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Zinc Fertilizers

Five different types of zinc compounds, which are used as zinc micronutrient fertilizers are: (i) Inorganic compounds (ii) Synthetic chelates and (ii) Natural organic complexes (iv) Inorganic complexes, and

  • (v) Organic manures.
  • (i) Inorganic compounds : These include zinc sulphate, zinc oxide, zinc carbonate and zinc chloride. Zinc sulphate is the most commonly used source in the world as well as in India. It has added advantage of having sulfur as well (11% S). It exists both in crystalline form (zinc sulphate heptahydrate) and granular form (zinc sulphate monohydrate) both are water soluble. Monohydrate is less soluble and not as effective as the crystalline form. Zinc sulphate is usually used to supply needed amount of zinc when dry fertilizer materials are used. This material can be either broadcast or incorporated or used in a starter fertilizer. Zinc oxide is insoluble in water and available in either granular or powder form. The granular form is less effective whereas powder form is difficult to use.
  • (ii) Synthetic chelates : ZnEDTA is the most popular chelate and is regarded as the most effective source of zinc as a micronutrient. It is 2-5 times more effective than zinc sulphate but it is also 5-10 times costlier as well. Chelates are applied to the soils in solid form (usually banded) or in solution form for foliar spray.
  • (iii) Natural organic complexes : Reacting zinc salts with organic by products from paper and pulp industry usually derives these complexes. These organic compounds include lignosulphonates and polyflavo- noids. These complexes are less expensive than chelates but less effective too.
  • (iv) Inorganic complexes: Amongst inorganic complexes, ammoni- ated zinc sulphate solution is very popular. This complex is a source of nitrogen (10-15%), zinc (10%) and sulphur (5%). It is often combined with ammonium polyphosphate as a starter fertilizer. This complex being in liquid form is compatible with most of the liquid fertilizers. In all there are 17 sources of zinc available globally, which are used for different crops. Of late zinc compounds blended/incorporated with fertilizers are becoming popular as it saves labour in application.
  • (v) Organic manures : In addition to the above sources of zinc, organic manures like compost, farmyard manures, green manures or azolla are rich sources of micronutrients. Organic manures play important role in maintaining long term fertility of soils through improvement of physico chemical and biological properties.

Integrated effect of organic manures and micronutrients is far more than micronutrients alone. It is estimated that use of farmyard manures, poultry and piggery manures is capable of reducing zinc requirements by about 50%. If all conceivable forms of organic residues are appropriately recycled and used in agricultural lands it is projected to supply approximately 3.34 million tonnes of micronutrients in soil. Against this vast potential estimation made by Ministry of Agriculture shows that currently only about 90 thousands tonnes are being exploited. Biogas slurry has the potential to be used as a source of micronutrients. Press mud from sugar mills is also a good source of micronutrients. Presently it is being used as a source of either nitrogen or phosphorous. About 55,78,000 tonnes of press mud is available in the country.

Zinc fertilizers available in India

In India there are four zinc compounds, which serve as zinc fertilizers. The fifth source is zinc incorporated with urea and known as zincated urea. These are :

Source of zinc

Zinc content (%)

1. Zince Sulphate Heptahydrate

21

2. Zinc sulphate Monohydrate

33

3. Zinc EDTA

12

4. Zincated Phosphate Suspension (12.9% P2O2)

19.4

5. Zincated Urea

2

Zinc sulphate heptahydrate is the most commonly used zinc source in India and it has the advantage of containing sulphur as well. One of the major problems with zinc sulphate is its quality control and a lot of spurious material is sold in the market. The use of other zinc sources is on limited scale and these are made only in small quantities. Some fertilizer manufacturers are making zincated urea on experimental basis.

Conclusion

It is concluded that coating of prilled urea with 1.0% zinc oxide in neem oil emulsion may be sufficient to get higher productivity and increased Zn efficiency over prilled urea alone in aromatic rice wheat system.

 
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