Accounting for surface cattle slurry in ammonia volatilization models: the case of Volt'Air

Abstract : Process based models have been developed to simulate ammonia (NH3) volatilization after surface slurry spreading, but none of them have managed to realistically represent slurry infiltration into the soil and the development of a specific slurry interface that modifies surface temperature and humidity conditions. To account for these physical effects, it is proposed to add to the model a layer of slurry on the surface of the soil. It is hypothesized that the slurry layer can be regarded as a soil layer from the hydrological point of view, characterized by its specific hydraulic parameters, and whose thickness depends on the quantity and bulk density of the slurry dry matter. An assessment was performed by comparisons with measurements of NH3 volatilization fluxes from two specific datasets. The addition of the slurry layer clearly improved the simulations of both the NH3 volatilization flux and ammoniacal nitrogen (NHX-N) distribution in the soil. This concept together with its parameterization proved to be relevant for accounting for effect of the slurry application rates on volatilization, and subsequent abatement obtained with band spreading. The efficiency factor was improved from -0.35 to 0.71. This concept also succeeded in describing the slurry layer state over the whole range from slurry ponding at the surface to the dried-out state, via a slurry in an intermediate drying state. This was actually a prerequisite for the good simulation of NH3 volatilization over the whole volatilization event. This approach is promising for extension to various organic materials present at the soil surface.