Purpose This study aims to compare crop rotation systems used in organic farming (organic rotation systems) with those of both conventional farming (conventional rotation systems) and continuous rice cropping systems. Life cycle assessment (LCA) is performed based on land-and product-based indicators. Methods Seven crop rotation systems for rice, barley, and soybeans and continuous rice production systems were evaluated in this study. These systems are practiced by farmers in the study region and were constructed using production records, statistics, and guidelines. Comparisons were then made between organic and conventional crop rotation systems and between these crop rotation systems and a continuous rice production system. We used land-oriented expression to analyze tradeoffs between physical and monetary productivity and the environmental impact per area unit and productoriented expression to analyze efficiency as measured by the environmental impact per product unit. Results and discussion Results are summarized as follows: (1) The product-oriented expression, which is equivalent to conducting product LCA, revealed that organic conversion tended to be efficient, irrespective of using physical productivity (the functional unit of product mass measured as averaged annual energy yield) or using monetary productivity (the functional unit of product mass measured as averaged annual income).(2) However, the land-oriented expression revealed that there were tradeoffs between physical productivity and environmental impacts, although these tradeoffs were converted to win-win relationships if monetary productivity was used instead of physical productivity, and (3) the alteration of a continuous rice production system into crop rotations tended to be efficient and enables a win-win relationship.Conclusions Organic rotation systems have the potential of being recommended as sustainable agricultural practices in comparison with conventional rotation systems and continuous (organic and conventional) rice production systems. However, it was not clarified which productivity concepts should be used as evaluation criteria. It is considered that further studies using mechanistic modeling of crop rotations are required to improve LCA practices.
Objective. Because most Japanese soybeans are cultivated in paddy fields under rotational cropping, life cycle assessment(LCA)of soybean production needs to take into account a whole crop rotation including rice cultivation. In order to investigate the environmental impact associated with organic soybean production in Japan, this study carried out comparative LCA of organic and conventional soybean-rice rotation systems including 3-year organic and conventional rotations and a 2-year organic rotation. The inventories of arable products were built in the SimaPro software with the NARO LCI database, and were analyzed using the impact categories of global warming, acidification, eutrophication, non-renewable energy consumption, and pesticide application. Results and Discussion. Organic soybean production reduced the environmental impact per 1 kg of soybeans in all the categories by more than 30% compared to conventional soybean production. The main contributors to the superiority of organic soybean production were decreases in direct field emissions and fertilizer consumption as well as the higher yield of organic soybeans. Sensitivity analysis demonstrated that organic soybean production remained more environmentally friendly than conventional soybean production, even if the yield of organic soybeans was assumed to decrease to 80% of the yield of conventional soybeans. However, the impact of organic rice production was significantly higher than that of conventional rice production in the categories of acidification and eutrophication due to overfertilization including rice bran and irregular soybeans for weed control. The impact of whole crop rotations was dominated in most cases by rice production owing to the higher yield of rice and the higher frequency of rice production. Consequently, the reduced impact of organic soybean production was canceled by the relatively large impact of organic rice production, depending on the impact categories; the impact of the organic rotation on acidification and eutrophication was higher than that of the conventional rotation. The 2-year organic rotation environmentally outperformed the 3-year organic rotation mainly because the effect of environmentally friendly soybean production had more influence on the former than on the latter. Conclusions. This study showed that the environmental impact of organic soybean production was definitely lower than that of conventional soybean production. However, comparative LCA of whole crop rotations showed unfavorable results particularly with regard to acidification and eutrophication. This paper suggests two solutions to reduce the total impact associated with the organic paddy rotation including organic soybean production; one is reduction of organic fertilization in organic rice production and the other is introduction of a 2-year soybean-rice rotation.
Increased public focus on agri-environmental issues and recent policies on agricultural sustainability have necessitated the construction of a life cycle inventory (LCI) database for agricultural production systems. However, the current progress of LCI database construction is far from being complete in both developed and developing countries. In this chapter, an integrated view for a data-construction methodology for agri-environmental assessment is proposed. The applications of computational methods to the construction processes are also proposed, with a special focus on Japanese case studies. After discussing the methods for construction, the implications of LCI construction are presented, which includes the following issues: how to make a transition to sustainability, and how to achieve informed and science-based policy decisions by increasing the applicability of life cycle assessment and the level of preparedness. The Japanese case studies should support assessment and decisions in developed and developing countries.
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