bluuebunny/crossref_metadata_2025_split huggingface dataset:
Smectite Mineralogy and Charge Characteristics along an Arid Geomorphic Transect
Authors: Reid D. A. , Graham R. C. , Amrhein C. , Douglas L. A. 
Published: July 2010

AbstractSmectites are a major mineral group often found in the clay fraction of soils. Our objective was to evaluate the effect of pedologic environments on smectites in the arid Carrizo Plain, California. Six pedons (one Argixeroll, three Haploxeralfs, one Natrargid, and one Salorthid) were described and sampled along a geomorphic and salinity gradient transect. The transect soils have formed in alluvial parent materials derived from Miocene marine sandstones, siltstones, and shales. The fine clay fractions of transect soils were studied using x‐ray diffraction, interlayer swelling with alkylammonium cations, and chemical analyses. Both beidellitic and montmorillonitic smectites occurred in the transect soils, suggesting multiple origins for these minerals. The chemical composition of the beidellites are similar to those of a tetrahedrally charged, dioctahedral mica. Since mica was identified in shale parent materials and in the fine silt and clay fractions of the soils, the beidellites are apparently a weathering product of mica. Minor variations in the chemical composition of mica precursors may account for observed differences in beidellite charge characteristics. The chemical composition of montmorillonites was variable, making a common origin for these minerals unlikely. Montmorillonites from saline pedons contained more Fe and Mg and less Al in the octahedral sheet than montmorillonites from nonsaline pedons. Montmorillonites in the nonsaline pedons are probably inherited from montmorillonites identified in parent materials, whereas montmorillonites in saline soils may be neoformed. Groundwater within the Salorthid was supersaturated with respect to both montmorillonite and beidellite.
Changes in Ponderosa Pine Site Productivity following Removal of Understory Vegetation
Authors: Busse M. D. , Cochran P. H. , Barrett J. W. 
Published: July 2010

AbstractCompetition from understory vegetation for water and nutrients can limit productivity of young forest stands. Less is known of the effect of understory vegetation on long‐term stand growth or soil organic properties. The effect of understory vegetation on periodic annual increments (PAIs) of basal area, height, and volume for ponderosa pine (Pinus ponderosa Dougl.) in central Oregon at 4‐ or 5‐yr intervals was examined for a 35‐yr period. Soil C, N, and microbial biomass C (MBC) were also quantified after 32 and 35 yr with and without understory vegetation on a sandy loam pumice soil (Xeric Vitricryand). Five tree spacings, ranging from 2.0 to 8.0 m (154–2469 trees ha−1), in combination with two understory treatments (understory vegetation present or continuously absent) were installed in 1959. Total understory vegetation cover averaged 35% between 1959 and 1994 for treatments with understory vegetation present, and was dominated by three shrub species: antelope bitterbrush [Purshia tridentata (Pursh) DC.], greenleaf manzanita (Arctostaphylos patula Green), and snowbrush (Ceanothus velutinus Dougl. ex Hook.). Covariance analyses of PAIs for each successive interval were performed using appropriate stand parameters at the start of each interval as covariates. Tree growth was reduced by competing understory vegetation during the first 12 to 20 yr only; understory vegetation did not reduce the adjusted PAIs during the last 15 yr. Soil C and N were measured incrementally to a depth of 24 cm. Presence of understory vegetation resulted in greater C and N in the O horizon and upper 4 to 12 cm of mineral soil. Seasonal MBC, measured at 14‐d intervals from May to November, was greater when understory vegetation was present. The results suggest that understory vegetation plays an important role in maintaining soil quality.
Hydraulic Conductivity in a Clay Soil: Two Measurement Techniques and Spatial Characterization
Authors: Reynolds W. D. , Zebchuk W. D. 
Published: July 2010

