Spring Maize Kernel Number and Assimilate Supply Responses to High‐Temperature Stress under Field Conditions

CORE IDEAS: Spring maize mono‐cropping system is shown to be a water‐saving and high‐yield maize farming system. Spring maize was traditionally planted in late April or early May but seldom obtained desirable yield. Altering sowing date reduced frequency of high‐temperature stress of spring maize around silking and grain‐filling stage. Altering sowing date improved assimilate availability of spring maize during the grain‐filling stage. Late May turned out to be the better sowing date, rather than traditional sowing dates in late April or early May under current conditions. The productivity of spring maize (Zea mays L.) in North China Plain (NCP) is primarily limited by high‐temperature stress (HTS) during the grain‐filling stage. To avoid HTS and promote productivity, variable sowing date (SD), treatments were established from 2013 to 2015 (early April, SD1; mid‐April, SD2; late April, SD3; early May, SD4; mid‐May, SD5; and late May, SD6). During the grain‐filling stage, the leaf area index (LAI) and dry matter accumulation (DMA) were greatest at the final SD (SD6) compared with all other treatments. Additionally, the daily mean air temperature (Tmean), daily maximum air temperature (Tmax), and cumulative stressful days (CSD) during this stage across 3 yr decreased at SD6 by 1.4 to 3.2°C, 1.0 to 2.7°C, and 5.7 to 14.7 d, respectively, compared with the values at SD1 to SD5. Planting at SD6 increased the final grain yield by an average of 5.4 to 19.3%. A linear regression analysis showed that the kernel number (KN) per plant increased by 4 with every 100 kg ha⁻¹ DMA. Kernel number was negatively correlated with Tmax and CSD from 15 d pre‐silking to 15 d post‐silking. Compared to SD1 and SD4, ear leaf at 15 d post‐silking under the SD6 treatment had the highest net photosynthetic rate (Pn) and the lowest ABA concentration. In conclusion, to avoid HTS and achieve the greatest corn grain yields in NCP, spring sowing maize should be postponed until late May.