bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial Variability of Nitrogen‐15 and Total Nitrogen in Some Virgin and Cultivated Soils
Authors: Broadbent F. E. , Rauschkolb R. S. , Lewis Kristine A. , Chang Grace Y.
Published: July 2010

Soil cores were taken from six locations representing three virgin and three cultivated soils in increments of 15 or 30 cm down to depths ranging from 120 to 300 cm. The number of samples of an individual soil profile varied from 20 to 96, though smaller numbers of some subsurface horizons were obtained at two locations where very rocky conditions were encountered. Frequency distribution analysis of δ15N values and of total N showed that they were log‐normally distributed in about half the groups of samples. Assumption of normal distribution in all samples would result in a maximum error of 37% in total N and 0.1% in 15N content if the real distribution were in fact log‐normal. Coefficients of variation of total N were somewhat lower in cultivated soils than in virgin soils, but C.V. values for atom %15N were comparable in the two groups of soils. It is concluded that the magnitude of natural variation in δ15N values at a given sampling site, both laterally and vertically, is so great as to preclude tracing biological events by means of natural abundances.
Properties and Classification of an Eroded Soil in Southeastern Nebraska
Authors: Lewis D. T. , Witte D. A.
Published: July 2010

Pedons representing soil properties within three mapping units of the Wymore soil series were studied to determine if they were correctly classified and named. Present concept of the three units suggests that they differ in slope and/or erosion class, but that they are within the concept of fine, montmorillonitic, mesic Aquic Arquidolls. Pendons representing the noneroded, 0–2% slope unit (Wt) and the noneroded, 2–7% slope unit (WtC) exhibited properties that supported their present classification. However, 64% of the pedons sampled in the delineations representing the eroded, 2–7% slope unit (WtC2), and consequently the pedon representative of the WtC2 unit, had an epipedon that appeared to have been formed through tillage of a subsurface horizon. Established criteria for the mollic epipedon and the agrillic subsurface horizon were not evident. An ochric epipedon and cambic subsurface horizon existed in this pedon. These features plus a high base saturation, lack of pedogenic lime and mottling in the solum supported placement of the pedon representative of the WtC2 unit in the subgroup Aquic Dystric Eutrochrept. This pedon is representative of > 45,000 ha in the region of its existence.
The Penetration Resistance in a Soil with Well‐defined Structural Units
Authors: Bradford J. M
Published: July 2010

Based on both laboratory and in situ probe penetration tests within each horizon of a soil with well‐defined structural units, the magnitude and variability of probe resistance values in relation to probe diameter and structural features are presented. Total penetration resistance was equal for 0.376‐ and 0.514 cm‐diam 60° angle probes; however, the resistance standard deviation and coefficient of variation were larger for the smaller probe. A pocket penetrometer gave significantly larger penetration resistances. There was a close relationship between probe penetration resistance of a 0.376‐cm‐diam probe and root length in natural B3 horizon.
Amorphous Material and Aluminum Interlayers in Quebec Spodosols
Authors: De Kimpe C. R. , Laverdiere M. R.
Published: July 2010

Clay fraction from spodic B horizons of Appalachian and Laurentian soils was recovered after organic matter and sesquioxides removal. Sodium citrate and sodium hydroxide further extracted various amounts of Al, Si, and Fe. Samples from the Appalachian sites released < 5% Al2O3 + SiO2 and < 1% Fe2O3. There were only small differences between the amounts of material extracted by both reagents. After citrate treatment, a moderate increase of CEC was observed and related to Al interlayer removal, while after NaOH + citrate treatment the CEC decreased slightly because of amorphous material removal. Samples from the Laurentian sites released from 9.3 to 30.0% Al2O3 + SiO2 in NaOH and subsequently 1.6 to 6.0% Fe2O3 in Na‐citrate. The presence of large amounts of amorphous material prevented the identification of clay minerals by X‐ray diffraction analysis, and its removal caused a strong decrease of the CEC. Citrate alone extracted this poorly crystalline material at a slower rate and for these samples, this was followed by a decrease of the cation exchange capacity.
Activities of Cu2+ and Cd2+ in Soil Solutions as Affected by pH
Authors: Cavallaro N. , McBride M. B.
Published: July 2010

The concentrations of free copper and cadmium ions in soil suspensions were measured by an ion‐selective electrode as a function of pH after equilibrating metal salt solutions with the soils. Similar experiments were done with water‐extractable organic matter. Free (uncomplexed) Cu2+ concentrations were strongly pH‐dependent in the soil systems, but well below the level where precipitation could have occurred. Free Cd2+ concentrations were much less affected by pH adjustment, and the nonacid soil systems approached saturation or oversaturation with respect to CdCO3 precipitation at high pH. Similiar dependence of the free metal ion concentration on pH was found in water extracted organic matter solutions. Precipitation of CdCO3 in oversaturated solutions containing the extracted organic matter was slow, while none of the copper‐organic matter solutions attained oversaturation with respect to Cu(OH)2 or Cu2(OH)2CO3.
The Effect of Nitrate on Nitrous Oxide Reduction in Organic Soils and Sediments
Authors: Terry Richard E. , Tate Robert L.
Published: July 2010