AbstractInfiltration, drainage, and chemical leaching are strongly influenced by the magnitude and spatial distribution of the field‐saturated soil hydraulic conductivity (Kfs). The Guelph permeameter (GP) method shows promise as an effective means for field measurement of Kfs and its spatial distribution, but its accuracy in medium‐ and fine‐textured soils is not well established. To further assess its accuracy and effectiveness, the GP method was compared with the auger hole (AH) method at the 0.5‐m depth at 68 grid locations in a texturally uniform silty clay soil that had stable but spatially variable structure. The two methods yielded similar geometric mean Kfs values (P < 0.001), as well as similar semivariograms. The two methods were also positively correlated (r = + 0.6565, P < 0.0001). We therefore concluded that the two methods gave equivalent estimates of Kfs at this field site, and that the GP method is capable of providing valid estimates of Kfs in at least some fine‐textured soils. The Kfs values were not correlated with soil texture, organic C content, or soil surface topography, but were negatively correlated (r = −0.7240 for GP method, r = −0.6070 for AH method, P < 0.0001) with antecedent volumetric water content (θa) measured in situ prior to the GP measurements using a down‐hole time domain reflectometry probe. The semivariogram for θa was similar to those for Kfs. These results suggest that the magnitude, range, and pattern of variability of the Kfs measurements were controlled primarily by the well‐developed and stable soil structure at the field site, rather than by texture, organic C content, or surface topography.
Characterization of Water Extracts of Two Manures and Their Adsorption on Soils
Authors: Liang B. C. , Gregorich E. G. , Schnitzer M. , Schulten H.‐R. 
Published: July 2010

AbstractTo uncover possible chemical differences between stockpiled and composted dairy manures, water extracts of these manures were analyzed by 13C nuclear magnetic resonance (NMR) and by pyrolysis‐field ionization mass spectrometry (Py‐FIMS). Judging from the 13C NMR, which took into consideration all of the organic C present, aliphatic and aromatic C in the composted and stockpiled manure extracts were similar but the composted manure extract appeared to be richer in protein C, phenolic C, and carboxylic C and poorer in carbohydrate C than the stockpiled manure extract. Major components of the extract of the stockpiled manure extract determined by Py‐FIMS, which measured only volatile organics, were N compounds > phenols + monolignins > carbohydrates > alkylaromatics > peptides = lipids > lignin dimers > sterols > fatty acids > suberins. On the other hand, the quantitative order of organic components of the composted manure extract was phenols + monolignins > N compounds > carbohydrates > peptides > alkylaromatics > lipids > fatty acids > sterols = lignin dimers > suberins. The relatively low total ion intensity of the water extract of the composted manure and its greater aromaticity suggested that composting increased polymerization and cross‐linking and so led to the formation of larger molecules. Water‐soluble organic C (DOC) extracted from the manures was used to study adsorption isotherms on soils varying in clay content from 3 to 54%. The adsorption of the DOC by the soils increased as the clay and organic matter contents and the surface areas of the soils increased. Increased adsorption of the DOC extracted from the composted manure appeared to be due to increased molecular weights of the major DOC components.
Using Field Data and Simulation Modeling to Determine Nitrogen Cycle Parameters
Authors: Larocque M. , Banton O. 
Published: July 2010

AbstractThe identification of representative parameter values is an important aspect of N modeling because many parameters are unavailable or difficult to evaluate. Reversed modeling was performed using a conceptual simulation model, AgriFlux, and NO3− concentrations from a field near Quebec City, Canada, to identify N cycle parameters. A sensitivity analysis of the model with regard to the unavailable N cycle parameters identified three parameters related to the organic N transformations that largely control soil N dynamics (efficiency of the internal synthesis of the microbial biomass, litter humification fraction, and humus mineralization rate). The available parameters and those of lesser influence were kept constant while various combinations of the three influential parameters were used for the simulations. An optimal parameter set was identified using the root mean square error procedure, and its uniqueness was confirmed by the isocontouring technique. For the site studied, low values of humus mineralization combined with low values for the efficiency of the microbial biomass and small transfers from the litter pool to the humus pool generated the NO3− concentrations that compared the most favorably with the measured values. However, a fitting difference was observed between simulated and measured concentrations that can be imputed to nonoptimized parameters or processes not differentiated in the model.
Diffusion Technique for Preparing Salt Solutions, Kjeldahl Digests, and Persulfate Digests for Nitrogen‐15 Analysis
Authors: Stark John M. , Hart Stephen C. 
Published: July 2010

