Showing papers in "Soil Science in 2008"

Determination of the point-of-zero, charge of manganese oxides with different methods including an improved salt titration method

Abstract: Manganese (Mn) oxides are important components in soils and sediments. Points-of-zero charge (PZC) of three synthetic Mn oxides (birnessite, cryptomelane, and todorokite) were determined by using three classical techniques (potentiometric titration or PT, rapid PT or R-PT, and salt titration or ST) and a modified salt titration method with a prolonged equilibration time (ST method with a prolonged equilibration time [PST]). The same methods have been applied to goethite, which was used as a reference material. The PZC values of goethite obtained by PT and R-PT methods were both 7.95, and those by the ST and PST method were 8.16 and 8.30, respectively, for birnessite cryptomelane, and todorokite. The PT method yielded PZC of 1.18, 1.98, and 3.98, and the RPT method yielded 1.60, 2.11, and 3.47, respectively, for birnessite, cryptomelane, and todorokite. In contrast to goethite, there was no PZC found with the ST method, even when the types and concentrations of the added electrolytes changed. However, when after KCl addition the equilibration time was prolonged 28 h, the PZC of birnessite, cryptomelane, and todorokite could be found and were 0.97, 1.74, and 3.39, respectively. The fact that the normal ST method failed for the Mn oxides is due to their low PZC, because at this low pH value, the oxides may start to dissolve. Compared with PT and RPT methods, the PST method is reliable, simple, and convenient. The PST approach seems also suitable for other similar colloid systems.

The Effect of Organic and Mineral Fertilization on Micronutrient Availability in Soil

Abstract: The application of organic amendments to agricultural soils may influence metal distribution in soil fractions and, in turn, can influence the availability of micronutrients to plants. However, in the literature, there is a great lack of data on micronutrient behavior in soils fertilized with compost from vegetable residues. The study was carried out on a loam soil, a Xerofluvent, in a field experiment. Soil received composted vegetable residues or was fertilized with conventional mineral fertilizer. This study compares Cu, Zn, Mn, and Fe availability in soil after 6 years under two different fertilization methods by using diethylenetriaminepentaacetic acid and ethylenediaminetetraacetic acid solutions. The sequential extraction method (Bureau Communautaire de Reference) was used to determine the chemical forms of the micronutrients. The results indicated that the addition of compost did not cause a significant effect on the total content of the soil but resulted in an increase in all extractable micronutrients compared with soil with mineral fertilization. The Bureau Communautaire de Reference sequential extraction indicated that the oxidizable fraction was always favored by the organic amendment, except in the case of Zn, which presented the opposite trend. However, the reducible fraction showed a high increase in the case of Zn and lower in Fe. The sum of the three extracting fractions was increased by compost addition, but they were significantly lower than the total content of Cu, Zn, and Fe, which means that these elements are specially bound to the residual fraction. This fraction accounts for more than 80% of the Fe and Cu and about 70% of the Zn in both fertilized soils.

The effect of different ammonical nitrogen sources on soil acidification

Abstract: Consecutive greenhouse cropping of wheat-maize-wheat-maize-wheat grown to maturity in 3 years was conducted to evaluate soil acidification by ammonium sulfate, urea, and ammonium nitrate. Three soils were incorporated with 100 kg N/ha for wheat and 200 kg N/ha for maize and the last crop (wheat). So

Interaction of Organic Phosphorus with Clays Extracted from Oxisols

Abstract: In highly weathered soils, such as tropical soils, organic phosphorus (P) may decline together with total P and could be represented by a relatively lower amount of inositol phosphates compared with temperate soils. The aim of this work was to understand the abiotic processes leading to inositol phosphate retention in highly weathered soils. Sorption of myo-inositol hexakisphosphate and inorganic phosphate (Pi) on two clay fractions (A and B) extracted from Brazilian oxisols was studied, examining both the extent of P retention and surface property modifications induced by anion sorption. The two clays were characterized by a high amount of crystalline iron oxides and kaolinite. In clay A, gibbsite was also present, plus a higher amount of organic matter. The two clays presented a similar specific surface area, but clay A had a lower microporosity. The amount of Pi sorbed on the two clays was similar, reaching a plateau at about 1.35 μmol m -2 , whereas the amount of myo-inositol hexakisphosphate was higher on clay A, 0.67 μmol m -2 , than clay B, 0.49 μmol m -2 . The retention of both P forms on the two clays was linked to the large presence of crystalline Fe and Al oxides. Whereas Pi adsorbed on the external surfaces and diffused into micropores, myo-inositol hexakisphosphate likely adsorbed only on the external surfaces. The precipitation of Al and Fe myo-inositol hexakisphosphate was also limited because of the small amounts of soluble Al and Fe forms. All these phenomena may contribute to justify the relatively low accumulation of these organic P compounds found in some highly weathered soils.

