Phosphorus Sorption Isotherms and Buffering Capacity in Rice Soils of North Kashmir

Phosphorus sorption isotherms have been used to characterize the P status and establish the fertilizer requirement of soils. Phosphorus sorption characteristics of sixteen representative soils of Zaingir command of Kashmir were evaluated and phosphorus sorption data was fitted in Temkin, Langmuir and Freundlich equations to determine the relative importance of the soil parameters in phosphorus retention and release. The soils differed considerably with respect to the retention of added phosphorus. All the three isotherm equations fitted well with experimental data and were reliable to describe the quantity and intensity relationships of P in these soils. The sorption and maximum phosphorus buffering capacity (MPBC) varied widely among the soils. Adipora soil (S1) showed maximum sorption (353.5 μg g⁻¹) of phosphorus along with highest MPBC (26.3 mL g⁻¹) while as Zonipora soil (S12) showed lowest MPBC (14.4 mL g⁻¹) and lowest phosphorus sorption capacity (19.5 μg g⁻¹). Such differences in phosphorus sorption and MPBC were attributed to differences in their pH, organic carbon content, available phosphorus pool of these soils and the amount of phosphorus added. Important sorption parameters such as sorption maxima (b), bonding energy constant (k), slope of the Temkin equation (B), and constants of Freundlich equation (K, n), which control phosphorus availability to rice in these soils, were related to each other. Distribution coefficient (Kd) and the percentage of added phosphorus sorbed (Xad) decreased with increasing solution phosphorus concentration. The Kd decreased with increased phosphorus adsorption maxima.