Cover Crop Biomass Production and Water Use in the Central Great Plains Under Varying Water Availability.

The water-limited environment of the semi-arid 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. Relative ranking of the 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.