The Use of Circular Economy in Horticulture Research: A Bibliometric Analysis

Abstract

This study explores the integration of circular economy (CE) concepts within horticultural research, assessing the reliability and depth of their application in scientific discourse. A bibliometric analysis was conducted on 221 articles published between 2016 and 2024, utilising the PRISMA framework, VOSviewer version 1.6.20, and MAXQDA version 24.6.0 software to analyse keywords, abstracts, and thematic patterns. The findings reveal a growing use of CE-related terminology in horticulture research, particularly post-2019, with increasing emphasis on resource efficiency, waste minimisation, and closed-loop systems. However, a discrepancy was identified between the usage of CE principles in article keywords and their representation in abstracts, indicating an incomplete alignment with CE fundamentals. Despite this progress, the study highlights the need for a more consistent and precise application of CE principles to bridge the gap between theoretical frameworks and practical implementation. This alignment is critical for advancing the sustainability of horticultural practices and ensuring their contribution to broader environmental and economic goals. By fostering a deeper integration of CE concepts, horticulture research can play a pivotal role in addressing global sustainability challenges.

1. Introduction

The growing global demand for natural resources, driven by the consumption patterns of the developed and emerging industrialised economies, threatens the planet. The standard of living in economies will continue to rise and, by 2060, the GDP per capita in the emerging countries is expected to reach the OECD levels [1]. Different studies have projected that the total resource use could more than double by 2050 if these trends continue [2,3]. Therefore, it is urgent to improve the efficiency with which resources are used by maximising their value and avoiding the possibility that the increase in globalised demand for resources leads to a shortage of supply that results in an increase in input costs, as well as the extraction of raw materials from nature at a much faster rate than the nature’s ability to recycle and return them to the environment. This is based on a linear model that assumes abundant reserves of cheap and readily available materials and energy sources as referred to by DGCEP [4].

The concept of a circular economy (CE) first emerged in the literature through three main pillars, known as the 3R principles: reduce, reuse, and recycle [5,6,7,8,9,10]. In this context, the CE model is presented as a key component to steer the world towards sustainability and help achieve the proposed goals. Subsequently, at the United Nations Environment Assembly, new variables were introduced to the CE model, describing it as “one of today’s sustainable economic models in which products and materials are designed to be reduced, reused, recycled or repaired (4R’s). This approach ensures that they remain in the economy for as long as possible, together with the resources from which they are made, while avoiding or minimising the generation of waste, especially hazardous waste, and reducing greenhouse gas emissions”. It should be noted that several systematic analyses have been carried out in order to determine the most appropriate definition, although it is an extremely complicated task due to the fact that numerous meanings of this term have been found, amounting to 114 definitions as highlighted by [11]. Other authors, such as Bressanelli [12], establish a link between the CE and the digital age, analysing the evolution of CE methods and the development of R&D in this context. Their work offers decision-makers a framework that connects digital technologies, product lifecycle stages, circular strategies, practices, and benefits, while also organising and mapping existing studies.

The need for the CE over the current linear model has gained recognition, as the latter harms the environment and depends on non-renewable resources and finite supply chains [13].

According to the United Nations, the agricultural sector occupies 50% of habitable land, contributes 25–30% of greenhouse gases, is responsible for 80% of deforestation and biodiversity loss, and consumes 70% of freshwater while causing over 80% of water pollution. Additionally, 89% of fisheries are overexploited or at capacity [13].

The present study explores the nexus between the CE and horticulture. It is imperative to elucidate that the agricultural sector consumes a greater quantity of natural resources per unit of value than any other sector, with 70% of freshwater withdrawals being allocated to this purpose. Moreover, over 60% of EU soils are confronted with degradation, which has a detrimental influence on food security, ecosystems, and human health. Consequently, the transition to the CE in agriculture is imperative for ensuring sustainability [13,14,15,16]. According to Jaskani and Khan [17], horticulture is the science and art of growing high-value plants, such as fruits, vegetables, ornamental plants, herbs, and medicinal plants, and it plays a key role in the global food value chain. Horticulture, in general, integrates intensive systems of agriculture, and due to that, it has shown the most relevant progress in adopting circular principles. Protected horticulture, such as greenhouse cultivation, can ensure high-quality production and contribute to global food security. It offers significant opportunities for circular production, optimising the use of resources by recycling at various levels, from individual farms to the regional level. The use of greenhouses promotes circularity through high productivity with reduced use of water and agrochemicals per unit of production, a production capacity per hectare of up to 10–15 times higher compared to open-field agriculture, and also its role as a potential tool for water and nutrient recycling [18]. The concept of CE is of great interest to both academics and farmers as it is considered a key criterion when operating sustainable firms. However, it remains a concept that sparks controversy [19,20]. The CE has gained popularity over time, and there are numerous actors, particularly among the stakeholders who adopt it, so its interpretation and implementation can be diffused, fragmenting its conceptualisation [11].

