bluuebunny/crossref_metadata_2025_split huggingface dataset:
Micromorphology of the Soil‐Saprolite Transition Zone in Hapludults of Virginia
Authors: Stolt M. H. , Baker J. C. , Simpson T. W. 
Published: July 2010

AbstractMost residual soils occurring in the southeastern USA have formed in saprolite. Between the saprolite and the argillic horizon lies a zone that divides material undergoing pedogenesis from that undergoing geochemical processes. We examined the physical, chemical, mineralogical, and micromorphological properties and characteristics of representative soils and saprolite formed from schistose or gneissic rocks of Virginia in order to describe and define the soil‐saprolite transition zone. Argillic horizons showed considerable oriented clay (3–16%), strong to moderate subangular blocky microstructure, porphyric coarse/fine related distribution patterns (c/f RDP), low (<0.5) coarse/fine ratios separated at 20 µm (c/f20µ ratios), and many planar voids. Oriented clay was absent from C horizons and microstructure was termed rock controlled to describe the apedal nature of these horizons. The c/f RDP was chitonic or gefuric, with the c/f20µ ratio at least double that of the argillic horizon. Microstructure of transition horizons was moderate subangular blocky to weak subangular blocky/rock controlled. The c/f20µ ratios and c/f RDP were intermediate between the argillic horizons and the saprolite. Transition horizons were designated as BCt, BC, or CB depending on percent oriented clay, rates of change with depth of clay, dithionite‐citrate‐bicarbonate (DB) extractable Fe, and sand contents. Weathering of mica grains showed slight to almost total pellicular and parallel linear alteration to hydroxy‐interlayered vermiculite (HIV), kaolinite, and an interstratified component of these minerals. Alteration of feldspar grains was generally <25% and occurred in the form of pellicular, or parallel, or cross‐linear patterns to kaolinite or gibbsite.
Repeated Fertilization Effects on Nitrogen Fluxes Measured by Sequential Coring
Authors: Whynot Tim W. , Weetman Gordon F. 
Published: July 2010

AbstractImproving site quality is an important goal of optimum‐nutrition trials where fertilizer is applied repeatedly to a site. Site quality is often measured by the rate of N mineralization, but commonly used agronomic methods for assessing N availability are often not suitable for forestry use; therefore, the merits of other methods need to be examined. To determine if four repeated N fertilizations at four rates in a young lodgepole pine (Pinus contorta [Dougl.] var. latifolia) stand had changed soil N‐mineralization rates, and to compare field and laboratory techniques for measuring N mineralization, the results of in situ sequential coring and anaerobic incubation were compared. Estimates of gross potential mineralizable N (laboratory‐incubated mineral N concentration) were consistent with field estimates, while net potential mineralization N (gross mineralizable N minus initial N concentration) estimates were not. While the data suggested increases in N fluxes, repeated N and P+K fertilization did not produce statistically significant increases (P > 0.05) in either N mineralization or uptake. Because sequential coring results in minimal soil disturbance and is sensitive to environmental processes, it is useful for evaluating other techniques for measuring N mineralization in forests, but requires intensive spatial and temporal sampling, which will limit its use. Because of variable flux rates following fertilization, mineralization should be measured two or more years following fertilization to determine if a significant change in site quality has occurred.
Iron Oxides in Selected Brazilian Oxisols: I. Mineralogy
Authors: Fontes M. P. F. , Weed S. B. 
Published: July 2010

AbstractTwelve Oxisols from the Triangulo Mineiro region, Minas Gerais state, Brazil, derived from four different parent materials were studied to provide insight into their Fe‐oxide mineralogy. The clay fraction (<2 µm) of all soils consisted of kaolinite and Fe oxides (hematite and/or goethite); gibbsite and anatase were found in most of the soils; maghemite was detected in several of them. Citratedithionite (CD) treatment of the soil clays showed hematite preferentially dissolved compared with goethite, and a higher dissolution rate for poorly crystalline than for well‐crystalline goethite. The calculated values for Al substitution in the Fe oxides, based on the CD extracts of the total clay corrected for Al soluble in acid ammonium oxalate, and of clay treated for gibbsite removal gave fair to good agreement with Al substitution determined by differential x‐ray diffraction (DXRD) for those samples in which the Fe‐oxide fraction was dominated by either goethite or hematite. Aluminum‐substituted maghemite, detected by DXRD, was present only in soils from mafic rocks, suggesting its formation through oxidation of the magnetite present in the parent material. Aluminum substitution, determined by DXRD, varied from 17 to 36 mol % for goethites, 6 to 15 mol % for hematites, and 16 to 26 mol % for maghemites. The mean crystallite dimension (MCDkkl) of some hematite samples determined from DXRD showed preferential crystal development in the X‐Y direction, suggesting a platy nature.
Synthetic Allophanes Formed in Calcareous Environments: Nature, Conditions of Formation, and Transformations
Authors: Farmer V. C. , McHardy W. J. , Palmieri F. , Violante A. , Violante P. 
Published: July 2010

