bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluation of Nitrogen‐15 Tracer Techniques for Direct Measurement of Denitrification in Soil: IV. Field Studies
Authors: Mulvaney R. L. , Vanden Heuvel R. M. 
Published: July 2010

AbstractField studies were conducted to determine whether underestimation occurs in measuring evolution of nitrous oxide (N2O) using an 15N‐tracer technique based on the assumption of isotopic uniformity. Microplots of 58, 553, or 1684 cm2 in area were treated with 15N‐labeled KNO3 (68.5 atom % 15N) at the rate of 100 kg N ha−1. Isotope‐ratio analyses of the NO−3 in soil cores collected from one plot of each size showed considerable spatial variability in 15N enrichment, but measurements of N2O evolution from these plots by gas chromatography (GC) and mass spectrometry (MS) usually did not differ significantly (0.05 level), demonstrating that appreciable error does not necessarily arise in the use of 15N‐tracer methodology to measure denitrification of NO−3 that is not isotopically uniform. In a subsequent study, replicate atmospheric samples were collected from three plots of each size following rainfall or irrigation for analysis of N2O by GC and MS. The measurements differed significantly (0.05 level) for approximately 60% of the collections that were made; however, the magnitude of the difference was usually small compared to spatial variability in N2O evolution. Significant differences occurred more often with medium or large plots than with small plots, and the greater value was usually obtained by GC. The extent of the difference was not affected by increasing the period of enclosure used in collection of atmospheric samples, but it was affected by subsequent application of fertilizer (25 kg N ha−1), which led to serious underestimation by MS of N2O evolved from most of the medium and large plots.
Microbial Release and Degradation of Catechol and Chlorophenols Bound to Synthetic Humic Acid
Authors: Dec Jerzy , Bollag Jean‐Marc 
Published: July 2010

AbstractThe binding of xenobiotics of humus occurs continuously in nature, and it is possible that this reaction can also be used for decontamination of the environment. It is not yet clear, however, to what extent the release of xenobiotics from humus may cause a delayed pollution problem. To evaluate this question, 14C‐labeled catechol (o‐dihydroxybenzene), 4‐chlorophenol, 2,4‐dichlorophenol, 2,4,5‐trichlorophenol, and pentachlorophenol bound to synthetic humic acid polymer were incubated with microbial soil populations, and the evolution of 14CO2 and release of radioactive compounds into the medium was monitored. The quantity of 14CO2 evolved varied with the source of the inocula and the chemical structure of the compound under investigation. After 13 wk of incubation, 14CO2 evolution ranged from 1.2 to 10.0% of the initially bound radioactivity. Radioactive substances, which were released into the media mostly in the form of the unchanged compound, varied from 0.4 to 12.4% of the initially bound radioactivity. Most radioactivity (54.7–88.9%) remained bound to the synthetic humic acid, suggesting that once chlorophenols are incorporated into humus their release is very slow and unlikely to adversely affect the environment.
Sulfur Transformations in Forest Litter and Soil: Results of Laboratory and Field Incubations
Authors: Watwood M. E. , Fitzgerald J. W. 
Published: July 2010

AbstractField incubations of litter (01 and 02 layers) and A horizon soil utilizing 35S‐labeled inorganic sulfate were conducted during July 1985 in an eastern white pine (Pinus strobus L.) and a hardwood forest. Samples were assayed for the capacity to form 35S‐labeled organic S, and in most cases these capacities were very similar to those determined in corresponding laboratory incubations. The A horizon soils from both watersheds formed approximately 3.0 nmol of organic S g−1 dry weight of sample during 2‐d field or laboratory incubations. No substantial increase in this amount was observed after 7‐d field incubations. Intrinsic S fractions of samples were quantified prior to and following field incubations, and organic S represented the majority of the total S in all cases. Total S ranged from 260 to 1180 and from 150 to 270 mg kg−1 in the litter layers and the A horizon, respectively. Sulfonate S (13–74% of total S) and nonphosphate extractable ester sulfate (16–82% of total S) were the largest organic S pools. Water soluble and phosphate extractable S pools were comprised of both inorganic sulfate and ester sulfate, and the latter was found to represent up to 8.1% of total S. The distribution of 35S following field incubations was determined, and organic 35S fractions in a variety of linkage groups were again found to predominate. Total C, moisture content, and throughfall sulfate concentrations during the field incubations were also determined.
Simulated Transport of Multiple Cations in Soil Using Variable Selectivity Coefficients
Authors: Mansell R. S. , Bloom S. A. , Selim H. M. , Rhue R. D. 
Published: July 2010

