bluuebunny/crossref_metadata_2025 huggingface dataset:
Sorption and Sorptive Interaction of Cadmium and Zinc on Hydrous Manganese Oxide
Authors: Zasoski R. J. , Burau R. G.
Published: July 2010

Adsorption of Zn, Cd, and Ca by δ‐MnO2 was measured at pH 4, 6, and 8 by a batch technique at steady‐state conditions. Fitting the data to Langmuir and Freundlich expressions suggested that there were two or more mechanisms or sites of sorption for both Zn and Ca. The “higher energy” site(s) (first to fill) showed preference for Cd over Zn, whereas the reverse was true for the lower energy site(s). Simultaneous addition of both Cd and Zn reduced adsorption of both ions. Cadmium and Zn adsorption diminished somewhat when Ca was present at higher Zn and Cd loadings but competition from Ca was minimal at low metal loadings. It is proposed that the high energy binding is an exchange sorption on the negatively charged oxide sites by displacement of surface and diffuse layer cations and protons, which binds Cd more strongly than Zn. On a relative basis at pH 6 and 8, Zn is more strongly bound than Cd. The higher surface charge density and greater proportion of Zn hydroxy solution phase species at higher pH may favor Zn sorption. Competition between Cd, Zn, and Ca was observed at pH 4, 6, and 8, suggesting that solution bulk precipitation was not controlling solution metal concentrations.
Differences in Humic Acid Characteristics as Determined by Carbon‐13 Nuclear Magnetic Resonance, Scanning Electron Microscopy, and Infrared Analysis
Authors: Lobartini J. C. , Tan K. H.
Published: July 2010

An investigation was conducted on the usefulness of 13C nuclear magnetic resonance (NMR) spectroscopy in the characterization of humic acids (HA) isolated from selected soils. Soil samples for extraction of HA were collected from Indonesia, USA, and Argentina. The analyses were conducted by liquid 13C NMR, scanning electron microscopy (SEM), infrared (IR), and chemical analysis. The NMR spectra indicated that all HA samples had in common aliphatic, polysaccharide, aromatic, and carboxyl groups. However, the NMR signals for the chemical groups were different in intensities, producing a distinctive spectrum for each HA studied. The NMR analysis demonstrated that HA from the tropical region soils were highly aliphatic in nature, with a combined carbohydrate and polysaccharide C content of 59.5 to 67.6%. On the other hand, HA from the seven temperate region soils contained more COOH and aromatic C. The highest aromatic C concentration together with the strongest NMR signals for aromaticity were exhibited by HAs of the Mascotte (Ultic Haplaquod) and the Argentina (suborder unknown) soil. The differences in NMR spectra were accompanied by differences in SEM micrographs and IR spectra. A significant correlation was noted between NMR and especially IR spectra. Humic acid samples with strong NMR signals for aromatic C exhibited IR spectra with strong bands at 1240 cm−1, whereas HA with weak NMR signals for aliphatic C had IR spectra with weak bands at 2980 to 2900 cm−1. Therefore, IR spectroscopy can also be an important tool in the characterization of humic matter when used in conjunction with 13C NMR.
Effects of Parent Material Weathering on Chemical and Mineralogical Properties of Selected Hapludults in the Virginia Piedmont
Authors: Wysocki Douglas A. , Lietzke D.A. , Zelazny L.W.
Published: July 2010

