bluuebunny/crossref_metadata_2025_split huggingface dataset:
Semiempirical Model of Soil Water Hysteresis
Authors: Nimmo John R. 
Published: July 2010

AbstractIn order to represent hysteretic soil water retention curves accurately using as few measurements as possible, a new semiempirical model has been developed. It has two postulates related to physical characteristics of the medium, and two parameters, each with a definite physical interpretation, whose values are determined empirically for a given porous medium. One parameter represents the fraction of the pore space that is not subject to Haines jump hysteresis. Its associated postulate is that a single value of this parameter characterizes a given medium, or, equivalently, that the medium is self‐similar with respect to the division between hysteretic and nonhysteretic pore space. The second parameter is the effective body‐to‐neck size ratio of the medium's largest pore. The second postulate specifies a particular relation between the size distributions of pore bodies and of pore necks. Tests of the model show that it provides high‐quality optimized fits to measured water content vs. matric pressure wetting curves for a wide variety of media. The parameter values obtained through optimization correlate plausibly with such media properties as uniformity of particles, complexity of structure, and degree of compaction. A practical use of this model is to provide a complete simulated main wetting curve for a medium where only a main drying curve and two points on the wetting curve have been measured. With additional development, it may be possible to do without the two measured wetting points if parameters can be evaluated from other measurements or known properties of the medium.
Ion Transport in an Allophanic Andisol under the Influence of Variable Charge
Authors: Ishiguro M. , Song K.‐C. , Yuita K. 
Published: July 2010

AbstractBecause the density of variable charge in a soil is influenced by the solution concentration and the pH, exchanging ion transport in the soil is also affected by them. In this study, the effect of variable charge on exchanging ion transport in an allophanic Andisol (Typic Hydrudand) that has negative and positive variable charges was investigated experimentally. Miscible‐displacement experiments were conducted under saturated and unsaturated (−1.96 kPa of soil water pressure) conditions. The cases studied here involved ion exchange under a constant total concentration condition and a constant pH condition. A SrBr2 solution was applied to the soil column, which was initially saturated with a CaCl2 solution. The miscible‐displacement experiments were carried out at different total concentration (0.001–0.1 molc L−1) and pH (4.2–7.65). Bromine flowed out slowly at lower pH due to the large anion‐exchange capacity (AEC). Strontium discharged slowly at higher pH due to the large cation‐exchange capacity (CEC). The counterion penetrated slowly at a lower concentration because the amount of the counterion contained in a unit of solution volume was small. Observed breakthrough curves (BTCs) agreed with those expected from measured exchange isotherms. Based on the relationship between the Sr BTC and the Br BTC, no notable differences were observed between the BTCs under saturated conditions and those under unsaturated conditions. The influence of the solution concentration and the pH cannot be ignored when considering ion transport in an allophanic Andisol.
Analysis of Fluorobenzoate Tracers by Ion Chromatography
Authors: Pearson R. J. , Inskeep W. P. , Comfort S. D. 
Published: July 2010

AbstractPentafluorobenzoic acid (PFBA), 2,6‐difluorobenzoic acid (2,6‐DFBA), and orthotrifluoromethylbenzoic acid (o‐TFMBA) are three fluorobenzoates that have recently been used as tracers to monitor soil water and solute movement in soil systems. These fluorobenzoates are typically analyzed by high‐performance liquid chromatography (HPLC) with ultraviolet (UV) detection and have reported retention times ranging between 9 and 12.5 min. Ion chromatography (IC) analysis of these fluorobenzoates using conductivity detection is possible and faster than the currently used HPLC methodology. This study demonstrates the reliability of IC for fluorobenzoate tracer analysis. Mixed and single standard solutions (0.10–25 mg L−1) of PFBA, 2,6‐DFBA, o‐TFMBA and LiBr were prepared and analyzed using IC‐conductivity detection. High resolution among all four tracers was achieved by the methodology presented. However, we found that Cl‐ interferes with o‐TFMBA analysis even at low concentrations (1.0 mg Cl‐ L−1). Retention times of o‐TFMBA, 2,6‐DFBA, and PFBA by IC analysis ranged between 1.79 and 2.62 min with a linear detection response achieved across a 0.25 to 25 mg L−1 concentration range. These results indicate that IC analysis is an accurate and expedient means of determining both single and multiple fluorobenzoate and Br‐ concentrations in soil solutions and natural waters.
Release of Nitrogen from Ureaform Fractions as Influenced by Soil pH
Authors: Tlustos P. , Blackmer A. M. 
Published: July 2010

