You live where you would normally plant a 3.8 variety, considered full-season for your area. Common logic has always held that if you go with the fullest-season variety for your area and get them planted on time, yield will be higher than if you plant an earlier variety for your area. Theory says it's because the full-season variety has more time to grow and take advantage of the growing season, and make maximum use of the growing season.
Shaun Casteel, Purdue University Extension soybean specialist, says that while that's one school of thought, he's impressed with the yielding power of some earlier-season varieties for given areas. For example, he's noted that in central Indiana results, some varieties rated at 3.2 maturity have yielded as well or better than 3.8 varieties, considered full season varieties for the area.
Using the group maturity rating system for soybeans, Northern Indiana farmers generally start with group 2 beans and perhaps some very early group 3 varieties. Central Indiana farmers grow varieties in the 3.0 to 3.9 range, depending upon location. Traditionally, the main reason for varying this strategy is if someone wants to harvest very early to either plant wheat behind beans, or try to catch a premium for early harvest if soybean supplies are running short. In southern Indiana, varieties in the 4.0 range are common, although some growers reach back and plant a few varieties in the latter part of the Group 3 range.
Looking at Purdue variety trials and from his own observations over the past few seasons, Casteel says there are many examples where soybean varieties considered shorter season in an area have yielded just as well or better than those traditionally counted as full season varieties.Casteel will explore this idea further in the January issue of Indiana Prairie Farmer. The new series, Soy Basics, returns to the magazine, working out on this issue. "I'm glad to get some press for soybeans," Casteel says. He believes farmers will be able to improve yields if they understand more about the crop.