Working range of tensiometer for determination of soil moisture is

Correct option is B

The correct answer is (B) 0 – 0.8 bar

Explanation:
• A tensiometer is a device used to measure the matric potential (tension) of soil water. It consists of a water-filled tube with a porous ceramic cup at the bottom and a vacuum gauge at the top.
• It works by allowing the water inside the tube to come into equilibrium with the soil water through the porous cup. As the soil dries, it pulls water out of the tube, creating a vacuum.
• The working range is limited to 0 to 0.8 or 0.85 bar. Beyond this point, air enters the ceramic cup (the "air entry value"), and the vacuum is broken, rendering the reading invalid.
• This range makes tensiometers ideal for sandy soils and for managing high-value crops where soil is kept relatively wet (near Field Capacity).

Information Booster:
• Field Capacity is usually at $0.33 bar$; thus, tensiometers cover the most critical range for plant growth.
• For drier soils (near Wilting Point at $15 bar$), other methods like Gypsum blocks or TDR (Time Domain Reflectometry) are used.
• Tensiometers are also known as Irrometers.

Additional Knowledge:
• 0-15 bar (Option A): Represents the entire range of available water, which no single physical suction-based instrument can measure continuously.
• Gypsum Blocks: Work best in the range of $1$ to $15 bar$, picking up where tensiometers leave off.