Widespread adoption of quality seed treatments in soybeans has led to increasingly early planting of soybeans by growers across the midwestern United States. For example, in 2021 by May 2, Illinois growers had completed 41% of soybean planting, compared to 14% average for the previous 5 years.1
Early in the planting season, growers are often faced with the decision of whether to plant corn or soybeans first.
This research was conducted with a goal of understanding the risks and benefits of planting corn and soybeans at various timings throughout the spring.
RESEARCH SITE DETAILS
Corn and soybeans were planted on simultaneous dates in both 2020 and 2021.
In 2020, a 3.6 relative maturity (RM) soybean product was planted and in 2021 a 3.5 RM product was used.
In 2020, a 114 day RM corn product was planted, while the 2021 data includes an average of 113 and 114 day RM corn products at each planting date.
In both 2020 and 2021, heavy frost reduced the soybean stands in the earliest planting dates.
UNDERSTANDING THE RESULTS
To compare data across years, results are presented as a percentage of the maximum yield for the year and corn/soybean product.
Although soybean stands can be reduced in early plantings (Figure 1), the surviving plants have additional time to grow compared to later plantings and can still attain high yields (Figure 2).
In 2021, emerged soybeans endured freezing temperatures for 2 consecutive nights (Figure 3) after emergence, killing 25.9% of them. Final stand was 67,846 plants per acre, with a yield of 77.7 bushels/acre (98.9% of maximum).
Soybean yield is consistently highest in early plantings, with a steady decline in progressively later plantings, while corn yield shows a peak with too early and too late plantings negatively impacting performance (Figure 4).
These data support the increasingly accepted practice of planting soybeans early in the growing season and waiting until conditions are more favorable for planting corn.
Generally, soybeans can be planted when soil moisture conditions are satisfactory, regardless of soil temperature and weather forecast. Corn, however, should only be planted when soil conditions (temperature and moisture) and the weather forecast are favorable.
1USDA National Agricultural Statistic Service. https://www.nass.usda.gov/Statistics_by_State/Illinois/Publications/Crop_Progress_&_Condition/2021/20210503-IL-Crop-Progress.pdf