Short‐term transport of cadmium during a heavy‐rain event simulated by a dual‐continuum approach

The transport of solutes in soils, and its intensification due to preferential flow, plays crucial role when problems related to the groundwater pollution are dealt with. The objective of this study was to examine transport of cadmium (Cd) in response to an extreme rainfall event for three different soils using numerical modeling. The ^115mCd²⁺ concentration profile had been measured in the Bodiky reference site (Danubian Lowland, Slovakia) by the radioactive‐tracer technique and used for the calibration of the dual‐continuum model S1D. The Cd transport during a single rain event was predicted with the S1D model for light, medium‐heavy, and heavy soil in the same region. The Cd transport through the soil profile was simulated by the one‐dimensional dual‐permeability model, which assumes the existence of two pore domains: the soil‐matrix domain and the preferential‐flow domain. The model is based on Richards' equation for water flow and advection‐dispersion equation for solute transport. A modified batch technique enables to distinguish process of adsorption in the matrix domain and the preferential pathways. Modeling with classical single‐permeability approach and dual‐continuum approach without considering the particle‐facilitated transport led to negligible Cd penetration. The rainfall event with extremely high rainfall intensity induced deep penetration of Cd in the medium‐heavy and heavy soil, which may indicate increased vulnerability to shallow groundwater pollution for the respective sites in Danubian Lowland region. The highest Cd leaching was predicted for heavy clay soil, where the preferential particle‐facilitated transport of Cd through the soil profile was significant due to the contrasting properties of the soil‐matrix domain and the preferential‐flow domain. The results of the sensitivity analysis suggested only slight effect of the transfer rate coefficients on simulated Cd leaching.     

Relation of dispersivity to properties of homogeneous saturated repacked soil columns

It is expected that solute dispersivity is determined by the physical properties of the transport medium. However, experimental investigations to date have not identified such a relationship. In this work, we examine the relation between soil physical parameters, experimental parameters and dispersivity. Experimental data were compiled for 291 repacked, saturated homogeneous laboratory column experiments reported in the literature. Using multiple stepwise regression and classification and regression tree analysis, the relationships between soil physical parameters (sand, silt and clay content, bulk density, water content), experimental parameters (pore‐water velocity, column length and diameter), and transport parameters (dispersion coefficient and dispersivity) were examined. Regression tree analysis showed that clay content was the most important factor controlling dispersivity, followed by column diameter. Columns of length less than approximately 10 cm generally resulted in greater dispersivities than longer columns. A scale effect appeared significant with increasing column diameter, but was not apparent with column length. These results suggest that it may only be possible to relate dispersivity to intrinsic soil properties by explicitly accounting for the experimental design, including column geometry, inlet dead volume and soil packing.     

Effects of compaction on soil hydraulic properties,penetration resistance and water flow patterns at the soil profile scale

The aim of this study was to quantify the effects of compaction on water flow patterns at the soil profile scale. Control and trafficked plots were established in field trials at two sites. The trafficked treatment was created by four passes track‐by‐track with a three‐axle dumper with a maximum wheel load of 5.8 Mg. One year later, dye‐tracing experiments were performed and several soil mechanical, physical and hydraulic properties were measured to help explain the dye patterns. Penetration resistance was measured to 50 cm depth, with saturated hydraulic conductivity (K_s), bulk density, and macroporosity and mesoporosity being measured on undisturbed soil cores sampled from three depths (10, 30 and 50 cm). Significant effects of the traffic treatment on the structural pore space were found at 30 cm depth for large mesopores (0.3–0.06 mm diameter), but not small mesopores (0.06–0.03 mm) or macroporosity (pores > 0.3 mm). At one of the sites, ponding was observed during the dye‐tracing experiments, especially in the trafficked plots, because of the presence of a compacted layer at plough depth characterized by a larger bulk density and smaller structural porosity and K_s values. Ponding did not induce any preferential transport of the dye solution into the subsoil at this site. In contrast, despite the presence of a compacted layer at 25–30 cm depth, a better developed structural porosity in the subsoil was noted at the other site which allowed preferential flow to reach to at least 1 m depth in both treatments.     

