The Mineral Content of Vineyards Soil and its Effects
Clay is very fertile and has the most available nutrients. Soils that have too much clay produce very high yields of large grapes with poor flavor concentration.
Some minerals found in clay are necessary for the vine to absorb certain nutrients. It is important that clay soils are on the low end of the spectrum in regards to cation exchange capacity (CEC). This type of clay is the most porous and the least water retentive. More importantly it is reluctant to over nourish the vine and produces quality wine grapes.
Sandy soils drain very well and do not contain a lot of available nutrients and water for grapes. If soils are too sandy and do not have enough clay minerals, vines will produce very lean, unflavorful grapes.
As limestone weathers, it releases carbonates which help break down organic matter. This leads to some clay and silt with better water retention. Granite breaks down to shale and gravel. Sandstone weathers to sand which also dries out quickly.
Soils with high iron content tend to produce wines with stronger tannins and therefore more aging potential.
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