PurposeThis study aims to investigate the effects of root exudates on the aggregate stability and permeability of loess and to further reveal the mechanisms of vegetation in preventing and controlling soil erosion beyond mechanical effects.Materials and methodsWetting tests were conducted to investigate how loess aggregate stability varies with curing time and root exudate concentration; and infiltration tests were carried out to examine the influence of root exudates on the infiltration characteristics of loess with varying degrees of compaction.Results and discussionThe results showed that the stability of loess aggregates significantly increased due to the application of root exudates. Curing could enhance the stabilizing effects of root exudates on loess aggregates; however, there existed a critical curing duration. The application of root exudates reduced the stable infiltration rate and hydraulic conductivity of loess. However, untreated specimens under lower degrees of compaction exhibited lower stable infiltration rate and hydraulic conductivity due to local structural damage. The stable infiltration rate of both treated and untreated specimens decreased with curing time.ConclusionsThe effects of root exudates can be attributed to their ability to function as stabilizing agents and promote aggregation, due to their high adsorption capacities and negatively charged groups on their surfaces. On the other hand, the presence of root exudates can significantly enhance the soil microbial activity, the microorganisms and their hyphae further strengthen the soil structure, fill pores and increase the soil hydrophobicity, thereby improving the aggregate stability while reducing the soil permeability.

Under saline-alkali stress conditions, inoculation with Rhizophagus irregularis or the application of biochar can both promote plant growth and improve soil physicochemical properties. However, the effects of their combined use on switchgrass growth and soil mechanical properties remain unclear. This study established four treatments: no Ri inoculation and no biochar addition (control, CK), biochar addition alone (BC), Rhizophagus irregularis inoculation alone (Ri), and their combination (RB). The aim was to investigate the effects of these treatments on the biomass, root morphology, and soil mechanical properties of switchgrass under saline-alkali stress. The results showed that compared to the CK treatment, the RB treatment significantly increased the root, stem, leaf, and total biomass of switchgrass by 67.55%, 74.76%, 117.31%, and 82.93%, respectively. Among all treatment groups, RB treatment significantly reduced soil bulk density, soil water-soluble sodium ions (Na+), soil exchangeable sodium percentage (ESP), and sodium adsorption ratio (SAR), while increasing soil porosity. Furthermore, RB treatment significantly improved infiltration rate and shear strength. Compared to the CK treatment, the stable infiltration rate and shear strength under 400 kPa vertical load increased by 70.69% and 22.5 kPa, respectively. In conclusion, the combination of Ri and biochar has the potential to improve soil mechanical properties and increase the biomass of switchgrass under saline-alkali stress.

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.

This study was conducted to explore the use of non-expansive soil as protective cover for expansive soil slopes. Laboratory model experiments were carried out on expansive soil systems with varying thickness of non-expansive soil cover. The models were subjected to three wet-dry cycles. Variation in soil moisture content was monitored using moisture probes. Surface and internal cracking of soil was observed using cameras. Variation of infiltration rate of the cover with wet-dry cycles was measured in-situ. Results of the study show correlation between cover thickness and evaporation rate and crack formation in the expansive soil. Crack size, quantity, depth, and interconnectivity in the expansive soil increased with decreasing cover thickness. Even the thinnest cover significantly reduced the the number and depth of cracks. The infiltration rate of the cover remained unchanged after three cycles wet-dry cycles. The final water content, after the third drying, in the expansive soil increased with increasing cover thickness.