ISSUE #478

478 Managing The Soybean Rotation Effect


Soybean acreage in the Red River Valley has dramatically increased in the past 10 years. Prior to 1995 few acres were planted north of Cass and Clay Counties. Today soybeans are commonly planted all the way to the Canadian border. Wheat and barley are becoming less profitable each year. Fusarium head flight, commonly called scab, has plagued small-grain crops often in the last 10 years. Small grain acreage has declined in recent years in sugarbeet producing counties with no reason to suspect this trend won't continue. These changing cropping patterns have greatly increased interest in planting sugarbeet after soybean.

Sugarbeet Production Following Soybean

American Crystal Sugar Company's database clearly showed reductions in sugarbeet yield and quality when following soybean versus wheat in the 1980s and 1990s, Table 1.

Table 1. Sugarbeet yield after wheat and soybean.

YearsPrevious CropRSA (lbs)Loss after Soybean (lbs)
1980-1989 Wheat 4,842  
1980-1989 Soybean 4,564 278
1990-1999 Wheat 5,759  
1990-1999 Soybean 5,233 526

A comprehensive study conducted by Dr. Alan Dexter and Dr. Larry Smith from 1986 to 1988 documented severe yield losses if sugarbeets were produced following soybean versus barley, Table 2. Yield losses of over 1,000 pounds of recoverable sugar per acre were observed. They determined that (1) excess nitrogen after soybean, (2) potentially reduced available soil water, and (3) increases in root disease did not cause observed yield losses. They did document that use of herbicides like Treflan with carryover potential increased yield loss by up to 2,000 pounds of recoverable sugar per acre following soybean.

Table 2. Influence of previous crop and previous herbicide on sugarbeet yield and plant population. Smith and Dexter, NDSU/UM, 1986-1988.

Previous CropPrevious HerbicideYield (T/A)SucroseExtractable Sucrose (lb/A)Sugarbeet Stand (plts/70 ft)
Barley Bronate 19.7 17.2 6,076 104
Soybean None 17.2 16.4 4,969 103
Soybean Sonalan 19.9 15.9 4,401 88
Soybean Treflan 14.6 15.7 3,920 80
  LSD (0.05) 1.5 0.2 367 14

Sugarbeet Production After Soybean 2001-2005

Sugarbeet production after soybean has resulted in nearly the same revenue per acre compared to production after wheat or barley since 2001, Table 3.

Why the observed change in impact of soybean on sugarbeet yields and quality? Possible reasons might be (1) wetter growing seasons, (2) earlier planting of soybean fields, (3) Roundup Ready soybean reducing weed pressure, (4) no herbicide carryover, and (5) cool springs with warmer soils after soybean allowing better germination and emergence.

Table 3. Effect of preceding crop on yield and quality, 2001 - 2005.

Preceding CropPlanted AcresTonsSugar (%)SLM (%)RSA (lbs)Rev/A ($)
Edible Beans 128,414 19.3 18.06 1.27 6,485 842
Soybeans 29,155 20.2 17.77 1.19 6,706 836
Barley 112,268 19.1 18.11 1.21 6,456 844
Corn 33,678 18.9 17.63 1.17 6,218 794
Potatoes 131,786 20.1 17.65 1.38 6,533 841
Wheat 1,663,266 19.2 17.87 1.22 6,394 826

Suggested Management Strategies for Sugarbeet Following Soybean

  • Plant early to maximize yield.
  • Be sure to use the 40 pounds/A soybean N credit.
  • Use a starter fertilizer to maximize yield opportunity.
  • Plant a spring cover crop on those prone-to-blow fields.
  • Watch out for herbicide carryover if not after Roundup Ready soybean.
  • Rhizoctonia root rot is common to both soybean and sugarbeet - monitor disease buildup.
  • Consider Amistar use for disease control on fields with a history of rhizoctonia.
  • Plant a resistant variety in fields with a rhizoctonia history.
  • Contact your agriculturist for a complete data history of sugarbeet after soybean.