bluuebunny/crossref_metadata_2025_split huggingface dataset:
Factor Analysis of Nutrient Distribution Patterns under Shrub Live‐Oak in Two Contrasting Soils
Authors: Brejda John J. 
Published: July 2010

AbstractIn shrub‐dominated ecosystems, many soil properties are correlated, confounding changes in nutrient distribution associated with soils and shrub canopies. The objectives of this research were to: (i) identify underlying patterns in soil properties using factor analysis, and (ii) analyze factor scores to determine how the factor patterns varied between soils, canopy covers, and depth. White House (fine, mixed, thermic Ustic Haplargid) and Romero (loamy‐skeletal, mixed, nonacid, thermic, shallow Ustic Torriorthent) soils were sampled at 0‐ to 4‐ and 4‐ to 8‐cm depths under shrub live‐oak (Quercus turbinella Greene) canopies and adjacent open areas and analyzed for sand, silt, and clay contents, cation‐exchange capacity (CEC), pH, organic C, total N, extractable P, and exchangeable K, Ca, and Mg. A three‐factor model accounted for 81.2% of the total variation in the data. The first factor had high positive loadings on organic C, total N, and extractable P, and represented aggrading soil processes produced by accumulated litter and organic matter under shrubs. The second factor had high positive loadings on silt and clay contents and exchangeable K, had high negative loading on sand content, and was influenced by textural changes resulting from the interaction between shrub canopies and the two soils. The third factor had high positive loadings on exchangeable Ca, Mg, and CEC, and varied significantly between the two soils but was not affected by the presence of shrub live‐oak canopies. Factor analysis provided a statistical tool for grouping the 11 correlated soil variables into three uncorrelated factors. Analysis of factor scores allowed independent assessment of soils, shrub cover, depth, and their interactions on soil properties.
Analytical Solutions for Solute Transport in Finite Soil Columns with Arbitrary Initial Distributions
Authors: Leij Feike J. , Toride Nobuo 
Published: July 2010

AbstractAnalytical expressions were derived for the solute concentration in soils with a nonuniform initial distribution and a finite outlet condition assuming a zero gradient at the soil outlet. The advection‐dispersion equation (ADE) was solved by successively using a Laplace transform with respect to time, variation of parameters, and two different inversion procedures. Solutions for two resident concentrations and a flux‐averaged concentration were derived for arbitrary and pulse‐type initial distributions. The solutions are applicable for a wide range of conditions. Particular attention was paid to cases involving small Peclet numbers and large dispersive fluxes associated with steep fronts in the initial distribution. Flux‐averaged concentrations may become negative or exceed the initial concentration, while solutions for the resident concentration, derived for first‐ and third‐type inlet conditions, can predict a substantial amount of upstream solute transport due to dispersion. This suggests that the conventional ADE is not always suitable to describe initial value problems where travel times are typically short and large concentration gradients may occur.
Reduction and Oxidation Effect on the Solubility and Transformation of Iron Oxides
Authors: Brennan E. W. , Lindsay W. L. 
Published: July 2010

AbstractReports on the solubility of Fe during fluctuating redox conditions in soils and sediments are often difficult to interpret. This study was undertaken to examine the solubility relationships of Fe in suspensions of amorphous Fe(OH)3, Fe2O3(hematite), and soils subjected to changing redox conditions. A decrease in pe + pH was accomplished by the addition of organic matter and H2(g) in soils, and by H2(g) with a Pt catalyst in Fe(III) oxide suspensions. Addition of H2(g) and a Pt catalyst to Fe(III) oxide suspensions resulted in their dissolution and subsequent precipitation of two distinct Fe3O4 products. With small additions of O2 (0.2 mL of air), equilibrium was maintained with Fe3O4(magnetite). X‐ray diffraction confirmed its presence. When large amounts of atmospheric O2(g) were added (15 mL of air), the precipitate designated Fe3O4(amorp) was formed with a mean log of the equilibrium constant based on activities (Ko) of 40.65 ± 0.11. X‐ray diffraction showed this precipitate to be amorphous. This precipitate controlled Fe solubility within the pe + pH range of 4.0 to 12.7. In soil suspensions subject to changing redox, the Fe3O4(amorp) precipitate and Fe(OH)3(amorp) appear to control Fe solubility. Crystalline Fe(III) oxides including Fe2O3(hematite) and FeOOH(goethite) can only control Fe solubility under more highly stable, oxidizing conditions. Only with prolonged and intensive reduction is Fe3O4(magnetite) expected to form and control Fe solubility.
Alleviation of Copper Rhizotoxicity by Calcium and Magnesium at Defined Free Metal‐Ion Activities
Authors: Parker David R. , Pedler Judith F. , Thomason David N. , Li Huiying 
Published: July 2010

