bluuebunny/crossref_metadata_2025_split huggingface dataset:
The influence of organic matter on aggregate stability in some British soils
Authors: CHANEY K. , SWIFT R.S. 
Published: July 2006

SUMMARYThe stability of aggregates from 26 soils selected from agricultural areas was measured by wet‐sieving and the results correlated with sand, silt, clay, nitrogen, organic matter and iron contents and with cation exchange capacity. Highly significant correlations were obtained for the relationships between aggregate stability and organic matter and some properties associated with it. No other soil constituent investigated had a significant relationship with aggregate stability, indicating that organic matter is mainly responsible for the stabilization of aggregates in these soils.The relationships between aggregate stability, and organic matter content plus some of its component fractions were examined in more detail using 120 soils. Total organic matter, total carbohydrate and humic material extracted by various reagents each gave highly or very highly significant correlations with aggregate stability. However, whilst it was not possible to distinguish whether any one organic component was more important than another, the results indicate that soil organic matter levels can be used diagnostically to identify soils which may show problems of structural instability.
The influence of clay mineralogy and diagenesis of Upper Carboniferous shales on soil formation in parts of Devon
Authors: GRAINGER P. 
Published: July 2006

SUMMARYThere is a correlation between variations in the clay mineral assemblages of the Crackington Formation (Upper Carboniferous) shales in parts of Devon, and the soil series mapped in the same areas. The differences in soil‐forming characteristics of the shales are not due to mineralogy alone, but to various states of diagenetic induration which they have achieved. Brown earths (Dunsford series) are formed on steeper slopes of more durable, illite‐chlorite dominated shales, whereas clayey soils (Tedburn and Halstow series) are typical of flatter, more poorly drained slopes of weaker illite and illite‐kaolinite clay mineral assemblages. This result adds the geological component to earlier views that the different soil series are simply a consequence of physiographic and hydrologic position.
Simultaneous nitrification and diffusion in soil. I. The effects of the addition of a low level of ammonium chloride
Authors: DARRAH P. R. , WHITE R. E. , NYE P. H. 
Published: July 2006

SUMMARYThe nitrification of NH4+ and the simultaneous diffusion of NH4+, NO3− and H+ following the addition of ammonium chloride to a fine sandy loam soil was analysed experimentally and theoretically. Experimentally, the concentration profiles of mineral N and pH were analysed 140h and 284 h after the homogeneous addition of 11 μmoles NH4Clcm−3 of soil to one part of a composite soil column. The mathematical model presented includes a kinetic model of nitrifier growth and activity, the adsorption equilibria of NH4+ and soil acidity with the soil solid phase and the influence of other ions on the diffusion characteristics of each diffusing ion. The predictions of the model were generated using parameters derived from independent experiments so that the predictions did not depend on data derived from the experimental concentration profiles. Good agreement was found between experimental and predicted profiles. The use of the model for predicting the penetration of NH4+ and NO3− into the soil is demonstrated.
Influence of organic matter content, moisture status and time after reworking on soil shear strength
Authors: DAVIES PATRICIA 
Published: July 2006

SUMMARYRecovery of soil shear strength was measured in disturbed samples of a calcareous clay loam soils, with four different organic matter contents. Repacked soil cores were put on tension tables at 25 or 50 cm water tension. Shear strength and water content were measured at one of eight time intervals, from 48 h to 7 weeks after the tension was applied. Soil strength increased with increasing organic matter content or increasing the applied tension. The major factor affecting strength, however, was the length of time that tension was applied. Because water contents showed little or no change with time on the tension table these results demonstrate thixotropic recovery of shear strength. This property is discussed with relevance to the soil's potential for mole drainage.
Ammonia volatilization from urea‐treated pasture and tillage soils: effects of soil properties
Authors: O'TOOLE P. , McGARRY S. J. , MORGAN M. A. 
Published: July 2006

