bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphology and Mineralogy of a Pre‐Wisconsinan Paleosol in Iowa
Authors: Thompson Michael L.
Published: July 2010

A paleosol covered by Wisconsinan till was studied to investigate pedological development before burial and to explore the effects of glacial overriding on certain morphological features. Samples of the paleosol were collected from an exposure in a limestone quarry. Particle size distribution, pH, total K2O content of the clay fraction, and clay mineralogical analyses were conducted on disturbed samples. Undisturbed samples were impregnated with a polyester resin and examined in thin section. The paleosol was divided into three zones that appeared to correlate with lithologic and/or pedologic discontinuities. The upper zone consisted of fine‐textured accretionary material that perhaps was deposited ahead of the advancing Wisconsinan ice. A lack of clay films in the field and pore argillans in thin section coupled with evidence of minimal smectite alteration suggested that this segment of the paleosolum was weakly developed. On the other hand, plasma separations, papules, and slickensides indicated that some physical reorganization of the soil had probably occurred. The middle zone, characterized by Al‐interlayered smectite in the clay fraction, illuviation argillans, and a sand content higher than the zone above, was interpreted to be an older segment of the paleosol developed in fine‐textured erosional debris of Pre‐Illinoian age under poorly drained conditions. The lower zone was heterogeneous with respect to both macromorphological and micromorphological features. It was interpreted to be a weakly weathered, Pre‐Illinoian till.
Variability of Nitrogen and Carbon in Surface Soils of Six Forest Types in the Oregon Cascades
Authors: McNabb D. H. , Cromack K. , Fredriksen R. L.
Published: July 2010

Soil samples were collected from sites typical of six forest habitat types in the western Oregon Cascades to determine the variability in total N, C, and mineralizable N. Within each type, 20 samples of surface soil (0‐15 cm deep) were removed from around the outside perimeter of a 0.25‐ha plot. Averages of 23, 28, and 70 samples were needed to estimate the population mean of total N, C, and mineralizable N, respectively, with an accuracy of ±10% at a 95% probability. Variability was not reduced by reporting data on the basis of mass per area rather than concentration, but the method of reporting data affected the relative ranking of sites. Within‐site variability was not generally related to microsite differences in slope or coarse fragment content.
Quantitative Evaluation of Feldspar Weathering in Two Boralfs (Gray Luvisols) from Saskatchewan
Authors: Mermut A. R. , Ghebre‐Egziabhier K. , St. Arnaud R. J.
Published: July 2010

Fine (0.10‐0.25 mm) and medium (0.25‐0.50 mm) sand size fractions of two Boralfs (Gray Luvisols) under Boreal forest were used in this study to characterize the nature of feldspars and the extent of their weathering in glacial till soils in northern Saskatchewan. Feldspars were separated into four different specific gravity fractions by heavy liquids. This facilitated subsequent x‐ray diffraction (XRD) and chemical analyses used for more accurate quantitative determination of feldspars. Distinctive etch pits were observed by scanning electron microscopy. Infilling of voids in the grains by mostly Fe oxides and some clay minerals was observed under the petrographic microscope. While there is evident recent weathering of feldspars within the solum horizons, there is also evidence of ancient weathering as observed in minerals within the parent materials. The studies verified the presence of microcline, orthoclase, and several solid solution series of plagioclase (mostly oligoclase with inclusions of labradorite‐anorthite series). Sodic plagioclases (An 10‐30) were dominant in both profiles, followed by K‐feldspars in Profile 1 and calcic plagioclases (An50‐100) in Profile 3; this confirmed some differences in mineral composition of the two soil parent materials. Stability of feldspars was calculated using a newly developed pedogenic index. As compared to the E horizons, the lower weathering rates in the Bt horizons were attributed to the illuvial clay, which may have played the role of a protective barrier around the feldspar.
Kinetics of Ion Exchange on Clay Minerals and Soil: I. Evaluation of Methods
Authors: Ogwada R. A. , Sparks D. L.
Published: July 2010

The effect of kinetic methodology on adsorption rate coefficients (ka) and energies of activation for adsorption (Eaa) were investigated using five different techniques. These techniques were: miscible displacement, batch, static, stirred, and vortex batch. Kinetics of K adsorption were studied on Ca‐saturated kaolinite, a Chester soil (fine‐loamy, mixed mesic Typic Hapludults) and vermiculite. The ka values were highest for kaolinite and lowest for vermiculite. The higher ka values observed for kaolinite would be expected since a relatively pure kaolin would exhibit only easily accessible planar surface sites for K exchange. The ka values for the Chester soil were a reflection of the intermediate properties of this soil between kaolinite and vermiculite. The type of kinetic technique greatly affected the time required for equilibrium to be attained in K adsorption. From greatest to least time, the order was: static > miscible displacement > batch > stirred > vortex batch. Both static and miscible displacement techniques yielded the lowest ka and Eaa values for all three colloids. This is primarily because these methods represent systems where the influence of diffusion on the rate of K adsorption is at its maximum. Only for kaolinite did the ka and Eaa values of both the stirred and batch techniques approximate, in magnitude, those of the vortex method. With the Chester soil and vermiculite, which contain appreciable interlayer sites, the stirred and batch techniques yielded ka and Eaa values much lower than those for the vortex batch method. These results indicate that in colloids where more significant intraparticle diffusion occurs, the batch or stirring technique as used in this study is not effective in eliminating the influence of diffusion.
Role of Extracellular Polysaccharide Production and Clays in the Desiccation Tolerance of Cowpea Bradyrhizobia
Authors: Hartel Peter G. , Alexander Martin
Published: July 2010

