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Sloping farmland has been one of the most important parts of cultivated land in the hills and mountains areas. It is a high demand to clarify the evolution characteristics and driving factors of the temporal and spatial pattern of sloping farmland, in order to rationally utilize resources and ecological functions. This study aims to reveal the spatial distribution characteristics and driving factors of sloping farmland in Chongqing City in southwest China. The aspects covered the temporal and spatial change characteristics, cold and hot spot patterns, as well as the driving factors of sloping farmland. Firstly, the local spatial autocorrelation (LISA) and cold hot spot were selected to determine the local spatial agglomeration characteristics of sloping farmland using the remote sensing data from 2000 to 2018. Secondly, the transfer of land use was obtained to overlay the land use data of each period. A transfer matrix of land use was then used to determine the transfer direction of sloping farmland. Finally, four dimensions were selected as the indicators, including the natural environment foundation, social living conditions, economic development level, as well as policy and institution. A geodetector was then used to determine the driving mechanism of sloping farmland change. The results showed that: 1) The area of sloping farmland decreased by 2.40% and 22 300 km2 in 2018, accounting for 59.35% of the cultivated land, compared with 2000. The average annual change dynamic degree of sloping farmland was greater than 1% in the six districts and counties (Yuzhong, Jiangbei, Jiangjin, Nan'an, Dadukou, and Shizhu). There was an outstandingly different change trend of sloping farmland areas in the different districts and counties. 2) Sloping farmland was significantly transferred from the forest land, grassland, paddy field, and construction land, where the transfer out and transfer in were generally balanced during the 18 years. The sloping farmland returning to the forest land was mainly concentrated in the regions of Shizhu, Wulong, Fengdu, and Yunyang counties in the Qin-Daba and Wuling Mountainous Areas. The area of sloping farmland showed a small decrease trend in the process of land use transfer. 3) There was significant heterogeneity of local spatial autocorrelation in the sloping farmland. The area of sloping farmland in most regions was in the state of high-high and low-low aggregation. The hot spots were concentrated in the northeast of the study area, whereas, the cold spots were distributed in the west and the main urban areas. 4) The factors in the forestry output value, per capita net income of rural residents, grain yield, rural employees, agriculture, forestry, and water expenditure greatly contributed to the slope farmland change, most of which were nonlinear and two-factor enhancement. Among them, the interactive driving factors with the greater explanatory power were the grain yield/slope (2005, 0.927), and per capita net income of rural residents/resident population (2018, 0.910). The leading factors of spatiotemporal characteristics were ranked as economic development, policy regulation, farmers' income, urban expansion, and socio-economic factors. A relatively less impact on the sloping farmland was found in the natural factors, including the altitude and rainfall. The findings can provide a scientific basis for the protection and pattern optimization of slope farmland in the mountainous and hilly areas of southwest China. [ABSTRACT FROM AUTHOR]

Cultivated land being an essential natural resource, has been increasingly occupied in the last 60 years with the acceleration of urbanization. It is necessary to be careful in land use, in order to ensure food security and human existence. In addition, the quality degradation of cultivated land has seriously threatened to food security due to the misuse of land. Slope farmland, one type of cultivated land, is widely distributed in the plateau and mountain areas in the central and western China. Scientific quality evaluation of slope farmland is closely related to local food security and ecological environment, further to implement national protection schemes, such as the “Trinity” of quantity, quality and ecology. However, there are some features of slope farmland, such as wide distribution, large slope, soil erosion, frequent seasonal drought, low soil quality, to make accurate evaluation difficult. The evaluation index and model are also lacking. Taking the slope farmland in Yunnan as a research area, this study aims to construct a quality evaluation system of slope farmland based on the framework of “element demand regulation”. The 30 m × 30 m grid (pixel) was selected as an evaluation unit for the comprehensive weight. The quality of slope farmland was evaluated quantitatively, together with its characteristics of spatial distribution. The results showed that: 1) Index system of the Minimum Data Set (MDS) in quality evaluation of slope farmland consisted of 14 indexes, including the effective thickness of soil layer, arable layer thickness, bulk density of soil, soil texture, pH value of soil, organic matter, effective phosphorus, available potassium, accumulated temperature (≥10 ℃), field regularity, contiguity, amount of rainfall, assurance rate of irrigation, and field slope. 2) Slope farmland Integrated Fertility Index (SIFI) was distributed between 0.36 and 0.81, with an average value of 0.59. Most evaluation units of SIFI was less than 0.6, showing a significant difference (P<0.05). The SIFI size relationship between five types of soil in slope farmland were ranked in order: Lateritic red earths, Red earths, Purplish soils, Yellow earths, Yellow-brown earths. SIFI increased with the elevation in the range of 0-1 000 m, while decreased larger than 1 000 m, indicating the variation of SIFI was related to the range of elevation. 3) The quality of slope farmland can be Grade 6, 5, 7 and 4, according the national standard. Specifically, the quality of slope farmland was relatively high Grade 4 and 5 at the southern border, central, southeast, and western Yunnan, whereas, northeast and northwest Yunnan indicated low Grade 6 and 7. The Lorenz curve of quality grade showed a pattern of “S-type” distribution in different regions, indicating a low grade in Yunnan province. This finding can provide a scientific basis to improve the quality evaluation system of slope land, thereby to efficiently implement geological regulation of slope farmland. [ABSTRACT FROM AUTHOR]

