Cobalt in Plants

Until recently, scientists believed that cobalt was not essential for plants, despite its vital importance to the animals and humans who eat those plants. In more recent years, it has come to light that cobalt is indeed an essential micronutrient for at least some plant species, particularly legumes.

Cobalt plays a special role in legumes by working with beneficial bacteria to help root nodules fix nitrogen. However, it appears that cobalt may provide other benefits to plants:

Serving as a constituent ingredient of several enzymes.
Promoting stem growth.
Enabling leaf expansion.
Aiding in ethylene production (necessary for ripening fruit).
Increasing seed drought resistance.

You may already be aware that cobalt is necessary for the formation of vitamin B12, a key nutrient for animal and human health. Vitamin B12 also appears to aid plants in cell division.

Natural Sources

Cobalt can be added to the soil by the application of healthy organic matter. Manure from animals that received adequate dietary cobalt is a good option. Kelp-based fertilizers are also useful.

Deficiency

Soils naturally vary in their cobalt levels. Furthermore, this nutrient is easily depleted in soils that are subject to erosion or leaching.

Even in soils that contain cobalt, signs of deficiency may appear if the pH is unbalanced. The soil pH must be around neutral to enable plants to take up the nutrient efficiently.

The symptoms of cobalt deficiency in plants tend to be vague, but may include the following:

Stunted growth.
Reddening of stems.
Uniform paling, yellowing, or reddening of leaves.
Small root nodules on legumes.
Nitrogen deficiency symptoms in legumes.
Reduced seed production.
Reduced germination of the next generation of seeds in dry conditions.

If you suspect cobalt deficiency in your plants, adjust the pH to about neutral and consider using a quality organic trace mineral fertilizer.

Toxicity

In plants, cobalt toxicity is much easier to spot than cobalt deficiency. Some soils naturally contain toxic amounts of cobalt, but this is very rare. It is more likely to find contamination from an outside source, usually runoff or irrigation water. In some cases, cobalt toxicity can be induced by nickel deficiency (it is interesting to note that in nature cobalt is often found with nickel).

Symptoms of cobalt toxicity include:

Stunted growth.
Pale leaves with discolored veins.
Leaf loss.
Failure to produce fruit.
Iron deficiency.
Plant death.

Because this condition is usually related to pollutants, remedying the situation will involve identifying and addressing the source of contamination. Also consider using a trace mineral fertilizer containing nickel.