This study aims to understand the causes of structural decline occurring in saline Vertisols as they become sodic through the combined effects of climate change and artificial drainage. It was motivated by the concern of land owners on this soil type in the Upper South East (USE) of South Australia. A representative site has been investigated over a variety of scales with EM31 and ground penetrating radar (GPR) and with soil morphology, chemistry and clay mineralogy of the soil profile. Previous research of sodic soils in southern Australia has predominately been conducted on Alfisols, with little known about its development or effects on soil behaviour in Vertisols.

Reductions in watertable levels have occurred along with a steady decline in annual rainfall throughout the USE since the early 1990's. Lowering of the watertable has facilitated the leaching of salts from the uppermost horizons of the soil profile with the consequent development of sodicity (ESP >30% in most cases). It is hypothesised that the location, geographic extent and severity of sodicity are a result of a seasonally variable saline watertable, landform, variability in soil type and properties of soil horizons.

An exploratory trench (60m long x 1m wide x 1.5 deep) was excavated to groundtruth the geophysics surveys, providing the opportunity to observe deep soil features on a flat landscape and to collect samples for analysis. Patterns in the morphology of the soils at depth, the presence, form and thickness of carbonate horizons and the accumulation of salts are described and are assessed against the chemical and mineralogical variability throughout the site. Soil pH varies from near neutral to >10 and the dominant smectites vary in their extent of interstratification. The results of this study are discussed with reference to different management practices and their effects on soil behaviour.