Soil Pan Research Articles

Changes in erosion susceptibility of a Chromic Haplustert pasture soil by some polymers under simulated rainfall

Due to the climate change that has become evident especially in the last ten years, ecosystems such as forests and pastures in the Mediterranean climate zone have become even more vulnerable to degradation. High erosive precipitation increases the amount of erosion in these soils with increasing their erodibility. The aim of this study was to determine to what extent some polymers, such as polyacrylamide and polyvinylalcohol, can prevent runoff and soil loss from erosion pans where a pasture soil was placed. For this purpose, aggregates of soil samples <8 mm from the A horizon of a Chromic Haplustert were used. Polyacrylamide and polyvinylalcohol solutions at different doses (0, 3.5, 7.0 and 14.0 kg ha-1) were applied to the aggregates by spraying. Erosion pans with slopes of 9% and 15% were exposed to simulated rainfall produced by a drop former rainfall simulator for one hour. The simulation trial was planned as 2 replications according to the randomized plots trial design. During simulated rainfall, runoff water and sediment from pans were collected at 10-minute intervals. Transported soils were expressed as dry weight, and runoff waters were expressed as volumetric. According to the results obtained, the highest runoff occurred from a 15% inclined soil pan (11.06 mm) without polymer applied (control). After one hour of simulated rainfall, runoff did not occur from some pans with high-doses of applied polymer. The amount of soil transported from the control pan by runoff and by splashing to the sides is 362 and 4241 kg ha-1, respectively. The pan, in which the least soil is carried by splashing, was the one with a 9% slope and the highest dose of polyacrylamide (97 kg ha-1). Statistical results show that polyvinylalcohol was  more successful than polyacrylamide in reducing soil and water losses especially on 15% slope. These results indicate that the application of polymer to pasture soils can be a valid way to combat erosion, but the treatments should be carried out by choosing the right dose, taking into account factors such as the slope of the land, the erodibility of the soil and the erosivity of rainfall. 

13C evidence for the selective loss of active and inert organic carbon in soil aggregates under rain-induced overland flow erosion

Due to the hierarchical structure of aggregates, raindrops cause changes in the composition, distribution and state of aggregate-wrapped organic carbon (OC) fractions during erosion, greatly affecting soil carbon turnover and sequestration. To explore these regulatory mechanisms, the selective transport of light (LFoc) and heavy (HFoc) fraction OC within aggregates of varying sizes was traced via the 13C/12C carbon isotope ratio (δ13C) under splash and sheet erosion conditions. A “three-zone” variable-slope soil pan was filled with loess soil with a high aggregate concentration to monitor rainfall erosion on a slope. The OC aggregate composition, aggregate stripping and δ13C values of the sediment aggregates of various particle sizes were measured. When the erosion intensity was low, the splash-eroded sediment was mainly enriched in 13C-rich HFoc, and as the rainfall intensity increased, the concentrations of 12C-rich LFoc and HFoc gradually increased. That is, under heavy rainfall, aggregate fragmentation exposed more large fragments rich in younger HFoc and LFoc, and these fragments underwent saltation. There was no obvious correlation between the trends in splash erosion and OC, so runoff transport was an important factor influencing the correlation between δ13C and OC (P < 0.05). Raindrop impact exposed HFoc-rich aggregate fragments of different sizes, e.g., stable mineral-associated OC. Runoff promoted the obvious preferential transport of LFoc and the redistribution of particulate OC (POC) among different sediment particles. Mineral-associated OC and 2–0.05 mm easily decomposable LFoc or POC were preferentially transported, causing OC with the highest and median δ13C values to be preferentially transported. Overall, the transport order of aggregate-exposed OC particles was clay + silt particle-bonded OC, POC, POC-bonded aggregate fragments and silt-bonded aggregate fragments. These results verified the selective loss of aggregate-detached OC fragments during erosion, which led to a change in the OC sequestration and reaggregation potential of OC in the eroded and deposited soil.

