Artificial drainage affects the physico-chemical properties of salt-affected heavy clay soils in the Upper South East of South Australia

Abstract

Artificial drainage has been widely adopted throughout the Upper South East of South Australia to intercept surface floodwaters and ameliorate dryland salinity. Land managers have reported a perceived decline in pasture productivity and the development of bare patches of soil at both drained and un-drained sites. This study aims to investigate the effects of artificial drainage on soil physico-chemical properties and to determine whether the observed plant decline is directly related to artificial drainage. Results show groundwater levels have fallen both with a decline in annual rainfall and the implementation of artificial drainage; facilitating the leaching of salts. Comparison with 1950 (pre-drainage) data confirms that a change in soil physico-chemical properties has occurred. The combination of high pH, extreme salinity and strong sodicity has led to soils that are both chemically hostile and structurally unstable; hence, plant growth is affected. Soil type and mineralogy were found to vary both across and within study sites; the un-drained smectite dominant soils exhibit the most hostile chemical conditions for plant growth. Nevertheless, the mineralogy of the soil governs the level of structural degradation when the soils are sodic, such that the illite/kaolinite-dominant soils are particularly degraded, resulting in the highly compacted form observed.