bluuebunny/crossref_metadata_2025 huggingface dataset:
Three‐region Campbell Model for Unsaturated Hydraulic Conductivity in Undisturbed Soils
Authors: Poulsen T. G. , Moldrup P. , Iversen B. V. , Jacobsen O. H.
Published: July 2014

A three‐region Campbell (TRC) type model for predicting undisturbed soil unsaturated hydraulic conductivity from water retention is presented. The model assumes that hydraulic conductivity follows separate Campbell functions within the macropore (matric head ψ > −10 cm H2O), the mesopore (−10 ≥ ψ > −350 cm H2O), and the micropore (ψ ≤ −350 cm H2O) regions, and that soil water retention and two reference‐point values of hydraulic conductivity are known. Conductivity and retention data for 100 undisturbed soils from the UNSODA database and 68 soils from a Danish database were used for model development. Conductivity for both highly structured (three‐region) and weakly structured (two‐region) soils mostly followed a piecewise linear function (with slope β) in a Log(conductivity) −Log(water content) plot, supporting the TRC model concept. A unique relationship between the Campbell soil‐water retention parameter, b, and the unsaturated conductivity parameter, β, was found valid for both meso‐ and micropore regions. It was shown that the values of b in the mesopore and micropore regions are not correlated, making the use of single‐region expressions (e.g., the Mualem–van Genuchten type models) questionable and suggests that a multiregion model with noncorrelated retention parameters between pore regions, such as the TRC model, may provide a conceptually more correct description of hydraulic conductivity. The TRC model yielded improved conductivity predictions in loamy and clayey soils whereas predictions for sandy soils were comparable to the single‐region Campbell and van Genuchten models. TRC model predictions compared well with independent data for three differently textured soil profiles.
Comparison of Redox Indicators in a Paddy Soil during Rice‐Growing Season
Authors: Gao S. , Tanji K. K. , Scardaci S. C. , Chow A. T.
Published: July 2014

The objective of this study was to compare three methods of evaluating redox status, i.e., conventional redox potential (EH) measurement, terminal electron‐accepting processes (TEAPs) and oxidative capacity (OXC) in pore waters of a paddy soil during the rice‐growing season. The redox potential can be measured readily which can monitor progressive development of reducing conditions and distinguish oxic from anoxic conditions but with little information on specific redox processes under anoxic conditions. Identifying dominant TEAPs requires intensive data collection and analysis. The sequence of TEAPs development basically followed theoretical predictions but overlapping, typically among Mn, Fe, SO2−4‐S reductions and methane production, was featured throughout the season. The measured dissolved H2 gas as the intermediate product, reflected the overlap among electron acceptors. Oxidative capacity integrated all the major oxidized and reduced species to a single conservative parameter and showed clearly the progressive redox status from oxic to postoxic and then to sulfidic conditions in the paddies with no apparent methanic condition during this particular growing season. In OXC computations, a more reliable method to estimate Mn and Fe oxyhydroxide concentrations as electron acceptors needs further testing. The measured EH showed a higher correlation to redox species Mn(II), Fe(II) and methane concentrations (r2 = 0.76, 0.73, and 0.76, respectively) than to dissolved O2 (DO), NO−3‐N, and SO2−4‐S (r2 = 0.53, 0.37, and 0.16, respectively). Measured EH was also highly correlated to OXC for low sulfate solutions. The three methods for evaluating redox status all indicated that more reducing conditions were developed in straw‐incorporated paddies than that with straw‐burned.
Kinetics of Arsenic Adsorption on Goethite in the Presence of Sorbed Silicic Acid
Authors: Waltham Catherine A. , Eick Matthew J.
Published: July 2014

The potential toxicity and availability of As in the environment is dependent on several factors including redox potential, pH, and the presence of ligands that can compete for adsorption sites on mineral surfaces. Silicic acid is a ligand ubiquitous in natural systems and strongly chemisorbs to Fe oxides. However, there are relatively few studies examining its influence on As adsorption on Fe oxides. This study examined the influence of silicic acid (0.10 and 1.0 mM) on the adsorption kinetics of arsenite and arsenate (0.10 mM) on goethite over a range of common soil pH values (4, 6, and 8). The rate of arsenic (III and V) and silicic acid adsorption was greatest at pH values near their pK1 value. However, silicic acid sorption was characterized by biphasic kinetics with rapid adsorption followed by a much slower adsorption reaction. The rate and total quantity of arsenite adsorption decreased in the presence of silicic acid at all pH values and concentrations of silicic acid. Approximately 40% less arsenite was adsorbed in the presence of 1.0 mM silicic acid at all pH values. At 0.10 mM, silicic acid had less of an effect on arsenite adsorption. In contrast, only the rate and not the total quantity of arsenate was reduced in the presence of silicic acid. The rate of arsenate adsorption decreased as pH and silicic acid concentration increased. This was attributed to a decrease in the goethite's surface potential upon specific adsorption of silicic acid and deprotonation of the arsenate molecule creating an unfavorable electrostatic field. These results demonstrate the importance of evaluating As speciation, reaction kinetics, and the influence of naturally occurring ligands on the adsorption of As on variable charge surfaces.
Maize root‐induced change in soil organic carbon pools
Authors: Liang B. C. , Wang X. L. , Ma B. L.
Published: July 2014

