bluuebunny/crossref_metadata_2025 huggingface dataset:
A Method for Studying the Effects of Soil Aggregate Size and Density
Authors: De Freitas P. L. , Zobel R. W. , Snyder V. A.
Published: July 2010

Soil macroproperties, such as bulk density, porosity, water conductivity, and aeration, have been utilized in order to evaluate soil structure effects on crop yields. It has been suggested that many of the limitations to crop growth can be explained by the physical properties of the aggregates. To explore some aspects of this, a method to simulate soil aggregates of different sizes and densities was developed and tested. A Collamer silt loam soil (fine‐silty, mixed, mesic Glossoboric Hapludalf) was dried, crushed, sieved, and compressed to different densities (1.4, 1.6, and 1.8 Mg m‐3). The resulting 25‐ and 50‐mm‐thick cylindrical soil slices were cut to two different cubical sizes (25‐ and 50‐mm sides). Cylinders with continuous horizontal and vertical macropores were assembled from these artificial aggregates to make six different treatment combinations of aggregate size and density. Corn (Zea mays L.) seedlings were transplanted into the cylinders and grown in a growth chamber for 27 d. Results show that high aggregate density limits crop growth and that, at intermediate densities, aggregate size assumes more significance as a limiting factor.
Pedogenesis of a Vernal Pool Entisol‐Alfisol‐Vertisol Catena in Southern California
Authors: Weitkamp W. A. , Graham R. C. , Anderson M. A. , Amrhein C.
Published: July 2010

Vernal pools are seasonal wetlands that have unique plant and animal species. More than 10 vernal pools are found on the basaltcapped mesas of the Santa Rosa Plateau Ecological Preserve in southern Riverside County, California. In this study, one vernal pool catena was investigated to determine the relationships between soil morphology, soil chemical properties, and water movement. Soils on the summit and backslope are shallow and coarse‐loamy, and are maintained as Entisols by extensive burrowing by rodents and their predators. Footslope soils are clayey Alfisols with strong prismatic structure. The basin and toeslope soils are Vertisols with strong angular blocky structure and slickensides. Iron oxides are concentrated in the upper slope soils, imparting 5YR hues and high chromas. Because Mn oxides are soluble at higher redox potential than Fe oxides, Mn has been preferentially dissolved, transported downslope with throughflow, and precipitated as oxides in the lower slope soils, which have 10YR hues and low chromas. Water infiltrates readily through the upper slope soils and moves downslope along the soil‐basalt bedrock contact and within the vesicular basalt. In the basin, the Vertisols are wetted unevenly as water moves downward through soil cracks and upward from throughflow in the underlying vesicular basalt.
Soil Mass, Surface, and Spectral Fractal Dimensions Estimated from Thin Section Photographs
Authors: Anderson A. N. , McBratney A. B. , FitzPatrick E. A.
Published: July 2010

Aspects of fractal geometry have been used to give quantitative measurements of soil structure. Fractal dimensions measured were the mass fractal dimension (Dm), surface fractal dimension (Ds), and the spectral dimension (d). We investigated the fractal component of a computer program, STRUCTURA, which measures the fractal dimension of soil from images of soil thin sections. Six thin sections, each showing different structural characteristics, were analyzed in order to obtain a range of fractal dimensions. The dimensions, in particular Dm and d, were shown to discriminate the different structures. The values of Dm and d ranged from 1.682 to 1.852 and 1.236 to 1.668, respectively. A further objective was to use these results, together with fractal theory, to show the potential fractal geometry has in predicting physical processes such as diffusion within the soil. To assist with the interpretation of fractal dimensions, the dimensions of different soil samples with the same porosity were compared.
Two‐Dimensional Model for Water, Heat, and Solute Transport in Furrow‐Irrigated Soil: II. Field Evaluation
Authors: Noborio K. , McInnes K. J. , Heilman J. L.
Published: July 2010

To maintain crop production in areas where irrigation water or soil contains a large amount of salt, proper management of water and soil is required. A model simulating salt movement in the field may be helpful for developing improved management practices. We developed a two‐dimensional Galerkin finite element model to simulate transport of water, heat, and solute in furrow‐irrigated soil. In this model, we considered the interaction of soil water content, temperature, and solute concentration on transport of water, heat, and solute. An energy balance equation was applied to each node along the simulated ridge‐furrow soil surface to provide boundary conditions for water and heat transport. The model was compared with field measurements acquired in a loamy sand plot near College Station, TX. In the soil profile, distributions of water content and electrical conductivity were measured with time domain reflectometry, and distributions of temperature were measured with thermocouples. Solute concentration was estimated from electrical conductivity. The overall performance of the developed model was favorable when simulating distributions of water content, temperature, and solute concentration.
Soil Textural Control on Decomposition and Soil Organic Matter Dynamics
Authors: Scott Neal A. , Cole C. Vernon , Elliott Edward T. , Huffman Steve A.
Published: July 2010

