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Review

Bibliometric Analysis of the Application of Soil Amendments in Improving Soil Infiltration and Storage Capacity over the Last 20 Years

by
Xiaolan Ju
1,2,
Xihuan Sun
1,2,*,
Lijian Zheng
1,2 and
Juanjuan Ma
1,2
1
College of Water Resource Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China
2
Key Laboratory of Collaborative Utilization of Water Resources in River Basin of Shanxi Province, Taiyuan 030024, China
*
Author to whom correspondence should be addressed.
Agriculture 2025, 15(7), 691; https://doi.org/10.3390/agriculture15070691
Submission received: 28 February 2025 / Revised: 16 March 2025 / Accepted: 24 March 2025 / Published: 25 March 2025
(This article belongs to the Section Agricultural Soils)
Browse Figures
Versions Notes

Abstract

:
The infiltration and water-holding properties of soil are essential for the efficient utilization of farmland water and the control of soil erosion. Soil amendments can enhance soil infiltration and storage capacity by increasing the cohesion between soil surface particles and maintaining a good soil structure. To understand the research status and development trend of soil amendments in improving soil infiltration and storage capacity, this study analyzed the annual publication volume, the major contributing institutions, the international cooperation relationships, and the research hotspots in this research field based on the Web of Science Core Collection database, using Citespace and VOSviewer software. The results showed that the number of publications on the application of soil amendments in improving soil infiltration and storage capacity had increased over the past two decades, with China, the United States, and Spain dominating in terms of publication volume and international influence. The current research hotspots mainly include soil aggregates, soil fertility, soil microorganisms, soil pore characteristics, organic amendments, and biochar. Future research should focus on the impact mechanisms of soil amendments, led by biochar, on reclaimed soil productivity when used to enhance soil infiltration and storage capacity. Additionally, further exploration should be conducted on the interaction between soil aggregates and surface runoff.

1. Introduction

Soil is one of the most crucial natural resources for human survival. However, due to the early exploitation and utilization of land resources, natural vegetation has been severely damaged, leading to significant issues such as soil compaction, poor water and air permeability, and low water retention capacity [1]. These problems result in a large amount of rainwater being unable to infiltrate the ground during rainfall, causing surface runoff and, consequently, soil erosion. Therefore, enhancing the soil’s infiltration and water retention capacity is a vital approach to preventing soil erosion. Soil amendments can alter the physical and chemical properties of soil and offer advantages such as low investment, short cycles, and quick results. They have been proven to positively impact soil’s infiltration and water retention capabilities [2,3,4,5].
The mechanisms by which soil amendments improve soil infiltration and storage capacity are mainly concentrated in two aspects: soil structure and soil hydraulic properties. By enhancing the soil structure and hydraulic characteristics, the soil infiltration and water retention capacity can be improved, thereby reducing surface runoff and soil erosion. The soil’s structure plays a critical role in influencing the transmission and retention of soil moisture [6]. Understanding the effect of soil amendments on the structure of soil is of great significance for formulating scientific and rational measures for the conservation of soil and water and for the efficient use of water resources. Numerous studies have indicated that the application of soil amendments can lead to changes in soil aggregate formation and stability [7,8,9,10,11], bulk density [12,13,14], pore morphology [15,16,17,18], and pore spatial distribution [19,20,21]. However, these changes may vary depending on factors such as the amendment type, application rate, and soil texture. The soil structure and hydraulic properties are interrelated, as changes in the soil structure directly affect soil infiltration, retention, and water conduction abilities. Extensive research has been conducted on the influence of soil amendments on soil hydraulic properties, focusing primarily on the soil water retention capacity [22,23,24], soil saturated hydraulic conductivity [9,16,25], soil unsaturated hydraulic conductivity [26,27], soil water infiltration rate [28,29,30], soil evaporation rate [31,32], and parameters related to the soil water characteristic curve [20,30]. The application of soil amendments holds significant importance in the prevention and control of soil erosion, primarily through their regulatory effects on surface runoff and soil erosion [8,33]. Soil amendments function by binding small soil particles to form large water-stable aggregates [34], effectively reducing the slope runoff volume [35] and decelerating runoff velocity. Concurrently, they enhance the soil infiltration capacity and resistance to scouring on slopes [36], thereby markedly mitigating the risk of soil erosion. Furthermore, extensive research has demonstrated that soil amendments can significantly improve the efficiency of soil water utilization in farmland [37,38,39]. In summary, previous studies have extensively investigated the role of soil amendments in enhancing soil infiltration and water retention capacity, particularly under rainfall conditions, revealing their efficacy in managing slope erosion. However, they have predominantly focused on the effects of single or a few types of soil amendments on the infiltration and water retention capacity of specific soils in particular regions. There remains a paucity of comprehensive analyses on the trends in soil infiltration and water retention capacity influenced by soil amendments over different periods.
In recent years, review articles and meta-analyses on the use of soil amendments to enhance infiltration and water retention capacity have provided researchers with foundational information and innovative guidance. Through a meta-analysis, Matisic et al. [40] extensively examined the effects of four organic amendments—compost, vermicompost, biochar, and fruit residue—on soil physical and chemical properties. Their findings revealed that the efficacy of these amendments varied depending on the soil texture, application rate, and cropping system, underscoring the need for tailored and sustainable soil management practices. Adjuik et al. [41] reviewed the impacts of bio-based and synthetic hydrogels on soil hydraulic properties, including water retention, hydraulic conductivity, soil water infiltration, and soil water evaporation. Ahmed et al. [42] provided an overview of biochar characteristics, their effects on improving soil physicochemical properties, and their long-term implications for the soil environment. However, traditional literature reviews have primarily focused on specific research topics, often lacking the systematic organization of knowledge structures and failing to comprehensively reflect the application of soil amendments in enhancing soil infiltration and water retention capacity, as well as future research trends. Therefore, it is imperative to conduct a comprehensive analysis of the literature in order to reveal publication trends, contributing institutions and countries, and keyword co-occurrence and evolution, and to visually highlight significant research directions in this field. Such an analysis would provide a holistic understanding of the application of soil amendments in improving soil infiltration and water retention capacity.
Bibliometrics, a quantitative analysis method grounded in mathematical statistics, has been extensively utilized to identify research hotspots and developmental trends in specific fields [43]. It plays a pivotal role in elucidating the research status and guiding future research directions [44]. VOSviewer 1.6.20 software has been used in other studies of bibliometric analysis in various areas of knowledge and excels in static network visualization, with intuitive visualizations that help quickly identify research hotspots and domain associations. Citespace 6.3.R1 software is effective in dynamic network analysis and time series visualization, which can effectively reveal hot topic evolution and knowledge structures in the research field, and is especially suitable for analyzing research trends and frontier fields. The combined use of these two tools can fully reveal the research characteristics of the application of soil amendments in improving soil permeability and storage capacity from both dynamic and static dimensions. In this study, we employ CiteSpace and VOSviewer software to conduct a bibliometric analysis of publications from the past two decades in the field of soil amendments for enhancing soil infiltration and water retention capacity. This analysis encompasses publication volume, contributing institutions, countries, keyword co-occurrence, and keyword emergence, thereby examining global research trends. Additionally, we provide a preliminary exploration of the current research hotspots and future trajectories. The objective of this study is to offer essential references for utilizing soil amendments to mitigate soil degradation, improve soil infiltration and water retention capacity, and promote the rational utilization of degraded soils.

