bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geochemistry of Dissolved Organic Nutrients in Water Percolating through a Forest Ecosystem
Authors: Qualls Robert G. , Haines Bruce L. 
Published: July 2010

AbstractDissolved organic matter (DOM) is a major vehicle for the translocation and loss of N and P from forest ecosystems. The chemical properties of DOM and its interactions with soil surfaces are crucial in determining the mobility of these organic nutrients. We fractionated DOM from throughfall, all soil horizons (Ultisols and Inceptisols), and stream water from an Appalachian mountain forest ecosystem into hydrophobic or hydrophilic acids, neutrals, and bases. We analyzed each fraction for dissolved organic C (DOC), N (DON), and P (DOP). Most of the DOC was in the acid fractions, with the humic fractions (hydrophobic acids and phenols) comprising 35 to 57% of the DOC in all samples except summer throughfall. Concentrations of all fractions declined with depth in the soil. As a percent of total DOC, the humics declined with depth, whereas the hydrophilic neutrals increased. Bases, which we expected to contain cationic amino groups, were < 2.5% of the DOC. Instead, most DON was in the humic, hydrophilic acid, and hydrophilic neutral fractions. Most DOP occurred in the hydrophilic acid, humic, and hydrophilic neutral fractions. The functional groups in which N and P occur had little influence on the behavior of most of the DOM as a whole since: (i) cationic DOM was such a minor component, and (ii) P was simply too rare to influence the anionic behavior of many molecules. Nevertheless, for those molecules in which P did occur, P may have influenced their behavior since a large percentage of the DOP was in the hydrophilic acid (i.e., anionic) fraction. The carboxylic and phenolic functional groups, or in some cases the neutrality, of the DOM molecules appeared to be much more important than N‐containing groups in influencing the behavior of the N carried passively by the DOM.
Capillary‐Wick Unsaturated Zone Soil Pore Water Sampler
Authors: Holder M. , Brown K. W. , Thomas J. C. , Zabcik D. , Murray H. E. 
Published: July 2010

AbstractExisting unsaturated zone soil water samplers have several deficiencies that jeopardize their utility for field sampling. Suction cups function only when a vacuum is applied, and sample from an unknown volume of soil. Pan samplers sample only saturated flow. A capillary‐wick sampler was developed to overcome these problems and was tested in both the laboratory and field to evaluate its performance. Breakthrough curves for selected inorganic ions and organic chemicals were established in the laboratory. No adsorption/desorption of these chemicals was found for the capillary‐wick sampler made entirely of glass. Banks of eight capillary‐wick samplers were installed in field plots of Padina sand (loamy, siliceous, thermic, Grossarenic Paleustalf), Weswood silt loam (fine‐silty, mixed, thermic Fluventic Ustochrept), and Lufkin clay (fine, montmorillonitic, thermic Vertic Albaqualf) soils. Saturated soil Br breakthrough curves were determined at each location and used to estimate the number of samplers required to characterize the flow of contaminants. To achieve 95% confidence in the chemical data from the three soils and plot sizes tested, 31 samplers were required for the sandy soil, six for the silt loam soil, and only two for the clay soil. The wick‐activated sampler collected soil solution samples from soils having soil water potentials ranging from 0 to −6.0 kPa. The capillary‐wick sampler collected samples continuously across this range of water potentials without the need for a continuous vacuum and is thus an improvement over existing samplers. While the capillary‐wick samplers usually collected sample volumes representative of the flux at potentials of −5 kPa, samples collected at greater and lesser potentials were not representative of the flux.
Modeling Root Water Potential and Soil‐Root Water Transport: I. Model Presentation
Authors: Lafolie F. , Bruckler L. , Tardieu F. 
Published: July 2010

