bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assessment of the effect of molecular size on the electrophoretic mobility of humic substances
Authors: DE NOBILI M. , FORNASIER F. 
Published: August 2005

SummaryThe basic principles of the electrophoretic behaviour of humic substances (HS) still need to be systematically investigated. HS extracted from a Cryorthod (HS–1) and from an Haplumbrept (HS–2) were first fractionated by ultrafiltration to obtain two series of fractions of reduced polydispersity with a nominal mean relative molecular mass (M) of 7500, 20000, 40000, 75000 and 200 000 Da. Fractions extracted from the same soil behaved like an homologous series when tested by size exclusion chromatography, showing a linear relation of M with molecular size. When plotted against their mean M, the elution volumes of HS fractions extracted from the two different soils originated lines of different slope. Absolute electrophoretic mobilities of the fractions were determined in polyacrylamide gel slabs of increasing polyacrylamide concentration using a single buffer system; in all gels there was a close linear relation between the electrophoretic mobility and the logarithm of the mean M of HS fractions. Extrapolation of mobilities of HS–1 at zero gel concentration gave intercepts that did not differ significantly, showing that there was a constant mobility for all fractions in free solution. These results mean that charge differences have little effect on the electrophoretic mobilities of HS extracted from the same soil and imply the theoretical possibility of determining M distributions of HS by polyacrylamide gel electrophoresis in a single buffer system. Mobilities of HS–2 fractions were compared with those of HS–1: the latter fitted the regression equations of mobility against logarithm of the molecular weight obtained from HS–1 humic substances only in gels of small acrylamide concentration. Deviations were larger at small M, probably because of the increasing fulvic character of the fractions, and increased in gels of greater acrylamide concentration, indicating that charge differences may not be negligible when comparing humic substances extracted from different soils.
Sorption of phosphate and oxalate by a synthetic aluminium hydroxysulphate complex
Authors: VIOLANTE A. , RAO M.A. , DE CHIARA A. , GIANFREDA L. 
Published: August 2005

SummaryWe studied the sorption of phosphate and oxalate on a synthetic aluminium hydroxysulphate complex and the associated release of sulphate from this complex. In the pH range 4.0–9.0 the presence of phosphate or oxalate tended to increase the release of sulphate. Much more phosphate than oxalate was sorbed, but in most cases oxalate caused more removal of sulphate than did phosphate. Only in acid systems may these results be partly attributed to the greater solubilization of the complex in the presence of oxalate than in the presence of phosphate. At pH > 8.0 in the presence of phosphate, and at pH > 6.5 in the presence of oxalate, the quantities of sulphate replaced were greater than the quantities of phosphate or oxalate sorbed, suggesting that hydroxyl ions competed with phosphate and oxalate for sorption sites and sulphate removal. Sulphate was only partly removed from the complex even after repeated washings with phosphate or oxalate solutions or after 120 h in the presence of these ligands at pH 6.0. When phosphate and oxalate were added as a mixture much more phosphate than oxalate was retained. Phosphate strongly inhibited oxalate sorption, whereas oxalate partly prevented phosphate sorption only at pH < 7.0. More sulphate was removed in the presence of both the anions than in the presence of phosphate alone, but less than that desorbed in the presence of oxalate alone.
Atomic force microscopy (AFM) investigations of the surface topography of a multidomain porous goethite
Authors: FISCHER L. , MÜHLEN E. ZUR , BRÜMMER G.W. , NIEHUS H. 
Published: August 2005

SummaryA multidomain goethite was analysed with atomic force microscopy (AFM) to obtain information about the size and shape of pores on the surface, which are important for sorption processes of cations and anions. Wedge‐shaped pores > 100 nm long at the surface occurred at the domain boundaries. They were 20‐30 nm wide, becoming narrower towards the interior of the crystals to 2 nm and less. The AFM showed these pores to be at least 4–6 nm deep. The shape of the pores suggests that smaller pores continue much further into the interior of the crystals. Besides the irregularities between domains, randomly distributed steps of < 1 nm occurred. Hydrothermal treatment did not change crystal size, but made the surfaces smoother and reduced both the size and number of the pores and also the BET surface area (from 75.3 to 35.1 m2 g−1). The existence of meso‐ (2–30 nm width) and micropores (< 2 nm width) in goethite crystals explains the slow diffusion of heavy metals, phosphate and other ions into goethite particles. Therefore, the external and internal surfaces of goethite crystals and their spatial heterogeneity have to be taken into account in models of ion adsorption by goethite.
Effects of associations between humic acids and iron or aluminium on the flocculation and aggregation of kaolin and quartz
Authors: ARIAS M. , BARRAL M.T. , DIAZ‐FIERROS F. 
Published: August 2005

