bluuebunny/crossref_metadata_2025_split huggingface dataset:
Compressive Strength for an Aggregated and Partially Saturated Soil
Authors: Nearing Mark A. 
Published: July 2010

AbstractSoil strength increases with the application of soil water suctions, which impart an increasing level of effective confining stress on the soil mass. The relationship between effective confining stress and suction is influenced by soil water content. For sands, effective confining stress is approximated by the multiple of soil water suction and total saturation of the soil pores. For aggregated soils this is not true. This study was undertaken to test the hypothesis that the saturation of interaggregate pores in aggregated soils controls the level of effective stress and, subsequently, soil strength relationships. The soil used is a highly aggregated, mixed mineralogy, Paulding clay (very‐fine, illitic, nonacid, mesic Typic Haplaquept) from northwestern Ohio. Unconfined compressive strength was measured for five different aggregate size groups across a range of soil water suction levels. Triaxial compression strength was measured on saturated soil samples for which effective confining stress was well defined within the triaxial test cell. Results indicated that axial stress at failure for the soil was linearly related to the product of soil water suction and the saturation level of the interaggregate soil pores. Also, the slope of the regression line was statistically equivalent to the slope of the line relating axial failure stress and effective confining stresses in the saturated triaxial tests. The experimental results support the hypothesis that interaggregate pore water controls the effective confining stress level, and hence compressive strength, for aggregated soil.
Effect of Flow Rate and Path Length on p‐Nitrophenol Biodegradation during Transport in Soil
Authors: Kelsey Jason W. , Alexander Martin 
Published: July 2010

AbstractThe effect of flow rate and path length on the biodegradation of p‐nitrophenol (PNP) during its transport through soil was measured in columns of unsaturated soil receiving a continuous application of the compound. The PNP concentration in the effluents increased to a maximum and then decreased. Within 3 to 4 d after the initial addition of PNP, the number of microorganisms capable of degrading PNP reached a density that was sufficient to degrade all of the applied compound. The percentage of PNP entering the effluents from the soil decreased as the flow rate was reduced or the path length was increased, presumably because of the longer period of contact between the micro‐organisms and the test compound. When PNP was still leaching into the effluent from a 10‐cm column of soil, the microorganisms able to degrade PNP grew extensively at the 2.5‐ but not the 7.0‐cm depth. At the time that all of the PNP flowing through the soil was degraded, microorganisms capable of transforming PNP were concentrated in the top one‐fourth of the soil column. The reasons for the lack of extensive growth of the PNP‐degrading population at lower depths in soil containing PNP are unknown.
Denitrification, Immobilization, and Mineralization in Nitrate Limited and Nonlimited Residue‐Amended Soil
Authors: McKenney D. J. , Wang S.‐W. , Drury C. F. , Findlay W. I. 
Published: July 2010

AbstractAlthough the use of cover crops and intercrops has been increasing, little information exists on effects these plant residues may have on soil microbial processes. Our objectives were to determine effects of several crop residues representing a range of C/N ratios (11.3–65.5) on mineralization, immobilization, denitrification, and dissimilatory NO3− reduction in Brookston clay loam with limiting and nonlimiting NO3− concentrations. Residues were obtained from two legumes, hairy vetch (HV; Vicia villosa L.) and red clover (RC; Trifolium pratense L.); two grasses, annual ryegrass (ARG; Lolium temulentum L.,) and reed canarygrass (RCG; Phalaris arundinacea L.); and corn (Zea mays L.). Nitrate consumption and NH4+, NO2−, NO, and N2O production were measured in soil with 10 g residue kg−1 in a gas flow system. In soil without added NO3−, during a 5‐d aerobic incubation, 86% of the existing NO3− was immobilized with RC, 66% with corn, 44% with HV and ARG, and 41% with RCG. Intense immobilization in the RC and corn treatments limited the amount of NO3− available for denitrification, whereas during the subsequent anaerobic phase, only HV, ARG, and RCG stimulated denitrification. The enhanced net immobilization with RC was surprising because the C/N ratio for this residue was relatively low (15:1). Ammonium production was greatest with the HV residue. Nitrate addition to HV‐amended soil further increased NH4+ production with 91 mg N kg−1 being produced during a 5‐d aerobic, 6‐d anaerobic incubation. The nature of the residue‐derived organic material is more important than simply the C/N ratio in regulating these microbial processes in these short‐term incubations.
Precipitation Use Efficiency of Soybean and Grain Sorghum in Monoculture and Rotation
Authors: Varvel Gary E. 
Published: July 2010

