Magnesium deficiency in tomato plants generally start with mottled chlorotic areas developing in the interveinal tissue of older leaves, often near the margin. In case of severe deficiency, the chlorosis progresses to the middle of the leaf and the small veins also become affected. Later on, the development of necrotic areas in the highly-chlorotic tissue gives the leaves a rugged and deformed aspect. Finally, the yellowing engulfs the whole leaf (main veins included), eventually leading to premature death and early shedding. The growth of the plant is impaired, and even though it is able to flower, fruit development and yield are compromised.
Magnesium deficiency is common in tomato, among other crops. It is particularly a problem in light, sandy or acidic soils with low nutrient and water retention capacity, and where magnesium can easily be leached away. Soils rich in potassium or ammonium, or the excess application of these nutrients, can also be problematic because they hinder the uptake of magnesium by the plant. Magnesium is an important part of the chlorophyll molecules. Without sufficient amounts of magnesium, the plants begin to degrade the chlorophyll in the older leaves to transfer it to newly developing ones. This explains the development of interveinal chlorosis .
Use manure, organic mulches or compost to balance the nutrient content in the soil. These contain organic matter and many nutrients.
Use soil or foliar fertilizers containing a magnesium complement. Magnesium oxide allows a slow release of the nutrient and is used in blends for an immediate supply of magnesium to crops. Magnesium sulphate releases the magnesium over a four to six week period to the soil and is ideal for a slow release requirement.
Check the pH of the soil and lime if necessary to get the optimal range.,Plan a good drainage of fields and do not over-water the crop.,Do not over fertilize with potash.,Use organic mulch to keep soil moisture stable.