Field-scale solute transport — spatially interpolating the parameters of a transfer function model

The results from a solute transport study done near Basel, Switzerland are reported. The experimental site was a 3.25 ha corn field consisting of well drained silt loam. A bromide tracer was applied to the surface of 40 plots, located at regular intervals on a grid. Soil cores were taken twice at each plot during the experiment. The first time, samples were collected at 10 cm intervals from the surface to 50 cm. During the second sampling, soil cores were taken to a depth of 100 cm in 20 cm increments. Four plots were sampled twice each time to assess small-scale heterogeneities. Solute transport was described as a convective-dispersive process with highly variable parameters within the test field. A poor correspondence between the apparent fraction of the soil volume that is active in transport and volumetric water content was found. This was interpreted as resulting from effects such as stagnant water, locally three-dimensional flow and infiltration water which bypasses the regions of the soil which contain the main mass of the tracer. The spatial distribution of the transport parameters within the test field could not be explained on the basis of soil physical properties. The fields of the transport properties showed spatial dependence and locally estimated parameters were interpolated over the entire test field by kriging.     

Effect of deep tillage on soil physical properties and maize yields on coarse textured soils

The effects of deep tillage on soil physical properties and maize yields were evaluated on a loamy sand soil in which the bulk density distribution did not show a distinct root-limiting soil zone. Sub-soiling, mould-board ploughing and deep digging to 45 cm were compared with conventional tillage with and without irrigation. The tillage operations slightly decreased the bulk density of soil at all working depths. Sub-soiling and deep digging decreased the soil penetration resistance in the 20–40-cm layer to one-tenth of that in the control. They induced deeper and greater rooting and increased profile water use compared with conventional tillage. Sub-soiling, mould-board ploughing and deep digging increased plant height by 30–35 cm and yielded 80–100% more stover and 70–350% more grain than the control in different experiments.     

Long‐term changes of aggregate‐associated and labile soil organic carbon and nitrogen after conversion from forest to grassland and cropland in northern Turkey

Soil management systems can have great effect on soil chemical, physical and biological properties. Conversion of forest to grassland and cropland can alter C and N dynamics. The objective of this study was to evaluate the changes in aggregate‐associated and labile soil organic C and N fractions after conversion of a natural forest to grassland and cropland in northern Turkey. This experiment was conducted on plots subject to three different adjacent land uses (forest, grassland and cropland). Soil samples were taken from 0–5, 5–15 and 15–30 cm depths from each land use. Some soil physical (soil texture, bulk density), chemical (soil pH, soil organic matter, lime content, total organic C and N, inorganic N, free and protected organic C) and biological (microbial biomass C and N, mineralizable C and N) properties were measured. The highest and lowest bulk densities were observed in grassland (1.41 g cm⁻³) and cropland (1.14 g cm⁻³), respectively. Microbial biomass C and total organic C in forest were almost twice greater than grassland and four‐times greater than cropland. Cultivation of forest reduced total organic N, mineralizable N and microbial biomass N by half. The great portion of organic C was stored in macroaggregates (>250 µm) in all the three land uses. Free organic C comprised smaller portion of soil organic C in all the three land uses. Thus, this study indicated that long‐term conversion of forest to grassland and cropland significantly decreased microbial biomass C, mineralizable C and physically protected organic C and the decreases were the greatest in cropland. Copyright © 2011 John Wiley & Sons, Ltd.     

Tillage effects on selected physical properties of Grantsburg silt loam

Abstract

The objective of the project was to determine the effects of tillage on soil physical properties. A tillage project, involving three treatments with eight replications [no‐tillage (NT), chisel plowing (CP), and moldboard plowing (MP)], was initiated in the spring of 1989 in southern Illinois. The soil on which the work was conducted was a Grantsburg silt loam (fine‐silty, mixed, mesic Typic Fragiudalf), with a root‐restricting fragipan found at an average depth of 64 + 14 cm from the soil surface. Corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] were grown on the plot area on a yearly rotation. The soil physical properties evaluated were: penetration resistance; bulk density; aggregate stability; and pore size distribution by water‐release. Tillage effects on soil penetration resistance were mainly confined to the plow‐layer (i.e. top 23 cm of soil). Generally, the cone index (CI) values for the top 23 cm of soil for all treatments were below 2MPa, except at midseason in 1991, a dry year. Penetration resistance differences due to tillage treatments were not caused by differences in soil water content. Soil bulk density was generally highest for NT at planting, however, the bulk density for CP and MP increased later in the season attaining values comparable to those of NT treatment. Chiseling and moldboard plowing reduced soil aggregate stability. Soil temperature at planting was lower for no‐tillage compared to the moldboard plowed system. Effects of tillage on pore size distribution, for the first two years of the experiment, were significant only at planting. Total porosity was higher for MP than CP and NT in both years. At midseason, 1991, total porosity was lower with MP than with NT and CP. The improved NT crop performance relative to the CP and MP treatments could also be related to better seed bed and root bed conditions following soybean (third year) than sod (first year) and better weed control. Initial crop yield advantages of MP over the conservation tillage systems (NT and CP) deteriorated over time, resulting in decreased soil aggregation, total porosity and soil productivity.     