SummaryThe aggregative effect of organic matter on soil particles is conditioned by its composition and concentration and the degree to which it is associated with metal ions and oxides in the soil. We treated suspensions of kaolin or quartz substrates at pH 5 with metal (Fe or Al; c. 3 to 23 mg g−1 of substrate) or humic acid (HA; 7 to 53 mg g−1 of substrate) or both. In the absence of added Fe or Al, the proportion of HA retained by the substrate decreased from 98.5 to 50.8% for kaolinitic samples, and from 35.8 to 23.4 for quartz‐based samples, as the HA dose increased. In the presence of Fe or Al, the proportion of HA removed from solution increased and was always >91%.Untreated kaolin flocculated between pH 2.0 and 4.5. This flocculation interval narrowed as the dose of HA increased, widened as the dose of HA‐A1 increased, but was barely affected by HA‐Fe. Similarly, the aggregative effect of HA‐Fe associations on kaolin was smaller than that of HA‐A1 associations, which induced formation of aggregates >100 μm that were essentially absent in the untreated substrate. There was a similar but less marked difference between the aggregative effects of HA‐Fe and HA‐A1 on quartz.
Cation exchange hysteresis scanning curves: mathematical description and interpretation
Authors: VERBURG K. , BAVEYE P. 
Published: August 2005

SummaryCation exchange reactions in clays and soils have repeatedly been shown in the literature to be hysteretic during typical laboratory experiments. Yet all existing models of solute transport in soils and aquifers assume these reactions to be thermodynamically reversible. To remedy this situation a mathematical description of cation exchange hysteresis is needed. In the present research isotherms were obtained for a K‐Mg exchange on Camp Berteau montmorillonite. Scanning curves were also measured, corresponding to arbitrary reversals of the direction of the exchange reactions. Three different Preisach‐hysteresis models were used to describe the scanning curves. The fit of each hysteresis model to the experimental observations was analysed in terms of the features of the model itself and, from a physical viewpoint, in terms of a recently proposed conceptual model of cation exchange hysteresis.
Influence of gravimetric water content and bulk density on the dielectric properties of soil
Authors: PERDOK U.D. , KROESBERGEN B. , HILHORST M.A. 
Published: August 2005

SummaryMoisture content and bulk density largely characterize physical and mechanical soil status and behaviour. A nondestructive determination of these soil properties is essential. Time domain reflectometry (TDR), although widely accepted for determination of volumetric water content, θ, has its limitations, and recently a frequency domain (FD) sensor has been developed and tested. An equation relating relative permittivity, ɛ′, to gravimetric water content, w, and bulk density, p, was established for three soil types (sand, sandy loam and clay). If ɛ′ and w are known, our model can be used to calculate bulk density and associated volumetric water content, θ, keeping in mind that θ= pw. Utilization is found in long‐term monitoring of moisture fluctuations or short‐term detection of traffic‐induced soil compaction.
Aggregate stability and assessment of soil crustability and erodibility: I. Theory and methodology
Authors: LE BISSONNAIS Y. 
Published: August 2005

SummaryCrusting and erosion of cultivated soils result from aggregate breakdown and the detachment of soil fragments by rain, and the susceptibility of soil to these processes is often inferred from measurements of aggregate stability. Here, theories of aggregate breakdown are reviewed and four main mechanisms (i.e. slaking, breakdown by differential swelling, mechanical breakdown by raindrop impact and physico–chemical dispersion) are defined. Their relative importance depends on the nature of the rain, as well as on the soil's physical and chemical properties. The relations between aggregate breakdown, crusting and water erosion are analysed, and existing methods for the assessment of aggregate stability are reviewed. A unified framework for the measurement of aggregate stability is proposed to assess a soil's susceptibility to crusting and erosion. It combines three treatments having various wetting conditions and energies (fast wetting, slow wetting, and stirring after pre‐wetting) and measures the resulting fragment size distribution after each treatment. It is designed to compare different soils, or different climatic conditions for a given soil, not to compare time‐dependent changes in that soil.
Lattice–gas approach to surface runoff after rain
Authors: GARCIA‐SANCHEZ L. , DI PIETRO L. , GERMANN P.F. 
Published: August 2005

