基于电阻率断层扫描技术的土壤砾石体积含量评估

为了对电阻率断层扫描技术应用于土壤中砾石含量的研究进行评估,该文对此应用进行了数值模拟研究。该研究假设石质土壤为由细土和砾石组成的二相介质,采用有线差分法对所建立土壤数值模型进行了电阻率断层扫描模拟,模型中砾石随机分布且相互独立,过程中对砾石尺寸和土壤中水分情况的影响进行了研究。结果表明对已知二相各自电阻率值的石质土壤,其等效电阻率与其中砾石体积含量相关,数值模拟结果与理论预测结果相符合,验证了电阻率断层扫描技术应用土壤中砾石体积含量估计的可适用性,同时指出在土壤较湿润时为该技术的适宜使用条件。该研究为土壤学分类研究及质量评价提供参考和指导。     

土壤中砾石含量的测定方法研究进展

石质土壤中含有大量砾石,大量砾石的存在会影响土壤理化特性和水力特性。土壤中砾石含量的研究会影响土石介质的生产力评估、水文及风化过程的研究水平。本文主要介绍了国内外土壤中砾石含量的现有测定方法,对环刀取样法、挖坑法、Viro插钎法,γ射线法、探地雷达及电阻率断层扫描技术的实际应用进行了讨论。在实际研究中应根据实际情况选择合适的砾石含量测定方法。土壤中砾石含量的测定应该引起国内相关研究的重视,为土壤研究提供重要信息并为土壤学研究水平的提高提供帮助。     

基于电阻率断层扫描技术探测林地土层厚度

土层厚度对林地生产力具有重要影响,是评价林地土壤质量的重要指标。为了对林地土壤的土层厚度进行调查,该文应用电阻率断层扫描技术对林地土壤土层厚度进行了研究,对其可适用性做出评价。通过在野外试验点对土壤电阻率的实地断层扫描,将其结果与实际测定得到的基岩特征电阻率相结合,预测土层厚度,并将预测值和实地基坑开挖数据进行比较。结果表明,研究区土层厚度多在小于2 m的范围内,电阻率断层扫描技术估测结果与实测结果相符(均方根误差为0.2678),初步表明该技术在估算林地土层厚度方面具有良好的适用性。该研究结果为土壤学方面相关研究提供重要手段,也将对土壤质量评价和土地利用等相关工作提供指导。     

基于电阻率成像技术的土层精细划分

土壤层次的精确划分关系到土壤学相关研究结果的精确程度。为对田间尺度上层状土壤进行无损精细分层,采用电阻率成像技术,同时结合电阻率曲线纵向上的变化特征精细划分土壤层次,并将精细分层结果应用于层状土壤电阻率空间变异性研究。结果表明:运用电阻率曲线法对反演电阻率数据进行精细划分后,形成结果图能很好的满足研究过程中可视化呈现及精细化表达等需要;根据温纳四极反演电阻率曲线法将研究区内的剖面浅层土壤划分为5—13,13—24,24—50,50—70cm 4个层次;5—13cm(耕作层)电阻率值的变异系数最高(0.28),13—24cm(犁底层)平均电阻率值最低(17.35Ω·m)。研究成果可为土壤水文学和精准农业等相关研究提供技术支撑。     

