Effect of Cover Crop Types on Cash Crop Yields in No-till.

Using cover crops as a fallow period replacement may have short and long-term benefits in cropping systems.  The objective of this study was to evaluate the effects of cover crops on yields of cash crops in a three-year, no-till rotation.  A no-tillage crop rotation of winter wheat (Tritcum aestivum)-grain sorghum (Sorghum bicolor L. Moench)-soybean (Glycine max) was established in 2007 with cover crops planted during the fallow period between wheat and grain sorghum.  All crops were included in each year.  Summer and fall-winter growing periods each contained one legume and one non-legume cover crop species.  Chemical fallow and double-crop soybean treatments were included as alternatives to cover crops.  Five nitrogen rates were applied to the sorghum crop after each fallow treatment.  Averaged over five years, soybean and wheat yields were unaffected by cover crop treatments, however wheat yield increased at a rate of 0.9 kg ha^-1 for each kg ha^-1 nitrogen applied to the sorghum crop.  Sorghum yields after the various fallow treatments were similar at the 135 kg ha^-1 and greater nitrogen application rates and were similar at all N rates after the winter legume cover crop compared to after the chemical fallow treatment.  The summer non-legume cover crop suppressed sorghum yields, but the winter non-legume, double-crop soybean, and summer legume increased sorghum yields with N applications of 90 kg ha^-1 and less.  In 2012, a year with above-average temperatures and below-average precipitation, grain crop yields were similar or improved with cover crops in the rotation compared to yields without cover crops in the rotation.  These results indicate that grain sorghum yield can be improved at low to intermediate nitrogen fertilization rates by including a summer legume (either double-crop or cover crop) or a winter brassica cover crop after the previous wheat harvest compared to chemical fallow.