bluuebunny/crossref_metadata_2025_split huggingface dataset:
Manganese and Iron Oxides as Reactants for Oxidation of Chlorophenols
Authors: Pizzigallo M. D. R. , Ruggiero P. , Crecchio C. , Mininni R. 
Published: July 2010

AbstractManganese and Fe oxides are capable of decreasing the concentration of chlorophenols, which are highly toxic pollutants in natural systems. Four di‐ and trichlorophenols were oxidized in oxide‐buffered solution suspensions at rates depending on the concentration of reactants, the number and position of the chloro substituents, the surface charge and point of zero charge of the metal oxides, and the environmental pH. Second‐order graphical plots were used to calculate the reaction constants and the half‐life times. The order of reactivity of the oxides was birnessite > pyrolusite > Fe(III) oxide in all systems. Their reactivity was maximum at pH 4.0. The 2,4,6‐trichlorophenol (TCP) was the substrate oxidized to the largest extent, whereas 2,3,5‐TCP showed the lowest reactivity. The quantity of chlorophenols removed per unit mass of birnessite increased as the concentrations increased, without any apparent saturation effect across a wide range of concentrations, whereas it tended to be constant at high equilibrium concentration when pyrolusite and particularly Fe(III) oxide were used as oxidants. From radioactivity measurements of the 14C recovered in liquid and solid phases after incubation of radiolabeled 2,4‐dichlorophenol and 2,4,5‐TCP with the metal oxides, the presence of less soluble oxidation products was shown. Oxidation products, such as quinones and traces of a dimeric compound, were detected by mass spectrometry. The effects observed support the general mechanism for a surface chemical reaction involving a metal oxide‐chlorophenol complex formation followed by a phenoxyl radical generation.
Soil Organic Carbon, Microbial Biomass, and Mineralizable Carbon and Nitrogen in Sorghum
Authors: Franzluebbers A. J. , Hons F. M. , Zuberer D. A. 
Published: July 2010

AbstractQuantifying changes in soil microbial biomass and mineralizable C and N is important in understanding the dynamics of the active soil C and N pools. Our objectives were to quantify long‐term and seasonal changes in soil organic C (SOC), soil microbial biomass C (SMBC) and N (SMBN), and mineralizable C and N in continuous sorghum [Sorghum bicolor (L.) Moench] and sorghum‐wheat (Triticum aestivum L.)/soybean [Glycine max (L.) Merr.] sequences under conventional tillage (CT) and no tillage (NT) with and without N fertilization. A Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in south‐central Texas was sampled after planting in April, during flowering in June, and following sorghum harvest in August. More crop residue C input was retained as SOC and SMBC under NT than under CT. Soil organic C, SMBC, SMBN, and mineralizable C and N were greatest at a depth of 0 to 50 mm under NT. Mineralizable C and SMBC averaged 18% greater in rotation than in monoculture, probably due to greater C input via crop roots and residues in rotation and a shorter fallow. Mineralizable N with N fertilization was 36% greater in continuous sorghum but not different in rotated sorghum. Mineralizable C and SMBC increased an average of 5%, but mineralizable N decreased 41% from planting to flowering, probably due to rhizodeposition. From planting to post‐harvest, mineralizable C and SMBC increased 9% but mineralizable N decreased 15% due to crop residue addition. Soil N availability was reduced by plant additions in the short term but enhanced in the long term.
Soil pH and Copper Effects on Young ‘Hamlin’ Orange Trees
Authors: Alva A. K. , Graham J. H. , Anderson C. A. 
Published: July 2010

AbstractSoil pH is an important factor affecting the forms of Cu in soils and, in turn, its effects on plants. A field experiment was conducted on a Candler fine sand (sandy, hyperthermic, uncoated Typic Quartzipsamment) to investigate the effects of high soil Cu (as a result of repeated spray applications of Cu on the soil surface in 14 doses, for a total of 120 kg Cu ha−1) on growth and mineral content in the foliage of young ‘Hamlin’ orange [Citrus sinensis (L.) Osbeck] trees on three different rootstocks at four soil pH regimes (pH 5.0–7.0 at 0.5‐unit increments). The recovery of Cu (15 mo after the last application), by Mehlich 3 (M3) extraction, in the top 15 cm of soil accounted for 22 to 80% of applied Cu depending on the soil pH. Stem diameter and canopy volume of the trees (3 and 5 yr old) were significantly influenced by soil pH, Cu, and rootstock. Effects of Cu on tree growth were more pronounced at pH 5.5 to 6.0 than at the lower or higher pH regimes. The concentration of Cu in mature spring flush foliage of the trees did not exceed the optimal concentration range. There was no significant relationship between M3 soil Cu and Cu concentrations in the foliage of the trees on all three rootstocks. A significant relationship was found between the concentrations of feeder root Cu and M3 soil, suggesting that the former can be used as an index of soil Cu status.
Pedogenic Carbonate in Soils of the Isaacks' Ranch Surface, Southern New Mexico
Authors: Gile Leland H. 
Published: July 2010

