Phosphate Sorption by Some Calcareous Soils From the Mediterranean Region

Abstract

The relationship between phosphate sorption and the soil properties of nine soils (pH: 6.8-7.8; 1-48 % carbonates) from the Mediterranean regions of TŸrkiye were investigated before and after treatments with selective dissolution reagents. Phosphate sorption, as evaluated with the single-point method of Bache and Williams (1), was correlated with CaCO3 dissolved in ammonium oxalate ("active lime") content but not which total carbonates. Fine carbonate particles were found to be important as P sorbing soil components. The increase in phosphate sorption after carbonate removal was interpreted as a result of the cementing action of fine carbonate in soil components. Selective and successive treatments for the removal of carbonates and "free" oxides were found to make the P sorption interpretation difficult by producing a disintegration and dispersion effect. The phosphate sorbing capacity of samples decreased more than four times on treatment with acid oxalate in darkness and light indicating that oxalate-soluble iron and aluminium (1.7%) are potentially important soil constituents in P sorption. Smectitic clay minerals played only a minor role.