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It is of great significance to determine soil aggregate stability in predicting agricultural production conditions and soil erosion risk. However, the problem exposed in the process of evaluating soil aggregate stability cannot be ignored: Can the effects of different mechanisms on the degree of soil aggregate breakdown be distinguished by selecting ethanol and water as dispersion media? Based on this question, natural soils with a gradient in soil textures of silty loam to loamy clay were used as the test materials. Deionized water, ethanol and hexane were employed as soaking solutions to quantitatively analyze the extent to which the aggregates were dispersed in static disintegration experiments. The results suggested that the soil hydrophilicity (SH) of six soils with a texture gradient were >1 by comparing the aggregate breakdown index (ABI) of soils undergoing ethanol and hexane dispersion. This indicated that the hydrophilic group (-OH) contained in ethanol interacted with the hydrophilic surfaces of the soil particles. Therefore, the soil hydrophilicity (hydration) should be determined by comparing the ABI values undergoing hexane and water dispersion. From silty loam to loamy clay, the average contribution of hydration to aggregate fragmentation decreases, and the process of aggregate breakdown with different textures is characterized by size selectivity. When the soil aggregates were fragmented into 2–0.25 mm aggregate fractions, for silty loam and sandy clay loam, 0.002–0.02 mm and <0.002 mm particles were preferentially moved; for clay loam and loamy clay, >0.002 mm particles were preferentially moved. When the soil aggregates were fragmented into <0.25 mm aggregate fractions for soils with different textures, the 0.002–0.02 mm and <0.002 mm particles all exhibited preferential migration characteristics. This work provides an idea for improving the methods of aggregate stability measurements in the future. [ABSTRACT FROM AUTHOR]

Ridge tillage is one of the essential tillage methods in China. It affects the soil structure by altering the soil-water environment. With the rapid development of agricultural mechanization, the mechanized ridge tillage technology that combines modern mechanized agriculture with conservation tillage has become a pertinent agricultural production technology in the hilly regions. However, to date, the effects of mechanized ridge tillage on soil structure have garnered little attention. In this study, a field plot experiment involving the following four treatments: conventional tillage with rice and winter fallow (CK1), conventional tillage with rice-rape rotation (CK2), wide ridge tillage with rice-rape rotation (BT), and narrow ridge tillage with rice-rape rotation (RT) was conducted to study the effects of mechanized ridge tillage with rice-rape rotation on soil aggregate stability and soil porosity. The results indicated that mechanized ridge tillage could reduce the porosity of pores > 30 μm in diameter and increase the porosity of pores < 0.5 μm. Furthermore, mechanized ridge tillage could increase soil aggregate stability; the order of average mass diameter and geometric average diameter was RT > BT > CK2 > CK1. The BT and RT treatments could increase the agglomeration degree of the soil particles, which followed the order of RT > BT > CK2 > CK1. Therefore, mechanized ridge tillage with rice-rape rotation is effective in enhancing soil structure. [ABSTRACT FROM AUTHOR]

The orderly circulation of land can affect the structure of the agricultural industry, improve the level of agricultural industrialization, and realize the sustainable development of agriculture. Located in the inland of southwest China, Chongqing is the core area of China's Three Gorges Reservoir area, with obvious mountain characteristics. The characteristics and influencing factors of land transfer here can guide the reformation of land policy in other rural areas. Therefore, based on the survey data of 1015 mountain farmers in Chongqing, this paper employs a multi-class logistic model to analyze the above issues. The results show the following: (1) The phenomena of "zero rent" and "non-agreement" are widespread, and the spontaneous internal transfer among farmers is the main influencing factor. The decline in land value, the low degree of foreign investment, and the low average level of farmers' understanding of land transfer policies are quite different from the economically developed plains in the east. (2) Different directions of land circulation have different influencing factors. (3) The main factors are the total population of rural households, the proportion of non-agricultural household income, the age of the head of the household, the education level of the head of the household, the degree of land division, and the quality of land grades that affect land transfer and development in mountainous areas. Thus, improving the education level or technological training of farmers, establishing effective market mechanisms, and increasing income from non-agricultural employment can effectively promote land transfer. Moreover, age-oriented land policy is easier to implement. [ABSTRACT FROM AUTHOR]

The economic and social orientation of cultivated land in underdeveloped mountainous areas is obvious. A study of the spatial agglomeration characteristics of cultivated land quality can provide guidance for regional economic and social development. Taking Pengshui County, Chongqing, China as the study area, the spatial agglomeration characteristics of cultivated land quality indexes at county, township and village levels were analyzed by using the auto-correlation analysis method. The results showed that: (1) At different spatial scales, the cultivated land quality index showed spatial agglomeration characteristics. (2) Moran's I values of the cultivated land quality index at county, township and village level decreased successively, but three indexes still showed significant positive spatial correlation. (3) The spatial scale affects the spatial agglomeration of the cultivated land quality index, and its influence is physical, with a utilization and economic quality grade index from large to small. In underdeveloped mountainous areas, the spatial agglomeration characteristics of township scale and physical quality grade index are the most stable and significant, which can be used as the direct basis for zoning of cultivated land protection and site selection of rural residents' agglomeration points. [ABSTRACT FROM AUTHOR]

The rural settlements in poverty-stricken mountainous areas are the "living fossils" of an economic society with the characteristics of spatial dispersion and are slowly changing. Spatial agglomeration is the development direction of rural settlements. In-depth exploration of the spatial agglomeration characteristics and influencing factors of rural settlements in poverty-stricken mountainous areas is a way to provide a basis for rural settlement restructuring. We selected Pengshui County, a national poverty-stricken county in the southwestern mountainous area of China, as the research area. Spatial buffer and kernel density analysis were used to analyze the agglomeration characteristics of rural settlements and influencing factors. The results show that: (1) The rural settlements are small in scale and the space is evenly dispersed. 55.63% of the rural settlements' sizes are less than 1000 m2, 84.15% of the rural settlements' sizes are less than 2500 m2, and 92.81% of the rural settlements are within 200 m. (2) The elevation and slope of topographic factors have a significant agglomeration effect on rural settlements. However, the slope direction has no agglomeration effect. 85.41% of rural settlements (52.75% of rural settlements are gathered between 400 and 800 m above sea level) are gathered at an altitude of 1000 m or less, and 77.59% of rural settlements are gathered with a slope of 6~25°. Additionally, there are few rural settlements with a slope of 0~2°. Moreover, the distribution of residential areas has no agglomeration effect on rural settlements. (3) The cultivated land exerts the most significant effect on rural settlements followed by roads and water sources, while the role of urban land is weak. 99.48% of rural settlements are concentrated in the 100 m area of cultivated land. Therefore, in the poverty-stricken mountainous areas in the southwestern mountainous areas of China, convenient farming is the primary condition for production and living. Rural settlements are highly correlated with cultivated land. Rural settlements are scattered and concentrated with the scattered cultivated land. The rural settlements were leaded by the distribution of cultivated land. Less high-quality cultivated land with less slope were occupied or not by rural residential areas' people. [ABSTRACT FROM AUTHOR]