bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectroscopic Characterization of Pyrophosphate Incorporation during Extraction of Peat Humic Acids
Authors: Francioso O. , Ciavatta C. , Gessa C. , Tugnoli V. , Sanchez‐Cortes S.
Published: July 2010

Extraction procedures represent a crucial point in the study of the molecular structure of humic substances (HS). Although alkaline extractants such as NaOH plus Na4P2O7 are usually employed for the extraction of the HS from soil and peat, little information concerning the interaction between extractants and humic acids is available. In this study, the results on the molecular structure of humic acids (HA) extracted and separated from a Sphagnum Irish peat sample with an alkaline pyrophosphate solution (0.1 M NaOH + 0.1 M Na4P2O7) are reported. The HA were redissolved in 5 mM NaCl, fractionated in six cut‐off fractions (nominal molecular weight: HA >300, 100–300, 50–100, 20–50, 10–20, and 5–10 kDa) using a tangential ultrafiltration system. All samples were dialyzed against distilled water and then freeze‐dried. Fourier‐transform infrared (FT‐IR) and 31P nuclear magnetic resonance (NMR) spectroscopies were applied to characterize the incorporation of pyrophosphate (PP) in both the unfractionated HA and in the six HA fractions. Spectroscopic analyses showed that it was possible to assign a given pattern of bands to define the structure of phosphate: PP was present only in the unfractionated HA, whereas orthophosphate was present in both the high molecular weight and lower molecular weight fractions. The high concentration of phosphate found in the lower molecular weight HA fractions has been attributed to the presence of metals and the oxygenated groups of HA. The changes in the relative intensity of the bands attributed to oxygenated functional groups observed in the FT‐IR spectra could be assigned to the interaction of phosphate groups with metal cations, which are involved in a coordination complex with the oxygenated groups.
Isotropic Smectite Coatings and Spheroids in Holocene Volcanic Deposits under Temperate Climate, France
Authors: Jongmans A. G. , Denaix L. , van Oort F.
Published: July 2010

Isotropic clay coatings and spheroids were observed in Holocene, excessively drained, basaltic scoria deposits underlying a Hapludand at the Puy de la Vache volcano in the Massif Central in France. The morphology, chemistry, and mineralogy of these neoformed clay fabrics were studied by optical microscopy and analytical scanning and transmission electron microscopy. Optical microscopy of samples taken at 1‐ to 3‐m depth in the deposit showed thin, isotropic coatings and spheroids inside vesicles of the scoria fragments. In addition, isotropic coatings, occasionally up to 200 µm thick, covered scoria fragments, forming bridges between them. The isotropic coatings indicated a post‐depositional, pedogenic origin. The internal fabric of coatings and spheroids were similar, suggesting a common genetic relationship. Although isotropic behavior of coatings generally points to an amorphous mineralogical composition, analytical electron microscopy showed the presence of small (<1 µm) crinkly dioctahedral phyllosilicate particles, forming a honeycomb pattern. Periodically restricted drainage conditions in the numerous meso‐ and microvesicular pores of the scoriae were assumed to cause local and temporary stagnation of Si‐rich soil solutions and, consequently, to favor smectite formation despite the overall high permeability. Since scoria fragments at 3‐m depth were unaltered, formation of the secondary clay coatings was ascribed to co‐precipitation of leached elements liberated by weathering in the overlying Hapludand. The small size and random orientation patterns of the smectite clay particles and their occasional association with amorphous compounds explained the isotropic properties of the clay coatings when observed under the polarizing microscope.
Simple Method for Determining Cable Length Resistance in Time Domain Reflectometry Systems
Authors: Reece C. F.
Published: July 2010

Time domain reflectometry (TDR) based electrical conductivity (EC) measurements underestimate solution conductivity (σ) as salinity increases unless a correction parameter, Rcable, is incorporated into the EC calculation. The parameter Rcable accounts for series resistance of cable, connectors, and cable tester. The main objective of this study was to propose and verify a simple method of directly measuring Rcable from the load resistance on waveguides that are shorted together. Also, the dependence of Rcable on cable length vs. other resistances was investigated. The parameter Rcable was found to be a function of cable length and a constant probe resistance. Errors caused by ignoring Rcable in EC determinations increased with both salinity and series resistance. Although there may be cases where Rcable has a negligible effect on EC determinations, there are also situations where it is important. This study shows that the measurement of Rcable is so simple that there is little reason not to routinely incorporate it in all TDR‐based EC determinations.
Complex Formation of Soil Minerals with Nitroaromatic Explosives and other π‐Acceptors
Authors: Weissmahr Kenneth W. , Haderlein Stefan B. , Schwarzenbach René P.
Published: July 2010

The ability of soil minerals to interact with organic solutes exhibiting π‐acceptor properties was studied using batch adsorption experiments. Among the major groups of naturally occurring minerals, only phyllosilicates were capable of forming strong electron donor‐acceptor (EDA) complexes with such solutes, including nitroaromatic explosives (e.g., trinitrotoluene [TNT]) and other priority pollutants. Depending on the minerals and the solutes involved, adsorption constants due to such EDA interactions may exceed those caused by nonspecific interactions by several orders of magnitude. Two major factors controlled the ability of phyllosilicates to form EDA complexes: the n‐donor properties of their siloxane oxygens and the accessibility of such sites for π‐acceptors. The donor properties of siloxane oxygens are enhanced by isomorphic substitution, but their accessibility for π‐acceptors is restricted by the steric effects of hydrated exchangeable cations. Relative adsorption constants (Kad values) for a given set of π‐acceptors were independent of the mineral structure, indicating that similar sites are involved in EDA complex formation on phyllosilicates. Thus, Kad values measured on any type of model phyllosilicate may be used to estimate the relative extent of adsorption of π‐acceptors to natural subsurface matrices, irrespective of the types and abundance of phyllosilicates present. Cation exchange on phyllosilicates is a crucial geochemical process that controls the accessibility of their siloxane sites to π‐acceptors due to the different sizes of the hydrated cations. Injection of electrolytes may be a promising but so far unexplored way to control the adsorption and thus the bioavailability and transport of TNT and other contaminants with significant π‐acceptor properties in the subsurface.
Critical Tissue Concentration and Chloride Requirements for Wheat
Authors: Engel R. E. , Bruckner P. L. , Eckhoff J.
Published: July 2010

