Phosphorus Movement and Retention by Two Calcareous Soils

Abstract

To predict P sorption and leaching behavior in calcareous soils, we examined the adsorption and movement of applied P in columns of two calcareous soils. Phosphorus and various other ions were monitored in the leachate of the soil column by passing a 100 mg P l⁻¹ solution through the soil column. Concentrations of P, K⁺, Ca²⁺, Mg²⁺, Na⁺, HCO⁻ ₃, Cl⁻, EC and pH were determined in the leachates. Movement of K⁺ and P ions was retarded due to K⁺ ion-exchange and P adsorption and precipitation, respectively. Phosphorus leaching was affected by supersaturation with respect to P-Ca minerals, but undersaturated with respect to Mg-P minerals. Phosphorus retention based on batch and miscible displacement experiments revealed profound discrepancies that can be attributed to the short residence time of P in the miscible displacement. Breakthrough curves of P and K⁺ were analyzed by a CXTFIT program. The equilibrium model provides good results to the transport process of P and K⁺. Results indicated that the mobility of P in these calcareous soils reflects that a high downward movement of water-soluble P in soils may occur and much attention should be paid to leaching of P and potential contamination of P to surface and ground waters.

Keywords:

• Phosphorus
• leaching
• solubility
• calcareous soils
• retention

Acknowledgements

The authors are especially grateful to Professor Sjoerd van der Zee for critical review, perceptive comments and editing on the manuscript on primary draft of the paper.