bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variability of Infiltration in a Field with Surface‐sealed Soil
Authors: Ben‐Hur M. , Shainberg I. , Morin J. 
Published: July 2010

AbstractThe infiltration rates (IR) for water were measured at 30 random sites within a 1‐ha field by sprinkler and flood infiltrometers. A portable rainfall infiltrometer was used to measure the infiltration rate under water‐drop impact conditions, and double‐ring infiltrometers were used to measure IR in flooded conditions. No spatial dependence of the steady‐state IR values measured with the two methods was found. The mean steady‐state IR measured with the flood infiltrometer was 57.8 mm h−1 with a coefficient of variation (CV) of 41.8%. The mean steady‐state IR measured with the sprinkler infiltrometer was 8.6 mm h−1 with a CV of 14.7%. This difference was due to the formation of a soil surface seal from the impact of falling drops. The seal's hydraulic conductivity was much lower and less variable than that of bulk soil. Frequency distributions of the steady‐state IRs measured with the two methods were different; that from the double‐ring infiltrometer had a small deviation to the left, while that of the sprinkler infiltrometer had a large deviation to the right. The distribution of steady‐state sprinkler IR values corresponds with the distribution in the cation exchange capacity (CEC) and exchangeable sodium percentage (ESP) in the field, verifying the known dependence between surface seal formation and the soil CEC and ESP relationship. This dependence was not found for the IR values measured by flooding. No correlation was found between the IR values measured by the two methods. Thus, for soils that seal, it is impossible to predict IR under water drops from measurements under flooding conditions.
Measurement of Waterdrop Impact Pressures on Soil Surfaces
Authors: Nearing M. A. , Bradford J. M. , Holtz R. D. 
Published: July 2010

AbstractLimited data on pressures induced by waterdrop impact on soil surfaces restricts our understanding the mechanism of soil detachment due to raindrop impact. Impact pressures on rigid surfaces are known but their application to soil surfaces is questionable. This study was undertaken to measure vertical pressures of waterdrop impact on soil surfaces. A 1‐mm diam piezoelectric transducer was developed and measurements of impact pressures as a function of radial distance from drop center were made. Dickinson loam (coarse‐loamy, mixed, mesic Typic Hapludoll) and Ida silt loam (fine‐silty, mixed [calcareous] mesic Typic Udorthent) with bulk densities of 1.0 and 1.2 Mg/m3 and with matric potentials of −0.5 and −2.5 kPa were used. The waterdrop had a diameter of 5.6 mm and a fall height of 14 m. Average peak impact pressures were greatest at a distance of 1.8 to 2.3 mm from center of impact and of the order of 190 to 290 kPa. These stress levels are almost two orders of magnitude less than those for impact on a rigid surface. Much of the difference between soil and rigid cases was due to nonrigid, nonhomogeneous nature of the soil material. The remainder of the difference in stress levels was thought to be due to the effect of soil granularity or to the presence of surface and shear waves generated by impact.
Field Procedure for Estimating Soil Thermal Environments
Authors: Flint Alan L. , Childs Stuart W. 
Published: July 2010

AbstractIntensive measurements are required to precisely define soil temperature, heat flux, and thermal properties of heterogeneous forest soils. Fifty detailed profiles of temperature, density, and water content were used with the conduction heat flow equation to estimate soil thermal properties for a clearcut harvest area in a mixed conifer forest in southwest Oregon. These profiles were used to determine the accuracy with which soil temperatures could be modeled and the number of soil layers required to characterize a given field site. The soil was modeled as a profile of between 1 and 21 layers of known (measured) volumetric heat capacity and measured initial and boundary conditions. Soil thermal conductivity for each layer was determined for each of 50 datasets using an iterative numerical procedure. The accuracy of the various models was assessed by comparing the error between measured and modeled profiles. For the skeletal soil studied, a numerical model and field measurements of four soil layers proved to be the best combination of accuracy and simplicity. The assumption of a homogeneous (1‐layer) profile was satisfactory in several cases. The need for detailed field measurements was assessed by comparing modeled and measured soil temperature: minimum and maximum temperature, duration of high temperature and low temperature events, and positive and negative heat flux. Models based on measurements from four or more soil layers predicted soil temperature within ±0.3°C of measured values. Models based on two or more measured soil layers were within ± 0.006 MJ m−2 of measured daily positive heat flux.
Determination of the Combined Nitrogen‐15 Content of Dinitrogen and Nitrous Oxide in Air
Authors: Strong W. M. , Austin E. R. , Holt L. S. , Buresh R. J. 
Published: July 2010

