Review. Use of psychrometers in field measurements of plant material: accuracy and handling difficulties

  • E. M. Martinez Departamento de Ingeniería Agroforestal. Universidad de Santiago de Compostela. Lugo
  • J. J. Cancela Departamento de Ingeniería Agroforestal. Universidad de Santiago de Compostela. Lugo
  • T. S. Cuesta Departamento de Ingeniería Agroforestal. Universidad de Santiago de Compostela. Lugo
  • X. X. Neira Departamento de Ingeniería Agroforestal. Universidad de Santiago de Compostela. Lugo
Keywords: hygrometric technique, irrigation, isopiestic technique, pressure chamber, psychrometric technique


The determination of leaf water potential is useful in the establishment of irrigation guidelines for agricultural crop management practices and requires the use of various methods, among which thermocouple psychrometers (TCP). TCP have been widely used for this purpose. However, the psychrometric technique is complex and difficult to understand and the instrumentation required is difficult to handle. For this reason, a profound knowledge of the different aspects involved in the technique —which have not been clearly explained in the literature— is required. This paper reviews a number of research areas of TCP and focuses on three very specific fields: a) main applications of phsychrometry in field studies; b) determination of the measurement accuracy of psychrometric equipment, accuracy per se and accuracy tested against alternative methods; c) main errors and handling difficulties of TCP in the field. Research in these areas provides an updated overview of TCP as a method for determining water relations in plant material that will contribute criteria to select the most suitable technique according to the type of plant material and the purpose of the research and will highlight the types of instruments, accuracies and errors that have detrimental effects on measurements.


Download data is not yet available.


Andraski B.J., Scanlon B.R., 2002. Thermocouple Psychrometry. In: Methods of soil analysis. Part 4. Physical Methods (Dane J.H.,Topp G.C., eds). Soil Sci Soc of Am, Madison, Wis, USA. pp. 609-642.

Auge R.M., Duan X., Croker J.L., Witte W.T., Green C.D., 1998. Foliar dehydration tolerance of twelve deciduous tree species. J Exp Bot 49, 753-759.

Ball R.A., Oosterhuis D.M., 2005. Measurement of root and leaf osmotic potential using the pressure-pressure osmometer. Environ Exp Bot 53, 77-84.

Barrs H.D., 1964. Heat of respiration as a possible cause of error in the estimation by psychrometric methods of water potential in plant tissue. Nature 203, 1136-1137.

Barrs H.D., 1965. Psychrometric measurement of leaf water potential: lack of error attributable to leaf permeability. Science 149, 63-65. PMid:17737791

Barrs H.D., 1968. Determination of water def icits in plant tissues. In: Water deficits and plant growth. Vol. I (Kozlowski T.T., ed). Academic Press, New York, USA. pp. 235-368.

Barrs H.D., Kramer P.J., 1969. Water potential increase in sliced leaf tissue as a cause of error in vapour phase determinations of water potential. Plant Physiol 44, 959-964. PMid:16657164 PMCid:396197

Baughn J.W., Tanner C.B., 1976a. Leaf water potential: comparison of pressure chamber and in situ hygrometer on five herbaceous species. Crop Sci 16, 181-184.

Baughn J.W., Tanner C.B., 1976b. Excision effects on leaf water potential of five herbaceous species. Crop Sci 16, 184-190.

Bennett J.M., Cortes P.M., 1985. Errors in measuring water potentials of small samples resulting from water adsorption by thermocouple psychrometer chambers. Plant Physiol 79, 184-188. PMid:16664367 PMCid:1074848

Bennett J.M., Cortes P.M., Lorens G.F., 1986. Comparison of water potential components measured with a thermocouple psychrometer and a pressure chamber and the effects of starch hydrolysis. Agron J 78, 239-244.

Bingham G.E., Johnson M.N., Lemon E.R., 1972. Influence of heat sink design on thermocouple psychrometer response. In: Psychrometry in water relations research. Proceedings of the Symposium on Thermocouple Psychrometers (Brown R.W., Van Haveren B.P., eds). Utah Agric Exp Stn Utah State Univ, Logan, USA. pp. 88-93.

