Effect of drought stress on maize phenology and yield components and its sim-ulation

Drought is one of the main limiting factors for maize production in Northeast China, and drought stress is particularly severe during the seeding and flowering stages of the crop. The occurrence of drought around anthesis affects the temporal separation of male (anthesis) and female (silking) floral maturity (referred to as the anthesis-silking interval, ASI), which leads to a reduction in maize kernel numbers. To examine the effect of drought stress during the "yield critical period" on maize phenology, yield and yield components as well as to assess the modeling results of phenology and yield simulated by a crop growth model under drought stress, a field experiment was conducted. Sowing was performed on different dates at 10-day intervals beginning from April 20 over a 5-year period (2011-2015). Observation data of maize yield and yield components, particularly phonology and yield data in the drought years of 2014 and 2015 were used to analyze the effect of drought stress on maize phenology and yield components. The results of simulation using the CERES-Maize model were assessed in this study. Further improvements for the CERES-Maize model under drought conditions were proposed. The findings revealed that drought during the yield critical period delayed silking much greater than anthesis. More than 90% of the plants reached the anthesis stage, whereas only 45%-88% of the plants reached the silking stage. Drought in 2014 and 2015 reduced the kernel numbers of maize by 32% and maize yield by 33%-78%. Grain yield was significantly (P < 0.001) and positively correlated with the number of kernels per ear. The CERES-Maize model showed good performance (normalized root mean square error (NRMSE) of yield simulation was 6.5% for 2012 and 10.8% for 2013) in the normal years, whereas its performance during the drought years was unsatisfactory (NRMSE of yield simulation was 21.6% for 2014 and 76.5% for 2015), which was attributed partly to the neglect of the longer ASI, failure to reach silking, or delayed phenology, causing a decrease in yield. Above all, drought stress during the yield critical period affected maize phonology (anthesis to silking stage) to some extent, affecting kernel number and grain yield. Thus, it is necessary to study the modeling of maize yield under drought stress based on ASI and silking dynamics by coupling the plant biomass framework.