AbstractA method for measuring the total 15N content of an air sample containing 15N‐N2O and 15N‐N2 has been developed. A high voltage arcing process is used to rapidly decompose N2O into N2 and NOx, to randomly distribute the N isotopes between the N2 and NOx pools, and to fix a sample of N2 as NOx. A routine mass spectrometric 15N analysis based on the 29:28 ion signal ratio of either the N2 pool or the NOx sample after conversion to N2 will be equivalent to the 15N content of the original sample. Two methods of 15N analysis were shown to be equally accurate and precise. The air sample may be arced and the N2 analyzed by direct inlet into the mass spectrometer while cryogenically trapping the NOx, or the NOx may be reduced to an NH+4‐N salt that can be stored and analyzed later. If only a small air sample is available, 10 mL of air (at ambient pressure and temperature) can be mixed with ultrapure O2 to a N2/O2 ratio of 9:91 in a 90‐mL arc vessel and arced at atmospheric pressure for at least 150 s to produce sufficient NOx to yield 1 mg of fixed N for mass spectrometric analysis. The arc method measures the combined 15N content of the major gas species produced by denitrification by a single analysis and may be applicable for field studies.
Layer Charge Properties of Smectites and Vermiculites: Tetrahedral vs. Octahedral
Authors: Malla P. B. , Douglas Lowell A. 
Published: July 2010

AbstractTotal layer charge and charge of octahedral sheets of 2:1 soil clays were estimated by combining alkylammonium ion exchange technique and the Hofmann and Klemen effect. The estimation of charge before and after Hofmann and Klemen effect (Li‐saturation and heat treatment) gave the total layer and tetrahedral charge, respectively. The difference of total and tetrahedral charge provided the charge contribution of octahedral sheets, assuming that a complete neutralization of octahedral charge was achieved by Li+ migration during the heat treatment. As much as 50% of the charge was found to be located in the octahedral sheets in soil smectites and soil vermiculites. Clays with total layer charge in the vermiculitic range that accommodated both double (1.8 nm) and single (1.4 nm) interlayers of glycerol in the interlayer spaces formed only double‐layer complexes after Li+ treatment, indicating a reduction in total layer charge, plus a random distribution of charge in both octahedral and tetrahedral sheets of each 2:1 layer. Trioctahedral vermiculites with a total layer charge comparable to the total layer charge of dioctahedral soil vermiculites gave only single layer complexes with glycerol after Mg‐saturation. These sorption characteristics can be explained in terms of Coulomb's law and the higher concentration of negative charge of trioctahedral vermiculites in the tetrahedral sheet compared with dioctahedral soil vermiculites.
Improved Performance of Zero‐Tension Lysimeters
Authors: Radulovich R. , Sollins P. 
Published: July 2010

AbstractPublished collection efficiencies (volume of water collected divided by percolating volume calculated from a water balance) of zero‐tension lysimeters are <10%, suggesting that samples collected by such lysimeters may not be representative of the water percolating downward. By increasing catchment area to 2500 cm2, and by pushing the lysimeter rim upward into the soil, collection efficiency was increased to 36% under grass and 17% under forest; failure rate (proportion of lysimeters yielding <50 mL) was decreased from 60 to 6% under grass and to 23% under forest.
Upper and Lower Bounds of the Ponding Time for Near Constant Surface Flux
Authors: Boulier J. F. , Parlange J.‐Y. , Vauclin M. , Lockington D. A. , Haverkamp R. 
Published: July 2010

AbstractUpper and lower bounds on the relation between the time course of cumulated infiltration into soil and water content at the soil surface are derived. These estimates can be used specifically to predict upper and lower bounds of the ponding time. The analytical results are derived for mildly varying surface flux. However, the accuracy of the limits is illustrated and discussed for Granoble sand with constant rainfall rates only. A numerical solution is also obtained that yields results outside the range of the more accurate analytical results. This confirms that errors are introduced in the numerical scheme during the early stages of infiltration. Less accurate, but easier to apply, analytical limits are also presented and discussed.
A Mechanism by which Organic Liquids Increase the Hydraulic Conductivity of Compacted Clay Materials
Authors: Brown K. W. , Thomas J. C. 
Published: July 2010

