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 (H<inf>2</inf>SO<inf>4</inf>) and phosphoric acid (H<inf>3</inf>PO<inf>4</inf>) 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-H<inf>2</inf>SO<inf>4</inf> or H<inf>3</inf>PO<inf>4</inf>), 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-H<inf>2</inf>SO<inf>4</inf> per 100 g of PLA significantly increases nutrient solubility, especially P, while increasing volumes of 1M-H<inf>3</inf>PO<inf>4</inf> 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 H<inf>3</inf>PO<inf>4</inf>. 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.