Novel evaluation of pedogenesis in Human-made soils constructed with Andosols

Understanding the spatiotemporal variation of soil properties is essential for modeling pedogenesis. However, few studies have explored the influence of soil formation on the spatial variation of soil properties. Human-made soils, particularly those with a rapidly forming ^A horizon and well-documented ages since construction, are suitable for the examination of spatiotemporal changes in soil formation. This study examined pedogenesis in Human-made soils using Andosols as embankment materials and evaluated the influence of soil formation on the spatial dependence of soil properties using semivariogram analysis on artificially constructed planting bases with known ages. The ^A horizon, characterized by darkened soil color and crumbly structure, was observed, and thus grid sampling was conducted at various depths, considering the soil horizons and the embankment of soil materials. Soil samples were analyzed for general properties, such as pyrophosphate-extractable aluminum, iron, and carbon contents (Al_p, Fe_p, and C_p), as well as nitrate, nitrite, and ammonium nitrogen content. The results demonstrate that total carbon contents (TC) and C_p increased significantly over time after afforestation. Semivariogram analysis showed higher coefficients of determination for most soil chemical properties in the ^A horizon compared to the ^C horizon. This indicates that the spatial dependence of soil properties developed through soil processes. A significant correlation between pyrophosphate extracts indicates that Al/Fe-humus complexation, promoted by the initial spatial distribution of active Al and Fe, influences the spatial dependence of soil organic matter accumulation. These results demonstrate that pedogenesis amplifies the spatial dependence of soil properties in Human-made soils. Understanding soil formation necessitates considering both temporal and spatial scales relative to specific soil properties.