Effects of a lowland rice crop and of gypsum on a saline alkali clay

Abstract

Lowland rice cropping for one season decreased the soluble salts, particularly the chlorides, in the top 30 in. of a saline alkali clay soil. The calcium:sodium ratio increased for soluble cations, but showed little change for exchangeable cations. The surface soil became slightly more water-stable, but below 3 in. the soil became easier to disperse. These changes had little effect on the growth of an irrigated annual pasture sown after rice cropping, except in the year of establishment. After 2 years' growth of the pasture, part of the soluble salts had returned to the top 30 in. of the soil. The application of gypsum at 2 and 8 tons/acre before growing the lowland rice crop increased the ca1cium:sodium ratio of both soluble and exchangeable cations and reduced clay dispersion. Rice seedling ,establishment and yields of stubble-sown subterranean clover were higher on the gypsum-treated plots.