bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microtopographical Characteristics of Artificially Formed Crusts
Authors: Levy G. J. , du Plessis H. M. , Berliner P. R. , van der Watt H. v. H. 
Published: July 2010

AbstractThe properties of artificially formed crusts have usually been studied on two widely different scales: (i) the whole crusted area on which infiltrability was measured and (ii) small samples of crust as used for scanning electron microscope (SEM) studies. A close inspection of some crusts revealed the presence of small mounds protruding from relatively smooth plains. The surface characteristics of artificially formed crusts of a Plinthustalf with two levels of exchangeable sodium percentage (ESP) were investigated on three different scales viz. (i) macro: the whole crusted area as used for bulk infiltration measurements (500 mm by 300 mm), (ii) intermediate: having the typical dimensions of mounds (8–10 mm in diam. where local permeabilities were determined), and (iii) micro: having the dimensions of samples used in SEM studies. Mounds and plains exhibited different permeabilitiees with the mounds maintaining higher values than the plains irrespective of the ESP of the soil. This was due to the structural differences between the two features. The mounds maintained a profile relatively similar to the profile of an uncrusted soil even though some loose clay particles were evident on the soil surface. Conversely, in the plains a dense layer of compacted particles was visible at the soil surface. The area occupied by the mounds decreased with an increase in cumulative rain and ESP. The trend of the weighted permeabilities obtained from the intermediate scale measurements corresponded to the observed trend in the bulk infiltration measurements.
Compaction and Nitrogen Placement Effect on Root Growth, Water Depletion, and Nitrogen Uptake
Authors: Garcia Fernando , Cruse R. M. , Blackmer A. M. 
Published: July 2010

AbstractZones of compaction and/or high nutrient concentration that exist with selected tillage systems can alter plant root growth. It is hypothesized that these alterations affect water and nutrient uptake patterns. A greenhouse experiment was conducted to study the effects of horizontally and vertically oriented compaction zones and nitrogen (N) fertilizer placement on corn (Zea mays L.) root growth patterns, soil water depletion, and N fertilizer uptake. Compaction treatments included a simulated plow pan, simulated wheel tracks in one or both interrows, and uncompacted soil. 15N‐enriched ammonium nitrate was point injected 0.1‐m deep at a rate of 80 kg N ha−1 either under the plant or in a simulated interrow region (0.13 m to the side of the plant); a check treatment (no N) was also included. Compaction and N treatments were factorially combined in five randomized blocks. Corn plants were grown for 26 d without rewatering. Measurements taken at 26 d included: shoot and root growth, plant 15N content, and soil water content, and distribution. Compaction treatments did not significantly affect total root growth, but N fertilization tended to decrease it. Root growth compensation, both enhancement in zones of favorable nutrient supply and redirection of growth to zones of more favorable physical conditions, was observed. Nitrogen placement had a greater impact on N uptake when compaction zones were present than when they were not present. Water extraction from a given zone was directly related to root density in that zone.
Effect of Tillage Practices on Infiltration and Soil Strength of a Typic Hapludult Soil After Ten Years
Authors: Radcliffe D. E. , Clark R. L. , Tollner E. W. , Hargrove W. L. , Golabi M. H. 
Published: July 2010

AbstractHighly weathered soils of the Southeastern USA are poorly structured and may present special problems under continuous no‐tillage production. Soil physical properties were examined in a long‐term tillage experiment starting in its 10th year to determine if there were differences due to tillage. Fall/spring tillage treatments consisted of moldboard plow/moldboard plow (CT), moldboard plow/no‐tillage (MT), and no‐tillage/no‐tillage (NT). Cone index measurements in NT exceeded 4 MPa at a depth of 0.10 to 0.20 m, indicating the presence of a compacted zone. Bulk density was significantly higher than CT at this depth also (1.60 vs. 1.40 Mg m−3). Spring planting traffic compacted the top 0.15 m in all treatments. Infiltration rates, measured with a sprinkler infiltrometer, were significantly higher in NT. The straw mulch (5000 kg ha−1) and layer of fine organic litter at the surface of NT prevented the formation of an impermeable surface crust. Removing the mulch and litter layer from NT sharply reduced the infiltration rate. Adding a mulch to CT increased the infiltration rate. We conclude that during short‐term summer rainfall events, infiltration in conventionally tilled soil is controlled by surface crusting.
Transitional Vermiculite‐Smectite Phases in Aqualfs of Southwestern Ohio
Authors: Ransom M. D. , Bigham J. M. , Smeck N. E. , Jaynes W. F. 
Published: July 2010

