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Rill erosion, mostly affecting steep and long hillslopes, is one of the most severe effects of deforestation and wildfires in natural ecosystems. Specific monitoring and accurate but simple models are needed to assess the impacts of these forest disturbances on the rill detachment process. To address this need, this study has simulated the rill detachment capacity (Dc) through flume experiments on samples of soils collected in hillslopes after deforestation and severe burning. The associations between Dc and organic matter (OM) and the aggregate stability of soil (WSA), two key parameters influencing the rill detachment process, have also been explored under the two soil conditions (deforested and burned soils) using multivariate statistical techniques. Finally, linear regression models to predict Dc from these soil parameters or the hydraulic and morphological variables (water flow rate, WFR, and soil slope, S), set in the flume experiments, have been proposed for both soil conditions. Higher Dc in samples from deforested sites compared to the burned soils (+35%) was measured. This Dc increase was associated with parallel decreases in OM (−15%) and WSA (−34%) after deforestation compared to the wildfire-affected sites. However, the discrimination in those soil properties between the two soil conditions was not sharp. Accurate linear equations (r2 > 0.76) interpolating Dc and the shear stress (τ) have been set to estimate the rill erodibility (Kr) to evaluate soil resistance in erosion models to be applied in deforested or burned sites. [ABSTRACT FROM AUTHOR]

[Objective］ Soil resistance reflects the characteristics of soil to mitigate erosion and is quantified by rill erodibility (K r) and critical shear stress (「)• To investigate the difference of soil resistance and its main controlling factors under different land use types through the flume scouring test, which provided a theoretical basis for revealing the dynamic mechanism of soil erosion in Northeast black soil area. Methods］ Seven typical land use types were selected in the Hebei small watershed of Heshan farm, located in Nenjiang city of Heilongjiang Province. K r and rc were determined using the measured soil detachment capacity by scouring test in a large hydraulic flume. The dominant factors influencing soil resistance were determined by correlation analysis and partial least square regression. Results］ (1) The estimated K，-varied from ().003 to ().372 s/m among different land use types. K r of road was the highest. Compared to cropland, K r of grassland, transverse forest belt, woodland, longitudinal forest belt, and shrub land decreased by 94.00%, 86.20%, 84.00%, 83.60%, and 71.6()%. The fittedranged from 4.84 and 13.85 Pa. Cropland and road had lowest (4.84 and 9.80 Pa). The differences inwere not significant between other land use types and were greater than 1 ().0() Pa. (2) Correlation analysis showed that K r was significantly correlated with clay content, aggregate stability and organic matter content (p〈().()l), and sand content, soil cohesion, root mass density and litter density mixed within topsoil layer negatively (p〈().()5). Tt was significantly correlated with silt content positively ().()1). was significantly related to silt content negatively (/>〈()•()1). Tt was significantly correlation with sand content and topsoil litter density (p

A root system is an important factor to increase soil resistance to detachment of soil particles. However, due to the large number of species, there is a need for studying the impacts of native plant species on soil quality and soil erodibility. This investigation did flume experiments at various soil slopes (9.2%, 18.1%, 25.1%, and 32.5%) and different water flow rates (0.56, 0.67, 0.74, 0.81, and 0.94 L/(m·s)), to evaluate sediment detachment capacity caused by rills (D c) and rill erodibility (K r) as well as the soil quality of hillslopes with three common species including Carpinus betulus (as a natural tree species), Alnus glutinosa (as a planted tree species) and Mespilus germanica (as a shrub species) in forestland of northern Iran. The variability of D c has been associated with soil properties and root characteristics of Carpinus betulus. D c was significantly lower (average, −45%) for soils under Carpinus betulus compared to soils with the two other plant species (p < 0.01). This was due to the higher values of soil properties including medium weight diameter of soil aggregates (MWD), organic carbon (OC), total nitrogen (TN), total phosphorous (TP), potassium (K), calcium (Ca), magnesium (Mg) as well as to the more extended root system, as confirmed by the negative correlations between D c and the studied variables. K r also was different among the studied soils and plant species. The root system of Carpinus betulus also played a useful role for increasing soil resistance to rill erosion yielding a safety factor (1.61) in the studied forest ecosystem. Overall, the current study supports a broader use of native species (such as Carpinus betulus) in areas exposed to surface erosion and instability, as an effective eco-engineering conservation technique and an alternative technology instead of utilizing artificial and expensive management practices. [Display omitted] • Sediment detachment capacity (D c) has been estimated by flume experiments for vegetated soils. • A natural species had lower D c compared to the planted and shrub species. • This reduction was due to higher soil quality and more extended plant roots. • Carpinus betulus species played a beneficial role for increasing slope stability. • The rill erodibility (K r) was the lowest in soils under Carpinus betulus species. [ABSTRACT FROM AUTHOR]

Gully erosion, considered as a type of intensive erosion, is the dominant source of sediment at small watershed scales in certain environments. Variation of vegetation may result in the changes in near soil surface characteristics, which likely further affect the resistance of gully systems to erosion. However, the potential effects of near soil surface characteristics of plant communities on resistance to erosion are still unclear in gully systems. This study was performed to investigate the variations in resistance of gully systems to erosion under different plant communities and to identify the dominant influencing factors leading to these variations on the Loess Plateau. Five typical plant communities (two grasses, two shrubs and one forest) that distributed on different gully systems were selected. Six hundred undisturbed soil samples collected from different sites of gully systems were subjected to detach by overland flow under six different shear stresses (6.66 to 15.02 Pa). The results showed that the mean soil detachment capacity of gully systems covered by grass and shrub communities was 0.15 and 0.37 times to that of gully system covered by forest. Compared to forest gully systems, rill erodibility reduced by 29.8% to 85.6% for the other four plant communities. The relative rill erodibility of different vegetation communities generally increased from grass to shrub and forest communities. The critical shear stress of forest gully system was 58.7% and 63.8% of gully systems covered by grass (6.22 Pa) and shrub (5.73 Pa) communities. Bulk density, soil cohesion, water stable aggregate, root mass density, and the thickness of biological soil crust were the dominant factors affecting the resistance of gully systems to soil erosion. Rill erodibility decreased logarithmically with increasing soil cohesion, water stable aggregate and root mass density. Critical shear stress increased with the increase of soil cohesion and root mass density as a power function, and linearly with the increase of water stable aggregate. These results show how vegetation can mitigate against the erosion induced by concentrated flow in relatively stable gully systems. [ABSTRACT FROM AUTHOR]

In croplands, soil erosion resistance varies with both natural processes and human disturbances. To clarify the temporal variation in soil erosion resistance, nine cropland plots with three treatments (continuous fallow, fallow after tillage and tillage with corn) were established in the dry–hot valley region of China. A total of 144 field runoff simulation experiments were conducted from May to October to measure the soil detachment rate (Dc), rill erodibility (Kr) and critical shear stress (τc). The results revealed that the natural dry—wet alternation had little influence on the continuous-fallowed soil erosion resistance. On the other hand, the tillage disturbance that occurred in May sharply increased the Dc and Kr to 2.24 and 3 times that of the continuous-fallow treatment, respectively. Then, the erosion resistance could be enhanced with surface consolidation for the fallow-after-tillage treatment. However, after three months of fallow, the Kr was still 89.5% of the fresh tilled soil. In contrast, crop growth could significantly improve aggregate stability and reduce the Kr to 38.2% in August and even further to 23.7% in October compared to the fresh tilled soil. It could be concluded that crop growth is more efficient in enhancing erosion resistance than the mechanical effect. The above results would benefit from the accurate modeling of cropland soil erosion dynamics and guide agricultural management in dry–hot climate regions. [ABSTRACT FROM AUTHOR]

Physical soil crust (PSC), a key component of surface soil structure, exists extensively in loess areas. PSC is considered to have a significant effect on soil detachment processes. However, the long-term effects and the corresponding mechanisms of PSC on soil detachment by overland flow are still not well understood, especially in natural environments. To investigate temporal variation in soil erosion resistance and the underlying factors during PSC formation, an 8 × 8-m soil plot was exposed to natural conditions in the Loess Plateau over a 524-day period spanning two rainy seasons and a winter between them. A flume test was conducted to determine soil detachment capacity (Dc) under six designed flow shear stress levels (5.66–22.11 Pa) using crusted (SC) and non-crusted (NSC) soil samples at different PSC development stages. Subsequently, two soil erosion resistance parameters, rill erodibility (Kr) and critical shear stress (τc), were calculated. Over time, in the SC and NSC treatments, Kr decreased from 0.516 to 0.120 s m−1 and 0.521 to 0.223 s m−1, respectively, while τc increased from 0.49 to 4.42 Pa and 0.26–2.46 Pa, respectively. Variation in soil erosion resistance was rapid in the first one to two months, and then slowed down, with slight fluctuations afterwards. In the SC treatment, Kr was 42% lower and τc was 67% greater than those in the NSC treatment. Soil properties changed greatly for both treatments. SCT increased from 0 to 7.09 mm in the SC treatment. Coh increased from 2.91 to 9.04 kPa and 3.01–4.78 kPa in SC and NSC treatments, respectively. Both soil erosion resistance parameters could be well predicted by SCT and Coh in the SC treatment (R2 ≥ 0.82), while their best predictor was Coh in the NSC treatment (R2 ≥ 0.90). The results demonstrate that PSC formation enhances soil erosion resistance in the soil detachment process in the loess region under natural conditions. Our study revealed the important role and complexity of PSC in the process of soil erosion, and provided theoretical and data support for accurate understanding and prediction of soil erosion.

