bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ionic Strength Effects on Sulfate and Phosphate Adsorption on γ‐Alumina and Kaolinite: Triple‐Layer Model
Authors: He L. M. , Zelazny L. W. , Martens D. C. , Baligar V. C. , Ritchey K. D. 
Published: July 2010

AbstractIt is known that PO4 is retained by soils through ligand exchange, i.e., inner sphere complexation, but the mechanism for SO4 adsorption at the mineral‐water interface has been in debate. By studying the effects of ionic strength on ion adsorption, it is possible to distinguish between inner and outer sphere ion surface complexes. This study was conducted to evaluate ionic strength effects on SO4 and PO4 adsorption on γ‐Al2O3 and kaolinite at varying solution pH (3–11), and to infer SO4 and PO4 adsorption mechanisms at the mineral‐water interface. The adsorption of SO4 on γ‐Al2O3 and kaolinite decreased monotonically with increasing solution pH and was markedly reduced by increasing the concentration of background electrolyte. On the other hand, PO4 adsorption on γ‐Al2O3 and kaolinite increased from pH 3 to 4 and decreased from pH 6 to 11, with an adsorption plateau between pH 4 and 6. Effects of change in ionic strength on PO4 adsorption varied with pH. At low pH, PO4 adsorption demonstrated a slight decrease with increasing ionic strength, whereas at high pH, PO4 adsorption increased slightly with increasing ionic strength, resulting in a crossover point where there was no ionic strength effect. The triple‐layer model (TLM) was applied to model the adsorption of SO4 and PO4 with both inner and outer sphere complexes using the FITEQL 3.1 computer program. Sulfate adsorption was better modeled by assuming outer sphere complex formation, while PO4 adsorption was better modeled by assuming inner sphere complex formation.
Combination Probe for Nitrogen‐15 Soil Labeling and Sampling of Soil Atmosphere to Measure Subsurface Denitrification Activity
Authors: Nielsen Tommy Harder , Well Reinhard , Myrold David D. 
Published: July 2010

AbstractInvestigations of subsoil denitrification have been hampered by the difficulty in adapting traditional methods for measuring denitrification in surface soils to subsoils. In this study, we present, and test, a combination probe constructed to detect denitrification in the vadose zone. The probe was designed to label a volume of the subsoil with 15NO‐3 and subsequently to collect gas samples from which the denitrifying activity in the surrounding soil can be estimated by isotopic analysis of N2. Gas samples were collected from the labeled soil volume by use of He‐flushed silicone tubing having high permeability for gases. No mass flow of gases through the soil was caused by the procedure. Nitrogen gas diffusing into the tubing can be collected after equilibration periods of 15 to 20 min. A combined tensiometer and sampler for dissolved ions was built into the probe to have direct estimates of soil water potential together with information about the 15N atom fraction of the dissolved NO‐3 in the surrounding soil. The probe was tested under laboratory conditions. The probe introduced 15NO‐3 into a roughly spherical volume of soil with a symmetric distribution of 15NO‐3. Estimates of the 15N atom fraction of the NO‐3 undergoing denitrification based on gas samples agreed favorably with destructive sampling of NO‐3. The accumulation of N2 derived from denitrification was consistent with expected trends and, along with computer simulations and 15N mass balance methods, was used to calculate denitrification rates. These different estimates of denitrification agreed well. This combination probe shows promise for measuring denitrification in subsoil.
Effect of Soil Water Content Variation on the Least Limiting Water Range
Authors: da Silva Alvaro Pires , Kay B. D. 
Published: July 2010

AbstractThe least limiting water range (LLWR), a proposed structural quality index, is the range in soil water content within which plant growth is least limited by water potential, aeration, and mechanical resistance. This study tested the hypotheses that the frequency of the soil water content falling outside the LLWR (pout) increases with decreasing LLWR and that the relation is influenced by tillage, position (row vs. interrow), and climatic conditions. Thirty‐two paired sampling sites were located along two parallel transects in a side by side comparison of no‐till and conventional tillage. The transects crossed three soil types: Aquic Hapludalf, Psammentic Hapludalf, and Typic Hapludalf. The LLWR was calculated for the 0‐ to 20‐cm depth at row and interrow positions. The site was planted to corn (Zea mays L.) and the study lasted three growing seasons. Logistic regression analysis, pout = exp(b0 + b1 LLWR)/[1 + exp(b0 + b1 LLWR)], showed that pout was negatively related to LLWR (R2 = 0.72, P > 0.01), regardless of weather, tillage, or position. Values of pout under no‐till were lower than under conventional tillage and the interrow position had a lower pout than the row position. The parameter b1 did not vary across weather, tillage, or position but b0 was influenced by these parameters. The analyses supported the hypothesis and emphasized the impact on pout of factors unrelated to structure.
Fractal Characterization of Soil Aggregation and Fragmentation as Influenced by Tillage Treatment
Authors: Perfect E. , Blevins R. L. 
Published: July 2010

