bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of Applied Anhydrous Ammonia in Soils and Germination Hazard to Winter Wheat
Authors: Jacobson J. S. , Westerman R. L. , Claypool P. L.
Published: July 2010

Current changes in residue management systems for winter wheat (Triticum aestivum L.) include anhydrous NH3 injection combined with herbicide application, planting, and other field operations. The feasibility of NH3 application during planting is dependent upon potential NH3 toxicity to germinating seeds. A laboratory experiment was conducted to study anhydrous NH3 movement in soils by injecting 124 and 180 mg N as NH3 into a Hollister clay (fine, mixed, thermic Pachic Paleustolls), Grant silt loam (fine‐silty, mixed, thermic Udic Argiustolls), and Norge clay loam (fine‐silty, mixed, thermic Udic Paleustolls) at 0.124 and 0.181 water (kg kg−1) contents. Soil samples were taken 1, 7, and 14 d after N application. Soil NH+4‐N and calculated NH3(aq) concentrations following NH3 injection generated a normal distribution curve with N concentrations highest near the injection point and decreasing with increasing distance. Calculated NH+4 diffusion coefficients decreased with time and water content and were soil dependent. Field studies were conducted in 1983 to determine the potential germination hazard from NH3 applied at 0, 56, 112, 168, 224, and 280 kg N ha−1 while planting, and in 1984 to winter wheat planted 0, 1, 3, 5, 6, and 7 d after applications of 0, 100, and 200 kg N ha−1. Stand counts, forage NO‐3‐N concentration, and yield were not influenced by NH3 applications during planting in 1983, but grain N concentration increased linearly up to 24.1 mg g−1 with 280 kg N ha−1. In the 1984 experiment, increasing NH3 rates did not decrease seedling stand, even though analysis of soil samples reflected increased soil pH and soil NH+4‐N concentration. Anhydrous NH3 placement at a sufficient distance from newly seeded rows will ensure the success of systems which include NH3 injection in conjunction with other field operations in residue management systems.
Experimental Evaluation of Two Operational Standard States for Montmorillonite in Metastable Hydrolysis Reactions
Authors: Peryea F. J. , Kittrick J. A.
Published: July 2010

Two conventions have been used to represent smectite formulas in mineral hydrolysis reactions: exchangeable cations are either included in (monophase structure) or excluded from (charged structure) the Standard State phase designation. Replicate mixtures of K‐saturated Belle Fourche montmorillonite, kaolinite, goethite, and magnesite were taken through a series of consecutive equilibrations with 0.01, 0.1 or 1.0 M KCl solutions using low solution/solid ratios. Apparent chemical equilibrium with respect to magnesite was used as an indication of system‐wide meta‐equilibrium. Following equilibration, the aqueous phases were recovered by immiscible displacement. Total soluble K, Mg, Si, pH, and ambient CO2 were measured. The solutions were chemically speciated using an ionassociation computer model. Hydrolysis reactions were developed based on the two smectite standard state phase designations. Reaction equilibrium constants and Gibbs free energies of formation (ΔG°) for montmorillonite were calculated. In the case of the monophase structure model, these parameters were functions of exchangeable cation composition. The mean ΔG° (montmorillonite) values for the charged structure and monophase structure models differed in absolute value but were equally precise. These results suggested that a characteristic metastable equilibrium was obtained in the experimental system. Justification for the selection of one convention over the other must be based on criteria other than precision.
Prediction of pH Errors in Soil‐water Extractors Due to Degassing
Authors: Suarez D. L.
Published: July 2010

Moisture samples taken from the unsaturated zone with soil water extractors undergo degassing and an upward shift in pH. The measured pH values from commercially available extractors are usually sufficiently in error that they cannot be used in a quantitative manner. A model has been developed that predicts the extent of CO2 degassing and the resulting pH error. Using this model measured pH values can be corrected back to in situ soil water pH provided that precipitation has not occurred in the extractor. Extractors are classified into two groups—single chamber and multichambered. The extractors are evaluated for both operation under constant vacuum (open to the source) and decreasing vacuum (evacuated and then sealed). Analysis of the data and model predictions indicates that the major factor controlling the pH error is the ratio of liquid volume to total extractor volume. Additional factors exerting major influence are the initial extractor gas composition and the total pressure in the extractor when sampled. Variations in soil solution composition and differences in soil CO2 concentrations in carbonate buffered systems had a major effect on pH values but a negligible effect on the extractor induced pH error. Under typical field conditions the multichambered extractor is predicted to give the most satisfactory results; the pH errors were sufficiently small that no corrections for degassing were necessary.
Single Column Ion Chromatography: III. Determination of Orthophosphate in Soils
Authors: Karlson U. , Frankenberger W. T.
Published: July 2010

A chromatographic procedure was developed to determine orthophosphate in aqueous soil extracts by single column ion chromatography (SCIC) with conductimetric detection. The eluent stream consisted of 1.5 mM phthalic acid adjusted to pH 2.7 with formic acid. The method allows precise (RSD = 1.1‐3.3%) measurements of trace amounts of orthophosphate (detection limit = 0.3 µg L−1) in the presence of high background levels of Cl‐ and NO‐3. Analysis of orthophosphate by SCIC closely agrees to those values obtained with an AutoAnalyzer based on the Mo blue chromophore reaction. Under the chromatographic conditions described, elution of orthophosphate occurred at 6 min while Cl‐ and NO‐3 had respective retention times of 11 and 20 min. Single column ion chromatography proves to be a rapid and routine method for determination of orthophosphate with greater sensitivity than the conventional colorimetric methods.
Relation Between Potassium Fixation and the Oxidation State of Octahedral Iron
Authors: Chen S. Z. , Low P. F. , Roth C. B.
Published: July 2010

