Cultivated Slopes Research Articles

Influence of relief characteristics and landscape connectivity on sediment redistribution in small agricultural catchments in the forest-steppe landscape zone of the Russian Plain within European Russia

Sheet, rill and gully erosion occurring in the snowmelt period (March–April) and rainfall season (May–September) is the main factor of soil degradation and mobilized hillslope sediment redistribution within cultivated lands of the Russian Plain. The evaluation of sediment redistribution for the period since 1986 within catchment sediment cascades was done based on an integrated approach for some representative dry valley catchments located in the western (the Plava River basin, Tula Oblast, Russian Federation) and eastern (the Temeva Rechka Creek catchment, the Myosha River basin, Republic of Tatarstan, Russian Federation) sectors of the forest-steppe landscape zone of the Russian Plain. All the catchments studied are characterized by a high proportion (within the range of 60–80%) of cultivated lands. The modified version of the Universal Soil Loss Equation (USLE), the Russian State Hydrological Institute's erosion model, and the LandSoil erosion model were applied to calculate soil losses within the cultivated lands. The morphological classification of interfluve slopes and hollow slope catchments, in combination with the sediment delivery ratio (SDR) assessment for slopes and hollow slope catchments of different configuration, were used to assess sediment transfer from the cultivated lands. The Chernobyl-derived 137Cs isotope was applied as a chronomarker for sediment dating in different sediment sinks located along pathways from cultivated slopes to river valley bottoms. We found that the morphological features of the dry valley catchments, including a pattern of the dry valleys of different Hortonian orders, dry valley and hollow density, dry valley incision depth, and proportion of slopes and hollow slope catchments of different configurations are the main parameters that determined a proportional input of the different sediment sinks to the sediment interception along the pathways from the cultivated slopes to the river valley bottoms. The land use/cover features are mostly responsible for the pattern of buffer zones within the interfluve parts of the catchments. The quantitative assessment of the sediment budget allowed us to conclude that the mean SDR coefficients for the dry valley catchments of second, third, and fourth Hortonian orders are 0.56, 0.33, and 0.07 respectively. The extrapolation of the study results of sediment redistribution evaluation, obtained from the studied catchments located within the Plava River basin, to the entire basin of the river also allowed us to evaluate the mean value of hillslope-to-river-valley-bottom SDR = 0.27.

Contribution of climate and land cover changes to reduction in soil erosion rates within small cultivated catchments in the eastern part of the Russian Plain during the last 60 years

The eastern part of the Russian Plain is an important agricultural region of European Russia with high proportion of cultivated lands in the steppe, forest-steppe and forest (southern part) landscape zones. Soil erosion is the main process of land degradation and surface water contamination there. Climate and land cover changes have been observed in this region during the last 30 years. However, field quantitative assessments of soil erosion rates are not available for the eastern part of European Russia due to the lack of monitoring data as well as the evaluation of erosion/deposition processes in cultivated catchments using other field methods. Three representative small cultivated catchments with high (> 80%) proportion of cultivated lands were selected in the forest (southern part), forest-steppe and steppe zones of the study region to evaluate sedimentation rates in dry valley bottoms of the catchments for two-time intervals (1963–1986 and 1987–2016) based on the application of the bomb-derived and Chernobyl-derived 137Cs isotope for sediment dating. The 3–4 depth 137Cs profiles were used to assess the sedimentation rates within the each investigated catchment. It was established that the sedimentation rates have considerably decreased (at least 2–3 times) over the last 30 years compared to 1963–1986 in all the investigated catchments. This is in agreement with results of erosion rate calculations using erosion models for the forest zone, however not consistent with erosion rates assessments for the forest-steppe and steppe zones. According to the model calculations, erosion rates show a slight decrease in the forest-steppe zone and increase in the steppe zone. The reduction in surface runoff during snowmelt period is one of the reasons for decrease in erosion rates within cultivated slopes for all the investigated catchments. The increase in proportion of perennial grasses in the regional crop rotation is another important reason for the decrease in erosion rates for the catchment located in the south of the forest zone. The importance of land cover changes in a major decrease of soil losses from the cultivated fields of the investigated catchments located in the forest-steppe and steppe zones cannot be identified due to the lack detailed information about crop rotation for those particular sites. However, available regional information about crop rotation changes for the two-time intervals (1960–1980 and 1996–2012) do not explain very high reduction in sedimentation rates in the dry valley bottoms after 1986.

