bluuebunny/crossref_metadata_2025 huggingface dataset:
Diagnosis and Recommendation Integrated System Modifications for Fraser Fir Christmas Trees
Authors: Rathfon R. A. , Burger J. A.
Published: July 2010

The Diagnosis and Recommendation Integrated System (DRIS) has been used successfully to diagnose the nutrition of many crops. Some practioners, however, cite problems in applying DRIS to certain crops. Among the problems are: identifying a suitable expression of yield, maintaining symmetry in DRIS index equations, and dealing with extremely variable micronutrients. The purpose of this study was to resolve problems as they were encountered in applying DRIS to Fraser fir (Abies fraseri [Pursh] Poir.) Christmas trees. A total of 107 Fraser fir plantations were sampled for foliage, soil, and diameter measurements. Foliage was analyzed for N, P, K, Ca, Mg, Zn, Mn, Fe, Cu, and B. Age‐adjusted diameter was used successfully as the growth‐response variable. The DRIS symmetry was maintained by including nonsignificant ratios, but setting their standardization functions equal to zero. This reduced the influence of the nondiscriminating nutrient ratios on the DRIS analysis. Norm ranges, as opposed to discrete norms, were used successfully to correct for the influence of extremely variable micronutrient ratios on the DRIS analysis. This combination of adaptations and modifications of DRIS should greatly enhance its use for this tree crop.
Comparison of Statistical and Standard Techniques to Classify and Delineate Sodic Soils
Authors: Seelig B. D. , Richardson J. L. , Knighton R. E.
Published: July 2010

Statistical estimates of soil variability within and among delineations of taxonomic units are useful in designing and checking classification systems. We compared soil classification and spatial differentiation of a landscape dominated by sodic soils. Both statistical methodologies and standard soil‐survey techniques were used to differentiate soils. Forty‐nine pedons at three landform positions were compared with canonical discriminant analysis, principal component analysis, and kriging. Statistical analyses improved soil classification and allowed a clearer view of the field distribution of soil properties, compared with standard soil‐survey techniques. Soils with properties indicative of strong leaching (Solods) are recognized as significantly different from other soil taxonomic components at the intermediate and wetland positions. Solods were extensive at the wetland position, but could not be differentiated from Typic Natraquolls solely by morphologic observation. Although Solods are related to other leached soils, Argiaquolls and Argialbolls, they also possess soil properties that are similar to associated sodic soils. Leptic Natriborolls and Udic Natriborolls were similar except for salinity. The salinity difference by itself does not produce significant statistical differentiation between the soils of the two natric subgroüps. High salinity would be better recognized as a soil‐series phase, not a separate subgroup of Natriborolls.
Soil‐Forming Processes in Alic Melanudands under Japanese Pampas Grass and Oak
Authors: Dahlgren R. A. , Ugolini F. C. , Shoji S. , Ito T. , Sletten R. S.
Published: July 2010

Current soil‐forming processes and the effect of Japanese oak (Quercus serrata Thunb.) tree invasion on soils developed under Japanese pampas grass (Miscanthus sinensis Anders.) were investigated in Alic Melanudands forming on recent dacitic tephra deposits in Japan. The Andisols examined are members of the nonallophanic group of Andisols whose clay‐sized mineralogy is dominated by Al/Fe humus complexes and hydroxy‐Al interlayered 2:1 minerals, rather than short‐range‐order aluminosilicates common to most Andisols. Two study sites were chosen that had similar soil‐forming factors except for the present vegetation. One site has remained under Japanese pampas grass, while the other site was invaded by Japanese oak 50 yr ago. To examine soil processes, soil solutions were collected for a 2‐yr period, using tension lysimeters. Results indicate that translocation of Fe, Al, and dissolved organic C is not a major process in these Andisols. Aqueous concentrations of Si are sufficient for the formation of allophane/imogolite; however, the Al appears to be preferentially incorporated into the interlayer of 2:1 layer silicates and Al‐humus complexes and is, therefore, unavailable for synthesis of short‐range‐order minerals. Invasion of the oak vegetation resulted in a lowering of soil solution pH due to production of organic acids from the decomposing oak litter, and to removal and storage of base cations in the oak biomass. The lowering of the solution pH resulted in increased Al concentrations and decreased HCO3 concentrations in the A horizons of the oak site. When compared with the pampas grass site, the oak vegetation appears to promote greater cycling of Ca, Mg, K, and Cl in the upper 20 cm of the soil profile.
Weathering Environments and Occurrence of Imogolite/Allophane in Selected Andisols and Spodosols
Authors: Ugolini F. C. , Dahlgren R. A.
Published: July 2010