AbstractPedogenic carbonate has potential as a chronological tool for vast areas of arid and semiarid regions. However, much more work is needed on variations in carbonate accumulation in soils of the same age. A long gully and study trench in southern New Mexico provide continuous exposures of soils of a drainageway and ridge of Isaacks' Ranch age (8000–15 000 yr). A fine‐loamy Typic Haplargid in the drainageway has a Stage II carbonate horizon and 108 kg/m2 of carbonate. Two coarse‐loamy Typic Haplargids of the ridge side have Stage II carbonate horizons and 78 and 97 kg/m2 of carbonate, distinctly less than for the soil of the drainageway. The difference is attributed to finer texture (which would slow the wetting fronts) in the drainageway, and more water there for movement of carbonate into the soil. At the ridge crest, a facies change from coarse‐loamy to sandy materials caused a change from Stage II nodules to Stage I coatings on grains. In the sandy materials, a Typic Torripsamment has 22 kg/m2 of carbonate. In the coarse‐loamy materials, a Typic Torriorthent has 60 kg/m2 of carbonate; the coarse‐loamy materials must have captured carbonate that moved to greater depths in the Torripsamment. Although the totals obtained must be considered estimates, they indicate that the amount of pedogenic carbonate in Isaacks' Ranch soils may range up to fivefold, that landscape position is an important factor in this range, and that texture of the parent materials can have a major effect on the amount of carbonate in soils of a given age regardless of landscape position.
Surface Soil Degradation and Soil Productivity Restoration and Maintenance
Authors: Bruce R. R. , Langdale G. W. , West L. T. , Miller W. P. 
Published: July 2010

AbstractIn the Piedmont of the Southern Appalachian region, soil degradation is most often expressed by crop water deficit that limits crop yield in the warm season. To evaluate the nature of variability on these cropped lands, soybean [Glycine max (L.) Merr.] yield and associated soil characteristics were measured across the range of surface soil conditions in 40 farm fields. Factor analysis of the data permitted identification of variables responsible for most of the yield variability. Carbon in the surface soil was identified as the manageable soil variable that could significantly influence crop water availability and curtail soil erosion. Subsequently, selected crop cultures that supplied a range in quality and quantity of crop biomass to the soil surface were applied on three soil erosion classes for 5 yr. Large increases in rainfall infiltration and reduced soil erodibility were associated with no‐till planting of grain sorghum [Sorghum bicolor (L.) Moench] into crimson clover (Trifolium incarnatum L. ‘Tibbee’) in comparison to conventional tillage of grain sorghum and soybean. The maintenance of a decomposing mulch by crop residue additions of about 12 Mg ha−1 yr−1 generated high soil C levels in the 0‐ to 15‐mm depth and a high water stability of aggregates in the 0‐ to 80‐mm depth in comparison to incorporated crop residues. In the 6th yr, grain yield of conventionally tilled soybean was 30 to 100% greater on the previously no‐till crop culture than on the conventionally tilled. The restoration and maintenance of soil productivity commensurate with inherent site resources was associated with maintenance of a decomposing mulch on the soil surface derived from an appropriate quantity and quality of crop residue produced in situ.
Raindrop‐Induced Soil Detachment and Sediment Transport from Interrill Areas
Authors: Sharma P. P. , Gupta S. C. , Foster G. R. 
Published: July 2010

AbstractPhysically based soil erosion simulation models require input parameters of soil detachment and sediment transport due to the action and interactions of both raindrops and overland flow. In this study, we report on the soil detachability and transportability parameters for raindrop‐impact‐dominated interrill erosion processes. The detachability parameter is derived by integrating estimated soil detachment due to single raindrop impact over all the raindrops occurring in a storm. Using artificial rainfall characteristics and soil properties as inputs, we simulated raindrop‐induced soil detachment rates for 33 cropland soils used in the USDA‐ARS Water Erosion Prediction Project (WEPP) experiments in the USA. The magnitude of difference between the predicted detachment rates and the measured interrill sediment delivery rates decreased with clay content. This suggests that in coarse‐textured soils, most of the rain‐detached sediments are redistributed within the interrill area. Small differences between detachment rates and sediment delivery rates in clayey soils indicate that the interrill erosion is detachment limited. A raindrop‐induced interrill transportability parameter is derived by dividing the measured sediment delivery rates with the product of rainfall rate and unit effective kinetic energy. The derived transportability parameter increases linearly with an increase in clay content, thereby suggesting the predominant role of raindrop impact in the sediment delivery process, specifically on up‐slope areas with shallow overland flow. The raindrop‐induced soil detachment and sediment transport processes can be represented by incorporating intensity and effective kinetic energy of rainfall into the basic interrill erosion model.
A Multiregion Model Describing Water Flow and Solute Transport in Heterogeneous Soils
Authors: Hutson J. L. , Wagenet R. J. 
Published: July 2010

