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Psychrometric Measurement of Soil Water Potential: Temperature and Bulk Density Effects¹

ABSTRACT

Changes in soil water potential with temperature were determined using thermocouple psychrometers on samples of four soils. Results indicate that change in soil water potential with temperature becomes greater as soils become drier. The finer textured soils showed a greater change in water potential with temperature than did coarser soils at similar water potentials.

Water potential change with bulk density also was determined for samples of three soils. Little change was noted except on a clay subsoil sample.

These results indicate that in most cases negligible differences will arise from measuring water potential at laboratory temperature rather than at the temperature existing in the field and from use of disturbed field samples with altered bulk density rather than undisturbed field soil. However, at water potentials below about –20 bars, temperature effects may become significant, especially in fine textured soils, and measurements on clay subsoils may be significantly affected by changes in bulk density.

¹ This investigation was supported, in part, by Western Regional Research Project W-68 and by the US Atomic Energy Comm. Project At (45-1)-1543, and is published as Scientific Paper no. 3459.

² Formerly Assistant Professor of Biophysics and Assistant Soil Scientist, now CPT. US Army Electronics Command. White Sands Missile Range, N.M., and Professor of Soils and Soil Scientist, Washington State Univ., Pullman.

Received for publication April 7, 1970. Accepted for publication July 17, 1970.