The effects of sowing date on maize: Phenology, morphology, and yield formation in a hot subtropical monsoon region

With abundant thermal resources, there is a long-time span for potential maize sowing in the hot subtropical monsoon region. However, with different sowing dates, maize may be exposed to elevated temperatures at different growth stages. This study aims to understand the impact of sowing date on maize growth and development and yield formation as temperatures increase. A 3-year field experiment was carried out in the typical subtropical monsoon region in China, with 11 sowing dates ranging from mid-March to late June with approximately 10-day intervals (named S1 to S11), and three main commercial varieties were included to validate the impact of sowing date. Following delayed sowing, maize plants were exposed to increased temperatures during the emergence (VE) to silking (R1) stages. Maize plants of the three varieties exhibited similar responses to delayed sowing dates in terms of growth, development, and yield performance. Vegetative growth was accelerated, while the anthesis-silking interval (ASI) and the vegetative-to-reproductive transition, that is, the interval of V12 (twelfth leaf) to R1 stages, were prolonged. The grain yield gradually decreased and reached a minimum at approximately S8-S10 (varied among varieties), which was in accordance with the decreased grain number. Further analyses revealed that the decreased grain number and yield were associated with a prolonged V12-R1 interval with delayed sowing. The duration of V12-R1 was significantly positively correlated with the maximum and minimum temperatures within a day, suggesting that the V12-R1 interval could be a parameter for evaluation of heat's impact on yield formation. Grain weight decreased as the temperature of the R1-R6 stage rose before S8 but increased as the temperature dropped after S8. Inconsistently, biomass accumulation, leaf area, and plant and ear height first increased and then decreased before and after S3-S6, respectively. Delayed sowing in hot subtropical monsoon regions exposes maize plants to elevated temperatures, leading to accelerated vegetative and reproductive growth but a prolonged vegetative-to-reproductive transition, and suppresses yield by reducing grain number and/or weight, resulting the yield decreased with the delayed sowing. By demonstrating the impacts of high temperature with different sowing dates on the phenology, morphology, and yield formation of maize, this study provides a basis for improving maize yield in practical production by optimizing the sowing date.