A study was conducted to determine the roles of extracellular poly‐saccharide and clays in the desiccation tolerance of cowpea bradyrhizobia. Seven nonmucoid strains of cowpea Bradyrhizobium were more resistant to drying in a sandy soil than five mucoid strains. A significant correlation was not observed (r = 0.26) between the amount of extracellular polysaccharide produced by these strains and their desiccation tolerance in a sandy soil. Investigation of two strains showed that they survived better in two sandy soils subjected to slow than to rapid drying, but the rate of drying had little effect in quartz sand. The percentage survival of the two strains in both soils was less at an inoculum density of 109 than at 106 cells/g of soil, but the reverse was true in quartz sand. The effect of desiccation on the number of survivors was similar if the drying was carried out with sterile or nonsterile soil. At the lower inoculation density, survival of the two strains in quartz sand increased if the clay fractions from the soils were added. The clay fractions consisted primarily of kaolinite. When the clay percentage of Ibadan soil was reduced by adding sand, the survival of the two strains was similar to that of Maradi sand. Thus, survival was affected by the amount but not the type of clay. The data suggest that inoculation density and the length of drying are important in the survival of cowpea bradyrhizobia undergoing desiccation in soil, and biotic factors and extracellular polysaccharide production are unimportant. Clay is important because it affects drying time.
Inhibition of Nitrification in Soil by Acetylenic Compounds
Authors: McCarty G. W. , Bremner J. M.
Published: July 2010

Recent work has shown that acetylene (ethyne) is a potent inhibitor of nitrification in soil. To discover if substituted acetylenes inhibit nitrification in soil, we determined the effects of seventeen monosubstituted (HC ≡ CR) acetylenes (propyne, 1‐butyne, 2‐ethynylpyridine, phenylacetylene, 3‐butyn‐2‐one, 1‐phenyl‐2‐propyn‐1‐ol, 1‐pentyne, 4‐phenyl‐1‐butyne, 5‐phenyl‐1‐pentyne, 1‐ethynylcycloh‐examine, 2‐propyn‐1‐ol, 2‐propyn‐1‐amine, 1‐hexyne, 3‐butyn‐1‐ol, 1‐heptyne, 1‐octyne, acetylene monocarboxylic acid) and of seven disubstituted (RC ≡ CR′) acetylenes (2‐butyne, 3‐phenyl‐2‐propyn‐1‐ol, diphenylacetylene, 2‐butyn‐1‐ol, 2‐butyn‐1,4‐diol, acetylene dicarboxylic acid, 2‐butynoic acid) on production of (NO‐3 + NO‐2)‐N in soils treated with (NH4)2SO4. The data obtained showed that most of the substituted acetylenes tested inhibited nitrification in soil and that some were potent inhibitors of nitrification. The results with the four gaseous compounds tested showed that acetylene, propyne, and 1‐butyne inhibited nitrification in soils at partial pressures as low as 0.1 or 1.0 Pa, whereas 2‐butyne had little or no effect on nitrification at partial pressures as high as 10 Pa. The data obtained with the 21 nongaseous compounds tested showed that 2‐ethynylpyridine, phenylacetylene, and 3‐butyn‐2‐one had the greatest inhibitory effect on nitrification and that acetylene monocarboxylic acid, acetylene dicarboxylic acid, and 2‐butynoic acid had the least effect. Studies to measure production of C2H2 in soils treated with the nongaseous compounds showed that the inhibition of nitrification observed with these compounds was not due to C2H2 formed by their decomposition in soil. Experiments reported indicate that 2‐ethynylpyridine and phenylacetylene compare favorably with nitrapyrin (N‐Serve) and etridiazole (Dwell) as soil nitrification inhibitors and have potential practical value for retarding nitrification of fertilizer N in soil.
Release of Nitrogen from Crimson Clover Residue under Two Tillage Systems
Authors: Wilson D. O. , Hargrove W. L.
Published: July 2010

The N contained in winter cover crops (particularly legumes) is a potentially important source of N for succeeding crops. The purpose of this study was to determine N release from crimson clover (Trifolium incarnatum L.) residue under no‐tillage and conventional tillage conditions. Residues contained in nylon mesh (53 µm) bags placed either on the surface of no‐tillage plots or buried at plowlayer depth in conventional tillage plots were removed for dry matter, C, and N determinations at 1, 2, 4, 8, and 16 weeks after placement in mid‐May. The rate of N disappearance was more rapid under conventional than no‐tillage conditions. The percentage of initial residue N remaining at 4 and 16 weeks under conventional tillage conditions was 40 and 31, respectively. The corresponding values for no‐tillage were 63 and 36% at 4 and 16 weeks. The C/N ratio of the residue remained relatively unchanged over the 16‐week period under no‐tillage conditions. However, under conventional tillage conditions, the C/N ratio declined from 15.9 to 12.7. Under humid, subtropical conditions, release of N from both surface and buried residue from winter legumes, is sufficiently rapid to be of significant benefit to the summer crop.
Physical Basis of the Length‐slope Factor in the Universal Soil Loss Equation
Authors: Moore Ian D. , Burch Gordon J.
Published: July 2010

