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Corn+Soybean Digest

Replanting Decisions

Replanting can be a gut-wrenching and costly decision. Today, for example, the cost to replant corn runs about $25-50/acre. Will the time and money invested pay?

“Replanting is not a big effort, but one of the most aggravating things we do as farmers,” says Doug Anderson of Mt. Sterling, OH. Anderson and his brother Tony replanted about 180 acres of corn and soybeans in 2003 due to one of the wettest springs on record.

Replanting paid off with very good corn yields and near average soybean yields. “More than 50% of the time it won't turn out that way,” Anderson says.

To figure a replanting payback, consider several factors. The current plant population and calendar date are the most important points when evaluating both corn and soybeans, says Mike Hellmer, a Pioneer agronomist from Mahomet, IL.

Although there are in-depth formulas to measure stands, Hellmer finds the easiest way is the tape method.

Use a tape measure to mark off the length of row to equal 1/1,000 of an acre. That will vary depending on planting width: In 30-in. rows the length is 17 ft., 5 in.; in 15-in. rows the length is 34 ft., 10 in.; and in 22-in. rows the length is 23 ft., 9 in. Take the number of plants in this area and multiply by 1,000 to find the plant stand per acre. “It's critical to evaluate several locations in a given corn or soybean field. Populations can vary dramatically in different areas of the field,” explains Hellmer.

In narrow-row soybeans, use a hula hoop to measure stands. Toss the hula hoop in 10 different areas, count the soybean plants in the hoop and average all the areas together. University of Illinois research shows that replanting soybeans is justified only if there's a 40% stand reduction.

Before you pull out the planter, give the crop time to emerge. “Don't make a final assessment on the extent of damage and stand loss too quickly,” says Ohio State extension agronomist Peter Thomison.

Pioneer's Hellmer agrees. Cool weather can delay corn emergence three to four weeks. “I've seen awfully impressive stands of corn develop after warmer temperatures and some sunshine,” says the agronomist. Soybeans require 21 days to emerge when the soil temperature is 50-55°F and only 10-12 days when the soil temperature is in the 60s.

Next, estimate the gaps or spacing between plants. Soybeans can compensate for low plant populations and gaps in the rows. With gaps of less than 2 ft. wide, neighboring soybean plants often branch out and fill in the space.

University of Illinois and University of Missouri research shows that, if there are 73,000 healthy, evenly spaced plants per acre, the stand is worth saving.

Corn, however, isn't as resilient to low populations. Small gaps — less than 4 ft. — can reduce corn stands by 2-5%. Bigger gaps, at 4-6 ft., can cut corn yields by 10-15%. Also look at the surviving plants. Dwarf plants yield 25% less than healthy plants.

Find the reason for the spotty stands. The culprits could be planting into a poor seedbed, lower-quality seed, inaccurate planter adjustments, planting too fast, soil crusting and environmental injury (pesticide drift, insects, disease, frost or hail).

Figure out when the stand loss hit. University of Minnesota research shows that soybean stands cut early in the season may not result in significant yield loss. Reducing stands in the late vegetative stage, can cut yields.

Also consider the replanting date. If soybeans are seeded in May, the plants are usually not affected by small delays — you lose one bushel for each week delay. But by seeding after mid-June, experts say, you lose a bushel a day for each day delay.

The calendar is even more critical when replanting corn. Unless the population is below 22,500 plants per acre, it generally doesn't pay to replant corn, points out Pioneer's Hellmer. In May, an even lower plant population is needed to justify replanting because yields are reduced due to the later planting.

Patching in or thickening existing corn stands might sound tempting, but it's not a good idea. The later-planted corn cannot compete effectively with the original corn plants for sunlight, water and nutrients, says Ohio's Thomison.

Check with your agronomist or local seed representative for a second opinion and to remove emotion from the replanting decision. Looking over the mosaic of green and yellow replanted soybeans, Anderson says, “Somebody with an objective view can hand down the dirty facts and say, ‘You lost 25% of the stand and can't regain it.’”

Take Steps Before You Rush To Replant

Before Replanting:

  • Determine the reason for the spotty stand.
  • Figure stand loss and spacing between plants.
  • Calculate yield of the existing stand.

Then Consider:

  • Current and forecasted weather.
  • Replanting date.
  • Replanting cost.
  • Yield potential of replanted field.
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