bluuebunny/crossref_metadata_2025_split huggingface dataset:
Equilibrium and Kinetics of Borate Adsorption‐Desorption on Pyrophyllite in Aqueous Suspensions
Authors: Keren R. , Grossl P. R. , Sparks D. L. 
Published: July 2010

AbstractThis study was conducted to elucidate the dynamic aspects of the adsorption‐desorption of borate ions on edge surfaces of 2:1 clay minerals. A pressurve‐jump relaxation method was used to evaluate the elementary processes involved in the adsorption‐desorption of borate ions by pyrophyllite in aqueous media at pH 9 and ionic strength of 0.01 (NaNO3). This clay was selected because of the small deviation from the ideal structural formula of the dioctahedral 2:1 clay minerals. At pH 9, 37% of the total B in solution is in the B(OH)−4 form, whereas of the total adsorbed B, the fraction of the adsorbed B(OH)−4 is assumed to be ≈ 0.99 at all levels of adsorbed B studied. This high fraction is probably due to the absence of repulsive forces associated with the planar surfaces. A linear correlation (R2 = 0.94) between the reciprocal value of the relaxation time, τ−1, and the sum of concentrations of the free adsorption sites and borate ions in solution at equilibrium was determined. The forward rate constant, k1, for the adsorption was 104.26 L mol−1 and the backward rate constant, k‐1, for the desorption was 101.11 s−1. The desorption rate constant was three orders of magnitudes smaller than the adsorption rate constant. The intrinsic equilibrium constant obtained from the kinetic measurements (log10 Kkinetic = 3.15) agreed relatively well with that calculated from the static studies (log10 Kstatic = 3.51). The suggested reaction scheme for the B‐pyrophyllite interaction is:
urn:x-wiley:03615995:saj2sssaj199403615995005800040016x:equation:saj2sssaj199403615995005800040016x-math-0001 or
urn:x-wiley:03615995:saj2sssaj199403615995005800040016x:equation:saj2sssaj199403615995005800040016x-math-0002
An Infiltration Equation to Assess Cropping Effects on Soil Water Infiltration
Authors: Ali A.‐S. I. , Swartzendruber D. 
Published: July 2010

AbstractThe effect of crop plants on the infiltration of water into soil has been difficult to characterize. This study was conducted to determine whether a new three‐parameter infiltration equation, obtained from a recent infiltration quasi solution, could be validated and used for improved characterization of infiltration. For field plots under different cropping conditions of corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], soybean [Glycine max (L.) Merr.], and fallow, water‐infiltration data from ponded double‐ring infiltrometers were fitted by nonlinear least squares to the new equation, and, for comparison, to the two‐parameter Philip form and to the strictly empirical Lewis equation. Physically problematic negative values of the sated (near‐saturated) hydraulic conductivity K were yielded by the Philip form in well over half of the data sets, but all were superseded with positive K values by use of the new equation which, of the three, also gave the best fit to the data, in keeping with the additional fitted parameter. Statistically, by using orthogonal‐contrast analysis of the several equation parameters, the new equation also produced the largest number of significant differences between crops and crop sequences (rotations). Grain sorghum created the largest sorptivity S, whereas corn decreased it. Soybean produced the smallest K, but corn and grain sorghum caused moderate and equal increases in K. The new equation and these findings offer promise for improved characterization and understanding of plant effects on water infiltration.
Neutron Probe Calibration in Unsaturated Tuff
Authors: Elder A. N. , Rasmussen Todd C. 
Published: July 2010

