Soybean interactions with soil microbes, agronomical and molecular aspects

• Published in: Agronomy for sustainable development 2011, Vol.31 (1), p.173-190
• Main Authors: Rodríguez-Navarro, D. N., Margaret Oliver, I., Albareda Contreras, M., Ruiz-Sainz, J. E.
• Format: Article
• Language: English
• Subjects: Agricultural sciences; Agriculture; Agrochemicals; Agronomy. Soil science and plant productions; Azospirillum; Bacteria; Biological and medical sciences; Biomedical and Life Sciences; Bradyrhizobium; Cortex; Crop rotation; Crops; Ecology, environment; Fertilizers; Flavonoids; Foliage; Food; Forestry; Fossil fuels; Fundamental and applied biological sciences. Psychology; Fungi; glucans; Glycine max; Hormones; Infection; Inoculation; Legumes; Life Sciences; Nitrogen fixation; Nodulation; Nodules; oligosaccharides; Organogenesis; Primordia; Proteins; Review Article; Rhizobium; Roots; Seeds; Signal transduction; Sinorhizobium; Soil; Soil fertility; Soil microorganisms; Soil Science & Conservation; Soybeans; Sustainable agriculture; Sustainable Development; Transcription
• ISSN: 1774-0746; 1773-0155
• DOI: 10.1051/agro/2010023

Soybean, Glycine max (L.) Merrill, is one of the most important food crops in the world. High soybean yields require large amounts of N fertilizers, which are expensive and can cause environmental problems. The industrial fixation of nitrogen accounts for about 50% of fossil fuel usage in agriculture. In contrast, biological fixation of N 2 is a low-cost source of N for soybean cropping through the symbiotic association between the plant and soil bacteria belonging to the genera Bradyrhizobium and Sinorhizobium , which are collectively called “soybean rhizobia“. In general, symbiotic nitrogen fixation in crop legumes not only reduces fertilizer costs but also improves soil fertility through crop rotation and intercropping. Biological nitrogen fixation is due to symbioses between leguminous plants and species of Rhizobium bacteria. Replacing this natural N source by synthetic N fertilizers would cost around 10 billion dollars annually. Moreover, legume seed and foliage have a higher protein content than that of non-legumes, and this makes them desirable protein crops. There is a wide knowledge of the industrial elaboration and use of commercial soybean inoculants based on bradyrhizobia strains. At present, the technology to prepare different types of inoculants, either solid or liquid, is sufficiently developed to meet market requirements, although further research and investments are still required to improve the symbiotic efficacy of rhizobial inoculants. Inoculation of soybeans under field conditions has been successful in the USA, Brazil and Argentina, which are the world leaders in soybean cultivation in terms of acreage and grain yields. There are, however, limitations to a wider use of rhizobial inoculants: the size of indigenous soil rhizobial populations can prevent the successful use of inoculants in some particular areas. For example, many Chinese soils contain more than 10 5 soybean rhizobia per gram of soil, which imposes a serious barrier for nodule occupancy by the soybean rhizobia used as an inoculant. The use of inoculants based on soil bacteria other than rhizobia has also increased in the last decades. An example is the genus Azospirillum , which can be used for its capacity to increase plant growth and seed yields through different mechanisms, such as the production of plant hormones and the increase in phosphate uptake by roots. In addition, co-inoculation with Azospirillum and rhizobia enhances nodulation and nitrogen fixation. Althoug