The time required for satisfactory stabilization depends primarily upon:
a. initial C:N ratio;
b. particle size;
c. maintenance of aerobic decomposition; and
d. moisture content.
If moisture content is in the optimum range, compost is kept aerobic, and particles of material are of such size as to be readily attacked by the organisms present - all factors that can be controlled in the composting operation - the C:N ratio determines time required for stabilization. Low C:N ratio materials are decomposed in the shortest time because the amount of carbon to be oxidized to reach a stabilized condition is small. Also, in low C:N ratio compost, a larger part of the carbon is usually in a more readily available form, while in higher C:N ratio materials more of the carbon is usually in the form of cellulose and lignin which are resistant to attack. The changing biological population in the changing environment attacks cellulose and lignin last. When the available C:N ratio is above 30, additional time is required for recycling nitrogen.
If material is not kept aerobic so that high temperatures can be maintained during the active decomposition period, or if the particle size is so large that the bacteria cannot readily attack the material, or that the interior of the particle becomes anaerobic, longer composting periods are required.
Under aerobic conditions at high temperatures and when the initial C:N ratio is in the optimum range or below, the material takes on the appearance and odor of humus after 2 to 5 days of active decomposition. However, active decomposition is not complete at this stage, and the C:N ratio may not have been lowered to the level desired for fertilizer.
The actual composting time is not particularly important, provided that it is sufficient for destruction of pathogens and parasites, and for nitrogen conservation.
So long as satisfactory compost can be produced, turning time of composting, storage, and other factors should be adjusted for home composting and for nitrogen conservation.