Environmental Life Cycle Assessment of Danish Organic Vegetables

Andreas Jensen

Publikation: Bog/antologi/afhandling/rapportPh.d.-afhandling

Abstract

Currently, agricultural production has severe environmental consequences, such as global warming, eutrophication and high consumption of fresh-water, and farming is a cause of the transgression of the planetary boundaries. Food systems reorganisation towards more plant-based food options is a key part of the proposed solution for a sustainable food system. Organic production is generally already associated with sustainable practices by consumers and can contribute to a more sustainable diet. However, so far sustainability assessments of organic vegetable production are sparse, also for Danish production conditions, which have a high degree of mechanisation and specialisation in production.
Hence, the aim of the present Ph.D. study was to investigate the environmental profile of organic vegetable production in Denmark, and to identify the main sources of environmental impacts and evaluate improvement options for lowering environmental impacts of production. A life cycle assessment (LCA) framework was applied, and the Ph.D. project also identified, evaluated and discussed methodological challenges for conducting LCA of organic vegetable production systems.
Danish organic tomato production in greenhouses was investigated with a LCA framework. To provide optimal growth conditions, heating is provided, and sometimes, depending on timing of planting, supplementary growth light.
The assessment revealed that energy consumption was the main factor responsible for environmental impacts related to climate and the marine environment, even though estimated energy efficiency of greenhouses has more than doubled since the latest Danish assessment in 2006. Earlier transplantation of tomatoes leads to higher total yield, but also require more energy input, as the plants are moved into the greenhouse in early winter. The analysis revealed that the higher yield could not compensate for increased energy use. A three-fold increase in climate impact due to a five-fold increase in energy use per kg tomato was observed. The planned increase of renewable energy shares in the electricity grid can lead to noticeable decreases in impacts, except resource depletion. Hence, producer’s seeking to lower their environmental impact could improve energy efficiency by investing in more well insulated greenhouses, and invest in heat pump technology for heat provision, which reduced all assessed impacts markedly, except resource depletion which was unchanged. A future production system with fully-closed greenhouses can achieve a high energy efficiency but risks to not comply with the organic principles.
Impacts of organic vegetables grown in open-field crop rotation with cereals and grass-clover were investigated as well. The organic vegetables assessed were pointed cabbage, cos lettuce and yellow onion production for retail distribution. These crops were chosen for study as they differ in their production and crop characteristics, and are common organic vegetable crops in Denmark. The high amount of applied fertiliser and nitrogen-rich crop residues when producing pointed cabbage was identified as a main contributor to climate impact, as nitrous oxide was responsible for 40% of the cradle-to-farm gate climate impact. Hence, improved management of crop residues would contribute to lower impacts. Furthermore, the production of vegetable seedlings was identified as a hotspot due to the use of sphagnum peat as substrate, especially for cos lettuce and onion, which are grown in pressed peat blocks. Ongoing innovation can lead to sustainable alternative growth media, and peat-free seedling production will increase sustainability. As identified for yellow onion production, improved energy efficiency of post-harvest storage would reduce impacts.
Realised yields of hand-harvested vegetables are generally lower than possible, as not all vegetables suitable for human consumption is harvested. An increase in obtained yield would lower all impacts, but non-technical barriers should be further investigated and addressed.
The LCA of organic farming systems identified several methodological challenges related to handling of multi-functionality and interactions between crops and production systems. This is especially a challenge when applying LCA for product labelling. Organic tomato production depends on animal production systems for import of nutrients. It was investigated how to determine the impact of imported nutrients. This depend on local availability, as the nutrients from animal systems can be defined as either a waste, a co-product or a residual from animal production. However, regardless of definition, the inclusion of associated environmental impacts from nutrient import was negligible in the life cycle perspective, when assessing organic tomato production.
A well-managed crop rotation is important in organic open-field vegetable farming, as it ensures sufficient nitrogen availability for successful vegetable production. This should be accounted for when evaluating organic farming systems. Several approaches for inclusion of crop rotation effects have been investigated, and the inclusion of the carry-over effect of nitrogen to the following crop as a co-product from cultivation was recommended. Even though a system approach more comprehensively account for interactions between crops, a system approach requires allocation, which affect estimated impacts for the single crops. The rules of allocation for product labelling have previously sparked controversy, as illustrated by the process of determining slaughter-house allocation rules in the Product Environmental Footprint process.
Overall, the Ph.D. study suggest pathways for improved sustainable organic vegetable production by outlining the current impact sources. The study serves as an introduction to a debate of how sustainable organic vegetable production is dependent on producer choices, as well as other actors in the supply chain. Furthermore, the discussion of modelling choices can inform decision-makers about consequences of procedures for handling multi-functionality in relation to labelling scheme guidelines.
OriginalsprogEngelsk
ForlagÅrhus Universitet
StatusUdgivet - aug. 2023

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