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.
- How is manure used in conventional and organic agriculture? What are some differences?
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 for at least 90 days before harvest of crops grown for human consumption.
Furthermore, sewage sludge is not permitted in organic agriculture. The use of sewage sludge, also known as biosolids, which comes from treated municipal waste water and other sources, is one of the three processes completely banned in organic production. The other two other banned processes are the use of any genetically modified organisms and the use of irradiation.
- What does the National Organic Program (NOP) Rule mandate regarding manure use in organic farm practices?
No other agricultural regulation in the United States imposes such strict control on the use of manure.
The U.S. regulations for organic production require that raw animal manure must be composted unless it is applied to land used for a crop not intended for human consumption; or is incorporated into the soil not less than 120 days prior to the harvest of a product whose edible portion has direct contact with soil; or is incorporated into the soil not less than 90 days prior to the harvest of a product whose edible portion does not have direct contact with the soil surface or soil particles. See 7 CFR 205.203 (c)(1) and (2).
The requirements for making compost are regulated as well, and are designed to encourage soil health while minimizing risks to human health or the environment.
- What is the definition of compost?
The use of manure in organic farm practices is covered in the National Organic Program Rule’s definition of compost (7 CFR 205.2):
Compost. The product of a managed process through which microorganisms break down plant and animal materials into more available forms suitable for application to the soil. Compost must be produced through a process that combines plant and animal materials with an initial Carbon:Nitrogen ratio of between 25:1 and 40:1. Producers using an in-vessel or static aerated pile system must maintain the composting materials at a temperature between 131 deg. F and 170 deg. F for 3 days. Producers using a windrow system must maintain the composting materials at a temperature between 131 deg. F and 170 deg. F for 15 days, during which time, the materials must be turned a minimum of five times.
- 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 only on lists of materials that acceptable or unacceptable in organic products. 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 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: “Industry-wide 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.