bluuebunny/crossref_metadata_2025 huggingface dataset:
Aggregate Stability of an Eroded and Desurfaced Typic Argiustoll
Authors: Gollany H. T. , Schumacher T. E. , Evenson P. D. , Lindstrom M. J. , Lemme G. D.
Published: July 2010

Aggregate stability is a measure of the ability of soil to withstand the disrupting forces of rain and nonsymmetrical wetting. Erosion may influence aggregate stability by exposing soil with properties different than the original soil surface. This study was conducted to determine: (i) the influence of antecedent soil water content on wet aggregate stability using aggregates prehumidified to near saturation; (ii) the effects of organic C and clay content on the soil water content‐aggregate stability relationship; and (iii) the effect of topsoil removal on aggregate stability. Seventy‐eight soil samples were taken from six profiles of Beadle clay loam (fine, montmorillonitic, mesic, Typic Argiustoll). These samples were analyzed for pH, organic C, texture, CaCO3, antecedent soil water content, cation‐exchange capacity (CEC), and aggregate stability. Isolated test plots were also saturated with an overhead sprinkling infiltrometer. Samples were taken periodically throughout a 4‐d period for aggregate‐stability determination. A modified wet sieving technique, which included pre‐humidifying of the sample to near saturation, was used to determine aggregate stability. A negative linear relationship was found between aggregate stability of prehumidified aggregates and antecedent soil water content. Prediction equations were developed that explain up to 77% of variability for the aggregate stability. Organic C was the most important of the independent variables, followed by antecedent soil water content in the multiple regression analysis. Topsoil removal by desurfacing and erosion reduced aggregate stability. Aggregate stabilities for soils with high organic C and clay content were less affected by antecedent soil water content.
Macroporosity of a Well‐Drained Soil under No‐Till and Conventional Tillage
Authors: Dunn G. H. , Phillips R. E.
Published: July 2010

Conventional tillage and no‐tillage have been shown to affect the hydraulic properties of soil. For this reason, a field experiment was conducted in 1987 and 1988 to determine the effect of tillage practice and cover crop on the macroporosity of a Maury silt loam (fine, mixed, mesic Typic Paleudalf). The field used for this study has been in continuous no‐till and conventional‐till corn (Zea mays L.) since 1970. Ponded steady‐state infiltration measurements were made using double‐ring infiltrometers; afterwards, a tension infiltrometer was used to measure water flux at −0.4, −0.9, and −1.4 kPa water pressure. These negative water pressures were used to calculate equivalent cylindrical pore diameters from the capillaryrise equation. Flux at a pressure of −0.06 kPa was determined from regression equations for each plot. Equivalent pore diameters of 5.0, 0.75, 0.33, and 0.21 mm correspond to −0.06, −0.4, −0.9, and −1.4 kPa, respectively. In June 1987, conventional tillage had significantly higher water flux than no‐till for the 5.0‐ to 0.75‐mm equivalent‐diameter pore size range. In 1987, rye (Secale cereale L.) cover crop plots had significantly higher water‐flux values than hairy vetch (Vicia villosa Roth.) plots for the same range of equivalent pore sizes. In June 1988, no‐till plots had significantly higher water‐flux values for all equivalent pore size ranges. In 1987, 73 and 80% of the total water flux at −0.06 kPa water pressure was transmitted through pores >0.21‐mm equivalent diameter in no‐till and conventional tillage plots, respectively. The corresponding values in 1988 were 83 and 73%.
Biomass and Soil Nitrogen Relationships of a One‐Year‐Old Sycamore Plantation
Authors: Tschaplinski T. J. , Norby R. J. , Todd D. E. , Johnson D. W.
Published: July 2010

Maximum efficiency in biomass production in short‐rotation woody crops requires a level of N fertilization that achieves a balance between maximum growth and minimum NO‐3 leaching into groundwater. The effects of urea‐N fertilizer applied under various timing regimes were investigated in a plantation of American sycamore (Platanus occidentalis L.), and different aspects of optimum fertilization were explored. A plantation of sycamore was established at Oak Ridge, TN, typically a N‐poor area. Nitrogen treatments consisted of differing schedules of urea application, including trees fertilized at the beginning of the growing season with 0, 50, 150, and 450 kg N/ha, and trees fertilized periodically (three times during the growing season) at 37.5 kg N/ha. Fertilization effects on stem and leaf biomass, leaf nutrient concentration, soil N characteristics, including available N, mineralizable N, nitrification potential, and NO‐3 leaching loss were determined. The greatest aboveground biomass accumulation (three times greater than that of unfertilized controls) was obtained with 450 kg N/ha, but with greater NO‐3 leaching. Nearly as much biomass was obtained with almost no NO‐3 leaching when much less N was added either early in the season (150 kg N/ha) or in periodic applications (37.5 kg N/ha three times). The rapid decline to control levels of soil available N in all treatments, and the results of the aerobic incubations, indicate high nitrification potential at the site. The results suggest that periodic, low N fertilization may be optimal on sites with a high nitrification potential, and that the lower rates tested minimize NO‐3 contamination of groundwater.
Steel Rod Oxidation as a Hydrologic Indicator in Wetland Soils
Authors: Bridgham Scott D. , Faulkner Stephen P. , Richardson Curtis J.
Published: July 2010

