NITROGEN TRANSFORMATIONS IN LIMED AND NITROGEN-FERTILIZED SOIL IN NORWAY SPRUCE STANDS

Nitrogen transformations in the soil, and the resulting changes in car bon and nitrogen compounds in soil percolate water, were studied in tw o stands of Norway spruce (Picea abies L.). Over the last 30 years the stands were repeatedly limed (total 6000 kg ha(-1)), fertilized with nitrogen (total about 900 kg ha(-1)), or both treatments together. Bot h aerobic incubations of soil samples in the laboratory, and intact so il core incubations in the field showed that in control plots ammonifi cation widely predominated over nitrification. In both experiments nit rogen addition increased the formation of mineral-N. In one experiment separate lime and nitrogen treatments increased nitrification, in the other, only lime and nitrogen addition together had this effect. In o ne experiment immobilization of nitrogen to soil microbial biomass was lower in soil only treated with nitrogen. Soil percolate water was co llected by means of lysimeters placed under the humus layer and 10 cm below in the mineral soil. Total N, NH4-N and NO3-N were measured, and dissolved organic nitrogen was fractioned according to molecular weig ht. NO3-N concentrations in percolate water, collected under the humus layer, were higher in plots treated with N-fertilizer, especially whe n lime was also added. The treatments had no effect on the N concentra tions in mineral soil. A considerable proportion of nitrogen was leach ed in organic form.