RZWQM2 simulated N2O flux: Nitrogen inhibitor and variable rainfall impact on spring wheat

Authors: Chatterjee, Amitava; THAPA, RESHAM - Tennessee State University; Malone, Robert

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2026
Publication Date: 9/17/2026
Citation: Chatterjee, A., Thapa, R., Malone, R.W. 2026. RZWQM2 simulated N2O flux: Nitrogen inhibitor and variable rainfall impact on spring wheat. Agronomy Journal. https://doi.org/10.1002/agj2.70551.
DOI: https://doi.org/10.1002/agj2.70551

Interpretive Summary: The cost of U.S. crop production is significantly influenced by fertilizer prices. To protect U.S. growers in the global food market, nitrogen losses from fertilizer should be reduced to optimize economic returns. Applying chemical inhibitors alongside fertilizer can help prevent nitrogen loss, thereby maximizing crop nitrogen uptake and improving the return on fertilizer investment. Crop models such as the Root Zone Water Quality Model (RZWQM2) can predict the efficiency of inhibitor application under various crop, soil, and management scenarios. In this study, we tested the RZWQM2 model to predict spring wheat grain yield and nitrogen loss through denitrification in western Minnesota. The model showed that inhibitor application could reduce denitrification losses by half, closely matching field observations. We ran the model over a 25-year period to evaluate the effectiveness of inhibitor application under normal rainfall conditions, wetter springs (+10% precipitation), and drier (-10% precipitation) springs. Wetter springs decreased the probability of high denitrification loss, while drier springs increased denitrification loss-findings consistent with other related studies. This study demonstrates that U.S. growers can benefit from inhibitor application through reduced fertilizer nitrogen losses. A model like RZWQM2 can serve as a valuable tool for U.S. farm stakeholders to calculate the economic benefits of using inhibitors.

Technical Abstract: Additions of urease- and nitrification inhibitors to nitrogen (N) fertilizers reduce N losses and improve crops’ N use efficiency (NUE). However, the benefits of inhibitors depend on interactions among crops, soils, and weather variables. Root Zone Water Quality (RZWQM2) models can simulate such complex interactions to predict N dynamics but need evaluation for systems with additions of inhibitors. For this study, RZWQM 2 model was used to simulate the dual applications of nitrification- and urease inhibitors (Inhibitor) on the spring wheat grain yield and denitrification loss of N in the form of nitrous oxide (N2O) in western Minnesota during 2014-2015 growing seasons. The RZWQM 2 model was calibrated for only urea application at 146 kg N ha-1. RZWQM2 reliably reproduced spring wheat yield across years and treatments, with simulated values closely matching observation (R2 = 0.64, NSE = 0.49, RRMSE = 0.14, MAPE= 11.5). Model overestimated flux under urea only treatment during dry season (2014) but consistently captured the relative reduction in denitrification N loss from inhibitor additions. Long-term scenario simulations (2000-2024) indicated that inhibitors clearly reduced N losses and that wetter springs (+10%) decreased the probability of higher N2O emissions, while drier springs (-10%) increased the flux which is consistent with other related studies. This study highlights the potential of inhibitors to reduce N losses over a long term and utility of RZWQM2 model to evaluate the effectiveness of inhibitor addition and sustaining spring wheat production in the Northern Great Plains.