Extractable Sulfate - Sulfur

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Readily soluble and adsorbed sulfate (SO4) is extracted with a monocalcium phosphate [Ca(H2PO4)2] solution containing 500 parts per million (ppm) of phosphorus. A 10-gram scoop of air-dried soil is combined with 25 milliliters of extracting solution and shaken for 30 minutes. Sulfate in the filtrate precipitates with Barium (added in the form of BaCl2) and the SO4 concentration is determined turbidimetrically on the Lachat QuikChem 8500 Flow Injection Analyzer. The results are reported as parts per million (ppm) of extractable Sulfate-S (SO4-S) in the soil.