Soybean plants respond to photoperiod — the day length. Soybeans have developed a sort of intelligence that lets them know if they have enough time to fill seed. A chemical in the leaves called phytochrome responds to day length and sends Soybean maturity groups signal to the meristem on nodes, where the flowers appear. That starts the reproductive process.
Plant breeders have identified and selected varieties that are just a little different in how the phytochrome reacts to day length.
Soybean yield is a product of the number of days of seed fill and the rate of fill. The more leaves, the greater the fill. So as you go up the maturity scale, from a group 1 to 2 and 3 and so on, you further Soybean maturity groups the signal to start flowering.
Each whole number as you move up adds about 10 days. The significance of this is that as you move up the maturity groups, the plants have a bigger factory before flowering begins. That should maximize yields.
Within certain maturity groups, we have a fair amount of leeway to get top yields. A few years ago, we did tests with three soybean varieties in maturity groups 1, 2, 3, and 4 and three planting dates of April, May, and June.
Groups 3 and 4 yielded almost identical and significantly better than groups 1 and 2.
The average yields were Again, the 3 and 4 groups were about the same. The group 6 soybeans suffered frost damage because they flowered too late.
Our soybean variety testing program in Missouri also sheds some light on this. Regardless of how you break out this data, groups 3 and 4 yield nearly the same in central and north Missouri.