The change process of cultivated layer quality for slope farmland at plot scale is influenced by the interactive effects between erosive rainfall and artificial farming activities at different temporal and spatial scales. For a slope surface, there exists a successive erosion process of rainfall-runoff-infiltration and the consequence is first reflected in the quality of cultivated layer. Among the factors induced the erosion process at plot scale, terrain is an important factor because it could redistribute the ratio of rainfall--infiltration, which directly cause a different erosion process for an erosive rainfall and the different degradation degree during a rainy season and a growth season. Taking purple soil slope farmland as an example, the paper firstly analyzed the varying characteristics of cultivated layer quality of slope farmland, then quantitatively evaluated the effects of four terrain factors, altitude, slope angle, effective soil thickness and slope position on cultivated layer quality and their sensitivity of impact, adopted principal component analysis and evaluation model. The results indicated: 1) Such soil properties as cultivated layer thickness, soil organic matter and soil bulk density of cultivated layer were all within the suitable scope and soil nutrient properties were generally at middle & low levels. The variation coefficients of soil bulk density and soil total porosity showed weak variability (CV<10%), presenting 7.97% and 8.36% respectively and the other soil properties showed moderate variability. 2)Minimum data set for cultivated layer quality evaluation of purple soil slope farmland consisted of eight soil parameters, bulk density, penetration resistance, soil organic matter, clay content, cultivated layer thickness, soil shear strength, saturated water conductivity and bioavailable phosphorus. Soil physical properties are more important than chemical properties except soil organic matter for erosion control and crop growth of slope farmland. Evaluation based on the MDS revealed that the cultivated layer quality varied spatially over the slope, being 0.458 in the low part of the slope, 0.443 in the middle part of the slope and 0.417 in the upper part of the slope and the quality value of the lower slope was 3.39% and 9.83% higher than that of the middle slope and upper slope positions, respectively. 3) The factors affecting cultivated layer quality divided into four types: slope-angle impacted type, slope location impacted type, effective soil layer thickness impacted type and altitude impacted type and they accounted for 38.89%, 22.22%, 14.81% and 24.08% of the total samples taken from slope farmland respectively. The slope angle was the main determinant of cultivated layer quality because it could induce directly many ecological processes at plot scale. The slope angle and effective soil layer thickness could be modified by such soil and water conservation measures as terrace, biological ridge and soil improvement methods. But the slope location and altitude could not be modified easily only by selecting suitable crop system. 4) The quality of cultivated layer had positive correlation with its thickness and location in the slope, and negative correlation with altitude and slope angle. Sensitivity analysis revealed that the determinants were ranked in the order of altitude (-0.399) > location in the slope (0.192) > slope angle (-0.112) > effective soil layer thickness (0.110) based on their impact on cultivated lay quality. These results could provide some useful evaluation parameters and its regulating direction for cultivated layer quality, which contributed to the sustainable utilization of purple soil slope farmland. Furthermore, other samples of slope farmland should be studied in order to find out the critical values of MDS according to 2 functions of cultivated layer, erosion control and soil productivity. [ABSTRACT FROM AUTHOR]

The degradation of cultivated-layer quality of sloping farmland shows the agro-ecological process of cultivated-layer profile damaged, soil nutrient depletion and the regulation ability of crops-ecological environment declined or even completed loss on the slope scale by the combining effects of nature and human factors. In order to analyze the characteristics of soil degradation and main factors affecting degradation of cultivated layer for slope farmland in southern red soil hilly area, taking the cultivated-layer soil (0-20cm) of red soil from a small watershed as research object, we analyzed the degradation characteristics of cultivated-layer quality by cultivated-layer degradation index (CLDI), identified the dominant factors and main driving factors of cultivated-layer degradation by principal component analysis and regression analysis, analyzed the variation characteristics of soil property parameters of different degradation degrees of cultivated-layer quality, and defined the main obstacle factors and obstacle amount of the cultivated-layer quality by the obstacle factor diagnostic model for red soil sloping farmland. The results showed that the distribution area of cultivated-layer quality was mainly medium