Quantification of root or root‐induced changes in soil organic C (SOC), water‐soluble organic C (WSOC), and microbial biomass C (MBC) is important for understanding processes of soil C storage. A greenhouse study was conducted on a Bainsville loamy sand (Typic Hapludoll) to evaluate root or root‐induced quantitative and compositional changes in various SOC pools by growing corn (Zea mays L.), a C4 plant, on a historically C3 soil. Significant shifts in 13C of SOC pools, most noticeably in WSOC and MBC were observed. During the course of a growing season, the proportion of C4‐derived C varied from 0 to 12.3% of whole SOC, from 0 to 30.7% of WSOC, and from 0 to 52% of MBC, indicating a major contribution of root or root‐induced C to various soil C components, especially WSOC and MBC. The amount of C4‐derived C in the entire soil estimated by the 13C natural abundance (δ13C) was remarkably consistent with the amount of C4‐C retained in the soil microbial biomass, WSOC, and corn roots, suggesting that measurements of 13C of the entire soil following the shift of C3 to C4 plants can be used as an indirect measure of root or root‐induced C pools during the growing period.
Tillage, Nitrogen, and Cropping System Effects on Soil Carbon Sequestration
Authors: Halvorson Ardell D. , Wienhold Brian J. , Black Alfred L.
Published: July 2014

Soil C sequestration can improve soil quality and reduce agriculture's contribution to CO2 emissions. The long‐term (12 yr) effects of tillage system and N fertilization on crop residue production and soil organic C (SOC) sequestration in two dryland cropping systems in North Dakota on a loam soil were evaluated. An annual cropping (AC) rotation [spring wheat (SW) (Triticum aestivum L.)–winter wheat (WW)–sunflower (SF) (Helianthus annuus L.)] and a spring wheat‐fallow (SW‐F) rotation were studied. Tillage systems included conventional‐till (CT), minimum‐till (MT), and no‐till (NT). Nitrogen rates were 34, 67, and 101 kg N ha−1 for the AC system and 0, 22, and 45 kg N ha−1 for the SW‐F system. Total crop residue returned to the soil was greater with AC than with SW‐F. As tillage intensity decreased, SOC sequestration increased (NT > MT > CT) in the AC system but not in the SW‐F system. Fertilizer N increased crop residue quantity returned to the soil, but generally did not increase SOC sequestration in either cropping system. Soil bulk density decreased with increasing tillage intensity in both systems. The results suggest that continued use of a crop‐fallow farming system, even with NT, may result in loss of SOC. With NT, an estimated 233 kg C ha−1 was sequestered each year in AC system, compared with 25 kg C ha−1 with MT and a loss of 141 kg C ha−1 with CT. Conversion from crop‐fallow to more intensive cropping systems utilizing NT will be needed to have a positive impact on reducing CO2 loss from croplands in the northern Great Plains.
Root Length Growth of Eight Crop Species in Haplustoll Soils
Authors: Merrill Stephen D. , Tanaka Donald L. , Hanson Jonathan D.
Published: July 2014

Quantifying the dynamics of root growth is necessary for knowledge about development of rhizoplane and rhizosphere structure, and will indicate potentials for soil C sequestration and for water and nutrient usage. Root growth was measured during 3 yr in spring wheat (Triticum aestivum L.) on fallow and in seven crops in spring wheat–winter wheat–alternative crop rotation under minimum tillage on Wilton silt loam (fine silty, mixed, superactive, frigid Pachic Haplustolls). Two types of minirhizotrons (standard [Stand MR] and pressurized‐wall [P‐wall MR]) were read with a microvideo camera. Average maximum rooting depths fell into agronomic groups: oilseeds safflower (Carthamus tinctoris L.), 1.64 m, and sunflower (Helianthus annuus L.), 1.45 m; spring wheat, 1.31 m; mustard family crops crambe (Crambe abysinnica Hochst. ex R. E. Fr.), 1.17 m, and canola (Brassica rapa), 1.13 m; and legumes dry bean (Phaseolus vulgaris L.), 1.00 m, soybean [Glycine max (L.) Merr.], 0.99 m, and dry pea (Pisum sativum L.), 0.99 m. Median depths of root length growth ranged from 0.92 m for safflower to 0.46 m for dry bean, and ratios of median to maximum depths averaged 0.51. Six out of eight crops showed greatest rooting depths in relatively wet 1995, likely because of wetter subsoil. Greatest total root length in safflower, crambe, canola, soybean and dry bean occurred in drier‐than‐average 1997, which is interpreted as a response to soil water deficit. Results indicate that diverse crop rotations have the potential to utilize water and nutrients and input C over different soil profile positions than spring wheat‐based monocropping.
Eastern Gamagrass Root Penetration in Adverse Subsoil Conditions
Authors: Gilker Rachel E. , Weil Ray R. , Krizek Donald T. , Momen Bahram
Published: July 2014

