bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal Transformations of Manganese in a Palustrine Emergent Wetland
Authors: La Force Matthew J. , Hansel Colleen M. , Fendorf Scott
Published: July 2010

Naturally occurring wetlands need to be investigated to assess their role in contaminant sequestration. Accordingly, aqueous‐ and solid‐phase analyses were conducted to monitor Mn response to changing physicochemical conditions within a Palustrine Emergent Wetland. A rhodochrosite‐like phase (MnCO3) was the dominant Mn bearing phase (by mass) within the solids throughout the year. Aqueous‐phase Mn concentrations were highly variable, but only two sampling sites in the interior of the wetland had pore‐waters supersaturated with respect to rhodochrosite. Despite that a rhodochrosite‐like material was the dominant quantity of Mn in the solids through the year, the reactivity of Mn solids, as measured by selective sequential extractions, did change seasonally. In spring, Mn was preferentially associated with the hydrofluoric acid‐extractable pool, comprising ∼35% of the total extractable Mn. The sodium acetate (SA)/acetic acid (AA) fraction appears elevated from spring through fall. Amorphous sulfide phases denoted by the difference between hydrochloric‐ and oxalic‐acid extractable Mn increased during the summer months and then decreased in early fall as the site dried. Furthermore, as the site dried, Mn associations with the MnCl2 (water soluble and exchangeable) extractable phase increased significantly (P < 0.05), comprising between 26 and 43% of the total extractable Mn. Manganese removed using hydroxylamine‐hydrochloride/AA (crystalline oxide) increased significantly (P < 0.05) in the summer to ∼40% of total extractable Mn. It is therefore apparent that seasonal changes in temperature and water level, with associated redox status, drive changes in surficial coatings of Mn phases and thus its reactivity.
Logistic Modeling to Spatially Predict the Probability of Soil Drainage Classes
Authors: Campling P. , Gobin A. , Feyen J.
Published: July 2010

Logistic models were developed to spatially predict the probability of drainage classes in a humid tropical area (58900 ha) using sampled terrain attributes from a digital elevation model, and vegetation indices from a LANDSAT‐5 Thematic Mapper image. Soil drainage classes were assigned on the basis of the local water table regime depth, determined by soil morphological indicators, to 295 pseudo‐randomly selected soil auger hole observations (calibration data set) and 72 soil pedon observations (validation data set). Six drainage classes were identified: excessively (D1), well (D2), moderately well (D3), imperfectly (D4), poorly (D5), and very poorly (D6). A nested dichotomous modeling strategy of progressively separating the six drainage classes was adopted, and resulted in five multivariate logistic models. The best performing model, predicting the probability of nonhydric (D1D2) soils versus hydric (D3D4D5D6) soils had a concordance of 99%, and the worst performing model, predicting the probability of imperfectly (D4) drained soils versus moderately well (D3) drained soils had a concordance of 65%. The most important spatial determinants were: elevation, slope, distance‐to‐the‐river channel (DC), and vegetation indices. The logistic models were combined in a geographic information system (GIS) to derive soil drainage class maps using the gridded data sets of the significant variables. The results showed that digital elevation models and vegetation indices from LANDSAT‐5 Thematic Mapper provide complementary information for developing statistical models to spatially predict and map soil drainage classes.
Denitrification Potential and Carbon Quality of Four Aquatic Plants in Wetland Microcosms
Authors: Hume Noah P. , Fleming Maia S. , Horne Alexander J.
Published: July 2010

The C quality of four aquatic plants found in wetlands explains the differences in their relative capacity to fuel denitrification. In replicated (n = 4) flow‐through microcosm experiments we compared nitrate removal using equal C additions of two emergent plants (Scirpus acutus, Typha latifolia) and two floating plants (Hydrocotyle umbellata, Lemna minor). As expected, plant litter with the highest initial C/N and lignin content (Scirpus acutus), required significantly (p < 0.05) higher dry matter addition to achieve the nitrate removals of the other plants studied. For all plants, losses in C content and significantly (p < 0.05) higher C/N ratios in leached litter is consistent with preferential hydrolysis of low molecular weight (MW) carbohydrates. Interestingly, plant‐specific differences in this denitrification potential were removed when nitrate removal data was compared on an acid‐soluble carbohydrate (ASC) basis. As an efficiency measure, high ratios of applied C to NO3–N decreased denitrification potentials, whereas increasing NO3–N loading at equal C additions increased denitrification potentials. Differences in denitrification potential resulting from carbohydrate and lignin content of the plants studied were generally smaller than relative differences in reported productivity. That much of the plant C left the microcosms before oxidation is consistent with overall electron acceptor limitation in wetlands and suggests observable differences in field‐scale denitrification performance may still arise with the presence or absence of highly productive reed (e.g., Scirpus sp., Typha sp.) stands.
Adapting a Drainage Model to Simulate Water Table Levels in Coastal Plain Soils
Authors: He X. , Vepraskas M. J. , Skaggs R. W. , Lindbo D. L.
Published: July 2010

