Indigenous populations of rhizobia, legume response to inoculation and farmer awareness of inoculants in East and Southern Africa

Abstract

The Rhizobium Ecology Network of East and Southern Africa (RENEASA) is a participatory research affiliation of microbiologists and agronomists which seeks to better understand biological nitrogen fixation (BNF) and promote the use of rhizobial inoculants. The Network was initiated in 1991 to describe the rhizobial populations in soils. In 1994, two new areas of research were included; green house testing of legume inoculation and implementation of a survey addressing farmer awareness of BNF. One or all of these topics were investigated by 13 collaborators in 10 countries. Indigenous rhizobial populations were characterised at 46 sites by plant infection counts of legumes from different cross-inoculation groups. Bradyrhizobium spp. were the most frequently observed species in the wet and semi-arid lowlands (2.37 and l.84log10 cells g soil-l, respectively), and were consistently high in the humid areas of Uganda. Rhizobia nodulating bean (Phaseolus vulgaris L.) were greatest in highland soils (3.01 log10 cells g soil-1), particularly in the Kenyan and Rwandan Highlands. Thirty-six legume inoculant experiments were conducted in cooperators' glasshouses involving twelve soils and six hosts. Overall, legumes responded to inoculation with a 47% increase in growth and a 36% increase in the frequency of effective nodules when compared to the uninoculated controls. Farmer awareness of biological nitrogen fixation appears to be a major limitation in the use of inoculants. Overall, l16 households were surveyed in 5 counties, 98% cultivated legumes, 59% applied nitrogen fertilizers, 40% were aware of the potential benefits of root nodulation, 15% were aware of inoculants and 9% were currently using them. Different patterns of farmer awareness were noted in different counties.