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• Parent material exerts a significant influence on the soil texture and pH. • Parent material affects the soil water-holding capacity by affecting the soil texture. • Quartz sandstone soil exhibits the lowest water-holding capacity. • Argillaceous limestone soil exhibits the highest water-holding capacity. • Argillaceous limestone soil exhibits the lowest erosion resistance. The parent materials play an important role in soil hydrologic properties. However, in subtropical hilly areas with complex geological conditions, it appears that there is a lack of full understanding about the effect of parent material on soil water-holding and erosion resistance, which can be helpful for agricultural production and conservation of soil and water. In this study, five red soils developed from shale (Ds), quartz sandstone (Dqs), argillaceous nodular limestone (Danl), argillaceous limestone (Dal), and limestone conglomerate (Dlc) in subtropical China were selected. Soil properties, soil water-retention curves (SWRCs), water-stable aggregate fractions, and soil erodibility factor (K) were tested and calculated. The results showed that there are significant differences in soil texture among soils developed from different parent materials, soils with higher clay content have stronger water-holding capacity, and the average water-holding capacity of the five soils followed the order Dal > Danl > Ds > Dlc > Dqs. Furthermore, the erosion resistance of soil is closely related to the clay content and the stability of soil aggregates, and the sequence of average K -value among the five soil types is as follows: Danl > Dal > Dlc > Ds > Dqs. Partial least squares regression revealed that the stability of aggregates has a more significant influence on soil erodibility than the clay content. Therefore, soils with higher mean weight diameter (MWD) and geometric mean diameter (GMD) are more resistance to erosion. This paper evaluated the distinctions in basic properties and hydraulic properties between different parent materials under similar climatic conditions, elevations and vegetation in subtropical hilly area of Southern China, which can serve as a scientific foundation for soil and water conservation in the environments characterized by complex geological conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Invasion by Spartina increased mineral-bound OC in mudflat soil. • Subsequently reclamation for aquaculture decreased soil mineral-bound OC. • Mineral-bound OC was correlated to nitrogen supply and soil clay content. • Habitat change affected Fe[Al]–OC more than Ca-OC and residual-OC. • Soil OC storage increased more strongly with increasing Ca-OC. The formation of mineral-bound organic carbon (OC) complexes is important for the long-term preservation of soil organic carbon (SOC) in wetlands. Many coastal wetlands globally have been threatened by plant invasion and land development, but information on the effects on mineral-bound OC is limited. We measured the soil contents of Ca-OC, Fe(Al)–OC and residual OC across 21 coastal wetlands in southern China that have gone through the same sequence of land cover change, from native mudflats (MFs) to Spartina alterniflora marshes (SAs) then to earthen aquaculture ponds (APs). Residual-OC was the main component of SOC (74.1–78.2 %), followed by Fe(Al)–OC (18.4–22.8 %) and Ca-OC (<3.5 %). All three components in the soil increased when MFs were converted to SAs, but decreased in subsequent conversion of SAs to APs. Land cover change affected Fe(Al)–OC the most, but SOC storage increased more strongly with increasing Ca-OC. Nitrogen supply in the form of NH 4 +-N and clay content both positively affected the changes in mineral-bound OC. Our results suggest that different land cover change scenarios had different effects on the amounts of mineral-bound OC and their liability to microbial turnover, resulting in different degrees of SOC preservation and carbon emissions. [ABSTRACT FROM AUTHOR]

• UAVs show promising utility in monitoring desert rodent activity on a regional scale. • Regional plant variation significantly influences desert rodent burrow density. • Significant lag effects of environmental factors on rodent burrow density. • Elevation, precipitation, vegetation and soil are the key factors influencing rodent. Timely and accurate prediction and early warning of rodent infestation are highly important for the sustainable development of desert ecosystems. This study combines data from 1376 UAV images of actual rodent burrows with natural environmental factor data, aiming to reveal the mechanism through which these factors affect rodent burrow density in the desert areas. The relationships between rodent burrow density and the 9 plant communities and 34 plant species in this area were analyzed by the K-W test and Spearman rank correlation analysis, respectively. The Boruta algorithm and the boosted regression trees (BRT) model were used to determine the six main factors influencing rodent burrow density from a total of 32 factors and to determine the distribution pattern of the burrows. The results show that (1) the density of rodent burrows in the Junggar Basin desert area gradually decreases from south to north and from west to east. (2) There were significant differences in rodent burrow density across the different plant community types (P = 0.048**). A total of 50.0 % of the species significantly influenced rodent burrow density at at least one level. (3) Among the 17 factors with lag effects, nine had the most significant correlation with rodent burrow density in April. Only two natural environmental factors demonstrated lag effects of less than one month. (4) The soil clay content, elevation, Normalized Difference Salinity Index (NDSI), vegetation cover, precipitation, and soil bulk density were the most important influencing factors on rodent burrow density. Considering the pairwise interactions among factors, the collective impact of these factors on rodent burrow density is at least sevenfold greater than the independent effect of a single factor. This study provides a theoretical basis for obtaining a timely and accurate understanding of the spatial distribution of rodent burrows, mitigating the degradation trend of desert ecosystems, and ensuring healthy and sustainable development. [ABSTRACT FROM AUTHOR]

[Display omitted] • Suitable plantations can mitigate global change events, if well-implemented. • China's plantations show increasing above- and below-ground carbon stocks with stand age. • C stocks and rates increase with temperature as compared to humidity. • Soil clay and fertility increase C stocks rather than annualized C rates. • C allocation between tree organs depends on climate and soil conditions. A significant proportion of the Earth's natural forests has been continuously degraded each year as a result of human activities and global environmental changes. Meanwhile, there has been a rise in the establishment of plantations through numerous planting trees initiatives, including those recently spearheaded by the United Nations (UN) Decade (2021–2030). Yet, considerable global uncertainty remains on drivers of carbon (C) sequestration (defined by C stocks and annualized accumulation rates) in plantations. By using the meta -data from 257 plantation plots in China, we quantified above- and below-ground C stocks and annualized C accumulation rates in tree organs, i.e., stems, branches, leaves, and roots, based on biomass allometric equations and scaling rules. Multiple linear regression models were used to explore the drivers (i.e., stand age, climate and soil factors) of plantation above- and below-ground C stocks and accumulation rates. We show that above- and below-ground C stocks increased with stand age (β = 0.55 to 0.66; P < 0.001) followed by temperature (β = 0.29 to 0.36; P = 0.001 to < 0.001), precipitation seasonality (β = 0.23 to 0.41; P = 0.013 to < 0.001), and somehow by climatic humidity (β = 0.17 to 0.35; P = 0.105 to 0.002), but decreased with isothermality (β = -0.14 to -0.16; P = 0.024 to 0.019). Soil clay content increased stem C stock (β = 0.15; P = 0.016) whereas soil cation exchange capacity increased branch C stock (β = 0.23; P = 0.003), even though soil factors did not significantly affect annualized C accumulation rates (β = -0.12 to 0.14; P = 0.908 to 0.078). This coarse-scale study suggests that C sequestration in China's plantations increases over time with increasing climatic temperature and soil fertility, thereby sustaining environmental conditions by capturing C from the atmosphere and storing it in tree organs. Thus, conserving environment-friendly plantations, having no disruption to native biodiversity, as land resources can reduce pressures on natural forest resources while improving environmental integrity through feedback. [ABSTRACT FROM AUTHOR]

