This study examined the effect of rate and time of fertilizer N application to corn on N2O emissions in 2 yr on commercial corn fields. All treatments received starter fertilizer at 45 and 59 kg N ha(-1) in 2004 and 2005, respectively, similar to grower practice. Treatments included a control, with no additional fertilizer N application, 75 or 150 kg N ha(-1) banded at sidedress or 150 kg N ha(-1) broadcast at emergence. There was no significant effect of N fertility treatment on corn grain or silage yield, indicating that all N applications were at or in excess of crop N requirement. Delay of fertilizer application to sidedress and reduced fertilizer N application were effective in reducing nitrate intensity, an index of soil nitrate availability calculated as the summation of daily soil NO3--N concentration for the 0- to 15-cm depth. However, there was no significant effect of N fertility treatment on cumulative N2O emissions, and nitrate intensity explained a small proportion of the variation in cumulative N2O emissions. This study provides evidence that improved fertilizer N management may not result in reduced N2O emissions under some conditions.
