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The declining Ogallala Aquifer beneath the Southern High Plains may necessitate dryland crop production and cotton (Gossypium hirsutum L.) is a well-adapted and potentially profitable alternative crop. The limited growing season duration of the Texas Panhandle and southwestern Kansas, however, imposes significant production risk due to incomplete boll maturation. Emphasizing earlier boll production that is usually confined to sites on lower fruiting branches may reduce risk, but offsetting high planting densities are needed to maintain desirable lint yield. Our objectives were to quantify planting: 1) row width and 2) in-row spacing effects on growth, yield, and fiber quality of dryland cotton. Field tests of row widths from 0.25 to 0.76 m and plant densities with in-row spacing ranging from 0.075 to 0.15 m were conducted from 1999 to 2005 on a nearly level Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) managed in a wheat (Triticum aestivum L.), cotton, fallow (W-Ctn-F) rotation. To expand the basis of comparison, cotton growth and yields were simulated using GOSSYM and long-term (1958-2000) weather records from Bushland, TX, as input for all combinations of 0.38 or 0.76 m row widths and plant spacing of 0.075, 0.10 and 0.15 m. Experimental and computer simulated plant height and harvested boll number increased significantly with increased row spacing and, occasionally, in-row plant spacing. Modeled lint yield for 0.38 m rows decreased by approximately 50% compared with the 582 kg·ha-1 yield for conventional row spacing, which was practically duplicated by field observations in 2001 and 2004. Measured fiber quality occasionally improved with conventional row spacing over ultra-narrow rows, but was unaffected by plant spacing. Because narrow rows and frequent plant spacing did not improve lint yield or fiber quality of dryland cotton, we do not recommend this strategy to overcome a thermally limited growing season.

Depletion of the High Plains Aquifer that supplies irrigation water for the semiarid Southern Great Plains may necessitate dryland production of crops like wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] using the wheat–sorghum–fallow (WSF) rotation. Reduced crop productivity without irrigation can be offset by intensifying the WSF rotation with cattle (Bos taurus) grazing. Biomass removal and soil trampling without tillage, however, may reduce rain infiltration and storage during fallow that increases with no-tillage (NT) over stubble-mulch (SM) tillage. Our objective was to quantify grazing and tillage effects on infiltration, sediment transport, and aggregate stability during fallow periods after sorghum and wheat. Using a split plot randomized complete block design, we compared wet aggregate size distribution of a Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll; 0.0–0.05 m) and sediment yield in runoff of simulated rain during the fallow-like idle period after wheat and the sorghum fallow. Sediment concentration and yield for both fallows were numerically larger (>40%) with grazing. Sediment concentration from SM tillage increased significantly over NT for either fallow, but soil loss differed only for wheat fallow. Mean final infiltration rate (IRf) and amount (IA60) did not differ significantly with grazing during either fallow, but IA60 was usually 20% lower for grazed than for ungrazed paddocks. Because SM tillage after grazed wheat significantly (P < 0.01) increased IRf and IA60 over NT, occasional SM tillage to disrupt compaction from trampling may increase water conservation for dryland cropping systems combining grazing with NT residue management.

The Ogalalla Aquifer is used to supplement insufficient precipitation for agricultural production in the semiarid Texas High Plains. However, decades of pumping combined with minimal recharge has resulted in decreased well capacity in most areas. A calibrated Soil and Water Assessment Tool (SWAT) model was used to compare simulated yields, crop water use, and required irrigation for crop rotations of the region using measured long-term (90 years) historical weather data. Crop rotations included continuous corn and cotton, corn–cotton, sorghum–cotton, cotton–winter wheat, and corn–winter wheat. Results demonstrated that a calibrated SWAT model simulated crop water use and yields well for all listed crops except cotton. The plant growth algorithms in SWAT appear unable to simulate representative cotton yields typical of cotton management in the Texas High Plains. A work-around for a limitation of the auto-irrigate function in SWAT to be suspended during the dormancy period of winter wheat was also used. Summary statistics for crop yield, crop water use, and irrigation were presented for all rotations. Long-term water use of simulations and irrigation probability exceedance statistics are presented for all simulated crops. These data may serve as a decision support tool for producers considering crop rotation strategies.

Soil can be degraded by several natural or human-mediated processes, including wind, water, or tillage erosion, and formation of undesirable physical, chemical, or biological properties due to industrialization or use of inappropriate farming practices. Soil degradation occurs whenever these processes supersede natural soil regeneration and, generally, reflects unsustainable resource management that is global in scope and compromises world food security. In North America, soil degradation preceded the catastrophic wind erosion associated with the dust bowl during the 1930s, but that event provided the impetus to improve management of soils degraded by both wind and water erosion. Chemical degradation due to site specific industrial processing and mine spoil contamination began to be addressed during the latter half of the 20th century primarily through point-source water quality concerns, but soil chemical degradation and contamination of surface and subsurface water due to on-farm non-point pesticide and nutrient management practices generally remains unresolved. Remediation or prevention of soil degradation requires integrated management solutions that, for agricultural soils, include using cover crops or crop residue management to reduce raindrop impact, maintain higher infiltration rates, increase soil water storage, and ultimately increase crop production. By increasing plant biomass, and potentially soil organic carbon (SOC) concentrations, soil degradation can be mitigated by stabilizing soil aggregates, improving soil structure, enhancing air and water exchange, increasing nutrient cycling, and promoting greater soil biological activity.