AbstractThe common “hardness cations”, Ca and Mg, are at least partially capable of alleviating the toxicities of metal ions, but quantitative data for their effect on Cu rhizotoxicity are lacking. We used 2‐d root elongation of wheat (Triticum aestivum L., cv. Yecora Rojo) in a simple medium (≥0.2 mM CaCl2) as a sensitive bioassay for examining how Ca, Mg, and pH affect Cu rhizotoxicity. A fourfold increase in solution CaT from 1 to 4 mM showed a slight alleviation of toxicity, but the effect could be completely ascribed to changes in ionic strength and thus in Cu2+ activity. Subsequently, a 25‐fold range in CaT (17‐fold range in Ca2+ activity) was found to improve Cu‐inhibited root elongation by some 30 to 35%. Increases in solution Mg2+ activity were equally or slightly more effective than comparable increases in free‐ion activity [denoted by parentheses, i.e., (Ca2+)] of Ca in alleviating Cu stress, an unexpected result because of reports of selective binding of Ca by apoplastic sites. Neither cation alleviated Cu rhizotoxicity as profoundly as they do with other metals such as Al. Lowering pH from 6.5 to 5.5 alleviated Cu stress slightly; a further decrease to pH 4.5 was more effective. Finally, seedlings were reared en masse in nine treatments selected from the previous root elongation studies, and root tips were analyzed for operationally defined apoplastic and symplastic Cu. Growth inhibition was only weakly correlated with symplastic Cu (or with apoplastic or total Cu), and the results suggested that Ca and Mg (but not H) afford some physiological protection against Cu that is not explained by simple competitive inhibition of Cu accumulation in the apical tissues.
Hydrology and Hydric Soil Extent within a Mollisol Catena in Southeastern Minnesota
Authors: Thompson James A. , Bell Jay C. , Zanner C. William 
Published: July 2010

AbstractA landscape perspective is essential when examining the relationships among soil hydrology, hydric soil conditions, and soil hydromorphic properties because pedogenic processes, which are mainly driven by the presence and flow of water, are not restricted to a vertical soil profile. The objectives of this study were to: (i) examine the soil geomorphic properties that control water movement over and through soils of a catena in southeastern Minnesota, (ii) describe this water movement using soil water monitoring data and terrain analysis, and (iii) relate these monitoring and modeling results to the distribution of hydric soils in this landscape. Local shallow groundwater flow is lateral along this hillslope and is governed by parent material stratigraphy, particularly the presence of a sandy colluvium subsoil layer over dense till in lower landscape positions. The topographic influence on surface and near‐surface water flow and storage predicts saturated surface conditions farther upslope of the drainageway int he vicinity of low‐order, low‐relief drainages perpendicular to the drainageway. The hydric soil boundary also occurs farther upslope in the vicinity of these same low‐order drainages.
High‐Resolution Time Domain Reflectometry Coil Probe for Measuring Soil Water Content
Authors: Nissen H. H. , Moldrup P. , Henriksen K. 
Published: July 2010

