Soil structural degradation has been identified in some Australian vineyards, where unsuitable irrigation practices have been applied to vulnerable soils. There is a need to quantify the extent of degradation occurring in vineyards, in terms of physical properties, and to identify the rate at which this is occurring. Soil structural degradation affects soil water availability, which describes the capacity of a soil to store water and to supply water to a plant at an efficient rate. An index of soil water availability is provided by the integral water capacity (IWC), which incorporates a range of soil physical properties within a single measure.

A paired-site investigation was undertaken to assess the impact of conventional drip irrigation on IWC at sites with different irrigation histories. Two field sites were selected (McLaren Vale, SA; and Nuriootpa, SA). Undisturbed soil cores were sampled from a vineyard and a non-irrigated site at McLaren Vale, and from a young vineyard, an established vineyard and a non-irrigated site at Nuriootpa. Cores were sampled at different depths and distances from the dripper along the vine row, and used to measure soil water retention, penetration resistance and hydraulic conductivity among other soil properties. Laboratory work was coupled with field measurements of saturated hydraulic conductivity. Findings suggest differences between the irrigated and non-irrigated sites, with trends of altered soil physical properties noted along the vine row away from the dripper. At McLaren Vale, regular gypsum application appears to have negated some of the deleterious impacts of irrigation.