Crop Micronutrient Supplementation

Most micronutrients influence growth. For example, manganese (Mn), iron (Fe) and copper (Cu) all influence photosynthesis, the process whereby plants use sunlight for growth.

Iron deficiencies are common – for example in seed fruits – where the effect is to reduce production of chlorophyll. As a result, crops struggle and younger leaves develop a severe yellowing or chlorosis.

Boron (B) is needed for the development of shoots and roots, and is essential during the flowering and fruiting phases of crops.

Zinc (Zn) is needed for the production of important plant hormones, like auxin. Zinc deficiency leads to structural defects in leaves and other plant organs.

Molybdenum (Mo) is involved in plant enzyme systems that control nitrogen metabolism.

Management tools to help with decision making

Make soil and plant tissue samples from affected and unaffected areas within the same field for a complete comparative analysis. This service is available from most soil testing laboratories. Call the laboratory for sampling details for a complete comparative test.

Keep good field records; know which fields have had previous problems with micronutrients; soil test annually; and, monitor each crop for symptoms. The amount of micronutrients needed varies by crop. Geo-reference micronutrient deficient areas within a field to make site-specific management easier. Micronutrients are expensive in comparison to macronutrients, so site-specific management makes economic sense.

Forms of micronutrient fertilizer

Sulphate (salts)

The sulphate form of micronutrients such as Cu, Zn, Fe and Mn represent a water-soluble form that is plant available. Borate is the equivalent plant available form for B. Sulphates are the most commonly used form for field crops. Sulphates can be applied to the soil or foliage. Sulphate products, applied at agronomically recommended rates, can provide long term residual value.


An oxysulphate is an oxide of a micronutrient that has been partially reacted with sulphuric acid. In the year of application, the oxide portion is not nearly as available as the sulphate portion. The amount of sulphate in the product varies by product.


Micronutrient elements (Cu, Zn, Fe, and Mn) bonded with oxygen form oxides. The bonds with oxygen are very strong, meaning these products are not soluble in water and are not in plant available form.


Micronutrients such as Cu, Fe, Mn, and Zn are held within ring-type compounds. Chelated micronutrients remain in plant-available form longer because the chelated structure slows the micronutrient reaction with soil minerals.


Livestock manure can be a source of micronutrients such as Cu and Zn, especially since these nutrients are often added to the feed rations.

Other forms

Carbonates and nitrates and mixtures with elemental forms are examples of other forms, but are seldom used.

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