bluuebunny/crossref_metadata_2025_split huggingface dataset:
Soil Aggregates and Clod Strength Dependence on Size, Cultivation, and Stress Load Rates
Authors: Hadas A. , Wolf D. 
Published: July 2010

AbstractA study was carried out (i) to determine soil clod fragmentation patterns' dependence on specific surface energy, aggregate or clod size, and stress loading rates; and (ii) to examine the hypothesis that the large clods produced during tillage operations performed on air‐dry soils are a result of soil compaction due to overtilling and machinery traffic on a moist soil during the cropping season. It was found that surface energy and specific energy required to reduce aggregate size are dependent on stress loading rates. Under a specific stress loading rate, suspected to be less than or equal to the stress wave velocity in the soil, both common methods—the unconfined compression test and the drop‐shatter test—are assumed to be equally efficient in determining the energy required for soil fragmentation. It was concluded, based on soil strength values obtained, that the fracture strength of the soils tested is attributed to CaCO3 bonding bridges and is practically uniform for all clod and aggregate size ranges tested. The observed huge clods created while tilling the air‐dry soils were size dependent on row spacing and tillage direction. These results are typical of fracturing patterns of material characterized by uniform strength. The fracture patterns for these materials follow the planes of maximal shear stresses unless obstructed by plants of lower strength (e.g., plant rows, major cracks); thus the size of fractured units depend on tillage direction, tillage implement, and row spacing.
Cone Index of Loamy Sands as Influenced by Pore Size Distribution and Effective Stress
Authors: Vepraskas M. J. 
Published: July 2010

AbstractTillage pans form in coarse textured soil horizons of the Atlantic Coastal Plain and develop high cone index values (soil strengths) which slow root growth and may decrease crop yields. Identification of soil properties that influence cone index may improve field identification of tillage pans and lead to the development of techniques to reduce their detrimental effects. This study examined the influence of pore size distribution, and effective stress on the cone index of loamy sand and loamy fine sand soil materials. Effective stress values were calculated from soil water characteristic curves and compared to cone index values for both natural cores and remolded materials. The remodeled samples of a loamy sand and a loamy fine sand developed different cone index values for relative saturations between 1.00 and 0.10, and these cone index differences were partially related to pore size distribution differences between materials. Pore size distribution influenced cone index by controlling effective stress. In both remolded samples and undisturbed cores of loamy sand, effective stress values ranged from 0 to 33 kPa for soil water potentials between 0.0 and −1500 kPa, respectively. For relative saturation values between 1.00 and 0.10, changes in effective stress closely conformed to changes in cone index for nondispersed soil materials. At a given effective stress, cone index was influenced by bulk density and soil particle characteristics that influence interparticle friction.
The Effects of Soil Properties on Nitrification and Nitrification Inhibition
Authors: Gilmour J. T. 
Published: July 2010

AbstractAn understanding of the impact of the soil environment on nitrification in the presence and absence of a nitrification inhibitor is important to proper use of this group of compounds. The objective of this study was to describe the kinetics of the nitrification process and define how a nitrification inhibitor, etradiazole (5‐ethoxy‐3‐trichloromethyl‐1,2,4‐thiadiazole), altered the reaction. Nitrification was found to obey zero‐order kinetics with the rate constant being a function of temperature, moisture, and pH. The absolute zero‐order rate was also a function of initial ammonium concentration. As temperature increased over the range of 16 to 28°C, the rate constant increased according to the Arrhenius equation. The relative influence of the inhibitor on the rate constant decreased with temperature increases. Below the optimum soil moisture for nitrification a linear decline in rate was observed as soil moisture decreased over the range of 0.20 to 0.12 g g−1 (−40 to − 140 kPa). This decline was greater in the control than in the soil amended with etradiazole. Nitrification linearly increased with soil pH over the range of 4.9 to 7.2. Using the above relationships, the rate of nitrification was predictable for an independent group of 19 soils. This same group of soils was evaluated for inhibition at two etradiazole rates at optimum moisture and 14°C. Inhibition decreased as organic carbon content increased above 13 g kg−1 with the extent of the decrease being modified by the amount of clay in the soil. As inhibitor rate increased, inhibition was enhanced by a constant amount, suggesting that the relationships described above remained in effect.
Effect of Water‐Filled Pore Space on Carbon Dioxide and Nitrous Oxide Production in Tilled and Nontilled Soils
Authors: Linn D. M. , Doran J. W. 
Published: July 2010

