Journal of the Indian Society of Soil Science

The effect of pH on sorption of Zn in an untreated and corresponding farmyard manure treated fine loamy, Typic Camborthid from a semi-arid region was investigated. The untreated and FYM treated soils were adjusted to three pH levels (i.e high 8; medium 7; low 5) and made homoionic with Ca The Ca-saturated soil samples were equilibrated with solutions having a wide range of Ca:Zn at 10 mmol L⁻¹ total chloride concentration. The pH of soil suspensions decreased with the increasing proportion of Zn in equilibrating solutions, the decrease being more pronounced in the high and medium pH samples. At comparable FYM, ΔG₀ steeply increased with the decrease in soil pH. In the high and medium pH range, ΔG₀ for the untreated and FYM treated soil samples were negative (−7.66 & -3.79 kJ mol⁻¹; -0.03 & -0.93 kJ mol⁻¹). In the medium pH range, the effect of FYM on AGo was only negligible (i.e. equivalent to 0.9 kJ mol⁻¹). In the low pH range, the values of ΔG₀ for the untreated and FYM treated soil samples were positive (6.44 & 4.24 kJ mol⁻¹). The results suggested that thermodynamic preference for Zn over Ca was higher in the high, nearly equal in the medium and low in the low pH range both in FYM treated and untreated soils.