bluuebunny/crossref_metadata_2025_split huggingface dataset:
Method to Estimate Water Diffusivity and Hydraulic Conductivity of Moderately Dry Soil
Authors: Globus A. M. , Gee G. W. 
Published: July 2010

AbstractWater diffusivity and unsaturated hydraulic conductivity of moderately dry soils are seldom measured directly, yet are often needed by numerical models to simulate flow processes. We propose a relatively simple method to obtain water diffusivity or hydraulic conductivity in moderately dry soils. Steady‐state profiles of water content and temperature in a closed, non‐isothermal soil column are used to determine Sw = DT/D(θ) = − dθ/dT where Sw is the thermogradient coefficient, DT is the thermal water diffusivity, D(θ) is the isothermal water diffusivity, and dθ/dT is the rate of change of water content with temperature. The relative constancy of DT allows D(θ) to be estimated as D(θ) = ‐DT(dT/dθ) where dT/dθ is measured at various locations along the soil column. Using water retention data, the steady water content profile can be transformed into a suction head profile and the above procedures for estimating D(θ) can then be applied to estimate hydraulic conductivity, K(θ). Soil columns ranging in length from 5 to 10 cm, exposed to thermal gradients of 1°C/cm for periods as short as 7 d, at initial suction values ranging from 0.1 to 1.5 MPa, can be used to estimate water diffusivity and hydraulic conductivity with uncertainties of a factor of five or less in the suction range from 0.03 to 3 MPa.
Assessing Temporal Variations in Soil Water Composition with Time Domain Reflectometry
Authors: Heimovaara T. J. , Focke A. G. , Bouten W. , Verstraten J. M. 
Published: July 2010

AbstractTime domain reflectometry (TDR) can be used to study temporal variations in volumetric soil water content (θ) and bulk soil electrical conductivity (σa). The variations in σa are associated with changes in θ and the soil water composition. Laboratory and field experiments were conducted to verify if TDR can be used to monitor the temporal variation in the soil water composition between solution sampling occasions. Effects of cable length and temperature on the σa measurement were evaluated. Including the series resistance of the cable and connectors in the analysis improves measurements at high electrical conductivity levels. The temperature factor of the bulk soil appears to be similar to the temperature factor of soil extracts. Laboratory experiments showed that the theoretical model giving σa as function of θ and the electrical conductivity of the soil solution (σw) combined with the water retention function was capable of describing σw measured on soil solution extracted with ceramic cup solution samplers under static water flow conditions. After optimization of a single parameter, the model was able to describe σw values of the soil solution obtained in the laboratory, whereas literature values were sufficient for field data. Concentrations of a number of solutes in a field data set spanning 3 yr were positively correlated with σw. Site‐specific regressions between solute concentration and σw combined with automated TDR measurements of σa and θ enable a more meaningful interpretation of the temporal variation of the concentration of major solutes present in the soil solution between sampling occasions.
Error Analysis of Heat Pulse Method for Measuring Soil Heat Capacity, Diffusivity, and Conductivity
Authors: Kluitenberg G. J. , Bristow K. L. , Das B. S. 
Published: July 2010

AbstractA dual‐probe heat pulse (DPHP) method was developed recently that allows for the simultaneous, automated measurement of soil thermal diffusivity (κ), volumetric heat capacity (ρc), and thermal conductivity (λ). Estimation of thermal properties is based on theory for the conduction of heat away from an infinite line source (ILS) that is heated for a short period of time. In this study, we examined possible sources of error in the use of the ILS theory by comparing it with other models that explicitly account for finite length and cylindrical shape of the actual heater. For probe geometry and heating times typical of our experimental work, the analysis of model error showed that assuming an infinite length for a heat source of finite length caused errors <2% in the estimated thermal properties. Assuming the cylindrically shaped heater to be a line heat source caused errors of <0.6% in the estimated thermal properties. Thus, the ILS theory appears to be appropriate for use in the DPHP method if probe geometry is considered carefully. However, small changes in probe geometry can lead to large model errors. First‐order error analysis also was used to predict how thermal property estimates will be affected by experimental errors in the measured inputs to the ILS model. The analysis shows that κ and ρc estimates are sensitive to measurement error in probe spacing (r), but λ is unaffected by error in r. Estimates of κ and λ were shown to be sensitive to measurement error in the time to the temperature maximum (tm), whereas ρc was affected only slightly by such error.
Kinetics of Cadmium and Cobalt Desorption from Iron and Manganese Oxides
Authors: Backes Clare A. , McLaren Ronald G. , Rate Andrew W. , Swift Roger S. 
Published: July 2010