Seasonal saturation in soils is expensive and time consuming to document, but the information is needed for land use assessments. Hydrologic models can be used to assess saturation occurrence quickly if the models are calibrated for individual sites. This study determined whether a drainage model (DRAINMOD) could predict water table levels in soils with and without a perimeter ditch. Water table levels were monitored for up to 3 yr at two toposequences that contained a total of 21 soil plots (3 m by 3 m). Soils included Typic Paleudults, Aquic Paleudults, and Umbric Paleaquults. Each plot was instrumented with a recording well to monitor daily water table levels. DRAINMOD was calibrated for each soil plot using measurements of in situ saturated hydraulic conductivity, soil water characteristic, depth to impermeable layer, depth of rooting, and rainfall. A plot's water table fluctuation was simulated by a system of virtual drains whose distance and depth were adjusted to produce simulated water table fluctuations in line with those actually measured. Further calibration adjusted drainable porosity in the upper 20 cm of the soil, depressional storage, evapotranspiration rate, and depth to impermeable layer. Adjustments were made by iteration to minimize the absolute average deviation between simulated and measured water table levels. Calibration had to be done by plot. Average absolute deviations were generally <20 cm for periods ranging from 1 to 3 yr. The results showed that DRAINMOD could be adapted to simulate water table levels in landscapes that do not contain a network of parallel drains.
Validity of First‐Order Approximations to Describe Parameter Uncertainty in Soil Hydrologic Models
Authors: Vrugt Jasper A. , Bouten Willem
Published: July 2010

Model nonlinearity and parameter interdependence violate the use of a first‐order approximation to obtain exact confidence intervals of parameters in soil hydrologic models. In this study, the posterior distribution of parameters in soil water retention and hydraulic conductivity functions is examined using observed water retention data and a laboratory transient multistep outflow experiment. Parameter uncertainties obtained with traditional first‐order approximations and uniform grid sampling strategies were compared with those obtained using the Metropolis algorithm, a Markov Chain Monte Carlo (MCMC) sampler. A diagnostic measure, based on multiple sequences generated in parallel, was used to test whether convergence of the Metropolis sampler to the posterior distribution had been achieved. Most significantly, as the Metropolis algorithm can cope with rough response surfaces generated by the objective function used, it not only successfully infers the multivariate posterior probability distribution of the model parameters, but also provides valuable insights in parameter interdependence in the full parameter space.
Content, Distribution, and Solubility of Cadmium in Arable and Forest Soils
Authors: Andersen Martin K. , Refsgaard Anne , Raulund-Rasmussen Karsten , Strobel Bjarne W. , Hansen Hans C. B.
Published: July 2010

Afforestation of former farmland decreases soil pH and thus increases the solubility of Cd in the soil, which may cause Cd leaching to streams and groundwater. The Cd concentration in soil and soil solution were determined in 11 pairs of Danish arable and forest soil profiles representing three different texture classes (sand, loamy sand, and sandy loam). The soil pH did not change or decrease with depth through the arable profiles, but did increase with depth in the forest profiles. Significantly higher Cd contents were found in the upper 30 cm of the arable soil compared with that of the forest soil. The total soil Cd concentrations correlated with the effective cation‐exchange capacity (ECEC), clay content, and organic matter content, but not the soil pH. The soil solution pH was unchanged or decreasing downwards through the arable profiles, but increasing with depth in the forest profiles. The soil solution concentration of Cd was significantly higher in the forest soils than in the arable soils. The Cd concentration in the soil solution decreased as pH increased. Both total soil and soil solution Cd concentrations were higher in the sandy loam soils compared with the loamy sand and sand soils. It is concluded that afforestation may lead to higher soil solution concentrations of Cd as decreasing pH and ECEC diminish Cd retention and reduces Cd concentrations in the forest topsoils.
Relationship Between Plant Phenolic Acids Released during Soil Mineralization and Aggregate Stabilization
Authors: Martens Dean A.
Published: July 2010

Phenolic acids (PAs) from plant and microbial sources have been implicated as important components in a variety of soil processes, but little information is available on the decomposition rates of plant‐derived PAs, synthesis of soil microbial PAs, incorporation of PAs into humic substances and stabilization of soil aggregate fractions. To obtain this information, a Webster soil (fine‐loamy, mixed, superactive, mesic Typic Endoaquoll) was amended with seven plant residues (2% w/w) and incubated at 22 ± 2°C. Duplicate samples were extracted after incubation for 9, 29, and 84 d and analyzed for PA composition. The plant residues contained large amounts of ferulic [3‐(4‐hydroxy‐3‐methoxyphenyl)‐2‐propenoic acid] and coumaric acids [3‐(4‐hydroxyphenyl)‐2‐propenoic acid] (both C6–C3, phenylpropyl type), which decomposed according to pseudo first‐order kinetics. Most of the remaining PAs showed little change in concentration after 9 d and only microbial synthesis of 4‐hydroxybenzoic acid was noted during the study. Analysis of six purified soil microbial polymers isolated from pure culture confirmed that the tested microbial extracellular polymers contained benzoic and benzaldehyde PAs (C6–C1, phenylmethyl type). Evaluation of humic acids isolated from different residue‐amended soil showed the majority of humic‐PAs were C6–C3PAs of plant origin. Increased mean weight diameter of soil aggregates was closely related to the increase in soil PA concentration and organic C content in the amended soil during incubation. The results suggest that plant PAs are extremely important in the soil C cycle, soil aggregation and in the formation of stable C, and measurement of soil ester‐linked PA composition can provide an index of plant‐derived C in soil.
Short‐Term Effects of Land Leveling on Soil Physical Properties and Microbial Biomass
Authors: Brye K. R. , Slaton N. A. , Savin M. C. , Norman R. J. , Miller D. M.
Published: July 2010