The declining High Plains or Ogallala Aquifer motivates U.S. producers to optimize water use and yield of drought-tolerant crops like cotton [Gossypium hirsutum (L.)]. Systematic sea surface temperature anomalies (SSTA) drive the El Nino–Southern Oscillation (ENSO), resulting in predictable weather patterns in North America that could be exploited by irrigation strategies. Our objective was to compare cotton yield response to irrigation as altered by La Nina, Neutral, or El Nino phases for the Texas High Plains. We used actual 1959 to 2000 weather records with the simulation model GOSSYM to estimate lint yields for three progressively later emergence dates under 50 or 75% initial soil water conditions and all combinations of irrigation duration (0, 4, 6, 8, and 10 wk) and rate (2.5, 3.75,and 5.0 mm d–¹). Simulated lint yield and its ratio to evapotranspiration generally decreased with emergence delays and increased with increasing irrigation amount and application rate. Growing season precipitation varied with ENSO phase, but April to June phase classification was inconsistent with fall conditions except for La Nina. Compared with yield estimates for Neutral and El Nino phases, limited rain during La Nina years reduced lint yields from 5 to 30% when initial soil water was 75 and 50%. Yield increased with increasing irrigation rate and duration during drier La Nina growing seasons, but irrigation benefits decreased during Neutral and El Nino years having greater precipitation. Early ENSO based extended forecasts for La Nina related consistently to irrigation effects on yield and could determine application strategies.

Sorghum ( Sorghum bicolor (L.) Moench), including sorghum-sudan crosses [ S. bicolor subsp. Drummondii (Nees ex Steud) de Wet & Harlan] (SS), represents a broad category of plants that includes those grown primarily for forage or grain. Sorghum cultivars can be further classified as brown midrib (BMR), nonBMR, photoperiod sensitive (PS) and nonPS. The objective of our study was to compare sorghum classes comprised of multiple cultivars in relation to forage and grain yield, agronomic characteristics (i.e. height, lodging, moisture at harvest), nutrient composition and fiber digestibility. Although common properties among different sorghum classes were detected, consistent differences in forage yield and quality factors emerged between classes. The study mean SS-PS forage yield of 19.0 Mg ha −1 was significantly ( P = 0.05) greater than all other non-PS classes and the FS-BMR class consistently yielded less than the corresponding FS class with an average reduction of 2.2 Mg ha −1 . Grain yield varied greatly among the forage sorghum (FS) and FS-BMR cultivars, ranging from 2.30 to 7.54 Mg ha −1 with some FS cultivars yielding as much as those in the grain class. Those sorghum classes with the BMR trait consistently had the lowest acid detergent fiber (ADF) and neutral detergent fiber (NDF), and were lower in lignin content. The BMR trait also increased digestibility of the NDF fraction (NDFD). In vitro-true-digestibility (IVTD) was highest with FS-BMR and grain sorghum (Grain) classes followed by the FS, FS-PS-BMR and SS classes with the SS-PS consistently having the lowest IVTD. Although mean percent IVTD among sorghum classes descended in the same order as was observed for the grain yield, we identified very little correlation ( r = 0.28) between grain yield and IVTD. Lodging was not increased in BMR cultivars compared with the nonBMR cultivars when harvested at the soft-dough stage and there was little correlation between lodging and lignin content, grain yield, or plant height.

Increased precipitation storage as soil water is crucial to dryland production of wheat (L.) and grain sorghum [ (L.) Moench] on the semiarid southern Great Plains. At the USDA-ARS Conservation and Production Research Laboratory at Bushland, TX, surface runoff from a Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) is typically greater with no-till (NT) than stubble-mulch (SM) tillage under the 3-yr wheat–sorghum–fallow (WSF) dryland crop rotation. Our objective was to quantify the effects of NT or SM tillage with bare or retained residue on infiltration of simulated rain, sediment transport, and related aggregate stability for continuous wheat (CW) and WSF rotation plots established in 1983. Compared with bare soil, the retained wheat residue cover increased mean 60-min cumulative infiltration across all tillage and rotation combinations by >25 mm and decreased soil loss. Cumulative rain infiltration and total soil loss did not vary significantly (< 0.05) with tillage, but the mean infiltration rate at 60 min was 15.0 mm h less for NT than SM. The CW rotation typically increased infiltration regardless of residue cover or tillage compared with the WSF rotation, which we attributed to greater aggregate stability. The greater aggregate stability for CW may have decreased soil loss compared with WSF, which was greatest for bare SM tilled sites. We conclude that residue cover significantly increases rain infiltration over bare soil conditions independent of any tillage or rotation treatment effects. Nevertheless, increased rain infiltration due to residue cover was not sustained in the absence of soil disturbance for NT.

