Rainfall Simulation Experiments Research Articles

Runoff and sediment reduction effects of different Paspalum wettsteinii‐planting measures on the slopes of Masson pine plantation in the red soil region of southern China

AbstractGrass‐planting measure is a crucial vegetation approach to mitigate understory soil erosion and improve ecological environment in the red soil region of southern China. This study aimed to quantify the effects of grass (Paspalum wettsteinii Hackel.)‐planting measures on runoff and sediment reduction on slopes of Masson pine plantations under rainstorm conditions. We conducted a rainfall simulation experiment at a rainfall intensity of 2.0 mm/min, comparing single strip (MT1, strip spacing: 145 cm), double strips (MT2, strip spacing: 70 cm), and triple strips (MT3, strip spacing: 45 cm) grass‐planting measures on slope surface runoff generation and soil erosion processes of the young Masson pine (MT0, no grass strip) plantation, and the bare slope (CK) was selected as the control. Results revealed that grass‐planting measures significantly decreased slope erosion parameters compared to CK and MT0. As the average grass coverage increased (MT1 from 10% to 25%, MT2 from 7.5% to 22.5%, MT3 from 7.3% to 25%), the slope surface erosion parameters under the grass‐planting measures decreased, resulting in significantly improved runoff and sediment reduction benefits. The runoff reduction effect could reach 32%, while the sediment reduction effect could reach 88%. Moreover, MT3 demonstrated superior performance over MT2 and MT1, with minimal runoff and sediment reduction effects observed for the MT0. Overall, this study suggests that grass‐planting measures, coupled with the increasing of grass coverage rates, significantly improve runoff and sediment reduction benefits on slopes in regions experiencing heavy rainfall. Among the tested configurations, MT3 emerged as most effective measure for controlling understory soil erosion in Masson pine plantations, especially when its average grass coverage rate reached 25%. These findings provide valuable insights for selecting appropriate grass‐planting strategies, as well as for understanding the underlying mechanisms of how these measures mitigate soil erosion. This scientific reference will aid in the design and implementation of soil and water conservation measures in the region.

Combined effects of soil colloid and soil extracellular enzymes on nitrogen loss from sloping farmland

The extracellular enzyme plays a crucial role in nitrogen (N) conversion. Soil colloid serves as an important transporter of N transport in hydrological processes. This study investigated soil colloid-mediated N loss co-transporting with soil extracellular enzymes. Five simulated rainfall experiments were conducted under four tillage treatments in a purple sloping farmland in Sichuan, China. The N concentrations, soil mineral colloids, and four carbon (C), N and phosphorus (P) acquisition extracellular enzymes (βG, AP, NAG, and LAP) in surface runoff and interflow were measured. The results showed that cross-slope tillage with straw returning practices significantly reduced the concentrations of TN, PN, NH4+, and DON in surface runoff. The activities of N and P acquisition enzymes in interflow were higher than in surface runoff, while C acquisition enzymes showed the opposite trend. The BG and AP enzymes dominated in surface runoff, while AP and NAG dominated in interflow. The concentrations of fine soil mineral colloids (SMC, φ<1 μm) and coarse mineral colloids (CMC, φ＞1 μm) in interflow were higher than that in surface runoff. The extracellular enzymes were found to co-transport with soil colloid migration during the hydrologic process. The involvement of colloid in extracellular enzyme migration in surface runoff was primarily due to SMC, while in interflow, it was the joint action of SMC and CMC. Surface runoff is always in N and P limits, while interflow is only in the P limits. With a SEM combined model quantitatively analysis, we found the synergistic transport of soil colloid and extracellular enzymes significantly impacted TN loss, explaining 95 % and 55 % of the differences between surface runoff and interflow N loss pathways. This emphasizes the importance of understanding the co-transport mechanism between soil colloid and extracellular enzymes in N loss processes.

