As South African agriculture faces mounting pressure to increase yields, improve quality and remain globally competitive, attention is once again turning to a nutrient that rarely makes headlines but quietly determines performance, namely zinc. According to Simon Norton, Director of the International Zinc Association (Africa), zinc may not receive the same attention as nitrogen, phosphorus, and potassium, but its role in plant physiology makes it indispensable.
“Zinc is the trigger that makes the engine run,” comments Norton. “While NPK fertilisers provide the bulk nutrition, zinc is the micronutrient that activates the hormonal systems responsible for structural growth. Without it, crops simply cannot reach their genetic potential.” NPK fertilisers are compound fertilisers that contain the three primary macronutrients plants need in the largest quantities, namely nitrogen, phosphorus, and potassium.
Zinc plays a central role in the production of auxins, particularly indole-acetic acid (IAA), the hormone responsible for leaf development and internode elongation. When zinc levels are insufficient, crops exhibit stunted growth and distorted leaf formation.
In vegetables, this often appears as rosetting, where leaves are small, narrow, and bunched because the stem fails to elongate properly. In fruit trees such as citrus and apples, deficiency can result in ‘little leaf’ disease, reducing the tree’s photosynthetic capacity and directly affecting fruit size and overall yield.
Zinc deficiency is an economic issue
“In fruit production, reduced leaf surface area translates directly into reduced sugar production,” explains Norton. “That ultimately means smaller fruit, lower yields, and compromised market value. Zinc deficiency is not a cosmetic issue but an economic one.”
South Africa’s unique soil profile presents additional challenges. Many of the country’s soils are ancient and highly weathered, making zinc deficiency more common than many farmers realise. In alkaline soils, particularly those with a pH above 8.4, zinc becomes chemically locked and unavailable to plants.
Excessive phosphorus, whether naturally occurring or the result of over-fertilisation, can further inhibit zinc uptake, even when soil zinc levels appear adequate. Low organic matter in sandy soils compounds the problem, as these soils struggle to retain micronutrients, allowing zinc to leach away during irrigation or rainfall.
“Phosphorus-induced zinc deficiency is one of the most common mistakes in vegetable farming,” says Norton. “Producers may believe they are applying sufficient nutrients, but antagonistic interactions in the soil can block uptake. Understanding the chemistry is critical.”
Selecting the correct zinc formulation
Selecting the correct zinc formulation is therefore essential. Zinc sulphate remains widely used due to its high solubility and cost-effectiveness, particularly in acidic to neutral soils. However, in high-pH or problematic soils, synthetic chelates such as Zn-EDTA are often more effective, as the chelated structure protects the zinc ion from reacting with other soil minerals.
Increasingly, fertiliser manufacturers are also incorporating zinc into coated NPK granules to ensure consistent micronutrient delivery throughout the crop cycle. Timing and method of application are equally important. In perennial fruit trees, foliar application can be more effective than soil application because zinc moves slowly from roots to leaves.
Citrus crops benefit most from application during the spring flush, while apples and pears respond well at the green tip stage and again after petal fall. For vegetables such as tomatoes and maize, combining early soil application at planting with a foliar spray during the rapid growth phase typically delivers optimal results
“Strategic zinc management is not about adding more inputs,” stresses Norton. “It is about adding the right input, at the right time, in the right form. When managed correctly, zinc delivers measurable returns in crop uniformity, fruit size and overall productivity.” As climate variability, soil degradation and rising input costs continue to shape the agricultural landscape, micronutrient management is emerging as a critical lever for resilience and profitability.
“The future of South African agriculture will depend on efficiency,” concludes Norton. “Zinc is one of the most cost-effective interventions available to producers seeking to maximise both yield and quality. It is time we stop treating it as optional and start recognising it as foundational.”
