bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pyrophosphate Hydrolysis in Soil as Influenced by Flooding and Fixation
Authors: Racz G. J. , Savant N. K. 
Published: July 2010

AbstractThe rate of hydrolysis of pyrophosphate (K4P2O7) in a noncalcareous soil maintained at field capacity moisture content or under flooded conditions was determined. Attempts were also made to study the influence of fixation of added pyrophosphate by soil on the rate of pyrophosphate hydrolysis. The initial rate of pyrophosphate hydrolysis was rapid and approximately the same for both flooded soil and soil maintained at field capacity moisture content. The first‐order reaction rate constants, obtained by plotting the log of the concentration of unhydrolyzed pyrophosphate vs. time were 8.14 × 10‐4 min‐1 and 8.37 × 10‐4 min‐1 for soil at field capacity and under flooded conditions, respectively. However, after about 3 days of incubation, flooded soil hydrolyzed pyrophosphate at a relatively greater rate (k = 2.0 × 10‐5 min‐1) than did soil maintained at field capacity (k = 1.3 × 10‐5 min‐1). This difference appeared to be due to an increase in pyrophosphatase activity in the flooded soil. The half‐life of the added pyrophosphate was approximately 2 days.Pyrophosphate adsorbed by an anion exchange resin or fixed by soil hydrolyzed at a slower rate than did pyrophosphate in solution. The ratio of orthophosphate to total phosphate (orthophosphate + pyrophosphate) extracted from phosphated soils by various extractants decreased in the order: water, 0.1N H2SO4, and 0.5N H2SO4. Water‐soluble or loosely bound pyrophosphate hydrolyzed at a much greater rate than did water‐insoluble or strongly bonded pyrophosphate.
Diffusion of Selected Herbicides in Soil
Authors: Don Scott H. , Phillips R. E. 
Published: July 2010

AbstractDiffusion coefficients of atrazine, simazine, prometone, prometryne, 2,4‐D, chlorpropham, diphenamid, fluometuron, trifluralin, and benefin, were measured in Lanton silty clay loam. The effects of soil moisture content and adsorption upon the diffusion coefficients were evaluated.Differences were observed in the magnitude of diffusion coefficients of the 14C‐labeled herbicides in the soil. The self‐diffusion coefficients of 2,4‐D, chlorpropham, diphenamid, and prometone decreased as diffusion time increased, which suggest that changes in the structure of these herbicides might have occurred. The self‐diffusion coefficients of fluometuron, atrazine, simazine, prometryne, trifluralin, and benefin were found not to be significantly changed as diffusion time increased.The rate of diffusion increased as the soil water content increased for all herbicides except trifluralin. Diffusion of trifluralin was higher at the lower moisture content and this was attributed to a greater amount of trifluralin moving in the vapor phase.Linear adsorption isotherms were obtained with all herbicides. The order of adsorption was 2,4‐D < fluometuron ≃ prometone < simazine ≃ atrazine ≃ diphenamid < prometryne ≪ chlorpropham ≪ trifluralin ≪ benefin. Correlation analysis showed that the diffusion coefficients of the nonvolatile herbicides were inversely related to the amount of adsorption indicating that most of the diffusion occurred in the solution phase. For those herbicides that are considered to be volatile, diffusion occurred in the vapor phase and the solution phase.
Equilibrium Relationships of Metal Chelates in Hydroponic Solutions
Authors: Halvorson A. D. , Lindsay W. L. 
Published: July 2010

AbstractStability‐pH diagrams were developed to describe the equilibrium relationships of metal ions with chelating agents in nutrient solutions for the following chelating agents: EGTA, EDTA, DTPA, CDTA, and EDDHA. These stability diagrams give the concentration of each chelated metal species in solution in the pH range of 4 to 9 and provide a reliable means for selecting appropriate chelating agents for specific purposes. With increased pH, displacement of Fe3+ from the following chelating agents by divalent cations is in the order EGTA > EDTA > DTPA > CDTA > EDDHA. Similar developments can be extended to other chelating agents and to nutrient solutions of different composition.
The Determination of Quinone Groups in Humic Substances
Authors: Schnitzer M. , Riffaldi R. 
Published: July 2010

