bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cadmium Sorption to Soil Separates Containing Layer Silicates and Iron and Aluminum Oxides
Authors: Zachara John M. , Smith Steve C. , Resch Charles T. , Cowan Christina E. 
Published: July 2010

AbstractIon exchange to fixed charge sites and surface complexation to hydroxylated sites are recognized to affect Cd aqueous concentrations in soil; however, the individual contribution of these reactions to Cd sorption in mineralogically complex material has not been documented. The objective of this study was to isolate the contributions of fixed charge and hydroxylated sites to Cd sorption in two Ultisol subsurface horizons that contained kaolinite, 2:1 layer silicates, and crystalline Fe and Al oxides. Cadmium sorption was measured on clay‐sized isolates (<2.0 µm) from the soil materials in NaClO4 electrolyte at ionic strength (I) = 0.1, 0.01, and 0.001 mol L−1 with pH ranging from 4 to 9 and Cd concentrations ranging from 2 × 10−8 to 3 × 10−5 mol L−1. Comparative experiments were also performed with smectite (SWy‐1), kaolinite (KGa‐1), and crystalline and amorphous Fe oxides to evaluate the potential contribution of ion exchange and surface complexation reactions on these phases to Cd sorption in the isolates. Ion exchange of Cd2+ on layer silicates dominated Cd sorption within the isolates when I was ≤0.01 mol L−1 and the pH was less than ≈6.5. Sorption of Cd on hydroxylated sites on the edges of the layer silicates or on Fe or Al oxides, and/or exchange of CdOH+ on the fixed‐charge sites of the layer silicates, dominated Cd sorption at I = 0.1 mol L−1, and when the pH was greater than ≈6.5 at any I. Below pH 6.5, the magnitude of the sorption was controlled by the cation‐exchange capacity of the isolates, which, in turn, was related to their relative proportions of kaolinite and 2:1 layer silicates. By comparing the Cd sorption on the isolates to that on (i) dithionite‐citrate‐bicarbonate (DCB) treated islates and (ii) DCB‐treated isolates augmented with Fe oxides, it was concluded that crystalline Fe oxides were not significant sorbents of Cd. Instead, the Fe oxides appeared to be associated with the layer silicates by a particle interaction that blocked access of Cd to fixed‐charge sites on the layer silicates.
Use of Magnetic‐Susceptibility Measurements in Assessing Soil Uniformity in Chronosequence Studies
Authors: Fine Pinchas , Singer Michael J. , Verosub Kenneth L. 
Published: July 2010

AbstractRecent observations show that soils with vertical morphological differentiation often exhibit a distinct ferrimagnetic profile with the magnetic susceptibility (MS) of eluvial horizons enhanced with respect to that of illuvial, Cr, or R horizons. In addition, pedogenic ferrimagnetic material is mostly superparamagnetic (SP) and single domain (SD) (<30 nm), whereas inherited titanomagnetites are predominantly multidomain (MD) grains. We suggest that the continuous pedogenic development of a soil profile in homogeneous parent material results in enhancement of MS and in a gradual shift from MD to SD and SP magnetic states, and that deviations from this pattern arise from discontinuities in the soil or from climatic or topographic changes. This hypothesis was tested on 18 northern California pedons, formed in four marine and river terrace systems and in volcanic parent material. The ages of the terraces range from 600 yr to 1.6 million yr and the MS of the parent materials range from 10 to > 1000 × 10−8 m3 kg−1. Established chronosequence members were used to determine that enhancement of MS and shifts in magnetic domain state are correlated with age. Exceptionally large or small magnetic susceptibilities throughout the soil profile, lack of magnetic enhancement, and discontinuous magnetic profiles in other soils could each be related to morphologically or chemically determined discontinuities. Thus, magnetic susceptibility, an easily measured soil attribute, can be used to evaluate the suitability of pedons for chronosequence studies.
Crop Response to Ferrous Sulfate in Banded Gels of Hydrophilic Polymers
Authors: Mortvedt J. J. , Kelsoe J. J. , Mikkelsen R. L. 
Published: July 2010

