ILSOYADVISOR POST

Seven Thoughts to R5

Once a soybean seed is placed into the soil, it is Mother Nature’s job to provide an opportunistic mouth to feed on it. Whether it is a bean leaf beetle feeding on the cotyledons or seedling disease such as Fusarium reducing the stand, let’s face it - Mother Nature does not care about cash rent rates or grain market values. That means it’s up to us to better understand how a soybean plant works and what the major items are that need strong consideration.

1. The seed that is in the soil needs good seed-to-soil contact to evenly imbibe soil moisture, which will allow the seed to swell and elongate the radical.

2. Next, the hypocotyl will start to elongate closer to the soil surface. This action is done in part by following heat and sunlight. The arc or hook will then pull the former seed out of the ground to now become the cotyledons on the above ground plant.

3. The cotyledons serve as food storage for the plant until the radical can begin actively bringing in nutrients and trifoliate are established to begin the photosynthesis process. These structures are protecting the growing point from damage caused by insects and frost.

4. A soybean plant will grow through several vegetative stages until it produces its first open flower on the main stem. Once the first flower is present, the plant is officially in R1.

  • Track how many trifoliate were developed throughout the season.
  • Each trifoliate will develop from a node and each node will produce a pod cluster.
  • Record how many Growing Degree Units (GDU) were accumulated to get the first flower.

5. During all of the above-ground vegetative growth, do not forget to monitor what is going on below ground. If a soybean plant needs 4-5 lbs of nitrogen for a bushel and a corn plant needs 0.9-1.2 lbs of nitrogen for a bushel, the question is: are we investing similar efforts into soybean as we do for corn? If the answer is no, then plan on digging up plants to evaluate the quantity and quality of the nodule population (pink is good).

6. As a plant enters reproductive stages R3 & R4, the flowers have been pollinated and the pod will begin to elongate past the flower and start to develop.  During this period, major stress can send hormone signals throughout the plant that it can’t support the number of pods that are starting to develop and must abort them in order to create an equilibrium within the plant. Most of the time, stresses are induced from heat, lack of moisture, lack of nutrients, combined with the compound stress of a disease and insect attacking the leaves.

7. All the hard work up to this point was to set up a healthy and happy plant during R5-R6 in order to fill as many pods as the plant is able to. For top end yield, R5-R6 is a very important growth stage for a plant to be strong and healthy with minimal stressors.

As you’re building the 2021 soybean game plan, how will your plan protect R5-R6?


Todd Steinacher
Steinacher is an ISA CCA Soy Envoy alum and currently supports ISA on agronomic content as well as serving as an Illinois CCA board member. Since 2015, he has been a regional agronomist with AgriGold in West Central Illinois. His previous experience includes 10 years as a sales agronomist in the GROWMARK-FS system. Steinacher has an associate degree from Lincoln Land Community College, a B.S. in agronomy and business from Western Illinois University and a master’s degree in crop science from the University of Illinois at Urbana-Champaign. If you have any questions for him about this article, he can be reached at steinacher@ilsoy.org.


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