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Although a number of studies have provided information on soil texture, soil classification, and depth to bedrock throughout China, few studies have combined this information, which is the basis for agricultural field management. A total of 81% of China's cultivated lands are distributed among the Middle–Lower Yangtze Plain (18.2%), arid and semiarid North China Plain (18.2%), Northeast Plain (17%), Huang-Huai-Hai Plain (16.1%), and Yunnan–Guizhou Plateau (11.6%). The Huang-Huai-Hai Plain has the highest density of agricultural land (58.5%) and the greatest depth to bedrock of cultivated land (243–402 m). The lowest cultivated depth to bedrock (4–84 m) is concentrated in the Sichuan Basin and its surrounding regions. The main cultivated soil types are Anthrosols, Fluvisols, Cambisols, Phaeozems, Luvisols, Kastanozems, Leptosols, and Acrisols, under the main topsoil texture classes of loam, clay loam, silty clay loam, silt loam, sandy loam, and clay. The Fluvisols had the largest depth to bedrock (156 m) on the Middle–Lower Yangtze Plain and Huang-Huai-Hai Plain, with the highest silt soil distributions but comparable lower sand contents. The Yunnan–Guizhou Plateau had the highest clay soil content. The cultivation under Kastanozems and Leptosols on the Qinghai–Tibet Plateau and in arid and semiarid North China and under Phaeozems on the Northeast Plain should be restricted and managed very cautiously facing erosion risk. The higher percentages of Anthrosols are on the Middle–Lower Yangtze Plain (37%), in Southern China (32%), and on the Yunnan–Guizhou Plateau (26%). The same cultivation aim (i.e., more crop 0production) has produced a similar range of properties over time among the soils developed on agricultural fields, which are classified as Anthrosols. However, various soil types can still be found in agroecosystems because of the variations in climate and topography. Our results highlight that the agriculture-based soil climate and topography shape the interaction of the soil development and not only the pedogenic history of the soil development under variations in the soil depth to bedrock but also the cultivation of distinct pedogenic features. This study provides cultivated soil information on the depth to bedrock, soil classification, and soil texture in China, as well as instructions for field strategies for sustainable agricultural development. [ABSTRACT FROM AUTHOR]

To accurately visualize the spatial distribution of heavy metal pollution and provide information that assists in remediating farmland soil, this study employed GIS technology and collected 0–20 cm-depth surface soil and shallow groundwater samples from farmland in Jianxin Village, Xiba Town, Wutongqiao City, Sichuan Province, China. The soil samples were decomposed using a high-temperature closed digestion method, and the contents of Cr, Cd, Pb, As, Cu and Zn were determined using ICP-MS. A geographic semi-variogram analysis was then conducted to delineate spatial variations in the heavy metal concentrations within the soil, and a spatial distribution map of heavy metals in the soil was drawn using ArcGIS10.2 software based on a GIS Kriging interpolation spatial structure analysis. The results showed that all heavy metal element concentrations exceeded the soil background values of Sichuan Province; the exceeded rates of Cr, Cd, and Zn were 100%. All Cd samples exceeded the soil baseline value, and the pollution accumulation of Cr, Cd, and Zn was determined as being serious. Through a comparison of cross-validation methods, a theoretical optimal semi-variogram model of six heavy metal elements was obtained. Indexes C0/(C0 + C) of Cd, Pb, As, Cu, and Zn were in the range of 48–75%, which showed that their contents related to structural factors, such as the soil parent material and topography, and also to non-structural factors such as human activities. The index C0/(C0 + C) of Cr was more than 75%, which indicates that its content is mainly related to non-structural factors and human activities. The spatial correlation followed the order of Cu > Cd > Pb > Zn > As > Cr. The vertical distribution of heavy metals was greatly affected by the soil physical properties: the Cu and Pb contents of sandy soil decreased at first and then increased with depth; the Cr, Zn, and As contents first increased and then decreased with depth; and the Cd contents decreased with depth. In clay soil, there was little change in the Cu content with depth; the Cd, Zn, Pb, and As contents first decreased and then increased with depth, and the Cr content increased first and then decreased with depth. These results show that visualizing the spatial distribution of heavy metal contamination using GIS technology is significant for providing information that can be used to remediate farmland soil. [ABSTRACT FROM AUTHOR]

