Predicting the effect of soil-water-air dynamics on ammonia volatilization from applied urea with a mechanistic model

Abstract

To assess the influence of varying soil water and soil air contents on ammonia volatilization from surface applied urea, a mechanistic model is used to simulate the system. The results are discussed in terms of the effects of soil-water-air dynamics on the movement of urea, ammoniacal-nitrogen and soil base, and on the rate of urea hydrolysis, and their influence on ammonia volatilization. Changing the soil moisture between 90% and 125% of field capacity did not have a marked influence on ammonia volatilization. The predicted losses were at their minimum with a moisture content slightly above field capacity, and increased sharply as the soil moisture fell below 90% of the field capacity. Ammonia volatilization losses measured by experiment at differentθf values agreed very well with those predicted by the model. The relative contribution of the liquid pathway over the gaseous pathway of movement of NH3 through soil increased with increase inθf, and, at a givenθf, decreased with increase in the pH.