Monitoring water and salt movement during a leaching irrigation using time domain reflectometry
Time domain reflectometry (TDR) has become an accepted method of measuring soil water content. Laboratory results have indicated that it may also be possible to measure soil electrical conductivity (EC) using TDR. The objectives of this experiment were to investigate the utility of TDR as a field measurement of EC and to illustrate a potential application of the technique. Field research was conducted at the Saskatchewan Irrigation Development Centre on a field which has been reclaimed from salinity over the past 10 years by the installation of tile drains and a fall leaching program. To test the accuracy of bulk soil EC measurements made by TDR (ECr), EC was also measured on water samples from suction lysimeters which sampled at the same depths as the TDR waveguides and converted to a bulk soil basis (EC8). Comparisons between ECT and EC8 were made three times during the 1992 growing season (when the soil was relatively dry) and four times during the fall leaching period (when the soil was much wetter). ECr was significantly correlated (p<0.001) to EC8. However, the measurement of ECT was affected by soil moisture content and an empirical function had to be used to eliminate this source of variability. Good agreement (R2=0.93) was obtained between ECT and EC8 when this function was applied. During the leaching irrigation, water and salt movement was monitored by TDR. At most sites, a salt bulge could be clearly identified moving downward through the profile as the volume of water applied increased. With further investigation into the relationship between ECT and water content, the rapid simultaneous measurement of water content and electrical conductivity made possible by TDR should prove useful in studies of salt movement.
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