bluuebunny/crossref_metadata_2025_split huggingface dataset:
Strength Characteristics of Three Indurated Horizons in Massachusetts
Authors: Pickering E. W. , Veneman P. L. M. 
Published: July 2010

AbstractIdentification of fragipans is often difficult due to the lack of quantitative differentiating criteria. The unconfined compression (UC) test was used to characterize strength properties of three indurated horizons. Tests were performed in the laboratory on undisturbed core samples equilibrated to one of four moisture conditions: wet, 0.1 MPa, 0.5 MPa, or air‐dried. Fragipans developed in basal till exhibited maximum UC strength values of about 100 kPa at moisture contents < 0.10 kg kg−1 and minimum UC strength of < 25 kPa at wetnesses of 0.14 kg kg−1 or more. Between these two critical moisture contents, strength varied inversely with wetness. A pan formed in post‐glacial colluvial deposits showed similar maximum UC strength values but still retained about 70% of its UC strength at the wet moisture condition. The UC testing data enabled separation of the fragipans developed in the glacial till from indurated horizons formed in the colluvial material. Pocket and Proctor penetrometers were investigated to determine their suitability for routine recognition of fragipan horizons in the field, especially during wet soil conditions. Their application did not improve upon current field techniques.
Variation in Alluvial‐Derived Soils as Measured by Landsat Thematic Mapper
Authors: Thompson David R. , Henderson Keith E. , Houston A. Glen , Pitts David E. 
Published: July 2010

AbstractLandsat thematic mapper (TM) data acquired over Mississippi County, Ark. were evaluated in order to determine the sensitivity of TM to soil properties under growing soybeans [Glycine max (L.) Merr.], and to determine whether or not established soil survey soil association boundaries were apparent on TM imagery of cropped fields. Ten fields of soybeans at the same growth stage were selected such that five fields had complex soil patterns and five fields had uniform soil patterns for the sensitivity evaluation. A detailed soil survey was available for the area. Landsat TM has six narrow spectral bands with 30 m ground resolution and a broad thermal band with 120 m ground resolution. While all bands provided useful information, the 0.76 to 0.90 µm (band 4), the 1.55 to 1.75 µm (band 5), and the 10.4 to 12.5 µm (band 6) were most useful in identifying soil association boundaries located by the USDA‐SCS general soil maps. Examination of the digital values of the individual TM bands indicated that the coefficients of variations increased as the within‐field variability of the soils increased for all TM bands; TM appears to provide information of within‐field variability related to soil differences and as reflected by the vegetation growing on the soil.
Long‐Term Effects of Tillage Method on Soil Tilth Independent of Wheel Traffic Compaction
Authors: Voorhees W. B. , Lindstrom M. J. 
Published: July 2010

AbstractField experiments were conducted on a Nicollet silty clay loam (fine‐loamy, mixed, mesic Aquic Hapludoll) in southwestern Minnesota to measure and evaluate the direct effects of tillage method on soil tilth independent of wheel‐induced soil compaction. The controlled wheel traffic concept was used on plots that had two forms of primary autumn tillage—either moldboard plow or conservation tillage (chisel plow or tandem disk). The degree of soil tilth was evaluated by measuring bulk density, clod density, and aggregate size distribution over a period of 9 y. Wheel‐induced compaction increased the density of the soil and the mean diameter of aggregates < 9 mm in diam. More importantly, wheel traffic essentially eliminated differences in tilth due to tillage method. When tilth parameters were measured in the nonwheel‐tracked soil, tillage method did have an effect on tilth, and this effect changed with time. Initially, moldboard plowing produced a more porous soil in the 0‐ to 15‐cm depth than did conservation tillage. This difference gradually changed with time, and after 3 to 4 y, conservation tillage produced a higher porosity than did plowing. A similar effect was measured in the 15‐ to 30‐cm layer, but about 7 y of conservation tillage were needed to produce a soil with porosity equal to that of plowing. Continuous conservation tillage produced larger diameter aggregates and more porous clods than did continuous moldboard plowing. These changes in soil tilth with time illustrate the need for long‐term experiments. More importantly, these studies show that wheel traffic of normal farming operations can negate or mask the true effects of specific tillage methods.
Effect of Placement Methods on Floodwater Properties and Recovery of Applied Nitrogen (15N‐Labeled Urea) in Wetland Rice
Authors: Cao Zhi‐hong , De Datta S. K. , Fillery I. R. P. 
Published: July 2010

