Bibliometric Mapping of Soil Chemicalization and Fertilizer Research: Environmental and Computational Insights

Abstract

Soil chemicalization, involving the use of synthetic chemicals like fertilizers, pesticides, and herbicides, has been crucial in modern agriculture but has raised concerns about soil degradation, environmental pollution, and long-term sustainability. Over the past few decades, research has evolved from studying the effects of heavy metals and pesticides to exploring emerging contaminants such as microplastics, biochar, and oxidative stress in soils. Despite this growing body of research, gaps remain in understanding long-term trends, shifts in research priorities, and dynamics of scientific contributions. Notably, bibliometric analyses specifically focused on soil fertilizer research and associated agricultural practices remain scarce and poorly represented in the scientific literature. This bibliometric study examines the development of soil chemicalization research from 1975 to 2025, using data from the Web of Science to analyze scientific output, international cooperation, and thematic patterns. Citation impact peaked in 2018, although recent declines reflect citation lag. China led in total output (1977 documents) but lagged in population-adjusted productivity compared to the U.S. and Australia. Thematic shifts moved from studies on heavy metals and pesticides to research on microplastics, biochar, and oxidative stress, with sustainable soil management becoming a critical focus. Keyword clusters emphasized agricultural sustainability, pollutant toxicity, and bioremediation. Leading institutions included Nanjing Agricultural University, while journals like Science of the Total Environment and Chemosphere led in publications. Challenges remain in evaluating the long-term ecological effects, optimizing sustainable alternatives, and addressing regional disparities. Future research should focus on integrated soil health assessments, emerging contaminants, and policy-driven approaches to minimize environmental risks while sustaining agricultural productivity.

1. Introduction

Soil represents a complex environment where interconnected processes determine nutrient availability for plant growth. Plants require approximately 18 essential nutrients, with soil quality influenced by both inherent composition and human management practices [1,2]. Microbial activity plays a central role in these processes, affecting plant development, crop yield, and overall production potential [3,4]. To meet the demands of a growing global population, fertilizers have evolved from basic organic substances to sophisticated products including synthetic nitrogen, phosphatic, and potassium-based formulations [3,5,6]. However, while chemical fertilizers have significantly increased agricultural productivity, they present substantial challenges including environmental threats, finite resource availability, and soil quality decline [4,5]. Modern innovations such as slow-release formulations, stabilized nitrogen fertilizers, and nano fertilizers reflect a shift toward more sustainable and efficient practices that balance productivity with environmental stewardship [3].

Soil enzymes serve as sensitive indicators of soil quality changes, playing key roles in nutrient cycling and providing insights into microbial activity [6,7,8]. These enzymes are influenced by both management practices and environmental contaminants, with pollutants such as heavy metals altering biological processes within the soil [9]. The extensive use of chemical fertilizers has triggered serious environmental and health concerns, as overapplication contributes to soil degradation, water contamination, greenhouse gas emissions, and eutrophication of aquatic ecosystems. Chemical residues in water and food pose health hazards including endocrine disruption and toxicity. Addressing these challenges requires sustainable alternatives such as biofertilizers and precision farming techniques to preserve soil fertility, minimize environmental impact, and safeguard food security without endangering ecosystem health or public well-being [10,11].

Recognition of long-term environmental consequences from intensive fertilizer use emerged from several landmark studies spanning multiple decades, as identified through our bibliometric analysis of the most-cited foundational works (1975–2000). Early research established soil organic carbon decline as a primary concern in continuous cropping systems [12], while comprehensive assessments revealed food chain contamination risks from heavy metals accumulated through fertilizer applications [13]. Foundational studies on soil microbial responses to chemical inputs [14] and long-term enzyme activity changes [15] demonstrated that soil biological systems serve as sensitive indicators of chemical stress. Parallel research revealed plant detoxification mechanisms [16] and biodegradation pathways [17] that form the basis for understanding plant–soil–chemical interactions under intensive agricultural management.

Soil chemicalization research has transitioned from identifying pollutants to understanding their biochemical impacts and developing sustainable solutions. Initially focused on heavy metals and pesticide residues, concerns about food safety emerged in the late 20th century. By the 2000s, studies began exploring molecular mechanisms of soil pollution and microbial responses. More recently, sustainability efforts have centered on biochar and nanofertilizers to improve soil health while minimizing environmental harm. The rise of novel contaminants like microplastics has broadened the scope, emphasizing the need for innovative strategies that balance agricultural productivity with ecological sustainability [18,19,20,21].

Bibliometric analysis has emerged as a powerful methodological tool for mapping research landscapes in agricultural and environmental sciences, revealing knowledge structures, collaboration patterns, and thematic evolution across diverse domains. Recent applications within soil science have examined organic carbon components, soil erosion modelling, and related processes, demonstrating the methodology’s capacity to identify research hotspots, institutional leadership, and temporal transitions from fundamental to applied research [22,23]. Bibliometric investigations have proliferated in adjacent areas including heavy metal phytoremediation, biochar applications, and climate-agriculture interactions, with studies utilizing VOSviewer and CiteSpace to map publication trends, international collaborations, and emerging research frontiers [24,25,26]. Comprehensive analyses spanning multiple soil science journals have documented the field’s evolution from soil fertility-focused investigations to problem-oriented research centered on ecological environments [27]. Despite this methodological expansion across related domains, a comprehensive bibliometric analysis specifically examining the integrated landscape of soil chemicalization and fertilizer research encompassing heavy metals, pesticides, emerging contaminants, and sustainable alternatives remains absent from the literature, representing the critical knowledge gap this study addresses.