Samples of the <2‐µm fractions of five pure smectites and six soil clays were reduced by sodium dithionite in the presence of a potassium citrate‐bicarbonate buffer. Subsequently, they were freed of excess electrolyte by dialyzing them in a deoxygenated, 10−3 M KCl solution. Subsamples of the resulting clays were used to determine Fe2+/total Fe, the ratio of ferrous Fe to total Fe; mw/mc, the mass ratio of water to clay, at a swelling pressure of 0.3 MPa; KT, the total K; KE, the exchangeable potassium; and KF, the fixed K. Identical samples of the same smectites and soil clays were subjected to the same experiments except that they were treated with sodium sulfate instead of sodium dithionite. Hence, they remained in the oxidized state. Then the differences in the experimental results for the reduced and oxidized samples were determined. For the several samples, it was found that ΔKF, the change in KF, was proportional to Δ(mw/mc), the change in mw/mc. Also, it was found that ΔKF was an exponential function of 1/ΔFe2+, where ΔFe2+ is the change in Fe2+, but that the constants in this function were different for the pure smectites than for the soil clays. From these findings it was concluded that K+ fixation is enhanced by the reduction of octahedral ferric Fe in the clay crystal and that the difference between the pure smectites and soil clays was attributable to nonsmectite minerals in the latter.
Response of Turfgrass to Various Nitrogen Sources
Authors: Landschoot P. J. , Waddington D. V.
Published: July 2010

Nitrogen sources with different properties and release characteristics are used to meet a variety of fertility management needs in turfgrass culture. Our objective was to determine the response of turfgrass to various urea‐formaldehyde reaction products; two particle sizes of oxamide; experimental sulfur‐coated ureas (SCU); products containing combinations of N sources; and an experimental composted sewage sludge. Nitrogen sources included for comparative purposes were isobutylidene diurea (IBDU); commercial SCU products; soluble sources; and Milorganite. In this 2.5‐yr study, 25 N source treatments were evaluated on ‘Merion’ Kentucky bluegrass (Poa pratensis L.) using 196 kg N ha−1 yr−1, split into two equal applications. Turf response was measured by weekly color ratings, weekly clipping yields, and N uptake for six growth periods during 2 yr. Urea‐formaldehyde reaction products containing no water‐in‐soluble N (WIN) gave results similar to those of conventional soluble N sources, while products containing WIN caused less initial color and growth responses, but gave a slight residual effect in the third year of use. Nitrogen uptake for powdered ureaform (66% of N as WIN) and the suspension FLUF (20% of N as WIN) was 44 and 75%, respectively, of that obtained with Formolene (0% WIN). Major differences in color and growth were found for the different particle sizes of oxamide, with the fine (<0.25 mm) material providing a faster release and less residual effect than the coarse (1‐3 mm) material. Turf fertilized with coarse oxamide responded similarly to that fertilized with coarse IBDU (0.7‐2.5 mm). Commercial SCU and fine particle SCU made with curtain granulated urea (94% of particles between 1.14 and 2.38 mm; dissolution rates: 6 and 15%) had pronounced residual effects, especially in the spring prior to fertilization. The experimental composted sewage sludge was inferior to Milorganite as a source of N for use on turf. N uptake with the compost treatment was only 32% of that obtained with Milorganite. Turf response from combinations of N sources generally reflected the amount and type of N source present. All N sources except the sludge compost were effective for turfgrass fertilization. Selection of an N source or combination of sources for turf fertilization should be dependent on quickness and duration of response desired, rate and frequency of applications, and various economic factors.
Copper Activity in Soil Solution: II. Relation to Copper Accumulation in Young Snapbeans
Authors: Minnich M. M. , McBride M. B. , Chaney R. L.
Published: July 2010

Soil solution Cu2+ activity measured in soil saturation extracts was compared with Cu accumulation in young snapbeans (Phaseolus vulgaris L.). Copper was supplied through sewage sludge mixtures of varied Cu concentrations and through Cu‐salt additions to the soil. Treatments were a factorial combination of four levels of Cu additions and four levels of total sludge additions. Soil and sludge pH values were limited to pH 5.0 to 5.5. Plant yield differences were minor. Data are reported showing the relationships of root, shoot, and total plant Cu contents with Cu2+ activity, with DTPA‐extractable Cu, with soluble Cu, and with sludge Cu concentration. The Cu source (sludge vs. salt) produced distinctly different curves in most every case. Sludge treatments demonstrated nonlinear relationships of Cu activity vs. Cu accumulation; these were fit with exponential functions. Higher shoot Cu concentrations occurred with the Cu salt treatments. Higher root Cu levels occurred at lower Cu2+ activity values with sludge as the Cu source. This probably reflects the superior ability of the sludge to replenish or maintain the Cu supply in soil solution. Total soluble Cu was not related to plant Cu. The proportion of Cu in the sludge was closely linked with shoot Cu (r2 = 0.94); root Cu levels also reflected the proportion of Cu in the sludge, but higher sludge rates resulted in increased root Cu. Increased labile, soluble, Cu‐organic complexes with increased sludge rates would explain both the observed differences between salt and sludge treatments and the positive correlation of root Cu and sludge rate. Physiological control of Cu translocation within the plant is implicit in this reasoning. Continual monitoring of soil solution ion activity or a buffering index is needed to improve predictions of plant ion uptake.
A Pedogenic Chronology for Kilbourne Hole, Southern New Mexico: II. Time of the Explosions and Soil Events Before the Explosions
Authors: Gile Leland H.
Published: July 2010

