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1.
Soil compaction and related changes of soil physical parameters are of growing importance in agricultural production. Different stresses (70, 230, 500, and 1000 kPa) were applied to undisturbed soil core samples of eight typical soils of a Saalean moraine landscape in N Germany by means of a confined compression device to determine the effect on (1) total porosity/pore‐size distribution, (2) saturated hydraulic conductivity, and (3) air conductivity to assess the susceptibility towards compaction. Different deformation behaviors after exceeding the mechanical strength particularly resulted from a combination of soil characteristics like texture and initial bulk density. The saturated hydraulic conductivity, as an indicator for pore continuity, was largely affected by the volume of coarse pores (r² = 0.82), whereas there was no relationship between bulk density and saturated hydraulic conductivity. Since coarsely textured soils primarily possess a higher coarse‐pore fraction compared to more finely textured soils, which remains at a high level even after compaction, only minor decreases of saturated hydraulic conductivity were evident. The declines in air conductivity exceeded those in hydraulic conductivity, as gas exchange in soils is, besides the connectivity of coarse pores, a function of water content, which increases after loading in dependence of susceptibility to compaction. A soil‐protection strategy should be focused on more finely textured soils, as stresses of 70 kPa may already lead to a harmful compaction regarding critical values of pore functions such as saturated hydraulic conductivity or air capacity. 相似文献
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Soil hydraulic properties as related to soil structure 总被引：5，自引：0，他引：5
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Tillage effects on near-surface soil hydraulic properties 总被引：1，自引：0，他引：1
J. G. Benjamin 《Soil & Tillage Research》1993,26(4):277-288
The processes for the formation of porosity are thought to differ between tilled and non-tilled cropping systems. The pores are created primarily by the tillage tool in the tilled systems and by biological processes in non-tilled systems. Because of the different methods of pore formation, the pore size distribution, pore continuity and hydraulic conductivity functions would be expected to differ among tillage systems. The objective of this study was to determine effects of three tillage systems — mold-board plow (MP), chisel plow (CP), and no-till (NT) — on hydraulic properties of soils from eight long-term tillage and rotation experiments. Tillage effects on saturated and unsaturated hydraulic conductivity, pore size distribution, and moisture retention characteristics were more apparent for soils with a continuous corn (CC) rotation than for either a corn-soybean (CS) rotation or a corn-oats-alfalfa (COA) rotation. Pore size distributions were similar among tillage systems for each soil except for three soils with a CC rotation. The MP system increased volume of pores >150 μm radius by 23% to 91% compared with the NT system on two of the soils, but the NT system increased the volume of the same radius pore by 50% on one other soil. The NT system had 30 to 180% greater saturated hydraulic conductivity than either the CP or MP systems. The NT system with a CC rotation showed a greater slope of the log unsaturated hydraulic conductivity; log volumetric water content relationship on two of the soils indicating greater water movement through a few relatively large pores for this system than for either the CP or MP systems. 相似文献
5.
N. R. A. Bird A. R. Preston E. W. Randall W. R. Whalley & A. P. Whitmore 《European Journal of Soil Science》2005,56(1):135-143
The water retention characteristic provides the traditional data set for the derivation of a soil's pore‐size distribution. However, the technique employed to achieve this requires that assumptions be made about the way pores interconnect. We explore an alternative approach based on stray field nuclear magnetic resonance (STRAFI‐NMR) to probe the water‐filled pores of both saturated and unsaturated soils, which does not require information relating to pore connectivity. We report the relative size distributions of water‐occupied pores in saturated and unsaturated samples of two sets of glass beads of known particle size, two sands, and three soils (a silty loam, a sandy loam and a loamy sand), using measurements of the NMR T1 proton relaxation time of water. The T1 values are linearly related to pore size and consequently measured T1 distributions provide a measure of the pore‐size distribution. For both the sands and the glass beads at saturation the T1 distributions are unimodal, and the samples with small particle sizes show a shift to small T1 values indicating smaller voids relative to the samples with larger particles. Different matric potentials were used to reveal how the water‐occupied pore‐size distribution changes during drainage. These changes are inconsistent with, and demonstrate the inadequacies of, the commonly employed