Inhibition of N2O reduction by NO3‐ in cultivated Pahokee muck was determined by measuring N2O accumulation in soil samples incubated in the presence and absence of acetylene. At NO3‐‐N levels of 40 mg/liter or greater, nearly 100% of the gaseous denitrification products were N2O in Pahokee muck. Reduction of the accumulated N2O proceeded rapidly after the NO3‐ was exhausted from the soil. In comparison, N2O was readily reduced in ditch sediment samples in the presence of comparable concentrations of NO3‐. With NO3‐‐N concentrations in the ditch sediments ranging from 90 to 39 mg/liter, < 10% of the gaseous denitrification products were N2O. Similarly, NO3‐ levels in soil samples from a vegetable field which had been flooded 22 days had negligible effect on N2O reduction. These data demonstrate that the inhibitory effect of NO3‐ on N2O reduction was less in sediments and in organic soils that had been subjected to prolonged flooding than in the cultivated soils.
Enzymatic Activities in Coniferous Leaf Litter
Authors: Spalding Brian P.
Published: July 2010

Assays for measuring the activities of cellulase, xylanase, mannase, amylase, β‐glucosidase, invertase, and protease employing buffered suspensions of ground coniferous and deciduous leaf litter exhibited zero‐order kinetics. Only a small percentage of the whole‐litter activities of invertase (3%), β‐glucosidase (3%), and protease (1%) were extractable into 0.05M potassium acetate, pH 5.0; however, extractable activities of cellulase and xylanase represented from 39 to 174% of the whole‐litter activities indicating their soluble exocellular nature. Extractable protease and amylase activities were best correlated (r=0.65 and 0.65, respectively) with the average daily rates of CO2 evolution in a group of 90 leaf litter samples equally representing 18 coniferous species. Enzymatic activities were readily detectable in extracts of all samples but classification of the samples by species provided little differentiation in the distribution of either enzymatic activities or rates of CO2 evolution. Mannase, cellulase, and xylanase activities were well‐correlated with each other (r=0.88) in all samples. Assays at‐tempting to measure a pool of readily‐metabolizable substances in litter by extractable reducing substances, ninhydrin‐positive substances, glucose, and phenolics failed to show correlation coefficients > 0.41 with rates of CO2 evolution. Addition of D‐(+)‐catechin to litter extracts, up to levels equivalent to those observed in the group of samples, did not inhibit any carbohydrase thus suggesting the lack of inhibition of litter‐decomposing enzymes by the concentrations of phenolics present in these coniferous leaf litters.
Use of Soil Survey Data in a Model for Simulating Regional Soil Moisture Regimes
Authors: Bouma J. , de Laat P. J. M. , Awater R. H. C. M. , van Heesen H. C. , van Holst A. F. , van de Nes Th.J.
Published: July 2010

Depth to water table and evapotranspiration rates were simulated with the computer program GELGAM for an area of 6 by 6 km, which was described by square nodal areas of 25 ha each in a grid with a mesh width of 500 m. Soils which occupied the largest part within a nodal area (as determined by analyzing a soil map) were considered representative for the nodal area and were characterized by basic data in terms of rooting depth, moisture retention curves and hydraulic conductivity curves. Four simulation runs were made with GELGAM, using increasingly detailed and costly basic data obtained by estimates and measurements in four phases as follows: (i) identical estimates for all nodal areas; (ii) estimates based on an existing soil map; (iii) estimates from one on‐site boring per nodal area, and (iv) measurements of physical data.

Estimates of physical data were based on extrapolation of data obtained for similar soil horizons elsewhere, using empirical relationships with soil texture, organic matter content, and bulk density. Such estimates, when based on descriptions of mapping units in the soil survey report, were good for surface horizons but poor for the deeper subsoil beyond the solum in the region of the fluctuating water table. Simulated depth to water table agreed well with measured depths in all phases, but only when using measured physical data for the deeper subsoil. Simulated evapotranspiration using phase 1 data produced poor results for individual nodal areas when compared with phase 4 data (reference level), while phase 2 data produced good results if measured physical data for the deeper subsoil were included. Physical variability of nodal areas was better characterized by the soil survey data than by results from a single boring (phase 3).

Use of existing soil survey data, in combination with selected on‐site investigations, could reduce the cost of data gathering in this study by an estimated 50% as compared with the common procedure of making systematic borings in each grid point. The degree of detail of interpretation of simulation results for nodal areas should be limited by the field variability observed.
A Scanning Electron Microscopy Evaluation of the Fabric and Mineralogy of Some Soils from Malaysia
Authors: Eswaran H. , Daud N.
Published: July 2010

Four pedons — an Aquic Dystropept, Typic Paleudult, Tropeptic Haplorthox, and Haplic Acrorthox — representing a sequence of soils on shales in Peninsular Malaysia were employed to evaluate the changes in plasmic fabric and related distribution patterns as a function of soil genesis. The decreases in sepic features when proceeding from the cambic to the oxic stage of soil formation is due to changes in colloid composition (micaceous to kaolinite‐sesquioxide), size of colloid (coarse to fine clay), and masking of the optical properties of the plasma by the free Fe. Complimentary SEM studies are presented to show the structure of the domains and the interdomain relationships which determine the plasmic fabrics and the related distribution patterns.

