Excess nitrogen may decrease maize grain yields when water is limited

Water limitation and nitrogen (N) availability interact antagonistically to constrain maize productivity, yet this critical relationship remains poorly quantified in semi-arid cropping systems. Using maize (Zea mays L.) as a model crop, we conducted a three-year (2021–2023) field experiment in the US Great Plains with two irrigation regimes (100% and 70% of plant evapotranspiration targets) and six N availability levels (50–327 kg N ha⁻¹, including fertilizer, irrigation, and residual soil inorganic N). Under full irrigation, maize grain yield and aboveground biomass increased with N availability. In contrast, excess N was detrimental under water-limited conditions, reducing grain yield, aboveground biomass, and root biomass relative to moderate N rates. Maximum grain yield under water limitation required, on average, 31% less N than under full water. Water limitation decreased maximum yields by 36%, 59%, and 30% in 2021, 2022, and 2023, respectively. Notably, yield reductions at high N availability persisted in 2023 despite lower fertilizer inputs due to residual soil N carryover. Nitrogen uptake increased with N supply and was higher under full irrigation; however, under water stress, elevated N uptake became decoupled from yield and biomass production. These results demonstrate that matching N inputs to water-limited yield potential is essential to maximize grain yield and resource-use efficiency. Adjusting N inputs based on soil N availability and yield potential will become increasingly critical as water scarcity intensifies in semi-arid cropping systems.