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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]

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]

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]