• Long-term expansion rates of 46 Urban Gullies in Kinshasa and Bukavu are quantified. • Gully widening is responsible for most of the gully expansion. • Expansion rates in sandy soils are mainly controlled by land cover and road density. • Expansion rates in clayey soils appear influenced by landslide dynamics. Urban gullies (UGs) are a growing concern in many tropical cities of the Global South. Addressing this new geo-hydrological hazard requires good insights into the rates and controlling factors of this process. Therefore, we investigate the expansion rates of a representative sample of UGs in Kinshasa (n = 17) and Bukavu (n = 29), two contrasting cities in D.R. Congo. We reconstruct long-term (10–17 years) expansion rates, making a distinction between headcut retreat and sidewall widening, and analyse the environmental factors potentially explaining these rates. Total expansion rates varying between 12.6 and 863 m2y-1. Most of this expansion happens through sidewall widening. In Kinshasa, which is mainly characterized by sandy soils, contrasts in expansion rates are mainly correlated to the characteristics of the upslope drainage area of the gullies. Especially the road density and a hypothetical runoff index (combining drainage area, land use and soil characteristics) explain a significant part of the observed variation. In Bukavu, such trends are less apparent. This is likely because the clayey nature of the soils provides more resistance against gullying, resulting in overall smaller and less actives UGs. Furthermore, the already low infiltration rates of these soils probably make the relative impact of urbanization on runoff production smaller. Our results also indicate that UGs located in recent landslides have higher gully expansion rates. The mechanisms behind remain poorly understood. Overall, our work opens promising perspectives to model and predict gully expansion rates in urban settings but may also guide efforts aiming to stabilize UGs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil silt/clay and nutrients increased with increasing distance from the shelterbelt. • Downslope deposition lead to an increase in plow pan thickness and a decrease in bulk density. • Erosion rate was primarily affected by shelterbelt distance, followed by elevation. • Sites closer to shelterbelt warrant particular attention due to coarse-texture materials. Soil erosion is the most severe form of land degradation globally. Farmland shelterbelts are important for reducing erosion, especially erosion caused by the co-occurrence of water and wind. However, few studies have focused on how the distance from the shelterbelt associated with farmland topography affects the redistribution of soil quality indicators. The aims of this study is to reveal the relative importance of these two factors to soil quality under typical wind and water erosion conditions concurrent with the Songnen Plain, China. Topsoils (0–10 cm) were sampled at seven distances from the shelterbelt with three replicates, where topography heterogeneity was also considered. We found that the silt/clay content and soil nutrients at sites farther from the shelterbelt were significantly greater than those at sites closer to the shelterbelt (P < 0.05). Similarly, deposition was dominant at sites farther from the shelterbelt and downslope positions, while erosion was dominant at sites closer to the shelterbelt and upslope positions. Moreover, we discovered that the relative influence of distance from the shelterbelt and farmland elevation varied with individual soil quality indicators. Soil nutrients increased through the deposition of more fine-textured soil (silt/clay) positions farther from the shelterbelt. The downslope region responds to soil deposition by enhancing the plough pan thickness and lowering the bulk density and pH. Overall, distance from the shelterbelt and farmland elevation had interactive effects on soil quality, and erosion was primarily affected by distance from the shelterbelt (63.4 %), followed by elevation (22.7 %). Furthermore, the sites closer to the shelterbelt (i.e., 20 to 420 m) warrant particular attention due to the deposition of coarse-texture materials here. This work is crucial for an improved understanding of the synergistic effects of long-term water and wind co-occurrence on soil quality evolution. [ABSTRACT FROM AUTHOR]

• Using in-situ measurements, size fractionation from soil to sediment was investigated for numerous calcareous soils. • The 0.2 mm was suggested as the boundary between high and low erodible fractions of calcareous soils. • Size range of 0.063–0.2 mm was found as the most susceptible fraction to wind erosion. • Soil fraction of 0.063–0.1 mm intensified calcareous soil potential for suspension-size sediment generation. • Critical values of various soil PSD criteria for wind erosion rate of calcareous soils were suggested. Soil texture and soil surface aggregate size distribution (ASD) are key factors to study soil erodibility by wind and sediment size distribution (SSD) in arid and semi-arid areas. However, less research has studied the effect of soil fractions on soil erodibility and wind-blown sediment size of calcareous soils. In the present study, we focused on the size fractionation and particle size distribution (PSD) of 60 calcareous soil samples collected from 20 semi-arid and arid areas in Fars province, southern Iran. Extensive in-situ wind tunnel experiments were conducted under controlled high wind speed to measure wind erosion rate (WER) and SSD. The results showed that the calcareous soils had different erodibility based on their PSD. Generally, the most erodible soils to the wind force were those with less than 10 % of clay and higher frequency of the 0.1–0.2 mm size class. However, when the soil clay content exceeds 20 %, ASD got dominated with the fraction of 0.4–0.8 mm and WER of the calcareous soils got limited. Besides, size range of 0.063–0.2 mm was suggested as the most wind erodible fraction of the calcareous soils. Furthermore, the mean weight diameter (MWD) of sediment particles averagely reduced 1.3 times as compared to that of the soil samples and WER got inhibited for regions in which the difference of soil and sediment MWD exceeded 0.05 mm. The SSD was significantly controlled by soil PSD and suspension-size sediments < 0.1 mm (SSS) were negatively proportional to soil clay, MWD, geometric mean diameter of soil particles (GMD), dry stable aggregates > 0.25 mm (DSA), and organic carbon as logarithmic equations. Moreover, the presence of the size fractions > 0.2 mm restricted the potential of calcareous soils to generate SSS, which would be quite beneficial for wind erosion combat and dust control of calcareous soils. [ABSTRACT FROM AUTHOR]

• Ca2+ promoted macropores develop toward spheres under Na+ presence. • Under Na+ presence, Mg2+ promoted macropores to develop in one/several directions. • Ca2+ increased macropore size by soil flocculation, but Mg2+ by soil cracking. • Ca2+ affected soil macropore area, but Mg2+ changed macropore number. Cations in soil solutions affect soil structural stability and thus soil quality and health. Ca2+ and Mg2+ could alleviate soil clay dispersion by replacing Na+, which was the main driver. However, Mg2+ could also cause soil disaggregation and weaken aggregate integrity. Currently, most studies on Ca2+ and Mg2+ mainly examine soil hydraulic characteristics and clay particle dispersion, rather than macropore geometry. We analyzed the impact of Ca2+ and Mg2+ on soil macropore morphology by measuring macropore length, aspect ratio, and area indices. An indoor soil column experiment was set up, and irrigation water was prepared with the same electrical conductivity (4 dS m−1) and different cation compositions (Na+-Ca2+ (NC), Na+-Ca2+-Mg2+ (NCM), Na+-Mg2+ (NM) and Na+-only (N) were added), and deionized water as the control (CK). The results indicated that N had the highest soil suspension turbidity among all treatments, with NM being higher than NC. The highest percentage of soil macropore aspect ratio < 2.0 was found in N, and the highest percentage of soil macropore aspect ratio for NCM was found in > 2.0. The macropore anisotropy of NM was closer to 1.0, and anisotropy of NC was closer to 0. The soil macropore morphology of NC developed towards a spherical shape, while the macropores of NM might extend along one or several similar directions. For Na+-Ca2+ dominated soil, Ca2+ mainly affected the macropore area. However, for Na+-Mg2+ dominated soil, Mg2+ primarily influenced the number of macropores. Ca2+ inhibited the negative effects of Na+, but Mg2+ promoted unidirectional extension of macropores, posing a risk of soil cracking. This study provided a better understanding to explore the differences in the effects of different cations on soil pore structure and helped to provide guidance for field water management. [ABSTRACT FROM AUTHOR]

• Patchiness caused significant reduction of SOC and TN stocks. • Reduced vegetation input and increased erosion output accounted for SOC and TN loss. • Grasslands with high patchiness had a great potential for C and N sequestration. Patchiness acts as an indicator of terrestrial ecosystem degradation and can lead to considerable loss of soil organic carbon and total nitrogen. However, quantitative assessments of the effects of patchiness on soil organic carbon and total nitrogen stocks and their associated mechanisms remain limited. This study aimed to explore the influence mechanisms of patchiness on soil organic carbon and total nitrogen stocks and to project the quantitative contribution of the further expansion of patchiness and vegetation recovery. Soil properties, soil organic carbon and total nitrogen stocks were investigated using a combination of field sampling and aerial photography in four grassland types, alpine meadow, alpine steppe, temperate grassland, and desert grassland, at 47 sites in northwestern China. Soil organic carbon and total nitrogen densities in the bare patches were 34–54 % and 23–41 % lower, respectively, compared to the original vegetation. At the plot-scale, current soil organic carbon and total nitrogen stocks ranged from 30.85 to 77.80 T/ha and 3.26 to 10.19 T/ha, respectively, across grassland types; with a 10–27 % and 7–24 % potential loss of soil organic carbon and total nitrogen stocks, respectively, from the further expansion of patchiness but a 10–50 % and 9–37 % potential increase in soil organic carbon and total nitrogen stocks, respectively, from vegetation recovery. Soil organic carbon and total nitrogen stocks were positively correlated with vegetation biomass, soil clay content, and precipitation (p < 0.001), whereas they were negatively correlated with patchiness (p < 0.001). In summary, patchiness reduced soil organic carbon and total nitrogen stocks by decreasing vegetation inputs and increasing erosion outputs, while vegetation recovery showed potential for increasing carbon and nitrogen stocks. Our results highlight that maintaining intact vegetation cover is critical for preserving terrestrial ecosystem carbon and nitrogen storage. [ABSTRACT FROM AUTHOR]

