A century ago, there were only Natural
Fertilisers - plenty of manure from the horses, cattle, pigs,
and all the horses in the towns and cities too. There were two aspects
to using it in the fields:-
1. The animals wastes added to their straw bedding made manure,
which put nitrogen and organic matter back into the fields when
it was ploughed back in.
2. The stuff had to be disposed of somehow - you couldn't dump it
in the rivers without poisoning the drinking water of the people
downstream
This was hard work ! In Victorian times, large quantities of guano
(bird droppings) were imported to use as concentrated fertiliser,
and many other 'natural' by-products are also used as fertilisers,
now mostly by gardeners rather than farmers. These include bone
meal, hoof and horn, and dried blood, which all have various short-
or long-term advantages for the gardener. The farmers now seldom
make manure - the slurry from the animals is usually disposed of
by spraying it on the fields, where it has some fertilising effect.
The principles of Artificial Fertilisers were already
well known 100 years ago - there are 3 basic chemicals involved
which are highly beneficial for plant growth:- Nitrogen (usually
supplied as a nitrate), Potassium (as K2O),
and Phosphorus (as P2O5).
In 1928 and 1978, the relevant annual usages in the UK were:-
| |
N |
K2O |
P2O5 |
| 1929 |
50,000 tons |
50,000 tons |
140,000 tons |
| 1978 |
1,115,000 |
400,000 |
400,000 |
Production has increased greatly, and also many new lines of
plant have been bred which give proportionately better increases
in yield for increases in fertiliser usage. However, the energy
usages are:-
In 1975, about 80 x 109 MJ of fuel were
used in agriculture, ( 1,900,000 tons of oil equivalent)
and, about 110 x 109 MJ of fuel were used
in fertiliser production.( 2,600,000 tons of oil equivalent)(ref.
1, p 21)
Industrial Fixation from Microsoft Encarta 96 Encyclopedia,
ref 3.
The principal industrial nitrogen-fixation process today is the
production of ammonia by passing a mixture of atmospheric nitrogen
and hydrogen over a metallic catalyst (see Catalysis) at 500°-600°
C (932°-1112° F). Ammonia is then oxidized to form nitric
acid, which is in turn combined with ammonia to yield ammonium
nitrate, used primarily in explosives and fertilizers (see Fertilizer).
In another method, cyanamide, which is used as a fertilizer or
in the production of cyanides, is produced by passing atmospheric
nitrogen over heated calcium carbide in the presence of a catalyst.
Current Situation. Artificial fertiliser usage is clearly
economic, otherwise farmers would not use it, however, it will
tend to lead to a reduction of organic matter in the soil, which
may lead to soil erosion, as it is not 'held together' as well
when the organic content of the soil reduces.
Future. World fertiliser production seems likely to increase,
however, it seems likely that there will eventually be shortages
of fuel to power the chemical processes, and that the economics
of this will change. In this sense, the current situation does
not seem sustainable. Hydroponics will probably increase. From
ref 2, p75, it has been necessary in
Holland to introduce a system of quotas for pig-keeping (the quotasare
tradeable) and a system of contracts for the disposal of slurry
to ensure that every Dutch pig breeder either has sufficient land
to spread his slurry, or sells it to someone who does, to ensure
compliance with European nitrate regulations
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