bluuebunny/crossref_metadata_2025_split huggingface dataset:
The extraction of soil water by the suction‐cup method: a review
Authors: GROSSMANN J. , UDLUFT P. 
Published: July 2006

SUMMARYThis article deals with the extraction of soil water using the suction‐cup method and its accompanying problems. This method has become well‐developed over the past 20 years. It allows continuous sampling during any period and, if necessary, at several different depths of a soil profile. The installation of the suction probe is easy and the profile is only negligibly disturbed. Some problems may occur when this technique is used. The spatial variability of the properties investigated is often underestimated and must be clarified by sufficient replication. An important point of discussion is the by passing of water flowing through macropores. The problems of alteration of the sample by the sampling system also deserve attention. These can be the ‘filter effect’ as regards macromolecules and colloids, the sorption of trace substances, and the gas exchange between the sample and the atmosphere of the sampling system.
Relationship between equivalent salt solution series of different soils
Authors: JAYAWARDANE N. S. , BLACKWELL P. S. 
Published: July 2006

SUMMARYEquivalent salt solution series have been previously defined as solutions with combinations of sodium absorption ratio (SAR) and electrolyte concentration (Ec) producing the same extent of clay swelling in a given soil. The present study shows that there is a high (r2>0.96) positive correlation between log Ec and log SAR of equivalent salt solutions series, in the equation:
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where a1 and b1 are constants for each equivalent salt solution series for a given soil.Log a1 could also be represented as a linear function of b1 resulting in the equation:
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where a2 and b2 are constants for a given soil. Solving this equation using any given value of b1 yields the combinations of SAR and Ec which make up each equivalent salt solution series for a given soil. The relationship between log a1 and b2 for three soils from western United States, namely Waukena, Pachappa and Grangeville, was similar, with their combined data having a r2 value of 0.96. This indicated that a single set of equivalent salt solution series values could be used for these three soils which have different clay contents and clay mineralogy.Prediction of hydraulic conductivity decreases with Ec reduction at given values of SAR in red‐brown and alluvial soils from southern Tasmania, using the equivalent salt solution series values for Waukena soil, showed similar patterns to measured values and also to those predicted using the equivalent salt solution values applicable to the respective Tasmanian soils.Thus, available data indicate that the same set of equivalent salt series could be applied to the five soils studied. If further testing shows that a single set of equivalent salt solutions values could be applied to all or large groups of soils, this would facilitate the application of the equivalent salt solution concept to predict salt solution flow in the field.
A model of ammonia volatilization from applied urea. V. The effects of steady‐state drainage and evaporation
Authors: KIRK G. J. D. , NYE P. H. 
Published: July 2006

SUMMARYRachhpal‐Singh & Nye's model of ammonia volatilization is expanded to account for the effects of steady‐state water movement by drainage or evaporation when the soil does not dry out to any great extent. The model shows how upward movement of water during evaporation increases volatilization by carrying urea‐derived NH4+ and HCO3− ions upward, thereby increasing the concentration of ammonia gas at the surface. Conversely, water drainage reduces volatilization by carrying the dissolved solutes into the soil. The model is used to assess the effects on volatilization of evaporating conditions and of irrigation or rainfall.
A model of ammonia volatilization from applied urea. VI. The effects of transient‐state water evaporation
Authors: KIRK G. J. D. , NYE P. H. 
Published: July 2006

SUMMARYRachhpal‐Singh & Nye's model of ammonia volatilization is further expanded to account for the effects of transient‐state water evaporation when the soil surface dries significantly. Full details are given of the derivation and numerical solution of equations describing transient‐state water movement, and the diffusion and convection in soil of urea and its hydrolysis products, and of acid generated by ammonia volatilization. For the wide range of soil hydraulic properties considered, the effects of a dry soil layer on the rate of volatilization supplement the effects of increased convective supply of NH+4 and HCO−3 ions to the soil surface. The dry layer results in increased gaseous NH3 diffusion through the soil, and thereby increases the flux of NH3 across the soil surface and the neutralization of H+ ions generated by volatilization.
The fractal structure of soil aggregates: its measurement and interpretation
Authors: YOUNG I. M. , CRAWFORD J. W. 
Published: July 2006

