Revision of Soils Taxonomy in the Classification of Low Activity Clay Soils

Recel, Modesto R.
Journal Title
Journal ISSN
Volume Title
Starting Page
Ending Page
Alternative Title
The dominant soils of the intertropical region are Oxisols and low activity clay (LAC) Ultisols and Alfisols, which are collectively termed LAC soils. Due to Insufficient knowledge of these soils, their classification was not as satisfactorily developed as the soils of the temperate areas, and consequently, two International Committees (International Committee on Classification of Alfisols and Ultisols with Low Activity Clays and International Committee on Classification of Oxisols) were set up in 1975 and 1977, respectively, to develop proposals for the refinement of Soil Taxonomy. Through circular letters and classification workshops, these International Committees have proposed several changes in the classification. The purpose of this dissertation was to evaluate these proposals, test their appropriateness and validity and where necessary, to suggest alternatives for consideration. The review draft of a proposal for reclassification of Ultisols and Alfisols with low activity clays which constitute the final report of the ICOMLAC by the SCS and ICOMOX Circular Letter No. 10, dated June 1, 1983 and January 11, 1983, respectively, were the basis for the final discussion and suggestions in this study. The methodology consisted of fitting 163 test pedons from the intertropical region into the ICOM's proposals through specially developed flow-diagrams. From these tests, suggestions were made for refinement. The basis for proposing any modifications were: (a) the modifications should result in marked improvements in the interpretation which could be derived in the taxa names; (b) the modification should result to a better expression of the soil-landscape relationships; (c) the modification should introduce significant advantage either or both in the field or laboratory evaluations; (d) the modification should result in mutually exclusive classes and should not conflict with the other parts of the system; and (e) the modification should not result in any soil in a landscape from not being classified. The criteria set in evaluating the impact of revision on agrotechnology transfer were: (a) revision should achieve groupings of soils having closely similar crop production potential; and (b) revision should stratify agroenvironment into distinct agroproduction niches. The ICOM's proposals improved the taxonomic placements of the LAC soils, but there were pedons that could be placed in more than one taxa. Amendments were suggested to overcome these limitations. Some of the diagnostic class limits were refined. Certain criteria were also recommended for deletion and/or addition. Finally, all the proposed changes were included in a key for the classification of these soils.
Geographic Location
Time Period
Related To
Table of Contents
Rights Holder
Local Contexts
Email if you need this content in ADA-compliant format.