A comprehensive bibliometric review, published in the Journal of Hazardous Materials Advances by Haotian Chen, Hao Yang, Xiaoyu Shi, Haoruo Li, Xinyi Wang, Qiran Ren, Aixing Deng, Zhenwei Song, and Weijian Zhang, provides an in-depth look at research trends concerning the application of exogenous organic amendments (OA) and their impact on soil leachingLeaching is the process where nutrients are dissolved and carried away from the soil by water. This can lead to nutrient depletion and environmental pollution. Biochar can help reduce leaching by improving nutrient retention in the soil.   More from 1964 to 2024. This study analyzed 8,430 articles from the Web of Science Core Collection database, revealing a significant and accelerating growth in publications, highlighting the increasing scientific and environmental relevance of this topic.

The research trajectory can be broadly divided into three distinct phases: an emergence phase (1966-1991), a growth phase (1992-2008), and a maturity phase (2009-2024). During the emergence phase, an average of only 10 papers were published annually. This number dramatically increased to 129 papers per year in the growth phase, with an annual increment of 11 papers. The maturity phase showed the most rapid expansion, averaging 391 papers per year and an annual increase of 23 papers, with annual publications reaching over 500 in 2024. This surge in research activity reflects growing environmental concerns and the catalytic influence of regulatory frameworks, such as the EU Nitrates Directive (1991) and the Waste Framework Directive (2008).

Geographically, China and the United States emerged as the leading contributors to this field, publishing 5,210 and 3,532 articles respectively. These two nations collectively account for a substantial 62% of the total publications. While the United States led early international collaborations, China has taken the lead in the maturity phase, collaborating with 62 different countries and co-authoring 188 publications with the United States.

Keyword analysis identified four major research clusters: N-related leaching, heavy metal-related leaching, nutrient leaching, and the role of biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More in mitigating leaching. Historically, N leaching, particularly nitrate leaching, has consistently dominated the research, accounting for over 50% of studies in the earlier phases, though this declined to 44% in the maturity phase. In contrast, research on phosphorus and heavy metal leaching has seen notable growth, with P-related studies increasing from 23% in the emergence phase to 34% in the maturity phase, and heavy metal research rising from 9% to 24% over the same period.

A significant shift in research focus has been observed from simply assessing the leaching risks associated with OA to developing effective mitigation strategies, with biochar application gaining significant prominence. Although biochar-related studies were absent during the growth phase due to a lack of formal definition, they experienced explosive growth in the maturity phase, becoming the most frequently occurring keyword. Biochar, defined as biomass-derived char applied to soil, is recognized for its porous structure and strong adsorption capacity, which helps alleviate soil contamination and control nutrient and pollutant leaching.

Despite the progress, the review highlights several knowledge gaps and future research directions. Emerging pollutants like antibiotics, antibiotic resistance genes (ARGS), and microplastics, which can migrate into deeper soil layers or water bodies, remain inadequately understood in terms of their leaching mechanisms. Existing regulations often lack specific provisions for these emerging contaminants. Furthermore, while biochar’s inhibitory effects on leaching are promising, most studies rely on laboratory simulations, necessitating more long-term field experiments to understand its environmental behavior and stability under real-world conditions. Future research should also focus on optimizing OA application rates and integrating multiple mitigation strategies, considering regional contexts and the variability of soil leaching under different cropping systems.

Overall, this comprehensive analysis provides an evidence-based foundation for rethinking OA strategies in agroecosystems and supports the development of adaptive, risk-informed policies for integrated nutrient and contaminant management.

Source: Chen, H., Yang, H., Shi, X., Li, H., Wang, X., Ren, Q., Deng, A., Song, Z., & Zhang, W. (2025). A bibliometric review of research trends in exogenous organic amendments application and soil leaching (1964–2024). Journal of Hazardous Materials Advances.