bluuebunny/crossref_metadata_2025 huggingface dataset:
Combined Magnetic, Spectroscopic, and Analytical‐Chemical Approach to Infer Genetic Information for a Vertisol
Authors: Gehring A. U. , Guggenberger G. , Zech W. , Luster J.
Published: July 2010

A Vertisol from a floodplain in southern Mali was investigated by a combination of magnetic and spectroscopic methods in addition to classical soil chemical and physical analyses. This combined approach allowed us to deduce the genesis of the soil. The Ustic Endoaquert profile extended to a water table at 1.2 m and was subdivided into four horizons, Ap (0–0.1 m), A2 (0.1–0.4 m), A3 (0.4–0.6 m), and Ag (0.6–1.2 m). Redoximorphic features were found at a depth between 0.6 and 0.8 m. Prevailing reducing conditions in the Ag horizon were documented by a maximum concentration of exchangeable Mn(II). High redox dynamics were indicated by minimum concentrations of total and extractable Fe in the A3 horizon as well as by minimum susceptibility and saturation isothermal remanent magnetization in the A3 and Ag horizons. The latter minimum was most likely caused by the reductive dissolution of lithogenic magnetite. Soil organic matter (SOM) was generally characterized by a high amount of aromatic compounds and a high degree of lignin decomposition with maxima in the Ag horizon as indicated by solution and solid‐state 13C nuclear magnetic resonance as well as fluorescence spectroscopies. These characteristics of SOM suggested formation under highly oxidative conditions. The presence of such characteristics, in particular in the lower part of the Vertisol with prevailing reducing conditions, suggests an allochthonous origin of the SOM. Pedoturbation in the upper part of the profile was documented by a higher contribution of primary resources such as lignin, cellulose, and hemicellulose in the Ap and A2 horizons.
Distribution of Mycorrhiza on Competing Pines and Weeds in a Southern Pine Plantation
Authors: Sylvia David M. , Jarstfer Amiel G.
Published: July 2010

Mycorrhiza are important in the uptake of nutrients by plants, yet little is known about the distribution and function of the diverse fungal symbionts associated with competing plant species. The objective of our research was to investigate effects of weed competition on mycorrhizal development in a slash pine (Pinus elliottii Engelm. var. elliottii) plantation in order to better understand the impact of arbuscular mycorrhizal (AM) weeds on ectomycorrhizal (EM) pines. Seedlings were planted in a typical Spodosol and samples were collected to a depth of 100 cm from weed‐free (herbicide‐treated) and weedy plots in the first and third growing seasons after outplanting. Pine roots were separated from weed roots before samples were assessed for fine root (<3.0‐mm diam.) length, surface area, and mycorrhizal status. Fine root length and surface area, as well as EM surface area, of pine generally decreased with depth and increased between Years 1 and 3. In contrast, fine root length of weedy species was fairly constant during the 3‐yr period. The AM colonization of weeds followed a trend similar to that of fine root development. The depth distribution of EM pine roots and AM weedy roots exhibited complex interactions with treatment, time, and depth. There was generally greater mycorrhizal colonization of both AM on weedy species and EM on pine in the A soil horizon. Weed competition significantly affected the number of EM root tips and the distribution of EM morphotypes. Thelephora was generally the most abundant morphotype, followed by a white, rhizomorph‐producing type (White Rhiz) and Cenococcum. An exception to this pattern was found in the near‐surface soil (0–10 cm) of the weed‐free plots, where White Rhiz was the most frequent morphotype. A challenge for the future is to evaluate the functional significance of changing patterns of EM in the field.
Aggregate Size Effects on the Sorption and Release of Phosphorus in an Ultisol
Authors: Linquist B. A. , Singleton P. W. , Yost R. S. , Cassman K. G.
Published: July 2010

Despite extensive research on soil‐P reactions, little is known of the effect of soil aggregation on these processes. This study was conducted to determine the role of aggregate size on the sorption and release of P in a Haiku clay (Typic Palehumult). A range of aggregate sizes up to 4 mm in diameter were used in this study. Autoradiography of sorbed 32P and P sorption studies indicated that added P was initially sorbed to a 0.188‐mm layer around aggregates and remained in this peripheral layer for up to 28 d. We defined this layer as the reactive mass. Analysis of P in aggregates from a 4‐yr P management field experiment on the same soil indicated that diffusion of P from this peripheral layer into the aggregate was slow, requiring >2 yr for aggregate P to reach equilibrium. When P was added to a combined mix of aggregate size fractions, P sorption increased from 55 to 245 mg P kg−1 as mean aggregate diameter decreased from 3.4 to 0.375 mm, and was linearly related to the aggregates' reactive mass (r2 = 0.96). Similarly, the reactive mass of aggregates was linearly correlated to P release from aggregates (r2 = 0.99) and to the linear buffer coefficients derived from P‐sorption isotherms (r2 = 0.98). Since aggregate size is related to P sorption, soil buffering capacity, and P release from soil, it is likely that aggregation affects short‐ and long‐term plant P availability. The effect of aggregate size, however, needs to be investigated for other soils.
Loess Stratigraphy and Fragipan Occurrence in the Lower Mississippi River Valley
Authors: Lindbo D. L. , Rhoton F. E. , Hudnall W. H. , Smeck N. E. , Bigham J. M.
Published: July 2010

