Agricultural life cycle assessment: a system-wide bibliometric research

As the methodology of LCA is further developing (going beyond traditional environmental assessment towards comprehensive sustainability assessment), involvement of social and economic issues via Social LCA (SLCA), Life Cycle Costing (LCC), an exploration of comprehensiveness and implementation of such methods in agriculture gain importance. Some reviews generalise the experi ence of LCC application in agriculture [6] and food waste chains [7]. Though, it's not enough to understand the expansion and comprehensiveness of LCA research in agriculture, given the sector's multifunctionality and variety of impacts.

Only few publications [27-31] reveal the broader context of LCA application in agriculture. Fan et al. [27] systematically reviewed publications indexed in the ISI Web of Knowledge concerning the LCA experience in crop production (limiting the collection by studies using more than one LCA indicator). They emphasised the need for further improvement of the LCA methodology: allocation procedure, functional unit selection, and LCA integration with other decision -making tools. Alhashim et al. [28] apply a similar approach - narrowing the collection by crop production and several impact categories - but consider only LCA studies with GHG and/or ecotoxicity categories, thus covering rather LCA of the impact of agricultural production on climate change and ecotoxicity, but not the full LCA's potential for sustainable agriculture transformation. Gava et al. [29] - reviewing academic publications indexed in Scopus and Web of Science in January 2019 with the keywords “life cycle assessment” and “agriculture” or “food” - found the growing attention to LCA application to justify waste circularisation and corresponding strategies, and the lack of systemic LCA practices in agriculture. The authors limited the collection to agricultural economics and policy subject areas, so the results do not reveal LCA's system-wide agricultural implementation. Ruviaro et al. [30] made a systematic literature review on LCA application in agriculture globally and in Brazil, which is the broadest. Scholars examined publications of government institutions and scientific literature for 2001-2011 (86 documents) and found an increase in the number of publications since 2007 (authors explained this as a response to public demand for greater transparency and monitoring of environmental impacts due to global agreements such as the Kyoto Protocol), a prevalence of LCA use to compare different production systems (organic and conventional, extensive and intensive, small and large, traditional and developed), evidence of LCA and other methods integration to obtain better results in terms of agriculture environmental impact assessment. Assessing the spread of LCA application among agricultural sectors, authors attributed the dominance of LCA in livestock production (58 %) compared to crop (36 %) and other agricultural products (6 %) to the ascendancy of EU-related research, where livestock production is more common. Like narrower research, this review [30] indicates the heterogeneity of LCA procedures and results, the incomparability of LCA outcomes, and the inability to extend conclusions to other product systems. Later, Claudino & Talamini [31] conducted a similar by-context bibliometric review of research devoted to the implementation of LCA practices in agribusiness; however, limiting only to the Brazilian experience. To the best of our knowledge, there is no recent review with the broader coverage of LCA application in agriculture globally, including environmental but also social and economic issues.

Methodology. This study covers publications indexed in Scopus because this database contains more unique records than the Web of Science [32; 33]. The following search query was applied for titles-abstracts-keywords: “agr*” within three words of “life cycle analysis” or “life cycle assessment” or “life cycle cost*” or “life cycle impact” or “*lca” or “*lcia” or “lcc” (as of October 3, 2022). The phrase choice to form the sample was made because of the complexity of agriculture (and possible lexical forms) and the diversity of agriculture impacts covered by different LCA types and procedures. The limitation of the words' proximity allowed for avoiding the so-called “informational noise”, i.e. including little related to agriculture LCA research. Through “agr*” wording, it was aimed to cover all possible synonyms: agrarian, agriculture, agricultural, agribusiness, agri-food, and others similar. Different variants of LCA type naming were added to the search query, allowing to cover the social context (for example, in the term “SLCA” via “*lca”). Initially, the search result contained 508 documents. The sample was limited by the type of sources and language - only English-language academic journals - resulting in 367 publications. The primary screening of the sample (titles and abstracts only related to agriculture and agri-food issues) was made to exclude irrelevant publications. In this step, research related to “latent class analysis” in medicine, land cover analysis or change (included due to “LCA” and “lcc” abbreviation), building and c onstruction issues, packaging, and education for nutrition were excluded. Reviews (bibliometric, systematic) were also excluded to avoid any bias caused by more frequent words in the reviews. The final sample covered 259 documents (supporting data are listed in [34]).

Results

Research dynamics, geographic and institutional patterns. Table 1 summarises the main parameters of the collection, allowing for performance analysis. Almost one thousand scholars are engaged in research on LCA application in agriculture, mainly within a research team of five members on average.

Table 1

Descriptive statistics for bibliographic collection

The share of single-authored publications amounts to only 4.6 % of the total collection: only one in ninety authors publish individually. The average number of citations is 4.398 per publication annually, and it takes over six years for a publication to be cited. The first publication in the sample dates to 1999; in 1999-2002, there was a growing interest concerning the LCA in agriculture, followed by the recession: no studies published in 2003-2004 were found in Scopus (Figure 1).

Figure 1. Historical development of the research field: annual scientific production

Source: authors' development via Biblioshiny.

