Katrin Kuka, Judith Schick, Elke Bloem and Sylvia Kratz: Circular economy research in the Baltic Sea Region

Almost two decades ago, in 2007, the Baltic Rim countries came together to set up the Baltic Sea Action Plan, aiming to improve the strong eutrophication of the Baltic Sea and the poor condition of the surface waters transporting excess nutrients from the Baltic Rim countries into it. Nutrient losses from agriculture were identified as one of the major causes of eutrophication. With the Baltic Sea Action Plan, a series of agricultural research projects was initiated with the major target to systematically develop sustainable nutrient management strategies for the Baltic Sea Region (BSR), to reduce environmental impacts, optimise resource use and move towards a circular bio-economy. From the start, Germany, represented by its Federal Research Centre for Cultivated Plants, was part of this process.

EcoRegion (2009-2012) was the first large scale research initiative emphasising the need for circular nutrient management in the BSR. The main objective of EcoRegion was to support the realisation of sustainable development practices in the BSR. To do so, different Best Management Practices from different sectors were collected and major obstacles for a sustainable development identified. With view to agriculture, focus was placed on collecting good agricultural practices minimising negative environmental impacts of food and feed production. Since immoderate manure applications were identified as major reasons for nutrients loss (especially of nitrogen [N] and phosphorus [P]) from agro-ecosystems into water bodies, causing the regular eutrophication of the Baltic Sea, practices aiming to reduce nutrient loss were of major interest. Among the strategies were improved manure handling techniques, the establishment of buffer zones and constructed wetlands to capture excess nutrients before they reach waterways, and optimised practices for balanced fertilisation. Based on these findings, policy recommendations to increase the sustainability of agricultural activities were formulated. EcoRegion brought together scientists, policy makers and farmers to discuss sustainable agricultural development. This multi stakeholder collaboration resulted in networks that would later facilitate the implementation of targeted nutrient reduction strategies across the region. EcoRegion was crucial in highlighting the urgent need for changes in agricultural practices, particularly in relation to manure management.

Baltic Manure (2010-2013) marked a paradigm shift in the perception of manure, transforming it from an environmental problem to a valuable resource for both nutrient recycling and bioenergy production. Until then, manure was often simply disposed of on agricultural land, leading to poor management practices resulting in nutrient loss, excessive emissions and pollution. Baltic Manure demonstrated the economic value of manure by exploring its potential for nutrient recovery and use in bioenergy production. A key aspect was the identification and evaluation of manure treatment technologies, including mechanical separation, biogas production and phosphorus extraction methods. These technologies were tested for their efficiency, environmental impact and economic feasibility. The project also developed business models for manure-based bioenergy and fertiliser production, demonstrating the potential for profitable nutrient recovery solutions. In addition, this project aimed to provide an overview of the P status in agricultural soils of sensitive areas in the BSR and to determine the risk of P loss to water bodies from these areas. To this end, methodological research was performed, comparing and inter-calibrating different soil P tests applied in the Baltic Rim countries to assess plant available P as well as P loss potential. By establishing the Baltic Forum for Innovative Manure Management Technologies, transnational knowledge exchange and collaboration between researchers, industry stakeholders and policy makers was facilitated, promoting the integration of recovered nutrients into the agricultural economy.

The focus of BONUS PROMISE (2014-2017) was on the recovery of P from organic waste streams. With global concerns about finite phosphate rock reserves, there was an increasing need to reduce dependence on mined phosphate fertilisers. The project aimed to evaluate, refine and improve P extraction technologies from both urban and agricultural waste sources, such as digestate, sewage sludge and livestock manure, and to ensure that the recycled products were safe for agricultural use. The main focus was on potential contaminants in recycled fertilisers. As organic waste streams can contain residues of antibiotics, pathogens and heavy metals, extensive research was conducted to determine how different processing methods affect their removal or persistence. The project investigated how these risk factors vary between different waste sources and what measures could be taken to minimise the risk of contamination when recycled fertiliser is used in agriculture. An important outcome was that the digestion process has only little potential to reduce organic and inorganic contamination. With respect to pathogenic microorganisms, a stricter control of process parameters in biogas plants was identified as crucial. It was also shown that thermo-chemical treatment can significantly reduce both inorganic and organic contaminants, and destroy pathogenic microorganisms - however most of the organic matter content will also be lost. Based on these findings, regional nutrient recovery and best management strategies that considered site-specific conditions were proposed.

As efforts to improve nutrient recycling progressed, it became clear that one of the major challenges in manure management was the lack of standardised methods for assessing the nutrient content of manure. Without reliable and comparable data on manure composition, farmers struggled to optimise fertilisation strategies, leading to inefficiencies in nutrient use, potential over- or under-application of fertiliser and increased environmental risks from nutrient runoff. Likewise, policy makers and extension services faced difficulties in developing coherent nutrient management regulations, as inconsistencies in manure data between regions hindered the formulation of effective policies. Manure Standards (2017-2019) addressed these challenges by providing a harmonised framework for manure sampling, nutrient analysis and data interpretation across the BSR. The core objective was to enable more efficient agricultural use of manure by improving the accuracy of nutrient content estimation and integrating this knowledge into farm-level decision making and regulatory frameworks. A key achievement was the development of standardised protocols for the analysis of N and P in manure that allow for reliable and comparable nutrient assessments across all Baltic Rim Countries. In addition, calculation tools were developed to help farmers and extension services to better estimate the nutrient value of manure based on standardised reference data. By integrating standardised manure composition data into national and EU-wide nutrient management plans, policy makers were better equipped to develop consistent regulations that control nutrient application rates, helping to prevent over-fertilisation and water pollution while ensuring adequate nutrient supply to crops.