Eastern gamagrass [Tripsacum dactyloides(L.) L] (EG) is reported to exhibit acid tolerance and root penetration through claypans. To study its root growth in these conditions, a greenhouse column study was conducted under simulated soil stress conditions, using EG and sordan [Sorghum×drummondii(Steud.) Millsp. & Chase] as a comparison species. Treatments consisted of incomplete factorial combinations of plant species (EG and sordan), soil water potential (−10 and –300 kPa), lime (pH 3.5 and 4.8), and soil bulk density (Db) (1.3 and 1.7 g cm−3). The treatments were arranged as a randomized complete block design (RCBD). For some of the response variables that were analyzed at different depths, depth was considered as a subplot factor. Treatments were applied to Al‐toxic Tatum Bt horizon material (clayey, fine, mixed, semiactive, thermic Typic Hapludults) used in the middle 30‐cm section of 15 by 60‐cm polyvinyl Cl (PVC) columns. Soil strength was determined at harvest by cone penetrometer resistance. Results indicated that EG tolerated acid, Al‐toxic conditions, while sordan roots were sensitive to the low pH conditions. Eastern gamagrass roots penetrated high soil strength layers that inhibited sordan root growth. The characteristics of acid, Al tolerance, and penetration of high soil strength make EG valuable in establishing grassed buffers, vegetative conservation barriers, and pastures in extremely acid or dense soils.
Abiotic Nitrogen Uptake in Semiarid Grassland Soils of the U.S. Great Plains
Authors: Barrett J. E. , Johnson D. W. , Burke I. C.
Published: July 2014

Soils represent the largest terrestrial sink for N, yet current understanding of nutrient cycling cannot account for some of the mechanisms and sinks that stabilize anthropogenic N. We assessed the influence of soil properties, particularly soil organic C, pH, and clay content on potential biotic and abiotic N assimilation in soils collected across a temperature gradient in the U.S. Great Plains. We pulse labeled HgCl2‐sterilized and unsterilized soils with 15N to examine the relative importance of abiotic and biotic N assimilation in short‐term laboratory incubations. Estimates of total N assimilation in unsterilized soils ranged from 1.21 to 2.40 mg N kg−1 soil. Soil C content accounted for 50 and 60% of the variance in estimates of biotic immobilization and total N assimilation, respectively. Estimates of abiotic N assimilation ranged from 0.089 to 0.80 mg N kg−1 soil. Abiotic N uptake represented a large proportion of total N assimilation (mean equals 20%) in short‐term laboratory incubations. In contrast to previous reports, abiotic N uptake was negatively correlated to soil clay content and pH, perhaps because of differences in mineralogy and soil organic matter composition across the gradient. These results emphasize the importance of nonbiological N uptake in semiarid soils and suggest that abiotic pools could be an important sink for N.
An Automated Vacuum Extraction Control System for Soil Water Percolation Samplers
Authors: Lentz R. D. , Kincaid D. C.
Published: July 2014

A vacuum applied to soil water percolation samplers permits collection of both macro‐ and matrix‐pore liquids. Performance of these field samplers is improved when the extraction vacuum is adjusted in accordance with the tension in the surrounding soil. This is particularly important when monitoring a network of spatially distributed samplers and for samplers installed in medium to fine textured soils. We designed a vacuum extraction system to more efficiently collect vadose‐zone soil solution samples. A single vacuum pump, vacuum tank, and air dryer provided a vacuum supply for 12 soil water sampling sites via a branching polyethylene pipe network. A vacuum controller containing two inexpensive pressure transducers, a voltage regulator, relay, and solenoid valve was developed and tested for field installation. Data loggers operated the controllers, monitored extraction vacuum and ambient soil water potential, and adjusted relative vacuum at each percolation sampling site. The automated vacuum controllers successfully maintained sampler extraction pressures at levels proportional to ambient soil water potential and provided the added benefit of recording the pressure values for use in subsequent data interpretation.
Myrosinase Activity in Soil
Authors: Al-Turki Ahmad I. , Dick Warren A.
Published: July 2014

Myrosinase (thioglucoside glucohydrolase; EC 3.2.3.1) is an enzyme that hydrolyzes glucosinolates to D‐glucose and allelochemicals that have biological potential to suppress weed seed germination in soil. This enzyme, found in some microorganisms and released to soils via root exudation and decomposition, can be assayed by adding sinigrin (2‐propenyl‐glucosinolate) to soil as a substrate. We describe a simple and rapid method to assay myrosinase activity in soils. In this method, 1 g of soil is treated with toluene (0.2 mL) and incubated at 37°C with 2.8 mL of a buffered solution (pH 7) of sinigrin (20 mM final concentration) for 4 h. Glucose released upon sinigrin hydrolysis is extracted and its concentration is measured spectrophotometrically. Tests showed that recovery of glucose was quantitative if toluene was included in the assay mixture. Myrosinase activity in five soils studied ranged from 71 to 338 μg glucose g−1 soil 4 h−1 The rate of sinigrin hydrolysis increased with temperature from 10 to 40°C. The activation energy of myrosinase in four soils ranged from 40.3 to 52.8 kJ mol−1 The Vmax values for sinigrin hydrolysis calculated by the three linear transformations of the Michaelis–Menten equation ranged from 76 to 518 (avg. 275) μg glucose g−1 soil 4 h−1 and the apparent Km values for myrosinase ranged from 5.3 to 12.9 (avg. 8.1) mM The method developed in this study is accurate, fast, and simple.
Soil Aggregation and Carbon and Nitrogen Pools under Rhizoma Peanut and Perennial Weeds
Authors: Sainju U. M. , Terrill T. H. , Gelaye S. , Singh B. P.
Published: July 2014

