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Experimental Control of Soil Water Content in the Vicinity of Root Hairs¹

ABSTRACT

A technique for controlling water content in the root hair zone of growing plants has been developed which involves growing plants on a fine screen placed over soil in such a way that only root hairs can extend through the screen into soil beneath. Gamma-ray attenuation is used to monitor the supply of water in the root hair zone. By means of controlling either the length of a hanging water column or the rate of water supply, the rate of water flow to the soil lamina beneath the screen can be so adjusted as to just offset the loss due to transpiration. A predetermined soil water content can be maintained to within 0.015 cm³/cm³ in the root hair zone of a growing plant.

Plant growth was affected by soil water potential. Reduction in elongation rate of corn (Zea mays L.) leaves was observed at matric potentials higher than –1 bars. Elongation essentially ceased at matric potentials of about –22 to –30 bars within the root hair zone. A large water content gradient existed adjacent to the root hair zone and extended to a depth greater than 10 mm.

¹ Contribution of the Department of Agronomy and Soils, Washington State University, Pullman 99163, based in part on data used by the senior author in fulfilling the requirements for the Ph.D. in Soils. The investigation was supported by the US Regional Research Project W-67. Presented before Div. S-1 and S-6 at the SSSA meeting in Ithaca, N.Y. Aug. 22, 1962, and published as Scientific Paper no. 3742, Washington Agr. Exp. Sta.

² Senior Research Scientist, Battelle Northwest, Richland, Wash.; and Professor of Soils, Assistant Prof. of Biophysics, and Assistant Soil Scientist, Washington State University, Pullman.

Received for publication October 8, 1971. Accepted for publication January 5, 1972.