bluuebunny/crossref_metadata_2025 huggingface dataset:
Acetonitrile and Acrylonitrile Sorption on Montmorillonite from Binary and Ternary Aqueous Solutions
Authors: Zhang Z. Z. , Sparks D. L. , Scrivner N. C.
Published: July 2010

The main objective of this study was to gain mechanistic information on clay‐organic interactions in aqueous environments containing multiple organics. Three different measurements were made to achieve this objective. The sorption of acetonitrile and acrylonitrile on K, Na, Ca, and Mg montmorillonite from binary and ternary aqueous solutions were determined using a 14C isotope tracer method. The infrared spectra of acrylonitrile in solution and adsorbed on montmorillonite were recorded on a Fourier‐transform infrared (FTIR) spectrometer and the c‐axis spacings of montmorillonites in the acrylonitrile solutions were determined by x‐ray diffraction. It was found that the sorption of acetonitrile and acrylonitrile from ternary solutions on K montmorillonite was competitive across the entire concentration range. The sorption was slightly competitive at lower concentrations on Na, Ca, and Mg montmorillonite, but enhanced at higher concentrations. The competitive sorption on K montmorillonite was probably associated with the decrease in the interfacial volume, since the layers of K montmorillonite were collapsed at higher concentrations, while the enhanced sorption on Na, Ca, and Mg montmorillonite appeared to be caused by an increase in the partition coefficient as more organic molecules entered the interfacial phase. These results led to the conclusion that the sorption of acetonitrile and acrylonitrile on montmorillonite was not due to specific bonding between the organic molecules and the clay surfaces, but rather to a partition between the interfacial phase and the bulk solution phase.
Microwave Radiation and Incubation Effects on Resin‐Extractable Nutrients: I. Nitrate, Ammonium, and Sulfur
Authors: Yang Jae E. , Skogley Earl O. , Schaff Bernard E.
Published: July 2010

The phytoavailability soil test (PST) is a resin‐extraction methodology being developed for use on fresh soil samples. Mineralization of N and S during shipment of samples to a soil‐testing laboratory is of concern with this soil‐test approach. The objective of this research was to investigate microwave‐radiation (MWR) treatment of soil samples to arrest microbial conversions of nutrients during incubation of fresh samples. Fresh samples from three Ap horizons of Montana soils (Haploborolls) with different fertility histories were subjected to MWR for 0 to 4 min, and then incubated at 20 °C for 0 to 12 d. Subsamples were also dried before being subjected to the same treatments. Nutrients were extracted with mixed‐bed ion‐exchange resin extractors placed in saturated pastes of each sample and by standard soil tests on dried soil samples. Results for NO3‐N indicate that MWR prevented nitrification, but extractable NH4‐N and S varied in a manner suggesting release of interlayer NH4 and thermal decomposition of organic components. Compared with standard soil tests, PST was similar in sensitivity to changes in NO3‐N and S and more sensitive to changes in NH4‐N. These soils had up to three times more NH4‐N than NO3‐N in either the fresh or dried condition. Based on these results, MWR is not recommended for arresting microbial activity prior to extraction for soil‐test purposes, either by standard or PST methods. Changes in the two forms of plant‐available mineral N occurring during shipment or increases in total mineral N or S may need to be dealt with through other means of microbial arrest, or through calibration adjustments.
Soil Sampling under No‐Till Banded Phosphorus
Authors: Kitchen N. R. , Westfall D. G. , Havlin J. L.
Published: July 2010

Uncertainty exists about the best sampling procedures for no‐till soils containing residual P‐fertilizer bands. This study was conducted to determine the distribution of residual P‐fertilizer bands and to define soil sampling procedures that minimize variability, while approximating the “true” P‐soil‐test value. A no‐till, banded‐P‐fertilization field study was conducted during 1986 and 1987 on three central Great Plains soils: Keith clay loam (a fine‐silty, mixed, mesic Aridic Argiustoll), Woodsen silt loam (a fine, montmorillonitic, thermic Abrubtic Argiaquoll), and Harney silt loam (a fine, montmorillonitic, mesic Typic Argiustoll). Soils were sampled laterally away from the band 1 to 2 yr after fertilization, and P was determined with NaHCO3 and acid‐fluoride extractions. Bands were accurately described by the exponential decay model (mostly r2 values of 0.98 or better). The derived exponential equations were used in computer evaluation of soil‐sampling procedures. When the location of P bands are known, sampling to include one in‐the‐band soil sample for every 20 between‐the‐band samples for 76‐cm band spacing, and for every eight between‐the‐band samples for 30‐cm band spacing, will result in a P soil test equal to the “true” P‐soil‐test mean. When the location of P bands is unknown and <20 subsamples are taken, paired sampling consisting of a first completely random sample and a second sample 50% of the band‐spacing distance from the first sample, perpendicular to the band direction, will reduce variability over completely random sampling. The greatest deviation from the “true” P soil test occurs when inadequate sampling includes rather than excludes the band, and will thus under‐estimate P‐fertilizer needs.
Agronomic Evaluation of Two Unacidulated and Partially Acidulated Phosphate Rocks Indigenous to Niger
Authors: Chien S. H. , Henao J. , Christianson C. B. , Bationo A. , Mokwunye A. U.
Published: July 2010

