Question

Which of the following is not a method of measuring crop evapotranspiration?

• A. Rational method
• B. Lysimeter method
• C. Field water balance method
• D. Climatological method

Hint:

Remember: \[ \boxed{ \text{Rational Method} \rightarrow \text{Runoff Estimation} } \] \[ \boxed{ \text{Lysimeter / Water Balance / Climatological Methods} \rightarrow \text{Evapotranspiration Estimation} } \]

Answer 1

The Correct Option is A

Concept: Crop evapotranspiration can be estimated or measured using several hydrological and climatological methods. Common methods include:
• Lysimeter method
• Soil moisture depletion method
• Field water balance method
• Climatological method The Rational method is unrelated to evapotranspiration and is mainly used for peak runoff estimation.

Step 1: Understanding the Rational Method. The Rational method is used in hydrology for:
• Estimation of peak runoff
• Storm drainage design
• Small watershed analysis Its basic formula is: \[ Q = CIA \] where:
• \(Q\) = peak runoff
• \(C\) = runoff coefficient
• \(I\) = rainfall intensity
• \(A\) = drainage area Thus it is not related to evapotranspiration measurement. Hence: \[ \boxed{ \text{Rational method is not an ET measurement method} } \]

Step 2: Understanding Lysimeter Method. A lysimeter directly measures:
• Water added
• Water drained
• Change in soil moisture This method accurately estimates evapotranspiration. Thus: \[ \boxed{ \text{Lysimeter method is an ET measurement method} } \]

Step 3: Understanding Field Water Balance Method. This method uses conservation of mass: \[ ET = I + P - R - D \pm \Delta S \] where:
• \(I\) = irrigation
• \(P\) = precipitation
• \(R\) = runoff
• \(D\) = deep percolation
• \(\Delta S\) = change in storage Therefore it is an evapotranspiration estimation method.

Step 4: Understanding Climatological Method. This method uses climatic parameters such as:
• Temperature
• Humidity
• Wind speed
• Solar radiation Examples:
• Penman method
• Blaney-Criddle method Hence it is also an ET estimation method.

Step 5: Checking all options carefully. Option (A): Not used for evapotranspiration. \[ \boxed{ \text{Option (A) is correct} } \] Option (B): Used for ET measurement. \[ \boxed{ \text{Option (B) is incorrect} } \] Option (C): Used for ET estimation. \[ \boxed{ \text{Option (C) is incorrect} } \] Option (D): Used for ET estimation. \[ \boxed{ \text{Option (D) is incorrect} } \] Final Conclusion: The Rational method is not used for measuring crop evapotranspiration. Hence the correct answer is: \[ \boxed{ (A) } \]