ILSOYADVISOR POST

Evaluation of Nodulation

Illinois producers spend a lot of time developing a strong corn nitrogen program and implementing it throughout the growing season. We know that nitrogen is very important to a growing corn crop, but it’s just as important to a soybean plant. However, realistically, how much time is spent managing soybean’s nitrogen needs? There’s still an ongoing debate regarding how much nitrogen a corn plant needs, but it will likely fall between 0.9 to 1.2 units of nitrogen per bushel produced. However, a soybean plant can utilize upwards of 4.5 to 5.0 units of nitrogen per bushel produced. With this increased demand compared to corn, how come more focus isn’t on managing nitrogen for soybeans? 

A soybean root showing good nodulation development
from a seed-applied inoculant.

Since a soybean plant is a legume, it can create a relationship between its root system and the bacteria living in the soil. This relationship results in nodules on the root system that when active (inside turns red), will supply plant-available nitrogen to the crop.

The nodules’ supply is directly related to the quantity and quality of active population living in the soil. The nodulation process will start around the V2-V3 growth stage. The quantity and quality of the nodulation can be impacted by crop rotation, drainage, tillage, pH, etc.  Since nitrogen is important to soybean yields, it’s important to evaluate nodulation throughout the season: How many nodules are there? Where are they located on the root? What color is the inside? If low numbers are found, it’s time to start asking questions and looking for possible solutions.

There are currently several seed treatment options on the market that can provide supplementary support to boost the population in and around the root zone. However, not all products are created equal and one must ask the right questions to select the right product. For example: some products can be used as a dry powder in the seed box, and others are added as a seed coat. All these products are providing a different longevity of the bacteria that is being treated—bottom line, do your homework.

A nodule split open. If the inside has a red-to-pink color,
this means it’s actively working.

Regardless of your seed treatment selection, rotation, tillage and drainage system, it’s always important to stop and dig up soybean roots throughout the season to evaluate nodulation. Even if it’s later in the season and the nodules are no longer active, one can still find the growth on the roots for evaluation.  


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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