bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural change induced by wetting and drying in seedbeds of a hardsetting soil with contrasting aggregate size distribution
Authors: BRESSON L.M. , MORAN C.J.
Published: August 2005

Hardsetting has been related to two main processes: (i) development of strength when the soil is still moist (–100 kPa) due to matric suction acting within interparticle and interaggregate bridges and (ii) temporary cementation of dry soil by poorly ordered silica and aluminosilicates. In both cases, hardsetting of a seedbed should depend on geometric aspects of macro‐ and micro‐structure. This study deals with aggregate breakdown and/or deformation on wetting and with the structural changes which follow on drying. Repacked seedbeds of a hardsetting red‐brown earth were wetted by capillary rise. Seedbeds with a coarse and a fine aggregate size distribution were examined. Before and after wetting, the bulk density of the seedbeds was measured at 5‐mm increments using a gamma probe. Replicate samples were air dried, gamma scanned and impregnated. Binary images of pore space (> 107 μm) of vertical faces were used to generate depth functions of structure attributes, including macroporosity. Bulk density measurements combined with image analysis resulted in successful structure characterization. Thin‐section observations were used to interpret the quantified changes in terms of physical processes. In both coarse and fine seedbeds the physical processes which determined structural change occurred upon wetting rather than on drying. Coalescence of aggregates under plastic conditions, partly due to overburden pressure and enhanced by microcracking and partial slaking, occurred at the bottom of the coarse seedbed. In the fine seedbed, the fine material agglomerated due to matric suction. These different processes led to rather similar, microporous microstructures which exhibited similar strength properties after drying.
Modelling surface roughness by a Boolean approach
Authors: BERTUZZI P. , GARCIA‐SANCHEZ L. , CHADOEUF J. , GUERIF J. , GOULARD M. , MONESTIEZ P.
Published: August 2005

A model for simulating surface roughness of an agricultural bare soil is described. The model used a random Boolean function. The primary function was a sphere with radius r lying on a plane. The intensity function, a(r), of the distribution of the sphere radius was described by a(r) =αrβexp(λr)

Microtopography data were collected during two sets of field experiments. The distribution of experimental heights was used for fitting the three parameters, (α, β, λ) of the intensity function a(r) with a pseudo‐likelihood method. Comparisons between experimental and simulated soil surfaces indicated that the simulated roughness was not unrealistic. However, they also showed that the model is currently limited by the primary function and the intensity function that were chosen.
Solubilization of phosphate by rice plants growing in reduced soil: prediction of the amount solubilized and the resultant increase in uptake
Authors: KIRK G.J.D. , SALEQUE M.A.
Published: August 2005

Previous work has shown that rice plants growing in reduced soil are able to solubilize P by inducing an acidification in the rhizosphere through H+produced in Fe2+oxidation by root–released O2, and by the direct release of H+from the roots to balance excess intake of cations over anions. In this paper, equations for the diffusion and interaction of P and acid in soil are developed to predict the resultant increase in P uptake by the roots. Good agreement was obtained between the profiles of P and pH in the rhizosphere measured in the previous experiments, and those predicted using the equations with independently measured parameter values. The equations showed that solubilization accounted for over 80% of the P taken up. Measurements of the solubilization parameters in a range of reduced rice soils showed that H+addition increased the quantity of P that could be desorbed per unit weight of soil and the concentration of P in solution, in all the soils tested. The quantity of P solubilized per unit H+added at a given solution P concentration varied about 50–fold between soils, with a median of 11.9 mmol P per mol H+. The native soil solution P concentration varied 50–fold (median = 0.91 UM) and the soil pP buffer power (the quantity of P desorbed per unit decrease in –log of the P concentration in solution) varied 100–fold (median = 0.36 mmol kg−1pP−1); the soil pH buffer power varied 7–fold (median = 0.075 mmol kg−1pH−1). Calculations indicated that, in most of the soils tested, rice plants would depend upon solubilization for the bulk of their P.
The effects of long‐term superphosphate application on soil organic matter content and composition from an intensively managed New Zealand pasture
Authors: MURATA T. , NGUYEN M.L. , GOH K.M.
Published: August 2005

