Soil Fractal Dimension Research Articles

Relationship Between Salt Accumulation and Soil Structure Fractals in Cotton Fields in an Arid Inland Basin

The relationship between soil structure and salt accumulation is unclear; thus, experiments on salt accumulation under different soil structures were conducted in cotton fields in arid areas of northwest China. Thirty-nine sets of soil samples were collected from the 0 to 180 cm profile of three experimental areas. The total salt content of the soil extracts and the particle size distribution of the soil samples were determined using a JENCO TDS and a laser particle size analyzer, respectively, and the fractal dimension of the soil structure was obtained using fractal theory. Pearson’s correlation analysis and Tukey’s test (p < 0.01) were used to analyze the correlation between soil salinity, soil particle size distribution, and fractal dimensions in the three profiles. The results showed soil salinity accumulation was affected mutually by soil texture and soil structure, and soil salinity tended to accumulate in fine-grained soil. The soil fractal dimension (D) could indicate soil texture and quantify soil salinity content. When the sand content was more than 50%, there was a significant positive correlation between the soil fractal dimension and soil salinity (correlation coefficient R = 0.943). The results provide valuable insights into cotton production in arid areas.

Effects of different sand fixation plantations on soil properties in the Hunshandake Sandy Land, Eastern Inner Mongolia, China.

Planting forests is an effective way to improve desertification. In order to elucidate the impacts of different vegetation types on soil development and restoration of degraded lands, we compared the properties of soils at different depths in three plantation forests in the Hunsandak Sandy Land in the Chinese agro-pastoral ecotone (Ulmus pumila, Pinus sylvestris var. mongolica, and Populus simonii). The results show that all three plantation forests were able to significantly improve the soil properties, and they resulted in soil nutrient enrichment in the surface layer. As the soil depth increased, the soil became progressively poorer in nutrients, the fine particle content decreased, and the bulk density and water content increased. The orders of the fractal dimension characterization and soil improvement effects of the different tree species were as follows: U. pumila > P. sylvestris var. mongolica > P. simonii. Compared with the bare sand, the soil bulk density under the U. pumila plantation was 19% lower; the soil water content was 74% higher; the soil organic matter, total N, P, and K were 336%, 207%, 106%, and 31% higher; the available N, P, and K were 41%, 125%, and 21% higher; and the clay and silt contents were 498% and 387% higher, respectively. The ranges of the soil fractal dimension were 1.67-2.08 for the bare sandy land and 2.14-2.32 for the planted forests. The soil fractal dimension was strongly correlated with the soil physicochemical properties, especially with the soil nutrients and fine particle content, which exhibited highly significant correlations (p < 0.01), and the correlation coefficients were all greater than 0.8. Therefore, we believe that U. pumila is a suitable sand-fixing plant species in this area. In addition, the soil fractal dimension can be used as an important reference index for characterizing soil properties in sandy areas.

The Spatial Variation of Soil Structure Fractal Derived from Particle Size Distributions at the Basin Scale

The accurate characterization of soil structure is fundamental to groundwater science, environmental ecology, and Earth systems science. To address the challenge of quantifying the high spatial variability of large-scale soil structures, this study used a laser particle size analyzer to measure the distribution of soil particle size in 207 samples from ten profiles across the Daqing and Ziya River basins in the North China Plain. The quantified soil structure, expressed as soil fractal dimension D, was derived using monofractal theory. Various spatial analysis techniques, including Moran’s I index, correlation analysis heat maps, the Kolmogorov–Smirnov one-sample test, and geostatistical semivariogram function, were jointly applied to investigate the spatial variability of soil structural fractals across different depths in the piedmont plain–coastal areas of the two river basins. The results indicate the following: (1) Quantitative analysis confirms that under the influence of piedmont alluvial and fluvial dynamics, soil D values homogenize from the piedmont to the coastal areas, with decreasing particle size differences closer to the coast. However, the spatial variability of the soil structural fractals in the Ziya River Basin was greater than that in the Daqing River Basin. (2) The combined effects of climate change, regional differences, and human activity led to greater spatial variability in the soil structural fractals in the Ziya River Basin than in the Daqing River Basin. The correlation between D values and burial depth was strongest in the Xianxian profile (−0.78), whereas the spatial correlation was strongest in the Hengshui and Dacheng profiles (−0.47). (3) The greatest spatial variability in soil D values occurred at depths of 1–2 m, with a coefficient of variation of 23.595%, which was significantly higher than those at depths of 0–1 (14.569%) and 2–3 m (16.284%).