Depth of rusting on steel rods has been proposed as an inexpensive means of determining depth to the water table and the reducing zone in wetland soils. The suitability of steel‐rod oxidation as a hydrologic indicator in wetland soils was tested in a series of laboratory and field experiments in both Histosols and a mineral soil (Typic Fluvaquent). In laboratory microcosms, the steel‐rod rusting depth exactly matched water‐table levels under both permanently flooded and drained conditions. But under a rapidly fluctuating hydrology, once heavy rust formed on the rods it did not dissolve upon partial reflooding. Field experiments showed a good correspondence between steel‐rod rusting depth and water‐table depth under both relatively constant and seasonally changing hydrology in Histosols (r2 = 0.80, slope = 0.81). In the Typic Fluvaquent, a close correspondence between steel‐rod rusting depth and water‐table depth occurred under relatively constant hydrological conditions but, with a rapidly dropping water table, rod oxidation showed a lag period in response. We conclude that the steel‐rod technique is valuable as a hydrologic indicator of the reducing zone in basic science studies. We recommend frequent sampling (monthly) and the use of other hydrological measures to ensure unambiguous results. The technique is unsuitable for jurisdictional delineation in areas with a fluctuating hydrology due to prolonged lag periods in rod oxidation under some conditions and the inability of previously formed rust to dissolve upon reflooding.
Simultaneous Measurement of the Spatial Distribution of Soil Water Content and Bulk Density
Authors: Phogat V. K. , Aylmore L. A. G. , Schuller R. D.
Published: July 2010

Continuous nondestructive measurements of the spatial distributions of soil water content and bulk density are essential prerequisites to the resolution of many problems in the study of soil‐plant‐water systems. Computerized axial tomography (CAT) was applied to dualsource (137Cs and 169Yb) gamma‐ray attenuation in soil columns to determine nondestructively the spatial distributions of volumetric water content (θv) and bulk density (ρs) for two soils that exhibit swelling to different degrees. Beam slice thickness was 2 mm and pixel dimensions 2 by 2 mm. The CAT scanning technique for average ρs and θv provided excellent agreement with the corresponding values obtained gravimetrically. Average standard deviations (σ) for ρs of pixels for the dry soils, although large, were highly reproducible and provide a measure of the structural status of the soils. Changes in the mean and σ of pixel ρs following wetting were related to the texture, structure, mineralogy, and Ca or Na exchange status of the soil. Systematic errors arising from the random nature of radioactive emissions, for count times of 2 s, resulted in large σ in estimated θv of pixels even for dry soils. Very large counting times (some 169 s for an individual ray‐sum and, hence, 112 h to complete a dual‐source scan) were required to achieve σ values of pixel θv, on the order of 0.025 cm3/cm3 for a uniform field of water. Such large count times limit this approach to steady‐state or only slowly changing systems. Thus, while the application of CAT to dual‐energy‐level scanning has the potential to become a major tool for nondestructive studies of soil water content, structural status, and stability, realization of this potential awaits substantial improvements in scanning geometry and counting electronics.
Liquid Ion Exchanger Microelectrodes Used to Study Soil Solute Concentrations near Plant Roots
Authors: Hamza M. , Aylmore L. A. G.
Published: July 2010

A technique for using Na+ liquid ion exchanger (Na+‐LIX) microelectrodes to accurately measure, repetitively, and in a nondestructive fashion, Na+ concentrations in the soil solution at single points is described. The method has been used to examine solute (NaCl) accumulation in proximity to single roots of lupine (Lupinus angustifolius L.) and radish (Raphanus sativus L.) plants subjected to two levels of transpirational demand and five soil solute concentrations. The results obtained indicate that, at soil water contents corresponding to matric water potentials >−140 kPa, back diffusion of solute significantly counteracts the tendency for solute accumulation at root surfaces during transpiration.
Effect of Sodium‐Humate on the Rheological Characteristics of Montmorillonite Suspensions
Authors: Zhang Yiping , Gan Huamin , Low Philip F.
Published: July 2010

Humic compounds are supposed to have an aggregating effect on soil particles. This study was conducted to determine whether Na‐humate aggregates montmorillonite, a common clay mineral. A rotational viscometer was used to investigate the rheological behavior of suspensions of Na‐montmorillonite containing different concentrations of Na‐humate. Thereafter, the pan of an electrobalance was submerged at a given depth in each suspension and the particle‐size distribution of the montmorillonite was determined by continually weighing the sediment that accumulated on the pan. The effect of Na‐humate on swelling of the clay was also investigated by means of a miniature pressure membrane apparatus and by an x‐ray diffractometer. It was found that θ, the extrapolated shear stress, and ηpl, the plastic viscosity of the suspensions, decreased rapidly with Na‐humate concentration up to 0.1% (w/w) and then remained nearly constant. However, there was essentially no change in the particlesize distribution and swelling of the clay. These results were interpreted to mean that, in a suspension of montmorillonite and Na‐humate, the humic polyanions absorb on the edges of the particles and, as a result, reduce the attractive force between them. This implies that the aggregating effect of organic matter on soils cannot be attributed to the Na‐humate present in the organic matter.
Enzymatic and Microbial Interactions in Response to Pitch Pine Root Growth
Authors: Tate Robert L. , O'Reilly Laurie , Parmelee Robert W. , Ehrenfeld Joan G.
Published: July 2010

