Minerals + Organic Matter + Microbes = Transformed Products for Soil Health
The final products evolving from organic matter break down by soil microbes are polysaccharides (complex sugars) and humus. About 10% of the organic carbon in soils is in the form of carbohydrate (polysaccharides). It serves an important function by binding soil particles into water - stable aggregates. Polysaccharides are derived from plant, animal and microbial digested materials and from extra-cellular gums of microbial origin. The polysaccharide fraction is potentially the most readily available microbial food in the soil organic matter but, despite its abundance, utilization by microorganisms is severely curtailed until most other food sources are no longer available in adequate quantities.
The humus component consists of three substances:
1) Humin is the black insoluble residue which has a closer association with the inorganic fraction of soils. The humin is removed from humus by an alkali solution.
2) Humic acid is precipitated from humus by a very acid solution and is the main component in humus. The major component of humic acid consists of plant polysaccharide residues protected from further degradation by the action of phenolic protein complexes.
3) The remaining solution from humus extraction contains the Fulvic acid fraction, about half of the bulk of the Fulvic acid consists of bacterial cell residues, amino acids and amino sugars. Fulvic acid generally has a lower molecular weight and a 10% higher carbon content than the acid portion, although humus represents the final stage of organic matter decomposition in soil, it would be a mistake to regard it simply as the digestion resistant residue of plants, animals and microbes. It is in fact a product of microbial biosynthesis, and furthermore, it remains subject to very slow microbial breakdown. The humus component appears to be the energy reserve for all soils, giving the soils the vitality we referred to earlier.
The biological attributes rather than physical factors control the development and cropping ability of the soil ecosystem. The physical environment sets limits as to how far development may proceed. It is also a factor in the pattern and rate of change. It is the microbial factor, however, which is generally seen to be of overriding significance.