Vermicomposting is becoming increasingly popular especially in urban areas where even households are using this technique for their balcony gardens. While many people only focus on the method involved, in this article we will dive into what this method actually entails for the plants, humans and the environment and provide in depth, intersectional analysis...
Vermicomposting is synonymous with ‘worm composting’. It is actually the material left behind after earthworms eat and digest biodegradable wastes like kitchen scraps, vegetable and fruit peels, etc. When the worm poop ages; it is known as worm castings. Vermicomposting entails a combination of digestion by the worms as well as a decomposition process that takes place after the material exits the worm. The worm poop rests for some period while bacteria, fungi, etc continue the decomposition of the same. The end product is a black humus-like substance that resembles, in theory, if not in practice, the material produced by bin composting.
As per a bulletin of Indian Council for Agricultural Research, compiled by Pronita Chettri (SMS, Agronomy): “Vermicompost is the product of composting using earthworms to create a homogeneous mixture of decomposing vegetable or food waste, bedding materials. It is the end-product of the breakdown of organic matter by earthworms containing water soluble nutrients. Vermicompost is an excellent, nutrient-rich organic fertilizer and soil conditioner. The process of producing vermicompost is called as vermicomposting.”
Dr Shivendra Dutt Shukla, microbiologist and deputy manager, POCT group, states: “Vermicomposting is like a soil conditioner. It is a wonderful technology which is a combination of vermiculture and vermicomposting in which vermiculture is a breeding method for raising earthworm under controlled climatic condition which is favourable for the organism. Earthworms can sustain on many types of organic waste viz. agriculture waste, forest litters, kitchen waste Cow dung etc. It is another method of waste management by which vermicompost is produced with high nutrient composition and it enhances the plant growth, reducing the disease factor in plants and also increasing porosity µbial activity in soil in addition to reducing the use of chemical fertilizers and deposition of chemicals in the landfills which deteriorating the fertility of the soil. Vermicompost accommodate water-soluble nutrients and is an exceptional, nutrient-rich organic fertilizer and soil conditioner. Vermicomposting can also be used for treatment of sewage.”
Which Earthworm species are the most suitable?
As per Pronita Chettri,the earthworm species most commonly used for Vermicomposting are:
•Eiseniafoetida or Eiseniaandrej
What are the methods involved in Vermicomposting?
Pronita Chettri states: “Vermicomposting may be carried out by two main methods- Large scale and Small scale.
Large Scale - There are two main methods of large scale vermiculture
• Windrow: It consists of bedding materials for the earthworms to live in and acts as a large bin; organic material is added to it.
• Raised bed or Flow-through system: This system is well suited to indoor facilities, making them preferred choice for operation in colder climates.
• Pits: Some farmers opt for vermicomposting pits, digging a large hole in which to bury the worms and organic waste material. Of course, before adding the worms and bedding, farmers must line the pit to prevent worms from escaping into the surrounding soil.
Small Scale - For vermicomposting at home a large variety of bins are commercially available, or a variety of adapted containers may be used. They may be old plastic containers, wood, Styrofoam or metal containers. Bins however need holes or mesh for aeration.
Vermicomposting- what actually happens inside and outside the worm?