AbstractRainfed cropping systems are highly dependent on water use efficiency of crops in the rotation, especially in subhumid and semiarid areas. Precipitation use efficiency (PUE), an alternative to water use efficiency, is equally effective for water use evaluation in long‐term rainfed studies. We hypothesized that crop rotation and N fertilizer rates altered PUE of soybean [Glycine max (L.) Merr.] and grain sorghum [Sorghum bicolor (L.) Moench]. To test this, soybean (five cropping systems) and grain sorghum (four cropping systems) were grown under rainfed conditions at Mead, NE, on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll), each at three N fertilizer rates. Precipitation use efficiency values for the 1984 through 1991 cropping seasons varied from 15.5 to 59.9 and 21.6 to 159 kg ha−1 cm−1 for soybean and grain sorghum, respectively. Soybean PUE values averaged 30 kg ha−1 cm−1 and varied from 25 to 33 kg ha−1 cm−1 for the 8 yr. Grain sorghum PUE values averaged 89 kg ha−1 cm−1 and with sufficient N fertilization varied from only 94 to 99 kg ha−1 cm−1 for the 8 yr. Similar PUE values for soybean and grain sorghum (with adequate N fertilizer) within a given year and similar PUE values during the study among cropping systems for each crop indicated that both of these crops would be excellent options for rotations in areas with similar precipitation patterns.
Inorganic Nitrogen Determined by Laboratory and Field Extractions of Two Forest Soils
Authors: Van Miegroet Helga 
Published: July 2010

AbstractTo assess the effect of a delay in soil processing on inorganic N levels in N‐rich soils, field and laboratory extractions were compared at two forested sites with high N mineralization and nitrification potential. At eight sampling dates in 1989 and 1990, five mineral soil cores per site were taken between 0‐ and 10‐cm depth and transported on ice to the laboratory for KCl extraction and NH4‐N and NO3‐N analysis. At three sampling dates in 1990, soil extractions were performed in the field immediately following sampling, and inorganic N concentrations were compared between extractions. Nitrate‐N increased four‐ to sevenfold (net release of 2–7 mg NO3‐N/kg dry soil) due to the transport and relatively short delay (<24 h) in the processing of the soil samples, either coinciding with increased net N mineralization or due to transformation of NH4‐N into NO3‐N. This study indicates that if possible, soil samples should be extracted in the field, especially at N‐rich sites. The concerns raised by this study may not necessarily apply to N‐poor soils characterized by slow N transformation rates.
Simulating the Effects of Erosion on Corn Productivity
Authors: Shaffer M. J. , Schumacher T. E. , Ego C. L. 
Published: July 2010

AbstractSoil erosion effects on corn (Zea mays L.) production are sparsely documented for the Corn Belt. Simulation of these effects would help identify important information gaps for the region and elsewhere and help in the understanding of basic soil‐plant processes and interactions that occur. The N Tillage Residue Management model was tested on nine field sites across the north‐central USA. The 119 site‐years of data simulated 78% (R2 of 0.78) of observed corn yield variability for a wide range of eroded soils. Slightly better predictions were made (R2 values of 0.82 and 0.80) for loess‐derived soils and soils in the eastern (wetter) study areas, respectively. Till‐derived soils and soils in the western (drier) areas had R2 values of 0.75 and 0.77, respectively. Crop yield predictions were most responsive to soil physical properties.
Surface Charge Characteristics of Podzolized Soil
Authors: Polubesova Tamara A. , Chorover Jon , Sposito Garrison 
Published: July 2010

AbstractRecently developed methods for the accurate measurement of surface charge components and the points of zero charge in soils containing both permanent‐ and variable‐charge constituents were applied to a Haplorthod that is typical of podzolized soils in North America, Scandinavia, and Russia. Independently measured values of the density of structural surface charge, net proton charge, and net adsorbed ion charge were obtained for soil samples from the E2 and Bhs horizons suspended in LiCl or Li2SO4 solutions of ionic strength 1 or 10 mmol kg−1. Data taken across the pH range 2 to 6 tested successfully for conformity to the law of surface charge balance. Relationships between the point of zero net proton charge and the point of zero net charge were consistent with the fact that, at any pH, increasing ionic strength favored an increase in the net adsorbed ion charge, whereas changing from Cl− to SO2−4 favored a decrease in the net adsorbed ion charge. The methodology and charge balance analysis are applicable to any podzolized soil.
Solution/Soil Ratio and Release of Cations and Acidity from Spodosol Horizons
Authors: Skyllberg Ulf 
Published: July 2010

