bluuebunny/crossref_metadata_2025 huggingface dataset:
Low energy electron diffraction using an electronic delay-line detector
Authors: Human D. , Hu X. F. , Hirschmugl C. J. , Ociepa J. , Hall G. , Jagutzki O. , Ullmann-Pfleger K.
Published: February 2006

A low energy electron diffraction (LEED) instrument incorporating a delay line detector has been constructed to rapidly collect high-quality digital LEED images with low total electron exposures. The system uses a position-sensitive pulse-counting detector with high bias current microchannel plates. This delay-line detector combined with a femtoampere electron gun offers a wide range of flexibility, with electron dosing currents ranging from 0.15pAto0.3fA. Using the highest current setting and collecting 1×106 counts per image, individual LEED images can be completed in 4s with an acquisition rate of 250kHz and a total electron exposure of 5×106 electrons. Under the latter conditions, images can be collected in 20min with an acquisition rate of 1kHz with a total electron exposure of 2×106 electrons. An angular width of 0.13° at 108eV is demonstrated, which means that domain sizes as large as 600Å can be resolved, depending on the surface quality of the crystal. The system electronics collect 2048×2048pixel images with a spatial resolution of about 75μm. The dynamic range of this system is 32bits∕pixel (limited only by physical memory). The construction of the detector results in a “plus”-shaped artifact, which requires that, for a given sample orientation, two images be taken at a relative angle of 45°. Identical current-voltage curves from an MgO(111)1×1H terminated sample, taken during several hours of exposure to the low current electron beam, demonstrate minimal electron induced H desorption.
Self-assembled monolayer as an antiadhesion layer on a nickel nanostamper in the nanoreplication process for optoelectronic applications
Authors: Lee Namseok , Choi Sungwoo , Kang Shinill
Published: February 2006

In this letter, self-assembled monolayer (SAM) was applied as an antiadhesion layer in the nanoreplication process to reduce the surface energy between the nanostamper and the polymeric nanopatterns. After electrochemical pretreatment process, n-dodecanethiol SAM was deposited on the nickel stamper using the solution deposition method. To examine the feasibility of the SAM as an antiadhesion layer, contact angle and lateral friction force were measured at room temperature. To verify the effectiveness of SAM for nanoreplication process, polymeric patterns were replicated by hot-embossing process using SAM-deposited nickel stamper. To apply our method to replication of sub-100-nm-scale nanopillar arrays, the nanopatterned substrate with nanopillar arrays was replicated using nanoinjection molding process with SAM-deposited nickel stamper.
Organic metal electrodes for controlled p- and n-type carrier injections in organic field-effect transistors
Authors: Takahashi Y. , Hasegawa T. , Abe Y. , Tokura Y. , Saito G.
Published: February 2006

Fine control of p-, n-, and ambipolar-type field-effect transistor (FET) operations is successfully demonstrated in prototypical single-crystal organic FETs with use of chemically tunable nature of Fermi energy in tetrathiafulvalene-tetracyanoguinodimethane-based organic metal electrodes. Carrier-type preference and rectifying nature in the organic-organic contacts are revealed in terms of the FET operations as well as of the all-organic Schottky diode characteristics.
Gate capacitance in electrochemical transistor of single-walled carbon nanotube
Authors: Shimotani Hidekazu , Kanbara Takayoshi , Iwasa Yoshihiro , Tsukagoshi Kazuhito , Aoyagi Yoshinobu , Kataura Hiromichi
Published: February 2006

In the electrochemical transistor of a single-walled carbon nanotube, we introduced the fourth terminal, which works as a reference electrode. This enables accurate control of change in gate voltage, i.e., potential difference between the electrolyte and the source electrode, and quantitative analyses of the gate capacitance. We found that the geometrical capacitance, which was ignored in the conventional model, makes a crucial contribution to the device characteristics, comparable to that from the chemical capacitance.
Improved organic thin-film transistor performance using novel self-assembled monolayers
Authors: McDowell M. , Hill I. G. , McDermott J. E. , Bernasek S. L. , Schwartz J.
Published: February 2006

