: Acuff fine sandy loam Location: Hockley County, Texas; in a cultivated field 500 feet west of unpaved county road, 0.2 mi south and 3.0mieastof State High- way 168, 5.2 mi south of Anton. Pedon description: Sample No. S85TX219-1-(1-5) Ap——0 to 7 inches; reddish brown (5YR 4/3) fine sandy loam, dark reddish brown (5YR 3/3) moist; weak medium subangular blocky structure; 15 slightly hard, friable; many fine and medium roots; common fine and medium pores; neu- tral; abrupt smooth boundary. Bt1—7 to 22 inches; reddish brown (5YR 4/4) fine sandy loam, dark reddish brown (5YR 3/4) moist; weak coarse pris- matic structure, parting to weak medium blocky struc- ture; hard, firm; common fine roots; few fine pores; thin patchy clay films; mildly alkaline; gradual smooth boundary. Bt2——22 to 34 inches; reddish brown (5YR 5/ 4) sandy clay loam, reddish brown (5YR 4/4) moist; weak medium blocky structure; very hard, firm; few fine roots; few fine pores; thin patchy clay films; few threads and films of cal- cium carbonate; calcareous; mildly alkaline; gradual smooth boundary. Bt3—34 to 54 inches; yellowish red (5YR 5/6) sandy clay loam, yellowish red (5YR 4 / 6) moist; weak medium blocky structure; very hard, firm; few fine roots; few fine pores; thin patchy clay films; few threads, films, and small con- cretions of calcium carbonate; calcareous; mildly alkaline; clear smooth boundary. Btk—54 to 70 inches; pink (5YR 8/4) clay, pink (5YR 8/4) moist; moderate medium blocky structure; very hard, friable; common fine pores; about 47 percent of the soil consists of masses and concre- tionsofcalciumcarbonate;cal- careous; moderately alkaline. Site N0. 12 Soil Type: Acuff sandy clay loam Location: Lynn County, Texas; in a cultivated field 1400 feet east of Farm Road 1730, 0.25 mi north of New Home. Pedon description: Sample No. S85TX305-1-(1-5) Ap—0 to 8 inches; dark reddish gray (5YR 4/2) fine sandy loam, dark reddish brown (5YR 3/ 2) moist; weak med- ium subangular blocky struc- ture; slightly hard, friable; many fine and medium roots; common fine and medium pores; neutral; abrupt smooth boundary. Bt1—8 to 19 inches; dark reddish gray (5YR 4/2) sandy clay loam,darkreddishbrown(5YR 3/2) moist; weak coarse pris- matic structure, parting to weak medium blocky struc- ture; very hard, firm; common fine roots; few fine pores; thin patchy clay films; mildly alka- line; gradual smooth bound- a . Bt2—19 to 27 inches; reddish brown (SYR 5/4) sandy clay loam, reddish brown (SYR _ 4/4) moist; weak medium blocky structure; very hard, finn; few fine roots; few fine pores; thin patchy clay films; mildly alkaline; gradual smooth boundary. Bt3-—27 to 48 inches; yellowish red (5YR 5/6) sandy clay loam, yellowish red (5YR 4/6) moist; weak medium blocky structure; very hard, firm; few fine roots; few fine pores; thin patchy clay films; few threads, films, and small concretions of calcium carbonate; calcareous; mildly alkaline; clear smooth boundary. . Btk—48 to 70 inches; pink (SYR 8/3) clay, pink (SYR 8/3) moist; moderate medium blocky structure; very hard, friable; common fine pores; about 33 percent of the soil con- sists of masses and concretions of calcium carbonate; calcare- ous; moderately alkaline. Based on the field descriptions, profiles at the various sites differed mainly in thickness, color, texture of the different horizons, and depth to the calcic horizon. Table 4 indicates which profiles are present at the dif- ferent sites. The Ap horizon is 7 to 8 inches thick at all sites, except Site 2 where it is 9 inches thick. Color is reddish brown at Sites 2, 3, 6, 7, 8, 9, and 11; dark reddish gray at Sites 4 and 12; and dark brown at Sites 1, 5, and 10. Surface textures determined in the field are clay loam at Sites 1 and 2; loam at Site 5; sandy clay loam at Sites 8 and 12; and fine-sandy loam at Sites 3, 4, 6, 7, 9, 10, and 11. This horizon represents mainly the plow layer. The differences in thickness and texture probably resulted from winnowing of the fine fraction by wind, and mixing the upper layers by plowing. The Btl horizon is mainly 1O to 14 inches thick, but its thickness ranges from 5 inches at Site 3 to 16 inches at Site 6. Texture is clay loam at Sites 1, 2, 3, 5, and 6; sandy clay loam at Sites 7,8, 9, 10, 11, and 12; and sandy loam at Site 4. Colors are mainly dark reddish brown, but range from dark brown at Sites 1, 5, and 1O to reddish brown at Site 6. The Bt2 horizon is commonly 10 to 14 inches thick, but thickness var- ies from 5 inches at Site 10 to 16 inches at Site 6. Texture is clay loam at Sites 2, 3, 5, 6, and 7; sandy clay loam at Sites 4, 8, 9, 10, 11, and 12; and clay at Site 1. Color is mainly reddish brown, but is dark brown at Site 10, dark reddish brown at Sites 9 and 12, yellowish red at Site 8, and dark red at Site 3. The Bt3 horizon is commonly 12 to 16 inches thick, but ranges from 6 inches at Sites 9 and 10, 21 inches at Site 12. Texture is mainly sandy clay Table 4. Horizons identified in Acuif soil profiles at the various sampling sites. Horizon Site County, state > "o OJ F! —L w F6 Q w Bt4 9 3' 1 Parmer, Texas 2 Castro, Texas 3 Lamb, Texas 4 Bailey, Texas 5 Curry, New Mexico 6 Hale, Texas 7 Lubbock, Texas 8 Lubbock, Texas 9 Dawson, Texas 10 Howard, Texas 11 Hockley, Texas 12 Lynn, Texas XXXXXXXXXXXX XXXXXXXXXXXX XXXXXXXXXXXX XXXXXXXXXXXX XXXXXXXXXXXX 16 loam, but is clay loam at Sites 1, 5, 7, and 9. Coloris mainly reddish brown or yellowish red, but is red at Site 8 and dark red at Site 7. Particle Size Distribution Results of the particle size distri- bution analyses are included in Table 5. The weighted mean sand content was highest at Sites 3, 8, 10, and 11; intermediate at Sites 4, 6, 7,9, and 12; and lowest at Sites 1, 2, and 5. Mean sand content, in general, decreased from southwest to northeast across l the region. The size distribution of the sand fraction varied for samples from the different sites as determined by the percent retained on standard sieves (Table 6). No samples con- tained a high amount of coarse sand, but the amount of fine and very fine sand in the samples, in general, in- creased from east to west across the region. , The distribution of sand within the profiles was variable. At most sites (Sites 1 and Sites 3 to 12), maxi- mum sand content was at the sur- face, but some deeper horizons had similar sand contents. At Site 2, maximum sand contents were in deeper horizons. Except for Sites 7, 9, and 10, subsoil sand contents tended to increase slightly with depth. However, the calcic horizons had lower sand contents than the overlying horizons. The weighted mean silt content was lowest at Sites 3, 8, 10, 11, and 12; intermediate at Sites 2, 4, and 9; and highest at Sites 1, 5, 6, and 7. These trends are opposite those for sand content. Silt content was also variable in the profiles, and no hori- zon had the highest or lowest silt content in all cases. The weighted mean clay content varied less among sites than sand and silt contents, ranging from a low of 26.0 percent at Site 4 to a high of 36.5 percent at Site 1. Except for the Bk horizon, clay content usually was highest in the Btl and/ or Bt2 hori- zons. Clay content was lowest in the Ap horizon. Bulk Density Bulk density of the Ap horizon (plow layer) was not determined because this horizon was loosened by tillage and remained loose at the N Table 5. Characteristics o1 the Acuti soil at the study sites. Particle size Water content Site, County distribution USDA Bulk Organic CaCO, at bars potential‘ and State Horizon Depth Sand Silt Clay Texture density matter Equiv. pH -1/3 -15 Plant-available water adjusted 1o 48-inch inches % % % glcm’ % % % by volume % in/in. in/hoz. depth’ 1, Parmer, Texas -1 Ap 0-8 37.9 35.3 26.8 Loam 1.25’ 1.74 - 7.3 27.4 17.1 10.3 0.103 0.82 -2 B11 8-20 33.3 28.9 37.8 Clay loam 1.58 1.12 - 7.3 35.1 26.3 8.8 0.008 1.06 -3 B12 20-33 31.6 28.4 40.0 Clay 1.46 0.72 - 7.5 33.8 24.3’ 9.5 0.095 1.24 -4 B13 33-45 37.6 24.6 37.8 Clay loam 1.47 0.41 - 7.5 30.6 22.0’ 8.6 0.086 1.03 -5 Btk 45-86 26.4 27.6 46.0 Clay‘ 1.56 0.25 56.5 8.0 - - - - - Weighted mean‘ 34.8 28.7 36.5 - 1.46 0.93 - 7.4 32.2 22.8‘ 