bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of solution calcium concentration and calcium sink size on the dissolution of Gafsa phosphate rock in soils
Authors: ROBINSON J. S. , SYERS J. K. 
Published: July 2006

SUMMARYThe dissolution of a reactive phosphate rock (Gafsa, GPR) was evaluated in a range of UK soils which varied considerably in calcium (Ca) status and in a soil that had been amended with different amounts of a cation exchange resin (CER) to provide a Ca sink of varying size. As expected, but not apparently previously reported, increasing solution Ca concentration caused a decrease in the dissolution of GPR, consistent with the solubility product principle. At 40 d, the extent of GPR dissolution was correlated more closely with soil solution Ca concentration (r=−0.91) than with either the number of unoccupied exchange sites for Ca or the Ca‐exchange capacity (CaEC) of the soil (r=0.61 andr=−0.35, respectively). Unoccupied exchange sites for Ca were only effective in influencing GPR dissolution when solution Ca concentration was sufficiently low (< 1 mmol dm−3) for the sites to be operating on the well‐buffered portion of the Ca‐exchange isotherm. The combined effects of an initial low solution Ca concentration and the presence of unoccupied Ca exchange sites caused the relationship between GPR dissolution and solution Ca concentration to become curvilinear, whereby the proportion of GPR dissolved at 40 d could be related to the initial soil solution Ca concentration by an exponential equation. A similar interaction was obtained for the relationship between GPR dissolution and CaEC (operating at solution Ca concentrations ≥0.6 mmol dm−3) following the addition of CER to the soil. The effectiveness of the additional sites for Ca in maintaining the product of ionic concentrations below the solubility product of GPR was such that the amount of GPR dissolved at 40 d correlated linearly and strongly (r= 1.00) with the CaEC of the soil‐CER mixtures.
Measuring the diffusion coefficient of rhizosphere exudates in soil. I. The diffusion of non‐sorbing compounds
Authors: DARRAH P. R. 
Published: July 2006

SUMMARYA quick, convenient and robust method is presented for measuring the effective diffusion coefficients of non‐sorbing solutes in soil. The method estimates the effective diffusion coefficient from a measured diffusion profile by optimizing the solution of a numerical simulation model describing the experimental system. The method was used to measure the effective diffusion coefficients of compounds found in root exudates.
Critical‐state soil mechanics parameters and their variation for Vertisols in eastern Australia
Authors: KIRBY J. M. 
Published: July 2006

SUMMARYCompression and shear tests were conducted on undisturbed samples from a range of Vertisols to determine the critical‐state parameters, their variation, and the relationships between these parameters and the moisture content and density of the soil. The soils varied considerably in their characteristics, with the liquid limit ranging from 0.39 to 0.88, and were tested over a wide range of moisture contents, densities and saturations.The critical‐state parameters describing compressional and shear properties varied with the moisture content, Atterberg limits and density of the soil, in contrast to saturated soils where these parameters are considered to be constants. It was found that the liquidity index (moisture content expressed as fractional distance between the liquid and plastic limits) explained the data significantly better than moisture content and also significantly better than did the suction. These data, therefore, supported suggestions that the Atterberg limits may serve as a useful basis for practical soil management guidelines. The measured parameters displayed considerable variation, demonstrating that any such guidelines need to be cast in terms of probabilities. The soil expanded when sheared if the normal stress during shear was less than about half the pre‐consolidation stress and compressed when sheared if the normal stress during shear was more than about half the pre‐consolidation stress. This behaviour was repeatable.
Properties and distribution of iron oxides and their association with minor elements in the soils of south‐western Australia
Authors: SINGH B. , GILKES R. J. 
Published: July 2006