AbstractIron deficiences are widespread and difficult to correct by soil application. Banded hydrogels containing FeSO4 have the potential to act as a matrix for minimizing contact of the applied Fe with soil. Three greenhouse pot experiments were conducted to determine response of grain sorghum [Sorghum bicolor (L.) Moench] to FeSO4 banded alone or with hydrated commercial gel‐forming polymers in Epping silt loam (loamy, mixed (calcareous), mesic, shallow Ustic Torriorthent), a calcareous, Fe‐deficient soil. Sorghum dry‐matter production and Fe uptake after 6‐wk growth periods were highest with FeEDDHA and lowest with FeSO4, each banded alone. Plant availability of applied FeSO4 was increased by banding FeSO4 in some hydrated polymers (mainly polyacrylamides). Apparently, the banded gels provided an environment that maintained the included FeSO4 in a more available form, which resulted in greater crop response to the applied Fe. Results of a laboratory experiment indicated that band application of FeSO4 in hydrated polymers did not affect the rate of oxidation of the applied Fe2+ to Fe3+. However, total extractable Fe (by 0.05 M HCl + 0.0125 M H2SO4 or by 1 M HCl) was higher in soil near banded hydrated FeSO4 with polymer formulations than FeSO4 banded alone. This suggests that the applied FeSO4 had reacted with soil to a much greater extent when it was banded alone rather than with the hydrated polymers.
Parameter Estimates of Field Solute Transport Models Based on Time Domain Reflectometry Measurements
Authors: Elrick D. E. , Kachanoski R. G. , Pringle E. A. , Ward A. L. 
Published: July 2010

AbstractA new technique using vertically installed time domain reflectometry (TDR) probes can be used to measure the mass flux of solute past the ends of the TDR probes and characterize the probability density functions of travel times. The procedure is applicable for a conservative tracer under steady‐state leaching conditions of constant surface volume flux density of water. The procedure is, however, limited to soils low in salts where the addition of a solute spike will cause a measurable reduction in the TDR signal. We developed the transport equations used to analyze the breakthrough data and obtain the appropriate parameters of two steady‐state models, the convective dispersion equation and the convective lognormal transfer function, as well as a moment analysis. Other models could also have been used. The TDR measurements (reduced in terms of the maximum measured value) for a Dirac‐delta function (spike) input of solute are shown to be equivalent to the solution of a step function input of pure water at the surface to a soil containing unit concentration to infinite depth, i.e., the complement of the flux‐averaged reduced concentration for a step function input of solute. Nonlinear curve‐fitting techniques were used to obtain the transport parameters. Fitting the measured TDR readings to the two models for both field and laboratory data gave good estimates of the transport parameters. The moment analysis, however, reflected the early breakthrough and tailing of the solute, resulting in a doubling of the variance. In addition, variances at the averaged field scale were found to be slightly more than double those at the local scale. The field TDR procedure is fast, inexpensive and nondestructive; the analysis presented yields needed parameters for model predictions.
Dynamic Oxygen and Carbon Dioxide Exchange between Soil and Atmosphere: I. Model Development
Authors: Ouyang Y. , Boersma L. 
Published: July 2010

AbstractThe rate of exchange of O2 and CO2 gases between soil and atmosphere is controlled by atmospheric and soil physical and biological conditions. Analysis and evaluation of problems in soil biology and soil ecology would be greatly facilitated by the availability of a mathematical model that predicts concentrations of these gases as a function of time and soil depth as well as the rate of gas exchange at the soil surface. Our objective was to develop such a model, driven by time‐dependent functions for solar radiation, rainfall, air temperature, and relative humidity of the atmosphere. Outputs of the model include concentrations of CO2 and O2, soil water content, soil temperature, and rate of consumption of O2 and production of CO2 by roots and soil microorganisms, all as functions of time and soil depth. Dissolution of O2 and CO2 in soil water, adsorption of O2 and CO2 onto colloidal surfaces of soil particles, and replacement of air by water due to soil wetting and vice versa are accounted for in the model. Rates of respiration by microorganisms and roots and rate of root growth are given as functions of O2 and CO2 concentrations. Not all of the processes or parameters could be included in the model development because of their large number and complexity. The structure of the model consists of time‐dependent simultaneous equations for vertical transport of water, heat, O2, and CO2 through unsaturated soils. Finite difference methods are used to solve the mathematical model.
Ionic Strength Effects on Acidity and Cations Leached from Forest Floor Cores
Authors: Ross Donald S. , Bartlett Richmond J. 
Published: July 2010

