Question

Ideal C : N ratio of the mature compost is

• A. $<$20:1
• B. 35:1
• C. 60:1
• D. 100:1

Hint:

The C:N ratio of humus in the soil is typically around $10:1$ to $12:1$.
Finished compost should be as close to this range as possible.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the standard Carbon to Nitrogen (C:N) ratio that indicates a well-finished, stable compost ready for soil application.
Detailed Explanation:

• C:N Ratio Concept: In composting, carbon ($C$) is the energy source for microbes, and nitrogen ($N$) is needed for building proteins and cell components.

• Composting Process: Fresh organic matter often has a high ratio (e.g., $40:1$ to $80:1$). As microbes break it down, carbon is lost as $CO_2$, and the ratio gradually drops.

• Maturity Standards: A compost is considered "mature" and "stable" when the C:N ratio drops significantly. An ideal ratio for mature compost is generally accepted to be between 10:1 and 20:1.

• Importance: If the ratio is too high ($>$30:1), microbes will compete with plants for soil nitrogen when the compost is added (nitrogen immobilization). If it's too low ($<$10:1), nitrogen might be lost as ammonia.
Final Answer:
Based on the options, the most appropriate range for mature compost is $<20:1$. Thus, option (A) is correct.