Previous research in the Pacific Northwest and Great Plains has provided evidence that wheat (Triticum aestivum L.) yields are often improved by Cl− fertilization. Published reports on critical tissue concentrations and Cl− requirements for wheat are few in number. Our objectives were to define a critical plant Cl− concentration (head emergence) for maximum yield, develop a Cl− fertilizer recommendation, and determine the effect of Cl− fertilizer on grain protein. Thirty‐two field experiments (18 winter and 14 spring wheat) were conducted in Montana between 1988 and 1995. Experiments included comparisons with multiple cultivars and Cl− rates (0–90 kg ha−). Relative yield vs. plant Cl− concentration relationships were assessed from 219 cultivar × experiment episodes. Three zones of Cl− status were identified: (i) a deficiency zone, plant Cl− <1.0 g kg−1, where significant (P < 0.10) yield responses to applied Cl− occurred in 59 of 86 episodes (69%); (ii) an adequate Cl− status zone, plant Cl− ≥4.0 g kg−1, where yield responses occurred in only 2 of 44 episodes (<5%); and (iii) a critical range between these two zones, where responses were observed in 25 of 89 episodes (28%). Regression of plant Cl− concentration on soil (0–60 cm) plus fertilizer Cl− revealed that deficient, critical range, and adequate Cl− zones were associated with <7.5, 7.5 to 32, and ≥33 kg Cl− ha−1, respectively. The proposed guideline for wheat is to add sufficient Cl− to reach the upper end of the critical range (4.0 g kg−1 plant Cl−). This recommendation ensures adequate Cl− nutrition for maximum yield and kernel weight, although at some sites a slight reduction in grain protein (0.5%) may result.
Hydraulic Device for Transect Sampling Soil
Authors: Janssen K. A. , Havlin J. L. , Horstick E. H.
Published: July 2010

A soil sampler capable of hydraulically coring, extracting, and sectioning rectangular columns of soil was constructed. The purpose was to facilitate our transect sampling of P in banded P and other nonuniform P‐fertilized soils. The soil sampler was constructed to attach to a tractor's three‐point hitch and to operate using the tractor's hydraulic system. The sampler consisted of a primary and secondary frame, two hydraulic cylinders, a rectangular‐shaped box corer, and a grid divider with press plate. The soil sampler performed well with our silt loam, claypan soil. Computer isoline maps of the concentrations of P in the soil cores we collected showed a wide diversity of distributions of P. Knowing the patterns of P and other nutrient distributions that result from different tillage and fertilization practices will be helpful for studying fertilizer‐placement effects on crops, and for formulating producer soil‐sampling strategies.
Applicator for Spreading Liquid Manures on Small Research Plots
Authors: Wetterauer Donald , Killorn Randy
Published: July 2010

Farm‐size liquid‐manure pressure or vacuum tanks are not well suited for applying manure to research plots. It is difficult to manuever the spreaders and accurately control the flow of manure. This report describes an inexpensive liquid‐manure spreader developed for use on research plots (i.e., 4.6 by 12.2 m). The spreader has been used to apply manure as broadcast or injected treatments at rates of 18 000 to 80 000 L ha−1. This spreader can also be used to hand‐apply manure to very small (1.5 by 1.5 m) plots.
Ionic‐Equilibrium Time inside Ceramic Cups in Unsaturated Porous Media
Authors: Riga P. , Charpentier S.
Published: July 2010

In order to improve the methodology of collecting soil solutions with porous ceramic cups without suction, we developed a method to estimate an ionic‐equilibrium time (tC/C∞) inside cups first filled with distilled water. Characterization of tC/C∞ was used to select the minimum interval time between two extractions with different water contents (θ) or water pressures (ψ). The method is based on an analytical solution of the general equation of cylindrical diffusion. The model is used for approximating the molecular diffusion coefficient (D) vs. θ or ψ and predicting the evolution toward ionic equilibrium inside the cups. It was satisfactorily validated, using KNO3 as a solute, with a fine sand, a silty clay soil, and a peat‐perlite mixture. The results showed that tC/C∞ is (i) dependent on molecular diffusion, which has a particular relationship with θ for each medium, and (ii) proportional to the squared radius of the cup. The best results obtained near saturation showed that the times necessary to obtain a concentration close to equilibrium with standard cups (22.6‐mm diam.) were ≈4 d with the peat‐perlite mixture and ≈2 wk for the sand and the silty clay soil. Furthermore, tC/C∞ can take up to 1 mo when diffusivity in sand decreases drastically with low water content. The length of time needed to reach equilibration limits the usefulness of this sampling method for conditions where changes in solute concentration with time are weak, such as diffusion phenomena with slow or nonexistent displacement of solute. Nevertheless, the equilibration time may be reduced to ≈30 h by using smaller cups (9.6‐mm diam.) with high‐water‐content media.
Integral Method for Estimating Soil Hydraulic Properties
Authors: Shao Mingan , Horton Robert
Published: July 2010