Water flow velocity over frozen and nonfrozen black soil slopes

AbstractIce‐ and snow‐melted water flow over partially thawed frozen soil of cultivated slopes causes serious soil erosion, which results in soil degradation and affects productivity in Northeast China. Water flow velocity over frozen and nonfrozen soil shows importance in understanding meltwater erosion. In this work, a series of laboratory experiments were conducted to measure water flow velocity over frozen and nonfrozen soil slopes. Experiments were performed using the electrolyte trace method under the pulse boundary model, under conditions of 4 slope gradients (5°, 10°, 15°, and 20°), 3 flow rates (1, 2, and 4 L/min), and 7 sensors positioned at 0.1, 1.0, 2.0, 3.0, 4.0, 5.0, and 6.0 m away from the electrolyte injection point. Results showed that velocities over frozen soil slopes increased with flow rate and slope gradient. Flow velocities over nonfrozen soil slopes increased with flow rate and slope gradients from 5° to 15° and stabilized at 15°. Flow velocities over frozen soil slopes were 30%, 54%, 71%, and 91% higher than those over nonfrozen ones at slope gradients of 5°, 10°, 15°, and 20°. Flow velocities over frozen soil slopes under different flow rates of 1, 2, and 4 L/min were approximately 52%, 59%, and 79% higher than those over nonfrozen soil, respectively. This study can help in assessing the erosion of partially thawed frozen soil by meltwater flow.

Variation Trend Analysis of Runoff and Sediment Time Series Based on the R/S Analysis of Simulated Loess Tilled Slopes in the Loess Plateau, China

The objective of this study was to illustrate the temporal variation of runoff and sediment of loess tilled slopes under successive rainfall conditions. Loess tilled slopes with four microtopography types (straight cultivated slope, artificial backhoe, artificial digging, and contour tillage) under five slope gradients (5°, 10°, 15°, 20°, 25°) were simulated and a rainfall intensity of 60 mm/h was adopted. The temporal trends of runoff and sediment yield were predicted based on the Rescaled Range (R/S) analysis method. The results indicate that the Hurst indices of runoff time series and sediment time series are higher than 0.5, and a long-term positive correlation exists between the future and the past. This means that runoff and sediment of loess tilled slopes in the future will have the same trends as in the past. The results obtained by the classical R/S analysis method were the same as those of the modified R/S analysis method. The rationality and reliability of the R/S analysis method were further identified and the method can be used for predicting the trend of runoff and sediment yield. The correlation between the microtopography and the Hurst indices of the runoff and sediment yield time series, as well as between the slopes and the Hurst indices, were tested, and the result was that there was no significant correlation between them. The microtopography and slopes cannot affect the correlation and continuity of runoff and sediment yield time series. This study provides an effective method for predicting variations in the trends of runoff and sediment yield on loess tilled slopes.

Evaluation of the influence of cultivation period on soil redistribution in northeastern China using magnetic susceptibility

Magnetic susceptibility has been shown to be a reliable, economic and rapid method for tracking soil redistribution; however, more case studies are necessary to verify the link between soil movement and magnetic susceptibility. In this study, we sought to evaluate soil redistribution in northeastern China using magnetic susceptibility on the basis of data collected from croplands with different cultivation periods. The results showed that the magnetic susceptibility values, whether low-frequency magnetic susceptibility (χlf) or frequency-dependent magnetic susceptibility (χfd), were markedly different between forestland and cropland, with larger differences for longer cultivation periods. The magnetic susceptibility increased dramatically in topsoils on forest slope, whereas the difference in magnetic susceptibility between topsoils and subsoils decreased in cropland as the cultivation period increased. The magnetic susceptibility values varied significantly across sites on a given slope, increasing gradually from the upperslope to the lowerslope, regardless of whether the slope was forestland or cropland. Longer cultivation periods resulted in larger differences between the upperslopes and lowerslopes which were particularly notable when the cultivation period was longer than 50 years. For middleslopes and lowerslopes, the soil loss of an 110-year cultivated slope was approximately two times higher than that of a 30-year cultivated slope. These findings suggest that the use of magnetic susceptibility is feasible for tracking soil redistribution and soil loss.

