bluuebunny/crossref_metadata_2025 huggingface dataset:
Potassium‐Calcium and Sodium‐Calcium Exchange on Kaolinite and Kaolinitic Soils
Authors: Levy G. J. , van der Watt H. v. H. , Shainberg I. , du Plessis H. M.
Published: July 2010

Potassium‐Ca and Na‐Ca exchange isotherms were obtained for two kaolinite samples and two kaolinitic soils (Hutton and Avalon forms). The Gapon, Vanselow, and Gaines‐Thomas corrected selectivity coefficients were usually greater for K‐Ca exchange than for Na‐Ca exchange, as was expected. The exchange isotherms and selectivity coefficients suggested a preference for K relative to Ca on all four exchangers. The contribution of micaceous impurities to the observed high affinity for K was taken into consideration, by reasoning that exchange sites with high affinity for K resulting from these impurities are first saturated with K [i.e., at low exchangeable potassium percentage (EPP) values]. It is suggested that the high charge density of kaolinite enhances K dehydration, resulting in a high affinity of kaolinite per se for K.
A Rapid Method to Determine Total Phosphorus in Soils
Authors: Bowman R. A.
Published: July 2010

Present methods for extracting total phosphorus (P) from soil samples are tedious and time consuming. A rapid and precise extraction procedure was developed in which sequential additions of concentrated H2SO3, H2O2, and HF were made to soil samples. This was followed by 10 min of heating (≃ 423 K) to eliminate excess peroxide. The entire procedure required about 30 min. The proposed method was compared to standard Na2CO3‐fusion and HClO4‐extraction methods. Almost equal amounts of P were extracted by the proposed and Na2CO3‐fusion methods. About 7% less P was found in HClO4 extracts. In the proposed method, treatment with H2O2 was used to oxidize P associated with the organic carbon. Treatment with HF was necessary to solubilize P associated with the aluminosilicate minerals found in sandy soils that are low in organic C. The proposed method is not only more rapid than those previously used, but is easily performed at minimal cost with simple laboratory equipment. It is especially useful for analyzing small numbers of soil samples, and should be useful to evaluate P dynamics in sediment transport (erosion) studies, and in soil formation and degradation studies.
Plant and Microbial Responses to Sorghum‐Soybean Cropping Systems and Fertility Management
Authors: Roder W. , Mason S. C. , Clegg M. D. , Kniep K. R. , Doran J. W.
Published: July 2010

Monoculture production of soybeans (Glycine max (L.) Merr.) and grain sorghum (Sorghum bicolor (L.) Moench) generally results in declining grain yields. To better understand biological and chemical interactions causing yield declines with continuous cropping, microbial biomass, crop root dry weight, soil organic matter, and total N content were measured in a cropping system experiment on a Sharpsburg silty clay loam (Typic Argiudoll). The cropping treatments included continuous soybeans, continuous sorghum, and sorghum‐soybean or soybean‐sorghum rotations. These treatments were initiated 5 y prior to taking the reported measurements. Fertilizer treatments consisted of no amendment (control), N (45 kg ha−1 on soybean plots and 90 kg ha−1 on sorghum plots), and manure applied at 15.8 Mg dry matter ha−1 yr−1. In summer 1986, the microbial biomass C for the 0–30‐cm layer of soil averaged across fertility treatments was 1.37, 1.49, 1.43, and 1.58 Mg ha−1 for continuous soybeans, rotated soybeans, rotated sorghum and continuous sorghum, respectively. Soil microbial biomass C and soil organic matter contents for manured treatments were 11 to 14% and 6 to 16% greater, respectively than those of unfertilized controls. Root dry weights for the 0–30‐cm depth were 26 and 77% higher for soybeans and sorghum if the previous crop was sorghum instead of soybeans. In summer 1986, microbial biomass in the 0–15‐cm depth was correlated with root density and water‐filled pore space in sorghum plots and with bulk density in soybean plots. Previous crop, present crop, and fertilizer treatment affected dry matter partitioning between above‐ and below‐ground plant parts and microbial biomass. With sorghum as a previous crop, a higher proportion of the total production occurred below ground as roots and microbial biomass.
Nitrogen Use Efficiency and Nitrogen Budget for Conservation Tilled Wheat
Authors: Sharpe R. R. , Harper L. A. , Giddens J. E. , Langdale G. W.
Published: July 2010

The understanding of nitrogen (N) cycling in the soil‐plant‐atmosphere is necessary to maximize N use efficiency and to develop N budgets for wheat (Triticum aestivum L.) production. The objectives of this study were to determine the relative uptake rates of residual soil N and fertilizer N in conservation tilled winter wheat. These data were combined with soil mineralization and aerial NH3 flux data to present a N budget for the soil‐plant‐atmosphere system. Fertilizer N uptake was determined using ammonium nitrate (15NH415NO3) tagged with 3.78 atomic % 15N. The buried polyethylene bag technique was used to determine N mineralization. Fertilizer N uptake and N mineralization rates were determined four times during the spring growing season. Amounts of NH4 and NO3 in the top 0‐ to 300‐mm soil layers were determined biweekly. Fertilizer N levels in the surface to 75‐mm soil layers decreased rapidly due to plant uptake and immobilization. Of the N fertilizer utilized by the plants, 61% was absorbed in the first 28 d after application. During early vegetative growth stages (Feekes stages 3–5), fertilizer N uptake was 1.33 kg ha−1 d−1. During the elongation stage (Feekes stages 5–8), however, fertilizer N was immobilized and uptake of fertilizer N ceased. This resulted in a period of soil N insufficiency which was associated with atmospheric NH3 influx to the plants. After 4 to 5 wk, mineralization of fertilizer N became apparent and fertilizer N uptake rates increased until harvest. Influx of atmospheric N was small but total NH3 efflux from the soil‐plant system was 15.5 kg N ha−1. About 21% of the spring applied fertilizer N was lost through NH3 volatilization and losses of this magnitude need to be considered in N balance studies. Placement of fertilizer N below the surface soil layer may decrease immobilization and increase plant uptake of N.
Nature of Cementing Materials in Ortstein Horizons of Selected Florida Spodosols: I. Constituents of Cementing Materials
Authors: Lee F. Y. , Yuan T. L. , Carlisle V. W.
Published: July 2010

