bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anion Sorption on a Calcareous, Montmorillonitic Soil—Arsenic
Authors: Goldberg Sabine , Glaubig R. A. 
Published: July 2010

AbstractArsenic sorption on a calcareous, montmorillonitic soil was investigated as a function of solution pH (2–11) at two initial As concentrations (2.0 and 20 mmol m−3). Arsenite sorption could not be determined because oxidation of arsenite occurred during the experiment. Arsenate sorption increased with increasing pH, exhibited a maximum near pH 10.5, and decreased at higher pH. Arsenate sorption as a function of pH was studied on reference minerals representative of the dominant inorganic constituents of the soil: montmorillonite, kaolinite, and calcite. Arsenate sorption on the two clay minerals increased at low pH, exhibited a peak near pH 5, and decreased at higher pH. Arsenate sorption on the calcite increased from pH 6 to 10, peaked between pH 10 and 12, and decreased above pH 12. The constant capacitance model was able to describe arsenate sorption on kaolinite over the entire pH range studied and on montmorillonite and soil below pH 9. The soil sorption maximum near pH 10.5 was much reduced after removal of carbonates, indicating that carbonates play a major role in arsenate sorption above pH 9. Arsenate sorption on soil and calcite was unaffected by the presence of equimolar selenite concentrations.
Evaluation of Nitrogen‐15 Tracer Techniques for Direct Measurement of Denitrification in Soil: I. Theory
Authors: Boast C. W. , Mulvaney R. L. , Baveye P. 
Published: July 2010

AbstractMass spectrometric procedures for determination of dinitrogen (N2) and nitrous oxide (N2O) evolved during denitrification in soil treated with 15N‐labeled fertilizer are based on the hypothesis that the nitrate (NO−3) undergoing denitrification can be assumed to exist in a single pool that is isotopically uniform. In the work reported, it is shown that 15XN (the average mole fraction of 15N in the NO−3 undergoing denitrification) will be overestimated when this assumption is invalid. Moreover, it is proved mathematically that the amount of N2 or N2O evolved is underestimated when 15XN does not exceed 0.5. This proof does not hold for higher values of 15XN, but it is concluded that underestimation also occurs in these cases, because no exceptions were found in over three million computer simulations involving evolution of N2 from multiple pools having 15N enrichments as high as 99.6 atom %.
Heat Units for Describing Carbon Mineralization and Predicting Net Nitrogen Mineralization
Authors: Honeycutt C. W. , Zibilske L. M. , Clapham W. M. 
Published: July 2010

AbstractRate constants that describe C and N mineralization vary due to the changing complexity of the C compounds decomposed. Both economic and environmental concerns point to the importance of predicting net N mineralization from plant materials whose decomposition is initially characterized by net N immobilization. This study was conducted to examine the potential of the heat unit concept for describing C mineralization and for predicting the onset of net N mineralization from soil amended with an organic material. Rates of 0 and 59 g kg−1 papermill sludge were added to a soil and incubated at 5, 10, 15, 20, 25, and 30 °C at constant water content in the laboratory. Carbon mineralization rates varied with temperature and apparent substrate complexity, but a nearly identical amount of C (4.7 to 5.3 g kg−1 soil) was mineralized before the beginning of net N mineralization. The cumulative heat input resulting in that amount of evolved C was within the same range (600 to 684 degree days) for the 10 to 25 °C treatments. The number of degree days accumulated until commencement of net N mineralization was also similar for these four temperature treatments. Field microplots were established with 0 and 59 g kg−1 papermill sludge amendment rates. Commencement of net N mineralization in the field occurred at approximately 649 degree days, a value in close agreement with laboratory study results. These data suggest the heat unit concept may be useful for collectively describing mineralization of C fractions with contrasting decomposability, it may allow prediction of the onset of net N mineralization, and it may also serve as a method for linking laboratory and field studies of such biological processes as those studied here.
Effect of Residual Profile Nitrate on Corn Response to Applied Nitrogen
Authors: Bundy L. G. , Malone E. S. 
Published: July 2010

