Advances in Understanding the Molecular Structure of Soil Organic Matter

We take a historic approach to explore how concepts of the chemical and physical nature of soil organic matter have evolved over time. We emphasize conceptual and analytical achievements in organic matter research over the last two decades and demonstrate how these developments have led to increased skepticism toward the humification concept and question the usefulness of operationally defined and artificially prepared "humic substances" as models of fractions of soil organic matter in real soils. We identify some of the still open questions about organic matter, and point out future research directions that are likely to refine those concepts of the physicochemical nature of soil organic matter which we put before the reader today.