bluuebunny/crossref_metadata_2025_split huggingface dataset:
The dissolution and dispersion of dicalcium phosphate dihydrate in soils
Authors: KIRK G. J. D. , NYE P. H. 
Published: July 2006

SUMMARYThe model of the dissolution of particles of DCPD in soil, presented in part III, was tested against experimentally determined rates of dissolution in soil at two pHs, 4.6 and 6.0. To measure the rates, 45Ca dissolved from labelled DCPD was recovered from the soil by shaking the mixture of soil and undissolved DCPD in a CaCl2, extractant. There was good agreement between the observed and predicted rates of dissolution.
Stability of aggregates of different size grades in allophanic soils from volcanic ash in New Zealand
Authors: CHURCHMAN G. J. , TATE K. R. 
Published: July 2006

SUMMARYSamples from six ash soils were chosen with a range of Fe and C contents. Stabilities over the aggregate size‐range from < 1 †m to > 2 mm were measured by selectively removing aggregating agents from fresh soil samples. Wet‐sieving was also carried out on both field‐moist and air‐dried 3.4–2.0 mm macroaggregates.Macroaggregate stabilities were closely related to C contents and were also enhanced by high contents of allophane and/or Feox. High water contents decreased the stability of field‐moist macroaggregates.Clay‐sized material was most readily dispersed with Na resin after pretreatment with hydrogen peroxide; removing the latter alone was usually ineffective in dispersing clays.
Plant uptake of exchangeable and non‐exchangeable potassium. I. Measurement and modelling for onion roots in a Chalky Boulder Clay soil
Authors: MITSIOS I. K. , ROWELL D. L. 
Published: July 2006

SUMMARYUptake of K was measured using a single onion root technique with four soil cylinder diameters, and measuring changes in exchangeable K in the soil. Baldwin's model fitted the measured uptake when only exchangeable K was taken up, but that of Heming & Rowell allowed predictions of uptake of both exchangeable and non‐exchangeable K (Knes) after fitting the necessary parameters. Release of Knex occurred in both 3 mm and 6 mm cells (root densities of 14cm cm”−3 and 3.5 cm cm−3) in 10 days. Predictions were made for longer times and differing soil water contents: after four weeks at a water content midway between field capacity and wilting point the contribution of Knex to total uptake was significant (up to 60%) for plants with high root densities.
Characteristics of soil organic matter in temperate soils by Curie‐point pyrolysis‐mass spectrometry. II. The effect of drainage and illuviation in B horizons
Authors: BRACEWELL J. M. , ROBERTSON G. W. 
Published: July 2006

SUMMARYB horizons from a set of 23 Scottish soils were examined by Py/MS multivariate analysis. These soils comprised phaeozems, cambisols, podzols and gleysols.The principal components analysis of 52 mass ion intensities partitioned the set of soils successfully according to morphological classes Bw, Bg and Bs, and established characteristic differences of organic composition between them. Reconstructed factor spectra for the factors effecting this partition showed distinct homologous groups of products to be responsible. These were principally pyrroles, alkenes and aromatic hydrocarbons of low molecular mass. Possible organic origins of these are discussed and related to the organic patterns found in the A horizons.The Bh (humus B) horizons of podzols gave pyrolysates richer in polysaccharide and lignin products than those of other B horizons, suggesting a less decomposed organic matter.
Effects of green manure on isotopically exchangeable phosphate in a dark‐red latosol in Brazil
Authors: LEMARE P. H. , PEREIRA J. , GOEDERT W. J. 
Published: July 2006

SUMMARYIn a field experiment on a dark‐red latosol (haplustox) in the Cerrado of Brazil, green manure, including maize residues, increased yield of maize grain. Samples of soil from the experiment were investigated in the laboratory. Green manure caused no effect on amounts of phosphate extracted by Bray's solutions, nor by anion exchange resin. Adsorption measurements showed that green manure did not affect the total amount of phosphate adsorbed by the soil, in relation to the amount added nor to the concentration of phosphate in solution. However, green manure increased the proportion of added phosphate that became isotopically exchangeable so that after desorbing some phosphate in two stages, 99% of the adsorbed added phosphate was exchangeable in soil with green manure, but 89% was exchangeable in soil without it. Green manure increased the concentration of phosphate in solution that was maintained by a specific amount of exchangeable phosphate held by the soil. Buffer power increased with time, without and with green manure; but it was less in its presence indicating that phosphate was less strongly held, and would be more mobile in soil in the field.The results indicate that easily decomposable organic material, such as green manure and crop residues, makes fertilizer phosphate more effective for crops growing in an oxisol.
Salt effect in a multicomponent variable charge system: curve of zero salt effect, registered in a pH‐stat
Authors: MEIJER E. L. , BUURMAN P. 
Published: July 2006

