bluuebunny/crossref_metadata_2025 huggingface dataset:
Moment Method Applied to Solute Transport with Binary and Ternary Exchange
Authors: Leij Feike J. , Dane J. H.
Published: July 2010

When modeling transport of exchanging solutes in soils, it is sometimes conveniently assumed that the solutes interact linearly with the solid phase of the soil. In this study, an attempt was made to quantify the influence of nonlinear cation exchange on solute spreading with the moment method. Theoretical expressions for the first four moments were derived based on the equilibrium and physical nonequilibrium models of the advection‐dispersion equation (ADE). Displacement experiments were conducted in which either a NaCl pulse (binary exchange) or a pulse of KBr and NaBr (ternary exchange) was applied to a CaBr2‐saturated medium. Values for the transport parameters were determined with moment analysis and curve fitting. The observed breakthrough curves were somewhat better reproduced with parameters obtained from curve fitting than from the moment method. However, the curve‐fitting program produced some unrealistic parameter estimates for the nonequilibrium model. A disadvantage of the moment method was that the fourth‐order moment sometimes yielded unstable results for the nonequilibrium model. Parameters form the anion displacement were used to estimate the theoretical variance due to hydrodynamic dispersion and nonequilibrium spreading for the cation breakthrough curves. The difference between the variance of the observed cation breakthrough curve and these theoretical variances was used as an approximation of the variance due to nonlinear exchange. Particularly for the ternary exchange, the variance due to nonlinear exchange was often several times greater than predicted according to the transport model. The results enabled us to quantify errors in dispersion coefficient (D) values directly determined from cation‐displacement experiments.
Hydrologic Modeling of Protective Barriers: Comparison of Field Data and Simulation Results
Authors: Fayer M. J. , Rockhold M. L. , Campbell M. D.
Published: July 2010

Protective barriers, which consist of layers of silt loam over sand and gravel, have been proposed as covers for waste sites located in semiarid south‐central Washington state. The ability of an uncalibrated model to predict water contents, water storage, and drainage in barriers was tested for durations as long as 1.5 yr. Eight nonvegetated lysimeters containing the barrier layering sequence have been monitored since November 1987. The lysimeters were subjected to one of three precipitation treatments: ambient, 2 × average, and breakthrough (i.e., until drainage occurred). Distributions of measured and simulated water contents with depth were similar; maximum differences ranged from 0.023 cm3/cm3 for the ambient treatment to 0.089 cm3/cm3 near the soil‐sand interface for the breakthrough treatment. Simulated storage followed the trend in the measured values, although differences as much as 5 cm were observed at certain times. Generally, the model overpredicted evaporation in the winter and underpredicted it in the summer. Root‐mean‐square errors were 1.47 and 2.21 cm for the ambient and 2 × ‐average treatments, respectively. Sensitivity tests revealed that the hydraulic‐conductivity function, snow cover, and potential evaporation were important to successful modeling of storage in a protective barrier. When the above parameters and processes were adjusted (though not optimized), the root‐mean‐square error for the 2 × ‐average treatment was reduced 63% to 0.81 cm. For the breakthrough treatment, simulated drainage was obtained only by using field‐measured sorption and saturated‐conductivity data. This result indicates that hysteresis is important to successful modeling of drainage through protective barriers.
Microrelief and Rainfall Effects on Water and Solute Movement in Earthworm Burrows
Authors: Trojan M. D. , Linden D. R.
Published: July 2010

Macropores have been implicated in preferential transport of water and solutes in soil, but mechanisms of transport are not fully understood. Our objective was to determine the effect of surface microrelief, microlandscape position, and rainfall intensity on water and solute transport in burrows created by the earthworm Aporrectodea tuberculata. Water, Br‐, and dye movements in burrows were determined in buckets packed with Waukegan silt loam (fine‐silty over sandy or sandy‐skeletal, mixed, mesic Typic Hapludoll) and incubated with earthworms. One centimeter of simulated rainfall was applied at intensities of 2, 4, 7, and 10 cm h−1, and an instantaneous application of water. As rainfall intensity increased, less Br‐ and dye were displaced from the soil surface, but displaced Br‐ and dye were distributed more evenly with depth and deeper in the soil. The same percentage of burrows conducted at low and high intensities, indicating that increased volumes of water were transported in conducting burrows as intensity increased. Burrows located at the lowest elevations in surface microdepressions showed deeper staining than other burrows for the instantaneous treatment and for all treatments combined. A small number of burrows were responsible for deep displacement of water and solute for each treatment. Models designed to predict flow in burrows must consider the quantity of water available to a burrow, which is a function of surface position, and flow within a burrow, which is a function of the internal characteristics of a burrow.
Effect of Sorption on the Biodegradation of Quinoline
Authors: Smith S. C. , Ainsworth C. C. , Traina S. J. , Hicks R. J.
Published: July 2010

