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[Display omitted] • The mixed planting of shrubs and grasses improved soil properties and permeability within 10 years. • Mechanized agricultural reclamation faced challenges like high bulk density and low permeability. • Soil pore conditions mainly controlled soil permeability in mining areas. The impacts of various reclaimed mine land use patterns on the soil properties and infiltration capacity of mine areas remain incompletely understood. This study was conducted in the northern Loess Plateau to assess the effects of reclamation patterns, specifically vegetation (shrub grassland planted for 3, 6, and 10 years) and agricultural reclamation (mechanized and non-mechanized farmland, both cultivated for 10 years), on the soil properties and permeability of an open-pit coal mine. Original grassland (OG) and farmland (OF) were used as controls. The results show that after 6 years of vegetation reclamation, the soil bulk density (BD, 1.38 g·cm−3), total porosity (TP, 47.88 %), and infiltration rates approached levels similar to those of the OG. After 10 years, the organic matter content (SOM, 8.37 g·kg−1) and average weight diameter (MWD, 0.82 mm) were restored almost to those of the OG. In comparison, after 10 years of agricultural reclamation, SOM (9.22–9.38 g·kg−1) approached the level of the OF. However, compared with the OF, the BD and MWD of mechanized farmland increased significantly by 17.37 % and 154.96 % (P < 0.05), respectively, and the infiltration rates of mechanized and non-mechanized farmland decreased significantly (P < 0.05). Soil porosity was the most important factor affecting soil permeability, accounting for 65.9 % of change in permeability. In conclusion, vegetation reclamation, particularly mixed shrub and grass, led to more pronounced improvements in soil properties and permeability in mining areas compared with agricultural reclamation over a period of 10 years. However, heavy agricultural machinery has a detrimental effect on the soil properties and infiltration capacity of mining areas and should be carefully monitored. [ABSTRACT FROM AUTHOR]

• Natural grasslands improve soil infiltration capacity in both plant and bare patches. • Patchy mosaic patterns make infiltration heterogeneity and redistribute water on slope scale. • Plant with tap root systems produce more effective macropores as preferential flow paths. • Fine roots have a significantly negative effect on the soil infiltration capacity. Soil infiltration capacity is an important factor affecting soil moisture, and is of great significance to plant growth and groundwater recharge in arid and semiarid areas. Patchiness of grasslands widely exist and have a crucial effect on hydrological processes in water-limited regions. This study investigated soil infiltrability under natural grasslands with patchy mosaic patterns based on a series of in-situ tests. Two dominated natural restoration vegetation communities (Bothriochloa ischaemum (B. ischaemum) with fibrous root systems and Artemisia gmelinii (A. gmelinii) with tap root systems) and abandoned land (as control) were selected in the loess hilly and gully region of the Loess Plateau, China. The results showed that natural restoration grasslands significantly improved soil infiltrability in both plant and bare patches, and the emergence of patchy mosaic patterns can result in infiltration heterogeneity to redistribute water on a hillslope scale. Compared to B. ischaemum , A. gmelinii are more likely to facilitate the formation of preferential flow, contributing to the increased soil infiltration rates. The initial, steady and average infiltration rates (IIR , SIR , and AIR , respectively) and soil infiltration capacity index (SIC) were all negatively correlated with both root length density (RLD) and root surface area density (RSAD) of fine roots (diameter < 2 mm) but positively correlated with those of coarse roots (diameter ≥ 2 mm). The main factors influencing the infiltration capacity were the mean weight diameter in the 10−20 cm layer and the RSAD of the fine roots in the 0−20 cm layer, which can explain 98.6 %, 81.7 %, 63.9 %, and 91.3 % of the total variance of IIR , SIR , AIR , and SIC , respectively. This work highlights the important roles of patchy mosaic patterns in affecting soil water redistribution and the stabilization of ecological systems, providing a scientific basis for vegetation selection in the process of vegetation restoration in water-limited regions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Vegetation restoration decreased deep soil water storage in the Loess Plateau. • Revegetation increased steady infiltration but reduced initial and mean rates. • Soil infiltration rates exhibited gradual decline trends along the slope. • The effect of vegetation type on infiltration was higher than slope position. • Soil water and clay content were key factors influencing infiltration rates. Vegetation restoration effectively mitigates soil erosion and improves soil properties, but in drylands, it can lead to soil water scarcity and disrupt ecological balance. Until now, limited research has examined the combined effects of vegetation restoration type and topography on soil water and infiltration in the Loess Plateau of China. Here, we investigated soil water content (SWC), soil water storage (SWS), soil infiltration rates and related soil properties in typical forestland, shrubland, and grassland across five slope positions on steep slopes, and compared them with cropland. The results indicated that vegetation restoration significantly decreased SWS compared to cropland. Across the entire 0–500 cm depth, reductions were observed at 30.9 %, 33.2 %, and 20.8 % for forestland, shrubland, and grassland, respectively, with forestland and shrubland demonstrating a more pronounced decrease, particularly in deeper soil layers. Shrubland had the lowest SWS on the upper, middle, and top slopes, while forestland showed the lowest SWS on the lower and foot slopes. In terms of infiltration, vegetation restoration generally increased steady infiltration rate but resulted in reduced initial and mean infiltration rates (except for shrubland). Shrubland had the highest infiltration rates, followed by forestland, while grassland had the lowest rates. Soil infiltration rates decreased gradually along the slope, indicating that the impact of vegetation restoration on soil infiltration improvement weakened with lower slope positions. Vegetation restoration type had a stronger direct and total effects on infiltration than slope position. Yet, the indirect influence of slope position through clay content and SWC outweighed that of vegetation restoration type. Our findings highlight the comprehensive assessment of the eco-hydrological effects of vegetation restoration is essential for identifying suitable species and designing optimal spatial distribution, ultimately maximizing the ecological benefits of the restoration. These insights can offer valuable guidance for ecological restoration and land management in fragile dryland ecosystems. [ABSTRACT FROM AUTHOR]

• Subsurface lateral flow often occurs at 10–40 cm depths along the hillslope. • Wet soil conditions are conducive to triggering hillslope lateral flow. • Variability of infiltration partitioning remains high in the deeper layers. • Dominant factors controlling PWSI are sand (0–10 cm), EL (10–40 cm), and n (40–80 cm). Infiltration is the process of water entering into, and routings through, the subsurface. It has a profound impact on hillslope and catchment runoff. However, because of the hidden and complex subsurface structures, our understanding of rainfall-related infiltration and how it partitions along a topographic gradient remains challenging. In this study, we used two years of field observations of volumetric soil moisture at 25 combinations of topographic positions and soil depths along a steep subtropical forested hillslope. The lateral partition patterns of infiltration and its control factors were investigated based on a new index, percentage of soil water storage increment at each site to all hillslope sites during a rainfall event (PWSI). Our results showed that the active soil layer involved in hillslope lateral flow was distributed within the depths of 10–40 cm. In deep soil depths (i.e., 40–80 cm), lateral flow was more evident under wet initial moisture conditions than under dry initial moisture conditions, whereas rainfall characteristics had a relatively weak effect on it. Unexpectedly, we found the variability of infiltration partitioning remained high in the deeper soil layers. Among the soil properties, sand, bulk density, n , K S , and SOM were conducive to infiltration, whereas clay had the opposite effect. The dominant factors controlling the lateral partition patterns of infiltration across soil depths were sand in the depths of 0–10 cm, topographic gradient in depths of 10–40 cm, and n (parameter of soil retention curve) in the depths of 40–80 cm. Findings of this study reveal the infiltration partitioning indices were useful to quantitatively describe the distribution patterns of infiltration after rainfall events at the hillslope, and provide new insights into the detection of hillslope lateral flow, which is valuable for understanding subsurface hydrological processes and improving water resource management in humid mountain ecosystems. [ABSTRACT FROM AUTHOR]

• Establishment of plantation forest reduced the surface soil infiltrability but enhanced the water retention capacity (20–30 cm). • Low initial water content was conducive to increase soil water content after infiltration. • Visualization of gravels and roots spatial distribution at the soil plot scale. • Gravels with better connectivity were more conducive to water infiltration. • Preferential flow was the main infiltration type in reforested areas. Plantation forests (PF) and natural secondary forests (NSF) are the primary reforestation approaches. The establishment of PF can affect forest hydrological processes by changing soil structure. To date, few studies have focused on these changes and the effects on hydrological processes for the paleo-periglacial landform. To reveal reforestation approaches effects on water infiltration, including soil water infiltration capacity, retention capacity, and waterflow path pattern, we conducted field dye-tracer investigations with rainfall and laboratory infiltration experiments for the paleo-periglacial landform of eastern Liaoning mountains, China. The results showed that (1) Soil physical properties (including total porosity (TP), capillary porosity (CP), non-capillary porosity (NCP), initial soil water content (IWC), field water capacity (FWC)) and root abundance (RA) decreased with soil depth in both PF and NSF, while the soil bulk density (BD) and distribution of gravel content showed opposite changes. (2) Establishment of PF reduced the infiltration capacity and water retention capacity in the 0–20 cm layer, but enhanced the water retention capacity in 20–30 cm layer. Low IWC was conducive to increase soil water content (SWC) after infiltration. (3) Infiltration capacity parameters (including saturated hydraulic conductivity (Ks), SWC , difference between SWC and IWC (SWC–IWC), dye coverage ratio (DC)) were significantly correlated with BD , TP , CP , NCP , FWC , and fine roots RA (P < 0.05). Better connectivity gravels were more conducive to water infiltration. (4) Preferential flow was the main infiltration type, but with different waterflow paths pattern, with the 'funnel', 'finger' shape for PF, NSF, respectively. Increasing infiltration could increase flow path connectivity. Our findings show that soil physical properties, roots, and gravel occurrence affected soil infiltration, and different reforestation approaches had varying impacts on soil infiltration, water redistribution, transportation, and storage of surface and groundwater, improving the understanding of ecohydrological processes and effects of water resources management in forest ecosystems of paleo-periglacial landform. [ABSTRACT FROM AUTHOR]