Despite the growing global concern over soil fertilization and its environmental impact, systematic bibliometric analyses specifically examining soil chemicalization research remain critically underrepresented in the scientific literature. While bibliometric studies have thoroughly examined related agricultural domains such as soil organic carbon components [22], soil erosion modelling [23] or soil stabilization research [28], precision agriculture applications and geostatistical methods [29], agricultural drone technologies and their implementation patterns [30], sustainability transitions within agrifood systems [31], and machine learning applications in sustainable agriculture [32], no comprehensive analysis has mapped the evolution of soil fertilizer research, identified key scientific contributors and collaboration patterns, or tracked the emergence of sustainable technologies in this field. This knowledge gap limits our understanding of how research priorities have shifted from early contamination studies to current sustainability-focused approaches, hindering evidence-based planning for future research directions.

This research aims to provide an in-depth bibliometric evaluation of the soil fertilizer field and associated practices, focusing on the research landscape, pivotal bibliometric parameters, and the rise of novel technologies. By utilizing machine learning techniques, the analysis will trace the development of soil fertilizer research and assess its implications on environmental and human health. The aim is to provide a nuanced understanding of how fertilizer use has evolved, highlighting the impact of various innovations and shifts in research priorities. This comprehensive analysis will offer valuable insights for improving fertilization practices and guiding future research directions in sustainable agriculture.

2. Materials and Methods

In this bibliometric analysis, a combination of software programs was utilised to achieve optimal results. The primary program employed in this analysis was VOSviewer (version 1.6.20, released on 31 October 2023) [33,34], which is indispensable for conducting bibliometric analyses. It facilitates the creation of bibliometric maps that allow for the visualisation of bibliometric data, as well as the export of essential data that was subsequently processed using Microsoft Excel. The third program employed in this bibliometric analysis was R-Studio, an integrated development environment for R, a language frequently used for statistical analyses. R was utilized through the Bibliometrix package (version 5.0.0), aided by the Biblioshiny web interface [35,36].

The strategy for the literature search was designed to identify relevant documents in the field under investigation. The search was conducted in the Web of Science (WoS) Core Collection database, which is recognised for its extensive coverage of high-quality scientific literature. We chose to use only the WoS Core Collection for this study to ensure reliable and consistent results. Multiple databases often have different ways of organizing information, counting citations, and categorizing publications, which can create problems when trying to combine their data. These differences make it difficult to compare findings accurately and can lead to misleading conclusions. The WoS Core Collection provides uniform data collection methods and standardized information formats across all publications. This consistency is particularly important for bibliometric studies because it allows us to make reliable comparisons between countries, institutions, and research themes. Using one well-established database also simplifies the analysis process and reduces the chance of technical errors that commonly occur when merging different data sources. This approach ensures that our findings reflect true patterns in soil chemicalization research rather than differences in how various databases collect and organize their information.

To ensure comprehensive coverage and minimize false positives, a structured search strategy was developed incorporating keywords organized into five thematic categories (

Table 1. Structured search strategy and thematic keyword categories used for literature retrieval.

Category	Focus	Terms	Example Keywords
A. Chemicalization	Agricultural chemical inputs and management	13	Chemicalization OR “soil chemicalization” OR “chemical fertiliz*” OR “agrochemical*” OR “soil treatment*” OR “soil amendment*” OR “soil management” OR “agricultural chemical*” OR “chemical input*” OR pesticid* OR herbicid* OR “mineral fertiliz*” OR “organic fertiliz*”
B. Biological Indicators	Soil enzymatic and microbial activity	19	enzym* OR “soil enzym*” OR “enzymatic” OR “enzyme activity” OR “biological activity” OR “soil biology” OR “soil biochemistry” OR “microbial activity” OR dehydrogenase OR phosphatase OR catalase OR “soil quality” OR “soil health” OR “soil degradation” OR “agricultural impact*” OR “environmental stress” OR “soil pollution” OR “soil contamination” OR “abiotic stress”
C. Climate	Climate change and related factors	11	“climate change*” OR “global warming” OR “climate warming” OR “greenhouse effect*” OR “climate impact*” OR “climatic factor*” OR “temperature change*” OR “precipitation change*” OR “drought stress” OR “weather extreme*” OR “climate extreme*”
D. Pollution	Environmental and soil contamination	11	“environmental pollution” OR “soil pollution” OR “agricultural pollution” OR “chemical pollution” OR “heavy metal*” OR “toxic substance*” OR “pollutant*” OR “contamina*” OR “xenobiotic*” OR “ecological damage” OR “environmental degradation”
E. Environmental Impact	Anthropogenic effects and assessment	10	“environmental impact*” OR “anthropogenic impact*” OR “human impact*” OR “environmental stress*” OR “environmental pressure*” OR “environmental risk*” OR “ecological impact*” OR “ecosystem change*” OR “environmental quality” OR “environmental assessment”

Search logic: (A) AND (B) AND [(C) OR (D) OR (E)]. *, truncation operator, facilitating the inclusion of all variants of a word.

), where categories A and B were required (AND operator) and at least one environmental dimension (C, D, or E) was mandatory (OR operator).

The Boolean operator ‘AND’ was employed to restrict the results to articles containing terms from all categories, thus ensuring thematic relevance. The ‘OR’ operator was used to expand the search within each category to include synonyms and related terms. Quotation marks were employed to search for exact expressions, while the asterisk (*) functioned as a truncation operator, facilitating the inclusion of all variants of a word (e.g., fertiliz* includes fertilization, fertilizer, fertilize, etc.). Figure 1 illustrates our systematic approach to developing and refining the search strategy.

