Cobalt in plant life
The content of cobalt in plants is on average 0.00002%. Its amount can vary from 0.021 to 11.6 mg per 1 kg of dry weight. A large amount is contained in the nodules of leguminous crops. It is also concentrated in generative organs, accumulates in pollen, accelerates its germination. In plants, about 50% of cobalt is in ionic form, 20% – in the form of cobamide compounds and as part of vitamin B12. Vitamin B12 is synthesized by microorganisms and enters plants from the soil; in nitrogen-fixing plants it is formed in nodules. In plants it is found in legumes, turnips, peas, onions. Up to 30% of compounds are unidentified stable organic compounds.
An activated (coenzyme) form of vitamin B12 – 5,6-dimethylbenzimidazolcobamide coenzyme – has been isolated. In combination with a specific protein, it forms methylmalonylisomerase, which catalyzes the conversion of propionate to succinate.
Cobaltmethylcorrinoid serves as a donor of methyl groups for t-RNA methylation. A coenzyme-dependent ribonucleotide reductase is known. Cobamide coenzymes are involved in DNA synthesis and cell division. The methylation reaction is involved in many processes, for example, in increasing plant resistance to some diseases: the causative agent of Fusarium wilt produces a toxin, Fusarium acid, which forms a non-toxic methylamide derivative as a result of methylation.
Cobalt is a metal with variable valence, which determines its redox potential in various environments in oxidation-reduction reactions. However, it is not found in the composition of the active groups of the respiratory chain enzymes or photosynthesis.
A number of studies have established the connection of cobalt with auxin metabolism and its effect on cell membrane stretching.
Cobalt is required by legume crops in the absence of bound nitrogen. The requirement is 1/330 of that of molybdenum, and the requirement of cobalt for nitrogen fixation is 1/10 of that for nodule growth. Cobalt changes the structure of nitrogen-fixing apparatus, the functioning of bacteroides is more active. Capsules around bacteroides form earlier and last longer. Positive effect on the reproduction of nodule bacteria.
The effect of cobalt on nitrogen fixation is also manifested in its participation in the synthesis of leghemoglobin. Under the influence of cobalt increases the activity of dehydrogenases, hydrogenases, nitrate reductase, increases the content of chlorophyll, total hematin and associated with chlorophyll vitamin E.
With cobalt content in feed less than 0.07 mg per 1 kg of dry hay the animals fall ill with acobaltosis, productivity decreases, with sharp insufficiency of cobalt it is possible death of animals. This conditions the use of cobalt fertilizers in meadows and pastures in areas of cobalt deficiency.
Cobalt content in soil
Under natural conditions associated with the geochemical cycles of iron and manganese, cobalt occurs in ionic forms of Co2+ and Co3+. In an acidic environment, cobalt is mobile and does not migrate in solutions due to sorption by iron and manganese oxides and clay minerals. At low pH values, Co2+ and Mn2+ are exchanged to form Co(OH)2, which precipitates on the surface of oxides. With increasing pH, sorption by manganese oxides increases sharply.
In soil solutions, the concentration of cobalt varies in the range from 0.3 to 87.0 µg/L. The distribution of cobalt in the soil profile is influenced by soil organic matter and the content of clay particles. Montmorillonite and illite clays sorb this element well. Organic chelates of cobalt are mobile, migrate in the soil and are available to plants.
The poorest are sod-podzolic light sandy soils. With liming of soils the need for cobalt increases. Positive effect is shown on soils provided with basic nutrients with a soil solution reaction close to neutral: chernozems, gray soils, cultivated sod-podzolic and chestnut soils. In neutral soils cobalt is in a sedentary form and is inaccessible to plants.
Cobalt fertilizers include cobalt sulfate CoSO4⋅7H2O (20-21%), cobalt chloride CoCl2⋅6H2O (24.8%), cobalt nitrate Co(NO3)2⋅6H2O (20.3%).
Application of cobalt fertilizers in agriculture
Under cobalt deficiency conditions of physiological and biochemical processes and plant growth worsen; productivity and yield quality decrease. Cobalt enrichment of plant products is very important. Crop yields take from 5 to 50 g/ha of cobalt.
In experiments on sod-podzolic soils, the yield of sugar beet roots when cobalt fertilizers were applied increased by an average of 3.5 t/ha, sugar content – by 0.8%, resulting in increased sugar yield by 1 t/ha. Lupine yield increase on sod-podzolic soils was 0.12 t/ha of seeds and 6.5 t/ha of green mass (yield on the control – 32.5 t/ha).
Cobalt-containing fertilizers show effectiveness at 1.0-1.1 mg/kg of soil in the Non-Black Soil Zone, 0.6-2.0 mg/kg of soil in the Black Soil Zone, 1.0-1.5 mg/kg of soil in the zone of sierozem and chestnut soils, 0.8-1.2 mg/kg of soil in flooded soils of rice fields in Kuban. However, to grow good fodder and food, it is necessary to apply cobalt fertilizers at 2.0-2.5 mg/kg soil.
Apply in an amount of 200-400 g/haYagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. – Moscow: Kolos, 2002. – 584 p.: ill. (0.5-2 kg/haAgrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, 2017. – … Continue reading) per element. For seed treatment 0.5% and for foliar feeding 0.01-0.1% aqueous solutions of cobalt salts are used. Foliar feeding is carried out before flowering at the rate of working solution 300 l/ha; seed treatment of cereal crops is carried out by half-dry method (10 l/t).
Optimal concentration for foliar dressing of peas is 0.05% solution, for sugar beet – 0.02% solution. Feeding peas is carried out in the phase of 6-7 leaves, sugar beets – at the closing of rows.
Legumes, sugar beets, wheat, rice, and grapes are the most sensitive to cobalt deficiency.
Plants are equally sensitive to shortage and to excess of this element in soil. At high levels in the soil can develop cobalt toxicosis, which for rice, for example, appears at a content in the soil over 25 mg/kg.
The use of cobalt-containing fertilizers is promising on chernozem soils for leguminous crops and grapes, cultivated sod-podzolic soils.
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/Under ed. B.A. Yagodin. – M.: Kolos, 2002. – 584 p.: ill.
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.