Agro hydrogel: An eco friendly polymer for sustainable water management in agriculture

Introduction

Water scarcity is one of the most pressing challenges in global agriculture. According to the Food and Agriculture Organization (FAO) [6] , agriculture accounts for nearly 70% of global freshwater withdrawals, yet irrigation efficiency remains below 50% in many regions (FAO, 2021). Climate change, population growth, and unsustainable farming practices exacerbate the demand for water, leading to soil degradation and reduced crop yields (UNESCO, 2020) [7] . In drought-prone areas, farmers face acute challenges in maintaining soil moisture, which directly impacts food security. Hydrogels, a class of superabsorbent polymers, have emerged as promising materials to address these challenges. Their ability to absorb water many times their own weight and release it gradually to plants makes them valuable for soil moisture management (Buchholz & Graham, 1998) [2] . Agro hydrogels specifically designed for farming applications can reduce irrigation frequency, improve nutrient availability, and enhance plant growth.

Comparative studies have demonstrated that hydrogels can increase soil water retention by 30-50% and improve crop yields by up to 20% under water-limited conditions (Montesano et al., 2015) [5] . However, performance varies depending on soil type, polymer composition, and additive incorporation. This highlights the need for tailored hydrogel formulations that balance efficiency, cost, and environmental safety. Despite significant progress, most commercial hydrogels remain expensive and are not optimized for diverse agricultural environments. Furthermore, limited studies have integrated multifunctional additives such as bentonite clay (for controlled release), potassium humate (for soil enrichment), Trichoderma (for fungal protection), and calcium nitrate (for root strengthening). This project addresses these gaps by synthesizing an agro hydrogel using free radical polymerization and evaluating its performance in terms of water absorption, soil moisture retention, pH stability, and plant growth enhancement.

Objectives

The objectives of this study are  To synthesize an agro hydrogel using acrylamide and BIS cross-linker via free radical polymerization.  To incorporate functional additives for enhanced performance.  To evaluate water absorption, swelling ratio, soil moisture retention, and pH stability.  To assess the impact of hydrogel application on plant growth under controlled conditions. This data underscores the urgent need for innovative water management technologies such as agro hydrogels, particularly in regions with low irrigation efficiency and high water demand.

Global Context of Water Use in Agriculture

Free Radical Polymerization

The agro hydrogel synthesized in this study is based on free radical polymerization, a chain-growth process where reactive radicals initiate and propagate polymer chains. Acrylamide (𝐶𝐻 2 = 𝐶𝐻𝐶𝑂𝑁𝐻 2 ) serves as the primary monomer, while N,N-Methylenebisacrylamide (BIS) acts as a cross-linker to form a three-dimensional network. Ammonium persulfate (APS) decomposes to generate sulfate radicals, which initiate polymerization. TEMED accelerates radical formation by reducing APS.

Reaction scheme

Cross-Linked Polymer Network

The incorporation of BIS introduces covalent bonds between polymer chains, creating a three-dimensional hydrogel matrix. This network traps water molecules within its pores, enabling high absorption and retention. The degree of cross-linking directly influences swelling capacity:  Low cross-link density → higher swelling, weaker mechanical strength.  High cross-link density → lower swelling, stronger mechanical stability.

Equation for swelling ratio

𝑄 = 𝑊 𝑤𝑒𝑡 𝑊 𝑑𝑟𝑦

Where: 𝑊 𝑤𝑒𝑡 is the swollen hydrogel weight and 𝑊 𝑑𝑟𝑦 is the initial dry weight.

Swelling Theory and Osmotic Pressure

Hydrogel swelling is governed by osmotic pressure differences between the polymer network and the surrounding solution. Hydrophilic groups (-CONH 2 , -COOH) attract water molecules, while cross-links prevent dissolution. The Flory-Rehner theory describes swelling equilibrium:

Where  Π= osmotic pressure  𝑣 2 = polymer volume fraction  𝜒= polymer-solvent interaction parameter  𝑁/𝑉= cross-link density

Functional Additives and Mechanisms

To enhance performance, several additives were incorporated:  Bentonite clay: Layered silicate structure that regulates water release and improves soil texture.  Potassium humate: Organic compound that enriches soil fertility, improves cation exchange capacity, and enhances nutrient uptake.