2种土壤磁性特征及其对磁性示踪实验的影响

通过磁性示踪耕作实验、土壤磁性背景值测定、土壤物理性质分析等方法研究了云南东川区蒋家沟流域2种土壤类型的磁性特征,并探讨了土壤磁性对耕作侵蚀磁性示踪实验的影响。结果表明:(1)砾石土磁性随粘粒和粉粒含量增加而明显增强(r=0.58,p0.05;r=0.67,p0.05),随砂粒增加而明显减弱(r=-0.71,p0.05);黄棕壤粘土因受磁性矿物影响大,随土壤中砂粒含量增加而增强,砾石土磁性随土壤含水量增加而明显减小(r=-0.68,p0.05)。(2)因受土壤侵蚀的影响,砾石土的磁性与坡度呈显著负相关关系(r=-0.701,p0.05),即随坡度增大而明显减小。(3)土壤成土背景差异导致2种土壤磁性存在明显差异,即黄棕壤粘土的磁性(1 451×10-5SI)是砾石土磁性(53×10-5SI)的27倍。在耕作侵蚀的磁性示踪实验中,磁性背景值低的砾石土比磁性强的黄棕壤粘土有更好的磁性敏感性,更能准确反映耕作侵蚀位移。当混入磁性示踪剂的土壤磁性是土壤磁性背景值的30倍时,耕作侵蚀磁性示踪实验较为准确和可靠,以此作参考,不同磁性的土壤可以确定一个科学的磁性示踪剂用量。     

三峡库区碎石含量对紫色土容重和孔隙特征的影响

土壤容重和孔隙分布特征是土壤重要的基本物理性质,但有关含碎石土壤的物理性质以及碎石含量对土壤结构影响的研究尚不多见。三峡库区紫色土中存在大量的碎石,为了深刻了解和评价土壤中碎石对容重与大孔隙形成的可能作用,通过野外调查、典型土样采集和室内分析实验,探讨了三峡库区典型土地利用类型下土壤中的碎石体积含量以及不同粒径碎石的基本物理性质及其对土壤容重和孔隙特征的影响。结果表明:土壤中碎石的孔隙度和饱和含水率随着碎石粒径的减小而增大,小碎石本身具有一定的持水、供水性能;碎石含量对土壤的总容重、细土容重有显著影响,随着碎石含量的增加,土壤的总容重逐渐增加,而细土容重与碎石含量呈线性负相关关系,土壤中碎石的存在有利于改善土壤的结构;土壤孔隙分布特征与碎石含量密切相关,随着碎石含量的提高,土壤总孔隙度和毛管孔隙度呈减少趋势,而非毛管孔隙度即大孔隙呈增加趋势,碎石的存在有利于改善土壤的透水性能。本研究为山区农用地灌溉与水分管理提供了科学依据。     

砾石对丘陵紫色砾质土持水性的影响

通过红棕紫泥、灰棕紫泥、棕紫泥原状土和扰动土的持水性实验,研究了砾石对丘陵紫色砾质土持水性的影响.结果表明,在考虑砾石的情况下,原状土饱和含水量减少0.70%～10.70%,田间持水量减少2.07%～4.33%;砾石含量＜10%,饱和含水量和田间持水量与砾石含量关系不明显;砾石含量＞10%,饱和含水量和田间持水量随砾石含量减少而增加;在0～30 kPa吸力段,原状土和扰动土的持水能力、幂函数拟合式的α值、原状土物理性黏粒含量、扰动土比水容量都随砾石含量减少而增大;原状土的比水容量随砾石含量减少而减小.     

砾石覆盖对土壤水蚀过程影响的研究进展

 土壤中砾石的存在对水蚀过程有着重要的影响,有关砾石特别是表土砾石覆盖对土壤水蚀影响的研究结果表明,表土砾石对溅蚀分散、细沟间及细沟侵蚀等坡面侵蚀过程有重要影响:1)泥沙溅蚀分散量与砾石覆盖度呈负相关关系;2)砾石覆盖与细沟间侵蚀的关系较为复杂,这取决于表土的结构、砾石的位置和大小以及坡度等因素,当砾石嵌入结皮表土时,二者呈负相关关系,当砾石置于表土之上或嵌入具有结构孔隙的表土时,二者呈正相关关系;3)砾石覆盖对细沟间侵蚀产沙的作用效率与砾石粒径呈负相关关系,砾石置于表土之上的表土产沙量总低于砾石嵌入表土的产沙量;4)表土砾石覆盖能抑制细沟的形成,增加细沟糙度,降低细沟径流速率以及径流的侵蚀速率。鉴于砾石对水蚀过程的重要影响,RUSLE、WEPP和EUORSEM等土壤侵蚀模型预报含砾石土壤流失量时对相关参数做了修正。     