SUMMARYIron oxides from 39 soils derived from various parent materials in south‐western Australia have been studied using a variety of techniques. Goethite and hematite were the only two Fe oxides present. The goethite/(goethite+hematite) ratio ranged from 0.18 to 1.0, and was highest in soils on acidic igneous rocks, decreasing for soils on alluvial and mafic parent materials. In a few soils derived from acid rocks only goethite was present. The redness rating of soils increased linearly with increasing amount of hematite. Al substitution in goethite ranged from 13 to 35 mol%, with higher values for soils on acid igneous rocks (median value = 26 mol%) than for soils on mafic (19 mol%) and alluvial (17 mol%) parent materials. Substitution of A1 in hematite ranged from 4 to 23 mol%, and was greatest in soils on mafic parent materials (median value = 12 mol% A1). A1 substitution in hematite was about half of that in associated goethite. The dehydroxylation temperature for goethite increased linearly with increasing A1 substitution. Goethite and hematite had similar crystal sizes (c. 20 nm), and both were in the form of irregular plates.Dissolution with 1 M HCl of iron oxides concentrated from the soils by 5 M NaOH digestion could be described both by the Cube Root Law and by Kabai's equation. Only one straight line was obtained for the dissolution data using Kabai's equation for samples containing both goethite and hematite, in contrast to the results of other workers. Major proportions of the Co, Cr, Cu, Mn, Ni and Zn in the soils were concentrated with the iron oxides, and the dissolution kinetics of these elements indicate that some may be present in the structure of the iron oxides.
A normal distribution model for the titration curves of humic acids
Authors: Manunza B. , Gessa C. , Deiana S. , Rausa R. 
Published: July 2006

SUMMARYTitration curves of humic acids extracted from different sources were fitted using a continuous distribution model. The mean pK values and distribution variances were calculated in the fitting procedure and they proved to be useful in differentiation of the humic acids under examination.
Soil organic matter accumulation, litter decomposition and humus forms under mediterranean‐type forests in southern Tuscany, Italy
Authors: van WESEMAEL B. , VEER M. A. C. 
Published: July 2006

SUMMARYThe amount of organic matter and rate of litter decomposition in relation to vegetation type under mediterranean‐type forests in southern Tuscany was studied. Since existing concepts are largely based on studies of soils on calcareous substrates in this region, particular attention was paid to soils on non‐calcareous materials. The humus type and distribution at five sites on acid metamorphic rocks and at one site on dolomitic limestone with different vegetation types was investigated. The input of above‐ground litter was also determined. On the metamorphic rocks, clear trends in humus profile development could be observed from deciduous through sclerophyllous to coniferous vegetation: there was a decrease in litter nitrogen content (9.3 to 5.8 g N kg−1DM), an increase in the amount of organic matter in ectorganic layers (2.53 to 4.66 kg m−2), a decrease in the decay constantk(0.26 ± 0.02 to 0.17 ± 0.03 a−1), and a decrease in soil faunal activity. The results indicate that, under eu‐mediterranean to sub‐mediterranean forests, decomposition rates are comparable to those under temperate deciduous forests, and that the dominant humus form is a leptomoder. The spatial variation in the amount of organic matter within the plots was considerable, and was related to vegetation type.
Growth and nitrogenous excretion of a common soil flagellateSpumellasp.—a laboratory experiment
Authors: Zwart K. B. , Darbyshire J. F. 
Published: July 2006

SUMMARYThe growth and nitrogenous excretion of a common soil flagellate,Spumellasp., isolated from a Scottish podzol and fed with the common soil bacterium,Pseudomonas fluorescens, were investigated. Video‐enhanced light microscopy and transmission electron microscopy were used to study the digestion process. Ingestion of the bacteria occurred rapidly at the base of the two flagella and involved the formation of a small protrusion, which surrounded the prey. The first signs of digestion appeared a few minutes after ingestion with the degradation of the outer membrane of the bacteria. Digestion was complete within 30–60 min, and the indigestible bacterial residues were then released into the medium. Ammonium nitrogen was the major form of nitrogen excreted. Some apparently intactP. fluorescensbacteria were also egested. For each division 130 bacteria were required. No feeding activities were observed at 5°C. Of the total bacterial protein, 42% was incorporated into biomass of flagellates.
The release and fate of nitrogen from catch‐crop materials decomposing under field conditions
Authors: JENSEN E. S. 
Published: July 2006