AbstractPlant water uptake has classically been supposed to depend on the leaf water potential (LWP) and LWP was assumed to control the stomatal conductance. A new approach to stomatal control has recently been proposed in which root water potential (RWP) determines stomatal aperture, and hence transpiration, by means of chemical messages. In such a case, models that provide precise calculations of RWP become essential for understanding soil‐root water transport. The objective of this paper is to propose a theoretical approach to calculate RWP and water uptake by roots in the X‐Y plane for any spatial root distribution. For the calculations of RWP, we assumed that the plant continuously adjusted its RWP so as to minimize the difference between the maximum evapotranspiration (MET) and the amount of water extracted by the root system. Water release from the roots in the soil was considered to be negligible, so roots in dry soil were temporarily removed from the pool of active roots. A Galerkin finite element method was used to solve Richards' equation. Examples of calculation are presented for a nonuniform root distribution under both wet and dry initial situations. Root water potential and the number of active roots varied greatly with time. Results suggested that no simple relationship existed between the plant water uptake and the root water potential. Furthermore, soil water‐potential maps showed a close relationship between water uptake and root positions, and great differences between RWP and the mean soil water potential could be calculated. A greater or lesser water redistribution toward the roots occurred during the night. Finally, the proposed approach may be validated with precise soil and plant measurements.
Equivalent Diameter of Simulated Macropore Systems during Saturated Flow
Authors: Dunn G. H. , Phillips R. E. 
Published: July 2010

AbstractUnder natural conditions, soil pore systems that conduct water vary in shape, cross‐sectional area, and continuity. Because of this, it is virtually impossible to predict the flow of water through these pore systems. We conducted an experiment to measure the equivalent spherical diameter, deq, of simulated nonuniform macropore systems for 11 combinations of lengths of three radii of cylindrical, straight‐walled glass tubing during saturated flow. Also, we wanted to determine if experimental data of deq of the simulated macropores are described by a derived theoretical equation where deq is a function of the total length of the three tubes, their individual lengths, and their radii. Three known, uniform‐i.‐d. tubes of differing lengths, of cylindrical, straight‐walled glass, in series configuration were used to simulate to a small degree the geometry of macropores as they occur in the field. Inside diameters were 5.08 (L), 1.88 (M), and 0.94 (S) mm. A constant length of 0.60 m was maintained for the pore system. The deq values of these non‐uniform pore systems were measured. Flux values were measured at eight hydraulic pressures. Equivalent diameters were calculated using Poiseuille's law from the measured flux. The data points of deq of the pore system were described well by the derived equation. The experimental saturated hydraulic conductivity (Ksat) was also well described by a derived function.
Phosphate‐Induced Release of Arsenic from Soils Contaminated with Lead Arsenate
Authors: Peryea Frank J. 
Published: July 2010

AbstractMixing high rates of monoammonium phosphate (MAP) or monocalcium phosphate fertilizers with orchard soil often stimulates growth of newly planted pome fruit trees. This practice may increase As solubility in soils contaminated with lead arsenate pesticide residues because of competitive PO4‐AsO4 exchange. Laboratory experiments were conducted examining As release in batch suspensions of five lead arsenate‐contaminated soils. Dissolved Pb concentrations were <5 µmol/L in all soil suspensions. Redox potential exceeded 500 mV in all suspensions, suggesting that the primary form of dissolved As was probably AsO4. Phosphate‐induced As release was dependent on soil type, occurring in four nonvolcanic soils but not in a pumiceous soil. Arsenic release was positively related to added PO4 concentration but was not significantly influenced by PO4 source. Ammonium sulfate did not enhance As release. Arsenic solubility was consistent with a mechanism of specific PO4‐AsO4 exchange, while PO4 solubility was consistent with control by metastable PO4 minerals. Phosphate‐released As was not appreciably resorbed after multiple wetting and drying cycles. These results explain enhanced As mobility, phytoavailability, and phytotoxicity observed in lead arsenate‐contaminated soils amended with MAP.
Organic Carbon Sorption in Arctic and Subalpine Spodosol B Horizons
Authors: Dahlgren R. A. , Marrett D. J. 
Published: July 2010

