Towards Sustainable Nitrogen Use Connecting Human Society and Nature

Progress and Results (2024 Year)

Research purpose and content

1) Objectives and background

Sustai-N-able (SusN) Project targets the nitrogen (N) issue that is a tradeoff between the benefits of N use as fertilizers, industrial materials, and energy sources and the threats of N pollution from local to global scales (9. Fig. 1). The purposes of SusN are to create a universal and globally applicable methods for assessing the N issue, future scenarios, and inter- and trans-disciplinary knowledge to address the N issue focusing mainly on Japan, but also in cooperation with international activities to resolve the N issue for 2050 with food equity and good health of humanity and nature, particularly supporting the international N management initiated by the United Nations Environment Programme (UNEP). SusN tries to achieve the following three breakthroughs during 5-year period: (1) developing a framework to visualize the benefits of N use and the threats of N pollution based on scientific knowledge of the driver–pressure–state–impact–response (DPSIR) of the N issue (N-DPSIR), (2) promoting recognition of the N issue still not well known among various stakeholders (N Recognition), and (3) designing sustainable N use in the future (Future N Design).

N pollution causes various impacts such as climate change, stratospheric ozone depletion, air pollution, water pollution, eutrophication, and acidification. The annual damage cost due to N pollution in 2000s in the world was estimated to be 340–3400 billion USD (UNEP, 2019a). The amount of anthropogenic creation of reactive N (Nr, N compounds other than inert and harmless dinitrogen [N2]) now exceeds the natural creation by biological N fixation (Fowler et al., 2013). However, the N use efficiency (NUE) of human activities is low, ca. 20% in the world (Sutton et al., 2013). A large amount of N waste is eventually generated, part of which is lost to the environment as Nr then causes the N pollution. It has been assessed repeatedly that the human alternation of the global N cycling has already transgressed the planetary boundaries (Rockstörm et al., 2009; Steffen et al., 2015; Richardson et al., 2023). The world-mean NUE of crop production is ca. 50% and that of livestock production ranges from 5% to 20% (Lassaletta et al., 2014; Bouwman et al., 2013). Preference for animal products, therefore, lowers the food system NUE, and food loss wastes all the N input to produce the lost food. Economic disparity of fertilizer availability results in regions with too much and too little N in the world (Schulte-Uebbing et al., 2022). Places of production and consumption often cross borders, causing that consuming countries contribute to the N pollution in producing countries (Oita et al., 2016). Global N waste has been increasing since 1961, approximately four times in 2005 and will be six times in 2050 compared to that in 1961 (Sutton et al., 2021). Agricultural N input in 2050 will increase to support future food demand that intensifies the surplus N in croplands (Mogollón et al., 2018). A new N use as fuel ammonia (NH3) is being created (Nishina, 2022). In addition to watching future progress, our N use should shift to a more sustainable one to mitigate the threats of N pollution.

Based on the estimation by Hayashi et al. (2021), the annual N waste in Japan from 2000 to 2015 was ca. 6 Tg N yr–1, and its per capita value was approximately double of the world mean. More than 80% of the N waste in Japan originated from the imported commodities. Therefore, limited recycling opportunities are available within the nation, and the exporting countries suffer N pollution during the production of exports. N flow with fish products is also important in Japan because that accounts for ca. 20% of the food N supply. Although the NUE of fish products can be hundreds of percent owing to natural catch, the sustainability of fishery resources can be violated. The Nr lost to the environment has showed a decreasing trend in Japan, where the decrease in nitrogen oxides (NOX) from transportation sector was remarkable. Meanwhile, Japan focuses on NH3 fuel in terms of decarbonization because combusted NH3 does not create carbon dioxide. The Ministry of Economy, Trade and Industry (METI) announced a plan in September 2021 that 25 Tg N yr–1 of NH3, corresponding to 18% of the world NH3 production in 2015, will be supplied for fuels in Japan in 2050 (METI, 2021). The NH3 supply will rely on imports due to cost efficiency. There are concerns of economic competition among N uses and of N pollution due to NOX emissions with NH3 combustion and NH3 leakage. The future N use in Japan is uncertain and its change will spread to the world via international trade. It is expected that policy, technology, and behavior changes for sustainable N use in Japan will contribute to solving the world’s N issue.

