Cover Crop, N-Rate Impacts on Corn Yield and Soil N.

Nitrogen fertilizer is a significant input expense for producers, as conversion of stable dinitrogen into plant available reactive forms such as NH₄ or NO₃ is energy intensive and costly.  These reactive forms of nitrogen (Nr), critical for crop production, can escape from agricultural systems into surface and ground waters, or into the atmosphere (e.g., N₂O) where they become environmental liabilities.  Strategies are needed to reduce and mitigate Nr loss from agricultural systems.  One strategy is to integrate cover crops into agricultural management systems, since cover crops can scavenge Nr while providing surface cover protection for reducing erosion. We hypothesized that use of cover crops couple with direct seeding would capture fall-available N, reduce the need for expensive N-inputs, provide surface cover; thus, simultaneously provide economic incentive, reduce erosion risk, attenuate Nr loss and its down-stream consequences.  A replicated and repeated study was conducted to determine if inclusion of annual ryegrass or forage radish as cover crops could reduce the amount on nitrogen needed by the subsequent corn crop will be discussed.  Cover crop biomass (shoot and root) and plant N concentration, and soil N (total N, NO3-N, and NH4) to 90 cm was measured in the fall.  Soil NO3-N, and NH4 was measured again the spring.  Corn growth and yield were monitored. Both years, corn yield responded to fertilizer application but inclusion of the cover crop did not did not offset the amount of nitrogen needed to sustain crop yield either year. In fact annual ryegrass cause 15 to 50% yield reduction without N-fertilizer compared to the Control.  Only at a full N-rate were the yields between the control and annual ryegrass similar.  Corn following forage radish had either reduced yield or comparable yield to the cover crop control. The question “what happened to the sequester N remains unanswered by this study?”