bluuebunny/crossref_metadata_2025 huggingface dataset:
Complexation of Glyphosate and Related Ligands with Iron (III)
Authors: McBride Murray , Kung King‐Hsi
Published: July 2010

The 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

In 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

Diffusion 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

This 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

Recently 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

Studies 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

When 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

It 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

The 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

Pyrophosphate (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

The 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

Carbonic 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

Infiltration 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

We 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

Matric 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.
Flocculation of Reference Clays and Arid‐Zone Soil Clays
Authors: Goldberg Sabine , Forster H. S.
Published: July 2010

The effect of electrolyte concentration, exchangeable sodium percentage (ESP), sodium adsorption ratio (SAR), and pH on the flocculation‐dispersion behavior of reference kaolinite, reference montmorillonite, reference illite, and the clay fraction of three arid‐zone soils was investigated. The clay mineralogy of the soils was dominated by either montmorillonite, kaolinite, or illite. The clays were Na‐ or Ca‐saturated and freeze‐dried before use. Critical coagulation concentrations (CCCs) were investigated in the range of pH 5.5 to 9.5, ESP of (here equated with percent Na clay) 0, 5, 10, 20, 40, 60, 80, and 100, SAR of 0, 5, 10, 20, 40, 60, 80, and ∞, and using electrolyte concentrations of 0 to 500 mmolc L−1. The CCC values increased with increasing ESP, increasing SAR, and increasing pH. The pH dependence of kaolinite and illite was greater than that of montmorillonite at all ESPs and SARs. The CCC behavior of the soil clays resembled that of illite, especially in its pH dependence at ESP 100 and SAR ∞. The CCC values of the soil clays, kaolinite, and illite showed a sharp increase at high ESP and SAR, whereas montmorillonite showed a sharp increase in CCC at low ESP and SAR. The CCCs for all soil clays were similar in magnitude, despite their differing clay mineralogies. The CCCs for the reference clays were much lower than those for the soil clays, indicating that extrapolation from reference‐clay results is not possible, and that additional factors such as organic‐matter content and Al‐ and Fe‐oxide content may influence the dispersion of soil clays.
Carbon‐13 Nuclear Magnetic Resonance Spectra of Soil Humic Substances Extracted by Different Mechanisms
Authors: Piccolo A. , Campanella L. , Petronio B. M.
Published: July 2010

Humic substances were extracted from an organic soil of Tuscany, Italy, with solutions operating by three different mechanisms: charge repulsion (NaOH under N2), ligand exchange (Na4P2O7 at pH = 7), and H‐bond disruption (dipolar aprotic solvents in mixture with dilute HCl). Solution‐state 13C‐nuclear magnetic resonance (NMR) spectra were obtained for the unpurified and purified (HCl‐HF treatment) extracts, revealing that humic matter obtained through the H‐bond‐disruption mechanism was different from materials extracted using the two other mechanisms. Extracts obtained using dipolar aprotic solvents (DMF, DMSO, acetone) showed better resolved spectra than those using NaOH and Na4P2O7. This was due to a lower content of coextracted silicate materials and lower molecular weights. Spectra of humic substances extracted with acetone and DMF had a higher percentage of aliphatic C than did the spectrum of the extract with DMSO. The latter was, in general, more similar to the spectra of stronger extractants. The H‐bond‐disruption mechanism of dipolar aprotic solvents appeared to have extracted more unsubstituted aromatic rings than NaOH and Na4P2O7, although percent of aromatic C was generally equivalent in the spectra of all extractants. Purification with a HCl‐HF treatment decreased mainly the content of aliphatic, carbohydrate, and amino acid components of all extracts. Poor agreement between values for total acidity of extracts calculated by NMR and those given by chemical methods was also observed in this study.
Decomposition and Interactions among Wheat Residue Components
Authors: Collins H. P. , Rickman R. W. , Elliott L. F. , Bezdicek D. F. , Papendick R. I.
Published: July 2010

