CAREER: Altering transient soil evaporation mechanisms through hydrophobicity

Kansas State University, Manhattan KS

Investigators

Abstract

Growing food with less water by reducing soil evaporation The production of food requires adequate fresh water, and the sustainable production of food is a critical focus of the Food, Energy, and Water nexus. Reductions in soil evaporation rates will lower irrigation demands and overall water consumption for crop production, thereby conserving water worldwide and in the Ogallala Aquifer in the Great Plains. This research project will understand the effects of hydrophobic soil (where water beads up) on evaporation compared to typically hydrophilic soil (where water spreads out) through laboratory studies. Glass beads will be coated to make them hydrophobic and these beads will be used to simulate soil. Evaporation will be studied from a few beads and a tray of beads under weather conditions similar to fields. Next, a type of soil called Ottawa sand will be coated to become hydrophobic and evaporation will be measured from the plain, hydrophilic sand and hydrophobic sand. These experiments will show how soil hydrophobicity affects evaporation from soil. Soil hydrophobicity can occur naturally due to minerals, organic materials, or waxes. Information from these laboratory evaporation studies will be used to determine best agricultural practices to reduce water losses since the Ogallala Aquifer provides water for over 20% of corn, wheat, sorghum, and cattle produced in the United States. Additionally, this research project will attract diverse students due to the importance of the research. The Principal Investigator (PI) and student researchers will use bread baking as an analogy for soil evaporation with groups of female High School students at the EXCITE workshop at Kansas State University (KSU) and the PI and researchers will showcase the research to first year, female undergraduate students at an annual Research Open House. The PI will also teach an interdisciplinary course on heat and mass transfer in the Food, Energy, and Water nexus to graduate students from multiple colleges at KSU. This research will investigate transient evaporative phase change in a three-phase (i.e., soil, water, and air) system. The objectives of this study are to understand the impacts of hydrophobicity on evaporation mechanisms including contact line dynamics, capillary transport, and enhanced water vapor diffusion. Glass and Teflon-coated beads will be used to simulate soil for pore-level experiments. Evaporation will be modeled and experimentally investigated using a high speed and IR camera for a range of surface temperatures and realistic environmental conditions (e.g., air temperature and relative humidity and simulated solar irradiation). Contact lines will be observed for water evaporating from hydrophilic or hydrophobic single pores. Using knowledge obtained from these single pore studies, evaporation fronts and mechanisms such as capillary transport and enhanced water vapor diffusion will be investigated for multiple pores; water will be dyed with fluorescent dye rhodamine B and excited using a Nd:YAG laser. Color shifts will be used to identify evaporation fronts and liquid capillary transport for a given cross section of the porous material. In the final phase of the research, evaporation will be studied from layers of naturally hydrophilic and artificially hydrophobized Ottawa sand to understand the impacts of hydrophobicity on capillary transport and enhanced water vapor diffusion. This study will numerically and experimentally assess the relative impacts of hydrophobicity on these three primary evaporation mechanisms (i.e., contact line dynamics, capillary transport, and enhanced water vapor diffusion) and create a mechanistic map to show the dominant evaporation mechanism for field environmental conditions. As a result, the improved understanding of hydrophobicity on soil evaporation can inform agricultural best practices.