3.1 High temperature, sunshine hours and rainfall during flowering and early grain filling period
Maize tasseling, pollen shedding, and silking mainly occurred in June and July in four experimental years. In this period, the average daily maximum temperature (Tmax) was above 30℃ and exceeded 35℃ in July in 2016-2018 (Supplementary Table S2). The daily maximum temperature (DMT, ℃) and sunshine hours (SH, h) during the 15 days bracketing the silking stage was significantly lower in the first sowing date than in the second sowing date in 2015 and 2016 (Supplementary Figure S1). Among four sowing dates in 2015 and 2016, there were the similar rainfall (RF, mm) in the first sowing date of 2015 and 2016, and the second sowing date of 2015, however, the lowest rainfall occurred in the second date of 2016. Early grain filling period in 2017 and 2018 occurred in late July, corresponding to a daily maximum temperature of ~36℃ (Supplementary Table S2). The SH and RF during the 15 days bracketing the silking stage have a similar level in 2017 and 2018, but still lower than the average value of 2015 and 2016.