A field study was conducted on a sandy soil in Niger to evaluate the agronomic effectiveness of various P fertilizers for millet production during 1985 to 1987. The P fertilizers tested were two finely ground phosphate rocks (PR) indigenous to Niger (Tahoua and Parc W rocks), PR partially acidulated with H2SO4 at 50% acidulation level (PAPR), single superphosphate (SSP), and triple superphosphate (TSP). In 1985, application rates were 0, 6.5, 13.0, and 19.5 kg P ha−1 for each of the P fertilizers. In 1986, half of the plots received the same rates of P as in 1985 and half of the plots received no additional P. In 1987, P additions were repeated only in half of the plots that received P during 1986. A significant (P = 0.05) millet response to P was observed in all the trials. The major findings of this study were: (i) finely ground Tahoua PR was more effective than Parc W PR because of its higher reactivity and was 82 to 91% as effective as SSP for millet production in both the initial and two subsequent seasons; (ii) partial acidulation of Parc W PR can significantly increase its agronomic effectiveness in the first year, but not in terms of residual effect; (iii) partial acidulation was not a desirable technology for increasing the effectiveness of Tahoua PR, because its high Fe2O3 plus Al2O3 content resulted in a product containing relatively low amounts of water‐soluble P; and (iv) over a period of 3 yr, one initial application of a large dose of P fertilizer was found to be more effective than three small annual applications in terms of total grain production.
Dispersive Erosion and Entisol‐Panspot Genesis in Sodium‐Affected Landscapes
Authors: Hopkins D. G. , Sweeney M. D. , Richardson J. L.
Published: July 2010

In Natriboroll complexes, commonly barren, eroded Entisol or remnant Natriboroll areas occur that are devoid of vegetation. This study investigates the genesis, stratigraphy, and characteristics of panspots. The study consists of a detailed grid sampling of 121 pedons in a 20 by 20 m area of panspots (Entisol), revegetated panspots (Entisol), and Glossic and Leptic Natriborolls. Topographic and soil morphological parameters were compared with electrical conductivity, soluble Ca, Mg, HCO3, Cl, SO4, exchangable H, sodium adsorption ratio (SAR), particle size, and water‐dispersible clay. Field evidence clearly showed dispersion‐induced erosion resulting from a documented rainstorm. Water‐dispersible clay supported these observations. Morphologic indicators of leaching intensity and results from a salinity survey showed soil properties consistently related to surface vegetation density. In barren panspots, no development was evident but, in revegetated panspots, a leaching regime was evident and modest structural development could be seen. Chemical and morphological data suggested two water‐movement regimes in panspot development. A diagrammatic model illustrates the role of throughflow and discharge of saline‐sodic water and mechanical/dispersive erosion in panspot genesis. Revegetated panspot zones result from a renewal of soil development that slowly reverses the effects of dispersive erosion. Lateral water flow in anisotropic, sodic parent materials is a major factor in the development of panspots.
Determination of Hydraulic Conductivity Using a Tension Infiltrometer
Authors: Reynolds W. D. , Elrick D. E.
Published: July 2010

A new procedure is presented for in situ determination of saturated and near‐saturated hydraulic conductivity [Kfs and K(ψ), respectively] from a sequence of steady infiltration measurements made at several tensions on a single infiltration surface. The method applies to tension infiltration from either a surface disk or from within a ring inserted a small distance into the soil. The analysis employs a modification of Wooding's solution for infiltration from a shallow pond, combined with numerically determined shape factors that account for the interaction effects between flow geometry and soil properties. The method is found, via numerical simulations, to have an overall accuracy within about ± 7%, regardless of whether the predicted K(ψ) function is flat with an indistinct air‐entry value, steep with a distinct air‐entry value, or very steep with no air‐entry value. Some important practical features of the method are that it does not require measurement of the often‐difficult square‐root‐of‐time infiltration behavior, no special considerations are required regarding the thickness of the contact layer, it minimizes the effect of local spatial heterogeneity by using only one infiltration surface per set of K(ψ) measurements, it avoids the use of potentially unstable simultaneous‐equations solution procedures, and it can be applied to tension infiltration from both disk and ring infiltrometers.
Evaluation of Procedures for Aggregating Nonlinear Sulfate Adsorption Isotherm Data
Authors: Shaffer Paul W. , Stevens Donald L.
Published: July 2010

As part of a study to assess potential regional surface‐water acidification in the southern Blue Ridge region of the USA, more than 700 individual soils were sampled from 35 watersheds and analyzed. Sulfate adsorption isotherms were generated for all mineral soil horizons. Subsequent use of these data in dynamic watershed chemistry models required aggregation of adsorption data to two or three isotherms (one per soil mineral horizon) per watershed. This study evaluated several techniques for aggregation of the nonlinear adsorption‐isotherm data. The objective of the analysis was to identify a procedure for aggregation that would generate a function providing a representative weighted average of the SO2‐4 adsorption partitioning coefficients (isotherm slopes) of several individual isotherms, and would do so over a range of dissolved SO2‐4 concentrations. The most effective procedure involved a sequence of: (i) fitting isotherms for individual soils, (ii) computing values of adsorbed SO2‐4 corresponding to several reference concentrations of dissolved SO2‐4, (iii) computing weighted averages of adsorbed SO2‐4 at each of the reference concentrations, and (iv) fitting a new isotherm to the set of weighted points. Two alternate procedures for aggregation, computation of weighted averages of the coefficients of isotherms fitted to data for individual soils, or fitting a single isotherm to the raw data points for several soils, gave highly variable results that were usually skewed to low estimates of slope. Although specific results of this analysis relate to aggregation of SO2‐4‐adsorption isotherms, the strengths and weaknesses of the various aggregations have significant implications for aggregation of data sets for other nonlinear functions and for subsequent use of data. Use of an inappropriate aggregation procedure can lead to erroneous estimates of the capacity, efficiency, or response time of the system being described or modeled, and is likely to result in ineffective or inefficient treatment to supply putative adsorbates to the solid phase or to remove pollutants from solution.
Lignosulfonate Effects on Phosphate Reactions in a Clay Soil: Causal Modeling
Authors: Xie R. J. , MacKenzie A. F. , O'Halloran I. P.
Published: July 2010

