bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pore‐Size‐Dependent Apparent Viscosity for Organic Solutes in Saturated Porous Media
Authors: Malik M. , Letey J. 
Published: July 2010

AbstractThe value of hydraulic conductivity under saturated conditions, K, depends on the nature of the porous medium and the physical properties of the perfusing fluid. The equation K = kρg/η, where k is the permeability, η is the fluid viscosity, ρ is the fluid density, and g is the gravitational constant, has been used to account for porous medium and fluid properties on K. A laboratory study was conducted to determine whether the equation properly accounts for viscosity effects of organic solutes on K. Hydraulic conductivity of 0, 25, 50, 100, 200, 300, and 400 mg L−1 solutions of large molecular weight polyacrylamides (PAM); 0, 10, 20, 30, 40 and 50% (v/v) of glycerol in distilled water; and undiluted n‐propanol was measured in two size fractions of quartz sand. The apparent viscosities of PAM and glycerol solutions were higher in the fine sand than in the coarse sand. The apparent viscosity of n‐propanol was about the same in the two sand‐size fractions. The above‐stated equation did not properly account for the effects of fluid properties of PAM and glycerol on K. Use of viscosity values as measured by a viscometer in the equation could result in a several‐fold error in prediction of K. Quantitatively characterizing those conditions under which the equation is valid may be important in analyzing the transport of environmental contaminants through soil, particularly when the contaminants may be organic chemicals of various molecular sizes and conformations.
Individual Sorbent Contributions to Cadmium Sorption on Ultisols of Mixed Mineralogy
Authors: Cowan Christina E. , Zachara John M. , Smith Steve C. , Resch Charles T. 
Published: July 2010

AbstractA multisite model was applied to Cd‐sorption data across a range in pH and at ionic strength (I) = 0.1 and 0.01 on specimen layer silicates and on untreated and dithionite‐citrate‐bicarbonate (DCB) treated isolates from two Utisols. The two isolates contained different mass concentrations of kaolinite, 2:1 layer silicates, Al‐substituted crystalline Fe oxides, and gibbsite. The multisite model included the exchange of Cd2+ on fixed‐charge sites on the layer silicates, complexation to hydroxyl sites on the layer silicates and Fe oxides, and electrostatic interaction between positively charged sites on Fe oxides and fixed‐charge sites on the layer silicates. Site concentrations for the specimen layer silicates and DCB‐treated and untreated isolates were estimated from cation‐exchange capacity (CEC) data and N2‐specific surface area. Equilibrium constants for specific surface reactions were estimated from Cd‐sorption data on the specimen layer silicates, KGa‐1 and SWy‐1, and the DCB‐treated soil isolates. The combined modeling results indicated that (i) Cd2+ ion exchange to fixed‐charge sites was the dominant sorption reaction for pH < 6.5 and I = 0.01, (ii) mass action with Na suppressed ion exchange at I = 0.01, (iii) Cd complexation to hydroxyl sites produced strong pH dependency in Cd sorption and was responsible for all the Cd sorption at I = 0.01 and above pH 6.5 at I = 0.01, and (iv) Fe oxides decreased Cd sorption by blocking access of Cd to exchange sites. The modeling results were unable to determine whether Fe oxides were important sorbents for Cd. Either with or without Cd sorption on Fe oxides, this model was able to describe the Cd sorption on the soil isolates reasonably well.
Sodium Adsorption Ratio Screening Procedure for Soils Using pH and Electrical Conductivity
Authors: Munk Lewis P. 
Published: July 2010