Data were extracted from the WoS Core Collection database on 18 January 2025. While our temporal scope spans 1975–2025, it is important to note that 2025 data represent a partial-year snapshot captured at the time of extraction, containing only publications indexed through mid-January 2025. The inclusion of this partial 2025 data was deemed valuable for capturing the most recent research trends, while acknowledging the inherent limitation that publication and citation count for 2025 are necessarily incomplete. This temporal specification ensures reproducibility, as researchers accessing the same database query on the specified extraction date would obtain identical results.

The network collaboration map and keyword co-occurrence maps were created using VOSviewer version 1.6.20, using the following parameters: layout and clustering techniques with association strength normalization (default method), clustering resolution set to 1.0 with minimum cluster size of 1, default layout parameters, and inclusion thresholds of minimum 10 documents for countries and minimum 100 occurrences for keywords. In the collaboration network map, the node size represents the number of documents published by each country, meaning that countries with a higher number of publications are depicted with larger nodes. In the keyword co-occurrence map, the node size reflects the number of occurrences of a specific keyword, so words with a higher occurrence are represented by larger nodes. The colour of the nodes indicates their belonging to a specific cluster. Items within the same cluster have a collaborative relationship (in the case of country collaboration) or a co-occurrence relationship (in the case of keyword co-occurrence). The thickness of the line connecting two nodes represents the strength of this relationship. For country-level metrics, keyword co-occurrence network, and country collaboration network, full counting methodology was employed. In full counting, every multi-authored document is fully credited to all participating countries. For example, a single paper co-authored by researchers from China, the USA, and India would be counted as one publication for each of these countries.

To assess the robustness of network structure to parameter selection, we conducted sensitivity analysis by varying the minimum keyword occurrence threshold (20, 50, 100, and 150 occurrences). The 100-occurrence threshold was selected for primary analysis as it balanced network interpretability with thematic comprehensiveness, yielding 151 keywords organized into four distinct clusters. Sensitivity analysis confirmed that core thematic groupings remained stable across thresholds (cluster count: 3–5; Supplementary Table S1, Supplementary Figure S1).

Data on publication trends, country-specific citation dynamics, journal impact (bibliometric data), institutional leadership, institutional publication metrics, and publication citation metrics were extracted and exported from Bibliometrix. The resulting charts were generated in Excel for improved readability. Country-specific metrics, including the number of publications, citations, and TLS (Total Link Strength), were exported from VOSviewer version 1.6.20 and subsequently analysed in Excel.

Population-adjusted productivity metrics (Docs/Million Population) were calculated using 2024 population data obtained from the World Bank World Development Indicators database. The calculation applied the formula: (Number of documents ÷ Population) × 1,000,000 to derive documents per million inhabitants for each country [37].

The changing dynamics of scientific knowledge over time are illuminated by thematic evolution maps, which, through co-word analysis and clustering in Bibliometrix, visually represent the evolution of research topics, highlighting shifts in focus and the rise and decline of specific areas within a field. Temporal periods for thematic evolution analysis were determined using statistical change point detection on annual publication data (1975–2024) to replace subjective periodization with data-driven segmentation. The PELT (Pruned Exact Linear Time) algorithm was applied using the ruptures package in Python version 3.12.3, testing multiple penalty parameters (1–5) to assess robustness. Statistical analysis identified two robust breakpoints: 2005 (detected across all penalty settings) and 2015 (detected in 4/5 penalty settings), corresponding to fundamental shifts in research productivity patterns. Mann-Whitney U tests confirmed significant differences between periods defined by these breakpoints (p = 0.000001 and p = 0.000142, with effect sizes of 4.16 and 1.94 respectively) (Supplementary Table S2). For this analysis, the following additional parameters were applied: a maximum of 250 words analyzed, minimum cluster frequency per thousand documents set to 5, inclusion index weighted by word occurrences with minimum weight index of 0.1, maximum of 3 labels per cluster, and clustering performed using the Walktrap algorithm. The Walktrap algorithm operates on the premise that random walks become confined within highly connected network subgraphs corresponding to communities, demonstrating particular effectiveness in bibliometric network analysis [38]. Temporal distribution of trending topics analysis employed a minimum word frequency of 3 occurrences per year.

Rigorous bibliometric analysis is dependent on accurate term normalization for harmonising variations in expression and maintaining data consistency. While names can be manually standardized due to their lower number (e.g., resolving United Kingdom and Wales), processing an extensive dataset of over 30,000 keywords necessitated an automated approach. The implementation of a normalization script written in Python was developed (Supplementary File S1), with a focus on a specialized thesaurus generator designed to enhance the analysis of keyword trends and the study of thematic evolution (Figure 2). The generator employs character-level TF-IDF vectorization with n-grams and cosine similarity metrics, in combination with comprehensive text preprocessing, to identify and cluster semantically and lexically related terms. The system processes data in memory-efficient batches, with each cluster designating the shortest term as the canonical representation. To demonstrate the impact of our thesaurus-based normalization approach, we provide a comparative keyword co-occurrence network map without normalization as Supplementary Figure S1, illustrating the fragmentation and imbalanced clustering that occurs when plural forms, spelling variants, and semantically equivalent terms remain unconsolidated. This process results in the creation of a standardized thesaurus that is compatible with VOSviewer, while implementing garbage collection and duplicate filtering for optimal performance.

