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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. One of the challenges is the potential for excessive groundwater depletion due to increased demand for food and fuel from irrigated Nebraska crops and increasing risks of water stress due to climate change. Therefore, it is has become essential for a deeper understanding of the soil-plant-atmosphere continuum to help producers make more informed management decisions. One of the most important variables is soil moisture. Soil moisture is an integral part of the hydrologic cycle and an essential component in understanding land-atmosphere interactions. Eight years of soil moisture and biophysical measurements from an irrigated and rainfed maize-soybean rotation, in growing seasons that ranged from abnormally dry and warm to unusually moist and cool, add to that understanding. It is shown that soil moisture is an excellent measure of the effectiveness of precipitation and that timing of precipitation can be as important as quantity. Dry spells occurred in most seasons in the study period, but the timing and duration of said dry spells were important. In seasons where adequate precipitation returned, measured evapotranspiration and gross primary productivity at the rainfed field increased to close to that of the irrigated field. Therefore, it is implied that stomatal conductance seemed to return to close to pre-dry spell levels and rainfed yields were not substantially reduced compared to the irrigated field. However, during a classic flash drought in the study period, prolonged soil moisture stress led to reduced stomatal conductance and significantly reduced maize yields. 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 for identifying water stress of a rainfed field.
Adviser: Brian D. Wardlow