The loess uplands adjacent to the Lower Mississippi River Valley (LMRV) are comprised of several different depositional units overlying either coastal plain or alluvial sediments. The occurrence and development of fragipan horizons in the region has been attributed to the presence of a specific stratigraphic unit. This study was conducted to investigate the stratigraphic relationship between loess units throughout the LMRV to determine if the existence of fragipans is limited to one loess deposit. The study utilized five field sites in the loess uplands between northwestern Tennessee and southeastern Louisiana. At all sites, each member of the Memphis catena (Memphis [fine‐silty, mixed, thermic Typic Hapludalf], Loring [fine‐silty, mixed, thermic Typic Fragiudalf], and Grenada [fine‐silty, mixed, thermic Glossic Fragiu‐dalf]) was sampled and preliminary stratigraphic breaks identified by changes in texture and color. These breaks were further refined in the laboratory by characterizing each horizon for clay‐free particle‐size distribution and mass magnetic susceptibility. Additionally, total Fe, K, Mg, Ca, Ti, and Zr were determined for the coarse silts (20–50 µm) from all Memphis horizons. The data were further evaluated by κ‐means cluster analysis to refine stratigraphic breaks in the loess and underlying coastal plain or alluvial deposits. Generally, stratigraphic breaks were distinguishable by changes in clay‐free sand, clay‐free medium and coarse silt, and mass magnetic susceptibility. Secondary clay maxima below 250 cm represented paleoargillic horizons that confirmed stratigraphic changes and buried surfaces. For the thick loess deposits (>3.5 m total loess thickness), fragipans developed entirely in Peoria Loess, but in thinner loess deposits (<3.5 m total loess thickness) fragipans crossed stratigraphic boundaries between Peoria Loess and underlying units. Thus, the development of fragipan horizons in these loess soils is independent of stratigraphic units.
Soil Aggregation and Fungal and Bacterial Biomass under Annual and Perennial Cropping Systems
Authors: Chantigny Martin H. , Angers Denis A. , Prévost Danielle , Vézina Louis‐P. , Chalifour François‐P.
Published: July 2010

Understanding the mechanisms controlling crop effects on soil aggregation is necessary to develop sustainable soil management practices. Changes in soil aggregation, carbohydrates, and fungal vs. bacterial biomass were monitored following a shift from fallow (bare soil) to various cropping systems. Faba bean (Vicia faba L.) and wheat (Triticum aestivum L.) were used as annual cropping systems, while alfalfa (Medicago sativa L.), timothy (Phleum pratense L.), bromegrass (Bromus inermis L.), and reed canarygrass (Phalaris arundinacea L.) were used as perennial cropping systems. Crops were established in spring 1989, on a silty clay loam (fine, mixed, frigid Typic Dystro‐chrept) and a clay loam (fine‐loamy, mixed, frigid Typic Humaquept) near Québec City (Canada). After three growing seasons, the mean‐weight diameter of water‐stable aggregates (MWD) was higher under reed canarygrass (2.26 mm in the clay loam and 2.45 mm in the silty clay loam) and timothy (2.13 and 2.26 mm) than under faba bean (1.92 and 1.89 mm) or wheat (2.06 and 1.57 mm). Intermediate values were found under alfalfa and bromegrass. Changes in MWD were not correlated with microbial biomass C. Acid‐hydrolyzable carbohydrates correlated with MWD in the silty clay loam (r2 = 0.42**) but the relationship decreased with higher carbohydrate levels in the clay loam (r2 = 0.05). Close correlations were found between MWD and both fungal glucosamine (r2 = 0.68***, soils combined) and bacterial muramic acid (r2 = 0.48***). Changes in MWD were mostly reflected in aggregates >2 mm, and the close relationship with fungal glucosamine suggests that fungi played a dominant role in soil macroaggregation. Measurement of muramic acid and glucosamine is proposed as a potential approach to compare bacterial vs. fungal contributions to soil aggregation.
The Pattern of Soil Variables Related to Artemisia tridentata in a Burned Shrub‐Steppe Site
Authors: Halvorson Jonathan J. , Bolton, Harvey , Smith Jeffrey L.
Published: July 2010

Artemisia tridentata Nutt. is a prominent shrub of cool deserts in the USA that influences the patterns of chemistry and microbiological activity in the soil in which it grows. However, little is known about the fate of these patterns following the death or removal of the live A. tridentata plant. We compared abutting burned and unburned sites to see if patterns in soil could be related to locations where shrubs were removed by fire 9 yr earlier. While most soil variables were significantly higher in the unburned site than in the burned site, total organic C and soil pH appear unaffected by the removal of A. tridentata or the fire itself. Differences between unburned and burned sites were greatest near the location of a plant axis. In contrast, burned soil was not distinguishable from unburned soil at distances greater than ≈ 50 cm away from a live A. tridentata axis or a charred stump indicating that soil patterns were most affected by removal of the plant and not by the fire. Nearly a decade after the fire, significant effects of A. tridentata on patterns of some soil variables in the burned site were still detectable. Significantly higher values for total organic C, total N, water soluble C, electrical conductivity, and soil microbial biomass C were observed near the location of charred A. tridentata stumps than at distances further away. These patterns are a significant source of soil variability that may be difficult to account for because they are not related to the obvious location of live plants.
Effect of Storage and Sieving on the Phosphorus Composition of Soil Solution
Authors: Chapman P.J. , Shand C. A. , Edwards A. C. , Smith S.
Published: July 2010

