bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors Determining Differences in Soil pH in Adjacent Conifer and Alder‐Conifer Stands
Authors: Binkley Dan , Sollins Phillip
Published: July 2010

Tree species may differ in their influence on biogeochemical cycles, leading to differing rates of soil acidification. Over time, quantitative and qualitative changes develop in the characteristics of the soil exchange complex. Three such characteristics regulate soil pH: (i) the quantity of acids present, which can be represented as the total cation‐exchange capacity (CEC); (ii) the degree of dissociation of the acids, commonly called base saturation; and (iii) the affinity of the acids for H+, or acid strength, which represents the composite pKa (negative log of the acid ionization constant) of the exchange complex. We examined the importance of these three factors in explaining the differences in soil pH between adjacent stands of conifers [primarily Douglas fir, Pseudotsuga menziesii (Mirbel) Franco] and conifers mixed with N‐fixing red alder (Alnus rubra Bong.). At a low‐productivity site (Wind River, WA), the pH of 0 to 0.15 m of soil from both alder‐conifer and conifer stands averaged 4.3 in 0.01 M CaCl2. The pH values were the same, however, only because higher base saturation in the alder‐conifer stand was offset by greater acid strength. At a more productive site (Cascade Head, OR), soil pH (in 0.01 M CaCl2) averaged 3.7 in the alder‐conifer stand but 4.4 in the conifer stand. The difference in pH resulted primarily from greater acid strength of soil organic matter under alder, and secondarily from lower base saturation of the exchange complex. These results underscore the importance of considering qualitative changes in soil organic matter as factors driving changes in soil pH and other parameters.
Predicting Cation Mobility in Montmorillonitic Media Based on Exchange Selectivities of Montmorillonite
Authors: Gaston L A. , Selim H. M.
Published: July 2010

Cation‐exchange reactions influence the distribution of species between soil solution and sorbed phases and, in turn, the rate of movement of species through the soil. This study was undertaken to determine whether cation‐exchange selectivity coefficients of montmorillonite could be used to adequately describe cation movement in a montmorillonitic soil. Literature data for Ca‐Mg, Ca‐Na, and Mg‐Na exchange on pure montmorillonite in ClO4 and Cl anionic backgrounds were used to calculate average values for binary exchange selectivity coefficients. These selectivity coefficients were subsequently used in transport models in attempts to describe experimental binary (Ca‐Mg or Ca‐Na) and ternary (Ca‐Mg‐Na) miscible displacement in columns of bulk montmorillonite (admixed with sand) and Sharkey clay soil (a very‐fine montmorillonitic, non‐acid, thermic Vertic Haplaquept) from Louisiana. In general, use of Ca‐Mg exchange selectivity coefficients produced transport simulations in good agreement with experimental results. Use of heterovalent exchange coefficients tended to predict somewhat later breakthroughs of Na than were observed. Although cation‐exchange selectivities of montmorillonite could be used to adequately describe Ca, Mg, and Na transport in Sharkey soil, generalization of these results requires additional confirmation using other montmorillonitic soils.
Kinetics of Sulfate Desorption from Soil
Authors: Sharpley Andrew N.
Published: July 2010

Sulfate desorption and mobility in soil can be of both environmental and agronomic importance. This study was conducted to describe the desorption of SO4 from agricultural soils under experimental conditions applicable to the movement of SO4 in overland flow and runoff waters. The kinetics of SO4 desorption from soil were investigated at five different water/soil ratios (10:1–400:1), five time periods (5–180 min), and four SO4 additions (0–200 mg kg−1). Sulfate desorption (Sd) was logarithmically related to contact time (t) and water/soil ratio (W) and was a linear function of the initial extractable SO4 content of soil (Se). The kinetics of SO4 desorption was described by the equation Sd = K Se tα Wβ, where K, α, and β are constants for a given soil. This equation has previously been shown to describe desorption of soil P and K. The kinetic constants, K (r2 = 0.88), α (r2 = 0.83), and β (r2 = 0.88), were related to extractable soil Al content for 107 U.S. soils. The uniformity of equation constants for a given soil and the ease with which they can be estimated from extractable soil Al indicate the potential use of the equation in modeling SO4 desorption from soil and subsequent movement in surface runoff water.
Phosphorus Chemistry and Mineralogy in Excessively Fertilized Soils: Quantitative Analysis of Phosphorus‐rich Particles
Authors: Pierzynski G. M. , Logan T. J. , Traina S. J. , Bigham J. M.
Published: July 2010

There has been little success with direct methodologies in isolating or characterizing phosphate minerals or P‐bearing solids in soils, due primarily to the fact that P solids represent a relatively minor component of the soil matrix. This study was conducted to evaluate a method for concentrating P in soils and to characterize P‐solids phases by a variety of direct mineralogical methods. Eleven soil samples representing six soil series from Illinois, Michigan, Wisconsin, and New York were fractionated according to particle size, with the clay‐sized fractions being further separated into the density ranges of <2.2, 2.2 to 2.5, and >2.5 Mg/m3. The density separates were examined by scanning transmission electron microscopy in conjunction with energy dispersive x‐ray analysis, x‐ray diffraction (XRD), and Fourier‐transformed infrared (FTIR) spectroscopy. Total P concentrations were generally highest in the clay‐sized fractions, compared with the sand‐ and silt‐sized fractions, and always highest in the lowest‐density separates, compared with the remaining two density fractions. Discrete P‐rich particles were found in most density separates, with the highest abundances occurring in the < 2.2 and 2.2 to 2.5 Mg/m3 fractions. Particles generally contained detectable quantities of Al and Si and various combinations of K, Ca, and Fe. Phosphorus concentrations within individual P‐rich particles were highly variable. Analysis of the density separates with XRD and FTIR spectroscopy was not successful in identifying discrete P minerals.
Hard and Soft Acid‐Base Model Verified for Monovalent Cation Selectivity
Authors: Xu Shihe , Harsh James B.
Published: July 2010

