WATER REFERENCE

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REPRINTS, COPIES
Brown, R.W. 1970. Measurement of water potential with thermocouple psychrometers: construction and applications. USDA Forest Service Research Paper INT-80. Intermountain Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture, Ogden, Utah 84401

Abstract: Basic theory of water potential in the soil-plant-atmosphere continuum is considered, together with a review of the use of thermocouple psychrometers. The construction, methods of water potential measurement, and calibration of thermocouple psychrometers are discussed in detail. The effects of protective ceramic cups on the rate of water vapor exchange between the soil mass and the internal psychrometer cavity are compared with the effects of fine screen cups. The ceramic cup imposes a much greater resistance to vapor exchange than the screen cups; the mangitudes of possible errors resulting from this resistance in estimates of water potential are discussed. Possible uses of thermocouple psychrometers for measuring water potentials of soils and plants under intensive forest management practices are considered.
Contents:
Introduction

Theoretical Considerations
Components of Water Potential
Methods of Measuring Water Potential
Nonpsychrometric Methods
The Thermocouple Psychrometer MEthod
Improved Design Criteria for Thermocouple Psychrometers
Considerations of Instrument Design
Construction and Equipment
Calibration and Measurement Procedures
Psychrometer Response to Changing Water Potentials
Discucssion
Evaluation of Thermocouple Psychrometers

Literature Cited
Appendix

Updated: Thursday, September 6, 2007.

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