Ion leaching before and after clear-cutting in a Norway spruce stand - Effects of long-term application of ammonium nitrate and superphosphate

Soil solution chemistry was measured in a Haplic Podzol in a Norway spruce (Picea abies, L. Karst) site in central Sweden that had received frequent low-dose applications of nitrogen (N) as ammonium nitrate (30-120 kg N/ha yr) and phosphorus (P) as superphosphate (20-40 kg P/ha about every third year) over a long period (22 yr). The aim was to investigate effects of added N on the ion leaching before and after clear-cutting. The N load corresponded well with actual loads in central Europe. Prior to clear-cutting, fertilization increased concentrations of several ions in the soil solution. Total losses of NO;, Al and Hf increased with the intensity of fertilization. However, since fertilization enhanced tree growth and nutrient uptake, differences between the total losses of several other ions tended to be equalized. After clear-cutting, the pH in the soil solution decreased, and the losses of Mn and Al increased with fertilizer load, probably because of increased N mineralization and nitrification. In the N treatments the concentration of SO42- in the soil solution decreased, probably owing to increased adsorption in the B horizon in response to the pH decrease. The effects of anthropogenic N deposition are discussed in the light of our findings and possible causes of temporal and spatial variation in soil solution chemistry and ion fluxes are suggested.