AbstractStudies at the International Rice Research Institute (IRRI) during the 1981 dry and wet seasons evaluated the effects of placement methods on recovery of fertilizer N by rice (Oryza sativa L.) using 15N‐labeled urea in field microplots. Uniform placement and point placement of urea supergranules (USG) gave the highest yield (6.4 Mg/ha) with efficiency of 51 kg rough rice/kg N in the dry season. In the wet season, point placement by USG produced the highest yield (4.4 Mg/ha) with efficiency of 40 kg rough rice/kg N. Higher floodwater pH and total N (urea + NH4‐N) concentration in floodwater were recorded after fertilization with split application and band placement of urea indicating the greater potential for NH3 volatilization and denitrification losses from these methods. Lower floodwater pH and low total N concentration in floodwater (5 mg/kg) were detected with uniform placement of prilled urea and point placement of USG, demonstrating that these methods can reduce N losses in lowland rice. Most fertilizer N (15N‐labeled urea) uptake occurred during the early crop growth stages. However, fertilizer N uptake was sustained with point placement of USG and uniform placement of prilled urea. Native soil N was taken up by the rice crop during the entire growing season, and was the major N source at the later part of crop growth in the wet season. Fertilizer 15N as high as 75% in the dry season and 65% in the wet season were recovered by the rice plant at harvest (grain and straw) with point placement of USG.
Profiles of Bromide and Increased Soil Moisture after Infiltration into Soils with Macropores
Authors: Germann P. F. , Edwards W. M. , Owens L. B. 
Published: July 2010

AbstractThe purpose of this study was to investigate bromide and water distributions in soils as the result of macropore structure and sprinkling rate. Water was found to have moved laterally from the macropores into the soil matrix. It also has moved deeper into the soil with higher macroporosity and when applied at higher rates, as was indicated by bromide tracer profiles. Evidence is presented that the soil volume measured with a double tube gamma‐ray probe was too small to follow the wetting process completely when macropores contributed to flow. A parameter, derived from the bromide profiles, can be used to characterize the hydraulic importance of macroporosity, based upon a simple approach to water flow along macropores.
Flux‐Concentration Relation‐Based Solution of Constant‐Flux Infiltration Equation: I. Infiltration into Nonuniform Initial Moisture Profiles
Authors: Boulier J. F. , Touma J. , Vauclin M. 
Published: July 2010

AbstractThe quasi‐analytical solution of the infiltration equation based on the flux‐concentration relation for constant flux condition and initially uniform water content profile is extended here to nonuniform moisture profiles for fluxes either smaller or greater than the saturated hydraulic conductivity. In the latter case, the solution is developed for the postponding stage. It is shown that the measured flux‐concentration relation is well‐approximated by F(θ*) = θ* and that no significant time dependence can be observed. The quasi‐analytical solution is then successfully compared with both laboratory experiments performed on a sandy soil column and numerical solution of the Richards equation for the nonponding, preponding, and postponding stages of infiltration.
Steady Infiltration from Circular Cylindrical Cavities
Authors: Philip J. R. 
Published: July 2010

AbstractThe problem of quasilinearized steady infiltration from circular cylindrical cavities, with the moisture potential fixed at the cavity surface, is solved exactly. Solutions are presented numerically and graphically for values of the dimensionless cavity radius, R0, ranging from 0.01 to 10. The dependence on R0 of the average infiltration rate around the cavity surface, and of the distributions of moisture content and potential, are examined. As R0 increases, the effects of gravity on the phenomenon increasingly dominate those of capillarity. Gravity very strongly distorts the moisture distribution from the symmetry produced by capillarity alone: for R0 as small as 0.01, the depth of the effectively wetted region exceeds 250 times its horizontal width on the cavity center line; and the ratio increases rapidly with R0, exceeding 50 000 for R0 = 5. An earlier small R0 approximation proves useful only for R0 ≤ 0.2. The cavity flow, evaluated by the present analysis, may be combined with the line source solution to give approximate results useful for the region deeper than 50 radii below the cavity.
Effects of Chemical Modifications and Extractants on the Carbon‐13 NMR Spectra of Humic Materials
Authors: Preston C. M. , Schnitzer M. 
Published: July 2010

