About Vermicomposting
(in much more detail)
Vermicomposting involves the bio oxidation and stabilization of organic material by the joint action of earthworms and microorganisms. Although it is the microorganisms that biochemically degrade the organic matter, earthworms are the crucial drivers of the process, as they aerate, condition, and fragment the substrate, thereby drastically increasing the microbial activity.
Earthworms act as mechanical blenders and by pulverising the organic matter they modify its physical and chemical status, by gradually reducing the nitrogen content and increasing the surface area exposed to microorganisms, thus making it much more favourable for microbial activity and further decomposition.
Therefore two phases can be distinguished:
(a) an active phase where the earthworms process the waste, modifying its physical state and microbial composition; and
(b) a maturation phase starting as the earthworms move toward fresher layers of undigested waste, and microorganisms take over further decomposition of the waste.
The duration of the active phase depends on the species and population density of earthworms.
Vermicomposting is an aerobic biodegradation process involving complex interactions between organic waste, earthworms, microorganisms, moisture and oxygen.
The organic waste contains indigenous mixed populations of microorganisms. Microbial activity increases when the moisture content and oxygen concentration are brought to a suitable level.
In addition to oxygen and water, microorganisms require a source of carbon, macronutrients such as N, P, and K, micronutrients, and certain amounts of trace elements for their growth and reproduction. The organic waste materials provide these requirements, allowing the microorganisms to reproduce rapidly.
The microorganisms (mainly bacteria, fungi and ciliates) produce enzymes that cause the biochemical decomposition of the organic matter.
Earthworms do not have cellulolitic systems developed enough to digest plant material and therefore much of their nutrition depends on the action of microbes either in the organic waste or inside the earthworms (which are called “endosymbiotic microbes”).
Earthworms (and other soil invertebrates) feed on and disperse the microbes throughout the organic matter. As organic matter passes through the gizzard of the earthworms, it becomes finely ground prior to digestion. Endosymbiotic microbes (which are inside the earthworms) produce extracellular enzymes that degrade cellulose and phenolic compounds, thereby enhancing the degradation of material ingested by the earthworms. The degraded organic matter passes out of the earthworm's body in the form of casts.
Earthworms can therefore be considered mechanical blenders because they break down organic material, increase the surface area exposed to microbes, and move fragments and bacteria-rich casts throughout the waste, thereby homogenizing the organic material.
Their burrowing and tunnelling activities aerate the substrate and enable water, nutrients, oxygen, and microbes to move through it.
Hence, earthworms are the crucial drivers of the process because they:
- stimulate microbial populations through fragmentation of organic matter which results in a greater surface area available for microbial colonization and a dramatic increase in microbiological activity; and
- modify microbial populations by digesting and then dispersing them in their casts, which affects the structure of the microflora and microfauna communities.
The successful outcome of the vermicomposting process is the presence of a vast array of microorganisms and soil invertebrates growing and interacting, contributing to the “cycle of matter”. Hence the vermicomposting system sustains complex food webs, and different chemical forms of several nutrient elements become modified into long-lived organic compounds that are important for nutrient dynamics as well as plant growth regulators.
Availability of minerals in the soil is determined by the life in the soil. It is the soil life that facilitates trading of minerals with exudates (plant-produced sugars) for plants. If the specific microorganism that makes a special mineral is not available, it has the same effect as not having the mineral available in the soil at all. Hence vermicompost by virtue of its rich and diverse microbial life makes many soil minerals available to plants.