Bower J.P., 1985. Some aspects of water relations on avocado Persea americana (Mill.) tree and fruit physiology. Doctoral thesis. University of Natal, Faculty of Agriculture, Pietermaritzburg.

Boyer J.S., 1966. Isopiestic technique: measurements of accurate leaf water potentials. Science 154, 1459-1460. PMid:17821568

Boyer J.S., 1967. Leaf water potentials measured with a pressure chamber. Plant Physiol 42, 133-137. PMid:16656476 PMCid:1086499

Boyer J.S., 1969. Measurement of the water status of plants. Ann Rev Plant Physiol 20, 351-364.

Boyer J.S., 1972a. Use of isopiestic technique in thermocouple psychrometry. I. Theory. In: Psychrometry in water relations research. Proceedings of the Symposium on Thermocouple Psychrometers (Brown R.W., Van Haveren B.P., eds). Utah Agric Exp Stn Utah State Univ, Logan, USA. pp. 51-55.

Boyer J.S., 1972b. Use of isopiestic technique in thermocouple psychrometry. II. Construction. In: Psychrometry in water relations research. Proceedings of the Symposium on Thermocouple Psychrometers (Brown R.W., Van Haveren B.P., eds). Utah Agric Exp Stn Utah State Univ, Logan, USA. pp. 98-102.

Boyer J.S., 1972c. Use of isopiestic technique in thermocouple psychrometry. III. Application to plants. In: Psychrometry in water relations research. Proceedings of the Symposium on Thermocouple Psychrometers (Brown R.W., Van Haveren B.P., eds). Utah Agric Exp Stn Utah State Univ, Logan, USA. pp. 220-223.

Boyer J.S., 1995. Measuring the water status of plants and soil. Academic Press Inc, USA. 495 pp.

Boyer J.S., Potter J.R., 1973. Chloroplast response to low leaf water potentials. Plant Physiol 51, 989-992. PMid:16658486 PMCid:366389

Boyer J.S., Cavalieri A.J., Schulze E.D., 1985. Control of the rate of cell enlargement: excision, wall rela-xation, and growth-induced water potentials. Planta 1163, 527-543.

Brown P.W., Tanner C.B., 1981. Alfalfa water potential measurement: a comparison of the pressure chamber and leaf dew-point hygrometers. Crop Sci 21, 240-244.

Brown R.W., 1969. Leaf sampler for relative water content measurements: design and application. Agron J 61, 644-647.

Brown R.W., Mcdonough W.T., 1977. Thermocouple psychrometer for in situ leaf water potential determinations. Plant Soil 48, 5-10.

Brown R.W., Oosterhuis D.M., 1992. Review and interpretation. Measuring plant and soil water potentials with thermocouple psychrometers: some concerns. Agron J 84, 78-86.

Brown R.W., Van Haveren B.P., 1972. Psychrometry in water relations research. Proceedings of the Symposium on Thermocouple Psychrometers (Brown R.W., Van Haveren B.P, eds). Utah Agric Exp Stn Utah State Univ, Logan, USA. 342 pp.

Brunini O., Thurtell G.W., 1982. An improved thermocouple hygrometer for in situ measurements of soil water potential. Soil Sci Soc Am J 46, 900-904.

Busso C.A., 2008. Uso de la cámara de presión y los psicrómetros a termocupla en la determinación de las relaciones hídricas en tejidos vegetales. Rev Internacional de Botanica Experimental 77, 327-350.

Campbell C.S., Mcinnes K.J., 1999. Response of in situ leaf psychrometer to cuticle removal by abrasion. Agron J 91, 859-862.

Campbell G.S., 1985. Instruments for measuring plant water potential and its components. In: Instrumentation for environmental physiology (Marshall B., Woodward F.I., eds). University Press, Cambridge, England. pp. 193-214. PMid:2993680

Campbell G.S., Campbell M.D., 1974. Evaluation of a thermocouple hygrometer for measuring leaf water potential in situ. Agron J 66, 24-27.

Campbell G.S., Gardner W.H., 1971. Psychrometric measurement of soil water potential: temperature and bulk density effects. Soil Sci Soc Amer Proc 35, 8-12.

Campbell G.S., Zollinger W.D., Taylor S.A., 1966. Sample changer for thermocouple psychrometers: construction and some applications. Agron J 58, 315-318.

