Irrigated vineyards in Australia have seen extensive adoption of drip irrigation. At the start of this project there was concern about the sustainability of drip irrigation based on previous field observations. Drip irrigation conserves water but the concentrated nature of its application was believed to cause serious soil structural decline directly under drippers. This project aimed to identify such decline under drippers in Barossa Valley vineyards, to establish the causes of the decline and to suggest management and monitoring strategies to deal with the problem.

To identify such decline we adopted a “paired site” approach and examined subsoil structural problems, at depths of 30-50 cm, directly under drippers, midway between well-spaced drippers (>2 m) and at nearby non-irrigated control points. While we were encouraged to find no evidence of any preferential subsoil structural decline under drippers, we were surprised to find that all the subsoils we examined were of such generally poor structure that there was little prospect of further decline. However, we also realized that application rates in the Barossa Valley are dwarfed by those used elsewhere and proceeded to extend our investigation to the finer-textured soils of Sunraysia and the Murrumbidgee Irrigation Area (M.I.A.). The story here was no different and it became clear that the structural status of subsoils in vineyards is generally poor and is probably undermining good water use efficiency by vines. In 22 distinct soils air-filled porosities were universally very low, resistance to root penetration was high and infiltration rates were frequently poor. A comparison of root length density with subsoil structural properties strongly suggests that poor aeration poses the chief limitation on root proliferation and water use efficiency.

There are few strategies available for subsoil structural improvement in the vine row. We confirmed that gypsum alone has no significant benefit in improving poor structure at depth when applied to a red-brown earth. An attempt to induce subsoil cracking by drying soil in an extended partial root zone drying experiment also failed to improve subsoil structure.

These are inherently poor subsoils and there is a clear need for greatly improved preparation procedures ahead of new plantings. There is also need for changes in the management of existing vineyards if efficiency of water use is to be improved. We believe these will necessarily include modified traffic, soil mounding and the use of calcium, mulching and cover crops in the vine row. Indeed, the recommendations of Cockroft for the stone fruit industry (Murray, 2007) seem just as relevant to viticulture but have not been demonstrated or adopted. In their review of soil properties in relation to vine performance, Lanyon et al. (2004) have also recommended that much closer attention be paid to soil preparation and management in vineyards.