AbstractParameters are needed to quantify tillage‐induced changes in soil structure. Our objective was to see if fractal parameters from ped mass‐ and number‐size relations could be applied to quantify such changes. Soil from long‐term conventional (moldboard plow, MP, plus two passes with a disk harrow, DH) and no‐till (NT) plots on a Maury silt loam (fine, mixed, mesic Typic Paleudalf) was air dried and sieved into six size classes ranging from 0.5–1 to 16–31.5 mm. The mass percentage and weight of 100 peds in each size class were used to calculate the mean mass per ped and number of peds as a function of scale. Fractal equations were then fitted to both data sets (R2 always ≥ 0.99). The resulting parameter estimates were Dm (mass fractal dimension) and km (mass of an aggregate of unit length) for the mass‐size relation, and Dt (fragmentation fractal dimension) and kf (number of fragments of unit length) for the number‐size distribution. Significant tillage effects were observed for Dm, Df, and kf. The Dm increased from 2.88 for NT to ≥ 2.94 for MP and DH, suggesting differential compaction of large aggregates by plowing and disking. The Df was always less than the Dm, as predicted by theory. Soil fragmentation was least for NT (Df = 2.02) and greatest for MP (Df = 2.55); for DH, the Df = 2.15 suggesting that disking broke up large fragments and/or coalesced small fragments following plowing. The kf, which was shown to be nonlinearly related to the Df, was least for MP and greatest for NT. Similar studies on other soils are needed to test the general applicability of these fractal relations to soil structure.
Short‐Term Effects of Cover Crop Incorporation on Soil Carbon Pools and Nitrogen Availability
Authors: Hu S. , Grunwald N. J. , van Bruggen A. H. C. , Gamble G. R. , Drinkwater L. E. , Shennan C. , Demment M. W. 
Published: July 2010

AbstractWinter cover crops are increasingly used to maintain water quality and agroecosystem productivity. Cover crop incorporation influences transient soil microbial dynamics and nutrient availability at an early growth stage of subsequent crops. Short‐term (≤35 d) effects of cover crop incorporation on soil C pools and N availability were evaluated using sandy loam soils from organically and conventionally managed fields. Field and incubation experiments were designed to investigate whether cover crop incorporation had differential effects on C pools and how they were related to N mineralization. Labile C pools (soil carbohydrates and soil microbial biomass C [SMBC]) and coarse organic debris (COD) increased two‐ to threefold, whereas total organic C increased by only 20% by Day 7 after incorporation. The COD decreased faster than other C pools and best predicted SMBC (P < 0.0001). A rapid decrease in SMBC after Day 21 was accompanied by an increase in available N. Discriminant analyses revealed that organic soils were distinct from conventional soils by their higher total C, N, and SMBC, and lower available N, but cover crop incorporation obscured the distinction in the first 14 d. Residue decomposition was slightly faster in organic soils than in conventional soils at the early stage (3–4 wk), but >30% of N in cover crop residues was mineralized in both soils by Day 35 after incorporation, suggesting that manipulations of soil microbial dynamics and N mineralization in the short term can be of particular significance in synchronizing N release with the need of subsequent crops.
Accelerated Diffusion Methods for Inorganic‐Nitrogen Analysis of Soil Extracts and Water
Authors: Khan S. A. , Mulvaney R. L. , Mulvaney C. S. 
Published: July 2010