Scanning electron microscopy (SEM) and thin‐section micrographs of secondary goethite and gibbsite are presented and based on the SEM morphologies, a silicification of the gibbsite to kaolinite is postulated in the surface horizons of the Acrorthox.
The Priming Effect on Rate of Tobacco Mosaic Virus Degradation in Soil Columns
Authors: Cheo P. C. , Nickoloff Jon A.
Published: July 2010

Soil columns were set up to monitor tobacco mosaic virus (TMV) degradation in a time sequence study. One set of columns received a constant input of virus for nearly 3 months (challenged columns) and an additional set of soil columns received only a single treatment of virus (fresh columns). Gradual degradation of TMV in the challenged columns netted negligible residual virus at the end of the challenging period, even though a total of 11.75 mg of TMV had been added. When a high titer of virus was introduced into both columns for comparison, a much faster rate of virus degradation occurred in the challenged columns, especially in the early stages. In fresh columns the rate of virus degradation was sluggish at the early stage but accelerated after 2 weeks. Therefore, repeated additions of a small amount of TMV stimulated the process of TMV degradation in soil. The rate of TMV degradation was comparatively higher in the upper (0–10 cm) layers of the soil column than the lower (10–20 cm) layers.
Nitrate Movement with Zero‐order Denitrification in a Soil Profile
Authors: Kanwar R. S. , Baker J. L. , Johnson H. P. , Kirkham D.
Published: July 2010

A theoretical analysis of the movement of nitrates in an unsaturated soil with zero‐order denitrification is presented. The transport equation and boundary conditions are established to represent a field situation (i.e., application of N to the surface of a soil that already has nitrogen present in its profile). An analytical solution is derived. For given values of the diffusivity, pore solute velocity, and the rate coefficients for denitrification, the relative concentration profiles are shown at different times. Comparison with published data is made and it seems that the theoretical relationship fits the data reasonably well.
Sodium/Calcium Exchange in Montmorillonite and Illite Suspensions
Authors: Shainberg I. , Oster J. D. , Wood J. D.
Published: July 2010

The effect of salt concentration and exchanger composition on Na/Ca exchange in montmorillonite and illite suspensions (0.02 to 0.08 g clay/g water) was studied, where the equivalent fraction of exchangeable Ca, ECa, ranged from 0.6 to 1. A theoretical evaluation based on double‐layer theory for montmorillonite indicates that the formation of tactoids and internal surfaces at the Ca3+ end of the exchange isotherm can cause the Vanselow selectivity coefficient, KV, to depend on exchangeable cation composition and total electrolyte concentration. Whereas for montmorillonite, KV increased with ECa (0.6 < ECa < 1), as predicted for internal surfaces, the reverse was true for illite, where external surfaces predominate. Likewise, for a given Na adsorption ratio, dilution of the equilibrium solution for illite (0.6 < ECa < 1) and for montmorillonite (ECa ≃ 0.6) decreased KV as predicted for external surfaces.

The average Gapon selectivity coefficient for the montmorillonite (0.011) and illite clays (0.023) with ECa ≤ 0.8, suggests that the value for soils, (0.0148) reflects their mixed mineralogy.
Exchangeable Aluminum and pH as Indicators of Lime Requirement for Corn
Authors: Farina M. P. W. , Sumner M. E. , Plank C. O. , Letzsch W. S.
Published: July 2010

Notwithstanding a voluminous body of literature on the subject there is still poor agreement regarding the relative merits of lime requirement indices based on exchangeable Al and those based on pH measurements. The work reported here was conducted in an effort to obtain greater clarity on the subject. Lime × P × Mg factorialized pot experiments were conducted on Mollisols, Ultisols, and Oxisols using corn as an indicator crop. Plant tissue was analyzed for several essential elements plus Al and the soils were tested for exchangeable cations, P, and pH. Yield responses fell into three categories: (i) those in which liming neither promoted nor depressed growth, (ii) those where growth was initially promoted by liming with no depressive effect and (iii) those where liming to neutral pH values depressed yield. The results showed that corn response to lime was essentially similar over a wide range of soils when Al saturation of the soil was used as the index of lime requirement. Corn response was poorly related to pH in water but the relationship improved when salt pH was used. As nearneutral pH values were approached, the uptake of a number of nutrients was reduced, suggesting that the long‐held view that such pH values have beneficial effects on nutrient availability warrants re‐investigation.
Soil Taxonomy and Regional Land Use Interpretations for Ohio
Authors: Olson K. R. , Wilding L. P. , Hall G. F.
Published: July 2010

Soil Taxonomy provides for interpretations at each of the categorical levels; order, suborder, great group, subgroup, family and series, plus their phases. The potential for interpretations is best at the series level, but is feasible at higher categories. Categorically and cartographically generalized maps with percent compositions between 56 and 76% were prepared for Ohio. Once these maps were prepared it was possible to develop interpretations for each level of generalization by (i) assembling all the physical environmental data available for the area, (ii) applying the differentiae and covariant phenomena of soil taxonomic terms associated with the soil classification at the higher taxonomic levels, (iii) analyzing the existing land use and its associated limitations and suitabilities, and (iv) predicting the response of soil in similar taxonomic classes to alternative land uses. The taxonomic system does permit the separation of single factor criteria which in themselves are pertinent to interpretations and planning decisions. Two such soil properties that are reflected at high categorical levels include potential for saturated upper soil horizons (aquic suborders) and fragipans (fragi great groups) as diagnostic subsurface criteria.
Effects of Bicarbonate on Sodium Hazard of Irrigation Water: Alternative Formulation
Authors: Miyamoto S.
Published: July 2010

