Question

The C:N ratio of the upper 15 cm of arable lands ranges from ........

• A. 8:1 to 15:1
• B. 20:1 to 30:1
• C. 30:1 to 40:1
• D. 50:1 to 60:1

Hint:

Soils with a balanced C:N ratio (8:1–15:1) ensure efficient decomposition and steady nitrogen supply.

Answer 1

The Correct Option is A

Step 1: Understanding C:N ratio.
The Carbon to Nitrogen (C:N) ratio is the proportion of organic carbon to total nitrogen in soils or organic matter.
It strongly influences decomposition, nutrient availability, and soil fertility.
Step 2: Typical values in soils.
- In arable soils, microorganisms require a balanced C:N ratio for decomposition.
- Too wide C:N ratio (above 30:1) leads to nitrogen immobilization.
- Too narrow C:N ratio (below 8:1) leads to rapid decomposition and nitrogen release.
- Ideal soil C:N ratio in cultivated lands is between 8:1 and 15:1.
Step 3: Analysis of options.
- (A) 8:1 to 15:1: Correct, typical of the upper 15 cm in cultivated lands.
- (B) 20:1 to 30:1: Too high, typical for undecomposed organic residues.
- (C) 30:1 to 40:1: Much wider, causing nitrogen immobilization.
- (D) 50:1 to 60:1: Extremely high, occurs only in fresh plant residues like straw.
Step 4: Conclusion.
Thus, the C:N ratio of upper 15 cm of arable lands usually ranges between 8:1 and 15:1.