bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of Microbial Respiration and Nitrogen Mineralization in Great Lakes Forests
Authors: Zak Donald R. , Grigal David F. , Ohmann Lewis F. 
Published: July 2010

AbstractRecent attention has focused on organic matter storage in forested ecosystems because climate change could potentially alter this process. Labile organic matter pools are especially important because they may be most strongly influenced by changes in soil temperature and water availability. We measured rates at which C and N were released from labile organic matter within the forest floor and mineral soil of jack pine (Pinus banksiana Lambert), red pine (P. resinosa Aiton), balsam fir [Abies balsamea (L.) Miller], sugar maple (Acer saccharum Marshall), and quaking aspen (Populus tremuloides Michaux) forests. Forest floor and mineral soil samples were assayed for microbial respiration and N mineralization using a long‐term (32 wk at 35 °C) laboratory incubation. Cumulative amounts of respired C and mineralized N were fit to first‐order rate equations; pools and rate constants were compared among forests. Labile (respired) C pools in forest floor ranged from 67 (jack pine) to 92 g C m−2 (sugar maple), four to six times less than that measured in mineral soil. Rate constants for microbial respiration were statistically different among forest types, but means ranged narrowly in forest floor (0.269–0.299 wk−1) and mineral soil (0.303–0.350 wk−1). Labile (mineralized) N pools ranged from 2.2 (red pine) to 4.1 g N m−2 (sugar maple) in forest floor, an order of magnitude less than those in mineral soil. Rate constants for N mineralization varied from 0.326 to 0.556 wk−1 in forest floor and from 0.043 to 0.069 wk−1 in mineral soil. Regional climatic variables were weakly correlated with labile C and N pools and with rate constants. Annual in situ estimates of microbial respiration and N mineralization were far less than respired C and mineralized N pools, suggesting that only a fraction of labile soil organic matter is annually metabolized within these forests. Local climate, rather than the chemistry of labile organic matter, appears to be an important factor constraining the annual in situ flux of C and N from this pool.
Nitrogen and Phosphorus Fate from Long‐Term Poultry Litter Applications to Oklahoma Soils
Authors: Sharpley Andrew N. , Smith S. J. , Bain W. R. 
Published: July 2010

AbstractWith the rapid growth of the poultry industry in eastern Oklahoma, information is needed on the impact of land application of associated litter on the area's soil and water resources. The effect of broiler litter application on the N and P content was investigated by sampling 12 soil profiles to 150 cm under ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] to which litter had been continually applied for 12 to 35 yr. Litter application averaged 6 Mg ha−1 yr−1 (dry wt.), which contributed approximate N and P amounts of 270 and 90 kg ha−1 yr−1. Adjacent soil profiles under idle native grass, which received no litter or mineral fertilizer, were sampled at the same time to a 150‐cm depth. On average, soil pH and organic C were 0.5 and 21 g kg−1 greater and bulk density 0.2 Mg m−3 lower in the surface 5 cm of treated than untreated soils. Below 25 cm, litter had little effect on these properties. The effect of poultry litter on N and P content was greatest in the surface 5 cm of soil, with NO3‐N and Bray‐I P (BP) averaging 49 and 188 mg kg−1 in treated and 13 and 9 mg kg−1 in untreated soils. Below 5 cm, N and P content decreased rapidly, with only slight NO3‐N accumulations (5 mg kg−1) between 50 and 100 cm and no movement of P below 30 cm observed. Poultry litter application decreased P sorption to a depth of 30 cm. Average 1.2‐ and 2.5‐fold increases in the total N and NO3‐N content of treated compared with untreated 0‐ to 100‐cm profiles were observed. For P, 2‐ and 13‐fold increases in total P and BP were found, with little accumulation as organic P. Overall, BP increased 22 mg kg−1 for each 100 kg P ha−1 added in litter. The greater portion of litter P (72%) than N (44%) retained in the soil profile reflects the differing sorption of these nutrients by soil, and greater plant uptake of N than P. It also emphasizes the need to carefully manage continual land applications of poultry litter to minimize potential environmental impacts.
Analyses of Slope and Runoff Factors Based on the WEPP Erosion Model
Authors: Huang Chi‐hua , Bradford Joe M. 
Published: July 2010