AbstractThe major limitation of diffusion methods for N analysis is the time required to obtain the results — typically from one to several days. Methods were developed that involve a much shorter period for diffusion. In these methods, 10‐ to 100‐mL samples of 2 or 4 M KCl soil extract or water were treated with MgO, or MgO plus Devarda's alloy, in a 473‐mL (1‐pint) wide‐mouth Mason jar to liberate NH4‐N, NO3‐N, and/or NO2‐N as NH3. The jar was placed on an electric griddle maintained at 45 to 50°C. Gaseous NH3 was collected in 5 mL of H3BO3 indicator solution in a petri dish attached to the Mason jar lid, for quantitative determination by acidimetric titration. Complete recovery of 4 mg of N was achieved from 10 or 20 mL in 1.5 to 5 h. Recovery from 50 or 100 mL was complete in 5 to 8.5 h with 1 to 2 mg of N. The methods permit 15N analysis of the diffused NH3‐N. Isotopic analyses of labeled soil extracts were accurate to within 3%, as determined by isotope‐dilution calculations. Diffusions from 10 to 50 mL were subject to very little, if any, interference from decomposition of alkali‐labile organic‐N compounds.
Nitrogen‐15 Recovery and Release by Rye and Crimson Clover Cover Crops
Authors: Ranells Noah N. , Wagger Michael G. 
Published: July 2010

AbstractA grass‐legume biculture may be preferred over a legume monoculture cover crop due to the scavenging ability of a grass species, especially when high residual soil N levels are present following summer droughts in the Atlantic Coastal Plain. Rye (Secale cereale L.) and crimson clover (Trifolium incarnatum L.) were grown in monoculture and as a biculture in a 2‐yr field experiment on a Typic Kandiudult to assess cover crop recovery of fertilizer 15N and the subsequent corn (Zea mays L.) uptake of cover crop residue 15N. Potassium nitrate labeled with 10 atom % 15N was applied to microplots at 50 kg N ha‐1 1 wk after seeding the cover crops, which were monitored for recovery of fertilizer 15N. Labeled residue was placed in a new microplot to monitor release of residue 15N and its recovery by corn. Averaged across both years, rye monoculture recovered 39% of the labeled 15N fertilizer compared with 19% in the rye‐crimson clover biculture and 4% in the crimson clover monoculture. Following corn harvest and averaged across both years, total recovery of 15N fertilizer from the original microplots (cover crop, corn biomass, and soil N) was 29% for crimson clover, 75% for rye, 55% for rye‐crimson clover biculture, and 20% for the native winter weeds. In 1993, corn recovery of residue 15N was lowest in the rye monoculture (4%) compared with other treatments (20–35%). Results indicated that a rye‐crimson clover biculture was capable of recovering greater residual 15N than a crimson clover monoculture, but less than rye monoculture.
Automated Chamber Measurements of Methane and Nitrous Oxide Flux in a Flooded Rice Soil: I. Residue, Nitrogen, and Water Management
Authors: Bronson K. F. , Neue H.‐U. , Abao E. B. , Singh U. 
Published: July 2010

AbstractMethane and N2O are gases that are several times more radiatively active than CO2. It is well known that flooded rice (Oryza sativa L.) soils are a globally important source of atmospheric CH4. Mitigation strategies for CH4 flux, such as mid‐season drainage, might have the opposite effect on N2O emissions. An automated chamber system at the International Rice Research Institute in the Philippines measured CH4 and N2O fluxes from flooded rice and fallow rice fields essentially 24 h a day between December 1992 and April 1994. This period included two irrigated dry rice‐growing seasons (DS) and one wet rice‐growing season (WS). Nitrous oxide fluxes were generally barely detectable during the growing seasons, but small peaks (maximum 3.5 mg N2O‐N m‐2 d‐1) appeared after N fertilizer applications. Methane fluxes, on the other hand, were evident throughout the rice‐growing seasons. Organic matter additions as straw (5.5 t ha‐1, dry) or green manure (GM; Sesbania rostrata L.; 12 t ha‐1, wet) stimulated CH4 flux severalfold. Seasonal CH4 flux with ammonium sulfate (AS) was one‐fourth to one‐third the flux with urea. During the DS, however, the seasonal N2O flux was 2.5 times higher with AS than with urea. Mid‐season drainage (2‐wk duration) at either mid‐tillering or panicle initiation was very successful in suppressing CH4 flux up to 60%. However, N2O flux increased sharply during the drainage period at mid‐tillering until reflooding, when it dropped back to near zero.
Automated Chamber Measurements of Methane and Nitrous Oxide Flux in a Flooded Rice Soil: II. Fallow Period Emissions
Authors: Bronson K. F. , Neue H.‐U. , Abao E. B. , Singh U. 
Published: July 2010

