bluuebunny/crossref_metadata_2025_split huggingface dataset:
Errors in Gamma‐ray Measurements of Water Content and Bulk Density in Nonuniform Soils
Authors: Nofziger D. L. 
Published: July 2010

AbstractRecent experimental study of freezing soils has shown gamma‐ray measurements of water content and bulk density are in error when the water content and bulk density are not uniform throughout the gamma‐ray beam. Many gamma‐ray measurements involve nonuniform soils. This study was conducted to determine the magnitude of errors due to nonuniform bulk density and water content. Errors in gamma‐ray water content and bulk density were determined for soil‐water systems with linear and step‐function changes in water content and bulk density and for measurements of water absorption by a nonswelling porous medium. Both single‐energy and dual‐energy gammaray systems were analyzed.Large errors in water content and bulk density determined by dualenergy gamma‐ray measurements can occur for highly stratified soils. The calculated values may fall outside the range of values within the gamma‐ray beam. Relatively small errors occur if the bulk density and water content change linearly in the collimated beam. Both single‐ and dual‐energy systems accurately measure the average water content in the collimated beam if the bulk density of the soil is constant. However, the average water content in the beam may not represent the water content at the middle of the collimated beam and the middle of the preset time period. Errors due to nonuniform soils can be evaluated using the equations and graphs presented.
Field Measurement of Denitrification: I. Flux of N2 and N2O
Authors: Rolston D. E. , Hoffman D. L. , Toy D. W. 
Published: July 2010

AbstractAbsolute amounts and rates of denitrification from a Yolo loam (Typic Xerorthents) field profile were studied in relation to the influence of soil‐water content, organic C source, and soil temperature. Field plots were intensely instrumented with soil atmosphere samplers, tensiometers, and thermocouples. Soil‐water contents were maintained constant with a spray irrigation system activated at frequent time intervals. The upper 15 cm of soil was maintained at soil‐water pressure heads (h) of −15 and −70 cm of water for the two different water regimes of the experiment conducted at a soil temperature (5 cm depth) of 23°C. Soil‐water pressure heads were maintained at −8 and −50 cm for the two water regimes conducted at 8°C. Plots cropped with ryegrass, uncropped plots, and plots to which manure was mixed in the top 10 cm of soil were used to establish three different C levels. Fertilizer was applied at the rate of 300 kg N ha−1 as KNO3 enriched with 20 and 40% 15N for the h = −15 or −8 and h = −70 or −50 cm treatments, respectively. The flux of gases at the soil surface was measured from the accumulation of N2O and 15N2 beneath an air‐tight cover placed over the soil surface for 1 or 2 hours per day. Denitrification from gas fluxes occurred for the 23°C experiment in order of decreasing magnitude in manure (h = −15 cm), manure (h = −70 cm), cropped (h = −15 cm), cropped (h = −70 cm), uncropped (h = −15 cm), and uncropped (h = −70 cm) plots. Approximately 70% of the fertilizer N was denitrified for the manure (h = −15 cm) treatment. Approximately 1% of the added fertilizer was denitrified in the uncropped (h = −70 cm) treatment. Denitrification from gas fluxes for the 8°C experiment occurred in the same order as that of the 23°C experiment except that rates and absolute magnitudes were much smaller. Approximately 11% of the fertilizer N was denitrified for the manure (h = −8 cm), and no measurable denitrification occurred in the uncropped (h = −50 cm) treatment. The amount of N2 produced was much greater than N2O for all plots. The N2O flux at the soil surface was dependent upon time and degree of anoxic development and varied between 5 and 26% of total denitrification.
Oxygen Flux Measurement in Unsaturated Soils
Authors: Rankin J. M. , Sumner M. E. 
Published: July 2010

