ABSTRACT
Like a tensiometer, the granular matrix sensor (GMS) is an instrument for measuring soil water potential.[1]
The GMS eliminates regular maintenance required by tensiometers. Granular matrix sensor technology reduces the problems inherent in gypsum blocks (slow response time and dissolution of the block) by using a mostly insoluble granular fill material held in a fabric tube supported in a metal or plastic screen.[2,3] Like gypsum blocks, GMS sensors operate on the principle of variable electrical resistance. The electrodes inside the GMS are embedded in the granular fill material above a gypsum wafer, with additional granular matrix below the wafer in the fabric tube where water enters and exits the sensor. The gypsum wafer slowly dissolves to buffer the effect of salinity of the soil solution on electrical resistance between the electrodes. Particle size of the granular fill material and its compression determine the pore size distribution in the GMS and its response characteristics.[2]
OVERVIEW
Granular matrix sensors have been calibrated in the field in the range of 10 kPa down to 75 kPa for the irrigation of water stress-sensitive plants.[1]
Calibrations have varied depending on the sensor model, soil, and other experimental conditions.[1,4-6]
These sensors are most useful on soils that maintain intimate hydraulic contact with the sensor and are usually least useful on coarse textured soils.
