bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measuring Instantaneous Solute Flux and Loading with Time Domain Reflectometry
Authors: Hart G. L. , Lowery B. 
Published: July 2010

AbstractTime domain reflectometry (TDR) can be used to measure water content and conservative tracer concentration in soils. An important contribution of TDR for assessing or monitoring water‐soluble contaminant loading in real time under transient flow may be possible because of the ability to acquire rapid, multiplexed measurements of variables necessary for calculating loading — the water flux and resident contaminant concentration. An empirically derived equation relating resident soil Br− concentration (CBr, mg L−1) to apparent soil bulk electrical conductivity (σa, dS m−1) and soil water content (θ, m3 m−3) was established for Sparta sand (mesic, uncoated Typic Quartzipsamment). This equation has the form CBr = ασaγθδ, where α, γ, and δ are empirical constants. Using TDR, we conducted real‐time monitoring of a Br− tracer transported through a repacked Sparta sand soil column at four depths. Under steady‐state and transient‐flow experiemntal conditions and assuming a unit gradient and uniform vertical flow, instantaneous water flux at each monitored depth was estimated from TDR‐acquired θ data and soil hydraulic conductivity. For steady‐state conditions, recovery of Br− ranged from 72% at 15 cm to 133% at 45 cm, while water recovery averaged 92% for all depths. Under transient conditions, Br− recovery ranged from 65% at 15 cm to 121% at 60 cm. Percentages of Br− recovery were congruent across depths between steady‐ and transient‐flow experiments, leading us to conjecture that nonhomogeneous flow patterns and pockets of immobile water had developed within the column.
Clay Particle Differentiation in Alluvial Soils of Southwestern Niger (West Africa)
Authors: Ducloux Jacques , Guero Yadji , Fallavier Paul 
Published: July 2010

AbstractIn arid lands, textural and structural differentiation between the surface soil and deeper horizons is commonly attributed to mechanical transfer of finer material by wind and runoff, but other processes may be influential as well. This study was conducted to determine whether physico‐chemical and mineralogical processes could participate in differentiation. The study area is in Sona (Niger Republic) on alluvial deposits of the Niger River. After a soil survey, soil samples were collected from eight profiles. The particle‐size distribution was determined by the sedimentation and centrifugation methods. The clay fractions were studied by x‐ray diffractometry, chemical analyses, transmission electron microscopy, and energy dispersive x‐ray analysis. The particle images were computed and displayed by an image analysis program. The surface horizons contained fewer particles <0.1 µm than the deeper horizons. However, they were relatively richer in <83‐nm particles and these were corroded on the edges and (001) faces. From a mineralogical viewpoint, detrital kaolinite and smectite clays presented wides x‐ray diffraction lines, indicating smaller, thinner particles with fewer silicate layers than in deeper horizons. Textural differentiation of the surface horizons was enhanced by weathering and dissolution of the smectite and kaolinite particles under acidolitic conditions caused by soil ultradesiccation.
Monitoring for Temporal Changes in Soil Salinity using Electromagnetic Induction Techniques
Authors: Lesch S. M. , Rhoades J. D. , Herrero J. 
Published: July 2010

AbstractElectromagnetic induction surveys are often used in practice to estimate field‐scale soil salinity patterns, and to infer changing salinity conditions with time. We developed a statistical monitoring strategy that uses electromagnetic induction data and repetitive soil sampling to measure changing soil salinity conditions. This monitoring approach requires (i) the estimation of a conditional regression model that is capable of predicting soil salinity from electromagnetic (EM) survey data, and (ii) the acquisition of new soil samples at two or more previously established survey sites, so that formal tests can be made on the differences between the predicted and observed salinity levels. We examined two test statistics in detail: a test for detecting dynamic spatial variation in the new salinity pattern and a test for detecting a change in the field median salinity level with time. We applied this monitoring and testing strategy to two EM survey‐soil salinity data sets collected at multiple points in time from the saline irrigation district of Flumen, Spain, Our results demonstrate that this monitoring approach was successfully able to quantify the temporal changes in the soil salinity patterns occurring within these two fields.
Screening a Selective Chelator Pair for Simultaneous Determination of Iron(II) and Iron(III)
Authors: Wang Tiangen , Peverly John H. 
Published: July 2010

