Theme 15: Advances in Rhizobial Research

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Rhizobia are well known for their capacity to establish a symbiosis with legumes. During this symbiosis the bacteria inhabit root nodules where they reduce atmospheric nitrogen and make it available to the plant. Biological nitrogen fixation (BNF) is an important source of nitrogen and the various legume crops and pasture species often fix as much as 200-300 kg nitrogen per hectare (Peoples et al., 1995). Globally, symbiotic nitrogen fixation has been estimated to amount to at least 70 million metric tons of nitrogen per year (Brockwell et al., 1995). Furthermore, in many cases nitrogen fertilizers are not efficiently used by crops and the environmental costs are high due to nitrogen losses from fertilizers (Peoples et al., 1994). The contribution of BNF has been suggested to be more open to management than fertilizer nitrogen (Peoples et al., 1995). Moreover, legumes stimulate the soil microflora and may favour the proliferation of plant pathogen antagonists while rhizobia may promote plant growth (Chabot et al., 1996; Schloter et al., 1997). Natural plant communities, legume crops, pastures, tree plantations and various integrated cropping systems such as alley cropping, intercropping and crop rotations can gain from nitrogen inputs by BNF (Wani et al., 1995; Thomas, 1995; Sanginga et al., 1995; Ikerra et al., 1999; Lehmann et al., 1999).

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Advances in Rhizobial Research – Progress Priorities in Temperate Areas

Rhizobia are well known for their capacity to establish a symbiosis with legumes. During this symbiosis the bacteria inhabit root nodules where they reduce atmospheric nitrogen and make it available to the plant. Biological nitrogen fixation (BNF) is an important source of nitrogen and the various legume crops and pasture species often fix as much as 200-300 kg nitrogen per hectare (Peoples et al., 1995). Globally, symbiotic nitrogen fixation has been estimated to amount to at least 70 million metric tons of nitrogen per year (Brockwell et al., 1995). Furthermore, in many cases nitrogen fertilizers are not efficiently used by crops and the environmental costs are high due to nitrogen losses from fertilizers (Peoples et al., 1994). The contribution of BNF has been suggested to be more open to management than fertilizer nitrogen (Peoples et al., 1995). Moreover, legumes stimulate the soil microflora and may favour the proliferation of plant pathogen antagonists while rhizobia may promote plant growth (Chabot et al., 1996; Schloter et al., 1997). Natural plant communities, legume crops, pastures, tree plantations and various integrated cropping systems such as alley cropping, intercropping and crop rotations can gain from nitrogen inputs by BNF (Wani et al., 1995; Thomas, 1995; Sanginga et al., 1995; Ikerra et al., 1999; Lehmann et al., 1999).