Soil water tension can be monitored at given point in the active root zone by electrical resistant moisture blocks or tensiometers. Soil tension or suction is a measurement usually expressed in centibars, and describes how tightly water is held to the soil particles. The amount of soil water deficit for a given tension reading can be estimated by the use of Table 6 if the soil texture is known. Tensiometers directly read soil tension between 0 and 80 centibars, and work best in sandy loam or lighter textured soils. Resistance blocks, although slightly less accurate than tensiometers, work in a wider range of soil textures.
Some types are as accurate in coarser textured soils as tensiometers.
To obtain representative soil tension readings with any sensor type, it should be installed and left throughout the irrigation season, preferably at two or more locations in the field. Two depths are generally desired at each location. Soil water deficit estimates for different soil textures and selected tensions. The soil water depletion of each sample can be estimated by feeling the soil and comparing its appearance to data in Table 7. Soil samples should be taken from the top six inches to 12 inches in the root zone and at several locations in the field.