CHAUVAUD D. (2001). THE TERROIRS OF THE A.O.C. MADIRAN AND PACHERENC OF VIC-BILH AREA : GEOMORPHOLOGICAL, GEO-PEDOLOGICAL AND CARTOGRAPHICAL ANALYSIS.

Abstract : The A.O.C. Madiran and Pacherenc of Vic-Bilh area is located in the northwestern piedmont of the Pyrenees. A systematic characterization of vineyard geo-pedological environment was released. This semi-theoric and semi-applied work constitutes a pluridisciplinary research theme. The geomorphological analysis guided this work. The extensive study of elementary relief's forms permitted to recount the main stages of the morphogenesis and to establish reference transects along the valley sides. Those illustrate the main types of catenary soil association related with varying combinations of forms and facies variations of parent rocks. A physiographic map at 1/50000 scale shows the association of relief's forms on the vineyard area, divided into four geomorphological sectors : the apex of ridges in the SE, the relief of dissymetrical valleys in the NE, the relief of ridges with flats in the SW and the relief of convex ridges in the NW. This map has been used to establish 37 topolithosequences, analysed with 227 soils profiles. Their description, completed by physico-chemical analysis permits to characterize 12 soils. Their consolidations creates units of two maps : the pedological map at 1/25000 scale for the Bergons basin test zone and the morpho-pedological map at 1/50000 scale for the A.O.C. area. A statistical analysis of physical and chemical parameters (pH, texture, CEC, clay minerals,...) shows the influence of substrate and relief's forms to the vertical and lateral variations, and the present and old dynamics of geo-pedological environment. The data synthesis defines wine producing aptitudes of soils, hierarchized in 4 classes : optimal, appropriate, unpropitious and unfavourable. This work represents a tool for the wine growers, the wineries, the I.N.A.O. and the I.N.R.A. It represents too a referential for geo-pedological studies with a large scale and for the « terroirs viticoles » mapping, associating the main environmental constituents.

Keywords : Vineyard, geo-pedological environment, geomorphological analysis, physiographic map, topolithosequences, pedological maps, statistical analysis, wine growing aptitudes of soils.

davidchauvaud@yahoo.fr