(224c) Moisture Retention in Emulated Soil Micromodels: Development and Performance of Sustainable Agriculture Biotechnology

Soil bacteria living near plant roots secrete exopolysaccharides (EPS), a polymeric substance which can help modulate soil moisture and promotes plant growth. EPS functions in several different ways: (i) EPS behave as hydrogel, swelling during wet soil conditions and remaining hydrated during dry soil conditions; (ii) EPS promotes aggregation of soil particles and thereby promotes water retention in dry soil conditions through stronger capillary forces; and (iii) EPS alters surface properties of soil, creating more water repellent surfaces to inhibit rapid re-wetting in wet soil conditions. EPS functions in concert with the physical microstructure of real soil; therefore, it is necessary to study EPS performance in physically realistic micro-structures. Here we show pore-scale changes in moisture distribution within emulated soil micromodels that have systematically varied physical microstructures and surface water repellencies, and can be loaded with well-defined pore solutions. Experimental results showed dilute EPS solutions took twice as long to dry compared with pure water in identical micromodels. Microstructure geometry was found to influence drying rate over a range of pore saturation values as well as control the spatial distribution of liquid and gas phases within unsaturated soil micromodels. Deionized water took four times longer to completely dry from micromodels with higher water repellency surfaces compared with micromodels with lower water repellency surfaces. These results illustrate the various mechanisms whereby EPS impacts the spatial distribution and evaporation resistance of soil moisture. We provide a systematic method to evaluate performance of natural EPS solutions in modulating soil water and promoting resiliency of terrestrial ecosystem; we anticipate our approach may speed the development of sustainable agriculture biotechnology to enable food production using less water.