Abstract
The previous paper indicated that high nitrogen (N) application during the low temperature treatment caused a considerable decrease of the pod setting rate and the fertility per cent of ovules. In this paper, the unfavorable effects of high N application on low temperature treated soybeans was examined for clarifying of the relationship between the N supply conditions including level, time and period of application, and the stage of flower development with solution culture method. Flower developing plants were treated with low temperature at 15°C for 15 days and compared with the plants grown under the control condition at 24°C-day19°C-night. The flowers used in this experiment were restricted in the number per node and the time of blooming. Variance analysis of the pod setting rate, fertility per cent and the number of ovules per pod gave the significance of the interaction at the 1% level between N supply conditions and temperature conditions. N application under the 24°C/19°C condition obtained better grain yield compared with N free plot; on the contrary, N supply accompanied with the low temperature treatment showed a decreasing tendency of the pod setting rate and of the fertility per cent. The pod setting rate of the plants treated with low temperature was closed related to the time of N application. N application before or during the first five days in the low temperature treatment caused a signiftcant decrease in comparison to the N free condition and the later application showed the less damage. However no difference was observed betwen the level supplied at l00 ppm and 40 ppm N. The fertility per cent of the plants treated with low temperature was decreased by N application and, especially, all plants showed a considerable decrease in the pod setting rate which were accompanied with a significant decline. But the relation between time of N application and the degree of injury was not so clear as seen in the pod setting rate. Fertile grains which were supposed to be in a constant number of flowers per plant were calculated in each plot. N supply from before the low temperature treatment, till five days after the end of the treatment, resulted in a decrease in grain number, particularly, before the period of treatment and during the earlier period of N application, caused the greater decrease.