SUMMARYMeasurement of the effect of KC1 addition to a soil suspension in pH‐stat experiments indicates that the pH titration curves of such a multicomponent system are characterized by a Curve of Zero Salt Effect (CZSE) rather than a Point of Zero Salt Effect (PZSE). This curve is most accurately measured as a functional relation between pH and KC1 molarity. The described method is very accurate and, by its rapidity, precludes long‐term changes in the sample which are the bane of classic batch experiments. In analogy, multicomponent soil systems will probably be characterized by a Curve rather than a Point of Zero Net Charge (PZNC).
A scheme for the quantitative description of soil macrostructure by image analysis
Authors: RINGROSE‐VOASE A.J. 
Published: July 2006

SUMMARYImages prepared from impregnated samples showing a range of structures were classified structurally. A Quantimet 720 image analyzer and the ANOPOR system separate the pore space in each image into its fissure, channel and packing pore/vugh components. Measurements are derived for each type.Overall structure is determined by the structural pore space consisting of fissures and packing pores/vughs. Paramenters relating to these types indicate the size and shape of structural units and their degree of development. Two scheme are proposed which describe several structural spectra.One treats fissures and packing pores as modifications of the same structural pore space, whereas the other treats the two separately.The effects of various processes of structural parameters are discussed, and the reliability of pore measurements is discussed.
Multi‐orientation thin sectioning for the determination of 3‐D morphology
Authors: SULLIVAN L. A. , KOPPI A. J. 
Published: July 2006

SUMMARYA new soil thin sectioning technique which gives thin cross‐sections (called sliver sections) of thin sections, is described. Optical analysis of soil thin sections and soil sliver sections, using plain, crossed polarized and circularly polarized light provides three‐dimensional information on the micromorphology of clay coatings. This new technique is applied to a common type of clay plug and shows that these features consist of a stack of bowl‐shaped clay coatings.
The effect of subsoil cracking on moisture deficits of Pleistocene and Holocene fluvial clay soils in the Netherlands
Authors: KOOISTRA M. J. , MIEDEMA R. , WÖSTEN J. H. M. , VERSLUIS J. , BOUMA J. 
Published: July 2006

SUMMARYComputer simulation of the soil water regime was used to calculate moisture deficits for Pleistocene and fluvial Holocene clay soils for a 30‐year period. Hydraulic conductivity (K‐h) and moisture retention (h‐θ) data were derived for major horizons in both soils as well as functions to characterize bypass flow and effects of horizontal planar voids on upward unsaturated flow of water from the water‐table to the root zone. Calculated moisture deficits in Holocene soils occurred earlier during the year and were more pronounced during the summer period. Differences between the two soils could be attributed to more pronounced formation of horizontal planar voids in the Holocene soil, which was associated with more pronounced swelling and shrinkage of the undisturbed soil material. The relatively low swelling and shrinkage of the undisturbed Pleistocene soil material was attributed to very dense packing of the elementary soil particles.
The basaltic soils of SE Nigeria: properties, classification and constraints to productivity
Authors: ESHETT E. T. 
Published: July 2006

SUMMARYFour basaltic profiles located in northern Cross River State of Nigeria are described and characterized. The soils are classified as Typic Tropohumult and show strong acidity, low effective CEC, low N and available P. Organic matter levels of the surface soils are high. All the soils are well drained in spite of high YO clay, which is apparently kaolinitic, with moderate to high A1 saturation. Higher agricultural productivity of these soils is restricted by low effective CEC and strong acidity. Measures to combat these problems are suggested.
The use of tension infiltrometers to assess routes and rates of infiltration in a clay soil
Authors: JARVIS N. J. , LEEDS‐HARRISON P. B. , DOSSER J. M. 
Published: July 2006

