Question

Given below are two statements:
Statement I: Crop coefficient (Kc) values are important for estimation of crop water requirement and water requirement varies from crop to crop.
Statement II: The value of Kc increases with duration of the crops.
In light of the above statements, choose the correct answer from the options given below:

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Hint:

Remember the shape of the $K_c$ curve over time: it is always trapezoidal or bell-shaped. It starts low, rises to a peak at mid-season (flowering), and then drops at late-season (maturity/harvest).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The crop coefficient ($K_c$) is a dimensionless ratio used to estimate a crop's actual evapotranspiration ($ET_c$) relative to a reference crop evapotranspiration ($ET_0$):
\[ ET_c = K_c \times ET_0 \] The value of $K_c$ changes as the crop grows, reflecting changes in leaf area, plant physiology, and ground cover over the course of the season.

Step 2: Detailed Explanation:
Let us analyze both statements:
1. Statement I: Crop coefficient (Kc) values are important for estimation of crop water requirement and water requirement varies from crop to crop.
This statement is correct.
Different crops have different leaf structures, stomatal behaviors, rooting depths, and growth stages.
This means their water requirements vary significantly.
The crop coefficient ($K_c$) integrates these crop-specific characteristics, allowing engineers to calculate accurate crop water requirements from reference climate data ($ET_0$).
Therefore, Statement I is true.
2. Statement II: The value of Kc increases with duration of the crops.
This statement is incorrect.
The value of $K_c$ does not increase continuously throughout the crop's duration.
Instead, it follows a characteristic curve (the crop coefficient curve) over the growth stages:
- Initial Stage: $K_c$ is low (typically $0.15$ to $0.4$) because the ground is mostly bare soil.
- Development Stage: $K_c$ increases as leaf canopy and soil cover increase.
- Mid-Season Stage: $K_c$ reaches its maximum peak (often $1.0$ to $1.2$) when the crop reaches full maturity and flowering.
- Late-Season/Harvest Stage: $K_c$ decreases significantly (dropping to $0.3$ to $0.5$) as the leaves age, senesce, and dry out prior to harvest.
Since the $K_c$ value peaks and then declines rather than increasing steadily over time, Statement II is false.

Step 3: Final Answer:
Statement I is true, but Statement II is false because the crop coefficient ($K_c$) curve peaks at mid-season maturity and then declines toward harvest.
Hence, the correct option is (C).