Soil texture affects litter decomposition by altering soil water availability, pore size distribution, nutrient availability, and surface area. We examined the direct and indirect effects of soil texture on litter decomposition and soil organic matter mineralization during 91‐d laboratory incubations. Treatments included texture (73, 55, and 40% sand), soil water pressure (−0.012, −0.033, and −0.30 MPa), and nutrient availability (with or without additional N and P). Wheat litter (Triticum aestivum L.) was placed on the surface or incorporated into the soil. Soil texture had no effect on litter decomposition (P >‐ 0.23). Litter decomposition was fastest for the −0.012 MPa treatment across all soil types (P < 0.01), and the difference between water pressure treatments was greatest in the loam (40% sand) soil. The effects of texture and soil water pressure could be combined into one variable (percentage water‐filled pore space), which accounted for more of the variability in litter decomposition and native soil C mineralization than either texture or soil water pressure alone. Surface‐applied litter decomposed significantly faster than incorporated litter, but the effect was not consistent across different soils (P = 0.04). Litter addition stimulated the mineralization of native soil C, the greatest effect occurring when litter was incorporated into the fine‐textured soil.
Soil Phosphorus Dynamics during Seventeen Years of Continuous Cultivation: Fractionation Analyses
Authors: Schmidt J. P. , Buol S. W. , Kamprath E. J.
Published: July 2010

Excluding fertilizer P, a finite quantity of soil P exists for plant uptake. To improve our understanding of sinks and sources of long‐term plant‐available P, soil P fractions to a depth of 30 cm were determined in soils under a continuous cropping system prior to fertilization (1975), after 10 yr of P fertilization (1985), and 6 yr after the last P fertilization (1992). Soil types for two study sites were Norfolk loamy sand (fine‐loamy, siliceous, thermic Typic Kandiudult) and Davidson clay loam (clayey, kaolinitic, thermic Rhodic Paleudult). Superphosphate was applied from 1975 to 1986 at rates of 0, 10, 20, and 40 kg P ha−1 yr−1. Average removal of P, via corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] cropping, was between 10 and 20 kg P ha−1 yr−1 from 1975 to 1992. Resin‐extractable soil P increased in the Norfolk soil with annual P applications that were in excess of crop removal and decreased with annual P applications that were less than crop P removal. Resin‐extractable soil P decreased to below 3 mg P kg−1 in the Davidson soil regardless of P application or removal rate. Inorganic soil P extracted with NaHCO3 and NaOH increased with excess P additions and decreased with deficient P additions for both soils. Organic soil P in the Norfolk soil extracted with NaOH represented a P sink at the 40 kg P ha−1 yr−1 treatment in 1985, but subsequently mineralized by 1992. In both soils, inorganic P extracted in the resin, NaHCO3, and NaOH fractions, and organic P in the NaOH fraction of the Norfolk soil, represented the biologically dynamic P.
Spatial Characteristics of Soil Properties along an Elevational Gradient in a Carolina Bay Wetland
Authors: Reese Rachel E. , Moorhead Kevin K.
Published: July 2010

Soil chemistry gradients exist in wetlands but information on the spatial variability of wetland soil properties is limited. Soils were collected from a small, depressional wetland (Carolina bay) in South Carolina to determine spatial patterns along an elevational gradient. The bay was divided into four quadrants and a transect was established in each quadrant. Plots were sampled at every 10‐cm rise in elevation along the four transects. Samples from the A and B horizons were analyzed for soil texture, organic carbon (OC), pH, cation‐exchange capacity (CEC), and exchangeable Ca, Mg, and K. Significant difference were noted for OC, clay content, CEC, and base saturation for the A horizon across the elevational gradient. The OC content of the A horizon decreased from 4.7% in the center of the bay to 2.7% near the rim. The CEC decreased from 26.0 cmolc kg−1 in the center to 13.9 cmolc kg−1 near the rim. Significant differences also were observed for pH, OC, CEC, sand, silt, clay, exchangeable Mg, Ca, and base saturation among the four transects. In the B horizon, there were no significant differences for any parameter across the elevational gradient, or among the four transects. The clay content of the B horizon was about 20%, compared with <10% in the A horizon. The differences in soil parameters in the A horizon may be a reflection of vegetation patterns or hydrology of the bay. Sampling protocol for soils of depressional wetlands may require an evaluation of elevation, hydrology, and vegetation patterns to determine spatial patterns of nutrient cycling.
Soil Water Content Determination Using a Digital Ground‐Penetrating Radar
Authors: Chanzy A. , Tarussov A. , Bonn F. , Judge A.
Published: July 2010

We evaluated the potential of a digital ground‐penetrating radar (GPR) for soil moisture determination. Ground‐penetrating radar offers a fast and nondestructive way for estimating the soil dielectric constant and may be an interesting tool for low‐cost mapping of soil moisture. Two modes of operation were considered: (i) the ground mode where signal propagation between the antennas placed on the surface was studied; (ii) the airborne mode where the antennas are raised 5–15 m above the soil surface. Variables describing the GPR response were defined and related to the soil moisture. It is shown from field experiments that the GPR measurements performed at 200 MHz in both modes are mainly affected by the moisture in the 10‐ to 20‐cm topsoil layer. In the ground mode, the obtained soil moisture error after calibration was lower than 0.03 m3/m3. In the airborne mode, soil moisture estimations were less accurate (0.046 m3/m3). The wave spreading loss characterization has to be improved to get an altitude‐independent GPR measurement.
Chloride Increases Cadmium Uptake in Swiss Chard in a Resin‐buffered Nutrient Solution
Authors: Smolders E. , McLaughlin M. J.
Published: July 2010