3. Results

3.1. Literature Overview

The WoS database encompasses documents published in this field since 1975. However, the annual publication rate of documents varied significantly over time. The temporal distribution of publications demonstrates three clearly defined phases of scientific productivity. During this initial phase (1975–1990), research output remained relatively modest, with annual publication rates fluctuating between 2 and 9 documents. A significant shift occurred in 1991, marking the beginning of sustained scientific interest in the field. There was a marked increase in the number of annual publications (30–100 papers per annum) until 2004. Subsequent to 2005, the field entered a period of substantial growth, with peak productivity being achieved in 2024 with the publication of 1077 documents. This steady increase reflects the transformation of soil science into a central pillar of global sustainability research, coinciding with technological breakthroughs in AI/machine learning integration [22,39] and advanced spectroscopic methods that reduced analysis costs, while increasing sample throughput exponentially [35]. The growth temporally aligns with major policy initiatives including the UN’s International Year of Soils (2015) and the 4 per 1000 climate initiative, which positioned soil research as a critical component of global climate mitigation efforts [40]. Figure 3 illustrates the annual publication trends, highlighting the dynamic evolution of scientific productivity in this field from 1975 to 2024.

Soil chemistry and environmental impacts have been central themes of numerous research publications over the past five decades. A bibliometric analysis of these works reveals distinct trends in citation impact across different periods. During the initial phase (1975–1989), citation impact was relatively modest despite long citation windows, with mean citations per year ranging from 0.07 to 1.62 and peaking in 1989 at 1.62. The 1990–1999 period marked a notable increase in citation rates, followed by sustained elevated levels from 2000 to 2017, even as citation windows gradually shortened. The 2018–2021 period saw the highest citation impact, with MeanTCperYear peaking at 6.09 in 2021. However, the 2022–2025 period experienced a decline in citation rates, attributed to the citation lag effect. The 2021 citation peak reflected the convergence of multiple research breakthroughs, as biochar research evolved from less than 100 publications in 2010 with new application methods gaining attention since [41]. Simultaneously, comprehensive toxicity assessments gained prominence with studies documenting the combined effects of heavy metals and pesticides on agricultural ecosystems [42], developments that occurred alongside policy frameworks like the European Green Deal positioning sustainable soil management as central to climate neutrality goals [43]. This convergence enabled highly-cited synthesis studies that established biochar’s multifunctional applications beyond carbon storage and comprehensive reviews of plant growth-promoting rhizobacteria as sustainable alternatives to chemical fertilizers [44,45]. These trends in citation impact over time are visualized in Figure 4.

3.2. Global Scientific Productivity in Soil Chemicalization

Of the 144 countries that participated in the scientific production in the field of soil chemicalization, the top country, China, leads in terms of number of documents (1977) and total citations (62,597), with a significant total link strength (1168). However, its average citations per document (31.66) and documents per million inhabitants (1.40) are relatively low. The United States, in second place, demonstrated a higher average citations per document (52.13) and population-adjusted productivity (3.75 documents per million), indicating a focus on both research quality and efficiency. China’s rapid ascent to research leadership temporally coincided with the comprehensive Soil Pollution Prevention and Control Action Plan (2016) and strategic policy initiatives that established research priorities for soil contamination management and sustainable agriculture [46,47]. India, with 1067 documents and 33,950 citations, exhibited lower average citations (31.82) and population-adjusted productivity (0.74 documents per million), suggesting a need for further development in this area. European nations, including France and Italy, demonstrated moderate population-adjusted productivity, aligning with their smaller populations but robust research infrastructures.

Table 2. Key metrics of scientific productivity in soil chemicalization by country (1975–2025).

Country	Documents	Citations	Average Citations/Document	Docs/Million Population	TLS
China	1977	62,597	31.66	1.40	1168
USA	1276	66,516	52.13	3.75	1050
India	1067	33,950	31.82	0.74	673
Spain	488	17,073	34.99	10.00	414
Germany	486	26,287	54.09	5.82	692
Brazil	469	12,941	27.59	2.21	265
France	447	20,892	46.74	6.52	474
Italy	442	17,900	40.50	7.49	411
Pakistan	311	12,003	38.59	1.24	520
Australia	290	18,790	64.79	10.66	490

TLS, total link strength, a value associated with each country, indicated the measure of country co-authorship strength.

includes the number of documents, total citations, and average citations per document, which are essential metrics for evaluating scientific productivity.

The evolution of country-specific contributions demonstrates a substantial shift in global research leadership. Historically, the United States dominated soil chemicalization research, contributing the most publications until the early 2010s. However, China’s rapid ascent, particularly post-2019, reflects its strategic investment in agricultural and environmental research. Figure 5 demonstrates the evolution over time of country scientific production. The rankings of the most prolific nations are subject to variation due to the divergent methodologies employed by VOSviewer and Bibliometrix in the calculation of document affiliations. Bibliometrix assigns articles to countries based on the affiliations of all authors, a process which can result in a single document being attributed to multiple countries if it is co-authored internationally. The use of full counting in this analysis accentuates both the productivity and the collaboration intensity of highly international research leaders. This effect is particularly evident for countries such as China (1977 documents, TLS: 1168) and the USA (1276 documents, TLS: 1050), whose extensive international partnerships yield higher publication counts and link strengths than would appear under fractional counting. While this approach does not allocate precise productivity shares, it supports our study’s objective of mapping global research partnerships.

3.3. Academic Influence and Impact of Journals

A total of 1794 sources were identified, having published documents captured by the search algorithm. Science of the Total Environment demonstrates remarkable impact with the highest number of documents (322) and total citations (14,756), alongside a leading h-index of 63. Chemosphere follows as the second most influential journal, with 240 documents and 11,563 citations, maintaining a strong h-index of 59. The productivity-to-impact ratio is particularly notable in Environmental Science and Pollution Research, which produced 264 documents garnering 8525 citations, though its h-index (42) suggests a more moderate overall impact. Older journals like Environmental Pollution and Science of the Total Environment dominate cumulative metrics (TC, H-index), while younger journals like Agronomy-Basel (2013) and Journal of Hazardous Materials (2007) exhibit competitive M-indices (1.615 and 1.737 respectively), signalling rising influence.

