Continuous Soybean Considerations

Economics and market fundamentals may prompt some farmers to abandon traditional crop rotation in favor of more soybeans this spring.

Growing continuous soybeans can be risky. Disease and insect concerns and yield drag, among other reasons, are often a deterrent. A study published in 2017 in the Agronomy Journal indicated a 10.3% yield drag, on average, is associated with continuous soybeans.

However, steps can be taken to manage agronomic challenges to get the most out of consecutive soybean crops.

"Some farmers see continuous soybeans as a viable option when prices are high," said Clarke McGrath, an agronomist and on-farm research and Extension coordinator for the Iowa Soybean Research Center at Iowa State University. "Farmers can reduce the risk, but not eliminate it, with good management. It can set them up for success."

Interest in continuous soybeans often escalates with prices, McGrath said. Soybean futures have soared about $5 per bushel since last summer. The March contract neared $14 per bushel in late January thanks to strong exports, especially to China, robust domestic use and supply concerns.

Planting soybeans after soybeans isn't an alternative for every farmer or every field, McGrath added. But many growers make it work.

Cole and Zach Bailey intend to plant more than 80% of the 12,000 acres they farm with their parents near Xenia, Illinois, to nongenetically modified soybeans this year. Corn and winter wheat are often part of the mix, but the family has long favored a soybean-centric rotation. Some years they grow soybeans exclusively.

The Bailey brothers see less risk growing soybeans than corn on their heavy, clay soils that are always "a week away from drought." They contend intense management can overcome agronomic challenges of continuous production to make the system productive and profitable.

"People say you need to rotate crops, (but) they aren't paying (the farm's) bills," said Zach Bailey. "You need to put pencil to paper. With soybean prices now, (continuous) soybeans is a no-brainer for some farmers.

"If you stay on top of management, you can grow a heck of a soybean crop year after year," he added. The Baileys' soybean yields average 45 to 50 bushels per acre (bpa). In Clay County, where their farm is based, the average soybean yield was 40.5 bpa in 2019, according to USDA.

Here are some tips for returning to soybeans after soybeans.

PICK FIELDS CAREFULLY

"I would say the No. 1 thing for farmers to consider is land," McGrath said.

Agronomists recommend choosing well-drained, productive fields. If possible, avoid ground with a history of heavy weed, disease and soybean cyst nematode (SCN) pressure. SCN is the top yield-robber in the nation.

Pat Holloway, a field agronomist with Beck's Hybrids, said farmers should test fields for SCN if they haven't already. "This is a key step. If SCN populations are moderate to high, farmers run the risk of escalating SCN pressure with soybeans-on-soybeans and reducing yields."

PRACTICE DISEASE AND PEST MANAGEMENT

Seedling diseases such as Pythium, Phytophthora and Fusarium can pose enhanced challenges in continuous soybeans since the disease cycle isn't broken by another crop. The same goes for foliar diseases such as frogeye leaf spot and brown spot. SCN and sudden death syndrome (SDS) are also a concern.

Tony Lenz, a technical agronomist with Stine Seed, said good pre-planting and in-season management is critical to continuous soybean success. Scout fields for disease and insect pressure during the growing season and treat for both as needed.

"With any continuous crop, you have to up your management," Lenz said. "Make sure soybean seed treatments have a good disease package and pick varieties that are defensive (fend off diseases better). Switch varieties, trait packages and chemistries to mitigate resistance issues in the future."

DEPLOY WEED CONTROL

Start with a clean field if possible. Use multiple herbicide sites of action, use recommended rates and spray weeds in a timely fashion. Consider a layered residual program and scout diligently.

The Baileys start with a clean, tilled field. A pre-emergent herbicide is applied. In-season applications are done as needed to prevent weeds growing more than 1-inch tall, if possible. Multiple residual herbicides are layered during the growing season.

"Herbicide resistant weeds and build-up of the weed seed bank are legitimate concerns," Zach Bailey said. "We rotate chemistries and traits. Next year, we'll switch to the Enlist platform."

FINE-TUNE FERTILITY

Pay close attention to soil fertility. Soil test as needed.

Potassium (K) is a key nutrient to watch. Soybeans remove about 1.4 pounds of K for every bushel of production. That's 98 pounds of K per acre for soybeans averaging 70 bpa. A pre-season potash or K application may be needed to ensure soils are at the recommended level, which can vary among soils and regions.

"Fields that are inherently low in potassium levels are not a good choice for continuous soybean," Holloway said. "Soybeans remove more than in a typical corn/soybean rotation."

Soil pH is also important. Agronomists recommend pH levels of six and above for soybeans. Anything lower could affect plant nutrient uptake.

Chicken litter is key to the Bailey fertility program. They typically variable rate 3 to 10 tons per acre to provide necessary K, phosphorus, nitrogen and micronutrients.

GATHER MARKET CLUES

IHS Markit, an international information and analytics company, recently projected 90.8 million acres of soybeans will be planted in the U.S. this year. That's 8% higher than 2020.

DTN Lead Analyst Todd Hultman said numbers may entice more farmers to plant continuous soybeans. USDA estimates U.S. soybean ending stocks for the 2020/21 marketing year at 140 million bushels, a seven-year low.

"Realistically, the U.S. is on track for having the tightest supply situation in U.S. history," Hultman asserted. "This is the main reason many farmers may want to increase soybean acres in 2021. The tight carry is apt to keep harvest prices higher than normal for new-crop soybeans."

The current soybean-corn price ratio based on new-crop futures prices is 2.58 to 1, which slightly favors soybean plantings, according to Hultman. That's above the 10-year average of 2.44 to 1.

December corn prices have tracked fairly close with soybeans and are apt to keep competing for acres as spring nears, Hultman said. USDA's ending stocks estimate of 1.55 billion bushels of corn in 2020-21 is also the lowest in seven years and has room to go lower by the end of the marketing year on Aug. 31. However, he added, corn does not show the same risk of running out.

"For that reason, the expectation of much higher soybean prices is a strong incentive for those willing to plant more soybeans in 2021," Hultman concluded.

Matthew Wilde can be reached at Matt.Wilde@DTN.com

Follow him on Twitter @progressivwilde

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