Tensiometers and irrometers
are used to monitor soil moisture for use in
hydrology studies. Monitoring soil moisture can
assist in watershed runoff studies and determining
optimum irrigation rates. Units are often left
installed as a permanent station, but some are
portable and can give readings within 3 minutes at
any location.
Tensiometers are the only
instruments that can directly measure "soil suction"
- the force that determines moisture flow. Each
instrument consists of a sealed water filled chamber
equipped with a special vacuum gage and a porous tip
that is installed in the ground at desired depths.
In dry soils, water is drawn out of the instrument
which creates a vacuum that registers on a gage.
Irrigation reverses this action, as water is drawn
back into the instrument.
