EUROPEAN SOIL BUREAU RESEARCH REPORT NO. 7 Soil Taxonomy: Provisions for Anthropogenically Impacted Soils WILDING Larry P. 1 and AHRENS Robert J.2 1 Department Soil and Crop Sciences, Texas A&M University, College Station, TX 77843, USA Email: [email protected] 2 USDA-NRCS-National Soil Survey Center, USDA-NRCS, Lincoln, NE 68508-3866, USA Abstract Soil Taxonomy accommodates anthropogenically-impacted soils in a variety of ways, but there are still pending questions about the adequacy of these provisions. For this reason we initiated the International Committee on Anthropogenic Soils (ICOMANTH) to address this matter. Diversity of opinion exists among US soil scientists regarding the best manner to accommodate anthropogenic impacts on soils. Recommendations include a new soil order for Anthrosols, revisions in current taxa to accommodate anthropogenically-impacted soils, development of new taxa in Soil Taxonomy based on prior knowledge of history and/or genesis of humanly-managed soils, and finally better design and description of mapping units in soil surveys to transfer knowledge about anthropogenically-impacted soils. The human factor is one of the biological components of soil formation but is not considered a process per se. Commonly anthropogenic effects are difficult to calibrate consistently with morphogenetic markers as diagnostic differentiae. Then the question is posed how much change in a soil is needed before one recognizes anthropogenic impacts (e.g. surface plowing, addition of agricultural chemicals, irrigation, drainage, accelerated soil erosion, strongly disturbed soils, etc.). In considering this question, it is important to review basic tenets in rationale used to construct Soil Taxonomy, namely: (1) soils are classified on the basis of observed or measured properties that are expressed contemporaneously; (2) cultivated and non- cultivated soils should be placed in the same taxa whenever possible; (3) preference should be given to taxa differentiae representing more permanent subsurface properties rather than temporal surface conditions; (4) preference should be given to taxa differentiae representing properties that carry the greatest number and most important accessory properties; (5) Soil Taxonomy should continue to evolve as a dynamic system, and (6) Soil Taxonomy should be fully bifurcated so all known soils within the landscape can be placed within the system. In this spirit, Soil Taxonomy has accommodated anthropogenic impacts on soils by application of the differentiae at the order, suborder, great group, subgroup, family, and series categories and with the following diagnostic horizons and features: anthropic and plaggen epipedons, agric and sulfuric horizons, aquic conditions (anthric saturation), and densic materials. This paper does not provide solutions for all the questions raised above, but does set the framework of how Soil Taxonomy functions in regard to anthropogenically- influenced soils. Undoubtedly with time and knowledge, further revisions in Soil Taxonomy will be needed, as we better understand how to manage, interpret and classify anthropogenically-influenced soils. Keywords: human factor, soil diversity, diagnostic properties, Anthrosols, ICOMANTH Introduction Soil Taxonomy (1999) accommodates anthropogenically-impacted soils in a variety of ways but there is still pending questions about the adequacy of these provisions. For this reason formal activities of the International Committee Anthropogenic Soils (ICOMANTH) began in August, 1995. The committee has had limited activity, partly because of competing activities of other international committees but perhaps even more important was the diversity of philosophy about how to best accommodate anthropogenically- impacted soils. The committee would welcome inputs from the soils community via its web site: Soil Taxonomy: Provisions for Anthropogenically Impacted Soils. Wilding & Ahrens 35 EUROPEAN SOIL BUREAU RESEARCH REPORT NO. 7 hppt://wwwscas.cit.cornell.edu/icomanth. ICOMANTH is charged with defining appropriate classes in Soil Taxonomy for human-altered soils (Bryant, et al., 1999). As a part of this charge the committee is requested to establish criteria for long-term changes in morphogenetic properties and soil behavior. New classes were to be defined that would provide for improved understanding, classification, management and interpretations of these soils. To date, the committee has developed two circular letters and hosted an International Workshop on Classification, Correlation, and Management of Anthropogenic Soils (Kimble, et al., 1999). Several difficulties in accomplishing the charges given to ICOMANTH are entrained in questions like how much difference in soil properties does it take before one recognizes