『Abstract
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 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.
Keywords: Agriculture; Forest sector; Nitrogen; Phosphorus; Substance
flows; Time series』
1. Introduction
2. Materials and methods
2.1. System borders
2.2. Agricultural sector
2.3. Forest sector
2.4. Deposition and phosphorus weathering
2.5. Uncertainty analysis
3. Results
3.1. Agriculture
3.1.1. Agricultural soil and crop production
3.1.2. Animal production
3.2. Forest
3.2.1. Forest soil and wood harvest
4. Discussion
4.1. Agriculture
4.2. Forest sector
4.3. Uncertainties
5. Conclusions
Acknowledgements
References