It is worth noting that the concept of CE becomes more diffuse in the field of agriculture. Several works have discussed the specific characteristics of the agricultural sector and the need to adopt CE methodologies in this area. Additionally, emphasis is placed on the need for more appropriate indicators to address the complexities of this sector, as emphasised by Velasco-Muñoz et al. [21]. The use of bibliometric analysis has become an essential tool for evaluating scientific production in various areas of knowledge. This approach makes it possible to identify patterns, trends, and relationships between publications, authors, institutions, and research topics. By applying bibliometric methods, it is possible to measure the impact of specific studies, map scientific collaboration networks, and explore the evolution of concepts over time [22,23]. Several bibliometric studies on the CE have been published recently, offering researchers a novel perspective on the subject. These studies have begun to explore the field from a business administration perspective, in addition to the traditional environmental sciences. Camón and Celma [24] identify key authors, publications, and themes in this area, noting a shift from production aspects to the growing importance of business organisation and its impact on structures.

Dominko et al. [25] conducted a comprehensive study on the CE using bibliometric analysis to explore trends in the CE. The study emphasised the focus on theoretical frameworks and technological solutions while observing a slow transition to practical implementation.

The research gap identified by the authors pertains to the dearth of studies examining the practical implementation of the CE within the domain of horticulture. While numerous studies have explored its theoretical underpinnings, there is a paucity of research that addresses its practical application in this sector. Geissdoerfer et al. [26] conducted a bibliometric analysis with Web of Science data to identify types of relationships between sustainability and the CE. While often used interchangeably, the study highlights that these concepts are poorly differentiated in the literature, limiting their application. By clarifying these distinctions, the work advances conceptual understanding and practical relevance in both public and private sectors. The authors identified obstacles in the interaction between the concepts previously discussed. D’ Amato et al. [27] examined the communication of three global concepts—CE, green economy (GE), and bioeconomy (BE)—and concluded that CE is the most prevalent and consistent concept. Limited links between the concepts were identified, with the CE–BE concept being the most significant, emphasising the efficiency of biological resources. Using these concepts, the thesis highlighted the role and limitations of business discourse in global sustainability efforts. In addition, it is necessary to determine the thematic and contextual areas in which the term “CE” is used in the horticulture sector. Furthermore, there is a lack of clarity regarding the utilisation of the concept by researchers, whether for the purpose of innovation, academic visibility, or securing funding.

The objective of this study is to address this research gap by undertaking an examination of the manner in which CE is employed in the field of horticulture and by identifying the thematic and contextual domains in which it is employed.

A further key question is whether academics are using the concept of CE for the sake of innovation, to increase the readership of their publications, or to enhance success in fundraising, and in which thematic and contextual areas is the term “CE” being used.

This article aims to evaluate whether CE principles are genuinely integrated into research aligned with their fundamental concepts or if the term is being misused to justify conventional approaches in areas such as phytopharmaceuticals and environmental agricultural technologies. While research on environmental and agricultural sustainability undoubtedly supports broader sustainability goals, this study emphasises the importance of using the term “CE” authentically, avoiding its superficial use or its use as a marketing tool. It is essential to clarify why this research is necessary when there are already numerous studies on the CE and horticulture.

Despite the abundance of studies about the CE, research specifically oriented towards the implementation of the CE paradigm within the domain of horticulture is conspicuous by its absence. This study thus seeks to elucidate how research has applied the concept of CE in the particular context of horticulture.

2. Materials and Methods

To achieve the proposed objective, a bibliometric analysis was carried out, focusing on the relationship between the keywords of articles related to horticulture and the CE, their abstracts, and the specific terminology associated with the CE. This analysis aims to uncover patterns, identify gaps, and ensure that the research attributed to the CE adheres to its fundamental principles of resource efficiency, waste minimisation, and the creation of closed-loop systems, reducing the pressure on natural resources and ecosystems. By critically evaluating the discourse around the CE in horticultural research, this study seeks to promote a more precise and meaningful application of the concept in scientific research.

