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David Moseley, LSU AgCenter Soybean Specialist
A soybean planting date was initiated by Dennis Burns at the LSU AgCenter Northeast Research Station. The first planting date was on March 1 in a no-till field following cotton with 15-inch row spacing (Figure 1). Soybean seeds were sown 1.25 inches deep at a rate of 140,000 seeds per acre and the soil temperatures were 67 degrees Fahrenheit at planting. One variety with a maturity group of 4.8 was planted. Subsequent planting dates are planned for every two weeks until approximately mid-May.
Figure 1. A soybean planting date location at the LSU AgCenter Northeast Research Station. The soybean seed was planted on March 1, 2023, in a no-till field after cotton. On March 6, the seed had not yet emerged.
On March 6, the seeds had germinated and were approximately half an inch from emerging (Figure 2). The days between planting and emerging were slower than in later planting dates due to cooler soil temperatures. The soil temperature at planting was above the recommended 60 degrees Fahrenheit, but the seed will still take longer to emerge than in warmer temperatures when seed can emerge within three to five days. Soybean seed should not be planted if the soil temperature is expected to be below 50 degrees Fahrenheit within 48 hours after planting to avoid seedling damage during the rapid water imbibition stage.
Figure 2. A soybean seedling that was planted 1.25 inches deep on March 1, 2023. On March 6, the seedling was approximately half an inch away from emergence.
Planting equipment and soil conditions should be considered when planting. Seed should be planted approximately 1 to 2 inches deep, depending on soil moisture conditions with good seed-to-soil contact. Planting into wet soil conditions can cause compaction of the seed furrow side walls and limit outward root growth.
Data from planting date trials conducted in 2020 and 2021 at the LSU AgCenter Dean Lee Research Station suggest the optimum planting timing for soybean is between the last week of March and mid-to-late April (Figure 3). Data suggest planting earlier than late-March or later than mid-April can result in lower yield potential. The amount of yield loss when planting earlier or later than the optimum timing will depend on the environment of the growing season. The yield difference in 2020 was greater than in 2021 due to an ideal environment from late-March to mid-May. In 2021, there was cool and wet conditions during late-March to mid-May and then there were mild temperatures and timely rainfall events in the summer months of 2021.
Figure 3. Data from soybean planting date trials conducting at the LSU AgCenter Dean Lee Research Station in 2020 and 2021. Each data point is the average of 12 varieties planted on the same date.
Even though the yield potential for a mid-March and late-April to mid-May seem to be similar (earlier and later than optimum planting timings), the plant can grow faster in warmer temperatures. In 2021, the canopy coverage at the R4 growth stage was 78% when planting in late-April to early-May versus 52% when planting in mid-March (Figure 4). The faster canopy coverage can help with weed control.
Figure 4. Canopy coverage and yield data from a 2021 planting date trial conducted at the LSU AgCenter Dean Lee Research Station. Each data point is the average of 12 varieties planted on the same date.
Last year the majority of soybean acres planted in Louisiana during April suffered significant damage from rain. Planting in April can help maximize yield potential; however, decreasing the risk of a severe weather event by spreading out the planting dates may be one strategy to consider. Planting in early-to-mid-March can help extend the planting season and prevent planting into mid-May or later. Planting in March does come with the threat of freezing temperatures that can kill plants. The National Centers for Environmental Information shows a map of the expected last freeze across the United States. The map shows the areas in north Louisiana can have a last freeze between March 16 – 30.
Additional information can be found in a “Science for Success : The Best Soybean Planting Date” factsheet on the Soybean Research and Information Network website.