In this study, the effects of storage and sieving of a mineral soil (Typic Fragiorthod) on the P chemistry of the soil solution have been quantified. Intact and sieved soil cores were stored for 0, 1, 3, and 8 d at 4°C prior to obtaining solutions, which were analyzed for total dissolved phosphorus (TDP), molybdate‐reactive phosphorus (MRP), dissolved organic phosphorus (DOP), and dissolved condensed phosphorus (DCP). Storage of both sieved and intact soil cores influenced the amount and chemical composition of P in solution. Concentrations of TDP, MRP, and DOP displayed a rapid decline with increase in storage time, whereas DCP concentrations, which were initially very low, increased. Concentrations of TDP were significantly (P < 0.05) different between solutions extracted from intact and sieved soils on the same day as sampling and this was accounted for by DOP and MRP, which were significantly (P < 0.05) larger in sieved soil. The proportions of MRP, DOP, and DCP were similar in solutions extracted from intact and sieved soils on the same day, even for Day 0 where a large difference in TDP was apparent. The MRP fraction was consistently larger for intact cores (44%) than sieved (38%) on all days and varied little with length of storage. The DOP component, which dominated initially, decreased with increase in storage time, while DCP increased to become the major fraction after 8 d of storage. This study has highlighted the potential effects of soil storage and sieving on the P concentration and composition of soil solution. The results also have important implications for soil solution sampling and subsequent data interpretation.
Impact of Funnel Flow on Contaminant Transport in Sandy Soils: Numerical Simulation
Authors: Ju S.‐H. , Kung K.‐J. S.
Published: July 2010

Agrichemicals have played an essential role in maintaining the productivity of arable lands in modern agriculture. Recently, it was found that preferential flow could greatly enhance the leaching of agrichemicals into groundwater. This study investigated how contaminant transport would be influenced by funnel‐type preferential flow paths in a sandy vadose zone. Numerical simulations were conducted in four 12‐m‐wide by 6‐m‐deep two‐dimensional hypothetical soil profiles with embedded coarse sand layers. The soil layering structures in these profiles were generated according to what was observed in the vadose zone of a Plainfield sand (sandy, mixed, mesic Typic Udipsamment) in central Wisconsin. Corresponding simulations were conducted in one‐dimensional profiles as controls. Results showed that contaminant breakthrough time in the two‐dimensional profiles was only 25% of that in one‐dimensional homogeneous profiles. The ratio of the total mass leached from the two‐dimensional profile to that from the one‐dimensional profile increased exponentially as the water application rate decreased. This implies that: (i) the impact of funnel flow on contaminant transport is most drastic when the net infiltration is low; and (ii) minimizing excess leaching by carefully controlling the water budget alone might not prevent groundwater contamination. For a pesticide with a degradation coefficient of 3 × 10−7 s−1 and an adsorption coefficient of 0.5 cm3 g−1 in the top 30 cm and 0.05 cm3 g−1 from 30 to 600 cm, about 4% of the total mass would reach the groundwater through two‐dimensional funnel flow paths with an averaged daily net infiltration rate of 1.15 mm d−1.
Geochemical Characteristics of a Loess‐Soil Sequence in Central Kansas
Authors: Feng Zhao‐Dong
Published: July 2010

This study focuses on a Barton County loess‐soil section in central Kansas in an attempt to retrieve the geochemical signature of the late Quaternary environmental change in the arid‐semiarid region and provide a data base of loess geochemical characteristics in the Great Plains. The data indicate that the elements (expressed as oxides) of the windborne fraction (<63 µm) that are easily solubilized and lost from the soil by chemical weathering and leaching are relatively sensitive to soil‐forming processes, whereas the insoluble elements of that fraction are controlled primarily by the chemical composition of the parent material. The geochemical imprint of pedogenesis superimposed on that of the loess parent material can be distinguished by comparing the magnetic susceptibility signature with the Fe2O3/Al2O3 ratio. Based on the geochemical imprint and radiometric dates (14C and thermoluminescence), the Bignell Loess (8000–5000 yr) is poorly weathered and the Brady Soil (10 000–8000 yr) is strongly weathered. The Peoria Loess (20 000–10 000 yr) has neither a traceable leaching nor weathering marker, and the Gilman Canyon pedocomplex (35 000–20 000 yr) is strongly leached. The reddish pedocomplex (70 000–35 000 yr) is the most strongly weathered, probably due to stable land surface conditions in a mild climate, and the Barton sand (92 000–70 000 yr) seems to have been subjected to a moderate weathering. Within the exposed portion of the Loveland Loess (260 000–92 000 yr), weathering indices are inversely correlated with the carbonate content and the carbonate‐rich soils were developed under warm dry environments before 92 000, around 193 000, and before 260 000 yr. The data also show that the geochemical background of Fe2O3 and Al2O3 is high in two portions of the section: from the Brady Soil to the Gilman Canyon pedocomplex and from LL1 to LL2 within the Loveland Loess. The geochemical background of Fe2O3 and Al2O3 in the loess‐soil sequence might have been dictated by that of eolian sources.
Cradle‐Knoll Patterns and Characteristics on Drumlins in Northeastern Wisconsin
Authors: Kabrick J. M. , Clayton M. K. , McSweeney K. , McBratney A. B.
Published: July 2010

