Phosphorus Forms and Sorption Characteristics in Soils of a Transect of Kohora Watershed of Assam, India

Phosphate sorption relating to soil properties in soils of Kohora watershed of Assam, India was studied. The soils were acidic in reaction with varying texture. Clay and CEC increased concomitantly down the slope. In all soils, Fe-P dominated over other P fractions contributing 29.9%. Phosphate adsorption data fitted better to Freundlich equation. Medium land soils had greatest affinity for P yielding highest sorption maxima (b = 2044.03 µg P g-1) and Freundlich K. Langmuir ‘b’ was significantly correlated with Fed, Ald, Fe2O3+Al2O3, Al-P and total-P while negatively with pH, OC and available P fractions. Bonding energy was greatly affected by Fed (r = 0.683*) only while maximum phosphate buffering capacity (MPBC) was typically affected by Al and Fe oxides. Phosphorous supply parameters of the soils increased unevenly with equilibrium P concentration. Negative ΔG values indicated spontaneous adsorption processes. Results suggest that these soils require higher external P for maintaining optimal solution concentration.