Soil Microorganisms

Soil microorganisms include bacteria (the most numerous group by cell count), fungi (which can dominate microbial biomass through extensive hyphal networks), archaea, and protozoa. Each group occupies different ecological niches, from rapid decomposition of simple compounds by many bacteria to the breakdown of more resistant organic material by fungi.

Mycorrhizal fungi

Fungi that form symbiotic associations with plant roots, extending the root’s effective reach for water and nutrients, especially phosphorus.

Rhizobia

Bacteria that form nodules on the roots of legumes and fix atmospheric nitrogen into plant-available forms.

Antagonistic microorganisms

Microbes that suppress pathogens through competition, antibiosis, or direct parasitism, contributing to natural disease suppression.

Microbial decomposition and mineralization release nutrients locked in organic matter into forms plants can absorb, making microorganisms central to nutrient cycling. Mycorrhizal and rhizobial symbioses can substantially improve plant nutrient and water acquisition. Some microbial communities also suppress soil-borne pathogens through competition for resources, production of antagonistic compounds, or direct parasitism, contributing to natural disease resistance in well-managed soils.

Microbial biomass carbon estimates the total living microbial mass in a sample, while soil respiration (carbon dioxide release) reflects overall metabolic activity. Phospholipid fatty acid (PLFA) analysis can characterize broad community composition, and DNA- or RNA-based sequencing methods provide detailed identification of which organisms are present and, in some cases, active.

Because microorganisms depend on organic carbon as an energy source, management that maintains a steady supply of residues and living roots, while minimizing unnecessary disturbance, tends to support a more active and diverse microbial community.

• Maintain organic matter inputs through residues, cover crops, and organic amendments
• Rotate diverse crops, including legumes, to support varied microbial symbioses
• Reduce tillage intensity to protect fungal networks and microbial habitat
• Consider microbial inoculants (such as rhizobial or mycorrhizal products) where appropriate for the crop and soil, following supplier and regional guidance