Cattle (Bos taurus) grazing intensifies production of the dryland wheat (Triticum aestivum L.)-sorghum [Sorghum bicolor (L.) Moench]-fallow (WSF) rotation in the U.S. Southern High Plains. Stubble-mulch (SM) tillage controls weeds and counteracts soil compaction. No-till (NT) increases soil water at planting and dryland crop yields, but added grazing effects are unknown. Our objectives were to quantify dryland winter wheat and sorghum yield responses to grazing and tillage practices. At the USDA-ARS Conservation and Production Research Laboratory, Bushland, TX, we established all WSF rotation phases in triplicate ungrazed and grazed paddocks beginning 1999 on a Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) using SM tillage. During spring 2004, NT or SM tillage were superimposed within grazing main plots. Cattle gain, soil water after fallow, and crop yield were compared during 2005 to 2009 using a split-plot randomized complete block design. Cattle, stocked at 1.8 Mg ha -1 , grazed sorghum stover and growing wheat an average of 29 d for a mean gain of 147 kg ha -1 . Soil water at plantingwas unaffected by grazing, but increased from 14 to 28 mm with NT. Although grazing seldom reduced yield of wheat or sorghum, NT in ungrazed plots increased crop yields sufficiently (0.96-2.6 Mg ha -1 ) in 2008 and 2009 to offset any value added by grazing. We conclude that cumulative grazing effects in NT plots reduced soil water storage and depressed yield. We recommend post-wheat-harvest SM tillage to disrupt soil compaction and restore grazed soil productivity.

Tillage-induced changes in soil properties are difficult to predict, yet can influence evaporation, infiltration and how water is redistributed within the profile after precipitation. We evaluated the effects of sweep tillage (ST) on near surface soil water dynamics as compared with an untilled (UT) soil during a 7-month period. Plots were established in a fallow field devoid of residue under stubble–mulch tillage management on a clay loam soil. Soil water contents were monitored using time-domain reflectometry at 0.05–0.3 m and using a neutron moisture gage to a depth of 2.3 m. Soil temperature and net radiation was also monitored. During a 114-day period from April through July, tillage with a sweep (0.07–0.1 m) significantly decreased net water storage above 0.3 m soil depth by an average of 12 mm ( P = 0.002) as compared with UT plots. After tillage, soil water contents at 0.05 and 0.1 m were significantly ( P P −1 ) despite the greater near-surface water contents of UT plots. Although ST plots exhibited 19 mm greater cumulative evaporation from July through October, this was offset by 26 mm greater infiltration compared with UT. A more advanced surface crust development and greater initial water contents were likely responsible for lower cumulative infiltration of UT compared with ST plots. Immediately after tillage, cumulative daily net radiation averaged 22% greater for ST compared with UT surfaces and these differences diminished with time. Increased evaporation under tillage was likely a result of enhanced vapor flow near the surface and greater absorption of radiation by a tilled surface with reduced albedo.

Under dryland conditions of the Texas High Plains, maize ( Zea mays ) production is limited by sparse and erratic precipitation that results in severe water stress particularly during grain formation. When plant populations are reduced to 2.0–3.0 plants m −2 to conserve soil water for use during grain filling, tillers often form during the vegetative growth and negate the expected economic benefit. We hypothesized that growing maize in clumps spaced 1.0 m apart would reduce tiller formation, increase mutual shading among the plants, and conserve soil water for grain filling that would result in higher grain yield. Studies were conducted during 2006 and 2007 at Bushland, TX. with two planting geometries (clump vs. equidistant), two irrigation methods (low-energy precision applicator, LEPA, and low-elevation spray applicator, LESA) at three irrigation levels (dryland, 75 mm and 125 mm in 2006; and dryland, 50 mm and 100 mm in 2007). For dryland plots in 2007, clump plants had only 0.17 tillers (0.66 tillers m −2 ) compared with 1.56 tillers per plant (6.08 tillers m −2 ) for equidistant spacing. Tillers accounted for 10% of the stover for the equidistant plants, but less than 3% of the grain. Clump planting produced significantly greater grain yields (321 g m −2 vs. 225 g m −2 and 454 g m −2 vs. 292 g m −2 during 2006 and 2007, respectively) and Harvest Indexes (0.54 vs. 0.49 and 0.52 vs. 0.39 during 2006 and 2007, respectively) compared with equidistant plants in dryland conditions. Water use efficiency (WUE) measurements in 2007 indicated that clumps had a lower evapotranspiration (ET) threshold for initiating grain production, but the production function slopes were 2.5 kg m −3 for equidistant treatments compared to 2.0 kg m −3 for clump treatments. There was no yield difference for method of irrigation on water use efficiency. Our results suggest that growing maize in clumps compared with equidistant spacing reduced the number of tillers, early vegetative growth, and Leaf Area Index (LAI) so that more soil water was available during the grain filling stage. This may be a useful strategy for growing maize with low plant populations in dryland areas where severe water stress is common.

Increasing pumping costs and declining well capacities in the Southern High Plains compel producers to seek irrigation strategies to maximize yield and water use efficiency (WUE), which is the ratio of yield to evapotranspiration (ET). Cotton (Gossypium hirsutum L.) is suited to deficit irrigation using wells ranging from 0.29 to 0.93 L s ―1 ha ―1 capacity to supply limited, 2.5 mm d ―1 , to complete, 8.1 mm d ―1 ET replacement. Our objectives were to (i) evaluate irrigation capacity and duration effects on lint yield, and (ii) compare application strategies that maximize yield and WUE. The simulation model GOSSYM was used with 1959 to 2000 weather records from Bushland, TX, to calculate yields of cotton grown on a Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) with 50 or 100% initial available soil water. We compared all combinations of irrigation duration (4, 6, 8, and 10 wk) and capacity (for ET replacement of 2.5, 3.75, and 5.0 mm d ―1 and dryland). Simulated lint yield decreased as irrigation decreased; however, yields for similar irrigation totals increased with increasing irrigation capacity. Simulated yields for cotton irrigated > 8 wk did not differ among irrigation capacities, but cotton irrigated at 5.0 mm d ―1 maintained yield with earlier irrigation termination at 6 wk. Based on mean yields, we determined that spreading water to deficit irrigate a field with 2.5 mm d ―1 yielded ∼5% less lint than concentrating that water to irrigate smaller fields at 3.75 or 5.0 mm d ―1 that were averaged with complementary (2:1 and 1:1) dryland areas.

