Adequate nitrogen fertilization is needed to obtain maximum crop yields.
Without sufficient nitrogen available to the plant, other inputs are
wasted. There are great differences between developed and develop- ing
areas of the world with regard to nitrogen-fertilizer production and
application, resulting in serious food deficits in some of the most
needy areas. Although nitrogen fertilizer is an inexpensive input in
comparison to the resulting yield increases, chemical fertilizers must
be purchased and do represent a direct cash outlay, sometimes the only
cash require- ment for the peasant farmer, often an insurmountable
obstacle in subsistence farming situations. If present economic trends
continue, poor farmers may find it increasingly more difficult to pay
for nitrogen fertilizers. Biological nitrogen fixation offers the most
promising alternative or supplement to chemical nitrogen fertilizers.
Furthermore, nitrogen fixation does not present any hazard to the
environment which may be the case with excessive application of chemical
nitrogen fertilizers. It is there- fore of utmost importance to promote
the use of nitrogen fixing crops, especially grain legumes which are
also an important source of dietary protein. Although legumes only
account for some 9% of the combined world dry matter yield of cereals
and legumes, they con- stitute as much as 24% of the total protein yield
of these crops because of the high protein content in legumes.