bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Soil Type and Water Flux on Solute Transport
Authors: Vanderborght J. , Vanclooster M. , Mallants D. , Feyen J. , Gonzalez C. 
Published: July 2010

AbstractPrediction of solute transport in soils requires appropriate transport models and model parameters. The most suitable solute transport model and its parameters are likely to depend on both soil type and water flux. This dependency was investigated by means of transport experiments that were carried out in three different soils (Plaggept, Hapludalf, and Glossudalf) for two water application rates (0.5 and 1.0 cm d−1). Solute concentrations were measured during the transport experiment at six different depths in undisturbed soil monoliths (1.0‐m length, 0.8‐m i.d.) using time domain reflectometry (TDR). For each depth, parameters of two solute transport models, (i) the convective lognormal transfer function (CLT) model assuming stochastic‐convective solute transport or no solute mixing and (ii) the convective‐dispersive (CDE) model assuming complete solute mixing, were derived. The transport in the Plaggept and Hapludalf soil was better modeled as a stochastic‐convective process. Furthermore, solute transport in these two soils was very heterogeneous, resulting from considerable differences in local advection velocity. In the Glossudalf soil, solute transport was more homogeneous and characterized as a convective‐dispersive process. The heterogeneity of solute transport in both Plaggept and Hapludalf soils increased with the applied water flux. This increase was more pronounced in the Hapludalf soil, as the higher water flux resulted in a larger contribution of macropores to flow and transport of solutes.
Simulating Impact of Funnel Flow on Contaminant Sampling
Authors: Ju S.‐H. , Kung K.‐J. S. , Helling C. S. 
Published: July 2010

AbstractSoil‐solution sampling methods developed more than 50 yr ago are still routinely used to monitor the fate of contaminants in unsaturated soils. The measured results, expressed as a function of depth or time, are called breakthrough curves (BTC). In this paper, BTC from limited samples are called SBTC, while ABTC are the BTC from the entire soil profile and MBTC are mass‐flux‐based BTC. Conventionally, assumptions have been that: (i) ABTC and MBTC are identical; and (ii) SBTC would accurately indicate MBTC when enough samples are collected. In soil with preferential flow paths, such assumptions may be invalid. The objectives of this study were to: (i) determine whether increasing the total number of samples would make SBTC an accurate indicator of contaminant loading; (ii) determine whether ABTC and MBTC are identical; and (iii) explore how to obtain representative MBTC with only a limited number of samples. Numerical simulations were conducted in three sets of four, two‐dimensional hypothetical profiles with inclined layers that could trigger funnel‐type preferential flow paths. Soil‐solution samplers at four different spacings were placed at four depths in each profile. Simulated results indicate that ABTC always significantly underestimate MBTC. By increasing the total number of randomly located samples, SBTC will never accurately indicate MBTC. The SBTC could be modified to better estimate MBTC when preferential weight is assigned according to the local water flux.
Determining Nitrogen‐15 in Ammonium by Producing Nitrous Oxide
Authors: Laughlin R. J. , Stevens R. J. , Zhuo S. 
Published: July 2010

AbstractStandard procedures for determining 15N in the NH4+ fraction of 2 M KCl soil extracts convert NH4+ to N2 prior to isotope‐ratio mass spectrometry. We developed a new gas‐phase method for determining 15N in NH4+ by producing N2O. Producing N2O means that atmospheric contamination by N2 at natural abundance is not a problem. The method is more sensitive than other methods at lower enrichments, and as accurate and precise as other methods. Nitrous oxide is produced as a by‐product during the oxidation of NH4+ by alkaline OBr−. The reaction is catalyzed by Cu2+ and is pH‐dependent. The best practical conditions for producing N2O were when the NH3‐absorbing solution contained 0.005 M H2SO4 with 0.5 mM CuSO4, and when the molarity of the NaOH in the NaOBr was 10 M. Background N (0.20 µmol test−1) significantly diluted the theoretical enrichments for amounts of N <10 µmol test−1. Corrected enrichment values were accurate for amounts of NH4+‐N ≥1 µmol test−1. For amounts of NH4+‐N ≥1 µmol test−1, precision was determined with a CV of 5.6% at 0.10 atom % excess and with a CV of 0.3% at 10.00 atom % excess. The method is suitable for any matrix and has the potential for better performance if the background contamination could be lowered.
Parameterizing Temporal Changes in Aggregation in a Sludge Amended Soil
Authors: Rasiah V. , Biederbeck V. O. , Curtin D. , Zentner R. P. 
Published: July 2010

