Next Article in Journal
Safety Assessment of Honeys from Northern and Southern Algerian Regions
Previous Article in Journal
Evaluating Environmental Sustainability: The Role of Agriculture and Renewable Energy in South Korea
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Agriculture
Volume 14
Issue 9
10.3390/agriculture14091502
agriculture-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Global Trends and Current Advances in Slow/Controlled-Release Fertilizers: A Bibliometric Analysis from 1990 to 2023

by
Xianhong Li
1,2 and
Zhonghong Li
3,*
1
Hangzhou Institute of National Extremely-Weak Magnetic Field Infrastructure, Hangzhou 310028, China
2
School of Instrumentation and Optoelectronics Engineering, Beihang University, Beijing 100191, China
3
School Environment and Energy Engineering, Beijing University of Civil Engineering and Architecture, Beijing 100044, China
*
Author to whom correspondence should be addressed.
Agriculture 2024, 14(9), 1502; https://doi.org/10.3390/agriculture14091502
Submission received: 22 July 2024 / Revised: 26 August 2024 / Accepted: 30 August 2024 / Published: 2 September 2024
(This article belongs to the Section Agricultural Soils)
Browse Figures
Versions Notes

Abstract

:
Slow/controlled-release fertilizers (SRFs/CRFs) occupy a critical position in agricultural advancement, enhancing productivity and sustainability by regulating nutrient release, improving fertilizer efficiency, reducing pollution, and promoting lasting agricultural progress. To attain an in-depth understanding of the current landscape, hotspots, and development trends in SRF/CRF research, this study employed the Bibliometrix toolkit in R, VOSviewer, and CiteSpace for the statistical and graphical analysis of pertinent literature in the Web of Science Core Collection (WOSCC) database from 1990 to 2023. In this study, several dimensions were evaluated to assess the research scope and impact, including the quantity of published articles, authorship, citation frequency, keywords, institutional affiliations, publication journals, and source countries. The results indicate a significant increase in scholarly publications related to SRFs/CRFs from 1990 to 2023, totaling 1676 published papers across 77 subject categories. Research activities spanned 69 countries/regions, with China and the USA leading contributions. A total of 1691 research institutions published on SRFs/CRFs, with the University of Florida, the Chinese Academy of Sciences, and China’s Shandong Agricultural University being preeminent. HortScience, Science of the Total Environment, and Communications in Soil Science and Plant Analysis were the top three journals. Keyword co-occurrence and burst analysis disclosed that current research primarily focuses on several key areas: nitrogen (N) use efficiency, the processes of nitrification and denitrification, degradation, the use of phosphate (P) fertilizers, urea, and factors affecting crop growth and quality. The findings revealed several critical areas and trends within the sphere of SRFs/CRFs, with future research specifically directed towards developing cost-effective, efficacious, and environmentally friendly alternatives. Furthermore, future progress will concentrate on addressing the enduring environmental ramifications of SRF/CRF utilization.

1. Introduction

The growing global population has led to increased food demand, while arable land availability has diminished and soil degradation has become widespread in many regions around the world. Consequently, a substantial portion of agricultural land has been categorized as highly degraded (25%) or moderately degraded (44%), and nearly 10% is currently recovering from deterioration [1]. Soil degradation can lead to nutrient depletion, salination, and diminished food production capacity [2]. Fertilizer utilization is crucial for addressing the growing demand for sustenance and ensuring global food security, yet excessive application may lead to significant fertilizer loss and reduced fertilization efficiency [3]. Characterized by high solubility, inadequate thermal stability, and minimal molecular quantities, conventional fertilizers often lead to nutrient losses during application, as these nutrients can either infiltrate the soil surface through surface runoff, denitrification, and leaching or escape into the atmosphere as greenhouse gases [4]. Plant growth requires significant amounts of nutrients and trace elements, such as potassium (K), phosphorus (P), and nitrogen (N). Typically, crops generally absorb merely 50–60% of N and K, and only 10–25% of P [5]. Excessive fertilizer consumption not only causes fertilizer loss but also contributes to environmental pollution and poses health risks. Research has indicated that nutrient loss due to the excessive and irrational application of fertilizers has emerged as a significant source of non-point source agricultural pollution in China [6].
Researchers have proposed slow/controlled-release fertilizers (SRFs/CRFs) as a solution to the mismatch between nutrient release rates and plant absorption rates. This fertilization technique effectively controls the nutrient release rate, extends the fertilization duration, enhances fertilizer efficacy, minimizes resource wastage, and improves utilization efficiency [7]. Simultaneous SRFs/CRFs can enhance crop yield, regulate soil nutrient and mineralization properties, and optimize crop physiological parameters. Additionally, they reduce environmental pollution and energy consumption, which are vital for sustainable agricultural development. In 2010, the European Committee for Standardization (CEN) established four criteria defining SRFs/CRFs: the nutrient release rate should not surpass 15% within 24 h and 75% within 28 days. Additionally, the nutrient release rate should not be below 75% at the prescribed time, and the release pattern must align with the corresponding nutrient absorption curve. As the practical applications of SRFs/CRFs evolve, SRF/CRF types have diversified, encompassing physical, chemical, and composite categories [8]. Over recent decades, researchers have published numerous reviews on SRFs/CRFs, emphasizing their remarkable properties, such as water absorption, biodegradability, water retention, and evaporation capabilities. Liu et al. discussed hydrogel and high-hydrogel composite preparation methods and their utilization as nutrient carriers in agricultural production [9]. Beig et al. reviewed various coating materials for natural and synthetic urea, along with numerous coating processes employed to decelerate urea-nitrogen release [10]. Chen et al. assessed the preparation methods, mechanisms, and applications of SRFs/CRFs due to their favorable release properties, bonding, and additional functions [11]. Nevertheless, no studies have yet performed quantitative analyses of the existing literature on SRFs/CRFs to summarize research advancements and development trends.
Different from a literature review, which summarizes and elucidates existing knowledge within a specific field, bibliometrics employs mathematical and statistical methods to analyze the quantitative characteristics and structural attributes of scientific literature, thereby providing researchers with a detailed overview of research progress and future trends in a specific field [12]. It has been extensively used in agriculture [13], environmental engineering [14], soil sciences [15], and forestry research [16]. This study presents an in-depth and comprehensive quantitative assessment of scholarly publications pertaining to SRF/CRF research, with a focus on the time period spanning from 1990 to 2023. Using a bibliometric methodology, it aims to elucidate the current state of research and to identify the prevailing tendencies and trajectories in the field of SRF/CRF research. The objectives and contributions of this paper, expanded upon below, seek to offer valuable insights and implications for both researchers and practitioners:
  • Provide a concise overview of the predominant types of SRFs/CRFs in contemporary use while detailing the challenges associated with these specific categories of fertilizers. Additionally, it highlights potential future developments in preparation techniques and emerging materials in the field.
  • Generate and visualize the publication trends regarding the literature associated with SRFs/CRFs.
  • Examine the collaborative networks among leading groups, as characterized by their geographic distribution, prominent collaborations, and highly productive authors in the field.
  • Examine the research focus and evolution of slow-release and controlled-release fertilizers (SRFs/CRFs) from 1990 to 2023.
  • Identify current research limitations and explore potential future directions in the field of SRFs/CRFs.

2. Methodology

2.1. Database and Search Strategy

The technical roadmap of the bibliometric research is shown in Figure 1. The WOSCC database encompasses the world’s most vital and influential research literature and is universally recognized as the preeminent literature search instrument on a global scale. The search period for this paper is from 1 January 1990 to 31 December 2023, and the search was conducted on 11 January 2024, using the following search criteria: Topic = (“slow release fertilizer*” or “controlled release fertilizer*” or “sustained release fertilizer*” or “stabilized fertilizer*”), and “document type” = “ARTICLE”. Subsequent to the initial search, the publications were screened based on titles and abstracts, and articles devoid of relevance to the investigation of SRFs/CRFs were discarded. Ultimately, a total of 1676 articles pertaining to SRFs/CRFs were obtained from the WOSCC database. The data extracted from the WOSCC database were exported in a TXT file format, including “Full Record and Cited References”.

2.2. Data Analysis

Bibliometric software can assist researchers in analyzing published results and citations, facilitating discussions on the hotspots and development trends in the research field, as well as promoting academic cooperation. This study employed the Bibliometrix toolkit in conjunction with the VOSviewer (version 1.6.19) and CiteSpace (version 6.3.R1) bibliometric analysis applications. Bibliometrix (version 4.3.0), an advanced bibliometric toolkit integrated within the R language, offers a comprehensive suite of indices such as author publications, citations, and co-citations. This tool facilitates efficient and detailed analysis and visualization of scientific literature, revealing intricate academic relationships and trends [17]. VOSviewer, developed by the Science and Technology Research Center at Leiden University in the Netherlands, is a sophisticated tool that facilitates cluster analysis and the generation of knowledge graphs through the construction of co-occurrence matrices based on literature keywords, authors, institutions, and other bibliographic metadata. This application adeptly visualizes diverse clustering topics and collaborative networks in a manner that is both visually intuitive and accessible, thereby enabling researchers to identify emergent trends, hotspots, and cutting-edge developments in their field of study [18]. CiteSpace, a literature analysis software developed in Java by Professor Chen Chaomei of Drexel University, generates scientific knowledge maps that illustrate relationships within the body of literature. This innovative tool aids in tracing historical research trajectories and facilitates the comprehension of future research prospects across various fields, thereby enhancing the understanding of complex academic landscapes [19].
The amassed literature was exported in a plain text format, to be subsequently analyzed using the Bibliometrix toolkit. The quantitative examination involved the assessment of published papers, highly cited literature, research institutions, authors, and countries, with graphical representations created employing Origin 2018. VOSviewer facilitated the analysis of keyword co-occurrence networks in SRF/CRF-related research. CiteSpace was employed to investigate the keyword burst of published literature pertinent to SRFs/CRFs.

