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Estimating Relative Leaf Water Content with a Simple Beta Gauge Calibration¹

Existing methods for periodically measuring plant water status require considerable instrumentation or time. The method described herein simplifies plant water measurement by providing a completely linear calibration between attenuated beta radiation through a plant leaf and its relative water content simply by measuring the radiation intensity through the leaf at only two water contents — full turgidity and complete dryness. A ¹⁴C beta source was used with leaf discs from sugar beets (Beta vulgaris L.). The method includes a means for drying the leaf discs while maintaining the original geometry. Measurements on leaf discs at relative water contents between O and 1 show that the method is accurate, and that a calibration can be established using a standard method to ensure full turgidity and complete dryness without the added necessity of determining the mass of the leaf. Thus, after proper calibration, only radiation intensity measurements are required to determine the relative water content of a leaf.

Key Words: Plant water status • Beta radiation • Carbon-14 • Relative turgidity • Sugar beets • Beta vulgaris L.

² Formerly student, now soil scientist, Soil Conservation Service, Klamath Falls, Ore., assistant professor of soil science, and professor of water science, Univ. of California, Davis, and research chemist, U.S. Water Conservation Laboratory, Phoenix, Ariz., respectively.

Received for publication December 4, 1974.