Template:Chapter 4.15

4.15 - Using worms to create manure (vermicomposting)

Dylan P. Harding, University of Guelph, Canada

Introduction

Livestock populations are declining in many developing nations, and with them the supply of manure. Animal manure is an important source of nutrients that will improve yields when applied to the soil. Where little or no animal manure is available, worms can be intentionally introduced to compost piles to help break down food waste and crop residue. This process, known as “vermicomposting” creates biologically active compost that will benefit soils in a similar manner to animal manure, especially in terms of providing organic matter and micronutrients. Vermicomposting has been demonstrated by several studies to improve the quality of the final compost product in comparison to regular composting by improving mineral availability and concentration (Arancon, Lee, Edwards, & Atiyeh, 2003; Bhattacharya & Chattopadhyay, 2002; Ndegwa, Thompson, & Das, 2000; Suthar, 2009).

Worms can be broadly classified according to their habitat. “Epigeic” worms are those that live on the Earth’s surface in decomposing materials and do not have permanent underground burrows (Munroe). Epigeic worm species such as Red Wrigglers (Eisinia fetida), African Night Crawlers (Eudrilis eugeniae), and Perionyx excavatus are the most commonly used species for vermicomposting because a compost pile is very similar to their natural habitats. Epigeic worm species will predominate in untended compost or other decaying plant matter, so these are generally good places to collect worms to use for vermicomposting. Most epigeic worm species can reproduce rapidly, because this is necessary for competition in the wild (i.e. they must quickly grow in number when food becomes available) (Munroe). With this in mind, worm species found in an untended compost pile will probably have naturally good growth and reproduction rates, and therefore will likely be suitable for vermicomposting. More information on find an appropriate worm species is included below under Feeding and Caring for the Worms.

Labour and Time Requirements

Vermicomposting generally requires more work than traditional composting, although a vermicomposting pile has the benefit of not needing to be regularly turned over. This is because the tunnels made by the worms will allow air into the compost in a similar way that turning it over would (Munroe). Keeping enough moisture in the pile will probably be most of the daily work involved with a vermicomposting pile. Food and bedding will also have to be added to the pile every few days, depending on the management technique.

The harvest of a vermicomposting pile requires separating the worms and the compost as much as possible. This generally requires more labour than simply taking an entire finished compost pile to a field. However, with proper management separating the worms and the compost can be done without too much extra work. See the section on Harvest (below), for further detail.

Vermicomposting can take more or less time than traditional composting. This depends largely on worm population density and the climatic conditions of the compost pile. Under ideal conditions, vermicomposting will require less time to produce finished compost than traditional composting (Munroe).

Feeding and Caring for the Worms

Worms can be fed with almost any crop or food waste (Munroe). Exceptions include materials that are high in protein such as meat, blood or offal or materials that are high in salts (Munroe). Pre-composting such materials before introducing them into the vermicomposting environment can make them more suitable. Citrus based materials should not comprise more than 1/5th of the feed material because of their acidity.

A bedding material must also be included in the compost environment to retain moisture and provide adequate carbon (an energy source for the worms). The most important characteristics for bedding materials are high water absorbance, resistance to compaction, and a high carbon to nitrogen ratio. Shredded waste paper or cardboard is ideal although most absorbent carbon based material can meet this requirement. See Table 1 of the OACC manual [(Munroe), link included below] for carbon to nitrogen ratios of commonly available bedding materials. Different materials also can be mixed to create bedding that retains moisture and resists compaction. For example animal manure, which is highly absorbent, can be mixed with straw, which resists compaction but is not very absorbent (Munroe). Manure from pasture animals (cattle, sheep, goats) should be pre-composted on its own before addition to the manure pile so weed seeds can germinate and die off well before the manure is introduced to fields (Munroe). The ideal ratio of bedding to feed material will vary depending on the materials used. Foul odours or persistently dry conditions can be an indication that the vermicompost pile requires more bedding relative to feed material.

The compost pile must be kept moist (> 50% moisture at all times, ideally 70 to 90%) (Munroe). This is important because the worms will die if they dry out. Basically, 70 to 90% moisture means that the bedding material should be as wet as possible without dripping. Worm compost piles will often require being sprayed or sprinkled with water to maintain their moisture (Munroe).

Temperature is also important for the survival of the worms, and should be as constant as possible (Reinecke, Viljoen, & Saayman, 1992). Shielding the compost pile from direct sunlight will help encourage constant temperature. If native worms species are being used for the project a shaded compost bin will likely be enough precaution to ensure their survival however if an imported worm species is being used their ideal temperature range for growth and reproduction should be considered.

Worms can be expected to eat approximately half of their weight per day, although this will change depending on the feed material being given to the worms and their environment (Munroe). If the worm reproduction or compost production rate is less than ideal despite good culture conditions, the purchase of a worm species specifically intended for composting can be considered, if available. A guide to feed material digestion over time is provided in Table 1.

Making a Vermicomposting Pile

Vermicomposting can be performed either above ground in a sturdy container, or in a pit dug into the ground. If a pit environment is chosen it should be lined with an impermeable material to prevent the escape of worms (Munroe). Plastic bags or similar material could be used, though there should be as few gaps in the lining as possible. Pits have the advantage of being very easy to build and maintain, as well as being insulated from temperature changes. Harvesting of a pit will be less convenient as it will be lower down and the operator will have to bend over further to access the compost. This will be a greater concern for some than others depending on age, height, physical health, etc.

Above-ground vermicomposting can either be performed either in containers or in open piles. Enclosed containers are recommended because they protect worms from predators and discourage their escape.

