Thin Soil Layer Research Articles

Influence of Hydrogel and Zinc Oxide Nanoparticles on the Germination and Establishment of Chenopodium quinoa.

The aim of this study was to assess the influence of hydrogel and zinc oxide nanoparticles on quinoa germination and establishment. Various doses of a commercial potassium-based hydrogel (0, 5, 7, and 9 g), each dissolved in one liter of rainwater, were applied. Additionally, 1.5 g of zinc oxide nanoparticles (ZnO-NP) and pre-crushed nitrogen fertilizer, at a rate of 1.6 kg/ha, were added to the solution to achieve a homogeneous mixture. Following the application of hydrogel in the 10-linear-meter rows corresponding to each treatment area in every block, 25 seeds per linear meter of the "Blanca de Juli" quinoa cultivar were sown with a 4 cm spacing between the seeds. Subsequently, a thin layer of soil, approximately 0.5 cm thick, was used to cover the seeds. Ten seedlings were randomly selected and labeled for subsequent evaluations. The experimental design employed in this research was a completely randomized block design. The collected data underwent an analysis of variance, and the means of all the treatments were compared using Tukey's test with a 5% probability. Height and diameter evaluations of the plant neck were conducted every 45 days. The doses used in this study (5, 7, and 9 g of hydrogel per liter of water) significantly enhanced seed germination and increased the number of plants per linear meter (from 82.00 to 90.33) compared to the control dose without hydrogel (14.66), which resulted in an average of one plant per linear meter.

Development of a new test design to investigate the degradation of pesticides in soil under sunlight conditions

Pesticides applied to soil surface are subject to photodegradation if the parent molecule is sensitive to UV-light absorption. Photodegradation studies are therefore mandatory for the registration of plant protection products to provide data on the degradation rate and on the nature of photoproducts formed. In general, sunlight is simulated in these studies with xenon lamps, e.g., a Suntest® device. Surface application on very thin soil layers followed by direct irradiation is common practice, but the control of the boundary conditions, i.e. soil temperature and moisture, to maintain the structure and viability of the soil is challenging. A homogeneous and stable soil microclimate is crucial to compare the degradation data of the test item from the irradiated soil samples to the dark controls as well as to the results from the aerobic soil metabolism study. After trying different scale-up test systems with the UV-sensitive herbicide imazamox as comparative test item, a new soil photolysis test system was developed which is manageable in the laboratory and enables a more favorable management of the boundary conditions, especially with regard to the soil moisture and temperature. For this, the solar simulator SolarConstant® 1200, equipped with metal halide lamps Radium HRI-TS 1000W/D/S/PRO, was installed by Atlas Ametek (Germany) in a temperature controllable walk-in incubation chamber with aluminum racks and reflectors to minimize diffuse light and to maintain a homogenous temperature of 22(± 1)°C within the irradiated soil. Borosilicate glass vessels with an inner diameter of 10 cm and a maximum height of 9 cm, covered by quartz glass, were used for the incubation of the applied soil under light. Contrary to the imazamox degradation half-lives obtained with the Suntest® test system, where an unusual slower degradation was observed under light compared to the dark controls, the results from the new SolarConstant® study design showed the expected faster degradation under light. Hence, it can be concluded that the experimental boundary conditions of the new test system are more suitable to maintain the viablity of the irradiated soil. Since no adjustments of the soil water content were needed, compared to daily water adjustments for thin soil layers incubated under a Suntest®, drying–wetting cycles are eliminated and microbial-induced soil processes are maintained.

A Prediction Method for Surface Subsidence at Deep Mining Areas with Thin Bedrock and Thick Soil Layer Considering Consolidation Behavior

A Prediction Method for Surface Subsidence at Deep Mining Areas with Thin Bedrock and Thick Soil Layer Considering Consolidation Behavior

Time domain reflectometry coil probes for measuring thin surface layer soil moisture: Field tests over 21 years (2002–2022) under highly variable climate conditions in Mongolia

