Humans have massively altered flows of nitrogen on our planet, leading to both benefits for food production and multiple threats to the environment. There are few places on Earth more affected than South Asia, with levels of nitrogen pollution rapidly increasing. The result is a web of interlinked problems, as nitrogen losses from agriculture and from fossil fuel combustion cause air and water pollution. This damages human health, threatens biodiversity of forests and rivers, and leads to coastal and marine pollution that exacerbates the effects of climate change, such as by predisposing reefs to coral bleaching. Altogether, it is clear that nitrogen pollution is something we should be taking very seriously. The amazing thing is that so few people have heard of the problem. Everyone knows about climate change and carbon footprints, but how many people are aware that nitrogen pollution is just as significant? One reason for this is that scientists and policy makers have traditionally specialised. Different experts have focused on different parts of the nitrogen story, and few have the expertise to see how all the issues fit together. This challenge is taken up by a major new research hub established under the UK Global Challenge Research Fund. The "GCRF South Asian Nitrogen Hub" is a partnership that brings together 32 leading research organisations with project engagement partners from the UK and South Asia. All eight countries of the South Asia Co-operative Environment Programme (SACEP) are included. The hub includes research on how to improve nitrogen management in agriculture, saving money on fertilizers and making better use of manure, urine and natural nitrogen fixation processes. It highlights options for more profitable and cleaner farming for India, Pakistan, Bangladesh, Nepal, Afghanistan, Sri Lanka, Bhutan and the Maldives. At the same time, the hub considers how nitrogen pollution could be turned back to fertilizer, for example by capturing nitrogen oxide gas from factories and converting it into nitrate. The fact that all the SACEP countries are included is really important. It means that lessons can be shared on good experiences as well as on whether there are cultural, economic and environmental differences that prevent better management practices from being adopted. It is also important from the perspective of international diplomacy, and provides an example to demonstrate how working together on a common problem is in everyone's interest. It puts the focus on future cooperation for a healthier planet, rather than on the past. The South Asian case provides for some exciting scientific, social, cultural and economic research challenges. The first is simply to get all the researchers talking together and understanding each other. There are dozens of languages in South Asia, matching the challenge met when different research disciplines come together. This is where developing a shared language around nitrogen can really help. There are lots of nitrogen forms ranging from unreactive atmospheric nitrogen (N2), to the air pollutants ammonia (NH3) and nitrogen dioxide (NO2), to nitrate (NO3-) which contaminates watercourses, and nitrous oxide (N2O) which is a greenhouse gas. The impacts of each of these are being studied to provide a better understanding of how they all fit together. The result is an approach that aims to give a much more coherent picture of the nitrogen cycle in South Asia: What is stopping us from taking action, and what can be done about it. One of the big expectations is that the economic value of nitrogen will help. India alone spends around £6 billion per year subsidising fertilizer supply. It means that South Asian governments are strongly motivated to use nitrogen better. At which point research from the South Asian hub can provide guidance on where they might start.

