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

Authors: Donovan, Tyler; Comas, Louise; SCHNEEKLOTH, JOEL - Colorado State University; SCHIPANSKI, MEAGAN - Colorado State University

Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2025
Publication Date: 4/22/2025
Citation: Donovan, T.C., Comas, L.H., Schneekloth, J., Schipanski, M.E. 2025. Nitrogen and water availability affect soil nitrogen mineralization and maize nitrogen uptake dynamics. Nutrient Cycling in Agroecosystems. 130:387-405. https://doi.org/10.1007/s10705-025-10406-8.
DOI: https://doi.org/10.1007/s10705-025-10406-8

Interpretive Summary: Nitrogen fertilization and water availability can independently affect soil and plant processes. Importantly, nitrogen and water affect nitrogen mineralization, the process through which soil microbes make nitrogen available to the crop system that provides a major source of nitrogen for crops like maize. To better understand these effects, we grew maize under two levels of water availability (full and limited) and 3 levels of nitrogen fertilization (low, optimal, and high). We found that nitrogen mineralization rates were highest early in the growing season before the main period of plant uptake. Later in the season when plants take up most of their nitrogen, high N fertilization under full water availability limited the amount of nitrogen available from mineralization, while low nitrogen fertilization under limited water availability also limited this nitrogen pool. Soil enzyme activities, which are associated with total nitrogen mineralization, increased with nitrogen fertilizer and were not affected by water availability. Further research is needed to better understand the opposing effects of nitrogen and water on the total nitrogen pool from mineralization and verify that the effect of soil enzymes on gross nitrogen mineralization. Lastly, although maize nitrogen uptake increased with fertilizer for both water availabilities, under limited water availability, the increased nitrogen accumulation in the plants did not lead to larger yield. This limitation was likely due to the impact of water stress during grain fill.

Technical 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.