One of the possible hypotheses to explain the high Cd availability at elevated Cl concentration in soil is that chloro‐complexes of Cd are available for root uptake. In order to test this hypothesis, Swiss chard [Beta vulgaris ssp. cicla (L.) Koch, cv. Fordhook Giant) was grown in nutrient solution continuously recirculated over a chelating resin (Chelex‐100) partially loaded with Cd. Treatments were increasing concentrations of Cl (0.01, 40, 80, and 120 mM) in the nutrient solution with fourfold replication. Solution Na concentrations and ionic strengths were equalized in all treatments by compensating with NaNO3. Increasing Cl concentrations in solution did not affect dry weights of either roots or shoots. Activity of Cd2+ in solution was well buffered during plant growth using the resin system. Complexation of Cd2+ by Cl increased soluble Cd in culture solutions but the calculated activity of Cd2+ was not significantly affected by increasing concentrations of Cl in solution. As solution Cl concentration increased, Cd concentrations in plant shoots increased from 6.5 to 17.3 mg kg−1 and in roots from 47 to 106 mg kg−1. We concluded that enhancement of Cd uptake by Cl in soils need not be related only to enhanced diffusion of Cd2+ through soil to the root but that (i) CdCl2‐nn (in addition to Cd2+) species in solution are phytoavailable and/or (ii) Cl enhances diffusion of Cd2+ through the unstirred liquid layer adjacent to the root surface or through the apoplast to sites of Cd uptake within the root itself.
Dynamics of Soil Physical Properties in Amazonian Agroecosystems Inoculated with Earthworms
Authors: Alegre J. C. , Pashanasi B. , Lavelle P.
Published: July 2010

The combined use of earthworm inoculation and organic inputs is considered an efficient way to improve traditional slash‐and‐burn agriculture in the humid tropics. This study tests the hypothesis that the resistant macroaggregate structure that results from earthworm activities is likely to promote sustainability by favoring water infiltration and soil aeration. Six successive crops (maize [Zea mays L.]‐rice [Oryza sativa L.]‐cowpea [Vigna unguiculata (L.) Walp.]‐rice‐rice‐rice) were grown from March 1990 to January 1993 on a fine‐sandy, siliceous, isohyperthermic Typic Paleudult previously covered by forest at Yurimaguas (Peruvian Amazonia). The experimental design included a combination of three organic residue treatments (without residues, with crop residues, and with crop residues plus green manure), with or without earthworm (Pontoscolex corethrurus) inoculation (36 g fresh weight m−2). Soil physical properties (bulk density, total porosity, infiltration, sorptivity, soil water tension, and aggregate‐size distribution) were measured before clearing and after harvesting each crop. The proportion of macroaggregates (>1 cm) increased from 25.1 to 32.7% in inoculated treatments, whereas the proportion of small aggregates (<2 cm) decreased from 33.2 to 26.1%, and no change was observed in the intermediate (2‐10 mm) category. In the control treatment, no significant changes were observed. Earthworm activities significantly increased bulk density (from 1.12 to 1.23 Mg m−3), and decreased porosity (from 58 to 53%) and sorptivity (from 0.45 to 0.15 cm s−1/2). Soil water tension was also affected by the presence of earthworms through increased water uptake by larger plants and changes in soil structure. Longer term experiments are necessary to confirm that the activity of the earthworm may not eventually have detrimental effects.
Factors Affecting Phosphate Rock Dissolution in Acid Soil Amended with Liming Materials and Cellulose
Authors: He Z. L. , Baligar V. C. , Ritchey K. D. , Martens D. C. , Kemper W. D.
Published: July 2010

Coal combustion by‐product (CCBP; a wallboard‐quality gypsum), limestone, and cellulose had been found to influence the dissolution of North Carolina phosphate rock (NCPR) in an acid Lily loam soil (fine‐loamy, siliceous, mesic Typic Hapludult). Laboratory and incubation experiments were carried out in this study to elucidate the mechanisms responsible for the reduced dissolution of NCPR from CCBP application. The major factors responsible for the reduced PR dissolution were (i) an increase in exchangeable Ca + Mg derived from the CCBP, (ii) an increase in soil pH from the small amounts of CaCO3 in the CCBP material; and (iii) sulfate released from the CCBP resulting in a decrease in P sorption capacity of the amended soil due to competitive sorption between sulfate and phosphate. The further reduction in NCPR dissolution by limestone addition was probably due to the increase in pH and exchangeable Ca relative to CCBP application alone. An increased NCPR dissolution from cellulose addition probably reflected an accelerated depletion of labile P by the cellulose‐induced microbial growth and, hence, biomass production. The four kinetic dissolution parameters, i.e., the half‐life (t1/2) from a first‐order rate equation, the initial dissolution rate‐ and the average dissolution rate‐related constants (A and b) from an Elovich equation, and the potential maximum dissolution of phosphate rock from a Langmuir equation were significantly correlated with pH, the content of exchangeable (Ca + Mg), and P sorption capacity of the CCBP‐amended soil. The t1/2 and A of NCPR in the acid soil could be predicted with 95% confidence by the three soil variables, i.e, soil pH, P sorption capacity, and exchangeable (Ca + Mg). Both t1/2 and A could serve as an indicator of the NCPR dissolution potential in soils.
Sustained Productivity of Forests Is a Continuing Challenge to Soil Science
Authors: Nambiar E. K. Sadanandan
Published: July 2010