From Field to Model: Determining EROSION 3D Model Parameters for the Emerging Biomass Plant Silphium perfoliatum L. to Predict Effects on Water Erosion Processes

The agricultural production of maize (Zea mays L.) increases the risk of water erosion. Perennial crops like cup plant (Silphium perfoliatum L.) offer a sustainable alternative to produce biomass for biogas plants. The assessment of soil conservation measures requires calibrated soil erosion models that spatially identify soil erosion processes. These support decision-making by farmers and policymakers. Input parameters for the physically based soil erosion model EROSION 3D for cup plant cultivation were established in a field study. Rainfall simulation experiments were conducted to determine the model input parameter’s skinfactor and surface roughness. The results showed a reduction of soil erosion and higher infiltration rates for cup plant resulting in higher skinfactors of 11.5 in June and 0.75 post-harvest (cup plant) compared to 1.2 in June and 0.21 post-harvest (maize). With the extended parameter catalogue of EROSION 3D for cup plant cultivation model simulations were conducted for a rainfall event in June (64 mm). The sediment budget would have been reduced by 92.6% through the growth of cup plant in comparison to conventionally grown maize. Perennial cup plant can, therefore, contribute to achieving the targets outlined in the European Green Deal by reducing soil erosion and enhancing soil health.

Study on Soil Stabilization and Slope Protection Effects of Different Plants on Fully Weathered Granite Backfill Slopes

The slope erosion in the distribution area of completely weathered granite is often relatively severe, causing serious ecological damage and property loss. Ecological restoration is the most effective means of soil erosion control. Taking completely weathered granite backfill soil as the research object, two types of slope protection plants, Vetiver grass and Pennisetum hydridum, were selected. We analyzed these two herbaceous plants’ soil reinforcement and slope protection effects through artificial planting experiments, indoor simulated rainfall experiments, and direct shear tests. The test results showed that the runoff and sediment production rates of the two herbaceous plant slopes were significantly lower than those of the bare slope, with the order of bare slope &gt; Vetiver grass slope &gt; Pennisetum hydridum slope. Compared with the bare slope, the cumulative sediment production of the Vetiver grass slope at 60 min decreased by 56.73–60.09%, and the Pennisetum hydridum slope decreased by 75.97–78.45%. The indoor direct shear test results showed that soil cohesion decreases with increasing water content. As the root content of Vetiver grass roots increases, soil cohesion first increases and then decreases, reaching a maximum value when the root content is 1.44%. As the root content of Pennisetum hydridum increases, soil cohesion increases. The internal friction angle increases slightly with increasing water content, while the root content does not significantly affect the internal friction angle. Therefore, the shear strength of soil decreases when the water content increases. The shear strength of the Vetiver grass root-soil composite reaches a peak at a root content of 1.44%, while the shear strength of the giant king grass root-soil composite increases as the root content increases. At the same root content, the shear strength of the Vetiver grass root-soil composite is slightly higher than that of giant king grass. The reinforcement effect of roots on shallow soil is better than on deep soil. Both herbaceous plants have an excellent soil-fixing and slope-protecting impact on the fully weathered granite backfill slope. Pennisetum hydridum’s soil and water conservation effect is significantly better than that of the Vetiver grass. In contrast, Vetiver grass roots slightly outperform Pennisetum hydridum in enhancing the shear strength of the soil. The research results can provide a theoretical basis for the vegetation slope protection treatment of fully weathered granite backfill slopes.

The effect of mosses on the relocation of SOC and total N due to soil erosion and percolation in a disturbed temperate forest

Forests cover one-third of the global land and are important components of carbon and nitrogen cycling. Anthropogenic disturbances, such as forest road systems or skid trails for timber harvesting, can dramatically change the nutrient cycling in these ecosystems. Skid trails increase soil erosion and thus the displacement of soil organic carbon (SOC) and total nitrogen (Nt). Additionally, runoff transports high amounts of dissolved organic carbon (DOC), which can have a negative impact on aquatic ecosystems. One of the most important countermeasures against soil erosion is the quick recolonization of vegetation. To date, the extent to which natural vegetation succession influences the relocation of SOC and Nt, and in particular the role of mosses in this context, has not been well investigated. This study investigates the influence of natural vegetation succession and in particular of mosses on the displacement process of SOC and Nt as well as DOC caused by soil erosion. To this end, we combine the results of a field study using in-situ rainfall simulations with small-scale runoff plots in skid trails of the Schönbuch Nature Park in southwestern Germany with the results of ex-situ rainfall simulation experiments with infiltration boxes containing the substrate from the respective skid trails. The eroded sediments of skid trails were on average enriched in SOC by 16% and in Nt by 35% compared to the original soil, which lead to a decrease of the C/N ratio in sediments. As vegetation succession progressed, the displacement of SOC and Nt was reduced, confirmed by a negative correlation between the enrichment ratios of SOC (ERSOC), Nt and total vegetation cover. However, mosses tended to reduce ERSOC more than vascular plants. Additionally, mosses significantly decreased DOC concentration in surface runoff compared to bare soils, while no difference in DOC concentration in percolated water could be observed. Future research should explore the role of mosses in the storage of SOC and Nt in the soil and their impact on soil stability. Thus, utilizing mosses could potentially minimize environmental impacts from soil disturbances in forests.

