A MECHANISTIC MODEL FOR ESTIMATING AMMONIA VOLATILIZATION FROM SLURRYAPPLIED TO BARE SOIL

The loss of ammonia by volatilization after slurry application may lea d to large losses of soil-plant nitrogen. It is also a major source of atmospheric ammonia. These fluxes must therefore be accurately measur ed. However, volatilization depends on many features of the soil, clim ate and slurry, so that it is difficult to predict, or even to interpr et and compare data from different experiments. We have developed a me chanistic model that simulates the influence of the various factors on volatilization, accounting for the transfers and equilibria in the to psoil and between the soil and the atmosphere. The model uses readily available input data, including soil, meteorological and slurry data. It includes energy balance and advection submodels, which make it suit able for field scale applications using simple meteorological data. Se nsitivity analysis showed that soil pH has a large influence on volati lization. The model is also sensitive to soil adsorption capacity and some hydraulic characteristics (saturation water conductivity, water c ontent at field capacity). It has been calibrated under real field con ditions using experimental data for ammonia fluxes measured over two w eeks after slurry application, with a micrometeorological method givin g data at 15-min intervals. The soil, climate and slurry factors were also measured. The model provides a fair picture of the ammonia fluxes throughout the volatilization, including the total ammonia volatilize d, the decrease in daily loss and their short-term (< 1 h) variations due to the influence of meteorological conditions on soil surface temp erature and atmospheric diffusion. Lastly the model has been used to s imulate the influence of various meteorological conditions and agricul tural techniques on ammonia volatilization. This model will make it ea sier to interpret data from different experiments and will help to imp rove the emission submodel of atmospheric ammonia deposition models. ( C) 1997 Elsevier Science B.V.