bluuebunny/crossref_metadata_2025 huggingface dataset:
Solute Transport as Related to Soil Structure in Unsaturated Intact Soil Blocks
Authors: Bejat L. , Perfect E. , Quisenberry V. L. , Coyne M. S. , Haszler G. R.
Published: July 2010

Concern about soil and groundwater pollution has resulted in numerous studies focused on solute transport. The objectives of our study were to investigate the effect of soil type and land‐use management on solute movement. Transport of water and Cl− were measured through intact blocks of Maury (fine, mixed, semiactive, mesic Typic Paleudalf) and Cecil (fine, kaolinitic, thermic Typic Kanhapludult) soils, under steady‐state, unsaturated flow conditions. Three replicate blocks for the Maury soil and two replicate blocks for the Cecil soil were studied per land‐use treatment. The land‐use treatments were conventional‐till corn (Zea mays L.) production and long‐term grass pasture. Individual blocks were instrumented with time domain reflectometry (TDR) probes at the 5‐, 15‐, and 25‐cm depths. The effluent Cl− and TDR breakthrough curves were fitted using the convection dispersion equation (CDE); the estimated parameters were pore water velocity (v), dispersion coefficient (D), and, for the TDR breakthrough curves, maximum bulk electrical conductivity (BECmax). The CDE fitted the data very well, with model R2 values ranging from 0.971 to 0.999. Volumetric water content (θ), total porosity, the soil water retention curve, and saturated hydraulic conductivity were determined on the same blocks. Volumetric water content increased as the slope of the water retention curve decreased. Increasing θ resulted in decreasing v and thus, because of the linear relationship between D and v , decreasing D Structural controls on solute dispersion in this study were mainly indirect, and related to variations in water content produced by differences in pore‐size distribution.
Percolation Theory and Hydrodynamics of Soil‐Peat Mixtures
Authors: Vidal-Beaudet Laure , Charpentier Sylvain
Published: July 2010

Great quantities of organic matter are added reconstituting soils in urban conditions. To evaluate the efficiency of organic matter on physical properties of reconstituted soils, we studied the effects of loading on intrinsic permeability of soils mixed with peat. Percolation theory associated with a statistical porosity approach was used to explain variation of permeability related to porosity. After compression, sample porosity was measured and the pore‐space morphology described by image analysis. An ellipse with major axis (a) and minor axis (b) was inscribed within each pore. All the pores appeared as lenses of different sizes which could be assumed to represent disk‐shaped cracks characterized by a diameter d and an aperture e The crack model was calculated by means of a percolation threshold, , along with values d and e as well as the measured porosity. This allowed a determination of the crack interconnection factor f During compression, the number of pores per unit area decreased. Increasing the loading closed off pores and modified flow pathways. Connected sites facilitating percolation became disconnected from each other and the flow was reduced. The effective porosity, which actually took part in flow, was determined for all the samples and was dependent on peat content.
Method for In Situ Field Calibration of Fiber Optic Miniprobes
Authors: Garrido Fernando , Ghodrati Masoud , Campbell Chris G.
Published: July 2010

A fiber optic miniprobe (FOMP) system, based on remote fluorometry, has been recently developed for in situ real‐time measurement of solute transport processes in soil. In order for the FOMP output light intensity measurements to be converted to fluorescent tracer concentration, an in situ calibration is necessary for each probe. The conventional calibration method consists of leaching the entire soil unit of interest with several pore volumes of tracer solution for each calibration step. The steady signal measured by the probes at each step is then related to tracer concentration. This procedure works well for typical laboratory soil columns but is impractical for fiber optic calibration in longer soil columns or field conditions because of the large amount of time and tracer required. As a result, a “point” calibration method has been developed that consists of injecting standard solutions directly into the small soil volume surrounding the measurement tip of the probe. Comparisons of the conventional leaching method with the injection calibration techniques confirmed the new procedures work well in both silica sand and clay loam soil columns. As a result, the new calibration technique was tested in a heterogeneous field soil and provided a simple and accurate approach to calibrating FOMPs for in situ real‐time measurement of solute transport processes in the field.
Improved Prediction of Unsaturated Hydraulic Conductivity with the Mualem‐van Genuchten Model
Authors: Schaap Marcel G. , Leij Feike J.
Published: July 2010

In many vadose zone hydrological studies, it is imperative that the soil's unsaturated hydraulic conductivity is known. Frequently, the Mualem–van Genuchten model (MVG) is used for this purpose because it allows prediction of unsaturated hydraulic conductivity from water retention parameters. For this and similar equations, it is often assumed that a measured saturated hydraulic conductivity (Ks) can be used as a matching point (Ko) while a factor SLe is used to account for pore connectivity and tortuosity (where Se is the relative saturation and ). We used a data set of 235 soil samples with retention and unsaturated hydraulic conductivity data to test and improve predictions with the MVG equation. The standard practice of using and resulted in a root mean square error for log(K) (RMSEK) of 1.31. Optimization of the matching point (Ko) and L to the hydraulic conductivity data yielded a RMSEK of 0.41. The fitted Ko were, on average, about one order of magnitude smaller than measured Ks Furthermore, L was predominantly negative, casting doubt that the MVG can be interpreted in a physical way. Spearman rank correlations showed that both Ko and L were related to van Genuchten water retention parameters and neural network analyses confirmed that Ko and L could indeed be predicted in this way. The corresponding RMSEK was 0.84, which was half an order of magnitude better than the traditional MVG model. Bulk density and textural parameters were poor predictors while addition of Ks improved the RMSEK only marginally. Bootstrap analysis showed that the uncertainty in predicted unsaturated hydraulic conductivity was about one order of magnitude near saturation and larger at lower water contents.
Flattened Residue Effects on Wind Speed and Sediment Transport
Authors: Sterk Geert
Published: July 2010