Pentacene-based organic thin-film transistors have been fabricated using a phosphonate-linked anthracene self-assembled monolayer as a buffer between the silicon dioxide gate dielectric and the active pentacene channel region. Vast improvements in the subthreshold slope and threshold voltage are observed compared to control devices fabricated without the buffer. Both observations are consistent with a greatly reduced density of charge trapping states at the semiconductor-dielectric interface effected by introduction of the self-assembled monolayer.
Photonic-crystal near-ultraviolet reflectance filters fabricated by nanoreplica molding
Authors: Ganesh Nikhil , Cunningham Brian T.
Published: February 2006

One-dimensional photonic-crystal reflectance filters operating in the near-ultraviolet wavelengths were fabricated using nanoreplica molding from a silicon surface structure “master” template, patterned using electron-beam lithography. The fabricated devices produce a narrow linewidth reflectance resonance at a wavelength of 411nm for TM polarized illumination and a broadband reflectance characteristic between 402 and 439nm for TE polarized illumination. The measured reflectance spectra are accurately predicted by Rigorous Coupled Wave Analysis computer simulations, which demonstrate the capability for designing similar filter performance for wavelengths <350nm through minor adjustment of the photonic-crystal lattice period.
Giant enhanced optical nonlinearity of colloidal nanocrystals with a graded-index host
Authors: Xiao J. J. , Yu K. W.
Published: February 2006

The effective linear and third-order nonlinear optical properties of metallic colloidal crystal immersed in a graded-index host fluid are investigated theoretically. The local electric fields are extracted self-consistently based on the layer-to-layer interactions, which are readily given by the Lekner summation method. The resultant optical absorption and nonlinearity enhancement show a series of sharp peaks, which merge in a broadened resonant band. The sharp peaks become a continuous band for increasing packing density and number of layers. We believe that the sharp peaks arise from the in-plane dipolar interactions and the surface plasmon resonance, whereas the continuous band is due to the presence of the gradient in the host refractive index. These results have not been observed in homogeneous and randomly dispersed colloids, and thus would be of great interest in optical nanomaterial engineering.
Interface dipole and effective work function of Re in Re∕HfO2∕SiOx∕n-Si gate stack
Authors: Liang Y. , Curless J. , Tracy C. J. , Gilmer D. C. , Schaeffer J. K. , Triyoso D. H. , Tobin P. J.
Published: February 2006

Fermi level pinning at the Re∕HfO2 interface and its contribution to the Re interface work function in the Re∕HfO2∕SiOx∕n-Si stack were investigated using x-ray and ultraviolet photoelectron spectroscopy in conjunction with capacitance-voltage (C-V) measurements. Photoemission results showed that the Fermi level was partially pinned at the Re∕HfO2 interface, resulting in a 0.5eV interface dipole and 5.0eV interface work function between Re and HfO2. In contrast, C-V measurement of the Re∕HfO2∕SiOx∕n-Si stack showed a 4.7–4.8eV interface work function. The difference in Re interface work functions is discussed in terms of contributions of additional interface dipoles in the stack.
Influence of current noise on the relaxation oscillation dynamics of semiconductor lasers
Authors: Van der Sande Guy , Soriano Miguel C. , Yousefi Mirvais , Peeters Michael , Danckaert Jan , Verschaffelt Guy , Lenstra Daan
Published: February 2006

We find experimentally that the relaxation oscillation peak in the relative intensity noise spectrum of a semiconductor laser has a higher damping and lower frequency when we add low frequency noise to the pump current. The broadening of the relaxation oscillation peak with increasing carrier noise level is interpreted as an increase of the nonlinear gain compression with noise strength.
Enhanced efficiency in polymer light-emitting diodes due to the improvement of charge-injection balance
Authors: Lin Yow-Jon , Chou Wei-Yang , Lin Shih-Ting
Published: February 2006

The authors report the enhancement of efficiency of polymer light-emitting diodes (PLEDs) in the study. According to the experimental results, we find that PLEDs, fabricated on irradiated indium-tin-oxide surfaces by KrF excimer laser, with an organic layer between the cathode and the emitting layer may lead to the improvement of charge-injection balance and prevention of cathode metal quenching, resulting in a remarkable increase in external quantum efficiency.
Optical tunneling effect of localized surface plasmon: A simulation study using particle-in-cell method
Authors: Lan Yung-Chiang
Published: February 2006

