News From Great Lakes Hybrids

SDSU: Replanting Soybeans: A Clouded Decision

Jun 11, 2018, 09:59 AM by Clint Hawks
A recent windstorm has left several South Dakota producers wondering what to do next with their affected soybean fields.

– 6/7/2018

Figure 1. The aftermath of a dust storm that occurred this past weekend near Miranda, SD. Photo by Roxanne Knock.


Written collaboratively by Sara Berg and Jonathan Kleinjan.

A recent windstorm has left several South Dakota producers wondering what to do next with their affected soybean fields. Extreme winds combined with dry conditions created a dust storm this past week. In fact, flying soil and debris sheared off or caused major damage to emerged soybean plants in some areas. Although wind storms are not a welcome sight, having a weather event like this happen early in the growing season (rather than late) provides producers with a reasonable window of replanting opportunity if it is deemed necessary; however, making the decision to replant is not an easy one, and several factors should be considered.

Crop Insurance

If you carry crop insurance, be sure to contact your insurance company before undertaking any field operations. Most providers have a waiting period after the damage has occurred and prior to replanting to properly assess damage and determine coverage.

Crop Damage

Assessing the damage requires more than a quick look at the field’s edge. The full extent of damage should be assessed 3-5 days following the weather event or after a few days of satisfactory growing conditions have returned. To assess stands:

  • Determine row spacing and ‘length of row’ or area to count.
    Row Spacing Length of Row (1/1000 ac.)
    38” 13’ 9”
    36” 14’ 6”
    30” 17’ 5”
    22” 23’ 9”
    20” 26’ 2”
    15” 34’ 10”
  • In drilled beans the “hoop method” is commonly used. Count the number of plants that fall within the hoop (hula hoops work easily).
     
    Hoop Size Multiplication Factor
    28” 10,000
    30” 8,900
    32” 7,800
    34” 6,900
    36” 6,200
  • Count plants within the set distance or hoop area in adjacent rows in several different parts of the field to develop an average count.
  • Multiply each count by the respective multiplication factor.
    • Counts made based upon ‘length of row’ measured should be taken x 1000 to equal plants per acre.
    • Counts made using a hoop should be multiplied by the listed multiplication factor to reach plants per acre.
  • Average all plant population figures to reach a final average plant count across a field or area.

When surveying the damage in your field, it can be difficult to determine whether a plant is still viable or not. Look for green tissue above the soil surface, this increases survivability. The soybean cotyledon is very important in cases like this; plants with one or more green cotyledon and other remaining green leaf tissue are candidates for survival. Soybeans cut below the cotyledon or entirely stripped of green tissue will most likely die.

If the remaining stand is uniform, and plants look relatively healthy but stand is reduced by 20%, good yield potential may still exist (~90%). Many research reports suggest that a final uniform stand of 80,000-100,000 plants per acre is enough to reach expected yields. If there are bare spots in a field, but the areas around them still have “good yield potential”, filling in these gaps may be a viable option if moisture allows. This technique may damage standing plants, and university research suggests that filling in areas of low yield potential does not increase yields over leaving the existing stand if there are more than 66,000 plants per acre to begin with. When replanting at this point, we advise choosing a soybean maturity that is about 0.5 relative maturity earlier than your normal selections.

Profitability

It is still early enough in the season that soybeans still have time to produce optimal yield potential with minor risk of late season diseases or early frost damage. When choosing a maturity group consider your ‘later than intended’ planting, but understand that vegetative growth time often correlates to yield. Soybean maturity is driven by day length, so early maturing varieties will move into pod set earlier in the season (regardless of plant height), which may cause yield loss.

Mother nature can make a beautiful stand turn into disaster very quickly, but being patient, and taking time to assess damage may be your most useful tool in this situation.

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