Phosphate adsorption reduces the effectiveness of P fertilizers. Lignosulfonate (LS) is expected to compete with P for adsorption sites on soil particle surfaces and reduce P retention. A Dalhousie clay soil (a fine, mixed, nonacid, frigid Typic Humaquept) was incubated with various amounts of CaLS (0–150 g kg−1 soil) and phosphate (0–792 mg P kg−1 soil) for 240 h under moist conditions. A subsample was extracted with deionized water and the supernatant analyzed for P, Ca, pH, and organic C. Additions of CaLS increased P retention, compared with zero addition, with maximum increase occurring with LS at 50 g kg−1 soil. Adsorption of organic C was greater with nondesugared (BD) than with desugared CaLS (SF), but P retention was greater with SF than with BD. Recursive causal modeling indicated that, with LS additions, P retention was mainly related to concentrations of P (path coefficient β = 0.79), Ca (β = 0.30), and organic C (β = −0.39), and retained LS‐C (β = 0.32). Supernatant pH was mainly a function of retained LS‐C (β = −1.22), and concentrations of Ca (β = 0.49) and P (β = −0.27). The data suggested that Ca added with CaLS precipitated P, probably forming hydroxapatite [Ca5(PO4)3OH]. Further studies with NH4LS showed low P retention with high NH4LS additions after soluble native Ca had been removed. The results confirmed that P retention was decreased by LS under the conditions that soil Ca was below the level required to form Ca‐P precipitates and that organic C had been adsorbed on the soil surface.
Separating Ion‐Exchange Resin From Soil
Authors: Thien Steve J. , Myers R.
Published: July 2010

Use of ion‐exchange resins in soil science lacks a suitable technique for separating loose resin from soil. Implanting porous, resinfilled bags has been used, but limits soil‐resin contact. Grinding soil fine enough to sieve the resin may not be appropriate for some applications. We have developed a technique for separating loose resin from soil. A 1.31 M sucrose solution was added to a soil‐resin mixture and centrifuged 3 min at 1900 × g. Density differences caused the soil (2.65 kg m−3), sucrose solution (1.17 kg m−3), and exchange resin (1.12 kg m−3) to separate. The resin accumulated on top where it could easily be recovered by decanting for further analysis. Average recovery of resin was 99.0% from eight different soils. Resin added and resin recovered were highly correlated (r = 0.99) and were independent of soil/resin ratio. The use of sucrose, a nonionic solution, had no effect on resin composition in this procedure.
Collimated Neutron Probe for Soil Water Content Measurements
Authors: Klenke John M. , Flint Alan L.
Published: July 2010

The use of uncollimated (undirected) neutron moisture meters is common in the biological and geophysical sciences. A collimated neutron probe was designed to enable measurements in specific directions from the access tube. To determine the size and shape of soil volume affecting the neutron counts, experiments were conducted to evaluate: (i) the vertical distance of soil above and below the probe that influences neutron counts, (ii) the horizontal distance away from the probe into the soil that influences neutron counts, (iii) the angle of soil viewed by the probe from the collimator, and (iv) the three‐dimensional thermal‐neutron density field. The distance and the angular dimensions of the volume of influence were defined as the horizontal distance of neutron penetration from the edge of the probe, the vertical distance above and below the center of the effective measurement point of the probe, and the angle from the center of the probe, which would allow the determination of relative water content to within 95%. The vertical distance was ≈0.5 m, the horizontal distance was ≈0.2 m, and the angle of soil viewed by the probe from the collimator was ≈120°. Thermal neutrons detected from distances or angles larger than these values influence the determination of relative water content by 5% or less.
Air‐Drying and Pretreatment Effects on Soil Sulfate Sorption
Authors: Comfort S. D. , Dick R. P. , Baham J.
Published: July 2010

Drying, freezing, and refrigeration are commonly employed to facilitate the handling and storage of soil samples on which chemical, biological, and physical analyses are to be performed. These laboratory protocol have the potential to alter soil chemical characteristics and may result in unrealistic estimates of in situ chemical processes. We determined the effect of air drying, storage temperature, and time on SO4‐sorption characteristics. Sulfate‐sorption experiments were conducted in the field on moist samples and compared with laboratory results for the same soils that had been kept frozen (−5 °C), refrigerated (4 °C) for 14 or 60 d, or air dried. Only air drying significantly altered SO4‐sorption characteristics. The impact of air drying on SO4‐sorption capacities was then determined on 29 pedons (84 horizons) from four northeastern USA (NE) and three southern Blue Ridge province states. A suite of physico‐chemical properties of soils whose sorption capacities were affected by drying were also measured. The SO4‐sorption capacity increased as much as 320% when dried soils were compared with field‐moist samples. Soils whose sorption capacities were most affected by air drying included the NE soils group, which had a higher percentage of the clay fraction in the form of amorphous minerals and were high in exchangeable acidity and total organic C. Air drying caused significant decreases in ethylenediaminetetraacetic acid (EDTA) extractable Fe and Al, oxalate‐extractable Al, and KCl‐extractable Al. This suggests the formation of new solids on drying, which increase SO4 sorption. Development of a multivariate model, however, indicated that total organic C, change in Fe extracted by pyrophosphate, dry minus moist; change in Fe extracted by oxalate, dry minus moist; and H+ solution concentration in 0.01 M CaCl2, dry minus moist were the best predictors of the change in SO4 sorption capacity with drying.
Potassium Quantity‐Intensity Relationships in Calcareous Vertisols and Inceptisols of Southwestern Spain
Authors: Jimenez C. , Parra M. A.
Published: July 2010