The International Nitrogen Initiative (INI) is an expert group officially launched in 2003. INI tackles the N issue, plans international projects, supports international organizations, and hosts international N conferences on a 3-year basis (INI, 2024). PL Hayashi was appointed as the director of INI East Asia Centre and a member of INI Steering Committee in November 2022. He is working to connect experts in East and Southeast Asia, link national and international activities, and prepare for the 10th International N Conference (N2026), scheduled for November 2026 in Kyoto. UNEP and INI worked on the International Nitrogen Management System (INMS) project (October 2017–June 2023) to apply scientific knowledge to international policies (INMS, 2024a). PL and several SusN members have contributed to INMS which has set a goal of halving global N waste in line with the UN Sustainable Development Goals (SDGs) and will release the International Nitrogen Assessment (INA) in fall 2025. PL is contributing to INA as an editor and author, and several SusN members as authors. SusN can be considered a spin-off of INMS (INMS, 2024b). The United Nations Environment Assembly (UNEA) is held on a 2-year basis and its fourth and fifth sessions adopted the Resolution on Sustainable Nitrogen Management (UNEP, 2019b; 2022). Following the first resolution, UNEP established the Working Group on Nitrogen (WGN) in 2020 to discuss and form the framework of international N management (WGN, 2024). Japan has also been part of the WGN since 2022, with the Ministry of the Environment (MoE) as the national focal point and the Ministry of Agriculture, Forestry and Fisheries (MAFF). PL and SusN member Nishina have been helping both ministries as experts since the 4th WGN. Although a renewed motion was not passed at the 6th UNEA in 2024, a response for the 7th UNEA scheduled for December 2025 is being discussed at the WGN meetings. In early 2024, RIHN joined the UNEP Global Partnership on Nutrient Management (GPNM), a multi-stakeholder group established in 2009 for sustainable nutrient use (GPNM, 2024) in January 2024 with PL as the contact person. Then, PL was appointed as a member of the GPNM Steering Committee in June 2024 for three years upon a recommendation of MoE.

Research on the N issue has made progress on individual topics, e.g., elucidation and numerical modeling of environmental N cycling processes, environmental monitoring, impact assessment of each pollution, N footprint development as an indicator, agri-environmental policy analysis, and technology development for industrial applications. However, many interdisciplinary themes to address the N issue remain. Examples include responses and impacts of natural ecosystems to Nr loading, precise quantification of N flows in human society with pathways to the environment and their future scenarios, material and economic effects of policy, technology, and behavior change on the N issue, and the visualization of causal relationships between N use and N pollution to develop a framework to support decision-making. Furthermore, a transdisciplinary approach with various stakeholders to co-create sustainable N use is essential. This is because N is deeply connected to all human activities through the production and consumption of food, goods, and energy. Future Design (FD), a method of creating ideas as imaginary future persons, is expected to be used for co-creating ideas to address the N issue, for which SusN has been working with the RIHN FD Project (PL: Nakagawa).

2)How does the research contribute to the solution of the global environmental problems?

SusN aims to deepen research in each field on the N issue and to make the following three breakthroughs: (1) N-DPSIR, (2) N Recognition, and (3) Future N Design. (1) provides a tool for quantitative evaluation (e.g., cost-benefit analysis [CBA]) and visualization of how N use and N pollution are changed by policy, technology, and behavior change. (2) compiles up-to-date interdisciplinary knowledge (e.g., various specialized books), transdisciplinary knowledge (e.g., narratives on the N issue), and approaches to each stakeholder. (3) practices FD with various domestic and international stakeholders and gains experience working with international N management by UNEP. The outcome of SusN is to provide quantitative information on the effects of various measures and behavior changes based on the causal relationship between N use and N pollution, to promote diverse stakeholders to make the N issue their own through inter- and trans-disciplinary knowledge of the N issue, and then to generate ideas of the sustainable N use for future generation. As a result, we expect that awareness of the N issue will increase both domestically and internationally, existing and new efforts toward sustainable N use will be strengthened, and breakthroughs will be made toward resolving the N issue.