and in a mildly degraded level (accounting for 70.4% of the total samples), severely degraded samples was 11.1%, and the samples of non-degraded cultivated-layer accounting for 18.5% in red soil small watershed. The main nature driving factors leading to cultivated-layer quality degradation were rainfall, slope and soil mother material, meanwhile, agricultural input per unit of sloping farmland, tillage measure, total mechanical power per unit of sloping farmland and amount of fertilizer applied per unit of sloping farmland were the main human-driving factors. In comparison with the no degraded soil, the cultivated-layer soil properties parameters in red soil sloping farmland showed characteristics in different degradation degree. The cultivated-layer thickness was gradually thinned. The pH value first decreased significantly and then tended to be stable, and the cultivated layer of degraded level was 9.8%, and lower than that of non-degraded cultivated layer. The thinning rate of severely degraded cultivated layer was 8.9%, compared with that of non-degradation cultivated layer, which was related to the water erosion and farmer’s improper tillage methods in daily farming. The soil clay content and soil shear strength increased gradually with the deterioration of cultivated layer soil. The main obstacles of the cultivated layer quality of red soil sloping farmland with highly soil clay content, lowly pH value, thinning cultivated layer and lowly soil shear strength, and their average obstacle amount were 0.15, 0.14, 0.13 and 0.10, respectively. However, the average obstacle amount of other soil property parameters was relatively low. The obstacle amount of soil clay content, pH value and cultivated layer thickness significantly increased with the degradation degree intensifying. However, the obstacle amount of soil shear strength decreased gradually, and other soil property parameters did not change significantly, which indicated that moderately sub-soiling about 30-48 cm and reasonable fertilization were effective measures to improve the cultivated layer quality of red soil sloping farmland. Our results could provide a theoretical basis and some parameter support to scientifically understand the degradation characteristics of cultivated layer quality, define the effective measures to improve the cultivated-layer quality and construct rational cultivated-layers for red soil sloping farmland. [ABSTRACT FROM AUTHOR]

Slope farmland is an important part of cultivated land resources in hilly areas of China. Identifying the spatio-temporal distribution and evolution characteristics of slope farmland resources is of great significance for rational planning and utilization of slope farmland resources and water and soil ecological environment construction. In this paper, using the land use data for 7 time points from 1980 to 2015, based on GIS spatial analysis technology, dynamic degree model, kemel density estimation and landscape pattern index model, the spatio-temporal distribution pattern and evolution law of slope farmland in Yunnan for nearly 35 years were quantitatively analyzed. The results showed that: 1) the area of slope farmland in Yunnan was 472.55×104 hm², accounting for 69.79% of the cultivated land area, and the average slope was 15.62°. The relationship between the area ratio of slope farmland in different agricultural divisions was: Southwestern Yunnan>Northeastern Yunnan>Northwestern Yunnan>Southern fringe>Western Yunnan> Southeastern Yunnan>Central Yunnan, and the average slope size relationship was: Northwestern Yunnan>Southwestern Yunnan>Northeastern Yunnan>Western Yunnan> Southern fringe >Southeastern Yunnan > Central Yunnan. 2) In the past 35 years, significant dynamic transfers had occurred in slope farmland, forest land, grassland and paddy fields, but the process of transfer in and out was generally balanced, and the area of slope farmland has a slight increase trend during the process of land use transfer. 3) The slope of most slope farmland was more than 8°, and the proportion of slope farmland with slope >15° was 78.54%. The area of slope farmland with different slopes in the past 35 years had a dynamic process. It showed an increasing trend for the slope farmland area with slope <15°, while decreasing trend for the slope farmland area with slope >15°. The area of slope farmland with different slopes has the dynamic process of “decreased→increased→decreased” or “decreased→increased→ decreased→increased”, and the fluctuation degree of >25° slope farmland was the largest. 4) With the evolution of spatio-temporal distribution of slope farmland in the past 35 years, the distribution characteristics of kemel density value in slope farmland have changed, but the change range was small. The distribution of slope farmland in most areas was in low-density value, and the area of high-density value was the smallest. Slope farmland distribution clusters were represented by four significant distribution zones: the Lincang distribution zone, the Lincang-Xishuangbanna distribution zone, the Pu’er distribution zone and the Zhaotong distribution zone. 5) Among the eight types of land use, the landscape dominance of slope farmland was in the middle position, and the fragmentation characteristics of slope farmland were the most significant among all land use types. In the past 35 years, the degree of fragmentation of slope farmland landscape has decreased, and the degree of contiguous use of slope farmland has been strengthened. The research results can provide theoretical support for the rational planning and utilization of sloping farmland and soil and water ecological environment protection in Yunnan. [ABSTRACT FROM AUTHOR]

