bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of the Phosphate Interaction with Calcite
Authors: Griffin R. A. , Jurinak J. J. 
Published: July 2010

AbstractThe kinetics of the phosphate interaction with calcite were studied. The results showed that the reaction did not proceed in the absence of the calcite surface. The kinetics of interaction could be described by two simultaneous reactions. The first reaction was second‐order and was ascribed to the adsorption of phosphate on the calcite surface. The second reaction was first‐order and was considered to be associated with the surface arrangement of phosphate clusters into calcium phosphate heteronuclei.Solubility criteria were used to show that at low phosphate concentrations the ultimate calcium phosphate surface mineral formed was hydroxylapatite.Desorption kinetics were studied by using an anion exchange resin technique. The desorption process could be described as two simultaneous first‐order reactions. The desorption mechanism was postulated to correspond to the dissolution of a surface nucleated calcium phosphate mineral, with the second reaction step being the desorption of phosphate from the calcite surface sites.The rate constants for adsorption and desorption were determined at four temperatures between 0C and 40C. The rate constants were used to compute the activation energies of adsorption and desorption. In addition, the thermodynamic parameters for the enthalpy of activation (ΔH†), the entropy of activation (ΔS†), and the free energy of activation (ΔG†), for both the adsorption and desorption processes were computed and discussed.
Nitrogen Mineralization‐Water Relations in Soils
Authors: Stanford George , Epstein Eliot 
Published: July 2010

AbstractThe relationships between soil N mineralization, soil water content, and matric suction were studied with nine soils of widely differing chemical and physical properties. Highest N mineralization rates occurred between matric suctions of ⅓ to 0.1 bar, in which range 80 to 90% of the total pore space was filled with water. In the range from optimum soil water content (⅓ to 0.1 bar) to 15 bars, a near‐linear relation generally existed between amounts of mineral N accumulated and soil water contents (percent of oven‐dry soil). With increasing dryness, N mineralization continued to decline. Water levels above optimum often reduced mineral N accumulations, presumably because of denitrification.Upon expressing the values for N mineralization (Y) and soil water content (X) for each soil on a relative basis with respect to maximum N mineralized (Y = 100) and associated optimum soil water content (X = 100), the regression of Y on X did not differ among soils. Regression coefficients for common (based on covariance) and total regressions, respectively, were 1.07 and 1.02. Corresponding Y‐intercepts were −2 and −4. A reasonable approximation of the relationships is expressed by Y = X. Possible application of the findings in predicting N mineralization under fluctuating soil water conditions is discussed.
Slash Pine Biomass Response to Site Preparation and Soil Properties
Authors: McKee W. H. , Shoulders Eugene 
Published: July 2010

AbstractOf slash pine (Pinus elliottii Engelm. var. elliottii) plantations on an imperfectly drained soil in Louisiana, those on elevated beds developed about one‐third more aboveground tree biomass by age 8 years than did those on flat‐disked or unprepared sites (51 metric tons/ha as compared with 34 and 39). Bedding increased average depth to free water and average redox potential of the surface soil during winter and reduced the percent of organic matter in the 0–10‐cm layer. Independently of site treatments, total aboveground biomass and the amounts of N, P, Ca, and Mg it contained varied directly with average depth to the water table and soil redox potential during winter. Phosphorus content of the biomass was weakly, if at all, associated with these indicators of root aeration. Results indicate that root environment during winter profoundly influences early growth of slash pine and utilization of nutrients.
A Simplified Determination of Reductant‐Soluble Phosphate in Soil Phosphate Fractionation Schemes
Authors: Weaver R. M. 
Published: July 2010

AbstractA simplified and more rapid procedure for the determination of reductant‐soluble phosphorus (P) was developed by a modification of the Murphy and Riley (1962) ascorbic acid method. The procedure which eliminated the interference of sodium dithionite by air‐oxidation and that of sodium citrate by addition of ammonium molybdate, was suitable for the determination of 0.1 to 0.7 µg P/ml in the presence of up to 3000 µg Fe/ml and 4.0 µg Si/ml.
Effect of Varying the On‐Off Time of Rainfall Simulator Nozzles on Surface Sealing and Intake Rate
Authors: Sloneker L. L. , Moldenhauer W. C. 
Published: July 2010