The presence of relevant publications every year since 2005 illustrates stability and relevance the research field was getting. The publication activity dynamics are wave-like, with an average annual growth rate of 12.1 %. Despite the periods of recession (2003-2004, 2008, 2016, 2019), the number of publications has grown exponentially and doubled in 2021 compared to 2015.

Even though there was a decline in the number of publications in 2008 (Figure 1), two articles published that year are among the most cited (Figure 2), having 173 total citations per article on average and 12.36 citations annually. Publications in 2000 (four articles) and 2001 (one article) also have high citation rates: 157.25 and 163 total citations per article on average.

In addition to the above, 25 articles published in 2017 are also highly cited annually: 53.64 citations per article on average and 10.73 per article per year.

Figure 2. Historical development of research field: average article citation per year

Source: authors' development via Biblioshiny.

This evidences the formation of a particular set of relevant research topics in 2000-2001, 2008, and 2017. Documents from the collection represent different fields of knowledge according to the Scopus classification (Figure 3), with a predominance of studies in the Environmental

Figure 3. Scopus subject areas

Source: Scopus data.

Science area constituting more than a third of the sample. Research in Energy, Engineering, Agriculture and Biological Sciences, Business, Management and Accounting amount to a little more than 50 % of the sample, with a predominance of the Energy area. The Journal of Cleaner Production and the International Journal of Life Cycle Assessment are the leading platforms for publishing research results on LCA application in agriculture (Figure 4): a little more than 40 % (41.31 %) of the documents from the analysed collection were published in these journals. The Journal of Cleaner Production holds leadership in annual publications; the International Journal of Life Cycle Assessment led only in 2009-2011 and 2019-2021.

Figure 4. Most relevant sources

Source: authors' development via Biblioshiny and MS Excel.

In 1999 and 2000, the Journal of Cleaner Production and the International Journal of Life Cycle Assessment were the only journals publishing research about LCA application in agriculture. The European Journal of Agronomy has also become a platform for disseminating research results in this field since 2001 when the first relevant article was published. The first publications in Agricultural Systems appeared in 2007 (one article), in Environmental Science and Technology - in 2012 (two articles), and the Science of the Total Environment - in 2016 (two articles). Although LCA originates from the environmental management field, specialised journals - the Journal of Environmental Management and the Integrated Environmental Assessment and Management - published the first relevant publications only in 2009 and 2017, respectively. Certain neglection of the sustainability dimension of agricultural LCA is also evident: the Frontiers in Sustainable Food Systems and the Sustainability (Switzerland) have published appropriate research only recently (in 2020 and 2019, respectively). Commenting on the sources' influence, one should note that the Journal of Cleaner Production has the highest h-index (31), and the International Journal of Life Cycle Assessment indicator is 19. Other journals from the top 20 have significantly lower h-index values varying from 2 to 7. However, such journals as the Science of the Total Environment (h-index = 7), Sustainability (Switzerland) (h-index = 4), and Agronomy (h-index = 2) have the m-index value of more than 1.0, being close to the m-index of the Journal of Cleaner Production (1.33).

Developed countries lead in this research field (Figure 5).

Figure 5. Country scientific production

Source: authors' development via Biblioshiny.

The following countries constitute the top five by the number of publications: France (80 publications), the USA (77), Italy (50), Spain (46) and Switzerland (40). In addition to the listed above, only ten countries exceed the value of an average number of publications per country (13): China (37), Germany (36), the UK (29), Australia (24), Denmark (21), Belgium (20), Brazil (20), Canada (20), Japan (17), the Netherlands (15). One should note the excessive number of publications made by scholars in the least developed countries like Pakistan (7), Indonesia (6), Malaysia (6), and Thailand (6) compared to the number of publications in some EU member states: the Czech Republic (5), Hungary (5), and others. In general, the eastern EU members demonstrate low research activity: Poland, Bulgaria, and Romania have only one publication each. Despite its role in global agriculture, the number of publications from India is also low (4).

Although only one publication in the collection was associated with Poland, this article ensured the country's leadership by the number of citations per publication (Table 2). In addition, Italy and France, leading in the number of total citations (1169 and 1041), have fewer citations per article than the top ten listed in Table 2 (44.96 and 38.56, respectively).

Table 2

The most and the least relevant countries

Note. *TC - total citations; **TCpA - total citations per article.

Source: authors' development via Biblioshiny.

The top five leading countries, measured by affiliation to the corresponding author, are somewhat different: France, Italy, the USA, Switzerland, and China (Figure 6).

Figure 6. Collaboration among the countries

Source: authors' development via Biblioshiny.

Corresponding authors from France, Switzerland and China are leaders in the number of research conducted by an international team (eight international publications for each country), while several European countries (Finland, Portugal, Austria, Hungary, Greece, Poland, Romania), Turkey, and some least developed countries (Indonesia, Kuwait, Malaysia, Uganda) lag behind, because they have no international research at all. The Czech Republic, Luxembourg, Argentina, Chile, Fiji , Mexico, Norway, and Pakistan have the highest ratio of international collaboration (1.0). agriculture bibliometric greenhouse mapping

Results of network mapping (Figure 7) indicate the closest research cooperation between developed countries (mainly European) and weak collaboration outside.

