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The quantification of percolation processes and deep drainage rates in cracking clays is challenging due to the existence of multiple flow pathways, including desiccation crack networks, and the effect of variability in antecedent soil moisture and rain event properties. While most previous research on this topic focuses on long‐term average rates, this study focusses on inter‐event dynamics. The study uses data from soil moisture sensors distributed vertically down 4 m profiles of Vertosol and Chromosol soils across 13 sites over an area of approximately 20 km2. The objectives were to estimate the temporal and spatial variability of deep drainage rates and to investigate the effect of antecedent soil moisture conditions and rain event properties on deep drainage rates and percolation dynamics. 35 deep drainage events over a 40‐month period contributed 78 % of the total deep drainage of 254 mm at 4 m depth. Average deep drainage estimates were about 15 % (ranging from 0 – 80 % between sites) of total rainfall and irrigation in the Vertosol and 8% (0 – 24 %) in the Chromosol. The event water travel times at 4 m depth were 0.25 – 38 hr and 14 – 39 hr in the Vertosol and Chromosol respectively. The event deep drainage rates averaged across sites were associated with event rainfall volumes (linear regression R2 = 0.40), with the effect of antecedent conditions evident only when looking at inter‐site differences. The percolation response time was strongly associated with higher rainfall intensities (R2 = 0.33) with no evidence from the linear regression of an antecedent moisture effect.

Opencast coal mining has a series of consequences on land resources and places enormous pressure on the ecological environment. Stripping, excavation, transportation and dumping have different effects on soil physical, chemical and biological properties. Moreover, the reconstructed landscape produces increased small-scale spatial heterogeneity of mined soils. Currently, growing concerns for the negative consequences of mining have highlighted the importance of reclamation in minesoil studies. This review has examined the mechanisms of coal mining and reclamation that affect soil properties (physical, chemical, biological) and described soil development in reclamation, with an emphasis on the reclaimed minesoil (RMS) properties of reclamation sites. The major conclusions of this review were: (i) The randomness of soil dumping increased the heterogeneity of minesoil properties, which in turn increased the complexity of reclamation practice. (ii) The negative or positive consequences of mining and reclamation processes on RMS need to be recognized by scientific observations such as soil property multi-index analysis and soil chronosequences, on which the minesoil reconstruction practice are based. (iii) Five phases of reclamation (i.e., geomorphic reshaping, soil reconstruction, hydrological stability, vegetation restoration, and landscape rebuilding) should be considered as a comprehensive system for the reconstruction of minesoils. (iv) The application of new technologies (e.g., micro-terrain reshaping and soil non-destructive detection) and new studies (e.g., systematic study, rebuilding animal habitat, and biodiversity research) to minesoil recovery practice would enhance the new concepts of land reclamation and ecological restoration in mining areas.

Poor soil physical conditions associated with low hydraulic conductivity and infiltration can limit salt leaching and reclamation; hence, land revegetation. Soil physical amendments such as wood chips and fine sand may be used to remediate the soil physical conditions and improve salt leaching, thus assisting with revegetation. To evaluate the success of soil amendments for the reclamation and revegetation of a saline-sodic soil under a typical climatic condition of a semi-arid environment, a water and solute transport model (HYDRUS-1D) was used. Synthetic climatic scenarios were generated using LARS-WG. Soil profiles (1 m depth) amended separately with 20% wood chips and 40% fine sand at the surface (0–10 cm) were defined for the simulation. A non-amended soil profile, which had physical properties of a disturbed soil, was used as a control. Salt leaching was more successful in the non-amended soil profile compared with the amended soil profiles. The likelihood and the success of Atriplex halimus L. seed germination were also higher in the non-amended soil (67.7%) compared with wood chips (13.98%) and fine sand (6.7%) amended soils. This study indicates that the addition of 20% wood chips and 40% fine sand to the depth of 10 cm of a saline-sodic soil may not be an effective approach for reclamation and revegetation under the semi-arid climatic conditions. This study suggests that a reduction in soil bulk density is sufficient to provide suitable conditions for successful land reclamation and revegetation in the investigated climatic conditions.

Purpose: The use of heavy machinery in mining areas increases during mining and dumping of waste soils, causing severe soil compaction and potentially affecting soil recovery. This study aimed to capture the features of complex compacted soil pore structure using computed tomography (CT) and to quantify soil pore distribution properties based on Minkowski theory. Materials and methods: A total of 45 cylindrical soil columns were extracted from different soil layer at 5 sampling sites that differed in compaction level in Pingshuo opencast coal mine in Shanxi Province of China. The penetration resistance at these sites ranged from 27.3 to 1023.1 kPa. Three-dimensional reconstruction software VGStudio was used to obtain the morphological characteristics (pore volume density, VD; surface density, SD; mean curvature density, MCD; and Euler number, EN) of soil pores after processing the X-ray scanned image. Results and discussion: Compaction generally reduced VD, SD, and MCD, which ranged from 0.10 to 0.20, 2.23 to 2.80 mm 2 mm −3 , and 10.75 to 15.64 mm mm −3 respectively in undisturbed site P0, whereas, they ranged from 0.02 to 0.07, 0.13 to 0.60 mm 2 mm −3 , and 1.61 to 4.27 mm mm −3 respectively in highly compacted site P4. The three index exhibited the similar trend, and decreased with the increase of compaction level. Soil compaction had positive effects on EN, which was low at the depth of 20- to 40-cm layers but showed an increasing trend with increasing soil compaction level. The value of EN varied from 28,878 to 129,861 in P0, whereas it varied from 1,169,967 to 2,281,998 in P4. Conclusions: All of macroporosity, mesoporosity, and microporosity were significantly affected by heavy machinery compaction, among which macroporosity exhibited the maximum decrease in P4 compared to that in P0 (P0 ranged from 14.2 to 26.4% and P4 ranged from 0.2 to 1.4%). The soil compaction in mining area significantly affected soil properties, thus artificial methods such as fertilizer application and deep tillage were needed.

