Chat Over Coffee? Diffusion of Agronomic Practices and Market Spillovers in Rwanda

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. Training increased knowledge and self-reported adoption, with smaller effects on audited adoption. At first glance, the program appeared effective: trained farmers had 4.6% higher yields than non-trained applicants within the same village and stronger social ties with co-trainees. However, knowledge did not diffuse, and control farmers with more treatment friends reduced audited adoption and input use. Villages with high trainee concentrations showed suggestive evidence of negative spillovers, likely due to competition for inputs – mulch, fertilizer, and labor. Declines in control farmers’ yields account for treatment-control differences, raising concerns both about this dissemination strategy and estimates that fail to consider potential negative spillovers.