Interrill Erosion Research Articles

Technical note: The influence of splashed soil material on sediment transported by rain-impacted flows

Soil material lifted by raindrop impacting flows a few millimetres deep are transported downstream as they fall back to the soil surface. That occurs not only with material that is lifted and remains in the flow, but also material lifted into the air that falls onto the surface of the flow. The amount lifted into the air varies with flow depth and the effect of the input from airborne material on sediment discharged by rain-impacted flows is not normally taken into account in experiments on, or models of, sheet and interrill erosion where flows are more than 1 mm deep. However, in very shallow flows, the airborne input to rain-impacted flows is high and the dominant transport mechanisms the operate in deeper flows no longer operate effectively. Further research into the mechanisms that operate in transporting sediment by rain-impacted flows on slopes with high gradient is warranted.

Equations for predicting interrill erosion on steep slopes in the Three Gorges Reservoir, China

Abstract The Three Gorges Reservoir region suffers from severe soil erosion that leads to serious soil degradation and eutrophication. Interrill erosion models are commonly used in developing soil erosion control measures. Laboratory simulation experiments were conducted to investigate the relationship between interrill erosion rate and three commonly hydraulic parameters (flow velocity V, shear stress τ and stream power W). The slope gradients ranged from 17.6% to 36.4%, and the rainfall intensities varied from 0.6 to 2.54 mm·min−1. The results showed that surface runoff volume and soil loss rates varied greatly with the change of slope and rainfall intensity. Surface runoff accounted for 67.2–85.4% of the precipitation on average. Soil loss rates increased with increases of rainfall intensity and slope gradient, Regression analysis showed that interrill erosion rate could be calculated by a linear function of V and W. Predictions based on V (R 2 = 0.843, ME = 0.843) and W (R 2 = 0.862, ME = 0.862) were powerful. τ (R 2 = 0.721, ME = 0.721) did not seem to be a good predictor for interrill erosion rates. Five ordinarily interrill erosion models were analyzed, the accuracy of the models in predicting soil loss rate was: Model 3 (ME = 0.977) > Model 4 (ME = 0.966) > Model 5 (ME = 0.963) > Model 2 (ME = 0.923) > Model 1 (ME = 0.852). The interrill erodibility used in the model 3 (WEPP) was calculated as 0.332×106 kg·s·m−4. The results can improve the precision of interrill erosion estimation on purple soil slopes in the Three Gorges Reservoir area.

Improved Stock Unearthing Method (ISUM) as a tool to determine the value of alternative topographic factors in estimating inter-row soil mobilisation in citrus orchards

The Improved Stock Unearthing Method (ISUM) was initially designed to assess soil mobilisation rates in vineyards; however, other grafted crops such as citrus orchards could also be successfully used. The results obtained from ISUM have been used for several goals, but have not yet been applied for computing the LS factor (length and slope) as a part of the Universal Soil Loss Equation (USLE), which could give useful information to improve soil management system plans. This investigation was conducted in an 8-year old clementine field located in Canals (Valencia, Spain) and values of the LS factor were calculated by means of two pre-established algorithms, which allowed us to calculate a Transect Length Index (TLI). Our results demonstrated that the micro-topographical changes can show frequent irregularities. For the values of the Transect Length Index (TLI), the mean values were 1.02% for the left side and 1.04% for the right one. The difference among the areas predicted at the moment of furrow construction and the moment of data survey permitted us to estimate a total volume of 56.9 m<sup>3</sup> of soil mobilized in 19 years. Taking into account the studied area (360 m<sup>2</sup>), the volume of mobilised soil, and the bulk density for the local soil (1.3 g cm<sup>-3</sup>), we estimated a total soil mobilisation of 8.3 mm yr<sup>-1</sup> or 10.4 kg m<sup>-2</sup> yr<sup>-1</sup>. We did not observe any evidence or indicator of rill and inter-rill erosion by natural rainfall events, suggesting that the runoff homogenizes the sediment distribution during heavy rains (corroborated by the TLI data) or tillage practices. The data created following the ISUM was suitable to be used to calculate the LS-factor values. The amount of soil mobilised as predicted by USLE was always lower than the ones predicted by ISUM.