AbstractThe clay mineralogy of two Aqualfs occurring on the Illinoian till plain of southwestern Ohio was investigated in order to (i) determine the clay mineral distribution with depth, (ii) examine the clay mineral weathering sequence, and (iii) identify the 2:1 mineral species in which hydroxy interlayers had formed. Despite the presence of multiple parent materials, no obvious discontinuities in clay mineralogy were observed. A weathering sequence involving the transformation of clay mica to vermiculite to low charge vermiculite/high charge smectite occurred. Alkylammonium ion exchange data indicated that weathering created a heterogeneous charge distribution in the 1.4‐nm (expandable) mineral phase resulting in mixed low‐and high‐charge interlayers. The low‐charge interlayers readily formed bilayer complexes with ethylene glycol (1.7 nm), and also accommodated double layers of glycerol (1.8 nm) when the mean layer charge was <0.65. Reductions in layer charge were correlated with the oxidation of octahedral Fe(II) and the expulsion of K and Mg from the mineral structure. The expansion of 2:1 layer silicates in horizons near the soil surface was restricted as a result of Alhydroxy interlayering. After interlayer materials were removed with boiling 0.33 M Na citrate, the previously interlayered minerals exhibited x‐ray diffraction effects following Mg saturation and ethylene glycol and glycerol solvation that were indicative of vermiculite.
Estimating Michaelis‐Menten or Langmuir Isotherm Constants by Weighted Nonlinear Least Squares
Authors: Persoff Peter , Thomas Jerome F. 
Published: July 2010

AbstractWe derive a nonlinear least squares fitting method for determining either Michaelis‐Menten equation or Langmuir adsorption isotherm constants from experimental data. Data points can be weighted unequally if their relative precisions are known. Comparison of this method with the commonly used linearization methods, using simulated data sets containing normally distributed random errors, showed that this method yields more accurate and precise estimates of the constants than any of the linearizations. A short BASIC program to facilitate computation is presented.
Selenite Adsorption on Alluvial Soils: III. Chemical Modeling
Authors: Sposito Garrison , de Wit J. C. M. , Neal Rosemary H. 
Published: July 2010

AbstractSelenite adsorption envelopes for five alluvial soils from the San Joaquin Valley, CA, were described with the constant capacitance model, which is based on the ligand exchange mechanism of anion adsorption. The adsorption envelope data covered the pH range 4 to 9 and referred to 1:25 (w/w) soil suspensions in a 50 mol m−3 NaCl background. The initial selenite concentrations used were 2 and 8 mmol m−3. Model application consisted of determining, for one of the five soils, the intrinsic surface complexation constants for the species, SHSeO03, SSeO‐3, and S2SeO03, (S represents a surface Lewis acid site) subject to constraints of mass and charge balance and assumed values of the surface acid‐base reaction constants and capacitance density parameter. The binuclear complex S2SeO03 was treated independently of the two monodentate surface species with respect to mass and charge balance. Optimization of the model with the adsorption envelope for a Panoche soil at an initial selenite concentration of 2 mmol m−3 was used to predict the adsorption envelopes for the four other soils at the same initial selenite concentration, as well as those for three soils at an initial selenite concentration of 8 mmol m−3. The model predicted adsorption envelopes whose qualitative agreement with the experimental data was satisfactory, but whose quantitative agreement ranged from excellent to poor.
Anion Sorption on a Calcareous, Montmorillonitic Soil‐Selenium
Authors: Goldberg Sabine , Glaubig R. A. 
Published: July 2010

