Impacts of climate change on the optimum planting date of different maize cultivars in the central US Corn Belt

Planting date and cultivar selection are major factors in determining the yield potential of any crop and in any region. However, there is a knowledge gap in how climate scenarios affect these choices. To explore this gap, we performed a regional scale analysis (11 planting dates x 8 cultivars x 281 fields x 36 weather years x 6 climate scenarios) using the APSIM model and pSIMS software for Iowa, the leading US maize (Zea mays L.) producing state. Our objectives were to determine how the optimum planting date (optPD)changes with weather scenarios and cultivars and the potential economic implications of planting outside the optimum windows. Results indicated that the mean optPD corresponds to the US Department of Agriculture, National Agriculture Statistics Service (USDA-NASS) 18.4% planting progress (April 28th) in Iowa. The opt optPD was found to be advancing by -0.13 d yr(-1) from 1980 to 2015. A 1 degrees C increase in mean temperature increased the length of the growing season by 10 days while the opt PD changed by -2 to + 6 days, depending on cultivar. Under a more realistic scenario of increasing the minimum temperature by 0.5 degrees C, decreasing the maximum temperature by 0.5 degrees C, increasing spring rainfall by 10% and decreasing summer rainfall by 10%, the optPD only changed by -2 days compared to current trends, however, yield increased by 6.6%. Analysis of historical USDA-NASS planting durations indicated that on average, the planting duration (1-99% statewide reported planting progress) is 44 days, while it can be as low as 21 days in years with favorable weather. A simple economic analysis illustrated a potential revenue loss up to $340 million per year by planting maize outside the optimum window. We conclude that future investments in planting technologies to accelerate planting, especially in challenging weather years, as well as improved optPD x cultivar recommendations to farmers, will provide economic benefits and buffer climate variability.