Why the Different Responses between Single and Split Nitrogen Applications?.

Split- opposed to single-nitrogen (N) applications may improve corn (Zea mays L.) production, N use efficiency, and lessen environmental impacts due to fertilization. However, these hypotheses have not been fully tested.

Single and split N applications were applied in eight US Midwestern states over a 3-year period (49 sites-years total) varying in soil characteristics and weather. A single (0 to 315 kg-N ha^-1 in 45 kg increments) and two split N applications [45 kg-N near planting + V9-sidedress (45SD), and 90 kg-N near planting + V9-sidedress (90SD) at a total of 180 and 270 kg-N ha^-1] were evaluated. The series of single N applications were used to evaluate their effect on soil N at the VT development stage. Only the 180 and 270 rates were used to compare the effect of single and split N applications on soil nitrate-N content at tasseling (VTSN), N uptake of corn at physiological maturity (PMN), and grain yield.

Before sidedress application, soil nitrate (0-60 cm depth) at the V5 development stage increased linearly as N rate applied near planting increased in 48 of the 49 sites. After sidedress application, 17 of the 49 sites had no differences between the single and two split N applications for soil N, N uptake, and grain yield. Greater VTSN by 45SD or 90SD relative to single only led to greater PMN in two- of the five-sites and greater grain yield in four- of the nine-sites where 45SD or 90SD was greater than single. This demonstrates that greater soil N at tasseling did not always lead to greater N uptake and grain yield. In only 5% of the response variable comparisons between 45SD and 90SD, were differences found, indicating that applying more N near planting for split applications did little to alter their effect on soil N, N uptake and yield. This presentation will demonstrate under what soil and weather conditions differences between single and split N applications were found and when each can improve soil N, N uptake, and yield.