Fertilizer Management Effects on Nitrate Leaching and Indirect Nitrous Oxide Emissions in Irrigated Potato Production

Potato ( Solanum tuberosum L.) is a N‐intensive crop, with high potential for nitrate (NO 3 − ) leaching, which can contribute to both water contamination and indirect nitrous oxide (N 2 O) emissions. Two approaches that have been considered for reducing N losses include conventional split application (CSA) of soluble fertilizers and single application of polymer‐coated urea (PCU). The objectives of this study were to: (i) compare NO 3 − leaching using CSA and two PCUs (PCU–1 and PCU–2), which differed in their polymer formulations, and (ii) use measured NO 3 − leaching rates and published emissions factors to estimate indirect N 2 O emissions. Averaged over three growing seasons (2007–2009), NO 3 − leaching rates were not significantly different among the three fertilizer treatments. Using previously reported direct N 2 O emissions data from the same experiment, total direct plus indirect growing season N 2 O emissions with PCU–1 were estimated to be 30 to 40% less than with CSA. However, PCU–1 also resulted in greater residual soil N after harvest in 2007 and greater soil–water NO 3 − in the spring following the 2008 growing season. These results provide evidence that single PCU applications for irrigated potato production do not increase growing season NO 3 − leaching compared with multiple split applications of soluble fertilizers, but have the potential to increase N losses after the growing season and into the following year. Estimates of indirect N 2 O emissions ranged from 0.8 to 64% of direct emissions, depending on what value was assumed for the emission factor describing off‐site conversion of NO 3 − to N 2 O. Thus, our results also demonstrate how more robust models are needed to account for off‐site conversion of NO 3 − to N 2 O, since current emission factor models have an enormous degree of uncertainty.