Five clusters of international research cooperation were automatically detected:

1) Central European led by France, Switzerland, and the UK;

2) American-European (the USA and Italy among the leaders) closely interacting with the Central European cluster;

3) Eastern (China, Pakistan, Australia), collaborating with the American- European cluster;

4) Eastern European cluster integrating scholars from Austria and the Czech Republic;

5) Asian-European (Iran, Korea, and Belgium in cooperation with Colombia).

Figure 7. Collaboration network map of the countries

Source: authors' development via Biblioshiny.

The collection includes documents authored by scholars affiliated with 436 institutions. The Technical University of Denmark and the University of Montpellier (France) are the most productive, with a total of 10 publications per institution (Figure 8).

Figure 8. Most relevant affiliations by articles published

Source: authors' development via Biblioshiny and MS Excel.

The Institute of Environmental Engineering (Switzerland) and the University of California (USA) have seven publications each and, together with the Colorado State University (the USA) having six publications, are among the top five the most productive institutions. The authors did not indicate affiliation in seven publications. The most productive scholars (by the number of documents fractionalised) are as follows: Hayashi (3.28), van der Werf (2.46), Nemecek (2.44), Gaillard (1.65), Nikkhah (1.58), Pfister (1.50), Basset-Mens (1.48), Teixeira (1.33), Brankatschk (1.20), Hansson (1.14), Antn (1.09), Finkbeiner, Blanco-Canqui, Hotta, Lindeijer, Mangmeechai (1.0 each). Other authors have less than one publication. The top five authors by the total number of publications include Nemecek (14 publications), Gaillard and van der Werf (nine each), and Basset-Mens and Hayashi (six each). Most of these scholars are also the most cited: the author H-index in this collection for Nemecek, Gaillard, van der Werf, Basset-Mens, and Hayashi is 10, 8, 8, 6, 4, respectively. The most productive and relevant authors systematically researched LCA application in agriculture, starting from 2007-2008 (Gaillard and Hayashi began in 2010 and 2012, respectively) - Figure 9.

Figure 9. Top authors' production over time

Source: authors' development via Biblioshiny.

Research content. The word cloud reveals the research context, illustrating the most frequent words (Figure 10).

Figure 10. Word cloud of author keywords

Source: authors' development via Biblioshiny.

The main corpus of research keywords consists of the following terms: “agriculture” (frequency is 31), “environmental impact” (26), “sustainability” (17), “carbon footprint” (16), “agricultural LCA” (12), “greenhouse gas emission” (12), “life cycle impact assessment” (12), “life cycle inventory” (11), “climate change” (10). In addition to the mentioned before, “biofuel”, “land use”, and “organic” are gaining popularity. In general, research mainly focuses on the environmental impact assessment of agriculture, the link between LCA and sustainability, climate issues, LCA of specific crops and livestock, and methodological issues (impact assessment, allocation, and life cycle analysis).

The thematic map complements the description of research field development by disclosing the key concepts' prevalence and relevancy (Figure 11). The author keywords were used to cluster the documents. As a result, 11 clusters were obtained.

The agricultural LCA research centres around the role of LCA in food security and agricultural sustainability, complemented by niche topics concerning bioenergy, irrigation, and nitrogen.

Basic themes (in addition to “food security”) include issues related to environmental impact and its assessment via LCA in agriculture, effects of climate change on agriculture and their mitigation (“global warming potential category”), and exploration of agricultural pract ices, systems, and products through LCA. Issues of LCA application to measure impacts related to resource depletion and inform agricultural policy represent niche themes that are less spread and relevant. Growing attention is given to LCA applications to measure greenhouse gas emissions and features of LCA procedures in agriculture (“agricultural LCA”). These themes drive the modern development of the research field.

The identified diversity of themes covered (Figure 11) proves the need to explore the historical evolution of the research field.

Thematic evolution map (by author keywords) is drawn according to previously identified time slices with the publication activity decline (2003-2004, 2008, 2016, 2019) (Figure 12). Scientific productivity decline followed by the increase may indicate the emergence of a new trend (new topic) in the research field.

Figure 11. Thematic map by author keywords

Source: authors' development via Biblioshiny.

Figure 12. Thematic evolution map by author keywords Source: authors' development via Biblioshiny.

The first period (1999-2002) indicates the emergence of agriculture as a new area for LCA studies that further (2005-2008) is complemented with the studies of methodological issues (life cycle inventory). In 2009-2016, new topics arose (global warming potential, allocation) with a focus on production. The systemic view of agriculture as an object of LCA marks 2017-2019, LCA's focus on environmental impact and biofuel, and the emergence of carbon footprint-related research. Research in the current period focuses on climate change issues, production side and methodological aspects (allocation, inventory, agricultural LCA).

Main research topics. For a brief overview of leading research areas, the documents were bibliographically coupled and clustered based on the Walktrap algorithm. Five clusters of studies were obtained (Figure 13).