Most soil organisms rely on organic matter for food. Each source of organic matter favors a different mix of organisms, so a variety of sources generally supports a variety of organisms. Maximize crop residue Crop residue is a convenient and valuable source of organic matter. Corn harvested for grain will grow 3 to 4 tons of surface residue per acre and 1 to 2 tons of root biomass. Dense, sod-type crops produce generous amounts of root biomass.
Soybeans generate notoriously little surface residue.
Fungi increase because they have some advantage over bacteria in digesting surface residue, though greener and younger plant residues are easy for bacteria to use. It also changes the moisture and temperature of the soil surface. Some pathogens will be increased by the residue, others will be decreased. Apply compost or manure Compost inoculates the soil with a wide variety of organisms and provides them with a high quality food source. Some species thrive in both compost and in the soil, but many do not.