Mulching with flattened crop residues is widely used to protect soils from wind erosion. Several wind tunnel and field experiments have shown decreased protection of some soil covers with increasing wind speed. In some studies, sediment transport was enhanced with flattened residue as compared with the bare soil condition. The purpose of this article was to determine the behavior of wind speed and sediment transport when the soil surface is covered with randomly applied, flattened crop residues. A literature review was conducted to evaluate recent insights in turbulent flow properties and related sediment transport. A conceptual model was then developed to explain decreasing soil protection of a certain residue quantity when the free stream wind speed increases. The main reason is the change in turbulent flow properties of the near‐surface wind when no‐erodible roughness elements are added to an otherwise smooth surface. The average wind speed is reduced by the roughness but the probability distribution of instantaneous wind speed becomes wider and positively skewed. If free stream wind speed increases, at a certain moment the changed turbulence will cause more wind gusts that exceed the threshold wind speed for soil particle movement than would occur over a bare surface. But it is likely that this only happens when soil cover is less than 10%. For higher soil covers, increasing wind speed will also cause a decrease in soil protection, but natural wind speeds are normally not sufficient to cause enhanced sediment transport, because average wind speed is sufficiently reduced.
Soil pH Affects Copper Fractionation and Phytotoxicity
Authors: Alva A. K. , Huang B. , Paramasivam S.
Published: July 2010

Phytotoxicity of copper (Cu) depends on the relative distribution of different chemical forms, which is a function of soil properties, such as soil pH and organic matter content. Sequential fractionation was conducted to partition the total Cu into exchangeable, sorbed, organically bound, precipitate, and residual forms. Three soils were sampled from existing citrus groves and 0 to 400 mg Cu kg−1 were added. The soils used were: Myakka fine sand (sandy, siliceous, hyperthermic Aeric Haplaquods; pH = 5.7), Candler fine sand (hyperthermic, uncoated, Typic Quartzipsamments; pH = 6.5), and Oldsmar fine sand (sandy, siliceous, hyperthermic Alfic Arenic Haplaquods; pH = 8.2). Phytotoxicity of added Cu was evaluated using citrus rootstock (Swingle citrumelo) seedlings grown for 330 d. In Cu‐unamended soils, the major portion of the total Cu was in the organically bound form in the low pH soils. However, in the high pH soil, the precipitate form was the dominant form. As the rate of Cu increased, the concentration of the readily soluble Cu forms (exchangeable + sorbed forms) increased in the low pH soils, that is, from 0.8 to 89.5 mg kg−1 (8.4–25.3% of total Cu) in the Myakka soil, and from 2.2 to 70.3 mg kg−1 (3.1–20.3% of total Cu) in the Candler soil. In the high pH Oldsmar soil, however, the concentration of readily soluble Cu forms increased only from 1.1 to 5.3 mg kg−1 In relation to the total Cu content this was equivalent to a decrease from 5.2 to 1.5%. The citrus seedling growth was negatively correlated with Cu concentrations in the readily soluble forms and positively correlated with those of the precipitate form. A 20% decrease in the top and root weights occurred at 2.5 mg kg−1 of readily soluble Cu in the Candler soil (pH = 6.5). The critical concentration was lower (1.7 mg kg−1) for root growth on the Myakka soil (pH = 5.7). The critical Cu concentration in the leaves varied from 60 to 68 mg kg−1, while that in the roots was 62 mg kg−1 in the Myakka soil, but increased to 270 mg kg−1 in the Candler soil. This study demonstrated that the readily soluble form of Cu is the most phytotoxic, and an increase in the precipitate form is, thus, responsible for a reduction in Cu phytotoxicity.
Factors Affecting Measurement of the Near‐Saturated Soil Hydraulic Conductivity
Authors: Bagarello Vincenzo , Iovino Massimo , Tusa Giuseppa
Published: July 2010

Different techniques and different technique application procedures are available to determine soil hydraulic conductivity (K). The objective of this study was to determine the dependence of the K values on the selected technique and application procedure. Soil hydraulic conductivity was determined on a sandy loam soil in the near‐saturated zone by the pressure infiltrometer, the tension infiltrometer field techniques, and the inverse method applied to laboratory outflow multistep experiments. Other experiments included a study of ascending and descending pressure heads (h) on the K values measured by the tension infiltrometer technique, and the effect of contact material on ponded infiltration rates. Differences between ascending and descending K means and coefficients of variation were <20% for low pressure heads (h ≤ −120 mm). Three successive ponding infiltration runs produced mean field‐saturated hydraulic conductivities decreasing from 42.7 to 81.8 mm h−1 to 12.9 to 20.6 mm h−1, whether or not contact material was present on the infiltration surface. The mean values of K obtained by the selected three methods ranged between 47.1 to 71.9 mm h−1 at saturation and The K(h) relationships obtained by the pressure with tension infiltrometer and multistep techniques were essentially overlapping. The pressure infiltrometer produced K(h) relationships that were different from those determined by the two other techniques. In conclusion, ponded infiltration measurements were not usable for estimating unsaturated soil hydraulic conductivity, but contact material and ascending vs. descending direction had no substantial effect on infiltration rate.
Adsorption of Phosphate and Tartrate on Hydroxy‐Aluminum–Oxalate Precipitates
Authors: De Cristofaro A. , He J. Z. , Zhou D. H. , Violante A.
Published: July 2010

