bluuebunny/crossref_metadata_2025_split huggingface dataset:
Independent Calibration of a Mechanistic‐Stochastic Model for Field‐scale Solute Transport Under Flood Irrigation
Authors: Jaynes D. B. , Rice R. C. , Bowman R. S. 
Published: July 2010

AbstractSolute leaching at the field scale can show considerable variability because of variations in the hydraulic properties of the soil. A simple mechanistic‐stochastic model for predicting solute transport on this scale during intermittent flood irrigation is described and a method of calibrating the model independent of any leaching measurements is presented. The model assumes that the pore water velocity varies horizontally across the field but is uniform in the vertical direction. Explicit expressions for chemical diffusion and hydrodynamic dispersion are not included in the model. Instead, horizontal variations in the velocity serve to disperse the solute when measured on a field wide basis. The model requires knowledge of the probability density function for the velocity and estimates of the function parameters. These parameters were estimated from variations in infiltration rates measured within 63 ring infiltrometers and from water retention data. Model simulations of Br− leaching agreed well with most measured data for both position of the tracer peak and the degree of solute spreading, indicating that at least under flood irrigation, variations in infiltration as controlled by soil hydraulic properties explain most of the observed variations in Br− leaching over a field.
Single‐Column Ion Chromatography: IV. Determination of Arsenate in Soils
Authors: Mehra H. C. , Frankenberger W. T. 
Published: July 2010

AbstractA method has been developed for the determination of arsenate (AsO3−4) in aqueous soil extracts by single‐column ion chromatography (SCIC) at trace levels. The eluent stream consisted of 6 mM p‐hydroxybenzoic acid (PHBA) at pH 7.0. Separation was carried out on a low‐capacity anion‐exchange resin column with the anion species being quantified by conductometric detection. Resolution between AsO3−4 and PO3−4 was Rs = 1.93. The method allows precise (RSD, relative standard deviation = 1.12 to 7.87%) trace amount measurement of AsO3−4 (detection limit, 0.092 mg L−1) in the presence of Cl, NO−3, PO3−4 and SO2−4. The AsO3−4 signal becomes masked limiting separation and detection when PO3−4 exceeds 30 mg L−1. Under the conditions described, arsenite (AsO3−3) was not detected. Analysis of aqueous soil extracts for AsO3−4 by SCIC agrees closely with those values obtained by atomic absorption spectrometry and inductively coupled plasma emission.
Salt‐induced Manganese Solubilization in California Soils
Authors: Khattak Riaz A. , Jarrell Wesley M. 
Published: July 2010

AbstractThe solubility of Mn in soil solution depends on soil pH, redox potential (Eh), amount and type of higher valency Mn oxides, and a variety of organic and inorganic soil constituents. Laboratory experiments were conducted to determine the extent of salt‐induced Mn release from a variety of California soils. To investigate the effect of salinity and time of incubation on Mn release, Redding (fine, mixed, thermic Abruptic Durixeralf) clay loam and Hanford (coarse‐loamy, mixed, nonacid, thermic Typic Xerorthent) sandy loam soils were saturated with 0, 75, and 150 mol m−3 NaCl‐CaCl2 solution (prepared on an isoequivalent basis) and incubated in a glasshouse for 0, 2, 4, 7, and 10 d. The Mn concentration in the soil saturation extract increased 2‐ to 4‐fold with time of incubation at all levels of salt solution and 7‐ to 16‐fold with increasing salt concentrations (ionic strength) at a given incubation time. Increases in [Mn] with time and increases in pH in the nonamended soil suggest reduction of Mn oxides while increases in [Mn] with increasing salt levels implicates the release of Mn into soil solution through reduction of Mn oxides, displacement by Na+ and Ca2+ and/or ligand (Cl−) complexation processes. In another experiment, Mn release by NaCl‐CaCl2 salinity was investigated in 20 California soils varying in pH, easily reducible Mn (hydroquinone + NH4OAc), total Mn (HF‐HNO3‐HClO4), and in total C concentrations. These soils were saturated with 0, 37.5, 75.0, 112.5, and 150.0 mol m−3 NaCl‐CaCl2 solution and extracted after 5 d of incubation in a glasshouse. Depending upon soil pH, easily reducible and total soil Mn levels, the [Mn] in soil saturation extracts increased from 10 to 4000 mmol m−3 for 150 mol m−3 NaCl‐CaCl2 levels over the nonsaline (deionized water) treatments. Although the order of magnitude of salt‐induced Mn release was high in soils low in pH and high in easily reducible Mn, a significant salt effect was noted for even high pH (above 7.0) soils. Multiple regression analysis showed that Mn solubility in salt‐amended soils was mainly related to soil pH, easily reducible and total Mn (R2 = 0.68***, significant at p < 0.001). This indicates that factors related to geochemical environments in which soils exist might explain the variations in Mn solubility in salt‐amended soils.
Residue Management Effects on Soil Temperature
Authors: Unger Paul W. 
Published: July 2010