AbstractSoils with sodium adsorption ratios (SAR) <10 are generally considered to be below the threshold for potential Na hazard. The impetus for developing this screening procedure was to reduce the resources dedicated to determining precise SAR values in situations when simply knowing that the SAR is below the designated threshold is sufficient. The model was developed using 1000 samples and validated on a 24 000‐sample data set from two different laboratories operating in the western USA. The screening procedure uses empirically derived combinations of saturated soil paste pH (pHs) and extract electrical conductivity (ECe) to predict if the SAR is above or below 10, or whether Ca + Mg and Na must be analyzed to determine the SAR. For some combinations of pHs and ECe, the ratio of Ca + Mg to estimated total cations [ETC = ECe(10)] is used to decide whether Na must be analyzed. On average, the model incorrectly predicted that the SAR was <10 when the actual value was > 10 in only six out of 1000 samples. In addition, about 20% of the samples required Ca + Mg and Na analyses when the SAR was < 10. For the data sets tested, the screening procedure could have reduced the number of Ca + Mg and Na analyses by 50% with little loss of information about the potential Na hazard of the soils.
Fertilizer and Organic Amendment Effects on Mine Soil Properties and Revegetation Success
Authors: Schoenholtz Stephen H. , Burger James A. , Kreh Richard E. 
Published: July 2010

AbstractNitrogen deficiency frequently limits mine‐soil revegetation in the eastern USA. Application of organic amendments to these systems may provide a long‐term source of N and eliminate the need for repeated fertilization. A factorial experiment was conducted using lysimeters to determine the degree to which (i) organic amendments (control, 50 Mg ha−1 of whole‐tree wood chips, or 500 Mg ha−1 of native topsoil) and (ii) inorganic N fertilizer (0 or 100 kg N ha−1 as NH4NO3) affected mine‐soil properties and establishment of herbaceous vegetation and pitch × loblolly hybrid pine (Pinus rigida L. × P. taeda L.) seedlings on a newly exposed mine soil from the central Appalachian region. Amendments were tilled into the soil surface prior to application of fertilizer and cover‐crop seed. After 3 yr, total N, mineralizable N, and organic C in the wood‐chip‐amended mine soil were 10, 50, and 18% higher, respectively, than the control. Tree growth after 2 yr was highest with wood chips. A lack of wood‐chip treatment effect on pine nutrition showed that higher soil moisture levels, resulting from lower evapotranspiration, probably accounted for improved tree growth. Topsoil replacement increased total N and mineralizable N by 23 and 46%, respectively, but did not significantly increase vegetation productivity over that of the control. Nitrogen fertilizer increased herbaceous biomass production by 87% during the first growing season but did not affect herbaceous or pine productivity in two subsequent years or produce lasting effects on soil nutrient levels. Organic amendment × fertilizer interactions were not significant for any measured parameters. Results show that the organic amendments provided more stable sources of soil N; however, early revegetation success was more a function of moisture than of soil nutrient availability.
Fiber Content and Degree of Decomposition in Peats: Review of National Methods
Authors: Malterer T. J. , Verry E. S. , Erjavec J. 
Published: July 2010

AbstractFiber content and degree of decomposition are important physical and chemical peat characteristics. However, there are no internationally accepted methods for their determination. We review selected national methods that measure degree of decomposition and fiber content, and evaluate their precision and their capacity to distinguish between classes of peat. We also relate one national method to another using scaled‐variable regression equations. The von Post humification method, a European field test, was used in the identification and sample collection of 10 humification (decompositional) peat classes, from sphagnum, herbaceous, and humus peat types. Subsequent statistical analyses of the samples revealed that only eight classes were significantly different. The USSR centrifugation method successfully identified all eight classes, while the ASTM fiber method successfully identified four of the classes, the USDA fiber methods identified three, four, or five classes, and the USDA pyrophosphate method identified three of the classes. These analyses indicate that the USSR centrifugation laboratory method and the von Post humification field method separate more classes of peat with greater precision than the ASTM, several USDA fiber volume, and USDA pyrophosphate methods. However, similar tests on woody peats and tropical peats are needed to test the universal acceptability of the USSR centrifugation and the von Post humification methods. Predictive regressions between methods had R2 values from 0.690 to 0.998 and CVs form 4.8 to 45.3%. Thirty‐eight percent of the between‐method regressions are parabolic, 43% linear, and the remainder cubic.
Reclamation of a Saline Sodic Soil Using Synthetic Polymers and Gypsum
Authors: Zahow M. F. , Amrhein C. 
Published: July 2010