AbstractThe pH value, exchangeable acidity, and effective cation‐exchange capacity (CECe) are often used to characterize soils. In addition to properties of the soil itself, these parameters are highly attributed to electrolytes and ionic strength in extraction solutions, as well as to the solution/soil ratio (s/s ratio, liters per kilogram). The influence of the s/s ratio on pH, exchangeable acidity, and cations were studied in soil suspensions of Spodosol O, E, and Bs horizon soil samples in distilled water, 0.01 M CaCl2, 1.0 M KCl, and 0.5 M CuCl2. An enhanced s/s ratio resulted in a release of H ions from O and E horizon soil samples in agreement with a weak acid equilibrium, whereas the Bs horizon samples showed a higher buffer intensity of pH. A simultaneous release of organic acids and Al and the fact that samples from the spodic horizons were close to the point of zero charge indicate a more complicated pH buffering mechanism in these horizons. The amount of Al ions released from O and E horizon samples in 1.0 M KCl (Ale) were simply diluted when the s/s ratio was increased. Therefore, Ale is suggested to be a quite finite subpool of totally bound Al (Alt; extracted in 0.5 M CuCl2). A solution of 0.5 M CuCl2 extracted all exchangeable K+, Na+, Mg2+, Mn2+, Fe3+, and Al3+ in O horizon samples, independent of s/s ratio, whereas the release of Ca2+ was slightly enhanced with increased s/s ratio. Hydrogen ions exchangeable in 1.0 M KCl (He, centimoles of charge per kilogram) increased by 17 to 22% in O and E horizons and by 32 to 33% in Bs horizons when the s/s ratio increased from 100 to 150. Consequently, estimated He and CECe pertaining to different samples can only be accurately compared if they are obtained at the same s/s ratio or corrected for differences in the s/s ratio by specific functions for different soil horizons.
Herbicide Leaching under Tilled and No‐Tillage Fields
Authors: Gish Timothy J. , Shirmohammadi Adel , Vyravipillai Raviraj , Wienhold Brian J. 
Published: July 2010

AbstractThe effect of no‐tillage practices on water quality exiting the root zone of deep, well‐drained fields is largely unknown. This project was initiated to determine herbicide leaching characteristics as influenced by tillage practice and herbicide formulation. The research site consisted of four adjacent (0.25‐ha) fields, two fields each dedicated to either tilled or no‐tillage management. One field in each tillage regime received a controlled‐release formulation of atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] and alachlor [2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl)‐acetamide, starch encapsulated], while the others received standard herbicide formulations of atrazine and alachlor. Both herbicide formulations were annually applied at the same rate: 1.7 kg ha−1 for atrazine and 2.8 kg ha−1 for alachlor. Atrazine, deethylatrazine [DEAT; 6‐chloro‐N‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine], alachlor, and Br− concentrations were monitored with 12 suction lysimeters (six each at 1.5‐ and 1.8‐m depths) in each field. Alachlor was detected in <3% of all samples collected, regardless of tillage practice or berbicide formulation, while atrazine was detected in >41% of the samples. Under no‐tillage, atrazine was detected in <28% of the samples with <13% exceeding the U.S. Environmental Protection Agency Health Advisory level of 3 µg L−1 atrazine. Under tilled conditions, 53% of the samples contained atrazine, with 35% exceeding 3 µg L−1 atrazine. Averaged atrazine metabolite concentration of DEAT under no‐tillage was 0.52 µg L−1 vs. 0.39 µg L−1 for tilled fields. Similar Br− transport between tillage practices and reduced atrazine levels under no‐tillage fields suggest that no‐tillage management, on deep well‐drained soils, can have a positive impact on groundwater quality.
Combined Microdiffusion‐Hypobromite Oxidation Method for Determining Nitrogen‐15 Isotope in Ammonium
Authors: Risgaard‐Petersen Nils , Revsbech Niels Peter , Rysgaard Søren 
Published: July 2010