[Display omitted] • Slope had the most significant negative effect on soil infiltration rates. • The effect of different vegetation on soil infiltration rates was significantly different. • Soil organic carbon content increases in average infiltration rates reached 47.70 %. • Non-capillary porosity increases in average infiltration rates reached 31.00 %. High Mountain Asia (HMA) surrounding the Tibetan Plateau (TP) is a critical gathering place for water resources. Investigating soil water infiltration properties in HMA is a vital component of comprehending the hydrological cycle processes in this region. Despite some experimental studies having analyzed the soil water infiltration properties under specific conditions in HMA, a systematic quantitative anlysis of this region's soil water infiltration properties remains lacking. To investigate the effect of soil water infiltration properties under different factors in HMA, we conducted a literature review and meta-analysis based on experimental data from the literature. Our study employed the initial infiltration rate (IIR), steady infiltration rate (SIR), and average infiltration rate (AIR) as response variables to quantify the variations in soil water infiltration properties under diverse conditions. Results revealed that (1) the most significant negative effect on soil water infiltration rates was due to slope (IIR: −48.31 %, SIR: −36.87 %, AIR: −51.81 %). The subgroup analysis indicated that the negative effect of slope on the three infiltration rates was more pronounced as the slope gradient increased. (2) The positive and negative effects of different vegetation types on soil water infiltration rates were significantly different. Among them, the trees + shrub group exhibited the most prominent positive effect on IIR and SIR (IIR: +206.49 %, SIR: +153.45 %). Conversely, the widely distributed alpine meadow in HMA had a significant negative effect on IIR (−39.35 %). (3) Contrary to conventional soil infiltration experiments, the increase of initial soil moisture (SM) in HMA had a positive effect on IIR and AIR (IIR: +13.88 %, AIR: +23.37 %). Considering the study of macropore flow, this may be related to soil texture and vegetation growth. (4) As the values of each soil physicochemical property increased, there was a significant positive effect of increasing non-capillary porosity (NCP) and soil organic carbon content (SOC) on AIR (NCP: +31.00 %, SOC: +47.70 %). At the same time, we found that soil water infiltration studies in HMA are subject to spatial and quantitative limitations. Considering the importance of soil water infiltration in HMA, we recommend more comprehensive studies of soil water infiltration in HMA. Such studies would provide a vital theoretical foundation for enhancing the HMA soil infiltration model and improving the terrestrial hydrological cycle process in the region. [ABSTRACT FROM AUTHOR]

• Shrub encroachment and severe degradation reduced Cyperaceae coverage and root biomass. • Shrub encroachment and severe degradation significantly increased soil non-capillary porosity. • Reduction of Cyperaceae spp. and increase of non-capillary porosity increased infiltration rate. • The two divergent successions both increased cumulative infiltration and evapotranspiration. • Short-term grazing exclusion presented little effect on soil infiltration rate. Alpine meadow ecosystem are undergoing the divergent successions under the influence of global climate warming and overgrazing by herbivores, which may profoundly impact the ecohydrology function of alpine meadow ecosystem. However, few studies reported the effects of the divergent successions on ecohydrological process of alpine meadow. Here, we report an in situ experiment to examine the effects of the divergent successions on soil pore structure, infiltration rate and evapotranspiration of the two types of divergent-succession meadows (the shrub-encroached meadow and the severely degraded meadow), compared to the normal alpine meadow. Results showed that both the shrub-encroached meadow and the severely degraded meadow significantly reduced the dominant Kobresia spp. (Cyperaceae family) coverage, soil compactness, and belowground biomass, but significantly increased soil non-capillary porosity (P < 0.05) compared to the normal alpine meadow. Soil infiltration rate was significantly negatively correlated with Kobresia spp. coverage, soil compactness and belowground biomass, while significantly positively correlated with soil non-capillary porosity (P < 0.05). Therefore, the shrub-encroached meadow and the severely degraded meadow increased soil infiltration rates not only by reducing the dominated Kobresia spp. (Cyperaceae family) coverage and belowground biomass, but also by increasing soil non-capillary porosity. Compared with the normal alpine meadow, the cumulative infiltration and evapotranspiration increased by 245.25% and 45.19% in the shrub-encroached meadows, and increased by 208.23% and 29.95% in the severely degraded meadow. However, short-term grazing exclusion presented little effect on soil infiltration rate in alpine meadows. Overall, the divergent successions of alpine meadows had a greater impact on soil water replenishment and evapotranspiration than the short-term grazing exclusion. These findings can help to better understand the impacts of the divergent community succession on the ecohydrological process in alpine grassland ecosystem. [ABSTRACT FROM AUTHOR]

Abstract Estimation of soil sorptivity (S) and hydraulic conductivity (K) is fundamental to model the water infiltration into the soil. This process can be affected by soil water repellency, which is defined as a reduction in soil wettability due to coating of soil particles by hydrophobic substances. Unlike to wettable soils, this phenomenon can generate infiltration curves with double-slope shape: a transient infiltration curve followed by a steady-state section. Because the topsoil final volumetric water content (θ 1) of the transient phase of the double-slope curve is not a measurable data, in principle, the standard model based on the Haverkamp et al. (1994) model cannot be used to estimate S and K. This work presents two different approaches based on the Haverkamp et al. (1994) equation, which allow estimating S and K from the first phase of a double-slope infiltration curve, when θ 1 data are not available. The methods, which are based on the analysis of both short-medium time transient infiltration curve (Tr) and the combination of both short-medium transient and steady-state infiltration steps (Mx), were applied on 20 soils affected by different degrees of water repellency. The Haverkamp et al. (1994) model was also valid for infiltration curves measured on hydrophobic soils, and the final volumetric water content was not an essential data to estimate K and S. Although the steady-state infiltration rate (q 1) calculated with Mx was about 26% larger than that estimated with Tr , comparable K and S values were obtained with both methods. Overall, a large dispersion on the estimate of θ 1 was observed with both methods. The gravimetric time, t grav , estimated in the studied soils was low, <500 s. While the Mx method required simpler numerical calculus, Tr looked like to be more robust and less subjective. Highlights • This work analyzes the first part of a bi-slope infiltration curve affected by SWR. • A first method (Tr) estimates K and S from the transient infiltration curve. • The second one (Mx) combines short-transient and steady-state infiltration analysis. • The methods were applied on 20 soils affected by SWR. • Mx requires less numerical calculus, but Tr was more robust and less subjective. [ABSTRACT FROM AUTHOR]

Abstract In the Alberta oil sands, many soils available for reclamation contain portions of oil sand referred to as aggregated oil sand material (AOSM). The objective of this study was to determine the infiltration rates of soils and AOSM from various salvage depths and with various concentrations of interstitial petroleum hydrocarbons (PHCs). The water infiltration rates of AOSM and surrounding soil were determined using a miniaturized infiltrometer, revealing that the soil allows significantly (P < 0.05) greater infiltration than the AOSM. Furthermore, highly-weathered AOSM which originate from the near-surface, exhibit significantly lower PHC contents and greater infiltration rates than medium- and low-weathered AOSM, which are found at depth. The infiltration of 95% ethanol indicates water repellency (WR) is present in both the AOSM and surrounding soil; however, the ethanol results also suggest that the reduced water infiltration rates of AOSM in comparison to the soil, are primarily due to structural differences such as reductions in total porosity and pore connectivity resulting from interstitial PHCs. The diminished infiltration of water into AOSM indicates the ability to slow the downward flow of water and increase the residence time of water in overlying coarse-textured soils, potentially altering the soil water regime and associated ecosite. Highlights • Infiltration rates of coarse-textured materials reduced by interstitial hydrocarbons. • Infiltration rates of coarse-textured materials decrease with increasing hydrocarbons. • Infiltration rates of oil sand increase with increasing extent of weathering. • Infiltration rates of oil sand decrease with increasing depth into the soil profile. [ABSTRACT FROM AUTHOR]

• Grassland had the highest soil infiltration capacity among the land use types with vegetation. • Soil infiltration capacity of anti-dip slope was significantly higher than that of dip slope. • The bedrock strata dip could be treated as an indicator of infiltration properties. • The common experience model was the most suitable for describing the soil infiltration characteristics. The dip of bedrock has a great influence on the infiltration of water into soil, and can control the spatial distribution of rainwater in fragile karst rocky desertification regions. Thus, it is necessary to scientifically assess the soil infiltration capacity of dip and anti-dip slopes in karst trough valleys. In this study, we comprehensively evaluated the soil infiltration capacity of dip and anti-dip slopes under different land use types using the cutting ring infiltration method. The results showed the following. i) Compared with the anti-dip slope, the dip slope had a higher bulk density, noncapillary porosity and pH and a lower soil water content, capillary porosity and soil organic carbon content (p < 0.05). In addition, the soil infiltration capacity of grassland was the highest among the studied land use types except for abandoned land. ii) Both the bulk density and the total soil porosity could be treated as indicators of the infiltration properties of dip and anti-dip slopes.iii) Based on the coefficient of determination, R2 , the common experience model was the most suitable for describing the characteristics of the soil infiltration rate. iv) Based on the principal component equation, the soil infiltration capacity and organic matter of the grassland on dip slopes and anti-dip slopes were higher than those of other land use types with vegetation, but not higher than those of abandoned land without vegetation. The results of this study provide a reference for the selection of the restoration method and the assessment of the soil infiltration capacity of dip and anti-dip slopes in karst trough valleys and other karst landforms with the same geological background. [ABSTRACT FROM AUTHOR]

