bluuebunny/crossref_metadata_2025 huggingface dataset:
Variability of Depth to Tosca in Udolls and Soil Classification, Buenos Aires Province, Argentina
Authors: Pazos M. Susana , Mestelan Silvia A.
Published: July 2010

In the Buenos Aires province, a layer of caliche ortoscaunderlies a large area of Udolls. Its presence under a humid climate is unusual, making it difficult to classify these soils withSoil Taxonomy(ST), both in the past and after recent changes. The aim of this paper is to characterize the variability of the tosca layer, particularly in depth, to improve the classification of these Udolls. Depth variability was analyzed from available information and detailed depth variability (DDV) was studied in two sample areas: Balcarce and Azul. In addition, in Azul the DDV of the tosca was related to elevation of the land surface and pH of the Bt/Btn horizons. The three dimensional diagrams show a greater variability in depth to tosca in Balcarce, associated with the proximity to the Sierras. In Azul, the pH of the Bt/Btn horizons is related to elevation but has no relationship with depth to tosca. In Balcarce, the index sand/coarse silt was calculated for four soil pedons and the underlying tosca. The differences in sand/coarse silt ratio between the present soil and the tosca layer are nonconclusive proof of lithological discontinuities for every pedon. Consequently both concepts of chronological and lithological discontinuity apply to characterize the present soil/tosca boundary. To homogenize the classification criteria, the subgroups defined in the Natrudolls, allow a better handling of the lateral transitions between pedons. Consequently, we suggest defining the Petrocalcic subgroup in the Argiudolls.
Predicting the Dielectric Constant–Water Content Relationship Using Artificial Neural Networks
Authors: Persson Magnus , Sivakumar Bellie , Berndtsson Ronny , Jacobsen Ole H. , Schjønning Per
Published: July 2010

Accurate measurements of soil water content (θ) are important in various applications in hydrology and soil science. The time domain reflectometry (TDR) technique has been widely used for θ measurements during the last two decades. The TDR utilizes the apparent dielectric constant (Ka) for estimations of θ. The Ka–θ relationship has been described using both empirical and physical models. Universal calibration equations that fit a wide range of different soil types have been developed. However, to achieve high accuracy, a soil‐specific calibration needs to be conducted. In the present study, we use an artificial neural network (ANN) to predict the Ka–θ relationship using soil physical parameters for ten different soil types. The parameters that give the most significant reduction in the root mean square error (RMSE) are bulk density, clay content, and organic matter content. The Ka–θ relationship for each soil type is predicted using the other nine for calibration. It is shown that ANN predictions are as good as a soil specific calibration with comparable coefficient of determination and RMSE. Thus, by using ANN, highly accurate data can be obtained without need for elaborate soil specific calibration experiments.
Dynamics of Soil Water and Temperature in Aboveground Sand Cultures Used for Screening Plant Salt Tolerance
Authors: Wang D.
Published: July 2010

There are increasing concerns about the feasibility of applying plant salt tolerance information obtained from artificial sand cultures in field soils. A main question concerns the similarity of growth conditions between the sand cultures and the field. This study was conducted to determine the dynamic variations of soil water and temperature in sand cultures and to compare them with the same parameters observed in a field soil. Results indicated that sand cultures filled with a reasonably well graded river sand exhibited values of minimum and maximum soil water content similar to those in the field. Soil volumetric heat capacity and thermal conductivity of the river sand were also comparable with values found in the field soil. A poorly graded silica sand, however, was found not suitable to reproduce soil water and temperature regimes that commonly occur in the field. If other environmental factors for plant growth can be simulated to match those found in the field, results of plant salt tolerance obtained from the sand cultures can be used to provide guidance for plant selection under field conditions. The approach of using particle‐size analysis information to derive the hydraulic and thermal properties should be readily adoptable by interested researchers in selecting the most appropriate grading of sand culture materials.
Determination of hydraulic behavior of hillsides with a hillslope infiltrometer
Authors: Mendoza Guillermo , Steenhuis Tammo S.
Published: July 2010

Watersheds, in many parts of the world, consist of sloping soils with a dense subsoil at shallow depth. Very few measurement techniques exist for realistically determining hydraulic properties in situ on these hillside soils. A hillslope infiltrometer, open at the bottom, top, and downhill sides, was developed that can measure the vertical saturated conductivity of the horizon sequence and lateral hydraulic conductivity of the horizon most conductive to water. The infiltrometer was tested on the steeply sloping soils in Honduras. Increasing rainfall intensities were applied and lateral flow rate was measured in several troughs at the downslope end of the hillslope infiltrometer. Vertical infiltration rates for the horizon sequence and lateral conductivity were calculated at each rainfall rate after steady state conditions were established. The hillslope infiltrometer proved useful in the characterization of subsurface flow on the steep slopes in Honduras.
Electrochemical Water Splitting at Bipolar Interfaces of Ion Exchange Membranes and Soils
Authors: Desharnais Brian M. , Lewis Barbara Ann G.
Published: July 2010

