Water Absorption Capacity and Agricultural Utility of Biopolymer-Based Hydrogels: A Systematic Review and Meta-Analysis

Abstract

This review aims to elucidate the relationship between hydrogel composition and water absorption capacity, with a focus on biobased hydrogels, the influence of their constituents on water absorption, and their relevance to agricultural applications. The most frequently used biopolymers are cellulose, starch, chitosan/chitin, and alginate, all of which are derivable from agroindustrial waste, offering sustainable and environmentally friendly sourcing. These polymers possess a high amount of hydrophilic functional groups, enhancing their affinity for water and enabling the formation of highly absorbent hydrogels. Cross-linking agents further affect the hydrogel's swelling capacity by altering the number of available hydrophilic groups. Among them, N,N'-methylenebis-(acrylamide) is the most prevalent due to its ability to form stable networks, favoring high water absorption. However, concerns persist regarding their persistence in soil and potential environmental toxicity upon degradation. Citric acid has emerged as a promising alternative, reflecting a shift toward environmentally safer strategies. Beyond water absorption and retention, hydrogels exhibit potential as carriers for fertilizers and bioactive compounds, enabling the controlled release and availability in soil. A few studies included in this review have explored the incorporation of beneficial microorganisms, such as , , and , into hydrogel matrices, offering a clean and effective approach for agricultural enhancement that remains underexplored. This review highlights the connection between hydrogel composition and water absorption properties, identifying ecofriendly alternatives for hydrogel synthesis and applications in agriculture. It also reveals gaps in the development of sustainable, efficient hydrogels that could contribute to more environmentally friendly practices.

Keywords: agriculture; agroindustrial waste; biopolymers; cross-linking; fertilizer carriers; mass swelling; soil conditioners; sustainable materials.

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Historical development of hydrogel research and applications. This figure was created using BioRender (https://www.biorender.com/), under a Creative Commons license.

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Flowchart illustrating the study selection process following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Steps of the initial screening, eligibility assessment, and final inclusion are depicted.

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Distribution of studies utilizing the most frequently employed natural materials for hydrogel production, as identified in the Web of Science and ScienceDirect databases from 2018 to 2024, based on the Preferred Reporting Items for Systematic Review and Meta-Analyzes (PRISMA) methodology.

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Forest plot representing cellulose-based hydrogels, detailing maximum and minimum water absorption capacities (g/g), odds ratios (ORs), summary effects, 95% confidence intervals (CIs), and the percentage of weight attributed to each study. The analysis follows an REM with a 95% CI for the mean effect size under fixed-effect meta-analysis.

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Forest plot representing starch-based hydrogels, detailing maximum and minimum water absorption capacities (g/g), odds ratios (ORs), summary effects, 95% confidence intervals (CIs), and the percentage of weight attributed to each study. The analysis follows an REM, with a 95% CI for the mean effect size under fixed-effect meta-analysis.