The sampled sulfidic material was spread thinly on plastic sheets and kept moist in order to oxidize sulfides to produce sulfuric acid (Eq. (2)) so as to manufacture “sulfuric horizon material” or a “sulfuric soil” (pHw = 3.8, pHOx = 2.7). The manufactured “sulfuric soil” was added to: (i) Falcon tubes to conduct the soil organic matter experiments (data presented in Figs. 2–5) and (ii) small pots (140 mm high and capacity 1.1 L) for the soil neutralization experiment (data presented in Figs. 6–8).