Imogolite and allophane have been found in various soil environments, but most commonly occur in Spodosols and Andisols. Controversy exists regarding the origin of these short‐range‐order aluminosilicates, especially in Spodosols. The proto‐imogolite theory suggests that imogolite forms in the surficial mineral horizons and is subsequently transported to the B horizons. In contrast, evidence from analyses of soil solutions collected from Spodosols in the Washington Cascades shows that Al is migrating primarily as an organic complex, with no proto‐imogolite detected in the percolating solutions. The Andisols we studied in Japan also show an absence of imogolite/allophane in the A horizons and an abundance of imogolite in the B horizons. Extremely low levels of Al are transported from the A to the B horizons, indicating that imogolite was not translocated from the overlying A horizons. The occurrence of imogolite/allophane in the B horizons of both the Spodosol and Andisol is best explained by in situ formation. Indeed, soil solution composition from the Spodosol indicates that imogolite is unstable in the E and Bhs, but stable in the Bs, BC, and C horizons. The B horizons containing imogolite in the Spodosol and Andisol have a similar weathering environment characterized by non‐Al‐complexing inorganic proton donors (e.g., H2CO3, HNO3), low concentrations of dissolved organic C, a pH between 5 and 6.5 that promotes Al polymerization, and Si concentrations adequate to support the stability of imogolite. In situ formation of allophane and imogolite is proposed for both the Spodosol and Andisol.
Ionic Factors Affecting the Formation of Short‐Range Ordered Aluminosilicates
Authors: Huang P. M.
Published: July 2010

The formation of short‐range ordered aluminosilicates is substantially influenced by organic and inorganic ligands, metallic cations, and montmorillonite. Chemical composition, size, number, and nature of the functional groups, and concentrations of non‐humified organic acids play a vital role in perturbing the formation of allophanes and imogolite. Humic substances also substantially perturb the interactions of hydroxy‐Al ions with orthosilicic acid and thus inhibit the formation of these aluminosilicates. Inorganic ligands such as phosphates and sulfates vary in their ability to impede the formation of these aluminosilicates. Iron has a stronger inhibiting effect than Mn on imogolite formation, resulting in the formation of poorly ordered mineral colloids. Adsorption of hydroxy‐aluminosilicate (HAS) in the interlayers of montmorillonite results in an expanded structure. The transformation of HAS ions to noncrystalline aluminosilicates can, therefore, be affected by naturally occurring expansible layer silicates such as montmorillonite. These ionic factors perturb the genesis of allophane and imogolite to various extents, resulting in the formation of ill‐defined aluminosilicate complexes, HAS‐interlayered expansible layer silicates, and/or precipitated hydroxy‐Al‐organic or ‐inorganic complexes. Organic and inorganic ligands with a strong affinity for Al significantly modify the nature of the soluble products, which range from proto‐imogolite sol complexed with organic or inorganic ligands to hydroxy‐Al‐organic or‐inorganic complexes.
Tiron Dissolution Method Used to Remove and Characterize Inorganic Components in Soils
Authors: Kodama Hideomi , Ross G. John
Published: July 2010

Treatments using NaOH and Na2CO3 have been widely used to remove poorly crystalline and noncrystalline aluminosilicates and hydrous oxides of Si and Al. However, NaOH treatment is often too harsh and Na2CO3 treatment is usually too mild and must be repeated. Treatment using alkaline Tiron (4,5‐dihydroxy‐1,3‐benzene‐disulfonic acid [disodium salt], C6H4Na2O8S2) was as effective as acid oxalate in the dissolution of allophane, imogolite, and poorly crystalline hydrous Fe oxides. In contrast to oxalate, Tiron effectively removed opaline silica, and the difference between extracted Si could be used to measure the amount of opaline silica. Unlike oxalate, Tiron dissolved little magnetite. As gibbsite is partially dissolved by Tiron, the rates of Al release by gibbsite (<2 µm) dissolution at different temperatures were used to estimate the gibbsite contents of soil clays containing this mineral. Generally, a single treatment with Tiron appears to be sufficient to mildly but effectively clean up samples for x‐ray diffraction of crystalline minerals with amounts of extracted Si, Al, and Fe indicating the presence and quantities of poorly crystalline and noncrystalline aluminosilicates as well as hydrous oxides of Fe, Al, and Si, including opaline silica.
Analytical Solution of Solute Diffusion and Biodegradation in Spherical Aggregates
Authors: Priesack E.
Published: July 2010

Microbial degradation and transformation of substances in soils plays a crucial role in the nutrient turnover of ecosystems. To quantify these processes, a mathematical description is needed. For this purpose, an analytical solution to a model of solute diffusion and biodegradation in soil aggregates was developed. The model is a first approach toward understanding the influence of geometric arrangement of microorganisms and substrates in structured soils. These soils are considered to consist of uniformly sized and shaped aggregates surrounded by surface films of the soil solution. The model simulates transient diffusion of finite substrate amounts from the surface films into spherical aggregates. Biodegradation is considered for the special case of unlimited microbial growth, and adsorption is assumed to follow a linear Freundlich isotherm. The system is represented by a composite sphere, the outer sphere being the solution film and the inner sphere representing the soil aggregate. The diffusion equations are solved by Laplace transformation. The model solution gives a direct relationship between the initial substrate and biomass concentrations, the diffusion coefficient, the specific growth rate, and the adsorption coefficient. Good agreement between this closed form solution and numerical solutions is obtained for diffusion with and without biodegradation. Since the substrate is exhausted by organisms close to the surface, the centers of large aggregates are not reached by the diffusing substrate. These unaffected centers become larger as the growth rate is higher, the diffusion constant is lower, and adsorption of the substrate is stronger.
Fractal Fragmentation, Soil Porosity, and Soil Water Properties: I. Theory
Authors: Rieu Michel , Sposito Garrison
Published: July 2010

