Advanced tensiometer for shallow or deep soil water potential measurements

Tensiometers are required for measuring soil-water potential at depths greater than several meters to quantify the direction and rate of soil-water movement. This paper describes a permanently installed tensiometer (advanced tensiometer) designed to measure soil-water potentials at any depth below land surface,This advanced tensiometer was designed with a removable pressure transducer to allow for field calibration and servicing and has two parts, a permanently installed outer tensiometer assembly and a removable transducer assembly. The permanently installed portion has a porous cup, an adapter containing a reservoir of water, and an outer guide pipe that extends to the land surface. The removable electronic pressure transducer assembly has a stopper on the bottom, a connector to attach the stopper to a pressure transducer, and an inner guide tube to raise and lower the assembly. The transducer assembly is lowered into the outer tensiometer assembly until the stopper connects and seals into the permanently installed adapter,This configuration of the advanced tensiometer allows it to be installed at any depth. Advanced tensiometers were operated with no maintenance at depths of 2 to 4.8 meters for periods of more than 3 months. The nearly constant temperature condition in boreholes provided stable, long-term water potential values and reduced field maintenance.