Sulfate is extracted by shaking 10 g of air dried soil in 25 mL of 0.008 M Ca(H2PO4)2.H2O for 30 minutes. After adding 0.10 g of activated carbon and shaking for an additional 3 minutes, the mixture is filtered. (Double the solution to soil ratio for peats and mucks.) The filtrate is analyzed on a Lachat QuikChem 8500 Flow Injection Analyzer BaCl is included to cause extracted sulfate to produce a BaSO4 precipitate, which is measured turbidimetrically at 420 nm.
(See Method Reference No. 23)