Because tuff was emplaced as a result of explosions that produced Kilbourne Hole, soils formed in the tuff should provide important clues concerning time of the explosions. Pedogenic carbonate of illuvial origin was used to estimate the age of a soil in the tuff. Age was estimated by calculating the amount of pedogenic carbonate in a soil column 1 m2 in horizontal cross section, and by comparing this amount with the amount of carbonate in a soil with estimated age in the nearby Desert Soil‐Geomorphology Project. The amount of pedogenic carbonate for a soil in the tuff is 73 kg m−2. The Desert Project soil is estimated to be about 11000 yr old and has 34 kg m−2 of pedogenic carbonate that accumulated at a rate of 3.1 kg m−2 kyr−1. Using the same rate of carbonate accumulation, the soil in the tuff dates from about 24 000 yr BP and the explosions that produced Kilbourne Hole and the associated tuff are thought to have taken place at about that time. A lava flow preceded the explosions that produced Kilbourne Hole, but a time of sedimentation and soil formation occurred between the two events as evidenced by a postlava, pre‐tuff deposit in which a soil formed. This deposit is attributed to a localized cycle of sedimentation initiated by presence of the lava. The combined ages of the soil in the tuff and the soil in the post‐lava, pre‐tuff deposit are believed to represent the approximate age of the lava. Based on carbonate amount and morphology, the lava is estimated to be about 0.1 million yr old. This contrasts with the most recently obtained K‐Ar date of 0.53 ± 0.03 million yr for the lava. The amount of pedogenic carbonate in desert soils has potential for widespread application as a chronological tool and as a cross‐check for other dating techniques. However, lack of agreement on the age of soils at chronological benchmarks can indicate that some of the dates obtained by chronological extrapolation should be considered tentative, including the date obtained in this study.
Exact Desorptivities for Power Law and Exponential Diffusivities
Authors: Lisle I. G. , Parlange J.‐Y. , Haverkamp R.
Published: July 2010

The desorption of water from a soil is analyzed for a soil‐water diffusivity function obeying a power or an exponential law, and precise numerical values for desorptivity are found. An effective reduction in the number of parameters allows the cumulative desorption for various boundary conditions to be calculated from a short table of results. For the power law case, desorptivity for arbitrary initial water content can be obtained from tabulated values by a simple scaling transformation. A similar scaling transformation yields the exponential desorptivity for arbitrary initial and surface water content. An approximate desorptivity formula of Parlange is discussed, and found to give an accuracy within 2.5% over the whole parameter range. In general, the present results should be useful to assess numerical and analytical procedures.
Effect of Exchangeable Cation and Electrolyte Concentration on Mineralogy of Clay Dispersed from Aggregates
Authors: Ali O. M. , Yousaf M. , Rhoades J. D.
Published: July 2010

The type of clay dispersed from aggregates of various arid land soils as influenced by sodium adsorption ratio (SAR) and electrolyte concentration was evaluated in Ca‐Na and Mg‐Na systems. It was observed that, in general, in the case of Fallbrook I, Fallbrook II, Pachappa, and Arlington soils, all the common clay minerals (kaolinite, clay mica, vermiculite, and montmorillonite) dispersed whenever disaggregation occurred inrrespective of SAR and electrolyte concentration levels. In Bonsall soil, kaolinite and mica clays were apparently more dispersive than montmorillonite, which, in turn, was more dispersive than mixed layer clays in Ca‐NaCl solutions. More intense x‐ray diffraction peaks were obtained, in general, in the Mg‐Na system compared to the Ca‐Na system.
Clay Dispersion and Hydraulic Conductivity of Some Salt‐Affected Arid Land Soils
Authors: Yousaf M. , Ali O. M. , Rhoades J. D.
Published: July 2010

Cumulative clay dispersion from four arid land soils are compared with their relative hydraulic conductivities as affected by electrolyte concentration and sodium adsorption ratio (SAR). As electrolyte concentration decreased and SAR increased, clay dispersion increased and hydraulic conductivity decreased correspondingly. Threshold relations between electrolyte concentration and SAR associated with clay dispersion of 5 g of clay per kilogram of soil corresponded well with hydraulic conductivity threshold relations. This correspondence between clay dispersion and sodicity‐related reductions in soil hydraulic conductivity can be utilized to provide an index based on clay dispersion for screening soils for their sodicity hazard sensitivity and for predicting reductions in soil hydraulic conductivity related to soil and water sodicity.
Phosphorus and Potassium Uptake by Corn in Conservation Tillage Systems
Authors: Mackay A. D. , Kladivko E. J. , Barber S. A. , Griffith D. R.
Published: July 2010

