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ainfall data for each location. Mean yield and standard deviation of yield were estimatedfor each genotype at each location.Results1. Yearly yield variation due to rainfall for a given conditionat transplantingThe simulated yield level at Ubon was generally low in these simulations becauseseeding occurred rather late (16 July), the deep percolation rate was high (6 mm d –1 ),and soil fertility was low.Figure 3 shows water levels in the field from transplanting to maturity for fourcontrasting years; 1980 was one of the highest rainfall years, with standing waterlasting until flowering, whereas 1986 had periods in early vegetative stages whenthere was no standing water and standing water disappeared rather early, resulting inyield of 0.93 t ha –1 . The third year, 1993, was a very dry year and standing waterdisappeared well before flowering, resulting in a low yield of 0.58 t ha –1 . In 1996, thewater level was low immediately after transplanting and standing water also disappearedabout 10 d before flowering.Yearly variation in yield was mostly accounted for by the variation in rainfallduring the period from transplanting to maturity (Fig. 4A). In years of high rainfall,Water level (mm)4000FF–400–800–1,2004000Simulated yield = 1.94 t ha –11980FSimulated yield = 0.93 t ha –11986F–400–8001993Simulated yield = 0.58 t ha –1Simulated yield = 1.79 t ha –11996–1,20040 60 80 100 120 140 40 60 80 100 120 140Days after sowingFig. 3. Simulated water levels during growth and flowering of genotype KDML105 forUbon Ratchathani in four selected years. The letter “F” indicates time of flowering.118 Fukai et al