Varietal Differences of Wet Endurance in Autumn Soybean Plants

The objective of this study was to examine the effects of excessive soil moisture on seed weight and yield components of autumn soybean cultivers and to find the varietal differences in their wet endurance. Twenty soybean cultivers, belonging to ecotypes of IIIc, IVc and Vc were grown in an upland field converted from paddy. The experiments were conducted in 1983 and in 1984. Excessive soil moisture treatment was conducted at the third or fourth foliage leaf stage and continued until the maturing stage. As the experiments yielded nearly the same results for both years, the data obtained in 1984 is presented in this paper. The seed weight of 12 cultivers was reduced but that of eight cultivers was not reduced by the treatment at the 5% significant level. The reduction ratio of seed weight, which was calculated as the mean value of excessive moisture plots divided by the mean value of control plots multiplied by 100, correlated positively with that of stem weight, branch number and total node number at the 0.1% significant level. As a result of regression analysis, the reduction ratio of the total node number had the greatest influence on the reduction ratio of seed weight. The results suggest that the smaller reduction in the seed weight of the wet endurance cultivers was caused by a smaller reduction in the vegetative growth e.g., the total node number, the stem weight and the branch number.