Physikalische Eigenschaften von drei Bodentypen unter Acker und Grünland

Physical conditions of three soil types under arable land and pasture To evaluate the effect of the use of agricultural heavy machinery on soil structure, physical properties of three soil types (Typic Chromudert, Aquic Hapludalf, and Typic Hapludalf) managed as cropland and permanent grassland were studied under the climatic conditions of Upper Bavaria (FRG). Bulk density, saturated hydraulic conductivity, and aggregate stability were adversely affected by heavy machinery down to soil depths of at least 50 cm. Only in some cases the bulk density of aggregates was significantly increased by heavy machinery, showing that heavy machinery causes soil compaction due to a rearrangement of small soil aggregates in comparison to permanent grassland.     

北方土石山区典型坡面优先流特征研究

以太行山区崇陵流域的典型坡面为研究对象,通过亮蓝(Blue-FCF)与KI染色示踪试验,利用图像处理软件技术,计算优先流形态特征参数,分析5个不同坡位的优先流形态特征变化规律。结果表明:(1)随着坡位升高,坡面土壤厚度、容重逐渐减小,而总孔隙度、渗透系数、饱和含水量逐渐增大,凋萎系数与田间持水量则呈现波动变化趋势;(2)随着坡位的升高,染色剂运移深度不断增加,基质流区域占比减小而优先流区域占比增大;各坡位染色面积比随深度缓慢下降,在40cm以下深度范围高坡位点的土壤水分与周围土体交互作用较低坡位点较弱;染色剂入渗体积随坡位升高而逐渐增大;(3)随着坡位的升高,优先流对实际水分运移的贡献增大,高坡位坡面水分以优先流为主要方式向下入渗;(4)土壤质地与容重是影响土石山区坡面不同坡位优先流差异的主要因素。     

A semi‐analytical model for solute transport in layered dual‐porosity media

The vulnerability of groundwater from chemical leaching through soil is a concern at some locations. Because measurements are laborious, time‐consuming, and expensive, simulation models are frequently used to assess leaching risks. But the significance of simulated solute movement through a layered soil is questionable if vertical homogeneity of physical soil properties has been assumed. In the present study, a semi‐analytical model for solute leaching in soils is presented. The model is relatively simple, but it does account for soil layers having different physical properties. The model includes the mobile‐immobile model (MIM) to describe one‐dimensional (1‐D) nonequilibrium, transient solute transport under steady‐state flow conditions. The MIM is rewritten as a second‐order differential equation and solved by a numerical scheme. Differing from fully analytical or fully numerical solutions, the new approach solves the differential equation numerically with respect to time and analytically with respect to distance. Numerical experiments for a single layered soil profile show that the semi‐analytical solution (SA‐MIM) is numerically stable for a wide range of parameter values. The accuracy of SA‐MIM predictions is comparable to that of analytical solutions. Numerical experiments for a multilayered profile indicate that the model correctly predicts effluent curves from finite layered soil profiles under steady‐state flow conditions. The SA‐MIM simulations with typical parameter values suggest that neglecting vertical heterogeneity of flow paths in a layered soil can lead to inaccurate prediction of soil‐solute leaching. The quality of predictions is generally improved if parameter estimates for the different soil layers are considered. However, the mobile‐immobile‐parameter estimates obtained in a number of previous studies may not be transferable to a field situation that is characterized by a slow and steady flow of water. Further field experiments to determine mobile‐immobile parameters under such conditions are desirable.     

石砾参数对土壤水流和溶质运移影响研究进展

土壤水流和溶质运移一直是土壤学研究的热点,溶质运移理论主要应用于地下水污染、污染物运移、土壤重金属污染研究等方面。溶质主要通过优先流和基质流进行运移,影响溶质运移因素很多,主要包括土壤结构、质地、水力传导率、体积质量、初始含水量、根系、石砾等。石砾作为土壤质地中的一个分级单位,与溶质运移关系较为复杂。本文综合介绍了石砾基本内涵以及石砾对土壤水流和溶质运移影响研究进展;系统阐述了石砾内部参数(石砾覆盖度、含量、粒径、空间异质性等)和外部参数(根石结构、干湿冻融、耕作等),指出目前研究主要量化土壤表面及土壤表层石砾参数对水文效应、土壤侵蚀、入渗以及径流的影响,然而石砾参数对溶质运移影响研究不够系统,石砾参数与溶质运移关系研究尚处于初步阶段,对土壤深层石砾研究缺乏;归纳了石砾参数研究技术手段及模型;探讨了目前石砾参数对土壤水流和溶质运移影响研究存在的问题以及今后研究趋势。     

