||Humusica 1 and 2 Applied Soil Ecology Special issues are field guides for humipedon classification. Contrary to other similar manuals dedicated to soil, the objects that one can describe with these guides are living, dynamic, functional, and relatively independent soil units. This is the reason to why the authors dedicated the whole article 2 to functional considerations even before readers could go in the field and face the matter to be classified. Experienced lectors can overstep many of the sections reported in this article. If the titles of sections �1. A functional classification“, ”2. What is a humus system?“and ”3. Energetic considerations in terrestrial systems� stimulate the reader�s curiosity, then we suggest to pass through them. Otherwise, only section �4. Climatic, plant litter, or nutritional constraints?� is crucial. Readers will understand how the soil works in terms of litter and carbon accumulation, which one(s) among climatic, vegetation, or geological factors intervene and strongly affect the formation of terrestrial (oxygenated) soils. The article concludes with a debate about a tergiversated question: can temperature influence humus decomposition? Preceding statements were used for explaining how the biological soil net can store in the soil a maximum of energy in the form of SOM, by raising a plateau partially independent of climatic conditions.