SUMMARYMean NH3 losses after nine days incubation at 18°C and 60% FC were 3.1±2.9% and 7.6±6.0% of applied urea‐N from the pasture and tillage counterparts of 10 soil series. These losses were highly correlated with buffered CEC and maximal pH values (pHm) generated three days after urea application. NH3 volatilization was apparently controlled by buffered CEC and initial pH (R2= 72–87%) and was related to variations in soil organic matter and texture (R2= 77–81%). Losses in the acid pasture soils were attributed largely to initial pH differences, and in the tillage soils to buffered CEC only.Evolution was greater from the tillage than from the pasture equivalent in eight series. This was attributed to differences in CEC, including buffered CEC and pH‐dependent charge, caused by differences in OM content primarily but also in texture between the two soil groups. Differences in NH3 evolution from urea in pasture and tillage soils, in general, are not related to pH differences.
Studies on aggregate stability. I. Re‐formation of soil aggregates
Authors: CHANEY K. , SWIFT R. S. 
Published: July 2006

SUMMARYWhen natural soil aggregates were destroyed by crushing, techniques traditionally used for re‐forming aggregates, such as wetting/drying and freezing/thawing cycles, did not produce any stable re‐formed aggregates. Incubation without amendment, was similarly unsuccessful, whereas incubation with glucose amendment did produce stable aggregates, and their stability was related both to the natural soil organic matter levels and to the original stability of the natural aggregates. However, the stability induced by incubation with glucose was of a transient nature and declined over a period of 12 weeks. This behaviour was attributed to the production of microbial, extracellular polysaccharides and their subsequent decomposition. Addition of microbial polysaccharides of known structure confirmed that such polymers were capable of producing stable re‐formed aggregates without the assistance of further microbial activity. Longer term incubation showed that the stability of the re‐formed aggregates also declined as soil micro‐organisms broke down the polysaccharide material.Neither the glucose incubation nor addition of extracellular polysaccharide was very successful in producing stable aggregates when used with soil which had been washed with salt solutions, and dialysed, to form mono‐ionic soils.
Sorption and desorption of cobalt by soils and soil components
Authors: McLAREN R. G. , LAWSON D. M. , SWIFT R. S. 
Published: July 2006

SUMMARYThe sorption of Co by individual soil components was studied at solution Co concentrations that were within the range found in natural soil solutions. Soil‐derived oxide materials sorbed by far the greatest amounts of Co although substantial amounts were also sorbed by organic materials (humic and fulvic acids). Clay minerals and non‐pedogenic iron and manganese oxides sorbed relatively little Co. It is considered that clay minerals are unlikely to have a significant influence on the sorption of Co by whole soils.Cobalt sorbed by soil oxide material was not readily desorbed back into solution and, in addition, rapidly became non‐isotopically exchangeable with solution Co. In contrast, Co was relatively easily desorbed from humic acid and a large proportion of the Co sorbed by humic acid remained isotopically exchangeable. Cobalt sorbed by montmorillonite was more easily desorbed than that sorbed by soil oxide but less easily than that sorbed by humic acid.Cobalt sorption isotherms for whole soils at low site coverage were essentially linear and the gradients of isotherms increased with pH. A comparison of isotherm gradients for whole soils and individual soil components supported the suggestion that Co sorption in whole soils is largely controlled by soil oxide materials.
The classification and mapping of potassium reserves in soils of England and Wales
Authors: GOULDING K. W. T. , LOVELAND P. J. 
Published: July 2006

SUMMARYPotassium was extracted from samples of 21 surface soils and nine subsoils using a calcium‐saturated cation exchange resin and concentrated HCI under reflux. Most of the important arable soils of England and Wales were represented in the samples. The two methods permitted determination of the amounts and rates of release of exchangeable K, K fixed in the weathered periphery of vermiculitic and illitic minerals, and K in the unweathered core of mica minerals. Potassium reserves in the soils were classified as High, Medium or Low according to the rate of release of fixed K and the amount and rate of release of mica K. The K reserves of soils in England and Wales could be mapped by soil series using this method of classification. Such mapping would provide data on the extent and availability of reserves in both the short term (i.e. to a crop over a growing season) and long term.
Choosing functions for semi‐variograms of soil properties and fitting them to sampling estimates
Authors: McBRATNEY A. B. , WEBSTER R. 
Published: July 2006