Effect of Long-Term Swine Effluent Application on Selected Soil Properties

Abstract: Improving swine effluent management practices requires understanding of the fate of nutrients derived from swine effluent in soil quality. This study was conducted to evaluate the effects of long-term swine lagoon effluent application on nutrient distribution in an alkaline Okolona silty clay, an ac

Competitive sorption-desorption kinetics of arsenate and phosphate in soils

Abstract: The competition between arsenate (AsO 4 -3 ) and phosphate (PO 4 -3 ) on mineral surfaces has the potential of increasing arsenic mobility and bioavailability in the soil and water environment. In this study, kinetics of competitive sorption of AsO 4 -3 and PO 4 -3 in three soils was investigated in batch systems by simultaneously introducing the ligands at different molar ratios. Adsorption was carried out at different retention times, and release was investigated using successive dilutions after adsorption. Nonlinear sorption isotherms of AsO 4 -3 and PO 4 -3 were observed for all soils. Rates and amounts of AsO 4 -3 adsorption were significantly reduced when PO 4 -3 concentrations in the soil solution increased. In addition, the relative sorption preference of AsO 4 -3 and PO 4 -3 did not exhibit changes with reaction time. Desorption and sequential extractions results indicated that a significant amount of AsO 4 -3 was irreversibly retained by all soils. Kinetic retention data of AsO 4 -3 and PO 4 -3 were successfully described using a mechanistic multireaction model that accounted for competitive retention. This study indicates that competition of AsO 4 -3 and PO 4 -3 for adsorption sites should be considered in models predicting arsenic release from soils receiving high phosphorus inputs.

Response of selected soil physical and hydrologic properties to manure amendment rates, levels, andtypes

Abstract: Manure amendments affect several soil physical and hydrologic properties. The objectives of this study were to evaluate the effect of (i) manure amendment rates (0, 168, 336, and 672 kg total N ha -1 ), levels (one-time application, and two-time application), and types (chicken manure [CM], dairy manure [DM], and swine manure [SM]) on bulk density (ρ b ), total soil porosity (θ t ), and saturated hydraulic conductivity (K sat ) of a highly weathered tropical soil (Waialua gravely clay variant, isohyperthermic Pachic Haplustolls) and (ii) measuring instruments (tension infiltrometer [TI] and double-ring infiltrometers [DR]) on K sat . For the two-time application level, all the plots received additional manure to compensate for the amounts decomposed during the first growing season. The field was tilled to the top 15-cm depth before and after manure application during the two growing seasons. Measurements of ρ b and θ t were conducted on undisturbed soil core samples collected from the top 10 cm of soil from a field cultivated with sweet corn (Zea mays L. subsp. mays) and irrigated with a drip irrigation system for two consecutive growing seasons. Saturated hydraulic conductivity was calculated from steady state infiltration rates measured with TI and DR. Results show that the increased manure amendment rates and levels significantly (P < 0.01) decreased ρ b and consequently increased θ t . The values of K sat increased significantly (P < 0.01) with increase in CM and DM amendment rates and levels. For SM treatments, the values of K sat decreased with increase in manure amendment rates and levels; these results concur with those reported in literature on liquid manures. Saturated hydraulic conductivity calculated from DR data was slightly greater than that from TI data for CM and DM treatments. Opposite results were found for SM treatments. However, a good agreement (R2 = 0.90) was observed between K sat values calculated from TI and DR data across treatments. We conclude that the CM and DM amendments increased θ t and K sat and may also temporarily improve soil aggregation; however, SM amendments result in decreased K sat . Thus, it is not recommended that slurry SM be applied to the soils with low hydraulic conductivity because it could further inhibit water infiltration and increase surface runoff and soil erosion.