AbstractStatistical comparison of the changes in aggregate size distributions (ASD) with time among treatments in a given soil or among soils is difficult. The objective of this study was to compare the use of fractal dimension (D), geometric mean diameter (GMD), and alpha (α) parameters as indices to characterize the temporal changes in ASD of a soil subsequent to the incorporation of an oily waste sludge. Soil samples for dry and wet aggregate size distribution (DASD and WASD, respectively) measurements were collected from a loamy sand during a 4‐yr period following sludge incorporation. Sludge incorporation produced a continuous oil content, i.e., 0, 1.0, 1.5, 3.0, and 7.0%, variable in the soil (by mass). The wind erodible fraction (WEF; <0.84 mm) in the sludge treated plots decreased from 80 to 38% but increased with time to 78% 4 yr later. The reduction in WEF was reflected as gains in larger size fractions which decreased with time. The 4.76‐ to 8‐mm water stable aggregates in the sludge treated plots increased from 10 to 80% but decreased with time to 40% 4 yr later. An opposite trend was observed for smaller size aggregates. After sludge incorporation, the D for DASD and WASD decreased with increasing oil content and increased with time. An opposite trend was observed for GMD and α. Initial oil content and time of sampling accounted for 91% of the variability in DASD characterized by GMD, 89% by D, and 60% by α. Initial oil content and time accounted for 78% of the variability in WASD characterized by D and 67% by GMD. Our results indicate that the temporal changes in DASD can be characterized equally well by GMD and D and the changes in WASD by D.
Forest Management Effects on Surface Soil Carbon and Nitrogen
Authors: Knoepp Jennifer D. , Swank Wayne T. 
Published: July 2010

AbstractChanges in surface soil C and N can result from forest management practices and may provide an index of impacts on long‐term site productivity. Soil C and N were measured over time for five watersheds in the southern Appalachians: two aggrading hardwood forests, one south‐ and one north‐facing, undisturbed since the 1920s; a white pine (Pinus strobus L.) plantation planted in 1956; and two regenerating hardwood forests, a whole‐tree harvest in 1980, and a commercial sawlog harvest in 1977. Soils on harvested watersheds were sampled before and for ≈15 yr after harvest. Surface soil C concentration on the undisturbed watersheds varied significantly among sample years. Concentrations fluctuated on the south‐facing and decreased on the north‐facing watershed. The pattern for total N was similar. Total N decreased significantly on the north‐facing but was stable on the south‐facing watershed. In the white pine plantation, C increased while N concentrations decreased during the 20‐yr period. Soil C and N concentrations generally declined the first year following whole‐tree harvest. Fourteen years after cutting, C remained stable, while N was greater compared with reference watershed soils. The commercial sawlog harvest resulted in large increases in surface soil C and N concentrations immediately after cutting. Carbon levels remained elevated 17 yr following cutting. Our data suggest that the forest management practices examined do not result in long‐term decreases in soil C and N. However, the high interannual variation on all watersheds suggests that care must be taken in selecting control sites to determine long‐term treatment impacts.
Soil Microbial Biomass and Mineralizable Carbon of Water‐Stable Aggregates
Authors: Franzluebbers A. J. , Arshad M. A. 
Published: July 2010