Under the influence of a direct current, the dissociation rate of water in contact with bipolar ion exchange membranes (BPMs) is 106 to 107 times faster than in free solution. This phenomenon, termed accelerated water splitting, is well known in industry where BPMs are designed for electrosynthesis of acids and bases. In this work, it is hypothesized that (i) accelerated water splitting can also take place at the bipolar interface between ion exchange membranes (IEMs) and the ion exchange surfaces of soils, and (ii) electroosmosis plays a key role. If the IEM has an electrostatic charge opposite in sign to the predominant charge on the soil colloidal particles, the interface is, in effect, bipolar. If an external electric field is then applied, conditions can give rise to accelerated water splitting. Laboratory experiments performed on various mixtures of Ottawa sand, bentonite, talc, and anion exchange resin indicate that accelerated water splitting occurs when the free pore solution in the low permeable soil moves away from the bipolar interfaces due to electroosmosis, thus causing an unsaturated zone at these interfaces. Accelerated water splitting then initiates at these interfaces since there are not enough counterions in contact with the IEMs to maintain an ionic current. Very little cation exchange capacity (CEC), anion exchange capacity (AEC), or clay is needed for water splitting to occur at a bipolar IEM and soil interface.
Changes in Microbial Nitrogen Across a 100‐Year Chronosequence of Upland Hardwood Forests
Authors: Idol Travis W. , Pope Phillip E. , Ponder Felix
Published: July 2010

Soil microorganisms mediate many of the major processes involved in soil N cycling. Also, they are strong competitors with plants for available soil N. Thus, changes in microbial N because of forest harvesting may have significant impacts on N availability and overall forest N cycling. A chronosequence of upland hardwood forest stands in southern Indiana, USA, ranging in age from 1 to 100 yr since last harvest, was chosen to evaluate changes in microbial N with stand development. Microbial N was measured in the A and B soil horizons during different seasons from 1997 to 1999. Peak levels of microbial N were highest in the youngest forest stand (1 to 3 yr old), but seasonal variability was greater than differences by stand age. Microbial N concentration (mg kg−1) varied significantly by season and soil horizon within stands ranging in age from 1 to 30 yr since harvest, but not in the mature, 80‐ to 100‐yr‐old stand. There were few significant differences in microbial N content (kg ha−1). Harvesting did not appear to have long‐term effects on microbial N, but spatial variability in microbial N appeared to be greater in the younger forest stands.
Horizontal Infiltration Method for Determining Brooks‐Corey Model Parameters
Authors: Wang Quanjiu , Horton Robert , Shao Mingan
Published: July 2010

Mathematical models have been widely used to predict water and solute transfer in soil and ground water. The accuracy of water flow and solute transport predictions obtained with these models depends to a large extent on the reliability and accuracy of the soil hydraulic properties. The main soil hydraulic properties are the water retention curve and hydraulic conductivity function. Most methods for determination of soil hydraulic properties that include flow measurements require elaborate instrumentation and a substantial amount of time. It is important to develop simple flow‐based experimental methods to estimate soil hydraulic properties. In this paper, an analytical method was developed to determine Brooks‐Corey model parameters. The problem of water absorption into a horizontal soil column was solved, and the relationships of cumulative infiltration, infiltration rate, and infiltration time with distance to the wetting front were obtained. Based upon these relationships, a method to estimate soil hydraulic properties was developed. Numerical simulations of water flow into horizontal soil columns were used to evaluate the analytical method. The analytical model was fitted to the numerical infiltration results with coefficients of determination ranging from 0.97 to 0.99. The results based upon the numerical data indicate that the estimated hydraulic properties agreed closely with the given values. The analytical method provides a simple and quick transient water flow approach to estimate soil hydraulic properties.
Alachlor Transport during Transient Water Flow in Unsaturated Soils
Authors: Selim H. M. , Zhou L. , Xue S. K.
Published: July 2010

In most herbicide mobility investigations, laboratory experiments are often restricted to the traditional miscible displacement methods where water saturated conditions and constant flux are maintained. In this study, we examine the mobility of alachlor herbicide under soil‐water unsaturated and transient conditions. Gigger (a Typic Fragiudalf) surface soil samples were collected from long‐term soybean management system under no‐till with wheat (NTW, Triticum aestivum L.), conventional tillage with wheat (CTW), and conventional tillage with hairy vetch (CTV, Vicia villosa Roth). Air‐dried soil was packed in columns which were horizontally maintained. The inflow end was connected to a water supply which was maintained at zero head. The input pulse was made up of tritium and 14C‐alachlor solution. During horizontal infiltration, the advance of the wetting front and volume infiltrated into the soil was monitored over time. When the wetting front reached 25 cm, the column was dismantled and the soil moisture and alachlor concentrations in each 1‐cm section quantified. All alachlor distribution profiles appeared retarded and did not show sharp solute fronts. Rather the concentration distributions were of moderately shaped fronts reaching some 10 cm from the source and followed by a gradual decrease up to 20 cm. Alachlor movement was modeled based on transient flow in unsaturated soils. Such results were compared with equilibrium type models of the linear and nonlinear type under steady and transient flow conditions. Parameters needed were soil water‐diffusivity, solute‐dispersion coefficients and retention parameters for alachlor for individual soils. Independently derived parameters provided a good description of the BTC under unsaturated conditions.
Vertic Soils in Alluvion‐Reclaimed Areas, Volturno River Plain, Italy
Authors: Ermice A. , Murolo M. , Pugliano M. L. , Buondonno C.
Published: July 2010

