Long-term influence of intensively cultured short-rotation Willow Coppice on nitrogen concentrations in groundwater

Nitrogen concentrations in groundwater were measured during 9 years in an experimental field mainly cropped with intensively cultured short-rotation willow coppice consisting of different clones of willow (Salix viminalis L. and Salix dasyclados Wimm.). The three hectare experimental field is located in south-west Sweden on a sandy soil in an area with alternating recharge and discharge groundwater conditions. Nitrogen was applied to the field in doses averaging 0–153 kg N ha−1 yr−1during the study period, as either liquid or solid fertiliser, and drip irrigation was performed to prevent water shortage. Nitrogen concentrations in groundwater were monitored at four sites within the field. Additional piezometers were installed at 14 sites in order to study the hydraulic situation in the field. Concentrations of nitrate nitrogen (NO3-N) and ammonium nitrogen (NH4-N) were generally below 0·5 mg l−1but occasionally exceeded 5 mg l−1during the first and third year of sampling. Harvest of the short-rotation willow coppice did not seem to affect groundwater nitrogen concentrations. In this study, we show that the impact of intensively cultured short-rotation willow coppice on nitrogen concentrations in groundwater can be very moderate. Thus intensive management of short-rotation willow coppice should not be considered a major threat to the quality of groundwater.