Question

Harvest index is the ratio of ________________

• A. Economic yield/Biological yield
• B. Economic yield/Straw yield
• C. Straw yield/ biological yield
• D. Biological yield/Straw yield

Hint:

Remember the formula:
\[ \text{HI} = \frac{\text{Economic Yield (Grain)}}{\text{Biological Yield (Grain + Straw)}} \]
A higher harvest index indicates a more efficient crop variety.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
In crop physiology and agronomy, plants capture solar energy and assimilate carbon to produce biomass.
The partition of this total biomass into usable, harvestable components is measured by the Harvest Index (HI).
Key Formula or Approach:
The Harvest Index is calculated as:
\[ \text{Harvest Index (HI)} = \frac{\text{Economic Yield}}{\text{Biological Yield}} \times 100 \]
Where:
- Economic Yield is the weight of the useful, marketable portion of the crop (such as grains, tubers, or cotton lint).
- Biological Yield is the total above-ground dry biomass produced by the crop, which includes both the economic yield and the crop residue (such as straw, stover, or husk).

Step 2: Detailed Explanation:
The Harvest Index indicates a crop's efficiency in partitioning photosynthates into harvestable food components.
Modern high-yielding varieties (such as semi-dwarf wheat and rice developed during the Green Revolution) owe their high yields primarily to an improved harvest index.
These varieties partition more photosynthates into grains rather than tall straw, increasing the harvest index from about $0.3$ in traditional varieties to $0.5$ in modern semi-dwarf varieties.
The other options represent different relationships:
- Economic yield to straw yield is not a standard physiological index.
- Straw yield to biological yield is the residue fraction, which is the complement of the harvest index.
Therefore, the correct ratio is Economic yield to Biological yield.

Step 3: Final Answer:
Harvest index is the ratio of Economic yield to Biological yield.