AbstractOxides of Fe and Mn in soils are capable of sorbing large amounts of trace metal ions and can therefore be important in controlling trace metal concentrations in soil solution, and hence trace metal bioavailability in soils. There is, however, relatively little information on the rates of desorption of trace metals from oxide materials or on the factors affecting desorption rates. The objective of this study was to examine the kinetics of desorption of Cd and Co from two Fe oxides, goethite and ferrihydrite, and from two Mn oxides, hausmannite and cryptomelane. The concentrations of Cd and Co specifically sorbed by the oxides at pH 6.0 were greater for the Mn oxides than for the Fe oxides. The metals were also much less readily desorbed from the Mn than the Fe oxides and, in general, Cd was more readily desorbed than Co from all four oxides. Increasing the initial sorption period from 1 to 15 wk substantially decreased the proportion of sorbed Cd or Co subsequently desorbed from goethite, with a similar but much smaller effect also observed with the Mn oxides. Desorption kinetics for both Cd and Co were found to be described well by assuming either the occurrence of two simultaneous first‐order desorption reactions, or by a continuous distribution of reaction sites, distributed lognormally with respect to desorption first‐order rate constant. With increasing initial sorption period, the parameters obtained from fitting either type of kinetic equation to the experimental data could be interpreted as indicating a movement of metal ions to sites with slower desorption reactions.
Formation and Activity of Urease‐Tannate Complexes Affected by Aluminum, Iron, and Manganese
Authors: Gianfreda Liliana , Rao Maria A. , Violante Antonio 
Published: July 2010

AbstractThe formation of active enzymatic complexes, obtained by the interaction of urease, tannic acid, and soluble and insoluble species of Al, Fe, or Mn, was studied. Tannic acid strongly inhibited urease activity (inhibition constant, Ki = 0.040 mM). The dependence of kinetic parameters (Vmax and Km) on tannic acid concentration suggests a pure uncompetitive inhibition mechanism. Soluble and insoluble urease‐tannate complexes were formed by increasing both the contact time and the tannic acid/urease ratios. Soluble (FeCl3, MnCl2, and OH‐Al polymers) and insoluble (Fe2O3 and MnO2) inorganic components differently influenced the interaction of urease with tannic acid molecules and the residual activity of the immobilized enzyme. An increased removal of urease molecules from solution as well as an enhanced residual enzymatic activity of urease complexes was observed in the presence of all the additives. Soluble species (FeCl3 and OH‐Al polymers) probably acted as flocculating agents or promoted the formation of more active enzymatic complexes. On the contrary, MnO2 showed a predominant polymerizing action on tannate molecules that gave rise to insoluble aggregates occluding urease molecules. Adsorption, as opposed to polymerization, probably occurred in the presence of Fe2O3.
Evaluation of Methods for Estimating Net Nitrogen Mineralization in a Semiarid Grassland
Authors: Hook P. B. , Burke I. C. 
Published: July 2010

AbstractMethods for estimating net N mineralization in semiarid grasslands are not well tested. We compared three in situ incubation methods to evaluate (i) effects of root density and length of incubations on methodological artifacts involving N immobilization, (ii) effects of sieving on estimates of net N mineralization, and (iii) effects of containment on soil water dynamics. We incubated intact soils and sieved soils with or without roots for 15 to 90 d in uncovered tubes and determined changes in NO3 and NH4. Net N mineralization was transient and usually declined after 15 to 30 d. Nitrogen immobilization may have contributed to decreases in extractable N, but root abundance was not a dominant control of net N mineralization. Greater root mass under blue grama grass [Bouteloua gracilis (Willd. ex Kunth) Lagasca ex Griffiths] plants was expected to promote immobilization, but net N mineralization was higher under plants than in bare areas. Removing roots from sieved soil enhanced net mineralization, but not consistently. Sieving soil caused problematic changes in N dynamics. Under plants, for example, N concentrations were higher in sieved than intact soil after 15 d, but lower after 60 d. Effects of sieving may reflect accelerated depletion of a small, biologically active organic matter pool during prolonged incubations. Soil in tubes was slightly wetter than bulk soil during moist periods, but water content in tubes tracked ambient conditions well. We recommend 15‐ to 30‐d incubations of intact cores to avoid artificially high rates of net mineralization caused by soil disturbance and to capture effects of environmental variation.
Spatial and Temporal Variations in the Chemical Weathering of Basaltic Pyroclastic Materials
Authors: Okuda Itaru , Okazaki Masanori , Hashitani Takusei 
Published: July 2010