Bioactivity and chemical characteristics of humic acids from tropical soils sequence

Abstract: Humic acids (HA) isolated from a sequence of six Brazilian tropical soils with different degrees of weathering were characterized to evaluate possible relationships among their structural features and bioactivities toward plant growth. The chemical properties of HA, including elemental, conformational, and spectroscopy characteristics, were related to the HA effects on the activity of the plasma membrane H+-ATPase, as a biochemical marker for HA-induced root growth processes. The HA isolated from highly weathered soils had a larger oxidized character than HA isolated from less weathered soils. Organic matter transformation in more weathered soil induced an increase in carboxylic acidity accompanied with a decrease in alkyl content, as well as fluorescence intensity and content of free radicals. These changes suggested an alteration of the originally condensed aromatic compounds (lignin units) into unsaturated carboxylic acids. The HA derived from less weathered soils stimulated the plasma membrane H+-ATPase activity and maize root growth about twofold more than HA isolated from more weathered soils. Hydrophobicity and acidic functional groups represented the HA characteristics mostly effective in the stimulation of plant bioactivity. These results revealed a still unexplored relationship between chemical and biological properties of soil organic matter as a function of the weathering degree of native soils. (Soil Science 2008;173:624-637)

The temperature correction for the electrical resistivity measurements in undisturbed soil samples : analysis of the existing conversion models and proposal of a new model

Abstract: One of the challenges in soil science is to understand the relationships between electrical resistivity and other soil properties. Indeed, electrical resistivity is a complex soil electrical property that is affected by various soil parameters that can interact. Soil temperature plays a central role

Linear regression models to estimate soil liquid limit and plasticity index from basic soil properties.

Abstract: In Soil Survey, there is a need to estimate liquid limit (LL) and plasticity index (PI) for areas where data are not available. The objectives were to determine if LL and PI prediction equations could be developed from readily available soil properties in Soil Survey, and to test two different data

Influence of soil solution salinity on boron adsorption by soils

Abstract: Boron (B) adsorption on two arid-zone soils from the San Joaquin Valley of California was investigated as a function of equilibrium solution B concentration (0–250 mg L j1 ), solution pH (3–12), and electrical conductivity (EC, 0.3 or 7.8 dS m j1 ). Boron adsorption on both soils increased with increasing pH, reached a maximum near pH 9, and decreased with further increases in pH. Boron adsorption as a function of solution pH was independent of solution salinity from pH 3 to 9. Above pH 9, B adsorption was increased from the solution of higher EC. Boron adsorption for both soils as a function of solution B concentration conformed to the Langmuir adsorption isotherm equation. The B adsorption maxima obtained with the Langmuir equation for both EC were not statistically significantly different at the 95% level of confidence. The constant capacitance model, a surface complexation model, was able to describe B adsorption as a function of solution B concentration and solution pH. Boron adsorption was predicted using the soil chemical properties surface area, organic carbon content, inorganic carbon content, and aluminum oxide content. The predictions are suitable for transport modeling and will be used to describe B movement in large soil columns. Our results are advantageous because they indicate that under agricultural conditions (pH 3–9), B adsorption can be described without consideration of changes in soil solution salinity. (Soil Science 2008;173:368–374)

Null Creation Of Air-filled Structural Pores By Soil Cracking And Shrinkage In Silty Loamy Soils

Abstract: Information about abiotic regeneration of air-filled porosity in silty soils is scarce. It could be a key mechanism to explain their low physical resilience. In the present work, we aim at evaluating whether changes in intrinsic soil properties (e.g., soil organic carbon, clay content, and clay mineralogy) caused by degradation affected soil volume response to wetting-drying cycles. Volume and size distribution of cracks and clod shrinkage curves were determined in silty loamy soils (Typic Argiudoll) of Argentina under nearby conventionally tilled (CT), eroded CT, and Pasture management. Crack volume increased from 1000 cm 3 in CT and Pasture soils to 6000 cm 3 in the more clayey and swelling eroded CT soil. Crack size distribution was similar in all studied soils with large cracks (first and second size order) prevailing over small ones (fourth and fifth size order). Clod shrinkage curves had no S-shape, thus showing the lack of structural shrinkage in all studied soil management regimens. Air content in structural pores was as low as 0.03 to 0.10 cm 3 g -1 at the air entry point. This little air entry during drying agreed with the lack of small cracks and can be related to the prevalence of plasma (i.e., silt and clay) over sand. Results showed that key intrinsic properties did not drive soil volume changes in the studied silty loamy soils. They change their volume during drying, but the creation of air-filled structural pores is little or null.