AbstractBiophysical alterations of agricultural soils following adoption of zero tillage (ZT) deserve investigation in order to better understand the processes of soil organic C (SOC) sequestration and turnover. We determined the vertical distribution of soil microbial biomass C (SMBC), C mineralized in 24 d under standard conditions, and basal soil respiration (BSR) in five water‐stable aggregate classes. Four soils (loam, silt loam, clay loam, and clay) from the Peace River region of northern Alberta and British Columbia were sampled following 4 to 16 yr under comparison of conventional shallow tillage (CT) and ZT. Macroaggregates (>0.25 mm) had greater SMBC, more C mineralized in 24 d, and higher BSR than microaggregates at a depth of 0 to 50 mm. Differences between macro‐ and microaggregates in these properties decreased with soil depth. Carbon mineralized in 24 d and SMBC were 9 ± 9% greater (mean of four soils ± standard deviation among soils) under ZT than under CT in macroaggregates, but were 6 ± 11% lower in whole soil due to lower amounts in microaggregates under ZT than under CT. Macroaggregate‐protected SOC to a depth of 200 mm was 6.7 ± 1.9 g m−2 under CT and 9.8 ± 2.6 g m−2 under ZT. Soil organic C in macroaggregates, which had high concentrations of active pools of SOC, appeared to have been shunted into the more stable microaggregate fraction after disturbance with CT. Unlike in temperate, humid climates, decomposition of SOC during the passage from macro‐ to microaggregates may have been limited by the frigid, semiarid climate.
Monitoring Near‐Surface Soil Water Storage in Turfgrass using Time Domain Reflectometry and Weighing Lysimetry
Authors: Young M. H. , Wierenga P. J. , Mancino C. F. 
Published: July 2010

AbstractMonitoring near‐surface soil water content with time domain reflectometry (TDR) could improve our understanding of water movement in a daily irrigated crop. But, TDR field validation is needed using weighing lysimeters to assess actual changes in soil water storage. In this study, we test the hypothesis that vertically installed TDR probes can be used to measure evapotranspiration (ET) in a full‐cover turfgrass environment. This was done by directly comparing changes in soil water storage measured with TDR against changes in mass measured with weighing lysimeters. The TDR probes (200, 400, 600, and 800 mm long) were installed vertically in two weighing lysimeters. The TDR water content and lysimeter mass determinations were made every 30 min for a 28‐d period during daily irrigation intervals, and during a 6‐d irrigation interval. Average water contents increased with increasing probe length; e.g., 600‐ and 800‐mm probes yielded average water contents of 18.1 and 18.5%, vs. 14.8% for the 200‐mm probe. These differences reflect the lack of transpirational uptake from deeper soil layers. All TDR probes underestimated water added and lost compared with the lysimeter during daily irrigation, with shorter probes exhibiting larger differences than longer probes. However, when the irrigation interval was increased to 6 d, the longer TDR probes were more suited to measuring water loss; for example, the 200‐, 400‐, 600‐, and 800‐mm probes measured 40, 77, 78, and 96% of the water loss recorded by the lysimeter, which only records ET. This shows that increasing amounts of water were taken up from deeper layers as the soil dried.
Time‐Dependent Changes in Pedogenic Processes on Marine Terraces in Coastal Oregon
Authors: Langley‐Turnbaugh S. J. , Bockheim J. G. 
Published: July 2010

AbstractVery little is known regarding soil‐forming processes on marine terraces along the Pacific Coast. This study examined a soil chronosequence on an elevated marine terrace sequence in south‐coastal Oregon in order to investigate changes in soil‐forming processes with time. The soils range in age from 80 000 to >500 000 yr, and with increasing age classify as Inceptisols, Spodosols, and Ultisols. Relevant pedogenic processes were studied using morphological properties; extractable Fe, Al, and Si; dissolved Fe, Al, and Si in soil solution; and micromorphology. Podzolization and in situ weathering of silt to clay are the dominant and contemporary processes on the young and intermediate‐aged terraces, and argilluviation and clay neoformation are dominant processes on the older terraces. Evidence for podzolization includes organically complexed Fe and Al that peak in Bs horizons and mineral grains coated by Fe as evidenced in thin section. In addition, up to 93% of the Fe and Al in solution in the E horizons is retained in the Bs horizons. In situ weathering of fine silt in the younger soils is indicated by irregular depth trends in fine silt/total silt ratios. Argilluviation is manifested by clay films observed in the field and in thin section, which increase in thickness and abundance with time. Evidence for clay neoformation includes the retention of up to 54% of dissolved silica in the Bt horizons of the older soils. Podzolization and in situ weathering decrease in importance with time, and argilluviation and clay neoformation become increasingly more significant.
Hydraulic Characteristics of Organomodified Soils for Use in Sorptive Zone Applications
Authors: Rakhshandehroo G. Reza , Wallace Roger B. , Voice Thomas C. , Boyd Stephen A. 
Published: July 2010