AbstractThe spatial and temporal distributions of 17 elements in basaltic pyroclastic materials originating from Mt. Fuji, Japan, were investigated. The relatedness of the profiles was established tephrochronologically, which then allowed a comparison of the chemical compositions of the various weathered pyroclastic materials in terms of their spatial (distance away from the volcano) and temporal (older to younger deposits) relations. The distributions of mobile elements (e.g., Ca, Mg, Na, and Sr) and resistant elements (e.g., Ti) are strongly affected by the extent of weathering, which increases with time and increases with distance from the volcano (the effects of the thickness and specific surface area of parent material). The application of a few weathering indices based on chemical composition was successful. Furthermore, a principal component analysis statistically extracted the expected dominance of the element mobility‐resistance, which accounts for 43% of the field‐scale variability of the distribution of the 17 elements. The second principal component explained 21% of variability, and discriminated soils developed from similar parent materials but different weathering‐soil‐formation factors (agricultural activities and the impact of a river).
Soil Physical Property Changes during Dung Decomposition in a Tropical Pasture
Authors: Herrick J. E. , Lal R. 
Published: July 2010

AbstractThe contributions of soil macroinvertebrates to the creation and maintenance of soil structure in tropical rangeland ecosystems are poorly understood, in spite of the fact that compaction is frequently cited as a limiting factor in pasture production. Decomposition of cattle dung (fecal material) is associated with high levels of soil macroinvertebrate activity. We hypothesized that bulk density and surface penetrometer resistance would be reduced in soil beneath decomposing cattle dung patches and that soil water infiltration capacity and drainable porosity would be increased. Cattle dung was deposited in patches during the dry and wet seasons of 1991 in a seasonally dry pasture located 5 km north of Cañas, Costa Rica, on a Typic Argiustoll. At the end of the wet season, surface 3‐cm bulk density was <0.93 Mg m−3 under dung patches, compared with 1.05 Mg m−3 in control plots. Drainable porosity, defined as air‐filled porosity at 0.006 MPa, increased from 13% in control plots to >21% under dung. Similar, but smaller, differences were recorded at dung patch edges and at a depth of 4 to 7 cm. At the end of the wet season, equilibrium infiltration rates averaged 71 mm h−1 in the patch plots and 34 mm h−1 in the controls. Changes in penetrometer resistance were transient and no treatment effects persisted to end of the wet season. The results of this study indicate that processes associated with dung decomposition play a role in reducing surface compaction.
Gaseous Exchange and Wetland Plant Response to Soil Redox Intensity and Capacity
Authors: Kludze H. K. , DeLaune R. D. 
Published: July 2010

