bluuebunny/crossref_metadata_2025_split huggingface dataset:
Factors Affecting the Formation of Quasi‐Crystals of Montmorillonite
Authors: Greene R. S. B. , Posner A. M. , Quirk J. P. 
Published: July 2010

AbstractLight scattering techniques and the development of flow birefringence by suspensions have been used to follow the rearrangement of elementary silicate sheets of Ca‐montmorillonite to form quasi‐crystals.Shaking transforms Ca‐montmorillonite particles in a 0.25M CaCl2 suspension from loose, fluffy floccs into stable, compact particles >2.0µ in lateral extent and as much as 20 to 30 layers thick, known as quasi‐crystals. Quasi‐crystals of similar lateral extent but only four layers thick took longer to form at low electrolyte levels, <10‐3M CaCl2, in which more extensive double layers are present. Dialysis of Ca‐montmorillonite suspensions also produced quasi‐crystals, which are intermediate in thickness between those formed by the above two preparations.The stability of quasi‐crystals was demonstrated by the fact that high energy ultrasonic radiation was required to disrupt their structure.Sodium montmorillonite suspensions subjected to similar conditions of mechanical agitation and dialysis failed to form quasi‐crystals, the only form of aggregation being into unstable floccs.
Unsteady Two‐Dimensional Flow of Water in Unsaturated Soils Above An Impervious Barrier
Authors: Selim H. M. , Kirkham Don 
Published: July 2010

AbstractThe unsteady two‐dimensional, water flow equation for unsaturated soils is solved by use of a finite difference approximation and an alternating‐direction implicit (ADI) method. The two‐dimensional flow medium is a homogeneous soil with an impervious barrier at some depth from the soil surface and having equally spaced trenches. The bottom of the trenches are wetted at time zero and are kept at a constant 0.50 cm3/cm3 water content, the initial soil water content of the flow medium is 0.20 cm3/cm3. Water movement from the walls of the trenches and the soil surface is neglected. Computer results of the water content with time at all locations in the flow medium are obtained for physical data from an Ida silt loam soil for two geometries. For trenches at 120 cm spacing, 30 cm deep, and 30 cm wide, the wetting front reaches a depth of 30 cm in 35 min, and reaches the soil surface in 140 min. For trenches at 60 cm spacing, 15 cm deep, and 15 cm wide, the wetting front reaches a depth of 30 cm in 45 min, and reaches the soil surface in 30 min. The ADI method proves valuable for use with a modern computer to solve unsteady two‐dimensional flow problems.
Diurnal Soil‐Water Evaporation: Time‐Depth‐Flux Patterns
Authors: Jackson R. D. , Kimball B. A. , Reginato R. J. , Nakayama F. S. 
Published: July 2010

AbstractTime‐depth patterns of soil water flux in the 0‐ to 9‐cm zone of a bare field soil are presented for four 24‐hour periods at 3, 7, 16, and 37 days after irrigation. On day 3, the flux at 0 cm (evaporation) dominated the flux patterns for all depths. As the soil dried, this flux decreased and those at the greater depths gradually became dominant. On all 16 days of measurement, downward flux was observed below 1 to 3 cm during several hours between sunrise and early afternoon. Only one period of downward flux was observed for day 3; whereas, 2 to 4 periods were noted for subsequent days. The data demonstrate the dynamic nature of soil water flux in the surface zone of a field soil subjected to diurnally varying environmental conditions.
Use of Indigenous Soil‐Rubidium Absorbed by Cotton Plants in Determining Labile Soil‐Potassium Pool Sizes
Authors: Hafez A. A. R. , Stout P. R. 
Published: July 2010

