Yield Observations When Shifting to Earlier Relative Maturity Soybean Products
A growing trend for soybean growers is to plant “early” soybean products (south of their normal adaptation) earlier in the season and managing them at a higher level with seed treatments and foliar applications of fungicide and insecticide. This phenomenon, dubbed “relative maturity (RM) shift” is becoming increasingly important in some locations.
There are many benefits of planting “early” soybean products including:
Earlier cover crop seeding
Risk management benefits
The objective of this study was to determine the yield impact of planting “early” (for the location) RM soybean products compared to planting normal RM products for the location.
RESEARCH SITE DETAILS:
The trial consisted of two sets – North and South.
Each set had three Iowa locations:
North Set – Storm Lake, Marble Rock, and Huxley
South Set – Huxley, Atlantic, and Victor
Each RM group consisted of three unique Channel® brand soybean products.
Three products were considered early RM for the location:
North Set – 1.2 to 1.6 RM
South Set – 1.8 to 2.4 RM
Three products were considered normal RM for the location:
North Set – 1.8 to 2.4 RM
South Set – 2.9 to 3.7 RM
The 1.8 to 2.4 RM group consisted of the same three products for both the North and South sets.
The trial was a mix of plot sizes, replications (reps), and row spacings:
Storm Lake (4 reps)—six row strips, 20-inch spacing
Atlantic (2 reps) and Marble Rock (4 reps)—four row strips, 30-inch spacing
Huxley (3 reps)—six row strips, 30-inch spacing
Victor (2 reps)—eight row strips, 30-inch spacing
During the growing season, all sites recorded 20+ inches of rainfall with Atlantic receiving 32 inches total.
The Marble Rock site received several heavy rainfall events.
UNDERSTANDING THE RESULTS
Delayed planting dates in the spring and late rains in the fall favored the normal RM group at the sites tested in 2019.
The normal RM group had a 6.0 bu/acre advantage over the early RM group at the North and South locations (Figures 1 & 2).
In 2019, the early RM products yielded, on average, 6.0 bu/acre less than the normal RM products and yields ranged between 3 to 10 bu/acre less than normal RM products.
In 2019, rainfall was plentiful with Marble Rock receiving the heaviest one-time event, and with Atlantic receiving over 32 inches total.
The 2019 growing season favored the normal RM products, especially with a few delayed planting dates and excessive late-season rainfall that the normal RM group was able to utilize.
More research needs to be conducted in the genetic pipeline to better understand which soybean products can be grown south of their main area of adaptability.
It should be noted that a RM shift may not be for every operation and that its benefits could be defined in terms other than yield.