AbstractThe percentage of soil pore space filled with water (percent water‐filled pores, % WFP), as determined by water content and total porosity, appears to be closely related to soil microbial activity under different tillage regimes. Soil incubated in the laboratory at 60% WFP supported maximum aerobic microbial activity as determined by CO2 production and O2 uptake. In the field, % WFP of surface no‐tillage soils (0–75 mm) at four U.S. locations averaged 62% at time of sampling, whereas that for plowed soils was 44%. This difference in % WFP was reflected in 3.4 and 9.4 times greater CO2 and N2O production, respectively, from surface no‐tillage soils over a 24‐h period as compared to plowed soils. At a depth of 75 to 150 mm, % WFP values increased in both no‐tillage and plowed soils, averaging approximately 70% for no tillage compared with 50 to 60% for plowed soils. Production of CO2 in the plowed soils was enhanced by the increased % WFP, resulting in little or no difference in CO2 production between tillage treatments. Nitrous oxide production, however, remained greater under no‐tillage conditions. Substantially greater amounts of N2O were produced from the N‐fertilized soils, regardless of tillage practice. Production of CO2 and N2O was primarily related to the % WFP of tillage treatments although, in several instances, soil‐water‐soluble C and NO‐3 levels were important as well. Calculations of relative aerobic microbial activity between no‐tillage and plowed soils, based on differences in % WFP relative to maximum activity at 60%, indicated linear relationships for CO2 and N2O production between WFP values of 30 to 70%. Below 60% WFP, water limits microbial activity, but above 60%, aerobic microbial activity decreases—apparently the result of reduced aeration.
The Correlation Between Extracellular Polysaccharide Production and Acid Tolerance in Rhizobium
Authors: Cunningham Scott D. , Munns Donald N. 
Published: July 2010

AbstractRhizobial isolates from six host genera (Cicer, Phaseolus, Leucaena, Lens, Melilotus and Trifolium) were screened for ability to colonize successively more acidic agar plates. Sufficient isolates from Cicer and Phaseolus were screened to show that relative tolerance to acidic conditions was normally distributed. Extracellular polysaccharide (EPS) was isolated by ethanol precipitation from 10‐d‐old solution cultures of the most and least acid tolerant of these strains. Acid‐tolerant isolates from Cicer, Phaseolus, Leucaena and Melilotus produced significantly more (P < 0.001) EPS than did those which were acid sensitive. The differences between isolates from Trifolium were significant at the P < 0.05 level. No significant difference in EPS production was found among the 8 isolates from Lens. The correlation between EPS production and acid tolerance was tested further with EPS isolated from 20 strains of Rhizobium phaseoli. The quantity of EPS produced varied from 18 to 75 mg 100 mL culture, was normally distributed, and was positively correlated with acid tolerance (P < 0.01), albeit with an r2 value of only 0.331. It is postulated that EPS could modify the microenvironment of the rhizobia and so decrease the stresses induced by an acid soil.
Comparison of Chelating Agents as Extractants for Metals in Diverse Soil Materials
Authors: Norvell W. A. 
Published: July 2010

