Relationship between granitic soil particle-size distribution and shrinkage properties based on multifractal method

The mechanical properties of granitic residual soils vary with depth due to changes in soil type and heterogeneity caused by weathering.The purpose of this study was to relate the spatial variation of particle-size distribution(PSD)of granitic soils with soil shrinkage parameters using multifractal theory.The heterogeneity of PSD and pedogenic processes were depicted in detail by multifractal dimensions.The PSD generally increased with the increase of profile depth in accordance with the variation of single fractal dimension(D)ranging from 2.45 to 2.65.The shrinkage limit was greatly influenced by the multifractal dimension parameters,including information dimension(D1)and capacity dimension(D0)(Adjusted R2=0.998,P<0.01),and the maximum linear extensibility(κv)was determined by spectral width(?α)and bulk density,with the latter explaining 89%of the total variance ofκv(P<0.01).Soil shrinkage characteristic curve was fitted by the modified logistic model(R2>0.97,root sum of squares<0.1),and the water variation corresponding to the maximum change rate of linear extensibility was determined by the silt content(R2=0.81,P<0.01).Overall,the shrinkage of granitic soils was primarily influenced by PSD and soil compactness.

Changes of soil quality induced by different vegetation restoration in the collapsing gully erosion areas of southern China

Understanding the influence of collapsing gully management restoration on soil quality and function is essential to the protection of the regional ecological environment in the collapsing gully erosion area.The primary objective of this study was to construct soil quality index(SQI)to assess the influence of different vegetation restoration types on soil quality in collapsing gully restoration.The influence of five vegetation restoration types on soil properties was investigated by using a path analysis,a comprehensive soil quality index(SQI),and a general linear model(GLM).Vegetation restoration was shown to significantly increase the saturated hydraulic conductivity(Ks),mainly due to the effect of the physical parameters of bulk density,soil cohesion,and soil water content.Meanwhile,pH,Ks,soil organic matter(OM),and sand content were revealed as reasonable indicators to evaluate the influence of vegetation restoration on soil quality.Moreover,vegetation restoration was found to significantly improve the soil quality,with the highest SQI value for natural restoration mixed forest(NF),followed by replanted arboreal forest(RA)and replanted scrubland(RS),which were all significantly higher than the SQI value of the erosion area(EA)in the collapsing gully.Additionally,vegetation type explained the most substantial proportion of total variability(46.41%),and restoration time showed a positive correlation with SQI.The results of this study can provide a reference for the restoration and protection of the regional ecological environment in the collapsing gully area.

Dynamic study of infiltration rate for soils with varying degrees of degradation by water erosion

Ultisols,widely distributed in tropical and subtropical areas of south China,are suffering from serious water erosion,however,slope hydrological process for Ultisols under different erosional degradation levels in field condition has been scarcely investigated.Field rainfall simulation at two rainfall intensities (120 and 60 mm/h) were performed on pre-wetted Ultisols with four erosion degrees (non,moderate,severe and very-severe),and the hydrological processes of these soils were determined.The variation of soil infiltration was contributed by the interaction of erosion degree and rainfall intensity (p < 0.05).In most cases,time to incipient runoff,the decay coefficient,steady state infiltration rate,and their variability were larger at the high rainfall intensity,accelerating by the increasing erosion severity.Despite rainfall intensity,the infiltration process of Ultisols was also significantly influenced by mean weight diameter of aggregates at the field moisture content,soil organic carbon and particle size distribution (R2 > 30%,p < 0.05).The temporal erodibility of surface soil and soil detachment rate were significantly and negatively correlated with infiltration rate (r <-0.32,p < 0.05),but less significant correlation was observed between sediment concentration and infiltration rate for most soils,especially at the high rainfall intensity.The variation of surface texture and soil compactness generated by erosion degradation was the intrinsic predominant factors for the change of infiltration process of Ultisols.The obtained results will facilitate the understanding of hydrological process for degraded lands,and provide useful knowledge in managing crop irrigation and soil erosion.

