Stocks and flows of nitrogen and phosphorus in the Finnish food production and consumption system

Nitrogen (N) and phosphorus (P) are two elements contributing to many environmental problems, such as eutrophication, global change (N) and acidification (N). Mitigation of the negative environmental impacts caused by these nutrients requires understanding of their amounts and linkages through inputs and outputs of the different parts of the ecological and societal system. In this study, the stocks and flows of nitrogen and phosphorus in the Finnish food production and consumption system were identified and quantified. An average of each stock and flow was calculated for the period from 1995 to 1999. Total inputs to Finnish agricultural soil were estimated to be 276 500 t N a^-1 and 48 100 t P a^-1, whereas total outputs were approximately 223 500 t N a^-1 and 24 500 t P a^-1. These figures indicate a calculatory nutrient surplus of ca. 29 kg N ha^-1 a^-1 and 13 kg P ha^-1 a^-1 on agricultural land. Currently, the Finnish food production and consumption nutrient system is open, and significant nutrient, especially nitrogen, losses to waters, air and soil (landfills) occur in several parts of the system. Main losses occur during the agricultural production phase. Even if it would be technically and economically possible to return all the nutrients in municipal organic waste to the agricultural soil, these could only replace ca. 17% of the nutrients annually applied in agricultural soil in form of inorganic fertilizers. Other ways to improve nutrient use efficiency are discussed. These include quality control and quality assurance of the production systems and education of farmers to achieve similar yields with less nutrient inputs or smaller agricultural area. Environmental subsidy system may also encourage more efficient nutrient cycling. Several factors, including variation in nutrient concentrations and dry weights and possible inaccuracy of statistics, affect the calculations. Results from an uncertainty analysis indicated that soil inputs varied between 248 400 and 311 300 t N a^-1 and 43 900 and 53 200 t P a^-1. The outputs varied between 174 200 and 303 400 t N a^-1 and 21 500 and 28 300 t P a^-1. Uncertainties were particularly high for N largely related to the difficulties in estimating N₂O emission and denitrification losses.