Interrill Soil Erosion Research Articles

Corrigendum to “Estimating WEPP Cropland Erodibility Values from Soil Properties”

Highlights Interrill erodibility Ki values presented in Elliot and Flanagan (2023) were incorrect, and correct values are given. Interrill erodibility can be estimated from a soil’s sand, very fine sand, and clay contents. Abstract. In Elliot and Flanagan (2023), the interrill and rill soil erodibility of 36 cropland soils was reported, along with correlations among soil erodibility and other soil properties, and equations to estimate erodibility from readily measured soil properties. Early versions of the Water Erosion Prediction Project (WEPP) model had linked interrill detachment rate to the square of the rainfall intensity and an interrill soil erodibility constant Ki1. By the time the WEPP model was released for general use in 1995, the developers had changed the interrill detachment rate to be a function of the product of rainfall intensity and runoff and a different interrill erodibility constant, Ki2. The interrill erodibilities (Ki2) with this altered relationship were not the same as Ki1 values developed to support earlier releases of the WEPP model. The authors, when reviewing some of the past literature supporting Elliot and Flanagan (2023), had mistakenly reported Ki2 values when the numbers reported were in fact Ki1 values. A closer examination of the entire data set and the identification of a published source for the correct Ki2 values confirmed this mistake. This corrigendum reports the corrected Ki2 values, the correlation of those revised values with other soil properties, and confirmation of a 1995 regression equation relating Ki2 to three readily measured soil properties: sand content, very fine sand content, and clay content. The coefficient of determination for the 1995 regression equation was 0.80. We recommend that all references to Ki2 in Elliot and Flanagan (2023) be changed to Ki1 except the discussion about the findings of Mirzaee and Ghorbani-Dashtaki (2021), discussion about Ki2 in Alberts et al. (1995), and equations 2 and A16. A marked up copy of Elliot and Flanagan (2023) showing these changes can be downloaded from https://www.fs.usda.gov/rm/pubs_journals/2023/rmrs_2023_elliot_w001_corr.pdf. Keywords: Cropland Soils, Interrill Erodibility, Water Erosion Prediction Project.

Roles of raindrop impact in detachment and transport processes of interrill soil erosion

To date the roles of raindrop impact in sediment entrainment and transport processes of interrill soil erosion are not yet fully quantified. The objectives are to 1) evaluate the effects of raindrop impact on sediment entrainment, 2) systematically quantify the relative importance of raindrop-driven and flow-driven transport, and 3) characterize sediment size distributions in different sediment transport regimes. A loam soil with 48.4% sand and 23% clay was packed into flumes (L × W × H: 1.8 × 0.5 × 0.1 m) and subjected to intensities of 60, 90, 120 mm h−1 at gradients of 5, 10, and 16°. Air filter and tarp covers were used to vary impact energy and flow length. Results show that sediment is largely entrained by raindrop impact and transported by raindrop-impacted flow. Interrill erosion consists of two composite processes: raindrop-induced detachment/entrainment and raindrop-impacted flow transport. The former includes direct detachment by raindrop impact and ‘flow detachment’. The latter includes raindrop-driven and flow-driven transports. The proportions between the two transports vary with slope steepness, slope length, flow depth (or flow discharge), rainfall intensity, and sediment characteristics. Raindrop-driven transport is competent but inefficient, while the opposite is true for flow-driven transport. Because raindrop impact plays dual roles in detaching soil (and/or entraining sediment) and enhancing sediment transport, a drop energy factor must be included in interrill erosion models to adequately simulate the dual roles. More studies are required to derive a drop energy function that takes into consideration the rainfall energy dissipation by canopies of various plants under natural conditions.