English

Land degradation is increasing in severity and extent in many parts of the world. Success in arresting land degradation entails an improved understanding of its causes, process, indicators and impacts. Various scientific methodologies have been employed to assess land degradation globally. However, the use of local community knowledge in elucidating the causes, process, indicators and effects of land degradation has seen little application by scientists and policy makers. Land degradation may be a physical process, but its underlying causes are firmly rooted in the socio-economic, political and cultural environment in which land users operate. Analyzing the root causes and effects of land degradation from local community knowledge, perception and adapting strategies perspective will provide information that is essential for designing and promoting sustainable land management practices. The main objective of this study was to analyze the perceptions of farmers’ on the impact of land degradation hazard on agricultural land productivity decline, associated with soil erosion and fertility loss. The study used a multistage sampling procedure to select sample respondent households. The sample size of the study was 120 household heads and 226 farm plots managed by these farmers. The primary data of the study were collected by using semi-structured Interview, focus group discussions and field observation. Both descriptive statistics and econometric techniques were used for data analysis. Descriptive results show that 57% of the respondents perceived the severity and its consequence on agricultural land productivity. The following indicators of soil erosion and fertility loss were generally perceived and observed by farmers’ in the study area: gullies formations, soil accumulation around clumps of vegetation, soil deposits on gentle slopes, exposed roots, muddy water, sedimentation in streams and rivers, change in vegetation species, increased runoff, and reduced rooting depth. The direct human activities which were perceived to be causing land degradation in the study area include: deforestation and clearing of vegetation, overgrazing, steep slope cultivation and continuous cropping. The farmers’ possibility of perceiving the impact of land degradation hazard on agricultural land productivity was primarily determined by institutional, psychological, demographic and by bio-physical factors. Farmers who perceive their land as deteriorating and producing less than desired, tend to adopt improved land management practices. On the other hand, farmers who perceive their land to be fertile tend to have low adoption of conservation practices. In order to overcome this land degradation and its consequent effects, the study recommended a need for the government to enforce effective policies to control and prevent land degradation and these policies should be community inclusive /participatory founded up on indigenous and age-honored knowledge and tradition of farmers' natural resource management as well as introduced scientific practices. Key words: Farmers’ perception, land degradation, impact of land degradation, agricultural land productivity.

Landslide susceptibility zonation mapping using frequency ratio and fuzzy gamma operator models in part of NH-39, Manipur, India

The hilly region of Manipur especially along the NH-39 road, which is the lifeline of the State, is prone to landslides every year particularly during the monsoon season. Anthropological factors, such as excessive deforestation, unsystematic changes in land use and land cover pattern and slope cultivation, etc. are indirectly initiate the process of landslides. In the present study, landslide susceptibility mapping was carried out using frequency ratio and fuzzy gamma operator models with the help of geomatics techniques. The landslide susceptibility mapping was prepared using landslide inventory data and nine landslide causative factors, i.e. lithology, land use and land cover, geomorphology, drainage density, lineament density, slope gradient, slope aspect, curvature, and elevation. These causative factors were prepared with the help of toposheet, high resolution IRS P6 LISS IV satellite imagery, cartosat DEM data and extensive field work. The landslide susceptibility maps were prepared by calculating the relationship between the landslide causative parameters with landslide areas using a frequency ratio model. To get the fuzzy membership values, the frequency ratio values were normalized between the ranges of 0 and 1. The landslide susceptibility maps were compared and prediction accuracy of both the models was derived using the area under curve (AUC) method. The success rate curves were obtained using both training and all landslide inventory dataset. For training landslide inventory dataset, the AUC value of the success rate curve for the frequency ratio model was found to be 0.8056, whereas for the fuzzy gamma operator (using γ = 0.99) model, it was calculated as 0.9150. In the case of all landslide inventory dataset, the AUC value of the success rate curve for the frequency ratio model and the fuzzy gamma operator model were 0.7921 and 0.8188, respectively. The landslide susceptibility index was also compared with the landslide validation inventory dataset to obtain the prediction rate curves. The AUC value of the prediction rate curve for the frequency ratio model was 0.5681, whereas in the case of the fuzzy gamma operator model, it was 0.6721.