AbstractSynthetic allophanes were prepared by adding excess CaCO3 to solutions containing Al(NO3)3 and Si(OH)4 (concentrations ≤1.5 mM) with molar Si/Al starting ratios ranging from 1:8 to 4:1. The systems were incubated at 20 and 80 °C until the concentration of Si(OH)4 in solution approached stability after 6 to 10 wk, when the allophanes were isolated and characterized by infrared (IR) spectroscopy and electron microscopy. At 20 °C, proto‐imogolite allophane, rather than Al(OH)3 species, formed when Si in solution exceeded about 50 µM, but hydrous feldspathoids, containing tetrahedral Al, were progressively formed when Si in solution exceeded about 150 µM. At 80 °C, partial or nearly complete transformation of these products to proto‐halloysite occurred for Si in solution above 50 µM. The presence of 1 mM Mg and K in the starting solutions did not affect the allophanes formed at 20 °C, but modified those formed at 80 °C. For starting Si/Al ratios of 1:2 and 1:1, the formation of proto‐halloysite was partially inhibited, but for starting ratios of 2:1 and 4:1, evidence for the initiation of 2:1 trioctahedral layer silicate saponite was obtained. It is postulated that an alkaline environment favors the transformation of allophanes to layer silicate clays, and that this may account for the scarcity of reports of allophanes in calcareous horizons. A marked decrease in Si in solution when acid soils are limed is explained.
Balloon and Core Sampling for Determining Bulk Density of Alluvial Desert Soil
Authors: Andraski B. J. 
Published: July 2010

AbstractSamples were collected from major strata in the upper 5 m of an alluvial soil profile in the Amargosa Desert of southern Nevada to compare rubber‐balloon and drive‐core bulk‐density measurement methods. For strate where the fine soil was <82% sand and <15% clay, differences between total and fine‐soil bulk‐density values determined by the two methods were typically <10 and 15%, respectively, even where rock‐fragment content was as great as 48% by volume. Outside this range of fine‐soil texture, where soil consistency was either very loose or very hard, the core method appeared to sample inaccurately, resulting in bulk‐density values >0.30 Mg m−3 less than those determined by the balloon method. Under the severe sampling conditions encountered, large decreases in the relative accuracy of the core method were not directly related to rock‐fragment content, but were related to extremes in the cohesiveness of the strata sampled.
Anthropic Epipedons in Oyster Shell Middens of Maryland
Authors: Kaufman Ian R. , James Bruce R. 
Published: July 2010

AbstractCitric acid extractable P is the principal criterion used in the taxonomic classification of soils to distinguish mollic and anthropic epipedons, but the method has not been standardized or evaluated for soils strongly influenced by low‐P, high‐CaCO3 shells in oyster middens. This method was used on oyster‐midden‐affected A horizon samples associated with Ultisols along the Chesapeake Bay in Maryland to clarify its utility for this type of human‐influenced soil. Five of six midden‐soil A horizons contained >250 mg of extractable P2O5/kg. The soil horizon meeting mollic criteria was clearly human influenced, with deposition of shells and other evidence of human settlement. The citric acid test appeared appropriate in most cases, but an anthropic subgrouping would aid in classifying these soils, especially for those soils with mollic epipedons that are visually identified as anthropogenic.
Physical and Morphological Characterization of Bypass Flow in a Well‐Structured Clay Soil
Authors: Booltink H. W. G. , Bouma J. 
Published: July 2010