AbstractUreaforms are slow‐release N fertilizers that have potential for minimizing problems associated with leaching of NO‐3 from soils and accumulations of NO‐3 in vegetable crops. We studied the effects of soil pH on rates of release of N from various ureaform fractions. Three fractions (soluble in cold water, insoluble in hot water, and soluble in hot water but insoluble in cold water) were separated from a 15N‐labeled ureaform, and mineralization of N from these fractions and from labeled urea was studied in six soils having pH values ranging from 5.2 to 7.8. The results showed that rates of inorganic N (NH+4 and NO‐3) release were extremely pH dependent; they varied > 100‐fold for the cold‐water‐insoluble fractions. The cold‐water‐insoluble fractions were largely responsible for slow release of N in acid soils, but these fractions and much of the cold‐water‐soluble fractions were essentially inert in soils above neutrality. The results suggest that successful use of ureaform fertilizers would require modifications in rates of application or composition of the ureaform to adjust for differences in soil pH.
Stability of Synthetic Sand‐Clay Aggregates after Wetting and Drying Cycles
Authors: Singer M. J. , Southard R. J. , Warrington D. N. , Janitzky P. 
Published: July 2010

AbstractWe hypothesized that the lack of structure and low aggregate stability characteristic of many California Central Valley soils was due, in part, to infrequent wetting and drying cycles. We created synthetic aggregates by drying a slurry of 0.1‐ to 0.5‐mm‐diam. acid‐washed quartz sand and varying amounts of Ca‐saturated reference smectite, kaolinite, or illite at 40 °C. The resulting dry mixtures were crushed and sieved, and the 0.5‐ to 1.0‐ and 1.0‐ to 2.0‐mm‐diam. synthetic “aggregates” were subjected to up to 80 wetting and drying cycles. The wet aggregate stability (Yoder method) of 1.0‐ to 2.0‐mm‐diam. aggregates with 5% clay decreased, regardless of clay type, after 32 wetting and drying cycles. The smectite and illite 0.5‐ to 1‐mm‐diam. aggregate stability did not change significantly after 32 cycles. Following a decrease after eight cycles, wet stability for the 0.5‐ to 1‐mm 5% kaolinite aggregates increased to equal the zero‐cycle stability after 32 cycles. Increasing clay content to 25% increased the initial smectite wet aggregate stability, but decreased the kaolinite and illite wet aggregate stability for both aggregate size fractions. Scanning electron micrographs of the smectite‐sand aggregates showed that the sand grains became more tightly packed and clay became more uniformly distributed over the grains and formed grain bridges with increasing number of cycles. We attribute variation in response to wetting and drying cycles to different clay‐clay and clay‐sand interactions caused by inherent structural differences among the clays.
Simultaneous Use of Transmitted and Incident Ultraviolet Light in Describing Soil Microfabrics
Authors: Hartmann C. , Tessier D. , Wilding L. P. 
Published: July 2010

AbstractA technique for studying thin sections using both transmitted and incident (reflected) ultraviolet (UV) light has been developed. These two light modes used simultaneously may clearly distinguish pore space, plasma (micromass), and skeleton grains (coarse fraction). For this purpose, either a simple binocular or a petrographic microscope can be used. This technique is complementary to classical methods described in the literature for thin‐section analysis and will, at least under conditions discussed here, help alleviate problems encountered in examining thin sections when the skeletal and plasma phases confound porosity identification and measurement.
Liquid Component of Evaporative Flow in Two Tilled Soils
Authors: Jalota S. K. , Prihar S. S. 
Published: July 2010