AbstractBecause in unsaturated soil systems the plateau of the current‐voltage curve is not well developed or is absent, O2 reduction at the platinum microelectrode is not diffusion controlled and consequently measured current depends continuously on applied potential. To overcome this difficulty an O2 flux meter has been designed which carefully controls and measures the applied potential and enables the effective potential at the electrode to be measured precisely. The instrument, which has facilities for measuring soil electrical resistance, electrode redox potential, and O2 reduction current is fully described together with a circuit diagram. Because the surface oxide condition of the microelectrode is crucial to reproducible results, electrode pretreatment involving gentle abrasion in wet fine sand is necessary to standardize conditions prior to measurement. The results show that the instrument is suitable for measuring O2 flux in unsaturated systems, and that measured current is closely related to soil airspace.
Nitrogen Mineralization and Denitrification in Organic Soils
Authors: Guthrie T. F. , Duxbury J. M. 
Published: July 2010

AbstractThe quantities of N mineralized when columns of Histosols were incubated at field capacity for periods up to 28 days corresponded to 500‐600 kg N/ha per year without correction for N lost by denitrification.An absorption train utilizing molecular sieve 5Å to collect N2O was used in denitrification experiments. Under an argon stream, 52‐53% of the added NO3‐‐N was recovered as N2O, whereas the maximum concentration of N2O accumulating in the headspace of closed vessels amounted to 65% of the added NO3‐‐N. The quantity of N2O either collected or accumulating in a headspace was reduced to 15‐41% of the NO3‐‐N denitrified when a second addition of NO3‐ was made to the soils. Denitrification occurred in both drained and flooded soil columns amended with NO3‐. The N2O recovered ranged from 2.5‐9% and 9‐19% of the NO3‐‐N denitrified in the drained and flooded columns, respectively. From 78‐98% of the N2O was recovered in leachate from the flooded columns and the corresponding range for the drained columns was 11‐52%.
Nitrate Reduction to Ammonium in Anaerobic Soil
Authors: Buresh R. J. , Patrick W. H. 
Published: July 2010

AbstractKnowledge regarding the pathway and soil conditions necessary for NO3‐ Conversion to NH4+ and organic N, a process which conserves soil N, is limited. The influence of rice straw (2.5 mg C/g soil), methanol (1.0 mg C/g soil), and glucose (1.0 mg C/g soil) on the fate of 100 µg/g 15N‐labelled NO3‐‐N was studied in Crowley silt loam. The fraction of the added NO3‐‐N in the NO3‐, N2, NH4+, and organic N forms was determined after 4‐day incubations under an Ar atmosphere at 30°C. In glucose‐amended soil 9 and 19% of the applied NO3‐‐N was recovered as NH4+‐N and organic N, respectively. A 1‐day preincubation with glucose (0.5 mg C/g soil) before the 4‐day incubation with added NO3‐ and glucose increased labelled NH4+‐N and organic N recovery to 36 and 34% of the added NO3‐‐N, respectively. The corresponding values for rice straw‐ and methanol‐treated soil and soil containing no added energy source were each less than 5%.Nitrate‐N reduction to NH4+‐N increased to 20.5% after a 4‐day incubation when soil with no C amendment was incubated under Ar for 20 days before NO3‐ addition. The redox potential was −260 mV upon NO3‐ additionTransformation of significant amounts of NO3‐ to NH4+ and organic N required intensely reduced soil conditions. The reaction was apparently not suppressed by NH4+. Evidence indicated that NO3‐ was reduced to NH4+ by a nonassimilatory pathway in which NO3‐ functioned as a terminal electron acceptor.
Effects of Heating on Some Changes in Soil Properties in Relation to an Ethiopian Land Management Practice
Authors: Sertsu Sahle M. , Sánchez Pedro A. 
Published: July 2010