AbstractCarbon‐13 NMR was used to study the effects of methylation, 6M HCl hydrolysis and 6M HCl hydrolysis followed by methylation on two humic acids (HA's) and one fulvic acid (FA), as well as the effect of extraction by 0.5M NaOH vs. 0.1M HCl on an FA. Spectra of methylated HA's and FA's indicate that almost all CO2H groups are attached to aromatic structures, and that phenolic OH's are significant functional groups. These spectra also exhibit fine structure in the 127‐ to 131‐ppm region, possibly due to benzenecarboxylic acid‐type structures, which have been proposed as major building blocks of humic materials. Other sharp signals are observed in the 133‐ to 146‐ppm region, due to C‐substituted carbons in aromatic or heterocyclic rings. Carbon‐13 NMR spectra of hydrolyzed HA's and FA indicate, in agreement with chemical analyses, that 6M HCl hydrolysis removes all amino acids, most carbohydrates and increases the aromatic C content (aromaticity) of the residues. Carbon‐13 NMR spectra of FA extracted by 0.5M NaOH and 0.1M HCl are similar.
Natural Nitrogen‐15 Abundance as an Indicator of Soil Organic Matter Transformations in Native and Cultivated Soils
Authors: Tiessen H. , Karamanos R. E. , Stewart J. W. B. , Selles F. 
Published: July 2010

AbstractThe natural N isotope composition of soil organic matter associated with organo‐mineral particle size fractions of two cultivated and two native grassland soils was studied. In the native soils, N associated with the coarsest (sand size) fraction showed a low enrichment (+7 per mil 15N enrichment) typical for recent plant materials. A similarly low enrichment was observed in the silt‐sized fractions (+9 δa 15N) whereas clays had a higher 15N abundance (>12 δa 15N), characteristic of residual material from microbially‐mediated N mineralization. Cultivation initially resulted in the incorporation of a large pulse of low‐enrichment plant material that could be detected in the sand and coarse silt fractions, as well as in the fine clays that contain a large portion of the soil's microbial products. The 15N abundance of fine‐silt and coarse‐clay‐associated N appeared relatively unchanged even after prolonged cultivation of 60 yr. Increases in the 15N abundance of the sand and silt fractions were attributed to reduced inputs of plant residues under cultivation. A large drop in the 15N abundance of the fine‐clay‐sized materials indicated a major change in the nature of microbial N transformations.
The Stratigraphy and Composition of a Lakeside Wetland
Authors: Johnston C. A. , Lee G. B. , Madison F. W. 
Published: July 2010

AbstractSoils were examined at 35 locations and described in detail at 22 locations to determine the stratigraphy and distribution of materials in a lakeside wetland in Wisconsin. Histic and mineral soil samples were analyzed for organic P, inorganic P, ammonium, nitrate, and organic N. Particle size distributions were determined for the mineral soils. It was found that soils formed in the wetland are young, not well developed, and derived from a variety of parent materials: glacial till, glacio‐fluvial deposits, lacustrine deposits, histic materials, colluvium, and alluvium. Major soils in the wetland include Borosaprists, Haplaquents and Fluvaquents. Phosphorus concentrations are highest in silt loam alluvium and histic deposits, and lowest in glacio‐fluvial deposits, marl, and sandy alluvium. Total P in the alluvium and glacio‐fluvial deposits is very highly correlated (P <0.01) with percent silt plus clay. Nitrate concentrations were highest in silt loam alluvial levees and lowest in a saturated Histosol, indicating that the build‐up of levees in the wetland has created aerobic soil conditions locally conducive to nitrification. The accumulation of histic materials and marl in the wetland has been an ongoing process since deglaciation, but deposition of alluvium appears to have occured primarily since logging and cultivation of the watershed began in the mid‐1800's. The rate of Histosol accumulation in the wetland was estimated by 14C dating as 0.17 cm/year, no more than one third of the rate of alluvial deposition. Since P concentrations are slightly higher in the silt loam alluvium than in the histic materials, alluvial deposition is more effective than Histosol formation for retaining phosphorus in the White Clay Lake wetland.
Relationships between Sesquioxides, Kaolinite, and Phosphate Sorption in a Catena of Oxisols in Malawi
Authors: Karim May I. , Adams W. A. 
Published: July 2010

