Nitrogen fertilizer equivalence of red clover when inter‐seeded into corn

Inter‐seeding red clover ( Trifolium pratense L.) provides an alternative method to incorporate cover crops into continuous corn ( Zea mays L.) in the Upper US Midwest. Red clover is a leguminous cover crop that can grow in low‐radiation environments and is winter hardy. Systems with red clover have demonstrated improved corn yield and a fertilizer N equivalence but understanding these effects with inter‐seeding warrants further investigation. The objectives of this study were to determine the effect of inter‐seeding red clover on (i) plant‐available N during and after red clover decomposition, (ii) optimum N rates for corn, and (iii) corn yields. The experimental design was a randomized, complete block‐split plot design, with cover crop as the main plot factor (treatments with and without inter‐seeded red clover) and N‐rate as a split‐plot factor (N‐rates between 0 and 315 kg‐N ha −1 in 45 kg‐N ha −1 intervals). Quadratic plateau response curves with a bootstrapping technique were used to determine differences in optimum N rate among treatments. Corn yields were evaluated with or without red clover inter‐seeded following the first inter‐seeding year. Red clover accumulated biomass values of 50 kg ha −1 up to 300 kg ha −1 pre‐termination when inter‐seeded with corn at the V4–V5 growth stage without detriment to yield. Corn yield was improved with clover treatments in one of four site years tested, resulting in a (15–17 kg ha −1 ) lower N requirement that year. Overall, our results indicate that inter‐seeding red clover into continuous corn did not provide an agronomically meaningful nitrogen fertilizer equivalence to the cropping system.