3. Results

3.1. Publication Trends

The graphical representation depicted in Figure 2 illustrates an upward trend in the annual publication of academic articles related to SRFs/CRFs, highlighting a growing scholarly interest in this field. Based on the growth pattern in article volume, the publications can be categorized into slow and high-growth stages. During the first stage from 1990 to 2012, scholarly attention towards SRF/CRF studies was comparatively limited, with the annual publication count in this research field consistently remaining below 50. Throughout this period, the growth in scholarly output was gradual, characterized by an average annual publication count of approximately 19.5 and an annual growth rate of 32.73%. In the second stage, from 2013 to 2023, the publication count of SRF/CRF studies saw a significant surge, marking a period of high growth. The number of publications increased from 37 in 2013 to 207 in 2023, with the average annual publication count escalating to approximately 111.5. This stage was characterized by an average annual increase of 17 publications. Notably, this stage accounted for 73.21% of all publications in this research field, with an impressive annual growth rate of 45.95%. Following 2013, a notable rise in researchers’ interest led to a substantial increase in published papers. SRF/CRF research became a prominent area of focus for scholars.
The origins of SRFs/CRFs date back to the 1920s, when the USA developed Achu sulfur-coated urea to address the recycling challenge posed by the by-product sulfur in the smelting industry. In 1948, K.G. Cart and colleagues in the USA synthesized urea-formaldehyde, the world’s first SRFs/CRFs, marking the onset of diversified development in this field. Countries such as Japan, the USA, Germany, the UK, and France continued advancing urea modification and SRF/CRF research. (1) Before 1960, SRFs/CRFs primarily utilized organic materials such as blood meal and bone meal to gradually supply plants with nutrients. However, the rudimentary preparation processes in place at the time posed significant challenges in achieving precise control over the release mechanisms. (2) In the 1970s, researchers explored chemical and physical methods to improve fertilizers’ slow-release properties, resulting in novel SRFs/CRFs such as phosphorylated aluminum and S-coated urea. Despite these advancements, the ability to accurately regulate release processes remained limited due to the simplistic nature of the preparation techniques employed. (3) SRFs/CRFs experienced rapid progress during the 1980s and 1990s, introducing additional varieties such as polymer-coated and resin-based fertilizers. These innovations yielded significantly enhanced release characteristics, exhibiting stable rates that cater to plant growth requirements while minimizing environmental damage. (4) The 21st century witnessed the introduction of advanced technologies and materials in the field of SRFs/CRFs, notably polymer nanomaterials and biodegradable substances. These innovative developments have been instrumental in achieving significant enhancements in the performance, sustainability, and cost-effectiveness of SRFs/CRFs, marking a pivotal shift in their application and impact.

3.2. Subject Categories

The literature pertaining to SRFs/CRFs from 1990 to 2023 encompasses 77 subject categories, as determined by statistical analysis. The top 15 discipline categories are represented in Figure 3. Environmental Sciences holds the highest number of publications, with 341 (11.71% of the total), followed by Agronomy with 225 (7.73%) and Soil Science with 215 (7.39%). Other prominent categories include Plant Sciences (197, 6.77%), Polymer Science (171, 5.87%), Horticulture (157, 5.39%), Environmental Engineering (145, 4.98%), Applied Chemistry (134, 4.60%), and Chemical Engineering, alongside Multidisciplinary Chemistry (125, 4.29%). Publications on SRFs/CRFs encompass a wide range of subject fields, primarily concentrating on Environmental Sciences, Agronomy, Soil Science, Plant Sciences, and Polymer Science, which collectively account for 40% of the total publications. Consequently, SRF/CRF research demonstrates a trend toward a multidisciplinary structure and diversification within the fields of environmental sciences, agronomy, soil science, and materials chemistry.

3.3. Contribution of Countries and Institutions

Statistical analysis revealed that 69 countries/regions have published a substantial number of research papers related to SRFs/CRFs. Figure 4A presents the top 10 countries/regions in SRF/CRF research. China and the USA are the predominant contributors, with 521 and 278 papers published, respectively. By comparison, Brazil ranks third with 140 papers, comprising 8.35% of the total, while other countries lag, underlining the pivotal position of China and the USA in SRF/CRF research. China and the USA outpace other countries/regions in single-country publications (SCPs) and multiple-country publications (MCPs) in the SRF/CRF field. China exhibits 417 SCPs and 104 MCPs, whereas the USA registers 249 SCPs and 29 MCPs. The findings indicate that China and the USA serve as the principal research countries/regions in the SRF/CRF research field, maintaining a substantial lead over other countries/regions.
A cooperation network map between different countries/regions was generated using a cooperative networks graph. In this graph, colored edges represent different countries/regions, the magnitude of the edges signifies the number of articles published, while the thickness of the interconnecting lines between the edges indicates the extent of cooperation between countries/regions. As depicted in Figure 4B, China and the USA occupy the largest square area, with the former and latter ranked first and second in the number of articles published, respectively. China maintains close cooperation with the USA, the UK, and Spain, while the USA cooperates closely with China, Brazil, and Egypt. The strongest bilateral cooperation exists between the USA and China.
The analysis of the collected literature indicates that 1691 research institutions have contributed to the publication of articles on SRFs/CRFs. Table 1 presents the top ten research institutions, among which six are from China, having collectively contributed 243 journal publications, which account for 14.50% of the total. Two American research institutions, the University of Florida and Purdue University, are ranked among the top ten, collectively contributing 117 journal articles, which account for 6.98% of the total number of publications in the field. Additionally, two Brazilian institutions, University Federal Sao Carlos and University Sao Paulo, hold the top ten positions, with 39 journal articles representing 2.33% of the total publications. These findings indicate that Chinese and American research institutions possess greater investment and capacity in the SRF/CRF field compared to other countries, reflecting their substantial influence in this field. In terms of total citations, the three leading research institutions are the University of Florida (USA), the Chinese Academy of Sciences (China), and Shandong Agricultural University (China), receiving 3217, 2534, and 1613 citations, respectively. Lanzhou University, USDA ARS, and the Federal University of Sao Carlos rank the highest in average citation times, with figures of 60.59, 49.19, and 35.45, respectively, signifying their significant impact on SRF/CRF research. Notably, Lanzhou University in China has only 22 publications, but its average citation frequency is 60.59, indicating the high-quality literature produced by this institution. Figure 5 displays the close collaboration among various research institutions worldwide, illustrating the widespread attention garnered by the SRF/CRF field.

3.4. Contribution of Journals

The statistics pertaining to major publishing journals in the field of SRF/CRF research are presented in Table 2. As indicated, HortScience ranks first among the top ten journals with the highest number of articles on SRF/CRF research, publishing 69 articles between 1990 and 2023 and accounting for 4.12% of the total number of articles. Science of the Total Environment and Communications in Soil Science and Plant Analysis follow in second and third place with 44 and 37 publications, respectively, representing 2.63% and 2.21% of the total retrieved literature. The Journal of Agricultural and Food Chemistry claims the highest total citations, reaching 1835, surpassing Science of the Total Environment with 1243 and the Journal of Cleaner Production with 926 citations. The average citation frequency for the Journal of Agricultural and Food Chemistry is 49.59, slightly higher than the Journal of Cleaner Production at 28.94 and Science of the Total Environment at 28.25. Notably, the Journal of Applied Polymer Science and International Journal of Biological Macromolecules exhibit low article counts but an average citation frequency exceeding 20, indicating their popularity in the SRF/CRF research field.

3.5. Contribution of Authors

Statistical results indicate that 5566 authors have contributed to the SRF/CRF research field. Table 3 presents the top 10 authors, all of whom have published more than 15 articles. The three leading authors are Zhang M and Yang YC from Shandong Agricultural University, and Gao B from the University of Florida, with 36, 23, and 23 publications, respectively (Figure 6). Among the top ten authors, eight are from Chinese research institutions and two are from American institutions, highlighting China’s significant contributions to SRF/CRF research.

3.6. Highly Impactful and Highly Cited Publications

Table 4 presents a detailed enumeration of the top 10 most cited articles on SRFs/CRFs, categorized by total citations and author information. Akiyama H’s study in Global Change Biology, titled “Evaluation of the effectiveness of enhanced-efficiency fertilizers as mitigation options for N2O and NO emissions from agricultural soils: meta-analysis”, secured the top position for total citations, with 532 citations and a total citation per year frequency of 35.47. The study conducted a comprehensive assessment of the effects of polymer-coated fertilizers on N2O and NO emissions, utilizing field experimental data compiled from 113 datasets and 35 studies published in peer-reviewed journals since 2008. The meta-analysis results demonstrated that polymer-coated fertilizers significantly reduced N2O emissions (−35%, −58% to −14%) and NO emissions (−40%, −76% to −10%), suggesting that using slow-release and controlled-release fertilizers in agricultural production can potentially reduce surface and groundwater pollution and decrease nitrogen oxide (N2O and NO) emissions [20]. Yao Y from the University of Florida contributed two highly cited papers focusing on P resource recovery through adsorption, and phosphoric acid ion enrichment in wastewater by biochar, combined with SRFs/CRFs to enhance soil fertility and improve agricultural production. The first paper, published in Environmental Science & Technology in 2013 and titled “Engineered biochar reclaiming phosphate from aqueous solutions: mechanisms and potential application as a slow-release fertilizer”, received a high number of citations and ranked second in terms of citation count. This research demonstrated that biochar derived from magnesium-rich tomato tissues can effectively serve as SRF/CRF, achieving a maximum phosphorus adsorption capacity exceeding 100 mg·g−1. This substantial adsorption capability significantly enhances the germination and growth of grass seeds [21]. Another paper, published in the Journal of Hazardous Materials in 2011, titled “Removal of phosphate from aqueous solution by biochar derived from anaerobically digested sugar beet tailings”, attracted attention and ranked third for citation frequency. The study employed anaerobically digested sugar beet waste as a feedstock for producing biochar, which demonstrated capability in recovering phosphate from water sources. Additionally, this biochar effectively reduced phosphate leaching from fertilized soils and functioned as SRF/CRF. These properties contribute to enhanced soil fertility and increased carbon sequestration, highlighting the multifunctional benefits of biochar in sustainable agricultural practices [22].

