Optimum Nitrogen Fertilizer Rate and Timing Management of Corn Following a Rye Cover Crop.

Despite rye (Secale cereale L.) cover crop (RCC) benefits (e.g., soil erosion, nitrate leaching, weed control), side effects including limited early-season nitrogen (N) availability and N immobilization causing corn (Zea mays L.) yield reductions has discouraged RCC adoption. To limit yield losses, current corn N fertilizer rate and timing recommendations may require adjustment when following a RCC. Trial objectives were to evaluate corn N uptake, yield, and agronomically optimum N rate (AONR) differences following a RCC and different N application timings. Treatments included no-RCC and RCC, six fertilizer N rates (0 - 303 kg N ha^-1), and two fertilizer N timings (34 kg N ha^-1 at-plant 5 cm to side and 5 cm below the seed starter (5x5) + remainder N applied prior to planting (Pre-plant) and 34 kg N ha^-1 5x5 starter + remainder N applied V6 sidedress (Split)) at one and three KY locations in 2018 and 2019, respectively. In 3 of 4 site-years corn yield response to N rate did not plateau up to the highest N rate applied (303 kg N ha^-1) for pre-plant N following a RCC, compared with 0 of 4 site-years for pre-plant N not following a RCC, suggesting a higher AONR is required when following a RCC and N is applied pre-plant. Whereas, corn AONR following a RCC was significantly decreased by an average of 16.4% in 2 of 4 site-years when N was split-applied. Results suggests split-applied N can improve corn yield and AONR regardless of cover crop presence. However, more frequent corn yield and AONR improvements were observed with split-applied N when following a RCC compared to no RCC.