Scientific uncertainties about ecosystem processes and greater awareness of the need for environmental care are sources of public anxiety over forest management. Partly because of this, the negative impacts of poor forestry practices are often emphasized, overlooking the achievements in sustainable forestry. The forest estates should be viewed and managed as a continuum so that the overall need for production of wood and the protection of environmental values can be met. We need practical goals of forest management. One goal should be to ensure that the trend in forest productivity is nondeclining or is positive through successive rotations and harvests, while maintaining and enhancing the quality of the soil resource base in perpetuity. The conflicts about the use of native forests for wood harvesting, while maintaining all conservation values, can be lessened if the value of each forest is ranked within a scale ranging from wood production to conservation. The growing demand for wood and concerns for land care can be met in part by expanding plantation forestry. Questions concerning management strategies for sustainable forestry are global in scope, but the genesis and application of practices for achieving this are local and are based fundamentally on the soil. The expectation of developing soil‐based sustainability indicators can be realized only if the expectation is backed by substantial research linking changes in soil properties, ecosystem processes, and productivity at the landscape level. Challenges are many and include interdisciplinary approaches to research and forest management, application to ensure economic prosperity, and positive approaches to communication.
Changes in the Biogeochemistry of Potassium following a Whole‐Tree Harvest
Authors: Romanowicz Rachel B. , Driscoll Charles T. , Johnson Chris E. , Fahey Timothy J. , Likens Gene E. , Siccama Thomas G.
Published: July 2010

A whole‐tree harvest (WTH) was conducted at the Hubbard Brook Experimental Forest, New Hampshire, in 1983–1984 to evaluate changes in the loss and supply of nutrients such as K in response to clear‐cutting. The WTH removed 554 mmol m−2 associated with forest biomass. During the first 2 yr following the WTH, there were marked increases in concentrations and fluxes of K in drainage waters (stream efflux 24 mmol m−2 yr−1), coinciding with elevated losses of NO3−. While these losses decreased within 3 yr, concentrations and fluxes of K remained high in Bs2 horizon soil water and streamwater (10.5 mmol m−2 yr−1) for 10 yr relative to the reference watershed (4.8 mmol m−2 yr−1). Soil exchangeable K pools increased within 3 yr after the WTH. In the high‐elevation zone of the watershed, soil pools returned to near‐preharvest values after 8 yr. In the remainder of the watershed, exchangeable K pools decreased after 8 yr but remained about 20% above preharvest pools. The increase in exchangeable K in the mineral soil probably contributes to the long‐term pattern of elevated K concentrations in streamwater after the WTH. Although stream and WTH removal of K (8.5 mmol m−2 yr−1) was large in comparison to preharvest exchangeable K pools (284 mmolc m−2), the increased release of K from mineralization of soil organic matter and weathering resulted in an increase in K on the soil exchange complex (43 mmol m−2 yr−1 in the first 8 yr). The increase in exchangeable K provided an available pool of K for the regrowing vegetation.
Testing an Artificial Neural Network for Predicting Soil Hydraulic Conductivity
Authors: Tamari S. , Wösten J. H. M. , Ruiz‐Suárez J. C.
Published: July 2010

Multilinear regression has been used extensively to predict soil hydraulic properties, both the θ(h) and K(h) relationships, from easily obtainable soil variables. As an alternative, this study investigated the performance of an artificial radial basis neural network in predicting some K(h) values from other variables. This kind of neural network may be seen as a multivariate interpolation technique, which can theoretically fit any nonlinear continuous function. Neural networks are characterized by parameters that must be optimized to solve a given problem. We used a fitting procedure requiring only two parameters to ensure a unique solution. These two parameters were determined by data splitting. Hypothetical data bases with uncertainties were simulated to analyze the performance of the neural network in predicting a nonlinear relation derived from a classical model for K(h). A soil data base covering a broad spectrum of soil horizons was used to test the neural network in solving multivariate problems. Numerical simulations showed that the neural network was sensitive to large uncertainties in the data base. It was more efficient than a multilinear regression when the uncertainties were small. Experimental results showed that the neural network was more efficient than the multilinear regression for predicting K(h = −1 m) or K(h = −2.5 m) from two qualitative and five quantitative soil variables. It was also more efficient than two independent multilinear regressions, one for the sandy samples and the other for the loamy and clayey samples. Provided that a large data base with accurate K values is available, artificial neural networks can be useful to predict θ(h) and K(h) over a broad spectrum of soils.
Simultaneous Measurement of Soil Microbial Nitrogen, Carbon, and Carbon Isotope Ratio
Authors: Bruulsema T. W. , Duxbury J. M.
Published: July 2010

