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Soil Water Flowmeters with Thermocouple Outputs¹

ABSTRACT

The construction and operation of two soil water flowmeters with microvolt outputs are described. One meter with a sensitivity of 0.1 mm of water flow per day is recommended for flux measurements in the surface meter of soil when the water matrix potential is greater than –0.8 bar. Calibration factors for three soils with different textures are presented as a family of curves. These curves may be interpolated for using the flowmeter in other soils, possibly without a loss of accuracy greater than the natural water flow variation from place to place in the field.

The second meter with a sensitivity of about 0.5 mm per day will require some additional development and testing before it can be recommended for routine use. It does offer the possibility of making measurements at soil water matric potentials less than –1 bar and at relatively deep soil depths.

The thermocouple flow transducer developed for the meters may be used to measure saturated soil water flow or other liquid flows as small as 1 ml/day.

¹ Contribution from the Snake River Conservation Research Center, ARS, USDA; Idaho Agr. Exp. Sta. cooperating. Presented before Div. S-1 and S-6 at the Soil Science Society of America, New York, Aug. 18, 1971.

² Soil Scientist, Kimberly, Idaho 83341.

Received for publication September 5, 1972. Accepted for publication November 29, 1972.