• Clay content and subfreezing temperature coupling affect soil FT deformation. • The clay aggregate evolution during FT accounts for the complex deformation. • Full-range evolution of soil structure is characterized via NMR and X-CT. • Quantitatively analyze contribution of micro/meso structure change to deformation. Climate change brought about significant freeze–thaw (FT) deformation of clayey soils distributed in cold regions, which resulted from soil structure evolution including pore size distribution change and crack development. However, the formation of clay aggregate that dominates the soil deformation behavior during FT remains unclear. This study investigated the effects of clay contents (5 %, 10 %, 15 %, and 20 %) and subfreezing temperatures (−5 °C, −10 °C, and −15 °C) on the soil FT deformation properties by isotropic isothermal FT tests. Meanwhile, the soil structure evolution was characterized via Nuclear Magnetic Resonance and X-ray Computed Tomography. The results indicated that the frost heave ratio (η) and thaw settlement coefficient (δ) non-linearly varied with clay content and subfreezing temperature. Specifically, the minimum η and δ were observed in the specimen with 10 % clay content, and the maximum η and δ were identified at −10 °C. This phenomenon can be attributed to the clay aggregate forming bimodal or unimodal pore size distribution (PSD) with different initial clay contents. The freezing characteristics of inter- and intra-aggregate pore water were determined by the solid-water interaction. Moreover, the FT action altered the structure of clayey soil by the change in PSD and the generation of cracks. The contribution of pore size change and crack development to the total volume change before and after FT was quantitatively analyzed. It demonstrated that pore size change was more important for the total volume change in specimens with lower clay content and higher subfreezing temperature, whereas crack development mainly contributed to the total volume change in the rest of the specimens. This study provides a deep insight into the deformation characteristics of clayey soils under different climate conditions in cold regions. [ABSTRACT FROM AUTHOR]

[Display omitted] • We analyzed 56 Northern long-term experiments to explore manure effect on SOC. • We developed a statistical model to determine the most effective practices. • SOC saturation occurred with a certain proportion of ley depending on soil texture. • Manure is most effectively used in the crop rotations with low proportion of ley. • Management and circumstances should be considered when targeting SOC sequestration. Soil carbon sequestration has a great potential in climate change mitigation. To maximise carbon stocks in northern agricultural soils, the carbon sequestration determinants of manure application are crucial. We quantified the effect of manure on soil organic carbon (SOC) depending on the application rate, proportion of leys relative to annuals in crop rotation, and soil texture. We compared the steady-state SOC concentration under farm-yard manure application to a control treatment with no manure application based on 56 individual long-term experiments at 27 locations north of 50 degrees north latitude. At a low application rate of manure such as 0.7 Mg C/ha/y, SOC gradually increased with increasing ley proportions. At a moderate manure rate, such as 1.3 Mg C/ha/y, an increase in the ley proportion led to a decreasing growth of, or even a decrease in, SOC. At a low fixed ley proportion in crop rotation such as 20 %, SOC linearly increased with an increasing manure application rate. As the proportion of leys increased, saturation occurred at a certain ley proportion depending on soil texture. When leys occurred on sandy soils more than once out of seven years and the proportion of leys in crop rotation on clay soils was higher than 45 %, increasing the manure application rate led to decreasing SOC accrual. Compared to the absence of manure application, high manure rates even decreased SOC. We conclude that manure application in crop rotation with a low ley proportion maximises SOC accrual in the topsoil. The most effective manure application rate and ley proportion leys in regard to SOC in the northern agricultural landscape can be determined using a statistical model that we developed, depending on the management system and soil texture. [ABSTRACT FROM AUTHOR]

• Surface soil recovery of bulk density in 23 years at 5 cm depth. • Fine root biomass no different in skid trails and controls at 13 years. • Higher CEC and organic C in skid trails when compared to control after 19 years. • Elevated levels of exchangeable Al still in skid trails after 26 years. • Soil compaction persists in skid trails 19 years after logging in a clay Ferralsol. Each year, thousands of km2 of humid tropical forest are logged in the Brazilian Amazon. Many of these areas are underlain by clay soils dominated by non-expansive kaolinite. Logging operations often entail the use of heavy machinery to drag logs through the forest on skid trails, which causes substantial soil disturbance. Therefore, the objective of this study was to investigate if soil recovery occurs over time in the studied Ferralsol. The hypothesis is that soil recovery has indeed occurred and that the trend of recovery is observable. In this endeavor, a chronosequence was established composed of four logging units that were logged 13, 19, 23, and 26 years ago, as well as a control in undisturbed old-growth forest. Samples in the upper topsoil were collected for soil bulk density (BD), fine root biomass (FRB) and various soil chemical properties. Results indicated a sequential recovery. Prior to the study period of 13–26 years after logging operations, FRB recovered. The predicted recovery of the cation exchange capacity was at approximately 15 years, which was followed by soil organic carbon at 20 years. Lastly, BD was recovered within 25 years. Overall, soil organic carbon demonstrated the greatest associations with recovery variables as it accumulated over time. Although surface soils in skid trails did indeed recover, it was a lengthy process that occurred over several decades. In this context, skid trails should be planned to minimize soil disturbance in the logging area to the greatest extent feasible. [ABSTRACT FROM AUTHOR]

• Ratio of peak areas of MIR quantified OM dynamics in soil. • Using ratio of peak area increases our understanding of soil aggregate dynamics. • High C/N OM resulted in slow decomposition and gradual aggregation. • Low C/N OM fostered rapid macroaggregate formation and subsequent reorganisation. • Assigning a MIR band to a C group indicating its stability can be misleading. Soil organic carbon is a crucial parameter for assessing soil quality, and it significantly contributes to soil aggregation. However, the influence of different organic carbon components and groups on the formation of soil water-stable aggregates has not been thoroughly investigated. To examine it, a clay soil amended with two different types of organic matter (OM) at four input levels for 84 days. The ratio of peak area (RPA) of the mid-infrared (MIR) spectra was used to investigate the dynamic of specific compounds and soil aggregation during the decomposition of OM. The results showed three important aspects. Firstly, the amount and nature of OM input strongly influenced the formation of organic compounds during incubation, as well as the degree of soil aggregation. Furthermore, we observed that the C groups identified by MIR spectroscopy were highly dynamic. Thus, the approach of using a band of soil MIR spectra to infer the stability of a C group can be misleading. Secondly, the low C/N of alfalfa stimulated more microbial activity with 1.1 to 2.3 times more cumulative respiration than high C/N barley straw. The rapid degradation of alfalfa immediately formed water-stable aggregates and subsequently, the macroaggregates were reorganized by microbial activities and physical disturbance. In contrast, the slow decomposition of barley straw built up aggregates gradually in a hierarchical manner and in proportion to the amount of OM added. Alfalfa amendment caused a significant increase in the mean weight diameter (MWD) and a strong correlation with the RPA in the range of 1747–1500 cm−1 (r = 0.78). While aggregation due to barley straw treatment led a stronger relationship between MWD and RPA of 3000–2800 cm−1 (r = 0.89). The results suggest MIR spectra can be used to understand the dynamics of OM that build stable aggregates. [ABSTRACT FROM AUTHOR]

• Studied forests in Western Ghats had weathered and mature profiles of Ultisols. • Abundance of 2:1 and mixed layer minerals in natural forests than plantation. • Co-dominance of gibbsite with 2:1 minerals discounts the antigibbsite hypothesis. • Losses of SiO 2 in the non-clay fractions indicate active weathering in all horizons. • Clay formation assessments provide insights into ecosystem regulated pedogenesis. Clay minerals formed during soil formation are imprints of ecosystem functioning and pedogenic processes in landscapes. The study evaluated the variations in taxonomy, soil weathering and pedogenic changes in contrasting forest soils in the Southern Western Ghats, India. Three different forest systems with comparable soil-forming factors vis-a-vis evergreen, moist deciduous and a man-made system (rubber plantation) were evaluated for physical, chemical, morphological, and pedogenic characteristics of the related soils. Soil profiles were dug up to 1.50 m in the selected ecosystems and horizon-wise soil samples were collected. All the pedons were classified in the soil order of Ultisols and subclassified as Ustic Palehumult (evergreen forest), Ustic Haplohumult (moist deciduous forest) and Typic Haplustult (rubber plantation), respectively. The soil pH was found to be acidic in all the ecosystems ranging from 4.6 to 5.8. Chlorite, hydroxyl interlayered vermiculite (HIV), mica, kaolinite, feldspars, gibbsite and quartz dominated the mineral assemblages in the clay fractions of soils of natural forest systems. The losses of SiO 2 in the non-clay fraction and corresponding enrichment of the component in the clay-sized fraction in all horizons indicated an active continuous weathering process in all the systems of this region. Clay accumulation by way of formation and translocation was highest in the lower horizons of the soils of evergreen (Bt2 at a depth range of 28–57 cm) and moist deciduous (Bt3C at a depth range of 23–150 cm) forest, whereas it was highest at Bt1 at a depth range of 15–28 cm in the plantation soil. The depth variations in the clay formations in natural and manmade forest systems provide insights into ecosystems regulated profile development under natural and man-made systems in the humid tropics, a vital information gap hitherto in soil pedogenesis of the humid tropics. Such pedogenic assessments along with the factors responsible for such modifications would provide important inputs in developing soil health management strategies in the humid tropics. [ABSTRACT FROM AUTHOR]