Manure Standards was a milestone in improving the efficiency of manure use. Still, there was an urgent need to translate its findings into practical policy frameworks and management strategies that could be implemented at the farm, regional, and national levels. The SuMaNu platform (2019-2021) was designed to bridge this gap by integrating scientific research into governance structures, ensuring that sustainable manure and nutrient management is effectively regulated and incentivised. Building on the results from several previous projects, including Baltic Slurry Acidification (investigating techniques to reduce ammonia emissions from manure), Manure Standards, GreenAgri (promoting environmentally sound organic manure management) and BONUS PROMISE, SuMaNu consolidated existing knowledge into coherent recommendations for improved nutrient management across the BSR. The project provided guidance on how to include manure-based fertilisers in agricultural nutrient management plans in line with existing EU and HELCOM regulations. Technical guidelines on manure storage, processing and application were developed to help farmers and policy makers adopt best practices to optimise N and P use efficiency and reduce nutrient loss. These guidelines emphasised the importance of proper manure treatment technologies, such as anaerobic digestion, composting and solid-liquid separation, which help preserve nutrient value while reducing greenhouse gas emissions and water pollution. SuMaNu actively promoted regional nutrient redistribution strategies. It was proposed to rebalance nutrient distribution by advancing the transport of surplus manure from livestock- intensive areas, processed into high quality, transportable recycled fertiliser, into growing regions suffering from nutrient deficiencies due to a lack of organic fertiliser. Thus, SuMaNu was instrumental in establishing the policy and regulatory framework needed to implement sustainable manure management practices at transnational as well as national and regional level.

LEX4BIO (2019-2024) was launched to explore how bio-based fertilisers (BBFs) could replace synthetic fertilisers in modern agriculture. The project aimed to reduce Europe's dependence on mineral N and P fertilisers by optimising the use of recycled nutrients from organic sources. One of the key achievements was the mapping of regional nutrient surpluses and deficiencies across Europe. Extensive data was collected on nutrient stocks, flows and imbalances, helping to identify opportunities for more efficient nutrient redistribution. The results indicated that, while synthesised N is still needed in the future for adequate crop supply, BBFs could most likely cover a large portion of the actual P demand, since many European agricultural soils can contribute large amounts of legacy P to satisfy plant needs. LEX4BIO also carried out life cycle assessments for different BBF production technologies, including composting, anaerobic digestion, struvite precipitation and thermochemical treatments, analysing their nutrient recovery efficiency, economic feasibility and environmental impact. A major focus was on assessing the fertilising potential of a large number of marketed BBFs in growth trials under different climatic and soil conditions. The results demonstrated that BBFs can be as effective as synthetic alternatives in supplying N and P to arable crops. Products containing organic carbon may also provide long-term benefits for soil quality. The analyses included potential contamination with organics and inorganics as well as pathogens. It could be demonstrated that the investigated BBFs kept all applicable EU benchmarks or threshold limits, indicating that these products do not pose a risk to human, animal or plant health, to safety or the environment. Based on the results, socioeconomic and political recommendations were provided for farmers, policy makers and industry stakeholders on how to optimise the use of BBFs, ensuring that recycled nutrients are used efficiently while minimising environmental risks.

LEX4BIO was instrumental in providing the scientific basis for the integration of BBFs into European agriculture and thereby helped to lay the foundations for the next phase: CiNURGi (2023–2026) puts these findings into practice by testing different recycled nutrient fertilisers (RNFs) in vegetation trials together with industrial partners. In these trials, products already available on the market are investigated for their practical applicability in sustainable agriculture, with a focus on soil health, nutrient efficiency and environmental impact. The results provide valuable insights into how well these products contribute to closing nutrient cycles and reducing reliance on conventional mineral fertilizers. At the same time, CiNURGi actively supports the development and refinement of new, innovative RNFs by providing targeted financial support to help bring them to market. By promoting technological advances and scaling up promising solutions, the project aims to ensure that these next-generation fertilisers are both economically viable and environmentally sustainable.

Through this dual approach - evaluating existing solutions while fostering innovation - CiNURGi thus continues to contribute to the long-term goals underlying the last two decades of agricultural research in the BSR: closing nutrient loops by recycling nutrient rich waste streams for fertilisation, reducing pollution and promoting a resilient, sustainable agricultural system in the BSR and beyond. Future efforts must focus on enhancing economically viable large-scale implementation of safe recycling technologies, increasing farmer adoption of recycled products, and strengthening regulatory and financial support to fully integrate circular nutrient solutions into sustainable agricultural systems.