Comparison between conventional and organic farming systems : an LCA study of milk production

Abstract: Agriculture has always been an important part in people’s daily life and has been developing over centuries with the development of technology and contributing to the rise of civilizations. Based on the production method, conventional and organic farming systems are currently the two main farming systems. The growing awareness of sustainability has forced people to think of how the future of these two farming systems would affect their sustainability performance.  Swedish milk production is of high intensity and highly specialized. Swedish dairy farmers have highest milk yields in Europe, 9500 kilos per cow per year on average, and 73% of milk production takes place in the south of Sweden. The animals are kept indoors most of the year and manure is managed as slurry and removed to outdoor storage units every day. Most of the feedings are produced in Sweden, while some protein feed, especially soymeal and rapeseed meal, are imported from Brazil. Following the LCA methodology, this study aims to investigate the environmental impacts of conventional and organic milk production in Sweden, and then make a comparison between these impacts from the two systems. It also aims to find out the most influenced impact categories and the processes and activities with greatest impacts. Finally, it aims to give possible suggestions on the development of Swedish milk production systems. Methods applied in this study include a literature review of studies on milk production, especially LCA studies of milk production, and an LCA on Swedish milk production.  Current LCA studies have made several improvements which are recommended in previous studies: a clear description of system boundary, a common functional unit, appropriate emission factors, and a range of impact categories. However, there are still some data gaps that need to be filled. The review shows that generally the functional unit is set to be 1 kg of energy corrected milk at farm gate, impact categories include energy use, land use, climate change, eutrophication, and acidification, cradle-to-gate boundary is used. Mass allocation, economic allocation and biological allocation are widely used. However, sensitivity analysis and uncertainty analysis are rarely conducted.  LCA in this study shows that organic farming system does not have clear advantages over conventional system. Organic milk production has lower emissions in categories of CO, COD, HC, NOx, SO2, N, and P, and less use of fertilizer and pesticide. It has similar emissions of CH4, N2O, and NH3 with conventional milk production. But organic system has higher emission levels of CO2, NO3, and K, and higher land use and energy use. Looking at the corresponding ecological effects, the two systems do not have much difference in global warming, acidification, and photo-oxidant formation, while organic system has a higher eutrophication potential.  To deal with environmental impacts, three types of strategies are discussed in this study. The first type concerns manure management. Improvement in manure management can reduce CH4 and N2O emissions and mitigate related ecological effects. The second one concerns milk yield, as CH4 from fermentation process, which is the main source of CH4, is lower at a higher yield. The last one is about transportation, including selecting origins of feed and transportation vehicles to reduce diesel use and replacing diesel with clean and renewable fuel.