Transitions Toward a Circular Economy in Protected Agriculture Across the Americas: A Bibliometric Analysis of Trends, Approaches, and Research Gaps

The transition toward a circular protected agriculture in the Americas represents a strategic challenge to harmonize productivity, sustainability, and environmental restoration. This study presents a bibliometric analysis of scientific production on the application of circular economy principles to greenhouse, nursery, and protected agriculture systems, based on 34 documents indexed in Scopus between 1994 and 2025, originating from the United States, Canada, Brazil, Argentina, and Colombia. The results show a steady increase over the last decade, driven by the expansion of the bioeconomy, the valorization of agricultural residues, and the pursuit of low-carbon food systems. The leading countries, the United States (47%) and Canada (26%), concentrate their studies on organic waste management, anaerobic digestion, and nutrient recovery, whereas in South America, emerging approaches focus on water reuse, substrate recycling, and energy efficiency in intensive greenhouse horticulture. The keyword co-occurrence analysis (VOSviewer) identifies three main conceptual axes: (i) waste management and soil fertility, (ii) bioeconomy and energy recycling, and (iii) sustainability in protected agriculture. Although the European model of Almería is widely regarded as a global technological reference, research across the Americas is shifting toward regional adaptation through appropriate technologies and ecological transition policies. Future research should prioritize life cycle assessment of materials and resources, the redesign of metabolic flows in greenhouses, the digitalization of circular systems, and multilevel governance that integrates science, policy, and producers. Strengthening inter-American research networks will be essential to consolidate a paradigm of circular protected agriculture that is resource-efficient, low-carbon, and climate-resilient, serving as a cornerstone for food security and environmental sustainability in the region.