bluuebunny/crossref_metadata_2025 huggingface dataset:
Denitrification Kinetics in Soil Systems: The Significance of Good Fits of Data to Mathematical Forms
Authors: Kohl D. H. , Vithayathil Francis , Whitlow Peggy , Shearer Georgia , Chien S. H.
Published: July 2010

The loss of NO3‐ added to two central Illinois soils was determined in experiments in which the soils were incubated under waterlogged conditions. The loss was measured as a function of substrate concentration in one experiment in which samples were incubated for a single time (24 hours) and as a function of time in a second experiment in which the concentration of the added NO3‐ was held constant (200 ppm NO3‐‐N). The rate of loss of NO3‐ was about 5.5 times higher in one of the soils than in the other. This difference was largely overcome by the addition of glucose (1% with respect to the soil) which also greatly enhanced the rate of denitrification in both soils.

The experimental points representing the rate of NO3‐ loss plotted as a function of the concentration of added NO3‐, were equally well fit by Michaelis‐Menten and exponential equations as well as by the solution to a pair of nonlinear differential equations representing a system in which the product of one reaction (e.g., the reductant generated by the oxidation of carbon compounds) is a substrate in a second sequence (e.g., the denitrification of NO3‐). The significance of such fits is discussed. The authors point out that while such fits have certain uses, it is not possible to infer from them the mechanism of the reaction.
Denitrification Measured Directly from Nitrogen and Nitrous Oxide Gas Fluxes
Authors: Rolston D. E. , Fried M. , Goldhamer D. A.
Published: July 2010

The amount of denitrification is generally the unknown in attempts to evaluate the fate of N fertilizers applied to soils. Substantial error can result when denitrification is determined from the difference between measurements of plant uptake, residual soil N, leaching, and the amount of N applied. An independent, direct measure of denitrification potentially has merit by containing only the error from direct measurement and not a cumulative error from several measurements. Nitrate at a rate of 300 kg of N/ha and enriched with 20 and 10 atom percent excess 15N was applied to laboratory columns and a field plot, respectively. The columns were maintained at soil‐water pressure heads of −22 and −70 cm. The field plot was maintained at a soil‐water pressure head of approximately −10 cm in the upper 10 cm of soil. The field plot was cropped with perennial ryegrass (Lolium perenne). The columns and field plot were instrumented with tensiometers, soil solution samplers, and gas samplers. The concentration and isotopic ratio of NO3, N2, and N2O were measured as a function of soil depth and time. The gaseous concentration gradients and measured apparent diffusion coefficients were used to calculate the fluxes of 15N2 and 15N2O gas from the soil. Residual soil N, plant uptake, and leaching were measured in order to calculate denitrification by difference. For the laboratory columns, the amount of denitrification determined directly compared favorably with that determined by difference. For the field plot, the disparity between denitrification calculated directly and by difference was attributable to the uncertainty in the gaseous concentration gradient near the soil surface and the spatial variability of the apparent diffusion coefficient near water saturation.
An Evaluation of Job's Method of Continuous Variations as Applied to Soil Organic Matter‐Metal Ion Interactions
Authors: MacCarthy Patrick , Mark Harry B.
Published: July 2010

The literature dealing with the application of Job's method of continuous variations to the study of soil organic matter‐metal ion interactions has been reviewed, and an introduction to the fundamental chemistry necessary for an understanding of these interactions is presented. The method of continuous variations was applied to simple systems consisting of metal ions and mixtures of discrete ligands. The behavior of these “model” systems was compared to that of the more complicated soil organic matter systems. Following a consideration of the fundamental principles of Job's method and of its boundary conditions and limitations, it was concluded that this method is not directly applicable to the study of soil organic matter‐metal ion interactions. This conclusion was substantiated by experiments carried out on the simple “model” systems as well as those on fulvic acid itself. Explanations are proposed to account for the deceptive results which were obtained when this method was erroneously applied by other workers to the investigation of soil organic matter‐metal ion interactions in the past. Possible interferences, due to scattering of light, during the study of soil organic matter‐metal ion reactions by UV‐visible absorption spectroscopy are considered.
Water Content and Bulk Density During Wetting of a Bentonite‐Silt Column
Authors: Nofziger D. L. , Swartzendruber D.
Published: July 2010

An improved method of dual‐energy gamma‐ray attenuation was used to measure water content and bulk density rapidly and accurately, during one‐dimensional, unsaturated water movement into a column of an equal‐part mixture of initially air‐dry, highly swelling bentonite and silt. The bulk density near the inlet end of the column decreased rapidly as water entered. Since the ends of the column were confined, the expansion of the wetted bentonite‐silt produced a compensating compression in the remaining air‐dry portion of the column. Several water‐content variables were plotted against the so‐called reduced material coordinate m/t1/2 (Boltzmann variable expressed in terms of the material coordinate m and time t). Neither the volumetric water content nor the volumetric water ratio would coalesce the data when plotted against m/t1/2. In contrast, a plot of water saturation vs. m/t1/2 did coalesce the data into a single curve, except for very early times at positions nearer than 1 cm to the water inlet.
Zinc Adsorption Isotherms for Soil Clays with and Without Iron Oxides Removed
Authors: Shuman L. M.
Published: July 2010

