Variability of Depth to Tosca in Udolls and Soil Classification, Buenos Aires Province, Argentina

Abstract

In the Buenos Aires province, a layer of caliche or tosca underlies a large area of Udolls. Its presence under a humid climate is unusual, making it difficult to classify these soils with Soil Taxonomy (ST), both in the past and after recent changes. The aim of this paper is to characterize the variability of the tosca layer, particularly in depth, to improve the classification of these Udolls. Depth variability was analyzed from available information and detailed depth variability (DDV) was studied in two sample areas: Balcarce and Azul. In addition, in Azul the DDV of the tosca was related to elevation of the land surface and pH of the Bt/Btn horizons. The three dimensional diagrams show a greater variability in depth to tosca in Balcarce, associated with the proximity to the Sierras. In Azul, the pH of the Bt/Btn horizons is related to elevation but has no relationship with depth to tosca. In Balcarce, the index sand/coarse silt was calculated for four soil pedons and the underlying tosca. The differences in sand/coarse silt ratio between the present soil and the tosca layer are nonconclusive proof of lithological discontinuities for every pedon. Consequently both concepts of chronological and lithological discontinuity apply to characterize the present soil/tosca boundary. To homogenize the classification criteria, the subgroups defined in the Natrudolls, allow a better handling of the lateral transitions between pedons. Consequently, we suggest defining the Petrocalcic subgroup in the Argiudolls. Copyright © 2002. Soil Science Society . Published in Soil Sci. Soc. Am. J.66:1256–1264.