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

Increasing groundwater nitrate (NO₃-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 NO₃-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 NO₃-N leaching by 31% and increased grain yield by 9.6% compared to preplant Urea in 2021. However, the split EEFs increased NO₃-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 NO₃-N leaching without compromising maize yield while offering greater economic returns in areas affected by groundwater contamination.