The life cycle assessment of subsurface drainage performance under rice-canola cropping system

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The life cycle assessment (LCA) concept is a widely used tool to assess the environmental aspects of any activity throughout its life cycle. This study is the first application of LCA for assessing the agro-environmental sustainability of subsurface drainage systems under rice-canola cropping rotation. The systems included D0.65L15, D0.65L30, and D0.9L30, consisting of two depths (D=0.65 and 0.9 m) and two spacing (L= 15 and 30 m) and a bi-level drainage system with alternate depths of 0.9 and 0.65 m with 15 m spacing (Bilevel). A paddy plot with conventional surface drainage and similar cropping system was considered as control (Control). Two water management strategies, including mid-season drainage (MSD) and alternate wetting and drying (AWD), were practiced during rice-growing period. Free drainage (FD) was adopted during canola-growing period. Required field data were collected during 2011–2016, including four rice-canola-growing cycles (two MSD-FD cycles and two AWD-FD cycles). Using the LCA concept, the effectiveness of different drainage systems were assessed under the cycles of MSD-FD and AWD-FD. The AWD-FD system showed 7% less environmental impacts than MSD-FD. Also, AWD-FD reduced human health, climate change, and resource depletion indicators by 7.7%, 9.9%, and 8.4%, respectively, compared with MSD-FD, which improved the ecosystem quality index by 7.2%. The Bilevel, D0.9L30, D0.65L30, and D0.65L15 drainage systems, respectively, reduced the environmental impacts by 11.8%, 11.1%, 2.6%, and 5.9% under AWD-FD and 25.4%, 17.6%, 25.1%, and 14.1% under MSD-FD compared with Control. On average, Bilevel reduced the environmental impacts by 18.6% compared with the conventional surface drainage system. Based on the results, the LCA concept can be used as a suitable tool to evaluate the performance of subsurface drainage systems before implementation on a large scale.