dramatically and now exceeds 50 million tons annu-
ally. The return on this energy expenditure is thus
large, in terms of both energy and protein, because
nitrogen is the primary source of much of our food
protein.
 Biological nitrogen fixation (BNF) is an alternative
to chemical fixation. Currently, publicly supported
U.S. expenditures on BNF research scarcely exceed $8
million annually and support has hardly kept pace
with inflation during the past five years. Basic BNF
research is one of the most neglected of the biological
and physical sciences.
 Four major BNF systems are relevant for agri-
culture, forestry and rangelands. They are Rhizobium-
legume; the Azolla-Anabaena, particularly valuable for
rice production in tropical and subtropical areas;
Actinomycetes-angiosperm for forest trees, and the
Spirillum-grass symbioses. The Rhizobium, Anabaena,
Actinomycetes and Spirillum are all microorganisms
that, in symbiotic relationships with higher plants,
may fix atmospheric nitrogen and make it available for
plant growth or crop production. The major nitrogen
fixers in Rhizobium-legumes and Azolla-Anabaena part-
nerships are known. In addition, there are about 160
species of non-leguminous angiosperms (forest trees)
that have in their root nodules Actinomycetes capable
of fixing nitrogen. Advances in BNF will be an increas-
ingly important factor in future crop productivity.
 The first opportunity in BNF lies in the establish-
ment of Rhizobial technology centers where efforts
should continue to increase the output of Rhizobium-
legume symbioses. Basic biological research should also
be devoted to trees that fix nitrogen biologically,
because lack of nitrogen commonly limits forest tree
growth. Trees in temperate zones with promise for
biological fixation include mesquite, thornless honey
locust and red alder. In addition, many trees in the
tropics have such capability.
 Secondly, basic BNF research is needed on the rela-
tions among crops and plants interplanted and grown
in rotations. Laboratory and field approaches to im-
prove BNF from legumes include advanced inoculation
technologies, improved strains of Rhizobia and host
plant cultivars, better matching of the Rhizobia strain
to the legume cultivar, energy use minimization,
development of nitrogen fertilizer systems to which
legumes respond, and decreasing photorespiration for
improvement of photosynthate production. Some of
these indirect approaches may be as important for in-
creasing BNF as the improvement of nitrogen fixation
per se.
 The third system includes the Azotobacter and
Spirillum-rhizosphere associations in the grasses, cereal
grains and non-legumes. Promising plants are those


that excrete carbon compounds to supply energy for
nitrogen-fixing bacteria on their roots. Symbiotic
nitrogen fixation is dependent on large amounts of
photosynthetic energy. These requirements may be
reducible with basic research.
 Fourth, it has been demonstrated that the blue-
 green algae, Azolla complex or partnership, can pro-
 vide up to 75 percent of the nitrogen requirements for
 California rice. A total of 465 kilograms of nitrogen per
 hectare were harvested from 22 crops of Azolla at the
 International Rice Research Institute over a period of
 335 days. Similar results have been achieved in Cali-
 fornia when phosphorus is added. It has also been
 reported that plantings of alfalfa and clover may yield
 up to 500 kilograms of biologically fixed nitrogen per
 hectare per year, depending on planting densities and
 depths of rooting.
 BNF research has produced much information of
disciplinary and academic interest during the past 20
years and has generated volumes of literature. Unfor-
tunately, there is still little of practical significance for
increasing crop productivity under field conditions.
Basic breakthroughs are still needed. Progress can be
hastened with better links between scientists engaged
in DISC research in the laboratory and those doing
mission-oriented SM and PS research in the USDA and
state Agricultural Experiment Stations. What is needed
is an interacting balance of both-not one or the other.
 Collaborative efforts among scientists in the United
States and in the various less-developed nations should
also be encouraged. BNF offers a unique opportunity
to apply science to national problems of resource con-
servation and to reduce costs of essential inputs while
contributing to food production and alleviating
environmental pollution. The income, resource base,
food security, food quality and environmental stakes
are high.
 Looking ahead at the role of biological nitrogen fixa-
tion in assuring further supplies of food, fiber and
forest products, we see a bright future. Much progress
has been made since the report of the World Food and
Nutrition Study (NAS, 1977). Top young as well as
older and more experienced scientists are now being
recruited and are forming critical masses of human
capital at national and international levels. They are
working across the range from basic research to field
applications, beginning with the enzyme nitrogenase,
and proceeding to the ecosystems for agriculture, range
and forestry. The U.S. Department of Agriculture,
through the competitive grants program of the
Cooperative State Research Service, supports this
research with $2.5 million to $3 million annually.
Similarly, a support program approximating $400,000
annually is available to U.S. scientists for research on