bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of moisture content in a deformable soil using time‐domain reflectometry (TDR)
Authors: Kim D. J. , Choi S. I. , Ryszard O. , Feyen J. , Kim H. S. 
Published: March 2003

SummaryTime‐domain reflectometry (TDR) is being used increasingly for measuring the moisture content of porous media. However, successful application for measuring water in soil has been limited to non‐deformable soils, and it would be a valuable extension of the technique if it could be used for soils that shrink on drying. We have recently investigated its application to soils rich in clay and organic matter and peats. Here we propose a method for determining moisture content in deformable soils based on the relation between the dielectric constant, K, and the volumetric moisture content, Θ, measured by TDR.Parallel TDR probes with a length of 15 cm and a spacing of 2 cm were placed horizontally in soil cores with a diameter of 20 cm and height of 10 cm taken from a forest. The soil is very porous with large proportions of both silt and clay. The sample weight and travel time of the electromagnetic wave guided by parallel TDR probes were simultaneously measured as a function of time, from saturation to oven‐dryness during which the core samples shrank considerably. Vertical and horizontal components of shrinkage were also measured to take the air‐exposed region of TDR probe into account in the determination of K. The effect of deformation on volumetric moisture content was formulated for two different expressions, namely actual volumetric moisture content (AVMC) and fictitious (uncorrected) volumetric moisture content (FVMC). The effects of air‐exposure and expressions of volumetric moisture content on the relation between K andΘ were examined by fitting the observations with a third‐order polynomial. Neglecting the travel time in the air‐exposed part or use of the FVMC underestimated the Θ for a given K. The difference was more pronounced between AVMC and FVMC than between two different dielectric constants, i.e. accounting for air‐exposure, Kac, and not accounting for air‐exposure, Kau. When the existing empirical models were compared with the fitted results, most underestimated the relation based on the AVMC. This indicates that published empirical models do not reflect the effect of deformation on the determination of Θ in our forest soil. Correct use of the Θ expression has more impact on determining moisture content of a deformable soil than the accommodation of travel time through the air‐exposed region of TDR probe.
Myriapod and isopod communities in soils contaminated by heavy metals in northern France
Authors: Grelle C. , Fabre M. ‐C. , Leprêtre A. , Descamps M. 
Published: March 2003

SummarySoil invertebrates suffer from contamination of the soil by heavy metals. We have studied the effects of contamination by cadmium, zinc and lead on their communities in soils in northern France by comparing polluted land with non‐contaminated sites. We have followed the seasonal variations and effects of soil properties. Saprophagous invertebrates (Diplopoda, Isopoda) and Chilopoda were sampled by pitfall‐trapping from February to November in fairly contaminated areas. In addition, a Berlese extraction of the litter in two very highly contaminated sites was conducted during autumn; animals were also trapped during June in the same locations. The most active period for myriapods was spring (April and May), whereas isopods were abundant from April to the end of summer. No clear relation was found relating dominant species or number of myriapods or isopods to concentration of heavy metal in the little‐contaminated soils. The dominant species seemed not to be related to pollution but to vegetation or soil characteristics. In the most contaminated sites, with metalliferous grassland and a thick undecomposed litter layer, a threshold in contamination values seemed to be reached: no isopods or millipedes were found, but only Chilopoda and Symphyla.
Effect of compaction on the porosity of a silty soil: influence on unsaturated hydraulic properties
Authors: Richard G. , Cousin I. , Sillon J. F. , Bruand A. , Guérif J. 
Published: March 2003

SummaryTillage and traffic modify soil porosity and pore size distribution, leading to changes in the unsaturated hydraulic properties of the tilled layer. These changes are still difficult to characterize. We have investigated the effect of compaction on the change in the soil porosity and its consequences for water retention and hydraulic conductivity. A freshly tilled layer and a soil layer compacted by wheel tracks were created in a silty soil to obtain contrasting bulk densities (1.17 and 1.63 g cm−3, respectively). Soil porosity was analysed by mercury porosimetry, and scanning electron microscopy was used to distinguish between the textural pore space and the structural pore space. The laboratory method of Wind (direct evaporation) was used to measure the hydraulic properties in the tensiometric range. For water potentials < −20 kPa, the compacted layer retained more water than did the uncompacted layer, but the relation between the hydraulic conductivity and the water ratio (the volume of water per unit volume of solid phase) was not affected by the change in bulk density. Compaction did not affect the textural porosity (i.e. matrix porosity), but it created relict structural pores accessible only through the micropores of the matrix. These relict structural pores could be the reason for the change in the hydraulic properties due to compaction. They can be used as an indicator of the consequences of compaction on unsaturated hydraulic properties. The modification of the pore geometry during compaction results not only from a decrease in the volume of structural pores but also from a change in the relation between the textural pores and the remaining structural pores.
Laser‐induced breakdown spectroscopy for soil diagnostics
Authors: Bublitz J. , Dölle C. , Schade W. , Hartmann A. , Horn R. 
Published: March 2003

