Estimation of the Carbon Footprint of Conventional Rice (Variety: Koshihikari produced in Toso Area, Chiba Prefecture)

Abstract

Objective. This study estimates the carbon footprint（CFP）of conventional rice（variety: Koshihikari produced in Toso area, Chiba Prefecture）. This estimation compares CFP calculation results of Toso area, Chiba Prefecture, with those of specially-cultivated rice in Shiga Prefecture, which have already been reported, and discusses the cause of the difference between them. In addition, the effects of decreasing the number of times the rice is cooked and the heat retention time of the cooked rice on CFP are considered from the viewpoint of environmental conscious behavior.

Method. The functional unit is adopted to express CFP per emission per kilogram of white rice. The lifecycle of rice is classified into five stages, each of which is further divided into seven processes, and CFP is calculated as the total amount of CO₂eq emitted from each process.

Results and Discussion. The estimated result of conventional rice CFP was 1,985.7g-CO₂eq/kg. Followings are the CFP results obtained for the five lifecycle stages: the raw materials procurement stage: 1467.8 g-CO₂eq（component ratio: 73.9%）, the production stage: 43.4g-CO₂eq（2.2%）, the distribution and selling stage: 229.8 g-CO₂eq（11.6%）, the operation and maintenance stage: 232.7 g-CO₂eq（11.7%）, and the disposal and recycling stage: 12.0 g-CO₂eq（0.6%）. Most of the CO₂ is emitted from the rice farming process of the raw materials procurement stage, especially from the nitrogen chemical fertilizer usage and the methane from paddy fields, which accounts for about one-third of the total conventional rice CFP.

Conclusions. Comparing the CFP of conventional rice in Toso area to that of specially cultivated rice in Shiga prefecture, both the varieties have almost the same values except for CO₂ emission from the raw materials procurement stage（CFP of Toso rice is slightly higher than that of Shiga rice）. Therefore, it is important to adopt an environmental conscious cultivation procedure in Toso area, as followed in Shiga area, to reduce CO₂ emission. In addition, it is clear that the total CFP slightly declines by decreasing the number of times the rice is cooked and the heat retention time of the cooked rice.