Coupling effects of enhanced efficiency fertilizers and nitrogen timing on groundwater quality and maize yield in northeast Nebraska

Increasing groundwater nitrate (NO 3 ‐N) contamination in Nebraska's Bazile Groundwater Management Area poses significant economic, environmental, and public health risks. This 2‐year (2021–2022) on‐farm study evaluated the effects of nitrogen (N) application timing (preplant vs. split) and source (with and without enhanced efficiency fertilizers [EEFs], including urease inhibitor [UI] and dual inhibitor [DI] combining urease and nitrification inhibitor) on NO 3 ‐N leaching, maize yield, and return to N with environmental cost (RTN Env ) in irrigated sandy soils. Six N treatments at 202 kg N ha −1 were compared to a zero‐N control: preplant urea, conventional split urea‐UAN (urea ammonium nitrate), preplant UI, split UI‐UAN, preplant DI, and split DI‐UAN. Porous suction cup lysimeters were installed at a depth of 120 cm to collect pore‐water samples within the growing seasons. Compared to conventional split urea‐UAN, preplant EEFs (preplant UI and preplant DI) reduced nitrate leaching by 75% and increased RTN Env by $537 ha −1 without significantly affecting maize yield. Split EEFs (split UI‐UAN and split DI‐UAN) reduced NO 3 ‐N leaching by 31% and increased grain yield by 9.6% compared to preplant Urea in 2021. However, the split EEFs increased NO 3 ‐N leaching by 139% compared to the preplant EEF treatments, with no corresponding yield improvement. These findings suggest that preplant application of EEFs can substantially reduce NO 3 ‐N leaching without compromising maize yield while offering greater economic returns in areas affected by groundwater contamination.