9.4 0.094 - Prolile total-in. - - - - - - - - - - - - 4.15 4.42 2, Castro, Texas -1 Ap 0-9 35.9 34.8 29.3 Clay loam 1.25 1.80 - 7.1 29.6 18.8 10.8 0.108 0.97 -2 B11 9-19 32.9 28.8 38.3 Clay loam 1.50 0.98 - 7.3 34.1 23.7 10.4 0.104 0.94 -3 B12 19-31 46.1 19.4 34.5 Clay loam 1.52 0.48 - 7.3 29.0 21.5 7.5 0.075 0.90 -4 B13 31-46 51.5 15.5 33.0 Sandy clay loam 1.56 0.30 - 7.4 27.3 20.5’ 6.8 0.068 1.02 -5 Btk 46-80 27.4 27.1 45.5 Clay’ 1.65 0.17 55.0 7.9 - - - - - Weighted mean 42.9 23.4 33.7 - 1.48 0.68 - 7.3 29.1 20.2’ 8.9 0.089 Prolile1o1al—in. - - - - - - - - - - - - 3.83 3.97 3, Lamb, Texas -1 Ap 0-8 69.2 13.3 17.5 Fine sandy loam 1.35 0.63 - 7.5 15.9 8.8 7.1 0.071 0.57 -2 B11 8-13 48.3 13.0 38.7 Clay loam 1.58 0.73 - 7.6 33.8 20.7 13.1 0.131 0.66 -3 B12 13-27 43.7 23.5 32.8 Clay loam 1.51 0.34 - 7.6 27.0 16.9 10.1 0.101 1.41 ~4 B13 27-41 57.6 13.4 29.0 Sandy clay loam 1.62 0.16 - 7.9 23.4 16.5 6.9 0.069 0.97 -5 B14 41-53 64.1 11.4 24.5 Sandy clay loam 1.63 0.12 - 8.0 20.8 12.4 8.4 0.084 1 01 -6 Btk 53-90 40.5 20.0 39.5 Clay loam’ 1.63 0.13 41.0 8.0 - - - - - Weighted mean 56.3 15.5 28.2 - 1.52 0.32 - 7.3 23.6 16.3’ 7.3 0.073 - Prolile total-in. - - - - - - - - - - - - 4.62 4.20 4, Bailey, Texas -1 Ap 0-7 63.1 23.7 16.8 Fine sandy loam 1.35 0.59 - 7.0 15.2 8.2 7.2 0.072 0.50 -2 B11 7-20 52.4 24.3 23.3 Sandy clay loam 1.29 0.86 - 7.2 20.8 12.9 7.9 0.079 1.03 -3 B12 20-32 50.3 20.2 29.5 Sandy clay loam 1.42 0.60 - 7.9 25.1 15.9 9.2 0.092 1.10 -4 B13 32-46 51.8 17.4 30.8 Sandy clay loam 1.46 0.40 - 8.0 23.4 14.7 8.7 0.087 1 22 -5 Btk 46-70 34.0 23.7 42.3 Clay’ 1.57 0.53 46.0 8.0 - - - - - Weighted mean 33.3 20.7 26.0 - 1.36 0.61 - 7.6 22.1 14.1’ 8.0 0.080 - Prolile1o1a|—in. - - - - - - - - - - - - 3.85 4.02 5, Curry, New Mexico -1 Ap 0-8 47.5 29.5 23.0 Loam 1.25 1.47 - 7.3 23.3 13.6 9.5 0.095 0.76 -2 B11 8-20 34.4 31.1 34.5 Clay loam 1.54 0.91 - 7.2 31.3 22.4’ 8.9 0.089 1.07 -3 B12 20-30 35.1 29.4 35.5 Clay loam 1.47 0.65 - 7.5 30.1 19.3‘ 10.8 0.108 1.08 -4 B13 30-46 38.7 28.3 33.0 Clay loam 1.46 0.33 - 7.8 26.6 18.7’ 7.9 0.079 1.26 -5 Btk 46-80 32.0 24.7 43.3 Clay’ 1.61 0.27 53.0 8.2 - - - - - Weighted mean 38.3 29.5 32.2 - 1.44 0.75 - 7.5 28.0 19.3’ 8.7 0.087 - Prolileto1al—in. - - - - - - - - - - - - 4.17 4.33 6, Hale, Texas -1 Ap 0-7 58.7 22.5 18.8 Sandy loam 1.35 0.95 7.2 18.5 10.6 7.9 0.079 0.55 -2 B11 7-23 45.5 25.5 29.0 Clay loam 1.48 0.72 - 7.3 25.9 17.7’ 8.2 0.082 1.31 -3 B12 23-39 44.3 24.4 31.3 Clay loam 1.44 0.33 - 7.8 25.2 17.4’ 7.8 0.078 1.25 -4 B13 39-51 48.1 26.9 25.0 Sandy clay loam 1.58 0.15 - 7.8 21.0 12.9 8.1 0.081 0.97 -5 Btk 51-82 37.2 24.8 38.0 Clay loam ’ 1.67 0.15 35.0 8.1 - - - - - Weighted mean 47.5 25.1 27.4 - 1.49 0.50 - 7.6 23.7 16.1 7.6 0.076 - Prolile total-in. - - - - - - - - - - - - 4.08 3.84 7, Lubbock, Texas -1 Ap 0-8 53.8 28.7 17.5 Sandy loam 1.35 0.89 - 7.1 17.3 9 6 7.7 0.077 0.62 -2 B11 8-19 46.2 27.0 26.8 Sandy clay loam 1.55 0.99 - 7.3 26.2 18.0’ 8.2 0.082 0.90 -3 B12 19-30 39.3 24.7 36.0 Clay loam 1.53 0.78 - 7.3 31.7 22.9 8.8 0.088 0.97 -4 B13 30-39 43.7 20.5 35.8 Clay loam 1.54 0.42 - 7.6 29.8 20.4 9.4 0.094 0.85 -5 Btk 39-70 35.4 25.3 39.3 Clay loam ’ 1.62 0.20 38.0 8.0 - - - - - Weighted mean 45.2 25.2 29.3 - 1.50 0.78 - 7.3 26.8 18.5’ 8.3 0.083 - Prolile total-in. - - - - - - - - - - - - 3.34 4.17 17 Table 5. Continued. Particle size Water content Site, County distribution USDA Bulk Organic CaCO, at bars potential‘ and State Horizon Depth Sand Silt Clay Texture density matter Equiv. pH -1/3 ~15 Plant-available water adjusted to 48-inch inches % % % g/cm’ % % % by volume % in/tn. in/hoz. depth’ 8, Lubbock, Texas __ — __ ‘i i _ i-‘i- _' __ ‘i -1 Ap 0 -7 67.3 10.9 21.8 Sandy clay loam 1.35 0.74 - 7.3 19.6 11.8 7.8 0.078 0.55 -2 B11 7-18 54.5 15.0 30.5 Sandy clay loam 1.64 0.88 - 7.4 29.1 21.2 7.9 0.079 0.87 -3 B12 18-26 52.3 16.9 30.8 Sandy clay loam 1.57 0.73 - 7.5 28.0 21.0 7.0 0.070 ~ 0.56 -4 B13 26-39 55.1 13.9 31.0 Sandy clay loam 1.46 0.40 - 7.6 25.5 15.9 9.6 0.096 1.25 -5 Btk 39-70 37.3 25.7 37.0 Clay loam ‘ 1.64 0.22 55.0 7.9 - - - - - Weighted mean 56.5 14.3 29.2 - 1.51 0.66 - 7.5 26.0 17.9‘ 8.1 0.081 - Prolile total-in. - - - - - - - - - - - - 3.23 4.09 9, Dawson, Texas -1 Ap 0-7 64.3 18.9 16.8 Fine sandy loam 1.35 0.71 - 7.4 15.8 8.6 7.2 0.072 0.50 -2 B11 7-14 61.3 18.7 20.0 Sandy clay loam 1.55 0.84 - 7.5 20.5 13.2‘ 7.3 0.073 0.51 -3 B12 14-23 46.2 22.0 31.8 Sandy clay loam 1.62 0.68 - 7.6 28.9 20.8‘ 8.1 0.081 0.73 -4 B13 23-29 43.1 22.9 34.0 Clay loam 1.53 0.40 - 7.6 28.3 20.3‘ 8.0 0.080 0.48 -5 B14 29-35 45.5 22.7 31.8 Sandy clay loam 1.55 0.22 - 7.7 26.0 18.6‘ 7.4 0.074 0.44 6 Btk 35-60 25.1 27.4 47.5 Clay‘ 1.57 0.26 38.0 7.9 - - - - - Weighted mean 50.7 22.5 26.8 - 1.52 0.59 - 7.6 23.9 16.3‘ 7.6 0.076 - Pro1iletotal—in. - - - - - - - - - - - - 2.66 3.62 10, Howard, Texas -1 Ap 0-7 67.3 14.7 18.0 Fine sandy loam 1.35 0.68 - 7.6 16.5 9.3 7.2 0.072 0.50 -2 B11 7-13 57.3 17.4 25.3 Sandy clay loam 1.57 0.67 - 7.4 23.7 16.2‘ 7.5 0.075 0.45 -3 B12 13-18 61.2 16.5 22.3 Sandy clay loam 1.76 0.65 - 7.4 23.0 16.4‘ 6.6 0.066 0.33 -4 B13 18-24 58.2 10.0 31.8 Sandy clay loam 1.59 0.60 - 7.5 28.2 17.6 10.6 0.106 0.64 -5 B14 24-35 58.3 7.0 34.5 Sandy clay loam 1.51 0.51 - 7.7 29.1 20.7 8.4 0.084 0.92 -6 Btk 35-72 40.0 19.0 41.0 Clay‘ 1.52 0.24 44.0 8.0 - - - - - Weighted mean 60.3 12.3 27.4 - 1.54 0.61 - 7.6 24.7 17.0‘ 7.7 0.077 - Profile total-in. - - - - - - - - - - - - 2.84 3 93 11, Hockley, Texas -1 Ap 0-7 65.3 17.9 16.8 Fine sandy loam 1.35 0.71 - 7.6 15.8 8.6 7.2 0.072 0.50 -2 B11 7-22 57.1 16.1 26.8 Sandy clay loam 1.21 0.66 - 7.4 21.7 13.1’ 8.6 0.086 1.29 -3 B12 22-34 56.1 17.1 26.8 Sandy clay loam 1.87 0.41 - 7.4 24.0 19.6‘ 4.4 0.044 0.53 -4 B13 34-54 58.3 12.9 28.8 Sandy clay loam 1.54 0.20 - 7.5 23.6 16.5’ 7.1 0.071 1.56 -5 Btk 54-70 49.9 14.6 35.5 Sandy clay ‘ 1.65 0.20 47.0 7.7 - - - - - Weighted mean 58.4 15.4 26.2 - 1.50 0.44 - 7.5 22.6 15.3’ 7.3 0.073 - Prolile total-in. - - - - - - - - - - - - 3.88 3.31 12, Lynn, Texas -1 Ap 0-8 62.3 11.4 26.3 Sandy clay loam 1.35 0.80 - 7.3 23.2 14.8 8.4 0.084 0.67 -2 B11 8-19 57.5 14.2 28.3 Sandy clay loam 1.55 0.84 - 7.4 26.6 18.4‘ 8.2 0.082 0.90 -3 B12 19-27 51.6 14.9 33.5 Sandy clay loam 1.58 0.60 - 7.5 29.4 21.2’ 8.2 0.082 0.66 -4 B13 27-48 49.0 19.0 32.0 Sandy clay loam 1.48 0.31 - 7.7 26.0 18.2‘ 7.8 0.078 1.64 -5 Btk 48-70 44.0 19.2 36.8 Clay loam ‘ 1.59 0.20 33.0 7.9 - - - - - Weighted mean‘ 53.6 16.0 30.4 - 1.49 0.56 - 7.5 26.2 18.1‘ 8.1 0.081 - Profile total-in. - - - - - - - - - - - 3.87 3.87 ‘Water contents at the -1/3 bar matric potential were calculated by Equation 1, Table 7 ol Unger (1975) and water contents at -15 bars matric potential marked by an asterisk (‘) were calculated by Equation 2. ‘Bulk density ol the Ap horizon was estimated lrom values obtained lrom other studies because this horizon was the loosened tillage layer and core sampling was not possible when the samples were obtained. ‘Adjusted to 48-inch depth lor all horizons by adding or subtracting plant-available water based on water retention ol the horizon above or the horizon occurring at the 48-inch depth. ‘The calcic horizon when present was not included in the weighted mean calculations. For water content, weighted means were calculated only to the depth to which data are presented. 