By Davidzo Chizhengeni
Vermicompost or worm compost is one of the highest-grade and most nutrient-rich natural fertilizers in the world. Its soil conditioning properties and plant-strengthening effect encourage the growth and yield of the crops. It is a black, odourless and crumbly substrate with a balanced nutritional composition for plant containing an above-average number of micro-organisms which revitalize the soil, and loose yet stable soil structure (clay-humus complexes).
Nutritional composition of vermicomposting and conventional compost
|Nutrient element||Vermicompost||Conventional Compost|
|N – Nitrogen||1.9%||1.4%|
|C/N – Carbon-Nitrogen ratio||13.6||20.6|
|P (%) – Phosphorous||2.0||1.8|
|K (%) – Potassium||0.8||0.7|
Eisenia fetida (hard workers) – Of the over 3,000 species of earthworms, the most frequently used species of compost worm is the red wiggler (Eisenia fetida), which is naturally predisposed towards high rates of conversion and reproduction. Eisenia fetida grow to a length of 6 – 13 cm on average. They are reddish in colour, with yellowish rings, making them easy to distinguish from other species.
Transformation Rates of Organic Material:
- Between half and the whole of the equivalent of its body mass a day
- Under perfect conditions: 3,500 worms (approx. 1 kg) devour 1 kg kitchen waste a day
- 200 – 300 worms can convert a volume of 1 m² and 20 cm depth into worm humus within 60 days
- Of the 100% source material, 15% is what remains in the form of worm compost
Reproduction- The good living conditions in the compost make the development cycle of Eisenia fetida the shortest of all earthworms, with a correspondingly high rate of reproduction. The young worms hatch 3 weeks after the eggs are laid and are sexually mature within another 9 weeks. The worm population doubles every 3 months (4 generations a year) resulting in 500 – 600 offspring per worm per year.
Feeding – Ideal feeding intervals are 10 – 30 days. Compost worms, have a huge appetite, they feed on almost anything from vegetable to animal sources. They feed on animal excrement from cattle, horses, sheep, pigs, poultry, goats, hares and donkeys. The worms are particularly partial to cattle excrement. For this reason, cattle manure is the most commonly used source material for worm composting. However, green and nutrient rich plant waste (hay, grass, silage, weeds, leaves foliage, banana, and orange peelings) is often also composted; matter which rots slowly on conventional compost heaps. The waste used should be of preference from organic agricultural sources. In terms of feed particle size, the basic principle is ‘the finer the material offered to these energetic workers (worms, microbes, microorganisms), the faster its conversion’.
Size of the Worm Compost – Most compost heaps are 1- 2 m wide, 30 – 50 cm high, and can be as long as desired. Since, Eisenia fetida is an epigeic species, i.e. a surface dweller which works in the upper layers of the soil, the compost should not be over 60 cm deep.
Location of Worm Compost – The compost heaps can be distributed between rows of trees, or housed in shelters.
Climate – The Eisenia fetida is very tolerant to a wide range of temperatures varying between 0 – 30°C, and is therefore, well suited to locations in the open air. To ensure that the earthworm bed does not get too hot, shade trees or a roof should protect it from direct sunshine. Fresh manure must first be pre-fermented. The humus should not be too moist since it can otherwise lead to an infection of the female reproduction organs.
Construction of a Vermicompost
- Bedding – To create a perfect climate, a “worm bed” is made by using coarse materials such as
shredded twigs, mulch or wood shavings/sawdust as a basis, varying according to what
is available locally. All the components should have been produced organically.
2. Feed – The next step is to cover the worm bed with a layer of feed matter consisting of vegetable
waste and manure.
3. Introducing the worms -The worms are added to the compost heap in batches.
4. Watering the compost – The amount of water needed depends on the climate (temperature, evaporation).
5. Cover the compost heap – In order to protect the worm population from predators such as birds, rats, snakes, cockroaches and ants, but also from heavy rains, the compost heap needs to be covered. The most suitable materials are: banana leaves, polyethylene foil, wood or corrugated sheeting.
Harvesting -The compost can be harvested in about 2 – 5 months. If the compost heap takes the form of a windrow, the source material is introduced to one end of the windrow and added to continuously. Care should be taken that the new material added is in contact with the old substrate. The compost worms move over to the fresh substrate and continue conversion. The older material can then be harvested and, if necessary, left to mature.
Vermicomposting Application Rates – The harvested material can be applied on any crop, at any stage, but it is more beneficial if mixed in soil after broadcasting.The rate of application is as follows;
~field crops 5 – 6 t/ha
~vegetables 10 – 12 t/ha
~flower plants 1-2 kgs/m2
~fruit trees 5 – 10 kg/ tree
Vermiculture and vermicompost need to be fully utilised in agriculture so as to harness the full potential of growing organic food, as well as to revatilise the soils.