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Topography is a critical factor that determines the characteristics of regional soil formation. Small-scale topographic changes are referred to microtopographies. In hilly mountainous regions, the redistribution of water and soil materials caused by microtopography is the main factor affecting the spatial heterogeneity of soil and the utilization of land resources. In this study, the influence of microtopography on pedogenesis was investigated using soil samples formed from mudstones with lacustrine facies deposition in the middle of the Sichuan Basin. Soil profiles were sampled along the slopes at the summit, shoulder, backslope, footslope, and toeslope positions. The morphological, physicochemical, and geochemical attributes of profiles were analyzed. The results showed that from the summit to the toeslope, soil thickness increased significantly and profile configuration changed from A–C to A–B–C. The total contents of Ca and Na decreased at the summit, backslope, and footslope, while the total contents of Al, Fe and Mg showed an opposite trend. On the summit and shoulder of the hillslope, weathered materials were transported away by gravity and surface erosion, exposing new rocks. As a result, soil development in these areas was relatively weak. In flat areas such as the footslope and toeslope with sufficient water conditions, the addition of weathered components and the prolonged contact between water, soil, and sediment led to further chemical weathering, resulting in highly developed characteristics. Microtopography may influence physicochemical properties, chemical weathering, and redistribution of water and materials, causing variations in pedogenic characteristics at different slope positions. [ABSTRACT FROM AUTHOR]

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]

The topography is a critical factor that determines the characteristics of regional soil formation. Small-scale topographic changes are defined as microtopographies. As a characteristic topographic condition in hilly mountainous regions, the redistribution of water and soil materials caused by microtopography is the main factor affecting the spatial heterogeneity of soil and the utilization of land resources. In this study, the influence of microtopography on pedogenesis was investigated using soil samples formed from mudstones with lacustrine facies deposition in the middle of the Sichuan Basin and developed into hill landforms by erosion of flowing water. Soil profiles were sampled along the slopes at the summit, shoulder, backslope, footslope, and toeslope positions. The morphological, physiochemical, and geochemical attributes of profiles were analysed. The results showed that the soil thickness increased significantly with changes in the soil profile configuration from the summit to the toeslope, and the profile configuration changed from A-C to A-B-C. The migration direction of Ca and Na at the summit, backslope, and footslope changed from enrichment to leaching, whereas that of Al, Fe, and Mg changed from leaching to enrichment. At the summit and shoulder of the hillslope, weathered materials are transported away by gravity and surface erosion, and new rocks are often exposed; therefore, the characteristics of soil development is relatively weak. However, in flat areas such as the footslope and toeslope with sufficient water conditions, the long-term contact between water, soil, and sediment leads to further chemical weathering, resulting in highly developed characteristics. Microtopography can affect physicochemical properties, chemical weathering, and redistribution of water and materials, resulting in differences in pedogenic characteristics at different slope positions. [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]

Hydrothermal treatment is popular in reforming biomass for light-emitting carbon dots for multiple applications, but until now no work has been done on the hydrothermal treatment of soil organic matter (SOM) for this transformation. This work translates the knowledge from the chemical synthesis of carbon dots to the monitoring of SOM by a facile hydrothermal treatment of soils without the usage of toxic chromate chemicals: hydrothermally treated soils produce light-emitting carbon dots whose light absorbance and photoluminescence (PL) was attempted to correlate with the content of SOM. The light absorbance of the carbon dots was found to be correlated very well (R2 around 0.7) with the SOM by Walkley-Black acid digestion, but the PL was poor in describing the SOM. The absorbance at 250 nm related to the π-π* transition was less affected by pH or but can be reduced by high concentration ammonia. While the absorbance at wavelengths longer than 300 nm was variable, but it still can be used for SOM quantification. The fundamental optical properties are explored via PL and PL excitation spectroscopies to provide an overview of the monitoring of SOM using facile light-absorbance method. [ABSTRACT FROM AUTHOR]

Uncertainty is a common feature of the present era. The plethora of uncertainties prompted frequent adjustment in the process of general land-use planning in China and, therefore, severely undermines the effectiveness of the entire land-use plan. Previous research mainly considered a macroanalysis of the causes, types, and treatments of the uncertainties, while research through case studies focusing on uncertainties are very rare. We analyzed the role of uncertainty in the general land-use planning schemes of the Jiangjin district of Chongqing Municipality, China, using the methods of comparative analysis and comprehensive induction. We discovered that the adjustments of the general land-use planning schemes consist of changes in land-use quota and layout, especially those of construction land. It can be found that the major internal uncertainties stem from the uncertainty of government action, base period, and technical specifications, while the major external uncertainties principally come from policy variation and economic development. The research results suggest that we need to further refine the land-use planning theory, optimize the land-use planning scheme, and strengthen the land-use planning legislation in order to decrease or eliminate the uncertainties so as to ensure the effectiveness of the general land-use plan. [ABSTRACT FROM AUTHOR]