The clay fraction from four predominant Georgia soils sampled at two depths was separated and the iron oxides removed from a portion of each clay sample. These clays were equilibrated with five Zn solutions to measure Zn adsorption. The data conformed to the Langmuir adsorption isotherm. Langmuir coefficients were used to evaluate the Zn adsorptive capacities of the clays and the bonding energies for Zn. Adsorptive capacities and CEC values for the clays from Decatur cl and Leefield ls soils were higher than those for clays from the Cecil sl and Norfolk ls soils. Differences in adsorptive capacities were not consistent between depths nor between samples with or without Fe oxides. However, removal of the Fe oxides increased the capacity to adsorb Zn in more instances than it decreased this capacity. Zinc adsorptive capacities were directly related to the CEC values for the clays. When comparing those samples with and without Fe oxides removed, bonding energies were inversely related to adsorptive capacities.
Decomposition of Specifically Carbon‐14‐labeled Ferulic Acid: Free and Linked into Model Humic Acid‐type Polymers
Authors: Martin J. P. , Haider K.
Published: July 2010

Side chain 1‐14C, 2‐14C, and 3‐14C, O14CH3 and ring 14C‐labeled ferulic acids were synthesized and incubated with Greenfield sandy loam top soil at rates of 100 and 1,000 ppm. The loss of the specifically labeled carbons as 14CO2 over a 12‐week period ranged from 44 to 78% and averaged 64 and 68% for the 100 and 1,000 ppm additions, respectively. The smallest loss occurred from the 2‐14C (side chain) and the greatest from the 3‐14C (side chain) and the O14CH3 carbons. Losses of 14CO2 from specifically 1 and 2‐14C‐labeled acetic, and 1‐, 2‐, and 3‐14C pyruvic acids and from 14COOH‐labeled vanillic and protocatechuic acids, all of which are common metabolic products noted during the microbial decomposition of ferulic acid, averaged about 84%. After linkage into model humic acid type polymers from hydroxyphenols and toluenes by phenolase oxidative polymerization, losses of 14C ranged from 7 to 25%. Greatest losses were from the 3‐carbon of the side chain and least from the ring carbons. Losses for ring and side chain carbons after linkage into polymers from hydroxybenzoic acids varied from 3 to 7%. Losses of about 21% occurred from the O14CH3 groups. When labeled ferulic or vanillic acids were added to cultures of Stachybotrys chartarum or Hendersonula toruloidea, from 11 to 52% of the ring 14C was incorporated into the humic acid‐type phenolic polymers formed in the nutrient solutions. Only 3 to 4% of the ring carbons of veratric acid were incorporated into the “humic acid” fraction of these fungi.
Soil Shear Strength Variation in Soils of a Batavia Silt Loam Mapping Unit
Authors: Veneman P. L. M. , Bouma J. , Edil T. B.
Published: July 2010

Soil shear strength values obtained in situ in soils in a mapping unit of the Batavia silt loam (Mollic Hapludalf, fine silty, mixed, mesic) with the vane shear test for a wide range of natural moisture contents were compared with values obtained with the widely used unconfined compression test in the laboratory. The comparison was made to evaluate the tests for soil survey characterization, to express soil variability within an important mapping unit and to define functional relationships between shear strength and different soil properties.

The vane shear test was preferred because: (i) tests required less time and involved less cost, (ii) tests could be made in relatively dry, pedal soil where the laboratory method did not work, and (iii) test results of both methods were not significantly different. Graphical representation of shear strength (X) as a function of the moisture content (θw = percent by weight) allowed an estimate of the minimum shear strength of the studied soils at any natural moisture content. A more accurate estimate of shear strength could be made by considering also the liquid limit (LL) and plasticity index (PI) of the soil material in a multiple regression equation as follows: X = −3.84 −0.18θw + 0.47LL −0.4PI. Clay content and bulk density were insignificantly correlated. This type of analysis may provide quantitative data for soil survey interpretations.
Measuring Hydrologic Properties of Soil with a Double‐ring Infiltrometer and Multiple‐depth Tensiometers
Authors: Ahuja L. R. , El‐Swaify S. A. , Rahman A.
Published: July 2010

A ring infiltrometer with varying width of buffer zone in combination with multiple‐depth tensiometers was tested for determining the hydrologic properties of a Typic Dystrandept (Tantalus silty clay loam) soil profile on a Hawaii forested watershed. With location of one multiple‐depth tensiometer at the vertical axis of the axi‐symmetric flow system and one or more at a given radius outside the inner ring, both vertical and radial hydraulic gradients could be simultaneously measured. It was thus possible to estimate the lateral flow components and determine vertical infiltration rates and hydraulic conductivities (at field saturation) of the different soil horizons. Lateral flow decreased with time during infiltration. Under the moist to wet conditions of the soil under study, lateral flow was not appreciable. From an inner ring of 30‐cm diameter, the latter was practically eliminated when a buffer ring of 90‐cm diameter was employed. Its effect on the final infiltration rate was negligible even when a buffer ring of 60‐cm diameter was used.
Viscosity of Interlayer Water in Montmorillonite
Authors: Low Philip F.
Published: July 2010