The length‐slope factor in the universal soil loss equation (USLE) is a purely empirical relationship that was derived from an extensive data base. A physically based length‐slope factor was independently derived in this paper by using unit stream power theory to describe the erosion processes associated with sheet and rill flow on hill‐slopes. It was shown that the two length‐slope factors are equivalent. Therefore, the USLE length‐slope factor is a measure of the sediment transport capacity of runoff from the landscape, but fails to fully account for the hydrological processes that affect runoff and erosion. The strength of the theoretically derived length‐slope factor is that it explicitly accounts for the dual phenomena of catchment convergence and rilling. The empirically derived factor can not account for changes in either surface flow or erosion processes, nor slope geometry, and this may explain why the values derived for other factors in the USLE, especially soil erodibilities, have been found to be inconsistent.
Recovery of Compacted Soils in Mojave Desert Ghost Towns
Authors: Webb Robert H. , Steiger John W. , Wilshire Howard G.
Published: July 2010

Residual compaction of soils was measured at seven sites in five Mojave Desert ghost towns. Soils in these Death Valley National Monument townsites were compacted by vehicles, animals, and human trampling, and the townsites had been completely abandoned and the buildings removed for 64 to 75 yr. The soils studied (generally sandy, mixed, Typic Calciorthids) were derived from granitic or volcanic alluvium at elevations from 1310 to 1730 m. Compaction measurements in the townsites, including penetration depth, penetration resistance, bulk density, and peak shear stress, indicated that only one site had completely recovered to ambient soil conditions after 75 yr. Recovery times extrapolated using a linear recovery model ranged from 80 to 140 yr and averaged 100 yr. The recovery times were related to elevation, suggesting freeze‐thaw loosening as an important factor in ameliorating soil compaction in the Mojave Desert.
Spatial Dependence and Interpolation of Soil Properties in West Sumatra, Indonesia: I. Anisotropic Variation
Authors: Trangmar B. B. , Yost R. S. , Uehara G.
Published: July 2010

Spatial and temporal interaction of soil‐forming factors and processes determine the distribution of soil properties within the landscape. This study relates anisotropic spatial dependence of particle size fractions, pH and 25% HCl‐extractable P to directional differences in the main soil‐forming factors in Sitiung, West Sumatra, Indonesia. Linear geometric anisotropic models were fitted to pooled directional semivariances for each of these properties. Directions of maximum variation coincided with the main southwest to northeast axis of volcanic tuff fallout, deposition of alluvium and the general sequence of soil weathering in the region. Anisotropy ratios ranged from 1.5 for subsoil pH to 5.2 for subsoil HCl‐P. Topsoil textural components and pH were more variable than in subsoils, having larger sample variances and larger anisotropy ratios. Punctual kriging of topsoil sand content using the linear geometric anisotropic model resulted in low estimation variances in densely sampled areas where weighting of neighbor samples by direction as well as distance took most effect. Quantitative analysis of anisotropic spatial dependence of soil properties can aid interpretation of soil genesis. Estimates of anisotropic spatial dependence can also be incorporated into kriging interpolation for optimal, unbiased spatial estimation with minimum variance.
Boron Adsorption and Silicon Release by the Clay Minerals Kaolinite, Montmorillonite, and Illite
Authors: Goldberg Sabine , Glaubig R. A.
Published: July 2010

Boron adsorption behavior on the clay minerals kaolinite, montmorillonite, and illite was investigated. Adsorption increased at low pH, exhibited a peak in the pH range 8 to 10, and decreased at high pH. It was assumed that B adsorbs by means of a ligand exchange mechanism with aluminol groups at the edges of the clay particles. The constant capacitance model was able to describe B adsorption on kaolinites over the entire pH range studied (3–12), using only one adjustable parameter: the boron surface complexation constant. The model was able to fit B adsorption on montmorillonites and illites using three adjustable parameters; however, the chemical significance of some of the surface complexation constants is uncertain. Silicon release to solution increased in the order: kaolinite ∦ illite < montmorillonite and exhibited a minimum in the pH range 8 to 9. Boron adsorption on kaolinites was reduced only slightly in the presence of added silicate despite considerable silicate adsorption. Boron adsorption on montmorillonites was unaffected by the presence of added silicate. It is suggested that B and silicate adsorb on specific sites and that little anion competition occurs.
Speciation of Hydroxy‐Aluminum Solutions by Wet Chemical and Aluminum‐27 NMR Methods
Authors: Bertsch Paul M. , Layton W. John , Barnhisel R. I.
Published: July 2010

Partially neutralized Al solutions with OH/Al molar (ñ) ratios ranging from 0.25 to 2.5 were studied employing 27Al nuclear magnetic resonance spectroscopy and the ferron‐timed colorimetric assay. The monomeric Al concentrations (Ala) estimated by the ferron assay were consistently higher than the actual concentration determined by NMR spectroscopy. The differences between the methods indicate the presence of a small polymer which reacts rapidly with ferron and is erroneously assigned to the monomeric Al fraction. The polymeric Al component (Alb) estimated by the ferron method could be partitioned into a more rapidly reacting fraction (≤1 h) and a slowly reacting fraction (>1 h). The amount of Al associated with the rapidly reacting polymeric fraction corresponded to the amount of [AlO4 Al12(OH)24(H2O)12]7+ polymer directly determined by NMR spectroscopy. The slower reacting component of the Alb fraction is believed to be a polymer of the hexameric ring morphology. Direct NMR measurements provided evidence for specific adsorption of Al13 to a cation exchange resin and differential precipitation kinetics of this polymer with added sulfate. These data indicate that characterizing hydroxy Al solutions without direct measurements can lead to erroneous interpretations concerning the distribution between monomeric and polymeric Al and the nature and types of polymeric Al present.
Anisotropy of a Fragipan Soil: Vertical vs. Horizontal Hydraulic Conductivity
Authors: Dabney S. M. , Selim H. M.
Published: July 2010

