Open access publications in the SLU publication database

Abstract

Highly increased use of biomass production is placing great demands on Swedish forests. Several silvicultural measures can be implemented to increase forest production and fertilization being addressed in this paper is one. Forest companies are now increasingly applying fertilizer, with the main nutrient needed for high forest growth being nitrogen (N). This study investigated how commercial N fertilization (150 kg N/ha, including also Ca, Mg and B) of the 45 ha forest catchment Risfallet in central Sweden affected chemical composition and runoff export in stream water during one year after the fertilization. This well-defined and long-term monitored catchment proved very suitable for studies of water quality and nutrient losses. The fertilizer consisted of ammonium nitrate (50/50 ammonium and nitrate, respectively), plus calcium (Ca, 22 kg ha (Mg, 12 kg ha boron availability. The study was carried out according to the paired catchment method using a control area and a calibration period. Data from the after treatment period were compared with previous 25-year monitoring data for the catchment and also data for a similar 83 ha control catchment, Gusseltjärn, in the same region. During the first year after treatment, the nitrate concentration in stream water increased from 0.05 mg L ammonium (300%), B (3-fold), Mg (80%), Ca (60%), potassium (K) (50%) and sodium (Na) (40%). The pH decreased in the first half-year by 0.2 pH-units. One year after treatment, 14% of the N applied had leached from the catchment.1) and magnesium1) to mitigate acidification and boron (B 1.1 kg ha1) to compensate for decreased1 to 3.3 mg L1 on average. Other elements showing increased concentrations were ammonium (300%), B (3-fold), Mg (80%), Ca (60%), potassium (K) (50%) and sodium (Na) (40%). The pH decreased in the first half-year by 0.2 pH-units. One year after treatment, 14% of the N applied had leached from the catchment.