Life cycle assessment of alfalfa production and potential environmental improvement measures in Northwest China

Alfalfa is an important legume forage crop and environmental impacts of producing it differ with its production systems and regions. Despite its high water consumption, a comprehensive assessment of combining water consumption with other environmental impacts has not been carried out. The objectives of this study were to evaluate water consumption and other important environmental indicators for four main alfalfa production systems in Northwest China and to investigate improvement measures to reduce environmental impacts. A life cycle assessment approach coupled with CropWat modelling was used for the study. Compared with the low agricultural input systems NFNI (no fertilization or irrigation) and AFNI (applying fertilizer without irrigation), the high agricultural input systems AFRI (fertilization and irrigated with river-water) and AFWI (fertilization and irrigated with well-water) achieved higher yields with lower land use (LU), but led to higher environmental impacts on water resource consumption (WRC), global warming potential (GWP) and other impacts. Except for LU, the NFNI system had the least impacts on almost all environmental indicators, while the AFWI had the most adverse impacts. A trade-off between LU, WRC, GWP and other impacts was observed when single improvement measures were taken in the systems AFRI and AFWI. However, optimised combination of the measures such as reducing N fertilizer rate, deficit irrigation and sprinkle-irrigating can generally decrease impacts for most environmental indicators, except for LU. It is difficult to achieve high alfalfa yield while saving water consumption and also reducing GWP and other environmental indicators in a specific production system. However, increasing average yield in the whole region and decreasing environmental impacts can be achieved to some extent through adjusting the production systems with optimised combination measures. Accordingly, the AFNI production system for the semi-arid area and the AFRI system for the arid area are recommended. The study highlights the importance of considering water and land resources along with assessing other impacts of agriculture products when performing a comparison between farming systems and improvement measures.