Table 3. Bibliometric indicator of leading journals in the field of soil chemicalization (1975–2025).

Source	h_Index	g_Index	m_Index	Total Citations	Publications	Publication Start
SCIENCE OF THE TOTAL ENVIRONMENT	63	108	1.8	14,756	322	1991
CHEMOSPHERE	59	94	1.788	11,563	240	1993
ENVIRONMENTAL POLLUTION	50	77	1.282	7615	185	1987
ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY	49	82	1.633	8411	198	1996
ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH	42	80	1.448	8525	264	1997
JOURNAL OF ENVIRONMENTAL MANAGEMENT	35	65	1.667	4459	96	2005
JOURNAL OF HAZARDOUS MATERIALS	33	52	1.737	3075	98	2007
AQUATIC TOXICOLOGY	33	72	0.943	5292	89	1991
PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY	26	39	0.531	1891	100	1977
AGRONOMY-BASEL	21	40	1.615	1862	112	2013

presents the bibliometric indicators for each journal.

3.4. Institutional Leadership in Soil Chemicalization Research

The data reveals a significant concentration of scholarly output within Chinese academic institutions. Nanjing Agricultural University emerges as the foremost contributor to soil chemicalization scholarship with 332 publications, followed by China Agricultural University (261 publications), Zhejiang University (201 publications), Northwest A&F University (180 publications), and South China Agricultural University (164 publications). This institutional dominance occurred alongside a coordinated national strategy that combined environmental policy mandates with unprecedented institutional expansion, including establishment of specialized colleges and research centers at major universities like China Agricultural University and Nanjing Agricultural University [48]. Figure 6 presents the most productive affiliations in the researched field.

The bibliometric analysis of document production over time indicates that Chinese institutions, although starting their publications in this field later (as shown in Figure 6), began publishing in 2003. From 2003 to 2010, the publication output was relatively modest, with fewer than 20 publications annually across all institutions, and little differentiation among the top five Chinese universities. This initial phase suggests an emerging focus on soil chemicalization research within China’s agricultural research framework. The period from 2011 to 2015 marked the onset of institutional stratification, with Nanjing Agricultural University taking an early lead in the field. The most significant expansion in research output occurred after 2015, characterized by rapid growth across all institutions. Nanjing Agricultural University maintained its leadership, experiencing particularly strong growth from 2019 onwards and reaching approximately 320 publications by 2025. Figure 7 illustrates the scientific production over time of the top five most productive institutions.

3.5. Publication Citation Analysis

A bibliometric analysis of the top 10 most influential publications in the field of soil chemicalization research reveals a pronounced thematic focus on the environmental impacts of agricultural practices and soil pollution. The highest-cited paper (Lehmann et al., 2011, 3408 citations) examines the effects of biochar on soil biota, reflecting the field’s emphasis on sustainable soil amendments. A significant portion of these highly cited works address the challenges of soil pollution from various sources, including heavy metals and pesticides (Alengebawy et al., 2021, Toxics), plastic mulching in agriculture (Steinmetz et al., 2016, Sci Total Environ), and nitrate contamination in groundwater (Rivett et al., 2008, Water Res). Other prominent themes include the role of oxidative stress in aquatic and terrestrial organisms due to environmental pollutants (Lushchak, 2011; Valavanidis et al., 2006) and the long-term benefits of organic amendments on soil fertility and carbon sequestration (Diacono & Montemurro, 2010).

Table 4. Top 10 most-cited publications in the field of soil chemicalization (1975–2025).

Paper/Source	TC	TC/Year	Normalized TC	DOI
LEHMANN J, 2011, SOIL BIOL BIOCHEM	3408	227.20	49.82	10.1016/j.soilbio.2011.04.022
BLOKHINA O, 2003, ANN BOT	2884	125.39	28.26	10.1093/aob/mcf118
LUSHCHAK VI, 2011, AQUAT TOXICOL	1883	125.53	27.53	10.1016/j.aquatox.2010.10.006
VALAVANIDIS A, 2006, ECOTOX ENVIRON SAFE	1352	67.60	16.64	10.1016/j.ecoenv.2005.03.013
RIVETT MO, 2008, WATER RES	1085	60.28	19.03	10.1016/j.watres.2008.07.020
DIACONO M, 2010, AGRON SUSTAIN DEV	1059	66.19	19.60	10.1051/agro/2009040
STEINMETZ Z, 2016, SCI TOTAL ENVIRON	1000	100.00	25.39	10.1016/j.scitotenv.2016.01.153
BACKER R, 2018, FRONT PLANT SCI	967	120.88	24.15	10.3389/fpls.2018.01473
REEVES DW, 1997, SOIL TILLAGE RES	869	29.97	14.61	10.1016/S0167-1987(97)00038-X
ALENGEBAWY A, 2021, TOXICS	858	171.60	28.19	10.3390/toxics9030042

TC, total citations; DOI, digital object identifier.

presents the most influential documents in the field of soil chemicalization published between 1975–2025.

