The behaviour of molybdenum is totally different from other trace elements in relation to soil pH: it
is not available in acidic soil but becomes very soluble and can be mobilised in basic soil.
The quantities involved are very small and require precision and moderation in the applications.
IMPORTANCE FOR THE PLANT:
Molybdenum is involved mainly in enzymatic mechanisms related to the assimilation of nitrogen
(nitrogenase and nitrate reductase).
Molybdenum is absorbed via the soil solution as anion.
Molybdenum works quite well in synergy with phosphorus.
Sulphur has an acidifying effect in the soil which impedes the availability of Mo.
Unlike other trace elements, molybdenum is unavailable in acidic soils. It is then strongly linked to
With increasing pH-value, molybdenum becomes mobile and its availability strongly increases.
Fresh organic matter ensures a good supply of Mo. This is obviously not the case for peat, which
develops under acidic conditions.
The graph shows the different forms of Mo depending on the pH-value in the soil. It clearly turns out
that the content of MoO 4 2- , the plant-assimilable form, strongly increases with higher pH-value.
Molybdenum is extracted specifically with oxalate. A soil analysis for Mo is not common but can be
done upon request.
Tableau de sensibilité
Echelle de sensibilité:
Apple & Pear
Tableau sensibilités & Symptômes
Symptoms of Mo deficiency are similar like symptoms of nitrogen deficiency in legumes. Since Mo is
necessary for the activity of nitrogenase and the fixation of N 2 , an N-deficiency can be observed.
On crucifers, interveinal chlorotic plaques appear on the leaves, with a greyish colour and a soft
consistency. In the most severe cases, the leaves of the plants are completely deformed.
Excès & Besoins
Excess molybdenum blocks copper and may induce deficiencies in cereals and fodder grasses.
Acidophilic crops, such as rubber, are sensitive to any excess of molybdenum.
The soil content varies greatly depending on the source rocks, the iron content and the level of
In general, assimilable Mo is higher in alkaline soils, soils rich in organic matter and young soils
derived from volcanic rocks, whereas soils rich in iron have low Mo contents.
Fertilizers contain Mo as sodium or ammonium molybdate.
Mo soil analyses are not routinely performed. However, a soil poor in Mo and rich in iron, induces a
deficiency for the demanding crops.
ORGANIC MATTER CONTENT:
A high organic matter content, may, in low pH, reduce the risk of deficiency. Regular inputs of
organic matter can provide soluble Mo for crops. Conversely, peat input creates a retention of Mo on
High temperature above 25° C increase Mo solubility in soils. Dry conditions, on the other hand,
cause deficiencies in Mo.
This is the most important factor for the absorption of Mo by plants. At high pH, Mo is very mobile.
INTERACTION WITH OTHER ELEMENTS:
Phosphorus facilitates the absorption and transport of molybdenum. This positive interaction is
found when Mo is combined with P.
High levels of iron contribute to limiting the assimilability of Mo.
An excess of copper as well as inputs of Cu decrease the absorption of Mo; an excess of manganese
shows the same effect.