AbstractFive chelating agents—DTPA, EDTA, EGTA, HEDTA, and NTA—were compared at pH 5.3 as extractants for Al, Fe, Mn, Zn, Cu, Cd, and Ni in 25 diverse soils. Extracting solutions contained 0.005M chelating agent, 0.01M CaCl2, and 0.1M acetic acid‐ammonium acetate buffer at pH 5.3. These extractants were compared to: a similar solution without added chelating agent, 0.1M HCl, and the DTPA soil testing solution (0.005M DTPA, 0.01M CaCl2, buffered at pH 7.3 by 0.1M triethanolamine). All extractants yielded clear filtrates that aspirated and burned cleanly during analysis by flame atomic absorption spectrometry. At the 5:1 extractant/soil ratio used, all buffered extractants maintained their pH satisfactorily. DTPA and HEDTA were among the most effective ligands for extracting all seven metals. EDTA extracted somewhat lower concentrations but was also a good extractant for all metals. NTA was among the best extractants for Al and Ni but among the least effective extractants for Fe, Mn, and Cu. EGTA was the least effective chelator of Fe, Zn, Ni, and especially Al. Despite its alkaline pH of 7.3, the DTPA soil‐testing solution was a moderately effective extractant for metals except Mn and ferrous Fe. Acid soils, reduced soils and sediments, and metal‐contaminated soils may release enough strongly complexed metal to reduce the effectiveness and the capacity of chelating extractants. Recently dredged lake sediment released particularly large concentrations of metals, primarily Mn2+ and Fe2+. Extracting metals effectively from metal‐rich soils may require increased concentration of chelating agents, higher extractant/soil ratios, or more than one extraction per sample.
Soil Survey Interpretations from Water Retention Data: I. Development and Validation of a Water Retention Model
Authors: McBride R. A. , Mackintosh E. E. 
Published: July 2010

AbstractThe prediction of spatial and temporal variations in the soil water regime provides the basis for a proposed soil survey interpretive system. A water retention model estimates the boundary desorption curve from saturation to pF 4.2 for mineral soils in situ using limited soil physical data (standard error of estimate <2.2% g g−1). The total porosity (structural parameter) and clay content (adsorptive parameter) define the position of the moisture characteristic in logarithmic coordinates and the silt content its configuration. Organic matter affects the structural parameter by reducing both the dry bulk and particle densities but only significantly influences the adsorptive parameter at organic matter contents of 5% or greater. Model validation shows that the state and quantity of water retained by field soils near equilibrium is dependent on the position of the phreatic surface. Under field conditions, the ψ(θ) relationship establishes an effective equilibrium midway between the predicted wetting and drying curves of the hysteresis loop.
Enriched Levels of Arsenic in Post‐Active Acid Sulfate Soils in Alberta
Authors: Dudas M. J. 
Published: July 2010

AbstractThree post‐active acid sulfate soils derived from weathered pyritic shale were analyzed for total As. Levels found in B and C horizons were nearly 10 times higher than normal background abundances. Secondary iron oxides formed from the weathering of pyrite acted as scavengers of As. Samples of segregated iron oxyhydroxide collected from B horizons contained up to several hundred mg As kg−1. Natrojarosite and clay separates from the same horizons contained from 30 to 50 mg As kg−1. Pyrite is believed to be the source of the elevated levels of As.
Sensitivity Analysis Applied to Unsaturated Flow Modeling of a Retorted Oil Shale Pile
Authors: Freshley Mark D. , Reisenauer A. E. , Gee G. W. 
Published: July 2010

AbstractCommercial recovery of oil from oil shale will require disposal of large quantities of retorted or spent shale. Because no commercial disposal piles have been constructed and monitored, uncertainties exist in predicting water movement through large spent‐shale disposal piles. To better understand these uncertainties, we investigated water movement through spent shale by numerical modeling. A first‐order sensitivity analysis was used as a part of the numerical investigation of water movement through a hypothetical pile of spent oil shale. The sensitivity analysis was useful in identifying the most important components of the flow model. Results indicate that the flow model is sensitive to parameters that directly supply water to or control extraction of water from the profile, namely the initial condition of spent shale, precipitation, and estimates of potential evapotranspiration. The flow model is less sensitive to parameters that control water movement, specifically hydraulic conductivity of the spent shale and soil cover. The sensitivity analysis demonstrates that the flow model is also sensitive to parameters describing the sink term, namely rooting depth and rooting density. To improve predictions of the flow model, the input parameters contributing the most to model sensitivity should be measured carefully; parameters that produce less model sensitivity can be estimated without as much effort.
Tensile Strength of Unsaturated Soils
Authors: Snyder V. A. , Miller R. D. 
Published: July 2010