3) Methodology, structure and schedule

There are many unknowns in the N issue embracing the whole of human society and nature. Thus, the first pillar of our research approach is to accumulate scientific knowledge covering the material aspects of nature and human activities, as well as the economic aspects of human activities, and to promote our own interdisciplinary research (e.g., field research, laboratory experiments, numerical analysis, questionnaire surveys, data development, and scenario building). To take action to address the N issue, a mechanism is needed to support policy making, to spread awareness of the N issue among different stakeholders, and to generate ideas to enable sustainable N use for future generations. Therefore, the second pillar will be transdisciplinary research that integrates existing and cutting-edge interdisciplinary knowledge and co-creates and implements breakthroughs with other stakeholders. The third pillar is to create positive synergies through close collaboration with N-related programs and projects in Japan and abroad, as there are limits to what SusN can accomplish on its own. Such collaboration will generate many spin-offs and increase the likelihood that a group of projects contributing to sustainable N use will continue after SusN ends.

SusN consists of three interdisciplinary research units (RUs): Natural Cycling Unit responsible for elucidating the unknowns of environmental N dynamics and providing information and data on the natural science aspects of N for analysis by other units, Human Society Unit responsible for calculating N flows associated with the production and consumption of food, goods, and energy, and the emissions of each N species to the environment and developing future scenarios for N use, and Economic Evaluation Unit responsible for measuring the social costs associated with human activities such as food production and consumption and clarifying behavioral changes and nudge effects related to N. SusN also has one transdisciplinary research unit; Future Design Unit to achieve three breakthroughs in collaboration with the other three units. In addition to establishing common analysis sites, the unit works on inter- and trans-disciplinary research from both bottom-up and top-down perspectives, linking local, national, regional, and global scales (9. Fig. 2).

The research roadmap is shown in section 8. The common research sites are Tokyo Bay area and Lake Biwa, etc., and each unit may establish its own sites (e.g., Yosano Town and Miyakojima Island for Future Design Unit). The four units work together to elucidate the actual state of the natural and social N cycle at each site and the DPSIR linkage (EEA, 1999; EEA, 2005; 9. Fig. 3), to elucidate the differences and similarities in the behavior of local stakeholders (e.g., producers and consumers) in each site with respect to the N issue, and conduct transdisciplinary research to spread awareness of the N issue and co-design future N use.

4)Expected results

The following are expected: significant enhancement of interdisciplinary knowledge, (e.g., spatio-temporal relationship between water quality and N deposition in mountain streamwater nationwide, N flows in human society and Nr emissions to the environment, social costs of N pollution control measures, etc.), collaborative research results in natural and social sciences (e.g., social experiments supported by natural sciences, N footprint and other indicators for economic evaluation and behavior change, an N-DPSIR visualization tool, etc.), various narratives based on inter- and trans-disciplinary knowledge (e.g. brochures and videos on the N issue [already produced], awareness of the N issue through various outreach activities, specialized books, Japanese Nitrogen Assessment [JaNA] as the final product, etc.), and ideas contributing to sustainable N use derived from FD practices with domestic and international stakeholders. Important achievements include contributions to N management by UNEP and that in Japan, publication of INA in mid-FR3 (PL is an editor), and hosting the 10th International N Conference in Kyoto in mid-FR4 (9. Fig. 4).

5)Project organization and membership

SusN consists of three RUs in charge of interdisciplinary research (Natural Cycling, Human Society, and Economic Evaluation) and one RU in charge of transdisciplinary research (Future Design). The three interdisciplinary RUs strive to deepen research in their respective fields of study, while also conducting collaborative research at the common research sites to accumulate cross-disciplinary knowledge on the N issue. Future Design Unit collaborates with the other RUs to co-create inter- and trans-disciplinary knowledge with other stakeholders. Future Design Unit sets up several missions, e.g., activities on N recognition, forming respective teams from interested members from all RUs. Each unit has a unit leader. Sub-unit leaders may be appointed by decision of the unit leader. Since Future Design Unit is responsible for the integrated task of co-creating transdisciplinary knowledge, PL also takes on the role of leader of this unit. The composition of leaders and members (as of 10 January 2025) is shown in Fig. 5 in Section 9.

