Now that your soybeans are up, take time to evaluate your soybean stand.
Once a soybean seed is planted it’s in the hands of Mother Nature. We rely on her to provide the moisture and heat needed for emergence to start. To insure optimum stands, it’s important to protect emerging cotyledons. These plant parts are storage structures that provide food the emerging plant needs through the first week of its emerged life cycle.
Emergence: Once a soybean has absorbed 50 percent of its weight in moisture along with heat that is supplied from the soil, it will begin to swell and initiate the development and movement of the radicle or first small rootlet. After the radicles are established, the hypocotyl starts to elongate towards the soil surface to form the hypocotyl arc, which will eventually pull the cotyledons though the soil surface (Figures 1 and 2.) Soil crusting will impact emergence. Once cotyledons are above the soil surface, so is the growing point.
Figures 1 and 2. Hypocotyl and cotyledon emerge through the soil surface
Evaluating the Stand: To evaluate a newly emerging soybean stand, the first step is to see how consistent the stand is across the field. Then, select representative sites and measure off 1/1,000 of an acre. Count the number of viable bean plants, then multiply by 1,000 to get plants per acre.
The charts below (Figures 3 and 4) provide examples for a 30-inch and 15-inch rows. These samples should be taken in several spots throughout the field to determine a stand average. It’s always good to compare this with the seed dropped to better understand planting efficiency and accuracy.
Figure 3. Example of calculating stand estimates in 15- and 30-rows.
Figure 4. Percent stand loss from planting to emergence.
Seedling Disease: Seedling diseases are more common when a young plant is undergoing stresses along with soil conditions that are conducive to disease activity.
Soil fungi and bacteria will start to attack the soybean seed and can damage the embryo. Therefore, it’s important to have a strong seed coat and seed treatment to protect the seedling from infection.
Soil temperatures during germination and emergence determine the diseases that may or may not show up in your field. Figure 5 shows four typical early soybean diseases that can reduce population stand. In most cases seed treatments do a very good job of protecting the young plant from being attacked. It all depends on the severity of the infection and how long the seedling is stressed. The longer a seedling is stressed the less likely its survival.
Figure 5. Soil conditions that influence development of different seedling diseases.
About a week after your soybeans are up, allowing time for complete emergence, make plans to scout fields for population, issues with crusting, and signs of seedling diseases and bean leaf beetle feeding.
CCA Todd Steinacher is an agronomist at AgriGold. He works with growers to better manage their nitrogen and weed control needs, along with understanding the best way to estimate cost to generate a strong ROI. He is a 2017 Illinois Soybean Association CCA Soy Envoy.