bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Diffusion on the Kinetics of Biodegradation: Experimental Results with Synthetic Aggregates
Authors: Scow Kate M. , Alexander Martin
Published: July 2010

The rates of biodegradation in soil often do not conform to the predictions of kinetic models, such as the first‐order and Michaelis‐Menten models, developed to describe metabolic processes occurring in solutions in which microorganisms and their substrates are well mixed. To test whether the kinetics of biodegradation in the presence of aggregates could be described by explicitly accounting for chemical diffusion, studies were conducted in well‐defined experimental systems. The kinetics of biodegradation of low concentrations of 14C‐labeled phenol and glutamate by Pseudomonas sp. Strain K in buffer containing spherical aggregates of kaolinite that exclude bacteria were significantly different from the kinetics measured in the absence of aggregates. Both the biodegradation rate and the percentage of the initial compound degraded were lower in the presence of aggregates than in their absence. Using measurements of biodegradation, diffusion rates, and physical properties of the experimental system as input parameters, the diffusion‐sorption‐biodegradation (DSB) model simulated the biodegradation of phenol and glutamate originating inside aggregates. The model also simulated the initial period of biodegradation of glutamate in an experimental system containing gel‐exclusion chromatography beads. Clay aggregates reduced the concentration of available p‐nitrophenol sufficiently to lower the apparent rate constant for its biodegradation. Microscopic mass‐transfer processes, such as diffusion, may be important to consider in quantitative descriptions of the biodegradation of organic chemicals in soil.
Liming Double‐Cropped Ryegrass and Sorghum
Authors: Morris D. R. , Joost R. E. , Corkern D. L. , Mason L. F.
Published: July 2010

The grower must apply lime to maintain crop yields when double‐cropping forage sorghum [Sorghum bicolor (L.) Moench] in summer and ryegrass (Lolium multiflorun Lam.) in winter on Coastal Plain soils of the U.S. Southeast. The purpose of this research was to determine the frequency and rate of liming needed for optimal growth of these crops and to identify soil properties having greatest effect on yield. The experiment was conducted on a Tangi silt loam (fine‐silty, siliceous, thermic Typic Fragiudult) during a 12‐y period. Dolomitic lime treatments were: 0 lime, 2.2 and 4.4 Mg lime ha‐1 applied every 2yr, and 2.2 and 4.4 Mg lime ha‐1 applied every 4 yr. Soil samples were taken annually and analyzed for pH, exchangeable Al, Ca, Mg, and K, and extractable P. Surface soil pH was maintained at 5.8 and 6.0 when lime was applied at 2.2 and 4.4 Mg ha‐1 every 2 yr. Soil pH declined when lime was applied every 4 yr. In unlimed soil, the pH declined from 5.6 to 4.7 during the 12 yr. Significant differences in forage yields between unlimed and limed treatments did not occur until the sixth year (for sorghum) and the 11th year (for ryegrass). Reduced yields of ryegrass first occurred when soil pH decreased to 4.8 ± 0.11; for sorghum, yields declined at pH 5.2 ± 0.078. Crop yields of limed treatments were not affected by liming frequency. It may take longer than 12 yr for soil property differences among lime treatments to be large enough to alter plant yields. Ryegrass yield was not correlated with any surface soil parameters; Sorghum yield was positively correlated with surface soil extractable Ca. Exchangeable Al tended to decline and extractable Ca and Mg tended to increase with lime applications. Neither extractable P nor K was signigicantly altered by lime treatment. In a double‐cropped system of ryegrass and sorghum, liming would be of more benefit to sorghum.
Nitrous Oxide Emissions in Irrigated Corn as Affected by Nitrification Inhibitors
Authors: Bronson K. F. , Mosier A. R. , Bishnoi S. R.
Published: July 2010

Nitrous oxide and N2 are the major denitrification products in irrigated corn (Zea mays L.). In addition, N2O is considered a gas that contributes to global warming and stratospheric O3 depletion. Minimizing N2O emissions in cropping systems is therefore an economic as well as an important environmental concern. In a 1989 field experiment, the nitrification inhibitor encapsulated calcium carbide (ECC) (0, 20, or 40 kg CaC2 ha‐1) or nitrapyrin (0.5 L a.i. ha‐1) was banded with urea (218 kg N ha‐1) 7 wk after planting corn. Between 1 and 14 wk after fertilization in 1989, N2O losses of 3226, 1109, 1017, and 1005 g N2O‐N ha‐1 from urea alone, urea plus nitrapyrin, urea plus 20 kg ECC ha‐1, and urea plus 40 kg ECC ha‐1, respectively, were measured from vented chambers. Nitrous oxide fluxes were positively correlated with soil NO3 levels, indicating that the nitrification inhibitors indirectly controlled N2O emissions by preventing NO3 from accumulating in the soil. Carbon dioxide emissions from the root zone were generally not affected by ECC or nitrapyrin. In 1990, losses of N2O were less than in 1989 (1651 g N ha‐1 with urea alone), probably because there were fewer irrigations. Nitrapyrin and ECC addition to urea resulted in 980 and 459 g N ha‐1 N2O being emitted the second year. Nitrification inhibitors appear to be a useful tool in mitigating N2O emissions in agricultural systems.
Interrill Erodibility of Some Ohio Soils Based on Field Rainfall Simulation
Authors: Bajracharya R. M. , Elliot W. J. , Lal R.
Published: July 2010

