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Figure 1. Raised wooden boxes for vermicomposting, open (left) and closed (right). |
Containers and box systems are more labour-intensive since batches have to be moved in order to add more wastes or water. It is however, the best technology for backyard vermicomposting of garden and kitchen wastes (Figure 1). Low cost beds or windrows are the simplest technologies commonly used in vermicomposting. The bed size may vary but it must be freely drained and covered. The cover is only removed when water or new feed is added. The production of vermicompost requires from three to six months.
Techniques and Terminologies
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Figure 2. Well cured vermicompost that is ready for use in potting mixtures or horticultural crop production. |
Vermicompost. A humic substance produced through an accelerated composting process that, when applied to soil, results in improved chemical, physical and biological properties and better conditions for plant growth.
Vermicomposting. This is the use of earthworms to transform organic materials into rich, organic fertilizers. The growth of earthworms in organic wastes is termed vermiculture while the processing of wastes using earthworms is known as vermicomposting or
vermin-stabilization.
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Box 1. Differences between composting and vermicomposting technologies
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Microorganisms decompose substrate
Takes a longer period to mature
Thermophilic stage must be attained
Compost is coarser textured
Risk of heavy metals in the compost |
Microorganisms and earthworms combine their activities to transform the substrate
Matures relatively faster than compost
No thermophilic stage is required
Vermicomposts are finer textured
Heavy metals are removed and accumulated within worm bodies |
Advantages of Vermicomposting
Vermicomposting is important in both smallhold and large scale agricultural production in several ways. Some of the reasons why farmers will choose to practice vermicomposting are summarized as follows:
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Vermicomposting is rapid and minimizes nutrient losses.
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Suitable earthworms are found throughout the world and the best worms are available through commercial channels.
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Suitable mixtures of organic feeds are widely available and the environmental range for vermicomposting is broad.
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Environmental conditions that affect the survival and distribution of earthworms, moisture, temperature, pH and aeration can be controlled within the vermicomposting bed.
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Vermicomposting processes organic material more rapidly than traditional composting yet the final products are very similar (Box 1).
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Farmers, especially smallhold farmers need inputs for crop production and vermicomosting offers an affordable source of organic fertilizer.
Vermicomposting Species
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Figure 3. Earthworm species that are well-suited for vermicomposting of agricultural wastes: Kenyan pigmented worm (left) and tiger worm (right). |
The tiger worm (Eisenia foetida). This is the most commonly used species in commercial vermiculture and waste reduction (Haimi and Huhta, 1990). The species colonizes many organic wastes and is active in a wide temperature and moisture ranges (Figure 3, right). The worms are tough, readily handled, and survive in mixed species cultures. It is closely related to Eisenia andrii, another useful vermicomposting species. The species is commonly used in the U.S., Europe and Australia under the name Lumbricus rubellus. This species is raised in Kenya by several flower farms in the Central Highlands and Rift Valley.
Kenyan highland forest pigmented earthworm. A not yet identified earthworm was recovered by the author from highland forest litter near Muguga, Kenya. This species performance is comparable to the well-known Eisenia foetida (Savala, 2003). It produces finer vermicomposts than E. foetida but the chemical composition is comparable (Figure 3, left).
African night crawler (Eudrilus eugeniae). This is a large prolific African worm that is cultured in the U.S. and elsewhere. When large worms are produced under optimum conditions, they are ideal for use as fish bait and in protein processing. It is somewhat difficult to raise because of its intolerance to low temperature and handling. The use of E. eugeniae in outdoor vermiculture is limited to tropical and sub-tropical regions because it prefers warmer temperatures and cannot tolerate extended periods below 160C (Viljoen and Reinecke, 1992).
Perionyx excavatus. This is a species well adapted to vermicomposting in the tropics. The earthworm is extremely prolific and easy to handle and harvest but it cannot tolerate temperatures below 50C, making it more suited to the tropics.
Dendrobaena venata. A large worm with potential to be used in vermiculture and that can also inhabit soils. It has a slow growth rate (Edwards, 1988) and the least suitable species for rapid organic matter breakdown.
Polypheretima elongata. The species is suited for use in reduction of organic solids, municipal and slaughterhouse waste, human waste and poultry and dairy manure but it is not widely available. It is restricted to tropical regions, and may not survive temperate winters.
Production of Vermicompost Using the Bed Technique
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Figure 4. A vermicomposting bed with rock walls and concrete floor (Step 1). |
Step 1. Construct the bed. Prepare a bed with a concrete, wood or plastic sheet bottom and construct walls 20 to 30 cm in height using wood, logs or stone. Place a wooden board across the bottom and line with chicken wire for better handling and aeration (Figure 4).
Step
2. Add coarse material.
Place a 10 to 15 cm layer of coarse organic materials such
as banana trash, maize stover, coffee husks and other crop residues on top
of the chicken wire (Figure 5). The material must not contain poultry
manure as the uric acid is harmful to worms. Composted poultry manure is,
however, suitable as feed.
