This part of ISO 14388 specifies a suite of methods used to determine net acidity in acid sulfate soils. This part of ISO 14388 specifies a method for the determination of pH in a 1 mol/l potassium chloride soil suspension (pH_KCl) and where required, titratable actual acidity (TAA). Following this, potassium chloride extractable sulfur (S_KCl), calcium (Ca_KCl) and magnesium (Mg_KCl) are determined. On a separate test portion, following digestion with 30 % hydrogen peroxide, peroxide pH (pH_OX), titratable peroxide acidity (TPA) and excess acid neutralizing capacity (ANC_E) are determined. Following this, peroxide sulfur (S_P), calcium (Ca_P) and magnesium (Mg_P) are determined. On samples where jarosite is present, or where pH_KCl is < 4,5, residual acid soluble sulfur (S_RAS) is determined on the soil residue remaining after peroxide digestion. Titratable sulfidic acidity (TSA), reacted calcium (Ca_A), reacted magnesium (Mg_A) and peroxide oxidizable sulfur (S_POS) are then determined by difference. For peat samples containing substantial levels of organic sulfur, the SPOCAS suite is generally unsuitable for estimating sulfide content, and the chromium reducible suite of procedures should be used instead.