Temporal persistence and stability of soil water storage after rainfall on terrace land

The “Grain for Green” Project on the Loess Plateau of China has converted a large area of cultivated slope farmland to terraces to reduce soil erosion and improve the ecological environment. The area of terraced land on the Loess Plateau was 32,600 km2 in 2010. Knowledge of the behavior of soil water storage (SWS) and its spatiotemporal distribution provides essential information concerning hydrological and ecological processes. This study aimed to analyze the temporal stability of SWS after rainfall for different time periods on terraces planted with jujube trees (Ziziphus jujuba Mill.). The SWS of 21 locations was obtained from July 19 to September 3 in 2014 and from August 01 to August 31 in 2015. Relative difference analysis and the nonparametric Spearman rank correlation test were used to check the temporal stability of SWS. The SWS on terraces was normally distributed and demonstrated moderate spatial variability. The SWS at three soil depths all showed strong temporal stability with stability in the order of 0–0.6 < 0–1.0 < 0–1.6 m. Rainfall significantly affected the temporal stability of SWS in the depth of 0–0.6 m. The number of representative locations of SWS was not constant. The best representative locations were not identical for different soil depths; however, a common representative location did exist for the different depths and periods. Moreover, the mean SWS generally increased from the upper to lower slope. The temporal stability of SWS was not significantly affected by rainfall but was significantly negatively correlated with sand content. The total root length and soil organic carbon content did not show any obvious correlations with mean SWS. It was feasible to use the representative locations of SWS to represent the mean SWS over a period of time. However, the cumulative absolute error increased with cumulative days. In conclusion, SWS in the deeper soil depths indicated greater temporal stability than that in shallow soil depth during wet period. The best representative locations for SWS were depth and time dependent.

An improved core sampling technique for soil magnetic susceptibility determination

The efficiency of acquiring soil magnetic susceptibility (MS) data is strongly influenced by time-consuming sampling and treatment procedures of the conventional MS technique (M1). It is necessary to find an optimized technique to save time and labor in soil-related research, especially at large scales with a large number of soil samples. An improved soil sampling technique (M2) based on an improved core sampler kit and a simplified sample treatment procedure was introduced. Sample treatment of M1 is similar to other common soil- and sediment-processing procedures, while M2 involves relatively limited procedures without grinding and sieving. A total of 360 samples from 5 soil layers at 12 sampling sites based on M1 and M2 were collected on a gentle cultivated slope in Northeast China. The tested black soils contain few gravel (>2mm) and other non-soil components. Results showed that M2 saves a considerable amount of time and labor for MS determination compared with M1. Assuming one person, 85% of the time processing 10,000 soil samples using M1 can be saved by using M2. Additionally, M2 produces MS data (χlf, χfd%) with satisfactory accuracy compared with M1. Pearson correlation coefficients for χlf and χfd% between M1 and M2 are 0.973 and 0.882 (n=180) at the 0.01 level of significance, respectively. The mean relative error in χlf and χfd% based on M2 is 8.5% and 8.2%, respectively, when compared with M1. These results indicate that M2 for MS determination is effective for soil related research at large spatial scales where large sample sets are required or representative samples are required in advance for other time-consuming or expensive analyses.

喀斯特地区坡耕地与退耕地土壤有机碳空间异质性及其影响因素

喀斯特地区坡耕地与退耕地土壤有机碳空间异质性及其影响因素

Identifying soil redistribution patterns by magnetic susceptibility on the black soil farmland in Northeast China

Erosion processes in the black soil region of Northeast China result in significant regional soil redistribution and crop production heterogeneity along slopes. It is difficult to link soil erosion and redistribution on a long-term scale using classical field plot monitoring or the costly 137Cs technique; however, magnetic susceptibility measurements can provide an economical tool to quantify soil redistribution over a large area and over a long duration. This study attempts to determine the variations of soil magnetic susceptibility on sloped farmland using soil sampling and to establish the relationship between patterns of soil redistribution and variations of magnetic susceptibility at different locations on a slope. Soil cores were collected along two typical transects on a cultivated slope and a reforested slope, respectively. The cores were 100cm deep and were spaced at an interval of 10cm; the samples were measured for mass-specific low-frequency magnetic susceptibility (χlf) and frequency-dependent magnetic susceptibility (χfd). The results showed that the χlf profiles at different slope positions on uncultivated reforested land were relatively homogeneous, revealing a similar pedogenic process across the entire slope. However, the χlf profiles at different slope positions on cultivated land were significantly different, exhibiting signs of a soil erosion and deposition process. Maximum soil loss (15.8%) occurred at the shoulder segment, and maximum soil deposition (25.1%) was observed at the footslope. However, at least 10.6% of the topsoil had been eroded and lost due to cultivation over the past 60years in the study area. The results imply that magnetic susceptibility can be used to determine soil redistribution.