anthropogenic effects (Bryant et al., 1999)? Does it require simply plowing the soil or is more drastic soil disturbance required? Will a few years of irrigation be sufficient or will hundreds to thousands of years be required to recognize significant effects of such management practices? Under highly variable spatial and temporal soil conditions, how does one recognize and categorize the effects due to anthropogenic activities from those due to other non- anthropogenic impacts? The human factor is certainly one of the biological components but is human activity really a pedogenic process that can be differentiated from other pedogenic processes that are not humanly induced? Commonly the pedogenic processes associated with anthropogenically-impact soils are similar to ones which occurred prior to human intervention. To further confound the challenges of ICOMANTH, the proposals to this committee varied from establishing a new soil order of Anthrosols, to revising current Soil Taxonomy provisions, designing new taxa based on prior historic knowledge, and improving the design and description of mapping units as soil complexes (Kimble, et al., 1999). The human impact on soils is recognized in a number of taxa, especially Entisols and Inceptisols, but in general the soils community is still striving to improve Soil Taxonomy’s capability to accommodate this human factor. Transformations of soils that have been impacted by humans is common. For example, Mollisols can be transformed to Alfisols by erosion and vice versa by heavy liming and manure applications; paddy soils can undergo secondary salinity and waterlogging under long-term rice culture; urban/industrial environments can be markedly modified by landfills, landfarming, earth movement, and heavy metal contamination; and drastically disturbed soils are common in regions where precious metals, rock aggregate, and fossil fuels have been mined. ICOMANTH is charged to address these issues, but solutions and revisions of Soil Taxonomy will be deliberate and debated by a larger community of soil scientists. Sencindiver and Ammons (2000) have recently summarized information on minesoil genesis and classification which touches on many of the points raised above. Fanning and Fanning (1989) also have shared their philosophy about genesis and classification of anthropogenetically-impacted soils. Burghardt and Dornauf (2000 a,b,c) have edited three volumes of proceedings dealing with humanly-influenced soils with a focus on urban, industrial, traffic, and mining areas. These contributions deal with soil quality, mapping, spatial variability, genesis, classification, and problems encountered in accommodating anthropogenically-impacted soils. All these sources provide excellent background to the topic covered herein but general solutions are not offered or warranted. The purposes of this paper are: (i) to discuss the philosophy of Soil Taxonomy construction relative to anthropogenically-impacted soils; (ii) to illustrate ways in which the system does accommodate anthropogenically-impacted soils; and (iii) to consider limitations and constraints of the system for this purpose. It will draw heavily on several published literatures for this information including Smith (1963, 1983, 1986), Cline (1949, 1963), Soil Survey Staff (1999), Ahrens and Engel (1999), Ahrens and Arnold (2000), and Wilding (2000a,b). Philosophy of Soil Taxonomy Before presenting ways in which Soil Taxonomy accommodates anthropogenically-impacted soils it is worthwhile as a prelude to remember some of the principles and philosophy of the system. These signposts provide rationale as to how the system handles humanly impacted soils. Smith (1983) provides a classical summary of construction of Soil Taxonomy. Cline (1963) described the logic of Soil Taxonomy and key requirements of the system. 36 Soil Taxonomy: Provisions for Anthropogenically Impacted Soils. Wilding & Ahrens EUROPEAN SOIL BUREAU RESEARCH REPORT NO. 7 Soil Taxonomy serves the Soil Survey Program in US The architects behind Soil Taxonomy agreed that the classification system must serve the soil survey program of the United States. The system was utilitarian in scope with its primary purpose to identify and locate soils, and to predict the consequences of alternative uses of soils. In countries where no classification system existed or in which the system did not adequately serve the needs of the soil science community, Soil Taxonomy was available to be tested, modified and used as deemed appropriate. Numerous countries took advantage of this opportunity and use Soil Taxonomy or some derivative of it. The founders of Soil Taxonomy believed the system should provide a basis for developing principles of soil genesis, and predictions of soil behavior