Saprolite is a parent material prevalent in the Piedmont of the USA. Chemical weathering during saprolite development, but prior to soil formation, may obliterate chemical and mineralogical influences due to parent rock differences. The Cullen series and associated red Hapludults mapped in the Piedmont are an example. Cullen soils are derived from saprolites weathered from rocks of varying mafic and felsic composition. The mafic influence (Fe content) is manifested in the Cullen series as a dark red (1OR or 2.5 YR 3/6) B subhorizon. Soils that lack this feature are presumed to be less productive. Family control section chemical and physical properties were consistent among pedons studied, and did not relate to parent rock type or B horizon color. Lesser amounts of extractable Al in the lower part of the series control section provide a clue as to why Cullen soils are preferred for agricultural use over other Hapludults. Fourteen of the pedons studied were in the mixed mineralogy class, two were oxidic, and none were kaolinitic. In the northern Piedmont kaolinitic soils do not appear to exist, except on mafic parent materials. Soils studied had a high iron oxide content (2.0–15%), which did not correlate with dark red colors or parent material. Conversely, they contain small amounts of gibbsite. This data and discrepancies in the oxidic definition question the validity of the present osidic family requirements as a means for identifying soils dominated by weathered minerals. Soils derived from saprolites weathered from a variety of parent rocks have reached a similar mineralogical and chemical state in the family control section.
Cationic Polymer Effects on Infiltration Rates with a Rainfall Simulator
Authors: Helalia Awad M. , Letey J.
Published: July 2010

The cationic polymer “CP‐14” was applied to three soils at concentrations of 0, 5, 10, 20, and 50 mg L−1 in synthesized canal water (CW) (0.05 dS m−1) and well water (WW) (0.7 dS m−1) through a rainfall simulator. This first cycle was followed after drying by two cycles with untreated water. In some cases, a fourth cycle was conducted with the same polymer concentration as the first cycle. The infiltration rate (IR) was measured in each case. With one exception, the IR increased as the polymer concentration increased for all soils and both waters. The IR was higher with WW than with CW in all cases. The IR decreased successively from the first through the third cycle due to dispersion at the soil surface caused by drop impact and chemical effects of the applied water. Although the IR increased during the first cycle with increasing polymer concentration, the highest effects were obtained at 5 and 10 mg L−1 concentrations with diminishing effects at higher concentrations. In most cases, benefits of the higher concentrations were observed during the two cycles when polymers were not added to the water. The IR during the fourth cycle with polymer addition was higher than for the second and third cycle but lower than for the first cycle. The clay concentration in the effluent from CW did not change with polymer addition but the IR changed significantly. In addition, the clay concentration in the effluent from WW was very much lower than for CW. The IR values in the present study were correlated with the results of a flocculation test at 5% significance. Therefore, the flocculation test appears to be a useful, quick technique for determining the relative effectiveness of water quality and polymer addition on IR.
Urea and Biuret Stimulate Growth of Douglas‐fir and Western Hemlock Seedlings
Authors: Miller Richard E. , Anderson Harry W. , Young Donald C.
Published: July 2010

Two experiments were conducted in a greenhouse to test a theory that biuret in urea fertilizer reduces growth of Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] or western hemlock [Tsuga heterophylla (Raf.) Sarg.]. Newly germinated seedlings in 2.5‐L pots were treated with 0, 0.224, 2.24, or 22.4 kg biuret ha−1 (40% N) in factorial combinations with 0, 84, or 168 kg N ha−1 as reagent‐grade urea (46% N). The biuret was applied as a solution to either the sandy loam soil or the foliage. Four of the eight replicates were harvested 203 d after treatment. For Exp. 2, the remaining seedlings were retreated as they were initially and harvested 305 d later. In both experiments, the two species responded strongly to urea; moreover, seedling dry weight increased with increasing biuret (P = 0.003). Averaged over all other factors, weight of seedlings treated with the highest biuret dosage was 14% more than the weight of seedlings with no biuret. Unfertilized hemlock responded as much to 0.2 kg biuret ha−1 (0.08 kg N ha−1) as to 84 kg N ha−1 as urea; this suggests that biuret functions as a hormone. The results indicated that biuret is unlikely to reduce growth of seedlings of either species even when urea heavily contaminated with biuret is applied at high dosage.
Effect of Nitrogen Source and Dicyandiamide on Growth and Water Relations of Cotton
Authors: Reeves D. W. , Touchton J.T. , Rickerl D. H.
Published: July 2010

