Abstract
The present study was conducted to investigate the influence of water stress during flowering on yield and yield components using determinate (cv. Enrei and Norin 2) and indeterminate (cv. Clark and Willliams 79) soybean cultivars grown in pots and in the field. During the non-irrigation period, leaf water potential ranged from −1.1 MPa to −1.5 MPa in the dry plot. Pod and seed number decreased significantly in the determinate cultivars, while seed number per pod and the 100-seed weight also tended to decrease under the water stress condition. In the indeterminate cultivars also, pod and seed number tended to decrease but only slightly, and the seed number per pod and 100-seed weight tended to be maintained under the water stress conditions. As a result, stress-induced yield loss tended to be lower in the indeterminate than in the determinate cultivars. In 1999 when the temperature was extremely high, the net assimilation rate (NAR) and crop growth rate in the plot subjected to water stress from flowering to pod formation stage tended to be higher in the indeterminate cultivars than in the determinate cultivars. This suggested a correlation between NAR and the degree of yield loss. In addition, the long sunshine hours in August, after the water stress period, was suggested to have compensated for the yield loss due to the water stress in the indeterminate cultivars.
