Irrigation Water Requirement for Dissolution of Gypsum in Sodic Soil

Abstract Laboratory studies were conducted to determine the effect of exchangeable sodium content of the soil and the particle size of gypsum on the irrigation water needs for dissolving gypsum mixed in sodic soils. Gypsum dissolution increased with an increase in the exchangeable Na content of the soil. About 4 cm of water was sufficient to dissolve all the agricultural grade gypsum of <0.26‐mm size. The amount of water required to dissolve the added gypsum and to reclaim a sodic soil did not increase with the amount of gypsum added, provided it equalled the gypsum requirement. The effect of particle size of gypsum on its dissolution and the applicability of the equal‐reduction hypothesis were examined. The dissolution of gypsum was approximately predicted by a dissolution equation based on particle surface area if the initial particle sizes were neither very coarse (<0.5 mm) nor very fine (>0.1 mm). The water required for complete dissolution of gypsum computed from a dissolution equation, increased from 2.8 cm to 15.9 cm as gypsum particle size increased from < 0.1 mm to 0.5–2.0 mm.