Prediction of soil erodibility and an understanding of erosion processes are vital to sustained productive use of agricultural land. Interrill erodibilities (Ki) of five Ohio soils were assessed and compared with predicted Ki using the Water Erosion Prediction Project equation (WEPP‐K). A portable rainfall simulator was used to apply ∼ 70 mm h‐1 intensity rain for 1 h on 0.75‐m2 field plots representing crop row sideslopes. The soils studied included Miamian (fine, mixed, mesic Typic Hapludalf) and Riddles (fine‐loamy, mixed, mesic Typic Hapludalf) silt loams, Crosby silt loam (fine, mixed, mesic Aeric Ochraqualf), Kokomo silty‐clay loam (fine, mixed, mesic Typic Argiaquoll) and Mechanicsburg loam (fine‐loamy, mixed, mesic Ultic Hapludalf). The value of Ki determined for each soil was related to selected physical and chemical properties. Values of Ki varied significantly between soils and ranged from 1.23 ± 0.09 to 1.97 ± 0.60 × 10‐6 kg s m‐4. Interrill erodibility was negatively correlated with water‐stable aggregates (WSA) >0.25 mm (r2 = 0.50), WSA > 0.5 mm (r = 0.49), and organic C (r2 = 0.61), and positively correlated with Middleton's dispersion ratio (r2 = 0.84) and the ratio of water‐dispersible clay to total clay (r2 = 0.70). The WEPP‐Ki differed from measured values by ∼ 10 to 40%, ranging from 1.1 to 2.0 kg s m‐4. There was no correlation between WEPP‐Ki and measured Ki.
Isotopic Composition of Hydration Water in Gypsum and Hydroxyl in Jarosite
Authors: Dowuona G. N. , Mermut A. R. , Krouse H. R.
Published: July 2010

Data on the isotopic composition of hydration water in gypsum and hydroxyl in jarosite are rare. This study was initiated to measure the δ18O and δD (deuterium) values of hydration water in gypsum and hydroxyl in jarosite and to determine their relationship with the isotopic composition of environmental water. Gypsum and jarosite in soils from different localities in Saskatchewan, Canada, were sampled for O and H isotope analyses. Two samples from Maryland and one from Thailand were included for comparison. The δD and δ18O values of hydration water in gypsum and hydroxyl in jarosite varied from ‐166 to ‐80‰ and ‐17 to ‐9‰, respectively. Gypsum and jarosite samples from Saskatchewan generally followed the gradient in isotopic composition of local precipitation with slopes of 8.9 and 8.6, respectively. Samples from Maryland and Thailand, which are located at lower latitudes, showed relative enrichment in D and 18O, compared with the samples from Saskatchewan. The δD and δ18O data of samples from Saskatchewan, Maryland, and Thailand plot along a straight line with a steep slope of 11.5 due to the relative D and 18O enrichment in samples from Maryland and Thailand. Because the isotopic composition of hydration water of gypsum and hydroxyl of jarosite reflect that of water in the soil environment, they may be useful as a proxy for the isotopic composition of soil moisture at depths where gypsum or jarosite precipitates.
Pool Size and Mean Age of Stable Soil Organic Carbon in Cropland
Authors: Hsieh Yuch‐Ping
Published: July 2010

Most modern surface soils are believed to contain a pool of very stable soil organic carbon (SOC) with a mean age (MA) that may reach several thousand years. The remaining SOC pools are much younger, perhaps no older than a few decades. The SOC can thus be divided into two major classes: very old (stable pool) and relatively young (active pool). Because active and stable SOC play very different roles in soil organic‐matter dynamics and nutrient cycling, it is desirable to know the pool size and turnover time of the two fractions in an ecosystem. Unfortunately, none of the physical or chemical fractionation methods can satisfactorily separate active from stable SOC. The pool size and MA of the stable SOC pool in the surface soil of the Morrow Plots (University of Illinois) and Sanborn Field (University of Missouri) were determined using the concept of management‐induced differential decomposition of active SOC in a pair of soil samples and the principle of radiocarbon dating. Pool size and MA of the stable SOC in the surface soil (0–20 cm) was estimated at 11.0 g/kg and 2973 yr for the Morrow Plots and 7.3 g/kg and 853 yr for Sanborn Field, respectively.
Soil Pattern Recognition with Fuzzy‐c‐means: Application to Classification and Soil‐Landform Interrelationships
Authors: Odeh I. O. A. , McBratney A. B. , Chittleborough D. J.
Published: July 2010

Soil variation is more continuous than discrete and therefore calls for a continuous approach to soil classification. Fuzzy set theory provides such an approach that quantitatively assigns individuals to geographically and taxonomically continuous classes. We hypothesized that the fuzzy‐c‐means algorithm, based on a fuzzy objective function, could be used to quantify pedons into intragrade and extragrade classes and that minimization of the function would allow for the most “precise” classification, which could be validated by mathematically heuristic methods. These methods assume that local extreme (or abrupt changes) in the value of the objective function or its derivatives indicate optimal grouping. This approach was applied on two transects traversing a subcatchment in the central Mount Lofty Ranges, South Australia. The resulting fuzzy soil classes were found to have reasonable spatial continuity and contiguity, which were associated with local variation in slope features and parent material. Thus the approach identified plausible groupings (substructures) among the soil individuals that realistically reflected changes in the external factors (principally landform and lithology) controlling the processes generating the substructures. The structure‐factor relationships could be used for further rapid soil pattern recognition embodied in soil classification and mapping.
Biodegradability of Dissolved Organic Matter in Forest Throughfall, Soil Solution, and Stream Water
Authors: Qualls Robert G. , Haines Bruce L.
Published: July 2010