Optical tunneling through thin metal films with periodic Gaussian-shaped grooves was studied using the particle-in-cell method. For a normally incident TM-polarized wave, the transmission coefficients are maximal in the localized surface plasmon (LSP) modes, which is similar to the predictions of the Drude model, but with lower transmission coefficients. The plasma-plasma interactions partially smear out the LSP modes, which has not been addressed in previous studies that involved the Drude model. Although various heating and cooling processes occur at the air-plasma interface, the temperature of the plasma only slightly affects the transmission coefficients.
Measurement of residual stresses in micromachined structures in a microregion
Authors: Sabaté N. , Vogel D. , Gollhardt A. , Keller J. , Michel B. , Cané C. , Gràcia I. , Morante J. R.
Published: February 2006

The use of a focused ion beam equipment is reported to find out the in-plane residual stress value of a microelectromechanical system structure by performing a local stress release. The ion beam column is used to mill stress-release slots of a few microns, whereas the scanning electron column captures micrographs of the milled area before and after the stress release process. The displacement component perpendicular to the slot is obtained from digital image correlation analysis of the captured high-resolution micrographs. The fitting of the experimental results with an analytical model together with the independent determination of the Young’s modulus allows one to find the residual stress value of the layer under study to a very good accuracy.
Silicon-on-insulator control impact-ionization-avalanche transistor
Authors: Dobrovolsky V. , Pavljuk S. , Rossokhaty V. , Cristoloveanu S.
Published: February 2006

In thin silicon-on-insulator structures, the gate effectively controls the longitudinal component of the electric field intensity in the pn+ junction, and thus the impact avalanche ionization of carriers. The present work proposes a device based on this operation principle: the control-impact-ionization-avalanche transistor, which achieves a transconductance of 0.14(A∕V)∕mm. According to the developed theoretical model and preliminary experimental data, the device can be optimized to achieve very high transconductance and frequencies such as several (A/V)/mm at frequencies of the order of 100MHz and lower, and about 1(A∕V)∕mm in 0.1–1THz range.
Reversible metal-semiconductor transitions for microwave switching applications
Authors: Dragoman M. , Cismaru A. , Hartnagel H. , Plana R.
Published: February 2006

This letter presents an original approach regarding the switching at high frequencies using reversible metal-semiconductor transitions displayed by various materials termed as Mott materials. The Mott materials experience a reversible semiconductor-metal transition when an external parameter (temperature, dc bias, hydrogenation, etc.) is varied. This transition can be used to allow or to stop the propagation of high-frequency fields, when a thin film of a Mott material is integrated with a planar high-frequency waveguide. This effect could have important applications in the area of communications, computing, and sensors.
Nanoindentation-induced deformation in Al–Pd–Mn single quasicrystals
Authors: Coupeau C. , Texier M. , Joulain A. , Bonneville J.
Published: February 2006

Nanoindentation experiments were performed at room temperature on Al–Pd–Mn single quasicrystals to induce plastic deformation in very localized areas and to examine microscopic mechanisms taking place in the bulk. Nanoindentation imprints investigated by transmission electron microscopy revealed the presence of grains and crystalline phases, but did not provide any evidence of dislocation activity. Pop-in events observed on the nanoindentation curves support the idea of grain formation and phase transformation just beneath the indenter, as shown by transmission electron microscopy.
Occurrence and simulation of nitrification in two contrasting sugarcane soils from the Australian wet tropics
Authors: Meier E. A. , Thorburn P. J. , Probert M. E.
Published: February 2006

The concentration of ammonium-nitrogen (NH4+-N) frequently exceeds that of nitrate-N (NO3−-N) in Australian wet tropical sugarcane soils. The amount of mineral N in soil is the net result of complex processes in the field, so the objective of this experiment was to investigate nitrification and ammonification in these soils under laboratory conditions. Aerobic and saturated incubations were performed for 1 week on 2 wet tropical soils. Net NO3−-N increased significantly in both soils during both types of incubation. A second series of aerobic incubations of these soils treated with NH4+-N and inoculated with subtropical nitrifying soils was conducted for 48 days. Nitrification in the wet tropical soils was not significantly affected by inoculation, and virtually all added N was nitrified during the incubation period. Mineral N behaviour of the 48-day incubations was captured with the APSIM-SoilN model. As nitrification proceeded under laboratory conditions and was able to be captured by the model, it was concluded that nitrification processes in the wet tropical soils studied were not different from those in the subtropical soils. Processes that remove NO3− from the soil, such as leaching and denitrification, may therefore be important factors affecting the proportions of NH4+-N and NO3−-N measured under field conditions.
Surface and sub-surface salinity in and around acid sulfate soil scalds in the coastal floodplains of New South Wales, Australia
Authors: Rosicky Mark A. , Slavich Peter , Sullivan Leigh A. , Hughes Mike
Published: February 2006