Quantity‐intensity (Q/I) curves and derived parameters provide general information about soil K availability. This investigation was conducted to study the relationship between the K Q/I parameters and the properties of 24 calcareous Inceptisols and Vertisols of southwestern Spain. Three Q/I parameters were considered: activity ratio at equilibrium (ARo), buffer power at equilibrium (BPo), and buffer power in the 20 × 10−3 to 30 × 10−3 activity‐ratio range (BP20‐30). Close linear correlations were found between buffer powers (BP20‐30 and BPo) and cation‐exchange capacity (CEC) (r2 = 0.949 and 0.888, respectively), and between ARo) and initial exchangeable K percentage (EPPo) (r2 = 0.762). A good correlation (r2 = 0.873) was also found between EPP and AR for all the soils within the range of K saturation studied. Twelve of the 24 soil samples were intensively cropped (nine wheat [Triticum aestivum L.] croppings); the K balance showed that 80% of the K extracted by the crops came from the nonexchangeable K pool. The Q/I curves of the soil samples after cropping were displaced upward with respect to the original ones, and the ARo values were, consequently, lower; the displacement of the Q/I curves was similar to the decrease in exchangeable K. Following cropping, the BP20‐30 values increased slightly. In spite of these changes, the shape of the Q/I curves remained nearly unchanged; therefore, this can be considered a characteristic of the soils studied. The good correlations between ARo and EPPo and between buffer powers and CEC allow prediction of the Q/I parameters of these soils.
Silica and Carbonate Sources for Aridisols on a Granitic Pediment, Western Mojave Desert
Authors: Boettinger J. L. , Southard R. J.
Published: July 2010

Three pedons on a granitic pediment in the western Mojave Desert, a Typic Durorthid, a noncalcareous Typic Haplargid, and a Typic Haplargid with carbonates below 80 cm, were studied to evaluate the potential of mineral weathering as a source of Si and Ca for the duripan and Bk horizons. Calcareous and noncalcareous soils occur as contiguous polypedons on the pediment surface, with calcareous soils overlying calcareous saprolite, and noncalcareous soils overlying noncalcareous saprolite. The irregular distribution of opaline silica and CaCO3 in these pedons cannot be attributed to a uniform input of eolian deposits across the pediment. Micromorphological and chemical evidence indicates that primary crystalline silicates in the calcareous horizons of these Aridisols have been weathered and replaced by opaline silica and calcite. Dissolution of plagioclase is a probable source of Ca in soil and saprolite carbonates. The lack of silt‐ and volcanic‐glass‐enriched vesicular A horizons suggests that eolian deposits of carbonates and volcanic ash are less significant in the formation of these soils than the contributions of weathering primary crystalline silicates in the granitic saprolite. The contribution of the weathering of crystalline silicates to soil formation in arid regions should not be overlooked.
Mechanical Strength of Clay Minerals as Influenced by an Adsorbed Polysaccharide
Authors: Chenu C. , Guérif J.
Published: July 2010

The water‐stabilizing action of polysaccharides on soil aggregates has been ascribed to the binding together of soil particles by polymer bridges. This study was conducted to investigate the ability of polysaccharides to increase the strength of interparticle bonds by measuring the mechanical strength of clay‐polysaccharide complexes. Kaolinite, montmorillonite, and the polysaccharide scleroglucan were used. Cores were prepared from dilute suspensions of the complexes, air dried, and manufactured either into small briquets or into spherical aggregates to measure respectively the modulus of rupture and the tensile strength. The polysaccharide increased the mechanical strength of both clay minerals. The modulus of rupture of montmorillonite increased from 265 to 580 × 105 Pa at the maximum adsorption of scleroglucan, which was 140 g kg−1 clay. In the case of kaolinite, modulus of rupture measurements indicated that particle‐orientation effects were small and could be neglected. The tensile strength of kaolinite increased from 1 to 20.6 × 105 Pa at the maximum adsorption of scleroglucan (29.9 g kg−1 clay). In this case, the mechanical properties were not due to changes in the clay microorganization, since scleroglucan affected neither the fabric nor the porosity of the kaolinite. Increases in strength were thus intercepted as the formation of polymer bridges between the clay particles and were related to the progressive coverage of the surface area of the clay by the polysaccharide. We concluded that the aggregating action of polysaccharides is predominantly due to an increased strength of interparticle bonds.
Chloride and Perchlorate Influence on Calcium‐Potassium and Magnesium‐Potassium Exchange
Authors: Karmarkar S. V. , Dudley L. M. , Jurinak J. J. , James D. W.
Published: July 2010