Reply to comments on “Characterizing detachment and transport processes of interrill soil erosion, Geoderma (2020) 114549”

Reply to comments on “Characterizing detachment and transport processes of interrill soil erosion, Geoderma (2020) 114549”

Comment on “Characterizing detachment and transport processes of interrill soil erosion, Geoderma 376 (2020) 114549”

Comment on “Characterizing detachment and transport processes of interrill soil erosion, Geoderma 376 (2020) 114549”

Impact of Land Use/Cover Changes on Soil Erosion in Western Kenya

This study examined the impact of land use/cover changes on soil erosion in western Kenya in the years 1995 and 2017. The study used the GIS-based Revised Universal Soil Loss Equation (RUSLE) modelling approach and remote sensing assessment. The results showed that the average soil loss through sheet, rill and inter-rill soil erosion processes was 0.3 t/ha/y and 0.5 t/ha/y, in the years 1995 and 2017, respectively. Of the total soil loss, farms contributed more than 50%, both in 1995 and 2017 followed by grass/shrub (7.9% in 1995 and 11.9% in 2017), forest (16% in 1995 and 11.4% in 2017), and the least in built-up areas. The highest soil erosion rates were observed in farms cleared from forests (0.84 tons/ha) followed by those converted from grass/shrub areas (0.52 tons/ha). The rate of soil erosion was observed to increase with slope due to high velocity and erosivity of the runoff. Areas with high erodibility in the region are found primarily in slopes of more than 30 degrees, especially in Mt. Elgon, Chereng’anyi hills and Elgeyo escarpments. This study forms the first multi-temporal assessment to explore the extent of soil erosion and seeks to provide a useful knowledge base to support decision-makers in developing strategies to mitigate soil erosion for sustainable crop production.

Characterizing detachment and transport processes of interrill soil erosion

Detachment and transport processes of interrill soil erosion are not yet fully understood and quantified due to their complexity. Understanding these processes and their interaction is essential to developing effective interrill erosion prediction models. Thus, the objectives are to (1) identify detachment-limiting and transport-limiting regimes by comparing measured total soil splash with total sediment load of flow wash, (2) estimate relative importance of raindrop-driven and flow-driven transports under selected flow conditions using a novel experimental protocol, and (3) test widely used erosion equations for use in both detachment-limiting and transport-limiting regimes under the experimental conditions never before used. Sediment discharge and raindrop splash were separately collected from two plots with a 2.5-cm gap between them. Three rainfall intensities of 60, 90, and 120 mm h−1 were applied to three slopes of 9, 18, and 27% under two cover treatments of screen and tarp. Screen cover is to simulate crop canopy for dissipating raindrop energy, which is to control upslope sediment inflow by reducing raindrop detachment without modifying runoff rates. Tarp cover is to control both water and sediment inflows by varying slope length. Results showed that total raindrop splash in the entire plot during an event was less than total flow wash in the screen treatment, indicating detachment-limiting scenarios. However, total raindrop splash was greater (less) than total wash at the 9% (27%) slope in the tarp treatment, indicating transport-limiting (detachment-limiting) cases. The results indicated that raindrop-impacted flow might be able to detach soil in some cases. This finding runs counter to the common wisdom that soil detachment in interrill erosion is solely caused by raindrop impact. If raindrop-impacted flow can detach soil, the determination of limiting process by direct comparison between splash and wash loads seemed overly simplistic. Raindrop-driven transport was estimated for the first time by a means of dissipating raindrop impact energy in this study. Raindrop-driven transport was found to increase with rainfall intensity and slope gradients. Stream power and an empirical multiplication-of–factor equation performed well in predicting interrill sediment delivery under all erosion regimes, suggesting that it is unnecessary to develop distinct predictive equations for different interrill erosion regimes.

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.

Determining and Modeling Dominant Processes of Interrill Soil Erosion

AbstractUnderstanding the dominant process of interrill soil erosion is imperative to better modeling interrill sediment delivery rates. The objectives are to (1) determine the limiting erosion process (detachment vs. transport) that controls interrill erosion under the study conditions, (2) quantify the effects of water and/or sediment influxes from upslope on downslope sediment transport and interrill erosion, and (3) evaluate the ability of commonly used hydraulic parameters for simulating interrill sediment delivery. Runoff, sediment delivery, and raindrop splash were simultaneously collected from two flumes (1.8 m × 0.5 m) and a 2.5‐cm slot between the flumes for three intensities of 60, 90, and 120 mm/hr at three slopes of 9%, 18%, and 27% under two cover treatments. Results showed that slot splash rates were consistently greater than flume wash rates, indicating that sediment transport capacity limited interrill sediment delivery under the study conditions. Soil detachment by raindrop impact was more influenced by surface water depth, while sediment transport capacity by flow velocity. The former played a bigger role in determining interill sediment delivery under detachment‐limited cases while the latter under transport‐limited conditions. Linear correlation coefficients between sediment delivery rates and hydraulic predictors were 0.545 for shear stress, 0.946 for stream power, 0.867 for unit stream power, and 0.948 for an empirical lumped model that includes a rainfall intensity term. Stream power and the empirical model were better predictors for interrill sediment delivery. However, their predictive abilities need to be assessed more rigorously at various impact levels of rainfall kinetic energy.