SummaryWe simulated the distribution of water flowing over the soil surface in small plots using a lattice‐gas approach. The numerical lattice‐gas algorithm consists in simulating a fluid as a finite set of particles which move in a discrete lattice obeying deterministic rules. With this technique, complex boundary conditions and transient flow regimens are handled with ease. The amount of depressional storage and the onset of runoff were considered as functions of rainfall intensity, surface roughness, slope angle and infiltration dynamics. Rainfall was simulated by spherical raindrops of fixed diameter, which were generated by a space and time Poisson process of constant intensity. The effect of infiltration on surface flow was simulated by removing liquid particles at the solid surface with a chosen rate function. Depressional storage and runoff then result from the intrinsic hydrodynamic behaviour of the model under the imposed rainfall, infiltration rate and surface geometry. Results of numerical experiments are presented. They show that the lattice‐gas approach is well‐adapted for simulating the formation of excess water and the roles of roughness and slope in attenuating runoff for any arbitrary complex surface geometry.
Improving the kriging of a soil variable using slope gradient as external drift
Authors: BOURENNANE H. , KING D. , CHÉRY P. , BRUAND A. 
Published: August 2005

SummaryUniversal kriging with a topographic variable used as external drift was compared with ordinary kriging, ordinary kriging with external drift, and universal kriging for predicting the thickness of a superficial deposit on part of the Beauce of central France. Thickness was recorded at 62 sites and at another 25 sites to obtain a sample for validation. A Digital Elevation Model (DEM) was computed from 484 sites where relative elevation was measured. The slope gradient which is significantly correlated to thickness was used as an external drift variable for kriging thickness. The sample for validation was used for testing the four prediction methods. In testing each of the methods, two indices were computed from the validation sample (observed data) and predicted values. These two indices are the mean error (ME) and the root mean square error (RMSE). The results show that universal kriging with the slope gradient used as external drift was more precise than the other kriging methods. Further analysis based on the mean ranks of performance confirmed these results.
Influence of soil properties and soya bean cropping history on the Bradyrhizobium japonicum population in some French soils
Authors: REVELLIN C. , PINOCHET X. , BEAUCLAIR P. , CATROUX G. 
Published: August 2005

SummaryAs French soils are naturally free of Bradyrhizobium japonicum, soya beans planted into new areas must be inoculated with this bacterium. Although, the B. japonicum inoculum can survive in soils for long periods of time even in the absence of a soya bean crop, re–inoculation may increase nodulation and grain yield. Thus, populations of B. japonicum can fall below optimum for plant growth. To identify the soil properties controlling survival of the inoculated bacteria samples of soil were collected from 52 sites from France that had previously grown soya beans. The samples were analysed for some physical and chemical characteristics and the B. japonicum population counted. The soil's CaCO3 content was the main factor affecting survival. The average B. japonicum numbers (per g soil) were 80 for calcareous soils and 15000 for non–calcareous soils. In the latter, silt and sand contents were correlated with the numbers of B. japonicum. The cropping frequency of soya bean and the time since the crop was last grown were other factors affecting Bradyrhizobium populations. Thus, there is a probability of enhancing economic benefit for farmers with re–inoculation of soya bean in calcareous and sandy soils.
Distribution of cation exchange capacity between organic matter and mineral fractions in acid forest soils (Vosges mountains, France)
Authors: TURPAULT M.‐P. , BONNAUD P. , FIGHTER J. , RANGER J. , DAMBRINE E. 
Published: August 2005