parallel‐capillary tube model of a soil pore space. We find that not all pores of the same size drain at the same matric potential. Further, we observe that the T1 distribution is shifted to smaller values beyond the distribution at saturation. This shift is explained by a change in the weighted average of the relaxation rates as the proportion of water in the centre of water‐filled pores decreases. This is evidence for the presence of pendular structures resulting from incomplete drainage of pores. For the soils the results are similar except that at saturation the T1 distributions are bimodal or asymmetrical, indicative of inter‐aggregate and intra‐aggregate pore spaces. We conclude that the NMR method provides a characterization of the water‐filled pore space which complements that derived from the water retention characteristic and which can provide insight into the way pore connectivity impacts on drainage. 相似文献
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Soil pore networks have a complex geometry, which is challenging to model in three dimensions. We use a Boolean model of pore space that has proved useful in modelling gas diffusion in dry structures to investigate the distribution of water in this pore space and to quantify the effects on pore connectivity to the soil surface. We first show how total porosity in dry soil influences connectivity via the percolation threshold. Then we show that our model simulation of the ‘ink-bottle effect’ can account for much of the hysteresis of the soil water. The differences in distribution of water between wetting and drying result in maintaining greater connectivity of the air-filled pore space during drying than during wetting. Hysteresis is large at small total porosities and slowly declines as porosity increases. During wetting much pore space is blocked when more than 40% of the pore space is filled with water, although during drying all non-isolated air-filled pores are connected to the surface. Even when soil is allowed to wet to near saturation, there are rapid increases in pore connectivity during drying, which may explain, for example, rapid increases in production and emission of nitrous oxide in soils near saturation. 相似文献
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The physical properties of a Luvisol derived from loess near Bonn, Germany, under different long‐term fertilization treatments were examined. For the investigation of the impact of farmyard manure (FYM) on soil strength at the mesoscale (100 to 300 cm3 soil cores), undisturbed samples were taken from two different depths (10 and 40 cm), either with no fertilization at all, with full mineral fertilization, with FYM only, and with both mineral and organic fertilization. We investigated hydraulic and mechanical parameters, namely precompression stress, pore‐size distribution, saturated hydraulic and air conductivity, and calculated pore connectivity. Long‐term organic fertilization resulted in significantly more and coarser pores which in addition were more conductant and mechanically stronger by trend. Mineral fertilization also increased pore volume by trend but not pore functionality. Mechanical strength generally increased with fertilization by trend, however, was reduced again when organic and mineral fertilization were combined. Nonetheless, FYM led to relatively higher soil strength as the FYM‐treated plots with lower bulk density attained similar soil strength as the unfertilized but denser plots and thus supported the soil‐improving impact of organic amendments. The subsoil physical properties were rather unaffected by fertilization, but were dominated by texture. 相似文献
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We investigated the possibility of inferring effective hydraulic properties of soil from the structure of the pore space. The aim was to identify structural properties, which are essential for water flow, so that physical experiments may be replaced by direct morphological measurements. The pore structure was investigated in three dimensions by serial sections through impregnated samples. The complex geometry of pore space was quantified in terms of two characteristics: pore-size distribution and pore connectivity. Only pores larger than 0.04 mm were considered. The results were used as input parameters for a pore-scale network model. The main desorption branch of the soil-water characteristic and the corresponding hydraulic conductivity function of the network model were calculated by numerical simulation. The simulation results, which are exclusively based on morphological investigations, were compared with independently measured results from a multi-step outflow experiment. This approach was demonstrated for two centrasting soil materials: the A and B horizons of a silty agricultural soil. The simulations were close to the experimental data, except for the absolute values of the hydraulic conductivity. The pore-size distribution and pore connectivity govern the shape of hydraulic functions and the applied morphometric methods are suitable for predicting essential characteristics of hydraulic soil properties. 相似文献
9.
