Efficacy of zinc oxides as fertilisers
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Background and aims
Human zinc (Zn) deficiency is prevalent in developing countries and Zn biofortification of grains is used to increase the Zn content of food staples. Agronomic interventions to biofortify grain involve fertiliser selection and management. The usefulness of a zinc compound as a fertiliser will depend on its solubility, bioavailability and the effect of its distribution in the soil profile.
Various sources of Zn oxide and Zn sulfate fertiliser were characterised for nutrient content, morphology, solubility, and fertiliser recovery when applied to the surface, banded near the seed or uniformly mixed.
Compared with Zn sulfates, Zn oxide fertilisers had very low water solubility and slow dissolution rates, because of a higher dissolution pH. This did not translate to a diminished ability to supply Zn to plants when both sources of Zn were mixed through the soil, but there was significantly less fertiliser recovery from Zn oxides than from Zn sulfates when the fertiliser was banded near the seed.
All sources will be equally effective if uniformly mixed through the profile. In no-till systems where fertiliser is banded near seed, Zn sulfate is superior to Zn oxide.
KeywordsFertiliser efficiency Isotopically exchangeable zinc Fertiliser dissolution Fertiliser solubility
Funding for this work was from the International Zinc Association. Thanks to Maria Manjarrez and Caroline Johnston for technical support and to the Department of Environment and Heritage for permission to undertake sampling for scientific purpose in the Ngarkat Group of Conservation Parks. Thanks to Fien Degryse, Rodrigo Coqui da Silva and Merv Probert for comments on earlier versions of the manuscript.
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