Interrill erodibility in relation to aggregate size class in a semi-arid soil under simulated rainfalls

Interrill erodibility can be affected by soil aggregates, especially by those aggregate size classes that are dominant in the soil. In the Water erosion Prediction Project (WEPP) model, interrill soil erodibility (Ki) is estimated using very fine sand content. Despite that some studies have indicated an effect of aggregate stability on the Ki, information on the relationship between the aggregate size class and Ki and factors controlling it, particularly in semi-arid region is limited. This study was conducted to determine the variation of Ki for different aggregate size classes under various rainfall intensities and evaluation of the WEPP model in estimating the Ki for different aggregate fractions. Five aggregate size classes (0.25–2, 2–4.75, 4.75–5.6, 5.6–9.75 mm, and 9.75–12.7 mm) were separated from a sandy clay loam soil sampled in an agricultural land and put in laboratory flumes of 100 cm × 50 cm. The flumes were placed on a 9% slope and exposed to ten sequential rainfall simulations varying from 10 to 60 mm h−1 for 30 min. The Ki of each aggregate size classes was determined using the interrill sediment delivery rate and compared this with the values estimated using WEPP. All physicochemical properties were also determined in the aggregate size classes. Organic matter content in the aggregate size classes was very low (0.65–0.73%) and didn't show strong relationships with the aggregate stability and hydraulic conductivity, whereas clay was major factor controlling determining these properties for the different aggregate fractions. Significant differences were found among the aggregate size classes in clay content (P < 0.05), aggregate stability measured using both wet-sieving method (P < 0.05) and water drop test method P < 0.05, saturated hydraulic conductivity (Ks), and measured Ki (P < 0.05). The measured Ki was about 34 and 90 times bigger than the estimated Ki for the fine aggregates and coarse aggregates, respectively. The fine aggregates showed higher susceptibility to interrill detachment with increasing rainfall intensity as compared with the coarse aggregates. Significant decrease was observed in the measured Ki with increasing the aggregate size which was associated with increases in clay content, aggregate stability and Ks. The stability of aggregates against raindrop impact (CND) was an important indicator describing the effect of aggregate size on the interrill erodibility in semi-arid soils. Therefore, this indicator can be taken into account as a soil structure measure to develop a proper equation for estimating interrill erodibility (Ki) for agricultural lands. The minimum use of tillage practices is essential to prevent aggregate breakdown and control interrill erosion in semi-arid regions.

Gaining insights into interrill erosion processes using rare earth element tracers

Increasing interest in developing process-based erosion models requires better understanding of the relationships among soil detachment, transportation, and deposition. The objectives are to 1) identify the limiting process between soil detachment and sediment transport for interrill erosion, 2) understand the dynamic relationships between transport and deposition by tracking sediment fate with multiple tracers, and 3) verify the effects of slope length on interrill soil erosion. Five rare earth element (REE) tracers were applied in five bands or segments to track sediment dynamics on a 10%, 4×4-m long uniform slope under simulated rainfall. A silt loam soil with 8% clay and 87% silt was used. Six rain events were applied, the first four with 60mmh−1 and the last two with 90mmh−1. Sediment in runoff and deposition along the slope were measured. Results confirmed that interrill soil erosion was controlled by the transport process. Thus soil erodibility estimated with many interrill erosion models was actually sediment transportability. As the slope length increased, soil erosion rates initially increased and then decreased, indicating that the upper section was dominated by erosion and the lower section by transport. Raindrop-driven creeping prevailed in the upper section while flow-driven rolling dominated in the lower section. Sediment influx from upslope clearly suppressed soil detachment downslope. Moreover, the steady state sediment discharge from a segment was positively correlated to the amount of sediment deposited downslope from that segment, implying that 1) re-detachment, transport, and deposition occurred simultaneously in the system and 2) sediment was transported in a form of bedload, mainly rolling or creeping on interrill areas. Sediment delivery ratios of each segment tended to slightly increase downslope, suggesting the flow-driven transport was more efficient than the raindrop-driven transport. The sequence of sediment discharged from different slope positions was inconsistent with the transport-distance theory. However, interrill erosion processes vary with soil, slope, and rainfall properties, and the findings here need to be verified in different conditions.