Sloping croplands could result in soil erosion, which leads to non-point source pollution of the aquatic system in the Three Gorges Reservoir Region. Mulberry, a commonly grown cash plant in the region, is traditionally planted in contour hedgerows as an effective management practice to control soil erosion and non-point source pollution. In this field study, surface runoff and soil N and P loss on sloping land under crop-mulberry management were investigated. The experiments consisted of six crop-mulberry treatments: Control (no mulberry hedgerow with mustard-corn rotation); T1 (two-row contour mulberry with mustard-corn rotation); T2 (three-row contour mulberry with mustard-corn rotation); T3 (border mulberry and one-row contour mulberry with mustard-corn rotation); T4 (border mulberry with mustard-corn rotation); T5 (two-row longitudinal mulberry with mustard). The results indicated that crop-mulberry systems could effectively reduce surface runoff and soil and nutrient loss from arable slope land. Surface runoff from T1 (342.13 m hm), T2 (260.6 m hm), T3 (113.13 m hm), T4 (114 m hm), and T5 (129 m hm) was reduced by 15.4, 35.6, 72.0, 71.8, and 68.1 %, respectively, while soil loss from T1 (0.21 t hm), T2 (0.13 t hm), T3 (0.08 t hm), T4 (0.11 t hm), and T5 (0.12 t hm) was reduced by 52.3, 70.5, 81.8, 75.0, and 72.7 %, respectively, as compared with the control. Crop-mulberry ecosystem would also elevate soil N by 22.3 % and soil P by 57.4 %, and soil nutrient status was contour-line dependent. [ABSTRACT FROM AUTHOR]

The paddy fields and water storage facilities are seriously damaged by the coal mine subsiding in the hilly post-mining and subsidence-stable areas in China, which make the farmers there being suffered greatly from the lack of water for traditional rice cultivation and daily life. The purpose of this paper is to find a method to restore the damaged paddy fields, thereby promoting sustainable development of land resources, and alleviating the contradiction between people and land, as well as creating a more inhabitable environment. The research methodology included field experiments, cultivated observation, and field investigation. This paper selected the Songzao Mining Area as the research area, and focused on the restoration technologies of damaged paddy fields, through the following four different measures at three experimental fields: (1) Traditional repeated cattle plowing (CK); (2) Water retention agent with repeated cattle plowing (W&C); (3) Film without holes under tilth depth (FO); and (4) Film with holes under tilth depth (FW). At last, a contrastive analysis of the four measures was made according to the results of the experiments. The results show that the use of water retaining agent with repeated cattle plowing (W&C) can be the most appropriate method to restore the damaged paddy field in the hilly post-mining and subsidence-stable area in southwest China. Compared with the other three measures, its water productivity is the maximum (0.81 kg/m3), and the net income is the highest (1 403 $/hm2). What's more, it is simple, short time-consuming, and low cost, which is benefit to generalize the use of this restoration technology [ABSTRACT FROM AUTHOR]

Nitrate pollution in oxygenated karst aquifers is common due to nitrification and anthropogenic inputs. However, the shift of nitrogen sources influenced by enhanced rural tourism activities and land use changes are not well understood. In this study, hydrochemistry and dual nitrate isotopes of water samples from a rural karst basin in Chongqing, southwestern China were employed to investigate the nitrate fate and its decadal change during the periods from 2007–2008 and 2017–2019. The results showed that δ15N–NO 3 and δ18O–NO 3 values at the groundwater basin resurgence averaged 9 ± 3.4‰ and 2.5 ± 3.4‰, respectively, with a mean NO 3 − concentration of 19.7 ± 5.4 mg/L in 2017–2019, clearly exceeding natural background levels. The dual isotope results suggested that nitrification occurred at the sampled sites. From 2007–2008 to 2017–2019, the mean δ15N–NO 3 values from the primary sink point and the resurgence of the underground river water samples increased from −0.2 ± 2.1 to 11.2 ± 4.8‰, 4.2 ± 0.9 to 9.0 ± 3.4‰, respectively. A Bayesian mixing model in R (MixSIAR) based on the isotopes revealed that soil organic nitrogen, and manure and sewage proportions for the groundwater increased by 34% and 23%, respectively, while chemical fertilizer and atmospheric precipitation proportions decreased by 32% and 25%, respectively. These decadal changes resulted from reforestation practices and enhanced rural tourism activities in the basin, which were evidenced by the change of land use patterns. The elevated nitrogen load from the rapid development of rural tourism is likely to increase this contamination in the near future if the infrastructure cannot meet the demands. The results from this study could contribute to minimizing environmental health risks in drinking water when rural tourism activities are increasing. [Display omitted] • Nitrate fate and decadal shift in a typical karst aquifer system were studied. • Nitrification was dominant due to oxidic conditions. • Proportions of soil organic nitrogen and manure and sewage increased the most. • Elevated manure and sewage source was a result of rural tourism activities. • Rural tourism is likely to increase nitrate contamination in the near future. [ABSTRACT FROM AUTHOR]