Factors affecting mineral nitrogen transformations by soil heating: a laboratory-simulated fire study

Abstract: Two forest soils from the Sierra Nevada Mountains of California were brought into the laboratory and subjected to simulated burning in a muffle furnace at several durations, oven temperatures, and water contents. Soils were analyzed for NO 3 -, NH 4 + , total N, total C, and C:N responses to the treatments. Ammonium, which was the dominant form of inorganic N, generally increased with greater burn temperatures and durations (interpreted as higher fire severity), but decreased at the highest severity in dry soils. Increasing initial water content (IWC) diminished these responses in one soil but not in the other. Nitrate responses varied between soils, but generally increased with increasing IWC. Little or no change was seen in total N, total C, and C:N ratio except at highest severity, where C and N decreased regardless of initial moisture content. Soil temperatures measured immediately after burning increased with greater applied furnace temperatures and durations to near 100 °C, leveled off for periods depending on IWC, and then increased to 300 °C to 400 °C at higher temperatures and durations. This experiment shows that low-severity fire can cause very large and highly variable changes in NO 3 and NH 4 + , with little or no change in total C or N. High-severity fire has varying effects on NO 3 - and NH 4 + , depending on IWC and soil type, but generally causes losses of total C and N.

Sorption and leaching of short-term-aged pahs in eight european soils : link to physicochemical properties and leaching of dissolved organic carbon

Abstract: Polycyclic aromatic hydrocarbons (PAH) are among the major contaminants in the terrestrial environment. In tools for ranking contaminated soils according to risks and cleanup measures, simple predictions of contaminant leaching rates and actual leaching concentrations need to be established preferab

Gypsum amendment and exchangeable calcium and magnesium effects on plant nutrition under conditions of intensive nutrient extraction

Abstract: In general, increasing the concentration of one cation species in soil solution can decrease levels of other cations in plants. It is not clear whether adjusting soil cation ratios or adding gypsum will improve plant growth. We studied the effect of adding gypsum to unleached soil, and the effect of changing soil-exchangeable Ca/Mg ratios on corn root and shoot growth and nutrient concentrations. Soil-exchangeable Ca/Mg ratios (8.0, 4.9, 1.8, 0.7, and 0.5) were obtained by leaching soil with Ca and Mg chloride, followed by leaching with Ca and Mg sulfate to remove chloride. An unleached soil treated with gypsum and an untreated control soil were also included. Corn plants were grown for 23 days in a replicated greenhouse experiment. Exchangeable Ca/Mg ratios did not substantially affect root and shoot growth in the leached soils, nor did gypsum addition to the unleached soil. However, growth in the leached soils was less than that in the unleached soils, probably because of removal of K in the leaching process. Shoots from plants from treatments with lower leached Ca/Mg ratios had less Ca and more Mg but showed no consistent changes in K. Addition of gypsum to unleached soil decreased P, increased K and Ca, and did not affect N and Mg concentrations in shoots.

Organic amendments increase soil solution phosphate concentrations in an acid soil: a controlled environment study

Abstract: Soil acidification affects at least 4 million hectares of agricultural land in Victoria, Australia. Low soil pH can inhibit plant growth through increased soluble aluminum (Al) concentrations and decreased available phosphorus (P). The addition of organic amendments may increase P availability through competition for P binding sites, solubilization of poorly soluble P pools, and increased solution pH. The effect of two organic amendments (lignite and compost) on P solubility in an acid soil was determined through controlled environment (incubation) studies. Three days after the addition of lignite and compost, both treatments increased orthophosphate and total P measured in soil solution, with the compost treatments having the greatest positive effect. Increased incubation time (26 days) increased soil solution P concentrations in both untreated and amended soils, with the greatest effect seen in total P concentrations. The measured differences in solution P concentrations between the lignite- and compost-amended treatments were likely caused by differences in solution chemistry, predominantly solution pH and cation dynamics. Soil amendment with lignite or compost also increased microbial activity in the incubation systems, as measured by carbon dioxide respiration. Based on the results presented, it is proposed that the measured increase in soil solution P with amendment addition was likely caused by both chemical and biological processes, including biotic and abiotic P solubilization reactions, and the formation of soluble organic-metal complexes.