Changes in quantity and composition of soil organic matter (SOM) in pasture receiving annual superphosphate (SP) applications for 41 years at 0 (control), 188 and 376 kg SP ha−1a−1were investigated in soil samples collected from 0–75 and 75–150 mm depths by determining total carbon (TC), total nitrogen (TN), biomass C (BC), biomass N (BN) and subjecting the soils to sequential extraction using cold water, hot water, a mixture of hydrochloric (0.1 M HC1) and hydrofluoric (0.3 M HF) acids (HCl/HF), and sodium pyrophosphate (Na4P2O7) followed by sodium hydroxide (NaOH) for extracting labile and stable SOM fractions. There were significant differences in some SOM fractions between control (0) and SP treatments (188 and 376), especially in the topsoil (0–75 mm) but these were not observed between the two SP treatments. Soil TN (0–75 mm), BN and BN: TN ratio (0–75 and 75–150 mm depths) and the proportion of hot–water–extractable C (HC) in soil TC (HC:TC) (0–75 mm) were significantly greater in the SP treatments than in the control. HC1/HF extractable C and the proportions of soil TC as HC1/HF extractable C (HC1/HF extractable C: TC) were smaller in the topsoil of SP treatments than in the control. Similar results were observed in humin N: TN ratio and the proportions of soil TC as cold–water–extractable carbohydrate (CWcC: TC) and of soil HC as hot–water–extractable carbohydrate (HWcC : HC). Increases in the proportion of labile fraction in SOM were reflected in values of BN, BC: BN, BN: TN, HWcC : HC and HC: TC whereas decreases in the proportion of stable fraction in SOM were found in humin N: TN and HCl/HF–extractable C: TC ratios. Increases in labile SOM (BN and N–containing compounds such as amino acids and amino sugars, which were extractable by hot water but were not present as carbohydrate) and decreases in stable SOM (HC1/ HF–extractable C and humin fraction) in soils under pastures treated with annual SP applications compared with the control were attributed to pasture improvement and the amelioration of P and S deficiency, resulting in a greater return of plant residues and animal excreta and also an increase in clover growth and associated biological N2fixation. The additional labile SOM in SP treatments compared with that of the control was not associated with the soil mineral Al and Fe components.
The effect of strong hydroxide solutions on the stability of aggregates and hydraulic conductivity of soil
Authors: LIEFFERING R.E. , McLAY C.D.A.
Published: August 2005

The effect of two hydroxides (NaOH and KOH) and two chlorides (NaCl and KCl) on aggregate stability and saturated hydraulic conductivity (Ks) was studied in three New Zealand soils using concentrations (0.003, 0.03, and 0.3m) typical of the range ofpH found in strongly alkaline industrial liquid wastes. The different solutions were used as pretreatments prior to aggregate stability measurements and as influent solutions forKsmeasurements.

The concentration of hydroxide appeared to be the most important factor affecting aggregate stability andKSin all soils. Aggregate stability andKsdecreased with increasing hydroxide concentration, but were generally unaffected by chloride solutions. RelativeKsdecreased to <2.5% of initialkSwith all hydroxide concentrations, but the time until a decrease ocurred depended on concentration. In contrast, relativekSremained > 100% with chloride solutions, but decreased substantially when distilled water replaced the chloride solutions. Differences in aggregate stability andKsdue to the cation present (either Na+or K+) appeared to be very small. A surface crust formed in the upper 1 cm of the soils leached with hydroxide solutions. This surface crust had substantially less organic carbon than the upper 1 cm of soil from the cores leached with chloride.

A two‐stage process explains the decrease inkswhen strongly alkaline solutions are applied to soil. First, organic matter dissolution decreases aggregate stability, with the rate of organic matter dissolution depending on hydroxide concentration; and second, increased repulsion of soil particles (due to increasedpH) causes movement of dislodged particles into pore spaces, resulting in decreasedKs.
Factors affecting the sorption and fixation of caesium in acid organic soil
Authors: HIRD A.B. , RIMMER D.L. , LIVENS F.R.
Published: August 2005

Radioactive caesium deposited on upland Britain following the Chernobyl accident in 1986 remains available for uptake by plants, despite the potential of the contaminated soils to fix Cs. The minimum concentration of Cs+ required to cause Cs+ fixation is 0.60 to 0.75 mm, and this is unlikely to be reached in any contaminated upland soil. It is suggested that the fixation is caused by interlayer collapse of the illitic clay. The observed Cs+ fixation in lowland mineral soils and its absence from acidic upland soils is explained by the action of K+ ions, which can also induce interlayer collapse.

Although Cs+ ions are unlikely to be fixed in acid organic soils, they can be strongly sorbed on any unoccupied Cs‐specific sorption sites in the narrow parts of illitic wedge zones. A method for determining the number of such sites is described. For two of the soils studied the number of sites ranged between 8 × 10−8 and 1 × 10−5 mmol kg−1; for two others there appeared to be no unoccupied Cs‐specific sites. Although Cs+ ions sorbed on such sites do not exchange with other ions, they can be desorbed if the concentration of Cs+ in solution is decreased. Thus, radioactive Cs in such soils will remain available for plant uptake, unless interlayer collapse can be induced.
Forms and rates of release of 137Cs in two peat soils
Authors: LIVENS F.R. , HOWE M.T. , HEMINGWAY J.D. , GOULDING K.W.T. , HOWARD B.J.
Published: August 2005

Cation exchange resin saturated with H+ and Ca2+ was used to extract 137Cs from peat soil at two sites in Britain affected by l37Cs deposition following the Chernobyl accident. The technique identified three classes of 137Cs, similar to those observed for K+ in soils: ‘Fast’, ‘Intermediate’ and ‘Slow’. These classes are probably related to the selectivity for 137Cs of the cation exchange sites on the organic matter and the clay minerals, and to the structure of the soil. With one exception, most 137Cs was in the ‘Slow’ form and was only very slowly released to the resins, if at all. However, there was enough l37Cs in the ‘Fast’ and ‘Intermediate’ forms to contaminate pasture and thus grazing animals for some years. Based on the resin technique, it is estimated that contamination will persist for several decades in uplands contaminated at these activity concentrations.
Signatures of lipid assemblages in soils under continental Mediterranean forests
Authors: ALMENDROS G. , SANZ J. , VELASCO F.
Published: August 2005

The analysis of free lipids in 12 soils from three representative types of Mediterranean forest has been carried out in an attempt to describe diagnostic molecules reflecting differences between the ecosystems and the intensity of the soil organic matter turnover. The study centred on the analysis by gas chromatography–mass spectrometry of the soil compounds extracted with petroleum ether from soils in central Spain, developed under monospecific formations of stone pine (Pinus pined), evergreen oak (Quercus rotundifolia) and Spanish juniper (Juniperus thurifera), the lipid extracts from their leaves also being analysed as reference material.

