Nutrient recycling in soil is generally performed by microorganisms. Both beneficial soil fungi and beneficial soil bacteria are the main players. Soil microbes will exist in large numbers in soils as long as a carbon source exists for energy. Interestingly, in undisturbed soils fungi tend to dominate the soil biomass, while in tilled soils bacteria, actinomycetes, and protozoa dominate the soils. This is due to the fact that the later are hardier species and can tolerate more soil disruptions.
The decomposition of organic matter serves two distinct functions for microorganisms. This process provides both an energy source and supplies carbon for cell growth and reproduction. Absent a reliable carbon source, there are fewer microorganisms and the organisms that are present tend to be in a dormant state. This is the condition found in dawn on the road in the forest in summer tilled and highly used soils.
In contrast, long term no tilled soils have significantly higher levels of microbes, higher levels of soil decomposition, more active carbon and more stored carbon. In other words, these soils have a greater degree of nutrient recycling and are healthier as a result. The overall health of soil is affected by the amount of organic carbon in the soil. This organic carbon is needed to support an active, healthy microbial population.
The breakdown of organic compounds by microorganisms is dependent on the carbon to nitrogen ratio (C:N). Bacteria generally start the decomposition process first. They have high nitrogen content in their cells but are typically less efficient at converting the organic carbon to new cells. Aerobic bacteria only metabolize and assimilate 5-10% of the available carbon leaving behind many waste carbon compounds.
The fungi are much more efficient at converting soil carbon into new cells. They can assimilate 40-55 % of the existing carbon. In particular, fungi are invaluable in consuming both cellulose and lignin. Protozoa and nematodes consume the nitrogen rich bacteria and help the nutrient recycling process. They release the nitrogen as ammonia. Ammonia and soil nitrates are converted back and forth in the soil. These microorganism communities change rapidly and continuously in the soil, as organic matter is added, consumed, and recycled.
In conclusion, microorganisms are critical to decomposing and nutrient recycling. To have healthy, productive soils both a thriving microorganism population and carbon source are necessary pieces of the puzzle.
Bill Baugh is a product manager for Custom Biologicals, Inc. a manufacturer and distributor of innovative microbial products. You can visit their website at Living-Soils.com and he can be contacted at 561.797.3008 or Bill@Custombio.biz.