High concentrations of dissolved organic matter (DOM) were leached into rainwater passing through the canopy and forest floor of an oak (Quercus spp.)‐hickory (Carya spp.) forest in the southern Appalachian Mountains. More than 95% of this dissolved organic C (DOC) and N (DON) was removed as water percolated through the soil profile and left the ecosystem in stream water. Our objective was to examine the importance of decomposition in the removal of DOC and DON. Samples of DOM from throughfall, forest floor water, soil water from A and B soil horizons, and stream water were all adjusted to a common initial DOC concentration, inoculated with soil and stream microbes, and incubated in solution for 134 d. In general, only 14 to 33% of the DOC in forest floor, soil solution, and stream samples decomposed during the incubation. The relative order of average decomposition of DOC from the various strata was, from fastest to slowest; throughfall, Oi horizon (forest floor), Oa horizon (forest floor), B horizon, stream, AB horizon, isolated fulvic acid, and upper A horizon. In short, biodegradability of DOM in the ecosystem profile declined vertically from throughfall to the A horizon and then increased with depth. The DON generally did not decay faster than the DOC — results consistent with the idea that hydrolysis of organic N is linked to mineralization of DOC rather than occurring selectively in response to the biochemical need for N. Throughfall DOM could be decomposed during its passage through the upper soil, but decomposition seems too slow to be responsible for the bulk of removal of DON and DOC that occurs in the mineral soil. Adsorption, rather than biodegradation, is more likely responsible for maintaining low DOC substrate concentrations in the mineral soil and preventing its loss into stream water.
Identification of Nutritional Influences on Cone Production in Fraser Fir
Authors: Arnold Roger J. , Jett J. B. , Allen H. L.
Published: July 2010

Fraser fir [Abies fraseri (Pursh) Poir.] is highly valued as a freshcut Christmas tree. Commercial cultivation is limited partly by seed scarcity. The purpose of this study was to develop foliar tissue nutrient norms for female cone yield to use in the Diagnosis and Recommendation Integrated System (DRIS), for ultimately improving cone yields. Two sets of these norms were developed, one set based on February and the other on July foliar nutrient levels. Neither single mineralnutrient concentrations nor other assessed tree parameters correlated with cone yield. However, nutritional discrimination between high‐and low‐yielding trees was obtained with July tissue. Discrimination with February needle samples was poor. Reasonable agreement was obtained for orders of nutrient limitations diagnosed from the two seasonally specific sets of norms. Results indicated the potential to use DRIS to aid in selection of clones and prescribing treatments to enhance cone yields.
Ridge‐Tillage Corn Response to Point‐Injected Nitrogen Fertilizer
Authors: Blaylock A. D. , Cruse R. M.
Published: July 2010

Management practices to improve N‐use efficiency have been studied repeatedly for conventional tillage and no‐till systems. Little work has been done, though, to identify efficient N‐placement methods for ridge‐tillage systems. The objective of this study was to test the hypothesis that point injection of N in the ridge can optimize N‐use efficiency and corn (Zea mays L.) production in ridge tillage, compared with broadcast N or injection between rows. Corn‐soybean [Glycine max (L.) Merr.] rotation studies were conducted between 1986 and 1988 on Webster and Marna silty clay loams (fine‐loamy, mixed, mesic Typic Haplaquoll and fine, montmorillonitic, mesic Typic Haplaquoll, respectively). Treatments consisted of a control (no N) and factorial combinations of three N‐placement methods (broadcast, point injection between rows, or point injection in rows) and five rates (22, 45, 67, 112, and 157 kg N ha−1) applied as urea‐NH4NO3 solution (UAN). Fertilizer‐N recovery by plants was determined at four growth stages in labeled‐N microplots. Corn yields, percentage of N derived from fertilizer, and percentage of fertilizer N recovered were significantly greater with injected N than with broadcast N. Injection position generally did not affect plant response. Point injection of N fertilizer can improve N‐uptake efficiency over broadcast methods in ridge‐tillage corn, but the importance of injection position was not substantiated.
Bypass Water Flow through Unsaturated Microaggregated Tropical Soils
Authors: Radulovich R. , Sollins P. , Baveye P. , Solórzano E.
Published: July 2010

Recent evidence suggests that bypass flow occurs in many soils even under unsaturated conditions, but experimental confirmation is lacking. We measured bypass flow in two microaggregated Inceptisols from the humid Atlantic region of Costa Rica under water‐application rates below those needed to produce ponding. Water was applied with a constant‐head rainfall simulator to undisturbed soil cores taken when soils were near field capacity. Mass of soil core and of water exiting the core (outflow) and time to first appearance of water at the bottom of the core (breakthrough) were recorded. For each application rate, steady‐state outflow was reached quickly at a core mass well below that corresponding to soil saturation. (In contrast, classical theory for sandy soils without macropores, based on the Richards' equation, predicts that breakthrough should take more than twice the time actually observed.) Successive step increases in application rate produced successively smaller increases in core mass and decreases in the lag time before outflow increased. Our results suggest that bypass flow will occur in the noncapillary interpedal pore space whenever the application rate exceeds the infiltration rate of individual microaggregates. Because values for matrix conductivity are extremely low (much less than typical rainfall rates), we suggest that bypass flow may be the rule rather than the exception in microaggregated soils with extensive interpedal noncapillary pore space.
Partitioning Dissolved Inorganic and Organic Phosphorus Using Acidified Molybdate and Isobutanol
Authors: Jayachandran K. , Schwab A. P. , Hetrick B. A. D.
Published: July 2010

