Planting corn early? Consider these factors first

By Dan Martens
University of Minnesota Extension

Jeff Coulter, University of Minnesota Extension corn agronomist, wrote recently about factors that play into decisions for planting corn earlier than normal. Catching a little rain mixed with some cooler weather could slow the urge to plant corn very early. Jeff offers the following:

For many growers, this unusually early spring may offer the earliest opportunity of all time for corn planting. This makes it especially important to weigh the risks and benefits of early planting:

1) Crop Insurance: For farmers with federal crop insurance, planting before the earliest allowable planting dates specified by the USDA-Risk Management Agency will result in loss of replant coverage, even if the need for replanting is due to factors other than freeze damage or poor emergence. (The earliest allowable planting date for corn is April 11 in Stearns, Benton and Morrison counties; and April 21 for soybeans.)

2) Yield: Rarely in Minnesota are soils fit for corn planting prior to the earliest date established for crop insurance. Corn planting date studies from 1988 to 2003 at Lamberton, show that planting dates ranging from April 21 to May 6 produced yields within 1 percent of the maximum.

These results are supported by a recent study from 2009 to 2011 at Lamberton, Morris and Waseca that was funded by the Minnesota Corn Growers Association. In these studies, the yield was optimum on average with planting dates of April 25 to May 10. In the 10 instances when planting occurred prior to April 18 in these studies, yields were 82 to 100 percent of the maximum (average equals 94 percent). In both studies, rapid decline in corn yield did not occur until planting was delayed beyond mid-May.

3) Frost Damage: A risk of early planting is frost damage to young corn plants, as experienced in much of Minnesota in 2010. Although the growing point on corn is below the soil surface until the five leaf collar stage (V5), new growth often has trouble emerging through frost-damaged tissue, resulting in buggy-whipped plants.

Frost damage to plants that are 6 inches or shorter can reduce yield by 9 to 15 percent (Bremer et al., 1995). This is likely related to the subsequent unevenness in the stand and competition among plants. For example, previous research from Lamberton found that when a corn plant was one leaf stage behind neighboring plants early in the season, its yield was reduced by 20 percent.

In comparison, when a corn plant was two leaf stages behind neighboring plants early in the season, its yield was reduced by 51 percent.

Corn that is emerging (spiking) is less affected by a freeze than corn at later growth stages (V1 or later). Since corn requires about 155 growing degree days to reach the V1 stage, one can assess the risk of frost damage by using expected air temperatures to calculate growing degree days and project the date at which corn would reach the V1 stage for a given planting date, and then compare that to historical frost-free dates. For most regions in Minnesota, planting dates earlier than April 15 are likely to result in corn plants at the V1 stage or larger prior to the long-term average frost-free dates.

Here are a couple more thoughts on the topic.

In a planting date trial at Rochester in 2010, corn was planted on April 9, 14, 21 and 27. Frost injury occurred on May 14 and 17 from V1 to V4 stage corn. Yields for plots planted on April 9, 14 and 21 were 10 bushels per acre less than corn planted on April 27.

Planting corn or soybeans before the crop insurance April 11 and April 21 dates carries more risk than most people should want to take. For corn, somewhere around April 18-20 might be as early as we’d care to plant much corn in this area.

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