AbstractUnder process‐based erosion model development, the source of sediment transported off a field is separated into that from interrill and rill areas, and separate detachment equations are developed. Limitation of this spatial separation is that, in many conditions, rill and interrill areas are not clearly defined a priori. We interpreted the erosion and deposition equations used in the current Water Erosion Prediction Project (WEPP) in an alternative fashion such that spatial separation of rill and interrill areas is no longer required. Analytic solutions were derived for the WEPP erosion and deposition equations under general conditions. Simplified solutions for a specific case, uniform rain on uniform slope, were examined closely for slope and runoff effects on sediment delivery. Under both erosion and deposition conditions, analytic solutions show a linear relationship between sediment yield, qs and slope, S. The dependency of qs on runoff, qw, is either linear or quadratic depending on whether the system is dominated by an erosion or deposition regime. These analytic findings explain results obtained from laboratory studies in which sediment yield was collected under variable slope and rain intensities.
Analytical Volume Change Model for Swelling Clay Soils
Authors: Tariq Ata‐ur‐Rehman , Durnford Deanna S. 
Published: July 2010

AbstractSwelling clay soils undergo volume changes as the moisture content varies. This volume change is typically described by a shrinkage characteristic curve. There is a need for a generally acceptable model to describe these curves without requiring extensive soil shrinkage measurements. Models that are presently available in the literature do not represent the shrinkage characteristic curve data adequately and, thus, have limitations to their application. We have developed an analytical volume change model that was derived using the theoretical boundary conditions at the endpoints of the four shrinkage ranges. Thus, the model describes all four shrinkage ranges better without additional input requirements. The proposed model describes a smooth shrinkage characteristic curve with continuous slopes at the endpoints of each shrinkage range. The analytical model was verified against measured shrinkage characteristic curves and was found to represent the data very well.
Reconciliation between Measured and Theoretical Temperature Effects on Soil Water Retention Curves
Authors: Liu Hui Hai , Dane J. H. 
Published: July 2010

AbstractBecause temperature has a considerable effect on water retention curves, it should be accounted for when modeling unsaturated soil water flow under nonisothermal conditions. Changes are commonly attributed to alterations in surface tension at the air‐water interface, to changes in the volume of entrapped air, and sometimes to the presence of contaminants at the air‐water interface. Predicted changes have, however, always fallen short of experimentally determined values reported in the literature. We propose a new theory that considers soil water to be composed of continuous water and isolated packets of water. Measured soil water pressure head values are assumed to be determined by the properties of continuous water only. We hypothesize that, when the temperature increases, water flows from isolated packets to the continuous water phase, thus resulting in an additional temperature effect on the water retention curve. Based on the assumption that the continuous water content changes linearly with the total water content, we derived expressions for the change in soil water pressure head with temperature. Calculated changes in points on the water retention curve were subsequently much closer to measured values than previously reported. The good agreement between measured and predicted results suggests that more definitive experiments be conducted to investigate the role of isolated water packets on soil water retention curves.
Colloid‐Assisted Transport of Trace Metals in Roadside Soils Receiving Deicing Salts
Authors: Amrhein C. , Mosher P. A. , Strong J. E. 
Published: July 2010

AbstractCalcium magnesium acetate (CMA) is an alternative to NaCl for deicing highways. It has been shown to be an effective, biodegradeable deicing salt that is less corrosive than Cl salts and less toxic to aquatic life. There has been some concern, however, that CMA may increase the mobility of trace metals from roadside soils. A calcareous roadside soil was leached with solutions of the deicing salts NaCl and CMA followed by deionized water to evaluate the potential for trace metal mobilization. Elevated concentrations of Cu, Pb, Ni, Cr, Fe, and organic matter were found in the deionized water leachate following the NaCl leaching. Ultrafiltration and dialysis tubing were used to separate dissolved matter from colloidal (1000 molecular weight cutoff) and to determine if the trace metals were preferentially sorbed to small organic molecules and Fe oxides. Under high salinity, there was little evidence of colloid‐assisted transport. Under low salinity, dispersion and mobilization of colloidal‐sized particles occurred. Effluent Cu, Pb, and Ni concentrations were correlated with organic colloid concentrations, while Cr was correlated with Fe‐oxide concentrations. Evidence for both Fe‐organic matter colloidal complexes and Fe‐oxide mobilization was found. These findings suggest that roadside soils impacted by NaCl from deicing operations could be contributing trace metals to groundwater via colloid‐assisted transport.
Soil Surface Charge Evaluation by Back‐titration: I. Theory and Method Development
Authors: Duquette Martin , Hendershot William 
Published: July 2010

