About 3ieThe International Initiative for Impact Evaluation (3ie) is an international grant-making NGO promoting evidence-informed development policies and programmes. We are the global leader in funding and producing high-quality evidence of what works, how, why and at what cost. We believe that better and policy-relevant evidence will make development more effective and improve people's lives. 3ie Impact Evaluations3ie-supported impact evaluations assess the difference a development intervention has made to social and economic outcomes. 3ie is committed to funding rigorous evaluations that include a theory-based design, use the most appropriate mix of methods to capture outcomes and are useful in complex development contexts. About this report3ie accepted the final version of this report as partial fulfilment of requirements under grant OW3.1216 issued under Open Window 3. The content has been copyedited and formatted for publication by 3ie. Due to unavoidable constraints at the time of publication, a few of the tables or figures may be less than optimal. All of the content is the sole responsibility of the authors and does not represent the opinions of 3ie, its donors or its Board of Commissioners. Any errors and omissions are also the sole responsibility of the authors. All affiliations of the authors listed in the title page are those that were in effect at the time the report was accepted. Any comments or queries should be directed to the corresponding author, Krishna B Kumar at kumar@rand.org Funding for this impact evaluation was provided by 3ie's donors, which include UKaid, the Bill & Melinda Gates Foundation, Hewlett Foundation and 12 other 3ie members that provide institutional support. A complete listing is provided on the 3ie website at http://www.3ieimpact.org/en/about/3ie-affiliates/3ie-members/ Suggested citation: Burger, N, Fu, M, Gu, K, Jia, X, Kumar, KB and Mingliang, G, 2015 ii AbstractIn China, a major agricultural challenge is the sub-optimal use of fertilizer and the environmental effects associated with overuse. The Chinese Ministry of Agriculture (MoA) is addressing this problem by instituting farmer field schools (FFS), but this initiative has not been rigorously evaluated. We used a randomised controlled trial to evaluate the FFS program in five counties in Anhui and Hebei provinces, for rice and tomato crops, respectively. We used a matched pair random assignment of villages into treatment and control groups, and we randomized additional farmers into an 'exposed' group to study diffusion effects. We found no significant effects of the FFS intervention on mean fertilizer use for either crop. However, we found that fertilizer usage is highly heterogeneous, and a simple comparison of means masks the differential response to the FFS programme at either end of the distribution. For rice farmers, the percentage increase in nitrogen fertilizer usage at the lowest quintile is significantly higher for the treatment group than that for the control group, with a less pronounced drop in usage in...