Some observations of the complexity of soil taxonomy

A critical evaluation was conducted on the complexity in teaching Soil Taxonomy to students of soil classification. Since its debut in the 1960 International Soil Science Conference under the name of "Soil Classification, Comprehensive System, 7th Approximation," Soil Taxonomy has brought radical changes in concepts and nomenclature. The principles of this new system are perhaps superior to any other soil classification system. However, frequent inconsistent application of definitions for assessing soil categories or names from order to subsequent lower levels of classification was a source of constant confusion in teaching the material to new students. One of the major criticisms of Soil taxonomy is its readability. In addition, many repetitions of criteria for divisions of orders, suborders, and great soil groups occur. The description of taxa following keys helps in understanding taxa but cannot serve as criteria for differentiating the taxa. Orders are, by definition, based on diagnostic epipedons or horizons; whereas great soil groups are distinguished by close similarities in kind and arrangement of horizons. In the actual assessment of soil classes, diagnostic epipedons are used more to differentiate among the great soil groups, whereas similarities in arrangement of horizons are used more for the orders. Differentiae for suborders and the variations observed provide for subjective interpretations. A proposal is presented to alleviate part of the problems by the use of revised definitions, showing explicit directives for application. Comprehension would have been helped if definitions had been applied equally to all members within a category, satisfying in this way the rules for a proper stratification in the classification system. Additional index words: Soil classification, 7th Approximation. S Taxonomy (15) was first introduced under the name Soil Classification, a Comprehensive System, 7th Approximation (14) at the International Soil Science Conference at Madison, Wisconsin, in 1960. An initial outburst of support in 1963 by key persons in soil classification in the U.S. (4, 5, 9, 11), and its further development through the 1966, 1967, and 1968 supplements were perhaps indications of its merit in fulfilling the demand to replace an earlier system based on zonality, intrazonality and azonality concepts. The earlier system, published by Baldwin et al. (1) in the 1938 Yearbook of Agriculture, Soils and Men, has since been adopted and quoted widely in many countries of the world. Although the latter system had been revised by Thorp and Smith (16), it became apparent through further use (10, 14) that even if great time and effort were to be spent in revising it, the revised system would still have unacceptable gaps and inconsistencies. Many soil series then being established could not be accommodated into the existing great soil groups or proposed new great soil groups without considerable modification (14), as knowledge in soil classification expanded with the years. The necessary drastic changes in concepts, principles, and nomenclature were introduced in Soil Taxonomy. Five fundamental changes were introduced (12, 13) including provision for cultivated as well as natural soils, emphasis of soil properties instead of theories of soil genesis, development of a totally new nomenclature, and revisions in definitions of classes or categories. The principles of the new system and provisions for future 1 Contribution of the Univ. of Georgia, College of Agriculture and Experimental Stations, College Station, Athens. Paper presented before Commission V, l l th Congress International Soil Science Society (1978), Edmonton, Alberta, Canada. This research was supported by State and Hatch funds allocated to the Georgia Agric. Exp.Stn. 2 Professor, professor, and associate professor, respectively, Dep. of Agronomy, Univ. of Georgia, Athens, GA 30602. 42 JOURNAL OF AGRONOMIC EDUCATION revisions make it one of the best soil classification systems currently in use. Although the present authors wholeheartedly endorse the adoption of the new system, they do find Soil Taxonomy difficult to read, and frequently inconsistent in application for assessing the soil’s name from order to subsequent lower levels of classification. Moreover, Soil Taxonomy has not received universal acceptance (7, 8), and some of the objections offered against its use appear to be well founded. In this paper we are offering for discussion areas in which we think Soil Taxonomy can be improved in the hope that eventually support will be gained for making the system still easier to teach and apply. Though the 7th Approximation of Soil Classification was not prepared for use by beginning students of soil classification (14) while Soil Taxonomy mentioned that knowledge of the Soil Survey Manual is necessary, the proposed modifications by the present authors may encourage its acceptance by a wider group of students. In this way, a wide variety of people may have easy access to the system and be able to apply it. PROBLEMS IN USE OF TEXT A proper text, simple to comprehend, is perhaps sine qua non in communications. It is common knowledge among scientists, in need of soils information, and especially those who are working in fields other than soil science, that parts of Soil Taxonomy are difficult to understand and apply (7, 8). Although the nomenclature has been improved in the 1975 edition (15), many the sentences are still ~umbersome. The liberal use of negative terms discourages some potential users from consulting it further. For instance, many persons, including the present authors, will have to exert considerable effort to apply the following definition: "Alfisols are mineral soils that 1. Have one of the following combinations of properties: a. do not have fragipan but have an argillic or natric horizon and have one or more of the following, etc..." 05). As defined above, the Alfisols have properties that they do not have. Therefore, the suggestion is made, that it is more logical to list the properties in a straightforeward way, rather than stating that Alfisols do have properties that they do not have. CRITERIA FOR DISTINCTION OF CATEGORIES