AbstractA better understanding of the nature of tensile failure in unsaturated soils is important if adequate theories explaining the behavior of soils under tillage or during processes such as frost heaving are to be developed. In this paper, the problem of tensile failure of uncemented soils is formulated by combining Aitchison's extension of the classic Haines‐Fisher model of capillary cohesion with Griffith's theory of the fracture of cracked elastic solids. Results suggest that once air intrusion has initiated desaturation, the maximum tensile strength which can be expected is about half the gauge pressure of the pore water. Effects of grain size on tensile strengths of moist soils are actually manifested through their effects on drying characteristic curves as demonstrated by similitude analysis. A parameter, χ, used to estimate tensil strength as a function of pore water pressure, is a function of the degree of pore saturation hardly influenced by the actual shapes of the drying characteristic curves. Results are presumably applicable to various analogues, including the initiation of ice‐filled cracks (ice‐lenses) in air‐free soils during the process of frost heaving.
Uptake of Nitrogen‐15 by Cotton under Salt Stress
Authors: Pessarakli M. , Tucker T.C. 
Published: July 2010

AbstractEvidence was gathered to evaluate the effect of salt stress on 15N absorption rate by plants, to indicate how plant parts (roots and shoots) react to NaCl stress conditions. Nitrogen (15NH4) absorption studies were on cotton (Gossypium hirsutum L.) grown in complete Hoagland nutrient solution in pots with various NaCl concentrations (0, −0.4, −0.8 and −1.2 MPa osmotic potentials). Low and medium levels of salinity (−0.4 and −0.8 MPa) failed to exhibit a significant effect on the 15N absorption rate, while high levels of salinity (−1.2 MPa) resulted in substantial reduction of 15N absorption rate. Concentration of 15N in plants was significantly higher under moderate salinity stress than in the controls. Absorption rate of water significantly decreased with increasing salinity levels, and was directly proportional to plant growth and total dry matter production. Water uptake rate and plant growth were affected to a greater extent than 15N absorption rate. The effect of salinity was more pronounced at vegetative than at reproductive stages of growth. Nitrogen concentration was greater in roots than shoots.
Illuvial Versus Inherited Clays in a Cryoboralf of the Boulder Batholith, Montana
Authors: McDaniel P. A. , Nielsen G. A. 
Published: July 2010

AbstractSome forested Mollic Cryoboralfs of the granitic Boulder batholith have smectite‐rich B horizons. A representative soil was studied to determine processes responsible for morphologically well‐developed argillic horizons in relatively young soils formed in coarsegrained quartz monzonite parent material. X‐ray diffraction and particle‐size analysis indicated that B horizons of this soil differ greatly from surface eluvial horizons in both type and amount of clay minerals present and in the degree of weathering of plagioclase feldspars. Illite is the dominant clay mineral in the andy loam eluvial horizons and plagioclase grains appear only slightly weathered when examined in thin‐section. In Bt horizons, smectite is the dominant clay mineral and few identifiable plagioclase grains are seen in thinsection. Soil fabric analysis indicated illite rather than smectite as the dominant clay mineral being translocated within the soil profile. Results suggest that smectite content of B horizons is most likely a result of in situ alteration of plagioclase by hydrothermal processes prior to soil formation. Thus, smectite inherited from parent material is primarily responsible for the mineralogical and morphological properties of the argillic horizon. Although some illuviation of clay has occurred, this process has played a relatively small role in influencing these properties.
Soil‐Saprolite Profiles Derived from Mafic Rocks in the North Carolina Piedmont: I. Chemical, Morphological, and Mineralogical Characteristics and Transformations
Authors: Rice T. J. , Buol S. W. , Weed S. B. 
Published: July 2010

AbstractThe chemical, morphological and mineralogical properties of two Enon sandy loam (fine, mixed, thermic Ultic Hapludalfs) soil‐saprolite profiles, one formed on gabbro and the other on metagabbro, are compared. Clay skins are scarce and stress cutans common in the argillic horizons of these soils. Iron‐manganese concretions are concentrated in soil horizons immediately above the argillic horizons. The high shrink‐swell capacities and slow permeabilities of the argillic horizons result in relatively shallow depths to paralithic contact with saprolite. The parent rock from the Enon profile near Albemarle, Stanly County, North Carolina is a medium‐grained metagabbro with chlorite, hornblende, quartz, and calcic plagioclase feldspar as the dominant primary minerals. Chlorite weathers to regularly interstratified chlorite‐vermiculite, which alters to randomly interstratified chlorite‐vermiculite and smectite. Particle size decreases with each mineral alteration. Hornblende weathers to smectite and goethite. Calcic plagioclase feldspar transforms to kaolinite in the saprolite and soil horizons. Quartz is relatively resistant to chemical weathering. The parent rock of the Enon profile near Concord, Cabarrus County, North Carolina is a coarse‐grained gabbro with hornblende and calcic plagioclase feldspar as the dominant primary minerals. Hornblende transforms to smectite and goethite. Calcic plagioclase feldspar alters to kaolinite in the saprolite and soil horizons.
Alteration of Basalt in Soils of Western Oregon
Authors: Glasmann J. R. , Simonson G. H. 
Published: July 2010