Experimental support was obtained for a quantitative ion‐exchange model based on the principle of hard and soft acids and bases (HSAB) applied to monovalent cation exchange on clay minerals, oxides, and exchange resins. According to the model, the thermodynamic exchange constant (Kex) can be obtained from the differences in absolute electronegativity (ϰ) and absolute softness (S) between the exchanging cations in binary exchange as follows:
urn:x-wiley:03615995:saj2sssaj198503615995004900030046x:equation:saj2sssaj199003615995005400060014x-math-0001 where the subscripts M and R denote exchange and reference cations, respectively, and α and β are coefficients dependent only on the exchanger surface properties, temperature, pressure, and ionic strength. This study was conducted to test the applicability of this model to monovalent cation exchange on clay minerals and ionic‐exchange resins. Exchange isotherms for Li, K, Rb, Cs, Ag, and Tl+ vs. Na on vermiculite, smectites, hydrous Zr oxides, silica gel, and ion‐exchange resins were obtained experimentally or from the literature and α and β were obtained by fitting the data to the above equation. An excellent fit (R2 ≥ 0.954, n = 5) of the alkali metal cation‐exchange data to the model resulted on all of the tested exchangers, whereas Ag and Tl+ exchange was successfully fit only on hard surfaces such as a vermiculite and on highly hydrated surfaces such as certain ion exchange resins. According to the HSAB model, coefficients α and β determine the relative contribution to Kex from ionic or covalent bonding in surface complexation. The |α/β| ratio depended on the layer charge of clay minerals and on the acid strength of the exchange resins and hydrous oxides.
Temporal Patterns of Soil Denitrification: Their Stability and Causes
Authors: Christensen Søren , Simkins Stephen , Tiedje James M.
Published: July 2010

The temporal stability of denitrification activity was assessed by monitoring N2O production in 30 rings installed in an acid sandy loam soil in which N2O was the only gaseous product of denitrification. When soil water was kept at field capacity or above, in the absence of NO3 limitation, some locations showed high denitrification compared with the average activity. These high‐activity locations persisted for up to several weeks. The ranking of locations with respect to denitrification rates was more stable over time than would have been expected due to chance alone. Additions of particulate organic matter (POM) that stimulated denitrification within 2 h in anaerobic soil slurries did not increase denitrification until 5 d after addition to soil cores. The increase in denitrification was preceded by an increase in respiration. The denitrification activity within the “hot spots” created by addition of POM was not limited by diffusion of NO3 in the soil. The addition of glucose 9 d before the injection of POM into field rings reduced the lag time preceding increased denitrification. Therefore, the delayed response of denitrification following POM addition in aerobic soil probably reflects the time required to establish an anaerobic soil volume.
Tillage Influence on Soil Sulfur Characteristics in Winter Wheat‐Summer Fallow Systems
Authors: Tracy P. W. , Westfall D. G. , Peterson G. A. , Elliott E. T.
Published: July 2010

Conversion of native prairie ecosystems to crop production leads to net losses of many essential plant nutrients. The purpose of this research was to monitor winter wheat (Triticum aestivum L.)‐fallow rotations for seasonal soil S fractions and S dynamics as affected by tillage. Soil samples from plots that had been subject to 15 yr of no‐till, stubble mulch, and conventional tillage were collected at monthly (cropped) and 2‐wk (fallow) intervals, from May through October at depth increments of 0 to 2.5, 2.5 to 5, 5 to 15, 15 to 30, and 30 to 60 cm. Sulfate‐S, carbon‐bonded S (CB‐S), and esterbonded S (HI‐S) concentrations were determined for each soil sample. During fallow, SO4‐S accumulation in the surface 0 to 5 cm was 1.5 times greater in no‐till than in tilled soils. After a rainfall of 49 mm, SO4‐S concentrations increased at 15 to 30 cm from 4.6 to 5.8 mg kg−1 in no‐till, 3.1 to 8.3 mg kg−1 in stubble mulch, and 3.4 to 11.2 mg kg−1 in plow treatments. No‐till soils contained higher amounts of HI‐S at 0 to 15 cm than either tilled soil. There was no difference in CB‐S concentration at 0 to 15 cm between no‐till and stubble mulch with both containing higher CB‐S contents than plowed soils. Lower surface concentrations of SO4‐S, greater SO4‐S leaching, and lower HI‐S and CB‐S in tilled than in no‐till soils indicates that S is conserved in low‐soil‐disturbance tillage systems.
Soils and Mineral Weathering on Phyllite Colluvium and Serpentinite in Northwestern California
Authors: Graham R. C. , Diallo M. M. , Lund L. J.
Published: July 2010

