Agriculture Reference
In-Depth Information
Site Selection Indices
A more complete approach to site selection than that of climate analysis alone
involves the development of a local site index (LSI), which combines knowl-
edge of the requirements of particular cultivars for the factors listed under
“Determining the Site.” Viticultural and soil experts are asked to identify the key
biophysical properties and weight them to form a composite index for sites in a
region. For example, when applied to assessing site suitability for wine grapes in
the West Gippsland region, Victoria, Australia, soil, climate, and topography were
weighted in the ratio 70:20:10 (reflecting the perceived order of their importance;
Itami et al., 2000).
A similar approach was used in the hilly and mountainous terrain of central
Virginia,—a region colder than West Gippsland. There, frost in spring and freez-
ing in winter were serious constraints, so the most important factor in the LSI
was altitude (affecting temperature). Altitude was weighted at 30%; followed by
soil, 25%; existing land use, 20%; slope, 15%; and aspect, 10% (Boyer and Wolf,
2000). Another example of an LSI is that developed for Cabernet Sauvignon in
the Hawke's Bay region, New Zealand, which has a maritime climate of cool win-
ters and warm to hot summers (Tesic et al., 2002). In this index, soil properties
such as maximum rooting depth, topsoil gravel content, and soil texture (affect-
ing water-holding capacity and soil temperature) were combined with climatic
variables, such as growing season rainfall and mean October and January tempera-
tures. The resultant index was better correlated with growth characteristics and
fruit quality than several purely climatic indices.
The LSI approach has been used to develop the concept of digital
terroirs
,
which are described in chapter 6. A grower is more appreciative of such indices
iftheprimarydataarespatiallydeinedusingaglobalpositioningsystem(GPS),
entered into a geographic information system, and displayed in a colored map.
Although “determining the site” is only the first step in a chain of events in
wine production, it is important because suitable land is becoming scarce in many
of the more desirable wine regions. Also, the investment per hectare (ha) in estab-
lishing a new vineyard is large, so mistakes made in site selection can ultimately be
costly. The remainder of this chapter focuses on the soil factor in site selection; it
presents methods of gathering soil data and modifying the soil-vine environment
to optimize vineyard performance.
Steps in Site Selection
Topography overall is important in site selection in respect of cold air drainage,
susceptibility to frost, and row orientation for safe use of machinery, as discussed
later. However, as indicated in “Site Selection Indices,” the soil also plays an
