A critical agronomic decision is the choice of soybean products and their associated optimum seeding rate. Though soybeans compensate well at different plant populations, soybean products respond differently and the search for the optimum seeding rate continues.
The objective of this study was to determine the yield potential of Asgrow® brand soybean products at different seeding rates.
Research Site Details
Fifteen Asgrow® brand soybean products ranging from 1.8 to 3.6 maturity group (MG) were planted at 100,000, 140,000, and 180,000 seeds/acre.
The trial was planted in 30-inch spacing, 4 rows per product per seeding rate, and 200-ft long plots.
Weed management consisted of a rye burndown with Roundup PowerMAX® herbicide and a post-emergence application of XtendiMax® herbicide with VaporGrip® Technology, Warrant® herbicide, and Roundup PowerMAX®.
Understanding the Results
The decrease in plant population across the trial between the V4 and R8 growth stages was partly due to wet and rainy conditions at the research site in May and June, followed by a dry July. Such conditions result in poor seedling health and reduced crop stands.
Seeding rate did not have an impact on lodging in most of the products tested, especially in the late MG products (Table 1 and 2). In the products in which there was an association (particularly in the early MG), lodging increased with increasing seeding rate.
In both the early and late MGs, yield increased as seeding rate increased in most of the products. In the other products, the 140,000 seeds/acre seeding rate produced the highest yields (Figure 1 and 2).
In both MGs, the biggest yield increase was from the 100,000 to 140,000 seeds/acre rate increase (Figure 1 and 2).
What Does This Mean for Your Farm?
With the current soybean seed cost at $62/bag and assuming the soybean grain was sold at $7.50/bu, a minimum of a 2.4 bu/acre yield increase is needed to justify a 40,000 seeds/acre seeding rate increase.
Thus, for all products in the early MG (except for AG20X9 and AG21X9), 180,000 seeds/acre was the highest yielding and most profitable seeding rate (Figure 1).
For the late MG, the median seeding rate of 140,000 seeds/acre was the most profitable, except for AG30X9, in which the 180,000 seeds/acre rate was both the highest yielding and most profitable (Figure 2).
This is our fourth year of research into germplasm response to seeding rate. Results from the 2015-2017 trials were product-specific and did not provide a consistent trend in response to seeding rate.1 The 2018 results are consistent across almost all products tested, providing a good benchmark for future decision making.
Growers should consult their trusted agronomists and dealers in choosing the best products for their operation.
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1Monsanto Learning Center at Huxley, Iowa Demonstration Reports, 2015-017.