Haplohumults and Argixerolls have formed in close proximity on phyllite colluvium and serpentinite residuum, respectively, in the Klamath Mountains of northwestern California. This study was conducted to compare their contrasting properties and to investigate soil mineral weathering. Thick, dark A horizons containing 20 to 50 g kg−1 organic C have formed in the Argixeroll under the influence of perennial grass cover with sparse conifers and shrubs. The Haplohumult, under dense Douglas fir [Pseudotsuga menziesii (Mirbel) Franco] forest, has a thin A horizon containing 10 to 20 g kg−1 organic C. Soil pH is in the range of 5.6 to 5.8 in the A horizons of both soils. In the Haplohumult, pH decreases slightly with depth, whereas pH increases to 6.5 in the Crt horizon of the Argixeroll. The mineralogy of the Haplohumult is relatively uniform throughout its 260‐cm depth. Chlorite, the dominant mineral in the phyllite parent rock, has altered to interstratified chlorite/vermiculite and poorly crystalline kaolin in the soil fine‐sand fraction. Chlorite/vermiculite and kaolin dominate the clay fraction, accompanied by gibbsite, talc, and Fe oxides. Serpentine weathering prevails in the Argixeroll. The serpentine content of the fine‐sand fraction decreases upward in the profile, whereas magnetite and chlorite resist weathering and are concentrated. Serpentine is the most abundant mineral in the clay fraction. Clay‐size smectite, a product of serpentine weathering, is absent from A horizons, but increases with depth to a maximum in the fine‐earth material from cracks in the Crt horizon. Chlorite in the clay fraction is inherited from the parent rock. Both soils have experienced minor surficial additions of amorphous silica phytoliths and volcanic glass shards.
Regional and Catenary Variations in Properties of Borolls of Southern Saskatchewan, Canada
Authors: Pennock D. J. , de Jong E.
Published: July 2010

The spatial pattern of soil properties results from systematic variations in the type and intensity of soil‐forming processes and from random variations superimposed on the systematic variations. We examined the thickness of A horizons and depths to CaCO3 at 21 sites in southern Saskatchewan to determine whether systematic differences occurred among soil‐moisture regimes of Borolls and among landform elements in catenas. The mean thickness of A horizons was thinnest for the aridic Borolls (x̄ = 15.3 cm) and ustic Borolls (x̄ = 15.2 cm) and thickest in the udic Borolls (x̄ = 18.4 cm), reflecting the regional moisture gradient. The regional differences in mean depth to CaCO3 were contrary to the expected pattern: mean depths were smallest for the ustic Borolls (x̄ = 29.9 cm) and greatest for the aridic (x̄ = 34.1 cm) and the udic (x̄ = 34.9 cm) Borolls. A consistent pattern was associated with landform elements in soil catenas. The smallest means for both properties were associated with shoulder and backslope elements with convex across‐slope curvatures, and the greatest means for footslope elements with concave across‐slope curvatures. The range in mean values of the two properties among landform elements within a catena was consistently an order of magnitude greater than the regional differences among soil subgroups.
Simulated Erosion and Fertilizer Effects on Winter Wheat Cropping Intermountain Dryland Area
Authors: Massee T. W.
Published: July 2010

Topsoil loss from erosion in the intermountain dry‐farming area reduces crop yields. This study tested the hypothesis that the effects of erosion on water storage and wheat (Triticum aestivum L.) yield could be partially alleviated by applying appropriate fertilizers. Two sites were used, one on Rexburg silt loam, a coarse‐silty, mixed, frigid Calcic Haploxeroll, and the other on Newdale silt loam, a coarse‐silty, mixed frigid Calciorthidic Haploxeroll. Topsoil‐depth treatments were +15, 0, −15, or −30 cm changes relative to the original surface. After making the soil depth changes, 54 kg P ha−1 were incorporated on one half of each topsoil depth plot and the other half received no P. These P or no P plots were split for applications of 0, 34 or 68 kg N ha−1. Phosphorus had no effect on wheat yield. Without fertilizer N, yields on −15 and −30‐cm plots were reduced 46 and 55%, respectively, but increased 69% from the addition of 15 cm of topsoil, compared with the 0‐cm plot. Removing 15 and 30 cm of topsoil also reduced the upper limit of N‐fertilized production to 80 and 65%, respectively, of production on undisturbed N‐fertilized plots. Three kilograms fertilizer N ha−1 each crop year offset each centimeter of soil removed, but only to the new lower production limit. All plots had similar amounts of stored, available soil water in the spring, but a large fraction of this water remained unused at harvest on plots with 15 and 30 cm of topsoil removed because the low‐yielding wheat did not use as much water. Profile water differences at harvest were no longer apparent by the next spring, following winter recharge. Unused water at harvest, which partially filled the soil profile, reduced winter infiltration and contributed to subsequent runoff from precipitation on those plots. Adding N fertilizer was only a partial solution to topsoil deficiencies.
Cation Removal during Application of Acid Solutions into Air‐Dry Soil Columns
Authors: Liu K. H. , Mansell R. S. , Rhue R. D.
Published: July 2010