Impacts of straw mulching in longitudinal furrows on hillslope soil erosion and deposition in the Chinese Mollisol region

In the Northeast Mollisol region of China, straw mulching has a great effect on preventing soil loss from ridge tillage, but how furrow straw mulching (FSM) impacts the spatial distribution of erosion-deposition and sediment sources in longitudinal ridge tillage systems is still unclear. Therefore, this study was to quantify the effects of the FSM on the spatial distribution of soil erosion-deposition and sediment sources in longitudinal ridge tillage systems by using the magnetism tracing methodology and indoor simulation rainfall experiments. The experimental treatments included two surface treatments: without the FSM (NFSM) and with the FSM of 0.30 kg·m−2 amount, two rainfall intensities of 50 and 100 mm h−1 were included; each experiment was run for 60 min at a soil pan with a 5° slope gradient, 6.2 m length, 1.3 m width and 0.7 m depth. The results indicated that, compared with the NFSM treatment, the total slope runoff and soil loss in the FSM treatment at two rainfall intensities were decreased by 41.6 % and 99.5 % and by 37.9 % and 97.7 %, respectively, and the reduction in slope runoff and soil loss decreased with an increase of rainfall intensity. The total mass of sediments intercepted by straw mulching on the entire slope accounted for 36.9 % and 10.4 % of the total soil loss in the NFSM treatment, respectively. Erosion regimes dominated on the hillslope of the NFSM treatment with strong-weak alternation at two rainfall intensities, while for the FSM treatment, only deposition regime was observed at 50 mm h−1 rainfall intensity; a slight change with erosion-deposition on the ridge tops was observed and deposition in the furrows was observed at 100 mm h−1 rainfall intensity. Furthermore, the FSM treatment changed the main sediment source from ridge tops to furrows on the hillslope compared to the NFSM treatment, whose sediment contributions from the ridge tops and the furrows at the two rainfall intensities were approximately 16.4 % and 83.6 %, respectively. In conclusion, FSM should be promoted due to its high efficiency in decreasing slope runoff and intercepting sediments. The findings of this study served as a scientific reference for effectively controlling soil erosion along slopes in the Chinese Mollisol region.

Derivation of physically based soil hydraulic parameters in New Zealand by combining soil physics and hydropedology

AbstractField‐characterised soil morphological data (to 1 m depth) and modelled soil water release characteristics are recorded in the S‐map database for soils covering approximately 40% of New Zealand's soil area. This paper shows the development of the Smap‐Hydro database that estimates hydraulic parameters by synergising soil morphologic data recorded in S‐map and soil physics. The Smap‐Hydro parameters were derived using the bi‐modal Kosugi hydraulic function. The validity of the Smap‐Hydro parameters was tested by applying them within an uncalibrated physically based hydrological model (HyPix) and comparing results with soil water content, θ, measured with Aquaflex soil moisture probes (0–40 cm deep) at 24 sites across New Zealand. The HyPix model provided an excellent fit with observed soil water content for 25% of the sites, a good fit for 33% of the sites and a poor fit for 42% of the sites. Applying the model to all soils in the S‐map database required adjustments for the occurrence of rock fragments, hydraulic discontinuities caused by soil pans and required the addition of boundary conditions for water tables and the occurrence of impermeable rock. A discussion on how we can further synergise the development of pedotransfer functions with knowledge of soil physics is provided.

Smart Garden on Chili Plants Based on IoT

Abstract:Cultivating chili plants requires special attention such as temperature and soil humidity. Internet of Things (IoT) technology is a technology that allows objects around us to be connected to the internet network. The widespread adoption of various internet of things technologies has a very pronounced influence in the domestic sector such as home and smart car applications, and the agricultural sector is no exception.Temperature monitoring system, humidityIoT-based soil pan on chili plants (smart garden) is an IoT-based monitoring system design to control temperature and soil moisture on chili plants which can make it easier for farmers to measure soil and plant conditions and to make it easier for farmers to monitor the quality of their agricultural land. The process of creating a monitoring system design begins with interviews to collect primary data and literature studies to collect secondary data. Then carry out system design, tool assembly and implementation. The system for monitoring and controlling temperature and soil moisture using IoT can be run using Windows operating system software. The hardware used is the DHT11 temperature sensor, Moisture Sensor, Arduino, and Nodemcu ESP8266. This system utilizes a pump and fan for its hardware, using an automatic system implementation from a microcontroller so that it can make the hardware run without user intervention.If the humidity value displayed on the LCD is &lt;70% then the pump will be on and the plants will be watered, and if the humidity is &gt;80% then the pump will be off and stop watering.

