Composting
Research Improves a Time-Tested Technique
By Sharon Durham
August 6, 2003 Composting continues to have a place
in farm animal operations, according to Agricultural Research Service scientists
who are finding ways to make composting even more feasible for animal
producers.
In field experiments by microbiologist Patricia Millner at the ARS
Environmental
Microbial Safety Laboratory in Beltsville, Md., 99.99 percent of
the pathogens Escherichia coli and Salmonella were eliminated
from manure after composting. But the scientists stressed that composting
for the right amount of time, and at the proper temperature, is the
key to controlling pathogens in compost.
Composting is one of several methods farmers can use to treat animal
manure, sewage sludge and other organic residuals that contain pathogens
or parasites of public health concern. The temperature of an aerated
compost pile—one that's turned frequently to allow air to penetrate
—must be at least 131 degrees Fahrenheit for three consecutive
days to reduce pathogens to safe levels. For unaerated compost piles—those
that are turned only five times—the temperature must reach 131
degrees Fahrenheit for two weeks.
In many states, untreated manure can be applied to farm fields. However,
this can introduce pathogens and parasites into soils, and even into runoff or
irrigation water. As organic vegetables and fruits gain popularity, the demand
for animal manure is expected to increase.
Millner is conducting research on what she calls hybrid composting systems.
Not only do these systems reduce numbers of pathogens like E. coli
and Salmonella, they also reduce excess available phosphorus and
keep the ratio of nitrogen to phosphorus within a range acceptable for use in
areas that have nutrient-management plans. This approach means that composting
can address nutrient, pathogen and odor concerns all at the same time.
More information about this research is in the
August issue of
Agricultural Research magazine.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.
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