Acidic deposition is considered an environmental problem that may be modifying the forest soil, and that affects the forest soil's cation‐exchange status. The primary purpose of this study was to determine whether cation removal from laboratory columns of Cecil soil (a clayey, kaolinitic, thermic Typic Kanhapludult) would be proportional to the proton concentration of the acidic input solution. A second purpose was to find the effective‐charge balance of major cations in the soil columns after termination of acid infiltration. Aqueous HCl solutions of pH 3.9 and 4.9 were applied with constant flux to columns of initially air‐dry topsoil and subsoil until approximately 30 pore volumes of effluent had been collected. Larger quantities of cations were leached by the pH 3.9 solution. The ratio of cations removed in the two cases was considerably less (<2‐fold) than the 10‐fold H ion ratio of the two input acid solutions. The effective‐charge balance error of major cations was greatest for the high‐pH solution. Differences in effective‐charge balance of major cations were greater for columns of subsoil than for topsoil. Application of acid (HCl) solutions definitely accelerated leaching losses of cations from the forest Cecil soil.
Effects of Urea‐Potassium Chloride and Nitrogen Transformations on Ammonia Volatilization from Urea
Authors: Gameh M. A. , Angle J. S. , Axley J. H.
Published: July 2010

Ammonia volatilization following fertilization with urea can be substantial. Losses via NH3 volatilization may be reduced with the concurrent application of KCl, which temporarily reduces soil pH. The objective of this study was to examine the influence of various urea‐KCl mixtures on NH3 volatilization and N transformations in two soils. Urea, granular urea plus KCl, urea plus KCl in solution, and urea coated with powdered KCl were added to a Matapeake silt loam (a fine‐loamy, mixed, mesic Typic Hapludult) and a Hagerstown silty clay loam (a fine, mixed, mesic Typic Hapludalf) at rates equivalent to 260 kg urea ha−1 (120 kg N ha−1) and 260 kg KCl ha−1 (135 kg K ha−1). During the first 13 d of incubation in the Matapeake soil, 26% of the N applied as urea alone was lost via NH3 volatilization. From the KCl‐coated urea, only 13% of the applied N was lost via volatilization. Ammonia losses from the Hagerstown soil were less than from the Matapeake soil but were still significantly reduced by the KCl coating on urea. Differences in NH3 volatilization between the soils were primarily attributed to the rate of urea hydrolysis and subsequent N transformations. These results indicate that coating urea with KCl may offer a significant advantage over uncoated urea, especially in K‐deficient soils.
New Technique for Measuring Volumetric Shrinkage in Soils
Authors: Overby Steven T. , DeBano Leonard F.
Published: July 2010

Volumetric shrinkage in soils is an important physical parameter used in soil erosion and soil mechanics studies. The American Society for Testing Materials D427 method for determining volumetric shrinkage was modified using a less toxic silicone‐mineral spirits mixture instead of liquid Hg. The silicone‐mineral spirits method yielded the same results in shrinkage as measured by the Hg method for a wide range of soils containing between 22 and 48% clay. Use of the silicone‐mineral spirits mixture decreases safety hazards associated with liquid Hg and is more economical.
Clay Mineral Type and Organic Compound Sorption by Hexadecyltrimethlyammonium‐Exchanged Clays
Authors: Jaynes W.F. , Boyd S.A.
Published: July 2010

In order to relate mineralogy to sorbent efficiency, organo‐clays were prepared from reference vermiculite, illite, smectite, and kaolinite clay minerals using the organic cation hexadecyltrimethylammonium (HDTMA). Adsorption isotherms using 14C‐HDTMA indicated stoichiometric adsorption of HDTMA up to the cation‐exchange capacity (CEC). Organo‐clays were prepared by adding HDTMA equivalent to the CEC and were evaluated as sorbents for nonionic organic compounds (NOCs) dissolved in water. X‐ray diffraction analysis of the HDTMA clays revealed basal spacings of 28 Å for the vermiculite and 23, 20, and 18 Å for the high‐charge, intermediate‐charge, and low‐charge smectites, respectively. The HDTMA vermiculite, illite, and smectites were all highly effective sorbents for NOCs, whereas Mg smectite was ineffective. The sorption isotherms of benzene, toluene, ethylbenzene, propylbenzene, butylbenzene, t‐butylbenzene, naphthalene, and biphenyl on the HDTMA clays indicated that sorption occurred by partition interactions with the HDTMA‐derived organic phase. In general, both the greater HDTMA content and the larger basal spacings of high‐charge HDTMA clays increased NOC sorption. Mineral‐charge effects on the sorption of unsubstituted aromatic compounds (benzene, naphthalene, and biphenyl) were less evident than for alkyl‐benzenes. Greater sorption of the alkylbenzenes by high‐charge HDTMA clays can be attributed to the capability of the large basal spacings to accommodate larger solute molecules. The formation of organic cation exchanged soil clays derived from vermiculite, illite, or smectite may greatly improve the ability of soils to immobilize organic contaminants.
Nitrogen Assimilation and Distribution in Field‐Grown Cowpea at Various Growth Stages
Authors: Awonaike K. O. , Kumarasinghe K. S. , Danso S. K. A.
Published: July 2010

The sources of N and the periods during which they are assimilated can influence the redistribution of N within different organs and, consequently, the final grain yield and N content of legumes. The 15N isotope‐dilution approach was used to measure the amounts of N derived from atmospheric N2 (Ndfa), soil (Ndfs), and fertilizer (Ndff) in the aboveground portion of field‐grown cowpea [Vigna unguiculata (L.) Walp.] at the following developmental stages: late vegetative, early pod filling, mid pod filling, and physiological maturity. The soil was classified as an Oxic Paleudalf. The principal sources of cowpea's N changed markedly during development. While Ndfs supplied 80% of the total N assimilated in the aboveground plant parts during the first 42 d of growth, Ndfa furnished over 80% of the N assimilated during the remaining and most N‐demanding period of cowpea growth. At physiological maturity, the total above‐ground plant N was composed of 100, 50, and 5 kg N ha−1 as Ndfa, Ndfs, and Ndff, respectively. The preexisting N pools in vegetative parts of cowpea did not contribute much N towards pod fill, with the currently assimilated N (predominantly as Ndfa) contributing 87% of the N for pod fill. At physiological maturity, the N in pods was only slightly in excess of Ndfa in the aboveground plant parts. We conclude that Ndfa can contribute significantly towards the N nutrition of field‐grown cowpea, serving also as an important source of N for pod development.
Soil Denitrification Dynamics: Spatial and Temporal Variations of Enzyme Activity, Populations, and Nitrogen Gas Loss
Authors: Parsons Laura L. , Smith M. Scott , Murray Robert E.
Published: July 2010