AbstractWhen diffusion techniques are used to prepare samples for 15N analyses, low or variable N recovery is sometimes observed. The effect of low recovery on estimates of 15N enrichment is unknown. Also, the suitability of diffusion techniques for use with a variety of salt solutions and digests containing very low N concentrations (<0.8 mg L−1) has not been determined. We evaluated a diffusion technique where NH3‐N is trapped on acidified filter paper disks that are sealed between two strips of Teflon [polytetrafluoroethylene (PTFE)] tape. Because the PTFE protects the acid trap from neutralization, large volumes of solution can be diffused in plastic specimen containers and the sample can be vigorously mixed during the diffusion period. Six days of diffusion at 22°C resulted in >92% recovery of 50 µg NH+4‐N from 75 mL of 2 M NaCl, total Kjeldahl digests, or 2 M KCl preserved with acid. Leaving sample containers open for 5 d after diffusion for NH+4 completely eliminated contamination of NO−3‐N by residual NH+4; however, recovery of NO−3 was inversely related to the length of the open period. Recovery of NO3−‐N from 0.5 M K2SO4 and alkaline persulfate digests after a 3‐d open period was 90 and 77%, respectively. Complete recovery of NH+4 or NO−3 was not required to obtain accurate estimates of 15N enrichment; however, when recovery was <100%, the method of blank correction was critical. When the mass of N contamination measured in diffusion blanks was used to blank‐correct 15N enrichments, diffused standards often had 15N enrichments that were significantly different from nondiffused standards; however, when the mass of N in blanks was estimated using an isotope dilution equation, there was excellent agreement between diffused and nondiffused standards, regardless of the degree of recovery.
Soybean Growth and Rhizosphere pH as Influenced by A Horizon Thickness
Authors: Yang J. , Blanchar R. W. , Hammer R. D. , Thompson A. L. 
Published: July 2010

AbstractCrop growth and yield are known to be limited by A horizon thickness and may be related to more abundant and metabolically active roots in A than B horizon soil. The influence of A horizon thickness on root distribution and rhizosphere pH was observed in the field. Soybean [Glycine max (L.) Merr.] were grown on plots of Mexico soil (fine, montmorillonitic, mesic Mollic Endoaqualfs) with A horizon thicknesses of 0, 12.5, 25, and 37.5 cm above Bt horizons. Plant height, root and shoot growth, and rhizosphere pH (pH in soil 0.5 mm from a root surface) were determined 25, 55, and 85 d after planting. Plant height and shoot and root weight decreased significantly as A horizon thicknesses decreased from 37.5 to 0 cm, and these differences were attributed to later emergence of soybean seedlings from the thinner A horizons. Root distribution with depth in the upper 30 cm was independent of A horizon thickness. Rhizosphere pH was 0.07 to 0.65 units lower than that of the bulk soil, depending on soil horizon, root morphology, and plant age. This pH difference (ΔpH) averaged 0.36 in the A horizon and 0.18 in the Bt horizon and was independent of measurement depth within each horizon. As bulk soil pH decreased from 6 to 5, the mean ΔpH for lateral and main roots decreased 0.28, 0.21, and 0.10 units at 25, 55, and 85 d, respectively. The mean ΔpH for lateral roots was 0.34 and for main roots was 0.20. The mean ΔpH for all roots and horizons was 0.41 at 25 d, 0.28 at 55 d, and 0.11 at 85 d. The changes in ΔpH with root age, morphology, and depth suggest that ΔpH may be an indicator of root activity.
Rain Infiltration as Affected by Wheat Residue Amount and Distribution in Ridged Tillage
Authors: Baumhardt R. L. , Lascano R. J. 
Published: July 2010

AbstractTexas South Plains production systems for conserving rainfall and reducing wind erosion in cotton (Gossypium hirsutum L.), a low‐residue crop, include the spring chemical termination of winter wheat (Triticum aestivum L.) overseeded post‐harvest into cotton. This practice often increases cotton lint yields under irrigation, but residues hinder weed control and increase production costs. This study characterized infiltration response to (i) residue weathering and soil consolidation with ridges, (ii) residue distribution on the ridge or in the furrow, and (iii) flat or standing architectures and residue amounts. Simulated rain was applied at 65 mm h−1 for 1 h into a bare Olton clay loam (fine, mixed, thermic Aridic Paleustoll). Mean cumulative infiltration was lowest for bare soil (28.7 mm), but increased curvilinearly with increasing residue amounts, leveling at 49.0 mm. Cumulative infiltration with residues distributed on the ridge (42 mm) or in the furrows (44 mm) were the same even though water in the furrow absorbed drop impact. A minimum amount of residue (0.7 Mg ha−1) to intercept raindrop impact was needed to increase rain infiltration, but increasing residue above a residue threshold of 2.4 Mg ha−1 had no effect because of sufficient drop impact interception. Increases in infiltration were related to the residue amount rather than to the bed or furrow location. Partial residue cover and tillage operations that lodge crop residues may increase infiltration.
Soil Heterogeneity and Root Distribution of Mature Loblolly Pine Stands in Piedmont Soils
Authors: Parker M. M. , Van Lear D. H. 
Published: July 2010

