Introduction

The term “organic” as applied to farming was first used in the US by Rodale in 1940. The Rodale Institute and their Organic Farming and Gardening magazine remains a primary source of organic information and advocacy. In England, the term was developed about the same time by Lord Northbourne who described an integrated farm as a “dynamic living organic whole” (Durham 2005). These workers shared an emphasis on the importance of soil organic matter for maintaining fertility, a rejection of chemical fertilizers and pesticides, and a reliance on livestock production as an essential component of the workings of the farm. Now, organic farming is practiced in approximately 100 countries throughout the world, with more than 24 million hectares under organic trade association (OTA).

Organic farming is a way of agriculture that relies on techniques such as crop rotation, green manure, compost, and biological pest control. Depending on whose definition is used, organic farming uses fertilizers and pesticides if they are considered natural, but it excludes or strictly limits the use of various methods for reasons including sustainability, openness, independence, health, and safety (Paull 2011). Organic agriculture is an ecological production management system that promotes and enhances biodiversity, biological cycles and soil biological activity. It is based on minimal use of off-farm inputs and on management practices that restore, maintain and enhance ecological harmony (Gold 2014). Organic agricultural methods are internationally regulated and legally enforced by many nations, based in large part on the standards set by the International Federation of Organic Agriculture Movements (IFOAM 2010).

Several studies have been conducted to better understand how farmers choose between organic and conventional production (Matthias et al. 2008), some of them based on qualitative analysis of in-depth interviews (Darnhofer et al. 2005; Duram 2000; Fairweather 1999; Fairweather and Campbell 2003; Lockeretz 1997), others on quantitative analysis of surveys (Burton et al. 1999; Midmore et al. 2001; Schneeberger et al. 2002) or farm accounting data (Pietola and Lansink 2001).

The desire for a sustainable agriculture is universal, yet agreement on how to progress towards it remains elusive. The extent to which the concept of sustainable agriculture has any operational meaning is discussed. Sustainability is considered in relation to organic farming a sector growing rapidly in many countries. The reason for the focus on organic agriculture is the rapid development of the organic sector in Europe and North America (Rigby and Cáceres 2001; Yuseffi 2004). The organic sector of the US agricultural and food industry is garnering increasing interest from producers, consumers, policymakers and those interested in farm, environmental and nutrition issues. Although it is not the only emerging niche in the food sector, it is one of the pioneering market segments over the past few decades. The innovative nature of organic marketing, together with a new national organic certification program, resulted in a high consumer profile and market presence. Thus, there may also be need for enhanced research, education and extension on production, marketing, policy and food science issues related to this sector (Thilmany 2006).

In numerous official documents, organic farming methods are said to contribute to food safety, greater product diversity, environmental benefits and provision of public goods linked to rural development (CEC 2002; LD 1999). Accordingly, policy makers actively seek to increase the number of organic farms through various initiatives. Proponents of organic farming argue that soil quality is best promoted in food production systems where biological, cultural, and physical practices are relied on to supply crops with adequate nutrition and suppression of pests (Badgley et al. 2007; Horrigan et al. 2002). Others maintain that the conventional farming systems which include the regular use of synthetic fertilizer and pesticides are the best option for providing an adequate global food supply while maintaining and even enhancing soil quality (Trewavas 2001, 2004; Conner 2008).

Recent published meta-analyses (De Ponti et al. 2012) suggest that widespread replacement of conventional with organic farming is not recommended if substantial increases in food production are needed to feed a population of 10 billion humans by 2050, as some have projected (Lutz et al. 1997). Seufert et al. (2012) and De Ponti et al. (2012) reported an average yield drag of 20 % when crops were grown using organic compared with conventional methods. Still, Reganold (2012) argued that organic farming has a place in supplying a sufficient and nutritious food supply in the future, pointing out that high yields can be produced by organic farmers. In addition, organic farming may be a better strategy for promoting the environmental and socio-economic sustainability of agrarian life than conventional farming (Reganold 2012).

Given the emergent significance of this topic, the aim of this paper was to analyze the knowledge structure of scientific research on organic farming integrating the analyses of productivity, collaboration, and scientific impact with subject category analysis, keyword analysis, social network analysis (SNA), and co-word analysis. The identification of the knowledge structure of scientific research on organic farming can help neophytes and newcomers to enter this field or to provide sufficient insight to leap forward in a new competitively advantageous research direction.