18 time of sampling. Other studies, however, have shown that the bulk density of this horizon is highly vari- able, depending on type and recency of tillage. For this study, a bulk density of 1.25 g/cm’ was assumed for the Ap horizon at Sites 1, 2, and 5 (Table 5). This value is the average for the Ap horizon in studies by Taylor et al. (1963), Unger (1969, 1972), and Unger et al. (1973) on Pullman clay loam, which is a simi- lar soil. A field bulk density of 1.35 g/cm’ was assumed for the Ap hori- zon for all other sites (Table 5). This value is an average for the Ap hori- zon on soils having sandy loam tex- tures. The assumed value is pro- vided for calculating the available water content of this horizon in a subsequent section. Bulk density of the Btl horizon ranged from 1.21 g/cms at Site 11 to 1.64 g/cma at Site 8. Densities usu- ally were highest in the Bt4 or Btk horizons, except at Sites 1 and 8 where it was highest in the B11 hori- zon (1.58 and 1.64 g/cm’, respec- tively) and at Sites 9, 11, and 12 where it was highest in the Bt2 horizon. Some unusually low bulk densities at horizons other than the Ap were 1.29 g/cm’ in the Btl at Site 4 and 1.21 g/cm’ in the Btl at Site 11. Bulk densities at different sites are not high enough to prevent root penetration if the soil water content is adequately high, but some reduc- tion in root penetration may occur. Resistance to root penetration is in- fluenced by soil strength, which is a function of soil bulk density and water content (Taylor and Gardner, 1963). For Amarillo fine sandy loam, Taylor and Gardner (1963) showed that some roots penetrated the soil at a bulk density of 1.75 g/cm’ if the soil matric potential was -1 / 2 bar or higher. For bulk densities equal to or less than 1.65 g/cm’, some root penetration occurred when the matric potential was -2/ 3 bar or higher. Resistance to root penetra- tion at similar soil matric potentials and bulk densities may be different in Acuff soils than in Amarillo soils. Also, the bulk densities measured by core samples may be consider- ablydifferent than those determined on individual soil clods. With core sampling, the bulk density repre- sents an average density of the sampled volume, which includes the Table 6. Sand content and size distribution oi the sand in Acuii soil. Percent oi sand retained on standard sieves with openings oi (mm) Site, county, Total 0.850 0.425 0.250 0.150 0.106 0.053 & state Horizon Depth sand (#20) (#40) (#60) (#100) (#140) (#270) in i % Site 1 Ap 0-8 37.9 0.2 2.1 4.3 9.8 45.2 38.4 Parmer, Texas B11 8-20 33.3 0.3 1.8 4.0 6.3 36.6 51.0 B12 20-33 31.6 0.3 1.7 3.7 7.3 34.7 52.3 B13 3345 37.6 0.8 1.7 3.6 7.7 36.4 49.8 Btk 45-86 26.4 4.0 3.9 4.6 7.2 35.2 45.1 Weighted mean‘ 34.8 0.4 1.8 3.6 7.6 37.5 48.8 Site 2 Ap 0-9 35.9 0.4 2.1 3.3 8.3 40.9 45.0 Castro, Texas B11 9-19 32.9 0.1 1.0 7.8 12.9 39.4 38.8 B12 19-31 46.1 0.2 1.0 6.6 12.9 39.3 40.0 B13 31-46 51.5 0.2 1.0 7.4 13.9 39.6 37.9 Btk 4680 27.4 1.4 2.0 8.0 11.8 36.7 40.1 Weighted mean 42.9 0.2 1.2 6.5 12.3 12.9 40.0 Site 3 Ap 0-8 69.2 0.1 1.3 15.4 44.8 21.6 16.8 Lamb, Texas B11 8-13 48.3 0.1 0.7 9.5 28.9 26.9 33.9 B12 13-27 43.7 0.1 0.7 10.4 30.8 26.2 31.8 B13 27-41 57.6 0.1 0.7 10.8 35.3 24.8 28.3 B14 41-53 64.1 0.1 0.6 10.8 35.7 25.0 27.8 Btk 53-90 40.5 0.8 1.5 7.9 20.4 30.3 39.1 Weighted mean 56.3 0.1 0.8 11.2 35.0 25.9 27.9 Site 4 Ap 0-7 63.1 0.3 3.2 4.1 14.4 49.3 28.7 Bailey, Texas B11 7-20 52.4 0.1 1.8 7.4 9.9 42.2 38.6 B12 20-32 50.3 0.3 2.5 3.1 8.5 46.9 38.7 B13 32-46 51.8 0.6 3.1 3.2 7.8 42.5 42.8 Btk 46-70 34.0 2.6 5.4 5.2 7.8 40.6 38.4 Weighted mean 53.3 0.3 2.6 4.5 9.6 44.6 38.4 Site 5 Ap 0-8 47.5 0.1 1.2 2.3 6.9 46.8 42.7 Curry, New Mexico B11 8-20 34.4 0.2 0.9 2.0 6.5 44.5 45.8 B12 20-30 35.1 0.3 0.9 0.9 6.9 44.7 46.4 B13 30-46 38.7 0.3 1.5 2.3 6.8 42.2 46.8 Btk 46-80 32.0 0.1 2.4 3.9 9.4 43.6 40.6 Weighted mean 38.3 0.2 1.2 1.9 6.8 44.1 45.7 Site 6 Ap 0-7 58.7 0.0 1.7 12.4 28.9 28.1 28.9 Hale, Texas B11 7-23 45.5 0.2 1.6 12.2 16.1 27.0 42.9 B12 23-39 44.3 0.2 1.8 10.7 12.7 25.0 49.6 B13 39-51 48.1 0.5 1.9 11.4 13.7 25.8 46.7 Btk 51-82 37.2 1.7 2.9 13.1 14.2 25.4 42.7 Weighted mean 47.5 0.2 1.7 11.6 16.2 26.2 43.9 Site 7 Ap 0-8 53.8 0.2 2.2 11.7 17.5 32.0 36.4 Lubbock, Texas B11 8-19 46.2 0.3 1.0 9.6 21.8 21.0 40.3 B12 19-30 39.3 0.5 1.6 11.5 19.6 25.6 41.7 B13 30-39 43.7 0.5 1.6 13.5 25.6 26.0 32.8 Btk 39-70 35.4 1.6 2.2 12.3 21.9 25.3 36.7 Weighted mean 45.2 0.4 1.6 13.0 21.2 25.7 38.2 ' Site 8 Ap 0-7 67.3 0.1 0.9 11.7 33.9 32.3 21.1 Lubbock, Texas B11 7-18 54.5 0.1 0.5 10.0 27.8 34.2 27.4 B12 18-26 52.3 0.2 0.7 9.5 26.6 34.3 28.7 B13 26-39 55.1 0.1 0.7 10.6 29.5 32.9 26.2 Btk 39-70 37.3 2.9 3.2 9.5 22.3 32.6 29.5 Weighted mean 56.5 0.1 0.7 10.4 29.2 33.4 26.1 Site 9 Apt 0-7 64.3 0.4 2.5 18.1 26.1 25.4 27.5 Dawson, Texas B11 7-14 61.3 0.3 3.2 18.5 24.8 24.0 29.2 B12 14-23 46.2 0.7 4.9 17.8 22.7 23.2 30.7 B13 23-29 43.1 0.7 5.8 16.4 20.7 22.2 34.2 B14 29-35 45.5 1 1 6.4 16.0 20.6 23.3 32.6 Btk 35-60 25.1 - - - - - - Weighted mean 50.7 0.8 4.9 17.1 22.5 23.6 31.1 Site 10 Ap 0-7 67.3 0.7 7.3 20.6 23.9 23.0 24.5 Howard, Texas B11 7-13 57.3 1.5 9.2 21.0 20.3 19.5 28.5 B12 13-18 61.2 1.5 12.9 22.0 20.8 18.5 24.3 B13 18-24 58.2 2.5 10.3 18.3 17.5 17.8 33.6 B14 24-35 58.3 2.9 10.7 19.6 20.0 17.5 29.5 Btk 35-72 40.0 6.6 13.7 20.6 19.5 18.3 21.3 Weighted mean 60.3 2.0 10.0 20.2 20.5 19.1 28.3 19 Tobie 6. Continued. Percent o1 sand retained on standard sieves with openings o1 (mm) Site, county, Total 0.850 0.425 0.250 0.150 0.106 0.053 8 state Horizon Depth sand (#20) (#40) (#60) (#100) (#140) (#270) in % % Site 11 Ap 0-7 65.3 0.3 1.0 10.0 30.3 32.8 25.6 Hockley, Texas B11 7-22 57.1 0.0 0.8 7.2 21.2 35.6 35.2 B12 22-34 56.1 0.2 0.8 7.4 19.6 33.3 38.7 B13 34-54 58.3 0.6 1.1 7.3 19.9 30.9 40.2 Btk 54-70 49.9 0.7 1.3 7.3 20.8 32.7 37.2 Weighted mean 58.4 0.3 0.9 7.6 21.5 33.0 36.6 Site 12 Ap 0-8 62.3 0.3 1.2 9.8 31.0 33.1 24.6 Lynn, Texas B11 8-19 57.5 0.2 1.0 6.5 21.1 30.5 40.7 B12 19-27 51.6 0.1 1.1 5.7 19.6 29.9 43.6 B13 27-48 49.0 0.5 1.3 6.2 20.2 33.4 38.4 Btk 48-70 44.0 2.1 2.3 6.9 19.8 30.5 38.4 Weighted mean 53.6 0.3 1.2 6.8 22.1 32.1 37.5 soil and the shrinkage cracks that develop as the soil dries. For indi- vidual clods, shrinkage cracks are not included in the sample volume. The density of the clods, therefore, may be considerably higher than those obtained by core sampling and may be high enough to prevent root penetration of the matrix in some horizons of the soil. Organic Matter Soil organic matter content usu- ally was highest in the Ap horizon and usually decreased progressively with soil depth (Table 5). For the Ap horizon, the organic matter content was lowest at Sites 3, 4, 8, 9, 10, and 11 (less than 0.75%) and next lowest at Sites 6, 7, and 12 (0.80 to 0.95%). These sites also had high sand con- tents in the Ap horizon. Higher organic matter contents (1.47 to 1.80%) were found in the Ap hori- zon at Sites 1, 2, and 5, all of which had more than 29 percent silt in this layer. Based on weighted means for the entire profile, organic mattercon- tents ranged from 0.32 percent at Site 3 to 0.93 percent at Site 1. A significant positive relationship be- tween soil organic matter and silt content was previously established for Texas soils (Unger, 1975). pH Soil pH (Table 5) varied from 0.50 to 1.0 pH unit throughout the pro- files at most sites. An exception was at Site 11, where the range was 0.30 unit. In general, pH increased with soil depth at all sites. The lowest weighted mean pH (7.3) occurred at Sites 2, 3,and 7. The highest (8.2) and lowest (7.0) pH for a horizon was at Sites 5 and 4, respectively. The soil was neutral to moder- ately alkaline in all cases (see profile descriptions), which corresponds with pH values of more than 7.0. Although alkaline, the pHis not high enough to suggest that field crops would be adversely affected. How- ever, plants sensitive to alkaline con- ditions may be affected and may require special treatments for good growth. Calcium Carbonate (CaCOs) Equivalent The CaCOa equivalent, which re- fers to the neutralizing power of the soil material, was determined for calcic horizons in the soil profiles. The CaCOa equivalents ranged from 33.0 percent at Site 12 to 56.5 percent at Site 1, but soil with such CaCOB equivalents is considered low grade in value forlimingpurposes (Lawton and Kurtz, 1957). Water Retention Cores were not obtained from the Ap horizon because this layer was loosened by tillage. Therefore, wa- ter contents at -1/3 and -15 bars matric potentials for this horizon (Table 5) were calculated by equa- tions developed by Unger (1975). The equations are based on the soil bulk density, organic matter con- tent, and clay content of the horizon. 