Recent changes in sediment redistribution in the upper parts of the fluvial system of European Russia: regional aspects

Abstract. Quantitative assessments of soil loss from cultivated land and sediment redistribution along pathways from cultivated fields to river channels have been undertaken using a range of different methods and techniques, including erosion models, detailed studies of sediment redistribution in representative catchments, monitoring of gully head retreat and evaluation of sediment deposition in ponds and small reservoirs. Most of the sediment eroded from arable land is deposited between the lower portions of the cultivated slopes and the river channels. Less than 15% of the eroded sediment is delivered to the river channels. Sediment redistribution rates in the upper parts of the fluvial system have declined during the last 25 years in both the western and eastern parts of the Russian Plain, because of a major reduction of surface runoff during snowmelt and a reduction of the area of arable land in some parts of the study area.

Restoration of Degraded Gidan Waya Forest Reserve

Land degradation is a matter of serious concern. Vast area of land all over the world has been converted into unproductive and degraded lands. Ecosystem restoration through plantation forest is the most effective technique to reclaim the degraded landscape. Measurement of slopes angles and correspondent rates of soil erosion were taken at different spots of cultivated slopes which have been occupied for particular period of time. This paper explores the impact of human activities as the main cause of land degradation and loss of biodiversity. The result indicated that cultivation on steeper slopes is more harmful and degradation is faster. Restoration of this area is possible when farmers receive environmental education through the planting of exotic tree species of Tectona grandis and G melina that grows faster in this region. The DPSIR (Driving force, Pressure, State, Impacts, Response) conceptual framework model is used to illustrate how degradation control could be more effective, tackling not only the drivers of change but also major developmental issues such as poverty and food insecurity. DOI: 10.5901/ajis.2014.v3n7p146

Establishing a sediment budget for a small agricultural catchment in southern Brazil, to support the development of effective sediment management strategies

Summary The rapid expansion of agriculture in Brazil has increased erosion rates and sediment yields, causing many negative environmental and economic impacts, both on- and off-site. However, to date, very few catchment-scale sediment budget investigations have been carried out in Brazil. Given the need to reduce the negative off-site impacts of increasing agricultural activity, there is an important need for such investigations in order to inform the development of effective sediment management strategies. Against this background, 137Cs measurements have been combined with measurements of sediment yield and fingerprinting the source of the fine sediment output, to establish a provisional sediment budget for a small (1.19 km2) agricultural catchment in southern Brazil. The catchment is located in an area of steep highly erodible basaltic terrain, which has been intensively cultivated with tobacco. An ongoing monitoring programme provided information on the sediment yield from the catchment and existing suspended sediment source fingerprinting investigations provided information on the main sediment sources contributing to the sediment load at the catchment outlet. 137Cs measurements have been used to estimate medium-term erosion and deposition rates along 17 transects across the cultivated slopes and to quantify sedimentation rates within valley floor sediment sinks. These data have been used to estimate sediment redistribution rates within the cultivated areas of the study catchment and sediment accumulation in the valley floor sinks. The information provided by the three primary data sources has been integrated to establish the sediment budget for the catchment over the past 57 years. The individual terms of the budget necessarily involve much uncertainty, but its closure adds confidence to the final result. The budget calculations indicate that the study catchment has a sediment delivery ratio of ∼15%. The implications of the key features of the budget for developing effective sediment management strategies are discussed.