• Combined measures were used to regulate rainwater in Pisha Sandstone areas. • Infiltration holes promoted deep rainfall infiltration into the weathered bedrock. • Infiltration holes with mulching improved the weathered bedrock soil water storage. • Fish-scale pits with grass mulching and infiltration holes was the most effective. Effectively regulating slope runoff and infiltrating maximum rainwater are essential to reduce soil and water loss, and promote vegetation restoration in the Pisha Sandstone areas of China, which are semiarid areas with shallow buried bedrock. However, the effects of individual or combined rainwater regulation measures, such as infiltration holes, mulch, and fish-scale pits (a semicircle-shaped pit), on soil water infiltration and restoration in such regions have not yet been fully explored. In this study, the responses of soil water to rainfall in the 0–1.6 m soil layer was investigated through in situ monitoring during the two main rainy seasons under four rainwater regulation treatments in the Pisha Sandstone area of China covered in thin soil layer (0–0.3 m): fish-scale pits with grass mulching and infiltration holes (PGH), fish-scale pits with grass mulching (PG), fish-scale pits without mulching (P), and slope land (control, CK). The results have shown that because of the relatively low permeability (0.08–0.17 m d−1) of Pisha Sandstone, individual torrential rainfall events (63.2 mm) increased the soil water only in the 0–0.3 m layer after 3 days under the CK, P, and PG treatments. However, the PGH treatment simultaneously and significantly increased the soil water in the 0–0.3 m and 0.7–0.8 m layers. Compared with the CK treatment, rainwater replenishment depths under the P, PG, and PGH treatments increased from approximately 0.4 m to 0.9 m, 1.0 m, and 1.1 m, respectively, and the average soil water storage increased by 27 mm, 34 mm, and 50 mm, respectively, in the 0–1.6 m soil layer. Moreover, the PGH treatment enhanced rainwater storage in deep soil (0.6–0.9 m), which decreased the potential for water loss by evaporation. We concluded that the PGH treatment was effective in increasing soil water storage and reducing soil erosion in areas with shallow buried bedrock. [ABSTRACT FROM AUTHOR]

• Couples time-lapse ERT and GPR with probing sensors to monitor a lab scale soil infiltration test. • Calibrated petrophysical relationships enable a more precise characterization of water content dynamics. • Reveals impacts of short-term transient hydrological process on joint surface geophysical survey. • Observed changes in soil electrical resistivity/ dielectric constant are converted to changes in infiltration rate. • Constructs an unsaturated flow model to describe the subsurface infiltration process. This paper presents an integrated geophysical method to characterize the vadose zone by conducting lab-scale infiltration experiments, during which time-lapse electrical resistivity tomography (ERT) sections and ground penetrating radar (GPR) profiles were simultaneously and continuously captured together with soil moisture and temperature probing devices installed at various depths. Time series water content data obtained from the moisture sensors, coupled with discreetly calibrated petrophysical relationships and time-lapse datasets from ERT and GPR, were combined to monitor the spatial–temporal evolution of soil water content during wetting and drying and to track the downward progression of wetting front. Reduction in electrical resistivity as well as increment in dielectric constant were converted to rising soil moisture, and then further scaled into cumulative infiltration through integration with corresponding wetting depth as observed through the experiment. Robust estimates regarding controlling vadose zone parameters such as infiltration rate and hydraulic conductivity were subsequently achieved by fitting the results from complementary investigations with an unsaturated infiltration model. With calibrated saturated hydraulic conductivity fitted well with reported and experimentally derived ranges, it's suggested that the model is capable of reflecting average changes in infiltration rate at the lab scale. However, the model intrinsically lacks the ability to provide spatial variations of hydraulic parameters, thereby further investigation is essential to establish a suitable model for characterizing the more complex vadose zone at field scale. [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSCs) are widespread in abandoned farmlands over the Loess Plateau after the “Grain for Green” project was implemented in 1999. However, few studies have been carried out to quantify the effects of BSCs on temporal variations of soil infiltration properties. This study was conducted to investigate the effects of two typical BSC (moss and cyanobacteria) on the temporal variations of soil infiltration properties reflected by soil sorptivities under different pressures of 0 ( S 0 ) and − 3 ( S 3 ) cm, saturated hydraulic conductivity ( K s ), and wetting front depth ( WFD ) on the Loess Plateau. Two BSC-covered sites and one bare soil site (as control) were selected to measure soil infiltration properties using a disc infiltrometer under two consecutive pressure heads of 0 and − 3 cm, and then the S 0 , S 3 , and K s were calculated. The WFD was measured quickly by a ruler after the measurement of soil infiltration. The experiments started from May 9 to October 8, 2015 for 7 times at approximately 3 weeks interval. Soil physicochemical properties and BSC thickness were also measured to explain the temporal variations of soil infiltration properties. The results showed that the thickness of moss and cyanobacteria crusts increased continually during the experimental period. BSC affected top-soil (0–5 cm) properties (soil water content, bulk density, texture, and organic matter content) significantly, and the effects of moss were greater than those of cyanobacteria. BSC was effective to impede soil infiltration. Compared to the control, the mean S 0 , S 3 , K s , and WFD of moss-covered soil reduced by 31.4%, 25.2%, 39.0%, and 22.7%. While, S 0 , S 3 , K s , and WFD of cyanobacteria-covered soil declined by 21.5%, 18.2%, 29.3%, and 11.9%, respectively. The temporal variations in infiltration properties of both moss- and cyanobacteria-covered soils were similar. S 0 , S 3 , K s , and WFD generally decreased over time. However, the related infiltration properties of bare soil fluctuated over time with no distinguish trend. The temporal variations in infiltration properties were closely related to the seasonal variations in BSC thickness and soil water content. [ABSTRACT FROM AUTHOR]

• Reseeded plants differently affecting soil water infiltration in a desert steppe. • Infiltration of grass higher than legume due to its optimized soil properties. • Infiltration of monocultures higher than mixtures due to optimized root traits. • Both soil properties and root traits determined by the volumes of fine roots. Infiltration of precipitation is the main source of water for soil water replenishment in arid and semiarid regions and plays a critical role in influencing the restoration of degraded grassland. However, the effects of reseeded vegetation on soil infiltration in grasslands remains unclear. Here, we measured soil infiltration rate (IR), root characteristics, and soil properties for four plant treatments (Agropyron mongolicum , Lespedeza potaninii , A. mongolicum × L. potaninii (1:1), and A. mongolicum × Astragalus melilotoides (1:1)) five years after reseeding and enclosure in degraded desert steppe, and continuously grazed steppe used as a control. Results showed that the IR among treatments presented as A. mongolicum > L. potaninii > A. mongolicum × A. melilotoides > A. mongolicum × L. potaninii > the grazed steppe. Correlation analysis indicated that root length density, root surface area, root volume, soil organic matter, non-capillary porosity, capillary porosity, and total porosity were positively correlated with initial, steady, and average IR (p < 0.05, or 0.01), yet root biomass and soil bulk density did not significantly influence IR (p > 0.05). The study also indicated that the higher IR of A. mongolicum was associated with higher soil organic matter and soil porosities at soil depths of 0–40 cm than in L. potaninii plots. Whereas, the higher IR of monocultures was associated with higher values of root length density, root surface area, and root volume at soil depths of 0–30 cm than mixtures. However, both root morphological characteristics and soil properties were significantly determined by the volumes of fine roots (diameter ≤ 2 mm). Therefore, in this study, the fine root volume played a crucial role in regulating soil infiltration via determining root morphological characteristics and forming soil pores and pathways. [ABSTRACT FROM AUTHOR]

Loess slopes are widely distributed throughout the northwestern region of China and are prone to slope failure in response to heavy rainfall. We undertook three groups of flume experiments in the laboratory to study loess slope dynamics under artificial rainfall conditions. Additionally, a laser scanner was used to observe loess landslide deformation characteristics and failure development. A numerical analysis of unsaturated seepage in loess slopes because of rainfall infiltration was performed. Moisture content, pore-water pressure, and slope deformation were monitored to quantify the relationship between rainfall infiltration and loess slope stability. Movement of the wetting front near the slope surface was triggered by rainfall and related to rainfall intensity and duration, which is consistent with the numerical solution. Rainfall infiltration increased pore-water pressure, producing gravity-driven landslides. We observed that landslide development began with local failure in the toe slope that gradually retreated toward the crown, forming a multi-sliding displacement, and eventually resulting in total slope failure. [ABSTRACT FROM AUTHOR]

