Effects of Late Sowing and Dense Planting on the Yield and Occurrence of Delayed Stem Senescence in Soybean (Glycine max (L.) Merr.) Cultivars in Kanto, Japan

The effects of late sowing (July sowing) and dense planting on the yield and the occurrence of delayed stem senescence in soybean cultivars “Enrei”, “Tachinagaha” and “Ayakogane” were examined on the experimental farm of Nihon University. The seeds were sown in the field in June at the normal density (June-normal plot) or in July at normal, high and super high densities July-normal, July-dense and July-super dense plots, respectively. Pot experiments were carried out to analyze the amount of cytokinin at the top of the plant. In all cultivars, the yield in the July-dense plot and July-super dense plot was higher than that in the June-normal plot. The yield in the June-normal plot was the same as that in the July-normal plot, although the number of seeds per pod was higher in the latter than in the former plot. The occurrence of delayed stem senescence was more frequent in the June sowing plot than in the July-sowing plot probably due to the damage of seeds by bean bugs, smaller amount of cytokinin, and water stress after the flowering time. In conclusion, the yield was not changed by changing the sowing time from June to July in these cultivars, but the occurrence of delayed stem senescence was decreased by sowing in July.