Increasing pumping costs and declining well capacities in the U.S. Southern High Plains have led to greater reliance on less productive and inherently riskier dryland cropping systems. Dryland wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] are typically grown in a 3-yr wheat-sorghum-fallow (WSF) rotation that may be intensified by integrating cattle (Bos taurus) grazing. Suitability of grazing dryland crops in the WSF rotation has not been evaluated. Our objectives were to quantify (i) cattle gain during limited grazing of dryland wheat and sorghum stover, and (ii) grazing effects on the growth and yield of the grazed wheat and subsequent sorghum crop. We established, concurrently, all WSF rotation phases in duplicate ungrazed and grazed plots in three replicated paddocks on a gently sloping Pullman silty clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) at the USDA-ARS, Conservation and Production Research Laboratory, Bushland, TX (35°11' N, 102°5' W). Cattle gain, fallow soil water storage, and the growth and yield of wheat and subsequent grain sorghum were compared from 2000 to 2007 within a randomized complete block. Dryland wheat was grazed an average of 31 d during 7 of 8 test years by cattle stocked at 1.7 Mgha -1 and produced a mean gain of 123 kg ha -1 . Wheat grain yield averaged 1.72 Mgha -1 without grazing and was not different from the 1.57 Mg ha -1 grain yield with grazing. Grazing decreased wheat straw yield, but subsequent soil water storage was unaffected. Sorghum grain yields of 2.26 Mg ha -1 in ungrazed plots were not different from grazed plots averaging 2.20 Mg ha -1 . Overall productivity of the WSF cropping system was increased using limited grazing of dryland wheat forage and sorghum stover with no significant reduction in wheat or sorghum grain yields.

The mention of trade names of commercial products in this article is solely for the purpose of providing specifi c information and does not imply recommendation or endorsement by the USDA.Soil Sci. Soc. Am. J. 72:677-682doi:10.2136/sssaj2007.0122Received 30 Mar. 2007.*Corresponding author (R.Louis.Baumhardt@ars.usda.gov).© Soil Science Society of America677 S. Segoe Rd. Madison WI 53711 USAAll rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

NOTE Quantifying the hydrologic balance at high temporal resolution is necessary to evaluate fi eld-scale management eff ects on soil water storage. Our objective was to develop and evaluate a hybrid procedure to estimate drainage, infi ltration, and evaporation based on changes in plot-scale soil water storage on a Pullman clay loam. Soil water contents were monitored in 2005 at 0.5-h intervals on 12 plots instrumented with time-domain refl ectometry probes at 0.05, 0.1, 0.15, 0.2, and 0.3 m depths, and weekly using a neutron moisture meter to a depth of 2.3 m in 0.2-m increments. During periods in August 2005 when either a plane of zero fl ux existed or when a wetting front penetrated into an upper soil layer at ?0.24 m, changes in soil water storage were used to iteratively fi t hydraulic parameters to estimate soil water fl uxes into and out of the control volume. Predicted hydraulic conductivities were not signifi cantly diff erent (p = 0.471) from hydraulic conductivities calculated using the iterative method during three other months in 2005 and yielded drainage rates that diff ered by less than 0.05 mm d −1 as compared to calculated changes in storage below the plane of zero fl ux. By considering the delayed response of water content measurements to precipitation inputs, cumulative infi ltration and evaporation throughout a month with 103-mm precipitation could be estimated from the measured changes in soil water storage with expected uncertainties of ± 5 mm. Th e proposed procedure permits the indirect estimation of soil water balance components useful for comparing plot-scale treatments and overcomes some of the diffi culties associated with weighing lysimeter and meterological approaches.

Increasing pumping costs and declining well capacities in regions like the Southern High Plains of Texas are requiring producers to adaptcroppingpracticesforusewithirrigation levelsthatvarybetween complete replacement of crop evapotranspiration (ET) to none (i.e., dryland production). Grain sorghum [Sorghum bicolor (L.) Moench] isacropsuitedtobothdrylandandvariousdeficitirrigationproduction systems. Our objectives were to (i) identify cultural practices (planting date, population, and cultivar maturity) that maximize sorghum grain yield for widely varying irrigation strategies; and (ii) consider effective means to allocate available water among irrigation strategies that maximizes the ratio of yield to ET, that is, water use efficiency (WUE). Using the model SORKAM and long-term (1958–1999) weather records from Bushland, TX, we simulated sorghum grain yields on a Pullman soil (fine, mixed, superactive, thermic Torrertic Paleustoll) under dryland (rain) and three deficit irrigation levels (rain 1 irrigation 5 2.5, 3.75, or 5.0 mm d 21 ) for all combinations of planting date (mid-May, 15 May; early June, 5 June; and late June, 25 June), cultivar maturity (early, 95 d; medium, 105 d; late, 120 d), and plant density (12and16plantsm 22 ).For2.5mm d 21 irrigation level,simulated grain yields were maximized with either early or medium-maturing cultivars planted in early June. In contrast, simulated sorghum yield and WUE increased with a mid-May planting date and later-maturing cultivars forirrigationlevelsof3.75and5.0mmd 21 .Weconcludethatspreading water to uniformly irrigate a field with 2.5 mm d 21 produces |16% less grain than concentrating the same water resources to variably irrigate a field at 3.75 or 5.0 mm d 21 with complementary (2:1 and 1:1) dryland areas.

