bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Rapid Flow Paths for Nitrogen Transformation in a Forest Soil A Field Study with Micro Suction Cups
Authors: Hagedorn Frank , Mohn Joachim , Schleppi Patrick , Fl u ¨ hler Hannes
Published: July 2010

Preferential flow is a common phenomenon in soils. This study was conducted to investigate the significance of rapid flow paths for N transformation in a forested Humaquept in central Switzerland. Fifty micro suction cups, each with a surface area of 12 mm2, were installed in a regular grid in the uppermost 5 cm. First, the location of each “microcup” relative to main flow paths was estimated based on the response to applications of a dye, SO2−4, and Cl− Then, a N‐addition experiment was carried out to study the N transformation at locations along flow paths and within the soil matrix. Only 23 of 50 microcups responded to the application of the dye within the first 24 h, which indicates that a large portion of the soil volume is not in contact with the infiltrating rainwater. Those microcups which responded to the added dye were regarded to be located along flow paths. At depths below 2 cm, under temporarily reducing conditions, sampling locations in or near flow paths had higher NO−3 concentrations (20–25 μM) than those of the soil matrix (below 12 μM). Within 24 h after a simulated rainfall, the ratio decreased more in the flow paths (between −2.4 and −4.9 mol mol−1) than in the soil matrix (−0.7 to −0.8 mol mol−1), which indicates an enhanced denitrification at these locations. In the subsequent dry period, nitrification started 2 d earlier and was more pronounced along flow paths. The results of this study suggest that flow paths are microhabitats with an increased N transformation compared with the soil matrix.
Influence of Nitrate and Phosphorus Loading on Denitrifying Enzyme Activity in Everglades Wetland Soils
Authors: White J. R. , Reddy K. R.
Published: July 2010

There has been recent concern about the impact of increased nutrient loading on the northern Everglades ecosystem. We investigated the spatial and temporal distribution of denitrifying enzyme activity (DEA) along a P‐enrichment gradient in the Water Conservation Area 2A (WCA‐2A) and determined the effects of added P and NO−3on DEA. The DEA in soil and detritus layers was measured under anaerobic conditions four times during 2 yr, using the acetylene blockage technique. The DEA ranged from 0.004 to 7.75 mg N2O–N kg−1h−1Highest rates of DEA were found in the detritus and surface (0–10 cm) soils, and rates decreased exponentially with increasing distance from the surface‐water inflow point, where nutrients are loaded to the wetland. Nitrate was found to be limiting, while the addition of P had no effect on the distribution of DEA in these soils. There was a seasonal effect on DEA, with higher activity observed during the summer when temperatures and hydraulic and nutrient loading were highest. Soils from outside the impacted zone demonstrated denitrifying potentials, within 10 h when spiked with inflow concentrations of NO−3, similar to DEA of soils from within the impacted zone. This suggests that soils from outside the impacted zone can increase denitrification rates when exposed to higher NO−3concentrations in a relatively short time. Agricultural drainage water discharge, and consequent NO−3loading, has created a zone of elevated DEA proximal to the S‐10C surface‐water inflow point in WCA‐2A.
Effects of Soil Organic Matter on the Kinetics and Mechanisms of Pb(II) Sorption and Desorption in Soil
Authors: Strawn Daniel G. , Sparks Donald L.
Published: July 2010

To improve predictions of the toxicity and threat from Pb contaminated soil, it is critical that time‐dependent sorption and desorption behavior be understood. In this paper, the sorption and desorption behavior (, ) of Pb in a Matapeake silt loam soil (Typic Hapludult) were studied by stirred‐flow and batch experiments. In addition, we studied the effects of soil organic matter (SOM) on sorption and desorption behavior by treating the soil with sodium hypochlorite to remove the SOM fraction, and using a soil with six times as much SOM (St. Johns loamy sand [Typic Haplaquods]) as the Matapeake soil. Lead sorption consisted of a fast initial reaction in which all of the Pb added to the stirred‐flow chamber was sorbed. Following this initial fast reaction, sorption continued and appears to be rate limited (indicated by a decrease in the outflow concentration when the flow rate was decreased, or when the flow was stopped). The total amount of Pb sorbed was 102, 44, and 27 mmol kg−1 for the St. Johns soil and the untreated and treated Matapeake soils, respectively. Desorption experiments were conducted on the soils with the background electrolyte as the eluent in the stirred‐flow chamber. In the St. Johns soil only, 32% of the total sorbed Pb was desorbed, while 47 and 76% of the sorbed Pb was released from the untreated and treated Matapeake soil, respectively. The correlation between SOM in the soils, and the percentage Pb desorbed from the soils suggests that SOM plays an important role in slow desorption reactions of Pb from soil materials. Aging experiments in which sorbed Pb was incubated for 1, 10, and 32 d showed that sorption incubation time had no effect on Pb desorption behavior. Analysis of the treated and untreated Matapeake soils by x‐ray absorption fine structure (XAFS) spectroscopy revealed that the local atomic structure of sorbed Pb is distinctly different in the two samples. In the soil treated to remove SOM, the data were well represented by theoretical models using O, Si, and Pb backscattering atoms. In the untreated soil, the XAFS data were best described by O and C backscatterers. These XAFS results confirm that the sorption mechanisms in the two systems are different.
Soil Organic Matter Pools and Their Associations with Carbon Mineralization Kinetics
Authors: Alvarez R. , Alvarez C.R.
Published: July 2010

