bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Equilibrium in Externally Loaded Unsaturated Granular Similar Media
Authors: Snyder V. A.
Published: July 2010

The physics of soil deformation under applied external loads is still very poorly understood. This is especially true in the case of unsaturated soils, where very complex internal force systems arise as a result of applied loads, stresses in the pore fluid phases, and surface tension forces in the air‐water interface. The present paper attempts a theoretical description of these forces, for the relatively simple case of nonswelling cohesionless granular soils in static equilibrium. The analysis concentrates on systems which are similar according to the rules defined by Miller and Miller (1956) in their theory of capillary flow phenomena in granular media. Applied loads, gravity, and stresses in the pore fluid phases are analyzed in terms of their effects on the interparticle contact forces which determine soil behavior. For isotropic similar media under similar applied loads, interparticle contact forces can be approximated as linear combinations of the scalar groups (σ̄‐µa) λ21, ρgλ31 and γλ1, where σ̄ is the mean applied stress, µa is the pore‐air pressure, ρ is particle density, g is the gravitational constant, γ is the surface tension of the air‐water interface, and λ1 is the microscopic characteristic length. The coefficients of these groups are dimensionless vector arrays (each vector corresponding to a particular interparticle contact point) which depend on the geometry of the soil‐air‐water system, but are independent of its characteristic length when gravitational effects on pore‐water pressure can be neglected relative to surface tension effects. The relationship of the theory to continuum mechanics and probabilistic approaches to force transmission in soils is briefly discussed.
Solutions for Transport of Two Sorbed Solutes with Differing Dispersion Coefficients in Soil
Authors: Angelakis A. N. , Kadir T. N. , Rolston D. E.
Published: July 2010

Simultaneous transformation and transport in the soil of two solutes with different dispersion coefficients were described by two, one‐dimensional linear partial differential equations. Linear, equilibrium adsorption‐desorption relationships for both solutes and irrerversible microbial first‐order kinetics as an overall transformational mechanism were assumed. Consecutive analytical solutions were developed using Laplace transforms for zero initial concentrations, pulse input conditions and semi‐infinite media. Special cases in which the first solute moved only by mass flow and both solutes described by the same dispersion coefficient were considered. Sample problems to demonstrate the applicability of the solutions and their sensitivity to dispersion coefficients of both solutes are presented. Computed concentration profiles of the first or second solute are sensitive to their respective dispersion coefficient, especially under low degree of adsorption of both species. The sensitivity of the concentration profiles of the second solute to the dispersion coefficient of the first species occurs, however, only under a low degree of adsorption and low decay rates of that species.
Models to Predict Water Retention in Semiarid Sandy Soils
Authors: Meng Tan Piow , Taylor H. M. , Fryrear D. W. , Gomez J. F.
Published: July 2010

Objectives of this research were to (i) develop statistical models for predicting water content at three matric potentials, using three levels of input data; (ii) compare predictive capability of the locally calibrated models with those of three published models; and (iii) illustrate the changes that occur in water retention when texture of sandy soils is altered by deep plowing or wind erosion. At −10 kPa, accuracy of predicting gravimetric water contents increased with increased number of inputs. The R2s and the slopes between predicted and measured water contents for 50 samples increased, and the intercepts came closer to zero as the inputs progress from clay only to soil texture plus organic matter and CaCO3 and on to sand separates plus texture, organic matter, and CaCO3. At the −33‐ and −1500‐kPa matric potentials, the clay‐only model predicted soil‐water content equally as well as the two local models with more inputs. A previously published clay‐only model that had been calibrated using semiarid soils performed almost as well as the locally calibrated models. Two other published models performed unsatis‐factorily in predicting water retention at any of the matric potentials. Deep plowing increased clay content of one specific soil from 4 to 14%. Wind erosion subsequently reduced clay to 6% after 5 yr. Predicted water contents were 0.281, 0.341, and 0.293 kg kg−1, respectively, at −10 kPa, and 0.012, 0.050, and 0.020 kg kg−1, respectively, at −1500 kPa.
Shrinkage Curve Indices to Quantify Cultivation Effects on Soil Structure of a Vertisol
Authors: McGarry D. , Daniells I. G.
Published: July 2010

Differences in selected parameters and derived variables of models fitted to soil shrinkage curves were used to investigate soil structural degradation of an irrigated Pellustert in northern New South Wales, Australia. Significant differences between clods taken from the same depths in land prepared for cotton (Gossypium hirsutum L.) when “dry” and “wet” were found in specific clod volume at zero water content, the slope of the line in the normal shrinkage zone, the airfilled specific pore volume throughout normal shrinkage, and the range in water content in the structural shrinkage zone. These indicators showed that this soil prepared wet exhibited increased bulk density, decreased porosity, loss of structural pores, and tended to have weak structural development.
Influence of Oak in Pine Forests of Central Arizona on Selected Nutrients of Forest Floor and Soil
Authors: Klemmedson James. O.
Published: July 2010