The soils above caves represent a membrane that regulates the connection between the underground environment and the outside atmosphere. In this study, soils from two different field sites (Cueva de Altamira and Cueva del Rull in Spain) are investigated. Field results are analysed and linked to laboratory tests. Several laboratory experiments are performed to quantify CO 2 diffusion coefficients and water infiltration rates in these soils under different degrees of soil water saturation and compaction. Tests confirm that the grain size distribution, organic matter content, mineral composition and water content of soils affect gas transport through the soil pore network. Both field and lab results reveal that Altamira soil has a coarser texture and therefore has higher CO 2 diffusion coefficients, infiltration rates and hydraulic conductivity values than Rull soil. Rull soil contains a higher proportion of fine particles and organic matter, which explains the lower fluid transport coefficients. When soils are near saturation, fluid transport does not depend on the physical properties of soil but depends on the soil water content. In this state, liquid transport regulates the available space within the soil pores, which leads to a reduction in the gaseous diffusion coefficient of the soil. After rainfall episodes, the connection between the exterior atmosphere and underground cavities is hindered due to a rise in the soil water content, which is responsible for the closure of the overlying membrane. This study demonstrates that soil-produced CO 2 reaches the underground atmosphere through diffusion processes that are controlled by the intrinsic properties of soil (porosity, grain size distribution, texture, mineralogy and organic matter content) and soil water content. [ABSTRACT FROM AUTHOR]

• Vegetation restoration enhances soil infiltrability and preferential flow. • Soil moisture and total porosity are the dominant factors affecting soil infiltrability. • Macroporosity plays a major role in influencing the degree of preferential flow. Soil infiltration plays a critical role in soil hydrological processes. Land use/cover changes are generally considered to influence soil infiltration. However, the effect of long-term vegetation restoration on the soil infiltration capacity and infiltration pattern is poorly understood. In the present study, we analyzed the infiltration capacity with a double ring infiltrometer and detected the degree of preferential flow using a dye tracer in a typical loess hilly gully catchment of China. Additionally, we identified the relationships between soil characteristics and infiltration capacity and preferential flow. The results showed that (1) converting cropland to forest, shrubland and grassland generally enhanced the soil infiltration capacity. Compared with cropland, the steady-state infiltration rate (SIR) and saturated hydraulic conductivity (K s) increased by 135 % and 155 % in shrubland, by 76 % and 91 % in forest, and by 22 % and 23 % in grassland. (2) Land use changes markedly increased the degree of preferential flow, following the order of shrubland > forest > grassland > cropland. (3) The decline in soil moisture (SM) and bulk density (BD) and the increase in total porosity (TP), macroporosity (MP) and soil organic matter (SOM) could cause higher infiltration capacity and preferential flow. SM and TP were the dominant factors affecting soil infiltrability, while MP was the greatest contributor to variations in preferential flow. Our findings demonstrated that vegetation restoration had a positive impact on soil infiltrability and preferential flow. This effect should be considered when assessing the influence of vegetation restoration on water resources in the Loess Plateau and other arid and semiarid regions. [ABSTRACT FROM AUTHOR]

• Soil infiltration and water flow paths were quantified in subtropical forest types; • Soil water infiltrability rate increased with forest succession; • The degree of soil preferential flow did not evolve along succession sequence; • Soil porosity, root systems and rocks jointly affect soil water flow patterns. Maintaining and improving the water conservation capacity of forest ecosystems is an important step in building regional ecological protection barrier. At present, there is a lack of knowledge about the patterns of soil water flow in different stages of forest succession. Therefore, this study quantified the change tendency of soil infiltration and water flow paths in subtropical different forest types, including pine forests (PF), mixed pine and broadleaf forests (MF) and monsoon evergreen broadleaf forests (BF), and analysed the effect of soil physical properties on hydraulic properties. Results showed that (1) both BF and MF were characterized by a smaller bulk density and the larger porosity than PF. (2) The saturated hydraulic conductivity of BF and MF was 2.1 times and 3.1 times higher than that of PF, respectively, showing that there were clear differences in the soil infiltrability resistance of the different forest types. The observed soil water exchange amount also showed that both BF and MF had higher water holding capacity than PF. (3) Macropore flow and lateral flow were the dominant preferential flow behaviors, but the degree of preferential flow did not evolve along succession sequence PF, MF and BF. The pattern of soil water flow was found to show obvious spatial variability, restricted by the joint influence of soil porosity, root systems and rocks. The above results suggest that soil infiltration improve with the sequence of forest succession, but that soil water flow patterns may be independent of forest succession due to the complex conditions of the soil. This study provided effective data information of forest soil hydrological antecedents. [ABSTRACT FROM AUTHOR]

• Soil infiltrability was differentially regulated by soil texture and plant roots. • The variations in regional soil infiltrability were more explained by soil texture. • Various root-soil combinations differentially affected regional soil infiltrability. • Soil texture had the strongest total effect on soil infiltrability on a reginal scale. Soil infiltrability controls precipitation input to soil and plays a crucial role in regulating soil eco-hydrological processes and ecosystem production in water-limited areas worldwide. The effects of root traits on soil infiltrability have been widely investigated at individual sites, but root-soil interactions and their effects on soil water infiltration over large spatial scales remain poorly understood. This study aimed to identify the unique characteristics of soil infiltration processes and different contributions of soil texture and root morphological traits to soil infiltrability. For this purpose, 153 plots of natural revegetated land with two contrasting plant species (Artemisia gmelinii Web. with tap root systems and Stipa bungeana Trin. with fibrous root systems) and bare land were selected in three regions along a texture gradient in the Loess Plateau of China. The results showed a distinct spatial variability of soil infiltration rates across the three regions with soil texture explaining the variability more strongly than plant species at several infiltration stages. Rooted soils had higher infiltration rates than bare soils, with nonsignificant inter-species difference under three soil texture types. Furthermore, soil texture and root morphological traits explained 92.03% and 74.75% of the total variance of soil properties (soil organic matter, aggregate stability, and soil porosity), and their interaction effects (73.09%), accounted for a considerable proportion. These findings suggest that soil texture and root morphological traits indirectly affect soil infiltrability by modulating soil properties, with soil texture having a higher contribution. In addition, the effects of root morphological traits on soil infiltrability were found to be dependent of soil texture on the regional scale. Therefore, the effects of soil texture and root-soil interaction deserves further attention in assessing soil hydrological processes on large spatial scales in the future. [ABSTRACT FROM AUTHOR]

• Thermal effects on soil hydraulic and mechanical properties were investigated. • An increasing temperature decreased the soil Ψ in the middle stage of SWRC. • The soil cohesion increased as the power function with increasing soil Ψ. • The soil friction angle increased as the linear function with increasing soil Ψ. • The increase in soil temperature decreased soil matric suction and shear strength. The soil hydrologic and mechanical properties play an important role in the slope stability in the red soil hilly region of southern China. In this study, the red soil layers in a collapsing gully wall were used to investigate the effects of temperature on the soil water retention curve (SWRC) and shear strength. The results showed that the SWRCs of the red soil under different temperatures could be accurately described by the van Genuchten (VG) model (R 2 > 0.95, root mean square error (RMSE) < 0.024). An increasing temperature significantly decreased the soil water holding capacity (WHC), especially in the intermediate range of the SWRCs of the red soil. The soil saturated hydraulic conductivity (Ks) increased linearly with temperature. The soil cohesion and soil friction angle decreased by approximately 44.13% and 30.40% respectively when the soil water content increased from 0.24 cm3 cm−3 to 0.42 cm3 cm−3. The mean soil cohesion and soil friction angle decreased approximately 8.56 kPa and 1.34° respectively when the soil temperature increased from 25 °C to 40 °C. Regression analysis showed that the soil cohesion increased as the power function with increasing matric suction (0–2000 kPa), and friction angle increased as the linear function with increasing matric suction. These results illustrated that an increase in temperature will decrease soil matric suction and shear strength but enhance the soil infiltration rate under certain soil moisture levels. Therefore, the stability of a collapsing gully wall will sharply decrease under the conditions of high temperature and heavy rain in summer. [ABSTRACT FROM AUTHOR]

• A method measured soil matrix infiltration (SMI) by double-ring was improved. • The SMI of eucalyptus plantations decreased with increasing forest age. • Soil properties changing with forest age inhibited SMI in eucalyptus plantations. • Soil texture dominates the SMI of differently aged eucalyptus plantations. In this study, we improved the method for measuring soil matrix infiltration by using a surface-positioned double-ring infiltrometer. The soil matrix infiltration processes of four differently aged (1, 3, 5, and 7 years) eucalyptus plantations were measured in situ in a southern subtropical area in China. Soil matrix infiltration characteristics (SMICs), including initial infiltration rate (IIR), stable infiltration rate (SIR), and cumulative infiltration (CI), were calculated using the experimental data of the soil matrix infiltration process. The physical and chemical properties of layered soil (0–60 cm with an interval of 20 cm), including soil textures, buck density (BD), soil organic matter (SOM), and soil water stable macroaggregate (WSMA) closely related to infiltration, were analyzed. Results showed that the IIR (140.33–233.14 mm h−1), SIR (116.24–194.04 mm h−1), and CI (118.42–217.20 mm) decreased with increasing forest age. In addition, the SIR and CI of the 1-year-old eucalyptus plantation were significantly higher than those of the other plantations. The decrease trend of SMICs with forest age was attributed to the soil properties changing in the eucalyptus plantations. The clay content, BD, SOM, and WSMA increased and sand content decreased with increasing forest age, thus inhibiting the SMICs. The results of stepwise regression analysis showed that the sand content of topsoil (0–20 cm) was the main factor affecting IIR, and the clay content of deep subsoil (40–60 cm) was the dominant factor affecting SIR and CI. The in situ soil matrix infiltration measurement in eucalyptus plantations was achieved with the improved method, and the main influencing factors were clarified. The results enhance understanding of soil matrix infiltration and its effect on precipitation redistribution and are helpful in quantifying the water storage capacity of plantation soil. [ABSTRACT FROM AUTHOR]