AbstractA chromatographic model for describing the transport of multiple cations in soil was modified to include both mobile‐immobile flow regions and variable ion exchange selectivity coefficients Kij for each binary combination of cation species in a ternary soil‐water system. The model was evaluated by comparing simulated results with published breakthrough curves (BTC) for Na+ and Mg2+ concentrations in effluent from columns of Yolo loam soil initially saturated with Ca2+ ions. Experimental BTC for the relatively uncompetitive Na+ species were adequately described when either constant or variable values of Kij were used in the model. For the more competitive Mg2+ species however, simulations using constant Kij coefficients described the relative location for maximum concentration but underestimated tailing for the BTC. When all of the soil solution was assumed to be mobile, description of tailing for Mg2+ BTC was improved by the use of variable Kij values in simulations, but retardation for Mg2+ transport tended to be overestimated. The combined use of mobile‐immobile liquid regions and of variable selectivity coefficients provided the observed tailing in Mg2+ BTC but minimized overestimation of retardation.
Disjunctive Kriging as an Approach to Management Decision Making
Authors: Yates S. R. , Yates Marylynn V. 
Published: July 2010

AbstractDisjunctive kriging is a nonlinear estimation technique that allows the conditional probability that the value of a spatially variable management parameter is greater than a cutoff level to be calculated. The method can be used in management decision making to help determine when some reclamation action is necessary. Two input parameters are required to use the technique: a cutoff level and the critical probability level. The use of disjunctive kriging as a decision making tool is illustrated using the regulation of septic tank setback distance as a means for minimizing the contamination of groundwater by viruses. Two examples are described: given a setback distance, the spatial distribution of the conditional probability that the virus concentration will be greater than acceptable levels is calculated; and given a critical probability level, calculating the spatial distribution of setback distances which satisfy that probability level. The study showed that, to be 90% confident that virus concentrations would be within acceptable limits, in many areas the setback distance would have to be severalfold higher than prescribed by current regulations.
Electrophoretic Mobility of Hydroxy‐Aluminum and Sodium‐Hectorite in Aqueous Solutions
Authors: Harsh James B. , Doner H. E. , Fuerstenau D. W. 
Published: July 2010

AbstractThe electrokinetic behavior of colloids titrated with acid or base in the presence of hydrolyzable metal cations is often modeled by assuming the substrate surface is partially or completely coated with the metal hydroxide. In aged OH‐Al‐clays much of the Al(OH)3 surface precipitate resides in the interlayer, but it is not known if the external surfaces of aged OH‐Al clays contain Al(OH)3. We precipitated Al(OH)3 on hectorite and measured electrophoretic mobility (µ), which is a function of the electric potential at the shear plane of the substrate, with varying pH, time, and ionic strength. The behavior was compared to that of Na‐hectorite in the presence and absence of AlCl3. We found that (i) the OH‐Al‐hectorite had a more positive µ than the Na‐hectorite between pH 3 and 5.5, but had a more negative µ between pH 5.5 and 7; (ii) µ became more negative with increasing NaCl concentration; and (iii) neither clay equilibrated rapidly with time. Ion exchange experiments showed that Na displaced exchangeable Al and Mg that originated from dissolution of the hectorite and Al(OH)3. There was no evidence for significant Al(OH)3 coating external surfaces, because this would have resulted in a more positive µ for the clay at all pH values below the point of zero charge of Al(OH)3 (pH = 9). Exchangeable cations on external surfaces primarily determined the shear plane potential in this system.
Acid Phosphatase Activity in Soils of the Appalachian Region
Authors: Baligar V. C. , Wright R. J. , Smedley M. D. 
Published: July 2010

AbstractAcid phosphatase (AP) activity was determined in 14 hill land soils of the Appalachian region. Soil samples were obtained from surface (A or Ap) and subsurface (E, BA, Bt, or Bw) horizons during spring, and subsamples were stored field‐moist at 4 °C and air‐dry (AD) for 36 wk prior to determination of AP activity. The average AP activities of surface and subsurface horizons stored field‐moist at 4 °C were 1.7 to 1.9 times higher than those of AD samples. The average AP activity of air‐dry surface horizons was 3.3 times higher than that of subsurface horizons. Significant positive relationships were found between the AP activities of AD and 4 °C samples, and total C and N content of soils. Positive relationships were observed between AP activities and various forms of soil P. The original soil moisture content by weight or volume and percent water‐filler pores (% WFP) were significantly related to AP activities of surface soil horizons. Each soil type has its own inherent level of phosphatase activity.
Denitrification in Soil Aggregates of Different Sizes
Authors: Seech A. G. , Beauchamp E. G. 
Published: July 2010

