Soybeans Following Soybeans

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High soybean prices relative to corn can favor shifting acreage away from corn to more soybean production.
In some cases, this may involve planting fields to soybeans in two consecutive years.
Planting soybeans in the same field in consecutive seasons is generally not recommended by extension agronomists; however, there are several management considerations that can help maximize productivity for growers pursuing this strategy.

Yield Potential

Growers should expect lower yields in second year soybeans.
Research results have varied, but a yield reduction of 3-5% compared to soybeans following corn is not an unreasonable expectation.
- 2.3% average yield reduction in an 8-yr Univ. of Kentucky study with individual year reductions up to 13% (Grove, 2017).
- 6.5% average yield reduction in a 4-yr study in Ontario
  (OMAFRA, 2009).
- 0% average yield reduction in a long-term Univ. of Wisconsin study (Lauer et al., 1997).
Plant stress caused by environmental conditions, diseases, weed pressure or insects can easily increase yield losses in second year soybeans

Avoid poorly-drained soils due to higher risk of Pythium, Phytophthora, sudden death syndrome, and brown stem rot.
Avoid fields with herbicide resistant weed species and fields where white mould has been a concern.
Consider cover crops in fields with slopes prone to erosion – soybeans produce less residue than corn and decompose more quickly.

Avoid planting a field to the same soybean variety two years in a row.
Select soybean varieties with high levels of disease resistance.
Test for SCN and select SCN-resistant varieties, be sure to rotate resistance sources.
- SCN proliferates in long-term soybean cropping systems.
- Resistant varieties can reduce SCN reproduction by 70-80%.

Use a fungicide seed treatment to protect against diseases such as Pythium and Phytophthora that can increase in severity under continuous soybean production.
Pioneer^® brand soybeans treated with ILeVO^® fungicide seed treatment provides control of sudden death syndrome and certain soil-borne nematodes such as soybean cyst and root knot nematodes.
- Soybeans treated with ILeVO fungicide treatment produced significantly higher grain yield (4.9 bu/acre) in high SCN environments in Pioneer testing (O’Bryan and Burnison, 2016).
- In moderate SDS environments the addition of ILeVO fungicide treatment increased grain yield 4.5 bu/acre.

Growers often routinely rely on carryover fertilizers for soybean when rotated with well-fertilized corn. Soybean after soybean may require additional fertilizer, especially potassium.

Many diseases can overwinter on soybean residue, some can be managed with fungicide, some cannot.
Stem canker and pod and stem blight can overwinter on residue but fungicides are not as effective on these.
Septoria brown spot and frogeye leaf spot are two diseases that can be managed with foliar fungicides.
Scout fields regularly to check for disease problems.

Any weed escapes in the previous soybean crop are likely to result in greater weed management challenges in second-year soybean.
Use multiple modes of action
Soil residual herbicides applied pre-emergence and with a post-emergence application can help manage problem weeds.

Authors: Dan Emmert and Mark Jeschke

March 2017

Lauer, J., P. Porter, and E. Oplinger. The corn and soybean rotation effect. Univ. of Wisconsin. http://corn.agronomy.wisc.edu/AA/A014.aspx.

O’Bryan, K. and M. Burnison. 2016. Performance of soybean seed treatments against SDS and SCN in on-farm trials. Pioneer Agronomy Research Update.

Image courtesy of Case IH.