2. Materials and Methods

2.1. Data Sources and Search Strategies

To reflect the scientific nature of the studies and to ensure the accuracy and reliability of the bibliometric analysis, we used the Web of Science Core Collection (WOSCC), a comprehensive database with the longest time span, a complete collection of documents, and systematic multidisciplinary reviews, as the data source for the literature search. The basic search method was used. This study conducted a literature search across three areas: “Soil amendments for improving soil structure”, “Soil amendments for improving soil hydraulic properties” and “Soil amendments for reducing soil runoff and erosion”. A keyword search was performed in the “TOPIC” field (equivalent to topic research) for “amendment” AND “aggregate stability” OR “soil porosity” OR “soil pore properties”, “amendment” AND “soil hydraulic properties” OR “soil hydraulic parameters”, “amendment” AND “soil runoff” OR “rainfall erosion”, with the time span set from 1 January 2004 to 31 December 2023. The search date was 13 April 2024, and the document type was limited to articles, yielding a total of 3327 documents. The resulting documents were exported as a text file containing “full record and citation data”. The “Data-import/export” function in Citespace software was used to remove duplicates of the retrieved literature, and only the unique records in the duplicate literature were retained. Then the remaining detailed manual retrieval results. The exclusion criteria included the following: (1) meta-analysis articles; and (2) incomplete keyword coverage. For example, when searching for the keywords “amendment” AND “aggregate stability”, only “amendment” OR “aggregate stability” is included in the abstract and keywords sections. (3) Test indicators: the research scheme of this paper does not involve the type of improvers and the determination of key word-related indicators. After screening, irrelevant literature were eliminated, and 1481 literatures were retrieved for bibliometrics and visualization analysis.

2.2. Data Analysis and Knowledge Graph

The literature data retrieved from the WOSCC were saved in text format. The retrieved and downloaded data were analyzed using Microsoft Excel 2021 to identify trends in the total number of publications per year and plotted using Origin 2018. Networks of research organizations and keywords were plotted using the software VOSviewer 1.6.20. Collaboration between countries was mapped using the software Scimago Graphica 1.0.49. A keyword hotspot analysis was conducted using CiteSpace 6.3.R1 software.

3. Results and Discussion

3.1. Bibliometric Review of Soil Amendments for Improving Soil Structure

3.1.1. Distribution of Publications over the Years and Major Contributing Institutions

Figure 1 shows the number of articles published on soil amendments for improving soil structure from 2004 to 2023. By the end of 2023, the WOSCC database contained a total of 859 articles on “soil conditioners for soil structure improvement”, and the number of articles generally showed an increasing trend year by year. According to the annual number of articles, this field can be roughly divided into two phases: 2004–2013, the starting period, with a total of 168 articles and an annual average of 16.80 articles, exhibiting slow development; and 2014–2023, the growth period, with a total of 691 articles and an annual average of 69.10 articles, exhibiting rapid development momentum. Figure 2 shows the institutional collaborative network of soil amendments used to improve soil structure from 2004 to 2023. The top three institutions in terms of the number of published papers are the Chinese Academy of Sciences, the Chinese Academy of Agricultural Sciences, and Northwest Agriculture and Forestry University, all from China. This indicates that China currently attaches great importance to research on soil amendments for improving soil structure, as well as emphasizing that, in this field, China not only holds a preeminent position but also strongly promotes the development of research. However, although the connecting lines between the institutions in Figure 2 indicate the existence of collaborative relationships, the links are weak, suggesting that they do not work closely with each other and lack cohesion, and that further exchanges and cooperation are needed.

