Studies show that the cultivation of corn in the United States (U.S.) will be affected by the changing climate. The cornbelt in the country is shifting northwards. Corn is one of the major contributors to the country's economy. In this research, growing degree days (GDD) data have been used to understand the effect of increasing temperatures on the corn yield in various U.S. states.

The base temperature for corn is 50°F (10°C). Above this temperature, corn starts to accumulate heat units also termed as GDD. Each stage of corn development needs a certain amount of GDD units. There are different varieties of corn, and each requires various amounts of GDD units to mature; higher GDD-requiring varieties give better yield. With temperature changes, GDD accumulation for corn will be affected. This study has tried to tabulate GDD trends for various U.S. states. GDD data based on 50°F (10°C) from local climatological data sites were directly used and statistically tested for significance. Trends in the annual accumulated GDD were studied. The relationship between the corn yield and the annual accumulated GDD over the last century was further analyzed. An online database has been prepared to make GDD data for all states available to the public at http://www.ndsu.edu/pubweb/flood/GDD/.

The GDD trends for various states in the country have shown varied results. The results depicted that 63% of the locations used in this study had significant trends (5% significance level) in the annual accumulated GDDs, among which 81% of the locations showed a positive trend in the annual GDD accumulation. These progressive trends can be attributed to the changing climate, and the numbers depict that the warming trend is more predominant in the United States. In the future, our study can be expanded to include factors, such as precipitation, soil moisture, solar radiation, technology and management practices to obtain a broader picture of all the factors causing changes in the corn yield.