# The Application of Computed Tomography to Study the Soil Porosity of Mountain Red Earth
## 3 Results and Discussion
### Parameter Quantization
This results in a reduction of structural pores associated with biological activity. Sudden changes in pore area observed at some locations can be attributed to the decay of roots or the slanting intrusion and extension of roots from the exterior of the soil column under study. Figure 7: Variation of the porosity with depth. Figure 8: Cumulative distribution of pore area percentage within each scale of pore including large pores, medium pores, small pores, and micropores. It can be seen that the percentage of pores area in each scale is different. Figure 9: Distribution of the number of pores in each scale of pore including large pores, medium pores, small pores, and micropores. It can be seen that there are obvious differences in the number of pores each scale. Observing the number of pores within each scale of pore (Figure 9), at various depths, the quantity of each type of pore aligns with their area proportions. Small pores are most numerous, followed by medium and large pores, while micro-pores are the least. With increasing depth, the total number of pores first increases and then gradually decreases. Although the topsoil layer contains a higher number of large pores, their overall area is larger despite the lesser quantity. Beyond a depth of 80.5 mm, there is a linear decrease in pore number, reaching its minimum at the bottom. In this process, within the surface layer of 80.5 mm, the number of large and medium pores is relatively higher compared to other layers, with numerous small pores as well. The distribution of medium and large pores is most abundant at a depth of 80.5 mm, which could be related to the greater root distribution within this range. In summary, litterfall on the forest floor provides a form of shelter, particularly for the large pores that significantly contribute to water conduction in the surface soil layer. This protective layer serves as a barrier that also mitigates the direct erosive impact of raindrops on the soil surface, thereby facilitating soil erosion prevention. However, the vegetation in the research area is somewhat homogenous, predominantly comprising _Dianthus carophyllus_ and _Pinus thunbergii_. Given their relatively low biological activity, the resultant layer of litterfall is correspondingly thin. With underdeveloped soil strata and a thin humus layer, the protective effect of the litterfall on the pore structure is somewhat limited. In the event of rainfall, the impact of raindrops could lead to the degradation of the pore structure or induce splash erosion, potentially leading to pore blockages. Roundness in soil can serve as an indicator for assessing soil texture and particle structure. Higher roundness typically signifies more homogeneous soil particles with more regular shapes. Such soil exhibits superior water permeability and aeration, and it can retain moisture and nutrients more effectively, thereby facilitating root system development and growth in slope vegetation. Considering the earlier discussion on the trends in pore quantity and area, we find that the roundness at the top of the soil column is lower compared to that near the bottom. This can be attributed to the number and diameter of pores distributed at these depths. The top area contains a larger proportion of medium and large pores, which are less spherical, resulting in lower roundness. However, as depth increases, the pores gradually transition to smaller scales, with both their number and area decreasing. As a result, their shapes become more spherical, leading to a higher roundness. Figure 10: Variation of roundness with depth. The results derived from the pore characterization via CT scanning suggest that although the surface layer's large pores are larger than those at other depths, they only account for a fraction of 15.9%, with this proportion decreasing with depth. The pore structure, particularly the large pores, is insufficient to absorb and facilitate the timely percolation of surface runoff generated by rain.