Root growth stimulates many soil metabolic and enzymatic activities through, in part, loss of photosynthate as root exudates. Because of the abundance and structural simplicity of the carbonaceous compounds comprising root exudates, compared with native soil organic matter, it can be hypothesized that not only the magnitude but also the relationship between various soil microbial and enzymological processes vary with proximity to the growing root. To test this hypothesis, metabolism of amino acids and glucose, microbial growth, microbial biomass C, and potential acid phosphatase, protease, and invertase activities were examined in pitch pine (Pinus rigida Miller) rhizosphere and near rhizosphere soils. The trees were grown in microcosms (total volume ≈145 cm3) in the greenhouse in O or A horizon soils (Lakehurst sand, a mesic, coated Haplaquodic Quartzipsamment) from the New Jersey Pinelands. The microbial and enzymological activities in the organic‐matter‐rich O horizon soil were 2‐ to 25‐fold greater than those detected in the organic‐matter‐poor A horizon soils throughout the study. Phosphatase activity and glucose and amino acid metabolic rates did not correlate with tree root mass, whereas protease activity, microbial growth rate, and microbial biomass C varied with root mass. No effect of proximity to the root on these relationships was detected. In the A horizon soil after 22 wk of growth, amino acids and glucose metabolic rates declined with increasing root mass, whereas the microbial growth rate increased. Phosphatase activity was not detected in the A horizon soil. The interrelationship of these activities was evaluated in O horizon soil. Significant (P <0.05) correlations were detected between microbial biomass C and the various indices of microbial activity, but glucose metabolism and phosphatase and proteolytic activities varied independently of microbial biomass C. In conclusion, significant effects of tree root growth on enzymatic and metabolic activities were detected, but, with a few minor exceptions, relationships between these enzymological and metabolic activities were not altered by proximity to the growing tree root.
Crop Residue Type and Placement Effects on Denitrification and Mineralization
Authors: Aulakh M. S. , Walters D. T. , Doran J. W. , Francis D. D. , Mosier A. R.
Published: July 2010

Nutrient release from legume and cereal crop residue is important to N crycling and the success of conservation and sustainable farming systems. Residue type, placement, and degree of incorporation, and soil water regimes largely control availability and loss of soil N and were evaluated in the laboratory. Four residues, i.e., vetch (Vicia villosa Roth.), soybean (Glycine max [L.] Merr.), corn (Zea mays L.), and wheat (Triticum aestivum L.) having C/N ratios ranging from 8 to 82 were applied on the soil surface or incorporated in repacked cores of a Nicollet loam (fine‐loamy, mixed, mesic Aquic Hapludoll) and incubated for 17 or 35 d at 60 and 90% water‐filled pore space (WFPS) with enriched 15N‐NO3 (76.7%). Denitrification losses from all treatments were negligible at 60% WFPS. At 90% WFPS, total denitrification losses from residue‐incorporated soils represented 87 to 127% of the initial soil NO3 level (80.5 mg N kg−1); losses increased with decreasing residue C/N ratio. Denitrification was greatest during the first 8 d, as was CO2 evolution. Initial denitrification with surface‐placed residues was less than with incorporated residues, but cumulative losses over 35 d did not differ significantly. Substantial N immobilization occurred with incorporated or surface‐placed wheat, corn, and soybean residue with wide C/N ratios at 60% WFPS, whereas, with low‐C/N‐ratio vetch, significant mineralization occurred. After 35 d, 51 and 36% of N in incorporated and surface‐placed vetch residue, respectively, was mineralized. Residue C/N ratio was inversely related to initial rates of residue decomposition, and effects of residue type and placement and soil water on denitrification and mineralization were most important during early (8‐10 d) decomposition.
Urea Transformations in Flooded Soil Columns: I. Experimental Results
Authors: Hongprayoon C. , Lindau C. W. , Patrick W. H. , Bouldin D. R. , Reddy K. R.
Published: July 2010

The main form of fertilizer applied to lowland rice (Oryza sativa L.) is urea, but very little is known about its movement and transformations under flooded soil conditions. Laboratory incubation studies were conducted to measure adsorption, movement, and transformations of urea and hydrolyzed ammoniacal N in flooded soil columns. Urea was added to the floodwater (750 mg N L−1, equivalent to 150 kg N ha−1) of sterilized and nonsterilized Crowley silt loam soil (fine, montmorillonitic, thermic Typic Albaqualf) columns and urea diffusion, urea hydrolysis, and subsequent NH+4‐N diffusion were measured during a period of 30 d. Urea adsorption by the soil increased with increasing concentration of added urea‐N and adsorption coefficients ranged from 0.037 to 0.064 but modeling found adsorption to be too small to be an important factor in urea movement and hydrolysis. Urea hydrolysis rates in the flooded soil columns increased with time and followed first‐order reaction kinetics. Rate constants measured in the soil varied from 0.036 to 0.288 h−1. The diffusion coefficient for both N forms (urea and NH+4) was estimated to be 3.5 × 10−10 m2 s−1 in the flooded soil columns. The basic urea data generated in this study should help provide a data base to model urea‐N behavior in submerged soils.
Nontronite Catalysis in Polycondensation of Pyrogallol and Glycine and the Associated Reactions
Authors: Wang M. C. , Huang P. M.
Published: July 2010

