Page 20 - Curriculum Visions Dynamic Book

Nitrogen-based fertilisers
Plants obtain their nitrogen as soluble nitrate compounds. Nitrogen-based fertilisers (in the form of soluble nitrate) are among the most important of all aids to producing more crops for the world to eat.
Using manure is the natural (“organic”) way of applying nitrogen fertiliser in addition to that in rainfall or produced by legumes and soil bacteria. Using manure is a way
of recycling waste products, and an added advantage is that manure contains a wide variety of elements in addition to nitrogen that can be used for the benefit of plants and the soil.
Manure tends to act slowly, relying
on bacteria to break down the waste organic matter. As part of the process
of breakdown, bacteria release nitrogen
as ammonia and soluble nitrates.
For more immediate, as well as sometimes more convenient, application, concentrated nitrogen-containing fertilisers, obtained from nitrate rock or produced from ammonia, are applied to a soil.
Applying nitrogen fertiliser
There are several methods of applying nitrogen fertiliser. On highly mechanised farms it may be applied in the form of an ammonia solution in water that
is injected about 15 cm under the soil’s surface to prevent the liquid from vaporising. More commonly, a solution containing ammonia compounds is sprayed onto
the fields.
To make the number of
applications less frequent, fertiliser can be applied in pellet form. The pellets dissolve and release nitrates throughout a growing season.
Artificial fertilisers do have limitations, however, and not just because they may pollute rivers and lakes. The rapid growth that can occur with some very concentrated formulations can cause the crop to have less taste, be “watery” and have other less desirable qualities. For these reasons, research continues into how to make more effective
use of natural nitrogen fixation, producing genetic engineering that may allow all plants in the future to fix their own nitrogen.
 A stick containing nitrate pushed into the soil of a house-plant.
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