Highlights - A slower water movement is associated with a greater salt leaching efficiency. - A greater rate of cation exchange can increase salt leaching. - Addition of bentonite can improve the reduction of soil salinity. Abstract Saline-sodic soils may be reclaimed through the addition of amendments to alter the soil pore system and hydraulic functions, therefore allowing salts to be leached from the soil. For the purpose of investigating the suitability of specific amendments for improving leaching and reclamation, soil percolation column studies were conducted to assess the influence of amendments on cation exchange, the potential for the release of cations and changes in hydraulic conductivity of the soil. A fine textured saline-sodic soil amended separately with 20% wood chips (wt/wt), 40% fine sand (wt/wt) and 2.5% bentonite (wt/wt) was used for this study as well as a non-amended soil as a control. The impact of amendments was evaluated by continuous leaching of the soil substrates with deionized water until the hydraulic conductivity and leachate chemistry stabilised. The bentonite amended soil had a greater increase (15.9 cmolc kg−1) in exchangeable Ca2+ and a higher reduction in exchangeable Na+ (12.29 cmolc kg−1) after the final leaching due to a greater rate of cation exchange for this soil substrate. The bentonite amended soil also had a greater reduction (92%) in Na+ content compared with the other soil substrates. The hydraulic conductivity of all soil substrates improved during leaching although the hydraulic conductivity of bentonite amended soil reduced after three pore volumes of leaching. This study suggests that a slower water movement (an increased percolation time) and a greater rate of cation exchange were associated with the greater leaching efficiency. Therefore, addition of bentonite improves and accelerates the reduction of salinity and sodicity.

Heavy machinery compaction in mining area is widespread, and seriously jeopardizes soil restoration. Characterization of soil macropores with three-dimensional methods is essential for understanding the reclaimed minesoil (RMS) development. The aim of this study was to demonstrate the application of X-ray computed tomographic (CT) scanning for analyzing soil macropore structure and to explore how soil compaction affects soil macropore properties. To achieve this, soil samples collected from Pingshuo opencast coalmine were tested through a laboratory scheme, which was conducted to simulate the real soil pore situation under increasing soil bulk density treatments of 1.3, 1.4, 1.5, 1.6, 1.7, and 1.8 g cm−3 (T1.3-T1.8). Three-dimensional (3D) macropore networks were observed via CT, and macroporosity, macropore number, area, volume and its connectivity were characterized. Soil compaction had a major impact on soil macropore characteristics. The macropores of the 1.3 g cm-3 treatment were well connected, whereas those of the 1.8 g cm-3 treatment were poorly connected and isolated from each other. Macropore number and macroporosity decreased significantly as the soil compaction increased. Moreover, a 3D visualization of soil pore connectivity results suggested that the macropore connectivity markedly decreased with increasing compaction level, with average Euler number increasing from 0.677 in the 1.3 g cm-3 treatment to 0.999 in the 1.8 g cm-3 treatment. Soil bulk density was negatively correlated with macropore throat number and thickness, indicating that the soil compaction causes a loss of pore connectivity. Despite using a coarse resolution, the combination of laboratory simulation tests and 3D visualization of soil macropores provides valuable data for identifying the differences in soil pore structure among compacted RMSs and monitoring the persistent effects of soil compaction caused by heavy machinery in the mining area. Furthermore, we recommend a new method combining 3D visualization techniques and hydraulic analysis in the study of compacted soils, and the establishment of soil restoration measurements to avoid further compaction in mining areas.

In this paper we discuss the use of a series of column experiments to improve understanding of the effect irrigation water chemistry (saline solutions) has on measurements of saturated hydraulic conductivity (Ksat) of a sodic clay soil. We highlight in particular the use of extended leaching periods to determine whether the duration of leaching affects the results. In the experiments, mixed cation solutions of two different salinity levels, 50 meq/L and 100 meq/L, were applied under constant head to columns of a repacked sodic clay soil using three replicates for each treatment. The maximum Ksat measured during leaching with the 100 meq/L solution was approximately double the maximum Ksat measured during leaching with the 50 meq/L solution. Measured flow rates were found to increase rapidly after flow commenced then decrease gradually until flow rates became stable. The final, stable flow rate was roughly 80% less than the maximum flow rate measured. Reasons for these changes in saturated hydraulic conductivity are discussed. The key finding from these experiments is that long term leaching, involving significantly more pore volumes than is commonly reported in the literature, is required to obtain a ‘stable’ Ksat. We recommend that further studies be carried out to (1) determine whether similar behaviour in Ksat occurs in a wide range of sodic clay soils and (2) to help build a better understanding of the causes and implications of the observed behaviour in Ksat.