AbstractWe treated fresh, intact forest floor core samples with three concentrations of artificial acidic precipitation. No differences in leachate pH were found between the acidic and nonacidic treatments at each concentration (30–300 µmolc L−1). A linear relationship was found between incoming ionic strength and leachate H+, the major cation leached in all treatments. Soil solution extracted in the field was chemically similar to the laboratory leachates. Our findings suggest that the downward movement of acidity in these soils is a function of the ionic strength of incoming leaching water, independent of short‐term incoming acidity.
Color Zonation Associated with Fractures in a Felsic Gneiss Saprolite
Authors: Schoeneberger P. J. , Weed S. B. , Amoozegar A. , Buol S. W. 
Published: July 2010

AbstractDarkly coated fractures are identified as a major type of macropore in most saprolites found in the Piedmont and Mountain regions of North Carolina. Morphological and mineralogical characteristics of various color zones associated with these Mn‐coated fractures were evaluated to determine their nature and assess their role in water flow through saprolite. Four distinct color zones (black, white, yellow, and red) were identified surrounding the Mn‐coated fractures in a typical saprolite derived from gneiss and schist parent rock in the Piedmont region. Two large, vertically oriented intact blocks (30 by 30 by 80 cm) containing fractures and associated color zones were removed from the 1.9‐ to 2.7‐m depth. Small undisturbed samples containing all color zones, and disturbed bulk samples from each color zone were analyzed for mineralogical and chemical composition using x‐ray diffraction, scanning and transmission electron microscopy, Mössbauer spectroscopy, electron microprobe scans, and HF digestion for total elemental analysis. Iron content was highest in the interior saprolite matrix (182 mg/kg of clay‐size fraction in the red zone) and diminished toward the fracture (black zone). The red zone was dominated by hematite (54% of Fe oxide present), the yellow zone was dominated by goethite (92% of Fe oxide present), and the white zone was almost free of Fe. In the black zone, Mn oxides occurred in substantial amounts and Fe was mostly in the form of goethite. Manganese was not detected in the other three color zones. Color patterns and relative amounts of Fe and Mn indicate historical preferential water movement along fractures. Measurement of saturated hydraulic conductivity, however, indicates that these fractures are no longer active macropores allowing rapid water flow through saprolite.
Differences in Soil and Leaf Litterfall Nitrogen Dynamics for Five Forest Plantations
Authors: Gower Stith T. , Son Yowhan 
Published: July 2010

AbstractVegetation can influence N cycling in forest soils; however, it is difficult to isolate the positive feedback of vegetation on N cycling because other factors are often not held constant. The objective of this study was to measure and compare leaf litterfall N and in situ and laboratory N mineralization rates for 28‐yr‐old northern red oak (Quercus rubra L.), European larch (Larix decidua Miller), eastern white pine (Pinus strobus L.), red pine (P. resinosa Aiton), and Norway spruce [Picea abies (L.) Karst.] plantations on a similar soil in southwestern Wisconsin. Average seasonal soil NO‐3 and NH+4 concentrations (mg kg −1) were 3.9 and 3.4 for red oak; 7.7 and 5.8 for European larch; 5.4 and 6.7 for white pine; 4.9 and 5.1 for red pine; and 5.2 and 6.2 for Norway spruce, respectively. Annual in situ net N mineralization in the top 20 cm of mineral soil differed significantly (P < 0.01) among species and ranged from 46 kg ha−1 yr−1 for Norway spruce to 117 kg ha−1 yr−1 for European larch. Annual in situ nitrification differed significantly (P < 0.001) among species and comprised from 42 (red oak) to 95% (European larch) of the total annual net N mineralized. Laboratory net N mineralization rates also differed significantly among the five species. Average annual leaf litterfall N content for a 2‐yr period ranged from 26 kg ha−1 yr−1 for white pine to 40 kg ha−1 yr−1 for Norway spruce but was not correlated to annual net N mineralization. We suggest that leaf litterfall lignin/N may be an important positive feedback mechanism that influences N mineralization.
Multifractal Model for Soil Aggregate Fragmentation
Authors: Perfect E. , Kay B. D. , Rasiah V. 
Published: July 2010