[Display omitted] • We studied the effects of moisture content, slope angle, and clay contents on mass failure. • A self-designed hollow model was used. • Indoor hollow-flume experiments were conducted under the condition of surface runoff. • Soils with 5%, 7.5%, and 10% initial water content generate fatal mass failure. • Soil mass failure occurs when critical water and clay contents are reached. Soil mass failure disasters are among the most destructive disasters in mountainous areas worldwide, and they continue to receive significant attention in the literature. However, factors that influence soil mass failure in hollows have not been explored via experimental approaches. In this study, we conducted a series of indoor hollow–flume experiments to exhibit how the three factors, namely, initial moisture content, slope angle, and clay content, influence the collapse of soil mass under surface runoff conditions. Our findings revealed that the major processes causing soil mass failure were internal seepage erosion resulting from subsurface runoff, migration of fine particles, development of tension cracks, increase in pore water pressure, and decrease in cohesion. Fluctuations in pore water pressure were characterized by two main trends: (1) an abrupt rise under static liquefaction and (2) a decrease before failure due to dilatancy. The time required for soil mass failure first decreased and then increased with the increase in moisture content. The soil mass with an initial moisture content of ∼12.5% was more critical to the failure. In addition, the time required for soil mass failure decreased with increasing slope angle, revealing a slope angle of 40° to be more prone to failure. The buildup of pore water pressure was found to increase with clay content; soil with a clay content of ∼7.5% required the shortest amount of time to initiate slides. Thus, our results provide a thorough insight into the processes and factors involved in the initiation and development of soil mass failure in hollow areas, which can be used by public agencies to improve monitoring, early warning, and forecasting systems. Notably, our study can help identify risk-prone source areas, and sensors can be installed to monitor potential mass failure locations. [ABSTRACT FROM AUTHOR]

• Total methane emissions from paddy fields in China are 8.20 Tg. • CH 4 emissions from early, late and single cropping rice are 1.12, 2.86 and 4.23 Tg. • Southern rice fields contribute 92% towards total CH 4 emissions. • CH 4 emissions hotspots were in Sichuan Basin, Heilongjiang, South and central China. • Water management, temperature and soil clay significantly affect CH 4 emissions. Methane (CH 4) emissions from rice fields across China were estimated using the DNDC (DeNitrification-DeComposition) model. The results showed that the CH 4 emissions from Chinese rice fields in 2012 were estimated to be 8.20 Tg CH 4 yr−1 (ranging from 4.80 to 11.40 Tg CH 4 yr−1); the values from early, late, and single cropping rice were 1.12, 2.86, and 4.23 Tg CH 4 yr−1. Rice fields in AEZ (agricultural ecosystem zoning) 7 (southeastern China) and AEZ 6 (central and southwestern China) were the two major sources, accounting for 92% of the total CH 4 emissions in China. The CH 4 emissions in AEZ 7 mainly originated from double cropping rice fields, while single cropping rice fields dominated the CH 4 emissions in AEZ 6. The CH 4 emission hotspots were in the Sichuan Basin of AEZ 6B (southwestern China), AEZ 6A (central China, except for Henan Province), AEZ 7 (except parts of Fujian and Zhejiang Provinces), and Heilongjiang Province. At the national scale, water management (positive correlation), air temperature (positive correlation), and the soil clay content (negative correlation) were the three dominant factors controlling the CH 4 fluxes in paddy fields. These results provide an understanding of the spatial distribution of CH 4 emissions from paddy fields and will help the government formulate policies to control CH 4 emissions at a regional scale. [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]