Effects of check dam construction on sediment production and topographic changes in a gully in the Loess Plateau: A rainfall simulation experiment

AbstractTo maintain a reasonable sediment regulation system in the Loess Plateau, it is critical to determine the effects of check dam construction on sediment production and topographic changes. An indoor simulation experiment was conducted to investigate sediment production at the outlet section of the gully and micro‐topographic changes within the channel before and after dam construction. The results showed that check dam significantly affected the run‐off and sediment transport processes in the watershed. Specifically, the cross‐sectional morphology index (η) and the width‐depth ratio increased by 10.23% and 40.44%, respectively, while sediment content and particle size decreased by 39.29% and 18.58%, respectively. Additionally, the relative importance of section parameters and micro‐topographic parameters that affect sediment production rate and particle size was ranked using the random forest algorithm. The roughness after check dam construction was identified as a relatively important topographic factor affecting sediment production and particle selection by erosion. These findings provide valuable information for future check dam construction and development in the Loess Plateau region.

Hedgerows enhance the size selectivity of eroded sediment from sloping farmland under simulated rainfall experiment

AbstractThe particle size distribution (PSD) of eroded sediment can effectively reflect changes in erosion processes. Hedgerows provide significant soil and water conservation benefits and influence erosion processes. However, the impact of hedgerows on the PSD of eroded sediment remains unclear. Therefore, three slope conditions (control check, CK; only hedgerow root, R; and whole hedgerow, P) involving the configuration of two slope gradients (15 and 25°) were established, and simulated rainfall experiments were conducted under three rainfall intensities (60, 90, and 120 mm/h). The PSD, sediment sorting process, and sediment particle agglomeration degree under the different slope conditions were compared to evaluate the influence of hedgerows on the size selectivity of eroded sediment during water erosion. Moreover, the direct and indirect effects of hedgerows on the sorting process and sediment particle agglomeration degree were revealed via correlation analysis and partial least squares path modelling (PLS–PM). Compared with those under CK slope conditions, the average clay, fine silt, and coarse silt contents under R slope conditions decreased by 1.37%, 0.06%, and 1.71%, respectively, whereas the sand content increased by 0.46%. Under P slope conditions, the average clay, fine silt, and coarse silt contents increased by 32.61%, 38.71%, and 36.14%, respectively, whereas the average sand content decreased by 47.30%. Under CK slope conditions, sediment sorting occurred primarily during the early stages of rainfall. R slope conditions caused an increase in the duration of early‐stage sediment sorting but caused a reduction in the degree of sorting, whereas P slope conditions exhibited interceptive sorting of sand throughout the rainfall event. Under R slope conditions, more aggregates were dispersed into individual particles due to raindrop impact, whereas under P slope conditions, more fine particles aggregated initially, but loose aggregates were dispersed into individual particles during the later rainfall stages. The enrichment rates of fine silt and coarse silt were positively correlated with slope conditions, whereas they were negatively correlated with the enrichment rate of sand. However, there was no significant relationship between the slope conditions and the aggregation rates of particles of various sizes. PLS–PM indicated that hedgerows directly and indirectly affect sorting processes and sediment particle agglomeration degree by regulating runoff and sediment erosion, and the direct effects exceed the indirect effects. These findings provide a comprehensive understanding of the influential mechanisms of hedgerows on controlling soil erosion.