AbstractThe water infiltration rate of saline sodic soils often limits the rate of reclamation. Column leaching studies were conducted to determine if water‐soluble, synthetic polymers would be beneficial in improving the hydraulic conductivity and aid reclamation of a heavy‐textured, salt‐affected soil. Soil samples from a swelling soil (fine, montmorillonitic [calcareous] Thermic Vertic Haplaquoll) were collected from a field site that had exchangeable sodium percentages (ESP) of 8, 12, 20, 25, 32, and 35. The air‐dried soil samples were treated with polyacrylamide polymers (one nonionic and two anionic) and one cationic guar‐derivative polymer at a rate of 50 mg kg−1. Polymer treatments had a highly significant effect on increasing the saturated hydraulic conductivity of the soil samples with ESP values <15, but had no significant effect on the samples with values > 15. The addition of gypsum increased the hydraulic conductivity from 0.0 to 0.063 mm h−1 in the soil with an ESP of 32. When polymers were used in conjunction with gypsum, the hydraulic conductivity increased to 0.28 mm h−1. We attributed the improvement in hydraulic conductivity with polymer treatment at low ESP values and in the gypsum‐treated soil to a reduction in soil slaking and dispersion. At ESP values > 15, an additional mechanism that may have been controlling the hydraulic conductivity was swelling, and none of the polymers reduced soil swelling.
Molecular Weight Distribution of Soluble Organics from Laboratory‐Manipulated Surface Soils
Authors: Homann Peter S. , Grigal David F. 
Published: July 2010

AbstractTransfer of organic matter from solid to solution phase is the first step in the redistribution by leaching of organic C and associated elements in forest soil profiles. To examine the effects of disturbances on solubilization of organics, three A horizons and one O horizon were exposed to air drying, waterlogging, addition of urea, addition of ash, and addition of ash in combination with heating at 250 °C. Following incuhation at 20 to 22 °C for 1 to 50 d, soluble organic C (SOC) was extracted with 0.5 mM SrCl2. The SOC was 0.2 to 0.7% of total organic C in controls. Urea and heat‐plus‐ash treatments yielded up to 17 times more SOC than controls, and other treatments yielded up to three times more than controls. Distribution of SOC among molecular‐weight classes, as determined by dialysis, was 21 to 32% in the <3500‐dalton class, 8 to 20% in the 3500 to 14 000‐dalton class, and 47 to 71% in the >14 000‐dalton class. Urea treatment yielded a higher proportion of SOC in the >14 000‐dalton class than in the controls, while air drying resulted in a lower proportion. Both the quantity and quality of soluble organics can be influenced by soil disturbances, but the specific response varies with the type of disturbance.
Field Solute Transport across a Soil Horizon Boundary
Authors: Hamlen C. J. , Kachanoski R. G. 
Published: July 2010

AbstractModels describing solute transport in a field soil need to account for transport through soil horizons and across horizon boundaries. This study investigated the effects of soil horizons on the transport of a conserving tracer and the validity of treating soil horizons as independent (uncorrelated) layers. The occurrence or absence of correlated solute travel times with depth was tested by comparing predicted solute travel time variances with variances measured from solute breakthrough curves. Steady‐state transport experiments were conducted on a Fox sand (fine‐loamy over sandy or sandy‐skeletal, mixed, mesic Typic Hapludalf) in Ontario, Canada. The transport of Cl through the Ap and the Ap + B horizons was measured at constant surface flux densities of 3.5 and 5.5 cm h−1. The upper 20 cm of soil was then excavated and the transport of Cl through the B horizon was measured independently at a flux density of 5.5 cm h−1. The horizons exhibited differences in solute velocity, spatial variations in velocity and in equilibrium water contents. At the transect scale, successful predictions of travel time variance were made at both flux densities when it was assumed that solute travel times were correlated with depth. At the local scale, the successful prediction of variance assuming correlated travel times occurred only at the lower flux density. At this site a correlated model is appropriate for describing solute transport at the transect scale. Independent estimates of transport properties from each horizon is not sufficient information to predict field transport. The nature of the boundary between horizons must be evaluated.
Ion Transport in Soil with Ion Exchange Reaction: Effect of Distribution Ratio
Authors: Ishiguro M. 
Published: July 2010