Cradle‐knoll microtopography has been shown to influence soil and vegetation. However, the scale of commonly used topographic maps is too coarse for representation of microtopography. The objectives of this study were to investigate the influence of cradle‐knoll microtopography on the distribution of trees, to develop a method to quantify the spatial patterns and characteristics of cradle‐knolls, and to test for pattern similarity of cradle‐knolls within and among drumlins in the Nicolet National Forest, Wisconsin. Six drumlins were selected for study. Tree species, tree diameter, and microsite location (e.g., cradle, knoll, or neither) within which each tree was found were inventoried in three, 10‐m‐radius plots across each drumlin. The spatial location, length, width, relief, and orientation of 220 cradle‐knolls were inventoried along 200‐m transects using a T‐square sampling technique on summit and backslope positions of each drumlin. Sixty percent of the trees inventoried were growing on knolls and only 2% were growing in cradles. The same number of knolls and cradles occurred among drumlins and among backslopes and summits within drumlins. Cradle‐knoll relief differed among drumlins, and knoll relief is greater on backslopes than on summits within drumlins. Cradle‐knoll orientation differed among slope positions. These findings suggest that treethrow rates and the size of the uprooted trees are roughly the same among and within drumlins. Differences in relief among drumlins are probably an indication of how recently treethrow has occurred. Greater relief of knolls among backslopes and summits is probably because of slope‐mediated differences in cradle‐knoll formation. Slope position also affects cradle‐knoll orientation in these landscapes.
Mineralogical and Physicochemical Differences between Mobile and Nonmobile Colloidal Phases in Reconstructed Pedons
Authors: Kaplan Daniel I. , Bertsch Paul M. , Adriano Domy C.
Published: July 2010

Ultisols can be highly dispersive and therefore a potential source for mobile colloids to underlying aquifers. In this study, mobile colloids were collected after a rain from 13.5‐m3 lysimeters containing reconstructed pedons of two Ultisols. The mobile colloids were enriched with kaolinite, Fe oxides, and gibbsite and were more dilute in quartz and hydroxy‐interlayered vermiculite (HIV) relative to the total clay fractions of the originating pedons. The colloids were <1000 nm in diameter and had a bimodal size distribution: the larger colloids (≈760 nm) consisted primarily of quartz and HIV; the much more abundant smaller colloids (≈230 nm) consisted primarily of Fe oxides, kaolinite, and gibbsite. The colloids also had exceptionally high negative surface charges that probably originated from organic coatings (10 g kg−1). These organic coatings indicate that the majority of the colloids originated from the surface horizon, the only horizons with measurable amounts of organic C. Soil minerals most likely to enter the mobile phase (Fe oxides, gibbsite, and kaolinite) were readily dispersible and in the <200‐nm fraction. The HIV in the reconstructed pedons was readily dispersible but because of its relatively large size (>200 nm), it was removed from the mobile phase during transport, presumably via a straining mechanism. Quartz was neither readily dispersible nor abundant in the <200‐nm fraction and, therefore, was not prevalent in the mobile phase. The ability of Ultisols to release colloids that can readily move through a pedon may make these soils and the underlying aquifers especially susceptible to colloid‐facilitated transport of contaminants.
Modeling Structural Influences on Soil Water Retention
Authors: Nimmo John R.
Published: July 2010

A new model quantifies the effect of soil structure, considered as the arrangement of particles in the soil, on soil water retention. The model partitions the pore space into texture‐related and structure‐related components, the textural component being what can be deduced to exist if the arrangement of the particles were random, and the structural component being the remainder. An existing model, based on particle‐size distributions, represents the textural component, and a new model, based on aggregate‐size distributions, represents the structural component. This new model makes use of generalized properties that vary little from one medium to another, thereby eliminating any need for empirically fitted parameters. It postulates a particular character of the structural pore space that in some ways resembles texture‐related pore space, but with pore shape related to the breadth of the aggregate‐size distribution. To predict a soil water retention curve, this model requires the soil's porosity and particle‐ and aggregate‐size distributions. Tested with measurements for 17 samples from two sources, it fits the data much better than does a model based on texture alone. Goodness of fit indicated by correlation coefficients ranged from 0.908 to 0.998 for the new model, compared with a range of 0.686 to 0.955 for the texture‐based model.
Influence of Organic Acids on Selenite Sorption by Poorly Ordered Aluminum Hydroxides
Authors: Dynes J. J. , Huang P. M.
Published: July 2010

Competition between low molecular weight (LMW) organic acids and selenite for sorption sites on hydrous metal oxides is an important factor affecting the dynamics of Se in soils and associated environments. Equilibrium and kinetic studies on the competition between selenite and 12 LMW organic acids (acetic, aspartic, citric, formic, glycine, glycolic, p‐hydroxybenzoic, malic, oxalic, salicylic, succinic, and tartaric) for the sorption sites on short‐range ordered Al hydroxides were investigated using the batch method. The equilibrium and kinetic results showed that the influence of the organic acids on selenite sorption by Al hydroxides depended on the concentration, structure, and functionality of the organic acids. The competitiveness of the organic acids with selenite for the sorption sites increased with increasing organic acid concentration. Generally, the larger the stability constant of the Al‐organic solution complexes (KAl‐L), the more effective the organic acid was in competing with selenite for the sorption sites of the Al hydroxides. However, some of the organic acids competed less successfully than expected based on their KAl‐L values. This is attributed to the stereochemical and electrostatic effects originating from both the surface of the Al hydroxides and the organic acids, which lowered the ability of some organic acids to compete with selenite for the sorption sites of the Al hydroxides. Moreover, the kinetic results revealed that the organic acids competed with selenite for the sorption sites primarily in the early reaction period (<3 h), and subsequently, it was this period that was largely responsible for the equilibrium level of selenite sorbed by the Al hydroxides. The findings are of fundamental significance in understanding the role of organic acids in influencing the fate of Se in the environment.
Fractionation of Iron, Managanese, Aluminum, and Phosphorus in Selected Sandy Soils under Citrus Production
Authors: Zhang M. , Li Y. C. , Calvert D. V. , Alva A. K.
Published: July 2010

