How Does Molybdenum Function in Plants?

Plants require the element Nitrogen (as a nutrient). In non-leguminous plants such as cauliflower, tomato, lettuce, and corn, molybdenum helps initiate a series of chemical reactions, enabling the plants to use the nitrogen absorbed from the soil.

In cases of Molybdenum deficiency, nitrates accumulate in the plant's leaves. Since these accumulated nitrates cannot be used for protein synthesis, it causes the leaves to turn yellow. This is because the unused nitrates cause the leaf tips to burn. We can also observe stunting of the plant due to the resulting nitrogen deficiency.

Yellowing of leaves is particularly common in indoor plants. The reason for this yellowing is often molybdenum deficiency. To correct this, fertilizers containing Sodium Molybdate or Ammonium Molybdate should be used.

It serves two purposes in legumes. The first is to help break down the nitrate absorbed from the soil. The second is to aid in the fixation of atmospheric nitrogen by root nodule bacteria.

How is Molybdenum Deficiency Detected?

Cauliflower is the key indicator plant for definitively diagnosing Molybdenum deficiency. Otherwise, identifying molybdenum deficiency is not a straightforward task. The first step in detection is to observe the plant's roots and leaves. However, it is not always correct to definitively conclude that these symptoms are caused solely by molybdenum deficiency.

For this reason, when solutions containing Sodium Molybdate and Ammonium Molybdate are applied to the plants, if a change is observed in the leaves and roots, we can determine the cause. That is, if the plant begins to produce healthy green leaves, it confirms that the molybdenum deficiency has been remedied.

Additionally, the occurrence of 'whiptail' in cauliflowers in the same area should be considered a strong indicator that the plants have a high need for molybdenum.

Molybdenum deficiency may be observed less frequently when farmyard manure is used. Additionally, a patchy or irregular distribution of symptoms among the plants can also be an indicator of molybdenum deficiency.

What is the Correct Molybdenum Dosage?

When using Sodium Molybdate and Ammonium Molybdate as a molybdenum source, the recommended application rate varies from 75 g to 1 kg/ha, depending on the crop and molybdenum requirement.

For alfalfa, Ammonium Molybdate or Sodium Molybdate can be mixed with superphosphate at a rate of 75 g/ha.

For vegetable crops, solutions of Ammonium Molybdate or Sodium Molybdate are applied at a dosage of 1 kg/ha.

For crops such as cauliflower, broccoli, cabbage, and tomatoes, application is made to the seedbeds where the seeds are sown. A solution of Ammonium Molybdate and Sodium Molybdate, dissolved in 40 L of water at 40 °C, is applied per 10m2 of seedbed.

What Problems Are Caused by High Molybdenum Levels in Plants?

While molybdenum deficiency causes slowed growth and leaf yellowing, high concentrations of molybdenum can also be toxic to plants. Molybdenum toxicity can lead to issues such as chlorosis, jaundice, and deformities in the leaves, endangering the plant's health.

Phosphate applications can be used to alleviate such problems.

Example Formulation for a Molybdenum Source

Sodium molybdate and ammonium molybdate are preferred sources. Molybdenum fertilizers typically contain 10-50% molybdenum. These fertilizers can be applied to the soil or as a foliar spray. Molybdenum fertilizer can be applied before sowing or during the growing season.