[Objective] The relationship between soil column pore structure and soil erosion resistance for soil columns with Bahiagrass was analyzed in order to provide a scientific basis for the optimal arrangement of plants for soil and water conservation and to assess the benefits of planting Bahiagrass. [Methods] This study was conducted using long-term experiments of Bahiagrass grown in soil columns. Four pore indicators (pore length density, bulk density, surface area density, and pore number density) of Bahiagrass soil columns were quantified by CT scanning technology. Flushing tests using a flume with variable slopes were carried out to quantify soil erosion resistance at three slopes (10°, 20°, and 30°) and five runoff rates (0.8, 1.6, 2.4, 3.2, and 4.0 L/s). The relationships between pore structure characteristics and erosion resistance factors were then determined. [Results] Bahiagrass root system development increased during the growth period, but decreased with soil depth. The values of four pore structure indicators in 0—5 cm soil layer were much higher than those in 5—10 cm soil layer, and the average soil rill erodibility (0.026 s/m) and critical shear stress (7.0 Pa) in 0—5 cm surface layer were 0.33 and 1.54 times the values of those respective parameters in 5—10 cm lower soil layer. [Conclusion] The pore characteristics of plant root development indicated soil erosion resistance. The four pore structure indicators obtained by CT scanning were significantly related to factors such as rill erodibility. The pore surface area density was most closely related to the erosion resistance factors.

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Soil erosion resistance is influenced by intrinsic soil properties and multiple external factors. This study investigated the effect of tea planting age on soil resistance to flowing water erosion (reflected by rill erodibility (Kr) and critical shear stress (τc)) in Three Gorges Reservoir Area. One slope farmland (as the control) and five tea plantations cultivated for 3 to 34 years were selected for sampling sites. The results indicated that bulk density (BD), soil cohesion (Coh), water stable aggregate (WSA), mean weight diameter (MWD), soil organic carbon (SOC), litter density (LD), and root mass density (RMD) increased generally with tea planting age. Compared to the control, Kr of tea plantations reduced by 71.1%-85.3%. The temporal variation in soil erosion resistance was controlled greatly by the variations in most near-surface characteristics. Kr decreased with WSA, Coh, LD, RMD, and SOC following a power function (P < 0.01); τc increased with MWD, LD, RMD, and SOC as an exponential function, with BD a power function, and Coh a logarithmic function (P < 0.01). In this study, Kr could be simulated well by WSA and LD with a power function, and τc could be simulated well by MWD and RMD with an exponential function.

In croplands, soil erosion resistance varies with both natural processes and human disturbances. To clarify the temporal variation in soil erosion resistance, nine cropland plots with three treatments (continuous fallow, fallow after tillage and tillage with corn) were established in the dry–hot valley region of China. A total of 144 field runoff simulation experiments were conducted from May to October to measure the soil detachment rate (Dc), rill erodibility (Kr) and critical shear stress (τc). The results revealed that the natural dry—wet alternation had little influence on the continuous-fallowed soil erosion resistance. On the other hand, the tillage disturbance that occurred in May sharply increased the Dc and Kr to 2.24 and 3 times that of the continuous-fallow treatment, respectively. Then, the erosion resistance could be enhanced with surface consolidation for the fallow-after-tillage treatment. However, after three months of fallow, the Kr was still 89.5% of the fresh tilled soil. In contrast, crop growth could significantly improve aggregate stability and reduce the Kr to 38.2% in August and even further to 23.7% in October compared to the fresh tilled soil. It could be concluded that crop growth is more efficient in enhancing erosion resistance than the mechanical effect. The above results would benefit from the accurate modeling of cropland soil erosion dynamics and guide agricultural management in dry–hot climate regions.

Copyright of Mountain Research (10082786) is the property of Mountain Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Soil Science & Plant Nutrition / Toprak Bilimi ve Bitki Besleme Dergisi is the property of Soil Science Society of Turkey and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the late 1980s, the USDA Agricultural Research Service, along with other federal agencies and multiple universities, collaborated to develop a new physically based soil erosion model, the Water Erosion Prediction Project (WEPP) Model. The WEPP model was intended to replace the Universal Soil Loss Equation and was to include estimates for upland runoff and erosion, sediment delivery to first order channels, and runoff and sediment routing through a downstream channel network. The WEPP technology estimated erosion from raindrop splash and sheet flow (interrill erosion) and concentrated channel flow (rill erosion). To make these erosion estimates, WEPP required new soil erodibility values for interrill erodibility (Ki). rill erodibility (Kr), and critical shear (𝜏𝜏 c) for concentrated flow erosion. The WEPP Core team determined that they needed to estimate these three erodibility values from measurable soil properties for a wide range of soil conditions. To develop relationships between WEPP soil erodibility variables and other soil properties, a field study was carried out using rainfall and runoff simulation to measure the three erodibility values for 36 soils. Sites were identified on croplands from Washington to Georgia and Maine to California, USA for erodibility measurement. Concurrently, the USDA Soil Conservation Service (SCS) carried out detailed soil surveys and laboratory analyses for all sites to provide a large database of soil physical, chemical, and engineering properties. Correlation and regression analyses were carried out to develop relationships between SCS measurable soil properties and WEPP soil erodibility values. This article provides a summary of the field procedures, data analyses, and subsequent predictive equations that were developed. The predictive equations that were finalized in the WEPP User Summary used sand, very fine sand, clay, and organic carbon contents to predict cropland soil erodibility, but the Coefficient of Determination (r²) values were 0.55 or less. More complex predictive equations were developed with soil physical, chemical, mineralogical, and geomorphic properties, with r² values up to 0.81. Most of the better predictive equations included terms for soil texture and clay mineralogy, often with additional chemical properties. A set of simplified erodibility equations using only the readily available properties of soil texture, organic carbon, cation exchange capacity, slope steepness, and taxonomic order were derived for use within the WEPP Model, with r² values greater than 0.5 for all three equations for estimating soil erodibility from measurable soil properties. [ABSTRACT FROM AUTHOR]

Purpose: Vegetation restoration types influence the physicochemical properties and near-surface characteristics of soil and likely affects soil resistance. However, variations in the characteristics of soil resistance under different vegetation restoration types have not been characterized in the severely eroded subtropical regions of South China. The objective of this study was aimed to identify the mechanism of soil resistance under different vegetation restoration types and simulate the prediction equation. Materials and methods: This study examined four typical vegetation restoration types that were restored by artificial planting forest (AF), orchard (AO), scrubland (AS) and grassland (AG) and compared them with unrestored eroded land (EL) as a control. The soil detachment rate was measured by scouring the soil with steel cutting rings with flowing water under five shear stress intensities (3.40–18.11 kPa). This study quantified the effects of typical types of vegetation restoration on soil resistance in severely eroded subtropical regions of South China by identifying the major factors and simulating a prediction equation. Results: The results showed that the eroded land had the maximum soil detachment rate (0.474 kg m−2 s−1), and then was the most easily detached. It was followed sequentially by the artificial grassland, the artificial scrubland, the artificial orchard and the artificial forest. The soil detachment rate was negatively correlated with clay content, capillary porosity, soil organic matter content, soil cohesion (p < 0.01) and soil initial water content (p < 0.05), and it was a positively correlated with silt content (p < 0.01). Near-surface characteristics also inhibited the soil detachment process to some extent. A similar trend was observed for rill erodibility, which was dominated mainly by soil organic matter content, root surface density and sand content (NSE = 0.806). The critical shear stress was significantly positively related to soil cohesion and biological crust thickness (NSE = 0.632). Conclusions: Based on the Water Erosion Prediction Project (WEPP) model, the soil detachment rate was simulated from easily measured factors, such as sand content, soil organic matter content, soil cohesion, biological crust thickness and root surface density (R2 = 0.812, NSE = 0.827). This observation provides a reference regarding the soil–water erosion process in severely eroded subtropical regions in South China. [ABSTRACT FROM AUTHOR]

Fertilizer application can affect the physicochemical properties of soil, such as the contents of large aggregates, humus, and exchangeable cations, thereby influencing soil erosion resistance. However, the rill erosion resistance and its key influencing factors of soil following long-term balanced fertilizer application remains unclear. This study aimed to analyze the change in rill erosion resistance following 44 years of balanced fertilizer application (No changes in the type of fertilizer) to non-calcareous soils and establish a Partial Least Squares Regression (PLSR) model of rill erodibility (k d) and soil critical shear stress (τ c) to changes in the physical and chemical properties of the soil. Five treatments were designed: (1) CK (no fertilizer applied), (2) N (nitrogen), (3) NP (nitrogen plus phosphorus), (4) NK (nitrogen plus potassium), and (5) NPK (nitrogen, phosphorus, and potassium). Compared to CK, the N, NP, NK, and NPK application significantly increased τ c by 49.6, 96.7, 73.6, and 36.2 %, respectively. Whereas, k d increased significantly only in the NPK treatment group. The optimal partial least squares regression model showed that mean weight diameter (MWD) had the greatest positive influence on soil critical shear stress, followed by fulvic acid (FA) content, whereas water-dissolved substances had a negative influence. Long-term balanced fertilizer application can increase MWD and τ c by combining micro-aggregates and humus into large aggregates. Ca2+ content had the greatest positive effect on k d. Compared with that of CK, exchangeable Ca2+ content increased significantly with NP and NPK application (7.9 and 34.3 %, respectively). Ca2+ can increase k d by binding to the polar functional groups in FA to promote the shedding of hydration shells in large aggregates. Among all treatments, the NP treatment showed the best performance for reducing k d and increasing τ c. This study could contribute to the understanding of the rill erosion process and modeling in non-calcareous soils and offer a reference for agricultural erosion control treatments. • Balanced fertilizer application for 44 years improved rill erosion resistance. • Balanced fertilizer application increased soil critical shear stress by up to 96.7 %. • Mean weight diameter was positively associated with soil critical shear stress. [ABSTRACT FROM AUTHOR]