AbstractA limiting factor for work with biological N transformations has been unsatisfactory procedures for analysis of 15N isotope labeling in small amounts of NH+4. Using the procedure described here, it is now possible to perform accurate determinations in NH+4 pools as small as 2 nmol. By diffusion of NH3 through a gas phase, N in NH+4 is transferred from the sample and into a hypobromite solution, where an oxidation to N2 occurs. The N2 originating from the oxidation is mixed with N2 initially dissolved in the sample, which functions as a carrier during subsequent mass spectrometry. Random isotopic pairing of the N atoms originating from NH3 oxidation makes it possible to calculate the original 15N abundance in the NH+4 pool from the relative amounts of 14N15N and 15N15N in the reaction container. The combined microdiffusion‐hypobromite oxidation method for 15NH+4 analysis proved to be very precise (standard error <0.15 atom %, n = 5) when applied on samples with an 15N enrichment >1 atom %, and interference was found only for volatile methyl amines.
Organic Matter and Water‐Stable Aggregate Distribution in Ridge‐Tilled Surface Soil
Authors: Unger Paul W. 
Published: July 2010

AbstractSoil surface conditions improve with increased organic matter (OM) and water‐stable aggregation (WSA), but surface variability may influence values obtained when soils are sampled to evaluate these factors. My hypothesis was that cultural operations for sorghum [Sorghum bicolor (L.) Moench] grown on ridges produce zones of differing soil OM and WSA. Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll) was sampled at the 0‐ to 4‐cm depth in furrows, on ridge tops, and on ridge sides before and after planting, after reforming ridges, and after harvest in 1992. Tillage (conventional [CT] and ridge [early (RT‐E) or late (RT‐L) stalk shredding]), position, and crop cycle (sampling) stage affected OM and WSA. Compared with ridges, OM in furrows was greater due to residue accumulations. Mean WSA was greater on ridges with CT than with RT‐E or RT‐L because disk‐bedding to build the CT ridges moved more stable aggregates to ridges than the other treatments. More thorough mixing of residues by CT may have been involved also. Ridge and furrow positions and possibly ridge sides require separate sampling for obtaining representative OM and WSA data from ridge‐tilled soil, especially where ridge tops are cleared at planting. Ridge clearing at planting should be limited to avoid residue reduction and lowered WSA that could lead to soil crusting and impaired seedling emergence.
Bromide Transport Detection in Tilled and Nontilled Soil: Solution Samplers vs. Soil Cores
Authors: Fleming J. B. , Butters G. L. 
Published: July 2010

AbstractExperimental validation of solute transport models is often met with unsatisfying or ambiguous results. Aside from the inherent difficulty in conducting these experiments, the lack of a standard set of methodologies employed in these studies may be an impediment. This study was conducted to determine if the method employed in the sampling of soil solutes could influence the results of model validation attempts. A narrow pulse of KBr was uniformly applied to two 25‐m2 plots, one tilled and the other undisturbed, on a level Ulm clay loam (fine, montmorillonitic, mesic Ustollic Haplargid). Solute movement was then monitored for the next 388 d using replicated ceramic cup solution samplers at depths of 0.15, 0.30, 0.80, 1.20, 1.60, and 2.00 m and by the periodic removal of replicate soil cores in 0.05‐m increments to a maximum depth of 3.70 m. Overall, the methods yielded consistent information regarding the mean convective transport of Br−. Both methodologies indicated deeper and more rapid movement of Br− in the nontilled soil, although the shallow solution samplers appear to miss the most rapidly moving solute. By the conclusion of the experiment, the difference between the centers of mass of the Br− plumes in the tilled and nontilled soil was at least 0.6 m. The soil core and solution sampler methods appear to yield inconsistent measures of the solute dispersion but we attribute the differences to the effects of incomplete mass recovery and, we argue, follow naturally from the instrument window of the sampling methodology relative to the observed soil heterogeneity.
Analysis of Aggregate Fractal Dimensions and Aggregate Densities Back‐Calculated from Hydraulic Conductivity
Authors: Logsdon S. D. 
Published: July 2010