A coil probe (CP) for time-domain reflectometry (TDR) with a sensor length of 40 mm (CP40) was developed for long-term field soil moisture measurements in a thin surface soil layer (0–3 cm depth). In laboratory, soil moisture measurements of CP40 were nearly identical to those of a traditional two-rod type TDR (2RTDR) probe (rod length: 15 cm, diameter: 0.3 cm, spacing: 3 cm). The CP40 measurement accuracy was between 0.01 m3/m3 and 0.03 m3/m3. For long-term field soil moisture measurements, five CP40 units were installed in the highly wetted soil at the Sanzai site (SS), which is in the permafrost area of the Taiga, and dry soil at the Mandalgobi site (MGS) in the semi-arid area of Mongolia. Four units accurately measured soil moisture at both sites over six years (2002–2007and 2008–2009). Three units succeeded in conducting precisely continuous soil moisture measurements between 2008 and 2022 at the MGS. Two units successfully measured soil moisture over 21 years at both the sites. The representativeness of the CP40 soil moisture measurements in highly wetted soils was low because of heavy rainfall and soil heterogeneity. The accuracy of CP40 soil moisture measurements in highly wetted soils was slightly lower than that of the traditional 2RTDR probe. However, the accuracy of the CP40 soil-moisture measurements in the dry soil was comparable to that of the traditional 2RTDR probe. CP40 units are durable and their field soil moisture measurements demonstrate stable and precise performance (bias, RMSE), even under severe environmental conditions.

The Growth and Carbon Sink of Tundra Peat Patches in Arctic Alaska

AbstractRecent amplified climate warming in the Arctic has caused profound changes in terrestrial ecosystems, with the potential for strong feedback on climate change. Arctic tundra landscapes have developed patchy and thin organic soil (peat) layers at the surface that may continue to grow into mature peatlands and become a larger carbon sink under future warming. Here we use paleoecological analyses of multiple soil and peat cores collected from the North Slope of Alaska to document and understand the formation and development histories of tundra peat patches and permafrost peatlands. We find a consistent peat development sequence for peat patches, first from mineral soils to sedge peat during the Little Ice Age, and then to Sphagnum peat during the recent warming with high carbon accumulation rates. These findings suggest that climate cooling is likely critical for the initial peat buildup on tundra soils due to reduced decomposition, whereas climate warming triggers the regime shift into an increased abundance of Sphagnum mosses that are likely central to enhancing their carbon sink capacity. Additionally, peat patches become similar to permafrost peatlands in the vicinity in terms of ecosystem processes and carbon dynamics, and therefore may have developed the same ecohydrological feedback system to maintain their long‐term stability. This study implies that the potential future expansion of peat patches into peatlands may strongly alter the carbon balance of Arctic tundra, supporting the new United Nations Environment Programme's report that calls for incorporating widespread shallow peat into understanding the peatland–carbon–climate nexus.

One-dimensional infiltration in a layered soil measured in the laboratory with the mini-disk infiltrometer

Abstract Layered soils can consist of a thin little permeable upper layer over a more permeable subsoil. There are not many experimental data on the influence of this upper layer on infiltration. The mini-disk infiltrometer set at a pressure head of –3 cm was used to compare infiltration of nearly 40 mm of water in homogeneous loam and clay soil columns with that in columns made by a thin layer (1 and 3 cm) of clay soil over the loam soil. For each run, the Horton infiltration model was fitted to the data and the soil sorptivity was also estimated by considering the complete infiltration run. For the two layered soils, the estimates of initial infiltration rate and decay constant were similar but a thicker upper layer induced 2.4 times smaller final infiltration rates. Depending on the infiltration parameter and the thickness of the upper layer, the layered soils were characterized by 2.2–6.3 times smaller values than the loam soil and 2.2–6.6 higher values than the clay soil. Sorptivity did not differ between the homogeneous clay soil and the layered soil with a thick upper layer and a thin layer was enough to induce a decrease of this hydrodynamic parameter by 2.5 times as compared with that of the homogeneous loam soil. Even a thin upper layer influences appreciably infiltration and hydrodynamic parameters. Layering effects vary with the thickness of the upper layer and the considered parameter. The applied experimental methodology could be used with other soils and soil combinations.

Source, distribution patterns and resources potential of selenium in soil of north Pakistan: Revealed by a national-scale geochemical mapping