The objective of this study was to investigate the catalytic power of nontronite (0.2‐2 µm) in the polycondensation of pyrogallol (1,2,3‐trihydroxybenzene) and glycine and the associated reactions involving the ring cleavage of pyrogallol and the decarboxylation and deamination of glycine in systems free of microbial activities. At the end of a 90‐h reaction period, nontronite catalyzed the ring cleavage of pyrogallol, as shown by the release of CO2. The release of CO2 in the nontronite‐pyrogallol system was six times higher than that for pyrogallol alone. Nontronite also catalyzed decarboxylation and deamination of glycine, as shown by the release of CO2 and NH3. The ability of nontronite to catalyze deamination of glycine was substantially enhanced by the presence of pyrogallol. Polycondensation of glycine and pyrogallol was greatly catalyzed by nontronite. This is indicated by the absorbances of the molecular visible absorption spectroscopy of the supernatants, yields of total N‐containing humic acids (HA) and fulvic acids (FA) and the fraction of glycine converted to nitrogenous polymer. The infrared (IR) and electron spin resonance (ESR) spectra of HA and FA formed in the supernatants of the reaction systems were similar to those of soil HA and FA. The sequence for the amounts of the total humic polymers formed in the system was: nontronite‐glycine‐pyrogallol > nontronite‐pyrogallol > glycine‐pyrogallol > pyrogallol. The catalytic effects of nontronite on the C turnover, N transformations, and humic substance formation in soils thus merit attention.
Modeling Root Water Potential and Soil‐Root Water Transport: II. Field Comparisons
Authors: Bruckler L. , Lafolie F. , Tardieu F.
Published: July 2010

In a previous article, a theoretical approach to the calculation of root water potential (RWP) and water uptake by roots in the two‐dimensional case was proposed. The RWP was assumed to show a threshold value that controlled plant transpiration by means of chemical messages triggered by roots. This article compares model predictions with data from field experiments. Measured maximum evapotranspiration (MET), basic soil hydraulic properties, and a map of soil‐root contacts in a soil profile (vertical case) were taken as inputs to the model. Field experiments were performed in a clay loam soil (a Typic Hapludalf) planted with maize (Zea mays L., F1 hybrid LG1), where sections were compacted using wide tractor wheels. At silking, precise maps of soil‐root contacts were drawn for vertical planes. Volumetric water content and matric potential measurements were performed during a 17‐d experiment under dry climatic conditions. Computed and field‐measured soil volumetric water content values showed large gradients between compacted and noncompacted zones. Calculated and measured mean root water‐uptake rates were similar, and depended strongly on root densities. Mean individual root water‐uptake rates were considerably greater in zones where the root density was low. Finally, the proposed model could be useful for calculating the root water potential if chemical messages from roots are confirmed as being an important control mechanism of stomatal conductance and photosynthesis.
Aluminum‐Binding Ability of Soluble Organics in Douglas Fir Litter and Soil
Authors: Tam Shuk‐Ching , McColl John G.
Published: July 2010

Organic matter from litter and soil are important metal‐mobilizing agents. This study was conducted to characterize the Al‐binding abilities of soluble organics from both Douglas fir litter and soil (fine‐loamy, mixed, mesic Ultic Haploxeralf). A modified ion‐pairing chromatographic technique was used to differentiate organics according to their Al‐binding abilities. Further identification with high‐performance liquid chromatography (HPLC) found gallic, catechol, salicylic, and phthalic as the most strongly Al‐binding ligands among the aromatic acids identified. Moderate binding ability was exhibited by 3,4‐dihydroxybenzoic acid; benzoic, vanillic and 4‐hydroxybenzoic acids were the least strongly binding. The identified aliphatic acids (shikimic, oxalic, succinic, fumaric, malic, and citric) were not differentiated, due to their weaker binding to Al and to the fractionation column. For the unidentified organics, suggestions are made on their functional structure that will be useful for more exhaustive studies. Greater amounts of Al‐binding ligands were found in litter than in soil. The effect of different litter types on Al solubilization in underlying mineral soils can be obtained by comparing their Al‐fractionation characteristics.
Upper Bounds on Evaporation Losses from Buried Sources
Authors: Philip J. R.
Published: July 2010

Evaporation losses at the soil surface are important in subirrigation. This study yields upper bounds on fractional evaporation loss from buried sources. Quasilinear solutions are given for evaporation at the soil surface from buried steady point and line sources at finite depth. These yield the very general result that e‐2z1 is the upper bound on the fractional evaporation loss from any arbitrary configuration of steady sources at dimensionless depth z1. This dimensionless depth is the ratio of the physical depth to the sorptive length 2α−1, where α is the sorptive number entering the quasilinear analysis. A simple general theorem gives the upper bound on fractional evaporation loss from arbitrary configurations of steady sources distributed throughout an arbitrary range of depths.
Identifying and Removing Spatial Correlation from Yield Experiments
Authors: Bhatti A. U. , Mulla D. J. , Koehler F. E. , Gurmani A. H.
Published: July 2010