AbstractResidual profile NO3 significantly affects crop N fertilizer requirements in semiarid regions, but little information is available on the influence of profile NO3 on crop response to applied N in humid climates. Experiments were conducted on three well‐drained silt loam soils to investigate profile NO3 accumulation and retention and to determine the effect of profile NO3‐N on corn (Zea mays L.) response to applied N under humid climatic conditions. In 1983, spring preplant N (0, 134, 268, or 402 kg N ha−1) was applied to corn at each location. Fall 1983 profile NO3‐N to 90 or 120 cm was linearly related to 1983 N rate and ranged from 52 to 644 kg N ha−1. Overwinter retention of fall profile NO3‐N varied from 45 to 66% among locations in a year with above normal fall to spring precipitation. Original plots at all locations were split in 1984, and preplant N rates of 0, 78, 156 or 234 kg N ha−1 were superimposed on each 1983 N treatment. Corn yields in the absence of applied N and yield response to added N were significantly affected by spring profile NO3‐N content. With no applied N, profile NO3‐N to 90 cm accounted for 84% of the variation in yield at the most responsive site. Grain yields were maximized (8.5 to 9.5 Mg ha−1) in the absence of applied N where profile NO3‐N to 90 cm was >150 kg N ha−1. Similarly, yields were not increased by applied N where profile NO3‐N exceeded 150 kg N ha−1. These results indicate that profile NO3‐N significantly affects corn response to applied N on some Wisconsin soils. Adjustment of N recommendations for profile NO3‐N should allow more accurate prediction of corn N fertilizer requirements on these soils when substantial overwinter carryover of profile NO3‐N occurs.
Variability of Northwest Florida Soils by Principal Component Analysis
Authors: Collins M. E. , Ovalles F. A. 
Published: July 2010

AbstractTwenty soil properties from 151 pedons were evaluated (i) to select the statistically‐important ones influencing soil variability and (ii) to test if these were actually differentiating properties. Approximately 83% of the pedons studied were Ultisols. Three sets of data were used for the statistical analysis of soil properties (i) weighted‐averages in individual pedons, (ii) data from the first A (A, Ap or Al) horizon, and (iii) data from Albany, Dothan, and Orangeburg soil series. The latter data were tested by a nested analysis of variance to find out if the properties selected were actually differentiating properties. Principal component analysis (PCA) was used as an unbiased method to make the selection. The first five principal components (PCs) explained more than 73% of the total variance. Analyses of eigenvectors, collinearity, and correlation coefficients between soil properties and PCs were also employed. Total sand, fine sand, clay, and organic carbon contents were selected by the PCA as the important properties. These properties except fine sand were validated by a nested analysis of variance. The analysis of variance indicated these properties had a large variation among soil series and/or among horizons within the same soil series.
Measuring the Spatial Variability of Soil Hydraulic Conductivity Using an Automatic Neutron Moisture Gauge
Authors: Moutonnet P. , Pluyette E. , El Mourabit N. , Couchat P. 
Published: July 2010

AbstractSoil internal drainage was measured along a 100‐m transect with 20 neutron probe access tubes at 5‐m intervals using an automatic neutron moisture gauge and a tensiometer data logger. Geostatistical analysis of the measurement results (in terms of hydraulic conductivity, K, vs. water content, θ) at depths of 60 and 90 cm, showed no autocorrelation among the sites. Measurement results related to depths of 120 and 150 cm were deleted because of the lack of a unit hydraulic gradient. Variance analysis indicated that the 60‐ and 90‐cm layers values could be considered together as a unique soil layer. The exponential regression equation computed from 240 K(θ) pairs, gave correlation coefficient of 0.90 for this soil layer. The K variation coefficient between 32 and 40% θ was 75% for the 60‐ and 90‐cm soil depths. This value is consistent with other published findings.
Phosphorus Adsorption by Kaolinite and Montmorillonite: I. Effect of Time, Ionic Strength, and pH
Authors: Bar‐Yosef B. , Rosenberg Rivka , Kafkafi U. , Sposito G. 
Published: July 2010