Spatial and temporal variation in N‐gas loss (N2O evolution with C2H2), denitrifying enzyme activity (DEA), and denitrifier biomass (as determined by most‐probable‐number [MPN] counts) was measured in two agricultural soils in central Kentucky in order to characterize the extent to which denitrifying enzymes are synthesized and expressed, and how environmental conditions influence the in situ growth and activity of denitrifying bacteria. Rates of N‐gas loss from intact cores ranged from 0 to 300 µg N m−2 h−1. Nitrogen gas loss was strongly seasonal, with both soils having the most frequent activity in the spring. Nitrogen gas loss was highly variable on a spatial scale with replicate measurements exhibiting coefficients of variation between 74 and 268%. Denitrifying enzyme activity in both soils ranged from 0.1 to 119 ng N2O‐N g−1 soil min−1 and varied spatially and temporally, but did not exhibit the same seasonal pattern as N‐gas loss. Increases in DEA often followed increases in soil moisture and were commonly associated with increases in soil respiration. Denitrifier populations ranged from 3 × 103 to 1 × 106 cells g−1 dry soil but did not show the same temporal pattern as N‐gas evolution.

When the entire data set was considered, none of the parameters measured, alone or in combination, adequately accounted for variation in N‐gas loss from either soil. When mean values of the parameters measured at each sampling date were considered, however, multiple‐regression models accounted for 74 to 91% of the variation in mean denitrification rate. Denitrifying enzyme activity and MPN population measurements were not good predictors of denitrification rate because N‐gas loss was not always tightly coupled to the synthesis of denitrifying enzymes or population growth.
Organic Matter Extraction from Soils with Water at High Pressure and Temperatures
Authors: Schnitzer M. , Schuppli P. , Schulten H.‐R. , Angers D. A.
Published: July 2010

The objective of this research was to develop a procedure for the more specific extraction of major organic matter (OM) components from soils. The method was tested on Ap horizons of a Haplaquoll, a Cryoboroll, and a Haploboroll, and on the Bh horizon of a Haplaquod. The four soils were extracted for 2 h with distilled water at a constant pressure of 17.2 MPa and at temperatures of 150, 200, and 250 °C. The OM extracts obtained were characterized by chemical methods, infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy, and pyrolysis‐field ionization mass spectrometry (Py‐FIMS). With one exception, relatively more of the soil N (18–53%) than soil C (17–40%) was extracted from the four soils at the three temperatures. Recoveries of N at 200 and 250 °C were superior to those reported for extractions by 0.1 M Na4P2O7 solution from the same soils, while C recoveries were higher from the Bainsville and Regina soils. In general, extracts obtained at 200 °C were richest in carbohydrates and especially in N components. The 13C‐NMR spectra showed that most of the C in the extracts was aliphatic, occurring in the form of noncarbohydrate carbons bonded to OH and O. The Py‐FI mass spectra indicated that the extracts contained polysaccharides, n‐fatty acids, n‐alkanes, n‐alcohols, sterols, N compounds (pyrroles and pyridines), and mono‐ and dilignins, all typical OM components. Extracts obtained at 150 °C were enriched in n‐alcohols and diols, whereas extracts at 250 °C were rich in fatty acids. For the extraction of carbohydrates and N components, we recommend an extraction temperature of 200 °C; for soils rich in clay minerals, extractions at 250 °C may be more efficient. For studies on paraffinic OM components, extraction at 150 °C may be appropriate.
Flow Injection Analysis of Urea Nitrogen in Soil Extracts
Authors: Sullivan D. M. , Havlin J. L.
Published: July 2010

Flow injection analysis (FIA) is a relatively new technique with advantages over traditional automated analysis methods in precision and sample throughput. A new procedure has been developed to measure urea in soil extracts using automated FIA. This procedure utilizes the diacetyl monoxime thiosemicarbazide colorimetric method, with a modified acid reagent that increases the rate of color formation and improves the mixing of sample with reagent in narrow‐diameter (0.8‐mm) tubing. Sixty samples can be analyzed per hour, with a detection limit of 0.01 mg urea‐N L−1. Residence time between sample injection and maximum absorbance is 130 s.
Nitrogen‐15 Recovery in Winter Wheat as Affected by Application Timing and Dicyandiamide
Authors: Bronson K. F. , Touchton J.T. , Hauck R. D. , Kelley K. R.
Published: July 2010

