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

Nitrogen (N) loss through ammonia (NH_3) volatilization in agricultural soils is a significant source of atmospheric NH_3 , contributing to low N use efficiency in crops, risk to human health, environmental pollution, and is an indirect source of nitrous oxide (N_2O) emissions. Our objective was to develop an ammonia volatilization method within the DayCent ecosystem model that incorporates key 4R N management practices (right type, right rate, right placement, and right timing) that influence NH_3 volatilization associated with application of urea-based nitrogen fertilizers to agricultural soils. The NH_3 volatilization method was developed with Bayesian calibration using sampling importance resampling methods and Bayes factors to select the level of complexity in the model that best represents NH_3 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 NH_3 volatilization with a root-mean-squared error of 158 (95