AbstractMethane and N2O are radiatively important gases that are emitted from waterlogged soils. Automated chamber measurements of CH4 and N2O fluxes were carried out at the International Rice Research Institute in the Philippines in flooded rice (Oryza sativa L.) and fallow rice fields 24 h a day between December 1992 and April 1994. This period included three 5‐ to 11‐wk rainfed fallow periods. During the first two fallows, the soil was generally aerobic, and moderate amounts of NO3 accumulated (7–20 kg NO3‐N ha‐1). Moderately high, continuous N2O fluxes were evident during these two fallow periods. This N2O was apparently emitted during nitrification of mineralized organic N in the topsoil and possibly from denitrification in the wet subsoil. Nitrous oxide fluxes were highest (up to 80 mg N2O‐N m‐2 d‐1) immediately after rainfalls >20 mm, and following the establishment of flooding for rice at the end of the fallows. Acetylene inhibition in intact cores at these times showed that more N2 was produced than N2O. Denitrification of accumulated NO3 was therefore occurring after the wetting events. Methane emissions were generally absent during the fallow periods. Two exceptions were immediately after rice harvest and 1 to 2 wk after the establishment of the permanent flood. Following flooding and green manure (GM; Sesbania rostrata L.) incorporation, CH4 fluxes appeared within 7 d. During the third fallow period, which was unusually wet, no NO3 accumulated in the soil. Nitrous oxide emissions were not significant, and low levels of CH4 fluxes persisted throughout this fallow period. This study demonstrates that rice soils in the fallow periods can be significant sources of N2O, and during wet fallow seasons, important sources of CH4 as well.
Soil Solution Electrical Conductivity Measurements under Transient Conditions Using Time Domain Reflectometry
Authors: Persson Magnus 
Published: July 2010

AbstractSeveral studies have shown that time domain reflectometry (TDR) can be used to measure water content and solute concentration during steady‐state experiments with constant soil water content. Few studies have been carried out to identify the relationship between bulk electrical conductivity (σa) and soil solution electrical conductivity (σw) to be used for transient conditions with varying water content. In this study, a single TDR probe was calibrated and found to accurately measure water content and σa. The σa measurements were fitted to σw using several previously published models. The accuracy of the σa and σw measurements increased with σa; however, the error in the σw estimation was <10% for σa higher than 5.7 mS m−1. The calibration was verified in a large sand column; σa measurements were fitted to σw measured in soil solution extracted with suction samplers. The calibration was also used in a transient solute transport experiment. If not accounted for, the temperature effects of the water content measurement introduce significant errors in the σw estimations.
Spatial Series Analysis of Horizontal Cores to Characterize Tracer Patterns in Soil Profiles
Authors: Powers W. L. , Shea P. J. , Troyer W. , Verhoeff R. L. , Parkhurst A. M. 
Published: July 2010

AbstractSurface topography, plant canopy, plant root distribution, and soil preferential flow paths cause variability in downward movement of agrichemicals in soil. To better understand this variability, tracers are often applied to the soil surface and their signatures (concentration patterns) are examined. To characterize Br− signatures within a Crete silt loam soil (fine, montmorillonitic, mesic Pachic Argiustoll), potassium bromide was applied to the soil surface at 200 kg ha−1. Four sets (two sets in June and two sets in August) of four 6.1‐m horizontal cores were taken in a vertical plane, perpendicular to corn plant rows at 20‐, 40‐, 80‐, and 120‐cm depths. Each 6.1‐m core was divided into 120 5.1‐cm sections and analyzed for Br−. Spatial series analyses were used to identify deterministic and combined deterministic‐stochastic models that described the cyclic nature of Br− concentrations at each depth. Periods for these sinusoidal cycles generally corresponded to the distance between plant rows or the distance between the wheel tracks of field equipment.
Immobile Water Content and Mass Exchange Coefficient of a Field Soil
Authors: Casey F. X. M. , Horton R. , Logsdon S. D. , Jaynes D. B. 
Published: July 2010

