Manure Facts
Consumers' heightened concerns about farm practices and food safety have resulted in much media coverage, and in some cases, confusion. Here are the answers to some of the key questions regarding agricultural practices, especially use of manure, and how those practices do or do not correlate to food safety issues.
- What type of agriculture uses manure as part of its regular farm practices?
Both conventional and organic agriculture utilize manure as part of regular farm soil fertilization programs. Certified organic farmers, however, must have a farm plan detailing the methods used to build soil fertility including the application of manure or composted manure. Certified organic farmers are prohibited from using raw manure less than 120 days prior to harvesting crops whose edible portion has direct contact with soil or soil surface, or less than 90 days prior to harvesting crops whose edible portion does not have direct contact with soil or the soil surface. No other agricultural regulation in the United States imposes such strict control on the use of manure. - Why is composted manure part of organic farming practices?
Composted manure is a primary source of soil fertility for organic farmers. It offers a natural means to cycle plant nutrients. As such, animal manure forms an important part of organic soil fertility programs.(Source: B.P. Baker, M. Lipson, and S. Alterman. Organic Farmers Growing Practices. Santa Cruz, CA. California Certified Organic Farmers.)
Organic farming practices are not based simply on lists of acceptable or unacceptable materials. Rather, organic farming strives to practice agriculture in a manner that achieves a balance similar to that found in natural systems. This includes a commitment to building or maintaining soil health practices through practices such as green manures, crop rotations and compost application. (Source: Organic Materials Review Institute, "Use of Manure, Compost and Sewage Sludge in the USDA/NOP Proposed Rule." April 1998) - What are the approved parameters for compost used by the organic industry?
According to the National Organic Standards implemented in 2002, composed plant and animal materials must be produced through a process that establishes an initial Carbon to Nitrogen ratio between 25:1 and 40:1, and that is maintained between 131 – 170 degrees Fahrenheit for three days using an in-vessel or static aerated pile system, or between 131 –170 degrees Fahrenheit for 15 days using a windrow composting system during which period the materials must be turned at least five times. - What are the benefits of using composted manure?
"Compost fosters the biological processes in the soil. Its use is a major tool in the creation and preservation of soil fertility." (Source: Grace Gershuny & Joseph Smillie, "The Soul of Soil, A Guide to Ecological Soil Management," AgAccess, Davis, Calif., 1995.)"Nutrients that leave farm soils must be replaced if crop production is to remain abundant. (Nutrients assist photosynthesis--the plant's use of light energy to transform carbon dioxide and water into organic compounds that give the plant its energy.) Organic wastes, many of which are rich in nutrients and organic matter, can be used to replenish soils. But the common practice in conventional agriculture is to rely primarily on manufactured fertilizer. . . . The acceptance of the ancient appreciation of organic material will be an important step toward building sustainable cities and farms." (Source: Gary Gardner, "Recycling Organic Wastes," STATE OF THE WORLD, 1998, Worldwatch Institute, W.W. Norton & CO., NY)
- Is there a connection between E. coli and manure?
"While not all manures carry E. coli, manure is a documented source of E. coli contamination and should thus be handled cautiously in a fresh produce production system. Well-composted manures are recommended over the use of raw manures." (Source: Jasper Hempel, Food Safety Initiative Steering committee, California Certified Organic Farmers) - What about E. coli and composted manure?
"E. coli, salmonella, and other pathogens found in manure can be reduced by proper composting. Compost should be maintained at temperatures of 55-60 degrees C (130 –149 degrees F) for a period of several days—if possible up to two weeks (Droffner, et al, 1995). Composting reduces pathogens in several different ways. One way is by generating temperatures unfavorable to the undesirable organisms. Temperature increases during composting are the result of microbial metabolism. The temperatures generated have the benefit of reducing populations of many pathogenic organisms." (Source: Organic Materials Review Institute Response to Docket Number: TMD-94-00-2, 1998)"Properly composted manure can be an effective and safe fertilizer. Uncomposted or improperly composted manure used as a fertilizer or soil amendment, or manure that enters surface waters, may contain pathogens and subsequently contaminate produce. Operators should carefully develop and follow good manure handling practices as a key to reducing the potential for pathogenic contamination of produce." (Source: "Industrywide Guidance to Minimize Microbiological Food Safety Risks for Produce – United Fresh Fruit & Vegetable Association, 1997)
- What methods do organic farmers use to improve the health of their soil?
Crop rotation: Crop rotation means changing the kind of crop produced in each field each growing season. Organic farmers may take five or more years before the same crop is planted again in a particular field. Organic farmers, including livestock producers, practice crop rotation in order to build and maintain soil health and to break the lifecycle of pests, thus reducing the need for synthetic fertilizer and pesticide applications.
"Green manure" or cover crops: Green manure is a crop that is grown then plowed into the soil or otherwise left to decompose for the purpose of soil improvement. Examples of cover crops used for green manure include soybeans, clover, rye, and others. Green manure does not mean raw manure.
Manure management: Manure offers a natural means to cycle plant nutrients. As such, animal manure forms an important part of organic soil fertility programs. Manure, either by itself or blended with crop residues, makes up much of the raw material for the compost used on organic farms. (Baker, et al., 1990)
Non-synthetically treated minerals: Organic farmers may use minerals such as limestone, rock phosphate langbenite (a sulfate of potash- magnesia), green sand, rock dust and others to improve the soil’s tilth. The tilth of soil is a composite of its texture, structure, aggregation, density, drainage, and water holding capacity.