“VERMICOMPOST: MAKING GARBAGE INTO GOLD”
Vermicomposting is a simple biotechnological process of composting, in which certain species of earthworms are used to enhance the process of waste conversion and produce a better end product. Vermicomposting differs from composting in several ways. It is a mesophilic process, utilizing microorganisms and earthworms that are active at 10–32°C (not ambient temperature but temperature within the pile of moist organic material). The process is faster than composting; because the material passes through the earthworm gut, a significant but not yet fully understood transformation takes place, whereby the resulting earthworm castings (worm manure) are rich in microbial activity and plant growth regulators, and fortified with pest repellence attributes as well! In short, earthworms, through a type of biological alchemy, are capable of transforming garbage into ‘gold.
Importance of vermicompost
Source of plant nutrients
Earthworms consume various organic wastes and reduce the volume by 40–60%. Each earthworm weighs about 0.5 to 0.6 g, eats waste equivalent to its body weight and produces cast equivalent to about 50% of the waste it consumes in a day. These worm castings have been analyzed for chemical and biological properties. The moisture content of castings ranges between 32 and 66% and the pH is around 7.0. The worm castings contain higher percent
age (nearly twofold) of both macro and micronutrients than the garden compost.
Plant growth promoting activity
Growth promoting activity of vermicompost was tested using a plant bioassay method. The plumule length of maize (Zea mays) seedling was measured 48 h after soaking in vermicompost water and in normal water. The marked difference in plumule length of maize seedlings indicated that plant growth promoting hormones are present in vermicompost.
Improved crop growth and yield
Vermicompost plays a major role in improving growth and yield of different field crops, vegetables, flower and fruit crops. The application of vermicompost gave higher germination (93%) of mung bean (Vigna radiata) compared to the control (84%). Further, the growth and yield of mung bean was also significantly higher with vermicompost application. Likewise, in another pot experiment, the fresh and dry matter yields of cowpea (Vigna unguiculata) were higher when soil was amended with vermicompost than with biodigested slurry.
Reduction in soil C:N ratio
Vermicomposting converts household waste into compost within 30 days, reduces the C:N ratio and retains more N than the traditional methods of preparing composts. The C:N ratio of the unprocessed olive cake, vermicomposted olive cake and manure were 42, 29 and 11, respectively. Both the unprocessed olive cake and vermicomposted olive cake immobilized soil N throughout the study duration of 91 days.
Role in nitrogen cycle
Earthworms play an important role in the recycling of N in different agroecosystems, especially under jhum (shifting cultivation) where the use of agrochemicals is minimal. It is reported that during the fallow period intervening between two crops at the same site in 5- to 15-year jhum system, earthworms participated in N cycle through cast egestion, mucus production and dead tissue decomposition. Soil N losses were more pronounced over a period of 15-year jhum system.
Improved soil physical, chemical and biological properties
Limited studies on vermicompost indicate that it increases macropore space ranging from 50 to 500 μm, resulting in improved air-water relationship in the soil which favorably affect plant growth. The application of organic matter including vermicompost favorably affects soil pH, microbial population and soil enzyme. It also reduces the proportion of water-soluble chemical species, which cause possible environmental contamination.
Types of earthworms
Earthworms are invertebrates. There are nearly 3600 types of earthworms in the world and they are mainly divided into two types: (1) burrowing; and (2) non-burrowing. The burrowing types Pertima elongata and Pertima asiatica live deep in the soil. On the other hand, the non burrowing types Eisenia fetida and Eudrilus eugenae live in the upper layer of soil surface. The burrowing types are pale, 20 to 30 cm long and live for 15 years. The non-burrowing types are red or purple and 10 to 15 cm long but their life span is only 28 months. The non-burrowing earthworms eat 10% soil and 90% 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 type of earthworms comes 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% soil and 10% organic waste.