Effect of nano clay and organic fertilizer amendments on the physico-chemical properties of soil affected by cold lava in Mount Marapi, Indonesia

Eruptions of Mount Marapi have left large deposits of cold lava and reduced the quality of the soil around the river, especially on agricultural land. The soil formed from this material is generally poor in nutrients, has a weak structure, and is difficult to bind to water, so its restoration requires proper ameliorant input. This study examines the effect of the combination of nano clay and manure (Pukan) on a number of physical and chemical properties of cold lava soils, including aggregation, organic carbon, N, P, K, cation exchange capacity (KTK), pH, content weight, and total porosity. The experiments were arranged in a complete factorial random design with several levels of nano clay and Pukan. Pukan significantly increased the C-organic content (up to 1.15%), N-total (0.22%), P-available (10.56 mg kg⁻¹), and KTK (43.51 cmol(+) kg⁻¹). The addition of nano clay mainly plays a role in raising soil pH (up to 5.32) and improving nutrient retention, but tends to decrease total porosity and increase content weight. Changes in aggregate stability and soil moisture content are relatively small. These results suggest that the application of Pukan is effective in improving chemical fertility, while nano clay functions more as a pH buffer and structural stabilizer. The combination of the two has the potential to be an ameliorant package to restore agricultural land affected by the Marapi cold lava.