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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]

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]