The labile component of soil organic matter (SOM) plays an important role in short‐term nutrient turnover. Our objectives were (i) to establish the relationships between carbon in soil density fractions with carbon mineralization and the microbial biomass under contrasting conditions, (ii) to compare the goodness of fit of different mathematical models to describe carbon mineralization, and (iii) to evaluate the relationships of the SOM pools and the mineralization parameters estimated by the best kinetic model. Twenty‐eight soil samples were collected from a fine, illitic, thermic Typic Argiudoll localized in Argentina. These samples differed in the soil management (pasture and agriculture), tillage systems (chisel tillage, plough tillage, and no‐tillage), crop rotation, or depths. Microbial biomass was highly correlated with total carbon and carbon in the SOM light density fraction (density < 1.59 g mL−1) but less strongly correlated to medium (density 1.59–2.0 g mL−1) and heavy (density > 2.0 g mL−1) soil fractions. Carbon in the soil light fraction was strongly related to the carbon mineralized at 10 and 160 d of incubation. The exponential and hyperbolic models showed a good description of the mineralization data (r2 > 0.982). The application of models which considered two organic matter pools could not describe the mineralization of some samples. The hyperbolic model estimated higher potentially carbon mineralizable pools (C0) and semidecomposition time periods than the exponential one. The C0 estimated by the exponential model were similar to the carbon content in the soil light fraction. This soil organic component seemed to be the driving variable of microbial activity and a good predictor of soil potential carbon mineralization.
Root‐Derived Carbon and the Formation and Stabilization of Aggregates
Authors: Gale W.J. , Cambardella C.A. , Bailey T.B.
Published: July 2010

It is hypothesized that particulate organic matter (POM) contributes to aggregate stability. However, little is known about the dynamics of the POM fraction or its role in aggregate formation. A simulated no‐till study was conducted to examine changes in free and aggregate‐associated POM during the decomposition of in situ 14C‐labeled roots during a 1‐yr incubation in a loess‐derived silt loam. Two water pretreatments (capillary‐wetted and slaked) were applied to soil samples collected during the incubation, and the samples were then wet sieved to obtain five aggregate size fractions. Densiometric separations were used to isolate free and released POM (frPOM) and intraaggregate POM (iPOM). Small macroaggregates (250–2000 μm) were enriched in iPOM‐14C on Day 0 which suggested that many of these aggregates formed around cores of new, root‐derived POM during the growth and senescence of the oat plants. Slaking resulted in the disruption of many of the small macroaggregates (250–2000 μm) and a large increase in frPOM‐14C on Day 0. The amount of 14C released into the frPOM pool with slaking declined with time. In contrast, there was a significant linear increase in the amount of new, root‐derived iPOM‐14C in large microaggregates (53–250 μm) that were released when unstable macroaggregates (>250 μm) slaked. These data support the hypothesis that new microaggregates are formed within existing macroaggregates and provide strong evidence that, in no‐till, aggregate formation and stabilization processes are directly related to the decomposition of root‐residue and the dynamics of POM C in the soil.
Salinity–Grain Yield Response Functions of Barley Cultivars Assessed with a Drip‐Injection Irrigation System
Authors: Royo A. , Arag u ¨ és R. , Playán E. , Ortiz R.
Published: July 2010

Success in breeding crops for yield and other quantitative traits depends on the use of convenient methods to accurately evaluate genotypes under field conditions. We report the evaluation of a drip‐injection irrigation system (DIS) for assessing the salt tolerance of barley genotypes. Ten barley cultivars were randomized within each of nine salinities imposed by a DIS in an experiment with two replications. Grain yields were regressed against soil salinity (ECe) using a sigmoidal growth response model to obtain the statistics Ym, ECe50, and p. The data fitted the model well; the average correlation coefficient was 0.89 (P < 0.001) when the observations for each cultivar in both replications were pooled, and the average SEs were <12% of the mean Ym and ECe50 estimates. We concluded that the DIS is a reliable system for estimating the salinity response functions of barley. The grain yields obtained in the control and intermediate soil salinity were highly correlated (, P < 0.01), indicating that the highest‐yielding cultivars under nonsaline conditions were also most productive under intermediate saline conditions. However, yields at high soil salinity were not correlated with the control yields. For the same set of genotypes, the estimates of ECe50 obtained with the DIS and with a triple‐line source system (TLS) were strongly correlated (, P < 0.01), even though the direct absorption of salts by the leaves, which is a feature of the TLS, had a deleterious effect on grain yields. Results from the DIS trial suggest that the salt tolerance of barley quoted in the literature for similar climatic conditions could be overestimated by 40%.
Nitrogen and Water Interactions in Subsurface Drip‐Irrigated Cauliflower I. Plant Response
Authors: Thompson Thomas L. , Doerge Thomas A. , Godin Ronald E.
Published: July 2010