Characteristics of Soil Particle Sizes and Fractal Parameters under Different Plantation Types of Populus alba

Vegetation plays a leading role in restoring desert ecosystems and increasing productivity. In this study, we elucidate the improvement effects of different restoration areas of Populus alba on the soil particle distribution, sedimentation environment, and fractal characteristics. We selected the restoration areas of P. alba × Caragana korshinskii (YN), P. alba × Hedysarum leave (YY), and P. alba × Hedysarum scoparium (YH), which have a history of twenty-one years. We analyzed the soil nutrients, soil particle size, soil particle size parameters, soil fractal dimension (D) values, and soil multifractal parameters at soil depths of 0–80 cm. We found that the YN, YY, and YH significantly increased the soil nutrients and soil fine particles (p &lt; 0.05) and changed the deposition pattern of the soil particles in the sandy area. The YN, YY, and YH promote soil particle refinement and reduce the sorting performance of the soil particles. The vegetation promotes extremely positive-skewed and very leptokurtic soil particle distributions. The D values in the YN, YY, and YH restoration areas increased by 7.62%–27.94%, 7.36%–26.28%, and 7.10%–17.92%, respectively, relative to those of the LS. The construction of the different restoration areas of P. alba has made the distribution of the soil particles nonuniform. Compared with the YY and YH plantations, the distribution range of the soil particles in the YN plantation is wider, and the distribution heterogeneity is greater. In addition, we found that the fractal parameters are influenced by the soil physicochemical properties, the depositional environment, and vegetation factors. Therefore, we believe that D values and multifractal parameters are necessary as additional information for desert soil texture improvement. The results of this study provide a scientific and theoretical basis for the future revegetation of deserts.

Sand-fixing measures improve soil particle distribution and promote soil nutrient accumulation for desert – Yellow River coastal ecotone, China

In the fragile desert ecosystems of the world, sand-fixing measures play an irreplaceable part in ecological restoration. However, it is unclear how the long-term establishment of sand-fixing measures affects soil particle distribution and soil nutrients for the desert – Yellow River coastal ecotone. Therefore, we selected sand-fixing measures that have been established for fifteen years: Pinus sylvestris (PS), Populus alba (PA), Elaeagnus angustifolia (EA), Hedysarum scoparium (HS), Salix psammophila (SC), Salix psammophila checkerboard barriers (SCSB), and mobile sandy land (LS). We analyzed soil physical properties, chemical properties, soil fractal dimension (D), and multi-fractal parameters in the top soil layer (0–20 cm). The results showed that the establishment of sand-fixing measures significantly increased the clay and silt, and decreased the sand (p < 0.05). Sand-fixing measures promote the heterogeneity of soil particle distribution and increase its dispersion. The soil nutrition content was significantly increased under different sand-fixing measures (p < 0.05), and soil organic carbon (SOC) and alkaline nitrogen (AN) changed significantly. The D value is between 2.18 and 2.39. The D value and multifractal parameters were driven by soil physicochemical properties and aboveground biomass (AGB). The regression model demonstrates a significant correlation between the D values and multi-fractal parameters (R2 = 0.58–0.77, p < 0.001). Therefore, we suggest that multifractal parameters can replace the D values as indicators of soil environmental changes in desertification. This study complements the information on the restoration of soils in the desert-Yellow River coastal ecotone by sand-fixing measures. In addition, we suggest that desert ecological management should be tailored to regional environmental differences to establish an integrated model of restoration of sand-fixing measures in the future. The results of this study scientifically provide a theoretical basis for the future reconstruction of ecologically fragile areas.