Robert Pavlis, in his books entitled ‘Garden Myths’ and ‘Soil Science’ states: “Worms eat soil and organic matter which travels down a long digestive tube that consists of several key sections. The esophagus adds calcium carbonate as a way for the worm to rid itself of the excess calcium. The food then moves on through the crop and into the gizzard. The gizzard uses small stones to mash the food into small particles. Enzymes are added to aid in digestion. The food then moves into intestine where fluids are added to further digest the food. Similar to our own intestine, it absorbs nutrients that are needed by the worm. This all sounds quite normal for an animal digestive system but there is one key ingredient- the microbes. The worm controls moisture and pH levels to favour the growth of microbial populations. These microbes play a major role in the digestion of organic matter. Along with the soil and organic matter, worms also ingest large amounts of microbes. In fact, the microbes are the primary source of food, not the organic matter. The entire digestive system is not very efficient and only 5-10 percent of the ingested food is absorbed by the worm. The rest is excreted as mucus coated particles called Vermicasts or Worm Castings. The worm casts contain undigested plant material, nutrients, soil and a large number of microbes. The microbial activity in worm cast is ten to twenty times higher than it is in soil or other forms of organic matter. The worm is not really doing much composting. It does some digestion, but its main contribution to the process is that it breaks organic matter into small pieces and mixes it with microbes. A point that is not emphasized enough is that much of the composting takes place after the casts exit the worm. This external processing may in fact be the most significant part of the composting process. I can only assume that in a worm compost bin, the casts get re-eaten by other worms. In a commercial setting, which is maximised by productivity, usable vermicompost is ready in as less as six weeks. In worm bins, receiving minimal management (mostly done in households by common people, it can take up to four to six weeks.”
Dr Archana Pant, in her paper entitled, ‘Recycling Organic Waste through Vermicomposting’ (University of Hawai), states that during vermicomposting, earthworms facilitate two sets of processes: 1) gut associated processes and2) cast associated processes. In gut associated processes, several events happen: fractionation and homogenizationof materials, addition of sugars, modification of microbial populations and addition of mucusand excretory compounds (e.g. urea and ammonia). In cast associated processes, decomposition bymesophilic bacteria (bacteria that grow best at moderate temperatures, between 25°C and 40°C),mineralization (break down of organic form of nutrient into plant available form) and stabilization of organic material take place under moist and dark conditions. Both of these processes result in high number and diversity of bacteria, relatively high maturity indicators of the composted materials and thus contribute to plant growth promoting response. The most commonly found bacteria in matured vermicompost are Pseudomonas, Bacillus and Microbacterium species. However, the bacteria associated with the vermicompost vary depending on the feedstock that is added into the vermicompost bin. Some functions of these bacteria in the vermicompost include: producing plant growth promoting agents e.g. auxins, cytokinins and gibberellic acid; producing enzymes that dissolve organic nutrients e.g. phosphates dissolves organic phosphorusin soil into a plant available form; enhancing enzymes activities that inhibit growth of pathogenic fungi or insect pests e.g. chitinase; protease and cellulase that suppress fungal and insect pests, amino cyclopropane carboxylate(ACC) deaminase that has broad spectrum anti-fungal activities, hydrogen cyanide (HCN)which is antagonistic to many root infecting fungi; producing siderophores which have high affinity to iron (Fe) in the soil making siderophore forming bacteria outcompete other microbes.
Should vermicomposting be discouraged or encouraged? Our experts explain the reasons:
Dr Shivendra Dutt Shukla states: “Vermicomposting should be encouraged as it is cost effective as it can be produced in any non-economic place with shades, high humidity and cool place. The operation cost of vermicompost in a year workout to be around Rs. 4.2/kg on an average thus it is quite profitable to sell the compost at Rs.10/kg according to ICAR (Indian Council of Agriculture Research) report. It has a near to nil opportunity cost and provides a great scope for earning extra income for the farmers. The farmers can also get the financial support for the setting up of vermicompost unit from NGOs or by forming the self-help group, consisting 15 or 20 members. Centralized bank like Central bank of India also offers loans to meet the investment credits or working capital requirement of farmers and or corporates for setting up and running vermicompost unit through schemes like Cent vermicompost scheme. A number of government schemes are there in place to support the practice, for example- Pararamparagat Krishi Vikas Yojna (PKVY), National mission for sustainable Agriculture (NMSA), Mahatma Gandhi National Rural Employment Guarantee Act (MGNREGA), Mission for Integrated Development of Horticulture (MIDH), etc.”