AbstractThe measurement of water content in unsaturated media using neutron moisture probes requires a calibration relationship between neutron counts and water contents. Techniques for obtaining the relationship in unconsolidated geologic media may be unsuitable for consolidated media due to the difficulty of extracting undisturbed samples for water content analysis. The calibration relationship, θ = α0 + (α1 + α2ρb)C = α3ρb, with C = neutron counts, and ρb = dry bulk density, provided a good predictor of volumetric water content, θ, for consolidated media at the Apache Leap Tuff Site. Four techniques were employed to obtain data necessary to construct this relationship. Two methods employed a neutron transport code to predict neutron counts from scattering and absorption neutron cross sections. The first method calculated cross sections from elemental compositions, while the second used cross sections obtained from rock samples placed in a graphite pile containing a neutron source. The third method used in situ neutron counts measured in two access holes constructed in unsaturated rock with known water contents estimated from rock fragments excavated surrounding the access holes using a pneumatic hammer. The fourth technique used neutron counts from crushed rock packed into containers and maintained at prescribed water contents. Neutron cross sections obtained from elemental analyses were smaller than graphite‐pile values, although the differences were insignificant at the 95% confidence level and the difference in rock water content predictions was small. The neutron transport model provided neutron count estimates consistent with in situ counts and counts from saturated crushed rock in containers.
Infiltration Characteristics under No‐Till and Clean‐Till Furrow Irrigation
Authors: Christensen N. B. , Jones T. L. , Kauta G. J. 
Published: July 2010

AbstractTillage or the lack of tillage affects infiltration and its variability across the field. To quantify infiltration characteristics of soil under no‐till and clean‐till furrow irrigated systems, a 3‐yr rotation of wheat (Tritium aestivum L.)‐sorghum [Sorghum bicolor (L.) Moench]‐fallow on a Pullman sandy clay loam soil (fine, mixed, thermic Torrentic Paleustoll) was initiated. Treatments were no‐till and clean‐till with or without wheel traffic. Soil water contents, water advance times down the furrow, wetted cross‐sectional area of flow, and cumulative furrow infiltration during three irrigations for each cropping event were determined. No‐till treatments conserved significantly more soil water (3.0 cm) during the fallow periods than clean‐till. Average water advance times to the end of the field were 301 and 175 min for no‐till and clean‐till, respectively. Wheel traffic significantly decreased advance times, by a factor of 1.98, during the initial irrigations at planting with no effect on subsequent irrigations. Wetted cross‐sectional area in no‐till furrows was significantly greater than in clean‐till during sorghum irrigations, averaging 0.0206 and 0.0093 m2, respectively. However, these factors did not contribute to a consistent increase in infiltration in the no‐till treatments. Grain yields for sorghum were significantly greater in no‐till than clean‐till: 4147 and 3584 kg ha−1, respectively, but clean‐till wheat yields (5414 kg ha−1) were significantly greater than no‐till yields (4657 kg ha−1). No‐till conserved more water during the fallow periods, but surface characteristics of planting wheat no‐till in sorghum residue may decrease uniformity over long furrows.
Cover‐Crop‐Enhanced Water Infiltration of a Slowly Permeable Fine Sandy Loam
Authors: Gulick S. H. , Grimes D. W. , Munk D. S. , Goldhamer D. A. 
Published: July 2010

AbstractInfiltration improvement in many sandy to medium textured soils of California's Central Valley is often hampered by unfavorable soil properties, unfavorable management practices, and the need to protect perennial crop roots. Minimum‐tillage practices using chemical sprays, mulches, and cover crops avoid soil structure deterioration due to high traffic, but some properties of these methods are not universally acceptable. Furrow irrigation water infiltration, water use, and ‘Thompson Seedless’ grape production were evaluated on a Hanford fine sandy loam (coarse‐loamy, mixed, nonacid, thermic Typic Xerorthent) for three management systems for 2 yr to develop a useful system. The compared systems were (i) continuous cover crop [winter ‘Blando’ bromegrass (Bromus mollis L.) followed by summer resident vegetation] (CC); (ii) winter bromegrass, herbicide treated to form a summer mulch (CHT); and (iii) bare soil, herbicide treated as needed (BHT). Cumulative infiltration for 8‐h irrigation periods, averaged for five irrigations, was 177 mm for CC, 125 mm for CHT, and 74 mm for BHT during the second season. Eight‐hour cumulative infiltration was unchanged from the first year to the second for BHT but increased with CC from 107 mm to 202 mm at the first irrigation of each year; the increase for CHT was intermediate. Cover cropping between vineyard rows increased soil water depletion in the between‐row zone profile by an average of 14 mm for CHT and 27 mm for CC for each drying cycle between irrigations. Soil water depletion beneath vine rows was unchanged by treatment.
Applications of X‐ray Absorption Fine Structure Spectroscopy to Soils
Authors: Fendorf S. E. , Sparks D. L. , Lamble G. M. , Kelley M. J. 
Published: July 2010

