bluuebunny/crossref_metadata_2025_split huggingface dataset:
A laboratory method for measuring the isotropic character of soil swelling
Authors: Michel J. ‐C. , Beaumont A. , Tessier D. 
Published: March 2003

SummaryAlthough the swelling of clays has been thoroughly studied, the mechanism by which this occurs in clay soils is not so fully understood. We have developed a technique to study the swelling and three‐dimensional deformation of a soil sample during wetting by adapting a triaxial apparatus. This equipment applies a controlled, confined and isotropic pressure to the periphery of the samples. A constant flow of solution is injected into the base of the sample while the lateral and axial deformations are simultaneously controlled. The development of the interstitial pressure, positive or negative, is measured. When the soil is thoroughly wetted, the equipment measures the saturated hydraulic conductivity.The swelling of the soil is not necessarily isotropic, and practically all the possibilities of lateral, isotropic and vertical swelling can be encountered. Furthermore, the swelling can be preceded by significant lateral shrinkage, caused by fissures. The results show the importance of confinement pressure when measuring the swelling of the samples.The adaptation of a triaxial apparatus to the study of the permeability and swelling of soils appears to be promising as it also allows the geometric development of the samples to be traced as well as the changes in the chemical composition of the percolating solutions.
Non‐equilibrium water flow characterized by means of upward infiltration experiments
Authors: Šimůnek J. , Wendroth O. , Wypler N. , Van Genuchten M. T. 
Published: March 2003

SummaryUpward infiltration experiments under tension were used to demonstrate the presence of non‐equilibrium flow in soils, the phenomenon that has important implications for the accelerated movement of fertilizers, pesticides, non‐aqueous liquids, and other pollutants. Data obtained from these experiments were analysed using the single‐porosity Richards equation, as well as a variably saturated, dual‐porosity model and a dual‐permeability model for characterizing non‐equilibrium water flow. The laboratory experiments were carried out on 0.10‐m‐long soil cores having an internal diameter of 0.10 m. Constant pressure heads of −0.10 and −0.01 m were used as the lower boundary condition. Each infiltration was followed by a single‐rate evaporation experiment to re‐establish initial conditions, and to obtain the drying soil hydraulic properties. Pressure heads inside the cores were measured using five tensiometers, while evaporative water loss from the top was determined by weighing the soil samples. The data were analysed to estimate parameters using a technique that combined a numerical solution of the governing flow equation (as implemented in a modified version of the Hydrus‐1D software) with a Marquardt–Levenberg optimization. The objective function for the parameter estimation was defined in terms of pressure head readings, the cumulative infiltration rate, and the final total water volume in the core during upward infiltration. The final total water volume was used, as well as the pressure head readings during the evaporation part. Analysis of flow responses obtained during the infiltration experiment demonstrated significant non‐equilibrium flow. This behaviour could be well characterized using a model of physical non‐equilibrium that divides the medium into inter‐ and intra‐aggregate pores with first‐order transfer of water between the two systems. The analysis also demonstrated the importance of hysteresis.
Abandoned anthills of Formica polyctena and soil heterogeneity in a temperate deciduous forest: morphology and organic matter composition
Authors: Kristiansen S. M. , Amelung W. 
Published: March 2003

