Biological Nitrogen Fixation Research Challenges - A Review of Research Grants Funded by the U.S. Agency for International Development (1994) / Chapter Skim
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1 GLOBAL INVESTMENT AND RESEARCH NEEDS
1 GLOBAL INVESTMENT AND RESEARCH NEEDS
Pages 5-32
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From page 5... ...
The free-living diazotrophs contribute little fixed nitrogen to agricultural crops. Associative nitrogen-fixing microorganisms are those diazotrophs that live in close proximity to plant roots (that is, in the rhizosphere or within plants)
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From page 6... ...
It is reasonable to expect that the need for fixed nitrogen for crop production will also at least double. If this is supplied by industrial sources, synthetic fertilizer nitrogen use will increase to about 160 million tons of nitrogen per year, about equal to that produced by the biological process.
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From page 7... ...
term substantially replace, the need for industrially produced fertilizer nitrogen. The Environment There are several significant environmental reasons to seek alternatives to chemically fixed nitrogen fertilizer: it affects the balance of the global nitrogen cycle, pollutes groundwater, increases the risk of chemical spills, and increases atmospheric nitrous oxide (N2O)
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From page 8... ...
Thus, fixed nitrogen from BNF will affect the global nitrogen cycle substantially less than will industrially fixed nitrogen. Groundwater Pollution Fertilizer nitrogen is used inefficiently by crops.
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From page 9... ...
The production of nitrogen fertilizer by industrial nitrogen fixation not only depletes our finite reserves of fossil fuels, but also generates large quantities of carbon dioxide, the principal greenhouse gas. Thus, increased use of fertilizer nitrogen may contribute substantially to the potential for global warming, and early replacement with BNF is desirable.
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From page 10... ...
Without question that situation will recur, with concomitant increase in the cost of fertilizer nitrogen produced by the Haber-Bosch process. Those exploiting BNF for crop production will be in a relatively favorable position.
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From page 11... ...
They are also major food sources in some regions. Symbiotic nitrogen fixation in legumes allows them to grow well without the addition of fertilizer nitrogen.
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From page 12... ...
Until the middle of the twentieth century, agricultural production depended mainly on soil nitrogen that had accumulated over time or was recently added by BNF and natural atmospheric deposition or animal manures rather than fertilizer. Soil organic matter, manures, and unharvested crop residues, especially those of legumes, can meet crop nitrogen needs in many circumstances where appropriate management is exercised.
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From page 13... ...
If these species could be genetically manipulated to form effective symbiotic or associative nitrogen-fixing systems, it would decrease or remove our major dependence on fertilizer nitrogen. The transformation of plants and microorganisms through molecular genetics offers promise for development of new symbiotic and associative BNF systems.
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From page 14... ...
The question arises as to who will benefit from increased BNF: the scientist creating the research breakthrough, the agribusiness firm developing and marketing it, the farmer adopting it, the farm laborer utilizing it, the financial institution providing the capital, the agribusiness processor or retailer selling the product, the consumer, or society in general? Previous analyses of the impacts of agricultural technology have focused almost exclusively on the producer, although in developed countries the consumer has been the major benefactor through the reduced cost of food.
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From page 15... ...
The first is underpricing of industrially produced fertilizer nitrogen for example, some governments subsidize the cost of producing or importing fertilizer nitrogen. The second is the overpricing of some farm products to keep farm income high.
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From page 16... ...
A few judged to be of the highest priority are mentioned below. · No BNF microbial associations or symbioses are known that produce significant amounts of fixed nitrogen for the major cereals corn, wheat, barley, and sorghum.
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From page 17... ...
Can this specificity be overcome without decreasing nitrogen-fixing ability? · The blue-green algae Azolla association with the aquatic fern Anabaena azollae has the potential to fix nitrogen in paddy rice, but needs improvements to be useful as a green manure.
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From page 18... ...
and their respective host legumes (Fischer and Long, 1992~. Rhizobial genes known to control host specificity and nodule induction fall into two groups: the structural nod genes and the regulatory nod genes.
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From page 19... ...
The rationale for investment in BNF research has grown with recognition of the negative environmental impact of overuse of chemical fertilizers and the increasing need for sustainable agricultural practices. These changes have substantially increased the need for BNF research with appropriate funding to attract and retain creative scientists.
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From page 20... ...
The eventual transfer of nodulation capacity to nonlegumes will probably require an understanding of the genes responsible in rhizobia and legumes, of the structural chemical bases of rhizobia/legume communication, and of the signal transduction pathways responsible for the finely orchestrated induction of the symbiosis-specific genes in both plants and microbes (de Bruijn and Downie, 1991; Fischer and Long, 1992)
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From page 21... ...
In addition, inoculation practices do not always result in a good distribution of microbes in the root zone. Therefore, studies on the ecology of nitrogen-fixing microbes in the rhizosphere is an essential component of BNF research.
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From page 22... ...
We also must study the mechanisms involved in microbial responses to nutrient limitations and other environmental stresses. The interaction of roots in mixed-cropping systems is poorly understood.
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From page 23... ...
Moreover, many tropical species have the C4 photosynthetic pathway, which more efficiently utilizes radiant energy. Charcoal can be produced from Pennisetum spp., a tropical grass with C4 photosynthesis, with a yield up to three times more per hectare than from eucalyptus, a fast-growing tree (NI.N.G.
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From page 24... ...
Site- and situation-specific research will be necessary to develop new and varied crop rotations, to optimize nitrogen fixation and other nutritional resources, and for pest control. Accrual of nitrogen can be attained by using legumes as green manures, and by returning legume crop residues to the soil.
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From page 25... ...
For centuries, the Azolla-Anabaena azollae association has been used in Southeast Asia to supply fixed nitrogen to paddy rice. After incorporation as a green manure, nitrogen released by the decomposition of the azolla supports rice growth.
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From page 26... ...
, respond poorly to nitrogen fertilizer in the field that is, they fix nitrogen abundantly and can derive most of their nitrogen from fixation. An understanding of why the broad bean symbiosis is so effective could provide guidance for improving the common bean and other legumes.
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From page 27... ...
There is a need to develop increased understanding of the microbial genes and plant and soil factors involved in rhizosphere and saprophytic competence. Also needed are studies on the mechanisms involved in microbial responses to nutrient limitations and other environmental stresses, especially those germane to the tropics.
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From page 28... ...
BNF Systems for Cereals The cereals rice, maize, wheat, sorghum, and millet are the major food crops in the world. In the 1960s and '70s, the Green Revolution greatly increased yields of rice and wheat through breeding and greater inputs of fertilizer nitrogen and irrigation.
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From page 29... ...
the effects of tillage practices on nitrogen cycling, as well as on how nitrogen fixation is affected by various sources of nitrogen and by quantity and quality of soil organic matter including composts and crop residues. Although there are data available from model-system studies on the factors that affect nitrogen fixation by legumes, there is little understanding of how the various environmental stresses may interact to affect the total nitrogen available to the plant.
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From page 30... ...
These collections, which constitute a basic resource for utilizing BNF to improve crop productivity, include rhizobia, associative nitrogen-fixing organisms for example, Azospirillum and Azotobacter spp. and Azolla spp.
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From page 31... ...
This suggests that the net effect of BNF is positive on society and on most sectors of the economy. BNF is in competition with industrial production of fixed nitrogen.
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From page 32... ...
Widespread adoption of farm-level BNF technology is also likely to lead to changes in land use. Thus, existing land-use policies and practices should be examined for their incentive or disincentive effects on BNF technology adoption and on the farm profitability and well-being of rural communities.
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