Trichoderma spores

Beneficial fungi that protect roots against pathogens and promote plant growth.

Calcium nitrate

Provides calcium ions for root strengthening and nitrate ions for improved nitrogen nutrition. accelerator.  Functional additives: bentonite clay, potassium humate, Trichoderma spores, calcium nitrate. All chemicals were of analytical grade and used without further purification.

Hydrogel Synthesis

The hydrogel was synthesized via free radical polymerization. The process involved three phases: formation, processing, and additive incorporation.

Preparation of Monomer Solution

The monomer solution is prepared by dissolving acrylamide and BIS in distilled water. Flowchart of experimental design showing synthesis → characterization → testing → plant growth evaluation.

Statistical Analysis

All experiments were conducted in triplicate. Results were expressed as mean ± standard deviation. Statistical significance was determined using ANOVA at 𝑝 < 0.05.

Water Absorption Test

The hydrogel demonstrated rapid water uptake within the first 30 minutes, reaching equilibrium absorption at 60 minutes. Result: Maximum absorption capacity = 25× its dry weight.

Observation Table 1: Water Absorption

Swelling Ratio Test

The swelling ratio was calculated using the formula:

This high swelling ratio indicates excellent hydrogel performance compared to commercial polyacrylate hydrogels, which typically range between 15-20 (Li et al., 2014) [4] . [4] Starch-based hydrogel 20 Ahmed, 2015 [1] 4.3 Soil Moisture Retention Test Hydrogel-treated soil retained significantly higher moisture compared to untreated soil. Result: Hydrogel extended soil moisture availability by ~3 days compared to untreated soil.

Observation Table 2: Soil

pH Analysis

The hydrogel exhibited a neutral pH range (6.8-7.2), confirming its suitability for agricultural applications.

Result

Hydrogel-treated plants showed ~50% greater height at day 12 compared to controls.

Statistical Analysis

All experiments were conducted in triplicate. Results are expressed as mean ± standard deviation. ANOVA analysis confirmed statistical significance at 𝑝 < 0.05for differences in water absorption, soil moisture retention, and plant growth between treated and untreated groups.

Interpretation of Polymer Chemistry Results

The agro hydrogel synthesized via free radical polymerization exhibited excellent water absorption and swelling properties. The high swelling ratio (25×) can be attributed to the presence of hydrophilic amide groups in acrylamide, which form hydrogen bonds with water molecules. The BIS cross-linker provided a stable three-dimensional network, preventing dissolution while maintaining elasticity. This balance between hydrophilicity and cross-link density is critical: too few cross-links lead to structural collapse, while excessive cross-linking reduces swelling capacity (Buchholz & Graham, 1998) [2] . The Flory-Rehner theory supports these findings, as the osmotic pressure difference between the polymer matrix and surrounding solution drives water uptake. The hydrogel's ability to reach equilibrium absorption within 60 minutes demonstrates efficient diffusion pathways created by the porous network, confirmed by SEM analysis.

Soil Moisture Retention and Plant Growth

The soil moisture retention test revealed that hydrogel-treated soil maintained 50% moisture after five days, compared to only 10% in untreated soil. This extended hydration period is consistent with studies by Montesano et al. (2015) [5] , who reported that biodegradable hydrogels improved water use efficiency by 30-40%. The gradual release of water from the hydrogel matrix aligns with the controlled hydration mechanism described in swelling theory.

Plant growth trials further validated the hydrogel's agricultural potential. Hydrogel-treated plants exhibited ~50% greater height after 12 days, reflecting improved root hydration and nutrient uptake. The incorporation of calcium nitrate likely contributed to stronger root development, while potassium humate enhanced soil fertility. The presence of Trichoderma spores provided biological protection, reducing stress from soil pathogens.

Comparison with Literature

Compared to commercial polyacrylate hydrogels (swelling ratio ~18), the agro hydrogel demonstrated superior performance (swelling ratio 25). Ahmed (2015) [1] reported similar improvements when natural additives were incorporated into hydrogel matrices. Guilherme et al. (2015) [3] emphasized the importance of eco-friendly formulations, noting that hydrogels based on polysaccharides achieved better biodegradability but often lacked mechanical strength.

