Definition

Selenium (Se) is a trace element found in soils and absorbed by plants. Its concentration in soil varies depending on factors such as organic matter content, soil type, and chemical properties.

Soils rich in organic matter generally contain higher levels of selenium, whereas sandy soils with low organic matter often have low selenium content.

Importance

For plants, selenium is not considered an essential trace element, unlike for animals where it plays a critical role in health. However, selenium uptake by plants can influence the nutritional quality of crops for animal and human consumption. Therefore, understanding selenium dynamics in soil is important for agricultural and food systems.

Factors affecting selenium availability

Several soil properties influence selenium availability to plants:

• Organic Matter: Higher organic matter typically increases selenium content.
• Soil pH: Selenium availability rises with increasing pH.
• Oxygen Balance: Redox conditions in the soil affect selenium forms and uptake.
• Soil Texture: Sandy soils often have lower selenium levels compared to clay or loam soils.

Selenium uptake by plants

Plants absorb selenium mainly in the form of selenate and selenite ions. The absorption process is influenced by:

• Soil aeration and moisture conditions.
• Interaction with other nutrients, such as sulphur (S), due to chemical similarities.

Relation to sulphur – The S-Index

The S-index refers to sulphur availability in soil, which can indirectly affect selenium uptake because both elements share similar chemical behavior. Managing sulphur levels may therefore influence selenium dynamics in crops.

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