Sorption of phosphate in the presence of low molecular mass organic ligands on hydroxy‐Al–organics coprecipitates may be the rule and not the exception in rhizospheric soils. We studied the competitive sorption of phosphate and tartrate on hydroxy‐Al–oxalate precipitates obtained by coprecipitating Al and oxalate at pH 7.0 and initial oxalate/Al molar ratios of 0, 0.1, 0.2, and 0.5. The noncrystalline precipitates showed different chemical and physicochemical properties. Oxalate was not homogeneously distributed throughout the solids, and the greater its content in the samples, the higher the surface area, reactivity, and solubility of the solids. Oxalate was released from each complex mainly at pH <5.0 and >7.0 and more in the presence than in the absence of phosphate or tartrate. More phosphate than tartrate was sorbed on the samples, but tartrate appeared to be more specific than phosphate in replacing oxalate. The quantity of phosphate and tartrate sorbed on the organomineral complexes, containing greater amounts of oxalate, was little affected by pH (4.0–9.0), probably due to the release of oxalate from the surfaces of the complexes by increasing the pH. When mixtures of equimolar amounts of the two ligands were added at pH 4.0 to 9.0, more phosphate than tartrate was sorbed on the organomineral solids. The sorbed tartrate/sorbed phosphate molar ratio was always <1.0, but usually increased by decreasing pH and increasing the content of oxalate in the precipitates. At pH ≤5.0 the presence of high tartrate concentrations reduced the phosphate sorption, releasing Al and Al‐bounded oxalate. Only at pH >5.0 could the decrease in sorption of phosphate be attributed mainly to competition in sorption between the organic and inorganic ligands for different sorption sites.
Degradation of 13C–U–Glucose in Sphagnum majus Litter Responses to Redox, pH, and Temperature
Authors: Bergman Inger , Lundberg Peter , Preston Caroline M. , Nilsson Mats
Published: July 2010

We studied the utilization of 13C–U–glucose by the microbial community in shallow Sphagnum majus (Russ.) C. Jens. ssp. norvegicum Flatb. litter and its regulation by pH, temperature, and redox conditions. The transformation of 13C–glucose was monitored by solution‐ and solid‐state 13C–nuclear magnetic resonance (NMR) spectroscopy. The aerobic microbial community used the glucose C for respiration and, to a lesser degree, for storage as mannitol, triglycerides, and polysaccharides. Under both aerobic and anaerobic conditions, the allocation of glucose C for storage was greater at pH 6.8 than at 4.3; however, the amount of C used for building new biomass was the same at both pH settings. At 15°C, 15 to 18% of the utilized C under aerobic conditions was found in new microbial biomass: less than the previously reported values of 40 to 72%. This indicates that peat soils may promote significantly different microbial growth patterns from other minerogenic and moor humus soils. The production of mannitol and triglycerides suggests that fungi dominated the microbial community and utilized the glucose under aerobic conditions. Using a combination of solid and liquid NMR techniques we were able, for the first time, to follow the anaerobic pathways of glucose degradation in a natural soil sample. The anaerobic microbial community produced mainly volatile fatty acids (VFA), ethanol, and CO2 from the added glucose, and only minor amounts were converted to methane, storage C, and new microbial biomass. Nuclear magnetic resonance spectroscopy allows nondestructive assays of metabolic events and, therefore, was shown to be an excellent tool for studying the microbial utilization of 13C–glucose in peat.
Quantifying Soil Morphology in Tropical Environments Methods and Application in Soil Classification
Authors: Gobin Anne , Campling Paul , Deckers Jozef , Feyen Jan
Published: July 2010

We tested the hypothesis that readily observed and easily measured morphological variables can be used to characterize the soils sampled and described in southeastern Nigeria for purposes of land use and management. Field tests were developed for estimating soil texture and amount of ironstone nodules. Two new soil color indices provided an immediate means of diagnosing the soil drainage regime in case of the color index (CI) and soil forming processes in tropical soils in case of the redness index (RI). The indices correlated negatively with organic C content and positively with dithionite‐extracted Fe2O3 (0.44) and Al2O3 (0.51). Inexpensive field tests for color, texture, and ironstone can be quantified using color indices and laboratory measurements. The local soil classification was quantified by means of color indices (RI, CI) and percentages of ironstone, sand, silt, and clay measured in the A horizon. A classification based on soil texture, ironstone, and color was used to define classes for the B horizon. The two first principal components (PC) extracted from soil morphological variables measured on the upper three horizons of 72 pedons explained 64.7% of the total variance. Nonhierarchical clustering performed on the two PCs produced seven clusters that compare well with the great groups of U.S. soil taxonomy. Principal component analysis on 20 soil chemical and morphological variables confirmed that soil texture, ironstone, and soil color account for most of the variation of the soils and provide an efficient means of characterizing tropical soils derived from sedimentary parent material.
Comparison of Fatty Acid Methyl Ester (FAME) Methods for Characterizing Microbial Communities
Authors: Schutter Mary E. , Dick Richard P.
Published: July 2010