Empirical and physical modelling of soil erosion in agricultural hillslopes

Abstract Soil erosion is a complex and highly heterogeneous process with a wide range of environmental and economic impacts. Its estimation is particularly challenging and modelling is typically used for erosion estimation over large areas. The aim of this study was to compare the two leading empirical and physical erosion estimation models, i.e. the Revised Universal Soil Loss Equation (RUSLE) and the Water Erosion Prediction Project (WEPP). The models were calibrated and validated using data collected from field experiments conducted in agricultural lands of Mexico. The simulated rainfall experiments involved measuring erosion from field plots subjected to four tillage systems (No crop, Conventional tillage, Conventional tillage + residues, and Handspike) under two antecedent soil moisture conditions (dry and wet). Different calibration approaches based on the factors K and C for RUSLE, and interrill erodibility and hydraulic conductivity in WEPP were tested. The best-performing methods in RUSLE involved measuring the K factor and adopting the recommended C factor by the National Forestry Commission of Mexico. In WEPP, the best results were obtained when interrill erodibility was estimated from experimental measurements. Overall, RUSLE outperformed WEPP in most of the treatments except for CT under WAMC.

Comparative Study of the Impacts of Maize and Soybean on Soil and Water Conservation Benefits during Different Growth Stages in the Loess Plateau Region

Maize (Zea mays L.) and soybean (Glycine max L. Merr.) are prevalent summer crops planted widely in the Loess Plateau region of China, which is particularly susceptible to severe soil erosion on the sloping farmland. However, which crop exhibits superior soil and water conservation capabilities while maintaining economic viability, and how their performance in soil and water conservation is affected by slope gradient and rainfall intensity remains unclear. The objective of this study was to compare the impacts of maize and soybean on regulating runoff and sediment through rainfall simulation experiments, and explore the main control factors of soil and water conservation benefits. Five slope gradients (8.7, 17.6, 26.8, 36.4, and 46.6%) and two rainfall intensities (40 and 80 mm h−1) were applied at five respective crop growth stages. Both maize and soybean effectively reduced soil and water losses compared with bare ground, although increasing slope gradient and rainfall intensity weakened the vegetation effect. Compared with slope gradient and rainfall intensity, vegetation coverage was the main factor affecting the performance of maize and soybean in conserving soil and water. The average time delay benefit (TDB), runoff reduction benefit (RRB), and sediment reduction benefit (SRB) of soybean (246.48 ± 11.71, 36.34 ± 2.51, and 54.41 ± 3.42%) were significantly higher (p &lt; 0.05) than those of maize (100.06 ± 6.81, 25.71 ± 1.76, and 43.70 ± 2.91%, respectively) throughout growth. After planting, the increasing rates of vegetation coverage, TDB, RRB, and SRB with time were consistently higher with soybean than maize. Moreover, under the same vegetation coverage, the TDB, RRB, and SRB of soybean were also consistently higher than those of maize. In conclusion, these findings indicate that soybean outperformed maize in terms of soil and water conservation benefits under the experimental conditions, making it more suitable for cultivation on sloping farmland. This finding offers crucial guidance for the cultivation of dry farming in regions plagued by severe soil erosion, facilitating a balance between economic objectives and ecological imperatives.

Exploring rational vegetation configuration to relative increase runoff, reduce erosion and soil organic carbon loss in gully-slopes on the Chinese Loess Plateau