Selective uneven enrichment of soil organic carbon among different-sized sediments under a rain-induced overland flow: 13C stable isotope evidence

Soil organic carbon (SOC) enrichment varies among sediments of different sizes during rain-induced overland flow erosion. This selective transport of SOC is complex in conjunction with the exposure of labile and stable organic carbon (OC), accompanied by heterogeneous aggregate disintegration under raindrop effects. Utilizing the variations in δ13C values of SOC fractions, we traced this selective transport, linking it to aggregate-wrapped SOC changes during erosion. A modified soil pan facilitated the simultaneous monitoring of splash and sheet erosion via artificially simulated rainfall, with control over the intensity and slope. Aggregate composition, SOC distribution, and δ13C values in the erosion samples were analyzed. The results indicated that distinct sorting existed within the aggregate fragments. Along with SOC variation among different sediment sizes, the proportions of clay and fine silt within sediment aggregates increased as a function of slope and rainfall intensity, whereas particulate OC within aggregates decreased. The SOC enrichment ratios (ERocs) and δ13C values in splash-eroded sediments were positively correlated with those in sheet-eroded sediments. The ERocs in splash-eroded sediments were lower than those in sheet-eroded sediments, but δ13C values were the opposite. Moreover, δ13C values of SOC enriched in sediment particles of all sizes from aggregate stripping were lower than those of the original soil. This indicates that raindrop hits promote heavy C loss during sheet erosion, which is different for mineral-associated and particulate OC. As the slope and rainfall intensity increased, δ13C values for all sediment sizes decreased over the course of erosion. Interestingly, the highest δ13C values were observed under a rainfall intensity of 60 mm h−1, whereas the highest SOC concentrations were noted on a 5° slope. These observations suggest divergent mechanisms affect δ13C values and SOC concentrations in eroded sediments. All these results verified that selective sorting existed for the light SOC fraction. Finally, the internal selective transport of one SOC fraction may explain the enhanced mineralization and reaggregation capacity of the deposited sediments.

Effect of slope borders in reducing splash erosion during sediment transport by rain‐induced overland flow

AbstractSplash erosion plays a vital role in the loss of eroded materials. Unlike those in slope central areas, laterally ejected splashed materials in slope border areas cannot be replenished easily because slope edges prevent splash erosion particles from entering the slope. Thus, splashed materials in slope border areas are less than those in slope central areas because of the lack of source areas for splash‐eroded materials. However, this phenomenon, called the slope border effect, has received minimal attention by researchers. The partially missing splash erosion induced by the slope border effect on sediment transport was investigated to understand the slope erosion mechanism further in this paper. A modified soil pan divided into four areas, namely, central erosion test area (length = 100 cm, width = 35 cm, depth = 45 cm), border erosion test area (length = 100 cm, width = 35 cm, depth = 45 cm), splash compensate border area (length = 110 cm, width = 30 cm, depth = 45 cm) and splash collection area (length = 100 cm, width = 2.5 cm, depth = 45 cm) was used to monitor diffusion and splash erosion under simulated rainfall. Results showed that the splash detachment rate increased with the increase in slope but initially decreased and then increased with the increase in rainfall intensity. The runoff rate and diffuse erosion rates for complete splash erosion (SE) treatments were higher than those without partial splash erosion (SEL). Under low rainfall erosive power and runoff transport capacity (e.g., 5° slope and 60 mm h−1), the transported clay in SE treatments was approximately 2% more than that in SEL treatments. This amount changed to more than 2% sand under high rainfall and runoff erosive power. However, the mass fraction accounted for by silt particles in the sediments of the SEL treatments was more than that in the SE treatments. Thus, the partially missing splash erosion can weaken the selective transport ability of runoff for sediments. The effect of missing partial splash erosion on diffuse erosion was enhanced with an increase in erosive power. The results of our paper will provide insights into the effect of the boundary effect zone of slope on soil erosion and its related mechanisms.