Methods used for analysis of soil microbial biomass N and C are limited in precision and are time consuming. A method involving direct combustion of evaporated soil extracts was developed for use with an automated nitrogen and carbon analyzer (ANCA). The objectives of this study were to: (i) evaluate the usefulness of ANCA determination of microbial C and N, and (ii) ascertain whether the microbial C isotope ratios determined by the ANCA method would reflect C contributions from actively growing crops of wheat (Triticum aestivum L.) and maize (Zea mays L.) differing in C isotope ratio. Cropped and fallow soils were sampled at planting, anthesis, and maturity. Field‐moist soils were fumigated with chloroform and extracted with 0.05 M K2SO4 for the ANCA method and with 0.5 M K2SO4 for Kjeldahl analysis. Small volumes of the 0.05 M K2SO4 extracts were evaporated on cone‐shaped tin disks that were analyzed using combustion at 1700°C and mass spectrometry. Reproducible values for C, N, and δ13C were obtained with less effort than that typically expended for Kjeldahl N analysis of similar extracts. Temporal changes in microbial δ13C occurred in both cropped and fallow soils during a single growing season. At maturity of the maize crop, an estimated 23% of the soil microbial C was derived from the plant material of the current maize crop. Carbon contribution from the wheat crop to the soil microbial biomass was not detected. Further refinements in the ANCA method may make the procedure routinely usable for enhancing the understanding of chloroform labile C and N as indicators of microbial dynamics in the soil.
Myrosinase Activity in Soil Extracts
Authors: Borek Vladimir , Morra Matthew J. , McCaffrey Joseph P.
Published: July 2010

Myrosinase (β‐thioglucoside glucohydrolase; EC 3.2.3.1) catalyzes the hydrolysis of glucosinolates to form a variety of potential allelochemicals. Although these allelochemicals may exert an influence on soil‐borne organisms, the extracellular preservation of plant‐derived myrosinase in soil has not been determined. Soil samples from a field of rapeseed (Brassica napus L.) and from a pasture were extracted with a 0.1 M mixture of K2HPO4 and disodium ethylenedinitrilotetraacetate (pH 7.9). Crude extracts were purified with dialysis and assayed for enzymatic activity using sinigrin (allyl glucosinolate) as a substrate. Myrosinase activity was evaluated by monitoring the hydrolysis product, allyl isothiocyanate, using gas chromatography. Reliability and limitations of the assay were verified with autoclaved samples amended with known amounts of enzyme of allyl isothiocyanate. Extracts of soil samples from a rapeseed field showed myrosinase activity, whereas extracts from a pasture soil showed no detectable activity. Highest myrosinase activity was detected in soil sampled directly from rapeseed rows, an activity equivalent to a myrosinase concentration of approximately 20 µg kg−1 soil. Soil sampled between rapeseed rows had a lower myrosinase activity equivalent to a myrosinase concentration of approximately 5 µg kg−1 of soil. The presence of extracellular myrosinase in soil indicates that glucosinolate hydrolysis in the rhizosphere of Brassica spp. and allelochemical impacts on organisms within the rhizosphere are possible.
Soil Surface Coatings at Costa Rican Recently Active Volcanoes
Authors: Jongmans A. G. , Groenesteijn K. , Buurman P. , Mulder J.
Published: July 2010

Unvegetated slopes of recently active volcanoes in perudic Costa Rica have locally thin, hard, laminated coatings at the soil surface. These coatings, which cover both ash deposits and boulders, are actively forming in some locations and eroding in others. We investigated the chemistry and formation of these coatings. Optical analysis of the coatings shows that they consist of anisotropic ash particles embedded in isotropic, translucent, fine‐textured amorphous material. Scanning electron microscope analysis clearly shows secondary coatings covering and cementing primary mineral grains and rock fragments. In situ microchemical analysis shows that the coatings consist predominantly of silica. Primary mineral grains in well‐developed coatings may also be replaced by silica. The internal fabric of the coatings suggests that accumulation of secondary silica and deposition of (reworked) ash are simultaneous processes and that all coatings were formed in various episodes. Precipitation of secondary silica from solution may occur where rapid weathering of primary minerals (volcanic ash) combined with high deposition of strong acids (HCl, H2SO4) from fumarolic and solfataric activity results in high dissolved Si concentrations. This process is further enhanced by evaporative concentration at the soil surface. Low pH precludes formation of secondary aluminium silicates and gibbsite. Erosion of the coatings seems to be largely due to episodically transported water.
Mineral and Organic Fractions of Two Oxisols and Their Influence on Effective Cation‐Exchange Capacity
Authors: Mendonça Eduardo S. , Rowell David L.
Published: July 2010

The mineral and organic fractions of a clayey Red Yellow Latosol (Typic Acrustox) and a sandy loam Dark Red Latosol (Typic Haplustox) sampled under the Cerrado Region of Brazil were characterized, and their influence on the effective cation‐exchange capacity was evaluated. Kaolinite and sesquioxides dominate the clay fraction of both soils, but the clayey soil is at a more advanced stage of weathering. It also holds a larger amount of organic matter and has more fulvic acid than humic acid throughout the profile. In the sandy soil, the reverse applies to the surface horizon, with equal amounts of humic and fulvic acids in lower horizons. More humic and fulvic acids were extracted from both soils by NaOH than by Na4P2O5, with CaHPO4 and water extracting similar small amounts of C. The total acidity, the carboxyl groups, and the phenolic‐OH groups were measured in humic and fulvic acids. The humic acid was about half as reactive as the fulvic acid in both soils. Fulvic acid is therefore the main source of charge in the clayey soil, but in the surface horizon of the sandy soil, humic acid contributes to more charge. The soils have low effective cation‐exchange capacity values, which decrease with depth and depend primarily on the content of organic matter, as shown by regression and multiple regression analysis.
Color Index for Identifying Hydric Conditions for Seasonally Saturated Mollisols in Minnesota
Authors: Thompson James A. , Bell James C.
Published: July 2010

