Continuous Soybeans Risks and Benefits

ANKENY, Iowa (DTN) -- Sky-high fertilizer costs, supply uncertainties and soybean profit potential may entice some farmers to stray from their traditional crop rotation and plant more continuous soybeans this spring.

"I think it will happen," said Mike Staton, a Michigan State University (MSU) Extension soybean educator, based on recent conversations with farmers.

However, growing soybeans back to back in the same field can be risky. Enhanced disease and pest pressure, among other concerns, can contribute to yield drag. A study published in the Agronomy Journal (https://www.mssoy.org/…) indicated a 10.3% yield drag, on average, occurs with continuous soybeans.

Steps can be taken, though, to mitigate and possibly eliminate yield loss growing continuous soybeans. With intensive management, central Ohio farmer John Buck said planting soybeans in the same field year after year does work. More soybeans than corn are usually grown on the 2,100 acres he farms (500 are custom acres) each year.

"I'm not seeing the (continuous soybean) yield drag that others are seeing, but I'm doing everything I can to mitigate it," said Buck, who farms near New Bloomington, about 60 miles northwest of Columbus. "I'm not saying you won't have a hiccup here and there. But my yields are consistently 60 to 80 (bushels per acre) and improving."

Buck embraces continuous soybean production out of necessity. Getting consistently high corn yields of 200 bpa or more is difficult, he said. Corn planting is often delayed in fields with heavy, clay soils that don't dry out well in the spring, which make up a good chunk of his farm ground. Some hilly, poor ground doesn't hold water well, which causes corn to suffer moisture stress in-season.

MORE SOYBEANS POSSIBLE

As of the beginning of March, Buck plans to plant two-thirds of his total acreage to soybeans and one-third to corn. That's a little more soybeans than he wanted this year, but high fertilizer costs and soybean prices dictated the decision, he said. Planting even more soybeans and less corn is still an option depending on future input costs, supplies -- fertilizer and herbicides -- and commodity prices, Buck added.

"Unless you have (fertilizer and chemicals) in your possession, there's no guarantee you can get them," he said, based on discussions with ag input suppliers.

Soybean profit potential exceeds corn in some projections by analysts. "That's a factor (in planting decisions)," Buck said.

Economics and market fundamentals prompted more continuous soybeans in 2021 than past years. (See that story on DTN at www.dtnpf.com/agriculture/web/ag/crops/article/2021/02/08/5-tips-want-grow-soybeans-soybeans-2.)

Even more soy-on-soy acres could be planted in 2022, which includes areas in the Western Corn Belt where the practice isn't as common as in the east. "If there's ever a temptation to stray away and plant more soybeans, this has got to be the year," said DTN Lead Analyst Todd Hultman.

Most fertilizer prices have doubled or tripled in the last year. Nitrogen products used in corn production, such as anhydrous ammonia and UAN, are at record highs. (See the latest DTN fertilizer price story at www.dtnpf.com/agriculture/web/ag/crops/article/2022/03/02/average-retail-fertilizer-prices.)

Corn production costs have skyrocketed since December when the USDA pegged the average price at $715.73 per acre. Factoring in higher fertilizer prices compared to when the USDA collected its cost figures in the late fall, Hultman estimated corn costs for many farmers at more than $900 per acre. Purdue University ag economist Michael Langemeier recently estimated expenses of up to about $1,100 per acre in highly productive ground.

Langemeier said soybean costs are up as well, but not as much as corn. Based on recent commodity prices and input costs, he projected 2022 soybean profit potential is $16 to $61 per acre better than corn, depending on the productivity of soil. The largest difference occurring on lower productivity soils.

"Soybean prices have strengthened so much in the last month. That's really contributed to the bullish outlook for soybeans," Langemeier said.

He added that farmers who haven't already purchased or applied fertilizer for this year's corn crop will be the most tempted to plant continuous soybeans.

Hultman's latest profit potential estimates, taking in account recent new-crop corn and soybean prices, input costs and trendline yields, give corn the profit potential advantage of $191 per acre compared to $150 per acre for soybeans.

"Price expectations for the fall can be different than current new-crop prices, which can factor in the decision of what to plant," Hultman said, along with fertilizer and chemical supply concerns.

Here are five tips to mitigate continuous soybean challenges.

