Characterizing climate change in the Midwest: Magnitude of warming and plausibility of adaptation strategies for maize-based systems
Michael J. Castellano
Maize-based agricultural systems dominate the U.S. Midwest landscape and maintaining productive systems in the short- and long-term are high priorities for the agricultural sector. Climate change has and will continue to alter the environment in which farmers produce their crops. Information and recommendations are necessary for understanding the magnitude of warming and adaptation strategies that can mitigate intensified precipitation events, moisture shortages, and increased temperatures. The multi-faceted changes in temperature were aggregated using thermal time as an agro-climate index to describe the warming relevant for producing maize. Across 1054 counties, the change in thermal time since 1950 was disproportionally warming for northern and eastern counties. Counties in the central and western regions have not warmed substantially. A future adaptation strategy may be the use of longer-season maize hybrids that have thermal requirements more closely aligned with the environmental thermal availability of an area. The feasibility of this adaptation strategy was assessed based on current hybrid choices. Pioneer brand hybrid sales were provided from Corteva Agriscience for 650 counties from 2000 to 2016. The difference between hybrid thermal requirements and environmental thermal availability varied with northern counties having a difference near zero Growing Degree Days (GDDs) while southern counties had up to 800 GDDs available following crop maturation. Over the 17-year period, hybrid maturities changed in 345 of 650 counties with an increase in 64 and decrease in 281; 305 were unchanged. An inverse relationship was identified for the majority of counties between long-term climate trend and hybrid choice such that as seasonal thermal time lengthened, hybrid maturity shortened. Finally, climate adaptation strategies for farmers often focus on mitigation of intensified precipitation events and increased temperatures through conservation and diversification practices that build system “resilience”. Twenty-three experiments located across eight Midwest states were used to assess maize yield response to “improved” management practices relative to a “standard”. Climate adaptation practices included: differing intensity of tillage, diversity of cropping systems, and management of drainage water. Research sites were binned relative to yield environment or soil organic carbon; the latter was most helpful as a characterization variable in separating treatment response.