Exploring the spatial and temporal distribution characteristics of heat resources utilization efficiency of summer maize in growth season could provide theoretical basis for the adjustment of summer maize variety layout and guarantee of a high and stable maize yield. Based on the daily meteorological data of 15 agricultural meteorological observation stations from 1981 to 2019, and the observation data of the growing period of summer maize and wheat in the later crop rotation in Hebei Province, the regression analysis and spatial interpolation methods are used to analyze the spatial and temporal variations of heat resources utilization efficiency of summer maize in growth season under climate change. The results show that the potential growing days of summer maize in Hebei Province had no significant change from 1981 to 2019, while the potential accumulated temperature increased significantly (P<0.05). The utilization efficiency of heat resources during growth season increased significantly (P<0.05), the utilization efficiency of growing days increased from 80.4% in 1981 to 94.5% in 2019, and the utilization efficiency of accumulated temperature increased from 84.5% in 1981 to 94.9% in 2019. The potential growing days and accumulated temperature of summer maize were more in the south and less in the north, and the utilization efficiency of growing days and accumulated temperature were lower in the south and higher in the north. There was higher utilization efficiency (more than 95%) of growing days and accumulated temperature in Langfang, while in Handan the utilization efficiency of growing days was lower (less than 85%). The accumulated temperature of summer maize increased at a rate of 19.6 ℃·d·(10 a)^-1 before anthesis and 58.7 ℃·d·(10 a)^-1 after anthesis. The increase rate of accumulated temperature after anthesis was obviously higher than that before anthesis, and the ratio of accumulated temperature showed an obvious downward trend, it fell 28.5% from 1.6 in 1981 to 1.1 in 2019. The results demonstrate that the utilization efficiency of climate resources of summer maize in the southern Hebei had some space for improvement. The medium and late maturing varieties with a longer growing season could be selected, and the varieties with a longer filling stage could be selected for breeding or cultivation, so as to make full use of the heat conditions in the growing season and improve maize yield.

The 40 summer maize varieties passing the certification were selected, variety comparison field trials were carried out at Xunxian located in northern Henan, Xuchang located in central Henan, and Fangcheng located in southern Henan. The high-yield and high-efficiency comprehensive evaluation index of summer maize varieties was constructed to carry out a comprehensive evaluation of the adaptability of summer maize varieties in three ecological regions from aspects of high and stable yield and climate resource utilization efficiency. The results show that the full growth period length of summer maize varieties was shortest at Fangcheng, with an average value of 108 days, and it was longest at Xunxian, with an average value of 111 days. The difference of the full growth period length of summer maize varieties ranged from 12 to 16 days in three ecological regions, and the full growth period length was correlated significantly with the flowering and grain period. The average yield of summer maize varieties at Fancheng was highest, while it was lowest at Xuchang, and yield difference between two ecological regions passed the 0.05 significance test. The highest utilization rates of light, temperature, water were at Fangcheng. The light and temperature utilization rate was higher at Xunxian than at Xuchang, but the water use efficiency was lowest at Xunxian. According to the ranking of high-yield and high-efficiency evaluation comprehensive index of summer maize varieties, 11 high-yield and high-efficiency summer maize varieties were selected including Weike 702, Qingyu 9, Xindan 68, Denghai 605, Dafeng 30, Zhengdan 1002, Fengdecunyu 10, Jundan 29, Zhengdan 538, Huaichuan 39 and SK1098.