In order to solve the water shortage, uncoordinated runoff-sediment relationship, and prevent carbon loss in the Yellow River Basin, there is an urgent need to explore the rational vegetation configuration in order to relative increase runoff, reduce sediment and prevent soil organic carbon loss in the gully-slopes on the Loess Plateau. To solve these problems, the simulated rainfall experiments with an intensity of 60 mm·h−1 were conducted in four types of plots: shrub-grass (SG), tap root grasses (GT), fibrous root grasses (GF) and bare land (CK). Four types of plots were built on one gully-slope with a slope of 35°–40° in situ. Compared with CK (mean runoff rate: 0.61 mm·min−1), the runoff reduction benefits of SG (0.27 mm·min−1), GT (0.04 mm·min−1) and GF (0.17 mm·min−1) plots were 54.9 %, 71.7 %, 92.2 %. Compared with GT and GF plots, the total runoff of SG plots was 1.6–5.8 times. Compared with CK, the sediment reduction benefits of three vegetation plots were more than 98 %. Shrub-grass is a more suitable vegetation combination for soil and water conservation: reducing sediment and relative increasing runoff. The soil organic carbon loss has been well alleviated through vegetation restoration, and vegetation plots all prevented over 98 % of soil organic carbon loss compared with the bare plot. Soil organic carbon loss equation based on runoff and sediment was established and validated. The R2, P and NSE results of the equations were 0.92–0.95, <0.001, 0.85–0.86, respectively, indicating that the fitted equations can be considered acceptable. The soil organic carbon loss in the gully-slopes was mainly from sediment (more than 85 %) compared with runoff. Therefore, controlling sediment is more effective than controlling runoff in preventing soil organic carbon loss in the gully-slopes on the Loess Plateau. These results can provide a basis for decision-making of high-quality development of contemporary soil and water conservation on the Loess Plateau.

Reduction and immobilization of Cr(VI)-contaminated soil using FeSO4 combined with (NH4)2HPO4: The remediation efficiency, mechanisms, and long-term stability

The chemical reduction technique is widely used to remediate Cr(VI)-contaminated soil due to its cost-effective and convenient operation. However, it also suffers from the "yellowing" issue and re-migration of Cr(VI) after on-site remediation. This study hence investigated a new combined treatment material, (NH4)2HPO4 and FeSO4, to enhance the immobilization of Cr(VI) in soil, ultimately inhibiting the "yellowing" phenomenon. The Cr(VI) remediation efficiency, mechanisms, and the long-term stability using FeSO4 with (NH4)2HPO4 were investigated. The Cr(VI) immobilization mechanisms were elucidated using the European Community Bureau of Reference (BCR) sequential extraction procedure, X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The results suggested that, following the reduction of Cr(VI) to Cr(III) by FeSO4, the presence of (NH4)2HPO4 promoted the formation of residual Cr (CrPO4). At the optimal dose of FeSO4:(NH4)2HPO4:Cr(VI), 5:10:1, 88 % of the 450 mg/kg Cr(VI) in soil was reduced, all the HOAC-extractable Cr (58.67 %) disappeared, while the residual Cr was increased from 6.74 % to 50.61 %. The H2O2 oxidation and simulated rainfall experiments suggested that the extra addition of (NH4)2HPO4 significantly inhibited Cr reoxidation and leachability, possibly due to the formation of residue CrPO4 and FexCr1-x(OH)3, especially when the rainfall`s SO42-:NO3- ratio was 8:1. It is believed that the combination of FeSO4 and common synthetic fertilizer (NH4)2HPO4 is a promising method for in-situ remediation of Cr(VI)-contaminated soil due to its strong resistance to oxidation and acid rain erosion.

Predicting the coupling effects of grass and shrub with biological crust on splash and sheet erosion

Vegetation plays an important role in preventing soil erosion in arid and semi-arid regions. However, the current research on soil erosion under vegetation conditions neglected the role of biological crusts (BSC). The impact of different combinations of grass and shrub vegetation with BSC on the soil erosion process were investigated in this study through indoor simulated rainfall experiments and field experiments. Additionally, the calculation formula for the splash and sheet erodibility coefficients (KSS) in the Rangeland Hydrology and Erosion Model (RHEM) model was revised and validated. The results showed that the ability of BSC to reduce erosion was gradually enhanced with an increase in BSC coverage. The significant erosion reduction effect of BSC under different vegetation coverages was found. As the BSC coverage increased to 40 %, the soil erosion process changed from transport-limited to detach-limited. When grass and shrub was combined with BSC, the average flow velocity was smaller than that of the individual vegetation treatments. Moreover, the proportion of BSC resistance was the highest among the various vegetation combinations consistently. When the coverage of the combined BSC exceeded that of the vegetation, the BSC dominated the soil erosion process through its direct physical protection and indirect alteration of soil properties. When the BSC coverage was incorporated into KSS, the determination coefficients of the revised KSS were all above 0.8. This study deepened the understanding of the coupling effects of grass and shrub with BSC on slope erosion processes, and improved the predictive accuracy of the RHEM model.

