Although soybeans generally supply up to 90% of their own nitrogen needs through their beneficial relationship with Rhizobium bacteria1 and via the soil2, there are several factors that can limit nitrogen uptake and cause soybean nutrient deficiency.
The most common causes of reduced nitrogen fixation include temperatures colder than 60 F or warmer than 80 F.
Additionally, high levels of soil nitrate, drought, high moisture and soil compaction can all create challenges.3
Keep reading to discover the symptoms of soybean nutrient deficiency and management solutions to help prevent yield reductions.
Soybean nutrient deficiency symptoms
Anything that interrupts soybean nitrogen fixation can have a detrimental effect on how plants grow and develop.4 That can directly harm yields if symptoms of nitrogen deficiency in plants are left untreated.
Although it’s best to analyze your soybeans’ well-being at the roots, there are several symptoms to scout for on multiple parts of the plant:
Minimal root nodules
This is the best way to quickly diagnose nitrogen problems, according to experts. If you see fewer than seven nodules on the roots of a single plant, it’s likely nitrogen deficient. Be sure to only count nodules 2 mm or larger, and include them in your tally only if they are red or pink inside.
Limited leaf nodes and branching
Short-looking plants with few leaf nodes and abnormal branching can point to nitrogen deficiency. Older leaves closer to the ground will fall off. This pattern will continue as the plant grows, and the plant will look increasingly weak, especially in hot or cold conditions.
Fewer and smaller pods
Soybean seeds won’t fill as thoroughly amid nitrogen deficiency. Plants will hold onto fewer pods, as well.
Leaf discoloration
The appearance of light green color on leaves can indicate chlorosis, a symptom of poor soybean nitrogen fixation.
Positive tissue test
If other signs are unclear, a tissue test can definitively diagnose soybean nutrient deficiency.
If you identify one or more of these indicators, implement a thorough management strategy to meet soybean nitrogen requirements.
Possible causes for nitrogen deficiency in soybeans
- Soil compaction, soil saturation, insects and/or disease limit root growth
- Low soil pH and/or lack of legumes in recent rotations inhibit Rhizobium activity
- Soil that’s sandy or has low organic matter has less available N and can leach rapidly
- Weeds outcompete soybeans for N
Management strategies for soybean nutrient deficiency
Once nitrogen problems are identified, you can protect soybean productivity and income by taking several proactive measures.5
Pre-planting: inoculation and rotation
If you are growing soybeans in an area known for nitrogen deficiency, you can use an in-furrow granular inoculant or a seed treatment in the form of a solid or liquid product.
You can use an inoculant such as Vault® SP Inoculant for Soybean from BASF:
- in fields that haven’t had soybeans for at least five years
- on acres previously enrolled in the U.S. Department of Agriculture’s Conservation Reserve Program (CRP)
- on land flooded for one or more weeks
- with soil whose pH is below 6.0 or above 8.5
Growing season: targeted N application and foliar fertilizer
If your soybean crop has already emerged, there are several other strategies available for management of nutrient deficiency symptoms in soybeans.
One option is to apply between 60 and 70 pounds. of actual nitrogen per acre. Make the application between R1 and R2. You’ll know you are in the right growth stage when half the plants have a single flower open. It’s possible to get good results at R3 as well, assuming the crop gets a drink from rainwater or irrigation once application is complete.
A second option is to make one foliar application of N-P-K fluid fertilizer. Be sure to use a product with low-salt K and low N proportion to limit leaf and yield damage. Recognize this approach won’t work if your soybean nutrient deficiency comes from root issues or soil problems, such as pH that’s too low or high.
Get the soybean nitrogen fixation help you need
Experts are available to help you make your decisions and mitigate the risk of soybean nutrient deficiency. Reach out to your seed retailer, a nearby extension office agent or a seed company professional such as your regional BASF representative.
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Endnotes
- Dillehay, David E., and Jeff Edwards. “Understanding Soybean Nodulation and Inoculation.” Oklahoma State University Extension, extension.okstate.edu/fact-sheets/understanding-soybean-nodulation-and-inoculation.html. Accessed 19 Mar. 2025.
- “Nitrogen Management in Soybeans.” University of Delaware Cooperative Extension, www.udel.edu/academics/colleges/canr/cooperative-extension/fact-sheets/nitrogen-management-soybeans/. Accessed 19 Mar. 2025.
- “Soybean Nitrogen Management.” South Dakota State University Extension, extension.sdstate.edu/sites/default/files/2020-03/S-0004-23-Soybean.pdf. Accessed 19 Mar. 2025.
- Casteel, Shawn, and Darcy Telenko. “Soybean Nitrogen Deficiency: Soil Factors and Plant Response.” Purdue University Extension, extension.entm.purdue.edu/newsletters/pestandcrop/article/soybean-nitrogen-deficiency-soil-factors-and-plant-response/. Accessed 19 Mar. 2025.
- Warncke, Darryl, and Michael Staton. “Are Your Soybeans Deficient in Nitrogen?” Michigan State University Extension, www.canr.msu.edu/news/are_your_soybeans_deficient_in_nitrogen. Accessed 19 Mar. 2025
- Rakkar, Mohammad K., et al. “Evaluating Soybean Response to Nitrogen Fertilization in the North Central United States.” Soil Science Society of America Journal, vol. 85, no. 6, 2021, acsess.onlinelibrary.wiley.com/doi/10.1002/saj2.20241. Accessed 19 Mar. 2025.