AbstractSoil temperatures are influenced by many factors, including surface residues. In turn, soil temperatures influence such factors as seed germination, plant growth, nutrient availability, insect populations, and pesticide degradation. Because of the increased use of conservation tillage involving surface residues, a better understanding of residue management effects on soil temperatures is needed. The objective of this study was to determine the effects of residue management practices on soil surface temperatures and on soil surface‐air temperature relationships for the southern Great Plains. Soil surface and air (at 2‐m height) temperatures were measured during the fallow period after winter wheat (Triticum aestivum L.) harvests in 1982 and 1983. Residue management treatments were disk, sweep, and no‐tillage (with standing or shredded residues). Minimum surface temperatures differed only slightly among treatments at different seasons of the fallow period (summer, fall, winter, spring). Maximum temperatures were highest with no‐tillage (standing residues) after dryland wheat in all periods, except in winter when they were highest with no‐tillage with shredded residues. Relationships between soil surface and air temperatures were highly significant (R2 = 0.931, P ≥ 0.001). The relationships developed from the 1983 to 1984 data were used to predict surface temperature from weather station air temperatures for the 1982 to 1983 period. Differences between observed and predicted mean temperatures were significant only for no‐tillage with standing residues in summer and fall and with shredded residues in spring. Normalized soil surface temperatures were affected more by season of the year than by residue management treatment.
Sequential Extraction of Iron, Manganese, Aluminum, and Silicon in Soils from Two Contrasting Watersheds
Authors: Arnseth R. W. , Turner R. S. 
Published: July 2010

AbstractSoil samples from two contrasting forested watersheds on the U.S. Department of Energy Oak Ridge Reservation in Oak Ridge, TN, were chosen for selective extraction of organics, Fe, Mn, and aluminosilicates. The extracts were analyzed for Fe, Mn, Al, and Si, and the results were evaluated in terms of pedogenic processes. The clay mineralogy was determined on a subset of the samples. Differences between the watersheds were observed in clay mineralogy and in the vertical distribution of extractable Mn. Walker Branch soils, developed on Knox Group carbonates, exhibit vertical flow paths capable of transporting soluble Mn deep in the profile before precipitation. Physically separated zones of Mn and Fe precipitation are observed in Walker Branch cores wherein mid‐depth maxima in citrate‐bicarbonate‐dithionite (CBD)‐extractable Fe are not mimicked in the Mn‐specific extractable Mn profiles. Melton Branch soils, developed on shaly carbonates of the upper Maryville Limestone, with shaly residua persisting to the surface in some areas, retain a structure that obstructs vertical flow, forces lateral flow, and provides microenvironments for water stagnation. When these microenvironments experience periodic desiccation and oxidation, Fe‐ and Mn‐oxyhydroxides are precipitated and coprecipitated. Therefore, clay mineralogy reflected differences in parent material whereas differences in the distribution of extractable Mn‐oxyhydroxides probably reflect the distribution of soil microenvironments conducive to Mn accumulation and oxidation with implications for soil water flow patterns.
An Inexpensive, Portable System for Drilling into Subsurface Layers
Authors: MacDonald Lee H. 
Published: July 2010

AbstractA relatively simple adaptation of rock drilling equipment to a portable two‐man power auger creates an inexpensive device capable of drilling 45‐mm diam. holes through both surface materials and moderately hard rock to a depth of at least 6 m. The equipment is portable and hence ideal for use in rugged terrain, but a local water source is required. The total cost for all the materials, including the power auger and water pump, is estimated at $1500. Drilling rates of 0.01 to 0.10 m min−1 were obtained in moderately hard to hard rocks in the Central Sierra Nevada of California, but the relatively low rotations per minute of a power auger suggest that drilling will be progressively less efficient in harder rocks. Use of this devise should allow more extensive investigations into the role of saprolites, fractured rock, and other subsurface layers in hydrologic and geomorphic processes.
Evaluation of Soil Recompaction by Transverse Wheeling of Tillage Slots
Authors: Blackwell P.S. , Jayawardane N. S. , Blackwell J. , White R. , Horn R. 
Published: July 2010

