Should We Be Using Soybean Maturity Group as a Tool for Variety Selection?

Over the last decade I have noticed a subtle shift across much of the northern soybean growing region towards planting later maturity group soybeans. This shift, either conscious or unconscious, may be attributed to earlier planting dates, relatively favorable fall harvest windows, and the drive for maximum yield as influenced by high commodity prices. As with all trends sooner or later, we have a correction year: 2014 was that year for many farmers. As farmers, consultants, and the battered and bruised seed suppliers sort through the plethora of product offerings for 2015, a common question arises: "In 2015, how much weight should we really give to maturity group in these seed decisions?". For those of you with short attention spans like me, the short answer for soybean is not much....for the rest of you please read on to understand my reasoning.

In 2011, the WI Soybean Research Program published an article in the journal Crop Management entitled: "Optimal Soybean Maturity Groups for Seed Yield and Quality in WI" (Furseth et al, 2011). In this data set we looked at 893 varieties across 6 growing seasons (2004-2009) and three production regions in WI . Within each region we identified the optimal maturity group range for maximum yield. Those were 2.6-2.9, 2.1-2.4, and 2.0-2.2 for our southern, central and north central regions respectively.  After I make this provocative statement this is usually where the audience either falls asleep, starts texting their neighbor about the lame and inept speaker (me), or uses the restroom and fails to hear as the great Paul Harvey would say ......the rest of the story.

Within each figure below you will also notice a maroon line directly below the black yield regression slope. This maroon line indicates the range of maturity groups that lie within 10% of maximum yield. These figures suggest that regardless of growing region in WI growers can select a variety that is almost one full maturity group earlier than the optimal maturity group range for maximum yield and still be within 10% of maximum yield.

These data further support Joe Lauer's assertion that "Every hybrid (or in our case cultivar or variety) must stand on its own" (Happy Thanksgiving JGL, you were positively quoted in a soybean article). In our recently released 2014 WI Soybean Variety Test Results book the maturity group range that included a starred variety (starred varieties do not differ from the highest yield variety in that test) was 1.9-2.8, 1.1-2.4,and 0.9-2.0 in our southern, central and north central regions respectively. This amplifies my assertion that the "relative" maturity group rating is trumped by individual cultivar genetic yield potential.

Lastly, since I brought it up lets also discuss our "relative" soybean maturity group rating system. If anyone has ever observed a multi-company variety trial in the fall, they may have notice many differences in maturity amongst varieties that have the same MG rating. For example in our 2014 Southern Region Glyphosate Tolerant Soybean Test we noted a 7 day maturity date range among all the 2.4 maturity group varieties listed. This may not seem important at the end of September, but in years when we plant late (Table 1), have a cool growing season and apply a fungicide those few days may matter. 

As seed decisions are made for 2015, it is fine to keep the relative maturity rating on your check list, just don't have it near the top!

Table 1. Calendar date for reaching R5 (beginning seed fill) and R7 (beginning maturity) growth stage (G.S.) by planting date and maturity group (M.G.) for the 2014 growing season at Hancock WI.

		Timing of G.S. Initiation
Planting Date	M.G.	R5	R7
5-May	1.9	29-Jul	3-Sep
	2.1	3-Aug	13-Sep
	2.1	29-Jul	3-Sep
	2.1	29-Jul	3-Sep
	2.3	29-Jul	3-Sep
	2.3	1-Aug	6-Sep
	2.4	3-Aug	6-Sep
	2.5	29-Jul	6-Sep
	2.5	30-Jul	6-Sep
	2.5	31-Jul	13-Sep
22-May	1.9	12-Aug	12-Sep
	2.1	9-Aug	20-Sep
	2.1	12-Aug	16-Sep
	2.1	12-Aug	20-Sep
	2.3	12-Aug	20-Sep
	2.3	9-Aug	20-Sep
	2.4	12-Aug	16-Sep
	2.5	12-Aug	16-Sep
	2.5	12-Aug	20-Sep
	2.5	12-Aug	20-Sep
11-Jun	1.9	23-Aug	27-Sep
	2.1	23-Aug	2-Oct
	2.1	23-Aug	30-Sep
	2.1	23-Aug	2-Oct
	2.3	23-Aug	2-Oct
	2.3	23-Aug	30-Sep
	2.4	23-Aug	1-Oct
	2.5	23-Aug	2-Oct
	2.5	23-Aug	2-Oct
	2.5	23-Aug	2-Oct

Literature cited: 

Furseth, B. J., Zhao, Y., Conley, S. P., Martinka, M., and Gaska, J. 2011. Optimum Soybean Maturity Groups for Seed Yield and Quality in Wisconsin. Crop Management. Online. Crop Management doi:10.1094/CM-2011-0622-01-RS.