bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of Three Methods for Soil Homogenization
Authors: Schumacher B. A. , Shines K. C. , Burton J. V. , Papp M. L. 
Published: July 2010

AbstractWe used the most common homogenization techniques, namely, grinding and sieving, riffle splitting (open and closed bin), and cone and quartering to homogenize four soils of differing textures. Our objective was to determine the effectiveness, efficiency, and extent of fine particle loss for each technique by examining particle‐size distribution, loss‐on‐ignition organic matter, and pH. Five passes should be used to effectively homogenize a sample, since the least replicate variability almost always occurred after the fifth pass. Riffle splitting was more efficient and had less loss of fines than cone and quartering and is, therefore, the recommended method for soil homogenization. The closed‐bin riffle splitter was apparently better able to contain the loss of fines than the open‐bin riffle splitter. Grinding and sieving (random sampling) was the most efficient process, yet it almost consistently showed greater replicate variability than the other homogenization techniques after the fifth pass, thereby reducing its value for soil homogenization.
Analytical Solution for Two‐Dimensional Heat Conduction beneath a Partial Surface Mulch
Authors: Kluitenberg Gerard J. , Horton Robert 
Published: July 2010

AbstractModels describing heat conduction in materials subjected to periodically varying surface temperatures are important in agricultural physics and other disciplines of applied physics. To date, most attempts to model soil heat conduction in two dimensions have relied on methods of numerical approximation to solve the heat‐conduction equation. We have developed an exact analytical solution to the heat‐conduction equation in a two‐dimensional region of constant thermal properties. The surface temperature is described by a wave that varies sinusoidally with time and that has mean temperature, amplitude, and phase constant as arbitrary functions of space. In addition to a general solution, a particular solution is presented for a surface temperature pattern corresponding to a partial surface mulch. Calculated temperature and heat‐flux profiles beneath a partial surface mulch indicate that, at certain times of the day, there are large vertical and horizontal spatial variations in temperature and heat flux but, at other times, temperatures are uniform and heat fluxes have similar magnitude and direction. The calculations also show that, near the soil surface, the horizontal component of the heat flux can be quite large.
Simulation of Water Flow from a Percolation Test Hole in Layered Soil
Authors: Jabro J. D. , Fritton D. D. 
Published: July 2010

AbstractIn order to better explain problems in the correlation of percolation test and soil hydraulic conductivity data, a finite‐element program (TWODEPEP) was used to solve Richards' water‐flow equation in cylindrical coordinates. Both saturated and unsaturated aspects of water flow from a percolation test hole were simulated. Inputs for the simulation model were the soil hydraulic conductivity, which was measured using the Guelph permeameter technique, and water‐retention data for each layer of a Monongahela silt loam soil (a fine‐loamy, mixed, mesic Typic Fragiudult). Pressure‐head distribution and rate of water flow were simulated. A thin (approximately 10‐mm) saturated zone near the water source, approximated by the region inside the zero‐pressure line, was nearly constant in size with time, but the wetting front continued to advance. It was also found that the horizontal movement of water in the soil was dominant over the downward vertical movement due to the movement of the water in both the upper and middle layer rather than the lower layer because the soil in these two layers was more permeable than the underlying layer. Simulated flow results agreed with the geometric mean of the field data obtained at six sites. The simulated results in the layered soil were compared with those in a uniform soil to show how soil layers significantly affect water flow from a percolation test hole.
Analysis of Infiltration through a Two‐Layer Soil Profile
Authors: Smith R. E. 
Published: July 2010

AbstractMost soils in nature exhibit some degree of layering, while infiltration theory is largely confined to homogeneous profiles. This study was conducted to describe general infiltration features of a two‐layer system, including the often‐studied crust case as a limit. The general analytic theory for infiltration models leads to several related robust relations for homogeneous soils. The resulting analytic expressions relate infiltrability, f, to infiltrated water, I. This type of expression is uniquely general in describing the decay of f with I for either saturation or flux boundary conditions, and in describing the onset of ponding for flux boundary conditions. This study explores the applicability of this theory when the soil profile is composed of two layers. A numerical solution of Richards' equation is used as an experimental tool, applied to a general set of possible soil changes that may occur at the layer interface. The special case of layers with “absorption matched” infiltrability parameters exhibits complex behavior when the interface is encountered at large I. The behavior of the layered system exhibits the same unifying f(I) response to flux boundary conditions as does a homogeneous profile, which lends unexpected generality to the I‐based analytical infiltration model.
Zinc Adsorption by a Lateritic Soil in the Presence of Organic Ligands
Authors: Chairidchai P. , Ritchie G. S. P. 
Published: July 2010