Fatty acid profiling is a popular method for characterizing microbial communities of natural systems. Direct extraction of microbial fatty acids in situ would be useful compared with methods that extract lipids first and subsequently release fatty acids from lipids. In this study, two methods for the direct extraction of fatty acids from soils were compared for three cultivated silt loams and one forested sandy clay loam. Fresh soils were analyzed for their fatty acid methyl ester (FAME) profiles by an ester‐linked (EL) method and the method of MIDI (Microbial ID, Inc., Newark, DE). Soils were stored four different ways (moist at 4°C, moist at −20°C, air‐dried at 25°C, and partially dry at 4°C) and analyzed for FAME profile changes after 30 and 90 d of storage. Eleven and 17 FAMEs were unique to the EL and MIDI method, respectively, but unique FAMEs generally were found in only minute amounts. Soils extracted with the MIDI method yielded more hydroxy FAMEs and short‐chain saturated and branched FAMEs. Conversely, EL‐extracted soils generally produced more long‐chain saturated and branched FAMEs, unsaturated FAMEs, and FAMEs with cyclopropane and methyl groups. Both extraction methods were able to differentiate among communities of different soil types, regardless if soils were fresh or stored. Changes in FAME profiles did occur in stored soils, but the effectiveness of each storage protocol for preserving FAME patterns over time was different among the four soils. While community analyses should be conducted on fresh soil, overall effects of storage were slight compared with those of extraction method and soil type.
Ammonium Adsorption and Desorption in Sandy Soils
Authors: Wang F. L. , Alva A. K.
Published: July 2010

Leaching of fertilizer N in sandy soils is both an agricultural and environmental concern and depends, in part, on the N holding capacity of the soils in the vadose zone. We examined NH4adsorption and desorption in surface (0–30 cm) and subsurface (30–60 cm) samples of Wabasso (sandy, siliceous, hyperthermic Alfic Alaquod) and Candler (uncoated hyperthermic, Typic Quartzipsamment) sands using a batch technique. Samples of a 90‐ to 100‐cm depth horizon of the Wabasso sand were also used in the study. The NH4quantity–intensity (Q/I) relations showed that the potential buffering capacity (PBC) of the soils ranged from 0.26 (Wabasso, 30–60 cm depth) to 3.9 (Wabasso, 90–100 cm depth) cmolckg−1M−1/2Labile NH4, as determined from the Q/I, was 4.9 × 10−3(Candler, subsurface) to 13.8 × 10−3(Wabasso, surface) cmolckg−1Positive linear relationships were observed between organic C content and Q/I plot parameters (potential NH4buffering capacity and labile NH4) of all soil samples except in the Wabasso 90‐ to 100‐cm depth horizon. Although NH4adsorption capacity of the surface soils was greater than that of the subsurface soils, desorption was greater from the former soils than that from the latter. This study clearly demonstrated that the potential NH4buffering capacity and labile NH4for the sandy soils studied were much lower than those for clay and silt loam soils.
Quantitative Determination of Recently Fixed Nonexchangeable Ammonium in Soils
Authors: Paramasivam S. , Breitenbeck G. A.
Published: July 2010

The importance of nonexchangeable NH4as a potential source of plant‐available N is widely recognized. However, quantitative determination of nonexchangeable NH4in soils poses a challenging analytical problem. The use of the KOBr pretreatment in the methods currently used to determine nonexchangeable NH4in soils was found to cause a substantial loss of this fraction. For example, a second KOBr pretreatment prior to digestion of air‐dried samples reduced recovery of fixed NH4by 6.4 to 32.8%. Therefore, a more reliable method was developed that avoids KOBr pretreatment. The proposed method quantitatively recovers (98–99%) nonexchangeable NH4including recently fixed (RF) as well as native clay fixed NH4while avoiding significant recovery (<1%) of N in soil organic matter or in microbial cells. Values obtained by the proposed method were similar to methods employing KOBr when the amounts of fixed NH4were determined in 17 air‐dried soil samples that ranged widely in clay and organic matter content. However, when these samples were treated to enrich RF NH4, values obtained by methods employing KOBr were an average of 35% less than those obtained by the proposed method. These differences were attributed to loss of RF NH4during KOBr oxidation. In the absence of KOBr pretreatment, determination of NH4by steam distillation resulted in values inflated by the partial recovery of organic N. The proposed method determines the amount of NH4–N in 5MHF:1MHCl soil digests by a NH3membrane diffusion technique that is highly accurate, minimizes recovery of organic N, and avoids the health hazards posed by the use of KOBr.
Soil Nitrogen Mineralization Influenced by Crop Rotation and Nitrogen Fertilization
Authors: Carpenter-Boggs Lynne , Pikul Joseph L. , Vigil Merle F. , Riedell Walter E.
Published: July 2010

An estimate of soil mineralizable N is needed to determine crop needs for N fertilizer. The objective of this research was to estimate soil net N mineralization in soils maintained in continuous corn (Zea mays L.) (CC), corn–soybean [Glycine max (L.) Merr.] (CS), and corn–soybean–wheat (Triticum aestivum L.)/alfalfa (Medicago sativa L.)–alfalfa (CSWA) rotations that have been managed since 1990 with zero N (0N), low N (LN), and high N (HN) fertilization. Soil samples were taken from 0‐ to 20‐cm depth in plots planted to corn in 1998. In order to produce more realistic time‐series data of net N mineralization, soils were incubated in filtration units in a variable‐temperature incubator (VTI) that mimicked field soil temperatures under a growing corn canopy. Rotation and N fertilization significantly affected net N mineralization in soil samples. Cumulative net N mineralized in a 189‐d field temperature incubation averaged 133 ± 6 kg ha−1 in CC, 142 ± 5 kg ha−1 in CS, and 189 ± 5 kg ha−1 in CSWA. Across rotations, average net N mineralized was 166 ± 9 kg ha−1 in 0N plots, 147 ± 10 kg ha−1 in LN plots, and 152 ± 10 kg ha−1 in HN plots. Inclusion of a legume, particularly alfalfa, in the rotation increased net N mineralized. Generally, more net N was mineralized from plots receiving no fertilizer N than from soil with a history of N fertilization. Variable‐temperature incubation produced realistic time‐series data with low sample variability.
GLEAMS, Opus, PRZM2β, and PRZM3 Simulations Compared with Measured Atrazine Runoff
Authors: Ma Qingli , Hook James E. , Wauchope R. Don , Dowler Clyde C. , Johnson A. W. , Davis Jessica G. , Gascho Gary J. , Truman Clint C. , Sumner Harold R. , Chandler Lawrence D.
Published: July 2010

