Question of the Week
Answer: The following provides a brief overview of composting systems. Keep in mind that if your operation is certified organic, you must meet the requirements for composting set by the USDA National Organic Program so as to not jeopardize your organic certification.
1. Passive or open-pile
These systems require only a low level of management for small- to medium-sized farms. Small piles are formed from organic materials and utilize natural air flow. Larger piles are more difficult to aerate, so it is recommended to not have pile exceed four feet in height. Under proper feedstock and moisture conditions, piles can generate a lot of heat and good compost. Loaders and manure spreaders are often used in these systems.
2. Windrow using loader for turning, mixing, and handling
These systems are most common for organic on-farm composting, as windrows are turned to actively manage the process. Turning improves air exchange and allows for materials to be evenly composted. The high interior temperatures generated can break down pathogens and destroy weed seeds and pest larvae. Your front-end loader can be very efficient for this type of system.
3. Windrow using a specialized turner
Depending on size, you can invest in a small PTO-driven windrow turner, or, for larger operations (4,000+ tons per hour), a self-propelled turner can be used.
4. Aerated static pile using perforated pipes
These systems are closely managed and can be either outdoors or covered. They utilize perforated pipes for air exchange that push out hot gases that are generated inside the pile. As mentioned, a blower can be hooked up to supply the air to the bottom of the pile or windrow. Wind chips or straw are used as the base and the pile dies need to have good structure to maintain porosity throughout the process. Initial height should be around five to eight feet.
5. Contained, or in-vessel, systems
These systems involve composting within a building, container, or vessel. They can be quite expensive and require a great deal of management. As a result, there is a lot more control. They can combine certain aspects of other systems and can be insulated for winter production.
There are many variables to consider in selecting the best type of system, including characteristics of the site, cost, equipment, and speed of composting. The first three systems mentioned above usually take place outdoors. The aerated and in-vessel systems are often covered and/or enclosed for better moisture control. The key is to mix the aerated static pile only once.
For more information on composting, see the ATTRA publication Composting: The Basics, available at https://attra.ncat.org/attra-pub/summaries/summary.php?pub=374. This publication provides a foundation of information for those interested in composting. It addresses a wide range of topics, from the materials that are needed to begin a compost pile to techniques for successfully managing the composting process. A troubleshooting list describing common problems and how to address them also is included. In addition, the basics of vermicomposting—using worms to generate compost—are described. Finally, the publication contains an introduction to composting for small agricultural operations such as market gardens.
Another useful resource is On-Farm Composting Handbook, available at: http://palspublishing.cals.cornell.edu/nra_order.taf?_function=detail&pr_booknum=nraes-54.
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