AbstractAlthough reports on plant responses to wetland conditions abound, limited information is available to relate such responses to well‐defined soil redox conditions. Laboratory experiments were conducted to evaluate differences in plant response to soil redox intensity (Eh) and capacity. Mississippi floodplain soil (Mhoon; fine‐silty, mixed, nonacid, thermic Typic Fluvaquent) and rice paddy soil (Crowley; fine, montmorillonitic, thermic Typic Albaqualf) were used to grow saltmeadow cordgrass [Spartina patens (Aiton) Muhlenb.] and rice (Oryza sativa L.), respectively. Plants were grown under controlled Eh levels of 100, 0, −100, and −200 mV to examine the effect of Eh on CO2 fixation. Treatments for the soil redox capacity experiment were imposed by application of different levels of extra energy source while maintaining Eh at ‐200 mV. Redox capacity effects on plant growth, CO2 fixation, root porosity (POR), radial oxygen loss (ROL), and CH4 emissions were also evaluated. In both test plants, CO2 fixation did not respond to soil Eh until −100 mV. Although POR was unaffected, plant growth, CO2 fixation, and CH4 emissions were significantly decreased with increase in soil O2 demand, thus suggesting a complex relationship between soil redox capacity and plant physiological functions. Plant O2 transport to the root environment (ROL) was also governed by soil redox capacity. Results indicate that plants may respond differently in magnitude to soil redox intensity and redox capacity. Evaluating responses, especially ROL, of flood‐tolerant plant species therefore requires proper quantification of the soil redox condition or substrate O2 demand in which the plants are grown.
Brittle Fracture of Fractal Cubic Aggregates
Authors: Perfect E. , Kay B. D. 
Published: July 2010

AbstractThe conventional Weibull model for brittle fracture assumes soil aggregates are Euclidean cubes. Recent developments in fractal theory suggest that fractal cubes may provide a more realistic representation of soil aggregates. We modified the Weibull model for fractal cubes, and compared the performance of the modified model with the conventional model using previously published brittle fracture data for air‐dry aggregates, ranging in equivalent cubic length from 1.19 to 25.275 mm, collected from different soils under the same crop, and similar soils under different crops. Goodness‐of‐fit statistics showed that the modified model fit the data much better than the conventional model. The modified model also produced a more accurate estimate of the spread in aggregate strength values. The modified model has an extra parameter. This parameter is the mass fractal dimension (D) of the solid phase. The theoretical range for D is zero to three. All of the estimates of D were less than three. However, 5% of the estimates were significantly less than zero. We attributed these negative estimates to the absence of any relationship between strength and size (within the range of length scales investigated) in the case of the weakest aggregates. The D increased with increasing clay content. We showed that the D for the solid phase is theoretically identical to the D for the pore‐size distribution. Thus, it may be possible to predict the pore‐size distribution of soil aggregates from brittle fracture data.
Surface Aggregates and Macropore Effects on Chemical Transport in Soil under Rainfall
Authors: Heathman G. C. , Timlin D. J. , Ahuja L. R. , Johnsen K. E. 
Published: July 2010

AbstractSoil surface aggregates and macropores have the potential to greatly influence the transport of surface‐applied agricultural chemicals in soil and to surface and groundwater. We studied the effects of a 1.0‐cm layer of 4.5‐ to 12.5‐mm surface aggregates, a 3‐mm artificial macropore, and their combination on the transport of surface‐applied Br− and Sr2+ tracers (as SrBr2) under simulated rainfall, with the underlying soil initially dry or prewetted to a certain depth (about 7 cm). Air‐dried Kirkland soil (fine, mixed, thermic Udertic Paleustoll), <3.5‐mm size, was packed in duplicate 15‐cm‐diam., 30‐cm‐long, sectionable Plexiglas columns (Cole‐Parmer Instrument Co., Niles, IL) to a bulk density of 1.26 Mg m−3. During the rainfall, surface runoff or macropore flow out of the column bottom was measured and analyzed for Br− and Sr2+. After the rain, the column was sectioned in 1.15‐cm increments to determine soil water, Br−, and Sr2+ content distributions. Without a macropore, the surface aggregates reduced the overall movement of Br− in soil and increased Br− in runoff, the effects being much greater in prewetted columns than in nonprewetted columns. A macropore, by itself, also reduced the movement of the main Br− pulse as it allowed surface solution (runoff) to move down and infiltrate laterally below the main wetting front. Surface aggregates greatly increased Br− content of the macropore flow and of the wetted soil around the macropore below the main wetting front. Aggregates or the initial condition did not change the Sr2+ movement much but increased Sr2+ content of runoff or macropore flow.
Surface Area of Soil Organic Matter Reexamined
Authors: Pennell K. D. , Abriola L. M. , Boyd S. A. 
Published: July 2010