Five pairs of ortstein and nonortstein spodic horizons of Haplaquods were studied in an attempt to identify the nature of cementing materials. The ortstein horizons had significantly larger amounts of dithionite‐citrate‐extractable Al, significantly higher silt plus clay contents, and significantly higher bulk density values than did nonortstein spodic horizons. Moist and air‐dried ortstein samples had similar shear strengths, but the strength significantly decreased by 14 to 82% for oven‐dried samples. The strength had a significant correlation with the dithionite‐citrate‐extractable Al. Energy‐dispersive spectra showed that Si and Al were major constituents of both ortstein and nonortstein samples. Ortstein samples had stronger Al peaks, however. More cementing materials were observed in the ortstein than nonortstein samples in scanning electron micrographs. These cementing materials consisted of gel‐like substances and fine particles. Cracks in dry gel‐like substances between coarse particles were also observed. Electron‐dot pictures revealed that the gel‐like substances were Al‐dominated.
Effects of Fallow Length on Organic Carbon and Soil Fabric of Some Tropical Udults
Authors: Wadsworth G. , Southard R. J. , Singer M. J.
Published: July 2010

Soil samples representing eight different ages of forest regrowth (0–50 yr following clearing) from fields in a pineapple slash and burn agricultural system were collected for organic carbon (OC) analysis and study of soil physical properties. The OC content of the surface soils decreased for 10 yr following clearing, then gradually increased close to the original level after 50 yr. Major micromorphological differences were apparent in surface horizons as a function of OC content. Soils with higher OC contents were more strongly aggregated and have more visible porosity than those with less OC. Bulk density and OC are statistically, significantly, negatively correlated (r2 = 0.64, p < 0.05), for combined data from all four representative pedons. Particle size distribution had a large effect on subsoil micromorphology. Argillic horizon fabric within the finest grained pedon was mostly mosepic with few discrete cutans suggesting that in situ weathering is a dominant clay forming process. Coarser textured pedons had well‐oriented argillans in the skelvosepic to vo‐masepic fabric of the argillic horizons. The short‐cycle slash and burn methods studied here have no observable effects on the micromorphology of the argillic horizons.
Polymer and Water Quality Effects on Flocculation of Montmorillonite
Authors: Aly Saleh M. , Letey J.
Published: July 2010

Wyoming Na‐montmorillonite (SWy‐1) was equilibrated with two synthesized waters, representing Friant‐Kern Canal or a typical well water of San Joaquin Valley (EC 0.05 and 0.7 dS m−1, respectively). Adsorption isotherms and flocculation patterns of the clay with three anionic and one nonionic polyacrylamide polymers and cationic, nonionic and anionic derivatized guar polymers, were observed. Polymer solutions of concentrations 0, 5, 10, 20, 50, and 100 mg L−1 were prepared and clay was added at a concentration of 1 g L−1. The test tubes were shaken and then periodically photographed to record floc formation and settling. Adsorption was in the general order: cationic > nonionic > anionic with the exception of the nonionic guar which was adsorbed about equally as the cationic guar. Adsorption of anionic polymers was greater from well water than canal water, whereas the opposite was true for the cationic polymer. Significant polymer water quality interactions on flocculation were observed. Anionic polymers promoted flocculation in the well water for polymer concentrations ≥ 5 mg L−1, but enhanced clay suspension stability in canal water. Floc volume increased with increasing cationic and nonionic polymer adsorption, whereas changes in floc volume were insignificant with anionic polymers. An optimal polymer concentration was found with well water. Flocculation with cationic polymer was attributed to charge neutralization, whereas flocculation with anionic polymers was explained by bridging and osmotic attraction.
Nonexchangeable Potassium Associated with Hydroxy‐Interlayered Vermiculite from Coastal Plain Soils
Authors: Harris W. G. , Hollien K. A. , Yuan T. L. , Bates S. R. , Acree W. A.
Published: July 2010

Hydroxy‐interlayered vermiculite (HIV) from a Quartzipsamment, a Haplaquod, and a Paleudult from Florida was studied to determine levels of nonexchangeable K associated with this mineral. Mineralogy was characterized by x‐ray diffractometry (XRD) and thermal analysis. A scanning electron microscope equipped with an energy‐dispersive x‐ray system was used to examine morphology of silt‐sized phyllosilicate grains and to qualitatively determine elements present. An electron microprobe equipped with a wavelength‐dispersive x‐ray system was used to obtain K x‐ray images and determine elemental oxide compositions of 82 randomly selected grains. Total K was determined for bulk samples using Na2CO3 fusion. Extractable K by double acid, HNO3, and H2SO4 was determined for clay fractions. Results confirmed that most phyllosilicate grains from quartz‐ and HIV‐dominated silt fractions of all samples contained sufficient K to be detected in K x‐ray dot images, though little or no mica was detectable by XRD. Mean K2O contents for mediumsilt grains from the Quartzipsamment, Haplaquod, and Paleudult were 2.3, 4.1, and 5.6%, respectively. Fine‐silt grains averaged 1.3, 1.3, and 2.3%, respectively, despite lack of infinite thickness. High K2O values, mica‐like grain morphology, and relatively large size of these grains suggest that they are transformation products of mica. Acid extracts from the clay also contained detectable levels of K. Nonexchangeable K may reside within grains as small occluded mica zones with insufficient periodicity for XRD detection, or could be retained in the 1.4‐nm structure. Results suggest a more direct transformation of mica to HIV rather than one involving a significant vermiculite intermediate.
Estimating Spatial Patterns in Water Content, Matric Suction, and Hydraulic Conductivity
Authors: Mulla D. J.
Published: July 2010

