Phosphorus sorption kinetics in calcareous soils of selected arid and semi-arid toposequences and its relationship with plant growth

An array of kinetic equations has been used to describe time-dependent sorption of P by soils. We investigated P sorption kinetics in calcareous soils at upper-, mid-, and lowerslope positions of two arid and two semi-arid landscapes and its relationship with plant growth and P uptake by wheat. The P sorption kinetics was described by the rival kinetic models in the order: power function Elovich > parabolic diffusion > first order > second order equation, all indicative of diffusion kinetics with a slow chemical reaction. The rate parameters showed positive correlations with CBD-extractable Al and active calcium carbonate contents and negative correlations with organic carbon content. The P sorption rate at 0.25 h and 72 h after initiation of the experiment (SRin and SRf, respectively) and the P sorption rate parameters derived from the Elovich (1/β), power function (ab) and parabolic diffusion (R) equations were significantly correlated with the shoot dry matter and P uptake by wheat. The soil P sorption rate and the P sorption kinetics parameters generally increased from upper to lower slope positions. This phenomenon was more significant in semi-arid than in arid toposequences.