There is some uncertainty regarding the effect of the background electrolyte on Ca‐Na and Mg‐Na exchange. We conducted a study to see if any of the effects attributed to the background electrolyte in heterovalent exchange with Na could be observed when K was the monovalent cation. The influence of the competing cations Ca2+ and Mg2+ on K+ exchange was evaluated by examining quantity/intensity parameters (Q/I), Gapon‐convention selectivity coefficients, and adsorbed metal charge with Cl and ClO4 as the background electrolyte. Exchange reactions were unaffected by the background electrolyte for four of the five soils studied. In those soils where exchange was unaffected by the background electrolyte, there was a significant difference between Ca‐K and Mg‐K Q/I curves and Gapon selectivity coefficients; Ca was preferred over Mg relative to K. The Q/I curves from Ca‐K and Mg‐K systems differed in the Cl media, but not in the ClO4 media. Further, the Ca‐K curve was affected by the media. Calcium‐K and Mg‐K selectivity coefficients differed in both Cl and ClO4 media. The Ca‐K selectivity coefficients determined in ClO4 media were closer to Mg‐K selectivity coefficients than those determined in Cl media. The adsorbed metal charge did not increase when the exchanger composition was changed from Mg‐K to Ca‐K in Cl media. The effect of the background electrolyte on Ca‐K exchange was attributed to competition between K+ and CaCl+ for external exchange sites.
Evaluation of an In Situ Method for Measurement of Gas Diffusivity in Surface Soils
Authors: Rolston D. E. , Glauz R. D. , Grundmann G. L. , Louie D. T.
Published: July 2010

Diffusion of gases across the soil/atmosphere interface is a major mechanism in water evaporation, soil aeration, and volatilization of N species, pesticides, and volatile organic compounds. Rapid methods to directly measure the soil‐gas diffusivity of surface soils in the field are needed. An in situ method for measuring the soil‐gas diffusivity was evaluated both theoretically and experimentally in order to provide guidelines for using the method with minimal experimental error. The method involves insertion of a cylinder into the surface of field soil and supplying a tracer gas to the confined soil core from a well‐stirred reservoir of finite volume placed over the inserted cylinder. An analytic solution for unsteady diffusion of a gas in one dimension in semiinfinite porous media is used to determine the soil‐gas diffusivity. In order to establish an estimate of the amount of time for which a diffusion experiment may be conducted without resulting in error due to finite soil core length, calculations of gas reservoir concentration were made for two extreme cases of the lower soil boundary condition. These calculations indicate that tests using a 10‐cm soil cylinder can be conducted for >50 min for soils with soil‐air contents (ε) <0.3 cm3 cm−3. For dry soil (ε > 0.3), soil cylinder depths of 15 or 20 cm should be used to extend the sampling time. Diffusivities determined from the in situ method are in reasonable agreement with cores removed from the field and analyzed in the lab using an independent method. The method should be used for times greater than ≈15 min in order to minimize errors associated with experimental measurements and perturbations associated with initiating the initial gas reservoir concentrations. The method offers a relatively rapid approach for measuring the diffusivity of surface soils in situ as long as the initial concentration of the tracer gas is accurately estimated and the assumption of uniform soil‐air content within the soil depth of interest is not greatly violated.
Soil Organic Matter Influence on Adsorption and Desorption of Boron
Authors: Marzadori C. , Antisari L. Vittori , Ciavatta C. , Sequi P.
Published: July 2010

The role of soil organic matter in B adsorption and desorption processes in soil is not yet clearly understood. Adsorption/desorption isotherms of B were compared in three soils before and after organic‐matter removal by NaOCl. The amount of B adsorbed was considerably greater after the organic matter had been removed from the soil, and the release of B showed a hysteretic trend or, in any case, the hysteretic nature of the B release increased. An increase in oxalate‐extractable Fe and Al occurred after destruction of the organic matter. It is suggested that a portion of the Fe and Al oxides, as well as other possible adsorption sites, are generally coated or occluded by organic matter and become active only after removal of the organic matter.
Pressure Solution: Possible Mechanism for Silicate Grain Dissolution in a Petrocalcic Horizon
Authors: Monger H. Curtis , Daugherty LeRoy A.
Published: July 2010

In the petrocalcic horizon of a middle Pleistocene soil in southern New Mexico, up to 58% of the silicate grains have dissolution features, such as embayed and serrated edges. The purpose of this study was to determine if pressure solution produced the dissolution features. Samples were analyzed in thin section using light and electron microscopy, and by measuring pH and Si concentration of saturated paste extracts. Four lines of evidence support the pressure‐solution mechanism in the petrocalcic horizon: (i) silicate grains are smooth where they contact pores, but serrated where they contact calcite; (ii) dissolution pits on silicate grains generally match the shapes of impacted calcite crystals; (iii) silicate grains are concentrated into horizonal layers in the upper petrocalcic horizon, which testifies to the pressure generated by crystallizing calcite; and (iv) outside the petrocalcic horizon where crystallization pressure is less, silicate grains coated with calcite crystals have fewer dissolution features than grains in the petrocalcic horizon. No relationship was apparent between silicate‐grain dissolution and petrocalcic‐horizon pH or Si concentration. The pH (7.6) was below, and the Si concentration (8.6 mg L−1) was above the levels required for dissolution. Thus, pressure generated by crystallizing calcite appears to have caused dissolution features on the silicate grains in the petrocalcic horizon.
Spatial Variation of Crop Residue Incorporated by Tillage
Authors: Staricka J. A. , Allmaras R. R. , Nelson W. W.
Published: July 2010

