A REVIEW OF SODICITY AND SODIC SOIL BEHAVIOR IN QUEENSLAND

The occurrence of sodic soils in Queensland is more related to soil ge netic factors of the past than to the current rainfall pattern, with l ower sodium accessions and smaller occurrence of saline lands than oth er areas of Australia. A soil sodicity map of Queensland is presented. On an area basis, 55% of soils in Queensland are non-sodic, 25% are s trongly sodic and 20% are of variable sodicity. The map was prepared u sing exchangeable sodium percentage (ESP) values at 0.6 m depth from 2 009 soil profiles, as well as the soil boundaries of the 1:2000000 At las of Australian Soils maps (Northcote et al. 1960-68). There is gene ral agreement with the earlier sodicity map of Northcote and Skene (19 72). The relationships between exchangeable sodium and field-measured soil hydraulic properties and plant-available water capacity are discu ssed. Behaviour of sodic soils depends on the exchangeable sodium perc entage, clay content, clay mineralogy and salt levels. The binary comp onent particle packing theory has been used to explain soil behaviour and identify those soils most susceptible to sodium. Cracking clay soi ls with dominantly smectite mineralogy and high clay contents are less susceptible to a given ESP level, as determined by their hydrological behaviour, than soils of moderate clay content and mixed mineralogies . The sodicity and the salt content of an irrigation water are importa nt in maintaining permeability of soils. The naturally occurring equil ibrium salinity-sodicity relationships of a wide range of subsoils in Queensland is compared to the published relationships between stable p ermeability and decreasing permeability based on sodicity and salt con tent. Aspects of management of sodicity under dryland and irrigation a re discussed.