The role of soil-forming processes in the definition of taxa in Soil Taxonomy and the World Soil Reference Base

Modern soil taxonomic systems, including Soil Taxonomy (ST) and the World Reference Base (WRB) for Soil Resources, classify soils using diagnostic horizons, properties, and materials. Although these systems are based on genetic principles, the approaches used have de-emphasized the role of soil processes in soil taxonomic systems. Meanwhile, a consideration of soil processes is important for understanding the genetic underpinnings of modern soil taxonomic systems and developing quantitative models of pedogenic systems. Seventeen generalized soil-forming processes are identified, briefly discussed, and linked to soil taxa and diagnostic horizons, properties, and materials in ST and the WRB. The processes are illustrated in simple diagrams and include: (1) argilluviation, (2) biological enrichment of base cations, (3) andisolization, (4) paludization, (5) gleization, (6) melanization, (7) ferrallitization, (8) podzolization, (9) base cation leaching, (10) vertization, (11) cryoturbation, (12) salinization, (13) calcification, (14), solonization, (15) solodization, (16) silicification, and (17) anthrosolization. The implications of soil-forming processes on present and future soil classification systems and pedogenic models are discussed.