Variability in environmental impacts during conversion from conventional to organic farming: a comparison among three rice production systems in Japan

Earlier applications of the life cycle assessment (LCA) to organic agriculture concern comparisons with conventional agriculture under the assumption that year-to-year variations of agricultural production are negligible. Although the comparisons based on averages are important, it is necessary to investigate the variability in environmental impacts during the conversion period, because the performance of organic farming in the conversion process from conventional farming is unstable. In this study, time-series data obtained from a five-year on-farm trial were applied to an LCA of three rice production systems in Japan: organic, environmentally friendly, and conventional. Four impact categories global warming, acidification, eutrophication, and non-renewable energy were used for the assessment. The results showed that only the environmental impacts associated with organic farming fluctuated widely over the years across all impact categories, and these fluctuations diminished over time. The environmental impacts of organic rice production were higher than those of the other two modes of rice production in four categories covered in the study on average. However, they decreased to the same level as that of conventional farming in the last stage of the conversion phase. The cause of higher variability in the impacts of organic farming at the initial phase was associated mainly with the instability of the organic rice yield. The results indicate that understanding the trends in inter-temporal variability is important for successful conversion to organic farming. (C) 2011 Elsevier Ltd. All rights reserved.