Developing effective management strategies that protect soil against erosion necessitates an understanding of residue decomposition. Predicting decomposition of crop residues requires knowledge of their chemical and physical composition. Wheat (Triticum aestivum L.) residue decomposition is influenced by the amount of residue, ratio of residue components, and chemical composition of component mixes. This study describes winter wheat residue components and chemical composition, and assesses the effect of mixing residue components on the rate of decomposition. Winter wheat residue levels were measured on 20 field sites having grain yields ranging from 1 to 6 Mg ha−1. Residue was positively correlated with grain yield for the 1984 and 1985 crop years (r2 = 0.99***, 0.94***, respectively [significant at P = 0.001]). Residue‐to‐grain ratios averaged 1.47 for 1984 and 1.17 for 1985. Ratios of stem (ST), leaf sheath (LS), chaff (CH), and leaf blades (L) averaged 37:30:20:13. Total C and N, soluble C, and nonstructural carbohydrate (NSC) concentrations were not correlated with residue or grain yield. Stem and LS components had greater lignin and NSC contents than L and CH components. Rates of C mineralization for components were: L > LS > CH = ST. When components were mixed at the ratio of 32:30:28:10 ST/LS/CH/L, cumulative CO2 evolution was 1.25 times greater than that predicted by summing cumulative CO2 evolved from individual components. Comparison of single‐ and multiple‐term exponential decay models showed that a single‐term model adequately described decomposition of wheat residues.
Organic Amendment Effects on Physical and Chemical Properties of a Sandy Soil
Authors: Tester Cecil F.
Published: July 2010

Effects of repeated applications of sewage‐sludge compost on soil properties have not been sufficiently evaluated with field trials. Field studies were established on an Evesboro loamy sand soil (mesic, coated Typic Quartzipsamment, 97% sand) to compare the effects of sewage‐sludge compost, beef manure, and fertilizer amendments on soil properties. The study site had been fallow for 26 yr and should have provided a positive response to the added organic matter. Compost application rates were based on the assumption that material would be applied either only once or annually. Application rates ranged from those that were too low to supply the total N requirement of a crop (e.g., 33 Mg ha−1) to excessively high rates that would produce maximum soil benefits from the added organic matter (e.g., 268 Mg ha−1). Soil properties such as strength (penetrometer resistance), bulk density, water retention, pH, surface area, total N and P contents, and organic matter were evaluated for 5 yr. Addition of sewage‐sludge compost significantly reduced penetration resistance when compared with the control and fertilizer‐amended soils. Compost significantly reduced bulk density, increased soil water content, and modified pH to greater depths. Specific surface area of the soils increased linearly with the addition of compost and C levels indicated that 24 and 37% of the annually added organic matter decomposed during the 1st yr from the sewage‐sludge compost and beef manure, respectively.
Nitrification Potential of Secondary‐Succession Upland Oak Forests: II. Regulation of Ammonium‐Oxidizing Bacteria Populations
Authors: Donaldson Jennifer M. , Henderson Gray S.
Published: July 2010

Field plots were treated with NH4‐N and Ca(OH)2 to test the hypothesis that NH4 and pH control nitrification in these soils. The most probable number (mpn) of autotrophic NH4‐oxidizing bacteria were estimated in treated and control soils at five dates within a 1‐yr period. Sampling dates coincided with periods of significant phenological development of the vegetation. The effect of the treatments on the population of NH4‐oxidizers was used to assess the treatment effect on soil nitrification potential. The results suggested that soil NH4 is a major factor regulating populations of these microorganisms; however, numbers of NH4‐oxidizers in both treated and untreated soils vary significantly with date of sample collection. The seasonal responses of these microorganisms indicate that vegetation affects NH4‐oxidizer populations, perhaps through the production and release of inhibitory compounds.
Exchange Fertilizer (Phosphate Rock plus Ammonium‐Zeolite) Effects on Sorghum‐Sudangrass
Authors: Barbarick K. A. , Lai T. M. , Eberl D. D.
Published: July 2010

Fertilizer systems that use an exchange medium in combination with slightly soluble phosphate rock could provide a slow, sustained release of P and avoid the potential problems (e.g., fixation) associated with a large, single application of an element. Consequently, the effectiveness of one NH4‐exchanged zeolite (clinoptilolite) in increasing phosphate‐rock solubility in two soils (Red Feather loamy sand, a Lithic Cryoboralf and Weld loam, an Aridic Paleustoll) was evaluated by measuring increases in dry matter, nutrient content, and nutrient uptake by sorghum‐sudangrass [Sorghum bicolor (L.) Moench‐S. sudanese (Piper) Stapf, ‘NB280S’]. Two phosphate‐rock applicationr ates of 170 and 340 mg P kg−1 soil were used in factorial combination with zeolite/phosphate‐rock ratios of 0, 1.5, 3, 4.5, 6, and 7.5:1. The largest dry‐matter yields through four plant cuttings from the Weld soil generally were found with the 340 mg P kg−1 rate and with increasing zeolite/phosphate‐rock ratio (linear response). Increasing zeolite/phosphate‐rock ratio in this soil generally increased plant P concentrations and uptake. The exchanger fertilizer system increased P availability in the Weld soil by producing lower soil pH (nitrification of NH4 released by the zeolite) than the 0:1 zeolite/phosphate‐rock ratio control and by the adsorption of Ca in the zeolite. The Red Feather soil, which was deficient in K, did not provide definite yield responses because the zeolite sequestered K, thereby reducing plant K concentrations and uptake even though the zeolite increased total P uptake. The NH4‐exchanged zeolite/phosphate rock combination used in the present study seems to be a promising P‐fertilizer system in nonalkaline soils if K or other plant‐essential cations are not limiting.
X‐ray Diffraction Indices for Relative Quantification of Interlayering in Phyllosilicates
Authors: Esser Kjell Bjørgen
Published: July 2010

