Question

The following are statements on fertilizer N use efficiency of crops. Which statement or the combinations are true?
(A) Partial factor productivity does not account for soil N-supply
(B) Agronomic efficiency requires data on soil N supply
(C) For soil N supply, the N-balance index is useful
(D) Soil N supply does not vary across soil types
Choose the correct answer from the options given below:

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

Hint:

Soil physical and biological properties vary significantly across different soil classes.
Therefore, any statement claiming that "Soil N supply does not vary across soil types" is factually incorrect.
Excluding (D) immediately points to the correct option.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Nitrogen Use Efficiency (NUE) indices are used to evaluate how effectively crops utilize applied nitrogen fertilizers.
These indices help researchers optimize fertilizer rates by taking into account both the applied nutrients and the native nutrient-supplying capacity of the soil.

Step 2: Detailed Explanation:
Let us evaluate each of the statements:
- Statement (A): "Partial factor productivity does not account for soil N-supply."
Partial Factor Productivity (\(\text{PFP}\)) is calculated as:
\[ \text{PFP} = \frac{Y}{F} \]
where \(Y\) is the crop yield and \(F\) is the rate of applied fertilizer.
Since it does not include a control yield value (yield with zero fertilizer), it does not account for the native soil nitrogen supply.
Thus, Statement (A) is true.
- Statement (B): "Agronomic efficiency requires data on soil N supply."
Agronomic Efficiency (\(\text{AE}\)) is calculated as:
\[ \text{AE} = \frac{Y_f - Y_0}{F} \]
where \(Y_f\) is the fertilized plot yield and \(Y_0\) is the control plot yield (with no fertilizer applied).
Since the control yield \(Y_0\) reflects the soil's native nitrogen-supplying capacity, calculating agronomic efficiency requires measuring this value.
Thus, Statement (B) is true.
- Statement (C): "For soil N supply, the N-balance index is useful."
The Nitrogen Balance Index (NBI) is a non-destructive optical measurement index that compares the ratio of chlorophyll (reflecting nitrogen status) to polyphenols.
It serves as a reliable indicator of soil nitrogen supply and plant nitrogen status under field conditions.
Thus, Statement (C) is true.
- Statement (D): "Soil N supply does not vary across soil types."
This is completely false.
Native soil nitrogen supply varies significantly depending on soil texture, organic matter content, soil temperature, moisture levels, and microbial activity.
Therefore, only statements (A), (B), and (C) are true.

Step 3: Final Answer:
The true statements are (A), (B) and (C) only.