The conventional equation using the saturation index does not satisfactorily account for the effect of bicarbonate on sodicity. We, therefore, examined the existing method and presented an alternative formulation. The alternative formulation was based on direct numerical solutions of well‐known carbonate equilibrium reactions, and consisted of the solution of the second‐ or the third‐order polynomial approximation. The analytical results were then compared with published laboratory, lysimeter, and field data. The comparison indicates that the conventional equation using the saturation index overestimates the sodicity of irrigation water having a high ratio of Ca to HCO3 and underestimates otherwise. The method also generally overestimates the sodicity of drainage water. The proposed third‐power polynomial approximation yields a satisfactory prediction of the sodicity of irrigation water, of drainage water, and of surface soils. The second‐order approximation can also be used for predicting the sodicity of drainage water if the pH of the drainage water is known. The proposed methods are somewhat more complex than the conventional method, but can be conveniently utilized with a programmable calculator or a mini‐computer.
Mineralogical Characteristics and Transformations of a Vertical Rock‐Saprolite‐Soil Sequence in the North Carolina Piedmont: II. Feldspar Alteration Products‐Their Transformations Through the Profile
Authors: Calvert C. S. , Buol S. W. , Weed S. B.
Published: July 2010

Feldspar minerals near the rock‐saprolite interface weathered directly to gibbsite, tubular halloysite, and amorphous aluminosilicate minerals. The gibbsite precipitated as aggregates of tiny plates deep in the profile. This mineral then resilicated into a tabular halloysite pseudomorphic after the gibbsite.

There was very little evidence of amorphous materials throughout the profile but apparently amorphous spheres formed on the surface of feldspars and quartz in the weathering rock. These amorphous spheres seemed to radially crystallize into tube‐shaped minerals, presumably halloysite. Halloysite in the deep saprolite later recrystallized, via a randomly‐interstratified phase, to plate‐shaped kaolin minerals. Morphology of the 1:1 layer aluminosilicates did not provide evidence for degree of crystallinity as determined by X‐ray diffraction; poorly crystalline plate‐shaped and more highly crystalline tube‐shaped kaolin minerals were found in the same profile.
Inhibition by Xanthates of Nitrification and Urea Hydrolysis in Soil
Authors: Ashworth J. , Akerboom Helen M. , Crépin J. M.
Published: July 2010

Inhibition of urease activity and of nitrification by potassium xanthates was measured by adding them to soil amended with urea or (NH4)2SO4 and determining the urea remaining or nitrate produced after incubation at 23°C. The xanthates of unsubstituted alcohols of low molecular weight were the best inhibitors of urease and nitrification. The effectiveness of nitrification inhibition was not well correlated with the amounts of CS2 evolved from soil treated with xanthates in sealed Conway units.
The Magnesium Problem in Nitrate Determination by Steam Distillation
Authors: Clausen C. , Bock B. R. , Peterson G. A. , Olson R. A.
Published: July 2010

Steam distillation of NH3 is commonly used to quantify the amount of mineral N in soil and plant materials. A problem with NO3‐ recovery by this method was encountered in an NH3 volatilization study. When NH4NO3 solutions were collected in acid and analyzed for NH4+‐N and NO3‐‐N, incomplete recovery of NO3‐ occurred. As the volume or normality of H2SO4 added to the distilling solution increased, more of the MgO used to raise the pH of the distilling solution was solubilized, which caused NO3‐ recovery in the first 25ml of distillate to decrease. Only 80% NO3‐‐N recovery was obtained with 20 ppm of Mg2+ in the distilling solution. Soils with 3 meq exchangeable Mg2+/100 g depressed NO3‐‐N recovery by 15% using the standard distillation procedure. An interaction between Mg2+ and Devarda's alloy evidently inhibits NO3‐ reduction.
Evaluation of Phosphorus Fixation Capacity of Tropical Savannah Soils of Western Nigeria
Authors: Ayodele Olufemi , Agboola Akinola A.
Published: July 2010

It is generally believed that tropical soils fix most Phosphorus (P) applied as fertilizers into forms not available to plants. To study fixation characteristics of savannah soils of western Nigeria, 22 surface soil samples varying in cropping histories, physical and chemical properties, and derived from igneous and metamorphic rocks were evaluated for capacities to fix soluble‐P with time.

The fractional recovery (FR) which is the proportion of added P extracted by Bray's P1 (0.03N NH4F + 0.025N HCl) decreased with time following a pattern of rapid decline during the first few days of incubation and a slower decline thereafter. The decrease suggests an exponential relationship, and fits into the equation

FR = ‐K ln t + C.

The equations were used in calculating probable residual values of applied‐P at times within or outside the range of the experimental period.

The high FR and residual values indicate that these soils fix little P in contrast to earlier‐held views about the P‐fixation capacity of tropical soils. The FR was significantly correlated with organic matter, clay, citrate‐dithionite‐extractable oxides of Fe and Al while there was no correlation with soil pH.
Trace Metal Complexation by Fulvic Acid Extracted from Sewage Sludge: I. Determination of Stability Constants and Linear Correlation Analysis
Authors: Sposito Garrison , Holtzclaw K. M. , LeVesque‐Madore C. S.
Published: July 2010

