Environmental evaluation with greenhouse gas emissions and absorption based on life cycle assessment for a Jatropha cultivation system in frost- and drought-prone regions of Botswana

摘要

Among biomass feedstock for energy, a promising option has emerged in Jatropha, which is drought-resistant and has potential for biodiesel production in arid and semi-arid regions. In the present study, we obtained empirical data for calculating the greenhouse gas (GHG) balance from a four-year field experiment on Jatropha cultivation in a frost-and drought-prone region of Botswana. Based on a cultivation protocol customized for this region, GHG emissions were evaluated using life cycle assessment for the actual activities of cultivation: field preparation, raising seedlings/cuttings, farming, and harvesting. Consequently, inputs related to irrigation (irrigation installation, watering, and maintenance) made up 88% of total GHG emissions, and were identified as the major source of GHG emissions in all seasons throughout the study period. Petroleum fuels and plastics for irrigation materials accounted for 50% and 42%, respectively, of all GHG emissions in the cultivation activities. GHG absorption was estimated by measuring Jatropha dry mass, and the GHG balance was addressed through comparison between emissions and absorption. As a result, the emissions and absorptions were calculated as 17 and 21 Mg ha(-1) in CO2-eq, respectively, suggesting that the absorption was 4 Mg ha(-1) greater than the emissions in four years of Jatropha cultivation. Although change in soil organic carbon in the Jatropha field requires further investigation in the future, the present study suggests that Jatropha cultivation may be effective in improving GHG balance in the frost-and drought-prone study region, despite heavy GHG emission from irrigation.