Mapping 25 Years of Hydrogel Research in Soil Health: Bibliometric Insights into Scientific Trajectories and Global Collaboration Gaps

Soil degradation and increasing climate variability are intensifying soil moisture limitations in many agricultural regions, particularly in arid and semi-arid environments. Hydrogels (superabsorbent polymers, SAPs), have emerged as promising soil amendments capable of improving soil water retention and enhancing crop performance under water-limited conditions. Despite the growing body of experimental research on hydrogel-soil interactions, the overall intellectual structure and thematic development of this research field remain insufficiently understood. This study provides a comprehensive bibliometric assessment of global research on hydrogels and superabsorbent polymers applied to soil systems during the period 2000-2025. A dataset of 652 peer-reviewed articles indexed in the Scopus database was analysed using the Bibliometrix R package and VOSviewer to examine publication trends, collaboration patterns, and conceptual research themes. Results indicate a strong and accelerating growth in scientific output, particularly after 2015, reflecting increasing global interest in polymer-based soil amendments for water management and climate resilience. Keyword co-occurrence and bibliographic coupling analyses revealed that the literature is primarily structured around four major research domains: soil water management and crop productivity, modification of soil physical properties and water retention, soil structural stabilization and aggregation processes, and hydrogel materials and polymer chemistry. Thematic evolution analysis further indicates a transition from early studies on synthetic polymers toward increasing research attention on biodegradable and bio-based hydrogels derived from natural polymers. However, biological responses of soil systems and socio-economic aspects of hydrogel adoption remain comparatively underexplored. This bibliometric synthesis clarifies the conceptual development of hydrogel research in soil systems and identifies priority areas for future interdisciplinary research on sustainable soil water management.