SUMMARYThe release and fate of nitrogen from15N‐labelled perennial ryegrass (Lolium perenneL.) and white mustard (Sinapis albaL.) catch crops were studied in field microplots. The initial decline in15N‐labelled organic N, after incorporation of the material in early December, was more rapid from mustard containing 2.6% N than from ryegrass containing 1.4% N. After 9 months of decomposition, the residual organic15N from the two materials declined at the same rate; the average decay constant for the following 2 years of decomposition was 0.30 a−1. After 33 months of decomposition, 23% and 34% of the mustard and ryegrass15N, respectively, was recovered in organic residues in the topsoil. Seven per cent of the ryegrass N was leached below 45 cm in micro‐lysimeters during the winter following incorporation. Three spring barley (Hordeum vulgareL.) crops, which succeeded ryegrass incorporation, accumulated 19%, 4% and 2%, respectively, of the ryegrass N in the above‐ground plant parts. Perennial ryegrass swards recovered a total of 26% of the ryegrass and 22% of the mustard catch‐crop N within 2 years. After 2 years of decomposition in unplanted soil, 82% of the ryegrass N was accounted for. The15N that was not accounted for may be present in the 10–45 cm depth, or it may have been lost by denitrification.
Gypsum crystals in soils
Authors: Jafarzadeh A. A. , Burnham C. P. 
Published: July 2006

SUMMARYGypsum is deposited in soils by capillary rise from water tables (per ascensum), or by movement downwards following incomplete wetting (per descensum). Both these situations were reproduced in artificial columns using a wide range of soil materials. Two soil profiles formed per ascensum on Bahrain Island and two per descensum in Iran were also studied. The size, shape and arrangement of gypsum crystals were determined by optical examination of specimens and thin sections and by using the scanning electrod microscope. A comprehensive scheme for their description is outlined. Tabular, prismatic, lenticular, acicular, fibrous, tubular and granular forms were found, often modified by features produced by partial solution and subsequent resumption of crystallization. The form of gypsum crystallization changes intricately in space, and is often ephemeral in time, making it difficult to draw firm conclusions linking crystal shape to particular environments or soil types.
Acquisition and analysis of three‐component digital images of soil pore structure. II. Application to seed beds in a fallow management trial
Authors: MORAN C. J. , McBRATNEY A. B. 
Published: July 2006

SUMMARYSeed beds of a tillage and fallow management trial were examined using the techniques of field impregnation and image analysis described in Part I of this paper. The trial was situated near Warwick on the Darling Downs, Queensland, Australia on a self‐mulching black earth soil with wheat as the test crop. The effects of both frequency of tillage operations and of burning vs. retention of stubble on the pore structure are examined. The only effect detected in the top 50 mm was due to stubble burning. The tilth layer was finer in the cultivated treatment. Cultivation was seen to reduce the connectivity of pore space. This effect was greatest when combined with burning of stubble. The image analysis results were found to be consistent with other data generated from the same trial.
Caesium sorption—desorption in clay—humic acid systems
Authors: MAGUIRE S. , PULFORD I. D. , COOK G. T. , MACKENZIE A. B. 
Published: July 2006

SUMMARYSoaking for 7 d with 0.05 M NaCl resulted in less caesium being sorbed by bentonite and kaolinite, but more by illite, compared to soaking for 2 d prior to addition of Cs. Overall the amount of Cs sorbed by the three clays was in the order bentonite > illite > kaolinite. Addition of humic acid to the clays depressed the sorption of Cs by all three clays, with illite showing the greatest effect. Desorption of added Cs was not totally reversible. The presence of humic acid resulted in an enhanced desorption of Cs from bentonite and to a lesser extent kaolinite. This enhanced desorption in the presence of humic acid was not seen for illite. The order of Cs retention following desorption for both clay and clay/ humic‐acid mixtures was illite > bentonite > kaolinite. A single Kd value could not describe the whole isotherm, but individual values were calculated at different Cs concentrations to cover the range of the isotherm. Kd values for desorption were higher than the corresponding Kd for sorption. For both sorption and desorption, the presence of humic acid resulted in lower Kd values than in its absence.
Influence of carbonate on the reaction of heavy metals in soils
Authors: MADRID L. , DIAZ‐BARRIENTOS E. 
Published: July 2006