Undisturbed core samples were obtained in vertical and horizonal directions from surface and subsurface horizons of an Olivier silt loam (Aquic Fragiudalfs, fine‐silty, mixed, thermic) in order to test for anisotropy. Saturated hydraulic conductivity, bulk density, penetrometer resistance, and volumetric moisture content at soil matric potential of 30 J kg−1 were measured. Hydraulic conductivity values within the Ap did not differ in horizontal and vertical sampling directions. However, within the Btx1 horizon, measured conductivity values were three times greater in vertical than in horizontal directions. This was attributed to the primarily vertical orientation of flow‐restrictive zones within the fragipan. Bulk density and moisture content differed between surface and subsurface horizons, but were not influenced by direction of core sampling. Penetrometer resistance did not differ between horizons or sampling direction, but was significantly greater in brown than in grey areas of the fragipan. The results of this study have relevance to models of soil water flow and the sampling methods described should be applicable to testing for anisotropy in other soils.
Method of Estimating the Travel Time of Noninteracting Solutes Through Compacted Soil Material
Authors: Horton R. , Thompson M. L. , McBride J. F.
Published: July 2010

The pollutant travel time through compacted soil material (i.e., when a pollutant introduced at the top first appears at the bottom) cannot be accurately predicted from the permeability (saturated hydraulic conductivity) alone. The travel time is also dependent on the effective porosity of the material; i.e., the portion of the total porosity that contributes significantly to fluid flow. Once permeability and effective porosity are determined for a selected material, the travel time of noninteracting pollutants through specified thicknesses of compacted material at specified hydraulic gradients can be predicted easily. Pollutant travel time is directly proportional to effective porosity and thickness of a compacted layer and inversely proportional to permeability and hydraulic gradient. This paper presents a straightforward method of determining the effective porosity of compacted soil materials. The determination of effective porosity is based upon the total porosity and the spread on a log scale in the pore sizes of a compacted sample. The total porosity is calculated from measurements of bulk and particle density. Pore size distribution information is obtained from the cumulative porosity curve of the sample as measured by a mercury‐intrusion porosimeter. Once the total porosity and pore size distribution information are obtained for a particular sample, the effective porosity can be determined directly by using a graphical relationship. This paper also compares measured and predicted solute breakthrough times for three compacted soil materials. Predicted travel times through compacted samples of glacial till, loess, and paleosol materials were reasonably close to measurements of CL‐ travel time.
Stratigraphy and Genesis of Polygenetic Soils on the Illinoian Till Plain of Southwestern Ohio
Authors: Ransom M. D. , Smeck N.E. , Bigham J. M.
Published: July 2010

Three pedons each of Clermont (Typic Glossaqualfs) and Avonburg (Aeric Fragiaqualfs) soils were investigated on the Illinoian till plain of southwestern Ohio in order to evaluate parent material stratigraphy and to determine if paleosols were substantially altered following burial by a thin mantle of loess. The relationship between fragipan development and paleosol properties was also examined. The soils were found to have formed in 57 to 69 cm of Late Wisconsinan (Peoria) loess overlying a composite Early Wisconsinan and Sangamon paleosol. The Sangamon paleosol, which was most strongly developed at approximately 150 to 200 cm, was formed in Illinoian till. The material from about 70 to 140 cm consisted of a mixture of Early Wisconsinan loess and Illinoian till with till characteristics dominating. Evidence for a mixed zone in the upper paleosol included (i) a higher silt content than the lower paleosol, (ii) a maximum in elemental Ca in the total silt fraction, and (iii) an abundance of pedotubules in up to 50% of some horizons suggesting that mixing was caused by bioturbation. Modification of the paleosols has occurred as evidenced by recharge with secondary carbonates and bases leached from the overlying loess. A fragipan was identified in only one Avonburg pedon that had a clay content of 27% in the upper part of the paleosol as compared to 31 to 38% for the other pedons. Fragipans appear to have formed in these soils only if the clay content of the upper part of the paleosol is currently less than about 30%.
Soils with Bx Horizons in the Upper Coastal Plains of South Carolina
Authors: Smith B. R. , Callahan L. L.
Published: July 2010