Interrill soil erosion processes on steep slopes

To date interrill erosion processes are not fully understood under different rainfall and soil conditions. The objectives are to 1) identify the interrill erosion regime and limiting process under the study condition, 2) characterize the interactive effects of rainfall intensity and flow depth on sediment transport competency and mode, and 3) develop a lumped interrill erosion model. A loess loam soil with 39% sand and 45% silt was packed to flumes and exposed to simulated rainfall. A complete factorial design with three factors was used, which included rainfall intensity (48, 62, 102, 149, and 170mmh−1), slope gradient (17.6, 26.8, 36.4, 46.6, and 57.7%), and slope length (0.4, 0.8, 1.2, 1.6, and 2m). Rain splash, sediment discharge in runoff, and flow velocity were measured. Results showed that rainfall intensity played a dual role not only in detaching soil materials but also in enhancing sediment transport. Sediment transport was the process limiting interrill erosion rate under the study condition. Two major sediment transport modes were identified: rainfall-driven rolling/creeping and flow-driven rolling/sliding. The relative importance of each mode was largely determined by flow depth. The competence of the flow in transporting sediment decreased downslope as flow depth increased due to increased dissipation of raindrop energy. The optimal mean flow depth for the maximal interrill erosion rates was <0.1mm, which is much shallower than the widely reported 2mm. Slope length was negatively related to interrill erosion rate. The negative correlation seemed stronger for heavier rains, indicating the cushioning effects of flow depth. Lumped interrill erosion models, developed from short slopes, are likely to overestimate erosion rates. Given transport as the limiting process, the so called erodibility value, estimated with those models, is indeed sediment transportability under the study condition. The effects of slope length on interrill erosion regimes need to be studied further under a wider range of conditions.

An evaluation on using soil aggregate stability as the indicator of interrill erodibility

Aggregate stability is a very important predictor of soil structure and strength, which influences soil erodibility. Several aggregate stability indices were selected for estimating interrill erodibility of four soil types with contrasting properties from temperate and subtropical regions of China. This study was conducted to investigate how closely the soil interrill erodibility factor in the Water Erosion Prediction Project (WEPP) model relates to soil aggregate stability. The mass fractal dimension (FD), geometric mean diameter (GMD), mean weight diameter (MWD), and aggregate stability index (ASI) of soil aggregates were calculated. A rainfall simulator with a drainable flume (3.0 m long ×1.0 m wide ×0.5 m deep) was used at four slope gradients (5°, 10°,15° and 20°), and four rainfall intensities (0.6, 1.1, 1.7 and 2.5 mm/min). Results indicated that the interrill erodibility (Ki) values were significantly correlated to the indices of ASI, MWD, GMD, and FD computed from the aggregate wet-sieve data. The Ki had a strong positive correlation with FD, as well as a strong negative correlation with ASI, GMD, and MWD. Soils with a higher aggregate stability and lower fractal dimension have smaller Ki values. Stable soils were characterized by a high percentage of large aggregates and the erodible soils by a high percentage of smaller aggregates. The correlation coefficients of Ki with ASI and GMD were greater than those with FD and MWD, implying that both the ASI and GMD may be better alternative parameters for empirically predicting the soil Ki factor.ASI and GMD are more reasonable in interrill soil erodibility estimation, compared with Ki calculation in original WEPP model equation. Results demonstrate the validation of soil aggregation characterization as an appropriate indicator of soil susceptibility to erosion in contrasting soil types in China.