Methods

Items under study were obtained from the Web of Science Core Collection (WOS) from Thomson Reuters. The terms used in the search strategy were Title = (“Ecolog* agriculture” OR “organic agriculture” OR “organic farm*”). To reach greater accuracy in the results, the search was conducted in the Title field because if applied in the Topic option, which includes the search fields Title, Abstract and Keywords (KW), many records obtained were not relevant. The terms were truncated using an asterisk to obtain all documents associated with the derived words (e.g., “organic farm*” allows for the recovery of items containing the terms “organic farm”, “organic farms”, “organic farmer”, “organic farmers” and “organic farming”. All records obtained were reviewed to ensure their relevance. The final records were exported to a relational database using the self-developed software Bibliometricos. We then proceeded to correct variations on signatures of names of the same institution to merge them into a single appellation and to standardise and group keywords in the records. We then analyse the records to identify in which journals the articles were published, the subject category of each article, the KW most frequently associated with subject categories, impact factor of journals and articles receiving higher citations. We used social network analysis (SNA) to identify the leading keywords, institutions and countries by means of quantifying the number of different co-occurrences in the set of papers revised. The software Pajek, specialized in the visualisation of networks, was used for the construction and graphical representation of the collaboration between institutions and countries, as well as the network of co-words (Batagelj and Mrvar 2002). The software VOSViewer was used for the construction of the density map of keywords. Data on country of publication of the journals and impact factor were extracted from the 2012 edition of the Journal Citation Reports.

Results

A set of 1009 published papers were collected: 916 original articles (90.8 %), 47 revisions (4.7 %), 4 notes (0.4 %), and 42 letters (4.1 %). The first article registered in WOS was published in 1954 (Fig. 1). The number of articles has increased steadily, from 34 in the period 1954–1984 (3.4 %) to 675 in 2005–2013 (66.9 %). This growth is more striking for original articles than for reviews.

Fig. 1
figure 1

Annual evolution of published papers

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Papers were published in 359 different journals. Table 1 lists the 41 journals that published more than five articles distributed by country of publication, WoS subject categories, quartile and impact factor in 2013. The most productive journals were the Agriculture Ecosystems Environment (n = 37), Biological Agriculture Horticulture (n = 33) and Renewable Agriculture and Food Systems (n = 26) and Journal of Sustainable Agriculture (n = 26). The majority of these 41 journals were published in the Netherlands (n = 11), UK (n = 11), US (n = 8) and Germany (n = 5). Journals with higher impact factor (in addition to Science, with an IF = 31,477) were Journal of Applied Ecology (FI = 4.754), Soil Biology and Biochemistry (FI = 4.410), Agriculture Ecosystems and Environment (FI = 3.203), Land Use Policy (FI = 3.134) and Journal of Agricultural and Food Chemistry (FI = 3.107), all of which ranked in first quartile in Journal Citation Reports.

Table 1 Journals of publication, WoS subject categories, quartile and impact factor
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Table 2 shows WOS categories with most published articles, most frequent key words and journals with most articles in each area. The list is ranked by Agriculture, Multidisciplinary category (n = 263) with the key words “Organic agriculture”, “Sustainable agriculture” and “Systems”, and the journals Agriculture Ecosystems and Environment, Journal of Sustainable Agriculture and Renewable Agriculture and Food Systems. Other two areas with more than 100 published articles were Agronomy (n = 138) and Environmental Sciences (n = 103). In Agronomy, the key word “Organic agriculture” is followed by “Nitrogen” and “Management” while in Environmental Sciences the key word “Organic agriculture” is followed by “Biodiversity” and “Farming”. Other represented areas were Environmental Sciences, Ecology, Soil sciences, Plant Sciences and Horticulture.

