Climatic resources and drought characteristics of maize sown in different dates in the hilly area of central Sichuan: A case study of Zhongjiang, Sichuan

The hilly area of central Sichuan is one of the main maize-producing areas in Southwest China, where seasonal drought is the main agro-meteorological disaster. It is of great significance to study the climatic resources and drought characteristics of maize at different growing periods with different sowing dates for maize drought avoidance and disaster reduction in this area. Using Zhongjiang County in the hilly area of central Sichuan as an example, based on the surface meteorological observation data of Zhongjiang Meteorological Station from 1981 to 2020, eight sowing dates with 20 days intervals were set from late March to early June to analyze the change laws of main agro-climate resources during maize growth periods under different sowing dates. At the same time, based on the crop water deficit index (CWDI), the drought characteristics of maize at different growth periods under different sowing dates were studied to provide a scientific basis for the selection of suitable sowing dates and the prevention of staged drought during the growth periods of maize in the hilly region of central Sichuan. The results showed that first, over the past 40 years, the changes in climatic resources during the maize growth season of each sowing date showed a trend of decreasing sunshine hours, increasing temperature, and decreasing rainfall. With the delay in sowing date, the daily average temperature, growing degree days, and heat degree days first increased and then decreased, while the sunshine hours gradually decreased and the rainfall gradually increased. Therefore, appropriately delaying the sowing date of maize is beneficial for improving the utilization of sunshine, heat, and rainfall resources. Second, with the delay in sowing date, the CWDI during the maize sowing–jointing and jointing–tasseling periods noticeably decreased, and the CWDI during the tasseling–filling of maize sown on the late-March was significantly higher than that on other sowing dates. Delaying the sowing date can reduce the risk of water deficits during the maize growth periods. Third, there were differences in most susceptible growing period to drought among different sowing dates. Maize sown in late March, late May, and early June had the highest drought frequencies during the sowing–jointing stage, and maize sown from early April to mid-May had the highest drought frequency during the jointing–tasseling stage. Fourth, the drought intensity at each growing period of maize sown in different dates was dominated by light and moderate drought, followed by severe drought, with extreme drought occurring the lowest. When the sowing date was delayed, the maize drought intensity decreased from moderate to mild. Appropriately delaying the sowing date of maize can reduce the frequency of drought, especially the frequency of severe and extreme drought. The proper sowing date of maize in the study area is before mid-May. When maize is sown in late March and early April, attention should be paid to drought resistance management prior to the grain-filling period. When sowing from mid-April to mid-May, attention should be paid to drought resistance management before tasseling to prevent high temperature risks during the filling-maturity stage.