THE NATURE, DISTRIBUTION AND MANAGEMENT OF SODIC SOILS IN NEW-SOUTH-WALES

Accurate data on the distribution of the various types of sodic soils in New South Wales are not available. However, general observations suggest that large areas are affected by structural instability as a result of sodicity, particularly on grey clays and red-brown earths of the Murray-Darling Basin. There is a strong need for new sodicity surveys because the production of crops and pasture often is well below potential on these lands. Exchangeable sodium data on their own do not adequately describe sodic soil behaviour, so information is also required about related factors such as electrical conductivity, exchangeable magnesium, clay mineralogy, pH, calcium carbonate content, degree of remoulding, and the frequency of continuous stable macropores. Critical limits for sodicity that are used by soil management advisory services need to be redefined. Considerable research into the reclamation and management of sodic soils has occurred in the irrigation areas and rainfed cropping districts of the Murray-Darling Basin in New South Wales. Mined and by-product gypsum, and to a lesser extent lime, have been shown to greatly improve the physical condition and profitability of production from soils with a dispersive surface. However, the responses to these treatments are less likely to be economical when sodicity is confined to the subsoil. Adequate supplies of gypsum and lime are available in New South Wales, but further research is required to determine economically optimal and environmentally acceptable rates and frequencies of application, particle sizes and chemical compositions for different farming systems that utilize the various types of sodic soil.