High‐intensity storms that occur shortly after chemical application have the greatest potential to cause chemical runoff. We examined how effectively current chemical transport models GLEAMS, Opus, PRZM2β, and PRZM3 could predict water runoff and runoff losses of atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] under such conditions, as compared with observations from a controlled field runoff experiment. The experiment was conducted for 2 yr using simulated rainfall on two 14.6‐ by 42.7‐m plots within a corn (Zea maysL.) field on Tifton loamy sand (fine‐loamy, kaolinitic, thermic Plinthic Kandiudults) under conventional tillage practices. For each plot‐year, atrazine was applied as surface spray immediately after planting and followed by a 50‐mm, 2‐h simulated rainfall 24 h later. A similar preapplication rainfall and four subsequent rainfalls during the growing season were also applied. Observed water runoff averaged 20% of the applied rainfall. Less runoff occurred from freshly tilled soil or under full canopy cover; more runoff occurred when nearly bare soil had crusted. Observed total seasonal atrazine runoff averaged 2.7% of that applied, with the first posttreatment event runoff averaging 89% of the total. GLEAMS, Opus, PRZM2β and PRZM3 adequately predicted water runoff amounts, with normalized root mean square errors of 29, 29, 31, and 31%, respectively. GLEAMS and PRZM3 predicted atrazine concentrations in runoff within a factor of two of observed concentrations. PRZM2β overpredicted atrazine concentrations. Opus adequately predicted atrazine concentrations in runoff when it was run with an equilibrium adsorption submodel, but significantly underestimated atrazine concentrations when it was run with a kinetic sorption submodel.
Potential of Earthworm Burrows to Transmit Injected Animal Wastes to Tile Drains
Authors: Shipitalo Martin J. , Gibbs Frank
Published: July 2010

Subsurface injection of animal manure is a best management practice (BMP) that reduces odors and promotes efficient nutrient usage. In tile‐drained fields, however, injected wastes have been observed emerging from tile outlets shortly after application. This appears to be a particular concern in no‐till fields whereLumbricus terrestrisL. are often numerous. Our objective was to determine if burrows created by this earthworm species can contribute to rapid movement of injected wastes to tile drains. A turbine blower was used to force smoke into a 0.6 m‐deep tile line in a no‐till field and 20 burrows 0.02 to 0.5 m from the tile that emitted smoke, and 18 burrows 0.8 to 4.7 m from the tile that did not produce smoke were flagged. A Mariotte device filled with dyed water was then used to measure infiltration rate for each burrow. Afterwards, plastic replicas of the burrows were made so their proximity to the tile and geometrical properties could be determined. Average infiltration rate for smoke‐emitting burrows (128 mL min−1) was twice that of the more distant burrows. Moreover, dyed water was observed in the tile when added to smoke‐emitting burrows, but not when added to burrows that did not produce smoke. Thus, earthworm burrows in close proximity to tile lines may expedite transmission of injected wastes offsite. Movement of injected wastes to tiles via earthworm burrows and other preferential flow paths may be reduced by using precision farming to avoid waste application near tile lines or by modifying application procedures.
Persistent Organic Pollutants in Native Grassland Soils along a Climosequence in North America
Authors: Wilcke Wolfgang , Amelung Wulf
Published: July 2010

Among the controls on the fate of harzardous persistent organic pollutants (POPs) in the environment, soil organic matter (SOM) and climate play an outstanding role. Thus, it may be possible to predict POP concentrations at background sites from SOM properties and climatic elements. We therefore related polycyclic aromatic hydrocarbon (PAH) and polychlorinated biphenyl (PCB) concentrations in 18 mollic epipedons under native grassland to SOM properties (lignin‐derived phenols, polycarboxylic benzoic acids [PCBAs], aromaticity, and polarity of alkali‐extractable SOM) and climatic elements. The sum of 20 PAH (∑20PAHs) concentrations ranged from 63 to 321 μg kg−1, and that of 14 PCB (∑14PCBs) concentrations ranged from 7.9 to 93 μg kg−1, except at one contaminated site (3136 μg kg−1). On average, phenanthrene (PHEN, 38% of the ∑20PAHs concentrations) and naphthalene (NAPH, 28%) were the most abundant PAHs, congeners 28 (22% of the ∑14PCB concentrations) and 101 (17%) were the most abundant PCBs. Soil organic C (SOC) concentrations correlated with the ∑20PAHs concentrations; the C concentration in the sum of eight PCBAs, a marker for black C, correlated with the concentrations of higher molecular weight PAHs, except in soils with cyric temperature regime. The ∑14PCBs concentrations was independent of any soil property. The contribution of NAPH to the ∑20PAHs concentrations and that of the up to tetra‐chlorinated PCBs to the ∑14PCBs concentrations decreased with increasing mean annual temperature (MAT). The percentages of PCB 101 increased with increasing MAT. However, the temperature effect was not strong. Mean annual precipitation (MAP) neither effected PAH nor PCB patterns. Our results indicate that the easily measured SOC concentrations may be used to predict PAH concentrations in native grassland soils of the prairie. Including MAT improves the prediction of NAPH concentrations. The influence of MAT on PCB concentrations is obvious, but the correlation is too weak to be used for reliable predictions.
Carbon Turnover and Carbon‐13 Natural Abundance in Organo‐Mineral Fractions of a Tropical Dry Forest Soil under Cultivation
Authors: Shang C. , Tiessen H.
Published: July 2010