AbstractBypass flow governs solute movement in well‐structured clay soils. Combined use of physical and morphological methods was made in this study to better characterize the process. Flow processes in five 200‐mm‐long undisturbed cores of 200‐mm diameter were monitored at 11‐min intervals by using 102 small transducer tensiometers, divided among five samples and installed at three depths. Flow patterns along macropores were stained with methylene blue. Twenty‐five tensiometers in or within a distance of a few millimeters of stained macropores reacted very quickly when 10 mm of simulated rain was applied at an intensity of 13 mm h−1, and showed a drying pattern after the end of the simulated rainfall. Forty‐three tensiometers inside peds reacted more slowly and showed continued wetting after the end of the simulated rainfall indicating internal catchment of water in the bottom of discontinuous macropores followed by redistribution of water. Internal catchment increased with depth in the samples, as indicated by both physical and morphological data. Using tensiometer measurements as a point count, it is estimated that 33% of the soil volume was in close contact with continuous macropores, while 42% was influenced by the effects of internal catchment. An average of 5.2 ± 0.96 mm of the applied 10 mm of water left the cores through bypass flow, while an estimated average of 3.3 ± 0.96 mm contributed to internal catchment. The observed patterns of water movement illustrate the inadequacy of the concept of mobile/immobile water.
Zinc Sorption by Manganese‐Oxide‐Coated Sand as a Function of pH
Authors: Stahl Randal S. , James Bruce R. 
Published: July 2010

AbstractManganese oxides in soils may be sites for sorption of heavy‐metal cations, but the roles of pH‐dependent charge and oxide mineralogy remain unclear as controls on exchangeability of the metals. A model soil‐oxide system tested the effect of pH on the amount and form of Zn retained in exchangeable or nonexchangeable fractions on birnessite‐hausmannite‐coated sand or pyrolusite‐coated sand. Two Zn treatments, 250 and 2500 µmol/kg sand, were used to determine the effect of Zn concentration on the form of Zn retained. Surface charge for the birnessite‐hausmannite‐coated sand and pyrolusite‐coated sand increased across the pH range from 4 to 7.6, but surface charge was found to be a poor predictor of the amount and form of Zn retained even though the oxides increased Zn sorption by the sand. The distribution between the exchangeable and nonexchangeable Zn fractions changed from predominantly exchangeable to predominantly nonexchangeable Zn due to the oxide coatings and higher pHs. The difference in the exchangeable and nonexchangeable Zn retention by the two sands was attributed to mineralogical constraints on the type of surface functional groups. The mechanisms proposed to account for the nonexchangeable retention of Zn on both oxide‐coated sand surfaces were hydrolysis of the Zn followed by chemisorption to the oxide surface.
Sodium‐Calcium Exchange on Brazilian Soils: Modeling the Variation of Selectivity Coefficients
Authors: Rieu M. , Touma J. , Gheyi H. R. 
Published: July 2010

AbstractBecause routine experimental determination of exchangeable cations is time consuming, models allowing for the prediction of the composition of the adsorbed phase based on that of the solution are of great interest. Thermodynamically based models allow the determination of exchange equilibrium constants from the variation of selectivity coefficients, as defined by Vanselow, Gapon, or Gaines‐Thomas, and usually modeled by a direct fit of experimental data. Empirical models, based on the relationship between the sodium adsorption ratio (SAR) and either the exchangeable sodium ratio (ESR) or the exchangeable fraction ratio (EFR) provide an estimate of adsorbed cation ratios. Both thermodynamically based and empirical models were tested on 74 Na‐Ca exchange equilibria measurements, carried out on calcic Cambisols representative of the Paraiba region of northeast Brazil. Because of their sensitivity to errors in measurement, questionable selectivity‐coefficient values were obtained by a direct fit of experimental data, so models involving these values appeared roughly approximate. Selectivity‐coefficient values calculated from empirical relations between SAR and either ESR or EFR were more accurate. Therefore, models of the variation of selectivity coefficients were derived from these relationships. Linear relations enabled consideration of the constancy of the selectivity coefficients across a range of SAR ≤60, as implicitly assumed by the well‐known relationship between SAR and ESR. Parabolic relations exhibited a restricted range of application, whereas power‐law relationships appeared very simple and accurate for producing both a direct estimate of the composition of the adsorbed phase and the calculation of the equilibrium exchange constant.
Determination of the Copper2+ Activity Required by Maize Using Chelator‐Buffered Nutrient Solutions
Authors: Bell Paul F. , Chaney Rufus L. , Angle Jay S. 
Published: July 2010