However, Gyaneshver Shukla, naturalist, is of the firm opinion that vermicomposting should be discouraged, primary reason being they have heavy metal toxicity. “Earthworms absorb, species specific heavy metals, in their body-fat cells. These heavy metals, upon the death and decomposition of their body, release these heavy metals, in the surrounding, in bio-available state, to the plants. If these plants are eaten, they carry the danger of bringing, heavy metals in food chain,” he reasons.
“The use of ‘Red Worm’ Eiseniafoetida, should be discouraged as it is an exotic species. It has all the features to be grouped in ‘Invasive Alien Species’ as it is fast multiplying and aggressive. Invasive Alien Species are known as a major threat to local biodiversity. The Red worm being voracious feeder, competes with local earthworm species and poses a threat to their survival. Indigenous species of earthworms, Pheritima, Lumbricus, Eutypheous and other local fauna face a major threat from these fast multiplying red worms. Local fauna of earthworms naturally decomposesthe biodegradable material without any special arrangements and enrich soil. This is their very nature. It is what the nature has mandated them to do. Spreading of biodegradable material on soil, agriculture field as mulch or otherwise, get composted, easily without any efforts. Hence, in my opinion, vermicomposting and vermicompost pose severe threats to nature and biodiversity aided by human efforts and should be discouraged. It has no added advantage to agriculture fields, which indigenous fauna in not providing. If use of agri-chemicals is regulated to save local biodiversity, vermicomposting becomes unnecessary,” he further adds.
Robert Pavlis states in his book Earthworm, castings in home garden often contain five to ten times more nitrogen, phosphorus and potassium than the surroundings. All that is nice science but the question is which compost results in better plant growth? Some studies may show one to be better than the next but the truth is that neither is superior. Actually, a lot depends on the specific conditions of soil, technologies used and input ingredients. It is incorrect to say that vermicompost produces better compost unless your soil needs more phosphorus and calcium. The high phosphorus actually means that bin composting or other methods might be better suited.
What is its impact on human health?
Gyaneshver Shukla states: “Since vermicomposting can leach heavy metals like cadmium, mercury, iron, etc into the food chain, it can have severe impact on human health. Heavy metal toxicity takes a long time to be noticed and it is also diagnosed very late. Treatment for such diseases is rare. This is especially harmful for children.”
Robert Pavlis states: “Additionally, every composting process produces some kinds of greenhouse gases. Because vermicomposting happens partially inside the worm, it is an anaerobic process that produces both nitrous oxide and methane. Both of them are even more harmful greenhouse gases than carbon dioxide (CO2).”
What are the organic farming methods that can be used as an alternative to improve soil fertility?
Gyaneshver Shukla states: “Vermicompost does not contain enough nitrogen and other nutrients, to be called as 'fertilizer' in the first place. In USA for example, it can't be marketed, as reported. The temperature fluctuations and seasonal changes are not suitable for round the year operations. Natural; traditional techniques of compositing are better, less cumbersome and as rise in temperature ensures, reduction of pathogens. This is not an advantage that we can have during vermicomposting. Till mid of 1960s, before, so-called 'Green Revolution' our agricultural practices were totally natural and organic and sustainable as there was no external inputs were employed. A careful observation and selective practices, with less external input are to be envisaged, according to local conditions and water table to ensure watershed management. Also, local market facility and processing facility of the harvest should be considered in planning of agriculture.”
Dr Priya Singh, a PhD scholar, department of Zoology, University of Lucknow, suggests an alternative- “Bio-predators like ladybird beetles can be used to control insect pest instead of excessive using of harmful pesticides."
The way forward
Robert Pavlis states: “Vermicompost is much like other kinds of compost. There is no scientific evidence to show that it is a superior product, as so many claim. On the other hand, it is a very suitable organic source to add to your garden. Like all organic sources, it will provide some immediate release of nutrients, and then go on to provide more nutrients in the long term. It will also improve soil structure since it adds organic matter, but too much organic matter can also be a problem.”
As the saying goes, moderation is a golden practice and excess of anything is bad.