Three Decades of Evolution in Approaches and Methods in Urban Soil Research (1995–2024). A Bibliometric Perspective

The article presents the results of a study on the formation and evolution of the global research field devoted to urban soils between 1995 and 2024. A database comprising 961 scientific articles published during this period was compiled and subjected to a detailed bibliometric analysis. The analysis included an assessment of the temporal dynamics of publication output, the identification of the most frequently publishing journals and countries with the highest research activity, an examination of international collaboration patterns, and the distribution of publication languages. The core part of the study involved an analysis of keyword co-occurrence in the collected literature. Based on these data, a network model was constructed to represent the variability and interconnections among keywords. Analytical methods derived from mathematical graph theory were applied to characterize complex network structures in terms of their coherence, vertex degree distribution, and the extraction of so-called p-layers. To isolate these layers, an original graph-layering technique was proposed, enabling a multilevel interpretation of relationships and hierarchies within the analysed network. The keyword co-occurrence analysis revealed that the development of urban soil research can be divided into two distinct phases. The first phase (1995–2010) represents the emergence of research awareness, while the second (2011–2024) corresponds to a “developmental” stage characterized by the expansion and deepening of knowledge about urban soils. Furthermore, the results indicate that research in this field has revolved around a limited number of central concepts (Urban Soil, Heavy Metals, Biochar), which serve as semantic reference points within the scientific discourse. The established prominence of these keywords positions them as enduring thematic anchors in a still relatively young yet dynamically developing research domain, which continues to evolve in parallel with growing public awareness of the importance of the urban environment.