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

The effect of farmyard manure (FYM) on sorption of Co in three soil samples (one alkaline soil sample from a semi-arid region and two acidic soil samples from a humid region), which widely differed in their pH, CE~, clay mineralogy and free iron oxide, was investigated. The FYM treated, homoionic (Ca-saturated) soil samples were equilibrated with solutions having a wide range of Ca:Co at 10 mmol V total chloride concentration. The pH_eq decreased with the increasing proportion of Co in equilibrating solutions. The pHeq and the values of selectivity coefficient of Co sorption (K_Co) in alkaline soil sample decreased and those in acidic soil samples increased with the addition of FYM. On FYM treatment, the AG₀ increased from -3.52 to -1.86 kJ mol⁻¹ in alkaline soil and decreased from 2.60 to 0.60 kJ mol⁻¹ and 5.91 to 2.45 kJ mol⁻¹ in acidic soils.