Roots of rhizoma peanut [(Arachis glabrata Benth.), a warm‐season perennial legume forage] and perennial weeds may influence soil aggregation and associated C and N pools. We compared aggregate‐size distribution and concentrations of organic C and N, NH4–N, NO3–N, potential C and N mineralization (PCM and PNM), microbial biomass C and N (MBC and MBN), and particulate organic C and N (POC and PON) in whole‐soil and aggregates under 10‐yr‐old rhizoma peanut and perennial weeds [dominated by henbit (Lamium amplexicaule L.) and cut‐leaf evening primrose (Oenothera laciniata Hill)]. Field plots were established on a Norfolk loamy fine sand in April 1991 in central Georgia. While soil aggregation and associated C and N pools were not influenced by treatments, whole‐soil NH4–N and PON at the 0‐ to 15‐cm, PCM at the 30‐ to 90‐cm, and MBC at the 0‐ to 30‐cm depth were 28 to 100% greater under peanut than under weeds. Under both treatments, the amount of soil present in the 4.75‐ to 2.00‐mm aggregate‐size class and mean‐weight diameter of aggregates were 21 to 47% greater at 15‐ to 60‐ than at 0‐ to 15‐cm, indicating improved aggregation in the subsurface compared with the surface soil. At 0 to 15 cm, concentrations of organic C and N, MBC, MBN, POC, and PON were greater in the <0.25‐mm than in the 4.75‐ to 0.50‐mm size class. At 0 to 30 cm, NO3–N was greater in the 4.75‐ to 0.85‐mm than in the 0.50‐ to 0.25‐mm size class. Although treatments did not influence soil organic C and N levels, rhizoma peanut may increase microbial activities and labile N pools compared with perennial weeds. Rhizoma peanut and perennial weeds may improve aggregation in the subsurface compared with the surface soil and C and N pools in aggregates <0.25 mm in diameter.
Non‐Flow‐Through Steady‐State Chambers for Measuring Soil Respiration
Authors: Hutchinson G. L. , Rochette P.
Published: July 2014

Soil respiration estimates obtained from non‐flow‐through steady‐state chambers (also called static, absorption, or alkali trap chambers) are considered by many investigators to be unreliable. We studied the accuracy, functioning, and design requirements of this chamber type using a gas diffusion model validated for this purpose by demonstrating that it matched the empirical relation between alkali‐measured flux and headspace CO2concentration. Simulated measurement error depended on (i) magnitude of the soil respiration rate, which spawned positive or negative error depending on the algebraic sign of the change in headspace CO2, (ii) absorption efficiency of the alkali trap, which was determined by headspace air mixing rates, the thickness of atmospheric interfacial layers, and especially the ratio of exposed alkali surface area to emitting soil surface area, (iii) the effective diffusivity and storage coefficient of CO2in underlying soil, which depended on the soil's air‐filled porosity (AFP) and pH, respectively, and (iv) the rate of CO2leakage between the chamber system and its surroundings. The results also indicated that although no single chamber design is universally applicable, striving for the ideal design in every situation is not required; for example, measurement error associated with the design used in our simulations was usually only ≈5% despite that headspace concentration rose more than 70% within 2 h. Larger errors occurred for chamber designs less well matched to the soil respiration rate they were intended to measure, but if such serious design deficiencies are avoided, the method offers a simple inexpensive means for obtaining multiple reliable time‐integrated estimates of soil respiration, even at remote locations.
Genesis of Tephra‐derived Soils from the Roccamonfina Volcano, South Central Italy
Authors: Vacca A. , Adamo P. , Pigna M. , Violante P.
Published: July 2014

The properties of seven pedons, formed in three different tephra deposits inside the main caldera of the Roccamonfina volcano, were examined to better understand the genesis of these soils. Three of these soils derived from trachytic ash deposits are deep and porous and have andic properties, imogolite, and high allophane content. In these ash‐derived soils, neogenesis of crystalline clays is limited but include halloysite and hydroxy‐interlayered vermiculite. Hydrated halloysite is present only in the deepest horizons of two of these pedons. By contrast, the deep and clayey soil formed from alkali basaltic scoria and the shallow and slowly permeable soils derived from consolidated trachyandesitic tuffs have weak andic properties. In these soils, allophane content is negligible and pedogenesis induces the neogenesis of crystalline clays dominated by halloysite. Unlike the ash‐derived soils, hydrated halloysite is present through most of the pedons. Climate, topography, and vegetation do not appear to be limiting factors for allophane formation in the area. The hydraulic properties of the parent material, possibly together with the time of pedogenesis, apparently affect the different pedogenetic trends of these soils. Allophanic soils developed in younger, porous, permeable ash deposits where rapid glass weathering is favored and Al and Si are readily available for allophane formation. By contrast, non‐allophanic soils developed in older, less porous, and less permeable scoria and consolidated tuffs where pedogenesis induces the neogenesis of crystalline clays and hydrated halloysite is probably formed by in situ weathering of volcanic glass. Allophanic and non‐allophanic soils are then coexisting in similar landscapes under similar climatic conditions.
A Single Irrigation to Improve Early Maturing Soybean Yield and Quality
Authors: Sweeney Daniel W. , Long James H. , Kirkham M. B.
Published: July 2014

