Characterisation of Bean Farming Systems Across Farm Types in Northern and Eastern Rwanda: Identification of Potential Niches for Legume Technologies
N2AFRICA is a development and research project focused on putting nitrogen fixation to work for smallholder farmers growing legume crops in Africa. Within this project, bean (Phaseolus vulgaris L.) farming systems in Northern and Eastern Rwanda were characterised and potential niches for grain legume technologies explored. Data were collected on resource flows, soil properties, crop productivity, field management, and biological nitrogen fixation (BNF) and on farmers assessment of production constraints. Farmers were classified according to regional specific resource endowment indicators, following the governmental household typology ‘Ubudehe’. Resource-poor farmers are permanently food insecure and are mainly constrained by land, labour, and inputs and achieve relatively low climbing bean yields of 1.18 Mg ha-1. Resource-rich farmers are food secure and have the capital to hire labour and rent land due to their market orientation and off-farm activities. Such farmers achieve average climbing bean grain yields of 2.27 Mg ha-1. BNF measured with the natural abundance method was relatively low with on average 50% N derived from the atmosphere and 93 kg N ha-1 fixed in all above- and belowground plant parts. Depending on farmers’ bean residue management, N-budgets per field ranged from -80 to 45 kg N ha-1 neglecting N returned to fields in animal manure after feeding bean residues. Resource-poor farmers, who all fed bean residues to animals, had an average negative N-budget of -43 kg N ha-1. Wealthier farmers, who retained part of the residues on fields, had an average N budget of -3 kg N ha-1. No evidence could be found that field distance from the homesteads influences soil fertility. Total N, organic C, and sand fraction are influenced by inherent factors (landscape) and do not correlate with bean grain yield. On the contrary, available P, and exchangeable Mg, Ca, and CEC correlate with grain yield and do not seem to be influenced by landscape. Beans play currently a major role in the farming systems in both sites. In Burera, climbing beans fit into a niche due to favourable agro-ecological, social, and economical factors. In Bugesera, recent droughts discouraged farmers to grow beans, but made groundnut, which is a more drought tolerant crop with high economic value, more popular.. This study shows that potential niches for legume technologies are site and farm type dependent. An increase in the area under climbing beans is not likely and opportunities for an increase in productivity and BNF are likely to be a better availability of quality stakes and higher application rates of organic manure. To achieve positive partial N-budgets on fields of resource- poor farmers, in addition an increased availability of alternative animal feed sources would be needed to reduce the losses of nitrogen in bean residues that are currently used as feed (because little manure is retuned). The limitation of stakes possibly also limits other technological improvements, including improved varieties, mineral fertilisers etc. especially in the case of the resource-poor farmers. From the provision of high yielding varieties, currently mainly resource-rich farmers profit since resource-poor do not keep the seed and have no long-term access to such varieties. Different bean variety preferences of farmers need to be taken into account, including varieties suitable for harvesting immature plant parts (pots and leaves). In Bugesera, strategies need to be implemented to stop the reductions of bean-cultivated area, the current decline in soybean cultivation and to further stimulate the already increasing cultivation of groundnut. Such strategies should include the promotion of drought tolerant bean varieties. The study highlights the complexity of smallholder farming systems in East/Central Africa and bean farming related trade-offs e.g. for bean residue management. This underlines the importance of studies on the farm rather than the single plot scale. Further, it shows that the ‘Ubudehe’ farm typology is useful to explain variations in resource use and productivity and is a potential tool for tailoring extension and technology services to the needs of farmers.