AbstractPhosphate reactions in soils are affected by various factors operating simultaneously. The objective of this work was to study specific effects of total P concentration, pH, ionic strength, and equilibration time on P partitioning between solid and solution phases of Ca‐ and K‐kaolinite and ‐montmorillonite suspensions as model systems of soils containing these minerals. Phosphorus concentration in the solution phase (Cp) stabilized within 24 to 48 h after introducing P into the system. Increased electrolyte concentration, which elevated the electrical conductivity (EC) from 0.2 to 5.0 dS/m, decreased Cp in both clay systems. Further increase to about 40 dS/m had a negligible effect on Cp. Phosphorus adsorption by Ca‐clay exceeded that by K‐clay. This, and the effect of EC on Cp are suggested to operate via their effect on the extent of the diffuse double layer, which determine the accessibility of P to adsorption sites on clays' edges. Phosphorus solution concentration as a function of pH was minimal in the studied clays around pH 6. In the investigated pH range (5–9), P partitioning was controlled by adsorption, which could be described by a modified Langmuir model. The model accounts for effects of Cp and pH on adsorption and considers retention of individual P species by the adsorbent.
Dynamics of Aluminum Complexation in Multiple Ligand Systems
Authors: Anderson Michael A. , Bertsch Paul M. 
Published: July 2010

AbstractThe role of complexing ligands in attenuating aluminum (Al) toxicity and in influencing Al transport in soils and waters has been recognized for some time though the kinetics of such complexation reactions within complicated multi‐ligand aqueous solutions have not been previously evaluated. As a result, this study was undertaken to examine the dynamics of Al complexation in the presence of multiple ligands, specifically fluoride (F), oxalate (Ox), and citrate (Cit), utilizing an ion chromatographic speciation method. The rate constant for formation (kf) of AlF2+ under the experimental conditions used in this investigation was found to be 12.3 ± 1.1 M−1s−1 in the absence of competing ligands, but was observed to increase to 23.4 ± 0.6 and 52.0 ± 5.7 M−1s−1 in the presence of Ox and Cit, respectively. The rate of formation of the AlOx+ complex was more rapid than that of AlF2+ (kf ≃ 100 M−1s−1) and was unaffected by the presence of F. Citrate complexed with Al sufficiently rapid that kf could not be determined. That kf for AlF2+ increased in the presence of competing ligands contradicts the accepted dogma on the kinetics of concurrent reactions, where reactions are envisioned to proceed independently and in relative isolation. This aberrance can be explained by one of two possible mechanisms: (i) the rapidly complexing Ox and Cit form reduced charge Al‐species with resultant increased rates of water exchange (k); the increased kH2O exceeds the reduction in the extent of outer sphere Al‐F association, thus creating a condition favorable for inner sphere penetration of F through displacement of a coordinated water molecule with ejection of inner sphere Ox or Cit; or (ii) F may exchange directly with inner sphere Ox or Cit, perhaps through HF. Additionally, AlCit formation in the presence of F was found to exceed the thermodynamically imposed equilibrium level and necessarily reequilibrated to a lower solution concentration as the slower Al‐F complexation reaction proceeded, though no such behavior was witnessed for AlOx+ formation in the presence of F.
Effects of Terpenoids on Nitrification in Soil
Authors: Bremner J. M. , McCarty G. W. 
Published: July 2010

AbstractIt has recently been hypothesized that vegetation in ponderosa pine (Pinus ponderosa Dougl.) ecosystems inhibits nitrification in these systems by releasing volatile terpenoids that retard oxidation of NH+4 by nitrifying microorganisms. This hypothesis is based largely on observations that exposure of a ponderosa pine ecosystem to fire decreased the amount of volatile organic compounds and stimulated production of NH+4 and NO−3 in the forest floor and that exposure of soil samples to vapors from a terpenoid mixture decreased production of NH+4 and NO−3 by mineralization of organic N in these samples. To test the validity of this hypothesis, we studied the effects of different amounts of six terpenoids (α‐terpinene, limonene, myrcene, α‐pinene, β‐pinene, and α‐phellandrene) on nitrification in soils incubated at 25 °C after treatment with (NH4)2SO4. The results showed that the terpenoids studied did not significantly affect nitrification in soil even when the amounts applied greatly exceeded the amounts that have been reported to occur in soil. They also indicated that the apparent inhibition of nitrification observed when soils were exposed to terpenoid vapors was due to immobilization of ammonium N by microbial activity stimulated by the organic C in these vapors.
Controls on Natural Nitrogen‐15 and Carbon‐13 Abundances in Forest Soil Organic Matter
Authors: Natelhoffer K. J. , Fry B. 
Published: July 2010

