Data/hora: 22/06/2024 06:52:35

Biblioteca(s): | Embrapa Soja.
Data corrente: | 13/03/2009
Data da última atualização: | 13/03/2009
Autoria: | HUNGRIA, M.
Afiliação: | Mariangela Hungria, CNPSo.
Título: | Biological nitrogen fixation: the brazilian experience.
Ano de publicação: | 2008
Fonte/Imprenta: | In: WORKSHOP ABOUT BIOLOGICAL NITROGEN FIXATION, Seattle, 2008. Abstracts...Seattle: Bill & Melinda Gates Foundation, 2008. CD-ROM.
Idioma: | Inglês
Conteúdo: | Brazilian's economy is based firmly on agriculture, and the high costs of mostly imported N fertilizers has resulted in a major research focus on biological N2 fixation (BNF) to enhance crop productivity and agricultural sustainability. One good example is the successful adoption of the soybean crop in the country, in large part due to the approach of BNF as a main component of the crop production. Selection programs towards superior symbiotic performance have been performed since the late 1960s and still continue, aiming at supplying the increased demands of more productive cultivars. Nowadays the area under cultivation with soybean in Brazil (~22 million ha) accounts for more than one third of world grain production and even though the great majority of the soils show high populations of soybean bradyrhizobia introduced by previous inoculations, most farmers practice seed inoculation every year, as the new strains and technologies result in grain yield increases averaged in 8%. Furthermore, N fertilizers do not benefit the crop. Rates of BNF with the soybean under field conditions can exceed 300 kg of N ha-1, providing up to 94% of total plant N and resulting in an economy to the country estimated at US$ 6.6 billion per year. In addition, release of N to the following crop has been reported, and cropping systems including soybean every one or two years are highly sustainable on N. Those numbers indicate higher rates of BNF than in other producing countries as U.S.A. and China, and explanations for such success include: 1) emphasis on selection of both soybean cultivars and bradyrhizobia with higher BNF capacity; 2) development of technologies aiming at increasing the contribution of the BNF; 3) education of the farmers towards the importance of spending time and money with inoculation; 4) establishment of a strong legislation controlling both the strains used and the quality of commercial inoculants. As a main conclusion we may say that a serious and long term effort to include BNF into the soybean cropping system returns today in economical and environmental benefits to the country, and if it works for Brazil it should work for any other country. A new challenge will be to make another successful story with the common bean crop, a legume representing the most important source of protein for Brazil, and also in most countries of South America and Africa. Very effective and competitive rhizobial strains, showing higher genetic stability under the environmentally stressful tropical conditions have been selected, and when used as inoculants result in yields of up to 4,000 kg ha-1 without any N fertilizer. The replacement of the N fertilizer recommended for the crop would immediately save about US$ 240 million per year. In a medium term, increasing the yields to 2000 kg ha-1 would result in an economy of N fertilizers estimated at US$ 720 million per year, and if we succeed, the technology can be adopted by other countries. Also, there are today in Brazil 142 rhizobial strains selected for the use of commercial inoculants for 96 legumes, and the BNF with those legumes must be better explored to improve soil fertility. Finally, non-symbiotic diazotrophic bacteria have been selected and proved to be highly effective with important non-legume species, as wheat and maize, thus the whole cropping system can highly benefit from BNF. Overall, we also have to show to the society the environmental benefits of BNF, and for that we have to estimate the benefits in terms of lower pollution of water resources by nitrate, lower emission of gases with greenhouse effects, and improvements on C sequestration. As a final message, it is important to highlight that BNF and the strategies reported here have a very low cost and may be applied in developing or industrialized countries, by large or small landholders, and for subsistence or cash legume crops.
Categoria do assunto: | --
Registro original: | Embrapa Soja (CNPSO)
Exemplares: | CNPSO - (28969-1) - UPC - SP - -- - 11603 -  - 11603 - DIS