257-L

The 257 determines soil water potential by measuring electrical resistance. When the 257 is wet, electrical resistance is low. As the 257 dries, resistance increases.

The 257 consists of two concentric electrodes embedded in a reference matrix material. The matrix material is surrounded by a synthetic membrane for protection against deterioration. An internal gypsum tablet buffers against the salinity levels found in irrigated soils.

The 257's construction can allow the sensor (in some circumstances) to be left in the soil all year, eliminating the need to remove the sensor during fallow periods.