Aims and Background Plants can exude large amount of carboxylates which ultimately increase phosphate ( P) availability. Both anions compete for adsorption onto soil minerals. Mechanistic modelling approach can be profitably used to understand these competitive interactions in soils. The aim of this study was to use such an approach to investigate citrate effect on P desorption in soils of contrasted mineralogy. Methods As Devau et al., 2011a, three adsorption models w ere used to simulate citrate and P competition onto the major sorbents of the studied soils; 1- pK Tr iple Plane, simple ion exchange and Nica- Donnan. Tested c itrate concentrations w ere representative of those found in the rhizosphere. We considered a large range of pH values. Results At high citrate concentration (100ìM), the larger increase of P availability was found at high pH in Luvisol and Chromic Cambisol and at low pH in Ferralsols. At low er citrate concentration (10ìM), the maximum increase w as predicted at acidic pH in Ferralsols. Surprisingly, a decrease of P availability was calculated in Luvisol and Chromic Cambisol. Conclusion The extent of P desorption is a function of citrate release, soil pH and mineralogy. Predicting the effect of citrate on P availability requires to account for the interactions with clay minerals, not only Fe oxides.