Recent efforts to characterize soil water properties in terms of porosity and particle‐size distribution have turned to the possibility that a fractal representation of soil structure may be especially apt. In this paper, we develop a fully self‐consistent fractal model of aggregate and pore‐space properties for structured soils. The concept underlying the model is the representation of a soil as a fragmented fractal porous medium. This concept involves four essential components: the mathematical partitioning of a bulk soil volume into self‐similar pore‐ and aggregate‐size classes, each of which is identified with a successive fragmentation step; the definition of a uniform probability for incomplete fragmentation in each size class; the definition of fractal dimensions for both completely and incompletely fragmented porous media; and the definition of a domain of length scales across which fractal behavior occurs. Model results include a number of equations that can be tested experimentally: (i) a fractal dimension ≤3; (ii) a decrease in aggregate bulk density (or an increase in porosity) with increasing aggregate size; (iii) a power‐law aggregate‐size‐distribution function; (iv) a water potential that scales as an integer power of a similarity ratio; (v) a power‐law expression for the water‐retention curve; and (vi) an expression for hydraulic conductivity in terms of the conductivities of single‐size arrangements of fractures embedded in a regular fractal network. Future research should provide experimental data with which to evaluate these predictions in detail.
Fractal Fragmentation, Soil Porosity, and Soil Water Properties: II. Applications
Authors: Rieu Michel , Sposito Garrison
Published: July 2010

The fractal model of Rieu and Sposito contains seven predictive equations that can be tested experimentally with data on aggregate characteristics and soil water properties for structured soils. However, data with which to test the model are extremely limited at present because of the need to have precise, concurrent measurements of aggregate physical properties (bulk density and size distribution) along with soil water properties for an undisturbed soil. For the five sets of suitable physical soil aggregate data currently available, good agreement was found with the fractal model bulk density‐aggregate size and size‐distribution relationships. For the single set of aggregate/soil water properties data available, good agreement also was found with the fractal model water‐potential scaling relationship, moisture characteristic, and hydraulic conductivity‐water content relationship. Model simulations of the last two soil water relationships for hypothetical sandy and clayey soils also were qualitatively accurate and showed the sensitivity of the model to the value of the fractal dimension. These encouraging results suggest that the model should have success in further experimental tests with natural soils.
Diffusion of Technetium in Dense Bentonite under Oxidizing and Reducing Conditions
Authors: Sawatsky N. G. , Oscarson D. W.
Published: July 2010

Diffusion is the principal mechanism by which most contaminants migrate through dense bentonite‐based barrier materials used in many waste‐containment strategies. Diffusion coefficients are, therefore, critical parameters for predicting migration rates of contaminants through these materials. Diffusion coefficients, D, were determined for Tc (99Tc is a relatively long‐lived radionuclide present in high‐level nuclear fuel waste) in compacted, nearly saturated bentonite under both oxidizing and reducing conditions. The D values were measured under oxidizing conditions at 25 or 80 °C in bentonite compacted to dry bulk densities, ρb, ranging from about 0.9 to 1.35 Mg/m3. In a reducing environment, D values were determined at 25 °C and ρb ≃ 1.3 Mg/m3; reducing conditions were established by mixing 1% (w/w) Fe(II)‐silicate with the bentonite and by conducting the experiment under a N2 atmosphere. Under oxidizing conditions at 25 °C, D ranged from 2.3 × 10−10 m2/s at ρb ≃ 0.9 Mg/m3 to 0.73 × 10−10 m2/s at 1.35 Mg/m3. The decrease in D with increasing density is largely attributed to an increase in the tortuosity of the diffusion path as the density increased. At 80 °C, D values were two to three times greater than those obtained at 25 °C at all densities; this is primarily due to a decrease in the viscosity of the saturating solution with increasing temperature. In a reducing environment, D was 6 ± 3 × 10−12 m2/s. The lower D values under reducing conditions are attributed to the reduction of TcO−4[Tc(VII)] to a less mobile Tc(IV) species. The results indicate that the migration of Tc through a bentonite‐based barrier material will be relatively slow in a reducing environment, such as that expected in a nuclear fuel waste disposal vault located deep in plutonic rock; this will mitigate the potential hazard associated with 99Tc in the long‐term disposal of nuclear fuel waste.
Phosphate Transport in Calcium‐Saturated Systems: II. Experimental Results in a Model System
Authors: Akinremi O. O. , Cho C. M.
Published: July 2010

This study investigated the diffusive transport of phosphate in a cation‐exchange‐resin model system. The objective was to demonstrate the effect of cation‐exchange reactions on the movement of the phosphate ion. To a cylindrical wax column of Ca‐saturated resin, 0.2 g of KH2PO4 was surface applied to simulate one‐dimensional diffusive transport. Other ions of interest were Ca2+, K+, and H+. Extraction and analysis of 2‐mm increments of the column after the desired incubation period (3, 7, and 14 d) revealed the following results. The pH of the system became low as a result of the interaction between added phosphate and Ca2+ from the exchange resin. The higher the cation‐exchange capacity (CEC), the lower the pH became. Calcium ions, present on the exchange sites, were displaced into solution by cation exchange with K+. The higher the CEC of the column, the higher was the amount of Ca2+ displaced into soil solution. The movement of K+ and phosphate ions was retarded in the system, and the degree of retardation increased with increasing CEC of the soil column. The retardation of K+ movement was due to ion‐exchange interaction with exchangeable Ca2+, while P movement was retarded as a result of chemical interaction with the displaced Ca2+. The experimental results showed the effect that the K‐Ca exchange reaction has on the diffusive movement of P. There is a need to take this into consideration in any model simulating P transport in the soil.
Zinc Sorption by Iron‐Oxide‐Coated Sand as a Function of pH
Authors: Stahl Randal S. , James Bruce R.
Published: July 2010

