Modeling the effects of fertilization and pH on dissolved inorganic phosphorus in soils
Résumé
We used a set of mechanistic (macro-scale) adsorption models within the framework of the component additive approach in an attempt to determine the effect of repeated massive application of inorganic P fertilizer on the processes controlling the concentration of dissolved inorganic phosphorus (DIP) in soils. We studied a Luvisol with markedly different total concentrations of inorganic P as the result of different P fertilizer history (i.e. massive or no application for 40 years). Soil pH was made to vary from acid to alkaline. Satisfactory results were obtained using generic values for model parameters and soil-specific ones, which were either determined directly by measurements or estimated from the literature. We showed that adsorption largely controlled the variations of DIP concentration and that, because of kinetic constraints, minor precipitation of Ca-phosphates may have occurred under alkaline conditions, particularly in the Pfertilized treatment. The adsorption of Ca2+ onto soil minerals promoted adsorption of phosphates through electrostatic interactions. The intensity of this mechanism was high under neutral to alkaline conditions. The variation in DIP concentration with pH can be related to changes in the contribution of the various soil minerals to P adsorption.