In conservation tillage systems surface application of P and K fertilizers and the annual return of corn residue to the soil surface can result in the stratification of these two nutrients in the topsoil. The extent to which this changes P and K uptake patterns of corn (Zea mays L.) has not been investigated. The objectives of this field study on a Chalmers silty clay loam (Typic Haplaquoll) were to compare the degree of stratification of P and K after 9 yr under conventional, no‐till, and ridge till systems, and to use this data along with root measurements in a model to calculate P and K uptake patterns by corn under these three tillage systems. Under conventional tillage Bray P1‐P and exchangeable K were distributed evenly throughout the topsoil (0–275 mm). Stratification of P and K, however, had occurred in the ridge till and no‐till systems after 9 yr. Of calculated P and K uptake from 30 to 47 d after planting, only 18 and 23%, respectively, came from the upper 75 mm under conventional tillage, compared with 52 and 58%, respectively, under no‐till for the same period. From 30 to 77 d, 39 and 52% of calculated P and K uptake, respectively, was from the upper 75 mm under no‐till compared with only 28 and 26%, respectively, under conventional tillage. Some deep placement of fertilizer P and K may be desirable after several years of continuous no‐till cropping, to provide P and K to roots growing deeper in the soil.
Diffusion of Strontium and Chloride in Compacted Clay‐based Materials
Authors: Robin M. J. L. , Gillham R. W. , Oscarson D. W.
Published: July 2010

This study examines the effect of pore solution composition and temperature on the measured and calculated diffusion coefficients (Dm and Dc, respectively) for Sr2+ in a compacted mixture of bentonite (50 wt%) and sand. Dm for Sr2+ and Cl‐ in the soil was determined at a dry bulk density of ∼1.7 Mg m−3 using deionized water (DW) and two synthetic groundwater solutions (SGW) with ionic strengths of 0.27 and 1.4 mol L−1 to saturate the soil, and at 25, 60, and 90°C. The Dc for Sr2+ was calculated from Dc = Doτ/(1 + ρbKd/θv), where Do is the diffusion coefficient of Sr2+ in free solution; τ is a tortuosity factor, obtained for the compacted soil from Cl‐ diffusion experiments; ρb is the dry bulk density; θv is the volumetric moisture content; and Kd is a distribution coefficient that accounts for the interaction of Sr2+ with the soil. Both Dm and Dc for Sr2+ increased with an increase in the ionic strength of the saturating solutions and with an increase in temperature. The Dm values were, however, always greater than Dc values by a factor of 6.2 to 8.0 for DW and 1.3 to 1.8 for the SGW with an ionic strength of 1.4 mol L−1. This difference is believed to be the result of obtaining Kd values in solutions that differed significantly from the pore solution of the compacted soil. Nevertheless, the results indicate that Dc values, which are often more convenient and less time‐consuming to obtain than Dm values, can at least be used to establish relationships and trends between the diffusion rates of some contaminants in clay‐based materials and the properties of these materials.
Microbial Role in Immobilization and Subsequent Mobilization of Cadmium in Soil Suspensions
Authors: Chanmugathas Pushparany , Bollag Jean‐Marc
Published: July 2010

The effect of microorganisms on the fate of Cd in soil suspensions was investigated. Samples of four soil types were suspended in growth media amended with Cd(NO3)2 (20 mg/L) and incubated aerobically or anaerobically at 28 ± 1°C. At various time intervals, aliquots were withdrawn, and Cd concentrations (total and free Cd2+) and pH were determined in the supernatant. The results of the short‐ and long‐term studies indicated that in all soils tested the extent of Cd disappearance (total and free Cd2+) in nonsterile soil supernatants was significantly greater than in the corresponding sterile controls. However, during the subsequent long‐term 8‐week aerobic incubation, a significant amount of Cd (including free Cd2+) was released into solution of nonsterile suspensions, while no increase in Cd concentration was observed in the sterile suspensions. Under anaerobic conditions, a continued disappearance of Cd from the non‐sterile soil supernatants was observed during an incubation period of up to 24 weeks. Under aerobic conditions, the pH of the nonsterile soil suspensions decreased to approximately pH 5.5, whereas the pH remained approximately 8.0 during anaerobic incubation. The rate and degree of Cd immobilization or mobilization was also dependent on the soil types used. Of the four soils tested, Morrison (Ultic Hapludalfs) sandy loam from a coniferous forest site exhibited the highest degree of Cd mobilization, accounting for up to 100% of total Cd immobilized. Our results suggested that soil microbial activity is responsible for both binding of Cd to and its subsequent release from soil.
Soluble Organic Nitrogen Losses Associated with Recovery of Mineralized Nitrogen
Authors: Smith S. J.
Published: July 2010

The extent and subsequent availability of soluble organic N in soil mineralization extracts were determined using initially air‐dry soil samples. Involved were eight Southern Plains agricultural soils comprising five soil orders. The major losses of soluble organic N occurred during the initial leaching prior to incubation, and are attributed to factors not directly associated with the mineralization procedure (e.g., freshly decomposed plant residues, pretreatments, etc.). Often, these losses were as high or higher than initial values for inorganic N. Thereafter, the organic N losses represented, on average, only about 5% or less of the inorganic N produced in surface soil samples during 84 d of aerobic mineralization. This was the case for both indigenous and fertilizer‐incorporated N. Subjecting the soluble organic N in the mineralization extracts to subsequent aerobic, anaerobic, or autoclave procedures indicated no excessive N availability. Distribution of the soluble organic N components in the extracts did not differ greatly from that of soil. In general, soluble organic N losses were not a major factor associated with recovery of mineralized N.
Chemical, Spectroscopic, and Biological Characteristics of the Organic Matter in Particle Size Fractions Separated from an Aquoll
Authors: Catroux G. , Schnitzer M.
Published: July 2010