Mineralogy of Fe‐oxide coatings in soils may influence pH‐dependent sorption of heavy metals, but exchangeability of retained metals needs to be better understood to improve predictions of bioavailability. A laboratory study tested the effect of pH on the amount and form of Zn retained in exchangeable (extractable with 1 M KNO3) or nonexchangeable forms on goethite‐ and hematite‐coated sand. Batch equilibrations with 250 and 2500 µmol Zn(NO3)2/kg coated or uncoated sand were used to determine concentration effects on the form of Zn retained. Cation‐exchange capacity (CEC) of the goethite‐ or hematite‐coated sand increased with pH (4–7.6), but surface charge was a poor indicator of the amount and form of Zn retained. The goethite‐coated sand retained the Zn principally in a nonexchangeable form, while the hematite‐coated sand retained the Zn in both exchangeable and nonexchangeable forms. The distribution between the exchangeable and nonexchangeable Zn fractions changed from predominantly exchangeable to predominantly nonexchangeable Zn retention as pH increased in both oxide systems. The dominance of nonexchangeable‐Zn sorption by goethite was attributed to surface‐induced hydrolysis by OH groups, while O atoms of hydrated hematite and uncoated sand surfaces were hypothesized to be sorbing Zn in exchangeable forms.
Fecal Coliforms in Soil Detected by Polymerase Chain Reaction and DNA‐DNA Hybridizations
Authors: Josephson K. L. , Pillai S. D. , Way J. , Gerba C. P. , Pepper I. L.
Published: July 2010

The application of sewage sludge on agricultural lands is a common practice in the USA. The survival of pathogens and indicator organisms added to soil via sludge needs to be determined. A rapid method utilizing polymerase chain reaction (PCR) and a gene‐specific probe was used to detect low numbers of fecal coliforms in soil. Two 23‐base primers were designed from a region of the lamB gene that codes for an outer‐membrane protein present specifically in fecal coliforms. Use of these primers for PCR amplification of a 179‐bp fragment of lamB allowed specific detection of fecal‐coliform indicator organisms. Sensitivity of amplification from whole‐cell lysates of pure cultures of Escherichia coli using detection via ethidium bromide was 104 colony‐forming units (CFUs). When detection of these cell lysates was via a lamB gene‐specific probe, a total of 4 × 102 CFUs could be detected from these pure cultures. When genomic deoxyribonucleic acid (DNA) preparations were made from these pure cultures, 100 ag (10−18) of DNA was detectable. Following the inoculation of E. coli into soil, cells were extracted with CaCl2, and concentrated and purified by sucrose density centrifugation. The DNA obtained by lysing the cells was amplified using a new “double PCR” 50‐cycle protocol. Escherichia coli were detected in Brazito sandy loam (mixed, thermic Typic Torripsamment) and Pima silty clay loam (fine‐silty, mixed (calcareous), thermic Typic Torrifluvent). Using a 5′ end‐labeled lamB‐specific probe to detect PCR products, one CFU of E. coli was detectable in 1 g of soil. One PCR‐amplificable CFU g−1 would be equivalent to many copies of amplificable target DNA, due to the presence of dead and lysed cells along with cells containing more than one copy of the genome. Sample processing and PCR amplification can be completed within 7 to 8 h. Thus, the use of PCR for sensitive detection of introduced bacteria in environmental soil samples is possible.
The Growth of White Lupine on a Calciaquoll
Authors: Moraghan J. T.
Published: July 2010

White lupine (Lupinus albus L.), an annual legume used for grain production in temperate climates, forms proteoid root (clusters of determinate rootlets on sections of lateral roots), accumulates Mn, and grows poorly on calcareous soils. This study was conducted to determine, under greenhouse conditions, the influence of P (0 vs. 120 mg NaH2PO4‐P kg−1), Fe (0 vs. 2 mg FeEDDHA‐Fe kg−1), and N source (inoculation with Bradyrhizobium lupini vs. 80 mg NH4NO3‐N kg−1) on growth of ‘Kiev’ white lupine on a Wheatville loam (coarse‐silty over clayey, frigid, Aeric Calciaquoll) low in available P, Fe, and N. Yield of white lupine shoots was increased by Fe and P fertilizers but was unaffected by N source. Wheat (Triticum aestivum L.) gave a three‐fold increase to N fertilizer under similar conditions. Inoculated white lupine plants were nodulated but uninoculated ones were not. Number and weight of nodules were stimulated more than twofold by application of Fe and P fertilizers. Plants without added Fe displayed leaf chlorosis that was increased by P and N fertilizers and decreased by added Fe and advancing plant age. The incidence of proteoid roots encased in hard‐to‐remove soil was depressed more than two‐thirds by P fertilizer, but was stimulated by inoculation. Concentration of Mn in white lupine shoots was depressed by P fertilizer, stimulated by inoculation, and little affected by added Fe. Iron deficiency detrimentally affected the growth of white lupine on the Wheatville soil, and its severity was intensified by N and P fertilization.
Chemistry of Smectitic and Illitic Phases in Interstratified Soil Smectite
Authors: Laird D. A. , Barak P. , Nater E. A. , Dowdy R. H.
Published: July 2010