AbstractDry aggregate size and strength distributions are important soil structural characteristics. We present a theoretical model based on multifractals for predicting one characteristic from the other. For a specified stress, σ, the strength of dry aggregates of normalized equivalent cubic length x* was expressed as a probability of failure, {P(x*)}σ. A method was developed for calculating {P(x*)}σ from tensile strength data. At intermediate levels of stress (0.3 ≤ σ ≤ 0.9 MPa), {P(x*)}σ decreased with decreasing x*. A Pareto distribution was used to model this scale dependency. The distribution's parameters, q and r, determine the probability of failure of the largest aggregate and the rate of change in scale dependency, respectively. The r increased and the q decreased logarithmically with increasing σ. The fractal dimension, D, was used to characterize the number‐size distribution of dry aggregates after fragmentation. For mass‐conserving cubic fragmentation, D is related to {P(x*)}σ by the multifractal spectrum, D ≅ log {8(2′ − qx*−r)}/log {2}. Previously published dry‐sieving data were reanalyzed. The number‐size distribution determined by visual counting gave a spectrum of fractal dimensions as predicted by the theory. Values of D ranged from 2.53 at x* = 4.7 × 10−2 to 3.46 at x* = 7.5 × 10−1. The multifractal spectrum was used to estimate q and r inversely. Further research is required to determine the level of stress associated with these values.
Improved Models of Particle‐Size Distribution: An Illustration of Model Comparison Techniques
Authors: Buchan G. D. , Grewal K. S. , Robson A. B. 
Published: July 2010

AbstractWe investigated a relatively unexplored area of soil science: the fitting of parameterized models to particle‐size distribution (a subject more thoroughly explored in sedimentology). Comparative fitting of different models requires the use of statistical indices enabling rational selection of an optimum model, i.e., a model that balances the improvement in fit often achieved by increasing the number of parameters, p, against model simplicity retained by minimizing p. Five models were tested on cumulative mass‐size data for 71 texturally diverse New Zealand soils: a one‐parameter (p = 1) Jaky model borrowed from geotechnics; the standard lognormal model (p = 2); two modified lognormal models (each with p = 3); and the bimodal lognormal model (p = 3). The Jaky and modified lognormal models have not previously been introduced into the soil science literature. Three statistical comparators were used: the coefficient of determination, R2; the F statistic; and the Cp statistic of Mallows. The bimodal model and one modified lognormal model (denoted ORL) best fit the data. The bimodal model gave a marginally better fit, but incorporates a sub‐clay mode (untestable with the present data), so we adopted the ORL model as the physically best benchmark for comparison of other models. The simple Jaky one‐parameter model gave a good fit to data for many of the soils, better than the standard lognormal model for 23 soils. The model comparison methods described have potential utility in other areas of soil science. The Cp statistic is advocated as the best statistic for model selection.
On the Interpretation of Labile Aluminum as Determined by Reaction with 8‐Hydroxyquinoline
Authors: Luster Jörg , Yang Andrew , Sposito Garrison 
Published: July 2010

AbstractThe interpretation of labile Al, as defined operationally by a 15‐s reaction with 8‐hydroxyquinoline, remains problematic. In solutions free of complexing ligands other than OH−, one question is whether the chemical species (Al(OH)+2 should be included. To resolve this issue, labile Al was measured in Al(ClO4)3 solutions at total Al (AlT) concentrations in the range 4 to 60 µmol kg−1 and pH in the range 4 to 6. In solutions equilibrated for 4 h without shaking, no effect of pH in the range 4 ≤ pH ≤ 5 on the values of labile Al was observed. Thus, Al3+ and all significant mononuclear hydrolytic species of Al that formed under the experimental conditions were reactive with 8‐hydroxyquinoline within 15 s. Shaking the sample solutions at pH 5 throughout equilibration, however, produced a gradual decline in labile Al with concomitant changes in light scattering that indicated the formation of colloidal or macromolecular Al species that were unreactive with 8‐hydroxyquinoline during a 15‐s period. Even in unshaken solutions, a decline in labile Al (and the inferred formation of colloidal Al species) was observed at pH 5 if solutions with AlT > 1 mmol kg−1 were used to prepare standard solutions for calibration. These results are important not only for the application of the 15‐s 8‐hydroxyquinoline method, but also for any experimental study of aqueous Al at pH values where Al hydrolysis is significant.
Alkaline Persulfate Oxidation for Determining Total Nitrogen in Microbial Biomass Extracts
Authors: Cabrera M. L. , Beare M. H. 
Published: July 2010

