A Comparison of Environmental Impacts Among Different Rice Cultivation Practices in Bimodal Agriculture.

Rice is usually cultivated bimodally (twice a year) in many subtropical and tropical districts including Taiwan. In the 1^st cultivation season, rice was transplanted in the spring and harvested in the summer. In the closely following 2^nd season, rice was transplanted in the summer and harvested in the autumn. The differences of climates between the 2 seasons would bring effects to the grain yield and environment surroundings. Rice production would bring many kinds of environmental impacts such as global warming potential (GWP), energy use (EU), acidification potential (AP), and eutrophication potential (EP). Meanwhile, many adjusted cultivation practices were developed (e.g. reducing fertilization, organic farming and integrated agriculture) for improving these environmental impacts. We applied Life Cycle Assessment (LCA) to assess the environmental impacts of two cultivation seasons and cultivation practices by using DNDC model and SimaPro software. In our results, 4 environmental impacts were all lower in the 1^st season than the 2^nd season, especially in the impacts of GWP and AP. Among cultivation practices, reducing fertilization cultivation brought lowest GWP and EP due to the low input of nitrogen. Organic and integrated cultivation had the advantages in EU and AP because 1. production of organic fertilizer was more energy-saving than chemical fertilizer. 2. releasing rate of organic nitrogen was slower and led to less NH₃ and NO emissions. We advised to make the 1^st season as main rice production rather than the 2^nd season. On the other hand, our results of these cultivation practices could be a reference for rice production under different environmental requirements (e.g. low carbon footprint or water purification).