Growing a crop in place of fallow may improve soil properties but result in reduced soil water and crop yields in semiarid regions. This study assessed the effect of replacing fallow in no‐till winter wheat (Triticum aestivum L.)–fallow with cover, forage, or grain crops on plant available water (PAW), wheat yield, grain quality, and profitability over 5 yr, from 2007 to 2012. Plant available water at wheat planting was reduced the most when the fallow period was the shortest (i.e., following grain crops) or when biomass production was the greatest. Winter and spring lentil (Lens culinaris Medik.) produced the least biomass, used the least soil water, and had the least negative effect on yield. For every 125 kg ha−1 of cover or forage biomass grown, PAW was reduced by 1 mm, and for every millimeter of PAW, wheat yield was increased by 5.5 kg ha−1. There was no difference in wheat yield whether the preceding crop was harvested for forage or left as standing cover. In years with above‐average precipitation, wheat yield was reduced 0 to 34% by growing a crop in place of fallow. However, in years with below‐average precipitation, wheat yield was reduced 40 to 70% without fallow. There was minimal negative impact on wheat yield growing a cover or forage crop in place of fallow if wheat yield potential was 3500 kg ha−1 or greater. Net returns were reduced 50 to 100% by growing a cover crop. However, net returns were increased 26 to 240% by growing a forage crop. Integrating annual forages into the fallow period in semiarid regions has the greatest potential for adoption.

Water is the driving variable in Great Plains agriculture and sustainability depends on efficient use of incident precipitation. Spring and winter wheat (Triticum aestivum L.)‐fallow (SWF and WWF) farming systems, as currently practiced, are not economically sustainable without government subsidies. This paper synthesizes information regarding the water use efficiency (WUE) of intensified cropping systems in cultivated dryland agroecosystems and proposes solutions to ensure sustainablity. Decreasing tillage and maintaining crop residue on the soil is requisite to improved efficiency. No‐till fallow efficiency, the percentage of the precipitation stored during fallow, reached 40% in the early 1970s. However, scientists in the 1980s and 1990s still report fallow efficiencies no greater than 40%, indicating that other major system changes must occur if progress is to continue. Residue levels in the Great Plains usually are < 3 tons/acre and this probably has capped fallow efficiency near 40%. No‐till management of crop residues after spring or winter wheat harvest increases soil water storage in the first portion of the fallow (July to May) compared with conventional fallow management, but the soil in the late fallow period (June to September for winter wheat and June to May for spring wheat) gains no more water, and may even lose water relative to the quantity present in the spring. Overall system efficiency is best evaluated by calculating grain WUE values. Modern no‐till wheat‐fallow (WF) systems, even with maximum fallow efficiencies, only had average grain WUE of 104 lb/acre per in. for spring wheat and 140 lb/acre per in. for winter wheat. WUE for 3‐yr cropping systems, like winter wheat‐corn (Zea mays L)‐fallow or winter wheat‐sorghum [Sorghum bicolor (L.) Moench]‐fallow, increased WUE in Central and Southern Great Plains. Three year system WUE averaged 180 lb/acre per in., a 28% increase compared with WF. In the Northern Plains, continuous spring wheat systems averaged 122 lb/acre per in., a 15% increase compared with SWF. Individual crops within systems had the following potential WUE values: corn = 245 lb/acre per in., grain sorghum =225 lb/acre per in., proso millet (Panicum miliuceum L). = 195 lb/acre per in., spring wheat = 216 lb/acre per in., and winter wheat = 150 lb/acre per in. Maximum system efficiency depends on choosing the most efficient plants for a given geographic area. Intensified cropping systems improve our ability to use precipitation efficiently. However, adoption of higher intensity cropping systems depends more on economic outcomes and government programs than on WUE or environmental effects. Research Question Water is the driving variable in Great Plains agriculture and sustainablity depends on efficient use of precipitation. If Great Plains agriculture is to be economically and environmentally sustainable, systems must be developed that maximize water storage efficiency and grain water use efficiency (WUE). The main objective of this paper was to synthesize existing information rega...

Replacement of fallow in crop–fallow systems with cover crops (CCs) may improve soil properties. We assessed whether replacing fallow in no‐till winter wheat (Triticum aestivum L.)–fallow with winter and spring CCs for 5 yr reduced wind and water erosion, increased soil organic carbon (SOC), and improved soil physical properties on a Ulysses silt loam (fine‐silty, mixed, superactive, mesic Aridic Haplustolls) in the semiarid central Great Plains. Winter triticale (×Triticosecale Wittm.), winter lentil (Lens culinaris Medik.), spring lentil, spring pea (Pisum sativum L. ssp.), and spring triticale CCs were compared with wheat–fallow and continuous wheat under no‐till management. We also studied the effect of triticale haying on soil properties. Results indicate that spring triticale and spring lentil increased soil aggregate size distribution, while spring lentil reduced the wind erodible fraction by 1.6 times, indicating that CCs reduced the soil's susceptibility to wind erosion. Cover crops also increased wet aggregate stability and reduced runoff loss of sediment, total P, and NO3–N. After 5 yr, winter and spring triticale increased SOC pool by 2.8 Mg ha–1 and spring lentil increased SOC pool by 2.4 Mg ha–1 in the 0‐ to 7.5‐cm depth compared with fallow. Triticale haying compared with no haying for 5 yr did not affect soil properties. Nine months after termination, CCs had, however, no effects on soil properties, suggesting that CC benefits are short lived in this climate. Overall, CCs, grown in each fallow phase in no‐till, can reduce soil erosion and improve soil aggregation in this semiarid climate.