AbstractThe physical, chemical, and mineralogical changes resulting from heating three soils up to 600° C for 48 hours were determined in the laboratory in an attempt to explain the effects of the “guie” (soil burning) practice common of Ethiopia. Heating to 200° C did not affect soil color, particle size distribution or clay mineralogy. Heating to 400 and 600° C changed colors to redder hues, the textures from clayey to sandy, produced the collapse of layer‐silicate clay minerals and probably fused clay particles into sand‐sized particles. Organic C started to decompose between 100 and 200° C and was essentially eliminated at 400° C. Total N decreased by half at 400 and 600° C. Ammonium nitrogen increased sharply at 200° C heating but decreased at higher temperatures. Soil pH values increased with heating temperature in acid soils but decreased in the alkaline soil up to 400° C. Changes in exchangeable Ca, Mg, K, Al, and available Fe, Mn, Cu, and Zn varied with soil properties. The most pronounced chemical change was a marked increase in available P in all soils when heated at 200° C or above. Although the different layers in the “guie” heaps are heated to different temperatures, the main beneficial effect of heating in the amorphous Ethiopian soils seems related to increases in available NH4+‐N and P at temperatures low enough to prevent drastic changes in particle size distribution or organic matter content.
Morphology of Discontinuous Phase Plinthite and Criteria for its Field Identification in the Southeastern United States
Authors: Daniels R. B. , Perkins H. F. , Hajek B. F. , Gamble E. E. 
Published: July 2010

AbstractPlinthite is defined in Soil Taxonomy as an iron‐rich material that hardens on repeated wetting and drying, especially when exposed to the sun. Many morphologically similar materials rich in iron oxides do not harden on repeated wetting and drying and are misidentified as plinthite. We propose that the following field‐tested criteria be used to distinguish plinthite from similar materials that will not harden and from material that has already irreversibly hardened. Plinthite has a color range from 10R to the 7.5 YR hues. It occurs as discrete bodies > 2 mm that can be separated from the matrix. It is firm when moist and hard to very hard when dry, yet it can be broken in the hands. A moist body of plinthite withstands moderate rolling between the thumb and forefinger, and either moist or air dry it will not slake when submerged in water even with periodic gentle agitation.Plinthite has platy and nodular forms. Platy plinthite bodies are red to yellowish red or strong brown about 1 cm thick and 2 to 4 cm long. They commmonly have a horizontal orientation. Nodular plinthite bodies have a similar color range but have an irregular to spherical shape. A horizon with about 10% platy plinthite will perch water. Horizons with nodular plinthite do not perch water, but the underlying reticulately mottled zone is a restrictive horizon that perches water. It is suggested that platy plinthite forms on level landscapes with a freely fluctuating water table. Nodular plinthite apparently forms on more sloping landscapes where lateral movement of water above a restrictive horizon is a contributing factor.
Size Distribution of Eroded Material From Simulated Rainfall: Effect Over a Range of Texture
Authors: Gabriels D. , Moldenhauer W. C. 
Published: July 2010

AbstractSize distribution of eroded materials has implications in deposition mechanics and in carrying capacity for pollutant materials. Dispersed clay stays in suspension virtually as long as water is moving. This dispersed clay, especially the expanding lattice types, has a high carrying capacity for pollutant materials. The aggregated materials high in clay settle according to their size and density. Their carrying capacity for pollutants is assumed to be much greater than that of single‐grained materials of the same size. Studies of the carrying capacities of the various sizes and compositions of aggregates are in progress. The present study reports size distributions and composition of material detached by water drops and transported in shallow flow.The size distributions of aggregates and primary particles in the splashed, washed, and seal material at different times during a laboratory simulated rainfall were compared for different textured soils. The wash had more finer material than did the splash. The wash and splash material at equilibrium were not different from the original soil, while the seal of all soils had a larger silt content than the original soils. The silt loam soil had seals with about the same clay content as the original soil, while silty clay soils had seals with less clay than the original soils.Of significance from this study is the low percentage of dispersed clay being eroded compared to the percent of clay in the original soil and that this percentage didn't change significantly with time. The most striking differences were between soils and these were influenced mainly by texture and aggregate condition of the original soils.
Effects of Nitrogen and Phosphorus Additions on Deciduous Litter Decomposition
Authors: Kelly J. M. , Henderson G. S. 
Published: July 2010