Leaching behavior of phosphorus in sandy soils amended with organic material

Abstract: Transport of phosphorus (P) from agriculture often causes eutrophication of surface water systems, which is particularly a concern in sandy soil regions because of low holding capacity of the soil for nutrients and moisture. Soil amendment is considered to be one of the best management practices in reducing P loss to water. A column leaching study was conducted to evaluate the effectiveness of organic amendment applied together with water-soluble fertilizer in reducing P leaching in two typical agricultural sandy soils (Spodosol and Alfisol) in south Florida. The Spodosol is an Alfic Alaquod, whereas the Alfisol is an Arenic Glossaqualf. Both soils have the same texture with sandy, siliceous, and hyperthermic properties. Organic material (OM) used in this study is marketed as a slow release organic fertilizer (GreenEdge; JEA Inc., Jacksonville, FL), which supplies essential nutrients for plant growth. The treatments consisted of chemical fertilizer (CF) alone, CF + 1.25 g kg -1 OM, CF + 5.0 g kg -1 OM, and CF + 10.0 g kg -1 OM. A control receiving no CF or OM was also included. Leaching of orthophosphate-P (PO 4 -P) and dissolved total P was similar. After seven leaching events, application of CF together with 10.0 g kg -1 OM reduced PO 4 -P and dissolved total P loss by 25.4% and 21.4% in the Spodosol and by 45.3% and 22.6% in the Alfisol and increased soil Olsen-P and Mehlich 3-extractable P by 54% and 31%, respectively, in the Spodosol and by 50% and 94% in the Alfisol, compared with CF alone. Increasing OM application rates increased NaHCO- and NaOH-extractable P but decreased water-extractable P in the two soils. Soil microbial biomass P (MBP) and the percentage of MBP in Olsen-P (MBP/Olsen-P) increased by 585% and 350%, respectively, in the leached Spodosol and by 190% and 127%, respectively, in the leached Alfisol with the treatment of CF together with 10.0 g kg -1 OM, compared with CF alone. It appears that the reduction in P leaching by OM amendment was related to the stimulation of microbial activities, which incorporate water-soluble P from applied CF into organic fractions and retained more P in soil against leaching but available to plants. These results indicate that organic amendment in combination with CF in a 10 g OM kg -1 soil level can increase P utilization efficiency by reducing P leaching and maintaining a larger available P pool in sandy soils.

Phosphorus sorption and desorption in semiarid soils of Senegal amended with native shrub residues

Abstract: Incorporation of organic residues into soils can improve P availability to crops in P-fixing soils. Perennial shrubs are commonly found in farmers' fields in Senegal, but little is known about their potential to reduce P sorption. Consequently, the residues of the two dominant shrub species, Guiera senegalensis and Piliostigma reticulatum were amended to soils where each is found, the Dior (Rubic Arenosol) and the Deck/ Dior (Mixed Haplic Ferric Lixisol), respectively, and compared with beef manure for P sorption characteristics. Amended soils (2% weight/ weight) were incubated at 24 °C for 30 or 75 days. Phosphorus isotherms were constructed using the batch technique, and sorption parameters were derived by fitting the Langmuir and Freundlich equations. All organic amendments decreased P adsorption maxima and affinity constants and increased P in the equilibrium solution (equilibrium P concentration) compared with the control. The amount of P desorbed from soils was greater in amended soils than in unamended soils. Soils beneath shrub canopy had lower P sorption capacity than soils outside shrub canopy in P. reticulatum-associated soils, which was reversed in G. senegalensis-associated soils. All organic amendments significantly increased soil pH. The longer incubation period of 75 days, over the 30 days, enhanced the effect of organic amendments in reducing soil P sorption and decreased soil pH. Manure amendments induced the greatest reduction in soil sorption capacity and showed the highest desorption rate. These results indicate that the addition of locally available plant residues to soil at a high rate can reduce P sorption and should be included in nutrient management recommendations of deficient P-fixing Sahelian soils.

