bluuebunny/crossref_metadata_2025_split huggingface dataset:
NEMIS, a predictive model of denitrification on the field scale
Authors: Hénault C. , Germon J. C. 
Published: March 2003

SummaryWe have developed a predictive model of denitrification in soils, NEMIS, based on data from a cultivated field composed of denitrification rates measured on undisturbed soil cores and the corresponding soil water‐filled pore space, nitrate content and respiration. This model is a multiplicative combination of a potential denitrification rate measured under standard conditions defined in this paper, and dimensionless functions of nitrate content, water‐filled pore space and temperature. The model was applied to two further databases obtained independently of its definition. Significant correlation was observed between the simulated and measured denitrification rates. The sensitivity of NEMIS to systematic variations of the input variables and of the coefficients included in the dimensionless functions was tested using these databases. NEMIS seems to be a very useful tool particularly adapted for interpolating a small number of denitrification measurements from a simple database composed of soil potential denitrification rate and the evolution of soil water‐filled pore space, nitrate content and temperature. Its main limitation is its high sensitivity to the water‐filled pore space from which denitrification starts to occur and which is included in the water function.NEMIS, un modèle prédictif de la dénitrification à l'échelle de la parcelle cultivéeRésuméNEMIS, un modèle prédictif de la dénitrification dans les sols, a été défini à partir d'une base de données obtenue dans un sol cultivé et composée de vitesses de dénitrification mesurées sur des échantillons de sol non remaniés et les valeurs correspondantes de taux de saturation en eau, de teneur en nitrates et de vitesses de respiration. Ce modèle est une combinaison multiplicative entre une vitesse potentielle de dénitrification mesurée dans des conditions standardisées définies dans ce papier et de fonctions sans dimension de la teneur en nitrates, du taux de saturation en eau et de la température du sol. Ce modèle a ensuite été utilisé sur deux jeux de données indépendantes et des corrélations significatives ont été observées entre mesures et simulations. La sensibilité du modèle lors de variations systématiques du niveau des variables d'entrée ainsi que des coefficients inclus dans les fonctions sans dimension a été testée sur ces jeux de données. NEMIS apparaît comme un outil très utile d'interpolation entre quelques points de mesures de dénitrification à partir d'un jeu de données relativement simple comprenant le potentiel de dénitrification du sol et l'évolution du taux de saturation en eau, de la teneur en nitrates et de la température du sol. La principale limite de NEMIS est sa grande sensibilité au taux de saturation en eau du sol à partir duquel le processus de dénitrification commence à fonctionner.
Quantifying dye tracers in soil profiles by image processing
Authors: Forrer I. , Papritz A. , Kasteel R. , Flühler H. , Luca D. 
Published: March 2003

SummaryDeveloping and testing models for solute transport in the field requires experimental data on the spreading of solutes in the soil. Obtaining such data is costly, and a substantial part of the total costs is in the preparation and chemical analysis of the tracing compounds in the gathered samples. We developed a cheap method to quantify the concentration of the mobile dye tracer Brilliant Blue FCF from digitized photographs of stained soil profiles, and we have tested it in the field. Soil sampling and chemical analyses were necessary only to establish a calibration relation between the dye content and the colour of the soil. The digital images were corrected for geometrical distortions, varying background brightness, and colour tinges, and then they were analysed to determine the soil colour at sampling points in the profiles. The resident concentration of the dye was modelled by polynomial regression with the primary colours red, green, blue and the soil depth as explanatory variables. Concentration maps of Brilliant Blue were then computed from the digitized images with a spatial resolution of 1 mm. Validation of the technique with independent data showed that the method predicted the concentration of the dye well, provided the corrected images contained only the colours included in the calibration.
Sorption of dissolved organic nitrogen by acid subsoil horizons and individual mineral phases
Authors: Kaiser K. , Zech W. 
Published: March 2003

