5 Commonly used Micro-Nutrient Fertilizers

This article throws light upon the five commonly used micro-nutrient fertilizers that are taken up by plants. The micro-nutrient fertilizers are: 1. Sulphate 2. Oxy Sulphate 3. Oxide 4. Chelate 5. Manure.

Micro-Nutrient Fertilizer # 1. Sulphate (Salts):

The sulphate form of micro-nutrients 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.

Micro-Nutrient Fertilizer # 2. Oxy Sulphate:

An oxy-sulphate is an oxide of a micro-nutrient 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.

Water solubility of oxy-sulphates can vary greatly. It is generally accepted that a minimum of 50 per cent water solubility is required for the micro-nutrient to be a readily available nutrient source. In general, the higher the water solubility portion, the better. Residual value is similar to sulphates.

Micro-Nutrient Fertilizer # 3. Oxide:

Micro-nutrient 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. An oxide of a micro-nutrient needs to be converted to a plant available form in the soil before being taken up by the plant.

Oxides represent the final form to which other forms are eventually converted under soil conditions, and may then be slowly converted back to plant available form. For crop response during the growing season, plant available forms (water-soluble forms) of micronutrients need to be used. Pure oxide forms are less common and may be of residual value.

Micro-Nutrient Fertilizer # 4. Chelate:

Micro-nutrients such as Cu, Fe, Mn, and Zn are held within ring-type compounds. Chelated micro-nutrients remain in plant-available pool for a longer period because the chelated micro-nutrients exhibit very less interactions with soil components preventing various harmful reactions undergoing in soils.

Chelated form of micro-nutrients show greater mobility in soils compared to inorganic salts. There are a large number of chelating agents.

For example a synthetic chelating agent is EDTA, and a natural chelating agent is citric acid. Chelated micro-nutrient products are not all equally available to the plant. Chelated micro-nutrients can be soil or foliar applied.

Chelates are generally many times more expensive than the sulphate or oxide forms on a per pound actual micronutrient basis, but this is partly compensated for in the low recommended rate of chelate product needed to supply the micro-nutrient.

Chelated products applied at label rates have no residual value. Soil applied chelates at recommended rates only last for one year. Follow label rates and directions. Chelates are more commonly used now than in the past.

About 90-95% of soil applied inorganic form of Zn is rendered unavailable to the plants due to its harmful reactions with different soil components and hence chelated form of Zn (Zn-EDTA) is one of the most important sources which can increase the use efficiency of applied Zn with the simultaneous increase in yield of crops.

Micro-Nutrient Fertilizer # 5. Manure:

Livestock manure can be a source of micro-nutrients such as Cu and Zn, especially since these nutrients are often added to the feed rations. Repeated applications of manure have been shown to increase the content of available Cu and Zn.