3.7. Keyword Analysis

3.7.1. High-Frequency Keywords

Keywords capture the essence and core of an article, providing a condensed summary of the research content and signifying the principal direction of ongoing investigations, thereby serving as pivotal indicators for the identification and retrieval of relevant literature [23]. The visual representation illustrated in Figure 7 displays the 50 most frequently utilized keywords throughout the period of 1990 to 2023. High-frequency keywords such as “slow release”, “controlled release fertilizer”, “nitrogen”, “urea”, “phosphorus”, and “polymer” proffer valuable insights for discerning the research orientation in the field of SRFs/CRFs. In conjunction with the aforementioned keywords, such as “biochar”, “hydrogel”, “cellulose”, and “chitosan”, commonly employed as slow-release carriers and encapsulation materials, also feature prominently. The pursuit of efficient, stable, degradable, and eco-friendly SRFs/CRFs embodies the foremost research hotspot in this field.
The exploration of coating materials constitutes a primary field of academic inquiry in the field of SRF/CRF research. Identifying and developing coating materials that originate from biological sources, which are cost-effective, environmentally benign, and modifiable and demonstrate superior nutrient release efficiency, represents imperative avenues for investigation in the field of SRF/CRF research. Coating materials for film-type SRFs/CRFs predominantly fall into two categories: inorganic materials and organic polymers. Inorganic coating materials primarily adhere to fertilizer granules via binding agents, which attenuate the contact between the fertilizer and water through a physical barrier effect, thereby facilitating a slow-release mechanism [24]. Inorganic coating materials predominantly include minerals such as sulfur, clay, gypsum, magnesium oxide, phosphate, silicate, humic acid, kaolin, bentonite, talc, zeolite, and sea foam. Sulfur-coated materials, extensively studied for SRFs/CRFs, are cost-effective and environmentally sustainable, making them valuable for long-term nutrient delivery in agriculture. They provide plants with slow-release salt-based ions without harming soil health, highlighting their potential for broad agricultural application. Guo et al. demonstrated that integrating humic acid into SRFs/CRFs culminated in augmented crop yield and N assimilation, as well as enhanced N utilization efficiency. Furthermore, this methodology contributed to a decrease in greenhouse gas emissions, thereby generating favorable outcomes for both crop productivity and environmental sustainability [25]. The utilization of an acrylic polymer as a binder in Dubey’s zeolite-coated urea has been found to regulate N release by 54.7%. Empirical investigations conducted on soil columns have demonstrated that the adoption of zeolite-coated urea as an N fertilizer with controlled release characteristics for the purpose of proficient crop N management leads to a reduction of N leaching by 65% [26]. However, inorganic film fertilizers are poorly elastic and brittle, which can easily cause large gaps between the fertilizer and the film. This hinders slow release of the fertilizer and controlled release of nutrients. Adjusting the thickness of the film and the amount of cover agent (paraffin) helps achieve controlled release of nutrients [27].
Polymer-coated SRFs/CRFs are achieved by coating the surface of the fertilizer with a layer of polymer material so that the fertilizer cannot come into direct contact with the external environment. Depending on the source of the coating material, polymer coating materials are divided into synthetic, semi-synthetic, and natural polymer materials. Natural polymer materials exist in large quantities in nature and include starch, cellulose, lignin, sodium alginate, chitosan, hydrogels, natural rubber, plant gum, and animal glue. Natural polymer materials are stable, film-forming, non-toxic to the soil, and inexpensive; however, they are easily decomposed by microorganisms in the soil, so the slow-release effect is poor and generally has to be modified before they can be used as coating materials for SRFs/CRFs [28]. Semi-synthetic polymers are formed by the modification of natural polymer materials, mainly cellulose derivatives such as hydroxy cellulose and carboxymethyl cellulose. Semi-synthetic polymers have good film-forming properties, easy hydrolysis, and broad application prospects. Synthetic polymers can be divided into solvent-based thermoplastic coating materials, water emulsion coating materials, and thermosetting resin coating materials based on their principles, including thermoplastic polyolefins (polyethylene, polyvinyl chloride, and polypropylene), acrylate polymers, urea–formaldehyde resins, and polyurethanes. Synthetic polymers allow for the controlled release of nutrients by controlling the thickness of the envelope, with low sensitivity to soil conditions, and the rate of nutrient diffusion is controlled by the chemical properties of the polymer.
Nanomaterials are materials in the nanoscale range (1–100 nm) in at least one dimension of a three-dimensional space, or materials composed of them as basic units [29]. Nanomaterials exhibit shared attributes, including diminutive dimensions, expansive surface area, and noteworthy interfacial effects. These traits confer enhanced benefits and prospects for optimizing the microstructure and enhancing the macroscopic performance of SRFs/CRFs. The incorporation of nanotechnology significantly enhances the coating properties of fertilizers. By utilizing nanoscale materials, it improves nutrient release dynamics, enabling more precise nutrient management and increasing both water stability and weather resistance. This advancement supports more efficient and sustainable agricultural practices [30]. Nanofertilizers primarily include nano-oxides, nanocellulose, nanocarbons, and nanoclays. Khan et al. prepared nano-biochar based SRFs/CRFs by leaching nutrients into pyrolytically synthesized wheat straw biochar. Compared with 300 °C, the nano biochar prepared at 350 °C had larger pores, better water retention, and slow release, and the water retention rate could reach 64%, and the release period of N, P, and K nutrients was more than 10 days [31]. Shen et al. employed micro- and nano-SiO2 that had been modified with trimethoxysilane to perform hydrophobic modification of the water-based polymer film layer of SRFs/CRFs through surface spraying. The hydrophobicity of the altered membrane was enhanced, as evidenced by an increase in the water contact angle from 49° to 98° [32]. Nanomaterials have shown great application value and potential for SRFs/CRFs.

