bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improved Computational Procedure for Retention Relations of Immiscible Fluids Using Pressure Cells
Authors: Liu H. H. , Dane J. H. 
Published: July 2010

AbstractThe capillary pressure‐saturation relation, or the capillary pressure head‐volumetric fluid content relation, is of widespread interest in modeling and predicting multiphase fluid flow. A common procedure to determine this relation is to use a pressure cell and assume uniform distributions of capillary pressure and volumetric fluid contents at static equilibrium. The pressure cell method, however, yields inaccurate results for certain combinations of multiphase fluids and porous media. The sensitivity analysis in this study shows that the pressure cell height, the positions of the pressure measuring devices, which can coincide with the in‐ and outflow ports, and the relative density difference of the fluids, can give rise to considerable errors in the determination of capillary pressure head‐volumetric fluid content relations by the standard procedure using pressure cells. We, therefore, propose a curve‐fitting method that considers nonuniform distributions of capillary pressure and volumetric fluid content of multiphase fluids. The method uses the same input data as commonly used procedures.
Dinitrogen Fixation in Pea: Controls at the Landscape‐ and Micro‐Scale
Authors: Stevenson F. C. , van Kessel C. , Knight J. D. 
Published: July 2010

AbstractTopography influences the distribution of water and N, thereby exerting an indirect control on N2‐fixing activity of legumes. A study was conducted to assess the (i) variability of N2 fixation in pea (Pisum sativum L.) in a rolling field, and (ii) degree of landscape‐scale control on N2 fixation. A 90 by 100 m sampling grid, with 10‐m spacings, was established in the field. Each sampling point was classified as either footslope or shoulder. The percentage of N derived from the atmosphere (% Ndfa) was estimated using natural 15N abundance and the A‐value approaches. Spring soil water content and inorganic N were most concentrated in the footslopes, whereas mean estimates of % Ndfa showed inverted spatial distribution patterns. At flowering, natural 15N abundance estimates of % Ndfa did not differ between shoulders and footslopes. In contrast, A‐value mean estimates of % Ndfa were 84% for shoulders and 92% for footslopes. The two approaches gave similar mean estimates of % Ndfa at maturity, with values of approximately 72 and 84% for footslopes and shoulders. A random spatial pattern existed for total aboveground N accumulation, indicating that pea was able to adjust its N2‐fixing activity according to the available soil N. Despite similar spatial patterns for % Ndfa estimated using the two approaches, the correlation between the A value and natural 15N abundance approaches was poor (r = 0.213 at flowering and r = 0.377 at maturity). The poor correlation suggests that N2 fixation by pea was partially controlled at the landscape scale, whereas strong micro‐scale controls may have existed that ultimately regulated N2 fixation.
Impact of Fertilizer Placement and Tillage System on Phosphorus Distribution in Soil
Authors: Rehm G. W. , Scobbie A. J. , Randall G. W. , Vetsch J. A. 
Published: July 2010

AbstractRepeated use of band applications, both surface and subsurface, of immobile nutrients applicable to a variety of tillage systems raises concerns about the collection of soil samples used for making fertilizer recommendations. This study was conducted to measure the effect of tillage system and fertilizer placement on soil test P in a major part of the root zone. Soil samples were collected from control treatments and from treatments where phosphate fertilizer supplying 29 kg P ha−1 yr−1 had been broadcast, applied as a surface band, or applied in a subsurface band for three consecutive years in a corn (Zea mays L.)‐soybean [Glycine max (L.) Merr.] rotation. These placements were used in both a chisel and a ridge‐till planting system. Soil samples were collected from depths of 0 to 7.5, 7.5 to 15.0, 15.0 to 22.5, 22.5 to 30.0, and 30.0 to 45.0 cm at distances of 0, 7.5, 15.0, 22.5, 30.0, and 37.5 cm from the row. Soil test P, to a depth of 15 cm at each position from the row, was significantly affected by fertilizer placement. Placement also had a significant effect on soil test P to a depth of 30 to 45 cm at a distance of 30 cm from the row. Tillage system had a significant effect on measured soil test P at sampling positions near the row. These results indicate that both tillage system and fertilizer placement could have a major effect on soil test values. If band locations are known, they should be avoided, if possible, during sample collection.
Phosphorus Transport during Transient, Unsaturated Water Flow in an Acid Sandy Soil
Authors: Chen J. S. , Mansell R. S. , Nkedi‐Kizza P. , Burgoa B. A. 
Published: July 2010

