Zinc deficiency in crop plants

Role of Zinc in Plant Physiology

Zinc is involved in several critical plant functions:

• Enzyme Activation: Zinc is a cofactor for over 300 enzymes involved in carbohydrate, protein, and nucleic acid metabolism.
• Auxin Synthesis: It plays a vital role in the synthesis of auxin, a plant hormone regulating growth and development.
• Membrane Stability: Zinc contributes to maintaining the integrity of cell membranes.
• Protein Synthesis: It is essential for ribosomal protein function and protein synthesis.
• Chlorophyll Formation: Though not a constituent of chlorophyll, zinc is necessary for its synthesis.

Symptoms of Zinc Deficiency

The symptoms of zinc deficiency vary depending on the crop species and severity of the deficiency. Common symptoms include:

• Interveinal Chlorosis: Yellowing between the veins of younger leaves.
• Stunted Growth: Reduced plant height and overall growth.
• Small Leaves: Development of abnormally small leaves, often referred to as ‘rosetting’.
• Reduced Internode Length: Shortening of the distance between leaves on the stem.
• Mottled Leaves: Irregular patches of yellow and green on leaves.
• Dieback: Death of shoots and branches.

For example, in maize, zinc deficiency manifests as interveinal chlorosis on older leaves, while in fruit trees, it causes ‘little leaf’ disease, characterized by small, distorted leaves.

Causes of Zinc Deficiency

Several factors contribute to zinc deficiency in plants:

• Soil pH: High soil pH (alkaline soils) reduces zinc availability as it forms insoluble compounds.
• Soil Texture: Sandy soils have low zinc-holding capacity.
• Organic Matter Content: Low organic matter reduces zinc availability.
• Phosphorus Levels: High phosphorus levels in the soil can induce zinc deficiency by forming insoluble zinc phosphates.
• Antagonistic Interactions: High levels of iron and calcium can interfere with zinc uptake.
• Root Growth: Poor root development limits zinc absorption.

Management Strategies for Zinc Deficiency

Various methods can be employed to correct and prevent zinc deficiency:

• Soil Application: Applying zinc sulfate (ZnSO₄) to the soil is a common practice. The dosage depends on the soil type, crop, and severity of deficiency.
• Foliar Spray: Spraying zinc sulfate solution directly onto the leaves provides a quick and effective remedy, especially for acute deficiencies.
• Seed Treatment: Coating seeds with zinc compounds enhances zinc uptake during germination.
• Chelated Zinc: Using chelated zinc compounds (e.g., zinc-EDTA) increases zinc availability, particularly in alkaline soils.
• Organic Amendments: Incorporating organic matter improves soil health and zinc availability.
• Zinc-Enriched Fertilizers: Utilizing fertilizers fortified with zinc.

Zinc Biofortification: Developing crop varieties with enhanced zinc accumulation in edible parts is a sustainable long-term solution. For instance, the development of zinc-biofortified rice varieties has shown promising results in reducing zinc deficiency in populations relying heavily on rice as a staple food.

Method	Advantages	Disadvantages
Soil Application	Cost-effective, long-lasting	Slow response, potential for fixation
Foliar Spray	Rapid response, efficient	Temporary effect, requires repeated applications
Seed Treatment	Early zinc supply, improved germination	Limited effect on mature plant growth