The eutrophication of Lake Tai in the mid-east of China caused by an excessive import of nutrients from agricultural non-point-source pollution impedes social and economic development. In our research we aim to improve the understanding of the farmers’ decision-making process applying chemical fertilizers. Based on data gained in household interviews in 2011 and 2012 we follow the question: Which factors influence the individual decision on the use of fertilizers? Our approach is twofold: first, we estimate a production function to assess nitrogen overuse. Second, based on qualitative data we analyse the influence of the institutional context on individual decision-making.