Phosphate sorption on some arid, semi-arid and dry sub-humid soils of north-west India.

摘要

Phosphate sorption was studied on 28 surface (0-0.15 m) soil samples of alkaline-calcareous soils belonging to Camborthids, Torripsamments, Ustochrepts, Hapludolls of arid, semi-arid and dry sub-humid regions of north-west India. The samples of each soil were equilibrated for 24 hrs at 25+or-2 degrees C with aqueous solution of KH₂PO₄ containing (0 to 500 micro g P mL-1) in a 1:20 soil:solution ratio. The amount of P sorbed increased and distribution coefficient (Kd) and percentage of added phosphate adsorbed (Xad) decreased with increasing solution P concentration. Phosphate sorption was satisfactorily described by the two surface Langmuir equation (R2=0.95-0.99, P=0.01) and Freundlich equation (R2=0.94-0.99, P=0.01). The values of b₂ (adsorption maxima of lower energy sites) were 1.41 to 11.11 folds as compared to b₁ (adsorption maxima of higher energy sites); whereas the values of k₁ (bonding energy constants of higher energy sites) were 0.95 to 41.52 folds of k₂ (bonding energy constants of lower energy sites). The contribution of high and low energy sites to total adsorption maxima ranged from 8.25 to 41.47 and 58.53 to 91.75%, respectively. Inverse relationship was observed between adsorption maxima and bonding energy constants. The adsorption maxima for both the regions increased with organic carbon, clay, CaCO₃ and extractable Al and Fe. The organic carbon and CEC had significant negative correlations with bonding energy constant k₂ of Langmuir and n of Freundlich equations, respectively. However, when the effect of individual property (e.g. clay or CaCO₃) was compared for soils not varying in other soil properties, it was found to be highly marked.