2.1. Bibliographic Search

At the outset, a systematic literature review on the CE and horticulture was conducted using the PRISMA method described by Page et al. [28] (Figure 1). The review focused exclusively on articles published in English in the database. This analysis only found articles from 2016 onward, and there were no data before that. A comprehensive literature search was conducted in two primary research databases (Scopus and Web of Science) in November 2024 using three keywords (horticulture, circular, and circular economy) in the title, abstract, and keywords. It was observed that by removing the keyword “circular,” the same results were obtained. A total of 222 articles were identified in both databases. Subsequently, “open publisher invited review” articles were excluded because they did not fit the research objective, resulting in 221 articles. The Web of Science (WoS) and Scopus databases were used for bibliometric analysis due to their comprehensiveness, data quality, and analytical resources: they include only rigorously evaluated journals, ensuring reliable information; cover various fields of knowledge, making them ideal for interdisciplinary analyses; and allow for the identification of the most productive authors, most cited journals, frequent keywords, and co-authorship and co-citation networks. For a complete bibliometric analysis, it is ideal to use both databases complementarily—WoS for quality and precision, and Scopus for broad coverage and visual analyses.

After examining the abstracts of these articles, all 221 studies were deemed relevant and included in the review.

2.2. Keywords Map

A keywords map is a visual representation of the frequency of co-occurrence between two terms or keywords within a dataset. This co-occurrence can be observed in the titles or abstracts of articles in a bibliographic database. Co-occurrence analysis is a method of identifying and illustrating relationships between terms, highlighting concepts or topics that frequently appear together in a network of nodes and links [29]. This method has been applied across various fields, including artificial intelligence, education, and healthcare [23]. Different software tools allow bibliometric analysis, including CitNetExplorer [30], SciMAT [31], Science of Science (Sci2) Tool [32], VOSviewer [29], and CiteSpace [33], among others. In this case, VOSviewer was used since it facilitates the graphical representation of bibliometric maps and is useful for displaying bibliometric maps of large size that are easy to interpret, as referred to by Aria and Cuccurullo [34]. Bibliographic searches from two databases were exported and imported into the software. Subsequently, a co-occurrence analysis was conducted, defining the minimum number of times a keyword should appear as three. Initially, a threshold of five occurrences was tested, but a threshold of three was chosen as it allowed for better noise filtering, thus achieving greater clarity of the map that allowed for a better interpretation of the results.

This clarity was achieved by improving the visualisation of connectivity. Low-frequency keywords often fail to show meaningful links with other terms, potentially leading to an incomplete understanding of the context. Therefore, this threshold enabled greater customisation of the analysis. In short, this number allowed for greater personalisation of the analysis. Additionally, the words that did not align with the research objective were eliminated, i.e., the terms that were related neither to horticulture nor the CE, such as “review” and “nonhuman,” resulting in the removal of five keywords.

2.3. Abstracts Map

As mentioned in the objective of this work, the aim was to determine whether the keywords are associated with the information contained in the abstracts, since the abstract offers a concise review of the results and can indicate whether it contains the CE or related words and whether there is a relationship with these words [23].

The abstract text-based map was utilised to explore and visualise the relationships, themes, and patterns within the abstracts of academic articles and other papers. A map of the abstracts was created using the VOSviewer version 1.6.20 software, with the bibliographic searches conducted in both databases. A minimum threshold was established, stipulating that a keyword must appear a minimum of three times. Terminology unrelated to the study’s objectives, i.e., terms not associated with horticulture or the CE, such as “Norway” or “case”, was excluded, resulting in the removal of a total of 35 words.

2.4. Quantitative Analysis of the Abstracts and Keywords

To identify the main research trends in the literature on the CE and horticulture, an approach based on the frequency of codes was used. The abstracts and keywords were analysed using the software MAXQDA version 24.6.0. The process began with a thorough reading of the abstracts from the selected publications. Subsequently, textual analysis techniques were applied to identify the occurrence of terms relevant to the CE within the abstracts.

We applied the same methodology to keyword analysis. This was accomplished by employing a predefined dictionary of keywords, which had been developed based on an exhaustive review of the extant literature on the CE [35,36,37,38,39]. In the present work, a total of 24 terms were identified as used in the construction of quantitative research related to the CE. The dictionary served as the foundation for the analysis and was constructed to account for the linguistic diversity inherent in CE research. It included synonyms, variations in verbal forms, and other alternative expressions commonly used in the field.

In order to ensure accuracy and relevance, the analysis adhered to three key criteria. Firstly, whole-word matching was employed, focusing on complete words to prevent partial matches from yielding irrelevant results. Secondly, case sensitivity was considered, with variations in uppercase and lowercase taken into account to capture differences in formatting and emphasis within the abstracts. Thirdly, regular expressions were applied to identify all variations of predefined terms, ensuring flexibility in recognising synonymous or rephrased expressions.

