There are several different types of humus found in soil, each formed under varying environmental conditions and decomposition processes. These types can be broadly categorized based on the oxygen levels present during their formation.
Humus Types in Upland Forests (Aerobic Conditions)
Under well-aerated conditions, such as those found in upland forests, three main types of humus develop:
-
Mor: Mor humus is characterized by a distinct, undecomposed layer of organic matter on the soil surface. It's often acidic and nutrient-poor, with slow decomposition rates. It forms a matted layer.
-
Moder: Moder humus represents an intermediate stage between mor and mull. Decomposition is more advanced than in mor, with some mixing of organic and mineral layers. It's less acidic than mor and has a higher nutrient content.
-
Mull: Mull humus is considered the most fertile type. It's characterized by rapid decomposition and close integration of organic matter with the mineral soil. It's typically found in soils with earthworm activity, which aids in mixing and aeration.
Humus Types in Wetlands (Anaerobic Conditions)
In wetland environments where oxygen is limited, different types of humus are formed:
-
Sapric: Sapric humus is the most decomposed form found in wetlands. The original plant structures are barely recognizable, and the material is a dark, amorphous mass.
-
Hemic: Hemic humus represents a partially decomposed state. Some plant fibers are still visible, but the material is significantly altered from its original form.
-
Fibric: Fibric humus is the least decomposed of the wetland humus types. It consists primarily of recognizable plant fibers and has a high water-holding capacity.
Humus Type in Wetlands with Fluctuating Conditions
- Muck: Muck humus forms in wetlands that experience alternating aerobic and anaerobic conditions. This fluctuating environment leads to a unique type of decomposition that results in a dark, highly decomposed organic material.
In summary, the types of humus are dictated by the level of decomposition and environmental circumstances of the soil.