A relatively rapid method for surveying and estimating field‐scale variability of water content, hydraulic conductivity, and matric suction using geostatistics is described. Two 660‐m long transects located 8 km west of Steptoe, WA were intensively sampled at 5‐m spacings for surface temperature. Soil samples were also collected to a depth of 12 cm at spacings of 20 m, and these were analyzed for sand, clay, and soil water content. The spatial variability in each property was described using spherical semivariograms. Kriging was used to estimate spatial patterns in clay and sand content along each transect at 5‐m spacings. Spherical cross‐semivariograms of surface temperature and water content were used along with cokriging techniques to estimate water content at 5‐m spacings. The geostatistical estimates of spatial patterns in water content, clay content, and sand content were used for texture‐based estimates of matric suction and hydraulic conductivity at 5‐m spacings along both transects. A comparison of texture‐based and laboratory‐based estimates of matric suction showed that although the two estimators gave similar spatial patterns and means, they had significantly different standard deviations. If it is important for a researcher to make quantitative predictions of matric suction, laboratory‐based estimates would be better than the texture‐based estimates. On the other hand, if what is important is estimating spatial patterns in matric suction, the texture‐based estimator would be acceptable.
A Comparison of Gas Diffusivity Models for Unsaturated Porous Media
Authors: Collin Marie , Rasmuson Anders
Published: July 2010

The effective gas diffusivity in a porous medium decreases rapidly with increasing water content. Comparisons are made between experimental diffusivity data for different materials at various moisture contents, and estimation methods from the literature. The estimation methods proposed by R.J. Millington and R.C. Shearer in 1971 give the best predictions of the effective diffusivity. The methods are extended here to account for the contribution of diffusion in the water‐filled pores. The method for aggregated media should be used for undisturbed clayey soils, and the method for nonaggregated media may be used for sandy soils and for other materials that are not aggregated, e.g., laboratory packed clayey soils. The experimental data show that very low effective diffusivities may be obtained in practice in soils with high moisture content.
Solubility of Barium Arsenate
Authors: Essington M. E.
Published: July 2010

Current thermodynamic data suggest barium arsenate [Ba3(AsO4)2(c)] to be a highly stable phase. However, sufficient evidence is available to question the validity of the current data. In order to determine the solubility (pKsp) and calculate the standard free energy of formation (ΔG°f) of Ba3(AsO4)2(c), an equilbrium solubility study was conducted. The equilibrium experiments were carried out under three different ionic strength conditions for reaction times up to 45 d. Equilibrium was approached from both undersaturated and supersaturated initial conditions. The pKsp for the dissolution of Ba3(AsO4)2(c) was calculated to be 21.62. Correspondingly, a ΔG°f of − 3101.2 ± 2.0 kJ mol−1 was calculated. This value is 166.9 kJ mol−1 more positive than the current literature value. Reevaluation of the solubility data from a previous work suggests that the pKsp for the dissolution of BaHAsO4 · H2O(c) is 24.64 and the corresponding ΔG°f is − 1587.0 ± 2.5 kJ mol−1.
Adsorption of Thiram and Dimethoate on Almeria Soils
Authors: Valverde‐García A. , González‐Pradas E. , Villafranca‐Sánchez M. , del Rey‐Bueno F. , García‐Rodriguez A.
Published: July 2010

The adsorption process of thiram and dimethoate on Almería (East‐Andalucía, Spain) soils from aqueous solution at 30 °C has been studied. The adsorption isotherms may be classified as L type of the Giles classification. The Kf values (Freundlich equation) vary between 4.81 to 13.73 for fungicide thiram (tetramethylthiuram disulfide) and between 1.06 to 8.95 for insecticide dimethoate [O,O dimethyl S‐(N methylcarbamoylmethyl) phosphorodithioate] depending on the soil type. In relation to the correlations between adsorption parameters and soil properties, the adsorption process of thiram seems be conditioned by the soil organic matter content whereas the adsorption of dimethoate is fundamentally conditioned by specific surface area and by cation exchange capacity.
Sulfur Supplying Capacity of Some Missouri Soils
Authors: Hanson R. G. , Haron K. B.
Published: July 2010