Cancela J.J., Dafonte J., Martínez E.M., Cuesta T.S., Neira X.X., 2006. Assessment of a water activity meter for rapid measurements of soil water potential.Biosyst Eng 94(2), 285-295.

Cavalieri A.J., Boyer J.S., 1982. Water potentials induced by growth in soybean hypocotyls. Plant Physiol 69, 492-496. PMid:16662235 PMCid:426236

Comstock J.P., 2000. Correction of thermocouple psychrometer readings for the interaction of temperature and actual water potential. Crop Sci 40, 709-712.

Daws M.I., Lydall E., Chmielarz P., Leprince O., Matthews S., Thanos C.A., Pritchard H.W., 2004. Developmental heat sum influences recalcitrant seed traits in Aesculus hippocastanum across Europe. New Phytol 162, 157-166.

Daws M.I., Cleland H., Chmielarz P., Gorian F., Leprince O., Mullins C.E., Thanos C.A., Vandvik V., Pritchard H.W., 2006. Variable desiccation tolerance in Acer pseudoplatanus seeds in relation to developmental conditions: a case of phenotypic recalcitrance? Funct Plant Biol 33, 59-66.

Dixon M.A., Tyree M.T., 1984. A new stem hygrometer, corrected for temperature gradients and calibrated against the pressure bomb. Plant Cell Environ 7, 693-697.

Dixon M.A., Grace J., Tyree M.T., 1984. Concurrent measurements of stem density, leaf and stem water potential, stomatal conductance and cavitation on a sapling of Thuja occidentalis L. Plant Cell Environ 7, 615-618.

Duniway J.M., 1971. Comparison of pressure chamber and thermocouple psychrometer determinations of leaf water status in tomato. Plant Physiol 48, 106-107. PMid:16657723 PMCid:396812

Easter S.J., Sosebee R.E., 1974. Use of thermocouple psychrometry in field studies of soil-plant-water relationships. Plant Soil 40, 707-712.

Ehlig C.F., 1962. Measurement of energy status of water in plants with a thermocouple psychrometer. Plant Physiol 37, 288-290. PMid:16655646 PMCid:549781

Ehret D.L., Lau A., Bittman S., Lin W., Shelford T., 2001. Automated monitoring of greenhouse crops. Agronomie 21, 403-414.

Ficus E.L., 1972. In situ measurement of root-water potential. Plant Physiol 50, 191-193.

Frank A.B., Power J.F., Willis W.O., 1973. Effect of temperature and plant water stress on photosynthesis, diffusion resistance, and leaf water potential in spring wheat. Agron J 65, 777-780.

Gee G.W., Campbell M.D., Campbell G.S. Campbell J.H., 1992. Rapid measurement of low soil water potentials using a water activity meter. Soil Sci Soc Am J 56, 1068-1070.

Gollan T., Turner N.C., Schulze E.D., 1985. The responses of stomata and leaf gas exchange to vapour pressure deficits and soil water content. III. In the sclerophyllous woody species Nerium oleander. Oecologia 65, 356-362.

Gounot M., Monteny B., 1967. Mise au point d'une méthode thermoélectrique (Effet Peltier) pour determiner le potentiel hydrique d'un tissu végétal ou d'un sol. Documents Techniques 31. Institut National de la Reserche Agronomique de Tunisie, Ariana. [In French].

Hardegree S.P., 1989. Xylem water holding capacity as a source of error in water potential estimates made with the pressure chamber and thermocouple psychrometer. Am J Bot 76, 356-360.

Hillel D., 1998. Environmental soil physics. Academic Press, USA. 771 pp. PMCid:1459797

Hoffman G.J., Splinter W.E., 1968. Water potential measurements of an intact plant-soil system. Agron J 60, 408-413.

Hoffman G.J., Rawlins S.L., 1972. Silver-foil psychrometer for measuring leaf water potential in situ. Science 177, 802-804. PMid:17840129

Hsieh J.J.C., Hungate F.P., 1970. Temperature compensated Peltier psychrometer for measuring plant and soil water potentials. Soil Sci 110, 253-257.