3.1.2. International Cooperative Relations

Using VOSviewer software to statistically analyze the articles published on soil amendments used to improve soil structure from 2004 to 2023, we obtained a network of the national cooperation in this research field, as shown in Figure 3. The top five countries in terms of the number of published articles are China, the USA, Spain, India, and Germany, indicating that these countries are in leading positions in the research field of soil amendments used to improve soil structure, and the related research has had a significant impact on the field. In Figure 3, it can also be seen that there are a variety of cooperative relationships between different countries; many countries are involved in research on soil amendments for improving soil structure and maintain a certain degree of cooperative links, forming a relatively stable cooperative network. In terms of the intensity of cooperation, the connecting line between China and the United States has the darkest color, indicating that the cooperation between them is the strongest, followed by China’s relatively close cooperation with the United Kingdom, Australia, Pakistan, and other countries. Regarding the number of cooperating countries, China ranks first in terms of the intensity of cooperation with other countries, followed by Germany.

3.1.3. Keyword Co-Occurrence Analysis

Keywords can greatly distill the main concepts and core points of an article and visually express the direction and value of the research results. In this study, we used VOSviewer to visualize and analyze the keywords in the literature retrieved from the WOSCC database and to draw a keyword knowledge map. Figure 4 shows a schematic diagram of the keyword co-occurrence network of soil amendments used to improve soil structure from 2004 to 2023. In order to display high-frequency keywords, the threshold was adjusted to 10, and a total of 162 high-frequency keywords were obtained. As can be seen in Figure 4, VOSviewer software generated five clusters, and the keywords headed by each cluster were biochar (red, with a link strength of 1510 and 197 co-occurrences), carbon (green, with a link strength of 1295 and 187 co-occurrences), aggregate stability (blue, with a link strength of 1434 and 221 co-occurrences), manage (yellow, with a link strength of 813 and 107 co-occurrences), and management (purple, with a link strength of 983 and 139 co-occurrences); these five clusters show the hotspots in research on soil amendments used to improve soil structure. Among them, cluster 1 focuses on the effects of soil amendments on soil physical properties, with the keywords “biochar”, “physical properties”, “impact”, “water retention”, and “hydraulic conductivity” appearing more frequently in this cluster. A global meta-analysis showed that biochar could be used to enhance soil physical properties, with it reducing soil bulk weight by an average of 9% and increasing the field water-holding capacity and wilting point by 1–51% and 5–47%, respectively [45]. Cluster 2 focuses on the relationship between soil amendments and soil nutrients and microorganisms, with the keywords “carbon”, “stability”, “management”, “matter”, and “nitrogen” appearing more frequently in this cluster. The storage of nutrients in soil microbial biomass and their subsequent release to plants through microbial turnover is an important process for high-quality crop production [46], and the addition of soil amendments can have an effect on soil microbial activity, which, in turn, alters soil nutrient availability [47,48]. Cluster 3 focuses on the relationship between soil amendments and crop growth, with the keywords “manure”, “growth”, “quality”, “composts”, and “yield” appearing more frequently in this cluster. Soil amendments can be used to improve infertile soils or to rebuild soils damaged by mismanagement so that they are kept at their peak and plants can take up nutrients through the root system to promote crop growth and development [49,50], which, in turn, improves quality and yield. Cluster 4 focuses on the effect of soil amendments on soil aggregates, with the keywords “amendment”, “aggregate stability”, “organic matter”, “organic carbon”, “sewage sludge”, etc., appearing more frequently in this cluster. The addition of soil amendments promotes the consolidation of small soil granular bodies and the formation of large granular bodies, thereby increasing soil aggregate stability. Cluster 5 focuses on the effect of tillage on soil runoff and erosion, with the keywords “tillage”, “erosion”, “runoff”, “erodibility”, and “loess plateau” appearing more frequently in this cluster. Conventional tillage can increase soil bulk density and reduce macroporosity, leading to reduced water and nutrient availability and severe soil erosion [51]. Conservation tillage is a new type of tillage relative to conventional tillage and differs from it in terms of operation, time, and production costs. Typically, conservation tillage controls soil erosion by altering soil properties or microtopography or by increasing surface cover [52].