SummaryLaser‐optical measurements and fibre optics are potentially attractive tools for applications in soil science because of their great sensitivity and selectivity and their capabilities for on‐line and in situ analysis. We have investigated laser‐induced breakdown spectroscopy (LIBS) for the quantitative detection of metal ions on the surface of natural soil samples from two sites (Hohenschulen and Oderbruch, Germany). The LIBS technique allows the spatially resolved investigation of adsorption and desorption effects of ions in soil. A frequency doubled (532 nm) and Q‐switched Nd:YAG laser with a pulse duration of 8 ns is focused on the soil surface and induces a plasma. Typical power densities are 150 mJ mm−2. The plasma emission is recorded in time and spectrally resolved by a gateable optical multichannel analyser (OMA). A delay time of about 500 ns between laser pulse and OMA gate was used to resolve single atomic and ionic spectral lines from the intense and spectrally broad light that is emitted by the plasma itself. The dependency of the LIBS signal of a single spectral line on the amount of water in the sample is investigated in detail. The results indicate that quenching of water in the plasma plume reduces the line intensities, while the interaction with aquatic colloids increases the intensity. The two processes compete with each other, and a non‐linear correlation between measured line intensities and the amount of water in the sample is obtained. This is verified by a simple computer simulation and has to be taken into account for the quantitative interpretation of LIBS signals, e.g. when absolute concentrations are estimated. In the present investigation natural calcium concentrations < 2 μg kg−1 were measured with the LIBS technique in the samples for the two test sites. In addition, measurements were made with dry and water‐saturated BaCl2 mixed soil samples, and no significant difference in the detection limit for barium was obtained.
Effect of sodium adsorption ratio and electrolyte concentrations on the saturated hydraulic conductivity of clay–sand mixtures
Authors: Aringhieri R. , Giachetti M. 
Published: March 2003

SummaryWe did flow experiments under saturated conditions on homoionic (Na+) kaolin–sand and illite–sand systems, containing 5, 10, and 15% clay, to validate a drainage model, and evaluate the effect of the different chemical composition of the percolating solutions on the hydraulic properties of the systems. Column drainage experiments, under a constant hydraulic head, were carried out using solutions with two sodium adsorption ratios (SAR 0 and ∞) and three electrolyte concentrations (10−2, 10−3, and 10−4 m). We calculated the saturated hydraulic conductivity, Ksat, of the systems using Darcy's law when these showed linear relationships between effluent volume and time. The drainage model was applied to characterize the flow of non‐steady‐state drainage of solutions through the porous systems. This model describes and characterizes quantitatively the drainage of solutions from soil columns that vary in intrinsic permeability, k, because of structural modifications that occur within the solid matrix of the systems. For both the systems investigated we always observed a decrease in the flow rate as electrolyte concentration decreased, or clay percentage increased. Under the same conditions the flow was faster for the kaolin system than the illite system, even though kaolin dispersed more than illite. Non‐linear relations were also observed at the smallest electrolyte concentration (10−4 m). In all cases, the equations proposed correlated well with the experimental data, confirming the soundness of the model. The flow rates observed in the experiments at SAR ∞ were unexpectedly greater than those observed at SAR 0, for the two systems, when leaching with solutions at 10−3 and 10−4 m. The values of pH and electrical conductivity of the eluates support the idea that the clay hydrolysis occurred during the saturation and, to a lesser extent, during the leaching phase of the flow.
Sources and composition of soil organic matter fractions between and within soil aggregates
Authors: Six J. , Guggenberger G. , Paustian K. , Haumaier L. , Elliott E. T. , Zech W. 
Published: March 2003

