Influence of Warm-Season Cover Crops On No-till Winter Wheat Production.

Due to the adverse economic and ecological consequences of the conventional-till, monoculture winter wheat production system that dominates the southern Great Plains, producers are interested in no-till farming practices and diversifying their cropping systems through crop rotation and cover crops.  In response to this interest, we evaluated winter wheat nitrogen requirement and final grain yield response to warm-season cover crops in a no-till, dual-purpose (grazing plus grain), continuous winter wheat production system. Experimental design was a split split-block with four replications (blocks). Whole plots were cover crop treatment (cowpea, soybean, guar, sorghum-sudangrass, pearl millet and fallow control) sown 18 June 2009 and chemically terminated 12 August 2009.  Sub plot treatment was winter wheat variety (Duster and Endurance) sown into the standing residue 29 September 2009.  Sub-sub plot treatment was topdress nitrogen application (a nontreated control receiving no nitrogen or nitrogen rate determined by sensor based nitrogen rate (SBNR) recommendation). Grass cover crops produced 6248 kg ha^-1 more biomass than legume cover crops.  In the SBNR plots, Endurance showed no significant yield difference between fallow, legume or grass cover crops, while Duster showed no significant yield difference between fallow and legume cover crops. In the nontreated control nitrogen plots, fallow increased grain yield as compared to legume and grass cover crops in both wheat varieties.  Overall, warm season cover crops had no effect to grain yield when nitrogen was applied according to SBNR recommendations but decreased grain yield when winter wheat received no additional nitrogen fertilizer.