AbstractNarrow, gypsum‐enriched slots are a technique for ameliorating texture‐contrast soils (Natrixeralfs) in Australia. It is expected that undisturbed soil adjacent to the slots will protect loosened soil within the slot from recompaction by wheel traffic. Vertical stresses in slots were compared to those in troughs formed by ripping, and to the stresses between slots and ripping troughs. Stresses were smaller in slots than outside, unless increased by downward movement of the whole slot contents. Inside troughs the stresses were similar to those outside. Macrostructure after zero, one, or four wheelings was also measured. There was more increase of density and loss of macroporosity in ripping troughs than in slots. However, the macrostructure in the slots could be seriously damaged after four consecutive passes over soil at water contents near the lower plastic limit. Thus gypsum‐enriched slots provide only a limited amount of protection from compaction and the amelioration technique needs to be associated with suitable techniques for the management of subsequent traffic.
Evaluation of Three Aluminum Assay Techniques for Excluding Aluminum Complexed with Fluoride or Sulfate
Authors: Alva A. K. , Sumner M. E. , Miller W. P. , Li Y. C. 
Published: July 2010

AbstractAluminon, 8‐hydroxyquinoline and ferron reagents are often used to measure Al in solutions. Since Al complexed with F‐ or SO2‐4 is less phytotoxic, in solutions containing these ligands an estimate of Al excluding that complexed with F‐ and/or SO2‐4 represents predominantly phytotoxic Al. In the present study, the capacity of the above reagents to exclude Al complexed with F‐ or SO2‐4 was evaluated in solutions containing 40 µM Al with 20 to 640 µM F‐ or 40 to 5120 µM SO2‐4 at pH 4.5. The effects of varying reaction time from 15 s to 30 min on the recovery of Al by the respective reagents was also investigated. The sum of predicted (by MINTEQ speciation model) concentrations of Al3+ and hydroxy‐Al monomers decreased to 45% or to 0.6% of total Al in solutions with 5120 µM SO2‐4 or 80 µM F‐. The concentration of Al measured by 8‐hydroxyquinoline (15‐ or 60‐s reaction) or aluminon (15‐s reaction) appeared to exclude entirely Al complexed with F‐. All three reagents, however, regardless of reaction time, failed to exclude Al complexed with SO2‐4. Therefore, 8‐hydroxyquinoline (15‐ or 60‐s reaction) aluminon (15‐s reaction) reactive Al would accurately represent phytotoxic Al in the presence of F‐, while ferron reagent is likely to overestimate the phytotoxic Al. In the presence of SO2‐4, however, all three reagents are likely to overestimate the phytotoxic Al.
Effects of Potassium and Lime Applied for Coastal Bermudagrass Production on Sandy Soil
Authors: Cripps R. W. , Young J. L. , Leonard A. T. 
Published: July 2010

AbstractThe deep sandy soils of eastern Texas are inherently low in available Ca and Mg. Also, Coastal bermudagrass [Cynodon dactylon (L.) Pers.] grown on these soils has exhibited K deficiency symptoms. This study was conducted to evaluate the effects of K fertilization and liming on (i) Coastal bermudagrass yield; (ii) plant tissue K, Ca, and Mg concentrations; and (iii) K, Ca, and Mg soil test values. The study was conducted on a Darco fine sandy loam (loamy, siliceous, thermic, Grossarenic Paleudults) from 1981 through 1983 using four rates of K fertilization (0, 140, 279, and 419 kg K ha−1 year−1) and six lime rates (0, 2.2, 3.6, 4.5, 9.0, and 18.0 Mg ha−1). Significant yield responses to both K fertilization and liming were observed in 1982 and 1983. Potassium fertilization resulted in increased plant K concentration and decreased plant Ca and Mg concentrations. Liming increased Ca and Mg concentrations. Maximum yields were obtained with K concentrations of about 22.0 g K kg−1 plant tissue. Increased plant K concentration did not depress Ca and Mg concentrations below 1.8 and 1.1 g kg−1, respectively. After 3 yr of K fertilization, soil test K values were increased only at the 419 kg K ha−1 rate. No yield response to liming was measured above 3.6 Mg lime Ha−1. At the conclusion of the study, soil pH and extractable Ca and Mg values in 3.6 Mg lime ha−1 plots were 5.3, 333 mg kg−1 and 30 mg kg−1, respectively.
Aluminum Leaching by Mineral Acids in Forest Soils: II. Role of the Forest Floor
Authors: James Bruce R. , Riha Susan J. 
Published: July 2010

