Of all the mineral nutrients in the soil,
nitrogen is generally the most difficult for plants to acquire. Even though
nitrogen is the most abundant element in the atmosphere,
plants alone, do not have the ability to
obtain (fix) it. Only plants,
that form a symbiotic relationship with nitrogen fixing bacteria i.e. rhizobia,
gram-negative bacilli that invaded the
roots of plants, can fix atmospheric
nitrogen fixation is an important factor in any sustainable agriculture program.
Biological nitrogen fixation is a
process in which
taken from its relatively inert molecular form (N2) in the
atmosphere and converted into nitrogen compounds useful for building plant
The best known nitrogen fixing
clover which contain
rhizobia bacteria within
in their root systems,
producing nitrogen compounds that help to fertilize the
soil. The great
majority of legumes have this association, but a few genera (e.g.
Styphnolobium) do not.
A few dollars
worth of rhizobia inoculant can replace hundreds of dollars worth of
nitrogen fertilizer and significantly improve soil and crop health.