Cobalt (Co) in crops: role, deficiency signs and how to correct it

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 to make vitamin B12, without which they cannot fix nitrogen. A cobalt-short legume looks nitrogen-starved, with pale leaves and poor nodules. Cobalt in fodder also matters for cattle and sheep, which need it for their own vitamin B12.

By Gafar Laiya and the Gujarat Bio Organics team. Updated November 2026.

What cobalt does in the plant

• Needed by nodule bacteria to make vitamin B12.
• Vitamin B12 is needed for the bacteria to grow and fix nitrogen.
• Supports nitrogen supply in pulses and other legumes.
• Fodder cobalt supplies cattle and sheep with what they need for vitamin B12.

How cobalt moves in the plant

Cobalt moves little in the plant; it matters mostly in the root nodules.

Signs of cobalt deficiency

• Legumes look nitrogen-starved: pale leaves and slow growth.
• Few, small or pale nodules.
• Poor pod set in pulses.
• In livestock grazing cobalt-poor fodder: weight loss and poor appetite.

Crop by crop

More crops and look-alikes: Cobalt deficiency signs in legumes and livestock fodder.

Where and why it happens

• Sandy, leached and highly weathered soils.
• Highly calcareous soils.
• Heavy liming.

How it works with other nutrients

• Cobalt and molybdenum are both needed for nitrogen fixation in nodules.
• Iron and manganese in excess can lower cobalt uptake.
• See nutrient interactions.

What happens if it is not managed

• Less nitrogen fixed by legumes, so more nitrogen fertilizer needed.
• Lower pulse yields.
• Cobalt-poor fodder for livestock.
• See the full picture of what unmanaged shortages cost.

How to confirm it

• Suspect it only after checking nodules, molybdenum, sulphur and Rhizobium inoculation.
• A soil or plant test at a lab that tests trace elements confirms.

How to correct it

• Seed treatment with Rhizobium culture, and cobalt where your agriculture officer advises it.
• Only tiny amounts are used, and excess is harmful.
• Do not apply without advice or a test.

Too much cobalt

• Excess cobalt is toxic to plants, causing yellow young leaves similar to iron shortage.
• Use only advised amounts.

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.