SUMMARYThis paper describes the design and operation of a simple tension infiltrometer which imposes pressure potentials at the soil surface (hb) of –0.5, – 2 and –9 cm water, corresponding to equivalent diameters (ed) of the largest conducting pore of 6, 1.5 and 0.3 mm respectively. Infiltration measurements obtained in Evesham series clay soil were fitted to Philip's (1957) two‐term infiltration equation. Results were interpreted using information on the number, type and size of conducting macropores obtained in a dye tracing experiment. Significantly larger values of effective hydraulic conductivity at hb=–0.5 cm were attributed to the flow of water in large shrinkage cracks which constituted nearly 90% of the total conducting macroporosity. Measured fluxes at hb=–9 cm were related to sorption and swelling in the clay matrix, since within the range of infiltration times considered (t<0.5 h), the gravity or steady state component of infiltration was negligible. Rainfall intensity/duration data for a large number of storms at Silsoe were used to demonstrate that in dry soil nearly 70% of rainfall infiltrates in the clay matrix, and that the infiltration capacity of macropores of ed≤1.5 mm is only rarely exceeded.
The contribution of sorbed sodium and calcium to the self‐diffusion of these cations in soils with different clay mineralogies
Authors: STAUNTON S. , NYE P. H. 
Published: July 2006

SUMMARYSelf‐diffusion coefficients of sodium and calcium were measured on a range of moist subsoils. The ratio of concentrations of each isotope in the liquid phase and on the surface at the water content of the diffusion run was obtained from both the extrapolation of ratios measured at a range of soil:solution ratios, and, where possible, by measurement on expressed soil solution.The diffusion coefficients were considerably greater than would be predicted if only the liquid phase contributed to diffusion. Surface phase impedance factors, fs, were calculated for each soil. fs for sodium was between 1/5 and 1/2 of the liquid phase impedance factor, fL; fs for calcium was between 1/9 and 1/20 of fL. Values of fs were not obviously related to the clay mineralogy, the proportion of internal to external cation adsorption, the volumetric water content, or the pH.
Chemistry of pedogenesis in Indo‐Gangetic alluvial plains
Authors: TOMAR K. P. 
Published: July 2006

SUMMARYFive soil pedons–two aquic and two udic Haplustalfs and one petrocalcic Natrustalf–from the Indo‐Gangetic alluvial plain of Western Uttar Pradesh were investigated to evaluate the pedogenetic processes. Sand/silt ratios indicate that parent material discontinuities are insignificant. Higher K content and lower SiO2/R2O3 ratios of the non‐clay fractions in Bt, rather than in the A, horizons suggest maximum weathering at or near the surface.An almost linear relationship between decrease in molar SiO2/R2O3 and % increase in clay to about 100cm depth in all the pedons, presence of clay argillans in Bt horizons (where % clay, fine/coarse clay ratio and bulk density values are greatest), all indicate that the development of argillic horizons in these soils was due, at least partly, to lessivage of clay. Fe in clay fractions decreases with depth whilst Al increases, but in the fine earth both increase steadily with depth. This, together with crystalline iron concretions in the lower Bt horizons, suggests that in Haplustalfs these horizons are gaining clay by neoformation/ reorganization of illuviated constituents, especially A12O3.
Effect of soil compaction by tractor traffic on soil structure, denitrification, and yield of wheat (Triticum aestivum L.)
Authors: BAKKEN L. R. , BØRRESEN T. , NJØS A. 
Published: July 2006

SUMMARYIn a field experiment with soil compaction by tractor traffic on a loam soil, the denitrification rate (using the C2H2 inhibition method), the soil structure, and the wheat yield were investigated. Tractor traffic on wet soil (> – 50 mbar matric potential) reduced the pore volume, doubled the percentage of large aggregates (> 20 mm), reduced the wheat yield by about 25%, and increased the N‐loss through denitrification by a factor of 3–4. Neither of these parameters were affected by tractor traffic at low soil moisture content. The weight of the tractor (1800 kg vs 4800 kg) did not significantly alter the effect of compaction on the measured parameters. There was a factor of 2–6 between the measured denitrification rate in compacted and that in uncompacted soil, and this factor showed little dependence on the average activity level on each date of measurement. Accumulated values for the measured denitrification during 75 days (May 23‐August 9) were 3–5 kg N ha–1 in uncompacted soil and 15–20 kg N ha–1 in soil which was compacted in wet condition.
Caesium and strontium diffusion through sodium montmorillonite at elevated temperature
Authors: JENSEN D. J. , RADKE C. J. 
Published: July 2006