Soil hydraulic properties are required to fully understand and predict soil water distribution. Soil hydraulic properties include the soil water characteristic curve and hydraulic conductivity. We used an integral method to solve the problem of water absorption into a horizontal soil column. The integral solutions to the problem were used to estimate the parameters α and n in the van Genuchten model for soil water characteristic curves. The two parameters, α and n, in the characteristic curve model were estimated by the length of the wetted zone, sorptivity, and saturated hydraulic conductivity. This new integral method uses both Richards' equation and the closed‐form equations of soil hydraulic properties. Six soils ranging from sandy loam to clay loam were used to test the method. Soil water characteristic curves estimated by the infiltration method are in good agreement with measured characteristic curves. The integral method provides a transient water flow approach to estimate the soil water characteristic curve instead of the usual equilibrium method. This is a new and simple means to determine soil hydraulic properties.
Supercritical Fluid Extraction of 2,4‐D from Soils: pH and Organic Matter Effects
Authors: Rochette E. A. , Harsh J. B. , Hill H. H.
Published: July 2010

Supercritical fluid extraction (SFE) recoveries of 2,4‐D (2,4‐dichlorophenoxyacetic acid) from spiked Washington soils depended on both pH and organic matter content. The soils used in this study spanned a wide range of organic C concentration (2–480 g kg−1). One of the soils (the Benge series A horizon) was adjusted to pHs from 1.8 to 8.3, and extracted with methanol‐modified supercritical CO2. Recoveries from this soil increased from 41 to 76% with decreasing pH. For soils at natural pHs, when a weak acid modifier (benzoic acid) was used in addition to methanol, the 2,4‐D recovery ranged from 21 to 86%, increasing with decreasing organic C concentration. Treating the samples to the lowest pHs practical (1.2–1.6) with HCl and extracting with methanol‐modified supercritical CO2 was more successful than utilizing the weak acid‐methanol modifier, except for the soil with very low organic C. Recoveries after HCl treatment ranged from 80 to 94%. Two soils from 2,4‐D‐treated fields yielded more 2,4‐D by modified SFE at pH 1.2 than by a modified version of the method recommended by the U.S. Environmental Protection Agency. The results suggest that organic acids like 2,4‐D can be successfully extracted at low pH, even from soils high in organic C. Low recoveries from soils high in organic C appear to result from proton consumption by natural soil organic matter during extraction.
Effect of Different Organic Ligands on Cadmium Sorption by and Extractability from Soils
Authors: Naidu R. , Harter R. D.
Published: July 2010

Soil solutions contain a variety of low molecular weight dissolved organics from breakdown of plant residues and exudation from plant roots, and complexation of metals by these organic ligands can play an important role in controlling metal solubility. The effect of the organic ligands acetate, citrate, fumate, malonate, maleate, salycylate, succinate, and tartrate on the extractability and sorption of Cd was investigated in a range of Cd‐treated soils varying widely in soil chemical characteristics. Experimental parameters were adjusted to investigate the effect of pH and organic ligand concentration on Cd extractability. The soils were also extracted with NaNO3 of equivalent pH and concentration. The organic ligands always extracted more Cd than did NaNO3, indicating that organic complexation increased the extractability of Cd from soil. Extractable Cd ranged from <0.30 to 1 µmol kg−1; the greatest Cd concentration in each soil was released in the presence of maleate. In general, the ability to desorb Cd followed the order: maleate > fumarate ≈ succinate > tartrate > malonate > oxalate > salicyclate when the pH of the extract was between 3.1 and 3.4; in this pH range competition for complexation between the metal ion and ligand anion is greater than the affinity of the metal ion for the soil surface. For all soils and organics, extractable Cd decreased with increasing pH of the ligand solutions. The amount of NaNO3‐extractable Cd also decreased with increasing pH, and the amount desorbed was not detectable at pH values exceeding 5.5, suggesting that at high pH values, Cd is released into soil solution only as metal‐organic complexes.
Removal of Nitrite Impurity from Nitrate Labeled with Nitrogen‐15
Authors: Malone John P. , Stevens R. James
Published: July 2010

Potassium nitrate labeled with 15N is often used as a tracer in studies of N dynamics in soil and water systems. Typically, 0.8% NO−2 impurity has been found in the batches of K15NO3 enriched to 99 atom % excess 15N that were purchased by our laboratory. Nitrite is an intermediate in several N cycling processes so its addition when adding NO−3 could produce misleading results. We have developed a safe, simple, and inexpensive method to remove NO−2 impurity from any NO−3 solution in a water matrix. The principle is the oxidation of NO−2 to NO−3 by UV light in the presence of a heterogenous TiO2 catalyst. A NO−2 concentration of 0.2 mM in 100 mL of 0.2 M NO−3 solution could be oxidized in 12 min using 0.5 g L−1 TiO2 in a specially constructed photoreactor with a 75‐W UV facial tanning lamp. For the routine removal of NO−2, use of the same TiO2 concentration in a standard beaker worked equally well when the irradiation time was extended to 2.5 h. After irradiation, the TiO2 is easily and totally removed from the solution by membrane filtration.
Simulating the Impact of Management Practices on Nitrous Oxide Emissions
Authors: Xu C. , Shaffer M. J. , Al‐kaisi M.
Published: July 2010

