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This study focuses on the collapsing gullies in tuffaceous sandstone area and investigates the slope direction and morphological characteristics of the main and branch gullies. Furthermore, we assess the structural characteristics of the rock joints within this area, including their strike, dip direction and dip angle. The results show that there are 405 collapsing gullies in the study area. The slope directions associated with collapsing gullies and the directions of the main gullies largely fall within the ranges of NE20°-NE90°, SE90°-SE160°, SW240°-SW270°, and NW270°-NW290°. The collapsing gullies include 1103 branch gullies in total, most of which have directions that fall within the ranges of NE20°-NE40°, NE50°-NE70°, NW280°-NW300°, and NW330°-NW350°. The joints in the bedrock are directional and regional, and they can be divided into two main groups. The number of southward dip directions is greater than the number of northward dip directions, and most of the measured dip angles are greater than 60°. The mean dip angle is greatest for joints with measured strike values of NW280°-NW290°, with a value of 85.2°. The development of collapse gullies is affected by both the slope direction and joints. The slope direction determines the direction of the main gullies, with a correlation coefficient of 0.809 (P

In southern China, collapsing gully erosion produces massive deposits of sediment on the plough layer of alluvial fan farmland, leading to reduced nutrients, increased erodibility, and even desertification. The aim of this study was to investigate soil erodibility (the factor K in the universal Soil Loss Equation, USLE) and physicochemical properties of the alluvial fans of the most severe collapsing gully erosion areas (Hubei, Jiangxi, Fujian, and Guangdong provinces) in southern China. The soils of the collapsing gully alluvial fans had a higher bulk density, but a lower total porosity, saturated water content, and silt and clay fractions than the control (CK) soils from the farmland without desertification. Soil quality gradually decreased from fan edge to fanhead. Significant decreases were found in soil pH, organic matter, cation exchange capacity, and total potassium, nitrogen, and phosphorus, as well as available nitrogen, phosphorus, and potassium, resulting in a gradual decrease in soil nutrients from the fanedge to the fanhead. Soil erodibility was greatest in the fanhead, and soil erodibility K values of the alluvial fans were 53.71%, 66.28%, 67.53%, and 71.68 % greater than that in those of the CK soils of Hubei, Jiangxi, Fujian, and Guangdong, respectively, indicating a significant correlation between the soil erodibility K values and physicochemical properties, particularly sand fraction and organic matter content. The results provide new insights into the relationship between soil physicochemical properties and erodibility of alluvial fans, and suggest that improving soil structure might increase soil fertility in the collapsing gully alluvial fan farmland.

The main goal of this research is to study the relationship between the soil suction stress and soil properties within four different soil profiles of collapsing gullies in the hilly granitic region of southern China. Large differences were found in the four soil layers between granite red soils, which are manifested in terms of soil bulk density, porosity, particle composition, clay minerals, micromorphology, organic matter, cation exchange capacity, permeability, oxide and hydraulics properties. The suction stress of the upper soils increases rapidly and almost linearly monotonously with the increase of matric suction, whereas C layers increases rapidly first, followed by a slow increase. The suction stress of the lower soils is significantly smaller than the upper soils under the same matric suction. These findings illustrate that the collapsing gully starts from the lower part of the granite red soil, and finally caused the gravity collapse in the upper soils, which is the main aspect that is different from the other types of soil erosion. Furthermore, suction stress has a very significant correlation with soil properties, with a positive correlation to the fine particle content, iron and aluminum oxide, and a negative correlation to coarse particles. In addition, suction stress can also be explained as being directly proportional to weathering degree. Our research provides a theoretical basis for the mass failures of the granite-derived red soil in southern China.

Permanent gullies are a serious type of soil erosion. A special type of permanent gully, called “Benggang” severly affects agricultural production in hilly areas. To reveal the influence of Benggang erosion on granitic soil restoration and fertility, we selected three stages (active, semi-stable and stable) of Benggang recovery in the subtropical granite hilly region, and corresponding soil samples were collected to analyze the spatial variation in the soil physical and chemical qualities in the early stage of recovery. The soil physical properties and nutrients were significantly different in the runoff direction of each Benggang gully. There were significant differences in soil chemical properties and no obvious differences in physical properties among the different Benggang recovery stages. The results of principal component analysis showed that the level of soil fertility in the different Benggang recovery stages, ranked from high to low, was as follows: stable, semi-stable and active. Benggang vegetation restoration was an important factor for soil fertility restoration. Benggang ecological restoration can significantly improve the physicochemical properties and fertility of the soil. However, the soil fertility in gully erosion areas in this study still needs to be improved.

