Molybdenum

Molybdenum (Mo) is one of the six ‘minor’ chemical elements required by green plants. The other five are iron, copper, zinc, manganese and boron. These elements are termed ‘minor’ because plants need them in only very small amounts (in comparison with the ‘major’ elements nitrogen, phosphorus, potassium, sulphur, calcium and magnesium). But they are essential for normal growth. Of these six minor elements, molybdenum is needed in smaller quantities than any of the others. As little as 50 grams of molybdenum per hectare will satisfy the needs of most crops. Molybdenum is often present in farmyard manure, in seeds or other planting material such as tubers and corms, and as impurities in some artificial fertilisers. The molybdenum supply from the seed appears to be significant only where the size of the seed is fairly large. For example, the molybdenum content of bean, pea and maize seed can be important, but that of tomato seed is probably of little significance.

Soil acidity
Molybdenum in acid soils tends to be unavailable to plants. This is why most molybdenum deficiencies occur on acid, rather than on neutral or alkaline soils.

Biological role
Molybdenum helps in the uptake of nitrogen and in root nodule activity in plants and is a cofactor to enzymes important in building amino acids. It is rare that a plant will suffer a deficiency in this nutrient.

Symptoms of deficiency
Chlorosis in older leaves Suppression of leaf growth Example is whiptail in brassicas.