Land leveling is a practice that facilitates more uniform delivery of irrigation water. However, the spatial variability and distributions of soil physical and biological properties, and the relationships between them, are not well characterized in agroecosystems that have been land leveled. The objectives of this study were to characterize the short‐term impacts of land leveling on the magnitudes, spatial variability, and spatial distributions of soil physical and biological properties, and to evaluate the relationships between these properties in a Stuttgart silt loam (fine, smectitic, thermic Albaqultic Hapludalf) used for irrigated soybean [Glycine max (L.) Merr.] and rice (Oryza sativa L.) production in eastern Arkansas. Bulk density and sand and clay contents significantly increased, while silt content and fungal and bacterial biomass significantly decreased, as a result of land leveling. Land leveling did not change the fungal/bacterial biomass ratio indicating that, despite the effect leveling had on the relative abundance of the fungal and bacterial biomass, the relative proportion of fungal/bacterial biomass, hence the structure of the soil microbial community, remained unaffected as indicated by soil‐sample staining methods. Land leveling significantly changed the variance associated with soil biological properties, but the variances of soil physical properties were unaffected. The relationships between soil physical and biological properties also changed significantly as a result of land leveling, but the ability to predict soil biological properties from soil physical properties was surprisingly poor. These results indicate that variability in soil biological properties may play an important role in restoring productivity to precision‐leveled soils.
Assessing Soil Genesis by Rare‐Earth Elemental Analysis
Authors: Aide Michael , Smith-Aide Christine
Published: July 2010

The soils of the St. Francois Mountains in Missouri are developed in loess and rhyolite residuum. Loess contributions may be expected to modify the texture, clay mineralogy, and nutrient availabilities, awarding characteristics significantly different from soils developed entirely in rhyolite residuum. The objective of this investigation is to assess the validity of using the rare‐earth elements (REEs) as a geochemical indicator to discriminate between two contrasting parent materials. Elemental analysis of the whole soil, the rhyolite residuum, and a representative loess deposit were analyzed by instrumental neutron activation analysis (INAA) and X‐ray fluorescence (XRF). Whole soil Ti contents are consistent with the local loess and incompatible with rhyolite residuum as the only parent material. The REE signatures of the whole soil are consistent with a mixture of local loess and rhyolite residuum. The clay fractions show a preferential REE accumulation, suggesting the REE may co‐illuviate with clay across soil profile boundaries. Neodymium, and to a smaller extent Eu, show dramatic associations with illuviated clay, altering the REE signatures and their interpretation. However, interhorizon transfers of the REE because of lessivage are not sufficient to render the use of the REE signatures ineffective for recognizing loess as a parent material. The migration potential of the REE must be further investigated before the method may be accepted as a diagnostic tool for recognizing lithologic discontinuities, especially for extremely weathered soils.
Taxonomic Structure, Distribution, and Abundance of the Soils in the USA
Authors: Guo Yinyan , Amundson Ronald , Gong Peng , Ahrens Robert
Published: July 2010

In this paper, we report the taxonomic structure, the spatial distribution, and relative abundance of soils in the USA. In the analysis, we used the STATSGO (1997 version) database, which contains information on 11 orders, 52 suborders, 232 great groups, 1175 subgroups, 6226 families, and 13 129 series. The analysis of taxonomic structure showed that the numbers of taxa in any category were distributed unevenly in relation to taxa present at the next higher category. This uneven distribution becomes more pronounced in the lower categories of the hierarchy. In addition, there is a trend for taxa to produce only one, or a very small number, of taxa in the next lower category at the lower categories of the system. The analysis of the spatial distribution of taxa showed that 10 662 (51.2%) out of 20 825 taxa exist only 1 Major Land Resource Area (MLRA), indicating that most soil taxa are not widely spread, and are specific to particular combinations of state factors. The area abundance of soil taxa is asymmetric with most taxa in a category having relative small area extent. Five (2.1%) great‐groups, 37 (2.1%) subgroups, 417 (6.7) families, and 827 (6.3%) series had total areas less than 10 km2, and were defined as rare taxa. Among the rare taxa, four (80%) rare great groups, 36 (97.3%) rare subgroups, 378 (90.6%) rare families, and 750 (90.7%) rare series were found in only 1 MLRA. The portion of rare soils might be much higher because not all the soils are included in STATSGO because of their too limited area. The spatial and area abundance analyses of the soils provides a perspective useful for discussions on the preservation of soil resources in the USA, a topic whose importance is likely to grow in conjunction with increasing interest in global biodiversity and more intense uses of the world's soil resources.
Tillage Effects on Nitrate Leaching Measured by Pan and Wick Lysimeters
Authors: Zhu Y. , Fox R. H. , Toth J. D.
Published: July 2010

No‐till (NT) is a recommended best management practice for reducing erosion in agricultural production. Because of potential increases in infiltration with NT, a better understanding of tillage effects on NO−3–N leaching is required. An experiment was conducted in central Pennsylvania on a Hagerstown silt loam (fine, mixed, semiactive, mesic Typic Hapludalf) to study NO−3–N leaching under chisel‐till and NT and to compare results from zero‐tension pan and passive capillary fiberglass wick lysimeters from May 1995 to April 2001. Pan lysimeters collected greater leachate volumes from NT than from tilled treatments during the growing season, likely due to greater macropore flow in NT soil. When leachate collection efficiency corrected values were used, pan and wick lysimeters collected equivalent masses of NO−3–N. Flow weighted NO−3–N concentrations in leachate in both lysimeter types were also similar. Tillage had no effect on total leachate collected during the 6‐yr experiment by either pan (228 mm yr−1) or wick (558 mm yr−1) lysimeters. Flow‐weighted NO−3–N concentrations and NO−3–N masses in leachate were not significantly different between tilled and NT, but increased with increasing N‐rate (at 0, 100, and 200 kg N ha−1, flow‐weighted NO−3–N concentrations were 3.5, 8.2, and 23.9 mg L−1 and NO−3–N masses were 17, 39, and 112 kg ha−1 yr−1, respectively). The results demonstrate that under our condition NT will not result in more NO−3 leaching than chisel‐tillage over a multiyear period.
Synthesis, Characterization, and Agronomic Evaluation of Iron Phosphate Impurities in Superphosphates
Authors: Prochnow L. I. , Chien S. H. , Dillard E. F. , Austin E. R. , Carmona G. , Henao J. , Singh U. , Taylor R. W.
Published: July 2010

