From Agricultural Byproducts to Value-Added Materials: Wheat Straw-Based Hydrogels as Soil Conditioners?

Herein, we present a simple synthetic approach to fabricate wheat straw-based hydrogels, starting from the unfractionated and carboxymethylated lignocellulosic matrix. Citric acid was used as a cheap and nontoxic cross-linker. The applied hydrogel characterizations can be essentially distinguished into investigations on the synthetic pathway and model-scale application-related tests. For the first part, three sample-specific values were introduced: gel yield (%), swelling ratio (g(water)/g) and gel stiffness (G', Pa). Optimized reaction conditions led to mechanically stable gels with a moderate swelling ratio (up to 50 g(water)/g). Moreover, dynamic vapor sorption analysis revealed that these gels reswell after complete drying. Finally, one selected hydrogel was incorporated into two different model soil substrates, assessing its impact on the soil's water retention. Our experiments showed that already low incorporation rates (0.2 wt %) increased the water content of a sandy soil by 70% (at pF 2.53). Overall, these results are promising and may lead to new soil amendments based on a sustainable source and a simple synthesis.