SUMMARYCounter ionic migration rates of dilute Cs+ and Sr2+ against sodium in a Na‐montmorillonite gel are measured using a radially perfused diffusion cell. Enhanced or surface diffusion for caesium is observed both at ambient and elevated temperature. To quantify these surface diffusivities the ion‐exchange properties of the diffusing species are required. Thus, exchange isotherms for caesium against sodium on montmorillonite at 22 and 90°C are given for 10−1, 10−2, and 10−3M background NaCl concentrations. Caesium counterion surface diffusivities at 22 and 90°C are 2.2*10−6 and 8.0 * 10−6 cm2 s−1, respectively. These values are found to be essentially independent of background ionic strength over the range 10−3 to 10−1m NaCl. Experimental evidence of enhanced transport through Na‐montmorillonite for the divalent cation Sr2+ is also confirmed with a surface diffusivity of 2 * 10−6 cm2 s−1 at 22°C and in 10−1m NaCl.
The numerical classification of soils: a case study using data from West Sussex, England
Authors: WICKRAMAGAMAGE P. , FISHER G. C. 
Published: July 2006

SUMMARYA set of numerical clustering strategies was applied to soil data for 65 profile descriptions from profiles in West Sussex. The numerical classifications were compared to an original (1967) traditional classification, and at the higher categorial levels the composition of groups was found generally to be different. Such differences were ascribed to attribute weighting, missing information and restrictions on the types of data which could be employed by certain methods. Wilks’ Criterion, A, was used to find the classification producing the most homogeneous groups and, on the basis of tests using a restricted number of quantitative variables, numerical methods were found to give better groupings. An agglomerative, heirarchical procedure based on similarities calculated by Mahalanobis D2 and clustering by minimizing error sums of squares was found most satisfactory, however, the difficulty of defining a best classification is discussed.
Ochre deposits and associated bacteria in some field drains in Scotland
Authors: WHEATLEY R. E. 
Published: July 2006

SUMMARYDrainage systems installed in highly organic soils, with the ground water pH near to neutral and affected by iron ochre deposition, were studied at six sites in Scotland. The iron ochre was composed of iron–encrusted filamentous bacteria entrapping amorphous material. The filamentous bacteria were identified as Gallionella spp., Sphaerotilus natans, Leptothrix ochracea and Leptothrix pseudo–ochracea. Heterotrophic iron–oxidizing bacteria were also present in the iron ochre, but Thiobacillus ferroxidans was not isolated. Differences in the proportion of species could not be correlated with peat type or the age of the drainage system. Sulphate reducing bacteria and bacteria capable of reducing Fe3+ were also isolated from the drainage water.A preliminary investigation of the importance of biotic factors in the kinetics of Fe2+ oxidation showed that the rate of Fe2+ oxidation in unfiltered drainage water, was about twice the rate in filtered water, at 10°C. Incubations over a range of temperatures showed that the differences in rates were greatest at low temperatures.
Gaseous nitrogen losses from soil under Sitka spruce following the application of fertilizer 15N urea
Authors: HULM S.C. , KILLHAM K. 
Published: July 2006

SUMMARYGaseous N loss, through denitrification and NH3−volatilization, was monitored throughout the growing season after spring application of 15N labelled urea fertilizer to peaty gley soils supporting N‐deficient Sitka spruce. From the 15N data, it was calculated that only about 0.28% of applied N was lost through NH3‐volatilization, almost all within the first few days after fertilizer application. Approximately 0.05% of applied N was calculated to be lost through denitrification. Denitrification decreased slowly over a 4‐month period after fertilizer application. Rates of NH3‐volatilization correlated with available NH4+ in the litter layer, while for the early part of the study when N‐losses were highest, denitrification rates correlated with available NO3− in the litter layer. Observations of gaseous N‐loss are also discussed in relation to data from lysimetry, changes in soil pH, and the soil moisture regime.
Testing a mechanistic model. VIII. The effects of time and temperature of incubation on the sorption and subsequent desorption of selenite and selenate by a soil
Authors: BARROW N. J. , WHELAN B.R. 
Published: July 2006

