calcareous is the technical adjective for geological materials that are ‘limy’, i.e. composed significantly of calcium carbonate. These include marl, limestone (and its subvarieties chalk and dolomite), and their associated soils (see geology). Calcaire is the French for limestone.
In cool, non-arid vineyards, calcareous soils allow better water movement and access to nutrients than more acid soils. This is because calcium carbonate, unlike most geological minerals, can dissolve in the water in the soil and react with its natural carbon dioxide content to form soluble bicarbonate, which tends to buffer the ph (see soil acidity and soil alkalinity) to around its optimum for nutrient availability. In addition, calcareous soils tend to flocculate clays, improving soil texture, microbial activity, and drainage. Limestone bedrock is normally highly fissured, and this also promotes water flow. Adding calcareous matter to overly acid soils (see lime) helps achieve the same results, although it can be overdone, causing the problems associated with vines growing on highly calcareous rocks or pure limestone (chlorosis, for example). These are vineyard effects; calcareous soils are unrelated to the acidity of a finished wine.
