Smart hydrogels from agro-waste to enhance soil water retention for climate-resilient agriculture

Intensive agriculture and extensive agrochemical use have increased food production but created significant environmental challenges, including greenhouse gas emissions, water contamination, and large volumes of waste. At the same time, water scarcity and climate‑induced droughts threaten crop productivity and food security. Superabsorbent hydrogels present a potential solution by improving soil moisture retention, reducing irrigation demand, and enhancing nutrient use efficiency. However, conventional synthetic hydrogels are non‑biodegradable and costly, limiting their use by smallholder farmers. This highlights the need for sustainable, bio‑based hydrogels derived from agricultural residues.

This study evaluated the feasibility of synthesizing hydrogels from sugarcane bagasse (SCB), rice straw (RS), and coconut husks (CH) to strengthen the resilience of the farming system under input scarcity and climate stress. The lignocellulosic agro-wastes were alkaline‑delignified to expose the cellulose, which was modified into carboxymethyl cellulose to improve its water‑swelling properties. Ionic and covalent crosslinking approaches were tested to optimize hydrogel yield and functionality.

Ionic crosslinking with single covalent crosslinking produced 36.69 g and 30.80 g of hydrogel (wet weight) from SCB and RS, equivalent to 14.68 and 12.32 metric tons per ton of biomass. Ionic crosslinking with double covalent crosslinking yielded 32.42 g from SCB and 25.94 g from RS, corresponding to 12.97 and 10.38 metric tons per ton. SCB is recommended where a high hydrogel yield is required, while ionic crosslinking with single covalent crosslinking favors bulk production. Future research should expand biomass-based and microbial synthesis pathways and improve hydrogel drying methods.