Spatial Variability of Soil Properties in a Tobacco Field of Central China

Abstract: Present nutrient management recommendations for flue-cured tobacco (Nicotiana tabacum) in central China are typically uniform for large regions. This results in overapplication in areas with high nutrient levels and underapplication in areas with low nutrient levels. Therefore, understanding the spatial variability of soil nutrients is essential in determining local fertilizer needs of tobacco. The objectives of this study were to (i) quantify the spatial variability of soil properties across tobacco plantation fields and (ii) generate contour maps for these variables. Soil samples (0-20 cm) were taken from 81 points on an approximately 100-m grid in March 2007 using global positioning system to define sample locations. Seven soil chemical properties and texture were analyzed by geostatistical techniques. Soil pH, total N, sand, and clay showed strong spatial dependence, with nugget/sill ratios ranging from 16% to 20%. Soil organic matter, available phosphorus (AP), available potassium (AK), cation exchange capacity, and silt showed moderate spatial dependence, with nugget/sill ratios ranging from 30% to 50%. Soil alkalytic N showed no spatial dependence (pure nugget effect) at the chosen sampling interval. Ranges of spatial dependence varied from 274 m (total N) to 1066 m (cation exchange capacity). The clearly patchy distribution and low extrinsic component of variability for AP and AK indicated that spatial distribution maps for AP and AK could be used for the basis of site-specific fertilizer application.

Influence of specific organic compounds on phosphorus sorption and distribution in a tropical soil

Abstract: Effects of organic matter on phosphorus (P) sorption are not completely understood, among others, because the molecular composition of organic matter seldom has been considered. Our objective was to investigate how surface modification of a tropical soil with specific organic compounds altered the P

Useful Soil-water Repellency Indices: Linear Correlations

Abstract: Water repellency (WR) has been classically characterized at fixed (usually oven-dry) soil water content (θ g ) in terms of the soil water contact angle (CA), a. However, a has been previously reported to depend upon θ g in a nonlinear fashion, such that WR increases from a wettable state close to saturation (θ g-min ) up to a maximum, α max , decreasing afterward either monotonically or rising again to a second local or absolute a maximum nearby the dried soil state. Hence, a CA versus water content (α-θ g ) curve may be described in terms of different WR parameters, such as θ g-min , θ g-max , α max , or the integrated area below the α-θ g curve, S. Based on previous α-θ g measurements carried out with the molarity of an ethanol droplet (MED) test, both in mineral and volcanic soils from different world regions, including cultivated and natural forest soils, and textures ranging from clay-loam to sandy, we confirm here the usefulness of the integrated area below the α-θ g curve (S) as a WR describing index for a large variety of α-θ g curve shapes. We found a simple relationship between S and the soil water content at which WR is triggered, θ g-min , such that S = 16.903 θ g-min (R 2 = 0.946), which provides an easy method for the rapid characterization of the overall WR degree of soils. S was also linearly correlated with the soil organic matter (SOM) content (R 2 = 0.817) for 1 g (100 g) -1 < SOM < 88 g (100 g) -1 , such that the best estimate of S was that obtained by combining linearly both θ g-min and the SOM content (R 2 = 0.990). Linear correlations were also found between θ g-max , that is, the soil water content at which a is maximum, and S (R 2 = 0.834) or the SOM content (R 2 = 0.705), and consequently between θ g-max and θ g-min (R 2 = 0.830). In addition, both θ g-min and θ g-max were found to depend linearly upon the soil water content at -33 kPa and -1500 kPa, respectively. Finally, a mean soil WR may be defined as the ratio S/θ g-min . We found that the maximum CA, α max , and the mean soil WR S/θ g-min were positively correlated (R 2 = 0.780), such that a particular soil with high (low) values of maximum CA is expected to exhibit a high (low) WR degree on average across the whole water regimen from -33 kPa down to oven-dry moisture. Such an estimate of the mean WR index S/θ g-min was further improved if both α max and the SOM content were available (R 2 = 0.825).

