Consolidating the current knowledge on urban agriculture in productive urban food systems: Learnings, gaps and outlook

Urban agriculture is of increasing interest for tackling a range of environmental and social issues of the current food systems. However, many questions remain unanswered regarding upscaling, the balancing of its multipurpose nature, and how it should be embedded into the broader urban system. This review looks at a breadth of novel insights that are indicative for sensible future development, including new possibilities for nutrient circularity, opportunities for increased sustainability and open questions regarding logistics and economics and development pathways. A thorough assessment of the existing self-sufficiency studies is provided to advance the debate on expected productivity, which is highly dependent on the intended outcomes and the choice of practices employed. Addressing resource circularity, decentralized anaerobic digestion and vermicomposting are presented as methods of utilizing organic waste in urban agriculture, in particular food and garden waste. Furthermore, critical aspects of sustainability are synthesized and promising developments, such as the co-location of micro-scale anaerobic digestion and greenhouses, are evaluated and research gaps regarding life cycle assessments and technical understanding identified. The review also identifies three aspects of urban agriculture upscaling that have not been well studied, namely logistics, economic performance and business models, and institutional and civil development. Finally, the realization of the transformative potential of urban agriculture based on industrial ecology and inclusive co-design is discussed. (C) 2018 Elsevier Ltd. All rights reserved.