Dynamics of nitrate leaching and 15N turnover in intensively fertilized and irrigated basket willow grown in lysimeters

A 13-month experiment was conducted to study the dynamics of nitrate leaching from basket willow (Salix viminalis), and the fate of fertilizer-N applied after the growing season. Lysimeters with or without plants were supplied daily with water and liquid fertilizer. Nitrate leaching and transpiration were quantified, as well as leaf-, stem- and root growth and N-uptake. 15N-labelled fertilizer was applied in autumn after leaf fall for the determination of the fate of fertilizer-N. The N-uptake by the willow plants was high during the summer and was correlated with transpiration. It decreased drastically in autumn in the absence of transpiration, but was still significant, which was also the case in early spring, the following year. A leaf rust infection during autumn led to a 9-times increase in nitrate leaching, whereas transpiration was reduced by 26%. After a fertilizer application for 10 days after leaf fall in autumn, an average of 8% of the fertilizer-N was taken up by the plants, and 32% was unaccounted for, of which a large portion was likely to be lost through denitrification. Recalculated on a hectare basis, the whole-season nitrogen budget shows that 191 kgN/ha was applied as liquid fertilizer during the first season, of which 98 kgN/ha was taken up by plants, 69 kgN/ha was leached, and 24 kgN/ha was unaccounted for (i.e. possibly denitrified). The amount of nitrogen taken up by plants or lost from the system (possibly through denitrification) corresponded to 36 kgN/tonnes of dry stem wood produced.