Runoff and soil loss from Pinus massoniana forest in southern China after simulated rainfall

Secondary forests with little understory vegetation and litter accumulation are facing a serious threat of erosion in the red soil region of southern China. To quantify the soil loss and develop prediction equations, 30 field rainfall simulation experiments were conducted with two rainfall intensities and five slope gradients in a 20-year-old Pinus massoniana forest. The results show that under the higher rainfall intensity, the runoff generation from the forest floor was high, even on gentle slopes. During simulated rainstorms, the initial soil losses increased rapidly and reached the peak value nearly at the same time as the peak runoff. Then soil loss decreased and runoff leveled out. Soil losses were significantly correlated with rainfall intensity, slope steepness and runoff rate. Further regression between soil loss as a dependent variable and runoff coefficient on different slopes verified that there exist interactions between slope and runoff factors in affecting soil loss. Stream power, which reflects the effect of both slope steepness and runoff rate can provide a more precise estimation (R2=0.71) of the soil loss rate than the single factors. Finally, an erosion model composed of rainfall, slope steepness and runoff rate was proved to be able to estimate interrill erosion for the large slope range data set of this study (R2=0.828). Therefore the model was proposed to predict the interrill soil erosion under the forest. The results will help us to understand the influential factors and build models to predict soil loss from forest with little understory vegetation in the red soil region of China.

Fatores relacionados à suscetibilidade da erosão em entressulcos sob condições de uso e manejo do solo

Neste trabalho foram avaliados fatores relacionados com a suscetibilidade a erosão em entressulcos de um Neossolo Litólico submetido a diferentes intensidades de uso e manejo do solo. O experimento foi realizado em condições de laboratório, utilizando-se amostras deformadas de solo colocadas em parcelas experimentais (0,23 m2) e declividade de 0,09 m m-1. O delineamento experimental utilizado foi em blocos casualizados, em que foram aplicadas chuvas simuladas com intensidade de 100 mm h-1 para os seguintes tratamentos: (I) solo cultivado com fumo sob preparo convencional (PC); (II) solo cultivado com fumo sob plantio direto (PD) e (III) solo sob mata nativa (MN). Para avaliar a suscetibilidade a erosão em entressulcos utilizaram-se índices referentes à relação energia cinética total (chuva e escoamento) sobre perda de solo, taxa média de desagregação e índice de estabilidade de agregados, cujos resultados mostraram que os fatores relacionados com a suscetibilidade a erosão em entressulcos estão associados não apenas com características e propriedades que conferem coesividade ao solo, mas, também, com condicionantes que afetam a hidráulica do escoamento e, consequentemente, a fase de transporte dos sedimentos.

Catchment-wide estimate of single storm interrill soil erosion using an aggregate instability index: a model based on geographic information systems

The main objective of this paper is to estimate interrill erosion after rainfall in the basin of Mourganis river (442 km2; Kalabaka province, Trikala prefecture, Thessaly, Greece). For the estimation of the interrill erosion, the method of Valmis et al. (1988) was used, in combination with Nearing et al. (1989). Input data of the algorithm include the slope angle of the ground surface, the rainfall, the ground cover type, the height of canopy, and the instability of ground of the study area. The spatial data were processed by standard GIS software. Soil samples were collected in the field to calibrate the model. The results comprise soil erosion maps for two specific rainfall scenarios. The first rainfall scenario refers to the most extreme rainfall in this catchment that happened on the 7/21/1959 with 48 mm/h. The second scenario is closer to average as the intensity rainfall is 3.54 mm/h. The total mass of eroded material ranges from 0.048 t/ha (assuming mean rainfall intensity) up to 3.5 t/ha (for the extreme scenario). We note that the western part of the Mourgani basin exhibits higher erosion than the eastern part.

