|Organic and Compost-based Growing Media for Tree Seedling Nurseries (WB, 1995, 90 p.)|
The most appropriate method to be used for making compost is dependent upon the following: the type of waste available; the quantity of raw material; available funds, labor, equipment and space; amount of compost needed; and climate or season. Methods will vary according to the amount of material and construction of the heap, the manner by which wastes are placed into the heap, and the frequency materials are turned. Compost heaps can be constructed as either enclosed or free-standing piles, in pits or trenches, or in windrows (elongated piles). A composting unit can be as small as one cubic meter or may contain up to 100 tons of raw material depending on nursery needs.
Composting is often a task for the less busy times in the nursery when labor is available to collect and process wastes, build piles, and turn the compost. Composting generally needs to be started at least 6 months before it is will be used, though actual time for processing will depend on the mixture, season, and climate. In the tropics, composting time is generally less than in temperate countries because of the higher ambient air temperatures.
Following are brief descriptions of three commonly practiced methods of comporting: Bangalore, Indore, and Berkeley. The single outstanding difference between methods is the frequency of turnings which affects the rate of decomposition. It is not essential to follow only one method and nursery managers should be encouraged to experiment and be flexible in their approach to composting.
The Bangalore method functions aerobically for several days and then becomes anaerobic, because no turning occurs. Although appropriate for both below- and aboveground composting, it is more commonly carried out in pits. After 4 to 5 months the composting process is complete. One drawback with this method is that without turning, the entire contents of the pit do not reach high temperatures and not all pathogens and weed seeds are destroyed. Fly breeding and odor problems are often associated with this method so the top exposed portions must be covered, usually with soil. Material near the outside of the pit should not be used, but transferred and incorporated into the next composting mix.
The Indore composting system relies on aerobic activity although portions of the pile or pit will likely become anaerobic between turnings. This method has better fly control, more rapid and uniform decomposition, and less moisture control problems than with the Bangalore method. During the period of active composting the contents are turned from 1-5 times over a period of 16 months. The longer the intervals between turnings the longer the composting process. Many smaller compost operations use this less labor intensive method.
The Berkeley method for composting is named after the University of California at Berkeley where it was developed. It is considered to be the quickest method of achieving finished compost, and it is the method which is likely to be the most effective method for production of either large or small quantities of compost. This method requires frequent turning and mixing of the heap, particularly during the initial stages of decomposition which intensifies the activity of microorganisms. The Berkeley method is normally carried out in above-ground stacks or windrows where air circulation is improved and the pile is accessible for turning. Since turning is frequent, problems associated with odors and flies are minimal. Compost should be ready for maturing within two or three weeks depending on the size of the heap, frequency of turning, initial C/N ratio, and moisture content. Labor requirements are higher with this method than the others, but the shorter composting period reduces the space needed for a site. Where large quantities of compost are produced a mechanized system is often used.
Further information on the basic methods of composting (preparation of raw materials, compost heap construction, management and monitoring, etc.) are given in Annex III.
The use of various species of worms can be used to rapidly and efficiently consume and break down vegetable, human, and animal wastes (See Annex VI). The resulting "vermicompost" has very good peat-like quality with excellent structure, porosity, aeration, drainage, and moisture holding capacity, and it contains a large quantity of 'inorganic nutrients (Edwards and Burrows, 1988).