SOIL-WATER CONTENT AND POTENTIAL MEASURED BY HOLLOW TIME-DOMAIN REFLECTOMETRY PROBE

A new soil probe used in conjunction with time domain reflectometry (TDR), tensiometry, and solution extraction devices and designed to allow simultaneous in situ measurement of soil-water content, matric potential, and solute concentration is proposed. Hollow stainless steel electrodes with a porous stainless steel tip serve as TDR wave guides in a standard two-parallel-probe configuration. The porous tip allows water inside the hollow rods to equilibrate with the soil water in an unsaturated or saturated system. A pressure transducer system is used to measure the soil matric potential around the porous tip. A vacuum pump can be used to withdraw soil solution through the permeable porous tip. A preliminary comparison between measurements of soil-water content obtained by a two-solid-wires TDR probe and the new probe gave encouraging results. Favorable agreement was obtained between measurements of the oil matric potential and depth to an artificial water table.