Confirmed S deficiencies on some Missouri soils necessitated a study to determine their capacities to supply S to plants. Surface (0–30 cm) and subsurface (30–60 cm) depths of two Alfisols (Bosket loamy fine sand, Dubbs fine loamy sand) and one Entisol (Malden fine sand) from southeastern Missouri, and surface depths (0–30 cm) of an Alfisol (Kennebec silty clay loam) and Mollisol (Mexico silt loam) from northern Missouri were used. The soil properties measured included pH, organic matter, cation exchange capacity (CEC), Bray & Kurtz P1 (BK1) and P2 (BK2), labile SO4 (LAS), SO4 buffer index (SBI), extractable SO4 (500 mg P L−1 in 2 M HOAc), and soil texture (sand, silt, and clay). Soils were amended with 0 and 22 mg S kg−1, and corn (Zea mays L., hybrid DeKalb 1189TX) dry matter yield and S uptake were measured through five 35‐d intensive cropping cycles. There was little S uptake from unamended Bosket (0–30 and 30–60 cm), Dubbs (0–30 and 30–60 cm), and Malden (0–30 and 30–60 cm) zero‐S soils after the second cropping cycle. The Kennebec and Mexico soils exhibited a plant growth response during the second and fifth cropping cycles, respectively. The significant increase in yield response to S fertilization suggests the Dubbs (0–30 and 30–60 cm), Malden (0–30 and 30–60 cm), and Bosket (30–60 cm) to have inadequate capacities to supply S to plants. Of these three southeastern Missouri soils, the Bosket 30‐ to 60‐cm depths yielded the highest plant S uptake. This suggests that soils of this region with similar surface textures may possess differences in total plant available S when subsoil available S is included in this total. The SO4 buffering index (SBI) correlated negatively with BK1 and BK2 available P suggesting that high or excess P fertilization would decrease the capacity of these soils to adsorb SO4. With the 22 mg S kg−1 treatment, using total SO4 (TSO4 = extractable SO4 + added SO4) as the independent variable, S uptake was not dependent on this TSO4 quantity during the first 35‐d cropping period. For the 0‐ to 70‐d cropping, S uptake was significantly dependent on the TSO4. The relationship (r = 0.99) between the extractable SO4 and SO4 labile pool (LAS), and their relationships to plant S uptake during the 0 to 35 d (r = 0.98, r = 0.97) and cumulative 0 to 70 d (r = 0.95, r = 0.95) cropping periods indicates that SO4 extracted with 500 mg P L−1 in 2 M HOAc to be a good estimate of plant available SO4‐S. The relationships (r = 0.84 for 0–35 d and r = 0.90 for 0–70 d) between CEC and plants S uptake suggests the need to investigate the potential mechanism of CEC to SO4 availability and other soil properties that may be correlated to CEC.
Comparison of Kinetic Models for Describing Net Sulfur and Nitrogen Mineralization
Authors: Ellert B. H. , Bettany J. R.
Published: July 2010

Net S and N mineralization in forested and cultivated Typic Cryoboralfic soils was monitored over 37 wk in a laboratory incubation experiment with intermittent leaching. Patterns of net S and N release depended on the management histories of the soils. Several kinetic models were evaluated for the ability to accommodate continuously decreasing rates, a large initial flush of mineralization, a mineralization lag within the first 13 wk of incubation, or a constant rate of release near the end of incubation. Mineralization in the forest E horizon was best described by a modified first‐order model with contributions from an easily mineralizable pool to account for an initial flush of S mineralization. Initial flushes of mineralization could be described by two simultaneous first‐order reactions, but the additional complexity of the model was unjustified, because contributions from the rapidly mineralizing pool did not extend beyond the first incubation interval. Soils from a field cultivated since 1905, a recently cleared field and, the organic layer from a native forest had fluctuating mineralization rates which appeared as lags in the cumulative amounts of inorganic element released over time. The lagged mineralization patterns were best described by consecutive reaction or Gompertz models. The Guggenheim method of fitting the first‐order model was demonstrated as an alternative to nonlinear regression. Fitting nonlinear kinetic models to incremental data from each incubation interval was superior to conventional approaches which use cumulative data obtained by summing the incremental observations. Information from net mineralization patterns was maximized by improving the methods of data analysis.
Characterization of a Pimple Mound‐Intermound Soil Complex in the Gulf Coast Prairie Region of Texas
Authors: Carty D. J. , Dixon J. B. , Wilding L.P. , Turner F.T.
Published: July 2010

Natural mound and intermound soil pedons were characterized to investigate native mound‐intermound formation and soil properties that may explain unfavorable plant growth that has been observed on sites of truncated mounds. Subrounded mounds average 26‐m apart, 15 m in diam., and 0.5 m in local relief. Mound soil has a thick silt loam A horizon, silt loam E, B/E, and BE horizons, and thick, weakly expressed Bt (argillic) horizons of silt loam to clay loam texture. Upper mound horizons are acid, and the lower Bt horizon is neutral to calcareous. Calcareous intermound soil, originally mapped as Morey (fine‐silty, mixed, thermic Typic Argiaquolls) silt loam, has a silt loam A horizon above clay loam cambic and calcic horizons. Better infiltration and drainage in the mound contrasts with very slow runoff and poor infiltration and drainage in the intermound. Mound and intermound mineralogy is similar, with mainly quartz in coarse silt and very fine sand separates, kaolinite and quartz in coarse clay, and smectite and kaolinite in the fine clay fractions. Carbonate, base saturation, pH, and illuviation argillan distributions suggest predominantly downward water flow with desiccation and rewetting cycles in the mound soil, contrasted with more prolonged periods of wetness in the intermound soil. Particle size and Ti and Zr distributions indicate a definite parent material break above the mound Bt horizon, but no clear break in the intermound. Properties of the loamy mound soil investigated are consistent with a mechanism of local wind or water deposition around clumps of vegetation. Soil surface exposed by mound truncation is a poor plant growth medium because it consists of acid, silty, slightly buffered material with low organic matter content and weak structure.
Exploitation of Soil Potassium in Layered Profiles by Root Systems of Cotton and Barley
Authors: Gulick S. H. , Cassman K. G. , Grattan S. R.
Published: July 2010