AbstractThe rubidium/potassium (Rb/K) ratios of natural soils and of most soil‐grown plants are higher than Rb/K ratios of many available fertilizer‐grade potassium salts as revealed by analyses of 24 samples of commercial K‐fertilizers. Low‐Rb K‐fertilizers of 0.02 mmoles Rb/mole K or lower may offer practicable means for field scale tracing of fertilizer‐K absorbed by crop plants when growing under normal management regimes. Whenever K‐fertilization results in lower Rb/K ratios appearing in fertilized plants, this dilution or “reversed‐tagging” of indigenous soil‐Rb with low Rb‐containing K‐fertilizers permits determinations of pool‐sizes of labile soil‐K. Four different soils were compared for NH4OAc extractable‐K, HNO3 extractable‐K, and the pool‐size of labile‐K as determined from Rb/K ratios of K‐fertilized cotton plants (Gossupium hirsutum L.). A large pool size of labile‐K does not necessarily mean that the K supplying power of a soil is large. The Rb/K ratios can also be used to calculate relative amounts of absorbed plant‐K originating from the indigenous soil‐pool vs. the plant‐K derived from a K‐fertilizer.
Weathering of Biotite in Soils of a Humid Tropical Climate
Authors: Ojanuga A. G. 
Published: July 2010

AbstractThe weathering of biotite in soils formed in saprolites derived from granite and gneiss was studied. The soils occurred in the Southwestern Upland of Nigeria which is characterized by a humid tropical climate.Vermiculite and montmorillonite are the usual products of biotite weathering in well‐drained temperature soils, whereas kaolinite appears to be the dominant product in the well‐drained, moderately acidic, tropical soils studied. The formation of kaolinitic pseudomorphs represented a stage in the kaolinization of biotite in the soils. A mechanism for the kaolinization of biotite has been suggested.
Dissolved Aluminum in Acid Sulfate Soils and in Acid Mine Waters
Authors: van Breemen N. 
Published: July 2010

AbstractAnalytical data on water samples from acid sulfate soils and acid mine spoils indicate that the upper limit of dissolved Al is regulated by a basic aluminum sulfate with the stoichiometric composition AlOHSO4. The observed solubility relationship, pAl + pOH + pSO4 = 17.23, can be useful in defining environmental conditions in terms of pH and dissolved sulfate for the occurrence of Al concentrations toxic to plants.
Liming as Related to Solubility of P and Plant Growth in an Acid Tropical Soil
Authors: Amarasiri S. L. , Olsen S. R. 
Published: July 2010

AbstractThe reactions between soil and fertilizer P at six levels of liming were investigated on an acid tropical soil. An acidic soil of pH 3.8 was limed to pH 7.0 in stages. Four levels of phosphorus were added to the soils.For any level of phosphorus, liming decreased soluble P and labile P until the pH reached about 6.5. The phosphate potentials did not lie consistently on known solubility isotherms, but the potentials approached hydroxyapatite at pH values between 6.9 and 7.0. A labile pool of P appeared to govern mainly the concentration of P in the soil solution. Limed soil had a higher maximum adsorption capacity for phosphorus than the unlimed soil. Adsorption of P by the freshly precipitated Fe and Al hydroxides apparently caused the greater inactivation of added phosphorus in the limed soils.Rye (Secale cereale L.) and millet (Setaria italica L.) were grown in the greenhouse at six levels of lime and four levels of phosphorus. The yields and percent P of rye were significantly increased by P without lime, but the response to added P was greater in the presence of lime. Lime with added P caused larger differences in yield and percent P of millet than in rye. Liming increased the yields of millet with added P until a pH of about 5 to 6 was reached, but further additions of lime decreased the yields. The percent P of millet increased with the initial applications of lime, but further additions resulted in a slight decrease of percent P. Plants were healthier and their root system better developed on the limed soil, which probably caused a higher percent P in the tops.
Uniformity of Limestone Mixing in Acid Subsoil as a Factor in Cotton Root Penetration
Authors: Pearson Robert W. , Childs Joel , Lund Zane F. 
Published: July 2010

AbstractCotton (Gossypium hirsutum L.) root growth response to different degrees of mixing limestone in strongly‐acid subsoil was determined, using both short‐term radicle elongation and full‐growth‐cycle root extension as criteria. The roots displayed no chemotropic response to limed pathways in the acid subsoil. Roots grew best when the entire subsoil mass was mixed with limestone. However, when applied at an adequate rate, even poorly‐mixed limestone increased rooting depth at least twofold. Both radicle elongation rate and final root pattern were closely related to percentage of total subsoil mass limed in the incompletely mixed treatments, even when the neutralized soil zones averaged as much as 7.6 cm apart.
Mulch and Tillage Relationships in Corn Culture
Authors: Van Doren D. M. , Triplett G. B. 
Published: July 2010

