Soil Biota
It consists of the microorganisms (bacteria, fungi, archaea and algae), soil animals (protozoa, nematodes, mites, spiders, insects and earthworms) and plants, living all or part of their lives in or on the soil or pedosphere.
Microorganisms (fungi, archaea, bacteria, algae and cyanobacteria) are members of the soil biota but are not members of the soil fauna.
The soil fauna is the collection of all the microscopic and macroscopic animals in a given soil.
The soil biota includes:
• Megafauna: size range 20mm upward. Example: moles, rabbits and rodents.
• Macrofauna: size ranges 2 to 20mm. Example: woodlice, earthworm, beetles, centipedes, slugs, snails, ants and harvestmen.
• Mesofauna: size ranges 100 micrometers to 2mm. Example: mites.
• Microfauna and Microflora: size range 1 to 100 micrometers. Example: yeasts, bacteria, fungi, protozoa, roundworms.
Decomposition of Organic Residue
Decomposition is a biological process that includes the physical breakdown and biochemical transformation of complex organic molecules of dead material into simpler organic and inorganic molecules.
The continual addition of decaying plant residues to the soil surfaces contributes to the biological activity and the carbon cycling process in the soil. Carbon cycling is the continuous transformation of organic and inorganic carbon compounds by plants, micro and microorganisms between the soil, plants and the atmosphere. In the decomposition process, different products are released: carbon dioxide, energy, water, plant nutrients and resynthesized organic carbon compounds.
Successive decomposition of dead material and modified organic matter results in the formation of a more complex organic matter called humus. This process is called humification. Humus affects soil properties. As it slowly decomposes, it colors the soil darker, increases soil aggregation and aggregate stability, increases the CEC and contributes N, P and other nutrients. Soil organisms, including microorganisms, use soil organic matter as food. As they break down the organic matter, any excess nutrients are released into the soil in form that plants can use.
This release process is called mineralization.
The waste products by microorganisms are also soil organic matter. This waste material is less decomposable than the original plant and animals’ material, but it can be used by a large number of organisms. The organic matter content, especially the more stable humus, increases the capacity to store water and store C from atmosphere.