Soybean Inoculant: When and How to Use Rhizobia
What soybean inoculant is, when it pays to inoculate, how to apply it, checking root nodules, and nitrogen fixation.
Soybeans form nodules on their roots with the bacterium Bradyrhizobium japonicum, which fixes nitrogen from the air. Where soybeans have not been grown in the last 3–5 years, or never, coating the seed with inoculant is essential; otherwise plants turn pale and yield poorly.
How to Inoculate
- Buy fresh inoculant specific to soybeans; check the expiry date.
- Apply to seed in the shade just before planting.
- Plant into moist soil soon after; sunlight and heat kill the bacteria.
Checking Nodules
About 4–6 weeks after emergence, dig a plant carefully: healthy nodules are numerous, pea-sized and pink or red inside. White or green nodules are not fixing nitrogen.
More Soybean Guides
- How to Grow Soybeans: The Complete Guide
- Soybean pests and diseases
- When to harvest soybeans and edamame
- Soybean yield per acre
Frequently Asked Questions
Do soybeans need inoculant every year?
Not in fields with recent soybean history, though many growers inoculate anyway as cheap insurance.
Why are my soybean leaves yellow?
Often poor nodulation, waterlogging or iron chlorosis on alkaline soils.
TarlaTapan guides focus on practical, field-tested growing advice. Corrections and suggestions are welcome at info@tarlatapan.tr.