Spatial distribution of crop residues incorporated by tillage is generally unknown even though the soil environment for roots, soil microbes, and water flux may be greatly affected. Variations in depth and concentration of oat (Avena sativa L.) residue and tracers (ceramic spheres and polyethylene chips) were measured after incorporation by disk, chisel, or moldboard plow as a primary tillage. Depth distribution of root tissue in an untilled area was also measured. In 1987 and 1988, 60 to 120 soil cores (1.8‐cm diam.) per treatment were taken to a 30‐cm depth immediately after tillage and sectioned into 2‐cm increments (a 5‐cm3 volume). Residue amount, tracer presence, and soil bulk density were measured in each 5‐cm3 sample. Moldboard‐plowing treatments incorporated crop residue to a depth of 28 cm; chiseling and disking incorporated residue to 10 cm. Despite differences in depth of incorporation between tillage treatments, residue and tracers were generally in a 10‐cm band of each 30‐cm‐deep core from all tillage systems. Frequency distributions of residue concentration in individual 5‐cm3 samples were not normal (Gaussian); rather, they were monotonic and positively skewed. Maximum concentrations of crop residue in a 5‐cm3 sample (135.0 mg cm−3 in 1987 and 48.1 mg cm−3 in 1988) were similar among tillage treatments and were greater than the average concentration by a factor of 10 for disk and chisel and 30 for moldboard plow. Samples containing incorporated residue had a distinctly higher soil porosity than samples in general. Primary tillage buries crop residue without effectively dispersing in a microscopic scale throughout the tilled zone. Ceramic spheres and polyethylene chips worked equally well as tracers for incorporated residue.
Soil Solution Phosphorus Dynamics in a Whole‐Tree‐Harvested Northern Hardwood Forest
Authors: Yanai Ruth D.
Published: July 2010

Forest harvest drastically alters nutrient cycling, yet stream water and mineral‐soil solutions typically show little change in P concentrations after forest disturbance. Changes in P availability and movement are more likely to be detected in forest‐floor solutions, since P can be strongly sorbed in soil. Tension‐free lysimeters were used to compare forest‐floor and mineral‐soil solution total‐P concentrations in whole‐tree‐harvested and undisturbed forest sites for 2 yr after harvest in the Hubbard Brook Experimental Forest in New Hampshire. Mean total‐P concentrations in solution in the forest floor (Oa horizon) were significantly higher in whole‐tree‐harvested sites (248 µg P L−1) than in undisturbed forest sites (67 µg P L−1), presumably due to reduced plant uptake of P. Mean P concentrations in mineral‐soil solution remained low after whole‐tree harvest (32 µg P L−1 in the Bh and 15 µg P L−1 in the Bs), consistent with the high P‐sorption capacity of the mineral soil. Phosphorus flux in soil solution from the Oa to the B horizon, calculated from monthly mean P concentrations and monthly water flux simulated by a hydrologic model, was greater in whole‐tree‐harvested sites (1.0 kg P ha−1 yr−1) than in undisturbed forest sites (0.3 kg P ha−1 yr−1) in the first 2 yr after the disturbance. This redistribution of P from the forest floor to the mineral soil far exceeds stream‐water export of dissolved P (0.02 kg P ha−1 yr−1) but is small compared with forest‐floor stores (85 kg P ha−1).
Calcination Effect on the Agronomic Effectiveness of Apatitic North Carolina Phosphate Rock
Authors: Chien S. H. , Hammond L. L.
Published: July 2010

Calcination of apatitic phosphate rock (PR) is one of the means to increase the grade (total P content) of the mineral. The objective of this study was to investigate the effect of calcination on the solubility and agronomic effectiveness of apatitic North Carolina PR in a greenhouse experiment. A Hartsells silt loam (fine‐loamy, siliceous, thermic Typic Hapludult) with pH 4.8 was used. Fertilizers were mixed with the soil at P rates of 0, 50, 150, and 300 mg P kg−1. Funks G5757 maize (Zea mays L.) was grown for 6 wk for each of two crops. The results showed that the degree of carbonate substitution for phosphate in the apatite structure was decreased from 1.20 to 0.32 mol after calcination. The corresponding decrease in neutral ammonium citrate solubility was from 2.7 to 0.8%. Dry‐matter yield and P uptake by maize in two successive crops also decreased due to calcination. Across the range of the P rates used in two maize crops, an average reduction in dry‐matter yield of 77% was calculated for the calcined PR relative to uncalcined PR. Thus, apatitic PR used for direct application should not be calcined, even though calcination can increase its total P content.
Estimation of Hydraulic Conductivity from Effective Porosity Data for Some Indiana Soils
Authors: Franzmeier D. P.
Published: July 2010

Hydraulic‐conductivity data are needed to predict how soils will respond to various uses. Saturated hydraulic conductivity (Ks), however, has been determined for only a few soils. Ahuja et al. proposed a model by which Ks can be estimated from effective porosity (φ3), the difference between total porosity and the volumetric soil water content at 33 kPa of suction. If this relationship were known, Ks could be predicted for many more soils using available water‐retention information. Previously, Ks had been determined in saturated soil horizons by the piezometer method for a set of soils in Indiana. These data were summarized by soil classes, called lithomorphic classes, based on origin of parent material, kind of soil horizon, and soil texture. More recently, bulk‐density and water‐retention measurements were summarized using similar classes. In this study, Ks is related to φe for some Alfisols and Mollisols of Indiana. The relationship is Ks = 5.01 × 10−3 × φ3.21e, where Ks is in m/s and φe is in m3/m3. This compares favorably with the relationships found by Ahuja et al.
Complexation of 1‐Naphthol by Humic and Fulvic Acids
Authors: Chen S. , Inskeep W. P. , Williams S. A. , Callis P. R.
Published: July 2010