Soil organic matter (SOM) turnover is more rapid in tropical than in temperate soils. One possible reason is a limited ability of tropical soils to stabilize SOM. To test this, we measured C turnover resulting from 12 years' cultivation of a forest soil with sorghum [Sorghum bicolor (L.) Moench]. Carbon‐13 natural abundance (δ13C) signatures of forest‐ and sorghum‐derived C were used to quantify C losses and gains in organo‐mineral fractions separated by particle size, and further by density (for sands and silts) and magnetic susceptibility (for clays). Nearly 50% of original C was in the silt‐sized fraction, mostly in microaggregates of intermediate density; 30% was held by clays, particularly those of intermediate magnetic susceptibility; and 20% was of sand‐size, low‐density, often recognizable plant residues. The δ13C values in the forest soil showed the more humified SOM to be associated with finer, denser, and less magnetic fractions. After cultivation, total C content was 28% lower, with 59% of this reduction in the silts, 28% in the sand, and 19% in the clays. Loss of forest‐derived C amounted to 45%. The sand fraction lost 54% of its forest C, the silts 45% (mostly from intermediate density fractions), and the clays 23% (mostly from intermediate magnetic fractions). Gains in sorghum‐derived C amounted to 32% of C in the sand fraction, 12% in the silts (relatively evenly distributed among densities) and 13% in the clays (mostly in the nonmagnetic fraction). Thus, losses of forest C and gains of sorghum C occurred in different organo‐mineral fractions, indicating that there were no unique active fractions corresponding with the concept of C pools with defined turnover characteristics used in models of organic matter turnover.
Carbonation of Wood Ash Recycled to a Forest Soil as Measured by Isotope Ratio Mass Spectrometry
Authors: Ohlsson K. E. Anders
Published: July 2010

In Sweden, large‐scale recycling of wood ash to forests is considered a means of replenishing base cations, particularly Ca, taken up by the trees and removed by logging. To minimize negative effects on the forest ecosystem, slow rates of dissolution of the ash and release of Ca would be preferred. Carbonation of wetted ash [Ca(OH)2] can reduce the rate of Ca dissolution. In this study, field experiments were performed to evaluate carbonation of ash following application to forest soil beneath a spruce [Picea abies (L.) Karst] stand. To accomplish this, a mass spectrometric analytical method was developed that allowed quantitative estimation and isotopic analysis of the ash carbonate concentration. The dynamic range was between 0.07 and 30 μmol of carbonate, measured as CO2 evolved from an acidulated ash sample, which corresponded with between 0.01 and 5 mg of a completely carbonated ash (dried) containing ≈0.30 g g−1 Ca. The method allowed spatially resolved measurements (≈1 mm3) of the amount of carbonate and the 13C/12C and 18O/16O isotopic ratios. Following field application, ash granules (8–11 mm o.d.) increased their degree of carbonation from ≈45 to >80% within 3 d and were >90% carbonated after 3 wk. For the initial 3 d, the rate of carbonation, Rc, was estimated to be 0.70 (± 0.33) μmol mg−1 d−1 carbonate. During the field carbonation process, the outer granule layer could either be enriched or depleted in carbonate relative to the interior parts, which is suggested to depend on the occurrence of rainfall. These results indicate that the rate of carbonation of ash granule Ca in the field is rapid and probably dominates over Ca dissolution, especially under favorable conditions.
Magnetic Susceptibility for Use in Delineating Hydric Soils
Authors: Grimley D. A. , Vepraskas M. J.
Published: July 2010

Field indicators are used to identify hydric soil boundaries and to delineate wetlands. The most common field indicators may not be seen in some soils with thick, dark, mollic epipedons, and do not form in Fe‐poor soils. This study evaluated magnetic susceptibility (MS) meter as a field tool to determine hydric soil boundaries. Five Mollisol‐dominated sites formed in glacial deposits in Illinois were evaluated along with one Ultisol‐dominated site formed in Coastal Plain sediments of North Carolina. Measurements of volumetric MS were made along transects at each site that extended from wetland into upland areas. One created wetland was evaluated. Field indicators were used to identify the hydric soils. Results showed that volumetric MS values were significantly (P< 0.01) lower in hydric soils than in nonhydric soils formed in glacial deposits. Volumetric MS values also decreased slightly with depth. In a created marsh, significant differences in MS were found between hydric and nonhydric soils at 15 to 30 cm but not at shallower depths where topsoil from a wetland had been artificially applied. No significant (P> 0.15) differences in MS were found for Coastal Plain hydric and nonhydric soils where MS values were low (<10 × 10−5SI). Critical MS values that separated hydric and nonhydric soils varied between 20 × 10−5and 30 × 10−5SI for the loessal soils evaluated in Illinois. Such critical values will have to be determined on site using field indicators until specific values can be defined for hydric soils within a given parent material. With a critical MS value in hand, a wetland delineator can make MS measurements along transects perpendicular to the envisioned hydric soil boundary to quickly and quantitatively identify it.
Osmotically Driven Water Vapor Transport in Unsaturated Soils
Authors: Kelly Shaun F. , Selker John S.
Published: July 2010

