04560nam a2200133 a 450000100080000000500110000800800410001910000160006024501390007626002640021530000120047952038950049165300400438620415032016-04-27       2016    bl uuuu     u00u1 u    #d1 aHUNGRIA, M.  aSimbiotic nitrogen fixation and approaches to increase inputs from nitrogen fixation in tropical grain legumes.h[electronic resource]  aIn: PAN-AFRICAN GRAIN LEGUME & WORLD COWPEA CONFERENCE, 2016, Livingstone. Sustainable grain legume systems for food, income and nutritional security in a rapidly changing climate: book of abstracts. Livingstone: Legume Innovation Laboratory: IITA: CIATc2016  ap. 212.  aFarmer's use of inoculants and research aiming at increasing biological nitrogen fixation (BNF) with grain legumes have been inversely related to economic and logistic facilities to get N-fertilizers. In Brazil, about 70% of the N-fertilizers are imported and quoted in foreigner currency; therefore, research aiming at increasing the contribution of BNF to plant’s nutrition has been persistent and often very successful in crops with economic value, such as soybean (Glycine max), contrarily to countries with low-cost N-fertilizers. In addition, for these legumes cropped in large scale a new horizon has been raised, relying on the global interest in mitigating greenhouse gases emissions (GGE). Unfortunately, in Brazil and in other countries, in family scale farms with low input of fertilizers, although there are promising results of contribution of BNF to important legumes used mainly for food, such as common bean (Phaseolus vulgaris), the adoption of the technology has been difficult. The rates of BNF that can be achieve with some legume crops is impressive. The soybean-Bradyrhizobium might be considered as the “perfect symbioses”, adapted to a variety of edaphoclimatic conditions and reaching rates of 300 kg of N/ha, in addition to about 30 kg N/ha left for the following crop. The estimated economy associated with BNF with soybean in Brazil is of around U$ 12 billion/year, in addition to the mitigation of about 65 million t of CO2 equivalent. To achieve this successful story, Brazil has heavily invested in research of BNF with soybean for half a century, and the research continues. Interesting, the best strains selected for the soybean crop in Brazil are also showing an outstanding performance in some field trials in Africa. Therefore, the possibility of transferring technologies related to BNF from southern hemisphere countries as Brazil and Australia to Africa seems feasible and can help to save money and time. On the contrary, it is a paradox that research has proven that it is possible to increase the contribution of BNF in critical crops for food as common bean, by the selection and massive inoculation of elite strains. Data from Brazil has shown that yields of 3,000 kg/ha can be achieved exclusively with BNF, more than three times the national average for this crop. Interesting, excellent results have also been obtained with other crops considered promiscuous in the ability of nodulating with indigenous rhizobia and thus with low probability of responding to inoculation, such as cowpea (Vigna unguiculata) and peanut (Arachis hypogaea). Especially for the cowpea, the adoption of BNF is impressively increasing among farmers that adopt a high level of technology, but is low among poor farmers with low level of technology. We may thus conclude that the success of BNF relies not only in having good plant and bacterial genotypes, but also in a large effort in educating farmers with low level of technology. Relevant results can also be achieved with the use of other plant-growth promoting rhizobacteria (PGPR), encompassing contributions by a variety of mechanisms including BNF, production of phytohormones, increased stress tolerance, antibiosis against pathogens, among others. The use of Azospirillum spp. with the maize crop, and co-inoculation of soybean, common bean and cowpea is increasing considerably in the last five years in Brazil. Finally, we must mention large progresses of the inoculant industry that is now producing inoculants at a very low cost, usually representing less than 0.1% of the establishment of the crop. Globally, in all countries we are perceiving an increasing use of microorganisms, either due to the low cost or to environmental concerns about chemical fertilizers. And Africa can take great advantage of the results obtained in decades of research with microbial inoculants in other countries.  aFixação biológica de nitrogênio