Nitrate leaching from lysimeter-grown short-rotation willow coppice in relation to N-application, irrigation and soil type

Abstract

The use of willow vegetation filters for wastewater treatment is gaining interest in Sweden. A study was conducted in order to determine reasonable rates of wastewater application to such vegetation filters. NO 3-N leaching loads and N-uptake by the plants were quantified in relation to nitrogen application rate, irrigation rate, shoot growth, and soil type during three years after planting of willow ( Salix viminalis) in sixteen 1200-l lysimeters filled with clay or sand soil. Nitrogen was applied at rates corresponding to 110– 244 kg N / ha yr combined with irrigation of 3– 6 mm/ day during 100– 110 days each growing season. NO 3-N leaching loads were very high the first year after plant establishment (on average 341 kg N / ha from clay and 140 kg N / ha from sand lysimeters). However, NO 3-N leaching loads decreased and were low or negligible during the second (43 from clay and 17 kg N / ha from sand lysimeters) and third year ( 3 kg N / ha from clay and less than 1 kg N / ha from sand lysimeters). Harvest of the plants after the second growing season did not seemingly affect NO 3-N leaching loads during the third year. Soil type and N application rate strongly influenced NO 3-N leaching loads, whereas irrigation rate had only a slight effect, and thus, dosing of wastewater should be based on N-amounts. Assuming an annual shoot growth of 10 tonnes (dry weight)/ha in a willow vegetation filter, wastewater could be applied at rates corresponding to 160– 190 kg N / ha without substantial NO 3-N leaching losses.