Prospects for Enhancing BNF in Farming Systems

5.1. Changes in management. To be able to fix atmospheric N2 it is necessary for the legume to form an effective symbiotic relationship with rhizobia in the soil. In its simplest form the symbiosis is established when indigenous rhizobia infect the roots of legumes to produce nodules. But populations of appropriate rhizobia are not always adequate or may be absent entirely such as when legumes are introduced to new areas. Under these conditions the only way to introduce the required rhizobia is through the inoculation of legume seeds before, at, or soon after sowing. Many studies have reported improvements in legume growth and grain yield in response to inoculation (van Kessel, Hartley 2000). However, with a few exceptions, inoculation technology has not been widely adopted by farmers. This reflects in part inadequate demonstration and promotion of the benefits of inoculation, difficulties in applying inoculants, limited potential for inoculant production and distribution, poor quality control, and economic constraints to resource poor farmers.

Promiscuously-nodulating soybean varieties is one approach being evaluated in Africa as a potential solution to these problems (Giller et al. 2000).

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