Optimisation of nutrient budget in agriculture Sustainable agricultural production systems not only deliver nutritious food and other raw materials, they are also key drivers of economic growth in rural areas. Roughly 25% of the annually produced terrestrial agricultural biomass is used by humans, about 70% [[A nutrient budget quantifies the inputs and outputs of nutrients in a system and can be used to understand better how the system soil-water-plant-nutrients works, and provide quantitative environmental and economic indicators for farms, regions and products.]](mostly from grassland, by-products, and inedible crop residues) converted through animals into food and manure, and the remainder goes into biofuel. Unsustainable agricultural systems can cause a variety of adverse environmental effects, such as climate change, loss of biodiversity, and air and water pollution due to poor management of nutrients.When possible, the holistic consideration of plant and animal nutrition within the agricultural production systems could contribute to more sustainability of the food chain by promoting the minimization of nutrients leakage and improved nutritional values of fertilisers, feed and food. This approach could cover the basic nutritional elements (carbon, hydrogen, nitrogen, oxygen), the macro elements (phosphorous, potassium, magnesium, calcium, sulphur) but also the trace elements (zinc, copper, iron, iodine, selenium, manganese). In line with the European Green Deal, the development of a nutrient budgeting approach could focus on the fluxes of carbon (C).However, there are substantial knowledge gaps regarding the measurement and understanding of the impacts of nutrients flow in different farming practices (conventional, agro-ecological and organic systems, specialised and mix farming systems) at various scales, from local to global, and the capacity to model those impacts.Proposals should build on existing and new knowledge, data, models (including in situ calibration measurement), artificial intelligence and tools to:Optimise and harmonise nutrient and water flow models, indicators and data for quantification and assessment to prevent or reduce environmental pollution caused by nutrients, across sectors, for different types of agricultural practices (conventional, organic and agro-ecological agriculture), and scales – farm, local, regional and river basin.Explore and assess safe alternative nutrient sources and pathways (e.g. organic vs inorganic), enhance management and recycling of organic wastes and explore nutrient recovery opportunities (e.g. by using treated sewage sludge or wastewater) as well as nutrient mobilisation through microorganisms;Build upon available results from previous EU projects funded under the Horizon 2020 topic CE-RUR-08-2018-2019-2020: Closing nutrient cycles.Enhance nutrient use efficiency at different levels.Analyse climate change effects of certain nutrient flows, including interactions between nutrient, water and carbon cycles.Develop biological models for nutrients flows remote sensing tools, in agricultural systems: for physical, chemical and biological parameters, using smart sensors and AI technologies.Develop digital platforms to allow precision nutrient management at farm scale and landscape scale. Proposals must implement the 'multi-actor approach’ and ensure adequate involvement of the farming sector and, as relevant, bio-based industry active in rural areas.In this topic the integration of the gender dimension (sex and gender analysis) in research and innovation content is not a mandatory requirement.