Khaira Disease: A Major Deficiency Problem
Khaira disease, caused by zinc (Zn) deficiency, is a prevalent disorder in lowland rice, particularly in areas with high soil pH, prolonged flooding, and high organic matter content. It was first identified in northern India but is now widespread across Asia, representing a major hurdle for resource-poor farmers. The deficiency can lead to severe stunting and even plant mortality if not addressed in time.
Symptoms of Khaira Disease
Symptoms of Khaira disease typically appear within 2–3 weeks after transplanting and can be identified by a series of distinct signs:
- Stunted growth: The plant's overall height and tillering are significantly reduced.
- Leaf discoloration: Leaves, particularly older ones, develop a bronze tint that starts at the margins and spreads inward.
- Brown blotches and streaks: Small, dusty brown or reddish-brown spots appear on the leaves, which may merge to cover the entire leaf surface.
- Reduced tillering: In severe cases, the number of tillers per plant decreases or stops completely.
- High mortality: Intolerant seedlings can die within 5–7 weeks after transplanting under severe deficiency.
Causes of Zinc Deficiency
Several soil and environmental factors can lead to zinc deficiency in rice crops:
- High pH (>7.0): In calcareous soils with high alkalinity, zinc becomes less available for plant uptake.
- Prolonged submergence: Flooded rice paddies can have low redox potential, causing a reduction in zinc availability.
- High organic matter: Soils rich in organic matter can sometimes bind zinc, making it inaccessible to the plant.
- High bicarbonate content: High concentrations of bicarbonate in the soil solution can hinder zinc uptake.
- Phosphorus-induced deficiency: Large applications of phosphorus fertilizer can cause imbalances that induce zinc deficiency.
Other Significant Nutrient Deficiencies in Rice
While Khaira is a common issue, rice can suffer from a lack of many other essential macro- and micronutrients. These deficiencies also manifest as specific symptoms affecting growth and yield.
Nitrogen (N) Deficiency
Nitrogen is a key nutrient for vegetative growth. Its deficiency is one of the most common problems in rice cultivation and can cause entire fields to appear yellowish. Older leaves become light green or yellow first, with the discoloration spreading to the rest of the plant as the deficiency intensifies. Plants appear stunted, have fewer tillers, and mature early.
Phosphorus (P) Deficiency
Phosphorus is vital for energy transfer and root development. A lack of phosphorus results in severely stunted growth and narrow, short, and very erect leaves that are often a "dirty" dark green color. Some varieties may develop a reddish-purple color on older leaves or leaf sheaths. Poor root systems and reduced tillering are also common signs.
Potassium (K) Deficiency
Potassium is crucial for enzyme activation and water regulation. Its deficiency first appears on older leaves, which develop yellowish-brown margins and brown necrotic spots. In severe cases, leaf tips turn yellowish-brown and eventually die. Symptoms can lead to smaller leaves, weak stems, poor grain filling, and increased lodging.
Iron (Fe) Deficiency
Iron deficiency, or iron chlorosis, mainly affects emerging and young leaves, causing interveinal yellowing while the veins remain green. It is more common in alkaline or waterlogged soils. If severe, new leaves can become very pale and eventually die.
Comparison of Major Nutrient Deficiencies in Rice
| Nutrient | Leaf Symptoms | Growth Symptoms | Causal Factors | Key Management |
|---|---|---|---|---|
| Zinc (Zn) | Bronze or dusty brown spots on older leaves, yellowing | Stunted growth, reduced tillering, high mortality | High pH soils, prolonged flooding, high bicarbonate | Foliar spray or soil application of zinc sulfate |
| Nitrogen (N) | General pale green or yellowish-green color on older leaves | Stunted growth, fewer tillers, early maturity | Low soil organic matter, improper N fertilization timing | Timely and split applications of N fertilizer |
| Phosphorus (P) | “Dirty” dark green leaves, reddish-purple discoloration | Stunted growth, inhibited root development | Low soil P, high iron oxides in flooded soil | Apply P fertilizers, use P-efficient varieties |
| Potassium (K) | Yellowish-brown margins and necrotic spots on older leaves | Stunted plants, weak stems, poor grain filling | Low K supply in soil, unbalanced N and P fertilization | Apply K fertilizers based on soil test |
| Iron (Fe) | Interveinal yellowing (chlorosis) on young leaves | Stunted growth, poor root development | Alkaline soils, waterlogged conditions | Organic matter application, foliar spray of iron sulfate |
Management Strategies for Nutrient Deficiencies
Successful management of rice nutrient deficiencies involves both short-term fixes and long-term soil health improvement. Key strategies include:
- Soil and plant analysis: Regularly test soil and plant samples to accurately diagnose specific nutrient deficiencies before symptoms become severe.
- Fertilizer application: Apply the correct type and amount of fertilizers based on identified needs. For zinc deficiency (Khaira), foliar spraying with zinc sulfate can provide a quick remedy, while soil application offers a longer-term solution.
- Water management: For deficiencies like zinc and iron, managing water levels, including periodic drainage and drying of flooded fields, can increase nutrient availability.
- Cultivar selection: Choose rice varieties that are known to be more tolerant or efficient at absorbing specific nutrients from the soil, such as zinc-efficient varieties for Khaira-prone areas.
- Organic matter incorporation: Incorporating organic materials like crop residues and manure can improve soil structure and nutrient-supplying capacity over the long term.
- Balanced fertilization: Ensure that the application of different nutrients, especially nitrogen, phosphorus, and potassium, is balanced to prevent one from inducing the deficiency of another.
Conclusion
Understanding what is the deficiency disease in rice is crucial for global food security, given that rice is a staple food for billions. While Khaira disease (zinc deficiency) is particularly notorious in lowland rice systems, numerous other macronutrient and micronutrient deficiencies can drastically impact crop health and yield. By recognizing the specific symptoms associated with each deficiency, farmers and crop managers can implement targeted solutions, including appropriate soil amendments, balanced fertilization, and water management. Early and accurate diagnosis, often confirmed by soil or plant tissue analysis, is the most effective approach to mitigating the damage caused by these nutritional disorders and ensuring a healthy, high-yielding rice crop. For more information on managing nutrient issues, visit the IRRI Rice Knowledge Bank: Nitrogen (N) deficiency - IRRI Rice Knowledge Bank.