Nitrification inhibitor amendment to fall‐applied N for winter wheat may reduce denitrification and leaching losses of N by maintaining N in ammoniacal form. A field study on a Norfolk loamy sand (fine‐loamy, siliceous, thermic Typic Paleudult) compared fall application of 15N‐labeled urea with and without dicyandiamide (DCD) and split urea application in fall and spring. Grain yield (mean 4.26 Mg ha−1) increased with N rate (67, 101, and 134 kg N ha−1), but was not affected by DCD or time of N application. Recovery of 15N in wheat the first year (mean 53%) was not affected by DCD or time of N application. Immobilization of 15N was 21, 20, and 15% with the fall N plus DCD, split‐applied N, and fall N treatments, respectively. Nitrogen‐15 leached at harvest was less with fall N plus DCD or split‐applied N than with fall N only. Denitrification estimates, calculated as 15N not accounted for, were not affected by DCD or timing of N. In the second year, 101 kg N ha−1 of unlabeled urea was split applied across the entire experiment. Grain yields averaged 2.07 Mg ha−1 and were not affected by N rate, DCD, or timing of N application from the previous year. Percent recovery of 15N averaged 1.0 and 0.9% in the grain and straw, respectively, or about 10% of the 15N immobilized the year before. Recovery of 15N in the second year was significantly higher in the straw and roots following split‐applied N or fall N plus DCD, compared with following fall N alone. This suggests that nitrification inhibitors can affect N uptake of a second‐year crop by enhancing biological immobilization of fertilizer N.
Cropping Systems Effects on Mycorrhizal Colonization, Early Growth, and Phosphorus Uptake of Corn
Authors: Vivekanandan M. , Fixen P.E.
Published: July 2010

A field study was established in 1986 on a Viborg silty clay loam (fine‐silty, mixed, mesic Pachic Haplustoll) soil in eastern South Dakota. The objectives were to quantify the influence of crop rotation, tillage, and residual P (254 kg P ha−1 applied in fall 1985) on the incidence of vesicular‐arbuscular mycorrhizae (VAM) of corn (Zea mays L.) and to define the relationship between VAM colonization, early growth response to P, and early P uptake of corn. Plant and root samples were collected periodically from plots that varied in tillage and previous crop. Crop rotation and tillage influenced the early growth and P uptake of corn. Large differences in early growth response to P were observed among cropping systems. Average relative growth response as compared with the check during both years ranged from 360% for the moldboard (MP) corn‐fallow rotation to 7% for the ridge‐plant (RP) corn‐soybean (Glycine max [L.] Merr.) rotation. Early dry‐matter production and P uptake in the check plots were highest in the RP corn‐soybean system and lowest in the MP corn‐fallow system. Generally, VAM colonization rates were significantly higher (P ≤ 0.10) in the RP systems than in the MP systems. Considerable reduction in VAM colonization rates were found with P fertilization (P ≤ 0.01) in all cropping systems. An inverse relationship was measured between VAM colonization and relative early growth response to P (Y = 647.0 − 49.4X + 0.97X2; R2 = 0.92; Y = growth response in percent, X = percent root length colonized). Considering early dry‐matter production, P uptake, and mycorrhizal association the RP corn‐soybean system appears to provide a good environment for P nutrition of corn during early vegetative growth.
Manganese Distributions in Acid Soils of the North Carolina Piedmont
Authors: McDaniel P. A. , Buol S. W.
Published: July 2010

Manganese is a dynamic component of soils that can be present in a variety of forms. This study was initiated to examine the distribution of Mn in Ultisols and Alfisols formed in gneisses of the North Carolina Piedmont. Secondary Mn (Mnd) and Fe (Fed) depth distributions were evaluated using a citrate‐bicarbonate‐dithionite extract; the distribution of Mn among organic and various inorganic soil fractions was determined using a sequential‐extraction procedure. Results indicate that accumulation of Mnd is related to interactions between landscape position and associated redox potential (Eh)‐pH environments rather than mineralogy of soil parent material. Spatial relationships between Mnd and Fed within soils reflect Eh‐pH‐potential gradients in these acid systems. Accumulations of secondary Mn occur in well‐drained surface horizons of soils occupying lower lying landscape positions. These accumulations occur in weathered hillslope sediments and are not related to mineralogy of the underlying residuum. As much as 50% of this Mn is associated with the organic‐matter fraction and the inorganic exchange complex. Secondary accumulations of Mn also occur in B/C horizons and saprolite residuum in soils of actively down‐wearing geomorphic positions. Most of this Mn is in the crystalline Mn oxide fraction. Data indicate a significant correlation (P < 0.01) exists between quantities of Mn found in the amorphous, exchangeable, and crystalline Mn oxide fractions.
Spatial Distribution of Soil Heat Flux and Growing Degree Days
Authors: Wolf J. K. , Rogowski A. S.
Published: July 2010

In agricultural areas, groundwater pollution by NO2‐3 from excessive fertilizer, manure, and amendment applications is becoming a serious problem. To control such pollution, assessment of the potentially most critical recharge zones is needed. Spatial parameterization of soil heat flux can delineate areas of high C and N mineralization and help identify such zones. Soil heat‐flux distributions were estimated on a central Pennsylvania farm and surrounding watershed from changes in the optical‐rotation angle of a sucrose solution, water content, and bulk density. The change in rotation angle is a function of soil temperature and occurs during the chemical reaction when sucrose is converted to glucose and fructose. Volumetric soil water content and bulk density were used to compute soil heat capacity. Estimates of soil temperature and heat capacity were combined to produce estimates of soil heat flux and growing degree days at different scales. Their spatial distributions were computed using geostatistical techniques. Measured and derived properties were found to exhibit anisotropic spatial structure related to soil‐forming factors and scale. Land‐use management implications suggest that this method identifies warmer or colder zones as well as areas with high or low C and N mineralization potential on farm and watershed scales.
Interactions of Microorganisms and Soil during Fenamiphos Degradation
Authors: Ou L.‐T.
Published: July 2010