In classical statistics, the effect of soil trends is compensated for by replication and randomization of treatments. Two field experiments were conducted at sites with significant soil trends to evaluate the use of semivariograms for identifying spatial correlation in plot yield, and evaluate the ability of nearest‐neighbor analysis (NNA) in removing trend. The first experiment involved a P‐fertilizer trial with winter wheat (Triticum aestivum L.) on an eroded hillslope in eastern Washington. The second experiment involved a N‐ and P‐fertilizer trial with cotton (Gossypium hirsutum L.) in Dera Ismail Khan, Pakistan. One of the difficulties in using semivariograms of plot‐yield data to evaluate spatial correlation in experimental errors is that yield is affected by the presence of trends as well as by the pattern in treatment randomization and replication. To remove the influence of treatment randomization, the measured mean for each treatment was subtracted from the measured yield for that treatment in each plot. Semivariograms of these deviations in yield relative to the treatment mean showed significant structure for both experiments, indicating spatial correlation between plots resulting from soil trends. We used NNA to adjust measured plot yields for the effects of spatial correlation. Semivariograms of yield deviations after this adjustment exhibited no spatial structure, indicating removal of spatial correlation between plots. Analysis of variance (ANOVA) on measured yields before adjustment by NNA in both experiments showed nonsignificant treatment effects, while block effects were highly significant. Thus, without adjustment, the experimental results showed no response to the applied fertilizer treatments. In contrast, ANOVA on adjusted yields after NNA showed highly significant treatment effects, while block effects were nonsignificant.
Improved Solute‐Sampling Protocol in a Sandy Vadose Zone Using Ground‐Penetrating Radar
Authors: Kung K‐J. S. , Donohue S. V.
Published: July 2010

Soil solution samples taken from a vadose zone by current monitoring techniques are randomly obtained because it is assumed that the representativeness of the samples is dependent on the total number of samples instead of the location of the samples. In the presence of preferential flow (i.e., “macropore”, “fingering”, or “funnel” flow), however, the locations as well as the number of samples and not just the number of samples determine the representativeness. The purpose of this study was to: (i) demonstrate that current sampling protocols could underestimate solute breakthrough in a soil with preferential flow; and (ii) show that ground‐penetrating radar (GPR) has great potential to nondestructively map the location of interbedded soil layers with textural discontinuities so that suction‐cup samplers could be correctly installed along the preferential paths triggered by funnel flow. A 24 by 24 m plot at the Hancock Research Station, Wisconsin, was scanned with GPR in 1989. Based on the GPR images, four ceramic suction‐cup samplers were installed at a depth of 1.85 m in locations with layering structures and abrupt textural discontinuities. Four other ceramic suction cup samplers were installed randomly at a depth of 1.5 m. The plot received a uniform pulse of Br solution. Breakthrough curves collected by samplers installed with the aid of GPR have higher concentrations than those collected by randomly installed samplers. This result indicates that random solute sampling in a sandy vadose zone exhibiting preferential flow could underestimate solute movement.
Selenate Reduction in an Alluvial Soil
Authors: Sposito Garrison , Yang Andrew , Neal Rosemary H. , Mackzum Adrienne
Published: July 2010

Recent studies of the mobility and solubility of Se in western San Joaquín Valley soils suggest that this potentially hazardous element can be managed by controlling its oxidation‐reduction reactions. The soluble species, SeO4, which is highly mobile and toxic, can, in principle, be reduced to SeO3, which is strongly adsorbed, or to organoselenium species, which may volatilize under suitable conditions. Chemical thermodynamics predicts that the reduction sequence in soils should be: NO3 → SeO4 → MnO2 at pH >5. The objective of this study was to establish the position of SeO4 in the kinetic reduction sequence for a representative western San Joaquín Valley soil incubated in suspension with its own saturation extract. In a series of replications of an incubation experiment, it was observed that native NO3 (plus NO2) concentrations became undetectable after 100 h in the soil suspension without O2 supply. Soluble Se, either added as Na2SeO4 or indigenous to the soil, disappeared after 50 to 200 h. Native soluble Mn began to rise after 50 h and showed a sharp increase after 100 h of incubation. Retardation of SeO4 reduction in the presence of added NO3 was noted. The results indicated that, at native levels of NO3, effective microbial catalysis of SeO4 reduction occurred in the soil under the conditions of the experiments, in agreement with the recent isolation of bacterial species that can respire SeO4 while oxidizing organic acids typical of suboxic soil environments.
High‐Elevation Forest Soils of the Southern Appalachians: I. Distribution of Parent Materials and Soil‐Landscape Relationships
Authors: Feldman S. B. , Zelazny L. W. , Baker J. C.
Published: July 2010

Because of geomorphic instability imparted both by present‐day slope processes and past periglacial activity, soils in the high‐elevation spruce‐fir (Picea rubens Sarg.‐Abies fraseri [Pursh.] Poir) zone of the southern Appalachians have similar morphological features that make it difficult to assess their variability on the landscape, despite widespread differences in parent material and local geology. We used multiple discriminant analysis to (i) determine whether soils from three extensive areas of southern Appalachian spruce‐fir forests could be separated by physical, morphological, chemical, and mineralogical properties, (ii) determine the relative effectiveness of these properties as differentiae, and (iii) assess the contribution of mineral weathering in offsetting potential base‐cation depletion induced by strong‐acid anion loading associated with atmospheric deposition. A total of 35 pedons at elevations >1450 m were characterized on the high mountain peaks of eastern Tennessee, western North Carolina, and southwestern Virginia. Physical and morphological properties used to separate and field classify these soils were not significantly different between study areas. Soil chemical and mineralogical properties inherited from different parent materials, however, were sufficiently different between study areas to result in the clear separation of soils into distinct groups with >95% classification accuracy. Soils formed from siliceous metavolcanic parent materials were dominated by K‐feldspar and quartz in both the sand and silt fractions. Soils with parent materials derived from more high‐grade metamorphic rocks were less quartzitic, had plagioclase as the dominant feldspar, and had high contents of expansible 2:1 phyllosilicates. Slope processes involved in the transport of solutes and sediments resulted in sorting of surficial materials, higher pH, and greater amounts of silt‐size mica and kaolinite in depositional areas.
Soil Temperature and Organic Matter in a Disturbed Forested Wetland
Authors: Aust W. Michael , Lea R.
Published: July 2010