Reclamation activities in alluvial depressions in Volturno River Plain resulted in the occurrence of soils with vertic characteristics and properties. We studied the genesis and properties of soils in alluvial areas known to be reclaimed by the alluvion system about 100 yr ago, and compared these soils with natural, adjacent alluvial soils. Soils in the reclaimed areas were characterized by cracks, slickensides, and high clay contents. Soils were satisfactorily classified within the existing Vertisol order of U. S. soil taxonomy. Soils with similar vertic morphology and properties also occurred in nonreclaimed adjacent alluvial areas, where they were associated with coarser textured Entisols. Since no important morphological evidence for the reclamation activity was identified in the soils in the reclaimed areas, the anthropogenic origin of such soils only emerged from historical records. The introduction of relational properties such as historical records is currently suggested to interpret and classify soils of various proposed taxonomic classes at different categorical levels. Therefore we discuss some critical aspects of the use of the historical records for classifying the soils in the reclaimed areas into genetic and technical soil categories that are currently being defined by the International Committee on Anthropogenic Soils (ICOMANTH).
Accelerated Soil Erosion of a Mississippian Mound at Cahokia Site in Illinois
Authors: Olson K. R. , Jones R. L. , Gennadiyev A. N. , Chernyanskii S. , Woods W. I. , Lang J. M.
Published: July 2010

About 1000 years ago prehistoric Indians built over 120 earthen mounds, including Mound 57, at the Cahokia site near Collinsville, IL. Loamy and clayey soil materials were apparently placed on the mound before 1100 CE by people of the Middle Mississippian culture. The objectives of this study were: (i) to determine the extent of soil formation during the past 850 yr, (ii) to determine the time period, extent, and direction of tillage, and (iii) to determine the erosion phase of soil on a mound and the extent of soil loss from erosion. The high amount and regular decrease in organic C with depth in 16 soil profiles suggested that since 1925 no tillage and little soil erosion had occurred on the sideslopes of M57. In the sideslope and footslope positions on the north, south, and east transects, the fine‐loamy soil materials with fly ash were thickest suggesting that any tillage translocation and soil erosion must have occurred after 1864. This resulted in the current elongated south to north axis which was parallel to the tract boundary and the direction of plowing. The amounts and distribution of the fly ash in the upper 20 cm indicated that cultivation between 1864 and 1925 may have mixed some fly ash into the 20‐cm deep tillage zone. Fly‐ash content of soil layers to the 40‐cm depth on the footslope was primarily a result of fly ash being deposited after the 1850s on the original soil surface and the subsequent deposition of sediment rich in fly ash.
Aggregate‐Protected Carbon in No‐tillage and Conventional Tillage Agroecosystems Using Carbon‐14 Labeled Plant Residue
Authors: Bossuyt Heleen , Six Johan , Hendrix Paul F.
Published: July 2010

No‐tillage (NT) management can result in higher soil organic matter (SOM) levels than conventional tillage (CT) practices. The objective was to investigate the underlying mechanisms in which C is protected under NT management, using 14C‐labeled plant residue as a tracer. Samples were collected from the Horseshoe Bend Research area in Athens, GA. Aggregate‐size distribution, total C, and 14C were measured together with different pools of aggregate‐associated C and 14C from 21‐d laboratory incubations of intact and crushed macro and microaggregates. Compared with CT, NT practices resulted in higher total C and 14C in all aggregate‐size classes of the 0‐ to 2.5‐ and 2.5‐ to 5‐cm layers, except for 14C in the <53‐ and 250‐ to 2000‐μm aggregate‐size classes at the 2.5‐ to 5‐cm layer. At the 5‐ to 15‐cm depth, more 14C was found in the >2000‐μm aggregate‐size class under NT than CT. In contrast, more 14C was found in the 53‐ to 250‐μm and <53‐μm size classes under CT than NT. Unprotected C and 14C pools, microaggregate‐protected and micro within macroaggregate‐protected C and 14C pools were significantly higher for the 0‐ to 2.5‐ and 2.5‐ to 5‐cm layers under NT than CT. Carbon‐14 pools were generally higher in CT than in NT at the 5‐ to 15‐cm depth, while total C did not differ between tillage treatments at this depth. The results indicate that (i) more young C (14C) is accumulated in the subsurface soil of CT than NT, but this C is not stabilized in the long term, and (ii) short‐ and long‐term stabilization of C is higher in the soil surface layers under NT compared with CT. This C stabilization occurs mainly at the microaggregate level.
Characterization of Soil Algal Bioavailable Phosphorus in the Minnesota River Basin
Authors: Fang F. , Brezonik P. L. , Mulla D. J. , Hatch L. K.
Published: July 2010

Soil algal bioavailable P (ABP) is the P fraction that contributes most directly to eutrophication in freshwaters affected by agricultural nonpoint‐source pollution. There are uncertainties regarding the algal bioavailability of P sorbed to calcareous glacial till soils in the upper Midwest. The ABP of soil samples with a broad range of pH and calcium carbonate content from six sites across the Minnesota River Basin (MRB) was measured by algal bioassay, and relationships with various soil physical and chemical properties were studied. For soils of the MRB, a major agricultural watershed in the upper Midwest, ABP was significantly correlated (p < 0.001) with Bray P, Mehlich‐III P, NaOH P, Oxalate P, and Fe‐paper P. Among them, Fe‐paper P approximated ABP best, particularly for calcareous soils. For acidic soils, amorphous Fe and Al apparently were the primary P retention agents in soil particles. Soil sorption data were well described by the linearized Langmuir sorption model. Although the P sorption maximum (Γ∞) could not be predicted from basic soil physical and chemical properties, the sorption energy constant (b) was highly correlated with soil pH, clay content, and organic matter (OM) content. A P saturation index (PSIs) that uses sorptivity (Γ∞ × b) as the measure of sorption capacity gave the best estimate of soil ABP among the predictors used in this study. Phosphorus saturated index itself can be approximated by the widely available Bray‐P value for soils in the MRB.
Sorption of Pyridine to Suspended Soil Particles Studied by Deuterium Nuclear Magnetic Resonance
Authors: Zhu Dongqiang , Herbert Bruce E. , Schlautman Mark A.
Published: July 2010

