bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatial Distribution of Soil Nutrients in a Northern Everglades Marsh: Water Conservation Area 1
Authors: Newman S. , Reddy K. R. , DeBusk W. F. , Wang Y. , Fisher M. M. , Shih G. 
Published: July 2010

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

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

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

AbstractMeasures of aggregate size and shape are needed in models to predict soil erosion, seed bed density, tensile strength, and solute diffusion. We hypothesized that size (i.e., equivalent cubic length Lc = [l1(l2l√2)(l3l√3)]1/3, where l1, l2, and l3 are the shortest, intermediate, and longest axial lengths, respectively) and shape (i.e., aspect ratios, l1/l3 and l2/l3) vary with soil type and tillage treatment. Caliper measurements of l1, l2, and l3 were made on 1800 aggregates from three sieved fractions (4–8, 8–16, and 16–31.5 mm) of a plowed, plowed plus disked, and no‐till Maury silt loam (fine, mixed, mesic Typic Paleudalf) and a no‐till Karnak silty clay (fine, montmorillonitic, nonacid, mesic Vertic Haplaquept). Overall means for l1/l3 (0.57) and l2/l3 (0.78) were close to those for a cube (0.58 and 0.82, respectively). The mean l1/l3 for Karnak was 18% lower than the corresponding value for no‐till Maury. The Lc was lognormally distributed. The mean log10(Lc) increased from 0.67 in the smallest fraction to 1.19 in the largest fraction. Soil effects on log10(Lc) were most evident in the 8‐ to 16‐mm fraction (1.01 for Karnak compared with 0.93 for no‐till Maury). Tillage effects on log10(Lc) were most evident in the 4‐ to 8‐mm fraction (0.68 for no‐till Maury compared with 0.66 and 0.65 for plowed and plowed plus disked Maury, respectively). The equation Lc = xl(m/mm)1/3, where xl is lower sieve aperture, m is aggregate mass, and mm is modal mass, explained 96% of the variation in Lc. This equation can be used to predict aggregate size from sieve aperture size and measurements of aggregate mass.
Determining the Hydraulic Properties of a Swelling Soil from a Transient Evaporation Experiment
Authors: Garnier P. , Rieu M. , Boivin P. , Vauclin M. , Baveye P. 
Published: July 2010

AbstractMost methods used to determine the hydraulic properties of swelling soils (i.e., the shrinkage curve [e(θ)], the moisture retention curve [h(θ)], and the hydraulic conductivity curve [K(θ)]) are time consuming because they require measurements of several different parameters (either in separate experiments or by using very expensive equipment). We propose a simple evaporation experiment to simultaneously determine all three soil hydraulic properties. The method is illustrated using samples of a Vertisol from the Senegal River valley. The value of e(θ) is determined during the experiment by horizontal and vertical linear deformation measurements, whereas an inverse parameter estimation method is used to determine h(θT) and K(θ). This method relies on a water flow model that takes into account the three‐dimensional and anisotropic deformation of the soil. The reliability of the estimated parameter values was checked and we compared the results with those obtained by a multistep outflow experiment. Good agreement was found between the results of the different procedures. The sensitivity of the method to deformation was also analyzed. In the soil investigated, the inverse method does not seem to require the use of a water flow model that takes into account deformation. However, a correction for deformation is needed if the characteristic functions are sought in terms of the volumetric water content of the soil.
Apparatus for Constant‐Head Solute Transport and Soil Water Characteristic Determination
Authors: Langner H. W. , Wraith J. M. , Inskeep W. P. , Gaber H. M. , Huwe B. 
Published: July 2010

AbstractWe developed a system to impose, maintain, and monitor constant matric head (h) and water content (θ) within large soil cores during saturated or unsaturated flow. Critical elements include: (i) delivery of water and chemicals to the column inlet using a modified disk permeameter; (ii) paired time domain reflectometry (TDR) and transducer tensiometer sensors; and (iii) solenoid valves at the outlet for uninterrupted negative pressure and simultaneous collection of large effluent volumes. Use of TDR and tensiometry provides detailed water retention data and allows hydraulic conditions within the soil to be continuously monitored during single or multiple experiments using the same soil column. Our experiences have emphasized the need to measure soil column h rather than infer its status based on applied pressure.
Influence of Soil Organic Matter Removal and pH on Oxalate Sorption onto a Spodic Horizon
Authors: Bhatti J. S. , Comerford N. B. , Johnston C. T. 
Published: July 2010