Slope farmland is an important part of cultivated land resources in hilly areas of China. Identifying the spatio-temporal distribution and evolution characteristics of slope farmland resources is of great significance for rational planning and utilization of slope farmland resources and water and soil ecological environment construction. In this paper, using the land use data for 7 time points from 1980 to 2015, based on GIS spatial analysis technology, dynamic degree model, kemel density estimation and landscape pattern index model, the spatio-temporal distribution pattern and evolution law of slope farmland in Yunnan for nearly 35 years were quantitatively analyzed. The results showed that: 1) the area of slope farmland in Yunnan was 472.55×104 hm2, accounting for 69.79% of the cultivated land area, and the average slope was 15.62°. The relationship between the area ratio of slope farmland in different agricultural divisions was: Southwestern Yunnan>Northeastern Yunnan>Northwestern Yunnan>Southern fringe>Western Yunnan> Southeastern Yunnan>Central Yunnan, and the average slope size relationship was: Northwestern Yunnan>Southwestern Yunnan>Northeastern Yunnan>Western Yunnan> Southern fringe >Southeastern Yunnan > Central Yunnan. 2) In the past 35 years, significant dynamic transfers had occurred in slope farmland, forest land, grassland and paddy fields, but the process of transfer in and out was generally balanced, and the area of slope farmland has a slight increase trend during the process of land use transfer. 3) The slope of most slope farmland was more than 8°, and the proportion of slope farmland with slope >15° was 78.54%. The area of slope farmland with different slopes in the past 35 years had a dynamic process. It showed an increasing trend for the slope farmland area with slope <15°, while decreasing trend for the slope farmland area with slope >15°. The area of slope farmland with different slopes has the dynamic process of “decreased→increased→decreased” or “decreased→increased→ decreased→increased”, and the fluctuation degree of >25° slope farmland was the largest. 4) With the evolution of spatio-temporal distribution of slope farmland in the past 35 years, the distribution characteristics of kemel density value in slope farmland have changed, but the change range was small. The distribution of slope farmland in most areas was in low-density value, and the area of high-density value was the smallest. Slope farmland distribution clusters were represented by four significant distribution zones: the Lincang distribution zone, the Lincang-Xishuangbanna distribution zone, the Pu’er distribution zone and the Zhaotong distribution zone. 5) Among the eight types of land use, the landscape dominance of slope farmland was in the middle position, and the fragmentation characteristics of slope farmland were the most significant among all land use types. In the past 35 years, the degree of fragmentation of slope farmland landscape has decreased, and the degree of contiguous use of slope farmland has been strengthened. The research results can provide theoretical support for the rational planning and utilization of sloping farmland and soil and water ecological environment protection in Yunnan. [ABSTRACT FROM AUTHOR]

Sloping farmland is an important part of cultivated land resources in Yunnan district. The evaluation of cultivated-layer soil quality and the appropriate range of parameters for sloping farmland are the basis for the development of reasonable plough layer. Based on the Soil Management Assessment Framework (SMAF), taking the cultivated-layer soil quality of sloping farmland in Yunnan province as the research object, this paper constructed a soil quality index evaluation model (CLSQI) for sloping farmland, and used the minimum data set (MDS) method to screen the evaluation indicators to evaluate the soil quality of sloping farmland in Yunnan, proposed the range of soil parameters for rational tillage in sloping farmland. The results showed that the minimum data set (MDS) of soil quality evaluation of sloping farmland in Yunnan region consisted of five indicators: pH value, total nitrogen, total porosity, soil shear strength and slope. The comparative analysis of AL-CLSQI (the cultivated-layer soil quality index calculated by all indicators) and AL-CLSQI (the cultivated-layer soil quality index calculated by the minimum data set index) showed that the evaluation accuracy of cultivated-layer soil quality based on MDS index was higher. In the primary selection index system, the weights of soil bulk density, total porosity, capillary porosity, shear strength, and slope grade were larger, while in the MDS index system, the weight of the slope and total nitrogen content was larger. The cultivated-layer soil quality index (CLSQI) of sloping cultivated land was between 0.39 and 0.84, the mean value was 0.59±0.11, and the coefficient of variation was 0.19. The cultivated-layer soil quality of sloping farmland was generally “medium”, and it was generally low. The CLSQI of the sloping farmland in different sampling areas was significantly different (P<0.05), and the size relationship was: Chuxiong＞Shuangbai＞Xuanwei＞Ninger＞Malong＞ Shilin. The 0～20 cm sampling depth sloping farmland CLSQI (mean value 0.59) was greater than >20 cm (mean value 0.56), and the CLSQI (mean value 0.61) of purple soil sloping farmland was larger than the red soil (mean value 0.54) (P<0.05), while the ridge and contour farming cultivation mode sloping farmland CLSQI was larger than that of the straight-plowing. The order of the CLSQI of the sloping farmland in different agricultural divisions was: Northeastern Yunnan＞Central Yunnan ＞Southwest Yunnan. According to the corresponding relationship between the soil quality of the cultivated-layer and the crop productivity and membership function, the cultivated-layer was in a relatively reasonable state when the soil quality grade of the sloping farmland was at a “higher” and above level (CLSQI≥0.6). The appropriate range of MDS indicators for cultivated-layer of sloping land in Yunnan were indicated as follows: the pH value of 5.58～7.82, the total nitrogen content of ≥1.37 g/kg, the total porosity content of ≥52.28%, the soil shear strength value of ≥5.19 kPa, and slope value of ≤11.79°. The suitable range of the above-mentioned cultivated-layer soil parameters can be used as the standard for the rational cultivated-layer diagnosis of sloping farmland in Yunnan. The research can provide theoretical basis and parameter support for the quality evaluation of ploughed plough layer and the construction of reasonable plough layer. [ABSTRACT FROM AUTHOR]

