Evaluating the Water Holding Capacity of Multilayer Soil Profiles Using Hydrus-1D and Multi-Criteria Decision Analysis

In semi-arid climate regions of China, vegetation restoration on open pit mining lands is limited by soil moisture. However, multi-layered soil profiles can impede water infiltration into deeper underground, leaving more water stored in the root zone. Here, three types of soils with contrasting texture, sandy loam (SL), sand (S), and silt loam (SiL), were used to construct four multilayer profiles: SL-SiL, SL-S, SL-S-SiL, and SL-SiL-S. Silt loam was taken from the humus layer, which is more conducive to plant growth than other layers, and it was allocated to the first layer in the four profiles, while sand and silt loam underlay the silt loam layer. Column experiments and Hydrus-1D simulation of the vertical infiltration and drainage process were performed: (1) The simulated results showed that when the sand layer underlay the sandy loam layer (SL-SiL and SL-S-SiL), the sandy loam layer could hold more water than the silt loam layer underlaying the sandy loam layer (SL-SiL and SL-SiL-S). The water content of the sandy loam layer in SL-SiL (95 cm) and SL-S-SiL (95 cm) was 28.3% higher than SL-SiL (74 cm) and 10.5% higher than SL-SiL-S (86 cm). (2) Both the measured and simulated cumulative infiltration and wetting front penetration time were positively related to the thickness of the silt loam layer and negatively related to the thickness of the sand layer. (3) The simulated infiltration rate, accumulation infiltration, and wetting front of the first layer were unaffected by the texture of the underlying layer. According to multi-criteria decision analysis, SL-S-SiL had the best water holding capacity and was suggested for land reclamation in the open pit mine in our research.