Although the role of soil organic matter (SOM) for the ecosystem services and functions of soils is very well accepted, the understanding of the mechanisms involved in its stabilization and the requirements for its sustainable maintenance is still scarce. The impact of pyrogenic organic matter (PyOM) on SOM formation and turnover rates has achieved increasing attention during the last decades; but the insufficient understanding of its long-term impact on size and properties of the different SOM pools does not allow a good description of its significance for global elemental cycles, pedogenic processes or long-term soil fertility and quality. Comparably, there is an increasing awareness of the close relationship between the N and C cycles. However, the understanding of the implication of those interactions for SOM dynamics is still scarce. In summary, it is evident that a better knowledge about the nature and function of SOM is strongly needed.
One of the earliest approaches to study SOM concerned the isolation of humic acids via alkaline extraction as it was performed by Achard in 1786. Of course, ever since, the perception of humic substances (HS) as an important component of natural organic matter (NOM) in soils, sediments and waters has undergone considerable changes. Whereas in the early days of HS research, different fractions separated according to solubility in aqueous solutions and color were assigned to specific chemical compounds, modern views consider that such approach is exclusively operational in nature and may produce “artifacts”. Although the fractionation scheme is arbitrary, it has been widely accepted since the isolated fractions differ in their reactivity and are often more suitable for further analysis as bulk NOM. This is of particular interest, when interactions between pollutants, nutrients, and NOM are studied.
However, during the last years, the concept of HS has been questioned in particular with respect to their suitability to improve our understanding of C and N cycling in soils. Therefore, aside from presenting new results within the area of SOM research, the intention of the present session is to bring together researchers with different conceptual backgrounds willing to present their newest findings and debating on fundamental and applied aspects of HS and NOM. We hope to induce a fruitful discussion which includes, but is not limited, to subjects such as:
i) structural and functional aspect of NOM
ii) myths and legends of humification processes
iii) the role of PyOM in soils and as part of the turnover of SOM
iv) The role of soil organic N for the stability of NOM
v) HS as a tool to study interaction with pollutants
vi) New analytical approaches in NOM research