Technical Note: The Vertical Distribution of Beryllium-7 Activity in Soil Profiles Determined by a Designed Device

Beryllium-7 (7Be) is an environmental radionuclide that is continuously deposited onto the surface of the earth as fallout. After depositing onto the earth, 7Be is rapidly and strongly adsorbed by soil particles. Beryllium-7 has a short half-life (53.3 days) and thus is primarily distributed in the upper 10 mm of the soil profile; it is therefore considered a useful tracer for documenting soil interrill erosion. The use of 7Be to document erosion is based on a comparison of the 7Be inventory at a sampling point with a reference value determined for a nearby reference site. The reference site is often very difficult to find; as a result, determining the reference value is usually the bottleneck for successfully using 7Be to document soil erosion. The objective of this study was to develop a device that can easily measure a 7Be reference inventory. A raingauge-like device was designed and used to determine the reference 7Be inventory and its vertical distribution with depth in three types of soil. The results show that the vertical distribution of 7Be in soil can be described by an exponentially decreasing function. The majority of 7Be was distributed in the first 10 mm of the soil surface. These results indicated that the device is valid to determine 7Be inventory as a reference, as well as its vertical distribution. According to the vertical distribution of 7Be, samples from the upper 4 mm of the soil surface should be less than 2 mm thick, while samples 2 to 3 mm thick can be used in the soil profile below 4 mm. The 7Be collector can be used to determine both the total 7Be inventory as a reference value and the distribution of 7Be at depths in a disturbed soil profile, which is important for estimating short-term interrill soil erosion.

Produção de sedimentos pela erosão em entressulcos em três Latossolos do Rio Grande do Sul

A distribuição de diâmetro do sedimento produzido pela erosão hídrica dependerá do tipo e da textura do solo. Este trabalho foi desenvolvido com o objetivo de avaliar a distribuição de tamanho de sedimentos produzidos por erosão em entressulcos, em três Latossolos do Rio Grande do Sul (Latossolo Vermelho aluminoférrico-LVaf, Latossolo Vermelho distroférrico-LVdf e Latossolo Vermelho distrófico-LVd), com diferentes classes texturais. Três repetições de chuva simulada com intensidade de 88 mm h-1 e duração de 90 min foram aplicadas sobre os solos, em parcela experimental com área útil de 0,36 m² e declividade de 0,09 m m-1. As amostras do sedimento foram coletadas em um conjunto de peneiras. A distribuição de diâmetro dos sedimentos variou conforme a textura do solo e os sedimentos produzidos apresentaram partículas e agregados de menor diâmetro que os do solo original. A maior parte dos sedimentos aportados no LVdf pertence à classe de 9,51 a 4,76 mm, enquanto no LVaf a classe predominante é a de 4,76 a 2,00 mm, os quais são os solos com maior teor de argila, carbono orgânico e óxidos de ferro e maior estabilidade de agregados em água. O Latossolo com menor estabilidade de agregados em água (LVd) foi o que apresentou sedimentos de tamanho menor (1,00 a 0,25 mm).

Evaluation of the EUROSEM model for predicting the effects of erosion-control blankets on runoff and interrill soil erosion by water

The European Soil Erosion Model (EUROSEM, Morgan et al., 1998) is an event-based soil erosion model which predicts runoff and sediment discharge for different environmental conditions. Applying geotextiles or erosion-control blankets (ECB’s) on the soil surface significantly affects surface seal formation and topsoil properties and therefore controls runoff and soil erosion rates during a rainfall event. Since these within-storm changes of soil surface characteristics and hydrological conditions are not incorporated in EUROSEM, errors in runoff and soil erosion predictions may occur for soil surfaces covered with ECB’s. Therefore, the objective of this paper is to evaluate and improve the performance of a research version of the physically-based erosion model EUROSEM (EUROSEM-2010; Borselli and Torri, 2010) for simulating the effects of ECB’s on runoff and interrill soil erosion by water during intense simulated rainfall events. Results of model simulations are compared with experimental results of interrill erosion using biological (i.e. natural) ECB’s and simulated rainfall. Because ECB’s applied on the soil surface retard seal formation, the differences between observed and predicted runoff rates and sediment discharges are rather high during the first 20–30 min of the simulated rainstorm. Therefore, a simple approach is proposed to cope with the dynamic evolution of some soil characteristics, i.e. saturated hydraulic conductivity, soil erodibility and soil cohesion, during an intense rainfall event. This time-dependent approach improves the predictions of runoff rate and sediment discharge during the first 20–30 min of a rainfall event and increases the model efficiency (i.e. a measure for the goodness of fit) from 0.84 to 0.98 and from 0.48 to 0.68 for the total runoff volume and soil loss, respectively. For most conditions, the predicted final sediment discharge is still considerably larger than the observed values, which can be partly attributed to the deposition of sediment in the bare soil patches (i.e. inter-weave open areas) of the ECB’s, which is not simulated by EUROSEM in this study. This model approach increases our understanding of the effects of ECB’s on within-storm changes in hydrological conditions and soil surface characteristics.