Stored soil water and growing season precipitation generally support early season growth of grain sorghum (Sorghum bicolor L. Moench) in dryland areas but are insufficient to prevent water stress during critical latter growth stages. The objective of this study was to determine if growing plants in clumps affected early season growth and subsequent grain yield compared to uniformly spaced plants. We hypothesized that growing grain sorghum plants in clumps would result in fewer tillers and less vegetative growth so that more soil water would be available during the grain-filling period. Results from 3 yr at Bushland, TX, and 1 yr at Tribune, KS, showed that planting grain sorghum in clumps of three to six plants reduced tiller formation to about one per plant compared to about three for uniformly spaced plants. Grain yields were increased by clump planting by as much as 100% when yields were in the 1000 kg ha 21 range and 25 to 50% in the 2000 to 3000 kg ha 21 range, but there was no increase or even a small decrease at yields above 5000 kg ha 21 . Our results suggest that planting grain sorghum in clumps rather than spaced uniformly conserves soil water use until later in the season and may enhance grain yield in semiarid dryland environments.

Grain sorghum [Sorghum bicolor (L.) Moench] is adapted for use in dryland and irrigated cropping systems on the southern High Plains. Irrigation in this region relies on the declining Ogallala aquifer, and applications are transitioning from full to deficit evapotranspiration replacement. Our objective was to identify optimum planting date, population, row spacing, and cultivar maturity combinations to maximize grain sorghum yield using the SORKAM model and long-term (1958–1999) weather records at Bushland, TX, for a Pullman soil (fine, mixed, superactive, thermic Torrertic Paleustoll) with reduced irrigation. Grain sorghum growth and yield was simulated under dryland and deficit- or full-irrigation conditions (rain 1 irrigation 5 2.5 or 5.0 mm d 21 ) for all combinations of planting date (15 May, 5 June, 25 June), cultivar maturity (early, 95 d; medium, 105 d; late, 120 d), population (12 and 16 plants m 22 ), and row spacing (0.38 and 0.76 m). Simulated grain yield was unaffected by planting population but increased 7% for narrow compared with wide row spacing independent of other treatment effects. Results suggest two alternative management practices to optimize yield for the southern High Plains depending on potential irrigation capacity: (i) where rain plus supplemental irrigation was ,0.2.5 mm d 21 , plant early-maturing cultivars during June and (ii) where rain plus supplemental irrigation approaches 5.0 mm d 21 , plant late-maturing cultivars on 15 May. Earlymaturity cultivars planted on 5 June were better adapted to dryland and deficit irrigation for optimum grain yield on a southern High Plains Pullman soil.

Agricultural systems produce both detrimental and beneficial effects on soil quality (SQ). We compared soil physical properties of long-term conventional (CON) and alternative (ALT) cropping systems near Akron, Colorado (CO); Brookings, South Dakota (SD); Bushland, Texas (TX); Fargo, North Dakota (ND); Mandan (ND); Mead, Nebraska (NE); Sidney, Montana (MT); and Swift Current, Saskatchewan (SK), Canada. Objectives were to quantify the changes in soil physical attributes in cropping systems and assess the potential of individual soil attributes as sensitive indicators of change in SQ. Soil samples were collected three times per year from each treatment at each site for one rotation cycle (4 years at Brookings and Mead). Water infiltration rates were measured. Soil bulk density (BD) and gravimetric water were measured at 0–7.5, 7.5–15, and 15–30 cm depth increments and water-filled pore space ratio (WFPS) was calculated. At six locations, a rotary sieve was used to separate soil (top 5 cm) into six aggregate size groups and calculate mean weight diameter (MWD) of dry aggregates. Under the CON system at Brookings, dry aggregates (>19 mm) abraded into the smallest size class (

Typical planting recommendations for dryland grain sorghum [Sorghum bicolor (L.) Moench] in the southern High Plains are to delay until soil water is adequate for crop establishment, but no population or cultivar maturity class are specified. Our objectives were to use the SORKAM simulation model, long-term (1958-1998) weather records at Bushland, TX, and known Pullman soil (fine, mixed, superactive, thermic Torrertic Pateustolls) properties to identify an optimum planting date, population, row spacing, and cultivar maturity combination to maximize dryland grain sorghum yield. We simulated sorghum grain yields for combinations of planting dates (15 May, 5 June, and 25 June), populations (3,6, and 12 plants m -2 ), row spadngs (0.38 and 0.76 m), and cultivar maturity class (early, medium, and late). SORKAM consistently (r 2 = 0.69, RMSE = 792 kg ha -1 ) simulated grain yields that averaged about 5% more than measured values and correctly simulated row width and population effects on yield. Simulated grain yields increased with narrow row-spacing ∼9%, independent of planting date or cultivar. Increasing plant population significantly decreased panicle seed number, seed mass, and plant tillers; however, the simulated grain yield was unchanged (3996-4106 kg ha ') by plant populations. Mean simulated grain yields were greatest for the 5 June planting dates with early and medium maturity cultivars that avoided late summer heat or water deficit stresses and matured before freezing weather. Our results show early or medium maturity cultivars, planted 5 June, in 0.38-m row widths, using 3 or 6 plants m -2 , achieve the greatest dryland grain yield on a southern High Plains clay loam soil.