Root and soil carbon distribution at shoulderslope and footslope positions of temperate toposequences cropped to winter wheat

Crop root residues are an important source of soil organic carbon (SOC) in arable systems. However, the spatial distribution of root biomass in arable systems remains largely unknown. In this study, we determined the spatial distribution of macro-root and shoot biomass of winter wheat at shoulderslope and footslope positions from four cultivated slopes within an arable field in western Denmark. In addition, soils from the shoulderslope and footslope positions of four slopes were characterized for physical and chemical properties. Root biomass dry matter (DM) was marginally higher (P=0.06) at footslope (1.2Mg DM ha-1) than at shoulderslope positions (0.9Mg DM ha−1), in particular in the subsoil. Likewise shoot biomass was higher (P=0.03) at footslope (10.3Mg DM ha−1) compared to shoulderslope (7.1Mg DM ha−1) positions. Soil bulk density increased with depth at shoulderslope positions, but was more variable with depth at footslope positions. Root C was significantly correlated with SOC in shoulderslope soils (r=0.98), but not in footslope soils. We conclude that, at shoulderslope positions, SOC originated mainly from root residues whereas at footslope positions, SOC was derived from both root residues and likely soil redistribution processes. Management practices that increase C input at shoulderslope positions potentially enhance soil carbon storage and increase crop productivity, which would probably not be the case for C rich footslope soils. These findings imply that models used to simulate or predict C dynamics and crop productivity should consider topography-controlled variations in root C input and SOC redistribution as well as their effects on soil properties, root growth and crop productivity.

基于斑块评价的三峡库区腹地坡耕地优化调控方法与案例研究

The center of the Three Gorges Reservoir area is an ecologically sensitive, economically poorest, and environmentally fragile region,and hence become a research hotspot for many researchers. There is a large amount of cultivated slope land( part of them being abandoned by local farmer) in the region and it is very difficult and sometimes impossible to return the lands with gradient 25° to forests. So,it is necessary to explore the optimization control theory and methods for the slop land with different characteristics in this region. Cultivated slope land optimization should consider the demands of local people' s production and living,and it is also a selection process of the combined efforts of natural resources,geographical accessibility and socio-economic conditions. This paper suggested that the control and optimization scheme should not only combine the spatial distribution pattern and the ecological functions of cultivated slope land,but also consider the current distribution and future trends of sloping farmland. In addition,this paper promoted six principles about how to control and optimize thecultivated slope land,plus the evaluation methods integrating the spatial patternsuitability to quantitatively assess farmers demand pressures. By applying the principles and evaluation,this paper chose Caotangxi watershed,a typical watershed in thecenter of the Three Gorges reservoir area,as a case study. According to the characteristics of the watershed three indices were selected to evaluate the suitability of the system,namely,the accessibility,the ecological functions and the feasibility of changing slope land into terrace. The accessibility means the distance from the settlements roads to the land; the ecological function means the land degradation( the soil erosion) and the distance from water and the large forest patches( that is the distance away from the rivers and ecological sensitive area);while the feasibility from slope land to terrace means the size of the farmland patches,aspect and the slope gradient At the same time,the pressure index of cultivated land and supplementary capability of orchards to farmer's demand were selected as evaluation indexes of the quantity regulation system. Accordingly,the cultivated slope land of the Caotangxi watershed were divided into four types,namely,the optimization utilization type,the key consolidation type,the type of gradually returning( farmland to forest) and the type of preferentially returning,which accounted for 30. 5%,32. 9%,29. 7% and30. 5% respectively. Finally,at the premise of reducing steep inappropriate cultivated land and soil erosion,this paper suggested four returning scenarios without increasing the pressure of cultivated land,based on the distribution of abandoned land of local farmers. The rational and validity were verified according to the indices for these scenarios. The result of this study provides a theoretical basis for the current cultivated slope land optimization as well as a certain guidance to the cultivated slope land regulation in the Three Gorges Reservoir area.

Recommendations for riparian buffer widths based on field surveys of erosion processes on steep cultivated slopes

Results of field surveys are used to build knowledge about erosion processes occurring on steep cultivated slopes next to watercourses, and to propose conservation measures with an emphasis on widths for riparian buffer strips. The surveys were conducted on a 108-km2 watershed in Portneuf region, Québec, Canada. Using a handheld global positioning system (GPS), measuring tapes, a 0.5-m resolution satellite image and a 1-m resolution Digital Terrain Model (DTM), 12 erosion-prone areas, totalling 53 ha, located close to river banks were surveyed during four days of the rainy and snowmelt period of April–May 2012. As a result, 328 erosion features were identified and classified into 10 categories. Predominant erosion features included rills, ephemeral gullies and sheet erosion (70% of all features observed). Rills and smaller gullies had lengths of 0.5–160 m, depths of 5–55 cm, and breadths of 5–130 cm. Most erosion features (n = 194) occurred on hillslopes > 8% and had lengths of 10–60 m. At present, most riparian buffer strips in the surveyed field are 1–3 m wide, which is the minimum dimension required by the provincial policy that regulates vegetated filters. In most places surveyed, ephemeral gullying on steep slopes simply extends through the thin 1–3 m buffer strip to easily discharge sediments and pollutants into flowing streams. Based on the local slopes assessed, it is proposed herein to convert these steep cultivated hillslopes into riparian buffer strips of 10–60 m, so that vegetated strips effectively act as boundaries between watercourses and damaging uphill erosion processes, which are sources of sedimentation and, in all likelihood, eutrophication.

