title: Development of an LCA-based approach for a regional assessment of the environmental impacts of nitrogen in crop production systems
Creators: name: Wowra, Karoline
Publisher: name: UNSPECIFIED
Year: 2023

description: Agricultural systems are dependent on nitrogen (N) inputs to achieve food security and, at the same time, put high pressure on environmental systems. Accordingly, global limits for N-cycles are already exceeded. However, the release of N compounds from agricultural cropping systems mainly impacts the regional level, for instance, by eutrophication or acidification of terrestrial systems. Therefore, avoiding the exceedance of regional boundaries is essential. Likewise, when assessing environmental impacts on agricultural cropping systems with Life Cycle Assessment (LCA), integration of regional N thresholds and, thus, regionalization plays a crucial role. This thesis aims to provide an LCA-based approach to comprehensively assess N on a regional level by integrating N thresholds as reference values and regionalization in LCA. This thesis is a cumulative dissertation consisting of three peer-reviewed publications. In the first publication, a comprehensive review following the LCA framework is presented by analyzing literature on regionalization approaches applied to agricultural cropping systems compared with general requirements of LCA and the scientific background of the N-cycle. Key factors are derived, formulating the basis for a targeted N assessment in LCA. The second publication presents the development of an approach for integrating regional N resilience as distance-to-target value in LCA. Therefore, regional carrying capacity based normalization references are derived for two N-related impact categories: terrestrial acidification and eutrophication. Additionally, regional background interventions comprising N-related emissions of non-crop production sectors are taken into account. Regional environmental interventions of cropping systems applying different yield scenarios are assessed for two regions. The newly developed approach is further developed within the third publication and applied to a case study including five NUTS-3 regions in Germany. The influence on regional N resilience is evaluated by assessing environmental interventions for four N management scenarios based on policy measures of the German Fertilizer Ordinance. The case study demonstrates that environmental interventions and exceedance of N resilience are lowest in N scenarios applying catch crops for both impact categories assessed. Furthermore, regional differences in the exceedance of N resilience were observed. Overall the analyses done within this thesis revealed that considering absolute sustainability references as regional N resilience in LCA is a valuable tool for agricultural decision-makers. This supports LCA practitioners by providing normalization references directly applicable for LCA and N-assessment of cropping systems. Additionally, it helps regional stakeholders to provide the possibility to evaluate and decide on the best options for N reduction strategies on the regional level and draw attention to vulnerable regions threatening N resilience. Finally, challenges, future research needs, and opportunities for application of the approach are outlined.