When irrigation sources are limited, deficit irrigation at selected growth stages may help avoid crop stress at critical times. The objective of this study was to determine the effect of a single irrigation at different reproductive growth stages on yield and quality of early maturing (Maturity Group I) soybean [Glycine max (L.) Merr.] cultivars. The experiment was conducted from 1991 through 1994 on a Parsons silt loam (fine, mixed, thermic Mollic Albaqualf). The experimental design was a randomized complete block with a split‐plot arrangement of treatments. Irrigation scheme (application of 2.5 or 5 cm at R4, R5, or R6) as the main plot was factorially arranged within each replicate, and cultivar (Hodgson 78 and Weber 84) was the subplot treatment. Also included was a randomized nonirrigated check whole plot planted with both cultivars. Yields from a single irrigation at R4, R5, or R6 were similar, and averaged approximately 20% more than yield with no irrigation (1.72 Mg ha−1). Irrigation at R4 increased seeds plant−1, whereas R5 and R6 irrigations increased weight per seed. Irrigation had minimal effect on seed protein and variable effect on oil content. Visual quality of harvested seed frequently scored poor and irrigation improved quality only in 1992 when maximum air temperatures were <35°C. A single irrigation at R5 in 1991 improved germination to nearly 60% compared with 30% with no irrigation. Germination averaged 81% in other years with no irrigation effects. These data show that a single irrigation at different reproductive growth stages can influence early maturing soybean yield and quality, but the improvements may be inadequate to justify the practice.
Soil Carbon Maps
Authors: Mueller T. G. , Pierce F. J.
Published: July 2014

The quality of soil property maps may be improved and spatial sampling intensities reduced by incorporating secondary data to enhance spatial estimates. The purpose of this study was to evaluate how scale of sampling and secondary spatial information (terrain attributes) affected the quality of spatial estimates of soil C. A field in Central Michigan was sampled using 30.5‐ and 100‐m regular grids and the samples were analyzed for total C. Extracting a 61‐m grid from the 30.5‐m regular grid (G30) data set created an additional data set. Total C maps were created at each scale using ordinary kriging, kriging with a trend model, cokriging, kriging with an external drift, and multiple regression. Each resulting map was compared with an independent validation data set (n= 24) to evaluate map quality. At the 30‐m grid scale, there were modest differences between maps created with ordinary kriging (root mean squared error [RMSE] = 2.9 g kg−1, isotropic model; RMSE = 3.0 g kg−1, anisotropic model), kriging with a trend model (RMSE= 2.8 g kg−1), cokriging (RMSE = 2.9 g kg−1), kriging with an external drift (RMSE = 2.6 g kg−1), and multivariate stepwise regression (RMSE = 3.2 g kg−1). Prediction errors were generally larger at the 61‐m grid scale and procedures that utilized secondary the terrain data (cokriging, RMSE = 3.8 g kg−1; kriging with an external drift, RMSE = 3.8 g kg−1; stepwise multiple regression, RMSE = 3.0 g kg−1) outperformed procedures that did not (isotropic ordinary kriging, RMSE = 4.3 g kg−1; kriging with a trend model, RMSE = 4.3 g kg−1). At the 100‐m grid (G100) scale, geostatistical procedures were not appropriate because of the small sample size (n= 12) yet multiple regression performed well (RMSE = 3.8 g kg−1). Maps of soil C created with regression most resembled the soil color patterns evident in an aerial photograph of the field.
Sampling‐Induced Increases in Net Nitrification in the Brush Brook (Vermont) Watershed
Authors: Ross Donald S. , Hales Heidi C.
Published: July 2014

Accurate measurement of nitrification rates in disturbance‐sensitive soils can be problematic. A series of experiments illustrated the extent of net nitrification increases and explored possible causes. In highly disturbed soils, weekly leachates of columns containing homogenized Oi/Oe material had NO−3 concentrations over 5 mmol L−1 after 20 wk and over 1 mmol L−1 after 2 yr. Small‐scale impact disturbance in the field (footprints) resulted in a tripling of NO−3 concentrations after a 2‐wk incubation. After disturbance by sampling, bulked Oa horizons showed rapid increases in NO−3 concentration, with change detectable within 1 h. Initial net nitrification rates were as high as 74 μmol kg−1 h−1 (300 mg N m−2 d−1). Ammonium concentrations increased over the first 10 h but decreased afterwards. Incubation with acetylene stopped nitrate accumulation but NH+4 continued to increase. Intact cores also showed increases in NO−3 after 1 to 3 d but at a much lower rate than bulked samples. Gross rates of nitrification in intact cores were much lower than net rates in bulk samples. The addition of NH+4 to intact cores caused an increase in net nitrate after 20 h. These results suggest that sampling stimulates nitrification rapidly through an increase in NH+4 availability. The NH+4 increase may be because of a stimulation of ammonification caused by mixing, a decrease in spatial heterogeneity, or a disturbance in other types of NH+4 consumption. In soils that exhibit these disturbance effects, nitrification rate measurements will not be accurate but still may represent the potential for nitrification with increased NH+4 supply.
Changes in Bicarbonate‐extractable Inorganic and Organic Phosphorus by Drying Pasture Soils
Authors: Turner Benjamin L. , Haygarth Philip M.
Published: July 2014