The comparison between the distribution patterns of alkanes and fatty acids in plant lipids and the corresponding soil lipids was used to assess the extent to which the former accumulate in soil or are substituted by other biogenic or diagenetic homologues. In general, the alkane patterns showed the greatest variation in soils under oak, and the differences between lipid patterns in plant and soil were greatest in the juniper forests. As indicators of the vegetation type, the soil fatty acids had little value.

Up to 60 major cyclic compounds were identified, including mainly di‐ and sesquiterpenes, in addition to some monoterpenes and nonterpenic naphthalenes and decalins. Of these major constituents, 33 compounds were found in soil but were not present in plant extracts, and 18 compounds were identified in plants but were not in the soils. The results suggest an arrangement of the soil samples based on the composition of the signature lipid assemblages.
Hyperfine splitting in the electron spin resonance solution spectra of humic substances
Authors: CHESHIRE M.V. , McPHAIL D.B.
Published: August 2005

Humic substances contain significant quantities of free radicals which have important functions in many biological processes in soil involving electron transfer. Such radicals may be detected by electron spin resonance spectroscopy in both solid and solution state and are usually reported as giving a single unstructured peak. Humic acids from a range of soil types varying in parent material and pH have been examined by electron spin resonance spectroscopy of their solutions in 0.1 m KOH. Spectra with an effective g‐value typical of an organic free radical were obtained. Observation of hyperfine structure was highly dependent on the instrument settings used. It was present at a modulation amplitude of 0.0142 mT, but not at 0.101 mT. Similarly, there was a reduction in resolution as microwave power was increased from 0.505–20 mW. This may explain the inability of some investigators to observe structure in soil humic acids. Resolution of hyperfine features was greatly enhanced by recording spectra in the second derivative mode. Using appropriate instrument settings all the humic acids showed hyperfine structure, although the intensity of these components varied by a factor of 100, being much greater in humic acid from highly acidic soils.
The 14C age and residence time of organic matter and its lipid constituents in a stagnohumic gley soil
Authors: BOL R. , HUANG Y. , MERIDITH J.A. , EGLINTON G. , HARKNESS D.D. , INESON P.
Published: August 2005

A combination of radiocarbon (14C) dating and biomarker analyses of the aliphatic hydrocarbons in soil lipids is proposed as a novel and improved method for studying the environmental history of peaty soils. The radiocarbon concentration of unfractionated bulk organic matter, hydrolysed soil residues and two lipid fractions (the aliphatic hydrocarbons and carboxylic acids) recovered from a stagnohumic gley soil, were compared using AMS (accelerator mass spectrometry) and radiometric 14C dating techniques. The radiocarbon ages recorded by the aliphatic hydrocarbon fractions were consistently older than those measured from the unfractionated soil, and were in most cases older than the residues remaining after acid hydrolysis. This pattern was observed at three different depths in the soil profile. The apparent age difference between the hydrocarbon fraction and its unfractionated substrate increased with depth. An abundance of long–chain n–alkanes, similar to those found in higher plant waxes, characterized the aliphatic hydrocarbon fraction from the deepest soil (at 21.5–24.5–cm depth). The radiocarbon age of this basal organic component (13470± 170 years bp) indicated that it derived from the initial re–establishment of vegetation on the local deglaciated landscape with the onset of the Windermere Interstadial (c. 14000–13000 14C years bp). Bulk organic detritus within the basal horizon dated at some 3000 years younger, and presumably as a result of the downward penetration and retention of some mobile organic residues produced later in the development of the soil profile. The survival and apparent stratigraphical stability of these recoverable aliphatic hydrocarbons provides the opportunity, via the development of AMS dating, to measure an unambiguous radiocarbon age for the origin of organic residues retained in soils and sediments.
Turnover of clay‐associated organic nitrogen in the different aggregate‐size classes of a cultivated silty loam
Authors: BALABANE M.
Published: August 2005