AbstractFactors that influence rooting patterns in mature forest stands are poorly understood. We examined the distribution of loblolly pine (Pinus taeda L.) roots in trench profiles and related rooting to selected soil physical features along a moisture gradient on the Clemson University Experimental Forest, Clemson, SC. Root density was greater on xeric and subxeric sites than on intermediate sites. Root density declined exponentially with soil depth. Fine roots (<4 mm) accounted for 83 to 95% of all roots and averaged 17 fold higher in root channels than in the soil matrix. Root density was also higher along rock‐soil interfaces than in the soil matrix. Soil morphological and physical features, as well as the relative position of the site in the landscape, influence root growth and survival and markedly affect the distribution of roots in mature loblolly pine stands.
Soil Respiration in Pits and Mounds Following an Experimental Forest Blowdown
Authors: Millikin Catherine S. , Bowden Richard Drew 
Published: July 2010

AbstractExtensive uprooting of trees by windthrow can create areas of severe soil disturbance in temperate forests. Specifically, uprooted trees leave shaded pits and mounds of exposed roots and mineral soil. To assess the contribution of pit and mound microenvironments to overall soil respiration in an experimental hurricane blowdown at the Harvard Forest Long‐Term Ecological Research site (MA), summer CO2 effluxes were measured on pit, mound, and undisturbed microsites. Mean CO2 effluxes were 45.4, 80.1, and 99.0 mgC m−2 h−1 for pit, mound, and control microsites, respectively. Although soil respiration is lower in areas of disturbed soil than in undisturbed areas, the total efflux contribution (5.3%) from pits and mounds to the overall flux rate at the site was small. The area‐weighted soil respiration estimate is 3.1% lower than the estimate obtained using flux measurements from control locations alone. Measurements taken from undisturbed plots represent a small but systematic overestimate of soil respiration across the site.
Assessment of Two Chemical Extraction Methods as Indices of Available Nitrogen
Authors: Jalil A. , Campbell C. A. , Jame Y. W. , Schoenau J. , Henry J. L. , Lafond G. P. 
Published: July 2010

AbstractA soil test for estimating mineralizable N in soil is needed to improve fertilizer use efficiency. Our objectives were to: (i) test the effectiveness of two chemical indices in estimating potentially mineralizable N (N0) in soils, and (ii) determine if these indices could be used to differentiate the impact of cultural practices on the N‐supplying capacity of soils. We collected samples from the 0‐ to 0.15‐m depth of 42 soils representing all agroecological regions in Saskatchewan, Canada. We determined (i) N mineralized (Nmin), N0, and the rate constant (k) by aerobic incubation at 35°C for 24 wk, and (ii) the NH4‐N extracted by (a) 2 M KCl heated at 100°C for 4 h, and (b) a steam‐distilled phosphate‐borate solution buffered at pH 11.2. The association between N0 and the hot 2 M KCl extracted NH4‐N was close (r2 = 0.78, significant at P < 0.001); the relationship between N0 and the phosphate‐borate NH4‐N was slightly less precise (r2 = 0.73, P < 0.001). When NH4‐N extracted with cold 2 M KCl was subtracted from the NH4‐N extracted with hot extractants, the association with Nmin was weaker (r2 ≤ 0.50). The value of k for the 42 soils was generally constant (avg. 0.067 ± Sxt 0.05 = 0.040 wk−1). In a second experiment, we compared the two chemical extractants vs. the N mineralized in a 24‐wk incubation regarding their effectiveness in differentiating the effects of eight 37‐yr crop rotation treatments on N‐supplying capacity. These three indices performed effectively in this regard. For example, the 2 M KCl NH4‐N was closely associated with N mineralized in 24 wk (r2 = 0.92), as was phosphate‐borate NH4‐N (r2 = 0.88; both significant at P < 0.001). We concluded that the chemical extractants may provide a quick test for assessing N‐supplying capacity of the soil.
Soil Quality: A Concept, Definition, and Framework for Evaluation (A Guest Editorial)
Authors: Karlen D. L. , Mausbach M. J. , Doran J. W. , Cline R. G. , Harris R. F. , Schuman G. E. 
Published: July 2010