Soils are commonly dried in the laboratory prior to the determination of P fractions, but this can profoundly influence the results. We investigated the impact of soil drying on bicarbonate‐extractable inorganic and organic P in 29 permanent lowland pasture soils from England and Wales (total C 29–80 g C kg−1 soil, clay 219–681 g kg−1 soil, pH 4.4–6.8) by extracting soils at approximate field moisture capacity and after air‐drying at 30°C for 7 d. Air‐drying increased the mean bicarbonate‐extractable inorganic P from 14.8 to 22.5 mg P kg−1 soil, and the mean bicarbonate‐extractable organic P from 17.4 to 25.7 mg P kg−1 soil. Proportional increases for individual soils following drying were between 11 and 165% for inorganic P, and between −2 and 137% for organic P, being greatest in soils with low P concentrations. The results are unlikely to influence tests for plant‐available P, because these are derived from analyses of air‐dried samples, but have important implications for attempts to relate bicarbonate‐extractable P fractions to processes operating under field conditions.
Yield Models Implied by Traditional Fertilizer Recommendations and a Framework for Including Nontraditional Information
Authors: Kastens Terry L. , Schmidt John P. , Dhuyvetter Kevin C.
Published: July 2014

Recently emerged technologies permitting precision farming provide opportunities to collect and evaluate vast amounts of data; yet, a formal method for incorporating additional yield‐affecting information into fertilizer‐yield response models is still largely unavailable to site‐specific managers. This research develops an integrated yield model that combines laboratory‐based fertilizer recommendations with data from multiple independent variables. Kansas wheat (Triticum aestivum L. sp. aestivum) was the target crop, and simulated soil test and yield data were characteristic of data from the literature and this geographic area. Independent variables in the plateau‐type yield model included fertilizer N and P, soil test N (STN) and soil test P (STP), and Z (representing all other causal factors). Consideration of the potential benefits of managing STP is an explicit outcome of this research. To expand the modeling procedures to include actual farm information, data from a northwest Kansas farm were used to replace the simulated Z variable. Additionally, maximum entropy (ME) was examined as a statistical technique for using the farm's N and P data to modify the predicted N‐ and P‐response of laboratory‐based models. Based on out‐of‐sample yield prediction accuracy, the ME models were generally the most accurate, improving root mean squared prediction error by as much as 14% relative to a model estimated with only farm data. Because the ME models were the most accurate and provided fertilizer recommendations similar to those from soil testing laboratories, this approach should provide a reliable framework for developing site‐specific fertilizer recommendations that depend on factors other than STN and STP.
Evaluation of a Model for Irrigation Management Under Saline Conditions
Authors: Feng G. L. , Meiri A. , Letey J.
Published: July 2014

Sustained irrigation agriculture is critical for food and fiber production to support the growing human population. Increasing salinity is a significant factor in many irrigated lands. Knowledge on the proper time and amount of water of various salinities to be applied for optimum yield of a given crop is important. Because of the numerous variables, computer simulation models would be valuable to partially replace expensive field experiments. Simulated relative yields of corn from the ENVIRO‐GRO model were compared with experimentally measured yields which had irrigation water electrical conductivities (ECs) of 1.7, 4.0, 5.0, 8.0, and 10.2 dS m−1 and average irrigation intervals of 3.5‐, 7‐, 14‐, and 21‐d treatments. The simulations were run for 5 yr although the field experiment was conducted only 1 yr. The simulated root‐weighted average matric and osmotic heads prior to irrigation were evaluated during the year. Depending on treatment, yields were depressed because of either osmotic or matric effects or a combination of the two. The agreement between simulated and measured yields was good for all treatments indicating that the model appropriately accounted for both osmotic and matric effects. On the basis of these results, the ENVIRO‐GRO model can be used with confidence in simulating the consequences of irrigation management options under saline conditions. The simulated yields were lower the second and subsequent years compared with the first year, emphasizing the fact that results from 1‐yr experiments cannot be used reliably for long‐term predictions because the results are highly dependent on the soil conditions at the beginning of the growing season.
Robust Estimation of the Generalized Solute Transfer Function Parameters
Authors: Javaux M. , Vanclooster M.
Published: July 2014

A method is presented to mathematically characterize a wide range of solute transport processes in soils from time‐domain‐reflectometry (TDR)‐based breakthrough curve (BTC) measurements. To do this, we combined the flexible generalized transfer function model (GTF) with the definition of the time normalized resident concentrations Crt* The GTF is a four‐parameter flexible transfer function able to describe both the convection‐dispersive (CD) and the stochastic‐convective (SC) process of dispersion in a soil. In addition, it allows other dispersion processes typical for heterogeneous soils to be modeled. To obtain robust estimations of the GTF model parameters, closed‐form expressions of the GTF time normalized resident concentrations Crt* and temporal moments of Crt* were defined. These expressions allow the transport parameters to be estimated from TDR‐based BTCs without relying on problematic probe calibrations and mass recovery assumptions. Since GTF is a four‐parameter model, the robustness of the parameterization procedure was tested by fitting the Crt* of the GTF model to numerically generated, error‐contaminated BTCs. Using the least‐square optimization technique, robust estimates of the GTF parameters could be obtained from TDR observations at two different soil depths. Application of the proposed method was also tested for a real undisturbed sandy subsoil and compared with the convective lognormal transfer (CLT) and CD models. For this case, it was shown that the GTF model improved greatly the goodness of prediction of the BTCs. The proposed method offers a new powerful tool for analyzing transport processes of nonreactive solutes in soil.
Does the Number of Irradiated Cells Influence the Spatial Distribution of Bystander Effects?
Authors: Belchior A. , Balásházy I. , Gil O. Monteiro , Vaz P. , Almeida P.
Published: July 2014