SUMMARYThe theory of fractal geometry is presented with reference to soil structure. Recent work on relating fractal structure to pore structure in soils is reviewed. It is suggested that the connection made in previous work between the fractal dimension and soil moisture retention curves is based on simplified assumptions that complicate the interpretation of results. A simple method for estimating the fractal dimension, D, of natural aggregates which circumvents some of these assumptions is presented. Preliminary results of aggregates from soils under different management systems show that, for the soils examined, D ranged from 2.75 to 2.93. The use of D to quantify heterogeneity in soil is explored.
The influence of soil deformations on the permeability to air
Authors: KIRBY J. M. 
Published: July 2006

SUMMARYSamples were reconstituted in the laboratory from a cracking grey clay soil. Some samples were created with a granular structure in which there was no preferred macropore orientation, others were created with a strongly preferred macropore orientation. The samples were compressed and their air permeability measured. They were then sheared and their air permeability measured again.In the samples with a granular structure the change in permeability was dominated by the change in the volume of the pore space. Volume increase led to permeability increase and volume decrease led to permeability decrease. At low shear strains and low volume increases there was some loss of pore continuity leading to small permeability decreases. In contrast, permeability change in the samples with a preferred macropore orientation was dominated by macropore continuity. Permeability decreased both when volume decreased and also over a wide range of volume increases. These results are interpreted in terms of critical‐state soil mechanics and used to construct ‘critical state for permeability’ lines analogous to the usual critical‐state lines.It is suggested that these forms of behaviour encompass the likely bounds of behaviour of soils in many circumstances.
A comparison of three methods of organic carbon determination in some New Zealand soils
Authors: GREWAL K. S. , BUCHAN G. D. , SHERLOCK R. R. 
Published: July 2006

SUMMARYA dry combustion (Dumas) reference method for measuring total organic C (T), is compared with two other methods: the wet acidified dichromate oxidation, Walkley‐Black procedure (an estimator of organic C) and loss on ignition (L) (an estimator of organic matter) for 40 samples from various depths from five New Zealand mineral soils, spanning a range of textures and cultivation treatments. Regression analyses reveal the following: (1) an excellent linear relation exists for all samples between Walkley‐Black procedure and reference method results, with a mean conversion factor 1.25, which compares with the original value 1.32 recommended by Walkley & Black (1934).(2)LandTare less well‐related by an equation of the formL=a+bT.In contrast to the traditional assumption thatb≃ 1.72 anda≃ 0, a strong ‘intercept effect’ (a> 0) is revealed, reflecting removal on ignition of non‐organic soil constituents. An improved regression of the formL=a+bT+cC, whereC= percentage of clay, obtained by inclusion of the clay as an independent variable, points to the role of clay in releasing these constituents, chiefly adsorbed water.
Aggregation of humic substances in aqueous media as determined by light‐scattering methods
Authors: REID P. M. , WILKINSON A. E. , TIPPING E. , JONES M. N. 
Published: July 2006

SUMMARYSamples of peat humic acid (PHA) and surface water humic (WBHA) and fulvic acids (WBFA) extracted from Whitray Beck in North Yorkshire, UK and previously studied by analytical (UV scanning) ultracentrifugation at low concentrations (10–20 mg dm−3) (Reid et al., 1990) have been investigated by dynamic and static light‐scattering methods at concentrations up to approximately 1700 mg dm−3. Dynamic light‐scattering gave very low diffusion coefficients for the humic acids (PHA and WBHA) suggesting the presence of aggregates. Static light‐scattering from the fulvic acid (WBFA) showed that the second virial coefficients of this material in various media were negative, which is characteristic of reversible aggregation. The aggregates, which consisted of approximately 20 smaller molecules, could not be dissociated completely by the detergents sodium n‐dodecylsulphate or Triton X‐100, although limited dissociation by the latter may occur. Sedimentation velocity measurements in the same concentration range as the light scattering gave sedimentation coefficients which increased with concentration also consistent with reversible aggregation.The studies illustrate the problems inherent in the characterization of humic substances from natural sources and demonstrate that, at least for lower molecular weight fulvic acids, static light‐scattering from solutions of relatively high concentration in combination with sedimentation equilibrium measurements at low concentrations distinguishes a system having a broad molecular weight distribution from one in which aggregation occurs.
Local disjunctive kriging of soil properties with change of support
Authors: WEBSTER R. 
Published: July 2006