PLANT COVER CROPS

For farmers who planted cover crops last fall, that may benefit continuous soybeans this year.

Seedling diseases such as Pythium, phytophthora and fusarium can pose challenges to back-to-back soybeans since the disease cycle isn't broken by a rotational crop. Laura Lindsey, an associate professor at Ohio State University specializing in soybean and small grain production, told DTN that planting a grass cover crop (cereal rye, oats, etc.) between soybean plantings can act as the rotational crop.

OSU conducted cover crop research in second-year continuous soybeans in 2018 and 2019 at two locations in the state. Researchers looked a slug, seedling disease and foliar disease pressure, insect defoliation and other problems associated with continuous soybeans, Lindsey said.

"We really didn't have any heavy disease, insect or slug pressure," Lindsey said, though she noted the test fields didn't have big problems with pests and disease prior to the study.

"I think there is a potential benefit (to minimize disease pressure) by planting a grass and not a legume," she added. "The grass cover would not be a host for a lot of soybean diseases in between soybean crops."

Continuous soybeans produce less crop residue compared to a rotation that includes corn, which can reduce organic matter in the soil. Staton said corn residue and cover crops build organic matter and improve soil health.

"One of the biggest components of soil quality is adding plant material to the soil," he said. "That is a good thing. It improves soil structure and feeds soil microbes ... to better cycle nutrients."

Cover croppers need to think of herbicide availability this year though.

Potential shortages of glyphosate -- a popular herbicide to terminate cover crops -- are expected in 2022, according to Kevin Bradley, a University of Missouri weed scientist. Glufosinate is also expected to be in short supply. Chemical prices are higher than in previous years as well.

"I'm also not sure who will have a shortage of these herbicides in 2022, and who won't," Bradley recently wrote on the University of Missouri's Integrated Pest Management website. "So, if you anticipate that you may be unable to source enough glyphosate or glufosinate for your needs this season, my advice is simply this; determine the best way for you to use the herbicide(s) that you do have available for the good of your overall weed management program."

CHOOSE FIELDS CAREFULLY

Choose well-drained, productive fields with minimal to no history of disease and heavy weed and pest pressure for continuous soybean production, if possible. Staton said that's a key step to successfully implementing the practice.

Avoiding fields with soybean cyst nematode (SCN), the top yield-robber in the nation, is especially important, Staton emphasized. Crop rotation is one of the most effective SCN management tactics. (See a recent DTN article focusing on that at www.dtnpf.com/agriculture/web/ag/crops/article/2022/02/15/know-scn-risks-planting-soybeans.)

"If you have SCN in a field, continuous soybeans give them a greater chance to reproduce and built up, so there are downsides," Staton warned.

KEEP PLANTS HEALTHY

Seedling diseases and foliar diseases, such as frogeye leaf spot and brown spot, can be exacerbated by continuous soybeans. So can sudden death syndrome.

Seed treatments to combat diseases are a must in continuous soybeans, Staton said. Also, scout fields regularly for disease and insect pressure during the growing season and treat for both as needed.

Staton said he's not afraid of yield loss from continuous soybeans if precautions are taken. "The biggest thing is just managing those pest (and disease) problems that carry over," he said.

Buck said picking seed varieties with proven resistance to diseases and pests, such as SCN, is important. Switching seed brands, varieties of seed, genetics and varietal resistance every year is recommended, he added.

"I don't even stay with the same seed company year after year," Buck said. "I make my seed advisors work."

Various biological products are part of Buck's soybean inputs, as either seed treatments or in-furrow applications, to protect soybeans from pests and diseases. He believes biologicals improve plant health.

WATCH WEED CONTROL

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

Buck routinely rotates chemistries and herbicide-tolerant seed traits to lessen weed pressure.

"I don't want the same (trait) repeatedly used," he said.

FINE-TUNE FERTILITY

Fertilize fields based on nutrient removal rates and soil tests.

Potassium (K) is a key nutrient to watch. Soybean remove about 1.4 pounds of K for every bushel of production, according to MSU. A pre-season potash or K application may be needed to ensure soils are at the recommended level, which can vary.

(Find crop removal rates at https://www.canr.msu.edu/….)

Matthew Wilde can be reached at matt.wilde@dtn.com

Follow him on Twitter @progressivwilde

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