Sodicity in South Australia - a review

Abstract

The current knowledge of the nature and distribution of sodic soils in South Australia is reviewed. The agriculturally developed area of South Australia lies south of latitude 32-degrees-S. and is mainly used for low intensity grazing and dry land cereal/sheep production. A high proportion of the State, including much of the high rainfall area, has soils which are sodic (>6% ESP) through a significant proportion of the profile but information on the precise nature of sodicity in these soils is limited. Where exchangeable cation data axe available, the analytical techniques used often did not precisely delineate between soluble salts in the soil and ions on exchange sites. Therefore, many of the datasets have major weaknesses and may be unreliable. Since many soils with ESP <6 also show dispersive characteristics typical of sodic soils, there is an urgent need for new sodicity studies relating to distribution and the criteria (ESP) used to identify dispersive soils. Information on the effect of sodicity on nutrient requirements of plants, especially the modern varieties, is scarce both locally and internationally, making development of management strategies for economically sustainable crop production difficult. Further, many different grades of gypsum are available in South Australia. Preliminary studies show the presence of impurities drastically influences gypsum dissolution characteristics. More effort is needed to assess the quality and reactivity of South Australian gypsum. Some effort has been directed by land managers towards reclamation and management of sodic soils by using both gypsum and lime either separately or as mixtures. However, there is neither a scientific basis for the application of gypsum-lime mixtures nor crop production data to support such management strategies.