Extended Reproductive Phases Is Associated with High Soybean Yield.

Soybean [Glycine max (L) Merr.] yield increases have often been associated with extending reproductive growth phases. There is evidence that exposing full-season cultivars to extended photoperiods for a few days after the onset of flowering can significantly lengthen reproductive phases and increase yield. To test the hypothesis that early planting coupled with full-season cultivar maturity selection can maximize the reproductive growth phases and yield, experiments were established at a number of sites in Illinois and one in Iowa. Trials included two planting dates and a set of cultivars chosen to represent a large range in maturity for that site. Averaged across sites, later-maturing cultivars yielded more than earlier ones, but this yield response leveled off at cultivar maturity of about 0.5 units longer than that of mid-season cultivars at that site. This leveling off was not as apparent at Champaign, where the relationship between length of reproductive development (R3 to R7) was linearly related to yield. These results indicate that well-adapted, full-season cultivars are likely to produce higher yields regardless of planting time, and while the duration of reproductive development is associated with yield, cultivars that mature much later than is typical for a site may be affected by other yield-limiting factors such as temperature and water supply near maturity.