SummaryDissolved organic matter is important in translocation and export of nutrients from forest ecosystems. Its mobility in soil is restricted by sorption to mineral surfaces which depends on its chemical properties. Carboxyl and hydroxyl groups form strong bondings to mineral surfaces, whereas the role of N‐containing functional groups in the sorption process is less well understood. We examined in laboratory experiments the binding of dissolved organic matter from the forest floor to amorphous Al(OH)3, goethite, kaolinite, and illite and to subsoils in order to compare the sorption and desorption of dissolved organic C with that of dissolved organic N. The mineral samples were equilibrated with acidic solutions of organic matter at pH 4. In the equilibrium solutions organic C and N and their contribution to two operationally defined fractions, namely the so‐called hydrophilic and hydrophobic fractions, were determined. We measured neutral and acidic amino sugars to discover the nature of the binding of organic N. Within the hydrophilic and hydrophobic fractions, the sorption and desorption of organic C and N did not differ, indicating that there was no preferential binding of N‐containing compounds. The hydrophilic fraction contained more N and sorbed less than the hydrophobic fraction, and so the overall retention of organic N by the mineral phases and subsoils was smaller than that of organic C. Among the amino sugar compounds, muramic acid was preferentially removed from the solution, whereas the neutral amino sugars were sorbed similar to organic C. The results suggest that the sorption of N‐containing compounds is favoured by acidic groups and not by amino groups.
Estimation of phosphate adsorption by Acrisols of western Spain from electrical conductivity of potassium dihydrogen phosphate extracts of soil
Authors: Serrano R. Espejo , Arias J. Santano , García E. Pardo , Fernández P. González 
Published: March 2003

SummaryEstimation of the phosphate adsorption capacity in highly weathered acid soils is crucial for adopting appropriate phosphate fertilization practices. In this work, the salt sorption effect was used to develop a method for estimating phosphate adsorption capacity from the decrease in electrical conductivity of a potassium dihydrogen phosphate solution brought in contact with acidic soil samples from surface and subsurface horizons of Acrisols. The method is fast and simple and requires only the use of a conductimeter.
Re‐evaluation of the structural properties of some British swelling soils
Authors: Groenevelt P. H. , Grant C. D. 
Published: March 2003

SummaryThe structural condition of swelling soils can be assessed from their shrinkage curves. We re‐evaluated data on six British swelling soils using modern methods to model the void ratio, e, as a function of the moisture ratio, ϑ. The points on the e–ϑ curve were fitted with a constitutive shrinkage equation using an unbiased least‐squares, curve‐fitting program. The shrinkage curves were then differentiated to obtain their slopes, σ(ϑ), which were used to calculate the overburden potentials, Ω. The slope functions were subsequently differentiated to obtain the curvatures, κ(ϑ), from which the maximum curvature at the wet end was used to separate the structural shrinkage, Sc, from the proportional (unsaturated) shrinkage. At the point of maximum curvature, Sc and the volumetric air content, θac, were calculated and found to correspond closely to those reported previously. Water retention curves were constructed and fitted using the van Genuchten equation, from which the α coefficient appears an important structural parameter. The structural condition of a swelling soil appears to be well described by its air content at the point of maximum curvature, its van Genuchten α coefficient, and a parameter describing the effect of the overburden potential.
Ultrastructural study of the biogeochemical cycle of silicon in the soil and litter of a temperate forest
Authors: Watteau F. , Villemin G. 
Published: March 2003