• Regional geochemical baseline values can well model the background values of studied metals. • Cd was the main pollutant in the riparian sediment. • The contamination and risk of Cd was high in upper downstream and site of 24. • Influencing factors explained variation of metals better at 1 km buffer scale. • Land use composition contributed most to the high explanation at 1 km scale. In this study, we assessed pollution status and potential risk of metals in riparian sediment of Yangtze River with geo-accumulation index (I geo), ecological risk index (RI) and health risk index (THQ) by calculated regional geochemical baseline (RGB) values. We explored the influence of natural factor (sediment property) and anthropogenic factors (land use composition and landscape configuration) at different buffers (500 m, 1 km and 5 km) on metals in sediment using redundancy analysis (RDA) and variation partitioning analysis (VPA). Results indicated that RGB values can effectively model background values of metals (p < 0.01). I geo and RI assessment showed that Cd was the primary pollutant, which showed no contamination to moderate contamination (I geo > 0) and moderate ecological risk (ecological risk factor > 40) in upper downstream of the river. Besides, Cd showed moderate to strong contamination (I geo > 2) and considerable ecological risk (ecological risk factor > 160) at site 24, which is located in the intersection of Poyang Lake and Yangtze River and strongly affected by natural erosion and human activities of Poyang Lake drainage. THQ assessment indicated low health risk of metals from consuming fish influenced by suspended sediment. RDA and VPA analysis indicated that explanation rate of land use composition, sediment property and landscape configuration on metals was 27.01–55.1 %, 36.66 %, 9.77 %-12.52 %, respectively. The total explanation rate was significantly higher at 1 km scale (82.5 %), which was mainly contributed by land use composition and its interaction with sediment property and landscape configuration (55.11 %). Specifically, percentage of farmland, grassland, wetland and forest, content of TN, TOC, silt and clay in soil and landscape configuration index of NumP were positively correlated with metals, and content of sand in soil and landscape index of MSI negatively correlated with metals in riparian sediment at different buffer scales. Our results offer valuable insights for safeguarding riparian zone. [ABSTRACT FROM AUTHOR]

• C:N ratios in soils and particle-size fractions were assessed in tropical highlands. • Sand C:N ratios increase with depth, whereas silt and clay C:N vary little. • C:N ratios decrease with increasing Ca and Mg contents, CEC, and clay activity. • N-enrichment in clays is likely controlled by mineralogy. • R-NH 3 + sorption onto clays can be critical to organic matter stabilization. Factors affecting soil organic carbon (SOC) retention in the tropics are relatively well known, but this is not the case for N retention and thus C:N ratios, a common proxy for organic matter stability. Recent data suggest that SOC and N concentrations vary with climate, whereas soil C:N ratios depend on particle-size fractions contents. However, such knowledge is still incipient for tropical soils, native vegetations and deeper soil layers, which are critical to understand how land use and climate change affect C and N fluxes. We assessed SOC, N and C:N ratios in bulk soils and sand, silt and clay fractions, and their correlations with other soil properties under native tropical forests in the highlands near Lavras, Brazil. Soil samples were collected to 1-m depth in soils of contrasting texture and mineralogy, formed on quartzite, sericite-schist, gabbro, itabirite, ironstone, meta -limestone, gneiss, and phyllite. Mean SOC and N concentrations were generally high, whereas mean soil C:N ratios varied from 9.5 to 18.7 among parent materials, and only in three soils C:N ratios varied considerably with depth. Enrichment factors (EFs) were generally < 1 in the sand and silt fractions for SOC and especially N. Conversely, EFs for clay were mostly > 1 for SOC and even higher (up to 6.58) for N. Such trend indicates that SOC and N are concentrated in clays, and more importantly, that N sorption is favored compared with SOC, and likely dependent on clay mineralogy. Soil C:N ratios decreased with increasing values of exchangeable bases, due to higher N in the most fertile soils, suggesting that a mechanism of R-NH 3 + cationic sorption is likely involved. Our results suggest that soil N is a critical component of the overall stabilization of soil organic matter onto clays of tropical soils, deserving further investigation also under temperate climate and other zones. [ABSTRACT FROM AUTHOR]

• A meta-analysis to test rubber stand age and altitude effects on soil properties. • Forest-to-rubber conversion significantly reduced SOC pools by 24%. • Rubber monoculture-to-intercropping significantly increased SOC pools by 6%. • Improvement of intercropping occurred in 0–20 cm soil and at 500–800 m altitude. The rapid expansion of rubber plantations may have greatly influenced the carbon stocks of the ecosystem, with potential impacts on mitigating climate change and future carbon fluxes. Therefore, soil carbon pools and other properties must be reliably estimated after rubber-based land cover transitions. The aim of this meta-analysis is to understand how various land use changes based on rubber plantations affect soil physicochemical properties, especially soil organic carbon (SOC) pools. This study focuses on three land use changes: (1) forest-to-rubber conversion; (2) rubber monoculture vs. intercropping; and (3) the age and altitude of the rubber stand over a chronosequence in rubber plots. Results showed that the conversion of forest to rubber plantation significantly reduced the SOC, microbial carbon (MBC), total nitrogen (TN) and total magnesium pools by 24%, 35%, 13% and 94% respectively, whereas rubber intercropping with different crops profoundly increased the SOC and MBC pools by 6% and 24% on average, respectively. The improvement of rubber intercropping on SOC and properties mainly occurred in the surface soil at 0–20 cm and at altitudes of 500–800 m, but these effects were diminished in the subsurface soil at 20–60 cm and at altitudes higher than 800 m. Rubber intercropping plantations can significantly alleviate soil acidification. Changes in the response ratio of SOC were closely related to the variations in soil clay, bulk density, and C/N ratio. These results suggest that rubber-based land use management policies should promote intercropping plantations, especially those with woody plants, and the altitude of rubber planting should be manipulated to minimize the loss of soil C, N, and other nutrients. [ABSTRACT FROM AUTHOR]

• The response of soil water content (θg) to vegetation restoration mode varied highly. • θg increased with soil depth and the distance from the ephemeral gully (EG) head. • θg was less on EG top with artificial plant than on EG top with natural plant. • Natural succession is recommended to control soil erosion and maintain soil water. Vegetation restoration in an ephemeral gully (EG) can alter the traits of soil, vegetation, and microtopography, and therefore likely influences soil water. Nevertheless, few results have been reported regarding the response of soil water regime to vegetation restoration modes in EGs in semiarid region. This research was designed to clarify the spatial variation in soil water in an EG with different restoration modes on the Loess Plateau of China. For the selected EG, the two banks of ephemeral gully were well restored by natural succession and artificial planting. Soil water content (θg) was quantified on the ephemeral gully floor (F), natural successional restored ephemeral gully top (NT), and artificial planted restored ephemeral gully top (AT) in both the vertical and longitudinal directions. A sloping farmland was selected as the control. The results revealed that θg increased significantly with soil depth (i.e., 0–1 m) and the distance from the ephemeral gully head (i.e., 0–60 m). In the vertical direction, the mean θg of the six test points of the ephemeral gully floor was 1.1 to 1.2 times greater than that of the control in each soil layer, while the mean θg of the six test points of NT and AT decreased by 12.3 % to 15.6 % and 29.2 % to 29.9 % compared to the control in each soil layer. Along the longitudinal direction, the θg (i.e., 0–1 m soil layer) abided by the pattern of F > NT > AT. The difference in θg between the three ephemeral gully units and their variations in the vertical and longitudinal directions were mainly driven by the variations in soil clay content, bulk density, organic matter content, plant root density, plant litter density, and the distance from the ephemeral gully head. The findings are useful to clarify the spatial variation in soil water and to select a reasonable vegetation restoration mode on hillslopes in semiarid regions. [ABSTRACT FROM AUTHOR]

• Digital mapping of soil clay types was performed using easily accessible covariates. • Multiple linear regression and random forest algorithms were compared. • Random forest resulted in higher prediction performance. • Topography and soil properties mainly affected palygorskite and kaolinite variation. • Soil properties were considered responsible for the spatial distribution of illite. Understanding the abundance variability of clay minerals, as fundamental soil components, will help the users to improve land management and address concerns over climate change and soil fertility. Therefore, this investigation aimed to model the abundance and spatial distribution of clay types, including palygorskite, illite, and kaolinite, and identify the most significant variables affecting their variability using a digital soil mapping (DSM) approach in Darab district, southern Iran. Multiple Linear Regression (MLR) and Random Forest (RF) techniques were applied to link clay types and environmental attributes that were obtained from a Landsat-8 operational land imager (OLI) and digital elevation model (DEM). A ten-fold cross-validation approach was applied to calibrate and validate the models, and 50 bootstrap models were used to quantify the prediction uncertainty. The models accuracy was defined by the coefficient of determination (R2), root mean square error (RMSE), and the ratio of performance to the interquartile range (RPIQ). Findings denoted that the RF model better predicts the abundance and variability of clay minerals in the study area (R2 = 0.56, 0.47, and 0.48, RMSE = 5.3, 1.91 and 0.63 % and RPIQ = 2.82, 3.28 and 2.62 for palygorskite, illite and kaolinite, respectively). Based on the feature selection analysis, topographic covariates and soil properties determined palygorskite and kaolinite content variations, while for illite, only soil properties could explain the spatial distribution. Besides, the RF produced a lower uncertainty for palygorskite compared to the other clay types. The present research can provide new insight into the spatial variability of clay minerals in arid and semi-arid regions of Iran that could be extended to other similar environments. Moreover, the results showed that the easily available environmental variables could provide reliable predictions. However, other environmental covariates, such as XRF analysis, Vis-NIR, and MIR spectroscopy, are also recommended as input variables for further studies. [ABSTRACT FROM AUTHOR]