SummaryAnts can modify the properties of soil when they build their nests. We have investigated the degree and persistency of changes of soil morphology and chemistry in abandoned anthills in a temperate, deciduous wood in Jutland, Denmark. For this purpose, we sampled surface soils (0–10 cm) from each of five abandoned anthills (Formica polyctenaFörster) and adjacent undisturbed sites, where anthills covered about 0.5% of the surface area. In addition, one soil profile in an abandoned anthill was sampled for morphological descriptions. All samples were analysed for pH, C, N, lignin‐derived phenol, and cellulosic and non‐cellulosic carbohydrate concentrations. The results showed that soils under the anthills were enriched in organic matter, were yellower and showed features of Podzol degradation. Former Podzols had to be reclassified to Umbrisols or Arenosols, whereas anthills on Luvisols affected soil classification only at the subdivision level. The C/N ratio and soil pH were not significantly affected by the ants' activity. However, lignin‐derived phenols and cellulosic polysaccharides were enriched inside the mounds by a factor of 6 and 7, respectively. This probably reflected collection of woody debris for nest construction while the nest was occupied, and large input of C from an increased root density. The degree of changes in the quality of the organic matter decreased with time since abandonment, but changes were still detectable within anthills left 20 years ago. As ant colonies are concentrated, and move regularly on a decadal timescale, formation ofFormicaanthills has an intrinsic influence on the heterogeneity of the soil within this forest ecosystem.
Interpretation of heteronuclear and multidimensional NMR spectroscopy of humic substances
Authors: Simpson A. J. , Burdon J. , Graham C. L. , Hayes M. H. B. , Spencer N. , Kingery W. L. 
Published: March 2003

SummaryMapping the chemical structures and organization of humic substances is vital for a fundamental understanding of their roles and interactions in the soil. One‐dimensional nuclear magnetic resonance (NMR) techniques have advanced our awareness of the composition of humic materials, but modern developments in two‐dimensional NMR are soon likely to make obsolete reliance on one‐dimensional spectra alone. The advantages of using heteronuclear two‐dimensional NMR spectroscopy are illustrated in this paper in studies of the structural units in a fulvic acid fraction isolated from the Bh horizon of a Podzol.The structures identified from the NMR (at 500 MHz) experiments can be summarized as: mono‐ and dicarboxylic acids (in about equal amounts), with an average chain length of about 10 carbon atoms (these are easily the major components); smaller amounts (about 10–20% of the acids) of esters and alcohols or ethers; some carbohydrate and amino acid residues (evidence from chemical shift data would suggest that these were likely to be in the form of chains); and very small amounts of 1,2‐, 1,4‐, and 1,3,4‐substituted benzenes and of cinnamic acids. The results suggest that applications of heteronuclear and multidimensional NMR spectroscopy will allow considerable progress to be made in understanding the nature of the structural units and their connectivities in humic molecules provided that the heterogeneity of the humic mixtures can first be decreased significantly.
Description and classification of soil structure using distance transform data
Authors: Holden N. M. 
Published: March 2003

SummaryClassification of soil based on structure is useful for conveying information about physical properties and soil processes. The distance transform is an image analysis technique suitable for quantifying soil structure. An analysis of distance transform data, in the form of cumulative area distribution curves for previously published images of soil structures of various types, is presented. The images were used to derive a quantitative classification of structure using maximum distance of solid from a macropore (Dmax, measured), the distance from macropore space containing 50% of the solid area (k, derived by fitting a sigmoidal function to the cumulative area distribution curve), the total interface length between pore and solid per area of sample (IA, measured), the porosity or the proportion of pores per area of sample (PA, measured) and the pore distribution characteristic (n, derived by fitting a sigmoidal function to the cumulative area distribution curve) which is related to the number, continuity and distribution of pores. The influence of image resolution was investigated, and within limits found to be fairly small. The final classification of soil structure was based on the hypothesized relations between the descriptors and structure‐forming processes.
Changes in variance and correlation of soil properties with scale and location: analysis using an adapted maximal overlap discrete wavelet transform
Authors: Lark R. M. , Webster R. 
Published: March 2003