A multi-domain model for the transport of chemicals in soils is developed. The solute flux is related to the microscopic water flux, which is modelled using concepts to estimate the hydraulic conductivity of porous media. The pore space of the soil is divided into an arbitrarily large number of domains each representing an equivalent pore radius. The domains are arranged on a structural coordinate, perpendicular to the direction of mean water flow. Transport in the flow direction takes place in each domain by convection and diffusion with pore-size specific velocities. Solute mixing between the domains is simulated as convective-dispersive transport along the structural coordinate. The model is solved numerically for one-dimensional steady-state water flux under unit-gradient conditions. Required input parameters are the unsaturated conductivity function of a soil and a pore interaction coefficient which characterizes the solute exchange between the pore domains. Simulations show a gradual change from convection dominated transport (isolated tube model) to convective-dispersive transport. The length scale where this change takes place depends on the lateral mixing intensity, pore-size distribution of the medium, and saturation degree. 相似文献
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基于CT图像的土壤孔隙结构三维重建及水力学性质预测 总被引：6，自引：4，他引：2
为了更好地了解土壤孔隙结构对水分运动过程的影响机制,该文利用黄淮海平原原状潮土CT扫描图像,通过数字图像分析和计算机重建技术对孔隙结构进行三维重建,根据图像分析获得的孔隙大小分布和连通性等形态学参数建立了用于描述孔隙尺度结构特征对水分运动影响机制的网络模型,据此预测了样本尺度(样本体积为385.84cm3)的土壤水力学性质。结果表明,模型预测的水力学性质和实测值基本吻合,变化趋势基本一致,二者的决定系数达0.94以上。结果表明相关网络模型可以较好地模拟孔隙尺度的水分运动过程,可用于预测土壤的非饱和水力学性质。 相似文献
11.
Vegetated buffer zones (BZs) between arable fields and bodies of water are commonly established to reduce erosion and run‐off of particle‐bound nutrients. Functioning of a BZ depends on soil structure, as it is important for water infiltration. Therefore, it is vital to understand how varying management practices affect soils of BZs. We studied the structural and hydraulic properties of three differently managed BZs established in a boreal Vertic Stagnic Cambisol (clay, 51%). The three management practices for vegetation were as follows: natural with no treatment, harvested yearly and grazed by cattle. We used bulk density and macroporosity, together with a pore geometry index (air permeability per unit air‐filled porosity), to describe the soil structural properties. Hydraulic properties were measured at different length scales by means of an aggregate sorptivity test, saturated hydraulic conductivity of the core samples and field‐saturated hydraulic conductivity. Vegetation management markedly affected the physical properties in the top 5 cm of the soil. Properties were least favourable for infiltration at the grazed site, with the greatest bulk density, least macroporosity and hydraulic conductivity or greatest pore tortuosity. In general, spatial variation in zones with restricted and good hydraulic conductivity together with reduced aggregate sorptivity in the deeper horizons made the soil prone to preferential flow when initially dry. Prolonged wetness, on the other hand, reduced saturated hydraulic conductivity significantly, resulting in surface run‐off. Harvesting was considered the best management practice due to its inherent capacity for reducing the soil nutrient content and because it has minor implications for soil physical properties. 相似文献
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P. Schjønning B.V. Iversen L.J. Munkholrn R. Labouriau O.H. Jacobsen 《Soil Use and Management》2005,21(3):265-275
Abstract Application of organic residues to soil is generally assumed to improve soil tilth. Only few studies have reported the long‐term effects on the more subtle aspects of soil porosity, and no reports have considered the potential effects of organic amendments on the pore system in the subsoil. We sampled undisturbed soil cores (100 cm3 and 6280 cm3) using metal cylinders in differently fertilized plots in the long‐term field experiment at Askov Experimental Station, Denmark. We selected the 0–60 cm soil layer of plots dressed for a century with either mineral fertilizers (labelled NPK) or animal manure (labelled AM) and unfertilized plots (UNF) as a reference. Both fertilization treatments were studied at two levels of nutrient application: ‘normal’ (labelled ‘1’) and 1.5 times ‘normal’ (labelled ‘1½’). Water retention, air permeability and air diffusivity were measured on the small cores, and we used the large cores for measuring near‐saturated and saturated hydraulic conductivity. In the plough layer, the AM and NPK soils displayed identical pore volumes in size fractions that were larger as well as smaller than 30 μm, while the UNF soil had a significantly smaller volume of pores < 30 μm. No clear trends were found in treatment effects on pore organization as calculated from air diffusivity and air permeability measurements. No significant differences in hydraulic conductivity were found in the plough layer. For the subsoil below ploughing depth, significantly larger macropore volumes and near‐saturated hydraulic conductivities were found for soil of plots receiving the larger (‘1½’) amount of nutrients compared with the ‘normally’ dressed soil. This effect was independent of fertilization system (AM or NPK). We attribute the larger volume of macropores to the improved root growth conditions in the soil with the higher nutrient level. We conclude that addition of animal manure at rates realistic in agriculture has only a modest effect on soil pore characteristics of the plough layer soil compared with the use of mineral fertilizers. For the subsoil below ploughing depth, a high level of nutrient application may increase soil macroporosity and near‐saturated hydraulic conductivity, but the origin of nutrients is of no significance. 相似文献
14.