In addition to identifying terms related to the CE, the analysis also focused on terms associated with horticulture, thereby creating a comprehensive framework to explore the intersection of these two domains. By leveraging these systematic approaches, the study ensured a robust and nuanced interpretation of the textual data, capturing the depth and diversity of concepts within the analysed publications. By combining frequency analysis with relational mapping, this approach provides a robust framework for understanding the evolution of research trends, highlighting key areas of focus and emerging opportunities for further investigation.

3. Results

First, the keywords were examined to determine their frequency, relationships, and significance in the literature reviewed. This step provided information on the main themes and research trends as represented in the keyword mapping process. The analysis was then extended to the abstracts of the articles. This deeper exploration allowed for a more comprehensive understanding of the context and focus of the studies, going beyond the superficial representation provided by the keywords. The integration of these two levels of analysis—keywords and abstracts—provided a holistic view of the research landscape, offering valuable insights into the interrelated topics of the CE and horticulture.

3.1. Keywords Map

The relative frequency of use of keywords and the relationships between them in the reviewed publications were analysed in a word map, as shown in Figure 2.

The larger the circle, the more frequently a given word appeared in the keywords of the reviewed articles. The size of the circle is proportionate to the frequency of a given word that appears in the keywords of the reviewed articles (see Figure 2). The figure also highlights the relationships between different keywords, with “CE” and “horticulture” being those with a higher presence. This was to be expected, given that they were part of the bibliographic search terms. The map generated is related to the clusters created by the software (

Table 1. Clusters of the keywords map.

Cluster	Keywords	Cluster	Keywords	Cluster	Keywords
Cluster 1	Agricultural waste	Cluster 2	Agriculture	Cluster 3	Agricultural land
	Anaerobic digestion		Circular economy		Bioenergy
	Animal		Economic aspects		Biomass
	Animals		Greenhouse gas		Environmental impact
	Compost		Horticulture		Environmental protection
	Composting		Pesticides		Recycling
	Fertilizer		Soil		Sustainable development
	Fertilizers		Soil amendment		Wastewater
	Human		Soil fertility		Waste reclamation
	Manure		Soils		Waste treatment
	Nitrogen		Sustainability		Water
	Nutrients		Waste management		Water pollution
	Phosphorus				Water supply

).

Analysing groups and relationships between keywords allows for meaningful interpretations of themes and focus areas in the research landscape. Each group represents a distinct thematic area, with clustering indicating shared concepts or topics of academic interest. The relationships between keywords within a group reveal interdependencies and synergies, providing an integrated perspective on aspects of the CE and horticulture. The prominence of specific keywords within a cluster indicates their importance in driving research trends and identifies emerging areas of focus aligned with sustainability, resource efficiency, and environmental protection. Understanding cluster relationships helps researchers to identify gaps in knowledge and underexplored areas for future research. Clusters not only visualise keyword relationships, but also serve as a framework for guiding further research. The clusters are analysed and interpreted to provide a deeper understanding of their thematic focus and relevance.

First cluster. Focuses on nutrient recycling, where waste is managed in such a way that it is converted into resources, minimising environmental impact and promoting sustainability. It highlights strategies to convert waste into valuable fertilisers, thereby minimising environmental impact and promoting sustainability, aligning with broader goals of reducing the ecological footprint of using chemical fertilisers. In this cluster, animals are critical players, converting vegetable biomass into organic fertilisers. Composting is another way to transform animal effluents and vegetable waste into fertilisers.

Second cluster. Reflects the interconnection between agricultural production and sustainability, with special attention to soil health. It emphasises the importance of practices that minimise environmental impact while promoting efficient resource use, with the CE being a key approach to achieving more sustainable and responsible horticulture. This perspective encourages the adoption of regenerative practices that enhance resilience and efficiency within agricultural systems by promoting resource efficiency, waste reduction, and the regeneration of natural systems. The CE balances environmental conservation and economic viability. It supports the transition to greener horticulture and emphasises the importance of resilience and long-term sustainability in the agricultural sector.

Third cluster. The valorisation of waste is the core of this cluster, reducing its environmental impacts. It emphasises the importance of sustainable management of water and land resources in horticulture, as well as the role of bioenergy, recycling, and the valorisation of agricultural byproducts in the CE as key components. It also highlights the need to protect the environment and minimise the impact of agriculture on ecosystems. The focus is on promoting long-term sustainable development by ensuring that horticultural practices are in line with environmental protection and resource optimisation and emphasising the urgent need to protect natural ecosystems from the negative impacts of agriculture. This includes reducing pollution, preserving biodiversity, and promoting practices that regenerate rather than deplete natural resources. The overall aim is to enable sustainable development that meets today’s needs while safeguarding the environment for future generations.