AbstractSorbent‐sorbate interactions heavily retard the movement of P during water flow in most soils. The effect of soil/solution ratio on sorption kinetics and movement of P during unsteady unsaturated water flow were investigated. A series of batch experiments with soil/solution ratios ranging from 0.1 to 6.4 Mg m‐3 were conducted to obtain sorption rate coefficients. Aqueous P solutions (100–800 g m‐3) were applied at two constant fluxes (1.4 × 10‐6 and 6.9 × 10‐6 m s‐1) to columns of an air‐dry spodic soil. The experimental data were simulated with a parallel two‐site nonlinear, nonequilibrium transport model during unsteady, unsaturated water flow. Phosphorous sorption followed Freundlich‐type reversible kinetics with a very fast reaction occurring in Type I sites and a slow reaction occurring in Type II sites. The sorption reaction of P in batch experiments was satisfactorily described by the model but the rate coefficients varied with the soil/solution ratio. Experimentally determined rate coefficients described P movement in column experiments at an influx rate of 6.9 × 10‐6 m s‐1, but not for the slower influx rate of 1.4 × 10‐6 m s‐1, hence calibration of rate coefficients was necessary for describing P movement during the slower water influx. We developed a technique for determining rate coefficients under water saturated‐unsaturated conditions that provides a way to validate P transport models during transient, unsaturated water flow.
Macroscopic Capillary Length, Sorptivity, and Shape Factor in Modeling the Infiltration Rate
Authors: Nachabe M. H. 
Published: July 2010

AbstractInfiltration tests in the field involve measurements of sorptivity and macroscopic capillary length. These two parameters are strongly related through the shape factor, which is a measure of the nonlinearity of the soil hydraulic diffusivity. In this study, relationships were developed between the macroscopic capillary length, the sorptivity, and the shape factor and the parameters of the Brooks and Corey and van Genuchten expressions of hydraulic conductivity and diffusivity. These relationships are important for users of numerical models who need to estimate the parameters of these expressions to predict water flow and contaminant transport in soils. Numerical simulations with a dimensionless form of Richards' equation show that the predicted infiltration rate will not be very sensitive to small variations in the shape factor, provided the macroscopic capillary length is the same. This result is encouraging because the shape factor is difficult to determine accurately in the field. The similarity of the dimensional infiltration solutions implies that the macroscopic capillary length is a scale factor, because (i) it renders predictions of infiltration rates fairly insensitive to the expressions of hydraulic conductivity and diffusivity used, and (ii) it reduces the number of parameters needed to characterize infiltration. Therefore, the infiltration curve into a particular soil can be deduced by choosing units of length and time (i.e., scaling) of a generalized infiltration solution.
Model Sensitivity to Measured and Estimated Hydraulic Properties of a Zimmerman Fine Sand
Authors: Wu L. , Allmaras R. R. , Lamb J. B. , Johnsen K. E. 
Published: July 2010

AbstractWater retention and hydraulic conductivity are necessary for simulating solute transport in process‐oriented models because of the fundamental role of water flow. Accuracy and extension of soil hydraulic properties are crucial for using models to give site‐specific predictions, yet these evaluations are infrequent and often lack rigor. The objectives of this study were to compare measured and estimated hydraulic properties and their effects on simulation of field soil‐water regime. Water contents (θ) and hydraulic conductivities (K) at specific matric potentials (ψ) alternatively measured in the laboratory and field or estimated from other soil properties were fitted to water retention and hydraulic conductivity functions to obtain parameters according to the van Genuchten formulation. The estimated parameters were inputs for the Root Zone Water Quality Model to simulate water movement in a Zimmerman fine sand (mixed, frigid Argic Udipsamment). Simulated and in situ measured water contents were compared to assess methods used for measuring or estimating hydraulic properties. Simulation using hydraulic functions generated from field‐measured θ(ψ) and K(ψ) was closest to measured total water depth in the 1.5‐m profile as well as water contents at the 0.2‐m depth. Arbitrary variations of α and n in the van Genuchten equations had larger effects on θ(ψ) and K(ψ) functions compared with variations caused by methods to measure and estimate hydraulic functions. This test demonstrated the crucial role and importance of soil hydraulic properties in simulating water storage and movement even in a sandy soil.
Determining Convective Lognormal Solute Transport Parameters from Resident Concentration Data
Authors: Vanderborght J. , Vanclooster M. , Mallants D. , Diels J. , Feyen J. 
Published: July 2010