Spin‐lattice relaxation times (T1) and chemical shifts (δ) of perdeuterated pyridine (α, β, γ deuterium of d5–pyridine) in aqueous solution (e.g., water, 0.001 M benzoic acid and phenol) are found to decrease with increasing pH values. This is because the concentration distribution of the two pyridine species, protonated and unprotonated, varies with solution pH. The T1 values of γ are lower than α and β deuterium in water and methanol compared with n‐hexane, indicating more anisotropic molecular movements of pyridine resulting from interactions between amine and the polar solvent. Spin‐spin relaxation times (T2) and δ of d5–pyridine in aqueous suspensions of water‐dispersible clay (WDC) soil components are highly pH dependent. The lowest T2 and the most downfield‐shifted δ compared with aqueous solution show that the strongest sorption occurs at the weak acidic condition (pH 6). The downfield shifts of δ observed in WDC suspensions are directly caused by the increased mole ratio of protonated pyridine through sorption. However, no significant changes in δ are observed for organic free minerals (H2O2–treated WDCs and a standard clay mineral) compared with aqueous solution, indicating interactions with mineral surfaces are negligible in pyridine sorption. A sorption mechanism of cation exchange between protonated pyridine and charged sites of soil organic matter (SOM) is inferred based on the measured δ values.
Sorption‐Desorption of Lead (II) and Mercury (II) by Model Associations of Soil Colloids
Authors: Cruz-Guzmán M. , Celis R. , Hermosín M. C. , Leone P. , Nègre M. , Cornejo J.
Published: July 2010

Sorption by soil colloids largely determines the bioavailability of heavy metals and their movement in soil and aquatic environments. Due to soil constituents' interactions, the sorption behavior of natural soil colloids may not correspond to the simple sum of their individual constituents. In this work, sorption of Pb(II) and Hg(II) ions by binary and ternary model particles containing Wyoming montmorillonite (SW), poorly crystallized ferrihydrite (Ferrih), and soil humic acid (HA) was investigated and the results obtained were compared with the sorption behavior of the individual constituents. For single sorbents, Pb(II) sorption was high on HA, moderate on SW and zero on Ferrih, whereas Hg(II) sorption decreased in the order: HA ≫ Ferrih > SW. Ferrihydrite coatings on SW had little effect on Pb(II) and Hg(II) sorption by the clay. Humic acid coatings on SW significantly enhanced sorption of both heavy metals, whereas, unexpectedly, HA coatings on Ferrih did not enhance heavy metal sorption. This last result was attributed to blockage of the functional groups of HA responsible for heavy metal sorption (such as carboxylic groups) as a result of their interaction with the Ferrih surface. A similar behavior was observed for Pb(II) in ternary particles containing HA. Sorption by the model associations was highly reversible. The results of this study confirmed that the sorptive behavior of colloidal particles for heavy metals is not the simple sum of the contributions of the single constituents, indicating the usefulness of considering polyphasic model sorbents to achieve a more realistic interpretation of the sorption process in soil.
Simulating Infertile Acid Soils with Nutrient Solutions
Authors: Wenzl Peter , Mancilla Lida I. , Mayer Jorge E. , Albert Roland , Rao Idupulapati M.
Published: July 2010

Aluminum toxicity limits plant growth in acid soils. Because of their advanced state of weathering, acid soils of the tropics also tend to be deficient in nutrients. A realistic assessment of plant adaptation to these soils would therefore require Al‐toxic conditions under which growth is simultaneously limited by nutrient deficiency. We developed and tested a nutrient solution for this purpose. We analyzed soil solutions of two Oxisols from the Colombian savannas. Nutrient concentrations were extremely low (ionic strength <1.7 mM). Nitrification during incubation of soil samples acidified soil solutions, resulting in a release of cations from the exchange phase, an increase in the activity of Al3+, and a decrease in that of H2PO−4 Predicted ion activities were taken as guidelines for designing a nutrient solution that simulates these soil solutions. Growth of well‐adapted signalgrass (Brachiaria decumbens cv. Basilisk) and less‐adapted ruzigrass (Brachiaria ruziziensis cv. Common) in this solution mirrored the interspecific difference in forage yield that had previously been observed in a field close to where one of the soils originated. This suggests that the designed solution may be a realistic approximation to chemical soil properties that limit forage productivity. The different growth response of the two grasses was apparently due to increased Al sensitivity of less‐adapted ruzigrass under low nutrient supply; neither Al toxicity nor nutrient deficiency alone resulted in a comparable growth difference between the grasses. These data highlight the importance of taking into account interactions among stress factors that occur in parallel in infertile acid soils.
Detecting Change in Forest Floor Carbon
Authors: Yanai Ruth D. , Stehman Stephen V. , Arthur Mary A. , Prescott Cindy E. , Friedland Andrew J. , Siccama Thomas G. , Binkley Dan
Published: July 2010

