bluuebunny/crossref_metadata_2025_split huggingface dataset:
Methanogenesis in saltmarsh soils of the North Sea coast of Germany
Authors: GIANI L. , DITTRICH K. , MARTSFELD‐HARTMANN A. , PETERS G. 
Published: August 2005

SummaryTemperate saltmarshes are a potential source of atmospheric methane. We have measured the concentration and emission of methane in typical saltmarsh soils (Salic Fluvisols) and humus‐rich saltmarsh soils (Thionic Fluvisols) from the German North Sea coast. We also measured the methane production rates of the latter. The methane content of typical saltmarsh soils reached 12.0 μmol 1−1, although values of 1–4 μmol 1−1 were usual. The sulphate concentrations of the pore‐water were about 10 mm, which means sulphate reduction is not limited and methanogenesis would be suppressed. Methane concentrations were generally largest in summer. Independent of the redox potential and the degree of soil development, methane concentrations were smallest in those soils poorest in humus. Methane emission rates were almost zero. In the humus‐rich saltmarsh soils, methane concentrations were roughly a thousand times larger than those in typical saltmarsh soils, reaching values of 23 mmol 1−1 The sulphate concentrations of the pore‐water were often less than 1 mM, indicating limited sulphate reduction. Methane production was up to 80 μg cm−3 day−1 and was not inhibited when we added sulphate. Methane emission rates reached up to 190 μg m−2 day−1 in summer, with values up to 20 μg m−2 day−1 at other times. The two kinds of saltmarsh soil behave quite differently: the typical saltmarsh soils act as a sink for methane; the humus‐rich saltmarsh soils are a source.
Effect of pH and some organic anions on the solubility of soil phosphate: implications for P bioavailability
Authors: STAUNTON S. , LEPRINCE F. 
Published: August 2005

SummaryThe effect of pH and the addition of carboxylates (acetate, oxalate, tartrate, salicylate and citrate) on the solubility of soil phosphate has been investigated to assess the possible effects of root exudates on phosphate availability. The soil was a neutral calcic Luvisol with a large pH buffer capacity. Various concentrations of strong acid (0–20 mmol kg−1) and anion (0–2 mmol kg−1) were applied to soil in suspension (0.5 g soil cm−3). The effect of 2 mmol kg−1 oxalate on the adsorption isotherm of phosphate was also studied. The rate of isotopic exchange was largely unchanged by any of the treatments. Neither pH nor acetate had an effect on phosphate solubility. The addition of di– and trivalent anions increased phosphate solubility somewhat. The effect increased with increasing concentration of anion, and was generally independent of pH and the proportion of anion adsorbed. Oxalate was more efficient in limiting the adsorption of freshly added phosphate than in desorbing native phosphate. The results illustrate that rhizosphere acidification does not necessarily increase phosphate solubility. However, carboxylates, the conjugate bases of organic acids, may play an important role in improving the availability of soil phosphate.
Zinc sorption–desorption by two Andepts: effect of pH and support medium
Authors: PARDO M.T. , GUADALIX M.E. 
Published: August 2005

SummaryLaboratory experiments were carried out to evaluate the effect of pH, ionic strength and electrolyte composition on zinc sorption–desorption by two Andepts from the Canary Islands (Spain). At the natural soil pH, the soils exhibited little net negative surface charge and small Zn sorption capacities. More than 75% of the sorbed Zn was apparently strongly bonded. The pH greatly influenced the sorption–desorption reactions. Sorption increased with increasing pH, and retention increased abruptly at pH > 6.0. Sorption also occurred at pH values below the point of zero charge (PZC) of the soils, when most of the surface sites are positively charged. Desorption decreased continuously with rising pH and became a trace at pH > 6.0. An increase in the ionic strength of the background electrolyte decreased Zn sorption and enhanced the amount of sorbed metal that could be subsequently released. In the two soils, Zn sorption diminished somewhat in the K and Ca electrolytes as compared with the Na electrolyte. However, this did not happen at small Zn loadings. Desorption was not affected by the type of electrolyte and cation used. The results are consistent with chemisorption being responsible for most of the sorption. The results also suggested a strong affinity sorption or even precipitation at high pHs.
The properties, genesis and significance of a man‐made iron pan podzol near Castletownbere, Ireland
Authors: CONRY M.J. , DE CONINCK F. , STOOPS G. 
Published: August 2005

