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Soybean Soil Fertility

 

Soybean Soil Fertility

Soybeans have among the highest nitrogen (N) demands of agronomic crops due to a high concentration of protein in the seed. Symbiotic fixation supplies about half of the plant’s N needs, and the remainder comes from the soil and/or fertilizer.

Despite their high demand for N, soybeans have historically received little or no N fertilizer. However, some studies have indicated that fixed N alone may not be sufficient to supply the N required to produce maximum yields. In fact, adequate N2-fixing capacity of soybeans declines rapidly after the R5 stage, which coincides with the peak soybean N demand for protein synthesis in seeds.

To better understand the potential for increased soybean productivity by using additional N, DuPont Pioneer conducted research trials to determine soybean yield response to late-season N applications.

Soybeans in field
 

In a 2011-2012 study conducted at 5 Illinois locations, 80 lbs N/acre was applied as a polymer-coated urea at the R2 growth stage. Results showed a significant positive yield response to the N fertilizer at all 5 research locations (p < 0.10). Yield increases ranged from 1.3 to 3.7 bu/acre (Figure 1).

Chart showing soybean yield increases with R2 applications of 80 lbs N/acre at 5 Illinois locations in 2011-2012.

Figure 1. Soybean yield increases with R2 applications of 80 lbs N/acre at 5 Illinois locations in 2011-2012. All locations showed a significant (p < 0.10) yield increase.

In addition, a larger study conducted at 55 Illinois and Indiana locations over 2 years also showed a positive yield response to 100 lbs N/acre applied at the R2 growth stage. Across all locations, the average yield increase from supplemental N application was 1.1 bu/acre (Figure 2). The yield response to the added N was 0.4 bu/acre for short-season (< 3.0 MG) varieties and 2.1 bu/acre for full-season (> 3.0 MG) varieties.

Influence of 100 lbs N/acre applied at R2 vs. no applied nitrogen on soybean yields at 55 research locations.

Figure 2. Influence of 100 lbs N/acre applied at R2 vs. no applied N on soybean yields at 55 research locations in Illinois and Indiana over a 2-year period.

An iron deficiency can also hinder soybean productivity. Soybean iron deficiency chlorosis (IDC) is a nutrient deficiency disorder with symptoms that include chlorosis (yellowing) of the soybean foliage and stunting of the plant. This condition is yield-limiting in many soybean fields in the northern and western Corn Belt as well as parts of the southern U.S. Because soybean varieties vary widely in tolerance to IDC, variety selection is the first and most important step in managing this problem.

 
Soybean interveinal chlorosis due to iron deficiency
 

DuPont Pioneer conducted a study to determine if an in-furrow application of an iron chelate treatment at planting would help to mitigate IDC symptoms at 11 locations with a history of IDC in Nebraska and Kansas. Results showed that several soybean varieties with a range of IDC tolerance scores had a positive yield response to the iron chelate treatment (Figure 3). Visual differences, such as greener and more robust plants, were noted as well.

Soybean yield response to iron chelate treatment averaged across 11 locations with a history of IDC in Nebraska and Kansas.

Figure 3. Yield response to iron chelate treatment averaged across 11 locations with a history of IDC in Nebraska and Kansas in 2012.

In another study, DuPont Pioneer and Auburn University investigated the use of a wheat cover crop to manage IDC on high pH soils in the Black Belt Region of Alabama.

Results from this 2012 study showed that using a cover crop increased yield of several soybean varieties that had a range of IDC tolerance scores. In fact, a cover crop increased the yield of the most IDC sensitive variety by 45 bu/acre. Other varieties showed yield increases ranging from 20 to 31 bu/acre in response to a cover crop (Figure 4).

Soybean yield response comparing the impact of a cover crop vs. a fallow field in 2012.

Figure 4. Soybean yield response comparing the impact of a cover crop vs. a fallow field in 2012. Pioneer® brand varieties used in the study were 95Y40 (RR), 95M82 (RR), 96Y70 (RR, STS), and 96M60 (RR).

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 Glyphosate Tolerant  Genuity® Roundup Ready 2 Yield® Soybeans

Always follow grain marketing, stewardship practices and pesticide label directions. Varieties with the Glyphosate Tolerant trait (including those designated by the letter “R” in the product number) contain genes that confer tolerance to glyphosate herbicides. Glyphosate herbicides will kill crops that are not tolerant to glyphosate.


Always follow grain marketing, stewardship practices and pesticide label directions. Varieties with the Genuity® Roundup Ready 2 Yield® (RR2Y) trait contain genes that confer tolerance to glyphosate, the active ingredient in Roundup® brand agricultural herbicides. Roundup® brand agricultural herbicides will kill crops that are not tolerant to glyphosate. Genuity®, Roundup® and Roundup Ready 2 Yield® are registered trademarks of Monsanto Technology LLC used under license. Individual results may vary, and performance may vary from location to location and from year to year. This result may not be an indicator of results you may obtain as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible.
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Roundup Ready® crops contain genes that confer tolerance to glyphosate, the active ingredient in Roundup® brand agricultural herbicides. Roundup® brand agricultural herbicides will kill crops that are not tolerant to glyphosate.
Pioneer is a member of Excellence Through Stewardship® (ETS).
Pioneer is a member of Excellence Through Stewardship® (ETS). Pioneer products are commercialized in accordance with ETS Product Launch Stewardship Guidance and in compliance with the Pioneer policies regarding stewardship of those products. Crops and materials containing biotech traits may only be exported to or used, processed, or sold in jurisdictions where all necessary regulatory approvals have been granted for those crops and materials. It is a violation of national and international laws to move materials containing biotech traits across borders into jurisdictions where their import is not permitted. Growers should discuss these issues with their purchaser or grain handler to confirm the purchaser or handler's position on products being purchased. Excellence Through Stewardship® is a registered trademark of the Biotechnology Industry Organization.

DuPont™ STS®    Varieties with the DuPont™ STS® gene (STS) are tolerant to certain SU (sulfonylurea) herbicides. This technology allows post-emergent applications of DuPont™ Synchrony® XP and DuPont™ Classic® herbicides without crop injury or stress (see herbicide product labels). NOTE: A soybean variety with a herbicide tolerant trait does not confer tolerance to all herbicides. Spraying herbicides not labeled for a specific soybean variety will result in severe plant injury or plant death. Always read and follow herbicide label directions and precautions for use. DuPont™, STS®, Synchrony® XP and Classic® are trademarks or registered trademarks of DuPont or its affiliates.
Hybrid and variety responses are variable and subject to any number of environmental, disease and pest pressures. Individual results may vary.
The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and management suggestions specific to your operation.
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