Indonesia has many areas with volcanic soils, especially pyroclastic materials that are rich in minerals important for plants such as calcium, potassium, and magnesium. These nutrients are bound to minerals that are difficult for plants to access, so the soil is often less productive. The use of organic materials such as humic substances and potassium-solubilizing bacteria can help accelerate the release of nutrients from pyroclastic materials because humic substances increase the solubility of minerals and provide essential nutrients. This study objectives on how humic substances and potassium-solubilizing bacteria work together to increase the release of nutrients from pyroclastic materials. This study was conducted by collecting pyroclastic samples at Mount Merapi and using soil from Mamuju, West Sulawesi, with a specific procedure (percolation). The results showed a pattern of nutrient release from pyroclastic materials, where Ca was always the most released element, followed by K and Mg, and this pattern was formed in all treatments. The combination (pyroclastic + humic substances + PSB) is the best treatment for nutrient release. The increase in nutrient release from the control and combination (pyroclastic + humic substances + PSB): Ca 788.84 mg - 1157.26 mg, K 123.96 mg - 206.69 mg, and Mg 50.65 mg - 59.65 mg. Humic substances improves the chemical properties of the soil and increases the activity of microorganisms, which helps in dissolving minerals, whereas bacteria produce organic acids that dissolve potassium from minerals.