The effect of humic substances and potassium-solubilizing bacteria on the release of nutrients from pyroclastic materials of Mount Merapi, Indonesia

Indonesia, which is in the Ring of Fire, has many active volcanoes, including Mount Merapi, whose eruptions produce pyroclastic material rich in essential minerals. Pyroclastic material comes out when a volcano erupts and contains various minerals containing nutrients which are easily weathered minerals. Although this material has the potential to be a source of nutrients for plants and is included in the category of easily weathered minerals, the process of leaching nutrients from minerals takes a long time to make them available to plants. This study aims to determine the effect of humic substances and potassium-solubilizing bacteria on releasing nutrients from pyroclastic materials from Mount Merapi using humic substances and potassium-solubilizing bacteria. The study was conducted by taking pyroclastic samples from Mount Merapi and carrying out a percolation process with variations in grain size (passing 2 mm and 0.05 mm sieves), pyroclastic doses (0, 9.375, 18.75, 37.5, 75, and 150 g/washing tubes), and the addition of humic substances and potassium-solubilizing bacteria. The results showed that the finer the size of the pyroclastic grains, the faster the release of nutrients, especially calcium (Ca), potassium (K), and sodium (Na). The combination of humic substances and potassium-solubilizing bacteria increases the release of nutrients from pyroclastic materials, making them more available to plants. The best dose is to provide 75 g of pyroclastic material, both fine and coarse-sized pyroclastic. This study offers an alternative in soil management by increasing the effectiveness of nutrient leaching from volcanic materials.