Cristofer Chambi, Julio Alegre Orihuela, María Pachés, Patricia Pacheco Umpire, Javier Montalvo Andia
Hydrogels (HGs) have emerged as promising multifunctional materials for sustainable agriculture due to their high water retention capacity and their ability to act as controlled-release platforms for agrochemicals, nutrients, microorganisms, and bioactive compounds. Their application has gained increasing attention in response to global challenges associated with climate change, water scarcity, soil salinization, and the low efficiency of conventional fertilizers, which contribute to environmental degradation and reduce crop productivity. This review provides a critical overview of hydrogel-based systems for agricultural applications, with particular emphasis on the encapsulation of bioactive components for soil remediation and crop protection under abiotic stress conditions. A systematic literature review following PRISMA guidelines was conducted using the Scopus database, resulting in the analysis of 548 studies published between 2003 and 2024. Bibliometric analysis revealed a marked increase in research activity since 2021, mainly driven by advances in water-retention technologies, nanocomposite hydrogels, controlled-release systems, and bioactive encapsulation strategies. The review discusses the main factors governing hydrogel functionality, including swelling behavior, crosslinking density, biodegradability, and interactions with soil-plant systems. Particular attention is given to recent developments involving the incorporation of microorganisms, nanoparticles, micronutrients, and agrochemicals into biodegradable hydrogel matrices to improve nutrient availability, mitigate salinity stress, and reduce agrochemical losses. Finally, the challenges associated with scalability, environmental stability, and field validation are discussed, highlighting the potential of hydrogel-based bioactive delivery systems for developing resilient and resource-efficient agricultural systems.