Collapsing gullies are one of the most serious soil erosion problems in the tropical and subtropical areas of southern China. However, few studies have been performed on the relationship of soil Atterberg limits with soil profiles of the collapsing gullies. Soil Atterberg limits, which include plastic limit and liquid limit, have been proposed as indicators for soil vulnerability to degradation. Here, the soil Atterberg limits within different weathering profiles and their relationships with soil physicochemical properties were investigated by characterizing four collapsing gullies in four counties in the hilly granitic region of southern China. The results showed that with the fall of weathering degree, there was a sharp decrease in plastic limit, liquid limit, plasticity index, soil organic matter, cation exchange capacity and free iron oxide. Additionally, there was a gradual increase in liquidity index, a sharp increase in particle density and bulk density followed by a slight decline, a decrease in the finer soil particles, a noticeable decline in the clay contents, and a considerable increase in the gravel and sand contents. The plastic limit varied from 19.43 to 35.93 % in TC, 19.51 to 33.82 % in GX, 19.32 to 35.58 % in AX and 18.91 to 36.56 % in WH, while the liquid limit varied from 30.91 to 62.68 % in TC, 30.89 to 57.70 % in GX, 32.48 to 65.71 % in AX and 30.77 to 62.70 % in WH, respectively. The soil Atterberg limits in the sandy soil layers and detritus layers were lower than those in the surface layers and red soil layers, which results in higher vulnerability of the sandy soil layers and detritus layers to erosion and finally the formation of the collapsing gully. The regression analyses showed that soil Atterberg limits had significant and positive correlation with SOM, clay content, cationic exchange capacity and Fed, significant and negative correlation with sand content and no obvious correlation with other properties. The results of this study revealed that soil Atterberg limits are an informative indicator to reflect the weathering degree of different weathering profiles of the collapsing gullies in the hilly granitic region.

Collapsing gully erosion is a specific form of soil erosion types in the hilly granitic region of tropical and subtropical South China, and can result in extremely rapid water and soil loss. Knowledge of the soil physical and chemical properties of farmland influenced by collapsing gully erosion is important in understanding the development of soil quality. This study was conducted at the Wuli Watershed of the Tongcheng County, south of Hubei Province, China. The aim is to investigate soil physical and chemical properties of three soil layers (0–20, 20–40 and 40–60 cm) for two farmland types (paddy field and upland field) in three regions influenced by collapsing gully erosion. The three regions are described as follows: strongly influenced region (SIR), weakly influenced region (WIR) and non-influenced region (NIR). The results show that collapsing gully erosion significantly increased the soil gravel and sand content in paddy and upland fields, especially the surface soil in the SIR and WIR. In the 0–20 cm layer of the paddy field, the highest gravel content (250.94 g kg−1) was in the SIR and the lowest (78.67 g kg−1) was in the NIR, but in the upland filed, the surface soil (0–20 cm) of the SIR and the 40–60 cm soil layer for the NIR had the highest (177.13 g kg−1) and the lowest (59.96 g kg−1) values of gravel content, respectively. The distribution of gravel and sand decreased with depth in the three influenced regions, but silt and clay showed the inverse change. In the paddy field, the average of sand content decreased from 58.6 (in the SIR) to 49.0% (in the NIR), but the silt content was in a reverse order, increasing from 27.9 to 36.9%, and the average of the clay content of three regions showed no significant variation (P