AbstractThe sorption capabilities of subsoils for organic contaminants can be enhanced by modification of soil clays with cationic surfactants. The use of these organomodified soils to establish permeable sorptive zones has been suggested as a potential means for attenuating the migration of contaminant plumes. The hydraulic feasibility of sorptive zones was evaluated by measuring the hydraulic conductivities and porosities of both modified and unmodified soils at different effective stresses when permeated with water. Samples with 6, 12, 18, and 24% fines content were prepared and batch treated with hexadecyltrimethylammonium (HDTMA) to 80% of their cation‐exchange capacities. Under the first load (24 kPa), all treated soils showed higher conductivities and similar or higher porosities than untreated ones. Higher loads decreased the difference in porosity between treated and untreated soils while increasing the difference between their conductivities. At the highest load (766 kPa), treated samples were 5 to 124 times more conductive than untreated ones depending on their clay contents. Differences in conductivities were explained in terms of the role of treated and untreated clays in controlling initial effective pore size and its change during consolidation. Creation of organomodified sorptive zones by batch soil processing is shown to be hydraulically feasible as evidenced by a marked increase in the conductivities of all treated samples compared with untreated ones. In addition, an increase in the sorptive capacity of the zone could potentially be achieved, without experiencing a loss in conductivity, by increasing the clay content during modification.
Infiltration and Redistribution of Perchloroethylene in Stratified Water‐Saturated Porous Media
Authors: Hofstee C. , Dane J. H. , Walker R. C. 
Published: July 2010

AbstractAlthough infiltration, redistribution, and drainage of dense nonaqueous‐phase liquids (DNAPLs) in water‐saturated soils and aquifers are known to be sensitive to stratifications of the solid phases of the porous media, little experimental evidence is available to explain the behavior of DNAPL movement. To improve our understanding of DNAPL movement under these conditions, physical simulations were conducted with various perchloroethylene (PCE) spills in initially water‐saturated, stratified porous media in nominally one‐dimensional glass columns and in an intermediate scale, nominally two‐dimensional laboratory flow container. The columns and flow container were packed with two distinct layers of coarse sand, with a fine sand layer in between. Volumetric water and DNAPL contents, as well as bulk densities, were determined with a dual‐energy gamma radiation system. To obtain additional information required for the explanation of the displacement processes, in‐ and outflow rates of water and PCE were measured during each experiment. In the sand columns, PCE accumulated on top of the fine layer, while in the flow container, considerable lateral movement was observed just above the fine sand layer. In general, these phenomena were attributed to the small conductivity values of the fine layers relative to those of the coarse layers rather than to displacement pressures not being exceeded. Overall our results suggest that in field situations, continuous PCE spills are more likely to penetrate horizontal fine layers than short intermittent spills.
Modeling Soil Water Balance of a Maize‐Sorghum Sequence
Authors: Maraux F. , Lafolie F. 
Published: July 2010

