Pot experiment

To evaluate the remediation ability of the slow-release nano fulvic-like acid fertilizer on soil acidification, pot experiment was conducted using acidic soil (pH 5.0) with seven different treatments in triplicate: waste milk, Control, ATP, K₂SO₄, COF, Product, and slow-release nano fulvic-like acid fertilizer. In each pot (height of 8.5 cm, bottom width and length of 7 cm, top width and length of 10 cm), acidic soil (120 g soil +280 g sand) was mixed with suitable amount of water to obtain a humidity of approximately 30%. Then 8 chickweed seeds were planted evenly at the soil depth of approximately 1 cm. The waste milk (1.4 mL), ATP (0.7 g), K₂SO₄ (0.14 g, equal to the content in 1.4 mL product), COF (1.5 g), product (1.4 mL), and slow-release nano fulvic-like acid fertilizer (1.5 g, made of 1.4 mL product and 0.68 g ATP) were spread evenly to the soil surface, respectively. During the whole growth period, 50 mL tap water was evenly sprayed onto the soil every three days. After harvest on day 21, the height, root length, fresh weight, dry weight, leaf area (leaf length × width), and germination rate of plants in each pot and chlorophyll contents of all leaves were recorded. Additionally, for each treatment, a total of 150 g soil was collected from triplicate pots (50 g each) for physicochemical properties (i.e. pH, total and available NPK, and soil organic matter) analyses. More detailed information about the pot tests were provided in Fig. S⁹.