AbstractUrea and concentrated superphosphate were applied to plots in a deciduous forest to examine their effects on decomposition of white oak leaves (Quercus alba L.) in litter bags and the associated populations of decomposer organisms. Urea applications decreased soil invertebrate populations by about 30% and caused a three‐ to four‐fold increase in bacterial populations while increasing decomposition rates by 1 and 3% at the 550 and 1,100 kg/ha N levels, respectively. Superphosphate additions caused bacterial populations to decrease by 30% at the highest addition rate and decreased decomposition by 4 and 6% at the 275 and 550 kg/ha P rates, respectively. Soil acidity changes following fertilizer additions appear to be primarily responsible for observed results although longer‐term changes in decomposition may be associated with changes in the nutrient status of the forest floor.
Adaptation of the Soxhlet Extractor for Pedologic Studies
Authors: Singleton G. A. , Lavkulich L. M. 
Published: July 2010

AbstractThe use of the soxhlet apparatus has had limited success in its application to pedogenic weathering studies. Modified designs of the original soxhlet eliminated problems of sample inundation, erosion, and leachate contamination. The modifications, which utilized extraction thimbles, were made either by reducing the height (A) or completely removing (B) the siphon tube. B‐modified extractors increased Ca extractability of a soil material from the original 50 ppm to 210 ppm compared to an increase to 125 ppm in the unmodified apparatus. Use of a CO2 atmosphere in modification A caused rapid change in reaction of the material from the initial pH 5.1 to 4.5 compared to pH 6.1 in unmodified units. The use of these modified soxhlets showed promise in simulating pedogenic processes.
Water and Salt Movement in Unsaturated Frozen Soil: Principles and Field Observations
Authors: Cary J. W. , Papendick R. I. , Campbell G. S. 
Published: July 2010

AbstractSoil temperatures, electrical conductivities, and water redistribution were measured at four field sites during a 30‐day period in which the soil was never completely thawed. The soil on each site was a silt loam with varying aspects and vegetation covers. Both upward and downward flow of water and solutes were observed. Assuming that liquid water flow in frozen soil is analogous to unsaturated liquid flow in unfrozen soil, led to a simple equation that in general agreed with the field observations. The equation requires knowledge of the soil temperatures, the solute concentrations, and two constants that characterize the soil's water release curve and saturated hydraulic conductivity.Infiltration and frost heaving are discussed with respect to this simple theory. Water in frozen soil flows from high to low temperatures and from high to low salt concentrations. Consequently, solutes in even very low salt soils are important in decreasing frost heave and increasing infiltration. The liquid flow is so closely coupled with temperature that heat flow must be considered simultaneously in any comprehensive analysis. This coupling, as expressed in the simple liquid flow equation, accounts for the effect of soil water content on frost heave rates and the effects of temperature on maximum heaving pressures.
A Drainage Model for a Reclaimed Surface Mine
Authors: Prunty Lyle , Kirkham Don 
Published: July 2010

AbstractStripmine reclamation for row‐crop production employing bench‐terraced geometry is under study and may become increasingly common. A simplified model of the postreclamation soil profile at the Iowa Coal Project Demonstration Mine No. I is created. The model is used to find the steady‐state water‐table shape if one tube drain per terrace is installed. Dupuit‐Forchheimer (D. F.) theory is used for the analyses. Water‐table curves are generated for a series of alternative drain‐tube locations. An analysis is made to find the best position for the drain tube. It is found that, for a recharge‐to‐soil‐conductivity ratio of 0.01 for terraces repeating at a 45.7‐m (150‐ft) interval, the best drain‐tube location is beneath the horizontal portion of the terrace 4.87 m (16 ft) from the toe of the backslope if the drain tubes are placed 2.44 m (8 ft) beneath the surface of soil underlaid by a barrier at 3.05 m (10 ft) depth. The horizontal portion of the bench terraces is 38.08 m (125 ft), and the vertical drop from one terrace to the next is 3.05 m (10 ft). A table of best drain locations is given for other drain depths and recharge rates. Previous work on D.F. theory for a uniformly sloped barrier is discussed briefly and compared with and contrasted to the present work for a barrier that parallels the bench‐terraced surface of the reclaimed surface mine.
Adsorption and Desorption of Sulfate and Charge Relationships in Allophanic Clays
Authors: Rajan S. S. S. 
Published: July 2010

