Estimation of nitrogen saturation on the basis of long-term fertilization experiments

The obvious changes in some properties of forest soil due to atmospheric nitrogen deposition under Finnish conditions were estimated on the basis of long-term fertilization experiments. The experiments were established during the years 1959–1965. Nitrogen fertilization was repeated three to four times. During the study period averaging 23 years, the cumulative amount of fertilizer nitrogen totalled about 400 kg N ha^-1. The main results are as follows. Nitrogen addition increased the quantity of organic matter in the humus layer, but has not clear effect on its quality. Nitrogen fertilization did not increase soil acidity.