Assessment of crusting effects on interrill erosion by laser scanning.

BackgroundCrust formation affects soil erosion by raindrop impacted flow through changing particle size and cohesion between particles on the soil surface, as well as surface microtopography. Therefore, changes in soil microtopography can, in theory, be employed as a proxy to reflect the complex and dynamic interactions between crust formation and erosion caused by raindrop-impacted flow. However, it is unclear whether minor variations of soil microtopography can actually be detected with tools mapping the crust surface, often leaving the interpretation of interrill runoff and erosion dynamics qualitative or even speculative.MethodsIn this study, we used a laser scanner to measure the changes of the microtopography of two soils placed under simulated rainfall in experimental flumes and crusting at different rates. The two soils were of the same texture, but under different land management, and thus organic matter content and aggregate stability. To limit the amount of scanning and data analysis in this exploratory study, two transects and four subplots on each experimental flume were scanned with a laser in one-millimeter interval before and after rainfall simulations.ResultsWhile both soils experienced a flattening, they displayed different temporal patterns of crust development and associated erosional responses. The laser scanning data also allowed to distinguish the different rates of developments of surface features for replicates with extreme erosional responses. The use of the laser data improved the understanding of crusting effects on soil erosional responses, illustrating that even limited laser scanning provides essential information for quantitatively exploring interrill erosion processes.

Effects of near soil surface components on soil erosion on steep granite red soil colluvial deposits

Vegetation restoration typically aims to control and restore collapsing gullies, which are prevalently and seriously eroded areas in South China. However, its effectiveness has rarely been evaluated, especially on steep colluvial deposits and during the prevalent high-intensity precipitation events. The effects of Melinis minutifora and Chrysopogon zizanioides on slope erosion, and the contributions of canopy, biocrusts, and roots were investigated in this study via rainfall simulation experiments. M. minutifora and C. zizanioides effectively reduced soil sediment yield rate (SR) on steep colluvial deposits by 98.1% and 86.6%, respectively. Overall, lower and denser canopies and greater fine root volumes indicated better performance of M. minutifora compared to C. zizanioides. Canopies of both plants exerted the strongest effects and contribution rates for reducing the SR and apparent interrill erodibility, while the effects and contribution rates of biocrusts were slightly higher than those of roots on average. These results highlight the importance of low plant canopies, fine roots, and the protection of biocrusts toward the reduction of rainfall erosion. The results add to the optimization of soil conservation and management practices for steep colluvial deposits.

Interrill erodibility of different sandy soils increases along a catena in the Caiuá Sandstone Formation

ABSTRACT Soil erosion in tropical areas is a major problem for sustainability in agriculture and soil stability. In the Northwest of Parana, cassava crop is produced using a conventional tillage system along a catena consisting of different soil classes: Ferralsols (near the summit), Lixisols (mid-slope), and Arenosols (foot-slope). Therefore, differential soil erosion rate and soil degradation are expected along the catena. Here, we test the erodibility of the three sandy soil classes in a representative catena of the Caiua Sandstone [...]

Impact of near‐surface hydraulic gradient on the interrill erosion process

AbstractThe impact of near‐surface hydraulic gradients on interrill erosion is still obscure. The objective of this study is to distinguish the dominant interrill erosion process in areas impacted by near‐surface hydraulic gradients. A series of rainfall simulations were conducted on a clay loam soil subjected to near‐surface hydraulic gradients that shifted from drainage/saturation conditions to seepage conditions under three rainfall intensities (30, 60 and 90 mm hr−1) and two slope gradients (5° and 10°). The results showed significant differences in soil loss between all the treatments. The sediment concentrations for seepage conditions were 0.57 to 7.02 times greater than those for drainage conditions. The correlation analysis indicated that the near‐surface hydraulic gradient was a governing factor affecting interrill erosion. The critical flow rate was larger than 90 mm hr−1, suggesting that thin sheet flow does not have sufficient power to detach soil particles without raindrop impact. Furthermore, the detachment rates by raindrop impact were 1.12 to 4.60 times greater for seepage conditions than for drainage conditions. As the near‐surface hydraulic gradient shifted from drainage conditions to seepage conditions, it transitioned from transport‐limited to detachment‐limited, and the contribution of interrill erosion to overall erosion increased from 20.19 to 75.30%. The critical point of dominant interrill erosion process transition existed between saturation (SA) and artesian seepage in 20 cm of hydrostatic pressure head (SP20). The results emphasize the importance of the near‐surface hydraulic gradients’ impact on the interrill erosion process. Further investigations need to be verified in different soil types, steeper slopes and natural storms.Highlights The impact of near‐surface hydraulic gradients on interrill erosion is only partially understood. Dominant interrill erosion processes are identified under near‐surface hydraulic gradients. The critical point of dominant interrill erosion process transition exists between SA and SP20. The dominant erosion process varied as a function of near‐surface hydraulic gradients.