SummaryThe magnitude of variation in soil properties can change from place to place, and this lack of stationarity can preclude conventional geostatistical and spectral analysis. In contrast, wavelets and their scaling functions, which take non‐zero values only over short intervals and are therefore local, enable us to handle such variation. Wavelets can be used to analyse scale‐dependence and spatial changes in the correlation of two variables where the linear model of coregionalization is inadmissible.We have adapted wavelet methods to analyse soil properties with non‐stationary variation and covariation in fairly small sets of data, such as we can expect in soil survey, and we have applied them to measurements of pH and the contents of clay and calcium carbonate on a 3‐km transect in Central England. Places on the transect where significant changes in the variance of the soil properties occur were identified. The scale‐dependence of the correlations of soil properties was investigated by calculating wavelet correlations for each spatial scale. We identified where the covariance of the properties appeared to change and then computed the wavelet correlations on each side of the change point and compared them. The correlation of topsoil and subsoil clay content was found to be uniform along the transect at one important scale, although there were significant changes in the variance. In contrast, carbonate content and pH of the topsoil were correlated only in parts of the transect.
Rock weathering promoted by embryonic soils in surface cavities
Authors: Certini G. , Corti G. , Ugolini F. C. , De Siena C. 
Published: March 2003

SummaryThe upper surfaces of trachyte outcrops and boulders in Tuscany and Latium have numerous cavities. The cavities have formed from the dislodgement of xenoliths and, if properly oriented, they collect water and accumulate mineral and organic debris. There is no drainage, and water stays in them for a long time, inducing a severe hydrological regimen, but supporting a variety of living organisms such as cyanobacteria, green algae and insects. The humic substances produced by the humification of organic matter and the organic acids released by organisms alter the underlying rock, thereby deepening and enlarging the cavities. Following the dissolution of the glassy cements, crystals detach from the matrix to join the accumulated material, where they are progressively comminuted and partly changed into clay minerals. With time, these accumulations increase in thickness sufficiently to allow the establishment of vascular plants and the development of horizons so as to become embryonic soils. We sampled the material from several such cavities and determined its chemical and mineralogical composition. We conclude that cavities contain miniature ecosystems supported by the tiny bodies of soil in them.
Spatial and temporal variations in resistance of loess‐derived soils to ephemeral gully erosion
Authors: Nachtergaele J. , Poesen J. 
Published: March 2003

SummaryPlanners would like a simple means of describing spatial and temporal variations in soil erodibility accurately. We have done a series of concentrated flow detachment experiments to investigate the feasibility. Four different soil horizons, typical of loess‐derived soils in Belgium, were sampled seven times during one year, so that a representative range of initial soil moisture contents was obtained. Undisturbed soil samples were subjected to five different combinations of slope gradient and concentrated flow discharge. Results showed that for a given soil horizon, variations in detachment rate could be related well to temporal variations in initial soil moisture content. For a given initial soil moisture content the ploughed topsoil horizon (Ap) and the underlying clay‐enriched horizon (Bt) had only one fifth of the erodibility of the loess horizon whether decalcified (C1) or still calcareous (C2). Combining knowledge on spatial distribution of soil profiles and initial soil moisture content allowed us to explain observed spatial and temporal variations in resistance to ephemeral gully erosion for soils in loess. Also, differences in ephemeral gully morphology (cross‐sections) could be explained from differences in initial soil moisture content and soil horizon. In the short term these results have important implications for spatial and temporal variations in erosion, while in the medium or long term information on spatial distribution of soil profiles is crucial when predicting the volumes and patterns of (ephemeral gully) erosion. Finally, the importance of combining the effect of water and tillage erosion with respect to soil profile evolution and consequent erosion risk is stressed.
The inherent ‘safety‐net’ of an Acrisol: measuring and modelling retarded leaching of mineral nitrogen
Authors: Suprayogo D. , Van Noordwijk M. , Hairiah K. , Cadisch G. 
Published: March 2003