AbstractOxalate is one of the dominant low molecular weight organic anions in many soils under forest ecosystems. Through its complexation reactions with Fe and Al, both in solution and at mineral surfaces, oxalate increases the availability of nutrients such as P in these soils. This investigation was designed to study (i) the influence of pH on the mechanism of oxalate sorption by the soil clay fraction and whole soil materials from a spodic horizon, and (ii) the effect of soil organic matter removal on oxalate sorption using Fourier‐transform infrared (FTIR) spectroscopy. The removal of soil organic matter and decrease in pH increased oxalate sorption significantly. There was a two‐ to threefold increase in oxalate sorption with removal of organic C at all pH values. Depending on pH, the molar ratio of OH ions released to oxalate sorbed was close to 1 or 2. These results suggest that oxalate formed mondentate and/or binuclear surface complexes at pH 3.5, and bidentate surface complexes at pH 4.5 and 5.5. With oxalate sorption, large amounts of organic C and Al were released from the soil clay fractions and whole‐soil samples. Seven to 10 mol oxalate kg−1 soil clay than by water.
Comparison of Reaction Products from the Transformation of Catechol Catalyzed by Birnessite or Tyrosinase
Authors: Naidja A. , Huang P. M. , Bollag J.‐M. 
Published: July 2010

AbstractBoth tyrosinase, a Cu‐containing polyphenoloxidase, and birnessite (δ‐MnO2) are able to catalyze the transformation of phenolic compounds through oxidative polymerization, a process that leads to humification, but the reaction mechanisms are not fully understood. The objective of this study was to characterize or identify the reaction products generated from catechol (1,2‐dihydroxybenzene) by birnessite or tyrosinase. Birnessite and tyrosinase catalyzed the transformation of catechol to oligomers, polycondensates, and fragments. The reaction products formed after catalysis by tyrosinase were brown colored, while those resulting from the birnessite‐catechol system were green colored; the former had a higher absorbance between 200 and 620 nm than the latter. This indicated a higher degree of aromatic ring condensation in products of the tyrosinase‐catechol system relative to those of the birnessite‐catechol system. In addition, the products of birnessite catalysis contained polycondensates and fragments, including aliphatic components, with lower molecular weights than did the products derived from catalysis by tyrosinase. Fourier‐transform infrared (FTIR) analysis and mass spectrometry indicated that the reaction products formed an organic coating on the birnessite granules.
Determining Soil Hydraulic Properties using Tension Infiltrometers, Time Domain Reflectometry, and Tensiometers
Authors: Wang Dong , Yates S. R. , Ernst F. F. 
Published: July 2010

AbstractTension infiltrometers have become a popular instrument for field determination of soil hydraulic properties. To develop and test different models for parameter estimation based on tension infiltrometer measurement, we obtained simultaneous measurements of transient tension infiltration rate, soil water content, and tension using small time domain reflectometry (TDR) probes and tensiometers installed at fixed locations relative to the infiltrometer disk. Infiltration was made with 10‐ and 20‐cm‐diam. disks under 1 and 5 cm of water supply tensions. The soil is an Arlington fine sandy loam (coarseloamy, mixed, thermic Haplic Durixeralf). Wooding's steady‐state approximate solution for water flow from a surface circular pond was used to estimate the saturated hydraulic conductivity (Ks) and an empirical parameter (αG) used in Gardner's exponential hydraulic conductivity function. These two parameters (i.e., Ks and αG) were then independently estimated using an integral form of the steady‐state Darcy‐Buckingham flux law. A sorptivity method was also proposed as an alternative to Wooding's steady‐state approach. Calculated Ks and αG with the Darcy‐Buckingham flux law method was in good agreement with estimates using Wooding's steady‐state approximation. The sorptivity method produced Ks estimates that were statistically similar to those obtained with Wooding's method. The K(h) inferred from measured θ(h) underestimated the conductivity close to saturation compared with estimates obtained from the infiltrometer measurements.
Proton Adsorption on a Titanium Oxide in the Presence of Bicarbonate
Authors: Schulthess C. P. , Belek J. Z. 
Published: July 2010

