Are the Maturity Group (MG) ratings we are accustomed to still accurate and do they reflect the maturity of the varieties we should be planting today?

Shawn Conley, Soybean Extension Specialist Soybean, and colleagues from the University of Wisconsin led an effort to reevaluate how maturity group rankings relate to today’s soybean growing environments. Constantly changing weather patterns (think global warming), and changes in genetics and approaches to management have led farmers to change management practices. The adaptability of soybean varieties needs to be routinely evaluated to see if their maturity group ratings make sense. And while photoperiod is still a constant, temperature and rainfall have increased.

Soybeans are grown across Illinois and over a range of environments from northern North Dakota to south Texas, from western South Dakota and eastern Colorado to the Atlantic coastline, and along the Gulf Coast from Texas to Florida. Soybean maturity is classified in Groups ranging from an MG of 000 in the Northern U.S. and Canada for the very early maturing varieties to an MG 9 for the later maturing varieties. Maturities can be further divided by adding a decimal point. The MG of a variety is determined largely by its response to photoperiod (day and night length) and temperature.

The authors of the study evaluated the yield of varieties with different MGs using data from variety performance trials from 27 states over 14 years. They developed an updated map showing optimal MG zones across the soybean producing areas of the U.S. (below).

Optimum soybean maturity groups and standard error across the examined region of the continental U.S. Courtesy of Delineating Optimal Soybean Maturity Groups Across the United States. Spyridon Mourtzinis, John M. Gaska and Shawn P. Conley. University of Wisconsin.

The authors concluded MG 3 varieties are best adapted to the northern half of Illinois and MG 4 to the southern half of Illinois. MG 2.5 is adapted to the northern two tiers of counties in Illinois and MG 4.5 is best adapted to the southern-most point of Illinois. While the contour lines may be different than earlier MG maps, the range of maturities recommended is primarily what growers are already planting today in those regions. However, if they plant an MG 3, for example, they plant a range from maybe 2.5 to 3.5.

To see the full study, visit Delineating Optimal Soybean Maturity Groups Across the United States to download the full extension report.

Agronomist Daniel Davidson, Ph.D. posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.