Changes over time in forest soils are important to global C balance and to local ecosystem function. Detecting change in C storage in the forest floor is hampered by high variability and the use of study designs that are not adequate to statistically detect change. Using estimates of variability from previous forest floor studies, mostly conducted in the northern USA and Canada, we conducted statistical power analyses to assess the ability of such studies to detect various magnitudes of change in forest floor C. The studies we surveyed were unable to detect statistically significant changes in forest floor C or mass smaller than 15 to 20%. Studies that remeasure plots or sites (i.e., paired designs) have greater statistical power to detect changes than those in which experimental units are independently located for the two sampling dates. The causal mechanisms of forest floor change influence the magnitude of the change, and accordingly our ability to detect such changes. The direct effects of climate change may be too small to be detectable by current designs, but larger changes in forest floor mass resulting from forest management, changes in tree species, changes in fire regime, or the introduction of earthworms are more likely to be detectable. With paired resampling and more efficient allocation of sampling effort, it should be possible for future studies to detect smaller changes.
Extending the Applicability of Laser‐Induced Breakdown Spectroscopy for Total Soil Carbon Measurement
Authors: Ebinger Michael H. , Norfleet M. Lee , Breshears David D. , Cremers David A. , Ferris Monty J. , Unkefer Pat J. , Lamb Megan S. , Goddard Kelly L. , Meyer Clifton W.
Published: July 2010

Soils are the major pool of terrestrial C globally. Estimating inventories and detecting changes in the soil C pool have remained elusive, largely because the spatial distribution of soil C varies considerably. New approaches are needed that enable more rapid, cost‐effective, and sensitive measurements of soil C and that reduce uncertainty in estimates of C pools and changes in those pools. In this note we extend the application of a new method of total soil C measurement: laser‐induced breakdown spectroscopy (LIBS). Carbon analysis using LIBS provides data in seconds from soils with little preparation, whereas conventional methods such as dry combustion require lengthy sample preparation and longer analysis times. Laser‐induced breakdown spectroscopy instruments, unlike conventional instruments, can be used while in the field. This promising new method, however, has potential drawbacks, namely interference with Fe at approximately 248 nm. Here we report results of using a different C line at 193 nm to solve the interference problem. We also use a two‐element standardization factor to demonstrate that the 193‐nm line is nearly as sensitive to C concentration as the C line at 247.8 nm, and that calibration curves can be readily replicated. Overall these results indicate that LIBS is a very promising method to estimate soil C pools and dynamics.
Time Dependence of Chlorobenzene Sorption/Desorption by Soils
Authors: Sharer Michael , Park Jeong-Hun , Voice Thomas C. , Boyd Stephen A.
Published: July 2010

Soil contact time with organic chemicals (aging) has been found to cause increased sorption coefficients and reduced isotherm linearity as well as increased environmental sequestration and persistence. In this study, the sorption/desorption behavior of chlorobenzene (CB) on four soils was evaluated after aging periods of 24 h and 14 mo. The four soils ranged in organic matter content from 0.69 to 13.4%. Sorption isotherms were performed after each aging period to observe changes in CB uptake. Desorption kinetic profiles were generated after each aging period to observe changes in CB release from soil, with desorption followed for a period of four months. These data demonstrated no increase in CB uptake by three soils between the 24‐h and 14‐mo sorption periods and only a slight increase (∼22%) by the fourth soil. The sorption isotherms were linear (r2 > 0.99) and did not display increased non‐linearity with aging. A three‐site desorption model was used to evaluate desorption parameters for both aging periods. Sorption/desorption was not fully reversible; non‐desorbable fractions (fnd) were observable after only 24 h of aging, and ranged from 0.17 to 0.27. Non‐desorbable fraction increased for all four soils with longer aging time; after 14 mo aging fnd ranged between 0.28 and 0.45. The CB sorption data were difficult to reconcile with current dual mode models that have been proposed to account for the sorption of organic contaminants and pesticides by soil organic matter.
Phenotypic and Genetic Diversity of Rhizobia Isolated from Nodules of Clover Grown in a Zinc and Cadmium Contaminated Soil
Authors: Delorme T. A. , Gagliardi J. V. , Angle J. S. , van Berkum P. , Chaney R. L.
Published: July 2010

Metal contamination can affect the diversity of microbes living in soil. We compared phenotypic and genetic characteristics of Rhizobium leguminosarum bv trifolii isolated from clovers (Trifolium pratense) found at a metal contaminated and a control site, or isolated from nodules of clovers used in most probable number (MPN) determinations of rhizobia in the metal contaminated soil. Analysis of variations in genetic patterns using BOX‐PCR was used for genetic characterization. Zinc and Cd tolerance of each isolate was also determined. Rhizobia isolated from the control soil compared with the metal contaminated soil differed both genetically and phenotypically. Genetic diversity, measured by AMOVA, was high and not related to the presence or the absence of high metal concentrations. Isolates originating from the metal contaminated soil were more tolerant to both Cd (minimal inhibitory concentration [MIC50] = 2.5 μM) and Zn (MIC50 = 92.9 μM) compared with those observed for isolates of control soil (Cd MIC50 = 2.0 μM and Zn MIC50 = 41.9 μM). Rhizobia originating from the metal contaminated soil expressed a higher number of metal phenotypes (9) compared with isolates of control soils (6). Slow rates of metal accumulation over the years favored an adaptation of the rhizobia to the metal rather than elimination of metal sensitive organisms and the selection of a few preexisting metal tolerant organisms.
Experimental Acidification Causes Soil Base‐Cation Depletion at the Bear Brook Watershed in Maine
Authors: Fernandez Ivan J. , Rustad Lindsey E. , Norton Stephen A. , Kahl Jeffrey S. , Cosby Bernard J.
Published: July 2010

