Cobalt is an element found in abundance in the earth’s crust and in low concentrations in most soils, depending on the source material, with a content that generally ranges between 1 and 40 ppm. Most of the nutrient is in the form of Co2+, participating in cation exchange reactions in the soil. Clay soils with a lot of organic matter tend to have higher concentrations of cobalt than sandy soils, where the nutrient has generally already been transported to deeper layers of the soil. There are many Cobalt derivatives, one of the most famous is Cobalt sulfate heptahydrate CAS# 10026-24-1.In soil, cobalt mobility is governed by pH and oxygen availability. The higher the pH, the greater the specific adsorption and precipitation of cobalt, reducing the nutrient content in the soil solution. The main man-made additions of cobalt to the soil are the application of cobalt-containing sludge, the application of phosphate fertilizers and atmospheric deposition from mining, combustion, refining or smelting activities.
Cobalt in plants
Cobalt is an essential component of several plant metabolism enzymes. It is absorbed by the roots in the form of Co2+, and transported to the shoots through the transpiration stream. As the element combines with organic compounds, movement from the leaf to the organs is limited. When these have a low concentration of cobalt, a small increase in content already stimulates plant growth. Cobalt is mobile in the phloem and partially mobile when applied via the foliar route, allowing the application of the nutrient during the vegetative period of some crops. The adequate concentration of the nutrient to obtain good yields is not yet known.In legumes, cobalt is important for nitrogen-fixing microorganisms, which live in symbiosis with legumes. In these microorganisms, cobalt is essential for synthesizing vitamin B12, necessary to form hemoglobin, which is necessary for the functioning of atmospheric nitrogen fixation. Thus, it is understood that cobalt deficiency can result in nitrogen deficiency in important crops such as soybeans. In the case of the crop, current technical indications recommend the application of 2 to 3 g of cobalt per hectare in the seeds.In non-legume plants cobalt is also beneficial, and possibly essential for many plants. Some effects include less leaf senescence, seeds with greater resistance to drought and regulation of alkaloid accumulation, in addition to blocking ethylene synthesis (stress hormone in plants), and being involved in plant respiration.
Cobalt in Soy
As previously described, cobalt is of fundamental importance for the nodulation of nitrogen-fixing bacteria in leguminous plants. Thus, it is understood that the nutrient is essential for the soybean crop, acting in the nitrogen cycle in the crop. Studies indicate that the application of cobalt and molybdenum (another fundamental nutrient for nodulation) in seeds, providing uniform distribution and good establishment of the association of rhizobium with soybean, promoted a 7% increase in productivity in relation to untreated seeds. As for the foliar application, there was an increase of 20% in relation to plants without nutrient application. When the application is done via seeds, it must be done before inoculation with the rhizobium, whereas when it is done via the leaves, it is done at stages V3 and V5. It is important to understand that when the plant is well supplied with these nutrients in the soil, the application will not result in increased productivity.This information does not represent fertilization recommendations. For this, always consult an agronomist.
