The growing importance of repurposing waste ash from biomass power plants as a fertilizer material is evident. This study systematically investigates the feasibility of employing manure ash obtained from a biomass power plant for applications in fertilizer production. In this study, initially, waste poultry manure ash (PMA) was attempted to be modified by HCl, H2SO4, and HNO3 to enhance the solubility of plant nutrients in its composition. SEM and XRD were used for the molecular and chemical characterization of the ash samples. The ash samples modified with acid were comparatively tested with triple superphosphate fertilizer (TSP) to determine their effects on the growth and nutrition of lettuce plants. The long-term use of ash and ash-derived fertilizer materials and whether they create a negative impact on soils have been determined through a simulation study. The most effective modification on the water solubility of nutrient elements, especially P, in PMA samples is achieved through modification with H2SO4. Similarly, in the plant experiment, PMA + H2SO4 treatment is superior to TSP. In the simulation study, it has been observed that the direct application of PMA in the long term further increases the pH in calcareous and high-pH soils, and the PMA + H2SO4 application is the most suitable for maintaining soil pH stability. It is well understood that effective recycling of PMA can provide an economical and alternative source of phosphorus. Additionally, PMA serves as a significant fertilizer due to the presence of other essential plant nutrients in its composition.