Effects of Different Hedgerow Patterns on the Soil Physicochemical Properties, Erodibility, and Fractal Characteristics of Slope Farmland in the Miyun Reservoir Area.

Soil erosion of sloping farmland in the Miyun reservoir area in Beijing has become a serious issue and has threatened the ecological environment and safety of the reservoir area. We used the Taishizhuang Village Non-point Source Pollution Prevention & Control Base in the Miyun reservoir as a study area and performed a comparative analysis of the physicochemical properties of soil of the upper, middle, and lower slopes of the Scutellaria baicalensis + Buchloe dactyloides plot (Treatment 1, T1), Morus alba + Buchloe dactyloides plot (Treatment 2, T2), Salvia miltiorrhiza + Cynodon dactylon plot (Treatment 3, T3), Platycodon grandiflorus + Cynodon dactylon plot (T4), and a barren land control plot (Control check, CK), to explore how different hedgerow patterns affect the soil’s physicochemical properties, anti-erodibility, and fractal characteristics. We found the following: (1) The primary soil mechanical composition included sand particles in the upper slopes, whereas it was soil fine particles in the middle and lower slopes. (2) The fractal dimension of the slope soil showed a significant negative correlation with sand particles (R2 = 0.9791) while being positively correlated with silt particles (R2 = 0.9635) and clay particles (R2 = 0.9408). (3) All hedgerow patterns increased soil nutrients, with the Morus alba + Buchloe dactyloides hedgerow plot increasing the soil total nitrogen (STN), soil total phosphorus (STP), and soil organic matter (SOM) content by 213.89–282.69%, 55.56–58.15%, and 29.77–56.04%, respectively. (4) The Morus alba + Buchloe dactyloides hedgerow plot significantly decreased the soil erodibility factor K value, improved soil anti-erodibility, and reduced soil erosion. (5) The K value of the soil erodibility was significantly negatively correlated with clay particles, soil fractal dimension, and STP (p < 0.01); positively correlated with sand particles; and negatively correlated with silt particles, STN, and SOM. Therefore, the Morus alba + Buchloe dactyloides hedgerow planting contributes to clay particle conservation, soil nutrient content improvement, soil structure optimization, and soil anti-erodibility enhancement.

Fragmentation of soil-root complexes in sloping landscapes during tillage and soil translocation

It is well known that roots play a significant role in reducing water erosion in soil, yet few studies have reported the influence of crop roots on soil translocation induced by tillage in sloping fields. To examine the relationship between soil-root complexes (i.e., complexes of wheat roots and soil) and soil redistribution caused by tillage, a series of tillage experiments were carried out on bare soil and areas of wheat sown by drilling ( DS ) and nesting ( NS) using nine slopes with gradients varying from 0.19 to 0.32 m m −1 . The magnetic tracing technique was used to determine soil translocation rates under hoeing tillage in sloping landscapes in response to soil-root complexes and bare soil. The results indicated that mean displacement distance for DS and NS in the downslope direction was 0.15 m and 0.16 m, respectively. This was much shorter than that of bare soil which was 0.26 m. Mean tillage erosion rates ranged from 14.58 to 19.15 Mg ha −1 per tillage pass for DS and 13.90 –21.10 Mg ha −1 per tillage pass for NS , while reached 31.23–36.31 Mg ha −1 per tillage pass for bare soil. Tillage transport coefficients ( k 3 and k 4 ) were 6.31 and 106.46 kg m −1 per tillage pass for DS , 6.58 and 118.68 kg m −1 per tillage pass for NS , and 28.12 and 151.07 kg m −1 per tillage pass for bare soil, respectively. A significant difference in cohesive force ( C ) was found between DS ( NS ) and bare soil ( P < 0.05), thereby resulting in an increase in the soil shear strength of soil-root complexes. Compared with those of bare soil, the soil fractal dimension of soil-root complexes decreased significantly due to an increase in the percentage of coarse clods (>100 and 100–80 mm) and a decrease in the percentage of fine clods (50–20 and < 20 mm). Mean soil displacement distance caused by tillage displayed a negative relationship with C and wheat root traits (the root density, the root length density, and the root area ratio) within the hilly landscape of soil-root complexes ( P < 0.05), implying that wheat roots played a crucial part in soil translocation and soil fragmentation during hoeing tillage. Our study revealed that soil-root complexes markedly reduce the soil downslope transfer process during tillage and prevent the break-up of large clods by tillage implements on sloping farmland. • Wheat root attenuated the mechanical breakage of clods during tillage operation. • Root systems increase soil shear strength and reduce fragmentation of soil clods. • Displacement distance for soil-root complexes was smaller than that for bare soil. • Tillage erosion decreased with increasing structure stability and cohesive force.

