bluuebunny/crossref_metadata_2025_split huggingface dataset:
Complexation of Glyphosate and Related Ligands with Iron (III)
Authors: McBride Murray , Kung King‐Hsi 
Published: July 2010

AbstractThe extent of chelation of aqueous Fe3+ by glyphosate [isopropylamine salt of N‐(phosphonomethyl)glycine] and the related ligands glycine, iminodiacetic acid and aminomethylphosphonic acid was estimated over a range of pH and ligand/Fe3+ ratios. Electron spin resonance (ESR) and UV‐visible spectroscopy were used to detect chelation, evidenced by changes in the inner‐sphere coordination environment of Fe3+. Generally, the spectroscopic methods confirmed the degree of chelation predicted from the known stability constants of these Fe3+complexes. The importance of the phosphonomoeity in conferring a high degree of stability to the complexes were confirmed and the Fe3+‐glyphosate soluble complex persisted in aqueous solution to pH 4 and higher. The Fe3+complexes without the phosphonate group failed to form or existed only in very acidic solution, since they were easily dissociated upon the hydrolysis of Fe3+ as the pH was raised. Infrared spectroscopy of glyphosate adsorbed on goethite confirmed direct coordination of the functional groups with surface Fe3+, and suggested that the strong adsorption of glyphosate on oxides is a consequence of the same chelation mechanism observed in solution.
Adsorption of Para‐substituted Benzoates on Iron Oxides
Authors: Kung King‐Hsi , McBride Murray B. 
Published: July 2010

AbstractIn order to understand the binding mechanism and adsorptivity of benzoic acids on Fe oxides, adsorption of parasubstituted amino, nitro, methyl, methoxy, and chlorobenzoic acids onto noncrystalline Fe hydroxide and goethite from aqueous solution and vapor state was studied. Adsorption on noncrystalline Fe hydroxide from solution phase was quantified by the determination of adsorption isotherms using UV spectrometry to measure the concentration of unadsorbed organic. Adsorption of the benzoic acids from the vapor phase was further studied, using Fourier‐transform infrared spectroscopy (FTIR) of self‐supported goethite films to identify the binding mechanism and relative bond strength of the organic anion‐oxide complex. Results showed that the higher the pKa of the benzoic acid (i.e., the smaller the Hammett Constant of the substituent) the more readily the organic was adsorbed from solution. From FTIR study, an inner‐sphere coordination of the carboxylate anion to surface Fe involving a ligand exchange process was identified. Quantity of adsorption from solution was correlated to surface Fe‐benzoate bond strength as deduced from FTIR of dry oxide films, with bond strengths of para‐substituted benzoate following the order: amino > methoxy > methyl > chloro > nitro. Bidentate coordination was deduced to be the binding mechanism for chemisorption on air‐dry surfaces; however, physical adsorption was also identified in the absence of competing anions. It is concluded that electron‐with‐drawing groups on the aromatic ring weaken the carboxylate bond to surface Fe atoms by withdrawing electron density from the carboxylate group. Conversely, electron‐donating groups increase adsorption by increasing the electron density of the carboxylate, strengthening its Lewis basicity.
Calcium, Magnesium, and Potassium Diffusion Coefficients in Soil Estimated from Electrical Conductance
Authors: Conkling B. L. , Blanchar R. W. 
Published: July 2010

AbstractDiffusion coefficients for Ca, Mg, and K in various horizons of four soils were calculated from electrical conductivity measurements. The soil materials studied were surface and subsurface horizons of a limestone derived soil, Bardley (fine, mixed, mesic Typic Hapludalf); a fragipan soil, Lebanon (fine‐silty, mixed, mesic Typic Fragiudalf); a loess derived soil, Marshall (fine‐silty, mixed, mesic Typic Hapludoll); and a claypan soil, Putnam (fine, montmorillonitic, mesic Mollic Albaqualf). A diffusion model that separates ion movement in solution from that along soil surfaces was used to estimate Ca, Mg, and K movement in a mixed‐ionic system. The equilibrium soil solution and exchangeable concentrations were estimated using the total salt concentrations, soil cation exchange capacity (CEC), and measured exchange constants. The molar conductivity of each ion in the soil solution and along surfaces was calculated using its published molar conductivity, estimated solution composition, exchangeable concentration, and the specific conductance of the soil measured at salt concentrations of 0.01 and 1 mol L−1. Diffusion coefficients were computed from molar conductivity. For Ca soil solution, diffusion coefficients ranged from 0.78 to 1.64 × 10−10, Mg from 0.69 to 1.46 × 10−10 and K from 2.13 to 4.49 × 10−10 m2 s−1. Surface diffusion coefficients for Ca varied from 0.20 to 0.44 × 10−10, Mg from 0.18 to 0.39 × 10−10 and K from 0.55 to 1.21 × 10−10 m2 s−1. The quantities of Ca, Mg, and K that diffused across a boundary were calculated from these diffusion coefficients and were the same order of magnitude when compared with the quantities measured.
Phosphorus Behavior in Flooded‐Drained Soils. I. Effects on Phosphorus Sorption
Authors: Sah R. N. , Mikkelsen D. S. 
Published: July 2010

