On the relevance of site specificity and temporal variability in agricultural LCA: a case study on mandarin in North Uruguay

Purpose Mandarin is a relevant citrus crop in Uruguay both in terms of yield and area. This study is aimed at assessing the environmental impacts of mandarin cultivation in the country to identify the environmental hotspots. Temporal variability is assessed by considering six harvest seasons and site specificity by developing a regionalized inventory using a Tier 3 to estimate nitrogen on-field emissions. Also, the effect of regionalizing specific impact categories is analyzed. Methods A cradle-to-farm gate assessment was carried out based on mass and area functional units. Primary data was gathered from a representative orchard of the region for the seasons 2016 to 2022. Nitrogen on-field emissions were modeled using LEACHN, a Tier 3 model that considers site-specific climatic and soil parameters as well as water and fertilizer applications at a daily scale. In addition, other modeling approaches were tested following the Environmental Product Declarations (EPD), Product Environmental Footprint (PEF), World Food LCA Database guidelines (WFLDB), and the updated IPCC and EMEP/EEA guidelines. The EN 15804 + A2 standard was followed to assess the environmental impacts, except for the categories concerning acidification, where IMPACT 2002 + v2.1 was used. In addition, to analyze the variations in the results when regionalizing impacts of on-field emissions, IMPACT World + was used. Results The main hotspots detected are on-field emissions, machinery operations, pesticides, and fertilizer production. Irrigation is the main hotspot in blue water scarcity. As for the models tested to estimate nitrogen emissions, significant differences were detected in marine eutrophication between LEACHN and WFLDB, regardless of the functional unit, and in terrestrial acidification, terrestrial eutrophication, and aquatic acidification per ha between LEACHN and PEF. Significant reductions in the results were observed by regionalizing the environmental impacts caused by the on-field emissions. Conclusions The development of site-specific inventories and impact assessment methods with spatial resolution is encouraged, although more research is needed to draw general conclusions about the convenience of mechanistic models to estimate nitrogen emissions in Uruguayan citriculture. The high variation coefficients obtained reaffirm the importance of considering temporal variability. Moreover, the relevance of considering different functional units is highlighted since different influencing variables are observed throughout the seasons depending on the functional unit used.