3.6. Mapping International Scientific Partnerships in the Field of Soil Chemicalization

The analysis indicates that collaboration among authors from different countries is essential for achieving high-impact results, with technology transfer contributing to the enhancement of document quality. China emerges as the largest node with extensive red connections, signifying its status as the primary research hub in this field. The USA represents another significant hub with blue connections, indicating robust international collaboration. India, positioned between the Western and Asian specific clusters, appears to serve as a conduit between these two regions. The red cluster, under Chinese leadership, appears to consist predominantly of Asian countries, the blue cluster, led by the USA, appears to be dominated by Western countries, and the green and yellow clusters appear to include a significant proportion of European countries. This multi-polar collaboration structure facilitates global knowledge exchange and reflects the transnational nature of soil chemicalization challenges, where environmental problems transcend national boundaries and require coordinated international research efforts to develop effective solutions. Figure 8 presents the global research collaboration network in the field of soil chemicalization, for the articles identified by the search algorithm.

3.7. Soil Chemicalization Trend Evolution

As illustrated in Figure 9, the evolution of the research landscape in soil chemicalization follows three statistically validated periods determined through change point detection analysis, showing distinct thematic transitions that align with fundamental shifts in publication productivity.

The first period (1975–2004) represents the foundational phase characterized by core environmental contamination themes. Heavy metals dominated research focus alongside specific pesticide studies on lindane and atrazine, while fundamental biomarker research examined glutathione s-transferase and liver-based metabolic responses using rat models. This period also established early applications of sewage sludge and basic soil management practices.

The second period (2005–2014) marked a mechanistic transition phase where oxidative stress became the central organizing concept. Research integrated pesticide studies with broader environmental and soil quality concerns, shifting from individual contaminant identification toward understanding biological response mechanisms and their environmental implications.

The third period (2015–2024) represents the solutions-oriented acceleration phase, where soil health emerged as the primary theme alongside persistent pesticide concerns. The prominent emergence of biochar research reflects the field’s evolution toward sustainable remediation approaches, demonstrating maturation from problem identification to practical solution development. The overall thematic evolution demonstrates a clear progression from pollutant-focused research through mechanistic understanding to solution-oriented approaches, reflecting the field’s development from environmental problem documentation to sustainable intervention strategies.

3.8. Temporal Dynamics of Research Trends

The temporal evolution of topics of interest demonstrates an advancement from methods such as radioimmunoassay to more intricate immunological methods, including enzyme-linked-immunoassay and enzyme-linked-immunosorbent-assay, in addition to biochemical analysis that references cytochrome-p-450 liver microsomes and monooxygenase. This progression signifies an augmented interest in the detection of substances of interest to ascertain their impact on biological systems. Moreover, the progression has been further fueled by the emergence of increasingly sophisticated techniques for the analysis of xenobiotics and pesticides, with a particular emphasis on the study of their toxicity and degradation in the environment. The data demonstrate a marked increase in research activities related to heavy metals and the optimization of detection methods, culminating in the recent advent of nanoscale technologies. It is also important to note the parallel development of studies on test organisms such as fish, yeasts and Escherichia coli, which have allowed a better understanding of the effects of these contaminants on living systems. This evolution reflects the field’s transition from primarily analytical and detection-focused research to application-oriented studies aimed at developing practical solutions for agricultural sustainability and environmental protection.

Recent trends suggest a move towards the optimization of agricultural production and the improvement of yields, probably in response to the challenges of climate change and the need for more sustainable agriculture, while maintaining a strong focus on the monitoring and understanding of the impact of pollutants on the environment (Figure 10).

3.9. Keyword Co-Occurrence Analysis in Soil Chemicalization Research

As outlined in Figure 11, which presents the network map of keyword co-occurrence, four distinct clusters were identified. The red cluster, which is the largest, encompasses a total of 51 terms, with ‘growth’ and ‘agriculture’ being the most prevalent, with occurrences of 541 and 528, respectively. This cluster includes terms such as “yield,” “plant growth,” “sustainability,” “amendment,” “compost,” “organic matter,” “climate change,” “drought,” and “temperature.” This thematic area represents the interface between soil management practices and environmental factors, particularly focusing on sustainable agriculture in changing climate conditions. The green cluster, comprising 49 keywords, is centred around the terms ‘pesticide’ (1560 occurrences), ‘toxicity’ (803 occurrences) and ‘oxidative stress’ (855 occurrences). The cluster’s focus is evident in the prevalence of keywords such as “organophosphorus,” “chlorpyrifos,” “risk-assessment,” “herbicide,” and enzymes like “acetylcholinesterase.” This emphasis on research into the molecular and cellular impacts of agricultural chemicals, particularly pesticides, on biological systems is further highlighted by the significant presence of the terms “oxidative stress” and “detoxification pathways.” The blue cluster, comprising 28 keywords, is centered around the concept of “degradation,” with associated terms including “bioremediation,” “removal,” “microbial-degradation,” “adsorption,” and “dissipation.” This cluster emphasizes research on strategies for mitigating and remediating chemicalized soils, emphasizing both natural and engineered approaches to addressing contamination. The yellow cluster, meanwhile, is concentrated around the keyword “heavy-metal” (occurring 736 times), and “cumulation” (occurring 431 times). This cluster contains 14 keywords, the majority of which concentrate on the risk associated with heavy metals, as well as examples of heavy metal contaminants. The interconnections between these clusters reveal the increasingly interdisciplinary nature of soil chemicalization research, where agricultural sustainability, toxicity assessment, remediation strategies, and contamination studies are becoming more integrated in addressing both environmental risks and agricultural productivity challenges.

