Soil MICROBIOLOGY – A BRIEF EXPLANATION

In agricultural areas across Australia, the average percentage of organic carbon in the soil is 1% or lower. Before European settlement, the organic carbon levels in Australian soil averaged around 13%. Records from the 1840’s showed 100 days in summer without rain in an area of NSW and despite this the grasses and many native plants per hectare that were growing in that area were noted as not being moisture stressed – this is because of the high carbon content of the soil which is like a sponge that holds moisture. The plants were also supported by an active network of micro-biology in the soil, which supplied all the nutrients that the many species of plants required. These plants were also able to access moisture from the atmosphere due to the soil microbes increasing their capillary suction ability to efficiently harvest moisture each evening during a dew.

“Every gram of carbon that we build in our soil can hold 8 grams of water”

Over 95% of the nutrients available in the soil is governed by microbial activity which includes mycorrhizal fungi. Mycorrhizal fungi are vitally important to the nitrogen fixing process in the soil because they transfer energy from the plants – in the form of liquid carbon to the associative nitrogen fixers in the soil.

The soil must always have green growing plants or trees that are photosynthesizing (transferring sunlight & carbon into energy) and feeding this carbon down through their roots into the soil which feeds the soil micro-biology. In exchange, the soil micro-biology feed the plants the nutrients that they require. This whole process which is called the ‘Green Bridge’ is what builds carbon in the soil.

Plants release exudates from their roots which is how they feed the soil microbes, the plants that are exudating microbes have more root hairs. Plants stop producing exudates when inorganic nitrogen is applied to them. Nitrogen must be fixed biologically for carbon to be fixed in a stable form in the soil.

Since the introduction of synthetic nitrogen (inorganic nitrogen) that is applied to crops and trees in most agricultural practices throughout the world, the supply of organic carbon to soil microbes has become inhibited and these microbes starve and die off which results in carbon depleted soils.

Inorganic Nitrogen is not able to be fully absorbed by the plant or the soil, 60% to 90% of inorganic Nitrogen volatilises into the atmosphere as Co2 emissions. It also produces clean plant roots which do not have rhizosheath’s limiting the plant’s ability to take up nutrients. This is because roots need to connect into the mycorrhizal fungi network to access nutrients.