Quantification of P‐mineralization rate in soil using isotopic dilution requires that soluble inorganic 32P (32Pi) be determined without interference from soluble organic 32P (32Po). Therefore, a method is needed to partition 32Pi and 32Po into physically separate solutions before radiation counting. A previously suggested method of extracting Pi into isobutanol with acidified molybdate was tested for efficiency of separation from Po. Inorganic P as KH2PO4 was completely recovered in the isobutanol phase with acid molybdate. Organic P (glycerophosphate) remained in the aqueous phase during the extraction. No Po hydrolysis was observed when sodium phytate, glycerophosphate, ribonucleic acid, adenosine 2′‐ and 3′‐monophosphate, and cytidine 2′‐ and 3′‐monophosphate were extracted, but detectable amounts of adenosine 5′‐triphosphate hydrolyzed. This technique was tested on four Kansas soils, and the levels of inorganic and organic P obtained by this method were the same as those detected by conventional analyses.
Nitric Oxide and Nitrous Oxide Production from Soil: Water and Oxygen Effects
Authors: Drury C. F. , Findlay W. I. , McKenney D. J.
Published: July 2010

This study was designed to determine the effects of water and O2 on the speciation of denitrification gases (NO and N2O). Nitric oxide was found to be the principal end product from soil incubated under low‐moisture conditions, whereas the relative amount of N2O increased under wetter moisture regimes. The total amount of NO plus N2O produced increased with increasing water content for the Brookston clay loam (fine‐loamy, mixed, mesic Typic Argiaguoll), whereas it peaked at 150 g kg−1 (15%) water content with the Fox sandy loam (fine‐loamy over sandy or sandy or sandy‐skeletal, mixed, mesic, Typic Hapludalf). The decrease in NO plus N2O at higher water contents was probably the result of the subsequent reduction of N2O to N2 in the Fox sandy loam soil. The residence time of the denitrification gases in the soil increased with increasing water content, hence facilitating the subsequent conversions of NO to N2O and N2. The thickness of the water film surrounding the microbes affected both the diffusion of O2 through the water and into the microbes as well as the diffusion of denitrification gases (NO, N2O, and N2) from the microbes into the atmosphere. In the sandy loam soil, O2 content and soil water affected both the amount and species of evolved denitrification gases. Oxygen was more effective in decreasing NO production at lower than at higher water contents.
Phosphorus Distribution in Loessial Fragiudalfs as Affected by Relief
Authors: Switzer R. E. , Pettry D. E.
Published: July 2010

Topographic effects on P form and distribution were determined in three loessial toposequences. Loring soils (fine‐silty, mixed, thermic Typic Fragiudalfs) were sampled in the top‐ and midslope positions. Slopes ranged from 1 to 2% in the topslope and 9.5 to 13% in the midslope pedons. Phosphorus distribution reflected changes in topographic position and the influence of fragipan horizons (Btx) in the pedons. Nonoccluded, occluded, organic, and total P decreased while Ca‐P increased as slope increased. Nonoccluded exceeded occluded P in the topslope Bt horizons, while occluded P dominated in the Btx horizons. Occluded P dominated midslope Bt and Btx horizons. Results suggest a loss of P and a reduction in weathering intensity as slope increased. Significant correlations were found between nonoccluded and occluded P and clay, dithionite‐ and oxalate‐extractable Fe, and total Fe while Ca‐P and organic P were correlated with pH and base saturation in the topslope pedons. In the midslope pedons, significant correlations were found between occluded P and clay and dithionite‐extractable Fe while Ca‐P and organic P were correlated with pH, base saturation, and organic matter. Maximum clay and total P occurred in similar Bt horizons in all topslope pedons. Changes in P distribution occurred into and below the Btx horizons, suggesting these changes occurred prior to and during fragipan formation.
High Dimensional Reflectance Analysis of Soil Organic Matter
Authors: Henderson T. L. , Baumgardner M. F. , Franzmeier D. P. , Stott D. E. , Coster D. C.
Published: July 2010

Recent breakthroughs in remote‐sensing technology have led to the development of high spectral resolution imaging sensors for observation of earth surface features. This research was conducted to evaluate the effects of organic matter content and composition on narrow‐band soil reflectance across the visible and reflective infrared spectral ranges. Organic matter from four Indiana agricultural soils, ranging in organic C content from 0.99 to 1.72%, was extracted, fractionated, and purified. Six components of each soil were isolated and prepared for spectral analysis. Reflectance was measured in 210 narrow (10‐nm) bands in the 400‐ to 2500‐nm wavelength range. Statistical analysis of reflectance values indicated the potential of high dimensional reflectance data in specific visible, near‐infrared, and middle‐infrared bands to provide information about soil organic C content, but not organic matter composition. Although reflectance in the visible bands (425–695 nm) had the highest correlation (r = −0.991 or better) with organic C content among the soils having the same parent material, these bands also responded significantly to Fe‐ and Mn‐oxide content. For soils formed on different parent materials, five long, middle‐infrared bands (1955–1965, 2215, 2265, 2285–2295, and 2315–2495 nm) gave the best correlation (r = −0.964 or better) with organic C content. Several wavebands were identified in which the soils were separable, but the reflectance response was dominated by soil factors other than organic matter content, indicating that choice of wavebands should not be based on spectral curve separability alone.
Infiltration Rate of a Sandy Loam Soil: Effects of Traffic, Tillage, and Plant Roots
Authors: Meek B. D. , Rechel E. R. , Carter L. M. , DeTar W. R. , Urie A. L.
Published: July 2010