Effective evaluation of alternative management strategies to control global warming requires tools for simulating emissions of N2O from soils across a range of soil properties, weather, and management inputs. We hypothesized that with modification to the nitrification and denitrification submodels of the Nitrate Leaching and Economic Analysis Package (NLEAP) model, we could simulate daily N2O emissions as a function of soil moisture, temperature, N content, and other factors. Field parameterization was conducted on an Ulm clay loam soil (a fine, montmorillonitic, mesic Ustollic Haplargid) and validation experiments for N2O gas emissions were performed on an on‐farm swine effluent study site on a Valent sandy soil (a mixed, mesic Ustic Torripsamment). The unitless model parameters reflecting the maximum fraction of selected N transformations emitted as N2O for nitrification (αN), wet‐period denitrification (αw), and dry‐period denitrifiation (αd) were calibrated as 0.065, 0.050, and 0.520 separately and then used in the validation study. The trends and magnitudes of simulated N2O emissions were statistically consistent with the results obtained from the field experiments (r = 0.78). Experimental results showed that the decline of N2O emission rates from 70 to 2 g N ha−1 d−1 during the growing season was related to soil N content decline from 33 to 4 mg kg−1. Simulated effects of field management on annual N2O emissions indicated that plowing decreased N2O relative to notillage corn (Zea mays L.), irrigation increased N2O 14% relative to dry‐land corn, and doubling fertilization N rates from 100 to 200 kg ha−1 increased N2O emissions 60%.
Distribution of Zinc and Lead Fractions within a Forest Spodosol
Authors: Johnson Chris E. , Petras Robert J.
Published: July 2010

Soil processes play a critical role in the fate of trace metals in forest ecosystems. To explore the nature of soil‐trace metal interactions, we estimated five fractions of Zn and Pb in Spodosols at the Hubbard Brook Experimental Forest in central New Hampshire: (i) soluble + exchangeable (EX); (ii) inorganically bound (IB); (iii) organically bound (ORG); (iv) amorphous oxide bound (AMOX); and (v) mineral lattice, or residual (RES). Organic matter is a critical factor in trace metal fractionation in Hubbard Brook soils; loss‐on‐ignition was strongly correlated to EX Zn (r = 0.91) and Pb (r = 0.85), and ORG Zn (r = 0.57) and Pb (r = 0.89). The Oa horizon accounted for only 1.9% of the soil mass above the C horizon, but contained 23% and 77%, respectively, of the EX Zn and Pb in the soil. Lead was more tightly held in the soil than Zn; the percentage of total metal in the EX fraction was greater for Zn than Pb in all horizons. Through biocycling, Zn is returned to the forest floor, helping to maintain labile pools in upper soil horizons. Nevertheless, the EX Zn pool (6.03 kg ha−1) is insufficient to replace the pool of Zn in aboveground tissues (6.87 kg ha−1). Lead, not a nutrient, has accumulated in the soil due to the combustion of leaded gasoline. Lead leached from the O horizon between 1926 and 1991 can account for 30% of the EX + IB + ORG Pb, or 14% of the labile Pb in the mineral soil.
Alteration of Arsenic Sorption in Flooded‐Dried Soils
Authors: McGeehan Steven L. , Fendorf Scott E. , Naylor Denny V.
Published: July 2010

Arsenic is known to be immobilized in soils through oxyanion sorption reactions involving metal (hydr)oxides. While the mechanisms involved in oxyanion sorption are relatively well characterized in aerobic systems, the response of (hydr)oxides to fluctuating soil redox conditions, and its impact on As sorption, is poorly understood. This study investigated the influence of soil flooding and drying on As sorption and Fe fractionation. Four soils exhibiting a range in As sorption capacity were incubated under flooded (anaerobic) conditions. After the flooding period, the pH and redox potentials of each soil suspension were measured and saturation indices were calculated for standard soil minerals. The suspensions were air dried at room temperature and the short‐range order Fe (oxalate‐extractable) and crystalline Fe (dithionite‐extractable) fractions determined. Separate flooded‐dried samples were resuspended in 0.1 M NaCl for AsO4 sorption measurements. Prolonged soil flooding resulted in a decrease in soil redox potential and an increase in dissolved Al, Fe, Mn, and Si. Drying the previously flooded soils resulted in an increase in As sorption. Selective extraction indicated that the flooding‐drying treatments increased the short‐range order Fe fraction while depleting the free oxide fraction. These changes in Fe mineralogy most likely increased the surface area and number of potential As sorption sites.
Determination of Parameters for Bimodal Hydraulic Functions by Inverse Modeling
Authors: Zurmühl Torsten , Durner Wolfgang
Published: July 2010

To determine the hydraulic properties of soils, transient flow experiments on soil samples and their evaluation by parameter identification methods have become common. In the past, the feasibility of this method has been investigated for soils exclusively with unimodal poresize distributions. In this work we investigated, both from a theoretical and from an experimental point of view, whether hydraulic properties of structured soils with bimodal pore‐size characteristics can be identified by inverse simulation. Multistep outflow experiments were simulated for three hypothetical soils with different degrees of bimodality. The outflow data thus created were then used in the inverse procedure, both in the original form and with an added random error. An analysis of sensitivity coefficients for the model parameters showed that if the bimodality of the pore system is well developed, the parameters of the bimodal hydraulic functions are uncorrelated and can be identified. This was confirmed by inverse optimization runs with simultaneous optimization of up to six parameters, which consistently converged from different initial values to the true parameter values, indicating uniqueness of the inverse problem. Attempts to fit the bimodal outflow data with simulations using unimodal hydraulic functions were not successful, as expressed by systematic disagreement between fitted and “observed” data and nonuniqueness of the inverse solution. We validated these theoretical results with experimental data from an undisturbed sandy forest soil, which showed that it is possible to determine the retention parameters of bimodal hydraulic properties by inverse modeling of multistep outflow experiments.
Texture and Electrical Conductivity Effects on Temperature Dependency in Time Domain Reflectometry
Authors: Persson Magnus , Berndtsson Ronny
Published: July 2010

