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| Agriculture
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| Agricultural Uses of Copper Compounds |
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Copper compounds have their most extensive employment
in agriculture where the first recorded use was in 1761, when it was
discovered that seed grains soaked in a weak solution of copper sulphate
inhibited seed-borne fungi. By 1807 the steeping of cereal seeds in
a copper sulphate solution for a limited time and then drying them
with hydrated lime became the standard farming practice for controlling
stinking smut or bunt of wheat, which by then was endemic wherever
wheat was grown. Flour milled from bunted wheat had to be fed to animals
or sold cheaply to ginger bread makers who had found a way of masking
its bad taste and colour with ginger and treacle. Within a few decades,
so general and effective had become the practice of treating seed
grains with copper sulphate that the appearance of more than a few
bunted ears in a field of wheat was looked upon as a sign of neglect
on the part of the farmer. So well have copper compounds controlled
bunt that today this seed-borne disease is no longer of any economic
importance.
The greatest breakthrough for copper salts undoubtedly came in the
1880's when the French scientist Millardet, while looking for a cure
for downy mildew disease of vines in the Bordeaux district of France,
chanced to notice that those vines, bordering the highways and which
had been daubed with a paste of copper sulphate and lime in water
in order to make the grapes unattractive to passers-by, appeared freer
of downy mildew. This chance observation led to experiments with mixtures
of copper sulphate, lime and water and in 1885 Millardet announced
to the world that he had found a cure for the dreaded mildew. This
mixture became known as Bordeaux mixture and saw the commencement
of protective crop spraying.
Within a year or two of the discovery of Bordeaux mixture, Burgundy
mixture, which also takes its name from the district of France in
which it was first used, appeared on the scene. Burgundy mixture is
prepared from copper sulphate and sodium carbonate (soda crystals)
and is analogous to Bordeaux mixture.
Trials with Bordeaux and Burgundy mixtures against various fungus
diseases of plants soon established that many plant diseases could
be prevented with small amounts of copper applied at the right time
and in the correct manner. From then onwards copper fungicides have
been indispensable and many thousands of tons are used annually all
over the world to prevent plant diseases.
As a generalisation, soils would be considered copper deficient if
they contain less than two parts per million available copper in the
context of plant health. However, where the soil contains less than
five parts per million available copper, symptoms of copper deficiency
may be expected in animals. The increasing use of chemical fertilisers
which contain little or no copper are denuding soils of readily available
copper and creating a deficiency of the element in plants and through
them in animals. Copper compounds are now being added to the ever
increasing copper deficient soils either direct or in combination
with commercial fertilisers. This is particularly the case where the
fertilisers are rich in nitrogen and phosphorus. Animals grazing on
copper deficient pastures or obtaining an inadequate amount of copper
through their normal diet will benefit from mineral supplements containing
copper.
Copper sulphate, because of its fungicidal and bacteriecidal properties,
has been employed as a disinfectant on farms against storage rots
and for the control and prevention of certain animal diseases, such
as foot rot of sheep and cattle. |
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