Settling and trafficking of a soil after tillage causes rapid changes in the soil physical condition until a new equilibrium is reached. In the soil studied, a Wasco (coarse‐loamy, mixed, nonacid, thermic Typic Torriorthent) sandy loam, soil compaction reduces infiltration rates, which under grower conditions could result in inadequate infiltration of irrigation water to supply crop requirements. Our objective was to evaluate important management practices as they relate to changes in the infiltration rate of a sandy loam soil. Factors evaluated were traffic, tillage between crops, and the formation of channels by roots of perennial crops. Tillage between crops increased the infiltration rate during the first part of the season in trafficked soils but decreased or had no effect on nontrafficked soil. Alfalfa (Medicago sativa L.) increased the infiltration rate fourfold during a 2‐yr period in a heavily compacted soil. An increase in bulk density from 1.6 to 1.8 Mg m−3 decreased infiltration rate 54% in the field. Hydraulic conductivity of undisturbed cores was at least seven times larger than that measured in columns of disturbed soil (same bulk density). This difference is believed to be the result of natural channels in the undisturbed soil that are destroyed when the soil is disturbed. Under controlled traffic, when surface seal is not a problem, tillage will not be necessary to obtain adequate infiltration rates except in the wheel paths.
Nitrogen and Phosphorus Release from Decomposing Needles of Southern Pine Plantations
Authors: Polglase P. J. , Jokela E. J. , Comerford N. B.
Published: July 2010

Fertilizer application and weed‐control treatments have increased biomass accumulation of loblolly (Pinus taeda L.) and slash pines (P. elliottii Engelm. var. elliottii) in north‐central Florida. While the effects of these treatments have been immediate, the long‐term influences on rates of nutrient cycling are unknown. This study measured rates of mass loss and changes in N and P contents in Oi horizon needles decomposing in the laboratory, and in Oi, Oe1, and Oe2 horizon needles decomposing in situ (litterbag study). The quality of organic‐matter substrates in needles (determined by laboratory incubation) was increased by both weed‐control and fertilizer treatments (P < 0.05), and litter quality of loblolly pine was greater than that of slash pine. However, these effects were not manifest in the field study. Across all treatments, an average of 31% of the original organic matter was lost after 1 yr of decomposition in situ. Generally, N was immobilized into Oi horizon needles but was released in modest amounts (<15% yr−1) from Oe1 and Oe2 horizon needles. In contrast, substantial release of P from Oi horizon needles (>35% yr−1) was followed by smaller release from Oe1 and Oe2 horizon needles (< 15% yr−1). More P was cycled per unit of organic matter in fertilized than nonfertilized plots, and loblolly pine cycled more P than slash pine. Changes in total P content of needles during decomposition were accounted for by changes in the pool of inorganic P. The rapid recycling of P in fertilized plots has the potential to enhance long‐term productivity beyond the immediately beneficial effects derived from fertilizer uptake.
Thiosulfate Inhibition of Urea Hydrolysis in Soils: Tetrathionate as a Urease Inhibitor
Authors: Sullivan D. M. , Havlin J. L.
Published: July 2010

Ammonium thiosulfate [ATS, (NH4)2S2O3, 12‐0‐0‐26S] added to urea‐ammonium nitrate (UAN) inhibits urea hydrolysis after application to soil. Thiosulfate itself does not inhibit purified jackbean urease, so products of S2O2‐3 oxidation in soil (tetrathionate [S4O2‐6], Fe2+, and Mn2+) are the probable urease inhibitor(s). The objectives of this study were to (i) identify the primary urease inhibitor produced by ATS in soil and (ii) determine why the efficacy of the inhibitor is improved by increasing UAN droplet size. Jackbean urease (urea amidohydrolase, Type III from jackbean, EC 3.5 1.5) was inhibited by Fe2+ (100% inhibition at 0.3 mM), Mn2+ (100% at 6.3 mM), Fe3+ (97% at 6.3 mM), and S4O2‐6 (39% at 7.8 mM). Thiosulfate did not inhibit jackbean urease at concentrations up to 18.8 mM. When applied in a simulated UAN fertilizer band, S4O2‐6 was as effective as S2O2‐3; it inhibited soil urease (24%) to the same extent as S2O2‐3 (26%) but more than FeSO4 (0%) in two soils. Urease inhibition by all species was low in unbuffered 5‐h soil incubations (Fe2+ [14%], Mn2+ [3%], S4O2‐6 [10%], and S2O3 [7%]) with 25 mmol S kg−1. Urease inhibition by S4O2‐6 increased from 9% at pH 7 to 30% at pH 8.5 in buffered incubations. Since pH during urea hydrolysis increases with UAN droplet size, the increased efficacy of ATS with application of large UAN droplets is probably due to greater activity of S4O2‐6 as a urease inhibitor at pH > 7. Tetrathionate is the primary urease inhibitor produced by ATS in soil. Reaction of urease sulfhydryl groups with S4O2‐6 is proposed as an inhibitory mode of action.
Association of Microcrystalline Goethite and Humic Acid in Some Oxisols from Brazil
Authors: Fontes M. R. , Weed S. B. , Bowen L. H.
Published: July 2010