• Reforestation and soil conservation heavily impact on rill detachment capacity (D c) • Soil and root characteristics were significantly different among undisturbed forests and treated sites. • Changes in D c are associated to soil and root characteristics. • D c is similar in natural and planted forests, and undergoes a noticeable reduction after treatments. • The discrimination in soil and root properties and D c is however not sharp. Rill erosion is particularly intense after deforestation on hillslopes with steep and long profiles. Since the rill detachment capacity ("D c ") shows a noticeable variability resulting from different soil properties and vegetation characteristics, there is a need to explore the changes in key soil properties and rill erosion rates under different natural or planted species and a variety of soil conservation practices after deforestation. This study evaluates the changes in four key soil properties (organic carbon content, bulk density and water-stable aggregates of soil, and weight density of plant roots) and rill detachment capacity in forest sites with natural tree species as well as in areas subjected to reforestation and soil conservation treatments in comparison to deforested sites. To this aim, 2000 soil samples have been collected in forestlands of Northern Iran. Sampling was done in deforested areas (assumed as reference condition), and in forest sites 14 plant species (natural or after reforestation). Deforested samples were subjected to five soil conservation treatments (using additives or hydromulching). On all soil samples, D c has been measured in a laboratory flume at five water flow rates (0.27 to 0.69 L/m s−1) and five soil slopes (5.9 to 31.7 %). All soil properties, when compared to the reference condition, were significantly different (between −50 % to 124 %) among the three soil conditions (natural forests, reforested soils and deforested and treated sites), the natural forests and the treated sites showing a better quality compared to planted forests. D c was noticeably lower in all conditions (0.022 ± 0.021 kg m−2 s−1) compared to the deforested and untreated sites (0.046 ± 0.023 kg m−2 s−1). Natural and planted forests showed a similar decrease in rill erodibility (−70 to 80 %), while a much lower reduction in D c (−36 %) was measured for the treated areas. Overall, the study demonstrates that the changes in soil properties due to plant species and soil management as well as the associated variability in rill detachment are noticeably site-specific, and greatly depend on soil conservation treatments. The results of this study may give landscape planners clear indications about the relationships between rill detachment and the associated soil properties among treated and untreated (natural or reforested) soils. [ABSTRACT FROM AUTHOR]

Biochar addition can change the physiochemical properties of soil, thus likely influencing soil's resistance to rill flow (reflected by rill erodibility (K r , s m−1) and critical shear stress (τ c , Pa). However, the persistent time effects of biochar on K r and τ c have remained unexplored. This study aimed to assess the impact of biochar composed of apple branches on K r and τ c , and to investigate the relationships between K r , τ c and soil properties. The undisturbed soil core samples to a depth of 5 cm were collected from field plots that had received biochar at rates of 0, 1, 2.5, 4, 5.5, and 7 % (w/w) after 1, 2, and 3 years, respectively. The K r and τ c of these samples were evaluated through a flume experiment, with scouring soil samples under three flow discharges (e.g., 0.00025, 0.00045, and 0.00065 m−3 s−1) and five slope gradients (e.g., 5.24, 8.75, 17.63, 26.79, and 40.40 %). The results revealed that the ranges of K r and τ c for no biochar treatments varied from 0.1947 to 0.2107 s m−1 and 1.6971–1.7314 Pa, with the averaged values of 0.2007 s m−1 and 1.7100 Pa, respectively. Compared with no biochar addition, the addition of 1–4 % biochar after 1–2 years generally resulted in a reduction in K r ranging from 20 % to 59 %, while increasing τ c by 2–4 %. Conversely, 5.5 and 7 % biochar addition increased K r by 31 and 5 %, and reduced τ c by 12 and 6 %. All biochar treatments after 3 years resulted in a 51 % reduction in K r and a 5 % increase in τ c relative to bare soil, showing an increasing trend with an increasing biochar addition rate. The fluctuations in K r and τ c could be elucidated by changes in cohesion (COH) and mean weight diameter of soil aggregates (MWD), with COH (total effect of −0.32 and 0.17, P <0.01) and MWD (total effect of −0.13 and 0.37, P <0.01) serving as reliable estimators of K r and τ c during the 1–2 years following biochar addition. After biochar addition for 3 years, total organic carbon (TOC) (total effect of −0.45 and 0.10, P <0.01) emerged as a significant factor influencing K r and τ c , making TOC a potential p r edictor of K r and τ c. The results demonstrate that biochar may be an effective measure for enhancing soil resistance to erosion on the Loess Plateau, especially when applied over the long term. • 1–4 % biochar increased rill erodibility (K r) but result was oppsite for 5.5 % and 7 % additions after 1–2 years. • Biochar addition after 3 years enhanced soil erosion resistance for all rates. • Total organic carbon (TOC) significantly affected K r as biochar addition duration increased. • MWD, soil cohesion and TOC could be used to estimate K r under biochar addition. [ABSTRACT FROM AUTHOR]

Various disputes exist regarding the critical shear stress (τc) of rill erosion determined by linear regression. Alternatively, some researchers have attempted to measure critical shear stress (τo) of rill erosion by observing the start of soil particle detachment and showed promising results. However, few studies have been conducted to evaluate the reliability of the method determining τo. Thus, this study was conducted to identify the reliability of the method determining τo by comparing the values of τc and τo and their relationships with rill erodibility (Kr) and influencing factors, using 360 disturbed soil samples (standing for the freshly tilled condition) from six sampling sites along a 330 km transect in the Loess Plateau. Results indicated that the mean τc was 1.90 times greater than that of τo. No significant relationship was found between τc and Kr. An inverse changing trend between Kr and τo was observed from Yijun to Zizhou, while both Kr and τo exhibited increasing trends from Zizhou to Yulin. The τo of six sampling sites all demonstrated increasing trends with slope gradient (S), which contradicted the statement of the WEPP model that τc was independent of S. The relationships between τc and the measured soil properties were poor, whereas the τo increased exponentially with soil organic matter. Generally, τo did not present significantly better results than τc; the reliability of τo also showed some uncertainties, such as the subjective judgment of the beginning detachment of soil particles. This result has great importance for deepening our understanding of the rill erosion mechanism. [ABSTRACT FROM AUTHOR]

Biocrusts affect soil detachment through above-ground (top crust's surface covering) and below-ground (sub-crust's binding and bonding, B&B) effects, which might vary with biocrust development or coverage. However, these effects in humid climates are still unclear. This study was conducted to apportion and quantify the surface covering and B&B effects of moss biocrusts with five coverage levels (1%–20%, 20%–40%, 40%–60%, 60%–80%, and 80%–100%) on soil detachment by overland flow in a subtropical humid climate. Two treatments with one being intact moss crusts and one removing the above-ground moss tissues were designed for each coverage level, and bare soil was used as the baseline. The results indicated that soil detachment capacity (Dc) and rill erodibility (Kr) decreased with biocrust coverage. After removing the above-ground moss tissues, the impeding effect of biocrusts on soil detachment weakened, but still increasing soil erosion resistance relative to bare soil. For intact crust, Dc was reduced by 50%–95% compared with bare soil, wherein 36%–55% and 14%–40% were attributed to the surface covering and B&B, respectively. The top crust contributed more than sub-crust to the soil detachment reduction, which were related to but not linear with biocrust coverage. When biocrust coverage reached mid-to-higher level (40%–100%), both top crust and sub-crust steadily contributed to soil detachment reduction with 60% and 40%, respectively. The findings advance a better understanding of the influencing mechanism of biocrusts on soil erosion in humid climates and highlight the importance of saving biocrusts as ecosystem functions. [ABSTRACT FROM AUTHOR]

Periodic submersion and exposure due to the operation of the Three Gorges Reservoir (TGR) alter the soil properties and plant characteristics at different elevations within the water level fluctuation zone (WLFZ), possibly influencing the soil detachment capacity (Dc), but the vertical heterogeneity of this effect is uncertain. Soil samples were taken from 6 elevation segments (5 m per segment) along a slope profile in the WLFZ of the TGR to clarify the vertical heterogeneity of Dc. Scouring experiments were conducted at 5 slope gradients (17.6%, 26.8%, 36.4%, 46.6%, and 57.7%) and 5 flow rates (10, 15, 20, 25, and 30 L min−1) to determine Dc. The results indicate that the soil properties and biomass parameters of the WLFZ exhibit strongly vertical heterogeneity. Dc fluctuates with increasing elevation, with maximum and minimum average values at elevations of 145–150 m and 165–170 m, respectively. Linear equations accurately describe the relationships between Dc and hydrodynamic parameters, for which the shear stress (τ), stream power (ω), and unit energy of water‐carrying section (E) perform much better than the unit stream power (U). Furthermore, a clear improvement is achieved when using a general index of flow intensity to estimate Dc. Furthermore, Dc is significantly and negatively correlated with the mean weight diameter (MWD, p < 0.05) and organic matter content (p < 0.01) but not significantly correlated with other soil properties (p > 0.05). The rill erodibility at elevations of 145–150 m and 170–175 m is greater than that at other elevations. The critical hydraulic parameters were highest in the 165–170 m segments. Both the rill erodibility and the critical parameters fluctuate vertically along the sloping surface. This research highlights the vertical heterogeneity of Dc and is helpful for better understanding the mechanisms responsible for soil detachment in the WLFZ of the TGR. [ABSTRACT FROM AUTHOR]