AbstractMany different processes influence chemical breakthrough patterns from soil columns, including chemical kinetics, diffusion, matrix geometry, and flow heterogeneity. TRANSMIT, a multiregion model that reflects many of these features, was used to simulate a suite of solute breakthrough curves from soil columns subjected to both transient and steady‐state flow. When utilized as a two‐region model. TRANSMIT matched analytical solutions for steady‐state flow through two‐region soils. The TRANSMIT model is easily expanded to describe a wide range of multiregion and two‐dimensional geometries and is applicable to transient and steady‐state flow typical of both laboratory experiments and field situations. Sorption and degradation parameters can be varied, and nonuniform surface boundary conditions, resulting from irrigation method and banded chemical placement, can be described.
Spatio‐Temporal Variability of Soil Temperature within Three Land Areas Exposed to Different Tillage Systems
Authors: Mohanty B. P. , Klittich W. M. , Horton R. , van Genuchten M. Th. 
Published: July 2010

AbstractThe rational (lateral) spacing between soil temperature sensors to obtain spatial independence of measurements in the field under various tillage systems is not well studied. In particular, properly positioning sensors in a tillage plot requires knowledge of the spatial dependence of the measurements. This study was conducted to measure the horizontal spatial variability of soil temperature and its diurnal fluctuation in three different tillage systems. Soil temperature was measured with copper‐constantan thermocouples at 49 positions in each system at the 1‐ and 10‐cm depths. The thermocouples formed a 7 by 7 grid with a spacing of 3.0 (east‐west) by 1.5 m (north‐south). The three management systems were fall moldboard plowing followed by spring disking and planter operation (MP), fall chisel plowing followed by spring disking and planter operation (CP), and ridge tillage slot planting (RN). Each management system had been under continuous field corn (Zea mays L.) for 8 yr. A novel finding of the study is that a hysteresis within the diurnal cycle existed between the mean and the sample variance. This hysteresis was presumably due to differences in soil surface heating and cooling rates during the diurnal cycle. Although no definitive relationships could be determined, semivariograms appeared to show a time dependence and anisotropy during the 24‐h observation period. Correlation distances were ≈9 m in the E‐W direction along crop rows and tillage operations but <1.5 m in the N‐S direction across crop rows and tillage operations. These spatial correlation distances will be useful in deciding the minimum (lateral) spacing between adjacent soil temperature sensors in the field.
Kinetic Behavior of Synthetic Organo‐ and Organo‐Mineral‐Urease Complexes
Authors: Gianfreda Liliana , De Cristofaro Annunziata , Rao Maria A. , Violante Antonio 
Published: July 2010

AbstractA study was conducted for characterizing the properties and the catalytic behavior of enzymatic complexes that are considered analogues of those usually present in soil. Active enzymatic complexes were formed at 10°C by interaction for 1 h of urease and tannic acid with and without Fe ions and OH‐Al polymers. The enzymatic complexes obtained in the presence of Fe3+ ions and OH‐Al species showed higher activity levels than urease‐tannate complexes. The pH optimum of immobilized urease did not differ significantly from that of free urease, except for the tannate complexes, which showed a pH optimum slightly shifted upwards by ≈0.5 units. Immobilized urease displayed the highest activity in a wider range of temperatures (60–80°C) compared with the free enzyme. The free enzyme showed a marked reduction in activity above 70°C. Higher values of energy of activation (Ea), enthalpy of activation (ΔHa), and the kinetic parameter (Km) were obtained for urease immobilized on tannate molecules. On the contrary, the complexes obtained with Fe3+ and OH‐Al species displayed kinetic and thermodynamic parameters similar to those of the free enzyme. Immobilized urease showed a catalytic behavior similar to the free enzyme, when the interaction with tannic acid occurred in the presence of Fe3+ ions and OH‐Al polymers. Evidently, both Fe ions and OH‐Al species favored the formation of enzymatic complexes in which conformational and catalytic features of the enzyme remained practically unchanged.
Chemical Structure and Biological Activity of A Siderophore Produced by Rhizopus arrhizus
Authors: Shenker M. , Chen Y. , Ghirlando R. , Oliver I. , Helmann M. , Hadar Y. 
Published: July 2010

