This year we have a Delaware Soybean Board project examining planting date effects on soybean yields, with the goal of planting early and evaluating issues with germination, disease, and general growth. Our first planting was April 12th, followed by April 28th, and May 10th. The first planting date took 14 days to emerge, while the second and third planting date only took 8 days to emerge.
Up until this week, the three planting dates were about 1 stage behind the other (e.g. V3 vs V2). The lowest germination rates appear to be in the first planting (April 12th). The earliest planting also has a large range in growth stages, with some plants having four trifoliates (V4) and others six (V6). Plants that were at V6 had their first flowers (R1) on June 9th but will continue vegetative growth even as flowers begin to form. Unless you are planting varieties greater than 4.5, your soybeans are most likely indeterminate, and will continue in their vegetative growth (leaves) even while flowers being to grow.
Earlier flowering this year could potentially lead to greater yields, although the loss of germinating seeds may cancel that benefit this year.