3.7.2. Keywords Co-Occurrence Analysis

Keywords represent the most critical elements in co-occurrence analysis, signifying a significant level of abstraction and summarizing the core research content of a manuscript. The prevalence of specific keywords within a field frequently serves as an indicator of emerging research hotspots, reflecting the focal points and trends in scholarly investigations [33]. A co-occurrence analysis of the keywords of SRFs/CRFs was performed in order to explore the research hotspots and future development trends of these topics (Figure 8 and Table 5). The clustering diagram enables the analysis of the interrelation between research themes and developmental trajectories in the field of SRFs/CRFs, furnishing a framework for guiding future research directions. Based on the keyword clustering outcomes, keywords pertaining to SRFs/CRFs were categorized into five distinct clusters (purple, red, yellow, blue, and green clusters).
The green cluster focused on the impact of SRFs/CRFs on N use efficiency as well as the nitrification and denitrification functions in soil–plant systems, with keywords such as “nitrous”, “nitrous-oxide emissions”, “nitrification inhibitors”, and “ammonia volatilization”. Overuse of N fertilizers in agroecosystems can adversely affect the environment through nitrate loss via leaching, runoff, or volatilization into the atmosphere as the greenhouse gas N2O [34]. SRFs/CRFs can progressively release N nutrients in alignment with plant requirements, thereby substantially enhancing plant absorption and improving the utilization of N fertilizers. This optimization leads to a reduction in the need for N fertilizer applications and diminishes the associated environmental impacts. Moreover, the slow release of N in SRFs/CRFs helps balance soil N content, temper the nitrification rate, and enhance N fertilizer efficiency while reducing soil-accumulated nitrate N. This indirectly curtails denitrification rates, diminishing the production and emission of harmful N oxides (N2O and NO), subsequently alleviating global warming and preserving the environment [35]. A global meta-analysis by Zhang et al., comprising 120 studies, revealed that substituting urea with controlled-release urea (CRU) led to a 5.3% increase in maize yield and a 24.1% improvement in N use efficiency. Furthermore, the replacement significantly reduced N2O emissions, N leaching, and NH3 volatilization by 23.8%, 27.1%, and 39.4%, respectively, while sustaining the same N application rate [36]. Tian et al. assessed the efficacy and potential role of CRU in enhancing cotton productivity in China using a meta-analysis. Their findings indicated that the adoption of CRU resulted in a 9.8% increase in cotton yield and a 19.4% improvement in N use efficiency compared to urea application under equivalent N conditions [37]. Consequently, the adoption of SRFs/CRFs constitutes a crucial step towards diminishing dependency on chemical fertilizers. N fertilizer usage plays an essential role in addressing challenges such as food security, environmental degradation, and climate change. The 15N isotope techniques serve as significant investigatory tools for examining N cycling processes within various ecosystems, including soil, atmosphere, water, and crop systems, particularly concerning fertilizer application [38]. By measuring the abundance of 15N in plants, the interaction between the N isotope of SRFs/CRFs and plants, soil, and microorganisms can be assessed. Moreover, 15N isotope technology facilitates direct tracking and quantification of how released N is absorbed by soil, plants, and microorganisms, thereby deepening the understanding of the impact of SRFs/CRFs on soil N cycling processes, such as nitrification and denitrification. In addition, the 15N isotope technique can swiftly identify the N loss pathways and their proportions, facilitating the evaluation of SRFs/CRFs effectiveness in reducing N loss [39]. Ultimately, 15N isotopes enhance the assessment of nitrogen use efficiency in SRFs/CRFs, reducing nitrogen loss and promoting environmental protection.
The purple cluster focuses on the degradation aspects of SRFs/CRFs. The release of nutrients from SRFs/CRFs primarily occurs through chemical decomposition and biodegradation, with the release rate being intimately connected to soil conditions, encapsulation materials, and preparation processes [40]. However, the nutrient release mechanism of SRFs/CRFs remains insufficiently explored. Prevailing release mechanisms encompass diffusion and rupture, with internal factors impacting release, including coating material, coating thickness, coating rate, and porosity. External factors influencing release encompass soil water content, temperature, and soil pH [41]. Future research should further investigate the degradation processes of SRFs/CRFs in various soil environments, focusing on physical, chemical, and biodegradation mechanisms. It is also crucial to study how environmental factors, such as temperature, humidity, and microbial activity, influence the degradation behavior of fertilizer coating materials. These insights will help optimize fertilizer efficacy and minimize environmental impacts. Establishing the nutrient release model of SRFs/CRFs enables expedited predictions of SRF/CRF nutrient release cycles, assisting in the selection of suitable SRFs/CRFs for various plants. Furthermore, following nutrient release by SRF/CRF film fertilizers, film materials persisting in the soil may pose considerable harm to the soil and crops if not easily degradable. Consequently, degradable film materials have attracted substantial research interest due to their environmentally friendly nature. Natural degradable materials, such as starch, humic acid, cellulose, lignin, and chitosan, have emerged as preferred alternatives. Nevertheless, these materials are prone to biodegradation and provide limited release control, necessitating modification for utilization as film materials in SRFs/CRFs.
The yellow cluster highlights the impact of SRFs/CRFs on the gradual and regulated release of P fertilizers, one of the three essential fertilizer components in agricultural cultivation. Ensuring an adequate phosphate supply in the soil is pivotal for boosting crop productivity. At present, 71% of worldwide phosphate ore is employed in phosphoric acid production, while 90% of phosphoric acid is utilized in manufacturing fertilizers [42]. Nevertheless, mined phosphate can no longer satisfy global agricultural needs. Therefore, rational phosphate fertilizer application and improved utilization efficiency are critical for addressing the P crisis. As P fertilizer readily combines with other soil ions to form insoluble P compounds, its water solubility is extremely low, leading to poor P fertilizer utilization by plants. SRF/CRF coating materials effectively inhibit P fertilizer nutrient diffusion to the soil, help balance soil P content, and reduce insoluble P compound formation caused by redox reactions and pH value fluctuations. Consequently, P remains in a plant-absorbable state. Furthermore, SRFs/CRFs exhibit slow or almost no P release during the early stages when crops require minimal P. The later-stage accelerated P release coincides with the crops’ greater P demands and enhanced absorption capacity. The shortened migration distance and residence time of available soil P result in faster absorption rates, while P-SRFs/CRFs’ continuous P supply throughout the growth stage ensures adequate plant P availability. This is conducive to improved P availability, utilization rate, and reduced P losses [43]. Sharma formulated a novel biodegradable hydrogel composite employing polyvinyl alcohol as the polymer matrix, kaolin as the mechanical binder, and poly(vinyl alcohol)/kaolin/diammonium hydrogen phosphate (DAhP) as the P fertilizer. The composite demonstrated an 88.8% phosphate water release rate and a 76.3% soil release rate. This formulation proficiently regulated DAhP discharge [44]. Currently, P-SRFs/CRFs’ primary benefits include enhanced P utilization rates, improved crop growth, increased soil P dynamics, and decreased environmental pollution. The rational combination of P-SRFs/CRFs, N-SRFs/CRFs, and K-SRFs/CRFs can yield substantial economic and ecological advantages in agricultural production. However, P-SRFs/CRFs’ application effectiveness under varying soil conditions may be influenced by factors such as soil type, pH value, and moisture. Therefore, further research is needed to optimize P-SRF/CRF application schemes under different conditions.
The blue cluster focuses on urea-based SRFs/CRFs. Urea, distinguished by its ease of transport and storage, high nitrogen concentration, and exceptional stability and safety, constitutes 50% of the total global nitrogen fertilizer supply, making it the most widely utilized N fertilizer. [45]. Nevertheless, approximately half of the N present in urea-treated soils is lost due to leaching, emissions, and volatilization [36]. Urea-based SRFs/CRFs control urea nutrient release rates in soil through coating technology, chemical modification, or combined application. This approach not only reduces N loss from volatilization and leaching but also alters N release kinetics, providing nutrients at a rate that better aligns with plant metabolic needs and fulfills crop growth nutrient requirements [46]. Tian et al. assessed the effectiveness and potential role of slow-release urea in enhancing cotton yield in China through a meta-analysis. Under equivalent N application rates, slow-release urea increased cotton yield and N use efficiency by 9.8% and 19.4%, respectively, compared to conventional urea [37]. Future research should focus on developing more efficient and environmentally friendly coating materials to enhance the slow-release properties of urea and reduce environmental pollution. Additionally, exploring specific chemical or biological synergists could significantly improve the efficacy and efficiency of urea fertilizers by optimizing nitrogen absorption and utilization in various soil conditions.
The red cluster focuses on the effects of SRFs/CRFs on crop growth and quality. SRFs/CRFs can deliver a continuous and stable nutrient supply for crops, catering to their temporal needs for N, P, K, and other elements. This subsequently improves seed germination rates, bud and root growth, chlorophyll content, photosynthesis, and abiotic stress tolerance in crops, ultimately enhancing crop yield and quality. Simultaneously, SRFs/CRFs can reduce greenhouse gas emissions, such as CO2, CH4, and N2O [47]. Moreover, SRFs/CRFs contribute to regulating the soil environment, augmenting soil structure stability and water retention capacity, thus fostering a more favorable growth environment for plants and potentially prolonging crop growth cycles. This facilitates the attainment of full crop growth potential, resulting in increased yields and quality [48]. Different types and application methods of SRFs/CRFs exhibit significant effects on crop yield. Guo et al. demonstrated that urea-based SRF/CRF application had a notably positive impact on rice crop yields. The use of polymer-coated urea, nitropyridine-treated urea, and effective microbial-treated urea resulted in average annual grain yield increases of 18.0%, 16.2%, and 15.4%, respectively, compared to farmer-applied treatments. Additionally, annual NH3, CH4, and N2O emissions decreased by 64.8%, 19.7%, and 35.2%, respectively [49]. Currently, investigations on SRFs/CRFs’ effects on crop growth and quality primarily involve determining and analyzing plant physiological indicators (e.g., biomass, photosynthetic parameters, root development, crop yield and quality, stress resistance, and plant hormone levels) for SRF/CRF-treated plants. However, the interaction mechanism between SRFs/CRFs and plant physiology and gene level remains obscure. In recent years, omics techniques, including transcriptomics [50] and metabolomics [51], have emerged as crucial methods for studying the interactions between fertilizers and plants. For example, Tian et al. investigated the triggers for organic acid secretion in root systems and the molecular mechanisms underlying the synergistic uptake of nitrogen and phosphorus in plants under low phosphorus conditions. The study revealed that in phosphorus-deficient environments, Arabidopsis root cell nuclei accumulate the key regulatory protein STOP1 [50].
However, some SRFs/CRFs may contain detrimental elements such as heavy metals and organic pollutants, which, if used excessively, can alter the soil’s physical, chemical, and biological properties, potentially leading to adverse environmental impacts. Such alterations could influence soil permeability, structure, consolidation, biochemical geo-cycling, as well as soil microbial diversity and structure, thereby impeding plant growth. In the future, there is a pressing need to undertake long-term studies on the application of SRFs/CRFs to investigate the potential ecological hazards associated with their usage. Evaluating the enduring effects of the multi-year application of these fertilizers on soil microorganisms, ecosystems, and crop production can be facilitated through omics methodologies such as transcriptomics, proteomics, and metabolomics. To comprehend the biological underpinnings of soil–plant–SRF/CRF interactions, a multi-scale examination of plant–SRF/CRF associations is warranted, spanning gene-level, physiological, and biochemical aspects, as well as crop yield and quality. Concurrently, crop varieties adapted to different nutrient supply conditions can be developed based on genetic improvements or gene-editing technology to enhance the application effectiveness of SRFs/CRFs. This approach would further contribute to improved crop quality regarding drought tolerance, pest and disease resistance, and quality enhancements.

