2026 年 35 巻 2 号 p. 49-58
Production of forage feed is rapidly expanding in Japan, with potential to improve self-sufficiency in animal feed. However, it is important to understand how this expansion will contribute to the broader context of agriculture’s sustainability. Production of forage feed uses inputs that are important sources of greenhouse gas (GHG) emissions. Life Cycle Assessment (LCA) is increasingly being used to inform decisions related to environmental sustainability. Most environmental impact assessments of agricultural supply chains have used Process LCA, which is limited in estimating indirect (embodied) GHG emissions, as it usually takes into account only one (but up to three) production stage (supply level) upstream of the farm. Thus, embodied GHG emissions from upstream supply levels are often underestimated, leading to potential biases in conclusions. Here we applied the Path Exchange hybrid LCA and Structural Path Analysis (SPA) methods, which integrate process and economic input-output data, to comprehensively quantify direct and embodied GHG emissions in the Japanese forage supply chain. Process LCA estimated GHG emissions of 0.052 kg CO2-eq/kg forage feed. Inclusion of embodied upstream impacts increased this by 18.6% (0.062 kg CO2-eq/kg forage feed). Structural Path Analyses showed that inorganic fertilizers, freight, and dairy cattle farming are the most important contributors of GHG emissions in the forage feed supply chain. These findings are important for policy consideration. If targeted only at the farm level, efforts to achieve environmental efficiency may significantly reduce direct GHG emissions, but will increase the contribution of embodied GHG emissions. The implications are that achievement of total environmental efficiency in the forage supply chains should take into account upstream indirect GHG emissions from carbon hotspot areas of inorganic fertilizers, freight, and dairy cattle farming.