AbstractUntil recently, surface charge chemistry of soils has been measured using two different approaches: ion adsorption and potentiometric titration. The former provides a good measure of both anion‐exchange capacity (AEC) and cation‐exchange capacity (CEC) as a function of pH, although the procedure is time consuming. Potentiometric titration is more rapid, but the resulting curve overestimates the change in surface charge with pH. The error is largely due to consumption of H+ and OH− by dissolution and hydrolysis reactions with dissolved ions instead of being limited to protonation‐deprotonation reactions of surface charge sites. Our objective was to develop the theoretical aspects of the determination of surface charge using a back‐titration method. After suspension in Ca(NO3)2, a subsample of the soil is titrated slowly to pH 3, and then back‐titrated to pH 8 or 10. A second subsample is similarly titrated to pH 3; the soil and the supernatant solution are separated by centrifugation and filtering; only the supernatant solution is back‐titrated. The difference between the two titration curves represents the consumption of OH− by surface reactions corrected for dissolution and other solution reactions. The proposed method provides a relatively rapid means of obtaining pH‐dependent surface charge using potentiometric titration while giving results comparable to those obtained by ion adsorption.
Soil Surface Charge Evaluation by Back‐titration: II. Application
Authors: Duquette Martin , Hendershot William 
Published: July 2010

AbstractMeasurement of net surface charge by potentiometric titration and ion adsorption methods often gives different estimates of pH‐dependent exchange capacity. One of the major problems has been that potentiometric titration measures the H+ or OH− consumption due to surface reactions as well as those associated with dissolution of the soil and hydrolysis of ions in solution. In general, potentiometric titration has overestimated pH‐dependent exchange capacity, compared with ion adsorption methods. The backtitration procedure presented here corrects for these errors by performing two titrations. After slowly titrating the soil sample, suspended in 0.1 M Ca(NO3)2, to pH 3, the suspension is either titrated with 0.005 M Ca(OH)2 or centrifuged and the supernatant alone titrated. By subtracting the amount of OH− required to titrate the supernatant from the amount required to titrate the soil‐solution suspension, the net OH− consumption is calculated. If a value for pH‐independent CEC is known, then the pH‐dependent surface charge curve can be adjusted to give results that correspond closely to those obtained by ion adsorption. The proposed method is simpler and more rapid than the ion adsorption procedures. The inflection points on the titration curve can also be correlated with the chemical composition of the soil. Preliminary results suggest that the pH‐dependent CEC curve can be predicted from knowledge of organic matter content and various forms of amorphous Fe and Al.
Labile and Nonlabile Aqueous Silica in Acid Solutions: Relation to the Colloidal Fraction
Authors: Xu Shihe , Harsh James B. 
Published: July 2010