AbstractWe used δ15N and δ13C measurements to study formation and decay of soil organic matter in surface soils of two oak (Quercus spp.) forests in Wisconsin. There were two controls of soil isotopic compositions: new litter inputs and overall isotopic fractionation during decomposition. Litter inputs lowered soil δ15N and δ13C values while decomposition increased δ15N and δ13C values. Leaf and root litter inputs averaged −3.8 and −1.6‰ δ15N and −27.3 and −28.2‰ δ13C, respectively. Field experiments showed that low surface soil δ15N and δ13C values resulted when litter inputs were high. Laboratory experiments showed that overall isotopic fractionation during decomposition left residual soil N and C enriched in 15N and 13C, and could explain the high δ15N and δ13C values observed in deeper forest soils (+5.9‰ δ15N and −23.6‰ δ13C for 10 to 20 cm soils). Our results suggest two pools of naturally labeled N in forest soils: surface N with low δ15N values and subsoil N with high δ15N values. Natural abundance measurements of soil N may be useful for following the importance of these two N pools in forest N cycles. We found no evidence for selective preservation of 13C depleted litter components, such as lignin, during long‐term decomposition in forest soils.
Comparison of Percolation Test Results and Estimated Hydraulic Conductivities for Mollisols and Alfisols
Authors: Bicki Thomas J. , Fenton Thomas E. , Luce Harvey D. , Dewitt Thomas A. 
Published: July 2010

AbstractPercolation tests were performed on an array of biosequences, topo‐drainage sequences, and stage of profile development sequences of soils in Iowa and results were compared to estimated subsoil hydraulic conductivities from Soil Interpretation Records. Within a biosequence, Mollisols had higher percolation rates and lower coefficients of variation than Alfisols. The difference in permeability was attributed to higher subsoil clay content, higher subsoil bulk density, more continuous argillans, and stronger subsoil consistence in Alfisols. High coefficients of variation for percolation rates in Alfisols were attributed to large diameter root channels, lateral flow of water on sloping sites, and increased distinctness of subsoil horizon boundaries. Percolation rates of Mollisols commonly exceed Soil Interpretation Records' estimates of hydraulic conductivity by a factor of two or three while percolation rates of Alfisols approximate estimated subsoil hydraulic conductivity. In soils without argillic horizons, percolation test results of topo‐drainage sequences are similar and reflect similar morphological characteristics. Soil Interpretation Records assign slower estimated hydraulic conductivity to some topo‐drainage sequences as drainage becomes more restrictive. Percolation rates decreased in topo‐drainage sequences of soils with argillic horizons as drainage became more restrictive, even though morphological characteristics were quite similar. Differences in percolation rates within topo‐drainage sequences may reflect errors inherent in the procedure. Additional permeability data is needed to quantify and more accurately estimate subsoil hydraulic conductivity. Criteria used to establish estimated hydraulic conductivity in Soil Interpretation Records should be applied consistently among biosequences and topo‐drainage sequences.
Estimating Confidence Bands for Soil‐Crop Simulation Models
Authors: Shaffer M. J. 
Published: July 2010

AbstractA general method is described that provides confidence bands for the ouput from soil‐crop simulation models. Stochastic data are generated for model inputs and model coefficients. These data reproduce the statistical characteristics of the climate, soil properties, and internal model coefficients including distributions, temporal, spacial and variable cross correlations, means, and standard deviations. Model output based on these inputs is then analyzed to produce means, standard deviations, and confidence bands. A typical application of the method is illustrated using a stochastic model for soils input data together with the nitrogen‐tillage‐residue management (NTRM) simulation model to generate confidence bands for soil NO3‐N profiles in Houston County, MN. Results indicate that 380 to 1800+ computer runs may be required to provide confidence bands for soil NO3‐N concentrations that are within 10% of the means, and that use of singular mean input data sets in a nonlinear model such as NTRM can produce deviations in the simulated results ranging from 0.7 to 101% of the mean output obtained from many runs.
Nature of Cementing Materials in Ortstein Horizons of Selected Florida Spodosols: II. Soil Properties and Chemical Form(s) of Aluminum
Authors: Lee F. Y. , Yuan T. L. , Carlisle V. W. 
Published: July 2010

