The decision about when to plant a soybean field is very important, because it will set the stage for how well the crop emerges and if it will ultimately establish a vigorous stand. In recent years there has been a movement to plant soybeans earlier to take advantage of early season sunlight accumulation (building more nodes and canopy to capture more energy).
Considerations for balancing the art and science:
- What are the current soil temperatures?
- What is the current soil moisture?
- What is the next 7- to 10-day weather forecast?
- What is the germination rate of the soybean seed?
- Does the reward of planting early offset the weather risk?
With this new trend, it’s important to understand both the Art and the Science that goes along with earlier planting dates. As soybean producers, one must balance the science with the art of planting soybeans to insure good seed-to-soil contact to allow for warm moisture to be absorbed (imbibed) into the seed to initiate a successful emergence. The increased yield potential with early planting beans doesn’t matter if we can’t get them out of the ground and growing because of marginal soil and environmental conditions.
The Science – To Maximize Yield:
- Planting early can provide a faster, more aggressive canopy to capture more sunlight through the growing season, ultimately leading to stronger, more consistent yields.
- Basic agronomy warns that planting early creates an increased risk to stand establishment due to early season disease. Fortunately, the industry has produced high-quality seed treatments that help mitigate the risk.
The Art – To Reduce Risk:
- When planting early it’s important to monitor the soil temperatures prior to planting and use local forecasting models to project air and soil temperatures for the next 7 to 10 days. Soil temperatures near 40 degrees or below will restrict the flow of water to be absorbed (imbibed) by the seed.
- Like corn, the “First Drink” is also important for soybeans seeds to initiate germination and the development of the radical and cotyledons. Knowing the temperature of the available moisture within the first 24 hours during germination will set the stage for success or failure.
- Respiration rates increase during germination, therefore soil compaction and flooded or saturated soil can reduce available oxygen and germination rates.
Once seed is placed into the soils, it starts to absorb moisture (imbibition), increasing from 13% to almost 50% moisture concentration. Therefore, a soybean seed will swell from available moisture and in an ideal situation this process can be accomplished within the first few days after planting.
However, this process can be compromised by low soil moisture, compaction and low soil temperature (less than 40° F within 24 hours of planting). It’s important to remember that the temperature of the “first drink” impacts the cellular integrity and stability of the radical, hypocotyl and cotyledonary seed leaves. During their development, energy is being consumed and cells are rapidly dividing and expanding. Therefore, soil and moisture temperature, and soil temperature in general will impact quality and timeliness of the germination process.
Once the seed has absorbed (imbibed) enough moisture to complete the germination process, it begins to develop and elongate the radical. From the radical it will develop its primary root system along with root hairs, which now become the primary systems for absorbing additional moisture