Almost two-thirds of the farms in southern Australia have a texture-contrast soil profile with sandy or loamy A and E horizons overlying clay B horizons. A common problem with some of these soils is the development of a perched watertable in winter, which causes severe reduction in crop yield and exacerbates land degradation. The aim of this study was to measure the extent of the variability in the duration of soil saturation in texture-contrast soils on slopes in a catchment in the Mount Lofty Ranges, South Australia. Furthermore, a method based on a topographic index was used to predict soil saturation at catchment scale, which was then compared to the conventional point-scale measurements.

In the relatively dry years of the study, water duration on the upper slopes was surprisingly higher than on the lower slopes but was rarely expressed at the soil surface. Furthermore, the cause of soil saturation on the mid- and upper slopes was different from that on the lower slopes. However, it was predicted that in wet years water would last longer on the lower slopes due to saturation by groundwaters. As the catchment-scale method was based on a topographic index, it should be useful for predicting the duration of saturation in wet years but not in dry years.

The information obtained on the variability and causes of waterlogging will be of benefit to farmers. It showed that the failure of some current management options to adequately control perched watertables on slopes is partly due to the lack of understanding of their causes and to inadequate prediction of their variability in catchments.