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Sampling for Pedographic Modal Analysis of an Argillic Horizon¹

ABSTRACT

Pedographic modal analysis expresses soil composition in terms of the relative amounts of constituents observed in thin sections. Data are presented on the sampling density necessary for pedographic modal analysis of an argillic horizon. Thirty-one randomly selected samples (100cc cores) were obtained from a 61 cm by 61 cm vertical exposure of the horizon. Four thin sections were made from each core. Six constituents were counted in each thin section by the point count method of modal analysis. Constituents less than 50 µ in diameter were classified as matrix, while those larger than 50 µ were classified as glaebules, pores, papules, argillans, or skeleton grains.

Results indicate that a sample adequate to measure these constituents in an argillic horizon with a standard error 10% of the mean would involve taking 21 cores, making 2 thin sections per core, and counting 1,000 points per thin section.

¹ Contribution from the Soil Survey Div., Wisconsin Geol. and Natur. Hist. Surv. and the Dep. of Soil Science, College of Agriculture, Univ. of Wisconsin. Published with the approval of the Director of the Wisconsin Geol. and Natur. Hist. Surv. and the Director of the Wisconsin Agr. Exp. Sta., Madison. Appreciation is expressed to Professor George R. Barr and Leo R. Hansen of the Dep. of Dairy Science, Univ. of Wisconsin, for assistance in computer programming and operation.

² Soil scientist, Wisconsin Geol. and Natur. Hist. Surv., Professor of Soil Science (in charge of the Soil Survey Div.), and Professor of Agronomy, Univ. of Wisconsin, Madison., respectively.

Received for publication February 7, 1966. Accepted for publication November 28, 1966.