Life cycle inventory-based analysis of greenhouse gas emissions from arable land farming systems in Hokkaido, northern Japan.

To assess their impacts on net global warming, total greenhouse gas emissions (mainly CO₂, N₂O and CH₄) from agricultural production in arable land cropping systems in the Tokachi region of Hokkaido, Japan, were estimated using life cycle inventory (LCI) analysis. The LCI data included CO₂ emissions from on-farm and off-farm fossil fuel consumption, soil CO₂ emissions induced by the decomposition of soil organic matter, direct and indirect N₂O emissions from arable lands and CH₄ uptake by soils, which were then aggregated in CO₂-equivalents. Under plow-based conventional tillage (CT) cropping systems for winter wheat, sugar beet, adzuki bean, potato and cabbage, on-farm CO₂ emissions from fuel-consuming operations such as tractor-based field operations, truck transportation and mechanical grain drying ranged from 0.424 Mg CO₂ ha⁻¹ year⁻¹ for adzuki bean to 0.826 Mg CO₂ ha⁻¹ year⁻¹ for winter wheat. Off-farm CO₂ emissions resulting from the use of agricultural materials such as chemical fertilizers, biocides (pesticides and herbicides) and agricultural machines were estimated by input–output tables to range from 0.800 Mg CO₂ ha⁻¹ year⁻¹ for winter wheat to 1.724 Mg CO₂ ha⁻¹ year⁻¹ for sugar beet. Direct N₂O emissions previously measured in an Andosol field of this region showed a positive correlation with N fertilizer application rates. These emissions, expressed in CO₂-equivalents, ranged from 0.041 Mg CO₂ ha⁻¹ year⁻¹ for potato to 0.382 Mg CO₂ ha⁻¹ year⁻¹ for cabbage. Indirect N₂O emissions resulting from N leaching and surface runoff were estimated to range from 0.069 Mg CO₂ ha⁻¹ year⁻¹ for adzuki bean to 0.381 Mg CO₂ ha⁻¹ year⁻¹ for cabbage. The rates of CH₄ removal from the atmosphere by soil uptake were equivalent to only 0.020–0.042 Mg CO₂ ha⁻¹ year⁻¹. From the difference in the total soil C pools (0–20 cm depth) between 1981 and 2001, annual CO₂ emissions from the CT and reduced tillage (RT) soils were estimated to be 4.91 and 3.81 Mg CO₂ ha⁻¹ year⁻¹, respectively. In total, CO₂-equivalent greenhouse gas emissions under CT cropping systems in the Tokachi region of Hokkaido amounted to 6.97, 7.62, 6.44, 6.64 and 7.49 Mg CO₂ ha⁻¹ year⁻¹ for winter wheat, sugar beet, adzuki bean, potato and cabbage production, respectively. Overall, soil-derived CO₂ emissions accounted for a large proportion (64–76%) of the total greenhouse gas emissions. This illustrates that soil management practices that enhance C sequestration in soil may be an effective means to mitigate large greenhouse gas emissions from arable land cropping systems such as those in the Tokachi region of northern Japan. Under RT cropping systems, plowing after harvesting was omitted, and total greenhouse gas emissions from winter wheat, sugar beet and adzuki bean could be reduced by 18%, 4% and 18%, respectively, mainly as a result of a lower soil organic matter decomposition rate in the RT soil and a saving on the fuels used for plowing. [ABSTRACT FROM AUTHOR]