The complexes formed between either Cd2+ or Pb2+ and fulvic acid extracted from sewage sludge mixtures were investigated by potentiometric titration of K/H fulvate with either Cd(ClO4)2 or Pb(ClO4)2 at pH 5.0 and 25°C, in an ionic medium of 0.1M KClO4. Formation functions were calculated from the titration data and analyzed by the Scatchard plot method. The results were similar to those obtained previously for sludge‐fulvic acid complexes of Ca2+ and Cu2+, in that two classes of complexes were found for both Cd2+ and Pb2+. The common logarithms of the measured conditional stability constants for the two types of complexes with sludge‐derived fulvic acid were hypothesized to be linearly correlated with the Misono softness parameter, which is a quantitative measure of the tendency to covalent bonding on the part of a metal cation. The resulting linear correlation equations had r2‐values ≥ 0.99 and, therefore, were used to predict conditional stability constants for complexes of sludge‐derived fulvic acid with Mg2+, Mn2+, Fe2+, Ni2+, and Zn2+, which cannot be investigated by the method of potentiometric titration.
Calcium Phosphate Precipitation: Identification of Kinetic Parameters in Aqueous Limestone Suspensions
Authors: Brown J. L.
Published: July 2010

Phosphate disappearance from aqueous calcitic limestone suspensions was described using an equation for interface‐, controlled crystal growth following addition of hydroxyapatite seed crystals. Phosphate removal from solution exhibited second order dependence on the phosphate concentration. Hydroxyapatite seed crystals were more important than limestone in governing phosphate removal. Limestone functioned primarily to buffer the activities of (Ca2+) and (OH‐). At pH 8.5, an increase of 0.1‐millimolar (mM) NaF caused a fivefold increase in the rate constant. Twenty successive reactions of limestone with phosphate caused a fourfold increase in the phosphate removal rate. A portion of freshly precipitated calcium phosphate probably served as seed for development of new crystals. Participation of both (F‐) and hydroxyapatite crystals suggests a mixture of fluorapatite and hydroxyapatite, or an apatite precursor formed in the experiments.
Residual Effects of Phosphorus Applications on a High Phosphorus Adsorbing Oxisol of Central Brazil
Authors: Yost R. S. , Kamprath E. J. , Naderman G. C. , Lobato E.
Published: July 2010

High crop yields on P‐deficient Oxisols are not possible without application of relatively high amounts of fertilizer P. Correction of P deficiency can be accomplished by an initial broadcast application of a high rate of P or by lower rates of P applied as a band treatment or combination broadcast and band treatment. The residual effect of such P applications is influenced by the rate and method of application. A field study was established on a Haplustox in the Cerrado of Contral Brazil to evaluate the residual value of applied P as measured by corn yields and soil P analyses.

Comparisons were made of the residual‐P effectiveness where a total of 140, 280, and 560 kg P/ha were applied initially as one broadcast application or, in equal increments as banded applications, to the previous four crops.

With a total application of 140 and 280 kg P/ha, the residual P from the banded applications gave greater corn yields and P uptake than the initial broadcast applications. At the 560 kg P/ha rate, where yields were nearly maximum, there were no differences in yield due to the application method.

Soil test P levels indicated a considerable residual effect from the higher rates of broadcast P. Fractionation of soil P indicated a conversion with time of more soluble forms of P to less soluble forms. Estimates of P requirements from P. sorption curves suggested a residual efficiency of 40–60% of the previously broadcast fertilizer P. Although clayey Oxisols have a high P requirement for maximum yields, there is a considerable residual effect of fertilizer P which needs to be included in estimates of the efficiency of P fertilization.
Effects of Litter Alteration on Carbon Dioxide Evolution from a South Carolina Pine Forest Floor
Authors: Reinke J. J. , Adriano D. C. , McLeod K. W.
Published: July 2010

A field study in the upper Coastal Plain of South Carolina was conducted to evaluate the impacts of several litter manipulations on carbon dioxide evolution from a longleaf pine (Pinus palustris Mill.) forest floor. These manipulations, which included prescribed burning, removal of the L‐layer material (red straw), and total litter (O1 and O2 horizons) removal, were compared with undisturbed control treatment using a static alkali absorption technique for CO2 measurement.

Though slight reductions were noted, the burning and removal of the L‐layer material had less effect on the evolution of CO2 from the forest floor than total litter removal. Total litter removal, however, significantly reduced the average rate of CO2 evolution by approximately 22% (p ≤ 0.05). The amount of CO2 evolved was sensitive to rainfall and air temperature, showing declines in periods of drought and cool temperature. However, on an annual basis, the air temperature was much more important than rainfall in estimating the CO2 evolution. The burning treatment increased the pH and nitrogen concentrations of the litter and the soil pH at the 0 to 5‐cm depth. The calculated net annual respiration (CO2‐C production), exclusive of root metabolism, was approximately equivalent to 95% of the C input from litterfall deposited on the ground during this period, indicating that perhaps the accumulation of litter has reached a steady state condition.
Influence of Spartina Alterniflora on Nitrogen Loss from Marsh Soil
Authors: Buresh R. J. , DeLaune R. D. , Patrick W. H.
Published: July 2010

The influence of Spartina alterniflora, a common salt marsh macrophyte, on loss of NH4+‐N from a Louisiana salt marsh soil was examined in the greenhouse. Labelled NH4+‐N, equivalent to approximately 100 µg N/g soil, was added in 10 installments over 18 weeks to undrained soil cores with and without stands of S. alterniflora. In the presence of S. alterniflora, 93% and 94% of the added N was recovered from constantly flooded and alternately flooded and dried soil, respectively. In the absence of S. alterniflora, loss of added NH4+‐N was greater; only about 56% of the added N was recovered from constantly flooded soil. Actively growing S. alterniflora apparently assimilated the inorganic soil N before it could be lost in gaseous form via nitrification‐denitrification reactions.
Automated Aluminum Analysis with the Aluminon Method
Authors: Bertsch P. M. , Alley M. M. , Ellmore T. L.
Published: July 2010

