Cobalt guide
Cobalt is a beneficial element. The plant itself is not shown to need it, but the Rhizobium bacteria in legume nodules do: they need cobalt...
Read the full guideCobalt and Rhizobium: the trace element behind nitrogen fixation
How cobalt lets Rhizobium bacteria fix nitrogen in pulse roots, why only a trace is needed, and why too much does harm.
Rhizobium bacteria in legume nodules need vitamin B12 to grow and fix nitrogen, and B12 contains cobalt. A trace of cobalt in the soil is enough in most fields; where it is short, nodules stay small and pale. Because excess cobalt is toxic, it is supplied only in tiny amounts, usually with seed treatment, and only where advised.
By Gafar Laiya and the Gujarat Bio Organics team. Updated November 2026.
How nodules work
- Rhizobium bacteria enter legume roots and form nodules.
- Inside, they turn nitrogen from the air into forms the plant uses.
- They need molybdenum for the fixing enzyme and cobalt for vitamin B12.
Good nodulation practice
- Use the right Rhizobium culture for the crop.
- Treat seed in shade and sow soon.
- Keep the soil well drained.
- Correct acid soils and sulphur shortage.
- Add cobalt or molybdenum only where advised.
Read more
Doses depend on the crop, soil and product, so this page gives methods, not amounts. Take the dose from your soil test report, the product label or your local agriculture officer or KVK. Results differ from farm to farm with soil, weather, crop and management. Farmer experiences on this site are their own reports, not a promise of results.
Read next
Cobalt deficiency signs in legumes and livestock fodder
How cobalt shortage shows in pulses and fodder legumes, how it affects animals that eat the fodder, and how to tell it from other nodulation problems.
Read the full guideHow Gujarat Bio Organics can help
Since 2006, lakhs of farmers from Kashmir to Kanyakumari have used Immunity products on almost every crop: from the mango farms around Somnath to the apple orchards of Himachal Pradesh and Kashmir, the tea estates of Assam and Darjeeling, and the banana, coconut and cardamom farms of Tamil Nadu, Karnataka and Kerala. Each Special is one formula made for one crop and its common problems. Tell us your crop, soil test and what you see, and our team will tell you what to check, whether a micronutrient correction is needed, and which Special fits your programme.
- Pulses guide and Immunity Pulses Special
- Groundnut (Mungfali) guide and Immunity Mungfali (Groundnut) Special
Results differ from farm to farm with soil, weather, crop and management. Farmer experiences on this site are their own reports, not a promise of results.
Questions
Does every pulse field need cobalt?
No. Most fields supply enough. It is used only where advised for the soil.
Can cobalt be mixed with Rhizobium culture?
Follow the culture label and your agriculture officer's advice.