Accuracy of soil thermocouple hygrometer measurements in desert ecosystems

TitleAccuracy of soil thermocouple hygrometer measurements in desert ecosystems
Publication TypeJournal Article
Year of Publication1987
AuthorsFonteyn P.J, Schlesinger W.H, Marion G.M
Date Published1987
Accession NumberJRN00050
Call Number00067
Keywordsarticle, articles, Gutierrezia,xylem sap potential, hygrometer, soil thermocouple, journal, journals, Larrea,xylem sap potential, soil water potential,technique, soil, thermocouple hygrometer, technique,soil thermocouple hygrometer, thermocouple, accuracy

The use of thermocouples in studies of soil and plant water relations began in the 1950's (Spanner 1951, Monteith and Owen 1958, Richards and Ogata 1958, Savage and Cass 1984). Initially, thermocouples were used only in laboratory studies because precise temperature control was thought to be essential for accurate measurements (Kramer 1972). Field applications began after Rawlins and Dalton (1967) and Wiebe et al. (1970) demonstrated that certain corrections eliminated the need for precise control. With the advent of commercial availability, thermocouples have been widely used by plant ecologists (see Turner and Kramer 1980 for examples). Despite their extensive use, many investigators are distrustful of data obtained with soil thermocouples. The prevelence of this distrust, although not expressed in the literature, is commonly expressed in discussions among scientists who have had field experience with thermocouples. We compared soil water potential data obtained with soil thermocouples to measurements ofpredawn xylem sap potential of desert shrubs (Scholander et al. 1965, Waring and Cleary 1967). The null hypothesis tested was that predawn xylem sap potentials would not differ significantly from soil water potential values measured with soil thermocouples in the dew point mode (hygrometers), because xylem sap potentials at that time are in equilibrium with rhizosphere water potential (Ritchie and Hinkley 1975).