Described herein is a process that converts an ash source such as, for example, a manure ash source to granules with increased nutrient solubility and phosphorus (P) content. In one aspect, the process involves admixing an ash source with a phosphorous-based acid to produce the granules. The granulated composition produced by the methods described herein have good packing properties and, thus, are easy to transport and apply as a fertilizer. The granular compositions produced herein can be readily used in conventional fertilizer equipment, mixes, and systems.