Manure

Fall 2000
By Eric Sideman, Ph.D., Director of Technical Services for MOFGA

I am deeply concerned about a new direction for policy that I see developing behind the scenes at the U. S. Department of Agriculture: A crusade is brewing to eliminate the use of livestock manure on vegetable farms. The forces behind the effort base their argument on their fear of pathogenic microbes. This fear has been heightened by many recent stories in the press, worldwide, about disease and death that may be traced back to food.

Salmonella, E. coli and other Latin names have become common household words, and researchers and policy makers can’t miss the opportunity to get some funding or public praise. I agree that a serious risk can accompany the use of manure, but let’s be reasonable. Let’s do our research to learn how to use manure safely and then set policy based on that research. Let’s not set policy that would have great negative effects on farming, farmers and the environment if that policy is unwarranted.

Everyone who keeps up with food and farming issues knows that manure can carry pathogens, such as E. coli 0157:H7, and we know that this and other pathogens have caused horrible outbreaks of food poisoning, sometimes resulting in death. But, the link has not been made: Not one case of food contamination has occurred when manure has been used according to good farming practices, such as those that the organic industry demands in its standards. Instead, every case has been traced back to contamination of food due to poor and unsafe manure handling practices or to a lack of sanitation when food was prepared.

Research-based standards have been developed, as reflected in the recommendations of the National Organic Standards Board and the second proposed Rule on organic agriculture from the USDA that is based on those NOSB recommendations. (Also, see my article, “E. Coli 0157:H7: A Primer for Farmers, The MOF&G, March-May 1997.) Then why is this anti-manure movement gaining support? Fear and opportunity. Some members of the public foster the “eeeewww” feeling about manure, and some microbiologists see only the risks from microbes and miss the benefits to the soil and the environment, so they just promote banning manure.

I am pleased to see studies of E. coli and its survival in manure continue, and I hope the USDA and others continue to support such work. I want manure to be used safely. I have great concern that the forces to eliminate manure from farming could win. I have even heard that the National Organic Program at the USDA is getting pressured to go against its own recommendation in the Proposed Rule and to come out with a final Rule that will not permit manure use on vegetable farms. After the past few decades of sustainable agriculture research to foster diversified farms and cooperation between neighboring livestock farms and crop farms, that would be a travesty.

Manure has always been a major part of agriculture. Before the advent of chemical fertilizers, most agriculture used manure as a source of nutrients for crops. When farmers turned to fertilizers instead of manure, they lost all of the other benefits of manure, including building soil fertility and soil structure. Fertilizers simply provide nutrients to the present crop. Many research institutions that spent many decades pushing fertilizer are now turning back to manure and manure products for just this reason. Let’s not let these efforts become lost in food safety fears but rather learn how to use manure even more safely.

Composting manure is one way to deal with E. coli 0157:H7 and other pathogens. Consequently, composted manure does not have to meet the same handling guidelines as uncomposted manure in organic standards or in the USDA’s Proposed Rule. However, composting is not the best practice for all farming systems, so we must keep our guidelines for using fresh or aged farmyard manure. Compost does not provide nearly the amount of available plant nutrients as manure, nor does it encourage soil microbial activity, since it has already been decomposed. New work at the University of Vermont has demonstrated that compost does not build soil structure as well as fresh manure does.

Many studies have emphasized the risk of contamination of food with manure and the direct result of serious food-borne illness. They all point to the potential for a robust population of pathogenic microbes in manure and the potential for those microbes to survive long periods in the manure. However, few studies have investigated the survival of pathogens under field conditions, so more work is needed. Those few field studies that were done point to radical declines in microbial populations once manure is spread, thus the risk of contamination is greatly reduced once manure is exposed to the natural environment of the soil in the field. In fact, research at the USDA Agricultural Research Service, New England Plant, Soil and Water Laboratory in Orono, Maine, is looking at the survival of human pathogens in soil after the soil has been amended with dairy manure. A steady decline in numbers has been observed over the growing season. Listeria became undetectable 10 weeks after manure application, and no E. coli was found on harvested potatoes.

Clearly, no scientific support exists for the effort to impose unreasonable restrictions on farmers’ use of manure, whether those farmers are organic or conventional. Studies show that all farmers must take great precautions when using manure as a source of nutrients for their crops. Let’s make sure the regulations from our government, for all farmers, are reasonable and promote the well-being of consumers, farmers and the environment.

About the author: Eric is MOFGA’s “extension agent.” You can address your questions about organic growing to him at the MOFGA office, or look for him at the Common Ground Country Fair.

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