Comparison of environmental performance of tractor and animal traction using a hybrid-LCA

Since the origin of agriculture and shortly after the end of the Second World War, animal traction has supported humans in most field operations. Animal traction allowed human populations to grow faster because it significantly increase agricultural yield with a minimum increase of energetic inputs. The introduction of mechanization in agriculture and forestry completely changed this. Nowadays, animal traction is largely used in the developing part of the World and, sometimes, in specific contexts such as mountain areas, due to the difficulties of using tractors, and for rural farm holidays for commercial appeal. Nevertheless a debate is carried out about the environmental sustainability of animal traction in comparison with tractors, because supporters of mechanical management highlight that tractor impacts are related to a small consumption of fuel related to the feed consumed by animals. Furthermore impacts of tractors have to be related to a larger amount of traction obtained by a traction compared to animals, due to the difference in power exerted by the two different “machines”. Therefore this study assess the environmental performance of animal traction in comparison of tractor traction, in a case study, using a combined functional unit consisting of two different operations: the management of 1000 m2 of soil for horticultural production and the deforestation needed to obtain 100 kg of wood. Impacts of both operations made by donkeys were evaluated in the “La Masca”farm in Roccaverano (Asti, Northern Italy) and by field data on the same operation made by tractors in a similar production system and then related to the specific functional unit. In order to compare the environmental burdens per working hour of donkeys and tractors, the impacts generated in the full life of the two “machines”were divided by the estimated working hours in their whole life. Therefore, in the case of donkey, the full feeding and stabling requirement were considered taking into account the real mechanical hay-making in Roccaverano to produce the hay. This was one of most challenging aspects of the study because it involved the modeling of the donkey. As several by-products or services are provided during the provision of the functional unit in the two systems of donkey and tractor management, it is not possible to consider it directly in a standard LCA. Therefore, we applied a hybrid input-output/LCA methodology in which the environmental contribution of services were accounted as the impacts per €, obtained by NAMEA (National Accounts Matrix including Environmental Accounts) evaluations. This hybrid method has both the typical strength and weakness of mixing a bottom-up approach with a top-down analysis. With this method all processes involved in the lifetime of donkeys and tractors are accounted (also services without basic goods) but, as the NAMEA matrix refer to the National level, the emission associated to a service may not be sufficiently accurate to the local context. The results show a better environmental performance of animal traction both per surface of managed soil and per weight of ready-to-be-sold wood. Considering just the Global Warming Potential category, animal traction operations reduce impacts by 50,45 kg CO2 eq. / 1000 m2 of managed soil (about 94%) in the agricultural operation and the impacts by 0,97 kg CO2 eq. / 100 kg of wood (about 72%) in the forestry operation.