Production of cauliflower (Brassica olearaceaL. var.botrytisL.) in the southwestern U.S. is highly dependent on inputs of water and N fertilizer to achieve optimum yields and quality. Subsurface drip irrigation offers what is likely the ultimate in control of the plant root zone for crop production. However, the water and N‐response characteristics of subsurface drip‐irrigated cauliflower have not previously been reported. Three field experiments were conducted in southern Arizona in 1993–1996. The objectives were to determine: (i) an optimum range of soil water tension for subsurface drip‐irrigated cauliflower, (ii) the effects and interactions of water and N fertilizer on crop yield and quality, and (iii) seasonal and daily N uptake for high‐yielding cauliflower. The experiments were randomized complete block factorial with three irrigation regimes (low, medium, high), four N rates (60–600 kg N ha−1), and four replications. Irrigation was applied daily to maintain target soil water tensions and all N was applied by fertigation. With respect to marketable yield, curd weight, and curd diameter, the optimum soil water tension was approximately 10 to 12 kPa in this sandy loam soil during the 3 years. Marketable yields across all treatments ranged from <5 to >30 Mg ha−1Yields and quality were generally more responsive to N rate than to irrigation and showed significant irrigation by N rate interactions during 2 of the 3 years. At equivalent N rates, excessive irrigation generally resulted in lower yields and quality. Cauliflower accumulated up to 250 kg N ha−1in the aboveground biomass and N‐uptake fluxes were as high as 5 kg N ha−1d−1at the 12‐leaf to folding growth stage.
Predicting the Gas Diffusion Coefficient in Undisturbed Soil from Soil Water Characteristics
Authors: Moldrup P. , Olesen T. , Schjønning P. , Yamaguchi T. , Rolston D. E.
Published: July 2010

The gas diffusion coefficient in soil (DP), and its dependency on soil physical characteristics, governs the diffusive transport of oxygen, greenhouse gases, fumigants, and volatile organic pollutants in agricultural, forest, and urban soils. Accurate models for predicting DP as a function of air‐filled porosity (ϵ) in natural, undisturbed soil are needed for realistic gas transport and fate simulations. Using data from 126 undisturbed soil layers, we obtained a high correlation (r2 = 0.97) for a simple, nonlinear expression describing DP at −100 cm H2O of soil water potential (DP,100) as a function of the corresponding air‐filled porosity (ϵ100), equal to the volume of soil pores with an equivalent pore diameter >30 μm. A new DP(ϵ) model was developed by combining the DP,100(ϵ100) expression with the Burdine relative hydraulic conductivity model, the latter modified to predict relative gas diffusivity in unsaturated soil. The DP,100 and Burdine terms in the DP(ϵ) model are both related to the soil water characteristic (SWC) curve and, thus, the actual pore‐size distribution within the water content range considered. The DP(ϵ) model requires knowledge of the soil's air‐filled and total porosities and a minimum of two points on the SWC curve, including a measurement at −100 cm H2O. When tested against independent gas diffusivity data for 21 differently textured and undisturbed soils, the SWC‐dependent DP(ϵ) model accurately predicted measured data and gave a reduction in root mean square error of prediction between 58 and 83% compared to the classical, soil type‐independent Penman and Millington‐Quirk models. To further test the new DP(ϵ) model, gas diffusivity and SWC measurements on undisturbed soil cores from three 0.4‐m soil horizons (sandy clay loam, sandy loam, and loamy sand) within the 4 to 7 m depth below an industrially polluted soil site were carried out. For these deep subsurface soils the SWC‐dependent model best predicted the measured gas diffusivities.
Prediction of Near‐Saturated Hydraulic Conductivity in Three Podzolic Boreal Forest Soils
Authors: Mecke M. , Westman C. J. , Ilvesniemi H.
Published: July 2010

Steady‐state infiltration fluxes into the soil were measured with a tension infiltrometer at supply potentials of −0.35, −0.70, and −1.10 kPa, and the near‐saturated hydraulic conductivities (K) were calculated using an exponential model. Measurements were conducted in four mineral soil horizons at three forest sites, representing contrasting textures. The analysis was concentrated on K at −0.35 kPa [K(−0.35)] since this potential corresponds to the 1‐mm pore diam., which is often considered to be the limit between macropores and mesopores. The average K(−0.35) of the site varied in the parent soils of the three sites from 0.46 to 40.98 cm h−1, while in the two uppermost horizons the variability was smaller: 0.30 to 0.69 cm h−1 Three multiple linear regression models of log[K(−0.35)] were constructed by stepwise regression analysis. The retained water content at the seven potentials; textural fractions; dry bulk density; and Al, Fe, and C contents were suggested as predictor variables. In addition, simple functions of these variables were suggested. In Model 1, all horizons were included ; in Model 2, all horizons except the upper illuvial horizon were included ; and in Model 3, only the lowest horizon was included Adding predictor variables increased r2 in all models. The water content at −100 kPa, which depends on pore‐size distribution and C content (which produce a strong retarding effect on water flow), were the most important predictors for K(−0.35). Similarly, by gradually excluding horizons where pedological and biological processes had changed the structure and pore‐size distribution, r2 increased from 0.86 (Model 1) to 0.99 (Model 3).
A digestion method for trace metals recovery from oil and grease contaminated soils
Authors: Cook Nicola , Turmel Marie-Claude , Hendershot William H.
Published: July 2010