AbstractTime domain reflectometry (TDR) is becoming a widely used nondestructive method for measuring soil‐water content (θ), but relatively little effort has been put into the development of TDR equipment and especially TDR probes. Therefore, TDR has been used with only limited success for measuring small spatial scale variations in θ. In this study a small‐scale TDR probe (length = 15 mm, diameter = 3.6 mm), applicable with common TDR equipment and easy and inexpensive to produce, was developed. Travel time in the probe is prolonged by forcing the electromagnetic waves to travel in a coil surrounded by four grounded wires. The apparent relative dielectric permittivity (Ka) measured by the coil probe (Ka, coil) was calibrated against Ka measured by a standard two‐rod TDR probe without a balun (Ka, ref) in (i) five soils during transient evaporation, and (ii) air and seven fluids. Calibration in air and fluids was fast and reliable compared with transient‐state calibration in soil. A two‐phase dielectric mixing model was used to describe the contributions of the probe materials and the surrounding media to Ka, coil. Soil volume of influence was found to be approximately 180 mm3, implying that the coil probe measurement can be considered close to a point measurement. By introducing the coil principle, a reduction in probe length of a factor of five was achieved without loss in the sensitivity of the probe to changes in the Ka of the surrounding soil.
Nitrogen Management for High Yield and Quality of Citrus in Sandy Soils
Authors: Alva A. K. , Paramasivam S. 
Published: July 2010

AbstractWe are in the process of developing N best management practices for citrus in sandy Entisols to increase N uptake efficiency and to minimize NO3 leaching below the rooting depth. We evaluated the effects of N sources as either dry granular form (DGF), fertigation (FRT), or controlled‐release fertilizer (CRF), and rates (56–280 kg N ha‐1 yr‐1) with optimum irrigation management on: (i) the fruit yield and quality and leaf nutrient concentrations of bearing ‘Hamlin’ orange [Citrus sinensis (L.) Osbeck] trees on ‘Cleopatra’ mandarin (Citrus reticulata Blanco) rootstock (planted in 1974) grown in a Tavares fine sand (hyperthermic, uncoated Typic Quartzipsamments) and (ii) changes in NO3‐N status in soil solution sampled from the vadose zone both within and below the root zone. For the DGF and FRT sources, 3‐yr mean fruit yield increased with an increase in N rates in the range of 112 to 224 kg ha‐1 yr‐1. For further increase in N rate, the fruit yield showed a diminishing response, which was quite marked for the DGF. The N requirements for 1 Mg of fruit, mean across all N rates, were 1.79, 2.58, and 2.75 kg N for the CRF, FRT, and DGF sources, respectively. Leaf N concentrations were maintained within the optimal range (25–27 g kg‐1) at N rates ≥168 kg ha‐1 yr‐1, regardless of source of N. Various N rates and sources did not significantly affect the fruit size, nor juice quality parameters. The improved management of irrigation and fertilizer placement and timing of application contributed to minimized leaching of NO3‐N below the root zone.
Evaluation of a Model for Predicting Compressibility of Forest Soils
Authors: Smith C. W. , Johnston M. A. , Lorentz S. A. 
Published: July 2010

AbstractSoil compressibility is an important soil physical property in the prediction of compaction behavior. The compression index, C, as a measure of compressibility, was determined for a wide range of South African forest soils and compared with existing models that utilize clay content as the independent variable. These models were tested using a model performance technique that distinguished between systematic (bias) and nonsystematic (random) errors. The maximum compression index, Cmax, was adequately predicted for all soil orders in this study and possessed a relatively low systematic error. The average compression index, Cmod, which was calculated in this study as the average of C values across a wide range of water contents, was generally underpredicted and showed a slightly higher systematic error than with Cmax. It is concluded that the slightly better performance of the models in predicting Cmax was due to the models being developed on moist to wet soils (Ψp > −100 kPa) when compression is at a maximum. Since compaction can also occur under moist to dry conditions, our results indicate that modelling compaction behavior for soils that occur in regions with a pronounced dry season will require compression indices developed across a wider range of water contents than is currently the case.
Estimating Soil Hydraulic Conductivity and Macroscopic Capillary Length from the Disk Infiltrometer
Authors: Zhang Renduo 
Published: July 2010

