May 26, 2010
You've selected high-yielding hybrids to fit your fields, applied the required fertilizer for your yield goals, prepared the seedbed, planted your desired plant population and monitored seedlings as they emerged. Yet, in spite of your best efforts, your corn stand could fall victim to heavy rain, hail, pests or poor germination. If your corn is damaged and your established stand is poor, should you consider replanting?
Growers should consider all factors before deciding to replant to determine whether the yield advantage of a replanted field will offset the added cost and the lower yield potential of the first planting.
"Analyzing the yield potential of the existing stand, replanting date, replanting cost, weed control implications, crop insurance adjustments and other factors can help determine if replanting is right in any given situation," says Jeff Housman, Mycogen Seeds customer agronomist.
To determine if replanting is appropriate, growers should follow these steps:
1. Calculate yield loss from a less-than-optimum plant population.
To determine potential yield loss due to a reduced stand, first determine the current plant population.
"Use a rope that measures the length of 1/1,000th of an acre to mark off a row. This length will depend on row spacing (refer to Table 1)," Housman says. "Then count the number of live plants in that row and multiply that number by 1,000 to determine plants per acre. Repeat this process in at least six places and then average the counts to estimate the plant population of the field."
Row Length Equal to 1/1000th of an Acre
Row Spacing Row Length
40 inches 13 feet 1 inch
36 inches 13 feet 6 inches
30 inches 17 feet 5 inches
22 inches 23 feet 9 inches
20 inches 26 feet 2 inches
15 inches 34 feet 10 inches
Make certain you do not count plants that emerge more than three weeks late as they generally do not contribute to final yield. Then compare the existing plant population to the original planting population to calculate yield loss.
Yield potential also can be lost due to non-uniform plant stands within fields. Large gaps of two feet or more in the stand can further reduce grain yield by about 5 percent in fields with existing populations of 14,000 to 28,000 plants per acre.
"If plants are uneven, increase the estimated yield loss due to stand reduction by an additional 5 percent," Housman says.
2. Estimate yield loss due to later replanting date.
Corn planted later than the optimum date for top yield potential within a given geography also can result in decreased yield. When comparing the date of replanting to the optimum planting date, refer to a local Extension or university source to determine specific yield loss due to later planting dates, as optimum planting dates vary by geography.
3. Compare yield potential to determine if replanting is worthwhile and consider all other factors.
"If the yield loss from a reduced stand is less than the yield loss from delayed planting, replanting may not be the most profitable choice," Housman says. "However, if there is yield to be gained by replanting after comparing existing stands and planting dates, be sure to factor in other costs and crop implications before making a final decision. Remember, replanting does not guarantee a better stand."
If corn is severely damaged late in the season, another option to consider is switching to a later-season alternative crop. If you do choose to replant, a local crop consultant or agronomist can help select hybrids with shorter relative maturities appropriate for your area.
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