The Rural Voice, 1978-04, Page 32Gardening
Should you use
organic or chemical
fertilizers
BY T.E.BATES
DEPARTMENT OF LAND RESOURCE
SCIENCE
People interested in the environment are
questioning the use of chemical fertilizers.
Can we use them without harming our
environment and what effects do chemical
fertilizers have on the food we eat?
We hear of "organic farming" and are
sometimes given the impression that all
organic compounds are safe to use. The
term "organic" can be misleading,
however. Organic compounds can range
from extremely toxic to quite beneficial to
plants or animals.
We cannot even separate safe com-
pounds from the unsafe by dividing them
into natural and manufactured categories.
Some plant parts such as potato or water
hemlock leaves and many ornamentals are
toxic if eaten by animals or people. Some
plant residues are toxic to other plants.
Quackgrass or rye green manure plowed
under can be toxic to the following crop, in
the early stages of decomposition.
Animal manure used carefully as a
fertilizer is an example of a beneficial
organic compound. Nutrients in the soil are
usually found in the same form, regardless
of organic or chemical fertilizers used.
There appear to be no simple rules for
dividing materials used for plant growth
into safe and harmful categories. Most
manures, composts and chemical fertilizers
can be very useful when used at
recommended rates, times and methods of
application. However, both organic man-
ures and chemicals, if seriously misused,
can reduce the growth of plants or make
them unfit for human consumption.
ORGANIC MANURES
Organic matter is important to the
productivity of soils. It adds to the
water -holding capacity. It helps to keep the
soil loose and friable for faster intake of
rain, oxygen and other gases, for growth of
plant roots and ease of tillage. It also acts
as a storehouse of plant nutrients,
releasing them gradually for plant growth
as the organic matter breaks down.
Organic wastes should not be discarded,
but should be used as a valuable resource.
USING ORGANIC MATERIALS
In general, organic materials produced
by plant growth return to the soil only
those nutrients the plants obtained from
PG. 32. THE RURAL VOICE/APRIL 1978.
the soil, less the amount removed by crops.
Therefore, the continued large scale
production of crops with only organic
wastes (crop residues, green and animal
manures) returned to the soil will, in most
cases, result in a gradual depletion of plant
nutrients and decline in yields.
Yield will eventually stabilize at a level
of production sustained by the nutrients
supplied through gradual decomposition of
soil minerals and absorption of small
amounts of nutrients from rainwater.
The home gardener has a special
opportunity to overcome this problem.
Using household wastes and other organic
materials which would otherwise be
wasted, he or she can in many cases,
supply all required nutrients from organic
sources even though this is quite
impractical on a field scale.
USING CHEMICAL FERTILIZERS
Nitrogen Fertilizers. Most of our
nitrogen fertilizers are made in chemical
factories where electrical energy is used to
combine the nitrogen from air with
hydrogen from natural gas to form
ammonium. This ammonium may be
further processed to form nitrate or urea.
Nitrogen and the products, ammonium
nitrate and urea, are the same as found in,
or formed from, plant and animal wastes in
soils.
Most chemical fertilizers are very
concentrated. Anhydrous ammonia, for
example, is a common fertilizer of which 80
percent is pure nitrogen compared to
barnyard manure which may contain one
percent nitrogen.
Modern fertilizers are concentrated
because most people like them that way. It
is much easier and frequently less
expensive to transport and apply a
50 -pound bag of ammonium nitrate
fertilizer containing 17 pounds of nitrogen,
than to transport and apply 1700 pounds of
manure containing the same amount of
nitrogen.
Application of too much nitrogen, from
either chemical or organic sources, can
seriously affect plant growth. In extreme
cases, where too much nitrogen is applied,
the nitrate content of plants can become so
high that they are unsafe for human
consumption. Some cases of high plant
nitrate content in Ontario have been
caused by excessive applications of both
chemical fertilizer and animal manure on
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