Seedling emergence is the crucial first step in crop establishment; however, crops frequently must penetrate or lift a thin, dense, soil layer called a crust, which is formed by drop impact or aggregate slaking during rainstorms and sprinkler irrigation. Shaping the soil surface into a small ridge or cap above the seed row may decrease crust strength and improve seedling emergence. Our objectives were to quantify the effects of surface soil geometry (25 mm high by 50 mm wide soil cap without removal) on (i) crust formation and strength, (ii) seedling emergence of selected crops, and (iii) seed zone soil temperature. Sieved (

Dryland wheat (Triticum aestivum L.) and grain sorghum (Sorghum bicolor (L.) Moench) are often grown using a wheat–sorghum-fallow (WSF) crop rotation on the semiarid North American Great Plains. Precipitation stored during fallow as soil water is crucial to the success of the WSF rotation. Stubble mulch-tillage (SM) and no-tillage (NT) residue management practices reduce evaporation, but the sparse residue cover produced by dryland crops, particularly sorghum, is insufficient to reduce soil crusting and runoff. Subsoil tillage practices, e.g., paratill (PT) or sweep (ST), fracture infiltration limiting soil layers and, when used with residue management practices, may increase soil-water storage and crop growth. Our objectives were to compare the effects of PT to 0.35 m or ST to 0.10 m treatments on soil cone penetration resistance, soil-water storage, and dryland crop yield with NT and SM residue management. Six contour-farmed level-terraced watersheds with a Pullman clay loam (US soil taxonomy: fine, mixed, superactive, thermic Torrertic Paleustoll; FAO: Kastanozems) at the USDA—Agricultural Research Service, Conservation and Production Research Laboratory, Bushland, TX, USA (35 ◦ 11 � N, 102 ◦ 5 � W) were cropped as pairs using a WSF rotation so that each phase of the sequence appeared each year. In 1988, residue management plots received PT or ST every 3 years during fallow after sorghum resulting in five treatments: (i) NT–PT, (ii) NT–NOPT, (iii) NT–ST, (iv) SM–PT, and (v) SM–NOPT. Cone penetration resistance was the greatest in NT plots and reduced with PT after 12, 23, and 31 months. Mean 1990–1995 soil-water storage during fallow after wheat was greater with NT than with SM, but unaffected by PT or ST. Dryland wheat and sorghum grain yields, total water use, and water use efficiency (WUE) were not consistently increased with NT, however, and unaffected by PT or ST tillage. We conclude, for a dryland WSF rotation, that: (1) NT increased mean soil-water storage during fallow after wheat compared to SM, and (2) ST and PT “subsoil” tillage of a Pullman did not increase water storage or yield. Therefore, NT residue management was more beneficial for dryland crop production than subsoil tillage. Published by Elsevier Science B.V.

Dryland winter wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] are often grown on the semiarid North American Great Plains using the wheat-sorghum-fallow (WSF) crop rotation. When used with WSF, no-tillage (NT) and stubblemulch tillage (SM) residue management reduce evaporation and increase yield, but more runoff occurs with NT compared to SM. Our objectives were to determine the effects of NT and SM residue management with paratill (PT) and sweep (ST) tillage on soil properties and rain infiltration into a Pullman clay loam (US soil taxonomy: fine, mixed, superactive, thermic Torrertic Paleustoll). Six contour-farmed level-terraced watersheds were dryland cropped using a WSF rotation with each phase of the WSF appearing all years as main plots. Residue management by tillage subplots of: (i) NT with PT, (ii) NT with NOPT, (iii) NT with ST, (iv) SM with PT, and (v) SM with NOPT were installed within these main plots after sorghum harvest. Approximately, 9 months later during the wheat phase (before planting), we measured selected soil characteristics and the infiltration rate and amount using a rotating disk rain simulator that applied cistern stored rainwater at 48 mm h -1 on the five tillage-residue management treatments. Cumulative infiltration at 1 h was similar among tillage treatments within residue management practices, i.e., infiltration into SM plots averaged 32.4 ± 3.9 mm compared to 21.9 ± 2.5 mm for NT plots. Regardless of residue management, PT and ST tillage caused no significant (P < 0.05) increase in infiltration compared to NOPT. Measured cone-penetrometer resistance, bulk density, and initial soil-water content decreased with ST and PT for NT residue management but not SM residue management. The data show that SM residue management compacted the soil beneath, the sweep implements; thus, negating any benefits of reduced soil bulk density and penetration resistance with PT. We conclude that reductions in soil density and penetration resistance due to PT were diminished by SM tillage and that infiltration was regulated at the soil surface by a rapidly forming crust, which negated PT effects on SM or NT. Published by Elsevier Science B.V.