AbstractMany erosion studies have been conducted using water drops formed by sprinkler irrigation nozzles. Rainfall intensity is controlled by varying the on‐off time. This study shows that after a certain point, the energy to initiate runoff is increased as the nozzle off time is increased. Water intake rate is increased as application rate is increased even though runoff is taking place.
Effect of Monosilicic Acid on Hydrolytic Reactions of Aluminum
Authors: Luciuk G. M. , Huang P. M. 
Published: July 2010

AbstractThe mechanisms and products of hydrolytic reactions of Al ions as influenced by Si(OH)4 were studied under the experimental parameters of degere of hydrolysis of Al (OH/Al molar ratios,) Si/Al molar ratios, Al concentrations of 1.39 × 10‐3M and 1.39 × 10‐4M, and time.As the degree of hydrolysis of Al increased, the amounts of Si along with Al initially precipitated and removed from the solution phase by ultrafiltration consistently increased. The coprecipitation data, infrared evidence, and stoichiometric considerations of Si(OH)4 removal and proton release strongly indicate that the predominant coprecipitation of Si(OH)4 with hydroxy‐Al ions is the condensation reaction involving the hydroxyl groups in hydroxy‐Al ions. At the OH/Al molar ratios of 1 and 2 and in the absence of Si(OH)4, precipitation of Al continued with aging; whereas at the Si/Al molar ratios of 0.5 and 1, the reaction products were metastable, and there was formation of a significant portion of nonextractable Al which was not removed by ultrafiltration.In the absence of Si(OH)4, the product was crystalline Al(OH)3 even at the OH/Al molar ratio of 1. Materials amorphous to X‐ray and electron diffraction were the only products at Si/Al molar ratios of 0.5 and 1, OH/Al molar ratios of 2 and 3, and both initial Al concentrations even after prolonged aging. Decreasing degree of hydrolysis of Al resulted in a distinct decrease in particle size for crystalline products, and in a decrease in the extent of aggregation for amorphous products. The thermal stability and Si/Al ratio of the reaction products were influenced by the Si/Al molar ratio of solution and the period of aging. The presence of Si(OH)4 in solutions also resulted in a decreased Cl inclusion in the reaction products.The results clearly show that the presence of Si(OH)4 affects the hydrolytic reactions of Al at all degrees of hydrolysis of Al. This knowledge is of basic significance for a further understanding of pedogenic processes, and the fate of certain nutrients and environmental pollutants.
Adsorption of Fenuron and Monuron (Substituted Ureas) by Two Montmorillonite Clays
Authors: Van Bladel R. , Moreale A. 
Published: July 2010

AbstractThe effect of the type of clay mineral, exchangeable cation, temperature, and electrolyte concentration on the adsorption of two substituted ureas was investigated.The adsorption was greater on a Bentonite than on a Camp Berteau montmorillonite, possibly because the lattice charge in the former originates from tetrahedral and octahedral layers whereas in the latter only from octahedral layers. The adsorption increased with the polarizing power of the exchangeable cation. Normal adsorption isotherms were exothermic but when the temperature effect on solubility was accounted for, the adsorption reaction tended to be more and more temperature independent as the electronegativity of the exchangeable cation increased. Relative thermodynamic data suggest that the favorable contribution to the adsorption energy arises mainly from enthalpy changes.The effect of salt concentration was almost negligible up to 1.0N and for a given electrolyte good agreement was obtained between the heat of solution of the herbicide and its adsorption.
Anion Adsorption by Allophanic Tropical Soils: I. Chloride Adsorption
Authors: Gebhardt H. , Coleman N. T. 
Published: July 2010

AbstractThe adsorption of Cl by Andepts from Mexico, Colombia, and Hawaii was measured in solutions of HCl, HCl + NaCl, and AlCl3. Chloride adsorption varied from 0‐8 meq/100 g at pH 6 to as much as 32 meq/100 g at pH 3.8. At given pH, adsorption was concentration‐dependent in a manner consistent with the Langmuir adsorption equation. For a B‐horizon sample from San Gregorio, Mexico, the Cl adsorption maxima, in meq/100 g, were 7.4 at pH 6; 10.7 at pH 4.8; 13.4 at pH 4.4; 17.3 at pH 4.2; and 31.6 at pH < 4. The average a from the Langmuir equation was 0.04 liter/meq. Adsorbed Cl was removed by leaching with water, and was exchanged by NO3.Chloride adsorption from HCl or HCl‐NaCl was accompanied by the consumption of protons; adsorption from AlCl3 resulted in the hydrolysis and precipitation of Al. Protons consumed or Al hydrolyzed exceeded Cl adsorbed by amounts corresponding closely to the effective CEC. The results suggest that protons are adsorbed to produce positively charged sites, which bind Cl nonspecifically.Chloride adsorption capacity can be conveniently measured by shaking soil with AlCl3 solution and measuring Cl uptake. Chloride capacities of soils and clay minerals, determined by the AlCl3 procedure, were, in meq/100 g, 7–30 for Dystrandepts; 16–18 for Hydrandepts; 2–4 for acid soils containing crystalline clay and oxide minerals; 4 for kaolinite; zero for montmorillonite and illite.
Anion Adsorption by Allophanic Tropical Soils: III. Phosphate Adsorption
Authors: Gebhardt H. , Coleman N. T. 
Published: July 2010

