Environmental accounting of closed-loop maize production scenarios: Manure as fertilizer and inclusion of catch crops

The agri-food sector has moved towards a more linear production economy, partly caused by worldwide food demand. One clear example is the intensification of livestock production, with consequent manure-management and feed-production challenges, the effects of which have led to large environmental problems. Currently, efforts are being made to move the agricultural sector towards closed-loop alternatives. To ensure high environmental performance of these alternatives, realistic quantification of environmental impacts is needed. Thus, using Life Cycle Assessment (LCA) tools, we analyzed the environmental profile of six closed-loop maize scenarios focusing on different combinations of mineral fertilizer, digested organic fertilizer (digestate) from a manure co-digestion biogas plant, and rotation with (or without) catch crops (CCs) as a strategy to prevent nitrate leaching to groundwater and as a co-substrate in the biogas plant. Results demonstrated that replacing a large portion of the mineral fertilizers with digestate could help offset much of the total potential impact of global warming (by 25–35 %), resource depletion (by 94–96%), photochemical ozone formation (by 17–22 %), ozone depletion (by 96–99%) or even avoid it entirely as in freshwater eutrophication. However, digestate production and application contributed greatly to acidification (51%) and particulate matter (51–52%) categories, with minor differences depending on the species of CC used. An optimal combination of both digestate and mineral fertilizers is recommended. The incorporation of CCs in a maize rotation can reduce freshwater eutrophication impacts but increase global warming potential. Conclusions were drawn suggesting better management strategies to decrease environmental impacts of maize production.

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