There is concern that changes in atmospheric deposition, climate, or land use have altered the biogeochemistry of forests causing soil base‐cation depletion, particularly Ca. The Bear Brook Watershed in Maine (BBWM) is a paired watershed experiment with one watershed subjected to elevated N and S deposition through bimonthly additions of (NH4)2SO4 Quantitative soil excavations in 1998 measured soil pools of exchangeable base cations 9 yr after treatments began. Stream sampling at the weirs on a weekly and event basis, and weekly precipitation sampling, were used for input‐output estimates. The treated watershed had lower concentrations of exchangeable Ca and Mg in all horizons, with evidence for the greater depletion in the O horizon compared to underlying mineral soils, and in softwoods compared to hardwoods. This difference between watersheds is interpreted to be treatment‐induced base‐cation depletion, which was reinforced by model simulations. The difference between watersheds was 66 and 27 kg ha−1 of exchangeable Ca and Mg, respectively, after accounting for soil mass differences between watersheds. This was comparable with the total cumulative excess stream Ca and Mg export in West Bear after 9 yr of treatment of 55 and 11 kg ha−1, respectively. Model simulations of watershed response to treatments predicted excess soil exchangeable Ca and Mg losses in the treated watershed of 47 and 9 kg ha−1, respectively. These results indicate that the response to a step‐increase in N and S deposition during the first decade of treatments in this experimental forested watershed was to invoke cation‐exchange buffering, resulting in a net decline in soil exchangeable base cations.
Origin of Talc, Iron Phosphates, and Other Minerals in Biosolids
Authors: Jaynes W. F. , Zartman R. E.
Published: July 2010

Biosolids (i.e., sewage sludge) contain as much inorganic as organic materials. The inorganic materials include local soils, sediments, and other materials washed down residential, industrial, and storm drains. In this study, the chemistry and mineralogy of the inorganic materials in New York, NY (NYC) biosolids applied to soil surfaces in western Texas from 1992 to 1999 were examined. Inorganic residues were 44 to 77% of whole biosolid weights after oxidation of the organics with H2O2Inorganic residues consisted largely of silt‐ and clay‐size particles with smaller amounts of fine and very fine sand. Selective dissolution and chemical analyses of the residues indicated >20% Fe phosphates, formed during anaerobic digestion, that contained Al, As, Cr, Cu, Hg, and Zn. X‐ray diffraction, selective dissolution, and surface area analyses showed that the Fe phosphates were poorly crystalline. The mostly quartz and feldspar sands also contained glass shards, textile fibers, and zircon grains. New York City area biosolids contained quartz, feldspars, kaolinite, mica, and expandable layer silicates. Electron microscopy and x‐ray spectra of the clay fractions revealed aggregates of layer silicates and Fe phosphates containing Al, Ca, and Ti. Pigment TiO2, commonly used in foods and cosmetics, contributed Ti to the layer silicate aggregates. Talc derived from cosmetic products was identified in silt and clay fractions by x‐ray diffraction and electron microscopy. Less talc occurred in the 1999 and 1997 biosolids relative to 1992, 1993, and 1994 biosolids suggesting reduced use of talc products. Nationally, cosmetic talc use decreased during that time, probably due to health concerns.
The Relationship between Carbon Input, Aggregation, and Soil Organic Carbon Stabilization in Sustainable Cropping Systems
Authors: Kong Angela Y. Y. , Six Johan , Bryant Dennis C. , Denison R. Ford , van Kessel Chris
Published: July 2010

One of our current challenges is to quantify the mechanisms, capacity, and longevity of C stabilization in agricultural lands. The objectives of this study were to evaluate the long‐term (10 yr) role of C input in soil organic carbon (SOC) sequestration and to identify underlying mechanisms of C stabilization in soils. Carbon input and SOC sequestration, as governed by crop management strategies, were assessed across 10 Mediterranean cropping systems. Empirically derived relationships between yield and aboveground plus belowground crop biomass as well as estimates of C contributions from crop residues and manure amendments were used to quantify cumulative C inputs into each cropping system. Soil samples were separated into four aggregate size classes (>2000, 250–2000, 53–250, and <53 μm) and into three soil organic matter (SOM) fractions within the large (>2000 μm) and small (250–2000 μm) macroaggregates. Aggregate stability increased linearly with both C input (r2 = 0.75, p = 0.001) and SOC (r2 = 0.63, p = 0.006). Across the 10 cropping systems, annual soil C sequestration rates ranged from −0.35 to 0.56 Mg C ha−1 yr−1 We found a strong linear relationship (r2 = 0.70, p = 0.003) between SOC sequestration and cumulative C input, with a residue‐C conversion to SOC rate of 7.6%. This linear relationship suggests that these soils have not reached an upper limit of C sequestration (i.e., not C saturated). In addition, C shifted from the <53‐μm fraction in low C input systems to the large and small macroaggregates in high C input systems. A majority of the accumulation of SOC due to additional C inputs was preferentially sequestered in the microaggregates‐within‐small‐macroaggregates (mM). Hence, the mM fraction is an ideal indicator for C sequestration potential in sustainable agroecosystems.
Sorption and Desorption of Ammonium from Liquid Swine Waste in Soils
Authors: Fernando W. A. R. Nishantha , Xia Kang , Rice Charles W.
Published: July 2010

