The force with which water is held in the soil by the soil particles, is referred to as soil suction, soil tension, or soil water potential. It indicates how tightly the water is bound in the soil, and how much energy must be exerted by plant roots to remove and use the water.
Jetfill tensiometers measure in the range 0-70 kPa. The tensiometer can measure very accurately small changes in soil water potential and because of the fast response these are immediate. The vacuum inside the tensiometer is measured by a vacuum transducer (ICTGT3-15), which gives a continuous analogue output signal. A resolution of 0.1 kPa is attained for this tensiometer transducer. Turf and vegetable crops are typically irrigated at 30kPa and cereal crops closer to 50 kPa.
The basic components of a tensiometer include a porous ceramic cup, a plastic body tube, water reservoir, and a vacuum transducer. The ceramic cup is placed in good hydraulic contact with the soil and allows transfer of water into and out of the tensiometer body according to the tension in the soil. The vacuum inside the tensiometer body equilibrates with the soil water tension, and there is direct response with a vacuum transducer.