CARBONATE CHEMISTRY, PH, AND PHYSICAL-PROPERTIES OF AN ALKALINE SODICSOIL 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 t he changes in carbonate chemistry, pH, and particle charge following t he application of gypsum, green manure, and glucose. Gypsum reduced th e pH from 9.38 to 7.89, increased Ca2+ in soil solution, and decreased the sodium adsorption ratio (SAR(1.5)) from 11.6 to 1.2. Green manure , due to increased CO2 production, reduced the pH to 8.68 and SAR(1.5) to 7.52. Green manure plus gypsum reduced pH to 7.67 and SAR(1:5) to 0.91. The interactive effect of gypsum and green manure on all soil pr operties was highly significant as shown by ANOVA analysis. Reduction of son pH was also reflected in the levels of carbonates in the soil s olution. Addition of glucose increased the microbial activity and prod uced fatty acids. The drastic reduction in pH (<60) was related to the amount of glucose added. The concentrations of Ca2+ and carbonates, a nd SAR(1:5) values, were inversely related to the soil pH after glucos e addition. The data on soluble Na2CO3 and NaHCO3, zeta potential, mec hanical dispersion, aggregate stability, and saturated hydraulic condu ctivity confirm the effects of pH reduction and carbonate solubility a s influenced by the amendments in alkaline sodic soil.