HUMIPEDON

The Humipedon corresponds to the part of the soil richest in organic matter, pedofauna, miroorganisms, seeds and roots of plants (Figure 1). It is also the most active part of the soil, where the processes of mineralization and humification of organic matter take place and also the making of the organo-mineral aggregate of the soil.

A soil profile may be parted in three sections^[1]: 

1) humipedon (horizons: H, O, A) [2] = organic and organo-mineral soil horizons;

2) copedon (horizons: E, B)^[2] = mineral soil horizons;

3) lithopedon (horizon: C, and R layer) = rocky part of the soil, altered rock, top part of the solid Earth crust.

Figure 1. The distinction of Humipedon, Copedon and Lithopedon, with the list of diagnostic horizons in Terrestrial and Semi-terrestrial conditions.

The Humipedons cover the entire surface of the planet Earth. They are essentially the physical spaces where, at the same time, both the decomposition of dead organic matter and the reconstruction of new organic matter take place. Depending on the environment of genesis and development, humipedons are different, as they are created by different organisms in equilibrium with the environment and with each other. In summary, we can say that these processes depend on the possibility of "oxidizing" the organic matter in the air or in water and of making the components thus obtained interact chemically and physically to create new organic, organo-mineral or mineral structures, in more or less environments. less rich in water. If the pores of the substrate in which these processes take place are full of water, there is no air, and vice versa. This aspect divides the humipedons into two broad categories: Terrestrial (rather in the air) and Semiterrestrial (more or less in water). However, there are also particular conditions of birth and development of these humipedons. The "young" ones differ from the more developed ones. When young, they are highly dependent on external and dominant groups of organisms that build them and assign a recognizable appearance to humipedon. As they evolve, they converge into typical systems that we could define as "adults", that is, characterized by a certain independence from the environment in which they develop. For this reason, central humus systems and satellite humus systems can be seen in Figure 2. The first are the Terrestrial (red), Histic (blue) and Aqueous (light green) systems; the second are the gray Para ones. In the central part there are also two anthropogenic systems of black color.

Figure 2. The humus system that cover planet Earth. Terrestrial (forests and grasslands): Mull, Moder, Mor, Amphi, Tangel; Histic (Fens and Bogs): Anmoor, Saprimoor, Anphimoor, Mesimoor, Fibrimoor; Aqueous (salty shores and bottom of the sea); Anthropogenic Agro (natural humipedons modified for agricultural purposes) and Techno (man made composts, dumps, hydroponic solutions,...). Para humipedons are represented as satellites of the other humipedons because they can either remain independent, or evolve towards the more developed ones in the central area. 

Main groups of humipedons

- Terrestrial^[3]: not or submerged for a few days a year;

- Semiterrestrial:
- Histic^[4]: submerged but not subjected to strong daily tides;
- Aqueous^[5]: by the sea, in salt water and affected by tides with a daily rhythm.

- Para^[6]: These are humipedons either of initial soils or of soils linked to specific "out of standard" environmental conditions. They are represented in gray circles on figure 2.

- Anthropogenic: Agro^[7] or Techno^[8] humipedons. The former are Terrestrial, Semiterrestrial or Para humipedons modified by man to be cultivated. They contain diagnostic horizons similar to the original natural ones. Techno instead are: 1) maniure humipedons (the different types of composts), 2) soil-free humipedons (from hydroponic solution to porous clay balls), 3) dump humipedons (various types of landfills).