Site Characteristics Influence the Value of in-Season N Application for Sustainable Midwestern Corn Production.

Applying nitrogen (N) at economically optimal rates (EONR) and at times of rapid crop uptake are practices that are thought to minimize the amount of residual soil nitrate (RSN) in the profile after harvest that may be susceptible to loss. The objective of this study was to evaluate the time of N application (at-plant (AP) or split (AP+V9 sidedress)) on EONR, profitability, fertilizer N uptake, and RSN. Studies were conducted from 2014 to 2016 at 49 site-years in Illinois, Indiana, Iowa, Minnesota, Missouri, Nebraska, North Dakota, and Wisconsin on soils with contrasting characteristics. At the EONR, RSN was significantly greater with split N compared to at-plant N application. Nitrogen application timing did not impact N uptake in above ground biomass as R6. Thus, when corn is fertilized for EONR, time of application influences when N will be lost from the system, ie. early season or post-harvest. On more poorly drained and excessively drained soils, split applications may be prudent to minimize the high risk of early season N loss. On well and moderately well drained soils, there is no clear benefit to split applications over at plant applications under typical weather conditions.