AbstractThe ability of concentrated organic chemicals, with low dielectric constants (E) to increase the hydraulic conductivity of compacted soils has been well documented. This study was undertaken to evaluate a mechanism by which these increases occur. Theory predicts that the spacing between adjacent clay particles diminishes as the E value decreases. Hydraulic conductivity measurements were made in fixed wall permeameters with a range of concentration of organic liquids in water. Marked increases in hydraulic conductivity occurred at concentrations above which the clay flocculated. Smectite d spacings increased when the clay was equilibrated with acetone and ethanol solutions having E values ranging from 65 to 77, but decreased when equilibrated with solutions having E values <35 to 50 as compared to that in water. All three clays tested exhibited reductions in electrophoretic mobility (µ) and the absolute value of the zeta potential|ζ| which would be associated with flocculation at low E values. Relative clay content measurements indicated that all three soils flocculated in solutions with low E values. At E values >49, all clays remained dispersed. When bulk samples were exposed to organic liquids, the volume changes were proportional to the E values of the permeant. The results indicate that when organic liquids or salts are sufficiently concentrated, soil particles will be drawn closer together until the clays flocculate. Thus, changes in the surface electrical properties of the clays cause shrinkage, resulting in cracking and increases in hydraulic conductivity. Flocculation tests and E values may be used as tools to predict the influence of a solution on the hydraulic conductivity of compacted soils.
Adsorption and Oxidation of Phenolic Compounds by Iron and Manganese Oxides
Authors: McBride M. B. 
Published: July 2010

AbstractThe adsorption and oxidation of catechol and hydroquinone by Fe and Mn oxides has been investigated by Fourier transform infrared spectroscopic (FTIR) analysis of the adsorbed molecules and by the measurement of O2 consumption by aqueous suspensions of these oxides. Evidence for direct coordination of catechol and salicylate to surface Fe3+ on iron oxides was obtained by FTIR. The promotion of catechol and hydroquinone oxidation by Fe and Mn oxides was confirmed by measured rates of O2 consumption and by the appearance of Fe2+ and Mn2+ in the solutions. However, only trace levels of soluble Fe2+ were detected, suggesting that oxidation by Fe(III) oxides was catalytic in that electron transfer between the phenols and Fe3+ generated Fe2+, which was rapidly reoxidized by O2. Other adsorbates introduced into these oxide/phenol systems, such as acetate, phosphate, and Cu2+, diminished O2 consumption rates, but the effect was generally attributable to a Iowered pH that inhibited oxidation. A model of surface oxidation by Mn and Fe is presented in which coordination of the organic at the surface is a prerequisite to electron transfer. Oxidation of organics can proceed with or without the uptake of O2, depending largely on pH, which determines the rate of reoxidation of the reduced metal ions by O2. The results emphasize the difficulty in interpreting the effects that chemical buffers have on oxidation reactions at oxide surfaces.
The Effect of Time and Temperature on Nitrogen Mineralization in Arctic Tundra Soils
Authors: Marion G. M. , Black C. H. 
Published: July 2010

AbstractThe objective of this work was to evaluate several mathematical models for describing N mineralization in three arctic tundra soils (Histic Pergelic Cryaquepts) as functions of time and temperature. Intact soil cores were collected in the field and incubated in a laboratory at 5, 15, 25, and 35 °C for 11 weeks. The exponential equation fit the data well at 35 °C but was generally unsuited for describing N mineralization at lower temperatures. The parabolic equation better fit the N mineralization data than the exponential equation except in a few cases where the data appeared to be approaching an asymptote. The parameters of the parabolic equation did not follow simple trends with respect to temperature, however, which made interpolating between experimental temperatures difficult. A second‐order polynomial equation with respect to both time and temperature was evaluated. This empirical equation gave R2 >0.98 in all but one case. The major advantages of the empirical, polynomial equation are that it assumes little about the nature of the N mineralization process, it is flexible, and it is accurate. The temperature data did not follow the Arrhenius relationship nor have a simple overall Q10 value because the mineralization rates at different temperatures did not follow similar trends with respect to time. Only a small fraction of the N that is potentially mineralizable is likely to be mineralized under the prevailing cold temperatures of these arctic soils.
Seasonal Variation of Potentially Mineralizable Nitrogen in Four Cropping Systems
Authors: Bonde Torben A. , Rosswall Thomas 
Published: July 2010