Two-metre-deep soil profiles at 10 acid sulfate soil (ASS) scalds along the coast of New South Wales (NSW), Australia, were examined for salinity indicators. At 5 of the sites, permanently vegetated areas adjacent to the ASS-scalded land were also tested. Throughout the profiles, most sites had high soluble chloride (Cl−) concentrations (≤17 mg/g soil) and high soluble sulfate (SO42−) concentrations (≤17 mg/g soil). Very low Cl− : SO42− ratios (≤3) indicated active pyrite oxidation. Soil salinity (measured as electrical conductivity, EC) was extremely high in the top 2 m of most of the ASS scalds when related to the growth requirements of the typical introduced pasture species that were planted in these areas following drainage. This allows salinity, in addition to the extremely low pH of the surface soils, to contribute to land denudation, which can instigate or perpetuate pyrite oxidation and ASS-related land scalding. Although the sites had shallow watertables and soil-moisture content was high, the surface soil (top 0.10 m) of the scalds had consistently higher soluble Cl− and SO42− concentrations and EC than adjacent vegetated areas. All coastal ASS areas investigated, typically freshwater backswamps used for cattle grazing, were underlain by estuarine-derived sediments containing saline ground water. The results demonstrate that revegetation of ASS scalds must include investigation and management of salinity, in addition to acidity, within the soil profile and at the soil surface.
Occurrence of magnetite in the sand fraction of an Oxisol in the Brazilian savanna ecosystem, developed from a magnetite-free lithology
Authors: Viana J. H. M. , Couceiro P. R. C. , Pereira M. C. , Fabris J. D. , Fernandes Filho E. I. , Schaefer C. E. G. R. , Rechenberg H. R. , Abrahão W. A. P. , Mantovani E. C.
Published: February 2006

It is relatively well established from many pedogenetic studies that, in deeply weathered Oxisols from Central Brazil, magnetite or maghemite are either inherited or transformed from magnetite of the mafic parent material. However, no similar pedogenetic pathways have been reported in the literature for other lithologies, such as limestone and pelitic rocks (shales and slates) of the Bambuí Group in Brazil. In these sedimentary, non-mafic lithologies, magnetic minerals are not likely to occur. Despite that, magnetic nodules were identified in a representative Oxisol pedon developed on this pedodomain, under savanna (Cerrado). Magnetic and non-magnetic fractions of nodules were separated with a hand magnet. Chemical and mineralogical compositions of these nodules were determined by conventional chemical methods, powder X-ray diffractometry (XRD), and 298 K Mössbauer spectroscopy. For the magnetic fraction, containing up to 84 dag/kg of Fe2O3 but also relatively rich in Al, Ti, Cr, and Si, Mössbauer measurements were also made at 4.2 K, without and with an externally applied magnetic field of 8 Tesla, and at 100 K. Mössbauer results and structural Rietveld refinement of the XRD data consistently suggest that the iron oxide mineralogy corresponds to approximately equivalent proportions of hematite and a partially oxidised magnetite, containing 3 dag/kg of iron as FeO. Laboratory tests were conducted in an attempt to produce magnetic material by heating this non-magnetic fraction. The sample was wrapped in filter paper and heated at 300°C for 30 min, and the results were compared with the naturally occurring magnetic nodules. The saturation magnetisation value of the thermally treated sample was found to be σ = 7 J/T.kg, well below σ = 16 J/T.kg of the magnetic soil nodules. Mössbauer and XRD results indicate that the iron oxide mineralogy of this laboratory-produced magnetic sample also corresponds to a mixture of partially oxidised magnetite and hematite. Two other parts of the same non-magnetic, naturally hematite-rich precursor were mixed with charcoal, to act as reducing agent, and oven-heated at 450°C and 600°C, respectively, for 1 h, producing increasing reduction of the hematite to magnetite. These laboratory simulations support the model in which magnetite in these hematite-rich nodules was formed under the influence of seasonal burning regimes of the covering vegetation, followed by partial re-conversion of the magnetite particles to hematite under long-term atmospheric exposure to air. This model is consistent with a long-term, seasonal fire history, assumed for the genesis of the Cerrado ecosystem in the Central Brazil, although a wider validity for the entire Bambuí Group area remains open.
Mathematical modelling of temperature profile of volcanic soils affected by an external thermal impact
Authors: Antilén Mónica , Fudym Olivier , Vidal Alvaro , Foerster Juan E. , Moraga Nelson , Escudey Mauricio
Published: February 2006