There is growing evidence that the radiation effects at low doses are not adequately described by a simple linear extrapolation from high doses, due, among others, to bystander effects. Though several studies have been published on this topic, the explanation of the mechanisms describing the bystander effects remains unclear. This study aims at understanding how the bystander signals are or can be propagated in the cell culture, namely if the number of irradiated cells influences the bystander response. An A549 cell line was exposed to several doses of α-particles, being the bystander response quantified in two non-irradiated areas. The radius of irradiated areas differs by a factor of 2, and the non-irradiated areas were optimally designed to have the same number of cells. Our results show evidence for bystander effects occurring in cells far away from the irradiated ones, meaning that bystander signals can easily spread throughout the cell culture. Additionally, our study highlights that the damage caused by radiation on the surrounding of irradiated areas could be different according to the number of irradiated cells, i.e., for the same dose value; the overall cellular damage could be different.
MCNP simulation of the dose distribution in liver cancer treatment for BNC therapy
Authors: Krstic Dragana , Jovanovic Zoran , Markovic Vladimir , Nikezic Dragoslav , Urosevic Vlade
Published: July 2014

The Boron Neutron Capture Therapy (BNCT) is based on selective uptake of boron in tumour tissue compared to the surrounding normal tissue. Infusion of compounds with boron is followed by irradiation with neutrons. Neutron capture on 10B, which gives rise to an alpha particle and recoiled 7Li ion, enables the therapeutic dose to be delivered to tumour tissue while healthy tissue can be spared. Here, therapeutic abilities of BNCT were studied for possible treatment of liver cancer using thermal and epithermal neutron beam. For neutron transport MCNP software was used and doses in organs of interest in ORNL phantom were evaluated. Phantom organs were filled with voxels in order to obtain depth-dose distributions in them. The result suggests that BNCT using an epithermal neutron beam could be applied for liver cancer treatment.
Threshold conditions and bound states for locally periodic delta potentials
Authors: Dharani Marappan , Sahu Basudeb , Shastry Chakrakodi
Published: July 2014

We present a systematic study of the conditions for the generation of threshold energy eigen states and also the energy spectrum generated by two types of locally periodic delta potentials each having the same strength λV and separation distance parameter a: (a) sum of N attractive potentials and (b) sum of pairs of attractive and repulsive potentials. Using the dimensionless parameter g = λV a in case (a) the values of g = g n, n = 1, 2, …, N at which threshold energy bound state gets generated are shown to be the roots of Nth order polynomial D 1(N, g) in g. We present an algebraic recursive procedure to evaluate the polynomial D 1(N, g) for any given N. This method obviates the need for the tedious mathematical analysis described in our earlier work to generate D 1(N, g). A similar study is presented for case (b). Using the properties of D 1(N, g) we establish that in case (a) the critical minimum value of g which guarantees the generation of the maximum possible number of bound states is g = 4. The corresponding result for case (b) is g = 2. A typical set of numerical results showing the pattern of variation of g n as a function of n and several interesting features of the energy spectrum for different values of g and N are also described.
Nutrition in acute pancreatitis: a review
Authors: Frutos Visitación , Herranz-Antolín Sandra , García-Martínez María
Published: July 2014

We perform an update about nutritional measures that have been adopted in patients with acute pancreatitis (AP). The nutritional support is an essential part of treatment in AP. When the AP is mild or moderate, there is no doubt that is not necessary to use an artificial nutritional support, and it is recommended that oral nutritional support should begin as soon as possible. If the AP is severe, the best way to provide nutritional support is through enteral nutritional (EN) because it reduces infection, length of hospitalization and mortality rate. Parenteral nutrition (PN) should be used only when EN is Impossible. However, there is no scientific evidence for recommending the most optimal route necessary to administer this type of nutritional support; we seek to uncover whether this is by gastric or jejunal route and the proper formula to use. There is an international agreement that the nutritional support should begin quickly, within the first 24 and 72 hours of hospitalization. As conclusion, more research needs to be done concerning nutritional support in AP, and many questions are not been answered yet.
Modelling of catalytic hydrocracking and fractionation of refinery vacuum residue
Authors: Manek Eduard , Haydary Juma
Published: July 2014

The main objective of this work was to create a kinetic model of refinery vacuum residue hydrocracking and to monitor the impact of the operating conditions on the product yields. Data and yield measurements were gathered from a residual hydrocracking unit (RHC). Reaction temperature ranged from 401°C to 412°C at the pressure of 18–20 MPa. A simplified kinetic yield model was applied; where the feed and each product fraction are represented by one lump (reactant or product of cracking) represented by the number of pseudo-components. The product fractions were determined by fractional distillation of the output mixture from the reactor. The kinetic model includes eight reaction steps and the following six fractions: vacuum residue, vacuum distillate, gas oil, kerosene, naphtha, and gas. In addition, a model for hydrodesulphurisation has been proposed. The average relative deviation between model and experimental yields was 5.36 %, and that for the sulphur conversion model was 1.04 %. An Excel file with the kinetic model was implemented in the Aspen Plus program using a user-defined model of the reactor. This model allows to input/output data between the Aspen Plus and Excel programs. The Excel subroutine calculates the reaction kinetics of cracking from the set temperature and residence time, and distributes the products into 30 pseudo-components created in the Aspen Plus program. The remaining part of the RHC unit was simulated in the Aspen Plus environment. The effects of the reaction conditions such as temperature and residence time on the conversion of the feed and on the distillation curves of the output mixture from the reactor were investigated. The model was verified by comparison of the distillation curves of simulated and real products.
Introduction to the GRADE Approach for Guideline Development: Considerations for Physical Therapist Practice
Authors: Austin Tricia M. , Richter Randy R. , Sebelski Chris A.
Published: July 2014

Background

Practice guidelines (guidelines) have an increasing role in health care delivery and are being published more frequently. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) is an approach for guideline development. The GRADE approach has been adopted by multiple national and international organizations producing guidelines related to physical therapist care.