Two of the most common impurities found in superphosphates (single superphosphate [SSP] and triple superphosphate [TSP]) in the forms of Fe3KH8(PO4)6·6H2O and Fe3KH14(PO4)8·4H2O were synthesized (H8‐syn and H14‐syn, respectively), characterized, and agronomically evaluated to investigate cost‐effective means to optimize the utilization of phosphate rocks (PRs) containing Fe impurities. A solubility study showed that more P was released from both compounds as pH increased in the 0.01 M KCl solutions (pH 3.0–7.5) and more P was released from H14‐syn than H8‐syn. The two Fe‐K‐P compounds were mixed and compacted with monocalcium phosphate (MCP) at 0, 25, 50, 75, and 100% of total P as MCP. In a greenhouse study, rates of P were applied at 0, 10, 20, 40 and 80 mg P kg−1 from H8‐syn, H14‐syn, and MCP, while the compacted mixtures were applied only at 40 mg P kg−1 to an Ultisol (thermic Rhodic Kanhapludults, pH 5.3) cropped with upland and flooded rice (Oryza sativa L.) for 65 d. The results showed that P uptake and dry‐matter yield were greater with H14‐syn than H8‐syn for both crops and both compounds were more effective for flooded rice than upland rice. The calculated values of relative agronomic effectiveness (RAE) of H8‐syn and H14‐syn with respect to MCP were 32 and 72% in dry‐matter yield for upland rice and 55 and 102% for flooded rice, respectively. To reach 90% of maximum dry‐matter yield obtained with MCP, it required approximately 43 and 35% of total P as water‐soluble P (WSP) in the mixtures of H8‐syn and H14‐syn with MCP for upland rice and only 17 and 11% for flooded rice, respectively.
Carbon Sequestration in Clay Mineral Fractions from 14C‐Labeled Plant Residues
Authors: Gonzalez Javier M. , Laird David A.
Published: July 2010

An understanding of organic C dynamics in soils is necessary to develop management options to enhance soil organic C sequestration. The objective of this research was to study the distribution of newly formed humic materials into mineralogically distinct clay‐size fractions of a silt loam soil. Oats (Avena sativa L. cv. Ogle), grown under simulated no‐tillage conditions, were pulse labeled with 14CO2 After senescence, the labeled surface residue was removed and replaced with unlabeled residue and the labeled roots were allowed to decompose in the soil for 360 d. The soil clay fraction (<2 μm) was separated into coarse, medium, and fine clay size‐fractions (0.2–2.0, 0.02–0.2, and <0.02 μm, respectively) by centrifugation. X‐ray diffraction indicated that quartz, illite, and kaolinite were the dominant mineral phases in the coarse clay fraction while smectite was the dominant mineral phase in the fine clay fraction. The organic C content in the coarse and fine clay fractions (3.70 and 3.93%, respectively) was similar. Scintillation analysis indicated an increase in 14C specific activity in all fractions after 360 d of incubation. For both sampling times, 0 and 360 d, the highest 14C specific activity occurred in the fine clay fraction (847.2 and 1529 Bq g−1 C, respectively), whereas the lowest 14C specific activity occurred in the coarse clay fraction (565.8 and 770.9 Bq g−1 C, respectively). The results suggest that new humic materials are preferentially forming or accumulating on smectite surfaces.
Anionic Polysaccharide Sorption by Clay Minerals
Authors: Dontsova Katerina M. , Bigham Jerry M.
Published: July 2010

An influence of clay mineral composition on C turnover in surface soils is widely assumed but poorly documented. The objective of this study was to evaluate the effect of various clay minerals on polysaccharide sorption under different environmental conditions, including pH, ionic strength, and cation type. Xanthan, an anionic polysaccharide produced by Xanthomonas campestris, was used to represent soil microbial exopolysaccharides. Highly significant effects (P > F < 0.0001) were observed for type of clay mineral, pH, xanthan concentration, and electrolyte concentration. Sorption decreased with increase in pH from 3 to 8, consistent with an increase in the negative charge of both the clay surface and xanthan molecules. The presence of 10 mmol L−1 Ca(NO3)2 made sorption possible at pH values above the pKa of xanthan. Divalent cations (Sr2+, Ca2+, and Mg2+) enhanced sorption to a greater degree than monovalent cations (K+, Na+, and Li+) at the same ionic strength, indicating that cations participated in the binding of xanthan to clay surfaces. Generally, sorption was smallest with kaolinite and greatest with a low‐charge (0.62 e layer charge per unit cell) smectite where layer charge originated mostly in the tetrahedral positions. Average sorption was two times greater for smectite than for kaolinite, indicating that clay mineral composition influenced polysaccharide sorption; however, contributions may not be significant on a field scale.
Microbial Properties of Mine Spoil Materials in the Initial Stages of Soil Development
Authors: Machulla Galina , Bruns Mary Ann , Scow Kate M.
Published: July 2010