SummaryThe biogeochemical cycle of silicon is closely linked to the plant cycle. We have studied the relations between silica and organic matter during humification in a temperate deciduous forest, an acid brown soil ecosystem, the characteristics of which suggest that plants play a major role in the recycling of soluble silica. Our ultrastructural approach consists in identifying the occurrence of biogenic silica in the beech roots, in young and old beech leaves in litter and in the underlying microaggregates of the topsoil. The microaggregates were either sampled directly in situ or isolated by size fractionation.Observations  of ultrathin sections by transmission electron microscopy at a micrometric scale were combined with electron energy loss microanalysis, which enabled us to identify the silica phases and their associated mineral and organic environments. Some silica deposits were identified in the cell walls of both the beech roots and the beech leaves, whereas pure silica occurred in the root cortical cells as a layer which was closely associated with polyphenolic substances. The ultrastructural study of the microaggregates showed a close association between Si‐cell wall residues and Si‐polyphenolic residues. We also identified a specific bacterial activity that seemed to be related to the degradation of siliceous cell walls. The microquartz in the topsoil showed morphological and analytical transformations that might be considered as weathering. Both ultrastructural observations and the electron energy loss microanalysis showed the presence of biogenic silica and silica‐organic material in litter and soil, and these techniques should enable us to follow the biogeochemical cycle in ecosystems and the bioavailability of silicon.
Vents and seals in non‐steady‐state chambers used for measuring gas exchange between soil and the atmosphere
Authors: Hutchinson G. L. , Livingston G. P. 
Published: March 2003

SummaryDespite decades of research to define optimal chamber design and deployment protocol for measuring gas exchange between the Earth's surface and the atmosphere, controversy still surrounds the procedures for applying this method. Using a numerical simulation model we demonstrated that (i) all non‐steady‐state chambers should include a properly sized and properly located vent tube; (ii) even seemingly trivial leakiness of the seals between elements of a multiple‐component chamber results in significant risk of measurement error; (iii) a leaking seal is a poor substitute for a properly designed vent tube, because the shorter path length through the seal supports much greater diffusive gas loss per unit of conductance to mass flow; (iv) the depth to which chamber walls must be inserted to minimize gas loss by lateral diffusion is smaller than is customary in fine‐textured, wet or compact soil, but much larger than is customary in highly porous soils, and (v) repetitive sampling at the same location is not a major source of error when using non‐steady‐state chambers. Finally, we discuss problems associated with computing the flux of a gas from the non‐linear increase in its concentration in the headspace of a non‐steady‐state chamber.
Analysing repeated measurements in soil monitoring and experimentation
Authors: Webster R. , Payne R. W. 
Published: March 2003

SummaryField monitoring, leaching studies, and experimentation in soil biology are often now being done non‐destructively using fixed installations so that measurements are made repeatedly on the same units. The resulting data for each unit (suction cup, lysimeter, incubation chamber) constitute a time series in which there may be autocorrelation. The usual methods of statistical analysis, such as the analysis of variance, must be modified or replaced by more suitable ones to take account of the possible correlation. This paper describes the split‐plot design of such experiments, shows how to assess the variance–covariance matrix of residuals for uniformity by the Greenhouse–Geisser statistic, and shows how to use this statistic to adjust the degrees of freedom in a formal test of significance. It also describes more recent methods. Ante‐dependence analysis identifies the extent of the temporal correlation in the data and provides approximate significance tests for the treatments. Alternatively, the paper also shows how the traditional analysis of variance may be replaced by a restricted maximum likelihood analysis which gives Wald statistics. The techniques are illustrated with data on CO2 evolved from soil incubated for 75 days in closed chambers, during which time the gas was measured on 24 occasions to give time series for three replicates of each combination of two soils (limed and unlimed) and three types of ryegrass amendment. An ante‐dependence structure (extending to ninth order) weakened the usual significance test within the subunit stratum. The Wald statistics showed that there was, nevertheless, a strong interaction between the treatments and time.
Effect of non‐linear adsorption on the transport behaviour of Brilliant Blue in a field soil
Authors: Kasteel R. , Vogel H.‐J. , Roth K. 
Published: March 2003

