Agronomy Journal Journal of Natural Resources and Life Sciences Education
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Published online 1 July 1968
Published in Agron J 60:408-413 (1968)
© 1968 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
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Water Potential Measurements of an Intact Plant-Soil System1

Glenn J. Hoffman and William E. Splinter2

Thermocouple psychrometers were used to measure the water potential of an intact plant-soil system. The system consisted of a young tobacco plant grown in a container of fine sandy loam soil. The effects of soil water potential, diurnal fluctuations, and atmospheric relative humidity on the leaf water potential within a leaf and at different locations on the plant were studied.

Water potential was found to decrease from the base of the leaf to the tip. Leaves at the base of the plant were found to have lower water potentials than leavesnear the middle. The soil water potential decreased linearly with time as evapotranspiration occurred in the system. The site of measurement on the leaf, atmospheric relative humidity, and diurnal variations were found to affect the relationship between leaf and soil water potential. At a constant relative humidity a linear relationship was obtained when the leaf water potential was measured at the base of the bottom leaves or at a given time each day to eliminate diurnal variations. In general, however, the relationship between leaf and soil water potential was not found to be linear. Soil water potential, atmospheric relative humidity, and diurnal variations were found to reduce the leaf water potential by at least 100% in tobacco if altered within the range found under field conditions.

Key Words: thermocouple psychrometer • water potential gradient

1 Contribution from the Dept. of Biological and Agricultural Engineering, North Carolina Agr. Expt. Sta., Raleigh. Published with the approval of the Director of Research as paper No. 2548 of the Journal series. Part of thesis submitted by the senior author in partial fulfillment of the requirements for a Ph.D. degree.

2 Formerly Research Assistant (now Agr. Engr., U. S. Salinity Lab., P. O. Box 672, Riverside, Calif. 92502) and Professor, Dept. of Biol. and Agr. Engineering, North Carolina State University, at Raleigh.

Received for publication December 30, 1967.




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The SCI Journals Crop Science Vadose Zone Journal
Journal of Natural Resources
and Life Sciences Education		 Soil Science Society of America Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome
Copyright © 1968 by the American Society of Agronomy.