Oil and grease contaminated soils are difficult to digest using the common HNO3–H2O2digestion method. Even after an overnight pre‐digestion with HNO3and subsequent heating, the addition of H2O2caused violent reactions in soils with oil and grease, resulting in the loss of the samples. At low metal concentrations at least a gram of soil needs to be digested to obtain concentrations measureable by flame atomic absorption spectrometry (FAAS) or inductively coupled plasma–atomic emission spectrometry (ICP‐AES). We developed a modified procedure using HNO3–HClO4for the analysis oftotaltrace metals that can be used on all types of soils including those with oil and grease. Recovery rates of 99, 94, 114, 92, and 83% for Cd, Cu, Ni, Pb and Zn, respectively, were obtained for standard reference material (SRM) NIST 2710 (Montana Soil). Soils with ≈1000 mg kg−1oil and grease were successfully digested and gave extract concentrations suitable for analysis on FAAS or ICP‐AES. Compared to the common HNO3–H2O2soil digestion method, the proposed method was as effective (no significant difference) in extracting Cu, Pb, and Zn and was significantly better in liberating Ni from the soil. With the HNO3–H2O2soil digestion method the Cd concentrations were often below the limit of detection by FAAS but were measureable in the HNO3–HClO4digests. Variability of results using the proposed method was reduced in some cases.
Temporal Changes in Small Depth‐Incremental Soil Bulk Density
Authors: Logsdon S. D. , Cambardella C. A.
Published: July 2010

Farmers are concerned that soil compaction will be a problem in the first few years after conversion to strict no‐till. The objective of this study was to determine if the changes in depth‐incremental soil bulk density during transition to no‐till were greater than density changes due to natural variation. We sampled six locations from a no‐till field and six locations from a disk field of a soybean [Glycine max (L.) Merr.]–corn (Zea mays L.) rotation and took 12 samples at each of the 12 locations. The soil types sampled were Clarion (fine‐loamy, mixed, superactive, mesic, Typic Hapludoll), Nicollet (fine‐loamy, mixed, superactive, mesic, Aquic Hapludoll), and Canisteo (fine‐loamy, mixed, superactive, calcareous, mesic, Typic Endoaquoll) soils. We divided each 300‐mm soil sample into 15 depth‐increments, and pooled the 12 samples for each location for each 20‐mm depth‐increment. Bulk densities ranged from 0.9 to 1.3 Mg m−3 in the top 0 to 20 mm, and 1.2 to 1.6 Mg m−3 for the depth‐increments below 20 mm. Comparing the first and last sampling dates for the no‐till field, no significant changes in bulk density were detected for any depth‐increment; however, for the disk field, increases in significant bulk density were detected in 10 out of 15 depth‐increments. Natural causes probably contributed to the bulk density changes that occurred over time in both fields. None of these bulk densities were high enough to restrict root growth. We concluded that concern about soil compaction under no‐till management is inappropriate for these structured soils.
Field‐Scale Mapping of Surface Soil Organic Carbon Using Remotely Sensed Imagery
Authors: Chen Feng , Kissel David E. , West Larry T. , Adkins Wayne
Published: July 2010

The surface soil organic C (SOC) concentration is a useful soil property to map soils, interpret soil properties, and guide fertilizer and agricultural chemical applications. The objective of this study was to determine whether surface SOC concentrations could be predicted from remotely sensed imagery (an aerial photograph of bare surface soil) of a 115‐ha field located in Crisp County, Georgia. The surface SOC concentrations were determined for soil samples taken at 28 field locations. The statistical relationship between surface SOC concentrations and image intensity values in the red, green, and blue bands was fit to a to a logarithm linear equation The distribution of the surface SOC concentrations was predicted with two approaches. The first approach was to apply the relationship to individual pixels and then determine the distribution; the second approach was to classify the image and then apply the relationship to determine the class boundaries and means. Eight levels of surface SOC concentrations were classified in both approaches, and there was good agreement between the two approaches with a probability value near one using a paired t‐test. The predicted and measured surface SOC concentrations, based on additional soil samples from 31 field locations, were compared using linear regression The surface SOC concentrations were correctly classified in 77.4 and 74.2% of cases for the two approaches. The procedures tested were accurate enough to be used for precision farming applications in agricultural fields.
Constructing Simple Wetland Sampling Devices
Authors: LaForce Matthew J. , Hansel Colleen M. , Fendorf Scott
Published: July 2010

Wetland soils and sediments are commonly monitored for nutrient or contaminant cycling. Oftentimes, sample collection and subsequent transport to the laboratory proves to be difficult. We detail the construction and use of three inexpensive devices for sampling and transporting sediment and solution in wetlands: dialysis cells (peepers) for solution measurements, a piston coring device for sediment sampling, and a portable vacuum‐chamber sample transporter. Peepers were fabricated using either 5‐ or 20‐mL filter tubes placed at 2‐ or 5‐cm intervals into slotted polyvinyl chloride (PVC) tubes. On the basis of a laboratory investigation, trace elements reached a steady state in our peepers within 10 d. The piston coring device was constructed from 1.9‐cm diam. PVC tubing and was used to remove intact sediment (≈20‐cm) cores. The transporter was constructed from 25‐cm diam. PVC pipe and was designed to carry field‐collected materials back to the laboratory while minimizing sample alteration caused by exposure to O2 Our results indicate that four purges at 0.05 MPa, followed by filling with N2, resulted in negligible O2 levels in this transporter.
Adsorption and Transport of Uranium(VI) in Subsurface Media
Authors: Barnett M. O. , Jardine P. M. , Brooks S. C. , Selim H. M.
Published: July 2010

