Dr. Dan Talks Agronomy

Continuous Soybean Questions

Dan Davidson
By  Daniel Davidson , DTN Contributing Agronomist
Can you outsmart the market and still get good yields with back-to-back soybeans? It takes good management. (DTN photo by Pamela Smith)

Back-to-back soybeans have traditionally been considered somewhat risky. However, the current costs of production are weighing against commodity prices to make the practice more enticing.

Disease concerns and a yield penalty are the common strikes against continuous soybeans. The question is are these risks as serious as we've been led to believe and can we manage around them?

Greg Anderson from Newman Grove, Nebraska, has been growing 100% continuous soybeans on over 1,000 acres for 26 years. "My yields are always above the Nebraska state dryland average and always above the county average. What's important is that yield isn't just maintaining, but are increasing," said Anderson.

Anderson doesn't have farm help and has found soybeans to be easier to handle and less labor-intensive than corn. "I can harvest earlier and am out of the field sooner in the fall. When Roundup Ready soybeans came available, growing continuous beans became much easier," he said.

"There is less grain to haul, no drying, and less inputs to purchase. The system is not going to gross the same as corn, but there is less expense and it is profitable," he said.

Lance Tarochione, a Monsanto technical agronomist based in western Illinois, doesn't believe the risk is as great as we might perceive. "In my career I have known a few producers who have planted soybeans after soybeans," said Tarochione. "Generally speaking, these fields turned out just fine and growers were satisfied with the outcome. This does not mean they were their best beans or their most profitable acres, but a good crop was still produced. Without the right changes to management, second-year soybeans probably yield less, but the yield loss is small enough it's hard to prove," he said.

University of Illinois agronomist Emerson Nafziger spoke to the subject at a meeting I attended in December 2015. While he doesn't recommend the practice, he said growers should expect a 4% to 5% yield penalty.

For those determined, Nafziger recommends choosing the right field, variety and seed treatment and using the same best-management practices for soybeans after corn. If you produce 60-bushel soybeans, a 2- to 3-bushel loss isn't much and the reduction in costs may easily offset the small loss in yield.

"There is no clear pattern of a higher penalty for continuous soybeans under stress conditions, like we sometimes see in corn," said Nafziger. "We also didn't see the penalty changing over time, so it doesn't seem that second-year soybeans are safer or riskier than soybeans grown more than two years continuously."

Here's Nafziger's list of do's and don'ts when planting a field back to soybeans:

-- Do expect some yield loss when soybeans follow soybeans.

-- Don't count on tillage to increase yields.

-- Don't worry about adding extra fertilizer.

-- Do pay attention, but there's no need for extra concern about fungal diseases.

-- Do be concerned about SCN.

-- Do remember that these are still soybeans and use the same best-management practices.

Tarochione agreed that field selection plays a major role. "If you have fields you know have a history of more disease pressure or SCN problems, you'll be better off selecting different fields for your second-year soybean acres and always choose the best fields," he said.

Anderson follows these practices when growing continuous soybeans on his Nebraska acres:

1. Pay close attention to soil fertility.

2. Choose best yield genetics.

3. Don't rely on a single seed brand and choose the best bean.

4. Plant in narrow rows and at a higher population.

5. Plant early, start April 20 to get crop off to an early start.

6. Treat seed to plant earlier and protect seed to get it out of the ground.

7. Inoculate seed with rhizobia.

8. Have a plan to apply an insecticide on aphids based on scouting thresholds.

9. Have to think about white mold in wet years.

10. Apply a foliar fungicide at R-3, depending on the year.

"It takes the right soil to grow continuous soybeans," Anderson said. "They have to drain and the [soil] pH needs to be between 6.5 and 6.8 and organic matter needs to be high. Continuous soybeans aren't for everyone, but work for me. Growers have to find the places that it will work and avoid fields where it won't," he said.

Dan Davidson can be reached at AskDrDan@dtn.com

(PS/AG)

Dan Davidson