AbstractThe disk infiltrometer is increasingly used to measure in situ soil hydraulic properties in the field. Several procedures have been proposed for determining soil hydraulic conductivity from disk infiltrometer data. However, the procedures require steady‐state infiltration rates at several tensions, which limits their applications in the field. In this study, two methods were developed to estimate soil hydraulic conductivity and macroscopic capillary length using soil water fluxes at any infiltration time under the disk infiltrometer. The proposed procedures do not require steady‐state infiltration rates but infiltration data at any time. Therefore, the time required for field infiltrometer experiments can be dramatically reduced. Meanwhile the new procedures provide high estimation accuracy of soil hydraulic conductivity and macroscopic capillary length. Extensive numerically simulated data were used to examine the methods for various soils and different radii and tensions of the disk infiltrometer. The proposed methods are especially useful for estimating soil hydraulic conductivity and macroscopic capillary length of fine‐textured soils, using infiltration data collected during a short experiment period with a relatively large infiltrometer.
Stability of Arsenate Minerals in Soil under Biotically Generated Reducing Conditions
Authors: Rochette E. A. , Li G. C. , Fendorf S. E. 
Published: July 2010

AbstractMining activities and arsenical pesticide applications can introduce arsenate compounds into soils and sediments. Under water‐saturated (flooded) soil conditions, arsenate solids are subjected to biotically generated reducing conditions and may undergo reductive dissolution. While thermodynamic calculations have been used to predict the conditions under which mineral‐associated As undergoes reduction, there is relatively little data from systems in which well‐characterized arsenate solids have been subjected to reducing conditions, and a limited amount of information about the reduction of mineral‐bound arsenate. In this study, the behavior of five arsenates was observed under reducing conditions generated by flooded soils. The apparent solubility of the arsenates decreased in the order CaHAsO4 = Na2HAsO4·7H2O > AlAsO4·2H2O > MnHAsO4 > FeAsO4·2H2O under oxic conditions; under anoxic conditions (redox potential <0 mV) the apparent solubility was FeAsO4·2H2O ≥ CaHAsO4 = Na2HAsO4·7H2O > AlAsO4·2H2O > MnHAsO4. Calcium and sodium arsenates completely dissolved under the initial oxidizing conditions. X‐ray absorption near‐edge structure (XANES) spectroscopy indicated that As in AlAsO4·2H2O rapidly transformed to solid‐phase As(III). Manganese arsenate yielded the least solution and solid‐phase As(III) of all of the minerals. Iron arsenate underwent reductive dissolution, releasing As(III) to solution and solid phases, and thus may yield solution or solid‐phase As(III) if prolonged anoxic conditions prevail.
Classing the Soil Skeleton (Greater than Two Millimeters): Proposed Approach and Procedure
Authors: Corti G. , Ugolini F. C. , Agnelli A. 
Published: July 2010

AbstractIn soil science, analytical procedures apply almost exclusively to the fine earth (<2 mm). Rock fragments or skeleton (>2 mm) are regarded as inert and discarded during sieving; however, we have found that the clasts display physical and chemical properties that can equal or surpass those of the fine earth. These properties depend largely on the degree of alteration of the clasts. In light of these findings, we developed a method to separate the rock fragments into weathering classes. This method has been applied to five European skeleton‐rich soils derived from different parent materials. Color intensity, roughness and irregularities of the surfaces, cracks, and surface features of the exposed minerals were considered reliable criteria for the separation of the clasts. We noticed also that the degree of alteration of the clasts corresponds to size: as size decreased, weathering increased. Consequently, sieving could be used for separating the weathering classes. On the basis of these criteria, clasts were differentiated into highly, moderately, and slightly altered. There are statistically significant differences among the weathering classes in terms of bulk density, porosity, organic C, total N, and cation‐exchange capacity. There are no statistically significant differences in pH. The results confirm that the procedure separates relatively homogeneous and different classes of rock fragments. We also compared the characteristics of the soil skeleton to those of the fine earth and fresh rock. We concluded that not characterizing the skeleton of the soils may provide distorted information on the capability of these substrata.
Properties of Permafrost Soils on the Northern Seward Peninsula, Northwest Alaska
Authors: Höfle Claudia , Ping Chien‐Lu , Kimble John M. 
Published: July 2010