AbstractBasalt alteration from different pedo‐microenvironments in western Oregon was studied using petrographic, electron microscope, X‐ray diffraction, and differential thermal techniques. Initial alteration was similar in each environment and consisted primarily of mineral dissolution associated with the formation of etch pits and hairline cracks and the development of isotropic domains within feldspar phenocrysts. The stage of alteration characterized by secondary mineral formation was distinctly microenvironment dependent. Smectite formed as the initial crystalline weathering product of basalts in the Oregon Coast Range, but was metastable with respect to hydrated halloysite along fracture zones in the weathering crust where more leaching micro‐environments occureed. Smectite altered to chloritic intergrade and halloysite in cyclic wet and dry pedoenvironments. The occurrence of gibbsite was related to the alteration of glassy basalt lithologies under acid leaching conditions. Goethite formed form the alteration of an initial non‐crystalline iron oxide phase.
Monte‐Carlo Simulation of Noninteracting Solute Transport in a Spatially Heterogeneous Soil
Authors: Persaud N. , Giraldez J. V. , Chang A. C. 
Published: July 2010

AbstractMonte‐Carlo data generation techniques were used to obtain 200 pairs multivariate lognormal values of the physical parameters D (dispersion coefficient) and v (pore‐fluid velocity) which appear in the differential equation describing downward leaching of a noninteracting solute in the soil profile under steady‐state percolation. The time (tmax), at which the maximum concentration is attained at given soil depth L after a pulse input of solute has been applied at the soil surface for a time to, was obtained for each pair of generated D and v values. Values of the ratio ΔL/Δtmax representing the average rate of movement of the maximum concentration between two depths were also calculated. The effect of changes in the variance of v and the levels of correlation between D and v on the frequency distributions of tmax–t0 was investigated. The lognormal and gamma distributions were fitted to the calculated distributions of tmax–t0. Good fits were obtained with both theoretical distributions to the values of tmax–t0. The lognormal distribution was better in describing the values of ΔL/Δtmax. The parameters and properties of these calculated distributions were sensitive to changes in the variance of v but were less sensitive to changes in the correlation between D and v. The ensemble average of 200 concentration versus time curves was computed by substituting the generated parameters D and v in the solution to the differential equation. This curve was compared to that obtained using the sample mean values of D and v. The dissimilarity between these curves was sensitive to changes in the variance of v.
Indigenous Soil Properties Influencing the Availability of Iron in Calcareous Soils
Authors: Loeppert R. H. , Hallmark C. T. 
Published: July 2010

AbstractIron chlorosis in plants is commonly associated with calcareous soils; however, soil factors other than total carbonate may also influence the plant's ability to obtain adequate Fe for growth. Twenty‐four calcareous soils, which represent the expected ranges of clay, CaCO3, Fe oxide, and organic matter contents of agronomically important soils in Texas, were sampled and examined extensively with respect to these phases along with extractable ion and soil solution composition. [Sorghum bicolor (L.) Moench] was grown under greenhouse conditions to evaluate chlorosis and Fe uptake. Although total CaCO3 content was important in influencing availability of Fe, the quantity, mineralogy, and crystallinity of the Fe oxide phase assumed a dominant role. Clay and organic matter contents were positively correlated with plant available Fe. The influence of these phases may be attributed to stabilization of a poorly crystalline Fe oxide phase. The contents of solution phase and exchangeable Mg2+ were also positively correlated with the incidence of Fe chlorosis due to the influence of this ion on soil alkalinity.