Soil temperature and organic‐matter content are useful indices of ecosystem recovery after disturbance. This study was designed to evaluate soil temperature and organic‐matter changes associated with different levels of disturbance within a forest wetland. Soil temperatures and organic‐matter contents were monitored in a palustrine water tupelo (Nyssa aquatica L.)‐baldcypress (Taxodium distichum [L.] Rich. var. disticum) wetland forest in southwestern Alabama for two growing seasons following timber‐harvest‐related disturbances. Three forms or levels of disturbance were applied: helicopter logging, rubber‐tired skidder logging, and helicopter logging followed by herbicide application. An adjacent undisturbed stand served as a reference area. Analyses of post harvest data revealed that during the 2‐yr postharvest period, soil temperatures in the reference area were coolest, helicopter and skidded areas were warmer, and herbicide plots had the warmest soil temperatures. Soil organic matter followed the same trend. Both parameters were related to vegetative cover and indicated recovery following timber harvest.
Adsorption of Atrazine on Smectites
Authors: Laird D. A. , Barriuso E. , Dowdy R. H. , Koskinen W. C.
Published: July 2010

Smectites may strongly influence the fate of pesticides in soils due to their large surface area and abundance in agricultural soils. This research was undertaken to determine the effects of smectite properties on the affinity of smectitic clays for atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1, 3, 5 triazine). Samples of the <2‐µm fraction were separated by sedimentation from 13 reference smectites and treated with H2O2 for removal of organic matter. A soil smectite sample was separated (<0.02‐µm fraction) from a H2O2 and dithionite‐citrate‐bicarbonate‐treated Webster (fine‐loamy, mixed, mesic Typic Haplaquoll) soil by a dispersion‐centrifugation‐decantation technique. All 14 samples were Ca saturated, dialyzed free of excess electrolyte, and freeze dried. The mineralogy of each sample was evaluated by a combination of x‐ray diffraction and chemical analysis. Values for cation‐exchange capacity (CEC), surface charge density (SCD), surface area (SA), and percent tetrahedral charge (TC) were based on structural interpretations of the chemical analyses. Freundlich adsorption isotherms for atrazine adsorption on each sample were determined using the batch‐equilibration method. Smectite was the dominant mineral in 13 of the clay samples; the 14th sample was a mixture of interstratified smectite‐illite, quartz, and kaolinite. For the smectitic clays, atrazine adsorption ranged from 0 to 100%, and the logarithm of the Freundlich adsorption constant [log(Kf)] decreased linearly with the CEC (r2 = 0.82) of the clays. Stepwise multiple‐regression analysis indicated that log (Kf) values were correlated with SCD and SA values (r2 = 0.83). Inclusion of TC and suspension pH as independent variables in the regression analysis did not significantly improve the correlations. The results indicate that the affinity of smectites for atrazine decreases with increasing SCD, which suggests that atrazine is primarily adsorbed by smectites as a neutral species.
Measuring Field Variability of Disturbed Soils for Simulation Purposes
Authors: Finke P. A. , Bouma J. , Stein A.
Published: July 2010

Spatial variation of soil profiles disturbed by leveling was inventoried on a field scale to obtain representative data for simulation purposes. Depth of occurrence, thickness, and morphology of functional layers, which are different pedogenetic horizons with comparable soil physical properties, were considered to be regionalized variables. The layers served as carriers of physical information, such as water‐retention and hydraulic‐conductivity characteristics and organic‐matter content. An impression of the variability within each layer was obtained by six fold sampling. Spatial variability, expressed by variations in thickness of functional layers, was inventoried in a two‐step soil survey. First, semivariograms were constructed using data obtained following a nested sampling scheme supplemented by a nugget estimation procedure. Variograms were used to evaluate cost/quality ratios at varying potential grid sampling densities, using the root of the prediction error variance (RPEV) to compare quality of interpolations. Based on these evaluations and a sequential sampling test, a grid mesh of 12 m was chosen. Second, a grid soil survey and an independent quality test were done, in which root mean square errors (RMSE) on test points were compared with RPEV. The RPEV to RMSE ratios varied between 0.7 and 1.1 for the sampled grid mesh, and had comparable values for other grid meshes. Estimations on test points by an hypothesized spatial mean, based on 26 measurements by a sequential sampling method, produced RMSE values not significantly different from RMSE values from kriging interpolations. However, sequential sampling required 26 observations whereas kriging required 153, a saving of 83%.
Micromorphology and Mineralogy of Cracking Soils from the Accra Plains of Ghana
Authors: Acquaye D. K. , Dowuona G. N. , Mermut A. R. , St. Arnaud R. J.
Published: July 2010

