In developing countries, specially sub-arid areas, agricultural development is mainly limited by drought, low soil fertility and energy supply of rural communities. Biogas technology can be a good alternative for organic matter and fuel production, in order to hold and increase soil fertility and to supply small pumping sets for irrigation. A continuous anaerobic fermenter, called "Transpaille", has been designed to process all types of agricultural residue (straw, cowdung, weeds…) without any pre-treatment. The fermenter is coupled to a small dual engine in the range up to 12 KW, Electricity generation is the most adaptable transformation of energy for different agricultural or social uses : pumping, grinding of grain, lighting, cooling…. After a finishing period, effluents of the fermenter can be spread in the fields, to increase crop yields. The complete system, including fermenter, engine, irrigation and compost spreading, has been field-tested in Senegal for 4 years with good results. Since 1985 a demonstration project phase has therefore begun in 4 African countries with different applications : irrigated areas of less than 5 hectares, corn grinding for animal or human consumption, and crop transformation, This paper presents the technical results of biogas and compost production and use, and the first socio-economic appraisal of the system for irrigated areas.