Humans have massively altered flows of nitrogen on our planet, leading to both benefits for food production and multiple threats to the environment. There are few places on Earth more affected than South Asia, with levels of nitrogen pollution rapidly increasing. The result is a web of interlinked problems, as nitrogen losses from agriculture and from fossil fuel combustion cause air and water pollution. This damages human health, threatens biodiversity of forests and rivers, and leads to coastal and marine pollution that exacerbates the effects of climate change, such as by predisposing reefs to coral bleaching. Altogether, it is clear that nitrogen pollution is something we should be taking very seriously. The amazing thing is that so few people have heard of the problem. Everyone knows about climate change and carbon footprints, but how many people are aware that nitrogen pollution is just as significant? One reason for this is that scientists and policy makers have traditionally specialised. Different experts have focused on different parts of the nitrogen story, and few have the expertise to see how all the issues fit together. This challenge is taken up by a major new research hub established under the UK Global Challenge Research Fund. The "GCRF South Asian Nitrogen Hub" is a partnership that brings together 32 leading research organisations with project engagement partners from the UK and South Asia. All eight countries of the South Asia Co-operative Environment Programme (SACEP) are included. The hub includes research on how to improve nitrogen management in agriculture, saving money on fertilizers and making better use of manure, urine and natural nitrogen fixation processes. It highlights options for more profitable and cleaner farming for India, Pakistan, Bangladesh, Nepal, Afghanistan, Sri Lanka, Bhutan and the Maldives. At the same time, the hub considers how nitrogen pollution could be turned back to fertilizer, for example by capturing nitrogen oxide gas from factories and converting it into nitrate. The fact that all the SACEP countries are included is really important. It means that lessons can be shared on good experiences as well as on whether there are cultural, economic and environmental differences that prevent better management practices from being adopted. It is also important from the perspective of international diplomacy, and provides an example to demonstrate how working together on a common problem is in everyone's interest. It puts the focus on future cooperation for a healthier planet, rather than on the past. The South Asian case provides for some exciting scientific, social, cultural and economic research challenges. The first is simply to get all the researchers talking together and understanding each other. There are dozens of languages in South Asia, matching the challenge met when different research disciplines come together. This is where developing a shared language around nitrogen can really help. There are lots of nitrogen forms ranging from unreactive atmospheric nitrogen (N2), to the air pollutants ammonia (NH3) and nitrogen dioxide (NO2), to nitrate (NO3-) which contaminates watercourses, and nitrous oxide (N2O) which is a greenhouse gas. The impacts of each of these are being studied to provide a better understanding of how they all fit together. The result is an approach that aims to give a much more coherent picture of the nitrogen cycle in South Asia: What is stopping us from taking action, and what can be done about it. One of the big expectations is that the economic value of nitrogen will help. India alone spends around £6 billion per year subsidising fertilizer supply. It means that South Asian governments are strongly motivated to use nitrogen better. At which point research from the South Asian hub can provide guidance on where they might start.

The agri-food system, producing 23% of UK emissions, must play a key role in the UK's transition to net zero by 2050, and through leadership in innovation can support change globally. Our Network+ will build on existing and new partnerships across research and stakeholder communities to develop a shared agenda, robust research plans, and scope out future research and innovation. The Network will design and deliver high-reward feasibility projects to help catalyse rapid system transformation to ensure the agri-food system is sustainable and supports the UK's net zero goal, while enhancing biodiversity, maintaining ecosystem services, fostering livelihoods and supporting healthy consumption, and minimising the offshoring of environmental impacts overseas through trade. The radical scale of the net zero challenge requires an equally bold and ambitious approach to research and innovation, not least because of the agri-food and land system's unique potential as a carbon sink. Our title, Plausible Pathways, Practical and Open Science, recognises the agri-food system as a contested area in which a range of pathways are plausible. Success requires that new relationships between natural and social science, stakeholders including industry, government and citizens, be forged in which distributed expertise is actively harnessed to support sectoral transformation. We will use our breadth of expertise from basic research to application, policy and engagement to co-produce a trusted, well-evidenced, and practical set of routes, robust to changing future market, policy and social drivers, to evolve the agri-food system towards net zero and sustainability. Marshalling our many existing stakeholder links, we will review and evaluate current options and use Network funding to catalyse new partnerships through retreats, crucibles, workshops, online digital networking and scoping studies to develop system approaches to transformation, reframe the research agenda and undertake novel research projects. We will co-design productive and creative spaces that enable the research community to engage with a wide range of stakeholders and thought leaders through the following framework: 7 Co-Is who govern the Network but are not themselves eligible for funding; 9 Year-1 Champions (with new appointments after Year 1) dynamically forging new connections across research communities; 11 Advisory Board members tasked with challenging business-as-usual thinking; and regular liaison with other stakeholders.