Effects of Different Vegetation Restoration Types on the Fractal Characteristics of Soil Particles in Earthy-Rocky Mountain Area of Northern China

The fractal characteristics of soil particle-size distribution (PSD) constitute an important soil physical property, and fractal models of soil PSD are increasingly used to describe the effects of vegetation on the improvement of soil-related properties. Based on the fractal theory, this paper selected four typical vegetation restoration types (Quercus acutissima, QAC; Robinia pseudoacacia, RPL; Pinus densiflora, PDS; QAC × PDS) in the Taiyi mountainous area as the research object, and the single-fractal dimension (D) and multi-fractal parameters of PSD and its correlation with soil-associated properties were studied. The results show that (1) QAC × PDS reduced the heterogeneity of soil sand distribution, which also increased the range and concentration of soil PSD in the dense area. Soil clay and silt contents showed QAC × PDS &gt; RPL &gt; QAC &gt; PDS. QAC × PDS significantly increased clay and silt content in 0–20 cm soil. (2) D varies among different vegetation restoration types, which was QAC × PDS &gt; RPL &gt; QAC &gt; PDS, and the D of 0–20 cm soil was greater than that of 20–40 cm. For the multi-fractal parameters of PSD, the capacity dimension (D0), information dimension (D1), correlation dimension (D2) and D1/D0 in 0–20 cm soil of different vegetation restoration types showed significant differences. (3) D and multi-fractal parameters were significantly positively correlated with clay and silt contents, which were significantly negatively correlated with sand contents. (4) QAC × PDS had the smallest soil bulk density and largest porosity. Fractal dimension was negatively correlated with soil bulk density and positively correlated with soil total porosity and capillary porosity. These results indicate that the soil fractal dimension can well characterize the vegetation improvement on soil structure and properties in the earthy-rocky mountain areas of northern China.

Effects of Population Density on Revegetation of Artemisia sphaerocephala and Soil Traits in a Desert Ecosystem

Soil desertification is a serious problem in arid northwestern China that threatens ecological sustainability. Artemisia sphaerocephala, a dominant shrub species, play an important role in the conservation of water and the restoration of soil in the desert ecosystem. However, the poor establishment of A. sphaerocephala often limits plant revegetation, and the optimal population density for sustainable growth is largely unknown. Here, we determined key soil properties and plant growth characteristics associated with different population densities of A. sphaerocephala (including from 1.1, 2.1, 3.1, 3.9 to 5.3 plants per m2) in the resource-limited Alashan desert of northwestern China. The results showed that plant population density was the primary factor determining the revegetation of A. sphaerocephala, followed by soil water availability. Soil N, P and K content, and soil fractal dimensions also contributed to the vegetation and productivity. Soil nutrients were mostly accumulated in the topsoil layers, coincidental with the root distribution pattern in which 57% to 82% of total roots were distributed in the top 20 cm soil layer. The concentrations of soil nutrients in higher population densities (3.9 to 5.3 plants per m2) were greater than those in lower population densities (1.1 to 2.1 plants per m2), suggesting that A. sphaerocephala may have the ability to promote nutrient cycling in the desert ecosystem. We conclude that the optimal population density for the best growth of revegetated A. sphaerocephala was 3 plants per m2.