Sensitivity analysis across varying occurrence thresholds (20, 50, 100, and 150) confirmed the robustness of core thematic structures while revealing expected threshold-dependent boundary effects. Network inclusion progressively narrowed from 869 keywords at 20 occurrences to 99 keywords at 150 occurrences, with cluster count stabilizing between 3–5 across all thresholds (Supplementary Table S1). High-occurrence keywords including “pesticide”, “degradation”, “oxidative stress”, and “heavy-metal” maintained their central network positions across all parameter settings. Core thematic groupings—pesticide-toxicity associations (red cluster), degradation-remediation themes (blue cluster), and agricultural sustainability concepts (green cluster) persisted across all thresholds, while the purple cluster merged at 100 occurrences and the yellow cluster consolidated at 150 occurrences, representing progressive thematic integration as peripheral keywords were excluded (Supplementary Figure S1).

4. Discussion

Early investigations into soil chemicalization, conducted from the early 1970s to the mid-1990s, yielded a limited number of publications, reflecting the nascent stage of the field. As awareness of soil degradation and its wider ecological impacts grew in the late 1990s, the number of published studies increased accordingly. This sustained growth into the early 2000s was likely driven by advancements in analytical techniques and increased funding for environmental research. The most significant expansion of the literature occurred post-2010, with a particularly pronounced increase after 2015, indicating a rapidly evolving understanding of this critical area. This era signifies a transformative transition in soil chemicalization research, propelled by growing global commitments to sustainable agricultural practices and soil conservation policies. The notable expansion in scientific inquiry corresponds with worldwide initiatives to combat soil degradation and enhance agroecosystem resilience against climate variability. The geopolitical landscape of soil chemicalization research has evolved significantly over time, reflecting changes in national research priorities and investments. The United States has shown an increased interest in this field since the early 1970s, leading the research in this area until the mid-2010s. China began to show an increased interest in this field starting in the mid-2000s, reaching the point where, by the early 2020s, it became the most prolific country in this field. This may be due to the ever-increasing interest in this country, as well as initiatives on the part of the state to carefully monitor both the methods of soil chemicalization and the increased interest in soil pollution. The increased interest in this field, both on the part of China and the rest of the contributing countries, underlines the international commitment to advancing knowledge in this field. With unique clustering patterns that demonstrate both regional relationships and cross-regional cooperation, the collaboration network map displayed an extensive web of research collaborations between nations. Collaborations between clusters demonstrate the global trend toward knowledge sharing, which is essential for advancing expertise in this field. While international collaborations across diverse countries are crucial, we cannot overlook the importance of regional collaborations, primarily represented by intra-cluster partnerships. These collaborations are significant not only in terms of shared priorities but also in addressing common challenges faced by neighboring countries, which are geographically close to one another.

The research on soil chemicalization and its environmental impacts has undergone a significant evolution, progressing from basic identification of contaminants to complex, interdisciplinary approaches addressing climate change and human health. In the 1990s to early 2000s, studies primarily focused on identifying specific contaminants (especially heavy metals and agricultural pollutants) as highlighted by McLaughlin et al. (1999) [13] that raised concerns about the risk of heavy metals and food safety. While other researchers focused on understanding basic degradation mechanisms of soil pollutants, with a highly influential paper on this subject published by Spain (1995) [17]. As suggested by the explored subjects this era set the groundwork for future investigations.

By the mid-2000s–2010s, there was a shift in focus towards the investigation of biochemical and molecular responses to pollution. The concept of oxidative stress became central, with studies like Valavanidis et al. (2006) [49] linking it to environmental pollutants in aquatic organisms. The early 2010s saw an escalating interest in sustainable soil management, with biochar applications becoming a focal point of research. Among the selected documents, Lehmann et al. (2011) [50] is the most cited paper. This paper highlighted biochar’s role in enhancing soil fertility and influencing microbial dynamics. This period marked an increasing awareness of the need for sustainable agricultural practices.

In more recent years, from the mid-2010s to the present, research has evolved to address emerging contaminants such as microplastics, with climate change considerations being integrated into soil management strategies. Studies like Steinmetz et al. (2016) [51] highlighted the risks of microplastic accumulation from agricultural practices like plastic mulching, revealing their persistence in soils and potential to disrupt microbial communities and nutrient cycles. Risk assessment also is becoming a central subject, Silva et al. (2019) [52] highlighting the risk of pesticides by highlighting residues in European soils. But still the focus of this period seems to be on sustainability, with documents like Alengebawy et al. (2021) [42] integrated heavy metal and pesticide risks with climate change impacts, advocating for biochar and organic amendments to sequester carbon while detoxifying soils.

The most influential research identified through our bibliometric analysis demonstrates clear pathways from fundamental discovery toward practical applications, with several breakthrough technologies establishing scientific foundations for real-world implementation. Comprehensive biochar research on soil biota interactions [50] has provided the scientific basis for understanding carbon sequestration and soil amendment mechanisms, while detailed frameworks for plant growth-promoting rhizobacteria applications [53] have established roadmaps for developing sustainable alternatives to synthetic fertilizers. Advanced research on oxidative enzymes has demonstrated significant potential for wastewater and soil treatment applications [54], and comprehensive studies on microbial degradation pathways have revealed promising approaches for bioremediation of organophosphorus compounds [55]. The practical knowledge extends to risk assessment frameworks, where systematic food safety research has established critical scientific understanding for managing heavy metal contamination in agricultural systems [13], and comprehensive pesticide residue documentation has provided essential data for environmental monitoring programs [52].

These research contributions have established robust scientific foundations that enable evidence-based decision-making and technology development across multiple domains. Advanced biosensor research has demonstrated the potential for enhanced monitoring of agricultural contaminants [56], while integrated approaches to crop productivity and resource efficiency have provided scientific frameworks for sustainable agricultural management [57]. The progression from fundamental research to applied frameworks illustrates how sustained investigation in soil chemicalization has generated the knowledge base necessary for addressing global challenges in food security, environmental protection, and sustainable agriculture, establishing the scientific foundations upon which future technological and policy innovations can be built.