SUMMARYThe semi‐variogram is central to geostatistics and the single most important tool in geo‐statistical applications to soil. Mathematical functions for semi‐variograms must be conditional negative semi‐definite, and there are only a few families of simple function that meet this demand. These include the transitive models with finite a priori variance deriving from moving average processes. The spherical and exponential schemes are the most often encountered members. The other major group is that of unbounded models in which the variance appears to increase without limit. The linear model is the most common in this group. If more complex models are needed they can be formed by combining two or more simple models.The usual estimator of the semi‐variance is often considered inefficient and to be sensitive to departures from normality in the data. It is compared with a robust estimator and shown to be generally preferable in being unbiased and having confidence intervals that are no wider. For routine analysis, fitting models to sample semi‐variograms by weighted least squares approximation, with weights proportional to the expected semi‐variance, is preferred to the more elaborate and computationally demanding statistical procedures of generalized least squares and maximum likelihood. The Akaike information criterion is recommended for selecting the best model from several plausible ones to describe the observed variation in soil, though for kriging it may be desirable to validate the chosen model.Examples of models fitted to soil semi‐variograms are shown and compared.
A comparison of tests of soil structural stability
Authors: MATKIN E. A. , SMART P. 
Published: July 2006

SUMMARYSamples from 70 horizons from UK soils were tested for structural stability, and a comparison was made between the results from the following six tests: (i) Emerson, (ii) Janse & Koenigs, (iii) Thorburn, (iv) Childs (soil moisture characteristic), (v) Williams & Cooke slump test, and (vi) wet sieving. Both correlations and systematic differences were observed between the tests, suggesting that different aspects of stability were emphasized by different test procedures. The tests leading to classes (i), (ii) and (iii) were found to be more subjective than those leading to indices. It is suggested that (v) may be applicable to less stable soils, and (vi) to more stable soils. Childs’ test was time consuming and subject to some erratic results; two new indices of stability are proposed to increase the reliability of this test.
Some problems associated with the use of the neutron probe in swelling/shrinkling clay soils
Authors: JARVIS N.J. , LEEDS‐HARRISON P.B. 
Published: July 2006

SUMMARYComparison of neutron probe count rate ratios measured at 10 cm depth, with bulk soil water contents measured 3–5m away from the access tubes, confirmed that in swelling/ shrinking clay soils, recharge may be over estimated. This is due to the drying soil shrinking form the access tube, creating an air gap and radial cracks which allow preferential re‐writing of the soil near the access tube. Installation of access tubes into dry soil was only a short‐term answer.Comparison of results obtained for bulk soil and for small colds shows that calibrating the neutron probe using small diameter cores may be lead to serious under estimates of changes in water content in shrinking clay soils.
Inorganic anion sorption and interactions with phosphate sorption by hydrous ferric oxide gel
Authors: RYDEN J. C. , SYERS J. K. , TILLMAN R. W. 
Published: July 2006

SUMMARYThe sorption of inorganic anions by hydrous ferric oxide gel (Fe gel) from 10 −1 M NaClO4 at pH 6.5 decreased in the order: orthophosphate (H2PO4)>arsenate (H2AsO4) = selenite (HseO3) > silicate (H4SiO4) > molybdate (MoO24−) > sulphate (SO24−) > selenate(SeO24−)>chloride (Cl−) = nitrate (NO−3). When each anion was added to Fe gel with an equimolar quantity of H2PO−4, there was no detectable effect of SO24−, SeO24−, Cl−, and NO−3 on the amount of H2PO−4 sorbed. Other anions depressed H2PO4 sorption in the order H2AsO4 >HseO3 > H4SiO4 > MoO24. At the lowest level of anion addition (500 mmol kg −1), H2PO4 sorption was depressed by no more than 6% of the sorption level in the absence of a competing anion. In contrast, at the highest level of anion addition (1700 mmol kg‐1 of each), H2AsO4 decreased H2PO4 sorption by 44%. The sorption of SO4− was completely eliminated when this anion was added with equimolar amounts of H2PO4. The ability of anions to compete with H2PO4 for sorption sites could not be explained solely by the results obtained for the sorption of each anion alone. Thus, H2AsO4 was more competitive than H2PO4 when added together, even though more H2PO4 than H2AsO4 was sorbed when each anion was added alone. Although H2PO4 was sorbed in larger amounts, there is no evidence to suggest that H2PO4. H2AsO4, and HseO3 were sorbed on different sites.
The elucidation of soil pattern in the Wyre Forest of the West Midlands, England. II. Spatial distribution
Authors: OLIVER M. A. , WEBSTER R. 
Published: July 2006

