Sporadic emergence of soybeans this spring could cause headaches for farmers all season long.
What exactly happened to emergence this season? To answer this question, it’s important to understand factors affecting seed germination.
Generally, the soil will dry out to the depth of tillage passes, usually the top 3 to 4 inches of soil. Without rainfall, by the time the planter reaches the field no moisture remains in the seedbed.
Soybean germination requires seeds to take up about 50 percent of their weight in water. In the photo provided by Soy Envoy Stephanie Porter (Figure 1) we see the dry soil conditions that were common at planting this spring. Some seeds didn’t germinate immediately and had to wait until after a rain event occurred to begin germination. Under these conditions, soybean seedlings will lag behind in development and reaching maturity, impacting crop management.
Heavy residue and dry soil conditions also can impact how deeply seed is placed in the soil. Remember as the soil dries, seed needs to be placed deeper into a more consistent moisture zone. Moving from 1.5-inch depth to a 2-inch depth would be beneficial under these conditions.
The chart below shows the duration of each reproductive growth stage in soybeans with each stage lasting a bit longer than the previous stage.
If you are faced with variable plant development across the field, whether due to sporadic emergence or replanting, you will need to address these management factors:
Weed control. Weed control in these fields could be tricky, since herbicide label restrictions specify the crop stage when a product can be used. I always recommend a good pre-emergence herbicide, such as an Authority®, Valor®, Boundary® or many others. However, the second (post) application will be trickier. In this situation, segregate the field to the best of your ability in order to avoid off-label applications.
Fungicide timing. With delays in plant growth development you may be asking yourself when to spray a fungicide. The ideal timing for fungicide application is when the soybeans have reached R3. However, studies have shown that earlier spraying is better. I would recommend spraying when the first emerging soybeans have reached R3. At that time, the second emerging soybeans will be in the latter half of the R2 stage.
Harvest concern. As we move toward harvest the soybeans that emerged at different rates will not mature at the same time. Planting date and rainfall events determine when the entire field will be ready. Generally, for every three days of delay in emergence we can expect a one-day delay in maturity. For example, if the soybeans took 15 days to emerge after planting, expect a five-day difference in maturity in the fall. That means some parts of the field will be ready to harvest and others will not. You may end up combining when parts of the soybeans are either too dry or too wet.
Nick Marley is an agronomist and Certified Crop Adviser. He has a B.S. in agronomy and crop science from the University of Illinois and is working on a Master’s in agronomy and crop science at Iowa State University. He is a 2017 Illinois Soybean Association CCA Soy Envoy.