3.7.3. Keyword Burst Analysis

CiteSpace’s burst-term analysis functionality enables the examination of terms exhibiting sudden emergence and rapid frequency increases, often signifying research frontiers in a given field [52]. The burst analysis of keywords pertaining to SRFs/CRFs suggests that research on SRFs/CRFs can be partitioned into three distinct stages across the 34 years from 1990 to 2023 (Figure 9). During the initial stage (1998–2011), keywords exhibiting the highest burst strength included “biodegradation”, “degradation”, and “bioremediation”. Although the utilization of SRFs/CRFs enhances fertilizer efficiency and reduces the quantity of fertilizers required to achieve equivalent yields, thereby diminishing soil and environmental pollution, the comprehensive resolution of pollution issues depends critically on the adoption of environmentally friendly, degradable materials. Furthermore, concerning contemporary soil organic pollution (e.g., crude oil pollution), SRFs/CRFs function as exogenous additives for in situ bioremediation technology. They contribute to increased populations of soil bacteria/fungi and actinomycetes, elevated soil enzyme activity, enhanced soil microbial functional diversity, and the reinforcement of indigenous or exogenous soil microorganisms in degrading soil organic pollutants. All the while, SRFs/CRFs release fertilizer to ensure crop growth, thereby achieving remediation of soil organic pollution [53].
The second stage (from 2011 to 2018) exhibited keywords with high burst strength, including “behavior”, “growth”, “nutrition”, “loss”, and “mineral nutrition”. Conventional fertilizers, once applied to soil, are subject to continuous nutrient losses through processes such as leaching, runoff, volatilization, and denitrification. These losses contribute to a range of environmental issues, including the eutrophication of aquatic ecosystems. In most instances, these fertilizers fail to satisfy plant growth requirements without continuous application [54]. SRFs/CRFs enable the regulation of essential nutrient release according to crop-specific demands. This controlled nutrient release bears considerable importance within the purview of soil properties and agricultural productivity and constitutes a vital strategy for boosting fertilizer utilization efficacy.
The third stage (from 2018 to the present) includes keywords with high burst strength, such as “polymer”, “biochar”, and “pyrolysis”. During this stage, the focus of SRF/CRF research gradually changed from conventional encapsulation materials to more eco-friendly alternatives, such as polymeric materials. Biochar, with its high specific surface area, elevated porosity, and numerous functional groups, has proven effective as a green material for SRFs/CRFs. Its ability to adsorb and retain nutrients enhances fertilizer efficiency and offers additional environmental benefits. Furthermore, investigations have revealed that biochar can positively influence a variety of soil physicochemical and biological properties. These include enhanced water retention capacity, improved ion exchange attributes, and an increase in soil pH levels. Such modifications contribute significantly to the overall health and productivity of soil ecosystems [55]. Besides, biochar holds the potential to function as a premium substrate for SRF/CRF production. Employing co-composting, co-pyrolysis, or co-application of biochar in combination with fertilizers can potentially increase N utilization efficiency, boost crop yield, and tackle the challenge of managing and disposing of agricultural and forestry residues [56].

4. Challenges and Future Research Prospects

4.1. Emerging Preparation Techniques and Materials for SRFs/CRFs

Amid escalating concerns about the ecological environment in agriculture and the pursuit of sustainable development, the study of SRFs/CRFs faces novel challenges. These challenges necessitate innovative approaches to enhance the effectiveness and environmental compatibility of these fertilizer technologies. Currently, the market offers a diverse array of SRFs/CRFs, each presenting unique characteristics and benefits. However, despite their diversity, these fertilizers often share commonalities in practical applications and may exhibit specific shortcomings that need to be addressed to optimize their effectiveness and environmental sustainability. For instance, SRFs/CRFs prepared through sulfur aluminum and chlorination processes demonstrate a level of maturity, yet the temperature increase stemming from the chemical reaction may compromise their controllability, and the reaction process may generate toxic waste, among other issues. For coated SRFs/CRFs, the utilization of coating materials that resist degradation and exhibit suboptimal slow-release performance could adversely affect the soil and may even contribute to microplastic pollution [57]. Moreover, the comparatively elevated material costs lead to higher prices for finished products, making the development of cost-effective and efficient biobased coating materials crucial for enhancing their market competitiveness and sustainability. In addition, nutrient release from SRFs/CRFs may not ideally align with the specific nutrient requirements of crops, and the coating materials used in these fertilizers may themselves pose environmental threats. Consequently, there is a pressing need to devise new materials and processes characterized by enhanced release efficiency, eco-friendliness, and reduced production costs. In the future, innovative preparation techniques such as microbial fixation, biodegradation technology, and nanotechnology (encompassing nano-encapsulation, nano-adsorption, and nano-N fixation), along with novel materials such as biodegradable substances (polyacrylate, polylactic acid, polyhydroxyl fatty acid esters, etc.) and nanomaterials (nano zinc oxide, nano silicon, nano iron oxide, etc.) can be incorporated. By integrating insights from material science, chemistry, and biology, the performance of SRFs/CRFs may be holistically enhanced, facilitating improved production efficiency, cost reductions, and a diminished environmental burden.
The controlled release effect of SRFs/CRFs is influenced by factors such as soil temperature, pH, humidity, and soil microbial content. Consequently, the development of intelligent SRFs/CRFs capable of responding to changes in the soil environment, such as pH levels, temperature, and moisture content, to achieve more precise control over nutrient release represents a significant future research direction in the field of SRF/CRF research. Responsive SRFs/CRFs are skillfully designed and fabricated utilizing special sensitive materials, allowing them to regulate nutrient release in accordance with soil environmental conditions, production demands, and crop growth stages [58]. Various types of responsive SRFs/CRFs, encompassing pH-responsive, temperature-responsive, humidity-responsive, and bioenzyme-responsive iterations, are prepared using materials such as pH-sensitive resins, temperature-sensitive polymers, and moisture-sensitive hydrogels [59]. Responsive SRFs/CRFs contribute to further enhancement of nutrient utilization efficiency, improvement in crop yield and nutrient utilization rates, and reduction in environmental strain.
Currently, the majority of SRF/CRF research concentrates on individual nutrient elements, primarily due to the relative maturity of single nutrient element slow-release technology and the ease of translating research findings into practical applications. Nevertheless, crops necessitate a diverse array of nutrient elements to attain healthy growth and development. Multi-element SRFs/CRFs encompass a variety of nutrient elements, typically including major elements (N, P, and K) and trace elements such as calcium, magnesium, sulfur, iron, and zinc, among others. Owing to their capacity to provide multiple nutrient elements simultaneously, multi-element SRFs/CRFs can diminish the complexity of fertilization management. A single application can satisfy the nutritional demands of numerous crops [60]. Thus, in SRF/CRF research, emphasis should be placed not only on the continued study of single-element SRFs/CRFs but also on the investigation and development of multi-element SRFs/CRFs.

4.2. Mechanism and Model Simulation of Nutrient Release from SRFs/CRFs

While SRFs/CRFs contribute to the reduction of nutrient loss and enhancement of nutrient utilization, their release rates might not precisely align with crop requirements. An overly rapid release could impede crop growth, whereas a prolonged release may adversely affect yield [61]. Thus, attaining a profound understanding of the release mechanism of SRFs/CRFs is imperative. Comprehending the nutrient release mechanisms and models of SRFs/CRFs facilitates more accurate predictions of nutrient release rates and strategies. This ensures that crops receive sufficient and timely nutrient supplies throughout their life cycle, diminishes nutrient loss, fosters the development of rational and dependable fertilizer management plans, and provides scientifically grounded fertilizer recommendations for farmers and decision-makers. Currently, the nutrient release mechanisms for some SRFs/CRFs have been identified, predominantly comprising coated SRFs/CRFs (where nutrient release rate is controlled by coating agents, involving diffusion, dissolution, and degradation mechanisms of membrane materials), biological SRFs/CRFs (impacted by microbial activities), and chemical SRFs/CRFs (e.g., in ammonium urate fertilizer, nutrient release is influenced by soil pH and water content) [62]. Researchers have engaged in mathematical modeling of the nutrient release process from SRFs/CRFs to enhance the accuracy of predictions regarding fertilization strategies. However, current models for nutrient release from SRFs/CRFs tend to oversimplify the dynamics involved. There is a notable deficiency in the exploration of various environmental factors that influence nutrient release, including soil type, climatic conditions, and microbial activity. Consequently, these models fail to adequately capture the complexity of nutrient release across diverse crop, environmental, and soil conditions. Currently, many models primarily focus on single-element fertilizers, such as N-SRFs, P-SRFs, or K-SRFs. This emphasis underscores the need to develop a more comprehensive nutrient release model that can effectively address the complexities associated with multi-element SRFs/CRFs.
A considerable portion of current SRF/CRF research relies on laboratory settings, which may not adequately represent the real-world agricultural environment. Furthermore, the fertilizer demands of various crops differ in distinct soil conditions, and the slow-release effect is often diminished due to regional, climatic, and soil disparities, among other factors. To achieve precise fertilization with SRFs/CRFs, it is essential to leverage digital agriculture, big data, and Internet of Things (IoT) technology and conduct comprehensive soil testing and analysis while utilizing nutrient release models and intelligent fertilizer systems that employ real-time sensors to monitor soil and crop needs, thereby adjusting release rates and optimizing the growing environment for enhanced agricultural efficiency and sustainability.

5. Conclusions and Limitations

This manuscript presents a comprehensive visualization assessment of the scholarly literature on SRF/CRF research, covering a period of 34 years from 1990 to 2023. This comprehensive appraisal critically evaluated the existing literature, exploring publication trends, prominent research themes, and emerging hotspots from a multidimensional perspective. By analyzing the relationships among various publications and identifying prevailing topics in the field, this investigation seeks to provide valuable insights for researchers and stakeholders. The key findings that emerged from this analysis are outlined as follows:
(1) First and foremost, the field of SRFs/CRFs has experienced substantial global growth, as evidenced by an increasing number of publications over the years, with the growth trajectory distinguishable into two discrete stages. China and the USA exhibit substantially elevated publication volumes within this specialty, outpacing other countries. Leading research institutions, including the University of Florida, the Chinese Academy of Sciences, and Shandong Agricultural University, serve as instrumental drivers in propelling the field forward. Research on SRFs/CRFs has been published in scholarly journals, including Hortscience, Science of the Total Environment, and Communications in Soil Science and Plant Analysis.
(2) High-frequency keywords, keyword co-occurrence, and burst analysis derived from the SRF/CRF literature reveal prevailing research hotspots, primarily focusing on carrier and encapsulation materials such as biochar, hydrogel, chitosan, zeolite, starch, and lignin, while scholarly emphasis also concentrates on the nitrogen cycling process within the soil–plant–atmosphere system and the effects of SRFs/CRFs on crop growth and quality. Despite advancements in SRF/CRF design and performance, significant challenges persist, including a lack of comprehensive research on the factors affecting nutrient release and the mechanisms behind fertilizer efficacy and sustained-release properties. The unclear nutrient release pathways and misalignment of release cycles with plant growth cycles hinder the enhancement of nutrient utilization rates, limiting the broader application of these fertilizers. Secondly, synchronizing nutrient release rates with crop nutrient uptake is crucial for advancing SRFs/CRFs. This involves aligning fertilizer release with plant growth demands by identifying and responding to nutrient demand signals from plants. Therefore, future research on SRFs/CRFs must focus on enhancing the development of fertilizers capable of intelligently regulating nutrient release based on soil conditions and crop requirements. Additionally, it is imperative to strengthen the systematic assessment of the long-term degradation processes of coated materials in soil, as well as their impacts on the environment and soil ecosystems.
(3) This study employed bibliometric methodologies to conduct quantitative assessments of the research landscape and trajectories of the literature pertaining to SRFs/CRFs in the WOSCC database. Although the WOSCC database encompasses a vast array of information across diverse disciplines, exclusive reliance upon this database may constrain the scope of the research, potentially omitting pertinent studies housed in alternative databases. To secure a more all-encompassing perspective of the research field, future bibliometric analyses could benefit from incorporating multiple databases, including Scopus, PubMed, Google Scholar, and Dimensions, to supplement coverage and enhance accuracy.