AbstractThis essay summarizes deliberation by the Soil Science Society of America (SSSA) Ad Hoc Committee on Soil Quality (S‐581) and was written to spur discussion among SSSA members. Varying perceptions of soil quality have emerged since the concept was suggested in the early 1990s, and dialogue among members is important because, unlike air and water quality, legislative standards for soil quality have not been and perhaps should not be defined. In simplest terms, soil quality is “the capacity (of soil) to function”. This definition, based on function, reflects the living and dynamic nature of soil. Soil quality can be conceptualized as a three‐legged stool, the function and balance of which requires an integration of three major components — sustained biological productivity, environmental quality, and plant and animal health. The concept attempts to balance multiple soil uses (e.g., for agricultural production, remediation of wastes, urban development, forest, range, or recreation) with goals for environmental quality. Assessing soil quality will require collaboration among all disciplines of science to examine and interpret their results in the context of land management strategies, interactions, and trade‐offs. Society is demanding solutions from science. Simply measuring and reporting the response of an individual soil parameter to a given perturbation or management practice is no longer sufficient. The soil resource must be recognized as a dynamic living system that emerges through a unique balance and interaction of its biological, chemical, and physical components. We encourage SSSA members to consider the concept of soil quality (perhaps as a marketing tool) and to debate how it might enable us to more effectively meet the diverse natural resource needs and concerns of our rural, urban, and suburban clientele of today and tomorrow.
Competitive Sorption of Dissolved Organic Matter Fractions to Soils and Related Mineral Phases
Authors: Kaiser Klaus , Zech Wolfgang 
Published: July 2010

AbstractExperiments with soils, Al(OH)3 gel, and goethite were conducted to investigate the competitive sorption of hydrophilic and hydrophobic dissolved organic matter (DOM) fractions and inorganic anions such as SO2−4 and H2PO4−. The DOM for the experiments was extracted from a mor layer. The ratio of hydrophilic to hydrophobic dissolved organic carbon was 37/63. The sorption of the hydrophobic DOM fraction was strongly favored over the binding of the hydrophilic fractions on soils and hydrous oxides. Under conditions of a limited number of available binding sites, the preferential sorption of hydrophobic DOM suppressed the binding of hydrophilic DOM or even resulted in a displacement of indigenous hydrophilic organic substances. Favorable chemical properties were assumed to be responsible for the strong sorption of hydrophobic DOM. The SO2−4 induced little reduction of the DOM sorption, whereas H2PO4− caused a strong decrease. The effects of both inorganic anions were more pronounced for the hydrophilic than for the hydrophobic DOM fraction. As the sorption of hydrophilic DOM was strongly affected by inorganic anions and hydrophobic DOM, hydrophilic DOM seems to be the most mobile organic component in soil solutions. The results give evidence that competitive interactions among the chemically heterogeneous DOM constituents need to be considered in DOM transport process in soils.
Climatic Effects on Soil Organic Matter Composition in the Great Plains
Authors: Amelung W. , Zech W. , Flach K.W. 
Published: July 2010

AbstractTo examine temperature and moisture effects on the chemical composition of soil organic matter (SOM), six soil profiles were studied from a climosequence in the native prairie of the Great Plains of the USA. After the removal of plant debris, the vertical distributions (0–60 cm) of soil organic carbon (SOC), N, lignin, and cellulosic and noncellulosic polysaccharides were determined. Samples of the topsoil horizons were additionally characterized by means of 13 C and 1H‐Nuclear Magnetic Resonance (NMR) spectroscopy. As annual temperature increased from 7 to 23°C at sites with <500 mm precipitation per year, the amount of polysaccharides decreased from 605 to 422 g kg−1 SOC in the topsoil (0–15 cm) and from 516 to 278 g kg−1 SOC in the subsoil (30–40 cm). Polysaccharide contents increased with increasing precipitation, reaching 726 g kg−1 SOC in the top 15 cm and 876 g kg−1 SOC at 50‐cm soil depth (830 mm annual precipitation, 12.6°C annual temperature). At all sites, the content of lignin‐derived phenols per kilogram SOC decreased with increasing soil depth. Polysaccharides decreased much less. It is suggested that polysaccharides were resynthesized during SOM alteration within the soil profiles and thereafter preferentially to lignin protected from decay in the mineral soil. The NMR spectra suggested that both polysaccharides and alkyl compounds reflected climatic influences on the SOM composition of the Great Plains.