AbstractAndepts from Mexico and Hawaii bound 30–70 mmole P/100 g air‐dry soil at pH 4.3–4.7 during a 1‐hour reaction with 0.05M mixed H3PO4‐NaH2PO4 solution. As much as 130 mmole P/100 g were taken up from H3PO4 at pH 2.4. A B‐horizon sample, San Gregorio from Michoacan, Mexico, adsorbed P from H3PO4 and consumed H in nearly equimolar amount, with 38 mmole/100 g of each removed from solution in bringing soil from an initial pH of 5.4 to 4.3. Larger additions of H3PO4 dissolved appreciable Al, gave pH < 4, and yielded solutions that were supersaturated with respect to variscite. An apparent adsorption maximum of 38 mmole/100 g compares with maxima of 27 and 30 mmole/100 g for Cl and sulfate, respectively. High‐affinity adsorption of P from H3PO4 appeared limited by the supply of H‐ions to protonate sites or react with displaced OH. San Gregorio B horizon took up phosphate from NaH2PO4, but with low affinity. Phosphate uptake from NaH2PO4 was accompanied by coadsorption of Na. At a given pH and level of tightly bound P established with H3PO4, addition of NaH2PO4 resulted in low‐affinity adsorption of P and coadsorption of Na. Around half of the P bound from NaH2PO4 was readily eluted with water. Phosphate bound from H3PO4 was virtually insoluble in water. Some P was eluted by 0.5M arsenate or selenite. The Andepts bound P through at least three mechanisms: high‐affinity adsorption on protonated sites; low‐affinity adsorption with co‐adsorption of Na; and formation of insoluble variscite‐like substances.
A Kinetic Study of Ammonium and Nitrite Oxidation in a Soil Field Plot
Authors: Ardakani M. S. , Schulz R. K. , McLaren A. D. 
Published: July 2010

AbstractDisappearance of NH4+ from percolating solution in a 40 m2 plot is at first attributable to both oxidation and to adsorption by the soil. Once a steady state was established and exchangeable NH4+ was equilibrated with NH4+ in soil solution, oxidation alone accounted for disappearance of NH4+ — N in the top 2.5 cm of the soil. Concentration profiles of NO2‐ and NO3‐ are described by a modified Michaelis‐Menten equation. Rate constants for oxidation of NO2‐ → NO3‐ and NH4+ → NO2‐ are 0.6 × 10‐3 and 2.5 × 10‐3 ppm/hour·cm3 per bacterium, respectively. These rates are in good agreement with the values found under controlled laboratory conditions.Growth and distribution in soil of Nitrobacter and Nitrosomonas sp. were followed by weekly estimates of their numbers at different depths. The former reached a maximum population of about 106/cm3 of soil but declined to a stable density of about 105 organisms/cm3; the latter approached a steady level of about 104 organisms/cm3. Both organisms showed higher densities near the soil surface where the concentrations of substrates were always highest.
Nitrogen Transformations in Soil During Leaching; I. Theoretical Considerations
Authors: Misra C. , Nielsen D. R. , Biggar J. W. 
Published: July 2010

AbstractTransport equations describing the movement and simultaneous oxidation of NH4+ to NO3‐ and reduction of NO3‐ to N2 by microbial and/or chemical means were set up and solved both for leaching of a pulse and for a continuous application of NH4+ and/or NO3‐ salt at the soil surface. Both ionic adsorption owing to cation exchange and microbiological transformations have been considered and distinguished as reversible and irreversible processes, respectively. The possibilities of the model extended to a sequential transformation during transport of more than two nitrogen species have been examined.
Nitrogen Transformations in Soil During Leaching: II. Steady State Nitrification and Nitrate Reduction
Authors: Misra C. , Nielsen D. R. , Biggar J. W. 
Published: July 2010