3.2. Abstracts Map

The first step was to analyse the relative frequency of the words used in the abstracts. This analysis provided insight into the prominence of specific terms and concepts within the field. Following this, the relationships between the keywords were examined to understand how they interact and cluster within the research landscape. These findings were visually represented in a word map, as shown in Figure 3.

The word map illustrates both the frequency of individual keywords and the strength of their relationships, offering a clear depiction of the central themes and interconnections shaping the discourse on the CE and horticulture. As referred to above, the larger the circle, the more frequently a given word appeared in the keywords of the abstracts of the articles reviewed. Figure 3 also shows the relationships between the different keywords found in the abstracts of the publications. The main keywords found were “water”, “compost”, “plastic”, “poultry manure”, and “management.”

As with the analysis of the keywords found in the reviewed articles, the clusters generated by the software were also examined, this time focusing on the abstract texts. This examination was particularly significant in determining whether, beyond the keywords assigned by the authors and the inclusion of these articles in the categories specified in the methodology, the abstracts also incorporated terms relevant to the context. Specifically, the analysis sought to identify whether the abstracts included references to “circular”, “circular economy”, and “horticulture”, aligning with the themes under investigation. The analysis, conducted using VOSviewer and in accordance with the methodology presented above, resulted in the generation of a map (Figure 3) comprising seven clusters (

Table 2. Clusters of the abstracts map.

C	Keywords		Keywords	C	Keywords	C	Keywords	C	Keywords	C	Keywords	C	Keywords
Cluster 1	Agricultural soil	Cluster 2	Cordia	Cluster 3	Clean water	Cluster 4	Agriplastic	Cluster 5	Added value	Cluster 6	Compost	Cluster 7	Food security
	Aquaponic system		Demand		Comparison		Bioplastic		Agroecosystem		Contamination		Goat
	Availability		Floral		Leafe		Field		Biostimulant		Disease		Urban
	Composting		Waste		Lettuce		Grower		Consumption		Farm		Agriculture
	Contaminant		Flower		Microalgae		Peat		Food		Composting
	Energy		Horticultural		Struvite		Plastic				Heavy metal
	Fish		Plant		Water		Processing				Mass
	Greenhouse		Management		Yield		Substrate				Soil quality
	Nitrogen		Nature
	Pesticide		Solution
	Poultry		Valorization
	Manure
	Risk

Note: C, cluster.

).

Cluster 1. The focal point of this cluster is the practices, challenges, and opportunities in modern horticulture through the lens of sustainability and the CE. A win–win relationship between animal and plant production is fostered, where outputs from one system are inputs for the other, to minimise waste and maximise resource efficiency. Strategies for reducing waste, recycling resources, and adopting environmentally friendly innovations in cultivation techniques are examined. The integration of advanced technologies and knowledge is central to the cluster’s objective of optimising production processes while also fostering environmental stewardship and promoting the interconnectedness of agricultural systems within a sustainable framework. This cluster includes the novel aquaponic system, where vegetable production is integrated with aquaculture. This system promotes the reduction of waste, the circularity of nutrients, and the symbiosis of the two systems.

Cluster 2. This cluster is related to floriculture production and sustainability. The transformation of floral and plant waste into valuable resources, such as compost and bioenergy, fosters eco-friendly practices aligned with nature-based solutions. Sustainable methodologies, including precision agriculture, organic farming, and lifecycle analysis, propel this transition, achieving a balance between economic productivity and ecological preservation. The integration of scientific innovations, policies, and stakeholder collaboration is pivotal in advocating for greener, resilient systems that meet the increasing demand for sustainable products and ensure long-term agricultural viability.

Cluster 3. This cluster emphasises the critical synergy between water quality and recycling, resource management, and sustainability in horticulture. It highlights the integration of alternative resources and byproducts, such as microalgae and struvite, into horticultural practices. Microalgae, known for capturing carbon dioxide and producing biomass, serve as sustainable sources of nutrients and biofertilisers, while struvite, a phosphorus-rich mineral recovered from wastewater, supports the CE by recycling essential nutrients. The cluster also underscores advanced irrigation techniques, such as precision drip systems and water recycling technologies, to optimise water usage. By prioritising resource efficiency, recycling, and environmental stewardship, this cluster advocates for scalable, eco-friendly solutions that align horticultural productivity with long-term sustainability and resilience.

