HOW SOIL FORMING PROCESSES DETERMINE SOIL-BASED VITICULTURAL ZONING
The aim of this study was to elucidate the soil forming processes of representative vineyard soils, and to discuss the implications on a soil-based viticultural zoning at very detailed scale. The study area is located in Priorat, Penedes and Conca de Barbera viticultural areas (Catalonia, North-eastern Spain). The studied soils belong to representative soil map units determined at 1:5,000 scale, according to Soil Taxonomy classification. The soil forming processes, identified through morphological and micromorphological analyses, have significant effects on some soil properties. For example, the different processes of clay accumulation in soils developed from granodiorites in Priorat or gravel deposits in Conca de Barbera, are primarily responsible for significant differences in clay content, available water capacity and cation exchange capacity. These soils properties, especially those related to soil moisture regime, have a direct influence on vineyard management and grape quality. However, soil forming processes are not always reflected on soil classification, especially in soils modified by man. We show that climate or geology alone cannot be used in viticultural zoning at very detailed scale, unless soil forming processes are taken into account.