The early years of soil genesis during mine spoil reclamation are critical for vegetative establishment and may help predict reclamation success. Mine spoils in the Halle‐Leipzig region of Germany were analyzed for microbial changes following a hay mulch‐seeding treatment without topsoil or fertilizer application. Microbial biomass carbon (Cmic) and dehydrogenase activity (DHA) of spoils were measured each year in the first 3 yr after treatment. In the third year, bacterial community DNA fingerprints were compared with those from a reference soil. Microbial indicators were measured at three depths in the upper 10 cm of spoils at three sites with contrasting parent materials: glacial till (sandy loam), limnic tertiary sediments (high‐lignite sandy clay loam), and quaternary sand and gravel (loamy sand). Before reclamation, Cmic means and standard deviations of surface spoils (0–1 cm) were 9 ± 6, 39 ± 11, and 38 ± 16 mg kg−1 for the loamy sand, high‐lignite sandy clay loam, and sandy loam spoils, respectively. Within one year, mean Cmic at the surface increased to 148 ± 70, 229 ± 64, and 497 ± 167 mg kg−1, respectively, and was significantly higher at 0 to 1 cm than at lower depths. Highest DHA and DNA yields were obtained in the 0‐ to 1‐cm depth of the sandy loam spoils. Microbial biomass C values exhibited significant correlations with DHA, DNA yield, and extractable C for all three mine spoils. Soil microbial indices were more responsive than plant measurements to differences in parent materials.
Tillage and Nitrogen Fertilizer Influence on Carbon and Soluble Silica Relations in a Pacific Northwest Mollisol
Authors: Gollany H. T. , Allmaras R. R. , Copeland S. M. , Albrecht S. L. , Douglas C. L.
Published: July 2010

Long‐term experiments are ideal for evaluating the influence of agricultural practices on soil organic carbon (SOC) accretion. Little is known about the influence of tillage and N fertilization on SOC distribution and silica (Si) movement in a soil. This study: (i) determined the effect of tillage and N fertilizer on SOC accretion in a Walla Walla silt loam (coarse‐silty, mixed, superactive, mesic Typic Haploxeroll), and (ii) examined the subsequent influence of fine organic matter (FOM) on Si movement. A long‐term wheat (Triticum aestivum L.)–fallow experiment was established in 1940, in a randomized block with split‐plot design. Soil cores (2‐cm increments) from two tillages (moldboard plow, MP; and sweep, SW) and two N rates (45 and 180 kg N ha−1) were used to measure coarse organic matter (COM), FOM, pH, bulk density (ρb), water‐soluble C (Cws), and water‐soluble Si (Siws). The FOM fraction (6.6 kg C m−2) in SW was 14% higher (5.8 kg C m−2) than in MP for the 180 kg N ha−1 rate. After 44 yr of N additions, the SOC storage (6.2 kg C m−2) for the 180 kg N ha−1 rate increased 3% above that for the 45 kg N ha−1 (6.0 kg C m−2). Total Siws in the B horizon were 34 and 39% greater than in the Ap horizon for the MP and SW systems, respectively. Interaction of tillage and N with Siws suggests that SOC provides a mechanism to suppress Si solubility, which impacts siliceous pan formation, reduces soil mechanical resistance, and enhances drainage and plant growth.
Gibbsite and Goethite Solubility
Authors: Essington Michael E. , Nelson Julia B. , Holden William L.
Published: July 2010

2‐Ketogluconate (kG) is a microbial byproduct that has been isolated from the rhizosphere of several plants and has been found to accumulate around bacteria adhering to rock surfaces. It has long been suspected that kG may play a role in enhancing the bioavailability of soil nutrients. However, quantitative information relevant to its behavior in soils, its reactions with mineral surfaces, and its aqueous complexation of metal cations is unavailable. The objectives of this research were to examine the influence of kG on gibbsite and goethite solubility and to describe these effects by considering the aqueous complexation of Al3+ and Fe3+ by kG. Secondary to this was to compare the impact of kG on mineral solubility to that of citrate. The equilibrium solubility of gibbsite and goethite was examined at ambient (20–22°C) or controlled (25°C) temperatures as a function of pH, ionic strength, and kG or citrate concentration. Both ligands were observed to significantly enhance mineral solubility (as determined by the total soluble concentrations of Al and Fe), with kG and citrate having similar impacts on gibbsite solubility, but with kG having a lesser impact than citrate on goethite solubility. The solubility data were employed to characterize the aqueous complexation chemistry of Al– and Fe(III)–kG and citrate. In the 4 < pH < 8.5 range, the mononuclear species AlkG2+(aq), Al(OH)2kG0(aq), and Al(OH)3kG−(aq) describe Al–kG speciation, with the latter two species mechanistically described by the bidentate complexation of AlOH2+(aq) and Al(OH)+2aq [also written as AlOH(H−1kG)0(aq) and Al(OH)2(H−1kG)−(aq)]. Iron(III)–kG complexation is described by the FekG2+(aq) and Fe(OH)3 kG22−aq or FeOHH−1kG22−aq species. For the citrate systems, the chemical models required to describe metal speciation differed from those reported in the literature: Alcit0(aq), Al(OH)2cit2−(aq), and Al(OH)3 cit3−(aq) for Al–citrate speciation and Fecit0(aq), Fe(OH)2 cit2−(aq), and Fe(OH)3cit3−(aq) for Fe(III)–citrate.
Soil Carbon Storage Estimation in a Forested Watershed using Quantitative Soil‐Landscape Modeling
Authors: Thompson James A. , Kolka Randall K.
Published: July 2010