Jobling J.J., Patterson B.D., Moradi S., Joyce D., 1997. A non-destructive method for measuring the water potential of fruit and vegetables. Postharvest Biol Tec 10, 1-8.

Johnson R.W., Dixon M.A., Lee D.R., 1992. Water relations of the tomato during fruit-growth. Plant Cell Environ 15, 947-953.

Joly R.J., 1985. Techniques for determining seedling water status and their effectiveness in assessing stress. In: Proceedings: evaluating seedling quality: principles, procedures, and predictive abilities of major test (Duryea M.L., ed). Workshop held, Forest Research Laboratory, Oregon State University, Corvallis, October 16-18, 1984. pp. 17-28.

Knipling E.B., Kramer P.J., 1967. Comparison of the dye method with the thermocouple psychrometer for measuring leaf water potentials. Plant Physiol 42, 1315-1320. PMid:16656657 PMCid:1086725

Kirkman M.B., 2005. Principles of soil and plant water relations. Elsevier Academic Press, New York, USA. 500 pp.

Lambert J.R., Van Schilfgaarde J., 1965. A method of determining the water potential of intact plants. Soil Sci 100, 1-9.

Li Y.Z., Lu H.F., Fan X.W., Sun C.B., Qing D.J., Dong H.T., Wang L., 2010. Physiological responses and comparative transcriptional profiling of maize roots and leaves under imposition and removal of aluminium toxicity. Env Exp Bot 69, 158-166.

Liu M.Z., Jiang G.M., Niu S.L., Li Y.G., Gao L.M., Ding L., Peng Y., 2003. Photosynthetic response to soil water contents of an annual pioneer C4 grass (Agriophyllumsquarrosum) in Hunshandak Sandland, China. Photosynthetica 41, 293-296.

Machado S., Paulsen G.M., 2001. Combined effects of drought and high temperature on water relations of wheat and sorghum. Plant Soil 233, 179-187.

Manoharan P.T., Shanmugaiah V., Balasubramanian N., Gomathinayagam S., Sharma M.P., Muthuchelian K., 2010. Influence of AM fungi on the growth and physiological status of Erythrina variegata Linn. grown under different water stress conditions. Eur J Soil Biol 46, 151-156.

Martínez E.M., Cancela J.J., 2011. Condiciones de contorno en las determinaciones del punto de marchitamiento permanente con water activity meters. Span J Rural Dev (in press). [In Spanish].

Martre P., 1999. Architecture hydraulique d'une talle de féstuque élevée (Festuca arundinacea Schreb.). Implications pour les relations entre la transpiration et l'expansion foliare. Doctoral thesis. Université de Poitiers, Poitiers, France. [In French].

Mcaneney K.J., Tanner C.B., Gardner W.R., 1979. An in situ dewpoint hygrometer for soil water potential measurement. Soil Sci Soc Am J 43, 641-645.

Mcburney T., Costigan P.A., 1984. Rapid oscillations in plant water potential measured with a stem psychrometer. Ann. Bot-London 54, 851-853.

Mcburney T., Costigan P.A., 1987. Plant water potential measured continuously in the field. Plant Soil 97, 145-149.

Mcburney T., Costigan P.A., 1988. Continuous measurement of plant water stress. Acta Hort (ISHS) 228, 227-234.

Merrill S.D., Rawlins S.L., 1972. Field measurement of soil water potential with thermocouple psychrometers. Soil Sci 113, 102-109.

Michel B.E., 1977. A miniature stem thermocouple hygrometer. Plant Physiol 60, 645-647. PMid:16660155 PMCid:542681

Millar A.A., Lang A.R.G., Gardner W.R., 1970. Four-terminal Peltier type thermocouple psychrometer for measuring water potential in nonisothermal systems. Agron J 62, 705-708.

Mullins C.E., 2001. Matric potential. In: Soil and environmental analysis. Physical methods (Smith K.A., Mullins C.E., eds). Marcel Dekker Inc, New York, USA. pp. 65-93.

