Phosphorus-Sorption Characteristics of Calcareous Soils in Arid and Semi Arid Regions

Understanding of phosphorus (P) sorption and desorption by soils is important for water quality. The objectives of this study are to: (1) estimate P-sorption parameters of calcareous soils; and (2) determine the factors affecting P sorption and the relation between equilibrium P concentration at zero-net P sorption (EPCo) and soil parameters. In this study selected samples of calcareous soils (CaCO3 % 34-60) were collected from the Al-Hashemiya area. Phosphorus sorption isotherms covering a wide concentration range of phosphate (0-500 mg/L phosphate) were determined at room temperature by batch experiments. The results indicate that as the P concentration in solution increased, the slope of the sorption isotherm changed abruptly. The abrupt change in slope of the sorption isotherms suggests that P precipitation at the carbonate surface began to dominate the process as concentrations increased beyond that of the point of inflection. Sorption isotherm results showed that these soils best fit Freundlich isotherm. Both Pearson correlation matrix and stepwise regression models indicated that Fe-oxide and soil cation exchange capacity (CEC) are the most significant effective (P<0.05) predictors on P availability and occurrence in calcareous soils, while carbonate content, soil pH, EC, and OM content were insignificant on P availability