The minimum data set (MDS) is the least indicators collection that can reflect the information of total soil quality well, which can effectively improve the real-time characteristic and application of soil quality assessment. In order to characterize the soil quality of cultivated layer for slope farmland in southern red soil hilly area, the paper established the MDS for quality diagnosis of cultivated layer for slope farmland by cluster analysis (CA) and principal component analysis (PCA) respectively, and furthermore analyzed soil quality characteristics of cultivated layer adopting 3 different soil quality indices (SQI), including SQI-T (data from total soil indicators), SQI-CA (data from CA indicators) and SQI-PCA (data from PCA indicators). The results showed: 1) Soil quality of cultivated layer for slope farmland varied significantly among different red soil sites. The average cultivated layer thickness of 19.93±4.9 cm was in suitable level for crop growth, and the soil organic matter content of 17.43±8.71 g/kg and the soil total nitrogen content of 0.97±0.42 g/kg were in moderately barren level, but the soil nutrients of effective phosphorus of 26.1±22.22 mg/kg and available potassium of 155.46±88.35 mg/kg were rich for crop growth. The soil pH value of 5.34±0.77 was faintly acidic. 2) The MDS on soil quality diagnosis of cultivated layer for red soil slope farmland included such indicators as cultivated layer thickness, soil bulk density, soil penetration resistance, soil organic substance, pH value and soil available phosphorus. The assessment results of soil quality of cultivated layer based on 3 different data sets are distinct greatly, the variation range and the mean of soil quality index were showed as SQI-T > SQI-CA > SQI-PCA and the variation coefficients presented as SQI-T < SQI-CA < SQI-PCA. Furthermore, the relevance and Nash efficiency coefficient between SQI-CA and SQI-T were higher than that between SQI-PCA and SQI-T, and the relative deviation coefficient and the average relative error between SQI-CA and SQI-T were lower than that between SQI-PCA and SQI-T, which illustrated that MDS-CA (MDS based on CA) was more appropriate than MDS-PCA (MDS based on PCA) to reflect the information of the total data set (TDS) for soil quality assessment of cultivated layer for red soil slope farmland. 3) From the perspective of soil and water conservation, fertilizer conservation and yield-increasing potential, the suitability thresholds of those diagnostic parameters for cultivated layer of red soil slope farmland were indicated as follows: the cultivated layer thickness of ≥20.39 cm, the soil bulk density of 0.92-1.21 g/cm3, the soil penetration resistance of ≤1.21 kg/cm3, the soil organic matter content of ≥18.82 g/kg, the pH value of 5.04-5.38 and the effective phosphorus content of ≥28.83 mg/kg. Rational deep-loosening is one of the effective measures for reasonable cultivated layer construction. These results can provide some useful parameters not only for the soil quality recovery of the cultivated layer but also for the suitability regulation of the crop growth and the control of soil and water loss of slope farmland, which are also conducive to the sustainable utilization of the slope farmland resources in red soil hilly area. [ABSTRACT FROM AUTHOR]

Great decrease in water retention function of various artificial disturbed landform units (DLU) caused by urbanization activities, when compared with original Landform units (OLU). is the mam reason and factor that not only cause urban water and soil loss but also aggravate urban waterlogging under the certain rainfall and special designed drainage network capability. Field investigations, physical laboratory analyses and analytic hierarchy process composite method were performed comprehensively to analyze the impacts of various DLUs on water retention function of OLU. Results indicated that: 1) >2mm particle content for various DLU was over 45%, and <2 mm particle content of OLU was more than 92%; natural repose angle of soil-sock mixture (34°-38°) in DLU were all higher than OLU; uniformity coefficient and curvature coefficient changed between 11.05-41.30 and 0.32-3.15. in which uniformity- coefficient decreased by 4.51%-80.27% than OLU. 2) The soil bulk density- of various DLU showed the order as construction road (CR, 1.74 g/cm3) >slope greening belt (SGB. 1.54 g/cm3) > 1 year disturbed soil accumulation (DSA1, 1.48g/cm3) > 2 year disturbed soil accumulation (DSA2, 1.34 g/cm3) >3 year disturbed soil accumulation (DSA3, 1.31 g/cm3). which increased by 33.85%, 18.46%, 13.85%, 3.08%, 0.77%, respectively, compared with sloping land; and the soil total porosity, field capacity' and saturated water content presented the contrary trends. 3) Soil infiltration capacity' of various DLU were lower than that of OLU, the soil stable infiltration rate presenting the order as DSA3 (2.89 mm/min) > SGB (2.65 mm/min) > DSA2 (1.89 mm/min) > DSA1 (1.64 nun/nnn) > CR (0.45 mm/min), at same time, the soil stable infiltration rate of OLU ranged between 2.83 and 6.22 mm/min; the conversion from forest to new-DSA had greatest impact on regulating function for rainfall and urban flood, while conversion to CR was the lowest. 