Cluster 4. This area of research examines the intricate interconnections between the materials employed in horticulture, including plastics, substrates, and other inputs, and their management, processing, and ultimate impact on sustainability. It addresses the growing concern over the environmental consequences of traditional materials, including conventional plastics and peat, which contribute to pollution and ecological degradation. The main aim of this cluster is the integration of bioplastics as an innovative and sustainable alternative. Bioplastics, derived from renewable biological resources, have the potential to replace traditional petroleum-based plastics, thereby reducing greenhouse gas emissions and reliance on finite resources. Furthermore, this cluster emphasises the importance of advanced material management strategies, including recycling, upcycling, and the development of biodegradable products.

Cluster 5. This cluster underscores the interconnectedness of horticultural production, sustainable consumption, and the CE, exploring the potential of responsible food production—encompassing the creation of added value, utilisation of biostimulants, and the health of agroecosystems. Concomitantly, conscious food consumption assumes a pivotal role in closing the loop of the CE. The integration of biostimulants, which enhance plant growth while reducing reliance on synthetic fertilisers, is a key innovation that the cluster highlights as being vital to achieving a sustainable future.

Cluster 6. This cluster reflects the importance of organic waste management and soil quality in horticulture. It explores practices such as on-farm composting and the application of compost to enhance soil fertility and structure, while simultaneously reducing pollution. On-farm composting and the use of compost can improve soil quality and reduce pollution, while concerns about heavy metals and disease underscore the need for sustainable practices. By addressing these issues, the cluster aims to create a more resilient and environmentally sustainable horticultural system.

Cluster 7. This cluster is concerned with the interrelated topics of food security, urban food production, and the role of animals, such as goats, in more sustainable agricultural systems. The necessity for agricultural practices that simultaneously address the population’s food requirements and promote sustainability and resource efficiency is emphasised. By integrating urban farming, small-scale livestock systems, and sustainable resource management, the cluster identifies innovative strategies to meet the food demands of growing urban populations. Furthermore, it emphasises the necessity of achieving a balance between food production and environmental conservation in order to ensure global food security in an increasingly urbanised world.

3.3. Quantitative Analysis of Keywords and Abstracts

A quantitative analysis of the terms related to the CE in the abstracts and keywords of academic publications was conducted (

Table 3. Results from the analysis of the abstracts of scientific papers.

Year	2016		2017		2018		2019		2020		2021		2022		2023		2024		Total
	k	Abs	k	Abs	k	Abs	K	Abs	k	Abs	k	Abs	k	Abs	k	Abs	k	Abs	k	Abs
No. of Articles	2	1	1	3	3	5	6	10	13	22	16	35	22	38	18	25	18	44
Rethink	0	0	0	0	0	0	0	0	0	0	0	0	0	2	0	0	0	0	0	2
Reduce	0	1	0	3	0	2	0	1	0	10	0	23	0	16	0	12	0	27	0	95
Reuse	0	3	0	2	0	5	0	1	1	6	0	8	0	3	0	8	1	11	2	47
Recover	0	0	0	2	0	4	0	2	0	4	2	11	0	9	1	4	0	17	3	53
Recycle	0	0	0	1	0	4	1	3	1	13	0	8	0	14	0	12	0	19	2	74
Resource efficiency	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	1
Soil health	0	0	0	0	0	0	0	0	0	0	1	0	0	0	1	0	0	1	2	1
Agroecology	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	0	1	0
Nutrient cycling	0	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	0	1	0	2
Circular bioeconomy	0	0	0	0	0	0	0	1	0	0	1	1	0	0	1	1	1	3	3	6
Closed loop systems	0	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	0	0	0	1
Sustainable intensification	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	0	1
Integrated pest management	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0	0	1
Sustainable	0	0	0	1	0	2	0	2	0	7	0	18	0	13	0	10	2	23	2	76
Sustainability	0	0	0	1	0	1	1	2	1	9	6	5	7	10	3	4	2	12	20	44
Circular economy	2	0	0	1	2	5	4	5	12	13	11	25	17	24	14	15	14	31	76	119
TOTAL	2	4	0	11	2	23	6	17	15	62	21	101	25	92	20	67	20	146	111	523
Total different keywords	1	2	0	7	1	7	3	8	4	7	5	10	3	9	5	9	5	11	27	70

Note: k, keywords; Abs, abstracts.

