Modeling ammonia volatilization from urea applied to agricultural soils in the DayCent model

Authors: GURUNG, RAM - COLORADO STATE UNIVERSITY; OGLE, STEPHEN - COLORADO STATE UNIVERSITY; WILLIAMS, STEPHEN - COLORADO STATE UNIVERSITY; BREIDT, JAY - COLORADO STATE UNIVERSITY; ZHANG, YAO - COLORADO STATE UNIVERSITY; Del Grosso, Stephen - Steve; PARTON, WILLIAM - COLORADO STATE UNIVERSITY; PAUSTIAN, KEITH - COLORADO STATE UNIVERSITY

Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2021
Publication Date: 5/2/2021
Citation: Gurung, R., Ogle, S., Williams, S., Breidt, J., Zhang, Y., Del Grosso, S.J., Parton, W., Paustian, K. 2021. Modeling ammonia volatilization from urea applied to agricultural soils in the DayCent model. Nutrient Cycling in Agroecosystems. 119:259-273. https://doi.org/10.1007/s10705-021-10122-z.
DOI: https://doi.org/10.1007/s10705-021-10122-z

Interpretive Summary: Nitrogen (N) loss through ammonia (NH3) volatilization in agricultural soils is a significant source of atmospheric NH3, contributing to low N use efficiency in crops, risk to human health, environmental pollution, and is an indirect source of nitrous oxide emissions. Our objective was to develop an ammonia volatilization method within the DayCent ecosystem model that incorporates key fertilizer management practices that influence NH3 volatilization associated with application of urea-based nitrogen fertilizers. The NH3 volatilization method was developed with Bayesian calibration to identify optimum values of parameters in model equations. The final model included urea hydrolysis and the influence of urease inhibitors; short term soil pH changes following fertilization; fertilizer incorporation into the soil (mechanically and through irrigation/precipitation); and specification of the fertilizer placement method (i.e. broadcast vs. banding and surface vs incorporated). DayCent can now predict NH3 volatilization with reasonably good accuracy and represents an important model extension. The new model incorporates key management options influencing NH3 volatilization related to placement method and fertilizer type with and without urease inhibitors that can be used to evaluate management options for reducing losses of NH3 from urea fertilization.

Technical Abstract: Nitrogen (N) loss through ammonia (NH3) volatilization in agricultural soils is a significant source of atmospheric NH3, contributing to low N use efficiency in crops, risk to human health, environmental pollution, and is an indirect source of nitrous oxide (N2O) emissions. Our objective was to develop an ammonia volatilization method within the DayCent ecosystem model that incorporates key 4R management practices that influence NH3 volatilization associated with application of urea-based nitrogen fertilizers to agricultural soils. The NH3 volatilization method was developed with Bayesian calibration using sampling importance resampling (SIR) methods and Bayes factors to select the level of complexity in the model that best represents NH3 volatilization given the observed data. The final model included urea hydrolysis and the influence of urease inhibitors; short term soil pH changes following fertilization; fertilizer incorporation into the soil (mechanically and through irrigation/precipitation); and specification of the fertilizer placement method (i.e. broadcast vs. banding and surface vs incorporated). DayCent predicts NH3 volatilization with a root-mean-squared error (RMSE), bias, and Bayesian R2 value of 158 (95% interval ranging from 133 to 192), 7 (95% interval ranging from -106 to 102) g NH3-N ha-1 day-1 and 0.39 (95% interval ranging from 0.17 to 0.62), respectively. Furthermore, the model incorporates key management options influencing NH3 volatilization related to placement method and fertilizer type with and without urease inhibitors that can be used to evaluate management and policy options for reducing losses of NH3 from urea fertilization.