4) The soil total reservoir storage, usable storage and flood control storage in various DLU were lower than that in OLU. soil total reservoir storage showing the order as DSA3 > DSA2 > DSA1 > SGB > CR, which presented decreases of 1.08%, 2.27%, 5.63%, 15.41% and 21.96%. respectively, compared with sloping land (453.70 t/hm2); the conversion process from grass to CR caused the greatest damage to storing water and regulating the overhand flow. 5) The water retention functions in DLU were all obviously weaker than that m OLU. and CR was weakest (0.421) while NF was strongest (0.651), the water retention function was influenced by factors such as soil depth, particle-size distribution, soil porosity', soil organic matter content, soil bulk density, and soil permeability', so more attentions should be paid to urban surface water, forest and grassland occupied area and its spatial distribution, short-term disturbed soil accumulation should also be conducted by temporary greening measures at the same time during urbanization process. These results could provide scientific basis for the function recovering of urban soil and water conservation ecological sen-ices, which also help for constructmg urban green belts and alleviating flood waterlogging durmg the urbanization construction process. [ABSTRACT FROM AUTHOR]

Cultivated layer soil quality is highly sensitive to both soil erosion and artificial farming tillage in Purple Hilly Area. Soil erosion is a key factor that causes soil degradation and soil productivity instability of cultivated layer for slope farmland. Taking slope farmland in purple hilly area as an example, this paper has conducted cluster analysis on soil quality, permeability and cultivated layer type of slope farmland with different land productivity grades, and further discussed the effect of soil erosion on thickness of cultivated layer and the soil body configuration with reasonable cultivated layers of slope farmland. Results indicated that: (1) The soil quality of cultivated layer for purple soil slope farmland presented a moderate variability, the variation coefficients were 12.18% and 37.26% for the effective soil layer thickness (15-80 cm) and the cultivated layer thickness (15-25 cm), respectively, and the variation coefficient was 94.51% for the soil available phosphorus, indicating that the variability of soil physical properties was weaker than that of chemical properties. The cultivated layer configuration below the third grade of land productivity was almost full virtual or full real profile structures, and meanwhile, the production of slope farmland with the fifth grade of land productivity fell by about 50%. (2) There were significant (P<0.05) differences in soil physical properties, water-retention properties and tillage performances of cultivated layer at different slope position and different vertical depth of purple soil slope farmland, in which the soil bulk density showed upper slope > lower slope > middle slope, and soil shear strength showed upper slope > middle slope > lower slope, the soil stable infiltration rate showed the contrary order, and the soil penetration resistance was middle slope > upper slope > lower slope. The soil bulk density, shear strength and penetration resistance all presented bottom soil layer > subsoil layer > cultivated layer except soil infiltration; about 70% of the rain stored in 0-40 cm soil layer of slope farmland could be used by crops. (3) The average annual thinning of cultivated layer thickness varied between 1.04 and 3.04 mm for the moderate erosion degree of slope farmland. The reasonable cultivated layer of slope farmland could be established effectively by regulating such means as the minimum data set (MDS), which included soil layer thickness, cultivated layer thickness, soil bulk density, soil shear strength, soil organic matter and soil infiltration capacity for evaluating the cultivated layer soil quality of slope farmland, and moreover, the reasonable cultivated layer configuration overall should maintain the type of upper part loose and lower part tight, the cultivated layer thickness of 20-25 cm and the effective soil layer thickness of 50-60 cm. (4) Purple soil slope farmland could be divided into 4 kinds of cultivated layer types, whose obstacle cultivated layer was mainly manifested as the effective soil layer thickness restricted type (Class II), the cultivated layer thickness restricted type (Class III) and the soil nutrients restricted type (Class IV), accounting for 30%, 10% and 3% of total cultivated layer, respectively; so the regulating of reasonable cultivated layer of purple soil slope farmland should focus on effective soil layer thickness and cultivated layer thickness. These results can not only deepen the objective understanding of relationship between soil erosion and cultivated layer degradation but provide some essential parameters and technical supports for constructing reasonable cultivated layer of slope farmland in purple hilly area. [ABSTRACT FROM AUTHOR]