In this work, the soil temperature at depth was measured in the laboratory, and a mathematical model to fit the temperature profile in volcanic soils classified as Ultisols and Andisols was used. The mathematical model considered the transient heat diffusion equation, and a numerical discrete method was used to solve the equations system.
The soil surface was heated for 2500 s and the temperature rose close to 700°C; the soil temperature decreased with depth; the temperature v. time curves showed a constant value when the temperature reached around 100°C, associated with water phase change and related to the water content of soils. The model was corrected by including the heat volumetric formulation. The observed relative errors are close to 10% in all fitted curves with respect to experimental data, showing the quality of the parametrisation chosen in the mathematical model. The fitting curve deviations were reduced when the actual position of thermocouples was considered, showing the sensitivity of the mathematical model.
The simplified mathematical transient diffusion model proposed, which considers 2 ranges of thermal conductivity of soils and the surface temperature, was able to describe the experimental temperature profile in volcanic soils with wide differences in mineralogy, organic matter, and moisture contents.
Dispersion and re-deposition of fine particles and their effects on saturated hydraulic conductivity
Authors: Dikinya Oagile , Hinz Christoph , Aylmore Graham
Published: February 2006

Measurements of saturated hydraulic conductivity (K) have been used to study the rates of structural breakdown and pore clogging which occurred during leaching of 2 contrasting soils, Balkuling agricultural soil and a mining residue. Soil columns were leached with solutions of different electrolyte concentrations under saturated conditions using a Marriotte constant-head device. Measurements were made with either abrupt change of concentration from 500 to 1 mmol/L or gradual decreasing concentration from 500 through 100, 50, 10, to 1 mmol/L of NaCl followed by deionised water. The relative hydraulic conductivity (K/Ko) decreased substantially with time and with decrease in electrolyte concentrations for both soils. The decreases were attributed to various extents of internal swelling, dispersion, and decreases of pore radii as a result of detachment followed by re-deposition of the clay fraction during leaching. There was little difference in ultimate reductions in permeability between the abrupt and gradual changes of concentration from 500 to 1 mmol/L for both soils. The mining residue was clearly more prone to structural deterioration than the agricultural soil. Whereas the effluent particles from the Balkuling soil included domains or aggregates of clay crystals, those from the mining residue columns appeared to consist essentially of primary clay crystals indicating the less cohesive nature of this disturbed material. We also estimated the extent of permeability reductions using theoretical investigations based on particle size distribution. Predicted simulations agreed reasonably well with experimental data for both soils following column leaching with 1 mmol/L, with the best agreement observed for the mining residue.
Organic matter increases jarosite dissolution in acid sulfate soils under inundation conditions
Authors: Chu Chengxing , Lin Chuxia , Wu Yonggui , Lu Wenzhou , Long Jie
Published: February 2006

A column experiment was conducted to examine the effects of added organic matter and thickness of surface water on the stability of jarosite in a coastal acid sulfate soil. The results show that dissolution of jarosite was negligible if no organic matter was added onto the soil. However, where organic matter was added onto the soils, the acidity and the concentrations of iron and sulfate in the leachate of the soil increased following water inundation, indicating the decomposition of jarosite in such conditions. Probably, the organic matter content of the soil was originally too low to enable the creation of reducing conditions that could sufficiently cause the breakdown of jarosite contained in the soil. Under the experimental conditions, the amount of added organic matter played a more important role than the thickness of the overlying water in the dissolution of jarosite.
Modelling water and chemical transport in large undisturbed soil cores using HYDRUS-2D
Authors: Phillips I. R.
Published: February 2006