SUMMARYThe reaction of Cu, Zn and Cd with soils with carbonate contents ranging from 0 to 75 mg g−1 was studied before and after removal of soil carbonates with acetate buffer at pH 5. Treatment with acetate buffer caused a strong decrease in metal retention by those soils containing carbonates, although if no carbonate was originally present, the treatment caused little effect or even an increase in the amounts sorbed. Before the treatment, adsorption of increasing amounts of Cu and Zn was accompanied by a continuous increase in Ca + Mg released, and those soils containing carbonate released Ca + Mg in excess of their exchangeable amounts, due to dissolution of carbonates and/or penetration of the heavy metal into the carbonate structure.It is suggested that Cu was preferentially retained by the treated soils through precipitation of Cu oxide, and by adsorption on the soil carbonates in the case of the original samples. Zn was removed from the solution by the original carbonate soils through formation of ZnCO3. Treated soils were likely to retain Zn by cation exchange and/or adsorption. Adsorption was probably the main process involved in retention of Cd.In all cases pH was the master variable in controlling the extent and probably the nature of the reaction.
Sulphur cycling in New Zealand hill country pastures. I. Laboratory sulphur, nitrogen and carbon mineralization studies
Authors: SAKADEVAN K. , HEDLEY M. J. , MACKAY A. D. 
Published: July 2006

SUMMARYLarge leaching losses of sulphate contribute to the inefficient use of sulphur (S) fertilizer in some grazed hill country pastures in New Zealand. Laboratory mineralization studies were conducted to measure S, nitrogen (N) and carbon (C) mineralization rates and the potential for S leaching from surface soils of low (LS, 0–12°) and medium (MS, 13–25°) slope positions on hill country pastures. The soils differed in C, N and S contents as a result of different fertilizer histories and the uneven redistribution of nutrients by the grazing animal. Soils were incubated in columns for 140 d and leached periodically with 0.01 M KCl to remove mineralized sulphate, nitrate and ammonium. The net amounts of N and S mineralized were greater in soils on low slopes than medium slopes and in soils from pastures which had received fertilizer continuously, compared with those hill pastures that had not received single superphosphate fertilizer in the previous 7 years. In both cases more mineralization was associated with smaller soil C:nutrient ratios. However, the amounts of C mineralized were greater in soils from medium slopes where C:nutrient ratios were larger. In general, the ratio of N:S mineralized was smaller than the N:S ratio of the soil organic matter, suggesting that N is conserved while S remains in the soil solution susceptible to leaching. It is suggested that the extent of S leaching loss under field conditions will reflect S mineralization potential.
Genesis and transformation of minerals in the formation of red (Alfisols) and black (Inceptisols and Vertisols) soils on Deccan basalt in the Western Ghats, India
Authors: BHATTACHARYYA T. , PAL D. K. , DESHPANDE S. B. 
Published: July 2006

SUMMARYSix noncalcareous pedons from the basaltic terrain of the Western Ghats in Maharashtra, India, were identified for the present study. Of these, two red‐soil pedons (Typic Haplustalfs) and one black‐soil pedon (Vertic Ustropept) are from the Bhimashankar plateau at an elevation of 1000 m above mean sea level, experiencing a humid (>5000 mm rainfall) tropical climate. The other three pedons of black soils (Typic Chromusterts and Typic Ustropept) are from the semi‐arid zone (500–1000 mm rainfall), at an elevation of 825–893 m.Clay mineralogical investigation indicated that interstratified smectite‐kaolin (Sm/K) is dominant in red soils whereas smectite is dominant in black soils. The Sm/K is formed by the transformation of montmorillonite, the first weathering product of Deccan basalts in a humid tropical climate. We suggest that the interstratification of kaolin with chloritized smectite may also be an important ephemeral stage during the transformation of smectite to kaolinite. The presence of zeolites provided sufficient bases to prevent the complete transformation of Sm/K to kaolinite. The presence of smectites and zeolites made the formation of black soils possible in microdepressions even in a tropical humid climate. The genesis of Sm/K and smectite in red and black soils, respectively, suggests that these soils formed through a progressive landscape reduction process. The presence of both Sm/K and smectite in black soil clays of semi‐arid climate suggests that the smectite of these soils was formed in an earlier humid climate.
Field determination of sorptivity as a function of water content using a tension infiltrometer
Authors: BONSU M. 
Published: July 2006