Aims Antecedent soil water content (ASWC) is an important factor affecting soil water infiltration, runoff and soil erosion on slopes but it is difficult to measure or forecast accurately and is not often reported in soil erosion databases. Methods Runoff plots (12 m × 5 m) were used to collect runoff and sediment during the rainy seasons between April 2010 and October 2013 on the Loess Plateau, China. The HYDRUS-1D model was calibrated and tested using the data collected from the plots. The relationships of ASWC with runoff and sediment yield were investigated using the model output values for ASWC. Results The model performance was satisfactory, with a mean Nash–Sutcliffe model efficiency coefficient of 0.411 and a root mean square error of 0.031 during the four study years. Runoff was directly affected by rainfall amount and rain intensity. Furthermore, runoff typically increased with ASWC. Conclusions HYDRUS-1D can provide temporal ASWC data that could be used for runoff prediction. [ABSTRACT FROM AUTHOR]

• Soil water in 0–1 m soil layer was unevenly distributed and varied by habitat. • Soil water content was lower on habitats with biocrusts than on bare areas. • Soil water content was higher on habitats with subshrub than on bare areas. • Biocrusts had little effect on plant biomass in well-watered habitats. • Soil water in 0–1 m soil layer affected by position of slope-gully system. The landscape position (LP) of slope-gully system (SGS) greatly influences the variations in soil water content, and development of biocrusts and vegetation. It is unclear the relationships between biocrusts, natural successional vegetation, and soil water content in the SGS with different LPs and habitats in semiarid regions. Therefore, this study aimed to clarify the relationships between moss-dominated biocrusts and natural successional A. sacrorum in the utilization of soil water; and investigate their spatial variation characteristics in a typical SGS. Soil water content in the 0–1 m soil layer, and biocrust and vegetation characteristics were measured at the summit, ridge slope, gully slope, and gully floor of an SGS in five habitats (i.e., bare areas (BA), moss-dominated biocrusts (BC), A. sacrorum (AS), A. sacrorum with biocrusts (ASB), and dead A. sacrorum with biocrusts (DASB)). The results showed that plant aboveground biomass and soil water content in the 0–1 m soil layer followed the pattern of DASB < ASB < AS and BC < DASBC≈ASB < BA ≤ AS for the summit, and ridge and gully slopes, respectively. While, those followed the pattern of DASB < ASB≈AS and BC < DASBC≈ASB≈BA≈AS for the gully floor, respectively. Compared to bare lands, soil water content and aboveground biomass were lower in habitats covered by biocrusts, which was likely related to reduced infiltration of biocrusts. This phenomenon was insignificant at the gully floor, which was attributed to the decreasing effect of biocrusts on soil water content with the improvement of water conditions. Soil water content of subshrub covered habitats were slightly higher than those of bare lands, which probably related to the reduced soil evaporation under shading conditions. This study showed that the relationships between biocrusts, subshrubs, and soil water were complex under natural succession conditions, and further observations are needed in the future in semiarid regions. [ABSTRACT FROM AUTHOR]

• ERT correlates well with FDR and helps reveal spatial subsurface heterogeneities. • Soil freezing depth in an undulating terrain varies with slope aspects. • Local terrain heterogeneities affect soil erosion initiating processes. The occurrence of freeze–thaw cycles modifies water infiltration processes and surface runoff generation. Related processes are complex and are not yet fully investigated at field scale. While local weather conditions and soil management practices are the most important factors in both runoff generation and surface erosion processes, local terrain heterogeneities may significantly influence soil erosion processes in catchments with undulating terrain. This paper presents a field-based investigation of spatial and temporal heterogeneities in subsurface soil moisture and soil temperature associated with freezing, thawing, and snowmelt infiltration. The field setup consists of a combination of traditional point measurements performed with frequency domain reflectometry (FDR) and electrical resistivity tomography (ERT). The transect was approximately 70 m long and spanned an entire depression with a north-facing slope (average slope of 11.5%) and a south-facing slope (average slope of 9.7%). The whole depression was entirely covered with stubble. Observed resistivity patterns correspond well to the measured soil moisture patterns. During the observation period, the north facing slope froze earlier and deeper compared with the south facing slope. Freeze–thaw cycles were less pronounced in the north-facing slope than in the south-facing slope. There were also differences in soil temperature and soil moisture patterns between lower and upper parts of the monitored depression. These indicate that initiation and development of runoff related processes, and consequently soil erosion, in regions with freeze–thaw cycles may differ significantly depending on local terrain characteristics. Consequently, it indicates that spatial terrain heterogeneities, especially slope aspects, may be important when studying soil erosion processes, water flow and nutrient leaching in lowlands where patchy snowpacks and dynamic freeze–thaw cycles are predominating. [ABSTRACT FROM AUTHOR]

Abstract: Knowledge of infiltration patterns and process is very important in understanding and managing slope hydrological processes, crop irrigation, soil erosion, and so on. This paper describes a study in which simulated rainfall events were used to study the effects of various factors (vegetation cover, rainfall intensity, and slope angle) on the soil moisture increase after rainfall and the infiltration recharge coefficient. Soils hosting three different plants (purple medic, PM; spring wheat, SW; and ryegrass, RS) were considered, along with bare soil (BL). These soil surfaces were tested with four different slopes (8.8, 17.6, 26.8 and 36.4%) and subjected to five different rainfall intensities (0.5, 0.75, 1.0, 1.5 and 2.0mmmin−1). The following key results were obtained: (1) The water distribution in BL boxes differed significantly from that in boxes with vegetation cover, but all boxes with vegetation cover exhibited similar distributions. Vegetation cover significantly increased the depth of the wetting front: under very similar conditions, the wetting front in the RS box reached a depth of more than 35cm, while that in the BL box reached only 25cm. (2) Vegetation cover (especially ryegrass) yielded a greater soil moisture increase than did bare land. The overall average soil moisture increase for RS boxes was 36.7±5.1mm, about twice than that of BL. (3) The water storage after rain across the whole soil profile initially increased and then decreased as the rainfall intensity rose. No differences in the average soil water content increase were found between various rainfall intensities. (4) As the slope increased from 8.8% to 36.4%, the water storage increase initially rose but then fell sharply. There were significant differences (p=0.05) between the water storage increases for gradual slopes (8.8 and 17.6%) and steep slopes (26.8 and 3.4%). (5) The recharge coefficient increased with increasing vegetation cover but decreased with increasing rainfall intensity, slope gradient, and initial soil water content. The average value for boxes with vegetation cover was 1.5 times that for BL boxes. The vegetation cover was the most important factor in determining the recharge coefficient. [Copyright &y& Elsevier]

Abstract: Tillage practices and depth of plow play an important role in altering the porosity and infiltration capacity of soils and hence surface runoff and soil water availability. A study was conducted to evaluate the effect of tillage method and depth on grain yield and irrigation water use efficiency (IWUE) during the dry season at Dire Dawa, eastern Ethiopia. Treatments for this study included were chisel plow at 150 and 250mm depth (CH150 and CH250), and disk plowing to 150mm and 250mm depths (DP150 and DP250); moldboard plow (MB150 and MB250) and “Maresha” (local plowing) (LP). Grain yield was determined by taking samples from three sections of the central furrow. Grain yields were adjusted to 10% moisture content. It was found that tillage method did not significantly affect the average grain and biomass yield and IWUE of grain and biomass. The grain yield for tillage method treatments averaged from 5325kg/ha for local plow to 5839kg/ha for disk plow. The effect of depth of plow on grain yield (kg/ha) ranges from 392 to 7108 for MB150 and DP250, respectively. The IWUE (grain, kg/hacm) for tillage depth treatments averaged from 16.73 for DP150 to 30.90 for DP250, and their respective IWUE (biomass, kg/hacm) averaged from 95.4 (MB150) to 124.6 (CH250). [Copyright &y& Elsevier]

Abstract: Andisols are soils with high structural development and aggregate stability, characteristics that play a major role in their high infiltration rate. They are, however, vulnerable to environmental changes, particularly those associated with land use modifications. The present work aims to ascertain the influence of modifications to land use as well as vegetation cover on the steady-state infiltration rate and associated properties of Andisols on the volcanic island of Tenerife (Canary Islands, Spain). Thirty two sites were selected in three categories of land use/vegetation cover (green forest, pine forest and cropped areas). The infiltration rate was studied using a double ring infiltrometer. Other soil properties which influence infiltration – organic matter content, texture, structure, bulk density, water retention capacity and water repellency – were also studied. Infiltration is extremely rapid under green forest (796 mmh−1) but falls considerably under pine forest (188mmh−1) and in formerly cropped soils (67mmh−1). The statistical analysis shows that the main soil properties affected by a change in land use/vegetation and which determine infiltration are soil aggregation, structural stability and, to a lesser extent, organic matter and bulk density. Compared to the green forest sites, a notable reduction in soil aggregation, structural stability and organic matter, and an increase in bulk density, are observed in the formerly cropped soils. Although less pronounced, the same tendency is seen also in the pine forest sites when compared to their green forest counterparts. The results confirm the vulnerability of Andisols'' soil properties and infiltration to land use modification, while also highlighting the influence of the type of forest cover present. [Copyright &y& Elsevier]