AbstractDirect determination of Fe(II) and Fe(III) is a fundamental technology for environmental Fe chemistry research. The key to accurate determination of Fe(II) and Fe(III) in soil, water, and plant samples is to stabilize Fe oxidation states during Fe extraction and analysis, but the goal has only been partially achieved in previous research. In this research, an approach to stabilizing the original oxidation states of Fe during extraction and analysis was studied. The following sequential procedures were conducted: computer simulation → colorimetric tests → Fe(III) reduction resistance tests → metal interference tests → sensitivity tests → determination of optimal pH for Fe extraction. Results indicated that EDTA (ethylenediamine‐N,N,N′,N′‐tetraacetate, disodium salt) and BPDS (bathophenanthroline disulfonate, disodium salt) were the most effective chelator pair with which to stabilize Fe oxidation states and that they may allow accurate, simultaneous determination of Fe(II) and Fe(III).
Model for Nonreactive Solute Transport in Structured Soils with Continuous Preferential Flow Paths
Authors: Wallach R. , Steenhuis T. S. 
Published: July 2010

AbstractA mathematical model for solute movement in a structured soil with well‐defined and continuous preferential paths was developed. The model divides the soil profile into one mobile and one “stagnant” pore group. For well‐structured soils, the mobile pore group consists of a few well‐connected pores that conduct the nonreactive solute downward very rapidly. Only a narrow matrix layer of stagnant solute along the interface between the two pore groups takes part in solute exchange with the preferential paths. Due to differences in time scales between convection and chemical transfer, the rate of chemical exchange between the preferential path and the active matrix layer for short and moderate times after chemical application is controlled mainly by the preferential flow concentration and, to a lesser extent, by the concentration in the matrix active layer. This is expressed mathematically by multiplying the concentration in the active matrix layer in the mass balance equation by a small dimensionless parameter, ɛ ≪ 1. A regular small perturbations problem is then obtained whose solution is expressed as the sum of the zeroth‐ and first‐order approximations. The simulated breakthrough curve (BTC) is made up of piecewise linear lines and shows a good fit to the measured solute concentration in the outflow of undisturbed columns that have significant preferential flow. Due to the model's simplicity, the transport parameters are estimated directly by fitting the model output to the measured BTCs.
Hydric Conditions and Hydromorphic Properties within a Mollisol Catena in Southeastern Minnesota
Authors: Thompson James A. , Bell Jay C. 
Published: July 2010

AbstractWetlands are characterized by wetland hydrology, hydrophytic vegetation, and hydric soils. The multiparameter approach to wetland identification and delineation requires independent evaluation of all three diagnostic characteristics. Hydric soils can be determined from data collected under saturated and anaerobic soil conditions or by using accepted field indicators. The objectives of this research were to: (i) evaluate the presence of wetland hydrology and hydric soil conditions, (ii) examine associations between observed soil hydrology and soil morphologic properties, and (iii) evaluate current field indicators of hydric soils for their applicability to presumed hydric Mollisols. We used wells, piezometers, and tensiometers to measure saturated conditions, and Pt electrodes to measure anaerobic and reducing conditions for five soils along a hillslope transect from summit to drainageway in southeastern Minnesota. Saturated conditions were observed within 25 cm of the soil surface for all five soils for at least a few days each year between 1992 and 1995, mainly in the early spring and the late fall when soil temperatures at 50 cm were not always >5°C. Only the soil in the drainageway was saturated and anaerobic during the microbial activity season in more than one year. Soil morphology reflects the presence of saturated and anaerobic conditions in the form of thick, black surface horizons. Absence of Fe concentrations and depletions in the upper 30 cm of presumed hydric soils may reflect the absence of Fe‐reducing conditions as a result of saturated conditions when soil temperatures do not facilitate abundant microbial activity.
Improved Transient‐Flow Air Permeameter Design: Dampening the Temperature Effects
Authors: Smith James E. , Robin Michel J. L. , Elrick David E. 
Published: July 2010