AbstractSelenite and selenate sorption on a calcareous, montmorillonitic soil was investigated as a function of solution pH (2–11) at two initial Se concentrations (1.9 mmol m−3 and 19 mmol m−3. Selenate sorption was not observed at any pH value for either initial Se concentration. Selenite sorption exhibited a maximum near pH 3, a sharp decline to pH 6, and a sorption plateau above pH 7. Selenite sorption as a function of pH was studied on reference minerals representative of the dominant mineral constituents of the soil: montmorillonite, kaolinite, and calcite. Selenite sorption on the clay minerals increased at low pH, exhibited a peak near pH 5, and decreased at higher pH. Selenite sorption on calcite increased from pH 6 to 8, peaked between pH 8 and 9, and decreased above pH 9. The constant capacitance model was able to describe selenite sorption on montmorillonite and kaolinite over the entire pH range studied and on the soil below pH 7. The soil sorption plateau above pH 7 virtually disappeared after removal of calcite, indicating that calcite plays an important role in selenite sorption of calcareous soils.
Influence of Phosphate Sorption Parameters of Soils on the Desorption of Phosphate by Various Extractants
Authors: Kuo S. , Jellum E. J. , Pan W. L. 
Published: July 2010

AbstractSeven different soils enriched with varying amounts of phosphate were extracted with NaHCO3, NaOAc, or NH4F‐HCl solution for determining how phosphate sorption parameters affect such extractions. While the amount of phosphate extracted increased with increasing amount of phosphate sorbed, it varied considerably among the soils. The fraction of added phosphate recovered by the extractants was highly correlated with phosphate sorption capacity (Xm), but not with either the phosphate affinity constant (K) or the maximum buffering capacity (KXm) estimated by the Langmuir isotherm. Since the affinity constant is a component of the maximum buffering capacity, poor correlation between the affinity constant and the phosphate recovery may have contributed to the relatively low correlation of the maximum buffering capacity with the phosphate recovery. The quantity of phosphate desorbed was not affected by the phosphate affinity constant but by the fraction of phosphate coverage of the soils. Regression equations were developed for estimating the amount of phosphate sorbed based on the amount of phosphate desorbed by the extractants. The amount estimated based on NaHCO3‐extractable phosphate was highly correlated with that based on NaOAc‐extractable phosphate, which suggests the feasibility of using the regressions to convert NaOAc‐extractable phosphate to NaHCO3‐extractable phosphate, or vice versa.
Complexation and Catalyzed Oxidative Polymerization of Catechol by Aluminum in Acidic Solution
Authors: McBride M. B. , Sikora F. J. , Wesselink L. G. 
Published: July 2010

AbstractThe role of soluble Al in catalyzing the abiotic oxidation of phenolic compounds has been investigated by monitoring the slow oxidation of aerated aqueous solutions of catechol containing Al. Spectroscopic analysis of the various oxidation products has demonstrated that aqueous Al3+ increases the rate of oxidation of catechol by O2, favoring the formation of highly colored polymeric products which may possess charge‐transfer properties. Spectral (UV‐visible, nuclear magnetic resonance, infrared, and electron spin resonance) properties of these products suggest that they have some similarities to polymers generated by alkaline oxidation of polyphenols, but they also have properties which suggest that they are related to melanins generated enzymatically byu fungi and plants. A proposed low‐pH mechanism for the role of Al in promoting oxidative polymerization is based on the concept that Al3+ cations tend to stabilize o‐semiquinone radicals at low pH and direct the manner in which these radicals polymerize. Aluminum may also stabilize charge‐transfer complexes by bridging oxidized and reduced molecules. Preliminary evidence is presented to suggest that the surfaces of Al oxides in soils may, by a similar mechanism, catalyze the oxidation of phenolic compounds by O2.
Phosphorus Fertilizer Placement and Tillage in a Wheat‐Fallow Cropping Sequence
Authors: Stecker J. A. , Sander D. H. , Anderson F. N. , Peterson G. A. 
Published: July 2010

