Lengthening of maize maturity time is not a widespread climate change adaptation strategy in the US Midwest

• Published in: Global change biology 2021-06, Vol.27 (11), p.2426-2440
• Main Authors: Abendroth, Lori J., Miguez, Fernando E., Castellano, Michael J., Carter, Paul R., Messina, Carlos D., Dixon, Philip M., Hatfield, Jerry L.
• Format: Article
• Language: English
• Subjects: Agricultural economics; Agricultural sciences; Availability; Biorefineries; Climate adaptation; Climate change; Climate change adaptation; Corn; Crop yield; Decision making; Drying; Economics; Ethanol; Farmers; Genetics; Grain; grain fill period; hybrid maturity; Hybrids; Labour; maize; Manganese; Maturity; Midwest; Physiological effects
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.15565

Increasing temperatures in the US Midwest are projected to reduce maize yields because warmer temperatures hasten reproductive development and, as a result, shorten the grain fill period. However, there is widespread expectation that farmers will mitigate projected yield losses by planting longer season hybrids that lengthen the grain fill period. Here, we ask: (a) how current hybrid maturity length relates to thermal availability of the local climate, and (b) if farmers are shifting to longer season hybrids in response to a warming climate. To address these questions, we used county‐level Pioneer brand hybrid sales (Corteva Agriscience) across 17 years and 650 counties in 10 Midwest states (IA, IL, IN, MI, MN, MO, ND, OH, SD, and WI). Northern counties were shown to select hybrid maturities with growing degree day (GDD°C) requirements more closely related to the environmentally available GDD compared to central and southern counties. This measure, termed “thermal overlap,” ranged from complete 106% in northern counties to a mere 63% in southern counties. The relationship between thermal overlap and latitude was fit using split‐line regression and a breakpoint of 42.8°N was identified. Over the 17‐years, hybrid maturities shortened across the majority of the Midwest with only a minority of counties lengthening in select northern and southern areas. The annual change in maturity ranged from −5.4 to 4.1 GDD year−1 with a median of −0.9 GDD year−1. The shortening of hybrid maturity contrasts with widespread expectations of hybrid maturity aligning with magnitude of warming. Factors other than thermal availability appear to more strongly impact farmer decision‐making such as the benefit of shorter maturity hybrids on grain drying costs, direct delivery to ethanol biorefineries, field operability, labor constraints, and crop genetics availability. Prediction of hybrid choice under future climate scenarios must include climatic factors, physiological‐genetic attributes, socio‐economic, and operational constraints. To adapt to climate change, farmers are expected to grow maize hybrids which mature later. In contrast, we show the length of time required for maturity has steadily decreased despite stable or increasing temperature trends. Records of commercial hybrid sales to US Midwest farmers from 2000 to 2016 reveal a shortening of hybrid maturities across the majority of counties. Hence, lengthening of maize maturity is not currently a widespread climate change