The productivity and response to inorganic fertilizers of species- rich wetland hay meadows on the Somerset Moors: nitrogen response under hay cutting and aftermath grazing

The productivity and response to fertilizer nitrogen (N) was measured in herb-rich wetland hay meadows within a Site of Special Scientific Interest (SSSI) in Somerset, UK. Output from hay cut after 1 July each year and from beef production at aftermath grazing was measured over a total of 4 years. Total utilized metabolizable energy (UME) output averaged from 40.6 GJ ha-1 year-1 without fertilizers to 61.7 GJ ha-1 at 200 kg N ha-1 (N-200), the highest rate used, with about two-thirds of this output from hay. N response was markedly curvilinear above about 50 kg N ha-1, but data from a concurrent experiment suggested that the comparatively low replacement rates of P and K applied were limiting at higher N rates. When hay cutting was delayed until early August in a wet year, yield response to N was lost because fertilized swards had passed a peak in yield several weeks before harvest. Compared with other published data, the results suggest that output and response to N is not constrained by the diversity of the flora or the damp conditions. The data will help to estimate the financial implications for farmers of restricted or zero fertilizer use within SSSIs and the wider Environmentally Sensitive Areas.