It’s not how you start; it’s how you finish – Jim George
Late Seeded Soybeans
As crop insurance deadlines come and go, seeding soybeans has been a major topic of discussion with growers over the past few weeks. Specifically, weather or not it made sense to seed soybeans as late as it has bean. By the time this article comes out, some will have managed to get soybeans in the ground and some will have opted to not seed soybeans. Either way, its good that we address all of the considerations leading up to that decision so that we can use this year to help make decisions in the future.
“Will my soybeans reach maturity before an early frost?”
“Should I plant an earlier season soybean instead of a late relative maturity?”
“What else am I risking seeding soybeans this late?”
Relative maturity is one factor to consider when answering these questions. That is, the amount of CHU (Corn Heat units) required for a variety of soybean to reach physiological maturity. This is a good bench-mark to recognize when trying to find a suitable variety for your region depending on relative heat unit accumulation for your growing area. Soybeans are also Photoperiod Sensitive, which means that plants are affected by day length and switch from vegetative to reproductive growth around when day-length begins to get shorter (Summer Solstice). Each variety will have a different sensitivity to this which will change how fast they decide to switch into reproductive growth. The speed at which the reproductive stages take place (R1 to R6) will be dictated by not only the length of the day (which continuously gets shorter past summer solstice) but also moisture, temperature and general plant health. Yield is optimized during these reproductive stages of growth where ideally; we want the plant to take its time with a sufficient amount of heat and moisture. Therefore, we want there to be enough CHUs distributed across the growing season for a vegetative stage before summer solstice that isn’t rushed and more importantly, the reproductive stages that follows. Regardless of CHUs, soybeans will make the switch from vegetative to reproductive and begin the journey to maturity once the days start getting shorter. But what is in question is the amount of heat that the plants will get after this switch, along with moisture.
Corn Heat Unit Accumulation
A shorter season soybean will have helped the case for anything that was late seeded. We can also be confident that the plants will get to maturity in time based on the amount of heat units we have accumulated thus far (fingers crossed we don’t have an early frost). From 30-year averages taken at the Brunkild weather station, we can typically expect 578 CHU to accumulate from May 1 to June 13th. Surprisingly, we have accumulated more CHU in the 2022 spring than many of us would have thought. Using the same weather station, we have accumulated a total of 540.2 CHU as of June 13th, which is 93% of the 30-year average.
Let’s conservatively assume we finish the growing season with the 90% of the 30-year average (2636.1 CHU). That would leave us with a total of 2372.5 CHU. Which would be sufficient for early-early/mid season soybeans. Just need to hope mother nature cooperates.
-Steve Tapley