Variability of interrill erosion at low slopes

AbstractNumerous models and risk assessments have been developed in order to estimate soil erosion from agricultural land, with some including estimates of nutrient and contaminant transfer. Many of these models have a slope term as a control over particle transfer, with increased transfer associated with increased slopes. This is based on data collected over a wide range of slopes and using relatively small soil flumes and physical principals, i.e. the role of gravity in splash transport and flow. This study uses laboratory rainfall simulation on a large soil flume to investigate interrill soil erosion of a silt loam under a rainfall intensity of 47 mm h−1 on 3%, 6% and 9% slopes, which are representative of agricultural land in much of northwest Europe. The results show: (1) wide variation in runoff and sediment concentration data from replicate experiments, which indicates the complexities in interrill soil erosion processes; and (2) that at low slopes processes related to surface area connectivity, soil saturation, flow patterns and water depth may dominant over those related to gravity. Consequently, this questions the use of risk assessments and soil erosion models with a dominant slope term when assessing soil erosion from agricultural land at low slopes. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Interrill erosion of carbon and phosphorus from conventionally and organically farmed Devon silt soils

Abstract Globally, between 0.57 and 1.33 Pg of soil organic carbon (SOC) may be affected by interrill processes. Also, a significant amount of phosphorus (P) is contained in the surface soil layer transformed by raindrop impact, runoff and crust formation. In the EU, the P content of a crusted (2 mm) surface layer corresponds to 4 to 40 kg ha− 1 of P on arable land (1.094 mil km2). Therefore, the role of interrill processes for nutrient cycling and the global carbon cycle requires close attention. Interrill erosion is a complex phenomenon involving the detachment, transport and deposition of soil particles by raindrop impacted flow. Resistance to interrill erosion varies between soils depending on their physical, chemical and mineralogical properties. In addition, significant changes in soil resistance to interrill erosion occur during storms as a result of changes in surface roughness, cohesion and particle size. As a consequence, erosion on interrill areas is selective, moving the most easily detached small and/or light soil particles. This leads to the enrichment of clay, phosphorous (P) and carbon (C). Such enrichment in interrill sediment is well documented, however, the role of interrill erosion processes on the enrichment remains unclear. Enrichment of P and C in interrill sediment is attributed to the preferential erosion of the smaller, lighter soil particles. In this study, the P and organic C content of sediment generated from two Devon silts under conventional (CS) and organic (OS) soil management were examined. Artificial rainfall was applied to the soils using two rainfall scenarios of differing intensity and kinetic energy to determine the effects on the P and C enrichment in interrill sediment. Interrill soil erodibility was lower on the OS, irrespective of rainfall intensity. Sediment from both soils showed a significant enrichment in P and C compared to the bulk soil. However, sediment from the OS displayed a much greater degree of P enrichment. This shows that the net P export from organically farmed soils is not reduced by a similar degree than soil erosion compared to conventional soil management. The enrichment of P and C in the interrill sediment was not directly related to SOC, P content of the soil and soil interrill erodibility. A comparison of soil and sediment properties indicates that crusting, P and C content as well as density and size of eroded aggregate fragments control P and C enrichment. Due to complex and dynamic interactions between P, SOC and interrill erosional processes, the nutrient and C status of sediments cannot be predicted based on soil P content, SOC or interrill erodibility alone. Clearly, further research on crust formation and the composition of fragments generated by aggregate breakdown and their transport in raindrop impacted flow under different rainfall conditions is required. Attaining this critical missing knowledge would enable a comprehensive assessment of the benefits of organic farming on nutrient budgets, off-site effects of interrill erosion and its role in the global C cycle.