During national scale geochemical mapping in Pakistan, 69 elements including selenium were analyzed in 2563 stream sediment samples, which filled the gap of selenium distribution in the middle section of Tethyan metallogenic belt. The sampling density was 1–2 sites /100 km2. The geochemical concentration of selenium in the samples range from 0.008 to 6.849 mg/kg with an average value of 0.306 mg/kg. The highest average concentration of Se was found in the Suleiman Fold and Thrust Belt (anomaly III3), whereas the lowest is in WKLT Kohistan-Ladakh Island Arc. The type of soil in Pakistan with the highest Se concentration is entisol. The high selenium anomalies are delineated in the northeast of Quetta, near Muslim Bagh, in Mekhtar-Musa Khel area and its southwest region, north of Quetta and Khushab. Three strong selenium anomalies have also been identified in the northeast of Islamabad, northwest of Rawalpindi and the east of Dargai, respectively. It is suggested that selenium anomalies, having a correlation with elements of Mo, CaO, S, Sr, are mainly caused by geological background of shale, coal and coal-bearing formations. Negative anomalies are mainly distributed in the northern Pakistan, which is mostly consists of bedrocks with no or very thin layer of soil. The product of anomaly intensity and variance are defined as prospecting favorable degree (Pfd). The product of Pfd and area (S) are defined as Quantity of Mineral (Qm). There are two anomalies with the highest Pfd in the east of Quetta city, and the anomaly in the southwest of Kundian ranks third. The selenium anomalies indicate the areas of potential Se enrichment and supply basic data and information for geochemical investigation on a larger scale or selenium relevant research.

Effectiveness of Phosphorus Solubilizing Bacteria on Enhancing Phosphorus Availability from Minjingu Phosphate Rock to Maize in Slightly Acid to Neutral Soils

The aim of this one-year field study was to evaluate the impact of phosphorus solubilizing bacteria (PSB) on increasing the availability of phosphorus locked up in insoluble Minjingu phosphate rock for the maize crop (Zea mays L.) in high soil pH. The study was carried out during one wet season in Nghumbi and Mlali villages in Kongwa District in the Dodoma Region, Tanzania. Based on the pH of their soil and the limiting nutrients, two farms from Mlali village and five from Nghumbi village were chosen at random for field trials. To determine the fertility status, composite soil samples were collected from the chosen farms and examined in a lab. Target treatments included the application of PSB inoculum in combination with various rates of Minjingu phosphate rock (MPR) (0, 20, 30, 40, and 60 KgP ha-1) as a basal fertilizer, placed beneath maize seed and covered with a thin layer of soil. Using a fully randomised block design, the treatments were set up three times. Inadequate levels of N, P, K, and Zn were found in the research area's soil samples. Results indicated the main effect of fields’ characteristics from field No.2 had the highest yield to other fields with significantly (P< 0.001) highest grain yield being 4.4 t ha-1, biological yield of 5.6 t ha-1, and Straw P uptake of 19.63 kg ha-1. Using P or an inoculant (Mx) produced a negligible yield of grain and straw, according to the major effect of treatments. For the studied variables, none of the treatments showed any significant (P =0.427) interaction effects. An intriguing revelation that the study's maize response to native P is provided by interaction effects area is a factor of soil and amount of P released to the soil. We recommend more research on PSB for more than one season in high soil pH before ascertaining the technology to farmers.

Variations in Bedrock and Vegetation Cover Modulate Subsurface Water Flow Dynamics of a Mountainous Hillslope

AbstractPredicting the hydrological response of watersheds to climate disturbances requires a detailed understanding of the processes connecting hillslopes and streams. Using a network of soil moisture and temperature sensors, electrical resistivity tomography monitoring, and a weather station we assess the above and below‐ground processes driving the hydrological response of a hillslope during snowmelt and summer monsoon. The transect covers bedrock and vegetation gradients, with a steep upper part characterized by shallow bedrock, and gentle lower part underlain by colluvium. The main vegetation cover is conifers on the upper, and grass and veratrum on the lower part. Combined with a simplified hydrological model, we show that the thin soil layer of the steep slope acts as a preferential flow path, leading to mostly shallow lateral flow, interrupted by vertical flow, mostly at tree locations, and likely facilitated by flow along fractures and roots. Vertical flow and upstream‐driven groundwater dynamics are prevailing at the colluvium, presenting a very different hydrological behavior compared to the upper part. These results show that subsurface structure and features have a strong control on the hydrological response of a hillslope and that those can create considerably varying hydrological dynamics across small spatial scales.

Analysis of Soil Chemical Properties and Their Relationship with Tobacco Plant Productivity in Dry Land

Dryland is defined as land that is never flooded or submerged in water throughout the year. Indonesia has a very large area of dryland, which is 11,876,881 hectares. Generally, drylands have low fertility and thin soil layers with low organic matter content. There are several types of plants that can be cultivated in drylands, one of which is tobacco. Environmental conditions such as soil conditions (physical and chemical properties of soil) affect the production and quality of tobacco, among others, soil status. In this topic, the descriptive method was used as an approach. Data collection techniques (literature) were carried out using books, articles, and scientific journals derived from previous research. It was concluded that an increase in C-organic content, CEC, and KB increased tobacco production. Conversely, an increase in pH can adversely affect tobacco production and quality.