The sorption and downward transport of trace metals and phosphate in soils are dependent, in part, on the distribution of various forms of Fe, Al, and Mn. The objectives of this study were to investigate (i) the distribution of various forms (exchangeable, organically bound, associated with Mn oxide, amorphous, and associated with crystalline Fe oxide forms) of Fe, Mn, Al, and P in the surface horizons, and (ii) the distribution of these elements in different depth horizons in six soil series in Florida representing Spodosols, Alfisols, and Entisols. Variation in concentration of total Fe with depth of soil was significantly correlated with clay content. Greater than 60 and 80% of total Fe was present in the amorphous and crystalline Fe oxide forms in soils with pH ≤ 6.5 and pH > 6.5, respectively. Total concentration of Mn was lower than that of Fe or Al in all the soils, and it changed very little with depth of sampling. Manganese in the surface horizon was present predominantly as the organically bound form in the Spodosols and as organically bound, oxide, and amorphous forms in the Alfisols and Entisols. The distribution of total and oxalate‐extractable P was significantly related to the content of amorphous Al and Fe and crystalline Fe oxides in the soils. The distribution of various forms of the metals and P was significantly influenced by the soil pH and organic matter content. In the surface horizon soils, Mn and Al were present predominantly as organically bound forms at pH < 6.5 or as Mn oxide and amorphous associated forms at pH > 6.5.
Methods for Comparing Spatial Variability Patterns of Millet Yield and Soil Data
Authors: Stein A. , Brouwer J. , Bouma J.
Published: July 2010

This paper investigates methods to compare spatial patterns of pearl millet [Pennisetum glaucum (L.) R. Br.] yield with spatial patterns of soil variables in a farmer's 1‐ha field on an undulating sand plain in Niger near ICRISAT‐SC. Spatial pattern comparisons are important for precision farming applications. Methods included the correlation coefficient, linear regression, a distance measure to compare separate maps and the cross‐correlation function. Millet grain yield varied from 0 to 2885 kg ha‐1 on 5 by 5 m sub‐plots. Pearl millet yield was correlated with measured soil variables at three different depths, elevation, and crust formation for two successive years. Only 30% of the total variation in millet dry yield was explained by regressing yield against soil variables. Detrended elevation showed a significant negative relation with yield (r = −0.421). The cation‐exchange capacity (CEC) at all the depths showed a significant negative relation with yield (r of −0.238 to −0.290) because crusting and erosion increase with CEC extending to distances up to 30 to 40 m. Pattern comparison using the cross‐correlogram related local hillocks in the area with high yields and local dips with low yields at a distance of 15 to 20 m. From this study, we concluded that the cross‐correlogram was beneficial to compare data at various distances. Yield patterns are best explained by soil variables related to erosion as the major determinign factor in the area.
Sodicity and Clay Type: Influence on Decomposition of Added Organic Matter
Authors: Nelson Paul N. , Barzegar A. Rahman , Oades J. Malcolm
Published: July 2010

Sodicity and clay type influence the decomposition of organic matter, and hence its accumulation in soil. In this study, the interaction of these two factors was examined. Two soils were prepared by mixing sand (57%) and silt (28%), separated from one soil, with clay (15%) separated from two soils. One clay type (Urrbrae) was composed mostly of illite and kaolimite, with a mean particle diameter of 1050 nm. The other (Claremont) was composed of smectite‐dominated materials, with a mean diameter of 104 nm. The prepared soils were brought to different values of exchangeable sodium percentage (ESP) by equilibration with solutions having sodium adsorption ratios (SAR) between 0 and 30. Pea (Pisum sativum L.) straw was added at 50 g kg−1 soil, and the samples were incubated moist. After 67 d, cumulative mineralization of C was 16% greater in the soils with Urrbrae clay than in those with Claremont clay. Sodicity had a slight negative effect on mineralization, but its interaction with clay type was not significant. Differences in the mineralization of C with time and between treatments were reflected in the chemical nature of the remaining C, as determined by 13C nuclear magnetic resonance (NMR) spectroscopy. The greater the loss of C, the lower the proportion of O‐alkyl C relative to other types of C. An implication of the findings is that, following a large addition of organic matter to a sodic soil, retention of organic C would not be improved by a prior reduction in ESP, irrespective of clay mineralogy.
Radiocarbon Dating for Determination of Soil Organic Matter Pool Sizes and Dynamics
Authors: Paul E. A. , Follett R. F. , Leavitt S. W. , Halvorson A. , Peterson G. A. , Lyon D. J.
Published: July 2010

