Poultry litter ash (PLA) is a valuable secondary raw material due to its high phosphorus (P) content and essential plant nutrients. This study focused on acidulating PLA with increasing volumes of 1 M sulfuric acid (H2SO4) and phosphoric acid (H3PO4) to improve nutrient solubility. Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) were used for the molecular and chemical characterization of the ash samples. The effects of PLA, acidulated-PLA (100 g of PLA was treated with 100, 200, 400, 600, 800, and 1000 mL of 1 M-H2SO4 or H3PO4), and triple superphosphate fertilizer (TSP) on the growth and nutrition of lettuce were comparatively tested in this study. Applying 600 mL or more of 1M-H2SO4 per 100 g of PLA significantly increases nutrient solubility, especially P, while increasing volumes of 1M-H3PO4 also improve nutrient solubility, though less effectively. Phosphoric acid increased the P concentration in PLA, with both PLA and acidulated PLA showing similar effects to TSP on plant growth and P levels. The magnesium (Mg) concentration in plants was the highest both TSP and acidulated with high volumes of H3PO4. TSP notably reduced the concentrations of iron (Fe) and zinc (Zn) in plants. However, compared to TSP, PLA with high-volume acidulation showed an increase in the concentrations of these elements. Acidified PLA, with its rich nutrient content, can serve as an alternative fertilizer source, while also playing a key role in the safe disposal of waste that could otherwise pose environmental pollution risks if not managed properly.