AbstractRhizopus arrhizus grown on low‐Fe medium produces a siderophore, the chemical structure of which was determined by means of 1H nuclear magnetic resonance (NMR), 13C NMR, and circular dichroism spectroscopy. The siderophore was identified as N1,N4‐bis(1‐oxo‐3‐hydroxy‐3,4‐dicarboxybutyl)‐diaminobutane, chemically identical to rhizoferrin produced by Rhizopus microsporus. Growth promotion of R. arrhizus by several unferrated chelates in Fe‐limited medium was studied in microtitration plates. The impact of rhizoferrin was much more pronounced than the effect of other siderophores. This growth promotion was used as a bioassay for the detection of rhizoferrin. Purified Fe‐rhizoferrin was found to be a very efficient Fe source for tomato plants [Lycopersicon lycopersicon (L.) Karsten] in nutrient solutions. Uptake and translocation of 55Fe mediated by rhizoferrin in a short‐term (10‐h) experiment were at levels higher than those obtained by other microbial siderophores. Iron‐rhizoferrin acted similarly to the synthetic chelate FeEDDHA [ethylenediamine di(o‐hydroxyphenylacetic acid)] on remedy of chlorosis in a long‐term (14‐d) experiment.
Isotopic Labeling of Soil Nitrate Pools Using Nitrogen‐15‐Nitric Oxide Gas
Authors: Stark John M. , Firestone Mary K. 
Published: July 2010

AbstractIn N cycling studies, soil NO−3 pools are typically labeled by adding solutions containing 15NO−3. The associated increase in moisture may perturb the system and preclude measurement of N‐cycle processes in relatively dry soils. This study examined the feasibility of using 15N‐NO gas to label soil NO−3 pools without addition of water. Soil samples (ashed, oven dry, or with soil water potentials ranging from −3.7 to −0.2 kJ kg−1 [1 MPa = 1 kJ kg−1]) were exposed to various quantities of NO gas (0–600 mg NO‐N kg−1 soil). Maximum recovery of NO‐N in soil NO−2 and NO−3 pools occurred after <2 h of exposure to the gas and ranged from ≈ 40% for moist soil samples to >90% in ashed soil. Relative increases in either NO−2 or NO−3 depended on the initial NO concentration and the soil treatment. In general, higher soil moisture resulted in higher NO−2/NO−3 ratios. Within 20 h of addition of 15NO, almost all of the NO−2 was converted to NO−3; however, a small amount was also converted to NH+4 and organic N. These results demonstrate that 15NO can be used to label soil NO−3 pools without addition of water. Depending on the objectives of the study, however, it may be necessary to monitor the enrichment of a variety of other soil N pools as well.
Nitrate Leaching through Lysimeters in a Corn‐Soybean Rotation
Authors: Owens L. B. , Edwards W. M. , Shipitalo M. J. 
Published: July 2010

AbstractLeaching of NO3‐N can be excessive under continuous corn (Zea mays L.) production. To reduce NO3‐N losses, corn might be rotated with soybean [Glycine max (L.) Merr.], which does not require fertilizer N. Six large, undisturbed monolith lysimeters (8.1‐m2 surface area, 2.4 m deep) were used to investigate NO3‐N leaching in a 6‐yr cornsoybean rotation study in eastern Ohio. Four lysimeters (Y103 A, B, C, and D) contained a moderately well‐drained Keene silt loam (fine‐silty, mixed, mesic Aquic Hapludalf) on a 6% slope, and two lysimeters (Y102 A and C) contained a well‐drained Rayne silt loam on a 13% slope (fine‐loamy, mixed, mesic Typic Hapludult). In the spring of each year, 224 kg N/ha as NH4NO3 was surface applied, and a rye (Secale cereale L.) winter cover crop was used following soybean. Nitrate‐N levels in lysimeter percolate varied seasonally from 1 to 20 mg/L and on a 2‐yr cycle, showing the influence of the crop rotation. The highest NO3‐N levels usually occurred during the dormant season following corn. During the 6 yr of the study, the flow‐weighted average NO3‐N concentration in the percolate was 10.5 and 14.3 mg/L from the Y103 and Y102 lysimeters, respectively. Mean annual NO3‐N losses in the percolate were 31.6 and 47.1 kg/ha, respectively. These NO3‐N losses are smaller than losses from continuous corn production previously measured with the same lysimeters. Thus, a corn‐soybean rotation may be one strategy for reducing NO3‐N loading to groundwater.
Hydraulic Conductivity of Saprolite as a Function of Sample Dimensions and Measurement Technique
Authors: Vepraskas M. J. , Williams J. P. 
Published: July 2010

