Selenium-containing fertilizers are microfertilizers that increase the content of the trace element selenium, essential for humans, in crop products.
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Selenium in plant life
Selenium is involved in reactions of chlorophyll formation, synthesis of tricarboxylic acids, in metabolism of long-chain fatty acids. The presence in plant cells of ferrodoxins containing selenium instead of sulfur indicates its participation in photosynthesis processes. It has an antagonistic effect on the absorption and transport of heavy metals, increases resistance to water stress, salt and drought tolerance. Excess and deficiency of selenium in nutrient medium has a negative effect on plant growth and development. An accumulation of free soluble amino acids and inhibition of protein synthesis are noted with selenium excess.
At present it does not belong to the microelements necessary for plants, but it is vitally important for warm-blooded animals. When deficiency occurs both specific trace element diseases and diseases of other etiologies. Selenium deficiency in humans leads to the development of cardiomyopathy – Keshan disease, cancer. Among the diseases of farm animals – white muscle dystrophy. Deficiency of selenium in food and drinking water – a pathogenic factor in necrotizing liver degeneration, lesions of the pancreas and intestines, exudative diathesis. Selenium helps protect the body from chemical mutagenesis initiated by toxic doses of heavy metals. With a deficit of selenium reduced immunity and mental development in children. The effect of selenium on iodine metabolism and thyroid activity was established.
The daily requirement of a person for selenium is 40-220 micrograms and depends on the phenotypic features of the organism, the form of incoming selenium, the content of proteins in food, vitamins C and E, to a lesser extent – on age and sex. The deficiency of selenium in food has a global nature: according to numerous studies, the majority of the population experiences a varying degree of selenium deficiency in the diet.
One promising way to correct selenium deficiency is to obtain plant products enriched with selenium. At the same time plants differ in their ability to accumulate selenium. In addition, selenium is unevenly distributed among plant organs. Thus, wheat stems and leaves contain about 2-3 times less selenium than grains and roots. In general, the concentration of selenium in plants varies from 10 to 1100 micrograms in 1 kg of air-dry weight.
Analysis of selenium content in plants of different families showed that the average content in most species is no more than 100 µg/kg.
Table. The content of selenium in plants of the Non-Chernozem zone, μg/kg dry weight[1]Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Ed. by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
| Poaceae | |||
| Fabaceae | |||
| Apiaceae | |||
| Brassicaceae | |||
| Asteraceae |
Maximum concentrations of selenium are in the legume, bluegrass, and aster families, while the lowest concentrations are in the celery family.
In countries where Keshan and Kashin-Beck diseases are common, such as China, foods are enriched with selenium. Another way is to import into a selenium-deficient region foods produced on soils with high selenium content. In Scandinavia, where soils, especially in the north, contain little selenium, selenium-containing fertilizers have been used for grain crops and forage grasses for the past 20 years.
Selenium content of soils
In the countries of Europe and Asia a large-scale mapping of selenium content in soils, waters, plants has been conducted, attempts are made to regulate selenium content in human foodstuffs and animal diets. In Russia extensive biogeochemical territories with varying degrees of selenium deficiency in the Nonchernozem zone, Southern Urals and Transbaikalia have been identified. Biogeochemical province with an excess of selenium is found in Uyug and Baryk valleys of Tuva.
Agroecological survey of the regions of the Non-Black Soil Zone of the European part of the country showed its low content – 61-729 µg/kg. The lowest amount up to 169 µg/kg is characteristic of podzolic and sod-podzolic soils, as well as soils on sandy soil-forming rocks. Maximum concentrations of selenium, from 521 to 727 µg/kg, were found in peaty, gleyed, iron oxide-enriched and carbonate-rock-formed soils. In most cases, soils contain up to 400 μg Se/kg soil, which refers to the deficit content.
There are complex interrelations of selenium in soils with other elements of mineral nutrition of plants. For example, the application of cobalt, zinc, nickel increases the microbiological formation of volatile selenium compounds, boron and manganese have no effect on these processes, molybdenum, mercury, chromium and lead inhibit the transformation of selenium compounds into volatile forms.
For several years in the laboratory of microelements of the Moscow Agricultural Academy of Sciences researches on cultivation of agricultural products enriched with selenium are carried out. In a series of experiments the effect of applied sodium biselenite on the yield, its quality and content in vegetable crops, wheat, rapeseed and lupine was studied.
The studied vegetable crops without selenium application accumulated in small amounts, 56-303 mg/kg dry weight. The application of sodium biselenite in increasing quantities from 25 to 500 micrograms of Se/kg of soil resulted in the increase of its content in dill plants by 2,5-15,7 times, in radish roots by 4 times, in parsley roots by 2,4-3,8 and in the above-ground part by 3,5-10,0 times. With the increase of sodium biselenite dose from 50 to 1000 μg Se/kg soil, its content in leaf lettuce increased by 10 times, in spring garlic by 3.7-16.0 times, in the green mass of yellow lupine by 3-11 times and in grain by 6-25 times. Foliar feeding of yellow lupine with 0.0005- and 0.002% sodium biselenite solution in field experiments increased the content in green mass by 4-9 times, in grain by 4-8 times.
Table. The content of selenium in some crops when fertilizing them with sodium biselenite[2]Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
Thus, in experiments on sod-podzolic soils, the application of selenium in doses of 25-1000 µg/kg of soil allows for significant enrichment of agricultural products with selenium without reducing yields. Garlic turned out to be the most pronounced concentrator among the tested crops.
As selenium-containing fertilizers in world practice use selenites and selenites for foliar dressing and seed treatment. The most effective and applicable method is the application of selenium to the soil together with macrofertilizers.
Sources
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.