As a special kind of soil erosion that severely deteriorates the qualities of soil in granite regions, collapsing gully is widely distributed in the tropical and subtropical areas of South China. In particular, collapsing-gully erosion produces a large amount of sediment deposited on the plough layer of alluvial fan farmland and causes increase of desertification, great reduction of nutrients and rapid enhancement of erodibility in the soil. This study was designed to evaluate the effects of different land uses on the soil physic-chemical properties and erodibility of collapsing-gully alluvial fan. Our results show that the physical properties of soil in alluvial fan were greatly improved with smaller bulk density, increased soil porosity, strengthened water holding capacity and a higher particulate matter content. The chemical properties of soil were also significantly improved, including pH, cation exchange capacity, and the contents of organic matter, total and available nitrogen, potassium and phosphorus. All the land uses were proved to improve the soil properties, especially in the tea garden, vegetable land and paddy field. The results of correlation analyses among the properties demonstrate that the physical and chemical properties were significantly correlated, indicating that improving the soil physical properties is an effective method to increase the soil nutrient in the farmland of collapsing-gully alluvial fan. In addition, the application of land uses included grass land, eucalyptus forest land, vegetable land, tea garden, sweet potato land, and paddy field reduced the erodibility of the soil compare to bare land. The erodibility K values of soils in grass land, eucalyptus forest land, vegetable land, tea garden, sweet potato land, and paddy field were 14.43, 16.97, 45.45, 33.12, 18.94, and 34.01% lower than those of bare land, respectively. The results of multiple linear regression analysis show that the soil erodibility had a significant correlation with the physic-chemical properties, especially the soil texture and the content of organic matter. In conclusion, our results demonstrate that different land use patterns are effective to improve the quality of the soil in collapsing-gully alluvial fan, including the improvements of the soil structure, nutrients and anti-erosion ability. Our findings provide important implications for the soil improvement in the farmland of collapsing-gully alluvial fan.

Collapsing gully erosion is the main important and specific soil erosion type in the red soil region of tropical and subtropical South China. Knowledge of the soil disintegration characteristics within different weathering profiles (surface layer, red soil layer, sandy soil layer and detritus layer) and its relationships with soil particle size distribution and soil properties is important in understanding the mechanism of the forming process and development of the collapsing gully. In this paper, we conducted an experiment on four collapsing gullies located four counties (Tongcheng County, Gan County, Anxi County and Wuhua County) in the hilly granitic region of southern China. The anti-disintegration ability of the different weathering profiles with two different moisture conditions (the air-dried condition and the natural state condition) were determined by the anti-disintegration index (Kc) and measured by the submerging test. The results show that the coarse particles are higher in the sandy soil layer and the detritus layer of collapsing gully than that in the surface layer and the red soil layer, but the finer particles show the inversed order. The Kc values reduce significantly from the surface layer to the detritus layer. In the surface layer and the red soil layer, the Kc values in the natural state condition are much higher than that in the air-dried condition. The results highlight that, the sandy soil layer and the detritus layer are easily to disintegrate compare with the surface layer and the red soil layer, and in the case of low soil water content, the soil in any layer of collapsing gully is easy to disintegrate. The regression equation shows a very significant and positive relationship between the Kc values and the < 0.002 mm particles contents and the SOM (soil organic matter) (p

Collapsing gully erosion is one of the most remarkable natural hazards in hilly granitic region of southern China. However, there have been few studies examining the changes of soil particle-size distribution (PSD) associated with soil profiles of the collapsing gullies. In recent years, the fractal method has become a new one to estimate soil structure. It has been proved to be a useful tool to examine soil properties and the relationships with other eco-environmental factors. To study the fractal dimension (D) of soil PSD in soils within different weathering profiles (surface layer, red soil layer, sandy soil layer and detritus layer) and its relationships with PSD and soil properties, we conducted an experiment on four collapsing gullies in four counties (Tongcheng County, Gan County, Anxi County and Wuhua County, labeled as TC, GX, AX and WH, respectively) in the hilly granitic region of southern China. The results showed that different weathering profiles exhibited a significant effect on soil physical–chemical properties and PSD. With the fall of weathering degree (from surface layer to detritus layer), as a result, SOM indicated sharp decrease, bulk density first increased sharply and then declined slightly, the finer soil particles (silt and clay) decreased, and especially the clay contents declined noticeably, whereas the gravel and sand contents increased considerably. D values varied from 2.883 to 2.597 of TC, 2.880 to 2.727 of GX, 2.921 to 2.644 of AX and 2.845 to 2.708 of WH, respectively, finer textures giving greater D values. The D values in the sandy soil layers and detritus layers were lower than those in the surface layers and red soil layers. The linear regression analyses showed that D was remarkable negatively correlated with gravel and sand content and positively correlated with clay contents, SOM. The second-degree polynomial equation was more adequate to describe the correlations between D and soil PSD. The results of this study revealed that fractal dimension can be used to characterize the soil grain-size characteristics and was regarded as an informative indicator for reflecting the weathering degree of different weathering profiles of the collapsing gullies in the hilly granitic region.

