bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Akaike Information Criterion for choosing models for variograms of soil properties
Authors: WEBSTER R. , McBRATNEY A. B. 
Published: July 2006

SUMMARYA problem in the application of geostatistics to soil is to find satisfactory models for variograms of soil properties. It is usually solved by fitting plausible models to the sample variogram by weighted least squares approximation. The residual sum of squares can always be diminished, and the fit improved in that sense, by adding parameters to the model. A satisfactory compromise between goodness of fit and parsimony can be achieved by applying the Akaike Information Criterion (AIC). For a given set of data the variable part of the AIC is estimated by
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where n is the number of experimental points on the variogram, R is the residual sum of squares and p is the number of parameters in the model. The model to choose is the one for which Â is least.The AIC is closely related to Akaike's earlier final prediction error and the Schwarz criterion. It is also equivalent to an F test when adding parameters in nested models.
Cation type and ionic strength effects on the solution composition of an acidic subsoil
Authors: MANSON A. D. , FEY M. V. 
Published: July 2006

SUMMARYSodium, potassium, magnesium and calcium chloride solutions of four concentrations (0.4, 1.0, 4.0, l0.0meq dm−3) and distilled water were equilibrated with the highly weathered, acidic subsoil of a Plinthic Paleudult from Natal at a soil:solution ratio of 2.2:1, then separated by centrifugation with an immiscible liquid and analysed for inorganic solutes. With each salt, increasing ionic strength resulted in lower solution‐pH (the maximum pH was 4.95 in the distilled water equilibration) and higher aluminium concentration and activity. These effects were much less marked for sodium (maximum ΔpH of 0.47) than for the other cations (maximum ΔpH of 0.83) and both the concentration and activity of aluminium were correspondingly lower (by tenfold at the highest chloride concentration) in the sodium solutions.Irrespective of the nature or concentration of the electrolyte added, pH and the activities of A13+ and silica in solution were consistently interrelated in a way which suggests that equilibrium with the gibbsite and poorly crystalline kaolinite in this soil had been closely approached. The results provide a basis for anticipating the effect of infiltrating solutions of fertilizer salts on subsoil acidity and suggest that a beneficial effect may accrue from the presence of sodium in the cation suite of acid soils.
Phosphorus accumulation in savanna termite mound in Venezuela
Authors: LÓPEZ‐HERNÁNDEZ D. , FARDEAU J. C. , NIÑO M. , NANNIPIERI P. , CHACON P. 
Published: July 2006

SUMMARYNasutitermes ephrataeare often abundant in seasonally flooded and dry Venezuelan savannas, where they play an important role in litter decomposition and nutrient cycling. Measurements were made of phosphorus forms and associated properties in 14 mounds and adjacent soils. Mounds contained on average over twice as much total phosphorus as adjacent soils. The difference was differentially distributed, mainly as inorganic forms. Mounds also display a relatively high organic matter content. ‘Available’ forms of P, especially water‐soluble P, increased several times as a result of termite activity. Concomitantly, P‐sorption was greatly reduced in mounds compared to surrounding soils.Mounds did not display higher phosphatase activity. The elevated organic carbon content, high level of soluble P, together with very high C/P0ratios found in mounds, probably inhibited phosphatase activity.
Effects of addition of bentonite on the hydrocarbon fraction of a podzol soil (A1 Horizon)
Authors: AMBLÈS A. , MAGNOUX P. , JAMBU P. , JACQUESY R. , FUSTEC E. 
Published: July 2006

SUMMARYLipids generally accumulate in surface horizons of soils deficient in clay minerals. Samples from a podzol (A1 horizon–no clay) were incubated with a supply of hetero‐ or homo‐ionic (Mg)‐bentonite for 4 months at 28 °C. A significant decrease of unbound lipids was observed. A detailed study of the mainly hydrocarbon fraction revealed that several processes were involved. A transfer of lipids, particularly hydrocarbons, occurred from the free to the bound phase. Consequently, reduced toxicity of these lipids towards soil microorganisms can be expected. The addition of clay resulted in a stimulation of oxidation processes, the extent of which varied with the exchangeable cations; heteroionic bentonite led to increased mineralization, whereas Mg‐bentonite promoted mild oxidation reactions. The increased microbial activity also produced short‐chain hydrocarbons; with Mg‐bentonite, unusual C21‐C35 n‐alkanes were detected. All of these microbial hydrocarbons were found in the bound phase.
Effects of pre‐sowing compaction on soil physical properties, soil atmosphere and growth of oats on a clay soil
Authors: McAFEE M. , LINDSTRÖM J. , JOHANSSON W. 
Published: July 2006