AbstractThe very high concentration of aqueous CO2 species below ground highlights a need to fully characterize the physicochemical behavior of this compound in the soil environment. This study focused on the adsorption of bicarbonates by a Ti oxide, and on its effects on the adsorption of protons, which was measured by the backtitration technique. The inorganic C adsorbed on the Ti oxide from pH 1.5 to 10 with a broad maximum at pH 4 to 6. For every molecule of inorganic C adsorbed (expressed as HCO3 adsorbed), an average of 2.3 protons were removed from the liquid phase (either by coadsorption or neutralization of the proton). The point of zero salt effect (PZSE) also increased from pH 5.7 to 6.2. The high stoichiometry of 2.3 suggests that the bicarbonate will also affect the desorption of cationic impurities; higher levels of Na, Ca, and Mg were measured in the liquid phase in the presence of inorganic C at pH 4. This study indirectly highlights that modeling the adsorption of protons by an oxide (even a “simple” one like Ti oxide) can be easily complicated by the presence of low levels of inorganic C or the presence of adsorbed cationic impurities.
Intercalation of Hydroxy‐Aluminosilicate and Hydroxy‐Aluminum in Montmorillonite and Resultant Physicochemical Properties
Authors: Sakurai K. , Huang P. M. 
Published: July 2010

AbstractBoth hydroxy‐aluminosilicate (HAS) and hydroxy‐Al (HyA) ions can be adsorbed into the interlayer spaces of montmorillonite (Mt), resulting in an expanded structure; however, the differences in the adsorption and the surface properties of the intercalated clay complexes still remain to be established. The objective of this study was to investigate the influences of the coexistence of silicic acid with HyA ions on the formation and surface properties of the HAS‐Mt complexes, in comparison with the HyA‐Mt complex and Mt. Most of the intercalation reactions of HAS and HyA ions by Mt came to apparent completion within 10 min. Compared with the original Mt, the HyA‐Mt complex had more external specific surface, pore area, and pore volume, and less internal specific surface; the HAS‐Mt complex had less external and internal specific surface, pore area and pore volume. The transmission electron micrographs and the analysis of the particle‐size distribution by small‐angle x‐ray scattering indicated that both HyA‐Mt and HAS‐Mt complexes formed domains of clay particles associated into larger particles. The HAS‐Mt complex exhibited a higher point of zero salt effect (PZSE) value than the HyA‐Mt complex. The pH‐dependent cation‐exchange (CEC) value was greater in the HAS‐Mt complex than in the HyA‐Mt complex; therefore, the variable charge in the former was more dominant than in the latter. The surface chemistry of HAS‐ and HyA‐intercalated clay complexes pertaining to dynamics of nutrients and pollutants in various pedogenic environments merits close attention.
Automated Near‐Continuous Measurement of Carbon Dioxide and Nitrous Oxide Fluxes from Soil
Authors: Ambus P. , Robertson G. Philip 
Published: July 2010

AbstractTrace gas fluxes often show temporal variability on the order of hours and accurate quantification may be difficult without continuous or near‐continuous measurements. We developed an automated near‐continuous trace gas analysis system (NCTGAS) to measure soil‐atmosphere gas fluxes on a several‐times‐per‐day basis. In this system, air is circulated in a closed sample loop between fully automated flow‐through chambers and a photoacoustic infrared trace gas analyzer (TGA). The TGA quantifies infrared active gases at ambient levels within 2 to 3 min. We tested sensitivity, stability, and calibration of the TGA, and the ability of the NCTGAS to measure fluxes of CO2 and N2O. In addition to static tests, fluxes of CO2 and N2O were simulated by bleeding known quantities of these gases into a test chamber. Gas samples were simultaneously analyzed by TGA and removed for independent analysis of CO2 by conventional infrared gas analysis and for N2O by gas chromatography. The TGA‐based flux measurements were statistically identical to the independent measurements of both CO2 and N2O. In situ fluxes of CO2 and N2O measured by the NCTGAS were 105 ± 6 and 93 ± 10%, respectively, of those measured from hand‐drawn samples. The TGA was as or more stable than conventional means for measuring CO2 and N2O in air at ambient concentrations, and was equally sensitive across the range of concentrations normally encountered in field measurements. Fast response time and ease of use offers significant advantages over conventional gas chromatography.
Three‐Parameter Soil‐Water Transient Equations in Horizontal Water‐Transport Analysis
Authors: Guerrini Ivan A. , Swartzendruber D. 
Published: July 2010