“旋松一体”耕作对潮土和砂姜黑土物理性质及作物生长的影响

为改善潮土和砂姜黑土容重大,穿透阻力强,犁底层紧实等结构障碍。研究提出一种“旋松一体”耕作方式,并在山东德州的典型潮土和安徽怀远的典型砂姜黑土进行试验。其中,潮土设置旋耕15 cm、旋松一体30 cm两个处理;砂姜黑土设置旋耕15 cm、深翻30 cm和旋松一体30 cm三个处理,研究旋松一体耕作对两种土壤0 ~ 40 cm土层土壤容重、紧实度、水分动态和小麦玉米根系及产量生长的影响。结果表明:与旋耕相比,旋松一体耕作显著降低了潮土和砂姜黑土容重和穿透阻力,与深翻相比,旋松一体耕作也显著降低了砂姜黑土容重和穿透阻力。旋松一体耕作显著提高了降水后土壤水分下渗速度、下渗量及下渗深度,进而提高潮土深层,砂姜黑土小麦季表层及玉米季深层土壤体积含水量。与旋耕相比,旋松一体耕作分别增加潮土和砂姜黑土小麦产量11.4%和7.1%,玉米产量6.7%和37%（受涝害胁迫）,提高直接经济收益1748和3277元hm?2。旋松一体耕作有效改善了潮土和砂姜黑土物理性质,提高作物产量和经济效益显著,可作为华北平原土壤耕层结构改良的新型耕作模式。     

Soil physical and hydrological properties under three biofuel crops in Ohio

Abstract

While biofuel crops are widely studied and compared for their energy and carbon footprints, less is known about their effects on other soil properties, particularly hydrologic characteristics. Soils under three biofuel crops, corn (Zea mays), switchgrass (Panicum virgatum), and willow (Salix spp.), were analyzed seven years after establishment to assess the effects on soil bulk density (ρ_b), penetration resistance (PR), water-holding capacity, and infiltration characteristics. The PR was the highest under corn, along with the lowest associated water content, while PR was 50–60% lower under switchgrass. In accordance with PR data, surface (0–10 cm) bulk density also tended to be lower under switchgrass. Both water infiltration rates and cumulative infiltration amounts varied widely among and within the three crops. Because the Philip model did not fit the data, results were analyzed using the Kostiakov model instead. Switchgrass plots had an average cumulative infiltration of 69 cm over 3 hours with a constant infiltration rate of 0.28 cm min^?1, compared with 37 cm and 0.11 cm min^?1 for corn, and 26 cm and 0.06 cm min^?1 for willow, respectively. Results suggest that significant changes in soil physical and hydrologic properties may require more time to develop. Soils under switchgrass may have lower surface bulk density, higher field water capacity, and a more rapid water infiltration rate than those under corn or willow.     

Investigating flow mechanisms in a forest soil by mixed‐effects modelling

Uniform and preferential flow produces typical infiltration patterns. We made three tracer experiments in a Norway spruce forest soil and qualitatively identified the dominant flow regime based on stained patterns. We analysed soil texture, fine root density and soil bulk density from preferential flow paths and the soil matrix by means of linear mixed‐effects models. These models can account for dependences in the data structure caused by hierarchical sampling and can deal with missing values. There were between 44% (topsoil) and 76% (subsoil) larger root densities in preferential flow paths than in the soil matrix. No significant differences in soil texture were detected. The bulk density was greater in the soil matrix by 0.12 g cm⁻³, which is probably because of a greater soil organic matter content of preferential flow paths. Using flow patterns and model results we identified the dominant flow mechanisms. At this study site, roots constituted the main preferential flow paths and induced macropore flow, especially in the topsoil. In the subsoil, root density decreased and inhomogeneous infiltration from preferential flow paths into the soil matrix caused unstable flow.     

