Evaluating nitrogen credits to corn following manured and non-manured alfalfa

Melissa Wilson

Nitrogen (N) credits for corn production systems typically come from manure that was applied in the previous year or from alfalfa that was grown into the previous two years. However, there is limited research on what to do when the two practices are combined. Would a N credit be taken for both? Since alfalfa N fixation is limited when there is sufficient N in the soil (like when manure was recently applied), it is unclear if the N credit is affected. This research aims to evaluate N credits following manured and non-manured alfalfa. We will leverage existing alfalfa research plots at the Rosemount and Southern Research and Outreach Centers (ROCs) that grew alfalfa for three years before it was terminated. Corn will be grown for two years following alfalfa termination during the 2024/2025 and 2026/2027 growing seasons at the Rosemount and Southern ROCs, respectively. The first year will have no additional N added while in the second year, the large plots will be split into smaller plots so that several different N rates (0-160 lbs. N/acre) can be evaluated. Overall, the goal is to develop best management practices for fertilizing corn following manured alfalfa and develop guidance for farmers using these practices.