Due to a cold and wet start many vineyards have been slow to grow. Vineyards on black cracking clays (Biscay Soils) have a naturally high fertility. In most seasons vines are healthy and yields are good. Sometimes, due to the alkaline limestone rock underneath, grapevines can have some nutritional problems but these are generally fixed once the weather warms up.
Look out for these symptoms particularly if your vineyard is on heavy black clay.
Currently in the vineyard nutritional disorders are easily seen on this soil type including Magnesium as shown (upper and lower left).
Above and Below: Iron Deficiency shows up as pale leaves.