Objective

The purpose of this article is to introduce physical therapists to the GRADE approach for guideline development.

Results

GRADE provides a consistent approach for guideline development and transparency in the communication of how the guidelines were developed and how the recommendations were reached, leading to informed choices by patients, clinicians, and policy makers in health care. GRADE leads to a clear distinction between the strength of the evidence and the recommendation. Both the direction (for or against) and the strength (weak or strong) of the recommendation are considered. For determining the strength of the recommendation, GRADE takes into account the quality of evidence, the balance of benefit and harm, uncertainty about or variability in patients' values and preferences, and uncertainty about whether the intervention is a wise use of resources.

Limitations

The GRADE approach has been used primarily with interventions and clinical questions and less often with questions related to diagnosis and prognosis.

Conclusions

The frequency of publication of guidelines is increasing. To make informed choices in the health care system, physical therapists should understand how guidelines are developed. The GRADE approach has been adopted by national and international organizations that produce guidelines relevant to physical therapist practice. Understanding the GRADE approach will enable physical therapists to make informed clinical choices.
Effect of local application of transforming growth factor–β at the nerve repair site following chronic axotomy and denervation on the expression of regeneration-associated genes
Authors: Sulaiman Wale , Dreesen Thomas D.
Published: July 2014

Object

Although peripheral nerves can regenerate after traumatic injury, functional recovery is often suboptimal, especially after injuries to large nerve trunks such as the sciatic nerve or brachial plexus. Current research with animal models suggests that the lack of functional recovery resides in the lack of sufficient mature axons reaching their targets due to the loss of neurotrophic support by Schwann cells in the distal stump of injured nerves. This study was designed to investigate the effect of one-time application of transforming growth factor–β (TGF-β) at the repair site of chronically injured nerve.

Methods

The authors used the rat tibial nerve injury and repair model to investigate the effects of application of physiological concentrations of TGF-β plus forskolin or forskolin alone in vivo at the repair site on gene and protein expression and axon regeneration at 6 weeks after nerve repair. They used gene expression profiling and immunohistochemical analysis of indicative activated proteins in Schwann cells to evaluate the effects of treatments on the delayed repair. They also quantified the regenerated axons distal to the repair site by microscopy of paraffin sections.

Results

Both treatment with forskolin only and treatment with TGF-β plus forskolin resulted in increased numbers of axons regenerated compared with saline-only control. There was robust activation and proliferation of both Schwann cells and macrophages reminiscent of the processes during Wallerian degeneration. The treatment also induced upregulation of genes implicated in cellular activation and growth as detected by gene array.

Conclusions

Addition of TGF-β plus forskolin to the repair after chronic nerve injury improved axonal regeneration, probably via upregulation of required genes, expression of growth-associated protein, and reactivation of Schwann cells and macrophages. Further studies are required to better understand the mechanism of the positive effect of TGF-β treatment on old nerve injuries.
Comparison of techniques for ventriculoperitoneal shunting in 523 patients with subarachnoid hemorrhage
Authors: Chalouhi Nohra , Whiting Alex , Anderson Eliza C. , Witte Samantha , Zanaty Mario , Tjoumakaris Stavropoula , Gonzalez L. Fernando , Hasan David , Starke Robert M. , Hann Shannon , Ghobrial George M. , Rosenwasser Robert , Jabbour Pascal
Published: July 2014

Object

It is common practice to use a new contralateral bur hole for ventriculoperitoneal shunt (VPS) placement in subarachnoid hemorrhage (SAH) patients with an existing ventriculostomy. At Thomas Jefferson University and Jefferson Hospital for Neuroscience, the authors have primarily used the ventriculostomy site for the VPS. The purpose of this study was to compare the safety of the 2 techniques in patients with SAH.

Methods

The rates of VPS-related hemorrhage, infection, and proximal revision were compared between the 2 techniques in 523 patients undergoing VPS placement (same site in 464 and contralateral site in 59 patients).

Results

The rate of new VPS-related hemorrhage was significantly higher in the contralateral-site group (1.7%) than in the same-site group (0%; p = 0.006). The rate of VPS infection did not differ between the 2 groups (6.4% for same site vs 5.1% for contralateral site; p = 0.7). In multivariate analysis, higher Hunt and Hess grades (p = 0.05) and open versus endovascular treatment (p = 0.04) predicted shunt infection, but the VPS technique was not a predictive factor (p = 0.9). The rate of proximal shunt revision was 6% in the same-site group versus 8.5% in the contralateralsite group (p = 0.4). In multivariate analysis, open surgery was the only factor predicting proximal VPS revision (p = 0.05).

Conclusions

The results of this study suggest that the use of the ventriculostomy site for VPS placement may be feasible and safe and may not add morbidity (infection or need for revision) compared with the use of a fresh contralateral site. This rapid and simple technique also was associated with a lower risk of shunt-related hemorrhage. While both techniques appear to be feasible and safe, a definitive answer to the question of which technique is superior awaits a higher level of medical evidence.