SummaryBeneath a layer of artificially deposited peat debris, an eluvial E horizon and thin iron pan (Bsm) has developed in the upper part of the Ap horizon of a brown podzolic soil (Haplorthod) near Castletownbere, Ireland. The thickness of the E horizon and the depth of the pan are directly related to the thickness of the layer of peat debris.The original soil (Haplorthod) was strongly podzolized with a significant accumulation of organic carbon, iron and aluminium in the spodic Bs. The iron pan of the upper sequum, on the other hand, is rich in iron. This iron pan seems to have developed as a result of reduction of iron in the E horizon, transport of divalent Fe2+ cations and precipitation in the Bsm as Fe2(OH)3, after the peat layer was deposited. We conclude that podzolization and iron pan development were fundamentally different processes.The study suggests a fundamental change in the iron pan‐blanket peat development sequence previously postulated by palaeoenvironmentalists in Ireland.
Macromolecular changes of humic substances induced by interaction with organic acids
Authors: PICCOLO A. , NARDI S. , CONCHERI G. 
Published: August 2005

SummaryTwo different humic materials, one from a forest soil and the other from wormcasts, were used to study the influence of mineral and organic acids on the conformational properties of humic substances. The macromolecular changes were followed by low pressure gel permeation chromatography after titrating humic material to low pHs with acids. All organic acids (mono‐, di‐, tri‐carboxylic, and oxy‐acids), added to humic solution prior to a gel permeation in an alkaline buffer, were able to shift the totality of absorbance of the humic chromatographic peak from high to low molecular sizes. Mineral acids, phenol, alcohols, dipolar aprotic solvents, could not produce the same shift and gave total absorbance at the column void volume as in the case of humic substances alone. The chromatographic peak shifted back to elution volumes proper of higher size molecules when the humic‐organic acid mixture was back‐titrated to high pHs before gel permeation. Elution in a much stronger alkaline buffer did not change the overall macromolecular behaviour.These results suggest that humic substances behave as micelles in solution and that hydrophobic bondings play an important role in holding humic molecules together. The organic acids enter the interior of the humic micelle‐like aggregates and alter the stereochemical hydrophobic arrangement of the humic material. In alkaline conditions the negative charges developed disrupt the apparent high molecular size configuration and disperse the humic aggregates into small micelles. Such conformational properties of humic substances appear to be a function of pH and of the concentration of organic acid.
Effect of water: soil ratio on phosphate release: P, aluminium and fulvic acid associations in water extracts from Andisols and Andic soils
Authors: NEGRÍN M.A. , ESPINO‐MESA M. , HERNÁNDEZ‐MORENO J.M. 
Published: August 2005

SummaryThe influence of water: soil ratio (w: s) on phosphorus fractions was studied in Andisols and Andic soils. Phosphorus was fractionated in 0.45‐μm filtered water extracts, and pH, monomeric Al and dissolved organic carbon (DOC) were determined. Speciation of dialysed extracts was also studied. Increasing w: s from 2.5 to 75 resulted in a release of dissolved reactive phosphorus (DRP), while DOC decreased significantly and pH increased moderately. For the 29 samples studied desorbed DRP =K (w: s)β, where β represents a P buffering term and ranged from 1 to 1.26 for DRP (mg kg−1). On dialysis, we observed a uniform partition between dialysable (DP) and non‐dialysable P (NDP) which was explained by the corresponding difference in DOC; these results were consistent with the existence of soluble P‐Al‐fulvic complexes. Study of solubility diagrams for determining solid‐phase controls on P activities in the extracts suggested that dissolution of Al‐phosphates could explain most of P release to water as free orthophosphate. Both this mechanism and organic P partition between solid and solution soil phases may be considered to reflect the main sources of P in Andisols: Al‐phosphate and organic‐Al‐P complexes.
Comparison of soil solution chemistry assessment using zero‐tension lysimeters or centrifugation
Authors: GIESLER R. , LUNDSTRÖM U. S. , GRIP H. 
Published: August 2005