3.1.4. Keyword Emergence Analysis

The emergence of keywords can allow for the characterization of rapid increases in the frequency of keywords in a research field in a certain period of time, thereby intuitively reflecting the trend of research hotspots and research directions. Using Citespace software to analyze the keyword emergence indices in the field of soil amendments used to improve soil structure from 2004 to 2023, we determined the keyword citation frequency in this research field, as shown in Table 1. According to the starting time of keyword emergence, the research on the soil amendments used to improve soil structure can be divided into three stages: In Stage I, 2004–2016, research mainly explored the mechanism of the effect of different organic amendments on the structure of cultivated soil, and the amendments mainly included compost, tufted mycorrhizal fungi, charcoal, and black carbon. The keywords “aggregate stability”, “charcoal”, “tillage”, “compost”, and “soil quality” had a greater emergence intensity, indicating that they received more extensive attention in this stage. In Stage II, 2017–2019, research mainly examined how soil structure changes affect crop growth after applying soil amendments to reclaimed soil, with the keywords “plant growth”, “size”, “water retention”, “pyrolysis”, and “remediation” emerging with greater intensity. In Stage III, 2020–2023, research mainly centered on “biochar”, “plant”, “productivity”, “retention”, and “crop yield”, indicating that the main focus in this stage was the effect of biochar on soil productivity. Biochar is a class of porous materials with complex void structures and abundant functional groups formed via the pyrolysis of biomass, capable of adsorbing organic matter and improving physical protection processes, thereby enhancing carbon sequestration in soils; its application as a potential soil amendment has been the subject of growing research interest [53]. The addition of biochar disrupts the original particle buildup in the soil matrix, and its elongated shape and irregularities alter the particle composition, thereby enlarging the soil pore space [54]. In addition, biochar can enhance soil erosion resistance by promoting aggregate formation [55] and increasing the soil microbial population [56], which increases total soil porosity and improves aggregate stability [19]. However, the physicochemical properties of biochar can vary greatly depending on its raw materials and pyrolysis conditions, and the physicochemical changes in the degradation process of biochar itself need to be further investigated. Accordingly, the long-term effects of biochar as a soil amendment to improve soil structure and its effect mechanisms on soil productivity and crop growth will be the focus of future research.

3.2. Bibliometric Review of Soil Amendments for Improving Soil Hydraulic Properties

3.2.1. Distribution of Publications over the Years and Major Contributing Institutions

Figure 5 shows the number of articles published on the study of soil conditioners for improving soil hydraulic properties from 2004 to 2023. As of the end of 2023, the WOSCC database contained a total of 412 articles on “soil conditioners for improving soil hydraulic properties”, and the number of articles generally shows an increasing trend year by year. According to the annual number of articles, this field can be roughly divided into two phases: 2005–2017, the starting period, with a total of 141 articles and an annual average of 10.85 articles, exhibiting slow development, and 2018–2023, the growth period, with a total of 271 articles and an annual average of 45.17 articles, exhibiting rapid development momentum. Globally, 596 institutions have contributed to the research on soil amendments for improving soil hydraulic properties. The acquired raw data were imported into VOSviewer software, and the minimum number of papers issued by the institutions was set to 1. The cooperative cluster co-occurrence of the issuing institutions was plotted, as shown in Figure 6. The top three institutions in terms of the number of published papers are the Chinese Academy of Sciences, Northwest Agriculture and Forestry University, and Shantou University, all from China. This indicates that research on soil amendments for improving soil hydraulic properties is currently highly emphasized in China. Figure 6 also shows that there are 22 clusters of institutions in the field of research on soil amendments for improving soil hydraulic properties, and the research institutions in the 22 clusters maintain close contact but cooperate less with other institutions; thus, there is a need for further exchanges and cooperation among different research institutions.

3.2.2. International Cooperative Relations

Using VOSviewer software to statistically analyze the articles published on soil amendments used to improve soil hydraulic properties from 2004 to 2023, we obtained a network of country cooperation in this research field, as shown in Figure 7. It can be seen that the top five countries in terms of the number of published articles are China, the USA, Germany, India, and Australia, which form the backbone of the research field, and the related studies have had a significant impact on the field. It can also be seen in Figure 7 that the intensity of cooperation is the strongest between China and the USA, followed by that between China and India, China and England, Egypt and Saudi Arabia, and China and Canada. In terms of the number of cooperating countries, China exhibits the greatest cooperation intensity with other countries and thus ranks first, followed by the USA. As can be seen in the diagram of the cooperative relationship network, many countries are involved in the research on the use of soil conditioners to improve soil’s hydraulic properties and maintain a certain degree of cooperative contact, forming a relatively stable cooperative network.

3.2.3. Keyword Co-Occurrence Analysis

Figure 8 shows a schematic diagram of the keyword co-occurrence network for the study of soil amendments for improving soil hydraulic properties from 2004 to 2023. In order to display the high-frequency keywords, the threshold was adjusted to 10, and a total of 80 high-frequency keywords were obtained. Four clusters were generated by VOSviewer software, and the keywords at the head of each cluster were biochar (red, with a link strength of 699 and 117 co-occurrences), aggregate stability (green, with a link strength of 354 and 62 co-occurrences), hydraulic conductivity (dark blue, with a link strength of 605 and 119 co-occurrences), and amendment (yellow, with a link strength of 731 and 137 co-occurrences); these four clusters indicate the hotspots in the research on soil amendments used to improve soil hydraulic properties. Among them, cluster 1 focuses on the effect of biochar type on soil hydraulic properties, with the keywords “biochar”, “hydraulic-properties”, “soil”, “sandy soil”, and “black carbon” appearing more frequently in this cluster. Biochar is a solid product obtained from the combustion of biomass (e.g., herbaceous plants, woody plants, and poultry manure) in an oxygen-limited environment, and it can improve agricultural productivity, especially soil hydrology and fertility [57]. Numerous studies have shown that different pyrolysis temperatures [58,59], particle sizes [58,60,61], and feedstock types of biochar [62,63] affect hydraulic properties. Cluster 2 focuses on the effect of soil amendments on soil aggregates and the response of crop growth and development to soil amendments. The keywords “aggregate stability”, “manure”, “carbon”, “quality”, and “water” appear more frequently in this cluster. Stabilized agglomerate formation is a key factor in securing plant growth and environmental quality [64]. Soil amendments help to increase the amount of organic matter in soil, as well as consume and transform organisms, providing binding agents that contribute to the formation of soil aggregates [65,66], which, in turn, promotes the formation of aggregate structures and creates pore spaces that can be filled with air and water, thus facilitating the growth of plant roots [48]. Cluster 3 focuses on the interaction between soil pore properties and soil hydraulic properties under different management measures, and the keywords “hydraulic conductivity”, “physical properties”, “organic matter”, “impact”, and “management” appear more frequently in this cluster. The application of soil amendments promotes the development of plant roots and changes the pore system through the mechanical movement of soil particles and aggregates, thus forming macropores [67], and the formation of soil macropores alters the soil structure and hydraulic conductivity, which leads to more water infiltration in the soil [16]. Cluster 4 focuses on the effect of soil amendments on soil infiltration and erosion resistance, and the keywords “amendment”, “water retention”, “infiltration”, “conductivity”, “nitrogen”, etc., appear more frequently in this cluster. Numerous studies have shown that the addition of soil amendments decreases soil bulk density [2,22,28,68,69,70], leading to an increase in total porosity, especially macroporosity. Macropores facilitate the transport of soil moisture, thereby increasing soil infiltration, reducing waterlogging, and decreasing the likelihood of land degradation due to surface runoff [71].