Nitrification inhibitors such as dicyandiamide (DCD) may improve N efficiency for cotton (Gossypium hirsutum L.) grown on sandy Coastal Plain soils. Research has demonstrated that cotton is sensitive to DCD, and field experiments suggest a possible link between cotton response to DCD and rainfall distribution. A green‐house experiment was conducted to investigate the effect of DCD and N source on growth and water relations of cotton on a typical Coastal Plain soil. Cotton (Deltapine 90) was grown in pots containing a Norfolk sandy loam (fine‐loamy, siliceous, thermic, Typic Paleudults). Nitrogen (50 mg kg−1) as NaNO3 or urea, and DCD (0, 2.5, 5, 10, 15, and 20 mg DCD‐N kg−1) were applied to the soil at first true leaf. Soil water content, leaf xylem water potential (ψ1), and stomatal conductance were monitored during a 3‐d drying period, commencing at first bloom, following which plants were harvested. Both N source and DCD affected plant growth and water relations, but there were no significant interaction effects. Fertilization with NaNO3 increased leaf dry weight 9.1% compared with fertilization with urea. Plants fertilized with NaNO3 depleted soil moisture faster than plants fertilized with urea, resulting in lowered stomatal conductances and more negative ψ1 throughout the drying period. Dicyandiamide lineraly reduced leaf area and dry weight, and stem dry weight. Dicyandiamide did not affect soil‐water depletion, ψ1, or stomatal conductance in the morning. Under more stressful afternoon conditions, DCD, especially at rates ≥10 mg DCD‐N kg−1, increased stomatal conductance over the range of available soil water. Dicyandiamide‐induced increases in stomatal conductance under conditions of nonlimiting soil water could increase photosynthesis and possibly lint yield. In years when soil water is limiting, however, additional stress from DCD phytotoxicity could result in yield reductions.
Column‐Profile Measurements Using Fiber‐Optic Spectroscopy
Authors: Kulp Thomas J. , Bishop Dorothy , Angel Stanley M.
Published: July 2010

Fiber‐optic spectroscopy was used to measure the flow of a fluorescent dye in a column packed with glass beads. Optical fibers inserted between the packed beads served as light pipes to transmit excitation light to the measurement zone at their distal end and to return fluorescent emission to a spectrometer. In this way, the dye concentration at the point of measurement was monitored. Data are presented demonstrating that flow can be monitored at several points in the column by multiplexing more than one fiber into a single spectrometer. This technique provides a tool to make fundamental flow measurements that have to date been experimentally impossible.
Phosphate Adsorption by Aluminous Hematites of Different Shapes
Authors: Barron V. , Herruzo M. , Torrent J.
Published: July 2010

The phosphate adsorption capacity of 43 synthetic hematites having widely different shapes, specific surface areas and Al2O3 mole fractions ranged between 0.19 and 3.33 µmol P m−2, with a mean value of 0.97 µmol P m−2. There was a significant decrease in the adsorption capacity when the diameter/thickness ratio of the particles increased; this agrees with the hypothesis that, because of the distribution and type of surface hydroxyls, the basal faces of hematites are not able to adsorb phosphate, in contrast with some of the nonbasal faces. The low adsorption capacity of the hematites studied here, as compared to many natural and synthetic goethites, gives a reason why, as reported in the literature, red (hematitic) soils adsorb less phosphate than similar yellow (goethitic) soils.
Effects of Field Methods and Soil Cover on Estimating Ammonia Loss from Nitrogen‐15‐Urea
Authors: Reynolds C. M. , Wolf D. C.
Published: July 2010