The thick surface accumulations of organic matter in Mollisols confound the possibility of recognizing soil morphological features such as redoximorphic features that indicate seasonally saturated and reduced soils. The most obvious morphological change in the soil across Mollisol hydrosequences in Minnesota is the thickening and darkening of the A horizon(s). Our purpose is to quantify this trend across the landscape and examine its correlation with duration of saturated and/or reducing conditions for distinguishing between hydric and nonhydric Mollisols. We examined trends in soil morphology and soil organic C in conjunction with hydrologic monitoring data across three Mollisol hydrosequences. We defined a new color index that is a function of the thickness and color of the A horizon(s) of Mollisols of three hillslopes in Minnesota. Coefficients of correlation (r) between this index and duration of saturated and reducing conditions at various depths in these Mollisols are as high as 0.69. This index is also linearly related to organic C content of the A horizon(s) of a single hillslope with a coefficient of correlation of 0.98. This index may be useful for identifying and delineating hydric soils and may be employed to examine soil C storage at a landscape scale; however, specific relationships will vary considerably with soil parent material and climate.
Early Teaching in USA of Dokuchaiev Factors of Soil Formation
Authors: Simonson Roy W.
Published: July 2010

Teaching of the factors of soil formation first recognized by Dokuchaiev began in the USA in the late 1920s and early 1930s. Reports on their functions had been available in English prior to and early in the 20th century, but Americans were not receptive to the Russian idea of five factors, still holding that soil formation consisted of rock weathering. Following the First International Congress of Soil Science and related activities in 1927, however, the Dokuchaiev factors were soon introduced in pedology courses, first by J.C. Russell in Nebraska and next by Charles E. Kellogg in North Dakota. Basically the same for the two men, the presentation of the five factors illustrated here is from the course taught by Kellogg in 1932. The presentation was chiefly a combination of lectures and reading assignments but included limited field study. Slightly less than half of the lectures in a three‐hour course were about the factors of soil formation. Evident now, the lectures and reading assignments reflect the state of knowledge of their day, including both gaps and errors. At the same time, the coverage is impressive when considered against the limited study of soils in the world accomplished up to that time.
Copper Solubility in Myersville B Horizon Soil in the Presence of DTPA
Authors: Vulava Vijay M. , Torrents Alba , James Bruce R.
Published: July 2010

Organic ligands greatly affect the speciation and solubility of heavy metals in soils, depending on complex interactions of pH, ligand‐to‐metal ratio, and the order of application of metals and ligands to soils. To understand how these variables influence the fate of metals added to soil, we investigated the solubility of Cu(II) in Myersville B horizon soil (Ultic Hapludalf) in the presence of diethylenetriaminepentaacetic acid (DTPA), a strong complexing agent. Copper solubility was studied as a function of soil pH, individual and relative concentrations of Cu2+ and DTPA, and the order of application of these components to the soil. In the presence of DTPA (1.0 and 10 mmol kg−1 soil), Cu(II) solubility (0.1 and 1.0 mmol kg−1 soil) increased with an increase in pH (4 to 7). However, this occurred only when DTPA concentration ≥ Cu(II) concentration, implying that the relative concentrations of DTPA and Cu(II) were critical in controlling Cu(II) solubility. The order of application of Cu(II) and DTPA to the soil also strongly influenced Cu solubility. The three orders of application of these components were (i) application of premixed stock solutions of Cu(II) and DTPA in specified ratios and concentrations to the soil, (ii) equilibration of Cu(II) with the soil followed by application of DTPA, and (iii) equilibration of DTPA with soil followed by Cu(II) application. Of these three, the highest Cu solubility was observed in the third case when DTPA > Cu(II). This was attributed to surface coordination of DTPA, which prevents Cu from binding with soils. Also, an increase in background electrolyte concentration was accompanied by a decrease in the pH and, therefore, a change in Cu(II) solubility. These results have several implications in the field of contaminant and nutrient management in soils.
Assessment of Soil Quality in Conservation Reserve Program and Wheat‐Fallow Soils
Authors: Staben M. L. , Bezdicek D. F. , Fauci M. F. , Smith J. L.
Published: July 2010