Uranium(VI) adsorption and transport in three natural, heterogeneous subsurface media were investigated in batch and column experiments. The rate of U(VI) adsorption to the natural samples was rapid over the first few hours of the experiments, and then slowed appreciably after 24 to 48 h. The adsorption of U(VI) to the samples was also nonlinear, suggesting a decreasing attraction for the surface with increased surface loading. The extent of adsorption on each of the media was strongly pH‐dependent, increasing sharply as the pH increased from 4.5 to 5.5 and then decreasing sharply over the pH range 7.5 to 8.5 as the concentration of dissolved carbonate and U(VI)–carbonate complexes increased. The similarities in the pH‐dependent behavior between the three materials despite differences in bulk mineralogy was likely due to the similar Fe contents of the materials. The transport of U(VI) through packed columns of the soils and sediments was significantly retarded but reversible. The local equilibrium assumption and the batch‐measured adsorption isotherms dramatically underestimated the degree of retardation observed in the columns. The U(VI) displacement experiments were modeled with the one‐dimensional advective–dispersive equation and several different model formulations describing the interactions of U(VI) with the solid phase. These models were able to fit the observed breakthrough curves within 0.1 root mean square error of the initial concentration.
Simulating Scale‐Dependent Solute Transport in Soils with the Fractional Advective–Dispersive Equation
Authors: Pachepsky Yakov , Benson David , Rawls Walter
Published: July 2010

Solute dispersivity defined from the classical advective–dispersive equation (ADE) was found to increase as the length of a soil column or the soil depth increased. The heterogeneity of soil is a physical reason for this scale dependence. Such transport can be described assuming that the random movement of solute particles belongs to the family of so‐called Lévy motions. Recently a differential solute transport equation was derived for Lévy motions using fractional derivatives to describe advective dispersion. Our objective was to test applicability of the fractional ADE, or FADE, to solute transport in soils and to compare results of FADE and ADE applications. The one‐dimensional FADE with symmetrical dispersion included two parameters: the fractional dispersion coefficient and the order of fractional differentiation α , 0 < α ≤ 2. The FADE reduces to the ADE when the parameter Analytical solutions of the FADE and the ADE were fitted to the data from experiments on Cl− transport in sand, in structured clay soil, and in columns made of soil aggregates. The FADE simulated scale effects and tails on the breakthrough curves (BTCs) better than, or as well as, the ADE. The fractional dispersion coefficient did not depend on the distance. In the clay soil column, the parameter α did not change significantly when the flow rate changed provided the degree of saturation changed only slightly. With the FADE, the scale effects are reflected by the order of the fractional derivative, and the fractional dispersion coefficient needs to be found at only one scale.
Impact of Preferential Flow on the Transport of Adsorbing and Non‐Adsorbing Tracers
Authors: Kung K.-J. S. , Steenhuis T. S. , Kladivko E. J. , Gish T. J. , Bubenzer G. , Helling C. S.
Published: July 2010

Field experiments were conducted by using a tile drain monitoring facility to determine the impact of preferential flow on the transport of adsorbing and non‐adsorbing tracers. Simulated rainfall with 7.5 mm h−1 intensity and 7.5 h duration was applied to a 18‐ by 65‐m no‐till plot. After 72 min of irrigation, a pulse of Br− and rhodamine WT (water tracer) was applied through irrigation, and 4 h later, a second pulse of Cl− and rhodamine WT was applied. The breakthrough curves (BTC) of these tracers were measured by sampling the tile. The same experiments were repeated in an adjacent conventional‐till plot, except the rainfall intensity was reduced to 5 mm h−1 The results showed that both the non‐adsorbing and the adsorbing tracers applied in the same pulse arrived at the tile line at the same time and their BTC peaked at the same time. This suggested that water dynamics of preferential flow paths dominated the initial phase of the contaminant transport, regardless of the retardation properties of contaminants. The tracers from the second pulse were detected at only 13 min after application. Among the four tracer pulses in two plots, the BTC from the second pulse in the no‐till plot had the longest period in which the non‐adsorbing and adsorbing tracers had identical patterns. This indicated that the wetter the soil profile, the longer the water dynamics of preferential flow paths dominate the contaminant transport. The BTC from the second pulse applied to the two plots had identical arrival and peak times.
Soil Community Analysis Using DGGE of 16S rDNA Polymerase Chain Reaction Products
Authors: Nakatsu Cindy H. , Torsvik Vigdis , Øvreås Lise
Published: July 2010

Separation of polymerase chain reaction (PCR)–amplified 16S rDNA products using denaturing gradient gel electrophoresis (DGGE) was tested as a means to study microbial community composition in bulk soil samples. DNA was extracted from six soils from agroecosystems in Norway and the USA under different agronomic treatments (crop, rotation, and tillage); one soil is contaminated with polyaromatic hydrocarbons (PAH, 700 mg kg−1). Two sets of primers specific for Bacteria (V3 and the V6/V9 regions of 16S rRNA) and another for Archaea (V3 region of 16S rRNA) were used to determine the contribution of each domain to the microbial community. Reproducible, characteristic profiles of the communities were obtained by DGGE separation of the PCR amplification products. The number of fragments resolved by DGGE indicated bacterial diversity was far greater than that of the Archaea in the agricultural soils examined. Only the soil contaminated with PAHs had reduced bacterial diversity, evidenced by a distinct DGGE profile. The results showed that the method is useful as an initial step to discriminate among communities because it is rapid and multiple samples can be easily screened. There are some limitations, but under highly selective conditions it is possible to distinguish communities from different soils and to indicate the presence of numerically dominant populations.
Fates and Losses of Nitrogen from a Nitrogen‐15‐Labeled Cover Crop in an Intensively Managed Vegetable System
Authors: Jackson L. E.
Published: July 2010

