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colation rate. In this case, the larger effect of variation in lateral water movement wasfound with lower water availability (–200 mm) at transplanting and a lower percolationrate. With the highest percolation rate of 6 mm d –1 , the water-stress effect wassevere and the effect of variation in C L was small.In these simulations, grain yield was directly related to the date of disappearanceof standing water relative to the flowering date for both locations and Figure 7shows the results for Ubon. Note that relationships obtained from the sensitivity analysesare similar to those obtained from the analysis of yearly variation (Fig. 4B,C).3. Response of genotypes with different phenologyto variation in water balance componentsFor the June planting in 1994 at Ubon, the yield of genotypes with different phenologyincreased with a delay in flowering until about 10 October with the lateral watermovement coefficient of 0.5 and until about 20 October with the coefficients of 1.0and 1.5 (Fig. 8). However, with seeding later in July, earlier flowering was advantageouswith a C L of 0.5, 1.0, and 1.25, whereas the phenology had a small effect whenthe coefficient was 1.5, with a slight advantage with later flowering. It should bepointed out that the order of flowering among genotypes changed between the twoseeding dates because of differences in photoperiod sensitivity. For example, the mildlyphotosensitive IR57514-PMI-5-B-1-2 flowered earlier than KDML105 when plantedon 16 June, but they flowered at almost the same time when sown on 16 July.In 1996, the water conditions were generally more favorable and the highestyield was obtained with the KDML105 phenology type for all values of C L in bothJune and July sowing.In Figure 6, where the water level throughout the growth period for the Julysowing is shown, flowering time of each genotype is also shown for both 1994 and1996. With a C L of 0.5 and 1.0, the three late genotypes flowered well after the standingwater disappeared from the lowland field and the yields were lower. With the C Lof 1.5, standing water was maintained until the last genotype flowered and the laterGrain yield (t ha –1 )321R 2 = 0.73Y = 1.89 + 0.025XFA50 mm–200 mm00–30 –20 –10 0 10 20 30–30 –20 –10 0 10 20 30Fig. 7. Relationship between the simulated grain yield and date of disappearance of waterrelative to flowering time for five genotypes. (A) with two levels of standing water at transplantingand (B) three levels of deep percolation rate at Ubon Ratchathani in 1996.321BR 2 = 0.97Y = 1.99 + 0.018XTime of disappearance of standing water(days to flowering)F6 mm d –14 mm d –11 mm d –1Modeling water availability, crop growth, and yield . . . 123