Investigating hydrogel potentialities for improving soil pore network by using X-ray computed microtomography

Hydrogels (HGs) are conventionally defined as a natural or synthetic polymeric 3D networks with high hygroscopicity and water-swelling properties. Over the decades, HGs have been widely utilized in various fields of cosmetics, food additives, tissue engineering, drug delivery, and pharmaceuticals. Only recently HGs have been studied also for agronomic purpose. Indeed, their unique physical properties, including their porosity and swellability, make them ideal platforms for water and nutrient delivering. The aim of this study was to investigate the potentialities of two HGs, one formed by polyacrylamide and one by cellulose added with clay and humic acids, for improving soil porosity of three soil types (sandy “SD”, silty “SL” and clay “CL”). Soil pore network was characterized with X-ray computed microtomography (µCT) at 50 µm resolution and subsequent image analysis measuring  total porosity (TP), pore size distribution (PSD), mean diameter (MD), connectivity density and degree of anisotropy. Soil samples were at first saturated and then dried trough freezing and drying cycles with acetone at -80°c.

Preliminary results showed that at water saturation HG increased TP of four- and two-fold, respectively for SL and CL soil, MD of 40 (SD), 519 (SL) and 164 µm (CL) while no effects were found on other pore architecture indices (e.g., connectivity or anisotropy). The PSD analysis highlighted that HG increased the macroporosity fraction (e.g., pore > 0.8 mm) only in SL (+36%) and CL (+11%) while the other pore classes were not affected. Present study demonstrated that in fine-textured soils at high water content, HG might be a valuable tool to increase not simply the TP but, in particular, the macroporosity fraction which may play a key role in soil functioning and ecosystem services. Future research will investigate the HG performances under dynamic soil moisture conditions on water holding capacity and hydraulic conductivity (Research supported by Fondazione CARIPARO, InnoGel, Progetti Eccellenza 2017).