Page 18 - Curriculum Visions Dynamic Book

Naturally fixed nitrogen
Nitrogen can be made in a chemical plant for
use as a fertiliser. However, there are natural processes that perform a much more efficient job of “fixing” nitrogen into a form that is available for plant use.
Several species of bacteria, fungi, and blue–green algae are able to “fix” nitrogen. They convert nitrogen into ammonia, a soluble material that can be absorbed by plants.
One of the most common nitrogen-fixing group of bacteria is called Rhizobium. These bacteria make the nodules, or galls, on the roots of legumes (plants like clover, beans, peanuts and alfalfa).
Both the bacteria and the plants benefit from this relationship. The bacteria need
the plants for food; the waste products of
the bacteria are nitrogen compounds, which are important to plant growth.
Natural nitrogen-producers are an
efficient method of applying nitrogen
fertiliser to a field. This is why, for several centuries, legumes have been grown alternately (in rotation) with “nitrogen-hungry” crops
like wheat and barley.
Nitrogen-fixing bacteria can also be used
to improve the yields of water-loving plants
such as rice. In the flooded rice paddy fields the nitrogen is fixed by blue–green algae
that live together with species of water fern.
By planting this fern in rice fields, nitrogen compounds are fixed and released into the water where they can be absorbed by the
roots of rice plants.
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