The Effects of Tillage Practices on Interrill Erosion in the Red Soil Region of China

HighlightsConservation practices (straw mulch, manure, peanut-orange intercrop) reduced soil and water loss vs. tillage.Reductions in soil loss were greatest under high rainfall intensity or low soil moisture.Measured interrill erodibility was relatively high in dry run tests and decreased with the final infiltration rate.ABSTRACT.Tillage practices have been adopted extensively to control runoff and soil loss from croplands. To quantify the effects of tillage practices on erosion processes in interrill areas, microplot rainfall simulation experiments were conducted in peanut fields with five tillage practices in the red soil region of China. The results showed that conservation tillage practices, including straw mulch cover (PC), manure fertilizer (PM), and peanut-orange intercropping (PO), could significantly conserve water and reduce soil loss rates by more than 50% compared with traditional furrow (PF) and peanut-radish rotation (PR) treatments. The variations in the hydrologic and soil loss indexes among the treatments were larger in the dry run tests than in the wet run tests. Accordingly, the efficiencies of the conservation practices in reducing soil loss were reflected mainly under a high rainfall intensity or low soil moisture in this study. Additionally, the runoff generation indexes were significantly correlated with the soil loss rate in all five treatments. The measured interrill erodibility was highest in the PR treatment (944,124 kg s-1 m-4) and lowest in the PO and PM treatments (571,797 and 584,238 kg s-1 m-4, respectively), as the organic matter content and aggregate stability were relatively high in the two conservation treatments. Influenced by the dynamics of loose materials and possible surface sealing, the interrill erodibility was relatively high and decreased with the final infiltration rate when measured under the dry run conditions. These results could guide cropland soil management and improve process-based erosion models. Keywords: Interrill erodibility, Interrill erosion, Rainfall simulation, Red soil region, Tillage practices.

Two-dimensional rainfall-runoff and soil erosion model on an irregularly rilled hillslope

The spatial characteristics of rills and non-planar hillslope could dramatically alter the mechanisms of the hydrologic and geomorphic processes, which were usually neglected in previous studies. Based on a two-layer soil infiltration model, a two-dimensional (2D) diffusion wave model, and modified WEPP erosion modeling approaches, a 2D distributed hillslope runoff and soil erosion model was developed to account for these effects. The interrill and rill areas are distinguished based on the high resolution topographic data. The model is tested against experimental erosion data from a hillslope subjected to three successive rainfall events, resulting in irregular rill networks. Good agreements between the modeled and observed results are found in runoff depth, erosion and its spatial distribution. A sensitivity analysis was also performed for the related parameters and found that the sensitive parameters for interrill erosion are rainfall intensity and interrill erodibility factor, while the sensitive parameters for rill erosion are the rainfall intensity, Manning’s friction coefficient, rill erodibility factor and soil critical shear stress. Moreover, the role of the dendritic rill network and concave hillslope have been examined and both of them can greatly affect the overland flow routing and increase the rill erosion, which is not accounted for in previous models such as WEPP. These results are valuable for rainfall-runoff and soil erosion prediction on irregularly rilled hillslopes.