Samples from the surface horizon of a cultivated Aquoll were ultrasonically dispersed and separated into particle size fractions. Humic acids (HAs) were extracted from the whole soil and each particle size fraction. Residual humic acids (RHAs) were obtained from the residue of each HA extraction by treating with HCl‐HF and reextracting. Chemical analyses showed that the fine silt fraction had the highest C and N contents. Although δ15N values and proportions of mineralizable N increased with decreasing particle size, C/N ratios decreased. Mineralizable N appeared to be related to both the total N content and the characteristics of the minerals with which the organic matter was associated. Nitrogen in sand and silt fractions was more resistant to mineralization than in clay fractions. Extractions with 0.5 M NaOH removed more of the C and N from the fine‐clay fraction than from the whole soil or any of the other fractions. Carbon‐13 nuclear magnetic resonance (NMR) spectra showed that HAs extracted from clays were more aliphatic than HAs extracted from larger particle sizes. The major aliphatic components in the clay size fractions appeared to be alkanoic and hydroxyalkanoic acids. Compared with HAs, RHAs, were more homogeneous, contained fewer proteinaceous materials and carbohydrates, were more aromatic, richer in phenolic OH and CO2H groups, had higher molecular weights, and contained more free radicals.
Soil Biology: Accomplishments and Potential
Authors: Lynch J.M.
Published: July 2010

A brief commentary is made of the accumulated knowledge, present activity, and future potential of topics in soil biology and the interaction of soil biology with related disciplines. New developments in biotechnology should be harnessed in soil and crop management, but this will only be achieved with even closer interdisciplinary cooperation.
Influence of Sample Size on Measurement of Soil Denitrification
Authors: Parkin T. B. , Starr J. L. , Meisinger J. J.
Published: July 2010

The influence of sample size on the magnitude and variability of soil denitrification was studied by collecting soil cores, ranging in size from 1.7 to 5.4 cm in diameter, from no‐till and conventionaltill corn plots. Estimates of natural denitrification rates were obtained by incubating intact soil cores with C2H2 and monitoring gaseous N2O production. In addition, maximum denitrification potential was determined by monitoring N2O production in anaerobic slurries amended with glucose, NO‐3 and C2H2. Natural rate estimates were highly skewed and approximated lognormal distributions. The spatial variability of denitrification was characterized by large variation at small distances of <10 cm and only weak spatial dependence at distances of 10 to 100 cm. Studies of the effect of sample size on denitrification suggest that soil cores >4.2 cm in diameter yielded the most reliable estimates of natural denitrification rates. Using a computerized random resampling technique, we estimated that approximately 10 to 15 kg of soil was necessary to obtain a representative soil mass for estimating natural denitrification rates. The results of this study are consistent with the hypothesis that the source of variability associated with the natural denitrification rates is the patchy distribution of denitrifying “hot spots” in soil. Some implications associated with the application of classical statistical methods to lognormal data are also discussed.
Physical Properties of a Typic Haplaquoll Under Conventional and No‐Tillage
Authors: Culley J. L. B. , Larson W. E. , Randall G. W.
Published: July 2010

Conservation tillage, particularly no‐till (NT), for corn (Zea mays L.) production on poorly drained soils in the U.S. Corn Belt often produces lower yields. Cone index (CI), bulk density (ρb), shrinkage, hydraulic conductivity (Ks), and water release charcteristics were all measured in a Typic Haplaquoll under NT and conventional tillage (CN) to characterize soil physical factors possibly related to the lower yields. Measurements in the interrows indicated that wheel traffic, associated only with crop establishment (planting and herbicide spraying), eliminated the benefits of lower CI and greater Ks associated with primary and secondary tillage. Cone index was a more sensitive indicator of these trafficking effects than was ρb. With the exception of the surface layer (0.0–0.1 m) of untracked interrows, Ks values under NT, as measured in vertically oriented soil cores, exceeded those in CN profiles. Because these tillage effects were not observed when Ks was measured in situ using a permeameter that integrated horizontal and vertical components of Ks, the high Ks measurements from cores were probably produced by flow in vertically oriented macropores although interfacial flow between sample ring and soil cannot be discounted. Untracked NT and CN surface layer macroporosities amounted to 5 and 0% of total porosity, respectively. Macropores did exist below the surface of the tilled layer, but they were susceptible to destruction by wheel traffic. However, tillage did not affect tile drain performance.
Particle Size of Interrill‐eroded Sediments from Highly Weathered Soils
Authors: Miller W. P. , Baharuddin M. K.
Published: July 2010

Fifteen highly weathered Alfisols and Ultisols from Georgia were used in runoff/erosion pan studies to delineate sediment character istics of interrill‐eroding soils and their relationship to soil particle size. Simulated rainfall was applied to the pans at 11.2 cm h−1, and runoff and sediment parameters were measured at 5‐min intervals for 25 min. Runoff rates and sediment concentrations varied consistently over time for the soils used, with concentrations increasing until peaking at 10 to 15 min, then decreasing as crust formation caused surface consolidation and decreased detachability, despite continued high runoff rates for most of the soils. Sediment particle size became finer after the initial sampling period, and was dominated by silt‐sized particles, with lesser amounts of primary clay and sand. Silt‐sized particles in the sediments were related statistically to a measure of water‐dispersible (0.5‐h shaking) soil silt, whereas primary sediment clay was related to both water‐dispersible (36‐h shaking) and total soil clay. Dispersible and total soil clay were also correlated with sediment concentration and soil loss rate, emphasizing the role of clay and its dispersibility in erosion and crust formation on these soils. A quadratic equation using soil clay described sediment clay content, showing greater relative enrichment of primary clay in sediments from sandy vs. clayey soils. The high proportion of easily transportable sediment generated by interrill erosion on these soils poses a serious environmental problem in areas of active soil erosion.
Mass Loss and Nutrient Changes in Decomposing Upland Oak and Mesic Mixed‐Hardwood Leaf Litter
Authors: Kelly J. M. , Beauchamp J. J.
Published: July 2010