Oxisols from the cocoa‐growing region of the state of Bahia, Brazil, may contain large amounts of Fe oxides and significant amounts of organic C to depths exceeding 2 m. The nature of the association of organic C and crystalline oxides was the objective of this study. Alkali extracts (0.1 M NaOH) of soil material taken from different depths in three Typic Hapludox and one Humic Hapludox were characterized by chemical analysis, x‐ray diffraction, Mössbauer spectroscopy, electron microscopy, surface area determination (N2 adsorption), Fourier‐transform infrared spectroscopy, and phosphate adsorption. Microcrystalline goethite was the only inorganic phase accompanying the humic acid in the alkaline solution and humic acid was essential for goethite to be extracted. Mössbauer spectra confirmed the absence of Fe oxides other than goethite in the humic‐acid extracts although hematite and ilmenite were identified in the total soil material. The goethite particles were 10 to 15 nm in diameter and nearly equidimensional. Infrared spectra of the humic acid‐goethite complex indicated that the COOH group was in the salt form, suggesting bonding through this group to the goethite surface. Phosphate adsorption was markedly higher on the humic‐acid‐free goethite than on the complex, indicating competition for adsorption on the goethite by the humic acid. Apparently, the interaction between the humic acid and the goethite involves iigand exchange in addition to coulombic attraction, and may significantly modify the properties of the Fe oxide.
Soil Gas Permeability as Influenced by Soil Gas‐Filled Porosity
Authors: McCarthy Kevin P. , Brown Kirk W.
Published: July 2010

The need to characterize the fundamental gas flow properties of soils has taken on new significance in recent years with the advent of induced soil venting as a remediation technique for contaminated soils. The purpose of this study was to characterize the relationship between soil gas permeability and soil gas‐filled porosity, and the effect of various soil physical properties on this relationship. A gas permeameter was developed to study gas flow through undisturbed soil cores from two horizons in each of three soil series. Measurements of the pressure difference across the soil core at varying flow rates were used to calculate gas permeability (k), from soil having a range of soil gasfilled porosities (Ea). Bulk density, pore‐size distribution, and particle‐size distribution were also measured on each soil. In soils containing <20% clay, the relationship between the gas‐filled porosity and the gas permeability was adequately represented by a linear equation across the range (0.4–33%) of gas‐filled porosities tested. The linear equation was unique to each soil studied and a general equation representative of all soils could not be established. Structured soils exhibited greater permeabilities than poorly structured soils, presumably due to the larger inter‐aggregate flow channels characteristic of structured soils. In poorly structured soils, finer textures were less permeable than coarser textures. Three of four soils with <20% clay exhibited anisotropic behavior, with higher permeabilities in the horizontal direction than in the vertical direction, related to their alluvial origin.
Interface Penetration Model Formulation for Analyzing Wall‐Separation‐Influenced Transient Hydraulic Conductivity Data
Authors: Jennings Aaron A. , Ravi Varadhan
Published: July 2010

Hydraulic conductivity values measured in permeameters can be influenced by the formation of preferential flow pathways that allow a significant fraction of flow to bypass the soil sample. Problems of this type are of particular concern when testing low‐permeability soils with aggressive permeants because reactions increase the possibilities for preferential flow pathways to develop. A wall‐separation preferential flow model is proposed based on the discrete interface penetration (DIP) modeling strategy. The formulation is specifically designed to help determine if observed transient hydraulic conductivity behavior may be attributed to soil‐permeant interactions, or may have resulted from a wall separation preferential flow pathway that developed after the start of the permeameter experiment. Analytical solutions are presented for two sets of boundary conditions. Example evaluations of experimental data are presented to illustrate how these solutions could be applied. Information is also presented on model parameter estimation and sensitivity. Possible extensions of the modeling strategy to additional problems of preferential flow are also discussed.
Pore‐Size‐Dependent Apparent Viscosity for Organic Solutes in Saturated Porous Media
Authors: Malik M. , Letey J.
Published: July 2010

The value of hydraulic conductivity under saturated conditions, K, depends on the nature of the porous medium and the physical properties of the perfusing fluid. The equation K = kρg/η, where k is the permeability, η is the fluid viscosity, ρ is the fluid density, and g is the gravitational constant, has been used to account for porous medium and fluid properties on K. A laboratory study was conducted to determine whether the equation properly accounts for viscosity effects of organic solutes on K. Hydraulic conductivity of 0, 25, 50, 100, 200, 300, and 400 mg L−1 solutions of large molecular weight polyacrylamides (PAM); 0, 10, 20, 30, 40 and 50% (v/v) of glycerol in distilled water; and undiluted n‐propanol was measured in two size fractions of quartz sand. The apparent viscosities of PAM and glycerol solutions were higher in the fine sand than in the coarse sand. The apparent viscosity of n‐propanol was about the same in the two sand‐size fractions. The above‐stated equation did not properly account for the effects of fluid properties of PAM and glycerol on K. Use of viscosity values as measured by a viscometer in the equation could result in a several‐fold error in prediction of K. Quantitatively characterizing those conditions under which the equation is valid may be important in analyzing the transport of environmental contaminants through soil, particularly when the contaminants may be organic chemicals of various molecular sizes and conformations.
Individual Sorbent Contributions to Cadmium Sorption on Ultisols of Mixed Mineralogy
Authors: Cowan Christina E. , Zachara John M. , Smith Steve C. , Resch Charles T.
Published: July 2010