AbstractThe reduction of quinone groups in humic substances by acid SnCl2 solution was found to be unsatisfactory. The experimental conditions are drastic, the systems are heterogeneous, favoring adsorption or complexing of the reducing agent by the humic materials, and so leading to excessively high quinone values.Reduction of humic substances by SnCl2 and Fe2+‐triethanolamine in alkaline solution at room temperature and atmospheric pressure appeared to be more suitable for the determination of quinone groups in these materials. There was good agreement between quinone groups determined by the two methods on seven humic and one fulvic acid. The quinone group content of the humic acids analyzed ranged from 1.4 to 2.2 meq/g, that of the fulvic acid was < 1.0 meq/g.No correlation was found between quinone groups and the free radical content of the humic materials. The results suggest that quinone groups in humic substances form part of complex chemical structures and not of simple compounds.The determination of quinone groups in humic substances is difficult because of the presence of substantial amounts of CO2H, OH, and ketonic C=0 groups, some or all of which may interfere. Thus, it is advisable to check each analysis by at least two different methods.
Uptake of Phosphorus by Plants Growing Under Field Conditions: II. Computed and Experimental Results for Corn Plants
Authors: Bar‐Yosef B. , Bresler E. , Kafkafi U. 
Published: July 2010

AbstractFluxes of P uptake by corn (Zea mays L.) plants growing in the field under high and low P fertilization levels, were both predicted by an uptake model, and obtained experimentally in the field by a new technique.The computed fluxes were averaged over a period of 1 week to give values of 4.8 × 10‐5 and 1.7 × 10‐5 µg P cm‐2 sec‐1 at the high and low P levels in the soil, respectively. These values were lower than the experimental weekly average fluxes which, at the critical growth period (between the 5th and 7th weeks), equaled about 6.8 × 10‐5 and 2.5 × 10‐5 µg P cm‐2 sec‐1, correspondingly. The deviation of the real conditions prevailing in the field from those assumed in the model tended, qualitatively, to explain the discrepancy.It is shown that the computed flux of P uptake is more sensitive to variations in the soil than in the plant parameters.
Vertical Mulch Effects on Soil Water Storage
Authors: Fairbourn Merle L. , Gardner H. R. 
Published: July 2010

AbstractSoil water storage for vertical mulch and furrow treatments on level soil surfaces and vertical mulch and nonmulch treatments with microwatersheds was evaluated in a constant temperature laboratory. The vertical mulch treatment on a level surface saved 30 to 40% more of the applied water than the furrow treatment. The efficiency of storage with vertical mulch was reduced by 17% when the surrounding soil surface was wet during water application. A microwatershed with vertical mulch stored 7 to 10% more of the applied water than a microwatershed without mulch. Depth of water infiltration and dry soil surface adjacent to the mulch appeared to be the factors that reduced evaporation losses from vertical mulch treatments. A comparison of scaled evaporation data with the diffusivity curve for the soil used demonstrated that the diffusivity equation was useful for predicting soil water loss by evaporation for microwatershed treatments of this experiment.
Cristobalite and Quartz Isolation from Soils and Sediments by Hydrofluosilicie Acid Treatment and Heavy Liquid Separation
Authors: Henderson J. H. , Clayton R. N. , Jackson M. L. , Syers J. K. , Rex R. W. , Brown J. L. , Sachs I. B. 
Published: July 2010

AbstractA qualitative method for the isolation of cristobalite or of quartz from soils and sediments was developed for the characterization of these SiO2 polymorphs by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and oxygen isotope analysis by mass spectrometry. The procedure, applicable to silt or sand size fractions, involved two steps. First the quartz was separated from the cristobalite by centrifugation of a polyvinylpyrrolidone (PVP) stabilized suspension in tetrabromoethane and nitrobenzene mixtures (specific gravity range from 2.28 to 2.38). Then selective chemical dissolution of the non‐SiO2 minerals was effected by HCl, NaOH, and H2SiF6 treatments. Minerals, such as magnetite, resistant to dissolution in these reagents, were subsequently removed by heavy liquid separation.Treatment of hydrothermal low‐cristobalite (Taiwan), having blocky SEM masses and δ18O = 14 ‰, with HCl, NaOH, and H2SiF6 removed amorphous silica and released the crystalline platelets of δ18O = 9 ‰. Little change in isotope abundance of the latter occurred on retreatment. When amorphous diatom skeletons (δ18O = 32.2 ‰) were treated with these reagents, 77% of the sample dissolved. The remaining skeletons had slightly lower δ18O value (29.1 ‰) but a similar diatom skeleton morphology by SEM.Quartz isolated from the A2 and Cl horizons of Parahaki soil of New Zealand had δ18O values of 9.6 to 10.0 ‰ The associated low‐cristobalite had δ18O = 8.3 to 9.1 ‰. The oxygen isotope data indicate that both of these SiO2 polymorphs had a hydrothermal or volcanic origin, and were not formed in the soil.
Influence of Water Content on Electrical Conductivity of the Soil
Authors: Gupta S. C. , Hanks R. J. 
Published: July 2010