SummaryIt is generally accepted that particulate organic matter derives from plants. In contrast, the enriched labile fraction is thought by many to derive from microbes, especially fungi. However, no detailed chemical characterization of these fractions has been done. In this study, we wanted to assess the sources (plants or microbes; fungi or bacteria) and degree of microbial alteration of (i) three particulate organic matter fractions – namely the free light fraction (1.85 g cm−3), the coarse (250–2000 μm) and the fine (53–250 μm) intra‐aggregate particulate organic matter fractions – and of (ii) three density fractions of fine‐silt associated carbon – namely < 2.0, 2.0–2.2 (i.e. enriched labile fraction) and > 2.2 g cm−3– by analysing the amino sugars, by CuO oxidation analyses, and by 13C‐, 1H‐ and 31P‐NMR analyses. Macroaggregates (250–2000 μm) were separated by wet‐sieving from a former grassland soil now under a no‐tillage arable regime. The three particulate organic matter fractions and the three density fractions were isolated from the macroaggregates by a combination of density flotation, sonication and sieving techniques. Proton NMR spectroscopy on alkaline extracts showed that the enriched labile fraction is not of microbial origin but is strongly degraded plant material that is enriched in aliphatic moieties partly bound to aromatics. In addition, the enriched labile fraction had a glucosamine content less than the whole soil, indicating that it is not enriched in carbon derived from fungi. Decreasing yields of phenolic CuO oxidation products and increasing side‐chain oxidation in the order coarse intra‐aggregate particulate organic matter < fine inter‐aggregate particulate organic matter < fine‐silt fractions indicate progressive alteration of lignin as particle size decreases. The light fraction was more decomposed than the coarse inter‐aggregate particulate organic matter, as indicated by (i) its larger ratio of acid‐to‐aldehyde of the vanillyl units released by CuO oxidation, (ii) the smaller contribution of H in carbohydrates to total extractable H as estimated by 1H‐NMR spectroscopy, and (iii) a larger contribution of monoester P to total extractable P in the 31P‐NMR spectra. In conclusion, the four fractions are derived predominantly from plants, but microbial alteration increased as follows: coarse inter‐aggregate particulate organic matter < light fraction ≈ fine inter‐aggregate particulate organic matter < enriched labile fraction.
The dynamics of organic matter in rock fragments in soil investigated by 14C dating and measurements of 13C
Authors: Agnelli A. , Trumbore S. E. , Corti G. , Ugolini F. C. 
Published: March 2003

SummaryRock 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 soil skeleton, a forgotten pool of carbon and nitrogen in soil
Authors: Corti G. , Ugolini F. C. , Agnelli A. , Certini G. , Cuniglio R. , Berna F. , Fernández Sanjurjo M. J. 
Published: March 2003

SummaryTo evaluate the contribution of rock fragments to the soil’s total carbon content, the soil of 26 sites, ranging from the Canadian Arctic to the Jordan desert, was analysed for the content of organic C and total N in both fine earth and skeleton fractions. The soils, uncultivated and cultivated, are derived from 11 parent materials: sandstone, mica‐schist, granite, gneiss, basaltic pyroclastites, trachyte, dolomite, beach deposits, clay schist, marl and serpentinite. For each soil horizon the contents of fine earth and skeleton were determined by volume. Both fractions were analysed for bulk density, total and organic C and total N. Our results indicate that rock fragments contain amounts of C and N that depend on the nature of the parent material and on its resistance to the weathering processes. The C and N of both fine earth and skeleton were used to calculate the contents of these elements for three depths. At each depth, the skeleton contributes C and N to the soil depending on its abundance. We conclude that the contribution of the rock fragments to the soil C and N cannot be predicted from the soil taxa, but can from the parent material. Calculations that exclude C and N of the skeleton could lead to errors in the estimates of these two elements in soils.
Organic matter in particle‐size fractions from A and B horizons of a Haplic Alisol
Authors: Schmidt M. W. I. , Kögel‐ Knabner I. 
Published: March 2003

SummaryThe organic matter in soils may be stabilized by its interactions with minerals. We have studied such interactions in a Haplic Alisol under forest in which clay and organic matter have migrated from an eluvial A horizon to accumulate in an illuvial B horizon. We have tried to trace the fate of organic matter in these horizons (Ah and Bvt) by determining clay mineralogy, carbon and nitrogen content, hydrolysable amino acids, lignin signature by alkaline CuO oxidation and carbon species by13C CPMAS NMR of bulk soils and particle‐size fractions. In both horizons, most of the organic matter was present in O–alkyl and methylene structures, each contributing one‐third to the bulk organic matter. In the Ah horizon the ratios of carbon‐to‐nitrogen, and yields for lignin and hydrolysable amino acids decreased as the particle‐size class decreased, but side‐chain oxidation of lignin compounds increased with decreasing particle size. In contrast to previous observations, the proportions of O–alkyl carbon increased as particle size decreased, constituting a major proportion of the organic carbon in the clay‐size fractions from both the Ah and Bvt horizons (≥ 38%), while proportions of methylene carbon decreased. Illite was the dominant mineral in the fraction ≤ 6 μm, whereas the mobile fine clay fraction (<0.2 μm) was rich in smectites – minerals with large surface areas. Our results support the hypothesis that potentially labile organic matter, such as O–alkyl carbon typically present in polysaccharides, may be stabilized against further degradation in organomineral complexes.
Defining the relation between soil water content and net nitrogen mineralization
Authors: Paul K. I. , Polglase P. J. , O'Connell A. M. , Carlyle J. C. , Smethurst P. J. , Khanna P. K. 
Published: March 2003

