Question

Lysimeter measures

• A. Runoff
• B. Transpiration
• C. Potential evapotranspiration
• D. Actual evapotranspiration

Hint:

Weighing lysimeter = Direct standard measurement of Actual Evapotranspiration ($ET_a$). Pan evaporimeter = Potential Evaporation ($E_p$).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
A lysimeter is a precision field measuring tank device containing an undisturbed soil block with growing vegetation to directly measure the hydrological mass balance of the root zone.
Key Formula or Approach:
\[ \text{ET}_{\text{actual}} = P + I - R - D \pm \Delta S \]

Step 2: Detailed Explanation:
In a field lysimeter (weighing, drainage, or floating type):
Inputs (precipitation $P$, irrigation $I$) and outputs (deep drainage drainage percolation $D$, runoff $R$, and change in soil water storage $\Delta S$) are directly measured.
This provides the direct, in-situ quantitative measurement of Actual Evapotranspiration (\(\text{ET}_a\)) under real soil moisture and crop growing conditions.

Step 3: Final Answer:
Therefore, a lysimeter measures Actual evapotranspiration, corresponding to option (D).