What Is the Best Soybean Maturity Group to Plant Behind Wheat?

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In recent years, 15-35% of North Carolina soybean acres are planted behind a small grain. This typically results in soybean planting dates from the second week of June through early July. Historically growers have planted a later maturing soybean variety as planting date was delayed. However with the increasing interest in earlier maturing soybean varieties for the associated yield gains, we have been getting more questions about the optimum maturity group to use in double crop soybean planting in North Carolina.

From 2019-2021, research was conducted across 11 NC locations to determine the best maturity group to use across diverse planting dates. More details about the methods used in this study can be obtained in this scientific publication. 

If you look at the mid-June planting dates, whether you were in a low or higher yielding environment, the MG4-7 varieties cut within 5 bu/A (Figure 1). Using varieties earlier than a MG4 should be avoided in double crop planting situations because those varieties will not get enough vegetative growth prior to flowering to drive photosynthesis because of the shorter night length needed to trigger flowering in earlier maturing varieties. At mid-July planting dates, the MG5-7 varieties were the highest yielding (Figure 1).

This data indicates that growers have some flexibility in which maturity group is used at later planting dates (MG4-7). So for those asking if using a MG4 variety will provide yield advantages when planting behind wheat; so far our data indicates there is not much of advantage or disadvantage of using an indeterminate MG4 compared to later maturing variety at this planting date. The SoyStage tool developed by the University of Arkansas is an excellent way to predict when soybeans will reach physiological maturity based on planting date and relative maturity. Growers should be making MG selection behind wheat based on desired harvest dates and needed disease resistance packages, as recent research across the United States indicates that foliar diseases are more problematic at lower latitudes when planting dates are delayed.

Figure 1. The impact of planting date and maturity group on soybean yield in high (n=5, blue) and low (n=6, red) yield environments across North Carolina from 2019-2021.