The current study bridges this gap by combining synthetic polymer stability with natural additive functionality. [4] Starch-based hydrogel 20 40% +30% Ahmed, 2015 [1]

Limitations

Despite promising results, several limitations must be acknowledged:  Overhydration risk: Excessive hydrogel application may lead to waterlogging and root rot.

 Cost considerations: Large-scale synthesis and additive incorporation may increase production costs compared to conventional hydrogels.  Soil variability: Performance may differ across soil types (sandy vs. clayey soils), requiring site-specific optimization.  Biodegradability: While additives are eco-friendly, the synthetic polymer backbone may persist in soil; long-term degradation studies are needed.

Practical Implications

The findings suggest that agro hydrogels can significantly reduce irrigation frequency, making them particularly valuable in drought-prone regions. Their neutral pH ensures compatibility with diverse crops, while functional additives provide multifaceted benefits: controlled hydration, soil enrichment, pathogen resistance, and root strengthening. Adoption of such hydrogels could improve crop yields, conserve water resources, and support sustainable farming practices.

Sustainability and Water Conservation

The agro hydrogel demonstrated significant potential for reducing water wastage in agriculture. By retaining soil moisture for up to three additional days compared to untreated soil, irrigation frequency can be reduced by 30-40%. This aligns with FAO projections that improved water management technologies could save up to 20% of global agricultural water use (FAO, 2021). In drought-prone regions, such savings directly translate into enhanced resilience and food security.

Eco-Toxicity Assessment

The hydrogel exhibited a neutral pH (6.8-7.2), ensuring compatibility with diverse crops and minimizing risks of soil acidification or alkalization. Unlike synthetic polyacrylate hydrogels, which may release residual monomers, the agro hydrogel's incorporation of natural additives (bentonite, humate, Trichoderma) reduces environmental toxicity. FTIR analysis confirmed complete polymerization, minimizing free acrylamide residues that could pose ecological hazards.

Contribution to Sustainable Agriculture

The agro hydrogel supports multiple pillars of sustainability:  Environmental: Reduced water wastage, improved soil health, eco-friendly additives.  Economic: Lower irrigation costs, potential yield improvements.

 Social: Enhanced food security in drought-affected communities.

Future Work

While the results are promising, further research is required to validate the hydrogel's performance under diverse agricultural conditions and to ensure scalability. The following directions are proposed:

Long-Term Field Trials

Conduct extended trials across different soil types (sandy, clayey, loamy) and climatic zones to assess hydrogel performance under real farming conditions. Monitoring crop yield, soil health, and biodegradation rates over multiple seasons will provide critical insights.

Integration with Precision Irrigation

Combine hydrogel application with smart irrigation systems (drip irrigation, IoT-based soil sensors) to optimize water delivery. This integration could maximize efficiency and reduce water wastage further.

Economic Feasibility Studies

Evaluate production costs, scalability, and farmer adoption rates. Comparative cost-benefit analyses against conventional irrigation methods will determine commercial viability.

Biodegradability and Environmental Safety

Investigate long-term degradation of the synthetic polymer backbone and its impact on soil ecosystems. Incorporating more natural polymers (e.g., starch, cellulose) could enhance biodegradability without compromising performance.

Functional Additive Optimization

Explore additional additives such as biochar (for carbon sequestration), micronutrients (for targeted fertilization), and beneficial microbes (for soil microbiome enhancement). Tailoring additive combinations could create crop-specific hydrogel formulations.

Acknowledgement

AcknowledgementThe authors sincerely thank ACIC-MEPCO Innovative Foundation for the financial support through Community Innovator Fellowship Scheme under ACIC-MIF.