On vermiculitic soils of the San Joaquin Valley, cotton (Gossypium hirsutum L.) often responds to K fertilization where other annual crops do not. These soils have markedly higher available K in surface soil than in subsoil. A pot study was conducted to compare rooting patterns, K uptake, and dry matter production of cotton and barley (Hordeum vulgare L.) in soil profiles with layered K availability. Topsoil (0.15 cmolc K kg−1) was layered to each of six depths above subsoil (0.09 cmolc K kg−1) in 17‐L pots with a total soil depth of 45 cm in all treatments. Two irrigation regimes were imposed and nutrients other than K were adequately supplied. For both crops, plant dry matter and K uptake increased linearly with increased topsoil depth but K uptake per unit increase in topsoil depth was 6.5‐ and 3.6‐fold greater by barley than for cotton with frequent and infrequent irrigation, respectively. Increased K uptake per unit increase in topsoil depth reflected coincident root and K distribution: barley root length density (RLD) was 2.7 times greater than RLD of cotton in topsoil layers but little different in subsoil layers. Poor exploitation of topsoil layers by the cotton root system was attributed to greater sensitivity to low soil water potential. A root system with little compensatory root development in the surface soil when the subsoil is low in nutrients may limit K uptake and crop productivity on layered soils in the San Joaquin Valley and may require management systems designed to promote more congruent root and nutrient distribution.
Contribution of Ferrimagnetic Minerals to Oxalate‐ and Dithionite‐Extractable Iron
Authors: Fine P. , Singer M. J.
Published: July 2010

Magnetic removal of magnetite particles to minimize Fe contribution from a well crystallized iron oxide to the acid ammonium oxalate (AAO) extractable iron (Feo) has been recommended as a pretreatment in chronosequence studies. Samples from two soil chronosequences in California were examined to determine the efficacy of using a hand magnet to remove magnetic particles from soils, and sediments. Magnetic susceptibility (χ) was used as a measure of treatment effect. Samples from 74 horizons retained 74 ± 20% of their original (χ) after treatment with a small hand‐held magnet. Clay and silt‐sized ferrimagnetic particles, which were responsible for 4 to 91% of the soils' χ, were not removed from the samples. Also sand‐sized ferrimagnetics could not be fully removed. Ferrimagnetics were more successfully removed from beach sand deposits. These retained only 14 ± 7% of their χ value. The AAO extraction of 31 magnetically depleted soil samples from typical soil horizons lost an additional 31 to 95% of their residual susceptibility, mostly as maghemite. The retention of a greater fraction of the ferrimagnetics within the soils, and their contribution to the Feo, proved the magnetic cleaning technique to be neither quantitative nor systematic. Magnetite was more resistant than maghemite to AAO. Magnetite was also fully resistant to the citrate‐bicarbonate‐dithionite (CBD) extractant whereas authigenic soil maghemite was completely dissolved in CBD. Magnetic monitoring of AAO‐ and CBD‐treated soils offers some insight into the nature and distribution of the ferrimagnetics in the soil profile.
Atmospheric Deposition and Ionic Concentrations in Forest Soils of Isle Royale National Park, Michigan
Authors: Stottlemyer Robert , Hanson David G.
Published: July 2010

A 64‐wk study of throughfall and soil solution was conducted on five ecosystem strata in Isle Royale National Park, MI, to examine the fate of atmospheric ionic inputs in mature boreal conifer and hardwood forests. Volume‐weighted pH of bulk precipitation was 4.65. Weighted bulk throughfall pH was 4.6 under spruce [Picea glauca (Muench) A. Voss] and 5.2 under aspen (Populus tremuloides Michaux)‐birch (Betula papyrifera Marsh). The forest canopy significantly increased the concentrations of Ca2+, Mg2+, and K+ in throughfall, and decreased the concentration in H+ beneath aspenbirch. Relative to precipitation, concentrations of Ca2+, Mg2+, Na+, and SO2‐4 significantly increased in soil solution of both forest types while NO‐3 decreased. Within the soil ecosystem, K+, NO‐3, and H+ were strongly conserved. Concentration of soil solution SO2‐4 is higher under conifers, and its flux two‐ to three‐fold greater. This suggests the possibility that boreal conifer forests may be more susceptible to cation leaching by mobile anions as SO2‐4 from atmospheric inputs.
The Monophase Model for Magnesium‐Saturated Montmorillonite
Authors: Kittrick J. A. , Peryea F. J.
Published: July 2010

Solubility data for Belle Fourche montmorillonite plotted on 2pH — pMg2+ vs. pSi (OH)04 axes, demonstrate that the monophase model can accurately represent smectite formulas in hydrolysis reactions. The smectite was equilibrated with gibbsite and goethite over a pH range of 3.26 to 8.16. Equilibration was from both undersaturation and supersaturation with regard to Si(OH)04, H+, and Mg2+. When the composition of the smectite phase actually controlling sample solubility was accurately known, experimental and predicted solubility results agreed within experimental error. Such favorable circumstances may be rare, but when they occur they show that metastable equilibria can be determined for complex aluminosilicates.
Potential Agronomic Value of Calcium in Some Phosphate Rocks from South America and West Africa
Authors: Hellums D. T. , Chien S. H. , Touchton J. T.
Published: July 2010