An automated method of aluminum analysis by the aluminon (ammonium salt of aurin tricarboxylic acid) procedure is described. The method employs ascorbic acid for removal of Fe(III) interference and eliminates, with proper sample pretreatment, the need for a protective colloid. The calibration curve has a correlation coefficient > 0.99 and a standard deviation around the regression line of ± 0.07 absorbance units up to 1.2‐ppm Al in solution. Standard autoanalyzer components are utilized in the system and computer interfacing is possible.
Properties of the Sorptivity for Exponential Diffusivity and Application to the Measurement of the Soil Water Diffusivity
Authors: Braddock R. D. , Parlange J. Y. , Lisle I. G.
Published: July 2010

For certain diffusivities, first integral techniques can be used to decouple the soil‐water diffusion equation, in similarity form, into a set of first‐order equations. Such a decoupling is possible where the diffusivity depends on the water concentration, as either a power law or as an exponential function. Here we show that the exponential case is related to the power law case, but with some resulting complications.

For this class of diffusivities, the solutions form a special class, and we generate some of their properties. In particular, the sorptivity can be represented by a simple relation to a universal function of the water content. This function is tabulated and compared with results obtained by another method, i.e., optimization. The results are applied to the measurement of soil‐water diffusivity.
Sodium‐Calcium Exchange in Nile Delta Soils: Single Values for Vanselow and Gaines‐Thomas Selectivity Coefficients
Authors: Sheta Tarek H. , Gobran George R. , Dufey Joseph E. , Laudelout Henri
Published: July 2010

Na‐Ca exchange measurements were carried out on 11 representative soils from the Nile Delta. Experiments were conducted over a wide range of exchanger compositions. Due to their common alluvial origin, all soils showed identical exchange properties.

The experimental data appeared to be well described either by a single Vanselow selectivity coefficient or by a single Gaines‐Thomas coefficient. The Gapon coefficient, as originally defined, increased linearly with the exchangeable calcium fraction (or decreased with ESP). After examining the sensitivity of those coefficients to experimental errors, as a function of the exchanger composition, values of 5.97 and 2.30 mol/liter were calculated for the Gaines‐Thomas and Vanselow coefficients, respectively. These correspond to a Gapon coefficient as redefined by Sposito equal to 48 (mol/m3)½.
Leaching of Fertilizer Ions in a Ultisol from the High Rainfall Tropics: Leaching Through Undisturbed Soil Columns
Authors: Pleysier J. L. , Juo A. S. R.
Published: July 2010

Downward movement of applied Ca3+, Mg2+, K+, and NO3‐ in a coarse‐textured, kaolinitic Ultisol profile was studied in the laboratory using undisturbed soil columns. The soil columns were leached with an amount of water equivalent to the annual rainfall of the sampling site (2,420 mm) through a rainfall simulator over a period of 72 days. Added nitrate in the forms of Ca, Mg, or K salts leached readily through the profile. Nitrate leached mainly with Al3+ ions. Cations leached differentially, depending upon the exchange selectivity of the soil and upon the surface loading of the cation in question. The leachability of the cations under the experimental conditions follows the order K < Al ≈ Ca ≈ Mg < Na.

The vertical distribution of added Ca in the leached profile may be predicted by Walter's formulation of ion exchange chromatography.

The limed soil columns retained more Ca in the surface layer than the columns treated with Ca(NO3)2 when an equal amount of Ca was applied.
Grazing of Blue‐Green Algae (Cyanobacteria) in Flooded Soils by Cypris sp. (Ostracoda)
Authors: Grant Ian F. , Alexander Martin
Published: July 2010

Grazing by the microcrustacean, Cypris, on five species of 14C‐labelled N2‐fixing blue‐green algae (cyanobacteria) in flooded soils indicated diet preferences among the algae. Animal size and floodwater temperature markedly affected feeding rates, but pH had little effect from pH 5.0 to 10.0. Control of feeding was achieved with low concentrations of lindane. Cell size of the blue‐green algae was not apparently responsible for diet selection, but cell age was significant with two species. It is suggested that nitrogen fixation by blue‐green algae in paddy fields may be increased by using inocula of algae not suitable for active grazing or by suppressing grazing by means of insecticides.
Long‐Term Recovery of Fertilizer Nitrogen Applied to a Native Mixed Prairie
Authors: Power J. F.
Published: July 2010

