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

Abstract

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.

Thermal Time Requirements for Maize Growth in Northeast China and Their Effects on Yield and Water Supply under Climate Change Conditions

“…Furthermore, farmers that used more than one variety often adopted drought resistant varieties. In areas prone to precipitation shortages, shortening the hybrid maturity may be a risk-averse strategy [17,34]. If farmers used more than one variety, the maize yield was about 150 kg/ha higher than farmers who only planted one variety [38].…”

“…A larger gap between rainfed and no water-stress yields also suggests that new adaption measures, other than a shift to longer-maturing varieties, are needed. In fact, factors other than thermal availability appear to more strongly impact farmer decision-making [17]. Under climate change conditions, new hybrids with droughttolerant qualities, applications of nitrogenous fertilizers and irrigation may be effective measures for semi-humid regions to maintain maize production [7].…”

“…In the Chinese Maize Belt, the sensitivity of maize production to water has increased, and water scarcity in China remains a serious problem [9]. In midwestern USA, lengthening the maize maturation time is not a widespread climate change-related adaptive strategy, and hybrid maturation times were shorter in fact in the majority of the region during 2000-2017 owing to production-related factors, such as decreasing grain drying costs and labor constraints [17]. In Europe, shorter-maturing oat varieties have been preferred in response to climate change because of concerns about late-season droughts [18].…”

“…In Europe, shorter-maturing oat varieties have been preferred in response to climate change because of concerns about late-season droughts [18]. Thus, in areas prone to precipitation shortages or heat stresses, shortening the hybrid maturation period may be a risk-averse strategy [17]. However, in China, would the adoption of longer-season cultivars be an effective strategy for the whole NEC to sustainably increase grain yield?…”

Trends and Climate Response in the Phenology of Crops in Northeast China

“…A warmer climate inevitably leads to shift in crop phenology, which ultimately determinate crop yields (Estrella et al, 2007;Tao et al, 2013;Xiao et al, 2017;Zhao et al, 2019). Quantitatively assessing the shift in crop phenology caused by climate change can help agricultural stakeholders to formulate effective climate change adaptation strategies (Mo et al, 2016;Abendroth et al, 2021). Therefore, the effects of climate change on crop phenology are a major concern for agricultural production (Wang et al, 2013;Xiao et al, 2013;Tao et al, 2014b;Bai et al, 2019).…”