AbstractAir permeability of soil is an important parameter for soil aeration and contaminant remediation techniques such as soil vacuum extraction. Transient‐flow air permeameters are inexpensive and portable, but have been shown to be sensitive to small changes in temperature in the air tank induced by the changing air pressure. We have developed a simple and inexpensive modification to the design of transient‐flow air permeameters that improves both the accuracy and precision of the method. The apparatus was modified by the addition into the air tank of a heat capacitor, i.e., fiberglass insulation. The fiberglass insulation filling the tank acts as a uniformly distributed heat source‐sink (capacitor) and thereby dampens the temperature changes. Data from the near‐isothermal air tank design were compared with data from the standard air tank design and data from a method that uses the standard air tank design but measures both pressure and temperature simultaneously. An air permeability value determined with a steadystate flow method was used as a reference. The results show that nonisothermal air tank data can produce large inaccuracies relative to the steady‐state permeability. Applying a temperature correction to the nonisothermal air tank data improved the results considerably, but this method requires additional temperature and pressure measurements of extreme precision. The permeabilities produced with the “nearly isothermal” air tank closely matched the steady‐state values without having to apply any correction to the data. It is therefore recommended that the air tank of transient air permeameters be filled with a heat capacitor, such as fiberglass insulation.
Thermodynamics of Bromide Exchange on Ferrihydrite: Implications for Bromide Transport
Authors: Brooks S. C. , Jardine P. M. , Taylor D. L. 
Published: July 2010

AbstractBecause Br‐ is often assumed to be nonreactive with mineral surfaces, it is frequently employed as a tracer in transport experiments. We investigated the thermodynamics of Br‐‐Cl‐ exchange on the synthetic ferric oxide ferrihydrite [Fe5O7(OH)·4H2O]. Even with 475 times more Cl‐ than Br‐ in solution, sites on the ferrihydrite surface selectively adsorbed Br‐. The implications of these results for Br‐ transport were examined in a series of column flow experiments. During flow through columns packed with ferrihydrite‐coated silica, Br‐ retardation increased from 0.912 to 2.42 as the pH of column experiments decreased from 7.8 to 5. This behavior is consistent with the variable‐charge nature of ferrihydrite, which exhibits increasing positive surface charge below the pH of its zero point of charge (pHzpc ≈ 7.5). These results show that Br‐ can behave as a reactive tracer under certain circumstances, thus leading to erroneous estimates of transport parameters that rely solely on the use of Br‐ as a nonreactive solute.
Retention and Turnover of Corn Residue Carbon in Some Eastern Canadian Soils
Authors: Liang B. C. , Gregorich E. G. , Schnitzer M. , Monreal C. M. , MacKenzie A. F. , Voroney R. P. , Beyaert R. P. 
Published: July 2010

AbstractAgricultural practices determine the level of soil organic C by influencing the amount of residue returned to, and retained by, soil. We conducted field experiments on four soils in Ontario and Quebec to test the hypothesis that short‐term changes in soil organic C and the proportion of corn (Zea mays L.)‐residue C retained in soils are affected by soil texture, fertility, and tillage management. We measured the amount of stover to estimate C input into the soils, and total soil C and 13C natural abundance to determine the soil C derived from corn residues. Only the sandy clay loam exhibited changes in total soil C, related to levels of fertilizer N and quantity of residues returned to the soil. The proportion of soil C derived from corn residues varied from 4 to 19%, depending on the time under continuous corn. Our data indicate a rapid increase in the proportion of cornderived C in the early stage of cropping to corn, but a markedly reduced rate of increase beyond 12 yr. Measured δ13C of archived samples of two soils with different clay contents (71 and 28% clay) but similar residue inputs (11 Mg stover ha‐1 yr‐1) indicated that the rate of increase in the proportion of corn‐derived C was higher in the soil with higher clay content (2.4 vs. 1.9% yr‐1). The results of this study are consistent with the hypothesis that the quantity of crop residue inputs and soil texture greatly influence the retention and turnover of crop residue C.
Parameter Uncertainty Analysis of Common Infiltration Models
Authors: Clausnitzer V. , Hopmans J. W. , Starr J. L. 
Published: July 2010