Previous research on perennial grassland soils has generally shown that a large part of any fertilizer nitrogen (N) added is immobilized in grass roots or in soil organic matter. Few studies have measured the amount of such immobilized N that eventually becomes mobilized and taken up by plant growth in subsequent years. In this experiment, up to 540‐kg fertilizer N/ha was applied to native mixed prairie in North Dakota during a 1‐ to 6‐year period, and residual effects of these treatments on grass production were followed until no further plant growth response was measured. When a total of 270‐ or 540‐kg N/ha had been applied, plant growth responses were measured for up to 9 years after fertilization ceased. As fertilizer N rate decreased, length of residual effects likewise decreased. Part of the residual response may have resulted from increased density of cool‐season grasses where higher N rates were applied. Growth responses after fertilization ceased were often greater when fertilizers were applied over a 6‐year period, rather than applying an equal quantity of fertilizer N all in 1 year. For the 540‐kg N/ha treatment, as much as 12% of the fertilizer N applied was recovered in top growth after fertilization ceased. Assuming that all increased inorganic N in the soil resulting from fertilization was used by plants during the residual period, and that the remaining fertilizer N taken up by top growth after fertilization ceased came from mobilization of fertilizer N present in grass roots in 1968, then an estimate can be made of availability of fertilizer N in roots. Maximum value for such an estimate was 44‐kg N/ha, leaving 60‐ to 160‐kg fertilizer N/ha permanently immobilized as this root material decomposed. Thus, when 270‐ or 540‐kg fertilizer N/ha was applied, typically about 30% was permanently immobilized by absorption into root material during the period of fertilization, 35% was removed in top growth, and 35% was either immobilized permanently in soil organic matter or lost by gaseous means.
Comparisons of Arithmetic Average Soil pH Values with the pH Values of Composite Samples
Authors: Baker A. S. , Kuo S. , Chae Y. M.
Published: July 2010

Close agreement was found between arithmetic mean pH values of limed samples and the pH values of composited samples. Agreement was consistently and considerably poorer when pH values were converted to H‐ion activities [(H+)] before averaging. Results are explained by the greater linearity between soil pH and base saturation (BS) in the acid range of mineral soils than between (H+) and BS. Linearity can be assessed by comparing average pH values with those of composited samples.
Release of NH4+ in Soils by Oven Drying
Authors: Frye W. W. , Hutcheson T. B.
Published: July 2010

There is often a pronounced increase in exchangeable NH4+ content when soils are dried, particularly when oven‐dried. The origin of the NH4+ is unknown. The objectives of this study were (i) to determine the effects of oven drying on the release of NH4+ in soils with different properties, and (ii) to evaluate possible sources that may account for the release. Samples form the Congaree, Davidson, Huntington, and Maury soils were oven‐dried at 110°C for 24 hours and analyzed for 2N KCl‐extractable NH4+ (exchangeable NH4+) and NO‐3. Values for moist samples of soils were subtracted from values for oven‐dried soils to determine the amounts of NH4+ released by drying. The amounts ranged from 5 to 20 ppm N, with the greatest amounts released from the top 30 or 45 cm of the Davidson and Maury soils. Generally, the amount of NH4+ released by oven drying decreased with depth in the soils. Monochloracetic acid (CH2ClCOOH) extracted more NH4+ than did KCl from oven‐dried surface samples of the Congaree and Davidson soils, but there was little or no difference in the amounts of NH4+ extracted by the two solutions from moist samples of Ap horizons or from samples below the Ap horizons, whether moist or oven‐dry. These results suggest an organic source of NH4+ in the Ap horizons. The relatively large amount released from deep in subsoils suggests the presence of an inorganic source also. We conclude that NH4+ is released from both organic and inorganic compounds during oven drying. Nonexchangeable NH4+ in interlayers of clay minerals usually increased with oven drying. We therefore conclude that nonexchangeable NH4+ is not a source of released NH4+. In fact, some of the NH4+ released by oven drying appears to be simultaneously fixed as nonexchangeable NH4+ in certain cases. The organic source of NH4+ is probably several constituents of rather highly decomposed soil organic matter. The inorganic source is thought to be NH4+‐phosphate complexes, perhaps taranakite‐like compounds. Further research is needed to identify specific sources.
Chemical Transformations of Urea‐Nitrogen and Movement of Nitrogen in a Shortgrass Prairie Soil
Authors: Stillwell M. A. , Woodmansee R. G.
Published: July 2010

This study, conducted on the Central Plains Experimental Range during the summer of 1979, was to (i) quantify the temporal dynamics of the transformations of nitrogen (N) in a simulated urine spot, (ii) determine the effect of urea hydrolysis on pH, and (iii) determine the depth of movement of nitrate by leaching. Miniplots of blue grama were established, and open‐ended aluminum cylinders 10 cm in diameter and 40 cm in length were embedded in each plot. Simulated urine was applied to two‐thirds of the plots at a rate of up to 45 g N m−2. The remaining plots were controls.

After the simulated urine application, only 6% of the added N remained as urea at 2 days; no urea‐N remained at 4 days. Maximum accumulation of ammonium‐N (39.9 g N m−2) was simultaneous with the disappearance of urea. Elevated levels of nitrate were first detected at day 12 when 6.7 g N m−2 had accumulated. No measurable nitrite accumulated during the experiment.

Through the first 4 days, 83% of the (urea + ammonium)‐N in the profile was in the top 15cm of the soil. With the rains near the end of the study, nitrification proceeded, and nitrate was leached through the profile to below the depth of the cores.