AbstractThis study examines the effects of flooding periods (FP), organicmatter (OM) addition, and temperature changes during soil flooding on P sorption in 10 flooded‐drained (FD) California soils. The soils were flooded for 0 to 90 d, drained, air dried, and used for P‐sorption studies at six (0.3–2.0 mM) initial P concentrations (Pi). Four soils, showing a wide variation in P‐sorption capacity, were evaluated for the effects of OM and temperature treatments. Using P‐sorption isotherms, a relationship between P sorption and FP was developed for a given final P concentration (Pf) for each soil. Flooding soil without added OM increased P sorption by 10 to 70% in half of the 10 soils. Organic‐matter treatment and elevated temperature during flooding further increased P sorption and shortened the FP at which P sorption reached maxima. The soils in which P sorption did not increase without OM treatment were low in either OM or reducible Fe. The largest increase in P sorption as a result of OM and temperature treatments was found in a soil that had low OM but a high level of reducible Fe. These findings suggest that OM and temperature are important factors determining the impact of FD conditions on P sorption.
Mineralogy and Classification of Andic Soils in Northeastern California
Authors: Southard S. B. , Southard R. J. 
Published: July 2010

AbstractRecently proposed changes to Soil Taxonomy will have a significant impact on the classification of soils with andic properties, most of which formed from volcanic materials. The vast majority of soils with andic properties occur in humid environments. A few have been identified in regions with semiarid to subhumid climates. Soils with andic properties and a xeric soil moisture regime are extensive in the Medicine Lake Highland and near the town of Burney in the Cascade physiographic province of northeastern California. Selective dissolution and x‐ray diffraction were employed to determine the mineralogy of six soils being mapped in the region. Four soils in the Medicine Lake Highland, formed mainly from air‐fall tephra and basalt, are mantled by rhyolitic pumice up to 81 cm thick. Soil pH in the 5 to 7 range favored initial allophane and smectite formation over formation of humus‐metal complexes. Subsequent desilication in upper horizons produced imogolite and kaolins there, but favored allophane stability in resilicated lower horizons. More intensive desilication of two soils formed from mixed basalt and tephra in the more humid Burney area favors the stability of a noncrystalline Al hydrous oxide (kliachite?), gibbsite, kaolins and crystalline Fe oxides. Three of the pedons in the Medicine Lake Highland meet the criteria for Xerands. The fourth, formed in the thickest pumice deposit, is a Vitrandic Xerorthent. Organic C contents, Al/Si ratios, and total annual precipitation suggest that the soil moisture regime in the Burney area may be udic, not xeric. The pedons in the Burney area are tentatively classified as Udands.
Apparatus for Precise Simultaneous Band Injection of Two Fluid Fertilizers
Authors: Stehouwer R. C. , Johnson J. W. 
Published: July 2010

AbstractStudies involving placement and transport interactions of fluid fertilizers require precise control of application rates of small amounts of fertilizer. An apparatus for use in fertilizer interaction studies was developed which permits simultaneous band injection of two fluid fertilizers. Either gaseous or liquid fertilizers can be used and the apparatus can be used to treat soils in containers for laboratory/greenhouse studies or for small plot field studies. The method allows precise application rates through control of liquid fertilizer delivery rate to injectors and travel rate of injectors. Fertilizers are introduced through opposite ends of a single injection tube which is passed through the soil simulating deep band injection by tractor‐drawn field applicators. Calibration of the apparatus showed CVs for the pressurized and nonpressurized fluid delivery systems were 1.0 and 1.2% respectively. Coefficient of variation for the injector rate of travel was 0.5%. For laboratory/greenhouse studies the apparatus treats multiple soil containers, each of which represents an undisturbed cross‐section of the fertilizer band. Precise radial sampling of the fertilizer band injected by the apparatus is possible in both laboratory/greenhouse and small plot field studies. Extraction of NH+4 and K+ from a 6‐cm radius band of soil treated with anhydrous ammonia and KCl solution gave CVs of less than 4.0 and 9.0% for laboratory and field operation respectively.
Seasonal Uptake Patterns of Fertilizer Nitrogen Applied in Split Applications to Rice
Authors: Wilson C. E. , Wells B. R. , Norman R. J. 
Published: July 2010

