Zonage et caractérisation des terroirs de l’AOC Côtes-du-Rhône: exemple du bassin de Nyons-Valreas

The southern Côtes-du-Rhône vineyard shows a significant variety of ecological facets over the Lower Rhone Valley. Intending to characterize such a variety of “terroir “called vineyard situations, a spatial approach based on identification of soil landscapes has been initiated. It was applied to a limited zone in part of the Valréas sedimentary basin, where local climate is likely homogeneous. Spatial distribution modelling of soil cover combine existing soil and geological data, using land survey, stereoscopic aerial photograph examination, satellite image processing. Map features are digitized within a Geographic Information System (GIS). 21 synthetic map units integrate 15 variables referring to soil, geomorphology, lithology, stratigraphy, vegetation, land form. The vine-growing terroirs, regarded as parts of agricultural lands consistent with both soil landscapes and harvestlwine response, are defined by clustering of the soil landscape units according to multivariate analysis. Terroir mapping is examined and validated in relation to wine response through Grenache harvest composition and its frequency over 1982-1996. Discriminant analysis is performed on the 1982-1996 must compositions of 14 sites related to 4 terroirs units. It shows that discrimination of the terroir units may be realized with the following variables: sugar content converted to expectable alcohol percentage (TAP, %), pH, titrable acidity (AT, g H₂SO₄/l.), weight of 200 berries (g/l), TAP/AT ratio.