• The ejection characteristics of soils with a textural gradient were investigated. • Distribution and size-selectivity of particle are determined according to texture. • Clay-and fine-silt-sized sediment were preferentially ejected in splash erosion. • Soil texture also indirectly governs particle ejection via surface crust formation. The ejection of surface soil particles caused by raindrops is an important stage of water erosion. Generally, surface soil is typically comprised of more complex structural units (e.g. crumb, block, or platy structures) rather than single granular structures (e.g. aggregate), especially on surface soil influenced by the different arrangement mode between soil particles. Thus, soil aggregate samples as a selected test material cannot properly characterise the particle ejection characteristics of surface soil with more complex structural units during rainfall. Considering this issue, undisturbed soil samples with a textural gradient were collected as test materials for this study and a needle-type raindrop simulator was used to simulate rainfall experiments. Our results demonstrate that, the first 6 min of rainfall is the key period for particle ejection. During this phase of the experiment, the clay-sized and fine-silt-sized particles were preferentially ejected, and the enrichment ratio (ER) of those particles decreased progressively from sandy loam to silty clay loam. With increased rainfall duration, the soils with a low clay content (e.g. sandy loam, silty loam and loam) were found to develop surface crusts more easily compared with clay loam and silty clay loam. Although the formation of soil crust reduced the size-selectivity of the splash-detached particles, the percentage of sand-sized particles in splash-detachment particles showed an increasing trend, while the percentage of clay-sized and fine-silt-sized particles showed a decreasing trend. The finding of this study suggests that identifying changes in the soil surface condition, as determined by soil texture, is the key factor affecting the ejection characteristics of surface soil particles during splash erosion. [ABSTRACT FROM AUTHOR]

Soil pore structure over a wide range of pore sizes regulates soil functions and relies heavily on pedogenic processes. To date, limited knowledge is available on the spatial variations of soil pore structure and underlying mechanisms over a broad geographic scale. Herein, seven typical zonal soils with increased status of soil development in heavy-textures were collected at different genetic horizons under forests along the mid-temperate to tropic climate gradient in eastern China. Pore size distribution (PSD, 0.006 ∼ 800 μm) of aggregates (sized ∼ 1 cm3) and other pore structure characteristics (void ratio, pore area and average diameter) were determined by mercury intrusion porosimetry. Differential PSD displayed tri- or bi-modal patterns and different pore size classes followed diverse geographic trends. Textural pores most influenced by soil type exhibited larger void ratio and pore area in highly than in moderately developed soils; structural porosity most influenced by soil horizon overall decreased with increased soil depth, indicating the decreased levels of hierarchical aggregation whatever soil type. Relative to soil texture and total organic matter (0.70≤|r|≤0.92), total and textural pores were more related to inorganic cementing agents (0.71≤|r|≤0.95, p < 0.001), where kaolinite and free iron/aluminum oxides (mainly crystalline form) exerted the positive effects on void ratio and pore area through clayey pores, in contrast to vermiculite and exchangeable cations; void ratio and pore size of structural pores could be separately promoted by sand-silt size organic matter and vermiculite (r = 0.79 and 0.73, p < 0.001). Additionally, clay-sized organic matter, sand, and free manganese oxides played a secondary effect (R2 = 0.04 ∼ 0.30, p < 0.05) and their specific roles differed with pore size class. The overall results suggest that the dramatic geographic variations of soil pore structure are controlled by both inorganic cementing agents and specific organic components to a large extent at the regional scale. [ABSTRACT FROM AUTHOR]

• Length dependent rill erosion processes seemed to be different on gentle slopes. • Equilibrium sediment transport was reached on the rills >7 m length under Q L. • Rolling of coarse particles affected by flow rates and rill length was evidenced. • Continuous head-cuts formation along long rills was an important affecting process. • Steady C and Dr of the 1-m-rill deviated from the Foster-Meyer conceptual model. Understanding the dynamic mechanisms of rill erosion is vital for accurately modeling of soil erosion. In this research, rill erosion was experimentally studied using different rill lengths. A flume, 11 m long and 0.2 m wide adjusted to 3% slope, was used for constructing rectangular rills of 0.05 m width and six different lengths (1 to 12 m). The experiments were carried out on a clayey calcareous soil from a semiarid region under two flow rates of Q L = 0.025 and Q H = 0.045 L s−1. Temporal sediment concentrations (C) were measured at the rill outlet for 40 min and the sediment size distribution (PSD) was recorded twice during each test. The common decreasing trend of C was affected by both flow rate and rill length. The formation of head-cuts along the bed of long rills was an important erosion process affecting C and PSD. The compiled data were used to determine the exponential models' parameters of both C and soil detachment rate based on the steady, unsteady, and event-average values. While, the equilibrium sediment transport occurred by increasing rill length beyond 7 m under Q L , the tested rills under Q H were not sufficiently long for the flow to reach its maximum transport capacity at the gentle slope used and for the calcareous soil tested. Based on the sediment PSD, the selective transport of coarse particles was evidenced. Selectivity transport was affected by rill length reached its maximum at the rill length of 7 m. The findings provides better understanding of rill erosion processes for calcareous soils on gentle slopes in semiarid regions. Further research is needed for better understanding of the rill erosion processes on short gentle slopes to provide experimentally supports for the existing theoretical concepts of rill erosion models. [ABSTRACT FROM AUTHOR]

• Surface activity on chronically subsided relief was analysed in a coal mining region. • Overall subsidence of 4–9 m from 1966 to 2013 pre-determined near-surface displacements. • Tree-ring records from Larix decidua Mill. showed the strongest activity in the 1970s. • One-year compression wood was discussed as a specific dendrogeomorphic signal. • Extreme rainfall contributes to surface activity in an area with more clayey soils. Tree-ring records from sites affected by underground mining provide valuable data on the long-term development of subsidence troughs. However, due to complexity of local conditions, it is unclear whether the surface displacements are actually the result of mining operations or shallow landslides caused by extreme rainfall. This paper compares surface movements at two nearby sites in the Upper Silesian Coal Basin (Central Europe) that have been affected by underground coal mining. Dendrogeomorphic data on subsidence-related movements were obtained from 360 increment cores (90 trees) of European larch (Larix decidua Mill.). Subsidence between 1966 and 2013 was calculated from the corresponding digital elevation models and the actual morphometric parameters of the sites were related to tree-ring records. The effect of precipitation on surface displacements was evaluated using logistic regression models incorporating rainfall data from a nearby meteorological station and dendrogeomorphic event years. The subsidence at the edges of subsidence troughs (study sites) between 1966 and 2013 reached 4–9 m, which is relatively low compared to nearby (5 km radius) directly undermined sites with subsidence up to 22 m. Most events were dated to the 1930s, 1970s, 1990s, and late 2000s with a peak of activity in 1973 and other noteworthy events in 1986, 1995, and 2009. Event years at the site with a flatter topography, and more waterlogged and clay soils are well explained by higher triennial precipitation and higher Simple daily intensity index, suggesting a possible influence of near-surface displacements on the chronology of recorded events, whereas the elevated site with step-block topography showed no relationship between precipitation extremes and event years. We concluded that not only the time of mining operation, but also the site-specific conditions are crucial for characterization of surface displacements in the forested post-mining landscape. [ABSTRACT FROM AUTHOR]

