Eric Hunt, doctoral student, will defend his dissertation at 9 a.m., May 19 in 901 Hardin Hall.
Hunt's dissertation is titled, "Analyzing the Relationship of Soil Moisture and Biophysical Variables in Wet and Dry Seasons at a Rainfed and Irrigated Fields in Eastern Nebraska." His adviser is Brian Wardlow.
Abstract:
Agriculture production, particularly of maize and soybeans, is a major component of Nebraska's economy and identity. However, agricultural production in Nebraska faces increasing challenges, particularly in areas dependent on irrigation. One of the larger concerns is the potential for excessive groundwater depletion due to increased demand for food and fuel from Nebraska crops and increasing risks of water stress in growing seasons due to climate change. Given the importance of agricultural production to the state and the increasing environmental risks, it has become essential for a deeper understanding of the soil-plant-atmosphere continuum to help producers make more informed management decisions. One of the variables that producers are starting to use for decision-making is soil moisture. Soil moisture is an integral part of the hydrologic cycle and an essential component in our understanding of land-atmosphere interactions. Improved understanding of soil moisture response under major cash crops, such as maize and soybeans, and insights into the dynamics of the soil moisture-crop-atmosphere continuum are needed to help producers in irrigated regions make more informed decisions.
This presentation will summarize a body of research that analyzed eight years of soil moisture and biophysical measurements from an irrigated and rainfed maize-soybean rotated fields at the UNL ARD over a range of growing season conditions that ranged from abnormally dry and warm to unusually moist and cool. The primary objective is to demonstrate the link between soil moisture and its relationship to crop biophysical variables under varying climate conditions to improve our understanding interactions and crop response. This work showed that soil moisture is a very suitable measure of the effectiveness of precipitation for soil recharge and that timing of precipitation can be almost be as important as quantity. Dry spells occurred in most years of the study period, but the timing and duration of these dry spells were important for determining how detrimental it was to the rainfed crop. In years where adequate precipitation was received, the measured evapotranspiration and gross primary productivity at the rainfed field increased to a level comparable to the irrigated field. However, during a classic flash drought, prolonged soil moisture stress led to declining stomatal conductance and a significantly reduced maize yield compared to the irrigated field. The flash drought case study not only showed the importance of irrigation during a prolonged dry spell, it also showed the utility of using short-term drought indices, such as the Standardized Precipitation Evapotranspiration Index (SPEI), for identifying water stress of a rainfed field. Thus, short-term indices can be used with more confidence when trying to determine locations where crop yields could be significantly reduced because of water stress.