SUMMARYDisjunctive kriging estimates from a set of measurements the conditional probability that true values of a regionalized variable such as a soil property exceed, or are less than critical thresholds. Estimates can be for sites equal in size to the supports of the samples and, by changing the support of the variogram, for larger blocks. The method also estimates the block averages and their associated variances.The underlying theory and steps in the analysis are described. They are illustrated using a case study from south‐east Scotland where the aim is to estimate the likelihood of copper and cobalt deficiency over whole farms or 1 km2 blocks of land using data from individual fields of 5 to 10 ha only. Maps show the conditional probabilities for 1 km2 squares that the available copper in the soil is less than 1 mg kg−1 and that cobalt is less than 0.25 mg kg−1.
Measuring gross nitrogen mineralization, and nitrification by 15 N isotopic pool dilution in intact soil cores
Authors: DAVIDSON E. A. , HART S. C. , SHANKS C. A. , FIRESTONE M. K. 
Published: July 2006

SUMMARYThe isotope dilution method for measuring gross rates of N mineralization, immobilization, and nitrification was applied to intact soil cores so that the effects of soil mixing were avoided. Soil cores were injected with solutions of either 15NH4+ or 15NO4−; gross mineralization rates were calculated from the decline in “N enrichment of the NH: pool during a 24‐h incubation; gross nitrification rates were calculated from the decline in 15N enrichment of the NO−3 pool; gross rates of NH4+ and NO3− consumption were calculated from disappearance of the 15N label. The assumptions required for application of this method to intact cores are evaluated. Sensitivity analysis revealed that homogeneous mixing of added “N with ambient pools was not a necessary assumption but that bias in distribution of added label, coincident with a non‐random distribution of microbial processes, would cause significant errors in rate estimates. Rate estimates were also sensitive to errors in initial 15N and 14N pool size estimates, In a silt loam soil from a grassland site, abiotic processes consumed over 30% of the added 15NH4+ within minutes of adding the label to sterilized soil. Extracting a subset of soil cores at the beginning of an incubation is recommended for obtaining initial pool size estimates. Gross immobilization is probably stimulated by addition of inorganic 15N substrate and, therefore, is overestimated by the isotope dilution method. As an alternative method, a non‐linear equation is given for calculating the gross immobilization rate from the appearance of 15N in chloroform‐labile microbial biomass; but incomplete extraction of biomass N may result in low estimates. Details of the isotope dilution methodology (injection rates, concentrations, experimental artefacts, etc.) are described and discussed. When care is taken to understand the underlying assumptions and sources of error, the isotope dilution method provides a powerful tool for measuring gross rates of microbial transformations of soil nitrogen in intact soil cores.
Image analysis and three‐dimensional modelling of pores in soil aggregates
Authors: GLASBEY C. A. , HORGAN G. W. , DARBYSHIRE J. F. 
Published: July 2006

SUMMARYThree cross‐sections of soil aggregates (2–5 mm diameter) were digitized at 5 μm resolution from montages (× 100) of scanning electron micrographs to produce binary images representing the soil pores and soil matrix. A three‐dimensional random Boolean process was chosen as a model of the soil pores and matrix. The soil matrix was simulated by randomly positioned, overlapping spheres with radii drawn from an exponential distribution. Simulation of a 1 mm cube of one soil aggregate showed that all but 0.1 % of the pore space was connected to the exterior, although only 50% appeared to be connected to the exterior in a cross‐sectional image. Pore spaces able to accommodate different sizes of microorganisms were also investigated. For example, a protozoan with a cross‐sectional diameter of 20 μm could be accommodated in 17% of the pores in a 1 mm3soil cube, although only 11 % of the pores would be accessible to those protozoa on the exterior of the cube.
Poorly ordered hydrous Fe oxides, colloidal dispersion and soil aggregation. I. Effect of humic macromolecules on surface and colloidal properties of Fe (III) polycations
Authors: BARTOLI F. , PHILIPPY R. , PORTAL J. M. , GERARD B. 
Published: July 2006

