Question

The combined loss of water from plants and soil surface is called

• A. Transpiration
• B. Evaporation
• C. Evapotranspiration
• D. Radiation

Hint:

Formula: $\text{Evapotranspiration (ET)} = \text{Evaporation (Soil)} + \text{Transpiration (Crop)}$.
- Only soil surface water loss = Evaporation.
- Only plant canopy water loss = Transpiration.
- Combined soil and crop water loss = Evapotranspiration.

Answer 1

The Correct Option is C

Concept:
In an agricultural ecosystem or cropped field, water is continuously lost to the atmosphere through both physical and biological pathways.
Solar radiation drives direct vaporization from the moist soil crust, while living crops lose water through their foliar surfaces.
Quantifying these simultaneous losses as a combined agro-meteorological parameter is fundamental to calculating crop water requirements and designing efficient irrigation systems.

Step 1: Understanding Individual Water Loss Pathways:
- Evaporation: The purely physical process wherein liquid water from wet soil surfaces, ponds, or mulches transitions directly into water vapor under solar radiation.
- Transpiration: The physiological process involving the vaporization and diffusion of water through the stomata, lenticels, and cuticular surfaces of living plant canopies into the ambient air.

Step 2: Defining the Combined Hydrological Term:
Because it is practically difficult to measure soil evaporation and crop transpiration separately in an open field, both processes are integrated into a single parameter.
The combined term for total water lost from the soil surface (evaporation) and the crop canopy (transpiration) is designated as Evapotranspiration (ET).

Step 3: Agronomic Relevance:
Reference evapotranspiration ($\text{ET}_0$) and crop coefficients ($K_c$) are standard values utilized globally to calculate actual crop water demand ($\text{ET}_c = K_c \times \text{ET}_0$).

Step 4: Final Answer:
Thus, the combined loss of water from plants and the soil surface is evapotranspiration, which corresponds to option (C).