Comparisons of soil organic carbon enrichment and loss in sediments among red soil, black soil, and loess in China

Water erosion could cause wide and serious soil organic carbon (SOC) loss, but differences in SOC loss and enrichment in sediments among red soil, black soil, and loess in China have received less attention. This study investigates the transport of sediments and generation regulation of runoffs during the erosion process by collecting data from indoor or outdoor artificial simulated rainfall experiments and selecting typical regional rainfall intensity and slope gradient for bare cultivate soil slopes as well as 5–8 m length and 1.5–2 m width runoff plots or soil pans. Then, the change in SOC loss for the three widely distributed and seriously eroded soils, from south to north in China, is clarified. Results show that the stable value and growth rate of soil and SOC loss rates followed the following order: black soil < red soil < loess. The SOC loss rate of loess was more sensitive to rainfall intensity and slope gradient than those of the two other soils. The SOC enrichment ratio (ERocs) of the sediments of the red soil and loess soil is higher than that of the black soil, and this difference increases as the soil loss rate decreases. ERocs generally has a negative exponential relationship with soil loss, but it has a negative logarithmic relationship with soil loss for the loess soil with high aggregate and clay contents. SOC and clay content determine the SOC enrichment in sediments for different soils. In addition, this study provides recommendations for improving SOC dynamic models for soil under water erosion.

Effects of Vertical Smashing Rotary Tillage on Root Growth Characteristics and Yield of Broccoli

Most of the soils of the cultivated land in southern China are Ferralsols, which are easily deposited and hardened. To date, rotary tillage (RT) has been the major tillage system used in China. This tillage system results in a shallow soil pan, which reduces broccoli growth and yield. A two-year field experiment was conducted in the Central Zhejiang Basin, China, to compare the effects of vertical smashing rotary tillage (VSRT), RT, and vertical rotary tillage (VRT) on the soil properties, growth characteristics, and yield of broccoli. VSRT reduced the bulk density and penetration resistance of the 0–40 cm soil layer, and increased the soil water content of the 10–40 cm layer. Compared with RT and VRT, VSRT significantly promoted broccoli root length and increased broccoli root dry matter accumulation (DMA). VSRT significantly increased the DMA rate during the growth period, and the size of the broccoli florets was more uniform. In 2020, compared with RT and VRT, VSRT increased yields by 7.8% and 19.5%, respectively; while in 2021, the corresponding increases in yield due to VSRT were 24.8% and 40.5%. Therefore, VSRT, as a deep tillage method, can improve soil characteristics before planting broccoli and ultimately increase broccoli yield.

Probabilistic modelling of the inherent field-level pesticide pollution risk in a small drinking water catchment using spatial Bayesian belief networks

Abstract. Pesticides are contaminants of priority concern that continue to present a significant risk to drinking water quality. While pollution mitigation in catchment systems is considered a cost-effective alternative to costly drinking water treatment, the effectiveness of pollution mitigation measures is uncertain and needs to be able to consider local biophysical, agronomic, and social aspects. We developed a probabilistic decision support tool (DST) based on spatial Bayesian belief networks (BBNs) that simulates inherent pesticide leaching risk to ground- and surface water quality to inform field-level pesticide mitigation strategies in a small (3.1 km2) drinking water catchment with limited observational data. The DST accounts for the spatial heterogeneity in soil properties, topographic connectivity, and agronomic practices; the temporal variability of climatic and hydrological processes; and uncertainties related to pesticide properties and the effectiveness of management interventions. The rate of pesticide loss via overland flow and leaching to groundwater and the resulting risk of exceeding a regulatory threshold for drinking water was simulated for five active ingredients. Risk factors included climate and hydrology (e.g. temperature, rainfall, evapotranspiration, and overland and subsurface flow), soil properties (e.g. texture, organic matter content, and hydrological properties), topography (e.g. slope and distance to surface water/depth to groundwater), land cover and agronomic practices, and pesticide properties and usage. The effectiveness of mitigation measures such as the delayed timing of pesticide application; a 10 %, 25 %, or 50 % reduction in the application rate; field buffers; and the presence/absence of soil pan on risk reduction were evaluated. Sensitivity analysis identified the month of application, the land use, the presence of buffers, the field slope, and the distance as the most important risk factors, alongside several additional influential variables. The pesticide pollution risk from surface water runoff showed clear spatial variability across the study catchment, whereas the groundwater leaching risk was uniformly low, with the exception of prosulfocarb. Combined interventions of a 50 % reduced pesticide application rate, management of the plough pan, delayed application timing, and field buffer installation notably reduced the probability of a high risk of overland runoff and groundwater leaching, with individual measures having a smaller impact. The graphical nature of BBNs facilitated interactive model development and evaluation with stakeholders to build model credibility, while the ability to integrate diverse data sources allowed a dynamic field-scale assessment of “critical source areas” of pesticide pollution in time and space in a data-scarce catchment, with explicit representation of uncertainties.