Enhanced degradation of a number of pesticides occurs in soils with a history of previous exposure to the chemical. Little is known, however, about the duration of enhanced degradation after a single field application of a pesticide or the microorganisms responsible for the enhancement. Soil samples collected 2, 3, and 4 yr after one application of the nematicide fenamiphos [ethyl‐3‐methyl‐4‐(methylthio)phenyl (1‐methylethyl) phosphoramidate] at a rate of 4.48 kg ha−1 to an experimental site planted in potato (Solanum tuberosum L.) near Hastings, FL, were used to determine mineralization rates and total‐toxic‐residue (TTR) disappearance rates. Both mineralization rates and TTR disappearance rates in samples collected 2 and 3 yr after field application were enhanced compared with the corresponding control samples. Half‐lives for TTR in soil samples collected 2 and 3 yr after field application of fenamiphos were 22 and 89 d, respectively, while half‐life values for the corresponding control samples were 131 and 130 d. During a 70‐d incubation period, 67.2, 27.8, and 9.8% of applied 14C‐fenamiphos was mineralized in soil samples collected 2, 3, and 4 yr after field application, while 10.8, 11.5, and 9.5% of applied 14C‐fenamiphos in the corresponding control samples was mineralized. Mineralization rates in soil collected 4 yr after field application were the same as in the control sample. Microorganisms capable of degrading fenamiphos could not be isolated from the soils. A mixed bacterial culture derived from soil collected 2 yr after the field application, in the presence of a small amount of this soil, however, did mineralize fenamiphos. Without the small amount of soil, the mixed culture did not mineralize the nematicide.
Determination of the Aromaticity of Humic Substances by X‐Ray Diffraction Analysis
Authors: Schnitzer M. , Kodama H. , Ripmeester J. A.
Published: July 2010

Aromaticity is an important indicator of the origin, stability, and chemical reactivity of soil humic materials. The only method available at the present time for measuring the aromaticity of these materials is 13C nuclear magnetic resonance (NMR), so that there exists a need for an alternate, independent method. With this in mind, we developed a method based on the x‐ray diffraction (XRD) analysis of humic materials. Total areas in XRD patterns are subdivided into areas due to G (aromatic) and γ (aliphatic) bands. The G‐band area, expressed as a percent of the total area, is assumed to be a measure of the aromaticity. The method was tested on 14 natural humic acids, one natural fulvic acid, and one synthetic humic acid. Aromaticities so measured were then compared with aromaticities computed from 13C‐NMR spectra. The agreement between the two methods was acceptable. This establishes the XRD method as a valid alternative to the 13C‐NMR method.
Equations for Estimating the Amount of Nitrogen Mineralized from Crop Residues
Authors: Vigil M. F. , Kissel D. E.
Published: July 2010

The amount of N mineralized or immobilized during the decomposition of a crop residue will influence the amount of N available for crop uptake and will ultimately impact N‐management practices and groundwater quality. The objective of this work was to determine quantitative relationship(s) between a crop residue's chemical properties and the potential net amount of N that would mineralize in a season. Eight experiments (six from the literature and two conducted by the authors) were combined to determine general relationships between net N mineralized and residue chemical characteristics. Regression analysis indicated that 75 and 72% of the variability in the measured amounts of N mineralized in the eight experiments could be explained using either the C/N ratio or the square‐root transformation of N concentration of the residue, respectively. The break point between net N mineralization and net immobilization was calculated to be at a C/N ratio of 40, which corresponds to a N concentration of about 10 g N/kg (assuming residue C is 400 g/kg). Eighty percent of the variability in the amount of N mineralized could be explained by a regression equation that included N and the lignin‐to‐N ratio as independent variables. The fitted equations provide estimates of the maximum amount of N that potentially will mineralize in a season from incorporated crop residues of different N contents.
Soil Genesis Associated with Periglacial Ground Wedges, Laramie Basin, Wyoming
Authors: Munn L. C. , Spackman L. K.
Published: July 2010

Periglacial ground wedges, indicative of former dry permafrost environments during the Pleistocene, occur in the high basins of Wyoming. At a study site in the Laramie Basin in southcentral Wyoming, a comparison was made between a soil developed in a ground wedge and the soil that was host to the wedge. The wedge soil has accumulated clay (315 kg m−2), carbonate (171 kg m−2), and gypsum (155 kg m−2). Both the soils developed in the wedges and the soils in the wedge host are Borollic Natrargids, but the wedge soils are more coarsely textured and have lesser accumulation of carbonate than the host soil. Mineralogy of wedge and host soils is similar, including quartz, calcite, plagioclase, smectite, and illite. Gypsum accumulation is superimposed over carbonate‐ and clay‐accumulation horizons in both soils. The wedges are thought to have been active in pre‐Wisconsin time. Soil genesis in these soils indicates progressive accumulation of clay and carbonate. Gypsum accumulation has apparently accelerated during the Holocene in these soils.
Organic Polymers' Effect on Soil Shear Strength and Detachment by Single Raindrops
Authors: Barry P. V. , Turco R. F. , Stott D. E. , Bradford J. M.
Published: July 2010

