Soil erosion, or soil loss, refers to the process of removing surface soil by natural forces such as water and wind or by human activities like agriculture and deforestation^[1]. Soil erosion is a major global issue, significantly affecting all continents, with regions such as sub-Saharan Africa, South Asia, and Latin America facing severe challenges due to intensive agriculture, deforestation, and overgrazing^[2-3]. Even in developed areas like the United States and Europe, soil erosion remains a concern despite adopting advanced conservation technologies^[4]. Approximately 75 billion tons of fertile soil are estimated to be lost yearly to erosion^[5].

The problems and impacts of soil erosion are multifaceted. The most immediate and obvious impact is the loss of topsoil, which is critical for plant growth and agricultural productivity^[6]. As topsoil erodes, the soil's structure and water-holding capacity deteriorates ^[7], and soil fertility significantly reduces^[8]. Facing the challenges of decreasing land fertility, farmers often need to increase their use of chemical fertilizers that further reduce soil quality and cause environmental harm^[9]. This is particularly problematic in arid regions where the balance between soil and vegetation is very fragile^[10]. In extreme cases, soil erosion can lead to desertification, turning fertile land into dry, barren areas^[11].

Runoff brings eroded soil particles to water bodies, resulting in sedimentation^[12]. Sedimentation not only diminishes water clarity but also disrupts aquatic ecosystems and the capacity of reservoirs and rivers to function effectively^[13-14]. Runoff transport of soluble nutrients, such as nitrogen and phosphorus, from agricultural fields can lead to eutrophication in nearby water bodies^[15]. Furthermore, the erosion process enhances non-point source pollution, where pollutants such as fertilizers and pesticides washed off from vast agricultural areas into water systems, complicating efforts to manage and mitigate pollution effectively^[16].

Economically, the reduction of land productivity and the increased costs associated with fertilizers and irrigation significantly impact farming communities^[17]. Decreased crop yields can cause an increase in food prices and poverty, eventually lead to food security issues^[5]. The overall impact of soil erosion on agriculture, biodiversity, and the environment is estimated to cost the global economy $8 billion annually^[18].

Additionally, soil erosion contributes to climatechange. Healthy soil acts as a carbon sink, but when it is eroded, the stored carbon is released into the atmosphere as CO₂^[19]. Soil erosion also leads to biodiversity loss because it destroys habitats and changes the structure of ecosystems, making them less adaptive to environmental changes^[20].

Given the far-reaching impacts of soil erosion, many countries have invested significant resources into researching this issue. According to Scopus, the world's largest literature database, there were 8 388 academic documents titled "soil erosion" or "soil loss" published between 1923 and 2023. Similar results were found in another authoritative citation database, Web of Science, which included 8 655 documents related to "soil erosion" from 1932 to 2013^[21]. Research on soil erosion primarily focuses on three aspects: Model-based soil erosion simulation, soil erosion estimation using Cs-137 technology, and the impact of soil erosion on the environment and agriculture^[21]. While early research was mainly conducted in the United States and Europe, China has made significant strides in recent decades that warrant attention.

To summarize the current status and development of soil erosion research in China, scholars have attempted to review relevant literature from various perspectives. For instance, Zhu et al.^[22] reviewed soil and water conservation and erosion control in China, Wang et al.^[23] examined the mechanisms and processes of soil erosion, and Zhang et al.^[24] explored the use of geographic information systems (GIS) for quantitative research on soil erosion. Although these reviews provide valuable insights, they often focus on specific fields, lacking a broad view of the research landscape.

In light of this, the present study conducted a bibliometric analysis of the literature on soil erosion in China indexed in the Scopus database to understand the current status and development trends in this field. Bibliometric analysis involves using quantitative methods to summarize, evaluate, track, and analyze the metadata of publications to describe and summarize the macro characteristics of a specific research field^[25]. Specifically, this study analyzed the number of documents, subject areas, research institutes, funding organizations, publishing journals, keywords, and international collaborations. This study can guide researchers in this field and attract more scholarly attention to soil erosion research in China.