SUMMARYSorptivity for tension wetting in the field was determined and weighted‐mean diffusivity calculated. Both tension sorptivity and weighted‐mean diffusivity could be described by an exponential function of the form aexp(bθ) where θ is either mean water content or dimensionless water content and a and b are parameters. This relation was valid for an initial water content between 0.016 and 0.047 m3 m−3 and a final water content between 0.154 and 0.316 m3 m−3. Tension sorptivity was more strongly correlated with average water content than dimensionless water content. However, in the case of weighted‐mean diffusivity, the correlations with both dimensionless water content and average water content were almost the same.
Factors affecting the nutrient status of forest sites in a mountain watershed in Nepal
Authors: SCHMIDT M. G. , SCHREIER H. , SHAH P. B. 
Published: July 2006

SUMMARYSoil and foliage samples were collected from 136 sample sites in forested areas of the Dhulikhel Watershed, Nepal. Analyses showed that the soils have small values for pH, base saturation, total nitrogen, carbon and available phosphorus. Sample sites were stratified on the basis of aspect and elevation, soil type, forest type and management and the strata were compared to determine the influence of site factors on forest soil fertility.Soils on south‐facing slopes at low elevation contained significantly less total nitrogen and organic carbon compared with soils from north‐facing slopes at high elevation. Foliage of both sal (Shorea robustaGaertn.) and chir pine (Pinus roxburghiiSargent) growing on red soils (Rhodustults and Haplustults) contained significantly less phosphorus compared with non‐red soils (Ustochrepts and Dystrochrepts). Soils under stands of sal have the poorest soil fertility levels in comparison with chir pine and hardwood sites. The continuous removal of base‐rich litter from sal sites may account for the poor fertility conditions. Soil fertility levels are greater on sites which have been protected from biomass removal for at least 15 years relative to sites which have come under protection in the past 7 years.
Root‐induced irreversible transformation of a trioctahedral mica in the rhizosphere of rape
Authors: HINSINGER P. , ELSASS F. , JAILLARD B. , ROBERT M. 
Published: July 2006

SUMMARYThe ability of the roots of rape (Brassica napus) to promote the transformation and dissolution of a phlogopite mica was studied in the rhizosphere. Rape was cropped for 1 to 32 d on 2–105 μm phlogopite as sole source of both K and Mg. The chemical balance of K and Mg revealed that rape was able to induce a significant release of interlayer‐K after 4 d, and even a significant release of octahedral‐Mg after 8 d of cropping. After 32 d, the root‐induced release amounted to 80 and 21 g kg−1 of total‐K and ‐Mg, respectively. The weathering products sampled in the close proximity of the roots were analysed by X‐ray diffractometry (XRD), and by energy dispersive X‐ray (EDX) microanalysis of resin‐embedded samples prepared for transmission electron microscopy. The XRD analysis of K‐saturated, oriented plates showed that part of the vermiculite formed by root activity behaved as a typical hydroxy‐aluminous interlayered vermiculite (HIV). The EDX microanalysis revealed that the release of interlayer‐K which occurred during the vermiculitization was compensated mostly by A1 and Mg originating from the octahedral sheet of the phlogopite. Such crystallographic and crystallochemical changes necessarily involved an acid dissolution of the mica structure, which may be related to the root‐induced pH decrease encountered simultaneously in the rhizosphere. Proton excretion by rape roots was thus the probable mechanism involved in the root‐induced irreversible transformation of the phlogopite.
Effect of organic matter on the distribution, extractability and uptake of cadmium in soils
Authors: HE Q. B. , SINGH B. R. 
Published: July 2006

SUMMARYDistribution and plant uptake of soil Cd as influenced by organic matter and soil type were investigated in a greenhouse experiment. Three soils (a sand, sandy loam and clay loam) were used. The rates of organic matter in its moist state added were 0,20,40, 80, 160 and 320 g kg‐1of the air‐dried soil on mass basis. Ryegrass (Lolium multörum L.) was used as a test crop. Soil Cd was analysed by a sequential extraction technique and by extraction with 1 M NH4NO3and 0.005 M DTPA. The exchangeable fraction of Cd as determined by 1 M MgCl2in the sequential extraction procedure increased, whereas the Fe‐Mn oxidebound fraction decreased, with increasing levels of organic matter addition in all three soils. The dry matter yields of ryegrass were not affected by the addition of organic matter, but the Cd concentrations in both cuts of ryegrass decreased with increasing amounts of organic matter added. The plant Cd was highly but negatively correlated to soil CEC. At any level of organic matter addition, the decrease in Cd concentration of ryegrass was in the order: sand > sandy loam > clay loam.