Ammonia loss from urea fertilizers is difficult to measure accurately in the field. In a field study we compared two methods for measuring NH3 loss from 15N‐urea surface applied to bare and bermudagrass (Cynodon dactylon L.) covered Captina silt loam (fine‐silty, mixed, mesic, Typic Fragiudult). The two methods were semiopen chambers and open microplots using 15N recovery. Labeled urea was applied at 100 kg N ha−1, and chambers and microplots were shaded and protected from rainfall. Estimates of NH3 losses from the bare soil after 357 h were 24.6 and 48.0% of the applied N from the semi‐open chambers and open microplots, respectively. Estimates of NH3 losses from the bermudagrass after 357 h were 34.5 and 42.7% of the applied N for the semi‐open chambers and open microplots, respectively. In the bermudagrass microplots, 78.6% of the applied 15N either remained in the plant‐thatch layer above the soil or was volatilized 18 h after urea application. Transport and transformations in the soil had little influence on NH3 loss from bermudagrass plots. These data indicated that measured NH3 loss from bare soil in semi‐open chambers was significantly less than NH3 loss in open microplots using 15N recovery techniques. Cumulative NH3 losses from urea retained on bermudagrass and thatch above the soil were similar in the semi‐open chambers and open microplots.
Basal Mixing Zones in Loesses of Louisiana and Idaho: II. Formation, Spatial Distribution, and Stratigraphic Implications
Authors: Miller B. J. , Schumacher B. A. , Lewis G. C. , Rehage J. A. , Spicer B. E.
Published: July 2010

Basal mixing zones of loess with different underlying materials in Louisiana and Idaho have been identified. Formation of basal mixed zones occurs when loess is deposited on a pedogenically active surface and becomes incorporated into the underlying stratigraphic unit through bioturbation and pedoturbation processes. Factors influencing basal mixed zone formation include climate, nature of stratigraphic materials underlying the loess deposits, and rate of loess deposition. The warm, humid climate in Louisiana is more conducive to the formation of thicker basal mixed zones than the cool, semiarid climate of Idaho. In Louisiana, thicker basal mixing zones were found where loess was underlain by coarse textured, unconsolidated materials than where underlain by unconsolidated materials with similar or finer textures. Amount and distribution of precipitation in Idaho appears to override the influence of underlying materials on basal mixed zone formation. A progressive thickening of basal mixing zones and thinning of the unmixed loess mantle was found as distance from the loess source increased until a point was reached where all loess was incorported or lost through erosion and the basal mixed zone occurred at the soil surface. Implications of the existence of basal mixed zones with respect to loess stratigraphy are discussed.
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

The 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

Zones 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

Highly 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

The 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

We 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

Selenite 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

Selenite 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

Seven 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

The 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

Since 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

Laboratory 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

Recognition 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

In 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

Mixtures 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

The 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

Disc 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.
Anion Sorption on a Calcareous, Montmorillonitic Soil—Arsenic
Authors: Goldberg Sabine , Glaubig R. A.
Published: July 2010

Arsenic sorption on a calcareous, montmorillonitic soil was investigated as a function of solution pH (2–11) at two initial As concentrations (2.0 and 20 mmol m−3). Arsenite sorption could not be determined because oxidation of arsenite occurred during the experiment. Arsenate sorption increased with increasing pH, exhibited a maximum near pH 10.5, and decreased at higher pH. Arsenate sorption as a function of pH was studied on reference minerals representative of the dominant inorganic constituents of the soil: montmorillonite, kaolinite, and calcite. Arsenate sorption on the two clay minerals increased at low pH, exhibited a peak near pH 5, and decreased at higher pH. Arsenate sorption on the calcite increased from pH 6 to 10, peaked between pH 10 and 12, and decreased above pH 12. The constant capacitance model was able to describe arsenate sorption on kaolinite over the entire pH range studied and on montmorillonite and soil below pH 9. The soil sorption maximum near pH 10.5 was much reduced after removal of carbonates, indicating that carbonates play a major role in arsenate sorption above pH 9. Arsenate sorption on soil and calcite was unaffected by the presence of equimolar selenite concentrations.
Evaluation of Nitrogen‐15 Tracer Techniques for Direct Measurement of Denitrification in Soil: I. Theory
Authors: Boast C. W. , Mulvaney R. L. , Baveye P.
Published: July 2010