AbstractAccurate hydraulic conductivity (K) data are needed to evaluate soils for on‐site waste disposal, but such data are difficult to obtain where K values vary with sample dimensions. This study evaluated the K of a quartz‐diorite saprolite (Cl horizon) by comparing saturated hydraulic conductivities (Ksat) for sample volumes of 347, 6280, and 675000 cm3. Unsaturated hydraulic conductivities [K(h)] for sample volumes of 347 and 6280 cm3 were compared using a one‐step outflow procedure and the crust test. A dye was also applied to the largest samples to determine the depth distribution of water‐conducting macropores. The mean Ksat value found for samples with volumes of 347 cm3 (0.04 cm h−1) was significantly lower than the mean Ksat values found for larger samples (0.16–0.20 cm h−1); means for the latter samples were not significantly different (P = 0.10). Means for K(h) also differed between the two sample volumes for soil water pressure heads of −5 and −10 cm. Channels were the major kind of water‐conducting macropore observed. The results from both the pore studies and K measurements showed that the minimum sample size needed in situ for K measurements in this horizon was ≈ 5000 cm3 for soil water pressure heads between 0 and −10 cm. Detached cores with smaller cross‐sectional areas could be used for measuring K(h) at soil water pressure heads of ‐20 cm or less.
Dithionite‐Citrate‐Bicarbonate‐Extractable Organic Matter in Particle‐Size Fractions of a Haplaquoll
Authors: Schulten H.‐R. , Leinweber P. 
Published: July 2010

AbstractThe influence of the dithionite‐citrate‐bicarbonate (DCB) extraction on soil organic matter (SOM) in five particle‐size fractions of a Haplaquoll was studied by pyrolysis‐field ionization mass spectrometry. By treatment with DCB, 4 to 19 g kg−1 of organic C (Cdcb; 17.8–44.4% of total C), 2.2 to 20.3 g kg−1 of Fe (Fedcb; 13.6–29.7% of total Fe), and 0.4 to 8.4 g kg−1 of Al (Aldcb; 0.6–8.0% of total Al) were extracted from the size fractions. The pyrolysis‐field ionization mass spectra recorded before and after DCB extraction and the proportions of six important compound classes of SOM showed that lipids, alkylaromatics, and lignin dimers were preferentially extracted. In the extraction residues of clay, fine silt, and medium silt, increases in total ion intensities, weight‐averaged molecular weights of the pyrolysate, and characteristic shifts in the pyrolysis thermograms toward lower temperatures were observed. These properties indicated a general destabilization of the SOM structure due to DCB extraction. We explained these results by the solubility of these SOM constituents in alkali or by associations with pedogenic oxides that stabilized the SOM structure. The results pointed also to unknown, possibly selective, losses of C species when DCB extraction is used to improve the quality of solid‐state (cross polarization/magic angle spinning)‐13C nuclear magnetic resonance spectra.
Nitrogen Mineralization and Microbial Biomass Nitrogen Dynamics in Three Alpine Tundra Communities
Authors: Fisk Melany C. , Schmidt Steven K. 
Published: July 2010

AbstractThe alpine tundra of the Colorado Front Range supports a variety of plant communities whose distribution corresponds to their topographic position. Our objectives were to: (i) determine patterns in net N mineralization and microbial N pools among three communities, Kobresia, Acomastylis, and Carex meadows, that span a topographic gradient, and (ii) relate any patterns to soil microclimate differences among these communities. Average yearly net N mineralization rates, measured with an in situ core incubation technique, were 1.2 g N m−2 in 1991 and 1.0 g N m−2 in 1992. No differences were detected in yearly N mineralization rates among the three communities; however, net nitrification and other soil properties were found to differ among communities. Net N mineralization rates and microbial N showed strong temporal variation, and this variation was related to different variables for each community. Seasonal variation in N mineralization was related to soil water and microbial N in Kobresia meadows, to soil temperature and microbial N in Acomastylis meadows, and to soil water and temperature in Carex meadows. Seasonal changes in microbial N were related to soil water in Kobresia and Acomastylis meadows. Large fluctuations in microbial N indicate that periodic losses from the microbial pool may be important to N availability in this alpine tundra site.