AbstractThe denitrification potential in different size aggregates of a silt loam soil was studied to explain spatial variability of denitrification. Seven aggregate size ranges (<0.25, 0.25–0.5, 0.5–1, 1–2, 2–5, 5–10, and 10–20‐mm diam.) were obtained by gentle dry sieving of the sampled soil. The denitrification rate was determined by the acetylene block method following imposition of several different treatments. It was observed that the denitrification rate was much larger with the smaller aggregates and generally decreased as aggregate size increased. Crushing of the aggregates to <0.25‐mm diam. resulted in some diminishment of this relationship. The supply of NO−3 was not limiting in the different size aggregates but the addition of glucose suggested that C substrate supply in larger aggregates was limiting denitrifier activity. Carbon dioxide production during aerobic incubation was greatest in microaggregates (<0.25 mm) and decreased with increasing aggregate size, further substantiating the deficiency in C substrate in large macroaggregates. It was found also that biomass C was greatest in microaggregates and decreased with increasing aggregate size when determined for both aerobic and anaerobic incubation conditions. The results of this study may be interpreted to suggest that considerable variability of available substrate C occurs in association with different size aggregates and could partly explain the large spatial variability of denitrification that occurs over relatively short distances in field soil
Calcium‐Aluminum Balance and the Growth of Soybean Roots in Nutrient Solutions
Authors: Noble A. D. , Fey M. V. , Sumner M. E. 
Published: July 2010

AbstractThe effect of varying two parameters having contrasting effects has been largely overlooked when describing Al phytotoxicity. Consequently the effects of varying pH (4.2, 4.5, and 4.8), Al (0, 20, 40, 80, and 160 µM Al) and CaSO4 (625, 1250, 2500, 5000, and 10 000 µM Ca) levels on root length of soybeans (Glycine max (L.) Merr.) were evaluated in a solution culture experiment. At a given pH and Al concentration, an increase in the level of CaSO4 resulted in a decrease in the activities of Al3+, AlOH2+ and Al(OH)+2 while the activity of AlSO+4 increased. Among the individual Al monomers, relative root length was most highly correlated with the calculated activity of Al3+ (R2 = 0.811) followed by AlOH2+ (R2 = 0.687), while AlSO+4 (R2 = 0.338) gave the poorest correlation. Thus, the AlSO+4 species appears to be less phytotoxic. Relative tap root length was poorly correlated with the concentration of monomeric Al determined by the modified Aluminon method, which also assays the less phytotoxic AlSO+4 species under the prevailing conditions. An expression termed CAB <Calcium aluminum balance = [2log(Ca2+)] − {3log(Al3+) + 2log[Al(OH)2+] + log[Al(OH)+2]}>, enabled the most precise assessment to be made of the effects of soluble Ca and Al, together, on root growth (R2 = 0.900). The coefficients in the CAB expression were introduced as a weighing to accommodate the assumed importance of valence in ion interactions at the plant root surface. The CAB was also found to be a better index of the solution conditions affecting root growth when applied to data from other published studies.
Using Texture and Other Soil Properties to Predict the Unsaturated Soil Hydraulic Functions
Authors: Wösten J. H. M. , van Genuchten M. Th. 
Published: July 2010

AbstractThe unsaturated hydraulic properties of soils are important but difficult to measure. Rather than measuring the hydraulic properties directly, we followed a different approach by fitting analytical expressions for the soil water retention and hydraulic conductivity functions to experimental data for a wide range of soils in the Netherlands. Analysis of the data shows the flexibility of the analytical expressions and also gives insight into how the different model parameters affect the calculated unsaturated hydraulic functions. Regression analyses are used to relate the estimated model parameters to more easily measured soil properties, such as bulk density and percentages silt, clay and organic matter. After calibration, the relations are used to predict the hydraulic functions of soils for which only the more easily measured soil properties are available. Accuracy of the predictions is analyzed in terms of functional criteria which are relevant to practical management problems. The predictive regression models are useful for estimating the unsaturated soil hydraulic properties of large areas of land, but need improvement for application to specific sites.
Transformation and Losses of Applied Nitrogen‐15 Labeled Ammonium in a Flooded Organic Soil
Authors: Meyer Michael L. , Bloom Paul R. , Grava John 
Published: July 2010