This study focused on the effect of Gambel oak (Quercus gambelii Nutt.), a common subdominant and understory species in a ponderosa pine (Pinus ponderosa Laws.) forest in central Arizona, on selected nutrient properties of the forest floor and soil. Samples of the L, F, and H layers (Oi, Oe, and Oa horizons, respectively) of the forest floor and the 0‐ to 5‐ and 5‐ to 15‐ cm layers of mineral soil from 33 randomly selected stands of ponderosa pine with varying amounts of Gambel oak (from 0 to about 75% of total basal area) were collected and analyzed for total N, P, S, total and exchangeable Ca, Mg, and K, and organic C. Chemical properties of fresh litterfall suggested the potential for oak to strongly influence soil fertility of the pine forest. In the forest floor as a whole, only C and Mg concentrations were not positively correlated with oak basal area. In separate layers (L, F, and H) of the forest floor, the concentration of all measured nutrients increased with oak. Increases in nutrient concentration for these layers ranged up to 133% for K in the H layer at 70% oak basal area. Increased oak influenced C and N concentration more than other nutrients in the 0‐ to 5‐ and 5‐ to 15‐ cm soil layers. Increase in oak basal area to 70% resulted in a downward shift (i.e., redistribution) of C, N, P, and S within the forest floor. Hence, these nutrients were more heavily concentrated in the H than in the L and F layers with increases in oak from 0 to 70% of total basal area. Elemental ratios (C/N, C/P, C/S, C/Ca, C/Mg, and C/K) for all layers of the forest floor declined sharply as percentage oak basal area increased.
Impacts of Acid Atmospheric Deposition on Woodland Soils in the Netherlands: II. Nitrogen Transformations
Authors: van Breemen N. , Mulder J. , van Grinsven J. J. M.
Published: July 2010

Inorganic N budgets were estimated for four oak‐birch (Quercus robur L.‐Betula pendula L.) woodland soils in the Netherlands, that receive high inputs (40–60 kg ha−1 yr−1) of atmospheric N, mainly as (NH4)2SO4‐. Budgets were based on measured inputs in through‐fall water, measured soil solution concentrations, and simulated soil‐water fluxes. Substantial nitrification occurred in both highly acidic (pH 3–4) and calcareous (pH 6.5–7.5) soils. The acidity formed during N transformations (3–9 kmolc ha−1 yr−1) accounted for a major part of all soil acidification taking place. Extreme soil acidification due to nitrification (4–14 kmolc ha−1 yr−1) in the 10‐cm surface soil in three of the four plots was partly alleviated at greater depth by removal of NO‐3. Presumably, most of this NO‐3 was removed by plants and microorganisms and, perhaps, in part by denitrification. In two of the four soils, leaching of inorganic NO‐3 exceeded atmospheric throughfall input. This trend indicates that N inputs were still higher, e.g., due to direct assimilation of atmospheric NH3 by tree leaves, or that the pool of soil N decreased by mineralization in excess of uptake. In one of the four soils, most of the atmospheric N2 was assimilated and soil acidification due to N transformations was relatively small. The differences in N budgets and associated soil acidification may be related to (i) consistent differences in N input over many years, and (ii) differences in accumulation of N in biomass. Variation in these two factors may be responsible for differences in the degree to which the ecosystems are now “saturated” with N.
Impacts of Acid Atmospheric Deposition on Woodland Soils in the Netherlands: III. Aluminum Chemistry
Authors: Mulder J. , van Grinsven J. J. M. , van Breemen N.
Published: July 2010

Annual element budgets for three acidic oak‐birch (Quercus robur L.‐Betula pendula L.) woodland soils in the Netherlands indicate high inputs of atmospheric (NH4)2SO4 (2.35–3.45 kmol NH4 ha−1 yr−1). Nitrogen transformations lead to strong acid inputs of 3.0 to 7.5 kmolc ha−1 yr−1 in these soils, which are neutralized primarily by solubilization of Al in the surface 20‐cm mineral layers (3–7 kmolc ha−1yr−1). We hypothesize that Al was relatively important in neutralizing strong acid inputs, due to the high acid loading and the low content of base cations. At the low pH (pH 3.27–4.26) dissolved Al in the mineral soil was mainly in aquo‐Al3+ form. Highest Al concentrations (up to 4 molc m−3) were reached in summer and coincided with high NO‐3 concentrations. In winter and spring, the export of Al with drainage water peaked and solute concentrations decreased. All Al mobilized in the surface layers of soil A was retained below the 40‐cm depth, probably due to cation exchange, since below this depth base saturation increased. In the deeper horizons of soils B and C, immobilization of Al was less, probably because base saturation was low. All subsoil solutions were undersaturated with respect to gibbsite and near equilibrium with jurbanite. Formation of jurbanite is unlikely, however, because mass balance calculations do not indicate net SO4 retention.
Interpretation of Alkylammonium Characterization of Soil Clays
Authors: Laird D. A. , Scott A. D. , Fenton T. E.
Published: July 2010

The alkylammonium method of characterizing the charge of layer silicates has recently been applied to soil clays containing mixed mineral assemblages. Various sharp, low‐angle x‐ray diffraction (XRD) peaks (e.g., 2.5 nm for tetradecylammonium‐treated samples) have been attributed to vermiculite or high‐charge smectite. To the degree that alkylammonium cations can replace interlayer K+, however, the observed low‐angle peaks may represent K+‐depleted soil illite as well as vermiculite. This hypothesis was tested by treating two reference illites with alkylamine hydrochlorides. The treated illites exhibited low‐angle XRD peaks similar to those observed in the soil clays. Moreover, the occurrence of these low‐angle peaks coincided with the release of K+ from the illites. Similarly, the alkylamine hydrochloride treatments for layer‐charge determinations released as much as 49% of the K+ from a soil clay. These data clearly show that the alkylammonium method can expand soil illites to give low‐angle XRD peaks, which may be misinterpreted as evidence of soil vermiculite.
Settling and Flocculation Value of Sodium‐Montmorillonite Particles in Aqueous Media
Authors: Keren R. , Shainberg I. , Klein Eva
Published: July 2010

