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2. Recommendations for zinc application

Sources of zinc

The evaluation of the efficiency of various chemical substances such as zinc sulphate hepta
hydrate, zinc sulphate mono hydrate, zinc oxide, zinc dust, zinc carbonate, zinc chloride,
chelated zinc such as Zn-EDTA, zincated super, zincated urea and multi-micronutrient
mixtureshas been done in different soils and crops. Economically, the zinc fertilizer with low
cost should be applied for maximum benefit of the farmers. From the extensive research
works and tests carried out, it is found that zinc sulfate is the most suitable and cheapest
source for all the soils and crops.Although in problem soils, chelated zinc is found to be more
effective than zinc sulphate but it is very costly.Zinc sulphate hepta hydrate, mono hydrate
and chelated zinc proved equally effective in most soil-crop situations. Details of the major
zinc fertilizers and content of Zn in them are given in Table 4.

Table 4. Different sources of Zn and their Zn content

Source Zinc content (%)
Zinc sulphate mono hydrate 33.0
Zinc sulphate hepta hydrate 20.5
Chelated zinc (zinc-EDTA) 12.0
Zinc oxide 67-80
Zinc carbonate 65.0
Zicated super or zincated urea 2.0
Zinc chloride 45.0

Recommendations based on zinc availability in soil

In soil testing, the level of available zinc soil is classified into various categories such as
acute deficient, deficient, marginally deficient, marginally sufficient, adequate and high. The
descriptions of different recommendations using zinc fertilizers for various levels of available
zinc in soil is given in Table 5.

Table 5. Recommendations for application of zinc-containing fertilizers based on soil
Zn availability

Available zincin Zinc fertility class Recommendation for zinc application in
soil (mg/kg) crops
≤0.3 Acute deficient 7.5 kg zinc / ha for each cropping system
or
3.75 kg zinc / ha for each crop
>0.3 to ≤0.6 Deficient 5.0 kg zinc / ha for each cropping system in
alternate year
or
3.0 kg zinc / ha for each cropping system
>0.6 to ≤0.9 Latent deficient 5.0 kg zinc / ha for every third year of cropping