Simple, numerical methods for routine interpretation of x‐ray diffractograms of soil samples are desirable but largely unavailable due to the prevalence of mineral intergrades. A set of indices is proposed that facilitates a comparative estimation of proportions of K‐collapsible vermiculite and smectite, proportions of hydroxy interlayers, and proportions of swelling interlayers. The indices are based on an estimation of the horizontal displacements of the centroids of x‐ray diffraction areas representing a range of d001 spacings after various saturation and heat treatments. A potassium contraction index (KCI), a contraction index at 300 °C (CI300), and a contraction index at 550 °C (CI550) express the degree of interlayer contraction upon K saturation, heating to 300 °C, and heating to 550 °C, respectively, relative to the Mg‐saturated sample. Subtracting the CI300 from the CI550 yields an (Al + Fe)/Mg interlayer index expressing the relative proportions of Al + Fe‐hydroxy interlayers and Mg‐hydroxy interlayers. The indices can be a useful supplemental tool in the study of mineral transformations when computer analysis of x‐ray diffractograms is unavailable.
Collection of Intact Cores from a Rocky Desert and a Glacial Till Soil
Authors: Lewis T.E. , Blasdell B. , Blume L.J.
Published: July 2010

A method involving the use of triple‐expanding polyurethane foam was developed for the collection of large intact cores from two problem soil types for use in anion/cation transport studies. Intact cores, 36‐ to 41‐cm diameter, were collected from a Jean series (sandy‐skeletal, mixed, thermic Typic Torriorthent) and a Colonel series (coarse‐loamy, mixed, frigid Aquic Haplorthod). A free‐standing pedestal was isolated. The circumference of the core was reduced, to allow encapsulation with a PVC pipe of appropriate inner diameter. The space between the soil and the PVC pipe was filled with polyurethane foam. After the foam cured overnight, the core was severed at the base by driving a steel plate beneath the PVC pipe. Endcaps were fastened to the PVC pipe and the cores were transported to the laboratory.
Pore Size, Particle Size, Aggregate Size, and Water Retention
Authors: Wu L. , Vomocil J. A. , Childs S. W.
Published: July 2010

Measurements of water retention and pore‐size distribution for a soil are time consuming and affected by changes in aggregate‐size distribution. A method of compared distribution curves was used to relate distributions of pore size (PO), particle size (PA), aggregate size (AG), and pore size from water retention (WR). Seven surface soils varying in texture and aggregation were tested. After normalization to 100% volume, the pore‐, particle‐, and aggregate‐size distribution, as well as water‐retention (converted to pore diameter) curves were each fitted to a linearly transformed logistic function to evaluate their interrelations using R(m/n), a coefficient for the ratio of the diameters of component m to component n. Identical distribution curves have an R(m/n) value of 1. The R(PO/PA) and R(WR/PA) for the seven soils ranged from 0.25 to 2.26 and from 0.18 to 1.34, respectively, indicating that the theoretical packing parameters of 0.225 to 0.414 do not hold for PA distribution. The R(PO/AG) ranged from 0.06 to 0.23 and R(WR/AG) from 0.04 to 0.16. Both ranges of R values smaller than the theoretical packing parameters suggests interactions may occur between large and small aggregates. However, R(PO/AG) and R(WR/AG) values were more consistent and were significantly related to aggregation level and bulk density, suggesting that AG distribution should be used as a parameter to predict PO distribution and water retention. Comparisons between water retention curves and PO distributions from Hg intrusion gave R(PO/WR) ranging from 0.78 to 2.59, showing that equivalent PO for a given soil is not the same when different measuring methods are used.
Reactions of Gypsum or Phosphogypsum in Highly Weathered Acid Subsoils
Authors: Alva A. K. , Sumner M. E. , Miller W. P.
Published: July 2010

