Salt content of lateritic profiles in the Darling Range, Western Australia

Abstract

Soil cores from some 40 complete laterite profiles as deep as 40 m in the Darling Range, W.A., have been examined for salt content, and in some cases, pH. The sites cover a range of topographic situations from divides to valley floors, and of rainfall from 560 to 1350 mm per annum. Increases in surface soil salinity and in the salt concentration of water yields following clearing of the native hardwood forest are related to the amounts of soluble salts stored in the lateritic pallid zones. Storage increases as rainfall decreases in all slope situations. In low rainfall areas (<800 mm per annum) the salt stored under unit area of landscape in the profile down to bedrock is five times greater than in high rainfall areas (≫1000 mm per annum). One area with an annual rainfall of 600 mm has an estimated storage of nearly a million kg of total salts per ha and marked increases in surface soil salinity have occurred within 10 years of clearing. Although in the past, increasing soil salinity has mainly affected agricultural land, the present emphasis on bauxite mining in the forested areas of the Darling Range, particularly in the drier parts, poses new problems in revegetating the exposed saline and acid pallid zone clays after mining operations have ceased.