AbstractWhen rice (Oryza sativa L.) is grown in a direct‐seeded, delayed‐flood system as used in the southern USA, split topdress applications of N fertilizer have proven to be one of the most effective methods for achieving relatively high grain yields and efficient fertilizer‐N uptake. Knowledge concerning the seasonal uptake patterns of fertilizer N applied in split applications is limited. Consequently, a field study was conducted to measure the seasonal uptake of N fertilizer from split applications made at preflood, 1.3‐cm internode elongation (IE), and 14 d after IE (IE + 14 d). To evaluate each fertilizer application, 15N‐labeled urea (2.42 atom% 15N) was applied at preflood (10 g N m−2), IE (5 g N m−2), or IE + 14 d (5 g N m−2). Fertilizer N contained in the soil as NH4, NO3, and organic N were determined periodically after each 15N application, along with the fertilizer and total N in the rice roots, shoots, and panicles. Plant uptake of fertilizer N from the preflood application was essentially complete within 21 d after application (63.2% of the applied N). Nitrogen uptake was essentially complete within 3 d after application of the midseason treatments. Three days after IE, 63.3% of the applied N had been taken up by the plant whereas the plant had taken up 70.1% of the applied N 3 d after the IE + 14 d N application. Approximately 20% of the fertilizer N was recovered in the soil organic fraction at maturity regardless of the time of fertilizer application. Fertilizer N incorporated into the soil organic fraction reached a maximum within 21 d after the preflood treatment.
System for Automating and Multiplexing Soil Moisture Measurement by Time‐Domain Reflectometry
Authors: Baker J. M. , Allmaras R. R. 
Published: July 2010

AbstractIt is often necessary to measure soil water content at multiple points in space and time. Our goal was to develop an automated and multiplexed measurement system using time‐domain reflectometry (TDR). Two systems are described; the first (A) uses an analog TDR unit, in which voltage signals sent from the TDR to a datalogger convey the shape of the waveform. The second (D) uses a digital TDR that communicates a digital representation of the oscilloscope wave to a personal computer. Both systems use the same multiplexing strategy, in which the TDR transmission line connects through a 12‐position rotary switch to various waveguides positioned in the soil and to further rotary switches. The switches are turned by stepping solenoids that are activated by the datalogger in System A and the computer in System D. System D uses software to automatically analyze the incoming waveforms and calculate volumetric water content. Some of the possible uses of each system include observation of infiltration at multiple points within a field and measurement of unfrozen water content as a function of space and time during freezing and thawing. The system has also been used to estimate the reproducibility of water content measurement by TDR, which was found to be in the range of ±0.006 to ±0.008. The systems described should be useful for field research on many subjects, including studies of transport and biological processes in soil, and validation of root water‐uptake models.
Adsorption and Heat of Adsorption of Organic Compounds on Montmorillonite from Aqueous Solutions
Authors: Zhang Z. Z. , Low P. F. , Cushman J. H. , Roth C. B. 
Published: July 2010