Abstract: A rainfall simulator is an ideal tool for infiltration, soil erosion, and other related research areas for replicating the process and characteristics of natural rainfall. In this study, a laboratory-scale rainfall simulator is developed. Rainfall characteristics including the rainfall intensity and its spatial uniformity, raindrop size, raindrop velocity, and kinetic energy confirm that natural rainfall conditions are simulated with sufficient accuracy. Pressure nozzles are used to spray water corresponding to rainfall intensities ranging from 45 to 105mmh−1. The simulator produces rainfall with uniformity coefficient changing between 82 and 89%. The raindrops falling with an initial velocity from a height of 2.43m have median diameters of 2.2–3.1mm. The impact velocities of the median size raindrops deviate from their terminal velocities with a relative error between 6 and 15%. The accompanying erosion flume can be given slope up to 20% in lateral and longitudinal directions. During the experiments, flow measurement is taken from two outlets at the end of the flume to distinguish the contribution of interrill areas into rills. Experiments result in typical rainfall-induced hydrographs and sedigraphs observed under natural conditions. This shows the ability of the rainfall simulator for use in sediment transport processes over hillslopes. [Copyright &y& Elsevier]

Abstract: Soil water content (SWC) has a vital role in a variety of hydrological processes such as infiltration, runoff and erosion. Mapping the spatial pattern of SWC is then essential for appropriate addressing of these processes. Geostatistics is often used to characterize the spatial variability of SWC. This information may be used for estimating SWC e.g., by ordinary kriging (OK) or modeling location-specific uncertainty (local uncertainty) of the estimates by indicator kriging (IK). Kriging-based algorithms however smooth out the details and are incapable of detecting multi-location uncertainty (spatial uncertainty) of SWC estimates. Sequential Gaussian simulation (sGs) can model the spatial uncertainty through generation of several equally probable stochastic realizations. In this study sGs is used to map SWC spatial distribution and to provide a quantitative measure of its spatial uncertainty in particular. The SWC measurements were performed on 157 soil samples taken from an 18 ha erosion experiment field in Lower Austria. The results show that the spatial pattern of SWC is well recognized using the sGs as the simulated models reproduce the sample statistics including histogram and semivariogram model reasonably well. The difference among realizations is used to provide a quantitative measure of spatial uncertainty of SWC estimates. Knowledge of spatial uncertainty is helpful to evaluate the delineation of vulnerable areas to erosion. [Copyright &y& Elsevier]

Abstract: Preferential flow may strongly affect hydrology at different scales. Measurement of preferential flow however remains very difficult. Tracer-infiltration profiles are often used to measure the degree of preferential flow at plot scale. These experiments are time-consuming, costly and destructive. As a result existing dye-tracer studies are often based on a limited number of profiles. The aim of this study is therefore to select a limited number of soil and landscape characteristics with high predictive value for the degree of preferential flow. 18 rainfall simulations with a dye-tracer and additional site measurements such as soil type, vegetation type and soil physical parameters were performed in a 1 km2 catchment in the Dehesa (Extremadura, Spain). A stepwise multiple regression procedure was used to select variables with a high predictive value for the degree of preferential flow. The infiltration patterns show that preferential flow is potentially present throughout the area and is spatially variable. At first inspection the spatial variability seems to relate to the site specific variables. This is corroborated by the stepwise multiple regression results, with R 2 values of 56% to 67% for the different preferential flow parameters (uniform infiltration front, maximum infiltration depth, total stained area and preferential flow fraction of stained area). A bootstrapping procedure however indicated that the bias due to stepwise variable selection with a large number of independent input variables and a low number of cases was high. Pre-selection of a limited set of variables (vegetation, texture, slope and location) based on expert knowledge gives lower but more powerful R 2 values (50% to 66%), without the bias due to stepwise variable selection. As a large part of the spatial variability of infiltration patterns can be explained with the selected site characteristics, the regression equations were used in combination with detailed maps of the four selected input variables to calculate maps of catchment scale spatial variability in infiltration patterns, thereby delineating sub-areas within the catchment with different infiltration patterns. [Copyright &y& Elsevier]

• Effect of grazing on soil hydraulic properties of gypseous soils were studied. • Three grazing intensities, High, Medium and Low, were compared. • Soil surface S and K c and subsurface ρ b , K s , θ s , α and n were measured. • H presented the highest ρ b and the lowest K c values. • In semiarid gypseous soils M did not have a negative effect of soil properties. Although is well known that grazing has a significant effect on the soil hydraulic properties and through them on the pasture productivity in semi-arid regions, there is still little data about the effect of this management on soils with high gypsum content. This work compares the effect of three increasing grazing intensities (low, medium, and high) on the hydraulic properties of the upper soil layers, measured on two areas with increasing gypsum content (56 and 73%, respectively) located in a semi-arid region of the Middle Ebro Valley (NE, Spain). 90 soil samplings were taken on bare soil surface areas. The measured soil parameters included the saturated sorptivity (S c) and hydraulic conductivity (K c) of the soil surface layer and the soil bulk density (ρ b), saturated hydraulic conductivity (K s), saturated volumetric water content, θ s , and α and n parameters of the water retention curve of the 1–8 cm depth soil layer. Increasing gypsum content increased the soil water infiltration but did not affect the water retention capacity and total porosity. All studied gypseous soils presented low water retention. High grazing intensities decreased the soil water infiltration. While soils with high gypsum content tended to attenuate the effect of the livestock trampling on ρ b , a significant influence of grazing on ρ b was observed in the fields with moderate soil gypsum content. No effect of livestock trampling on the soil water retention characteristics was observed. Moderate grazing, which did not show negative effects on the soil hydro-physical properties, could be an acceptable management for soil conservation in these semiarid regions of soils with high gypsum content. [ABSTRACT FROM AUTHOR]

• Some forest areas of northern Iran are characterized by extreme water repellency. • An adapted version of SWAP4 model used to compute soil water fluxes and runoff. • Water repellency decreases water infiltration and increases runoff generation. • Water repellency reduces evaporation from the soil surface. Water repellent or non-wetting soils show poor water infiltration, which leads to an increased runoff in both natural and agricultural setting. Some forest areas of northern Iran are characterized by extreme water repellency, which makes their soil hydrological response highly complex. A field experiment was carried out to study the effect of water repellency on water movement and runoff in coarse-textured soil covered in Pinus teada in northwestern Iran. An adapted version of the popular agrohydrological model SWAP (Soil, Water, Atmosphere and Plant) has been used to evaluate the modelling of soil water flow and runoff generation. Water repellency was accounted for by multiplying the soil water content and the unsaturated hydraulic conductivity of soil with the F factor. This factor is equal to the volumetric fraction of soil occupied by preferential flow paths. Twenty-seven rainfall experiments were carried out under artificial rainfall using soils with various wettability levels and various rainfall intensities (14 mm/h, 27 mm/h and 34 mm/h). The result show that during the summer and early autumn (May to October) the soil became extreme repellent and runoff was formed when the soils were dry (θ < 2 %) and the rain intensity was more than 27 mm/h. Also, we investigated the role of the repellent layer on evaporation losses. The results of laboratory and simulation data confirm that water repellency reduces evaporation from the soil surface. Comparing modelling results with field data shows that an assumption of uniform flow in water repellent soil leads to an overestimation of soil water content and an underestimation of runoff. After incorporating water repellency in SWAP with the mobile–immobile concept, the agreement between measured and model simulation data considerably improved. [ABSTRACT FROM AUTHOR]

• Temporal BD and Ks changes were investigated along a 500 km transect. • Ks exhibited greater temporal variation compared to BD along the transect. • Climate had no significant effect on BD and Ks along the transect. • Land-use type determined BD variation. • Sampling time significantly affected BD and Ks variability along the transect. Soil bulk density (BD) and saturated hydraulic conductivity (Ks) are two critical soil physical parameters that affect soil water holding capacity, infiltration, carbon stocks, and many land and surface processes. Although variations in spatial and temporal BD and Ks are widely recognized and known to differ at different scales, little large-scale data is available. This study explores changes in spatial and temporal BD and Ks along a 500 km transect on the Chinese Loess Plateau (CLP). On seven different occasions, we took BD and Ks measurements in undisturbed soil samples within the surface (0–10 cm) and subsurface (10–20 cm) soil layers from August 2015 to October 2018 along this long transect. This transect covers two climate zones (subhumid and semiarid) and mainly includes five land - use types. BD and log10-transformed Ks (LogKs) exhibited weak and moderate spatial variations during different sampling periods along the long transect, respectively. The highest LogKs values of the two soil layers were observed in summer. Only BD (LogKs) in the surface soil layer of semiarid zone was significantly higher (lower). Grassland had slightly lower BD and higher Ks compared to the other land - use types. Climate had no significant effect on BD and Ks variability. Land - use type and season separately had a significant impact on BD and Ks variability, while sampling time significantly influenced both BD and Ks variability. Ks was negatively correlated with soil water content in spring, summer and autumn. In this long transect, spatial and temporal variations in BD and Ks are determined by land - use types, seasonal changes, sampling time and soil water condition. Understanding temporal BD and Ks variations and their dominant factors will help in the selection of soil physical parameters to optimize hydrological models more accurately at a regional scale. [ABSTRACT FROM AUTHOR]