Challenges and achievements for this year

1)  Project overall progress

- Results including methodological development and project organization formed

To create actions to address the N issue, support for decision-making such as policies, awareness rising of the N issue, and a mechanism to generate free ideas to realize sustainable N use for future generations are required. They will be achieved by the three SusN breakthroughs, (1) N-DPSIR, (2) N Recognition, and (3) Future N Design. While the Natural Cycling, Human Society, and Economic Evaluation Units conduct interdisciplinary research, several missions are set that would lead to transdisciplinary research by the Future Design Unit to achieved the three breakthroughs, and a team is formed for each mission with participants from all units, e.g., cost-benefit analysis (CBA), analysis in the Tokyo Bay area, and FD practices with various stakeholders. After having selected Tokyo Bay, Lake Biwa, Matsushima Bay, and Lake Kasumigaura as common study sites, activities in FR2 are converging on Tokyo Bay and Lake Biwa as our main targets. Meanwhile, activities in Miyakojima Island and Yosano Town are gaining momentum as local stakeholder collaborations, and the area covering Minami Aso Village, Kumamoto City, and Minamata City is next candidate for collaborations. For the Seto Inland Sea, where oligotrophication is a problem, we expect that specific collaboration will begin as municipal-scale activities associated with the “Japan’s National Action Plan on Sustainable Nitrogen Management” (MoE, 2024) in the future. SusN has collaborated with other programs and projects such as JST COI-NEXT Gastronomy Geopolitics (PL: Matsubae, Human Society Unit leader), Environment Research and Technology Development Fund JpNwst (PL: Nishina, Natural Cycling Unit member), NEDO Moonshot N Cycling (PL: Kawamoto, AIST), life cycle impact assessment (LCIA) LIME (Itsubo, Waseda University), INI, and UNEP as well as activities in RIHN. Our highest priority is to foster human connections among diverse inter- and trans-disciplinary fields. The four SusN RUs have been strengthened with the participation of leading researchers in the fields of biogeochemistry, isotopic chemistry, environmental engineering, industrial ecology, agronomy, agricultural economics, environmental economics, life history, and policy studies, as well as experts in unique activities from inter- and trans-disciplinary aspects of agriculture, food culture, cooking, environmental education, and media. SusN has hired RIHN researchers who are expected to be future leaders in research and actions that contribute to addressing the N issue, and research associates to support our various activities.

In FS, SusN published Japanese N budgets (Hayashi et al., 2021a), held many symposia and workshops, and published “Picture Book of Nitrogen and the Environment” (Hayashi et al., 2021b). In PR, SusN published many reviews, books, and articles on the N issue. In FR1, SusN supported the “Mountain Health Checkup” project (Kyoto University, 2022), a nationwide mountain streamwater survey using a citizen science method, and organized several co-host events. The “Mountain Health Checkup” was a precursor to the survey that SusN originally planned to conduct in FR1 and a follow-up to the 2003 nationwide survey by the RIHN Environmental Valuation Project. Activities with the RIHN FD Project, workshops on interpreting the N issue through systems thinking and creating strategies to spread awareness of the N issue (Loftwork, 2024a; Hayashi et al., 2025a), and activities in Miyakojima Island and Yosano Town were also implemented. From the end of FS to early PR, study meetings on the N issue were held for MAFF, MoE, METI, and Ministry of Land, Infrastructure, Transport and Tourism (MLIT), and after several inquiries from MoE, N management was identified as an administrative need for the FY2023 Environment Research and Technology Development Fund, and the proposed project was adopted as JpNwst (PL: Nishina). JpNwst contributes to the realization of breakthroughs (1) and (3) through the development of Japanese N inventory and the evaluation of reduction potential of N waste. PL ran for INI East Asia Centre Director in PR and was the first Japanese to be selected. In FR2, publication of the results of each RU has progressed, including the nationwide analysis of nitrate concentrations in mountain streamwater (Makino et al., 2024), the footprint of household food residues (Shigetomi et al., 2024), and the economics of sustainable agriculture (Kuriyama, 2024). The JaNA editorial board was formed to prepare its writing guidance and draft contents. The Future Design Unit held strategy-making workshops twice, had various opportunities to give lectures and talks, held a Chronological Table of Meals workshop in Miyakojima, and committed to the Smart Green Village Establishment Council of Yosano Town. The exhibition “Ghost Story and Nitrogen” in collaboration with art and design was a success (Loftwork, 2024b; 2024c). An FD experience package was developed and put into practice at the 22nd International N Workshop (N Workshop, 2024). A symposium with speakers from MoE and MAFF was organized at the 2024 Annual Meeting of Japanese Society of Soil Science and Plant Nutrition (Hayashi et al., 2025b). SusN contributed to the Japan’s Action Plan on Sustainable N Management (MoE, 2024). Internationally, SusN has contributed to the WGN and GPNM and will host the 10th International N Conference in Kyoto in 2026. Detailed information is given in 3. 1).