SUMMARYModel humic macromolecules, obtained by auto‐oxidation of the catechol‐glycine system, were adsorbed on poorly ordered hydrous iron oxides, Fe(OH)2.8. The pH was nearly constant at c. 6 in order to simulate natural soil and river environments. When the amount of organic carbon adsorbed on 1 g of poorly ordered ferrihydrite increased from 0 to 70 mg, the ligand OH exchange was very small, but the zero point of charge of suspensions progressively shifted from 7.3 to 5.6, and net surface charge, which was initially positive, progressively became negative, suggesting an adsorption mechanism with positive charge neutralization. Consequently, colloidal stability changed from rapid to slow flocculation. The ferrihydrite‐haematite exothermic reaction partially shifted from 400°C to higher temperatures as a function of adsorbed organic matter, and ferrihydrite solubility progressively increased by formation of soluble iron‐organic complexes.These results were explained more satisfactorily by the concept of colloidal organ‐ mineral association than by organic coatings on surfaces.
Evaluation of similar‐media scaling and a one‐parameter model for estimating the soil water characteristic
Authors: WILLIAMS R. D. , AHUJA L. R. 
Published: July 2006

SUMMARYTwo simple methods for estimating the soil water characteristic curve from saturated soil water content, or even just the soil bulk density, plus one other measured point on the curve (such as the water content at a matric potential of –33 kPa) were evaluated. A similar‐media scaling approach and the one‐parameter model of Gregson et al. were compared for eight diverse soils from within the USA. The scaling method also requires knowledge of one complete curve to serve as a reference. The one‐parameter model was extended to include the residual water content, and the soils were divided into three textural groups for the analysis. Visual comparison of the calculated vs. measured soil water content for both methods showed less scatter in the relationship to the 1:1 line, concomitant with smaller calculated error terms, for the one‐parameter model. These results demonstrate that the one‐parameter model is better than similar‐media scaling in estimating soil water content.
Effect of iron oxide on phosphate sorption by calcite and calcareous soils
Authors: HAMAD M. E. , RIMMER D. L. , SYERS J. K. 
Published: July 2006

SUMMARYPure calcite (AR grade CaCO3) was treated with ferrous perchlorate solution to give a surface coating of iron (Fe) oxide. Maximum sorption (xm) of phosphate (P) by the calcite increased from 18.2 to 160 mg P kg−1 as the amount of coating increased from 0.00 to 16.0 g Fe2O3, kg−1 CaCO3. Evidence for Fe oxide coatings on carbonate minerals in two Sudanese soils was obtained by optical microscopy and electron‐probe microanalysis. The relative contributions of carbonate and Fe oxide minerals, and Fe oxide coatings to P sorption in these soils were calculated, based on an assumed model of oxide distribution. Separate‐phase Fe oxide was the major contributor (30–40%) to P sorption in the soils; the Fe oxide coatings on carbonate minerals were only minor contributors (< 6%), and the contribution of uncoated carbonate minerals was found to be negligible (<1 %). These results suggest a very minor role for carbonate minerals, even when coated with Fe oxide, in the sorption of P by these calcareous, Sudanese soils.
Determination of aluminium activity from measurements of fluoride in acid soil solutions
Authors: MUNNS D. N. , HELYAR K. R. , CONYERS M. 
Published: July 2006

SUMMARYTrivalent aluminium (Al) in solutions extracted Centrifugally from soils with pH ranging from 3.3 to 5.8 in 0.01 M CaCl2was estimated from: (i) iterative computation using total Al (pyrocatechol violet), pH, major ions and Al ligands (PCV + GEOCHEM); (ii) 15‐s reaction with 8‐quinolinol (8Q); and (iii) electrode measurements of free and Al‐complexed fluoride. Fluoride and hydroxyl complexes were major Al‐components. With decreasing pH, complexed and total F increased along with Al, but free F decreased. Results from PCV + GEOCHEM and 8Q were consistent with each other and with solubilities of the clay minerals in the soils. Relative to these, the F‐electrode method increasingly overestimated Al as pH increased and Al decreased; its evident failure was not attributable to La interference, OH interference, or the uncertainty of electrode calibration at F activities below 10−6M.
Selenium retention in the organic matter of Swedish forest soils
Authors: GUSTAFSSON J. P. , JOHNSSON L. 
Published: July 2006

