Residual Effects of Cover Crop Species, Tillage, and Manure Application on Corn Yield and Soil Nitrogen Dynamics in Organic Management Systems

Nitrogen (N) management remains a primary challenge in organic grain systems, particularly in rotations where heavy N-consuming crops, such as corn and wheat, follow one another. Daikon radish (Raphanus sativus L.) is widely adopted for its ability to scavenge residual soil nitrate between cash crops; yet the subsequent availability of scavenged N to the following crop is inconsistent and often negligible. This 4-year field study (2014–2017) at the University of Minnesota Southwest Research and Outreach Center evaluated whether planting daikon radish in polyculture with berseem clover, and either annual oats or winter rye could improve N retention and timed release compared to daikon radish monoculture. Three cover crop treatments were tested across three common organic management systems: no manure with no tillage, manure with tillage, and manure plus shallow tillage incorporation before cover crop seeding. Polycultures, especially those including winter rye, produced significantly more fall biomass (up to 6435 kg ha−1) than daikon radish monoculture (573–1272 kg ha−1). Manure incorporation consistently increased total and daikon radish biomass, as well as the percent living cover. Despite substantial biomass differences, mid-season and fall soil inorganic N, potentially mineralizable N, permanganate-oxidizable C, and enzyme activities showed few consistent treatment effects. Corn grain yield was highest following manure with tillage incorporation but was significantly reduced after the winter rye polyculture in all years, likely due to N immobilization and delayed corn planting caused by late rye termination under wet spring conditions. Results indicate that while polycultures with winter rye maximize biomass and soil cover, they do not reliably enhance N recycling to the subsequent organic corn crop and can reduce yield.