SummaryThe composition of soil solutions obtained from the field varies with the method of extraction. Variations in sampling methods and the difficulties in extracting representative samples from soils in space and time, can explain divergent results. In this study we compared soil solutions from a forest soil in northern Sweden obtained by a centrifuge drainage technique and by zero‐tension monolith lysimeters. Zero‐tension lysimeters were destructively sampled, and centrifuge solutions from this soil were compared with that from soil outside. In our study we found three major differences in the solute composition between the centrifugate and the lysimeter leachate: (i) larger concentrations of most solutes in the mor layer centrifugate than in the mor layer leachate, (ii) accumulation of nitrate in the lysimeters, and (iii) larger concentrations of base cations in the zero‐tension lysimeters below 0.3 m depth. Water contents within the lysimeters were up to 3.5 times greater than under natural conditions and the water yields from the lysimeters indicate that water residence time ranged from < 1 to >5 years. This study shows that differences in results from the two methods are due to inherent differences in the methods themselves and not just to the collection of different soil waters. The hydrological anomaly and disturbance induced by the zero‐tension lysimeters affects the solute chemistry and thus the applicability of the results to field conditions.
Mobilization of phosphate from phosphate rock and alumina–sorbed phosphate by the roots of ryegrass and clover as related to rhizosphere pH
Authors: HINSINGER P. , GILKES R.J. 
Published: August 2005

SummaryThe mobilization of phosphate by two pasture species was studied in an alumina sand with P added as phosphate rock (PR–P) and as phosphate sorbed on to alumina (A12O3–P). The experiments were performed with a cropping device which enables the collection of rhizosphere material at defined distances from the roots of ryegrass (Lolium rigidum L.) and clover (Trifolium subterraneum L.). Nitrogen was supplied as nitrate alone or in combination with ammonium, which stimulates proton excretion by plant roots. Whatever the phosphate source, rhizosphere pH decreased relative to control pots without plants when ammonium was supplied. The pH decrease was larger for ryegrass than clover and reached 1.5 pH units when phosphate was supplied as A12O3–P. When nitrogen was supplied as nitrate only, rhizosphere pH remained close to the near neutral pH of the control. Root–induced dissolution of PR ranged between 20% of applied PR–P for nitrate–fed ryegrass and 40% for ammonium–fed ryegrass. Most of the P dissolved from PR was sorbed on to alumina and accumulated as alkali soluble P in the rhizosphere of both species, whilst dissolved Ca from PR also accumulated. The excretion of protons by roots of clover and ryegrass was thus the driving force for the root–induced dissolution of PR. When P was supplied as A12O3–P, ryegrass grew more than clover and took up more phosphate whatever the nitrogen source. Depletion of alkali soluble P, that is phosphate sorbed on to alumina, occurred only for ryegrass and extended up to two millimetres from the roots. These differences between the two plant species suggest that the mobilization of A12O3–P was not simply related to rhizosphere pH. Instead, the superior ability of ryegrass to mobilize A12O3–P relative to clover might be related to the ability of its roots to cope with smaller solution P concentration (smaller external P requirement).
Defining monitoring strategies for runoff and erosion studies in agricultural catchments: a simulation approach
Authors: JETTEN V. , BOIFFIN J. , DE ROO A. 
Published: August 2005