Author Contributions

Conceptualization, Z.L.; software, X.L.; writing—original draft preparation, X.L.; writing—review and editing, Z.L.; visualization, X.L.; supervision, Z.L. All authors have read and agreed to the published version of the manuscript.

Funding

Supported by the China Postdoctoral Science Foundation (No. 2023M740176).

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. El-Naggar, A.; Lee, S.S.; Rinklebe, J.; Farooq, M.; Song, H.; Sarmah, A.K.; Zimmerman, A.R.; Ahmad, M.; Shaheen, S.M.; Ok, Y.S. Biochar application to low fertility soils: A review of current status, and future prospects. Geoderma 2019, 337, 536–554. [Google Scholar] [CrossRef]
  2. Sim, D.H.H.; Tan, I.A.W.; Lim, L.L.P.; Hameed, B.H. Encapsulated biochar-based sustained release fertilizer for precision agriculture: A review. J. Clean. Prod. 2021, 303, 127018. [Google Scholar] [CrossRef]
  3. Cole, M.B.; Augustin, M.A.; Robertson, M.J.; Manners, J.M. The science of food security. npj Sci. Food 2018, 2, 14. [Google Scholar] [CrossRef] [PubMed]
  4. Wesolowska, M.; Rymarczyk, J.; Gora, R.; Baranowski, P.; Slawinski, C.; Klimczyk, M.; Supryn, G.; Schimmelpfennig, L. New slow-release fertilizers—Economic, legal and practical aspects: A Review. Int. Agrophys. 2021, 35, 11–24. [Google Scholar] [CrossRef]
  5. Bi, S.; Barinelli, V.; Sobkowicz, M.J. Degradable controlled release fertilizer composite prepared via extrusion: Fabrication, characterization, and release mechanisms. Polymers 2020, 12, 301. [Google Scholar] [CrossRef]
  6. Li, Y.; Zhang, W.; Ma, L.; Huang, G.; Oenema, O.; Zhang, F.; Dou, Z. An analysis of China’s fertilizer policies: Impacts on the industry, food security, and the environment. J. Environ. Qual. 2013, 42, 972–981. [Google Scholar] [CrossRef]
  7. Timilsena, Y.P.; Adhikari, R.; Casey, P.; Muster, T.; Gill, H.; Adhikari, B. Enhanced efficiency fertilisers: A review of formulation and nutrient release patterns. J. Sci. Food Agric. 2015, 95, 1131–1142. [Google Scholar] [CrossRef]
  8. Fu, J.; Wang, C.; Chen, X.; Huang, Z.; Chen, D. Classification research and types of slow controlled release fertilizers (SRFs) used—A review. Commun. Soil Sci. Plant Anal. 2018, 49, 2219–2230. [Google Scholar] [CrossRef]
  9. Liu, Y.; Wang, J.; Chen, H.; Cheng, D. Environmentally friendly hydrogel: A review of classification, preparation and application in agriculture. Sci. Total Environ. 2022, 846, 157303. [Google Scholar] [CrossRef] [PubMed]
  10. Beig, B.; Niazi, M.B.K.; Jahan, Z.; Hussain, A.; Zia, M.H.; Mehran, M.T. Coating materials for slow release of nitrogen from urea fertilizer: A review. J. Plant Nutr. 2020, 43, 1510–1533. [Google Scholar] [CrossRef]
  11. Chen, J.; Fan, X.; Zhang, L.; Chen, X.; Sun, S.; Sun, R.C. Research progress in lignin-based slow/controlled release fertilizer. ChemSusChem 2020, 13, 4356–4366. [Google Scholar] [CrossRef]
  12. Li, X.; Li, Z.; Du, C.; Tian, Z.; Zhu, Q.; Li, G.; Shen, Q.; Li, C.; Li, J.; Li, W.; et al. Bibliometric analysis of zerovalent iron particles research for environmental remediation from 2000 to 2019. Environ. Sci. Pollut. Res. 2021, 28, 34200–34210. [Google Scholar] [CrossRef] [PubMed]
  13. Rocchi, L.; Boggia, A.; Paolotti, L. Sustainable agricultural systems: A bibliometrics analysis of ecological modernization approach. Sustainability 2020, 12, 9635. [Google Scholar] [CrossRef]
  14. Zhang, Y.; Pu, S.; Lv, X.; Gao, Y.; Ge, L. Global trends and prospects in microplastics research: A bibliometric analysis. J. Hazard. Mater. 2020, 400, 123110. [Google Scholar] [CrossRef]
  15. Xu, Y.; Lyu, J.; Liu, H.; Xue, Y. A Bibliometric and visualized analysis of the global literature on black soil conservation from 1983–2022 based on CiteSpace and VOSviewer. Agronomy 2022, 12, 2432. [Google Scholar] [CrossRef]
  16. Duan, G.; Bai, Y.; Ye, D.; Lin, T.; Peng, P.; Liu, M.; Bai, S. Bibliometric evaluation of the status of Picea research and research hotspots: Comparison of China to other countries. J. For. Res. 2020, 31, 1103–1114. [Google Scholar] [CrossRef]
  17. Aria, M.; Cuccurullo, C. Bibliometrix: An r-tool for comprehensive science mapping analysis. J. Informetr. 2017, 11, 959–975. [Google Scholar] [CrossRef]
  18. van Eck, N.J.; Waltman, L. Software survey: VOSviewer, a computer program for bibliometric mapping. Scientometrics 2010, 84, 523–538. [Google Scholar] [CrossRef] [PubMed]
  19. Chen, C.M. CiteSpace II: Detecting and visualizing emerging trends and transient patterns in scientific literature. J. Am. Soc. Inf. Sci. Technol. 2006, 57, 359–377. [Google Scholar] [CrossRef]
  20. Akiyama, H.; Yan, X.; Yagi, K. Evaluation of effectiveness of enhanced-efficiency fertilizers as mitigation options for N2O and NO emissions from agricultural soils: Meta-analysis. Glob. Chang. Biol. 2010, 16, 1837–1846. [Google Scholar] [CrossRef]
  21. Yao, Y.; Gao, B.; Chen, J.; Yang, L. Engineered biochar reclaiming phosphate from aqueous solutions: Mechanisms and potential application as a slow-release fertilizer. Environ. Sci. Technol. 2013, 47, 8700–8708. [Google Scholar] [CrossRef] [PubMed]
  22. Yao, Y.; Gao, B.; Inyang, M.; Zimmerman, A.R.; Cao, X.D.; Pullammanappallil, P.; Yang, L.Y. Removal of phosphate from aqueous solution by biochar derived from anaerobically digested sugar beet tailings. J. Hazard. Mater. 2011, 190, 501–507. [Google Scholar] [CrossRef]
  23. Li, C.; Wu, K.; Wu, J. A bibliometric analysis of research on haze during 2000–2016. Environ. Sci. Pollut. Res. 2017, 24, 24733–24742. [Google Scholar] [CrossRef] [PubMed]
  24. Ghumman, A.S.M.; Shamsuddin, R.; Nasef, M.M.; Yahya, W.Z.N.; Abbasi, A.; Almohamadi, H. Sulfur enriched slow-release coated urea produced from inverse vulcanized copolymer. Sci. Total Environ. 2022, 846, 157417. [Google Scholar] [CrossRef] [PubMed]
  25. Guo, Y.; Ma, Z.; Ren, B.; Zhao, B.; Liu, P.; Zhang, J. Effects of humic acid added to controlled-release fertilizer on summer maize yield, nitrogen use efficiency and greenhouse gas emission. Agriculture 2022, 12, 448. [Google Scholar] [CrossRef]
  26. Dubey, A.; Mailapalli, D.R. Zeolite coated urea fertilizer using different binders: Fabrication, material properties and nitrogen release studies. Environ. Technol. Innov. 2019, 16, 100452. [Google Scholar] [CrossRef]
  27. El Assimi, T.; Lakbita, O.; El Meziane, A.; Khouloud, M.; Dahchour, A.; Beniazza, R.; Boulif, R.; Raihane, M.; Lahcini, M. Sustainable coating material based on chitosan-clay composite and paraffin wax for slow-release DAP fertilizer. Int. J. Biol. Macromol. 2020, 161, 492–502. [Google Scholar] [CrossRef]
  28. Tyagi, P.; Agate, S.; Velev, O.D.; Lucia, L.; Pal, L. A critical review of the performance and soil biodegradability profiles of biobased natural and chemically synthesized polymers in industrial applications. Environ. Sci. Technol. 2022, 56, 2071–2095. [Google Scholar] [CrossRef]
  29. Zhang, Z.; An, Y. Nanotechnology for the oil and gas industry—An overview of recent progress. Nanotechnol. Rev. 2018, 7, 341–353. [Google Scholar]
  30. Jakhar, A.M.; Aziz, I.; Kaleri, A.R.; Hasnain, M.; Haider, G.; Ma, J.H.; Abideen, Z. Nano-fertilizers: A sustainable technology for improving crop nutrition and food security. Nanoimpact 2022, 27, 100411. [Google Scholar] [CrossRef]
  31. Khan, H.A.; Naqvi, S.R.; Mehran, M.T.; Khoja, A.H.; Niazi, M.B.K.; Juchelkova, D.; Atabani, A. A performance evaluation study of nano-biochar as a potential slow-release nano-fertilizer from wheat straw residue for sustainable agriculture. Chemosphere 2021, 285, 131382. [Google Scholar] [CrossRef] [PubMed]
  32. Shen, Y.; Zhou, J.; Du, C.; Zhou, Z. Hydrophobic modification of waterborne polymer slows urea release and improves nitrogen use efficiency in rice. Sci. Total Environ. 2021, 794, 148612. [Google Scholar] [CrossRef] [PubMed]