Complexation of organic solutes with dissolved humic substances may have a significant effect on the chemistry and fate of contaminants in natural systems. The complexation of 1‐naphthol with dissolved humic and fulvic acids (HA and FA) in 0.01 M KCl was studied using fluorescence quenching. No increase in quenching at elevated temperature and an increase in quenching ratio at higher viscosity both indicated that the quenching was due to the formation of naphthol‐HA water‐soluble complexes. Conditional equilibrium constants for the association of 1‐naphthol with humic and fulvic acids were estimated from the Stern‐Volmer equation, and ranged from 9.7 to 33.4 L/g C. In general, HA showed a stronger affinity for 1‐naphthol than FA. The ionic strength of the solution, adjusted using KCl and CaCl2, did not significantly affect the complexation of 1‐naphthol with HA. The quenching ratio increased as the pH of the solution increased, suggesting that changes in the dispersion of HA polymers or additional binding mechanisms result in increased HA complexation of naphthol at higher pH. The complexation of 1‐naphthol with HA was enhanced in the presence of Cu2+ and Zn2+ at a pH higher than the dissociation constant (pKa) of 1‐naphthol (9.34). This suggests that cation bridging between functional groups of anionic organic solutes and humic or fulvic acids is an additional binding mechanism for the association of organic solutes with soluble humic substances.
Ethylene Inhibition of Ammonium Oxidation in Soil
Authors: Porter Lynn K.
Published: July 2010

Small quantities of ethylene (C2H4) are produced by bacteria and fungi in soils. Ethylene is produced when nitrogenase activity is measured by acetylene (C2H2) reduction. Acetylene has been used as a nitrification inhibitor and has been shown to produce C2H4 in flooded rice soils. Whether C2H4 affects the oxidation of NH4 by the soil's nitrifying organisms and at what concentrations was the focus of this study. A Weld clay loam surface soil (fine, montmorillonitic, mesic Aridic Paleustoll) was treated with (NH4)2SO4, subjected to various partial pressures of C2H4 and incubated at 30 °C. At designated incubation times, the atmospheres of the incubation flasks were analyzed for O2, CO2, and C2H4 by gas chromatography (GC) and the soil was analyzed for NH4, and NO3 plus NO2 by steam‐distillation procedures. At a C2H4 partial pressure of 0.017 kPa, NH4 oxidation was similar to untreated samples. At a C2H4 partial pressure of 0.17 kPa, NH4 oxidation was partially inhibited and, at a C2H4 partial pressure of 4.55 kPa, inhibition was nearly complete.
Injection of Nitrogen‐15 into Trees to Study Nitrogen Cycling in Soil
Authors: Horwath William R. , Paul Eldor A. , Pregitzer Kurt S.
Published: July 2010

Most 15N dilution techniques disturb either the soil or N‐pool size. The objective of this study was to develop a method of labeling the roots of Populus trees with 15N without physically disturbing the soil. Such a method would enable the direct measurement of the flux of 15N from dead roots into the soil organic matter. Leaf and root biomass were labeled by injection of 15N directly into the vessel elements of hybrid Populus trees during their second growing season. The 15N was uniformly distributed throughout the canopy and root system. The rate and amount of 15N turnover from plant tissue can be determined by pool transfer or through differences in plant 15N concentrations. The 15N was detected in the dead‐root pool 8 wk after injection, indicating root turnover. Results demonstrate the ability to measure the contribution of fine‐root litter to N‐cycling processes without disturbing the soil environment.
Bromide and Nitrate Movement in an Irrigated Cotton Production System
Authors: Silvertooth J. C. , Watson J. E. , Malcuit J. E. , Doerge T. A.
Published: July 2010

A field experiment was conducted for the purpose of determining the worst‐case potential for solute leaching under furrow‐irrigated conditions, and to assess the spatial variability associated with solute movement. The experiment was carried out on a Mohall sandy loam soil (fine‐loamy, mixed, hyperthermic Typic Haplargid) within a field of upland cotton (Gossypium hirsutum L.), with uniformity of all management factors including fertilizer N and irrigation water. Six mainplot areas were identified throughout the study area to provide characterization of spatial variability. Within each main plot, five subplots (1 m2 each) were further identified. To each subplot area, 20 g KBr was applied in 500 mL of solution using the Br‐ as a biologically conserved tracer. Soil from each subplot was sampled to a depth of 180 cm and separated into 30‐cm depth increments. Soil samples were then subjected to a 1:1 (soil/water) extraction and analyzed for Br‐ and NO‐3‐N. Appreciable amounts of solute movement were measured, with a very high degree of spatial variability. The highest degree of leaching potentials was measured early in the season, when soil water depletions were the lowest and crop root development would not be extended past very shallow regions of the soil profile. The results reinforce the need to split fertilizer‐N applications throughout the course of a growing season, and to base fertilization rates and frequency on properly calibrated plant‐tissue tests.
Fiberglass Wicks for Sampling of Water and Solutes in the Vadose Zone
Authors: Boll J. , Steenhuis T. S. , Selker J. S.
Published: July 2010