The objective of this investigation was to determine the elemental composition and mineralogy of the smectitic and illitic phases in interstratified smectite‐illite from a typical upper Midwestern agricultural soil. A sample of soil clay (<2‐µm fraction) from the Ap horizon of a Webster (fine‐loamy, mixed, mesic Typic Haplaquoll) pedon was fractionated by centrifugation to prepare various fine‐clay (<0.020‐, <0.026‐, <0.036‐, <0.045‐, <0.060‐, and <0.090‐µm size fractions) samples. X‐ray diffraction analyses indicated that interstratified smectite‐illite was the only mineral present in significant quantities in the fine‐clay samples. Elemental analyses of the fine‐clay samples were performed by inductively coupled plasma‐atomic emission spectroscopy using suspension nebulization. The elemental analyses revealed significant linear correlations for the K vs. other element relationships (P < 0.001 for K vs. Si, Al, Fe, Ca, Ti, Mn, and Zn, and P < 0.01 for K vs. Mg). A nonlinear parameter optimization technique, based on elemental mass balance, was used to estimate the elemental compositions and proportions of the smectitic (K‐free) and illitic (K‐bearing) phases in the fine‐clay samples. The results for the elemental mass balance optimization were independently verified by water mass balance. The smectitic phase was a high‐charge (0.482 per formula unit), Fe‐rich montmorillonite (46.6% tetrahedral charge). The illitic phase consisted of dioctahedral, tetrahedrally charged (86.9% tetrahedral charge) elementary illite particles. Layer charge for the illitic phase was 0.473 per formula unit, which is substantially below the lower limit for classification of illite. The interstratified smectite‐illite comprised at least 60% of the whole (<2‐µm fraction) soil clay and the illitic phase comprised at least 36% of the interstratified smectite‐illite.
Solute Transport in a Two‐Layer Medium Investigated with Time Moments
Authors: Leij Feike J. , Dane J. H.
Published: July 2010

The study of solute transport in porous media requires knowledge of the transport parameters. These transport parameters can be determined from data collected during displacement experiments using a number of mathematical procedures, among them the moment method. An advantage of this method is that it can also be used to theoretically analyze, and therefore enhance our understanding of, transport problems. We present theoretical time moments as derived from analytical solutions of the advection‐dispersion equation in the Laplace domain for a step‐ and pulse‐type solute input applied to a two‐layer soil with steady flow transverse to layering. These moments were used for investigating the mean breakthrough time, µ1, and variance, µ2. It was shown that, theoretically, more retardation and spreading occurs for a third‐ than for a first‐type boundary condition, but that the presence of the interface, as such, does not affect spreading for either boundary condition.
Tensile Strength of Thirty‐Three Saturated Repacked Soils
Authors: Nearing M. A. , Parker S. C. , Bradford J. M. , Elliot W. J.
Published: July 2010

Interaggregate strength in saturated soils is important in terms of erosion processes and surface sealing during rainstorms. The objective of this study was to ascertain the soil properties that influence interparticle binding of unconsolidated, saturated soil as measured by tensile failure of disturbed samples. Tensile strength of 33 soils was measured in the laboratory. The measurements were performed on 0‐ to 1‐mm, 2‐ to 4‐mm, and mixed aggregate size class materials. Factor analysis was used to understand the patterns of relationships and correlations among all the variates, and then to select appropriate variables (from among 39 measured soil properties) for use in regression relationships for tensile strength. Clay amount and surface properties were dominant in terms of explaining the variance of tensile strength. Other important factors included variables related to soil dispersion (Na and Na‐adsorption ratio), silt, coarse sand, aggregation, and electrical conductivity. This study presents the use of a laboratory tensile test for loose, saturated soil as applied to a wide variety of soil types from across the USA.
Cesium‐Adsorption Method for Measuring Accessible Structural Surface Charge
Authors: Anderson Sharon J. , Sposito Garrison
Published: July 2010

Measurements of the separate contributions of structural and pH‐dependent charge are essential to understanding and predicting surface‐chemical reactions in soils and other heterogeneous adsorbents that contain a mixture of surface functional groups. An ion‐adsorption method was developed to measure the accessible structural charge density (σ0) in adsorbents that comprise both structural‐charge and variable‐charge surface functional groups. The method is based on the preference of siloxane surface sites for Cs+ over Li+ and on the much lower selectivity of ionizable surface groups for Cs+. To estimate σ0, CsCl‐saturated adsorbents were reacted with 0.05 mol CsCl kg−1 at pH 7, washed with ethanol to reduce the entrained CsCl concentration, dried at 65 °C to promote the formation of inner‐sphere surface complexes between Cs+ and permanent‐charge sites, and then extracted with 0.01 mol LiCl kg−1 to displace Cs+ from variable‐charge adsorption sites, which exhibit little or no preference for Cs+ over Li+. Finally, Cs+ was displaced from permanent‐charge sites by repeated NH4OAc extraction until no Cs was present in the equilibrium supernatant solution. According to this method, σ0 represented about 85 and 70% of the accessible cation‐adsorption sites at pH 7 on <2‐µm Wyoming montmorillonite and <106‐µm Silver Hill illite, respectively; 15% and 30%, respectively, were variable‐charge sites. These results were consistent with published reports of the amount of pH‐dependent cation adsorption on montmorillonite and with model calculations of the relative contributions of edge and structural charge in montmorillonite and illite. When the method was used to measure Cs‐accessible σ0 in four soils, the percentage of structural charge ranged from 1% in an Oxisol to 65% in an Alfisol. The method is appropriate for adsorbents that contain montmorillonite, illite, and repotassified (nonexpandable) vermiculite. It may be suitable for adsorbents that contain clay‐sized, but probably not coarse‐grained, expandable vermiculite.
Electrolyte Concentration and Composition Effects on Sulfate Sorption by Two Spodosols
Authors: Courchesne François
Published: July 2010