AbstractThe concept of potentially mineralizable N is discussed and data that support the identification of N0 as an active fraction of soil organic N are presented. Aerobic medium‐term incubations (13 weeks) were used to measure the potentially mineralizable nitrogen (N0) in four cropping systems on four different occasions from early spring to late autumn. The cropping systems consisted of barley (Hordeum distichum L.) with no N fertilizers (B0), barley receiving 120 kg N ha−1 yr−1 (B120), meadow fescue (Festuca pratensis Hudson) ley receiving 120 + 80 kg N ha−1 yr−1 (GL), and lucerne (Medicago sativa L.) ley with no N additions (LL). The amounts of N mineralized during the 13‐week incubations (37°C) ranged from 188 to 483 kg N ha−1, and the cropping systems ranked in the order GL > LL > B120 > B0 and showed a steady decline in all systems from spring to harvest and a subsequent increase from harvest to autumn. The seasonal differences were as large as the differences between systems. Three related models were employed to describe the kinetics of N mineralization during the incubations: (i) first‐order, (ii) two‐component (sum of two first‐order models), and (iii) a simplified special case of the two‐component model. In all cases, the special case of the two‐component model offered the best description of the curves of accumulated mineral N. Based on the mineralization course and an observed relationship between literature values of N0 and the rate constant (k), it is hypothesized that the mineralization is mediated by two distinct populations: an opportunistic, mainly immobile, population (bacteria) and a generalistic, mobile one (fungi), and that the k value is influenced both by the amount of substrate and its quality. The fact that the amount of mineralizable N decreases during the growing season and increases in autumn as a result of organic matter input provides evidence for the existence of an active fraction of soil organic matter.
Basin Properties and Postglacial Erosion Rates of Minor Moraines in Iowa
Authors: Burras C. L. , Scholtes W. H. 
Published: July 2010

AbstractTwo minor moraine basins in Story County, Iowa, were examined to determine the extent and effect of postglacial erosion on the present landscape and stratigraphy. Minor moraines are subtle repeating ridge and valley landforms with relief of approximately 2 m. The stratigraphy was examined in this study using grid and transect borings. A mantle of locally derived postglacial sediment blanketed the Late Wisconsinan till in both basins. In places, a strata of coarse diamicton separated the till and sediment. The postglacial sediment was identified primarily on particle size distribution and bulk density. After determining the extent and thickness of sediment in each basin, the sediment volume and mass were calculated. Previously, the Late Wisconsinan till in central Iowa was dated as being deposited 14 000 RCYBP (radio carbon years before present). This age was used to calculate a gross annual rate of postglacial erosion. The basin with modern relief of 2.7 m had a 0.9 Mg ha−1 yr−1 erosion rate and the basin with modern relief of 1 m had a 0.7 Mg ha−1 yr−1 erosion rate.
Landscape Position and Particle‐size Effects on Soil Phosphorus Distributions
Authors: Day L. D. , Collins M. E. , Washer N. E. 
Published: July 2010

AbstractThe objectives of this study were to investigate the effects of pedogenesis and landscape position on (i) the association of total P with particle‐size content and with various particle‐size separates, (ii) relative abundance of different forms of P, and (iii) P distributions between horizons and soils representing five landscape positions on an Ultisol hillslope in northwest Florida. Total‐P content in soil seemed to be directly associated with the amount of clay in the lower landscape positions. This association may be the result of the activity of the mineralogy dominant in the clay fraction. Total P in the clay and P‐fraction values indicated that some P had been redistributed between horizons and possibly between soils on the landscape. Coarser sands commonly had more total P than finer sand fractions. The sand fractions were composed primarily of quartz and ironstone. The amount of ironstone in the sand fraction was probably responsible for the amount of total P. Among P fractions, a large portion of P was in the residual form, especially in lower horizons, implying that the soils are intensely weathered or developed from parent materials that contained considerable residual‐P, which was occluded in sesquioxides prior to deposition of the sediments. The P forms were present in the order of decreasing abundance as residual‐P, Fe‐P, Al‐P, and Ca‐P. Water‐soluble P was not detected in any of the soils.
Phosphorus Redistribution from Cultivated Fields into Riparian Areas
Authors: Cooper J. R. , Gilliam J. W. 
Published: July 2010