Multisensor capacitance probes (MCAP) are an alternative to gravimetric or nuclear soil water content (θ v , m 3 m -3 ) measurements. Their θ, measurements are more convenient than gravimetric, and don't carry the nuclear regulatory burdens. Previous studies noted potential salinity and temperature effects on MCAP 0, determinations. Our objectives were to calibrate and verify MCAP 0, measurement accuracy in two soil materials, two water salinities (1.3 and 11.3 dS m -1 ), and with diurnal temperature fluctuations. The surface and calcic horizons of an Olton soil (fine, mixed, superactive, thermic Aridic Paleustoll) were packed into triplicate, 0.5-m-tall, 100-L columns and wetted. We compared θ v determined by volumetric measurements, time domain reflectometry (TDR), and MCAPs. The TDR θ v were within ±0.01 m 3 m -3 of volumetric determinations for air-dry and saturated soil. The factory supplied universal MCAP calibration provided accurate 0, estimates for air dry (± 0.01 m 3 m -3 ) surface and calcic soil materials but not after wetting (-0.05 m 3 m -3 ). Also, imprecise MCAP sensor positioning during water frequency parameter determination was problematic and biased initial θ v measurements. After calibration against TDR, the MCAP θ v varied ±0.01 m 3 m -3 from measured Θ v for air-dry and saturated conditions for both soil materials, which were then pooled to obtain one calibration. Column resaturation with saline water affected permittivity and elevated MCAP θ v 0.25 m 3 m -3 above the available pore space. Cyclical soil temperature fluctuations of 15°C induced similar fluctuations in indicated θ v throughout the column (0.04 m 3 m -3 for MCAP and 0.02 m 3 m -3 for TDR), which was attributed to variations in permittivity.

Natural rainstorms have dynamic intensities; thus, a large portion of total predpitation may be received during a short time. Natural rainstorms also have both variable drop sizes and kinetic energy. Accurate studies of sediment transport and infiltration require realistic duplication of natural rain kinetic energy and intensities. Rain simulator designs must be capable of producing dynamic multiple intensities and corresponding multiple drop sizes to simulate variable kinetic energies. Many simulators are capable of producing rain with multiple and, in some cases, dynamic intensities, but a simulator that can vary both the intensity and kinetic energy is needed. Our objective was to design and build a rain simulator for field use that realistically duplicated natural rain storms. A computer-controlled solenoid-valve multiple nozzle type rain simulator was developed. The computer not only controls solenoid valve activation of the rain simulator during operation but also measures runoff and records rain application and runoff data to a log file for processing. The simulator has control software that controls and monitors all processes. The rain simulator is capable of uniformly applying water (coeffident of uniformity = 84-94%) with a dynamically changing intensity of up to 200 mm h -1 and kinetic energies ranging from 15.0 to 23.5 J m -2 mm -1 . Uniformity of application was achieved by oscillating the nozzles in two directions. Field operation of the simulator is enhanced by its portability. The measurement area is easily modified using in-line handrail connectors to change support frame dimensions, thus accommodating infiltration and chemical or sediment transport studies.

Texas South Plains production systems for conserving rainfall and reducing wind erosion in cotton (Gossypium hirsutum L.), a low-residue crop, include the spring chemical termination of winter wheat (Triticum aestivum L.) overseeded post-harvest into cotton. This practice often increases cotton lint yields under irrigation, but residues hinder weed control and increase production costs. This study characterized infiltration response to (i) residue weathering and soil consolidation with ridges, (ii) residue distribution on the ridge or in the furrow, and (iii) flat or standing architectures and residue amounts. Simulated rain was applied at 65 mm h -1 for 1 h into a bare Olton clay loam (fine, mixed, thermic Aridic Paleustoll). Mean cumulative infiltration was lowest for bare soil (28.7 mm), but increased curvilinearly with Increasing residue amounts, leveling at 49.0 mm. Cumulative infiltration with residues distributed on the ridge (42 mm) or in the furrows (44 mm) were the same even though water in the furrow absorbed drop impact. A minimum amount of residue (0.7 Mg ha -1 ) to intercept raindrop impact was needed to increase rain infiltration, but increasing residue above a residue threshold of 2.4 Mg ha -1> had no effect because of sufficient drop impact interception. Increases in infiltration were related to the residue amount rather than to the bed or furrow location. Partial residue cover and tillage operations that lodge crop residues may increase infiltration.

Dryland agricultural cropping systems emphasize sustaining crop yields with limited use of fertilizer while conserving both rain water and the soil. Conservation of these resources may be achieved with management systems that retain residues at the soil surface simultaneously modifying both its energy and water balance. A conservation practice used with cotton grown on erodible soils of the Texas High Plains is to plant cotton into chemically terminated wheat residues. In this study, the partitioning of daily and seasonal evapotranspiration (Et) into soil and plant water evaporation was compared for a conventional and a terminated-wheat cotton crop using the numerical model ENWATBAL. The model was configured to account for the effects of residue on the radiative fluxes and by introducing an additional resistance to latent and sensible heat fluxes derived from measurements of wind speed and vapor conductance from a soil covered with wheat-stubble. Our results showed that seasonalEt was similar in both systems and that cumulative soil water evaporation was 50% ofEt in conventional cotton and 31% ofEt in the wheat-stubble cotton. Calculated values ofEt were in agreement with measured values. The main benefit of the wheat residues was to suppress soil water evaporation by intercepting irradiance early in the growing season when the crop leaf area index (LAI) was low. In semiarid regions LAI of dryland cotton seldom exceeds 2 and residues can improve water conservation. Measured soil temperatures showed that early in the season residues reduced temperature at 0.1 m depth by as much as 5°C and that differences between systems diminished with depth and over time. Residues increased lint yield per unit ofEt while not modifying seasonalEt and reducing cumulative soil water evaporation.