AbstractRelative effects of soil mulch cover and various tillage practices on corn (Zea mays L.) yield were studied as functions of previous crop and rainfall on a typic fragiudalf soil. Residues (mulch from previous crops of corn or tall fescue) were removed from the soil prior to tillage, manipulated according to action of the tillage implements, or replaced on the soil surface after tillage. Eight tillage treatments consisted of all possible combinations of moldboard plowing, disking, and post emergence cultivation.Mulch cover produced three times as great a yield effect as any other single variable, with the effect (kg/ha) = 36.2M − 0.00218 MS, where M is percent of the soil surface covered with mulch and S is yield in kg/ha of the plowed plus cultivated treatment. Tillage variables increased yield in order of cultivation > plow > disk, and results are expressed in terms of mulch cover required to produce an equal yield effect. Most tillage and mulch effects were additive.The major reason for mulch and tillage effects on corn yield is assumed to be their influence on soil water content. Possible extrapolation of these results to other soils and climates is discussed.
Water Vapor Movement Through Mulches Under Field Conditions
Authors: Kimball B. A. 
Published: July 2010

AbstractThe loss of water vapor through 0.5‐, 1‐, and 2‐cm depths of water repellent mulches was measured under field conditions with lysimeters. Concurrent measurements were made of wind velocities, air vapor pressures, and temperatures at the soil‐mulch interfaces. Mulches used included 0.5‐, 1‐, and 2‐mm glass beads and 1‐mm glass bead aggregates.By assuming that the relative humidity of the soil air at the soil‐mulch interface was essentially 100%, effective diffusion coefficients for field conditions were calculated. The average effective diffusion coefficient for afternoon periods was 1.26 times greater than the molecular diffusion coefficient. An error analysis revealed that the value could have been as low as 0.90 or as high as 1.63, but these values would have been realized only if the effects of several possible systematic errors were completely additive.Little correlattion was found between wind velocity and effective diffusion coefficient. However, the generally low range in wind velocities observed and the smoothing required for the reduction of the lysimeter data may have prevented detection of such a correlation.
Water Transport Through Plant Tissues in the Presence of a Diffusable Solute
Authors: Molz Fred J. , Hornberger George M. 
Published: July 2010

AbstractBecause water transport through soils and plants are closely related and interdependent phenomena, it is logical to attempt to develop a quantitative description of water flow in the plant portion of the soil‐plant‐atmosphere continuum comparable to that which exists for the soil portion. The present paper utilizes the theory of nonequilibrium thermodynamics to develop a quantitative description of water transport through aggregations of plant cells containing both permeating and nonpermeating solutes in aqueous solution. Application of the theory results in two linear, coupled, partial differential equations with a water potential‐related term and the diffusable solute concentration as dependent variables. As the permeability of the diffusable solute approaches zero, the system of equations reduces to a single equation first derived by Philip (1958d), wherein the dependent variable is water potential. Using the Crank‐Nicolson method, the one‐dimensional forms of the equations are solved numerically for the case of a fully turgid tissue placed in a solution of diffusable solute at time zero. The solution shows that the resulting transport process is entirely different from the classical case in which the cell membranes are permeable to water only.
The Partial Molal Volumes of Several Ionic Forms of Montmorillonite in Dilute Suspensions
Authors: Miller Raymond J. , Schepers J. , Hassett J. , Brown D. S. 
Published: July 2010

AbstractA high precision magnetic float densitometer was used to determine the density of dilute aqueous NaCl solutions. The method of intercepts was then used to calculate the partial molal volume of the water and the NaCl salt. These values compared favorably with those in the literature.Using the above methods, the molal volumes of dilute suspensions of Na+, Li+, K+, and Al3+‐montmorillonite were determined. The partial molal volumes of the homoionic saturated clays were corrected for the exchangeable cations using the additive principle. From these values an apparent density for the four clays was determined. The calculated values are consistent with literature values for dilute suspensions. The data indicates that there are clay‐water‐ion interactions such that the partial molal volume of the clay is greater than expected and the apparent density is less. These differences depend on the exchangeable cation and suggest that the clayion associated water is different than normal water.
Adsorption of Picloram (4‐Amino‐3,5,6‐Trichloropicolinic Acid) on Panoche, Ephrata, and Palouse Soils: A Thermodynamic Approach to the Adsorption Mechanism
Authors: Biggar J. W. , Cheung M. W. 
Published: July 2010