AbstractThe accumulation of P in sediments deposited within riparian areas was measured to study the role of these areas as P sinks. The sediments originated from the cultivated fields and forests of the uplands and were deposited during the last 20 to 25 years. The riparian areas were studied in the Atlantic Coastal Plain and consisted of four field‐forest edges, four ephemeral streams and four flood plains of intermittent streams that flowed into a flood plain swamp. Selective sorting and deposition of sand and silt near the field‐forest edge (0–20 m) and clay deposition downstream (1–4 km) on the flood plains and swamps explained much of the total P distribution in the riparian areas. The P in the sediments increased with percent clay, R2 = 0.80. Laboratory measurements of the equilibrium phosphorus concentration (EPC) in flood plain swamp sediments were two to three times higher than P concentrations in the overlying water (1.0 vs. 0.4 µmol P L−1) during high flow stages of winter and spring. During summer and fall the ortho‐P concentrations of isolated pools and base flow ranged from 1.0 to 1.3 µmol P L−1. Approximately 260 kmol of P were deposited in the riparian areas of the 1850 ha watershed during the past 20 to 25 years. The amount of P deposited was equal to the amount estimated to have been removed from the watershed in the drainage water. Thus about 50% of the P leaving agricultural fields appeared to be removed from the runoff water in the riparian areas. Riparian areas between the field edge and a perennial stream were sinks for P because of the continual deposition of fresh sediment from upland areas.
Soil‐water Regimes of a Typic Haplaquoll under Conventional and No‐tillage
Authors: Culley J. L. B. , Larson W. E. , Allmaras R. R. , Shaffer M. J. 
Published: July 2010

AbstractComputer simulation models are needed to help describe the dynamic nature of soil‐water regimes. A simple water budget and an integrated soil‐plant‐atmosphere simulation model (NTRM) were each evaluated for predicting water regimes under no‐till (NT) and conventional tillage (CN) of a well‐structured soil. Estimates of soil physical properties related to the retention and movement of water, which were required as input for the models, were obtained from laboratory measurements on undisturbed soil cores. An in situ drainage experiment, using Br‐ labeled water, also provided information on field capacity water retention properties. Ponded water containing Br‐ moved rapidly through the surface 0.5‐m profiles of both tillage treatments. Redistribution of the added water was effectively completed within about 8 h. Field capacity matric potentials of both profiles were above −6 kPa. Chromatography theory indicated that the labeled water may have mixed with only 43 and 25% of the initial soil water in the CN and NT profiles, respectively. Despite these observations, both models, which assumed complete mixing within each soil layer, were reasonably satisfactory at predicting soil‐water contents under corn (Zea mays L.) through the 1984 growing season at a southern Minnesota location. Output from the NTRM model agreed better with experimental data showing water contents lower under CN than NT.
Effects of Combinations of Triple Superphosphate and a Reactive Phosphate Rock on Yield and Phosphorus Uptake by Corn
Authors: Chien S. H. , Adams F. , Khasawneh F. E. , Henao J. 
Published: July 2010

AbstractA combination of finely ground phosphate rock (PR) and triple superphosphate (TSP) represents a method that can improve the agronomic value of PR at a lower cost than would be required to manufacture the conventional, fully acidulated fertilizers from that same rock. A reactive PR from North Carolina was evaluated for its effectiveness as a P source when used in conjunction with TSP at P rates up to 266 mg P kg−1 in a short‐term (6‐week) greenhouse experiment. The soil used was a limed Mountview silt loam (Typic Paleudult) with pH 6.2. As measured by dry‐matter yield and P uptake, P availability from PR appeared to increase with increases in the proportions of TSP to PR in the TSP‐PR mixtures. Although PR alone was less effective than TSP, PR was just as effective as TSP when mixed with TSP at a P ratio of at least 1:1. Because plants responded to both TSP and PR, and because there was an interaction between TSP and PR in the soil, neither water solubility nor total citrate solubility could be used to predict the effectiveness of TSP‐PR mixtures with different P ratios.