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

Citation

Bamber, N., Jones, M., Nelson, L., Hannam, K., Nichol, C., Pelletier, N. (2020). Life cycle assessment of mulch use on Okanagan apple orchards: Part 1 - Attributional. Journal of Cleaner Production, [online] 267 http://dx.doi.org/10.1016/j.jclepro.2020.121960

Plain language summary

Life cycle analyses are used to assess the environmental impact of producing, using and discarding a product. ‘Attributional’ life cycle analyses are used to determine the environmental impacts associated with making a product using currently available alternative technologies. In this case, an attributional life cycle analysis was used to compare the environmental impact of producing apples in the Okanagan Valley with and without the use of surface mulches of wood and bark chips. Surface mulching with wood and bark chips has been shown to reduce the release of a powerful greenhouse gas, nitrous oxide, from the soil surface in apple orchards. However, it was unclear if the greenhouse gas emissions associated with producing, transporting and applying the wood chip mulch outweighed the environmental benefits in terms of reduced nitrous oxide emissions. This life cycle analysis tried to account for a whole suite of other possible costs and benefits of mulch application, e.g., from the perspective of water quality, irrigation water needs, soil acidification, orchard productivity, etc. The analysis found that apples produced using wood and bark chip mulch probably produce more greenhouse gasses than those produce without wood and bark chip mulch. However, the analysis also showed that critical data remain unavailable. Better information on the effect of wood and bark chip mulches on soil carbon sequestration, herbicide and pesticide requirements, fertilizer and irrigation water requirements and nutrient leaching losses are needed to make accurate recommendations to apple producers on the issue of mulching with wood and bark chips

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.

Publication date

2020-09-10

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