The important role of selenium in soil

Selenium is a trace element in soil that is very low in content. Although selenium is very small, it plays an important role. The soil tester can help us to quickly and accurately determine the content of various trace elements in the soil and provide guarantee for our future soil management and scientific fertilization. Today we are talking about the important role of selenium in the soil.

Selenium enters the food chain mainly through the "soil-plant" system, which affects human health and the ecological environment. However, only a small part of the selenium in the soil is directly absorbed and utilized by plants. The environmental bioavailability of selenium is only related to its content, and depends on its occurrence form in the soil.

The forms of selenium in the soil include the two main modes of valence and combination. From the perspective of environmental pollution, Tang Hongqi attributed the chemical form to four categories: valence state, chemical state, structure state and bonding state. The form of selenium in the soil described in this paper mainly refers to the chemical form or combination of the valence state and the chemical state. It can be seen that the study of selenium in the soil has an important theoretical and practical significance for elucidating the bioavailability of selenium in the soil and the entire ecological environment.

1 The chemical form of selenium in the soil

Selenium in soil and sediment can be divided into organic selenium and inorganic selenium. Among them, organic selenium is one of the main parts of selenium in soil, which mainly comes from the decomposition of selenium-containing plants. Volatile selenium and some organic selenium are found in microorganisms. Decomposed to form gaseous volatile alkyl selenium compounds (volatile selenium), selenium poisonous soil and its special odor emitted by growing plants is alkyl selenium [16]; inorganic selenium exists in the form of selenate, selenous acid Salts, selenides, and elemental selenium. The form of soil selenium can be divided into six levels according to the valence state: elemental selenium (Se), in the soil content is very small, very inactive, can not be used by plants; selenide (Se2-), semi-arid region The main form of selenium in soils without intensive weathering of sulfur-rich and pyrite; selenite (SeO32-), both the main form of selenium in soil and the main form of inorganic selenium absorbed by plants. Selenate (SeO42-) is the highest valence of selenium in the soil of temperate and humid regions and is easily absorbed by plants. It is mainly found in alkaline and aerated soils.

2 Combination forms of selenium in soil

Because the soil itself is a complex system, the migration and transformation of selenium in the soil is affected by many factors, and the process of biosorption of selenium is a complex physiological process. Therefore, the bioavailability of selenium is studied from the perspective of the chemical form of selenium. Sex is not practical.

Although elemental analysis technology has made great progress since the 1970s, the chemical extraction method is still the main method for studying the selenium element form in sediments of soil, river and lake. Based on the solubility of selenium in different forms, domestic scholars have used continuous extraction method to separate selenium from soil into soluble (water-soluble), exchangeable and carbonate bound, iron-manganese oxide bound, organic-sulfide Bond state, element state, residue state. The direct correlation between soluble selenium and selenium uptake by plants has become a consensus. Therefore, water-soluble selenium is often used as a method to determine the bioavailability of selenium in soil.

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