Phosphate rock (PR) has been used for decades as a P fertilizer for plants. Apatite is a basic P mineral that could have agronomic value as a source of Ca. Little information is available in literature on this possibility, however. A greenhouse experiment (6 wk) was conducted to compare the Ca value of six PRs (Bahia Inglesa, Chile; Bayovar, Peru; Capinota, Bolivia; Tilemsi Valley, Mali; Tahoua, Niger; and Hahotoe, Togo) with respect to CaCO3. The soil used was an acid (pH 4.5) Bladen sandy loam (Typic Albaquult). Calcium was applied at rates of 0, 200, 400, and 800 mg kg−1. All treatments received 400 mg P kg−1 as KH2PO4 so that P was not a limiting factor on plant (maize) growth. In general, the effectiveness of Ca response by maize to various PRs followed the order of the PRs' reactivity except in the case of Capinota PR which had a substantial amount of free carbonates. Dry‐matter yield, Ca uptake, and soil exchangeable Ca increased with increasing Ca rates from the various Ca sources. The relative agronomic effectiveness (RAE) of various PRs with respect to CaCO3 (100%) in terms of increasing dry‐matter yield and Ca uptake ranged from 28 to 88% and from 8 to 58%, respectively. The results showed that PRs with medium or high reactivity have potential Ca value, in addition to their use as a P source, when directly applied to acid soils.
Fate of Subsurface‐Banded and Broadcast Nitrogen Applied to Tall Fescue
Authors: Raczkowski C. W. , Kissel D. E.
Published: July 2010

The purpose of this study was to determine why N uptake and forage production by tall fescue (Festuca arundinacea Schreb.) in southeastern Kansas are greater from subsurface‐banded (knifed) than from broadcast N applications. The fate of urea N fertilizer applied to tall fescue either broadcast or banded in 1982 was determined using a urea ammonium nitrate (UAN) solution containing 15N tagged urea and measuring various components of the N balance. Plant uptake of residual urea N was measured during 1983. In 1982, 62% of the banded urea N was recovered in harvested forage, whereas only 40% was recovered in the broadcast treatment. Tagged N remaining in the soil as residual N at the end of 1982 amounted to 40 and 45% for broadcast and band treatments, respectively. Most of this residual N was not available to plants in 1983 since only 1.4 kg fertilizer N ha−1 (5–6% of the residual N) was recovered in the forage. About 1% of the banded N was unaccounted for, indicating that gaseous losses (denitrification and ammonia volatilization) were about 1% of the applied urea N, whereas 23% of the broadcast urea N was unaccounted for, indicating probable significant gaseous losses. These results suggest that the improved efficiency of knifed N over broadcast N observed in southeastern Kansas may be due to reduced gaseous N losses.
Characterization of Garnets in a Typic Cryoboralf (Gray Luvisol) from Saskatchewan, Canada
Authors: Ghabru S. K. , Mermut A. R. , St. Arnaud R. J.
Published: July 2010

Garnets separated from the 250‐ to 2000‐µm sand fractions of a Typic Cryoboralf (Orthic Gray Luvisol) and beach sands by a liquid magnetic separator, heavy liquid, and an optical microscope were used to study to composition, surface morphology, and distribution with regard to garnet weathering in a present day Boreal environment. Garnets constituted 0.2 to 0.3% of the 250‐ to 2000‐µm sand fractions and 16 to 29% of the heavy mineral fractions in the profile. The sand garnet/total soil quartz ratios for soil horizons were relatively constant, ranging between 3 × 10−3 to 4 × 10−3 within the profile. There were no striking differences in weathering among the garnets within the profile or between the soil and lake garnets, suggesting very limited pedogenic weathering since the last deglaciation of the area. The pits that were attributed to dissolution were likely produced by ancient weathering. Despite the high Fe content, and evident surface weathering that had taken place before the last glaciation of the area, it is concluded that these garnets are highly resistant to chemical weathering in present Boreal soils. The association of diatoms with soil and lake garnets suggests that the parent material is of lacustrine origin. Light pink and dark pink garnets were the two varieties present. X‐ray diffraction and chemical analyses revealed their composition was close to the end member almandine. Scanning electron microscopic studies showed extensive evidence of crescentic and several other morphological pits in all the samples. Different type of hillocks were also present, but they were less frequent than the pits. The type of pits and hillocks varied from grain to grain and also within individual grain surfaces. Limited occurrence of vein‐like poorly crystalline tubules were observed in the primary fissures of some garnet grains.
Prediction of Cadmium Complexation in Solution and Adsorption to Montmorillonite
Authors: Hirsch D. , Nir S. , Banin A.
Published: July 2010

Effects of inorganic complexation in solution, ionic strength, and clay concentration on Cd adsorption to montmorillonite were investigated. Increased ionic strength decreases Cd adsorption. The presence of a complexing anion such as Cl‐ inhibits Cd adsorption. When the complexing anion was HCO‐3, disappearance of Cd from equilibrium solution was enhanced compared to the case where the anion was ClO‐4, which does not form complexes with Cd. The explanation of the latter phenomenon is still incomplete, the two possibilities being either strong binding to the clay of the complex CdHCO+3, or precipitation of otavite (CdCO3). Raising clay concentration enhances Cd adsorption. A model that predicts cation binding and cation exchange in clay suspensions and calculates the surface potential, the concentrations of the species bound to the clay surface, in the double layer and in the equilibrium solution, was coupled with a subroutine to calculate complexation reactions in solution. Agreement between observed and calculated values of adsorbed Cd was fairly good. The binding coefficients that best fit the data are 1, 10, and 30 for Na+, Cd2+, and CdCl+, respectively.
Infection Unit Method of Vesicular‐Arbuscular Mycorrhizal Propagule Determination
Authors: Franson Raymond L. , Bethlenfalvay Gabor J.
Published: July 2010

