The Rural Voice, 1989-02, Page 20S
MANURE MANAGEMENT
by Ian Wylie-Toal
Manure is a natural resource — and a valuable one. It is also a toxic
pollutant. Here in Canada we're fortunate: not only do we have a reasonable
density of livestock relative to land area, but farmers as a group are
conscientious in managing this resource carefully. Keep up the good work:
preading manure on farm
land is a practice as old as
agriculture itself. In early
pastoral societies, the animals them-
selves "spread" manure, which had an
obvious beneficial impact on pasture
land. Later, when animals were
allowed less range space or confined
in barns, it was only reasonable that
their manure be collected and used as
fertilizer for the next year's crop.
Animal density was low, and the
amount of land available to receive
manure was very high, ensuring that
the process was environmentally safe.
But while animal manure is a
valuable fertilizer, it can also turn into
a source of pollution, contaminating
lakes and streams. According to Dr.
Eric Beauchamp of the Department of
Land Resources Science at the Univer-
sity of Guelph, Canada definitely has
some pollution problems associated
with animal manure, although our
problem is not as severe as the prob-
lems in some European countries.
In Britain, for example, a 1979
Royal Commission on Environmental
Pollution recommended that manure
from modern farms should be class-
ified as industrial waste and treated
accordingly.*
The root of any problems caused
by manure is indeed the intensification
of agriculture. Large farms depend on
close -confinement housing, which
concentrates large volumes of animal
waste in a small area. Large opera-
tions may also be located on relatively
small fauns, increasing the amount of
manure produced relative to each unit
of land.
Intensive farming has also changed
how manure is handled, making it into
a more potent pollutant. Manure used
to be mixed well with straw and was
stored in solid piles before being
spread on the land.
Now manure is usually handled
as a liquid. This liquid is a powerful
pollutant (liquid cattle manure is 100
times more potent than untreated hu-
man sewage) and is harder to contain
than a solid. A solid manure pile stays
Liquid manure is a
powerful pollutant —
liquid cattle manure is 100
times more potent than
untreated human sewage.
where it is put — it can't escape from
its container and flow over a field or
seep into the ground. Liquid manure
is mobile — it can seep through soil
into the groundwater system, and can
run off land into rivers and streams.
There are two general types of
pollution caused by manure: chronic
pollution of water sources by chemi-
cals in the manure, and acute pollution
caused by an accidental spill. In each
instance, different properties of the
manure are responsible for the type of
pollution produced.
CHRONIC POLLUTION
With chronic pollution, the
nitrogen and phosphates found in the
manure cause the problems.
Nitrogen and ammonia in manure
are converted by soil bacteria into
nitrates, compounds that are easily
soluble in water. Nitrates are washed
by rain through the soil and into the
water table, where they show up in
drinking water. They can also wash
off the soil and make their way into
rivers and lakes.
Dr. Tom Adiscott, a soil scientist at
the Rothamsted Experimental Station
in England, has written that a high
concentration of nitrate in drinking
water "can make babies ill and might
somehow be linked to stomach cancer,
although medical studies have yet to
show a direct link."*
Too much nitrate in lakes and riv-
ers, he says, speeds up plant growth,
clogging waterways with plants and
algae and ultimately decreasing
oxygen levels in the water.
Nitrate pollution has been blamed
on the heavy use of fertilizer, but Dr.
Adiscott says that work done at
Rothamsted shows that little of the
nitrogen applied in the spring remains
in the soil after the crop comes off.
Instead, he points to organic matter in
the soil as the cause. Nitrogen bound
up in organic matter is degraded to
nitrate by soil bacteria, especially in
the fall when there is no crop to take
up the nitrate and plenty of water to
wash it down.
Plots "regularly given farm -yard
manure contain as much as 100
kilograms more nitrate per hectare at
the critical period in autumn than plots
receiving chemical fertilizer," Dr.
Adiscott says. This is because manure
gives the microbes more organic
nitrogen to break down, and they
receive most of it during the critical
autumn period when manure is most
commonly applied.
Obviously the nitrate problem
would be worse if farmers were to use
18 THE RURAL VOICE