Cover crops are known to decrease leaching of NO−3–N during the winter fallow period in vegetable crop systems, but soil N dynamics following cover crop incorporation are not well understood. The ability of microbes and plants to assimilate and retain N from cover crop residue was studied in a sandy soil in a field under intensive vegetable production in California. The purpose was to describe changes in soil responses and15N fates after adding a15N‐labeled cover crop under field management conditions. Fresh residue (478 g dry weight m−2) of15N‐labeled phacelia (Phacelia tanacetifoliaBenth.) (C/N of 19) was added to miniplots contained within large cylinders. Microbial biomass and NO−3–N increased rapidly, then began to decline 2 wk later. Microbial biomass C declined faster than microbial biomass N. Only a small amount of15N was ever found in microbial biomass, but NO−3–N was enriched with substantial15N. Percentage recovery of the added15N after 4 mo was 60.7% as soil organic N; 20.7% in plants; 1.4% as inorganic N; 1.4% in microbial biomass; 4.7% in ion exchange resin (IER) bags, leached below a depth of 60 cm; and 11.1% as unexplained loss. Losses of15N during the first lettuce (Lactuca sativaL.) crop after the cover crop were relatively low, most likely due to low rainfall and appropriate scheduling of fertilizer and irrigation. Total soil15N at 0‐ to 30‐cm depth declined for the first 7 mo, and thereafter cover crop N was apparently no longer readily mineralizable. Microbes may have assimilated C from the plant residue, met their N demand mainly with soil‐derived N, and released cover crop‐derived N that was rapidly mineralized and nitrified. The resulting NO−3–N was either taken up by plants, leached, or denitrified. Proper management of water and fertilizer inputs after incorporation of low C/N plant material is important for avoiding N loss before plants are established, especially since NO−3–N is readily available, and microbes do not retain much of the cover crop N in this intensively managed soil.
Soils and Landscapes of Kärkevagge, Swedish Lapland
Authors: Darmody Robert G. , Thorn Colin E. , Dixon John C. , Schlyter Peter
Published: July 2010

Kärkevagge, a glacially eroded valley above the Arctic Circle in Sweden, is of particular interest because research findings there in the 1950s challenged the view that chemical weathering is insignificant in cold climates. Because of the wide elevation range, diverse landscapes, steep slopes, and proximity to tree line, soils in the watershed are quite variable and recent changes to Soil Taxonomy have complicated the classification of cold soils. This paper presents an overview of our findings based on 37 pedons. Research site elevations ranged from 505 to 1585 m and slopes from 1 to 78%. Mean annual soil temperatures (MAST), based on a 1‐ to 2‐yr record, ranged from 2.5 to −3.4°C. Although MAST was <0°C at sites above 1200 m, Gelisols were not found below 1500 m because estimated depth to permafrost exceeds 2 m, a critical boundary in the new Soil Taxonomy. The common mineral soils can be divided into four groups on the basis of elevation and landscape position: (i) Haplocryods at low elevation and on more stable landscapes; (ii) Cryofluvents within the valley on slopes <25% and on flood plains; (iii) Cryorthents at higher elevations and on steeper slopes; and (iv) Dystrocryepts on the gently sloping ridge tops where depth to permafrost presumably exceeds 2 m. Other soils identified include Cryosaprists in isolated bedrock depressions at lower elevations and a Mollisol, perhaps the most northern in the world. The soils are typically coarse‐loamy with <5% clay. Coarse fragments are common, ranging up to 68% by volume, most are channers derived from the local mica schist. The soils are micaceous, again reflecting the geology. Soil pH tended to be slightly acidic except near marble bedrock outcrops, which, along with the presence of interstratified minerals, demonstrates the importance of chemical weathering and pedogenesis in this arctic environment.
Calibration of a Frequency Domain Reflectometry Sensor for Humid Tropical Soils of Volcanic Origin
Authors: Veldkamp Edzo , O'Brien Joseph J.
Published: July 2010

Recently, a frequency domain reflectometry (FDR) was developed for measuring soil water content. It has a multivibrator that sends electromagnetic waves along its probes, and it measures the frequency of the reflected wave, which varies with water content. This FDR sensor has several advantages over time domain reflectometry (TDR); it is less expensive, has a lower power consumption, and continuous monitoring of soil moisture at several remote locations is easily automated using dataloggers. Our goal was to derive a calibration function for the FDR sensor with the following criteria: it should be applicable to soils with high clay and organic matter contents and with bulk densities between 0.7 and 1.1 g cm−3 We used undisturbed soil samples to account for the natural heterogeneity in soils. Our results show that the calibration functions derived from a three‐phase mixing model performed better than the manufacturer's empirically derived function for the soil volumetric content (θ) range of 0.45 to 0.70 m3 m−3 Separate values of the geometry parameter (α) and of the specific output period for soil matrix (Pers) were established both for the topsoil (0–0.5 m depth) and for the subsoil (>0.5 m depth). The manufacturer's calibration function underestimated the soil water content by up to 0.15 m3 m−3 The three‐phase mixing model uses a physical basis for the derivation of the calibration function in that the soil porosity is used for volumetric partitioning among soil components. This physical basis renders the calibration function widely adaptable.
Soil Sampling Strategies for Precision Agriculture Research under Sahelian Conditions
Authors: van Groenigen J. W. , Gandah M. , Bouma J.
Published: July 2010

