Molybdenum is needed by the plant in the synthesis and activation of nitrate reductase, an enzyme that reduces nitrate to ammonium in the plant. It is also required for symbiotic fixation of Nitrogen within legume root nodules and for the conversion of inorganic Phosphorus to organic forms in the plant.
Unlike other micronutrients, Molybdenum availability in the soil increases with higher soil pH. Sandy soils are more likely to be deficient in Molybdenum. Heavy Phosphorus fertilization can increase Molybdenum uptake by plants from the soil, while Sulfur fertilization reduces Molybdenum uptake.