A life cycle assessment of liquid pig manure transport in line with EU regulations: A case study from Germany

The transport of excess manure to crop farming systems is a core measure of livestock farmers to comply with environmental regulations like the EU Nitrates Directive. The German implementation of the directive has recently been revised and will lead to a distinct increase of manure transport. We quantify the environmental impact of 1 m³ of pig manure excreted in scenarios with and without manure transport by life cycle assessment, focusing on farming systems in North-West Germany. Furthermore, we assess how the environmental impact is linked to the regulation which is causing the transport. Compared to a reference scenario without transport, manure transport lowers all assessed impact categories and no trade-off between environmental impacts is found. Major reductions are realized for global warming (39%), freshwater (61%) and marine eutrophication (54%) as well as particulate matter formation (10%). Furthermore, the depletion of fossil fuels and phosphate is lowered. Reductions are mainly caused by an increase of nutrient use efficiency and the savings in chemical fertilizer. However, in a scenario where manure transport is caused by strict regulations regarding phosphate, needed nitrogen leaves the exporting farm likewise and chemical fertilizer use rises at the exporting farm. Caused by the increased fertilizer use, the positive environmental effect of manure transport diminishes, even leading to a rise of fossil fuel depletion by 20% and slight rise of global warming potential by 3%. However, we find that the use of lorries which combine manure and grain transport and, thereby, reduce empty drives, can prevent this trade-off. Our results show the potential of manure transport to reduce the environmental burden caused by the geographical concentration of livestock production. However, the impact of manure transport on global warming and fossil fuel depletion highly depends on the transport distance. Agronomic measures are needed to prevent the increase of chemical N fertilizer use on the exporting farms and policy makers should be aware of possible trade-offs between strict regulations regarding phosphorus and fossil fuel depletion.