AbstractRecently, aggregate size distributions (ASDs) have been characterized by fractal dimension (D, i.e., slope of the log of cumulative aggregate number as a function of the log of aggregate size). To simplify the laboratory work, aggregates are often considered to have scale‐invariant density (ρ). The D describes the completely fragmented ASD after sampling and sieving the aggregates, but a bulk Dr describes an incompletely fragmented ASD in situ. The Dr requires an estimate of scale‐variant ρi for each class. Then the ASD may be used to determine pore distributions and hydraulic conductivity (K) of the soil. The objectives of this study were to start with K determinations to back‐calculate ρi, D, Dr, and scale‐invariant ρ, and compare these with measured ρ and D from measured ASDs taken near the locations of the K measurements. Back‐calculated ρi was not significantly different between class sizes for aggregates >2.8 to 5 mm, and the ρi differences between aggregate sizes 1.26 to 25.2 mm would be difficult to determine with the precision (0.03–0.1 g cm−3) of current methods for determining ρi. The calculated ρi and scale‐invariant ρ were all significantly less than measured ρ. The D from back‐calculated ASD were all greater than three, but they should have been less than the Dr from back‐calculated ASD, which were all less than three. The D and Dr from back‐calculated ASD were significantly different from D for measured ASD. Further study is needed to determine the relationship between ASD and K.
Elevated Atmospheric Carbon Dioxide Effects on Cotton Plant Residue Decomposition
Authors: Torbert H. A. , Prior S. A. , Rogers H. H. 
Published: July 2010

AbstractAssessing the impact of elevated atmospheric CO2 concentration on the global environment is hampered due to a lack of understanding of global C cycling. Carbon fixed within plant biomass ultimately enters the soil via plant residues, but the effects of elevated‐CO2‐grown plant material on decomposition rates and long‐term soil C storage are unknown. The objective of this study was to determine the decomposition rate of plant residues grown under an elevated CO2 environment as affected by soil type. Cotton (Gossypium hirsutum L. ‘Delta Pine 77’) samples were collected from a free‐air CO2 enrichment (550 µL L−1) experiment. The plant residues were incubated under ambient CO2 conditions to determine decomposition rates of leaves, stems, and roots and potential N and P mineralization‐immobilization in three soil series: a Blanton loamy sand (loamy siliceous, thermic Grossarenic Paleudult), a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudult), and a Houston clay loam (very fine, montmorillonitic Typic Chromudert). No significant difference was observed between plant residue grown under CO2 enrichment vs. ambient CO2 conditions for soil respiration or P mineralization‐immobilization. Significantly greater net N immobilization was observed during the incubation in all soil types for plant residue grown at elevated CO2. These results indicate that while decomposition of plant residue may not be reduced by CO2 enrichment, N dynamics may be markedly changed.
Potential Soil Respiration and Relationship to Soil Properties in Ridge Tillage
Authors: Liebig M. A. , Jones A. J. , Doran J. W. , Mielke L. N. 
Published: July 2010

AbstractDifferences in traffic and tillage intensity among positions in ridge tillage create distinctly different environments for microbial activity. This study was conducted to assess the impact of long‐term controlled wheel traffic on soil respiration in ridge‐till and to use correlation analysis to identify relationships between soil respiration and soil physical and chemical properties. Soil respiration was evaluated from 0 to 30 cm in one row, one tractor‐trafficked interrow, and one nontrafficked interrow of continuous corn (Zea mays L.) and continuous soybean [Glycine max (L.) Merr.]. Soil respiration was measured on disturbed samples at three levels of water‐filled pore space (WFPS) by gas chromatography for 25 d. Properties assessed included bulk density, soil strength, texture, aggregate‐size distribution, saturated hydraulic conductivity (Ksat), water retention characteristics, organic C, and total N. Soil respiration was greatest at 0 to 7.5 cm in each position and decreased significantly below that depth. Correlation analysis indicated microbial activity in ridge‐till varied spatially in relation to changes in the soil physical environment. Soil respiration was negatively correlated with bulk density at each WFPS. The Ksat was positively correlated with soil respiration at 0 to 7.5 cm for each WFPS. Under drier soil conditions, as exemplified by 47% WFPS, aggregates <1.0 mm and gravitational water were positively correlated with soil respiration at the 0 to 7.5 cm. Soil environments characterized by bulk density <1.4 Mg m−3 and Ksat >10 cm h−1 were associated with respiration rates >4 and 12 mg CO2‐C L−1 soil d−1, respectively.