Nelsen C.E., Safir G.R., Hanson A.D., 1978. Water potential in excised leaf tissue. Comparison of a commercial dew point hygrometer and a thermocouple psychrometer on soybean, wheat, and barley. Plant Physiol 61, 131-133. PMid:16660227 PMCid:1091813

Neumann H.H., Thurtell G.W., 1972. A Peltier cooled thermocouple dewpoint hygrometer for in situ measurement of water potentials. In: Psychrometry in water relations research. Proceedings of the Symposium on Thermocouple Psychrometers (Brown R.W., Van Haveren B.P., eds). Utah Agric Exp Stn Utah State Univ, Logan, USA. pp. 103-112.

Niu S.L., Li L.H., Jiang G.M., Gao L.M., Li Y.G., Peng Y., Liu M.Z., 2004. Gas exchange and chlorophyll fluorescence response to simulated rainfall in Hedysarum fruticosum var. mongolicum. Photosynthetica 42, 1-6.

Nonami H., Boyer J.S., 1993. Direct demonstration of a growth-induced water potential gradient. Plant Physiol 102, 13-19. PMid:12231794 PMCid:158741

Oosterhuis D.M., 1987. A technique to measure the components of root water potential using screen-caged thermocouple psychrometers. Plant Soil 103, 285-288.

Oosterhuis D.M., Savage M.J., Walter S., 1983. Field use of in situ leaf psychrometers for monitoring water potential of a soybean crop. Field Crop Res 7, 237-248.

Peck A.J., 1968. Theory of the Spanner psychrometer, 1. The thermocouple. Agr Meteorol 5, 433-447.

Peck A.J., 1969. Theory of the Spanner psychrometer, 2. Sample effects and equilibration. Agr Meteorol 6, 111-124.

Rawlins S.L., 1964. Systematic error in leaf water potential measurements with a thermocouple psychrometer. Science 146, 644-646. PMid:17794038

Rawlins S.L., 1966. Theory for thermocouple psychrometers used to measure water potential in soil and plants samples. Agric Meteorol 3, 293-310.

Rawlins S.L., Dalton F.N., 1967. Psychrometric measurement of soil water potential without precise temperature control. Soil Sci Soc Am Proc 31, 297-301.

Rawlins S.L., Campbell G.S., 1986. Water potential: Thermocouple Psychrometry. In: Methods of soil analysis. Part. I: Physical and mineralogical methods, 2ª ed. (Klute A., ed). Am Soc Agron, Madison, WI, USA. pp. 597-618.

Richards L.A., Ogata G., 1958. Thermocouple for vapour pressure measurement in biological and soil systems at high humidity. Science 128, 1089-1090. PMid:17741841

Rodrigues O., Didonet A.D., Roman E.S., 2003. Avaliação do potencial hídrico foliar em plantas de trigo. Circular Técnica Online 15. Available on line at . [01 june 2010]. [In Brazilian].

Savage M.J., Cass A., 1984a. Measurement errors in field calibration of in situ leaf psychrometers. Crop Sci 24, 371-372.

Savage M.J., Cass A., 1984b. Measurement of water potential using in situ thermocouple hygrometers. Adv Agron 37, 73-126.

Savage M.J., Wiebe H.H., Cass A., 1983. In situ field measurement of leaf water potential using thermocouple psychrometers. Plant Physiol 73, 609-613. PMid:16663267 PMCid:1066515

Scanlon B.R., Tyler S.W., Wierenga P.J., 1997. Hydrologic issues in arid, unsaturated systems and implications for contaminant transport. R Geophys 35, 461-490.

Scanlon B.R., Andraski B.J., Bilskie J., 2002. Miscellaneous methods for measuring matric or water potential. In Methods of soil analysis. Part 4. Physical methods (Dane J.H., Topp G.C., eds). Soil Sci Soc of Am, Madison, Wis, USA. pp. 643-670.

Schaefer N.L., Trickett E.S., Ceresa A., Barrs H.D., 1986. Continuous monitoring of plant water potential. Plant Physiol 81, 45-49. PMid:16664805 PMCid:1075280

Shackel K.A., 1987. Direct measurement of turgor and osmotic potential in individual epidermal cells. Independent confirmation of leaf water potential as determined by in situ psychrometry. Plant Physiol 83, 719-722. PMid:16665324 PMCid:1056435

Shackel K.A., 1984. The theoretical and experimental error for in situ measurements of plant water potential. Plant Physiol 75, 766-772. PMid:16663701 PMCid:1066990

Spanner D.C., 1951. The Peltier effect and its use in the measurement of suction pressure. J Exp Bot 11, 145-168.