Soils with firm, dense Bx horizons are extensive in the Upper Coastal Plains including the Sandhills of Georgia, North Carolina, and South Carolina. The Bx horizons are slightly brittle to brittle, but prisms with bleached, vertical faces are often weakly developed or absent. Three pedons of a series representative of these soils were studied in detail to characterize the soils, to determine if they have fragipans, and to determine if they are properly classified. Particle size distribution data show that the Bx horizons also meet the criteria of argillic horizons, as do many fragipans. Bulk densities are high in the Bx horizons. Free Fe oxide contents are highest in the Bt or Bx horizons, just as are clay contents. Clay mineralogy in the surface horizons is predominately hydroxy‐Al interlayered vermiculite (HIV) and kaolinite with substantial amounts of gibbsite. HIV and gibbsite decrease and kaolinite increases with depth. Micromorphological examinations reveal dense packing of quartz skeleton grains with a mixture of clay minerals and Fe oxyhydroxides and very few voids in the Bt, Bx, and C horizons. Yellow illuviation argillans and red illuviation ferriargillans are fairly common in the Bt and Bx horizons. Some segregation of Fe oxyhydroxides has occurred in the soils. Brittleness of the Bx horizons is restricted to the reddish‐colored material. This indicates that weak cementation by Fe oxyhydroxides in the presence of clay minerals is at least partly responsible for the brittleness. The Bx horizons are brittle in approximately 45 to 50% of the volume and have many of the properties of fragipans. The establishment of a Fragic subgroup of Hapludults is proposed for these and similar soils.
Three‐Minute Analysis of Chloride, Nitrate, and Sulfate by Single Column Anion Chromatography
Authors: Barak Phillip , Chen Yona
Published: July 2010

Accepted techniques of single column ion chromatography of inorganic anions were extended to separation of chloride, nitrate, and sulfate using 15 mM phthalic acid as an eluent, permitting reduction of column length to 30 mm and thereby reducing analysis time to three min. Using a 50 µL sample loop, detection limits were 0.05 mmolc L−1 and coefficient of variation values ranged from 0.8 to 1.7% using peak height measurements and 0.8 to 8.1% using peak area measurements. This configuration is appropriate for routine analysis of soil water extracts and ground water.
Ion‐selective Electrode Determinations of Exchangeable Potassium in Soils
Authors: Farrell R. E. , Scott A. D.
Published: July 2010

Procedures using ion‐selective electrodes (ISEs) for the accurate determination of NH+4 ‐and Ba2+‐exchangeable K+ in soil extracts are described. The exchangeable K+ in 30 soil samples was extracted with neutral solutions of 1.0 M NH4OAc and 0.5 M BaCl2 and determined by atomic absorption spectrometry (AAS) to establish the K+ levels sought with the electrodes. Potentiometric measurements were then made with electrochemical cells consisting of either a valinomycin‐based K+‐selective electrode (VKE) or a cationic glass‐membrane electrode (CGE) and a double‐junction sleeve‐type reference electrode assembly with a saturated LiOAc salt bridge. The electrochemically analyzed solutions (1:5 extract/water dilutions) had a common ionic strength and a pH near 7 or a LiOH‐adjusted pH of 11.6. A comparison of the AAS values for the Ba2+‐ and NH+4‐exchangeable K+ demonstrated the feasibility of using either extractant for an evaluation of ISE methods. Interferences from NH+4 and Li+ limited the use of the CGE to the neutral BaCl2 extracts, where it yielded exchangeable K+ values that were only poorly correlated (r = 0.655) with those obtained by AAS. However, the Ba2+‐exchangeable K+ values obtained with the VKE were highly correlated (r = 0.983) with and not significantly different (α = 0.05) from those obtained by AAS with the neutral extracts and even more so with solutions at pH 11.6 (r = 0.998; α = 0.01). Accurate direct‐potentiometric determinations of the exchangeable K+ in the NH4OAc extracts were not feasible, even at pH 11.6. But the NH+4‐exchangeable K+ values obtained with the VKE and a modified standard additions technique were highly correlated (r = 0.987) with and not significantly different (α = 0.05) from those obtained by AAS.
Spectrofluorometric Investigation of Trace Metal Complexation by an Aqueous Chestnut Leaf Litter Extract
Authors: Blaser P. , Sposito Garrison
Published: July 2010

Fluorescence spectroscopy was investigated as a method for quantitating trace metal complexes with the organic ligands in a water extract of chestnut (Castanea sativa L.) leaf litter. Copper(II) and aluminum(III) were selected as environmentally significant metals with which to characterize the method as applied to the leaf litter extract. Solutions of Cu or Al mixed with the extract exhibited fluorescence that decreased in relative intensity as the total metal concentration and/or the pH increased. Data were obtained in the pH range 5 to 8 for total Cu concentrations up to 160 mmol m−3 and in the pH range 4 to 8 for total Al concentrations up to 100 mmol m−3. The fluorescence intensity data for Cu were comparable to those obtained in previous studies for solutions of Cu and soluble humic materials. A conventional equation was used to calculate an overall stability coefficient for metal complexation by the leaf litter extract. The pH‐dependence of this stability coefficient was modeled mathematically in terms of pH‐independent conditional stability constants through a new application of the Scatchard quasiparticle model. The quasiparticle species Cu(OH)nH0.9L (n = 0 or 1; L = organic ligands) were sufficient to model the Cu data with the two pH‐independent conditional stability constants, cβ0/0.9 = 1012.6 and cβ1/0.9 = 105.3. For the Al data, the conditional stability constants cβ0/0 = 108.55 and cβ2/0 = 10−1.8 were obtained for the quasiparticle species Al(OH)nL (n = 0 or 2). These stability constants can be used in computer speciation programs to estimate organic complexation of Cu(II) or Al(III) by the leaf litter extract, but otherwise have no molecular chemical significance.
Organic Matter Leaching as a Component of Carbon, Nitrogen, Phosphorus, and Sulfur Cycles in a Forest, Grassland, and Gleyed Soil
Authors: Schoenau J. J. , Bettany J. R.
Published: July 2010