Nylon net litterbags (30 by 30 cm) containing ∼10 g of upland oak leaf litter were collected at 30‐d intervals over a 1110‐d period from two upland oak (Quercus sp.)‐mixed hardwood stands on the Cumberland Plateau of Tennessee. Statistically significant differences (P ≤0.01) in losses of mass, N, K, Ca, and S were found between sites, whereas P and Mg losses did not differ. Litterbags containing mesic mixed‐hardwood leaf litter were collected at 30‐d intervals over a 810‐d period from mesic mixed‐hardwood stands located on the same watershed study sites as the upland oak stands. Statistical comparisons indicated significant differences in mass, N, P, K, Ca, Mg and S loss between sites. Constant rate projections of the time required for the upland oak litter weight to reach 10% of the original bag content based on 365, 730, and 1095 d of data were 960, 1530, and 1770 d, respectively, at the Camp Branch Watershed and 870, 1230, and 1410 d at the Cross Creek Watershed. Estimates of decomposition times derived from constant rate projections for both cover types were considerably less than observed values. In an attempt to obtain more realistic projections of weight and nutrient loss, several mathematical models commonly used to examine decomposition data were evaluated. A modified exponential model gave the best data fit and provided estimates of 3240 and 2370 d as the time required to reach the 10% mass‐remaining value for the upland oak litterbags at Camp Branch and Cross Creek, respectively. Estimates for the mesic mixed‐hardwoods were 1590 and 2490 d at Camp Branch and Cross Creek, respectively. The weight of most nutrients in the litterbags was modeled with limited success by the modified exponential model. However, N and particularly P weights could not be described by the model since they generally increased with time ove rthe study period. The results of this analysis, in addition to suggesting that a longer time is required for decomposition than is normally projected, also suggest that a single model may not be appropriate to describe all response variables. Data presented here along with the modeling work also reiterate the fact that a decay rate derived from a single species or group of species must be applied with caution over larger landscape units because of the potential differences both within and among sites.
A Critical Assessment of Surface Adsorption Models
Authors: Schulthess C. P. , Sparks D. L.
Published: July 2010

The theory on variable ionization energy of surface sites is criticized based on inconsistencies of traditional potentiometric titration data (singular reference curve methods) with electrophoretic mobility (EM) data, and on the nature of dissolution of the solid phase. The mathematical consequences of including the Boltzmann distribution term in models using intrinsic equilibrium constants are most probably merely to track the solubility behavior of the solid phase. The EM of an Al oxide was studied with respect to pH. The isotherm showed clear maximum mobility at low and high pH values with the zero point of charge (ZPC) ranging from pH 9.5 to 9.8. The ZPC lowers with increasing electrolyte concentration due to the increased competitive behavior of the cations in solution for the surface sites. Assuming a constant ionization energy of the surface sites, a mass balanced model that predicted both anion‐cation adsorption data and potentiometric titration data (backtitration technique) also correlated well with the EM data. The EM behavior was modeled based on the varying mobility of each type of surface species present on the oxide at various pH values. Whereas traditional models treat the oxide as being capable of forming a surface charge that induces ion adsorption, this model treats the oxide as being capable of undergoing ion exchange or substitution reactions resulting in surfaces that exhibit mobility in an applied electric field. The proposed model assumes that anion adsorption results in positive mobility, and cation adsorption results in negative mobility.
Sorption Characteristics of Organic Compounds on hexadecyltrimethylammonium‐Smectite
Authors: Boyd Stephen A. , Mortland Max M. , Chiou Cary T.
Published: July 2010

When hexadedyltrimethylammonium (HDTMA) ion is exchanged for metal cations like calcium in smectite, the sorptive properties of the clay are greatly modified. The resultant HDTMA‐smectite complex behaves as a dual sorbent, in the sorption of organic compounds, in which the mineral fraction functions as a solid adsorbent and the organic (HDTMA) phase as a partition medium. Capacities of mineral adsorption and partition uptake by HDTMA in the HDTMA‐smectites are illustrated by sorption of benzene, trichloroethene (TCE), and water as vapors on the dry sample and by sorption of benzene and TCE from water. The exchanged HDTMA in clay is found to be a much more powerful partition medium than ordinary soil organic matter in the uptake of benzene and TCE. Based on this finding, HDTMA‐smectite appears to be an effective sorbent for removing organic contaminants from water. It is suggested that such sorptive organo‐clay complexes could be used to enhance the containment capabilities of clay landfill liners and bentonite slurry walls.
Relationship Between Microbial Biomass and Elemental Sulfur Oxidation in Agricultural Soils
Authors: Lawrence J. R. , Germida J. J.
Published: July 2010