AbstractA catenary sequence of Oxisols was examined to determine the phosphate sorption capacity of the oxic horizon and to identify the minerals responsible for this property. The phosphate sorption capacity of the six soil samples taken along the sequence was found to increase downslope as far as the midslope, then to decrease towards the valley bottom. All samples contained quartz, kaolinite, goethite, and hematite; gibbsite was identified in one sample. Aluminium‐substituted goethite was found to be the mineral mainly responsible for phosphate sorption capacity and the one that caused variations in this property along the slope sequence. Significant correlations between phosphate sorption capacity and both Fe and Al extracted by citrate‐dithionite are explained by their occurrence in this oxide. Amounts of noncrystalline oxides were low and there was no correlation between phosphate sorption capacity and amounts of either Fe or Al extracted by oxalate. Kaolinite was calculated to account for 12 to 29% of the phosphate sorption capacities of the soils but there was no significant correlation between the two. Hematite, which showed a progressive decrease in content downslope, had no measurable influence on phosphate sorption capacity. The distribution of Fe oxides along the sequence suggests rather slow pedogenetic change in the horizons sampled with goethite, the main oxide product of contemporary soil‐forming processes.
Trace Metal Profiles in the Forest Floor of New England
Authors: Friedland A. J. , Johnson A. H. , Siccama T. G. , Mader D. L. 
Published: July 2010

AbstractPrevious studies in New England have revealed high levels of trace metals in the forest floor of remote regions and evidence of increases in trace metal concentrations and amounts over time. In this study, forest floor profiles collected from a boreal forest in Vermont, a northern hardwood forest in New Hampshire and white pine (Pinus strobus L.) stands in Massachusetts were analyzed for Pb, Cu, Zn, Ni, Cd, and organic matter. Concentrations of Pb, Cu, Zn, Ni, and percent organic matter showed similar trends with depth in all three forests. Cadmium occurrence differed according to site. Concentrations of Pb, Cu, Zn, and Ni were greatest 2 to 4 cm below the surface of the forest floor in all three forests. As expected, percent organic matter decreased with depth in the profile. Concentration and accumulation of trace metals appear to occur in the Oe horizon.
Optimal Prediction of Saturation and Wetting Fronts during Trickle Irrigation
Authors: Lockington D. , Parlange J.‐Y. , Surin A. 
Published: July 2010

AbstractThe nonlinear diffusion equation in spherical geometry describes water movement from a point source into a porous medium. This situation occurs, for example, in the early stages of trickle irrigation. Prediction of the saturation and wetting front positions during irrigation is of obvious practical importance. In the present paper, a general formula which predicts the positions of the two fronts is found by optimization. For particular soil properties the exact numerical solution of the diffusion equation can be easily found and is used to check the accuracy of the optimization formula. This formula proves to be extremely accurate. A simple asymptotic solution is also obtained which compares favorably with the above results in the long‐time limit. The maximum error associated with neglecting gravity is quantified using this solution and proves to be quite acceptable for most practical applications. In those few cases when this error is too large to be neglected and gravity needs to be included in the theory, other effects, e.g., instability, should also be considered.
Optimal Analysis of the Effect of a Surface Crust
Authors: Parlange J.‐Y. , Hogarth W. L. , Parlange M. B. 
Published: July 2010

AbstractRecently, experiments have been presented for the horizontal flow of water by soil with a surface crust and compared to an analytical model. It was found that the water content at the surface was consistently less than predicted by about a 1% water content. Such a small discrepancy may seem to be more of theoretical rather than practical interest. In fact, due to the rapid variation of soil properties near saturation, a very small error in water content at the surface implies that the model is unreliable to predict the relationship between cumulative absorption and soil water content at the soil surface, especially in the early stages of infiltration. A new model is developed here, based on an optimal principle. The results from this model are closer to the experimental observations, but some discrepancy remains. To eliminate the possibility of experimental error a simple theoretical example is also considered, where an exact solution exists, which illustrates in detail the accuracy of the optimal model.
Anisotropy of Unsaturated Soils
Authors: Mualem Yechezkel 
Published: July 2010