If not accounted for, temperature effects on the water content and electrical conductivity measured with time domain reflectometry (TDR) will introduce significant errors. In this study, an automated TDR system was used to quantify the temperature dependence of the apparent dielectric constant and electrical conductivity in wet soils. Sandy, clayey, and organic soils were used to examine the effect of soil texture. The temperature correction factor for water content measurements was predicted, by using different dielectric mixing models, to lie between −0.00253 and −0.00419θ°C‐1, the negative value of the temperature correction factor indicating a decrease in the water content measurements with increasing temperature. These values agreed well with the correction factor measured in sandy soils: −0.00269θ°C‐1. In soils with large specific surface, i.e., clayey and organic soils, however, the temperature dependence was significantly lower. Large specific surface combined with high soil solution electrical conductivity resulted in a positive correction factor, i.e., water content measurements increased with increases in temperature. The temperature dependence of the bulk electrical conductivity was investigated using different soils and soil solutions. The temperature dependence was close to that of the soil solution and was independent of soil texture.
Nitrogen Application Timing Effects on Nitrogen Efficiency of Dry‐Seeded Rice
Authors: Wilson, C. E. , Bollich P. K. , Norman R. J.
Published: July 2010

Optimum N application timing contributes significantly to successful rice (Oryza sativa L.) production. In many areas of the southern U.S. Rice Belt, where rice is produced in a dry‐seeded, delayed‐flood system, optimum fertilizer timing has traditionally been achieved by applying 50 to 65% of the total N required onto dry soil immediately prior to establishing the permanent flood and the remainder in one or two applications near the beginning of reproductive growth. Field studies were conducted during 1992 and 1993 at two locations to evaluate the optimum timing for midseason N applications. ‘Laccassine’ rice was grown in microplots (0.58 m2) established with galvanized steel collars. Nonlabeled urea was applied at the four‐ to five‐leaf growth stage at rates of 0, 67.2, and 134.4 kg N ha‐1 just prior to flooding. Nitrogen‐15 labeled urea was applied at midseason at a total rate of 67.2 kg N ha‐1 in four different treatments: (i) 67.2 kg ha‐1 at panicle initiation (PI) (PI‐1), (ii) 67.2 kg ha‐1 at panicle differentiation (PD) (PD‐1), (iii) 33.6 kg ha‐1 each at PI and PI + 10 d (PI‐2), and (iv) 33.6 kg ha‐1 each at PD and PD + 10 d (PD‐2), in addition to a zero‐N treatment. Plant samples were collected to measure total dry matter, fertilizer and total N uptake, and grain yields. Fertilizer N uptake was not affected by midseason N application timing during 1992 and was only slightly affected during 1993. Increasing the pre‐flood N rate significantly increased midseason fertilizer N uptake efficiency, total N uptake, total dry matter accumulation, and grain. Midseason N applications increased total dry matter accumulation, total N uptake, and grain yields compared with no midseason N at one location, but were minimally influenced at the other location. Results suggest that no real advantage is gained from split application of midseason N compared with a single application at midseason and that it can be made from PI to PD growth stage.
Phosphorus Diffusive Flux as Affected by Phosphate Source and Incubation Time
Authors: Villani E. M. A. , Barros N. F. , Novais R. F. , Costa L. M. , Neves J. C. L. , Alvarez V. V. H. , Comerford N. B.
Published: July 2010

Phosphorus supply to eucalypts is deficient in many Brazilian soils and must be augmented with fertilizers to promote economic growth of plantations. Diffusion is generally considered to be the major mechanism of P fertilizer movement in these types of soils; therefore, we studied the effect of P fertilizer source and time of incubation of fertilizer with soil on the P diffusive flux in four Oxisols. Five soluble P sources [Ca(H2PO4)2, NH4H2PO4, (NH4)2HPO4, Na2HPO4·2H2O, and K2HPO4] were applied to the soils at a rate of 500 g P m‐3 soils. Microscope slides were covered with anion‐exchange paper (filter paper impregnated with Fe hydroxide) and laid between two soil layers in a diffusion chamber. Fifteen days later, P was extracted from the exchange paper and analyzed. Five hundred grams P m‐3 soil as the Ca source were also applied to soil samples and incubated for 30 d. Phosphorus diffusive flux was measured as described above. The Ca source of P reduced P diffusive flux by as much as 77% compared with the other sources. This reduction was attributed to the effect the P source had on soil pH. Sandy soils showed less difference between P sources than did clayey soils because the P applied to the sandy soils was in excess of their maximum sorptive capacity. Incubation for 30 d reduced P diffusive flux by up to 81%. Different P sources affect the availability of P in these soils by influencing mobility. Choosing the best source can increase diffusive flux by up to 242% under these soil conditions.
Soil Warming: Consequences for Foliar Litter Decay in a Spruce‐Fir Forest in Maine, USA
Authors: Rustad Lindsey E. , Fernandez Ivan J.
Published: July 2010