The cost of soil samples to characterize field variability is a key problem in precision agriculture. This study was conducted to investigate whether yield maps can be used to optimize soil sampling for characterizing soil variables that determine yield variability. Using an inexpensive, low‐tech scoring technique, yield maps of pearl millet [Pennisetum glaucum(L.) Br.] were produced for a zero‐input farm in Niger. The soil was classified as a typic Plintustalf. The Spatial Simulated Annealing (SSA) algorithm was used to optimize three sampling schemes. Scheme 1 optimized coverage over the whole area. Scheme 2 covered the whole yield range. Scheme 3 covered the low‐producing areas. Yield varied from 0 to 2500 kg ha−1, measured per planting hill. Using correlation coefficients, Scheme 2 found significant correlations between five soil variables and yield. Scheme 1 found only one significant correlation and explained 37% of the variation in yield using multivariate regression of yield on soil variables. Scheme 2 explained 70% of the variation in yield. Differences between Scheme 3 and Scheme 1 proved to be significant for distance to shrubs, relief, soil pH, and cation‐exchange capacity (CEC). We concluded that shrubs are the main factor influencing millet yield by means of catching eroded materials and improving soil fertility. The possibilities of planting shrubs to improve soil fertility should be investigated. Variograms of relief and yield suggested that spatial correlation is largely confined to distances of 3 to 5 m. Since Scheme 2 was most effective in establishing soil–yield relationships, we concluded that yield maps can be used to optimize soil sampling.
Bromide and Atrazine Leaching in Furrow‐ and Sprinkler‐Irrigated Corn
Authors: Butters G. L. , Benjamin J. G. , Ahuja L. R. , Ruan H.
Published: July 2010

Irrigation method is an important consideration in the management of nutrients and pesticides. A 2‐yr study was undertaken to evaluate Br− and atrazine [6‐chloro‐N‐ethyl‐N'‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] leaching following uniform spray application in a corn (Zea mays L.) field under three irrigation treatments: (i) furrow irrigation with water placement in every furrow (EF), (ii) furrow irrigation with water placement (at twice the rate) in alternate furrows (AF), and (iii) sprinkler irrigation (SP). The soil, a Fort Collins clay loam (fine‐loamy, mixed, superactive, mesic Aridic Haplustalf), was ridged and furrowed for all irrigation treatments. In both years of the study, Br− movement under all three irrigation treatments was dominated by lateral flow into the ridge and/or dry furrow positions. The deepest Br− leaching was found in the SP treatment, but with irrigation scheduled at 100% of evapotranspiration (ET) in no case in either year did Br− mass below the root zone (1.2 m) exceed 3% of applied mass. Comparing the furrow irrigation treatments, applying water at twice the rate to alternative furrows neither increased nor decreased the plot averaged downward movement of Br− Atrazine movement was largely unaffected by the type and placement of irrigation, though in each treatment the downward leaching of atrazine was much greater than expected, suggesting nonequilibrium conditions and/or movement with a mobile reactive phase. A modified version of the unsaturated flow and transport code CHAIN‐2D, which included two‐dimensional root water and solute uptake with partitioning of the soil water into mobile and immobile regions, accurately simulated the Br− concentration profiles. The model will be useful in evaluating management alternatives for the placement of water and chemicals that minimize losses below the root zone.
Tillage Influence on Soluble Salt Movement in Silt Loam Soils Cropped to Paddy Rice
Authors: Wilson C. E. , Keisling T. C. , Miller D. M. , Dillon C. R. , Pearce A. D. , Frizzell D. L. , Counce P. A.
Published: July 2010

Rice (Oryza sativa L.) produced in a dry‐seeded, delayed‐flood system common to the southern USA is extremely sensitive to excessive accumulation of soluble salts during the seedling growth stage. Recent observations have been made by producers, county agents, and researchers that the use of conservation tillage systems, particularly no‐till systems, may increase the level of salinity in the rice root zone in dry‐seeded, delayed‐flood systems during the 4‐ to 6‐wk period prior to permanent flood establishment. With the use of conservation tillage practices for rice production steadily increasing in the southern USA, it is important to determine if these practices increase potential for accumulation of soluble salts, to determine the mechanisms involved, and to develop management strategies to overcome the problem. A 2‐yr study was initiated in the fall of 1994 to monitor salt distribution within the soil profile under different tillage regimes. A conventional system, a para‐till operation, a chisel plow operation, and a no‐till system were implemented in the fall and Br− was applied to monitor salt movement. ‘Kaybonnet’ rice was seeded during 1995 and 1996 and soil samples were collected from each plot at the two‐ to three‐leaf growth stage. Salt accumulation at the rice seedling growth stage near the soil surface was higher in the no‐till treatment than in any of the other tillage treatments based on higher electrical conductivity, Cl− concentration, and NO−3 concentration in the top 2.5‐cm depth. At this depth, the electrical conductivity was 30 to 40% greater, the Cl− concentration was 30 to 160% greater, and the NO−3 concentration was 10 to 160% greater in the no‐till treatment than in the other tillage treatments. Salt distribution within the profile was similar for all treatments beyond the 2.5‐cm depth. The data suggest that tillage does tend to reduce the potential for salt accumulation in the root zone.
Forest Soil Chemistry and Terrain Attributes in a Catskills Watershed
Authors: Johnson Chris E. , Ruiz-Méndez Javier J. , Lawrence Gregory B.
Published: July 2010