Knowledge of the transport processes of bulk fertilizers and other solutes in soils and porous media is vital to understanding the environmental and economic impacts of many agricultural and waste disposal practices. Previous experimental research shows that significant water movement can occur towards regions of high salt concentrations in unsaturated porous media. It is hypothesized that in unsaturated media, large gradients in aqueous osmotic potentials cause significant water‐vapor fluxes towards regions of high solute concentrations. A physically based model to describe this process is developed by combining existing theories of liquid‐water and water‐vapor transport with aqueous electrolyte theory. A simplified solution, demonstrating these water‐vapor transport processes, is compared with experimental results from discontinuous soil column experiments previously published by Wheeting (1925) The results confirm that large osmotic potentials created in the presence of high solute concentrations in unsaturated porous media, can account for the quantities of water vapor movement observed. This redistribution of pure water vapor complicates modeling of ion diffusion in these systems and is an important process to include in solute transport models when high solute concentrations exist in unsaturated soils.
Water Repellency and Critical Soil Water Content in a Dune Sand
Authors: Dekker Louis W. , Doerr Stefan H. , Oostindie Klaas , Ziogas Apostolos K. , Ritsema Coen J.
Published: July 2010

Assessments of water repellency of soils are commonly made on air‐dried or oven‐dried samples, without considering the soil water content. The objectives of this study were to examine the spatial and temporal variability of soil water content, actual water repellency over short distances, and the variations in critical soil water contents. Between 22 Apr. and 23 Nov. 1999, numerous samples were collected from a grass‐covered dune sand (typic Psammaquent), at six depths, eight times in transects and two times in soil blocks. The water drop penetration time (WDPT) test was used to measure the actual water repellency of the field‐moist samples and the potential water repellency after drying the samples at 25, 65, and 105°C. Highly spatial and temporal variability in water content and persistence of actual water repellency was found between the samples from all soil depths. At each depth we established an upper water content, below which samples were water repellent and a lower water content, above which samples were wettable. This water content range, called the transition zone, was different for each depth, and, for example, assessed at 0‐ to 2.5‐cm depth between soil water contents of 18 and 23% (vol./vol.), and at 16.5‐ to 19‐cm depth between 2 and 5% (vol./vol.). The potential water repellency of samples dried at 25 and 65°C was on some days less severe than the actual repellency of field‐moist samples on other days, thus underestimating the maximal persistence of water repellency that can occur in the field. Drying of the samples at 105°C significantly increased the potential water repellency.
Restoration of Microbial Residues in Soils of the Conservation Reserve Program
Authors: Amelung W. , Kimble J. M. , Samson-Liebig S. , Follett R. F.
Published: July 2010

To elucidate the role of microorganisms for C and N sequestration in arable soils converted to grassland (sites of the Conservation Reserve Program; CRP), we determined amino sugars as indicators for microbial residues in surface samples (0–5 cm) obtained from each of 10 adjacent native grassland, CRP, and cropland sites across the U.S. Great Plains. The CRP sites were 6 to 10 yr and the cropland sites were >80 yr old. Compared with native grasslands, the CRP sites had lost between 17 and 50% and the cropland sites between 32 and 94% of their surface soil organic matter (SOM). The C/N ratio was not significantly different among the three land‐use systems, indicating that C and N losses occurred at similar intensity. The mean amino sugar concentrations decreased in the order native grassland (70 g kg−1 C; 750 g kg−1 N) > CRP (53 g kg−1 C; 570 g kg−1 N) > cropland (47 g kg−1 C; 450 g kg−1 N). This decrease in the element‐normalized concentrations of amino sugars indicated that they responded faster to management than other C or N containing compounds. The response of individual amino sugars related to soil compaction and the temperature regime. We suggest that the resequestration of C and N into the residues of bacteria and fungi requires several years, but as it depends on land use it could be manipulated using, for example, soil decompacting techniques to improve CRP efficiency.
A pressure cooker method to extract glomalin from soils
Authors: Wright S. F. , Jawson L.
Published: July 2010

Glomalin, a glycoprotein produced by arbuscular mycorrhizal fungi, is an important constituent of soil organic matter. Glomalin is insoluble in water or salt solutions commonly used in soil extractions. Solubilization of glomalin does occur in the presence of citrate at the temperature achieved by an autoclave (121°C, 103 kPa). Most soil‐testing laboratories have access to all of the instruments required for glomalin analysis except an autoclave. Small (4‐L) and large (14‐L) pressure cookers were compared with a bench‐top autoclave to test glomalin extraction from three soils using 50 mM citrate, pH 8.0 as the extracting agent. Glomalin concentrations, as measured by the Bradford protein assay, were identical for extracts from the autoclave and the 14‐L pressure cooker when 103 kPa (121°C) was achieved in both vessels. The 4‐L pressure cooker extracted less glomalin than the other vessels. A pressure cooker that will achieve 103 kPa is a low‐cost substitute for an autoclave to extract glomalin from soils.
Quality of Amended Mine Soils After Sixteen Years
Authors: Bendfeldt Eric S. , Burger James A. , Daniels W. Lee
Published: July 2010

