bluuebunny/crossref_metadata_2025 huggingface dataset:
Release of cationic aluminium from acidic soils into drainage water and relationships with land use
Authors: ADAMS W. A. , ALI A. Y. , LEWIS P. J.
Published: July 2006

The concentration of cationic monomeric aluminium (A13+) was determined in streams draining areas in different land use. Relationships between the concentrations of A13+ and companion ions were examined both for streams and for eluates from soil leached in the laboratory with simulated rainwater that ranged in pH and salt concentration.

The concentrations of A13+ were consistently greater in streams draining Sitka spruce woodland than in streams in adjacent catchments draining rough grazing. In no case was the A13+ concentration governed by the solubility product of gibbsite. The concentrations of A13+ were very closely correlated with excess anions (total inorganic anions minus basic cations) both for stream water and for eluates from soil leached with simulated rainwater at a constant pH equal to that of the soil (3.8).

Exchangeable A1 was the source of A13+ in leachates from soil in the laboratory and the displacement of exchangeable Al was the dominant process accounting for the levels of A13+ in acidic streams. Hydrogen ions were much more important than basic cations in displacing exchangeable Al from the acidic soil used in the laboratory experiments and probably from soils in the field. The greater excess of inorganic anions in streams from Sitka spruce woodland probably resulted from a greater anion excess in the input water (acid rain) together with a greater NO, production in the soil. All three major anions, CI, SO4 and NO3 contributed to the greater anion excess.
The effects of fulvic and humic acids on soil aggregation: a micromorphological study
Authors: FORTUN A. , BENAYAS J. , FORTUN C.
Published: July 2006

The influence of soil amendment with fulvic + humic acid (FH) fractions, obtained from manure or peat, upon the shape, size and numerical density of aggregates in a sandy loam and a clay soil was examined using micromorphological techniques and image analysis. The effect of the FH fraction from manure (FHM) was to produce larger aggregates from the smaller ones, while the FH from peat (FHP) gave rise to a higher numerical density of smaller aggregates. Although the type of structural change was similar in the two soil types, the extent of change per g of FH was greater in the clay soil. Aggregate shape varied with treatment and soil type, but both kinds of organic matter produced vughs and a narrowing of the planes in the two soils which can be considered as signs of structural improvement.
Retarded leaching of nitrate in acid soils from the tropics: measurement of the effective anion exchange capacity
Authors: WONG M. T. F. , HUGHES R. , ROWELL D. L.
Published: July 2006

Delay in the leaching of nitrate was measured in laboratory columns of repacked soils (Oxisols, Alfisols, Ultisols and Inceptisols) from South America, Africa and South‐East Asia. Between one and five pore volumes were required for the frontal displacement of chloride by nitrate (2 mM adjusted to the natural pH of the soil). The delay was in good agreement with that calculated from charge (0 to 1.7 cmol positive charge kg−1). Measurement of charge by batch equilibration with 0.5 M and then 2 mM NH4CI at the pH of the soil overestimated the effective charge, probably due to removal of sulphate in the washings. A leaching method using only 2 mM NH4CI gave a better estimate.
Microbiology of soils at opencast coal sites. I. Short‐and long‐term transformations in stockpiled soils
Authors: JOHNSON D. B. , WILLIAMSON J. C. , BAILEY A. J.
Published: July 2006

The microbiology of soils subjected to stripping and stockpiling at opencast mine sites was investigated using a combination of and biomass fumigation plate‐count techniques. Mounds varied in age from a few weeks to 11 years, and soils included both mineral and organic variants. Results showed that after an initial stimulation of bacteria, microbial populations declined in stockpiles. Numbers of viable fungal propagules, and to a lesser extent actinomycetes, declined with depth in mounds, particularly below about 1 m, and this trend was accentuated with increased time of storage. However, stockpiled soils were highly variable in terms of microbiological status and displayed considerable lateral as well as vertical heterogeneity.
Microbiology of soils at opencast coal sites. II. Population transformations occurring following land restoration and the influence of ryegrass/fertilizer amendments
Authors: WILLIAMSON J. C. , JOHNSON D. B.
Published: July 2006

Data from field work and pot experiments gave insight into transformations occurring in soil microbial populations at opencast coal sites during the first year of land restoration. Total bacterial biomass increased markedly immediately following restoration, while pot experiments revealed that this flush was confined to soil stored below 1 m depth in stockpiles, where anaerobic conditions develop. Fungal and actinomycete propagules declined at the outset of restoration, but rallied during the first year, while the bacterial flush subsided. Fungal hyphae, which accounted for 50% of microbial biomass in surface mound and freshly restored soils, accounted for > 99% one year after restoration. Experiments involving fertilizer and ryegrass amendments showed the biomass of restored soil to be limited by carbon, rather than nitrogen or phosphorus.
Modelling water and solute transport in macroporous soil. I. Model description and sensitivity analysis
Authors: JARVIS N. J. , JANSSON P‐E. , DIK P. E. , MESSING I.
Published: July 2006