A method is presented for quantifying infectivity of vesicular‐arbuscular mycorrhizal (VAM) fungal inocula by directly counting infection units in roots. Inocula of five isolates of VAM fungi [Glomus etunicatum Becker and Gerd., Glomus pallidum Hall, and Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe from California, Florida and Nevada] were assessed. Sorghum bicolor L. was grown for 14 d under controlled conditions in 100 mL growth tubes containing 48, 12, 3, or 0.75 g of each inoculum (96, 24, 6, or 1.5 for G. etuicatum) mixed with sterile soil to provide a total growth medium of 96 g. Discrete infection units were found for all isolates at all inoculum density levels, except for G. etunicatum (no infection at lowest density) and G. mosseae‐California (coalescing infection units at highest density). The relationship between inoculum density and discrete infection units per gram root fresh weight was linear (P < 0.01). This relationship is particularly suitable for determining amounts of inocula of equivalent potential for use in short‐term experiments.
On the Phytotoxicity of Polynuclear Hydroxy‐Aluminum Complexes
Authors: Parker D. R. , Zelazny L. W. , Kinraide T. B.
Published: July 2010

In a previous study we demonstrated the phytotoxicity of polynuclear hydroxy‐Al, a finding that disagrees with a number of existing reports. The objectives of this study were to examine how toxicity of polynuclear Al might vary with experimental conditions or with choice of test plants, and to identify and characterize the toxic polynuclear species. Wheat (Triticum aestivum L. cv. Tyler or Seneca) or soybean (Glycine max (L.) Merr. cv. Stafford) seedlings were cultured for 2 d in dilute CaCl2 solutions containing 15 µM total Al at a basicity (initial molar OH/Al ratio) of 2.0. Increasing rate of base addition, solution age, or levels of added phosphate decreased the fraction of reactive polymers (Alb) and increased that of precipitated Al (Alc) as determined by the ferron method. Mononuclear Al was consistently ≤3 µM and did not contribute to toxicity. Inhibition of root growth was well correlated with [Alb] for both plant species. That only 3 to 4 µM [Alb] was required to fully inhibit wheat root growth suggested that detection of toxic polynuclear Al may at times be difficult in chemically complex media. All plants tested were considerably more tolerant of Al3+ than of Alb, suggesting fundamental physiological differences in the toxicity of the two types of Al. This conclusion was further supported by the finding that the two wheat cultivars exhibited differential tolerance to Al3+, but not to Alb. Several analyses suggested that Alb was composed primarily of the so‐called Al13 polymer, which may form as a consequence of synthesis conditions. Given uncertainties in the occurrence of this polymeric species, both in the laboratory and in nature, several lines of future investigation are suggested.
Landform and Stratigraphic Influences on Variability of Loess Thickness in Northern Delaware
Authors: Rebertus R. A. , Doolittle J. A. , Hall R. L.
Published: July 2010

A detailed study of the relationships between landform, surficial geology, and variability of loess thickness on uplands was conducted at two 2.32‐ha study sites in northern Delaware. The purpose of the study was to determine what factors are responsible for the short‐distance variability in loess thickness observed in this region. Thickness of loess and paleotopography of the subjacent Pensauken (Columbia) Formation were measured using ground‐penetrating radar at 1326 grid points within each plot. Present topography was measured using a transit at 676 points in one plot and 1326 points in the second plot. Surface grid diagrams and isopleth maps show a lack of relationship between loess thickness and landform and relief except along ephemeral drainages. Over short distances, the thickness and even the occurrence of loess is dependent on the topography of the paleosurface. The loess was deposited upon an uneven erosional surface and conforms on a gross scale to that paleosurface but has filled the concavities and low points, thus producing a more regular present topography. Modern denudation of the present land surface occasionally exposes the coarser‐textured Pensauken sediments at the surface over high points in the paleolandscape. The irregular erosional paleosurface has resulted in a high degree of short‐distance variability in loess thickness that is difficult to predict except where headslope dissection has been severe enough to produce gullying and the formation of ephemeral drainages. These drainages closely conform to the occurrence of paleodrainages. The high degree of variability in loess thickness and occurrence presents mapping difficulties that need to be addressed in design, naming, and description of soil mapping units.
Geochemistry of Hydric Soil Salinity in a Recharge‐Throughflow‐Discharge Prairie‐Pothole Wetland System
Authors: Arndt J. L. , Richardson J. L.
Published: July 2010

The saturation‐paste extract (SPE) chemistry of samples collected in the wet‐meadow and shallow‐marsh zones of seven North Dakota wetlands was related to SPE electrical conductivity to investigate the development of hydric‐soil salinity. Study wetlands represent a local, depression‐focused groundwater‐flow system. Recharge wetlands recharge the groundwater whereas discharge wetlands receive the majority of their water as groundwater discharge. Throughflow wetlands receive water from as well as yield water to the system. Development of soil salinity generally followed the Hardie and Eugster model of closed‐basin brine evolution, which considers the composition of solutions undergoing evaporation to be the result of chemical changes imposed by the successive formation of evaporite minerals. Hydric soils of recharge wetlands were nonsaline and free of calcite (CaCO3) and gypsum (CaSO4·2H2O). The chemistry of these soils results from evapotranspiration, recharge hydrology, ionic mobility, and exchange relationships. Increases in SPE Mg2+, Na+, and SO2‐4 dominance in more saline throughflow and discharge wetlands are caused by calcite and gypsum precipitation, with the former controlling alkalinity and the latter Ca2+ concentrations. At high salinities produced by concentration through freezing, mirabilite (Na2SO4·10H2O) crystallizes and controls Na+ levels, resulting in hypersaline solutions enriched in Mg2+ and SO2‐4. Additional variation in the patterns of salinity development can be explained by dominance of recharge over discharge, mixing with fresh or chemically discrete water, and valence dilution effects.
Identification of Clay Coatings in an Older Quaternary Terrace of the Allier, Limagne, France
Authors: Feijtel T. C. , Jongmans A. G. , van Doesburg J. D. J.
Published: July 2010