Siderophore Promoted Dissolution of Pyromorphite

Abstract: Apatite amendment to lead (Pb)-contaminated soils has been investigated in the last decade as a method of Pb remediation. Phosphate released by apatite dissolution combines with Pb to form highly insoluble and supposedly nonbioavailable pyromorphite (PY). As a first approach to determining whether Pb present in PY might be susceptible to remobilization by microorganisms, we investigated the dissolution of PY in the presence of the trihydroxamate microbial siderophore desferrioxamine-B (DFO-B) as a function of pH (from 2 to 11), temperature, DFO-B concentration, and different solution/solid ratios in batch experiments. Desferrioxamine-B strongly complexes Pb in solution approximately above pH 6, and we observed enhancement of the net release of Pb from PY at pH 6 to 11. Dissolution in the presence of DFO-B was stoichiometric. Modeling using PHREEQC indicated that the increase of PY solubility can be accounted for by an increase in concentration of Pb-DFO-B complexes. Based on the enthalpy of dissolution reaction (ΔH r = -199.35 kJ/mol), dissolution of PY is exothermic, and PY solubility decreases with temperature. However, in the presence of DFO-B, the equilibrium-dissolved concentrations of Pb and P, along with the rate of net Pb and P release, increase with increasing temperature from 4°C to 50°C, suggesting that Pb-DFO-B complexation constants likely increase with temperature. Our results indicate that Pb may be mobilized from PY by microbial siderophores over the pH range of many soils, and that the potential effects of microorganisms on Pb remobilization thus need to be considered in Pb remediation strategies that rely on PY formation.

Loss of bioactive phosphorus and enteric bacteria in runoff from dairy manure applied to sod

Abstract: Information on the concurrent release and interactions between manure-borne phosphorus (P) and enteric bacteria to runoff from a live or dead grass sod is limited. A study of simulated runoff and an enzyme-based fractionation of runoff P forms from dairy manure applied on grass-covered soil in runof

Simple and rapid method for measuring gas dispersion in porous media: Methodology and applications

Abstract: In this article, a simple and rapid method for measuring gas dispersion coefficients in porous media is proposed. The method is easy to apply and requires only relatively inexpensive equipment. It is based on the use of atmospheric air and nitrogen as tracer gases combined with a fast oxygen electrode for oxygen concentration detection. The method was tested using 103-cm-long, 14-cm-diameter columns containing a homogeneous filter sand. The sand columns were packed to different dry bulk densities ranging from 1.06 to 1.55 g/cm 3 and gravimetric water contents ranging from 0.005 to 0.1 g H 2 O/g solids. Oxygen and nitrogen breakthrough curves were measured on these columns for pore gas velocities ranging from 6 to 35 cm/min. The data were fitted to the advection-dispersion equation yielding values for gas dispersion coefficients that were then used to calculate gas dispersivity values as a function of pore gas velocity, dry bulk density, and gravimetric water content.

TRANSPORT OF 17β-ESTRADIOL AND TESTOSTERONE IN A FIELD LYSIMETER

Abstract: 17β-Estradiol (E2) and testosterone (T) are present in sources such as waste treatment effluent and manures, and can potentially disrupt aquatic organisms at low concentrations. Laboratory studies consistently indicate limited mobility and rapid attenuation of E2 and T in soils; however, these hormo

A pulse-chase method to 13carbon-label douglas-fir seedlings for decomposition studies

Abstract: Tracking litter decomposition and root carbon (C) flow via stable isotopes, such as 13 C, is gaining popularity because of reliable and affordable mass spectrometry. Although model 13 C-labeled compounds such as glucose or acetate are available commercially, there is a need for large quantities of 13 C-labeled plant materials to realistically study decomposition, C cycling, and biogeochemical processes in situ or in the laboratory. The objective of this research was to determine whether a pulse-labeling technique to label Douglas-fir seedlings with 13 CO 2 would result in significant quantities of 13 C-labeled needles, stems, and roots that would be sufficiently enriched for in situ tracking of plant C into soil organic matter fractions. Once a week, for up to 9 weeks, 670 Douglas-fir seedlings were exposed to 13 CO 2 in a closed chamber. The 13 CO 2 (99 at.%) was injected into the chamber in quantities proportional to the photosynthetic rate, providing about 3 L of 13 CO 2 in total. More than 1.5 kg of seedling dry matter was produced, and the 13 C distribution was relatively similar among plant parts, with 1.57 in needles, 1.45 in stems, and 1.36 atom% 13 C in roots compared with control litter that had less than 1.084 at.% 13 C. Adding an additional pulse to one half the seedlings at 9 weeks resulted in needles and stems being further enriched over seedlings that had received 13 CO 2 pulses over 8 weeks. A 2-month field incubation study showed that for microcosms amended with labeled needle or root materials, 13 C could be tracked into whole soil, free particulate organic matter, or the humin fraction (recalcitrant C pool that is insoluble in strong base or acid). The pulse-labeling technique and chamber design provide large quantities of 13 C-labeled plant material that can be used to trace residue decomposition rates in field or laboratory studies.