[Display omitted] • The total root morphological traits decreased markedly from 20° to 30° slope. • The reduction rates of soil detachment capacity did not differ with slope gradient. • The rill erodibility and critical shear stress peaked at 30° slope. • Soil detachment capacity declined exponentially with the increase of root morphology. Plant roots interact closely with soils and significantly affect soil erosion, which can be reflected in various root traits. Slope gradient is a topographic factor that considerably affects the interactions between root traits and soil erosion. However, little is known about the relationships between root traits and soil erosion, which are affected by slope gradient. This study investigated the responses of root traits and soil detachment to variable slope gradients in a representative purple-soil sloping grassland. Topsoil samples with vetiver (Chrysopogon zizanioides L.) roots (VT) and without roots (CK) were collected at three gradients (20°, 30°, and 40°) to determine the soil detachment capacity, the rill erodibility and critical shear stress. The root mass and morphology of the VT were also measured. The results showed that root mass density and root morphological traits related to the total roots (irrespective of root diameter) and roots with diameter ≤ 1.0 mm decreased markedly from 20° to 30°. The proportions of root morphology with diameter > 1.0 mm increased as slope gradients increased, suggesting that steep slopes could promote coarse roots. The soil detachment capacity was 34.1–49.6 % lower in VT than in CK under studied slope gradients, whereas these reductions did not differ with slope gradients. Lower rill erodibility and higher critical shear stress were found in VT under each slope than in CK, highlighting the role of roots in enhancing soil erosion resistance. Our results contribute to understanding the mechanisms by which roots on control soil water erosion in complicated, changing environments. [ABSTRACT FROM AUTHOR]

Biological soil crusts (biocrusts) are important landscape components that exist in various climates and habitats. The roles of biocrusts in numerous soil processes have been predominantly recognized in many dryland regions worldwide. However, little is known about their effects on soil detachment process by overland flow, especially in humid climates. This study quantified the effects of moss-dominated biocrusts on soil detachment capacity (Dc) and soil erosion resistance to flowing water in the Three Gorges Reservoir Area which holds a subtropical humid climate. Potential factors driving soil detachment variation and their influencing mechanism were analyzed and elucidated. We designed five levels of coverage treatments (1%–20%, 20%–40%, 40%–60%, 60%–80%, and 80%–100%) and a nearby bare land as control in a moss-dominated site. Undisturbed soil samples were taken and subjected to water flow scouring in a hydraulic flume under six shear stresses ranging from 4.89 to 17.99 Pa. The results indicated that mean Dc of moss-covered soil varied from 0.008 to 0.081 kg m−2 s−1, which was 1.9 to 21.0 times lower than that of bare soil (0.160 kg m−2 s−1). Rill erodibility (Kr) of moss-covered soil ranged from 0.0095 to 0.0009 s m−1, which was 2 to 20 times lower than that of bare soil (0.0187 s m−1). Both relative soil detachment rate and Kr showed an exponential decay with increasing moss coverage, whereas the critical shear stress (τc) for different moss coverage levels did not differ significantly. Moss coverage, soil cohesion, and sand content were key factors affecting Dc, while moss coverage and soil bulk density were key factors affecting Kr. A power function of flow shear stress, soil cohesion, and moss coverage fitted well to estimate Dc (NSE=0.947). Our findings implied that biocrusts prevented soil detachment directly by their physical cover and indirectly by soil properties modification. Biocrusts could be rehabilitated as a promising soil conservation measure during ecological recovery to enhance soil erosion resistance in the Three Gorges Reservoir Area. [ABSTRACT FROM AUTHOR]

Soil detachment is the initial stage of soil erosion, which refers to the process of soil surface particles detached from the original soil under the action of rainfall splash or runoff, and is the main source of erosion sediment. The slope after freeze-thaw provides a large number of effective materials for water erosion. In recent decades, as the global climate tends to be warmer, the effects of freeze-thaw in the areas of high latitude and high elevation have been intensified. This study was conducted to investigate the effects of freeze-thaw on soil detachment capacity and erosion resistance by means of indoor simulation freeze-thaw and runoff scour tests. Soil samples were collected from the top 20 cm of abandoned land in Loess Plateau of China. To remove stones, grass, and other debris, air-dried soil samples were sieved through a 5 mm mesh. Soil samples were stored in polyvinyl chloride (PVC) cylindrical boxes based on the bulk densities in the field. Then the samples were frozen at -10 ℃ for 12 hours and thawed at room temperature between 5℃ and 10℃ for 12 hours to simulate the natural phenomenon of night freezing and day thawing. Soil detachment capacity was measured in a 4.0 m long, 0.15 m wide flume. The loessal soil was subjected to 0, 1, 5, 10 freeze-thaw cycle times before it was scoured, while the slope and flow discharge of flume experiments were 10°, 15° and 12, 18, 24 L/min, respectively. The results showed that slope, flow discharge and freeze-thaw cycle times all had significant effects on soil detachment capacity (P<0.05), with contribution rates of 17.94%, 19.96% and 18.43%, respectively. Soil detachment capacity basically increased with the increase of slope and flow rate. The mean value after freeze-thaw (5.28±2.48 g/(cm² ·min)) was significantly higher than that before freeze-thaw (2.39± 1.71 g/(cm2 ·min)), but the degree of increase after freeze-thaw was significantly lower than that before freeze-thaw. Under different slope and flow rate conditions, soil detachment capacity increased significantly after first freeze-thaw (P<0.05). The variation trend of soil detachment capacity with the times of freeze-thaw cycles was significantly different. Only when the slope and flow rate were both small (10° and ≤18 L/min) or large (15° and ≥18 L/min), the trend increased significantly. After 1, 5 and 10 times of freeze-thaw cycle, the rill erodibility increased by 1.25, 1.66 and 1.72 times respectively, and gradually became stable with the increase of freeze-thaw cycle times. The critical shear stress decreased significantly after freeze-thaw cycles and had no significant relationship with freeze-thaw cycle times. After freeze-thaw, the means of soil bulk density, water stable aggregates and shear strength decreased by 6.61%, 24.77% and 21.35%, respectively. Under the condition of freeze-thaw, rill erodibility was negatively correlated with water stable aggregates and shear strength, but positively correlated with soil porosity. This study can provide reference for the study of complex erosion of freeze-thaw and water. [ABSTRACT FROM AUTHOR]

Plant litter can be incorporated into topsoil by a natural process, affecting the soil erosion process. This is a widespread phenomenon in erosion‐prone areas. This study was conducted to investigate the effect of litter incorporation on the process of soil detachment on the Loess Plateau, China. Four common plant litters (Bothriochloa ischaemum L. Keng., Artemisia sacrorum Ledeb., Setaria viridis L. Beauv., and Artemisia capillaris Thunb.) were collected, then incorporated into the silt loam soil at five rates (0.1, 0.4, 0.7, 1.0, and 1.3 kg m−2) on the basis of our field investigation. Twenty litter–soil treatments and one bare soil control were prepared. After 50 days of natural stabilization, 30 soil samples of each treatment were collected. We used a flume test to scour the soil samples under six flow shear stress conditions (5.66, 8.31, 12.21, 15.55, 19.15, and 22.11 Pa). The results showed that the different incorporated litter masses and morphological characteristics, such as litter tissue density (ranging from 0.52 to 0.68 g cm−3), length density (2.34 to 91.00 km m−3), surface area density (LSAD; 27.9 to 674.2 m2 m−3), and volume ratio (0.003 to 0.050 m3 m−3), caused varied soil detachment capacities (0.043 to 4.580 kg·m−2·s−1), rill erodibilities (0.051 to 0.237 s m−1), and critical shear stresses (2.02 to 6.83 Pa). The plant litter incorporated within the soil reduced the soil detachment capacities by 38%–59%, lowered the rill erodibilities by 32%–46%, and increased the critical shear stresses by 98%–193% compared with the bare soil control. The soil containing B. ischaemum (L.) Keng. litter was more resistant to erosion. By comparing different parameters, we found that the contact area between the litter and soil was the main factor affecting the soil detachment process. The soil erosion resistance increased with the increasing contact area between the soil and litter. Furthermore, the litter incorporation effect on rill erodibility can be comprehensively reflected by LSAD (R2 =.93; Nash–Sutcliffe efficiency = 0.79), which could be used to adjust the rill erodibility parameter in physical process‐based soil erosion models. [ABSTRACT FROM AUTHOR]

Land use has significant effects on the erosion process, since it influences the soil detachment capacity by causing an overland flow (Dc). The effects of different land uses on the rill detachment capacity have not been explained in depth, and the hydraulic parameters providing accurate estimates of this soil property have not been completely identified. This study quantifies Dc at low flow rates in woodland and forestland, compared to two other land uses (cropland and grassland), in the Saravan watershed (Northern Iran), and develops prediction models of Dc and rill erodibility (Kr). Dc was measured on undisturbed soil samples, collected in the four land uses, and characterized in terms of the main physico-chemical properties in a flume experiment, simulating five slopes and five shallow water flows. The results showed that Dc was significantly lower in woodland and forestland compared to cropland and grassland, as the consequence of the changes in the main soil properties and the more developed vegetation cover and structure. Dc was positively correlated to clay and silt contents of soils, and negatively correlated to sand content, aggregate stability, root density, and organic matter. The stream power and unit stream power were found to be very accurate predictors of Dc in woodland and forestland, respectively. Kr values, which assumed the lowest values in woodland and forestland, were provided by interpolating Dc and the shear stress of water flow. Overall, this study has confirmed that vegetation cover and improved soil properties in forestland and woodland may help to reduce erosion in delicate environment ecosystems, such as the forests of Northern Iran. [ABSTRACT FROM AUTHOR]