3.2.4. Keyword Emergence Analysis

Using Citespace software to analyze the keyword emergence indices in the field of soil amendments used to improve soil hydraulic properties from 2004 to 2023, we determined the keyword citation frequency in this research field, as shown in Table 2. According to the starting time of keyword emergence, the research on soil amendments used to improve soil hydraulic properties can be divided into two stages: In Stage I, 2007–2009, the hot keywords include “fertilizer”, “manure”, “coal fly ash”, and “soil amendment”, indicating that, in this stage, research mainly focused on the effect of different types of amendments on soil hydraulic properties. In Stage II, 2010–2023, research mainly examined the effect of biochar on the hydraulic properties of reclaimed soil, with the emergent keywords including “soil”, “management”, “black carbon”, “tillage”, “charcoal”, “organic matter”, “reclamation”, “biochar”, “plant available water”, “chemical property”, and “soil hydraulic properties”. The results show that biochar from different raw materials had different effects on soil hydraulic properties. The different chemical compositions and structural organizations of raw materials for biochar preparation will cause biochar to have different elemental compositions and chemical properties, and biochar prepared at different pyrolysis temperatures has different physicochemical properties and application areas. Therefore, in future research on the use of biochar as a soil amendment to improve soil hydraulic properties, the focus will be on how different types of biochar regulate soil moisture and the influence mechanism on reclaimed soil fertility and crop growth.

3.3. Bibliometric Review of Soil Amendments for Reducing Soil Runoff and Erosion

3.3.1. Distribution of Publications over the Years and Major Contributing Institutions

Figure 9 shows the number of articles published on the use of soil amendments to reduce soil runoff and erosion from 2004 to 2023. By the end of 2023, the WOSCC database contained a total of 210 articles on “soil amendments for reducing soil runoff and erosion”, with a fluctuating trend in the number of articles published annually. Globally, 275 organizations have contributed to the research on soil amendments for reducing soil runoff and erosion. The acquired raw data were imported into VOSviewer software, and the minimum number of articles published by the institutions was set to 1. The cooperative clustering co-occurrence of the publishing institutions was plotted, as shown in Figure 10. The top three institutions in terms of the number of published papers are the Agricultural Research Service, University of Arkansas, and Purdue University, all from the USA. This indicates that the current research on soil amendments for reducing soil runoff and erosion is highly emphasized in the USA. Figure 10 also shows that there are 20 clusters in the research field of soil amendments for reducing soil runoff and erosion, and the research institutions in the clusters maintain close contact but cooperate less with other institutions; thus, there is a need for further exchanges and cooperation among different research institutions.

3.3.2. International Cooperative Relations

Using VOSviewer software to statistically analyze the articles published on soil amendments for reducing soil runoff and erosion from 2004 to 2023, we obtained a network of the national cooperation in this research field, as shown in Figure 11. The top five countries in terms of the number of articles are the USA, China, Iran, Spain, and Ireland, indicating that these countries are in leading positions in the field of research on the use of soil amendments to reduce soil runoff and erosion, and the related research has had a significant impact on the field. It can also be seen in Figure 11 that there are cooperative relationships between different countries, but they cooperate less with each other. In terms of the intensity of cooperation, the connecting line between China and the USA has the darkest color, indicating that the cooperation between them is the strongest, followed by the cooperation between Ireland and the USA, which is also relatively strong. In terms of the number of cooperating countries, Germany is in first place, with the greatest intensity of cooperation with other countries, followed by India. As can be seen in the diagram of the cooperation relationship network, only 41 countries are involved in research on soil amendments used to reduce soil runoff and erosion, forming a less stable cooperation network. By enhancing international cooperation, different countries can not only work together to solve the challenges in the field of soil amendments for reducing soil runoff and erosion but also realize the sharing of resources and technology, and promoting the further development of this research field.

