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

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Abstract
Protected agriculture across the Americas ranges from high-technology greenhouses in North America to lower-cost protected systems in Latin America, yet both depend heavily on water, nutrients, energy, and synthetic materials. These technological and regional contrasts create unequal capacities to implement circular production models. This study aimed to characterize the evolution, collaboration patterns, conceptual structure, and research gaps of circular economy applications in protected agriculture across the Americas. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) framework, 144 Scopus-indexed documents published between 1996 and 2025 were analyzed using VOSviewer version 1.6.20, and the Bibliometrix R package version 5.4.1. Performance indicators, co-authorship, keyword co-occurrence, and thematic mapping were examined. The annual growth rate of 12.57% and an international co-authorship rate of 44.03% indicate an expanding and increasingly collaborative field; however, production remained concentrated in the United States, Brazil, and Mexico. The conceptual structure was dominated by hydroponics, aquaponics, nutrient recycling, wastewater management, and water quality, showing that circularity has been operationalized mainly through water and nutrient loops. The thematic structure highlights connections among production technologies, water treatment, and nutrient management. The studies discussed illustrate advances in these areas and identify the need to evaluate resource recovery alongside crop performance, microbiological quality, energy requirements, and environmental impacts. Thus, the regional research agenda should prioritize these thematic gaps while strengthening collaboration with countries that remain weakly represented. These priorities can guide funding and coordinated research toward circular strategies adapted to the technological diversity of protected agriculture in the Americas.

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