AbstractFor data obtained from horizontal soil column experiments, the determination of soil‐water transport characteristics and functions would be aided by a single‐form equation capable of objectively describing water content θ vs. time t at given position xt. Our study was conducted to evaluate two such possible equations, one having the form of the Weibull frequency distribution, and the other being called a bipower form. Each equation contained three parameters, and was fitted by nonlinear least squares to the experimental data from three separate columns of a single soil. Across the θ range containing the measured data points obtained by gamma‐ray attenuation, the two equations were in close agreement. The resulting family of θ(xf,t) transients, as obtained from either equation, enabled the evaluation of exponent n in the tn dependence of the positional advance of a given θ. Not only was n found to be <0.5 at low θ values, but it also increased with θ and tended toward 0.5 as θ approached its sated (near‐saturated) value. Some quantitative uncertainty in n(θ) does arise due to the reduced number of data points available at the higher water contents. Without claiming non‐Boltzmann behavior (n < 0.5) as necessarily representative of all soils, we nonetheless consider n(θ) to be worthy of further study for evaluating its significance and implications.
Aluminum Speciation in Aluminum‐Silica Solutions and Potassium Chloride Extracts of Acidic Soils
Authors: Hiradate Syuntaro , Taniguchi Satoru , Sakurai Katsutoshi 
Published: July 2010

AbstractTo differentiate chemical species of Al in soil solutions, a method using nuclear magnetic resonance (NMR) was applied to laboratory preparations of hydroxyaluminum (HyA) and hydroxyaluminosilicate (HAS) ions ([OH]/[Al] = 2.0), and 1 M KCl extracts from acidic soils. The Al in a Al‐OH‐Si(OH)4 mixture was separated into three fractions: Al13 ([AlO4Al12(OH)24(H2O)12]7+), AlSYM, and AlNON. The Al13 and AlSYM were quantitatively determined by 27Al‐NMR at 63 and 0 ppm, respectively. The AlNON was defined as the Al that cannot be determined by 27Al‐NMR. The AlSYM was attributed to electrically symmetric octahedral Al including monomer (and dimer) HyA ions, and the AlNON was attributed to electrically asymmetric Al including HAS and polymer HyA ions. The concentrations of Al13 decreased with increasing Si/Al molar ratio of the mixed solutions, and Al13 was not detected at Si/Al ≥ 0.28. With increasing Si/Al molar ratio, the concentration of AlSYM increased slightly, while AlNON increased significantly. In the KCl extracts from soils, the Al13 was not detected at all. This result suggests that Al13 is not formed in these soils, or that the persistence of Al13 in the soil solution is strongly inhibited by adsorption or precipitation reactions. The presence of organically complexed Al (AlORG) was also directly detected in KCl extracts from upper horizons by 27Al‐NMR spectra. The chemical shift of resonance peak of AlORG was close to that of the 1:1 complex of Al oxalate. On average, 92 and 96% of the KCl‐exchangeable Al existed as AlSYM and AlSYM plus AlORG, respectively.
Revegetation in Semiarid Zones: Influence of Terracing and Organic Refuse on Microbial Activity
Authors: Garcia C. , Hernandez T. , Albaladejo J. , Castillo V. , Roldan A. 
Published: July 2010

AbstractRevegetation of areas under semiarid conditions is difficult due to both the water shortage and the poor quality of the soils of semiarid areas. Two techniques of soil management (manually and mechanically built terraces), as well as soil amendment with organic materials were used for revegetation in a semiarid area. In this work the effect of such techniques on the microbial activity of a soil revegetated with Aleppo pine (Pinus halepensis Miller) was studied. The content of the different labile C fractions studied (water‐soluble C, water‐soluble carbohydrates, and polyphenol compounds) substantially increased in soils with mechanically built terraces and with addition of organic refuse. The highest values of these labile C fractions were found in soil samples collected in spring (rainy season) while those collected in January (dry season) showed the lowest values. The activity of oxidoreductases such as dehydrogenases as well as that of hydrolases involved in the biogeochemical cycles of important nutrients (ureases, proteases, phosphatases, and β‐glucosidases) were stimulated by the addition of organic matter to the soil. The lowest values of microbial biomass and enzyme activities were detected when revegetation was carried out on mechanical terraces without addition of organic materials. The simultaneous use of both soil management techniques, mechanical terracing and amendment with organic refuse, clearly improved soil microbial activity and hence soil biological quality. Plant growth was also improved with these techniques.