Soil Organic Carbon Stock and Distribution in Cultivated Land Converted to Grassland in a Subtropical Region of China

Land-use change from one type to another affects soil carbon (C) stocks which is associated with fluxes of CO2 to the atmosphere. The 10-years converted land selected from previously cultivated land in hilly areas of Sichuan, China was studied to understand the effects of land-use conversion on soil organic casrbon (SOC) sequestration under landscape position influences in a subtropical region of China. The SOC concentrations of the surface soil were greater (P\0.001) for converted soils than those for cultivated soils but lower (P\0.001) than those for original uncultivated soils. The SOC inventories (1.90–1.95 kg m-2) in the 0–15 cm surface soils were similar among upper, middle, and lower slope positions on the converted land, while the SOC inventories (1.41–1.65 kg m-2) in this soil layer tended to increase from upper to lower slope positions on the cultivated slope. On the whole, SOC inventories in this soil layer significantly increased following the conversion from cultivated land to grassland (P\0.001). In the upper slope positions, converted soils (especially in 0–5 cm surface soil) exhibited a higher C/N ratio than cultivated soils (P = 0.012), implying that strong SOC sequestration characteristics exist in upper slope areas where severe soil erosion occurred before land conversion. It is suggested that landscape position impacts on the SOC spatial distribution become insignificant after the conversion of cultivated land to grassland, which is conducive to the immobilization of organic C. We speculate that the conversion of cultivated land to grassland would markedly increase SOC stocks in soil and would especially improve the potential for SOC sequestration in the surface soil over a moderate period of time (10 years).

Soil Surface Roughness Effects on Infiltration Process of a Cultivated Slopes on the Loess Plateau of China

Infiltration is the only way water enters soil on the cultivated slopes of the China’s Loess Plateau, so infiltration plays an important role in conserving soil moisture. The objective of this study was to investigate how a soil wetting front created by simulated rainfall migrated in soil with different types of surface roughness. The three types of soil surface treatments studied included surfaces of smooth, medium rough and rough soil. The results showed that, 1) compared with a smooth surface texture, medium rough and rough surface textures have a higher infiltration capacity; 2) the infiltration rate gradually decreases as the wetting front deepens and the rate tends stabilize over time. This change could be described by a logarithmic function; 3) at the early stage of rainfall, the wetting front of medium rough and rough surface textures varied greatly, while the variability of the wetting front decreases markedly after the infiltration rate stabilizes; 4) with increasing depth of the wetting front, the similarity between the wetting front and soil surface profile decreased significantly for the medium rough and rough surface textures. These results indicate that the process of infiltration on cultivated slopes on the Loess Plateau changed from a non-uniform pattern to a uniform pattern as time passed during a rainfall event. Overall, soils with rougher soil surfaces experienced a larger effect of roughness on the process of infiltration.

Difference between Organic Materials of Distinct Slope Soils in Hilly Area of Sichuan Province, China

Organic materials in soils mainly consist of alkanes, esters, aromatic compounds and plant secondary metabolites, but they are different from one another in material type and quantity, depending on the types of slopes. This paper conducts a comparitive study on soils from slopes along the Suining-Chongqing Railway. Preparing soil samples from the rocky slope, the cultivated and uncultivated slopes by using ultrasonic methods, we measured the organic materials with a chromatograph mass spectrometer (QP2100). The results show that the number and types of organic materials decrease from the cultivated slopes to uncultivated slopes and then to rocky slopes. No contaminant appears in artificial soils on rocky slopes, but it is found in natural soils. Hence, it can be concluded that the reconstruction of soils on engineering slopes is beneficial not only for ecological restoration, but also for the prevention of pollution.