Analysis of Temperature Impacts during Critical Yield Formation and Development Growth Stages in Irrigated Maize.

Title: Analysis of temperature impacts during critical yield formation and development growth stages in irrigated maize. Recent statistical analyses of maize yield patterns suggest significant yield reductions due to high growing season temperatures. However, other climate factors likely impact yield, alone and in conjunction with air temperature.ÊOur goal is to distinguish the climate conditions where high temperatures affect maize yields in order to improve projections of climate change impacts on yield. Ê Irrigated maize yield data from hybrid performance trials (2005 to 2013), and yield contests (National Corn Growers Association) (2005 to 2012) for Nebraska, Kansas, and Missouri were analyzed. We focused on irrigated maize yields so that the impact of high temperature, if any, on yield could be determined independent of crop water stress. We calculated cumulative incident solar radiation and heat stress factors during critical phenological stages of yield formation and development for these data. Heat stress factors included cumulative Ôkilling degree daysÕ (average daily T > 29 C) and cumulative daytime and nighttime hours above reported threshold temperatures. These factors were calculated using both air temperature and estimated canopy temperature determined from analyses of flux tower data and application of the Penman-Monteith equation. A statistical model was developed to quantify the impact, if any, of the stress factors and cumulative solar radiation on yield, independent of management practices and underlying yield trends due to improved maize genetics over the study period. Stress factors calculated from either air T or estimated canopy T, were only weakly correlated with yield across the phenological stages examined. A positive correlation between cumulative incident solar radiation and yield during grain fill indicated a possible indirect impact of temperature on yield via accelerated phenological development. These results suggest that previously identified statistical relationships between high temperatures and yield are likely to be indirect, and may not be due primarily to direct negative impacts of high temperature on maize physiology. 2