Phased regulatory mechanism of sowing date-meteorological factor interaction on maize yield formation and resource use efficiency in Southwest China hilly region under climate warming conditions.

Introduction: Climate warming has increased extreme weather events, threatening maize yield stability in Southwest China. Optimizing sowing date is crucial for matching meteorological resources with crop growth demands, yet the stage-specific regulatory mechanisms remain unclear. Methods: A five-year field experiment (2015-2016 and 2019-2021) with five sowing dates (March to May) was conducted at the Zhongjiang Experimental Station in the Sichuan Basin. Meteorological factors, grain yield, and its components were measured, and correlation analyses were performed. Results: The climate in the study area has warmed significantly over the past 35 years, with a substantial increase in the frequency of extreme heat events. Early sowing (SD1) significantly increased maize yield and enhanced its stability. For each day of sowing delay, dry matter accumulation decreased by 77.4 kg ha-1, leading to a yield reduction of 58.0 kg ha-1. The coefficient of variation for yield increased significantly for sowings in May, primarily attributed to the increased frequency of adverse weather conditions, such as high temperatures and heavy rain, during the pollination and grain-filling period. Different yield components were governed by dominant meteorological factors specific to key growth stages. Total dry matter accumulation was primarily driven by solar radiation (Sr), growing degree days (GDD) and diurnal temperature range (DTR) over the entire growth period. The kernel number per ear was sensitive to the maximum temperature (Tmax) during the 10 days before and after silking, with temperatures exceeding 33 ℃ causing significant reduction. The 1000-grain weight was positively regulated by Sr and GDD during the grain-filling period but negatively correlated with precipitation (for each 1 mm increase, the 1000-grain weight decreased by 0.063 g). With delayed sowing date, solar radiation and temperature utilization efficiency during the grain-filling period exhibited a linear decline. Discussion: This study identified late-March as the optimal sowing date for maize in the Sichuan Basin, as it achieved the best meteorological resources matching across all growth stages. The findings revealed the interaction mechanism of sowing date-meteorology-maize yield formation from a stage-specific perspective, providing a theoretical foundation and technical pathway for achieving high- and stable-yield in Southwest China under climate change.