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 18 unique soybean products.

  • Nine products were considered early RM for the location:   
    
    • North Set – 1.3 to 1.8 RM
      
    • South Set – 2.0 to 2.6 RM 
      
  • Nine products were considered normal RM for the location:
    • North Set – 2.0 to 2.6 RM
      
    • South Set – 3.3 to 3.6 RM
      
  • The 2.0 to 2.6 RM group consisted of the same nine 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. 

   

• With later planting dates in 2019, the normal RM group showed a clear advantage of 6.0 bu/acre over the early RM group (Figure 1).

• Over the two years of this trial (2018-2019, Figure 2) the normal RM group had an average advantage of 3.8 bu/acre.  In 2018, the early RM group had a yield advantage at three locations (Victor, Storm Lake, and Atlantic).

• In 2019, the early RM products yielded, on average, 6.0 bu/acre less than the normal RM products and yields ranged between 4 to 11 bu/acre less than the 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 two-year data indicates that early RM soybean products can be competitive if the proper genetics are selected.

• 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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