A model of ammonia volatilization from applied urea. V. The effects of steady‐state drainage and evaporation

SUMMARY Rachhpal‐Singh & Nye's model of ammonia volatilization is expanded to account for the effects of steady‐state water movement by drainage or evaporation when the soil does not dry out to any great extent. The model shows how upward movement of water during evaporation increases volatilization by carrying urea‐derived NH 4 + and HCO 3 − ions upward, thereby increasing the concentration of ammonia gas at the surface. Conversely, water drainage reduces volatilization by carrying the dissolved solutes into the soil. The model is used to assess the effects on volatilization of evaporating conditions and of irrigation or rainfall.