Soil aggregates are known to protect organic matter against microbial attack, and thereby stabilize it. The scale at which aggregation is effective and the degree of control it exerts on organic matter transformations are not well known. I investigated whether rapid and slow pools of organic nitrogen bound to the <2‐μm clay fraction could be related to different locations of the clay fraction in the soil structure. Dry aggregates were separated from soil to which 15N had been added for 4 years in a field experiment. Soil samples were at maximal immobilization of a labelled inorganic N dressing, and after 1 and 3 years of the beginning of the remineralization phase. Clay‐sized particle fractions (< 2 μm) were.separated from the different aggregate‐size classes, and their total C and N contents, and 15N isotopic excess, were determined. It seems that recently immobilized N associated with the clay fraction was rapidly sequestered in microaggregates (< 0.1 mm). The results also suggest a relation between the fast decay of part of the clay‐associated N and its location on the macroaggregate scale (>0.1 mm) of soil structure.
Changes in chemical properties of organic matter with intensified rice cropping in tropical lowland soil
Authors: OLK D.C. , CASSMAN K.G. , RANDALL E.W. , KINCHESH P. , SANGER L.J. , ANDERSON J.M.
Published: August 2005

Rice systems in Asia have intensified rapidly in the past 30 years, and significant areas of irrigated lowland rice are now supporting two or three rice crops per year. Our objective was to compare the chemical composition of soil organic matter (SOM) from four fields with different histories of rice cropping intensity and soil submergence: (i) a single‐crop rainfed, dryland rice system without soil submergence, (ii) an irrigated rice and soybean rotation, and irrigated (iii) double‐ or (iv) triple‐crop rice systems in which soil remains submerged during much of the year. In all four soils, extracted mobile humic acid (MHA) and calcium humate (CaHA) fractions were of modern age by 14C‐dating, and represented about 20% of total N and organic C. The MHA was enriched in N and hydrolysable amino acids (AA) compared with CaHA in all soils. With increased frequency of irrigated rice cropping, however, there was a large increase in phenolic content of SOM. We speculate that slower lignin decomposition caused by deficiency of O2 in submerged soil leads to incorporation of phenolic moieties into young SOM fractions. The increased phenolic character of these fractions may influence N cycling and the N supplying capacity of lowland soils supporting two or three annual crops of irrigated rice.
Field evaluation of models of denitrification linked to nitrate leaching for aggregated soil
Authors: VINTEN A.J.A. , CASTLE K. , ARAH J.R.M.
Published: August 2005

Dynamic simulation models of the nitrogen cycle are an important aid for predicting the effect of land management on nitrate concentration in ground and surface waters. These models often neglect, or treat in a highly empirical way, the process of denitrification. The solute leaching model SLIM, suitable for use in aggregated soil, was linked to two alternative denitrification submodels ('simple structure'and ‘aggregate assembly’ treatments). The linked models can be used in dynamic simulation of the fate of nitrate in soil. The models were calibrated using water release and soil respiration data from two field sites (a clay loam and a sandy loam). The fate of Br−1and 99 atom percentage15NO−3tracers on drained plots was measured at these sites. Both models predicted less denitrification from plots receiving small inputs of fresh organic residue than was actually lost; both did better where residue inputs were large. The ‘aggregate assembly’ model predicted short‐term losses immediately after incorporation of residues more successfully than did the ‘simple structured’ model. The simulated dynamics of denitrification during the autumn and winter in the two models were also very different. Overall N balances were better predicted in the clay loam than the sandy loam. Possible reasons for discrepancies between model output and real data include immobilization (especially when large inputs of residues were incorporated), denitrification in the subsoil, and an inadequate description of the way in which degradation of organic matter depends on temperature.
Improving the calibration of dielectric TDR soil moisture determination taking into account the solid soil
Authors: MALICKI M.A. , PLAGGE R. , ROTH C.H.
Published: August 2005

The influence of soiľs solid phase on the dielectric constant of the soil over a range of moisture contents has been studied. Samples of soil, soil‐like, and also other porous materials were analysed using Time Domain Reflectometry (TDR) to determine the contribution of bulk density and porosity to the function that relates dielectric constant to water content.

The study showed that bulk density, and thus also porosity, substantially affects the relation between dielectric constant and water content. Two equivalent, empirical, normalized conversion functions were found, one accounting for bulk density and the other for porosity. Each of them reduced the root mean square error of the dielectric TDR determinations of moisture to 0.03, regardless of the materialľs bulk density and porosity.
A simple model of soil organic matter complexation to predict the solubility of aluminium in acid forest soils
Authors: WESSELINK L.G. , VAN BREEMEN N. , MULDER J. , JANSSEN P.H.
Published: August 2005

A simple equilibrium model for competitive binding of Al and protons to soil organic matter shows that Al activities in soil solutions of acid mineral soils are controlled by complexation reactions with soil organic matter. The model successfully explains the relation between pH and the activity of dissolved Al in several forest soils. Furthermore, we found evidence that pools of organically bound Al may be depleted fairly quickly. Kinetically controlled dissolution of inorganic soil Al compounds, which may be considerable, is the main cause for the re‐supply of the organically bound Al in the soil. The previously reported decrease in Al solubility that accompanies measured decline in organically bound Al in three Dutch soils was found quantitatively consistent with the model for organically bound Al proposed here.
Comparison of chemical composition of soil solutions collected by zero‐tension plate lysimeters with those from ceramic‐cup lysimeters in a forest soil
Authors: MARQUES R. , RANGER J. , GELHAYE D. , POLLIER B. , PONETTE Q. , GŒDERT O.
Published: August 2005

