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Continuous Soybean Management Practices
March 28, 2017
Continuous soybean production has become more attractive to some growers due to favorable market prices and lower input costs when compared to corn production.
Growing a crop year after year in the same field can result in a build-up of pathogens and insect pests which may result in yield penalties.
Certain management practices such as product disease or insect resistance can help mitigate these issues.
Field and Product Considerations
Though continuous soybean production is generally not recommended, some farmers have reported stable yields with no downward trend after nearly 20 years or more of planting soybeans continuously in the same field.1 Successes like these tend to occur in areas where soils are not prone to holding excessive moisture and where disease and soybean cyst nematode (SCN) problems are minor. Low lying fields and fields with poor drainage are not ideal for continuous soybean production due to the increased potential for disease development. Greater yield penalties and smaller profit margins, due to increased pest control costs, may be expected when soybeans are planted continuously in fields that have a history of insect and disease problems.
Product selection is critical for continuous soybean production. Products should be selected based on yield potential, maturity, and resistance to key insects and diseases. It is a good idea to plant different genetics each year to minimize the proliferation of diseases.
Figure 1. Soybeans damaged by sudden death syndrome.
Disease Management
Disease inoculum can build up on crop debris and in the soil each growing season when in the constant presence of a host crop. A field with disease or nematode issues may see a dramatic reduction in yield after the third or fourth year of continuous soybean production.2 Diseases such as white mold, sudden death syndrome (SDS), brown stem rot, certain root rots, and SCN remain in the soil or crop residue for several years after a host plant is removed.
Without crop rotation to break pest and pathogen life cycles, other management approaches will be needed. Often, planting a product with disease or insect resistance is the most effective management approach. Phytophthora root rot can be managed by selection of soybean products with racespecific resistance, designated Rps. Products with the appropriate Rps designations relative to the races in a field, combined with partial resistance, will provide the best control.3 No soybean products are completely resistant to white mold or SDS. Selecting soybean products with partial resistance to these diseases may help reduce damage.
If white mold occurred in the previous year, crop rotation is the most effective cultural practice for preventing future damage. With continuous soybeans, other cultural practices must be considered. Alternative control strategies for managing diseases include lower seeding rates or wider row widths to increase air flow in the canopy for suppression of foliar diseases. Planting later in the season or planting soybean products with shorter relative maturities can help to avoid disease outbreaks during sensitive growth stages.
Seed Treatments
Seed treatments are a critical component in continuous soybean production. Broad-spectrum fungicidal seed treatments can protect soybeans from early-season diseases including Pythium, Phytophthora, Fusarium, and Rhizoctonia. Broad-spectrum insecticidal seed treatments can protect soybeans from damage by early-season insect pests such as bean leaf beetle, soybean aphid, seed corn maggot, wireworm, and white grub. Some seed treatments can also protect against early-season SCN damage by making young soybean roots unattractive to the nematodes.
Weed Management
Weed control is more difficult in continuous soybean production. With crop rotation, alternating spray schedules and herbicides with different sites of action are more likely to be used for weed management. The practice of planting soybeans each year and spraying the crop with the same herbicides at the same time every year is not recommended. This practice can favor the survival of weeds that are less sensitive to the herbicides and weeds that reproduce when the herbicides are not being used, as well as increase the potential for the development of herbicide resistant weeds. It is important to tank mix herbicides with different effective sites of action on the weed species present in a given season and to vary weed control practices in subsequent years. Residual herbicides should be applied preemergence and potentially postemergence to aid in control of problematic weed species.
Soil Fertility
Soil nutrient levels should be carefully monitored to ensure that adequate phosphorus (P) and potassium (K) are available to the crop. Because a soybean grain harvest typically removes more K than a corn grain harvest, this nutrient may need to be supplied more often in continuous soybean production. Nutrient inputs should be based on soil test recommendations, which should be conducted every three to four years.
Sources
1 Howe, D. 2006. Risky business or good business? Corn and Soybean Digest. http://cornandsoybeandigest.com/risky-business-or-good-business.
2 Soybean following soybean. 2008. www.extension.org.
3 Dorrance, A.E. and Mills, D. 2009. Phytophthora damping off and root rot of soybean. Fact Sheet AC17-09. Ohio State University Extension. http://ohioline.osu.edu.
4 Koenning, S. 2000. Management of soybean cyst nematode. North Carolina State University Extension. www.ces.ncsu.edu.
Other sources:
Davidson, D. 2014. Planting continuous soybeans. Illinois Soybean Association. www.ilsoyadvisor.com/agronomy/2014/december/planting-continuous-soybeans. Pedersen, P. 2009.
Soybean after Soybean. Iowa State University Extension. http://crops.extension.iastate.edu/cropnews/2009/04/soybean-after-soybean.
Web sources verified 8/30/15. 130905060207