A comprehensive study of erosivity and soil erosion over a small tropical islet: Round Island, Mauritius

AbstractRound Island, a small (219‐ha) volcanic island 22.5 km north of Mauritius, has steep slopes and thin soils. This small tropical island was previously subjected to overgrazing by goats and rabbits, which detrimentally affected ecosystem functioning. Classified as a nature reserve since 1957, Round Island houses the last remnant of palm savannah that has been lost on mainland Mauritius and is a refuge to several endemic and endangered species. Landscape restoration and ecosystem functioning on Round Island are key conservation objectives, but soil erosion remains a significant hindrance to habitat restoration and ecosystem functioning. Here, we investigate soil erosion on Round Island and assess the implications for conservation and management. Sediment movement was monitored monthly (2015–2018) at seven soil erosion plots coupled with rainfall and erosivity measurements. A mean annual sediment movement rate of 0.2136 t ha−1 yr −1 is calculated. Although this rate of sediment movement is low for humid tropical regions, the barren landscape and low contemporary rates of soil erosion suggest that most of the erodible soil has already been eroded. Interrill erosion of the shallow soils and friable parent material is closely correlated with rainfall erosivity and exacerbated by limited vegetation cover. Continued revegetation is recommended to retard soil erosion and restore ecosystem functioning. The paper also emphasises that rainstorms are the greatest single phenomena affecting earth surface processes on and around the island of Mauritius. As such, long‐term monitoring of the interaction between the surface and climate is required to provide insights for conservation management.

Effects of interrill erosion on the distribution of soil organic and inorganic carbon in different sized particles of Mediterranean Calcisols

In this study, the potential effect of the selective transport and deposition by interrill erosion on the spatial distribution of eroded soil and associated soil organic (SOC) and inorganic carbon (SIC) in carbonate-rich soils was investigated in Mediterranean cultivated Calcisols. Particular attention was paid to the role of calcium carbonate in the stabilization of SOC and its impact on soil structure and the settling behavior of soil particles in suspension. The settling velocity is a key variable in controlling the transport and fate of eroded sediment and sediment-associated carbon, which accounts for soil particle / aggregate size and density. The objectives were to analyze the settling behavior of cultivated soils at two contrasting slope positions, representative of erosion and deposition sites, in an interrill area and compare with those of uncultivated and undisturbed soils (not affected by deposition or erosion processes). Besides we examined the distribution of SOC and SIC associated with different particle size classes.Soils were fractionated into five size classes (>250, 125–250, 63–125, 32–63 and ≤32 μm) using a settling tube procedure and carbon contents (SOC and SIC, %) were measured at each settling size classes. The results indicated that the particle size selectivity of interrill erosion affects the distribution of soil particles and associated SOC and SIC spatial variability. As a result of erosion processes, cultivated soil at the upper part of the slope was enriched in finer fractions compared to the lower part where mainly coarse particles were deposited and the finer material was transported and washed out. Cultivation leads to a depletion of SOC and of the >250 μm fraction in comparison with uncultivated and undisturbed soil, where the SOC content was two times higher than in cultivated soil. Lighter and smaller settling size classes (≤63 μm) had the highest SOC content in uncultivated and cultivated downslope soils. This is contrary to what occurs with SIC that acts as a cementing agent and promotes aggregation formation affecting soil structure. Therefore, sand-sized and silt-sized carbonates were accumulated in coarser size fractions in these soils, mainly in downslope positions. This study provides a first insight into the role of selective processes by interrill erosion and their impact on soil organic/inorganic carbon distribution affected by different particle selective transport process, soil aggregate size distribution and associated carbon in Mediterranean agroecosystems.

