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Field Capacity in Laboratory Columns¹

ABSTRACT

It is shown that the material decrease in downward movement observed as soils approach field capacity cannot be explained in terms of capillary conductivity alone. Instead, the combined effects of decreasing capillary conductivity in the drying zone, hysteresis and reduced hydraulic gradients at all levels are involved. The capillary conductivity of the drying zone is always greater (probably much greater) than that of the wetting zone. Hysteresis effects, if present, ought to result in larger reductions in hydraulic gradient for an increment of water transfer than would occur without hysteresis. The hydraulic gradients at all levels ought to decline during drainage.

Experimental evidence is presented which is in general agreement with expectations. Hysteresis effects were large, and the hydranlic gradients greatly diminished after 48 hours of drainage.

¹ Contribution of the Department of Soils, University of California, Berkeley 4, Calif. Presented before Division I, Soil Science Society of America, Cincinnati, Ohio, Nov. 19, 1952.

² Assoc. Prof. Soil Physics, Cornell Univ., (formerly Ass't. Soil Physicist, Univ. of Calif.) and graduate assistant, Univ. of California, respectively.

Received for publication December 12, 1952.