PLACEMENT OF MATERIALS FOR COMPOSTING
Various arrangements such as bins, barrels, pits and windrows have been used or suggested for composting organic matter. Open piles, windrows, or bins are by far the most widely used methods for aerobic decomposition and maturing of organic refuse. The exact use and arrangement of these systems depends on the local requirements of materials, labor, cost of systems, climatic conditions such as temperature, rainfall, and wind.
To aerobically maintain the composting process by frequent turning for aeration, windrows, piles and bins above the surface of the ground appear to be more efficient than pits. On the other hand, if the decomposition is to be entirely anaerobic or aerobic only during a short initial period, pits 3 to 4 feet deep and varying in length and width in accordance with the daily quantity of raw material should be used.
WINDROWS, PILES AND BINS
The material in aerobic composting piles should be loosely stacked to allow as much space for air in the interstices as possible. The windrows or piles may be of any convenient length, but the height of the pile is somewhat critical. If piled too high, material will be compressed by its own weight, thus reducing pore space which results in increased turning labor (costs) or longer composting time as anaerobic conditions develop. In some instances, the maximum practical height may be governed by the equipment used for stacking the refuse, or by the tendency of the pile to become excessively hot. Large piles in warm weather may reach temperatures excessively high for bacterial life.
Piles that are too low lose heat rapidly. Optimum temperatures for destruction of pathogenic organisms and decomposition by thermophiles (high temperature microorganisms) are not obtained. Also, if the piles are too small, the loss of moisture may be excessive, especially near the edges, and decomposition slows.
Five to six feet is about the maximum height for any refuse, and 3 feet is the minimum for most shredded fresh municipal refuse. The height can be greater in cold weather than in warm weather.
Thoroughly mixing compost materials in bins, windrows or piles provides quickest and most complete decomposition. The pile may normally be started directly on the ground. However, to provide aeration to the bottom of the pile and improve drainage, dig a trench across the base of the area and cover with stiff wire mesh (hardware cloth) before adding material.
Daily quantities of materials available for home gardeners will often be too small to permit the satisfactory use of windrows. In this case circular or rectangular piles approximately 6 feet in diameter and 3 to 5 feet high, with a rounded top for running off of the rain water, would be best.
For shallow pits, either the walls and bottom of the pit are lined with brick or masonry or the natural earth is tamped and packed. The material is stacked to a height of 1 foot or more above the ground, making a total of 3 to 4 feet. The material can be turned in the pit as often as necessary to provide the high temperatures and aerobic conditions as required. When pits are used, a smaller stack surface is exposed to the air, and the walls and bottom of the pit provide some insulation against heat and moisture loss.
Any type of pit should be lined and is usually provided with a chimney and trenches, or a porous bottom, for aeration and drainage of liquid seepage from the pile. The same shape trenches without aeration and drainage channels and without masonry lining may be used. But unless pits are lined, the walls are apt to crumble and the shape of the pit becomes irregular. When hand labor is used, turning the material in a pit may be about the same as in a stack on the ground surface.
We suggest composting in pits approximately 3 feet deep by a system of providing aerobic conditions and high temperatures for the first few days and then anaerobic conditions for 4 to 6 months. The material is mixed in the pit. There is sufficient oxygen in the initial stack for a high temperature to be produced by aerobic organisms during the first few days. Apparently, the high temperature is retained for some two weeks, owing to the insulating properties of the stack, even though anaerobic conditions exist after the first few days. The material is left to compost in the pit with no turning for about three months under conditions that are primarily anaerobic.