• Soil clay and moisture mediate the decoupling of C, N and P cycling along an elevational gradient. • Total organic C pools were highest where the clay content was highest. • Soil organic N pools were controlled by clay and soil moisture effects on microbial stabilisation. • Soil P pools were not related to clay and soil moisture. • Soil organic P was decoupled from soil organic C and N pools along the hillslope. Grasslands extend across a variety of topographies including non-flat hilly areas with varied soil texture and moisture that can mediate soil biogeochemical cycling of carbon (C), nitrogen (N) and phosphorus (P). In this study we examined soil organic C, total N and P pools (both inorganic and organic), as well as gross N mineralisation (GNM, as a measure of microbial activity and N dynamics) and microbial C, N and P in winter and spring along a grassland hillslope. Our results showed that variation in soil clay and associated soil moisture were the most important mediators affecting C and N dynamics along the grassland elevational gradient. Total organic C pools were highest where the clay content was highest, likely because of the sorption capacity of clay stabilising organic matter against microbial decomposition. Likewise, the variation in soil organic N pools along the hillslope was mostly controlled by clay and soil moisture effects on microbial stabilisation of organic N. Furthermore, microbial C, N and GNM increased with increased soil moisture, suggesting that microbial activity was limited by soil moisture. In contrast, soil P pools were not related to clay and soil moisture, while soil organic P was decoupled from soil organic C and N pools along the hillslope. Possibly, differences in microbial stabilisation and mineralisation pathways (oxidation for C and N, hydrolysis for P), microbial homeostatic regulation of C, N and P, and P fixation resulted in a decoupling of P from C and N cycling in this grassland. We conclude that variation in clay and associated soil moisture along grassland hillslopes can have important but non-unidirectional effects on soil C, N and P cycling. [ABSTRACT FROM AUTHOR]

[Display omitted] • FTIR spectroscopy of clay is sensitive to temperature during bushfires. • Boron leached from combusted bark decreases d11B of clays. • No direct influence of combustion temperature on d11B of clays. • Clays have higher d11B after experiencing a high severity fire. • Both FTIR spectroscopy and B isotope could be viable fire proxies. Bushfire occurrences will likely be exacerbated by climate change, thus requiring a model to forecast and manage their impacts. However, a robust bushfire model requires new proxies that can infer fire severity responses to past climate variability. A key test to the viability of new fire proxies is whether they record fire severity in the affected soil. We address this by testing Attenuated Total Reflectance- Fourier Transform Infrared (ATR-FTIR) spectroscopy and boron (B) isotopes in soil clay fractions from Yengo National Park, southeastern Australia, as proxies for bushfire severity. The isotopic results were also compared to that of clays that reacted with experimentally combusted bark. ATR-FTIR spectroscopy constrains the soil temperature to between 225 and 500 °C during high severity fires, based on the lack of dehydroxylation peak characteristics and the increased aromatic to aliphatic organic peak ratios in clays, compared to that of low severity sites. The isotope composition of the non-exchangeable B fraction in clays is lighter after reacting with leaching solutions of bark combusted at higher temperatures. Combustion temperature does not affect the B isotope fractionation during B adsorption onto clays. Changes to the B isotope composition of clays could instead be justified by the varying B concentration and B isotope compositions of the leaching solutions. In Yengo soil clay fractions, sites that experienced a high severity fire show higher δ 11B values by about 1.5 ‰, compared to low severity sites- at odds with observations from our experiment using combusted bark. The combustion of leaves from tree crowns in high severity fires could account for the increase in δ 11B of clays post-fire. In summary, FTIR spectroscopy of clays could be useful for constraining soil temperature during bushfires, while the B isotope composition of clays appears as a promising proxy for fire severity. [ABSTRACT FROM AUTHOR]

• Biochar from sewage sludge, sugarcane, and green coconut increased the water retention in the sandy soil. • Sugarcane and green coconut biochars improved the water holding capacity of all tested soils. • Biochar reduced the bulk density of the sandy soil but not the clayey soil. • Biochar proved distinct benefits for the hydraulic properties of soils with different textures. Most of the Brazilian soils have severe water limitations to crop growth and, therefore, can benefit from organic amendments. For instance, biochar is known to improve soil water dynamics and use efficiency by increasing the water holding capacity and availability. This study assessed the effect of sewage sludge (SSB), green coconut residues (GCB), and sugarcane bagasse (SCB) biochars on the water retention capacity and availability of three tropical soils (Typic Quartzipsamment-TQ, Ultisol, and Luvisol). Control treatments (no biochar) were included as references. Soil bulk density, water holding capacity (WHC), water retention curves, and plant available water (AW) were determined. We also measured soil pH, organic matter content, and electrical conductivity (ECs). Biochar (SCB and GCB) increased the WHC by 62% in the Typic-Quartzipsamment, 38% in the Ultisol, and 18% in the Luvisol. The SCB increased the AW in the TQ and Ultisol by 40% and 10%, respectively. Conversely, SCB and GCB reduced the AW in the Luvisol by 22.5% and 17.5%, respectively. Biochar improved the WHC of the coarse-textured soils. In the clayey soil, biochar improved soil porosity and water transmission. We conclude that biochar can be an excellent amendment to soils across a range of textures. [ABSTRACT FROM AUTHOR]

• Clay minerals in soils formed from marls in temperate climate were studied. • High pH hampers pronounced clay minerals transformation. • Clay minerals in soils are mainly inherited from parent material. • Slight changes detected in mixed-layered clay minerals and interlayer space. Five young soil profiles, formed from Miocene marls and argillaceous limestone, were investigated to determine changes in their clay mineralogy. Soil profiles were described, sampled, and their basic properties analyzed (particle size distribution, pH, cation exchange capacity (CEC), CaCO 3 and organic C contents). The soils were classified according to the WRB classification as: 1) Calcaric Mollic Leptosol (Humic); 2) Calcaric Lithic Leptosol (Humic); 3) Calcaric Regosol (Loamic, Relocatic); 4) Calcaric Regosol (Siltic); and 5) Calcaric Cambisol (Densic, Endoloamic, Episiltic). Mineralogy was determined via X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) on bulk samples and clay fractions, and chemical composition was determined by inductively coupled plasma emission spectroscopy (ICP-ES). Calcite, quartz and some plagioclase alongside phyllosilicates were identified in parent material. Dolomite was found in the parent material of younger age. Clay fraction from parent material consists of expandable clays (smectite-rich illite-smectite and vermiculite), illite and kaolinite, with chlorite present in younger parent materials. In most soil horizons dissolution and leaching of less stable phases (calcite, dolomite, chlorite) occurred. Initial stage soil formation is consistent with the dominant influence of parent rock mineralogy on soil clay mineral assemblage. Analyses showed substantial homogeneity between and within profiles; nevertheless, slight changes in the clay mineralogy were noted: decrease of illite layers in illite-smectite in topsoil samples and occurrence of mixed-layered chlorite-vermiculite and/or hydroxyl or organic matter interlayering in soil horizons. Chemical composition of bulk samples indicated mobility only of alkali elements, confirming weak chemical weathering. The results show slight changes in clay mineralogy, which can be detected in young soils developed from calcareous parent material under high pH conditions. Those weak alterations of parent clay minerals assemblage, often through unstable phases, can modify soil properties, but are also indicators of subtle clay transformation in calcareous soils in temperate climate. [ABSTRACT FROM AUTHOR]

[Display omitted] • We studied the effects of moisture content, slope angle, and clay contents on mass failure. • A self-designed hollow model was used. • Indoor hollow-flume experiments were conducted under the condition of surface runoff. • Soils with 5%, 7.5%, and 10% initial water content generate fatal mass failure. • Soil mass failure occurs when critical water and clay contents are reached. Soil mass failure disasters are among the most destructive disasters in mountainous areas worldwide, and they continue to receive significant attention in the literature. However, factors that influence soil mass failure in hollows have not been explored via experimental approaches. In this study, we conducted a series of indoor hollow–flume experiments to exhibit how the three factors, namely, initial moisture content, slope angle, and clay content, influence the collapse of soil mass under surface runoff conditions. Our findings revealed that the major processes causing soil mass failure were internal seepage erosion resulting from subsurface runoff, migration of fine particles, development of tension cracks, increase in pore water pressure, and decrease in cohesion. Fluctuations in pore water pressure were characterized by two main trends: (1) an abrupt rise under static liquefaction and (2) a decrease before failure due to dilatancy. The time required for soil mass failure first decreased and then increased with the increase in moisture content. The soil mass with an initial moisture content of ∼12.5% was more critical to the failure. In addition, the time required for soil mass failure decreased with increasing slope angle, revealing a slope angle of 40° to be more prone to failure. The buildup of pore water pressure was found to increase with clay content; soil with a clay content of ∼7.5% required the shortest amount of time to initiate slides. Thus, our results provide a thorough insight into the processes and factors involved in the initiation and development of soil mass failure in hollow areas, which can be used by public agencies to improve monitoring, early warning, and forecasting systems. Notably, our study can help identify risk-prone source areas, and sensors can be installed to monitor potential mass failure locations. [ABSTRACT FROM AUTHOR]