SUMMARYThe effects on a number of soil physical and aeration parameters of compaction during spring pre‐sowing operations were measured on a clay soil (49% clay). A soil‐tyre contact stress of 200 kPa was applied by tractor tyres.Yield of an oat crop was reduced by 30% as a result of compaction. Total porosity of the soil was reduced by 6% v/v owing to loss of pores > 60 μm, and water retention was increased. The resultant decrease in air‐filled porosity greatly reduced gas diffusion and air permeability coefficients of the soil, and, for a time, O2 content of the soil atmosphere was significantly lowered in the compacted treatment. Penetrometer resistance after sowing was 3.5 MPa in the control and 4.5 MPa in the compacted treatment; in the latter, root growth was inhibited until the soil dried and cracked. By the end of June, canopy temperature measurements indicated water stress in the oat crop on compacted soil but not in that on the control.The results obtained indicated that air permeability, measured in the field, of 1 mm s−1 provides a satisfactory single value below which crop growth is likely to be reduced.
Aeration changes after irrigation in a clay soil
Authors: McAFEE M. , LINDSTRÖM J. , JOHANSSON W. 
Published: July 2006

SUMMARYThe effects on soil aeration of varying both the intensity and quantity of water applied per irrigation were investigated in a field experiment on a clay soil. Soil physical and soil aeration parameters were measured before, and for up to 7 days after irrigation. Irrigation increased the volumetric water content of the surface layer by approximately 8% v/v. However, periods of waterlogging were short on this soil. Significant decreases in soil oxygen content in the days after irrigation were caused by increased soil and root respiration. In terms of subsequent crop growth, the practice of applying 30 mm irrigation water at an intensity of 5 mm h−1 was shown to be superior to irrigations providing half this quantity (15 mm) or double this intensity (10 mm h −1). The lower intensity irrigations decreased soil permeability by homogeneous wetting and swelling, and thus more of the water applied was recovered in the soil. Approximately one third of the water applied at the higher intensity was lost through cracks, and wetting of the soil was less uniform.
Scaling the saturated hydraulic conductivity of an alfisol
Authors: BONSU M. , LARYEA K. B. 
Published: July 2006

SUMMARYAlfisols exhibit a high degree of spatial variability in their physical properties. As a result, it is difficult to use information on physical parameters measured at one location to model larger‐scale hydrologic processes. In this study, the saturated hydraulic conductivity, KS, of an Alfisol was determined on 109 undisturbed monoliths using the falling‐head permeameter method. The model developed by Arya & Paris (1981) was used to calculate the pore volume from sand and clay fractions. Scaling factors were calculated from the measured Ks, sand pore‐volume, clay pore‐volume, clay content and effective porosity, using the similar media concept. Prediction of Ks of gravelly Alfisol using clay pore‐volume is confounded by high gravel content which, when discounted, improves the prediction remarkably. The scaled mean saturated hydraulic conductivity K* for all horizons of the Alfisol was approximately l.0x 10−5ms−1.
A comparison between acetone and dioxane and explanation of their role in water replacement in undisturbed soil samples
Authors: CHARTRES C. J. , RINGROSE‐VOASE A. J. , RAUPACH M. 
Published: July 2006

SUMMARYUndisturbed, moist samples from the A horizon of a swelling grey clay were treated with acetone or dioxane with or without para‐dichlorobenzene to replace soil water. They were then either impregnated with polyester resin whilst still solvent‐wet or after drying. Structural changes in samples treated with dioxane and then impregnated while solvent‐wet indicated little evidence of either disintegration or shrinkage resulting from the treatment. However, samples treated with acetone were prone to disintegration, but this was mitigated somewhat by the addition of para‐dichlorobenzene. Allowing either solvent to evaporate before impregnation caused shrinkage.X‐ray diffraction and infra‐red studies of treated clay separates indicated that dioxane prevented the marked swelling and potential dispersion found with acetone. It was concluded that dioxane breaks structural bonds within clay interlayers and between soil crumbs, thus limiting both collapse of clay minerals and sample shrinkage on drying. No changes to plasmic fabrics could be seen under a petrological microscope. Because of their appropriate size and shape, dioxane molecules could also enter clay interlayers so preventing marked shrink/swell movements. There is some indication that they may also form epoxide‐like compounds that themselves form structural ‘cements’.
Directional strength in aggregates as affected by aggregate volume and by a wet/dry cycle
Authors: HADAS A. 
Published: July 2006

SUMMARYReduction of aggregate size in the upper, tilled soil layer as a result of one wet/dry cycle was observed for sandy soil and clay soils. Bulk density of aggregates tended to increase as their size diminished for the clay after the wet/dry cycle, whereas similar changes in bulk density for the loam were observed only for aggregates smaller than 5.6 cm. Slaking and water‐drop impact seem to be the major factors in reducing the aggregate size of the sandy loam, while swelling and shrinkage affect clay aggregates of all size groups, but only aggregates smaller than 4.0 mm for the sandy loam.Tensile strength of the sandy loam aggregates was related to the axis along which the stresses were applied. A definite directional dependence of tensile strength was observed, e.g. the shorter the axis, the larger the tensile strength. The directional strength dependence was apparently not affected by one wet/dry cycle.
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

SUMMARYThe 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

SUMMARYThe 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

SUMMARYDelay 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

SUMMARYThe 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

SUMMARYData 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

SUMMARYA 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

SUMMARYLaboratory 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

SUMMARYDecomposing 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

SUMMARYSoil 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

SUMMARYAmmonia 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.