Soil Properties under Artificial Mixed Forests in the Desert-Yellow River Coastal Transition Zone, China

Mixed forests play a key role in the environmental restoration of desert ecosystems and in order to address the improvement of soil properties by different mixed vegetation types. We selected four typical mixed vegetation types (including: Populus alba var. pyramidalis × Caragana korshinskii, P. pyramidalis × Hedysarum mongdicum, P. pyramidalis × Hedysarum scoparium and Hedysarum scoparium × Salix cheilophila) that have been restored for 22 years and the moving sandy land in the transition zone between the desert and the Yellow River in northern China. We compared the differences in soil properties using a total of 45 soil samples from the 0–30 cm soil layer (10 cm units). We found that revegetation had a significant positive effect on fine particles, soil nutrients, soil bulk density (SBD), and soil fractal dimension (D) values. Soil D values under different types of vegetation range from 2.16 to 2.37. Soil nutrients and fractal dimension showed highly significant or stronger negative correlations with SBD and sand and highly significant or stronger positive correlations with clay and silt. The construction of P. pyramidalis × C. korshinskii improved the soil texture better than other vegetation restoration types. Compared to the mobile sandy land, organic carbon (SOC), available phosphorus (AP), available potassium (AK), alkaline hydrolysis nitrogen (AN), total nitrogen (TN), total potassium (TK), clay, and silt increased by 161%, 238%, 139%, 30%, 125%, 69%, 208%, and 441% respectively. As mentioned above, P. pyramidalis × C. korshinskii is a suitable type of mixed vegetation restoration for the area. In addition, establishing vegetation with high nitrogen fixation rates in desert ecosystems tolerant to drought and aeolian conditions is beneficial in reversing the trend of desertification. This research will suggest vegetation building strategies for controlling desertification.

Seepage–Fractal Model of Embankment Soil and Its Application

Over time and across space, the hydraulic conductivity, fractal dimension, and porosity of embankment soil have strong randomness, which makes analyzing seepage fields difficult, affecting embankment risk analysis and early disaster warning. This strong randomness limits the application of fractal theory in embankment engineering and sometimes keeps it in the laboratory stage. Based on the capillary model of porous soil, an analytical formula of the fractal relationship between hydraulic conductivity and fractal dimension is derived herein. It is proposed that the influencing factors of hydraulic conductivity of embankment soil mainly include the capillary aperture, fractal dimension, and fluid viscosity coefficient. Based on random field theory and combined with the embankment parameters of Shijiu Lake, hydraulic conductivity is discretized, and then the soil fractal dimension is approximately solved to reveal the internal relationship between hydraulic gradient, fractal dimension, and hydraulic conductivity. The results show that an increased fractal dimension will reduce the connectivity of soil pores in a single direction, increase the hydraulic gradient, and reduce the hydraulic conductivity. A decreased fractal dimension will lead to consistency of seepage channels in the soil, increased hydraulic conductivity, and decreased hydraulic gradient.

Study on the Fractal Characteristics of the Plant Root System and Its Relationship with Soil Strength in Tailing Ponds

To study the fractal characteristics of plant roots in tailing ponds and their effect on soil strength, the rhizosphere soil and roots of Amorpha fruticosa and Hippophae rhamnoides, which are widely distributed in ecological restoration areas, were collected. The fractal dimension, root fractal characteristics, soil strength characteristics, and interaction relationships of the two rhizosphere soils were studied. Fractal theory was used to derive the formula for calculating the safety factor of the slope considering the soil and root fractals. The results showed that (1) the fractal dimension of rhizosphere soil of A. fruticosa and H. rhamnoides decreased with increasing vertical profile depth. (2) The fractal dimensions of roots of A. fruticosa and H. rhamnoides decreased with increasing soil depth. (3) The cohesion of the root-soil complex first increased and then decreased, and the fractal dimension of roots was significantly positively correlated with the increase in cohesion. (4) The slope safety factor was positively correlated with the fractal dimension of the soil and root system. It established the theoretical formula of the slope safety factor modified according to the fractal dimension.