Reply to comments on the paper “Evaluating and modelling splash detachment capacity based on laboratory experiments” by P.I.A. Kinnell (2019). Catena 183, 104189

In this study, we used a new approach to measure and determine the splash detachment based on theories of soil erosion, the large number of articles published on the topic and simulated rainfall experiments. It is a necessity to use and improve new methods to accurately evaluate and quantify the processes of soil erosion. In this experiment, a soil pan with three areas, which consisted of a test area, complementary border area and a splash collector for slots, was used to obtain the ability of soil to undergo splash detachment. In this study, the soil surface was uniform and composed of a smooth slope and depth of thin layer flow that was < 0.43 mm. When raindrop splash occurs on the soil surface covered by a thin layer flow, all the soil materials detached by raindrop splash can only depart the soil surface and penetrate through the thin layer flow into the air and then fall to the soil surface. Splashed soil particles were collected and measured in our experimental setup to represent the amount of detached soil material that instantaneously fell on the test area. This material was quantified in mass per unit area per unit time, which is equal to the sample sediment mass divided by the slot area and the sample time. Thus, it is an expression of the raindrop splash detachment capacity observed in this study. Soil particles occupy all the spaces next to each other, and there is no space for the splashed soil material to move parallel to the soil surface within the soil mass. They may only depart from the soil mass itself. The thin layer flow has a very small depth. The detached soil materials cannot obtain enough space in the water depth to enter and to be maintained within the water depth. They easily penetrate the thin layer flow and enter the air. Once the splashed materials have entered the air, they can quantitatively be observed to represent the splash detachment using the soil pan with three areas in this study. Consequently, the splashed soil materials that were collected using this facility were all soil materials that were detached by the splashing of raindrops during the experiments.

Rill development and its change rate: a field experiment under constant rainfall intensity

Rill erosion is a widespread form of soil erosion on loess slope surfaces. The rill formation, evolutionary mechanism, and the quantitative expression of rill erosion dynamic changes in a micro-topographic level are currently lacking, primarily owing to lack of finer-scale measurements. This work presented the rill erosion evolutionary process and their dynamic changes at different slope gradients, (12°, 18°) in a millimeter-scale analysis. We achieved it by constructing an artificial excavation in the field and performed a soil pan with dimensions of 8 m in length and 2 m in width, which were subjected to a constant rainfall intensity of 100 mm h−1. The multiphase micro-geomorphologic changes during each rainfall phase were monitored using high-resolution terrestrial laser scanner (TLS). We noticed that the larger overland flow in the rill corresponded to more pronounced fluctuations in the cross-section lines of the rill bed. Also, with more the number of rills, the more easily the overland flow was dispersed, which required a larger slope gradient to resume the erosion and fill processes. Erosion rate and fill rate were highly correlated in general, and they increased abruptly at 70–90°. Due to the presence of swelling minerals, the loess surface expanded rapidly after encountering water in the early stage of rainfall. Therefore, the amount and rate of erosion on the slopes were underestimated. Understanding the detailed evolution process of rill erosion from a micro-perspective can provide a valuable reference for the development law of the initial stage of slope erosion in the loess region where erosion is extremely serious.

Rill network development on loessial hillslopes in China

AbstractRill network development not only potentially affects hillslope and drainage network evolution, but also causes severe soil degradation. However, the studies on rill network development remain inconclusive. This study aimed to investigate the temporal and spatial development of hillslope rill networks and their characteristics based on rainfall simulations and field observations. A soil pan (10.0 m long × 3.0 m wide × 0.5 m deep) on a 20° slope was applied three successive simulated rains at two intensities of 50 and 100 mm h–1. The field observations were performed on two bare hillslope runoff plots (10.0 m long × 3.0 m wide) at 20°. Three typical erosive natural rainfall events were observed in the field, and rills were measured in detail, similar to the laboratory rainfall simulation. The results indicated that with increases in rainfall events, the rill network morphology varied from incipient formation to the maximum drainage network density. Four rill network development indicators (rill distribution density, distance between rills, rill bifurcation number, and confluence point number) exhibited different changes over time and space. Among the four indicators, the rill bifurcation number was the best indicator for describing rill network development. Rill flow energy increased and decreased cyclically on a slope ranging between ~3 and 4 m. Moreover, rill networks on loessial hillslopes generally evolved into dendritic rather than parallel forms. The development characteristics of the rill network were relatively similar between the laboratory simulation and natural field conditions. Over time, rill erosion control measures become increasingly difficult to implement as the rill network develops. The morphology of eroding rills evolved over time and space, which led to corresponding rill network development. Further study should quantify the impacts of rill network development on soil degradation and land development. © 2020 John Wiley &amp; Sons, Ltd.