AbstractExchanging ionic‐solute transport through soil columns is significantly affected by ion exchange reaction. The breakthrough curve (BTC) for the input ion based on time or pore volume shifts to the right as the ion‐exchange capacity increases or the input ion concentration decreases. The shapes of the BTCs with different mean breakthrough times are easily compared when the BTCs are normalized by the mean breakthrough times. The influence of the distribution ratio, Dg, the ratio of the amount of ions adsorbed in the soil to that in the solution in a unit volume of the soil, on normalized BTCs with nonlinear exchange isotherms was evaluated. The cases studied here involved ion exchange in a binary system at a constant total concentration under steady‐state water‐flux conditions. The BTCs were calculated and interpreted using a normalized, one‐dimensional advective‐dispersive equation. It was determined that the effect of the nonlinear isotherm on the BTC increases as Dg increases. It was also shown that, when Dg is much greater than unity, an increase in Dg has no effect on the BTC. These results were confirmed with experimental data on actual soil columns of an allophanic Andisol. When the BTCs had a similar nonlinear exchange isotherm and Péclet number, the deviations among them were easily interpreted by the Dg values.
Compaction Effect on the Gas Diffusion Coefficient in Soils
Authors: Xu Xia , Nieber J. L. , Gupta S. C. 
Published: July 2010

AbstractGas diffusion is important in determining the aeration status of soils for crop production and in providing estimates of transport of volatile chemicals at waste disposal or chemical spill sites. This study investigated the effects of compaction on the gas diffusion coefficient in four soils. The experiment involved equilibrating bulk loose soil to a known matric potential in a pressure chamber, compressing the equilibrated moist soil in metal cores at a given applied stress, and measuring the concentration of N2 diffusing through these cores into a diffusion chamber. The diffusion coefficient was calculated by fitting an analytical solution of the transient diffusion equation to the measured N2 concentration in the diffusion chamber as a function of time. The diffusion coefficient of N2 in four soils at four water contents and four applied loads varied exponentially as a function of air‐filled porosity and was nearly the same function for all four soils. At an air‐filled porosity of ≈ 10%, the diffusion coefficient was close to zero, reflecting a discontinuity in the pathways at an air‐filled pore space of 10% or lower. A model for predicting the diffusion coefficient of gases in soils based on the diffusion coefficient of individual soil constituents was tested with the data set. For known shape factors for soil solid and soil water, the model overpredicted the diffusion coefficient for all four soils. A reduction factor suggested in the literature to account for blocked air slightly improved predictions. The ratio of the measured to predicted diffusion coefficient vs. degree of air‐filled saturation suggests a second‐degree correction factor to account for blocked air in soils.
Organic and Inorganic Anion Effects on Reference and Soil Clay Critical Flocculation Concentration
Authors: Frenkel H. , Levy G. J. , Fey M. V. 
Published: July 2010

AbstractMaintaining adequate soil permeability and favorable soil structure is largely dependent on the flocculation‐dispersion characteristics of the soil clay fraction. The critical flocculation concentration (CFC) of the clay fraction of three strongly structured clay soils from Natal (two dominated by smectite and one by kaolinite) was compared with that of smectite (bentonite from Wyoming) and kaolinite (from Georgia) in Na‐ and Ca‐saturated forms. The soil clays had much higher CFC than their reference mineral counterparts in both NaCl and CaCl2 systems. The addition of humic acid extracted from one of the soils and of citrate, formate, orthophosphate, carbonate, and silicate to the reference clays increased the CFC by as much as a factor of 50. Kaolinite was approximately 10 times more sensitive than bentonite to this dispersion effect of specifically adsorbing ligands. The results suggest that natural levels of soil humus, and possibly of certain inorganic anions, may be sufficient to impart a high degree of dispersion on the soil clay fraction. There is, therefore, some doubt as to the quantitative importance of clay mineral composition in the dispersion behavior of soils.
Reevaluation of Calcite Supersaturation in Soils
Authors: Suarez D. L. , Wood J. D. , Ibrahim I. 
Published: July 2010