AbstractThe significance of polymeric Al‐Si complexes and Si associated with colloids on Si speciation in acidic solutions is unknown. To characterize Si solutions, the kinetics of the color reaction of Mo with Si in various synthetic Al‐Si solutions was determined and a method to quantify the labile fraction of Si was developed. We determined labile Si, dialyzable Si, and nonpositively charged Si in both synthetic and natural solutions, and total Si in solutions passing through 0.45‐, 0.2‐, and 0.1‐µm filter membranes. Silica in various solutions was divided into labile and nonlabile Si according to the rates of the reaction of Si species with Mo in 0.05 M H2SO4. Silica species in the labile fraction were <0.001 µm in diameter and were either nonpositively charged or were converted to nonpositively charged species during passage through a cation‐exchange column. The major portion of nonlabile Si was associated with colloidal particles, some of which could pass through a 0.45‐µm filter membrane. At pH 4 to 5.5, the quantity of polymeric Al‐Si complexes with sizes between 0.001 to 0.1 µm was not significant in solutions in contact with soils or soil clays except for those from a Spodosol that contained allophane and imogolite. Therefore, ignoring soluble polymeric Al‐Si complexes will not introduce a significant error in Al and Si speciation in this pH range in the absence of allophane and imogolite. Incomplete removal of colloidal particles may, however, cause significant overestimation of soluble Si and Al, if nonlabile fractions are determined.
Flocculation of Kaolinitic Soil Clays: Effects of Humic Substances and Iron Oxides
Authors: Kretzschmar Ruben , Robarge Wayne P. , Weed Sterling B. 
Published: July 2010

AbstractDispersion of clay affects soil physical properties and can result in clay transport with surface runoff or with percolating water moving through soil macropores. The water‐dispersihle fine clay (<0.2 µm) is probably the most mobile fraction with percolating water. This study was conducted to characterize the mineralogy and flocculation behavior of water‐dispersible fine clays isolated from surface horizons (Ap) of three Ultisols in North Carolina, and to study the effects of treating the clays for removal of organic substances and Fe oxides. Critical coagulation concentrations (CCC) of dilute suspensions (0.5 g clay L−1) in CaCl2 and KCl solutions were determined for: (i) untreated clays; (ii) clays treated with NaOCl for removal of organic substances; and (iii) clays treated with NaOCl and dithionite‐citrate‐bicarbonate for removal of organic substances and Fe oxides. Suspension pH was varied between 4.5 and 9.0. Analysis by x‐ray diffraction (XRD), thermogravimetry, and Mössbauer spectroscopy showed that the mineralogy of the clays was dominated by kaolinite and hydroxy‐Al‐interlayered 2:1 clay minerals (HIM), with smaller amounts of gibbsite and poorly crystalline, Al‐substituted Fe oxides (hematite and goethite). The untreated clays contained between 17 and 32 g total C kg−1, and difference infrared spectra between the untreated and NaOCl‐treated clays were typical for humic substances. Treatment of the clays for removal of organic substances markedly decreased the CCC values in both CaCl2 and KCl solutions in the entire pH range studied. Treatment for removal of Fe oxides had little effect on CCC values. All fine clays exhibited high electrophoretic mobilities (u) at pH 6 (±0.6) in 0.001 M CaCl2, with u ranging between ‐2.95 × 10−8 and −5.11 × 10−8 m2 s−1 V−1. For two of the soil clays, u was not clearly affected by either of the clay treatments, indicating that there was little change in surface charge density. The results of this study strongly support the hypothesis that naturally occurring humic substances increase the colloidal stability of kaolinitic soil fine clays in aqueous suspensions. The data suggest that a combination of electrostatic stabilization and steric stabilization is responsible for this effect, with steric stabilization possibly being the more important mechanism.
Soluble Anthrone‐Reactive Carbon in Soils: Effect of Carbon and Nitrogen Amendments
Authors: DeLuca T. H. , Keeney D. R. 
Published: July 2010

AbstractStudies were undertaken to determine the effect of plant residues on levels of soluble sugars measured as anthrone‐reactive carbon (ARC) in soils. Three different soils were amended with 10 g kg−1 of grain sorghum [Sorghum bicolor (L.) Moench], soybean [Glycine max (L.) Merr.] straw, or soybean straw plus 100 mg N kg−1 as glycine. The treated soils were maintained at 40% water‐holding capacity and 30 °C and observed for changes in soluble ARC, microbial biomass C, and extractable NO−3 and NH+4 at 0, 5, 10, 20, and 30 d. Changes in soluble ARC also were observed in soil treated with 2 g kg−1 cellulose with or without N added as glycine or as (NH4)2SO4. Soluble ARC in soil is initially increased by plant residue addition to soil as a result of the free sugar associated with the plant tissue. Levels of soluble ARC decline rapidly, but grain sorghum and soybean straw plus glycine treatments maintained soluble ARC at levels above the background. Soybean straw alone resulted in an N‐limited environment in which soluble ARC declined to background levels after 10 d. Microbial biomass C increased in all treated soils. Cellulose additions to soil increased soluble ARC only in the presence of added N, demonstrating the relation of free sugars to microbial activity. Soluble ARC reflects the level of free sugars associated with plant residues and that made available by microbial activity.
Properties of Iron—Manganese Nodules from a Sequence of Eroded Fragipan Soils
Authors: Rhoton F. E. , Bigham J. M. , Schulze D. G. 
Published: July 2010

