June 8, 2006: The ideal sustainable livestock
farm is a closed system made up of crops grown to feed the livestock
and humans who live there, and manure that is returned to the soil
to ensure fertility. As with everything else in life, however, the
ideal is rarely attained.
Vegetable farmers need manure to feed their crops. Dairy and meat
producers usually have more manure than they can use. It would seem
the perfect arrangement for vegetable growers to haul away the manure
from a nearby farm (in some cases, your neighbors are happy to deliver
it) to apply it to fields. But modern agricultural inputs—especially
those used in confined, intensive settings—means that growers,
especially those who are certified organic, need to ask a few questions
before accepting that generous offer.
Recent studies have shown that manure can contain residues of antibiotics
and other medications routinely given to livestock, as well as pesticides
and heavy metals such as copper, zinc, arsenic, cadmium and lead.
Appropriate composting may take care of some of these substances,
but some it will not.
Organic certification standards allow raw manure to be spread on
fields at least 90 days before harvesting crops where the edible
portion does not touch the soil (i.e. sweet corn) and 120 days where
the edible portion does touch the soil (lettuce, carrots, onions,
etc.). All other animal manure must be composted, and standards
require that manure be shaped into a windrow, turned a minimum of
five times in 15 days and achieve a recorded temperature between
133°F and 170°F in order to be considered finished compost.
Anything else is termed “raw manure,” regardless of
how long it has been piled up behind the barn.
Organic standards prohibit the use of sewage sludge, sometimes
called biosolids, because of the possibility of heavy metal contamination.
Municipal yardwaste, such as grass clippings and leaves, fall under
the same category as manure—not prohibited, but demanding
scrutiny as to possible contamination from pesticides, herbicides
and synthetic fertilizers.
||"Residues of antibiotics and other
drugs, such as Ivermectin, a popular worming medication, have
been found in animal manures, and traces of these drugs can
be found in plants grown in soil where residue-laden manure
Antibiotics, such as tetracycline, are routinely fed to swine,
poultry and dairy cattle. Residues of antibiotics and other drugs,
such as Ivermectin, a popular worming medication, have been found
in animal manures, and traces of these drugs can be found in plants
grown in soil where residue-laden manure was applied. In a study
published in the Journal of Environmental Quality in October,
2005, Kumar et.al. found that antibiotic residues were detected
in green onions, corn and cabbages grown with the addition of manure
containing antibiotic residues. In another article in the same publication,
Chandler et.al. found that antibiotic residues in manure still retained
their bacteria-killing properties and could be contributing to the
formation of new strains of antibiotic-resistant bacteria. These
manures were not composted.
Other substances that can contaminate manure are metals such as
copper and zinc, which are part of the recommended minerals added
to livestock feed, and cadmium and lead, which can enter the chain
through crops grown in contaminated soil or air pollution in industrial
areas (see sidebar). In a paper published in The Scientific
World in 2002, researchers Allan Barker and Gretchen Bryson
found that composting can significantly reduce pesticide residues
and can bind heavy metals and reduce their uptake by plants.
One substance of particular concern is arsenic. Recent news stories
reported that arsenic was found in several commercial brands of
chicken and samples from ten fast food restaurants. The study was
conducted by Dr. David Wallinga, Director of Food and Health for
the Institute for Agriculture and Trade Policy (www.iatp.org),
a Minnesota-based, nonprofit advocacy group promoting sustainability
and family farms.
Arsenic is included in Roxarsone, a medication sometimes fed to
broilers raised in confinement to protect against outbreaks from
coccidia. The fact that arsenic is detectable in the meat of chickens
begs the question: How much is ending up in the manure, and where
is it going then?
Arsenic: common additive, complex agricultural
Brian Baker, research director of the Organic Materials Review
located in Eugene, Oregon, is trying to answer that question. “We're
looking at ways to reduce the accumulation of heavy metals, and
arsenic is of particular concern,” Baker said. “Arsenic
toxicity is problematic in a number of ways. The arsenic substitutes
for phosphates causing a deficiency in plants. Beans, peas and other
nitrogen fixing plants are very susceptible to this phosphate deficiency.”
Arsenic was one of the first-generation herbicides and was used
as a pesticide in apple orchards. Soil scientists noticed that orchards
with high arsenic content in the soil couldn’t grow clover
(another nitrogen fixer) as an under crop.