3.3.3. Keyword Co-Occurrence Analysis

Figure 12 shows a schematic diagram of the keyword co-occurrence network for soil amendments for soil runoff and erosion reduction research from 2004 to 2023. In order to display the high-frequency keywords, the threshold was adjusted to 10, and a total of 47 high-frequency keywords were obtained. As can be seen in Figure 12, four clusters were generated by VOSviewer software, and the keywords headed by each cluster were erosion (red, with a link strength of 253 and 51 co-occurrences), manure (green, with a link strength of 125 and 33 co-occurrences), amendments (dark blue, with a link strength of 279 and 60 co-occurrences), and runoff (yellow, with a link strength of 418 and 94 co-occurrences); these four clusters indicate the hotspots in the research on soil amendments used to reduce soil runoff and erosion. Among them, cluster 1 focuses on the effect of organic amendments on soil erosion resistance, with the keywords “erosion”, “biochar”, “aggregate stability”, “impact”, and “physical properties” appearing more frequently in this cluster. Organic amendments can provide substrates for soil microorganisms and facilitate their transformation into compounds that act as “glue” between soil particles [72,73], thereby improving soil aggregate stability [74], protecting the overall surface of soil particles from rainfall impacts, and reducing soil erodibility [75]. Cluster 2 focuses on the effect of soil amendments on nutrient loss due to soil runoff, and the keywords “manure”, “water quality”, “nitrogen”, “phosphorus”, “soil”, etc., appear more frequently in this cluster. Nutrients and organic matter required for plant growth are mostly concentrated in the soil surface, and when surface runoff occurs, the soil surface is washed away, resulting in the formation of a fragmented soil aggregate structure, leading to reduced soil water and nutrient retention [76,77], reduced land productivity [78], and, consequently, reduced soil fertility and arable land degradation. Soil amendments can improve nutrient availability by improving soil aeration, porosity, and infiltration rates and by reducing soil erosion, bulk density, and runoff [79]. Cluster 3 focuses on the effects of different types of soil amendments on soil infiltration and adsorption capacity, and the keywords “amendments”, “infiltration”, “polyacrylamide”, “gypsum”, and “adsorption” appear more frequently in this cluster. Due to the different compositions and inherent properties of different types of soil amendments, the infiltration capacity [29] and adsorption capacity [80] of nutrients such as nitrogen, phosphorus, and potassium in agricultural soils may be affected to different degrees. Cluster 4 focuses on the influence of soil management on soil erosion characteristics, and the keywords “runoff”, “soil erosion”, “management”, “sediment yield”, “organic matter”, etc., appear more frequently in this cluster. The intensification of land management, especially since the introduction of mechanized agriculture, has led to unprecedented soil erosion and widespread soil degradation [81]. Proper soil management strategies can improve soil quality, increase soil organic matter, and provide the nutrients required by plants.

3.3.4. Keyword Emergence Analysis

Using Citespace software to analyze the keyword burst indicators in the field of soil amendments for reducing soil runoff and erosion from 2004 to 2023, we determined the keyword citation frequency in this research field, as shown in Table 3. According to the starting time of keyword emergence, the research on soil amendments used to reduce soil runoff and erosion can be divided into two stages: In Stage I, 2006–2012, research centered on “energy”, “losses”, and “polymers”, mainly examining the effect of soil amendments on soil loss under different rainfall kinetic energies. In Stage II, 2013–2023, research mainly examined the effect of soil amendment application on the relationship between soil aggregates and surface runoff, and the emergent keywords included “surface”, “runoff”, “aggregate stability”, and “impact”. The application of soil amendments can promote the formation of soil aggregates and improve the stability of aggregates, thus affecting the generation and flow of surface runoff. However, the relationship between soil aggregate stability and surface runoff is affected by a variety of factors, such as climatic conditions, vegetation cover, land use practices, soil texture, and environmental factors (rainfall intensity, temperature, and humidity), which increases the difficulty of studying this relationship. Therefore, future studies should further examine the mechanism of surface runoff erosion affected by soil aggregates, especially the dispersion, transport, and deposition of aggregates during rainfall erosion. Strengthening the research on the formation and stabilization mechanisms of soil aggregates, as well as carrying out more field experiments and simulations, will help gain a deeper understanding of the relationship between soil aggregate stability and surface runoff and provide scientific bases for work on agricultural production and soil and water conservation.

4. Conclusions and Prospects

Using bibliometric visualization software, this study conducted a bibliometric analysis of the application of soil amendments to improve soil infiltration and storage capacity over the past two decades. The following conclusions were drawn:
(1)
The number of research publications on the application of soil amendments in improving soil infiltration and storage capacity during the period of 2004–2023 generally shows an upward trend. In China, research on the application of soil conditioners to improve soil structure and soil hydraulic properties is dominated by the Chinese Academy of Sciences, the Chinese Academy of Agricultural Sciences, Northwest Agriculture and Forestry University, and Shantou University, with these institutions making great contributions to this field. The USA holds the leading position in terms of research on the reduction in soil runoff and erosion, with the Agricultural Research Service, University of Arkansas, and Purdue University making the greatest contributions. China and the USA show the closest cooperation with other countries in various fields of research.
(2)
The current research hotspots in this field mainly include soil aggregates and aggregate stability, soil nutrients and fertility, soil microorganisms, soil pore properties, organic amendments, and biochar.
(3)
Future research should focus on studying the long-term effects of porous materials, including biochar, on the productivity of reclaimed soils and the growth of crops when used as soil amendments to improve soil infiltration and storage capacity. Additionally, future research should further explore the effects of the interactions between soil aggregates and surface runoff, particularly the processes of aggregate dispersion, transportation, and deposition during rainfall erosion, and clarify the key factors affecting their changes.
In this study, Web of Science Core Collection (WOSCC), a comprehensive database with the longest time span, complete collection files and systematic multidisciplinary reviews, as the data source for the literature search, providing high-quality data support for this study. However, it should be noted that the inclusion of literature in WOSCC may be affected by factors such as language preferences, subject coverage, and journal coverage, resulting in certain incomplete or biased data in specific fields. In addition, differences in citation habits and publication frequency across disciplines may also affect the objectivity of the results.