Four soil profiles, uncultivated and cultivated examples of Akuse and Prampram series from the Accra Plains of Ghana, developed in situ from garnetiferous hornblende gneiss, were examined in this study to establish their physical and chemical properties, macromorphology, micromorphology, and mineralogy. Cracking is well expressed in both soils; however, slickenside formation is found only in the deeper and moderately weathered Akuse soils. Although the clay content of the soils is only slightly >30%, the soils are still capable of developing cracks. The cation‐exchange capacity (CEC) values are all >32 cmolc kg‐1 and smectite is the dominant clay mineral. Moderate to minor amounts of vermiculite, chlorite, mica, and kaolinite occur throughout the profile. The amount of kaolinite is largest in the coarse‐clay fraction, which also contains considerable amounts of quartz and feldspar, especially in the Prampram soils. Weathering of amphiboles, micas, and feldspars in the solum is responsible for the formation of swelling clay minerals and Fe‐Mn nodules. Total chemical composition of both the coarse and fine clays suggests that clay minerals contain considerable structural Fe. The large proportion of vughs and interconnected vughs makes these soils unique and separates them from other cracking soils with higher clay contents. The Akuse soils have greater frequency of voids than the Prampram soils. Carbonate nodules with dendritic Fe‐Mn precipitation, and Fe‐Mn nodules are particularly distinct pedogenic features. A greater concentration of Fe‐Mn nodules in the Akuse than the Prampram soils represents a greater mobility of Fe and Mn because of long‐term moisture retention. A majority of the nodules at depth are formed in situ, but those at the surface are probably displaced upwards by the swell‐shrink process. Considering the overall soil properties, the Akuse soils may be classified as Typic Haplusterts and the Prampram soils, because of the absence of slickensides, as Vertic Ustochrepts.
Conceptual and Statistical Modes to Characterize Soil Materials, Landforms, and Processes
Authors: Evans C. V. , Roth D. C.
Published: July 2010

Within landscape units of interest to soil surveyors and to soilgenesis researchers, economic and physical constraints generally prohibit collection of sufficient data to develop adequate predictive models of spatial variability. Conceptual models are more legitimate at these scales, and modal concepts based on central‐tendency values can be used effectively to develop these models. Our objectives were to obtain central‐tendency values for genetically important properties of two similar New Hampshire soils, to use these values to quantify modal concepts of each soil, and to relate these modal concepts to depositional processes. We examined central‐tendency values of particle‐size distribution, porosity, landform relief, and drumlin axis ratios in nine map‐unit delineations of Becket and Marlow series (coarse‐loamy, mixed, frigid, Typic Haplorthods) in southern New Hampshire. Modal concepts of Becket and Marlow were successfully defined by these parameters: Marlow soils were significantly finer and less porous, and occurred on steeper, more linear drumlins than Becket soils. These properties indicate that till lodgement is singularly influential in the genesis of Marlow soils. Becket soils also exhibit some degree of till lodgement, but subsequent melting of ice lenses accounts for removal of finer particles, higher porosity, and lower relief and linearity. The modal concepts defined in this study enabled soil scientists to discriminate more efficiently between Becket and Marlow soils in mapping, and to develop process‐oriented models of these soils.
Stemflow, Rain Throughfall, and Erosion under Canopies of Corn and Sorghum
Authors: Bui Elisabeth N. , Box James E.
Published: July 2010

Modern soil erosion prediction technology, such as the Water Erosion Prediction Project, requires detailed information about plant status in the interrill and rill erosion processes. The total amount of rain that reaches the soil and is available for erosion under vegetated surfaces is a function of rain throughfall and stemflow. The objective of our research was to determine the effects, including the production of stemflow of canopies, of corn (Zea mays L.) and sorghum (Sorghum bicolor [L.] Merr.) on interrill soil erosion. A series of rainfall simulations of similar intensity (6.35 cm h‐1) was performed in 1989 and 1990 on experimental plots of Cargill SX 383 corn and Garst 5503 sorghum grown on Cecil soil (clayey, kaolinitic, thermic Typic Kanhapludult). Runoff and sediment were collected at 5‐min intervals over a 1‐h period for two sets of treatments each under corn and sorghum: canopy and canopy minus stemflow. Stemflow, plant‐height, and leafarea data were collected from a total of 18 corn and 16 sorghum plants and used to estimate stemflow. Rain throughfall was estimated as the difference between total rainfall and calculated stemflow and was compared with observed runoff. Both corn and sorghum were observed to have high stemflow, the amount being highly correlated to total leaf area. Runoff under sorghum indicated that all the stemflow was potentially available for infiltration. Under corn, however, about one‐third of the stemflow may have contributed to runoff. The average sediment concentration was not sensitive to canopy type. Erosion due to stemflow appeared negligible compared with that caused by throughfall.
Time Domain Reflectometry Response to Lateral Soil Water Content Heterogeneities
Authors: Hokett S. L. , Chapman J. B. , Cloud S. D.
Published: July 2010

