Geochemical processes, particularly adsorption/ desorption, which control inorganic phosphorus (P) soil availability were affected by plant rhizospheric functions. In this study, we intended to characterize the influence of pH variations which occurred in rhizosphere on process controlling P availability. We used an approach combining chemical extractions and geochemical modelling to study the speciation of P in Mediterranean chromic cambisol soils. First, one dataset where soil pH was adjusted manually ranging from acidic to alkaline conditions (pH ≈ 3 to 10) were used. In second, three sub-samples were chosen and soil pH was modified by wheat growth with NO 3 - applications. All the samples were analysed with CaCl2 extractions which is equivalent of aqueous P. We used the CD-MUSIC model in attempt to simulate P sorption based on CaCl2 extracts. For the first dataset, the fit between simulated and measured P-CaCl2 was quite good (R² = 0.80 and RMSE = 0.034 mg kg -1 ). This suggest that P available was controlled by sorption process in the soils studied [1]. The adsorption capacity of minerals and P surface complexes, both explained P-CaCl2 variations as a function of pH. Modelling of the second dataset showed us that the increase of P-CaCl2 in soils with plants was not fully explained by pH, we also need to consider citrate exudation. This model must be validated on other P-deficient soils.