土壤中砾石存在对入渗影响研究进展

石质山区的土壤中含有大量砾石,土壤中大量砾石存在会影响土壤物理特性和水力特性,从而对土壤入渗规律造成影响。本文主要介绍了国外土壤中砾石存在对土壤物理特性、水力特性以及入渗规律影响研究的现有研究成果,国外现有研究结果表明,土壤中砾石存在对入渗影响较为复杂,砾石覆盖/含量与入渗量之间既有正相关关系,也有负相关关系。     

电阻率成像法在土壤水文学研究中的应用及进展

缺乏有效的监测技术是制约土壤学和水文学中尺度问题研究的主要瓶颈。近年来,以电阻率成像法为代表的地球物理学方法被引入到非饱和带土壤水文过程的研究中来,为解决尺度问题提供了新的强有力的工具。结合土壤电阻率与土壤特性之间的岩土物理学关系,电阻率成像法可以实现对土壤特性或状态的多尺度无损连续监测。阐述了电阻率成像法的基本过程、特征及其在土壤水文过程研究中的初步应用。同时,深入探讨了电阻率成像法应用于非饱和带水文过程研究中存在的问题和未来的应用潜力。     

Effects of rock fragments on physical degradation of cultivated soils by rainfall

To understand better the role of rock fragments in soil and water conservation processes, the effects of rock fragments in maintaining a favourable soil structure and thus also in preventing physical degradation of tilled soils was studied. Laboratory experiments were conducted to investigate the effects of rock fragment content, rock fragment size, initial soil moisture content of the fine earth and surface rock fragment cover on soil subsidence by rainfall (i.e. change in bulk density by one or more cycles of wetting and drying). A total of 15 rainfall simulations (cumulative rainfall, 192.5 mm; mean intensity, 70 mm h⁻¹) were carried out. Before and after each rainfall application the surface elevation of a 19-cm thick plough layer was measured with a laser microrelief meter. In all experiments, the bulk density of the fine earth increased with applied rainfall volume to reach a maximum value at about 200 mm of cumulative rainfall. From the experimental results it was concluded that the subsidence rate decreased sharply for soils containing more than 0.50 kg kg⁻¹ rock fragments, irrespective of rock fragment size. Fine earth bulk densities were negatively related to rock fragment content beyond a threshold value of 0.30 kg kg⁻¹ for small rock fragments (1.7–2.7 cm) and 0.50 kg kg⁻¹ for large rock fragments (7.7 cm). Initial soil moisture content influenced subsidence only in the initial stage of the experiments, when some swelling occurred in the dry soils. Surface rock fragment cover had no significant effect on subsidence of the plough layer. Therefore, subsidence of the plough layer in these experiments appears to be mainly due to changing soil strength upon drainage rather than the result of direct transfer of kinetic energy from falling drops. The relative increase in porosity of the fine earth as well as the absolute increase in macroporosity with rock fragment content will cause deeper penetration of rainfall into the soil, resulting in water conservation. Therefore, crushing of large rock fragments into smaller ones is to be preferred over removal of rock fragments from the plough layer.     

Electrical resistivity tomography to detect the effects of tillage in a soil with a variable rock fragment content

Electrical resistivity tomography (ERT) is a promising non‐destructive tool to characterize agricultural soils where management effects are superimposed on natural variability. The aim of our study was to test whether ERT was capable of detecting stones and tillage effects in a soil with a variable rock fragment content. Field experiments were conducted by performing a set of three two‐dimensional (2D) resistivity tomographies across two management systems (tillage/no tillage) replicated twice on each transect, using dipole‐dipole configuration and 0.25‐m inter‐electrode spacing. Soil texture, bulk density and water content were measured destructively. Greater average electrical resistivity (ER) was found in tilled plots, with maximum values of up to 1700 Ohm m. However, when the spatial correlation structure was considered in a mixed‐effects model, no significant difference in ER was found between tilled and untilled plots. Empirical semivariograms showed less spatial continuity and more noise in tilled plots. Resistivity was strongly correlated with rock fragment content (r = 0.68), with greater average values in ploughed plots, which may possibly be linked to kinetic sieving after ploughing. ERT was able to identify the position of gravel lenses and was also sensitive to the presence of clay (r = ?0.45): a linear trend in resistivity across the field (r = 0.80) was consistent with a decreasing clay content (r = ?0.68). Resistivity was correlated with rock fragments, clay and an interaction variable (water × rock fragments). There was a poor fit for the tilled plot where resistivity peaks could be linked to the presence of voids, but their detection would have required a resolution greater than that which we adopted.     

