Ameliorative Effect of Humic Acid Extracted from Imperata cylindrica Compost on Selected Chemical Properties of Soil in Coastal Region of Indonesia

Acid Inceptisols are commonly found in coastal region of Bengkulu Province, Indonesia. This particular soil faces serious problem such as low pH, high aluminum (Al) saturation and low fertility. Humic acid extracted from cogon grass (Imperata cylindrica) benefits to improve chemical properties of the soil. The present study aims to evaluate the effect of humic acid derived from cogon grass compost on the improvement of selected chemical properties of soil from coastal region. The study employed Completely Randomized Design (CRD) with treatments of humic acid dosages consisting of 0 (control), 1, 2, 3, and 4 g kg-1. Each treatment was replicated 3 times. The experimental procedure was carried out by incorporating 100 g of air-dried soil with assigned rate of humic acid in a 100 ml plastic bin. The mixer was incubated for 14 days with additional distilled water to maintain field capacity moisture content. After the incubation, the soil was analyzed for selected soil chemical properties. The result indicated that the application of humic acid at a rate of 4 g kg-1 substantially increased soil organic-C by 49%, available P by 58%, exchangeable K by 33%, and cation exchange capacity (CEC) by 51.4% compared to control. However, soil pH significantly declined with the application of humic acid, thereby an application rate of 1-2 g kg-1 is adequate to prevent further decrease in soil pH. In addition, humic acid application had no prominent effect on soil total N, C/N ratio and electrical conductivity (EC) of the soil. These findings suggest that humic acid extracted from cogon grass compost has strong potential to improve acid Inceptisols in coastal regions, thereby supporting sustainable agricultural management.