Life cycle assessment of mulch use on Okanagan apple orchards: Part 1 - Attributional

Abstract

Food production contributes substantially to anthropogenic environmental impacts, including 19–29% of greenhouse gas (GHG) emissions. Use of wood and bark chip mulch as a soil cover has previously been found to reduce direct N2O emissions and increase soil organic carbon on apple orchards. The current study expanded the scope of this prior investigation to include the “upstream” processes that support production and transportation of the mulch used on orchards using ISO-compliant life cycle assessment. An “attributional” life cycle assessment was conducted to determine the net life cycle environmental impacts of the production of apples on an Okanagan orchard, focusing on the relative contribution of bark and wood chip mulch used as a soil amendment, both compared to other life cycle stages and processes, and to a system producing apples without the use of mulch. This research focused on only the orchard-level GHG reductions benefit associated with mulch use. A variety of environmental impact categories were examined including human toxicity, freshwater aquatic ecotoxicity, depletion of abiotic resources (elements, ultimate reserves), photochemical oxidation, ozone layer depletion, terrestrial ecotoxicity, acidification potential, climate change, eutrophication, land use – land competition, and energy use (including non-renewable: fossil, nuclear, primary forest; and renewable: biomass, geothermal, solar, water and wind). When the entire life cycle was considered, apples produced using mulch had higher life cycle GHG emissions than those without mulch, as well as higher impacts in all of the other impact categories considered. Due to these higher emissions with mulch, the results do not support the recommendation of mulch application on orchards as a GHG mitigation strategy, nor with respect to the other impact categories considered.