SummaryThe food dye Brilliant Blue FCF (Color Index 42090) is often used as dye tracer in field studies for visualizing the flow pathways of water in soils. Batch studies confirmed findings of other researchers that non‐linear sorption is important for Brilliant Blue, especially at small concentrations (< 10 g l−1 for our soil), and that retardation increases with decreasing concentrations as well as with increasing ionic strength of solutions. Therefore, it is not obvious if it can be used as an indicator for water flow paths as is often done. In this study, we compared the mobility of Brilliant Blue in a field soil (gleyic Luvisol) with that of bromide. Brilliant Blue and potassium bromide were simultaneously applied as a 6‐mm pulse on a small plot in the field, and the tracers were displaced with 89 mm of tracer‐free water using a constant intensity of 3.9 ± 0.2 mm hour−1. Both tracer concentrations were determined on 144 soil cores taken from a 1 m × 1 m vertical soil profile. The transport behaviour differed in both (i) mean displacement and (ii) spatial concentration pattern. We found the retardation of Brilliant Blue could not be neglected and, in contrast to the bromide pattern, a pulse splitting was observed at the plough pan. Numerical simulations with a particle tracking code revealed that the one‐dimensional concentration profile of bromide was represented fairly well by the model, but the prediction of the double peak in the Brilliant Blue concentration profile failed. With additional assumptions, there were indications that Brilliant Blue does not follow the same flow paths as bromide. However, the question of Brilliant Blue taking the same flow pathways as bromide cannot be adequately answered by comparing both concentration distributions, because we look at two different transport distances due to the retardation of Brilliant Blue. It became obvious, however, that Brilliant Blue is not a suitable compound for tracing the travel time of water itself.
The influence of soil pH on denitrification: progress towards the understanding of this interaction over the last 50 years
Authors: ŠImek M. , Cooper J. E. 
Published: March 2003

SummaryResults from the pioneering research on the interactions between pH and denitrification in soil from the 1950s to the present are reviewed, the changing perceptions of this complex relationship are discussed, and the current status of the subject is assessed. Facets of this relationship that are analysed in detail include the direct or indirect influence of pH on overall denitrification rates in soils, changes in the composition of gaseous products that depend on pH, methods for measuring the process, the concept of an optimum pH for denitrification, and the adaptation of microbial denitrifying communities to acidic environments. The main conclusions to be drawn are as follows. Total gaseous emissions to the atmosphere (N2O, NO and N2) have repeatedly been shown to be less in acidic than in neutral or slightly alkaline soils. This may be attributable to smaller amounts of organic carbon and mineral nitrogen available to the denitrifying population under acid conditions rather than a direct effect of low pH on denitrification enzymes. Numerous laboratory and field studies have demonstrated that the ratio N2O:N2 is increased when the pH of soils is reduced. The relation between soil pH and potential denitrification as determined by various incubation methods remains unclear, results being influenced both by original conditions in soil samples and by unknown changes during incubation. The concept of an optimum pH for denitrification has been frequently proposed, but such a term has little or no meaning without reference to specific attributes of the process.
The effect of reducing conditions on the solubility of phosphorus in a diverse range of European agricultural soils
Authors: Scalenghe R. , Edwards A. C. , Ajmone Marsan F. , Barberis E. 
Published: March 2003

SummaryThe effects of reducing conditions on solubility of phosphorus (P) can directly influence water quality. The release of P is enhanced although the P is not directly involved in reduction processes. We here compare the responses to flooding of 12 overfertilized agricultural soils in widely varying pedological and management regimes, belonging to seven World Reference Base groups. The redox potential initially ranged from 305 to 515 mV and decreased to −157 to −195 mV within 32 days. The onset of reducing conditions led to an increase in the concentration of soluble P. The maximum rate of solubilization occurred within 1–3 weeks under reducing conditions, and the steady‐state concentrations of P never exceeded 200 μmol dm−3. Four stages in the development of the reduction process are identified, and a simple empirical model describes the change in concentrations of soluble P. The potential of P release under reduction is positively correlated with the soil saturation with P. Flooding over a few weeks triggered the release of large amounts of P. Constant pe + pH is related to constant concentration of molybdate‐reactive P, suggesting that soluble P is effectively buffered so that P will be immobilized. In general the solubilization of P under reducing conditions is likely to be aggravated by the increased soil P status that has resulted from overfertilization of agricultural land with P. These findings bear on the establishment and long‐term effectiveness of riparian buffer zones where phosphorus is likely to accumulate by the interception of drainage.
Humus forms and metal pollution in soil
Authors: Gillet S. , Ponge J. F. 
Published: March 2003