• The mulching film is conducive to field drainage after excessive water input. • The mulching film reduces loss of soil water and improves water use efficiency. • The irrigation amount is assessed based on whether it is covered by plastic film. In arid areas, where water resources are extremely scarce, the consumption of agricultural water resources is generally higher than 80% of the total water resources. Reasonable irrigation practices and effective water conservation methods are critical to the efficient utilization of water resources. In order to analyze the rationality of existing irrigation mode and evaluate the effect of plastic mulch on irrigation water migration, this research monitored the hydrogen and oxygen stable isotopic composition of soil water in Minqin oasis farmland located in the arid area of Northwest China. We used the soil water balance equation and the Craig-Gordon model to quantify the infiltration and evaporation of soil water. The result shows: (1) After irrigations in the corn growing season, the average irrigation water of 29.9 ± 4.2% (29.0 ± 6.7 mm), 29.6 ± 2.9% (28.4 ± 2.7 mm) and 30.3 ± 4.3% (29.0 ± 3.5 mm) penetrated into the soil layer of 0–10 cm, 10–50 cm, and 50–100 cm respectively. The field drainage under plastic film mulching was higher than that of no film mulching. (2) Plastic film mulching is the main reason for the difference in SWlc-excess of the surface layer. The evaporative loss of 0–5 cm soil water in non-mulched soil was generally higher than that of plastic-mulched soil. During the whole corn growing season, plastic film mulching effectively reduces evaporation losses of surface soil water and improves water use efficiency. The results of the reserch are very useful for understanding the hydrological process of agricultural lands in arid oases, improving agricultural irrigation water utilization rates, and optimizing water conservation models. [ABSTRACT FROM AUTHOR]

• Observations of seasonal soil moisture using 4D ERT in the US sagebrush steppe. • Demonstrates use of 4D ERT for monitoring soil moisture distribution seasonally. • Shows in 3D how soil structure effects moisture infiltration. • 4D non-invasive observations of preferential flow paths. The semi-arid sagebrush steppe in the western United States faces pressures from the agriculture industry, recreation use, invasive grasses, and a changing climate. A key to facilitating the healthy management of this ecosystem is understanding the distribution and behavior of soil moisture in the vadose zone in both natural and agricultural settings. Within unsaturated environments, soil moisture is spatially and temporally heterogeneous, and changes in porosity and permeability within arid soils complicate characterization of soil hydrologic properties. Importantly, accumulations of 'caliche' or pedogenic calcium carbonate in arid soils can greatly limit permeability; however, observing the role that caliche plays in the hydrologic process is difficult because the installation of in situ instruments disturbs the soils and only provides information at a single point. To investigate vadose zone processes on a broad temporal and spatial scale, we installed a 7x8m2 electrical resistivity tomography (ERT) array at the Reynolds Creek Critical Zone Observatory in southwestern Idaho. Existing soil moisture observations show that infiltration is limited to depths less than 60 cm at this site, as compared to at least 90 cm at other sites in the watershed. To capture the seasonal wetting and drying of the soils, as well as the soils' response to rainfall events, we monitored the site bi-weekly during the spring, summer, and fall of 2015 and 2016. A time-lapse ERT array was placed adjacent to coaxial impedance dielectric reflectometry (CIDR) probes so that the time-lapse ERT data could be referenced to precise measurements of volumetric water content. In addition to the measurements provided by the ERT array and CIDR probes, soil texture analysis and soil profile descriptions from a near-by soil pit show typical arid soil morphology, with accumulations of clays and calcium carbonate in the B horizon. The resulting ERT inversions show the following soil structure: (1) a high-resistivity top layer corresponding with minor amounts of pedogenic calcium carbonate; (2) a low-resistivity intermediate layer at depths corresponding with substantial accumulations (stage IV) of carbonate; and (3) a high-resistivity deep saprolite. The resistivity of the top layer varies seasonally with changes in precipitation, while the intermediate carbonate soil layer does not. This agrees well with the changes in soil moisture with depth measured by the CIDR probes and suggests that the top of the carbonate soil layer limits infiltration. However vertical structure and cracks within the carbonate soil layer create vertical preferential flow paths; resistivity within these flow paths responds to large precipitation events and seasonal changes in soil moisture. This implies that the preferential flow paths are a conduit for soil moisture flow that is not captured by the CIDR probes. From the combined interpretation of the ERT and CIDR we conclude that soil structure and the presence of calcic soil horizons inhibits soil moisture infiltration during both the summer dry months and the winter wet flux period; however, preferential flow paths provide an important vertical connection between the deep and shallow portions of the critical zone. [ABSTRACT FROM AUTHOR]

[Display omitted] • Indoor rainfall simulation with undisturbed soil monoliths. • Rain intensity and antecedent moisture affect transport pathways for organic carbon. • Rain intensity and antecedent moisture affect organic carbon losses. • Rain intensity and antecedent moisture affect quality of organic carbon losses. Under conditions of climate change, the severity and probability of storm events and droughts are expected to increase, this may affect the partitioning into surface and subsurface runoff. However, there is still a debate on how such extreme weather conditions affect the leaching of soil organic carbon. The aim of this study was to ascertain the impact of rainfall intensity (63 vs 79 mm h−1) and antecedent soil moisture (Matric potential: −10 hPa vs −450 hPa) on flow partitioning in the transportation (fluxes and timing) of dissolved (DOC) and particulate organic carbon (POC). Rainfall simulation experiments using undisturbed soil monoliths (1 m × 0.5 m × 0.3 m) allowed to monitor the transport of water, sediments, DOC, and POC via surface and shallow subsurface runoff. In addition, the composition of the leached organic matter was analysed using photometric and fluorometric methods. Most of the organic carbon was transported as POC via surface runoff. In the surface runoff, the influence of antecedent soil moisture on POC loss was larger than rainfall intensity, while rainfall intensity had a greater influence on DOC losses. Under initially unsaturated conditions, surface sealing reduced the infiltration rate, thus fuelling the total surface runoff, which, in turn, enhanced the transported total sediment and POC load of the surface runoff. While POC dominated surface runoff, DOC played a crucial role in the subsurface runoff with higher DOC concentrations under unsaturated conditions. In contrast to other treatments, DOC exported from unsaturated soils rained with high intensity had a unique composition with the highest proportion of humic-like peaks (A, M, C), protein-like peaks (T) and components (C4), suggesting a concentrating effect on DOC at those soils. Altogether, this research acquires new insights into how flow partitioning under extreme weather conditions affects organic carbon losses and which transport mechanism might pose a risk for aquatic systems. [ABSTRACT FROM AUTHOR]

• Sorting and transport of particles in partially saturated sandy loam soil were investigated. • Stress characteristic of soil particles is important in affecting transport process. • Eroded sediments transport with suspension/saltation by a unimodal distribution. • Distribution, sorting of sediments are controlled by aggregation state of particles. Infiltrating water accumulates in the plough pan because of the low permeability of this layer, which results in saturation or partial saturation (soil water contents between the field water capacity and saturated water content) of the cultivated layer during continuous rainfall. Even in sloping farmlands, soil infiltration via large pores created by roots, wormholes and straw rot continuously increases, and the infiltrating water forms subsurface flow above the plough pan, causing the soil in the cultivated layer to become partially saturated. The processes and characteristics of soil particle sorting and transport in partially saturated soil were investigated in the laboratory using scouring experiments. The results showed that the stability of the aggregates was destroyed when the soil was in a soaking state and tended to be saturated, which produced a unimodal distribution of eroded sediment finer than 0.021 mm, and the main transport mechanism along the partially saturated soil was suspension/saltation. The eroded sediment in the erosion process was mainly composed of silt-sized particles, accounting for approximately 44–60% of the sediment load. Destruction of aggregates during erosion can easily enrich the soil in fine particles, especially clay-sized particles. Most fine and coarse sand-sized particles were predominantly aggregates of other finer particles; the aggregation of fine sand-sized particles was relatively poor, and a certain number of fine sand-sized particles were transported as single particles. The results reported in this study have important implications for an in-depth understanding of sediment transport in partially saturated soil. [ABSTRACT FROM AUTHOR]

• Traditional genetic algorithm (GA) is modified. • The improved GA is available for determining parameters in modified VG model. • Inversed soil parameters can be used to predict soil water under 2070 kPa. • Only a 2-hour 1D infiltration is sufficient for obtaining hydraulic parameters. • Kostiakov model is the best model to predict infiltration for biochar-amended soil. Biochar has been globally recognized as a soil amendment to ameliorate the degraded soil structures. We investigated the different biochar percentages contributed to the changes in soil water retention, soil infiltration, and water-holding capacity of one dimensional scale. Besides, infiltration models were compared, and an improved genetic algorithm (GA) combined with multi-objective optimization and elitist strategy was proposed to upgrade the modified van-Genuchten (VG) model. Results indicated that observed cumulative infiltration displayed reductions by 14.06%, 46.62%, and 71.78% for the soil mixed with 5%, 10%, and 15% biochar, respectively, relative to the pure soil. The Kostiakov model was more effective than the Philip model in predicting cumulative infiltration. Furthermore, the constructed modified VG model based on the inversed hydraulic parameters was capable of predicting soil moisture at suction less than 2070 kPa (i.e., 1.38 times wilting point) but caused an underestimation beyond it. This research has the potential to replace the soil water retention curve (SWRC) measurement by one-dimensional infiltration experiment with parameters inversed from the improved GA combined with a modified VG model. It is time-saving and efficient during the SWRC study. [ABSTRACT FROM AUTHOR]