AbstractDetermining the local chemical environment of a species is often a necessity for evaluating its reactivity in the environment. However, obtaining direct molecular‐level information is often problematic and may only be possible with severely invasive techniques. We discuss the physical and chemical aspects of x‐ray absorption fine structure spectroscopy (XAFS) and its application in soils. This technique can determine the local chemical and structural surroundings of a particular elemental species in soil and water or other natural systems, without the need to subject the sample to a foreign atmosphere. Electronic information and a fingerprint of the x‐ray absorbing element's local environment is provided with XAFS and can be used to determine the speciation of an element in media like soils. Precise structural information (bond distances within 0.02 Å) can also be ascertained with this method, although this precision is often difficult to obtain in heterogeneous materials. Nevertheless, XAFS is a method that can contribute significantly to our knowledge of soils and soil reactions.
Efficacy of Dicyandiamide as a Soil Nitrification Inhibitor in Citrus Production
Authors: Serna M. D. , Legaz F. , Primo‐Millo E. 
Published: July 2010

AbstractNitrification inhibitors such as dicyandiamide (DCD) help reduce leaching losses by retaining applied N in the ammoniacal form. Research objectives were to evaluate dicyandiamide added to ammonium sulphate nitrate (ASN) as a nitrification inhibitor in cultivated soils (Xeropsamments) and its effect on N uptake by citrus (Citrus sinensis (L.) Osbeck). In a greenhouse experiment, 10 g N as ASN either with or without 2% of DCD‐N were applied to plants grown in 50‐L pots filled with peat and sand (2:1). Addition of DCD to ASN resulted in significantly higher levels of NH+4‐N in the substrate than the ASN treatment, for at least 100 d. Drainage water from the ASN‐DCD treated pots was lower in NO−3‐N concentration during the first 60 d. Inclusion of DCD with ASN resulted in greater uptake of the fertilizer N by citrus plants. Under field conditions, fertilization of adult trees with ASN (600 g N tree−1) either with or without DCD (2% DCD‐N) was compared. In the ASN‐amended soil, nitrification was much more rapid than when DCD was added to the ASN. Fertilization with ASN + DCD maintained relatively high levels of NO−3‐N in soil longer than ASN alone. In another experiment, 60 g N as ASN either with or without DCD (2% DCD‐N) were applied to 3‐yr‐old citrus plants grown individually outdoors in containers and the distribution of NH+4‐N and NO−3‐N in the soil profile after consecutive flood irrigations was monitored. After the third irrigation, 68% of applied N was leached below 0.45 m in ASN amended soils, whereas only a very small amount of the applied N was retained above this depth. When DCD was added, only 20% of the applied N was lost by leaching at this time. The DCD nitrification inhibitor improved the N fertilizer efficiency and decreased NO−3 losses so as to minimize the economic and environmental risks that are inherent in irrigated production of citrus.
Methane Emissions and Growth of Spartina patens in Response to Soil Redox Intensity
Authors: Kludze H. K. , DeLaune R. D. 
Published: July 2010