2O The water contents at -1 / 3 bar matric potential for other horizons were also calculated by the equation of Unger (1975) because values determined for this study were generally lower than expected or previously deter- mined values for this soil. The -15 bar values were also calculated for some horizons below the Ap when data were missing or unrealistic re- sults were obtained by the pressure- plate method. The calculated values should be valid because correlation coefficients obtained when develop- ing the equations were significant at ' the 0.1 percent level (Unger, 1975). For other than the Ap horizon, de- tennined values are given for water contents at -15 bars matric potential. The water contents (Table 5) at -1/3 bar matric potential are calcu- lated on a volume basis. The -15 bar values on a volume basis were ob- tained by multiplying the deter- mined values (weight basis) by the soil bulk density. The plant avail- able water (PAW) contents for the different horizons are the differences between the -1 / 3 and -15 bar values, presented on a percent-by-volume basis. This difference is referred to as water retention difference (WRD). Water contents for individual hori- zons were obtained by multiplying the horizon thickness by the WRD. Totals for the profile are summa- tions of the values for individual horizons. Plant-available water contents were determined only for horizons above the calcic horizon. This depth wasused because rootsof most crops do not penetrate the calcic horizon. Because of its shallow depth (35 inches), the profile at Site 9 had the lowest total PAW storage capacity (2.66 inches). The profile at Site 10 also was only 35 inches deep, and it had a PAW capacity of 2.84 inches. On a weighted mean basis, the stor- age capacity per inch of soil was identically low (0.073) at Sites 3 and 11. The highest weighted mean stor- age capacity per inch of soil (0.094) was at Site 1, but because of a depth of only 45 inches, total PAW at Site 1 was less than at some other sites. To obtain a better comparison of water retention among profiles, all profiles were adjusted to a 48-inch depth with the assumption that any calcic horizon had a water holding capacity equal to that of the horizon immediately above it. Profile depths greater than 48 inches were disre- garded. For profiles adjusted to a 48-inch depth, maximum PAW holding ca- pacity of 4.42 inches occurred at Site 1. The minimum was 3.31 inches at Site 11, resulting in an overall range of 1.11 inches. In general, the higher the sand content, the lower the PAW holding capacity. These results are similar to expectations and previous studies (Unger, 1975; Unger and Pringle, 1981). Even though total PAW holding capacities varied from site to site, the results suggest that no major differ- ences in management are needed to use the soil effectively as a water storage reservoir for crops. First, the values in Table 5 should serve only asaguide because actual amounts of soil water storage and subsequent use by plants are influenced by many factors, and field values seldom cor- respond with laboratory values. Second, crops with well-developed root systems often extract soil water to lower values than reported -15 bar values. Third, tin undetermined ~ amount of water is made available by upward capillary movement as plants use water from (dry out) the overlying horizons. Probably the most important factor with respect to PAW holding capacity is that the soil be managed so that the storage reservoir is readily refilled with wa- ter from precipitation or irrigation. This requires that conditions be maintained for effective infiltration of water into the soil. Soil manage- ment is further discussed in a subse- quent section. Water Infiltration The results of infiltration mea- surements (Table 7) show the amount of water infiltrated at 10 min and 20 hrs, and the infiltration rates at times from 10 min to 2O hrs after water application begins. The values pre- sented were determined at each site under varying surface, plow layer, and residue conditions. (See remarks, Table 7.) Based on individual sets of obser- vations, infiltration at 10 min was highest at Site 10 (3.96 inches) and lowest at Site 6 (0.05 inch). At 20 hrs, infiltration was highest at Site 12 (27.89 inches), which had been sub- jected to profile modification by deep plowing, and lowest at Site 1 (1.49 inches). The highest infiltration at 20 hrs (16.76 inches) where discemableprofilemodification was not present was at Site 6. One factor that apparently had a major influence on infiltration was bulk density (BD) 0f the Ap horizon, which was determined when the in- filtration measurements were made (Table 7). At Sites 6 and 12, where total infiltration at 20 hrs was 16.76 and 27.89 inches, respectively, BD was 1 .10 g/cms. At Site 1, which had the lowest total infiltration at 20 hrs (1.49 inches), BD was 1.77 g/cm’. Total infiltration at 20 hrs also was low (1.56 inches) at Sites 6 and 7, where BD of the Ap horizon were 1.76 and 1.82 g/cm’, respectively. A close relationship between BD of the Ap horizon and water infiltra- tion was confirmed by resultsof mul- tiple regression analyses (Table 8). Total infiltration at 10 min and 20 hrs was significantly influenced by BD of the Ap horizon, both with a rank- ing of 1. Sand content also was sig- nificantly related to total infiltration at 20 hrs, with a ranking of 2. Only infiltration rate at 10 min was sig- nificantly related to some other vari- ables considered. For infiltration rate at 10 min, rankings of the vari- ables were 1, 2, 3, and 4 for sand, silt, clay, and BD, respectively. No vari- ables that were considered signifi- cantly affected infiltration rate at 20 hr. For the Btl horizon, sand content and BD (determined when infiltra- tion was measured) were signifi- cantly related to total infiltration in 10 min and 20 hr, and to infiltration rate at 10 min. The ranking was 1 for BD for total infiltration, but 2 for infiltration rate at 10 min. As for the Ap horizon, no variable considered affected infiltration rate at 20 hrs. For the Bt2 horizon, total infiltra- tion in 10 min was related only to horizon thickness. No variables con- sidered affected total infiltration in 20 hrs or infiltration rate at 10 min. Infiltration rate at 20 hrs was related to BD (ranking of 1) and horizon thickness. Analyses involving BDs of the Ap and Btl horizons (as determined 21 when infiltration was measured) and BD of the Bt2 horizon (determined when initial sampling was done at the sites) showed that BD of the dif- ferent horizons had variable results on total infiltration and infiltration rate (Table 9). At 10 min, total infil- tration was significantly related to BD of the Ap (ranking of 1) and Bt2 horizon, whereas infiltration rate was related only to BD of the Ap horizon. Total infiltration in 2O hrs was related to BD of the Btl horizon (ranking of 1) and BD of the Ap horizon. Infiltration rate at 20 hrs was significantly related only to BD of the Bt2 horizon. Lack of effect of most profile con- ditions and major effect of BD of the Ap horizon on total water infiltra- tion suggest that management prac- tices that alter the density of the plow layer (Ap horizon) have a ma- jor influence on most water infiltra- tion variables and, consequently, on water storage in the profile. Effects of management on tillage zone con- ditions and, subsequently, on BD of the Ap and Btl horizons and rate of water infiltration at 20 hrs are shown in Table 10. These results are a sum- mary of the infiltration and related data presented in Table 7. For loose surface soil with residues on the sur- face and absence of tillage pans or surface crusts, the infiltration rate at 20 hrs ranged from 0.20 to 0.40 inch/ hr. Waterinfiltration rates decreased as soil density increased, surface resi- dues decreased, crusts became evi- dent, and / or tillage pans developed. With severe compaction, for ex- ample, the bulk density of the Ap horizon was 1.77 g/cma and the in- filtration rate was only 0.02 to 0.04 inch / hr. The differences in water infiltra- tion rate and amount at the various sites may not be representative of all fields in the vicinity of the particular sites. The prevailing conditions un- doubtedly reflect past management on the fields such as tillage methods, crops grown, and residue manage- ment practices. Therefore, farmers should evaluate