SUMMARYFractions of selenium present in the soil profiles of three Swedish podzols were analysed using a sequential extraction scheme to characterize Se distribution among the organic and inorganic fractions. The process by which selenite deposited from the atmosphere is retained in a podzolic profile rich in organic matter was studied in a column experiment. Selenium present in organic fractions accounted for most of the Se extracted by Na4P2O7/NaOH. All soil organic matter fractions, particularly those in the B horizons, were considerably enriched with Se as compared with plant biomass. The most enriched fraction was that containing hydrophobic fulvates which had C to Se ratios ranging from 33 000 to 80 000. The distribution of Se among the organic fractions differed markedly from that of sulphur.Selenite applied to columns continuously for 67 d was fixed very rapidly upon entering the forest floor layers, with 77% being recovered in the top 2 cm of the forest floor after the experiment. In column leachates from the surface layers, C to Se ratios decreased progressively following Se application. No effect specifically related to Se application was observed for leachates and soil horizons underlying Bs1. The mechanism responsible for the efficient and rapid Se immobilization by organic matter is unknown.
Denitrification losses of nitrogen fertilizer applied to winter wheat following ley and arable rotations as estimated by acetylene inhibition and 15N balance
Authors: GOULDING K. W. T. , WEBSTER C. P. , POWLSON D. S. , POULTON P. R. 
Published: July 2006

SUMMARYWe studied the fate of 222 kg N ha−1 applied in spring as K15NO3 to winter wheat test crops which followed either continuous arable cropping (Arable) or a rotation in which a 3‐year grass/clover ley preceded the wheat (Ley). Denitrification losses (measured by an acetylene‐inhibition method) of over 1 kg N ha−1 d−1 were measured for short periods following heavy rain in mid‐May. However the generally dry and cool weather resulted in accumulated losses by denitrification between fertilizer application and anthesis equivalent to only 5.3% and 3.6% (±2%) of the applied N for the arable and ley treatments respectively. The smaller loss from the ley was despite this treatment containing more inorganic N and available carbon. 15N balance indicated that, at anthesis, 1.5% and 11.5% (± 7%) of the labelled N was lost from the arable and ley treatments respectively. Given the precision of the 15N and the acetylene‐inhibition methods, the results are not significantly different. However, the larger difference between methods for losses from the ley treatment may be an underestimate because 15N balance does not measure losses of unlabelled N. These were probably very small on the arable treatment but could have increased total N loss by 25% to c. 32 kg ha−1 on the ley treatment compared with the 8 kg ha‐1 measured as denitrified. Such a large difference is unlikely to be an error but was probably due to ammonia volatilization from this crop which was severely infected by mildew. The results were thus a poor test of the acetylene‐inhibition method, but revealed another loss process which could be significant in some situations.
Influence of electrolyte composition and pH on cadmium sorption by an acid sandy soil
Authors: BOEKHOLD A. E. , TEMMINGHOFF E. J. M. , Van der ZEE S. E. A. T. M. 
Published: July 2006

SUMMARYExtraction of soil with CaCl2, has been recommended as a measure of bioavailability of heavy metals. Interpretation of soil extraction data in terms of plant uptake potential may improve when the chemical behaviour of heavy metals in these extracts is ascertained. The effect of pH, Cd complexation by Cl, and competition between Cd and Ca on Cd sorption was studied at an ionic strength of 0.03 m. Sorption of cadmium was measured in 0.01 m CaCl2, in 0.01 m Ca(NO3)2, in a mixture of 0.02 m NaCl and 0.01 m NaNO3, and in 0.03 m NaNO3, at different values of pH ranging from 3.8 to 4.9. Adsorption isotherms were all linear, with a negative intercept on the y‐axis. This intercept indicated (linear) desorption of only part of the initial soil Cd content. About 50% of the Cd in solution was complexed in the presence of 0.02 m Cl at ionic strength of 0.03. Due to competition between Cd and Ca, sorption of Cd was reduced by 80% in the Ca‐electrolytes as compared with the Na‐electrolytes. Sorption was highly sensitive to pH as each 0.5 unit increase in pH resulted in twice as much sorption of Cd. An empirical factor in the sorption equation that accounts for this effect of pH showed a similar response to changes in pH as a mechanistic factor. This mechanistic factor was developed by assuming that Cd and protons sorb onto the same sites and that a two‐site Langmuir sorption isotherm for protons was able to describe the titration curve of the soil. This similarity may explain the successful application of the empirical factor in this and previous studies.