Global water shortage is a crisis for all living systems, including agricultural cropping systems. Water absorbent hydrogels from synthetic polymers can retain moisture from irrigation or rainfall and release it in response to crop water demands, but have a limited functional lifespan and may release byproducts that are harmful to plants or pollute the soil environment. Hydrogels fabricated from plant-based polymers are more suitable for agricultural cropping systems because they could improve the soil water availability to the crop and gradually biodegrade to harmless carbon dioxide and water. The objective of this work was to determine how biodegradable lignin hydrogel affected the soil water availability to maize grown under drought conditions. The lignin hydrogel was applied at 0.3% and 0.6% (by weight) in pots subjected to water deficit or sufficiency, and compared to sodium polyacrylate hydrogel that was applied at the same rates. Maize plants were taller, had greater phosphorus content and more biomass when grown in soil with lignin hydrogel and sodium polyacrylate hydrogel than without hydrogel. Furthermore, soil receiving 0.6% lignin hydrogel produced significantly (P<0.05) greater maize biomass and relative leaf water content, with an 86% reduction in leaf proline content and 10% less electrolyte leakage under severe drought conditions than without hydrogel. There was more soil soluble Na and Na uptake by maize in the sodium polyacrylate-amended soil due to solubilization of the Na+ ions from the sodium polyacrylate. We recommend lignin hydrogel as a soil additive to increase water availability to crops experiencing drought stress that will not release undesirable byproducts into the cropping system.

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