AbstractThe CHCl3 fumigation‐extraction method for determining soil microbial N involves the extraction of CHCl3‐fumigated and CHCl3‐unfumigated samples with 0.5 M K2SO4, followed by determination of total N in the extracts. Total N is typically determined by Kjeldahl digestion (TKN) with the inclusion of NO−2 and NO−3 present. The determination of total N by TKN has several procedural constraints such as an initial concentration step, long digestion times, and considerable bumping caused by catalyst salts. In contrast, a persulfate oxidation method (TPN) commonly used for determination of total N in sea‐ and freshwater samples does not require a concentration step and is much simpler and faster than TKN. The objective of this study was to evaluate and adapt the TPN method to measure total N in 0.5 M K2SO4 extracts for determination of soil microbial biomass N. Studies were conducted to optimize reagent/sample (R/S) ratio and autoclaving time, and to evaluate the effects of C and N concentrations. These studies showed that complete N recovery can be obtained with a R/S ratio of 1 and an autoclaving time of 30 min in extracts containing as much as 250 mg glucose‐C L−1 at a C/N ratio of 10:1. A comparison of the optimized TPN method to TKN for extracts of 12 CHCL3‐fumigated soils indicated that the methods gave the same N recoveries. The use of the TPN method in 0.5 M K2SO4 extracts should facilitate more rapid and efficient measurements of soil microbial biomass N.
Dentrification and Mineralization in Soil Amended with Legume, Grass, and Corn Residues
Authors: McKenney D. J. , Wang S. W. , Drury C. F. , Findlay W. I. 
Published: July 2010

AbstractSince cover crops and intercrops are increasingly used to reduce soil erosion and N loss and provide efficient N utilization, it is important to evaluate the consequences of crop residue to N cycling processes. The objectives of this study were to determine effects of incorporating hairy vetch (HV, Vicia villosa Roth subsp. villosa), red clover (RC, Trifolium pratense L.), annual ryegrass (ARG, Lolium multiflorum Lam.), reed canarygrass (RCG, Phalaris arundinacea L.), and corn (Zea mays L.) residues on denitrification, dissimilatory NO−3 reduction, and N mineralization‐immobilization in a Brookston clay loam (fine‐loamy, mixed, mesic Typic Argiaquoll). A gas flow system was used with 5 or 10 g residue kg−1 amended soil. With only anaerobic incubation, all residues stimulated denitrification about equally with net NO and N2O production rates two to three times greater than in the control soil. Ammonium accumulation over the 48‐h anaerobic period was 5 to 11 mg N kg−1. When a 5‐d aerobic incubation preceeded the anaerobic phase, losses of NO + N2O amounted to 5 to 17 times that in the control soil during the anaerobic phase. These losses were: 59.4, 47.1, 25.1, 24.4, 17.6, and 3.5 mg N kg−1 for HV, RC, ARG, RCG, corn, and the control, respectively. Mineralization in the HV treatment occurred from the third to the fifth day of the aerobic incubation and NH+4 continued to increase during the subsequent 2‐d anaerobic period, reaching 58.4 mg NH+4‐N kg−1. Nitrite accumulated during the anaerobic phase in all treatments, with 46 and 49 mg N kg−1 for ARG and HV, respectively, during with the 2‐d aerobic/2‐d anaerobic incubation. With the 5‐d aerobic/2‐d anaerobic incubation, NO−2 levels were lower in all but the ARG treatment.