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Think Before Replanting Soybeans

Taking stand counts can help you better make this tough decision.

Replanting soybeans is akin to soybean farmers entering The Twilight Zone. Should they replant and incur extra expense? Or should they let it ride and hope all turns out well this fall? Or is there somewhere in between?

In some areas of South Dakota, extreme windstorms recently sheared off emerged soybean plants. The good news – if you can call it that – is that this occurred early in the growing season. This gives farmers a reasonable window of replanting opportunity, say Sara Berg and Jonathan Kleinjan, South Dakota State University Extension agronomists. Here are some tips Berg and Kleinjan give to help soybean farmers make that decision. 

Be sure to contact your crop insurance agent before you undertake 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, say Berg and Kleinjan.

Thoroughly assess damage. The full extent of damage should be assessed three to five days following the weather event or after a few days of satisfactory growing conditions have returned. 

Determine row spacing and length of row or area to count.

Row spacing (inches) Length of row (1/1000 acre)
38 13 feet, 9 inches
36 14 feet, 6 inches
30 17 feet, 5 inches
22 23 feet, 9 inches
20 26 feet, 2 inches
15 34 feet, 10 inches

In drilled beans, the hoop method is commonly used. Count the number of plants that fall within a hula hoop. Then, 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.

Hoop size    Multiplication Factor
28 inches    10,000
30 inches  8,900
32 inches  7,800
34 inches  6,900
36 inches    6,200

Carefully assess plant viability. Look for green tissue above the soil surface, as this increases survivability. Also, focus on soybean cotyledons. 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 reduced 20%, but is uniform and packed with healthy plants, up to 90% of yield potential may still exist. Many research reports suggest that a final uniform stand of 80,000 to 100,000 plants per acre is enough to reach expected yields. 

If bare spots exist, but areas around them appear to have good yield potential, filling in these gaps may be a viable option if moisture allows. However, this technique may damage standing plants. Meanwhile, university research suggests that filling in areas of low yield potential does not increase yields over leaving the existing stand if more than 66,000 plants per acre exist at the start. When replanting at this point, choose a soybean maturity that is about 0.5 relative maturity earlier than 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. However, 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, say Berg and Kleinjan.

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