AbstractAmmonia volatilization, denitrification, and mineralization‐immobilization turnover rates (MIT) in a flooded organic soil were estimated using 15N‐labeled NH4Cl fertilizer. The soil was placed in 15‐cm columns either under dark or illuminated conditions. Volatilization of NH3‐15N was 8 and 4% of the initial fertilizer N added to the dark and illuminated columns, respectively. The rates of fertilizer N and total N denitrification in the dark columns were constant over the experiment at 1.2 and 2.1 mg N kg−1 d−1, respectively. After 74 d 22% of the initial amended fertilizer N had been denitrified. The rate of net mineralization of N in the anoxic zone was constant with time at 1.5 mg N kg−1 d−1. Mineralization and immobilization turnover fit the model y = ymax (1 − e‐kt), where y is the quantity of N mineralized or immobilized and k is the rate coefficient. For gross mineralization ymax = 480 mg N kg−1 d−1 and k = 0.00914 d−1. For immobilization ymax = 160 mg N kg−1 d−1 and k = 0.025 d−1. Mineralization and immobilization were not affected by the concentration of extractable NH4‐N. Algae increased immobilization in illuminated columns. No priming effect of added NH+4 on N mineralization was found. The impact of MIT on calculation of fertilizer efficiency is illustrated.
Effect of Saline Irrigation Waters on Soil Manganese Leaching and Bioavailability to Sugar Beet
Authors: Khattak Riaz A. , Jarrell Wesley M. 
Published: July 2010

AbstractUse of saline water for irrigation has shown considerable promise. However, its effect on the solubility and bioavailability of native soil nutrients is not well understood. This study was conducted to evaluate the extent of the salt‐induced Mn solubility and phytotoxicity to sugar beet [Beta vulgaris (L.) USH 11] under a soil‐plant‐leachate system. Sugar beet grown in the glasshouse on four diverse California soils was irrigated with either deionized water or 22.5 and 45.0 mol m−3 NaCl‐CaCl2 solution. Saline irrigation waters significantly (P < 0.001) increased (27 to 97%) the Mn concentration ([Mn]) and total Mn accumulation (48 to 130%) in sugar beet tops in all soils. The [Mn] in the soil solution leachate increased significantly with net increases of 55.3, 35.5, and 2.6 mg Mn kg−1 in Maymen, Aiken‐Tehama, and Aiken‐ElDorado soil, respectively, for the highest salinity, but only traces of Mn were detected in leachate of a high pH (8.23) Mojave soil. Diethylenetriamine pentaacetic acid (DTPA)‐extractable soil Mn significantly increased with salinity levels in irrigation waters in Maymen (92%), Aiken‐ElDorado (68%), and Mojave (47%) soils, but decreased (37%) in Aiken‐Tehama soil of low pH (5.10) and low C (3.60 g kg−1). The multiple regression analyses produced R2 = 0.864*** (P < 0.001) when shoot [Mn] was regressed on ECe, soil solution [Mn], soil pH, and DTPA‐extractable soil Mn. Since sugar beet tops contained in excess of 1000 mg Mn kg−1 top tissue, it was concluded that salt‐induced Mn accumulation under saline irrigation can be potentially toxic.
Infuence of Micaceous Minerals on Mineralogy Class Placement of Loamy and Sandy Soils
Authors: Rebertus R. A. , Buol S. W. 
Published: July 2010

AbstractIn Soil Taxonomy, mineralogy classes of pedons that have a fragmental, sandy, sandy‐skeletal, loamy, or loamy‐skeletal particle‐size class are defined by weight percent minerals in the coarse silt and larger fractions of the control section. However, a footnote to the key to mineralogy classes states that percentages by weight are estimated from grain counts of one or two of the dominant separates from a conventional mechanical analysis. The relationship of grain count number to volumetric percentage depends upon grain shape, size and cleavage, and the counting method used, making weight estimations, or even volumetric estimations impracticable. Revisions in the key to mineralogy classes are suggested because presently the key requires determination of grain size and shape relationships as well as the identification of minerals and their densities where often there is a gradation of mineral compositions and properties. According to the estimates used in this study, a line count of 80 to 85% micaceous minerals is needed to classify a pedon as micaceous; however, field classification of micaceous occurred at around 70% line count micaceous grains. This paper discusses limitations of grain counts for quantitative mineralogical analysis of the coarser fine‐earth fractions, presents a case for the revision of the key to mineralogy classes through use of actual mineralogic data, and recommends adoption of the line count method of determining composition for the purpose of mineralogy class placement.
Changes in Infiltration Under Alfalfa as Influenced by Time and Wheel Traffic
Authors: Meek B. D. , Rechel E. A. , Carter L. M. , DeTar W. R. 
Published: July 2010

