The following article will guide you about how to build and manage a compost heap.
Building a Compost Heap:
Size of the Compost Heap:
A good basic size for a compost heap is 2 to 2.5 metres (about 6.5 to 8 feet) wide and 1.5 and 2 metres (about 5 to 6.5 feet) high. If the heap is too broad or too high aeration will be poor. The minimum size of a compost heap is usually recommended to be 1 metre3 (about 1 yard3).
Frequently more organic matter is needed to build a compost heap to the desired size than the inexperienced compost builder would expect. This can only be learnt through trial and error.
If it is difficult for an individual to collect sufficient organic material to build a compost heap it might be worth working with other farmers or householders, or even organizing the whole community into building their compost heaps together. Alternatively, extra material such as roadside cuttings or the organic by-products from local processing plants could be considered. The correct balance of slow and fast decomposable material, however, must be maintained.
Labour:
Building a compost heap should be timed to fit in with the slack periods of labour. Some composting procedures e.g., regular turning, and some methods are more labour intensive than others.
Availability of Animal Feed:
Much of the organic material suitable for composting is also suitable as animal feed. If animal feed is scarce it may be inappropriate to compost it. The farmer must make his decision based on his own circumstances. If organic material is used as animal feed (e.g., kitchen compost for pigs, crop residues for cattle) it is likely there will still be other types of unwanted organic compost. Even if it takes longer to collect sufficient material it can still be worthwhile.
Water Availability:
If water is scarce, it may be better to use available water directly for irrigation rather than for producing compost. However, compost added to the soil can improve its water holding capacity and, in the long term, would reduce the amount of the water required to irrigate the crops.
Methods to reduce the water requirements of a compost heap include:
(1) Covering the heap, thus reducing evaporation;
(2) Siting the heap in a shaded area;
(3) Enclosing the heap entirely within a wall of mud;
(4) Building the heap in a pit.
If a rainy season can be expected a good compromise is to concentrate on compost building when more water is available.
Pit or Heap:
A heap is the most common form of composting. However, where water is scarce composts can be built in pits. This minimizes water loss, although watering is still required. Where there are heavy rains of a high water table compost built in a pit can easily become too wet.
Managing the Compost Heap:
Water Content:
In dry conditions, the heap will probably require water to be added about twice a week. The moisture content can be tested by placing a small bundle of straw in the compost heap. If the moisture is acceptable then the bundle will be damp when removed after about five minutes. If the heap becomes too wet it should be opened up and mixed with more dry organic material or allowed to dry in the sun before being rebuilt.
Ingredients:
Nearly all organic material, plant or animal can be used in a compost heap. However, organic material breaks down at different rates ranging from a rapidly rotting fruit to the slow breakdown of a dry maize stalk. When building a managed compost heap it is important to have a good balance between slow and fast rotting material.
These two main categories of organic material he to be balanced correctly because of the proportions of carbon and nitrogen they contain. Broadly speaking, young, living material that decomposes fast contains low levels of carbon relative to high levels of nitrogen. Though, often dead material, for example straw, decomposes slowly and has a high ratio of carbon to nitrogen. This is called the C : N ratio; the higher the ratio the slower the rate of decomposition.
Building the Heap:
In order to produce the conditions required by a compost heap it should be built in a particular way. First, a layer of course plant material such as stalks or twigs to ensure good air circulation and drainage is needed. Following that, organic material should be placed in layers, alternating between materials that is easily decomposed with material that decomposes slowly. A good thickness for each of these layers is 10 cm (about 4 inches).
If manure is used it should be applied in layers of 2 cm (1 inch), and soil applied even thinner. Water should be applied after each sequence of layers. With each layer of organic material, the edges should be laid down first, followed by the centre. This ensures that the heap edges will be firm and not collapse. Alternatively, a wire mesh or similar supporting structure that allows air to pass through can be used.
Air Vents:
These are made of bamboo canes with holes cut in them and placed both vertically and horizontally throughout the heap, can improve aeration. A large pointed stick should be driven into the heap at a slant to monitor the temperature.
The heap should then be covered to protect it against moisture loss and/or heavy rain. Sacking, grass thatch or banana leaves are all suitable.
Within three week the volume of the heap will have decreased considerably.
Digestion:
Aerobic composting or digestion of livestock composts can be accomplished by placing the manure in windrows.
The Super Digested Compost:
Application of super phosphate at 5 % over the raw compost materials during composting improves the manurial value of compost. Application of this compost to acidic, calcareous and heavy soils increases the P availability.
1. Windrows:
They are elongated piles that are turned periodically to aerate the organic composts. They can be of any convenient length, about 2.5 to 4.0 m wide and 1.5 to 2 m high. The height of the windrow is critical and should be carefully managed in order to obtain good results. If piled too high, the material will be compressed by its own weight which will destroy the spore space and cause anaerobic conditions.
2. The Height of the Pile:
It is also critical from the standpoint of controlling temperature. Windrows stacked too high may retain too much heat and develop temperatures above 70°C. Temperature in this range will destroy many of the microorganisms, slowing down the process and causing anaerobic conditions.
Shallow piles may dissipate heat too rapidly, preventing optimum conditions for thermophilic organisms to be reached. Loss of moisture may also be excessive, causing the rate of composting to be retarded. In drier climates, the cross-section of the windrow is usually trapezoidal, with the angle of repose being approximately 30°. In rainy climates, if no overhead protection is provided, the cross-section of the windrow should be semi-circular in order to shed water.
3. Turning the Pile Frequently:
It is essential for obtaining a rapid, nuisance-free composting action characteristic of the thermophilic aerobic process. In order to ensure a uniform and rapid decomposition, the compost must be thoroughly mixed. One method is to turn the outer edges into the center of the pile. This procedure causes weed-seeds, fly larvae, and pathogenic organisms which might survive near the cooler surface to be exposed to the lethal temperatures at the interior of the windrow.
Turning is also useful for reducing the moisture content and aerating a pile that has become anaerobic. Turning can be accomplished by using a front-end loader or a clam-shell bucket. Commercially available machines are also available for mixing windrows.
These machines are designed to straddle the windrow and mix the compost by means of long tines mounted on a rotating drum. Under normal conditions, when the moisture content is between 50 and 60%, the windrow should be turned at 3-day intervals. If the moisture level exceeds 60%, the windrow should be turned at 2-day intervals to prevent the occurrence an anaerobic conditions.
Curing:
After the compost has gone through a period of active decomposition, the composted material must be removed from the windrow and allowed to cure. Curing is a process that allows the compost to continue its stabilization process at a slower rate under mesophilic conditions. Curing can be done in the open or placed under cover. After the compost is cured it is ready to be stored or utilized as a soil conditioner.
Maturation of the Compost:
Once the compost heap has cooled down the heap should be left to mature. However, as long as most of the original material is no longer recognizable, and has turned into a brownish-black colour the compost can be used. If left to mature a finer product will be produced with a wider range of uses.
Maturation can take place on the ground, although the heap should be kept covered to protect it from the rain and sun. If the compost is kept for too long before use it may lose some nutrients and may also become a breeding place for unwanted insects.