The major problem of agriculture in Africa has been the low productivity of the traditional sector. The general thrust of development strategies to this point has been towards providing opportunities to small-holders and ‘encouraging agricultural development within existing peasant production units’. This essentially laissez-faire approach has emphasised the need to improve producer incentives and the necessary infrastructure, as well as to provide new crop varieties and modern agricultural inputs in general. Social scientists, in turn, have studied the general question of how farmers respond to changes in incentives and, especially, to the availability of technological innovations.