Zinc Application in Wet Paddy Fields: Combating Khaira Disease to Secure 25% Higher Yields

Rice (*Oryza sativa*) is the primary staple food for over half the world's population. In submerged, flooded paddy fields, zinc deficiency is the single most widespread and yield-limiting nutritional constraint, responsible for the devastating physiological disorder known as Khaira Disease.

1. Why Flooded Paddy Soils Suffer Severe Zinc Lock-Up

When a paddy field is submerged under water, anaerobic microbial respiration triggers radical chemical shifts in soil solution:

• •pH Neutralization: Acid soils increase in pH while alkaline soils decrease toward neutrality.

• •Formation of Insoluble Zinc Compounds: Free zinc ions (Zn2+) react with soluble carbonates, iron oxides, and sulphides to form insoluble zinc carbonate (ZnCO3) and zinc sulphide (ZnS), rendering native soil zinc unavailable to rice roots.

2. Identifying Khaira Disease Symptoms

Khaira disease manifests 14 to 21 days after transplanting young seedlings:

• •Symptom 1: Lower leaves develop small, rusty-brown, irregular spots that coalesce into uniform reddish-bronze pigmentation.

• •Symptom 2: Root growth ceases, root tips turn blackish-brown, and tillering is severely suppressed.

• •Symptom 3: Affected patches in the field appear stunted and unthrifty, resembling an apparent disease outbreak.

3. Recommended Fertilizer Schedule for Maximum Tiller Count

• •Basal Puddling Application: Broadcast 10 kg per acre of Zinc Sulphate Monohydrate 33% or 15 kg per acre of Zinc Sulphate Heptahydrate 21% during the final puddling stage just before transplanting.

• •Foliar Rescue Application: If Khaira symptoms emerge post-transplanting, dissolve 5 kg of Zinc Sulphate 33% + 2.5 kg of agricultural lime in 500 liters of water per hectare. Spray twice at a 7-day interval.