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Soil Investigations and the Seventh Approximation¹

ABSTRACT

The Seventh Approximation was developed because of the need for precise soil classification for agricultural and other uses. It incorporates recent advances in soil science and allows classification of all soils, whether cultivated, eroded, or virgin. Classes are defined in terms of morphology although the grouping of classes is based on genetic relationships. The Seventh Approximation presents challenges to soil characterization research because classes must be defined by measurable parameters and to soil genesis research because parameters at high categorical levels must reflect important soil-forming processes. Precise definition of classes may, in turn, aid in evaluating the relative importance of soil-forming factors and in the application of the results of research on one soil to similar soils in widely separated areas.

¹ A contribution of the Soil Conservation Service, USDA. Presented before Div. V, Soil Science Society of America, St. Louis, Mo., November 27, 1961.

² Soil Scientist, SCS, Riverside, Calif.

Received for publication May 9, 1962. Accepted for publication June 2, 1962.