Chemical and microbial aspects of soil quality are an important consideration when evaluating the benefits of soil conservation efforts such as the Conservation Reserve Program (CRP). The objective of this study was to evaluate the quality of CRP and wheat‐fallow (W‐F) soils using soil biological and chemical parameters and C and N mineralization processes. The study was conducted on 20 CRP/W‐F paired sites in eastern Washington, on Ritzville silt loam (coarse‐silty, mixed, mesic Calciorthidic Haploxerolls). Soils collected from the paired fields were analyzed for chemical and biological parameters that have been suggested as indicators of soil quality. Potential enzyme activities and soil N were higher in the CRP soil than the W‐F soil. Although there were no significant differences in total organic carbon (TOC) or microbial biomass carbon (MBC) the C mineralization potentials and C pools were significantly different between the CRP and W‐F soils. Soil biota measurements showed there was greater active bacterial biomass in the CRP soil but greater fungal‐feeding nematodes, flagellates, and amoebae in the W‐F soil. The C mineralization study suggests that there is a significant increase in the secondary C pool of the CRP soil, which may indicate a buildup of higher quality soil organic matter and the potential for higher enzyme levels. When grass or straw was added to each soil type, the W‐F soil produced more CO2 with either substrate than the CRP soil, indicating C limiting conditions in the W‐F soil. Since it is unknown what constitutes good soil quality, these shifts in chemical and biological parameters may seem subtle. However, in general, trends in the data indicated that soil quality in the CRP was improved after 4 to 7 yr, compared with its previous management in W‐F cropland.
Soil Zinc Map of the USA using Geostatistics and Geographic Information Systems
Authors: White J. G. , Welch R. M. , Norvell W. A.
Published: July 2010

The geographic distribution of soil Zn is important to agriculture, nutrition, and health. A map illustrating the total Zn content of soils of the conterminous USA was developed using geostatistics and geographic information systems. Data were combined from a U.S. Geological Survey study targeting nonagricultural soils in 47 states, and a U.S. Department of Agriculture‐U.S. Environmental Protection Agency‐U.S. Food and Drug Administration study targeting agricultural soils in 33 states. Semivariograms indicated spatial correlation at distances up to 470 km. A significant quadratic trend was modeled, but detrending had little effect on the semivariogram or on interpolation via kriging. The data exhibited some anisotropy, but it had little effect on kriging. An exponential semivariogram model was fit using least squares and used to krige a grid covering the conterminous USA. The resultant map depicted soils north of about 37°N latitude or west of about 109°W longitude as generally having more Zn than the average of 55 mg kg−1. Soils southeast of this boundary tended to contain less Zn than average, with exceptions of soils developed on Mississippi alluvium and in Piedmont valleys and ridges. High estimate standard deviations occurred where data were sparse. The map will be useful in future research to determine the geographic distribution of plant‐available soil Zn, regional patterns of plant, animal, and human Zn deficiencies, the relationship of Zn to soil parent material, genesis, and surficial geology, and in considering the consequences of land disposal of Zn‐laden wastes.
Factors Influencing Heavy Metal Distribution in Six Oklahoma Benchmark Soils
Authors: Lee B. D. , Carter B. J. , Basta N. T. , Weaver B.
Published: July 2010

Six contrasting benchmark Oklahoma soils underlain by sedimentary rock were selected and sampled by horizon to parent material or a 2‐m depth. Total Co, Cu, Ni, Pb, and Zn concentrations by horizon in total soil and clay fractions were determined by x‐ray fluorescence. Total concentration of heavy metals in these soils is dependent on clay content. There are fivefold more Cu, twofold more Zn and Ni, and 1.5‐fold more Co and Pb in the clay fraction than in the total soil. The clay fraction of surface horizons contains a greater concentration of Cu, Zn, and Co than subsoil horizons due to biogeochemical cycling of these micronutrients from the subsoil to the surface during melanization. Biogeochemical cycling reduces the total amount of heavy metal loss from surface to subsoil horizons by clay translocation but doesn't offset the illuviation of total heavy metals sorbed to clay. Higher levels of total heavy metals in each profile for each element are found in the B horizons than the A horizons (77% of the samples). Characterization of soil for total heavy metal content should include a sample from the B horizon especially in soil with higher clay content in the B than the A horizon. Soil parent material discontinuities cause changes in concentration of several heavy metals within two of the six soil profiles. Identification of soil parent material discontinuities is not a consistent factor causing change in heavy metal concentration within the soils studied.
Effectiveness of Organic Matter Incorporation in Reducing Soil Compactibility
Authors: Zhang Haiquan , Hartge K. H. , Ringe H.
Published: July 2010

Incorporation of organic matter (OM) into soil can reduce its susceptibility to compaction. However, the significance of incorporated OM for different soil and soil water conditions is not well documented. We investigated the effectiveness of incorporated OM at different soil and soil water conditions and the OM effect on strength and structure recovery of compacted soils. A sandy soil (sandy Orthod), a silt loam (loamy Udalf), and a clay soil (clayey Umbrept) were amended with up to 80 g kg−1 of highly and slightly humified peat. The peat‐soil mixtures were compacted at different water contents using the standard Proctor procedure. Soil strength was determined with a penetrometer. Structure recovery was determined by bulk density changes and disintegration of clods through wetting‐drying cycles. For the cohesive silt loam and clay soils, OM was most effective at reducing compactibility at water contents lower than those for maximum Proctor compaction. For the sandy soil, OM was most effective at the Proctor‐optimum water content. The slightly humified peat had a greater effect than the highly humified. We found that OM is most effective for soils with high compactibility. The maximum penetration resistance, Pmax, of the clay soil was reduced from 0.49 to 0.30 MPa, and that of the sandy soil increased from 0.64 to 1.08 MPa. For the silt loam, 30 g kg−1 peat content had the highest Pmax. After five wetting‐drying cycles, bulk densities showed no significant differences among treatments. Clod disintegration was hindered by the OM incorporation. Although soil compactibility was reduced by OM incorporation, OM was more effective as soil compactibilty increased and at water contents lower than or close to the Proctor‐optimum water content. Structure recovery of compacted soils was not improved. The penetration resistance after compaction is not consistently related to the incorporated OM.
Incorporating Spatial Trends and Anisotropy in Geostatistical Mapping of Soil Properties
Authors: Crawford Carol A. Gotway , Hergert Gary W.
Published: July 2010