AbstractSulfate adsorption by a synthetic and a natural allophane increased with increasing solution concentration. Initially both the materials had net positive charges. With the progressive adsorption of sulfate the positive charges were neutralized, followed by increases in the negative charges. Sulfate adsorption released OH‐ into the solution and linear relationships were obtained between the two parameters. Very little Si was released on sulfate adsorption. From the relationships between the various parameters studied it is proposed that on a net positive surface sulfate is adsorbed as a bidentate forming a six‐membered ring, displacing either two aquo or hydroxyl ligands. On a neutral or a negative surface sulfate is adsorbed as a monodentate displacing one aquo or one hydroxyl ligand and this makes the surface more negative.The desorption studies showed that aquo and hydroxyl ligands from the solution exchanged with the sulfate on the surface and, depending on the surface charge, a 1:1 or 1:2 stoichiometry apparently exists between the moles of sulfate desorbed and the ligands adsorbed. Irrespective of the initial concentration of sulfate on the clay surface the amount left on the surface after desorption was about the same.
Organic Carbon Determination by the Walkley‐Black and Dry Combustion Methods in Surface Soils and Andept Profiles from Costa Rica
Authors: Bornemisza E. , Constenla M. , Alvarado A. , Ortega E. J. , Vasquez A. J. 
Published: July 2010

AbstractThe efficiency of oxidation of organic C by the Walkley‐Black method was studied by comparing with determinations using dry combustion equipment and gravimetric determination for the evolved CO2. Fifty surface soils (0–30 cm) were studied, in groups of 10, each one belonging to one of the following taxonomic suborders: Fluvents, Andepts, Tropepts, Udults, and Ustults. Samples from 17 Andept profiles were also analysed to study changes of oxidation efficiency with depth.The results for the surface samples indicated that the commonly used conversion factor was somewhat too small. It is recommended that 75% oxidation be used as the base for conversion to total C, as 86% of the studied samples deviated in < 2% from this value.It was observed that the organic matter in the deeper horizons is more easily oxidized through the Walkley‐Black procedure, perhaps because plant residues are less abundant and there is an accumulation of fulvic acids. In some cases the oxidation is almost complete. This oxidation is rather variable and it was not correlated with the texture or pH of these soils. It is believed that the extent of oxidizability can allow conclusions on the relative age of horizons in Andept profiles and indicates the presence of buried horizons.
Decomposition and Stabilization of Ring‐14C‐Labeled Catechol in Soil
Authors: Martin J. P. , Haider K. , Linhares L. F. 
Published: July 2010

AbstractDecomposition percentages for ring‐14C‐labeled catechol and coumaryl alcohol and anisic acid for comparison over a 12‐week incubation period at 1000 ppm in Greenfield sandy loam (pH 7.0) were 20, 50, and 75, respectively. When linked into model humic acid type polymers carbon losses were 10% for a catechol only polymer and 5 to 7% for polymers containing 17 additional phenolic units. In Chino loam (pH 5.6) losses of catechol carbons were about 28% at concentrations ranging from 1 to 10,000 ppm. In San Jacinto loam (pH 8.0) losses were 6% for the 1 ppm addition and 14% for concentrations of 10 to 10,000 ppm. When the soil was initially sterilized and reinoculated from 14 (1 ppm) to 50 (1,000 ppm) % of the C was evolved as CO2 from the acid soil and about 10% was lost from all concentrations in the alkaline soil. After 1 week only a trace to 12% of the added catechol could be recovered by soil extraction. Under sterile conditions 6 and 90%, respectively, could be extracted from the alkaline and acid soils. After 5 weeks a small amount of catechol was still present in the sterile acid and neutral soils and in addition 8 other phenolic compounds could be separated by TLC. About 50% of the catechol present in model humic acid reaction mixtures was recovered in polymer form when phenolase was used as a catalyst. Over 90% was recovered when peroxidase was used. The study indicates that the apparent high stability of catechol in soil is caused by a rapid polymerization into phenolic polymers or into existing soil phenolic polymers brought about by the action of existing phenolase enzymes in the soil, by phenolases associated with living organisms, and by autoxidation.