References

1. Ahmed EM. Hydrogel: preparation, characterization, and applications. J Adv Res. 2015;6(2):105-121.
2. Buchholz FL, Graham AT. Modern superabsorbent polymer technology. New York: Wiley; 1998.
3. Guilherme MR, et al. Superabsorbent hydrogels based on polysaccharides for agricultural applications. Eur Polym J. 2015;72:365-385.
4. Li A, et al. Preparation and application of polyacrylamide based hydrogels. Polym Int. 2014;63(5):891-898.
5. Montesano FF, et al. Biodegradable hydrogel improves water use efficiency and crop yield. Agric Water Manag. 2015;152:39-46.
6. Food and Agriculture Organization. The state of food and agriculture. Rome: Food and Agriculture Organization of the United Nations; 2021.
7. United Nations Educational, Scientific and Cultural Organization. World water development report. Paris: UNESCO; 2020.
8. Kaur P, Agrawal R, Pfeffer FM, Williams R, Bohidar HB. Hydrogels in agriculture: prospects and challenges. J Polym Environ. 2023;31:3701-3718.
9. Buitrago Arias C, et al. Analysis of the growth of hydrogel applications in agriculture: a review. Gels. 2025;11(9):731.
10. Hasan AMA, Abdel Raouf MES. Cellulose based superabsorbent hydrogels. Carbohydr Polym. 2019;245:267-278.
11. Peppas NA, et al. Hydrogels from polysaccharide based materials: fundamentals and applications. J Phys Chem B. 2008;112(3):497-505.
12. De Fraiture C, Wichelns D. Satisfying future water demands for agriculture. Agric Water Manag. 2010;97:502-511.
13. Wu J, Huang G. Hydrogels for agricultural applications. J Mater Chem A. 2016;4(9):3001-3012.
14. Thakur VK, Thakur MK. Recent advances in hydrogels for agricultural applications. Int J Biol Macromol. 2015;72:102-110.
15. Yang L, et al. Biodegradable starch based hydrogels for agricultural water retention. Carbohydr Polym. 2018;181:100-110.
16. Zhang J, et al. Chitosan based hydrogels for sustainable agriculture. J Appl Polym Sci. 2019;136(12):472-481.
17. Chen J, et al. Controlled release fertilizers using hydrogel matrices. J Agric Food Chem. 2017;65(12):234-242.
18. Singh N, et al. Biopolymer hydrogels for soil conditioning. Environ Sci Pollut Res. 2020;27:112-124.
19. Gao Y, et al. Hydrogel composites with bentonite for water retention. Appl Clay Sci. 2016;132-133:75-82.
20. Luo H, et al. Potassium humate modified hydrogels for soil fertility. Soil Sci Soc Am J. 2019;83(4):765-774.
21. Harman GE, et al. Trichoderma species in agriculture. Phytopathology. 2004;94(2):138-150.
22. Sharma S, et al. Calcium nitrate supplementation in hydrogel systems. Plant Soil. 2018;426(1-2):45-56.
23. Ahmed K, et al. Hydrogel based drought mitigation strategies. Sustainability. 2021;13(5):2789.
24. Zhang X, et al. Smart hydrogels for precision irrigation. Sensors. 2020;20(12):3456.
25. Wang Y, et al. Hydrogel degradation and soil impact. Environ Chem Lett. 2019;17:1585-1594.
26. Chen S, et al. Hydrogel composites for nutrient release. J Control Release. 2018;271:1-10.
27. Liu M, et al. Hydrogel based soil conditioners. J Agric Eng Res. 2017;162:120-130.
28. Zhao Y, et al. Biodegradable hydrogel for crop yield improvement. Field Crops Res. 2016;193:12-20.
29. Kumar R, et al. Hydrogel applications in horticulture. Scientia Hortic. 2019;252:215-222.
30. Singh A, et al. Eco friendly hydrogels for sustainable farming. J Clean Prod. 2022;330:129-140.
31. Zhang H, et al. Hydrogel composites with biochar. Agric Syst. 2018;162:45-53.
32. Chen L, et al. Hydrogel microbe interactions in soil. Appl Soil Ecol. 2021;165:103-112.
33. Patel R, et al. Hydrogel based nutrient delivery systems. J Plant Nutr. 2020;43(12):1789-1802.
34. Huang X, et al. Hydrogel impact on soil microbiome. Soil Biol Biochem. 2019;135:1-10.
35. MDPI Review. Hydrogel development, processing and applications in agriculture. Polymers. 2024;16(2):345367.