Understanding the sorption and desorption behavior of NH4+in soils associated with animal waste is important because of the potential for the formation of NO3−and subsequent leaching that affects ground water quality. Batch equilibration experiments were conducted to evaluate the sorption and desorption of NH4+in two soils exposed to a complex matrix (liquid swine waste) and a simple matrix [aqueous solution of 0.01MCaCl2containing (NH4)2SO4]. Kennebec silt loam (fine‐silty, mixed, mesic Cumulic Hapludolls) and Haynie very fine sandy loam (coarse‐silty, mixed, calcareous, mesic Mollic Udifluvents) were used. This study revealed that the sorption and desorption behavior of NH4+in soils exposed to (NH4)2SO4solutions with a 0.01MCaCl2matrix is significantly different from that in soils exposed to liquid swine waste. Faster sorption rate, lower sorption capacity, and higher desorption capability were observed for NH4+in soils exposed to the (NH4)2SO4solution compared with soils exposed to the liquid swine waste. Sequential extraction could not extract nonexchangeable NH4+in both soils exposed to liquid swine waste, while a significant amount of nonexchangeable NH4+was extracted from the two soils that were initially exposed to the (NH4)2SO4solutions. The high dissolved organic C (DOC) content coupled with the high pH in swine waste appears to stimulate the sorption and retard desorption of NH4+in the two soils. This study revealed that batch equilibrium studies using solutions with simple matrixes may underestimate the sorption or overestimate desorption of NH4+in soils associated with swine waste.
Pre‐ and Post‐Mined Bauxite Soils of Jamaica: Physical and Chemical Properties
Authors: Greenberg W. A. , Wilding L. P.
Published: July 2010

Earthy bauxite (aluminum ore) deposits over limestone bedrock cover over 20% of Jamaica's surface area. With the shortage of arable land in Jamaica, there is great interest in using post‐mined bauxite lands for agriculture. The purpose of this study was to compare physical and chemical properties of pre‐ and post‐mined bauxite soils that are relevant in assessing suitability of these lands for small‐scale agriculture. Pedons were described and sampled for characterization at two pre‐mined sites and four post‐mined sites near Mandeville, Jamaica. Post‐mined soils were generally steeper, shallower, and higher in limestone rock fragments than pre‐mined soils. Pre‐mined soils consisted of Ap and Bo horizons making up clayey Oxisols with low charge and low bulk density. The new caret (^) symbol, which indicates horizons formed from human transported material, was helpful in describing pedons of post‐mined soils. Post‐mined soils consisted of ^Ap horizons (replaced topsoil) and 2^C horizons (fill material) over limestone. Some post‐mined pedons also had 2Bob or 3Bob horizons (Bo in situ buried by replaced topsoil and/or fill material). Post‐mined soils had higher bulk density in the ^Ap horizons than pre‐mined Ap horizons and higher pH throughout due to the incorporation of limestone rock fragments. In ^Ap horizons, organic matter and granular structure increased with time after reclamation and establishment of grass cover.
A Conceptual Model to Predict the Deflation Threshold Shear Velocity as Affected by Near‐Surface Soil Water
Authors: Cornelis Wim M. , Gabriels Donald , Hartmann Roger
Published: July 2010

A conceptual model to predict the threshold shear velocity, which should be overcome to initiate deflation of moist sediment, was recently developed by Cornelis et al. The model relates the threshold shear velocity to the ratio between water content and the water content at a matric potential of −1.5 MPa, and contains one proportionality coefficient that accounts for the effect of near‐surface wetness. The present study was conducted (i) to determine that proportionality coefficient and hence calibrate the model, and (ii) to verify the calibrated model. The model calibration was achieved through curve fitting the expression against a data set from wind‐tunnel experiments that were conducted on different sized sand particles and soil aggregates. Each sediment sample tray was prewetted, and subjected to different shear velocities and hence to different evaporation rates that dried the sediment. Once particle entrainment became sustained as recorded with a saltiphone, samples were taken to a depth of 1 mm to determine water content gravimetrically. To verify the calibrated model, threshold shear velocities simulated with our expression were compared with values obtained with Chepil's model of 1956. It was observed that the soil had to dry out to 75% of the water content at a matric potential of −1.5 MPa for deflation to occur. A single proportionality coefficient value could be used for the different sized sand and soil particles. Very good agreement was observed between our model and the model of Chepil.
Temporal Variability of Soil Carbon Dioxide Flux
Authors: Parkin Timothy B. , Kaspar Thomas C.
Published: July 2010