SummaryThe number of runoff and erosion studies in cultivated catchments in north west Europe is increasing. Measurements are usually costly and time‐consuming, in particular of soil hydrological properties because agriculture causes considerable spatial and temporal variation. A subdivision of the catchment is necessary to optimize the choice of sampling sites and to define extrapolation procedures. Four sampling strategies were examined, consisting of subdividing the catchment according to the crops (1), or according to the surface structure (2), followed by increasing the number of sampled fields by adding fields that are presumed to have maximum runoff activity (3) or intermediate activity (4). These strategies were compared by modelling the runoff and erosion in a virtual catchment, containing 15 arable fields with various crop sequences, at three times during a winter season. Strategy 2 gave better results than 1, because of the large variability of surface structure of the bare fields, which was not correlated with the crop type. Runoff prediction benefited from extra sampling only when groups of fields with a large heterogeneity in hydrological behaviour were included. The quality of erosion prediction increased when the steeper fields were included in the sampling scheme. A monitoring strategy is proposed that consists of: (i) repeated, fast and exhaustive descriptions of the soil surface using surface structure classes, (ii) subdivision of the catchment into groups of fields with identical surface characteristics before measurements are made, and (iii) sampling and extrapolation according to these groups.
Application and sensitivity analysis of process‐based erosion model GUEST
Authors: MISRA R.K. , ROSE C.W. 
Published: August 2005

SummaryAs long‐term measurement of erosion is expensive, models are required to predict spatial and temporal variation in erosion accurately for various land uses and to develop suitable practices for soil conservation. Details of the steady‐state, process‐based erosion model GUEST are presented with emphasis on the behaviour and sensitivity of the model to a fundamental erodibility parameter J. The model is developed to interpret temporal fluctuation in sediment concentration from bare soil in single erosion events. It incorporates the simultaneous effects of rainfall and runoff and of deposition on sediment concentration. An example of its application to temporal variation in sediment concentration for varying slopes and soil strengths show reasonable agreement between the measured data and the limits of sediment concentration predicted by the model. Sensitivity analysis indicated the model to be most sensitive to land slope and a defined sediment characteristic called depositability, but not as sensitive to frequency and dimensions of rills.
Nature and origin of soluble lipids shed into the soil by rainwater leaching a forest cover of Pinus maritima sp.
Authors: COLINA‐TEJADA A. , AMBLÈS A. , JAMBU P. 
Published: August 2005

SummaryWe have studied the ability of rainwater leaching a pine (Pinus maritima sp.) forest cover to solubilize lipid components. The nature and origin of straight‐chain hydrocarbons, alcohols and monoacids shed into the soil by rainwater was determined. Rainwater falling from branches and pine needles (RF) and rainwater running down the tree trunks (RR) were collected separately. The compounds were quantified and identified by gas chromatography used alone or coupled with gas chromatography. The dominant fraction of soluble lipids was aliphatic alcohols (alkanols) in RR and monoacids in RF. The concentration in water of total hydrocarbons and of total alkanols was the greatest in winter. In contrast, the proportion of alcohols with a number of carbon atoms < C20 in total alcohols and of branched monoacids in total monoacids were the highest in summer. Hydrocarbons were almost solely of bacterial origin but alcohols and monoacids showed components both of bacterial and of higher‐plant origin, the latter being more abundant in RR than in RF.
An investigation into sources of soil crack heterogeneity using fractal geometry
Authors: PRESTON S. , GRIFFITHS B.S. , YOUNG I.M. 
Published: August 2005

SummaryFractal dimensions were used to quantify the complex geometry of soil cracking patterns. Two fractal dimensions were measured to provide an adequate description of soil cracks: the mass fractal dimension, DM (which provides a measure of crack heterogeneity) and the spectral dimension, d (which provides a measure of crack connectivity). The cracking patterns generated by four soils were compared and related to their textural characteristics. As the clay content of the soil increased (6·1%–24·3%), so did DM (1·29–1·43), and d (1·03–1·33). Correlations indicated that there was a significant (P < 0·01) linear relation between the soil's clay content and the DM and d of cracks, the correlation coefficients obtained being equal to 0·965 and 0·840, respectively. Significant correlations (P < 0·01) were also observed between structural stability indices of the soil and the fractal dimensions of its cracks, increases in the stability of the soil, particularly of the clay fraction, being associated with cracks with greater fractal dimensions.
Aggregate stability and assessment of soil crustability and erodibility: II. Application to humic loamy soils with various organic carbon contents
Authors: LE BISSONNAIS Y. , ARROUAYS D. 
Published: August 2005