The effect of pH, particle size, and clay concentration on the flocculation value (FV) and the settling rate of Na‐montmorillonite in dilute suspension was studied in solution of various NaCl concentrations. Flocculation values increased with increasing pH, being 10, 13, 31, and 44 mmol dm−3 of NaCl at pHs 5, 7.5, 8.5, and 9.8, respectively. The final gel volume of the samples at all pHs was high (0.35 < gel volume < 0.49 m3 kg−1), and the corresponding thickness of the water film associated with the clay surface was approximately 500 nm. The high gel volume indicates that a three‐dimensional “card‐house” structure was formed. The presence of a negative charge on the broken edges at pH 9.8, the high FV (44 mmol dm−3 NaCl) and the high gel volume suggest that an open structure with a face‐to‐face association predominates. Face‐to‐face association between two platelets may take place at surfaces having either a lower or higher specific charge density than the average montmorillonite value of 0.117C m−2. At pHs equal or below the point of zero charge of the edges, edge‐to‐edge or edge‐to‐face association may occur. The time that it takes to establish a boundary between the gel and the supernatant depends on the size of the clay particles. The smaller the particles, the longer is the settling time. The settling rate depends also on the clay concentration. The boundary between the gel and the clear solution was observed after 1 and 4 d for clay concentrations of 0.1% and 0.05%, respectively, but at higher clay concentrations (0.2 and 0.5%) the suspensions remained stable for more than 7 d.
Effect of Application Method on Availability of Elemental Sulfur in Cropping Sequences
Authors: Chien S. H. , Friesen D. K. , Hamilton B. W.
Published: July 2010

There have been indications that many rice‐growing areas in developing countries are becoming deficient in S. This greenhouse study was conducted to compare the effectiveness of elemental S (ES) mixed with soil (incorporated) or deep‐placed in a band to that of incorporated gypsum on crop growth in sequences of rice‐rice (Oryza sativa L.) or rice‐maize‐maize (Zea mays L.). The soil used was an S‐deficient Josephine sandy loam (Typic Hapoxerults). Rates of S applied were 0, 14, 28, 42, 56 or 112 mg S kg−1. Incorporated elemental S and gypsum were equally effective in increasing grain and straw yields of the first rice crop, whereas deep‐placed ES was less effective. Deep‐placed ES became more effective than incorporated ES and gypsum for the subsequent crop of rice in terms of increasing plant dry‐matter yield. Two statistically distinct relationships were obtained between S uptake by the second rice crop and P‐extractable SO4‐S in the soil prior to that crop: one for incorporated ES and gypsum treatments, and the other for deep‐placed ES treatments. A weak S response was observed for the first maize crop after rice, regardless of sources and methods of S application. However, a strong S response was obtained with the second maize crop (the third crop in the sequence). At lower initial rates of applied S, the residual effect of deep‐placed ES was greater than that of incorporated ES and gypsum. A single relationship for all the S treatments was obtained between total S uptake by the second maize crop and P‐extractable SO4‐S in the soil after the first maize crop.
Revegetation of a Brine‐killed Forest Site
Authors: Auchmoody L. R. , Walters R. S.
Published: July 2010

Natural invasion of herbaceous plants and forest tree seedlings on a brine‐killed forest site in northwestern Pennsylvania was evaluated over a 4‐yr period. Brine generated from producing oil wells and accidently discharged to the soil of an Allegheny hardwood stand killed all of the vegetation it contacted, leaving the site unproductive and a visual nuisance. Once the brine source was eliminated, heavy spring rains quickly reduced brine concentrations in the soil to below toxic levels, allowing invasion of vegetation to proceed rapidly. Herbaceous plants and tree seedlings became established in the first year, and by Year 2 the site had regenerated naturally to full stocking with a desirable mix of forest trees. Results show that forest sites damaged by brine from oil wells can heal rapidly without mitigative treatment if the brine source is removed and there is abundant precipitation to flush the soil.
Biological Reduction of Structural Iron in Sodium‐Nontronite
Authors: Wu Jun , Roth Charles B. , Low Philip F.
Published: July 2010

To test the possibility that the structural Fe3+ in clay minerals can be biologically reduced, nontronite was mixed with sucrose and an aqueous extract from a Chinese paddy soil and incubated for 14 d at room temperature. Reflectance spectra, x‐ray diffraction patterns and Fe2+/Fe3+ ratios were determined for the nontronite in the mixture and for the nontronite in its nonreduced and chemically reduced states. It was found that the results for the nontronite in the mixture resembled those for the chemically reduced nontronite but differed markedly from those for the nonreduced nontronite. Therefore, it was concluded that microorganisms from the soil extract were able to reduce the structural Fe3+ in nontronite.
Transformations of Organic Matter Solubilized by Anhydrous Ammonia
Authors: Norman R. J. , Gilmour J. T. , Gale P. M.
Published: July 2010