Increased rates of litter decay due to projected global warming could substantially alter the balance between C assimilation and release in forest soils, with consequent feedbacks to climate change. This study was conducted to investigate the effects of soil warming on the decomposition of red spruce (Picea rubens Sarg.) and red maple (Acer rubrum L.) foliar litter at Howland, ME. Experimentally increased Oa horizon soil temperatures (increase of 4–5°C) were maintained during the snow‐free season from 1993 through 1995 in replicated 15 by 15 m plots using heat‐resistance cables. For red maple litter, significant treatment effects included greater loss of mass (27%) and C (33%), and greater accumulation of Zn (54%) during the first 6 mo of decay in the heated plots than the control plots. After 30 mo of decay, significant treatment effects were no longer evident for red maple litter. Few treatment effects were observed for red spruce litter during the initial 18 mo of decay. However, after 30 mo of decay, significant treatment effects included greater loss of mass (19%), C (19%), N (24%), Ca (27%), Mg (12%), K (4%), Zn (60%), and cellulose (40%) in red spruce litter in the heated plots than the control plots. We conclude that a modest increase in Oa horizon soil temperature (4–5°C) can significantly increase litter decay rates and alter litter decay dynamics in this coniferous forest stand, and that these changes exhibit variations in their temporal development as a function of species and litter quality attributes.
Nitrous Oxide Emissions from Agricultural Soils of the Boreal and Parkland Regions of Alberta
Authors: Lemke R. L. , Izaurralde R. C. , Malhi S. S. , Arshad M. A. , Nyborg M.
Published: July 2010

The contribution of agricultural soils to atmospheric N2O in the Boreal and Parkland regions of Alberta is largely unknown. Field data are required to quantify the flux of N2O from these regions, as are methodologies to scale up from site‐specific measurements to large geographical areas. Climate‐soil‐management combinations (CSMCs) aggregated to an ecodistrict level have recently been proposed as a technique for scaling up greenhouse gas flux estimates for Canadian agriculture. Our objective was to calculate seasonal N2O losses and investigate large‐scale spatial variability using field data from selected sites in the Boreal and Parkland regions. We used vented soil covers to measure N2O emissions during spring and summer of 1993 and 1994, and the spring of 1995, from six representative CSMCs in five ecodistricts in Alberta. Substantial and consistent differences in the magnitude of N2O‐N loss among sites were observed, with annual estimated losses of N2O‐N ranging from 0.4 to 2.6 kg ha‐1. Up to 70% of the total annual N2O‐N loss occurred during brief but intense bursts at spring thaw. Soil clay content was found to be strongly correlated with annual N2O‐N loss. This relationship suggests that clay content, readily available from soil data bases, could be used as a N2O‐loss predictor variable when applying scaling‐up methodologies.
Water Table Dynamics in Tile‐Drained Fields
Authors: Skaggs T. H. , Mohanty B. P.
Published: July 2010

We present a method for simulating water table dynamics in tile‐drained fields that are subject to intermittent precipitation or irrigation. A stochastic state equation for the water table height midway between drain laterals is obtained by adding a random noise term to van Schilfgaarde's deterministic drainage model. The random term accounts for dynamics not modeled by van Schilfgaarde's equation, which is based on numerous simplifying assumptions. The continuous‐discrete Kalman filter is used to obtain an estimate of the time variation of the water table height, as well as the variance of the estimate. The method is demonstrated using experimental data from the literature and is shown to have advantages over alternative approaches. Additional testing is necessary to fully assess the validity of the stochastic state equation and the utility of the filtering procedure.
Organic Matter Stabilization in Two Semiarid Tropical Soils: Size, Density, and Magnetic Separations
Authors: Shang C. , Tiessen H.
Published: July 2010

Soil organic matter (SOM) in many tropical soils is less stable than that of temperate soils, in part due to faster decomposition processes in the tropics, but possibly also due to different mechanisms of organomineral stabilization. We studied the mineral associations of SOM in the surface horizons of two semiarid tropical soils (an Oxisol and an Alfisol) using particle‐size, density, and magnetic separations. The inorganic phases of fractionated materials were examined using chemical extraction and x‐ray diffraction. Organic matter associated with the sand fraction accounted for 21 to 30% of soil C, mostly as coarse, floating material. This coarse material was more abundant in the Alfisol. One‐half the organic C of both soils was associated with the silt‐sized fraction, which contained a substantial portion of microaggregates resistant to sonication. Carbon in silt‐sized aggregates was mainly stabilized by association with poorly crystalline oxides and by aggregation with crystalline oxides and clays. The C as light matter (<1.8 g cm‐3) liberated from silt‐size microaggregates by successive sonication treatments accounted for ≈23% of total soil C for both soils. The SOM in the <1.8 g cm‐3 fraction seemed younger and less decomposed than the organic materials in the temperate soil fractions with similar density and equivalent sizes. In clays, C was concentrated in fractions of intermediate magnetic susceptibility, whereas both the highly magnetic fraction of predominantly well‐crystallized Fe and the nonmagnetic fraction were C poor. The study points to the important role of particle size and crystallinity of Fe oxides and of microaggregation between oxides, organic matter, and other minerals in stabilizing tropical soil organic matter.
Seasonal Distribution of Nitrous Oxide Emissions from Soils in the Parkland Region
Authors: Lemke R. L. , Izaurralde R. C. , Nyborg M.
Published: July 2010