The spatial variation in soil parameters often differs with direction. These differences may occur naturally or may be due to management practices. Regardless of their origin, they present a challenge in geostatistical mapping of soil parameters. Recommendations pertaining to the selection of an appropriate geostatistical method based on the current literature are often incomplete or contradictory. The purpose of this investigation was to provide a unified description, comparison, and discussion of different geostatistical methods for handling trend and anisotropy that may be present in measured soil properties. Soil organic matter content of the 0‐ to 20‐cm depth from a field in continuous ridge‐tilled corn (Zea mays L.) was used to compare five geostatistical methods: ordinary kriging with an isotropic semivariogram (OKI); ordinary kriging with an anisotropic semivariogram (OKA); ordinary kriging within local neighborhoods (OKN); universal kriging (UK); and median polish kriging (MPK). Organic matter maps produced from the five methods showed similar large‐scale features but marked differences in the finer features. A comparison of percentage of total area in each organic matter range among mapping methods also showed strong similarities; however, the proportion of the field assigned to each range differed by as much as 7%. Larger differences would be expected at large sample spacing. Although the five methods produced similar maps, selection of the “best” technique should be based on selection of an associated model that best accounts for and describes the nature of the cause of the variation.
Wetland Denitrification: Influence of Site Quality and Relationships with Wetland Delineation Protocols
Authors: Groffman Peter M. , Hanson Gay C.
Published: July 2010

Denitrification, the microbial conversion of NO3‐ to N gases, is important to wetland biogeochemistry and water quality maintenance functions. We measured denitrification along toposequences from forested upland‐wetland transition zones to red maple wetlands in Rhode Island. The sites were located on different soil parent materials derived from different geomorphic features including glacial outwash, granitic glacial till, basaltic glacial till, and alluvium. Each toposequence contained four or five different natural soil drainage classes. We assessed spatial and temporal variation in denitrification relative to site quality (parent material), water table dynamics, hydric soil and hydrophytic vegetation status, and a “growing season” defined as soil temperature >5°C. Denitrification rate was measured by intensive sampling during a 2‐yr period using an acetylene‐based intact soil core method. Annual estimates of denitrification were produced by extrapolating measured rates over the intervals between sample dates. Soils that were very poorly drained or that had developed on nutrient‐rich parent materials had higher denitrification than more well‐drained and/or less fertile soils. Nitrogen inputs from adjacent ecosystems also appeared to be a key regulator of denitrification rates. Annual denitrification ranged from 1 to >130 kg N ha−1 yr−1 and was lower in Year 2 than in Year 1 in all soils. There were poor relationships between spatial and temporal patterns of denitrification and patterns of hydric soils and hydrophytic vegetation within the wetlands. Wetland delineation and classification protocols based on soils, vegetation, or hydrology do not appear to encompass the capacity of a wetland to support denitrification.
A Two‐Stage Procedure for Determining Unsaturated Hydraulic Characteristics using a Syringe Pump and Outflow Observations
Authors: Wildenschild D. , Jensen K. Høgh , Hollenbeck K. J. , Sonnenborg T. , Butts M. B. , Illangasekare T. H. , Znidarcic D.
Published: July 2010

A fast two‐stage methodology for determining unsaturated flow characteristics is presented. The procedure builds on direct measurement of the retention characteristic using a syringe pump technique, combined with inverse estimation of the hydraulic conductivity characteristic based on one‐step outflow experiments. The direct measurements are obtained with a commercial syringe pump, which continuously withdraws fluid from a soil sample at a very low and accurate flow rate, thus providing the water content in the soil sample. The retention curve is then established by simultaneously monitoring the capillary pressure. The measured retention curves were compared with those obtained by static methods and found to agree closely. Subsequently, a transient outflow experiment is carried out on the same soil sample, in the same apparatus, and the information is obtained on a time‐scale of days. The one‐step outflow data and the independently measured retention data are included in the objective function of a traditional least‐squares minimization routine, providing unique estimates of the unsaturated hydraulic characteristics by means of numerical inversion of Richards equation. As opposed to what is often assumed in practical applications, we found it necessary to allow the exponent (γ) of van Genuchten's hydraulic conductivity expression to vary to obtain satisfactory estimates. Optimized hydraulic conductivity estimates were ultimately compared with directly measured values, and visual agreement was quite satisfactory. However, we encountered numerical instabilities of the optimization code used (SFIT), a flaw that may constitute a potential problem when using this code for the optimization.