AbstractShallow tillage is generally considered to reduce evaporation by checking upward liquid flow within and across the tilled layer. To verify this contention, we partitioned the total water loss from tilled soil into loss from the tilled (5‐cm‐deep) layer per se and upward flow across the interface of the tilled layer and untilled soil. This was done to verify the occurrence and extent of liquid flow across the junction of tilled and untilled soil and within the tilled layer, and to facilitate modeling evaporation from tilled soil. The determinations were made in 10‐cm‐i.d., 95‐cm‐deep columns filled with silt loam and sandy loam soils. For 1 or 2 d after tillage, water loss from the tilled layer constituted a major portion of the total flux. However, it became negligible after 7 d in the sandy loam and 12 d in the silt loam while the flux across the interface increased. Liquid flux across the interface in 30 d of drying after tillage amounted to 72 and 42% of total loss under low and high atmospheric evaporativity, respectively, in the silt loam and 20 and 30%, respectively, in the sandy loam. The total liquid flux, taken as the difference between the experimentally determined total loss from the tilled soil and the vapor flux computed from the tilled layer by Hanks' (1958) equation, was identical in both time pattern and magnitude to that computed from the moisture profiles predicted numerically from the water‐content gradients, diffusivity D(θ), and hydraulic conductivity K(θ). Thus, the upward capillary flow was not completely cut off by tillage; it was only retarded because of the change in D(θ).
Soil‐Macropore and Layer Influences on Saturated Hydraulic Conductivity Measured with Borehole Permeameters
Authors: Wu L. , Swan J. B. , Nieber J. L. , Allmaras R. R. 
Published: July 2010

AbstractThe borehole permeameter technique can produce erratic saturated hydraulic conductivity (Ksat) in soils with macropores and abrupt layers because operating theory assumes homogeneous and isotropic conditions. Dye application during an infiltration test demonstrated water movement in macropores and erratic Ksat or matric flux potential (ϕm). To evaluate the effects of macropores, cracks, and layered soil on Ksat and ϕm, a finite element solution of the Richards equation was used to simulate infiltration from a borehole (0.03‐m radius and 0.50 m deep) with a constant head (H) of 0.05 or 0.10 m. Borehole infiltration (for 2 h) was simulated for a Rozetta silt loam (fine‐silty, mixed, mesic Typic Hapludalf) with four configurations: homogeneous, layered, a cylindrical macropore centered at the borehole base, and a crack intersecting the borehole wall. Simulated flow rates were increased by 29% (with H = 0.05 m) and 21% (with H = 0.10 m) when a cylindrical macropore (4 mm by 0.10 m) was located at the borehole base. Respective increases were 25% (H = 0.05 m) and 20% (H = 0.10 m) when a crack extending 0.1 m laterally intersected the borehole wall. Three methods were tested for calculating Ksat. The simultaneous‐equations approach (SEA) using either the Guelph or the Philip model for a homogeneously configured borehole estimated Ksat within a factor of 2 from input Ksat, but the Laplace analysis method overestimated input Ksat by a factor of 5 to 12. The fixed α value (α = Ksat/ϕm) method with either the Guelph or Philip model estimated Ksat close to input Ksat when a proper α value was chosen, but the proper α value differed by soil and model. A negative Ksat was computed using the SEA with the Guelph model when macropores intersected the base of a borehole; negative Ksat or ϕm were produced when cylindrical macropores laterally intersected the borehole wall, depending on the vertical locations of the macropores. Soil with layered hydraulic properties also produced unrealistic Ksat.
Evaluation of the Relationship between Compressibility and Shear Strength of Andisols
Authors: McNabb D. H. , Boersma L. 
Published: July 2010

AbstractAndisols, and other soils with low bulk density, are often considered less susceptible to compaction than soils with higher bulk densities. This study was initiated to test the hypothesis that high soil strength reduces the compressibility of soils with low bulk density. The compressibility and shear strength of three Andisols were compared with that of a fine‐textured soil of crystalline mineralogy with a higher bulk density. Soil compressibility was measured in one‐dimensional consolidation tests and shear strength was measured in direct shear tests. Cores of undisturbed soil were collected from the 7‐ to 12‐cm depth of four forested soils in western Oregon. Cores were saturated prior to testing. Compression indexes were 0.231 for the coarse‐textured Andisol, 0.262 and 0.275 for two fine‐textured Andisols, and 0.320 for the fine‐textured soil of crystalline mineralogy, which was significantly higher than that of the Andisols. The angle of internal friction of the Andisols ranged from 33.0 to 33.7°, but was 28.9° for the fine‐textured soil of crystalline mineralogy. A nonlinear model was successfully adapted to describe the relationship between bulk density and normal stress using data of these sample sets. These samples had different initial and compressed bulk densities. We concluded that Andisols are less compressible than other denser soils because of a high shear strength. The question of the susceptibility to compaction of soils with low bulk density must be reconsidered.
Unsaturated Transport Processes in Undisturbed Heterogeneous Porous Media: II. Co‐Contaminants
Authors: Jardine P. M. , Jacobs G. K. , O'Dell J. D. 
Published: July 2010