This study obtained document data from Scopus because of two reasons. First, Scopus is the world's largest bibliographic database, containing over 90 million document records^①. This extensive coverage allows researchers to conduct in-depth analyses of research trends, collaboration patterns, and citation evaluation of a research field. Second, its rigorous quality control and standardized citation metrics contribute to Scopus's reputation as a reliable and valuable resource for bibliometric research^[26].

① Elsevier. Scopus Content Coverage Guide, 2023. https://www.elsevier.com/products/scopus/content.

While Scopus provides comprehensive coverage of documents, many Chinese journals are not indexed due to non-compliance with its selection criteria^①. Consequently, this study offers an international perspective on soil erosion research in China, focusing specifically on global insights rather than delivering a comprehensive review of domestic advancements. This approach is essential for understanding China's global recognition and influence in this field.

① Elsevier. Content Policy and Selection, 2024. https://www.elsevier.com/products/scopus/content/content-policy-and-selection.

The data query was conducted on June 1, 2024. As Scopus is regularly updated, the data for this article is based on the records available on that date. The initial query for this study included ("soil erosion" OR "soil loss") AND "China" in the "Title/Abstract/Keywords, " resulting in a total of 7 335 documents. The second query round filtered for documents published in "academic journals, " reducing the count to 6 811 documents. Only "original articles" were selected in the third query round, narrowing the count to 6 588 articles for bibliometric analysis.

After exporting the literature data from Scopus, the records were checked for errors, omissions, or duplications. The data was then organized and analyzed using an Excel spreadsheet, focusing on bibliometric information, including the number of documents, subject classification, and the country of publication. By analyzing the changes in the number of soil erosion research publications in China, it is possible to understand the research intensity and development trends in this field. Additionally, analyzing the subject areas of the literature reveals the main research directions and interdisciplinary aspects.Examining research institutes and funding organizations helps identify the primary research strengths and funding sources. Furthermore, analysis of publishing journals and common keywords highlights the main content and research hotspots^[27]. Finally, VOSviewer was used for co-occurrence and co-authorship analysis to identify themes, development trends, and international collaborations in soil erosion research in China.

Scopus first indexed a research article on soil erosion in China in 1934, but indexing was inconsistent until 1980. Since then, three distinct stages of development can be identified, characterized by an increasing number of publications. In the early stage (1981-2001), there was a gradual rise in publications, likely due to China regaining social stability following the implementation of economic reforms in 1978. The State Government of China introduced policies and measures to prevent soil erosion and protect the ecological environment. For example, promulgating and implementing the Soil and Water Conservation Law of the People's Republic of China provides legal protection for soil erosion prevention and control^[28]. The second stage (2002-2017) marked a period of rapid growth. The number of articles surged approximately sevenfold, increasing from 43 in 2002 to 315 in 2017. This growth can be attributed to China's accession to the World Trade Organization, which accelerated economic development and allowed for significant investments in education and research throughout the 2000s. The government prioritized expanding access to higher education and increasing funding for scientific research^[29]. The spike in publications is closely linked to national policies promoting soil conservation^[30]. In the third period (2018 to present), the number of articles continued to rise, reaching a peak in 2023. By June 1, 2024, a substantial number of articles had been indexed, totaling 380 within the first five months of the year (Fig. 1).

图 1(Fig. 1)

Fig. 1 Number of articles during the period 1981-June 2024

The most popular subject area for soil erosion research in China (Tab. 1) is "environmental science" (n=3 772; 57.3%), followed by "Agriculture and Biological Sciences" (n=2 915; 44.2%) and "Earth and Planetary Sciences" (n=2 122; 32.3%) (Tab. 1). Other popular subject areas are "Social Sciences" (n=926; 14.1%) and "Engineering" (n=524; 8%). Then there are "Energy" "Biochemistry, Genetics and Molecular Biology" "Computer Science" "Interdisciplinary" "Medicine" and "Decision Sciences" all with rates < 5%.

