Effects of Cover Crops and Nitrogen Rate on Sorghum Yield, Dry Matter, Nitrogen Uptake and Use Efficiency Under No-till Cropping System.

Nitrogen (N) is the most yield limiting nutrient in sorghum cropping systems. Both legume and non-legume cover crops (CCs) can affect N fertilizer management by enhancing nutrient cycling and reducing N losses, resulting in lower or greater fertilizer N requirement for succeeding cash crops depending on N immobilization. This study aimed to evaluate the effects of different cover crops and N rates on sorghum grain yield, dry matter (DM) production, N uptake and N utilization efficiency (NUE). This experiment was conducted on a three-year wheat/cover crop-sorghum-soybean rotation containing six different cover crop and check treatments (chemical fallow, CF; double-crop soybeans, DSB; summer legume, SL; summer non-legume, SNL, winter legume, WL; winter non-legume, WNL) and three N rate (0, 90 and 180 kg ha^-1). Samples for sorghum biomass and plant tissue nutrient analysis were collected after sorghum physiological maturity. Sorghum plots were harvested with a plot combine for yield determination. Total N uptake, NUE, grain yield and DM were all significantly affected by previous cover crop and N rate. In summary, total N uptake, DM and grain yield were approximately 46, 25 and 24% higher in sorghum planted after SL than after SNL, respectively. Moreover, where no N fertilizer was applied, sorghum yield was 18% higher after SL than after CF. NUE values ranged from 48.5 (after SNL) to 38.8 kg grain kg^-1 N (after SL). Overall, after eight years of management in no-till and three full cycles of the rotation, total N uptake, DM and grain yield of sorghum were greatest in the SL treatment and were not different from the double-crop soybean treatment. These results suggest that legume CCs or double crop soybeans have the potential to replace chemical fallow and to contribute N to the following cash crop.