Nitrogen leaching from short-rotation willow coppice after intensive irrigation with wastewater

Short-rotation willow coppice is being used in several locations in Sweden as vegetation filters for wastewater treatment. An experiment was conducted in order to quantify the leaching of nitrogen and the toxic effects on the plants after application of wastewater under “worst case” conditions. Eight 1200-1 lysimeters (4 with clay and 4 with sand) were irrigated-fertilised with wastewater from dewatering of sewage sludge or with liquid fertiliser during 8 days, resulting in doses corresponding to 320 kg N ha−1. Thereafter, plants were daily irrigated with tapwater at a rate of 10 mm d−1 for 123 days. Nitrate-N leaching loads from May until October were approximately 70 kg N ha−1 for clay and 90 kg N ha−1 for sand lysimeters (not significantly different). Leaching loads of ammonium-N and organic N were low (approximately 10 kg N ha−1 for all treatments). The high nitrate-N leaching loads were mainly attributed to the high nitrogen application rate and not to the chemical composition of the fertilisers. No short-term damages to the plants caused by the application of wastewater were observed.