AbstractNitrogen transformations were examined by means of a miscible displacement technique that permitted passage of air with different levels of oxygen through the soil. With the use of steady state solutions of equations describing the convective transport of NH4+ and NO3‐ ions in Columbia silt loam, first‐order reaction rate constants k1 and k2 were ascertained for NH4+‐oxidation and NO3‐‐reduction, respectively. Values of k1 were measured to be ten‐fold greater than those of k2. At an oxygen level of 0.5% in the gaseous phase, nitrification was apparently inhibited.
Isolation of Microorganisms from a Texas Soil Capable of Degrading Urea Derivative Herbicides
Authors: Lopez C. E. , Kirkwood James I. 
Published: July 2010

AbstractSamples of Hockley fine sandy loam were perfused with 500 µg/ml concentrations of monuron 3‐(p‐chlorophenyl)‐1, 1‐dimethylurea or diuron 3‐(3,4‐dichlorophenyl)‐1, 1‐dimethylurea for 2 weeks to isolate microorganisms tolerant to these concentrations. A fungus of the genus Fusarium and two unidentified bacteria were isolated by plating out small samples of the treated soil on Czapek's solution agar without sugar with 20 ppm of both herbicides added. The three isolates were tested for their ability to grow in solid and liquid media with different concentrations of the herbicides as sources of carbon. The same optimal growth of the fungus on Czapek's solution agar without sugar with 1 g/liter concentration of yeast extract was attained at 10 and 20 ppm monuron. When the yeast extract was excluded, best growth was attained at 2 ppm monuron. In Czapek's solution agar without sugar, and with 50 mg/liter of yeast extract, the fungus produced the highest amount of dry mycelia with 20 ppm monuron.Cultures of the three isolates in Czapek's solution agar without sugar containing 20 ppm diuron, including 0.5 ppm of carbonyl 14C‐diuron, were incubated for 2 weeks. The organisms grew profusely, but no breakdown products of diuron were detected from the extracts of these cultures as analyzed by TLC (thin layer chromatography) and strip scanning techniques. Approximately 3.5% of the added diuron was collected as 14CO2 from soil samples incubated for 80 days with carbonyl labeled 14C‐diuron and a mixture of the three isolates. Periodic analysis of soil samples from these experiments did not indicate any breakdown products of diuron apparently due to insensitivity of the instrumentation and procedures. However, data from the fungal growth and CO2 evolution experiments suggest that these organisms can use monuron and diuron as a source of carbon.
Nonuniform Phosphorus Distribution in the Root Zone of Corn: Growth and Phosphorus Uptake
Authors: Stryker R. B. , Gilliam J. W. , Jackson W. A. 
Published: July 2010

AbstractThe implications of nonuniform P distributions in the root zone of corn (Zea mays L.) on growth and P uptake were explored utilizing a split root system. Maximal dry matter accumulation occurred only when the entire root system was exposed to an external P supply. Reduction in shoot growth of nearly 20% was associated with those P distributions in which part of the root system was devoid of an external P supply. There was a concomitant decrease in root growth in “no P” zones such that shoot/root ratios remained constant regardless of whether all or part of the root system was exposed to P. The growth rate of roots dependent on an internal supply of P via translocation (roots in “no P” zones), as contrasted to that of roots with an external supply, is considered to have been limited by the rate at which inorganic P was supplied to the growing points.These effects were not due to the lack of total P uptake for it was shown that a portion of the root system could take up high amounts of P if the external supply was sufficient.For P distributions with one root zone devoid of an external P supply, significant differences in P concentrations, leaf widths, and dry weight occurred between opposite sides of some leaves. It is postulated that these nonuniform effects on leaves were the result of nonuniform P transport from the roots to leaves.
Distribution of Free Iron and Organic Carbon as Related to Available Water in Some Forested Sandy Soils
Authors: Shetron Stephen G. 
Published: July 2010

AbstractThe amount of available water (0.1–15 bar tension) in the B21 horizons of six sandy soil series increased as amount of free iron and organic carbon increased. Soils of the Typic Udipsamment subgroup had the lowest, and soils of the Typic Haplorthod subgroup the highest available water retention values. Retention of available water in the C horizons of these soils was positively correlated with free iron and specific surface. Cubic meter volume growth per hectare per annum for hardwood and pine stands increased as amounts of free iron, organic carbon, and available water increased.
Prediction of Water Loss from a Fallow Field Soil Based on Soil Water Flow Theory
Authors: Gardner H. R. 
Published: July 2010

