Effect of Dissolution Rate on the Efficiency of Industrial and Mined Gypsum in Improving Infiltration of a Sodic Soil

The dissolution rate of gypsum from three sources (analytical, mined, and industrial—a by‐product of the phosphate fertilizer industry) in solutions containing various initial NaCl concentrations was studied at 25°C. The total Ca concentration in 0.05 and 0.1 N NaCl solutions at a given time was about 1.3 and 1.5 times that in distilled water, respectively. The dissolution rate of the industrial gypsum was much higher than that of the mined gypsum, whereas the dissolution coefficients of the analytical, industrial, and mined gypsum were the same for a given surface area. The probable reasons for these findings are discussed. The efficiency of the industrial and mined gypsum in maintaining a high infiltration rate in a sodic soil under simulated rain conditions was studied. The efficiency of the industrial gypsum was found to be much higher than that of the mined. The high efficiency of industrial gypsum in maintaining a high infiltration rate is attributed to its high rate of dissolution.