Mass spectrometric procedures for determination of dinitrogen (N2) and nitrous oxide (N2O) evolved during denitrification in soil treated with 15N‐labeled fertilizer are based on the hypothesis that the nitrate (NO−3) undergoing denitrification can be assumed to exist in a single pool that is isotopically uniform. In the work reported, it is shown that 15XN (the average mole fraction of 15N in the NO−3 undergoing denitrification) will be overestimated when this assumption is invalid. Moreover, it is proved mathematically that the amount of N2 or N2O evolved is underestimated when 15XN does not exceed 0.5. This proof does not hold for higher values of 15XN, but it is concluded that underestimation also occurs in these cases, because no exceptions were found in over three million computer simulations involving evolution of N2 from multiple pools having 15N enrichments as high as 99.6 atom %.
Heat Units for Describing Carbon Mineralization and Predicting Net Nitrogen Mineralization
Authors: Honeycutt C. W. , Zibilske L. M. , Clapham W. M.
Published: July 2010

Rate constants that describe C and N mineralization vary due to the changing complexity of the C compounds decomposed. Both economic and environmental concerns point to the importance of predicting net N mineralization from plant materials whose decomposition is initially characterized by net N immobilization. This study was conducted to examine the potential of the heat unit concept for describing C mineralization and for predicting the onset of net N mineralization from soil amended with an organic material. Rates of 0 and 59 g kg−1 papermill sludge were added to a soil and incubated at 5, 10, 15, 20, 25, and 30 °C at constant water content in the laboratory. Carbon mineralization rates varied with temperature and apparent substrate complexity, but a nearly identical amount of C (4.7 to 5.3 g kg−1 soil) was mineralized before the beginning of net N mineralization. The cumulative heat input resulting in that amount of evolved C was within the same range (600 to 684 degree days) for the 10 to 25 °C treatments. The number of degree days accumulated until commencement of net N mineralization was also similar for these four temperature treatments. Field microplots were established with 0 and 59 g kg−1 papermill sludge amendment rates. Commencement of net N mineralization in the field occurred at approximately 649 degree days, a value in close agreement with laboratory study results. These data suggest the heat unit concept may be useful for collectively describing mineralization of C fractions with contrasting decomposability, it may allow prediction of the onset of net N mineralization, and it may also serve as a method for linking laboratory and field studies of such biological processes as those studied here.
Effect of Residual Profile Nitrate on Corn Response to Applied Nitrogen
Authors: Bundy L. G. , Malone E. S.
Published: July 2010

Residual profile NO3 significantly affects crop N fertilizer requirements in semiarid regions, but little information is available on the influence of profile NO3 on crop response to applied N in humid climates. Experiments were conducted on three well‐drained silt loam soils to investigate profile NO3 accumulation and retention and to determine the effect of profile NO3‐N on corn (Zea mays L.) response to applied N under humid climatic conditions. In 1983, spring preplant N (0, 134, 268, or 402 kg N ha−1) was applied to corn at each location. Fall 1983 profile NO3‐N to 90 or 120 cm was linearly related to 1983 N rate and ranged from 52 to 644 kg N ha−1. Overwinter retention of fall profile NO3‐N varied from 45 to 66% among locations in a year with above normal fall to spring precipitation. Original plots at all locations were split in 1984, and preplant N rates of 0, 78, 156 or 234 kg N ha−1 were superimposed on each 1983 N treatment. Corn yields in the absence of applied N and yield response to added N were significantly affected by spring profile NO3‐N content. With no applied N, profile NO3‐N to 90 cm accounted for 84% of the variation in yield at the most responsive site. Grain yields were maximized (8.5 to 9.5 Mg ha−1) in the absence of applied N where profile NO3‐N to 90 cm was >150 kg N ha−1. Similarly, yields were not increased by applied N where profile NO3‐N exceeded 150 kg N ha−1. These results indicate that profile NO3‐N significantly affects corn response to applied N on some Wisconsin soils. Adjustment of N recommendations for profile NO3‐N should allow more accurate prediction of corn N fertilizer requirements on these soils when substantial overwinter carryover of profile NO3‐N occurs.
Variability of Northwest Florida Soils by Principal Component Analysis
Authors: Collins M. E. , Ovalles F. A.
Published: July 2010

