chalk, a soft and crumbly, highly porous (35 to 40%) type of pure white limestone and a word often used erroneously as synonymous with it. Chalk-derived soils are valued in viticulture for their excellent drainage, combined with a capacity of the subsoil to store substantial amounts of water. Because vine roots can usually penetrate to chalk bedrock, continuity of moisture supply is assured regardless of short-term fluctuations in rainfall. Pure chalk is of low fertility, resulting in a rather low vine vigour and naturally good canopy microclimate.