Co-evolution among soil thickness, epikarst weathering degree, and runoff characteristics on a subtropical karst hillslope

Carbonate landscapes make up one-fifth of the terrestrial land area, a better understanding of the coupling relationship between the soil–epikarst form and hydrological function is imperative for hydrology and landscape evolution modeling. In this study, we monitored a total of 158 rainfall-runoff events on a karst slope between 2019/4 and 2022/5 in southwest China, while simultaneously examining the soil–epikarst architecture (924 pairs of soil thickness and epikarst weathering degree). The results indicated that soil thickness increased with the underlying epikarst weathering degree, and soil thickness was positively correlated with epikarst thickness (P<0.001). Additionally, a significant positive relationship (P<0.001) was observed between surface runoff (SR) and soil thickness, as well as a significant negative relationship (P=0.0018) between subsurface runoff (SSR) and soil thickness. These findings imply the dominance of SR and SSR (under normal rainfall conditions) in runoff plots with deep soil layers and thin soil layers, respectively. The soil thickness threshold at which the hillslope discharge shifted from being SSR-dominated to SR-dominated was approximately 50 cm. Nonetheless, a positive relationship was found between SR and SSR under extreme rainfall events, indicating the establishment of hydrological connectivity between the surface and subsurface. Moreover, the hillslope discharge when the rainfall depth is lower than 50 mm is primarily composed of either SR or SSR from different plots. In other words, the hillslope discharge is typically influenced by both SR and SSR when the rainfall depth exceeds 50 mm. We finally proposed a positive feedback loop among soil thickness, epikarst weathering degree, and the hydrological function of the soil–epikarst system (water storage and release). These findings enhance our understanding of the complex interactive relationships in hillslope hydrology by illuminating the physical links between critical zone structures and hydrological processes on the karst slope.

Analytical solutions for one-dimensional nonlinear large strain consolidation of soft soils with high compressibility under a multi-stage loading

At present, many achievements have been made in the analytical theory of large strain consolidation. However, the consideration of nonlinearity of compression and permeability is not yet sufficient. In this study, a large number of compressibility and permeability test data have been investigated to verify the advantages of log-log relationships in describing nonlinear characteristics of compressibility and permeability of soft soils under both large strain and small strain, and the variation range of parameters in log-log relationships are also presented. Also, based on the log-log relationships, a one-dimensional nonlinear large strain consolidation model of thin soft soil layer is established by considering excess pore pressure as a variable, and the analytical solutions of the consolidation model are obtained under three conditions, respectively. Then, the reliability of analytical solutions is verified by comparing with the results observed in the field and degenerate solution, respectively. Finally, the influence of loading method, final load, compressibility and permeability parameters on consolidation behavior are analyzed. This study provides theoretical supports for the calculation of nonlinear large strain consolidation of actual soft soil layer.

Landslide risk evaluation and its causative factors in typical mountain environment of China: a case study of Yunfu City

The urban area of Yunfu City is a typical mountain environment with the thin surface soil layer, broken terrain, and the fragile geological environment, which is a landslide hazard prone region, seriously threatening the safety of residents' lives and property. It is crucial to accurately reveal the landslide risk and its causative factors to develop regional geological disaster prediction and mitigation strategies. However, the risk assessment and cause analysis of landslides in Yunfu City are rarely studied at present. Therefore, this study selects 11 causative factors (elevation, slope, slope aspect, bedding structure, distance from fault, lithology, precipitation, distance from water, normalized vegetation index (NDVI), distance from road, and land use), and integrates the modified frequency ratio model and geographic detector method to analyze the spatial distribution pattern of landslide risk and its causative factors. The results indicate that the maximum predicted area under the receiver operating characteristic curve (AUC) and the average predicted AUC of the modified frequency ratio model perform best at the precision of 5, with the values of 0.83921 and 0.81872, respectively, which can accurately reveal the landslide risk evaluation in the study area. According to the experimental results, the landslide risk in the study area generally shows a trend of high in the north and low in the south. Besides, the overall risk of landslide hazards is low, with the area of very low grade and low grade accounting for 75.20% of the total area. Among the selected 11 potential factors, precipitation, NDVI, slope aspect, distance from water and slope are the main causative factors to induce landslide hazards. Furthermore, this study also describes in detail the combination of factors that are conducive to landslide hazards, which can provide a decision basis for relevant departments to carry out regional landslide hazards prevention and mitigation strategies, and can also provide a reference for geological hazard risk evaluation study in other mountain environment.