AbstractThe adsorption of 1,4‐dioxane, urea, ethanol, phenol, and the acetate anion by <2µm Na‐ and Ca‐saturated Upton montmorillonite from dilute aqueous solutions was determined at different concentrations by using their 14C‐labeled isotopes. The heat of adsorption of each compound at each concentration was also determined. All the neutral organic molecules were positively adsorbed and the acetate anion was negatively adsorbed. Except for the adsorption of 1,4‐dioxane and phenol on Ca montmorillonite, the adsorption isotherms of the neutral molecules were linear. The linear adsorption isotherms mean that the adsorbed molecules were not held to the surface by specific bonds but were distributed proportionally between interfacial and bulk phases. Preference of the neutral molecules for the interfacial phase was due to their increased interaction with the surrounding water molecules. Preference of the acetate ion for the bulk phase was attributed to its electrostatic repulsion by the clay. The adsorption reactions of the 1,4‐dioxane and urea with the Na montmorillonite were exothermic; the other adsorption reactions were endothermic. Had specific bonds formed between the organic molecules and the surface of the montmorillonite, the adsorption reactions would have been exothermic. Hence, the endothermic adsorption reactions confirm the absence of such bonds for the ethanol, phenol, and acetate anions. The adsorption isotherm of 1,4‐dioxane on Ca montmorillonite was of the Langmuir type, explained in the conventional way. The adsorption isotherm of phenol on the same clay exhibited upward curvature. We postulate the existence of interlayer regions containing phenol as a separate phase that grew disproportionally as the phenol concentration in the bulk phase increased.
Zinc Sorption, Desorption, and Fractions in Three Autoclaved Soils Treated with Pyrophosphate
Authors: Xie R. J. , MacKenzie A. F. 
Published: July 2010

AbstractPyrophosphate (PP) is used as a P fertilizer. Unlike orthophosphate, PP can sequester soil Zn. In addition, PP sorption may affect Zn sorption and have implications for fertilizer practice. Pyrophosphate effects on Zn solubility were examined with autoclaved top‐ and subsoil samples from three Quebec soils. Soils were equilibrated sequentially with PP solutions, then with Zn solutions, and finally with solutions containing neither P nor Zn. The effects of PP sorption on soil cation exchange capacity (CEC), PP desorption, and Zn sorption and desorption were determined. Zinc from treated soils was extracted sequentially with KNO3 (ZnKNO3), NaOH (ZnNaOH) and concentrated HNO3 + H2O2 (ZnHNO3) solutions. One mmol sorbed P kg−1 as PP resulted in CEC increases of 0.52 to 0.89 mmolc kg−1 soil. Increased Zn sorption was equivalent to 7 to 12% of the increase in CEC induced by sorbed PP in the Uplands (Typic Haplorthod), and 0.3 to 2.8% in the St. Bernard (Typic Eutrochrept) and the Dalhousie (Typic Humaquept) soil samples. Sorbed PP reduced Zn desorption in the Uplands and St. Bernard soils but not in the Dalhousie soils. Positive correlations between sorbed PP and extractable Fe or Al materials, clay, and organic C suggested that PP sorption was related to surfaces of Fe materials (especially crystalline Fe), or clay‐organic complexes. Zinc addition improved correlations between desorbed PP and soil parameters. Added PP at 90 mmol P kg−1 soil reduced ZnKNO3, by about 50% (except with the Uplands subsoil), while added PP increased ZnNaOH and ZnHNO3 in all soils, indicating that Zn sorption and PP‐Zn interactions were mainly related to Fe or Al oxides, and increased Zn sorption with PP was related to increased specific sorption sites.
Soil Tilth: A Review of Past Perceptions and Future Needs
Authors: Karlen D. L. , Erbach D. C. , Kaspar T. C. , Colvin T. S. , Berry E. C. , Timmons D. R. 
Published: July 2010

AbstractThe concept of soil tilth has many facets, ranging from the relatively simple effects of tillage to the physical condition of the soil created by integrating the effects of all physical, chemical, and biological processes occurring within a soil matrix. The objectives of this review are to examine historical perceptions of soil tilth, review research conducted to address soil tilth, and identify research needed to quantitatively understand soil tilth to improve management of our nation's soil and water resources. The four sections of the review trace the origin of the term, summarize research conducted prior to 1955, discuss research since 1955, and present some of the unsolved soil tilth research goals and needs. We believe the current Soil Science Society of America (SSSA) definition for soil tilth is too restrictive to accurately reflect this dynamic, multifaceted concept. Hence, a modified description of soil tilth is proposed to replace the current SSSA glossary definition. A new term, “tilth‐forming processes,” also is proposed and defined. Relationships between tilth and several soil and water management problems such as surface and groundwater quality, soil erosion, productivity, and long‐term sustainability are discussed.
Carbon Dioxide Dynamics in Acid Forest Soils in Shenandoah National Park, Virginia
Authors: Castelle A. J. , Galloway J. N. 
Published: July 2010