Table 2 WoS subject categories, most frequent key words and most productive journals in each category
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Papers that received 100 or more citations are shown in Table 3. Three papers stand out from the others with more than 300 citations. The more cited paper was published in 2002 by Mader et al. in Science (n = 606), a team of researchers belonging to the Research Institute of Organic Agriculture (Frick, Switzerland). The topic of this paper is about soil fertility and biodiversity in organic farming. The second most cited paper (n = 349), published in 2005 in the journal Biological Conservation by Hole et al., a British research team, discusses the question of whether organic farming benefits biodiversity. The third paper (n = 334), published in 2005 in the Journal of Applied Ecology by Bengtsson, Ahnstrom and Weibull, a team from the Swedish University of Agricultural Sciences—SLU (Uppsala, Sweden), is a meta-analysis on the effects of organic agriculture on biodiversity and abundance.

Table 3 Most cited papers
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Collaborative networks between institutions are shown in Fig. 2. The network with 8 components is mainly composed of Danish institutions and has Aarhus University as center. Other participating Danish centers are Technical University of Denmark, University of Copenhagen and National Environmental Research Institute. Aarhus University is connected with other four foreign centers: Robert Gordon University (UK), China Agricultural University, Australian National University (ANU) and Empresa Brasileira de Pesquisa Agropecuária—Embrapa. The second network integrates three centers form Switzerland (Research Institute of Organic Agriculture-FiBL, University of Basel and Swiss Federal Research Station for Agroecology and Agriculture) and two from The Netherlands (Wageningen University and Louis Bolk Institute). The network with four components is integrated by French centers that have Institut National de la Recherche Agronomique-INRA as central institution. The two networks with three components correspond to Spanish and Swedish centers. The largest number of articles published in collaboration has occurred between Louis Bolk Institute and Wageningen University (n = 6), INRA—Institut National de la Recherche Agronomique and ISARA Lyon (n = 5), and Lund University with Swedish University of Agricultural Sciences—SLU (n = 5).

Fig. 2
figure 2

Network of collaboration between institutions that collaborate in 3 or more papers (networks with 3 or more research centers)

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Papers productivity by countries is as follows: USA (n = 152; 14.3 %), Germany (n = 77; 7.6 %), UK (n = 77; 7.6 %) and Denmark (n = 70; 7 %). In the network of collaboration between countries (Fig. 3) emerge 16 countries. The country establishing more collaborative relationships with other countries is Germany, with 10 relations, followed by UK and The Netherlands, both with 8. Other countries that hardly stand in the network are Denmark, Switzerland and Sweden.

Fig. 3
figure 3

Network of collaboration between countries

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Figure 4 corresponds to a density collaboration map between key words. This map is useful to obtain a general scope of the key words that represent the documents and allow appreciating the weight that some concepts have in the published articles and the relations with other concepts. The names of the words whose papers have set more relations with other ones are shown with different black intensity. The warmer colours (red) indicate a higher density whereas the colder colours represent lower densities. The map highlights the place of greatest centrality in organic agriculture, and other relevant words are management and systems agriculture. Around organic agriculture the related key words are crooping system, quality, crops and soil. Related with management are found nitrogen and biodiversity. Finally, related to agriculture systems are sustainable agriculture, organic and nitrogen.

Fig. 4
figure 4

Density map of key words that appears in more than 20 papers. (Color figure online)

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Discussion

This work has enabled to characterize the global scientific production, impact, main topics covered and collaborations between institutions and countries in the scientific literature published on organic agriculture included in Web of Science.

Some of the most striking results are the increasing number of published articles and that two-thirds of the articles have been published in the last decade, especially since the early 2000s. This growth is in line with the increased interest in organic agriculture shown by most of the countries and the rapid development of the organic sector in Europe, North America and Australia (Rigby and Cáceres 2001; Yuseffi 2004). According to The World of Organic Agriculture 2014 report, edited by the Research Institute of Organic Agriculture (FiBL) and the International Federation of Organic Agriculture Movements (IFOAM), Australia is the country with most million hectares of organic agricultural land (n = 12), followed by Argentina (n = 3.6), USA (n = 2.2), China (n = 1.9) and Spain (n = 1.6). The observed positive trend remains unbroken and consumer demand increases (with 10 % market growth in the world’s largest organic market, the US); more farmers cultivate organically (+5 %) and a bigger land surface is organically certified (+0.5 %) (FIBL and IFOAM 2014).

