The researchers studied how different acidic materials affect the pH of calcareous soil. They found that phosphoric acid can effectively lower the soil pH, with 3.27g per 100g of soil being the optimal amount. Using phosphoric acid or sulfuric acid with a pH of 5.5 is not practical for acidifying calcareous soil. NH_4H_2PO_4 not only acidifies the soil well but also maintains the acidic condition longer. Adding 2.3g of NH_4H_2PO_4 per 100g of soil can lower the pH from 8.89 to 6.39. Additionally, adding sulfur (S) at 5% of the soil can decrease the pH from 8.90 to 7.0-7.5 in 30 days.