AbstractSince water and wind erosion are serious problems during fallow in most western winter wheat (Triticum aestivum L.) growing areas and available soil P is often low, field studies were conducted at three locations in western Nebraska on a Keith silt loam (fine‐silty, mixed, mesic, Aridic Argiustoll). These studies compared the performance of broadcast, knife and seed placement of fertilizer P with and without a residue treatment of 13.5 Mg ha−1 in a plow, no‐till, and stubble mulch tillage system. Plowing generally tended towards the highest and no‐till the lowest grain yield and P uptake. Delayed maturity resulting from abnormally cool spring temperatures was believed to be a contributing factor to lower yields in no‐till. Without applied residue, grain yields were increased by P placement methods in the order of seed = knife > broadcast similar to other reported research. When residue was applied, knife placement was less effective and broadcast more effective compared to seed placement at the low P rate (8.4 kg ha−1). At the high P rate (16.8 kg ha−1) seed placement produced the highest yield of all treatments. Seed placement showed higher P uptake in no‐till than other tillage treatments at one location while broadcast P resulted in higher P uptake with plowing than with stubble mulch or no‐till at another location. The colder soil temperatures associated with surface residues apparently favored seed placement of P. There was a trend for grain yield and P uptake to be lower when P was knifed in the presence of surface residues.
Subsoil Saturated Hydraulic Conductivity in Relation to Soil Properties in the North Carolina Coastal Plain
Authors: Southard R. J. , Buol S. W. 
Published: July 2010

AbstractLaboratory measurements of saturated hydraulic conductivity (Ksat) of soil cores from nine North Carolina Coastal Plain Ultisols demonstrate that Ksat generally decreases with increasing depth, while grade of blocky structure generally becomes stronger with depth. The best single predictor (second‐order polynominal, r2 = 0.81, p < 0.001) of Ksat is the proportion of pores with diameters >30 µm (LP) as calculated from water retention characteristics, followed by the coefficient of linear extensibility measured on soil pastes (COLE paste, r2 = 0.50). Total porosity is correlated negatively with Ksat (r2 = 0.16, p > 0.10). Multiple regression of Ksat on LP and COLE paste decreased correlation slightly (R2 = 0.77, p <0.001). Weighted mean ped diameter (WMPD), which is an indication of structure size and grade, is not significantly (p < 0.10) correlated with Ksat. Inter‐ped planes of weakness are not well developed in these weakly structured soils and do not contribute much to saturated flow. Stratification of pedons by drainage class and clay content had minor effects on regression correlation. Large pores are the dominant conduits for saturated water movement in these soils as measured by the method used in this study. The proportion of large pores, probably mostly of biological origin, decreases with increasing soil depth as biological activity is attenuated. The COLE paste measurement provides an index of the potential for swelling of clay minerals and resultant constriction of water‐conducting channels when soils are saturated.
Accumulation of Pedogenic Gypsum in Western Oklahoma Soils
Authors: Carter B. J. , Inskeep W. P. 
Published: July 2010

AbstractRecognition of pedogenic gypsum is particularly needed in parts of arid and subhumid climates to apply the suffix “y” to master horizons and to understand soil‐forming processes. Soil micromorphology provides correlation between field and laboratory observations, and recognition of pedogenic gypsum for the refinement of the “y” horizon suffix designation. Seven soils were described and sampled to (i) identify pedogenic gypsum, (ii) determine the distribution of pedogenic gypsum across a hillslope, and (iii) explain the occurrence of gypsum in residual‐derived soils. Gypsum content, saturated paste extracts analyzed for Ca2+ and SO2‐4, and micromorphology indicated gypsic horizon formation within the summit position. Small amounts of pedogenic gypsum occurring with allogenic and bedrock gypsum were identified in soils using micromorphology. Pedogenic gypsum accumulation was greatest in soils with higher contents of total gypsum and relatively longer periods of soil formation. In situ dissolution of gypsum during wet springs (March–June) followed by reprecipitation during hot dry summers (July and August) is proposed to explain the formation of pedogenic gypsum. An accumulation of pedogenic gypsum in the B horizon may indicate a net upward movement within the solum or a lateral movement of gypsum within the landscape. The compaction of diagenetic gypsum during geologic burial is proposed to explain gypsum form and formation within veins and joints in Cr and R horizons. Rock fragments containing vein and joint fillings of gypsum persisted within the solum and were identified as bedrock gypsum.
Ammonia Volatilization from Surface‐applied Urea as Affected by Several Phosphoroamide Compounds
Authors: Beyrouty C. A. , Sommers L. E. , Nelson D. W. 
Published: July 2010