Effects of woodland slope on heavy metal migration via surface runoff, interflow, and sediments in sewage sludge application

Sewage sludge (SS) application to forest plantation soils as a fertilizer and/or soil amendment is increasingly adopted in plantation forest management. However, the potential risks of SS-derived heavy metals (HMs) remain a concern. Many factors, including woodland slope may affect the risks, but the understanding of this issue is limited. This research evaluated the HMs migration via surface runoff, interflow, and sediments when SS was applied in woodlands of varying slopes. We conducted indoor rainfall simulations and natural rainfall experiments to clarify the effect of slope on the migration of HMs via runoff (including surface and interflow) and sediments. In the simulated rainfall experiment, HMs lost via sediments increased by 9.79–27.28% when the slope increased from 5° to 25°. However, in the natural rainfall experiment, when the slope of forested land increased from 7° to 23°, HMs lost via surface runoff increased by 2.38% to 6.13%. These results indciate that the surface runoff water on a high slope (25°) posed high water quality pollution risks. The migration of HMs via surface runoff water or interflow increased as the steepness of the slope increased. The total migration of Cu, Zn, Pb, Ni, Cr and Cd via sediment greatly exceeded that via surface runoff and interflow. Particles ≤ 0.05 mm contributed the most to the ecological risks posed by sediments. Cd was the main source of potential ecological risks in sediments under both experimental conditions.

Characteristics, Sources, and Mechanisms of Soil Respiration under Simulated Rainfall in a Native Karst Forest in Southwestern China

Rainfall significantly affects soil respiration rates by altering microbial activity and organic matter decomposition. In karst regions, it also impacts carbonate dissolution and precipitation, further influencing soil CO2 flux. Investigating the mechanism of rainfall’s impact on soil respiration is essential for accurately evaluating and predicting changes in terrestrial ecosystems. However, our understanding of the interaction between rainfall and soil respiration in the extensive karst ecosystems of southwestern China remains limited. This study conducted field-based simulated rainfall experiments to examine variations in soil respiration rates and elucidate the associated control mechanisms through stable carbon isotope composition analysis. Simulated rainfall significantly increased the CO2 release via soil respiration. We observed significant differences in the δ13C value of soil-respired CO2 before and after simulated rainfall. Following the rain, the δ13C of soil-respired CO2 was enriched compared to that before the rain. Through isotope data analysis, we found that the increased soil CO2 emissions were primarily driven by heterotrophic respiration, likely stimulated via changes in soil moisture, affecting microbial growth conditions. Furthermore, the variation in soil moisture affected carbonate dissolution and precipitation, potentially increasing the soil CO2 release after rainfall. In conclusion, these findings expand our understanding of rainfall’s effects on soil respiration in the native karst forests of southwestern China, contributing to the prediction of carbon cycling processes in such ecosystems. The data from this study have significant implications for addressing the release of greenhouse gases in efforts to combat climate change.

A study on soil aggregate stability and splash erosion under exogenous electrolyte conditions in the karst region of Southwest China

Study areaKarst region in Guangxi Province, Southwest China. Study focusBoth soil properties and rainfall characteristics have a critical influence on splash erosion and aggregate stability. However, the impact of electrolytes on splash erosion has received less attention. In this study, soils from 4 typical land use types (cropland, orchard, artificial forest and secondary forest) in karst region were utilized as the research objects. NaCl, KCl, and MgCl2 solutions of different concentrations were used to determine the stability of the aggregates via fast wetting (FW) treatment of Le Bissonnais (LB) method and the characteristics of splash erosion via simulated rainfall experiments. New hydrological insights for the regionResults revealed that both the land use types and electrolyte significantly influenced the soil aggregate stability and splash characteristics. Specifically, the change in land use from cropland to orchard, artificial forest and secondary forest significantly increased the aggregate stability, thus decreasing soil erodibility. The aggregate stability decreased and the total splash rate increased as the electrolyte concentration increased. The total splash erosion rate of the 4 soils was positively correlated with the <0.5 mm particle size released by aggregate fragmentation under simulated rainfall conditions. The results can provide a theoretical basis for soil erosion control and soil quality improvement in the karst region of Southwest China.