The ability of HYDRUS-2D (HYDRUS) to simulate water and chemical transport in large, undisturbed cores of a Vertosol and a Podosol soil was investigated. Parameters required by HYDRUS for simulating water and chemical transport, and nitrogen transformation, were obtained from previously published laboratory studies. HYDRUS simulated the measured cumulative drainage and cumulative chloride (Cl–) leaching behaviour very closely for both soil types, and also provided a very good description of coupled nitrogen transformation (conversion of ammonium to nitrate) and leaching (coefficient of model efficiency ∼1). There was little correlation between measured and predicted potassium (K+) leaching from the Podosol, suggesting that the mathematical equations governing the transport of reactive chemicals did not adequately reflect K+ behaviour in this coarse-textured soil. The reason for this discrepancy is unclear but may have been related to the use of sorption parameters obtained from batch rather than miscible displacement techniques, or mechanisms controlling K+ sorption were not well represented by the general non-linear sorption equation used by HYDRUS. The ability of HYDRUS to accurately simulate water and non-reactive chemical transport agrees with previous studies; however, more investigation into its suitability for predicting the movement reactive chemicals in soil is warranted.
Energy use and efficiency in two Canadian organic and conventional crop production systems
Authors: Hoeppner J.W. , Entz M.H. , McConkey B.G. , Zentner R.P. , Nagy C.N.
Published: February 2006

A goal in sustainable agriculture is to use fossil fuel energy more efficiently in crop production. This 12-year study investigated effects of two crop rotations and two crop production systems (organic versus conventional management) on energy use, energy output and energy-use efficiency. The grain-based rotation included wheat (Triticum aestivumL.)–pea (Pisum sativumL.)–wheat–flax (Linum usitatissimumL.), while the integrated rotation included wheat–alfalfa (Medicago sativaL.)–alfalfa–flax. Energy use was 50% lower with organic than with conventional management, and approximately 40% lower with integrated than with the grain-based rotation. Energy use across all treatments averaged 3420 MJ ha−1yr−1. Energy output (grain and alfalfa herbage only) across treatments averaged 49,947 MJ ha−1yr−1and was affected independently by production system and crop rotation. Energy output in the integrated rotation was three times that of the grain-based rotation; however, this difference was largely due to differences in crop type (whole plant alfalfa compared with grain seed). Energy output was 30% lower with organic than with conventional management. Energy efficiency (output energy/input energy) averaged to 17.4 and was highest in the organic and integrated rotations. A significant rotation by production system interaction (P<0.05) indicated that energy efficiency increases due to crop input reduction (i.e., shift from conventional to organic management) were greater in the integrated than in the grain-based rotation. Greater energy efficiency in the integrated rotation under organic management was attributed to the fact that the forage component was less sensitive to chemical input removal than grain crops.
Great Plains cropping system studies for soil quality assessment
Authors: Varvel G. , Riedell W. , Deibert E. , McConkey B. , Tanaka D. , Vigil M. , Schwartz R.
Published: February 2006

Interactions between environmental conditions and management practices can significantly affect soil function. Soil quality assessments may improve our understanding of how soils interact with the hydrosphere and atmosphere. This information can then be used to develop management practices that improve the capacity of the soil to perform its various functions and help identify physical, chemical, and biological soil attributes to quantify the present state of a soil and detect changes resulting from management. In protocols established by the Great Plains cropping system network, sampling and testing procedures were selected to identify physical, chemical, and biological soil attributes responsive to management that may serve as useful indicators in assessing the effects of management on the soil resource. Eight existing long-term studies from throughout the Great Plains in the central USA were used to make these assessments because, (1) many years are required for certain soil properties to change measurably; (2) annual weather causes variation in system performance; and (3) the soil pools of interest are spatially variable. This paper includes detailed descriptions of the treatments and sites, and both long-term and short-term (1999–2002) data on precipitation, temperature, and yields for each location.
Cropping system influences on soil physical properties in the Great Plains
Authors: Pikul J.L. , Schwartz R.C. , Benjamin J.G. , Baumhardt R.L. , Merrill S.
Published: February 2006