Quantifying and modeling sediment yields from interrill erosion under armouring

Surface soil properties can change as a result of soil disturbances, erosion, or deposition. When soils contain rock, surface soil properties can also change over time as a result of the process of soil armouring, which is the selective removal of finer particles by erosion, leaving an armoured layer of coarser particles that may reduce further soil loss. Rapid armouring is typically reported in steep and bare slopes on mine sites, construction sites, road embankments, and also rangelands. Changes in surface soil properties over time induced by armouring are not accounted for in current erosion models such as WEPP or RUSLE2 because little is known about rates of armouring over time as a function of rainfall intensity, rock content, slopes, and other factors. In this paper we simulate soil armouring induced by interrill erosion in two sets of experiments and propose ways to account for the process in WEPP and RUSLE2 without modifying the science behind the models. The first set of experiments was conducted to demonstrate and quantify the effect of armouring on sediment yields under varying rainfall intensities. Rainfall with intensities ranging from 22 to 80 mm h−1 was simulated on 0.56 m2 plots at slopes of 18 degrees (32.5%) using topsoil with high rock content from a mine restoration site. Results showed a clear relationship between rainfall intensity and armouring. There was an over 75% reduction in total soil loss under 22 mm h−1 rainfall between freshly applied soils and highly armoured soils at the same slope. A second set of experiments was conducted to understand the relationships between soil rock content, rate of surface rock cover change, slope change and sediment yields. Sediment yields and surface rock cover were quantified for non-cohesive soils consisting of glass beads with a diameter range of 45 to 90 μm and 0, 20 and 40% rock content in 0.22 m2 plots at a 15° (26.8%) slope under 80 mm h−1 simulated rainfall. Linear relationships were observed between cumulative sediment yields and rock cover, and exponential relationships between total runoff and rock cover. The armouring process was modeled at the experimental scale with WEPP and RUSLE2 by iteratively altering the rock cover and the slope over time. WEPP event based simulations at this scale resulted in reasonable predictions of sediment yields throughout the armouring process, and RUSLE2 required modification of soil erodibility values to account for high rock content and changes in runoff over time. Automation of this process, however, would require modifications of the models to expose rock cover and change slope over time. A method for doing this is discussed for interrill processes, but interactions between rill erosion and armouring need further study. The effect of long-slope high-energy rill flows on armouring also needs further investigation through field scale experiments, as this study did not examine the extent to which rock is uncovered and/or moved on long slopes differently from the residues already modeled in WEPP and RUSLE2.

Rainfall simulation experiments indicate that biochar addition enhances erosion of loess‐derived soils

AbstractBiochar addition to soil has increasingly demonstrated the potential to improve soil and mitigate climate change. However, the effects of biochar additions for sloping cropland amendments and soil erosion remain unclear. In this study, experiments with simulated rainfall (25, 50, 75, and 100 mm hr‐1) were conducted on a soil box (0.45‐m length × 0.3‐m width) to assess the effects of different biochar addition rates (2%, 5%, and 8% [wt/wt]) and incubation time (i.e., 140 days) on runoff, soil loss, and interrill erodibility. The soil and biochar were loess‐derived Miami soil and commercial charcoal made from seasoned oak and hickory hardwoods, respectively. Compared with the control soil, biochar addition decreased the total runoff by 2.4–10.8% (p > 0.05) and significantly increased the total soil loss and interrill erodibility (p < .05) by 20.8–50.8% and 20.4–29.2%, respectively. The changes in runoff, soil loss, and interrill erodibility were ruleless with an increase in the rate of biochar addition from 2% to 8%. The differences in runoff, soil loss, and interrill erodibility were nonsignificant among most biochar‐added treatments. After a 140‐day incubation period, total runoff and soil loss increased by 1.5–6.2% and 5.7–10.3%, respectively, and interrill erodibility increased for the 2% biochar addition and decreased for the 5% and 8% biochar additions. However, nonsignificant differences in runoff, soil loss, and interrill erodibility were observed before and after incubation. Our results implied that biochar addition to soil could increase the risk of erosion on sloping croplands, and thus, one should exercise caution when amending soil with biochar on sloping croplands.

The measurement, estimation and monitoring of soil erosion by runoff at the field scale: Challenges and possibilities with particular reference to Britain

Soil erosion is widely acknowledged as a global problem but attempts to measure and estimate its significance are frustrated by our inability to develop reliable, cheap and easy methods of assessment. The limitations of qualitative methods such as GLASOD, errors and inaccuracies inherent in modelling based on small-scale plot experiments, and problems with 137Cs approaches, mean that alternative strategies are required. For runoff-related erosion on arable land we propose the use of a well-tried estimation technique: volumetric measurement of rills, gullies and fans. Amounts of wash and interrill erosion can also be estimated. This approach allows for the estimation of erosion rates at the field scale, rather than relying on extrapolations from plot-based data. Measurements are based on sampling the population of rills and gullies and can be adapted to the aims of the project for ‘broad-brush’ or detailed data. Monitoring of large areas to produce regional assessments of erosion risk is frequently required and volumetric estimates provide these data. Thus predictions of the extent, frequency and amounts of erosion can be made and the vulnerability of particular crops becomes clear.

