Managing Global Resources for a Secure Future

Both double crops and cover crops provide opportunities to intensify crop rotations, but the potential exists for negative impacts on cash crop yields in environments where water supply often is a limiting factor. The objective of this study was to quantify the effect of double-crop soybeans and cover crops on grain yields in a wheat-sorghum-soybean rotation. The 3-year rotation was completed six times from 2008 through 2016 because all crops were present every year. The rotation was intensified by growing double-crop soybeans or summer legume, summer non-legume, winter legume, or winter non-legume cover crops between wheat harvest and sorghum planting. Sorghum yield responded to nitrogen (N) fertilizer rate, cover crop treatments, and/or their interaction in every year, but the response varied with year. Only in 2008 was there no positive sorghum yield response to fertilizer N, likely due to residual soil N. Soybean yield varied in response to treatment factors or their interaction in every year, but the magnitude of the responses were small or variable. Wheat yield varied with cover crop treatment only 2012, an extreme drought year. In other years, wheat yields either had no response to treatment factors or increased slightly with increasing N applied in the sorghum two years previously. Total grain yields for the 3-year rotation revealed a consistent advantage for the treatment including double-crop soybeans, although differences were greater when less N fertilizer was applied to the sorghum. Total 3-year rotation yields for treatments including cover crops differed from the chemical fallow check treatment only in the 2008-11 cycle when the sorghum-sudangrass cover crop reduced yields at the two lowest N rates, and in the 2009-12 cycle when inclusion of summer legume, winter legume, or winter non-legume cover crops resulted in greater yields than for the chemical fallow or the sorghum-sudangrass cover crop treatment.