AbstractA simple technique based on soil water flow theory to predict evaporation from nonhomogeneous field soils is presented. From cumulative evaporation measurements on undisturbed cores of soil, a dimensionless curve is drawn relating fractional water loss to the square root of time divided by the amount of water available for evaporation. A procedure is described to account for the residual water left in the soil from one rainfall event to the next. Predictions of cumulative evaporation made by the use of the dimensionless curve were compared with 4 years' of lysimeter data on Rago silt loam. The system would work best in an area with high average potential evaporation and low rainfall such as the Great Plains.
Time‐Dependent Linearized Infiltration. I. Point Sources
Authors: Warrick A. W. 
Published: July 2010

AbstractWater flow from a point source is analyzed using a linearized form of the moisture flow equation. Time‐dependence is assumed with the results simplifying to those of previous investigators for steady‐state conditions. Discrete time‐distributed inputs such as might occur for trickle or high frequency irrigation is amenable to the solution. Numerical simulations include (i) the advance of a wetting front during infiltration, (ii) moisture variation resulting from a cyclic input as during irrigation, and (iii) the matric flux potential field for a two‐source problem.
Soil Factors Affecting the Adsorption of 2,4,5‐T
Authors: O'Connor G. A. , Anderson J. U. 
Published: July 2010

AbstractFactors expected to affect the adsorption of 2,4,5‐T (2,4,5‐trichlorophenoxyacetic acid) on four soils of the western USA were studied. The effects were examined by equilibrating solutions of 2,4,5‐T with soils in their natural condition, after Casaturation, and with samples of the same soils treated to remove soil constituents expected to affect adsorption. Organic matter was an important contributor to 2,4,5‐T adsorption, and, in some soils, was the only adsorbent of significance. Oxides of Fe and Al did not contribute much to adsorption in the soils studied although the pH of soils studied was only slightly acid to alkaline. Allophane was apparently an effective adsorbent when the Si/Al ratio of the allophane was high.
Splash Correction Factors for Soil Erosion Studies
Authors: Farrell D. A. , Moldenhauer W. C. , Larson W. E. 
Published: July 2010

AbstractMany research workers in soil erosion have measured soil and sand splash from impacting water drops or raindrops. Size and shape of the soil containers have varied. A theoretical study was made to determine the possible effect of the geometric parameters on the measurement of soil splash. The results show that estimates of soil detachment by raindrop impact could be substantially affected by the size and shape of the container.
Determining Effective Soil Water Diffusivities from One‐Step Outflow Experiments
Authors: Gupta S. C. , Farrell D. A. , Larson W. E. 
Published: July 2010

AbstractA method is developed whereby effective or weighted mean diffusivity, D̄, can be estimated by using outflow data. These estimates can further be analyzed for soil water diffusivity, D(θ), with the help of a step‐wise function and the relationship given by Crank (1956). The suggested procedure for estimating soil water diffusivity is more accurate than previous methods because no assumption of constant diffusivity either over the pressure increment or over the length of the soil core is required. Moreover the procedure does not use the early part of the outflow curve and thus reduces the effect of membrane impedance on the estimates of D(θ).The method was tested by simulating outflow experiments on a digital computer, and using data obtained to calculate diffusivities. Our estimates of diffusivity were in better agreement with the actual diffusivities than those obtained with the earlier “one‐step” method.
Chloride and Tritiated Water Flow in Disturbed and Undisturbed Soil Cores
Authors: McMahon M. A. , Thomas G. W. 
Published: July 2010

AbstractColumns of disturbed and undisturbed Eden, Maury, and Pembroke soils were eluted with CaCl2 in tritiated water. The chloride was used as a substitute for nitrate since it is not affected biologically. The experiments were carried out to investigate the effects of natural soil structure on the flow of water and chloride. In all three soils flow was less stable in the undisturbed cores judging from the shape of the curve and the points of initial tritiated water and chloride breakthrough. Chloride moved through the undisturbed Eden and Maury soils faster than through the disturbed columns. Both soils exclude anions to a significant extent. In the Pembroke soil, which adsorbs anions, the chloride was retarded in the undisturbed column as compared to the disturbed column. The results suggest that field movement of water and anions is not described very well by columns of disturbed, packed soils.