The profiles of a forest (Typic Cryoboralf), grassland (Aridic Haploboroll), and gleyed (Argiaquoll) soil were examined to assess the role of organic matter leaching in determining organic matter composition in genetic horizons of soil profiles. An increasing proportion of NaOH extractable C, N, P, and S was found in the fulvic acid (FA) fraction as depth in the profiles increased, suggesting that fulvic acids produced in biologically active surface horizons have been translocated to B and C horizons by percolating water. The fulvic acid in B and C horizons was highly enriched in N, P, and S relative to the humic acid and fulvic acid in surface horizons, indicating that the organic matter being translocated downward is richer in N, P, and S than fractions not susceptible to leaching. Leaching of nutrient‐rich organic matter thus provides a valid explanation for the observed narrowing of soil organic matter C/N, C/P, and C/S ratios with increasing depth. The lowest HA/FA ratios coincided with the depth of CaCO3 accumulation, revealing a possible role of Ca and other basic cations in precipitation of organic matter from solution. Of the four elements studied, P appeared to be the most susceptible to deep leaching in the organic form. This is believed to reflect the predominance of organic P in the low molecular weight, mobile fraction of soil organic matter. Loss of labile, nutrient‐rich organics from surface horizons by leaching may be important in controlling element turnover rates and nutrient distribution within soil profiles. It may also represent a major nutrient export mechanism.
Spatial Variation of Soil Properties and Rice Yield on Recently Cleared Land
Authors: Trangmar B. B. , Yost R. S. , Wade M. K. , Uehara G. , Sudjadi M.
Published: July 2010

Crop yields on cleared forest land of the humid tropics are often highly variable due to spatial heterogeneity of soil properties. This study aimed to characterize spatial variation of soil chemical properties and yield components of upland rice (Oryza sativa) on a 0.1‐ha field of recently cleared land in West Sumatra, Indonesia. Plants were taller, stover and grain yields higher on sites where forest rash had been piled and burned, compared to the surrounding soils and other sites where topsoils had been removed. This pattern was largely caused by lower levels of Al saturation and higher concentrations of exchangeable cations in burned sites compared to other parts of the plot. The range of spatial dependence for soil acidity and exchange characteristics was 3 to 4 m, but increased to 7 m for organic C, total N, and extractable P. Semivariograms of crop components were better structured and had longer ranges (up to 20 m) than the soil chemical properties. Block kriging gave more precise local estimation of grain yield at unsampled locations than terrain unit means because it utiliized the inherent structure of variation determined from quantitative spatial analysis of observed values. Block kriged values of grain yield ranged from 11 to 355 g/m2 with estimation standard deviations ranging from 9 to 24 g/m2, depending on distance of interpolated cells from the 122 sample locations.
Silty Deposits of a Low, Pleistocene‐age Terrace in Eastern Arkansas
Authors: West L. T. , Rutledge E. M.
Published: July 2010

A segment of Terrace Qtb3 of the Western Lowlands of Arkansas was transected to determine if the silty material capping the terrace is loess or silty alluvium. Four sites along an east‐west transect were sampled to test the hypothesis that the material is loess with its source area immediately east of the terrace segment. Three deposits dominated by silts were identified at each site by morphology, fine‐earth and clay‐free particle size distribution, and by distribution of total Ca and K in the coarse silt fraction. The lowest of the silty deposits was identified as alluvium by its sand contents and stratification in the lower part. The morphology of the upper two deposits was similar to that of loess on other terraces in the area. However, relationships between clay‐free particle size distribution and log distance from the proposed source area were not those expected for loess. Thus, these two deposits are also interpreted as silty alluvium. Geomorphic relationships indicate that the terrace is younger than Illinoian, but no minimum age can be deduced from current data.
Seed Zone Soil Temperature and Early Corn Growth with Three Conservation Tillage Systems
Authors: Al‐Darby A. M. , Lowery B.
Published: July 2010

Detailed data are needed to quantify the effect of conservation tillage (CT) on corn (Zea mays L.) emergence and early growth in the Northern Corn Belt. Corn was grown using three CT systems: till‐plant (TP), chisel (CH), and no‐till (NT) and conventional moldboard plow (CN) on a Griswold silt loam soil (Typic Argiudoll) during the 1982 to 1984 growing seasons. Soil temperature at the seed depth (5 cm) was measured hourly. Daily means and cumulative growing degree days (GDD) based on seed zone temperatures were calculated. Corn emergence was monitored. Leaf area and dry matter per hectare were measured at different growth stages. Relative growth rates (RGR) were calculated from daily measured plant heights. Soil temperature at the 5‐cm depth ranked CN > TP > CH > NT. Initial corn emergence rates with the NT system were depressed compared to CN; the emergence rate ranked CN > TP = CH > NT. However, time to 100% emergence was delayed by 8, 2 to 3, and 2 d for NT compared to CN in 1982, 1983, and 1984, respectively. All tillage systems started to emerge at 40 to 55 GDD and reached a maximum emergence at 70 to 80 GDD. During the first 5 weeks after emergence, corn growth parameters (plant height, leaf area, dry matter) of NT were consistently lower, and in some cases significantly lower than CN. These growth parameters were highly correlated with GDD. The RGR fluctuated in the same manner as the daily 5‐cm soil temperature during the first 5 weeks after emergence. The correlation coefficients of log RGR vs. daily mean soil temperatures were highly significant and followed the soil temperature trends. Thus, the lower soil temperature associated with CT systems, especially NT, is one of the main factors affecting emergence and seedling growth and development.
Subsurface Water Movement in an Upland Coastal Plain Soil as Influenced by Plinthite
Authors: Blume L. J. , Perkins H. F. , Hubbard R. K.
Published: July 2010