AbstractHydroponics is a useful method to study micronutrient deficiencies in plants. Problems in using this method to study Cu deficiencies are: (i) control of Cu supply to induce any degree of deficiency is difficult, (ii) purification of reagents is required to induce severe deficiency; and (iii) when chelators are added to induce Cu deficiency, the chelators may inactivate Fe, making Fe unavailable to plants. Mild to severe Cu deficiencies were induced in maize (Zea mays L.) without the purification of reagents using chelators HEDTA [N‐(2‐hydroxyethyl)ethylenediamine triacetate] with and without BPDS (4,7‐diphenyl‐1,10‐phenanthrolinedisulfonic acid) to bind and inactivate Cu. GEOCHEM‐PC was used to calculate the quantity of free and chelate‐bound Cu. A wide range in leaf and root Cu concentrations was observed from plants grown in HEDTA solutions with calculated solution Cu2+ activities of 10−15.4 to 10−12.4 M. The calculated Cu2+ activity associated with a 20% reduction in yield was 10−14.5 M (control plants yielded 15 g dry matter at 18 d). Solutions containing HEDTA with BPDS and the lowering of nutrient‐solution Ca concentrations were evaluated as means of inducing severe Cu deficiency. Maize grown in BPDS‐added solutions were severely stunted regardless of Ca treatment, and had significantly lower shoot Cu, Mn, and Fe concentrations than those found in other treatments. Results indicated Cu availability to maize was controlled by Cu2+ and not Cu+ activity. HEDTA, especially in combination with BPDS, can effectively induce Cu deficiency and supply adequate Fe to maize.
Liming Effects on the Stability and Erodibility of Some Brazilian Oxisols
Authors: Castro C. , Logan T. J. 
Published: July 2010

AbstractThe effects of liming on the aggregate stability and erodibility of three Oxisols in Parana State, southern Brazil, were studied. Two soils from Londrina, one in a 10‐yr coffee (Coffea sp.) plantation (LC), and the other in a secondary mixed hardwood forest (LM), were compared with a third Oxisol from Cascavel, also under secondary mixed hardwood forest (CA), to give a range of surface organic‐C contents in the order CA > LM > LC. Lime was applied to replicated field plots at each site to neutralize 0, 25, 50, 100, 200, and 400% of total exchangeable acidity. Acid was also added to the Londrina soils to reduce initial soil pH to that of the Cascavel soil. Changes in aggregate stability, soil splash, and water erosion were measured. Lime application decreased the weight percentage of 2.0 to 4.0‐mm‐diam. aggregates and mean weight diameter (MWD) of aggregates in Cascavel soil, but had no effect on the other two soils. Liming decreased the apparent clay content of all three soils, and increased water‐dispersible clay on the LC soil. There were no significant effects of liming on soil splash, in part because of the high experimental variability of measurement. Soil erosion, measured on the field plots with a portable rainfall simulator, was in the order LC > LM > CA, a trend that corresponded to the decreasing organic‐C contents of the soils. Liming significantly decreased erosion on the LC soil, and had no effect on the other two soils. The study suggests that, while there may be some short‐term structural degradation caused by liming, the long‐term effect is to reduce water erosion.
Soil Response to Acid Deposition, Wind River Mountains, Wyoming: II. Column Leaching Studies
Authors: Clayton James L. , Kennedy Debora A. , Nagel Terry 
Published: July 2010

AbstractBoth base exchange and SO4 adsorption were important proton consuming processes in a laboratory leaching study of western, high‐elevation Inceptisols. Two soils formed from granitic parent materials are present in the watershed: a highly organic Humic Cryaquept (HCA) located adjacent to streams and on lake margins, and an upland Dystric Cryochrept (DCO). Large, single‐horizon soil columns were leached sequentially with deionized H2O (six pore volumes [PV]), pH 4 H2SO4 (12–16 PVs), and pH 3 H2SO4 (11–16 PVs). These treatments were equivalent to 3 to 6 yr of runoff and 50 to 100 times annual S‐deposition rates. Proton exchange for base cations was very effective at buffering all horizons for the distilled H2O and pH 4 treatments. Following three to five PVs of pH 3 H2SO4, leachate pH dropped to 5 in the B horizon and 4.2 in the C horizon of the DCO. The Al(OH)3 dissolution then stabilized the pH in those two experiments. The A horizon of the DCO and both HCA horizons had sufficient cation‐exchange capacity (CEC) and base saturation to resist large pH depressions during the pH 3 treatment. Cation exchange was the dominant neutralization process, accounting for 56 to 96% of total proton consumption. Sulfate adsorption was important in DCO horizons (20–35% of protons consumed), but not in the organic HCA soil. Postleaching analysis of soils indicated that exchangeable Na and Mg decreased to about one‐half of original values, but Ca and K remained unchanged. Apparently, hydrolysis of abundant primary minerals can resupply these cations under the conditions of these experiments.
Phosphate Rocks Compacted with Superphosphates vs. Partially Acidulated Rocks for Bean and Rice
Authors: Menon R. G. , Chien S. H. , Gadalla Abd el Nabi 
Published: July 2010