- Level of achievement in the whole research plan

For breakthrough (1), the input part of CBA is being prepared. PR collected information on CBA cases in the INMS project. The COVID-19 delayed INMS greatly and the release of its final product, INA, was finally postponed to 2025 autumn. Therefore, in FR1, we started the Life Cycle Impact Assessment (LCIA) of sewerage systems as a collaborative study for the CBA, and in FR2, we continued this work and started calculating damage factors of eutrophication.

For breakthrough (2), SusN has produced various narratives for information dissemination, obtained numerous outreach opportunities, developed strategies to spread awareness, and collaborated with art and design. We feel that awareness of the N issue is gradually spreading. Talk events for the public have been organized since IS, and the Nitrogen Cycling Symposium was co-hosted in FS, PR, and FR1, all of which were attended by several hundred people. A picture book of the N issue was published in FS (Hayashi et al., 2021b). SusN brochure was produced in PR (165, 166), and a 2-min video introducing the N issue was produced in FR1 (RIHN & Loftwork, 2024a; 2024b). They are all available in both Japanese and English. The editorial board for the SusN final product, JaNA, was formed in FR2.

For breakthrough (3), direct contribution to N management at domestic and international levels have been realized. In Japan, SusN supported to develop the National Action Plan (MoE, 2024), and internationally, SusN has supported these activities through INI, UNEP WGN, and GPNM. The research aspect of FD was promoted, some of which was published (Nakagawa et al., 2024), and an FD experience package was produced and put into practice at the 22nd International N Workshop (225). Furthermore, we have successfully bid for N2026 in Kyoto (November 2026).

- Outcomes beyond expectation

The election of the PL as the INI East Asia Director and a member of the INI Steering Committee (from November 2022) is the result of a review process, and is self-evaluated as a recognition of the efforts of SusN and PL. The press release of the Japanese N budgets in FS (Hayashi et al., 2021a) generated inquiries from government agencies, and through study meetings and discussions with relevant ministries in PR and FR1, SusN was able to assist MoE in developing its N management and action plan. As a result of the recommendation by MoE, PL was adopted as a member of the GPNM Steering Committee. SusN also provided support to MAFF and successfully organized a symposium in FR2 with speakers from both ministries (80 participants in-person). PL and several SusN members contributed to the committee for the national action plan (MoE, 2024). These were the desired outcomes of SusN, and it is noteworthy that they were realized earlier than expected and to a greater extent than anticipated.

- Challenges encountered and their possible solutions

The impact of COVID-19 has subsided and the speed of research has returned to normal. However, its impact on the delay in activities remained, and the publication of INA was delayed until fall 2025. The CBA framework to be published in INA is information that we want to refer to in the SusN breakthrough (1). While waiting for INA, we have been working with LCA researchers on a pilot LCIA and CBA study. From the second half of FR2, the BRIDGE project led by Itsubo (Waseda University) was launched that will contribute to accelerating our analysis combining CBA and LCIA.