The size and turnover rate of the resistant soil organic matter (SOM) fractions were measured by 14C dating and 13C/12C measurements. This involved soils archived in 1948, and recent samples, from a series of long‐term sites in the North American Great Plains. A reevaluation of C dates obtained in the 1960s expanded the study scope. The 14C ages of surface soils were modern in some native sites and near modern in the low, moist areas of the landscape. They were much older at the catena summits. The 14C ages were not related to latitude although this strongly influenced the total SOM content. Cultivation resulted in lower C contents and increased the 14C age by an average of 900 yr. The 10‐ to 20‐cm depths from both cultivated and native sites were 1200 yr older than the 0‐ to 10‐cm depth. The 90‐ to 120‐cm depth of a cultivated site at 7015 yr before present (BP) was 6000 yr older than the surface. The nonhydrolyzable C of this depth dated 9035 yr BP. The residue of 6 M HCl hydrolysis comprised 23 to 70% of the total soil C and was, on the average, 1500 yr older. The percentage of nonhydrolyzable C and its 14C age analytically identify the amount and turnover rate of the old resistant soil C.
Pedogenesis and Cementation in Calcareous Till in Indiana
Authors: McBurnett S. L. , Franzmeier D. P.
Published: July 2010

Glacial till is extensive in the north central USA. In Indiana, it is calcareous and dense and has high strength and low hydraulic conductivity. It limits root growth and water movement. Its strength has been attributed to compression by thick glacial ice resting on till during deposition. It is not known if chemical cementation also contributes to its strength. In some soils, argillans coat the large prisms in the till‐derived C horizons, and in others, calcans coat the prisms. The objective of this study was to learn if the kind of cutans indicates how water moves through till and if some of the till's strength is due to chemical cementation. We sampled six pedons in Delaware County, Indiana, to a depth of 3 m. Soils with argillans in the till‐derived upper C horizon had outwash strata 2 to 3 m below the surface, and those with calcans lacked outwash. We postulate that argillans indicate that water moves through planar voids in the till and into outwash strata and calcans indicate that the planar voids end in the till. To look for possible cementing agents, we extracted soil samples with acid oxalate (o), citrate‐bicarbonate‐dithionite (d), and NaOH (n) and determined Fe, Al, and Si in the extracts. We also determined soil strength with a modulus of rupture test. Strength was higher in Cd horizons than in the solum, so strength was lost during soil formation. Strength was positively correlated with extractable Si (Sio, Sid, and/or Sin) and CaCO3 equivalent and was negatively correlated with clay and extractable Fe and Al. We conclude that the strength of the glacial till C horizons is due in part to weak cementation by silica, carbonates, or both.
Woody Debris Decomposition in the Atchafalaya River Basin of Louisiana following Hurricane Disturbance
Authors: Rice Michael D. , Lockaby B. G. , Stanturf J. A. , Keeland B. D.
Published: July 2010

The contribution of woody debris to some biogeochemical functions of forested wetlands was examined in the Atchafalaya River Basin in Louisiana following disturbance by Hurricane Andrew. Woody debris decomposition processes were characterized in terms of mass, C, N, and P dynamics. These were compared between different diameters of debris, areas recieving different intensities of disturbance, and between different positions relative to the soil. Disturbance intensity (as defined by canopy closure) had little effect on decomposition processes when compared with soil orientation (i.e., whether in contact with or suspended above the soil). Rates of mass loss varied between 0.055 and 0.068 for suspended and ground‐contact coarse woody debris, respectively. Fine woody debris rate coefficients averaged 0.060 and 0.085 for the same respective orientations. In general, woody debris displayed strong source activity for P but a greater tendency toward sink behavior for N. In terms of biogeochemical transformations, these data suggest that woody debris might act as a phosphate source during sheet flow events but could provide short‐term retention of inorganic N associated with floodwaters.
Reaction of Nitric Oxide with Acetylene and Oxygen: Implications for Denitrification Assays
Authors: McKenney D. J. , Wang S. W. , Drury C. F.
Published: July 2010

Nitric oxide reacts with C2H2 at ambient temperature under aerobic conditions with relatively large quantities of O2 present. We used a gas‐flow system at 20°C to determine the extent, if any, of reaction of NO with C2H2 under nearly anaerobic conditions with addition of trace (<500 µL L−1) quantities of O2, and to determine whether the process could account for the apparent C2H2 inhibition of NO production in soil. Results showed that reaction occurred only when critical trace quantities of O2 were present. For example, if [NO] was in the range 0.5 to 2.5 µL L−1, which is typical of concentrations in our soil studies, approximately 200 to 300 µL O2 L−1 was required before measurable NO loss was observed. The reaction was first order with respect to NO and variable order, becoming zero order, with respect to O2 when [O2] exceeded ≈400 µL L−1 and maximum NO depletion rates (≈0.01–0.06 µL L−1 s−1) were obtained. The effect of C2H2 on NO production with addition of O2 (≈20–730 µL L−1) in Brookston clay loam (fine‐loamy, mixed, mesic Typic Argiaquoll) and Fox sandy loam (fine‐loamy over sandy or sandy‐skeletal, mixed, mesic Typic Hapludalf) under conditions similar to the gas‐phase studies was also investigated. Depletion of NO in the presence of C2H2 vs. [O2] followed the same pattern with similar rates as the gasphase process. A simplified C2H2‐catalyzed scheme for the oxidation of NO to NO2 provides a plausible, partial explanation for these results. Since NO depletion requires only trace amounts of O2, the results suggest that in many previous studies involving assays of NO or N2O production based on C2H2 inhibition, significant gas‐phase reaction may have occurred leading to serious errors of interpretation.
Equilibrium and Kinetic Study of Ammonium Adsorption and Fixation in Sodium‐Treated Vermiculite
Authors: Shen Siyuan , Tu Shu‐I , Kemper W. Doral
Published: July 2010