AbstractMeasurement of dynamic salinity and water content profiles under laboratory conditions were needed to test a model developed to characterize the simultaneous flow of water and salts in soils. Methods were needed for measuring salinity in place in a system where rapid water movement occurred. Because of the time lag in salinity sensors, other methods were considered for evaluating salinity.The four‐probe system of measuring electrical conductivity of soil eliminates the time lag error, but introduces the problem of correcting the changes in conductivity caused by water content. Units were constructed and samples prepared to evaluate the influence of water content, and salt concentrations on the four‐probe conductivity (K4P). Two soils were studied. Regression equations developed to estimate saturation or 1:5 extract electrical conductivity from four‐probe conductivity and water content (π) gave correlation coefficients of 0.75 and 0.90, respectively. Correlations for individual soils were generally higher than the combined soils. The regression equation relating the ratio of K4P to four‐probe conductivity at saturation (K 4PS) with water content was 4K4P/K4PS = − 0.26 + 2.49π with a correlation coefficient of 0.88 for the combined soil data.
Solutions for Miscible Displacement of Soil Water with Time‐Dependent Velocity and Dispersion Coefficients
Authors: Warrick A. W. , Kichen J. H. , Thames J. L. 
Published: July 2010

AbstractMiscible displacement processes with time‐varying velocity and dispersion coefficients are examined. Simplified solutions utilizing arbitrary initial conditions are presented and used to simulate step and slug inputs of solutes into soil during infiltration of water. The solutions are used in the analysis of experimental data, both for field infiltration with a slug of solute and for psychrometric measurements of salt fronts in a laboratory sand column. Experimental data obtained for solute movement was more accurately described using time‐increasing dispersion relationships than for constant values.
Characteristics of Phosphorus Adsorption by Some Nigerian Soils
Authors: Udo E. J. , Uzu F. O. 
Published: July 2010

AbstractTropical acid soils adsorb a large portion of phosphorus added to them. In order to study the characteristics of phosphorus adsorption in 10 Nigerian acid soils, 2 g of soil were equilibrated in 0.01M CaCl2 containing various amounts of phosphorus for 48 hours. The phosphorus disappearing from solution was taken as the amount adsorbed. The capacity to adsorb phosphorus varied among the soils, but in general the more strongly weathered soils from the eastern area adsorbed more phosphorus than those from western Nigeria. At low concentrations of phosphorus in the equilibrium solution, the adsorption could be satisfactorily described by Langmuir Isotherm equation. The adsorption was significantly correlated with sesquioxides and the exchangeable forms of Al and Fe as well as the clay content and pH. The citrate‐dithionite and the oxalate extractable oxides were of equal significance in the phosphorus adsorption, but the role of Al was more important than that of Fe.
Interacting Diffuse Layers in Mixed Mono‐Divalent Ionic Systems
Authors: Bresler Eshel 
Published: July 2010

AbstractA numerical solution of the electric double‐layer problem, for the case of overlapping diffuse layers in mixed monovalent‐divalent ion systems, is used to obtain a series of graphs for various cation compositions in the external solution. In these graphs, the electric potential is expressed as a function of the surface charge density, the concentration of the two cations in the equilibrium solution, and the distance between platelets in various ionic mixtures. The graphs cover most of the situations usually encountered in soil systems, and are not sensitive to the valency of the anions present. They are used to estimate the electrostatic effect on cation exchange equilibria, swelling pressures, and electrokinetic phenomena in mixed‐ion clay systems. Application of these estimates to theoretical analyses and comparisons between theoretical models and experimental data are illustrated. Some of the examples used for this illustration are based on work previously published by others.
Effect of Phosphate Salts as Saturating Solutions in Cation‐Exchange Capacity Determinations
Authors: Schalscha E. B. , Pratt P. F. , Kinjo T. , Amar A J. 
Published: July 2010

AbstractCation‐exchange capacities with KCl or NaNO3 in volcanic ash soils varied from 6 to 18 meq/100 g whereas CEC with KH2PO4 or NaH2PO4 varied from 78 to 188. Cation‐exchange capacities with NaH2PO4 and NaNO3 were 28 and 6, respectively, for an alfisol and 12 and 2, respectively, for an oxisol. The ratios of CEC with H2PO4‐ as compared to Cl‐ or NO3‐ varied from about 4 to 30. The effect of the H2PO4‐ is explained as a result of neutralization of positive charge in the soil with a simultaneous release of negative charge.
Effect of Freeze‐Thaw Cycles on Aggregate Stability and Hydraulic Conductivity of Three Soil Aggregate Sizes
Authors: Benoit George R. 
Published: July 2010

