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 harvest 
    • 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.




  • 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 Asgrow® brand soybean products.
    • Three products were considered early RM for the location:  
      • North Set – 1.1 to 1.7 RM  
      • South Set – 2.0 to 2.3 RM
    • Three products were considered normal RM for the location:
      • North Set – 2.0 to 2.3 RM
      • South Set – 2.9 to 3.2 RM
    • The 2.0 to 2.3 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. 




  • Delayed planting dates in the spring and late rains in the fall favored the normal RM group at the sites tested in 2019.
  • At the North locations, the normal RM group had a 6.0 bu/acre advantage over the early RM group (Figure 1) and at the South locations, the normal RM group had a 4.0 bu/acre advantage over the early RM group (Figure 2).




  • In 2019, early RM products yielded, on average, 5.0 bu/acre less than normal RM products and yields ranged between 4 to 8 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.




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