A detailed mechanistic model of water movement and transport of non‐reactive solute in a macroporous soil is described. One important feature of the model is that it may be run in either one or two flow domains using the same values for the hydraulic properties characterizing the soil. Water and solute movement in the micropores is calculated with the Richards and convection‐dispersion equations and, in two domains, this is coupled to fluxes of water and solute in the macropores by empirical interaction terms. These interaction terms are redundant in the one‐domain model, which simply reduces to the non‐steady state convection‐dispersion equation.

A sensitivity analysis is presented showing how it is possible to identify conditions under which a macropore flow domain may need to be considered. In part II (Jarvis et al., 1991), the model is evaluated under field conditions in chloride breakthrough experiments in soil monolith lysimeters.
Water flow characterization and test of a kinematic‐wave model for macropore flow in a highly contrasted and irregular double‐porosi medium
Authors: DI PIETRO L. , LAFOLIE F.
Published: July 2006

Laboratory experiments to characterize water flow through a column consisting of an artificial double‐porosity medium are described. A gamma‐attenuation device was used to measure water storage in the intra‐ and inter‐aggregate porosity domains after successive infiltrations. Several days after macropore flow had ceased, a significant proportion of the water that had infiltrated was retained within the aggregates.

After the column had been brought to its water retention capacity, several rains with different intensities were applied, and the drainage hydrographs were recorded and analysed in order to characterize water transport in the coarser pores and to test the kinematic‐wave approach to macropore flow proposed by Germann (1985). Reasonable fits of calculated hydrographs to experimental data were obtained for high input intensities, but the model was unable to reproduce the hydrographs recorded at low intensities. In particular, the model could not simulate the high dispersion of the input signal observed at low rain intensities.
Chemical changes in decomposing forest litter in response to atmospheric sulphur dioxide
Authors: WOOKEY P. A. , INESONT P.
Published: July 2006

Decomposing needle and leaf litter, from a pine(Pinus sylvestrisL.) stand and a mixed deciduous woodland, respectively, were exposed to arithmetic mean SO, concentrations of up to 50 nl l−3(mm3m−3) in controlled field‐based experiments lasting up to 215 d. The objectives of the study were: (1) to evaluate whether SO, concentrations, known to occur in parts of Europe, could alter the chemical composition of forest litter and leachates, and (2) to use such information to complement results obtained during microbiological studies (Wookeyet al., 1991).

Dry deposition of SO, on the litter resulted in the production of sulphate during damp conditions or when the litter was moist. The formation of SO2−4and associated H+ ions led to cation exchange processes whereby Mg2+and Ca2+in particular were leached from the litter. This resulted in significant (P<0.01) depletion of magnesium and calcium in both litter types, even at the lowest SO2concentrations tested (15 nl l−1). Incomplete buffering by base cations resulted in acidification of leachates.

The magnitude of cation leaching and depletion within the litter was not always linearly related to SO, or leachate SO2−4concentrations, and the role of microbial processes and litter quality as modifiers of such responses is considered.
Structure and self‐similarity in silty and sandy soils: the fractal approach
Authors: BARTOLI F. , PHILIPPY R. , DOIRISSE M. , NIQUET S. , DUBUIT M.
Published: July 2006

Soil structure was studied using the concept of fractals and related to soil texture and aggregate properties such as surface charges and aggregate stability. The mass and porosity fractal dimensions (Dm and Dp) of silty and sandy soils were determined on in situ soils using a variety of soil sections (thin, very‐thin and ultra‐thin), by image analysis on a continuous scale from m to 10−9 to 10−1m. Surface fractal dimensions (Ds) of these soils were determined on < 2 mm air‐dried samples using mercury porosimetry and the fractal cube generator model. The results suggest that soils are not pore fractals but mass and surface fractals with Dm= 1.1 Ds when the dimension of the embedding Euclidean space d is 3. The soil structures could possibly be described by fractal diffusion‐limited aggregation with complex interconnected aggregates or by fractal cluster–cluster aggregation models. As a preliminary conclusion, the fractal approach appears to be a potentially useful tool for understanding the underlying mechanisms in the creation or destruction of soil structure.
Use of CaCl2to decrease ammonia volatilization after application of fresh and anaerobic chicken slurry to soil
Authors: WITTER E.
Published: July 2006

