Question

[(Grain yield Biological yield) x 100] =

• A. Harvest Index (HI)
• B. Relative Growth Rate (RGR)
• C. Crop Growth Rate (CGR)
• D. Net Assimilation Rate (NAR)

Hint:

Remember:
Biological Yield = Total dry matter produced (Straw + Grain).
Economic Yield = Harvested useful part (Grain).
Harvest Index (HI) tells us how efficiently the plant converted its vegetative mass into harvestable yield.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Crop yield is determined by two main factors: the total dry matter produced by the crop canopy (biological yield) and the proportion of that dry matter partitioned into the harvested organs, such as grain or fruit (economic yield).
Key Formula or Approach:
The efficiency of carbon partitioning into the harvested economic sink is quantified by the Harvest Index (HI):
\[ \text{Harvest Index (HI)} = \left( \frac{\text{Economic Yield (Grain Yield)}}{\text{Biological Yield}} \right) \times 100 \]

Step 2: Detailed Explanation:
Let us evaluate each of the options:
1. Harvest Index (HI) (A): First introduced by Donald in 1962, the Harvest Index is the ratio of economic yield (such as grain yield) to total biological yield (total shoot dry matter, including leaves, stems, and grains).
It is expressed as a percentage.
Modern breeding programs (such as the Green Revolution) dramatically increased crop yields not by increasing total biological yield, but by improving the harvest index (e.g., from \( 30\% \) to over \( 50\% \)) using semi-dwarf cultivars that partition more carbon to the grains.
2. Relative Growth Rate (RGR) (B): RGR is the increase in dry mass per unit of pre-existing dry mass per unit of time.
3. Crop Growth Rate (CGR) (C): CGR is the gain in plant dry mass per unit of ground area per unit of time.
4. Net Assimilation Rate (NAR) (D): NAR represents the net increase in dry mass per unit of leaf area per unit of time, serving as a measure of average photosynthetic efficiency.

Step 3: Final Answer:
The ratio of grain yield to biological yield multiplied by 100 represents the Harvest Index, corresponding to option (A).