Vermicomposting is a type of composting in which certain species of earthworms are used to enhance the process of organic waste conversion and produce a better end-product. Vermicomposting is a mesophilic process utilizing microorganisms and earthworms. Earthworms feeds the organic waste materials and passes it through their digestive system and gives out in a granular form (cocoons) which is known as vermicompost. Like regular compost, vermicompost also benefits the environment by reducing the need for chemical fertilizers and decreasing the amount of waste going to landfills/dumpsites.
Vermicompost is primarily earthworm excrement, called castings, which can improve biological, chemical, and physical properties of the soil. The chemical secretions in the earthworm’s digestive tract help break down soil and organic matter, so the castings contain more nutrients that are immediately available to plants.
Earthworms consume various organic wastes and reduce the volume by 40–60 percent. Each earthworm weighs about 0.5 to 0.6 gram, eats waste equivalent to its body weight and produces cast equivalent to about 50 percent of the waste it consumes in a day. The moisture content of castings ranges between 32 and 66 percent and the pH is around 7.0. The worm castings contain higher percentage (almost twice) of both macro and micronutrients than the garden compost. About 2-3 kg of earthworms is required for 1000 kg of biomass, whereas about 1100 number earthworms are required for 1 m2 area.
There are nearly 3600 types of earthworms and they are mainly divided into two types: (1) burrowing; and (2) non-burrowing. Red earthworm species like Eisenia foetida and Eudrillus enginae are most efficient in compost making. The non-burrowing earthworms eat 10 percent soil and 90 percent organic waste materials; these convert the organic waste into vermicompost faster than the burrowing earthworms. They can tolerate temperatures ranging from 0 to 40°C but the regeneration capacity is more at 25 to 30°C and 40–45% moisture level in the pile. The burrowing types of earthworms come onto the soil surface only at night. These make holes in the soil up to a depth of 3.5 m and produce 5.6 kg casts by ingesting 90 percent soil and 10 percent organic waste.
A wide range of agricultural residues, all dry wastes, for example, straw, husk, dry leaves of crops and trees, stalks, vegetable wastes, weeds etc can be converted into vermicompost. In addition, animal manures, dairy and poultry wastes, food industry wastes, municipal solid wastes, biogas sludge and bagasse from sugarcane factories also serve as good raw materials for vermicomposting.