AbstractDetermining the preferential flow characteristics of a soil is important because agrichemicals can contaminate groundwater via preferential flow pathways. A model that predicts solute transport due to preferential flow is the mobile‐immobile solute transport model, which partitions the total water content (θ, m3 m−3) into a mobile fraction (θm) and an immobile fraction (θim). Recently, an in situ method was proposed for determining the mobile‐immobile model parameters of θim and mass exchange coefficient (α) between the fractions by using a tension infiltrometer to apply a series of four fluorobenzoate tracers. The objective of this study was to test the in situ technique at 47 sites along a transect in a ridge‐till corn (Zea mays L.) field of Nicollet soil (fine‐loamy, mixed, mesic Aquic Hapludoll). The immobile fraction (θim /θ) ranged from 0.394 to 0.952 with a median of 0.622. The mass exchange coefficient ranged from 0.000237 to 0.00481 min−1 with a median of 0.00123 min−1. These values are similar in magnitude and range to values reported by other investigators, and they follow the same relationships. The values of θim/θ and α along the transect indicated no obvious spatial trends or spatial correlations. Significant linear correlations did exist between α and soil water flux, α and θim, and θ and θim.
Soil Salinization Processes in Rice Irrigation Schemes in the Senegal River Delta
Authors: Ceuppens J. , Wopereis M. C. S. , Miézan K. M. 
Published: July 2010

AbstractSoil salinization constitutes a major threat to irrigated agriculture (mainly rice, Oryza sativa L.) in the Senegal River Delta. It is generally hypothesized that salinization is caused by (i) capillary rise from a saline water table and (ii) concentration of salts in the field due to lack of adequate drainage facilities. The impact of field water management and rice cropping intensity on salinization in the Delta was determined using an electromagnetic conductivity meter (Geonics EM38). More than 4000 measurements were made in 40 rice fields on a typical heavy clay soil (Vertic Xerofluvent). Thirty EM38 measurements per field (0.25 ha) estimated average field soil salinity with a relative error of 20%. A multiple linear regression model based on EM38 readings explained 60 to 75% of the variability in conductivity of 1:5 saturation extracts at 0‐ to 5‐, 10‐ to 15‐, and 30‐ to 35‐cm depths. Higher cropping intensity limited upward salt transport from the water table. Average horizontal and vertical EM38 measurements increased in the following order: two rice crops per year with drainage: 0.73 and 0.98 dS m−1; one rice crop per year with drainage: 1.26 and 1.76 dS m−1; one rice crop per year without drainage: 2.23 and 2.98 dS m−1; and abandoned fields: 4.77 and 4.29 dS m−1. Results indicate a beneficial effect of flooded rice on salinity for this type of heavy clay soil. Irrigation development in the area needs to be accompanied by monitoring of water table depth.
Changes in Soil Organic Matter under Different Tillage and Rotation: Mathematical Modeling in ecosys
Authors: Grant R. F. 
Published: July 2010

AbstractReductions in both tillage and fallowing may increase soil organic C. The effects of tillage and fallowing on soil C could be estimated under site‐ and climate‐specific conditions by mathematical modeling. The simulation model ecosys predicts changes in soil C by calculating C added through fixation by plant communities and C lost through oxidation by microbial communities. During a 14‐yr simulation of a field experiment in a semiarid environment, ecosys predicted that 18 and 20 g m−2 yr−1 more C would be sequestered in the upper 0.15 m of soil in continuous wheat (W‐W; triticum aestivum L.) than in wheat‐fallow (W‐F) under conventional tillage (CT) and no tillage (NT), respectively. During the same period, ecosys predicted that 14 and 12 g m−2 yr−1 more C would be sequestered in the upper 0.15 m of soil under NT than under CT in W‐W and W‐F, respectively. These increases were compared with those measured from the field experiment of 9 and 19 g m−2 yr−1 in W‐W than W‐F under CT and NT, respectively, and of 13 and 4.5 g m−2 yr−1 under NT than CT in W‐W and W‐F, respectively. The sensitivity of simulated changes in soil C to doubled atmospheric CO2 and a 3 or 6°C increase in air temperature was then tested. Similarity in the direction and magnitude of simulated and measured changes in soil C lend initial support to model hypotheses. However, there are some issues concerning the modeling and measurement of soil C that require further clarification.