SummaryThe inherent features of Acrisols with their increasing clay content with depth are conducive to reducing nutrient losses by nutrient adsorption on the matrix soil surfaces. Ammonium (NH4+) and nitrate (NO3−) adsorption by a Plinthic Acrisol from Lampung, Indonesia was studied in column experiments. The peak of the H218O breakthrough occurred at 1 pore volume, whereas the median pore volumes for NH4+and NO3−ranged from 6.4 to 6.9 and 1.1 to 1.6, respectively. The adsorption coefficients (Kain cm3g–1) measured were 1.81, 1.51, 1.64 and 1.47 for NH4+and 0.03, 0.09, 0.10 and 0.17 for NO3−, respectively, in the 0–0.2, 0.2–0.4, 0.4–0.6 and 0.6–0.8 m soil depth layers. The NH4+and NO3−adsorption coefficients derived from this study were put in to the Water, Nutrient and Light Capture in Agroforestry Systems (WaNuLCAS) model to evaluate their effect on leaching in the context of several cropping systems in the humid tropics. The resulting simulations indicate that the inherent ‘safety‐net’ (retardation mechanism) of a shallow (0.8–1 m) Plinthic Acrisol can reduce the leaching of mineral N by between 5 and 33% (or up to 2.1 g m−2), mainly due to the NH4+retardation factor, and that the effectiveness in reducing N leaching increases with increasing depth. However, the inherent ‘safety‐net’ is useful only if deep‐rooted plants can recover the N subsequently.
Influence of prolonged arable cropping on lignin compounds in sandy soils of the South African Highveld
Authors: Lobe I. , Du Preez C. C. , Amelung W. 
Published: March 2003

SummaryThe preservation of plant residues is important for sustainable arable cropping. Lignin is a marker for plant residues in soils. We have investigated influences of the length of cultivation on the dynamics of lignin. Composite samples were taken from the top 20 cm of soils that have been cropped for periods varying from 0 to 98 years in each of three different agro‐ecosystems in the Free State Province of South Africa. Lignin‐derived phenols were determined in the <2 µm (clay), 2–20 µm (silt), 20–250 µm (fine sand) and 250– 2000 µm (coarse sand) size separates. With increasing length of cultivation, the concentration of such phenols decreased to 36% of that in the grassland. The lignin contents as proportions of the total carbon did not change during cultivation, suggesting that there was no selective enrichment of lignin moieties as C was lost as a result of cultivation. The loss rate constants of lignin concentrations in particle‐size fractions increased in the order clay (0.17 year−1) ≤ silt (0.18 year−1) < fine sand (0.20 year−1) < coarse sand (0.22 year−1). Increasing ratios of phenolic acids to aldehydes in bulk soil, silt and fine sand fractions with increasing length of cultivation indicated that side chains were being oxidized. The ratios in the silt fraction, however, decreased after 10–20 years. We attribute this to a loss of lignin together with silt by wind erosion, resulting in a rejuvenation of lignin compounds in the remaining silt‐sized pools of C.
Depletion of soil phosphorus as assessed by several indices of phosphorus supplying power
Authors: Yli‐ Halla M. , Hartikainen H. , Väätäinen P. 
Published: March 2003

SummaryThis study attempts to clarify the advantages and shortcomings of various laboratory tests that are used to characterize the status and dynamics of soil phosphorus (P). We analysed a set of soil samples differing in P status for inorganic P fractions, water‐soluble P (Pw60) and bicarbonate‐extractable P (POlsen) both before and after a pot experiment in which soil was depleted. Their P exchange characteristics were determined by Q/I plots, fitted by a modified Langmuir equation, and the supplying power was further assessed by extracting soil samples with various amounts of water. The sensitivity of the P tests in assessing the decrease in inorganic reserves of P was expressed using a response index that was defined as the ratio between the decrease in inorganic P and the decrease in soil P test value. For POlsen, the index ranged from 6 to 11 and for Pw60 from 10 to 26. Desorption curves obtained by extracting soil samples with different amounts of water indicate increased buffering power and that large reserves of P were released from soil in weak solutions (P < 0.030 mg l−1) around soil particles. Although the constants of the Langmuir equation responded reasonably well to the changes in reserves of P in the soil, the results suggest caution is needed in the quantitative interpretation of the constant Q0 (instantly labile P) of the Langmuir equation.
A re‐interpretation of ‘Aluminium solubility mechanisms in moderately acid Bs horizons of podzolized soils’ by Gustafsson et al.
Authors: Farmer V. C. , Lumsdon D. G. 
Published: March 2003