Elemental sulfur oxidation in 28 agricultural soils was correlated with the size and activity of the microbial biomass. Sulfur oxidation increased linearly with microbial biomass C (r = 0.68, P < 0.01) and soil respiration rate (r = 0.88, P < 0.01). Canonical analyses of the same data set further emphasized the strong interrelationship of sulfur oxidation, microbial biomass C, and respiration. These results indicated that the size and activity of the microbial biomass determined the rate of elemental S oxidation in agricultural soils. Increasing the heterotrophic biomass by glucose additions caused an increase in sulfur oxidation that was proportional to the increase in biomass C. Application of cycloheximide or chloramphenicol to a Weyburn soil decreased S oxidation by 57%. When the two inhibitors were added together an 84% decrease was observed. These results and the absence of detectable populations of elemental S oxidizing autotrophs indicated that S oxidation in these soils was primarily a heterotrophic process.
Determination of Gaseous Selenium‐75 Evolved from Soil
Authors: Karlson U. , Frankenberger W. T.
Published: July 2010

A rapid, cost‐effective and inexpensive method was developed to determine volatile microbial metabolites of Se. Labeled inorganic Se was applied to soil, and the gaseous products were captured in a specially designed activated C trap. After removal for sampling, the C trap was counted directly for 75Se, without further sample preparation. Maximum sampling intervals were 101 to 263 h, depending on Se emission rates. The limit of quantification was 8.2 ng Se using a specific activity of 5 Ci kg−1 Se. The relative standard deviation ranged from 1.3 to 4.1%. Recovery for the added label was 97.5%. The technique is well suited for large‐scale environmental kinetic investigations.
Dry Matter Yield and Nitrogen‐15 Uptake by Tomatoes Under Sodium Chloride Stress
Authors: Pessarakli M. , Tucker T. C.
Published: July 2010

An absorption study was conducted in nutrient solution with seedlings of tomato (Lycopersicon esculentum Mill.; cv. Columbia) to observe the effects of NaCl on (15N) uptake and distribution in plant roots and shoots. The 14‐d‐old seedlings were grown for 16 d (14 d as group of 6 plants per container and 2 d after the final transfer of 2 plants per container) in complete Hoagland solution no. 1, then salinized (except the controls, −0.03 MPa) to −0.3, −0.6, and −0.9 MPa osmotic potentials with NaCl. Nutrient solutions were sampled daily for N loss after addition of 15NH415NO3 to the pots. The cumulative 15N loss was considered to be absorbed by plants. Lowering the osmotic potential of the culture solution decreased total N uptake at all salinity levels, and 15N uptake of the plants at medium (−0.6) and high (−0.9 MPa) salinity levels. A low level of salinity (−0.3 MPa) did not affect 15N uptake compared with the control (−0.03 MPa). Water uptake and dry matter yield were affected to a greater extent than 15N absorption. Nitrogen‐15 concentration was slightly higher in roots than in shoots.
Rheology of Aqueous Suspension of Sodium/Calcium Montmorillonite
Authors: Keren R.
Published: July 2010

The rheological characteristics of montmorillonite suspension as a function of exchangeable sodium percentage (ESP), (when the complementary cation is Ca2+), Na‐polymetaphosphate adsorption by clay, and suspension pH were studied in aqueous media at a clay concentration of 25 g kg−1 and temperature of 25 °C. The differential viscosity (the derivative of shear stress with respect to the shear rate at a given shear rate), the extent of deviation from Newtonian flow, and the extrapolated shear stress values all increased with ESP at the range between 20 and 60%, but the values remained constant at 60 < ESP < 100. The rheology of Na‐montmorillonite suspension changed from non‐Newtonian to Newtonian as the Na‐polymetaphosphate (NaPO3)13 concentration in suspension increased. The rheology of montmorillonite suspension was pH‐independent when the clay was saturated with Ca ions, but pH‐dependent when the clay was saturated with Na ions. The differential viscosity increased as the pH decreased. At pH 10.0, Na‐montmorillonite suspension showed a Newtonian behavior, whereas at pH 7.0 non‐Newtonian behavior was observed. The power law coefficients and the extrapolated shear stress values indicate that the particle‐particle linkages increase by introducing Na ions to the exchangeable complex in the range 10 < ESP < 60. The edge surfaces were associated with the formation of linkage between clay platelets and were responsible for the pseudoplastic characteristics of the suspension.
Stability of Soil Aggregates as Inferred from Optical Transmission of Soil Suspensions
Authors: Abu‐Sharar T. M.
Published: July 2010

Stability of the semiarid Zezia soil aggregates was evaluated by measuring the optical transmission (%T) of suspensions of two size fractions (<2 and <5 µm) dispersed at decreasing electrolyte concentration of constant sodium adsorption ratio (SAR). At a given SAR, the %T decreased linearly with decreasing electrolyte concentration. Slopes of the equations decreased with increasing SAR; indicating a decreasing dependence of %T on electrolyte concentration as SAR increased. Such slopes were called stability indices (SIs). The clay‐SI was on the average 5.6 times greater than that of the <5‐µm fraction. At a given SAR, electrolyte concentrations corresponding to maximum clay dispersion (minimum %T values of 10) or very little clay dispersion (%T values of 20) were called critical concentrations (CCs) and threshold concentrations (TCs), respectively. At SAR values of 0, 5, 10, 25, and ∞, the CCs were 1.0, 3.7, 5.4, 10.3, 10.0, and 13.0 mol m−3, respectively, and the TCs were 2.2, 5.5, 9.2, 16.7, 17.8, and 32.6 mol m−3, respectively. Both CCs and TCs increased linearly with increasing SAR to a limiting value of 20. The TC for the <5 µm dispersed size fraction also increased linearly with increasing SAR. The TCs were 11.8, 40.4, 49.0, and 61.7 mol m−3 at SAR 0, 10, 15, and 20, respectively. These relatively high values imply that slaking of soil aggregates into sizes >2 µm can take place without a significant clay dispersion.
Simultaneous Determination of Urea and Ammonia Nitrogen in Soil Extracts and Water by High Performance Liquid Chromatography
Authors: Abshahi A. , Goyal S. S. , Mikkelsen D. S.
Published: July 2010