AbstractSoluble Zn in soils and its availability to plants may be influenced by the presence of organic ligands, particularly in the rhizosphere, where soluble organic matter may be present in high concentrations. Zinc adsorption by a lateritic podzolic soil was measured in the presence of 0 to 3 mmol L−1 of acetate, oxalate, citrate, tricarballylate, salicylate, or catechol, or 0 to 3 mmolc L−1 of humate. Zinc remaining in solution was measured by atomic absorption spectrometry after shaking the soil for 17 h at a soil/liquid ratio of 1:5 in a 0.003 mol L−1 KCl solution containing 0 to 500 µmol L−1 Zn and the ligands. In the absence of organic ligands, more than 95% of the zinc was adsorbed. The amount of adsorption was linearly correlated with pH and the concentration of ZnOH+ in solution after shaking (r2 = 0.98; multiple regression). Zinc adsorption and pH decreased in the presence of each of the ligands except catechol. Seventy four percent of the variation in adsorption was accounted for by the combined effects of the concentration of zinc‐ligand complex (Zn‐L) and the concentration of ZnOH+ that were present in solution after adsorption. However, other factors such as changes in the number of sites available for adsorption, the point of zero salt effect (pzse) of the soil, and the charge of zinc species also contributed to the magnitude of zinc adsorption.
Fluorescence Quenching and Polarization Studies of Naphthalene and 1‐Naphthol Interaction with Humic Acid
Authors: Morra M. J. , Corapcioglu M. O. , von Wandruszka R. M. A. , Marshall D. B. , Topper K. 
Published: July 2010

AbstractAlthough it is known that the environmental behavior and fate of synthetic organic compounds are altered on association with humic materials, the nature of this interaction has been a source of controversy. Fluorescence quenching and polarization techniques were used to study the interaction between water‐soluble humic acid and naphthalene and 1‐naphthol. Stern‐Volmer plots constructed using intensity values for these fluorophores dissolved in humic acid solutions (0–25 mg L−1) were linear. The ultraviolet/visible (UV/VIS) absorption spectra of each fluorophore in the presence and absence of the humic acid quencher were identical. This, in addition to the observed increase in quenching with temperature, indicates a dynamic (collisional) mode of quenching. Fluorescent lifetimes of the probes decreased in the presence of humic acid, providing further evidence of dynamic quenching. However, the slopes of Stern‐Volmer plots constructed with lifetime values were considerably smaller than plots obtained with intensity values. Calculated bimolecular quenching constants of 5.2 × 1010 M−1 s−1 for naphthalene and 4.8 × 1011 M−1 s−1 for 1‐naphthol are above the maximum considered possible for a diffusion‐controlled interaction. Fluorescence‐polarization measurements indicate no rigid association between unquenched 1‐naphthol and humic acid. The interaction of naphthalene and 1‐naphthol with humic acid in aqueous solution occurs through a loose association in which humic acid surrounds the fluorophore in a cage‐like manner. This pseudomicelle confines the probe without rigidly binding it, promoting frequent quenching collisions and a combination of dynamic and static quenching.
Citrus Root Growth as Affected by Soil Aluminum Level under Field Conditions
Authors: Lin Zhongyan , Myhre Donald L. 
Published: July 2010

