Passive Composting of Manure Piles

Passive composting involves simply stacking the materials in piles to decompose over a long time period with little agitation and management. The process has been used for composting of animal wastes. Needless to mention that simple placement of manure in a pile does not satisfy the requirements for continuous aerobic composting. Without considerable bedding material, the moisture content of manure exceeds the level, which enables an open porous structure to exist in the pile. Little, if any, air passes through it. Under these circumstances, the anaerobic micro-organisms dominate the degradation.

All of the undesirable effects associated with anaerobic degradation occur including low temperatures, slow decomposition, and the release of hydrogen sulphide and other malodorous compounds.

When a livestock management system relies on bedding to add to livestock comfort and cleanliness, the bedding becomes mixed with the manure and creates a drier, more porous mixture. This provides some structure and, depending on the amount of bedding, enables the mixture to be stacked in true piles. The bedding also tends to raise the C:N ratio of the manure.

A mixture of manure and bedding requires a considerable proportion of bedding to provide the porosity necessary for composting. At least equal volumes of bedding and manure are required. If the amount of bedding is too low to provide a porous mix, then additional dry amendments must be provided by either increasing the bedding used in the barn or adding amendments when piles are formed. Manure from horse stables or bedded manure packs can often compost in piles alone, whereas non-bedded manure from dairy, swine, and many poultry barns needs drying or additional amendments.

The pile must also be small enough to allow passive air movement, generally less than 6 feet high and 12 feet wide. This passive method of composting is essentially windrow composting but with a much less frequent turning schedule. It is a common method used for composting leaves. It demands minimal labour and equipment. Passive composting is slow because of its low aeration rate, and the potential for odour problems is greater.

1 Source: FAO 1980 A Manual of Rural Composting. FAO/UNDP Regional Project
RAS/75/004 FieldDocument 15
2 Source: NRAES 1992 On-farm composting (Ed. Rynk, Robert). Natural Resource,
Agriculture, and Engineering Service, Cooperative Extension, Ithaka,
New York

Aerobic Decomposition through Passive Aeration