Tensiometer Measures Soil Capillary Potential
A tensiometer is a scientific instrument used in agriculture and soil science to measure the soil capillary potential, also commonly referred to as matric potential or soil suction.
Understanding Tensiometer Function
- A tensiometer works by measuring the tension (negative pressure) with which water is held in the soil pores.
- It consists of a porous ceramic cup filled with water, connected via a tube to a vacuum gauge or manometer.
- As the soil dries, water is pulled out of the ceramic cup through capillary action, creating a vacuum inside the tensiometer, which is then measured.
- This measurement directly indicates the energy status of the soil water, specifically related to the forces of adhesion and cohesion acting within the soil matrix.
Why Capillary Potential?
- The capillary potential represents the potential energy of soil water due to the capillary forces that hold water in the soil pores against gravity.
- Tensiometers are designed to capture this matric potential, which is a major component of the overall soil water potential.
- Higher readings on the vacuum gauge (more negative pressure) indicate drier soil conditions where water is held more tightly by capillary forces.
Evaluating Other Options
- Soil permeability: This measures how easily water flows through the soil and is typically assessed using permeameters.
- Soil moisture content: This refers to the amount of water present in the soil, usually expressed as a percentage by weight or volume, measured by methods like gravimetric analysis or electronic moisture sensors.
- Osmotic suction: While related to water potential, osmotic suction specifically relates to the dissolved solutes in the soil water and is measured using different techniques, often important in saline conditions. Tensiometers primarily measure the matric component.
Therefore, a tensiometer is specifically used to measure the capillary potential of the soil.
Important Questions from Soil Moisture Measurement
- An undisturbed soil sample is collected from a field with core cylinder having an internal diameter of $60\text{ mm}$ and length of $100\text{ mm}$. The weights of moist soil and oven dried soil are $0.48\text{ kg}$ and $0.44\text{ kg}$, respectively. Assuming density of water as $1000\text{ kg.m}^{-3}$, the water depth (in metres per metre depth of soil) is ________
(Rounded off to two decimal places) - In-situ volumetric soil moisture content measuring method(s) is/are:
- The elevations of pressure gauge and porous cup of the tensiometer installed in unsaturated zone are 145.8 m and 144.2 m, respectively. Pressure measured at the gauge is $-19.62\times10^3$ $N$ $m^{-2}$. The specific weight of water is 9810 $N$ $m^{-3}$. The estimated pressure at the porous cup is ________ $N$ $m^{-2}$.
Undisturbed soil sample is collected from a field when the soil moisture is at field capacity. The inside diameter of the core sampler is 7.5 cm with a height of 15 cm. Weight of the core sampling cylinder with moist soil is 2.81 kg and that with oven dry soil is 2.61 kg. The weight of the core sampling cylinder is 1.56 kg. Assuming $\pi = 3.14$, the water depth in centimeter per meter depth of soil (rounded off to two decimal places) is__________.
- Match the following items between Column-I and Column-II with the most appropriate combinations:
Column-I Column-II 1) Neutron Probe P) Open channel flow 2) Pressure Plate Apparatus Q) Deep percolation 3) Tipping Bucket R) Aquifer parameters 4) Current Meter S) Soil moisture 5) Pumping Test T) Rainfall intensity 6) Lysimeter U) Soil-moisture characteristic curve