表 1(Tab. 1)

Tab. 1 Subject areas of articles on soil erosion in China Rank Subject area Articles Percentage/% 1 Environmental Science 3 772 57.3 2 Agricultural and Biological Sciences 2 915 44.2 3 Earth and Planetary Sciences 2 122 32.3 4 Social Sciences 926 14.1 5 Engineering 524 8.0 6 Energy 249 3.8 7 Biochemistry, Genetics and Molecular Biology 217 3.3 8 Computer Science 164 2.5 9 Multidisciplinary 148 2.2 10 Medicine 143 2.2 11 Decision Sciences 116 1.8 Notes: Only those having 100 or more articles are listed. Also, the total count exceeds the actual number of articles because some documents are classified under multiple subject areas.

Tab. 1 Subject areas of articles on soil erosion in China

The articles cover multiple subject areas because soil erosion has broad and complex implications. The intersection and integration of disciplines provide a multi-angle and multi-level vision for soil erosion research. For example, environmental science focuses on the impact of soil erosion on ecosystems, agricultural and biological sciences focus on the impact of soil erosion on agricultural production, and earth and planetary sciences focus on the geological processes and landform changes of soil erosion. This multi-disciplinary integration helps to comprehensively and systematically understand and solve soil erosion issues^[31].

Tab. 2 lists the research institutes that have published over 100 papers on soil erosion in China. The Chinese Academy of Sciences is the most productive institute (n=3 367). Notable contributing institutes within the Academy include the Institute of Geographic Sciences and Resources (n=404), the Center for Ecological Environment Research (n=238), he Hazards and Environment Institute (n=224), and the Northeast Institute of Geography and Agroecology (n=102). The Northwest Agriculture & Forestry University ranks second in the list (n=1 796), including a significant contribution from the Institute of Soil and Water Conservation, Chinese Academy of Sciences & Ministry of Water Resources (n=841). Universities, such as the University of Chinese Academy of Sciences (n=789) and Beijing Normal University (n=563), as well as government bureaus like the Ministry of Education (n=622) and Ministry of Water Resources (n=586), are important players in this field.

表 2(Tab. 2)

Tab. 2 Productive institutes on soil erosion in China Rank Research institute Articles 1 Chinese Academy of Sciences · Institute of Geographic Sciences and Natural Resources Research · Center for Eco-Environmental Sciences · Institute of Mountain Hazards and Environment · Northeast Institute of Geography and Agroecology 3367 (404) (238) (224) (102) 2 Northwest Agriculture & Forestry University · Institute of Soil and Water Conservation, Chinese Academy of Sciences & Ministry of Water Resources 1796 (841) 3 University of Chinese Academy of Sciences 789 4 Ministry of Education 622 5 Ministry of Water Resources 586 6 Beijing Normal University 563 7 Beijing Forestry University 258 8 Huazhong Agricultural University 197 9 Xi′an University of Technology 147 10-11 China Institute of Water Resources and Hydropower Research Southwest University 137 12 Lanzhou University 133 13 Peking University 129 14 Ministry of Agriculture and Pural Affairs 127 15 China Agricultural University 122 16 Ministry of Natural Resources 119 Notes: Only those having 100 or more articles are listed.

Tab. 2 Productive institutes on soil erosion in China

Collaborations at the institutional level have strengthened the capacity for research in China. Take the Institute of Soil and Water Conservation, Chinese Academy of Sciences & Ministry of Water Resources as an example. Although the Institute is affiliated with Northwest Agriculture & Forestry University, it also receives direct support from the Chinese Academy of Sciences and the Ministry of Water Resources.

Tab. 3 lists the important funding organizations for soil erosion research in China. The largest funder is the National Natural Science Foundation of China (n=3 032), followed by the National Key Research and Development Program (formerly known as the National Key Basic Research Development Program (973 Program)) (n=946), the Chinese Academy of Sciences (n=616), the Fundamental Research Funds for Central Universities (n=272), the Ministry of Science and Technology (n=162), and the China Postdoctoral Science Foundation (n=153). The number of projects funded by other funding organizations is below 100 each.