AbstractMost research on the effects of Al on citrus rootstocks has been limited to nutrient‐solution studies. This study employed an implanted soil‐mass technique to determine the effects of Al level in soils on growth and mineral content of fibrous citrus roots under field conditions. The implanted soil, E horizon material from an Immokalee fine sand (sandy, siliceous, hyperthermic Arenic Haplaquod), had a pH of 4.2 and a very low exchangeable‐Al content. It was either limed, unamended, or amended with three levels of Al using AlCl3. Each of the five treatments was replicated 15 times. Mesh bags containing the treated soil were placed in holes at the drip line of mature trees (Citrus aurantium L. sour orange rootstock) in a producing citrus grove. The bags were removed after 46 d. Results showed that, at a concentration of 9.14 mg Al L−1 of soil saturation extract, root density was twice that of the unamended treatment (0.13 mg Al L−1) and equaled that of the lime treatment (0.03 mg Al L−1). More roots grew into the bag, and they produced more lateral roots. Aluminum concentrations in roots were lower than those in the unamended treatment, however. Root‐length density decreased to about 60% of the value for the unamended treatment when Al concentration increased to 34.60 mg L−1. The optimum Al concentration for root growth appears to be 10 mg L−1 calculated by a curvilinear regression equation. In general, the concentrations of Zn, Fe, and Mn in roots decreased with increased Al application to the soil, while concentrations of Ca, Mg, K, P, and B were unchanged.
Plant Availability of Phosphorus in the Water‐Insoluble Fraction of Commercial Triple Superphosphate Fertilizers
Authors: Mullins G. L. , Bartos J. M. , Bryant H. H. , Sikora F. J. 
Published: July 2010

AbstractWater‐insoluble complexed P fractions can form during the production of phosphate fertilizers, and there is some concern regarding the potential impact of these chemical impurities on fertilizer performance. A greenhouse study was conducted to evaluate the plant availability of P in water‐insoluble residues from five commercial triple superphosphate (TSP) fertilizers. Fertilizers manufactured from rock‐phosphate sources in Florida, North Carolina, Idaho, and Morocco were evaluated. Each fertilizer was washed with deionized water to remove its water‐soluble P. The resulting water‐insoluble fertilizer residues, reagent‐grade monocalcium phosphate [MCP: Ca(H2PO4)2] and reagent‐grade dicalcium phosphate (DCP: Ca‐HPO4) were applied to a Mountview silt loam soil (fine‐silty, siliceous, thermic Typic Paleudult) to supply 0, 10, 20, 40, 60, and 80 mg P kg−1 soil. Sorghum‐sudangrass [Sorghum bicolor (L.) Moench] was harvested for forage yields at 21 and 42 d after planting. Each P source gave different (P ≤ 0.01) yield and P‐uptake responses to the rate of the sum of the water‐soluble and the citrate‐soluble P applied. Water‐insoluble fertilizer residues were a better source of P than reagent‐grade DCP, but they were not as effective as reagent‐grade MCP. Results from this study demonstrate that the plant availability of P in the water‐insoluble fraction of TSP fertilizers is source dependent, and that P in this fraction is not as available as P in pure MCP. The sum of the water‐soluble and the citrate‐soluble P overestimated available P in the fertilizer residues.
Laumontite in Soils of the San Gabriel Mountains, California
Authors: Taylor Kelly , Graham Robert C. , Ervin Jarel O. 
Published: July 2010

AbstractLaumontite, a Ca‐rich zeolite, is widespread and locally abundant in the San Gabriel Mountains of southern California. It occurs in hydrothermally altered rocks of various origins and is inherited by the overlying soils. The objectives of this study were to determine the distribution and properties of laumontite in these soils. Laumontite was found in soils derived from anorthosite, arkosic sandstone, and granodiorite. All of the soils were Entisols, composed largely of colluvium, on steep, chaparral‐covered slopes. Soil depths ranged from 16 to 32 cm over 25 to 40 cm of saprolite (Cr horizon). Soil pH ranged from 5.0 in the A horizon of the soil on sandstone to 7.2 in the Cr horizon of the anorthosite‐derived soil. Laumontite was found in sand, silt, and clay fractions of the soils. Its particle‐size distribution in the soil depended on its grain size in the parent rock and its weathering within the soil. Comparisons of laumontite grain morphology using scanning electron microscopy showed grains in the A horizons to be rounded, dissolution pitted, and crusted with weathering products, whereas those in the Cr horizons tended to have more angular, fresher crystal faces. Halloysite tubes have formed on some laumontite grain surfaces. Although the low Si/Al ratio of laumontite indicates a high cation‐exchange capacity, only 17 cmolc kg−1 of native cations were extracted by shaking in 1 M NaCl solution for 17 d. Fewer cations were displaced by Ba, Sr, Cs, and NH4. Apparently, diffusion of cations from the one‐dimensional channels of laumontite is very slow. Laumontite does not contribute significantly to the cation‐exchange capacity of these soils, which also contain smectite and vermiculite.
Perturbation of Imogolite Formation by Humic Substances
Authors: Inoue K. , Huang P. M. 
Published: July 2010