Effect of tillage, slope, and rainfall on soil surface microtopography quantified by geostatistical and fractal indices during sheet erosion

Abstract Tillage and slope will influence soil surface roughness that changes during rainfall events. This study tests this effect under controlled conditions quantified by geostatistical and fractal indices. When four commonly adopted tillage practices, namely, artificial backhoe (AB), artificial digging (AD), contour tillage (CT), and linear slope (CK), were prepared on soil surfaces at 2 × 1 × 0.5 m soil pans at 5°, 10°, or 20° slope gradients, artificial rainfall with an intensity of 60 or 90 mm h−1 was applied to it. Measurements of the difference in elevation points of the surface profiles were taken before rainfall and after rainfall events for sheet erosion. Tillage practices had a relationship with fractal indices that the surface treated with CT exhibited the biggest fractal dimension D value, followed by the surfaces AD, AB, and CK. Surfaces under a stronger rainfall tended to have a greater D value. Tillage treatments affected anisotropy differently and the surface CT had the strongest effect on anisotropy, followed by the surfaces AD, AB, and CK. A steeper surface would have less effect on anisotropy. Since the surface CT had the strongest effect on spatial variability or the weakest spatial autocorrelation, it had the smallest effect on runoff and sediment yield. Therefore, tillage CT could make a better tillage practice of conserving water and soil. Simultaneously, changes in semivariogram and fractal parameters for surface roughness were examined and evaluated. Fractal parameter – crossover length l – is more sensitive than fractal dimension D to rainfall action to describe vertical differences in soil surface roughness evolution.

Effects of rainfall intensity and topography on rill development and rill characteristics on loessial hillslopes in China

Rill development is a major soil erosion process that causes severe soil degradation. This study examined the effects of representative rainfall intensities (50 and 75 mm h−1), slope gradients (10° and 15°), and slope lengths (7.5 and 10.0 m) on rill development and rill characteristics on loessial hillslopes in China. Loessial soil was collected from the cropland of Ansai Town, Yan’an City, Shaanxi Province. The soil with 28.3% sand, 58.1% silt, and 13.6% clay was packed into a soil pan to conduct rainfall simulations in 2012. The results showed that the time of the knickpoint occurrence (5–16 min), the rill headcut extension (9–33 min), and the mean headward erosion rate (1.7–5.0 cm min–1) were better representative indicators for reflecting the changes in the rill development than other indicators used in this study. For a quick evaluation of the rill erosion severity, the rill coverage ratio (1%–12%, generally increasing with an increase in the rainfall intensity) was better than the other indicators for treatments with different rainfall intensities, and the rill width-depth ratio (1.56–2.27, generally decreasing with an increase in the slope gradient) was better than the other indicators for treatments with different slope gradients. Furthermore, the rill inclination angle (8.2°–19.1°, significantly increasing with an increase in the slope length) and rill density (0.19–1.34 m · m−2, generally increasing with an increase in the slope length) were more suitable for evaluating the rill erosion severity on hillslopes with different slope lengths. Therefore, the representative indicators could reflect the differences in the rill development and rill characteristics under different rainfall and topographic situations. The study greatly improved the evaluation of rill erosion severity and the prediction of the development of rills for loessial hillslopes.

