The main objectives of the project described in the present and four following papers are: 1. To study tree growth and nutrient status of forest soil as influenced by atmospheric depositions of S and N. 2. To study the influence of plant growth, liner decomposition and atmospheric depositions on soil acidity. 3. To study the influence of atmospheric deposition on the release of N2O from soil. One field plot experiment in a Scots pine forest and one lysimeter experiment were established in 1990 on weakly podzolized soils (Cambic arenosol). The experiment was established in a young Scots pine forest. N, Mg and P were applied in a factorial design. The experiment includes 12 treatments and three blocks. Soil was collected in a long-term field experiment with acid rain acid filled into lysimeters (bucket type) by horizon. Under each horizon tension lysimeters were installed. The lysimeters were under a roof to avoid input of natural precipitation. S was applied as sulphuric acid diluted to pH levels of 5.5, 4.0, 3.5 and 3.0 and applied in a quantity of 1000 mm ''rain'' yr(-1). Nitrogen (NH4NO3) was applied in three quantities: 0, 30 and 90 kg N ha(-1) yr(-1). Seedlings of Scots pine were planted in the lysimeters. Lysimeters with no trees were also established. The experiment includes four replicates.