Soil quality research has focused on intensively managed agricultural and forest soils, but the concept and importance of soil quality is also pertinent to reclaimed mine soils and other disturbed ecosystems. Adding organic amendments has been used as a means for ameliorating mine soils and improving their quality, but the long‐term effects of amendments on soil quality are not known. In 1982, a mined site was amended with seven different surface treatments: a control (nothing added), 30 cm of native soil, 112 Mg ha−1sawdust, and municipal sewage sludge (SS) at rates of 22, 56, 112, and 224 Mg ha−1Four replicates of each treatment were installed as a randomized complete block design. Each plot was split and planted with pitch × loblolly pine hybrid (Pinus rigida×taeda) trees and Kentucky‐31 tall fescue (Festuca arundinaceaSchreb.). During the 16‐yr period, organic matter content, total organic N, N mineralization potential, aggregate stability, and other physical and chemical properties were measured as mine soil quality indicators. The comparative ability of these organic amendments to positively affect organic matter content, total N, and other parameters was most apparent and pronounced after 5 yr. However, after 16 yr, soil organic matter (SOM) content and total N appeared to be equilibrating at ≈10 000 and 750 kg ha−1, respectively. Organic matter inputs by vegetation alone across the 16‐yr period in the control plots resulted in organic matter and N mineralization potential values comparable to levels in the organically‐amended plots, indicating the overriding importance of vegetation in the soil recovery process. After 16 yr, there appears to be no lasting soil quality improvements due to addition of organic amendments to this mine soil. Amendments improved short‐term production, but their cost of transport and application may be difficult to justify based on long‐term soil quality improvement.
Phosphorus Sorption and Desorption Properties of the Spodic Horizon from Selected Florida Spodosols
Authors: Villapando R.R. , Graetz D.A.
Published: July 2010

The chemistry of P in the spodic (Bh) horizon of Florida Spodosols has generated considerable interest in recent years, particularly where water quality problems have been reported. Early studies suggested that the Bh horizon can function as a sorption sink for P moving through nonretentive sands. However, the conditions under which P can be retained in or released from the Bh horizon have not been adequately investigated. This study evaluated the P sorption and desorption properties of the Bh horizon from 16 Florida Spodosols. The samples exhibited P sorption capacities that were reflective of their citrate‐dithionite‐bicarbonate (CDB)‐extractable Al contents. Mean Langmuir sorption maximum (Smax) values of 7.55, 11.08, and 17.49 mmol P kg−1 were obtained for low‐, medium‐, and high‐Al soils, respectively. The CuCl2–extractable Al (organic matter bound) was the single most important chemical property contributing to P retention, accounting for >60% of the variability in P sorption. Though anaerobic incubation altered P sorption and release, the effect was generally small and inconsistent. Such treatment reduced P sorption by low‐Al soils and slightly increased that of high‐Al soils. The lack of response to anaerobic incubation was attributed to generally low levels of reducible Fe in the soils. The samples also exhibited varying degrees of P sorption–desorption hysteresis. Irreversibility was most pronounced for high‐Al soils, where >70% of the added P remained sorbed after nine successive extractions. The relationships between Al contents and P sorption capacities should be useful in formulating site criteria for control and management of wastewater from dairy and other agricultural operations located on Florida Spodosols.
HEDTA–Nitrilotriacetic Acid Chelator‐Buffered Nutrient Solution for Zinc Deficiency Evaluation in Rice
Authors: Trostle Calvin L. , Bloom P.R. , Allan D.L.
Published: July 2010

Chelator‐buffering methods with N‐(2‐hydroxyethyl)ethylenedinitrilotriacetic acid (HEDTA) are used to elucidate Poaceae growth response to micronutrient metal activities including (Zn2+), but reliable hydroponic methods that maintain stable (Zn2+) for evaluating Zn deficiency in rice (Oryza sativa L.) have not been reported. The objective was to develop a chelator‐buffered method that gauges rice growth response to (Zn2+) in an otherwise chemically stable environment. Using GEOCHEM‐PC to estimate solution activities, an aerobic HEDTA–nitrilotriacetic acid (NTA) dual‐chelator method was developed that imposed five (Zn2+) levels on cv. IR‐36 seedlings for 21 d after transplanting (DAT) in a growth chamber. Control of pH 5.50 ± 0.05 using 3.0 mM 2‐(4‐morpholino)‐ethanesulfonic acid (MES) combined with periodic adjustment was critical to preserving target (Zn2+). Solution treatments ranged from Zn deficient, where (Zn2+) = 10−10.0 M (0.25 μM total chelated Zn), to fully Zn sufficient where (Zn2+) = 10−8.8 M (4.00 μM total chelated Zn). Using 200.0 μM total chelated Fe(III), adequate Fe was maintained at (Fe3+) = 10−14.3 M Phosphorous supply was controlled to prevent toxic P accumulation at low (Zn2+). With increasing (Zn2+), total biomass at 21 d ranged from 0.94 to 1.90 g plant−1 Shoot Zn responded to (Zn2+), not total chelated Zn2+, and roots responded similarly. Critical (Zn2+) for normal growth was 10−9.1 M, and leaf Zn‐deficiency symptoms were observed at (Zn2+) ≤10−9.4 M (≤28 mg Zn kg−1 shoot). The HEDTA‐NTA method provides a rapid and reliable means for evaluating Zn deficiency tolerance in IR‐36 via diagnostic visual and physical symptoms in response to a range of (Zn2+) levels.