Vermicast Fertilizer Characteristics
Nutrients
Vermicast nutrient content varies with earthworm feed type, but feeding waste to earthworms does cause nitrogen mineralization, followed by phosphorous and sulphur mineralization after egestion. A typical nutrient analysis of casts is C:N ratio 12–15:1; 1.5%–2.5% N, 1.25%–2.25% P2O5 and 1%–2%, K2O at 75%–80% moisture content. The slow-release granules structure of earthworm casts allows nutrients to be released relatively slowly in sync with plant needs.
Salinity
Ammonium is the main contributor to salinity levels. Earthworms are repelled by salinity levels above 5 mg/g. Therefore, if the starting material is low in salt, the resulting vermicast will be as well. In fresh vermicast, ammonium mineralized in the earthworm gut is nitrified over 2 weeks.
Pathogens
Pathogen levels are low in vermicast, which is considered a Type A biosolid when excreted by earthworms. This is a lower pathogen level than in typical composts. Vermicast is low in pathogens because earthworms consume fungi, and aerobic bacteria do not survive low oxygen levels in the gut. Low pathogen levels could also be due to the fact that vermicasting does not build up heat, which allows disease-suppressing organisms to survive the vermicasting process and outcompete pathogens.
Digestion
Red wigglers can consume 75% of their body weight per day. Earthworms weigh about 0.2 g and require oxygen and water, both exchanged through their skin.
As organic matter passes through the earthworm gut, it is mineralized into ammonium (later nitrified) and other plant nutrients. The grinding effect of its gizzard and the effect of its gut muscle movement result in the formation of casts. Most pathogens are consumed in the earthworm gut, since earthworms feed on fungi, and pathogenic bacteria cannot survive in the low-oxygen environment inside the earthworm gut.
Feed Preferences
The ideal feed for earthworms is food or animal waste and fresh, green, plant waste, rich in nitrogen or precomposted (for up to 2 weeks to make it easier to digest). Ideally, earthworm feed has a 25:1 carbon-to-nitrogen (C:N) ratio and a pH between 6.5 and 8 (close to neutral) – sudden pH fluctuations repel earthworms. ( my opinion anything over 7.0 pH is too alkaline , most sources and forums agree with the 6.5 to 7.0 pH range)
Ideal earthworm feed is:
porous, allowing oxygen to penetrate
warm (25°C): worms can survive in temperatures 0°C–35°C, but at lower temperatures they are not as active and die at freezing temperatures
moist, but not wet: 75% moisture is ideal, like wet soil at field capacity (earthworms migrate out of wet materials)
not too dense: below 640 kg/m3 (40 lb/ft3) – like the fluffy density of peat moss
not salty: below 0.5% salinity – higher is too toxic
devoid of toxins such as de-worming medicine, detergent cleansers, pesticides and tannins
Online calculators for optimizing worm feeds are available. Search online for "vermicasting, feed mixtures with optimal characteristics." The calculation uses the percentage nitrogen, percentage carbon, water content and density of each feed material, plus the total desired feed quantity.< ( I've never seen any online calculators for configuring worm feed
)
Light Sensitivity
Earthworms have eye-cells on their skin that trigger pain when exposed to any light but blue light, keeping them underground during daylight. They will try to leave any material if it does not meet their feed requirements, but if a light is shining at the surface of the material, they will stay where they are.
Bin or Reactor Design
The goal for any vermicasting system is to:
provide worms with a palatable feed
have worms digest waste at the highest rate possible
keep worms from migrating out of or to the edge of the windrows, raised beds or bins
Waste must:
have the required pH and salinity levels
be moist but drained of excess water
be neither too cold nor too hot
be stacked in thin layers that diffuse air
Drainage and Aeration
For appropriate drainage and aeration, container walls, bottom and side walls must be made of a perforated material. Many commercially available vermicasting bins have a few holes at the bottom for drainage, but this is not enough. A screen-type floor surface allows drainage, unlike common bedding materials. A screen size of 4 mm (5/32 in.) will keep most waste particles in.
Earthworms will not fall through this size of hole but they can burrow through this size of hole to get to fresh wastes if need be.
Some commonly used bedding types are dense and can become waterlogged, not allowing air to diffuse through the drainage/aeration holes in the bin bottom. Instead, consider using a layer of finished vermicast on the bin bottom for the start-up period because worms will burrow through it, resulting in good aeration and drainage. Starting with a vermicast layer also provides room to keep the worm stocking density lower than the maximum 300 worms/L of material. Higher densities reduce worm efficiency. Keep an air space of at least 5–10 cm depth (2–4 in.) below the screen floor for free drainage. Earthworms could burrow through the 4-mm screening on the bottom of the bin, but they choose not to because there is no food there, just open air. Leachate draining through can be collected and reintroduced to the bin.
Moisture
Waste materials should have a moisture content of 75% (field capacity), never more than 85%. Regular watering, or automatic sprinkling in the case of large scale systems, is usually needed. If waste materials with elevated levels of water content are added, such as food waste (fruits and vegetables are about 90% moisture), watering is not necessary, and drainage will correct the moisture level if it exceeds 75%.
Thickness of the Waste Layer
To prevent anaerobic conditions (lack of oxygen), which can result in fermentation and heat build-up, design the vermicasting bin, raised bed or windrow pile to keep the waste layer at a thickness of 30 cm (1 ft) or less. This thickness allows air to passively diffuse into the material, aided by the canals burrowed by earthworms. This keeps the pile aerated and cool, which earthworms prefer. A thin layer of waste helps prevent compaction of the bottom of the waste pile, which might cause poor aeration, fermentation and heat, all of which repel earthworms.
Active aeration, mixing and temperature control of such a thin layer of waste occurs through the burrowing action of the earthworms. The earthworms do the work, unlike an active composting system where aeration, mixing and temperature control are accomplished by fans and/or machinery.
Temperature
Since earthworms require a temperature range of 0°C–35°C (optimum is 25°C), year-round vermicasting systems must be designed carefully for the Ontario climate. The process is odourless but does not generate heat on its own, so one option is to place the bin indoors. If this is not possible, insulate bins and place them partly underground in a sheltered location to help temper outside temperature fluctuations.
Odours and Flies
Odorous gases (volatile organic compounds) and heat are produced during fermentation, which can occur in poorly aerated (anaerobic) organic materials. This is often a problem in compost piles if they are not aerated or mixed. However, earthworms thrive in aerobic conditions, where fermentation and the resulting heat and odours do not occur. If designed properly, vermicasters do not produce odours.
When a vermicaster does produce odours and flies, it is likely due to excess water. Proper drainage using raised screen surfaces (4 mm) at the bottom of the container and/or reducing the thickness of the waste to no more than 30 cm should resolve this situation.
( I copied this from here ) >
http://www.omafra.gov.on.ca/english/engineer/facts/10-009.htm
