Nitrogen and water availability affect soil nitrogen mineralization and maize nitrogen uptake dynamics
Tyler C. Donovan, Louise H. Comas, Joel P. Schneekloth, Meagan E. Schipanski
Abstract
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.