New insights into sorption and desorption of organic phosphorus on goethite, gibbsite, kaolinite and montmorillonite

With the increasing use of organic resource for P fertilization, the adsorption and desorption dynamics of various organic phosphorus (OP) forms remain an important gap of knowledge to bridge in order to improve P availability. In this study, we examined the adsorption and desorption dynamics of various OP (myo-inositol hexakisphosphate, myo-IHP; glycerophosphate, GLY; and glucose-6-phosphate, G6P) compounds to and from several soil minerals including Fe and Al oxides (goethite and gibbsite, respectively) and clays minerals (kaolinite and montmorillonite). Overall, myo-IHP was the most adsorbed form followed by G6P and then GLY which reflected that OP adsorption increased according to the number of phosphate groups and/or the size of the organic molecule. Fe and Al oxides showed higher OP adsorption capacity than clays, as adsorption followed the trend kaolinite < montmorillonite < goethite ≪≪ gibbsite. Desorption experiments revealed that the adsorption was not fully reversible as only 30% could easily desorbed. On Fe and Al oxides, G6P and GLY were more desorbed than myo-IHP while the opposite trend was found on clay minerals. In addition, OP desorption from soil minerals followed the trend gibbsite < goethite < kaolinite < < montmorillonite. The clay-OP complex released P rapidly but over a short period of time, whereas the Fe- and Al-OP complex released P slowly but over a longer period of time. The comparison between the P adsorption and desorption properties of montmorillonite and other soil minerals are only valid for the K-saturated montmorillonite used here. The results could be different if the montmorillonite were saturated with Al or Ca. By deciphering the interactions between soil minerals and the predominant forms of OP in soils and organic fertilizers, our results provide new insights for the sustainable management of P in agroecosystems.