While it has been established that liquid anhydrous NH3 (LAA) solubilizes soil organic C, the transformations of the solubilized organic C have not been defined. In order to determine the mechanisms of these transformations, LAA was applied to a Drummer silty clay loam (Typic Haplaquoll) in the laboratory. At 1, 5, 12, 20 and 35 d after LAA application a set of LAA‐treated and nontreated (control) samples were analyzed for soil inorganic N, NH3‐N volatilized, soil pH, water‐soluble organic C (WSOC) and CO2‐C evolved. Biomass C and total hydrolyzed C were estimated. The WSOC concentration increased from 25 mg C kg−1 prior to LAA application to 282 mg C kg−1 on the first day after LAA application. By 35 d after LAA application, the WSOC had decreased to 89 mg C kg−1. Dissimilation, CO2‐C evolved, was an important conversion mechanism for the organic‐C solubilized by the LAA. The LAA‐treated soil had a cumulative CO2‐C production of 630 mg C kg−1 compared to about 200 mg C kg−1 for the control soil over the 35 d after LAA application. Estimations of assimilatory conversion of WSOC to biomass C at microbial efficiencies (E) ranging from 0 to 0.6 indicated that assimilatory conversions could range from 0.25 to 1.5 times the dissimilatory (CO2‐C) conversions, respectively. Total hydrolyzed (CO2 + biomass + WSOC)‐C directly attributable to the LAA at efficiencies of 0 and 0.4 were 445 mg C kg−1 and 701 mg C kg−1, respectively. In a separate experiment it was determined that soil pH had no significant effect on the decrease in WSOC concentration. Consequently, transformations of WSOC were attributed to the microbial processes of assimilation and dissimilation.
Soil Hydrology in Lodgepole Pine Ecosystems in Southeastern Wyoming
Authors: Nyberg Ray C. , Fahey Timothy J.
Published: July 2010

The rates and pathways of water movement through the soil were examined in several lodgepole pine (Pinus contorta ssp. latifolia) forests in southeastern Wyoming to improve our understanding of the dynamics of solute flux in forest ecosystems. We employed internal drainage and tracer pulse methods to determine hydraulic conductivity, and we examined snowmelt infiltration and drainage water chemistry on contrasting soils supporting lodgepole pine forests. Saturated hydraulic conductivity (Ko) values were lognormally distributed for 27 plots at each of two sites examined. The median value was significantly higher at a site on a gravelly, loamy‐sand (median Ko = 1.20 cm/h) than on a bouldery, sandy‐loam (Ko = 0.49). At these sites the high range in both Ko values and in the transit time for a Cl‐ pulse were suggestive of highly variable water flow pathways through the soil. Early in the spring snowmelt period much of the infiltrating water circumvented the soil matrix, probably flowing around entrapped air pockets and through macropores. Although large systematic differences in chemistry were not observed between soil solutions collected with tension and tensionless lysimeters, saturated flow (collected as drips from the ceiling of soil tunnels) contained about three times lower cation concentrations than the lysimeter solutions. To obtain more accurate estimates of nutrient leaching from the tree rooting zone better quantification of the chemistry of percolating soil water is needed.
Consolidation of an Unsaturated Illitic Clay Soil
Authors: Nearing M. A. , West L. T. , Bradford J. M.
Published: July 2010

Soil stabilizes with time after disturbance as a function of thixotropy and soil water stress. This study was undertaken to delineate the effects of soil water suction history and thixotropy on soil stabilization and effective stress. Unconfined compressive strength, tensile strength, density, and effective stress as a function of water stress history and time were obtained for a Paulding clay soil (very fine, illitic, non acid, mesic Typic Haplaquepts). Compressive strength was five times greater at 64 kPa suction than at 4 kPa suction, and twice as great at 32 d than at 4 d. Density also increased with suction and time. Compressive strength at 2 kPa suction was 1.8 and 3.2 kPa for prestress suctions of 4 and 32 kPa, respectively; and was 4.4 and 8.9 kPa for prestress suction of 64 kPa after 4 and 32 d, respectively. Prestress and time had no effect on tensile strength apparently because no volume change was allowed. The data supported the hypothesis that strength in unsaturated soil was controlled by soil water stress history. Prestress due to drying induced bonding, which persisted after suction was released if volume change was not restricted. Effective stresses due to soil water suction were greater for strength than for volume change and were influenced by soil structure for the case of strength, but not for the case of volume change.
Prediction and Prevention of Iron‐related Rice Seedling Chlorosis on Everglades Histosols
Authors: Snyder G. H. , Jones D. B.
Published: July 2010

Rice (Oryza sativa L.) drill‐seeded in certain Histosols in the Everglades Agricultural Area germinates well, but after a few weeks it becomes chlorotic and grows poorly. The condition is termed “rice‐seedling chlorosis.” After flooding, chlorotic seedlings generally assume normal color, except that some seedling mortality occurs, particularly in areas with excessively deep water. Studies were conducted to identify soil and cultivar susceptibility to seedling chlorosis, and then to develop methods for preventing its occurrence. Problem soils were identified on the basis of their total Fe content. Seedling chlorosis occurred in soils containing up to 3.4 g Fe kg−1. Susceptible soils produced a nearly white ash when heated in a muffle furnace for 2 h at 550 °C. Seedling chlorosis was alleviated in all cultivars examined by drilling water‐soluble Fe compounds with the seed at rates of 20 to 30 kg Fe ha−1. The effect of seedling chlorosis on yield varied with cultivar and, to some extent, with experimental conditions. The cv. Leah was very susceptible to chlorosis, and yield was increased by Fe treatment. By contrast, even though visual symptoms were apparent, yield of cv. Labelle evidently was not reduced by seedling chlorosis because Fe treatment did not increase yield. Yield of cv. Lebonnet increased with Fe treatment in two out of three trials. Although the studies did not permit determination of the cause of seedling chlorosis, it appeared that the chlorosis did not result from a simple Fe deficiency.
Effect of Long‐term Tillage Systems and Nitrogen Addition on Potassium Quantity‐Intensity Relationships
Authors: Evangelou V. P. , Blevins R. L.
Published: July 2010

