Life cycle analysis of soybean production in typical district of the North China Plain

In recent years, the low self-sufficiency ratio of soybeans has become an urgent issue in China. Gaocheng District of Shijiazhuang City of Hebei Province is an important county for soybean production in the Huang-Huai-Hai area. Although soybean has symbiotic nitrogen fixation efficiency, excessive inputs like fertilizers and pesticides still cause environmental pollution. Therefore, scientific evaluation of the eco-efficiency of soybean production is conducive to promoting the sustainable development of the soybean industry in the Gaocheng District. Based on a survey of 50 farmer households in the Gaocheng District, we evaluated the environmental impact and eco-efficiency of local soybean production using a life cycle assessment (LCA) and a super-efficiency slakck-based measure (SBM) model (super-SBM). The environmental impact results showed that the four indices, global warming potential (GWP), terrestrial eco-toxicity potential (TETP), acidification potential (AP), and eutrophication potential (EP), were the dominant potential environmental impact categories in soybean production. The sowing-to-seedling stage contributed to the largest part (1.45E−5) of GWP, the largest part (5.34E−6) of AP, and the largest part (3.21E−6) of EP; the largest part (5.85E−6) of TETP was attributed to the flowering-to-podding stage. Among the four indicators, GWP, TETP, and EP of large-scale farming were the highest according to the planting scale. Concerning irrigation methods, GWP and AP were highest in trickle irrigation, and TETP and EP were highest in furrow irrigation. Based on the planting areas, GWP, AP, and EP in northern Gaocheng were higher than in southern Gaocheng. The eco-efficiency analysis showed that the mean value of all farmers’ eco-efficiency was 0.84, indicating that local soybean production was inefficient and had room for improvement. Concerning the planting scales, eco-efficiency followed the order of large-scale > mid-scale > small-scale. Concerning irrigation methods, eco-efficiency decreased in the order of trickle irrigation, sprinkling irrigation, no irrigation, and furrow irrigation. Concerning the planting areas, the eco-efficiency in southern Gaocheng was higher than that in northern Gaocheng. Moreover, six redundancy indices were compared under three planting scales. The range of redundancy ratio (max−min) in pesticides was the highest (5.89%), indicating that the change in planting scale had the greatest impact on the use of insecticides. Six redundancy indices were compared under four irrigation methods, and the range of redundancy ratio in water was the highest (8.40%), indicating that irrigation methods had the greatest influence on irrigation water. Six redundancy indices were compared under two planting areas. The range of the redundancy ratio in fertilizer was the highest (2.79%), indicating that the difference in planting area had the greatest impact on fertilizer application. Overall, to ensure the yield and improve the ecological efficiency of soybean production in Gaocheng District, we suggest farming soybean at a large scale, constructing water conservancy facilities, developing trickle irrigation, and controlling the use of fertilizers and pesticides at the different stages of soybean production. These results provide a reference basis for the eco-efficiency evaluation of local soybean production that might benefit the sustainable development of the soybean industry in the Gaocheng District.