AbstractDepartment of Energy facilities involved in defense‐related activities have generated huge quantities of low‐level radioactive mixed waste during the past several decades. The waste is composed of organically complexed contaminants, also known as co‐contaminants, which are typically disposed in shallow land burial sites. The objective of this study was to provide an improved understanding of the geochemical processes controlling co‐contaminant transport in heterogeneous, unsaturated subsurface media. Large undisturbed columns were isolated from a proposed waste site consisting of fractured saprolitic shale, and the steady‐state unsaturated transport of Co(II)EDTA2−, Co(II)EDTA−, and SrEDTA2− was investigated at −10 cm pressure head. Subsurface Fe and Al sources effectively dissociated the SrEDTA2− co‐contaminant and Sr was transported as a reactive, uncomplexed species. The EDTA readily complexed with Fe and Al, resulting in significant solid‐phase modification of the porous media via chelate‐enhanced dissolution and redox alterations. Displacement of Co(II)EDTA2− through the subsurface media was characterized by a MnO2‐mediated oxidation of the co‐contaminant with subsequent formation of Co(III)EDTA−. The latter co‐contaminant was an extremely stable complex that was transported through the subsurface as a single, reactive entity and exhibited an overall retardation that was similar to the uncomplexed contaminant Co2+. Modeling results using equilibrium and nonequilibrium formulations of the convective‐dispersive equation suggested that a large portion of the transported Co(III)EDTA− was controlled by time‐dependent sorption reactions with the solid phase. Although the solid‐phase retention of Co(III)EDTA− and Co2+ were similar, the sorption kinetics of the former were more sluggish relative to Co2+ and contaminant transport was accelerated in the presence of EDTA.
Growing Corn Root Effects on Interrill Soil Erosion
Authors: Bui Elisabeth N. , Box James E. 
Published: July 2010

AbstractThe relationship between plant roots and interrill soil erosion is important in dynamic soil erosion predictions. Rainstorm simulations of similar intensity (63.5 mm h−1) were conducted in the summer of 1989 on 1 by 1 m field plots of Cecil sandy loam (clayey, kaolinitic, thermic Typic Kanhapludult) to study the effect of different root length densities, Lv (cm cm−3), of corn (Zea mays L.), during vegetative, preanthesis, and anthesis plant developmental stages on interrill soil erosion. Sediment loss and runoff data were assigned to treatments, Lva, on the basis of Lv range to reduce rooting variability associated with plant developmental stage. To avoid confounding by canopy cover, corn plants were cut at the stem base and removed for the first four sets of simulations. A reference set of simulations was performed on a fallow plot containing no roots, Lva0. Runoff and detached sediment were collected in buckets from each plot during successive 5‐min intervals over a 1‐h period. Thirty cores, 5 cm in diam. and 5 cm deep, were taken from each 1‐m2 plot and roots were washed from the cores and measured. Means for runoff and detached sediment were generally not significantly different for the high Lv or Lva, and Lva0. When Lva was <1.5 cm cm−3, runoff and detached sediment were significantly lower during the first 30 min of simulated rainfall. High densities of live corn roots did not reduce interrill soil erosion from a moldboard‐plowed Cecil sandy loam.
Evaluating Nitrate Recovery by Ion‐Exchange Resin Bags
Authors: Wyland L. J. , Jackson L. E. 
Published: July 2010

AbstractIon‐exchange resin (IER) bags were tested as traps for leached soil NO−3‐N. In laboratory experiments, IER bags recovered 84.7% of the NO−3‐N from solutions containing 0.09 to 40.74 g NO−3‐N kg−1 resin, but recovery decreased at higher concentrations. In soil columns, NO−3‐N recovery was poor (36.2%) when NO−3‐N moved slowly through the soil profile after a rapid single pulse, but improved (87.1%) when higher flow was sustained. In the field, estimates of leached NO−3‐N using IER bags fell within the range of values estimated from soil cores and suction lysimeters. Advantages of IER bags are attributed to cumulative recovery of NO−3‐N during passive interception of gravitational water flow.
Plant Responses to Sulfate and Chloride Salinity: Growth and Ionic Relations
Authors: Curtin D. , Steppuhn H. , Selles F. 
Published: July 2010