“Organic farmers don’t want arsenic in the soil,”
Baker pointed out. “It will accumulate in crop tissue and
can pose a human health hazard. Everything goes somewhere. We've
been looking at [arsenic] levels in the 30-40s ppm range. We’re
not sure yet what the levels should be, but it definitely should
be a concern.”
||"If a grower has to choose between
manure that may contain antibiotic residue and manure that may
contain arsenic, Baker recommends staying away from the arsenic.
Antibiotics break down quickly and the composting process should
take care of them. Not so with arsenic."
If a grower has to choose between manure that may contain antibiotic
residue and manure that may contain arsenic, Baker recommends staying
away from the arsenic. Antibiotics break down quickly, and the composting
process should take care of them. Not so with arsenic. “Heavy
metals are more of a concern,” Baker said. “Organic
growers are better off with dairy or layer manure.”
So perhaps organic growers should avoid importing manure altogether
and stick to buying compost and fertilizers? That isn’t a
fool-proof solution either. Prepared fertilizers are expensive,
and Baker recommends staying away from commercial compost unless
growers can be absolutely sure what is in it. According to Baker,
during the debate on whether to allow sewage sludge in organic farming,
the question of manure from factory farms was raised. Unlike the
European Union, The U.S. has no definition of Concentrated Animal
Feeding Operation (CAFO) or “factory farms” and does
not prohibit this manure from being used by certified-organic growers.
Many scientists and sustainable farming activists are of the opinion
that manure from factory farms contains as many heavy metals as
sewage sludge and should be prohibited in organic agriculture. The
EPA limits the amount of heavy metals in sewage sludge, but manure
from factory farms is unregulated. “There are operations that
will take sludge, CAFO manure and urban green waste and make it
into commercial compost,” Baker said.
Always know your source and their ingredients
The best insurance with imported manure is to know your source.
An organic grower for almost 20 years, Darrell Frey of Three
Sisters Farm in northwestern Pennsylvania has imported many
tons of manure to his farm. He had a long-standing agreement with
a race-horse stable where he parked his dump truck at the stables
and the owners filled it up for him every week.
The manure was then driven back to the farm and composted. Some
of it was formed into windrows to be used in the vegetable gardens
outside and some was loaded into bins in the bioshelter, or solar
greenhouse, to be used in the indoor planting beds and in potting
soil. The composting process also provides bottom heat for starting
seedlings on top of the compost chambers, and fans can be used to
circulate heat through the indoor growing beds.
Like many vegetable growers, Frey doesn’t have the time or
space for farm animals. The bioshelter is home to a flock of laying
hens that are fed organic feed from which they produce enough manure
in a year to fill one of the compost chambers. To meet the rest
of his compost needs, Frey must either import manure or use approved
fertilizers. Fertilizer can be expensive, but manure has its drawbacks,
too. “My biggest problem with imported manure was weeds,”
Frey said. “Every year we seemed to find new varieties.”
||"As with most aspects of sustainable
farming, education is your best bet. Talk to neighbors about
what they are feeding their animals and the possible effects
it could have."
Frey is currently getting his manure from a nearby farmer who owns
horses and other livestock. Before making the agreement, Frey went
to the farm and checked out the agricultural practices to ensure
that he wouldn’t be bringing anything onto the farm that he
According to Baker, this is a good idea. “No matter what
nutrient source you use, it's not going to be perfectly clean,”
Baker said. “Feed sources need to be monitored as well. Choose
manure from feed sources that are relatively uncontaminated.”
Baker also recommends layering suspect poultry or dairy manure with
high-carbon organic matter during composting. This should take care
of antibiotics and pesticide residues.
Where, what and how
The most important considerations when importing manure are these:
- Where is it coming from?
- What did the animals eat?
- How will it ultimately impact my crops?
A grower’s best bet is horse manure, because antibiotics
are usually not a concern, followed by dairy and layer manure. Baker
recommends staying away from manure from factory farms, particularly
hog and broiler operations which may rely heavily on drugs. Another
consideration is that manure from confined hogs often contains high
levels of copper.
As with most aspects of sustainable farming, education is your
best bet. Talk to neighbors about what they are feeding their animals
and the possible effects it could have. Chances are they will be
just as concerned about what is going into the soil as you are—especially
if they are buying your potatoes and chard.