AbstractLaboratory experiments were conducted to determine the influence of soil redox intensity (Eh) on the growth, root porosity (POR), radial O2 loss, and CH4 production, oxidation, and emission in Spartina patens (Aiton) Muhlenb. (salt meadow cordgrass). Plants were grown for 50 d in a Mississippi alluvial soil (silty‐clay loam, Typic Fluvaquent) under controlled Eh values of 200, −200, and −300 mV. Plant growth decreased with increase in Eh intensity. Root dry weights decreased by 37% and shoot dry weights by 25% between the soil redox intensity treatments of 200 and −300 mV. Root air space formation was enhanced by a decrease in Eh up to about 30 d when further development appeared to cease and levelled off in all the redox treatments. Methane production was generally enhanced by the intensity of reduction. Plant‐mediated emissions were commensurate with production levels but were influenced by plant related factors, especially POR. No differences (P < 0.05) existed between emissions in light and in the dark, which suggests a lack of stomatal influence on CH4 emissions from S. patens. Plant‐mediated CH4 oxidation was higher at −200 mV than at −300 mV by a factor of 16%. Results of this study demonstrate how soil redox intensity initiates physiological changes in S. patens, which in turn modulates the gas transport in the plant. Although the experimental conditions do not represent the natural environment, the results provide a theoretical understanding of the influence of soil redox intensity on the growth, CH4 production, and gas exchange in S. patens.
Transport of Reactive Solutes in Soils: A Modified Two‐Region Approach
Authors: Selim H. M. , Ma Liwang 
Published: July 2010

AbstractA modified two‐region approach that accounts for chemical and physical nonequilibrium of solute behavior in soils was developed. Chemical nonequilibrium was described by a second‐order two‐site model, while physical nonequilibrium was represented by a two‐region (mobile‐immobile) approach. Model validity was based on predictions of atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino‐s‐triazine] miscible displacement experiments in a Sharkey clay soil (very fine, montmorillonitic, nonacid, thermic Vertic Haplaquept) for different aggregate sizes, flow velocities, column lengths, and flow interruption. Independently measured model parameters from kinetic batch experiments were used in model validation. Two model formulations were evaluated. Model I was based on the classical two‐region approach where the soil matrix was divided into two fractions. In Model II, we assumed that the rate of reaction within each soil region was a function of the total number of vacant sites in the soil. Thus, the partitioning coefficient f of the two‐region concept, which is difficult to measure, need not be specified and the amounts retained by each soil region is solely a function of reaction rate coefficients. Model I with f = F (F = θm/θ, mobile/total water contents) provided the worst atrazine predictions. Moreover, based on Model I predictions with f = 1 and f = 0, the significance of physical nonequilibrium was dependent on experimental constraints such as aggregate size and flow velocity. Based on root mean squares, however, the best overall predictions were obtained using Model II. We concluded that Model II, which requires fewer parameters, is superior to Model I in its prediction capability for transport results.
The Philosophical Basis of Soil Classification and Its Evolution
Authors: Haskett Jonathan D. 
Published: July 2010

AbstractThe system of soil classification used in the U.S. system of soil taxonomy has been criticized as being based on the flawed 19th century logic of John Stuart Mill. Mill postulated that objects have self‐evident properties that will be apparent to any observer. Further, these properties reflect inherent differences between objects. However, language shapes perception to a great extent, and knowledge of external reality can be obtained only by observation. It cannot be assumed that all observers, particularly those using different languages, will find the same things important. Therefore, different observers are likely to categorize in different ways. In order to avoid arbitrary classifications, an inductive method is used based on tests of predictive ability. This allows the creation of a classification system that follows the regularities of nature, within the constraints on perception imposed by any linguistic division. Classification in natural history as well as in soil science has moved from a noncontextual naming of independent objects to a bounded self‐consistent system in which each entity is defined in relation to all others in the system. This represents an evolutionary process that proceeds through the adoption of the inductive method and ultimately leads to the creation of a classification system consistent with the underlying principles of the discipline. The current system of soil classification is consistent with the progressive nature of this process and is not in need of fundamental modification.
Models and Modeling of Hydrogeologic Processes
Authors: Narasimhan T. N. 
Published: July 2010

AbstractJ.R. Philip recently articulated a concern of many earth scientists that computer‐based mathematical models are impacting soil science practice and soil science education in an undesirable way. Unrealistic faith in the ability of these models to predict the future has encouraged overzealous use of models at the expense of the observational enterprise. These real concerns draw attention to the fact that much needs to be learned about the proper use of models in general and computer‐based models in particular in the earth sciences. I was impressed by Philip's thoughts, and here reflect on the current status and the role of models of hydrogeologic processes. While agreeing with Philip's concerns about the improper use of models, I advance a perspective that models (analytical or numerical) are tools with inherent limitations. Despite their overenthusiastic use, computer‐based models are potentially capable of helping us advance our knowledge of earth processes in unprecedented ways. As we seek to exploit this tool to its full potential, we may be challenged to reexamine and refine our conceptual foundations so that hydrologic processes are described more precisely than has hitherto been possible.
Developments in the Physics of Infiltration
Authors: Youngs E. G. 
Published: July 2010

