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A Test for Natural Soil Groups Within the Willamette Catena Population¹

ABSTRACT

A sample of 114 soil individuals, from Marion County, Oregon, representing the five soil series of the Willamette catena, was tested for the existence of natural soil groups. Natural soil groups are those separated by minima in frequency distributions of single or combined soil characteristics.

Eighty-five morphological, chemical, and physical properties were quantitatively measured on each individual. Frequency distributions were tabulated for each property and examined for the presence of minima. Frequency distributions for depth to evidence of impeded drainage, cation-exchange capacity of the B₂ horizon, and exchangeable magnesium of the B₃ horizon showed minima.

Discriminant function analysis was used to test the combined differentiating abilities of several selected characteristics. Minima were observed in frequency distributions for those combined functions which included a differentiating characteristic. The natural groups separated by these minima corresponded to the recognized soil series.

¹ Technical Paper No. 1405, Oregon Agr. Exp. Sta., Corvallis. Based on the Ph.D. thesis of the senior author, which is available for limited distribution. Supported in part by the Oregon Agr. Exp. Sta. Basic Research Committee.

² Graduate Research Fellow and Associate Soil Scientist. The senior author is now Assistant Professor of Soils, Agronomy Department, University of Maryland. The authors gratefully acknowledge the assistance of L. D. Calvin in statistical treatment, and of L. A. Alban in determination of cation-exchange capacity and exchangeable cations.

Received for publication June 7, 1961. Accepted for publication June 22, 1961.