AbstractCarbonic acid, derived from soil CO2, may strongly affect stream‐water chemistry. The spatial and temporal variability of soil CO2 levels was examined in the White Oak Run watershed of Shenandoah National Park, Virginia. This watershed is in a mountainous, forested region that is being studied to monitor the effects of atmospheric acidic deposition. Two soils—one comprised of alluvial infill on a valley bottom, the other covering a steep hillslope—were monitored for CO2 levels and soil temperature and moisture. Carbon dioxide concentrations varied from atmospheric levels during the winter to nearly two orders of magnitude higher in late summer. There were strong correlations of CO2 with soil air temperature, but correlations with soil moisture content were weak. The strong seasonal fluctuations of CO2 may explain variations in White Oak Run stream‐water alkalinity and base‐cation concentrations.
Spatial and Temporal Variation of Ponded Infiltration
Authors: Starr J. L. 
Published: July 2010

AbstractInfiltration of water into soil is controlled by a complex set of soil and biotic factors, and may be an important factor affecting the fate of water and agrochemicals under different tillage systems. This study was conducted to assess the spatial and temporal variation of ponded infiltration as affected by plow‐ (PT) and conservation‐tillage (CT) corn (Zea mays L.) systems under different plant and row location conditions. Ponded‐infiltration rates were measured on eight dates from 3 June to 7 November. Saturated hydraulic conductivity and sorptivity, Ks and S, were estimated by fitting a mechanistic infiltration model to the data. Subsequently, a third parameter, the cumulative 1‐h infiltration, I1, was calculated from the model using the derived Ks and S values. All three infiltration parameters were used to assess treatment and sampling‐position effects on infiltration. Frequency distributions for Ks, S, and I1 were highly skewed with quasi‐log‐normal distribution. Temporal variation gave rise to a strong seasonal impact on infiltration, resulting in I1 values under CT that were significantly greater than those under PT from June through August. An abrupt change in Ks occurred by early October, resulting in PT and CT then having similar infiltration characteristics.
Radiative and Conductive Transport of Heat through Flail‐Chopped Corn Residue
Authors: Shen Y. , Tanner C. B. 
Published: July 2010

AbstractWe know of no experiments on thermal radiation (3–100 µm) and sensible heat transfer in crop residues, although data are needed to model the energy balance of conservation tillage systems. The objective of this study was to develop methods for measuring the transmittance of thermal radiation in crop residues and the thermal conductance of the residue, and then to use the measurements to test a model of radiation and sensible heat flow in a crop residue. The extinction coefficient for thermal radiation through uniformly distributed, flail‐chopped corn (Zea mays L.) residue was measured as 1.57, which is more than 50% greater than that expected for black, randomly distributed, horizontal residue pieces (1.0). We believe the larger extinction coefficient resulted because the residue pieces were distributed more nearly uniformly than randomly. This indicates the need to measure extinction coefficients for different kinds of residue, since the residue pieces usually are not spread randomly. The total heat flux densities (radiation plus sensible heat) through residues with areal densities of 0.95 and 0.48 kg m−2 were measured under thermally stable and unstable conditions. Buoyancy‐driven convection was suppressed in the residue. The calculated sensible heat conductivity of flail‐chopped corn residue was only 2% greater than still air. Even with 0.95 kg m−2 of residue and a large extinction coefficient, thermal radiation contributed over 60% of the total heat flow. Modeled total heat flows ranged from 0.91 to 1.15 times measured flows. We believe the disagreement between measured and modeled values resulted from differences in radiation transfer caused by small differences in residue element packing.
Hydraulic Conductivity of Porous Media at Low Water Content
Authors: Toledo Pedro G. , Novy Robert A. , Davis H. Ted , Scriven L. E. 
Published: July 2010

AbstractMatric potential ψ and hydraulic conductivity K at low water content θ often obey power laws in θ, but the exponents of these are largely empirical. Theories of fractal geometry and of thin‐film physics provide a basis for the observed power‐law behavior of ψ and K. Specifically, they lead to ψ ∝ θ−1/(3‐D) and K ∝ θ3/m(3 − D), where D is the Hausdorff dimension of the surface between the pore space and grains or matrix, and m is the exponent in the relation of disjoining pressure II and film thickness h, i.e., II ∝ h−m. These power laws may increase the reliability of extrapolating measurements of ψ and K at low θ. Using the data of Nimmo and Akstin (1988) to test our ideas, we found that, in the case of water in soils, m < 1 and, across length scales between 5 µm and 20 µm, 2.1 < D < 2.7. In the limit of smooth pore walls, D = 2. The measured hydraulic conductivities lie between upper and lower bounds of K(θ) that we computed using three trial distributions of pore radius.