Interpreting Temperature- and Precipitation-related Scientific Information for the Agricultural Community In the U.S. Corn Belt

Climate change has been widely recognized in the U.S. Corn Belt, but what does it really mean to the agricultural community? In an era of explosive information, isolating useful climate change data and interpreting these data in usable ways is critical to the success of the broad corn production industry. In this study, three key questions are answered: (1) How have temperature and precipitation changed in the Midwest since 1980? (2) What is the best method to estimate thermal time for corn when temperature data are limited to a daily timescale? and (3) What are the historical effects of temperature and precipitation on field-level corn grain yield under irrigated and rainfed conditions? Different high-quality and representative datasets have been used for the study, together with several scientifically-proven statistical methods and spatial analysis tools. The results show that: (1) Growing season for corn has become warmer over the Midwest, mainly caused by the statistically significant increases of minimum temperature in early season in the southeast part and maximum temperature in late season in the northeast part. Meanwhile, growing season for corn has become wetter (not statistically significant), due to increased precipitation in early season outweighing a drier late season. (2) In Nebraska, six methods have been commonly used to estimate thermal time for corn by different agricultural groups. Among them, the single- and double-sine methods generally perform better estimations with one exception where the Tavg-based rectangle method outperforms them. However, the most widely used adjusted Tmax and Tmin rectangle method provides the poorest estimation for total degree-days during the active growing season for corn. (3) In the past decade, temperature and VPD plays a more important role on corn grain yield at the irrigated and rainfed sites near Mead, Nebraska, respectively. For the variance in corn grain yield, variation in growing season DD35+ explains 46% of it at the irrigated continuous corn site; variation in daytime air temperature during the 31-day period centered around silking explains 88% of it at the irrigated corn-soybean rotation site; variation in reproductive stage VPDmax explains 87% of it at the rainfed corn-soybean rotation site. Advisor: Martha D. Shulsk