Evaluation of criteria for argillic horizons (Bt) of soils in Canada

Abstract

Studies of 71 pedons in Canada showed that improvements are required in the estimation of argillic horizon development by both macro- and micro-morphological methods. Fifty-four of the pedons were considered by pedologists of the area to have argillic horizons but only 32 of them had at least 1% oriented, illuvial clay as estimated by point counting of thin sections. A high proportion of the soils thought to have argillic horizons but that lacked 1% oriented clay were either soils from semi-arid areas or soils of very high clay content. However, several clayey soils with COLE values more than 5% had well-developed argillans on ped surfaces and more than 1% oriented, illuvial clay. The results indicate that reference pedons and reference thin sections would be useful in improving the uniformity of designation of horizons as argillic. Useful estimates can be made of illuvial clay by rapid scanning of thin sections at a magnification of approximately 100 if reference sections with established point count values are available. Current criteria of argillic horizons are adequate except that the 1% oriented clay criteria should not be applied rigidly and that clay skins probably should be required in clayey soils of frigid and cryic temperature regimes (cool to very cold temperature classes in Canada).