An appraisal of phosphate supply characteristics of some soils in humid sub-tropic and semi-arid regions of India

Relationships between soil characteristics and phosphate supplying parameters were determined in well defined soil series of Assam and Haryana. Available P and phosphate supplying capacity were significantly and positively correlated with pH, electrical conductivity and exchangeable sodium percentage and negatively with different fractions of iron and aluminium. Phosphorus adsorption parameters viz adsorption maxima and energy involvement of phosphorus adsorption were determined as per the method of standard batch technique. Adsorbed P at 0.2 μg mL⁻¹ of equilibrium P solution, distribution coefficient, equilibrium phosphate potential, differential phosphate potential buffering capacity, Langmuir's adsorption maxima (b₁ and b₂) and Freundlich's K were correlated negatively with pH, EC, ESP and positively with different fractions of iron and aluminium. Adsorption maxima and bonding energies were not related with each other and total energy of P adsorption was always constant with negative correlation between k₁ and k₂ (r =-0.545**).