Quinoline is an N‐containing heterocyclic contaminant associated with creosote wastes and may be biologically degraded under aerobic and anaerobic conditions. Quinoline‐degrading bacteria were utilized to investigate the rate of quinoline desorption from smectite clay at low surface concentrations and its subsequent mineralization. Fluorescence spectroscopy and 14C‐quinoline mineralization techniques were used to compare the observed desorption rates to mineralization rates. Microbial utilization was desorption‐rate limiting. Desorption and microbial utilization may be modeled as pseudo‐first‐order reactions whose first‐order rate constant (kobs) is independent of surface concentration. The difference between quinoline disappearance from solution and from the clay surface as observed by fluorescence spectroscopy was comparable to the difference between microbial utilization of the solution and the surface‐bound species. The utilization of quinoline from solution was about 30 times more rapid than surface‐bound quinoline. The surface‐bound species appeared to be protected from microbial attack and, hence, desorption was required prior to utilization. The desorption process is suggested to be a chemical‐reaction‐controlled process rather than film diffusion controlled, as is typically suggested for an exchange process. The biotransformation of quinoline to 2‐hydroxyquinoline, observed in solution by fluorescence spectroscopy, was about five to eight times faster than the subsequent disappearance of 2‐hydroxyquinoline. When quinoline was sorbed, however, no 2‐hydroxyquinoline was observed in solution or on the surface of the clay. It is suggested that quinoline may be transformed to 2‐hydroxyquinoline at the cell surface and that 2‐hydroxyquinoline is the species that is transported into the cell prior to further degradation.
Ameliorating Chlorosis‐Inducing Soils with Rock Materials of Varying Porosity and Iron Content
Authors: Clemens Gerhard , Singer Arieh
Published: July 2010

Lime‐induced chlorosis is a severe problem, affecting many crops in arid‐ and semiarid‐zone soils. Applications of Fe chelates are expensive and only effective in the short term. The ameliorating effects of rock materials on three chlorosis‐producing calcareous soils from Israel were determined in pot tests and in the field. Chlorophyll concentrations of peanut plants (Arachis hypogaea L.) grown in pots with additions of up to 15% (v/v) pumice or tuff‐lapilli to the soils were compared with controls and Fe‐ethylenediaminedihydrochloric acid (EDDHA) treatments. Additions of 10% (v/v) tuff‐lapilli were more effective than those of pumice in small‐pot tests of all three soils. Positive effects persisted for a second growth period. In large‐pot tests, only 15% (v/v) additions were effective in two soils. In field tests, the three soils were treated with pumice or tuff‐lapilli (10% v/v) or basalt powder (5.5% w/w). Basalt powder was the most effective in raising chlorophyll concentrations to levels similar to or greater than those obtained from Fe‐EDDHA. Basalt powder was also the most effective in increasing pod and hay yields on two soils. Also, basalt appeared to have long‐term effects. Only where chlorosis was not severe and where poor aeration appeared to be an additional factor were the effects of tuff‐lapilli and pumice equal or even superior to those of basalt powder. On two soils with severe chlorosis, addition of porous, Fe‐poor materials had no effect. Either because the soils were well aerated or because CO2 production was low, CO2 in the soil air was low and not a major factor determining HCO3‐ in water extracts.
Redox Processes and Diagnostic Wetland Soil Indicators in Bottomland Hardwood Forests
Authors: Faulkner S. P. , Patrick W. H.
Published: July 2010

The presence of unique hydrologic, vegetative, and soil characteristics separates wetlands from nonwetlands. The hydrophytic nature of bottomland hardwood forest vegetation emphasizes soil and hydrologic parameters that are often inferred from soil profile characteristics. Our objectives were to determine the relationships among hydroperiod, soil redox processes, and diagnostic wetland soil indicators. Five transects traversing nonwetland, transitional, and wetland habitat were established parallel to the natural moisture gradient in alluvial bottomlands with mature hardwood forest overstory in Louisiana and Mississippi. Soil redox potential and O2 content at 15, 30, 60, and 120 cm were monitored monthly from September 1982 to August 1985 with permanently installed equipment. Water‐table depth in the upper 120 cm of the soil was also measured during this time. Oxygen and redox patterns at 30 cm were analyzed for each site. These patterns were conclusive enough to classify five sites as nonwetland and eight sites as wetland; however, additional data (hydric soils, soil profile descriptions) were needed to delineate the remaining 11 sites. The quantitative data supported the qualitative diagnostic wetland soil indicators, hydrologic regime, and wetland status of 18 of the 24 sites. Bottomland hardwood wetlands in the lower Mississippi River Valley that are seasonally inundated may be oxidized and aerobic throughout the root zone for 60 to 80% of the growing season. Many bottomland hardwood soils would be considered hydric by the current wetland delineation procedure. Hydrology is the determining factor for these sites and proper assessment of the current hydroperiod is critical.
Alfalfa Emergence and Survival Response to Irrigation Water Quality and Soil Series
Authors: Bauder J. W. , Jacobsen J. S. , Lanier W. T.
Published: July 2010

Irrigation with saline‐sodic water has increased in the northern Great Plains, due to development of marginal soils and extended drought in the region. A greenhouse study was conducted to determine the effect of irrigation water salinity and sodicity on alfalfa (Medicago sativa L.) seedling emergence and mortality in soils with differing textures. Emerged, live seedlings (designated as percent live seedlings, i.e., percentage of planted seeds that developed into emerged seedlings) were counted at 2‐day intervals for 20 d in a randomized block, 3 × 3 × 3 factorial experiment (irrigation water salinity × Na adsorption ratio × soil series). Total dissolved solids (TDS) concentration of irrigation water was maintained at 0.75, 1.15, and 1.65 g L−1 (−4.2 × 10−2, −6.5 × 10−2, and −9.3 × 10−2 MPa osmotic potential); sodium adsorption ratio (SAR) was maintained at 1.1, 5.1, and 9.6. Two supplemental studies of similar design were conducted to determine water quality and soil effects independently on seedling survival. Irrigation water quality treatments caused the percent live seedling counts to be lower than for distilled water. Little seedling mortality occurred. Irrigation with distilled water had a negative effect on germination and emergence in all three soils, but did not increase seedling mortality after germination. Soil series and preplant TDS‐SAR of the soil had the greatest effect on survival. Irrigation water TDS significantly affected seedling emergence among soil series. Emergence ranged from 65 to 85%, with the highest emergence occurring in the coarse‐textured soil irrigated with the lowest TDS‐SAR water. Mortality ranged from 25 to 45%, with the greatest survival occurring in the fine‐textured soil and intermediate TDS‐SAR combinations. Emergence and mortality were high on well‐drained soils irrigated with high TDS and high SAR water. Results of this study indicate that pre‐emergence alfalfa seedbed irrigation should be (i) limited to well‐drained soils with low indigenous salinity and sodicity, and (ii) confined to periods when salinity and sodicity of irrigation water are lowest.
Soil and Environmental Effects on Urease Inhibition by Ammonium Thiosulfate
Authors: Sullivan D. M. , Havlin J. L.
Published: July 2010

Soil urease inhibition by ammonium thiosulfate [ATS, (NH4)2S2O3 12‐0‐0‐26S] in fluid fertilizer mixtures with urea‐ammonium nitrate (UAN, 32‐0‐0) has been demonstrated for a limited number of soils. The objectives of this study were to (i) identify soil properties affecting ATS efficacy, (ii) measure ATS effects on gaseous NH3 losses, (iii) evaluate the effects of soil moisture and temperature on ATS efficacy, and (iv) measure the S species present after application of UAN + ATS. Urea hydrolysis inhibition by ATS ranged from 18 to 48% in eight Kansas soils varying in pH, clay, organic C, and carbonate content in an incubation at 20 °C and −0.1 MPa soil matric potential. Ammonia loss was significantly reduced in seven of the eight soils tested (48% in four noncalcareous soils and 22% in three calcareous soils). Urea‐hydrolysis inhibition averaged 29% at 20°C and 37% at 30°C; inhibition averaged 28% at −0.03 MPa and 38% at −0.1 MPa. Tetrathionate (S4O2‐6) was the dominant S anion produced by S2O32‐ oxidation, ranging from 17 to 88% of the applied S. The amount of S4O2‐6 present was not significantly correlated with the degree of ureahydrolysis inhibition. Ammonium thiosulfate inhibited urea hydrolysis in all soils; its efficacy was greatest for soils low in clay and organic C at high temperatures and low soil moisture contents.
Modeling the Transport and Retention of Cadmium in Soils: Multireaction and Multicomponent Approaches
Authors: Selim H. M. , Buchter B. , Hinz C. , Ma L.
Published: July 2010

A major challenge in modeling the mobility of solutes in soils is to take into account the time‐ dependent retention of reactive solutes in a transport model that can be evaluated by independent experiments. The kinetics of retention and transport of Cd in two soils were investigated in this study. Time‐dependent batch experiments were carried out to describe the extent of Cd sorption by two soils. Miscible‐displacement experiments were conducted to quantify Cd transport in soil columns that received single and multiple Cd pulses. A multi‐reaction convective‐dispersive transport model inadequately predicted effluent concentrations for both soils when independently measured parameters of retention‐release rate coefficients were obtained from batch data sets. We developed a multicomponent approach that accounts for reversible and irreversible Cd retention during transport in soils. Retention mechanisms considered include instantaneous equilibrium ion exchange and a specific sorption process that was based on a second‐order (Langmuir) kinetic reaction. The multicomponent model adequately predicted the observed breakthrough results. The use of kinetic ion exchange and specific sorption for irreversible retention provided improved overall predictions of the results. Parameter values used for the rates of specific sorption (kt) and that for kinetic ion exchange (α), which provided improved predictions for single‐pulse applications, were similar to those used for multiple‐pulse applications. This finding was consistent for both soils and was considered to add credence to our multicomponent model.
Shrinkage of Bare and Cultivated Soil
Authors: Mitchell Alan R. , van Genuchten M. Th.
Published: July 2010

The surface subsidence of shrink‐swell soils may be used to estimate the soil profile water content and soil behaving. Roots are known to affect cracking patterns by anchoring the soil mass, thus influencing soil shrinkage. Our hypothesis was that plant roots will influence soil shrinkage measured by vertical surface subsidence. We tested this hypothesis by measuring shrinkage in a large weighing lysimeter for bare soil with no root system and for soils under wheat (Triticum turgidum L.) and alfalfa (Medicago sativa L.) crops possessing fibrous and tap root systems, respectively. The volume‐loss shrinkage curves for both bare and cultivated soil were found to conform to the straight‐lines model, with distinct changes in shrinkage zones, in spite of uneven water‐content distributions in the profile. The shrinkage characteristic (i.e., the differential change in bulk volume divided by the change in volume water) was greater for fallow (0.677) than for wheat (0.380) and alfalfa (0.377), with the cultivated conditions being similar. These data suggest that plant roots may have large effects on in situ soil shrinkage rates and the water‐content zones throughout which they occur. This result means that a soil's shrinkage characteristic may change depending on the cropping condition. It also means that shrinkage measurements from soils without rooting systems (e.g., small cores or clods) are not necessarily representative of actual shrinkage properties observed in the field.
Cadmium Sorption to Soil Separates Containing Layer Silicates and Iron and Aluminum Oxides
Authors: Zachara John M. , Smith Steve C. , Resch Charles T. , Cowan Christina E.
Published: July 2010

Ion exchange to fixed charge sites and surface complexation to hydroxylated sites are recognized to affect Cd aqueous concentrations in soil; however, the individual contribution of these reactions to Cd sorption in mineralogically complex material has not been documented. The objective of this study was to isolate the contributions of fixed charge and hydroxylated sites to Cd sorption in two Ultisol subsurface horizons that contained kaolinite, 2:1 layer silicates, and crystalline Fe and Al oxides. Cadmium sorption was measured on clay‐sized isolates (<2.0 µm) from the soil materials in NaClO4 electrolyte at ionic strength (I) = 0.1, 0.01, and 0.001 mol L−1 with pH ranging from 4 to 9 and Cd concentrations ranging from 2 × 10−8 to 3 × 10−5 mol L−1. Comparative experiments were also performed with smectite (SWy‐1), kaolinite (KGa‐1), and crystalline and amorphous Fe oxides to evaluate the potential contribution of ion exchange and surface complexation reactions on these phases to Cd sorption in the isolates. Ion exchange of Cd2+ on layer silicates dominated Cd sorption within the isolates when I was ≤0.01 mol L−1 and the pH was less than ≈6.5. Sorption of Cd on hydroxylated sites on the edges of the layer silicates or on Fe or Al oxides, and/or exchange of CdOH+ on the fixed‐charge sites of the layer silicates, dominated Cd sorption at I = 0.1 mol L−1, and when the pH was greater than ≈6.5 at any I. Below pH 6.5, the magnitude of the sorption was controlled by the cation‐exchange capacity of the isolates, which, in turn, was related to their relative proportions of kaolinite and 2:1 layer silicates. By comparing the Cd sorption on the isolates to that on (i) dithionite‐citrate‐bicarbonate (DCB) treated islates and (ii) DCB‐treated isolates augmented with Fe oxides, it was concluded that crystalline Fe oxides were not significant sorbents of Cd. Instead, the Fe oxides appeared to be associated with the layer silicates by a particle interaction that blocked access of Cd to fixed‐charge sites on the layer silicates.
Use of Magnetic‐Susceptibility Measurements in Assessing Soil Uniformity in Chronosequence Studies
Authors: Fine Pinchas , Singer Michael J. , Verosub Kenneth L.
Published: July 2010

Recent observations show that soils with vertical morphological differentiation often exhibit a distinct ferrimagnetic profile with the magnetic susceptibility (MS) of eluvial horizons enhanced with respect to that of illuvial, Cr, or R horizons. In addition, pedogenic ferrimagnetic material is mostly superparamagnetic (SP) and single domain (SD) (<30 nm), whereas inherited titanomagnetites are predominantly multidomain (MD) grains. We suggest that the continuous pedogenic development of a soil profile in homogeneous parent material results in enhancement of MS and in a gradual shift from MD to SD and SP magnetic states, and that deviations from this pattern arise from discontinuities in the soil or from climatic or topographic changes. This hypothesis was tested on 18 northern California pedons, formed in four marine and river terrace systems and in volcanic parent material. The ages of the terraces range from 600 yr to 1.6 million yr and the MS of the parent materials range from 10 to > 1000 × 10−8 m3 kg−1. Established chronosequence members were used to determine that enhancement of MS and shifts in magnetic domain state are correlated with age. Exceptionally large or small magnetic susceptibilities throughout the soil profile, lack of magnetic enhancement, and discontinuous magnetic profiles in other soils could each be related to morphologically or chemically determined discontinuities. Thus, magnetic susceptibility, an easily measured soil attribute, can be used to evaluate the suitability of pedons for chronosequence studies.
Crop Response to Ferrous Sulfate in Banded Gels of Hydrophilic Polymers
Authors: Mortvedt J. J. , Kelsoe J. J. , Mikkelsen R. L.
Published: July 2010

Iron deficiences are widespread and difficult to correct by soil application. Banded hydrogels containing FeSO4 have the potential to act as a matrix for minimizing contact of the applied Fe with soil. Three greenhouse pot experiments were conducted to determine response of grain sorghum [Sorghum bicolor (L.) Moench] to FeSO4 banded alone or with hydrated commercial gel‐forming polymers in Epping silt loam (loamy, mixed (calcareous), mesic, shallow Ustic Torriorthent), a calcareous, Fe‐deficient soil. Sorghum dry‐matter production and Fe uptake after 6‐wk growth periods were highest with FeEDDHA and lowest with FeSO4, each banded alone. Plant availability of applied FeSO4 was increased by banding FeSO4 in some hydrated polymers (mainly polyacrylamides). Apparently, the banded gels provided an environment that maintained the included FeSO4 in a more available form, which resulted in greater crop response to the applied Fe. Results of a laboratory experiment indicated that band application of FeSO4 in hydrated polymers did not affect the rate of oxidation of the applied Fe2+ to Fe3+. However, total extractable Fe (by 0.05 M HCl + 0.0125 M H2SO4 or by 1 M HCl) was higher in soil near banded hydrated FeSO4 with polymer formulations than FeSO4 banded alone. This suggests that the applied FeSO4 had reacted with soil to a much greater extent when it was banded alone rather than with the hydrated polymers.
Parameter Estimates of Field Solute Transport Models Based on Time Domain Reflectometry Measurements
Authors: Elrick D. E. , Kachanoski R. G. , Pringle E. A. , Ward A. L.
Published: July 2010

A new technique using vertically installed time domain reflectometry (TDR) probes can be used to measure the mass flux of solute past the ends of the TDR probes and characterize the probability density functions of travel times. The procedure is applicable for a conservative tracer under steady‐state leaching conditions of constant surface volume flux density of water. The procedure is, however, limited to soils low in salts where the addition of a solute spike will cause a measurable reduction in the TDR signal. We developed the transport equations used to analyze the breakthrough data and obtain the appropriate parameters of two steady‐state models, the convective dispersion equation and the convective lognormal transfer function, as well as a moment analysis. Other models could also have been used. The TDR measurements (reduced in terms of the maximum measured value) for a Dirac‐delta function (spike) input of solute are shown to be equivalent to the solution of a step function input of pure water at the surface to a soil containing unit concentration to infinite depth, i.e., the complement of the flux‐averaged reduced concentration for a step function input of solute. Nonlinear curve‐fitting techniques were used to obtain the transport parameters. Fitting the measured TDR readings to the two models for both field and laboratory data gave good estimates of the transport parameters. The moment analysis, however, reflected the early breakthrough and tailing of the solute, resulting in a doubling of the variance. In addition, variances at the averaged field scale were found to be slightly more than double those at the local scale. The field TDR procedure is fast, inexpensive and nondestructive; the analysis presented yields needed parameters for model predictions.
Dynamic Oxygen and Carbon Dioxide Exchange between Soil and Atmosphere: I. Model Development
Authors: Ouyang Y. , Boersma L.
Published: July 2010

The rate of exchange of O2 and CO2 gases between soil and atmosphere is controlled by atmospheric and soil physical and biological conditions. Analysis and evaluation of problems in soil biology and soil ecology would be greatly facilitated by the availability of a mathematical model that predicts concentrations of these gases as a function of time and soil depth as well as the rate of gas exchange at the soil surface. Our objective was to develop such a model, driven by time‐dependent functions for solar radiation, rainfall, air temperature, and relative humidity of the atmosphere. Outputs of the model include concentrations of CO2 and O2, soil water content, soil temperature, and rate of consumption of O2 and production of CO2 by roots and soil microorganisms, all as functions of time and soil depth. Dissolution of O2 and CO2 in soil water, adsorption of O2 and CO2 onto colloidal surfaces of soil particles, and replacement of air by water due to soil wetting and vice versa are accounted for in the model. Rates of respiration by microorganisms and roots and rate of root growth are given as functions of O2 and CO2 concentrations. Not all of the processes or parameters could be included in the model development because of their large number and complexity. The structure of the model consists of time‐dependent simultaneous equations for vertical transport of water, heat, O2, and CO2 through unsaturated soils. Finite difference methods are used to solve the mathematical model.
Ionic Strength Effects on Acidity and Cations Leached from Forest Floor Cores
Authors: Ross Donald S. , Bartlett Richmond J.
Published: July 2010

We treated fresh, intact forest floor core samples with three concentrations of artificial acidic precipitation. No differences in leachate pH were found between the acidic and nonacidic treatments at each concentration (30–300 µmolc L−1). A linear relationship was found between incoming ionic strength and leachate H+, the major cation leached in all treatments. Soil solution extracted in the field was chemically similar to the laboratory leachates. Our findings suggest that the downward movement of acidity in these soils is a function of the ionic strength of incoming leaching water, independent of short‐term incoming acidity.
Color Zonation Associated with Fractures in a Felsic Gneiss Saprolite
Authors: Schoeneberger P. J. , Weed S. B. , Amoozegar A. , Buol S. W.
Published: July 2010

Darkly coated fractures are identified as a major type of macropore in most saprolites found in the Piedmont and Mountain regions of North Carolina. Morphological and mineralogical characteristics of various color zones associated with these Mn‐coated fractures were evaluated to determine their nature and assess their role in water flow through saprolite. Four distinct color zones (black, white, yellow, and red) were identified surrounding the Mn‐coated fractures in a typical saprolite derived from gneiss and schist parent rock in the Piedmont region. Two large, vertically oriented intact blocks (30 by 30 by 80 cm) containing fractures and associated color zones were removed from the 1.9‐ to 2.7‐m depth. Small undisturbed samples containing all color zones, and disturbed bulk samples from each color zone were analyzed for mineralogical and chemical composition using x‐ray diffraction, scanning and transmission electron microscopy, Mössbauer spectroscopy, electron microprobe scans, and HF digestion for total elemental analysis. Iron content was highest in the interior saprolite matrix (182 mg/kg of clay‐size fraction in the red zone) and diminished toward the fracture (black zone). The red zone was dominated by hematite (54% of Fe oxide present), the yellow zone was dominated by goethite (92% of Fe oxide present), and the white zone was almost free of Fe. In the black zone, Mn oxides occurred in substantial amounts and Fe was mostly in the form of goethite. Manganese was not detected in the other three color zones. Color patterns and relative amounts of Fe and Mn indicate historical preferential water movement along fractures. Measurement of saturated hydraulic conductivity, however, indicates that these fractures are no longer active macropores allowing rapid water flow through saprolite.
Differences in Soil and Leaf Litterfall Nitrogen Dynamics for Five Forest Plantations
Authors: Gower Stith T. , Son Yowhan
Published: July 2010

Vegetation can influence N cycling in forest soils; however, it is difficult to isolate the positive feedback of vegetation on N cycling because other factors are often not held constant. The objective of this study was to measure and compare leaf litterfall N and in situ and laboratory N mineralization rates for 28‐yr‐old northern red oak (Quercus rubra L.), European larch (Larix decidua Miller), eastern white pine (Pinus strobus L.), red pine (P. resinosa Aiton), and Norway spruce [Picea abies (L.) Karst.] plantations on a similar soil in southwestern Wisconsin. Average seasonal soil NO‐3 and NH+4 concentrations (mg kg −1) were 3.9 and 3.4 for red oak; 7.7 and 5.8 for European larch; 5.4 and 6.7 for white pine; 4.9 and 5.1 for red pine; and 5.2 and 6.2 for Norway spruce, respectively. Annual in situ net N mineralization in the top 20 cm of mineral soil differed significantly (P < 0.01) among species and ranged from 46 kg ha−1 yr−1 for Norway spruce to 117 kg ha−1 yr−1 for European larch. Annual in situ nitrification differed significantly (P < 0.001) among species and comprised from 42 (red oak) to 95% (European larch) of the total annual net N mineralized. Laboratory net N mineralization rates also differed significantly among the five species. Average annual leaf litterfall N content for a 2‐yr period ranged from 26 kg ha−1 yr−1 for white pine to 40 kg ha−1 yr−1 for Norway spruce but was not correlated to annual net N mineralization. We suggest that leaf litterfall lignin/N may be an important positive feedback mechanism that influences N mineralization.
Multifractal Model for Soil Aggregate Fragmentation
Authors: Perfect E. , Kay B. D. , Rasiah V.
Published: July 2010

Dry aggregate size and strength distributions are important soil structural characteristics. We present a theoretical model based on multifractals for predicting one characteristic from the other. For a specified stress, σ, the strength of dry aggregates of normalized equivalent cubic length x* was expressed as a probability of failure, {P(x*)}σ. A method was developed for calculating {P(x*)}σ from tensile strength data. At intermediate levels of stress (0.3 ≤ σ ≤ 0.9 MPa), {P(x*)}σ decreased with decreasing x*. A Pareto distribution was used to model this scale dependency. The distribution's parameters, q and r, determine the probability of failure of the largest aggregate and the rate of change in scale dependency, respectively. The r increased and the q decreased logarithmically with increasing σ. The fractal dimension, D, was used to characterize the number‐size distribution of dry aggregates after fragmentation. For mass‐conserving cubic fragmentation, D is related to {P(x*)}σ by the multifractal spectrum, D ≅ log {8(2′ − qx*−r)}/log {2}. Previously published dry‐sieving data were reanalyzed. The number‐size distribution determined by visual counting gave a spectrum of fractal dimensions as predicted by the theory. Values of D ranged from 2.53 at x* = 4.7 × 10−2 to 3.46 at x* = 7.5 × 10−1. The multifractal spectrum was used to estimate q and r inversely. Further research is required to determine the level of stress associated with these values.
Improved Models of Particle‐Size Distribution: An Illustration of Model Comparison Techniques
Authors: Buchan G. D. , Grewal K. S. , Robson A. B.
Published: July 2010

We investigated a relatively unexplored area of soil science: the fitting of parameterized models to particle‐size distribution (a subject more thoroughly explored in sedimentology). Comparative fitting of different models requires the use of statistical indices enabling rational selection of an optimum model, i.e., a model that balances the improvement in fit often achieved by increasing the number of parameters, p, against model simplicity retained by minimizing p. Five models were tested on cumulative mass‐size data for 71 texturally diverse New Zealand soils: a one‐parameter (p = 1) Jaky model borrowed from geotechnics; the standard lognormal model (p = 2); two modified lognormal models (each with p = 3); and the bimodal lognormal model (p = 3). The Jaky and modified lognormal models have not previously been introduced into the soil science literature. Three statistical comparators were used: the coefficient of determination, R2; the F statistic; and the Cp statistic of Mallows. The bimodal model and one modified lognormal model (denoted ORL) best fit the data. The bimodal model gave a marginally better fit, but incorporates a sub‐clay mode (untestable with the present data), so we adopted the ORL model as the physically best benchmark for comparison of other models. The simple Jaky one‐parameter model gave a good fit to data for many of the soils, better than the standard lognormal model for 23 soils. The model comparison methods described have potential utility in other areas of soil science. The Cp statistic is advocated as the best statistic for model selection.
On the Interpretation of Labile Aluminum as Determined by Reaction with 8‐Hydroxyquinoline
Authors: Luster Jörg , Yang Andrew , Sposito Garrison
Published: July 2010

The interpretation of labile Al, as defined operationally by a 15‐s reaction with 8‐hydroxyquinoline, remains problematic. In solutions free of complexing ligands other than OH−, one question is whether the chemical species (Al(OH)+2 should be included. To resolve this issue, labile Al was measured in Al(ClO4)3 solutions at total Al (AlT) concentrations in the range 4 to 60 µmol kg−1 and pH in the range 4 to 6. In solutions equilibrated for 4 h without shaking, no effect of pH in the range 4 ≤ pH ≤ 5 on the values of labile Al was observed. Thus, Al3+ and all significant mononuclear hydrolytic species of Al that formed under the experimental conditions were reactive with 8‐hydroxyquinoline within 15 s. Shaking the sample solutions at pH 5 throughout equilibration, however, produced a gradual decline in labile Al with concomitant changes in light scattering that indicated the formation of colloidal or macromolecular Al species that were unreactive with 8‐hydroxyquinoline during a 15‐s period. Even in unshaken solutions, a decline in labile Al (and the inferred formation of colloidal Al species) was observed at pH 5 if solutions with AlT > 1 mmol kg−1 were used to prepare standard solutions for calibration. These results are important not only for the application of the 15‐s 8‐hydroxyquinoline method, but also for any experimental study of aqueous Al at pH values where Al hydrolysis is significant.
Alkaline Persulfate Oxidation for Determining Total Nitrogen in Microbial Biomass Extracts
Authors: Cabrera M. L. , Beare M. H.
Published: July 2010

The CHCl3 fumigation‐extraction method for determining soil microbial N involves the extraction of CHCl3‐fumigated and CHCl3‐unfumigated samples with 0.5 M K2SO4, followed by determination of total N in the extracts. Total N is typically determined by Kjeldahl digestion (TKN) with the inclusion of NO−2 and NO−3 present. The determination of total N by TKN has several procedural constraints such as an initial concentration step, long digestion times, and considerable bumping caused by catalyst salts. In contrast, a persulfate oxidation method (TPN) commonly used for determination of total N in sea‐ and freshwater samples does not require a concentration step and is much simpler and faster than TKN. The objective of this study was to evaluate and adapt the TPN method to measure total N in 0.5 M K2SO4 extracts for determination of soil microbial biomass N. Studies were conducted to optimize reagent/sample (R/S) ratio and autoclaving time, and to evaluate the effects of C and N concentrations. These studies showed that complete N recovery can be obtained with a R/S ratio of 1 and an autoclaving time of 30 min in extracts containing as much as 250 mg glucose‐C L−1 at a C/N ratio of 10:1. A comparison of the optimized TPN method to TKN for extracts of 12 CHCL3‐fumigated soils indicated that the methods gave the same N recoveries. The use of the TPN method in 0.5 M K2SO4 extracts should facilitate more rapid and efficient measurements of soil microbial biomass N.
Dentrification and Mineralization in Soil Amended with Legume, Grass, and Corn Residues
Authors: McKenney D. J. , Wang S. W. , Drury C. F. , Findlay W. I.
Published: July 2010

Since cover crops and intercrops are increasingly used to reduce soil erosion and N loss and provide efficient N utilization, it is important to evaluate the consequences of crop residue to N cycling processes. The objectives of this study were to determine effects of incorporating hairy vetch (HV, Vicia villosa Roth subsp. villosa), red clover (RC, Trifolium pratense L.), annual ryegrass (ARG, Lolium multiflorum Lam.), reed canarygrass (RCG, Phalaris arundinacea L.), and corn (Zea mays L.) residues on denitrification, dissimilatory NO−3 reduction, and N mineralization‐immobilization in a Brookston clay loam (fine‐loamy, mixed, mesic Typic Argiaquoll). A gas flow system was used with 5 or 10 g residue kg−1 amended soil. With only anaerobic incubation, all residues stimulated denitrification about equally with net NO and N2O production rates two to three times greater than in the control soil. Ammonium accumulation over the 48‐h anaerobic period was 5 to 11 mg N kg−1. When a 5‐d aerobic incubation preceeded the anaerobic phase, losses of NO + N2O amounted to 5 to 17 times that in the control soil during the anaerobic phase. These losses were: 59.4, 47.1, 25.1, 24.4, 17.6, and 3.5 mg N kg−1 for HV, RC, ARG, RCG, corn, and the control, respectively. Mineralization in the HV treatment occurred from the third to the fifth day of the aerobic incubation and NH+4 continued to increase during the subsequent 2‐d anaerobic period, reaching 58.4 mg NH+4‐N kg−1. Nitrite accumulated during the anaerobic phase in all treatments, with 46 and 49 mg N kg−1 for ARG and HV, respectively, during with the 2‐d aerobic/2‐d anaerobic incubation. With the 5‐d aerobic/2‐d anaerobic incubation, NO−2 levels were lower in all but the ARG treatment.
Controlled Wheel Traffic Effects on Soil Properties in Ridge Tillage
Authors: Liebig M. A. , Jones A. J. , Mielke L. N. , Doran J. W.
Published: July 2010

Ridge‐till is gaining widespread use on highly erodible land. Matched‐width equipment has allowed producers to establish permanent traffic lanes in ridge‐till. The establishment of permanent traffic lanes and a lack of preplant tillage has increased concern about soil compaction. The purpose of our study was to assess the effects of long‐term controlled tractor wheel traffic on soil properties of a ridge tillage system. This research was conducted on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll) in southeastern Nebraska. A split‐split‐plot design was employed to evaluate differences in soil properties among corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] crops; row, trafficked interrow, and nontrafficked interrow positions; and depths of 0 to 7.5, 7.5 to 15, and 15 to 30 cm. Axle load of the tractor used on the plots was 4 mg. Sampling was conducted in the summer after ridging. Most variability in soil properties among positions was confined to the 0‐ to 7.5‐cm depth. Bulk density, soil strength, aggregate mean weight diameter (MWD), water content at field capacity (FC), and water content at wilting point (WP) tended to be highest in the trafficked interrow and least in the row. Saturated water content and gravitational water (GW) were generally highest in the row and least in the trafficked interrow. Soil strength in the trafficked interrow was 56% greater than the nontrafficked interrow and 104% greater than the row. Similar, but less pronounced differences among positions were also observed for bulk density. Aggregate mean weight diameter in the trafficked interrow indicated that wheel traffic resulted in larger aggregates while ridging resulted in smaller aggregates in the 0‐ to 7.5‐cm depth of the row. Mean saturated hydraulic conductivity (Ksat) in the trafficked interrow was approximately one‐quarter of the mean value for the nontrafficked interrow and row. Organic C and TN were greater in the row than the interrow positions. The influence of tractor wheel traffic on soil properties was largely dissipated by the 15‐ to 30‐cm depth. Because of the dissimilarity in soil properties among positions, ridge‐tilled fields should be conceptualized and managed as three distinct soil zones, not as a single unit.
Soil Burrowing and Mixing by a Crayfish
Authors: Stone E. L.
Published: July 2010

Observation of rapid lateral water flow through, rather than over, the surface of a level, clayey, mixed, thermic Typic Albaquult (Bladen series) prompted study of the abundant burrows of a crayfish, Procambarus rogersi rogersi Hobbs. The area was a 20‐yr‐old experimental plantation of slash pine (Pinus elliottii Engelm. var. elliottii), with a wide range in tree growth, ground vegetation, and O‐horizon thickness. The objective was to better understand the elaborate macropore system and its consequences for mixing the surface layers of a very poorly drained soil where other burrowing animals were lacking. Excavation of burrows and burrow casts revealed galleries, 4 to 10 cm in diameter, > 1.5 m long, chiefly in the upper 30 cm of soil but with vertical shafts to >1 m in depth. Fifty to 80% of randomly located 0.1‐m2 subplots in well‐forested plots had from one to five openings through the mineral soil surface into surficial burrows, demonstrating widespread distribution of the latter. Bands of rock phosphate broadcast on the surface 20 yr previously provide a marker of cumulative mixing; almost one‐half of the residual P had been mixed into the 5‐ to 15‐cm depth by crayfish activity.
Controls on Soil Solution Chemistry in a Subalpine Forest in North‐Central Colorado
Authors: Arthur M. A. , Fahey T. J.
Published: July 2010

High‐elevation ecosystems in the western USA are potentially susceptible to increased inputs of strong acids. A long‐term research project was established to identify the processes controlling surface water chemistry and to evaluate the sensitivity of Loch Vale Watershed in Rocky Mountain National Park, Colorado, to acid precipitation. Using lysimeters, we estimated the concentration and flux of major solutes in the Oie and B horizons in an old‐grown Englemann spruce (Picea engelmannii Parry ex Engelm.) and subalpine fir [Abies lasiocarpa (Hook.) Nutt.] forest, and in an adjacent site disturbed by a snow avalanche. In the forested site, most solutes were highly concentrated in soil solutions during the initial stages of snowmelt, and concentrations declined rapidly to low levels in the first 4 to 6 wk of snowmelt. Surface water chemistry in Loch Vale Watershed is controlled principally by mineral weathering. During the early stages of snowmelt, however, the flushing of solutes, especially N, S, and C, from forest soils (which comprise only 6% of the study area) exerts an important influence. Rates of cationic denudation per unit area were 3.5 times higher in the forest (131 µmolc m−2 yr−1) than in the whole watershed (38 µmolc m−2 yr−1) probably because of H+ exudation from roots during nutrient uptake and the generation of organic acids in the forest soils. Rates of N mineralization and nitrification as well as concentrations of NO3 in the soil solution were higher in the second year after forest disturbance from a snow avalanche than immediately following the disturbance, indicating a delayed nitrification response. Significant amounts of NH4 and NO3 were temporarily stored in extractable forms in the soil during the first year after the disturbance. Although precipitation inputs and theoretical mineral weathering can explain the total annual solute flux from Loch Vale Watershed, the effects of forest soil solutes may be important during the initial stages of snowmelt and following large‐scale disturbance.
Errors Associated with the Combination Method for Estimating Soil Heat Flux
Authors: Massman W. J.
Published: July 2010

Errors are common to all methods of measuring soil heat flux. This study examines some of the errors that result when estimating the heat storage term (employed by the combination method) from measurements of the time rate of change of soil temperatures. Based on analytical models of the vertical profiles of soil temperature, my results indicate that errors of ±3 to 10% in the estimate of soil beat flux can result from following recommended procedures. For homogenous soils, these errors can be reduced by about 67% using two soil thermometers with unequal weighting to estimate the heat storage term. However, minimizing these errors for inhomogeneous soils may not be possible without detailed information on the vertical structure of the soil thermal properties.