As soon as the organic matter is partially decomposed and competition for nutrients begins among soil microorganisms, beneficial effects begin. Pathogens now are suppressed or killed, and beneficial microorganisms thrive, including mycorrhizal fungi. The structure of the soil is improved, which results in improved water retention under dry weather conditions and better drainage during periods of high precipitation. Soil fertility is affected also. While organic matter decomposes, nutrients are released and fulvic acids are formed.
Fulvic acids are resistant to decomposition and polymerize to form humic substances in soils.
Fulvic and some humic acids remain dissolved in water in soil early during the decomposition process. These acids chelate trace elements, such as iron, zinc, manganese, copper, etc., and improve the availability of these elements in soils. Highly stabilized sources of organic matter, such as that in muck soils or peat, as well as humic substances in mineralized farm soils, do not provide these same beneficial effects. Pathogens typically cause heavy losses in such soils unless pesticides are used. Composts prepared from yard wastes, manures, and sewage sludges tend to release significant quantities of nutrients for plant growth.