• Rill morphology evolution on 4 coarse-textured topsoils is studied by laser scanning. • Rill headward and downward erosion are two mutually reinforcing processes. • Soil erosion intensity can be indirectly evaluated by geomorphologic comentropy. The sheet and rill erosion phases dominate the erosion process of the catchment area and up-slope of Benggang (a special gully) area, and its evolution has a vital impact on erosion characteristics in the erosion feedback loop. Here, the rill development processes, morphological characteristics and corresponding soil loss were investigated by laser scanning on the four coarse-textured granite topsoils defined as WH, TC, GX, and CT for the counties of Wuhua, Tongcheng, Ganxian, and Changting in China, respectively. A soil flume (3 × 0.8 m) at a slope gradient of 16.7% was treated with rainfall-inflow at the upslope inflow rate of 2 L min−1 and rainfall intensity of 90 mm h−1. Results showed that soil erosion rate increased with erosion evolution (sheet erosion, rill advance, and rill maturity phases). A comparison of the four different soils exhibited that the soil erosion rate showed a downtrend with the increase of soil clay and gravel contents. Specifically, the CT soil with high clay and gravel content showed the minimal soil erosion rate (0.024 kg m−2 min−1), rill density (0.95 m m−2), headward erosion rate (0.41 cm min−1), and surface evolution rate. The maximal soil erosion rate and rill depth were observed on the WH slope, with the rill headward erosion rate reaching the maximum of 20.59 cm min−1. Despite no significant difference in the geomorphologic comentropy of the four soils, their variation trend and rate could reflect dynamic changes in erosion. The total sediment transport efficiency was improved by rill formation and development, with rill erosion contributing to about 70% of total soil loss for the four soils. This study can enrich our understanding of the rill erosion process and surface morphology of coarse-textured topsoils. [ABSTRACT FROM AUTHOR]

• Litter and tree roots modify the proportion of soil aggregate fractions. • Extensive agriculture implies similar soil carbon storage than agroforestry. • Agroforestry increases the carbon associated with the small soil aggregate fractions. The land use sector currently represents ∼25% of the global greenhouse gas emissions, thus this human activity is having a huge impact on climate change. Semi-arid climate areas, which are widely distributed, are particularly influenced by such climate change. In these areas, land use changes have transformed the entire landscape and increased the greenhouse gas emissions. However, in semi-arid climate areas, the information on the effect of climate change is scarce and usually centred on one single type of land use. For the land uses (forest, agricultural and agroforestry) traditionally found in the semi-arid area in South Portugal, this study aimed to evaluate (i) the soil chemical (pH) and physical properties (bulk density and percentage of different soil aggregate fractions: 250–2000; 53–250 and <53 μm) and (ii) the carbon (C) storage in whole soil and each soil aggregate fraction in land with over 100 years of the same use. The results show that after >100 years with the same land use, C storage in the whole soil was similar in the plots with extensive agriculture based on the agroecology principles to that in the agroforestry plots. However, the concentration and storage of C in the microaggregates (53–250 μm) and the silt + clay soil fraction (<53 μm) were generally higher for the forest and agroforestry land uses than for the agricultural land use due to the tree effect. This C associated with the smallest soil fractions is very stable and is retained in the soil in the long term. In this context, agroforestry systems improve the soil C storage in the long term at the same time that agricultural production is allowed compared to the traditional forest systems. Therefore, the establishment and maintenance of agroforestry systems in the semi-arid climate areas is a sustainable land use for climate change mitigation. [ABSTRACT FROM AUTHOR]

• Mixed forests show a higher soil erosion control benefit than monocultures. • Tree-shrub mixtures reduce runoff and sediment more than tree-tree mixtures. • Mixed forests have the strongest positive impact on soil erosion control in dry areas. • Mixed forests are found to affect soil erosion most efficiently after 20 years of tree growth. • Mixed forests have the highest impact on soil erosion control on slopes of 16–20°. Soil erosion poses a major threat to the sustainability and stability of global terrestrial ecosystems. Mixed forests have more advantages in restoring degraded land and enhancing soil fertility than monocultures, but their influence on soil erosion remains uncertain. Therefore, we presented a meta -analysis consisting of 261 paired observations of mixed forests and the corresponding monocultures from 65 studies to evaluate the effect of tree diversity on soil erosion in China. The results showed that compared with monocultures, mixed forests significantly reduced the annual runoff and sediment yield by 17.4% and 23.6%, respectively. Tree-shrub mixtures showed more efficiency in reducing runoff (24.2%) and sediment yield (32.1%) than tree-tree mixtures. However, the positive effect of mixed forests on soil erosion control was significant > 20 years after stand establishment. Mixed forests showed the highest capacity to control soil erosion at slope angles of 16°-25° (runoff: 27.7%; sediment yield: 37.7%). In terms of soil textures, mixed forests performed better with respect to soil erosion control on sandy soils (runoff: 21.4%; sediment yield: 30.1%), whereas significant differences were not observed between different stand types on clayey soils. In addition, in the dry areas (humidity index (HI) < 30), mixed forests conferred the greatest benefits in reducing runoff and sediment yield (25.8% and 33.0%, respectively). Our results indicate that increasing tree species richness is a suitable approach to controlling soil erosion in China. This research provides a scientific basis for the management and sustainable development of forest ecosystems in the future. [ABSTRACT FROM AUTHOR]

• The bimodal pore size distribution was studied from soil water retention curves (SWRCs). • Hydraulic properties were predicted from structural and textural SWRCs. • The most frequent pore sizes of that bimodal distribution were from the macro and cryptopore classes. • Fe and Al oxides played a major role in structure formation and hydrology of Oxisols. • Microaggregates promotes high saturated hydraulic conductivity in clayey Oxisols. The soil water retention curve (SWRC) and soil hydraulic conductivity (K) are important soil hydraulic properties. In Oxisols, the degree of microaggregation depends on the amount of iron and aluminum oxides, kaolinite and biological activity engaged in modifying the pore size distribution (PSD) of the soil porous system. The objectives of this study were (i) to characterize four Brazilian Oxisols in terms of SWRC and PSD, using undisturbed (structural SWRCs) and disturbed (textural SWRCs) soil samples; (ii) to apply the van Genuchten-Mualem (vGM) model to the prediction of K and (iii) to correlate the classes of porosity and saturated hydraulic conductivity (K sat) with the physical, chemical and mineralogical properties. Four soils were studied: Xantic Kandiustox, Rhodic Haplustox, Anionic Acrustox and Typic Hapludox. The soil samples were collected from the Bw horizon of each soil. The structural SWRCs were determined by Haine's funnels and Richards' chambers, whereas the textural SWRCs were determined by dew point meter. K sat was evaluated by constant head permeameter and, additionally, soil chemical and mineralogical analyses were prepared. It was concluded that: (i) the four soils showed bimodal PSD; (ii) the four soils presented the maximum frequency of equivalent radius in the class of macropores (structural SWRCs) with r max varying between 43.37 and 88,98 μm, and in the class of cryptopores (textural SWRCs) with r max varying between 0.012 and 0.014 µm; (iii) the higher the K sat , the higher the K predicted by the vGM model over the entire soil water content range of the structural SWRCs, except for Xanthic Kandiustox and Typic Hapludox in which this phenomenon occurred closer to saturation ; (iv) the K values estimated by the vGM model from textural SWRCs were very low, varying approximately from 10−25 to 10−11 mm h−1 for the four soils; (v) the degree of microaggregation of Rhodic Haplustox and Anionic Acrustox resulting from the high levels of Fe and Al oxides, leading to the formation of greater inter-aggregate space, had an influence on the high K sat and showed that the mineralogy of the clay fraction was decisive in the physical-hydric behavior of these soils. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coarse-textured soil surface morphology evolution is studied by simulated rainfall. • Surface enriched coarse grains are quantified by photography and binarization. • Soil loss in inter-rill areas is controlled by surface coarse-grain coverage. • Soil clay content and stream power is shown to fit erosion prediction. The evolution of slope surface morphology directly affects the hydrological process and forms a dynamic feedback loop with the runoff and sediment production. However, the unique erosion processes and feedback mechanism for the surface morphological changes of coarse-textured granite soils have been rarely studied previously. Here, a series of rainfall simulation experiments (intensity of 90 mm h−1) were conducted under continual intermittent rainfall conditions (duration of 20 h) on a 0.8 m by 3.0 m soil flume packed with the four coarse-textured granite soils (sieved soils from the counties of Tongcheng, Ganxian, Changting, and Wuhua, China, defined as TCA, GXA, CTA and WHA, respectively) to measure the surface roughness, coarse grain coverage, soil erosion rate, stream power and sediment sorting. The results showed: 1) the coarse grain coverage of the four soils gradually increased with rainfall duration, with the final maximum (74.89%) for CTA soil, which corresponded to the enrichment of fine particles in the sediments; 2) the mean soil erosion rate of the four soils ranged from 0.090 to 0.76 kg m−2 min−1 with the decrease of clay content from 24.19% to 13.60% in the original soils, coinciding with the surface roughness controlled by rill erosion around the coarse grains; 3) the coarse grain cover provided a protective layer to reduce further soil loss in inter-rill areas; 4) the model of soil clay content and stream power was shown to be suitable for soil erosion prediction of coarse-textured soils (R2 = 0.93). The results highlighted soil mechanical composition and coarse grain coverage on the surface as the key factors affecting the coarse-textured soil erosion. This study facilitates our understanding of the unique erosion processes and the erosion feedback mechanism of coarse-textured soils. [ABSTRACT FROM AUTHOR]

