Effect of vegetation types on moisture migration in eco-protected loess slopes, China
WANG Juntian1, WANG Yunyi1, BAO Han1,2,*(), YAN Changgen1, WANG Geng1, DONG Qi1,3, JIANG Ziyang4
1School of Highway, Chang'an University, Xi'an 710064, China 2State Key Laboratory of Loess Science, Xi'an 710054, China 3Shaanxi Science and Technology Holding Group, Xi'an 710061, China 4Shaanxi Province Highway and Transportation Society, Xi'an 710064, China
Slopes in arid and semi-arid areas typically have low vegetation cover and are highly susceptible to extreme precipitation-induced hazards such as landslides and debris flows. Although ecological slope protection can regulate soil water dynamics through canopy interception, transpiration, and root water uptake, the specific moisture-regulation roles of different vegetation types remain unclear. In this study, Festuca arundinacea Schreb. (tall fescue) and Medicago sativa L. (alfalfa) were selected as representative slope-protecting species. Long-term field monitoring combined with HYDRUS 2D/3D numerical simulations was employed to analyze soil moisture dynamics under precipitation events. The results indicated that the dense canopy of tall fescue effectively delayd surface runoff and enhanced infiltration, increasing shallow soil moisture to 33.400%; however, its strong transpiration caused rapid post-precipitation depletion, with moisture decreasing by approximately 1.500%. In contrast, the sparse canopy of alfalfa leads to lower surface soil moisture (32.800%), while its deep taproot system facilitated downward water migration, gradually increasing deep soil moisture and maintaining post-precipitation stability. Numerical simulations further revealed distinct interspecific differences in precipitation response, soil moisture evolution, and vertical water redistribution. Shallow-rooted tall fescue exhibited rapid, short-term responses in the shallow layer, whereas deep-rooted alfalfa demonstrated deep-layer water storage and long-term stability. The findings demonstrate that vegetation type exerts distinct regulatory effects on overall slope moisture dynamics, offering a scientific foundation for optimizing slope-protection plant selection and enhancing hydrological regulation under extreme climatic conditions in arid and semi-arid areas.
Received: 27 November 2025
Published: 30 June 2026
Conceptualization: WANG Juntian; Data curation: WANG Yunyi, WANG Geng; Writing - original draft preparation: WANG Juntian, WANG Yunyi; Project administration: YAN Changgen, BAO Han; Formal analysis: BAO Han, WANG Juntian; Writing - review and editing: WANG Juntian, HanBao; Validation: WANG Yunyi; Methodology: DONG Qi; Visualization: JIANG Ziyang; Investigation: WANG Yunyi, WANG Geng. All authors approved the manuscript.
WANG Juntian, WANG Yunyi, BAO Han, YAN Changgen, WANG Geng, DONG Qi, JIANG Ziyang. Effect of vegetation types on moisture migration in eco-protected loess slopes, China. Journal of Arid Land, 2026, 18(6): 1014-1030.
Fig. 1Structural design of the slope model test chamber. (a), front view; (b), left view; (c), right view.
Layer
Thickness (cm)
Loess (%)
Guar gum (%)
Wood fiber (%)
SAP (%)
Modifier (%)
Base layer
5
97.300
1.000
1.500
0.100
0.100
Surface layer
2
94.300
0.500
5.000
0.100
0.100
Table 1 Composition and mixing ratios of slope base materials
Fig. 2Schematic diagram of moisture monitoring of the model slopes with tall fescue (a) and alfalfa (b)
Fig. 3Flowchart of sample preparation for slope model test. SAP, super absorbent polymer.
Fig. 4Grid division of the slope in the HYDRUS 2D/3D software. (a), slope with tall fescue; (b), slope with alfalfa.
Fig. 5Daily precipitation and cumulative precipitation from 24 July to 31 December, 2024
Precipitation type
Count
Proportion (%)
Total precipitation (mm)
Average precipitation (mm)
Proportion (%)
Trace
0
0.000
0.0
0.0
0.000
Light
25
78.100
62.2
2.5
27.900
Moderate
5
15.600
65.0
13.0
28.900
Heavy
1
3.100
34.2
34.2
15.400
Extreme
1
3.100
61.8
61.8
27.800
Total
32
100.000
224.2
7.0
100.000
Table 2 Precipitation characteristics
Fig. 6Comparison of soil moisture content between the two planting slopes in 2024. (a), moisture at the interface; (b), moisture at the 5 cm depth; (c), moisture at the 15 cm depth; (d), moisture at the 30 cm depth. G and Z denote tall fescue and alfalfa, respectively. Numbers indicate monitoring points.
Fig. 7Growth status of alfalfa (left) and tall fescue (right) monitored every two weeks. (a), 2nd week; (b), 4th week; (c), 6th week; (d), 8th week; (e), 10th week; (f), 12th week; (g), 14th week; (h), 16th week; (i), 18th week; (j), 20th week.
Fig. 8Comparison of canopy coverage (a) and leaf area index (LAI; b) between tall fescue and alfalfa
Fig. 9Pn (net photosynthetic rate) of tall fescue and alfalfa measured every three weeks. (a), 3rd week; (b), 6th week; (c), 9th week; (d), 12th week; (e), 15th week.
Fig. 11Soil water characteristic curves (SWCCs) for slopes with different vegetation types. (a), tall fescue; (b), alfalfa.
Fig. 12Measured and simulated soil moisture in monitoring points of the slope with tall fescue (a) and alfalfa (b)
Fig. 13Contour maps of soil moisture content for slopes with different vegetation types. (a), tall fescue slope under pre-precipitation condition; (b), alfalfa slope under pre-precipitation condition; (c), tall fescue slope under post-precipitation condition; (d) alfalfa slope under post-precipitation condition; (e), simulated tall fescue slope under post-precipitation condition; (f), simulated alfalfa slope under post-precipitation condition.
Vegetation type
Depth
RMSE (%)
Vegetation type
Depth
RMSE (%)
Tall fescue
Surface
0.231
Alfalfa
Surface
0.232
5 cm
0.178
5 cm
0.178
15 cm
0.163
15 cm
0.163
30 cm
0.189
30 cm
0.188
Table 3 RMSE (root mean square error) of soil moisture simulations at different depths and vegetation types
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