Agricultural yields across sub-Saharan Africa are falling. We can create better seeds, fertilisers and insecticides which has the potential to increase agricultural yields. But what stops that potential being realised? We put a lot of attention on how to influence the behaviour or the choices of farmers, but what can policy also do to help the firms, large and small, that provide the inputs that farmers use? 

Hope Michelson of the University of Illinois is one of the authors of a new review of agricultural input markets. She tells Tim Phillips about the important gaps in our knowledge of how those markets are working.