Abstract Soil detachment capacity (Dc) is a key parameter in many soil erosion models and is typically estimated using hydraulic parameters. However, the accuracy of predicting Dc and its relationship to hydraulic characteristics remains poorly understood for many soil types. This study investigates the predictability of Dc with hydraulics by simulated scour rill flow and quantifies erosion vulnerability to rill erosion as reflected by rill erodibility and critical hydraulic values for an Entisol from Southwestern China. Small samples (10 cm in diameter, 6 cm in depth) of sandy clay loam of Entisol were subjected to scouring by simulated rill flow under the combinations of flow discharges (18.8, 26.3, 46.6, 54.4, 64.6 l min−1) and slope gradients (3.5%, 8.7%, 17.6%, 26.8% and 36.4%). The results showed that Dc increased as a power function with flow discharge irrespective of slope gradients, and at low discharge gradients Dc increased as a power function with slope and with transitions to a linear function at higher discharge gradients. The association of flow discharges and slope gradients was a better predictor of Dc than flow depths and slope gradients. Shear stress and stream power were similar and better predictors of Dc than flow velocity, unit stream power and unit energy. Rill erodibility related to all hydraulic parameters were significantly different from zero under combination of flow discharges and slope gradients, and this was true for critical hydraulic values related to comprehensive data. Relatively higher rill erodibility and lower critical hydraulic values compared with other soils demonstrated that sandy clay loam of Entisol is susceptible to detachment. These results highlight the erosion vulnerability of Entisols and provide deeper insights on the reliability of hydraulic parameters which strongly affect soil detachment modeling. Graphical abstract Unlabelled Image Highlights • Detachment capacity of sandy clay loam Entisol determined by simulated rill flow scour • Power function can predict relationship between detachment capacity and hydraulics. • Shear stress and stream power have similar predictability of detachment capacity. • Sandy clay loam of Entisol is highly susceptible to erosion by detachment. [ABSTRACT FROM AUTHOR]

Abstract Steep gully slopes are widespread and have been recognized as the main sediment source on the Loess Plateau. Different vegetation growth may lead to the differences in soil properties and plant roots, and thus likely affects soil resistance to flowing water erosion, reflected by rill erodibility and critical shear stress. However, few studies have been conducted to evaluate this effect on steep gully slopes on the Loess Plateau of China. This study was performed to investigate the effects of vegetation growth on soil resistance to flowing water erosion on steep gully slopes, and quantify the main potential influencing factors on the Loess Plateau. Three typical shrub communities and four typical grass communities that distributed on different gully slopes were selected. 240 undisturbed soil samples were collected from these seven gully slope lands and one slope farmland (control), and were subjected to detachment by overland flow under six different shear stresses (6.64 to 17.85 Pa). The results showed that the mean detachment capacity of slope farmland was 6.9 to 47.8 times greater than those of steep gully slopes covered with different plant communities. The rill erodibilities of steep gully slopes covered with different plant communities reduced greatly by 77.0% to 95.1% compared to the control slope. The critical shear stress of slope farmland (2.72 Pa) was only 57.2% and 39.6% of that of shrubland (4.76 Pa) and grassland (6.88 Pa). Both shrub and grass communities were effective in reducing soil detachment capacity and rill erodibility, and increasing critical shear stress on steep gully slopes. But the effects were more obvious for the grass communities. The differences in rill erodibility between slope farmland and gully slope lands were mainly explained by the changes in root mass density (82.4%). Plant roots had strong direct effects on increasing soil cohesion (0.78), organic matter content (0.56), and water stable aggregation (0.92). Rill erodibility was negatively related to root mass density as an exponential function (p < 0.05), and soil cohesion and water stable aggregation as power functions (p < 0.05). Critical shear stress was positively related to root mass density and soil water stable aggregation following a logarithmic function. Highlights • Vegetation recovery effectively promoted soil erosion resistance on gully slopes. • K r negatively related to root mass density, soil cohesion and aggregate stability. • τ c positively related to root mass density and soil aggregate stability. [ABSTRACT FROM AUTHOR]

• Soil erosion resistance was significantly affected by straw incorporation. • Land degradation regulated the roles of straw incorporation in mitigating erosion. • Clay and organic matter contents were the key to improve soil erosion resistance. • Straw incorporation was not recommended in strong degraded cropland. Soil erosion resistance (reflected by rill erodibility and critical shear stress) is a useful parameter for evaluating soil erosion subjected to concentrated flow. The changes in soil properties and root trait induced by straw incorporation and land degradation likely affect soil erosion resistance considerably. Nevertheless, few studies have been conducted to quantify the effects of straw incorporation on soil erosion resistance of degraded croplands in the black soil region. In this study, a large hydraulic flume (5.0 m in length and 0.4 m in width) was utilized to quantify the impacts of straw incorporation on soil erosion resistance of four croplands with different degradation degrees (non-degradation, light degradation, moderate degradation and strong degradation) and further to determine the related influencing mechanisms in Northeast China. The results showed that straw incorporation reduced rill erodibility by 44.9%, 41.2%, 27.1% and −11.4% for non-degradation, light degradation, moderate degradation and strong degradation croplands, respectively. Land degradation degree had much stronger influence on soil erosion resistance than that of straw incorporation and regulated the roles of straw incorporation in mitigating erosion. Rill erodibility was significantly and negatively correlated with clay content, organic matter content, aggregate stability, soil cohesion, physical crust thickness and root mass density, whereas positively correlated with silt content. The increase in soil organic matter and clay content was the key to improve soil erosion resistance and prevent land degradation. Straw incorporation was suggested in non-degradation, light degradation and moderate degradation croplands, but vegetation restoration was recommended in strong degraded cropland. The results are helpful to understand the mechanism of straw incorporation to improve soil erosion resistance and make reasonable agricultural management strategies in semi humid region. [ABSTRACT FROM AUTHOR]

[Display omitted] • Rill detachment capacity (D c) has been calculated using a hydraulic flume in unburned (control) and burned soils. • D c was higher, more than twice, in the burned soils compared to the unburned soil. • These reductions are due to the changes in soil properties including the organic matter content and aggregate stability. • The soil organic matter and aggregate stability had a negative correlation with D c. • The model developed can predict the D c with well accuracy. It is well known that forest fires affect physico-chemical characteristics of soils. However, few investigations have explored the effects of human-caused fires on soil erosion processes, particularly for the parameters used in rill erosion on steep slopes. To fill this gap, this study has evaluated the effects of human-caused fires on the rill detachment capacity (D c) and rill erodibility (K r) in the burned soils, compared to the unburned soils, as control soils, in a forest of Guilan province (northern Iran). For measuring D c , the slopes (3.9, 9.1, 15.3, 23.9, and 32.7%) and water discharges (0.28, 0.38, 0.46, 0.54, and 0.63 L/m s−1) were adjusted to the desired values using a laboratory flume. Moreover, three properties of soils including the organic matter, bulk density and aggregate stability were determined. The results showed that D c and K r were significantly higher in the burned soils, compared to the unburned soils (both more than twice), as the consequence of the significant changes in organic matter content, bulk density and aggregate stability (p < 0.01). Compared to unburned soils, when soil organic matter and aggregate stability decrease, D c increases in burned soils and these differences led to rill development. These changes in soil properties were confirmed by principal component analysis, which did show a clear discrimination between the burned and unburned sites. The model developed can predict the rill detachment capacity according to a simple linear relationship of the selected soil properties and may be used for an appropriate hydrological management of forest soils. [ABSTRACT FROM AUTHOR]

• Both rill detachment capacity (D c) and rill erodibility (K r) were lower in the hydromulched soil containing Nano silica powder (HNS) compared to the control soil. • These reductions are due to the improvement the root characteristics in the HNS soil. • Root length, root biomass and root weight density had a significant negative correlation with D c. • The root diameter had a significant positive correlation with D c. It is well known that hydromulching is an appropriate method for controlling runoff and soil erosion. Also, the addition of silica nanoparticles (Nsi) in soil in various ways has been found to be a beneficial technique to improve root characteristics. However, few studies have explored the effects of silica nanoparticles produced from rice husk (as a crop that is exceedingly plentiful in many Asian countries) on soil erosion processes, particularly rill erosion due to overland flow in deforested lands. To fill this gap, this study has evaluated the impacts of root growth induced by silica nanoparticles (Nsi) on the rill detachment capacity (D c) and erodibility (K r) in the hydromulched soil samples, compared to the control soil samples in deforested lands of Northern Iran. Dc has been measured by a hydraulic flume under four bed slopes (7.3, 13.9, 18.5, and 23.4%) and five water discharges (0.25, 0.36, 0.47, 0.59, and 0.72 L m−1 s−1) with six replications per experiment. Moreover, after the application of hydromulch on soil surface and the growth of grass, root traits (root diameter, root length, root biomass and root weight density) were measured. The results show that rill detachment capacity was lower (on average −59%) in the hydromulched soil with the presence of silica nanoparticles compared to the untreated plot (P < 0.01). Dc was negatively correlated with the root length, root biomass and root weight density. Conversely, as the root diameter increased, the Dc increased. Rill erodibility, obtained by regressing Dc on shear stress, was noticeably lower (-86%) in the hydromulched soil with the presence of silica nanoparticles compared to the bare plot. Overall, the results of this study confirm that the effects of silica nanoparticles on growth development of root traits and the reduction of soil erosion appear to be impactful, especially on steep slopes. [ABSTRACT FROM AUTHOR]