Quantification of upslope and lateral inflow impacts on runoff discharge and soil loss in ephemeral gully systems under laboratory conditions

Overland flow through an ephemeral gully (EG) system integrates flow from upslope areas and lateral side slopes. Lateral overland inflow creates tributaries to the main EG channel for runoff and sediment discharge which exacerbates the EG erosion and local soil degradation. However, research concerning tributary formation by overland flow, especially contributions of overland upslope and lateral inflows to EG erosion, are still lacking. Thus, simulated rainfall and inflow experiments under two erosive rainfall intensities (50 and 100 mm h−1) and two typical slope gradients (15° and 20°) were conducted under representative lateral and upslope overland inflow conditions using an 8-m long, 2-m wide and 0.6-m deep soil pan. The results showed that upslope and lateral inflow both contributed to the runoff connectivity of the EG channel and lateral rills in the EG system. For these simulated conditions, upslope inflow contributions to total runoff and soil loss were 62–78% and 65–81%, respectively, while lateral inflow only contributed around 10%. The contribution differences could be attributed to flow hydrodynamic characteristics in that shear stress and stream power in the EG channel were 4.9–8.6 times greater than those on the lateral slopes. Lateral inflow was important to lateral rill formation, which contributed to imbricated landform and lateral gradient formation process, and consequently promoted runoff and sediment connectivity of the EG system. Soil erosion induced by concentrated flow in channels and sheet flow in interill areas coarsened soil textures, soil particles lager than 0.02 mm increased 12.6% on average, which may contribute to reduction of local soil productivity. This work demonstrates the critical need of preventing both upslope and lateral drainage into EG channels.

The effects of rock fragment content on the erosion processes of spoil heaps: a laboratory scouring experiment with two soils

Spoil heaps on newly engineered landforms create extensive artificially accelerated erosion, especially when there are catchment areas above spoil heaps, erosion caused by runoff will be much greater than that induced by rainfall. This study investigated the erosional characteristics of clay loam and sandy loam spoil heaps and proposed an appropriate hydraulic parameter to simulate the variation in erosion rate. A laboratory scouring experiment was conducted using a soil pan (dimensions 5 m × 1 m × 0.5 m deep) with a discharging arrangement to test four samples of clay loam and sandy loam containing rock fragments (0%, 10%, 20%, and 30%) by mass. The slope of simulated spoil heaps was 53.2% with a discharging inflow rate of 15 L min−1. The rock fragments used were those commonly used in construction works, having a diameter of 2–3 cm and irregular shape. Twenty-four scouring tests for eight treatments with duplication were accomplished in total. Average erosion rates showed a negative linear correlation with rock fragment content in clay spoil heaps (R2 = 0.94) and a positive linear correlation in sandy loam spoil heaps (R2 = 0.92). Rill width evolution of clay loam spoil heaps mainly developed at the early scouring stage (0–15 min), and rills developed even more rapidly during later scouring times (30–60 min) in sandy loam spoil heaps. Grey relational analysis showed that sheer stress and stream power both had higher Grey relational degrees with erosion rate for both soils, regression analysis showed that stream power can efficiently describe the erosional process of clay loam and sandy loam for each rock fragment content, but sheer stress only did well in sandy loam heaps. Adding rock fragments to spoil heaps resulted in significantly opposite effects in the different soils; great attention should be paid to sandy loam spoil heaps due to their more severe erosion with increasing rock fragment content; stream power is an appropriate hydraulic parameter to simulate the soil erosion process of spoil heaps for both soil types.

Experimental study on soil erosion prediction model of loess slope based on rill morphology

Rill erosion frequently occurs in agriculturally disturbed dry areas. Despite many research efforts over recent decades, the characteristics of rill erosion and its intrinsic mechanisms remain unclear. The objectives of this study were to investigate the impacts of rill morphology evolution on rill erosion processes. A soil pan (5 m long, 1 m wide, and 0.6 m deep and with an adjustable slope gradient of 0–30°) was subjected to rainfall simulation experiments under three intensities of representative erosive rainfall (66, 94, and 127 mm h−1). The rill morphology evolution exhibited significant nonlinear change regulation and the stronger the rainfall intensity, the clearer the nonlinear feature. The equation between rill morphological characteristics with geomorphological comentropy and bifurcation ratio was generated, which indicated that the contribution rate of geomorphological comentropy to sediment yield was 80%, and the contribution rate of bifurcation ratio was 20%. For the experimental treatments, a soil erosion model was constructed with and without rill development and the coefficient to describe the influence of rill development on slope erosion was obtained. The rill erosion coefficient was embedded into an existing soil erosion model for steep slopes. As a result, when rill erosion occurred on the slope, the contribution of the rill morphology to the rill erosion was fully realized by the model. Verification indicated that the accuracy of the model was significantly improved. In previous studies, the accuracy of slope water erosion prediction model was low because the evolution process of slope topography was not considered. Our results solve the spatial variability problem in the slope erosion prediction model, and improve the simulation accuracy of the soil erosion prediction model on a loess slope.