SummarySurface crusting results from aggregate breakdown under raindrop impact. It reduces the infiltration rate and may induce erosion by increasing runoff. Soil crustability and erodibility generally increase as organic carbon content decreases. Samples of topsoil were collected from fields cropped continuously for maize after land clearance at various dates. Organic carbon content ranged 4–30 g kg‐1. Aggregate stability was assessed by measuring fragment size distribution after different treatments. Samples were also subjected to simulated rainfall. The size of fragments forming the seal when the rain ceased and the infiltration rate during the rainfall were measured to characterize seal structure and hydraulic properties. Development of the seal and infiltration capacity were related to aggregate stability, which was itself a function of organic carbon content. The relations between aggregate breakdown, crusting and infiltration enabled us to predict soil physical behaviour from measurements of aggregate stability which are easier to make than direct measurements under rainfall. The proposed tests offer the opportunity to evaluate actual or potential soil physical degradation and erosion risks without extensive field measurements.
Deformation of saturated clays under mechanical and osmotic stress and its relation with the arrangement of the clays
Authors: CHARPENTIER S. , BOURRIÉ G. 
Published: August 2005

SummaryThe relation between physical and mechanical responses and the structure of clay has been studied. Deformation in response to mechanical stress was measured on samples of Wyoming mont‐morillonite and Saint Austell kaolinite in solutions of NaCl (0·005; 0·05; 0·5 and 5 M). Salt concentration was expressed in terms of osmotic potential of water and loading in terms of envelope pressure potential of water, and deformation was measured precisely under small mechanical stress. During shrinking and swelling, deformation was small and reversible, and consolidation was related to the largest mechanical stress applied previously in its history. The arrangement of the clay at equilibrium depends foremost on the type of clay mineral and physico‐chemical properties of the liquid phase. For Na‐montmorillonite suspensions, transition between gels with tactoids and rigid media with quasicrystals is abrupt and occurs at a potential of about −2000 J kg−1, whether the stress is osmotic or mechanical. Swelling indexes obtained under osmotic and mechanical stress are of the same order of magnitude. Deformation of smectite results from modifications of interassemblage and intra‐assemblage organization.
The absorption of water into a porous solid consisting of two dissimilar layers
Authors: WILSON M.A. , HOFF W.D. 
Published: August 2005

SummaryAnalytical modelling of the movement of water through porous solids consisting of more than one homogeneous layer is a problem in soil science and in construction engineering. In this paper equations based on the Green and Ampt model describe the absorption of water into a two‐layer composite bar for the cases of absorption through a material of large sorptivity into one of smaller sorptivity and vice versa. These predictions are compared with experimental results. There is broad agreement between theory and experiment at all times. We conclude that the absorption of water into a two‐layer composite is ultimately controlled by the second material in the absorbing sequence irrespective of whether this material has the larger or the smaller sorptivity.
Solubility of a proto‐imogolite sol in oxalate solutions
Authors: LUMSDON D.G. , FARMER V.C. 
Published: August 2005

SummaryThe amounts of aluminium liberated from a proto‐imogolite (P‐I) sol by 1–3 mM oxalate at pH 4·8–7·1 are found to be in excellent agreement with those calculated on the basis of the solubility product of the P‐I sol, and the stability constants for aluminium oxalate complexes established earlier. Calculated solubility curves are presented for proto‐imogolite sols in the presence of 10−3, 10−4 and 10−5 M total oxalate over the pH range 4–8, and also for the case where oxalate concentrations are controlled by solid calcium oxalate in the presence of 0·05, 0·5 and 5 mM calcium ion. We conclude that the presence of a proto‐imogolite allophane in podzol B horizons of pH 5·0 requires oxalate concentrations less than 10−5 M. For fertile agricultural soils with typical calcium concentrations (approximately 5 mM) in the soil solution, aluminium oxalate concentrations would be limited by calcium oxalate solubility to less than 10−6 M in the presence of proto‐imogolite allophane at pH values exceeding 5·5. In leached podzolic soils calcium concentrations are generally less than 0·05 mM, and would not limit the formation of aluminium oxalate complexes.