Fertilizer and Irrigation Management Effects on Nitrous Oxide Emissions and Nitrate Leaching

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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.