Five long-term tillage studies in Kansas were evaluated for changes in soil properties including soil organic carbon (SOC), water holding capacity (WHC), bulk density, and aggregate stability. The average length of time these studies have been conducted was 23 yr. Soil properties were characterized in three depth increments to 30 cm, yet changes due to tillage, N fertility, or crop rotation were found primarily in the upper 0-to 5-cm depth. Decreased tillage intensity, increased N fertilization, and crop rotations that included cereal crops had greater SOC in the 0-to 5-cm soil depth. Only one of five sites had greater WHC, which occurred in the 0-to 5-cm depth. Aggregate stability was highly correlated with SOC at all sites. No-tillage (NT) had greater bulk density, but values remained below that considered root limiting. Soil organic C levels can be modified by management that can improve aggregate stability, but greater SOC did not result in greater WHC for the majority of soils evaluated in this study. MATERIALS AND METHODS Five long-term study sites were selected across the state of Kansas as described in Tables 1 and 2, and located in Fig. 1.

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Agricultural sustainability in the USA's west‐central Great Plains depends on efficient use of water—the primary yield‐limiting factor in the region. With perennially water‐short status, the efficient capture and storage of precipitation in soil, and the yield responsiveness of crops to water, are emphasized. Our objective was to quantify grain sorghum [Sorghum bicolor (L.) Moench] and winter wheat (Triticum aestivum L.) yield responses to stored soil water and precipitation by using data gleaned from research conducted from 1973 to 2004 near Tribune, KS on Ulysses silt loam (fine‐silty, mixed, superactive, mesic Aridic Haplustolls) and Richfield silt loam (fine, smectitic, mesic Aridic Argiustolls) soils. Soil water content was measured gravimetrically to the 183‐cm depth at crop emergence. Grain yield was related to available soil water at emergence (ASWe) (increased 221 kg ha−1 cm−1 in sorghum and 98 kg ha−1 cm−1 in wheat). Grain yield was also related to in‐season precipitation (ISP) (increased 164 kg ha−1 cm−1 in sorghum and 83 kg ha−1 cm−1 in wheat). From response‐surface analyses, 63% (sorghum) and 70% (wheat) of variations in grain yield were explained by variations in ASWe and ISP. In data sorted by tillage, yield response to water supply (WS) was greater with no‐till than with conventional tillage in both crops (184 vs. 129 kg ha−1 cm−1 in sorghum; 138 vs. 86 kg ha−1 cm−1 in wheat). This finding supports the concept that less tillage and more residue lead to more efficient use during the growing season of ASWe and ISP.

Use of fallow to store soil water is a common practice in semiarid regions. In the central Great Plains, the most common dryland cropping system is winter wheat (Triticum aestivum L.)‐fallow. Stubble mulching involving tillage is the predominant weed‐control practice during the 14‐mo fallow period. As a result of tillage, soil organic matter content has declined 40 to 70% since the early 1900s. This decline has called for development of cropping practices that control soil erosion and increase soil organic matter. Green fallow is the practice of growing a legume during the time period not devoted to crop production. Water is a major limiting factor for crop production in the central Plains, and water use by the legume could reduce grain yields. Field studies were conducted near Tribune, KS, from 1990 to 1994 to evaluate green fallow in the central Great Plains. The objectives were to (i) evaluate the production potential of several dryland forage legumes, (ii) quantify the water use of dryland legumes as a function of growth period, and (iii) measure the effects of legume growth on grain yield of subsequent crops. Of 11 legume species evaluated, hairy vetch (Vicia villosa Roth) and yellow sweetclover (Melilotus officinalis Lam.) were the most promising in terms of biomass production and weed control. Hairy vetch was planted in a green fallow system and allowed to grow for selected periods of time. In all cases, green fallow depleted soil water and reduced grain yield of subsequent crops. Allowing hairy vetch growth throughout the fallow period reduced soil water by up to 178 mm and reduced grain yield by 42 to 83%. For every millimeter of soil water depletion by vetch, grain yields decreased by 15 kg ha−1. Although green fallow is too detrimental to subsequent crop yields to be recommended in the central Great Plains, dryland legumes may have potential as forage crops.

Compaction can be a problem in some no‐till (NT) soils, but accumulation of soil organic C (SOC) with time may reduce the soil's susceptibility to compaction. Relationships between SOC and soil maximum bulk density (BDmax), equivalent to maximum soil compactibility, have not been well documented, particularly in NT systems. We assessed near‐surface BDmax using the Proctor test under long‐term (>19 yr) moldboard plow (MP), conventional tillage (CT), reduced tillage (RT), and NT conditions in the central Great Plains and determined its relationships with SOC, particle size distribution, and Atterberg consistency limits. The experiments were located on silt loam soils at Hays and Tribune, KS, and loam soils at Akron, CO, and Sidney, NE. The near‐surface BDmax of the MP soil was higher than that of the NT soil by 13% at Sidney, while the near‐surface BDmax of the CT was higher than that of the NT soil by about 6% at Akron, Hays, and Tribune. Critical water content (CWC) for BDmax in the NT soil was higher than in the CT and MP soils except at Tribune. The BDmax decreased with increase in CWC (r = ‐0.91). The soil liquid limit was higher for NT than for MP by 82% at Sidney, and it was higher than for CT by 14, 9, and 31% at Akron, Hays, and Tribune, respectively. The SOC concentration in NT soil was higher than in MP by 60% at Akron and 76% at Sidney, and it was higher than in CT soil by 82% at Hays. The BDmax decreased (r = −0.64) and the CWC increased (r = 0.60) with an increase in SOC concentration. Across all soils, SOC concentration was a sensitive predictor of BDmax and CWC. This regional study showed that NT management‐induced increase in SOC improves the soil's ability to resist compaction.