Vegetative-hydraulic parameters generated by agricultural crops for laminar flows under a semi-arid environment of Pernambuco, Brazil

The structural parameters of vegetation have an important influence on the resistance imposed to shallow flow under the soil, being important in the control of floods, water erosion and sediment transport in the watersheds. Therefore, in order to obtain the hydraulic characteristics of overland flow, the variables of hydraulic resistance generated by the vegetation to surface flow, and the interrill erosion rates under semi-arid region led to the introduction of agricultural crops, through which shallow flows were generated on elephant grass (Pennisetum purpureum), corn (Zea mays sp.) and in a bare Entisol, placed in a toeslope landscape position. Results showed that the flow regime was slow, laminar and interrill erosion occurred (Re < 500 and Fr < 1). Nevertheless, the hydraulic characteristics of overland flow (Vm, h, q and log f) were probably affected by the proximity to the water table, a hypothesis supported by the obtained values for the infiltration. However, corn and principally elephant grass showed high hydraulic resistance to superficial flow and interrill erosion conferred by the highest ground coverage (lowest Ci = 0.198), by the effect of the sub-factors CiI, CiII and CiIII, and the lowest values of sediment concentration (CS), runoff coefficient (C), interrill detachment rate (Di), and soil loss (SL). Our results support the purpose of introducing agricultural crops in the Brazilian semi-arid region since increasing resistance to interrill erosion can be provided. Elephant grass is a more appropriate crop to be inserted under land management protocols in the semi-arid environment.

Plot-based experimental study of raindrop detachment, interrill wash and erosion-limiting degree on a clayey loessal soil

Better understanding of raindrop detachment, interrill wash and erosion-limiting degree in interrill processes is critical for accurately modelling interrill erosion and implementing proper anti-erosion strategies. Simulated rainfall experiments were conducted on a clayey loessal soil at three rainfall intensities (42, 60 and 90 mm h−1), five slope gradients (7°, 10°, 15°, 20° and 25°) and rainfall duration of 40 min. Results showed that raindrop detachment rate initially decreased rapidly within a few minutes and then reached a relative steady state during rainfall. The initial and steady raindrop detachment rate increased with increased rainfall intensity. Interrill wash rate peaked early and then decreased to a relative constant rate during the rainfall. The initial, maximum and steady interrill wash rate increased with increased rainfall intensity and slope gradient. Erosion-limiting degree (ELD), defined as the ratio of interrill wash rate to raindrop detachment rate, ranged from 10.99% to 35.70% under experimental conditions, indicating that interrill erosion system was transport-limited. The ELD decreased with rainfall intensity and increased linearly (R2 = 0.90) with slope gradient. The higher the rainfall intensity, the stronger the transport-limiting in interrill erosion processes; the steeper the slope gradient, the weaker the transport-limiting in interrill erosion processes. Raindrop detachment is the dominant process in detaching soil particles, whereas interrill flow contributes to washing out detached sediments. The findings of this study, especially ELD, largely improved the understanding of interrill erosion processes.

Selamento superficial e formação de crosta em solos representativos do Estado da Paraíba

The formation of seal and surface crust in the soil has direct consequences for the development of the crops and environmental quality, altering the soil structure, reducing the availability of water to the plants and favoring the erosion. The objective of this study was to evaluate the changes caused by successive rainfall events on the soil surface. Four soils were evaluated: Ferralsol; Acrisol; Leptsol; Luvisol. The selection criterion was based on pedogenetic development. The experiment was conducted under simulated rainfall, in experimental plots with a useful area of 0,3481 m², uncovered soil and slope of 0.10 mm-1. The tests were performed with mean precipitation intensity of 85 mm h-1 for 75 min, applied in three consecutive events at 7 day intervals, to determine the effects of surface sealing during rainfall and crust formation after the soil drying period. The hydraulic flow variables, the soil losses (PSi), soil disaggregation rate in interrill (Di) and the interrill erodibility factor (Ki) were evaluated. The formation of sealing and surface crusts were observed with increase of the flow velocity and liquid discharge, and the decrease of water sheet height, as well as in the changes in PSi, Di and Ki, being in the first event of simulated rainfall the greater contribution to formation of superficial crusting. TX showed the most stable after the successive events of simulated rainfall, even though the surface roughness was modified, did not present significant changes in the soil losses, disaggregation rate and soil interill erodibility. Keywords: Interill erosion, semiarid, sediment concentration, surface roughness, hydraulic flow variables.

