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Field Capacity Approximation Based on the Moisture-Transmitting Properties of the Soil¹

ABSTRACT

A new field capacity approximation is reported. This approximation was compared both with the field capacity and with various estimates of the field capacity of 23 soils. The field capacity approximation was found to be related to the field capacity by the equation: FC = 0.959FCA + 1.17. The data presented support the view that field capacity is the moisture content of a well drained soil when, after the soil has been thoroughly wet, drainage has decreased the moisture content to such an extent that the consequent decrease in capillary conductivity materially impedes further drainage of water. A statistical test of significance showed that the field capacity approximation is a significantly better over-all estimate of field capacity than the moisture equivalent, buchner funnel percentage, and -atm. percentage. The test further indicated that the field capacity approximation is not a significantly better estimate of field capacity than a modification of the Wilcox (7) method. However, the field capacity approximation is much more convenient, reproducible, and time conserving than the modified Wilcox method.

¹ Contribution from the Department of Soils, University of Wisconsin, Madison, Wis. The material is taken from a thesis submitted by the first author in partial fulfillment for the degree of Doctor of Philosophy and supplemented with data taken from a thesis submitted by the second author in partial fulfillment for the degree of Master of Science. This work was supported in part by a grant from the Research Committee of the Graduate School from funds supplied by the Wisconsin Alumni Research Foundation. Presented before Div. I, Soil Science Society of America, Dallas, Texas, Nov. 17, 1953.

² Agent (Soil Scientist) B.P.I.S. & A.E., U.S.D.A., Manhattan, Kans. (Formerly Graduate Assistant, University of Wisconsin), Graduate Assistant, and Assistant Professor of Soils, respectively.

Received for publication December 15, 1953.