表 3(Tab. 3)

Tab. 3 Funding organizations supporting research on soil erosion in China Rank Funding Organization Articles 1 National Natural Science Foundation of China 3032 2 National Key Research and Development Program of China (formerly known as National Basic Research Program of China (973 Program)) 946 3 Chinese Academy of Sciences 616 4 Fundamental Research Funds for the Central Universities 272 5 Ministry of Science and Technology 162 6 China Postdoctoral Science Foundation 153 7 Ministry of Education 90 8 China Scholarship Council 89 9 Youth Innovation Promotion Association of the Chinese Academy of Sciences 72 10 Ministry of Water Resources 66 Notes: Only those having 50 or more articles are listed.

Tab. 3 Funding organizations supporting research on soil erosion in China

A total of 98 international journals have published articles on soil erosion research in China. Tab. 4 lists international journals that are popular publication outlets for soil erosion research in China. The four most prolific journals are Catena (n=451), Science of the Total Environment (n=236), Chinese Journal of Agricultural Engineering (n=225), and Chinese Journal of Ecology (n=207). The rest of the journals published less than 200 articles each.

表 4(Tab. 4)

Tab. 4 Prolific journals on soil erosion in China Rank Journal Citescore (2023) Impact factor (2023) Articles 1 Catena 10.5 5.4 451 2 Science of the Total Environment 17.6 8.2 236 3 Transactions of the Chinese Society for Agricultural Machinery 4.1 N/I 225 4 Acta Ecologica Sinica 2.5 N/I 207 5 Land Degradation and Development 7.7 3.6 151 6 Sustainability (Switzerland) 6.8 3.3 142 7 Soil and Tillage Research 13.0 6.1 138 8 Science of Soil and Water Conservation 1.0 N/I 128 9 Ecological Frontiers (formerly known as Acta Ecologica Sinica (international)) 5.3 4.7 123 10 Chinese Journal of Applied Ecology 2.5 N/I 121 11 Journal of Hydrology 11.0 5.9 121 12 Water (Switzerland) 5.8 3.0 112 13 Ecological Indicators 11.8 7.0 109 Notes: Only those having 100 or more articles are listed. N/I= Not indexed in the Science Citation Index Expanded (SCIE), Social Sciences Citation Index (SSCI), or Emerging Sources Citation Index (ESCI).

Tab. 4 Prolific journals on soil erosion in China

Journals publishing soil erosion research in China are roughly categorized into three groups. One is journals that focus on water and soil, such as Catena and Water (Switzerland); the other is journals with ecology as the core, such as Ecological Frontiers and Ecological Indicators; and its three broader environmental journals, such as Science of the Total Environment. These prestigious journals help increase the international visibility of China's soil erosion research. For example, Catena and Science of the Total Environment are top journals in the fields of soil science and environmental science, respectively. Research results published in these journals can attract widespread attention and recognition from the international academic community.

Four Chinese journals, namely Transactions of the Chinese Society for Agricultural Machinery (农业机械学报), Acta Ecologica Sinica (生态学报), Science of Soil and Water Conservation (中国水土保持科学), and Chinese Journal of Applied Ecology (应用生态学报), were among the most prolific journals on soil erosion. Additionally, Ecological Frontiers, formerly known as Acta Ecologica Sinica (international), is sponsored by prestigious Chinese institutions. These journals highlight China's global influence and reputation in this field.

It is worth mentioning that some influential journals, e.g., International Soil and Water Conservation Research (since 2013) and Journal of Chinese Soil and Water Conservation (since 2013), respectively, were added to Scopus recently. Due to the short indexing history, they do not appear as prolific journals. Nevertheless, their impacts on soil erosion research in China cannot be overlooked.

There are a total of 13 701 keywords in Chinese soil erosion research articles, and Tab. 5 lists the keywords that appear more than 400 times. The most frequently occurring keywords are "China" (n=4 865) and "Soil Erosion" (n=4 098). Other popular keywords include "Soil" (n=2 147) and "Loess Plateau" (n=1 638), "erosion" (n=1 576), "rainfall" (n=1 139), "sediment" (n=1 129), "soil and water conservation" (n=1 127) and "runoff" (n= 1 112). Other keywords appear less than 1 000 times.

