| Abstract | Water stress is unpredictable, and which regularly affects maize production under rainfed condition in Thailand. This study was therefore conducted to determine the effect of varying dry periods occurring during selected critical growth stages on growth and yield of maize, and to simulate and compare the performance using CERES-Maize model in DSSAT version 4.0.2.0 using concurrent weather data. The study comprised of three separate experiments. In the first experiment, 10-day dry period was imposed during four critical growth stages of maize [viz. 36-45 days from seeding (DFS), 46-55 DFS, 56-65 DFS, and 66-75 DFS] together with a control (regular irrigation once a week) for two maize hybrids, i.e. Suwan 4452 and Pacific 224. Experiment was arranged in a split plot design with four replicates and conducted from December 2006 to April 2007, under controlled irrigation. Soil moisture content (SMC) at 0-15cm and 15-30cm depths reached near the lower limit of readily available water (RAW) in six days after the cessation of irrigation, which further lowered between RAW and permanent wilting point (pWP), but did not reach PWP during the 10-day period. Leaf area index (LAI) (ranged from 4.3 to 4.6), plant height (ranged from 2.24 to 2.36m) and biomass (ranged from 6.8 to 7.6 t/ha) at silking were not significantly affected by treatments, except height, and Pacific 224 was significantly taller than Suwan 4452. Number of grains per cob, 100-grain weight, grain yield and the harvest index remained unaffected due to treatments. In the first experiment, CERES-Maize model showed excellent results in predicting time to silking, LAI and biomass at silking, 100-grain weight, grain yield and the harvest index. However, some deviations were found in Suwan 4452 for time of silking, LAl and grain number per cob, and of Pacific 224 in the grain number per cob and 100-grain weight. Comparisons showed that simulations were very much close, except for soil moisture content. The other model predictions were similar to the actual values in this study. In the second study 15-day dry period was imposed during four selected growth stages (viz. 26-40, 46-60, 53-67 and 69-83 DFS) for Pacific 224 together with a control having irrigation at weekly interval until physiological maturity (PM) in pots in the greenhouse at the Agricultural System Research Farm of the Asian Institute of Technology Thailand. The design was a complete randomized design with four replications. Soil moisture content reached near PWP in treatments exposed to dry period during 53-67 DFS at both 0-15 and 15-30cm profiles, and this shortened the time to tasseling, prolonged the time to silking and widened tasseling-silking interval (TSI). The effect continued to reduce both grain number per cob and 100-grain weight thus lowering grain yield and harvest index (HI). In the 15-day dry period during 46-60 DFS, SMC was below RAW, which resulted in the lowest grain number per cob and reduced 100-grain weight. These two collectively lowered both grain yield and HI. However, the dry period imposed during 69-83 DFS showed moderate reduction in 100-grain weight and which reflected moderate reduction in grain yield and HI. The above change in SMC also reduced time to PM and biomass at harvest. There was not significant effect on leaf area per plant and plant height. CERES-Maize model simulations were close for time to silking with bias ranging from a to 2.0 days, and also close for the time to PM with bias ranging from 5.5 to 13.5 days. Prediction of grain yields under control was even so close (bias of 6.7g/plant), but other parameters deviated with a wide bias, among which SMC was one of the parameters. In the third experiment, 20-day dry periods were imposed at five selected critical growth stages (viz. 21-40, 30-49, 36-55, 43-62 and 57-76 DFS) and tested together with a control maintained with weekly irrigation using the same two maize varieties in a factorial experiment using split plot design with four replicates. Soil moisture content at 0-15cm and l5-30cm depths reached the lowest limit RAW in eight days after suspension of irrigation, but did not reach PWP during the remaining period. Both LAl and plant height decreased (p=0.05) in treatments subjected to dry period during 21-40 and 30-49 DFS when compared to the control. The grain number per col decreased (11.3%) when dry period prevailed during 21-40 DFS, and as a result, grail yield and HI decreased by 11.2% and 13.5%, respectively. In other treatments, grain yield remained unaffected compared to control. Suwan 4452 had a higher grain number per col than Pacific 224, but 100-grain weight was higher in Pacific than Suwan variety. CERES Maize model showed excellent performance in predicting the time to silking and biomass at silking, PM, 100-grain weight, grain yield and HI. There was variability in simulated values of LAI and number of grains per cob. The CERES-Maize showed its ability to provide information enabling appropriate decision making in the event of extending dry period up to 20-days |