Effects of transport distance and flow discharge of overland flow on destruction of Ultisol aggregates

The destruction of soil aggregates upon transport by overland flow may produce a significant effect on sediment transport capacity and general intensity of erosion. The particle size distribution of destructed soil aggregates has a close relation to the surface runoff and permeability of soils. The objective of this study is to quantify the effects of transport distance and flow discharge of overland flow on the destruction of aggregates of Ultisols in a 3.8 m long flume with a fixed bed. A series of experiments were carried out at a slope of 17.6%, including six transport distances （9-108 m） and eight discharges （0.4-1.2 L/s）. The results indicate that （1） the extent of the destruction of aggregates became weaker with the decrease in size over the same transport distances or at the same discharges; （2） the aggregates derived from Shale were rapidly abraded and had more serious destruction as compared to the aggregates from Quaternary red clay during the transport process, which was relevant to the stability difference of the two parent materials： （3） two stages of aggregate breakdown could be identified in terms of the coefficient c~ during transport, that is, the aggregates were rapidly abraded and became round and were predominantly broken down into smaller fragments at the first stage, while the smaller fragments and the round aggregates were weakly abraded with reduction in weight and their shape became regular; and （4） the extent of the destruction decreased with increasing discharge, which was due to the changes in the hydraulic properties （flow depth and friction factor） and in movement modes during the transport process. The analysis of the characteristics on aggregate destruction by overland flow can contribute to the development of soil erosion models.

Effect of joint structure and slope direction on the development of collapsing gully in tuffaceous sandstone area in South China

This study focuses on the collapsing gullies in tuffaceous sandstone area and investigates the slope di-rection 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<0.01). The branch gullies are mainly affected by joints, with a correlation coefficient of 0.876 (P<0.01). The joint structure also influences the degree of development of the collapsing gullies, and the average depth of the gullies that parallel the dominant joint orientation is significantly larger than that of gullies with other directions. Moreover, the average depth of the gullies associated with the dip angle of 85.2° measured relative to the joint strike is 6.89 m, which is significantly greater than that associated with lower dip angles. The dip angles of joints have an important effect on the infiltration of water, and high dip angles accelerate the erosion associated with collapsing gullies.

Soil organic carbon stock and fractional distribution across central-south China

The stock and stability of soil organic carbon(SOC)are critical to soil functions and global carbon cycle,but little quantitative information is available on the precise location and chemical components of SOC for soils across a wide range of climatic gradients.Here,a broad range of zonal soils were collected in forest land at topsoil(0-15 cm)and subsoil(15-30 cm)from temperate to tropical climatic gradient in central to south China.The stock and stability of SOC were determined in terms of aggregate and humic fractionation.SOC in bulk soils with a less significant geographic variation was comparably higher at Haplic Luvisoils in temperate regions(3637.61 g m^(−2))and Rhodi-Humic Ferrosols in tropical regions(3446.12 g m^(−2))than in the other experimental soils,but a consistent decreasing trend was observed along the soil profiles with the SOC stock was 1.11-1.97 times higher in the topsoil than in the subsoils.In addition,insoluble humin residue(HMr)as the dominant components of SOC ranged from 643.95 to 2696.90 g m^(−2) and decreased from temperate to tropical regions,which was consistent with the zonal variation of humic acids(HAs),but contrary to the zonal variation of fulvic acids(FAs)that fluctuated in a range of 39.67-389.55 g m^(−2) across the experimental sites.According to the results of partial correlation analysis,the variation of FAs stock was significantly attributed to soil pH,bulk density,iron and aluminum oxides,clay,and clay mineral content(|r|>0.61,p<0.05),while these soil physical properties showed a contradictory effects on HAs,iron-linked humin(HMi),clay-combined humin(HMc),and HMr.Moreover,the aggregate-associated carbon stock was mainly stored in macroaggregates(36.34-76.09%)for both SOC and its chemical components,especially in topsoils,and its zonal variation was associated with that of bulk soils.In general,the redundancy analysis(RDA)revealed that mean annual precipitation(MAP)accounted for 81.8%and 13.8%of the variance in SOC chemical and physical fractionation,respectively,while the corresponding contribution of mean annual temperature(MAT)was 1.5%and 34.7%.With the increase of MAT and MAP,the chemical stability of SOC decreased in the molecular structure,and the physical protection of SOC by aggregate exhibited a unimodal trend.The obtained results would facilitate the development of regional soil carbon prediction and land management against global warming.