边喝咖啡聊天？卢旺达农艺实践的扩散与市场溢出效应

Agricultural extension programs often train a subset of farmers and rely on social networks for knowledge dissemination. We evaluate this approach through a two-stage experiment of an agronomy training program among Rwandan coffee farmers. The first stage randomized trainee concentration at the village level; the second randomly selected participants within villages. The program increased knowledge and self-reported adoption of the taught practices. It also reshaped farmers’ social networks by creating new social ties primarily among co-trainees. At first glance, the intervention appeared modestly effective, with treated farmers exhibiting higher yields than control applicants within the same village, although this difference is not statistically significant. However, knowledge did not diffuse, and control farmers with more treatment friends at baseline reduced audited adoption and input use. Villages with high trainee concentrations showed suggestive evidence of negative spillovers, consistent with reallocation of labor and other shared inputs toward treated farmers, as formalized in a simple model in which social ties shape access to inputs. Relative declines in the yields of control farmers in these villages account for treatment-control differences, raising concerns both about this dissemination strategy and estimates that fail to consider potential negative spillovers.