SummarySmelters in northern France are a serious source of soil pollution by heavy metals. We have studied a poplar plantation downwind of an active zinc smelter. Three humus profiles were sampled at increasing distance from the smelter, and the thickness of topsoil horizons was measured along a transect. We analysed the vertical distribution of humus components and plant debris to assess the impact of heavy metal pollution on the humus forms and on soil faunal activity. We compared horizons within a profile, humus profiles between them, and traced the recent history of the site. Near the smelter, poplar trees are stunted or dead and the humus form is a mor, with a well‐developed holorganic OM horizon. Here faunal activity is inhibited, so there is little faecal deposition and humification of plant litter. At the distant site poplar grows well and faunal activity is intense, so there are skeletonized leaves and many organo–mineral earthworm and millipede faecal pellets. The humus form is a mull, with a well‐developed hemorganic A horizon. The passage from mor to mull along the transect was abrupt, mor turning to mull at 250 m from the smelter, though there was a progressive decrease in heavy metal deposition. This indicates that there was a threshold (estimated to be 20 000 mg Zn kg−1) in the resilience of the soil foodweb.
Simulation of the redistribution of soil by tillage on complex topographies
Authors: Van Oost K. , Van Muysen W. , Govers G. , Heckrath G. , Quine T. A. , Poesen J. 
Published: March 2003

SummaryTillage redistributes soil and contributes significantly to the within‐field soil variation, especially on topographically complex terrain. Although the basic principles of the redistribution are well understood, models for simulating the redistribution are poor predictors. This paper presents a modelling structure that allows a simulation of the redistribution of soil constituents on complex topographies for various tillage implements. The model simulates the redistribution of soil constituents by convoluting the probability distribution of the tillage displacement with the spatial distribution of the soil constituents. The probability distributions in two dimensions are derived from a series of tillage experiments conducted with a mouldboard plough at various positions in the landscape. Furthermore, the effects of topography and tillage direction on the probability distributions were characterized and implemented in the model. A first application showed that the direction of tillage significantly affects the long‐term redistribution of soil constituents. The inclusion of other implements in the model was explored, and we found that data in the literature could be used for simulating the long‐term effects of tillage.
Testing the adequacy of measured data for evaluating nitrogen turnover models by the dot‐to‐dot method
Authors: Smith J. U. , Smith P. , Richter G. M. , Agostini F. A. , Welham S. J. 
Published: March 2003

SummaryDynamic models of nitrogen turnover in soil are being used increasingly in agricultural science. To be of value, a model must be thoroughly evaluated, and the expected accuracy of simulated values must be defined. Frequent field measurements are time‐consuming and costly, and so models are often evaluated against only few data. However, this mismatch between the measured and simulated values can result in error statistics that are themselves subject to large errors and therefore unreliable. The dot‐to‐dot method quantifies the error associated with having too few measured values by interpolating linearly between measured data (hence, dot‐to‐dot) and evaluating the simulation at each time step using interpolated data where actual measurements are unavailable. A large error will be seen if the measured data do not capture the fluctuations predicted by the model. Other quantitative methods can be used to evaluate the performance of a model, but the dot‐to‐dot method can be used in conjunction with these to estimate whether or not the data are adequate for testing the model. If the performance of the model at the measured points is within the acceptable error, then the dot‐to‐dot method is used to judge whether there are too few points to evaluate the model's performance, and so to determine whether the evaluation of the model is valid.