Spatial terroir characterization and grape composition in the Southern Côtes-du-Rhône vineyard (Nyons-Valreas Basin)

Abstract

In order for the characterization of terroir in vineyard situations to benefit both viticultural and wine making practices, it is necessary to consider the spatial aspect of the vineyard environment. An exploratory approach at characterising terroir in the Nyons-Valreas Basin (figure 1) considers both the spatial analysis and frequency analysis of the harvest. Data gathered from stereoscopic aerial photographic examination, satellite image processing, land surveys, and the Digital Elevation Model are combined and structured within a Geographic Information System along with the existing soil and geological data (figure 2). The result is a comprehensive soils model applicable to a relatively large area (11,340 ha). The Nyons-Valreas Basin is a neogene and quaternary sedimentary basin, and the soils found there are described by 21 soil landscape units which integrate 15 variables (table I). The area examined is considered to be representative of the surrounding regional diversity. The variables used in characterising terroir include soil types, geomorphology, lithology, stratigraphy, vegetation, land form, and land use. The various viticultural terroirs are regarded as parts of agricultural land consistent with both soil landscapes and harvest/wine responses. Multivariate clustering of the soil landscape units indicates that there exists 7 distinct viticultural terroirs, essentially on the basis of geomorphology and soils (figures 3 and 4, table II). Four distinct terroirs were compared (figures 5 and 6) using data gathered from 14 sites over the course of 15 vintages (1982-1996). Grenache is the grape variety planted at each site, and the variables measured at harvest (pH, sugar content, titratable acidity, the weight of 200 berries, and the sugar/acidity ratio) appear to significantly discriminate the sites examined according to the terroir modeling performed (tables III, IV and V).