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Figure 5. Many coarse-textured materials placed on the floor bed are suitable for vermicomposting (Step 2). |
Step 3. Add fine material and water. Place a 5 to 10 cm layer of manure on top of the coarse material. Cattle, pig, sheep or goat manure are suitable. Green manure, such as tree leaves or grass cuttings may be substituted. Mix some of the fine material with the coarse layer. Mixtures of fine materials such as grass cuttings, bean threshing, maize or wheat bran and brewery waste are preferable. If the fine material is available in short supply, then use it to surround specific areas where earthworms are released. Moisten the organic materials prior to the introduction of the worms. Sufficient water should be applied so that no pockets of dried material remain. Wet materials such as banana trash and fresh manure need little watering while dried materials may require as much as 30 liters of water per m2 of bed.
Figure 6. Clusters of earthworms are introduced into a well-watered composting bed (Step 4). |
Step 4. Release worms. Release the earthworms into the moist bed. Avoid handling individual worms, rather place small handfuls of material rich in earthworms (clusters) into “holes” spaced about 0.5 m apart (Figure 6).
Figure 7. Fresh banana leaves used to cover the bed. Epigeic earthworms avoid light so beds should be covered (Step 5). |
Step 5. Cover the bed. Cover the bed with banana leaves (Figure 7) or dark polythene plastic. Inspect the bed regularly during composting for moisture and the presence of predators. Ants will usually leave the bed if the underlying chicken wire is violently and repeatedly shaken. Add new layers of banana leaves occasionally as the worms consume older leaves.
Step 6. Feed the bed. Organic materials may be applied to the bed regularly as additional layers or in discrete locations. A common practice is to periodically apply additional organic wastes by burying them in different positions within the bed. Vermicompost is ready after three to six months. Additional feeding prolongs the vermicomposting process but yields larger amounts of vermicompost. Withhold feed about three weeks before the vermicompost is collected to obtain a finer and more homogeneous and finished product.
Figure 8. Collecting earthworms that aggregate within the drying vermicompost for use as feed, bait or starter for the next batch of compost (Step 7). |
Step 7. Recover worms and vermicompost. When the vermicompost is ready, worms are harvested and compost processed. Place a fine feed material on the bed prior to vermicompost harvesting to facilitate the collection of worms from subsequent “batches”. Wheat bran, brewers’ waste or fresh cattle manure are particularly good feeds that lure earthworms. Collected worms may also be fed to fish and poultry. Spread vermicompost in the sun to collect other pockets of worms by hand as the vermicompost dries.
Once worms are collected, the vermicomposting cycle may be repeated. The finished vermicompost is uniform, dark and fine textured. It is best used as the main ingredient in a seedling or potting medium after passing it through a 5 or 10 mm mesh. A typical nutrient content from a manure-based vermicompost using E. foetida is 1.9% N, 0.3% P and 2.7% K.
Conclusion
Earthworms are useful in organic waste recycling. If a large number of adult worms (200 to 300) are introduced into one square meter of a 20 cm-deep compost substrate, covered with fine material and optimum conditions provided, mature vermicompost can be produced within as little as 60 days. Vermicomposts have excellent chemical and physical properties that compare favorably to traditional composts. Furthermore, the diversity among epigeic earthworms enables them to be utilized across a wide range of environments and in processing many different organic materials. Earthworms transform wastes into valuable products and a clever resource manager can discover many advantages through this process.
Vermicomposts are best applied to higher-value crops as a source of plant nutrients. The material is also excellent as a major ingredient of potting mixtures and to raise seedlings for transplanting. After vermicomposting, the worms may also be recovered for use as fishing bait or feed for poultry and fish. Earthworms provide an excellent source of protein that could even be consumed by humans but current food preferences tend to discourage this practice. Worm burger anyone?
References
Appelhof, M., Webster, K. and Buckerfield, J. 1996. Vermicomposting in Australia and New Zealand. Biocycle 3:63-66.
Ceccanti, B. and Masciandaro, G. 1999. Vermicomposting of municipal paper mill sludge. Biocycle 6:71-72.
Edwards, C.A. 1988. Breakdown of animal, vegetable and industrial organic wastes by earthworms. Agricultural Ecosystems and Environment 24:21-31.
Haimi, J. and Huhta, V. 1990. Effect of earthworms on decomposition processes in the raw humus forest soil: A microcosm study. Biology and Fertility of Soils 10:78-183.
Masciandaro, G., Ceccanti, B. and Garcia, C. 2000. In situ vermicomposting of biological sludges and impacts on soil quality. Soil Biology and Biochemistry. 32:1015-1024.
Savala, C.E.N. 2003. Vermicomposting of Agricultural Waste in Central Kenyan Highlands. M.Sc. Thesis. Department of Soil Science, University of Nairobi, Kenya.
Viljoen, S.A. and Reinecke, A.J. 1992. The temperature requirements of the epigeic earthworm species Eudrilus eugeniae (Oligochaeta): A laboratory study. Soil Biology and Biochemistry 24:1345-50.