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.

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.

The water‐limited environment of the semiarid Central Great Plains may not produce enough cover crop biomass to generate benefits associated with cover crop use in more humid regions. There have been reports that cover crops grown in mixtures produce more biomass with greater water use efficiency than single‐species plantings. This study was conducted to determine differences in cover crop biomass production, water use efficiency, and residue cover between a mixture and single‐species plantings. The study was conducted at Akron, CO, and Sidney, NE, during the 2012 and 2013 growing seasons under both rainfed and irrigated conditions. Water use, biomass, and residue cover were measured and water use efficiency was calculated for four single‐species cover crops (flax [Linum usitatissimum L.], oat [Avena sativa L.], pea [Pisum sativum ssp. arvense L. Poir], rapeseed [Brassica napus L.]) and a 10‐species mixture. The mixture did not produce greater biomass nor exhibit greater water use efficiency than the single‐species plantings. The slope of the water‐limited yield relationship was not significantly greater for the mixture than for single‐species plantings. Water‐limited yield relationship slopes were in the order of rapeseed < flax < pea < mixture < oat, which was the expected order based on previously published biomass productivity values generated from values of glucose conversion into carbohydrates, protein, or lipids. Residue cover was not generally greater from the mixture than from single‐species plantings. The greater expense associated with a mixture is not justified unless a certain cover crop forage quality is required for grazing or haying.

Crop production systems in the water‐limited environment of the semiarid central Great Plains may not have potential to profitably use cover crops because of lowered subsequent wheat (Triticum asestivum L.) yields following the cover crop. Mixtures have reportedly shown less yield‐reducing effects on subsequent crops than single‐species plantings. This study was conducted to determine winter wheat yields following both mixtures and single‐species plantings of spring‐planted cover crops. The study was conducted at Akron, CO, and Sidney, NE, during the 2012–2013 and 2013–2014 wheat growing seasons under both rainfed and irrigated conditions. Precipitation storage efficiency before wheat planting, wheat water use, biomass, and yield were measured and water use efficiency and harvest index were calculated for wheat following four single‐species cover crops (flax [Linum usitatissimum L.], oat [Avena sativa L.], pea [Pisum sativum ssp. arvense L. Poir], rapeseed [Brassica napus L.]), a 10‐species mixture, and a fallow treatment with proso millet (Panicum miliaceum L.) residue. There was an average 10% reduction in wheat yield following a cover crop compared with following fallow, regardless of whether the cover crop was grown in a mixture or in a single‐species planting. Yield reductions were greater under drier conditions. The slope of the wheat water use–yield relationship was not significantly different for wheat following the mixture (11.80 kg ha−1 mm−1) than for wheat following single‐species plantings (12.32–13.57 kg ha−1 mm−1). The greater expense associated with a cover crop mixture compared with a single species is not justified.

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