# The Application of Computed Tomography to Study the Soil Porosity of Mountain Red Earth
## 1 Introduction  
Mountain Red Earth, a type of soil predominantly found in southern China, is characterized by its high iron oxide content, imparting a distinctive reddish hue to the soil. This soil type plays a significant role in agricultural production and the ecological environment. Its unique properties and composition make it a subject of considerable interest in soil science and environmental studies [1]. In recent years, due to the influence of natural factors and human activities, the erosion and degradation of Mountain Red Earth has caused various ecological and environmental problems, such as ecological degradation and sediment deposition, and these problems have attracted worldwide attention [2]. Regions where Mountain Red Earth is found typically exhibit uneven terrain and soil with a complex pore structure, leading to significant spatial variability in permeability. Areas with low vegetation cover are especially vulnerable to soil erosion during rainy seasons, which thins the soil layer and severely impacts the regional ecological environment. Regarding soil-water loss in red soil, many scholars have focused on how different scale structures and particlesize compositions affect mechanical characteristics. This includes the impact of soil regulation on soil structure and its relation to red soil's erosion resistance [3; 4; 5]. Previous studies have mainly concentrated on agricultural soils, noting that different land use and cropping methods significantly affect runoff and soil erosion [6; 7]. Red soil is characterized by low levels of organic carbon, total nitrogen, available nitrogen, available potassium, and calcium [8], along with a poor aggregate structure, making it prone to rapid erosion [9]. Additionally, red soil is susceptible to physical crusting, which leads to faster runoff and greater damage under rainfall conditions [10; 11], especially during rapid rainfall events. Undoubtedly, the structure and physicochemical properties of red soil [12], particularly its pore structure and permeability, are critical intrinsic factors determining soil erosion [13]. Conducting systematic quantitative research on the pore structure characteristics of Mountain Red Earth is theoretically significant for understanding the processes and mechanisms of soil erosion. Currently, the soil slicing method is a commonly used but destructive technique for observing the microscopic pore structure of soil. This method involves preparing soil slices using epoxy resin impregnation, which, despite its complexity and potential to disrupt the native soil structure, is less destructive than earlier methods and facilitates easier shaping. However, it remains inconvenient for large-scale samples. With further optimization, it is now possible to produce 30 um thick soil thin sections through processes, including air-drying, oven-drying, impregnation, curing, slicing, and grinding [14; 15; 16]. In summary, the soil slicing method is often overly complex and prone to disrupting the native structure, and due to technical limitations, it remains unsuitable for widespread application. Non-destructive research methods such as the dye tracing technique (DTT) and moisture penetration methods are generally more applicable. The DTT method tracks soil moisture to construct an intact and high-precision native soil structure. While effective for pore structure analysis, it is challenging to obtain sufficient stained profiles in field conditions to comprehensively reconstruct soil structure, so it is often used to validate related studies [17]. In recent years, the agricultural sector has utilized ultrasonic sensing methods to measure the porosity of arable land. This method is unique in its ability to measure porosity in a non-invasive and relatively straightforward manner [18]. Computed Tomography (CT) technology has played a crucial role in soil and geological research and has achieved significant development with the progress of electronic computer technology.