Journal of the Indian Society of Soil Science

A few Alfisols and related soils from arid, semi-arid and sub-humid climatic regions of India varying in texture, organic carbon, CaCO₃, DTPA-Fe and exchangeable Al contents were analysed for phosphorus using different extractants. Of the P extracted by various extractants, the water extractable P (r = 0.70*), Olsen's P (r = 0.66*), Kumar's extractant P (r = 0.70*) and P extracted by Soltanpur and Schwab's method (r = 0.70*) correlated with saloid bound P which was the important source of plant available P in soil. Phosphorus adsorbed at 0.2 mg VI equilibrium solution concentration of P in these soils ranged from very low (9 mg kg⁻¹ soil) in semi-arid soil to medium (144 mg kg⁻¹ soil) in sub-humid soil. A substantial part (42–60 per cent) of added P was desorbed during two successive desorptions with 0.5M NaHCO₃ (pH 8.5). The first desorption released considerably more P than the second. The adsorption data significantly fitted to modified Freundlich, Freundlich and Langmuir equations. Correlation studies indicated a close relationship between P adsorption and DTPA-extractable Fe (r = 0.88**), organiccarbon(r = 0.88**), clay(r = 0.72*)and CaCO₃ content(r = 0.76*) in the soils suggesting the important role played by these constituents in P sorption phenomena.