5 MIN READ

Deciding Whether to Plant Corn or Soybean Based on Field Conditions

March 7, 2023

TRIAL OBJECTIVE

  • Widespread adoption of soybean seed treatments has led to an increase in early soybean planting by growers across the midwestern United States. As an example, Illinois growers planted 41% of the soybean crop by May 2, 2021, compared to the five-year average of 14%.1
  • Early in the planting season, growers are often faced with the decision of whether to plant corn or soybean first.
  • This research was conducted with a goal of understanding the risks and benefits of planting corn and soybean at various timings throughout the spring.

RESEARCH SITE DETAILS

  • Corn and soybean were planted on simultaneous dates across two growing seasons.
  • In 2020, a 3.6 maturity group (MG) soybean product was planted. A 3.5 MG soybean product was planted in 2021 and 2022.
  • In 2020, a 114-day relative maturity (RM) corn product was planted, while the 2021 data includes an average of 113- and 114-day RM corn products at each planting date.
  • 2022 data includes an average of 111- and 114-day RM corn products.

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UNDERSTANDING THE RESULTS

  • In both 2020 and 2021, heavy frost reduced the soybean stands in the earliest planting dates.

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Figure 1. Soybean stands can be thin in early planting dates.
Frosted soybean cotyledons after freezing nighttime temperatures. In 2021, 25.9% of emerged soybean seedlings were killed after two consecutive nights of freezing temperatures. Final stand was 67,846 plants/acre, with a yield of 77.7 bu/acre (98.9% of maximum).
Figure 3. Frosted soybean cotyledons after freezing nighttime temperatures. In 2021, 25.9% of emerged soybean seedlings were killed after two consecutive nights of freezing temperatures. Final stand was 67,846 plants/acre, with a yield of 77.7 bu/acre (98.9% of maximum).
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Figure 4. To compare corn and soybean data across years, results are presented as a percentage of the maximum yield for the year for the crop.
  • Highest soybean yields were consistently found with early planting dates. Soybean yield steadily declined in progressively later plantings.
  • Conversely, corn yield was negatively affected by too early and too late planting dates.

KEY LEARNINGS

  • These data support the increasingly accepted practice of planting soybean early in the growing season while waiting until conditions are more favorable for planting corn.
  • As a general rule, soybean seed can be planted when soil moisture conditions are satisfactory, regardless of soil temperature and weather forecast.
  • However, corn planting should wait until favorable weather is forecasted and proper soil conditions (temperature and moisture) prevail.
Sources:

1Illinois Crop Progress and Condition. May 3, 2021. United States Department of Agriculture Statistic Service. https://www.nass.usda.gov/Statistics_by_State/Illinois/Publications/Crop_Progress_&_Condition/2021/20210503-IL-Crop-Progress.pdf


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