Carbon storage in soils is important to forest ecosystems. Moreover, forest soils may serve as important C sinks for ameliorating excess atmospheric CO2 Spatial estimates of soil organic C (SOC) storage have traditionally relied upon soil survey maps and laboratory characterization data. This approach does not account for inherent variability within map units, and often relies on incomplete, unrepresentative, or biased data. Our objective was to develop soil‐landscape models that quantify relationships between SOC and topographic variables derived from digital elevation models. Within a 1500‐ha watershed in eastern Kentucky, the amount of SOC stored in the soil to a depth of 0.3 m was estimated using triplicate cores at each node of a 380‐m grid. We stratified the data into four aspect classes and used robust linear regression to generate empirical models. Despite low coefficients of correlation between measured SOC and individual terrain attributes, we developed and validated models that explain up to 71% of SOC variability using three to five terrain attributes. Mean SOC content in the upper 30 cm, as predicted from our models, is 5.3 kg m−2, compared with an estimate of 2.9 kg m−2 from soil survey data. Total SOC storage in the upper 30 cm within the entire watershed is 82.0 Gg, compared with an estimate of 44.8 Gg from soil survey data. A soil‐landscape modeling approach may prove useful for future SOC spatial modeling because it incorporates the continuous variability of SOC across landscapes and may be transportable to similar landscapes.
Fractal Analysis of Soil Water Desorption Data Collected on Disturbed Samples with Water Activity Meters
Authors: Perfect E. , Kenst A. B. , Díaz-Zorita M. , Grove J. H.
Published: July 2010

We combined water activity meters and fractal modeling to facilitate rapid, physically based characterization of the soil water retention curve. Desorption data (6 points per sample) were collected in the tension (h) range 2.0 × 102to 1.5 × 105kPa using the gravimetric method to measure water content (w) and water activity meters to measurehThirty‐two disturbed samples from a long‐term nitrogen fertilization and tillage comparison study on a silt loam soil were analyzed. A new form of an established fractal equation was derived:w=ahD−3−ρw/ρs, whereais a compound parameter including the bulk density (ρb) and air entry tension (ha),Dis the mass fractal dimension, ρwis the density of water, and ρsis the particle density. This model was fitted to the measured water retention curves by nonlinear regression analysis. TheaandDparameters were estimated, while ρwand ρswere fixed at 1.00 and 2.65 Mg m−3, respectively. Convergence was always achieved and the equation fitted the data extremely well; residual sums of squares ranged from 1.2 × 10−6to 6.7 × 10−5, with a median value of 2.2 × 10−5Estimates ofa(0.62–0.74) andD(2.948–2.963) were physically reasonable, and sensitive to soil management practices. Theaparameter increased,r= 0.80 (P< 0.01), (signifying decreasing ρband/orha) whereasDdecreased,r= −0.75 (P< 0.01), (signifying more rapid capillary drainage) with increasing soil carbon content. Additional research is needed to test this approach on other soil types, and to assess the influence of soil disturbance and variations in ρson the model's performance.
On the Construction and Calibration of Dual‐Probe Heat Capacity Sensors
Authors: Ham J. M. , Benson E. J.
Published: July 2010

Dual‐probe heat‐capacity (DPHC) sensors can be used to measure soil heat capacity (C), water content, and temperature. Research was conducted to test design factors that affect sensor calibration, including: (i) calibration media, (ii) diameter and length of the needle probes, (iii) sensor body material, and (vi) duration and total power of the applied heat pulse. All sensors were calibrated in media with known C, including: agar (water), water‐saturated glass beads, and dry glass beads. Calibration consisted of collecting heat pulse data in a given media and then calculating the apparent probe spacing (rapp, distance between heater and detector needles) that yielded correct value of C An ideal sensor would have the same rapp regardless of media type. The rapp for all sensor designs increased as C decreased, on average changing by 6.7% between agar and dry beads. This undesirable result was consistent with previous studies that showed DPHC sensors calibrated in agar overestimated C in drier soils. Needle diameter (1.27 vs. 1.65 mm), sensor body material (urethane vs. high‐conductivity epoxy), and shortening of the detector probe had a small effect on rapp Sensors made with urethane bodies, 1.27‐mm diam. needle probes, and shortened temperature probes showed less sensitivity to calibration media and are therefore recommended. The rapp for this design only increased by 2.6% between dry and water‐saturated wet beads. Apparent probe spacing was not affected by changes in total applied power (400–1600 J m−1) or heat pulse duration (2–16 s) when the correct analytical model was used to compute C
Kinetics of Selenite Adsorption on Hydroxyaluminum‐ and Hydroxyaluminosilicate‐Montmorillonite Complexes
Authors: Saha U. K. , Liu C. , Kozak L. M. , Huang P. M.
Published: July 2010