Ammonia losses after surface application of fresh chicken slurry (15% solids) and anaer‐obically stored chicken slurry (10% solids) to a silty clay soil (pH 6.9) at a rate equivalent to 34 m3ha−1were studied in a laboratory incubation experiment. Total NH3‐N losses amounted to 29% of the initial uric acid‐N+urea‐N+NH+4‐N content of the fresh slurry and 28% of the initial NH+4‐N content of the anaerobic slurry. Peak rates of ammonia volatilization took place between 24 h and 48 h after application of the fresh slurry and within 5 h of application of the anaerobic slurry. The addition of CaCl2at a rate of 36 mg Ca g−1(dry wt) slurry decreased peak rates of ammonia volatilization from the fresh slurry by 73% and total losses by 37%. The decrease in total ammonia losses through CaCl2addition to the anaerobic slurry was only 8 %. The addition of CaCl2decreased CO2output from both slurries through precipitation of HCO3−as CaCO3, thereby removing a source of alkalinity from the solution. The failure of the CaCl2addition to decrease significantly ammonia losses from the anaerobic slurry suggested that HCO3−was an important source of alkalinity driving ammonia volatilization in the fresh slurry, but not in the anaerobic slurry.

CaCl2, addition did not affect urea hydrolysis, nor net nitrogen mineralization. The decrease in ammonia loss achieved through CaCl2addition was however not associated with a parallel increase in ammonium concentrations in the soil. Further experiments showed that the ammonia retained by the CaCl2, was probably fixed by the soil and rendered non‐extractable by KCl.
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

The 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

A 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

Compression 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

Iron 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

Titration 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

The 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

The 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

The 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

Gypsum 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

Seed 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

Soaking 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

The 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

Large 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

Six 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

Sorptivity 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

Soil 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

The 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

Distribution 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.
The influence of temperature and water table position on carbon dioxide and methane emissions from laboratory columns of peatland soils
Authors: MOORE T. R. , DALVA M.
Published: July 2006

Laboratory columns (80 cm long, 10 cm diameter) of peat were constructed from samples collected from a subarctic fen, a temperate bog and a temperate swamp. Temperature and water table position were manipulated to establish their influence on emissions of CO2 and CH4 from the columns. A factorial design experiment revealed significant (P < 0.05) differences in emission of these gases related to peat type, temperature and water table position, as well as an interaction between temperature and water table. Emissions of CO2 and CH4 at 23°C were an average of 2.4 and 6.6 times larger, respectively, than those at 10°C. Compared to emissions when the columns were saturated, water table at a depth of 40 cm increased CO2 fluxes by an average of 4.3 times and decreased CH4 emissions by an average of 5.0 times. There were significant temporal variations in gas emissions during the 6‐week experiment, presumably related to variations in microbial populations and substrate availability. Using columns with static water table depths of 0, 10, 20, 40 and 60 cm, CO2 emissions showed a positive, linear relation with depth, whereas CH4 emissions revealed a negative, logarithmic relation with depth. Lowering and then raising the water table from the peat surface to a depth of 50 cm revealed weak evidence of hysteresis in CO2 emissions between the falling and rising water table limbs. Hysteresis (falling > rising limb) was very pronounced for CH4 emissions, attributed to a release of CH4 stored in porewater and a lag in the development of anaerobic conditions and methanogenesis on the rising limb. Decreases in atmospheric pressure were correlated with abnormally large emissions of CO2 and CH4 on the falling limb. Peat slurries incubated in flasks revealed few differences between the three peat types in the rates of CO2 production under aerobic and anaerobic conditions. There were, however, major differences between peat types in the rates of CH4 consumption under aerobic incubation conditions and CH4 production under anaerobic conditions (bog > fen > swamp), which explain the differences in response of the peat types in the column experiment.
A device for determining the sorptivity of soil aggregates
Authors: LEEDS‐HARRISON P.B. , YOUNGS E.G. , UDDIN B.
Published: July 2006

A device that infiltrated water over a small circular surface area having a radius ranging between 1.45 mm and 2.5 mm was used to measure the sorptivity of initially air‐dry aggregates of size greater than 20 mm. The small infiltration area caused the water uptake to be dominated by capillarity that allowed the use of a simple formula to obtain the sorptivity from the steady‐state flow rate that occurred very early after the start of imbibition. The results of measurements of sorptivity made on a fine sand agreed with those obtained from measurements on one‐dimensional water infiltration into columns of the sand. Sorptivity measurements on stabilized aggregates of a clay soil and on air‐dried field aggregates of a clay soil were easily made. The simplicity and rapidity of the method allowed measurements to be conveniently replicated.
Retention of vanadium (V) by three Finnish mineral soils
Authors: MIKKONEN A. , TUMMAVUORI J.
Published: July 2006