We present a new method of characterizing the void structures of soils from water retention curves as the primary source of data. The method avoids the problems of other current approaches, which use smoothing curves and can miss the subtleties of soil structure, and usually ignore the shielding of large pores by the small connecting throats surrounding them. In the new method, software we have named ‘Pore‐Cor’ is used to generate simple three‐dimensional networks of voids that have the same water retention characteristics and porosities as the soils. To find the geometry of the required networks, we have introduced a Boltzmann‐annealed simplex which works in four parametric and three Boolean dimensions of parameter space. Also, a more robust measure of the difference between the experimental and simulated water retention curves has been developed. The method is applied to water retention curves for a wide range of English and Welsh soils, both experimental and generated from a pedotransfer function. The resulting simulated void structures have void sizes that change as expected across the soil texture diagram, have different structures as highlighted by the locations of retained water, but have connectivities (number of connecting throats per pore) that vary little. A wide range of other calculations of wetting and non‐wetting fluid transport properties, and calculations of the behaviour of fluid‐borne pollutants, are now possible. The main bar to further progress is a lack of sufficiently accurate and comprehensive data for water retention, and for saturated and unsaturated hydraulic conductivity. 相似文献
15.
土壤水力性质是研究非饱和带中水分和溶质运移的重要参数 ,可以用孔隙网络模型进行预测。通常采用的网络模型中的参数是任意指定的 ,无法真实反映土壤孔隙空间的形态特征。本文采用了一种基于孔隙形态学的网络模型来预测土壤的水力性质 ,即通过图像分析来直接测定孔隙的大小分布及其连通性 ,并将其结合到网络模型中 ,最大程度地再现了三维的土壤孔隙结构。本文根据河南封丘地区采集的砂壤土样本图像分析结果 ,采用形态学网络模型预测了其水力性质 ,同时也进一步评价了这种模型的优缺点及其应用前景。 相似文献
16.
Although crop residue management is known to affect near‐surface soil physical quality, little is known about the temporal variability of these indicators over short time intervals. This study evaluates the temporal changes of nine indicators of soil physical quality. These are organic carbon content, structural stability index, bulk density, macroporosity, air capacity, relative field capacity, plant available water capacity, Dexter's S‐index and saturated hydraulic conductivity. A second set of soil physical indicators, based on the distribution of soil pore volume, was also evaluated. The indicators were determined in three different times during the growing cycle of winter durum wheat cultivated within a long‐term field research carrying out in Southern Italy and comparing two types of crop residue management, that is, burning (B) and soil incorporation (I). Only the bulk density changed over time for both treatments, although the air capacity also changed for the incorporation of wheat residues. Residual effects of the autumnal soil tillage and soil compaction were a common source of variability, irrespective of which treatment was used. Based on the existing guidelines for evaluating the physical quality of these agricultural soils, optimal or near‐optimal values were detected in about half of the cases under consideration. This suggests that both B and I create sufficiently good conditions for crop growth during the crop cycle. The comparison between observed and optimal soil pore distribution function was always poor. The pore volume distributions showed lower densities of small pores and relatively higher densities of large pores than the proposed optimal distribution. This study also suggests that the considered optimal or references curves probably cannot be applied successfully to a wide range of agricultural soils. 相似文献
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Morphological determination of pore connectivity as a function of pore size using serial sections 总被引：9，自引：0，他引：9
H. J. VOGEL 《European Journal of Soil Science》1997,48(3):365-377
The geometry of pore space in soil is considered to be the key in understanding transport of water, gas and solute. However, a quantitative and explicit characterization, by means of a physical interpretation, is difficult because of the geometric complexity of soil structure. Pores larger than 40 μm within two soil horizons have been analysed morphologically on 3-dimensional digital representations of the pore space obtained by serial sections through impregnated specimens. The Euler-Poincaré characteristic has been determined as an index of connectivity in three dimensions. The pore connectivity is quantified as a function of the minimum pore diameter considered leading to a connectivity function of the pore space. Different pore size classes were distinguished using 3-dimensional erosion and dilation. The connectivity function turned out to differentiate between two soil materials. The pore space in an upper Ah horizon is intensely connected through pores between 40 and 100 μm, in contrast to the pore space in the AhBv beneath it. The morphological pore-size distributions were compared to the pore-size distribution obtained by water retention measurements. The discrepancy between these different methods corresponds to the expectation due to pore connectivity. 相似文献
18.