• Soils rich in rock fragments are characterised by tri-modal pore size distribution. • The new combined model captures the presence of macro-, structural, and textural pores. • SOC and coarse fragment contents are crucial for pore size distribution in shallow soils. • Rock fragment content negatively correlated with textural porosity and water retention. • Coarse fragments significantly increased the macro-porosity and soil air capacity. Rock fragments are key components of soil systems. However, the role of rock fragments is only sporadically researched and therefore it is essential to establish how they control soil physical, biological and chemical properties and to assess the impacts of land-use on soil functions. Further, rock fragments affect soil water retention and infiltration capacity, and this is relevant for the fate of soils because water determines soil biota and weathering and decomposition processes in the soil system. Herein, we investigated abandoned arable, meadow and forest soils to determine the effect of land-use on soil water retention properties in soils containing rock fragments. Results showed that forest soil had the highest content of rock fragments and that previous ploughing on shallow abandoned arable soil on dolomite bedrock ensured that this had higher rock fragment content than meadows. We then compared coarse rock fragment effects on water retention in three research plots. Measured points in the water retention curves depict the total porosity and water retention determined at 3–1000 hPa suction in the undisturbed soil samples and 1.5 MPa in disturbed samples. Two models with different macro-porosity expressions were applied to the experimental data, and their derivatives provided pore size distribution curves with maxima for textural, structural and macro-pores. However, a new combined model with six independent fitting parameters has proven more suitable to approximate tri-modal soil water retention curves. The textural porosity was highest in the meadows due to the direct effect of organic carbon content and the indirect influence of coarse fragments which reduced the volume of small pores in the soil. Organic carbon content positively affected water retention properties in these soils. This included the permanent wilting point, field capacity and plant available water capacity, but the coarse fragment content negatively correlated with these properties. In addition, the results highlighted the stones' positive effect on structural pores in forest soils and on macro-pore formation in all soils, while structural pores in all soils were mainly influenced by organic carbon content. The combined structural and macro-pores determine the soil air capacity and this is positively influenced by the increased content of coarse rock fragments. The soil air capacity was therefore highest in the forest soil. Finally, although the irreversible increase in rock fragment content in the abandoned soil has negative impact on agricultural use, the coarse fragment influence on macro-pore volume is positive and this increases soil infiltration capacity and reduces surface runoff and soil erosion, as confirmed in the literature review. [ABSTRACT FROM AUTHOR]

• Soils from ground pine forest road are water repellent. • The degree of water repellency depends on the type of road neighbourhood habitat. • The wettability of unpaved forest roads varies along the road cross section. • Zisman's critical surface tension values ranged from 37.5 to 56.4 mN m−1. • The severity and persistence of potential soil water repellency were correlated. Forest roads play a crucial role in commercial forestry. Most of them are unpaved and exposed to increased surface runoff and the occurrence of soil erosion. Therefore, these roads constantly require repairs and maintenance, which are associated with the high cost of earthworks. Soil water repellency causes retardation of water infiltration into soil, which affects the generation of surface runoff, leading to the destruction of the active road layer. This phenomenon is well recognized in forest habitat soils, but poorly investigated in terms of soils constituting roads and communication routes. Therefore, the aims of this research were to determine the severity and persistence of potential water repellency in the case of soil collected from two unpaved roads in coniferous forest and to investigate the dependence between the severity of soil water repellency and its persistence. Soil samples (Dystric Brunic Arenosols) were collected from three points of the roadway, i.e., centre line, rut and roadside, from two different sites located in fresh coniferous and fresh mixed coniferous forest (Poland). The severity of soil water repellency was assessed, based on measured values of the wetting contact angle (Wilhelmy plate method) and the critical and 90° surface tensions. For this purpose, contact angle measurements of the solid phase, wetted by water–ethanol mixtures, were used and data results were analysed using the Zisman approach. The persistence of potential soil water repellency was assessed using the water drop penetration time test. The severity and persistence of soil water repellency depend on the forest habitat type surrounding the road and point locations on the road cross section. The soil samples collected from the roadside were more water repellent than samples taken from the centre line or rut. A strong relationship was found between the water drop penetration time and the advancing contact angle, the critical surface tension and the 90° surface tension. [ABSTRACT FROM AUTHOR]

• Multiple Linear Regression and Random Forests were used to predict infiltration rate. • Measured soil infiltration ranged from 0.29 to 81.7 mm h−1 with a mean of 13.6 mm h−1. • Channel networks, sand, distance-from-river, NDSI, and elevation were important. • Random Forest best predicted the spatial distribution of infiltration rate. Knowledge of the spatial variation of soil infiltration is necessary for managing water conservation, salinity, and precision agriculture in drylands. In this study, the spatial variation of soil infiltration was investigated using digital soil mapping methods in the Sistan plain, an arid, low-relief flood plain in eastern Iran where a large irrigation project is being implemented to irrigate lands. Information about the spatial variation in soil infiltration will assist the planning of this irrigation project. 138 sampling locations were selected using stratified sampling based on existing polygon-based soil maps. Steady state soil infiltration was measured at each sampling location using the double ring infiltrometer method. Twenty-three environmental covariates were derived from digital elevation models and satellite imagery as well as predictive maps of clay, sand, and silt that were derived from kriging the collected soil samples. A simple (multiple linear regression) and a complex (random forests) model were used to link covariates and infiltration measurements. Ten-fold cross-validation was used to determine model accuracy. Measured soil infiltration ranged from 0.29 to 81.7 mm h−1 with a mean of 13.6 mm h−1. RMSE of the infiltration rate predictions were 13.4 mm h−1 for random forest and 13.9 mm h−1 for multiple linear regression. MAE was 10.5 for random forest and 10.9 for multiple linear regression. The most important covariates were channel networks, sand concentration, normalized difference salinity index (NDSI), and elevation in the random forest model and distance-from-river and sand concentration in the multiple linear regression model. Accuracy metrics for both models were comparable, but the random forest predictions were judged to be closer to reality based on visual review, thus random forests was chosen to make predictive maps of soil infiltration. [ABSTRACT FROM AUTHOR]

The accurate measurement of soil infiltration rates is a challenging task in hydrological studies, as they are governed by complex interactions between the plant and soil components. To explore the effects of plant roots and soil moisture (SM) on infiltration process, an automatic measurement system based on a point source device was used to determine infiltration rates at different cultivated grasslands (leguminous, gramineous and mixed) in an arid region of China. The results showed that SM and plant roots significantly affected the infiltration process at different stages in the three grasslands. The soil infiltration rates were negatively correlated to SM, but a positive correlation was observed with the below-ground biomass (BGB). SM was the main factor influencing the infiltration rates in the initial stage of infiltration, whereas both SM and BGB determined the steady-state infiltration rates. The influence of the combined effects of SM and plant roots decreased over infiltration time. The decreased rate of determining coefficient showed that SM was more influent than plant roots. These results may contribute to interpret the observed higher soil infiltration capacity in the leguminous grasslands than in the gramineous and the mixed grasslands, and were conducive to better understand the effects of plant and soil properties on infiltration processes in arid areas. • Soil moisture and plant roots determined soil infiltration capacity by stages were studied. • Soil moisture is a main factor to influence negatively infiltration capacity in initial stage. • Soil moisture and plant roots codetermined the infiltration rate in steady stage. • Influences of soil moisture and roots are diminishing with the duration of infiltration time. [ABSTRACT FROM AUTHOR]

Time to runoff initiation (TRI) is an important factor related to water infiltration, runoff generation, and hillslope erosion. This study assesses TRI values for six different plots and investigates the effects of rainfall intensity, surface soil moisture content at depths of 0–5 cm, soil and water conservation measures (longitudinal ridges, cross ridges, grass, forest, and flat field under fruit trees), and vegetation on TRI for bare soil, longitudinal ridges under maize, cross ridges under peanut crops, grass, forest, and flat field under fruit trees. Results showed that bare soil exhibited the shortest TRI, followed by the longitudinal ridges under maize and cross ridges under peanut crops. The remaining three plots did not generate runoff. The first principal component affecting TRI was soil moisture content, which contributed 69.87%, 64.88%, and 85.73% to the TRI of bare soil, longitudinal ridges under maize, and cross ridges under peanut crops, respectively. The second major component of these three plots were combined rainfall intensity, comprehensive rainfall and vegetation factors, and vegetation factors, which contributed 27.98%, 33.73%, and 14.27%, respectively. Maximum load factor was generated during runoff with maximum rainfall intensity (0.969), stalk diameter (0.985), and maize height (0.864). In conclusion, soil moisture content are the main factors influencing TRI, and soil and water conservation measures provided key benefits for improving the time to runoff initiation and reduction of runoff erosion in the farmlands. • The effects of multi-factor on the time to runoff initiation (TRI). • Of the factors studied, soil water content is the main influential factor of TRI. • Bare soil exhibited the shortest TRI,followed by maize and peanut crop plots. • The experiment is carried out under natural rainfall. [ABSTRACT FROM AUTHOR]