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Approximation of the Field Maximum Soil Moisture Content¹

ABSTRACT

Field maximum moisture content is defined as the recurring maximum moisture content of a soil layer in its natural position. An approximation of the field maximum is needed when daily moisture records are not available for selecting the recurring peak values. This paper presents the approximation of the field maximum moisture content from equations relating various soil and site properties.

Of the several factors investigated, the 0.06-atm. soil moisture tension value was the only single factor that correlated significantly with the field maximum; it accounted for about 68% of the variation in the field maximum values. With a simultaneous analysis, the sand content and the wetness index of the soil layer also were found to be primary factors in estimating the field maximum moisture content. Wetness index is an arbitrary classification that rates the potential maximum wetting of the 0- to 12-inch layer of soil and is dependent on the depth to a water table and the depth of wetting. Organic content and clay content were found to be secondary factors in the 0- to 6- and 6- to 12-inch layers, respectively. Equations using all factors accounted for about 80% of the variation in the field maximum values. The usefulness of the equations was evaluated by application to 533 sites located throughout the United States.

¹ Contribution from Army Mobility Research Center, U. S. Army Engineer Waterways Exp. Sta., Corps of Engineers, Vicksburg, Miss., in cooperation with the Vicksburg Research Center, Southern Forest Exp. Sta., Forest Service, USDA. Presented before Div. V-A, Soil Science Society of America, Nov. 13, 1956, at Cincinnati, Ohio.

² Soil Scientist.

Received for publication February 13, 1959. Accepted for publication August 21, 1959.