Few reports exist on the influence of electrolyte concentration and composition on SO4 retention, although sorption experiments have been conducted with a variety of supporting electrolytes. Sulfate sorption by the B horizon of two forest Spodosols from Quebec was measured as a function of supporting electrolyte concentration and cationic composition, solution pH, and reaction time. The solutions had an ionic strength (I) of ≈0 (deionized H2O), 0.001, 0.01, 0.1, and 1.0 M NaCl, 0.01 M KCl, and 0.01 M CaCl2. Increasing the ionic strength of the electrolyte (NaCl) always decreased SO4 sorption at pH 4.25. It was proposed that increased Cl‐ ion competition for sorption sites and the formation of NaSO‐4 aqueous complexes (2.8, 14, and 55% of total SO4 at 0.01, 0.1, and 1.0 M NaCl) contributed to the observed trend. Increasing electrolyte concentration also lowered SO4 sorption by both horizons in the range of pH 3.0 to 5.2. Moreover, the influence of pH on sorption was more pronounced at low electrolyte concentration. At a constant I value, the cationic composition of the electrolyte also had an impact on SO4 sorption. The presence of Ca2+ and K+ favored sorption, compared with Na+. A mechanism involving the formation of a surface complex between Ca2+ or K+ and SO2‐4 is proposed to explain the experimental data. The results of this study support the hypothesis that the composition and concentration of the electrolyte influence SO4 sorption by Spodosols and that both should be considered when comparing the SO4‐sorption capacity of soil materials from distinct experiments or when projecting laboratory results to field conditions.
Zinc Sorption by B Horizon Soils as a Function of pH
Authors: Stahl Randal S. , James Bruce R.
Published: July 2010

Better information is needed to predict how soil acidity affects exchangeability of heavy metals in soils dominated by Fe and Mn oxides with pH‐dependent charge. Our laboratory study sought to separate exchangeable and nonexchangeable Zn sorbed by four B horizon soil materials with varied mineralogy and sesquioxide contents. A Myersville silt loam (fine‐loamy, mixed, mesic Ultic Hapludalf), a Jackland sandy loam (fine, mixed, mesic Aquic Hapludalf), a Christiana sandy loam (clayey, kaolinitic, mesic Typic Paleudult), and an Evesboro loamy sand (mesic, coated Typic Quartzipsamment) were compared for the exchangeability of Zn as a function of pH. Surface charge was measured across the pH range of 3.5 to 7.6, a 175 µmol ZnCl2/kg soil treatment was applied, and sorbed Zn was exchanged with K. Cation‐exchange capacity (CEC) was positively correlated with nonexchangeable but not with exchangeable Zn forms. All four soils retained nearly the same amount of Zn, even though CEC ranged from <10 to >80 mmolc/kg. An abrupt transition from exchangeable to nonexchangeable Zn occurred in the pH range 5.6 to 5.9 of the Myersville, Evesboro, and Christiana soils. Differences in oxide mineralogy and proton buffering intensity appeared more important than CEC as controls on the exchangeability of Zn in these soils. This result is germane to predicting retention of heavy metals in sewage‐sludge‐amended agricultural soils.
Supercritical Carbon Dioxide Extraction of Long‐Chain Aliphatics from Two Soils
Authors: Schulten H.‐R. , Schnitzer M.
Published: July 2010

Current trends in soil organic‐matter research are focused on developing methods for the extraction of specific organic‐matter components. One such method is the supercritical gas extraction of soils using CO2. To examine the applicability of this approach to whole soils, we used supercritical CO2 for extracting two soils. The resulting extracts were analyzed by chemical methods, infrared (IR), 13C nuclear magnetic resonance (NMR), and by field‐ionization and field‐desorption mass spectrometry. Major components identified in the extracts were C15 to C41 n‐alkanes, the C8 alkene, the C29 n‐alcohol, C14 to C40 n‐fatty acids, C17 to C41 unsaturated fatty acids, the C18 and C26 dioic acids, the C28 and C30 n‐ketones, C38 to C64 n‐alkyl monoesters, the C52 n‐dioic acid dimer, and the C78 n‐dioic acid trimer. Of special interest was the presence in the extracts of 10‐nonacosanol (C29), a biomarker for coniferous epicuticular waxes. Supercritical CO2 was found to be a mild and specific extractant for the removal of long‐chain aliphatic materials from soils.
Land‐Use Changes Affecting Classification of a Costa Rican Soil
Authors: Wielemaker W. G. , Lansu A. L. E.
Published: July 2010