六盘山香水河小流域典型坡面的土壤电阻率空间变异

为了解坡面土壤水文特征的空间分布,采用多电极电阻仪法(ERT),于2009年5月初在宁夏六盘山香水河小流域一个长约600 m的华北落叶松人工林典型坡面上,设置了从坡顶至坡底的1条纵向样线及处于不同坡位的水平分布的3条横向样线,多点测定了多层土壤的电阻率值并分析其空间变异特征。结果表明,土壤电阻率在纵向样线上总体有较好的空间连续性及一定的空间变异性,随着坡位下降,电阻率呈现出由坡上至坡中上逐渐减小和然后又恢复性增大的过程。由于局部特殊的土壤特征、地貌及植被分布差异,使土壤电阻率沿坡面纵向变异程度大于不同坡位的横向变异程度。在土层垂直方向上,由于石砾含量和岩石比例随深度逐渐增多,电阻率表现为随深度增加逐渐增大。电阻率与土壤总孔隙度和体积含水率相关最紧密,尤其与体积含水率相关较好,说明通过测定坡面电阻率推求土壤水分等土壤特性的坡面变化是可行的。     

The dynamics of organic matter in rock fragments in soil investigated by 14C dating and measurements of 13C

Rock fragments in soil can contain significant amounts of organic carbon. We investigated the nature and dynamics of organic matter in rock fragments in the upper horizons of a forest soil derived from sandstone and compared them with the fine earth fraction (<2 mm). The organic C content and its distribution among humic, humin and non‐humic fractions, as well as the isotopic signatures (Δ¹⁴C and δ¹³C) of organic carbon and of CO₂ produced during incubation of samples, all show that altered rock fragments contain a dynamic component of the carbon cycle. Rock fragments, especially the highly altered ones, contributed 4.5% to the total organic C content in the soil. The bulk organic matter in both fine earth and highly altered rock fragments in the A1 horizon contained significant amounts of recent C (bomb ¹⁴C), indicating that most of this C is cycled quickly in both fractions. In the A horizons, the mean residence times of humic substances from highly altered rock fragments were shorter than those of the humic substances isolated in the fine earth. Values of Δ¹⁴C of the CO₂ produced during basal respiration confirmed the heterogeneity, complexity and dynamic nature of the organic matter of these rock fragments. The weak ¹⁴C signatures of humic substances from the slightly altered rock fragments confirmed the importance of weathering in establishing and improving the interactions between rock fragments and surrounding soil. The progressive enrichment in ¹³C from components with high‐¹⁴C (more recent) to low‐¹⁴C (older) indicated that biological activity occurred in both the fine and the coarse fractions. Hence the microflora utilizes energy sources contained in all the soil compartments, and rock fragments are chemically and biologically active in soil, where they form a continuum with the fine earth.     

The effect of soil moisture on the vertical movement of rock fragments by tillage