The no‐tillage (NT) management of soils is expected to have an influence on the K+ adsorption characteristics of these soils due to organic matter accumulation. The purpose of this study is to investigate this influence as affected by nitrogen (N) additions. The effect of 16 yr continuous corn (Zea mays L.) production under conventional tillage and no‐tillage management on potassium quantity‐intensity (Q/I) relationships was investigated on soil samples taken at 0–50 mm and 50–150‐mm depths of a Maury silt loam (fine‐silty, mixed, mesic Typic Paleudalfs) from central Kentucky. The results show that the Q/I plot components, labile K+, activity ratio for K+ at equilibrium (ARKo) and linear potential buffering capacity for K+ (PBCK) were affected by tillage and N additions. The no‐tillage soil with and without N fertilizer had the highest quantity of labile K+ at the 0–50 and 50–100‐mm depth. The ARKo was also the highest for the no‐tillage with and without N in comparison to conventional tillage for the two depths. The highest PBCK value was that of conventional tillage no N at the 0–50‐mm depth. The lowest PBCK value was that of no‐tillage no N also at the 0–50‐mm depth. The BaCl2 CEC determination along with the relative affinity for K+ (determined from the slope of plots of ExK/CEC vs. ARK; where ExK = BaCl2 extractable K+) were the best predictors of the relationship PBCK = CEC KGo. The relative affinity for K at the linear portion of the Q/I plots appears to be influenced by organic matter content and pH. Finally, the increase in organic matter content is shown to have a positive influence on the magnitude of high affinity K+ sites.
Soil and Saprolite Characteristics of Vertic and Aquic Hapludults Derived from Triassic Basin Sandstones
Authors: Griffin R. W. , Buol S. W.
Published: July 2010

The chemical, morphological, and mineralogical properties of two soil‐saprolite profiles from the Durham Triassic Basin were determined. The relationship between clay mineralogy and shrink‐swell activity of the soils was also determined. The parent rock from the Vertic Hapludult profile was a fine‐grained red sandstone with muscovite mica, quartz, and feldspars as the dominant primary minerals. The parent rock from the Aquic Hapludult profile was a coarse‐grained gray sandstone with feldspars, muscovite mica, and quartz as the dominant primary minerals. The argillic horizons in both profiles had cracks, slickensides, high clay contents, moderate to high coefficient of linear extensibility (COLE) values, and smectite as the dominant clay mineral. The COLE values are greatest in horizons that display evidence of shrink‐swell activity (cracks and slickensides). The COLE values do not correlate well with either fine or total clay content, which implies that factors other than fine or total clay content influence COLE values. Base saturation percentage increases abruptly below the paralithic contact requiring close examination for correct Ultisol or Alfisol placement.
Soil Aggregate Instability Index and Statistical Determination of Oscillation Time in Water
Authors: Valmis S. , Kerkides P. , Aggelides S.
Published: July 2010

A new method for classifying soils on the basis of aggregate stability is presented. The method, based on the concept of an instability index β is simple, quick, and gives reliable results comparable to those obtained with the laborious more commonly used methods. The optimum time of oscillation for the determination of the instability index, β was determined by statistically analyzing data for nine soils. According to this analysis, β is a reliable index of the relative aggregate water‐stability when oscillation times of at least 4 min are used.
Statistical Inferences of Soil Properties and Crop Yields as Spatial Random Functions
Authors: Bresler Eshel , Laufer Asher
Published: July 2010

Crop yields are often highly variable due (partly) to spatial heterogeneity of soil properties. The conditional multivariate normal (CMVN) method is systematically described and applied to 24 spatial random functions. These include: 12 soil properties, four soil variables, and two yield components of each of four field crops [wheat (Triticum aestivum L.), vetch (Vicia sativum L.), corn (Zea mays L.), and peanut (Arachis hypogaea L.)]. The statistical parameters characterizing the joint probability density function in a two‐dimensional field were estimated, from 20 to 60 measurements, by the maximum likelihood procedure. An estimation procedure for three parameters of four covariance models (piecewise linear, exponential, spherical, and Gaussian), constant mean, and linear drift, is described. It was found that the covariance function of all the 24 spatial functions can be represented by the four models and that there is a significant two‐dimensional linear drift of the mean. The parameter that represents the nugget effect (i.e. the variance of uncorrelated values of the spatial function) is estimated to be either zero or nonsignificant for the soil properties but has a small significant value for most crop yield components. Soil properties as well as crop yield components are characterized by the existence of a significant correlation scale on the order of 10 to 30 m. Estimations of conditional expectation, conditional covariance, the variance, and the variance of the estimated variance were made and demonstrate that the CMVN method can be applied to real field data. The specific covariance model used generally has a small effect on the estimated results. Comparisons with kriged values and kriging variance demonstrate the similarity and differences in the results.
Evaluation of Nitrogen‐15 Tracer Techniques for Direct Measurement of Denitrification in Soil: II. Simulation Studies
Authors: Vanden Heuvel R. M. , Mulvaney R. L. , Hoeft R. G.
Published: July 2010