• The stable macroaggregate structure makes the erodibility of forest soil at a low level. • Mean weight diameter and rill erodibility has a negative power function. • Acidobacteria and Basidiomycota are the key groups in resisting soil rill erosion. • SOC has strong regulatory effects on the soil key group of microorganisms. How microbial communities respond to soil aggregation and rill erosion resistance has rarely been addressed. Such a knowledge gap hinders the practice of guiding sustainable soil management. Herein, the community composition of bacteria and fungi was evaluated by 16S rRNA gene sequencing. We measured critical shear stress (τc) and rill erodibility (k d) by self-made jet device. The effects of microorganism on soil aggregation and rill erosion resistance were quantitatively analyzed under different land uses. The results indicated that the forest soil supported the colonization and enrichment of Acidobacteria and Basidiomycota on account of the unique vegetation and higher soil organic carbon (SOC). The forest and shrubland contained higher macroaggregate and mean weight diameter (MWD) than those of cropland and bare land, while rill erodibility (k d) was the opposite. MWD and k d had a negative power function (y = 105.64x−0.69). The biotic factors explained 73.50% of the variation in rill erosion resistance and soil aggregation, indicating microorganism are more important in acting on rill erosion resistance. This study suggests that SOC had strong regulatory effects on the soil key groups of bacteria and fungi assemblages; furthermore, their interaction facilitated the formation of stable macroaggregates. The stable macroaggregate structure and vegetation cover make the erodibility of forest soil at a relatively low level. However, cropland are not conducive to stability of aggregates, which easily causes soil erosion. Improving soil SOC and maintaining the relative abundance of key groups of microorganism would be conducive to soil sustainable developing. [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSCs) have impacts on soil detachment process through surface covering, and binding and bonding (B&B) mechanisms, which might vary with successional stages of BSCs. This study was conducted to quantify the effects of surface covering, binding and bonding of BSCs on soil detachment capacity by overland flow in a 4 m long hydraulic flume with fixed bed. Two dominant BSC types, developed well in the Loess Plateau (the early successional cyanobacteria and the later successional moss), were tested using natural undisturbed soil samples collected from the abandoned farmlands. Two treatments of undisturbed crusts and one treatment of removing the above-ground tissue of BSCs were designed for each BSC type. For comparison, bare loess soil was used as the baseline. The collected soil samples were subjected to flow scouring under six different shear stresses, ranging from 6.7 to 21.2 Pa. The results showed that soil detachment capacity ( D c) and rill erodibility ( K r) decrease with BSC succession, and the presence of BSCs obviously increased the critical shear stress, especially for the later successional moss crust. For the early successional cyanobacteria crust, D c was reduced by 69.2% compared to the bare loess soil, where 37.7% and 31.5% are attributed to the surface covering and B&B, respectively. For the later successional moss crust, D c decreased by 89.8% compared to the bare loess soil, where 68.9% and 20.9% contributed to the surface covering and B&B, respectively. These results are helpful in understanding the influencing mechanism of BSCs on soil erosion and in developing the process-based erosion models for grassland and forestland. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Landscape position has significant effects on soil properties and plant roots, and thus probably affects soil resistance to rill erosion, reflected by rill erodibility and critical shear stress. However, the potential effects of landscape positions on soil resistance to rill erosion are still unclear. Therefore, this study was conducted to investigate the spatial variations in soil resistance to rill erosion under different landscape positions, and to identify the main factors controlling these variations in a small catchment of the Loess Plateau. 540 undisturbed soil samples were collected from 18 typical sampling sites of natural succession grassland under six landscape positions and subjected to scour under different flow shear stresses. The results showed that landscape position significantly affected the spatial variation of rill erodibility. The mean rill erodibility decreased gradually from the top of ridge to footslope and increased linearly with elevation. Significant differences were detected in rill erodibility between three grass species. No significant difference was found in critical shear stress between six landscape positions. Soil erosion and soil water content dominated the regular spatial changes of soil properties and root mass density along six landscape positions. All of these factors collectively resulted in the regular decrease of rill erodibility from the top of ridge to footslope. A negative relationship was identified between critical shear stress and clay content. Rill erodibility could be satisfactorily estimated by the median soil grain size, soil cohesion, water stable aggregate and root mass density. [ABSTRACT FROM AUTHOR]

Plant litter has been accumulated greatly along with vegetation restoration on the Loess Plateau. Besides covering soil surface, plant litter can be incorporated into topsoil under natural circumstances by soil splash, sediment deposition, and soil-dwelling animal activities. The distribution (covering soil surface or incorporated into surface soil) and the decomposition of plant litter can modify soil physical properties (including soil detachment capacity and soil erosion resistance) which are closely related to soil detachment process by overland flow. This study was conducted to investigate the effect of vegetation restoration on soil detachment process for black locust (Robinia pseudoacacia L.) stand with different ages of returning farmland on the Loess Plateau. The experiments were performed in the Zhifanggou small watershed (36°46'28"-36°46'42"N, 109°13'46"-109°16'03"E) in August, 2015. After a complete watershed survey, altogether 6 sampling sites were selected, including 1 corn (Zea mays L.) field and 5 black locust stands of 10, 15, 20, 30, and 40 years. Soil samples were collected from the top 5 cm soil layer using a circular steel ring with 10.0 cm diameter and 5.0 cm depth. Soil detachment was measured in a 4.0 m long, 0.35 m wide flume. Prior to the test of soil detachment capacity, soil samples were saturated in a container for 8 h and drained for 12 h. Then the soil samples were inserted into a hole (0.5 m away from the outlet of flume) on the flume bed and were scoured by flowing water under designed flow shear stress. A total of 180 soil samples were collected from different aged black locust stands and scoured under 6 flow shear stresses. In this study, 6 combinations of flow rates and slopes were applied to obtain 6 different flow shear stresses (5.4-17.4Pa) with similar intervals. Rill erodibility is defined as the increase in soil detachment capacity per unit increase in flow shear stress. Critical shear stress is a threshold parameter defined as the value above which a rapid increase in soil detachment capacity per unit increase in shear stress occurs. When the measured detachment capacity was plotted against the flow shear stress, rill erodibility and critical shear stress could be determined from the slope of the fitted straight line and its intercept on the X axis. The results showed that the density of plant litter in 0-5 cm surface soil was 0.065, 0.175, 0.316, 0.289 and 0.171 kg/m2 for 10, 15, 20, 30, and 40-year-old black locust stands, respectively, with the mean value of 0.20 kg/m2. The 40-year-old black locust stands had more capillary porosities, soil organic matter, and water stable aggregates, and smaller soil bulk density. Soil detachment capacity decreased by 49.8%, 73.9%, 85.0%, 86.0%, and 87.0% for 10, 15, 20, 30, and 40-year-old black locust stands, respectively, compared to the control. The soil detachment capacity decreased significantly over time as an exponential function (R2=0.97, P=0.006). The control (corn field) had the biggest rill erodibility (0.29 s/m), and the 40-year-old black locust stand had the smallest rill erodibility (0.04 s/m). Compared to the control, the rill erodibility for 40-year-old black locust stand was reduced by 86.3%. The black locust stand with 20 years had the biggest critical shear stress (4.78 Pa), and the control had the smallest critical shear stress (4.15 Pa). The critical shear stress increased by 10.1% for 40-year-old black locust stand compared to the control. The critical shear stress increased significantly with litter density as a linear function (R2=0.67, P=0.046). Rill erodibility was better than critical shear stress in the respect of reflecting the variation of soil detachment. The soil-plant litter system has a larger erosion resistance to flowing water than the control. Importantly, the soil-root system may have a larger structural stability and erosion resistance to flowing water than soil-plant litter system. [ABSTRACT FROM AUTHOR]

The knowledge of soil resistance to runoff (reflected by rill erodibility, K r , and critical shear stress, τ c ) of steep croplands from laboratory flume experiments and their influencing factors are unclear at a larger scale. Therefore, the disturbed soil samples (representing the freshly tilled steep croplands) of 36 soil types were collected from eastern China and scoured under different flow shear stresses to investigate the spatial variations in K r and τ c and their influencing factors. The results showed that the soil “Argi-Udic Ferrosols” had the lowest K r , while the soil “Aqui-Sandic Primosols” had the highest K r . The K r values of the 36 soil types showed a high spatial variability. The mean K r of the northwest Loess Plateau was significantly greater than that of the other five secondary water erosion regions. Soil texture with moderate clay and sand content had the highest K r . τ c showed moderate spatial variability, and no obvious correlation was detected with soil types, the six secondary water erosion regions, or soil textures. K r was significantly correlated with the measured soil physical and chemical properties. No significant correlation was found between τ c and measured soil properties. K r could be satisfactorily estimated by the silt content, sand content, the geometric mean particle diameter of the soil ( D g ), cation exchange capacity ( CEC ) and soil organic matter ( SOM ) ( R 2 = 0.70). [ABSTRACT FROM AUTHOR]