表 5(Tab. 5)

Tab. 5 Frequently occurred keywords in the field of soil erosion in China Rank Keywords Occurrences 1 China 4 865 2 Soil erosion 4 098 3 Soils 2 147 4 Loess Plateau 1 638 5 Erosion 1 576 6 Rainfall 1 139 7 Sediments 1 129 8 Soil conservation 1 127 9 Runoff 1 112 10 Watersheds 999 11 Land use 852 12 Landforms 791 13 Rivers 687 14 Vegetation 653 15 Sediment transport 488 16 Water conservation 455 17 Environmental protection 445 18 Agricultural land 444 19 Climate change 420 20 Land use change 418 21 Erosion control 408 22 Vegetation coverage 404 23 Soil moisture 403 Notes: Only those exceeding 400 times of occurrences are listed.

Tab. 5 Frequently occurred keywords in the field of soil erosion in China

Taking keywords that co-occur at least 40 times as the threshold for co-word analysis, VOSviewer found 49 keywords, combined them into 4 clusters, and displayed them in different colors (Fig. 2). The four clusters respectively represent the four main research themes of soil erosion in China, reflecting the breadth and depth of the research content. The red cluster "soil erosion and land degradation" consists of 17 keywords (China, Loess Plateau, human activities, land degradation, land use change, climate change, ecological restoration, soil conservation, afforestation, vegetation coverage, ecosystem services, precipitation, soil moisture, soil properties, water erosion, wind erosion, sustainable development). The green cluster "erosion dynamics and drivers" has 14 keywords (soil loss, soil, erosion, purple soil, rainfall, rainfall intensity, runoff, surface runoff, slope gradient, vegetation, sediment, sediment yield, phosphorus, simulated rainfall). The blue cluster "soil erosion process and mechanism" has 13 keywords (soil erosion, rainfall erosivity, soil erodibility, aggregate stability soil organic carbon, gully erosion, check dam, black soil, northeast China, Cs-137, karst, spatial distribution, vegetation restoration). The yellow cluster "erosion monitoring technology" has 5 keywords (GIS, remote sensing, RUSLE, land use, landscape pattern).

图 2(Fig. 2)

Fig. 2 Keyword clusters on soil erosion research in China

These four themes reflect the major directions of soil erosion research in China, reflecting the breadth and depth of the research content. For example, the theme "soil erosion and land degradation" focuses on the impacts of soil erosion problem and land degradation, and Loess Plateau as an example; the theme "erosion dynamics and drivers" focuses on the process of soil erosion and its influencing factors; the theme "soil erosion process and mechanism" focuses on the relationship between soil physical and chemical properties and soil erosion; the theme "erosion monitoring technology" focuses on using GIS and remote sensing technologyfor soil erosion monitoring and assessment.

VOSviewer color-coded the keywords according to the average time of occurrence (Fig. 3). Purple and blue keywords appear earlier, while green and yellow keywords appear later. Earlier research was more interested in "GIS" "remote sensing" "Cs-137" and "landscape pattern". Research interests turn to "soil erosion" "soil loss" "loess plateau" "runoff" "soil conservation" "ecological restoration" "simulated rainfall" "black soil", etc., and the latest research focuses on "climate change" "ecosystem services" "soil erodibility" "gully erosion" "RUSLE" and "vegetation restoration".

图 3(Fig. 3)

Fig. 3 Average time of occurrence of keywords on soil erosion research in China

The 98 countries have published research articles on soil erosion in China. Among the 6 588 articles included in this study, China accounts for the most (n=6 307; 95.7%), followed by the United States (n=525, 8.0%), the United Kingdom (n=170; 2.6%), and Canada (n=164; 2.5%), Australia (n=149; 2.3%) and Germany (n=128; 1.9%).