AbstractPossible differences in soil characteristics between ortstein and nonortstein Spodosols were studied. Organic C, fine particles (silt plus clay), and extractable Al by dithionite‐citrate, pyrophosphate, acid NH4 oxalate, and NaOH were all higher in Bh than other horizons, except silt plus clay contents in Btg horizons of the St. Lucie County soils. While dithionite‐citrate‐extractable Si was higher at the surface, larger amounts of Fe seemed to occur in lower horizons. Both contents were much lower than extractable Al with the exception of Si in the A and E horizons. Quartz, gibbsite, kaolinite, and hydroxy‐Al interlayered vermiculite were dominant clay‐size minerals. In general, no consistent differences were found in soil properties between the paired ortstein and nonortstein Spodosols except that the ortstein horizons contained more clay and more extractable Al. The cementing materials were shown to dissolve in reagents commonly used for Al and Fe extractions. The dithionite‐citrate reagent was the most effective extractant. The amounts of extractable Al and Fe by dithionite‐citrate, acidic oxalate, and NaOH were small after the ortstein samples were treated with pyrophosphate. These findings suggested that Al in the cementing materials was likely in organic complex form. Ratios of pyrophosphate‐extractable Al to oxalate‐extractable Al and the percentage of maximum Al‐organic complexes supported this assumption. Higher fulvic‐C contents and higher fulvic‐C to humic‐C ratios in ortstein than in nonortstein spodic horizons indicated the complex probably was an Al‐fulvate form.
Effect of Clay Charge Density and Adsorbed Ions on the Rheology of Montmorillonite Suspension
Authors: Keren R. 
Published: July 2010

AbstractThe rheological characteristics of montmorillonite suspension as a function of exchangeable sodium percentage (ESP), (when the complementary cation is either Ca2+ or Mg2+) and specific electrostatic charge density were studied in aqueous media at a clay concentration of 25 g kg−1, at pH 7 and temperature of 25 °C. The suspension showed a Newtonian rheology when the clay was saturated by either Ca2+ or Mg2+, but the differential viscosity (the derivative of shear stress with respect to shear rate at a given shear rate) of Mg‐clay (2.3 mPa s) was higher than that of Ca‐clay (1.5 mPa s). The higher value for the Mg‐clay suspension is due to the smaller average number of platelets in a tactoid of Mg‐montmorillonite than in the Ca‐montmorillonite suspensions. Introducing Na+ at a low percentage (10%) into the exchange complex of Mg tactoid was enough to break down some of the tactoids to smaller ones, whereas the Ca tactoids remained stable. The differential viscosity at high shear stresses increases with increases in ESP, showing higher values for Na/Mg systems at a low ESP range. At higher ESPs, no difference in differential viscosity between Ca and Mg systems was observed. The higher extrapolated shear stress values for Na/Mg‐montmorillonite suspensions suggest that the number of linkages between clay particles per unit weight of clay is higher than that found in Na/Ca‐montmorillonite for the same ESP and clay concentrations. The differential viscosity and the extrapolated shear stress values for the various smectites (the electric charge density varied between 0.91 and 1.22 molc kg−1) suggest that the extent of particle‐particle interaction in clay suspension decreases with increases in electrostatic charge density of smectites.
A Computer Simulation of Fe(III) and Fe(II) Complexation in Limited Nutrient Solution: I. Program Development and Testing
Authors: Schwab A. P. , Lindsay W. L. 
Published: July 2010

AbstractThe mechanism by which Fe‐stressed roots increase Fe availability was determined with the assistance of a computer model (written in PASCAL) that predicted the effects of redox and pH on the stability of Fe chelates. The program solves a series of simultaneous equilibrium equations to calculate the concentrations of all species in a nutrient solution containing Fe, Ca, and two competing chelating agents as a function of pH and redox potential. Experimental data were used to test the model. Model calculations based on results published by other investigators supported the theory that Fe‐deficient soybean [Glycine max (L.) Merr.] plants have the ability to lower the redox potential near their roots. It also showed that this phenomenon is the primary means by which iron‐stressed plants are able to increase the availability of Fe. The redox potential of a nutrient solution at pH 5 must be below pe + pH 7 to account for observed trends in the stability of ferric chelates and the availability of Fe to soybean.