). The results reveal a clear upward trend in research output over the years, reflecting a growing academic interest in the CE. Specifically, the number of articles analysed increased progressively, from only two publications in 2016 to 44 in 2024. This growth highlights an expanding focus on sustainability-related research and its associated practices in the field of CE. Comparing the trienniums 2016–2018 and 2021–2023, the number of articles analysed increased almost nine times, while the horticulture-related publications increased only 33.3% during this period [40].

Terms such as “CE” and “Sustainability” are the most used, with a notable increase in the number of mentions over the years, especially in the abstracts (31 mentions for “CE” in 2024). Other key terms such as “reduce,” “recover,” and “recycle” have also shown significant increases, indicating a continued focus on reduction and reuse practices, signalling a sustained focus on fundamental CE principles, specifically, reduction and reuse strategies. This growing prevalence underscores their central role in framing the discussion on CE practices. However, the analysis also highlighted the relatively low use of emerging and complementary concepts such as “biomimicry,” “permaculture,” and “carbon farming,” which barely appear in the publications. This may reflect the lower integration of these concepts into the academic discourse on the CE or their recent incorporation into the topic. These terms appeared infrequently in the publications analysed, which may indicate limited integration into the dominant academic discourse on the CE. Alternatively, their sparse occurrence may reflect their recent introduction into the field or a niche that has yet to gain widespread recognition.

Finally, although there is a gradual diversification of terms specific to both CE and horticultural topics, especially in the abstracts, reaching up to 11 terms in 2024, the total number of terms used in the abstracts shows a constant increase year after year, reaching 146 mentions in 2024, while the keywords only reached 20 in the same year. Overall, the analysis suggests that while the CE continues to gain traction in the academic literature, there is considerable room for integration of emerging concepts and expansion of the use of specific terminology, particularly in keyword selection. In addition to the terms listed in Table 3, the following keywords were also included in the search: “repair”, “refuse”, “regenerative agriculture”, “biomass valorization”, “zero waste farming”, “carbon farming”, “permaculture”, and “biomimicry”. However, none of these terms were found during the search, and as such, they are not included in Table 3.

4. Discussion

This article presents a bibliometric analysis to explore the connection between the concepts of the CE and horticulture. The analysis focuses on the relationship between the keywords, the abstracts, and the core principles of the CE. Additionally, the study seeks to ascertain whether the terminology employed in the research is consistent with the keywords, the abstract content, and the CE concepts.

Table 4. Synthesis of the results.

	Keywords	Abstracts
The core of the clusters	Nutrient recycling (animals as recyclers) Soil health and environmental impacts Waste valorisation and reduction of environmental impacts	Circularity between animal and plant production Floriculture and circular economy Water quality and water recycling Bioplastics and substrates Food and responsible consumption Soil health and composting Food security and urban agriculture
Most frequent terms: 4R	Recover	Reduce; recycle; recover; reuse
Most frequent terms: concepts	Circular economy; sustainability	Circular economy; sustainable; sustainability

presents a synthesis of the results of this research.

The analysis of the article abstracts reveals a clear increase in the use of terms related to the 4Rs (reduce, reuse, recover and recycle), especially after 2019. Of these, the term “reduce” is the most frequently mentioned, indicating a focus on the minimisation of resource consumption in horticultural practices. It is related to the concept of eco-efficiency, i.e., using fewer natural resources to obtain one unit of product. Furthermore, terms such as “repair” are conspicuous by their absence, which is likely attributable to the inherent characteristics of horticulture, where repair concepts are less applicable than in mechanical or product-focused domains.

Furthermore, the analysis demonstrates that broader CE-related terms, such as “sustainable”, “sustainability,” and “CE”, had only sporadically appeared in the literature up until 2020. Despite an examination of 221 articles with the keywords “horticulture” and “CE”, it can be concluded that the integration of CE terminology remained limited during this period. This indicates that these concepts are not yet fully embedded in horticultural research. It is noteworthy that the terms “CE” and “sustainability” appear in both the keywords and the abstracts, though they are more frequent in the latter. This higher frequency indicates that these terms serve as anchor concepts, deliberately selected to attract researchers interested in these specific topics. Such anchor terms play an important role in enhancing the visibility and discoverability of articles in academic databases, thereby extending their reach within relevant academic communities. There is a strong association in each year between the number of abstracts with the term “CE” and the number of abstracts with the term “sustainable” (or “sustainability”). The results show the emergence of the term “circular bioeconomy” since 2019, but only a few times and not consistently.