AbstractSoil processes in permafrost regions differ markedly from those of the mid and low latitudes. Permafrost soils are cold during the short growing season and frozen the rest of the year. This study was conducted to describe permafrost soils on the tundra coastal plain of northern Seward Peninsula with emphasis on soil characteristics below the active layer and cryogenic structures, both aspects which were widely neglected in previous studies of permafrost soils. We used cryogenic structures to determine active layer depths. In describing these soils, we applied the previous soil taxonomy and tested the utility of the new Gelisol order. Seven pedons were excavated and described in different topographic positions. Most pedons are influenced by frost action, as evidenced by irregular and broken horizons and weakly developed soils. Mineral horizons have predominantly reduced colors. Organic horizons of 7‐ to 50‐cm thickness occur in the study area. All soils contain segregated ice and ice wedges. Segregated ice includes ice lenses, ice nets, and ataxitic ice concentrations at the base of the active layer. With the identification of these cryogenic features, it was possible to determine active layer depths independently of thaw season. For describing the properties of permafrost soils, the new Gelisol order is shown to be a significant improvement on the previous soil taxonomy.
Evaluating Central Tendency and Variance of Soil Properties within Map Units
Authors: Hammer R. David , Young Fred J. , Williams Frederick 
Published: July 2010

AbstractUsers are demanding that soil surveys contain statistical information about soil and map unit properties. Numerous sampling and statistical methodologies are available, but statistical methods should be appropriate for both sampling methods and data distributions. Rigorous investigations of soil property distributions are rare, and statistical methodologies have received little attention for soil survey applications. Two hypotheses were tested: (i) frequency distributions of soil properties within map units are non‐normally distributed, and (ii) variability estimates will depend on the statistical assumptions and methods. Twelve transects were randomly selected in a Boone County, Missouri soil survey map unit and 12 soil attributes were investigated from a population of 120 soil cores. Three methods were used to estimate variances: (i) simple random sampling, (ii) cluster sampling, and (ii) two‐stage random sampling. Frequency distributions were significantly skewed for 11 of the soil properties. The median is an appropriate estimator of central tendency for these properties. The random sampling approach provided the samplest variances, but is conceptually questionable. Two‐stage sampling is conceptually most correct, but requires dubious assumptions about population size. Non‐parametric confidence intervals for variable medians were appropriate, but are wide for most properties. None of the applied assumptions and techniques are universally applicable. Statistical assumptions and methodologies should be tested across a spectrum of depositional, weathering, and land‐use conditions to determine the most suitable approaches for particular user needs and soil conditions.
Landscape and Pedogenesis of an Oxisol‐Inceptisol‐Ultisol Sequence in Southeastern Brazil
Authors: Anjos L. H. , Fernandes M. R. , Pereira M. G. , Franzmeier D. P. 
Published: July 2010

AbstractThe topographic sequence of Oxisols, Inceptisols, and Ultisols is frequently observed in tropical hilly surfaces in the southeastern region of Brazil. The purpose of this study was to relate pedogenesis to major geomorphic surfaces (MGS) in the Caetés watershed, located in Paty do Alferes, Rio de Janeiro State. The landscape is characterized by steep bedrock hills and cliffs of pre‐Paleozoic gneiss, granite, and related metamorphic rocks rising above long, nearly level, accordant ridge crests, convex hills, and narrow fluvial plains. Intense soil development, with deep weathering and kaolinite formation in the gneiss‐granite rock, took place on the ridges and convex hills. Six pedons were examined using field investigation and laboratory soil characterization techniques. The degree of pedogenesis on the various geomorphic surfaces supports the landscape evolution theories of Penck and King. A Typic Hapludox, with the greatest degree of pedogenesis, formed on the stable summit position, MGS1. The upper part of the retreating slope, MGS2, bevels MGS1, and the material eroded from MGS2 moved downslope and formed a surface with lower gradient, MGS3. Dystrochrepts are on shoulder positions and shallow Hapludox are on backslope positions of the geomorphic surface MGS2, and Kandiudults formed on footslopes, MGS3. Eutrochrepts are on the youngest surface MGS4, a toeslope position.