Tensiometer

A tensiometer is a device used to determine matric water potential $Psi\_m$ (soil moisture tension) in the vadose zone. The tensiometer consists of a glass or plastic tube with a porous ceramic cup, and is filled with water. The top of the tube has either a built-in vacuum gauge or a rubber cap used with a portable "puncture tensiometer" instrument, which uses a hypodermic needle to measure the pressure inside the tensiometer. The tensiometer is buried in the soil, and a hand pump is used to pull a partial vacuum. As water is pulled out of the soil by plants and evaporation, the vacuum inside the tube increases. As water is added to the soil, the vacuum inside the tube pulls moisture from the soil and decreases. The actual gauge reading will vary according to the type of soil, the moisture content, and due to hysteresis, according to the saturation history of the soil.

Tensiometers are used in irrigation scheduling to help farmers and other irrigation managers to determine when to water. In conjunction with a water retention curve, tensiometers can be used to determine how much to water. With practice, a tensiometer can be a useful tool for these purposes. Tensiometers can also be used in the scientific study of soils and plants.

References

* Rawls, W.J., Ahuja, L.R., Brakensiek, D.L., and Shirmohammadi, A. 1993. "Infiltration and soil water movement", in Maidment, D.R., Ed., Handbook of hydrology, New York, NY, USA, McGraw-Hill, p. 5.1–5.51.

ee also

*Capillary action
*Piezometer
*Surface tension

External links

* [http://www.experimental-hydrology.net/wiki/index.php?title=Soil_matric_potential_-_tensiometer_%28T4%29 The Experimental Hydrology Wiki Soil matric potential - tensiometer (T4)]
* [http://www.experimental-hydrology.net/wiki/index.php?title=Soil_matric_potential_-_tensiometer_%28T5%29 The Experimental Hydrology Wiki Soil matric potential - tensiometer (T5)]