We analysed the chemistry of solutions collected from soil by zero‐tension plate lysimeters and cup lysimeters connected to a constant suction (600 hPa) under Douglas fir in the Beaujolais mountains (France). The chemistry of zero‐tension lysimeters' (ZTL) and tension lysimeters' (TL) solutions differed enormously: TL solutions were most concentrated in Si, NH4‐N, NO3‐‐N, Cl−, Mg2+ and A13+ and TOC, whereas Ca2+ and K+ concentrations were greater in ZTL solutions. Organic matter (OM) greatly influenced the solution chemistry in both ZTL and TL. The chemistry of ZTL solutions was affected mainly by OM mineralization in the forest floor and upper soil horizon, and that of TL solution seemed to be related to destabilization of humified compounds under the new vegetation. Nitrification was important: residual nitrification led to excess protons neutralized in weathering or ion exchange reactions, mobilized cations, mainly A13+. Selectivity coefficients calculated both for ZTL and TL solutions formalized the differences between the two types of solutions. Nevertheless, these coefficients remained most often within the same order of magnitude indicating relations between them. Solutions from the two devices provided different information and should not be used for the same objectives. Solutions from ZTL are suited for ecosystem input‐output budgets, whereas TL solutions are more useful when equilibrium between the solution and solid phase or when plant nutrition are considered.
Three‐dimensional analysis of a loamy‐clay soil using pore and solid chord distributions
Authors: COUSIN I. , LEVITZ P. , BRUAND A.
Published: August 2005

Examples of pore and solid chord distributions obtained for ideal porous media are presented, and the distributions of the porous and solid phases of a soil have been studied by pore and solid chord distributions. Serial sections, 100 μm apart, were cut in a soil core, impregnated with resin, and images were obtained of them. The 2D images from 160 sections were used to build a 3D reconstruction of the core. The initial 2D images, the 3D reconstructed medium and 2D computed images from the latter were studied. We found that the solid matrix of the particular soil is homogeneous and isotropic at the scale studied, and it could be characterized with a single 2D image. For pores ranging from 500 μm to 2 mm we also found similar pore chord distributions for the 2D images in the three orthogonal directions and the 3D medium. A single 2D image can be used to study these pores. For larger pores more than one 2D image is required, and we showed that eight 2D images are sufficient to describe these pores.
Physical and chemical variations within prisms of a saline polder clay in relation to seasonal changes
Authors: HALLAIRE V. , AZIB M. , CURMP P. , CHEVERRY C.
Published: August 2005

The prismatic structure and soil behaviour were studied on a saline clayey soil in the polder of the Marais de ľQuest (France). Three profiles with different histories were examined, and the structure under wet and dry conditions, ionic concentrations, and changes in void ratio and water suction were measured on prisms sampled between 5 and 40 cm deep, in four places (base, centre, top and side). Seasonal dynamics were accompanied by reorganization within the prismatic structure, changing both the size and distinctiveness of the blocky substructure. Chemical and physical characteristics were closely related to the sharpness of these two imbricated structures. In the absence of blocky substructure the salinity increased horizontally from the centres of the prisms to their sides (the latter acting as exchange surface between the soil and the atmosphere), and no physical gradient was apparent. These results emphasized the permanence of lateral hydraulic continuity in individual prisms. On the other hand, where the blocky substructure was well developed there was no lateral variation of salinity within the prisms, whereas the swelling potential varied from the centres to the sides: the sharpness of the substructure therefore caused a decrease in lateral water transfer. The internal structure of the prisms appeared to determine the seasonal behaviour of the soil.
The significance of organic separates to carbon dynamics and its modelling in some cultivated soils
Authors: BALESDENT J.
Published: August 2005

Soil organic matter (SOM) dynamics are usually described by compartmental models. We have sought SOM separates that might be related to SOM dynamic compartments. The turnover of C in various separates from long–term field experiments with maize was measured using the natural 13C labelling technique. The Rothamsted carbon model gave a good prediction of the observed C turnover. Primary particle–size fractions coarser than 50 μm had short lives, and could be associated with the plant structural compartment of models. Water–extractable components are enriched in young C but cannot be associated with labile compartments. None of the chemical separates obtained by acid hydrolysis, wet oxidation, thermic oxidation, pyrolysis or alkaline extraction, were enriched either in young or old C. The results showed neither a sequential relation between fulvic acids and humic acids nor a resistance of nonhydrolysable material. The range of lifetimes of soil C seems to be determined more by physical position and protection than by the chemical nature of SOM.
Land‐use and fertilization effects on P forms in two European soils: resin extraction and 31P‐NMR analysis
Authors: GUGGENBERGER G. , CHRISTENSEN B.T. , RUBÆK G. , ZECH W.
Published: August 2005