conditions on their farms and adjust their practices ac- cordingly. For example, if a plowpan is hindering water infiltration, a till- ageoperation such as chiseling,deep sweep plowing, or even moldboard plowing may be required to disrupt Table 7. Amount and rate of water infiltration and related data from Acuff soils. Cumulative Bulk density infiltration at Infiltration rate at Site 8- county LTZ Subsoil 10 min 20 hr 10 min 30 min 1 hr 2 hr 5 hr 10 hr 20 hr Remarks g/cm’ ' in/hr Site 1 1.15 1.49 1.81 9.75 2.91 1.32 1.11 0.91 0.61 0.36 0.24 No crusting, wheat stubble, loose bulked surface Partner, Texas 1.15 1.45 1.92 11.28 2.95 1.68 1.11 0.72 0.62 0.35 0.25 No crusting, wheat stubble, loose bulked surface 1.15 1.51 2.04 10.15 2.64 1.92 0.85 0.81 0.51 0.36 0.24 No crusting, wheat stubble, loose bulked surface 1.77 1.58 0.48 1.49 1.44 0.24 0.12 0.08 0.03 0.03 0.03 Settled crusted surface, severe LTZ‘ compaction 1.78 1.56 1.21 1.81 1.44 0.18 0.08 0.05 0.02 0.02 0.02 Loose uncrusted surface, severe LTZ compaction Site 2 1.55 1.46 1.81 5.41 3.25 0.25 0.25 0.25 0.21 0.21 0.16 Loose bulked surface, no residues, slight LTZ compaction > Castro, Texas 1.57 1.49 1.63 5.16 2.52 0.36 0.31 0.25 0.25 0.21 0.14 Loose bulked surface, no residues, slight LTZ compaction 1.30 1.49 0.84 9.12 2.88 1.22 0.61 0.54 0.49 0.43 0.27 Loose bulked surface, no residues, no LTZ compaction 1.65 1.65 0.95 3.31 1.35 0.45 0.36 0.31 0.18 0.11 0.06 Cotton, no residue, no crust, severe LTZ compaction 1.69 1.64 0.84 2.16 1.21 0.12 0.12 0.12 0.11 0.08 0.04 Cotton, no residue, no crust, severe LTZ compaction 1.11 1.50 0.96 10.13 2.38 1.44 1.14 0.91 0.58 0.45 0.21 Cotton, no residue, no crust, no LTZ compaction Site 3 1.76 1.59 0.81 3.05 2.71 0.72 0.25 0.11 0.11 0.08 0.08 Soybeans, no crust, no residue, severe LTZ compaction Lamb, Texas 1.81 1.59 0.96 2.28 2.91 0.21 0.18 0.08 0.05 0.05 0.05 Soybeans, no crust, no residue, severe LTZ compaction 1.64 1.59 0.82 6.96 2.75 0.61 0.36 0.24 0.18 0.16 0.14 Soybeans, no crust, no residue, severe LTZ compaction 1.11 1.36 1.51 19.12 5.76 2.52 1.94 1.25 0.96 0.81 0.75 Soybeans, no crust, no residue, modified upper profile 1.11 1.35 2.41 21.36 8.64 2.16 1.44 1.11 0.96 0.96 0.91 Soybeans, no crust, no residue, modified upper profile 1.11 1.35 2.41 24.11 7.21 2.16 1.72 1.21 1.05 0.96 0.96 Soybeans, no crust, no residue, modified upper profile Site 4 1.10 1.30 1.68 23.31 5.76 1.44 1.21 1.21 1.21 1.11 0.95 Cotton, no crust, modified upper profile Bailey, Texas 1.10 1.42 2.41 16.68 8.64 1.21 0.72 0.72 0.72 0.72 0.72 Cotton, no crust, modified upper profile 1.77 1.59 1.41 2.59 4.32 0.11 0.11 0.11 0.09 0.06 0.03 Cotton, crusted surface, severe LTZ compaction 1.69 1.59 2.04 5.32 6.48 0.51 0.21 0.21 0.18 0.18 0.10 Cotton, crusted surface, severe LTZ compaction 1.69 1.59 1.81 4.95 5.18 0.38 0.24 0.16 0.16 0.12 0.10 Cotton, crusted surface, severe LTZ compaction Site 5 1.66 1.56 1.73 3.02 3.02 0.55 0.25 0.12 0.11 0.08 0.06 Wheat stubble, bulked surface, severe LTZ compaction Curry, New Mexico 1.66 1.54 1.73 3.29 2.74 0.41 0.25 0.15 0.12 0.08 0.06 Wheat stubble, bulked surface, severe LTZ compaction 1.11 1.48 1.45 13.44 3.96 2.52 2.16 1.44 0.72 0.36 0.31 Wheat stubble, no crust, no LTZ compaction 1.28 1.45 2.04 10.44 4.25 2.16 1.21 0.84 0.41 0.31 0.24 Wheat stubble, weak crust, no LTZ compaction 1.10 1.46 1.45 12.86 3.75 1.81 1.31 0.86 0.53 0.45 0.35 Wheat stubble, no crust, no LTZ compaction Site 6 1.68 1.59 0.31 3.61 1.31 0.58 0.43 0.36 0.18 0.18 0.12 Cotton, crusted surface, severe LTZ compaction Hale, Texas 1.76 1.59 0.05 1.56 0.18 0.18 0.18 0.18 0.14 0.11 0.06 Cotton, crusted surface, severe LTZ compaction 1.52 1.55 0.72 5.81 2.16 0.86 0.62 0.48 0.29 0.24 0.18 Cotton, crusted surface, moderate LTZ compaction 1.11 1.55 2.45 16.76 4.88 1.31 1.08 0.99 0.62 0.59 0.51 Cotton, no crust, no LTZ compaction 1.11 1.55 2.18 11.02 4.08 0.77 0.51 0.45 0.45 0.45 0.45 Cotton, no crust, no LTZ compaction Site 7 1.81 1.61 0.61 2.88 2.16 0.24 0.14 0.11 0.11 0.08 0.04 Cotton, crusted surface, severe LTZ compaction Lubbock, Texas 1.82 1.59 0.05 1.56 0.31 0.21 0.16 0.16 0.12 0.09 0.04 Cotton, crusted surface, severe LTZ compaction 1.25 1.54 2.16 11.69 8.64 1.80 1.15 0.79 0.45 0.35 0.35 Bulked surface, no crust, no LTZ compaction 1.25 1.54 2.31 11.46 5.04 1.44 1.01 0.72 0.46 0.43 0.34 Bulked surface, no crust, no LTZ compaction 1.11 1.45 2.68 16.48 8.21 2.23 1.58 0.91 0.75 0.61 0.51 Bulked surface, no crust, no LTZ compaction 1.25 1.57 2.21 9.28 4.32 1.58 1.01 0.61 0.31 0.25 0.25 Bulked surface, no crust, no LTZ compaction Site 8 1.69 1.59 1.48 4.42 5.62 0.46 0.34 0.22 0.22 0.11 0.08 Cotton, crusted surface, severe LTZ compaction, no resi- due Lubbock, Texas 1.68 1.59 1.25 5.22 4.32 0.48 0.38 0.24 0.18 0.18 0.09 Cotton, crusted surface, severe LTZ compaction, no resi- due 1.62 1.59 1.44 6.72 4.32 0.52 0.48 0.36 0.24 0.22 0.22 Cotton, no crust, no LTZ compaction, no residue Site 9 1.10 1.40 1.92 25.01 5.04 2.90 2.16 1.44 1.32 0.94 0.94 Cotton, no crust, modified upper profile Dawson, Texas 1.10 1.42 2.88 15.60 6.48 3.60 2.60 1.58 0.60 0.36 0.36 Cotton, no crust, modified upper profile 1.62 1.55 0.91 9.96 5.46 1.44 0.72 0.62 0.55 0.38 0.30 Cotton, no crust, moderate compaction Site 10 1.61 1.55 1.92 7.97 4.32 0.72 0.38 0.31 0.24 0.22 0.22 Cotton, no crust, moderate LTZ compaction Howard, Texas 1.69 1.55 3.07 5.93 2.88 0.60 0.26 0.18 0.12 0.12 0.10 Cotton, no crust, severe LTZ compaction 1.12 1.50 2.40 11.16 2.88 0.72 0.48 0.48 0.42 0.42 0.42 Cotton, no crust, no LTZ compaction 1.12 1.41 2.40 23.09 5.40 1.92 1.32 1.08 0.96 0.96 0.96 Cotton, no crust, modified profile 1.12 1.40 3.96 18.96 4.32 1.44 1.08 0.72 0.72 0.72 0.72 Cotton, no crust, modified profile Site 11 1.68 1.60 1.44 5.52 4.30 1.10 0.72 0.45 0.18 0.15 0.10 Wheat stubble, bulked surface, dense LTZ Hockley, Texas 1.56 1.60 1.21 9.48 4.40 1.44 1.08 0.84 0.48 0.30 0.24 Wheat stubble, bulked surface, moderate LTZ compaction 1.68 1.60 1.31 7.01 5.04 1.08 0.72 0.48 0.30 0.24 0.14 Wheat stubble, bulked surface, dense LTZ 1.61 1.60 1.44 6.24 4.08 1.15 0.62 0.24 0.24 0.24 0.20 Wheat stubble, bulked surface, slight LTZ compaction 1.58 1.60 1.56 7.21 4.25 1.45 0.61 0.28 0.24 0.22 0.22 Wheat stubble, bulked surface, slight LTZ compaction Site 12 1.15 1.61 1.36 6.10 3.85 1.15 0.36 0.24 0.22 0.19 0.19 Gr. sorg. after cotton, moderate LTZ compaction Lynn, Texas 1.15 1.66 1.25 5.90 3.74 1.71 0.48 0.30 0.24 0.18 0.16 Gr. sorg. after cotton, moderate LTZ compaction 1.11 1.52 2.61 11.82 7.65 1.92 1.10 0.75 0.48 0.42 0.36 Gr. sorg. after cotton, no LTZ compaction 1.12 1.55 2.41 10.72 5.04 1.36 0.72 0.43 0.36 0.36 0.36 Gr. sorg. after cotton, no LTZ compaction 1.10 1.25 1.98 27.89 2.88 2.52 1.56 1.32 1.21 1.21 1.19 Cotton, no crust, profile modified to depth of 24 inches 1.10 1.38 1.98 17.62 2.88 2.13 1.44 0.91 0.72 0.68 0.65 Cotton, no crust, profile modified to depth of 24 inches 1.10 1.45 2.38 12.25 2.95 1.55 0.72 0.48 0.48 0.45 0.41 Cotton, no crust, profile modified to depth of 24 inches ‘Lower tillage zone 22 Table 8. Summary of multiple linear regression analyses associating total infiltration and infiltration rates at 10 min. and 20 hr. with Ap, Bt1, and Bt2 horizon characteristics of Acuff soil obtained at 12 sites in Texas and New llexlco. Rankings based on standardized partial regression coefficients‘ and levels of significance oi partial regression coef1icients'based on T-value follow the partial regression coefficient. Soil horizon and independent variable‘ dependem variable Intercept Sand Silt Clay BD HT R’ ‘ Partial regression coefficients L____ Total infiltration in 10 min — in Total infiltration in mm-m infiltration rate at 10 min — in/hr infiltration rate at - - 20 hr- in/hr Bt1 Total infiltration in 10 min — in Total infiltration in mm-m infiltration rate at 10 min —- in/hr infiltration rate at - - 20 hr — in/hr Bt2 Total infiltration in 10 min — in Total infiltration in - - 20 hr- in Infiltration rate at - - 2O min — in/hr infiltration rate at 20 hr- in/hr 3.9736 - 28.9969 -54.6877 6.4924 101.3884 12.9231 3.0343 -13.2250 - 0.1262(2) 0.6541 (1 )' o.029e(2)' 0.2150(2)" 0.0600(1)’ 