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.

Recent recommendations advocating the use of cover crop mixtures instead of single-species in semi-arid environments require rigorous scienti c studies. One of those stated bene ts is greatly reduced water use by cover crops grown in mixtures. e objectives of this study were to characterize soil water extraction patterns and determine water use of cover crops grown in singlespecies plantings and in a 10-species mixture and to compare cover crop water use to evaporative water loss from no-till fallow.e study was conducted at Akron, CO, and Sidney, NE, during the 2012 and 2013 growing seasons on silt loam soils. At each location there were a dryland treatment and an irrigated treatment. Soil water contents were measured by neutron scattering and time-domain re ectometry at six depths (0.0-1.8 m, Akron) or four or ve depths (to 1.2 m or 1.5 m, Sidney). ere were no consistent signi cant di erences in soil water contents or growing season crop water use with the single-species plantings compared with the 10-species mixture. Cover crop water use (216 mm) averaged 1.78 times greater than evaporative water loss (122 mm) from the no-till fallow treatment with proso millet (Panicum miliaceum L.) residue. ere appears to be no evidence from data collected in this semi-arid environment, even when irrigated to simulate higher rainfall environments, to support the conclusion that cover crops grown in multi-species mixtures use water di erently than single species-plantings of cover crops.

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.

This research documented water use, grain yield, and water use efficiency of wheat following a 10‐species cover crop mixture and single‐species plantings (planted no‐till into proso millet residue) compared with winter wheat following a no‐till fallow period. The study was conducted under varying water availability conditions in western Nebraska and northeastern Colorado. Earn 0.5 CEUs in Soil & Water Management by reading this article and taking the quiz at http://www.certifiedcropadviser.org/certifications/self-study/775.