AbstractTo simulate the effects of forest floor organic horizons on leaching of labile and nonlabile forms of Al from underlying mineral soil horizons by acid precipitation, albic (E), ochric (A), and spodic (Bs) mineral horizons were leached in the laboratory with 1.0 mM HNO3, 0.5 mM H2SO4, or NH4NO3 control solutions at ionic strength 0.01 with or without an Oi‐Oe‐Oa forest floor horizon sequence (FF) above each mineral horizon. Adding 2 and 0.5 cmolc (H+)/kg to the organic horizons and mineral soils, respectively, simulated snowmelt additions to the soils in mountainous regions of the northeastern USA, where lake acidification has been attributed to acid precipitation leaching of forest soils. Total Al concentrations in leachates from soil columns containing the E or A horizon below the FF were greater than the sum of the concentrations in leachates from the FF and mineral horizon when leached separately. This positive synergistic behavior of the FF‐mineral horizon sequences was also observed in the FF‐Bs horizon sequence when leached with the control solution, but the synergism was negative for both forms of Al when leached with the acids. Sulfuric acid leached less Al from the Bs horizon than did HNO3, regardless of the presence of an FF, but HNO3, H2SO4, and control solutions leached similar concentrations of Al from the E and A horizons. The FF effects on the mineral soil leachates were attributed to effects of Ca, SO4, NO3, and dissolved organic C leached from the FF to the mineral horizons since the FF removed nearly all added H+.
An Economical, Digital Meter for Gypsum Soil Moisture Blocks
Authors: Fowler W. B. , Lopushinsky W. 
Published: July 2010

AbstractMost meters for soil moisture blocks are designed for use with relatively moist soils. This paper describes a meter that utilizes a frequency output proportional to block resistance and that is usable over a relatively wide range of soil moisture. Advantages of this meter are digital display, easy and reliable operation, low power drain, and simple economical design. It is stable with changes in temperature, lead length to sensors, and battery voltage. The meter functions satisfactorily with several types of commercially available gypsum blocks and provides good resolution of matric water potential in the range of −0.06 to −1.5 MPa.
Effect of Access Hole Properties on Soil Water Content Determination by Neutron Thermalization
Authors: Amoozegar A. , Martin K. C. , Hoover M. T. 
Published: July 2010

AbstractInstallation of snugly fitted neutron access tubes in uniformly sized holes is difficult to achieve in many soils. This is especially true for areas not readily accessible by heavy machinery. We evaluated the effect of access hole diameter and a kaolinite soil slurry placed around loosely fitted access tubes on soil water content determination by neutron thermalization. Uniformly sized 5.1 (control hole), 7.6, and 9.1‐cm diam. holes, and a nonuniformly sized 5.5‐ to 6.75‐cm diam. hole were constructed at the vertices of five 80‐ by 80‐cm square plots on a Cecil soil (clayey, kaolinitic, thermic Typic Hapludult) within a small pasture. An additional uniformly sized 5.1‐cm diam. hole was constructed 80 cm from the control hole at each plot. A 2‐in. Al irrigation pipe was used as access tubing. The access tubes were fitted tightly in the 5.1‐cm holes and were placed at the center of the larger holes. A kaolinite‐soil slurry was placed around the access tubes in the nonuniformly sized holes. Count ratios obtained at various depths in each hole type were linearly regressed against the count ratios for the corresponding control hole at each plot. While there was a statistically significant one to one relationship between the count ratios in the control and 5.1‐cm holes, the coefficient of determination (r2) was only 0.69. The r2's for the relationship between the count ratios for the control hole and the other three hole size treatments were between 0.61 and 0.72, and the regression coefficients (b) decreased with increasing access hole diameter. The calibration curve r2's for the 5.1‐, 7.6‐, 9.1‐cm holes and the slurry backfilled holes were 0.71, 0.62, 0.76, and 0.61, respectively. The slope of the calibration curves generally increased with increasing hole size indicating some loss of sensitivity with the larger holes.
A Simple Approximate Equation to Calculate Diffusivities from One‐Step Outflow Experiments
Authors: Valiantzas J. D. 
Published: July 2010