AbstractThe calcite saturation status of soil‐water systems in semiarid regions was reexamined taking into consideration organic ligand alkalinity and Ca‐organic complexation. These factors have been forwarded as the reason for earlier reports of calcite supersaturation in soil‐water systems. We examined groundwaters beneath irrigated lands, soil‐water suspensions in the laboratory using four soils and two levels of CO2, and soil water extracted from the root zone of an irrigated, cropped field. Total alkalinity and net inorganic C alkalinity were determined by titration. Calcium activity values calculated from total concentrations using the speciation program WATEQ4F were compared with Ca2+ activity values measured with an ion‐specific electrode. In all our systems, total alkalinity and inorganic C alkalinity were almost equivalent and thus organic C alkalinity was negligible. Calculated Ca2+ activity was generally 5 to 25% greater than Ca2+ activity determined with an ion‐specific electrode. Although these data suggest the presence of additional Ca complexes not included in the speciation routines, the determined dissolved organic C values are too low for Ca‐organic complexes to be the cause of these differences in Ca2+ activity. Ion activity products based on either measured Ca2+ activity values or calculated Ca2+ activities indicated that all systems were supersaturated, with saturation ratios of two to three.
Calibration and Validation of a Soil‐Landscape Model for Predicting Soil Drainage Class
Authors: Bell James C. , Cunningham Robert L. , Havens Matthew W. 
Published: July 2010

AbstractThe soil‐landscape relationships frequently used for soil mapping activities are seldom documented. We developed a statistical model that relates soil drainage classes to eight landscape parameters describing slope morphology, proximity to surface drainage features, and soil parent material. Soil profiles and landscape parameters were described at 305 randomly selected sampling points within the Mifflintown 7.5‐min topographic quadrangle in the unglaciated ridge and valley physiographic province of central Pennsylvania. Variables defining the spatial structure of the landscape were derived from digitized 1:24 000 scale maps of streams and drainageways, surficial geology, bedrock geology, and a digital elevation model. These data were stored in a geographic information system and overlaid with the sampling point locations to define a database of 305 known soil‐landscape combinations. These soil‐landscape combinations were used to derive a statistical soil‐landscape model using multivariate discriminant analysis and class frequency information. For soil drainage class, a 74% overall agreement with field observations was found for the model using a cross‐validation approach, compared with 69% for the published soil survey. The model correctly predicted a majority of the observations within each drainage class and provided a consistent method of extrapolating point information about soils to the three‐dimensional landscape.
Plant Water Uptake Terms Evaluated for Soil Water and Solute Movement Models
Authors: Cardon G. E. , Letey J. 
Published: July 2010

AbstractTwo root water uptake terms, representative of the two major types commonly employed in soil‐based models of water and solute movement, were evaluated. Simulations were run to test the sensitivity of the two terms to salinity and water content and to investigate the details of their respective form and function. The two root water uptake terms tested were: (i) a mechanistic equation based on Darcy's law (Type I), and (ii) an empirical equation relating soil water potential to relative water uptake (Type II). The Type I term was insensitive to salinity where no reduction in transpiration was shown for increasing irrigation water salinity from 0.0 to 6.0 dS/m and applying water equal to potential transpiration. The Type II term was sensitive to salinity and showed a 35% reduction in water uptake by increasing water salinity from 0.0 to 6.0 dS m−1 and applying water equal to potential transpiration. Predicted reduction in water uptake due to matric potential was of the same magnitude as that due to salinity. The Type I term resulted in abrupt shifts in water uptake between full and zero transpiration, occasionally resulting in long periods of computed zero transpiration, uncharacteristic of conditions in the field. It was concluded that the Type I water uptake term may not be appropriate for models incorporating root water uptake, particularly under saline conditions.