Bibliometric analysis provides a robust framework for the quantitative assessment of research impact and performance. The methodology’s primary strength lies in its capacity to process and analyze vast quantities of scholarly data. This enables researchers to identify past research trends, emerging research directions, collaboration patterns, and influential works across extensive academic fields. Recognizing the inherent biases in this field is crucial, but bibliometric analysis offers a more objective framework for evaluating research than depending only on the subjective opinions of experts, especially when handling the complexity of large datasets. By using quantitative measures like publication counts, citation rates, and other derived indicators, bibliometrics provides a foundation for comparing and monitoring research output over time. Efforts to enhance open-access scholarship, along with an increasing focus on data-sharing practices, are greatly improving the accessibility of research resources. The rise of open repositories and researchers’ willingness to share their datasets are broadening the range of materials available for bibliometric analysis. This level of transparency not only empowers scholars by encouraging cooperation across disciplines but also accelerates the exchange of knowledge, thereby advancing scientific progress. Furthermore, as digital archives continue to develop and diversify, the amount and quality of data available for bibliometric research are projected to increase, making this vital research methodology more accessible to everyone.

Although integrating multiple databases may appear beneficial, it inherently introduces systematic biases due to differences in indexing policies, citation counting practices, and coverage, thereby potentially undermining analytical reliability. Conversely, relying on a single database ensures methodological consistency; however, future research should focus on developing robust strategies for integrating multiple sources to achieve a more comprehensive representation of global scientific output. Furthermore, while bibliometric analysis provides valuable insights, its scope remains limited by an overreliance on journal articles as the primary data source. Although bibliometric analysis offers important insights, its limitations arise from an overly narrow emphasis on journal articles as the main data sources. This method frequently disregards various scholarly outputs, including monographs, edited volumes, conference papers, policy documents, and raw datasets. Such omissions can skew evaluations of academic impact, especially in disciplines where alternative publication formats are significant and widely shared within academic circles. Moreover, relying solely on bibliometric indicators yields a surface-level comprehension of academic ecosystems. Statistical measures such as citation frequency and publication volume might map trends in scholarly visibility, yet they remain disconnected from the conceptual depth that drives these trends. Such metrics cannot appraise a work’s methodological robustness, creative breakthroughs, or societal value. Foundational elements including research design, paradigm-shifting innovations, or applied outcomes of discoveries are left unaddressed, preventing a nuanced appraisal of a study’s interdisciplinary reach or its capacity to inform policy, practice, or future inquiry. Additionally, when bibliometric analysis extends to examining temporal relationships between policy events and research trends, further interpretative limitations arise. Although our analysis identifies notable temporal alignments between major policy initiatives and research output patterns, these correlations cannot establish definitive causal relationships. The exponential growth trajectory characterizing soil chemicalization research creates inherent difficulties in distinguishing potential policy influences from the natural expansion dynamics of an emerging scientific field. Observed increases in publication activity following policy implementations may equally reflect ongoing scientific progression, technological developments that enhance research capacity, shifting funding landscapes, or complex interactions among multiple contributing factors.

5. Conclusions

This bibliometric analysis demonstrates that soil chemicalization research has undergone a fundamental transformation from a specialized subdiscipline to a critical component of global sustainability science. The field’s evolution reflects broader shifts in environmental awareness, technological capabilities, and international cooperation, positioning soil health as central to addressing interconnected challenges of food security, climate change, and ecosystem preservation. The emergence of distinct research clusters and collaborative networks indicates a maturing scientific community capable of addressing complex, multiscale environmental problems through coordinated international effort.

The trajectory of soil chemicalization research has evolved significantly, reflecting a shift from problem identification in the 1990s and 2000s to solution-oriented approaches in the 2010s, and now towards systems thinking in the 2020s. This evolution underscores the growing emphasis on balancing agricultural productivity with environmental sustainability, while considering climate resilience and circular economy principles. The field’s increasing interdisciplinary nature is evident, with a growing focus on producing policy-relevant science that addresses complex challenges at the intersection of soil health, climate change, and food security.

Thematic and methodological advancements have reshaped the research landscape. Early investigations focused on identifying pollutants like heavy metals and pesticides, laying the foundation for understanding soil chemistry’s ecological ramifications. By the 2000s, the field pivoted to mechanistic studies, exploring oxidative stress detoxification pathways and bioremediation strategies. Recent decades have witnessed a surge in interdisciplinary approaches, incorporating climate resilience, nanotechnology, and precision agriculture to address complex challenges such as soil salinization and the persistence of contaminants.

The identified research patterns reveal both the field’s growing sophistication and persistent knowledge gaps that limit comprehensive understanding of soil chemicalization impacts. While technological advances have enabled unprecedented analytical capabilities, the concentration of research capacity in specific geographical regions creates potential blind spots in global knowledge systems. The transition from problem identification to solution-oriented research approaches suggests the field is well-positioned to inform evidence-based policy frameworks, though greater integration between scientific findings and practical implementation remains essential for maximizing societal impact.

Recent publications demonstrate accelerating interest in advanced analytical technologies, with nanoscale analysis and computational modeling emerging as trending topics in 2020–2025. The integration of these technological approaches with policy frameworks aimed at tackling contamination and enhancing agricultural sustainability represents a clear directional shift in contemporary research priorities. Building on these observed trends, by prioritizing open-source data platforms and democratizing access to cutting-edge tools, the field can empower global stakeholders to address soil degradation with unprecedented precision.