Rainfall and inflow effects on soil erosion for hillslopes dominated by sheet erosion or rill erosion in the Chinese Mollisol region

Erosion agents and patterns profoundly affect hillslope soil loss characteristics. However, few attempts have been made to analyze the effects of rainfall and inflow on soil erosion for hillslopes dominated by sheet erosion or rill erosion in the Chinese Mollisol region. The objective of this study was to discuss the erosive agent (rainfall or inflow), hillslope erosion pattern (sheet erosion or rill erosion) and slope gradient effects on runoff and soil losses. Two soil pans (2.0 m long, 0.5 m wide and 0.5 m deep) with 5° and 10° slopes were subjected to rainfall (0 and 70 mm h–1) and inflow (0 and 70 mm h–1) experiments. Three experimental combinations of rainfall intensity (RI) and inflow rate (IR) were tested using the same water supply of 70 mm by controlling the run time. A flat soil surface and a soil bed with a straight initial rill were prepared manually, and represented hillslopes dominated by sheet erosion and rill erosion, respectively. The results showed that soil losses had greater differences among treatments than total runoff. Soil losses decreased in the order of RI70+IR70 > RI70+IR0 > RI0+IR70. Additionally, soil losses for hillslopes dominated by rill erosion were 1.7–2.2 times greater at 5° and 2.5–6.9 times greater at 10° than those for hillslopes dominated by sheet erosion. The loss of <0.25 mm soil particles and aggregates varying from 47.72%–99.60% of the total soil loss played a dominant role in the sediment. Compared with sheet erosion hillslopes, rill erosion hillslopes selectively transported more microaggregates under a relatively stable rill development stage, but rills transported increasingly more macroaggregates under an active rill development stage. In conclusion, eliminating raindrop impact on relatively gentle hillslopes and preventing rill development on relatively steep hillslopes would be useful measures to decrease soil erosion and soil degradation in the Mollisol region of northeastern China.

Identifying sediment transport capacity of raindrop-impacted overland flow within transport-limited system of interrill erosion processes on steep loess hillslopes of China

Interrill erosion processes typically involve such scientific issues as detachment-limited and transport-limited erosion behaviour. An accurate estimation of the sediment transport capacity (Tc) by raindrop-impacted overland flow is critical for interrill erosion modelling and for evaluating sediment budgets under erosion-limiting conditions. Simulated rainfall experiments with rainfall intensities from 0.8 to 2.5 mm min−1 over a three-area soil pan with slope gradients from 12.7% to 46.6% were conducted to identify the transport-limited cases and determine Tc by raindrop-impacted overland flow within the transport-limited systems of interrill erosion processes. Results indicated that Tc increased as a power function of rainfall intensity and slope gradient (R2 = 0.84, NSE = 0.75), and Tc was more sensitive to rainfall intensity than to slope gradient. In terms of R2 and NSE, stream power was the key hydraulic parameter that influenced Tc among flow velocity (R2 = 0.64, NSE = 0.39), shear stress (R2 = 0.53, NSE = 0.23), stream power (R2 = 0.76, NSE = 0.52) and unit stream power (R2 = 0.49, NSE = 0.16). The addition of rainfall physical parameters in response equations of Tc in addition to hydraulic parameter, could improve an accuracy of Tc modelling. Stream power combined with rainfall kinetic energy can best describe the Tc of raindrop-impacted overland flow within the transport-limited system of interrill erosion processes by a power-exponent function (R2 = 0.90, NSE = 0.72). Rainfall kinetic energy can reduce the Darcy-Weisbach resistance coefficient of raindrop-impacted overland flow and thus benefit sediment transporting. This study provides another method for directly identifying the Tc of raindrop-impacted overland flow in interrill erosion processes on steep loess slopes, and points out that rainfall impacts should be particularly considered when studying Tc by raindrop-impacted overland flow.