Influences of dichlorodimethylsilane treatment on soil hydrophobicity, thermal conductivity, and electrical conductivity

Abstract: Soil water repellency occurs in a wide range of conditions, and it influences heat, water, and solute transport in soils. Dichlorodimethylsilane (DCDMS) has been used as a hydrophobizing agent to create waterrepellent soil materials by mixing the chemical with wettable soil samples. Little is known about how DCDMS treatment affects soil thermal and electrical properties. This study examines the influences of DCDMS treatments on soil water repellency, thermal conductivity, and electrical conductivity. Laboratory studies were performed on DCDMStreated soil samples with different degrees of water repellency. Soil thermal conductivity (1) and bulk electrical conductivity (Ab) were determined with the heat pulse method and time domain reflectometry technique, respectively, on repacked soil cores of various water contents. The results showed that DCDMS was able to hydrophobize soil samples, but reduced 1 and increased Ab at water contents greater than a critical value compared with wettable soil samples. Our analysis indicated that the increase in soil Ab was a result of salt dissolution from solid particle surfaces, which probably altered the hydration state of the solid particles. We concluded that DCDMS was effective in producing water-repellent soil samples, but the treatment also changed other soil properties, such as 1 and Ab. (Soil Science 2008;173:425‐432)

Phosphorus Fractionation in Chicken and Duck Litter Burned at Different Temperatures

Abstract: Disposal of poultry litter (PL) is one of the major concerns of poultry farmers. Burning of PL is an economically viable and environmentally safe method for poultry waste management. Phosphorus (P) fractionation in waste material is important for predicting its bioavailability. The objective of this study was to evaluate the effects of different temperatures on the release of P fractions in the chicken litter ash (CLA) and duck litter ash (DLA). The material was ashed at five temperatures: 200, 400, 600, 800, and 900 °C. Phosphorus was fractionated into readily plant-available P, labile inorganic P (another plant-available fraction), sesquioxide-associated P, and Ca-associated P by sequentially extracting with deionized water, 0.5 M of NaHCO 3 , 0.1 M of NaOH, and 1 M of HCl, respectively. Total P was determined by acid digestion. The inorganic P was also determined using Peterman citric acid and citric acid extractions. Loss-on-ignition, electrical conductivity (EC), and pH were measured. The experiment showed that weight loss was highly varied under different temperatures. As expected, increasing temperature increased weight loss. Except water-soluble P, all P fractions in samples increased with the increasing temperature. For both manures, P release decreased in the order: Ca-associated P > labile inorganic P > sesquioxide-associated P > readily plant-available P. Regardless of the burning conditions, sesquioxide- and Ca-associated P were higher in DLA than CLA, whereas the labile inorganic P (NaHCO 3 -P) was higher in CLA. For CLA, the sum of inorganic P that was found at its peak at 600 °C was 4.2-fold higher than unburned CL, whereas for DLA, the sum of inorganic P was 4.7-fold higher than unburned DL. Total P was higher in CLA than DLA with its highest amount at 900 °C. Peterman citric acid and citric acid-extractable P was substantially higher in CLA samples. Citric acid P was found more than Peterman citric acid P, and highest values were recorded at 600 °C. Irrespective of temperature, water-soluble P significantly decreased with burning. The burning practice seemed to affect the exchangeable cations. Magnesium was highest, whereas Ca 2+ was lowest at 600 °C. The K + was enhanced by temperature. The Ca 2+ and Mg 2+ contents were higher in DLA as compared with CLA. Potassium was highest in CLA. The CLA exhibited higher EC and lower pH values than DLA. Both EC and pH increased with temperature. The low water-soluble P in ash could suggest that the use of burned PL would be less of a water pollution problem in the fields.