Question

Four distinct growth stages are used to estimate crop evapotranspiration for which crop coefficients vary from one stage to another. In general the highest crop coefficient is at the stage :

• A. Initial or early stage
• B. Crop development stage
• C. Mid-season stage
• D. Late season or harvest stage

Hint:

The mid-season stage corresponds to the peak vegetative growth, flowering, and yield formation of the crop. This is when the plant transpires the most water, yielding the maximum $K_c$ value.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The crop coefficient ($K_c$) represents the ratio of crop evapotranspiration ($ET_c$) to reference crop evapotranspiration ($ET_0$).
Its value changes dynamically throughout the growing season based on canopy cover and crop growth stage.
Detailed Explanation:
Let us analyze the $K_c$ curve across the four growth stages:
- Initial or early stage (A): The crop is small, soil is mostly bare, and transpiration is minimal. $K_c$ is at its lowest level.
- Crop development stage (B): Canopy cover increases, and transpiration increases, causing $K_c$ to rise steadily.
- Mid-season stage (C): The crop reaches full effective canopy cover, flowering, and grain-filling. Water consumption and transpiration are at their peak. This is when the crop coefficient reaches its highest value ($K_{c,\text{mid}}$).
- Late season or harvest stage (D): Crop leaves begin to age and dry out (senescence), causing water requirements and $K_c$ to decline.

Step 2: Final Answer:
The highest crop coefficient occurs during the mid-season stage, matching Option (C).