In mass spectrometric procedures developed at the University of Illinois for determination of 15N‐labeled dinitrogen (N2) and nitrous oxide (N2O) evolved from soils, the assumption is made that the nitrate (NO−3) undergoing denitrification exists in a single pool that is isotopically uniform. Computer simulation studies were conducted to identify trends associated with errors in measuring denitrification of NO−3 that exists in two or more pools having different enrichments. The results indicate that, for a constant mean 15N enrichment, the magnitude of the error increases as the range of enrichment becomes greater and can increase or decrease with increase in the number of NO−3 pools, depending upon whether there is an increase in the range of enrichment. The error is also affected by the extent to which evolution is distributed among the various pools, but it does not depend upon the overall evolution rate or the 15N enrichment of the fertilizer applied.
Monitoring Saturated Zones in Soils Containing Coarse Fragments
Authors: Burk D. G. , Miles R. J. , Broderson W. D. , Sievers D. M.
Published: July 2010

A design for an in situ lateral piezometer constructed of polyvinyl chloride (PVC) components is presented for use in monitoring zones of saturation in soils with appreciable amounts of coarse fragments in dissected hillslope landscapes. This design allows replicated monitoring of water levels in steeply sloping areas which contain up to 60% by volume coarse fragments. Field results from over 150 piezometer units in 36 monitoring sites have shown that matched pairs of piezometers at the sites give consistent results that correlate well with observations in freshly dug profile exposures. This piezometer design is relatively easy to install, inexpensive, and allows correlation of zones of saturation with soil morphological properties.
Constant Rate Rainfall Infiltration in a Bounded Profile: Solutions of a Nonlinear Model
Authors: Broadbridge P. , Knight J. H. , Rogers C.
Published: July 2010

We present new exact solutions to a versatile analytic nonlinear model of single phase vertical unsaturated flow during constant rate rainfall infiltration in a bounded soil profile with an impermeable base. The nonlinear flow equation in a fixed finite region is transformed to a linear diffusion problem with boundary conditions on a shrinking domain. The linear problem is treated by King's method of Laplace‐transform boosts. The analytic solutions illustrate the theoretical differences in the basement moisture build‐up when the water content dependence of the soil hydraulic properties varies from strong to weak. When the rainfall rate exceeds a critical value which is estimated here, surface ponding precedes basement saturation. In this case, time to ponding is approximated well by the expression for the infinite column. When the rainfall rate is less than the critical value (which is greater than the conductivity at saturation), basement saturation precedes surface ponding. In this case, the time to basement saturation is close to the time taken for the rainfall to fill the available pore space.
Estimation of the Standard Free Energy of Formation of Metal Arsenates, Selenates, and Selenites
Authors: Essington M. E.
Published: July 2010

An empirical method developed for estimating the standard free energy of formation (ΔG°f) of solid phases is evaluated for metal arsenates, selenates, and selenites. A free energy function of a solid phase is found to be linearly correlated to a function of the metal oxide ΔG°f and the aqueous metal ion ΔG°f for the compound groups examined. The values estimated by this method are, on average, within ± 10.9, 10.4, and 12.0 kJ mol−1 of the experimental arsenate, selenate, and selenite values, respectively. A method for estimating the ΔG°f of hydrated metal arsenates and selenites is also evaluated. The estimated standard free energy of formation values of hydrated arsenates and selenites, on average, are within ± 23.7 and 10.0 kJ mol−1, respectively, of the observed values. The error involved in estimating metal arsenate, selenate, and selenite ΔG°f values are comparable to those obtained when the estimation technique was applied to other compound types.
Phosphorus Adsorption by Kaolinite and Montmorillonite: II. Organic Anion Competition
Authors: Kafkafi U. , Bar‐Yosef B. , Rosenberg Rivka , Sposito G.
Published: July 2010

The mechanisms by which roots affect the release of phosphate from soil surfaces into the solution is not clear. This study was undertaken to investigate the competition of several agents, reported as root exudates, with P on adsorption sites on kaolinite and montmorillonite. The agents studied were acetate, bicarbonate, citrate and oxalate, and the amino acids phenylalanine and alpha‐amino isobutyric acid. The adsorption or desorption of P on the clays in the presence of the noted agents at various fixed pHs and known ionic strength, and the effect of slurry density on P adsorption, were determined. Citrate, bicarbonate and oxalate decreased, and acetate and the amino acids increased P adsorption to the clays. A decrease in the solution‐to‐clay ratio from 100 to 10 L/kg resulted in enhanced P adsorption. The unifying principle that explains these findings is that P adsorption on a clay depends on the extent of the depression of the negative potential of the clay platelets. Bicarbonate and citrate anions at pH > 8 compete with P for active Al sites on the clay. The increased P adsorption in the presence of amino acids is suggested to stem from the fact that H‐bonding of the amino groups causes a decrease in interlamellar spacing, and produces quasicrystals. The quasicrystals reduce the spillover of negative charge from the surface to the edges and allow closer approach of the phosphate ion to the Al site.
Rapid Introduction of Acetylene into Large Assay Chambers for Acetylene Reduction Experiments
Authors: Peck R. L. , Hern J. L.
Published: July 2010

A rapid and facile procedure has been developed for preparing the desired acetylene concentration in large sealed chambers for acetylene reduction assays. The gas dilution system incorporated an inexpensive manometer to monitor evacuation of a known amount of air from the chamber. A simple valving system then allowed for easy injection of acetylene to produce the desired assay conditions. Although 34‐L chambers were used, the procedure is amenable to sealed chambers of any size. The entire procedure takes <1 min and exhibits excellent precision. This technique facilitates the use of very large assay chambers, and resolves the cumbersome problems and time involved in handling large volumes of gas.
Effects of Carbon and Trace Element Addition on Alkylselenide Production by Soil
Authors: Karlson U. , Frankenberger W. T.
Published: July 2010