AbstractInfiltration rates were measured for alfalfa, (Medicago sativa L., cv. WL514) subjected to treatments where wheel traffic was varied in terms of area covered and time of application on a Wasco sandy loam (coarse‐loamy, mixed, nonacid thermic Xeric Torriorthent). Traffic treatments were (i) No‐traffic, (ii) Preplant, (iii) Repeated, and (iv) traffic similar to what a grower would apply. Infiltration rates increased for all treatments, with increases being 240% for treatments without harvest traffic and 140% for treatments with harvest traffic. Increases in infiltration were related to decreases in stand density. Slight packing (traffic) applied before the soil was flood‐irrigated in 1983 increased infiltration rates 20% compared to flooding loosened soil (no traffic). Harvest traffic resulted in slower water movement in the soil.
Distance and Distribution Effects of Phosphorus Fertilizer on Corn
Authors: Eghball B. , Sander D. H. 
Published: July 2010

AbstractFertilizer P distribution and distance of application from the plant can affect fertilizer P efficiency. Ammonium polyphosphate solution tagged with 32P was injected into Sharpsburg sicl (Typic Argiudoll) 10‐cm deep on circle located 16, 32, 48, and 64 cm from five corn seeds (Zea mays L.) planted in the center. The P fertilizer for each plot was divided into 10 equal parts and was injected into 10 spots on the circle's circumference at five different spacings. To study the movement of P in the soil, seven concentrations of P fertilizer were injected into the soil 5‐cm deep. Results indicate that after 90 d P fertilizer moves outward from the injected point to form a near perfect sphere whose volume was related in a quadratic manner to the P application rate. At early stages of growth, seed placement of P fertilizer and placement up to 16 cm resulted in greater plant P from fertilizer than other P distances. At maturity little or no effect of P application distance was observed. Plant P from fertilizer increased as the surface area of the fertilizer P‐effected soil increased, indicating surface area is an important factor involved in determining the probability of root‐fertilizer contact. Plant P from fertilizer increased as the spacing between injection points increased because surface area of the fertilizer P‐effected soil was increasing. Plant P from fertilizer decreased with time indicating that a greater proportion of plant P was from soil P late in the growing season.
Transport of Inorganic and Natural Organic Tracers Through an Isolated Pedon in a Forest Watershed
Authors: Jardine P. M. , Wilson G. V. , Luxmoore R. J. , McCarthy J. F. 
Published: July 2010

AbstractThe transport of several inorganic ions (Mg2+, NH+4, Br‐, and NO‐3) and natural dissolved organic C (DOC) through the upper 1.2 m of an isolated in‐situ forest pedon was investigated. The purpose of the study was to investigate the spatial heterogeneity and the rate of nutrient transport in a forest soil. The tracers were added as a pulse to the soil surface during saturated flow in three separate experiments sequentially involving MgBr2, NH4NO3, and DOC, respectively. The temporal patterns of NO‐3 and Br‐ concentration observed at selected profile locations in the pedon were described by the convective‐dispersive (CD) equation using flux‐type boundary conditions with effluent concentrations treated as flux‐averaged concentrations. Skewed breakthrough curves (BTC) indicative of preferential flow were obtained at all measurement positions. Modelfitted velocities (v) agreed well with saturated infiltration rates established in‐situ for soils of the adjacent forest watershed. Although the CD equation could describe the temporal mobility of the nonreactive Br‐ and NO‐3 tracers at any given point in the pedon, it could not adequately describe the tracer concentration profiles with depth at selected times after tracer addition. Observed BTCs for Mg2+, NH+4, and DOC indicated that these tracers were reactive with the soil but also demonstrated that a significant quantity of these tracers moved through the soil via preferential flow. The temporal patterns for reactive tracer movement through the pedon could be modeled with the CD equation when adsorption was reversible.