Implementation of the effect of urease inhibitor on ammonia emissions following urea-based fertilizer application at a Zea mays field in central Illinois: A study with SURFATM-NH3 model

Agriculture is the main source of ammonia (NH3) emissions in the atmosphere. NH3 is precursor to secondary fine particulate matter, which is of concern for its impacts on health and visibility. There are a limited number of field measurements of NH3 emissions from fertilizer application in the US, and this limits our understanding of the importance of individual NH3 source and sink processes in controlling timing and magnitude of NH3 emissions. In this study, a new parameterization of the effect of urease inhibitor on NH3 emissions from urea-based fertilizer was developed on the basis of experimental results found in the literature. This parameterization was combined with an existing operational parameterization of soil and stomatal emission potentials (Γg, Γs) and was implemented in a surface-atmosphere transfer model for NH3 (SURFATM-NH3) in order to evaluate the bi-directional fluxes of NH3 at the field scale. The model was evaluated with field measurements obtained by the flux-gradient (FG) and relaxed eddy accumulation (REA) methods in a fertilized corn field in central Illinois. By integrating the effect of urease inhibitor, the timing of the highest NH3 emission peak was successfully predicted and its magnitude was close to that measured (predicted 2106 ng m−2 s−1, measured by FG 2312 ± 582 ng m−2 s−1). Based on the model results, urease inhibitor has a considerable effect on the dynamics and order of magnitude of NH3 fluxes. Furthermore, the model simulated the inhibiting action of N-(n-butyl) thiophosphoric (nBTPT) and suggests that it can reduce NH3 volatilization by 32%. The model also successfully predicted environmental parameters, such as soil temperature. Finally, this new version of SURFATM-NH3 is a valuable tool to estimate the NH3 bi-directional fluxes at the field scale, which describes dynamic modeling of Γs and Γg by taking into account the effect of urease inhibitor which is commonly used in the US to improve the efficiency of urea fertilizers.