Abstract
In this study, we examined the effects of the field type, planting density, seeding time, fertilizer and soil type, on the content and composition of isoflavone in soybean seeds for three years. The total isoflavone content of 12 soybean cultivars was higher in the order of upland field with regular seeding time (UR) < drained paddy field with regular seeding time (DR) < upland field with late seeding time (UL). The ratio of highest to lowest total isoflavone content was 3.0, 2.2 and 2.3, respectively in the 12 cultivars in UR, DR and UL. Moreover, the interannual coefficient of variation in total isoflavone content tended to be increased in the order of UL (4-31%) < UR (6-27%) < DR (10-44%). No significant difference was observed in either the content or composition of isoflavone among the three planting densities ranging from 8.3 to 16.7 hills/m2 and the content was unrelated to yield in 'Suzukari' and 'Tachiyutaka'. On the other hand, the isoflavone content increased as the seeding time was delayed in 2000. The effects of the soil type and fertilizer on the contents and compositions of isoflavone, were examined using'Fukuibuki' grown at Fukushima Agricultural Experiment Station in 2001. The kuroboku soil conditions, as compared with the grey lowland soil conditions, gave high isoflavone contents, but the composition was not changed. These results suggest that soybean with constantly high isoflavone content may be produced by late-season culture at a high planting density on fertile soil.