AbstractThe sorption of dissolved organic carbon (DOC) on B horizons from arctic and subalpine Spodosols was investigated at low temperatures typical of these soils. The arctic Spodosol, from northern Alaska, had an inverted horizon sequence (Bs overlying Bhs) and other properties inconsistent with the metal‐fulvate theory of podzolization. The subalpine Spodosol, from the Cascade Range of Washington state, developed in a mixture of volcanic and glacial materials and had classic Spodosol morphology. Batch studies were conducted under the following conditions: 3 °C, pH of 4.5, C/metal ratio of 59, a 10:1 solution/soil ratio, and an ionic strength of 10−3 M. Final pH, DOC, Fe, Al, and Si concentrations were determined. Between 30 and 50% of the adsorption/desorption occurred within the first 0.25 h and steady‐state DOC concentrations occurred between 4 and 12 h. Only the subalpine Bs horizon adsorbed DOC, while both Bhs horizons and the arctic Bs horizon desorbed DOC. Dispersion of fine colloids (<0.2 µm) affected desorption in arctic soils at reaction times >4 h. The results suggest that the main mechanism of DOC immobilization involved initial solubilization of metals, which lowered C/metal ratios in solution, followed by adsorption of the organo‐metal complexes. The ability of the subalpine Bs horizon to effectively adsorb DOC may be due to the large concentration of uncoated short‐range‐order materials (imogolite and ferrihydrite) present in this horizon.
Legume Mulch and Nitrogen Fertilizer Effects on Soil Water and Corn Production
Authors: Corak S. J. , Frye W. W. , Smith M. S. 
Published: July 2010

AbstractHairy vetch (Vicia villosa Roth), as a winter annual legume cover crop, can increase grain yield of no‐till corn (Zea mays L.). Optimizing management of this system depends on understanding beneficial effects. This field study examined effects of hairy vetch (HV) and N fertilizer on soil water content, crop growth, N assimilation, and water‐use efficiency. Cover‐crop treatments, each with 0 and 255 kg ha−1 of fertilizer N, were (i) winter fallow, (ii) aboveground HV removed at corn planting, (iii) HV left in place, and (iv) HV left in place and supplemented with that removed from (ii). Transpiration by HV before corn planting reduced soil water content, decreasing early growth of corn during years of low spring rainfall. By 2 to 4 wk after planting, however, soil water cotnent under HV mulch was similar to winter fallow. Soil water content was higher with HV mulch only during the second 4‐wk period following planting and only in the upper 7.5 cm of the profile. Greater soil water use associated with N fertilizer occurred after about 8 wk in 2 of the 3 yr. Hairy vetch treatments at the zero‐N fertilizer level increased corn growth, N assimilation, grain yield, and water‐use efficiency. The high‐N treatment negated these benefits of HV. Because of this and the lack of mulch effects on soil water during later stages of crop growth, we concluded that N supplied to no‐till corn was the principal, immediate benefit of HV during this study.
Freezing Effects on Aggregate Stability Affected by Texture, Mineralogy, and Organic Matter
Authors: Lehrsch G. A. , Sojka R. E. , Carter D. L. , Jolley P. M. 
Published: July 2010

AbstractAggregate stability, an important property influencing a soil's response to erosive forces, is affected by freezing. The objectives of this laboratory study were to determine how constrainment, number of freeze‐thaw cycles, and water content at freezing affect the aggregate stability of six continental USA soils differing in texture, mineralogy, and organic‐matter content. Moist aggregates, after being frozen and thawed either zero, one, three, or five times, were vapor wetted to 0.30 kg kg−1 and analyzed by wet sieving. Soils with clay contents of 17% or more and organic‐matter contents >3% were the most stable after freezing. Aggregate stability for fine‐ and medium‐textured soils generally decreased linearly with increasing water content at freezing. This linear decrease in stability was more rapid for constrained samples than for unconstrained samples. The stability of field‐moist aggregates generally increased from zero to one or three freeze‐thaw cycles. For at least one low‐organic‐matter soil, stability increased from one to three freeze‐thaw cycles, but then decreased at five cycles. After thawing, aggregates at water contents of 0.15 kg kg−1 or more that were constrained when frozen were always significantly less stable than aggregates that were unconstrained when frozen.
Forest Soil Sampling Efficiency: Matching Laboratory Analyses and Field Sampling Procedures
Authors: Mroz Glenn D. , Reed David D. 
Published: July 2010

AbstractSoil characteristics can be extremely variable, both spatially and temporally, and the cost of sampling to achieve high levels of precision may be prohibitive. Researchers are often faced with the need to obtain the best possible precision within a fixed budget. We present methods of determining the optimal number of field composite samples, the number of field samples per composite, and the number of laboratory analyses per composite. Example problems illustrate methods of obtaining both a desired precision at a minimum cost and the greatest possible precision at a given cost. Calculations to compare and select among alternative laboratory procedures are also illustrated. Often, less precise but inexpensive laboratory procedures may result in greater overall precision than highly precise but expensive procedures.
Vegetation‐Soil Relationships on Thin or Shallow Range Sites in Western South Dakota
Authors: White E. M. 
Published: July 2010

