R G V Bramley

CSIRO Land and Water and Cooperative Research Centre for Viticulture
Private Bag No. 2, Glen Osmond, SA 5064, Australia

Yield monitoring equipment for winegrape harvesters, which has now been commercially available since the 1999 vintage, presents grape and wine producers with opportunities to tailor production of both grapes and wine according to expectations of vineyard performance and desired goals in terms of both yield, quality and the environment. Indeed, the fact that yield mapping in the Clare Valley, Coonawarra, Padthaway and Sunraysia districts during the 1999 and 2000 vintages suggests that the range of yield variation in Australian vineyards can be expected to be at least 4-fold and more typically 8 or 10-fold, indicates that an ability to manage vineyards in a way that accounts for, and/or reduces such variation may offer very significant economic and environmental benefits. However, successful adoption of Precision Viticulture (PV) depends, amongst other things, on an understanding of the factors driving vineyard variability and of the temporal stability of spatial variation in vineyard performance. This paper discusses the results of research being conducted at Australian sites with contrasting soils, climate and management.

At sites in both Coonawarra and Sunraysia, yield variation was substantial and of a similar order of magnitude in both 1999 and 2000 in spite of a substantial difference in the mean yield between the two years. The pattern of yield variation at both these sites was remarkably consistent over the two years as evidenced by a comparison of the normalised yields obtained for the two years. Accordingly, it has been possible to identify potential management zones for which targeted differential management within vineyard may be appropriate.

A moving window regression analysis of soil depth and bulk soil conductivity as assessed by EM38 survey suggests that for the shallow (< 700 mm) terra rossa soils of Coonawarra (light red clays over limestone), EM38 provides a useful means of inferring soil depth (ie rooting volume and potentially available soil water) and therefore has value as an aid in better targeting irrigation; low yielding areas correspond to zones of shallow soil. A similar analysis at a site in Sunraysia, where a variable depth of riverine sand overlies a clayey B horizon, suggests that clay content and depth to the sand-clay interface exert similar control over water availability to the vines, and in particular, the risk of waterlogging during winter/spring; the sandy A horizon is at its shallowest, and the slowly permeable clay subsoil closest to the surface, in the lowest yielding zone of the vineyard. EM38 is also being used at a site in the Clare Valley to delineate areas at greatest risk of lost productivity due to the effects of salinity.

Whilst the results obtained to date suggest that careful soil management could promote greater control over variation in grape yield and some aspects of quality, covariation of soil and vine/grape indices does not appear to be constant in space. Thus, an improved understanding of the relationships between the inputs to grape production systems and their outputs will be required if targeted management is to be successful.

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