Soil Microbes Overview

Soil looks lifeless but a quarter of a teaspoon of soil (1 gram) contains many microbes - 100 million bacteria, 1 million actinomycetes and 5 metres of fungal filaments.

Soil is certainly living! In pastures grazed by sheep near Armidale, NSW, Australia, we have measured the weight of microbes in soil and calculated that there is the equivalent weight of soil microbes of 88 sheep/ha.

above ground

below ground

Since the pastures were grazed with only 20 sheep/ha above-ground, there was the equivalent weight of 4 sheep (as microbes) in the soil to every real sheep grazing above. Scientists in England and New Zealand have calculated that they have equivalent weights of 110 sheep/ha in microbes in pasture soil. These English and New Zealand soils would be moister and have more organic matter food for microbes than our Australian pasture soil which has periodic droughts and where organic soils are rare.

Ways of feeding: Bacteria and fungi have similar ways of feeding. Their main food is organic detritus in leaf litter, soil, dung and carrion. In contrast to invertebrate animals which engulf food and digest it within their bodies, microbes digest their food outside themselves by secreting digestive enzymes over their food. Under the action of the enzymes, organic matter breaks down into simpler molecules external to the microbe, which then re-absorbs the simpler products of digestion through its cell wall. Microbes have a vast number of enzymes to do this job – 50 to 60 different ones have been discovered. Few invertebrates possess this many digestive enzymes.