A lack of understanding about the selenite adsorption behavior on hydroxyaluminum (HyA)‐ and hydroxyaluminosilicate (HAS)‐interlayered phyllosilicates led us to conduct the present study. The kinetics of selenite adsorption on montmorillonite (Mt), HyA(OH/Al = 2.0)‐Mt, HAS1(OH/Al = 2.0; Si/Al = 0.24)‐Mt, and HAS2(OH/Al = 2.0; Si/Al = 0.48)‐Mt were studied at pH 4.5, with an initial selenite concentration of 0.025 mM, a clay concentration of 0.5 g L−1, temperatures of 288, 298, 308, and 318 K, and background electrolyte concentration of 10−2 M NaNO3 Of the six different kinetic models tested, the second‐order rate equation best described the kinetic data obtained for the initial fast reaction (5–30 min) followed by a slow reaction (30–180 min) in the adsorption systems. Elevated temperatures brought about a substantial increase in the rate constants. Compared with Mt, different HyA/HAS‐Mts had 2 to 21 times higher rate constants for the fast reaction and up to five times higher rate constants for the slow reaction. Silication of HyA‐Mt to form HAS1‐Mt and HAS2‐Mt substantially lowered the rate constants for both the fast and slow reactions. For the fast reaction, Mt had the highest activation energy and HyA‐Mt had the lowest activation energy (around four times lower than Mt); silication increased the activation energy of selenite adsorption on the HAS‐Mts. The pre‐exponential factor, an index of the frequency of selenite collision with the clay surface, was remarkably lower for the HyA/HAS‐Mts in comparison with Mt. The data obtained in the present study are of fundamental significance in understanding the role of Al interlayering and coating and silication of Al polymers on expansible phyllosilicates in influencing the dynamics of Se in soil and related environments.
Soil Lime Requirement By Direct Titration with Calcium Hydroxide
Authors: Liu Min , Kissel D. E. , Vendrell P. F. , Cabrera M. L.
Published: July 2010

A simple method for titrating acidic soils could be used by soil testing laboratories as an alternative method for routinely determining the lime requirement (LR) of soils. Because soil pH as a function of added base is linear in the pH range of 4.5 to 6.5, it may be possible to determine the slope of this relationship by regression analysis using a minimum number of base additions. The LR could then be determined by calculating the corresponding amount of lime required to reach the target pH using the regression equation. Our objectives were to determine reaction times needed for saturated Ca(OH)2 solution to reach an equilibrium pH with 17 widely different soils, and then test a simple titration procedure for its ability to predict the LR, determined first by a full titration curve and then by a standard incubation method. All titrations were performed in a 1:1 soil/water ratio with calcium hydroxide as the base. Using the regression procedure to estimate LR, equilibration times of 30 min between base additions gave greater LRs than 15‐min equilibration, but the same as 45‐min equilibration. When all 17 soils were considered, the LR from extrapolation of the linear regression yielded the same, as did the full titration curve (TC). The LR from titration with three base additions and 30‐min equilibration time between additions estimated an average of 80% of the LR determined by the 3‐d incubation. The Adams‐Evans (AE) buffer procedure overestimated and underestimated the LR for soils with relatively low‐ and high‐LRs, respectively. Based on these results, titration appears promising for routine use, but it needs more research to determine whether it can be simplified further.
Preferential Accumulation of Microbial Carbon in Aggregate Structures of No‐Tillage Soils
Authors: Simpson Rodney T. , Frey Serita D. , Six Johan , Thiet Rachel K.
Published: July 2010

We examined the effect of reduced tillage on the accumulation of fungal‐ versus bacterial‐derived organic matter within the soil matrix by quantifying the amino sugars glucosamine (Glc), galactosamine (Gal), and muramic acid (MurA) in aggregate‐size fractions isolated from no‐tillage (NT) and conventional‐tillage (CT) soil. Intact soil cores (0‐ to 5‐ and 5‐ to 20‐cm depth) were collected from the long‐term tillage experiment at Horseshoe Bend in Athens, GA. Four water‐stable aggregate‐size fractions were isolated: large macroaggregates (>2000 μm), small macroaggregates (250–2000 μm), microaggregates (53–250 μm), and the silt + clay fraction (<53 μm). Small macroaggregates were further separated into coarse particulate organic matter (POM) (>250 μm), microaggregates contained within macroaggregates, and the silt + clay fraction. Amino sugars were extracted from all fractions, purified, and analyzed by gas chromatography. Fungal‐derived amino sugar C (FAS‐C) comprised 63%, while bacterial‐derived amino sugar C (BAS‐C) accounted for 37% of the total amino sugar C pool under both tillage treatments. No‐tillage soil contained 21% more amino sugar C than the CT soil across the entire plow layer. Both, the percentage of total organic C as FAS‐C and BAS‐C were significantly higher in the silt + clay fraction of NT versus CT soil. The percentage of total organic C as FAS‐C was significantly higher in small macroaggregates of NT versus CT soil due to a preferential accumulation of FAS‐C in the microaggregates contained within these macroaggregates. These results indicate that microbial‐derived C is stabilized in NT soils, due primarily to a greater fungal‐mediated improvement of soil structural stability and concurrent deposition of fungal‐derived C in microaggregates contained within macroaggregates.
Long‐Term Corn Residue Effects
Authors: Wilts A. R. , Reicosky D. C. , Allmaras R. R. , Clapp C. E.
Published: July 2010

A better understanding of C turnover, with estimates of root‐derived C, is needed to manage soil C sequestration. The objective was to evaluate the long‐term treatment and environmental effects on unharvestable soil C components. Two N fertilizer treatments and a control were imposed during 29 yr of continuous corn (Zea mays L.) with stover removal as silage vs. stover return during grain harvest with moldboard plow (MB) tillage. Soil organic carbon (SOC) declined and natural 13C abundance (δ13C) increased during the 29‐yr period. Field averages of SOC and δ13C (0–30 cm) were 96.4 Mg ha−1 and −17.3‰ in 1965; respective values in 1995 were 78.9 Mg ha−1 and −16.6‰. Loss of SOC was greater with stover removed or no fertilization, but δ13C increased for all treatments. Stover yield (SY), SOC, and δ13C data were applied to a model to estimate unharvestable C and predict total source C (SC) input from corn. The SC for 29 yr totaled 172 to 189 Mg ha−1 when stover was harvested and 268 to 284 Mg ha−1 when stover was returned. The SC input from unharvestable sources was 1.8 times more than SC from aboveground stover when N was added and 1.7 when N was not added. The root‐to‐shoot ratio was 1.1 when N was added and 1.2 with no N. Only 5.3% of the SC was retained as SOC. Unharvestable C contributions to rhizodeposition are much larger than suggested from controlled studies including C‐enriched CO2 followed by soil respiration or CO2 efflux measurements.
Physical and Hydrological Characteristics of Reclaimed Minesoils in Southeastern Ohio
Authors: Shukla M. K. , Lal R. , Underwood J. , Ebinger M.
Published: July 2010

