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Zinc – Choose the right source!


Recent seasons have yet again confirmed the high yield potential of the current maize cultivars. Possible yield constraints must be identified in the production process and rectified to avoid yield reductions. This led to involuntarily identifying Zinc as a nutrient.

Soil samples over the past thirty years have shown that zinc analyses has remained constantly low in soil and has declined in some cases. Work done in the sixties by Carel Koch at Losdoorns in the Wesselsbron district showed that the addition of zinc to fertilizer has some benefits.

The question is why there are zinc deficiencies and why there responses to the administration of zinc? In the NWOFS there is inherently low zinc in the soil. The whole of South Africa is classified as being “zinc-poor”.

Yields have increased in recent years and no provision is made for the additional zinc need.

Allegations that zinc can easily built up in the ground, is disallowed by soil analysis done, where zinc analyses as low as 0,6dpm are seen. There are few locations where built or adequate zinc levels occur. Because of built-phosphorus in the soil, zinc is less accessible, phosphate resources like MAP which are used in the manufacturing of blends can require zinc to be supplemented by less accessible sources such as zinc oxide.

This source of zinc is highly insoluble and although according to standards the mix has sufficient zinc, it is not available to the plant.

Looking at the role of zinc in the plant it shows that it is very important in the synthesis of carbohydrates and proteins involved in the plant as building blocks of the yield that will be achieved, natural disease resistance, photosynthesis, growth regulation and fertility. Plants differ in their susceptibility to zinc deficiency and maize is identified as one of the most sensitive.

Root distribution which has always been identified as a problem in many cases that cause a poor yield, are also negatively affected by poor accessibility and low zinc analyses. Poor root distribution due to soil preparation problems and compaction can cause the problem to worsen.

A fact emphasized by health circles is that the human diet has a shortfall of adequate zinc, leading to various diseases. Making sure that plants and animals receive sufficient zinc can solve this problem.

The problem with zinc deficiency can be summed up in low and inaccessible applications of zinc. This can also be subject to periodic dry conditions due to fluctuating rainfall. Zinc uptake can be further harmed by cold wet conditions occurring, especially in early planting and root development which is not yet sufficient.

Research done overseas, has shown an increases of up to 800% in the yield of maize while sorghum and potatoes show a 25% increase. Work done by Dr. Arrie van Vuuren on the influence of two zinc sources namely, zinc oxide and zinc sulphate on root mass showed that zinc sulphate gave the best results (See chart. Source: Zinchem manual addendum to Farmers Weekly, 17 Dec 2010). Observations over the past seasons have shown visually improved growth and development on maize plants when using zinc sulphate as zinc source rather than zinc oxide.


- Johann Jordaan -



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