|Gypsum Block Soil Suction Sensor|
Unlike the CS616 and TDR probes, the gypsum blocks measure soil water tension (or matric potential) rather than soil water content. This sensor consists of a pair of electrodes encased in a porous gypsum block. The resisitivity of the elctrodes is continuously logged and changes with respect to the amount of water penetrating the block, which in turn is determined by the matric potential (soil suction).
Gypsum blocks have a limited range (60-600 kPa) and only operate in relatively wet conditions (that are not often encountered in the Murrumbidgee). Furthermore, they have a limited life span before they break down and merge into the surrounding soil.