AbstractTime Domain Reflectometry (TDR) has become a popular method to obtain time series of resident concentrations in solute transport studies, so effective interpretation of TDR data is very useful. In this study, we evaluated three procedures to determine the parameters of the convective lognormal transfer function (CLT) model from such time series. In a first approach, the CLT model travel time probability density function (pdf) was related to time series of time‐integral‐normalized flux concentrations, Cf*(z,t). The normalization was based on mass balance calculations performed with time series of resident concentrations measured at several depths. The Cf*(z,t) data thus obtained were very erratic leading to a high parameter uncertainty. In a second approach, the CLT model travel depth pdf was related to time series of depth‐integral‐ or mass‐normalized resident concentrations, Crm*(z,t). This approach suffered from uncertainty regarding calibration coefficients relating TDR measured impedance to resident concentrations and from uncertainty regarding the solute mass crossing the sampling volume of the TDR probe. The third approach used the relation between travel time and travel depth pdf for a stochastic‐convective transport process to formulate a new expression relating time‐integral‐normalized resident concentrations, Crt*(z,t), to the CLT model parameters. No information is needed about calibration coefficients while no a priori assumptions about the solute mass detected by the TDR probe are required. This approach yielded better CLT model fits to observed concentration data, and the variability of parameters fitted at different locations can be related to heterogeneity of solute and water flow after averaging across the TDR measurement window.
Fractal Characterization of Aggregate‐Size Distribution: The Question of Scale Invariance
Authors: Logsdon S. D. , Gimenez D. , Allmaras R. R. 
Published: July 2010

AbstractAggregate‐size distributions are often described as fractal based on the power law relationship between cumulative aggregate number and aggregate size. The slope of the natural log of cumulative number of aggregates as a function of natural log of diameter is the fractal dimension. If aggregate density, shape, and relative diameter (diameter as a fraction of the smallest diameter of the size‐class) are scale invariant, then aggregate number can be calculated from mass. These three factors can be combined into a single unknown factor, Gi. The objectives of this study were to test the assumption of a scale invariant Gi and to compare the fractal dimension from calculated cumulative number of aggregates with the fractal dimension from counted cumulative number of aggregates. Numbers of aggregates were counted for each size class of two data sets. Calculations for the 48 samples of Data Set I spanned six classes ranging from sizes 1 to 32 mm, and calculations for 12 samples of Data Set 2 spanned four classes ranging from sizes 0.5 to 8 mm. The fractal dimension from counted cumulative number of aggregates was significantly smaller than the fractal dimension determined from calculated cumulative number of aggregates for Data Set 1 (2.44 vs. 2.51) but significantly larger for Data Set 2 (2.41 vs. 2.03). The Gi factor was significantly different across many of the size classes for both data sets. Since Gi consisted of subcomponents (density, shape, relative diameter), we cannot be certain which subcomponent(s) was (were) scale variant. Scale variant Gi complicates the use of fractal mathematics to describe dry soil aggregate distributions.
Respiratory Activity and Oxygen Distribution in Natural Aggregates in Relation to Anaerobiosis
Authors: Sierra Jorge , Renault Pierre 
Published: July 2010

AbstractA reliable estimate of the anoxic regions in soil is essential in predicting the activity of microbial processes such as denitrification. In this study, two models were tested that have been previously proposed to estimate anaerobiosis within saturated aggregates. The first model assumes O2 consumption is constant as long as O2 is present; in the second model, O2 consumption depends on O2 concentration. The test was based on the overall respiration of natural aggregates of different sizes placed at different O2 concentrations. Some physical, chemical, and biological properties of the aggregates were also analyzed to verify the basic assumptions of the models. This analysis included direct measurements of O2 concentration within aggregates. The second model better described aggregate respiration, but some discrepancies were found between data and theory. Oxygen profiles indicate a steep fall of O2 near the aggregate surface. This suggests that the potential of respiration was not homogeneously distributed as assumed by the model, but decreased toward the center of the aggregates. The coefficient of variation of the respiration of 4‐mm aggregates placed at 0.21 m3 O2 m−3 was approximately 40%. This interaggregate variability must be incorporated into the model to prevent underestimation of the real and potential rates of respiration. Physical heterogeneities affected O2 transport within aggregates and induced irregularities in the O2 distribution. However, there was no evidence of any effect of such heterogeneities on the aggregate respiration.
Elevated Atmospheric Carbon Dioxide and Leaf Litter Chemistry: Influences on Microbial Respiration and Net Nitrogen Mineralization
Authors: Randlett Diana L. , Zak Donald R. , Pregitzer Kurt S. , Curtis Peter S. 
Published: July 2010