2)  Amendments to research objectives, methodology and organization as applicable

No major changes in research objectives, methods, and organizational structure. However, the research structure has been enhanced as needed, and new collaborative researchers were appointed also in FR2, and two research associates were appointed to prepare for increased administrative work related to JaNA and N2026. Although the sub-leader of SusN retired at the end of PR, no new sub-leader will be appointed.

3)  Results achieved this year

- Research results

As for breakthrough (1) N-DPSIR, the methodology and key results of the Mountain Health Checkup project (Makino et al., 2024); footprint for the climate change aspects of household food residues (Shigetomi et al., 2024); feasibility for fertilizer reduction in Japan (Nishina et al., 2024); and a book of agricultural and environmental economics (Kuriyama, 2024) were published. A paper on creating a strategy for awareness rising of the N issue using systems thinking was accepted (9. Figs. 6 and 7; Hayashi et al., 2025a), a paper on biogas and rice cultivation was submitted (under review), and an English translation of the abovementioned book (Kuriyama, 2024) is in progress. Regarding RU collaborations, the Natural Cycling and Human Society Units are writing a paper on the results of field survey in Matsushima Bay, and the Natural Cycling and Economic Evaluation Units are deepening their discussion of the results of model evaluation in the Tokyo Bay area. As an N CBA study, we have been working on LCIA for sewage systems (Sjyadi et al., 2024) and started to calculate damage factors for eutrophication in collaboration with the BRIDGE LCIA project from the latter half of FR2. SusN has collaborated with the team at the University of Virginia that developed the N footprint concept to make a content in its website “N-Print” that enables calculation of the N footprint of Japanese people with Japanese notation. A provisional content was released in FR2 (N-Print, 2024). A paper published in FR1 (Hayashi & Itsubo, 2023) was cited in the Global Nitrous Oxide Assessment (UNEP & FAO, 2024) published in conjunction with the UNFCCC COP29.

As for breakthrough (2) N Recognition, more than 2,500 pieces of the SusN brochures were distributed, and the two-min video on the N issue was used as an effective material to spread awareness. The events co-hosted by SusN were Sustai-N-able Island Day: Connecting Food and Environment in Miyako, Yosano Town Report Meeting, a symposium on the Sustainable Gastronomy Day, Future Design experience events at the 22nd International N Workshop, Symposium VI of the 2024 Annual Meeting of the Japanese Society of Soil Science and Plant Nutrition, and the exhibition Ghost Story and Nitrogen. The activities in Miyakojima and Yosano Town are expected to be a model for local scale efforts. The Symposium VI (attended by 80 people in person) provided an opportunity to exchange opinions of future N management with speakers from MoE and MAFF. PL feels that the awareness of the N issue is gradually spreading, as some of the listeners appear to have a certain understanding of the N issue. The Ghost Story and Nitrogen exhibition held in Kyoto in collaboration with Loftwork was so well received that it was decided to add an exhibition in Tokyo, and it was decided as top five projects among 250 projects undertaken by the company this year. SusN also participated in the exhibition Anima Rave, a collaboration between RIHN and the 21st Century Museum of Contemporary Art, Kanazawa. The editorial board of JaNA was formed, its chapter structure was worked out, the writing guidance was made in consultation with the Kyoto University Press, and selection of candidates for the lead authors of each chapter is underway.

As for breakthrough (3) Future N Design, two FD experience events were held at the 22nd International N Workshop. N management specified in the Sixth Basic Environment Plan released on 21 May 2024 (MoE) is a result of the online study meeting to MoE in April 2022 (attended by ca. 70 people) and the subsequent multiple inquires for opinions. MoE started to formulate a national action plan for N management in the latter half of FR1, where PL contributed by chairing its committee, and the action plan was launched on 27 September 2024 (MoE, 2024). ML and SusN member Nishina supported UNEP WGN, and PL was selected as a member of the GPNM Steering Committee. In this way, SusN was able to establish a foothold for direct and indirect contributions to N management in Japan and abroad (9. Fig. 8).