AbstractGrowing salt‐tolerant crops is one of the more cost‐effective strategies for coping with soil salinity, which is a significant factor affecting crop production and agricultural sustainability on the Canadian prairies. This study was carried out to determine if salt tolerance data, generated by traditional Cl (NaCl/CaCl2) salinization procedures, are appropriate to the prairies, where SO4 salinity predominates. Barley (Hordeum vulgare L., cv. Bonanza) and kochia [Kochia scoparia (L.) Schrad.] seedlings were grown in sand culture and salinized with either Cl or SO4 salts. The latter system was designed to mimic the natural salinity of prairie soils. The results showed that plant responses to salinity depend on the kind of salts (sulfates or chlorides) contributing to salinity as well as on the total electrolyte concentration. Growth was significantly better (by an average of 17%) on the SO4 system. However, barley salinized with SO4 salts developed severe Ca deficiency at high salt concentrations (electrical conductivity [EC] 17.5–27.5 dS m−1) because of low solubility of Ca. Kochia, which is more efficient than barley in absorbing Ca, was not limited by Ca. Barley and kochia tended to have higher selectivity for nutrient cations (Ca, Mg, and K) over Na when the plants were grown on the Cl salt system. This may be an indication of a beneficial effect of the high Ca supply in the NaCl/CaCl2 salt system on membrane selectivity. Our results show that there are many possible interactions between salt concentration, salt type, and plant nutrition. The significance of these interactions for salt tolerance testing may vary from crop to crop and may depend on factors such as the nutrient concentration in the growing medium. From a practical standpoint, however, response functions generated by NaCl/CaCl2 salinization probably provide an acceptable measure of the tolerance of most crops to SO4 salinity.
Modeling Water Flow from Subirrigation with Drainage
Authors: Kirkham Don , Horton Robert 
Published: July 2010

AbstractThe stream function for a flow domain, if properly chosen, can be used analytically to generate the boundary conditions of the domain and obtain flow velocities at all points in it. To illustrate the procedure, we developed and mathematically analyzed a physical model that describes saturated water flow from a subirrigation system with drainage. The theory takes the radius of drain and irrigation tubes into account and thus refines earlier work, which hypothesized slit irrigation tubes and slit drain tubes of thin rectangular cross section rather than circular ones. The theory additionally shows how the subirrigation water table changes when the drain tubes are switched to an irrigation mode. A series of three flow nets are included representing subirrigation alone, subirrigation with simultaneous drainage, and dual‐pipe subirrigation. The three cases show how the problem parameters influence heads and flows and thus give insight into strengths and weaknesses of the three water management systems.
Soil Solution Sampled with and without Tension in Arable and Heathland Soils
Authors: Magid Jakob , Christensen Niels 
Published: July 2010

AbstractThe composition of soil solution is of importance in many aspects of soil science. It is therefore of interest to reach an understanding of when to apply a certain sampling method in preference to others. For this reason we evaluated both zero‐tension and tension samplers for use in long‐term monitoring of soil solutions sampled fortnightly in a sandy arable soil plot from 1987 to 1990 and in a sandy calluna heathland plot from 1986 to 1990. Compared with tension solution, the zero‐tension solution in the arable plot was more influenced by the soil solution composition from the upper fertilized plow layer, and in the heathland plot the zero‐tension solution was more influenced by the composition of rainwater. On both plots the temporal variability in the amount of nonsorptive solutes, as well as systematic differences in the amount of sorptive solutes sampled by these techniques, give support to the notion that zero‐tension samples represented the flux concentrations, whereas the tension samples were approximations of resident concentrations. In conclusion, if the objective of sampling soil solution is to gain insight in internal processes in a specific soil layer, tension methods are most appropriate. On the other hand, if the objective is to study the loss of solutes from a given layer, zero‐tension methods should be used. Using less mobile water as a basis for the estimate of leaching processes may lead to biased results, especially when considering sorptive solutes. The estimates of nonsorptive solute leaching may also become biased, dependent on the coincidence of high drainage with biased concentration measurements.