Macroporous anion‐exchange resin extraction and 31P‐NMR spectroscopy of dialysed NaOH extracts were used to investigate the effects of land use (Taubenberg, Bavaria: spruce forest, deciduous forest, permanent grass, arable) and fertilization (Askov, Denmark: unmanured, mineral fertilizer, animal manure) on forms of phosphorus in soil with emphasis on the potentially labile organic (Po) and inorganic (Pi pools. Carbon content ranged from 12.5–118.1 g kg−1 and total P (Pi) content from 511 to 2063 mg kg−1. For all soils, the C:Po ratios of SOM decreased in the order: whole soil, 150: 1–44:1; alkali extract, 57:1–41: 1; resin extract, 20:1–9:1; suggesting an increasing P functionality of the OM with increasing Po lability. Analysis of functional relation showed a close relation between resin Po and 31P‐NMR estimates for diester‐P including teichoic acid‐P, indicating that these species contributed significantly to the labile Po pool as determined by the resin method. The most marked effects of land‐use were an increase in Pi under grass and arable, a concurrent sequestration of Po and SOM under grass, and a depletion of Po under arable. The amount of resin Pj appeared to be a function primarily of fertilization, and amounted to around 100 mg kg−1 in the fertilized soils irrespective of the SOM content and P source. The forest soil and the unfertilized agricultural soil had much smaller resin Pj values. The soil under grass had the largest amounts in resin Po and diester‐P including teichoic acid‐P, indicating a rapid turnover of Po with build‐up of a large potentially labile, microbially derived Po pool. 31P NMR also showed large proportions of labile Po species in soils where microbial activity is restrained by acidity (Taubenberg spruce forest, phosphonates) or where highly microbially altered OM is relatively enriched (Taubenberg arable, diester‐P including teichoic acid‐P).

We conclude that the resin used in this study isolates a structurally and functionally reasonably uniform pool of potentially labile soil Po.
Infant mortality and soil type: a case study in south‐central England (with discussion)
Authors: MUNRO L.J.A. , PENNING‐ROWSELL E.C. , BARNES H.R. , FORDHAM M.H. , JARRETT D.
Published: August 2005

We have analysed the differences in infant mortality for 1981 to 1990 in areas of contrasting soil types in south‐central England. The soils overlie rocks of varied lithology and hydrology, ranging from porous and permeable Chalk and limestones, to the generally wet and impermeable Oxford and Lower Jurassic Clays. The study area comprises 504 administrative wards, for each of which the soil has been classified as being predominantly‘Wet’, ‘ Intermediate’ or ‘Dry’, depending on the degree of seasonal or periodic waterlogging. The soil classes used are those mapped by the Soil Survey of England and Wales and relate closely to the underlying geology. We find proportionately more infant deaths on the‘Wet’ soils, and a gradation towards lower infant mortality rates on the drier soils. Overall, infant mortality on the‘Wet’ soils is 31·9 percent greater than on the‘Dry’ soils, for reasons that remain unexplained. This relation between infant mortality and soil moisture remains after the effect of social class has been removed.
Predicting soil properties over a region using sample information from a mapped reference area
Authors: VOLTZ M. , LAGACHERIE P. , LOUCHART X.
Published: August 2005

A method for mapping soil properties at a regional scale with acceptable precision and cost was investigated. It combines soil classification and interpolation, and uses sample information from a reference area and simple soil observations over the region. The method consists of two stages. First is the prediction of soil properties at a set of sites covering the region by classifying each site according to the soil classification of the reference area, and then by assigning to each site the values of soil properties measured at the representative profile of its soil class. The second is by interpolating the predictions of the properties from the classes at the observation sites. Three methods were considered: kriging, inverse squared distance and nearest neighbour. The performance of classification combined with interpolation was evaluated for mapping water content at wilting point in an area of 1736 ha in a physiographic region of Southern France. The method was compared with conventional methods, namely kriging with actual data and prediction from a soil map at a scale of 1:100000. Estimates from classification combined with kriging were more precise than those from the 1:1OOOOO soil map in all instances, and close to those of ordinary kriging with actual data when prediction points were near the observation points. Classification combined with inverse squared distance or with nearest neighbour interpolation was always less precise than classification with kriging. However, it was more precise than classification at the 1:100 000 scale except when prediction points were far from the observation points.
Critical state soil mechanics analysis of the constant cell volume triaxial test
Authors: KIRBY J.M. , O'SULLIVAN M.F.
Published: August 2005

We have developed a critical state, stress‐strain analysis that predicts the entire sequence of states from start to the end of a constant cell volume triaxial test in p‐q‐v‐ɛz, space, where p is the spherical stress, q is the deviator stress, v is the specific volume and ɛz is the axial strain. The analysis requires five soil properties to be specified, these being the critical state properties (M, λ and κ) and two elastic properties (any two of E, η, G and K—all four can be found from any two).

In order to test the analysis, properties taken mostly from one series of constant cell volume triaxial tests are used to simulate the behaviour in a second test series. In both series the two soils (a sand loam and a clay loam) were tested at several different water contents. The first (property estimation) series of tests was performed using large samples, whereas the second (verification) series involved small samples. The behaviour is quite different in the two series. The elastic property E was not determined in the first series of tests but was estimated from the second series. Furthermore, for three very wet samples, λ had to be estimated by fitting the analysis to the data. The verification was not therefore fully independent of the input test data, particularly for the three wet samples. The stress strain analysis simulated the behaviour of both series of tests in all four dimensions of the p‐q‐v‐ɛz space. The match in p‐q‐v space was good for all samples. On a q‐ɛz plane, the value of q was under‐estimated for several samples, but for most of the samples the match was good on this plane. The analysis was generally as good as, and sometimes better than, a previous analysis that deals only with the end point of the test in p‐q‐v space. The previous analysis did not take account of the elastic properties. The stress‐strain analysis therefore seems to offer a useful framework for parameter estimation from constant cell volume triaxial tests. This extends the usefulness of the test itself, as the elastic properties may now be accounted for. The success of the analysis also strengthens the record of success of the critical state concept for unsaturated soils.
Effects of crystallinity of goethite: II. Rates of sorption and desorption of phosphate
Authors: STRAUSS R. , BRÜMMER G.W. , BARROW N.J.
Published: August 2005