SUMMARYThe spatial distribution of soil in the Wyre Forest of England was analysed in two phases. In the first the soil was examined at sites chosen using a five‐stage nested design with spacings increasing geometrically from 6 m to 600 m. Some 80% of the variance was contributed by components for the spacings between 6 m and 60 m. Measurements were then made on transects at 5 m intervals and semi‐variograms estimated to 70 m. Except for those of pH the semi‐variograms of the soil properties had the same general transitive form and a common effective range of about 40 m. This short range meant that very intensive sampling, approximately one point per 400 m2, is needed to map the soil variation. A survey was made of a small portion of the forest on a 20m × 25 m grid to test the inference. Maps of clay and sand content were made successfully by kriging from the data. The mutual correlations between soil properties and the common range of their semi‐variograms enabled a general purpose and spatially coherent soil classification to be created from the data. Its mapping confirmed the intricacy of the soil pattern in the Forest.
Andosols developed from non‐volcanic materials in Galicia, NW Spain
Authors: GARCIA‐RODEJA E. , SILVA B. M. , MACÍAS F. 
Published: July 2006

SUMMARYA set of well‐drained soils in Galicia, formed from gabbros, amphibolites and schists, with udic moisture and mesic temperature regimes, are studied. All but one of the surface horizons show an‘exchange complex dominated by amorphous material’(ECDAM); consequently, most soils are classified as Andosols (FAO) or as different subgroups of Dystrandepts (Soil Taxonomy). The soils on gabbros and amphibolites frequently have‘andic properties’so, following the ICOMAND proposals, five of the 12 soils studied may be characterized as Andisols. Many of the five soils have properties comparable to those of soils from volcanic areas, especially to those called‘non‐allophanic Andosols’, which have an abundance of active‐Al, mainly in the form of Al‐humus complexes.
Extraction and characterization of water–repellent materials from Australian soils
Authors: MA'SHUM M. , TATE M. E. , JONES G. P. , OADES J. M. 
Published: July 2006

SUMMARYOrganic materials responsible for water–repellency in some Australian soils were extracted with an amphiphilic mixture of iso‐propanol/15.7 m ammonia (7:3, v:v) in a Soxhlet apparatus, after which the water–repellent soils were rendered wettable. The successful extraction by an organic solvent system indicates that the bulk of hydrophobicity in these soils is not covalently linked to the surface of the sand. The extracted materials restored hydrophobicity on acid washed sands or ignited sands at levels comparable to the original soils.Spectroscopic and chromatographic examination of the extracted materials indicated that both free and esterified long–chain, 16–32 carbon atom, fatty acids were present with a bimodal distribution showing maxima at C16 and C22. The 13C–NMR and infrared spectra of the most hydrophobic extract suggest that hydrophobicity is caused by molecules with extensive polymethylene chains. Calculations with model compounds indicate that at least a close packed monolayer is required before measurable hydrophobicity can be detected with the molarity of ethanol droplet penetration test.
The significance of gley features in soils derived from grey parent materials
Authors: MOFFAT A. J. , JARVIS M. G. 
Published: July 2006