AbstractWater infiltration is a driving force influencing crop growth, soil erosion, and chemical leaching processes. Knowledge of the relative precision and accuracy of infiltration models is needed for best characterization of the infiltration parameters. The two‐parameter Green‐Ampt and Philip, three‐parameter Horton, Mezencev, Swartzendruber, and Parlange et al., and four‐parameter Barry et al. infiltration models were compared for their precision and accuracy of estimated parameter confidence intervals using simulated infiltration reference data. To account for potential levels of uncertainty, three levels of measurement error were included using a Monte Carlo analysis. Reference data were generated for a clay and a sandy loam soil using an adaptive‐grid finite‐element code. Results show that extending the measurement period provided parameter estimates with higher confidence, a more precise estimate of that confidence, and better defined minima in the objective function. The empirical Horton model resulted in the worst fits due to model bias, which also prevented estimation of parameter uncertainty for this model. The semianalytical Swartzendruber and the physically based Parlange et al. and Barry et al. models provided the best fits. Considering all selected criteria, the Swartzendruber model was a reasonable compromise under the conditions imposed in this study.
Copper(II) Activity in Aged Suspensions of Goethite and Organic Matter
Authors: McBride M. , Martínez C. E. , Sauvé S. 
Published: July 2010

AbstractSuspensions of natural organic matter and iron oxide (FeOOH) were equilibrated with a wide range of concentrations of added Cu2+ (50–5000 mg kg‐1) for as long as 400 d, in order to observe the time‐dependent solubility of the free Cu2+ ion. Adsorption was conducted at two pH ranges (5.0–5.5 and 6.5–7.0) and in the presence and absence of phosphate. The Cu2+ activity, measured by ion‐selective electrode, was one to two orders of magnitude lower for the organic systems at all Cu loadings investigated when the pH was near 5.5, indicating that the organic matter was a more effective adsorbent for Cu2+ than goethite. Longer reaction times generally caused the Cu2+ activities to decrease due to drifting pH and slow reactions. At higher pH, organic matter again resulted in lower Cu2+ activity than the oxide at all Cu loading levels, but the difference was generally less than at low pH. A downward pH trend in the organic system initially at pH 6.5 caused the Cu2+ activity to increase with longer reaction times. Most of the long‐term changes in Cu2+ activity could be attributed to shifting pH, although an aging effect on activity could be discerned. Phosphate added to the oxide or organic matter had little effect on the activity of Cu2+. The EDTA extracted a larger fraction of Cu2+ adsorbed on organic matter than on the oxide, suggesting that strong chelating agents selectively extract metals in quantities not directly related to activity or potential toxicity.
Bacterial Composition in the Rhizosphere of Nodulating and Non‐Nodulating Soybean
Authors: Cattelan A. J. , Hartel P. G. , Fuhrmann J. J. 
Published: July 2010

AbstractLittle is known about the particular species of bacteria that are favored for growth in the rhizosphere. Obtaining this information will facilitate a better understanding of root colonization and competitiveness of rhizosphere organisms. We used fatty acid methyl ester (FAME) analysis to identify bacteria in two different soils and in the rhizosphere of nodulating and non‐nodulating ‘Lee’ soybean [Glycine max (L.) Merr.]. In a light‐room experiment, bacterial isolates from each soil and soybean rhizosphere were selected at 3 (emergence), 6 (V1 stage) and 15 (V2–V3 stage) d after planting (DAP). Of 1131 bacterial isolates examined, 572 (50.6%) were identified. The majority of the identified isolates were Bacillus (324 isolates), Pseudomonas (121 isolates), and Arthrobacter (48 isolates). Of the 49 total bacterial species identified, 29 were detected in only one soil or the other. Numbers of Bacillus spp. were lower in the rhizosphere of nodulating and non‐nodulating soybean than in root‐free soil, and these lower numbers were usually offset by higher numbers of Gram‐negative bacteria, especially Pseudomonas spp. Principal components analysis showed a distinct clustering in each of the two soils. The percentages of isolates identified from each habitat, and the clusters derived from the FAME analysis, showed differences between soybean rhizosphere and root‐free soil and, to a lesser extent, between nodulating and non‐nodulating soybean rhizosphere. These results suggest that each soil offered specific populations of bacteria and from these populations, soybean roots favored growth of certain bacteria. To a lesser extent, this specificity was also apparent between nodulating and non‐nodulating soybean.
Climatic Effects on Soil Organic Phosphorus in the North American Great Plains Identified by Phosphorus‐31 Nuclear Magnetic Resonance
Authors: Sumann M. , Amelung W. , Haumaier L. , Zech W. 
Published: July 2010