AbstractElevated atmospheric CO2 has the potential to influence rates of C and N cycling in terrestrial ecosystems by altering plant litter chemistry and slowing rates of organic matter decomposition. We tested the hypothesis that the chemistry of leaf litter produced at elevated CO2 would slow C and N transformations in soil. Soils were amended with Populus leaf litter produced under two levels of atmo‐spheric CO2 (ambient and twice‐ambient) and soil N availability (low and high). Kinetic parameters for microbial respiration and net N mineralization were determined on soil with and without litter during a 32‐wk lab incubation. Product accumulation curves for CO2‐C and inorganic N were fit to a first order rate equation [y = A(1 − e−kt)] using nonlinear regression analyses. Although CO2 treatment affected soluble sugar concentration in leaf litter (ambient = 120 g kg−1, elevated = 130 g kg−1), it did not affect starch concentration or C/N ratio. Microbial respiration, microbial biomass, and leaf litter C/N ratio were affected by soil N availability but not by atmospheric CO2. Net N mineralization was a linear function of time and was not significantly different for leaves grown at ambient (50 mg N kg−1) and elevated CO2 (35 mg N kg−1). Consequently, we found no evidence for the hypothesis that leaf litter produced at elevated atmospheric CO2 will dampen the rates of C and N cycling in soil.
Kinetics of Phosphate Rock Dissolution in Acidic Soil Amended with Liming Materials and Cellulose
Authors: He Z. L. , Baligar V. C. , Ritchey K. D. , Martens D. C. , Kemper W. D. 
Published: July 2010

AbstractPhosphate rock (PR), coal combustion by‐product (CCBP), limestone, and organic materials are promising amendments for low P, acid soils, and two or more of the amendments are commonly applied to improve crop yields in acid soil. However, the interactions between these amendments in acid soil are not fully understood. The effects of CCBP, limestone, and cellulose application on dissolution of North Carolina phosphate rock (NCPR) in an acid Lily loam (fine‐loamy, siliceous, mesicTypic Hapludult) from West Virginia were examined in an incubation study. Based on the ΔP‐NaOH estimation method, ≈ 30% of the added NCPR was dissolved after 60 d of incubation. The NCPR dissolution decreased drastically with increasing rate of CCBP, particularly when it was applied together with limestone, whereas cellulose addition tended to enhance NCPR dissolution. Dissolution of NCPR was well described by first‐order, Elovich, and Langmuir kinetic equations. The average r2 values between the experimental data of NCPR dissolution and the three models were 0.829*, 0.851**, and 0.930**, respectively, for 17 soil samples with and without amendments. Half‐life (t1/2) from the first‐order reaction could be employed as a simple measure of the NCPR dissolution rate. Constants A and b derived from the Elovich equation were related to the initial and average dissolution rate of NCPR. The potential maximum dissolution of PR from the Langmuir equation provided an estimate of the dissolution extent of NCPR. All four kinetic parameters, particularly t1/2 and A, were closely correlated with CCBP application rates. These parameters appeared useful in evaluating the effects of CCBP application on NCPR dissolution in the acid soil and might also be applicable to predicting PR dissolution for a wide range of soils with different properties.
Factors Affecting Phosphate Rock Dissolution in Acid Soil Amended with Liming Materials and Cellulose
Authors: He Z. L. , Baligar V. C. , Ritchey K. D. , Martens D. C. , Kemper W. D. 
Published: July 2010