Nevertheless, the relatively low representation of CE-related terms in the keywords indicates that horticulture research is not yet fully positioned within the broader CE framework. While the abstracts frequently address themes such as resource efficiency, waste reduction, and the 4Rs, this alignment is not consistently reflected in the keywords. However, the importance of reducing, recycling, recovering, and reusing is demonstrated by the presence of these terms in the abstracts. This gap presents a valuable opportunity for researchers to more clearly establish a connection between their work and the fundamental principles of the CE. By selecting more specific and representative keywords, authors could enhance the visibility of their research and further integrate CE concepts into horticultural studies. It would be beneficial for future research to improve the alignment between the content of the abstracts and the selection of keywords. This would ensure a stronger connection to CE principles and enhance the overall impact of the research.

There is a strong presence of the 4Rs, especially after 2019. The most frequent term (in the abstracts) is “reduction” (95 times), followed by “recycling” (74 times) and, to a lesser extent, the terms “recover” and “reuse” (53 and 47 times, respectively). These results indicate an alignment between circularity, the 4Rs and sustainability, and the prioritisation of actions in research into circular horticulture. We can conclude that there is a priority to reduce the use of inputs (namely those with higher environmental impact, such as nitrogen, phosphorus, and pesticides), followed by a concern about the recycling of materials, especially nutrients.

Cluster visualisation shows the main lines of research in circular horticulture, highlighting composting and the circularity of nutrients through animal production, waste valorisation, soil regeneration and soil health, water quality and water recycling, the problem of plastics, and the sustainability of food production and consumption. However, these clusters are not very consistent within each cluster, particularly in the case of the abstracts, or there is a great diffusion between the various clusters, as can be seen by viewing the keywords map.

The results of this study align with those of other recent research, which has also observed a growing trend in the popularity of the concept of CE over time. However, the concept is often vague and unclear, and it is still in the phase of validity challenges and development, heading in a progressive and promising direction [11,41]. Furthermore, other works indicate that this concept is still in the explanatory phase and lacks a confirmatory approach and empirical validation [42]. There is also a notable lack of methodologies and indicators that allow for the assessment of the application of CE across different sectors [10,43]. As referenced by Ghazanfari [44], the extant literature suggests that circularity is an essential strategy for achieving sustainable development. However, as emphasised by Ghazanfari’s work, while circularity is a key research area, advancing the CE requires greater involvement from governments and stakeholders to increase awareness.

The exploration of the CE as a model for promoting sustainability continues, and many researchers concur that its full implementation necessitates a more profound comprehension of its underlying principles, more precise definitions, and more robust methods for measuring impact. The ongoing challenge is twofold: to refine the concept and to create actionable frameworks that can evaluate and enhance the CE in various domains, whether in business, agriculture, or urban planning. As research progresses, it is becoming evident that the success of the CE will depend on its adaptability to different contexts and its ability to provide measurable real-world benefits.

This study did not consider the impact of publications, which would allow us to differentiate (or not) the relevance of the different clusters and the relationship between the impact of publications in the area and the temporal evolution of the number of publications. The study has limitations typical of an analysis based on bibliometrics, such as the geographical and linguistic coverage of the papers and the format of the publications. It should also be noted that this study does not allow us to determine the influence of the socioeconomic, cultural, and geopolitical context on the attitudes of researchers towards the CE and its principles. Considering these limitations, and in order to deepen our knowledge on the subject, it will be pertinent to study the influence of contexts on the attitudes of researchers towards the CE principles through more qualitative methods, such as interviews and focus groups.

5. Conclusions

Considering that this study aimed to analyse the role of the CE in scientific research in horticulture, it is observed that although the literature review was conducted using the keywords “horticulture” and “CE”, it is only after 2019 that the term “CE” has appeared more than 10 times in the abstracts of research papers. The association among the frequencies of the terms “CE”, the 4Rs, and “sustainability” suggests that the terminology associated with the CE is being used as a way of linking research to the sustainability and CE concepts. However, these economic concepts do not necessarily appear explicitly in the abstracts themselves.

This complexity highlights the need for further research to better understand how authors integrate and explore CE concepts in their research. Furthermore, there is a notable incoherence between the concepts highlighted in bibliographic research, the actual keywords chosen by the authors, and the broader academic curricula. This inconsistency may reflect a gap in the adoption or understanding of the CE within horticultural research, warranting a deeper exploration of how sustainability is incorporated into research focus, methodology, and outcomes.

In conclusion, while there is growing interest in linking horticultural research to CE principles, integration remains partial and inconsistent. Addressing this gap requires a more systematic analysis of how the CE framework is embedded in research practices, conceptual frameworks, and academic curricula.