Crop responses to gypsum or phosphogypsum (PG) amendment to acid soils have been highly variable in different soils. Therefore, soil properties influence the mechanisms of amelioration of acid‐soil infertility by gypsum or PG. The effects of gypsum or PG amendments on soil‐solution composition and surface reactions were studied in subsoils (0.6–0.8 m) from cultivated and woodland sites representing three soil series (Bladen: Typic Albaquult; Cecil and Wedowee: Typic Hapludults). Soils were equilibrated in the laboratory with either deionized water or saturated solutions (2.0 g L−1) of either PG or reagent‐grade CaSO4·2H2O (gypsum) at 20, 40, and 60% (v/w) soil moisture contents. Soil solution was displaced by centrifugation. Depletion of Ca and SO4 from gypsum or PG solution during equilibration was due to sorption of the respective ions by the soil. The sorption of Ca and SO4 was considerably greater in the woodland soils than in cultivated soils. The sorption of Ca from PG solution was equivalent to the increase in negative charge in the Cecil and Wedowee soils. In the Bladen soil, the increase in surface charge was lower than the sorption of Ca. The increase in exchangeable cations in the Cecil and Wedowee soils, after equilibration with PG solution, was very similar to sorption of SO4. Equilibration of the soils with PG or gypsum solution decreased the exchangeable Al by 40, 21, and 6 to 7% in the Cecil, Wedowee, and Bladen soils, respectively. The amelioration of acid‐soil infertility by gypsum or PG was due to a combination of SO4‐induced surface charge development, increased cation retention, and a decrease in exchangeable Al. The ameliorative effects of acid‐soil infertility by gypsum or PG amendment were greater in soils dominant in variable‐charge characteristics than in those dominant in permanent‐charge characteristics.
Alkali Basalt Gravel Weathering in Quaternary Allier River Terraces, Limagne, France
Authors: Veldkamp E. , Jongmans A. G. , Feijtel T. C. , Veldkamp A. , van Breeman N.
Published: July 2010

Weathering of alkali basalt pebbles was studied in three Quaternary Allier terraces of different ages. The isovolumetric method and Ti‐constant method were applied to quantify compositional changes due to weathering. Bulk density of fresh gravel in the younger terraces (Weichselien and Holocene) was adequately estimated from geochemical data by a multiple linear regression model (R2 = 0.81**, significant at P = 0.01). Since no chemical and micromorphological differences could be demonstrated between fresh gravel and the unweathered cores of partly weathered gravel, the regression model was also applied to calculate the bulk density of the cores of partly weathered pebbles in the oider terraces. The decrease in bulk density of the rind, compared with that of the core, was used as a measure of weathering intensity. The chemical composition of the weathering rind revealed a relative increase in the contents of Ti, Al, Fe, and Mn and a decrease of K, Na, Ca, and Si. Changes were estimated considering Ti essentially immobile. Except for Fe and Mn, all elements tended to decrease in the rind. The relative elemental mobilities were as follows:

K > Na > Si > Mg > Ca > P > Al > Ti

No relationship was found between weathering intensity and the age of the two oldest terraces or sampling depth. Differences in weathering intensity are predominantly a function of chemical (= mineralogical) composition of the alkali basalt pebbles.
Responses of Biopore Channels from Roots to Compression by Vertical Stresses
Authors: Blackwell P. S. , Green T. W. , Mason W. K.
Published: July 2010

The channels created in soil by roots and soil animals (biopores) play an important role in the subsequent movement of water, air, and new roots through irrigated clay soils in southeastern Australia. The maintenance of these biopores is critical for both crop productivity and erosion control. If these biopores are to remain open, they must be able to withstand the vertical stresses associated with vehicle and animal traffic. This study had three aims: (i) to examine the influence on porosity and permeability of naturally occurring channels, (ii) to determine the magnitude of vertical stresses that artificially created channels could withstand, (iii) to test the effect of channel angle to the direction of the stress. Air‐filled porosity of soil cores at −10 J/kg was decreased in a linear fashion as the applied stress was increased from 50 to 400 kPa. The reduction in air‐filled porosity was relatively independent of the size or the presence of biopores. However, the intrinsic permeability of the soil cores to air was positively correlated with the diameter of the biopores, and the permeability was little affected by applied stresses up to 200 kPa if the initial diameter of the biopores was >3.5 mm. The resistance of the channels to stresses was greatest if the vertical stress was parallel to the axis of the channels. Agricultural practices on these soils should not only encourage formation of biopores, but should also minimize stresses >200 kPa to the subsoil so that these biopores can remain open.
Polymer Effects on Erosion under Laboratory Rainfall Simulator Conditions
Authors: Ben‐Hur M. , Shainberg I. , Letey J.
Published: July 2010

