Molybdenum
The nutrient crops need least of by weight and cannot do without — it runs nitrogen fixation in legumes and clears "whiptail" in cauliflower.
- Composition
- Mo ~54% (ammonium molybdate)
- Form
- White crystalline powder
- Price
- High, but a tiny dose per acre
- Best for
- Legume nodulation; cole-crop whiptail
Overview
Molybdenum is a trace micronutrient — plants need it in smaller amounts than any other nutrient — yet its two jobs are critical: it is essential for the nitrogen-fixing bacteria in legume nodules, and for the enzyme (nitrate reductase) that lets any crop use nitrate nitrogen. A shortage shows as poor nodulation and nitrogen-deficiency symptoms in pulses, and as the classic "whiptail" — narrow, strap-like, distorted leaves — in cauliflower and other cole crops.
It behaves opposite to most micronutrients: molybdenum becomes less available as soil turns acidic, so deficiency is worst on acidic soils, and simply liming an acidic soil to correct its pH often fixes the molybdenum problem too. When a direct dose is needed it is applied in tiny quantities as a seed treatment or foliar spray — ammonium molybdate (about 54% Mo) is the usual source.
What it is and when to reach for it
- A trace micronutrient for legumes and cole crops — reach for it when cauliflower shows "whiptail" or pulses nodulate poorly, especially on acidic soils.
- It is needed in extremely small amounts, so a little goes a very long way.
- It pairs naturally with Rhizobium on legumes, because molybdenum is what the nitrogen-fixing bacteria need to work.
How to use it well
- On acidic soils, correcting the pH with lime is often the simplest fix — it makes native molybdenum available again.
- Seed treatment: coat the seed with a very small measured quantity of ammonium molybdate (a few grams per kg of seed, per local recommendation) before sowing.
- Foliar: a dilute spray (around 0.1% ammonium molybdate) corrects a standing deficiency; keep the dose small and measured.
What it can and cannot do
- It corrects a genuine molybdenum shortage; on soils that are not deficient it does nothing useful, and because the requirement is so tiny, excess is easy and wasteful.
- Deficiency is a pH problem as much as a supply problem — on acidic soils, liming alone often solves it without a molybdenum product.
- Very high molybdenum in fodder can cause "molybdenosis" (a copper imbalance) in grazing livestock, so do not over-apply on forage crops.
Common mistakes
- Over-applying because the dose is small — the crop needs only a trace, and more is waste, not benefit.
- Adding molybdenum to an acidic soil without liming, when raising the pH would have released the soil’s own molybdenum.
- Confusing whiptail (molybdenum) with boron or nitrogen problems in cole crops and treating the wrong nutrient.
Organic alternative
Lime + FYM
On acidic soils, liming to correct pH (with regular FYM) frees the soil’s own molybdenum and is often the whole fix in an organic system.
Crops it is used on
Open a crop for its full nutrient schedule.
Common questions
What is "whiptail" in cauliflower?
Whiptail is the classic symptom of molybdenum deficiency in cauliflower and other cole crops: the leaf blade fails to develop properly, leaving narrow, strap-like, distorted leaves — sometimes little more than the midrib. It is most common on acidic soils and is corrected by liming and a small molybdenum dose.
Why does molybdenum deficiency happen on acidic soils?
Unlike most micronutrients, molybdenum becomes less available as the soil gets more acidic. So molybdenum deficiency is a problem of acidic soils, and raising the pH by liming often releases the soil’s own molybdenum and corrects the deficiency without a separate molybdenum product.
Which crops need molybdenum?
Legumes (pulses, groundnut, soybean) need it for nitrogen fixation in their root nodules, and cole crops like cauliflower and cabbage need it to avoid whiptail. The amounts required are tiny, so it is applied only where a deficiency is confirmed, usually as a seed treatment or dilute foliar spray.
Composition and doses follow ICAR / Soil Health Card guidance; prices are the notified subsidised rates for the season shown and are guidance, not a quote. A soil test for your field always beats a general rate. See our editorial policy.