Water movement in a Tifton loamy sand (Plinthic Paleudult) was monitored using bromide as a tracer for 86 weeks under natural rainfall conditions following treatment in late summer. Potassium bromide (KBr) was placed at depths between 10 and 43 cm and 60 and 102 cm in a soil having a 4.4% slope. Bromide content of water from piezometers at distances up to 60 m downslope was determined at 2‐ to 4‐week intervals during periods of perched water starting 22 weeks after the injection date. Determinations were then made for a 65‐week period. Soil samples taken at depths to 4.72 m 1 yr after treatment were analyzed for bromide content. A perched or secondary water table occurred during periods of high rainfall and low evapotranspiration. Data indicate that subsurface flow downslope occurred primarily above and within the plinthic horizon during periods when a perched water table was present. Data from soil samples collected 1 yr after KBr treatment indicate that bromide moved slowly through the plinthic layer, was interceted by subsurface layers of high density, and was retained in the watershed until removed by lateral flow.
Soil Genesis Associated with Periglacial Ice Wedge Casts, Southcentral Wyoming
Authors: Munn L. C.
Published: July 2010

The development of ice and sand wedges (nonsorted polygon features) in Wyoming's high basins during the late‐Pleistocene glaciation allows determination of soil development on pre‐Wisconsin and late‐Wisconsin surfaces on the same landform. Pre‐Wisconsin soils on an old alluvial terrace in the Great Divide Basin (later hosts to ice wedges) exhibited clay translocation and accumulation followed by a period during which carbonate accumulated. Soils developed in the noncalcareous fill‐materials of the ice‐wedge casts show B horizon accumulation of clay and carbonate. The late‐Wisconsin soils developed in the ice wedge casts showed clay enrichment of 13 kg m−2 and CaCO3 enrichment of 113 kg m−2. The pre‐Wisconsin soil had CaCO3 enrichment of 250 kg m−2. Parent material stratification prevented determination of absolute clay enrichment in the host soil but its clay maximum is 33% compared to 15% in the late‐Wisconsin soil. The Bt horizons in the pre‐Wisconsin soils are also much thicker. Profile morphology indicates that the present semi‐arid environment probably developed immediately as the climate warmed at the end of the Wisconsin. Clay mica and kaolinite have become enriched in surface horizons and smectite in C horizons of both wedge and wedge‐host soils.
Sphericity and Roundness of Sand in Coastal Plain Soils and Relationships with Soil Physical Properties
Authors: Vepraskas M. J. , Cassel D. K.
Published: July 2010

Sand grain roundness and sphericity were evaluated for 50 soil samples from Atlantic Coastal Plain soils to determine relationships of sand grain roundness and sphericity to the soils' cone index (mechanical impedance), bulk density, and the dense soil angle of repose. A previous investigation collected undisturbed cores from 50 tillage‐induced pans in the Atlantic Coastal Plain, and determined cone index, bulk density, and the dense soil angle of repose. One hundred sand grains were isolated from each of the 50 soil materials. Roundness was determined for each grain by comparing the grain's projected image to standard images in published roundness charts. Sphericity was also determined for the 100 grains per soil by measuring selected grain axes. Mean values for roundness and sphericity were determined for each soil sample. Mean roundness values ranged from 0.44 to 0.57 across sites, but 74% of the sites had mean roundness values between 0.45 and 0.49 inclusive. Mean sphericity values ranged from 0.74 to 0.81, but 72% of the sites had mean sphericities between 0.78 and 0.81 inclusive. Correlation coefficients for relations of cone index, bulk density, and dense soil angle of repose to roundness and sphericity were generally ≤0.26 and not significant (0.10 level). Sphericity and roundness were not significant variables in regression models describing variations in cone index and the dense soil angle of repose. Roundness was not a significant variable in regression models describing variations in bulk density among sites, but sphericity was a significant variable in models that were based on particle size characteristics alone.
A Simple Method for the Estimation of Calcium and Magnesium Carbonates in Soils
Authors: El Mahi Y. E. , Ibrahim I. S. , Abdel Magid H. M. , Eltilib A. M. A.
Published: July 2010

A simple titrimetric method is described for the estimation of Ca and Mg carbonates in soils. It involves the determination of acid‐soluble Ca and Mg of the carbonate phase after the removal of soluble and exchangeable cations by ammonium acetate (NH4OAc). Twenty‐six tropical soils, which contain free carbonate, were used in this study. The results obtained by the proposed method were compared with those obtained by acid neutralization, calcimeter, and titrimetric methods. Analysis of variance revealed no significant difference between the percent CaCO3 equivalent obtained by the four methods when the acid neutralization method was corrected against proton adsorption. However, the proposed method has the advantage of estimating Ca and Mg carbonates. The proposed method requires no special equipment and is less time‐consuming if it follows the routine determination of exchangeable cations or the cation exchange capacity (CEC).
The Influence of Organic Complexing Agents on Iron Mobility in a Simulated Rhizosphere
Authors: Erich M. S. , Duxbury J. M. , Bouldin D. R. , Cary E.
Published: July 2010