AbstractThe study reported here was conducted to determine freeze‐thaw influences on the vertical hydraulic conductivity of soil. To accomplish this three soil aggregate sizes (0.0 to 0.8 mm, 0.8 to 1.2 mm, and 1.2 to 2.0 mm) were packed in aluminum cores, equilibrated at two water levels (maximum water‐holding capacity and 0.5 bar of pressure) and subjected to 20 freeze‐thaw cycles at two freezing temperatures (−4C and −18C). Hydraulic conductivity and aggregate stability were determined for all cores before and after the freeze‐thaw cycles.Generally, water‐stable aggregate breakdown was statistically greater at maximum water holding content. The percentage of water‐stable aggregates in the 0.0‐ to 0.8 mm aggregate class increased by a factor of 1.26 from initial values after freezing and thawing at the 0.5 bar water level and −4C freezing temperatures.Freezing and thawing caused the greatest decrease in vertical hydraulic conductivity of those cores with large aggregates and high water content subjected to the −18C freezing temperature. Freezing and thawing of cores at 0.5‐bar water content generally increased hydraulic conductivity. An exponential relationship seems to exist between the change in the ratio of final to initial hydraulic conductivity and the soil water content at freezing. Drainage of soil water from surface horizons could induce freeze‐thaw improvement of the soil's vertical hydraulic conductivity.
Chloride Movement in Undisturbed Swelling Clay Soil
Authors: Kissel D. E. , Ritchie J. T. , Burnett Earl 
Published: July 2010

AbstractRelatively large, continuous soil pores were important pathways of downward Cl‐ movement in saturated, swelling clay soils. Using water‐soluble fluorescein as a tracer for downward water and Cl‐ movement in field basins, distinct small areas of the soil contained fluorescein, whereas nearby areas contained no visible fluorescein after Cl‐ and fluorescein was ponded at the surface for 1.5 days. Chloride contents in the areas containing fluorescein were considerably higher than in nearby areas. Breakthrough curves of a large saturated core of undisturbed swelling clay soil indicated that Cl‐ was moving quite rapidly through large connected pores. In the undisturbed swelling clay soil, the volume of soil water not containing Cl‐ was about 60%; when the disturbed soil was repacked to the same density this value decreased to 40%.More of the original soil solution was eluted from long undisturbed cores than from short undisturbed cores of the same diameter before Cl‐ appeared in the effluent. Apparently the longer core wall blocked more connected flow paths which were not vertical.
Mobility of Polyphosphates in Soil
Authors: Hashimoto Isao , Lehr James R. 
Published: July 2010

AbstractAmmonium ortho‐, pyro‐, tripoly‐, tetrapoly‐, and long‐chain polyphosphates and cyclic ammonium tri‐ and tetrametaphosphates were surface applied to soil columns. After 1, 2, and 4 weeks the soil columns were sliced into 1‐mm sections and examined for the distribution of P along the columns. Each soil section was analyzed for total and orthophosphate P in both the water‐soluble and the immobilized (NaOH‐extractable) fractions. The general features of the distribution patterns usually were established by the first week, after which soluble P moved much more slowly and the amount of immobilized P increased slowly. The total distance of movement and the distribution patterns of water‐soluble P were similar for all the phosphates tested, but the polyphosphates differend markedly in the degree of immobilization of P and differed significantly in the positions of maximum retention of P in the soil columns. These positions of maximum retention had no apparent relation to the degree of condensation of the polyphosphates.
Interactions with Soil Lipase Activation and Inhibition
Authors: Pancholy Sunil K. , Lynd J. Q. 
Published: July 2010

AbstractSoil lipase interactions of Psammetic paleustalf, Eufaula loamy sand, were determined with a fluorometric assay of enzymatic cleavage converting nonfluorescent 4‐methyl umbelliferone butyrate (4‐MUB) to the highly fluorescent 4‐methyl umbelliferone (4‐MU). Soil lipase activity accelerated with manipulation of base cation levels. Combination effectiveness as reaction activators at 2.0M × 10‐4 was Ca + Mg + Na or K or Na + K > Ca + Mg > Ca > Mg > Na or K. Highly significant competitive lipase inhibition was induced with 0.1M Cu2+ > S2‐ > EDTA at MUB substrate levels of 12.5 to 75.0 × 10‐4M. Iron3+ noncompetitive inhibition was near constant.
X‐Ray Diffraction, Electron Microscopy, Electrophoretic Mobility, and pH of some Stable Smectite‐Protein Complexes
Authors: Harter Robert D. , Stotzky G. 
Published: July 2010