Simulated urine significantly affected soil pH to 15 cm. From an initial pH near 6.0, urea hydrolysis increased soil pH from 0.6 to 1.3 units. As nitrification prodeeded after day 40, the pH decreased to below control levels.
Classification and Genesis of Spodosols in the Central Appalachians
Authors: Stanley Scott R. , Ciolkosz Edward J.
Published: July 2010

Seventeen well‐drained pedons were sampled in Pennsylvania and northern West Virginia. Sixteen of the pedons had well‐expressed Spodosol morphology while one had very marginal Spodosol morphology. These pedons were classified according to Soil Taxonomy and the Canadian soil classification system. The degree of spodic horizon development in relation to soil temperature was examined. Only three of the 17 pedons studied met the chemical criteria of Soil Taxonomy for Spodosol identification, while 13 met the chemical criteria of the Canadian system. Three pedons were examined for cracked coatings on sand grains and dark pellets of coarse‐silt size; all three pedons qualified as Spodosols on the basis of these criteria. These data indicate that more emphasis should be placed on the field criteria described in Soil Taxonomy and less on the chemical criteria or that the chemical criteria should be amended.

The spodic horizon (Bh and Bir) in each of the 17 pedons contained the largest amount of illuvial Al, Fe, and C of the various horizons of the soil. As the mean annual soil temperature (MAST) of these soils increased, the Fe (pyrophosphate extracted) and C (total organic) content of the spodic horizon decreased (correlation coefficients of −0.70 and −0.46, respectively). The thickness of the spodic horizon was also related to soil temperature. There was a weak correlation (r = −0.31) of decreased thickness with increased MAST. In addition, Al (pyrophosphate extracted) content in the spodic horizon and the depth to the top of the spodic horizon showed a very weak correlation to MAST (correlation coefficients of −0.27 and 0.23, respectively). Although weak, these correlations show that Al, Fe, and C accumulate in spodic horizons of well‐drained soils in colder areas of the Appalachians to a greater extent than in warmer areas, and result in a more strongly expressed Spodosol in the cooler areas. The lack of stronger relationships may be a reflection of the effect of varying vegetation types (e.g., hemlock vs. maple) in the mixed hardwood‐conifer forest that was the natural vegetation of these soil pedons, or of varying vegetation during the development of these soils.
Effect of Differential Adsorption of Potassium and Magnesium in Soils on Magnesium Uptake by Corn
Authors: Stout W. L. , Baker D. E.
Published: July 2010

Indices of the differential adsorption of potassium (K) and magnesium (Mg) were used to explain the differences in magnesium uptake by corn seedlings (Zea mays L.) grown on two widely different soils of the Rayne (a fine‐loamy, mixed, mesic Typic Hapludult) and the Hublersburg (a clayey, kaolinic, mesic Typic Hapludult) series. The differential adsorption of potassium was found to be the controlling factor in the uptake of magnesium by corn seedlings in these two soils. The differential adsorption concept may be useful in predicting which soils may or may not respond readily to magnesium fertilization.
Interrelationship Between the One‐Step and Increment Methods of Determining Diffusivity
Authors: Prunty Lyle
Published: July 2010

The “one‐step” and “increment” methods for determining soil‐water diffusivity (D) are shown to be fundamentally the same. Only a slight modification of the development of the outflow equation for the increment method is needed in order to obtain identical formulas for calculating D by either method.
Portable System for Furrow Irrigation of Small Plots
Authors: Heatherly Larry G. , Ginn L. H.
Published: July 2010

A portable apparatus designed for furrow irrigation of small plots was constructed with a 3,800‐liter water wagon and a piece of gated aluminum irrigation pipe mounted laterally on the wagon. The pipe is long enough to water the middles of a four‐row plot. It is clamped by two brackets to a frame which is hinged at two points on the underside of the wagon. The hydraulic system of a standard row‐crop tractor is used to operate two double‐action hydraulic cylinders which are pivoted on the underside of the wagon and to each arm of the support frame for the gated pipe. A pump mounted on the rear of the wagon is attached to the water tank by noncollapsing suction hose and to the gated pipe by flexible fire hose. A graduated sight gauge on the pump end of the water tank allows for accurate measurement of applied water. The maximum output of the system is 380 liters/min.; a fully‐loaded trailer can provide 10 cm of water to a plot with four 100‐cm‐wide rows 9.1 m long without refilling.
An Adaptive Finite Difference Scheme for The One‐Dimensional Water Flow Equation
Authors: Dane J. H. , Mathis F. H.
Published: July 2010

The pressure bead form of the general flow equation for water in a porous medium was numerically solved using a scheme that allowed both the time step (Δt) and the space increment (Δz) to be changed during the flow process. The mass balance equation was used as a check for the accuracy of the simulation. A fixed number of grid points in the space direction was continuously redistributed to allow for small Δz values in regions of large changes in pressure head gradients while allowing large Δz values in regions of small changes. The method, which is unconditionally stable, is demonstrated for an infiltration and an evaporation process.
Thermodynamics of Sodium‐Copper Exchange on Wyoming Bentonite at 298°K
Authors: Sposito Garrison , Holtzclaw Kenneth M. , Johnston Cliff T. , LeVesque‐Madore C. S.
Published: July 2010

The exchange of copper (Cu2+) for sodium (Na+) at 298°K on Wyoming bentonite was investigated in a perchlorate background medium maintained at pH 5.0 to 6.0 and at a total normality of 0.01N. It was found that the exchange process could be well characterized by a Vanselow selectivity coefficient that was equal to 1.32, independent of the exchanger composition, and by a similarly constant apparent adsorbed metal charge equal to 0.92 ± 0.05 eq kg−1. These results are in conflict with previous data obtained at 295°K for Na+‐Cu2+ exchange on montmorillonite in a 0.01N chloride background medium. It was concluded that a principal cause for the differences between the two sets of data could be the presence of CuCl+ complexes in the chloride medium.