CAREER: Altering transient soil evaporation mechanisms through hydrophobicity

通过减少土壤蒸发来用更少的水种植粮食粮食的生产需要足够的淡水，而粮食的可持续生产是粮食、能源和水关系的关键重点。土壤蒸发率的减少将降低灌溉需求和作物生产的总用水量，从而在世界范围内和大平原的奥加拉拉含水层节约用水。这项研究项目将通过实验室研究了解疏水土壤(水珠向上)与典型亲水性土壤(水扩散)对蒸发的影响。玻璃微珠将被涂覆，使其疏水，这些微珠将被用来模拟土壤。在类似田野的天气条件下，将研究几个珠子和一盘珠子的蒸发。接下来，一种名为渥太华沙的土壤将被覆盖以变得疏水，并将从平原、亲水性沙子和疏水沙子测量蒸发量。这些实验将展示土壤疏水性如何影响土壤蒸发。土壤疏水性可由矿物、有机物质或蜡自然产生。这些实验室蒸发研究的信息将被用来确定减少水分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、高粱和牛提供水。此外，由于研究的重要性，本研究项目将吸引不同的学生。首席研究人员(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将面包烘焙作为土壤蒸发的类比，PI和研究人员将在一年一度的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多所学院的研究生讲授一门关于食品、能源和水之间的热质传递的跨学科课程。这项研究将研究三相(即土壤、水和空气)系统中的瞬时蒸发相变化。这项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、毛细输运和增强的水蒸气扩散。玻璃和特氟龙包裹的珠子将被用来模拟土壤进行孔隙度实验。将使用高速红外相机对蒸发进行模拟和实验研究，以适应不同的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的太阳辐射)。将观察到从亲水性或疏水性单孔中蒸发的水的接触线。利用从这些单孔研究中获得的知识，将研究多个孔的蒸发前沿和机制，如毛细管传输和增强水蒸气扩散；水将被荧光染料罗丹明B染色，并使用Nd：YAG激光激发。色移将被用来识别给定横截面的多孔材料的蒸发前沿和液体毛细管传输。在研究的最后阶段，将研究自然亲水和人工疏水的渥太华沙层的蒸发，以了解疏水性对毛细传输和增强水蒸气扩散的影响。这项研究将从数值和实验上评估疏水性对这三种主要蒸发机制(即接触线动力学、毛细输运和增强的水汽扩散)的相对影响，并创建一张机制图来显示田间环境条件下的主要蒸发机制。因此，更好地了解土壤蒸发的疏水性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.