Site selection and soil composition of a vineyard is one of the most important viticultural considerations when planting grape vines - that will have the greatest impact on wine quality.
Wine growers look for moderately fertile soils that do not promote an overly vigorous vine. It's no surprise that grapevines can often be found on ground that farmers deemed unsuitable for any other crop.
The ideal circumstance for a vine is an area of thin topsoil and subsoil that sufficiently retains waters but also has good drainage so that the vine roots don't become too saturated. The ability of the soil to retain heat and/or reflect it back up to the vine canopy is also an important consideration that affects the ripening of the grape.
There are several minerals that are vital to the health of grape vines that all good vineyard soils have. These include calcium which helps to neutralize the soil pH levels, iron which is essential for photosynthesis, magnesium which is an important component of chlorophyll, nitrogen which is assimilated in the form of nitrates, phosphates which encourages root development, and potassium which improves the grape vines metabolism and increases its health for next year's crop.
However, nutrients are essential to plant growth and ultimately to the ripeness of the grapes. It can therefore be argued that, indirectly, nutrients are essential to the production of high quality wine. It is the absorption of these minerals, the timing and amount during the growing cycle that is key.
Poor absorption creates imbalances, excesses or shortages, each with their causes and effects on vine growth and grape development. It is especially critical in relations to nitrogen and potassium content in the soil as their impact is largest.
When it comes to two of the greatest vineyards in the world - Château Lafite Rothschild and Domain de la Romanee Conti - soil quality is best expressed. There is a unique richness and you can taste it in the wine (Goût de terroir), a smell of aroma that emblazes into the mind. What is reflected in the soil is reflected in the plant, and in the taste of the wine.