Retention of V(V) by three Finnish mineral soils from 10−4m and 10−5m sodium vanadate solutions was investigated at room temperature in the pH range 2.3–7.5. In adsorption experiments, 0.02 m KCl was used as ionic medium, and the samples were left to equilibrate for 72 h. The solid: solution ration was 1:100 (m: v). Maximum adsorption occurred at pH ∼4, where 70–80% of the added V (350–400 μg g−1 from 10−4m solution and 35–40 μg g−1 from 10−5m solution) was retained by each soil. Retention was significant even at pH 6, where adsorption of a similar anion, molybdate, is negligible. Desorption of the retained V was measured by adding 50.0 cm3 of 0.02 M KCl into weighed soil samples and shaking for 17 h in a mechanical stirrer. Only a minor part of retained V could be removed from each soil by the KCl treatment.

Retention of different ionic species of V from 10−5m solution is approximated using values of log K obtained from the literature. In these calculations, kaolin is used as a reference material.
Coupled diffusion and oxidation of ferrous iron in soils: III. Further development of the model and experimental testing
Authors: KIRK G.J.D. , SOLIVAS J.L.
Published: July 2006

Equations are developed to predict the distribution of Fe2+between solid and solution phases in a reduced soil undergoing oxidation at different pHs, based on cation‐exchange equilibria and electrical neutrality in the solid and solution. The equations satisfactorily explained experimental results. They are incorporated in the model of Fe2+diffusion and oxidation developed in Part II, and the model is also extended to allow for O2consumption in processes other than Fe2+oxidation. The resultant predictions are tested against measured profiles of Fe(II), Fe(III) and pH in cylinders of reduced soil exposed to O2at one end. When oxidation rate constants measured in stirred soil suspensions were used to run the model, the predicted rates of O2consumption were too great and the spread of the oxidation front too small. Satisfactory agreement was achieved for oxidation rate constant values about one‐eighth of those measured in the stirred suspensions. The findings are consistent with the rate of Fe2+oxidation in soil being controlled by access of O2to Fe2+sorption sites, as suggested in Part I. The revised model allows a study of the effects of Fe2+oxidation on the mobility of other cations in reduced soils, e.g. nutrient cations in the rice rhizosphere. Fez+ oxidation and the accompanying acidification may greatly impede cation mobility in reduced soils.
THE EFFECT OF DEPTH OF BURYING AND FREQUENCY OF CULTIVATION ON SURVIVAL AND GERMINATION OF SEEDS OF WILD OATS (AVENA FATUA L. AND AVENA LUDOVICIANA DUR.)
Authors: THURSTON J. M.
Published: July 2006

Summary. Seeds of Avena fatua and A. ludoviciana were sown at a depth of 15 cm or mixed into the top 5 cm of soil in small field‐plots at Rothamsted and subjected to 5 different regimes of depth and frequency of cultivation for 3 years, after which all plots were dug to 15 cm in spring and autumn for a further 4 years. Seedlings were counted and no plants were allowed to produce seeds. After 7 years, soil‐samples showed that very few intact seeds of A. fatua and none of A. ludoviciana remained, although less than 20% of the seeds sown had produced seedlings. Laboratory tests after 4 to 8 years’dry slorage showed seeds of both species to be viable. The maximum survival of viable seeds, estimated by seedling‐emergence, was 61 months for A. fatua and 33 months for A. Indoviciana. Seeds of A. fatua survived slightly longer at 15 cm than in the top 5 cm of soil. Survival of A. ludoviciana was less affected by depth and cultivation, except that birds ate some shallow‐sown spikelets in the first fortnight after sowing. A. fatua germinated in spring and autumn, and A. tudoviciana in winter, irrespective of age of seed and cultivation of soil. Frozen soil delayed emergence of A. ludoviciana seedlings lor varying periods between December and March. Seedlings of A. ludoviciana were slightly more winter‐hardy than A. fatua. More seedlings of A. fatua appeared in the second spring than at any other time, but 80% of the seedlings of A. ludoviciana appeared in the first autumn and winter.