Effects of Intercropping on Fractal Dimension and Physicochemical Properties of Soil in Karst Areas

Suitable soil structure and nutrient security are important for plant growth and development. The fractal dimension of soil, along with the distribution of physical and chemical properties and their interactions, plays an important role in studying the stability of soil structures and water and fertilizer cycles. As a sustainable management model, intercropping has positive benefits for erosion control, the spatial optimization of resources, and improving system productivity. The effects of four intercropping methods on the fractal dimension and physicochemical properties of soil were investigated by intercropping Salvia miltiorrhiza with forage and S. miltiorrhiza with forest under typical karst rock desertification habitats in Guizhou. The results showed that the soil nutrient content when intercropping was significantly higher than that of monoculture. The organic carbon content of soil grown under forest is higher than other treatments, and there was a non-significant change in soil water content when intercropping compared with monoculture. The soil fine-grained matter when intercropping was significantly higher than that of monoculture, while the soil fractal dimension showed a tendency to become larger with an increase in fine-grained matter. Intercropping planting, due to its component types and spatial and temporal configurations, leads to differences in soil water and fertilizer interactions, which can be combined with other ecological restoration measures to optimize the composite model and jointly promote the restoration and development of ecologically fragile areas.

Soil organic carbon and soil aggregate stability associated with aggregate fractions in a chronosequence of citrus orchards plantations

Soil aggregates and their associated C may serve as accurate diagnostic markers for changes in soil characteristics in response to different agricultural management practices. However, there is limited knowledge regarding the effects of various chronosequences on soil organic C (SOC) pool in aggregates of different particle sizes in citrus plantations. Surface soil (0–20 cm) samples were collected from 120 citrus orchards (Yongxing County, Hunan Province, China) of different plantation ages (0-10y, 11-20y, and 21-30y). Plantation age dramatically affected the composition of soil aggregates of different particle sizes and their associated SOC, with the strongest macroaggregate fraction observed in the 0-10y orchards. Soil mean weight diameter (MWD) and geometric mean diameter (GMD) gradually decreased with plantation age (by 12.58% and 20.30% in 21–30y orchards, respectively). However, soil fractal dimension (D) and erodibility (K) gradually increased with plantation age (by 3.95% and 2.15% in 21–30y orchards, respectively). Furthermore, the SOC content and pool of aggregates and contribution of aggregates to SOC decreased with decreasing particle size. Multivariate analysis identified the aggregate fraction with a particle size over 2 mm as the main factor affecting the stability of soil aggregates in citrus plantations. The SOC content of aggregates was positively correlated with soil MWD and GMD but negatively correlated with soil D and K. The distribution of organic matter in soil aggregates can help us better understand the stability of soil structure and reduce the risk of soil erosion in successive citrus planting (<30y).

Fractal characteristics of soil particle size in loess hilly areas with different years of conversion

The purpose of this study was to investigate the change of soil particle composition and its effect on the fractal dimension of grassland under different years of conversion. The changes of soil particle composition and soil fractal dimension were analyzed by taking the 8-year grassland and 31-year grassland in the Yuanzegou watershed of the loess hilly region as the research objects, and taking the sloping farmland as the control. The results showed that the clay content of soil was increased by 69.6%, 47.6% and 8.80%, 8.7%, respectively, in the 31-year grassland and the 8-year grassland in the 0-20cm, 20-40cm. The decrease of sand content was 38.7%, 18.2% and 15.6%, and 13.5%, respectively, which were significantly different from that of the 31-years grassland (P<0.05). The contents of particles in the 40∼60cm soil layer did not change significantly. fractal dimension range from 2.6 to 2.7, the expression for the conversion of 31 years grassland>grassland>changing slope farmland 8 years, the fractal dimension of soil particles increased along with the increasing length of the grass farmland, in 0∼20, 20∼40cm soil layer, the conversion of 31 years grassland soil particles fractal dimension D and slope have significant difference (P<0.05). The fractal dimension of soil particle volume was positively correlated with soil clay (P<0.01), and positively correlated with soil particle size on farmland and grassland after 31 years of conversion (R2=0.6970, 0.6701), but not on grassland after 8 years of conversion. There was a negative correlation between soil sand content and fractal dimension of soil particles in the three plots, but there was only a significant difference in slope farmland.