Microbial volatilization of selenium (Se) may be applicable for detoxifying Se‐contaminated soils, if high rates of volatilization can be maintained. This study was conducted to evaluate some of the factors affecting the rates of microbial production of alkylselenides. Field‐moist Los Baños clay loam, representing soils from Se‐affected areas, was treated with 100 mg kg−1 Se(IV), labeled with 75Se(IV). Gaseous Se was determined by direct gamma counting of activated charcoal traps. Without C amendments, the volatilization potential was 2.9% in 13 d; amendments with 2 g C(pectin) kg−1 soil increased that potential to 8.8%. With other C sources volatilization in 13 d was 6.6% [corn (Zea mays L.) leaves], 5.2% (starch), 3.7% (dairy manure), 3.3% (cellulose), and 2.7% (sewage sludge). Volatilization rates decreased as C was depleted, but increased again upon C reload. The addition of molybdenum (Mo), mercury (Hg), chromium (Cr), and lead (Pb) greatly inhibited Se volatilization, while arsenic (As), boron (B), and manganese (Mn) had little effect. The presence of cobalt (Co), zinc (Zn), and nickel (Ni) at relatively high levels (25 mmol kg−1) increased Se volatilization rates up to 2.5‐fold. After 37 d of incubation, recovery of added Se(IV) as alkylselenides was as high as 34, 30, and 23% with Co, Zn and Ni, respectively, applied along with C amendments. Zinc, Co, and Ni most likely serve as cofactors in the methylation reaction. Low levels of N in the presence of added C slightly enhanced alkylselenide production, while without C amendments, N had a slightly inhibitory effect.
Long‐term Annual Manure Applications Increase Soil Organic Matter and Nitrogen, and Decrease Carbon to Nitrogen Ratio
Authors: Sommerfeldt T. G. , Chang C. , Entz T.
Published: July 2010

The effects of long‐term annual applications of cattle (Bos taurus) feedlot manure on the accumulation, decomposition (amounts and rates), and movement of organic matter (OM) and Kjeldahl‐determined N (total N) in soil were determined. Manure was applied annually since 1973 at three different levels to nonirrigated and irrigated Dark Brown Chernozemic (Typic Haploborolls) clay loam soil. Significant increases in soil OM and total N content in the first 8 and 6 yr, respectively, as affected by the level of manure application, were limited to the surface 30 cm of soil of the nonirrigated and irrigated land. Tillage did not affect the amount of OM and total N accumulated in the soil, but it did affect their distribution within the 0 to 30‐cm depth, which is attributed to placement during incorporation. The accumulation of OM and total N were similar under nonirrigated and irrigated conditions. Manure (C/N ratio of ca. 10.2) lowered the C/N ratio of the soil (ca. 8.2) by small amounts. The accumulation of OM and total N was described by a Michaelis‐Menten type of function. A response surface was generated for the accumulation of OM and total N with increasing levels and years of manure application, from which the rates of accumulation and decomposition were derived. The rates of accumulation decrease with years of application such that after two or three decades increases will be small. The model can be used to develop general guidelines for use and disposal of feedlot manure under similar conditions.
Effect of Soil pH and Clay Content on the Zinc Soil Test Interpretation for Corn
Authors: Lins I. D. G. , Cox F. R.
Published: July 2010

Soil test interpretations are usually improved by considering at least one soil property in addition to the extractable nutrient concentrations. Greenhouse and field experiments were carried out to evaluate the effects of soil pH and clay content on the Zn soil test interpretation for corn (Zea mays L.). In a greenhouse experiment, four Oxisols with 68, 63, 57 and 21% clay were adjusted to pH 5.2, 5.7 and 6.2. Five Zn levels within each soil pH were created by applying Zn at 0, 0.8, 1.6, 3.2 and 6.4 mg L−1. Three crops of Cargill 111‐S corn were grown, each for about 4 weeks. Soil Zn extracted with Mehlich‐1 was not affected by changes in pH, but plant Zn decreased as soil pH was increased. Plant growth was depressed at the highest soil pH and lowest soil Zn concentration, and the prediction of dry matter as a function of soil Zn was markedly improved by including soil pH for three of the four soils. The soil‐Zn critical level was calculated and was not affected by clay content, but did increase with an increase in pH. The critical levels in the greenhouse were 1.0, 1.4, and 2.0 mg L−1 for soils of pH 5.2, 5.7, and 6.2, respectively. In the field, the same variety of corn was grown one season in a residual experiment on a Typic Haplustox. Lime and zinc levels had been established by treatments imposed 13‐yr prior. Current pH ranged from 6.0 to 6.7, and the soil Zn from 0.6 to 1.6 mg L−1. The results were similar to those obtained in the greenhouse. The effect of pH on the soil Zn critical level, however, was not as striking, perhaps because of the high average and more narrow range in soil pH.
Vertical Distribution in Soil of Unincorporated Surface‐applied Phosphorus Under Sprinkler Irrigation
Authors: Lauer D. A.
Published: July 2010

