Release of Ions from Calcium Carbonate Treated Alkali Soil as Influenced by Organic Matter and Moisture Contents

The release of Ca²⁺ + Mg²⁺, Na⁺ and HCO₃⁻ ions was studied in an alluvial alkali soil treated with four levels of calcium carbonate viz 0, 10, 20 and 30% (on air-dry weight basis of soil). The treated soil samples were incubated at 32±1°C for 120 days at different moisture regimes i.e. half field capacity, field capacity, saturation and submergence at two levels (0 and 1%) of added organic matter (FYM). Soil sampling was done after 30, 60, 90 and 120 days of incubation and Ca²⁺ + Mg²⁺, Na⁺ and HCO₃⁻ concentration were analyzed in saturation extracts. The release of Ca²⁺ + Mg²⁺ increased due to dissolution of CaCO₃ with increasing level of CaCO₃, moisture content, and the effects were more pronounced in the presence of organic matter. Sodium ions increased significantly at submergence and saturation as compared to other moisture regimes. Due to proportionately higher release of Ca²⁺ + Mg²⁺ than Na⁺, there was a net decrease in SAR and more so, at higher moisture regimes and CaCO₃ levels. Different kinetic models viz. first order, power function, parabolic diffusion rate and Elovich equations were used to fit the Ca²⁺ + Mg²⁺ release data. The value of standard error of estimates (SE) was lowest for first order rate equation and was higher for power function equation, parabolic diffusion rate and Elovich equation. The results suggest that release of Ca²⁺ + Mg²⁺ will be more precisely predicted by first order rate equation than others. The higher “a” constant value for organic matter added soils in all the models suggested an instantaneous rate of release of Ca²⁺ + Mg²⁺.