SummarySimulation models of net mineralization of nitrogen (N) in soil need to be able to incorporate the effect of soil water. Our objective was to identify and define the best way of expressing soil water and its effect on net mineralization across a range of soil types. We collated data from 12 laboratory incubation studies, including a total of 33 different soils, where rates of net mineralization of N were determined from the net accumulation of mineral N under a range of water contents at near‐optimal temperatures. Measurements of water potential and limits of water content observed in the field were available for most of these soils. The percentage of pore space filled with water was estimated from measurements of soil bulk density. We found that relative water content, particularly when expressed relative to an upper and lower limit of water content observed in the field, was the best descriptor for net mineralization. The next best descriptions were soil water potential, water content relative to the optimal water content for mineralization, and percentage of pore space filled with water, with water content alone being poor. Although various functions may be used to describe the relation between relative water content and net mineralization of N, an equation for a sigmoidal curve provided the best fit, and explained 78% of the variation.
Denitrification in river sediments: relationship between process rate and properties of water and sediment
Authors: García‐ruiz  , Pattinson  , Whitton  
Published: March 2003

1. A survey was made of denitrification and nitrous oxide (N2O) production in river sediments at fifty sites in north‐east England during one season in order to investigate the relationship between rates and environmental factors likely to influence these processes. The sites were chosen to represent a wide range of physical and chemical conditions. Denitrification rate and N2O production were measured within 5 h of sampling using the slurry acetylene blockage technique.2. Denitrification rate ranged from less than 0.005–260 nmol N g–1 DW h–1, tending to increase in a downstream direction. N2O production ranged from negative values (net consumption) to 13 nmol N2O‐N g–1 DW h–1 and accounted for 0–115% of the N gases produced.3. Denitrification rate and N2O concentration in the sediment were correlated positively with nitrate concentration in the water column, water content of the sediment and percentage of fine (< 100 μm) particles in the sediment.4. The variation in denitrification rate was satisfactorily explained (64% total variance) by a model employing measurements of water nitrate and water content of sediments. No simple or multiple relationship was found for N2O production.
Differences in predation among morphotypes of the rotifer Asplanchna silvestrii
Authors: Hampton Stephanie E. , Starkweather Peter L. 
Published: March 2003

Summary1. Interactions were observed between three morphotypes of the predatory rotifer Asplanchna silvestrii and six different prey (Brachionus plicatilis, B. rotundiformis, B. pterodinoides, B. satanicus, Hexarthra jenkinae and copepod nauplii) to understand the differences in feeding abilities among morphotypes that may have led to the evolution of this predator polymorphism. The outcome of predation events was affected significantly, both by predator morphotype and prey type. Predator morphotypes also interacted differently with different prey types.2. The two smaller morphotypes, the saccate and the cruciform, responded similarly to prey overall, except that the smallest morphotype (saccate) was unable to ingest the most mobile prey (nauplii) and less able to ingest relatively large prey (B. plicatilis). The largest morphotype, the campanulate, had the highest encounter rate with prey, but the lowest probability of attack after encounter, so that it consumed far fewer prey per feeding bout than did the smaller morphotypes. This may have been because campanulates prefer larger prey than used in this study.3. Highly mobile prey (H. jenkinae and copepod nauplii) were much less susceptible to predation than the less mobile Brachionus species. While evasiveness reduced attacks by saccates and cruciforms, campanulates did not have a significantly lower attack rate on H. jenkinae and copepod nauplii than on less evasive prey. Large body size moderately defended B. plicatilis against ingestion by saccates only. The short‐spined B. satanicus was the only prey that was rejected after capture, resulting in lower ingestion probabilities for B. satanicus than other brachionid prey.