AbstractGardner's approximation for determining soil water diffusivities, D(Θ), from one‐step outflow experiments may deviate significantly from actual D(Θ) values. By the systematic analysis of a weighting function which corrects the Gardner's solution, a new simple and accurate equation is derived. Numerical outflow experiments were performed for a variety of arbitrary D(Θ) functions to demonstrate the validity of the equation. Results indicate that the suggested procedure is applicable even for nonlinear ln D(Θ) functions and is more accurate than other previous methods. The present equation has been applied to analyze one‐step outflow experiments in two soils. Numerical predictions of the outflow volumes are in good agreement with laboratory measurements.
Competitive Ion Exchange Behavior on Oxides
Authors: Schulthess C. P. , Sparks D. L. 
Published: July 2010

AbstractCation adsorption data using MnCl2 and the proton isotherm of a Si oxide were compared with pH as the variable. The cation adsorption data quantitatively correlated with the proton isotherm analysis; the H+/Mn2+ exchange ratio was 6.0. The presence of adsorption plateaus are due to pH‐dependent (step) reactions; this was suggested as the only reasonable explanation for adsorption isotherms covering several pH units. These plateaus are very important to surface adsorption modeling, and may be significant in determining experimental conditions for other soil and colloidal research. The proton isotherm obtained using the backtitration technique had some pH‐ and salt‐dependent shifts that may involve competitive reaction mechanisms between the ions in solution and the oxide surface. Cation adsorption studies were also used to determine the total number of sites available; this resulted in an initial estimate of 13.6 µmol m−2. The authors review several topics related to ion exchange modeling and data interpretation; emphasis is placed on avoiding an oversimplified view of the chemical nature of the solidaqueous phase.
Kinetics of Calcium‐Magnesium Exchange on Soil Using a Stirred‐Flow Reaction Chamber
Authors: Seyfried Mark S. , Sparks Donald L. , Bar‐Tal Asher , Feigenbaum Sala 
Published: July 2010

AbstractIon exchange reaction kinetics may significantly affect effluent concentrations under both laboratory and field conditions. One limitation to the study of exchange reaction kinetics has been the lack of appropriate methods. A stirred‐flow method that uses a constantly stirred reaction chamber with constant, steady inflow of the reactant solution and outflow of reactants and products was tested. The method allows for continuous sampling and accommodates a wide range of soil particle sizes. The basic assumption of a well mixed solution in the chamber has not been tested, however. That assumption was tested over a wide range of flow rates and found to be applicable. The measurable reaction rates using the stirred‐flow method were estimated using a simple empirical equation that allowed the use of the reaction half‐time (t1/2) to describe reaction rates. Values of t1/2 of 3 min and greater were detectable while a 0.3 min t1/2 was not detectable under the experimental conditions. Calcium‐Mg exchange on a Nordya sandy loam (Typic Rhodoxeralf) soil from Israel was investigated. Measured effluent concentrations were compared with values calculated assuming no adsorption preference for Ca or Mg, and assuming local equilibrium between adsorbed and solution phases prevailed. Effluent concentrations were accurately predicted when the reaction direction was from equilibrium with Ca solution to equilibrium with Mg, but not for the reverse. These results suggest that either the local equilibrium or the nonpreference assumption was not appropriate. Flow rate reduction and stoppedflow experiments indicated that local equilibrium prevailed. Equilibrium exchange isotherms obtained using the chamber indicated a preference for Ca over Mg.
Rheology of Mixed Kaolinite‐Montmorillonite Suspensions
Authors: Keren R. 
Published: July 2010

AbstractThe rheological characteristics of mixed kaolinite‐montmorillonite suspensions as a function of adsorbed ion (Na+ or Ca2+), montmorillonite concentration and suspension pH were studied in aqueous medium at a total clay concentration of 50 g kg−1 and 25 °C. The suspensions of kaolinite showed a Newtonian rheology regardless of the adsorbed ion and pH, indicating that neither structural breakdown nor orientation occurs during the flow. Non‐Newtonian rheology was observed when small amounts of montmorillonite (saturated by Na+ or CA2+ ions) were introduced into the kaolinite suspensions at pH values of 4.0 and 7.0. An association between kaolinite and montmorillonite platelets appears to take place, with the intensity (as inferred from the extrapolated shear stress and viscosity) higher at pH 4.0 than at pH 7.0. This association is probably due to the attraction between the positive charge on the pH‐dependent charge surfaces of kaolinite and the negative charge associated with the planar surfaces of montmorillonite. When the pH increases well above the point of zero charge of the pH‐dependent charge surfaces, the association between kaolinite and montmorillonite platelets is negligible.