Standard operating procedure for saturated soil paste extract
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Salt-affected soils severely limit crop growth, reduce yield, and cause plant stress and soil structure degradation. Therefore, soil salinity/alkalinity interpretation is essential to develop and apply sustainable agricultural practice and suitable irrigation techniques in semiarid and arid environments. Salinity is a soil condition characterized by a high concentration of soluble salts, generally defined as one in which the electrical conductivity (EC) of saturate soil paste extract (ECe) in the root zone exceeds 4 dS m-1 at 25 oC (Richards, 1954). Sodic soils are those with a percentage of exchangeable sodium (ESP) greater than 15. Because of the considerable experimental errors involved in ESP determination, emphasis has been placed on using the sodium adsorption ratio (SAR) of the equilibrium soil solution instead of the ESP for classification purposes. The electrical conductivity of saturation soil extracts may vary, but usually remains below 4 dS m-1 at 25 °C. The pH of saturated soil paste in sodic soils is 8.2 or higher, and in extreme cases may exceed 10.5. However, many crops exhibit a yield reduction at a lower ECe because soil salinity/alkalinity affects a number of morphological, physiological and biochemical processes and water and nutrient or toxic elements uptake (FAO, 2018; Filipovic et al, 2018).
The main aim of this SOP is to prepare a saturated soil paste to measure electrical conductivity (ECe) and soluble salts of a soil from a saturated paste extract.