Modeling Ammonia Volatilization from Surface‐Applied Swine Effluent

Ammonia volatilization is an important issue in agricultural production and environmental protection. Experimental methods and numerical models exist to estimate the rate and amount of ammonia volatilization from commercial fertilizers and animal manures applied to a field. The existing models imposed assumptions on water movement in a soil profile that were judged to be inadequate for surface-applied swine (Sus Domesticus) effluent. In this research, a computer model was developed to estimate short-term ammonia volatilization from swine effluent applied to a field by flood or sprinkler irrigation. The model simulates simultaneous water flow, heat flow, and the transport and transformation of ammoniacal N in a soil profile using the finite difference method. Submodels were developed to evaluate concentrations of ammoniacal N in the infiltration pond of a flood irrigation event and in the droplets of sprinkler irrigation. The governing equations for the water flow, heat flow, and chemical transport modules and the irrigation submodules were derived from mass balance and energy balance employing constitutive laws established empirically. The model was tested against data from field experiments using parameters obtained from independent sources. The simulation results were in excellent agreement with experimental data in three out of six experiments. In the other three experiments, the predicted cumulative volatilization exceeded the measured amount by 5 to 30 kg ha -1 at the end of 1 wk. The differences were primarily in the first sampling period after the application. The simulated cumulative volatilization was most sensitive to temperature, pH of the soil system, and pH of the effluent applied.