Effect of Farmyard Manqre on Copper Sorption in Soils from Semiarid and Humid Regions

The effect of farmyard manure on sorption of Cu in three soil samples (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, homoionic (Ca-saturated) soil samples were equilibrated with solutions having a wide range of Ca: Cu at 10 mmol L⁻¹ total chloride concentration. The pH_eq decreased with the increasing proportion of Cu in equilibrating solutions. The pH_eq of alkaline soil sample decreased and those of acidic soil samples increased with the addition of FYM. At comparable FYM, ΔG₀ was maximum for highly acidic soil, followed by moderately acidic and then alkaline soil sample. The ΔG₀ increased in alkaline soil and decreased in acidic soil samples on FYM treatment. The negative values of ΔG₀ suggested thermodynamic preference for Cu over Ca, irrespective of soil samples and FYM treatment.