rich topsoils contributes sediments and phosphorus to
animals from the use of animal manures, if large quanti-
streams and lakes, polluting surface waters. When very
ties of high-metal-content manure are applied over the
high phosphorus buildup occurs from the continual
years, soil testing should be used to track the buildup.
application of manure at rates to satisfy crop nitrogen
Another potential issue is the finding that plants can
needs, it may be wise to switch the application to other
take up antibiotics from manure applied to soil. About
fields or to use strict soil conservation practices to trap
70% of the antibiotics used in animal agriculture ends
sediments before they enter a stream. Including rota-
up in the manure. Although the amounts of antibiotics
tion crops, such as alfalfa—that do not need manure for
taken up by plants are small, this is an issue that may be
N—allows a “draw-down” of phosphorus that accumu-
of concern when using manures from concentrated ani-
lates from manure application to grains. (However, this
mal production facilities that use considerable amounts
may mean finding another location to apply manure. For
of these substances.
a more detailed discussion of nitrogen and phosphorus
management, see chapter 19.)
SUMMARY
Farmers that purchase much of their animal feed
Animal manures can be very useful sources of amend-
may have too much manure to safely use all the nutri-
ments for building healthy soils. They are high in nutri-
ents on their own land. Although they don’t usually
ents needed by plants and, depending on the species
realize it, they are importing large quantities of nutri-
and the amount of bedding used, may help build and
ents in the feed that remain on the farm as manures. If
maintain soil organic matter levels. Because of the wide
they apply all these nutrients on a small area of land,
variability of the characteristics of manures, even from
nitrogen and phosphorus pollution of groundwater and
the same species—depending on feeding, bedding, and
surface water is much more likely. It is a good idea to
manure handling practices—it is important to analyze
make arrangements with neighbors for use of the excess
manures to more accurately judge the needed applica-
manure. Another option, if local outlets are available,
tion rates. When using manures, it is important to keep
is to compost the manure (see chapter 13) and sell the
in mind the potential limitations—pathogen contamina-
product to vegetable farmers, garden centers, landscap-
tion of crops for direct human consumption; accumula-
ers, and directly to home gardeners.
tions of potentially toxic metals from high application
Poultry and hogs are routinely fed metals such as
of certain manures; and overloading the soil with N or P
copper and arsenic that appear to stimulate animal
by applying rates that are in excess of needs, as demon-
growth. However, most of the metals end up in the
strated by soil test and known crop uptake.
manure. In addition, dairy farmers using liquid manure
systems commonly dump the used copper sulfate solu-
SOURcES
tions that animals walk through to protect foot health
Cimitile, M. 2009. Crops absorb livestock antibiotics, science
shows. Environmental Health News. http://www.environmen-
into the manure pit. The copper content of average liq-
talhealthnews.org/ehs/news/antibiotics-in-crops.
uid dairy manures in Vermont increased about fivefold
Elliott, L.F., and F.J. Stevenson, eds. 1977. Soils for Management
between 1992 and the early 2000s—from about 60 to
of Organic Wastes and Waste-waters. Madison, WI: Soil Sci-
ence Society of America.
over 300 ppm on a dry matter basis—as more farm-
Endres, M.I., and K.A. Janni. Undated. Compost Bedded Pack
ers used copper sulfate footbaths for their animals and
Barns for Dairy Cows. http://www.extension.umn.edu/dairy/
disposed of the waste in the liquid manure. Although
Publications/CompostBarnSummaryArticle.pdf.
there are few reports of metal toxicity to either plants or
137
Building SoilS for Better CropS: SuStainaBle Soil ManageMent