A tensiometer is a device used to determine matric water potential (
soil moisturetension) in the vadose zone. The tensiometer consists of a glassor plastictube with a porous ceramiccup, and is filled with water. The top of the tube has either a built-in vacuum gaugeor a rubber cap used with a portable "puncture tensiometer" instrument, which uses a hypodermic needleto 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 schedulingto help farmers and other irrigationmanagers 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.
* 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.
* [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)]
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