Nitrogen and water availability affect soil nitrogen mineralization and maize nitrogen uptake dynamics

More frequent water limitations likely change plant N demands, but few studies have explored the effect of water and nitrogen (N) together on soil N dynamics. A field experiment was conducted to examine in-situ net N mineralization (Nmin), soil enzyme activity, maize N uptake and grain yield in the Great Plains Region in response to two levels of water availability (100% and 70% crop evapotranspiration, ET) and three levels of N fertilization (22–275 kg ha−1; low, optimal, and excess N). During the main growing-season, net Nmin was regulated by a N and water interaction where Nmin decreased with N fertilizer inputs under full water availability but increased with N fertilizer inputs under limited water. The interacting effects on Nmin may have been due to N availability suppressing further Nmin with full water, and increased microbial N turnover as soils underwent dry–wet cycles with limited water. Enzyme L-leucine amino peptidase (LAP) activity, which is associated with gross Nmin, increased with N fertilizer and maize N uptake under both water availabilities. Increased LAP activity suggested an increase in bioavailable N in response to heightened maize N demands, a positive feedback response. Plant- mediated mechanisms (i.e. N uptake and root exudation) likely explain the different responses of net Nmin and enzyme activity. With limited water, excess N constrained grain yield while yield increased with N inputs under full water. As water limitations become more frequent, ensuring that N is not in excess will help mitigate N losses while achieving high yields.