DR. Paul Research Update
Compost technology continues to evolve
New research offers insight to the great livestock question “what to do with the poo”

July 1, 2004: Livestock operations often struggle with the best way to effectively dispose of their animals' waste. Straight application of manure to the land can give off dangerously high emissions of ammonia, odor and greenhouse gases, and lead to groundwater contamination. While composting can be a viable alternative to direct application and is especially effective in returning valuable nutrients back the to soil, it too has left livestock farmers wondering what to do about escaped atmospheric gases.

Composting by forced aeration--a common composting practice that requires regular turning--causes high emissions of ammonia during the initial stages of composting. Biofilter or acid scrubbers can be used to prevent the ammonia gas from entering the environment, but this is not easily accomplished on-farm. Intensive, forced-aeration composting can also be expensive and impractical for some livestock operations.

Another method of composting, called passively-aerated composting, has proved to be a better option for livestock farmers. Unlike intensive composting, passively composted beds do not need to be turned; instead they rely on the temperature of the compost bed to facilitate the composting process. The passive process releases comparatively low levels of ammonia gas. The difficulties of the passively aerated system stem lie in ensuring the compost reaches the correct temperate. Too high, and it could lead to anaerobic regions and emissions of methane and odors. Too low, and the temperature is insufficient to kill pathogens.

Temperature in a passively aerated system cannot be directly controlled. In the past, there was a lot of guess work and crossed fingers in hoping the pile would reach but not exceed optimum temperature. Now, new research suggests that temperature can be controlled through the initial porosity and structure of the compost bed.

The Dutch researchers who conducted the study show that pile texture and cover are crucial to efficient composting and reducing ammonia and methane losses. If a compost pile density of 1100 kilograms per cubic meter was used, conditions quickly become starved for oxygen, resulting in high methane losses. If a pile density of 560 kg/cu m was used, no heating occurred and pathogens and weed seeds were not killed. Optimum heating and minimized losses were found at 700 kg/cu m pile density.

Lead researcher Adrie Veeken and his co-workers also found that covering the compost pile with a layer of straw trapped ammonia and prevented its loss to the environment. Use of natural filters composed of materials such as straw and clay provide a means to trap otherwise harmful emissions for beneficial use as soil amendments.

While loss of nitrogen during composting is inevitable, from an environmental standpoint the emission of nitrogen as a gas is preferable to emissions of nitrous oxide (a greenhouse gas emitted by storage and direct application of raw manure.)

Composting may never be able to solve the problems created by modern concentrated animal feeding operations (CAFOs), and further research still needs to be done to evaluate the contribution of passively aerated composting to global warming. However, this research does provide exciting new possibilities for responsible, environmentally-conscious livestock operations and manure management.

Veeken et al., 2002, Passively aerated composting of straw-rich pig manure, Compost Science and Utilization 10(2): 114-128

Dr. Paul Hepperly manages the research and training programs for the Rodale Institute. Paul has over 45 years farm and 25 years experience in conducting and managing agricultural research. Prior to accepting his current position he worked with ginger farmers in India and Hawaii to resolve major disease losses.

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