An investigation was conducted to identify the characteristics of heavy metals in orange ecosystem in three areas in the Three Gorge Reservoir Region by using the modified Tessier sequential extraction procedure. The contents of Cu and Pb in different speciation fractions of the soils can be ordered as the Residual (F6)>Reducible (F4)>Oxidable (F5)>Water soluble (F1)>Carbonate (F3)>Exchangeable (F2), and the contents of Zn and Ni follow the order of the Residual (F6)>Oxidable (F5)>Reducible (F4)>Water soluble (F1)>Carbonate (F3)> Exchangeable (F2), and those of Cd follow the order of the Reducible (F4)>Oxidable (F5)>Exchangeable (F2)>Carbonate (F3)>Residual (F6)>Water soluble (F1). The concentrations of Cu in the different organs of oranges follow the increasing sequence of pulp>leaf>pericarp, those of Zn and Ni following the increasing sequence of leaf>pulp>pericarp, and those of Pb and Cd follow the increasing sequence of leaf>pericarp>pulp. Correlation degrees of different forms of same heavy metals in soils are according to the order of Cu>Zn>Cd>Pb>Ni. Correlation degrees of different heavy metals in same forms are according to the order that the forms of Reducible (F4), Oxidable (F5) and Residual (F6) are higher than the forms of Water soluble (F1), Exchangeable (F2) and Carbonate (F3). There are either positive or negative correlations between heavy metals in leaves and in pulp, while there are all positive correlations between heavy mentals in leaves and in pericarp. There are significant correlations between the concentrations of some heavy metals in leaves, pericarp or pulp, and those in speciation fractions in the soils. [ABSTRACT FROM AUTHOR]

Abstract Permanently flooded rice fields, widely distributed in south and south-west China, emit more CH4 than those drained in the winter crop season. For understanding CH4 emissions from permanently flooded rice fields and developing mitigation options, CH4 emission was measured year-round for 6 years from 1995 to 2000, in a permanently flooded rice field in Chongqing, China, where two cultivations with four treatments were prepared as follows: plain-cultivation, summer rice crop and winter fallow with floodwater layer annually (convention, Ch-FF), and winter upland crop under drained conditions (Ch-Wheat); ridge-cultivation without tillage, summer rice and winter fallow with floodwater layer annually (Ch-FFR), and winter upland crop under drained conditions (Ch-RW), respectively. On a 6-year average, compared to the treatments with floodwater in the winter crop season, the CH4 flux during rice-growing period from the treatments draining floodwater and planting winter crop was reduced by 42% in plain-cultivation and by 13% in ridge-cultivation (P < 0.05), respectively. The reduction of annual CH4 emission reached 68 and 48%, respectively. Compared to plain-cultivation (Ch-FF), ridge-cultivation (Ch-FFR) reduced annual CH4 emission by 33%, and which was mainly occurred in the winter crop season. These results indicate that draining floodwater layer for winter upland crop growth was not only able to prevent CH4 emission from permanently flooded paddy soils directly in the winter crop season, but also to reduce CH4 emission substantially during the following rice-growing period. As an alternative to the completely drainage of floodwater layer in the winter crop season, ridge-cultivation could also significantly mitigate CH4 emissions from permanently flooded rice fields. [ABSTRACT FROM AUTHOR]

• Particle characteristics of clay rock derived soils were analyzed. • A determination method of multi-mineral sand particles (MSPs) was established. • MSP content in shale-derived soils was higher than that in mudstone-derived soils. • Characteristics of clay rock soils lie on the process of diagenesis and pedogenesis. Multi-mineral sand particles (MSPs), commonly found in upland soils, can change the erosion properties, structure, moisture level, porosity, and permeability of soil; however, their effects are generally neglected in previous studies. In this study, we explored the morphology using scanning electron microscopy (SEM), particle size distribution (PSD), aggregation state, and mineralogy of soils derived from two types of clay rocks containing MSPs: shale and mudstone. The results showed that: (1) small lamellate bodies formed granules and blocks in a face-to-face or side-to-side manner and that the aggregation particles ranged from several to tens of microns in diameter, which increased gradually in a downslope direction; (2) the sand content in shale- and mudstone-derived soils decreased from 41.0% and 31.3%, respectively, on the summit to 19.6% and 18.4%, respectively, on the toeslope, whereas their clay content increased from 23.3% and 20.2% to 45.0% and 38.9%, respectively; (3) regarding the aggregation states of soil particles, the content of 0.25–2 mm MSPs in the shale- and mudstone-derived soils decreased from 62.9% and 45.2%, respectively, on the summit to 7.1% and 1.4%, respectively, on the toeslope, with averages of 42.3% and 20.8%, respectively. The content of 0.25–2 mm aggregates in the shale- and mudstone-derived soils increased from 9.1% and 6.2%, respectively, on the summit to 44.4% and 21.1%, respectively, on the toeslope, with averages of 21.5% and 14.2%, respectively; and (4) the mineralogy of the clay rock-derived soils and MSPs was generally dominated by illite, montmorillonite, vermiculite and calcite, which was similar to the mineralogy of the parent rocks. Therefore, a large amount of MSPs was found in clay rock-derived soils whose particle characteristics were determined by the environment of diagenesis and the physical weathering of pedogenesis. [ABSTRACT FROM AUTHOR]