The viscosities of water in Na‐montmorillonite systems at various water contents were calculated by different equations using data from experiments conducted by different investigators on: (i) viscous flow of water at different temperatures, (ii) self‐diffusion of water, and (iii) neutron scattering by water. The results were remarkably consistent and showed that the viscosity of the interlayer water is greater than that of bulk water and increases exponentially with decreasing water content. Evidence was also presented to show that the viscosity of this water depends on the b‐dimension of the associated montmorillonite. By combining the data on viscosity with data on hydraulic conductivity, it was possible to determine the permeability of the montmorillonite at different water contents.
Ammonium Diffusion as a Factor in Nitrogen Loss from Flooded Soils
Authors: Reddy K. R. , Patrick W. H. , Phillips R. E.
Published: July 2010

The role of NH4+‐N diffusion in a flooded soil on nitrogen (N) loss through the nitrification‐denitrification process was investigated under laboratory conditions. The distribution of applied NH4+‐N in both the aerobic and anaerobic soil layers of a flooded soil was experimentally determined and compared with the values obtained from theoretical equations. The total loss of NH4+‐N from the flooded soil system (15‐cm depth) by nitrification‐denitrification was equivalent to 12.43 g N/m2 for a 120‐day incubation period when the initial concentration of NH4+‐N was 44.84 g N/m2. Diffusion of NH4+‐N from the anaerobic soil layer to the aerobic soil layer accounted for more than 50% (7.16 g N/m2) of the total NH4+‐N loss with the remainder being lost from NH4+‐N originally present in the aerobic layer. The NH4+‐N that diffused upward into the aerobic soil layer was nitrified to NO3‐‐N, which readily diffused back down into the anaerobic soil layer and was subsequently denitrified. The experimental distributions of NH4+‐N were not in close agreement with calculated distributions in the surface aerobic soil layer, but were in close agreement in the anaerobic soil layer. It is possible that the rate constant (k) for NH4+‐N oxidation varied considerably with depth in the aerobic soil layer and thus resulted in the disagreement. The total NH4+‐N loss calculated from the experimental distributions tended to agree with the values obtained theoretically from rate constant (k) values of 3.18, 5.00, and 6.67 µg cm‐3 day‐1. The first rate constant value was obtained from an independent experiment (for same soil), the second from matching the concentration of NH4+‐N at the aerobic‐anaerobic layer interface of the theoretical and experimental distribution at 90 days after flooding, and the third from the NH4+‐N disappearance in the aerobic soil layer of the soil columns described in this study. These rate constants indicate that the rate of nitrification is one of the factors controlling N loss from flooded soil.
Effect of Pretreatment on Loss of Nitrogen‐15‐labelled Fertilizer Nitrogen from Waterlogged Soil During Incubation
Authors: McKenzie E. , Kurtz L. T.
Published: July 2010

Soil preparation treatments (field‐moist, intact cores; oven‐dried, intact cores; and oven‐dried, crushed, screened soil) greatly influenced fertilizer nitrogen loss under waterlogged conditions in the laboratory. Nitrogen (300 pp2m) as 15N‐labelled calcium nitrate was added to samples from selected horizons of Drummer silty clay loam (Typic Haplaquol) and they were subsequently covered with water and incubated for 0, 4, 8, 16, and 32 days. Samples of upper (above 51 cm) soil horizons were incubated at 21°C while those from deeper horizons were incubated at 18°C.

Oven‐drying and crushing of the soil during preparation increased fertilizer nitrogen loss. Only 34% of the fertilizer nitrogen disappeared from field‐moist, intact soil cores while approximately 90% disappeared from both oven‐dried, intact cores and crushed screened samples.

Maximum rate of dentrification of fertilizer nitrogen in field‐moist, intact cores was 3.58% of the applied nitrogen per day. This rate was approximately one‐third of that in the oven‐dried, intact cores and one‐ninth of that in the oven‐dried, crushed samples.

Apparently oven‐drying and crushing soil samples increased the accessibility of the energy source for the denitrification process. However, crushing apparently did not increased the quantity of energy since total nitrogen losses after 32 days were similar for both oven‐dried, intact‐ and oven‐dried, crushed samples.
Evaluation of the Parameters of Soil Phosphorus Availability Factors in Predicting Yield Response and Phosphorus Uptake
Authors: Dalal R. C. , Hallsworth E. G.
Published: July 2010

The importance of quantity, intensity, capacity, and rate factors of soil P availability to account quantitatively for the variation in P uptake and wheat grain yield in pot and field experiments was studied. Among the parameters of the quanitity factor (L, E, Ec, E1.0, Q0 value, NH4F‐P, NaOH‐P, H2SO4‐P, organic P, Olsen P, Colwell P, carbonate P, and anion‐exchange resin, AER‐P), L value was found to be highly correlated with P uptake at 35 and 150 days after planting (maturity) when all the soils were considered. However, the carbonate P (soil P extracted for 16 hours with 0.25M NaOH‐0.1M Na2CO3 at a soil/solution ratio of 1:100) was found to be the best parameter of the quantity factor when the soils containing high amounts of hematite/goethite (> 20%) were excluded. The parameters of the intensity factor (0.01M CaCl2 soluble P, aH2PO4i and phosphate potential) were significantly correlated with P uptake at early growth (35 days) whereas the parameter of the capacity factor (maximum buffering capacity, Mb) was bezter correlated with P uptake at the later stage (150 days). The rate factor, as measured by AER was better correlated with P uptake at 35 days than with P uptake at 150 days after planting. The quantity factor as measured by the carbonate P accounted for 75 and 93% of the variation in P uptake and grain yield, respectively. The capacity factor, Mb when combined with the quantity factor accounted for more of the variation in P uptake (150 days) from 75 to 86%. The intensity and the rate factors had a smaller effect.
Distribution of Water and Ions in Soils Irrigated and Fertilized from a Trickle Source
Authors: Bar‐Yosef B. , Sheikholslami M. R.
Published: July 2010

