This report contains a meta-analysis of results from field trials with nitrogen application to leys which were carried out during 1997-2015. The analysis deals with the response to nitrogen fertilisation with respect to dry matter and crude protein content in the harvested biomass. The analysis shows that the yield level without any nitrogen application, and the response to nitrogen (kg dry matter/kg N applied), is greater in these trials compared to data from older trials. This applies to both pure grass leys and mixed grass/clover leys. The crude protein content is positively correlated with nitrogen application in pure grass leys. In mixed grass/clover leys this response depends on clover content, but is generally negative in the last cut