Chiselling in air-dry soils can rapidly create inverse grading of the plough layer as field experiments showed, i.e., the largest particles (rock fragments) are brought to the surface and the smallest particles concentrate at the bottom of the plough layer. Since no information about the effect of soil moisture and fine earth characteristics on this process is available laboratory experiments were conducted to examine the effect of soil moisture and fine earth characteristics on the vertical movement (segregation) of rock fragments due to tillage. An experimental trough, 120×60×40 cm³, was filled with three layers (each 4 cm thick) of fine earth (sand or silt loam), and rock fragments (1.2–2.2 and 2.7–4.0 cm). Tillage was simulated by moving a hand-held cultivator through the mixture. The results for the sandy soil matrix showed that inter-particle percolation was slowed down by soil moisture, however, at the same rate for different moisture levels. This was attributed to water-films that surround the sand particles. In the silt-loam soil matrix inter-particle percolation was stronger than that occurring in the sandy matrix at similar volumetric moisture contents but vertical movement was impossible at higher moisture contents (0.17 m³ m⁻³) because of a strong increase in stickiness. The results imply that at low moisture contents farmers in areas threatened by desertification can use moderate tillage as a means to create a surface rich in rock fragments which helps to increase water infiltration and decrease erosion.     

含碎石土壤的含水量测定误差分析

碎石的存在增加了土壤含水量测定的难度,为便于应用,一些学者将碎石当作细土或不透水介质处理,这在一些情况下可能产生很大误差。本文对忽略碎石或其含水量所引起的土石混合介质和细土含水量的误差进行了分析,并用室内实验验证了所得到的结果与相对误差的关系。结果表明,细土和土石混合介质含水量的相对误差与碎石含量以及碎石与细土含水量的比值有关。当碎石与细土含水量比值很大时,即便碎石含量很低也会产生很大误差;而当碎石与细土含水量比值很小时,高的碎石含量同样导致很大误差。此外,碎石与细土含水量的相对大小并非常数,而是随含水量变化的。因此,对土石混合介质田间水分状况的准确监测,以及水分和溶质迁移过程的定量模拟需要考虑碎石特性的影响。     

Fine-earth translocation by tillage in stony soils in the Guadalentin, south-east Spain: an investigation using caesium-134

Tillage erosion is increasingly recognised as an important soil erosion process on agricultural land. In view of its potential significance, there is a clear need to broaden the experimental database for the magnitude of tillage erosion to include a range of tillage implements and agricultural environments. The study discussed in this paper sought to address the need for such data by examining tillage erosion by a duckfoot chisel plough in stony soils on steep slopes in a semi-arid environment. Results of the investigation of coarse fraction (rock fragment) translocation by tillage in this environment have been presented elsewhere and the paper focuses on tillage translocation and erosion of the fine earth. Tillage translocation was measured at 10 sites, representing both upslope and downslope tillage by a duckfoot chisel plough on five different slopes, with tangents ranging from 0.02 to 0.41. A fine-earth tracer, comprising fine earth labelled with ¹³⁴Cs, was introduced into the plough layer before tillage. After a single pass of the plough, incremental samples of plough soil were excavated and sieved to separate the fine earth from the rock fragments. Translocation of the fine-earth tracer was established by analysing the ¹³⁴Cs content of the samples of fine earth. These data were used to establish translocation distances for each combination of slope and tillage direction. Translocation distances of the fine earth were not significantly different from translocation distances of the coarse fraction. For all sites, except uphill on the 0.41 slope, translocation distances were found to be linearly related to slope tangent. The soil flux due to tillage for each site was calculated using the translocation distance and the mass per unit area of the plough layer. For slopes with tangents <0.25, the relationship between soil flux and tangent was linear and the soil flux coefficient derived was 520–660 kg m⁻¹ per pass. This is much larger than the coefficients found in other studies and this high magnitude is attributed to the non-cohesive nature and high rock fragment content of the soil in this investigation. A second contrast with previous studies was found in non-linearity in the relationship between soil flux and tangent when steeper slopes were included. This was a product of variation in plough depth between the steepest slopes and the remainder of the study area. On the basis of the study it is suggested that an improved understanding of tillage erosion may be obtained by considering the dual processes of tillage detachment (mass per unit area of soil subject to tillage) and tillage displacement (equivalent to translocation distance per pass) in assessing, comparing and modelling tillage translocation. An improved model is proposed that recognises the complexity of soil redistribution by tillage, provides a framework for process-based investigation of the controls on tillage fluxes, and allows identification of potential self-limiting conditions for tillage erosion.