Question

Most problems in rice cultivation are?
(A) Zinc deficiency and toxicity
(B) Iron deficiency and toxicity
(C) Boron deficiency and toxicity
(D) Sulphur deficiency and toxicity
Choose the correct answer from the options given below:

• A. (A) only.
• B. (B) and (D) only.
• C. (A), (B), (C) and (D).
• D. (C) and (D) only.

Hint:

Submerged soils promote reduced forms (causing Fe toxicity and Zn deficiency), while aerobic soils promote oxidized forms (causing Fe deficiency).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Rice is cultivated under highly diverse ecosystems, ranging from saturated, anaerobic wetland soils to aerobic, dry upland soils.
These varying water regimes dramatically influence chemical reduction and oxidation in the rhizosphere, altering the availability and toxicity of micronutrients.

Step 2: Detailed Explanation:
Let us analyze how each nutrient listed presents issues in rice cultivation:
1. Zinc (Zn): Zinc deficiency is the most widespread micronutrient disorder in wetland rice, causing "Khaira" disease. This is due to zinc precipitating as insoluble zinc sulfide (\(\text{ZnS}\)) or zinc carbonate under anaerobic flooded conditions. Conversely, over-application or industrial contamination can lead to toxicity.
2. Iron (Fe): In flooded acid-sulfate soils, the reduction of \(\text{Fe}^{3+}\) to highly soluble \(\text{Fe}^{2+}\) causes severe iron toxicity (bronzing of leaves). In contrast, under dry, aerobic upland conditions, iron is oxidized and becomes highly deficient, especially in alkaline/calcareous soils.
3. Boron (B): Boron deficiency is common in leached acidic soils, whereas boron toxicity is highly prevalent in coastal saline soils where rice is often grown.
4. Sulphur (S): Sulphur deficiency has become widespread due to the use of sulphur-free fertilizers (like Urea and DAP). Under prolonged submergence, excess hydrogen sulfide (\(\text{H}_2\text{S}\)) can also cause sulphide toxicity (Akiochi disease).
Since all four micronutrients present major deficiency or toxicity issues in various rice-growing soils globally, the most inclusive answer is the correct choice.

Step 3: Final Answer:
Therefore, the correct choice is (A), (B), (C) and (D).