AbstractPhosphate rocks (PR), which have low reactivity and contain large amounts of Fe and Al oxides, may be both ineffective as direct‐application fertilizers and unsuitable for partial acidulation. Such PRs can be made more effective by mixing them with soluble phosphates and compressing the mixture into pellets. The agronomic effectiveness of such pelletized mixtures was compared with that of partially acidulated phosphate rocks (PAPR), in pot trials with upland rice (Oryza sativa L.) and kidney bean (Phaseolus vulgaris L.) as indicator crops. Capinota PR, (CPR) which is low in reactivity and contains 8.8% Fe2O3 + Al2O3, and moderately reactive Huila PR (HPR), with 2.3% Fe2O3 + Al2O3, were mixed with triple superphosphate (TSP) to provide 50% of the total P in water‐soluble form in the mixture. The mixtures were then compacted into pellets. A Hartsells silt loam (fine‐loamy, siliceous, thermic Typic Hapludult, pH 4.5) was used in the study. With TSP as the standard (assuming 100% effectiveness), pelletizing it with CPR increased the CPR's relative effectiveness from 43% before treatment to 80% after for rice grain production and from 51% before treatment to 92% after for bean biomass yield. Likewise, P uptake by rice increased from 47 to 79% and uptake by beans from 51% to 92% of that of TSP for CPR compacted with TSP. The moderately reactive HPR, low in Fe2O3 + Al2O3, the Huila PAPR (HPAPR), and the compacted HPR pus TSP were 83 to 86% as effective as TSP in increasing grain yield of rice and 75 to 81% as effective in promoting P uptake. For bean, the relative effectiveness of HPR, HPAPR, and compacted HPR plus TSP was 88 to 95% for biomass yield and 80 to 88% for P uptake. This study confirms that, for some PRs that have low reactivity and high Fe2O3 + Al2O3 contents, compaction with soluble P fertilizers is agronomically more effective than partial acidulation.
Field Measurement of Solute Travel Times Using Time Domain Reflectometry
Authors: Kachanoski R. G. , Pringle E. , Ward A. 
Published: July 2010

AbstractA limiting step in our understanding of solute transport through unsaturated field soils is the lack of experimental data. Field solute transport characteristics such as the travel‐time density functions, FL(T), for different soil depths are often very difficult and time‐consuming to measure. The objective of this study was to develop a method to measure FL(T) for a conserving tracer added as a pulse under conditions of constant surface water flux density. The method uses vertically installed time domain reflectometry (TDR) probes. At constant soil volumetric water content, ϑ, the TDR estimate of bulk electrical conductivity, ECE, is related to the average pore water concentration of an added solute tracer, which in turn is related to the total specific mass (g m‐2) of the tracer between the TDR probes. The change in EC*E with time is shown to be linearly related to the mass flux of the solute past the ends of the TDR transmission rods. Solute mass flux out of a laboratory column was very similar to that measured using the TDR method. Excellent agreement was also obtained between solute‐mass‐flux measurements in the field (0.2‐m depth), using ceramic solution samplers, and the new TDR method. The method measures mass flux of the solute at a particular depth and not solute concentration. Thus, no assumptions about local water flux density are necessary in estimating FL(T). The method also has the advantage that ϑ can be measured at the same location (soil volume) where the solute mass flux is measured. The method is limited to soils where addition of a solute pulse will cause a measurable reduction in the reflected signal. This depends on steady‐state soil water content, ECE at steady state, and the depth of measurement.