Fertilizer source and mulch effects on nitrate‐N leaching and corn yield in irrigated sandy loam soil

Abstract

Improving nitrogen (N) use efficiency while minimizing nitrate leaching remains a major challenge in irrigated sandy soils of the US Midwest. This 2‐year field study (2022–2023) in northeast Nebraska evaluated the effects of N source (inorganic fertilizer vs. beef manure) and surface mulch application on soil N dynamics, nitrate leaching, and corn ( Zea mays L.) yield. Both growing seasons experienced below‐average precipitation, increasing reliance on irrigation and influencing N behavior in the soil profile. Early‐season pore water nitrate concentrations peaked in inorganic fertilizer treatments, especially without mulch, reflecting poor synchronization between N availability and crop uptake. In contrast, manure maintained lower and more stable nitrate concentrations, reducing leaching risk by up to 84%. Mulch further moderated nitrate levels, lowering concentrations by 14% in 2022 and 29% in 2023, although its effect was less pronounced when paired with manure. Seasonal nitrate leaching loads averaged 8.5 kg N ha ^{− 1} in inorganic treatments in 2022, compared to only 1.8 kg N ha ^{− 1} under manure. Agronomic responses indicated a tradeoff: inorganic fertilizers without mulch enhanced early growth, N uptake, and grain yield but at the cost of higher leaching potential. Conversely, manure and mulch improved soil N retention and reduced losses but slightly decreased yield and nitrogen use efficiency. Residual soil analyses confirmed that manure and mulch sustained more stable ammonium pools and minimized nitrate accumulation. These results highlight the importance of integrating manure and mulch into conventional inorganic nitrogen fertilizer management to balance agronomic performance and environmental protection in irrigated sandy soils vulnerable to nitrate leaching.