Question

Which of the following statement(s) is/are true for tensiometer?
(A). It measures soil water potential.
(B). It is simple in operation and very useful for scheduling irrigation.
(C). It can also be used for measuring soil water flux.
(D). Although limited to $<$ 1 bar matric potential, this range can be increased by increasing the permeability of its porous cup.
Choose the correct answer from the options given below:

• A. (A), (B) and (C) only
• B. (A), (B) and (D) only
• C. (A) and (D) only
• D. (D) only

Hint:

The operating range of a standard tensiometer is strictly limited to 0 to 0.85 bar because air bubbles enter the tube or the water column cavitates at high tensions.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
A tensiometer is an instrument used to measure the energy state of soil water, specifically the matric potential (tension).
It consists of a water-filled tube with a vacuum gauge and a porous ceramic cup at the bottom.

Step 2: Detailed Explanation:
- Statement (A) is true because a tensiometer measures matric suction, which is a major component of total soil water potential in unsaturated soils.
- Statement (B) is true because it is a low-cost, user-friendly instrument widely implemented for irrigation scheduling in orchards and field crops.
- Statement (C) is true because by installing tensiometers at two adjacent depths, the hydraulic head gradient can be calculated.
This gradient can be used with Darcy's law to estimate soil water flux.
- Statement (D) is false because the physical limitation to $<$ 1 bar (typically ~0.85 bar) is due to water column cavitation.
Increasing cup permeability decreases the air-entry (bubbling) pressure, which actually reduces the measurement range.

Step 3: Final Answer:
Statements (A), (B), and (C) are correct.