超多収水稲生産システムのLCA：地球温暖化への影響およびエネルギー投入量による慣行システムとの比較

Abstract

Objective. The purpose of this paper is to conduct comparative life cycle assessment of super high-yield and conventional rice production systems. Since super high-yield rice production needs further energy and resource inputs as compared with the conventional production, the judgment of relative superiority should be based on the assessment of whole systems. Therefore, life-cycle energy use and life-cycle CO2 emissions are used for the comparison.Results and Discussion. Super high-yield rice production consumes much more fuels than conventional production due to drying of the unhulled rice and fertilizer production, and thus it needs much more energy inputs and emit much more greenhouse gases than the conventional production if we use the functional unit of unit area. Energy inputs per ha were 44 GJ for the super high-yield rice production and 42 GJ for conventional production. GHG emissions per ha were 8.0 t CO2 eq. for the super high-yield rice production and 7.5 t CO2 eq. for the conventional production. However, if we utilize the functional unit of 1 kg of brown rice, we have another result as follows: energy inputs per 1 kg of brown rice were 5.46 MJ for the super high-yield rice production and 7.70 MJ for the conventional production; GHG emissions per 1 kg of brown rice was 1.00 kg CO2 eq. for the super high-yield rice production, and 1.39 kg CO2 eq. for the conventional production. That is, energy inputs and GHG emissions per 1kg of brown rice for the super high-yield rice production were lesser than conventional production. The breakdown of the environmental impacts showed that the production of agricultural machines, materials, fertilizer, agrochemicals and fuels accounts for more than 70 % of all energy inputs. This means that the extension of the lifetime of machines and materials and the reduction of fertilizers and pesticides are effective in reducing energy inputs. In addition, since energy inputs to the drying of the unhulled rice were comparatively large, the reduction of the fuel consumption for drying will be important.Conclusions. This study clarified the environment load of super high-yield and conventional rice production systems. Improving rice yields was considered to be an effective way in decreasing energy inputs and GHG emissions per 1kg of brown rice. It was shown that we should use the inventory data of rice production for energy in LCA of the biofuel production.