Applicability of biochar for limiting interrill erosion and organic carbon export of sloping cropland in a semi-arid area of China

As a recalcitrant carbon source, the residence time of biochar is estimated to be hundreds to thousands of years. Since biochar is now being applied as a soil amendment in many areas of the world, the effects of long-term stationary biochar and its applicability for limiting soil erosion and nutrient export must be considered. To this end, this study investigated the effects of biochar on interrill erosion processes and total organic carbon (TOC) export by sediment and runoff at five slope gradient levels (5°, 10°, 15°, 20°, and 25°). A silt loam soil was incubated with or without wheat straw-derived biochar for 3 years in the field before carrying out a simulated rainfall experiment, in which a rainfall intensity of 60 mm h–1 was applied for 90 min. Compared with the non-biochar control, biochar-amended soils showed decreased interrill erosion potential by up to 21.34%, due to improved soil aggregate stability and organic carbon (OC) content. No substantial differences in runoff rate were detected between the control and biochar treatments. Light soil particles with a higher OC content were transported preferentially on gentle sloping cropland (≤15°) and there was a negative correlation between the enrichment ratio of OC and sediment loss rate. The OC in sediment was the primary source of TOC export from sloping cropland, while a limiting effect of biochar for reducing this TOC export occurred between 15° and 20° slope gradients. Biochar amendment reduced the relative TOC export and protected sloping cropland from soil degradation. Although the biochar application enhanced soil erosion resistance, it was deemed more appropriate to use biochar as a soil amendment to ≤15°-sloping cropland given its pronounced effect on TOC export.

Quantitative assessment of rill and interrill soil erosion in Romania

AbstractSoil erosion is an important geomorphological process with potential negative consequences especially on land agricultural potential. Unsuitable agricultural practices may increase soil erosion, leading to rapid loss of soil fertility and decrease of crop production. It is therefore important to correctly quantify soil erosion rates in order to adapt agricultural practices and implement proper conservation measures. This study attempts to assess the rill and interrill erosion in Romania, using the Romanian soil erosion model and GIS techniques. The database includes the digital terrain model, the soil map of Romania, the land use map of Romania and the rainfall erosivity regions. The results show that the high and very high erosion risk classes include 4.1% of the Romanian territory (9,627 km2). Most of this land is present in the hilly and plateau areas (Subcarpathians, Moldavian Plateau, Getic Plateau, Western Hills, Dobrogea Plateau). The model was validated by comparison of its predictions with long‐term erosion measurements from different locations in the country. Comparison with previous non‐GIS assessments of soil erosion at national level shows that the total estimated rill and interrill erosion in our study was very close to previous estimates. Comparison with the RUSLE 2015 model computed for Europe as a whole reveals that the two models assign almost 54% of their shared area to the same erosion class, while for 39% of the territory there is one class difference between the models. The results can be used for evaluations of erosion risk at national and regional scales.

Rainfall erosivity in interrill areas: Insights about the choice of an erosive factor

Defining a suitable erosive factor for interrill erosion has been a long-going discussion that was not resolved by experimental results. In this paper, by using computational fluid simulations of individual raindrop impacts, the relevance of four erosive factors was assessed for a range of soil resistance, rainfall type and water layer depth. Computation results show that the erosivity exponent associated to the erosive factors had a very low sensitivity to soil resistance. This confirms the common practice of separating rainfall erosivity from soil erodibility. The erosivity exponent was found to be very sensitive to the rainfall type. Therefore, an universal exponent could not be found, its value depending on the rainfall type. As a result of the balance between the shear stress development and the protective effect of the water layer, the soil detachment rate was maximum for a specific water depth. This supports to better account for the water layer depth in erosion models. Overall, the computational approach shows that the choice of an erosive factor may not be of practical importance. It also encourages for new experimental designs, able to evaluate soil detachment by raindrops — and not only the amount of splashed soil.