Microorganism Populations

The microorganism groups to be measured are heterotrophic (aerobic) bacteria, anaerobic bacteria, yeasts and molds (fungi, actinomycetes, pseudomonads, and nitrogen fixing bacteria. These are some of the major soil bacterial and fungal groups, with some overlap between the categories. Microbial density and diversity and the ratio of one species to another change over time in compost. The population of any onegroup varies with available nutrients, moisture, temperature, substrate type, oxygen content, and other environmental factors.

Microorganisms are responsible for the decomposition of organic matter and the release of plant available nutrients.

Heterotrophic bacteria are aerobic bacteria. In other words, they use oxygen in their growth. This group includes many species of bacteria. A large population indicates that the windrow is well-aerated.

Anaerobic bacteria are capable of growth without oxygen. The population count of these includes facultative anaerobes, or bacteria which can live with or without oxygen. A high population of these indicate low aeration due to water logging, infrequent turning, or compaction.

Yeasts and molds are fungi. Fungi are most abundant in well-aerated environments. Some fungi are pathogenic, however, others are capable of breaking down complex compounds, such as lignin and cellulose. Many other soil microorganisms are unable to break these substances dawn. Fungi also enhance soil structure. Finally, fungi can tolerate acidic soils.

Actinomycetes are aerobic bacteria They are capable of breaking down complex compounds. They are typically found in neutral to alkaline environments.

Pseudomonads are bacteria, also. They are capable of breaking down a wide variety of compounds, both natural and synthetic. Some are associated with the control of certain plant pathogens.

Nitrogen-fixing bacteria take atmospheric nitrogen and convert it into organic nitrogen, When nitrogen is available, nitrogen is not fixed. However when a deficit occurs, nitrogen is fixed.