Sampling solute concentrations in the vadose zone provides an early‐warning system for groundwater pollution. Various sampling devices are available. This study evaluates the functionality of fiberglass wicks in a soil solution sampler. Fiberglass wicks act as a hanging water column, drawing water from the undisturbed field soil without external application of suction. Flow characteristics of wicks were observed in the laboratory by miscible‐displacement tests using Br and an organic dye. The matric potential in the wick as a function of flow rate was measured. Fiberglass wicks behaved like a porous medium that effectively could apply a suction to the soil while only minimally retarding the organic dye. The relationship between matric potential, moisture content, and unsaturated conductivity was determined for several wicks. Based on these relationships, a set of curves was produced depicting travel time of nonadsorbed chemicals and the matric potential in the wick as a function of flow rate. These curves can be used for selecting optimum wick length and diameter for a given sampler configuration.
Nitrogen Uptake of Mesquite Seedlings at Conventional and Exponential Fertilization Schedules
Authors: Imo M. , Timmer V. R.
Published: July 2010

Exponential nutrient additions have been shown to induce steady‐state nutrition in plants and enhance seedling growth and nutrient status, which suggests improved nutrient efficiencies during the growing season. The objective of this study was to compare periodic growth, plant nutrient status, and N uptake of desert mesquite (Prosopis chilensis Mol.) seedlings that received 200 mg N seedling−1 as complete fertilizer delivered either conventionally (as single dose or constant top dressing) or exponentially (as pure or modified exponentially increasing additions) during a 12‐wk rotation. Steady‐state nutrition (characterized by a stable tissue nutrient concentration) was induced for the cultural period in the modified‐exponential fertility regime. The nutrients were supplied exponentially except for higher initial amounts that compensated for the incomplete accessibility of growing medium to the small root systems. These seedlings showed consistently higher N accumulation that matched dry‐matter production, reflecting higher fertilizer‐N uptake efficiency throughout the growing season. During the same growing season, pure exponential nutrient‐addition rates appeared to achieve steady‐state conditions 4 wk later because of incomplete interception of applied nutrients by small root systems during establishment. Conventional fertility regimes caused nutrient dilution in plants with time. Nutrient uptake did not match growth in these seedlings, resulting in nutrient stress at varying stages of seedling development.
Analysis of Soil Textural Porosity Relative to Skeleton Particle Size, Using Mercury Porosimetry
Authors: Fiès J. C.
Published: July 2010

Soil textural porosity represents the pore space due to packing of soil particles. The characteristics of this pore space are affected by particle‐size distribution. Binary mixtures of clay and skeleton (<2‐µm and coarser particles, respectively) were studied to evaluate whether the textural‐space division into clay‐fabric pore space and its complementary space, lacunar pore space, could be modified by decreasing skeleton size. Skeleton particles with diameters of 400 µm (glass beads), 20, 13, 6, and 4 µm (silt) were mixed in the wet state with various clay contents (5–90%), then dried. Mercury porosimetry was used to characterize textural pore space by volumetric pore density distribution curves (VPD) and volumes intruded into small pores of diameter <0.05 µm (VSP). For clay‐bead (400‐µm) mixtures, bimodal VPD curves occurred for all clay‐content levels, corresponding to distinct intrusion of either lacunar or clay‐fabric pores. Values of VSP, however, were only related to intrusion into clay‐fabric pore space. In clay‐silt mixtures, unimodal VPD curves occurred, and VSP values were greater, when the clay content was >60 to 70%. Similarly, VSP values and the unimodal VPD curve were both explained by hidden lacunar pores, i.e., lacunar pores intruded only via clay‐fabric pores. Clay‐fabric pore space and lacunar pore space were always present in clay‐silt mixtures, but the proportion of hidden lacunar pore space increased with clay content and at a greater rate the smaller the particle size.
Interactions between Organic and Inorganic Components in Particle‐Size Fractions Separated from Four Soils
Authors: Schnitzer M. , Kodama H.
Published: July 2010

Little information is available in the literature on the mechanism(s) of interaction of organic matter (OM) and inorganic crystalline and noncrystalline components in particle‐size fractions. To obtain a better understanding of this subject, five particle‐size fractions, ranging from coarse silts to fine clays, were separated from two soils from eastern Canada (Armadale and Bainsville) and from two prairie soils (Melfort and Regina). Each size fraction was characterized by chemical and mineralogical methods. Humic acids (HAs), fulvic acids (FAs), and humins were found to accumulate in size fractions ranging from medium silts to coarse clays, while aliphatics were concentrated in fractions from medium silts to fine clays. Amino acids tended to be enriched in clay fractions of the two prairie soils, but accumulated in the silt fractions separated from the two soils from eastern Canada. Except for one soil, NH3‐N accumulated in the fine silt and finer fractions, which were rich in expandable phyllosilicates. In general, amounts of OM, aliphatics, and NH3‐N tended to accumulate in fractions rich in noncrystalline inorganics. Noncrystalline inorganics separated from the two prairie soils were rich in Si, which appeared to contribute to the preferential accumulation of humin, HA, and neutral amino acids. On the other hand, noncrystalline components from the two soils from eastern Canada were rich in Al, which may have been associated with the accumulation of NH3‐N and acidic amino acids in these soils. The pH‐dependent charges of noncrystalline inorganics may also have contributed to the accumulation of OM.