Taking the co-authorship at least 20 times as the threshold for co-authorship analysis, VOSviewer found 18 countries and identified two clusters. The large cluster is centered on China, connecting some European Union countries, and India and Pakistan. This is followed by a small cluster of commonwealth countries headed by the United Kingdom. The rest are bilateral collaborations between two countries that do not form networks. Relatively strong bilateral collaboration relationships are China-United States, China-Canada, China-Japan, and China-Australia.These international collaborations help enhance the international influence of China's soil erosion research. For example, through collaboration with the United States and Europe, Chinese researchers can learn from advanced research methods and technologies to improve their research levels^[32]; through collaboration with developing countries, they can jointly address the global challenges of soil erosion^[33].

This study exported the data of 6 588 research articles on Chinese soil erosion from Scopus and conducted bibliometric analysis. First, by analyzing the changes in the number of soil erosion research literature in China, the research intensity and development trends in this field are revealed.Second, by analyzing the subject distribution of the literature, the main directions of research and interdisciplinary situations are determined. Third, the main research forces and funding sources in this field are identified by analyzing research institutes and funding organizations. Then, the main content and research hot spots of the research are revealed by analyzing the publishing journals and common keywords. Finally, the research's main themes, development trends, and international collaboration are revealed by co-occurrence analysis and co-author analysis. Overall, this study successfully systematically sorted out and summarized the current status and development trends of soil erosion research in China and provided reference and guidance for researchers in this field. At the same time, this study hopes to attract more scholars' attention to soil erosion issues and promote further development in this field.

This study proposes several further research directions to promote the development of soil erosion research in China. First, multidisciplinary interdisciplinary research should be strengthened, especially integrating environmental sciences, agricultural and biological sciences, earth and planetary sciences, and other disciplines. This will help to deeply understand and solve the problem of soil erosion from multiple angles and levels. Second, technological innovation and application are the keys to improving research levels. The accuracy and efficiency of soil erosion monitoring and assessment can be significantly improved using new technologies such as remote sensing technology, GIS, and model simulation. In addition, soil erosion research should be closely integrated with policy formulation and practical application, promote the transformation and application of research results, and provide scientific basis and technical support for formulating and implementing prevention and control measures.

This study has a few limitations that should addressed in future research. First, although Scopus provides valuable insights into the international impact of research, its focus on English-language and internationally recognized journals may under-represent national research outputs, particularly those published in local Chinese journals not indexed by Scopus. This bias may limit understanding of China's contributions to soil erosion research. To address this issue, future studies should consider incorporating data from Chinese databases (e.g., China National Knowledge Infrastructure (CNKI), Chinese Science Citation Database (CSCD)) to capture a more complete view of national efforts. This approach would provide a balanced perspective, encompassing both global and local significance, and offer richer insights into China's scholarly achievements^[34]. Second, bibliometric analysis mainly relies on quantitative data. Although it can reveal macro characteristics, it lacks an in-depth understanding of the research details. Therefore, future studies should use both quantitative and qualitative methods to further explore the depth and details of the research content through in-depth literature reviews and case studies^[35]. In addition, future research should also focus on the practical application and policy impact of soil erosion prevention and control, explore the combination of scientific research with policy formulation and practical application, and promote the transformation and application of research results. Third, bibliometric analysis has inherent limitations related to its counting methods. One key issue is the interpretation of citations. A citation doesn't always signify endorsement; it can also represent a critical reference or a discussion of erroneous results^[36]. This ambiguity challenges the assumption that more citations equate to higher quality or positive recognition ^[36]. Moreover, authorship attribution can also lead to skewed perceptions of contribution^[37]. Typically, bibliometric systems assign equal credit to all co-authors of a paper. For example, in a paper authored by two individuals, each author receives credit for every citation as if they were the sole author rather than sharing the credit. This can lead to inflated productivity of individuals and institutes, as indicated by the fact that the total number of articles in Tab. 2 is more than 6 588. Therefore, bibliometric results should be interpreted carefully and supplemented with qualitative assessments to provide a more comprehensive evaluation of research contributions and impact.

Looking forward, international collaboration and exchanges should be strengthened, advanced international research methods and technologies learned from and absorbed, and the global challenges posed by soil erosion should be jointly responded to. Through these improvements and deepening, future research will be ableto more comprehensively and deeply reveal the current status and development trends of soil erosion research in China, providing a more solid scientific basis and guidance for the sustainable development of this field.