AbstractCoal combustion by‐product (CCBP; a wallboard‐quality gypsum), limestone, and cellulose had been found to influence the dissolution of North Carolina phosphate rock (NCPR) in an acid Lily loam soil (fine‐loamy, siliceous, mesic Typic Hapludult). Laboratory and incubation experiments were carried out in this study to elucidate the mechanisms responsible for the reduced dissolution of NCPR from CCBP application. The major factors responsible for the reduced PR dissolution were (i) an increase in exchangeable Ca + Mg derived from the CCBP, (ii) an increase in soil pH from the small amounts of CaCO3 in the CCBP material; and (iii) sulfate released from the CCBP resulting in a decrease in P sorption capacity of the amended soil due to competitive sorption between sulfate and phosphate. The further reduction in NCPR dissolution by limestone addition was probably due to the increase in pH and exchangeable Ca relative to CCBP application alone. An increased NCPR dissolution from cellulose addition probably reflected an accelerated depletion of labile P by the cellulose‐induced microbial growth and, hence, biomass production. The four kinetic dissolution parameters, i.e., the half‐life (t1/2) from a first‐order rate equation, the initial dissolution rate‐ and the average dissolution rate‐related constants (A and b) from an Elovich equation, and the potential maximum dissolution of phosphate rock from a Langmuir equation were significantly correlated with pH, the content of exchangeable (Ca + Mg), and P sorption capacity of the CCBP‐amended soil. The t1/2 and A of NCPR in the acid soil could be predicted with 95% confidence by the three soil variables, i.e., soil pH, P sorption capacity, and exchangeable (Ca + Mg). Both t1/2 and A could serve as an indicator of the NCPR dissolution potential in soils.
Pyrolysis‐Field Ionization Mass Spectrometry of the Four Phases of Cow Manure Composting
Authors: van Bochove Eric , Couillard Denis , Schnitzer Morris , Schulten Hans‐Rolf 
Published: July 2010

AbstractPyrolysis‐field ionization mass spectrometry (Py‐FIMS) was used to analyze organic matter formed by the composting of cow manure. Analyses were done on samples withdrawn during the four characteristic phases (mesophilic, thermophilic, cooling, and maturation) of the composting process. The organic components that were identified included carbohydrates, phenols, monomeric and dimeric lignins, n‐C38 to n‐C51 n‐alkyl monoesters, n‐C15 to n‐C34 fatty acids, sterols, and heterocyclic N. Sterols of animal and plant origins were detected in relatively large amounts. Among the heterocyclic N forms, indole predominated. During the thermophilic phase, carbohydrates and n‐fatty acids increased. During the cooling phase, concentrations of carbohydrates increased, while dimeric lignins degraded to monomeric lignins and complex plant waxes to n‐fatty acids. The maturation phase was characterized by decreases in concentrations of all identifiable components, indicating the formation of chemically more complex structures.
Imaging a Pseudomonad in Mineral Suspensions with Scanning Force and Electron Microscopy
Authors: Fendorf Scott E. , Li Guangchao , Morra Matthew J. , Dandurand L.‐M. 
Published: July 2010

AbstractTechniques for imaging bacteria in their physical environments yield information potentially relevant to better understanding the role of soil and sediment colloids in altering microbial activity. Although cell structure and morphology of bacteria have been previously investigated using light and electron microscopies, both approaches are not without deficiencies. Our objective was to demonstrate the utility of scanning force microscopy (SFM) to image cell morphologies and to observe interactions between bacteria and clay minerals. Pseudomonas fluorescens (Migula), strain 2–79 RN10, was imaged in pure culture and in suspensions of kaolinite and montmorillonite using both SFM and, for comparison purposes, SEM (scanning electron microscopy). Largescale SFM and SEM images were similar, thus confirming the lack of artifacts introduced by SFM. Images of bacteria in kaolinite suspensions were not obtained with either technique, a result attributed to bacterial isolation in large pores of the kaolinite matrix. Imaging of montmorillonite‐bacteria suspensions showed that bacteria were closely associated with the larger mineral particles. In addition, the high resolution of SFM revealed what appeared to be small hexagonal montmorillonite platelets adhering to cell surfaces. The features of SFM allow for this unique ability to image whole cells as well as the microtopography of cell surfaces within hydrated environments. Scanning force microscopy provides valuable information concerning microbial cell morphology and the interaction of bacterial cells with montmorillonite.