It is well known that soil CO2 flux can exhibit pronounced day‐to‐day variations; however, measurements of soil CO2 flux with soil chambers typically are done only at discrete points in time. This study evaluated the impact of sampling frequency on the precision of cumulative CO2 flux estimates calculated from field measurements. Automated chambers were deployed at two sites in a no‐till corn/soybean field and operated in open system mode to measure soil CO2 fluxes every hour from 4 March 2000 through 6 June 2000. Sampling frequency effects on cumulative CO2–C flux estimation were assessed with a jackknife technique whereby the populations of measured hourly fluxes were numerically sampled at regular time intervals ranging from 1 d to 20 d, and the resulting sets of jackknife fluxes were used to calculate estimates of cumulative CO2–C flux. We observed that as sampling interval increased from 1 d to 12 d, the variance associated with cumulative flux estimates increased. However, at sampling intervals of 12 to 20 d, variances were relatively constant. Sampling once every 3 d, estimates of cumulative C loss were within ±20% of the expected value at both sites. As the time interval between sampling was increased, the potential deviation in estimated cumulative CO2 flux increased such that sampling once every 20 d yielded potential estimates within +60% and −40% of the actual cumulative CO2 flux. A stratified sampling scheme around rainfall events was also evaluated and was found to provide more precise estimates at lower sampling intensities. These results should aid investigators to develop sampling designs to minimize the effects of temporal variability on cumulative CO2–C estimation.
A System for Studying the Dynamics of Gaseous Emissions in Response to Changes in Soil Matric Potential
Authors: De Wever Helene , Strong David T. , Merckx Roel
Published: July 2010

An incubation system was developed to study the dynamics of greenhouse gas emissions from soil cores at different matric potentials. It combines the facility to establish and easily alter matric potential in soil columns, contained in nine parallel incubation chambers, with the feature of highly time resolved measurements of NO, N2O, N2, O2, and CO2 Studies on chamber performance demonstrated that the repeated application of specified suctions or pressures gave highly reproducible water contents and that the water release curves were similar to those obtained with traditional methods. The system was used to examine how soils preincubated at −5 or −75 kPa for 90 d responded to matric potential increases during a subsequent anaerobic incubation. The data showed that as large pores were filled with water rates of both CO2 evolution and total denitrification increased up to −2 kPa. This is in contrast to aerobic studies that show a decline in CO2 evolution at such high matric potentials. The data suggest that C that was not decomposed in large air‐filled pores during the aerobic preincubation became colonized only when these pores became water‐filled in the subsequent anaerobic incubation and provided substrate for denitrifying organisms. These studies demonstrate the capacity of the incubation system to explore the complex interaction between soil structure and the microbially mediated soil processes responsible for gaseous N and C emissions. This interaction is crucial to understanding factors controlling gaseous emission rates but has historically been difficult to be examined directly.
Aggregate Sizes and Stability in Cultivated South Dakota Prairie Ustolls and Usterts
Authors: Eynard A. , Schumacher T. E. , Lindstrom M. J. , Malo D. D.
Published: July 2010

Soil structural stability often decreases as the intensity of cultivation increases. The effect of three different management systems (grass, no‐till, and till) on soil aggregate stability and sizes were studied in six Ustolls and two Usterts on central South Dakota farms. Soil structure was morphologically described throughout the profile. Stability of dry and wet aggregates in the topsoil was tested by dry and wet sieving. Most structural changes were observed in the top 0 to 0.20 m. Granular structure was dominant under grass, whereas plates, blocks, and compacted layers were most common in conventionally tilled and no‐till soils. The largest mean weight diameters (MWD) of dry aggregates were found in no‐till soils (10 mm vs. 7 in till and 6 in grass). Wet aggregate stability was higher in grass (87%) than in cultivated soils (70%). After about 10 yr of no‐till management, no‐till soil aggregates were significantly more stable (5% for wet and 32% for dry aggregates) than till aggregates only in the top 0 to 0.05 m. The structural stability of cultivated soils was greater in Usterts than in Ustolls.
Differences in Phosphorus Retention and Release in Soils Amended with Animal Manures and Sewage Sludge
Authors: Siddique Muhammad Tariq , Robinson J. Stephen
Published: July 2010

Excessive levels of P in agricultural soils pose a threat to local water quality. This study evaluated (i) time‐dependent changes in soil P sorption (expressed as a phosphorus sorption index, PSI) and P availability (as resin P) during incubation (100 d) with poultry litter, cattle slurry, sewage sludge, or KH2PO4, added on a P‐equivalent basis (100 mg P kg−1), and (ii) the subsequent kinetics of P release, measured by repeated extractions with a mixed cation‐anion exchange resin. Soil exchangeable Ca and ammonium oxalate‐extractable Fe and Al were also determined at 100 d of incubation. The small decrease in P sorption in the litter and sludge treatments (25%), compared with that in the slurry and KH2PO4treatments (52%) between 20 and 100 d of incubation was attributed partly to the formation of new adsorption sites for P. Subsequent P release was described by a power equation: Resin P =a(extraction number)b, where the constantsaandbrepresent resin P obtained with a single extraction and the rate of P release per resin extraction, respectively. On average, the rate of P release decreased in the order: KH2PO4and slurry > litter > sludge, and was inversely related to exchangeable Ca content of the incubated soils (R2= 0.57). The slower rates of P release in the litter and sludge treatments (P< 0.001) are attributed to the large values for exchangeable Ca (1050–2640 and 1070–2710 mg kg−1, respectively) in these amended soils. Future research concerned with short‐term declines in environmentally harmful levels of P in recently amended soils should consider the differential effects of the amendments on soil P dynamics.