EUROPEAN SOIL BUREAU RESEARCH REPORT NO. 7 Facing basic problems in the discipline of soil classification: Conclusions based on 35 years practice and teaching LANGOHR Roger Ghent University, Soil Science, Krijgslaan 281/S8 B-9000-Ghent, Belgium Email: [email protected] Abstract Thirty-five years teaching soil classification to MSc fellows, mainly from developing countries, allows one to detect where the main problems are when young soil scientists are trying to use the standard handbooks for soil classification. Although the quality of these documents has increased in the last 25 years, still much can be improved. Mainly the index, the glossary and the redaction of the diagnostic requirements for horizons, materials, properties and taxa can still be markedly improved. Comprehensive studies by MSc and PhD research in soil classification allow one to conclude that the soil databases are mostly very poor. Missing and unreliable field and laboratory data for classifying soils are detected in nearly all the pedon databases. A method is proposed to lessen this major problem. This procedure will also permit improved recording of soil data in the future. It is also observed that soil scientists, in general, proceed too fast when they check the soil data for classification purposes. Keywords: soil classification, soil database, education Introduction Since 1971 the author has been a staff member of the International Training Centre for Post-graduate Soil Scientists at the Ghent University (ITC-Ghent). The late Prof. Rene Tavernier, head of the Belgian Soil Survey, launched this centre in 1963 to provide MSc level basic teaching in soil science and training in the various aspects of soil survey to scientists from developing countries. UNESCO supported the initiative. Up to now about 900 fellows, from 90 countries participated in this programme, most of them from developing countries. Through the years, the MSc programme changed because of new demands in applied soil science. Also the title was changed in 1997 to Master of Science in Physical Land Resources. The weight of the lectures and training in soil classification decreased with this evolution but remained in the programme. Today, soil classification is still part of the basic introductory courses in soil science, but the special training course in this subject became optional The author completed the ITC-Ghent programme in 1965. Dr. Guy D. Smith, leader of the project to develop a new soil classification for the United States Department of Agriculture (USDA) lectured to the class on the «7th Approximation» (Soil Survey Staff 1960). Since the beginning of the fifties Tavernier also organised several meetings in Ghent where heads of the soil surveys from many European countries, including those from behind the Iron Curtain, could discuss the progress of many soil classifications systems that where built in this “golden age of the soil survey”. One of these meetings, in 1952, can be called the “time zero of modern soil classification” (Eswaran, 1999). In the years 1970 through 1981 the author had many informal discussions on soil classification with G. Smith who lived then most of the time in Ghent. Conclusions based on 35 years practice and teaching. Langohr 15 EUROPEAN SOIL BUREAU RESEARCH REPORT NO. 7 In 1971 the author became a permanent staff member of the ITC-Ghent and was responsible, in the beginning for the training, and later also for the basic teaching in soil classification. In these years the ITC- Ghent programme focussed on both the FAO and the USDA soil taxonomies. This document provides an overview of the problems met by MSc students and PhD fellows, mainly from developing countries, when learning and training in these two taxonomies. It also reflects the difficulties the author met when applying these documents in his research and soil survey activities. In order to facilitate the further reading the following abbreviations will be used. • 7th Approximation: Soil Survey Staff 1960. • US ST 1975 and US ST 1999: first and second edition of the comprehensive handbook about the USDA Soil Taxonomy (Soil Survey Staff 1975 and 1999). • US ST 1998: the eighth edition of the “Keys to Soil Taxonomy” (Soil Survey Staff 1998). • FAO 1974: Legend of the FAO-UNESCO Soil Map of the World (FAO-UNESCO 1974). • FAO 1990: the Revised legend, Reprinted (FAO 1990a). • WRB 1998: the most recent edition of the World Reference Base for Soil Resources (ISSS/ISRIC/FAO 1998). • FAO, ST, WRB: the respective classification systems without precision of the edition. For the soil classification systems discussed in this paper, we consider the terms classification and taxonomy as synonyms. Also the FAO system is a taxonomy. It is not because it was built up as a tool for mapping soils that it would not be a taxonomic system but only a soil map legend (FAO 1990a, page 8). If this approach would be accepted, most classification systems, including US ST, would not be classification systems, or taxonomies. What and how to teach Teaching soil classification, just as any other classification system, can be a relatively easy task. After an introductory chapter where the basic terminology of the discipline is explained, the whole classification system can be discussed in length and width. Eventually some exercises can complete the programme. This approach is considered boring by most students and favours large memory capacities rather than comprehension of how to deal correctly with the subject. At ITC-Ghent the teaching programme was oriented toward preparing students to classify soils correctly rather than memorising numerous diagnostic requirements and taxa. An MSc degree is a high level of university teaching. It is the responsibility of the teaching staff to prepare professionals who, after the programme, can perform the job alone. Preference was given to: • teaching the rationale behind the systems, • warning of problems in the discipline as related to: o reputation, o quality of handbooks, o quality of database, o complexity of terminology, o complexity of keys for determination, • training on how to face these problems in order to classify soils correctly. Guy D. Smith mentioned in his Interviews (Smith 1986) that it was decided not to explain in the US ST handbook the reasons behind the decisions on the diagnostic criteria and definitions. The rationale was that readers would pay too much attention to these reasons, rather than on the definitions themselves. However, when we have to teach such a complex matter, the information provided to the students about the rationale is very important to help them link the rather abstract terminology and the diagnostic criteria to the problems met in the various applied aspects of soil science. From this point of view the publication of the Guy Smith Interviews (Smith 1986), eleven years after the first edition of US ST, was very helpful. Facing the status horribilis of soil classification as a discipline Overall, soil classification has a poor reputation. Severe criticism on the discipline is not uncommon. Comments such as “too many classification systems”, “changing too frequently”, “too many characteristics”, “data too difficult to obtain”, “too complex”, “too difficult terminology”, “specialists 16 Conclusions based on 35 years practice and teaching. Langohr EUROPEAN SOIL BUREAU RESEARCH REPORT NO. 7 disagree on the exact names of the soils”, “useless” are frequently heard. Pronounced by outsiders, these could be understandable. Unfortunately such sentences are also heard from soil science colleagues. In the presence of scientists from other disciplines, students, or layman, this has a damaging impact on the status of soil science in general. This bad reputation is at least partly responsible for soil classification being absent from many teaching programmes in soil science. Many younger soil scientists do not receive any training in classifying soils and thus, they do not even comprehend a classification system. A large part of this criticism about soil classification is not valid. The existence of many classification systems, based on soil characteristics that are frequently updated, should be considered as “normal”. The main arguments are the following. • Soils have a very high number of morphological, chemical, physical, mineralogical characteristics. • The applications of soil science are numerous and deal with topics such as fertility for crop production, irrigation/drainage, rangeland management, forest productivity, waste deposits, pollution risks, toxicity remediation, sport fields, palaeo-environment reconstruction, nature reserve management, road and house construction, and urban planning. Each of these disciplines constructs a different hierarchy of importance among the numerous soil characteristics. • In zoology and botany, in natural conditions, sexuality largely rules the combinations that are possible. This allows considering all races of dogs and all races of cats as two distinct species. Also in mineralogy and petrography numerous combinations of elements are impossible because of the crystal structures or the exclusivity among chemical components. In soils, on the contrary, it is difficult to formulate strict rules about the exclusivity among the numerous characteristics. This is because soils are capable of retaining characteristics that are related to past environmental conditions. It is, for example, possible to observe: o soils with a Bt horizon also containing secondary carbonates; o soils mainly composed of kaolinite