Rill erosion is one of the main sediment sources. Rill erodibility and critical shear stress are essential parameters for soil erosion prediction for Water Erosion Prediction Project (WEEP) model. Soil subsurface hydraulic gradient on soil loss is important to an accurate prediction of soil erosion and channel initiation. The objectives of this study were 1) to quantitatively explore the response of parameters of WEPP to different subsurface hydraulic gradients; and 2) to investigate the relationship between measured and calculate values in WEPP of critical shear stress. Taking typical yellow soil as example, runoff scouring experiment and a method of measuring critical shear stress were conducted by using a V-shaped soil pan under a slope of 5%. The experiments were carried out in Jinyun Mountain of the upper and middle reaches of the Yangtze River, China (106°22′E, 29°45′N). A total of 5 hydraulic gradients were -1.43, -0.71, 0, 0.71 and 1.43 m/m and 3 discharges were 0.55, 1.58 and 2.51 L/min, respectively. Average runoff, average sediment, soil detachment rate and shear stress were determined by collecting runoff samples every 30 s intervals in 8 minutes for each experimental treatment. Rill erodibility and critical shear stress were calculated in WEPP model. The measured value of critical shear stress was determined by varying the flow rate until erosion began when soil particles were continuously detached. Results showed that the average runoff for all the experiments increased with the increase of hydraulic gradient. The average sediment increased with the increase of hydraulic gradient when discharges were 0.55 and 1.58 L/min, showing a change range of 2.55-5.77 and 14.58-28.74 g, respectively. However, when the hydraulic gradient was increased from -1.43 to 0 m/m and then to 1.43 m/m for 2.51 L/min discharge, the average sediment exhibited a trend of first sharp decrease from 46.10 to 24.48 g and then slight increase from 24.48 to 29.21 g. When the discharge was increased from 0.55 to 1.58 L/min and then to 2.51 L/min under the drainage conditions (hydraulic gradient from -1.43 to -0.71 m/m), the average sediment increased by 217.40%-217.39% and 64.38%-66.20%, respectively. However, when the discharge was increased from 1.58 to 2.51 L/min under the saturation/seepage conditions (hydraulic gradient from 0 to 1.43 m/m), the average sediment only increased by 1.64%-17.41%. The average sediment under the drainage conditions was 42.24%-88.32% higher than that under saturation/seepage conditions for 2.51 L/min discharge. The soil detachment rate decreased firstly and then changed stably with the increase of scouring time under the saturation/ seepage conditions, and the similar trend of soil detachment rate was found under the drainage conditions for 0.55 L/min discharge. However, the change tread of soil detachment rate were fluctuated under the drainage conditions with the increase of discharge, and the fluctuation of soil detachment rate under 2.51 L/min discharge was stronger than that under 1.58 L/min discharge. The average value of rill erodibility for the 5 hydraulic gradients was 2.51×10-2 s/m. The value of rill erodibility under the saturation/seepage condition was 3.07×10-2 s/m, and was then 1.78 times higher than that under drainage conditions. When the hydraulic gradient was -1.43 m/m, the critical shear stress was nearly equal between the calculated value in WEPP and the measured value. However, when hydraulic gradient ranged from -0.71 to 1.43 m/m, the calculated value overestimated from 14.24% to 55.02% with an average overestimate of 36.85% compared to the measured value. Moreover, an exponential relationship was fitted between the calculated value in WEPP model and the measured value of critical shear stress (R2 was 0.77, Nash coefficient was 0.66, P value was smaller than 0.01). This study not only provides a guidance for controlling soil erosion on yellow soil region, but also offers an important database for correcting critical shear stress of rill erosion in WEPP. [ABSTRACT FROM AUTHOR]

Biochar addition to soil has been found to be a useful practice to control erosion. However, few studies have explored the effects of biochar produced from husk of rice on rill erosion, due to overland flow in deforested areas. This study has evaluated the rill detachment capacity (D c) and erodibility (K r) in soil samples treated with rice husk biochar in comparison to untreated sites (control), collected in deforested hillslopes of Northern Iran. D c was measured in a lab-scale hydraulic flume at four-bed slopes (9.7, 14.3, 19.5, and 24.2%) and five water discharges (0.24, 0.36, 0.47, 0.59, and 0.69 L m−1 s−1). Moreover, organic carbon, aggregate stability and bulk density of soils were measured. D c was lower (on average − 32%) in the treated soil compared to the control. D c was not correlated to the other physico-chemical properties of soil. K r , estimated by linear regressions between D c and shear stress, was noticeably lower (−79%) in the treated soil compared to the control. These results evidence that rice husk biochar is effective at controlling and mitigating soil detachment, and at improving organic matter content and aggregate stability in deforested hillslopes. The proposed values of rill erodibility and shear stress of deforested hillslopes (treated or untreated) are helpful to model soil resistance to rill erosion in process-based erosion models. • Scarce knowledge exists about biochar effects on rill detachment capacity (D c). • D c was lower by 32% in the soil treated with biochar compared to the untreated soil. • This reduction was due to organic matter addition to soil treated with biochar. • D c was not correlated to the other physico-chemical properties of soil. • Rill erodibility was lower (−79%) in the soil treated with biochar. [ABSTRACT FROM AUTHOR]

• The 43 years of manure application can improve rill erosion resistance. • Pig manure significantly increased soil critical shear stress by up to 101.4%. • Exchangeable calcium ions had positive effect on soil critical shear stress. • Soil mean weight diameter was controlled by sodium ions and organic carbon. Application of organic fertilizers is a potential practice to prevent soil erosion by changing the physicochemical properties of the soil, such as macroaggregates, soil organic carbon (SOC) content, and exchangeable cations. However, the practical performance of organic fertilizer in soil erosion after a long-term application has scarcely been reported. To reveal the response of soil erosion resistance (i.e., the soil susceptibility to resist external erosion force) to 43 years of organic fertilization, five treatments were investigated: (1) CK (no fertilizer), (2) NPK (mineral fertilizer), (3) M (pig manure), (4) MN1 (pig manure + 138 kg N ha−1), and (5) MN2 (pig manure + 276 kg N ha−1). The results showed that NPK, M, MN1, and MN2 significantly increased soil critical shear stress (τ c) by 54 %, 87 %, 101 %, and 67 %, respectively, compared to CK. However, rill erodibility (k d) was increased significantly only in the MN2 treatment. The optimal partial least squares regression model showed that the increase in soil exchangeable Ca2+ was the dominant contributor to the τ c increase, while soil mean weight diameter (MWD) had the greatest negative effect on k d. Compared with CK, the soil exchangeable Ca2+ in M and MN1 increased significantly by 123 % and 135 %, respectively. The MWD in M and MN1 increased by 86 % and 83 %, respectively, compared with that in CK. The application of pig manure was beneficial for decreasing exchangeable Na+ and increasing SOC content, which could improve MWD. Manure with a high N content did not increase MWD due to SOC decomposition. Our results indicate that the long-term application of manure, alone or combined with moderate N, improves rill erosion resistance. [ABSTRACT FROM AUTHOR]

Plant litter can be incorporated into topsoil under natural circumstances by soil splash, sediment deposition, and soil-dwelling animal activities. The incorporated litter can change the mechanical properties of soil and the decomposition of the incorporated litter can improve soil structural stability. Those changes likely influence soil detachment process by overland flow. This study was undertaken to quantify the effects of incorporated plant litters into topsoil on the temporal variation in soil resistance to detachment by overland flow using natural soil samples collected from four different plots (one control and three litter incorporation treatments) and then scoured under six different flow shear stresses in a hydraulic flume. The experiment started from April 19 to October 5, 2015 for 10 times at approximately 20 days sampling intervals. Soil properties and environmental parameters were also measured at each sampling time to explain the temporal variations in rill erodibility and critical shear stress. The results showed that the incorporated plant litter was effective to enhance soil resistance to flowing water erosion. Compared to bare soil, rill erodibilities of litter incorporated soils of black locust, sea buckthorn, and green bristle grass decreased by 24.3%, 33.5%, and 34.8%. The temporal variations in rill erodibility of bare and litter incorporated soils were similar. Rill erodibility decreased significantly over time as an exponential function for both bare and litter incorporated soils. The relative rill erodibility of three litter incorporated soils increased over time as a power function. The fitted critical shear stress increased exponentially over time. The temporal variations in rill erodibility could be explained by the temporal variations in soil consolidation, water stable aggregate, and litter decomposition. Rill erodibility could be well estimated by soil bulk density, water stable aggregate, and litter mass density ( r 2 = 0.92). [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSCs) cover up to 60 to 70% of the soil surface in grasslands after the 'Grain for Green' project was implemented in 1999 to rehabilitate the Loess Plateau. However, few studies exist that quantify the effects of BSCs on the soil detachment process by overland flow in the Loess Plateau. This study investigated the potential effects of BSCs on the soil detachment capacity ( Dc), and soil resistance to flowing water erosion reflected by rill erodibility and critical shear stress. Two dominant BSC types that developed in the Loess Plateau (the later successional moss and the early successional cyanobacteria mixed with moss) were tested against natural soil samples collected from two abandoned farmland areas. The samples were subjected to flow scouring under six different shear stresses ranging from 7.15 to 24.08 Pa. The results showed that Dc decreased significantly with crust coverage under both moss and mixed crusts. The mean Dc of bare soil (0.823 kg m−2 s−1) was 2.9 to 48.4 times greater than those of moss covered soil (0.017-0.284 kg m−2 s−1), while it (3.142 kg m−2 s−1) was 4.9 to 149.6 times greater than those of mixed covered soil (0.021-0.641 kg m−2 s−1). The relative detachment rate of BSCs compared with bare soils decreased exponentially with increasing BSC coverage for both types of BSCs. The Dc value can be simulated by flow shear stress, cohesion, and BSC coverage using a power function (NSE ≥ 0.59). Rill erodibility also decreased with coverage of both crust types. Rill erodibility of bare soil was 3 to 74 times greater than those of moss covered soil and was 2 to 165 times greater than those of mixed covered soil. Rill erodibility could also be estimated by BSC coverage in the Loess Plateau (NSE ≥ 0.91). The effect of crust coverage on critical shear stress was not significant. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Many process-oriented erosion prediction models reproduce rill erosion as affected by site-specific parameters, as for example, rill erodibility, and thus, their practical application requires the measurement of these parameters or their estimate. The aim of this paper was establishing a method for indirectly measuring field rill erodibility. A simple mathematical approach based on a known soil detachment equation and accounting for the rill erosion dynamic process is applied. Field measurements carried out for seven natural rainfall events occurring at the plots of the Sparacia experimental station, southern Italy, are used for indirectly measuring the rill erodibility of the investigated soil. This method needs only the knowledge of the geometric characteristics of the rills at the end of the erosion event and the event duration. The method was also tested by using the Water Erosion Prediction Project database, and this analysis showed that a reliable value of rill erodibility can be obtained by the proposed Equation . The proposed method has the following advantages: (i) to be applicable at field scale, being more realistic than the laboratory scale because the soil structure is not destroyed, and (ii) to avoid the disadvantages of field experiments such as the cumbersome experimental set-up and the large volume of water inflow needed. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A erosão em sulcos caracteriza-se pelo escoamento superficial concentrado de uma lâmina d'água com tensão de cisalhamento suficiente para desagregar o solo, que deforma o sulco e altera as características hidráulicas do escoamento responsável pela dinâmica de formação dos sulcos. Os objetivos deste trabalho foram: avaliar as condições hidráulicas do escoamento em sulcos de erosão, que podem fornecer subsídios importantes às relações de erosão, e determinar as taxas de desagregação do solo, a erodibilidade do solo e a tensão crítica de cisalhamento, além de quantificar o transporte de sedimentos em sulcos por meio de expressões baseadas em variáveis hidráulicas. Para tanto, sulcos foram pré-formados em um solo de textura franco-argilo-arenosa, num campo com declive médio de 0,067 m m-1, e submetidos à aplicação de chuva simulada com intensidade de 74 mm h-1, durante 80 min, tendo sido aplicados nos sulcos, nos últimos 20 min, fluxos extras de escoamento superficial de 0, 10, 20, 30, 40 e 50 L min-1. Os resultados mostraram que o regime de escoamento nos sulcos caracterizou-se como sendo de transição subcrítico a turbulento subcrítico. As taxas de desagregação do solo obtidas foram lineares às tensões de cisalhamento desenvolvidas, para uma erodibilidade em sulcos (Kr) de 0,0024 kg N-1 s-1 e uma tensão crítica de cisalhamento (tauc) de 2,75 Pa. Duas funções baseadas na potência do escoamento foram ajustadas para estimar o transporte de sedimentos nos sulcos de erosão, as quais explicaram 53 % da variação experimental, refletindo não só a dificuldade de ajuste de modelos de estimativa do transporte sólido às lâminas de escoamento pouco espessas que ocorrem nas áreas de cultivo agrícola, mas também a diversidade física e mineralógica das partículas e dos agregados do solo estudado.Rill erosion is characterized by concentrated surface water flow, with enough shear stress and detachment capacity to deform the rill and alter flow hydraulics, responsible for rill formation dynamics. The objective of this study was to evaluate flow hydraulic conditions that can provide important information on erosion relationships, soil erodibility and sediment transport in furrows of a recently-tilled Palleudult. Rills were pre-formed in a sandy clay loam soil with an average slope of 0.067 m m-1. Simulated rainfall with an intensity of 74 mm h-1 was applied during 80 min, while rainfall and extra inflows of 0, 10, 20, 30, 40, and 50 L min-1 were jointly applied for the last 20 min of each run in the rill. Results indicated that the rill flow regime varied from transitional subcritical to turbulent subcritical. The rill erosion detachment rates were linear to shear stress. Rill erodibility (Kr) was 0.0024 kg-1 s-1 N and critical shear stress (tauc) was 2.75 Pa. Two functions to predict sediment transport based on stream power explained 53% of data variability, which indicates the inherent difficulty of predicting solid transport through shallow flows on eroding agricultural lands, and the physical and mineralogical diversity of particles and aggregates of the studied soil.