Water‐content heterogeneities can occur between the parallel rods of the time domain reflectometry (TDR) probe if TDR is used in cracked soils or in laboratory studies with probes oriented in a variety of directions. The accuracy of water‐content measurements using TDR under such heterogeneous conditions was investigated in a series of laboratory experiments. Two cases were studied: (i) one TDR rod in dry soil and the other in wet soil; and (ii) an artificial soil crack filled with water or air between the two TDR rods. In Case 1, TDR readings were heavily biased toward the water content of the dry soil. This effect occurs because the electromagnetic wave (EMW) reaches the end of the waveguide quicker in dry than in wet material. Because the time delay of the earliest reflection signal is read from the TDR, the travel time of the dry material is measured. In Case 2, the air‐filled crack between the waveguide rods had only a small effect on measured water content when the soil was dry; however, water‐content measurements were reduced by as much as 46% in wetter soils. The effect of water‐filled cracks was small in both dry and wet soils. The effect of soil cracks is explained by a static capacitance model. Results from the experiments do not contradict previous work that demonstrated that TDR measures the average water content of heterogeneous layers oriented perpendicular to the TDR probe axis. In the two cases examined here, knowledge of the orientation of soil water heterogeneities relative to the TDR waveguide rods is necessary for correct data interpretation.
Fractal Scaling of Soil Particle‐Size Distributions: Analysis and Limitations
Authors: Tyler Scott W. , Wheatcraft Stephen W.
Published: July 2010

Fractal scaling has recently been proposed as a model for soil particle‐size distribution (PSD). In this work, the cumulative number of soil grains greater than a characteristic size, N(R > r), and the cumulative mass distribution, M(r < R), are developed and shown to be proportional to R3‐D and R3‐D, respectively, where r is the grain size, R is a specific measuring scale, and D is the fractal dimension. The cumulative‐number approach to estimate D is shown to be sensitive to the assumed grain density and characteristic size, while the mass distribution is less sensitive to the assumed grain density and characteristic size, and therefore more appropriate for the analysis of field soils. These two models of fractal PSD behavior also constrain the fractal dimension to lie between 0 and 3 for field soils. With constraints on the fractal dimension, soils displaying strict fractal scaling in grain‐size distribution are shown to be a rather small subset of those soils commonly encountered in the field. Earlier work has shown fractal scaling in many soil PSDs with fractal dimensions exceeding 3.0 using the number‐based analysis. The fractal scaling and magnitude of the fractal dimensions found in previous work are shown to be an artifact of the plotting algorithms and assumptions on grain density and size. Although fractal scaling plays an important role in soil water retention and porosity, PSD data alone are not sufficient to fully characterize this scaling.
Evaluation of a Triple Line Source Sprinkler System for Salinity Crop Production Studies
Authors: Aragüés R. , Royo A. , Faci J.
Published: July 2010

Numerous line source sprinkler experiments have been described in the literature, but they do not provide an in‐depth analysis of their potential use for salinity crop studies. This work evaluates the advantages and limitations of a triple line source sprinkler system for use in salinity crop tolerance studies. Two outer laterals are used to apply fresh water, while a third lateral centered between them applies saline water. This layout provides duplication of a salinity gradient on each side of the center line while maintaining a uniform application of water. Applied saline water and soil salinity gradients that developed across the laterals on both sides of the center line were correlated (P < 0.001). These gradients were generally linear (P < 0.01) in the 4 yr studied and were not significantly different (P > 0.05) when the laterals were installed parallel to the prevailing wind direction in soils with good infiltration. Soil salinity was uniform at a given distance from the laterals, as indicated by the low coefficients of variation (≤13%) of the electromagnetic sensor readings. Soil salinity increased during the growing season and was higher in the top portion than in the lower portion of the soil profile. This profile distribution was due to limited soil water infiltration. Most of the leaf injury due to foliar absorbed salts was restricted to the lower, older portion of the canopy. This method proves to be useful for salinity crop studies if soils are selected that allow for high leaching fractions, foliar absorption of salts by the crop selected is relatively low, and the system is operated under low wind conditions.
Organic Carbon Distributions in Shallow Soils of Pinyon‐Juniper Woodlands
Authors: McDaniel P. A. , Graham R. C.
Published: July 2010

Properties of soils associated with pinyon (Pinus edulis Engelm.)‐juniper (Juniperus spp.) communities of the western USA reflect a mosaic of canopy and interspace environments. This study was initiated to examine the influence of these contrasting environments on organic carbon (OC) distributions and associated soil properties of shallow soils in a pinyon‐juniper woodland of east‐central Utah. The mosaic of interspace and canopy environments results in a complex of soils with two distinct OC distribution patterns. In both interspace and canopy soils, color values and root distributions are related to measured OC. Tree roots are concentrated just above the lithic contact in transitional R/A and Cr/A horizons in all soils. Decay of this root material represents the dominant organic‐matter input to interspace soils, which are essentially devoid of vegetation and lack O horizons. As a result, OC increases with depth and the highest OC contents and darkest soil colors are found in R/A and Cr/A horizons of these soils. Canopy soils also have relatively high OC contents just above lithic contacts but contain maximum OC and darkest soil colors in A1 horizons underlying litter layers. All soils exhibit increases or irregular decreases in OC with depth and have similar distribution patterns for total N and NaHCO3‐extractable P. The OC distribution patterns result in inappropriate classification of some of these shallow upland soils as Fluvents according to the U.S. soil taxonomy.