Humus forms: visible field characters of main biogeochemical topsoil interacting systems.

Beginning with few anecdotes and presenting a Humus group born in Trento (Italy) in 2003, the intervention focuses on the classification of topsoils corresponding to specific types of interface soil-vegetation. The survey of few main morphological soil features (with intrinsic biological, chemical and physical contents) reveals the existence of different humus systems. Recognizable by naked eyes in the field, each humus system is confined in an ecological frame (climate, vegetation, substrate and soil) and results from a specific process of collaboration between plants and soil organisms. The scope of this cooperation is to implement and store in the ecosystem a maximum of energy/biomass. The goal is reached thanks to different topsoil structures that allow the storage in the soil of organic matter, a sort of “energy reserve” whose availability is controlled by plants and soil organisms in each given ecological frames. In 2011 the Humus group published a key of classification of these humus forms. A revised and enriched version of this classification is on the road with the shape of a field manual. The final slides of the presentation show the general scheme of the book and illustrate the main humus systems and forms covering our planet.