Effect of long-term organic and mineral fertilizer on physical properties in root zone of a clayey Ultisol

To explore the effects of long-term organic and mineral fertilization practices on the physical properties in Ultisol of south China, a study was conducted since 1998 to investigate the effects of a control (CK), application of chemical fertilizers (NPK), application of organic manure (OM), and NPK fertilizer plus straw returning (NPK + straw). Results showed that OM significantly increased soil water retention capacity at all tensions but with larger increment in low tension at depths of 0–10 cm and 10–20 cm (p < 0.05) when compared with the CK. On the contrary, NPK and NPK + straw led to a decrease in soil water retention capacity under chemical treatments. In the field both in wet and dry periods, soil water content was significantly higher in OM than in NPK + straw and NPK (p < 0.05) since soil hydraulic conductivity (saturated and unsaturated) are lower in OM than in other treatments (p < 0.05). OM was also found to have the lowest soil bulk density and penetration resistance of the four treatments. A high negative correlation was observed between the soil organic carbon and the bulk density and the penetration resistance (p < 0.01). In this way, the application of OM improved the clayey soil physical properties.     

土壤渗透参数空间变异性及其影响因子研究

土壤渗透参数的空间变异性是地形因子以及土壤理化性质综合作用的结果,是影响水以及溶质迁移转化的关键因素。在坡地随机布设24个点位,测定30cm土壤的渗透参数、地形指数、容重、颗粒组成、有机质、交换性钠、CEC(阳离子交换量)和ESP。在经典统计学以及Kolmogorov—Smiromov(K—S)正态分布检验概率(Pk—s)检验基础上对数据进行了空间结构分析。结果表明,Kfs、容重、砂粒、黏粒、有机质、CEC等符合正态分布,交换性钠和ESP等属于对数正态分布;粉粒属于均匀分布;Kfs、容重、砂粒、黏粒、有机质、交换性钠和ESP等空间结构明显,CEC空间变异性较大;并以相关分析和主成分分析相结合的方法,分析了土壤渗透参数空间变异的主要影响因子。     

Changes in the physical properties of typical chernozems of Kursk oblast under the conditions of a long-term stationary experiment

The light clayey typical chernozems were studied on the fields of a long-term experiment on continuous fallowing performed by the Kursk Research Institute of Agroindustrial Production. The experiment was initiated in 1964. It includes the following variants: bare fallow, fallow with NPK application, fallow with manure application, idle land, and cropland under traditional cereal rotation. The fundamental physical properties of the chernozems, such as the particle-size distribution, the aggregate-size distribution, the water stability of the aggregates, the specific surface (as determined by the methods of the equilibrium desorption of water vapor and nitrogen), the mechanical stability of the air-dried aggregates, and the penetration resistance have not changed significantly under the impact of fertilizers and manure application. At the same time, reliable changes have taken place in the physicomechanical properties of the chernozem, including, in particular, the strength of the aggregates and the dependence of the penetration resistance on the water content. This attests to changes in the structural bonds between the soil particles under the impact of the fertilizers. An exponential equation describing the dependence of the penetration resistance on the soil’s water content in the range from the liquid limit to the plastic limit has been suggested. The analysis of the approximation parameters of this equation shows that the application of manure increases the dilatant characteristics of the chernozem and lowers its penetration resistance at the given water content. Reliably higher values of the penetration resistance have been found in the soil of the cropland, which may be related to the somewhat coarser soil texture in this experimental variant.     

Soil physical properties and wheat root growth as affected by no-tillage and conventional tillage systems in a Mediterranean environment of Chile

No-tillage systems affect soil properties depending on the soil, climate, and the time since its implementation. In heavy no-tilled soils a surface compacted layer is commonly found. Such layer can affect root growth and soil water infiltration. In several cases, surface organic carbon can buffer these problems. The aim of this study was to evaluate the effect of 4- and 7-year-old conventional (CT) and no-tillage (NT) treatments on soil physical properties, root growth, and wheat (Triticum turgidum L. var. durum) yield in an Entic Haploxeroll of Central Chile. In both tillage treatments we study soil water retention, bulk density (ρ_b), soil particle density (ρ_s), soil water infiltration, mean-weight diameter of soil aggregates (MWD), penetration resistance, grain yield, and root length density (L_v) up to a depth of 15 cm. The MWD and the penetration resistance were higher under NT as compared to CT. For the top 5 cm of soil, L_v was greater under NT as compared to CT. Differences of L_v between NT and CT were 2.09, 7.60, and 4.31 cm root cm⁻³ soil during the two leaves, flowering and grain filling phenological stages, respectively. Generally, the effect of NT on these properties was more evident near the soil surface. In contrast, fast drainage macropores, ρ_s, and soil water infiltration rates were higher under CT than under NT. Tillage treatments did not significantly affect ρ_b and yield. A longer time under no-tillage enhanced aggregate stability, however, other soil physical properties were negatively affected.