Land-Use Conversion Effects on Phosphate Sorption Characteristics in Soils of Forest and Rangeland Sites from Zagros Area, Western Iran

Abstract

This study was performed to assess the effects of clearing and cultivation on phosphate sorption kinetics and equilibria as well as phosphate buffering behavior of soils in forest and rangelands from Zagros area, western Iran. Total phosphorus and its organic and inorganic fractions were also determined for the soils according to reference methods. The results showed that clearing and cultivation practices caused a significant increase in soil total and total inorganic phosphorus in the forest soils, but a decrease was observed in the rangeland study area. The concentration of soil organic phosphorus, however, decreased in both forest and rangeland soils after long-term cultivation. Phosphate sorption behavior of the soils was also affected by the land-use changes. The time-dependent sorption data for soils of both protected and disturbed sites were adequately fitted by Power function, Elovich and Parabolic diffusion equations. Kinetic parameters related to rate of phosphate sorption including “specific sorption rate at unit time” and “apparent diffusion coefficient” derived from the models were markedly increased after the land-use conversion. The equilibrium-based phosphate sorption on the soils was significantly described by Langmuir and Freundlich isotherms. Sorption capacity and buffering indices of phosphate, calculated from the isothermal equations, also increased in the cultivated soils as compared to the corresponding soils of the protected sites. The results demonstrated that land-use conversion from natural forest and rangeland to agriculture could significantly influence the distribution and sorption of phosphate in the studied soils which should be considered in sustainable land management in the Zagros area.