Salinity – Sodic Soils

Salinity fact sheet_NRCS

EC_guide_NRCS

saline_sodic_newsletter_NDSU

pH_guide_NRCS

WHAT IS SODICITY

Soil electrical conductivity (EC) is a measure of the amount of salts in the soil (salinity of the soil). It is important because it affects crop yields, crop suitability, plant nutrient availability, and the activity of soil microorganisms, which influences key soil processes. Excess salts hinder plant growth by affecting the soil-water balance.

Saline Soil  is a salt-affected soil with a high content of soluble salts that affects productivity.

Areas of saline soils need to be identified and managed differently than areas of nonsaline soils. The number of soil microorganisms’ declines as EC increases. This impacts important soil processes such as respiration, residue decomposition, nitrification, and denitrification.

SODIC SOILS

Soils with high levels of exchangeable sodium (Na) and low levels of total salts are called sodic soils. Sodic soils may impact plant growth.  Sodic soils tend to develop poor structure and drainage over time because sodium ions on clay particles cause the soil particles to deflocculate, or disperse. Sodic soils are hard and cloddy when dry and tend to crust. Water intake is usually poor with sodic soils, especially those high in silt and clay.  A soil pH above 8.4 typically indicates that a sodium problem exists and plant nutritional imbalances may occur. The term “alkali” is often used to describe soils that are high in salt but sometimes people use the term to mean high pH and at other times to mean high sodium. Sodium levels in soil are often reported as the sodium adsorption ratio (SAR). This is a ratio of the amount of cationic (positive) charge contributed to a soil by sodium, to that contributed by calcium (Ca) and magnesium (Mg). The SAR is determined from a water extract of a saturated soil paste. If the SAR is above 13, the soil is typically classified as sodic.

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