As for breakthroughs (2) and (3), Future Design Unit held member workshops twice to develop our strategies to promote awareness of the N issue and strengthen concrete local-scale activities. As a part of all breakthroughs, an appeal to the INI Steering Committee to invite the 10th International N Conference to Kyoto was unanimously adopted. Currently, organization and preparation of the overall structure are underway.

- What part of the project final outcome has been achieved

Breakthrough (1): Interdisciplinary knowledge has been enriched. The entrance part of the CBA was prepared, where the LCIA of sewage systems from FR1 and the calculation of damage factors for eutrophication of terrestrial ecosystems in collaboration with the new LCIA project from the latter half of FR2 will contribute to the CBA. Breakthrough (2): Awareness of the N issue has gradually spread and interest in the N issue has increased. Based on the strategies to raise awareness of the N issue (Hayashi et al., 2025a), efforts were made to strengthen outreach. Successful exhibition in collaboration with art and design was effective to N recognition (Loftwork, 2024c). We began work on the SusN final product, JaNA. Breakthrough (3): Direct contributions to domestic and international N management such as the Japan’s Action Plan on Sustainable N Management (MoE, 2024) and activities of INI, UNEP WGN and GPNM. An FD experience package incorporating the N issue was implemented at the 22nd International N Workshop. We realized the invitation of N2026, which will enable multistakeholder discussions towards sustainable N use for future generations.

4)  Results can be evaluated as having overfulfilled

The most important result was the realization of our involvement in N management both domestically and internationally. The success of the study meetings held in FS to the ministries and the responses to their inquiries resulted in the JpNwst project (FY2023-25) which works with SusN to promote complementary N management research in Japan. At the same time PL served as a link between MAFF and MoE practitioners in PR and fostered an atmosphere of free exchange of ideas between the two ministries. MoE has participated in UNEP WGN since 2022 as the Japan’s focal point (MAFF also joined), and at the request of MoE, PL and SusN member Nishina have been supporting the WGN as experts since mid-FR1. With the faith of MoE, PL was nominated and adopted as a member of the GPNM Steering Committee, strengthening our commitment to international N management. As a result, MoE became the first in the world to launch a national action plan for N management in mid-FR2 (MoE, 2024), and we have contributed to the formulation of this action plan. Furthermore, one of the two co-chairs of GPNM from November 2024 was elected from MoE, which is expected to further strengthen the collaboration with PL as a GPNM Steering Committee member. We will continue to support MoE and other ministries in these activities. PL was also elected as the INI East Asia Center Director and Steering Committee Member for a three-year term starting in November 2022 (up to two terms). The PL's commitment to INI, an expert group of working to address the N issue, will empower SusN’s international activities, especially in the development of international N management and transdisciplinary research with multi-stakeholders in the world. INI has hosted International N Conferences on a three-year basis in principle, the last one 9th Conference was held in New Delhi in February 2024. PL proposed that the 10th Conference be held in Kyoto (2–6 November 2026) and received unanimous approval, and preparations are proceeding diligently.

5)  Points to be evaluated that the goals were not reached

Regarding the breakthrough (1) N-DPSIR, the formulation of a CBA framework has been delayed. The main reason is that the publication of INA (the final product of the INMS project), which contains a global-scale CBA that we want to refer to, has postponed until fall 2025. PL is one of the INA editors and has confirmed that INA is certainly a useful reference. In response to this situation that arose in FR1, LCIA and CBA for sewage systems were started as a pilot study and is continuing in FR2. In the second half of FR2, a new LCIA-related collaborative project, BRIDGE, was initiated, and we expect to accelerate research activities to conduct CBA for the N issue in FR3, including the calculation of damage factors for eutrophication. Although the development of a causal analysis tool is challenging, we will at least serve to summarize the world's research achievements, provide a perspective on research issues, and link them to successors in FR5.