• The k d and τ c decreased with straw incorporation time prolonged. • The straw amount was the key factor influencing rill erosion resistance. • The k d and τ c could be linearly fitted by soil aggregate greater than 0.25 mm. The widely implemented wheat straw incorporation returning combined with nitrogen fertilizer and newly-developed secondary plant metabolites such as polyphenol, could result in variations of rill erosion resistance, and then soil detachment and channel scour. However, the variation pattern and its key influencing factorsremain unclear. Taking a silt loam soil as the research object, this study used the orthogonal table of L 9 (34) to arrange four influencing factors at three levels: straw length (2, 5, 8 cm), straw returning amount (2000, 4000, 8000 kg h m−2), nitrogen amount (100, 140, 180 kg hm−2), and polyphenol amount (0, 40, 80 kg hm−2). Rill erodibility (k d) and soil critical shear stress (τ c), representing the soil resistance to rill erosion, were measured twice by submerged jet equipment in August 2020 and 2021. The results presented significant temporal variations in k d and τ c with changes in straw decomposition and soil properties after straw incorporation. Compared with the results on day 60 following straw incorporation, k d and τ c decreased by 57.07% and 25.11% on day 425, respectively. On day 425, the straw length, straw returning amount, and nitrogen amount had significant effects on k d (P < 0.05), with the contributions of 7.97%, 42.06%, and 7.62%. Conversely, the straw returning amount and polyphenol amount had significant effects on τ c , with respective contributions of 50.88% and 11.24%. The variation of k d and τ c could be linearly fitted by the soil aggregate greater than 0.25 mm, with R2 values of 0.71 and 0.87, respectively, which could be used to estimate rill channel scour depth in the Soil and Water Assessment Tool in the absence of measured data on soil resistance to rill erosion. [ABSTRACT FROM AUTHOR]

In this paper, the contributions of rill and interrill components to total soil erosion monitored at event scale at the Sparacia experimental area, southern Italy, were first compared and the dominance of the rill component was detected. Then, the reliability of two empirical relationships between the rill length and its eroded volume and among the morphological variables (length, width, depth, and volume) describing the channelized process was tested using both direct measurements of rills, carried out for the October 3, 2011, event, and those of ephemeral gullies surveyed on February 2010 at Sparacia. The measurements of rills detected by the direct field relief were compared with those obtained using a survey that allowed the generation of a digital elevation model of the rilled area. Finally, plot rill erodibility values were estimated and their spatial and time variability were analyzed. Spatial variability of rill erodibility was negligible whereas a temporal variability was detected. [ABSTRACT FROM AUTHOR]

Land use can significantly affect soil properties, root systems, and tillage practices, and hence probably influence rill erodibility ( K r ) considerably. Nevertheless, there is little quantitative research on the effects of land use on K r . The objectives of this study were to evaluate the influence of land use on K r , quantify its potential influencing factors, and develop a regression model to estimate K r in a small Loess Plateau watershed. Undisturbed samples were collected from four different land uses on red Loess soil and seven different land uses on yellow Loess soil. Soil detachment capacity by overland flow was measured in a sand-glued hydraulic flume under six different shear stresses (5.59–18.31 Pa) to determine K r . The results indicated that K r was affected by soil type significantly and the average K r of yellow Loess soil was 1.5 times greater than that of red Loess soil. K r was also significantly influenced by land use. For the red Loess soil, cropped land had the maximum K r and followed by orchards, shrub land, and grassland. For the yellow Loess soil, cropped land also had the maximum K r , which was 1.74, 9.17, 11.65, 26.34, 28.88, and 42.57 times greater than those of roads, orchards, shrub land, woodland, grassland, and wasteland, respectively. K r increased with silt content, and decreased with soil cohesion, water stable aggregate, soil organic matter, and root mass density. A nonlinear regression showed that K r could be estimated well ( NSE = 0.87) by silt content, soil cohesion, water stable aggregate, and root mass density in the Loess Plateau. [ABSTRACT FROM AUTHOR]

• Soil moisture had different impacts on critical shear stress and rill erodibility. • Rill erodibility and critical shear stress were measured using hydraulic flume. • Rill erodibility and critical shear stress were not constant for all soil types. Antecedent soil moisture is known to exert a complex, perhaps controversial, effect on rill erodibility and critical shear stress. To understand their dynamic nature as a function of antecedent soil moisture, the rill erodibility and critical shear stress for sandy loam and silty loam soil, representing coarse-grained and fine-grained soil, respectively, were measured using a hydraulic flume under six antecedent soil moisture contents, i.e., 3, 6, 9, 12, 15, and 18%. The results show that antecedent soil moisture had a different effect on critical shear stress and rill erodibility for the two different soil textures. As antecedent soil moisture increased, rill erodibility for the fine-grained soil first increased and then decreased, whereas for coarse-grained soil, rill erodibility exhibited a decreasing pattern. Conversely, as the antecedent soil moisture increased, the critical shear stress decreased first and then increased for the fine-grained soil, but for coarse-grained soil, the critical shear stress decreased after a slight increase. These different patterns can be interpreted by aggregate slaking, capillary force, soil cementation, and water separation. However, when the patterns of critical shear stress and rill erodibility were neglected, the differences in critical shear stress and rill erodibility between the coarse- and fine-grained soils were not statistically significant (P < 0.05). Therefore, indiscriminate treatments of critical shear stress and rill erodibility for different textural soils under changing antecedent soil moisture regimes may cause errors in soil erosion modeling. The relationship between rill erodibility and critical shear stress for coarse- and fine-grained soils could be fitted by a power and a polynomial function, with R 2 value of 0.94 and 0.78, respectively. Future work should include additional soil textures to study the influence of soil physical characteristics in combination with antecedent soil moisture on soil erosion. [ABSTRACT FROM AUTHOR]

Soil rill credibility (Kr) is an important parameter for process-based soil erosion models since it reflects the soil's ability to resist concentrated flow detachment. Detailed information on the temporal variability of Kr remains scarce but critical to accurately predict rill erosion. This study was conducted to investigate the temporal variations in Kr of a silt loam loess soil using the undisturbed topsoil samples collected from four typical croplands (corn [Zea mays L.], millet [Setaria italic], soybean [Glycine max], and potato [Solanum tube-rosum L.]) and to further quantify the potential factors causing those changes in the Loess Plateau of China during one growing season from early April to late September of 2012.The results showed that the measured mean rill erodibility varied greatly with types of cropland. The potato land had the maximum mean Kr, and followed by corn, soybean, and millet. The Kr of the four croplands fluctuated considerably over time and tended to decline with root growth. Temporal variations in Kr were closely related to tillage operations, soil consolida-tion, water-stable aggregates, and root growth. The rill erodibility could be well predicted with root density, soil cohesion, and initial soil moisture content (NSE > 0.82). Further stud-ies are needed to detect the effects of root diameter of different plant types on rill erodibility. [ABSTRACT FROM AUTHOR]