In order to test the efficacy of conservation tillage and optimized fertilization on reducing N and P runoff losses, a 4-year (2007–2011) runoff plot experiment was conducted in the Chaohu Lake region, East China. There were four treatments including: (1) conventional tillage (CT, basal fertilization without mulch), (2) conventional tillage with straw mulching (CTS), (3) optimized fertilization (OPF, split applications) and (4) no-tillage with straw mulching plus optimized fertilization (NTS + OPF). Results showed that CTS and NTS + OPF exhibited significant reduction of seasonal runoff and soil losses compared with CT (P

Collapsing gullies are among the most severe soil erosion problems in the tropical and subtropical areas of southern China. However, few studies have examined the relationship of soil particle size distribution (PSD) changes with land-use patterns in the alluvial fans of collapsing gullies. Recently, the fractal method has been applied to estimate soil structure and has proven to be an effective tool in analyzing soil properties and their relationships with other eco-environmental factors. In this study, the soil fractal dimension (D), physico-chemical properties and their relationship with different land-use patterns in alluvial fans were investigated in an experiment that involved seven collapsing gully areas in seven counties of southern China. Our results demonstrated that different land-use patterns of alluvial fans had a significant effect on soil physico-chemical properties. Compared to grasslands and woodlands, farmlands and orchards generally contained more fine soil particles (silt and clay) and fewer coarse particles, whereas significant differences were found in the fractal dimension of soil PSD in different land-use patterns. Specifically, the soil fractal dimension was lower in grasslands and higher in orchards relative to that of other land-use patterns. The average soil fractal dimension of grasslands had a value that was 0.08 lower than that of orchards. Bulk density was lower but porosity was higher in farmlands and orchards. Saturated moisture content was lower in woodlands and grasslands, but saturated hydraulic conductivity was higher in all four land-use patterns. Additionally, the fractal dimension had significant linear relationships with the silt, clay and sand contents and soil properties and exhibited a positive correlation with the clay (R2 = 0.976, P

Collapsing gully erosion is one of the most serious natural hazards in the hilly granitic region of south China. However, few studies have been performed on the relationship of soil Atterberg limits with soil profiles of the collapsing gullies. Soil Atterberg limits, which include plastic limit and liquid limit, have been proposed as indicators for soil vulnerability to degradation. Here, the soil Atterberg limits within different weathering profiles and their relationships with soil physico-chemical properties were investigated by characterizing four collapsing gullies in four counties (Tongcheng County, Gan County, Anxi County and Wuhua County, labeled as TC, GX, AX and WH, respectively) in the hilly granitic region of southern China. The results showed that with the fall of weathering degree (from surface layer to detritus layer), there was a sharp decrease in plastic limit, liquid limit, plasticity index, soil organic matter, cation exchange capacity and free iron oxide, a gradual increase in liquidity index, a sharp increase in particle density and bulk density followed by a slight decline, as well as a decrease in the finer soil particles (silt and clay), a noticeable decline in the clay contents, and a considerable increase in the gravel and sand contents. The plastic limit varied from 19.43 to 35.93 % in TC, 19.51 to 33.82 % in GX, 19.32 to 35.58 % in AX and 18.91 to 36.56 % in WH while the liquid limit varied from 30.91 to 62.68 % in TC, 30.89 to 57.70 % in GX, 32.48 to 65.71 % in AX and 30.77 to 62.70 % in WH, respectively. The soil Atterberg limits in the sandy soil layers and detritus layers were lower than those in the surface layers and red soil layers, leading to the loss of bottom soil layers, the collapse of upper soil layers and finally the occurrence of collapsing gully erosion. The regression equation showed that soil Atterberg limits had significant and positive correlation with SOM, clay content, CEC and Fed, significant and negative correlation with sand content and no obvious correlation with other properties. The results of this study revealed that soil Atterberg limits are an informative indicator to reflect the weathering degree of different weathering profiles of the collapsing gullies in the hilly granitic region.

