Recycled Nitrogen for Regenerative Agriculture: A Review of Agronomic and Environmental Impacts of Circular Nutrient Sources

Abstract

Global agriculture faces the twin challenges of meeting rising food demand while minimizing environmental impacts, necessitating transformative approaches to nutrient management. Recycled nitrogen fertilizers (RNFs), derived from diverse organic and waste sources such as urine, manure, compost, digestate, biosolids, and struvite, offer a groundbreaking pathway to close nutrient loops, reduce reliance on synthetic inputs, and foster regenerative agroecosystems. This comprehensive review synthesizes peer-reviewed studies published over the last two decades, selected based on relevance, study quality, and applicability to agronomic and environmental outcomes. Unlike earlier reviews that focus on individual RNF types, this work provides a novel cross-sectoral synthesis linking agronomic performance, environmental trade-offs, and socio-economic feasibility within the regenerative agriculture framework. Using a structured analytical framework, we critically assess RNF technologies and applications across agronomic efficacy, ecological implications, economic viability, and socio-regulatory landscapes. Despite promising benefits, including enhanced soil health, greenhouse gas mitigation, and alignment with circular economy principles, widespread RNF adoption remains constrained by logistical complexities, variable nutrient quality, regulatory uncertainties, and social acceptance challenges. By integrating multidisciplinary evidence and identifying system-level synergies and bottlenecks, this review advances a unified understanding of how RNFs can be strategically scaled in regenerative agricultural systems. Key knowledge gaps and integrated research and policy strategies are identified to unlock the full potential of RNFs. Embracing recycled nitrogen within tailored, context-sensitive frameworks has the potential to revolutionize sustainable agriculture, delivering resilient food systems, restoring ecosystem services, and advancing global climate goals.