The effect of complexing agents on Fe mobility was investigated using a simulated root‐soil system that consisted of 0.24‐mm o.d. cellulose fibers embedded in a clay‐agar matrix. Complexing agents diffused into the clay‐agar matrix from a solution flowing through the fibers and their effect on Fe flux to the fiber surface was determined by following Fe concentration in the effluent solution from the fibers. Experiments with the chelating agents ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), ethylenediamine di‐(o‐hydroxyphenylacetic acid) (EDDHA), and ethylene glycol‐bis‐(2‐amino‐ethylether) tetraacetic acid (EGTA) demonstrated that solubilization of Fe qualitatively followed patterns predicted from known thermodynamic stability constant‐pH relationships. The concentration of Fe in the fibers 24 h after introduction of either EDTA, DTPA, or EDDHA was increased from close to 0 to 30 to 100 g Fe L−1, whereas EGTA had no measurable effect on Fe solubility. The measured fluxes of Fe were compared with calculations based on diffusion and reaction. An equilibrium model, where the complexing agent was assumed to equilibrate instantaneously with the soil (reaction rate constant Kr = 1), predicted concentrations of Fe 103 times greater than those observed. A first‐order kinetic model, which was solved by numerical methods, gave results similar to those found experimentally when Kr was on the order of 10−7. The partial success of the thermodynamic stability constant approach was reconciled with the kinetic model by considering Kr to combine both kinetic and equilibrium factors.
Relating the Fertility Capability Classification System to Tobacco Response to Potassium Fertilization
Authors: Denton H. P. , Peedin G. F. , Hawks S. N. , Buol S. W.
Published: July 2010

The Fertility Capability Classification (FCC) system is a technical soil classification system developed to evaluate soil properties affecting crop response to fertilization and to aid in making fertilizer recommendations. It was developed primarily for use in lesser developed countries. Results from a series of experiments involving application of K to flue‐cured tobacco (Nicotiana tabacum L.) in North Carolina were used to determine the usefulness of the FCC system for predicting crop response to fertilization in the southeastern USA. Six rates of K, ranging from 0 to 224 kg ha−1, were applied to flue‐cured tobacco at 13 locations for 3 yr. Tobacco leaf yield response to K differed significantly among FCC soil groups. Optimum rates by soil group varied from 0 to 112 kg ha−1, compared with 84 kg ha−1 across all soils. The highest optimum rates occurred on soils with sand or loamy sand surfaces >0.5 m thick, whereas the lowest rates were on soils with loamy surfaces. Extractable soil K level in the Ap horizon (soil test K) was not related to response to K, either overall or within FCC groups. The FCC system was useful in evaluating tobacco leaf yield response to fertilization. It appears that the FCC system could be used to improve fertilizer recommendations.
Soybean Response to Available Potassium in Three Silt Loam Soils
Authors: Grove J. H. , Thom W. O. , Murdock L. W. , Herbek J. H.
Published: July 2010

The range in soil environments has likely contributed to variation in the determination of that level of K availability at which no further yield increase to K is expected. Potassium response of soybean [Glycine max (L.) Merr.] from three different soil environments was studied in the field to determine if a single index of K availability could be found. Relationships between grain yield, R1‐R2 leaf K concentration, ammonium acetate exchangeable K, Ca, Mg, and water soluble K, Ca, and Mg were determined. Significant (P ⩽ 0.05) yield responses to added K were found at all three sites, as were increases in R1‐R2 leaf K. Water soluble K, K/Mg, and K/(Ca + Mg)1/2 were more stongly related to plant response than extractable K, K/Mg, or K/(K + Ca + Mg). All soils provided optimal K nutrition to soybeans at soil test levels ≤100 mg K kg−1 soil, as determined by neutral, molar ammonium acetate solution. Determinations of soil solution phase composition may improve our understanding of the role(s) of soil properties on divergent patterns of response to K nutrition.
Correspondence of Soil Properties and Classification Units with Sagebrush Communities in Southeastern Oregon: I. Comparisons between Mono‐taxa Soil‐vegetation Units
Authors: Lentz R. D. , Simonson G. H.
Published: July 2010

A preliminary second‐order soil survey (1:15840) of Squaw Butte Range Exp. Stn., Oregon, identified a single shallow upland soil that supported six contrasting sagebrush communities. Six delineations of this soil, each associated with different vegetation, were sampled intensively to objectively determine if soil properties and classification differed between delineations. Plant communities represented six different sagebrush (Artemisia) habitat types: A. longiloba/Agropyron spicatum, A. longiloba/(fescue) Festuca idahoensis, A. arbuscula/F. idahoensis, A. tridentata ssp. wyomingensis/A. spicatum, (F. idahoensis), and A. t. ssp. vaseyana/F. idahoensis‐A. spicatum. Morphological properties of profile samples were statistically compared by defining aggregate horizons (tiers) that were common to all profiles. Stepwise discriminant analysis selected elevation, aspect, presence of E and BA horizons, clay content of the Bt horizon, and sand content of surface strata as those which best distinguished between plant communities. Evidence suggests that series separations are justified based on family and class distinctions of higher categories or differences in range of soil properties, including variations in horizonation, volumetric rock fragment content of A and Bt horizons, and structure of BAt horizons. Phase separation criteria suggested include aspect, parent material, slope, and surface texture. Structure type of subhorizons, subhorizon position, and nutrient content are soil properties that may also provide important discrimination between soils possessing different range potentials.