What do these microbes contribute to soil health?
Actinomycetes are a type of bacteria that decompose the toughest plant materials like cellulose that form the plant walls. They generate the earthy smell from freshly turned soil or a newly opened compost pile. When you dig into a compost pile, the actinomycetes colonies may be seen as gray web-like filaments in the outer 4 to 6 inches of the pile.
Bacteria are the most numerous of the soil microbes, but there are different types of bacteria. Some bacteria convert plant nutrients to forms that the plant can use, and other types work to decompose plant material in the soil. The decomposers work on plant material after the actinomycetes and fungi are done with the heavy work, and these soil bacteria generate the heat found in the center of a compost pile. Also, soil bacteria release a sticky mucus-like substance that binds the soil particles and builds soil tilth and structure.
Some forms of soil bacteria are pathogens and are responsible for soil-borne disease. However, the beneficial soil bacteria form a protective shield around the plant roots to keep the harmful bacteria away. Also, the beneficial bacteria attract other types of soil microbes that feed on the harmful bacteria and reduce their numbers. The key to soil disease prevention is to maintain strong and activity colonies of beneficial bacteria.
Mycorrhizal fungi also form a protective shield around the plant roots and help protect the plant from soil pathogens. They also send out root-like vessels known as hyphae that can extend several feet away from the roots to carry water and nutrients back to the plant. Like the beneficial bacteria, mycorrhizal fungi generate sticky substances that help to build soil structure. Other types of fungi are like the actinomycetes and decompose cellulose, and the fungi in a compost pile may be seen as fluffy gray colonies on or near the surface.