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Measuring Soil Matric Potential in situ by Sensing Heat Dissipation within a Porous Body: II. Experimental Results¹

ABSTRACT

A sensor described previously to measure the matric potential of soil water in situ was tested in soil-plant systems. Experiments were performed in the laboratory in a controlled environment and in the field. In the field, temperatures obtained by the sensor were used to predict optimum time for measurement to avoid error caused by diurnal temperature drift in the soil. The error caused by temperature drift was eliminated completely by using two matched diode sensors and taking a temperature difference measurement.

The accuracy of the matric potential sensor proved to be as good as or better than that of other techniques used to measure matric potential. Sensors with high sensitivity in the 0 to –2 bar matric potential range had an accuracy of ±0.2 bar. The accuracy decreased progressively to ±1 bar at a matric potential of –10 bars.

¹ Contribution from the US Salinity Laboratory, SWC, ARS, USDA, P. O. Box 672, Riverside, Calif. 92502, and a part of the senior author's Ph.D. thesis, University of California, Riverside.

² Physicist, Research Soil Scientist (Physics), and Research Agricultural Engineer, respectively.

Received for publication September 14, 1970. Accepted for publication December 1, 1970.