Ammonium fixation in vermiculite affects the movement of N in many soils. The effects of particle size, solution concentration, pH, and associated anions on NH+4 fixation in vermiculite are also important information for reducing N leaching from soils. In this study, the retention of NH+4 on the exchangeable and nonexchangeable sites of Montana vermiculite was determined in batch experiments. In the NH+4‐K+ exchange isotherm, the exchangeable sites of the vermiculite exhibited a preference for K+ to NH+4, while the nonexchangeable sites preferred NH+4 to K+. The nonexchangeable sites of the sand fraction had a higher preference for NH+4 at lower solution NH+4 concentration and a lower preference at higher NH+4 concentration. An opposite case was observed for the NH+4 concentration effect on the preference of nonexchangeable sites in the clay fraction. The retention isotherm of total NH+4 in the vermiculite exhibited S‐shape curves that can be described by the “two‐surface” Langmuir‐Freundlich equation. In the kinetic study, the clay fraction adsorbed the largest amount of exchangeable NH+4, but the silt fraction fixed the most NH+4 on its nonexchangeable sites. The retention of NH+4 in vermiculite increased with solution NH+4 concentration. Ammonium adsorption on the exchangeable sites increased at low solution pH, while NH+4 fixation was unaffected by pH change. The effect of associated anions was insignificant, except they caused a pH difference in solution.
Approximating the Impact of Sorption on Biodegradation Kinetics in Soil‐Water Systems
Authors: Gamerdinger A. P. , Achin R. S. , Traxler R. W.
Published: July 2010

Naphthalene sorption and biodegradation were quantified in three soils of varying organic C content using miscible displacement and batch incubation techniques. As anticipated, sorption increased with organic C content; the sorption rate coefficient and equilibrium sorption constant (Kd) were inversely related. Organic matter in solution (NOM) from the high‐organic‐matter soil decreased apparent sorption, which was also quantified using methanol as a cosolvent. A cosolvency power of 3.8 or 4.1 was determined. The initial biodegradation rate decreased with increasing sorption and was a function of naphthalene concentration in solution. The extent of biodegradation was greatest in the high‐organic‐matter soil and decreased when NOM was removed from the system. The observed dependence of biodegradation kinetics on sorption (this study and in the literature) prompted us to develop a simple approach for approximating a biodegradation rate constant for soil‐water systems. This approach combines independently determined sorption parameters with the biodegradation rate constant determined for aqueous (soil‐free) solution. The approach was applied to our data and to published data where sorption was shown to control naphthalene biodegradation. The approximated biodegradation rate constant was within 10% of the measured values for three cases, 20% for a fourth case, and was underestimated by five‐to sevenfold for the high‐organic‐matter soil. The approach will be useful when applying management models for predicting contaminant fate and transport that require a degradation rate constant, or for estimating biodegradation rates in situations where cultured organisms are introduced for biodegradation.
Flow Velocity Effects on the Retardation of FD&C Blue no. 1 Food Dye in Soil
Authors: Perillo Catherine A. , Gupta Satish C. , Nater Edward A. , Moncrief John F.
Published: July 2010

Dyes are often used as tracers of water and solute flow in soil. However, there has been little published research on the effects of flow velocity on the relative movement of dye and wetting fronts. Recently, the FD&C Blue no. 1 dye has been used as a tracer of preferential water flow paths in soils, and has attractive properties suggesting it will be used increasingly in the future. The objective of this study was to characterize the effects of flow velocity on the adsorption characteristics of the FD&C Blue no. 1. We performed a series of laboratory experiments on the characterization of the equilibrium adsorption isotherm as well as the effect of flow velocity on adsorption characteristics of the FD&C Blue no. 1 in three horizons of Verndale sandy loam (coarse‐loamy over sandy, mixed, frigid Udic Argiboroll). Batch equilibration (24 h) measurements resulted in linearized Freundlich distribution coefficients (Kd) of 4.33, 23.95, and 4.59 L kg−1 for the Ap, Bt, and C horizons, respectively. Neither organic C nor clay content differences accounted for the variation between horizons. Leaching experiments with a 1 g L−1 dye solution and repacked soil columns containing either Ap, Bt, or C horizon material showed that the dye was retarded relative to the wetting front, and that the extent of retardation was inversely related to the time period during which dye solution was applied. Therefore, this dye (and perhaps others) should not be used to make inferences about the movement of water or other solutes until the effect of the application rate is evaluated for the flow conditions in the system(s) of interest.
Surface Roughness Related Processes of Runoff and Soil Loss: A Flume Study
Authors: Helming K. , Römkens M. J. M. , Prasad S. N.
Published: July 2010

