Life cycle assessment and fertilization scheme optimization of paddy field crops in South China

Abstract

Although the application of synthetic fertilizers remarkably improves crop yields, their excessive application can bring about serious environmental pollution. However, previous studies largely focused on life cycle assessment about environmental risk and impact through measuring environmental emissions, or fertilization scheme recommendation with single optimization goal based on field experiments. In this study, we used soil testing and formulated fertilization field data from the experimental region (Ezhou, South China) to acquire the optimal application scheme of synthetic fertilizers for paddy field crops. Based on four crops (i.e. rapeseed, early rice, middle rice and late rice) and two rotation systems (i.e. rapeseed-rice rotation and rice-rice rotation), we applied the life cycle assessment method to analyze life cycle inventories and assess environmental impacts. The fertilizer production and resource consumption were defined as the initial boundary, and the crop production and environmental emissions were defined as the terminal boundary. Four crops were assessed and compared under 1t crop grain functional unit and 1hm2 cropland area functional unit, and two rotation systems were assessed and compared under 1hm2 cropland area functional unit. The environmental impact categories assessed were energy consumption, climate change, eutrophication, environmental acidification, land use and water consumption. Based on three fertilization schemes (i.e. fertilization on benchmark value (Schemeb), yield balance value (Schemeyb) and threshold value (Schemet)), we subsequently simulated crop yields and environmental emissions of fertilization schemes. The results show that the estimated environmental impact category indicators assessed by life cycle per t of rapeseed were higher than rice, and that per hm2 of rapeseed-rice rotation were lower than rice-rice rotation. Eutrophication contributed the most (over 80%) to the environmental impact of producing 1t crop, followed by environmental acidification. Ammonia (NH3) emission accounted for a high contribution to eutrophication (about 30%) or environmental acidification (about 90%), and nitrate ion (NO3-) loss contributed the most to eutrophication (about 40%). The results also show that paddy field crops reached maximum yields but caused greatest environmental impact under the Schemeyb. Whereas, the Schemet could guarantee paddy field crops to keep average yields but cause minimum environmental impact, which was the optimal fertilization scheme. Our study indicates that producing 1t rice and 1hm2 rapeseed-rice rotation had higher environmental benefit than producing 1t rapeseed and 1hm2 rice-rice rotation respectively. Eutrophication could lead to the biggest threat to ecological environment, and the key to alleviating this environmental impact was reducing NH3 volatilization and NO3- loss. Our work implies that the optimal fertilization scheme can both guarantee food sufficiency and reduce environmental pollution, which is applicable combining with soil testing and formulated fertilization technology in Ezhou.