AbstractImogolite formation is influenced by ionic factors. This study was conducted to investigate the perturbation of imogolite formation by humic substances. Interactions of hydroxy‐Al ions with orthosilicic acid as influenced by humic substances were studied at the Si concentration of 1.6 mM, a Si/Al atomic ratio of 0.5, an OH/Al molar ratio of 2.0, and concentrations from 1 to 1000 mg humic acid (HA) L−1 and 1 to 300 mg fulvic acid (FA) L−1. Chemical analyses of filtrates (<0.01 µm) and x‐ray diffraction patterns, infrared (IR) spectra, and electron micrographs of the precipitation products (>0.01 µm) clearly showed that the degree of perturbation of the formation of imogolite increased with the rising concentration of humic substances, leading to the formation of ill‐defined aluminosilicate complexes. These complexes are similar in IR spectra to allophane‐like constituents or freeze‐dried protoimogolite and are associated with humic substances. In addition, pseudoboehmite and hydroxy‐Al‐humus complexes were present in the reaction products. The formation of imogolite was completely inhibited at concentrations >30 to 50 mg FA L−1 and 300 HA L−1. These results reveal that the pedogenic significance of humic substances in impeding the formation of imogolite and in promoting the formation of ill‐defined aluminosilicate or hydroxy‐Al‐humus complexes in the Andisol A and Spodosol Bh horizons merits attention.
Shrinkage Geometry of a Heavy Clay Soil at Various Stresses
Authors: Bronswijk J. J. B. 
Published: July 2010

AbstractThe shrinkage geometry of a clay soil drying from saturation to oven dryness was investigated. Undisturbed samples in rings measuring 232 cm3 were taken in the field at depths of 0.0, 0.20, 0.40 and 0.60 m. Overburden pressures at these four depths were determined by wet bulk‐density determination. Samples were oven dried with various loads applied on top. Surface subsidence and total volume decrease after drying were measured. It appeared that, for each soil layer, shrinkage at overburden pressures equal to or larger than field pressures was isotropic. When the load was removed during drying, subsoil samples showed relatively large cracking in comparison with surface subsidence.
Analytical Expression for Soil Water Diffusivity Derived from Horizontal Infiltration Experiments
Authors: Meyer J. J. , Warrick A. W. 
Published: July 2010

AbstractA technique is developed that utilizes a rational function θ = (A1 + A3λ)/(1 + A2λ) to fit water content (or other liquid) profiles resulting from horizontal infiltration as used in the Bruce‐Klute method for determining soil water diffusivity. In the above function, θ is water content (L3 L−3), λ is the Boltzmann variable, and A1, A2, and A3 are constants. The Boltzmann variable, λ, is equal to xt‐0.5, where x is the distance from the inlet of a horizontal soil column and t is time from the commencement of liquid imbibition. The function is easily fit to experimental data by either linear or nonlinear regression techniques and leads to analytical expressions for sorptivity and soil water diffusivity without further numerical approximation or fitting. If boundary conditions are specified, only one of the three coefficients is left to be determined. The rational function provided excellent approximations to liquid distribution for water and alcohol horizontal infiltration experiments in this study and is adequate for representation of experimental data of several other researchers. An example is included to illustrate that the approach is also applicable to determination of diffusivity for the hot‐air method.
Spatial Variation in Denitrification: Dependency of Activity Centers on the Soil Environment
Authors: Christensen Søren , Simkins Stephen , Tiedje James M. 
Published: July 2010