  33. Ouyang, W.; Wang, Y.; Lin, C.; He, M.; Hao, F.; Liu, H.; Zhu, W. Heavy metal loss from agricultural watershed to aquatic system: A scientometrics review. Sci. Total Environ. 2018, 637, 208–220. [Google Scholar] [CrossRef]
  34. Zheng, W.; Zhang, M.; Liu, Z.; Zhou, H.; Lu, H.; Zhang, W.; Yang, Y.; Li, C.; Chen, B. Combining controlled-release urea and normal urea to improve the nitrogen use efficiency and yield under wheat-maize double cropping system. Field Crop Res. 2016, 197, 52–62. [Google Scholar] [CrossRef]
  35. Liu, L.; Shen, T.; Yang, Y.; Gao, B.; Li, Y.C.; Xie, J.; Tang, Y.; Zhang, S.; Wang, Z.; Chen, J. Bio-based large tablet controlled-release urea: Synthesis, characterization, and controlled-released mechanisms. J. Agric. Food Chem. 2018, 66, 11265–11272. [Google Scholar] [CrossRef] [PubMed]
  36. Zhang, W.; Liang, Z.; He, X.; Wang, X.; Shi, X.; Zou, C.; Chen, X. The effects of controlled release urea on maize productivity and reactive nitrogen losses: A meta-analysis. Environ. Pollut. 2019, 246, 559–565. [Google Scholar] [CrossRef]
  37. Tian, X.; Fan, Z.; Zhao, Y.; Sun, S.; Li, T.; Yu, N.; Zhai, S. Controlled-release urea improved cotton productivity and nitrogen use efficiency in China: A meta-analysis. Agron. J. 2021, 113, 2251–2259. [Google Scholar] [CrossRef]
  38. Khalsa, S.D.S.; Smart, D.R.; Muhammad, S.; Armstrong, C.M.; Sanden, B.L.; Houlton, B.Z.; Brown, P.H. Intensive fertilizer use increases orchard N cycling and lowers net global warming potential. Sci. Total Environ. 2020, 722, 137889. [Google Scholar] [CrossRef]
  39. Coskun, D.; Britto, D.T.; Shi, W.; Kronzucker, H.J. Nitrogen transformations in modern agriculture and the role of biological nitrification inhibition. Nat. Plants 2017, 3, 17074. [Google Scholar] [CrossRef]
  40. Wang, Y.; Guo, H.; Wang, X.; Ma, Z.; Li, X.; Li, R.; Li, Q.; Wang, R.; Jia, X. Spout fluidized bed assisted preparation of poly(tannic acid)-coated urea fertilizer. ACS Omega 2020, 5, 1127–1133. [Google Scholar] [CrossRef]
  41. Hamidi, R.M.; Siyal, A.A.; Luukkonen, T.; Shamsuddin, R.M.; Moniruzzaman, M. Fly ash geopolymer as a coating material for controlled-release fertilizer based on granulated urea. RSC Adv. 2022, 12, 33187–33199. [Google Scholar] [CrossRef] [PubMed]
  42. Li, B.; Ng, S.J.; Han, J.C.; Li, M.; Zeng, J.; Guo, D.; Zhou, Y.; He, Z.; Wu, X.; Huang, Y. Network evolution and risk assessment of the global phosphorus trade. Sci. Total Environ. 2023, 860, 160433. [Google Scholar] [CrossRef] [PubMed]
  43. Guelfi, D.; Pereira Nunes, A.P.; Sarkis, L.F.; Oliveira, D.P. Innovative phosphate fertilizer technologies to improve phosphorus use efficiency in agriculture. Sustainability 2022, 14, 14266. [Google Scholar] [CrossRef]
  44. Sharma, N.; Singh, A.; Dutta, R. Biodegradable fertilizer nanocomposite hydrogel based on poly(vinyl alcohol)/kaolin/diammonium hydrogen phosphate (DAhP) for controlled release of phosphate. Polym. Bull. 2021, 78, 2933–2950. [Google Scholar] [CrossRef]
  45. Yang, J.; Liu, T.; Liu, H.; Zhai, L.; Wang, M.; Du, Y.; Chen, Y.; Yang, C.; Xiao, H.; Wang, H. Dimethylolurea as a novel slow-release nitrogen source for nitrogen leaching mitigation and crop production. J. Agric. Food Chem. 2019, 67, 7616–7625. [Google Scholar] [CrossRef] [PubMed]
  46. Mustafa, A.; Athar, F.; Khan, I.; Chattha, M.U.; Nawaz, M.; Shah, A.N.; Mahmood, A.; Batool, M.; Aslam, M.T.; Jaremko, M.; et al. Improving crop productivity and nitrogen use efficiency using sulfur and zinc-coated urea: A review. Front. Plant Sci. 2022, 13, 942384. [Google Scholar] [CrossRef]
  47. Rahman, M.H.; Haque, K.M.S.; Khan, M.Z.H. A review on application of controlled released fertilizers influencing the sustainable agricultural production: A Cleaner production process. Environ. Technol. Innov. 2021, 23, 101697. [Google Scholar] [CrossRef]
  48. Lu, S.; Feng, C.; Gao, C.; Wang, X.; Xu, X.; Bai, X.; Gao, N.; Liu, M. Multifunctional environmental smart fertilizer based on L-aspartic acid for sustained nutrient release. J. Agric. Food Chem. 2016, 64, 4965–4974. [Google Scholar] [CrossRef]
  49. Guo, C.; Ren, T.; Li, P.; Wang, B.; Zou, J.; Hussain, S.; Cong, R.; Wu, L.; Lu, J.; Li, X. Producing more grain yield of rice with less ammonia volatilization and greenhouse gases emission using slow/controlled-release urea. Environ. Sci. Pollut. Res. 2019, 26, 2569–2579. [Google Scholar] [CrossRef]
  50. Tian, W.H.; Ye, J.Y.; Cui, M.Q.; Chang, J.B.; Liu, Y.; Li, G.X.; Wu, Y.R.; Xu, J.M.; Harberd, N.P.; Mao, C.Z.; et al. A transcription factor STOP1-centered pathway coordinates ammonium and phosphate acquisition in Arabidopsis. Mol. Plant 2021, 14, 1554–1568. [Google Scholar] [CrossRef]
  51. Alami, M.M.; Liu, S.; Gong, D.; Guo, S.; Shaohua, S.; Mei, Z.; Alami, M.J.; Yang, G.; Wang, X. Effects of excessive and deficient nitrogen fertilizers on triptolide, celastrol, and metabolite profile content in Tripterygium wilfordii Hook F. Ind. Crops Prod. 2023, 206, 117577. [Google Scholar] [CrossRef]
  52. Zhong, S.; Chen, R.; Song, F.; Xu, Y. Knowledge mapping of carbon footprint research in a LCA perspective: A visual analysis using CiteSpace. Processes 2019, 7, 818. [Google Scholar] [CrossRef]
  53. Rong, L.; Zheng, X.; Oba, B.T.; Shen, C.; Wang, X.; Wang, H.; Luo, Q.; Sun, L. Activating soil microbial community using bacillus and rhamnolipid to remediate TPH contaminated soil. Chemosphere 2021, 275, 130062. [Google Scholar] [CrossRef] [PubMed]
  54. Rehana, M.; Gladis, R.; Joseph, B. Controlled Release of Nutrients for Soil Productivity- A Review. Curr. J. Appl. Sci. Technol. 2022, 41, 34–46. [Google Scholar] [CrossRef]
  55. Ye, L.; Camps-Arbestain, M.; Shen, Q.; Lehmann, J.; Singh, B.; Sabir, M. Biochar effects on crop yields with and without fertilizer: A meta-analysis of field studies using separate controls. Soil Use Manag. 2020, 36, 2–18. [Google Scholar] [CrossRef]
  56. Liao, J.; Liu, X.; Hu, A.; Song, H.; Chen, X.; Zhang, Z. Effects of biochar-based controlled release nitrogen fertilizer on nitrogen-use efficiency of oilseed rape (Brassica napus L.). Sci. Rep. 2020, 10, 11063. [Google Scholar] [CrossRef]
  57. Mbachu, O.; Jenkins, G.; Kaparaju, P.; Pratt, C. The rise of artificial soil carbon inputs: Reviewing microplastic pollution effects in the soil environment. Sci. Total Environ. 2021, 780, 146569. [Google Scholar] [CrossRef]
  58. Xie, J.; Yang, Y.; Gao, B.; Wang, Y.; Li, Y.C.; Cheng, D.; Xiao, T.; Li, K.; Fu, Y.; Xu, J.; et al. Magnetic-sensitive nanoparticle self-assembled superhydrophobic biopolymer-coated slow-release fertilizer: Fabrication, enhanced performance, and mechanism. ACS Nano 2019, 13, 3320–3333. [Google Scholar] [CrossRef]
  59. Li, T.; Lu, S.; Yan, J.; Bai, X.; Gao, C.; Liu, M. An environment-friendly fertilizer prepared by layer-by-layer self-assembly for pH-responsive nutrient release. ACS Appl. Mater. Interfaces 2019, 11, 10941–10950. [Google Scholar] [CrossRef]
  60. Ardali, T.R.; Ma’mani, L.; Chorom, M.; Motamedi, E.; Gharebaba, M.F. A biocompatible NPK+Fe+Zn slow release fertilizer: Synthesis and its evaluation in tomato plant growth improvement. Sci. Rep. 2024, 14, 4640. [Google Scholar]
  61. Jariwala, H.; Santos, R.M.; Lauzon, J.D.; Dutta, A.; Wai Chiang, Y. Controlled release fertilizers (CRFs) for climate-smart agriculture practices: A comprehensive review on release mechanism, materials, methods of preparation, and effect on environmental parameters. Environ. Sci. Pollut. Res. 2022, 29, 53967–53995. [Google Scholar] [CrossRef] [PubMed]
  62. Kassem, I.; Ablouh, E.H.; El Bouchtaoui, F.Z.; Kassab, Z.; Khouloud, M.; Sehaqui, H.; Ghalfi, H.; Alami, J.; El Achaby, M. Cellulose nanocrystals-filled poly (vinyl alcohol) nanocomposites as waterborne coating materials of NPK fertilizer with slow release and water retention properties. Int. J. Biol. Macromol. 2021, 189, 1029–1042. [Google Scholar] [CrossRef] [PubMed]
