BackgroundIn the Loess Plateau region, significant engineering activities have led to many exposed loess slopes. These slopes have undergone a series of shallow failures under rainfall, significantly affecting their stability. Vegetation can somewhat restore the ecological damage to the slope surfaces and enhance their stability. Thus, studying the spatiotemporal evolution of soil moisture migration under vegetation protection on loess slopes is crucial.MethodsEmploying experimental designs with slope gradients of 45 degrees and 60 degrees, this investigation is structured around a trio of core objectives: to delineate the processes of rainfall infiltration and its redistribution within the slope, to chart the evolution of soil water within the loess soil matrix, and to discern the impacts of slope inclination on soil water dynamics. Critical to this study are the monitoring of volumetric moisture content, matric suction, and the external variables of rainfall and temperature, alongside an analysis of soil water potential and moisture movement as observed in laboratory setups and simulated through Hydrus-2D.ResultsThe study revealed that slope angle significantly affects soil moisture infiltration and redistribution. The steeper slope (60 degrees) exhibited more pronounced fluctuations in soil water potential, particularly during the rainy season, reflecting the dynamic nature of water movement. This slope also demonstrated sharper transitions in soil moisture during drying periods, indicating a greater sensitivity to weather changes. Water movement parallel to the slope surface was faster on steeper slopes, especially under drying conditions, with more pronounced lateral downslope flow at the surface layer. In contrast, the gentler slope (45 degrees) showed more consistent moisture retention during wet periods, with slower and more uniform soil moisture movement, leading to a steadier moisture gradient and prolonged upslope movement. Vegetation plays a crucial role in modulating soil moisture dynamics, with grass growth being more effective on the steeper 60 degrees slope. The extensive root network on this slope enhanced water retention, increased soil permeability, and reduced erosion. During the drying phase, deeper root systems significantly reduced volumetric water content at shallower depths, promoting higher moisture content in the middle sections of the slope.

A vertical tube surface drip irrigation system was designed to address the damage caused by soil drought and high surface temperature to sand-fixing seedlings in a plant sand-fixation area. Numerical simulation and experimental verification were used to study soil water movement with vertical tube infiltration and surface drip irrigation for four aeolian sandy soils with different hydraulic conductivity (Ks), drip discharge (Q), vertical tube diameter (D), and vertical tube buried depth (B). The results show that a power function relationship exists between the soil-stable infiltration rate (if) and Ks, D, and B given the condition of vertical tube water accumulated infiltration, and its coefficient is 0.17. The power function indices of Ks, D, and B are 0.87, 1.89, and -0.37, respectively. The if can be used to determine the maximum drip discharge (Qmax) of the dripper in the vertical tube to ensure that the sand-fixing plants are not submerged during drip irrigation through the vertical tube (Qmax=if). The wetting front transport distance in the three directions increased with increasing Ks and Q but decreased with increasing D and B. After determining the time required for water to reach the bottom of the vertical tube, an estimation model of soil wetting body transport for vertical tube surface drip irrigation, including Ks, Q, D, and B, was constructed. Compared with the experimental data, the root mean square error (RMSE) is between 0.17 and 0.42 cm, and the Nash-Sutcliffe efficiency (NSE) is at least 0.88. Therefore, the model is appropriate and can provide valuable practical tools for the design of vertical tube surface drip irrigation in different plant sand fixation areas. A surface drip irrigation system and pipe protection technology were combined to form a vertical tube surface drip irrigation system to address the damage caused by soil drought and high surface temperature to sand-fixing seedlings. However, this irrigation technology has the problem that it is difficult to quantify the matching of drip discharge and pipe parameters (vertical tube diameter and burial depth), wetted soil volume, and plant roots due to the single soil sample used in the laboratory experiments. This paper considers the influence of soil differences in diverse plant sand-fixing areas and establishes a stable infiltration rate model to determine the maximum drip discharge. Additionally, a soil wetted volume prediction model was developed by combining HYDRUS-2D simulations and experimental verification. The model is simple and has high prediction accuracy, which is convenient for designers to determine the appropriate vertical tube parameters for different plant sand-fixation areas.