Effects of deforestation and ensuing land use were studied on an Andic Humitropept developed from fluvio‐laharic deposits in the perhumid climatic zone of Costa Rica. Drastic changes in soil climate and land use after deforestation caused compaction and clay mobilization, particularly in the profiles under maize (Zea mays L.) and pasture. The latter process resulted in a change of classification at the order level from Inceptisol to Ultisol.
Neoformation of Palygorskite in a Southern New Mexico Aridisol
Authors: Monger H. C. , Daugherty L. A.
Published: July 2010

Palygorskite is the dominant clay mineral in a petrocalcic horizon of the Rotura soil series (a coarse‐loamy, mixed, thermic, Typic Haplargid), a soil of middle Pleistocene age in southern New Mexico. The purpose of this study was to determine if palygorskite is eolian in origin, inherited from its alluvial parent material, or neoformed in the soil. The origin of palygorskite was determined by examining clay mineral distribution, soil‐water extract chemistry, and palygorskite fiber morphology. An eolian origin of palygorskite is unlikely because it is absent in upper soil horizons and no palygorskite was captured in dust traps during a 10‐yr study. An inherited origin is also unlikely because palygorskite is not an inherent component of Rio Grande alluvium. Scanning electron microscopy revealed that delicate palygorskite fibers radiate perpendicularly into pore spaces, which indicates neoformation. The petrocalcic horizon may foster palygorskite neoformation because it is the site of high Mg content and abundant sand‐ and silt‐grain dissolution.
Stable Carbon Isotopic Composition of Carbonate in Holocene Grassland Soils
Authors: Kelly Eugene F. , Amundson Ronald G. , Marino Bruno D. , DeNiro Michael J.
Published: July 2010

Stable C isotope ratios (13C/12C) and amounts of soil carbonate were measured at six sites of differing temperature, moisture, and vegetational make‐up in the northern Great Plains of the USA in order to determine climatic and biotic influences on the stable C isotope chemistry of these soils. With approximately constant precipitation, total carbonate decreased with increasing temperature. With decreasing precipitation, the total carbonate in the soils increased. For all but one soil, the 13C/12C ratios of segregated carbonate conformed to values expected if the carbonate formed from CO2 derived from soil organic matter. In the nonconforming site, the 13C/12C ratios of the carbonate suggest that the vegetation and soil organic matter have recently become dominated by C4 plants, which use the Hatch‐Slack photosynthetic pathway, and organic matter derived from them. The 13C/12C ratios of disseminated carbonate reflect the proportion of pedogenic and parent‐material carbonate in the sample. The 13C/12C ratios of pure, pedogenic carbonate at each site could be constrained by: (i) measured 13C/12C ratios of soil organic matter, (ii) measured 13C/12C ratios of carbonate nodules, and (iii) calculated 13C/12C ratios using a diffusion model designed by others. Estimates of the percentages of disseminated pedogenic carbonate in the soils suggested that, as the amount of weathering at sites increases and the total carbonate decreases, the percentage of carbonate that remains becomes more dominated by carbonate of pedogenic origin.
Growth Characteristics of Legume Cover Crops in a Semiarid Environment
Authors: Power J. F.
Published: July 2010

To select the best legume cover crop to grow for a given cropping situation, the producer needs knowledge of relative growth rates, N2‐fixation and N‐uptake rates, and water use for various potential planting dates. Such an experiment was conducted for 2 yr at Mandan, ND, in which 10 legume species were planted on or shortly after the first day of May, June, July, and August each year. Soil and plant samples were collected periodically after each planting date to evaluate rates of dry‐matter production, N accumulation, and water use. Potential N2‐fixation rate was measured in one season only. For the first 40 to 90 d after planting, large‐seeded annuals such as faba bean (Vicia faba L.), field pea (Pisum sativum L.), and soybean (Glycine max [L] Merr.) generally exhibited most rapid growth, N accumulation, and water use (these three parameters were generally closely related for all samplings). With more than 90 d growth, species such as Korean lespedeza (Lespedeza stipulacea Maxim.), yellow sweet clover (Melilotus officianalis L.), and alfalfa (Medicago sativa L.) also began to exhibit rapid growth. One surprising result was the outstanding growth of May‐planted subterranean clover (Trifolium subterraneum L.) in one (ample moisture) of the two seasons. For the shorter growth periods, faba bean exhibited good growth characteristics at all planting dates, and field pea was satisfactory at most. July and August planting of slower growing species generally resulted in relatively little growth by the end of the season. In most instances, water‐use efficiency was greatest for the May planting, and highest values were often recorded for field pea, faba bean, and subterranean clover. These results identify those legume species best adapted for a given planting date and duration of growth under the climatic conditions of this experiment.
Motor‐Driven Portable Soil Core Sampler for Volumetric Sampling
Authors: Hendrickx J. M. H. , Ritsema C. J. , Boersma O. H. , Dekker L. W. , Hamminga W. , van der Kolk J. W. H.
Published: July 2010

An improved soil core sampler was tested for measuring bulk densities and volumetric water contents of field soils. The improvements consist of (i) a portable gasoline‐driven mechanical hammer and (ii) a wide cut‐out trough with removable cover. The improved hammer uses high‐frequency vibrations to drive the core sampler into the soil at an even speed without interruption, thus preventing compaction. The new trough allows free access for sampling the soil core with 205‐cm3 steel cylinders. Samples were taken by the improved soil core sampler and by hand in sand, silt loam, and clayey peat soils. Comparison of these samples showed that the improved soil core sampler provides volumetric soil samples that are sufficiently accurate in bulk density and volumetric water content as those taken manually.
Spectroscopic Study of Surface Redox Reactions with Manganese Oxides
Authors: Risser Jeffrey A. , Bailey George W.
Published: July 2010

