Fertilizer and irrigation management effects on nitrous oxide emissions and nitrate leaching

Irrigation and N fertilizer management are important factors affecting crop yield, N fertilizer recovery efficiency, and N losses as nitrous oxide (N₂O) and nitrate (NO₃^-). Split application of conventional urea (split-U) and/or one-time application of products designed to perform as enhanced-efficiency N fertilizers may mitigate N losses. The objective of this study was to compare the effects of controlled-release polymer-coated urea (PCU), stabilized urea with urease and nitrification inhibitors (IU) and split-U on direct soil-to-atmosphere N₂O emissions, NO₃^- leaching, and yield for fully irrigated and minimum-irrigated corn in loamy sand. Indirect N₂O emissions due to NO₃^- leaching were estimated using published emission factors (EF₅). Split-U increased yield and N uptake compared with preplant-applied PCU or IU and decreased NO₃^- leaching compared with PCU. Direct N₂O emissions were significantly less with IU or split-U than with PCU, and there was a trend for greater emissions with split-U than with IU (P = 0.08). Irrigation significantly increased NO₃^-leaching during the growing season but had no significant effect on direct N₂O emissions. After accounting for significantly increased yields with irrigation, however, N losses expressed on a yield basis did not differ and in some cases decreased with irrigation. Post-harvest soil N and soil-water NO₃^- in spring showed the potential for greater N leaching in minimum-irrigated than fully irrigated plots. Indirect emissions due to NO₃^- leaching were estimated to be 79 to 117% of direct emissions using the default value of EF₅, thus signifying the potential importance of indirect emissions in evaluating management effects on N₂O emissions.