Zinc Deficiency

Symptoms

Zinc deficiency symptoms vary between species but several effects can be generalized. Many species show yellowing of leaves, often with main leaf veins remaining green. In some species, young leaves are the most affected, but in others both old and new leaves show the symptoms. New leaves are often smaller and narrower and have wavy margins. Over time, the yellow (chlorotic) spots can turn a bronze color and dead (necrotic) spots may start to develop from the margins. In some crops, zinc-deficient leaves often have shortened internodes, so leaves are clustered on the stem (rosetting). Leaf deformation and reduced growth may occur, caused by restricted development of new leaves (dwarf leaves) and reduced internode length.

Hosts

Trigger

Zinc deficiency is mainly a problem in alkaline (high pH) sandy soils that are low in organic matter. High levels of soil phosphorus and calcium (calcareous soils) also affect the availability of zinc to plants. In fact, phosphorus application can show negative effects on zinc uptake. The addition of calcium-rich materials such as limestone or chalk (liming) also offsets soil acidity and reduces the uptake of zinc by the plants (even though the levels in the soil remain unchanged). Zinc deficiency can also become a problem when soils are cool and wet during the vegetative phase.

Organic Control

Application of organic manure to the seedbed or field a few days after transplanting helps to reduce the chance of zinc deficiency occurring.

Chemical Control

- Use a fertilizer containing zinc (Zn). - Example: Zinc sulphate (ZnSO4) is commonly used for foliar sprays. - Consult your agricultural advisor to know the best product and dosage for your soil and crop. Further recommendations: - It is recommended to do a soil test before the start of the cropping season to optimize your crop production. - Soil application of zinc should be done before sowing. - Seed coating with zinc can provide the nutrient to the crop.

Preventive Measures

• Apply organic manure before seeding or transplanting.
• Do not lime soils as this increases the pH and hinders zinc uptake.
• Choose varieties that are tolerant to zinc deficiency or better at mining zinc from the soil.
• Use fertilizers including zinc compounds.
• Use fertilizers based on urea (that generate acidity) rather than on ammonium sulfate.
• Make sure not to over-fertilize with phosphorus.
• Monitor the quality of the irrigation water regularly.
• Allow permanently flooded fields to drain and dry out periodically.