Phosphate adsorption by dark alkaline vertisols in Greece

Phosphorus adsorption isotherms are presented for samples from agricultural areas in central Greece. The soils contain montmorillonitic clays, have high exchange capacities and range in pH from 6.8 to 8.1. The amounts of P adsorption are high for surface and subsurface samples and are comparable to the adsorption observed in acid kaolinitic soils. The fit of the Freundlich equation to the experimental data was significantly improved when NaHCO₃ extractable P was used as an estimate of the labile soil P to account for P already adsorbed in the soil. No conclusive relationship was established between the Freundlich parameters and selected soil properties though in some cases a values (capacity term) increased with increasing organic carbon content.