0.6054(2)‘ 0.5645(6)‘ - 1.6672(1)"- -19.06a7(1)"* - 2.2695(4)" - - 4.1632(1)" - -67.4020(1)"- - 6.5604(2)’ - 7.6264(1)“ 0.426" 0.722'" 0526'" 0.388" 0797'" 0.341" - -1 .1a2o(1 )" 0.320" 0.1760(2)’ 0.346" ‘Rankings are shown in parentheses immediately after partial regression coefficients. Rankings in order from 1 (highest) to 4 (lowest). ‘Levels of signifitznce of partial regression coefficients are '(0.05), "(0.01), "'(0.001), and NS (not significant). These are shown after the rankings. ‘independent variables are % sand content, % silt content, % clay content, and g/cm’ bulk density, and inches horizon thickness. ‘Coefficient of correlation. Levels of significance are "(0.01) and "’(0.001). the plowpan and increase water in- filtration and storage in the soil. Implications for Management Plant-Available Water (PAW) The total amount of PAW retained in the soil profile was influenced by depth to the calcic horizon and by ‘the PAW holding capacity of soil in different horizons. Total amounts, based on the adjusted value for a 48- inch depth, ranged from 3.31 inches at Site 11 to 4.42 inches at Site 1 (Table 5). Therefore, a crop could extract about 34 percent more water from the soil at Site 1 than at Site 11, provided both profiles were initially filled to capacity with water and the crop root system had explored and extracted water from the entire soil volume to the 48-inch depth (Table Table 9. Summary of multiple linear regression analyses associating total Infiltration and infiltration rates at 10 min and 20 hr with Ap, Bt1, and Bt2 horizon bulk densities of Acuff soil obtained at 12 sites in Texas and New Mexico. Rankings based on standardized partial regression coefficients‘ and levels of signifi- cance of partial regression coefficients’ based on T-value follow the coefficients. independent variables’ Dependent variable intercept BD of AP BD of Bt1 BD of Bt2 Fl“ Total infiltration 1.1649 -1.6168(1)"' - 1.7569(2)‘ 0.521 '9" in 10 min — in Total infiltration 89.8322 -11.3530(2)"' -42.3249(1)"' - 0.833"' in 20 hr — in infiltration rate at 8.1859 3.0764(1)" - - 0.231’ 10 min — in/hr infiltration rate at -7.5516 - - 5.2127(1)" 0.237" 20 hr — in/hr ‘Rankings are shown in parentheses immediately after partial regression coefficients. Rankings in order for 1 (highest) to 2 (lowest). ‘Levels of significance of partial regression coefficients are '(0.05), "(0.01), and "'(0.001). These are shown after the rankings. ‘independent variables are bulk density (g/cm’) of Ap, Bt1, and Bt2 horizons. ‘Coefficient of correlation. Levels of significance are '(0.05), "(0.01), and "'(0.001). 23 Table 10. Summary of the effects of tillage zone characteristics of Acuff soils on average water infiltration rate at 20 hours. Average Average in-place bulk infiltration rate densiy at Tillage zone conditions (Tilth) Ap Bt 2O hours g/cm’ in/hr Loose, bulked surface layers with heavy residues on 1.10 1.34 > 0.75 or near the soil surface; absence of tillage pans 1.10 1.40 0.61-0.74 and surface crusts. Evidence of profile 1 10 1.50 0.51-0.60 modification by deep plowing. Loose, bulked surface layers with moderate 1.50 0.36-0.50 residues on or near the soil surface; absence 1.51 0.31-0.35 of tillage pans and surface crusts. Settled surface layers with little residue on or 1.34 1 53 0.21-0.30 near the soil surface and weak crusts present. Settled surface layers with little or no residue on 1.46 1.57 0.16-0.20 the soil surface and weak crusts present. Early stages of tillage pan development are evident. Readily discernable compaction in the form of 1.64 1.57 0.11-0.15 wheel track furrows or well developed tillage pans; with or without loose, bulked surfaces and residue on or near the surface. Readily discernable compaction in the form of 1.70 1.58 0.07-0.10 tillage pans; with or without residue on or near the surface, or loosened surfaces. Severe compaction in the lorm of tillage pans; 1.72 1.60 0.04-0.06 with or without crusts, residues, or loosened surface layers. Severe compaction in the form of tillage pans; 1.77 1.58 0.02-0.04 with or without crusts, residues, or loosened surface layers. 5). Both conditions, however, often are not fulfilled under field condi- tions at all locations. Based on PAW holding capacities (Table 5) and the measured infiltra- tion rates (Table 7), profiles at all sites could be completely refilled with water (for example, by irriga- tion) in less than 20 hrs, except at sites where severe subsoil compac- tion had occurred. If severe compac- tion in the form of tillage pans is present, water application for much longer than 2O hrs would be required. With severe compaction, total infil- tration was 1.65 inches at 20 hrs at Site 1. Hence, under the infiltration conditions prevailing at 20 hrs, ad- ditional time required to refill the profile would be about 92 hrs at Site 1. Less additional time (beyond 20 hrs) would be needed at other sites having severely compacted subsoils. In most cases, prolonging the time of irrigation to fill the profile with wa- ter is not practical under the prevail- ing conditions, and the profiles at some sites normally would not be refilled with water, except during prolonged wet periods or occasion- ally with repeated irrigations. Pro- files in most cases would be filled with PAW when irrigated for less than 2O hrs and would, therefore, provide considerable water for plant use. Root penetration into a soil varies with plant species and soil water status. Sunflower roots have grown into and used water from the calcic horizon on Pullman clay loam at Bushland. In contrast, sorghum gen- erally extracts water only from the horizons overlying the calcic. The Pullman soil is similar morphologi- cally to the Acuff soil, and root pro- liferation would probably be similar on both soils. Therefore, even though there are differences in water hold- ing capacity and soil depth at the different sites, the management re- quired (for example, irrigation fre- quenCy) to obtain similar yields with a given amount of water may be 24 nearly identical at all sites, at least for crops that do not root deeply. The water application rate, however, may need to be varied because of infiltration rate differences. Crops that root deeply, tolerate stress, and deplete soil water to low levels would probably perform well on dryland and would require less frequent irri- gation (if irrigated) than crops that root less deeply, are sensitive to stress, and fail to extract all PAW. Marked differences in water extrac- tion by sunflowerand grain sorghum have occurred on Pullman soil at Bushland. When grown on adjacent fallowed plots, sunflower extracted more water from the soil at all depths than sorghum (Unger and Pringle, 1981). Similar differences would probably occur on Acuff soils. Water Application Furrow irrigation (Figure 11) is widely practiced on Acuff soils, com- monly with furrow lengths of one- quarter mile. Because of the gener- ally low infiltration rates associated with high soil bulk densities com- monly observed in clean tillage sys- tems, it is believed that deep perco- lation of water can be controlled on this soil. However, infiltration mea- surements at the various sites (Table 7) suggest that considerable deep percolation may be occurringat some sites, even when set times are 12 hrs or less. Consequently, irrigation re- quires a knowledge of the delivery capacity and soil water storage ca- pacity to make efficient use of the water. Because of water quality con- cerns coupled with energy costs, deep percolation should be avoided. To evaluate irrigation practices, as- sistance is available through the water conservation districts and the Soil Conservation Service (Figures 15 and 16). Where excessive deep percolation is a problem under fur- row irrigation, set times may need to be shortened. Other alternatives are to use higher flow rates per furrow with shorter set times, smooth fur- row bottoms for more rapid water advance, use the surge-irrigation system (Figure 13), or irrigate alter- nate packed furrows (Musick and Pringle, 1986). Further water sav- ings can be achieved by using un- derground pipelines