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Magnesium-deficient plants generally develop a mottled pale green or chlorotic pattern in the interveinal tissue of older leaves, often starting near the margin. In cereal, leaves with mild deficiencies develop a green linear beading that progresses to interveinal chlorosis. In severe cases, the chlorosis progresses to the middle of the leaf and the small veins also become affected. Reddish or brown spots appear on the leaf blade. 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, eventually leading to premature death and early shedding. Root growth is inhibited, resulting in poor plant vigor.
Magnesium deficiency is a common problem in light, sandy soils or acidic soils with low nutrient and water retention capacity. In those soils, nutrients can be easily leached away. Soils rich in potassium or ammonium or the excess application of these nutrients can also be problematic, because they compete with magnesium in the soil. Magnesium is involved in sugar transport and 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 the newer, developing ones. This explains the development of interveinal chlorosis. Light intensity influences the development of the symptoms. High light worsens the effects of a deficiency.
Apply substances that contain magnesium such as algal limestone, dolomite or limestone magnesium. Use manure, organic mulches or compost to balance the soil nutrient content. They contain organic matter and many nutrients that are release slowly into the soil.
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 period of weeks to the soil and is ideal for a quick release requirement.