Micronutrient required by plants in small quantities
Involved in improving nitrogen use efficiency (NUE)
Deficiency symptoms include poor grain set, poor leaf formation and yellowing of older leaves
The main role of molybdenum is to improve the ability plants to take up and utilise nitrogen, otherwise known as Nitrogen Use Efficiency (NUE).
Molybdenum is a component of two enzymes which help convert nitrate to ammonium within the plant, enabling the synthesis of amino acids.
It is required for the symbiotic fixation of atmospheric nitrogen by Rhizobia bacteria in root nodules of leguminous crops such as beans, peas and clover.
Where there is a lack of molybdenum, the conversion of nitrogen to protein within the plant is likely to be poor.
In animals, molybdenum is a component of several enzymes which are involved in electron transfer.
The level of molybdenum in an animals blood should be kept below 3ppm to avoid inducing copper deficiency.
Molybdenum is available for plant uptake in its ionic form (MoO42-). Its negative charge means it is unable to bind to negatively charged clay particles, therefore it is vulnerable to leaching losses.
Soils high in molybdenum are likely to induce copper deficiency.
Molybdenum deficient plants present with poor grain set due to reduced pollen viability.
In maize, deficiency signs include reduced tasseling, flowering and pollen formation.
Molybdenum deficiency in cauliflower results in poor leaf development.
Due to its role in improving nitrogen efficacy, molybdenum deficiency plants can also present with nitrogen deficiency symptoms including yellowing of the older leaves.
Where is the risk of deficiency highest?
A Broad Spectrum (BS) soil analysis can help determine the quantity of molybdenum which is likely to be available for crop uptake and can be used to tailor fertiliser plans and to help prevent deficiencies within the season.
Tissue testing is also useful to determine the molybdenum concentration of the plant mid-season in order to compare against optimum levels. Although laboratory results may be available too late to correct the deficiency in the current crop, they can be useful for decisions on molybdenum use for future crops.