Simultaneous distributions of water, NO3‐N and P in clay and sandy soils irrigated daily from a trickle source were studied in the laboratory. Hydraulic conductivity data, water retention curves and adsorption isotherms to the soils were determined to enable verification of mathematical models against the experimental results obtained under various conditions. It was found that when adding identical amounts of water, but increasing the trickle discharge rate in the sandy soil from 250 to 2,500 ml/hour, the vertical movement of the wetting front increased and the horizontal movement decreased. In a sequence of three cycles of irrigation with a nutrient solution, losses of nitrate were observed in the clay soil, probably due to denitrification processes. The restricted mobility of the phosphate ions, even in the sandy soil, implies that a preirrigation mixing of P in the soil, supplemented by its addition to the irrigation solution, is necessary to obtain a uniform P concentration in the soil volume.
Use of the Green‐Ampt Equation with Variable Conductivity
Authors: Ahuja L. R. , Tsuji G. Y.
Published: July 2010

A comparison with Phillp's two‐term equation, derived from a series solution involving t1/2, indicates that the hydraulic conductivity in the Green‐Ampt equation of vertical infiltration varies with time when the soil water content of the transmission zone is assumed to be constant. Use of the Green‐Ampt equation with a continuously variable conductivity or a piecewise application of the equation as an extension of Philip's two‐term equation resulted in improved prediction of infiltration in two Hawaii soils. Both these forms of application require three parameters, hydraulic conductivity, sorptivity, and constant A, which have well‐established physical meaning.
Spatial Distribution of Soil Heat Flux Under a Sour Cherry Tree
Authors: Fritton D. D. , Martsolf J. D. , Busscher W. J.
Published: July 2010

This paper presents data on the spatial variability of surface soil heat flux in an orchard (Prunus cerasus L.), evaluates the error involved in estimating the surface soil heat flux, and develops a method by which a spatial average may be taken. Surface soil heat flux was calculated from measurements of the heat flux at the approximately 5‐cm depth and of the heat stored above the heat flux plate. The heat flux plate calibrations were corrected for the thermal conductivity of the soil as measured in situ. Measurements were made at six sites both under an orchard tree and in the open between trees. Results showed that the nighttime flux under the tree was occasionally < 50% of the values measured in the open. In contrast, the daytime spatial and temporal variability was very high and occasionally a small upward flux was recorded under the trees while a near maximum downward flux was being recorded in the open or under the tree a short time earlier or later. A spatial average was calculated by weighting the soil heat flux values by the area of the orchard they represented using an integration procedure. The spatial averages showed that 50–80% of the nighttime net radiation loss from the orchard was derived from the soil.
Stability Constants of Cu2+, Pb2+, and Cd2+ Complexes with Humic Acids
Authors: Stevenson F. J.
Published: July 2010

Application was made of the potentiometric titration method for determining apparent stability constants for the complexes between Cu2+, Pb2+, and Cd2+ and three humic acids from diverse sources. Complexes of Cu2+ and Pb2+ were considerably more stable than those for Cd2+. Log K2 values, obtained from the relationship kj = bj/Ki (Ki = ionization constant) increased rather dramatically with decreasing salt concentration and were of the order of those reported in the literature for metal complexes with known biochemical compounds. Average log K2 values for the three humic acids (absence of neutral salts) were 8.9 for Cu2+, 8.7 for Pb2+, and 6.9 for Cd2+. Differences between humic acids in their ability to bind metal ions were slight. At least two major sites were involved in the binding of metal ions.
Phosphorus‐zinc Interaction in Relation to Absorption Rates of Phosphorus, Zinc, Copper, Manganese, and Iron in Corn
Authors: Safaya N. M.
Published: July 2010

The effects of P and Zn on growth, nutrient content in tops and roots, and the rates of absorption of P, Zn, Cu, Mn, and Fe per unit fresh weight of roots for two growth periods of corn (Zea mays L.) were studied in soil culture under greenhouse conditions. Visual symptoms of Zn deficiency appeared in plants when the level of applied P was raised to 75 µg P/g soil. Phosphate decreased tissue‐Zn concentration and Zn flux through roots. Zinc deficient plants had higher concentration of P in their tissues. Phosphate flux was mostly reduced with Zn, but during 27–48 days growth, Zn‐supplied plants retained near identical rates of P absorption (approximately 14 µg/g fresh root/day) irrespective of the level of P supplied. The rate of Cu absorption was reduced with both P and Zn as the plants aged. Manganese flux was initially stimulated by P but later on drastically reduced by Zn. Iron concentration in plants decreased with Zn application but significant reduction in Fe flux with Zn occurred during early growth of 25 ppm P‐supplied plants only. In general, nutrient fluxes diminished with plant age.
A New Method of Measuring Shrink‐Swell Potential Using Soil Pastes
Authors: Schafer William M. , Singer Michael J.
Published: July 2010

A new method of measuring shrink‐swell potential of soil was developed using < 2‐mm sieved soil. Results obtained by this method were significantly correlated with COLE determined on natural soil clods (p < 0.001, r2 = 0.83). The new method is fast, requires little equipment, and should be a valuable test of shrink‐swell potential when clods cannot be obtained or when equipment for measuring COLE by the standard method is not available.
Evaluation of a Capillary Bundle Model for Describing Solute Dispersion in Aggregated Soils
Authors: Rao P. S. C. , Green R. E. , Ahuja L. R. , Davidson J. M.
Published: July 2010

A simple capillary bundle model was evaluated for describing solute dispersion in two well‐aggregated soils of Hawaii. The model enables the use of pore‐water velocity distribution rather than an average pore‐water velocity. The pore‐size distribution was calculated from the soil water characteristic data. The position and relative shape of the break‐through curves calculated by the capillary bundle model was dependent more on the pore‐water velocity distribution than on dispersion owing to mixing within a pore. The predicted breakthrough curves were extremely skewed and did not describe the measured curves. The mixing of solute between adjacent flow paths, a process not accounted for in the model, apparently resulted in failure of the model. A measure of pore accessibility and interconnectedness of pore sequences is essential for quantitative description of the influence of soil pore geometry on solute dispersion.
Coupling Phenomena in Saturated Homo‐ionic Montmorillonite: II. Theoretical
Authors: Groenevelt P. H. , Elrick D. E.
Published: July 2010

A theory is presented for the formulation of flux equations which describe the transport of water, salt, and electric charge through clays. This theory is based on thermodynamic principles. Model considerations lead to analytical expressions for the transport coefficients. These model calculations are based on electric double layer theory and produce a symmetric matrix of coefficients.

The difference with former theories and model calculations is that the analysis is for electrodes which are reversible to the anions instead of the cations. The impact of this difference on the magnitude of some of the coefficients and on some of the physico‐chemical responses of the system is formidable.
Potassium Status of Some Alluvial Soils in Kentucky
Authors: Rasnake Monroe , Thomas Grant W.
Published: July 2010

Six alluvial soils from Kentucky were intensively cropped to ‘Midland’ bermudagrass (Cynodon dactylon L. Pers.) to determine K availability in each soil. Potassium removal by the bermudagrass was compared to exchangeable K, to labile K estimated from Beckett quantity/intensity plots and to Gapon coefficients before and after cropping. Exchangeable K was not a good measure of uptake (r = 0.61 not significant), but labile K determined on soils before cropping and the Gapon coefficient after cropping gave highly significant linear correlations with K removed by bermudagrass. Exchangeable K after cropping changed an average of only 23 ppm K in the soils, but availability of K to plants was lowered drastically in all soils. This study shows that exchangeable K is an insensitive measurement of K availability to plants. Exchangeable K is a useable measurement only because wide ranges are used in determining classes of availability in soil testing.
Weathering of Serpentinite in Matanzas Province, Cuba: Mass Transfer Calculations and Irreversible Reaction Pathways
Authors: Dirven J. M. C. , van Schuylenborgh J. , van Breemen N.
Published: July 2010

Weathering processes of serpentinite rock in the Province of Matanzas, Cuba, were studied by means of detailed mineralogical and chemical analyses of three pedons in a toposequence. The observed mineralogical composition was compared with that predicted theoretically by mass transfer calculations.

All soils are extremely rich in ferric oxides. The lowest, poorly drained soil, a Gleysol, is smectitic and contains carbonates (magnesite and siderite). Its subsoil appears to meet the requirements for application of the model most closely. Here weathering proceeds at high CO2 concentrations leading to the formation of siderite, magnesite, smectite, and amorphous silica. Reduction of colluvial goethite to siderite may be involved also. Carbonates are lacking in the two well‐drained soils (Chromic Cambisols) which contain appreciable kaolinite in addition to smectite. This agrees with the stronger leaching at the well‐drained sites. Yet, the presence of amorphous silica implies that the rate of leaching only slightly exceeds the rate of weathering.

Published water analyses from serpentinite areas are in good agreement with the water composition predicted by the model.
Geomorphic Surfaces and Soil Development in the Upper Rogue River Valley, Oregon
Authors: Parsons R. B. , Herriman R. C.
Published: July 2010

Soil‐geomorphology studies in the upper Rogue River Valley in Jackson County, Oregon have related soil distribution to a step sequence of six geomorphic surfaces ranging in age from late Holocene to middle Pleistocene. Haploxerolls of the two flood plains have only A horizons. The soils of the low Holocene terrace have developed an argillic horizon within 2,350 years and are classified as Argixerolls. Durochrepts and Argixerolls of the two late Pleistocene surfaces have two kinds of periglacial patterned ground and one soil has a duripan that greatly affects land use. The middle Pleistocene surface has Haploxeralfs and Chromoxererts. The surfaces and soils are compared to those previously studied in the Willamette Valley.
Transport of Reactive Solutes through Multilayered Soils
Authors: Selim H. M. , Davidson J. M. , Rao P. S. C.
Published: July 2010

Solute transport through saturated and unsaturated multilayed soils was studied using laboratory experiments and finite difference approximations of the solute transport equation. Soil‐water and physical characteristics as well as solute sorption properties were measured and/or calculated for each soil layer. Linear and nonlinear equilibrium and kinetic adsorption processes were used to predict adsorption in each layer. Water flux was assumed constant for water‐saturated and unsaturated layered soil profiles. For all adsorption processes considered, the calculated results showed that the order in which the soil layers were stratified in a water‐saturated profile did not influence the effluent solute concentration distribution. For unsaturated layered soil profiles, the results showed that effluent solute distributions can be predicted with an average water content within individual soil layers. Experimental results from the miscible displacement of 36Cl and 14C‐labeled 2,4‐D [(2,4‐dichlorophenoxy) acetic acid], through a two‐layered soil column (Norge loam and Eustis sand) supported the calculated results.
Predictions of the Soil Water Flux Based upon Field‐measured Soil‐water Properties
Authors: Warrick A. W. , Mullen G. J. , Nielsen D. R.
Published: July 2010

Predictions of soil water flux are made taking into account spatial variability of the soil water parameters. A conductivity of the form K = Ko exp [α(θ − θo)] is utilized where θ is the volumetric water content with Ko and θg the values of hydraulic conductivity and water content for steady‐state intake from water ponded on the soil surface. The value of α is an empirical constant for each site and for each depth. Monte Carlo simulations are used to simulate the flux distribution from the simplified drainage equation JL = Ko (1 + α Ko t/L)‐1. The flux of JL is a random output dependent upon the stochastic nature of Ko and α. Long‐normal distributions of Ko and α are chosen from field data published for Panoche soil. Output of JL is approximately lognormal for all times studied. The mean value of JL is larger than the flux calculated using the average Ko and α values in the above equation. Sample numbers necessary to estimate the means of the flux at t = 0, 1, and 10 days are plotted. For t = 0, samples of 1,000, 100, and 50 result in estimates of JL within 16, 50, and 60% of the true mean 95% of the time. For t = 1 and 10 days similar figures for samples of 1,000, 100, and 50 are 4, 14, and 20%. Values of water content stored in the profile using the above equations are also examined as a random function. Unlike the flux values the range in values stays about the same for at least 20 days. The research points out a need for meaningful methods for sample stratification in order to reduce variances.
Fritted Glass Bead Materials as Tensiometers and Tension Plates
Authors: Chow T.L.
Published: July 2010

A maximum temperature of 655°C which was reached in six steps with approximately 100°C/step/hour for 90 min was used to frit glass beads. Tensiometer or tension plate with desired dimension and operational characteristics can be constructed from the product. Uniformity tests on the product indicate negligible horizontal temperature variations during the fritting process and slow heat dissipation during the cooling phase tends to limit its thickness. Tests on the particle size distributions suggest that glass beads graded to very narrow distribution are required to produce fritted material with both the maximum saturated hydraulic conductivity and maximum air‐entry value.
Ion Exchange Reactions in Nondried Chambers Montmorillonite Hydroxy‐Aluminum Complexes
Authors: Keren Rami , Gast R. G. , Barnhisel Richard I.
Published: July 2010

The extent and mechanisms by which hydroxy‐Al interlayers may reduce the CEC of Chambers montmorillonite were studied using 22‐Na labeled clay. Clay‐hydroxy‐Al complexes were formed by added AlCl3 and NaOH at pH 7.5–9.5 (OH/Al ratio of about 2.80). AlCl3 was added at 4, 8, or 16 meq/g clay and either before, after, or simultaneously with NaOH. Addition of 16 meq AlCl3/g clay followed by NaOH resulted in CEC reductions of 60, 40, and 10% at pH 7.5, 8.5, and 9.5 as measured by Na adsorption. However, there was no trapped or nonexchangeable 22‐Na observed in any of the systems. Since the charge on the hydroxy‐Al is negligible at these pH's, the CEC reduction is apparently due to trapped Al. CEC reduction was much less when NaOH was added prior to rather than after AlCl3 even though X‐ray results indicated the presence of Al‐interlayers after drying in all except physical mixtures of hydroxy‐Al and clay. Since CEC reduction is apparently due to formation of hydroxy‐A1 interlayers and entrapment of A1 on the surface of the clay, it will vary with the amount and sequence in which AlCl3 and NaOH are added and the pH of the system due to varying solubility of the hydroxy‐Al and charge on the precipitate. As a result, studies where AlCl3 and NaOH are added simultaneously may give varying results depending on which is leading during the titration. Studies using 137‐Cs and 85‐Sr labeled Cs‐and Sr‐clay were conducted to further confirm the mechanism of hydroxy‐Al interlayer formation and subsequent CEC reduction.
Chemical Reduction of Nitrite and Nitrous Oxide by Ferrous Iron
Authors: Moraghan J. T. , Buresh R. J.
Published: July 2010

Little is known about the reduction of NO2‐ and N2O by Fe2+ in the pH range from 6 to 8, a range of importance in many natural environments. Reduction of 25 mg NO2‐‐N (approximate concentration=25 ppm) and 5 mg N2O‐N in a distilled‐water medium containing 800 mg Fe2+ with a helium atmosphere in the presence and absence of Cu2+ at pH 6 and 8 was studied at 26°C. Reduction of NO2‐ to N2O (the principal product), N2 and NH4+ was rapid and quantitive at pH 8 and not greatly affected by Cu2+. However, addition of Cu2+ decreased the mole ratio of N2O to N2 in the evolved gas mixture from 4.2 to 3.1. Reduction of NO2‐ at pH 6 was incomplete, but was favored by Cu2+ addition. Nitrous oxide was the dominant reduction product at this pH value. Small quantities of NO accumulated at pH 6.

Irrespective of Cu2+ addition, N2O was stable in the Fe2+ medium at pH 6. In the pH 8‐system in the presence of Cu2+ 84% of the N2O was reduced to N2. Nitrous oxide was relatively stable at pH 8 in the absence of Cu2+. Small quantities of H2 accumulated in the atmospheres of vessels containing the pH 8, plus Cu2+ N2O − N treatment. No H2 accumulated in the NO2‐ series of treatments.
The Nitrogen Isotope Effect Associated with Nitrate and Nitrite Loss from Waterlogged Soils
Authors: Chien S. H. , Shearer Georgia , Kohl Daniel H.
Published: July 2010

Changes in the isotopic composition of added NO3‐, during the course of its disappearance from two central Illinois soils are reported. The only known difference in the two soils is the cultural history of the fields from which they were taken. A large (approximately three‐fold) difference between the two soils was observed in the isotopic fractionation factor associated with NO3‐ loss. Large differences in the two soils with respect to both the rate of NO3‐ loss and the isotopic fractionation associated with it were apparently related to differences in the two fields rather than to temporal or spatial variation within the fields. Addition of glucose (1% with respect to dry soil weight) caused the difference between the two soils to disappear. It also appreciably reduced the apparent isotopic fraction factor in both soils.

When NO2‐, rather than NO3‐, was added as substrate, the isotopic fractionation factor associated with its loss was the same in the two soils. The effect of glucose was similar whether NO3‐ or NO2‐ was the substrate; i.e., the isotopic fractionation factor was substantially reduced.

Possible explanations for the observed variations in isotope effect associated with substrate loss are discussed. In addition, the implications of these variations for the study of denitrification in natural systems are discussed.
Evaluation of Soil Nitrogen Mineralization Potentials under Modified Field Conditions
Authors: Smith S. J. , Young L. B. , Miller G. E.
Published: July 2010

Amounts of mineral N obtained by a calculation procedure and measurement in fallow plots were compared during two cropping seasons and annually with eight Oklahoma soils. The calculation procedure involved adjusting the N mineralization potentials for varying soil temperature and water content. The field N measurements involved the use of soil in plastic bags and glass filter tubes. Cropping season and annual field amounts for the eight soils, on the average, ranged from 54 to 78 ppm N. In general, the calculated amounts compared favorably to the field amounts, differences frequently being <10 ppm N. Calculated amounts correlated as well or better with the field amounts than a variety of other N availability indexes.
Soil Formation on Loess in Southwestern Indiana: II. Distribution of Clay and Free Oxides and Fragipan Formation
Authors: Harlan P. W. , Franzmeier D. P. , Roth C. B.
Published: July 2010

Fourteen soil profiles from southwestern Indiana were studied to determine the effects of loess thickness and natural soil drainage on the profile distribution of clay and free oxides (CBD‐extractable) of Fe, Al, Mn, and Si. In all soils, Fe and Al curves follow the clay curve, suggesting that the oxides are adsorbed on clays and move with them. Natural soil drainage had little effect on profile distribution of clay, Si or Fe. Free Al2O3 contents increase slightly with poorer drainage. With thinning loess, clay and free Fe2O3 distribution changes little, free Al2O3 contents increase slightly, free MnO2 curves have more pronounced minima and maxima, and free SiO2 increases significantly in fragipan horizons. We propose that free silica moves down the profile in solution and precipitates, possibly with aluminum hydrous oxides on clays. The resulting silica or alumino silicate binds particles together to form the hard, brittle soil material of fragipans.
Soil‐landscape Relationships in the Occidental Plateau of São Paulo State, Brazil: II. Soil Morphology, Genesis, and Classification
Authors: Lepsch I. F. , Buol S. W. , Daniels R. B.
Published: July 2010

Nine profiles representing the major soils in the Occidental Plateau of São Paulo State, Brazil, were characterized after detailed geomorphic and soil mapping were completed on a 70.8 km2 area. The stable upland geomorphic surface had Oxisols, surrounded by younger erosional surfaces with Ultisols, Alfisols, and Inceptisols. Mollisols formed where the erosional surfaces exposed calcareous sandstone. The argillic horizons of the Ultisols and Alfisols in these positions apparently have formed in material that would qualify as an oxic horizon before it was exposed. Laterally moving water at these sloping sites is believed to initiate free Fe removal and lessivage. Lateral water movement at the contact between the surficial deposits of oxic composition and the underlying calcareous sandstones appears to supply the bases for the Alfisols developed in the oxic material.

Kaolinite dominates the clay mineralogy of the soils formed in unconsolidated deposits, but attapulgite and smectite are present in the calcareous sandstone. In the soils shallow to calcareous sandstone the attapulgite apparently has weathered to smectite within a few centimeters of the rock.
Gully Wall Stability in Loess‐derived Alluvium
Authors: Bradford J. M. , Piest R. F.
Published: July 2010

A field study was made on an instrumented vertical slope to investigate the triggering mechanisms that initiate gully wall failure in loess‐derived alluvium. The relevance of hydrology, soil morphology, and soil mechanics to an understanding of gully slumping is examined. Conventional limit equilibrium slope stability methods were of little value in predicting failure volumes or in understanding the failure mechanics. The geometry and time of failure are greatly influenced by the structural features of loess‐derived alluvium and by the dependence of the shear strength on the pore water pressure within the soil.
On the Chemical Foundation of the Sodium Adsorption Ratio
Authors: Sposito Garrison , Mattigod Shas V.
Published: July 2010

The theoretical chemical basis of the sodium adsorption ratio (SAR) was examined in order to clarify two important issues that arise in connection with the problem of estimating potential sodium hazard: (i) the relation between SAR and the theory of cation exchange, and (ii) the implications of the universal practice of replacing SAR by what may be termed the practical SAR, which employs total concentrations of Na, Ca, and Mg instead of their free cationic concentrations. In regard to (i), it was confirmed that SAR can be given a chemical basis in terms of the Gapon cation exchange equilibrium constant which is provided in this paper with a rigorous derivation for the first time. The Gapon constant is shown to differ from the Vanselow exchange constant only because of the (arbitrary) convention adopted as to what entity is termed the ligand in the cation exchange reaction. In regard to (ii), it was shown through a direct calculation of SAR and the practical SAR for 161 different soil solutions or water extracts, utilizing a comprehensive chemical equilibrium computer program, that an exact functional relationship between the two parameters does not exist. Only a statistical correlation between SAR and practical SAR could be established because of the random variation in the composition of metal‐complexing anions in the soil solutions or water extracts. These anions reduce the free cationic concentrations of Na, Ca, and Mg, but their amounts are not chemically related to the presence of the metals and, therefore, to the value of the practical SAR. It follows that the practical SAR has no exact chemical relation to the theory of cation exchange, although its use in strictly empirical studies of Na hazard may be justified, in a statistical sense, by its acknowledged practical value.
Destruction of Organic Matter by Hydrogen Peroxide in the Presence of Pyrophosphate and Its Effect on Soil Specific Surface Area
Authors: Sequi Paolo , Aringhieri Roberto
Published: July 2010

The effectiveness of hydrogen peroxide in oxidizing soil organic matter was markedly increased by the presence of 0.1M sodium pyrophosphate at pH 7, with residual C after treatment being reduced up to 20 times lower compared to conventional soil peroxidation. “Electropositive” (Orange II) and external (N2) surface areas increased, whereas “electronegative” (cetyl pyridinium bromide) surface area values generally decreased after H2O2 treatment, supporting the assumption that metals released from organic matter may precipitate as hydroxide coatings that hinder further oxidation. Some soil sorption sites appear to be occluded by organic matter, so that changes in soil properties after peroxidation cannot be solely attributed to organic matter.
Information Provided on Humic Substances by E4/E6 Ratios
Authors: Chen Y. , Senesi N. , Schnitzer M.
Published: July 2010

The ratio of optical densities or absorbances of dilute, aqueous humic and fulvic acid solutions at 465 and 665 nm (E4/E6) is widely used by soil scientists for the characterization of these materials. While it has been suggested that the E4/E6 ratio is related to the degree of condensation of the aromatic carbon network, carbon content, and molecular weight of humic substances, little rigorous experimental evidence is available in the literature to confirm these hypotheses.

The results of this investigation show that the E4/E6 ratio of humic and fulvic acid is: (i) mainly governed by the particle size (or particle or molecular weight); (ii) affected by pH; (iii) correlated with the free radical concentration, contents of O, C, CO2H and total acidity in as far as these parameters are also functions of the particle size or particle or molecular weight; (iv) apparently not directly related to the relative concentration of condensed aromatic rings; (v) independent of humic acid and fulvic acid concentrations, at least in the 100–500 ppm range. Our data show, in agreement with M. M. Kononova (1966), that E4/E6 ratios for humic and fulvic acids should be determined between pH 7 and 8. This can best be done by dissolving the humic material in 0.05N NaHCO3 solution at concentrations of 200–400 ppm.
Effects of pH Level on Yields and Compositions of Pearl Millet and Alfalfa in Soils with Differing Degrees of Weathering
Authors: Lanyon L. E. , Naghshineh‐Pour B. , McLean E. O.
Published: July 2010

Bulk samples of soils representative of widely differing degrees of weathering (Mollisols, Alfisol, Ultisols, and Oxisols) were collected. Aliquots of each were adjusted to different pH levels, fertilized, and cropped successively to one cutting of pearl millet (Pennisetum glaucum L. Willd.) and three cuttings of alfalfa (Medicago sative L.).

As postulated, the trends in crop response to pH differed with crop and with degree of soil weathering. Pearl millet responded very little to increase in pH, except that with very highly weathered soils yields increased significantly up to pH 5.6 to 6.2 followed by a significant decrease at higher pH. Significant increases in alfalfa yields with increased pH were obtained on all soils. However, yields from some of the soils increased prograssively to the highest pH; others leveled off at an intermediate pH, and still others decreased at the highest pH. The latter generally occurred in the most highly weathered soils. Soil and plant analyses as well as visual symptoms suggested that toxic levels of Mn (all soils) and insufficient Ca and high Al (one soil only) were major causes of low alfalfa yields at low pH. Depressed yields of alfalfa in the highly weathered soils at higher pH levels may be related to low levels of available P.

The yield response to soil pH vs. degree of weathering relationship was not as clear cut as postulated, but this may not be so much a shortcoming of the hypothesis as it is a consequence of the difficulty in selecting individual soils representative of the highest levels of soil classification, and of the effect of specific parameters important to crop response‐soil pH relationships which transcend such soil groupings.