Nitrogen and Phosphorus Flows in the Finnish Agricultural and Forest Sectors, 1910-2000

摘要

In this study, the main changes in the flows of nitrogen (N) and phosphorus (P) in the Finnish agricultural and forest sectors during the 20th century were identified and quantified and their future trends were considered. Both the inputs and outputs of N and P to agricultural soil increased during the 20th century. We estimated that biological N fixation in agricultural soil was highest in the 1930s, when it accounted for approximately 40-50% of the N fertilization level at the turn of the Millenium. The total N input to agricultural soil increased almost fourfold between 1910 and 1980-1990 and P input increased nearly eightfold between 1910 and 1970 resulting in an apparent soil surplus of N and P. However, during the last decades, the apparent soil surplus significantly decreased, following the reduction in fertilizing and increasing nutrient outputs in crop yields. The nutrient flows in the forest sector are considerably smaller than agricultural flows. Although the current land area used for forestry in Finland is about 8 times larger than that used for agricultural production, N inputs to the agricultural soil are about 2.5 times and P inputs about 4 times higher than to the forest soil. N outputs (harvest) from the agricultural soil are about 5 times and P outputs about 6 times higher than from forest soil. The observed surpluses have enabled the increase in nutrient losses to water (N, P) and air (N) or their accumulation in soil (N, P), and further, contribution to several environmental problems such as eutrophication of lakes and the Baltic Sea.