Eight samples of goethite ranging in surface area from 18 to 132 m2 g‐1 were mixed with phosphate at a range of pH values for periods which ranged from 0·5 h to 6 weeks. The sample with a surface area of 18 m2 g‐1 had been hydrothermally treated to improve its crystallinity. Its rate of reaction with phosphate depended on pH but was complete within a day. Its maximum observed reaction was close to the theoretical maximum for surface adsorption of 2·5 μmol m−2. For the other samples, phosphate continued to react for up to 3 weeks and exceeded the value of 2·5 μmole m−2. The duration and extent of the reaction depended on the crystallinity of the goethite. The results were closely described by a model in which the phosphate ions were initially adsorbed on to charged external surfaces. The phosphate ions then diffused into the particles. This was closely described using equations for diffusion into a cylinder.

Samples of goethite which had been loaded with phosphate dissolved more slowly in HCl, and had a longer lag phase, than phosphate‐free goethite. For the hydrothermally treated goethite, HCl removed much of the phosphate when only a small proportion of the iron had been dissolved. For a poorly crystallized goethite, it was necessary to dissolve much more of the iron to obtain a similar removal of phosphate. Brief treatment with NaOH removed most of the phosphate from the hydrothermally treated goethite but only half the phosphate from a poorly crystallized goethite. These results are consistent with the idea that phosphate ions were not only bound on external surface sites but had also penetrated into meso‐ and micro‐pores between the domains of the goethite crystals and were then adsorbed on internal surface sites. This penetration tied the domains together more firmly thus increasing the lag phase for dissolution. Differences between sites for phosphate adsorption are therefore caused mainly by their location on either external or internal sites. Models that ignore this are incomplete.
Computer modelling of partial specific volumes of humic substances
Authors: BIRKETT J.W. , JONES M.N. , BRYAN N.D. , LIVENS F.R.
Published: August 2005

The determination of the structure of humic substances from peat soils and natural waters is a major problem in soil science. Humic substances are chemically heterogeneous and consist of molecules covering a wide distribution of molecular size. A quantity related to both molecular size and structure in the hydrated state is the volume of the humic molecules per unit mass or partial specific volume (ν2). The partial specific volumes of humic substances have been estimated from atom and chemical group volume contributions for 17 proposed structures of fulvic and humic acids taken from the literature. The results show that the partial specific volume reflects the composition of humic substances, decreasing with increase in the carbon: hydrogen (C:H) molar ratio. The more oxidized the humic material the smaller is its partial specific volume. These trends agree with our experimental measurements of partial specific volumes for a range of humic materials (aquatic fulvics, aquatic and peat humics). The predicted values of partial specific volumes for the proposed structures, however, are overestimated by approximately 15% compared to the experimental values. There is little difference between values of ν2 calculated from the detailed humic structures and those calculated from their empirical formulae; calculations of partial specific volumes using a random modelling approach leads to overestimation by approximately 37%. It seems that the estimates based on additivity of atom and chemical group volumes do not take into account an overall contraction of the structures because of hydrophobic interactions. In general terms the values of the partial specific volumes of humic substances suggest they are more compact molecules than globular proteins, and intrinsic viscometry studies suggest that aqueous salt solutions approach θ‐solvent conditions for humic substances.
Some microscopic mineral particles of biological origin in soil solutions
Authors: KELLER C.
Published: August 2005

Soil solutions leaching from lysimeters and soil suspensions were observed under Transmission Electron Microscopy to reveal small particles (400 nm to few micrometers) of apparently biological origin. Some of the particles are displayed: most of them are scales of protists such as Paraphysomonas(algae), Gyromitus, Acanthocystis and Thaumatomastix (flagellates) which have not been observed previously in soil or soil solutions.
Carbonate redistribution and hydrogeochemical processes in two calcareous soils with groundwater in a Mediterranean environment
Authors: BOUZIGUES R. , RIBOLZI O. , FAVROT J.C. , VALLES V.
Published: August 2005