SummaryGustafsson et al. in a recent paper in this Journal reported the effects of adding HCl, AlCl3 and Si(OH)4 on the pH and concentrations of Al and Si in 1:1 soil:solution systems at three different temperatures, using samples of soil from an allophanic Bs horizon. Contrary to their conclusions, their observations are compatible with Al in the soil solution being in equilibrium with a proto‐imogolite allophane; it is neither necessary nor even plausible to postulate a hypothetical Al hydroxide. Concentrations of 0.2–0.4 mm Si in the equilibrated solutions at pH 5 could arise from an amorphous silica, probably phytoliths. They cannot come from the allophane.
Field calibration of the Optical Plankton Counter with respect to Calanus finmarchicus
Authors: Heath M.R. , Dunn J. , Fraser J.G. , Hay S.J. , Madden H. 
Published: March 2003

Zooplankton in the Faroe–Shetland Channel and north‐western North Sea were sampled concurrently with a profiling serial net system and an Optical Plankton Counter (OPC) during January and March 1995. Calanus finmarchicus, together with a small proportion of Calanus helgolandicus (< 3% overall), made up > 75% of the zooplankton in the region, with C. finmarchicus being predominant below 500 m depth. Sensitivity analysis of the OPC data was carried out to determine the particle size range providing the highest correlation between the concentrations of stage CIV–CV and stage CVI C. finmarchicus estimated from net catches, and particle concentrations from the OPC. Significant correlations were obtained for particle size ranges that corresponded closely with microscopic measurements of the dimensions of copepodites. The highest correlations were obtained for stages CIV–CV in January.According to the net sampling, the concentration of C. finmarchicus in January varied by at least four orders of magnitude over the survey region (< 0.05 to > 500 m−3), although only 4% of the samples contained > 100 m−3. When C. finmarchicus was present at concentrations of around 120 m−3, similar estimates of its abundance were obtained from the OPC data as from the net samples. At lower concentrations, the OPC increasingly overestimated the net catches, and the overestimate reached 40:1 at the detection limit of the nets (0.05 m−3). The average overestimate, taking into account the distribution of concentrations, was 2.5:1. This over‐estimate could not be wholly accounted for by the occurrence of other zooplankton species or potential errors associated with the OPC or net system, and the conclusion was that it arose mainly from the detection of detrital aggregates by the OPC. Thus, the OPC was effective at resolving the peak concentrations (> 100 m−3) of C. finmarchicus in the survey region, but was less effective at delineating the marginal areas of the distribution where C. finmarchicus was outnumbered by other similarly sized particles. Nevertheless, the results indicated that, with the application of calibration data such as described here, the OPC is a valuable tool for broad scale surveys of the spatial distribution of C. finmarchicus during the winter, when the animals are concentrated at depths > 500 m in areas such as the Faroe–Shetland Channel.
Availability of horse mackerel (Trachurus trachurus) in the north‐eastern North Sea, predicted by the transport of Atlantic water
Authors: Iversen Svein A. , D. Skogen Morten , Svendsen Einar 
Published: March 2003

AbstractOne of the clearest relationships between a single marine climate variable and fisheries yield is found between the transport of Atlantic water into the North Sea in the winter and catches of horse mackerel (Trachurus trachurus L.) in the northern North Sea 6 months later. A three‐dimensional numerical model, the NORWegian ECOlogical Model system (NORWECOM), has estimated this inflow during the winter from 1976 to 2000, which is strongly correlated with the Norwegian fleet's catch of horse mackerel (r2 = 0.70) in the following autumn. It is hypothesized that a large influx of this relatively warm and nutrient rich water during the winter may support an early spawning of zooplankton and high biological production during the spring and summer. This might be the biological reason for a large fraction of the horse mackerel stock migrating into the North Sea during strong inflows.