• Sediment transport capacity is the dynamic and spatial equilibrium value. • Subsurface hydrology affects sediment size distribution and sediment transport rate. • Fractions of coarse-sized particles increased from saturation to seepage conditions. • Sediment transport capacities increased from free drainage to seepage conditions. Sediment size distribution and sediment load are important factors for the estimation of sediment transport processes. Subsurface hydrologic conditions including drainage, saturation, and seepage can affect the sediment selectivity process and sediment transport, given that downward infiltration under drainage and upward exfiltration under seepage can add one more force on surface particles compared to saturation conditions. The aim of this study was to investigate characteristics of sediment selectivity and transport rates under different subsurface hydrologic conditions in small laboratory flume channels. Series of experiments were conducted with an Opal clay soil under four subsurface hydrologic states ranging from free drainage to 10 cm seepage head conditions with water discharge rates from 0.0003 to 0.0008 m2 s−1 at three slope gradients from 4.56% to 12.17%. Results showed that the fraction of coarse-sized particles increased from saturation to 5 cm and 10 cm seepage head conditions. Compared to saturation conditions, the greater proportion of coarse particles leaving in flow in the free drainage experiments may have been caused by infiltration enhancing the deposition processes and regenerating a coarser surface when reaching the dynamic equilibrium. As slope gradients increased, the subsurface hydrologic impacts decreased on the sediment selectivity process. Both the sediment size distribution and the sediment transport rate changed dynamically and spatially before reaching an equilibrium condition. The determination of sediment transport capacity should consider both dynamic and spatial equilibrium conditions. For the Opal soil, the sediment transport capacity values greatly increased from free drainage to saturation conditions, and the differences between these two subsurface hydrologic conditions increased for greater water discharge rates and slope gradients. From saturation to 5 cm and 10 cm seepage head conditions, the sediment transport capacity values increased slightly, and the differences were stable for the slope gradients and water discharge rates studied. [ABSTRACT FROM AUTHOR]

• The content of soil MBC and DOC increased by 9.5% and 12.3% after DWC. • The effect size of MBC continuously increased with the number of DWC. • The number of DWC and D/T had a positive effect on the effect size of MBC. • The increase in the number of DWC had a negative effect on DOC. Climate change may significantly increase drying-wetting cycles (DWC) in terrestrial ecosystems. However, the effects of DWC on soil microbial biomass carbon (MBC) and dissolved organic carbon (DOC) remain elusive. Therefore, we used a meta -analysis including 187 observations to clarify the effects of DWC on soil MBC and DOC. The results showed that DWC increased soil MBC by 9.5%. The effect size was negatively related to soil clay content, SOC, total nitrogen, while it was positively related to soil sampling depth, and the ratio of drying days over the total number of days in a DWC (D/T). Simultaneously, DWC increased soil DOC by 12.3%. Moreover, the effect size of MBC continuously increased with the number of DWC, while that of DOC decreased with the number of DWC. This result may explain why the CO 2 pulse after rewetting continues, but its amplitude decreases gradually with the increase of DWC number. Overall, our results help understand the responses of soil MBC and DOC to DWC in terrestrial ecosystems, and could improve the prediction of soil carbon emissions under more variable soil moisture regimes in the future. [ABSTRACT FROM AUTHOR]

• Redox potential decreased with increasing clay content and was lowest in eluvial horizons. • Ferrihydrite dissolution is an ongoing process in eluvial horizons of Midagahara peatland. • Higher pH and redox potential limits dissolution of iron oxides in the subsoil horizons. • Redox potential decreased in forest soil under heavy snow cover during winter. • Reducing conditions in winter and low pH are favorable for formation of eluvial horizon. Although eluvial (E) horizons of podzols typically form on sandy soils, they can also form in acidic clayey soils. Two non-exclusive hypotheses for E-horizon formation in clayey soils are podzolization and the reductive dissolution of iron (Fe). To analyze the effects of redox reactions on Fe solubilization in montane soils in regions with heavy snowfall, we measured the redox potential (Eh), pH, and Fe2+ concentration in soil solutions sampled from the Midagahara peatland of Mt. Tateyama and Mt. Naeba. We also conducted continual in situ Eh monitoring of soils under snow cover in a beech forest on Mt. Naeba. In the Midagahara peatland, Eh decreased with increasing clay content and was lowest in E horizons. A mineral stability diagram of the soil solution data, in which (pH + 3pe) was expressed as a function of log [Fe2+], suggests that ferrihydrite dissolution from the E horizons and precipitation of the other Fe oxides (lepidocrocite or goethite) in the B horizons are ongoing processes. A combination of low pH and reducing conditions in clayey soils can increase the loss of Fe oxides to form impermeable E horizons. Continual monitoring of Eh in the soil of Mt. Naeba revealed a sharp drop in Eh under heavy snow cover during winter. The reducing conditions in winter, along with consistently low pH, are favorable for the formation of E horizons in clayey soils, which lead to poor drainage and summer flooding. The combination of clayey E horizons and flooding with snowmelt are required for peat accumulation in the Midagahara peatland. [ABSTRACT FROM AUTHOR]

[Display omitted] • Weathering pedogenic process were main source of heavy metals in tea garden. • Organic matter and redox process control transfer of As, Pb, Cd and Hg. • Geochemical behaviors of Cr, Cu, Ni and Zn were related to pH and iron oxides. • Tea type, bedrock, soil texture and fertilizer affected metals transfer mainly. • High risk by Pb and Cd existed in area with granite/granodiorite and shale. As one of the most popular beverages around world, factors influencing transfer of heavy metals from soil to tea leaves is crucial to investigate and assess health risk through tea drinking. Parent material (PM), soil and tea samples from Anhui province, typical tea producing area in China were collected in this study. To find out distribution characteristics of heavy metals in tea and soil, and influencing factors for transfer process, variables of plantation factors, soil properties and geological background were taken into account. The results showed that weathering pedogenic process could be the main release source of heavy metals in soil under the acid environment for tea growth. More than 75% of soil Cd, Hg, Pb and Zn exceeded background. However heavy metals in tea samples were below the limits of China, WHO and EU standards. Soil organic matter and redox process influenced the distribution and transfer of As, Pb, Cd and Hg in soil and tea. While geochemical behaviours of Cr, Cu, Ni and Zn were mainly related to soil pH and iron oxides in tea garden. The method of classification and regression trees (CART) showed clones of tea type, bedrock type, soil texture, soil organic and fertilizer application were identified as the main factors influencing transfer factors of heavy metals from soil to tea. The specific types of tea grown in the soil with sandy clay and bedrock of granite/granodiorite and shale should be given more monitoring. The non-carcinogenic hazard quotients (HQ) and cancer risk (Risk) through tea drinking were primarily caused by Pb and Cd respectively. To reduce the potential health risk from tea, application of organic and/or compound fertilizer were thought to be the effective management strategy for tea plantation. [ABSTRACT FROM AUTHOR]

• New functions to predict K sat improved prediction compared to other PTFs. • Prediction of water characteristic curve was improved by newly developed functions. • Accounting for soil solution composition improves PTF performance on soils. Saturated soil hydraulic conductivity (K sat) and the soil water characteristic curve have been predicted from soil texture, bulk density, and other soil physical properties. These previous functions do not account for soil clay mineralogy or soil solution composition. The objectives of this study were to: (1) analyze the performance of previously developed pedotransfer functions (PTFs) on saline and sodic soils, (2) predict hydraulic properties of saline and sodic soils with a range of clay mineralogy, and (3) develop PTFs that account for clay mineralogy and solution composition. Most PTFs do not perform well on soils with smectitic clay mineralogy and usually over-estimate K sat and under-estimate soil water characteristic on smectite clay dominant soils. Accounting for soil cation exchange capacity (CEC) as an indicator of soil clay types and solution composition improved the prediction of K sat which had a geometric root mean squared error of 3.28 cm day−1 compared to 6.04 cm day−1 for the best performing PTF from the literature. A PTF we developed to predict soil water characteristic curve was able to predict soil water characteristic curve with a root mean squared error of 0.032 g g−1 compared to 0.082 g g−1 for the best performing previously published PTF. The PTFs developed in this study improved prediction of soil hydraulic properties on salt affected soils by using soil CEC to account for soil clay behavior and responsiveness to the soil solution composition. The PTFs reported here can easily be used to predict the K sat and the soil water characteristic curve of soils in response to changes in irrigation water quality. [ABSTRACT FROM AUTHOR]