SummaryThe cation exchange capacity (CEC) of 18 samples (<2 mm) of five acid soils developed on granite or gneiss was measured before and after H2O2 treatment from pH‐unbuffered extraction solution (1 N KCl). The pH in water of the soils ranged from 3.4–4.7. The samples were separated into seven fractions (<2 μm, 2–20 μm, 20–50 μm, 0.05–0.2 mm, 0.2–0.5 mm, 0.5–1 mm and 1–2 mm) and the CEC of each measured. Thus the contribution of each size fraction and of organic matter to the CEC was obtained. From CEC measurements on the different fractions and particle size distribution data, a balance calculation was carried out to verify the methodology. According to the hypotheses used and soil characteristics, the CEC of organic matter was found to vary from 35 to 165 cmolc kg−1 and so represented from 10 to 85% of the total soil CEC in the upper soil horizons. In these sandy soils developed on granite or gneiss which were frequently affected by hydrothermal alteration, the CEC of silt and sand fractions was large. It can represent from 35 to 80% of the total soil mineral CEC. The specific contribution of the 0.2–2 mm fraction can reach 50% of the total soil mineral CEC with values ranging from 0.5–5.2 cmolc kg−1. The mineralogical description showed that hydrothermal white micas and neoformed smectites (precipitated during weathering) were present in all the fractions even in the coarsest ones. In some subsoils, albite grains containing smectite have a CEC as large as 21 cmolc kg−1. This study shows that the CEC of acid soils was not always located in the organic matter and in the clay fraction. The sand fraction can contribute substantially to the soil CEC.
Side‐effects of herbicides on the size and activity of the soil microflora: DNOC as a test case
Authors: ROUARD N. , DICTOR M.‐C. , CHAUSSOD R. , SOULAS G. 
Published: August 2005

SummaryRecent advances in measuring soil microbial biomass by chloroform fumigation–extraction (CFE) and microbial heterotrophic activity interpreted by quantitative concentration–activity relations (QCAR) have renewed interest in assessing side–effects of agricultural chemicals on soil microorganisms. We have studied the effects of a herbicide, 4,6‐dinitroorthocresol (DNOC), taken as a test chemical, on the rate of microbial carbon turnover and the size of the soil microbial biomass. We used the CFE technique in combination with in‐situ labelling of the soil biomass. Exposure of prelabelled soil samples to the herbicide resulted in a significant increase in 14CO2 production during which the radioactive carbon content of the microflora decreased exponentially without apparent reduction in the size of the biomass. The extra production of 14CO2 by DNOC‐treated soil over control, or carbon‐enriched soil, is the expression of an increased rate of endogenous metabolism to compensate for shortage in energy caused by a decoupling of ATP generation at the oxidative phosphorylations level by the DNOC. To assess the influence of DNOC on soil microbial communities we also compared the advantages of short‐term respirometric tests with those resulting from application of heterotrophic activity measurements in connection with QCAR. Both procedures detected modifications in the metabolic behaviour of soil microorganisms when faced with chemical stress. Short‐term respirometric tests showed that DNOC causes a decrease in the respirometric activity of the soil microflora. Measuring heterotrophic activity also makes it possible to interpret microbial responses in terms of changes in the physiological traits of the microbial communities. DNOC provokes an apparent enrichment in microorganisms with a smaller saturation constant, Km and, as a consequence, a greater affinity for carbon substrates.
Influence of the nature of soil organic matter on the sorption‐desorption of 4‐chlorophenol, 2,4‐dichlorophenol and the herbicide 2,4‐dichlorophenoxyacetic acid (2,4‐D)
Authors: BENOIT P. , BARRIUSO E. , HOUOT S. , CALVET R. 
Published: August 2005

