By Gerrit Bezuidenhout
Zinc’s contribution to living systems is often underestimated. Worldwide, a lack of zinc in crops hampers yields and causes human health problems.
A zinc fertiliser helps with soil corrections and contributes to higher-quality crops, better yields, and food security. Since approximately 40% to 50% of South Africa’s agricultural soil is poor in zinc, paying attention to fertilisation with this trace element is essential.
Simon Norton, director of the International Zinc Association in Africa (IZA), emphasises that zinc is an essential micronutrient for crop growth and development. The IZA is an industry association exclusively focused on the interests of the zinc sector, operating both locally and internationally to highlight zinc’s significant role in plant production. “On the African continent, where nutrient-poor soil is a common challenge, zinc fertiliser is a powerful tool for boosting agricultural production and ensuring the sustainability of food systems,” Norton states.
Zinc deficiencies are a problem on every continent, particularly in Mexico, Brazil, India, parts of China, and Australia. The lack of zinc is one of the most common soil nutrient deficiencies globally, according to Prof. Ismail Cakmak of Sabanci University in Istanbul, Turkey, who spoke at a Fertasa symposium. “About a third of the world’s population is disadvantaged due to their diet, particularly grain foods, which contain too little zinc.”
Zinc deficiencies are widespread in children. Mortality rates among children, especially those under five, are often linked to this issue. This situation is particularly evident in countries where the soil lacks sufficient zinc and grains are the primary food source. Consequently, zinc fertilisation contributes to higher crop yields and the production of more nutritious food.
Efficient uptake
Raw materials such as zinc sulphate, which is the most common in South Africa, zinc oxide, and chelated zinc compounds are utilised to manufacture zinc fertiliser. These raw materials are sourced from mined zinc ore or recovered from by-products of industrial processes.
“The manufacturing process involves mixing zinc with supporting nutrients, after which the mixture is granulated. Finally, the product is dried and packaged,” says Norton. Fertiliser is purposefully designed to ensure that zinc transfer to the plant is as efficient as possible.
The granules are designed for even distribution and to enhance nutrient uptake. This ensures that plants receive the nutrients they require to thrive. Surfactants are employed to increase the solubility and stability of the active ingredient, ensuring that the zinc ion reaches the appropriate location in the soil to promote crop growth. Zinc fertiliser can be applied through various practices tailored to specific farming needs.
“The broadcast spreading of zinc fertiliser is ideal for large fields. It ensures even distribution and the limitation of nutrient losses,” says Norton.
“Band placement, where the zinc fertiliser is placed close to the plant roots, improves the availability of the fertiliser and reduces the amounts used to fertilise effectively.
“Foliar sprays are applied to quickly address zinc deficiencies in crops with visible symptoms.”
Zinc can also be included as a treatment for seeds before planting to ensure that the seedlings immediately have access to this essential nutrient.
Fertigation is another option, and zinc can be supplied through irrigation systems for precise control over fertilisation. According to Norton, each method has its advantages, and the choice of fertilisation depends on the crop, soil conditions, and the farmer’s goals. Zinc availability also plays a crucial role in plants’ ability to manage stress conditions successfully. “Healthy, zinc-rich crops are significantly more resistant to stress caused by drought and pests.”
Zinc influences, among other things, the photosynthetic pigment levels in plants, which are essential for efficient energy production. Research has shown that zinc application increases the chlorophyll content of crops, which in turn improves photosynthesis, especially under drought stress. It helps plants generate more energy, even when under stress.
Increased food quality
Zinc directly influences plants’ immune response against pathogens and pests.
It stimulates the production of protective properties; at higher concentrations, it can even be toxic to certain pests. “Plants that have sufficient zinc are therefore better equipped to resist infection and can respond more swiftly to attacks by pathogens,” he says.
“Zinc is a crucial micronutrient that not only promotes growth and development, but it also plays an important role in helping plants protect against various stress factors, such as drought, pathogens, and oxidative damage.”
Zinc’s contribution extends beyond crop protection and increased yields. It also helps to improve nutritional quality. “This is extremely important in Africa, where zinc deficiencies can directly impact human health. Eliminating zinc deficiencies has implications that extend beyond primary agriculture. Zinc is essential for human nutrition. Ensuring that our crops contain sufficient zinc levels contributes to healthier communities and addresses malnutrition and other growth restrictions,” says Norton.
How zinc benefits different crops
- Wheat, rice, and corn benefit from zinc’s role in grain filling and root development.
- Legumes, such as beans and lentils, achieve better nitrogen fixation, which results in higher seed quality.
- When zinc is applied, vegetables and fruits, from tomatoes to citrus, have better yield, quality, and disease resistance.
- Oil and tuber crops: zinc significantly enhances growth and resilience in sweet potatoes, potatoes, soybeans, and sunflowers.
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