Soil erosion by water is a serious problem in several parts of the world. Incorporation of polymers into water applied to soil by a rainfall simulator can improve infiltration rates. This study was conducted to determine the effects of nonionic, anionic, and two charge densities of cationic derivatized guar products on erosion and infiltration rates. The polymers were mixed with distilled water at concentrations from 0 to 20 g m−3 and applied through a rainfall simulator in the laboratory. Untreated distilled water was applied to an Arlington sandy loam soil (Haplic Durixeralf) with the soil surface both unprotected and protected by a fiberglass sheet placed 0.5 cm above the soil surface. All polymer treatments were applied to the unprotected soil surface. Distilled water drop impact greatly reduced infiltration rate and increased erosion, compared with no impact. The anionic and nonionic polymers did not significantly affect erosion or infiltration rate, compared with distilled water. The cationic polymers significantly increased infiltration rate and erosion, compared with distilled water. The higher charge cationic polymer produced significantly higher values than the lower charge polymer at the same concentration. The distilled‐water treatment with impact caused severe aggregate disruption and dispersion, producting a layer of fine material at the surface that decreased infiltration rate. Apparently, the very‐fine particulates became imbedded in the soil matrix, which made them less susceptible to lateral transfer with flowing water. The flocculating action of the cationic polymer created larger particulates, which had very little effect in reducing infiltration rate but were more susceptible to erosion. Under the conditions of the experiment, particulates between 0.05 and 0.25 mm were most susceptible to transport by a thin sheet of flowing water.
Macroporosity and Its Relation to Saturated Hydraulic Conductivity under Different Tillage Practices
Authors: Logsdon S. D. , Allmaras R. R. , Wu L. , Swan J. B. , Randall G. W.
Published: July 2010

Tillage management influences the distribution of macropores (biopores, cracks, interpedal planes, and packing voids) that may provide pathways for rapid infiltration of water. To aid in predicting ranges of saturated hydraulic conductivity (Ksat), macropore distribution in situ was characterized by exposing selected horizontal planes and tracing macropores on clear polyethylene sheets. A methylene blue solution was used to indicate macropore continuity through the pressure pan. Sixteen undisturbed cores were taken in a grid pattern from each Ap horizon and adjacent subsoil for determination of Ksat. Field marking on plastic sheets was superior to photographic slides as a technique to characterize macropores because film noise (false pores) was eliminated, overall analysis time was reduced, and different features could be separated for analysis. Unfortunately, a bias of pore size between observers was possible. Four sites with four different soil series were examined: Nicollet (fine‐loamy, mixed, mesic Aquic Hapludoll), Rozetta (fine‐silty, mixed, mesic Typic Hapludalf), Waukegan (fine‐silty over sandy or sandy‐skeletal, mixed, mesic Typic Hapludoll), and Normania (fine‐loamy, mixed, mesic Aquic Haplustoll). Below the maximum tillage depth, macropores were present at all locations, but tillage disrupted continuity of pores from the surface. No‐till had macropores throughout the upper 70 cm with continuity observed in the 0‐ to 35‐cm range. Numbers of pores (>0.4‐mm diam.) per m2 ranged from 100 to >3000, representing 0.1 to 2% of the total area. When present, horizontal crack length ranged from 1.7 to 19.3 m m−2. Measured Ksat on undisturbed detached cores ranged from 1.1 to 180 µm s−1 with CVs ranging from 44 to 197%. The Ksat could be estimated within a range (out of eight classes) from descriptions of biopore area, cracks, soil structure, and soil texture.
Tall Fescue Response to Placement of Urea/Ammonium Nitrate Solution
Authors: Moyer J. L. , Sweeney D. W.
Published: July 2010

Several studies have shown that cool‐season grasses may respond more to subsurface (knife) applications of fluid fertilizer than to surface applications. However, optimum depth of knife application has not been clearly identified. A field study was conducted from 1984 to 1986 to determine the effects of 5‐, 10‐, and 15‐cm knife and surface band (dribble) and broadcast applications of urea/NH4NO3 solution at 84 and 168 kg N ha−1 on forage yield and N use of tall fescue (Festuca arundinacea Schreb.), and on soil N levels. The soil is a Parsons silt loam (fine, mixed, thermic Mollic Albaqualf). In 1985 and 1986, 168 kg N ha−1 resulted in higher final forage yields than 84 kg N ha−1. Knife applications at 10 cm generally resulted in the highest forage yield, though not always significantly higher than other placements. Knife placement at 15 cm resulted in lower N uptake in early grass clippings (intermediate harvests), compared with surface and shallower knife applications. The N concentration, N uptake in the final spring harvest, and apparent fertilizer‐N recovery by the forage were usually increased by 10‐cm placement. Knife applications of N at or below 10 cm resulted in higher inorganic soil N concentrations at intermediate harvests than did surface applications.