Research on Multi-Factor Effects of Nitrogen Loss in Slope Runoff

To study the characteristics of nitrogen (N) loss on slopes, different vegetation (bare soil, alfalfa), slopes (5°, 10°, 15°), and rainfall intensities (40, 60, 80 mm/h) were set as variable factors in simulated rainfall experiments. Surface runoff accounts for 60.38–96.16% of total runoff and most N loss (57.69–88.67% of NO3−-N). Alfalfa can reduce average concentrations of N loss in runoff and reduce N loss in surface runoff by more than 48.29%, as well as subsurface runoff by 3.8%. Average N loss in subsurface runoff exceeds that of surface runoff. Rainfall intensity most affects N loss from surface runoff in bare soil conditions, and slope most affects N loss in subsurface runoff. Rainfall intensity in alfalfa treatments most influences runoff volume and N loss. The comprehensive effects of rainfall intensity, slope, and vegetation cover on the total loss of various forms of nitrogen in surface runoff can be described using a linear correlation equation, with a correlation coefficient between 0.84 and 0.91.

Sugarcane leaf return and mixing significantly reduce slope runoff and soil loss

AbstractImproper management of sugarcane cultivation may cause severe soil erosion, especially in lateritic red soil hilly areas. Crop straw return to the field can effectively improve the soil structure, but there is a lack of evaluation studies of the soil and water conservation benefits of sugarcane leaf mixing and return to the field, and the underlying regulatory mechanism has rarely been described. Thus, we conducted a series of simulated rainfall experiments to investigate the impact of returning different mixed sugarcane leaf weights (0, 3, 6, 9, 12 and 15 t/ha) to the field on erodible lateritic red soil slopes that support sugarcane production under various slopes (5°, 10°, 15° and 20°) in different rainfall events (60 and 120 mm/h). The results indicated that returning sugarcane leaves into farmland could effectively regulate the process of runoff and sediment production on lateritic red soil slopes, and the optimal mixing amount was 9 t/ha. Under a low rainfall intensity, the erosion process was mainly affected by the slope, and the benefits of applying the sugarcane leaf mixing treatment to the slope to reduce runoff and sediment could reach 13.37–53.04% and 23.86–77.55%, respectively. However, under a high rainfall intensity, the sugarcane leaf mixing amount was the main influencing factor, the benefits for reducing runoff and sediment could reach 4.64–38.72% and 30.87–93.14%, respectively. The sugarcane leaf mixing amount exhibited a linear relationship with the Reynolds number (R2 &gt; 0.63), whereas the runoff velocity (R2 &gt; 0.96), Froude number (R2 &gt; 0.94) and drag coefficient (R2 &gt; 0.85) exhibited well‐fitting exponential function relationship with it. This study provides a reference for future endeavours regarding the inhibition mechanisms of sugarcane leaves mixed and returned to the field for decreasing slope erosion.

Conducting an in situ evaluation of erodibility in a Mediterranean semi-arid and conventional vineyard in Granada province (Southern Spain) through rainfall simulation experiments

AbstractVineyards in Europe has been fundamental for food, drink and cosmetic production, and job creation; however, in recent decades due to increased cultivation intensity, numerous negative consequences, including erosion, have been observed. Erodibility or susceptibility to erosion is a little-studied parameter in vineyards but is crucial for analyzing the vulnerability of this crop. Therefore, in this research, a small portable rainfall simulator was used as a useful tool for assessing erodibility, combined with other methods such as soil analyses or infiltration measurements in a semi-arid vineyard located in the Granada province (Spain) considering 20 different hotspots at diverse hillslope positions along the inter-rows and close to the traffic roads. The experiments were conducted in spring 2022 under dry soil conditions. Our results display susceptibility to erosion, particularly on steeper parts such as the shoulder and backslopes. In these areas, runoff gained momentum, carrying a significant sediment load, diminishing the effectiveness of stone cover, and occasionally leading to its removal, especially near the roads. Nevertheless, it is observed that increased roughness plays a mitigating role by slowing down runoff. Using linear correlation analysis and Spearman rank coefficient, we observed this effect is linked to factors such as stoniness, vegetation, and moderate tillage. Conversely, in the flatter zones, primarily in lower areas, reduced runoff and delayed onset are primarily influenced by factors such as roughness, type of cover, material composition, and organic matter content. We concluded that this study case can demonstrate that erodibility in vineyards can shed light as an extra parameter to inform farmers, rural inhabitants, and policymakers about the extreme problem of the vulnerable soils of vineyards.