SUMMARYDetailed observations of gley features in soils derived from grey Upper Greensand rocks have been compared with their moisture regimes as determined by water‐levels in dipwells. There was good correlation between the incidence of grey ped face and matrix colours of low chroma, prominent ochreous mottling within the matrix and duration of waterlogging. Careful examination of soil macromorphology can be used, despite inherent greyness, to assess the drainage status and Wetness Class of these soils.Physical and micromorphological analyses suggest that the wetness of some Upper Greensand soils is due to the combination of low vertical permeability in the underlying rock, and moderate horizontal permeability in the overlying horizons. Such circumstances allow perched water‐tables to form in wet weather, sustained by lateral flow when rainfall has ceased.
The role of diffusion in the kinetics of phosphate desorption: the relevance of the Elovich equation
Authors: PAVLATOU ATHENA , POLYZOPOULOS N. A. 
Published: July 2006

SUMMARYVarious kinetic expressions were tested with phosphate desorption data from four contrasting soils and found inadequate, but the data supported a model recently proposed by Aharoni and Suzin. This model assumes that chemisorption reactions are kinetically controlled by diffusion and integration of Pick's equation, under appropriate boundary conditions, results in an expression for the time dependence of adsorption or desorption, that can be approximated by a sequence of equations‐parabolic, Elovich and exponential–at small, intermediate and large times, respectively. Thus, full or even partial conformation of data to such a sequence would suggest diffusion control of the rate determining step, a suggestion usually relying on a time relationship alone.Since true rate constants could not be derived from the other expressions tested, calculation of physically meaningful activation energies was not possible. An approach to the calculation of activation energies at different stages of the process, based on the model of Aharoni and Suzin, and the difficulties encountered are also discussed.
The use of ignition loss to estimate bulk density of forest soils
Authors: HONEYSETT J. L. , RATKOWSKY D. A. 
Published: July 2006

SUMMARY136 samples were collected from soils under wet schlerophyll forest in southern Tasmania. The samples were from different depths and covered a wide range of bulk density and organic matter content. A simple linear relationship between specific volume (the reciprocal of bulk density) and low‐temperature ignition loss was established. Since the variance about the regression tended to be homogeneous with bulk density rather than specific volume, the relationship was fitted as a generalized linear model using bulk density as the dependent variable with an ‘inverse’ link and normal error assumption.For soils with loss‐on‐ignition at 375 ± 5°C (I) ranging from 1.8% to 87.9%, the bulk density, pb was given by an equation of the form l/pb=α+βI, where α and β are constants related to the bulk densities of the mineral and organic matter of the soils studied.The existence of the simple linear relationship in the deterministic part of the model implies that these soils are made up of a mineral framework and organic matter, with neither of the two components penetrating the interstices of the other.
Testing a mechanistic model. IX. Competition between anions for sorption by soil
Authors: BARROW N. J. 
Published: July 2006

SUMMARYA model which describes the reaction of anions and cations with soil when they are added separately was applied to the results of Roy et al. (1986a,b) in which pair‐wise combinations of phosphate, arsenate, and molybdate competed for sorption on three soils. The model postulates that the reaction is between ions in solution and charged surfaces of the soil particles. The surfaces are assumed to be non‐uniform and to differ in their electric potential. Competition comprises both ordinary competition between ions for adsorption sites and the electrostatic interactions which occur because reaction with one anion makes the surface more negative and, therefore, less favourable for reaction with a second anion. The equations of the model were expressed in such a way that the outcome was related to the initial anion concentrations.With appropriate choice of parameters, the model described sorption both when the anions were added singly and when they were added in competing pairs. This shows that the model is comprehensive in that it can be extended to competing pairs of ions. It also shows that simpler descriptions of competition which neglect the electrostatic effects are unlikely to be comprehensive.
A method for the dehydration and impregnation of clay soil
Authors: MORAN C. J. , McBRATNEY A. B. , RINGROSE‐VOASE A. J. , CHARTRES C. J. 
Published: July 2006

SUMMARYDifficulty is sometimes experienced in achieving dehydration and acceptable impregnation of undisturbed specimens of clay soil. It is necessary to avoid shrinkage when removing water and disruption of brittle dehydrated specimens when impregnating. Methods for dehydrating clayey soil for structural studies are reviewed. A method using continuous flow and dehydration of acetone or 1,4 dioxane followed by slow impregnation is outlined. Inexpensive techniques for measuring the water content of these two solvents are described.