AbstractThe adsorption of picloram (4‐amino‐3,5,6‐trichloropicolinic acid) was studied on Panoche clay loam (at pH 4.2 and 1.2), Ephrata sandy loam, and Palouse silty loam. The adsorption processes could be described by the Freundlich equation with Freundlich constants, K, 1/n, and percentage of adsorption at 25C: respectively, 0.210, 0.92, and 3–5.6% for Panoche at pH 4.2; 2.5, 0.93, and 30% for Panoche at pH 1.2; 0.172, 0.99, and 1.9–3.6% for Ephrata; and 1.74, 0.92, and 26–33% for Palouse. Also evaluated were the standard free energy, entropy, and enthalpy associated with the adsorption processes. The values of ΔG° (kcal/mol), ΔS° (cal/mol per degree), and ΔH° (kcal/mol) were: respectively, −1.2±0.1, −14±2, and −5.3±0.6 for Panoche at pH 4.2; −2.98±0.05, −59±2, and −20±1 for Panoche at pH 1.2; −1.80±0.06, −24±3, and −9±1 for Ephrata; and −3.11±0.05, −3.3±1.5, and −4.1±0.4 for Palouse. Thermodynamic parameters were useful in assigning adsorption mechanisms to the four picloram‐adsorbent‐water systems.
Chemical and Physical Processes that Affect Atrazine and Distribution in Soil Systems
Authors: Swanson Roger A. , Dutt Gordon R. 
Published: July 2010

AbstractInteractions studied included adsorption and desorption of atrazine by Ca2+, Mg2+, and Na+ saturated soil material and the effect of chloride salts of the above cations on solubility of crystalline atrazine. It was found that adsorption isotherms follow the Freundlich equation. The desorption isotherm had the same shape as the adsorption isotherm but followed a different path back to the starting point. This hysteresis effect encountered indicates that adsorption and desorption of atrazine are irreversible reactions. The desorption isotherm was also found to fit the Freundlich equation where the exponential desorption coefficient was equal to the exponential adsorption coefficient divided by 2.3.The effect of exchangeable cations was found to be within experimental error, and the solubility of crystalline atrazine was found to be exponentially related to the ionic strength of the solution. Using the equation developed, a computerized model for predicting atrazine distribution and movement in soil systems was prepared. Predicted breakthrough and elution curves were in agreement with those found for effluents from soil columns. It was concluded that the skewed nature of the experimental curve was primarily due to differences in the adsorption and desorption of atrazine.
Self‐Diffusion Coefficients of Selected Herbicides in Water and Estimates of Their Transmission Factors in Soil
Authors: Scott H. D. , Phillips R. E. 
Published: July 2010

AbstractSelf‐diffusion coefficients of selected herbicides were measured in aqueous solution by the capillary tube method. The diffusion coefficients were approximately 0.6 × 10‐5 cm2/sec at 23C and were not particularly related to the configuration of the herbicide molecule. Values calculated for the transmission factors of these herbicides differed with the more mobile compounds being associated with the higher values.
Controlled Instantaneous Application of Free Water to a Porous Surface
Authors: Swartzendruber D. , Asseed M. S. 
Published: July 2010

AbstractInstantaneous application of free water to a porous‐medium surface is achieved essentially by a device in which the central feature is a plastic plate perforated with small holes. The pressure head of the water can be controlled at a preselected value between 0 and 1 cm. Water enters the porous mdium at essentially zero external flow resistance, while volume and time of entry can be measured accurately. No lateral flow of free water occurs, thus eliminating the disturbing effects of such flow on the porous‐medium surface.
Measurement of Hydraulic Conductivity By Means of Steady, Spherically Symmetric Flows
Authors: Dirksen C. 
Published: July 2010