Knowledge of soil chemistry is useful in assessing the sensitivity of forested areas to natural and anthropogenic disturbances, but characterizing large areas is expensive because of the large sample numbers required and the cost of soil chemical analyses. We collected and chemically analyzed soil samples from 72 sites within a 214‐ha watershed in the Catskill Mountains of New York to evaluate factors that influence soil chemistry and whether terrain features could be used to predict soil chemical properties. Using geographic information system (GIS) techniques, we determined five terrain attributes at each sampling location: (i) slope, (ii) aspect, (iii) elevation, (iv) topographic index, and (v) flow accumulation. These attributes were ineffective in predicting the chemical properties of organic and mineral soil samples; together they explained only 4 to 25% of the variance in pHw, effective cation‐exchange capacity (CECe), exchangeable bases, exchangeable acidity, total C, total N, and C/N ratio. Regressions among soil properties were much better; total C and pHwtogether explained 33 to 66% of the variation in exchangeable bases and CECeTotal C was positively correlated with N (in Oa horizons and mineral soil, respectively), exchangeable bases, and CECe, indicating the importance of organic matter to the chemistry of these acidic soils. The fraction of CECeoccupied by H explained 44% of the variation in pHwSoil chemical properties at this site vary on spatial scales finer than typical GIS analyses, resulting in relationships with poor predictive power. Thus, interrelationships among soil properties are more reliable for prediction.
Morphological Changes in Soils Produced When Hydrology Is Altered by Ditching
Authors: Hayes W. A. , Vepraskas M. J.
Published: July 2010

A soil's hydrology (seasonal saturation occurrence) must be estimated in the field to delineate jurisdictional wetlands and to evaluate soil suitability for on‐site waste disposal. It is difficult to predict soil hydrology on lands that contain ditches, because the areal extent of hydrologic alteration by an individual ditch is generally unknown. This study evaluated whether morphological changes occurred in soils after a drainage ditch had been installed. Four transects of plots were established parallel to a ditch with plots at distances of 7, 30, 60, and 80 m from the ditch. Each transect contained plots in the following soils: Aquic Paleudults, Aeric Paleaquults, and Typic Paleaquults. Soils within 30 m of the ditch had a significantly (0.10 level) greater volume of Fe masses at depths of 40 to 100 cm than soils further from the ditch. Duration of saturation did not vary significantly with distance from the ditch, but within 30 m of the ditch water tables fluctuated more frequently than those in soils further away. Concentrations of Fe(II) in groundwater at a depth of 60 cm were higher at 7 m from the ditch than at 60 m, but redox potentials at a depth of 60 cm were <500 mv for shorter periods of time at 7 m than at greater distances from the ditch. We hypothesized that groundwater flowing into the soils within 30 m of the ditch introduced Fe(II) into the Bt horizons. The Fe(II) oxidized and formed Fe masses as the water table fell. Our results indicate that soil colors can change within 30 yr as a result of ditching. We suggest that the major area of soil influenced by the ditch can be identified by where the Fe masses in the argillic horizons increase as one approaches the ditch.
Adsorption of Mercury(II) by Kaolinite
Authors: Sarkar D. , Essington M. E. , Misra K. C.
Published: July 2010

Adsorption of Hg(II) by kaolinite was investigated as a function of solution pH, ionic strength, and the competitive or complexation effects of ligands (Cl, SO4, PO4) and metals (Ni and Pb). Mercury(II) adsorption from a 0.6 μM Hg(II) solution was primarily influenced by pH. The Hg(II) adsorption edge was described by a pH50 (pH where 50% adsorption occurs) of 3.4 and a pHmax (pH where maximum adsorption occurs) of 4.4. At pH values above the pHmax, Hg(II) retention decreased with increasing pH. Chloride and Ni shifted pH50 from 3.4 to 7 and 4.1, respectively. Nickel and Pb reduced the amount of Hg(II) adsorbed throughout the pH range examined. Ionic strength and the presence of SO4 and PO4 had relatively little impact on the Hg(II) adsorption envelope. The adsorption of Hg(II) was predicted through the application of the triple layer model (TLM) by assuming that the kaolinite surface was composed of equal proportions of silanol and aluminol groups. The TLM model suggests that the silanol group was responsible for retaining the bulk of the adsorbed Hg(II), through the formation of the ≡SiO−‐HgOH+ outer‐sphere, and the ≡SiOHg OH−2 and ≡SiOHgCl0 or ≡SiOHgOHCl− (Cl system) inner‐sphere species. The ≡AlO−‐HgOH+ outer‐sphere complex accounted for a small percentage (<15–35%) of the adsorbed Hg(II). The TLM results suggested that Hg(II) adsorption by both ≡SiOH and ≡AlOH sites on kaolinite should be considered to predict adequately Hg(II) retention.