[Diffusion on new bean varieties in Rwanda]
1991
Sperling, L. | Loevinsohn, M.
In Rwanda, the primary channel of diffusion of new varieties is through farmer-to-farmer distribution. Studies at ISAR assessed the rate of such diffusion for four varieties, tested on-farm in three regions. Results show that the small average farm size influences the rate of multiplication by initial recipients: two or more seasons are needed until sufficient quantities are available for sale or exchange. Further, the initial small quantities and widespread poverty make farmers unusually vulnerable to losing even appreciated varieties during the first seasons: out of necessity, seed may be consumed, ill-health may prevent a farmer from harvesting, etc. Distribution tends to be socially-restricted and many farmers are reluctant to circulate varieties at all. The diffusion of new varieties and its speed can be understood as the resultant of two processes: 1) the rate at which new users are created through distribution after the initial period of multiplication and 2) the rate of disappearance of a variety from individual farms. Borrowing techniques from demography, it was found that the life expectancy, the mean longevity of a variety in farmers' fields, is correlated with the mean number of secondary recipients of the variety per season. The doubling time of appreciated varieties ranges from three to five seasons. The study has several implications: 1) It suggests that the process of diffusion may be qualitatively different for small than large farmers; precisely those who most need improved cultivars may have the greatest difficulty keeping them. 2) It presents a usefull model for measuring expansion which realistically incorporates varietal loss as well as adoption. 3) It outlines a strategy for improving the access to new varieties by small farmers in areas where central seed distribution services are weak. (AS)
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