The ability for microorganisms to produce and release various metabolites stimulating plant growth and favourable health is considered to an important factor in soil fertility.
What are Secondary Metabolites
Secondary metabolites are organic compounds with complex chemical structures and diverse physiological functions. Secondary metabolites include antibiotics, pigments, and other bioactive compounds. Many of these compounds have important agricultural and medical applications. Microorganisms, especially actinomycetes and filamentous fungi both of which are in EM, are noted as a rich source of bioactive secondary metabolites. The below image illustrates the many effects soil microbes influence plant growth and development.
How EM produces these Metabolites
Through fermentation of this diverse blend of beneficial microbes these organisms produce organic acids, plant hormones (e.g., auxin, gibberellin, and cytokinin), vitamins and antibiotics. These products of microbial metabolism can benefit the growing plant by
- Improving availability of nutrients with limited solubility, e.g., rock phosphate
- Limiting heavy metal uptake by plants
- Providing simple organic molecules such as amino acids for direct uptake
- Protecting the plant from soil-borne pathogens, insects and diseases
- Stimulating plant growth and increasing the yield and quality of crops
- Improving the chemical and physical properties of soils
When all these beneficial effects of microbial metabolism are integrated it can optimize soil productivity and crop production.
Plant Growth Regulators
I wanted to highlight plant growth regulators as it is well known that plant hormones play an important role in root growth and plant development. But what isn’t well know is that soil microbes will produce these substances in Rhizosphere to boost plant health and growth.
The microbial species listed here in this table (extracted from the book Nature Farming and Microbial applications), are all present in EM, and have all been shown to produce various PGR’s as published. These include the above mentioned Auxins, Cytokinins and Gibberellins among others. Note that GA stands for Gibberellic Acids and IAA stands for Auxins. Ethylene is a naturally occurring substance, which was one of the first plant growth regulators to be discovered and used successfully for enhancing ripening in fruit.
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