Eco-balance analysis of land use combinations to minimize environmental impacts and maximize farm income in northern Japan

摘要

Relationships between global warming potential (GWP), farmland surplus nitrogen (FSN) and income for major land uses in Ikushunbetsu watershed were compared using the eco-balance method. An empirical model was created for carbon dioxide, methane and nitrous oxide for both uplands and paddy rice using monitoring data from 22 fields. The greenhouse gas emissions were converted into GWP, whereas yield and FSN were obtained from farmers' interviews and literature survey. Land use distribution was obtained by ground surveys in 2002, 2005 and 2007. The analysis showed that paddy rice and soybean were characterized by a high GWP, low FSN and high income, whereas onions and vegetables had a high FSN but low GWP and moderate income. Wheat showed a negative GWP in some years and abandoned areas always exhibit negative values. The total GWP for the region was 14184, 11085 and 8337 Mg CO2 yr^[-1] for 2002, 2005 and 2007, respectively. The contribution of paddy rice to GWP was highest, ranging from 40% to 75%. To find optimal land use combinations that have higher income and lower GWP and FSN than present, all possible land use combination was analyzed by changing the land use proportion from 0 - 100% at an interval of 10%. The number of land use combinations meeting the requirements in the three investigated years was 205. Abandoned area which had the smallest environmental load was included in every land use combination, indicating that land uses with low environmental impacts should be maintained at a certain proportion to mitigate the environmental load accompanying land uses with high production.