CAREER: Altering transient soil evaporation mechanisms through hydrophobicity

通过减少土壤蒸发用更少的水种植粮食粮食生产需要充足的淡水，可持续的粮食生产是粮食、能源和水关系的关键焦点。土壤蒸发率的降低将降低灌溉需求和作物生产的总用水量，从而在全球和大平原的奥加拉拉含水层中节约用水。本研究项目将通过实验室研究，了解疏水土壤（水呈珠状）与典型亲水土壤（水向外扩散）对蒸发的影响。玻璃珠将被涂上一层使其疏水，这些珠将被用来模拟土壤。在类似于田间的天气条件下，将从几个珠子和一盘珠子中研究蒸发。接下来，将一种叫做渥太华砂的土壤涂上疏水涂层，然后测量平原、亲水性砂和疏水性砂的蒸发情况。这些实验将显示土壤的疏水性如何影响土壤的蒸发。土壤疏水性可以自然发生，由于矿物质，有机物质，或蜡。来自这些实验室蒸发研究的信息将用于确定减少水损失的最佳农业实践，因为奥加拉拉含水层为美国生产的20%以上的玉米、小麦、高粱和牛提供了水。此外，由于研究的重要性，这个研究项目将吸引不同的学生。首席研究员（PI）和学生研究人员将在堪萨斯州立大学（KSU）的EXCITE研讨会上与一群女高中生一起用面包烘焙作为土壤蒸发的类比，PI和研究人员将在年度研究开放日向一年级的女本科生展示这项研究。PI还将向来自KSU多个学院的研究生教授关于食品，能源和水关系中的热量和质量传递的跨学科课程。本研究将探讨三相（即土壤、水和空气）系统中的瞬态蒸发相变。本研究的目的是了解疏水性对蒸发机制的影响，包括接触线动力学、毛细输送和增强的水蒸气扩散。玻璃和聚四氟乙烯涂层珠将用于模拟土壤孔隙水平的实验。将利用高速红外照相机对一系列表面温度和实际环境条件（例如，空气温度和相对湿度以及模拟太阳辐照）进行蒸发模拟和实验研究。接触线将被观察到水从亲水性或疏水性单孔蒸发。利用从这些单孔研究中获得的知识，蒸发前沿和机制，如毛细输送和增强的水蒸气扩散将在多孔中进行研究；用水荧光染料罗丹明B染色，用Nd:YAG激光激发。色移将用于识别蒸发前沿和液体毛细管输送的给定截面的多孔材料。在研究的最后阶段，将研究天然亲水性和人工疏水性渥太华砂层的蒸发情况，以了解疏水性对毛细管输送和增强水蒸气扩散的影响。本研究将通过数值和实验评估疏水性对这三种主要蒸发机制（即接触线动力学、毛细输送和增强的水蒸气扩散）的相对影响，并创建一个机制图来显示野外环境条件下的主要蒸发机制。因此，提高对疏水性对土壤蒸发的理解可以为农业最佳实践提供信息。

Growing food with less water by reducing soil evaporationThe 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.