One of the important reasons that could have contributed to this growth may be the health benefit of organic agriculture. Recently, an international team of experts led by Newcastle University (UK), has proved in a meta-analyses based on 343 peer-reviewed publications that organic crops and organic crop-based foods are up to 60 % higher in a number of key antioxidants than conventionally grown crops. The meta-analysis also reported lower Cadmium concentrations (Baranski et al. 2014). As it is well known, numerous studies have linked antioxidants to a reduced risk of chronic diseases, including cardiovascular and neurodegenerative diseases and certain cancers (German and Walzem 2000; Ruf 2003; Guilford and Pezzuto 2011; Giacosa et al. 2012; Aleixandre et al. 2013).

As observed, journals with most published articles are devoted to the main aspects covered by the organic farming, such as agriculture, environment, ecology, agronomy and soil, among others. This is the case of the most productive journal, Agriculture, Ecosystems and Environment. It publishes scientific articles dealing with the interface between agroecosystems and the natural environment, specifically how agriculture influences the environment and how changes in that environment impact agroecosystems. The second ranked journal, Biological Agriculture and Horticulture, aims to study alternative systems of husbandry, and particularly the biological approach to food production. Other relevant publishing journals deal with renewable and sustainable agriculture, soil use, ecology and food science and technology, among others. Particularly striking is the presence of the multidisciplinary high-impact factor journals such as Science, which may be due to the importance and interest that is currently drawing the organic agriculture as highest area of research. The diversity of subject categories of journals contributes to understand these features.

The subject analysis has revealed that the key words prioritization in organic agriculture-related scientific journals depends on the addressed subject area. In the subject categories Agriculture, Multidisciplinary and Environmental Studies is frequent the key word “sustainable agriculture”; in Agronomy, Soil Science, Plant Sciences, Horticulture, Agriculture, and Dairy and Animal Science, a common word is “Nitrogen”; for Environmental Sciences and Ecology, an important word used is “Biodiversity”; Agronomy, Soil Science and Plant Sciences have however the key word “management” as most usual.

The topic analysis of the most cited papers allows knowing which topics attract more interest in the research. As we can see, these are issues that are linked to the relationship between organic farming and biodiversity, the possibility that enhance or reduce the nutritional value of plant foods, the organic farming as a global food supply, the agronomic and environmental implications and impact, the sustainability of agricultural systems and the innovation in the conversion to organic farming, among others.

It is striking that the most productive institutions belong to north Europe small countries such as Denmark, The Netherlands or Sweden. This is consistent with the importance that the consumption of products derived from organic farming has in these countries (Oesch and Schaer 2008). The countries of northern and central Europe such as Germany, UK, The Netherlands, Denmark, Sweden and Switzerland are leaders in the EU in consumption of organic products; being USA the leader country within the global framework. Only Denmark alone consumes about 7 % of the European total (European Union 2010). The same applies to the network of collaboration between countries, since these are the countries with major number of papers written in cooperation. This network highlights four non-European countries along with the US: Canada, Australia, Brazil and China, the latter two included within the BRIC emerging countries.

It must be understood that some research limitations are inevitable in this kind of analysis. For example:

  1. 1.

    The purpose of this study was to characterise knowledge structures generated by research papers on organic farming, integrating subject categories of journals, key words of papers and social network analysis. However, this method is only an approach which could be complemented by a deeper analysis, for example analysing the content of papers.

  2. 2.

    The quality of the results extracted from the co-word analysis and the validity of maps depend on the quality of KW chosen to conceptualise the scientific papers by the authors or indexers.

Future research in this area must focus on the process of more professional journals from other bibliographic databases and on the study of the thematic content of the papers, which will enable a wider analysis. It will also be interesting to see whether the growth trend remains in the coming years, as well as the consolidation of current research groups and the emergence of new groups and countries involved in this field.

Conclusions

The interests of producers, consumers, policymakers, and the widespread belief in the beneficial health effects of organic agriculture in modern society encourages a greater allocation of resources for research in this area, resulting in a greater number of publications. This research has taken place in recent years. The issue of organic farming has thus become an emerging field of research that requires a systematic analysis of the structure of knowledge. This study contributes to a better understanding in this field and identifies the main lines of research, the sources chosen for their scientific dissemination and the major scientific players.