AbstractIron‐manganese nodule concentrations increase in Ap horizons of Fragiudalfs in the lower Mississippi River Valley as profile thickness is reduced by erosion. This study was conducted to determine how nodule mineralogy and chemistry change with profile depth and after incorporation into the plow layer. Nodules larger than 1.0 mm were separated from each horizon of uneroded, slightly, moderately, and severely eroded pedons. Nodules were ground to <45 µm and analyzed for organic C, in addition to Fe, Mn, and P following extraction with dithionite‐citrate‐bicarbonate (DCB) and acid ammonium oxalate (AAO). Nodules from the E/Bx horizons of the least eroded pedons had the highest DCB‐extractable Fe (Fed) contents. Distributions of AAO‐extractable Fe (Feo) fluctuated with depth; however, Feo/Fed ratios reached a minimum in E/Bx horizons. In A horizon nodules, Fed increased with degree of erosion, ranging from 70 (uneroded) to 99 g kg−1 (severely eroded). Conversely, Feo and Feo/Fed decreased in Ap horizon nodules as erosion increased. Phosphorus contents in DCB extracts followed the Fed depth distribution curve. Manganese extracted by DCB decreased with profile depth and severity of erosion. Although Feo/Fed ratios suggested the presence of ferrihydrite, goethite was the only Fe‐oxide mineral identified from differential x‐ray diffraction (DXRD) scans. Goethite XRD peak intensities tended to reflect Fed contents, reaching a maximum in the E/Bx horizons and A horizons of the more severely eroded pedons. The color of the crushed nodules from the A horizons became progressively lighter as degree of erosion increased, due to increases in Fed and decreases in Mnd and organic C. Manganese had the greatest effect on color, accounting for 93 and 85% of the variability in value and chroma, respectively. However, no crystalline Mn‐oxide minerals were identified. Incorporation of E/Bx nodules in Ap horizons by gradual erosion and removal of finer materials is probably responsible for the observed changes in nodule color, chemistry, and mineralogy.
Laboratory Method for Studying Pesticide Dissipation in the Vadose Zone
Authors: Rambow Jürgen , Lennartz Bernd 
Published: July 2010

AbstractA laboratory apparatus was constructed to study the leaching behavior of soil‐applied herbicides in disturbed and undisturbed soil columns under vadose zone conditions. The setup was built in such a manner that a broad variety of field conditions regarding rainfall characteristics and soil water tension could be simulated. Long‐term transport experiments up to 3 mo required an automatic withdrawal of the soil percolate and a continuous control and recording of the soil water tension, the applied vacuum, and the amount of precipitation. During the sampling of the leachate, a newly designed lock guaranteed a constant vacuum at the bottom end of the soil column. First experiments with the new apparatus showed an earlier break‐through of terbuthylazine (2‐chloro‐4‐ethylamino‐6‐terbuthylamino‐s‐triazine) and a larger solute dispersion under transient water flow than under steady‐state water flow in a sandy soil.
A Simple Method for Predicting the Spatial Distribution of Soil Hydraulic Properties
Authors: Lascano R. J. , Stroosnijder Leo 
Published: July 2010

AbstractWe developed a method to calculate the statistical distribution of a scaling factor from soil‐water retention curves. The method consists of measuring the particle‐size distribution by laser scattering, computing soil water retention curves using the Arya and Paris model, and calculating a scale factor for each function. The method was tested by comparing measured and predicted soil‐water retention curves. The advantage of this method is in its simplicity and ease of use. The applicability of the method to a given soil texture depends on the verification of the calculated soil‐water retention functions.