Vineyard nutrient management. Magnesium (Mg)

Symptoms usually occur in light, acidic soils low in magnesium. Sandy soils with a high concentration of potassium, as well as calcareous soils can also favor the appearance of magnesium symptoms. Excessive use of ammonia and potassium fertilizers can also cause problems (Pearson and Goheen, 1988).

In species of the genus Vitis spp, deficiency symptoms occur mainly in two forms. At the beginning of the vegetative period in the form of interneural chlorosis, and later in the form of interneural yellowing. Later in the vegetative period, deficiency symptoms appear mainly on base leaves, while the first signs of deficiency usually appear shortly before flowering, as small green brown spots near the margin and in the interneural tissues of young leaves (Pearson and Goheen, 1988).

Magnesium intake was studied by Conradie (1981). The intake of magnesium was relatively stable during the vegetative cycle of the plant, so its addition is timely from just before flowering and until normal leaf fall.

As with other nutrients, the type of subject can affect magnesium intake. Garcia et al. (2001) examined the effect of three different subjects (101-14, 3309 C, SO4) on their ability to take up magnesium.

The results showed that plants grafted on the 3309 C rootstock showed the highest magnesium concentration, followed by 101-14 and SO4. In line with other nutrients, the establishment of a magnesium fertilisation programme should also take into account the rootstock used.