AbstractX‐ray diffractometry, electron microscopy, electrophoretic mobility, and pH measurements have been used in an attempt to understand the mechanisms involved in the formation of stable clay‐protein complexes. Pepsin was apparently adsorbed to positive edge sites on the smectite, and all other proteins were adsorbed on planar surfaces. Casein, chymotrypsin, lysozyme, and ovomucoid intercalated the H and Na‐smectites, and catalase may have intercalated the H‐smectite. All proteins, except catalase, appeared to intercalate the clays when the weight ratio of protein‐to‐clay exceeded about 1:5. Catalase did not appear to intercalate the Ca, Al, La, or Th‐smectites, even though the ratio of adsorbed protein‐to‐clay exceeded 1:5. The electrophoretic mobility of the H, Na, and Th‐smectites became less negative upon adsorption of proteins, indicating a physical or chemical covering of the negative clay surface charge and a flocculation of the complex. When protein was adsorbed by Ca, Al, and La‐smectites they either showed little change or increased in electrophoretic mobility, indicating a tendency for clay tactoids to be broken. The pH of all protein‐clay complexes tended to approach neutrality. In the acid clays (H, Al, and Th‐smectite), especially, this indicated a cation exchange reaction, since the exchanged inorganic ions would be subsequently removed from the clay.
A Multichannel Syringe Pump for Steady State Flow in Soil Columns
Authors: Wierenga P. J. , Black R. J. , Manz P. 
Published: July 2010

AbstractA multichannel syringe pump3 was designed for maintaining a constant rate of outflow over long periods of time. Low flow rates are obtained by using a timer‐control which causes the pump to make one cycle per set time interval. The pump is not pulse free, but for many studies requiring steady state water movement in soil columns this is not considered too great a disadvantage. Measured over a 10‐day period at a rate of outflow of 173 ml/day, the mean day‐to‐day variation was less than 0.2 ml/day.
The Chemistry and Phytotoxicity of Arsenic in Soils: II. Effects of Time and Phosphorus
Authors: Woolson E. A. , Axley J. H. , Kearney P. C. 
Published: July 2010

AbstractArsenate from sodium arsenate changes to less soluble compounds in soils with time. To study these changes, the arsenic soluble in 1N NH4Cl, 0.5N NH4F, 0.1N NaOH, and 0.5N H2SO4 solutions was determined. These dissolved arsenates were designated as WS‐As (water soluble), Al‐As, Fe‐As, or Ca‐As, respectively. The percent of WS‐As present was proportional to As added and inversely proportional to time, and to the Fe and Al content. Fe‐As was the predominant form of As in Hagerstown silty clay loam while Al‐As predominated in Lakeland loamy sand. Growth of corn (Zea mays) increased with increase in time of As incubation in the soil before planting.Arsenic phytotoxicity and As in the plant were altered by P additions. Arsenic residues in the Lakeland soil became more phytotoxic, while residues in the Hagerstown soil became less phytotoxic with P additions. This plant response was related to the availability of As and P in these soils. Leaching with 0.05M KH2PO4 removed 77% of the total As from a contaminated Dunkirk fine sand. The distribution of the forms of As in this soil changed during leaching.
Water Movement and Caliche Formation in Layered Arid and Semiarid Soils
Authors: Stuart D. M. , Dixon R. M. 
Published: July 2010

AbstractIn soils, downward water movement is restricted when finetextured materials are underlain by sand or gravel layers. Water accumulates in arid and semiarid soils at the interface of the fine‐ and coarse‐textured materials and may rarely enter the coarse‐textured materials. Calcium carbonate, silica, and other salts are deposited at or near the top of the sand or gravel layers as water is removed by evapotranspiration. With time, silica, calcium carbonates, and other salts become cemented or indurated, forming calcareous crusts at these interfaces. The sands and gravels are not wet uniformly when water does enter, because it enters relatively small areas. Calcareous concentrations may form in these small, wetted areas and may be seen as calcareous cemented columns surrounded by noncal careous sands or gravels.
Horizontal Infiltration of Water in Soils: A Theoretical Interpretation of Recent Experiments
Authors: Parlange Jean‐Yves 
Published: July 2010

AbstractA general theory of water movement is used to describe the horizontal infiltration of water when the diffusivity increases exponentially with moisture content. The results can be expressed in simple analytical form and are in excellent agreement with experimental observations. The results confirm that the theory is accurate because water diffusivity varies with water content.