AbstractIn an attempt to reduce ammonia (NH3) losses from surface applied urea to ultimately increase plant N use efficiency, a field experiment was conducted to compare the effects of six phosphoroamide urease inhibitors on NH3 volatilization from urea surface applied to no‐till (NT) and conventionally tilled (CT) soils. Urea prills (200 kg N ha−1) with and without phosphoroamide inhibitors (4.0 kg a.i. ha−1) were broadcast on the surface of microplots. Ammonia evolution was measured using a semiopen‐static system in which the volatilization chambers were moved periodically to compensate for soil environmental changes induced by the enclosures. Environmental and soil conditions affected the cumulative and daily losses of N. Losses were greater and more rapid under warm, moist soil conditions than hot and dry conditions. The low specific humidity during the hot, dry conditions prevented complete dissolution of prills until 6 d after application thus reducing hydrolysis and NH3 volatilization. Phenylphosphorodiamidate (PPD) most consistently reduced cumulative NH3 losses on NT and CT. Ammonia loss with the addition of PPD was 10 to 54% of the NH3 loss with unamended urea in three of four tests. Trichloroethyl phosphorodiamidate and N‐(diaminophosphinyl)‐cyclohexane were the only other compounds to significantly reduce NH3 losses compared to unamended urea, but these compounds were effective in only one‐half the tests. Both field and laboratory studies showed significantly greater NH3 losses from urea applied to residue covered soil than to bare soil. Addition of PPD or thiophosphoric triamide to residue reduced N losses to 43 and 39% of applied urea‐N, respectively. The effectiveness of PPD in retarding NH3 losses was decreased as the soil pH increased from 5.6 to 7.2.
Characterization and Quantification of Aluminum‐Substituted Hematite‐Goethite Mixtures by X‐ray diffraction, and Infrared and Mössbauer Spectroscopy
Authors: Amarasiriwardena D. D. , Bowen L. H. , Weed S. B. 
Published: July 2010

AbstractMixtures of aluminous goethite and hematite with varying amounts of Al substitution up to about 25 mole % were analyzed by x‐ray diffraction (XRD), Fourier‐transform infrared spectroscopy (FTIR), and Mössbauer spectroscopy. Crystalline dimensions decreased with Al substitution for both the hydrothermally‐synthesized goethites and the hematites prepared from them by heating at 500 °C. Band positions in the infrared shifted to higher wave numbers with Al substitution for both the bending modes of goethite and the O‐displacement modes of hematite. Mössbauer spectra obtained at 80 K down to 16 K were fitted with a distribution of hyperfine fields. Both the average and maximum‐probability field decreased with Al substitution. The mixtures exhibited linear correlations of peak intensity with hematite concentration for all three techniques, although XRD and Mössbauer spectroscopy were more sensitive than FTIR for detection of small proportions (<50 g/kg) of hematite. Sensitivity of XRD decreased with Al substitution. The field distribution analysis was essential for obtaining quantitative ratios of hematite to goethite from Mössbauer spectra of mixtures where the hematite proportion was low.
Length of Incubation Time Affects the Parameter Values of the Double Exponential Model of Nitrogen Mineralization
Authors: Cabrera M. L. , Kissel D. E. 
Published: July 2010

AbstractThe double exponential model has been used to describe nitrogen N mineralization in disturbed soil samples, allowing the separation of two N pools that mineralize according to first‐order kinetics. We fitted the model to data from various incubation times to study the effect of incubation time on the parameter values of the model. In general, as the incubation time increased, the apparent size of the two N pools increased, whereas their rate constants of mineralization decreased. These results call for caution when comparing parameter values obtained with different incubation times.
Designs for Disc Permeameters
Authors: Perroux K. M. , White I. 
Published: July 2010

AbstractDisc permeameters are designed to measure hydraulic properties of field soils containing macropores and preferential flow paths and are particularly useful in soil management studies. We present here designs for disc permeameters for both positive and negative water supply heads. The effects of the water supply membrane and soil contact material on permeameter performance are examined using approximate quasi‐analytic solutions to the flow equation. This analysis provides approximate criteria for the selection of membrane and soil contact materials. Limitations to performance caused by restricted air entry are considered and design criteria are given also. We present in situ tests of the disc permeameter for the early stages of one‐dimensional infiltration and an example of the deterministic variation of sorptivity of a field soil with supply potential. Finally, we use ponded and unsaturated sorptivities measured in situ with disc permeameters to find the saturated hydraulic conductivity and flow‐weighted mean characteristic pore dimension of a field soil.