Corn optimum nitrogen fertilizer rate and application timing when following a rye cover crop

Farmers and researchers continue to question the impact of rye (Secale cereale L.) cover crops (RCC) on the optimal N fertilizer rate and grain yield of corn (Zea mays L.). In addition, minimal research has addressed the role of N fertilizer timing on reducing corn N stress and yield loss following a RCC. In this research, our objectives were to evaluate corn N fertilizer requirement following a RCC and different N fertilizer timings. Trials were established at three locations (2017–20) to evaluate corn response to N fertilizer rate (0 – 303 kg N ha⁻¹) following a RCC and no RCC with preplant and split-applied N fertilizer. A lower plant-available N supply, indicated by lower soil inorganic N and corn chlorophyll content, as well as a reduced plant stand were observed following a RCC. A RCC reduced corn grain yield by 20% at the 0 kg N ha⁻¹ due to apparent N deficiency, but did not reduce corn yield at the agronomic optimum N rate (AONR) or the economic optimum N rate (EONR). The AONR and EONR were statistically similar regardless of RCC presence and N application timing. However, corn chlorophyll content, agronomic efficiency, and yield was increased following a split N application. In addition, a quadratic-plateau regression analysis indicated greater yield increase per unit N applied for a split application than a preplant application. Our results suggest that farmers in similar production environments may benefit from a split N application to improve corn N use efficiency and yield regardless of the presence of a RCC. However, split application may be appealing following a RCC, where lower plant-available N supply requires more efficient fertilizer delivery to limit a higher N fertilizer rate.