Combining the separation efficiency of high performance liquid chromatography (HPLC) and the catalytic solid phase urease reactor, a simple, sensitive, and highly specific method for simultaneous determination of urea and ammonia nitrogen is possible. In this system the immobilized urease catalyzes the hydrolysis of urea to ammonium ions, which is then measured fluorometrically after postcolumn derivatization with o‐phthalaldehyde (OPA). The fluororphore is detected on‐line with a fluorometric detector, 344(ex) and 455(em) nm. The method is rapid and can be used to accurately monitor the urea and ammonia‐N content of soil, water, and fertilizer materials.
Quaternary Cation Exchange on Silver Hill Illite
Authors: Thellier Catherine , Sposito Garrison
Published: July 2010

The simultaneous exchange of Na, K, Ca, and Mg on Silver Hill illite suspended in 5 mol m−3 perchlorate background at pH 7 was investigated systematically. Composition data for both the exchanger and the equilibrium aqueous solution phase were obtained directly. The data showed that the total adsorbed metal charge was independent of exchanger composition provided that all four cations were considered. Analysis of the composition data with exchange isotherms and calculated Vanselow selectivity coefficients showed that: (i) K+ was preferred over Na+, Ca2+, and Mg2+, and the preference decreased as EK decreased (E = charge fraction on the clay mineral); (ii) bivalent cations were preferred only slightly over Na+ for ENa > 0.01, whereas for ENa ≤ 0.01, the reverse was true; (iii) no preference was shown in Ca‐Mg exchange at ENa values between 0 and 0.13.
Determination of Soil Characteristics from Thematic Mapper Data of a Cropped Organic‐Inorganic Soil Landscape
Authors: Lee Kyoo‐seock , Lee G. B. , Tyler E. J.
Published: July 2010

Methods of determining soil characteristics from thematic mapper (TM) data were investigated at a site in southern Wisconsin. These methods utilized the soil‐sensitive spectral region of TM. Because there was little correlation between soil mapping units (soil phases) and the TM soil spectral classes, the former were grouped by wetness class, as determined from natural soil drainage classes, and by organic matter content. Agreement between wetness class and the April and September classifications, with absolute radiance and raw ratio transformation was 65.1, 61.3, 64.0, and 64.7%. When organic matter content was used instead of wetness class, the agreement ratio with TM was 74.0, 73.9, 68.4, and 66.0%. The April image correlated better with the soil map than the September image. Vegetative cover was a primary reason for difficulty in interpretation. The soil brightness image contributed most to classification accuracy, and can be used for manual soil interpretation. The stretched thermal IR image was also effective in discriminating between mineral soils and Histosols.
A New Technique for Evaluating the Presence of Preferential Flow Paths in Nonstructured Soils
Authors: van Ommen H. C. , Dekker L. W. , Dijksma R. , Hulshof J. , van der Molen W. H.
Published: July 2010

A new technique for determining the presence of preferential flow paths in a nonstructured soil profile is described. The presented method is easily applicable in the field, and is based on the formation of an intensely colored complex of I2 with starch. Moreover, the method can be applied to all kinds of nonstructured soils, irrespective of their color. An illustration of the technique is given in case of water and solute movement in a water‐repellent soil, where formation of preferential flow paths was known to occur.
Comparison of a Laboratory Procedure and a Textural Model for Predicting In Situ Soil Water Retention
Authors: Schuh W. M. , Cline R. L. , Sweeney M. D.
Published: July 2010

A physico‐empirical model proposed by L.M. Arya and J.F. Paris in 1981 for predicting the soil moisture characteristic curve using particle size and bulk density data was compared with a commonly used laboratory method using undisturbed core samples and a pressure plate extractor, for precision in estimating in situ water retention measured with paired neutron probe and tensiometer installations. An empirical factor for the Arya and Paris (A&P) model was found to average close to the value (α = 1.38) proposed by its authors. Values for this experiment were different between texture classes. Loam and silt loam values were constant, while values for soils of sand, loamy sand, and sandy loam texture were nonconstant. The empirical factor was calibrated for (i) loam and coarse loam; (ii) silt loam; and (iii) sand, loamy sand, and sandy loam texture groups. The sandy soil values required linear calibration as a function of soil water potential. Results for the calibrated A&P model compared well, overall, with laboratory determinations on soils ranging in texture from sand to loam and silt loam. Laboratory estimates were slightly better for A and B horizon materials, while A&P estimates were better for C horizons. Error for estimation of field volumetric water content using A&P and lab methods was approximately twice the error for estimation of θ using a second field neutron‐tensiometer installation within one meter of the first field apparatus.