Optimizing Straw Mulching Methods to Control Soil and Water Losses on Loess Sloped Farmland

Straw mulching is a key method for controlling soil and water losses. Mulching costs may be reduced by applying it in strips rather than over entire areas. However, the effect of different straw mulching methods on the effectiveness of reducing soil erosion is unclear. In this study, the effects of straw mulching strip length (covering 1/4, 1/2, 3/4, and 4/4 of the slope length) and coverage rate (0.2, 0.5, and 0.8 kg m−2) on interception, infiltration, runoff, and soil erosion were investigated at the plot scale using rainfall simulation experiments. The further complex correlations between these variables were analyzed using structural equation modeling (SEM). Bare slopes were used as a control group. The rainfall intensity was chosen to be 60 mm h−1. The results showed that (1) the modified Merriam interception model can describe the change in interception with time under straw mulching conditions well (R2 &gt; 0.91, NSE &gt; 0.75). (2) A total of 35.39–78.79% of the rainwater is converted into infiltration on straw-covered slopes, while this proportion is 36.75% on bare slopes. The proportion of rainwater converted to infiltration was greatest (78.79%) when the straw covered 3/4 of the slope length at a coverage rate of 0.5 kg m−2, which was the most conducive to rainwater harvesting on the slope. (3) Straw mulching protects the topsoil from the impact of raindrops and directly affects the sediment yield (direct effect = −0.44). Straw mulching can also indirectly affect sediment yield by increasing interception, reducing runoff, and decreasing the sediment carrying capacity of runoff (indirect effect = −0.83). Compared with bare slopes, straw covering at least 1/2 of the slope length can significantly reduce runoff yield, but straw covering only 1/4 of the slope length can significantly reduce sediment yield. Moreover, once the straw mulch slope length reaches 3/4 and the coverage rate reaches 0.5 kg m−2, further increases in mulch slope length and coverage rate will not significantly reduce the runoff and sediment yields. These results assessed the effectiveness of different straw mulching methods in controlling soil and water losses on sloping farmland.

Does century-old biochar affect soil interrill erodibility on cropland soils? A study on pre-industrial kiln sites

Adding biochar to soils is being advocated to mitigate soil erosion. However, given biochar aging and persistency in soils, the effects of biochar on soil in the long-term are important to investigate yet remain largely unknown. The objective was therefore to determine the long-term effect of biochar on interrill erosion on cropland soils. Experiments were conducted using topsoil from three fields of different textures (silt loam, loam and sandy loam). Each field was characterized by the presence of kiln sites containing century-old charcoal used as proxy to investigate the long-term impact of biochar. Aggregate stability was measured using the method of Le Bissonnais (1996), whereas interrill erosion was studied using two successive (24-h apart) rainfall simulation experiments (84 mm h−1, 90 min.). The presence of historical charcoal in kiln sites did not affect soil aggregate stability, irrespective of charcoal-C content or soil type. For the first rainfall simulation only, the century-old charcoal reduced both the final runoff and soil loss rates by, respectively, 15.4 mm h−1 and 12.1 g m−2 h−1 for each percent increase in charcoal-C content. As a result, Meyer’s interrill erodibility decreased with increasing charcoal-C content. However, because the final runoff and soil loss rates decreased to a similar extent with increasing charcoal-C content, Kinnell’s interrill erodibility was unaffected by charcoal-C content. These effects on interrill erosion parameters were independent of soil type and could not be related to changes in soil chemical properties. The measured reduction in runoff and soil loss were attributed to delayed crust development, which could be related to increasing proportions of clods in the soil samples with increasing charcoal-C content. Further research may be needed to confirm the observed trends and underlying mechanisms over a wider range of soil types.