Nutrient leaching from energy forest production on arable land in southern Sweden

For nine runoff seasons (1984 - 1993) the nutrient leaching from two drainage systems under an energy forest field (Salix viminalis) and under an adjacent agricultural field with normal crop rotation has been monitored. In 1991 the agricultural field turned into permanent non-fertilized grazing ley. Originally both fields were managed as a unit agricultural field plot with common soil conditions. The purpose of the project has been to investigate the long term leaching effect (nitrates and phosphates) from energy forest and differences in this leaching from normal agricultural practice. Statistical evaluation of the nine seasons shows no significant difference with respect to phosphate. The variations are large, and extreme values occur simultaneously. In fact, the mean leaching values was larger from the energy forest. Other factors than crops seem to influence the leaching. It should be emphasized, however, that only soluble phosphates with the drainage water have been recorded. Phosphorous with erosion has not been studied. The leaching of nitrate shows no statistical difference between the systems for the first five seasons. During this period the energy forest reacts as normal agricultural crops. From there on, the water as well as nitrate leached decrease significantly compared to normal agricultural crops. The nitrate concentrations are however influenced by heavy fertilizer application. This influence remains over a couple of seasons. Moderately or non fertilized energy forest thus seems to protect against nitrate leaching on a long term basis and compared to normal crop rotation, although less obvious compared to permanent grazing ley. 8 figs, 8 tabs