SummaryThe sorption–desorption properties of three organic pollutants, 4‐chlorophenol (4‐CP), 2,4‐dichlorophenol (2,4‐DCP) and the herbicide 2,4‐dichlorophenoxyacetic acid (2,4‐D) on soil organic matter (SOM) were studied using kinetic and equilibrium measurements in aqueous suspensions. Chestnut wood, wheat straw, Kraft lignin, composted straw and a soil humic acid were chosen as sorbents to model different states of humification. Physico–chemical characterization using chemical fractionation, potentiometric titration and IR spectroscopy was done on all sorbents. The microbial biomass, sizes of total bacterial and fungal microflora and phenoloxidases activities were determined for the plant materials. The irreversibility of sorption was revealed by the desorption isotherms. Only a small proportion of 2,4‐D, which has little affinity for the fresh organic materials, was desorbed. Sorption of 2,4‐DCP was strong on straw but was reversible to a large extent, indicating weaker interactions. By comparison, the sorption of 4‐CP was significantly less reversible. Thus, the nature of SOM and the properties of the chemicals strongly influenced the extent of sorption and the type of interactions, and it controlled subsequent desorption and possible transformation of the sorbed species.
Micro‐scale variation of solid‐phase properties and soil solution chemistry in a forest podzol and its relation to soil horizons
Authors: GÖTTLEIN A. , STANJEK H. 
Published: August 2005

SummaryIn order to evaluate micro‐scale heterogeneities 55 micro suction cups were placed in an array at 15 mm intervals in a profile face of a cambic podzol. The chemistry of soil solution (mineral anions, pH, UV absorption as a measure for DOC) was compared with solid‐phase properties from soil samples (2 cm3 volume), which had surrounded the suction cups. Sequential extraction techniques (water, NF4Cl, hydroxylamin‐hydrochloride, citrate‐bicarbonate, oxalate, dithionite‐citrate‐bicarbonate) and base titrations were applied to characterize the solid phase. Although the average soil solution concentrations between horizons often differed significantly, the spatial distributions of pH and SO42− did not correlate with soil horizon borders. Even if concentration isolines and soil horizon borders were parallel, marked concentration gradients could be observed within individual soil horizons. The less intense the interaction between solute ion and soil matrix, the greater was the variation in solution concentration within a soil horizon. For the soil solid phase only a weak correlation of slow buffer reactions to soil horizons was found. The distribution of extractable Fe and Al was typical for a podzol profile, however, with very steep gradients within single soil horizons. Except for pH, which was related mainly to citrate‐bicarbonate extractable aluminium, no solid‐phase characteristic showed a clear correlation with soil solution chemistry.
Effects of crystallinity of goethite: I. Preparation and properties of goethites of differing crystallinity
Authors: STRAUSS R. , BRÜMMER G.W. , BARROW N.J. 
Published: August 2005

SummaryWe prepared five samples of pure goethite and three samples of aluminous goethite with mole fractions of aluminium ranging from 0·05 to 0·20. One of the samples of pure goethite was repeatedly heated in an autoclave at 150°C. We studied the samples using transmission electron microscopy and XRD and we measured the surface area (BET), rate of dissolution of the samples in acid, the surface charge in four concentrations of sodium nitrate from pH 4–10, and the sorption of calcium and chloride from a dilute solution of calcium chloride. Surface areas ranged from 18 to 132 m2 g−1. The BET adsorption‐desorption isotherms had hysteresis loops which increased as the surface area increased. These showed that there were pores present with diameters smaller than 2 nm and that the number of pores increased as the surface area increased. All samples of goethite showed typical X‐ray diffraction patterns but with peak heights decreasing, and width increasing, as surface area increased. Mean coherence lengths, as determined by XRD line broadening, were smaller than those determined by transmission electron microscopy. This was because each crystal was composed of several domains, and the XRD data reflect the size of the domains. Heating one of the goethite samples in an autoclave caused most of the domains to coalesce and slightly decreased the surface area. As the surface area of the eight goethite samples increased, the mean coherence length in the direction of the a, b and c axes decreased. The better crystallized samples dissolved more slowly in acid and the dissolution curves were sigmoid because the acid was able to penetrate between the domains allowing access to a larger surface area and consequently accelerated dissolution. The points of zero charge increased with increasing surface area of the goethite. The charge carried by the goethite at pH values distant from the point of zero charge increased as the surface area increased. This may indicate movement of protons or hydroxyl ions into pores or other defects in the crystal. The effects of pH and of salt concentration on surface charge were closely described by the variable‐charge/variable‐potential model. This model also closely described adsorption of Ca2+ and Cl− from calcium chloride solutions requiring only the allocation of constants for these ions. The substitution of aluminium for iron did not affect the charge properties of goethite.