A COST EFFECTIVE SOIL MOISTURE INSTRUMENT BASED ON TIME-DOMAIN TRANSMISSION MEASUREMENT

A cost effective soil moisture instrument based on time-domain transmission (TDT) measurement has been developed. A fast-rising pulse is applied to one end of the probe and the time of the pulse arriving at the other end of the probe is measured. The relationship between the one-way transmission time and volumetric soil water content has been established. This TDT technique doesn’t require acquisition of a graphic reflection waveform nor automatic interpretation of the waveform, therefore the circuit is simple compared to typical Time-Domain Reflectometry (TDR) instruments. A series of tests have been conducted in sandy, loamy, and clayey soils with different level of salinity. Results show that for soil consisting of less than 40% of clay and with electrical conductivity (saturated extract) less than 2 dS/m, the accuracy, resolution and repeatability of a TDT instrument is very comparable to TDR instrument performance.

Sun, Z.J.*, G.D. Young, R. A. McFarlane, B.M. Chambers
E.S.I. Environmental Sensors Inc.
Victoria, British Columbia, Canada.