AbstractModeling plant‐soil‐water interactions for long periods of time is important for crop management strategies. Because it is difficult to assess soil hydraulic properties, mechanistic models are rarely used for simulating soil water balance. Models less complicated with respect to soil water flow are more often used. Although simple water balance models are easy to use, however, they do not always provide good approximations of plant transpiration and soil‐water status. Our objectives were to test the ability of a model, mechanistic with respect to soil‐water flow and empirical for soil‐plant and plant‐atmosphere interactions, to predict soil‐water balance components for long periods of time when input parameters are measured or estimated independently. A data set gathered in Nicaragua during several months was used for this purpose. Soil hydraulic properties were measured independently and parameters taken from the literature were used for plant processes modeling. The model predicted reasonably well the soil‐water balance for a maize (Zea mays L.)‐sorghum [Sorghum bicolor (L.) Merr.] sequence and for a grass sod. Periods of crop water stress were also correctly reproduced. Adjusting some plant parameters slightly increased the goodness of the predictions. Results indicated that plant water uptake was not well predicted when topsoil layers were dry and deep soil layers wet. In addition, the model predicted the upward water flux into the root zone and its important contribution to plant water uptake. During drought periods, the upward water flux reached 2 mm d−1 while the actual evapotranspiration of the crop was between 2 and 4 mm d−1.
Soil Water Dynamics Using Multisensor Capacitance Probes in Nontraffic Interrows of Corn
Authors: Starr J. L. , Paltineanu I. C. 
Published: July 2010

AbstractWater is often the primary factor limiting plant growth, and it is the primary agent for moving plant nutrients and pesticides to streams and groundwater. This study was conducted to assess the capabilities of recently developed multisensor capacitance probes and monitoring systems to measure the dynamics of soil water content under long‐term field‐scale conditions, and to quantify in real time the spatial variation of soil water content under plow‐tillage (PT) and no‐tillage (NT) corn (Zea mays L). Probes were placed at eight nontraffic interrow locations, with cable lengths ranging from 25 to 125 m, on a 0.5‐ha field site. The capacitance sensors were centered at four soil depths and readings were taken every 10 min by the data‐logging system. Real‐time dynamics of soil water change following 82 mm of rainfall in the spring were used to identify the apparent water‐holding capacity within the sensor depths (5–55 cm) under NT as 171 mm and 155 mm under PT. Rates of soil water loss with a full canopy of corn were 90% of high evapotranspiration (ET) demand. Breaking points were observed and calculated between high and low rates of soil water loss, under full canopy and high ET demand. Changes from high to low rates of soil water loss were more evident in PT plots (62% reduction) than in NT plots (46% reduction). At the end of three drying cycles during the growing season, there was an average of 37 mm more water (5–55‐cm soil depth) under NT than PT. The multisensor capacitance probes proved to be highly sensitive and robust for field‐scale, real‐time, soil water research.
Carbon, Nitrogen, and Sulfur Pools in Particle‐Size Fractions as Influenced by Climate
Authors: Amelung W. , Zech W. , Zhang X. , Follett R. F. , Tiessen H. , Knox E. , Flach K.‐W. 
Published: July 2010

AbstractThe response of soil organic matter (SOM) dynamics to climate change may be deduced from changes in the distribution of SOM among different C pools. The distribution of soil organic carbon (SOC), total N, and total S in particle‐size fractions were measured to assess the influences of climate. Clay (<2 µm), silt (2–20 µm), fine sand (20–250 µm), and coarse sand (250–2000 µm) fractions were obtained from composite soil samples from the top 10 cm of 21 native grassland sites along temperature and precipitation transects from Saskatoon, Canada, to southern Texas, USA. The clay fraction contained about 43% of the total SOC, 56% of the total N, and 62% of the total S. The SOC and total‐N concentrations in the clay fraction, relative to those in the bulk soil, increased significantly across sites with increasing annual temperature, decreasing annual precipitation, and decreasing clay content (multiple R2 = 0.80*** [significant at P = 0.001] for SOC and 0.83*** for N); the concentration of SOM in the fine sand fraction showed the opposite trends. Principal axis component analyses confirmed that both clay and fine sand fractions comprised sensitive SOC and N pools related to climate, whereas S seemed to be controlled by factors other than those regulating the dynamics of SOC and N. These results suggest that SOM is preferably decayed from pools of the fine sand fractions with increasing temperature, resulting in a relative enrichment of SOM stabilized on clay.