Quantification of 3D macropore networks in forest soils in Touzhai valley (Yunnan, China) using X-ray computed tomography and image analysis

Abstract

The three dimensional (3D) geometry of soil macropores largely controls preferential flow, which is a significant infiltrating mechanism for rainfall in forest soils and affects slope stability. However, detailed studies on the 3D geometry of macropore networks in forest soils are rare. The intense rainfall-triggered potentially unstable slopes were threatening the villages at the downstream of Touzhai valley (Yunnan, China). We visualized and quantified the 3D macropore networks in undisturbed soil columns (Histosols) taken from a forest hillslope in Touzhai valley, and compared them with those in agricultural soils (corn and soybean in USA; barley, fodder beet and red fescue in Denmark) and grassland soils in USA We took two large undisturbed soil columns (250 mm×250 mm×500 mm), and scanned the soil columns at in-situ soil water content conditions using X-ray computed tomography at a voxel resolution of 0.945 × 0.945 × 1.500 mm3. After reconstruction and visualization, we quantified the characteristics of macropore networks. In the studied forest soils, the main types of macropores were root channels, inter-aggregate voids, macropores without knowing origin, root-soil interface and stone-soil interface. While macropore networks tend to be more complex, larger, deeper and longer. The forest soils have high macroporosity, total macropore wall area density, node density, and large macropore volume, hydraulic radius, mean macropore length, angle, and low tortuosity. The findings suggest that macropore networks in the forest soils have high inter-connectivity, vertical continuity, linearity and less vertically oriented.