Effets de la profondeur d'enfouissement des graines et de la fréquence des façons culturalles sur la longévité et la germination des semences de Folle‐Avoine (Avena fatua L. et A. ludoviciana Dur.)
THE CONTROL OF RANUNCULUS REPENS (L.) IN RASPBERRIES
Authors: ROBINSON D. W.
Published: July 2006

Summary. Experiments conducted in Northern Ireland between 1956 and 1960 show that Ranunculus repens may be controlled by MCPA‐salt or ‐ester applied in November or December. These compounds are more effective than salt or ester formulations of 2,4‐D and salt formulations of MCPB and 2,4‐DB. Three varieties of raspberry were uninjured when a salt formulation of MCPA was applied during December at 2.2 kg/ha to the same plots for three successive years. Five other varieties were uninjured after one year's treatment. Wetting the dormant canes to run‐off with MCPA‐salt at 2000 ppm caused no injury but, in one experiment, MCPA‐salt at 4.5 kg/ha reduced the number of shoots the following season. The margin of safety is not high but, in the absence of any alternative chemical means of controlling R. repens in raspberries, a late November or December application of MCPA‐salt at 2.2 kg/ha is recommended in Northern Ireland where this weed is prevalent. In two trials, raspberries appeared to be slightly more tolerant of 2,4‐D than of MCPA but in general, control of R. repens with winter applications of 2,4‐D was inadequate except where the weeds were young or active.

La lutte contre Ranunculus repens L. dans les framboisiers
THE RELATIONSHIP BETWEEN THE HERBICIDAL EFFECT OF 2,6‐DICHLOROBENZONITRILE AND ITS PERSISTENCE IN THE SOIL
Authors: BARNSLEY G. E. , ROSHER P. H.
Published: July 2006

Summary. A series of experiments with 2,6‐dichlorobenzonitrile is described. It is demonstrated that 2,6‐DBN is highly phytotoxic when applied as a soil drench or preemergence spray in the greenhouse, but measurement of crop and weed responses in the field, accompanied by quantitative assessment of the chemical residues in the soil, indicates that the persistence of 2,6‐DBN following surface application is short under both tropical and temperate (winter) conditions. It is, however, extended from a few days to several weeks if the chemical is incorporated into the soil immediately after application. Under tropical conditions the effect of 4 lb/ac applied to the surface is roughly equated to 2 lb/ac immediately watered‐in, 1.5 lb/ac immediately raked‐in, or 1 lb/ac both watered‐ and raked‐in, and a delay of 4 hours between application and incorporation is shown to reduce the effectiveness of the chemical by about half. The lack of persistence of 2,6‐DBN when applied to the soil surface, and the modifying influence of soil incorporation and watering is attributed to its high vapour pressure (5 × I0−4 mm Hg at 20° C) and its relatively low solubility in water (20 ppm at 25° C).

Le rapporl entre l'activité herbicide du 2,6‐dichlorobenzonitrile et sa persistance dans le sol
THE REACTION OF TRIFOLIUM REPENS (L.) IN GRASSLAND TO 2,4‐D, MCPA AND MIXTURES OF 2,4‐D AND MCPB
Authors: ELLIOTT J. G.
Published: July 2006

Summary. Eight experiments were carried out on a range of pasture lypes under different management and in different years to lest the reaction of white clover (Trifolium repens in grasstand to doses of up to 4 lb/ac of the herbicides MCPA‐sodium or‐potassium and 2,4‐D‐amine. The initial effect of the treatments was to reduce the amount of dover in the sward, the size of the reduction varying greatly from field to field for any one dose. In general, the higher the dose, the more severe was the depression of the clover 1 month after spraying. Both herbicides at 2 and 4 lb/ac caused substantial depressions on some of the fields. The growth of the treated clover was examined during the year following spraying. The ability of the clover to recover from the initial depression varied considerably in the different fields; on some, recovery started in the year of spraying and on others in the following year. Quick recovery was usually associated with a high initial resistance but there were fields in which the clover showed contrasting rates of recovery following similar depressions. The experiments produced no clear‐cut evidence as to why the initial resistance and speed of recovery varied in different fields. In one experiment the effects of MCPB‐sodium and 2,4‐D‐amine on white clover were compared separately and in a series of mixtures. An examination made 6 weeks after spraying showed that MCPB at up to 8 lb/ac had no significant effect on the clover, whereas 2,4‐D at 1 lb/ac caused a 22% reduction. Mixtures containing up to 0.37 lb 2,4‐D and up to 6 lb MCPB caused no reduction while those containing 0.75 lb 2,4‐D and 4 lb MCPB were not significantly different from 1 lb 2,4‐D alone.

Reaction de Trifolium repens (L.) en prairie au 2,4‐D, au MCPA, et aux mélanges de1, 2,4‐D et de MCPB