rather than Figure 16. Equipment used by Water Conservation District and Soil Conservation Service personnel to evaluate irrigation systems. open ditches to convey water to the irrigation furrows. On sites where the infiltration rate is low, tailwater runoff may be high from furrow irrigation unless cut- back flow rates are used. Some of the tailwater can be recycled through recovery systems, but building the systems and pumping more water adds to production costs. Pumping costs are higher for sprinkler systems than for furrow irrigation because of the extra head required to pressurize the system. However, labor requirements for sprinkler systems such as center- pivot systems are lower than for fur- row systems. The water can also be applied with sprinklers at rates com- patible with infiltration rates. In an ideally designed sprinkler system, the water should be applied at a rate slightly less than the soil infiltration rate. This minimizes the potential for water collecting on the surface, which could result in runoff losses. High-pressure sprinkler systems apply water over a relatively large area, minimizing runoff problems. These systems, however, are energy intensive and may result in high evaporation losses from the falling droplets or fine spray. Low pressure sprinklers require less energy, but apply water over a smaller area (Fig- ure 13). Evaporative losses should be lower, but runoff losses could be higher unless special provisions are made to reduce runoff. Lyle (1979) controlled runoff and used water efficiently with a low-pressure, pre- cision application system used with furrow dikes (Figure 17). Another possibility would be to add booms with attached nozzles at right angles to the main frame of the sprinkler, thus applying water to a larger area at the same time. Water Infiltration Variation The data in Table 7 show more than a nine-fold variation among the observations in total water infiltra- tion at 10 min and even greater dif- ference in infiltration rates at differ- ent times. This variation seemed to be most closely associated to bulk density of the Ap horizons, but total water infiltration and infiltration rates also varied considerably among measurements within some sites. Such variation resulted from local conditions such as surface crusting and soil compaction, which suggests that soil behavior on a given field near the sampling sites may differ considerably from that indicated by the data in Table 7. Where infiltration is much lower than expected, a compacted zone such as a plow pan may have devel- oped in the soil. Deeper-than-nor- mal plowing or chiseling while the soil is relatively dry is a possible remedy for overcoming infiltration problems associated with soil lay- ers. Another possible remedy is the use of reduced- or no-tillage crop- ping systems, which minimize soil compaction because of less traffic across the field. These systems pro- tect the soil surface, decrease rates of runoff, and reduce evaporation losses (Figure 18). However, be- cause soil crusts are left undisturbed and become stronger and thicker with time, infiltration rates may not be significantly improved. Based on the measurements, large variations in infiltration are possible at all sites on Acuff soils. Where problems are suspected, appropriate corrective measures should be taken to increase Figure 17. Combination of low pressure irrigation system on furrow-diked land gives energy savings, precision placement, and reduce evaporation. 25 Figure 18. Corn planted by no-tillage method in wheat residues benefits in several ways. Surface residues are conducive t0 rapid water infiltration, they reduce soil water evaporation, and reduce chance of early plant injury caused by blowing silt. Figure 19. Much of the grain produced on Acuffsoils is consumed by cattle in feedlots such as the one pictured in the background. infiltration where it is too low, 0r decrease it where deep percolation occurs. Crop Sequences Wheat, grain sorghum, corn, sun- flower, sugarbeet, alfalfa, and veg- etable crops such as potato (Solanum tuberosum) and onion (Allium cepa) are adaptable and grown through- out some part or the entire area of Acuff soils. Much of the grain pro- duced in the region is stored in el- evators, then transported to area feedlots (Figure 19) or to seaports for export to foreign countries. Whether the crops are grown continuously or in rotations depends on such factors as crop prices; water availability; fer- tilizer cost and availability; weed, insect, and disease problems; and producer preferences. When irri- gated crops that do not root deeply are grown continuously, some wa- ter generally moves beyond the depth of plant rooting and, there- fore, reduces water use efficiency for crop production. Unless a deep- rooted crop is subsequently grown, this water may be lost for crop pro- duction unless it eventually reaches the aquifer from which it could be pumped again. 26 Water losses from deep percola- tion can be minimized by growing deep-rooted crops in rotation with shallower-rooted crops. The effec- tiveness of deep-rooted crops for extracting water from deep in the profile is enhanced when these crops are grown without irrigation, or with a limited amount of irrigation. In either case, adequate water must be available throughout the profile so that root growth is not restricted by a dry zone in the soil. Tillage and Cropping Practices Concern about the steady decline of water in the Ogallala Aquifer, which supplies water to irrigate Acuff soils, and rising production costs have triggered an interest in conservation of irrigation water. More emphasis is being placed on the conservation and use of precipi- tation for crop production. Studies conducted on Pullman soil, which is morphologically similar to Acuff, can aid in understanding the effects of conservation practices on Acuff soils. Under dryland conditions, more water from precipitation was con- served and grain yields were higher where stubble mulch tillage was used instead of one-way disk tillage in continuous wheat or wheat-fallow cropping systems (Johnson and Davis, 1972). Other practices that have conserved water and increased crop yields on dryland are conserva- tion bench terraces 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 Hudspeth, 1976; Clark and Jones, 1981) (Figure 20). These practices retained potential runoff water where it fell or retained it on 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 (Figures 21, 22) generally were not adequate to greatly reduce evaporation, even when all residues were maintained on the surface in no-tillage systems (Army et al ., 1960, 1967). t. Figure 20. Blocked furrows (with furrow dikes) retain water on the land; runoff occurs from open furrows (photo provided by O.R. Iones, LISDA-ARS). Figure 21 . The amoimt of residue produced by dryla nd winter wheat generally is low. In contrast to the lack of response to surface residues for increasing water storage from precipitation in no-tillage systems on dryland, ma- jor increases in water storage were obtained when residues from irri- gated wheat (Figure 23) were man- aged on the surface with no-tillage systems compared to working them into the soil with tillage (Musick et 27 al., 1977; Unger, 1984; Unger et al., 1971; Unger and Wiese, 1979). The additional stored water decreased the amount of irrigation water needed for irrigated grain sorghum (Musick et al., 1977) and resulted in good growth (Figure 24) and yields of dryland grain sorghum (Unger, 1984; Unger and Wiese, 1979). In a controlled-residue-level study, wa- ter storage during fallow, and sub- sequent grain sorghum yields, in- creased as surface residues were in- creased from 0 to about 11,000 lbs/ acre (Unger, 1978b). Dryland wheat residue yields often are only about 1,500 to 2,500 lbs/ acre at Bushland. In contrast, irrigated wheat residue yields of 4,000 to 6,000 lbs/ acre are common and amounts of 10,000 or more lbs / acre have been obtained in some years (Unger, 1977, 1 986; Unger et al., 1971). The residue amounts produced by irrigated wheat are in the range that substantially