AbstractThe specific surface area of soil organic matter has traditionally been considered to range from 550 × 103 to 800 × 103 m2 kg−1, based on the change in ethylene glycol (EG) retention before and after treatment of soils with H2O2. Recent studies, however, indicate that when N2 is used as the adsorbate, the surface area of soil organic matter is approximately 1 × 103 m2 kg−1. To investigate this large discrepancy, the surface areas of four H2O2‐treated soils were determined by EG retention and the N2‐Brunauer, Emmett, and Teller (BET) method. After exposure of the soils to H2O2, retention of EG decreased, while N2 adsorption increased. The surface area of soil organic matter calculated from the reduction in EG retention ranged from 65 × 103 to 481 × 103 m2 kg−1 and was dependent on the initial organic C content of the soil. In contrast, the N2‐BET data yielded negative estimates of soil organic matter surface area that varied from −13 × 103 to −410 × 103 m2 kg−1. These results demonstrate that techniques based on the removal of organic C fail to provide consistent and reliable values for the surface area of soil organic matter. Due to the complex nature of interactions between soil organic matter and EG, including cation solvation, partitioning, and surface adsorption, it is recommended that EG retention be regarded as an estimate of the total uptake capacity of soils for polar liquids, rather than a measure of surface area.
Effects of Sugarbeet Residues on Soil Redox Potential and Nitrous Oxide Emission
Authors: Flessa H. , Beese F. 
Published: July 2010

AbstractThe influence of the incorporation of fresh sugarbeet (Beta vulgaris L.) plant residues (green weight, 36.5 t ha−1; N content, 113 kg ha−1) on microbial activity, soil redox potential, and N2O emissions was studied using soil microcosms with an automated registration of N2O and CO2 emissions. The experiment was conducted in well‐drained soil columns (water‐filled pore space 63%) and in soil columns with temporary water‐logging (water‐filled pore space continuously increased to 81‐89% for 5 to 7 d). The cumulative CO2 losses during 45 d were equal for the well‐drained and the temporarily water‐logged soils and amounted to ≈30% of the total residue C added. For the well drained soils, the total N2O‐N emission during 45 d was 35‐fold higher than for the control without added plant residues and amounted to 0.37% of the residue‐bound N. Water logging increased the N2O‐N losses to ≈1% of the N added with the sugarbeet residues. The period of increasing N2O release coincided with the starting net mineralization of the residue N and decreasing redox potentials in the vicinity of the plant material. The greater availability of NO−3 combined with enhanced metabolic activity led to the formation of anaerobic microenvironments within and around the plant residues, providing favorable conditions for denitrification. The results emphasize the importance of anoxic zones in the soil caused by respiratory O2 consumption for N2O production in well‐aerated soils and indicate that N2O emission from N‐rich plant residues could be in the same order of magnitude as reported for mineral N fertilizers.
Wheat Responses to Vesicular‐Arbuscular Mycorrhizal Fungal Inoculation of Soils from Eroded Toposequence
Authors: Mohammad M. J. , Pan W. L. , Kennedy A. C. 
Published: July 2010

AbstractLow fertility of eroded soils is often attributed to the loss of topsoil, an important source of nutrients for microorganisms and plants. Vesicular‐arbuscular mycorrhizal (VAM) fungi are known to improve nutrient uptake by plants from infertile soil. The objective of this study was to determine whether wheat (Triticum aestivum L.) responses to VAM fungal inoculation differ among eroded and noneroded soils from the same toposequence. Spring wheat plants were grown under growth chamber conditions in soils collected from three landscape positions of a typical toposequence in eastern Washington, with and without VAM fungal inoculation. Noninoculated soils exhibited 13 to 26% VAM root colonization, while inoculation increased VAM colonization up to 49 to 55% by 5 wk after planting. The VAM fungal inoculation of eroded soils increased shoot dry weight and tiller number, advanced the leaf stage, and increased root length compared with the noninoculated controls. Shoot concentrations of P and Zn were increased by VAM inoculation. In contrast, shoot concentrations of Cu and Mn were unchanged, while Fe was decreased. While VAM fungal inoculation also increased P, Zn, and Cu concentrations in water‐stressed plants, Mn and Fe concentrations decreased. No responses to VAM fungal inoculation were observed in soil from a noneroded toeslope, although VAM colonization was similar to that observed in the eroded soils. These results indicate the potential role of VAM fungi for improving dryland wheat productivity on eroded soils.