Movement of water through well developed calcic horizons, present in many North American Great Plains soils, is critical to groundwater recharge and crop water management; however, information about the hydraulic properties of these horizons is scarce. This study was conducted to measure physical an

Greater infiltration of precipitation increases water available for cotton (Gossypium hirsutum L.), wheat (Triticum aestivum L.), and sorghum [Sorghum bicolor L. (Moench)] production on the semiarid Texas South Plains. The objective of this study was to determine the short-term effects of tillage and crop residues on water infiltration into an Olton clay loam (fine, mixed, thermic Aridic Paleustoll), a Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll), and an Amarillo loamy fine sand (fine-loamy, mixed, thermic Aridic Paleustalf). Cropping treatments included (i) conventional tillage of continuous cotton (CVT), (ii) no-tillage, limited residue, of continuous cotton (C-NTL), and (iii) no-tillage of cotton grown in rotation with limited grain sorghum (S-NTL), or (iv) wheat (W-NTL) residues [...]

The objectives of this study were to determine: (1) the degree of seal development at incipient ponding, and (2) the relationship between the hydraulic conductance of developing seals and rainstorm characteristics, i.e. the rain intensity and kinetic energy rate. Laboratory columns of an Atwood soil (Typic Paleudalf) were subjected to rainstorms with different combinations of duration, intensity, and kinetic energy rate. Seal conductance was determined from measured infiltration data and a solution of the Richards' equation for vertical infiltration through an infinitely thin seal. The results show that the hydraulic conductance of the sealing zone decreased rapidly during early stages of rainfall commencing before incipient ponding. The analyses indicate that for storms of relatively brief duration (less than 2 h) the hydraulic conductance of the sealing zone depends on the cumulative rainfall energy and on the rainstorm intensity.

(20,000 km 2 area) in a bench terrace system in the semiarid High Plains in Texas (USA). Deep plowing was followed by conventional tillage. Boreholes were drilled in deep plowed cropland (three boreholes) and also beneath conventionally tilled cropland (four) and natural ecosystems (three) to provide baseline controls. Soil samples were analyzed for water content, chloride concentrations, and matric potentials to quantify subsurface water movement. Bulges of chloride that accumulated beneath natural ecosystems during the past 9,000–14,000 years (Holocene period) provided a marker to quantify timeintegrated response of subsurface drainage to hydrologic forcing in deep-plowed cropland. Displacement of chloride bulges to depths of 10.7, 12.3, and 13.7 m beneath deep-plowed cropland indicate minimum drainage rates of 58, 60, and 81 mm/a, whereas drainage beneath conventionally tilled cropland ranged from 0 (nonterraced) to 9 and 14 mm/a (bench terraced). Deep plowing slightly increased crop yield during wet years by reducing waterlogging. If deep plowing were applied to 10% of the Pullman soils, it could increase regional volumetric recharge by 0.1 km 3 /a, which is similar to the current regional

Rain infiltration is often controlled by a less permeable layer known as a seal. Infiltration through this layer was modeled numerically by continuously updating the seal properties as a function of rainfall characteristics. The seal remains unchanged until the surface has reached incipient ponding. Subsequently, a rapid change in the hydraulic properties of the seal is imposed to reflect the effect of raindrop impact. Finally, an equilibrium state develops between seal formation due to raindrop impact and seal erosion due to the rainstorm intensity effects. Model-predicted infiltration was similar to that observed during simulated rainstorms having various combinations of intensities and kinetic energy rates per millimeter of rain. A sensitivity analysis was performed to determine the effects of changes in seal and bulk soil properties, as well as simulation parameters, on infiltration. Seal formation was dependent on cumulative rainfall energy and the rainstorm intensity.

Bulk electrical conductivity (σ a ) can dominate the low frequency dielectric loss spectrum in soils, causing changes in the permittivity and errors in estimated water content. We examined the dependence of measured apparent permittivity ( K a ) on σ a in contrasting soils using time-domain reflectometry (TDR), a digital time-domain transmission (TDT) sensor, and a capacitance sensor (5TE) during near saturated solute displacement experiments. Sensors were installed in columns packed with fine sand or a clay loam soil. Displacement experiments were completed by first equilibrating columns with 0.25 dS m −1 CaCl 2 , introducing a step pulse of ∼4.7 dS m −1 CaCl 2 and, after equilibration, displacing the resident solution with 0.25 dS m −1 CaCl 2 . Using TDR, measured K a increased with increasing σ a ; however, the slope of this response averaged 3.47 m dS −1 for clay loam compared with 0.19 m dS −1 for sand. The large response in the clay loam was attributed to relaxation losses that narrowed the effective bandwidth from 821 to an estimated 164 MHz. In contrast, the effective frequency in sand averaged 515 MHz. Permittivity measured using the TDT probe exhibited little or no sensitivity to σ a ( −1 ) in both media. Measured K a using the 5TE probe declined with increasing σ a up to 1 to 1.8 dS m −1 and then increased thereafter with net negative responses for sand (Δ K a /Δσ a = −3.1 m dS −1 ) and net positive responses for the clay loam (Δ K a /Δσ a = 2.9 m dS −1 ). Consideration of the K a –σ a response is required for accurate soil water content estimation (±0.03 m 3 m −3 ) in the presence of solution EC variations using TDR in fine-textured soils or the 5TE sensor in all media. Large differences in the sampling volumes between 5TE-measured bulk EC and permittivity confounded the K a –σ a response in the presence of a concentration gradient.