The temporal variability of soil‐derived N2O emissions presents a major challenge to the accurate quantification of N2O‐N losses from agroecosystems. We characterized the seasonal distribution of N2O emissions from two agricultural sites in the Parkland region of Alberta during 1993 and 1994. Treatments studied were fallow, and spring wheat (Triticum aestivum L.) with and without urea fertilizer, under conventional till management. Gas samples were collected from vented static soil chambers and were analyzed for N2O with a gas chromatograph equipped with a 63Ni electron capture detector. Soil water content and concentrations of NO‐3‐N, NH+4‐N, and water‐soluble organic C (WSOC) were measured several times during the season. A brief burst of N2O emission was recorded at both sites during and immediately following spring snow melt. A second period of activity occurred between mid‐June and mid‐July. Between 16 and 60% of estimated annual N2O‐N loss occurred during spring thaw, while >80% of cumulative annual N2O‐N loss had occurred by mid‐July. Mean soil NO‐3‐N concentration explained up to 65% of the temporal variability in geometric mean N2O emissions. A multiple regression model that included fall soil concentrations of NO‐3‐N, NH+4‐N, and WSOC explained 94% of the variability in estimated cumulative N2O‐N loss during the following spring thaw. Most N2O‐N losses in the Parkland region appear to occur during spring thaw and early summer; therefore, sampling schedules need to focus on these time periods. Management practices that minimize N availability during spring thaw may be an effective mitigation strategy for this region.
Direct vs. Indirect Nitrogen‐15 Approaches to Estimate Nitrogen Contributions from Crop Residues
Authors: Stevenson F. C. , Walley F. L. , van Kessel C.
Published: July 2010

The benefit of including a legume in a cropping system often has been attributed, in part, to N2 fixation and the additional N that legume residues can supply to the succeeding crop. In this study, we estimated the N contribution from pea (Pisum sativum L.) to a succeeding wheat (Triticum aestivum L.) crop directly, using 15N‐labeled crop residues, and indirectly, using the A value. The A value provides an index of soil N availability and was used to indirectly estimate the N contribution of crop residues to the subsequent crop. Pea‐wheat and wheat‐wheat rotations were established at four sites using a small‐plot research approach and at one site using a landscapescale research approach. Nitrogen‐15‐labeled residue and 15N‐labeled fertilizer were applied to unlabeled areas within each rotation following the first growing season. When estimated directly using 15N‐labeled residues, pea residue contributed 10 kg N ha‐1 to the subsequent wheat crop, whereas wheat residue contributed only 3 kg N ha‐1. According to indirect estimates of N contribution, the A value in the second year of the pea‐wheat rotation was, on average, 119 kg N ha‐1 higher than for the wheat‐wheat rotation. The difference in A values was equivalent to an additional contribution from pea, relative to wheat residues, of 4 kg N ha‐1 in the small‐plot study and 38 kg N ha‐1 in the landscape‐scale study. The direct approach considers only the N contribution from the aboveground portion of the previous crop residues. In contrast, indirect estimates of the N contribution from crop residues based on the A value includes the contribution of all belowground N sources and the influence of non‐N rotation effects, such as root diseases, on the ability of a succeeding crop to access soil N reserves.
Iron Oxides Erodibility Interactions for Soils of the Memphis Catena
Authors: Rhoton F. E. , Römkens M. J. M. , Lindbo D. L.
Published: July 2010

In the Memphis catena, the well‐drained Memphis (fine silty, mixed, active, thermic Typic Hapludalfs) is more erodible than the moderately well‐drained Loring (fine silty, mixed, active, thermic Oxyaquic Fragiudalfs) and Grenada (fine silty, mixed, active, thermic Glossic Fragiudalfs). We hypothesized that soil wetness and Fe oxide status affects the erodibility of these soils. Samples (<2 mm) of A‐ and B‐horizons, collected from representative pedons at five locations, were characterized for standard physical and chemical properties. Simulated rainfall was applied (64 mm h‐1) to additional samples (<8 mm) in a rainfall simulator pan that had a 0.6 m × 0.6 m test area. Water dispersible clay (WDC) and soil loss averaged 7.2% and 9.21 Mg ha‐1 for Memphis, 6.8% and 8.85 Mg ha‐1 for Loring, and 6.1% and 8.71 Mg ha‐1 for Grenada. Sediment Feo, Fed, and Feo/Fed ratios were about 0.80, 1.5, and 0.50 times that of the soil, respectively. Correlation coefficients (r) for WDC and soil loss vs. Fe oxide variables exceeded 0.90 in some horizons, whereas, organic C (OC) and % clay were generally <0.60. However, OC vs. % sediment <53 µm had r values of 0.87 compared to 0.59 for some Fe oxide variables. Regression models derived for WDC and soil loss had Fe oxide parameters as principal variables in the best fit models and coefficients of determination that ranged from 0.208 to 0.922 (significant at P ≤ 0.01). Results suggest that Fe oxides are more important than OC and clay content for determining the erodibility of these soils, particularly Feo/Fed ratios which are negatively correlated with WDC and soil loss.
Nitrate‐Nitrogen, Soluble, and Bioavailable Phosphorus Runoff from Simulated Rainfall After Fertilizer Application
Authors: Gascho G. J. , Davis J. G. , Hook J. E. , Wauchope R. D. , Dowler C.C. , Johnson A. W. , Truman C. C. , Sumner H. R.
Published: July 2010

Runoff from crop land can enhance eutrophication of fresh water and hypoxia in sea water. We simulated rain at 25 mm hr‐1 for 2 hr, 8 d prior and 1, 14, 29, 49 and 108 d after fertilization and planting of corn (Zea mays L.). Experimental sites received 50 kg N, 45 kg P, and 125 kg K ha‐1 as granulated fertilizer broadcast and incorporated to a depth of 150 mm. An additional 118 kg N ha‐1 was surface‐banded as solution fertilizer at Day 28, which was 1 d prior to the Day 29 rain. The study was conducted for 2 yr on a Tifton loamy sand (fine‐loamy, siliceous, thermic Plinthic Kandiudults) with a slope of 4.5%, on micro‐ (5.57 m2) and meso‐scale (622 m2) plots. Runoff was equal for the two scales of plots. There were greater runoff losses of soluble‐P from meso‐ (1.4 kg ha‐1) than from micro‐plots (1.0 kg ha‐1). Nitrate‐N losses averaged 2.7 kg ha‐1 and bioavailable‐P losses were 2.3 kg ha‐1. Greatest NO3‐N and soluble‐P losses occurred the day after application of the soild fertilizer, whereas bioavailable‐P loss was greatest at Day 14 and 29. No increase in NO3‐N losses was found 1 d after the application of urea ammonium nitrate solution, possibly indicating that liquid fertilizers are not as susceptible to runoff losses as solid fertilizers. Results of this study should encourage the use of small plots, thereby saving research time and expense and provide data useful for estimating losses at similar sites.
Evaluation of the Test‐Mineral Method for Studying Minesoil Geochemistry
Authors: Monterroso C. , Macías F.
Published: July 2010