J. A. CURRIE 《European Journal of Soil Science》1983,34(2):217-232
Gas diffusion coefficients for hydrogen through air in packings of 1–2 mm crumbs from a clay loam (both under grass and under arable) and from a sandy loam were measured over a range of water contents as the soils were wetted. Diffusion coefficients decreased with increasing water content (decreasing air content) in three stages: in the first, to specific water contents of 0.08–0.10 gg1, decreases were small indicating the filling of pores less effective for diffusion; in the second, to crumb saturation, decreases were greater, and in the third, to complete saturation, decreases were greatest. Two of these stages are related to swelling: in the first, any slight swelling is contained within the crumb and there is loss to the gas of crumb pores only; in the second, the crumbs swell and there is simultaneous loss of crumb pore space and, more important, inter-crumb space; in the third, swelling is complete, so, as in nonswelling soil, there is loss of inter-crumb space only. Pore size and pore shape in the three soils, and pore distribution (intra-crumb structure) in the grassland clay loam, may also affect diffusion but to a lesser extent: these influences are discussed. On subsequent drying there was little evidence of hysteresis in diffusion with water content, and only a slight indication in the arable clay loam of decreases due to structural degradation during the measurements. 相似文献
19.
A. R. Russell 《European Journal of Soil Science》2010,61(3):412-424
A soil with double porosity is modelled as a collection of aggregated particles, in which a single aggregate is made up of discrete particles bonded together. Separate fractal distributions for pore sizes around and within aggregates are defined. The particle size distribution of the double porosity soil is also modelled using a fractal distribution, which may have a fractal dimension very different to those defining the pore sizes. The surface areas of the particles and the pores within the aggregates are assumed to be equal, enabling an expression linking two fractal dimensions to be defined. It is necessary to introduce ratios between maximum and minimum particle and pore sizes into the expression. A theoretical soil‐water characteristic curve is then derived for a double porosity soil. The curve, and the underlying assumptions regarding the distributions of pore and particle sizes, showed good agreement with experimental data for a range of soils having double porosity. A discontinuity is observed in the soil‐water characteristic curve at a second air entry value related to the maximum pore size within the aggregates, a feature also observed in experimentally obtained soil‐water characteristic curves for double porosity soils. 相似文献
20.
The structure of two alluvial soils in Italy after 10 years of conventional and minimum tillage 总被引：6，自引：0，他引：6
Micro and macroporosity, pore shape and size distribution, aggregate stability, saturated hydraulic conductivity and crop yield were analysed in alluvial silty loam (Fluventic Eutrochrept) and clay soils (Vertic Eutrochrept) following long-term minimum and conventional tillage. The soil structure attributes were evaluated by characterizing porosity by means of image analysis of soil thin sections prepared from undisturbed soil samples.
The interaggregate microporosity, measured by mercury intrusion porosimetry, increased in the minimally tilled soils, with a particular increase in the storage pores (0.5–50 μm). The amount of elongated transmission pores (50–500 μm) also increased in the minimally tilled soils. The resulting soil structure was more open and more homogeneous, thus allowing better water movement, as confirmed by the greater hydraulic conductivity of the minimally tilled soils. The aggregate stability was less in the conventionally tilled soils and this resulted in a greater tendency to form surface crusts and compacted structure, compared with the minimally tilled soils. The latter tillage practice seemed to maintain, in the long-term, better soil structure conditions and, therefore, maintain favourable conditions for plant growth. In the silt loam, the crop yield did not differ significantly between the two tillage systems, while in the clay soil it decreased in the minimum tilled soil because of problems of seed bed preparation at the higher surface layer water content. 相似文献