Life cycle assessment of organic paddy rotation systems using land- and product-based indicators: a case study in Japan

Abstract

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. 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 product-oriented expression to analyze efficiency as measured by the environmental impact per product unit. 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. 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.