6)  Notable achievements and challenges as to contribution to the RIHN programs

The three goals of the affiliated program, i.e., elucidation of the relationship and linkage between various human activities and nature to reduce dualities and increase synergies, development of communication methods, and transformation of the relationship between human and nature for sustainable future, correspond to SusN breakthroughs (1) N-DPSIR, (2) N Recognition, and (3) Future N Design, respectively. With the release of Japan’s Action Plan on Sustainable Nitrogen Management (MoE, 2024), it is expected that activities to realize both the goals of the affiliated program and the breakthroughs of SusN will become possible in the initiatives of each local government that will be launched in the future.

Future tasks

1) Research plan for next year

The plans of respective RUs in FR3 are described below.

Natural Cycling Unit: 1) Evaluate the impact of sewage treatment plants on river and coastal water quality; 2) Integrate and analyze water quality data from the atmosphere to mountains, rivers, and coasts to visualize the change patter of N dynamics in a nationwide watershed scale using GIS; 3) Use past and present data and machine learning to evaluate the vulnerability to N deposition in forested watersheds nationwide; and 4) Analyze the N cycle in the common study sites and support the analysis of the InVEST model of the Economic Evaluation Unit.

Human Society Unit: 1) Elaborate N footprint analysis (e.g., input-output analysis, N loss due to resource and energy consumption, revision of virtual N factors); 2) Advance scenario analysis of future N use can be used for CBA (e.g., NUE improvement in food production, reuse and recycling of resources, tradeoff between low-carbon technology and the N issue); 3) Collaboration with JST COI-NEXT Gastronomy Geopolitics (Higasimatsushima City, Shima City).

Economic Evaluation Unit: 1) Analyze the effects of information and financial incentives for consumers using household accounting app purchase data for plant-based food; 2) Conduct a choice experiment on environmental conservation using the InVEST model in the Tokyo Bay area in collaboration with Natural Cycling Unit; and 3) Conduct data analysis of a questionnaire survey targeting agricultural producers. 

Future Design Unit: 1) Consider using the INA international CBA, promote CBA and LCIA for sewage systems, and calculate damage factors of eutrophication that can be used for these purposes; 2) Develop an AI app for N footprint calculation in collaboration with Human Society Unit; 3) Conduct outreach through lectures, talks, and other means to spread awareness of the N issue actively; 4) Work with local-scale stakeholders in Miyakojima, Yosano, Minamiaso, and Minamata to co-create ideas for addressing the N issue; 5) Contribute to domestic (MoE and MAFF) and international (UNEP and INI) N management efforts and strengthen networking; 6) Work with all RUs and external experts to write JaNA; and 7) Prepare for the N2026 and support activities being linked (e.g., Osaka Expo, youth initiatives, etc.).

2) Tasks for the next fiscal year onward

PD Taniguchi advised us that a stronger cultural approach is necessary. Although there are member experts in food culture, viewing culture from other angles is also important. To expand our research in FR3 to Minamata, one of the four major pollution areas of Japan in the past, we are establishing connections with key local people there. PL recognizes that efforts are still needed to facilitate free exchanges of ideas and spontaneous project promotion by many members. PL will continue to closely share information and exchange opinions among the core members. PL will encourage members’ activities through each RU leader and individual activities as necessary. PL thinks that the absence of a sub-leader is not a problem; however, it may be necessary to hedge the risk of a situation where PL is unable to lead research.

We would like to request support of the Public Relation Unit in outreach activities as appropriate. Regarding Lake Biwa among the common study sites, we request that RIHN facilitates the use of its research achievements. Since SusN’s contribution to international networking and international N management is beneficial to the international missions of RIHN. Therefore, we would like to request that PL makes efforts to share information with RIHN, and RIHN provides necessary support, e.g., cooperation with activities related to Future Earth. We organize N2026 on 2-6 November 2026 at the Kyoto International Conference Center. We hope that RIHN co-hosts N2026 and organizes a public symposium and an international workshop at N2026. This is the first time that an international N conference is held in Japan, and its co-hosting will be an important achievement for RIHN. JaNA as the final product of SusN will be published as RIHN Book Series both in Japanese and English. Support of RIHN for these productions is also requested.