Contour hedgerow agroforestry has been studied for soil erosion control and soil fertility improvement in subtropical China. However, below-ground competitive and complementary interactions between tree hedges and crops have received relatively little attention in the scientific literature. A field experiment was conducted to explore the effects of a leguminous shrub hedge, false indigo (Amorpha fruticosa) and a non-legume gramineous hedge, vetiver (Vetiveria zizanioides), on the growth of soybean (Glycine max). Pot experiments were also carried out to determine the effect of below-ground interactions on nitrogen uptake between two contour hedgerow agroforestry with a 15N isotope method and root partition, i.e., a sheet barrier, a mesh barrier and no barrier. The results showed that the relative disadvantage of intercropping, expressed as land equivalent ratio, were 0.96/0.97 for the A. fruticosa–soybean system and 0.99 for the vetiver–soybean system, based on the dry matter (DM) production and N acquisition. Both area-adjusted yield and N content of soybean were significantly decreased in two intercropping treatments compared to those in the sole soybean treatment. The DM production of soybean, for example, was decreased by 10% and 5% under A. fruticosa and vetiver, respectively, when compared to the sole soybean. The intercropping disadvantage was mainly due to interspecific competitive interaction. The result was proved by lower yields and biomasses adjacent to the hedgerows. The 15N-based estimates of N uptake, in the vetiver–soybean system, of soybean with mesh separation (6.11 mg pot−1) was lower than that (13.85 mg pot−1) with no root separation, for vetiver the higher 15N uptake was observed in no root separation (13.90 mg pot−1). In the A. fruticosa–soybean system, the lower 15N uptake of soybean (1.53 mg pot−1) and A. fruticosa (6.42 mg pot−1) were observed in no root separation. It is concluded that the growth of soybean was unexpectedly suppressed in two intercropping systems. The growth of A. fruticosa was clearly suppressed due to below-ground interactions, yet the growth of vetiver was improved to a great extent.

The Three Gorge Project (TGP) of China necessitates the resettlement of over 1 million population (mostly farmers) to more rugged and isolated areas than their original settlements. Soil erosion is a serious environmental and production problem in this area. To decrease the risk on environmental impacts, there is an increasing demand for sound, and readily applicable techniques for soil conservation planning in the Three Gorge Areas (TGA). The objectives of the study were to develop and validate a soil erosion-predicting model based on the revised Universal Soil Loss Equation (RUSLE) in a geographic information systems (GIS) environment. The use of GIS to develop conservation-oriented watershed management strategies in the Wangjiaqiao watershed is presented. Data used for the RUSLE were either determined or taken from published literature pertaining to the Wangjiaqiao watershed. In combination with IDRISI, GIS software (Eastman, R.J., 1997. IDRISI for Windows: User's guide (Version 2.0). Clark University, Graduate School of Geography, Worcester, MA, Chapters 4–17) was used to evaluate different agricultural management strategies in terms of predicted soil loss in the watershed. This model allowed for easy assessment of soil erosion hazards under different crop and land management options over the entire watershed. The study revealed that the annual average soil loss rate from relatively flat agricultural land was approximately 26 t/ha, whereas 52 t/ha was found on the cultivated sloping lands, which constitutes a large proportion of soil loss in the watershed. In the watershed, approximately 38 ha of agricultural land had slopes >47% (25°) and should be reforested or returned to pasture. Contour tillage (CT) and contour farming with a seasonal no-till ridge (CTN) were most effective in reducing soil loss rates. If CT and CTN were implemented, approximately 31% and 70%, respectively, of the areas with soil loss > T EP would be reduced to T EP . T EP is soil loss tolerance for economic planning and was set at ≤10 t/ha year. In addition to soil loss reduction, the CTN has the potential to increase crop yield. Soil erosion hazards may be alleviated in over 91% of the agricultural lands if combined conservation measures including terraces, CTN, CT, and crop rotations were implemented in the watershed. The results of the study indicate that the RUSLE-GIS model is a useful tool for resource management and soil conservation planning. This technology is readily transferable and accessible to other land managers and agronomists in the TGA.

The characteristics of Pb2+ adsorption on the surface of birnessites with different average oxidation states (AOS) of Mn, synthesized under acidic and alkali conditions, were investigated. The results indicated that the amount of adsorbed Pb2+ increased with the increase of Mn AOS in birnessites. The amount of Pb2+ adsorbed positively correlated with the amount of released Mn2+, H+, and K+ (r = 0.9962 > 0.6614, n = 14, α = 0.01). The released Mn2+, H+, and K+ were derived mostly from the corresponding cations adsorbed on the vacant sites. The maximum amount of adsorbed Pb2+ increased with the increasing vacant cation sites, leading to an increase of the total amount of released Mn2+, H+, and K+, and the increased likelihood for two Pb2+ adsorbed in the region of one side of a vacant site.