The test‐mineral method was evaluated as a means of assessing the chemical environment and soil processes in mine soils. This study was carried out on lignite mine tailings at As Pontes (northwestern Spain). The spoils are heterogeneous and mainly consist of carbonaceous and noncarbonaceous clays and slates, often containing pyrite. Vermiculite was used as a reference mineral and placed in ionpermeable polyamide bags that were then buried in various reclaimed minesoils. One bag was recovered from each soil after 13, 26, and 52 wk and analyzed for pH, elemental composition, exchangeable cations, cation‐exchange capacity (CEC), extractable Al and Fe, and mineralogy (x‐ray diffractometry [XRD], differential thermal analysis [DTA], and thermogravimetry [TGA]). Vermiculite rapidly underwent geochemical and mineralogical changes (in <13 wk). The greatest changes took place in soils developed from minespoils rich in sulfides; exchangeable Na on the vermiculite was replaced with Ca, Mg, Al, or H and there was an important decrease in CEC due to interlayer Alpolymerization. This behavior is typical of an acid environment. By contrast, the CEC of vermiculite in the low‐sulfide soils did not change and exchangeable Na (principal cation in original vermiculite) was displaced by Ca, with virtually no involvement of other cations. This test vermiculite proved to be an excellent indicator of the chemical environment of minesoils.
Refinement of the Anion Exchange Membrane Method for Soluble Phosphorus Measurement
Authors: Cooperband L. R. , Gale P. M. , Comerford N. B.
Published: July 2010

The proper use of anion exchange membranes (AEMs) to assess phosphorus availability in situ requires a more thorough understanding of their function under a wide range of soil biophysical conditions. We evaluated the ability of AEMs to sorb selected organic P compounds, determined possible interference of low‐molecular‐weight organic acids and humic substances on AEM‐P sorption, and assessed the efficiency of AEM‐P sorption in the presence of wetland sediments and soil‐sediment microbes. We collected soils, swamp water, and sediments from a cypress swamp‐pine flatwoods ecosystem in north central Florida. Membranes recovered nearly 100% of both ortho and organic P in a study using aqueous solutions of ortho P and organic P compounds. Membrane sorption of ortho P with varying concentrations of oxalate and protocatechuate was close to 100%. There was a reduction of 15 µg P per membrane when AEMs were placed inside low‐molecular‐weight‐cutoff dialysis tubing (<1000 MWCO) in P‐spiked swamp water; however, there was no significant tubing effect in non‐spiked swamp water. In an experiment exploring effects on AEM‐P sorption of P additions to swamp water with or without sediments, AEMs recovered six times more P than measured in non‐spiked swamp water with sediments. When swamp water was treated with chloroform, AEMs sorbed an equal or greater amount of ortho P than ortho P measured in swamp water with no AEMs. Results suggest that AEMs can be used to measure soluble and readily desorbable P in low‐P status soils and sediments with organic acids.
Microbial Utilization of Heterocyclic Nitrogen from Atrazine
Authors: Bichat F. , Mulvaney R. L. , Sims G. K.
Published: July 2010

Radiotracer studies have provided indirect evidence that heterocyclic N in atrazine [2‐chloro‐4(ethylamino)‐6‐(isopropylamino)‐1,3,5‐triazine] may be utilized by microorganisms as a source of N; however, no data are available from investigations using 15N as a tracer. Studies were conducted to examine microbial utilization of atrazine ring‐15N in soil and pure cultures of Pseudomonas sp. strain ADP, Agrobacterium radiobacter J14a, or bacterium M91‐3. Atrazine [U‐15N‐ring] was synthesized from labeled urea. To investigate the effect of exogenous N on atrazine degradation, pure cultures were supplemented with unlabeled atrazine and labeled N as (NH4)2SO4, KNO3, urea, or glycine. Under C‐limiting conditions, cells of Pseudomonas sp. strain ADP incorporated side chain‐N into biomass and liberated ring‐N as NH4. When N was limiting, ring‐N was also recovered in biomass. Degradation of atrazine by Pseudomonas strain sp. ADP and A. radiobacter was unaffected by the presence of exogenous N, whereas no degradation occurred with bacterium M91‐3 in media containing urea or NH4‐N. The fate of double‐labeled [U‐14C, U‐15N‐ring]‐atrazine (15 mg kg‐1) was examined after incubation of a Bloomfield soil (sandy, mixed, mesic Psammentic Hapludalf) amended with NH4‐ or NO3‐N (75 mg kg‐1), with or without an inoculum of Pseudomonas sp. strain ADP (1.06 × 1013 cells kg‐1). In uninoculated soil, mineralization of atrazine‐14C was inhibited by inorganic N, whereas in the inoculated soil, 87% of the atrazine was mineralized, regardless of the N treatment. The C/N ratio was much lower for amino acids isolated from soil than for the atrazine ring, suggesting preferential assimilation of N over C by microorganisms.