SUMMARYSeveral levels of both selenite and selenate were incubated with separate samples of soil for periods of up to 30 d and at temperatures between 5 and 60°C. The concentrations of selenite or of selenate which caused neither desorption nor further sorption–that is, the null‐point concentrations–were then measured at 25°C. In addition, the rate of desorption was measured after incubation at 60°C for 10 d. The ability of a mechanistic model to describe the results was tested.There were large decreases in the null‐point concentrations of selenite with both increasing period and increasing temperature of incubation. These effects were modelled as due to a relatively rapid diffusive penetration and a large activation energy for diffusion. Only a small proportion of the sorbed selenite was desorbed within 3 d but, at large solution:soil ratios, desorption appeared to be still continuing. These effects were fairly well predicted by the model applied to the sorption data. For example, the continuing desorption was ascribed to the slow reversal of the diffusive penetration. For selenate, the effects of period and temperature of incubation were much smaller. These effects were modelled as due to a slower diffusive penetration and a lower activation energy. Desorption was quicker and was more nearly complete. According to the model, a large proportion remained in the adsorbed form and was more quickly removed when desorption was induced. It is argued that the behaviour of selenite is consistent with diffusion into a crystal and the large activation energy is required to enable jumps over energy barriers. On the other hand, the lower activation energy for selenate is consistent with diffusion being limited to pores or cracks.It is suggested that the residual value of selenite fertilizers would decrease because of the continuing reaction, but that this effect would be unimportant for selenate.
Measurements of the yield surfaces and critical state of some unsaturated agricultural soils
Authors: KIRBY J. M. 
Published: July 2006

SUMMARYYield surfaces and the critical‐state condition have been measured on unsaturated agricultural soils using a standard uniaxial compression test and a constant‐volume direct shear test. The yield surfaces and critical‐state line are all readily described in terms of applied or total stresses, and such an approach offers practical advantages over approaches based on effective stresses. Four soils were tested, these being a silt, a tilth with aggregates mostly from 5‐15 mm, a cracking clay and a red‐brown earth.Each soil was tested at a single constant moisture content in all tests, although the moisture content differed from soil to soil. The range of saturation covered by the four soils was approximately 20‐98%. All the soils displayed yield and deformation behaviour qualitatively consistent with the critical‐state concept. All approach a condition of shear with no volume change (the critical state) under continuing shear. All show collapse with shear in states looser than critical, and expansion with shear in states denser than critical. The silt, being a non‐cohesive soil, cannot support shear stresses much above the critical‐state line, whereas the other three soils can support much higher shear stresses in the overconsolidated condition. The yield surfaces of the silt and the tilth, which were tested at low saturation, are similar in shape with increasing stress level. However, the other two soils, tested when near saturation, display yield surfaces that are not constant in shape with increasing stress level. While the critical‐state concept is applicable both qualitatively and quantitatively, unsaturated soils may be considered to have properties that differ in detail from those of saturated soils.
Determination of the exponential unsaturated hydraulic conductivity function by parameter identification
Authors: BRANDYK T. , ROMANOWICZ R. , SKAPSKI K. 
Published: July 2006

SUMMARYThe parameter identification technique for the evaluation of the exponential unsaturated hydraulic conductivity function is described. The identification is performed using the indirect approach with an output error criterion for steady soil moisture flow through peat‐muck soil columns. The identification procedure uses the Levenberg‐Marquardt algorithm to the solution of the stated least‐square optimization problem. Examination of the evaluated parameters from laboratory experiments justifies the use of this simple identification method for the whole soil profile when the variation of the soil properties in the soil profile is not too large. For layered soil profiles with relatively large differences of soil properties between layers, the parameters of the exponential function must be evaluated separately for each layer.