Author Contributions

Writing—original draft preparation, X.J.; writing—review and editing, X.S., L.Z. and J.M.; funding acquisition, X.S. and J.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was financially supported by the National Natural Science Foundation of China (52379044), and the Central Government-Guided Local Science and Technology Development Fund Project (YDZJSX20231A016).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The data presented in this study are available in the article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Agriculture 15 00691 g001
Figure 1. Number of published studies on the use of soil amendments to improve soil structure from 2004 to 2023.
Figure 1. Number of published studies on the use of soil amendments to improve soil structure from 2004 to 2023.
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Figure 2. Research institutions using soil amendments to improve soil structure from 2004 to 2023. Note: The thickness of the connecting lines represents the closeness of cooperation between institutions, with thicker lines indicating closer cooperation between institutions. The size of the nodes represents the number of papers published by the author’s institution; the same as below.
Figure 2. Research institutions using soil amendments to improve soil structure from 2004 to 2023. Note: The thickness of the connecting lines represents the closeness of cooperation between institutions, with thicker lines indicating closer cooperation between institutions. The size of the nodes represents the number of papers published by the author’s institution; the same as below.
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Agriculture 15 00691 g003
Figure 3. The national cooperative network for research on the use of soil amendments to improve soil structure from 2004 to 2023. Note: The color of the connecting lines represents the closeness of cooperation between countries, with darker colors indicating closer inter-agency cooperation; the same as below.
Figure 3. The national cooperative network for research on the use of soil amendments to improve soil structure from 2004 to 2023. Note: The color of the connecting lines represents the closeness of cooperation between countries, with darker colors indicating closer inter-agency cooperation; the same as below.
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Agriculture 15 00691 g004
Figure 4. Co-occurrence network of keywords in the study of soil amendments used to improve soil structure from 2004 to 2023. Note: Keyword co-occurrence is manifested as the appearance of correlation curves between circular nodes, with different colors representing different clusters of nodes and nodes of the same color constituting duplicate clusters; the same as below.
Figure 4. Co-occurrence network of keywords in the study of soil amendments used to improve soil structure from 2004 to 2023. Note: Keyword co-occurrence is manifested as the appearance of correlation curves between circular nodes, with different colors representing different clusters of nodes and nodes of the same color constituting duplicate clusters; the same as below.
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Agriculture 15 00691 g005
Figure 5. Number of research papers on the use of soil amendments to improve soil hydraulic properties from 2004 to 2023.
Figure 5. Number of research papers on the use of soil amendments to improve soil hydraulic properties from 2004 to 2023.
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Agriculture 15 00691 g006
Figure 6. Research institutions using soil amendments to improve soil hydraulic properties from 2004 to 2023.
Figure 6. Research institutions using soil amendments to improve soil hydraulic properties from 2004 to 2023.
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Agriculture 15 00691 g007
Figure 7. National cooperative network for research on the use of soil amendments to improve soil hydraulic properties from 2004 to 2023.
Figure 7. National cooperative network for research on the use of soil amendments to improve soil hydraulic properties from 2004 to 2023.
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Agriculture 15 00691 g008
Figure 8. Research on the use of soil amendments to improve soil hydraulic properties from 2004 to 2023.
Figure 8. Research on the use of soil amendments to improve soil hydraulic properties from 2004 to 2023.
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Figure 9. Number of research papers on the use of soil amendments to reduce soil runoff and erosion from 2004 to 2023.
Figure 9. Number of research papers on the use of soil amendments to reduce soil runoff and erosion from 2004 to 2023.
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Agriculture 15 00691 g010
Figure 10. Research institutions using soil amendments to reduce soil runoff and erosion from 2004 to 2023.
Figure 10. Research institutions using soil amendments to reduce soil runoff and erosion from 2004 to 2023.
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Agriculture 15 00691 g011
Figure 11. National cooperative network for research on the use of soil amendments to reduce soil runoff and erosion from 2004 to 2023.
Figure 11. National cooperative network for research on the use of soil amendments to reduce soil runoff and erosion from 2004 to 2023.
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Agriculture 15 00691 g012
