Soybeans differ from corn when it comes to relative maturity (RM). How?
Corn hybrid relative maturity is solely based on heat unit accumulation, while soybean variety RM is based on day length.
Soybean plants are photosensitive, which means that when day length shortens at Summer Solstice (marking the onset of summer and the longest day of the year), soybean plants are stimulated to begin the reproductive stage of development (though day length varies between latitudes across the United States and Canada). Of course, other factors, such as planting date, moisture availability and temperature can influence maturity of soybeans as well, but to a lesser degree.
Groups were formed with the 42nd parallel as the center of soybean production (Interstate 80 follows close to the 42nd parallel as a reference point). Soybean maturity group numbers relate to the date in the month of September that the soybean is expected to reach physiological maturity (R8).
Groups are 10 days apart in maturity, with groups from 00 to 10. Each group is then subdivided into 10 subgroups behind a decimal point.
Another example of a soybean Group 3.4 would reach R8 on October 4. Each seed company sets the RM of their seed; therefore, RM may differ by as much as three days between seed companies.
Generally, the longer the soybean RM, the more yield that can be expected. New soybean genetics developed in recent years have helped to decrease some of the yield differences between relative maturities.
Be sure to consider RM when you’re considering soybean varieties for your farm and how it relates to other factors in your seed selection, such as:
moisture availability
temperature, like average frost date
disease resistance
seeding rates
management practices