A multisite model was applied to Cd‐sorption data across a range in pH and at ionic strength (I) = 0.1 and 0.01 on specimen layer silicates and on untreated and dithionite‐citrate‐bicarbonate (DCB) treated isolates from two Utisols. The two isolates contained different mass concentrations of kaolinite, 2:1 layer silicates, Al‐substituted crystalline Fe oxides, and gibbsite. The multisite model included the exchange of Cd2+ on fixed‐charge sites on the layer silicates, complexation to hydroxyl sites on the layer silicates and Fe oxides, and electrostatic interaction between positively charged sites on Fe oxides and fixed‐charge sites on the layer silicates. Site concentrations for the specimen layer silicates and DCB‐treated and untreated isolates were estimated from cation‐exchange capacity (CEC) data and N2‐specific surface area. Equilibrium constants for specific surface reactions were estimated from Cd‐sorption data on the specimen layer silicates, KGa‐1 and SWy‐1, and the DCB‐treated soil isolates. The combined modeling results indicated that (i) Cd2+ ion exchange to fixed‐charge sites was the dominant sorption reaction for pH < 6.5 and I = 0.01, (ii) mass action with Na suppressed ion exchange at I = 0.01, (iii) Cd complexation to hydroxyl sites produced strong pH dependency in Cd sorption and was responsible for all the Cd sorption at I = 0.01 and above pH 6.5 at I = 0.01, and (iv) Fe oxides decreased Cd sorption by blocking access of Cd to exchange sites. The modeling results were unable to determine whether Fe oxides were important sorbents for Cd. Either with or without Cd sorption on Fe oxides, this model was able to describe the Cd sorption on the soil isolates reasonably well.
Sodium Adsorption Ratio Screening Procedure for Soils Using pH and Electrical Conductivity
Authors: Munk Lewis P.
Published: July 2010

Soils with sodium adsorption ratios (SAR) <10 are generally considered to be below the threshold for potential Na hazard. The impetus for developing this screening procedure was to reduce the resources dedicated to determining precise SAR values in situations when simply knowing that the SAR is below the designated threshold is sufficient. The model was developed using 1000 samples and validated on a 24 000‐sample data set from two different laboratories operating in the western USA. The screening procedure uses empirically derived combinations of saturated soil paste pH (pHs) and extract electrical conductivity (ECe) to predict if the SAR is above or below 10, or whether Ca + Mg and Na must be analyzed to determine the SAR. For some combinations of pHs and ECe, the ratio of Ca + Mg to estimated total cations [ETC = ECe(10)] is used to decide whether Na must be analyzed. On average, the model incorrectly predicted that the SAR was <10 when the actual value was > 10 in only six out of 1000 samples. In addition, about 20% of the samples required Ca + Mg and Na analyses when the SAR was < 10. For the data sets tested, the screening procedure could have reduced the number of Ca + Mg and Na analyses by 50% with little loss of information about the potential Na hazard of the soils.
Fertilizer and Organic Amendment Effects on Mine Soil Properties and Revegetation Success
Authors: Schoenholtz Stephen H. , Burger James A. , Kreh Richard E.
Published: July 2010

Nitrogen deficiency frequently limits mine‐soil revegetation in the eastern USA. Application of organic amendments to these systems may provide a long‐term source of N and eliminate the need for repeated fertilization. A factorial experiment was conducted using lysimeters to determine the degree to which (i) organic amendments (control, 50 Mg ha−1 of whole‐tree wood chips, or 500 Mg ha−1 of native topsoil) and (ii) inorganic N fertilizer (0 or 100 kg N ha−1 as NH4NO3) affected mine‐soil properties and establishment of herbaceous vegetation and pitch × loblolly hybrid pine (Pinus rigida L. × P. taeda L.) seedlings on a newly exposed mine soil from the central Appalachian region. Amendments were tilled into the soil surface prior to application of fertilizer and cover‐crop seed. After 3 yr, total N, mineralizable N, and organic C in the wood‐chip‐amended mine soil were 10, 50, and 18% higher, respectively, than the control. Tree growth after 2 yr was highest with wood chips. A lack of wood‐chip treatment effect on pine nutrition showed that higher soil moisture levels, resulting from lower evapotranspiration, probably accounted for improved tree growth. Topsoil replacement increased total N and mineralizable N by 23 and 46%, respectively, but did not significantly increase vegetation productivity over that of the control. Nitrogen fertilizer increased herbaceous biomass production by 87% during the first growing season but did not affect herbaceous or pine productivity in two subsequent years or produce lasting effects on soil nutrient levels. Organic amendment × fertilizer interactions were not significant for any measured parameters. Results show that the organic amendments provided more stable sources of soil N; however, early revegetation success was more a function of moisture than of soil nutrient availability.
Fiber Content and Degree of Decomposition in Peats: Review of National Methods
Authors: Malterer T. J. , Verry E. S. , Erjavec J.
Published: July 2010

Fiber content and degree of decomposition are important physical and chemical peat characteristics. However, there are no internationally accepted methods for their determination. We review selected national methods that measure degree of decomposition and fiber content, and evaluate their precision and their capacity to distinguish between classes of peat. We also relate one national method to another using scaled‐variable regression equations. The von Post humification method, a European field test, was used in the identification and sample collection of 10 humification (decompositional) peat classes, from sphagnum, herbaceous, and humus peat types. Subsequent statistical analyses of the samples revealed that only eight classes were significantly different. The USSR centrifugation method successfully identified all eight classes, while the ASTM fiber method successfully identified four of the classes, the USDA fiber methods identified three, four, or five classes, and the USDA pyrophosphate method identified three of the classes. These analyses indicate that the USSR centrifugation laboratory method and the von Post humification field method separate more classes of peat with greater precision than the ASTM, several USDA fiber volume, and USDA pyrophosphate methods. However, similar tests on woody peats and tropical peats are needed to test the universal acceptability of the USSR centrifugation and the von Post humification methods. Predictive regressions between methods had R2 values from 0.690 to 0.998 and CVs form 4.8 to 45.3%. Thirty‐eight percent of the between‐method regressions are parabolic, 43% linear, and the remainder cubic.
Reclamation of a Saline Sodic Soil Using Synthetic Polymers and Gypsum
Authors: Zahow M. F. , Amrhein C.
Published: July 2010