Reclamation of disturbed soils is done with the primary objective of restoring the land. Therefore, measurement of physical and chemical properties of reclaimed minesoils (RMS) is essential for understanding the process of soil restoration. This study was designed to assess soil quality of two reclaimed sites and two nearby undisturbed sites in Jackson and Vinton counties, Ohio. Three different rates of fertilizers applied annually to the RMS at Jackson and Vinton County sites from 1979–1994 were: no fertilizer (FL1), 112‐25‐46 kg NPK ha−1(FL2), and 224‐50‐92 kg NPK ha−1(FL3). Bulk and core samples were obtained for only 0‐ to 10‐cm depth for undisturbed (unmined) soil (UMS) and for 0 to 10 and 10 to 20 cm for RMS. A comparison within UMS and RMS showed that water‐stable aggregation and mean weight diameter of aggregates (MWDs) were significantly higher for UMS than RMS for both sites (P< 0.05). Apart from soil bulk density (ρb) for Vinton, no significant differences were observed in ρb, electrical conductivity (EC), pH, saturated hydraulic conductivity and water infiltration for the 0‐ to 10‐cm depth among fertility treatments in RMS and UMS for both Jackson and Vinton County sites. Average soil organic C (SOC) 5 yr after reclamation in 1981 was 14.2 Mg ha−1for Jackson and 15.1 Mg ha−1for Vinton site for the 0‐ to 10‐cm depth. In 2001, average SOC was 28.7 Mg ha−1for Jackson and 30.24 Mg ha−1for Vinton site. A two‐fold increase in SOC was obtained at both sites between 1981 and 2001. Soil pH was >6.4 and was favorable for root development and biomass production at both reclaimed sites. No significant differences in several soil properties between UMS and RMS showed that fertility treatments improved the soil quality of RMS.
Soil Hydraulic Properties Influenced by Stiff‐Stemmed Grass Hedge Systems
Authors: Rachman Achmad , Anderson S. H. , Gantzer C. J. , Alberts E. E.
Published: July 2010

The effectiveness of stiff‐stemmed grass hedge systems in controlling runoff and soil erosion is influenced by the water transport properties of the soil under grass hedge management. This study evaluated soil hydraulic properties within a grass hedge system 10 yr after establishment. The study was conducted at the USDA‐ARS research station near Treynor, IA in a field managed with switchgrass (Panicum virgatum) hedges. The soil was classified as Monona silt loam (fine‐silty, mixed, superactive, mesic Typic Hapludolls). Three positions were sampled: within the grass hedges, within the deposition zone 0.5 m upslope from the grass hedges, and within the row crop area 7 m upslope from the hedges. Intact soil samples (76 by 76 mm) were taken from the three positions at four depths (100‐mm increments) to determine saturated soil hydraulic conductivity (Ksat), bulk density (ρb), and soil water retention. The grass hedge position had significantly greater (P < 0.05) macroporosity than the row crop and deposition positions in the first two depths and greater than the deposition position in the last two depths. TheKsatwithin the grass hedge (668 mm h−1) was six times greater than in the row crop position (115 mm h−1) and 18 times greater than in the deposition position (37 mm h−1) for the surface 10 cm. Bulk density and macroporosity were found to provide the best two‐parameter regression model for predicting the log‐transformedKsat(R2= 0.68). These results indicate that grass hedges significantly affected soil hydraulic properties for this loess soil.
Calibrating Hydric Soil Field Indicators to Long‐Term Wetland Hydrology
Authors: Vepraskas M. J. , He X. , Lindbo D. L. , Skaggs R. W.
Published: July 2010

Jurisdictional wetlands are required to be saturated to the surface for 5% or more of the growing season in 5 out of 10 yr, but practical field methods for confirming this are lacking. This study determined whether hydric soil field indicators were related to wetland hydrology requirements. Water table levels were monitored daily for 2.5 yr in a toposequence of nine soil plots that included well to poorly drained members (Oxyaquic Paleudults and Typic Albaqualfs). Monitoring data were used to calibrate a hydrologic model that simulated water table levels from inputs of hourly rainfall data. Forty years of rainfall data were then used with the model to compute long‐term daily water‐table levels in each plot. These data were summarized as “saturation events”, which are the frequency that water tables were at or above preselected depths for at least 21 d. Twenty‐one days was the average period needed for Fe reduction to begin in these saturated soils. This condition must occur for hydric soil field indicators to form. Regression equations were developed to relate saturation events to percentages of redoximorphic features. The r2 values for relationships between percentages of redoximorphic features and saturation events were >0.80 for depths of 15 cm, and >0.90 for depths between 30 and 90 cm. Results showed that the depleted matrix field indicator, in which redox depletions occupy >60% of the horizon, occurred in soils that were saturated for 21 d or longer at least 9 yr out of 10. This indicated the depleted matrix indicator occurred in soils that were saturated nearly twice as long, and more frequently, than the minimum requirements needed to meet wetland hydrology requirements.