Organic matter is known to influence soil erodibility, but little work has been done to determine the effects of specific organics on erosional processes. Our study was designed to assess the influence of organic polymers known to increase aggregate stability on nearsurface soil shear strength and soil detachment by single raindrops during time. An index of shear strength was obtained with a Swedish fall‐cone device and detachment was based on soil loss in the splash of a single raindrop. Two soils with similar texture but differing organic‐matter contents were used. Amendments studied were polyvinyl alcohol (PVA), an experimental starch graft polymer (SGP), and a mixture of a microbial polysaccharide rich in levans and other cellular material (LEV). The amendments initially induced significant increases in soil shear strength ranging from 1.5 to 5.5 times greater than untreated soil. The pattern of change of shear strength during time was nearly identical for all treatments, and was attributed to an aging process. Significant changes induced by the amendments in the amount of soil detached varied with time. The patterns of change during time seen in the PVA‐amended soils were similar to the controls, while the LEV and SGP response curves differed. In conjunction with decomposition‐rate data, it was concluded that the transformation products formed during the decomposition of the LEV and SGP were causing temporal changes in the soil that the Swedish fall‐cone device was insensitive to, but influenced the response of the soil to raindrop detachment.
Time Domain Reflectometry Measurements of Water Content and Electrical Conductivity of Layered Soil Columns
Authors: Nadler A. , Dasberg S. , Lapid I.
Published: July 2010

The major argument for measuring the soil salt concentration and water content at the same position is their high correlation and spatial variability. Time domain reflectometry (TDR) was used for simultaneous measurement of soil water content, θ (derived from the soil dielectric constant ε), and bulk soil electrical conductivity, σa (from the attenuation of a transmitted pulse), for uniform and layered soil profiles in the laboratory. The purpose of the study was to test the different concepts of travel time and attenuation by using independent estimates of θ and σa. Both parallel (two‐rod) and simulated coaxial (three‐rod) probes resulted in essentially the same ε. The three‐rod probe measurements were easier to interpret and did not necessitate an impedance‐matching transformer. The TDR measurements of θ for layered profiles were not always accurate, especially when wet soil was overlying dry soil, due to erroneous interpretation of the TDR trace. In this case, the pulse travel time should be measured at the inflection point, which is sometimes difficult to identify, and not at the minimum of the TDR trace. This study reports a new method of calculating σa, which is based on a direct measurement of the transmission‐line load by TDR. This new method, which is simpler than the previous ones and independent of multiple reflections, was found to correlate better than the previously published methods with another, independent method for σa measurement (four‐electrode technique).
Mathematical Analysis of One‐Dimensional Solute Transport in a Layered Soil Profile
Authors: Leij Feike J. , van Genuchten M. Th. , Dane J. H.
Published: July 2010

Solute transport studies involving layered media are important for investigating how restricting layers affect rates of solute migration in the soil profile and, more generally, for examining the influence of soil heterogeneity on solute transport. Analytical solutions of the one‐dimensional advection‐dispersion equation (ADE) were obtained with the help of Laplace transforms for transport in a two‐layered soil profile. Assuming that the layers are, in effect, semi‐infinite, solutions were obtained for first‐type (constant concentration) and third‐type (constant flux) conditions at both the inlet boundary and the interface of the two layers. Concentration profiles were also obtained for a finite first layer via numerical inversion of the Laplace transform solution, using a third‐type condition at the inlet, and, simultaneously, a first‐ and third‐type condition at the interface. Volume‐averaged or resident‐type concentrations were used in all cases. First‐type conditions did not meet our criterion of mass conservation, whereas third‐type conditions caused discontinuities in the concentration at the interfaces of layers with differing transport parameters. The concentration at the interface was found to be continuous, and no mass‐balance error occurred, when first‐ and third‐type conditions were imposed simultaneously at the interface. Serveral example calculations show the effect of soil layering on solute transport in a one‐dimensional soil profile.
Weathering of a Mica by Roots and Rhizospheric Microorganisms of Pine
Authors: Leyval C. , Berthelin J.
Published: July 2010

The weathering of minerals within the rhizosphere has been demonstrated many times; however, only a few studies have been concerned directly with root‐microorganism interactions. This study was conducted to determine the influence of symbiotic (mycorrhizal) and nonsymbiotic microorganisms on rhizospheric weathering of mica. A lysimetric experiment was performed in a greenhouse to study the weathering of a mica (phlogopite) by roots and rhizospheric microorganisms of pine (Pinus sylvestris L.). Pine roots were inoculated or not with an acid‐producing rhizobacteria (Agrobacterium sp.) and an ectomycorrhizal fungus (Laccaria laccata [Scop.: Fr.] Berk. and Broome). In noninoculated pine, rhizospheric phlogopite particles were smaller than control phlogopite particles and partially transformed into vermiculite. Inoculation of pine roots with the bacteria increased cation‐exchange capacity and losses of K from the mica flakes. Losses were attributed to increased production of organic acids in the rhizosphere by the bacteria. Fewer losses of K were observed in pine mycorrhizosphere as monitored by x‐ray diffraction. Electron microscopic observation with a microprobe, however, demonstrated that K losses were greater for the phlogopite particles closely attached to the mycorrhizae. The mycorrhizal effect was attributed to an increase of exchange surface area, rather than to an increase in acidification. Dual inoculation significantly promoted mycorrhizal infection and phlogopite cation‐exchange capacity, compared with inoculation with the bacterium or the fungus alone.