Corn yield response to late‐split nitrogen fertilizer

Multiple applications of N fertilizer on corn (Zea mays L.), with the last application as late as tasseling (VT) or early reproductive stages, is regarded as having potential to lower N requirements or to increase yields, or both. To test this, we conducted trials with N rates ranging from 0 to 280 kg N ha−1, applied at or near planting (early), or with 56 kg N ha−1 retained and dribbled near the row at VT stage (late split). Averaged across eight trials with corn following soybean [Glycine max (L.) Merr.], economically optimum nitrogen rate (EONR) values were 159 and 169 kg N ha−1 for early and late‐split N, and predicted yields at the economically optimum nitrogen rate (YEONR) were identical, at 14.8 Mg ha−1. The net return to nitrogen (RTN) at the EONR averaged $537 ha−1 for early N and $525 ha−1 for late‐split N. Averaged over six trials with corn following corn, EONR values were 171 and 170 kg N ha−1, YEONR values were 14.1 and 14.0 Mg ha−1, and RTN values were $745 and $731 ha−1 for early and late‐split N, respectively. Within each set of trials, t tests revealed no significant differences due to N timing on EONR, YEONR, or RTN. With little or no agronomic benefit and added costs for late application, applying late‐split N is unlikely to be profitable in productive Corn Belt soils.