The water infiltration rate of saline sodic soils often limits the rate of reclamation. Column leaching studies were conducted to determine if water‐soluble, synthetic polymers would be beneficial in improving the hydraulic conductivity and aid reclamation of a heavy‐textured, salt‐affected soil. Soil samples from a swelling soil (fine, montmorillonitic [calcareous] Thermic Vertic Haplaquoll) were collected from a field site that had exchangeable sodium percentages (ESP) of 8, 12, 20, 25, 32, and 35. The air‐dried soil samples were treated with polyacrylamide polymers (one nonionic and two anionic) and one cationic guar‐derivative polymer at a rate of 50 mg kg−1. Polymer treatments had a highly significant effect on increasing the saturated hydraulic conductivity of the soil samples with ESP values <15, but had no significant effect on the samples with values > 15. The addition of gypsum increased the hydraulic conductivity from 0.0 to 0.063 mm h−1 in the soil with an ESP of 32. When polymers were used in conjunction with gypsum, the hydraulic conductivity increased to 0.28 mm h−1. We attributed the improvement in hydraulic conductivity with polymer treatment at low ESP values and in the gypsum‐treated soil to a reduction in soil slaking and dispersion. At ESP values > 15, an additional mechanism that may have been controlling the hydraulic conductivity was swelling, and none of the polymers reduced soil swelling.
Molecular Weight Distribution of Soluble Organics from Laboratory‐Manipulated Surface Soils
Authors: Homann Peter S. , Grigal David F.
Published: July 2010

Transfer of organic matter from solid to solution phase is the first step in the redistribution by leaching of organic C and associated elements in forest soil profiles. To examine the effects of disturbances on solubilization of organics, three A horizons and one O horizon were exposed to air drying, waterlogging, addition of urea, addition of ash, and addition of ash in combination with heating at 250 °C. Following incuhation at 20 to 22 °C for 1 to 50 d, soluble organic C (SOC) was extracted with 0.5 mM SrCl2. The SOC was 0.2 to 0.7% of total organic C in controls. Urea and heat‐plus‐ash treatments yielded up to 17 times more SOC than controls, and other treatments yielded up to three times more than controls. Distribution of SOC among molecular‐weight classes, as determined by dialysis, was 21 to 32% in the <3500‐dalton class, 8 to 20% in the 3500 to 14 000‐dalton class, and 47 to 71% in the >14 000‐dalton class. Urea treatment yielded a higher proportion of SOC in the >14 000‐dalton class than in the controls, while air drying resulted in a lower proportion. Both the quantity and quality of soluble organics can be influenced by soil disturbances, but the specific response varies with the type of disturbance.
Field Solute Transport across a Soil Horizon Boundary
Authors: Hamlen C. J. , Kachanoski R. G.
Published: July 2010

Models describing solute transport in a field soil need to account for transport through soil horizons and across horizon boundaries. This study investigated the effects of soil horizons on the transport of a conserving tracer and the validity of treating soil horizons as independent (uncorrelated) layers. The occurrence or absence of correlated solute travel times with depth was tested by comparing predicted solute travel time variances with variances measured from solute breakthrough curves. Steady‐state transport experiments were conducted on a Fox sand (fine‐loamy over sandy or sandy‐skeletal, mixed, mesic Typic Hapludalf) in Ontario, Canada. The transport of Cl through the Ap and the Ap + B horizons was measured at constant surface flux densities of 3.5 and 5.5 cm h−1. The upper 20 cm of soil was then excavated and the transport of Cl through the B horizon was measured independently at a flux density of 5.5 cm h−1. The horizons exhibited differences in solute velocity, spatial variations in velocity and in equilibrium water contents. At the transect scale, successful predictions of travel time variance were made at both flux densities when it was assumed that solute travel times were correlated with depth. At the local scale, the successful prediction of variance assuming correlated travel times occurred only at the lower flux density. At this site a correlated model is appropriate for describing solute transport at the transect scale. Independent estimates of transport properties from each horizon is not sufficient information to predict field transport. The nature of the boundary between horizons must be evaluated.
Ion Transport in Soil with Ion Exchange Reaction: Effect of Distribution Ratio
Authors: Ishiguro M.
Published: July 2010

Exchanging ionic‐solute transport through soil columns is significantly affected by ion exchange reaction. The breakthrough curve (BTC) for the input ion based on time or pore volume shifts to the right as the ion‐exchange capacity increases or the input ion concentration decreases. The shapes of the BTCs with different mean breakthrough times are easily compared when the BTCs are normalized by the mean breakthrough times. The influence of the distribution ratio, Dg, the ratio of the amount of ions adsorbed in the soil to that in the solution in a unit volume of the soil, on normalized BTCs with nonlinear exchange isotherms was evaluated. The cases studied here involved ion exchange in a binary system at a constant total concentration under steady‐state water‐flux conditions. The BTCs were calculated and interpreted using a normalized, one‐dimensional advective‐dispersive equation. It was determined that the effect of the nonlinear isotherm on the BTC increases as Dg increases. It was also shown that, when Dg is much greater than unity, an increase in Dg has no effect on the BTC. These results were confirmed with experimental data on actual soil columns of an allophanic Andisol. When the BTCs had a similar nonlinear exchange isotherm and Péclet number, the deviations among them were easily interpreted by the Dg values.