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Published in Soil Sci Soc Am J 34:570-574 (1970)
© 1970 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Measurement of Water Potential and Osmotic Potential in Soil with a Combined Thermocouple Psychrometer and Salinity Sensor1

R. D. Ingvalson, J. D. Oster, S. L. Rawlins and G. J. Hoffman2

ABSTRACT

A combined thermocouple psychrometer and salinity sensor, which is embedded in a single ceramic body, is described. This design makes possible the measurement of the water and osmotic potentials of soil water at the same location in the soil. Errors produced by spatial variations in soil solution concentration, shown to be large, were eliminated by the instrument's ability to make both measurements on a single sample of soil solution. The instrument was tested in a soil-plant-water system, and the data obtained are reported. Desaturation of the ceramic at matric potentials more negative than –2 bars was shown to have a significant effect on conductance of the salinity sensor. Correction for this effect is discussed. Measurements showed that cotton plants extracted more water from the less saline zones in the soil. This had the effect of lowering the water potential to approximately the same value at two depths in the soil profile at the end of a drying cycle.

NOTES

1 Contribution from the U. S. Salinity Laboratory, Soil & Water Conservation Research Division, ARS, USDA, P. O. Box 672, Riverside, Calif. 92502.

2 Chemist, Research Soil Scientists, and Research Agricultural Engineer, respectively.

Received for publication January 12, 1970. Accepted for publication March 11, 1970.






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Copyright © 1970 by the Soil Science Society of America.