Soil surface roughness greatly affects surface sealing and runoff generation, yet little information is available about the effect of roughness on the spatial distribution of runoff and on flow concentration. This study tested the hypothesis that runoff distribution and flow concentration differ with roughness and affect the amount of soil loss. Sequences of four rainstorms of constant rainfall amount but decreasing intensity (60, 45, 30, and 15 mm h−1) were applied to the Ap horizon material of a loess soil (Glossic Fragiudalf) packed into a 0.6 by 3.7 m flume. Rough, medium, and smooth soil surfaces were studied at 17, 8, and 2% slope steepness. Surface roughness and flow pathways were visualized with digital elevation maps obtained from laser microrelief measurements. On the smooth surfaces, runoff was uniformly distributed during the first two rainstorms and soil losses were 0.23, 0.07, and 0.12 kg m−2 for the first and 2.26, 0.35, and 0.2 kg m−2 for the second storm at 17, 8, and 2% slope steepness, respectively. On the rough and medium surfaces, flow concentrated in pathways between clods and soil losses were up to eight and three times that on the smooth surfaces during the first and second storms, respectively. During the last two storms, flow concentrated also on the smooth surfaces and soil losses were similar for the three initially different surface configurations. Surface roughness effects on runoff amount were minor, but roughness affected the spatial distribution of runoff, thereby affecting the amount of soil loss.
Retardation of Fluorobenzoate Tracers in Highly Weathered Soil and Groundwater Systems
Authors: Seaman John C.
Published: July 2010

Fluorobeuzoate (FBA) compounds have been used extensively as hydrologic tracers based on the assumption that they are not significantly sorbed or degraded in most soil and groundwater environments. However, previous batch studies have indicated that such compounds may be readily sorbed by organic matter and hydrous Fe oxides, such as goethite. This study was conducted to evaluate the transport properties of FBA tracers within the highly weathered sediments of the southeastern Coastal Plain. Repacked columns of coarse‐textured alluvial soil and aquifer sediments were leached with tracer solutions (pH ≈5.0) containing various fluorobenzoates with negative logs of the acid dissociation constants (pKas) ranging from 3.83 to 2.85. Bromide was included in many of the solutions to evaluate the influence of ionic strength and competition for anion‐exchange sites on FBA mobility. Despite possible differences in the mechanisms of sorption, retardation within surface and subsurface materials increased with increasing pKa of a given FBA compound. Retardation was attributed to partitioning to the organic fraction for the surface soil and to sorption by Fe oxides for the subsurface sample. For the transport of mixed‐benzoate solutions through surface soil, 2,6‐di‐FBA, 2,3,4,5‐tetra‐FBA, and Br− yielded transport velocities consistent with those observed for 3H; however, 3,4,5‐tri‐FBA and 3,4‐di‐FBA were significantly retarded, most likely due to partitioning to the organic fraction. For the subsurface sample, all of the FBA tracers and Br− were retarded compared with 3H, with FBA retardation increasing with pKa. At higher ionic strengths, retardation was reduced in the subsurface sample due to competition with Br− for anion sorption sites.
Soil Organic Matter Recovery on Conservation Reserve Program Fields in Southeastern Wyoming
Authors: Robles Marcos D. , Burke Ingrid C.
Published: July 2010

Soil C and N changes following cessation of cultivation in semiarid soils is not well understood. We hypothesized that returning cultivated fields in southeastern Wyoming to perennial grasses through the Conservation Reserve Program (CRP) would (i) increase labile pools of soil organic matter (SOM), and (ii) increase small‐scale heterogeneity of SOM. Carbon and N in labile and passive pools of SOM were measured in CRP fields seeded with perennial grasses intermediate wheatgrass (Elytrigia intermedia [Host] Nevski ssp. intermedia), pubescent wheatgrass (Elytrigia intermedia [Schur.] A. Löve ssp. barbulata) and smooth brome (Bromus inermis Leysser), and in winter wheat (Triticum aestivum L.)‐fallow fields. Mineralizable C increased from 0.37 g m−2 d−1 in wheat‐fallow fields to 0.99 g m−2 d−1 in CRP fields; mineralizable N and coarse particulate C were consistently but not significantly higher in CRP fields. Fine particulate and total soil C and N were not significantly different between CRP and wheat‐fallow. Within CRP fields, mineralizable C was significantly higher under grasses than in interspaces (1.96 vs. 0.73 g m−2 d−1, respectively), and mineralizable N and coarse particulate C and N were consistently but not significantly higher under grasses than in interspaces. Soil C and N have increased only slightly after 6 yr of CRP management, and future changes in land use management on these CRP fields, including grazing and cropping, may accrue some small benefits associated with improved soil fertility status.
Parameter Estimation Analysis of the Evaporation Method for Determining Soil Hydraulic Properties
Authors: Šimůnek Jiří , van Genuchten Martinus Th. , Wendroth Ole
Published: July 2010

Soil hydraulic properties are important parameters affecting water flow in variably saturated soils. We estimated the hydraulic properties from a laboratory evaporation experiment using both a parameter estimation method and the modified Wind method. The parameter estimation method combined a one‐dimensional numerical solution of the Richards equation with the Marquardt‐Levenberg optimization scheme. In our study we used both numerically generated data and data measured in the laboratory. Two experiments were carried out on 10‐cm‐high soil cores containing two different soils. Pressure heads inside the cores were measured with five tensiometers, while evaporative water loss from the top was determined by weighing the soil samples. The objective function for the parameter estimation analysis was defined in terms of the final total water volume in the core and pressure head readings by one or several tensiometers. An analysis of numerically generated data showed that the optimization method was most sensitive to the shape factor (n) and the saturated water content (θs) and least to the residual water content (θr). Pressure heads measured close to the soil surface were found to be more valuable for the parameter estimation technique than those measured at lower locations. The optimized hydraulic parameters corresponded closely with those obtained using Wind's analysis. All optimizations gave similar results for the soil hydraulic properties within the range of measured pressure heads (0 to −700cm). Extrapolation beyond this range involved a high level of uncertainty because of high correlation between parameters θr and n.