As a typical agroforestry system, bio-embankments formed by planting trees, shrubs or herbaceous in terrace ridge are effective farming measures for soil and water conservation in Purple Hilly Area. Bio-embankments not only could prevent soil erosion from slope farmland, but also greatly improve the soil quality and agricultural production conditions for cultivated land. The bio-embankment of slope farmland is often prone to collapse under heavy rainfall condition, which mainly attributed to the deformation and failure of slope caused by soil drying-wetting effect during the continuous raininginfiltration- evaporating process. Soil shear strength is one of the important determinants for slope stability of bio-embankments, which mainly influenced by soil structure, soil particle morphology and soil moisture content. The soil moisture of bio-embankments is often constantly changing along with the drying-wetting-drying circulation under a single rainfall condition, which would greatly weaken stability of bio-embankments. Recently, soil shear strength mainly focused on indoor simulation experiment conducted under such single factor as soil water content, soil bulk density, root system, soil particle composition, and some multi-factor combination experiments were also carried out. However, the changing characteristics of soil content and soil shear strength under drying-wetting-drying circulations caused by a natural raining and evaporating effect is unclear. The study mainly discussed the following facts as: 1) the variation trend of soil moisture for different bio-embankment layers under three-types natural rainfall condition; 2) the effects of different bio-embankment types on soil moisture variation; 3) the response characteristics of soil cohesion and soil internal friction angle of different bio-embankments on wetting-drying effect of rainfall and evaporation. Taking the bio-embankments with mulberry (SS) and zanthoxylum (HJ) planted in terrace ridge of slope farmland in purple hilly area of Southwest University, Chongqing as objects and bio-embankment with natural grass as control (CK), the paper systematically analyzed the attenuation and recovery effect of soil moisture and soil shear strength of bio-embankments under drying-wetting condition of different natural rainfall. The method of field and laboratory tests were conducted to observe soil moisture, soil cohesion, soil internal friction angle and root characters before and after different natural rainfall intensity such as light rain (0.64 mm/h), heavy rain (1.37 mm/h) and rainstorm (3.46 mm/h) from the field experiments were carried out from June to September 2014. The results indicated that: 1) The soil moisture of bio-embankments under drying-wetting condition presented a variation trend as sharp increase—sharp decrease—fluctuation stable, of which the changes amplitude and interaction depth increased with increasing rainfall intensity. The soil moisture showed obvious change in soil layer of 0-20 cm under light rain (0.64 mm/h), and varied obviously in soil layer of 0-30 cm under heavy rain (2.37 mm/h) and rainstorm (3.46 mm/h), which tended to be stable in 5h,7h, 9th day after natural rainfall stopped, respectively. 2) Both the soil cohesive strength and soil internal friction angle of bio-embankments showed a change trend as decaying sharply—stabilizing relatively—recovering gradually under the condition of drying-wetting. The soil cohesion strength and soil internal friction angle of bio-embankments were enhanced in 9th day after light rain, of which the enhancement showed a decreasing trend with increasing soil depth. Compared with the state before the rain, the soil cohesion strength of HJ, SS and CK increased by 2.46%, 2.95% and 0.66% respectively; meanwhile, their internal friction angle increased by 2.40%, 3.17%, and 1.19%, respectively. 3) The soil cohesion and soil internal friction angle decreased in 9th day after rainstorm compared with the original state before rain. Bio-embankments with mulberry and zanthoxylum could significantly weaken the deterioration effect of drying-wetting on soil shearing strength, and the effect of mulberry measures was better than the other two. Compared with CK, the soil cohesion degradation rates of HJ and SS bio-bio-embankments decreased by 44.03% and 65.05%, respectively, and the degradation rates of soil internal friction angle of HJ and SS bio-embankments decreased by 42.47% and 45.70%, respectively. The research results could provide some technical supports for design of bio-embankment design and soil and water utilization of cultivated-layer for slope farmland in purple hilly area. [ABSTRACT FROM AUTHOR]

Various engineering accumulations, caused by all man-made activities during mining process, have resulted in serious artificial soil and water loss in the coal mine area because of great difference in material composition, slope structure and runoff and sediment characteristics from original landforms, which would make great potential risk for the mining safety production and the surrounding areas. Recently, researches begin to focus on artificial soil and water loss in project areas, however, mechanism of runoff erosion on engineering accumulation slopes is still unclear, especially hydrodynamic characteristics in the process of runoff erosion needs further study. Taking typical coal mine engineering accumulation as example, soil test method and field scouring experiment were conducted to study the runoff erosion characteristics and critical hydrodynamic conditions of engineering accumulation slopes in the coal mine area. In this paper, some physical properties, hydraulic properties and runoff erosion process on slopes of engineering accumulations with different producing sources were all comparatively studied. Field scouring experiments were carried out from July to August 2013 at the Soil Erosion Experiment Site for production and construction projects in Southwest University, Chongqing. The field scouring experiments contained 5 flow discharges (i.e. 10, 15, 20, 25 and 30 L/min) and 4 slope gradients (i.e. 25°, 30°, 35° and 40°). The paper mainly studied the hydrodynamic characteristics of engineering accumulation slopes in order to reveal the characteristics of runoff and sediment yield and soil erosion rate, and to analyze the relationship between soil erosion and critical hydrodynamic conditions and the critical slope gradient under different flow discharges. The results indicated that: 1) During runoff erosion process, both flow velocity, flow shear stress and runoff power of engineering accumulation slopes exhibited different degrees of fluctuation, showing a range of 0.187-0.526 m/s, 24.336-126.542 Pa and 2.763-46.861 N/(m·s), respectively, however, resistance coefficient existed a fluctuation from weak to strong in the range of 2.236-19.337. 