Chemical Reactions Within Root Zone of Arid Zone Soils

Abstract

The quality of an irrigation water, in both its total salinity and individual constituents, influences the chemical character of the soil solution and irrigation return flows including drainage waters. Dissolution, precipitation, adsorption and exchange reactions modify the salt load and composition of return flows. The effects of these reactions can be manipulated by varying the leaching fraction. A change from significant increase in total salts to substantial precipitation of calcite (soil lime) and gypsum can occur as the leaching fraction is reduced. Such a reduction in ieaching fraction and the concomitant reduction in applied water will also reduce the rate at which native salts in the return flow pathway are displaced into receiving waters. Methodology exists, as illustrated by several examples, to evaluate potential consequences of reduced leaching and chemical reactions on soil solution composition and on the salt loads of irrigation return flows.