The morphology of the soil is closely associated with water regime and redistribution of solutes. We studied in detail two calcareous soils with groundwater representative of the two main hydro‐geological regimes, one on the plateau and the other in the central depression, of an experimental catchment near Roujan in the South of France. We recorded macro‐and micromorphological features, and measured the level of the water table and the saturating solution. The morphological features were primarily those associated with carbonate redistribution. The forms associated with iron and manganese added information. The two groundwater systems behaved differently over 3 years. The temporary perched groundwater of the plateau was characterized by a small partial pressure of CO2 (pCO2) and a large pO2, with rapid lowering of the water table (4–6 cm d−1). The permanent groundwater of the depression, in contrast, had a larger pCO2 and a small pO2. The water table fell more slowly (1–2 cm d−1). Higher up, rapid drying of the profile and release of CO2 leads to over‐saturation of the soil solution with respect to calcite, favouring the formation of poorly crystallized micrites, which are characteristic of the plateau system. In the lower part of the catchment, persistent waterlogging leads to more marked anaerobiosis (large estimated pCO2) favouring the development of large stable rhombohedral crystals characteristic of more stable hydrodynamic conditions. In both situations, iron and more particularly manganese redistribution agrees with the waterlogged state of these soils.
Release and fixation of potassium by a loamy soil as affected by initial water content and potassium status of soil samples
Authors: SCHNEIDER A.
Published: August 2005

To understand the contribution of non exchangeable potassium to plant nutrition the release and fixation of K was studied on a range of soil samples of varying K status, obtained from a long‐term fertilizer trial. The soil samples were either air‐dried or not prior to use so as to determine the influence of pretreatment on release and fixation of K. Sorption and desorption of K were measured by following the changes in solution K and exchangeable K, and calculating the relative contributions of exchangeable and non exchangeable K to K dynamics in the soil‐solution systems. The change in the amount of non exchangeable K is proportional to the difference between the initially imposed concentration and the concentration for which neither sorption nor desorption occurred. Whether release or fixation occurs depends on the sign of this difference. Soils containing much K release more K than those containing little K at the same initial or final concentration in solution. The threshold exchangeable potassium and the threshold K concentration for which release becomes large increase when K content increases in the soil. For air‐dried soils K‐enriched soils fixed less K than those containing little K. But when kept moist the soils fixed no K. The threshold exchangeable potassium of release and the minimal exchangeable potassium, i.e. that part of exchangeable potassium extracted by ammonium acetate but which is not in exchange equilibrium with Ca, are useful criteria to assess the meaning of the exchangeable potassium when used as a fertility indicator.
The response of soil organic matter to manure amendments in a long‐term experiment at Ultuna, Sweden
Authors: GERZABEK M.H. , PICHLMAYER F. , KIRCHMANN H. , HABERHAUER G.
Published: August 2005

In a long‐term field experiment started in 1956 on a clay loam soil at Uppsala, Sweden, changes of organic carbon in the topsoils receiving various organic amendments at the rate of 200 kg C ha'1 year'1 were studied to determine soil organic matter characteristics, variations of δ13C in the soil and to estimate a carbon balance. Fallow and mineral fertilizer without N led to a significant decrease of soil organic matter (SOM) in the soil, green manure maintained the SOM content, and animal manure and peat increased the SOM content significantly. The stable portion of the added organic materials after 37 years of continuous input was 12·8, 27·3, and 56·7%, for green manure, animal manure and peat, respectively. This was reflected by half‐lives of organic carbon originating from the amendments between 3·0 (green manure) and 14·6 years (peat). The isotopic composition of SOM changed both due to mineralization (continuous fallow) and the addition of amendments is topically different from soil humus (green manure, animal manure). The isotopic effect was used to calculate the percentage of carbon derived from animal manure present for the year 1993. This value (55·4%) was larger than that derived from the carbon balance, which indicated a priming effect of the animal manure on the initial soil humus. Mineralization of microbially available organic substances led to an increase in the degree of humification on plots not receiving organic amendments. Adding peat and animal manure resulted in a decrease of the humification index due to the continuous input of poorly humified material. The extinction ratio (E4/E6) and ratio of fulvic acid to humic acid changed considerably in the peat treated plots. Fourier transform infrared (FTIR)‐measurements of the extracts showed that peat characteristics can be detected in peat treated soils. The other amendments did not alter the characteristics of the extractable humic substances.
Short‐term kinetics of residual wheat straw C and N under field conditions: characterization by 13C15N tracing and soil particle size fractionation
Authors: AITA C. , RECOUS S. , ANGERS D.A.
Published: August 2005

Summary A clear understanding of the short‐term decomposition and fate of crop residues is necessary to predict the availability of mineral N in soil. The fate of 13 C15N‐labelled wheat straw in a silty soil (Typic Hapludalf) was studied using particle size fractionation and in situ incubation in which the equivalent of 8 t dry matter per ha of straw was incorporated into the soil over 574 days. Soil samples were separated into five particle‐size fractions by wet sieving after disruption of aggregates. The weight, C and N contents, and 13C and 15N atom excess of each fraction were determined. Straw‐derived C disappeared rapidly from the > 2000‐μm fraction with an estimated half‐life of 53 ‘normalized’ days (equivalent of 10°C and −0−01 MPA water potential). Straw‐derived C appeared to be only temporarily stored in the intermediate fractions (1000–2000 and 200–1000 pm). The maximum net 13C accumulation in the 50–200‐μm fraction was 4·4% of added 13C. Straw‐derived C accumulated most rapidly and preferentially in the 50‐μm fraction, which stabilized after 265 days and accounted for 70% of the residual 13C on day 574. Although there was more residual 15N than 13C, the distributions and kinetics of the two isotopes in the fractions were similar.