AbstractA conceptual model is applied for quantitative evaluation of the anisotropy factor during desaturation. The soil is assumed to consist of many thin parallel layers having different hydraulic properties. A uniform density distribution function is used to represent the saturated hydraulic conductivity probability of the various layers. A power function relationship is assumed between the hydraulic conductivity and the capillary head. The exponent in the hydraulic conductivity‐capillary head relationship and the air entry value are allowed to be variables. The model indicates that the degree of anisotropy of unsaturated soil may vary considerably from its value at saturation. Reducing the capillary head gradually from zero, the anisotropy factor first decreases to a minimum and then increases rapidly as the soil dries. In some cases, the anisotropy factor can reach values several orders of magnitude higher than at saturation. Soil layers with very low permeability tend to diminish anisotropy on desaturation. Conversely, large variation of the hydraulic properties of the layers would enhance anisotropy in the unsaturated state.
Ion Activities: An Historical and Theoretical Overview
Authors: Sparks D. L. 
Published: July 2010

AbstractA knowledge of ion activities in soil‐water systems is essential to a proper understanding of the physicochemical behavior of soils and to the environment of plant roots in the soil. However, with the notable exception of soil acidity, perhaps no other topic in soil chemistry has provoked such fierce arguments as the meaning of ionic activities as they apply to the soil solution. The purpose of this paper is to present an historical and theoretical overview of the use of ion activities in soil chemistry. Attempting to incorporate ionic species into a thermodynamic analysis of the soil solution is a convenient mathematical device, since an ionic species cannot be described in thermodynamic terms. Ionic species are strictly molecular or microscopic concepts. It is demonstrated in this paper that when ionic equilibria between aqueous solutions and solid phases are investigated, the division of the electrochemical potential into a term in electrical potential (φ) and a term in chemical potential (µ) is entirely arbitrary. Additionally, the early 1950s arguments of Jenny, Marshall, Peech, Coleman, Overbeek, and Babcock dealing with junction potentials, suspension effects, and mobilities of ions is reviewed. The importance of soil solution activities in relation to nutrient uptake and plant growth is also presented.
The Future of an Illusion: Ion Activities in Soil Solutions
Authors: Sposito Garrison 
Published: July 2010

AbstractThe thermodynamic significance of the single‐ion activity is limited to its use, through a self‐consistent set of conventions, to predict accurately the activities of electrolytes. Despite this fact, single‐ion activities appear to be of increasing importance in the study of soil‐plant relationships and in the surface chemistry of soils. Thus it is worthwhile to suggest a practical algorithm for the estimation of single‐ion activities in soil solutions: (i) Extraction and determination of the composition of the soil solution. (ii) Speciation of the extracted solution with an ion‐association computer model. (iii) Calculation of ion activities based on species concentrations and the Davies equation. This self‐consistent approach can be tested successfully with the performance criteria of: (i) adherence to Debye‐Hückel theory and Young's rules and (ii) accurate prediction of both conditional equilibrium constants and electrolyte activities that are important in soil chemistry.
Phosphate Sorption by Soils: I. A Model for Phosphate Reaction with Metal‐Oxides in Soil
Authors: van Riemsdijk W. H. , Boumans L. J. M. , de Haan F. A. M. 
Published: July 2010

AbstractA model for P sorption is described which is based on previous studies concerning the interaction of phosphate with gibbsite and with a sandy soil. Formation of coatings of metal phosphate on metal oxide particles constitutes the presumed mechanism of the sorption process. Diffusion of phosphate ions through the surface coating is taken as the rate‐limiting step. The relating diffusion equation is first solved with the condition of constant concentration for reactive particles of well defined geometry. Then it is shown that for any assembly of reactive particles the sorption as a function of the concentration‐time product should yield one curve, irrespective of the reaction pathway. The form of this curve can only be predicted for very specific cases. The above curve, however, can be determined experimentally, allowing the calculation of the phosphate sorption rate for any combination of concentration and sorption values. This is very useful in modeling the transport of P through soil systems. Experimental evidence is given which supports the model theory.