Towards enhanced nutrient circularity: Lessons from a multidisciplinary conference

The global agricultural sector faces the dual challenge of ensuring food security while minimizing the environmental repercussions of conventional farming practices. The use of waste-derived materials as fertilizers has gained global attention for improving nutrient circularity in agricultural systems. However, regulatory, environmental, and agronomic barriers still limit widespread adoption. To identify knowledge gaps and research opportunities, a multidisciplinary international conference was held in Lincoln, Nebraska, in September 2024. The event featured 22 expert presentations and drew participants from 12 countries, including researchers, regulators, industry, and farmers. This synthesis summarizes key insights from presentations and stakeholder discussions covering biosolids, struvite, digestate, biochar, and emerging contaminants such as PFAS and antibiotic resistance genes. Presenters shared findings from lab, greenhouse, and field studies, including novel methods for fertilizer stabilization (e.g., mechanochemical urea), life cycle assessment of bio-based fertilizers, and risk analyses involving microbial and chemical hazards. Post-conference survey data and expert panels identified major priorities for future work: establishing fertilizer-grade quality criteria, standardizing contaminant risk assessment, increasing long-term field trials, and developing guidance to support regulatory integration. Farmer and industry input emphasized cost-effectiveness and clarity in policy implementation. Overall, this synthesis demonstrates that circular fertilizers are scientifically viable but require coordinated regulatory and agronomic frameworks to accelerate adoption. A set of interdisciplinary research questions and policy recommendations is proposed to guide future work across scales.