AbstractDevelopments in the physics of infiltration, particularly the many theoretical contributions of John Philip, have been based on solutions of Richards' equation for flow in unsaturated soils. Solutions for constant surface soil‐water pressure and constant surface flux into soils initially at a uniform water content have given the physical basis for infiltration that generally takes place in conditions described by more complex initial and boundary conditions. The Green and Ampt step function and Gardner's exponential function models for the relationship between hydraulic conductivity and soil‐water pressure head are often employed to facilitate solutions. However, Richards' equation makes assumptions in the physics of the flow that do not take account of many complicating factors that may vitiate theories based on it. These factors include the influence of the air phase on the soil‐water movement, the effects of soil heterogeneity, soil swelling, soil aggregation and soil instability, deviations from Darcy's law, thermal effects and the hysteresis in soil‐water relationships. These factors need to be addressed in order to provide a better physical understanding of infiltration behavior in the field, first by understanding simple systems, as with much of John Philip's work, and then by progressing to more complex situations.
Liquid Flow in Swelling Soils
Authors: Smiles D. E. 
Published: July 2010

AbstractTheory of flow of water in media that change volume with water content change owes much to the insights of John Philip. In particular, his development and explanation of a one‐dimensional model in Eulerian space that correctly accounts for the statics and dynamics of the phases in a two‐phase swelling system is a paradigm of the combination of the models of mathematics with clear physical insights. In addition, transformation of the approach from Eulerian to Lagrangian space permits use, for swelling systems, of all the methods of analysis developed in soil physics to describe water flow in nonswelling soils. The approach has been used to describe important practical problems of filtration, sedimentation, centrifugation, and consolidation of colloidal and soil systems in chemical, civil, and mine tailings engineering. Regrettably, material coordinates, rather than the more familiar spatial coordinates, continue to present conceptual difficulties for many engineers and soil scientists, as does the effect of volume change on the potential of the water. Furthermore, the approach has yet to be satisfactorily extended to unsaturated systems and to multidimensional ones. Its use in agriculture thus remains uncertain despite the great importance of water management in swelling and cracking soils. This review discusses some of these issues and specifically identifies the energetics and mechanics of cracking, overburden effects in unsaturated porous materials, and structural effects of the equilibrium ambient solution type and concentration in swelling systems as practically important areas for further study.
The Role of Edge Surfaces in Flocculation of 2:1 Clay Minerals
Authors: Keren R. , Sparks D. L. 
Published: July 2010

AbstractThe effect of pH on the flocculation, settling rate, and gel volume of pyrophyllite in dilute suspension was studied in solutions of various NaNO3 concentrations to evaluate the role of the edge surfaces in particle‐particle interaction. The critical flocculation concentration (CFC) increased with increasing pH, being 1.6 × 10−4, 4 × 10−4, 1.5 × 10−3, 9.5 × 10−3, 1.6 × 10−2, and 0.1 molc L−1 at pH 3.2, 4.4, 5.3, 6.0, 7.4, 8.5, and 10.2, respectively. The CFC increased significantly in the presence of small amounts of sodium hexametaphosphate in the suspension. The changes in CFC from low values in the absence of the polymer to higher values in the presence of it support the hypothesis that the edge surfaces are involved in particle‐particle interactions. The settling rate of the clay particles at pH 8.5 increased as the electrolyte concentration was decreased. The effect of electrolyte concentration on settling rate was explained by the presence of an electrical field associated with the edge surfaces. The gel volume, after reaching a stable volume, increased with the increasing of electrolyte concentration. This increase in water content, indicating an open structure of clay platelets, also supports the hypothesis that edge surfaces are associated with clay flocculation. The electrical field associated with the edge surface also has an effect on the gel volume.