Carbonate chemistry, pH, and physical properties of an alkaline sodic soil as affected by various amendments

A greenhouse experiment evaluated the chemical and physical changes of a Natrixeralf (with alkaline pH 9·4 and 5% CaCO3), as influenced by the changes in carbonate chemistry, pH, and particle charge following the application of gypsum, green manure, and glucose. Gypsum reduced the pH from 9·38 to 7·89, increased Ca2+ in soil solution, and decreased the sodium adsorption ratio (SAR1:5) from 11·6 to 1·2. Green manure, due to increased CO2 production, reduced the pH to 8·68 and SAR1:5 to 7·52. Green manure plus gypsum reduced pH to 7·67 and SAR1:5 to 0·91. The interactive effect of gypsum and green manure on all soil properties was highly significant as shown by ANOVA analysis. Reduction of soil pH was also reflected in the levels of carbonates in the soil solution. Addition of glucose increased the microbial activity and produced fatty acids. The drastic reduction in pH (6·0) was related to the amount of glucose added. The concentrations of Ca 2+ and carbonates, and SAR1:5 values, were inversely related to the soil pH after glucose addition. The data on soluble Na2CO3 and NaHCO3, zeta potential, mechanical dispersion, aggregate stability, and saturated hydraulic conductivity confirm the effects of pH reduction and carbonate solubility as influenced by the amendments in alkaline sodic soil.