Twenty soil properties from 151 pedons were evaluated (i) to select the statistically‐important ones influencing soil variability and (ii) to test if these were actually differentiating properties. Approximately 83% of the pedons studied were Ultisols. Three sets of data were used for the statistical analysis of soil properties (i) weighted‐averages in individual pedons, (ii) data from the first A (A, Ap or Al) horizon, and (iii) data from Albany, Dothan, and Orangeburg soil series. The latter data were tested by a nested analysis of variance to find out if the properties selected were actually differentiating properties. Principal component analysis (PCA) was used as an unbiased method to make the selection. The first five principal components (PCs) explained more than 73% of the total variance. Analyses of eigenvectors, collinearity, and correlation coefficients between soil properties and PCs were also employed. Total sand, fine sand, clay, and organic carbon contents were selected by the PCA as the important properties. These properties except fine sand were validated by a nested analysis of variance. The analysis of variance indicated these properties had a large variation among soil series and/or among horizons within the same soil series.
Measuring the Spatial Variability of Soil Hydraulic Conductivity Using an Automatic Neutron Moisture Gauge
Authors: Moutonnet P. , Pluyette E. , El Mourabit N. , Couchat P.
Published: July 2010

Soil internal drainage was measured along a 100‐m transect with 20 neutron probe access tubes at 5‐m intervals using an automatic neutron moisture gauge and a tensiometer data logger. Geostatistical analysis of the measurement results (in terms of hydraulic conductivity, K, vs. water content, θ) at depths of 60 and 90 cm, showed no autocorrelation among the sites. Measurement results related to depths of 120 and 150 cm were deleted because of the lack of a unit hydraulic gradient. Variance analysis indicated that the 60‐ and 90‐cm layers values could be considered together as a unique soil layer. The exponential regression equation computed from 240 K(θ) pairs, gave correlation coefficient of 0.90 for this soil layer. The K variation coefficient between 32 and 40% θ was 75% for the 60‐ and 90‐cm soil depths. This value is consistent with other published findings.
Phosphorus Adsorption by Kaolinite and Montmorillonite: I. Effect of Time, Ionic Strength, and pH
Authors: Bar‐Yosef B. , Rosenberg Rivka , Kafkafi U. , Sposito G.
Published: July 2010

Phosphate reactions in soils are affected by various factors operating simultaneously. The objective of this work was to study specific effects of total P concentration, pH, ionic strength, and equilibration time on P partitioning between solid and solution phases of Ca‐ and K‐kaolinite and ‐montmorillonite suspensions as model systems of soils containing these minerals. Phosphorus concentration in the solution phase (Cp) stabilized within 24 to 48 h after introducing P into the system. Increased electrolyte concentration, which elevated the electrical conductivity (EC) from 0.2 to 5.0 dS/m, decreased Cp in both clay systems. Further increase to about 40 dS/m had a negligible effect on Cp. Phosphorus adsorption by Ca‐clay exceeded that by K‐clay. This, and the effect of EC on Cp are suggested to operate via their effect on the extent of the diffuse double layer, which determine the accessibility of P to adsorption sites on clays' edges. Phosphorus solution concentration as a function of pH was minimal in the studied clays around pH 6. In the investigated pH range (5–9), P partitioning was controlled by adsorption, which could be described by a modified Langmuir model. The model accounts for effects of Cp and pH on adsorption and considers retention of individual P species by the adsorbent.