Assessing soil fractal and sorting characteristics based on geostatistics and modeling approaches in a typical basin of North China plain

Fractal dimension is a parameter that quantitatively describes the complexity of fractal set. In order to understand the spatial variation characteristics of soil fractal dimension and its influencing factors, different geomorphic units in a typical basin of the North China plain were selected for sampling. And the grain size distribution of 180 soil samples were measured by laser diffraction. Fractal dimension was analyzed by the software of SPSS26 and Voxler4.3 to search for significant influencing factors. Then, in the same coordinate system as fractal dimension, models of soil particle sorting were built. There was a decreasing trend from the sloping plain at the southwest piedmont (1.6244) towards the alluvial plain (1.2164) about fractal dimension. In piedmont plain, fractal dimension was significantly correlated with the minimum particle size and proportion of clayey particles, respectively. In coastal plain, fractal dimension was extremely significantly correlated with the maximum particle size and the proportion of sandy particles, respectively. The spatial variability of soil structures in the study area was significant. The models features of sorting and fractal dimension are similar, and a linear relationship existed between fractal dimension and standard deviation as follows: D = 1.236σ1 + 0.082. This research supports quantitative and visual characterization of spatial variability of soil structure and sorting of soil particles.

The validity of laser diffraction system to reproduce hydrometer results for grain size analysis in geotechnical applications.

The grain size analysis plays a significant role in any geotechnical study. The grain size analysis, by means of sieving, is usually used for coarse material of particle size > 75 μm. For the fine material; the sedimentation methods are frequently adopted (e.g., hydrometers). Other methods also exist such as electron microscopy, digital image analysis and laser diffraction. The fine geomaterials commonly undergo agglomeration which makes the recognition of individual grain size using digital image analysis or electron microscopy challenging. To facilitate and enhance the grain-size analysis, this study was conducted using the Laser Diffraction System (LDS). Seven samples with different nature (composition and texture) and sources were analyzed by hydrometer and LDS. For LDS, various factors were studied such as air pressure, sonication, dilution, refractive index, and distribution method (volume or number). The results were compared qualitatively and quantitatively based on soil classification systems, fractal dimensions, and other parameters. Furthermore, this study provided a novel criterion to determine which LDS distribution method (volume or number) is to be used depending on the Liquid Limit. A combined sieve-LDS system is recommended to obtain the entire grain size distribution. It is concluded that the LDS is a viable technique that can replace the time-consuming hydrometer method to assess the grain-size distribution.

Fractal Features of Soil Particle Size Distributions and Their Implications for Indicating Enclosure Management in a Semiarid Grassland Ecosystem

Soil particle size distribution (PSD) is becoming an increasingly useful tool for the objective description of soil structure and intrinsic links between soil and the environment. Here we examined the fractal features of PSD and its correlation with soil physiochemical properties in grasslands under grazing and protected from grazing (enclosure) animals, before and after plant growing periods in a semiarid grassland ecosystem, in northern China. Our results showed that sand content was significantly higher in grassland soils under grazing compared with the enclosure at both sampling times (May and September), whereas their silt and clay contents followed the reverse pattern. The fractal dimensions of PSD (Dm) under enclosure were significantly greater than those found under grazing. The soil clay, silt contents and Dm were positively correlated with soil total N, total C, soil pH, and moisture content. By contrast, the soil sand content declined with increasing total N, total C, pH, and moisture content of soil. The soil fractal dimension of PSD had a positive correlation with soil clay and silt content, whereas it had a negatively correlated with sand content. From these results, we conclude installing enclosures can promote soil clay, silt, and soil particles' fractal dimension, with the latter could be used as a quantitative indicator of soil fertility characteristics. But it is unnecessary to use the fractal dimension of PSD as an index to evaluate the effects of enclosure management on degraded grassland.