AbstractThe spatial variation in field denitrification rates was studied in an acid soil where the sole denitrification end product was N2O. The rate of N2O accumulation was measured under a soil cover at 30 fixed sampling locations arranged in a grid. Water and NO3 were added prior to all measurements to provide soil water contents at or above field capacity and excess NO3 for denitrification. No significant differences in N2O production rates were observed in samples incubated with or without C2H2, indicting that nitrification is not a significant source of N2O in this soil. Denitrification was found to occur in “hot spots” in moist soil and throughout the soil volume if the soil was flooded. Denitrification rates followed a skewed frequency distribution when soil water content was at field capacity: most locations had low activity, and a few locations exhibited high activity. The frequency distribution of denitrification rates was less skewed in samples after flooding, following large additions of glucose, or when the vegetation underwent decay in the fall. The intensity of denitrification was much higher after flooding than following glucose addition. A few sample locations occasionally showed outstandingly high denitrification rates when at field capacity, as well as when flooded. The activity in these hot spots approximated the potential denitrification activity of that soil.
Chemical Restrictions of Roots in Ultisol Subsoils Lessened by Long‐Term Management
Authors: Hardy David H. , Raper C. David , Miner Gordon S. 
Published: July 2010

AbstractExchangeable Al in subsoils of Ultisols in the southeastern USA can restrict rooting depth. Downward movement of basic cations (Ca, Mg, and K), applied as lime and fertilizer, may diminish that restriction over time. Materials from the argillic horizon were collected from three paired sites, having managed (long‐term cropping) and nonmanaged topsoils (Typic Paleudults and Hapludults). One managed site was cropped continuously for 15 yr while the others were cultivated for more than 30 yr. Concentrations of extractable cations and other nutrients from the paired sites were compared to determine the magnitude of change due to management. The ability of the subsoils to support plant growth was evaluated in a missing‐nutrient greenhouse experiment with sorghum [Sorghum bicolor (L.) Moench]. Subsoils of managed sites had greater effective cation‐exchange capacity (CEC) and base saturation than those of nonmanaged sites. While availabilities of Ca, Mg, and K in subsoils of nonmanaged sites were inadequate to support maximal plant growth, they were adequate in subsoils of managed sites. Compared with nonmanaged sites, KCl‐exchangeable Al in subsoils of managed sites was 23% lower at the 15‐yr location and 65 and 100% lower at the two other locations. In the absence of lime, sorghum growth was almost totally inhibited on nonmanaged subsoils amended with optimum nutrients. On the managed subsoils, where 100, 65, and 23% of the nonmanaged exchangeable Al had been neutralized by topsoil fertilization and liming, growth reductions under the same conditions were 0, 50, and 100%, respectively. Thus, relatively long‐term management had improved these Ultisol subsoils for root growth and development.
Prediction Technology for Soil Erosion by Water: Status and Research Needs
Authors: Nearing M. A. , Lane L. J. , Alberts E. E. , Laflen J. M. 
Published: July 2010

AbstractThis is a review of research related to soil‐erosion prediction technology. The trend in erosion prediction technology in the USA, Australia, and Europe is toward the development of process‐based simulation models. The emphasis in erosion research on strictly empirically based models, such as the Universal Soil Loss Equation, is declining. With the process‐based technologies come a new array of research needs. In the USA, The USDA Water Erosion Prediction Project (wepp) has produced a new generation of soil‐erosion prediction technology based on fundamentals of hydrologic and erosion science. The development of the new computer‐based wepp erosion model for estimation of rill and interrill erosion required an extensive review and analysis of current knowledge of the science of soil erosion by water. Research needs were identified. The relative importances of identified research needs were evaluated using a sensitivity analysis of the wepp model, which identified the more important of the input variables required to execute the model. The review of research reported here, along with a discussion of associated current needs for research, addresses four general areas: (i) fundamental erosion relationships, (ii) soil and plant parameters related to erosion, (iii) data bases, user interfaces, and conservation system design, and (iv) erosion model development and analysis.