Agriculture 14 01502 g001
Figure 1. Flowchart of the research methodology.
Figure 1. Flowchart of the research methodology.
Agriculture 14 01502 g001
Agriculture 14 01502 g002
Figure 2. Annual publication on SRF/CRF research from January 1990 to December 2023.
Figure 2. Annual publication on SRF/CRF research from January 1990 to December 2023.
Agriculture 14 01502 g002
Agriculture 14 01502 g003
Figure 3. The top 15 subject categories for SRFs/CRFs from 1990 to 2023.
Figure 3. The top 15 subject categories for SRFs/CRFs from 1990 to 2023.
Agriculture 14 01502 g003
Agriculture 14 01502 g004
Figure 4. (A) Top 10 most productive countries/regions that contributed to SRF/CRF research publications from 1990 to 2023. (B) Cooperation between countries in the field of SRF/CRF research from 1990 to 2023.
Figure 4. (A) Top 10 most productive countries/regions that contributed to SRF/CRF research publications from 1990 to 2023. (B) Cooperation between countries in the field of SRF/CRF research from 1990 to 2023.
Agriculture 14 01502 g004
Agriculture 14 01502 g005
Figure 5. Cooperation between major research institutions in SRF/CRF research during January 1990 to December 2023.
Figure 5. Cooperation between major research institutions in SRF/CRF research during January 1990 to December 2023.
Agriculture 14 01502 g005
Agriculture 14 01502 g006
Figure 6. Cooperation between major authors in SRF/CRF research from 1990 to 2023.
Figure 6. Cooperation between major authors in SRF/CRF research from 1990 to 2023.
Agriculture 14 01502 g006
Agriculture 14 01502 g007
Figure 7. (A) Annual and (B) cumulative top 50 keywords with the highest frequency in the field of SRF/CRF research from 1990 to 2023 (the presence of null values is visually represented by gray squares).
Figure 7. (A) Annual and (B) cumulative top 50 keywords with the highest frequency in the field of SRF/CRF research from 1990 to 2023 (the presence of null values is visually represented by gray squares).
Agriculture 14 01502 g007
Agriculture 14 01502 g008
Figure 8. Network visualization of keyword co-occurrence network.
Figure 8. Network visualization of keyword co-occurrence network.
Agriculture 14 01502 g008
Agriculture 14 01502 g009
Figure 9. The burst word information on SRF/CRF research during 1990–2023.
Figure 9. The burst word information on SRF/CRF research during 1990–2023.
Agriculture 14 01502 g009
Table 1. Top 10 most productive institutions in SRF/CRF research from 1990 to 2023.
Table 1. Top 10 most productive institutions in SRF/CRF research from 1990 to 2023.
RankInstitutionCountry and RegionRecords% of 1676Total CitationsAverage Cited Times
1Univ FloridaUSA975.79321733.16
2Chinese Acad SciChina794.71253432.08
3Shandong Agr UnivChina684.06161323.72
4Univ Chinese Acad SciChina291.7365322.52
5USDA ArsUSA261.55127949.19
6Langzhou UnivChina221.31133360.59
7Purdue UnivUSA201.1942221.10
8Univ Fed Sao CarlosBrazil201.1970935.45
9Chinese Acad Agr SciChina191.1332116.89
10Univ Sao PauloBrazil191.1346624.53
Table 2. Top 10 most productive journals in SRF/CRF research from 1990 to 2023.
Table 2. Top 10 most productive journals in SRF/CRF research from 1990 to 2023.
RankJournal NameRecords% of 1676IF2023Total CitationsAverage Cited Times
1Hortscience694.121.981511.81
2Science of the Total Environment442.639.8124328.25
3Communications in Soil Science and Plant Analysis372.211.867218.16
4Journal of Agricultural and Food Chemistry372.216.1183549.59
5Journal of Plant Nutrition372.212.148012.97
6Horttechnology321.911.041212.88
7Journal of Cleaner Production321.9111.192628.94
8Agronomy—Basel301.793.71876.23
9International Journal of Biological Macromolecules281.678.261421.93
10Journal of Applied Polymer Science281.673.072225.79
Table 3. Top 10 most productive authors in SRF/CRF research from 1990 to 2023.
Table 3. Top 10 most productive authors in SRF/CRF research from 1990 to 2023.
RankAuthorRecordsTotal CitationsInstitutionAverage Cited Times
1Zhang M36832Shandong Agr Univ23.11
2Gao B231845Univ Florida80.22
3Yang YC23765Shandong Agr Univ33.26
4Zhou JM21446Chinese Acad Sci21.24
5Du CW20430Nanjing Institute of Soil Science, Chinese Academy of Sciences21.50
6Shen YZ18287Nanjing Institute of Soil Science, Chinese Academy of Sciences15.94
7Jacobs DF17468Purdue Univ27.53
8Liu MZ161110Lanzhou Univ69.38
9Liu ZG16391Shandong Agr Univ24.44
10Li YC15730Shandong Agr Univ48.67
Table 4. Top 10 cited publications related to SRF/CRF research from 1990 to 2023.
Table 4. Top 10 cited publications related to SRF/CRF research from 1990 to 2023.
TitleFirst AuthorYearJournalTotal CitationTC per Year
Evaluation of effectiveness of enhanced-efficiency fertilizers as mitigation options for N2O and NO emissions from agricultural soils: meta-analysisAkiyama H2010Global Change Biology53235.47
Engineered biochar reclaiming phosphate from aqueous solutions: mechanisms and potential application as a slow-release fertilizerYao Y2013Environmental Science & Technology50942.42
Removal of phosphate from aqueous solution by biochar derived from anaerobically digested sugar beet tailingsYao Y2011Journal of Hazardous Materials44231.57
Ammonia volatilization from synthetic fertilizers and its mitigation strategies: A global synthesisPan BB2016Agriculture Ecosystems & Environment34638.44
Preparation and characterization of slow-release fertilizer encapsulated by starch-based superabsorbent polymerQiao DL2016Carbohydrate Polymers25928.78
Fertilizer source and tillage effects on yield-scaled nitrous oxide emissions in a corn cropping systemVenterea RT2011Journal of Environmental Quality22716.21
Recycling of manure nutrients: use of algal biomass from dairy manure treatment as a slow release fertilizerMulbry W2005Bioresource Technology22011.00
Environmentally friendly slow-release nitrogen fertilizerNi BL2011Journal of Agricultural and Food Chemistry21015.00
Use of controlled release fertilizers and nitrification inhibitors to increase nitrogen use efficiency and to conserve air and water qualityShoji S2001Communications in Soil Science and Plant Analysis2068.58
Controlled-release fertilizer encapsulated by starch/polyvinyl alcohol coatingHan XZ2009Desalination20312.69
Table 5. The main keywords in different keyword clusters.
Table 5. The main keywords in different keyword clusters.
ClustersMain KeywordsResearch Topic
Red clusterNitrogen, plants, growth, quality, plant growth, plant nutrition, plant qualityThe impact of SRFs/CRFs on crop growth and quality
Blue clusterUrea, slow release, super-absorbent, Urea-based SRFs/CRFs
Yellow clusterPhosphorus, recovery, biomass, struvite, adsorption, kinetics, mechanism,Phosphorus fertilizer slow and controlled SRFs/CRFs
Green clusterSoil, management, use efficiency, nitrous, nitrous-oxide emissions, nitrification inhibitors, ammonia volatilizationImpact of SRFs/CRFs on N use efficiency, nitrification and denitrification functions in soil–plant systems
Purple clusterBiogradation, bioremediation, bioavailabilityDegradation aspects of SRFs/CRFs
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Li, X.; Li, Z. Global Trends and Current Advances in Slow/Controlled-Release Fertilizers: A Bibliometric Analysis from 1990 to 2023. Agriculture 2024, 14, 1502. https://doi.org/10.3390/agriculture14091502

AMA Style

Li X, Li Z. Global Trends and Current Advances in Slow/Controlled-Release Fertilizers: A Bibliometric Analysis from 1990 to 2023. Agriculture. 2024; 14(9):1502. https://doi.org/10.3390/agriculture14091502

Chicago/Turabian Style

Li, Xianhong, and Zhonghong Li. 2024. "Global Trends and Current Advances in Slow/Controlled-Release Fertilizers: A Bibliometric Analysis from 1990 to 2023" Agriculture 14, no. 9: 1502. https://doi.org/10.3390/agriculture14091502

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop