bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluidized Bed Combustion Bottom‐Ash Effects on Infiltration and Erosion of Variable‐Charge Soils
Authors: Reichert José Miguel , Norton L. Darrell
Published: July 2010

Highly weathered soils generally maintain low electrolyte levels (EC) in soil solution, which, along with raindrop impact, causes aggregate dispersion and enhanced erosion. This study was conducted to determine if application of fluidized bed combustion bottom ash (FBCBA) could control erosion of variable‐charge soils. Seven highly weathered soils (six Oxisols and one Ultisol) were prewetted and then subjected to high‐intensity rainfall (110 mm h‐1) for 2 h. The FBCBA was surface applied at a rate of 5 Mg ha‐1. Infiltration, runoff, and erosion were measured throughout the rains. The FBCBA increased EC and pH of the soil solution, because it contained CaO (23%), Ca(OH)2 (3%), and CaSO4 (73%). Steady‐state infiltration rates (Is) ranged from 7.2 to 54.8 mm h‐1 for the control and from 9.5 to 44.4 mm h‐1 for the FBCBA. The FBCBA had either a favorable, an unfavorable, or no effect on the parameters tested, depending on the soil. On soils with a favorable response to FBCBA, Is was increased by 1.7 to two times, total runoff reduced by two times, and total erosion reduced by 2.2 to 2.4 times. On soils with an unfavorable response, Is was decreased by 1.2 to 1.6 times, total runoff increased by 1.2 to 1.6 times, and erosion increased by 1.6 times. The increased infiltration and reduced erosion and runoff occurred only for soils that had low pH (ΔpH ≤ 0.6) and negative charge (≤ 2.0 cmolc kg‐1). Unfavorable responses were found when ΔpH was >2.1, charge increase was at least 6.8 cmolc kg‐1, and final pH was >9.
Organic Matter Fractions from Organically and Conventionally Managed Soils: I. Carbon and Nitrogen Distribution
Authors: Wander M. M. , Traina S. J.
Published: July 2010

Chemical and physical fractionation techniques were used to study the effects of organic and conventional management practices on soil organic matter (SOM) characteristics. We isolated SOM from: (i) organic animal‐based, manure‐amended (ORG‐AN), (ii) organic cash‐grain‐based, cover cropped (ORG‐CC), and (iii) conventional, cash‐grain‐based (CONV) rotations. We quantified the total C and N contents of humin (HN) and humic substances (HS), and light (LF), heavy (HF), fine organo‐clay, and organo‐sand fractions. Management changed the quantity and distribution of C and N in physically and chemically isolated fractions. The ORG‐CC soil had significantly greater quantities of C in its HN, HS, LF, and HF fractions than the CONV soil. Management impacted the distribution of C and N only in the LF fraction. The ORG‐CC had a larger percentage and proportion of C and N in its LF than the other soils. The percentage of soil N in HS was higher in the ORG‐AN and ORG‐CC than in the CONV soil. Even though the quantity of N in the CONV's HN equaled the other soils, it had the highest percentage and proportion of N allocated to this fraction. Farming systems did not significantly alter the C and N contents of HS or the quantity of C associated with selected particle‐size fractions; however, the C content of fine clay isolated from aggregated soil was significantly greater than the C content of clay isolated from loose soil. By isolating macroorganic matter (LF) in concert with HS and HN fractions, we were able to assess management practice impacts on SOM characteristics.
Drip Irrigation in Heterogeneous Soils: Steady‐State Field Experiments for Stochastic Model Evaluation
Authors: Or Dani
Published: July 2010

In many drip‐irrigated fields, spatial variations in soil properties induce variations in wetting patterns about the drippers, resulting in uncertainty in the interpretation and use of sensor‐based soil water information. In previous work, analytical tools to quantify the effects of spatial variation in soil hydraulic properties on wetting patterns were developed. The objective of this study was to validate some of these analytical results. Following the characterization of the soil hydraulic properties in the study site, water was supplied from arrays of surface and subsurface point sources at constant flow rates. About 160 tensiometers and 100 time domain reflectometry (TDR) probes were installed at fixed positions relative to the source (for each flow rate and source location) and were monitored daily. The resulting spatial moments of matric head and water content were compared with analytical model predictions. Results revealed a large discrepancy between measurements and predictions based on the field‐estimated variability in α (the exponent of the unsaturated hydraulic conductivity function). Better agreement was obtained when a reduced variability in α was used. This suggests that soil hydraulic properties measured under ponding may be biased by the presence of large pores. Overall, the analytical model was capable of using information on the (permanent) spatial variability in soil hydraulic properties to predict the variability in flow attributes. However, even with better soil characterization and smaller soil variability, model predictions should be viewed as first approximations of the extent of variability in matric head and water content.
A Quasi‐Analytical Model for Soil Solute Movement under Plant Water Use
Authors: Connell L. , Haverkamp R.
Published: July 2010

Solute accumulation in surface soils through capillary rise transport, driven by evaporation, is a serious management issue. In particular, for soils under a saline shallow water table, salt buildup can have a serious detrimental impact on agricultural productivity. For vegetated surfaces, evaporation is the sum of water loss directly from the surface and that taken up by plants for transpiration. We developed a procedure for the prediction of solute migration in soils under plant water use in a shallow water‐table environment. For this situation, the advection‐dispersion equation is shown to be linear with nonconstant coefficients. To solve this equation, the root zone is divided into a series of layers and for each layer the governing equation is approximated by a constant coefficient form with layer‐averaged values for properties. We derived a solution to this equation in Laplace space, which is coupled to its neighbors by requiring the flux and concentration be constant across the layer boundaries. At each time level, a matrix system is posed for the equation coefficients and concentration resolved by numerical inversion from Laplace space. The good agreement between model predictions and solutions obtained from a finite‐element analysis indicates that the procedure presented is of high accuracy and could offer computational savings over purely numerical procedures. The multilayer approach allows the representation of nonuniform plant water use functions, dispersivities, soil properties, and initial conditions.
Release Rates of Phosphorus, Ammonium, and Potassium in Clinoptilolite‐Phosphate Rock Systems
Authors: Allen E. R. , Hossner L. R. , Ming D. W. , Henninger D. L.
Published: July 2010

Controlled release of P, NH4, and K can be accomplished in synthetic soils through dissolution and cation‐exchange reactions by phosphate rock (PR) and the zeolite mineral, clinoptilolite (Cp). The power‐function equation has previously been found to adequately describe transport kinetics of the nutrient release process. Research was conducted to evaluate factors affecting P, NH4, and K release rates in Cp‐PR systems. Data was collected using a continuous‐flow thin‐disk technique. Results were evaluated with the power‐function equation. Materials included a Texas Cp and North Carolina and Tennessee PRs. Variables examined included the Cp/PR ratio, the mole fraction of NH4 and K on the Cp, and the type of PR. The power‐function model indicated that initial release rates and cumulative nutrient release in Cp‐PR mixtures were increased by using a higher Cp‐PR ratio and by using a more reactive PR. Nutrient release rates were also affected by changes in the proportion of NH4 and K occupying Cp exchange sites and reflected ion‐selectivity characteristics of Cp. The results indicate that Cp and PR may be used to obtain a controlled release of NH4, P, and K in a synthetic soil.
Soil Carbon Dioxide Fluxes from Conventional and No‐Tillage Small‐Grain Cropping Systems
Authors: Fortin M.‐C. , Rochette P. , Pattey E.
Published: July 2010

Conversion to conservation tillage systems increases soil C content by reducing soil erosion and the rate of organic matter oxidation. We hypothesized that these effects could impact soil emission of CO2. This study (i) determined if CO2 emissions were reduced in the first years after conversion to no‐tillage (NT) relative to conventional tillage (CT), (ii) evaluated whether differences in soil CO2 emissions between tillage treatments were related to soil temperature differences, and (iii) determined if soil CO2 emission measurements provided an early estimate of soil management practice impact on soil organic C. In 1992 and 1993, CT and NT plots were planted to small‐grain cereals in Ottawa, Ontario, on a Dalhousie silt loam (mixed, mesic, Typic Endoaquoll). Fluxes were measured using closed chambers connected to a portable CO2 analyzer. During growing season 1992, the CO2 emissions varied from 0.05 to 0.18 mg CO2 m−2 s−1 with an average of 0.12 mg CO2 m−2 s−1 for CT and of 0.10 mg CO2 m−2 s−1 for NT. In 1993, the CO2 emissions varied from 0.06 to 0.35 mg CO2 m−2 s−1 with an average of 0.15 mg CO2 m−2 s−1 in both tillage treatments. Differences in soil CO2 fluxes between treatments were related to differences in soil temperature (r2 = 0.62), giving an estimate of 75 g C m−2 yr−1 difference in organic C transfers to the atmosphere between CT and NT. These results were validated using an independent estimation derived from long‐term field experiments. Thus, soil CO2 flux measurements using dynamic closed chambers can provide early estimates of soil management impacts on soil organic C.
Ion‐Chromatographic Analysis of Low Molecular Weight Organic Acids in Spodosol Forest Floor Solutions
Authors: Krzyszowska Anna J. , Vance George F. , Blaylock Michael J. , David Mark B.
Published: July 2010

Low molecular weight organic acids (LMWOA) from root exudates, decomposing organic matter, and other sources are important lignads involved in solution complexation reactions as well as ligand exchange reactions at mineral surfaces. The purpose of this study was to (i) develop an ion chromatography method that could be used to determine LMWOA in soil solutions from Spodosols, (ii) assess methods for preserving LMWOA in soil solutions, and (iii) evaluate LMWOA concentrations in forest floor solutions during a growing season. Solutions were collected weekly from zero‐tension lysimeters installed within the forest floor (forest floor leachate collectors). Limits of quantitation for acetic, formic, malonic, oxalic, phthalic, and citric acids were 0.35, 0.14, 0.43, 0.41, 0.07, and 0.04 µM, respectively, which in some cases are an order of magnitude lower than reported in previous studies. Freezing soil solutions after filtering resulted in the best recoveries (between 90 and 100% for all LMWOA); other methods of preservation, such as filtering alone and filtering and storing at 4°C, resulted in lower recoveries. The average concentrations of LMWOA in the forest floor solutions were 10 µM acetic acid, 0.7 µM formic acid, and 3.3 µM oxalic acid. Dissolved organic C from the forest floor contained a maximum concentration of 2.0% acetic acid, 0.01% formic acid, and 0.15% oxalic acid. There were no apparent temporal patterns in LMWOA concentrations, except for a decrease in LMWOA concentrations from late September to a minimum in October.
Moment Analysis to Estimate Degradation Rate Constants from Leaching Experiments
Authors: Das B. S. , Kluitenberg G. J.
Published: July 2010

First‐order degradation rate constants (γ) are often estimated from the results of solute leaching experiments by using curve‐fitting procedures. However, uniqueness problems can make curve‐fitting a challenging task if multiple parameters are estimated simultaneously. Several attempts have been made to compute γ by employing batch degradation theory to analyze the results of leaching experiments. This theory requires an estimate of the mass recovery fraction (MRF) and the degradation time. The degradation time is replaced with an average solute travel time when batch theory is applied to the results of a leaching experiment. This approach is flawed because the simultaneous occurrence of sorption, dispersion, and convection confounds the time available for degradation in a leaching experiment. We have used statistical moments to show that when degradation follows first‐order kinetics, the degradation time is an adjusted convection time (ACT). It is defined as the harmonic mean of m1/R and the convection time (L/v), where m1 is the first moment of the breakthrough curve (BTC), R is the retardation factor, L is the length of the soil column, and v is the pore water velocity. The adjustment in the convection time scale is required because of the simultaneous occurrence of dispersion and degradation. We show that these two processes interact to reduce the true convection time for the leaching event (ACT < L/v). We have tested our result by generating artificial BTCs with known values of γ and then successfully estimating γ by obtaining the MRF and ACT from the generated BTC. We have outlined a procedure to estimate γ from the information generated in a typical leaching experiment.
Sodium‐Copper Exchange on Wyoming Montmorillonite in Chloride, Perchlorate, Nitrate, and Sulfate Solutions
Authors: Zhang Z. Z. , Sparks D. L.
Published: July 2010

The effect of anions on the Na‐Cu exchange reactions on montmorillonites is not well understood and discrepancies exist in the literature. This study was conducted to examine the role of anions on the Na‐Cu exchange reaction on Wyoming montmorillonite. The copper exchange capacity (CuEC) and Na‐Cu exchange reactions on Wyoming montmorillonite were studied in Cl−, ClO−4, NO−3, and SO2−4 solution media at a constant total metal charge concentration of 0.0200 molc L−1. We found that the values of CuEC were similar in Cl−, ClO−4, NO−3, and SO2−4 electrolyte media, and the quantity of Cu extracted by Na2‐EDTA solution was only 1.0 to 1.2% of the CuEC and was not affected by anions. The apparent adsorbed metal charge, Q, and Vanselow selectivity coefficients, Kv, were determined across a wide range of exchanger phase composition, with Cu2+ occupying 30 to 95% of the charge sites. We found that the values of Q increased with Cu saturation in each of the anionic media, and the increase was not affected by anions. The increase in Q was attributed to decrease in negative adsorption of anions. We observed that Kv was independent of exchanger composition in each of the four anionic media. The values of Kv in the SO−4 medium were lower than those in other anionic media because of the complexation reaction between Cu2+ and SO2−4. The data showed that Cu2+ ions were not specifically adsorbed under our experimental conditions and that the exchanger phase behaved as an ideal mixture. It was concluded that no detectable monovalent complexes such as CuCl+ and CuNO+3 were adsorbed on Wyoming montmorillonite in the Na‐Cu exchange reaction.
Origin and Properties of Smectite in Loess‐derived Soils of Western Ohio
Authors: Burras L. , Smeck N. E. , Bigham J. M.
Published: July 2010

Expanding phyllosilicates have been identified in soils of western Ohio for >40 yr, yet little is known about the origin or properties of these clays. The objective of this study was to ascertain the origin of the smectite component of the expanding phyllosilicates from a representative Udalf‐Aqualf‐Aquoll toposequence derived from Peoria loess in western Ohio. The content, distribution, and layer charge of the smectite were evaluated using chemical and x‐ray techniques. Results from these analyses show the smectite present in these soils is a medium‐charge dioctahedral species. Alkylammonium chloride exchange indicated the layer charge of the smectite is between 0.36 and 0.38 mole charge per half unit cell. The smectite generally comprised 50% or more of the total clay content in the B and C horizons of each pedon. The presence of high contents of smectite in the C horizons of all three pedons demonstrates a detrital origin and suggests that Peoria loess was an important source of expanding phyllosilicates in soils of western Ohio.
Influence of Hydroperiod on Litter Conversion to Soil Organic Matter in a Floodplain Forest
Authors: Lockaby B. G. , Wheat R. S. , Clawson R. G.
Published: July 2010

Lignin and cellulose dynamics were followed for 23 mo during degradation of foliar litter in an oligotrophic floodplain forest located in south Georgia. Litter was placed in microcosms, which were subjected to hydroperiod variation in terms of duration and nutrient inflow. Treatments were compared in terms of rates of lignin and cellulose loss and the degree to which a theoretical asymptotic value of the ratio of lignin to lignin plus cellulose (LCI) was approached. Flooding strongly stimulated loss rates of lignin and cellulose, and results suggest that a single, relatively brief flooding event promoted loss rates to the greatest extent. The elevation of N inflow reduced lignin degradation rates compared with other flooding treatments. Observed temporal patterns of LCI ratios did not follow theorized patterns and may suggest that, in warm climates such as south Georgia, lignin loss is greater than in boreal forest systems where theoretical LCI relationships were developed.
Improved Soil Particle‐Size Analysis by Gamma‐Ray Attenuation
Authors: Oliveira J. C. M. , Reichardt K. , Vaz C. M. P. , Swartzendruber D.
Published: July 2010

The size distribution of particles is useful for physical characterization of soil. This study was conducted to determine whether a new method of soil particle‐size analysis by gamma‐ray attenuation could be further improved by changing the depth and time of measurement of the suspended particle concentration during sedimentation. In addition to the advantage of nondestructive, undisturbed measurement by gamma‐ray attenuation, as compared with conventional pipette or hydrometer methods, the modifications here suggested and employed do substantially decrease the total time for analysis, and will also facilitate total automation and generalize the method for other sedimentation studies. Experimental results are presented for three different Brazilian soil materials, and illustrate the nature of the fine detail provided in the cumulative particle‐size distribution as given by measurements obtained during the relatively short time period of 28 min.
Winter Cover Crop Effects on Soil Organic Carbon and Carbohydrate in Soil
Authors: Kuo S. , Sainju U. M. , Jellum E. J.
Published: July 2010

Winter cover crops may increase soil organic carbon (SOC) levels or reduce their rate of depletion. Selection of appropriate cover crops to increase SOC requires an adequate knowledge of the quality and quantity of plant biomass produced and its rate of decomposition in soil. This study examined the SOC and carbohydrate concentrations in soil as affected by several leguminous and nonleguminous cover crops after 6 yr of a corn (Zea mays L.) cover crop double cropping system in a temperate, humid region. The vegetation in the control treatment without cover crops was primarily shepherd's‐purse [Capsella bursa‐pastoris (L.) Medikus]. The cover crops had a variable effect on SOC and soil carbohydrate concentrations due to a significant difference in total organic C and carbohydrate produced by the cover crops. The buried bag technique showed that the biomass C from the aboveground biomass of the cover crops decomposed rapidly in the soil with a half‐life averaging 30.9 ± 9.4 (SD) d in 1992 and 55.2 ± 7.8 (SD) d in 1993. The decomposition of carbohydrate in the aboveground biomass in the soil was also rapid with an average half‐life of 40.0 ± 13.1 (SD) d in 1992 and 50.5 ± 11.8 (SD) d in 1993. The overriding cover crop effect on SOC and carbohydrate was due to the magnitude of the C inputs from the cover crops. With more than 4 Mg ha−1 of top biomass, cereal rye (Secale cereale L.) and annual ryegrass (Lolium multiflorum Lam.) were better suited as winter cover crops for building SOC levels in this region than Austrian winter pea (Lathyrus hirsutus L.), hairy vetch (Vicia villosa Roth), and canola (Brassica napus L.).
Genesis of Non‐Allophanic E Horizons in Tephra‐Influenced Spodosols
Authors: McDaniel P. A. , Falen A. L. , Fosberg M. A.
Published: July 2010

Holocene volcanic ash from the cataclysmic eruption of Mount Mazama in southwestern Oregon is an important component of many soils of the Pacific Northwest region. High‐elevation forested soils of northern Idaho containing Mazama tephra have developed E‐Bhs horizon sequences and are accordingly classified as Spodosols. In this study, we report on the formation and expression of E horizons in a developmental sequence of volcanic‐ash‐influenced Spodosols from this region. Results suggest that development of E horizons in these volcanic‐ash‐influenced soils proceeds systematically along an elevational gradient. The lightest colored, thickest E horizons are associated with the highest elevation soils of the subalpine fir [Abies lasiocarpa (Hook.) Nutt.] forest zone, and E horizons are more weakly expressed and then absent with decreasing elevation. Microprobe analysis of volcanic glass shows that E and Bhs horizons contain the same tephra, indicating that substantial pedogenesis has taken place in these horizons. Formation and eluviation of Al‐humus complexes has given rise to E horizons whose mineralogy and chemistry are consistent with that of non‐allophanic Andisols and differ markedly from underlying horizons. Beidellite, an Al‐rich smectite, dominates the clay fraction of the well‐developed, very strongly acid E horizons at the expense of allophanic clays and metal‐humus complexes; other than beidellite, opaline SiO2 is the major secondary Si‐bearing phase. Chemical and mineralogical properties of illuvial B horizons are consistent with those of allophanic soils; short‐range‐order aluminosilicates and metal‐humus complexes dominate the clay fractions. Results indicate that coupled eluvial‐illuvial processes associated with podzolization are responsible for the non‐allophanic character of E horizons and the allophanic character of Bhs horizons in these forested, volcanic‐ash‐influenced ecosystems.
Mapping Wind‐Blown Mass Transport by Modeling Variability in Space and Time
Authors: Sterk G. , Stein A.
Published: July 2010

Field observations of wind‐blown particle transport are often characterized by a considerable spatial variation, which makes quantitative modeling of wind erosion difficult. This study examines how the horizontal distribution, or pattern, of mass transport can be determined from a limited number of point measurements. Twenty‐one sediment catchers were installed in an experimental plot in the Sahelian zone of Niger, on a sandy, siliceous, isohyperthermic Psammentic Paleustalf. Mass transport values during four storms ranged from 24.0 to 213.6 kg m−1, 7.2 to 26.0 kg m−1, 9.6 to 68.9 kg m−1, and 68.9 to 282.7 kg m−1. Geostatistical theory was applied to produce storm based maps by modeling the spatial correlation structure with the variogram. To estimate the variogram from 21 observations, the four storms were treated as independent temporal replicates. Two geostatistical mapping techniques were applied. Kriging (a spatial interpolation technique) produced maps of mass transport providing the best possible estimates of net soil losses from the plot, equal to 12.5, 2.0, 4.6, and 26.8 Mg ha−1, respectively. To overcome smoothing, possible realizations of actual mass transport were created by stochastic simulations with simulated annealing. The simulated maps reproduced the statistical properties of the observations and allowed a distinction between erosion and deposition areas within the experimental plot.
Growth and Survival of Jack Pine Exposed to Simulated Acid Rain as Seedlings
Authors: MacDonald Neil W. , Ducsay Brandon J.
Published: July 2010

In a previous study, jack pine (Pinus banksiana Lambert) seedlings grown under pH 2.5 simulated rain had larger shoot/root ratios and altered nutrition compared with seedlings grown with pH 4.7 rain. The objective of this study was to determine if these differences in initial seedling characteristics produced long‐term effects on survival or growth of outplanted seedlings. Significantly (P < 0.05) greater diameter increment (4.3 vs. 4.0 cm) between ages 6 and 10 of jack pine treated with pH 2.5 rain as seedlings was consistent with a carryover effect from the initial treatments. However, no differences between treatments in jack pine diameter, height, or survival persisted to age 14. Results support recent recommendations that extended measurement periods may be necessary to fully assess the long‐term effects of pollutant increases or decreases on growth of immature trees.
Field Evaluation and Error Analysis of Soil Water Content Measurement using the Capacitance Probe Method
Authors: Ould Mohamed S. , Bruand A. , Raison L. , Bertuzzi P. , Bruckler L.
Published: July 2010

The volumetric water content of a silty clay loam soil was measured using the capacitance probe method (CPM) for three successive winter‐spring periods. The results were compared with those obtained using the neutron scattering method (NSM). The CPM was calibrated using gravimetric water content measurements, whereas the NSM was calibrated using a theoretical calibration which requires chemical analysis of soil samples. The calibration curves of CPM were linear for volumetric water content ranging from 0.25 to 0.40 m3 m−3. The correlation coefficients (r) ranged from 0.87 to 0.98. The advantages of the CPM were discussed, and it was demonstrated that, for low differentiated soils, this method can be a better alternative to the NSM, which is commonly used for the determination of soil water content. The CPM and NSM measurements were compared and root mean squared errors between these two methods ranged from 0.0098 to 0.0159 m3 m−3. The precision of NSM and CPM in a field calibration exercise was calculated. For CPM, this study discusses unbiased and biased statistical treatments to establish the calibration curves. The unbiased treatment greatly decreased the total variance in volumetric water content. The standard deviation of volumetric water content ranged from 0.0194 to 0.0248 m3 m−3 and from 0.0108 to 0.0136 m3 m−3 for biased and unbiased statistical method, respectively. Finally, the soil water storage and associated errors were calculated using CPM and NSM.
Concentration of Uranium Particulates from Soils Using a Novel Density‐Separation Technique
Authors: Elless M. P. , Timpson M. E. , Lee S. Y.
Published: July 2010

Soils contaminated with heavy metals or radionuclides at concentrations above regulatory limits pose an environmental and human health risk. Whereas regulatory limits are only concerned with the “extent” of the contamination, knowledge of the “nature” of the contamination (e.g., oxidation state and mineralogy of the contaminant, particulate vs. adsorbed form, etc.) is necessary for developing optimal treatment strategies. Mineralogical identification of the contaminants provides important information concerning the nature of the contamination because once the mineral form is known, its properties can then be determined from geochemical data. To this end, a new density‐fractionation technique called the Magstream density separator was used to concentrate U particulates from U‐contaminated soils at a former U.S. Department of Energy U‐metal production facility. Results from neutron‐activation analysis of each density fraction showed that the U had been concentrated (up to 11‐fold) in the heavier fractions. Mineralogical analyses of the density fractions of these soils using x‐ray diffraction, scanning‐electron microscopy, and an electron microprobe showed the predominance of an autunite [Ca(UO2)2(PO4)2 · 10–12 H2O]‐like mineral with lesser amounts of uraninite (UO2) and coffinite (USiO4) as the U‐bearing minerals in these soils. The presence of reduced forms of U in these soils suggests that the optimal remediation strategy requires treatment with an oxidizing agent in addition to a carbonate‐based leachant to solubilize and remove U from these soils.
Time Series Analysis of Field‐Measured Water Content of a Sandy Soil
Authors: Wu L. , Jury W. A. , Chang A. C. , Allmaras R. R.
Published: July 2010

Prediction of the field soil water regime is important for assessing agrochemical transport and scheduling irrigation. This research was conducted to evaluate the potential for employing the time series analysis technique to predict average water content (WAVG) of a soil profile and water content at depths of interest from measurements made at a single depth. Volumetric water content of a Zimmerman fine sand (mixed, frigid Argic Udipsamment) in Princeton, MN, was measured in situ by time domain reflectometry at six depths during the early 1993 growing season. The time series made up of hourly measurements of soil water content was first‐order differenced to obtain stationarity. The differenced data were used to conduct analyses in the frequency domain to evaluate the coherence and cross‐amplitude between two soil water content time series and were subsequently fitted to autoregressive moving average models to obtain coefficients for the transfer function models in the time domain. The transfer function models were then used to predict water contents at depths of interest (50‐, 75‐, and 100‐cm depths) and WAVG in the top 100‐cm profile from measured water content at the 25‐cm depth. Overall, the predictions were reasonable, with accuracy increasing as the separation distance from the 25‐cm depth decreased.
Statistical Mixing Model for the Apparent Dielectric Constant of Unsaturated Porous Media
Authors: Friedman Shmulik P.
Published: July 2010

A statistical model is proposed that relates the apparent dielectric constant of an unsaturated porous medium to its porosity and volumetric water content. It is assumed that the solid, water, and air components are randomly distributed in space. The unsaturated soil, or other porous media, are considered as a three‐dimensional network of capacitors, with a distribution of capacitance values according to the volume fractions of the three components. Taking into consideration the simplifying assumptions embedded in the model and the fact that no calibration is required, a fair agreement was demonstrated between its prediction and the widely used empirical function of Topp. The basic model presented can be further developed to account for other soil properties by lifting some of the simplifying assumptions. The objectives of this study were to provide some additional insight into the way the volume fractions of the three soil phases determine its apparent dielectric constant, and to introduce a new approach for further investigation of this phenomenon. It is not intended to propose a new universal model relating the volumetric water content to its measured apparent dielectric constant.
Inorganic Nitrogen in Soil Solution Collected with Tensionic Samplers
Authors: Moutonnet P. , Fardeau J. C.
Published: July 2010

Traditionally, porous ceramic cups are used for monitoring ion concentration in soil solutions with time and depth. To calculate the actual N losses through leaching, the cups must be associated with tensiometers, which provide the hydraulic head gradient. This study was conducted to assess how tensionics can determine mineral‐N concentration in soil solution, compared with traditional porous ceramic cups. In field conditions under maize (Zea mays L.), five sets of four tensionics buried at depths between 40 and 130 cm were used throughout the 1992 growing season to assess the concentrations of NO3‐N, NO2‐N, and NH4‐N in the soil solution. Samples were obtained every 10 d for 60 d using two successive methods. The first method was the “tensionic mode” functioning by ionic diffusion through the porous ceramic cup and requiring an 8‐ to 10‐d time step. The second method was the more standard method using soil solution samplers kept 4 h under vacuum to extract the soil solution. For both methods, the same devices were used. Regression analysis on >100 samples showed that NO3‐N recovery was similar for both methods (slope = 0.91; r2 = 0.93). With the tensionic method, NO2‐N and NH4‐N concentrations were, respectively, 5.4 and 7.9 times greater than those obtained by the standard method. These results are explained on the basis of the different ionic concentrations contained in the macro‐ and micropores of the soil. Samples obtained throughout the season (12 series) with devices working in “tensionic mode” were analyzed for inorganic‐N content. In 1992, a rather rainy year, NO3‐N leaching occurred with a surprising downward flux of NO2‐N, which at certain times during the year might pose a threat to groundwater quality.
A Selective Dissolution Analysis Optimized for Measurement of Weathering Products in a Soil
Authors: Benoit Gaboury , Rozan Tim F. , April Richard H.
Published: July 2010

Soil weathering is an important source of nutrient cations and P for development of forested ecosystems, but the rates at which these nutrients are released are not well known. Measurement of weathering products can be used in long‐term (5–10 yr) mesocosm studies to evaluate soil weathering rates. In this study, a method was developed to optimize extraction of nutrient cations in weathering products (organic matter, transition‐metal oxyhydroxides, and amorphous Al and Si compounds) while dissblving minimal amounts of primary minerals. For organic matter destruction, dry ashing was compared with peroxide oxidation. Reducing agents (hydroxylamine hydrochloride, oxalate, dithionite) were evaluated for efficacy in extracting transition‐metal oxyhydroxides. Treatment with hydroxide solutions (NaOH, NH4OH) was tested for dissolving amorphous and poorly crystalline Al and Si compounds. Two methods were used to test for undesirable destruction of unweathered minerals: (i) parallel extraction tests on pure primary minerals, and (ii) release of Rb. The greatest variability in effectiveness of the extractants involved the reduction step. For most elements, the completeness of extraction followed the sequence dithionite > oxalate > hydroxylamine. A wash with HCl was needed to redissolve any carbonates that precipitated in the dithionite step. The best overall protocol involves (i) dry ashing, (ii) extraction with a mixture of citrate, bicarbonate, and dithionite, (iii) washing with HCl, and (iv) treatment with NaOH. This last step was found to release mainly Al and Si and only negligible amounts of cations (K, Ca, Mg, Fe, Mn). With this procedure, destruction of primary minerals can be held to ≈0.4%, well below the quantity of weathering products.
Sensitivity of Isotopically Exchangeable Phosphate in Soil Suspensions to the Supporting Solution
Authors: Morel C. , Torrent J.
Published: July 2010

The isotopically exchangeable quantity (Et) of phosphate measured in 1:10 soil/solution suspensions with deionized water has been identified as the reserve of plant‐available phosphate in agricultural soils. We studied the effects of two supporting solutions, 0.01 M CaCl2 and deionized water, on Et values in 27 calcareous agricultural soils. For three soils, Et was also measured after adding increasing phosphate quantities as KH2PO4, and equilibrating for 24 h, to assess changes in Et with phosphate concentration in solution (Cp). In unamended and phosphate‐enriched soils, Cp(CaCl2) was smaller than and related to Cp(H2O). The initial rapidly and the subsequent slowly isotopically exchangeable phosphate were both affected by the use of CaCl2 solution. Since both the rapid and slow isotopically exchangeable phosphate are Cp dependent, the overall effect of CaCl2 solution was analyzed considering two components: (i) a nonspecific effect attributed to the decrease in Cp and (ii) a specific effect attributed to phosphate reactions (i.e., adsorption or precipitation) in calcareous soils. Modifications in Et are the result of both nonspecific and specific effects. The change in Et due to the use of 0.01 M CaCl2 instead of deionized water varies with the soil sample, and can be positive, negative or nil depending on the time of exchange. For instance, after 24 h of exchange, the ratio {[E24h(CaCl2) − E24h(H2O)]100/E24h(H2O)} ranged from −30 to 340% for the 27 soils. The 0.01 M CaCl2 solution thus introduces complex and unpredictable changes in isotopic exchanged phosphate, and its use is not recommended to estimate plant‐available phosphate in soil.
Competition‐Induced Reductions in Soil Water Availability Reduced Pine Root Extension Rates
Authors: Ludovici K. H. , Morris L. A.
Published: July 2010

The relationship between soil water availability, root extension, and shoot growth of loblolly pine seedlings (Pinus taeda L.) was evaluated in a rhizotron sand mixture in the absence and presence of crabgrass (Digitaria spp.) competition. Heights and diameters of seedlings grown with crabgrass were reduced 33 and 50%, respectively, compared with seedlings grown in pine monoculture. Furthermore, survival of seedlings was reduced by 16% in the mixed species treatments compared with pine monoculture cells. Soil water contents at all depths were at least 50% lower in mixed species treatments compared with pine monocultures during a dry‐down cycle. Maximum loblolly pine root extension rate was 0.10 m wk−1 in pine monoculture compared with 0.02 m wk−1 in the presence of grass. Pine seedling root extension ceased in the presence of grass during prolonged periods of induced water stress. Crabgrass roots extended at a rate of 0.6 m wk−1, a rate largely unaffected by watering regime or differences in water content within the rhizotron. Pine root distributions, at the end of one growing season, were different for seedlings grown with grass than for those in pine monoculture; however, when seedlings of similar size were compared, root distributions were not different. Our results indicate that competition‐induced reductions in soil water availability reduced the rate of pine root extension and thus the volume of soil exploited, thereby reducing resource availability and three growth.
Improving Exposed Subsoils with Fertilizers and Crop Rotations
Authors: Robbins C. W. , Freeborn L. L. , Mackey B. E.
Published: July 2010

Irrigation‐induced erosion and land leveling have decreased crop yields on approximately 800 000 ha of south‐central Idaho silt loam soils. Previous attempts to increase subsoil productivity to that of the topsoil have not been successful on these soils. This study was conducted to find a method(s) for increasing the productivity of freshly exposed subsoil to that of the topsoil and to determine the factor(s) limiting subsoil production. A 4‐yr study was initiated by removing the surface 0.3 m of topsoil from strips between undisturbed topsoil strips of a Portneuf silt loam (coarse‐silty, mixed, mesic Durixerollic Calciorthid). Different crop rotations were established within the strips and fertility treatments were applied across the strips. The fertilizer treatments were conventional fertilizer application according to soil test, dairy manure, and two cottage cheese (acid) whey rates. During the fourth year, dry edible bean (Phaseolus vulgaris L., cv. Viva) were grown on the entire plot area as a test crop. The application of 44 Mg manure ha−1 in the spring and 93 Mg manure ha−1 in the fall of 1991 (first year of study) was the only treatment that restored subsoil bean production to that of the topsoil plots. Plant Zn and soil organic C concentrations were the only measured factors that correlated with bean yield increases on the subsoil.
Methane Emission from a Freshwater Wetland in Belgium
Authors: Boeckx Pascal , Van Cleemput Oswald
Published: July 2010

Some factors influencing methane emission from a freshwater wetland in Belgium were studied. Seasonal fluctuations of methane emission rates, influence of drainage capacity and depth of methane production on methane emission, as well as in situ methane oxidation were monitored. From March until December, methane fluxes varying between 0 and 102 mg CH4 m−2 d−1 were measured. During this period, a total emission of 60 kg CH4 ha−1 was calculated. Statistical analysis of these emission data showed that soil moisture was a more important controlling parameter than soil temperature. Depending on the drainage capacity of the selected area, different emission rates were observed. Sites with a “bad natural drainage” and a “fairly bad natural drainage” showed average fluxes of 5.41 and 2.04 mg CH4 m−2 d−1, respectively, during July. The area with an “insufficient natural drainage” had an emission of 1.44 mg CH4 m−2 d−1. Using methyl fluoride as a specific inhibitor for methane oxidation, it was found that 34 to 67% of the produced methane could be oxidized. Methane emission was found to decrease with increasing soil depth. With diffusion chambers placed on the soil surface, a CH4 release of 40.0 kg CH4 ha−1 (March–June) was found. With chambers placed at 150‐ and 300‐mm depths, emission rates of 11.3 and 3.3 kg CH4 ha−1, respectively, were calculated. Obviously, most of the emitted methane was produced in the upper organic soil layer.
Spatial Distribution of Soil Nutrients in a Northern Everglades Marsh: Water Conservation Area 1
Authors: Newman S. , Reddy K. R. , DeBusk W. F. , Wang Y. , Fisher M. M. , Shih G.
Published: July 2010

The Florida Everglades developed as a nutrient‐poor, rain‐fed ecosystem. However, for the past 30 yr, the Everglades have received nutrient‐enriched surface water runoff from the adjacent Everglades Agricultural Area (EAA). This study examines the response of a pristine wetland, Water Conservation Area 1 (WCA 1), part of the northern Florida Everglades, to nutrient loading as documented by soil nutrient concentrations. During 1979 to 1988, WCA 1 received 138 t total P (TP) and 4919 t total N (TN), retaining 53% of the TP load and 58% of the TN load. Analyses of the spatial distribution of soil N and P showed steep gradients of TP along the western canal boundary, adjacent to inflow points importing EAA runoff. Surficial soils (0–10 cm depth) at interior marsh sites had a mean TP concentration of 368 mg kg−1, compared with 1028 mg kg−1 measured at sites adjacent to the western canal. Similar trends were observed for soil Ca and Mg, while C and N did not show the same boundary effects on spatial enrichment. Nutrient‐enriched sites also had higher porewater soluble reactive P (SRP; 0.15 mg L−1) and NH4‐N (1.65 mg L−1) than unenriched sites (SRP = 0.02 mg L−1, NH4‐N = 0.85 mg L−1). Of the 90 sites sampled, 66 sites consisted of sloughs and sawgrass (Cladium jamaicense Crantz); the remaining 24 sites were either cattail (Typha spp.) dominated or had a significant cattail presence. These 24 cattail sites were closest to the nutrient inflow areas and had the highest soil nutrient concentrations.
Thermally Induced Water Transfer in Salinized, Unsaturated Soil
Authors: Nassar I. N. , Horton Robert , Globus A. M.
Published: July 2010

Natural soil surfaces are exposed to nonisothermal conditions. Resulting thermal gradients cause water to redistribute. The combined effects of solute concentration and temperature gradient on water transfer has not been fully studied. In this work, a model describing the simultaneous transfer of heat, water (liquid and vapor), and solute in porous media was used to predict water transfer under different initial solute concentrations and mean temperatures in closed soil columns. The initial solute concentrations ranged from 0.0 to 3.085 mol kg−1, and mean soil temperatures ranged from 17 to 37°C with thermal gradients of 100°C m−1. The predicted water contents were compared with observed values obtained from soil column experiments. Both the predicted and observed values of water content showed accumulation of water at the cold ends of the soil columns. The predicted and measured net water transfer decreased nonlinearly as the solute concentration increased. Net water transfer increased as the mean temperature increased. Both the predicted and measured solute concentrations showed an increase at regions close to the hot end of the soil columns. The soil column with initial water content of 0.232 m3 m−3 had a large accumulation of solute at the hot end relative to columns with 0.132 or 0.072 m3 m−3 initial water contents. This suggested that water moved mostly in liquid form under the initial water content of 0.232 m3 m−3, whereas it moved primarily in vapor from under initial water content of 0.072 m3 m−3.
Particulate Organic Carbon Content and Potential Mineralization as Affected by Tillage and Texture
Authors: Franzluebbers A. J. , Arshad M. A.
Published: July 2010

Conservation of soil organic carbon (SOC) is important for improving soil quality. Increasing the pool of particulate organic carbon (POC), thought to have a “slow” or medium turnover rate, with conservation tillage may be a critical step in improving the quality of agricultural soils. We determined the standing stock and potential mineralization rate of POC (defined as material >53 µm diam.) at depths of 0 to 50, 50 to 125, and 125 to 200 mm in four Boralfs (loam, silt loam, clay loam, and clay) under conventional shallow tillage (CT) and 4 to 16 yr of zero tillage (ZT) in northern Alberta and British Columbia. Standing stock of POC was consistently different between tillage regimes only at a depth of 0 to 50 mm, averaging 0.63 kg m−2 under CT and 0.76 kg m−2 under ZT. However, the ratio of specific POC mineralization to specific whole‐SOC mineralization averaged 23% greater under ZT than under CT, suggesting that POC was of higher quality (i.e., more mineralizable) under ZT relative to other pools of SOC. With increasing clay content of the original soil, specific mineralization rate of POC increased after clay was removed by dispersion. This result suggests that clay may play an important role in sequestering POC by protecting its decomposition. Particulate organic C content was a more sensitive indicator of tillage‐induced changes in SOC than the total amount of SOC. Zero tillage in this cold semiarid climate may increase both the active and slow pools of SOC within several years.
Soil and Tillage Effects on the Characteristic Size and Shape of Aggregates
Authors: Perfect E. , Zhai Q. , Blevins R. L.
Published: July 2010

Measures of aggregate size and shape are needed in models to predict soil erosion, seed bed density, tensile strength, and solute diffusion. We hypothesized that size (i.e., equivalent cubic length Lc = [l1(l2l√2)(l3l√3)]1/3, where l1, l2, and l3 are the shortest, intermediate, and longest axial lengths, respectively) and shape (i.e., aspect ratios, l1/l3 and l2/l3) vary with soil type and tillage treatment. Caliper measurements of l1, l2, and l3 were made on 1800 aggregates from three sieved fractions (4–8, 8–16, and 16–31.5 mm) of a plowed, plowed plus disked, and no‐till Maury silt loam (fine, mixed, mesic Typic Paleudalf) and a no‐till Karnak silty clay (fine, montmorillonitic, nonacid, mesic Vertic Haplaquept). Overall means for l1/l3 (0.57) and l2/l3 (0.78) were close to those for a cube (0.58 and 0.82, respectively). The mean l1/l3 for Karnak was 18% lower than the corresponding value for no‐till Maury. The Lc was lognormally distributed. The mean log10(Lc) increased from 0.67 in the smallest fraction to 1.19 in the largest fraction. Soil effects on log10(Lc) were most evident in the 8‐ to 16‐mm fraction (1.01 for Karnak compared with 0.93 for no‐till Maury). Tillage effects on log10(Lc) were most evident in the 4‐ to 8‐mm fraction (0.68 for no‐till Maury compared with 0.66 and 0.65 for plowed and plowed plus disked Maury, respectively). The equation Lc = xl(m/mm)1/3, where xl is lower sieve aperture, m is aggregate mass, and mm is modal mass, explained 96% of the variation in Lc. This equation can be used to predict aggregate size from sieve aperture size and measurements of aggregate mass.