In calcareous soils the dynamics of phosphorus is controlled by calcite and iron oxides such as goethite which strongly retain P and consequently maintain low P concentrations in soil solution. Plants can drastically change chemical conditions in the rhizosphere, in particular by releasing HC or OH or by excreting organic anions. By modifying the dissolution/precipitation and desorption/adsorption equilibria, roots can influence the mobility of soil P. The aim of this work was to test whether HC or OH release can induce the mobilization of P in the rhizosphere of maize and rape supplied with NO3-N or NH4-N and grown on synthetic phosphated calcite or goethite as sole source of P. With P-calcite, the mobilization of P was generally related to the acidification of the rhizosphere. With P-goethite, rhizosphere acidification induced some increase of DTPA-extractable Fe and hence dissolution of goethite. Rhizosphere P was concomitantly depleted but the mechanisms involved are less clear. The difference in behavior of the two species is discussed.