AbstractConsidering the influence of the climate is important in studying the dynamics of P in soils. In this study, we investigated the effect of climate on the composition of organic P in uncultivated soils of the North American prairie. We present 31P nuclear magnetic resonance (NMR) spectra of alkaline extracts of bulk samples and clay fractions along gradients of mean annual temperature (MAT) and mean annual precipitation (MAP) across the Great Plains. Orthophosphate monoesters (monoester‐P) accounted for 32 to 71% and orthophosphate diesters (diester‐P) for 7 to 40% of the total signal intensity. Compared with bulk soils, diester‐P structures were enriched in the clay fractions (P < 0.01). In contrast, monoester‐P structures were enriched in particle‐size classes coarser than clay (P < 0.05). As MAT increased, the proportion of diester‐P increased, whereas that of monoester‐P decreased. These statistically significant correlations were more pronounced for both diester‐P (r = 0.91) and monoester‐P (r = −0.87) in the clay fractions than in the bulk soils. As MAP increased, the proportions of diester‐P also increased at the expense of monoester‐P. This correlation was more significant for bulk soils (r = 0.70 for diester‐P and r = −0.47 for monoester‐P) than for the clay fractions. We believe that temperature and precipitation strongly influence the organic P in North American grassland soils through their influence on microbial activity and plant production.
Cadmium Fixation in Soils Measured by Isotopic Dilution
Authors: Smolders E. , Brans K. , Földi A. , Merckx R. 
Published: July 2010

AbstractThere is conflicting evidence on the effect of time of contact between soil and Cd on Cd availability to plants. If Cd can be fixed in soil by aging, higher soil contamination may be tolerated. Fixation of Cd by soil can be studied by adding small quantities of 109Cd to the indigenous soil Cd. The ratio of 109Cd to indigenous Cd in soil extracts or in plants gives information on the lability of Cd in soil. This isotope exchange technique was used to measure the labile and fixed Cd fractions in 10 Belgian agricultural soils (Soils A‐I) with both background and elevated Cd content (0.33–6.5 mg Cd kg‐1). The isotopically exchangeable Cd pool (E value) was measured after equilibrating 109Cd spiked soil suspensions in CaCl2 0.01 M for 7 d. The %E values (the E value relative to aqua regia soluble Cd) ranged from 62 to 90% in the eight soils where %E values could be detected. The plant labile Cd pool, relative to aqua regia soluble Cd (%L value) was measured from the specific activities in wheat (Triticum aestivum L.) seedlings grown for 16 to 21 d on soils spiked with 109Cd. The Cd %L value varied from 55 to 109% (mean: 82%) with five soils having a significant (P < 0.05) fixed Cd fraction. Varying the soil incubation procedure after soil spiking and before plant growth marginally affected the specific activity of Cd in plants. The %L values always exceeded the respective %E value between 1.05‐ and 1.4‐fold. It is concluded that Cd fixation, where found, is not very pronounced.
Influence of Available Nitrogen and Rice Genotype on Associative Dinitrogen Fixation
Authors: Malarvizhi P. , Ladha J. K. 
Published: July 2010

AbstractRice (Oryza sativa L.) genotypes with a high ability to support biological N2 fixation are of interest because they would enhance N gains in the rice‐soil system without changing existing cultural practices. Pot experiments were conducted in a greenhouse during the 1994 wet season to determine the amount of N2 derived from the atmosphere (Ndfa) by 10 rice genotypes grown in three soils with varying levels of initial soil‐NH+4‐N. Enriched 15N and natural abundance δ15N dilution methods were employed. Flooded soils were puddled with and without 99.5 atom 15N%‐labeled urea to minimize spatial variation of the isotope. The integrated 15N enrichment of plant available N, calculated using a model that accounts for temporal changes in the isotopic composition, was used as a reference to estimate genotypic differences in Ndfa. The 15N enrichment of soil available N declined exponentially and was half the original level at 122 d. The δ15N values correlated with atom 15N% excess of enriched 15N for the rice genotypes grown in two out of three soils. Percentage Ndfa for the genotypes across three soils ranged from 4.2 to 32.2 when calculated using as a reference plant, and from 10.8 to 35.9 when calculated using 15N enrichment of soil available N as a reference. Genotypic differences were significant and more pronounced at low soil‐NH+4‐N (11 mg kg‐1) than at higher soil‐NH+4‐N (79 and 92 mg kg‐1); they ranged from 14.9 to 35.9% at low N and from 10.8 to 23.6% at high N. Some genotypes consistently gave either high or low Ndfa. Because of the low levels and narrow range of genetic differences in associative N2 fixation, the potential for its improvement through breeding appears to be limited.