Elucidating the impacts of trees on landslide initiation throughout a typhoon: Preferential infiltration, wind load and root reinforcement

AbstractTyphoon‐induced landslides are widespread, damaging and deadly. In this study, we elucidated their spatiotemporal features through investigations in Southeast coastal China and proposed a numerical model that involves typhoon wind load, preferential infiltration and root reinforcement. The wind load is calculated through a combination of the autoregressive method and a multi‐degree‐of‐freedom tree swaying mode, transmitting to the slope through the wind–tree interaction. Taproots of trees are modelled as piles, and root–soil interfaces are modelled as preferential infiltration boundaries. Using the numerical model, we quantitatively assessed the impacts of wind load, rainfall infiltration and root reinforcement on the slope stability and compared results with cases in Waipaoa and Wairoa (New Zealand). Results suggest that the impacts of trees depend heavily on meteorological and geological conditions. Trees play a destabilizing role in Southeast China during a typhoon but a stabilizing role in the cases in New Zealand. For slopes in Southeast China with a thick soil layer (&gt;root depth), strong wind load and preferential flow resulting from root–soil interfaces, rather than slope surface infiltration, significantly decrease the slope stability in a short time. Slope failure occurred in all scenarios that account for the preferential infiltration, and its combination with a Force 14 typhoon wind load can fail the slope at 10 h after the typhoon initiation. Differently, tree roots in cases in New Zealand can penetrate through the thin soil layer (&lt;1 m) and provide considerable additional resistance to stabilize the slope.

FEM Modelling of Thin Weak Layers in Slope Stability Analysis

Modelling the presence and the effect of a thin weak layer of soil or rock in a slope stability analysis performed through the finite element method (FEM) presents several problems of purely numerical nature. This paper deals with a parametric analysis of three different 2D numerical case studies (both ideal and real) of unstable or potentially unstable slopes containing a thin soft band (or weak layer). The FEM software used is RS2 (Rocscience®). The aim is investigating the influence of some geometrical and numerical characteristics of the soft bands in the stability analyses. The Mohr–Coulomb elastic-perfectly plastic constitutive model for all the involved materials was assumed, and the mechanical parameters were kept constant. Instead, other fundamental parameters of the weak layer, such as the type of mesh elements, the mesh density, and the geometry, in terms of both thickness and outcrop shape, were changed, and results in terms of the critical Strength Reduction Factor (SRF) were compared. The main outcomes of this study represent practical suggestions on some numerical and technical aspects to users of FEM slope stability analyses, in order to obtain a precautionary assessment of slope stability.

Numerical modeling of a cohesively separating soil layer in consideration of locally varying soil distribution

Predicting the cleaning time required to remove a thin layer of soil is a challenging task and subject of current research. One approach to tackle this problem is the decomposition into physical sub-problems which are modelled separately and the subsequent synthesis of these models. In this paper, an existing model for adhesive detachment is extended for the prediction of the cleaning time of cohesively separating soil layers. The extension is based on measurements of the pull-off forces and their correlation to the local water mass fraction. The resulting new model is validated using cleaning experiments with starch in a fully developed channel flow. Furthermore, an inhomogeneous soil distribution and its effect on cleaning results like cleaning time and removal rate is investigated. It is shown that accounting for the local soil distribution in the model leads to a significant improvement of the prediction of the cleaning behaviour.

Determination of non-linear shear strength and volume changes on remolded granitic residual soil due to membrane penetration

Membrane penetration is the term used to describe the displacement of the rubber membrane into the spaces between the cylindrical specimens during triaxial testing in the consolidation stage. Membrane penetration from elevated cell pressure during the consolidation stage might have a negative effect on the interpretation of stress-strain data and specimen volume calculations during the shearing stage. To assist engineers in making knowledgeable judgments, additional study is needed to examine membrane penetration in granitic residual soil. In this study, membrane penetration was investigated using a modified graphical technique. Triaxial tests on grade V granitic residual soil were conducted as part of the study at effective confining pressures of 50 kPa, 100 kPa, 200 kPa, 300 kPa, and 400 kPa. In the tests, real specimens constructed of compacted granitic residual soil with initial diameters of 50mm and 100mm, and dummy specimens made of a thin soil layer containing a solid, rigid cylindrical core, were both employed. Without considering the impact of specimen compression, the behaviour of membrane penetration was only examined in the dummy specimens. The graphical method has to be altered as a result of the fines. The findings demonstrated that the effect of membrane penetration increased with a rise in effective confining pressure and became less relevant at confining pressures of 300 kPa or lower.