Turner N.C., 1981. Techniques and experimental approaches for the measurement of plant water status. Plant Soil 58, 339-366.

Turner N.C., Schulze E.D., Gollan T., 1984a. The responses of stomata and leaf gas exchange to vapour pressure deficits and soil water content. I. Species comparisons at high soil water contents. Oecologia 63, 338-342.

Turner N.C., Spurway R.A., Schulze E.D., 1984b. Comparison of water potentials measured by in situ psychrometry and pressure chamber in morphologically different species. Plant Physiol 74, 316-319. PMid:16663415 PMCid:1066675

Turner N.C., Schulze E.D., Gollan T., 1985. The responses of stomata and leaf gas exchange to vapour pressure deficits and soil water content. II. In the mesophyc herbaceous species Helianthus annus. Oecologia 65, 348-355.

Turner N.C., Shackel K.A., Le Coultre I.F., 2000. Leaf-cutter psychrometers. Agron J 92, 538-541.

Villar J.M., Ferrer F., 2005. Técnicas de medida y control del agua en el suelo. In: Agua y agronomía (Martín F., López P., Calera A., eds). Ed Mundi-Prensa, Madrid. pp. 23-86.

Vogt U.K., 2001. Hydraulic vulnerability, vessel refilling, and seasonal courses of stem water potential of Sorbus aucuparia L. and Sambucus nigra L. J Exp Bot 52, 1527-1536. PMid:11457913

Waister P.D., 1965. Precision of thermocouple psychrometers for measuring leaf water potential. Nature 205, 922-923.

Walker S., Oosterhuis D.M., Savage M.J., 1983. Field use of screen-caged thermocouple psychrometers in sample chambers. Crop Sci 23, 627-632.

Walker S., Oosterhuis D.M., Wiebe H.H., 1984. Ratio of cut surface area to leaf sample volume for water potential measurements by thermocouple psychrometers. Plant Physiol 75, 228-230. PMid:16663578 PMCid:1066868

Wiebe H.H., Brown R.W., 1979. Temperature gradient effects on in situ hygrometer measurements of soil water potential. II. Water movement. Agron J 71, 397-401.

Wiebe H.H., Brown R.W., Daniel T.W., Campbell E., 1970. Water potential measurements in trees. Bioscience 20, 225-226.

Wright G.C., Rahmianna A., Hatfield P.M., 1988. A comparison of thermocouple psychrometer and pressure chamber measurements of leaf water potential in peanuts. Exp Agr 24, 355-359.

Wullschleger S.D., Dixon M.A., Oosterhuis D.M., 1988. Field measurement of leaf water potential with a temperature-corrected in situ thermocouple psychrometer. Plant Cell Environ 11, 199-203.

Xanthopoulos G., 2002. Sap pressure (plant water potential) Measurement: method. EUFIRELAB. 21 pp. XU Z., ZHOU G., 2008. Responses of leaf stomatal density to water status and its relationship with photosynthesis in a grass J Exp Bot 59, 3317-3325.

Yubing L., Engguo Z., Xingrong L., Gang W., 2007. Protective mechanism of desiccation tolerance in Reaumuria soongorica: leaf abscission and sucrose accumulation in the stem. Sci China Ser C-Life Sci 50, 15-21. PMid:17393078

Zanstra P.E., Hagenzieker F., 1977. Comments of the psychrometric determination of leaf water potentials in situ. Plant Soil 48 347-367.

Zollinger W.D., Campbell G.S., Taylor S.A., 1966. A comparison of water-potential measurements made using two types of thermocouple psychrometer. Soil Sci 102, 231-239.

Zou C., Sands R., Sun O., 2000. Physiological responses of radiate pine roots to soil strength and soil water deficit. Tree Physiol 20, 1205-1207. PMid:12651497

How to Cite
Martinez, E. M., Cancela, J. J., Cuesta, T. S., & Neira, X. X. (1). Review. Use of psychrometers in field measurements of plant material: accuracy and handling difficulties. Spanish Journal of Agricultural Research, 9(1), 313-328.
Soil science