2) Both runoff yield rate and sediment production rate of engineering accumulation slopes exhibited a trend of first increase and then stability during runoff erosion process except for the 10 L/min flow discharge. The runoff yield rate tended to 0.5, 3.0, 3.8, 6.3 and 9.0 L/min, respectively, under different flow discharges (10 to 30 L/min), however the sediment yiled rate varied between 0 and 27.51 kg/min and the soil detachment rate changed between 9.570 and 4616.064 g/(m2·min). 3) There were great difference in critical flow shear stress and critical runoff power among engineering accumulation slopes with different slope gradients. At sheet erosion stage, both the critical flow shear stress and critical runoff power of 30° engineering accumulation were the minimum, whose values were 23.95 Pa and 1.76 N/(m·s), respectively; at rill erosion stage, however, the critical flow shear stress of 25° engineering accumulation was the minimum and the critical runoff power of 40° engineering accumulation was the least; and the soil erosion rate had a significant linear relationship with the flow shear stress and runoff power. 4) When flow discharge was 10-30 L/min, the critical slope gradients of engineering accumulations were 34.8°, 35°, 33.7°, 34° and 35.2°, respectively. These results not only could provide essential technical-parameters for predicting soil and water loss caused by mining production, but also would help to arrange some vegetation measures for soil and water ecological restoration of these engineering accumulations. [ABSTRACT FROM AUTHOR]

Engineering accumulation, a kind of loose soil-sock mixture consisted of soil, parent rock and stone caused by various artificial engineering during producing and constructing process, is the most serious erosion-landform in production and construction areas because it can greatly change the terrain, soil and vegetation conditions of original landform in a very short term, thereby causing great soil and water loss under a certain rainfall-runoff condition, and making more difficult for ecological restoration in these project areas. In order to revel the runoff erosion mechanism and its process for engineering accumulations with different slopes and soil-rock ratios, we carried out field scouring experiments from August to November 2012 at the Soil Erosion Experiment Site for production and construction projects in Southwestern University, Chongqing (29° 48' 50.2" N, 106° 24' 48.8 "E). The field scouring experiments were conducted under the simulated runoff conditions according to the regional rainstorm occurrence frequency with the 5, 10, 15, 20, 25 L/min for purple soil deposits and 5, 7.5, 10, 12.5, 15 L/min for yellow sand deposits, respectively. In the experiment, some physical properties, hydraulic properties and runoff erosion process on underlying surfaces of engineering accumulations with different producing sources and soil-rock ratios were all comparatively studied. The results indicated that material composition and infiltration capacity of the two loose engineering accumulations were remarkably different from original landform. The yellow sand deposit was dominated by ≤ 0.25 mm particles with particles variation coefficient as high as 1.2-2.0 times than its original landform and its stable infiltration rate was 1.70-4.07 times than original landforms, respectively; while purple soil deposit was well-distributed, its' variation coefficient of particles was 2.2 times than original landform and the stable infiltration rate was 7.02-11.59 times than original landforms. The experiments also showed that soil-rock ratio change could influence the slope infiltration performance for the two engineering accumulations and the effects of engineering construction on the purple soil deposits were more powerful than that of the yellow sand deposits. Some dynamic parameters on underlying surfaces of engineering accumulations increased with increasing flow discharge, in which flow velocity of yellow sand deposits ranged from 0.155 to 0.318 m/s, flow shear stress varied between 27.632 and 57.154 N/m2, and soil detachment rate changed from 0.337 to 77.071 g/(m2·s); while the flow velocity, flow shear stress and soil detachment rate of purple soil deposits were 0.184-0.281 m/s，35.525-53.600 N/m2 and 1.445-61.910 g/(m2·s), respectively. For rocky underlying surfaces, runoff yield rate had continuously waving variations within 9 min after runoff yielded. When flow discharge increased gradually from 5 to 25 L/min, the average runoff yield rate of rock underlying surface from yellow sand deposit increased by 510.38%, 531.96 % and that of purple soil deposit increased by 73.20% and 57.61%, respectively; for same conditions, the cumulative runoff of underlying surfaces showed the similar trend of partial soil deposits larger than rocky deposits, and that of yellow sand deposit higher than purple soil deposit. For rocky underlying surfaces, sediment yield rate presented continuously multi-peak multi-valleys. When flow discharge increased from 5 to 25 L/min gradually, the average sediment production rate of rock underlying surface from yellow sand deposit were 0.001, 0.03, 0.542 kg/(m2·min), respectively, while that of purple soil deposit were 0.0003, 0.012, 0.034 kg/(m2·min), respectively. The collapse on gully wall caused by gravity from underlying surfaces was an important cause for the fluctuating variations of the sediment yield rate. These results provide essential parameters and technical supports for predicting soil water loss caused by production and construction projects and for selecting vegetation measures for soil and water conservation in similar areas. [ABSTRACT FROM AUTHOR]