Microorganisms in the soil are a crucial link in nature’s energy cycle. Some of the beneficial traits of these microorganisms can also be employed by farmers to take care of their soil.
(The terms beneficial/harmful apply only where a certain outcome is desired. There is no way to say what is beneficial or non-beneficial. In nature, both exist and play a part.)
Some common microorganisms beneficial to the soil and the plants are:
1. Lactic acid bacteria
These bacteria feed on sugar and carbohydrates and produce lactic acid. Lactic acid increases rate of decomposition and suppresses the growth of harmful microorganisms. By feeding on the foul smelling ammonia released during decomposition, these bacteria keep the decomposing matter odour free.
We also culture lactic acid bacteria for fermentation to make curd, pickles and so on.
Some people add lactic acid bacteria to animal feeds to improve their digestion and immunity while some also use it in animal beddings to prevent foul odour.
2. Photosynthetic bacteria
Photosynthetic bacteria can produce their own food by using sunlight and otherwise harmful substances for the plants and turn them into proteins which promote plant growth and health.
3. Fermenting fungi
Fermenting fungi (similar to lactic acid bacteria) feed on organic matter very quickly to produce alcohols and anti-microbial substances thereby suppressing bad odours and diseases from other microbes and insects.
We know yeasts as the fungus that helps us in making bread. Yeast is also very useful to a farmer as it produces substances that promote active cell division and thus can be helpful as a growth promoter.
The rhizobium bacteria lives in the soil in a symbiotic relationship with leguminous plants like beans, pease etc. The bacteria inhabits small lumps on the roots feeding on carbohydrates from the plant and providing the plant with soluble nitrogen compounds (ammonia and nitrates) by fixing atmospheric nitrogen gas.
An estimated 95% of all plant species form symbiotic associations with mycorrhizae (with the exception of the Brassicaceae- mustard, cabbage, radish etc. and Chenopodiaceae- beetroot, spinach etc.).
The plant shares the food it synthesises with the mycorrhizae fungi and the fungi shares some of the nutrients it gathers with the plant. The fungi also increase uptake of water and nutrients by forming an extensive hyphal network on the roots, increasing their effective absorptive surface area. A plant with mycorhiza association is often more competitive for nutrients and water and is able to tolerate environmental stresses.
One way to identify wether a microorganism is beneficial or not, is by observing its effect on decaying biomass. If the biomass gives a sweet fermented smell, the microorganisms growing on it are beneficial, if, however, the biomass smells foul or even pungent, putrefaction is taking place and the microorganisms growing on it could be harmful.
Indigenous microorganisms (IMOs) are a mix of beneficial microorganisms living in a particular region or ecosystem or on a specific plant/animal. These microorganisms live in close associations with the local plants and animals and play a crucial role in decomposition, releasing nutrients from organic matter and preventing the soil/plants/animals from diseases.
The IMOs can be harvested easily, cultured and proliferated in the soils that seem to be lacking them. Harvesting IMOs is done in the presence of oxygen so that beneficial microorganisms are favoured over the harmful ones.
Periodic application of beneficial microorganisms is believed to have helped in increasing the diversity of microorganisms in the soil which supports a diversity of plants that can grow in it.
Different kinds of plants require different kind of microbial ecology around them. The vegetables grow in a largely bacterial soil ecosystem while trees grow in a fungal dominated soil ecosystem.