Micromorphologically three types of coatings were observed in B horizons of two planosol profiles (Albaqualfs): (a) nonlaminated isotropic limpid clay coatings, (b) nonlaminated anisotropic limpid clay coatings, and (c) microlaminated anisotropic dusty clay coatings. Micromorphological observations suggested that coating types (a) and (b) were genetically similar, resulting from weathering and neoformation. Coating type (c) originated from clay illuviation. Elemental compositions of clay coatings were obtained with a scanning electron microscope‐energy dispersive x‐ray analyzer technique. Alumina contents decreased from 38% in isotropic coatings to about 28% in illuviation coatings. The Al content was inversely related to contents of K, Mg, Ca, and Fe. Factor analysis indicated that two factors accounted for 56.5 and 22.8% of the total elemental variance. The first factor associated with coating type revealed the antithetic behavior of Al vs. K, Mg, Ca, and Fe, and accounted for about 90% in the variability of Al. The second factor associated with the sample location explained >70% of the variability in Ti and Si. Chemical classification of investigated samples was based on elemental similarity. Cluster analysis revealed that coatings of the same type were more alike than coatings originating from the same profile. About 83% of grouped samples were classified correctly as isotropic and anisotropic weathering coatings, and anisotropic illuviation coatings. Clay minerals associated with individual coatings were identified with an x‐ray step‐scan method after sampling microquantities of these coatings with a microdrill. Anisotropic illuviation and weathering coatings consisted of illite and kaolinite. Anisotropic weathering coatings, however, were found to contain less illite than illuviation coatings. Isotropic coatings were x‐ray amorphous, suggesting the presence of Al‐Fe‐Si gel.
Limited Release of Soluble Organics from Roots During the Centrifugal Extraction of Soil Solutions
Authors: Zabowski D.
Published: July 2010

Radioactive isotopes were used to determine if the extraction of soil solutions via centrifugation was rupturing biological tissues and introducing cellular contents into the solution. Fungal cells labeled with 32P and root cells labeled with 14C were added to soil samples prior to centrifuging. No 32P was detectable in the soil solutions, and a maximum of 1% of the 14C in the roots was recovered in solution. A comparison of dissolved organic C extracted using low‐ and high‐speed centrifuging showed no change in soluble C at the higher centrifugal force. This suggests that cell contents are not being introduced into soil solutions during centrifuging.
Undisturbed Soils, Landscapes, and Vegetation in a North Carolina Piedmont Virgin Forest
Authors: McCracken R. J. , Daniels R. B. , Fulcher W. E.
Published: July 2010

The North Carolina Piedmont has been farmed for nearly 200 yr and there is considerable concern about the effect of soil erosion on the productivity of Piedmont soils. Most attempts to assess the effect of erosion on soil properties and productivity have few comparable virgin areas to use for baseline data. Fortunately, a 12‐ha virgin tract, mapped as Cecil sandy loam, B and C slopes, was located on the Guilford College campus in Greensboro, NC. The purpose of our study was to quantify the physical and chemical properties of a virgin Cecil soil map unit and to compare soil properties and distribution to that of cultivated sites. Detailed studies of the surficial sediments, geomorphology and soil morphology were made along five transects run at right angles to the topographic trend. Maps of hillslope sediment thickness and geomorphic surfaces were made using the information from the transects and bore holes. Pedons were sampled by landscape position for laboratory analyses. Horizon thickness and depth to residual material varied with landscape position. Nutrient status of all virgin soil horizons are very low, especially when compared to cultivated sites.
Effect of Traffic and In‐Row Chiseling on Mechanical Impedance
Authors: Radcliffe D. E. , Manor G. , Clark R. L. , West L. T. , Langdale G. W. , Bruce R. R.
Published: July 2010

A compacted layer at 0.15 to 0.25 m frequently occurs in soils of the southern Piedmont. This hardpan can be caused by disk or other tillage but the effect that wheel traffic may have in the formation of this layer has not been shown. The objectives of this study were to determine the extent traffic may contribute to hardpan formation, the effectiveness of shallow in‐row chiseling, and the possible correlation of the hardpan with a morphologically identifiable soil horizon. A long‐term tillage experiment where traffic had been controlled was examined at the end of its eighth year. The soil was a slightly eroded Cecil sandy loam (clayey, kaolinitic, thermic Typic Kanhapludult). Summer crops of soybean [Glycine max (L.) Merr. ‘Ransom’] and grain sorghum [Sorghum bicolor (L.) Moench, DeKalb BR‐64] were double‐cropped with winter wheat (Triticum aestivum L. Thell, ‘Coker 747’, 1979–1982, ‘Stacy’, 1983–1986). Spring tillage treatments consisted of disk tillage (DT), in‐row chiseling (IC), and coulter planting or reduced tillage (RT). All tillage treatments were disked in the fall before planting wheat. Cone index was measured in 1987 and 1988 in five positions relative to the row and showed that a hardpan was present in all positions at 0.15 to 0.25 m. The hardpan was a result of disk tillage and wheel traffic. Traffic caused compaction to a depth of 0.28 and 0.18 m in DT and RT, respectively. In‐row chiseling was effective in disrupting the hardpan to a depth of 0.26 m and contributed to significantly increased yields in grain sorghum. The hardpan coincided with the Ap2 horizon in this soil. The top of the Bt horizon may act to confine compactive stresses to the soil horizon above.