AbstractLittle bluestem (Schizachyrium scoparium [Michx.] Nash) and/or big bluestem (Andropogon gerardii Vitman) stands often occur adjacent to western wheatgrass (Agropyron smithii Rydb.) stands on thin or shallow range sites and closely related sites. The purpose of this study was to identify soil properties that cause the nonrandom distribution of the grasses. Particle size, pH, organic matter, total N, total PO4, and available PO4‐P were determined on 17 soil profiles that supported different grass distributions. Soils with western wheatgrass had more plant‐available PO4‐P than soils with bluestem, but usually less organic matter. Western wheatgrass needs a large supply of available PO4‐P because it grows rapidly in the spring. The bluestems grow when temperatures are higher and the microbial‐chemical release of plant nutrients is greatest. The distribution of the grasses is related to soil properties that in turn, are perpetuated by bluestems supplying more organic matter to the soil surface layer that western wheatgrass. Sideoats grama (Bouteloua curtipendula [Michx.]) can grow under conditions intermediate to those suited for bluestems and western wheatgrass.
Simulation of Crop Response to Polyolefin‐Coated Urea: I. Field Dissolution
Authors: Gandeza A. T. , Shoji S. , Yamada I. 
Published: July 2010

AbstractPolyolefin‐coated urea (POCU) is a controlled‐release granular fertilizer whose dissolution is primarily temperature‐dependent. The coating is made of ethylene vinyl acetate, polyolefin, and talc to control N release. Dissolution doubles for every 10 °C rise in temperature, a Q10 matching that of plants. This study was conducted to understand its N release under Andisol field conditions and show its temperature dependency. Cumulative N release (CNR) with time between 10 and 30 °C is described by a quadratic equation in the general form CNR = a + b(day) + c(day)2. The equation corresponding to the mean daily soil or air temperature was used to calculate CNR. The CNR gradually increased with time and reached about 80% of the total N content at about 126 d after application. Two‐year experiments showed that observed CNR and predicted CNR determined using either soil or air temperature expressed as functions of time were closely correlated. Using cumulative temperature (CT) as the variable, CNR is given by the relation CNR = a + b(CT) + c(CT)2. This means that N dissolution from POCU can be predicted. Such behavior of N dissolution has significant implications on N supply to plants, fertilizer efficiency, and efforts to minimize environmental pollution.
Simulation of Crop Response to Polyolefin‐Coated Urea: II. Nitrogen Uptake by Corn
Authors: Shoji S. , Gandeza A. T. , Kimura K. 
Published: July 2010

AbstractControlled‐release N fertilizers are more desirable if release characteristics are synchronized to plant uptake. This study was conducted to determine the relationship between N dissolution from polyolefin‐coated urea (POCU) and N uptake by corn (Zea mays L.) under Andisol field conditions. Cumulative N release (CNR) followed a quadratic curve as a function of either time or cumulative air temperature (CAT). Rate of N dissolution was high at the early growth stages, but gradually decreased with time. The CNR reached about 80% of the total N content of the fertilizer at around 126 d after application or when CAT had reached about 2300 °C. Nitrogen uptake from the fertilizer followed a typical sigmoid curve. Therefore, the fertilizer can supply the N requirements of corn throughout the whole growing period. Since N dissolution can be simulated, it may also be possible to simulate N uptake from POCU by crops. Nitrogen uptake by corn can be predicted in terms of the total amount of N dissolved. Actual recovery of the fertilizer was very high compared with highly soluble fertilizers like (NH4)2SO4 or urea. Since POCU releases N gradually, depending on variations in temperature when soil moisture is sufficient, recovery by crops is less likely to be influenced by variations in climate, such as the occurrence of heavy rains; hence N losses are minimized. Such characteristics of the fertilizer increases nutrient efficiency and contributes to efforts in controlling pollution.
Stability of Iron Oxides in Two Soils with Contrasting Colors
Authors: Bigham J. M. , Smeck N. E. , Heckendorn S. E. , Jaynes W. F. 
Published: July 2010