Figure 12. Co-occurrence network of keywords in the study of the use of soil amendments to reduce soil runoff and erosion from 2004 to 2023.
Figure 12. Co-occurrence network of keywords in the study of the use of soil amendments to reduce soil runoff and erosion from 2004 to 2023.
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Table 1. Keyword emergence analysis of soil amendments for soil structure improvement studies.
Table 1. Keyword emergence analysis of soil amendments for soil structure improvement studies.
KeywordsStrengthBeginEnd2004–2023
compost6.1220052011Agriculture 15 00691 i001
amendments4.2520052013Agriculture 15 00691 i002
structural stability4.1120052014Agriculture 15 00691 i003
organic amendment3.4120052006Agriculture 15 00691 i004
arbuscular mycorrhizal fungi3.1320052006Agriculture 15 00691 i005
tillage6.420062014Agriculture 15 00691 i006
erodibility4.720072011Agriculture 15 00691 i007
erosion4.5720072012Agriculture 15 00691 i008
decomposition3.320072010Agriculture 15 00691 i009
nitrogen3.1720072008Agriculture 15 00691 i010
dynamics320072011Agriculture 15 00691 i011
aggregate stability9.9420082013Agriculture 15 00691 i012
chemical property4.0920112016Agriculture 15 00691 i013
organic matter3.320112015Agriculture 15 00691 i014
charcoal6.7220132017Agriculture 15 00691 i015
soil quality6.1120132018Agriculture 15 00691 i016
black carbon5.1620132017Agriculture 15 00691 i017
size5.4420172021Agriculture 15 00691 i018
soil amendment4.4320172019Agriculture 15 00691 i019
waste3.820172019Agriculture 15 00691 i020
plant growth7.1420182021Agriculture 15 00691 i021
water retention5.420182019Agriculture 15 00691 i022
pyrolysis4.6320182021Agriculture 15 00691 i023
quality3.3920182019Agriculture 15 00691 i024
yield3.0220182019Agriculture 15 00691 i025
remediation4.5520192021Agriculture 15 00691 i026
porosity3.8120192020Agriculture 15 00691 i027
plant4.5320202023Agriculture 15 00691 i028
productivity4.4520202023Agriculture 15 00691 i029
retention4.220202023Agriculture 15 00691 i030
microbial biomass3.9520202021Agriculture 15 00691 i031
plant available water3.4920202021Agriculture 15 00691 i032
responses3.4820202023Agriculture 15 00691 i033
heavy metals3.0620202023Agriculture 15 00691 i034
biochar5.3420212023Agriculture 15 00691 i035
crop yield4.0520212023Agriculture 15 00691 i036
density3.2320212023Agriculture 15 00691 i037
Note: Agriculture 15 00691 i038 stripes indicate the years in which the keyword did not appear, Agriculture 15 00691 i039 stripes indicate the time interval from the year in which the keyword first appeared to 2023, and Agriculture 15 00691 i040 stripes indicate the time period in which the keyword exploded and gained the strongest attention; the same as below.
Table 2. Keyword outburst analysis of soil amendments used to improve soil hydraulic properties.
Table 2. Keyword outburst analysis of soil amendments used to improve soil hydraulic properties.
KeywordsStrengthBeginEnd2004–2023
fertilizer3.4420082011Agriculture 15 00691 i041
manure3.3820082009Agriculture 15 00691 i042
coal fly ash3.1220082010Agriculture 15 00691 i043
soil amendment3.7420092014Agriculture 15 00691 i044
management4.8120102017Agriculture 15 00691 i045
black carbon4.7520102017Agriculture 15 00691 i046
tillage4.7220102016Agriculture 15 00691 i047
charcoal4.3920102014Agriculture 15 00691 i048
organic matter4.0120102014Agriculture 15 00691 i049
chemical property3.1720102017Agriculture 15 00691 i050
soil hydraulic properties3.0220132018Agriculture 15 00691 i051
soil5.1420192021Agriculture 15 00691 i052
reclamation3.7620202023Agriculture 15 00691 i053
plant available water3.2220202021Agriculture 15 00691 i054
biochar3.2620212023Agriculture 15 00691 i055
Table 3. Keyword outburst analysis of soil amendments used to reduce soil runoff and erosion.
Table 3. Keyword outburst analysis of soil amendments used to reduce soil runoff and erosion.
KeywordsStrengthBeginEnd2004–2023
energy3.7720062011Agriculture 15 00691 i056
polymers3.0820062009Agriculture 15 00691 i057
losses3.5520112012Agriculture 15 00691 i058
surface runoff4.7320162020Agriculture 15 00691 i059
aggregate stability3.5320182019Agriculture 15 00691 i060
impact3.6120192023Agriculture 15 00691 i061
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Ju, X.; Sun, X.; Zheng, L.; Ma, J. Bibliometric Analysis of the Application of Soil Amendments in Improving Soil Infiltration and Storage Capacity over the Last 20 Years. Agriculture 2025, 15, 691. https://doi.org/10.3390/agriculture15070691

AMA Style

Ju X, Sun X, Zheng L, Ma J. Bibliometric Analysis of the Application of Soil Amendments in Improving Soil Infiltration and Storage Capacity over the Last 20 Years. Agriculture. 2025; 15(7):691. https://doi.org/10.3390/agriculture15070691

Chicago/Turabian Style

Ju, Xiaolan, Xihuan Sun, Lijian Zheng, and Juanjuan Ma. 2025. "Bibliometric Analysis of the Application of Soil Amendments in Improving Soil Infiltration and Storage Capacity over the Last 20 Years" Agriculture 15, no. 7: 691. https://doi.org/10.3390/agriculture15070691

APA Style

Ju, X., Sun, X., Zheng, L., & Ma, J. (2025). Bibliometric Analysis of the Application of Soil Amendments in Improving Soil Infiltration and Storage Capacity over the Last 20 Years. Agriculture, 15(7), 691. https://doi.org/10.3390/agriculture15070691

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