The effect of climatic and edaphic factors on soil organic carbon turnover in hummocks based on δ13C on the Qinghai-Tibet Plateau

Hummocks (thúfur, pounus) are peculiar landforms usually formed by repeated freeze–thaw processes and differential frost heave, and are common in frost soil regions, especially in the Qinghai-Tibet Plateau. However, little is known about the response of δ13C in soil organic carbon (δ13CSOC) to soil and climate properties in hummocks. The β value indicates the decomposition rate of soil organic carbon (SOC) in soil, and was obtained from the slope of the regression between the log10-transformed SOC concentration and δ13CSOC in soil depth profiles. In this study, we investigated δ13CSOC and SOC contents along a soil profile (0–60 cm), together with edaphic and climatic properties, both in hummocks and control plots (alpine grasslands) on the northeastern Qinghai-Tibet Plateau. Then, the variations in δ13CSOC and β values, and the main factors affecting them, were analyzed. The results show that δ13CSOC increases with soil depth, while SOC decreases both in the hummocks and control plots. However, β values in the hummocks were significantly (P < 0.05) higher than in the control plots while δ13CSOC showed no difference between hummock and control. Redundancy analysis showed that altitude is the main control factor for δ13CSOC and β in the hummocks. Climate type was the main factor affecting δ13CSOC in the control plots, while mean annual precipitation and soil fractal dimension were the main factors controlling β. Overall, climate, rather than soil, is the key factor that affects the carbon turnover rate in the hummock in the northeastern QTP. The findings of this study will expand our understanding of the soil carbon cycle and δ13CSOC changes, especially in the case of hummocks.

Composition and fractal features of soil micro-aggregates in microsites of different types of treefall gaps

Through field survey and laboratory analysis, we examined the composition and fractal features of soil micro-aggregates in different types of treefall gaps and microsites (pit bottom and mound top) in broad-leaved Korean pine forest and spruce-fir-Korean pine forest. Results showed that the contents of soil microaggregates under the classes of 0.25-2 mm and 0.05-0.25 mm were higher in both forest types, ranging from 25.7% to 50.7% and from 27.0% to 42.8%, respectively, and that of <0.002 mm was the lowest, ranging from 4.4% to 8.9%. In the pit bottom and mound top of gaps, soil bulk density was higher in both forest types. Soil nutrient content in mound top was higher than that in pit bottom and was higher in broad-leaved Korean pine forest than spruce-fir-Korean pine forest. Soil microaggregates of <0.002 mm had no correlation with soil physical and chemical properties, whereas that of 0.25-2 mm and 0.002-0.02 mm had significantly positive and negative correlation with soil non-capillary porosity, total porosity, aeration porosity, organic matter, total phosphorus, total nitrogen and organic carbon, respectively. On the whole, soil fractal dimension (D) and the proportion of characteristic soil micro-aggregates (PCM) in broad-leaved Korean pine forest were larger than those in spruce-fir-Korean pine forest, and the ratio of soil microaggregates diameter (RMD) in mound top and pit bottom was increased in two forest types. Soil D and PCM had no significant correlation with soil physical and chemical properties, while RMD was negatively correlated with capillary porosity, total porosity, soil bulk density and aeration porosity. In two forest types, the formation of mound and pit microsites could decrease the larger size micro-aggregates and the stability of soil micro-aggregate, increase soil D and PCM, and signifi-cantly increase RMD. RMD could be used as a quantitative index of soil physical and chemical properties in pit and mound microsites of forest.