Effect of Farmyard Manure on Cadmium Sorption in Soils from Semiarid and Humid Regions

The effect of farmyard manure on sorption of cadmium in three soils (one from a semi-arid and two from a humid region), which widely differed in their pH, CEC, clay mineralogy and free iron oxide, was investigated. The FYM treated (i.e., FYM @ 0,25 and 50 g kg⁻¹ soil), homoionic (Ca-saturated) soil samples were equilibrated with different solutions having Ca:Cd range of 1 - 0 at 10 mmol L⁻¹ total chloride concentration. The pH of equilibrium soil solution (pH_eq) decreased with the increasing Cd in equilibrating solutions. The pH_eq of alkaline soil sample decreased and that of acidic soil samples increased with the addition of FYM. The standard free energy of Cd sorption (ΔG₀) increased from -3.86 to -2.97 kJ mol⁻¹ in the alkaline soil from Hisar and decreased from 5.22 to 1.71 kJ mol⁻¹ and 5.78 to 2.42 kJ mol⁻¹ in acidic soils from Kuptipara and Beltola on FYM treatment. The negative AGo in alkaline soil suggested thermodynamic preference for Cd over Ca and the positive AGo in Kuptipara and Beltola soils for Ca over Cd.