Enhanced efficiency fertilizers, potato production, and nitrate leaching in the Wisconsin Central Sands

Maintaining yield goals while reducing nitrate-nitrogen (NO₃-N) leaching to groundwater is a challenge for potato (Solanum tuberosum) production in the Wisconsin Central Sands as well as across the United States. The objectives of this study were to quantify the effect of conventional and enhanced efficiency nitrogen (N) fertilizers on NO₃-N leaching, crop yield, and N uptake in potatoes. We compared five N treatments, which include a 0 N control and 280 kg ha^-1 as ammonium sulfate and ammonium nitrate (AS/AN), polymer-coated urea (PCU), urea with a urease inhibitor (Urea+UI), or urea with a UI and a nitrification inhibitor (Urea+UI+NI). The study occurred on grower fields during the 2009, 2010, and 2011 growing seasons, and NO₃-N leaching was measured with equilibrium tension lysimeters. PCU resulted in a reduction in NO₃-N leaching and an increase in yield compared to AS/AN in a year with large early-season rainfall; Urea+UI also reduced NO₃-N leaching in this year. In 2010, large plot-to-plot variation and 250 kg ha^-1 of additional N applied by the grower masked our ability to see differences among fertilized treatments. In 2011, a year with less intense rainfall events, no differences among treatments were observed. Collectively, these results show a potential benefit to PCU, but these benefits are only realized under specific seasonal weather conditions. Overall, the percentage of applied N lost to leaching during the growing season and removed in biomass was relatively low, suggesting substantial amounts of NO₃-N leaching outside of the growing season.