SOLUBILIlY OF DIFFERENT GYPSUM SIZE-GRADES IN SYNTHETIC SALINE-SODIC \VATERS

For reclaiming calcareous sodic and saline-sodic soils, various amendments like gypsum, calcium chloride, hydrochloric acid and sulphuric acid can be used. These amendments either change insoluble soil calcium to soluble form or supply calcium directly to replace the adsorbed sodium from sodic and saline-sodic soils. Out of all these amendments, gypsum is the most commonly used one due to its cheap availability in Pakistan (Ghafoor et al., 1985a, b). The fineness to which gypsum must be ground is a matter of economic consideration. Grinding to a very fine size entails higher cost, though it will give higher availability of soluble calcium to replace the exchangeable sodium. Simultaneously, the higher sodium adsorption ratio (SAR) of sodium-problem soils as well as of irrigation waters may increase the solubility of gypsum due to decreased activity coefficient (Bohn et al., 1985) which is the only its demerit. The present study was planned to see the effects of different levels of water SAR