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Calculation of Capillary Conductivity from Pressure Plate Outflow Data¹

ABSTRACT

The flow equation describing the movement of water out of a soil sample in the pressure plate apparatus has been solved for a special case. It is assumed that during the outflow process (a) the capillary conductivity is approximately constant, and (b) the relation between the water content and the suction is linear. Both of these conditions can be met if the pressure increment which causes the outflow is made sufficiently small. By measuring the outflow from the sample as a function of time and using the solution of the flow equation, the capillary conductivity can be calculated for each suction interval.

Conductivity measurements on three soils indicate that the conductivity decreases approximately as the inverse square to cube of the suction. By using the pressure membrane apparatus, the range of suction over which measurements were made was extended up to 15 bars.

¹ Contribution from the U. S. Salinity Laboratory, Soil and Water Conservation Research Branch, A.R.S., U.S.D.A., Riverside, Calif., in cooperation with the 17 Western States and the Territory of Hawaii.

² Physicist.

Received for publication August 15, 1955.

This article has been cited by other articles:

				W. R. Gardner and C. F. Ehlig Impedance to Water Movement in Soil and Plant Science, October 26, 1962; 138(3539): 522 - 523. [Abstract] [PDF]