Above-ground containers can be made from most materials, although metal is not recommended because it transfers heat quickly and is likely to rust. Concrete is a popular option for its sturdiness and availability (Munroe). Large plastic containers can also be successfully used if available. Wood containers can be made but will require more frequent maintenance because of their tendency to rot (Munroe). Pressure-treated wood should be avoided because of its toxicity. Rammed earth could also be used to create the worm environment if the techniques for its construction are known in the area. If practical, the sides of an above ground container should have some vent holes to encourage air flow through the worm environment, as well as some kind of drainage outlet to remove excess moisture (Munroe).

The worm population for a new compost pile should be 2.5 to 5 kg worms per m2 of bedding and worm feed. An established vermicomposting pile should have 5 to 10 kg of worms per m2 (Munroe). Producers should use higher stocking densities when maximum compost creation is desired, and lower stocking densities when maximum worm production is desired (see Table 1).

Physical Protection

Protection is the main benefit from using gloves. Repetitive motions, such as when pounding grain, can cause irritation to the skin. When collecting firewood the sticks and logs can scratch or cut the skin (Food and Agriculture Organization, 2016). Weeds can be rough and by scratching their hands many times they can become cut and sore (Espasandín-Arias & Goossens, 2014). By lifting and pulling heavy items the top layer of your skin will separate from the next, causing a blister, by wearing gloves they now will prevent blistering because the glove will act as the top layer of skin and prevent the actual skin from separating (Schaffner, 2013). Manure has a lot of bacteria in it which are harmful if they are swallow, so keeping them away from the hands used to eat with is very beneficial (Furlong, et al., 2015). If farmers are working with firewood or in construction the cloth gloves will work better because they are more durable (Food and Agriculture Organization, 2016). The disposable rubber gloves would be the worst to use in this scenario because they are so thin, stick to jobs were the main goals are to keep hands dry and dirt free when using disposable rubber gloves.

The compost pile should be no more than a meter deep (Munroe). Because surface dwelling worms are used for vermicomposting, they will not perform well if covered by an excess of material due to lack of available oxygen (Munroe). As long as the vermicomposting pile is not excessively deep, its shape can vary depending on the desired management technique. Smaller piles will be easier to harvest but will generally require more labour per unit of compost harvested. With this in mind, compost piles should be as large as can be reasonably managed for harvesting. A rectangular shape will be more convenient for some harvesting techniques, for more information see Harvesting section below.

The construction of a vermicomposting container is very flexible and a wide variety of designs can potentially be successful. The most important characteristics of a container’s design are air flow, moisture retention, drainage, and accessibility, particularly for the removal of finished compost. Additionally, the container should prevent the escape of worms from the compost environment. Non-biodegradable materials should be used if available as they will require less frequent replacement.

Harvesting

There are two broadly practiced, low-tech methods of harvesting worms. In the “vertical harvesting” method, the finished compost is spread on well-lit surface (daylight is ideal). The worms will burrow downward in the compost to avoid the light, and the upper level of worm free compost can be removed in layers. Worms will continue to move downward as the upper layers are removed (Munroe). This method is best suited to smaller worm composting operations.

In the “horizontal harvesting” method, new feed material is added only to one side of the compost pile at a time. As one side of the pile approaches completion, the worms will migrate to the side of the pile where the new material is being added. After material on one side is completely digested, most worms will have migrated to the other side of the pile and the completed compost can be removed with minimal loss of worms (see Table 1 for approximate timing). Addition of new feed material can then begin on the just-harvested side of the compost pile. The horizontal harvesting method is less time consuming but is more likely to cause some loss of worms.

A final method of harvesting worms can be used with open compost piles. In this method new material should be added in thin layers (approximately 10 cm thick) evenly to the top of the pile. When this layer is close to being fully digested, a new layer can be added on top. The worms will then migrate up into the new food material. In this system, the lower levels of the windrow remain fairly free of worms. When harvesting is required, it should be performed a few days after a new feed layer is added. The top layer (containing most of the worms) can then be removed and added to a new pile or used for feed and the lower layer can be applied to crops with minimal loss of worms (Munroe).

Species

As mentioned above, African Nightcrawler (Eudrilus Eugeniae), Red Wriggler (Eisenia Fetida), and Perionyxexcavates have all been identified as ideal species for vermicomposting because of their suitability to the compost environment and high rates of growth and reproduction. In Africa, African Nightcrawler worms as well as other potentially suitable epigeic worm species can commonly be found in the environments described in Table 2. Those interested in vermicomposting should first try gathering worms from the environments described in this table. If the collected worms are not surviving or showing poor growth in the compost pile, the purchase of one of the popular vermicomposting species can be considered if available.

In general a temperature in the mid-twenties (˚C) that is kept as constant as possible is ideal for the growth of worms. Temperatures over 35°C should be avoided. Excessively cold temperatures are not likely to be limiting factors on worm growth for farmers in tropical climates.

Other Uses

Worms are a dense source of high-quality protein, and could be used to supplement livestock diets (Sun, Liu, Sun, & Song, 1997). Producing worms for feed could potentially be a small business opportunity for farmers if there is demand in their area, however available studies report that worms reproduction rates must be very high for this kind of system to be economically viable (Reinecke & Albert, 1994). Further study in this field is required.

Limitations

There will usually be more day-to-day work required to maintain a vermicomposting pile in comparison to traditional composting (especially in ensuring adequate moisture for the worms), although careful management (especially to limit moisture loss) can limit the additional labour required.

There is limited information available on the cultural acceptance of vermicomposting. This will obviously vary widely between communities and individuals, however it is likely that some people will not like handling worms. This could be a barrier to the uptake of vermicomposting techniques over traditional worm-free composting methods in some areas. It is possible that children (especially little boys) may find worms fun and could potentially be employed when handling worms is necessary.

Additional Reading:

http://www.villagevolunteers.org/wp-content/uploads/2011/05/Vermicomposting.pdf