AbstractTwo soils formed from sedimentary rocks with contrasting colors (dark reddish brown, 2.5YR 3/4 vs. olive, 5Y 5/3) were studied to assess the origin and relative stability of their constituent Fe oxides. Field morphology and total elemental analyses of the silt fractions for Ti, Zr, and K indicated that both soils had developed in uniform residuum overlain by approximately 30 cm of late Wisconsinan loess. The residual 2Bt horizons were contrasting in color but similar in clay content (50–65%), mineralogy (smectitic), and chemistry (pH = 4.5–6.0, base saturation = 50–60%). X‐ray diffraction studies of Fe‐oxide‐enriched specimens obtained through high‐gradient magnetic separations of the soil clays showed goethite to be the only detectable Fe oxide in the pedon formed from olive (5Y 5/3) shale. Red pigmentation in the companion soil was due to the presence of lithogenic hematite associated with varying amounts of goethite and lepidocrocite. Lepidocrocite occurred only in the solum and was most abundant in the clayey argillic horizon. Hematite grains from the 2C horizon consisted of thin, pseudohexagonal crystals with diameters <0.5 µm, whereas those isolated from overlying horizons were rounded and exhibited dissolution cavities attributable to instability within the modern pedoenvironment. Ratios of dithionite‐extractable to total Fe (Fed/Fet) indicated that goethite had formed primarily by pedogenic weathering of silicate minerals in the profile developed from olive shale. In contrast, sufficient Fe was apparently mobilized by dissolution of lithogenic hematite in the red soil to suppress the release of Fe from silicates and to exceed the solubility products of associated goethite and lepidocrocite on at least a seasonal basis.
Water Infiltration into Soil in Response to Ponded‐Water Head
Authors: Swartzendruber D. , Hogarth W. L. 
Published: July 2010

AbstractThe pressure head of water ponded on the soil surface can increase the infiltration of water into soil, but the effect has often been complicated to describe mathematically. This study was conducted to devise a simpler mathematical description without undue sacrifice of accuracy. A new three‐parameter infiltration equation was examined for its capability in describing the effect of soil‐surface‐ponded water head, h, on the cumulative quantity of water infiltrated into the soil with time. The infiltration equation, as reduced to two‐parameter dimensionless from, was fitted by nonlinear least squares to dimensionless data generated from mathematical descriptions of infiltration that included the effect of h in somewhat complicated parametric form. The fitted two‐parameter equation gave an excellent description of all the generated data, in terms of both goodness of fit and in recovery of the dimensionless ponded head p used as an input into the generated data. From an overall perspective, recovery of h was achieved within a relative error of ±1.4% across the complete range of the generated data, thus validating the new and relatively simple equation in its description of the general effect of ponded head on the cumulative infiltration process.
Topographic Effects on Spring Wheat Yields and Water Use
Authors: Halvorson Gary A. , Doll E. C. 
Published: July 2010

AbstractWater redistribution in a complex landscape needs to be quantified in order to determine field productivity. Landscape effects on water use and spring wheat (Triticum aestivum L.) yields were studied by monitoring two fields at each of two locations in North Dakota for 5 years. Four soil series at different positions within each field were monitored: the Zahl loam series (fine‐loamy, mixed Entic Haploboroll) on hilltops and shoulder positions, the Williams loam series (fine‐loamy, mixed Typic Argiboroll) on side slopes and hilltops, the Bowbells loam series (fine‐loamy, mixed Pachic Haploboroll) on footslopes and toeslopes, and the Tonka silt loam series (fine, montmorillonitic, frigid Argiaquic Argialboll) in small undrained depressional areas. Topographic factors were calculated at each site by measuring the slope in four directions, 90° apart, and adding the slopes together. If a slope was downward toward a site, it was considered positive, if a slope was upward toward a site it was considered negative. This number, if positive, would indicate that runon water would be added to the site and, if negative, water would be lost from the site due to runoff. Topographic factors were calculated 3, 6, 15, and 30 m from each site. As expected, wheat yields from the four soils were in the order Tonka > Bowbells > Williams > Zahl. Spring wheat grain yields ranged from 5.1 Mg ha−1 on Bowbells in 1985 to no yield in 1988 at the Underwood location. Spring wheat grain yields were generally correlated to total water use. When the topographic factor was added into the regression of yield vs. total water use, the coefficient of determination, R2, increased in the first 3 yr. The last 2 yr of the study were drought years and the topographic factor accurately reflected the lack of water redistribution in those years. Topographic factors measured 15 m from the site gave the highest R2 values.