Stand biomass decreases towards the edge of a range expanding invasive plant, Mikania micrantha, but only on thick soil layers

During spread in the new range, invasive plants may evolve distinctive traits that make them rapidly occupy the suitable and empty sites at the invasion front, such as rapid growth rate and high seed dispersal ability. However, less is known about how competitive ability evolves during range expansion, and no study has examined whether stand biomass (i.e. biomass production of dense monocultural stands, which may indicate the invasion speed and impacts of invasive plants) changes during range expansion. In this study, using 27 populations of an invasive plant, Mikania micrantha, which is expanding its range on Hainan island of China, we examined how competitive ability and stand biomass change along the invasion route. We grew plants of M. micrantha either singly or with common intraspecific competitors originating from different populations in 3 liter pots to evaluate competitive ability, and grew six plants from the same population together in 3 or 11 liter pots to evaluate stand biomass. When grown alone or with competitors, plant biomass and competitive ability did not correlate with distance from invasion center. Stand biomass was negatively correlated with distance from invasion center in 11 liter pots with a thick soil layer, but not in 3 liter pots with a thin soil layer. Stand biomass was negatively correlated with root to shoot ratio (RSR) in 3 liter pots but not in 11 liter pots, possibly because excessive allocation to roots for belowground competition reduced the overall performance at the stand level when soil space was highly limited. Stand biomass was unrelated to competitive ability. Our results indicate that edge populations of invasive plants may have reduced stand level performance in habitats with thick soil layers. In habitats with shallow soil layers, populations of invasive plants may evolve greater allocation to roots and reduced stand level performance.

Combining infiltration hole and mulching techniques with fish-scale pits effectively improved soil water storage in semiarid areas with shallow buried bedrock (Pisha Sandstone) in China

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.

Quantitative analysis of rainwater redistribution and soil loss at the surface and belowground on karst slopes at the microplot scale

On karst slopes, soil and bedrock form soil-rock structural units (SRSUs), leading to complicated soil erosion for which quantitative attribution can hardly be achieved through whole-slope tests. This study aimed to quantify the role of different SRSUs in the soil erosion process, including rock covering the soil (RCS), bedrock exposed at the surface (RES), and a thin soil layer covering bedrock (SCR). Surface flow (SF), subsurface flow (SBF), infiltrated rainwater entering underground bedrock fissures (UF) and transported sediments were measured in soil boxes representing these SRSUs on karst slopes (5° and 25°) under 50 mm/h rainfall. The results indicated that among the three SRSUs, SF accounted for < 1% (2.5%-4.2%) of the total rainfall on the 5° slope (25° slope); SBF of the SCR, RES and RCS SRSUs accounted for 12.9% (37.9%), 14.9% (46.9%) and 10.8% (35.9%), respectively, of the total rainfall on the 5° slope (25° slope), and UF accounted for 28.6% (6.5%), 25.7% (10.0%) and 32.3% (3.7%), respectively, of the total rainfall. The SBF values of the SCR and RES SRSUs were 23% higher than that of the RCS SRSU on average. The UF values of the SCR and RES SRSUs were 16% lower than that of the RCS SRSU on the 5° slope and were 125% higher than that of the RCS SRSU on the 25° slope on average. Soil loss mainly occurred through SF, and the amount of soil lost through SBF or UF was < 0.01 g/L. These results suggest that both the type of SRSU and slope could greatly influence rainwater redistribution in soil and that the rain-driven soil loss through underground bedrock fissures was low on karst slopes. This occurred because the infiltrated rainwater or rock surface flow reaching the rock-soil interface (RSI) underground became preferential flow (RSI-PF). Thereafter, part of RSI-PF entered bedrock fissures as UF, whereas the remaining RSI-PF likely seeped into the soil and contributed to SBF or SF. Therefore, on the whole slope, which comprises different SRSUs with high heterogeneity, the soil erosion process is very complex because of the interaction between the surface and subsurface.