increased water storage and grain sorghum yields (Unger, 1978b). Therefore, residues from crops such as irrigated wheat are a resource that can be managed to increase water use efficiency for crop production on Pullman soils and, by inference, on Acuff soils. The benefits from surface residues result from greater total infiltration and less evaporation of water. Be- cause of their greater water storage capacity, profiles at Sites 1, 3, 4, 5, 7, and 8 with over 4.00 inches PAW may derive more benefit from sur- face residues than those at Sites 2, 6, 9, 10, 11, and 12. Soils with less storage capacity are more readily filled with water because less water is required, provided water infiltra- tion rates are sufficiently high. The greater response to surface residues on Pullman soils at a deep site at Bushland compared with a shal- lower site near Lubbock was veri- fied by Baumhardt (1 980), who com- pared the effects of disk and no- tillage after wheat on water storage during fallow and subsequent growth and yield of grain sorghum. Because rainfall essentially filled the lower-capacity profile with water with both tillage methods near Lub- bock, sorghum yields were not sig- nificantly differentdueto tillage. At Bushland, where the storage capac- Figure 22. The amount of residue produced by dryland grain sorghum generally is low, which results in bare soil areas that enhance runoff during rainstorms. Figure 23. Substantially increased residue remains after harvest of irrigated winter wheat. ity was greater, no-tillage signifi- cantly increased grain yields of sor- ghum over those obtained with disk tillage when the sorghum was not irrigated. With irrigation, sorghum yields were similar with both treat- ments. A benefit from lower evaporation with surface residues is the pro- longed time that the surface layer remains wet enough to beneficially influence seed germination. Whereas rapid decreases in surface soil water content from evaporation may cause poor germination on rela- tively smooth bare soil, slower evaporation on mulched soils may result in favorable germination of crops. Ranching and Livestock Production Ranching and livestock produc- tion are important agricultural en- terprises on the High Plains. Native 28 Figure 24. Dryland grain sorghum ben- efits from residues from the previous irrigated winter wheat crop that are managed on the soil surface by no-tilI- age methods. grassland on Acuff soils covers about 278,840 acres, or 25 percent of the total land area. Most ranches are cow-calfoperations, though stocker steers make up a significant percent- age of many herds (Figure 25). Usu- ally, these stocker cattle are placed in nearby feedlots for finishing. On many ranches, the forage pro- duced on rangeland is supplemented by crop stubble (Figure 26) and small grain. In winter, the native forage is often supplemented with protein concentrate. Creep feeding of calves and yearlings to increase market weight is practiced on some ranches. . The native vegetation in many parts of the area has been greatly depleted by continued excessive use (Figure 27). Forage production now may be less than half of the original Figure 26. Stubble from a summer crop such as grain sorghum often provides some forage for cattle grazing on wheat pastures during the winter season. production. Range productivity can be increased by using management practices that are effective for spe- cific kinds of soils and range sites. Where climate and topography are similar, differences in the kind and amount of climax vegetation pro- duced 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 climax plant commu- nity and the expected percentage of each species on a typical clay loam range site are given in Table 11. The potential total annual dry matter pro- duction of vegetation in favorable, normal, and unfavorable years is about 2,000, 1,600, and 1,000 or less lbs / acre, respectively. In addition to knowing soil prop- erties and climax plant community, range management requires evalu- ating the present condition of the range vegetation in relation to its production potential. Range condi- tion on a particular site is determined by comparing the present plant com- munity with the climax plant com- munity for the site. The more closely the existing community approaches the climax community, the better the range condition (Figure 28). The objective in range management gen- erally is to control grazing so that 29 plants growing on a site are similar in type and percentage composition to the climax plant community for that site. Such management gener- ally results in the maximum produc- tion of vegetation, conservation of water, and control of erosion. Some- times, however, a range condition somewhat below the climax meets grazing needs, provides desirable wildlife habitat, and protects soil and water resources. The major management concern on most rangeland is to control graz- ing so that the types and percent- ages of plants that make up the cli- max plant community can become reestablished. Controllingbrush and minimizing soil erosion by wind and water are also important manage- ment concerns. Aids to good range management include adequate fenc- ing so that different tracts can be grazed on a rotational basis and stra- tegic positioning of water (Figure 29) and mineral supplement sources so that the livestock will visit differ- ent parts of the tracts during their daily quest for forage, water, and minerals (Merrill, 1983). If sound range management based on soil in- formation and rangeland invento- ries is applied, the potential is good for increasing the productivity of rangelands. Summary With a land area of 1.12 million acres, Acuff soils are among the ma- jor arable soils in Texas. A small area of Acuff soils also occurs in eastern New Mexico. The area of Acuff soils is bounded by the Pullman soil area on the north and east, the caprock escarpment at the High Plains-Roll- ing Plains boundary on the south- east, the Edwards Plateau escarp- ment on the south, and a catena of sandy soils extending from Stanton, Texas, to Clovis, New Mexico, on the southwest. Acuff soils occupy about 30 percent of the land within this area. The remaining area is com- posed mainly of soils having similar morphology and occupying similar landscape positions. About 73 percent of the Acu ff soil area is cropland, 25 percent is ran ge- land, and the remainder is in towns, roads, and other non-agricultural uses. Irrigation is used on about 52 Figure 27. Excessive grazing results in poor range conditions, as shown to the left of the fence pictured. percent of the cropland area. Major crops are cotton, wheat, grain sor- ghum, and com. To determine the variability of soil characteristics, Acuff soils were sampled at 12 widely separated lo- cations. The profiles were described in the field at sampling time, and samples were analyzed in the labo- ratory for sand, silt, and clay con- tent; pH; bulk density; CaCOa equivalent; and water retention. Plant-available water was calculated from horizon thickness, bulk den- sity, and water retention values. Water infiltration was measured at the sampling sites. The thickness of the profiles was highly variable, ranging from a depth of 35 inches to a calcic horizon at Sites 9 and 1O in Dawson and Howard Counties, Texas, respec- tively, to 54 inches at Site 11 in Hockley County, Texas. In general, the profiles had less sand and more silt and clay in the northern prov- ince than in the southern province. Associated with the higher silt and clay contents were higher organic matter contents and higher mean Figure 28. Well-managed rangeland provides good forage for grazing livestock. water retention values, which gen- erally resulted in a greater capacity to store plant available water. Total water infiltration and infil- tration rates at 1O min were highly variable and seemed more closely 3O related to bulk density of the Ap horizon at the time measurements were made than to any other deter- mined profile characteristic. Total infiltration at 20 hrs ranged from 1.49 inches at Site 1 in Parmer County, . . .-.;..-">S:-:~:»:-:-:-: