Controlling Soil Loss Research Articles

Study on Soil Properties of an Erosion Gully in Yanghe Basin in China

Controlling erosion gully caused by soil and water erosion is an important content of ecological restoration. In order to better allocate soil and water loss control measures, the total nitrogen content and water content in the surface soil of gully were analyzed by taking typical erosion gully in Yanghe basin as the research area. The results show that the erosion gully surface soil total nitrogen content was 0.215-1.459 g/kg, saturated moisture content ranged in 35-44%, and the permeability was between 0.0975-0.2925 mm/min. Combined with actual investigation and the experimental results, we conclude that the total nitrogen content and water content of the surface soil in the erosion gully are greatly affected by climate and vegetation conditions.

WATER EROSION IN EUCALYPTUS FOREST IN THE MUNICIPALITY OF OTACÍLIO COSTA (SC)

ABSTRACT Water erosion is the main factor of degradation and reduction of the productive capacity of the soil, requiring management operations that minimize water and soil losses and at the same time maximize crop productivity. The research aimed to quantify losses by water erosion and, in the runoff water, determine the levels and total losses of P and K during the development of Eucalyptus (Eucalyptus benthamii). Eucalyptus was planted in three types of soil preparation: minimum preparation in the direction of the slope, minimum preparation in the contour of the slope, and semi-mechanized preparation, in an experiment in southern Brazil on a Haplic Dystrudept soil. We observed that the mechanical preparation of the soil carried out in the direction of the slope is less effective in controlling soil losses than the mechanical carried out perpendicularly to the slope and also less effective than the manual in pits, in which the soil losses are equivalent to 10% of those that occur in the direction of the slope. As for the control of water losses, manual preparation in pits is more effective than the two mechanized preparations. The greatest losses of soil occur in the fall, with losses 27 times greater in relation to the other seasons of the year, and the greatest losses of water occurred in the mechanized preparation perpendicular to the slope and in the manual preparation. Water losses vary less than soil losses, regardless of the type of soil preparation and the season. The losses of phosphorus and potassium by the Runoff water vary with the contents in the soil, with the type of soil preparation and with the moment of evaluation.

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

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

Drought-Induced Reductions and Limited Recovery in the Radial Growth, Transpiration, and Canopy Stomatal Conductance of Mongolian Scots Pine (Pinus sylvestris var. mongolica Litv): A Five-Year Observation

Determining plant–water relationships in response to drought events can provide important information about the adaptation of trees to climate change. The Mongolian Scots pine (Pinus sylvestris var. mongolica Litv), as one of the major tree species to control soil loss and desertification in northern China, has experienced severe degradation in recent decades. Here, we aimed to examine the impacts of a two-year consecutive drought and another year of drought on the radial growth, transpiration, and canopy stomatal conductance of Mongolian Scots pine over a five-year period, especially in terms of its recovery after drought. The study period during 2013–2017 consisted of a ‘normal’ year, a ‘dry year’, a ‘very dry’ year, a ‘wet’ year, and a ‘dry’ year, according to annual precipitation and soil moisture conditions. Based on measurements of the sap flow and diameters at breast height of 11 sample trees as well as the concurrent environmental factors, we quantified the reductions in tree radial growth, transpiration, and canopy stomatal conductance during the drought development as well as their recovery after the drought. The results showed that the tree radial growth, transpiration, and canopy stomatal conductance of Mongolian Scots pines decreased by 33.8%, 51.9%, and 51.5%, respectively, due to the two consecutive years of drought. Moreover, these reductions did not fully recover after the two-year drought was relieved. The minimum difference of these parameters between before and after the two-year consecutive drought period was 8.5% in tree radial growth, 45.1% in transpiration levels, and 42.4% in canopy stomatal conductance. We concluded that the two consecutive years of drought resulted in not only large reductions in tree radial growth and water use, but also their lagged and limited recoveries after drought. The study also highlighted the limited resilience of Mongolian Scots pine trees to prolonged drought in semi-arid sandy environmental conditions.

Nano-biochar reduced soil erosion and nitrate loss in sloping fields on the Loess Plateau of China

The effects of biochar on soil erosion and nutrient loss on the Chinese Loess Plateau have been well reported, but the huge required application rate of biochar limits the biochar use. The specific nano-treatment can improve the distribution and properties of biochar (e.g., increase the specific surface area). To investigate the migration processes of runoff, sediment and nutrients on the nano-biochar (NB) applied sloping land during rainfall events, different mass content of NB (0.0%, 0.1%, 0.5%, 0.7%, and 1.0%) were used on the three types of vegetation covered sloping land (bare, caragana, and maize). The effects of NB and vegetation on runoff volume, sediment yield, and nitrate loss were studied under simulated rainfall in the northeastern region of the Loess Plateau. The main results were as follows: the application of NB effectively reduced runoff (39.7–74.4%), sediment yield (8.9–41.8%), and nitrate loss (13.6–59.8%) in all treatments. Losses of nitrate in runoff and sediment were negatively correlated with increased content of NB (when NB application rate was 1.0%, the maximum nitrate loss in runoff and sediment were 27.43 and 6.25 mg, respectively). The equivalent model of convection was more suitable for analyzing the nutrient transfer process with the application of NB. The effective mixing depth decreased with NB content and could be well described by a power function. NB might promote the nitrate migrate to deep soil and reduce nitrate loss in runoff and sediment. With NB application, the peak value of nitrate distribution in the profile moved downward, and the maximum value was obtained at 10–15 cm. Moreover, the most effective NB content for reducing nitrate loss were 1.0%. Comparing with bare and maize, caragana had the most significant effect on reducing runoff, sediment and nutrient loss. In addition, Synergistic effect of NB and caragana showed the great potential on soil and water loss control. The findings in this study provide an efficient and economic method for controlling soil erosion and nutrient loss on the Chinese Loess Plateau.

Exploring the interaction of surface roughness and slope gradient in controlling rates of soil loss from sloping farmland on the Loess Plateau of China

AbstractSurface roughness and slope gradient are two important factors influencing soil erosion. The objective of this study was to investigate the interaction of surface roughness and slope gradient in controlling soil loss from sloping farmland due to water erosion on the Loess Plateau, China. Following the surface features of sloping farmland in the plateau region, we manually prepared rough surfaces using four tillage practices (contour drilling, artificial digging, manual hoeing, and contour plowing), with a smooth surface as the control measure. Five slope gradients (3°, 5°, 10°, 15°, and 20°) and two rainfall intensities (60 and 90 mm/hr) were considered in the artificial rainfall simulation experiment. The results showed that the runoff volume and sediment yield increased with increasing slope gradient under the same tillage treatment. At gentle slope gradients (e.g., 3° and 5°), the increase in surface roughness prevented the runoff and sediment production, that is, the surface roughness reduced the positive effect of slope gradient on the runoff volume and sediment yield to a certain extent. At steep slope gradients, however, the enhancing effect of slope gradient on soil erosion gradually increased and surpassed the reduction effect of surface roughness. This study reveals the existence of a critical slope gradient that influences the interaction of surface roughness and slope gradient in controlling soil erosion on sloping farmland. If the slope gradient is equal to or less than the critical value, an increase in surface roughness would decrease soil erosion. Otherwise, the increase in surface roughness would be ineffective for preventing soil erosion. The critical slope gradient would be smaller under higher rainfall intensity. These findings are helpful for us to understand the process of soil erosion and relevant for supporting soil and water conservation in the Loess Plateau region of China.

Surface microrelief changes affect the soil and water conservation benefits of rainwater harvesting tillage operation during rainfall events

AbstractReservoir tillage (RT) improves the soil rainwater harvesting capacity and reduces soil erosion on cropland, but there is some debate regarding its effectiveness. The objective of this study was to further verify the effect of RT on soil erosion and explore the reasons for this effect by analysing microrelief changes during rainfall. Rainfall intensities of 60, 90, and 120 mm/hr and three slope degrees (5, 15, and 25°, representing gentle, medium, and steep slopes) were considered. A smooth surface (SS) served as the control. The microrelief changes were determined based on digital elevation models, which were measured using a laser scanner with a 2‐cm grid before and after rainfall events. The results showed that compared with the values for the SS, RT reduced both the runoff and sediment by approximately 10‐20% on the gentle slope; on the medium slope, although RT also reduced the runoff in the 90‐ and 120‐mm/hr intensity rainfall events, the sediment increased by 158.90% and 246.08%; on the steep slope, the sediment increased by 92.33 to 296.47%. Overall, when the runoff control benefit of RT was lower than 5%, there was no sediment control benefit. RT was effective at controlling soil loss on the gentle slopes but was not effective on the medium and steep slopes. This is because the surface depressions created by RT were filled in with sediment that eroded from the upslopes, and the surface microrelief became smoother, which then caused greater soil and water loss than that on an SS at the later rainfall stage.

Effects of forest litter cover on hydrological response of hillslopes in the Loess Plateau of China

Forest litter layer plays an important role in controlling water and soil loss; however, few studies have examined how litter cover affects hydrological processes. In this research, the effects of forest litter cover on interception, runoff, infiltration and soil erosion were investigated using rainfall simulation on a loess hillslope in China. Field experimental plots (10 m × 1.5 m, 5°) with two litter species (needle-leaf species and broad-leaf species) and three litter masses (300, 500 and 800 g m−2) were exposed to two rainfall intensities (30 and 60 mm h−1) for 40 min. A modified Merriam interception model as well as a WEPP (Water Erosion Prediction Project) Hillslope model were subsequently employed to analyze the experimental data of litter interception as well as runoff generation and soil erosion, respectively. Results showed that litter interception storage capacity ranged from 0.55 to 2.10 mm; thus, 1.8–9.2% of total rainfall was intercepted by the litter layer. Interception storage increased with increasing litter mass and rainfall intensity, and broad-leaf litter could intercept more rainwater than needle-leaf litter. Litter cover reduced runoff rates from plots covered with needle-leaf and broad-leaf litter by 18.6% and 25.9%, respectively, compared to the bare plot. Although runoff rates were slightly lower in litter-covered plots than in the bare plot, soil loss was effectively controlled when litter mass levels reached a threshold value of 500 g m−2. Compared to that from the bare plot, the mean soil loss rate for litter-covered plots was lowered by 58.5%, 74.5% and 78.3% for litter masses of 300, 500 and 800 g m−2, respectively. These results indicate that the litter layer was more conducive to controlling soil loss than runoff generation. Furthermore, the determination coefficient and Nash-Sutcliffe efficiency coefficient of the modified Merriam model ranged between 0.838–0.998 and 0.912–0.998, respectively, indicating that this model could successfully simulate the litter interception process. The WEPP model predictions also agreed well with the measured runoff and soil loss rates, but may have under-estimated the measured data in low rainfall intensity events and over-estimated the measured data in high rainfall intensity events. The performance of the WEPP model could be obviously improved by reducing the effective hydraulic conductivity and soil erodibility. Overall, this study will enable the development of more accurate modeling approaches and lead to a better understanding of hydrological processes under litter cover conditions.

Soil loss: Effect of plant litter incorporation rate under simulated rainfall conditions

AbstractPlant litter can control land degradation by increasing soil organic matter and decreasing soil erosion by covering the soil surface or being incorporated into topsoil. However, the effect of litter incorporation on soil erosion is not clear. This study aimed to investigate the effect of litter incorporation into topsoil on interrill erosion. The poorly decomposed litter was collected from the field and incorporated into topsoil (5 cm) at six rates (ranging from 0 to 0.5 kg m−2). Laboratory rainfall (80 mm hr−1) experiments were conducted under five slope gradients (ranging from 9% to 47%). The results showed that the soil loss rates declined exponentially with increase in litter incorporation rate on slope gradients between 9% and 36%. However, on slope gradient of 47%, litter incorporation caused an increase in the soil loss rate. The efficiency of litter incorporation in controlling soil loss varied from −21.7% to 40.5% with a mean of 10.8%. It decreased linearly with the slope gradient (R2 = 0.34). The decrease can be explained by two simultaneous but opposite effects: the effect of preventing erosion and that of promoting erosion. The former was induced by decreases in the effective erosive force of raindrop and overland flow exerted on soil, and soil erodibility, along with increases in sediment interception. The latter was caused by rapid saturation of the surface soil and concentrated overland flow. The results demonstrate the complexity of the effect of litter incorporation on soil erosion and can improve our understanding of litter in soil loss control.

Estimation of Soil Erosion to Define the Slope Length of Newly Reconstructed Gentle-Slope Lands in Hilly Mountainous Regions

Farming plot construction engineering in hilly areas plays an important role in the mechanization, large-scale production and industrialization of agriculture. The method is undertaken to improve water and soil conservation, enhance soil fertility and extend machinery agriculture. However, the positive effects of engineering require years to mature. The properties of newly reconstructed soil are not sufficient, i.e., with poor structure and low water holding capacity, resulting in deterioration of its physical properties and erosion. To date, most studies on plot characteristics and soil properties in farming plot construction engineering have neglected the influence of soil erosion. This paper addresses soil erosion characteristics at sites to define the appropriate slope length for newly reconstructed gentle-slope lands. Six field plots with a 10° slope gradient and different lengths (5, 10, 20, 30, 40, and 50 m) were established under natural rainfall and simulated overland flow conditions. The soil detachment rate, runoff shear stress and stream power exhibited the same trends as runoff and soil loss. The soil erosion characteristics varied at sites with different slope lengths, and the degree of soil erosion reached its minimum on gentle-slope land sites of 30 or 40 m. Therefore, 30–40 m slope lengths may be the recommended range to control soil loss from newly reconstructed gentle-slope lands. The conclusions of this study provide theoretical guidance for farming plot construction engineering, which can promote the sustainable development of cultivated land resources in hilly mountainous regions.

Eco-morphological characteristics of fern species for slope conservation

Degradation of slopes due to shallow landslide and the subsequent erosional processes are a big challenge on the application of soil bioengineering techniques; that is the use of plants as main structural components of a slope protection and conservation system. An optimal application of soil bioengineering techniques should include not only the technical factor of plants as structural components but also the ecology of species and the plant adaptations to disturbances, which is crucial if a longterm successful slope restoration system is intended. Ferns are a dominant understory vegetation species in the forest of Japan, but its characteristics and influences on the recovery of shallow landslide scars have not been fully studied yet. This study aims to find out the ecological characteristics of fern species through the calculation of ecological indicators and the quantification of the morphological features of specimens growing on disturbed and non-disturbed forest slopes in Japan. Gleichenia japonica was found as the vegetation species with biggest ecological indicators on both slopes. The analysis of morphological characteristics of the specimens growing on both sites showed that the development of the specimens is focused in below-ground characteristics. The pull-out force of Gleichenia japonica root system as an indicator of ecological adaptation to a constraint environment and morphological characteristics quality is influenced by height and root length according to the principal component analysis. The eco-morphological characteristics of species can be used as an indicator of an optimal element in soil bioengineering establishment for slope conservation proposes. The long and fibrous root system could be placed on forest roads, steep or small slopes where space limitation is an issue for the establishment of bigger species and if the slope conditions allow it, it can control soil losses due to rainfall and provide stability.

Sediment Grain-Size Characteristics and its Sources of Ten Wind-Water Coupled Erosion Tributaries (the Ten Kongduis) in the Upper Yellow River

Understanding the composition and sources of deposited sediments in watersheds has great significance on exploring the processes of sediment erosion and deposition, and controlling soil losses in rivers. In this paper, we investigate the grain-size composition parameters and their reflections on sediment erosion, transport and deposition processes in the Ten Kongduis, which are large arroyos carrying a large volume of coarse sediment into the upper Yellow River. The sediments delivered by the Ten Kongduis come from three kinds of sources, including the clasolite (mudstone, sandstone and conglomerate) and loess in the upstream reaches and the aeolian sand in the middle stream reaches. A portion of the sediments is carried to the Yellow River and another portion is deposited in the alluvial fans in the lower reaches of the kongduis. We found two types of deposits in the drilling cores on the alluvial fans and in the sediment profiles, i.e., the sediments deposited by hyperconcentrated flows and those by non-hyperconcentrated or ordinary sediment-laden flows. The deposits of hyperconcentrated flows were only found in some natural sediment profiles exposed on the riverbank slopes. They have a mean size in a narrow range of 0.016-0.063 mm but are very or extremely poorly sorted according to nine samples collected from four kongduis. Most of the sediments carried by the non-hyperconcentrated flows have a mean grain size in the range of 0.05–0.25 mm. We calculated the contributions of sediment from the sources using the grain-size fingerprint method based on grain-size data of the sediment sources and deposits in the alluvial fans for both the hyperconcentrated flows and non-hyperconcentrated flows. It was found that a proportion of 69% or above of sediment carried by the hyperconcentrated flows mainly comes from the clasolite and loess strata in the upper reaches, and 8%–31% from the desert in the middle reaches. The clasolite and loess strata contribute 64%, on average, of the particles above 0.05 mm carried by the hyperconcentrated flows, and the desert in the middle reaches contributes the other 36% or so. The sediments carried by non-hyperconcentrated flows down to the alluvial fans come from the clasolite, loess and dune sand in different proportions in different kongduis with the contributions of both clasolite and dune sand being related roughly to the ratio of upper drainage area to the width of desert in the middle reaches of kongduis. Over 90% of the sediments carried by the non-hyperconcentrated flows into the Yellow River are below 0.05 mm.

Computational Fluid Dynamics Simulation of Airflow through Standing Vegetation

Abstract. Maintaining vegetative cover on the soil surface is the most widely used method for control of soil loss by wind erosion. We numerically modeled airflow through artificial standing vegetation (i.e., simulated wheat plants) using computational fluid dynamics (CFD). A solver (simpleFoam within the OpenFOAM software architecture) was used to simulate airflow through various three-dimensional (3D) canopy structures in a wind tunnel, which were created using another open-source CAD geometry software (Salomé ver. 7.2). This study focused on two specific objectives: (1) model airflow through standing vegetation using CFD, and (2) compare the results of a previous wind tunnel study with various artificial vegetation configurations to the results of the CFD model. Wind speeds measured in the wind tunnel experiment differed slightly from the numerical simulation using CFD, especially near positions where simulated vegetation was present. Effective drag coefficients computed using wind profiles did not differ significantly (p <0.05) between the experimental and simulated results. Results of this study will provide information for research into other types of simulated stubble or sparse vegetation during wind erosion events.HighlightsMeasured airflow through a simulated canopy was successfully modeled using CFD software.Effective drag coefficients did not differ between the experimental and simulated results.Results of this study provide 3-D simulation data of wind flow through a plant canopy. Keywords: 3-D canopy structure, OpenFOAM, Wind erosion, Wind tunnel studies.

Effects of Rainfall Intensity and Vegetation Cover on Erosion Characteristics of a Soil Containing Rock Fragments Slope

Rainfall events coupled with shallow and gravelly sloping farmland have led to serious soil erosion and associated problems in the Three Gorges reservoir. Previous studies have shown that the use of vegetation is an effective way to control soil erosion. Therefore, an artificial, simulated rainfall experiment study is conducted to determine the effect of rainfall intensity and vegetation cover on runoff volume, sediment load, and runoff hydraulics characteristics. The experiment consists of seven vegetation treatments subjected to three rainfall intensities on a soil that contains rock fragments on a slope of 30°. The results indicate that the runoff volume and sediment load of the bare plot were greater than those of vegetation‐covered plots under three different rainfall intensities. When Cynodon dactylon and Indigofera amblyantha were applied together, the plot displayed the best performance for soil loss control, with a reduction of 87.88%–99.11%. According to a redundancy analysis, the change in rainfall intensity had the least impact on the Reynolds number and the runoff volume of the herb‐shrub mixed plot in this study. These findings suggest that the effect of combining Cynodon dactylon and Indigofera amblyantha and increasing the vegetation coverage is an effective solution for soil and water loss conservation. The application of this method can alleviate environmental stress on the Three Gorges reservoir.

The impact of straw mulching and salvage logging on post-fire runoff and soil erosion generation under Mediterranean climate conditions

Forest fires-affected landscapes enhance sudden runoff discharges, high sediment loads and extreme soil erosion rates. Different soil stabilisation treatments, such as mulching, can be applied to avoid runoff and soil erosion after wildfires. To characterise the post-fire soil erosion rates and runoff generation, we selected a Mediterranean forest affected by a wildfire in Lietor (Spain) to determine the sediment yield (dry sediment (DS), total suspended sediment (TSS), total dissolved sediment (TDS)) and runoff discharge in twelve 200 m2 (10 × 20 m) plots. Immediately after the wildfire, six plots were covered by straw and six other plots were set up as controls. Three months after the wildfire, logging activities were performed and the experimental designs were as follows: mulching + logging (three replicates), non-mulching + logging (three replicates), non-mulching + non-logging (three replicates) and mulching + non-logging (three replicates). During the period after wildfire and before salvage logging, the straw mulch controlled the soil erosion rates (DS, TSS and TDS) versus the non-mulched plots, but straw had no real impact on runoff discharge. For the period after salvage logging, once again runoff did not differ when comparing all the treatments. DS was higher in the non-mulched and non-logging plots, whereas the highest TSS was found in the non-mulched plots (in logged or non-logged plots). TDS was higher in the mulched and non-logged plots. We conclude that straw mulch is efficient management in recent fire-affected mountainous terrains to control soil loss immediately after wildfire. Moreover, logging operations done 3 months after wildfire did not necessary generate higher DS, TSS, TDS rates, mainly because of the type of machinery used for forest operations.

Managing runoff and soil loss in asparagus production systems

On slightly sloping land, current asparagus cultivation practices (including prolonged periods of bare soil, surface capping and compaction of wheelings) can lead to runoff and soil loss. This can result in on-site impacts to crops and field operations and offsite impacts on the wider environment. Research into soil and water management in green asparagus production has been undertaken in the UK since 2010. This paper details two separate runoff and erosion trials conducted in 2012 and 2013 on commercial asparagus fields. Each trial has tested the efficacy of a range of treatments applied to inter-row wheelings including green waste compost (of PAS:100 quality protocol standard) and wheat straw mulch at different application rates, both with and without shallow soil disturbance. It was realised early on that compost was ineffective in runoff and soil loss management where application quantity was restricted by nitrogen regulations in Nitrate Vulnerable Zones. Straw mulch alone has consistently reduced soil loss across both trials by 72 to 87% as compared to the bare soil control. Shallow soil disturbance alone reduced soil loss by 4 to 13%, with no significant differences observed between various tillage implements tested. Despite the reductions observed in soil loss, runoff sediment concentration still exceeds that stipulated by EU Directive for surface water quality; risking pollution of any receiving water bodies. The knowledge gained from these studies should be used to develop more effective runoff and soil loss control in order to ensure the future sustainability of asparagus production.

Soil and water conservation measures reduce soil and water losses in China but not down to background levels: Evidence from erosion plot data

The efficacy of soil and water conservation measures (SWCMs) on reducing the loss of soil and water has been widely tested at the plot scale in China. However, an integrated comparison of the efficacy and an overall investigation of the controlling factors of the efficacy is absent. Therefore, an extensive dataset compiling erosion plot measurement of applying SWCMs on controlling soil loss and runoff in China was established in this study. In total, 848 erosion plots representing 2494 plot years were retained in this dataset which compiled from 108 publications and 2 data reports. The 15 most frequently tested SWCMs were identified and described. Soil loss ratio (SLR) and runoff ratio (RR) of each SWCMs was calculated to assess the efficacy of an SWCMs on reducing soil and water loss. The potential controlling factors, such as slope, slope length, annual precipitation, were evaluated for the controlling factor for both SLR and RR. Our results suggested that in general, applying the SWCMs can reduce soil loss by ca. 70% (overall SLR is 0.39 ± 0.02) and runoff by ca. 50% (overall RR is 0.54 ± 0.05), respectively. However, erosion rates on plots with SWCMs in China were, in general, still significantly higher than erosion rates measured under permanent vegetation cover land and, on average, ca. one order of magnitude higher than soil formation rates which required for a soil-neutral agriculture. On overall, the SLR presented a significant relation with topographic factors: positive with slope gradient and negative with slope length. This suggests that the support practice factor (P factor) of RUSLE model might be overestimated when values measured from plot scale are directly applied to larger areas (catchment or region scale). The SLR and RR values presented in this study can be applied for the planning of SWCMs in China and can be used to estimate the P factor when applying RUSLE model whereby the effect of topographic factors on SWCM efficacy can be accounted for.

Partition-coordinated control of soil and water loss for chestnut forests in the Yanshan Mountain Region, China

Soil erosion from chestnut forests is one of the most important factors causing land degradation in the Yanshan Mountain Region. A 2-year field study was done to compare the effects on erosion of a control plot (CP), a repaired and maintained horizontal ditch built with an engineering baffle every 6 m (MP 1), and a repaired and maintained horizontal ditch built with an engineering baffle every 8 m (MP 2). The results showed that the slope runoff of chestnut forests was influenced by rainfall characteristic factors. No single rainfall characteristic factor showed dominance for hill slope runoff. The runoff reduction effect of the partition-coordinated erosion control measures (MP 1 and MP 2) was substantial for chestnut forests under high rainfall intensity conditions. However, the runoff reduction efficiency was higher under the conditions of heavy rainfall and low average rainfall intensity than for storms with higher intensity and lower total rainfall. The reduction effect of the partition-coordinated erosion control measures on the runoff and sediment yield of chestnut forest slopes was MP 2 > MP 1 > CP. The runoff reduction rate and erosion reduction rate of MP 2 reached 61.70% and 97.41%, respectively, and that for MP 1 was 54.15% and 85.31%, respectively. Therefore, after a comprehensive comparison, MP 2 was determined to be more effective for soil erosion control for a sloping chestnut forest.

Effects of Soil and Water Conservation Practices on Runoff, Sediment and Nutrient Losses

Rainfall is a major dynamic source of soil erosion and nutrient loss on slopes. Soil and water conservation practices and agricultural activities can change the soil surface morphology and thus affect erosion and nutrient losses. This study focused on the effects of several typical soil and water conservation practices and agricultural land, for the purpose of: (1) determining how these practices prevent erosion and nutrient loss and identifying the hydrodynamic mechanisms; and (2) determining the application conditions for different practices. Runoff, sediment, total nitrogen (TN) and total phosphorus (TP) in fish-scale pits, agricultural land, narrow terraces, shrub cover and bare land, under rainfall events in rainy seasons (from May to November) during the 2010–2015 period, were monitored. Slope hydrodynamic mechanisms and application conditions of these practices were also investigated. The results showed that compared with bare land, fish-scale pits performed the best in preventing runoff, sediment, TN and TP, followed by 30% shrub coverage, narrow terraces and agricultural land, successively. Total runoff, sediment, TN and TP losses in fish-scale pits site were 19.70%, 2.03%, 10.10% and 35.97% of those in bare land of the same area, respectively. Soil and water conservation practices could change the hydraulic characteristics of slopes, decrease Re (Reynolds) and Fr (Froude) numbers, thereby decreasing runoff, sediment, TN and TP losses. Fish-scale pits were suitable for the areas with small single rainfall and good water permeability. When rainfall was greater than 60 mm, narrow terraces had highest efficiency in reducing sediment loss; therefore, they were suitable for the areas with relatively high rainfall intensity and soils similar to the sandy loams of the study area. As to the practice of covering land with plants, the effect was sustainable due to the plants’ long-term growth. Agricultural land was not recommended since the losses on it were relatively higher due to the impact of human activities. In reality, these practices may be applied in combination so as to effectively control water, soil and nutrient losses.

Predicting soil loss and sediment characteristics at the plot and field scales: Model description and first verifications

Soil loss models are useful tools for making land management decisions to prevent soil and water quality problems. Several soil loss models have been developed, including the process-based Water Erosion Prediction Project (WEPP) model and the empirical Revised Universal Soil Loss Equation (RUSLE). Although process-based models provide accurate soil loss estimates, they are infrequently used for conservation planning because of their complexity and data need. On the other hand, models such as RUSLE cannot predict the soil loss nor the sediment composition associated with individual events, both of which are critical for designing accurate soil and water conservation practices. Therefore, the objective of this study was to develop a model for estimating sediment delivery on an event scale while predicting its clay, silt and sand fractions. For this purpose, the WEPP model was implemented using measured soil and climate data from Central Chile to generate a soil loss database for many hillslope configurations and management practices. More than 200,000 erosion events were generated using data from 83 sites. Using multiple regression analysis, the main variables controlling soil loss were identified, which included rainfall erosivity, soil erodibility, hillslope geometry, antecedent soil moisture and total precipitation. These variables were incorporated into a soil loss model, which was calibrated using data from 32 sites (R2 = 0.81–0.83) and validated for the remaining 51 sites (R2 = 0.66–0.89). The model provided accurate estimates for the clay and silt fractions (R2 = 0.86 and 0.78, respectively) but showed difficulties for predicting the sand fraction (R2 = 0.31). Contour plowing and vegetative filter strip routines were also incorporated into the soil loss model, providing reliable soil loss (R2 = 0.51–0.78), clay (R2 = 0.54–0.75), and silt (R2 = 0.57–0.68) estimates. The developed model is remarkably easy to use and, due to its simplicity, allows incorporating other soil conservation routines, providing a flexible tool for soil conservation planning. This study provides a detailed description and methodology for building such a model and discusses its advantages and limitations.