Redox reactions involving soil minerals and materials are important processes in environmental chemistry, but unfortunately they only have been characterized in the solution phase. The lack of a suitable method has prevented investigations of the mineral surface component of redox reactions. We present a model system in which ultraviolet‐visible spectroscopy is employed to observe a surface redox reaction. A synthetic MnOx is reacted with Cr(III), resulting in Cr oxidation to the hexavalent state and the reduction of the MnOx mineral. A scattered transmission accessory allowed us to observe spectroscopically both the appearance of Cr(VI) and the attenuation of MnOx in a suspension. Loss of absorbance intensity by MnOx suspensions may be useful as a general method to follow redox reactions as a function of the solid phase rather than relative to a specific reactant. This spectroscopic approach provides the capability to monitor in situ reactions of solid‐phase components and is useful for examining transformations of metallic and organic wastes and naturally occurring materials in the environment.
Sources of Nitric Oxide and Nitrous Oxide following Wetting of Dry Soil
Authors: Davidson Eric A.
Published: July 2010

When dry soil is wetted, significant fluxes of NO and N2O have been reported. The sources of these gases have been difficult to identify because a number of biological and abiological processes can produce both gases. Soil sampled from an annual grassland in central California at the end of the dry season was wetted to soil water contents above and below field capacity. Production of NO and N2O began within minutes of adding water. Below field capacity, the net production of NO exceeded N2O, whereas above field capacity the production of N2O exceeded NO. Production of NO was inhibited by acetylene (C2H2) at both water contents, indicating that the NO source was dependent on nitrification. In contrast, N2O production was inhibited by C2H2 only when soil water was below field capacity, indicating that denitrification was the dominant source when soil water was above field capacity. Addition of NO‐2 also stimulated NO production in both sterile and nonsterile soil, suggesting that abiological reactions could contribute significantly to NO emissions. Production of NO‐2 and H+ by NH+4‐oxidizing bacteria, followed by chemodenitrification of a small fraction of the NO‐2 produced, could account for the observed NO fluxes from dry and moist soil. Nitrifying and denitrifying bacteria appear to be well adapted to surviving extreme drought and to becoming active with minutes of wetting dry soil.
Early Cropping‐Induced Changes in Soil Aggregation, Organic Matter, and Microbial Biomass
Authors: Angers D. A. , Pesant A. , Vigneux J.
Published: July 2010

Crop management practices influence the amount and quality of organic matter and the state of aggregation in soils. The objective of this study was to determine the early changes in organic and microbial‐biomass C contents and in water‐stable aggregates of two loamy soils (Typic Fragiaquept and Typic Haplaquept) following plowing of a meadow and subsequent planting of either corn (Zea mays L.) or barley (Hordeum vulgare L.). The effects of 1, 2, and 3 yr of cropping with these two crops were compared with an undisturbed and a recently plowed meadow. Plowing decreased the organic and microbial‐biomass C contents of the surface soil (0–6 cm) by an average of 40 to 50%, but, when the whole surface horizon (0–24 cm) was considered, there was no effect. Further cropping with either corn or barley resulted in no net loss of organic matter and microbial biomass but only a redistribution in the surface soil profile. Microbial‐biomass C was not preferentially affected by cropping relative to total organic C. The mean‐weight diameter of water‐stable aggregates decreased not only with plowing but also with length of cropping both in the surface soil (0–6 cm) and throughout the top 24 cm. There was little difference in the specific effects of the two crops on organic C, microbial‐biomass C, or aggregation.
Effect of Diffusion and Sorption on the Kinetics of Biodegradation: Theoretical Considerations
Authors: Scow Kate M. , Hutson John
Published: July 2010

Organic chemicals subject to biodegradation by microorganisms in soil are often limited in their availability by sorption and diffusion to unavailable sites. To quantitatively describe biodegradation under conditions of substrate limitation, a process‐based deterministic model called the diffusion‐sorption‐biodegradation (DSB) model was developed to describe the biodegradation of an organic chemical in the presence of spherical aggregates. Diffusion is described by Fick's second law, sorption by a linear isotherm, and biodegradation by one of various rate equations including first‐order kinetics. Sensitivity analyses were performed to determine the dependence of a chemical's half‐life on soil physical and chemical properties. Half‐lives in the presence of aggregates were substantially greater than equivalent half‐lives in the absence of aggregates when the sorption partition coefficient was ≥3.2 dm3kg‐1 and the aggregate radius was ≥0.32 cm. The two‐compartment model provided a better fit than did a simple first‐order model to simulations of the biodegradation of a sorbing chemical in the presence of large (0.25‐cm radii) aggregates, whereas there was no difference between the two models for aggregates of much smaller radii. When simple first‐order kinetics was assumed without accounting for diffusion and sorption, long‐term extrapolation of chemical persistence in the presence of aggregates overestimated the degradation of a chemical with a sorption partition coefficient of 10 dm3kg‐1. Considering that many organic pollutants sorb strongly and numerous soils have some degree of aggregate structure and organic matter, taking into account the physical and chemical processes affecting a chemical's concentration may greatly improve kinetics models of biodegradation in soil.