Determining vertical distribution of P is important in irrigated conservation cropping systems for evaluation of P fertilization because soil‐immobile phosphorus accumulates near the soil surface where limited tillage reduces soil mixing. The objective was to determine in field and laboratory experiments the vertical distribution of P from surface‐applied monoammonium phosphate (MAP; 227 g P kg−1), triple superphosphate (TSP; 197 g P kg−1), and ammonium polyphosphate (APP; 149 g P kg−1). Following P application, vertical distribution was determined from 2‐cm depth increment samples in a Quincy sand (mixed, mesic, Xeric Torripsamments), a Warden silt loam (coarse‐silty, mixed, mesic, Xerollic Camborthids), and a calcareous subsoil of the Warden. There was little effect on P distribution from antecedent moisture; fertilizer rates at 30, 60, 120, or 240 kg P ha−1; or from preirrigation reaction times of 1, 4, or 16 d. Continuous postapplication irrigation totals of 40 or 160 mm at 10 mm d−1 moved P somewhat deeper into the soil, principally at 160 mm on the Quincy sand. Overall mean penetration depths of P were as follows: (i) APP moved the farthest in the Quincy sand (mean = 6.1; SD = 1.05 cm); (ii) penetrations were practically the same for MAP or TSP on the Quincy sand (mean = 5.4; SD = 1.32 cm) and on the noncalcareous Warden silt loam (mean = 5.5; SD = 1.25 cm); (iii) depth of penetration was intermediate for APP on the noncalcareous Warden (mean = 4.0; SD = 0.98 cm); and (iv) downward movement in the calcareous Warden of P from all fertilizer P materials was much more restricted (MAP/TSP: mean = 3.1; SD = 0.10 cm and APP: mean = 3.3; SD = 0.52) than on the two noncalcareous soils. Overall, the most apparent conclusion from this study is that the reactivity of P fertilizer material with the soil is the dominant and overriding determinate of the vertical distribution of surface‐applied P.
X‐ray Technique to Evaluate Pedon and Erosion Variability of an Ava Map Unit
Authors: Olson K. R. , Darmody R. G. , Steiner J. S. , Beavers A. H.
Published: July 2010

An uneroded map unit of Ava soil was examined to determine the presence of and variability in depth to the upper and lower boundaries of the argillic horizon, the second parent material, the horizon of maximum x‐ray mass absorption coefficient, the fragipan, the A and E horizons, and the clay maximum prior to accelerated erosion. Twelve pedons from six pits were examined to address the depth variability of selected soil features. These features have often been used as reference markers to provide a basis from which to estimate the soil loss from erosion. Considering all sampled pedons in an Ava map unit on a ridgetop, all selected soil parameter boundaries but the depth to the upper boundary of the fragipan were found to be reliable reference markers. The mean depth to the lower boundary of the horizon with the maximum coefficient of x‐ray mass absorption coincided with the mean depths to the lower boundary of the clay maximum, Fe maximum, and top of the second parent material, but did not coincide with the mean depth to the lower boundary of the argillic horizon. Iron content and x‐ray mass absorption coefficient were highly correlated because elements with high mass, such as Fe, increase the x‐ray mass absorption coefficient in a horizon. Where accelerated erosion occurred on a landscape segment, the lower boundary of the horizon of maximum x‐ray mass absorption coefficient, as well as other lower boundaries of subsoil parameters, could be used as reference markers to provide a basis for estimating soil loss from erosion.
Characteristics of Histic Materials in Wisconsin as Arrayed in Four Classes
Authors: Lee G. B. , Bullington S. W. , Madison F. W.
Published: July 2010

Samples of histic materials were collected throughout Wisconsin and analyzed for characteristics common to these materials. On the basis of resistant fiber content, they were ordered into four classes. Fibric and Hemic materials are similar to those in Fibrist and Hemist suborders. Sapric A materials are defined here as those containing from 8 to 20% fiber; sapric B materials contain 0 to 7%. Fiber, moisture, and organic C content decrease from fibric to sapric B material. Sodium pyrophosphate extract color (SPEC) values and C/N ratios follow the same trend. Percentage N and ash content increase in value, as does pH and bulk density. The low fiber content, which is indicated directly by volume and indirectly by SPEC values, low moisture content and C/N ratios, high N and bulk density values, and ash content, are characteristic of sapric B materials, and should be used in further definition of this class.
Time Series Analysis for Statistical Inferences in Tillage Experiments
Authors: Roseberg R. J. , McCoy E. L.
Published: July 2010

Spatial dependence of soil physical properties often invalidates parametric inferencing of tillage treatment effects. Spectral analysis was examined as a possible means to generate inferences on tillage treatments from an observation set that is spatially dependent. The method was tested using surface elevation data from a long‐term tillage study. Three tillage treatments were imposed on a continuous corn cropping system in a randomized complete block design beginning in 1962. Surface elevations were measured in 1971, 1976, 1980, and 1987 along four transects oriented perpendicular to the imposed treatments with each transect running the length of the field. The power spectrum from the 1971 observations yielded a significant spectral peak at a wavelength equal to one‐plot width. The power spectra from the 1976, 1980, and 1987 observations yielded a significant spectral valley at a wavelength equal to one‐plot width. The significant spectral valleys in the 1976, 1980, and 1987 power spectra represent low variance within the plot spacing as compared to variance between plots. In a randomized complete block design, this significant spectral valley represents an inference on the effect of tillage on surface elevation using spectral analysis. Calculation of number of observations needed to show significant spectral differences at wavelength equal to one‐plot width compared to within and beyond plot wavelengths indicate that 75, 161, 223, and 149 observations were necessary for 1971, 1976, 1980, and 1987 sampling dates, respectively.