AbstractThe dependence of hydraulic conductivity upon pressure head can be determined from a series of steady, spherically symmetric flows: at any point the hydraulic conductivity is equal to the rate of change of the steady flux per unit solid angle with respect to the pressure head of that point, divided by its radial distance from the center of the water source. This method is very attractive for in‐situ measurements in the field since it requires only one controlled boundary condition, but does not require one‐dimensional flow. Experimental procedures are described and some results given. Hydraulic conductivity values derived from the pressure head in the source cavity itself were the same as those derived from tensiometer measurements near the source. A range of hydraulic conductivity values can be obtained faster with a series of different, steady pressure heads in the source cavity, rather than by measurements on a series of tensiometers located at several distances from the source.Gravity tends to distort the spherical symmetry of the flow. An analytical solution for steady flow from a point source, for a soil with an exponential dependence of the hydraulic conductivity upon the pressure head, indicates that for most soils the effect of gravity near the cavity is small enough to obtain satisfactory hydraulic conductivity values. Gravity has no effect on the pressure head distribution directly below the cavity, suggesting that this is a preferred location for tensiometers. Actually, the analytical solution obtains the hydraulic conductivity in an exact manner for any position. The radius of the cavity should be kept as small as possible.
Solute Movement Through Disturbed and Undisturbed Soil Cores
Authors: Cassel D. K. , Krueger T. H. , Schroer F. W. , Norum E. B. 
Published: July 2010

AbstractDisplacement of nitrate and 36Cl through disturbed (reconstituted horizon by horizon) and undisturbed soil profiles of Aberdeen loam and Beotia loam representing strong and moderate soil structure, respectively, were investigated. Each soil core was 30 cm in diameter and at least 80 cm high. Mean water content θ̄ of the undisturbed soil profile was greater and mean bulk density D̄b less than the corresponding values for the disturbed cores for each soil. For example, disturbance increased θ̄ by 0.07 cm3/cm3 for Beotia with a 0.01 g/cm3 decrease in D̄b; disturbing Aberdeen decreased D̄b from 1.47 to 1.30 g/cm3 but increased θ̄ only 0.03 cm3/cm3. The disturbed soils required greater throughout volume of distilled water to displace the solutes and had smaller dispersion coefficients (D) than the undisturbed soils although not even a twofold difference in D was found. For a given effluent sample, relative nitrate concentration was consistently greater than relative 36Cl concentration due to nitrification occurring within both the disturbed and undisturbed soil profiles during the 24‐week period.
Buffer Intensities and Equilibrium pH of Minerals and Soils: I. The Contribution of Minerals and Aqueous Carbonate to pH Buffering
Authors: van Breemen N. , Wielemaker W. G. 
Published: July 2010

AbstractThermodynamic equilibrium considerations are used to calculate pH buffer intensities for a number of aqueous systems involving 16 common soil and rock minerals (viz. gibbsite, kaolinite, allophane, hematite, limonitic iron oxide, quartz, amorphous silica, calcite, siderite, hydrated magnetite + amorphous Fe(OH)3, microcline, albite, anorthite, Mg‐montmorillonite, two illites, and Mg‐chlorite), gaseous CO2 and 26 dissolved species. The calculation of buffer intensities is outlined for simple oxides and carbonates (analytical evaluation) and for silicate minerals during congruent and incongruent dissolution (graphical differentiation). Silicate minerals, carbonates and gibbsite provide strong buffering upon addition of strong acid under slightly alkaline to slightly acid conditions. Carbon dioxide at constant partial pressure is far more effective than any of the minerals considered in counteracting the effect of an increase in alkalinity.
Buffer Intensities and Equilibrium pH of Minerals and Soils: II. Theoretical and Actual pH of Minerals and Soils
Authors: van Breemen N. , Wielemaker W. G. 
Published: July 2010

AbstractEquilibrium pH values of different clay minerals, oxides and carbonates at pCO2 = 10‐2 atm. are between 4.5 and 8, i.e., in the range typical for most soils. The agreement between the calculated pH and the abrasion pH for most minerals is reasonable. The pH of a number of soils can be explained by partial equilibrium between the soil solution and kaolinite, allophane, gibbsite, montmorillonite or calcite. For illite the agreement is less satisfactory. The effects of reducing conditions and the possible role of pH buffering by organic matter are discussed briefly. Application of the phase rule indicates that the specific mineral assemblage of acid sulfate soils provides a nearly ideal pH‐stat, i.e., addition of moderate amounts of sulfuric acid or lime hardly affects the pH.