Agricultural systems produce both detrimental and beneficial effects on soil quality (SQ). We compared soil physical properties of long-term conventional (CON) and alternative (ALT) cropping systems near Akron, Colorado (CO); Brookings, South Dakota (SD); Bushland, Texas (TX); Fargo, North Dakota (ND); Mandan (ND); Mead, Nebraska (NE); Sidney, Montana (MT); and Swift Current, Saskatchewan (SK), Canada. Objectives were to quantify the changes in soil physical attributes in cropping systems and assess the potential of individual soil attributes as sensitive indicators of change in SQ. Soil samples were collected three times per year from each treatment at each site for one rotation cycle (4 years at Brookings and Mead). Water infiltration rates were measured. Soil bulk density (BD) and gravimetric water were measured at 0–7.5, 7.5–15, and 15–30 cm depth increments and water-filled pore space ratio (WFPS) was calculated. At six locations, a rotary sieve was used to separate soil (top 5 cm) into six aggregate size groups and calculate mean weight diameter (MWD) of dry aggregates. Under the CON system at Brookings, dry aggregates (>19 mm) abraded into the smallest size class (<0.4 mm) on sieving. In contrast, the large aggregates from the ALT system abraded into size classes between 2 and 6 mm. Dry aggregate size distribution (DASD) shows promise as an indicator of SQ related to susceptibility of soil to wind erosion. Aggregates from CON were least stable in water. Soil C was greater under ALT than CON for both Brookings and Mead. At other locations, MWD of aggregates under continuous crop or no tillage (ALT systems) was greater than MWD under CON. There was no crop system effect on water infiltration rates for locations having the same tillage within cropping system. Tillage resulted in increased, decreased, or unchanged near-surface BD. Because there was significant temporal variation in water infiltration, MWD, and BD, conclusions based on a single point-in-time observation should be avoided. Elevated WFPS at Fargo, Brookings, and Mead may have resulted in anaerobic soil conditions during a portion of the year. Repeated measurements of WFPS or DASD revealed important temporal characteristics of SQ that could be used to judge soil condition as affected by management.
Cropping system effects on soil biological characteristics in the Great Plains
Authors: Liebig M. , Carpenter-Boggs L. , Johnson J.M.F. , Wright S. , Barbour N.
Published: February 2006

Soil biological quality can affect key soil functions that support food production and environmental quality. The objective of this study was to determine the effects of management and time on soil biological quality in contrasting dryland cropping systems at eight locations in the North American Great Plains. Alternative (ALT) cropping systems were characterized by greater cropping intensity (less fallow), more diverse crop sequences, and/or reduced tillage than conventional (CON) cropping systems. Soil biological properties were assessed at depths of 0–7.5, 7.5–15, and 15–30 cm from 1999 to 2002 up to three times per year. Compared to CON, ALT cropping systems had greater microbial biomass and potentially mineralizable N. ALT cropping systems also had greater water stable aggregates in the surface 7.5 cm, but only at four locations. Total glomalin (TG), an organic fraction produced by fungi associated with aggregate stability, differed only at one location (Mandan), where the ALT cropping system had 27% more TG than the CON cropping system. Fatty acid methyl ester (FAME) profiles were highly location dependent, but total extracted FAME tended to be higher in ALT cropping systems. Soil biological properties fluctuated over time at all locations, possibly in response to weather, apparent changes in soil condition at sampling, and the presence or absence of fallow and/or legumes in rotation. Consequently, preplant and post-harvest sampling, when weather and soil conditions are most stable, is recommended for comparison of soil biological properties among management practices. Overall, ALT cropping systems enhanced soil function through: (1) improved retention and cycling of nutrients and (2) maintenance of biodiversity and habitat, implying improved agro-ecosystem performance over time.
Cropping system effects on soil quality in the Great Plains: Synthesis from a regional project
Authors: Wienhold B.J. , Pikul J.L. , Liebig M.A. , Mikha M.M. , Varvel G.E. , Doran J.W. , Andrews S.S.
Published: February 2006

Soils perform a number of essential functions affecting management goals. Soil functions were assessed by measuring physical, chemical, and biological properties in a regional assessment of conventional (CON) and alternative (ALT) management practices at eight sites within the Great Plains. The results, reported in accompanying papers, provide excellent data for assessing how management practices collectively affect agronomic and environmental soil functions that benefit both farmers and society. Our objective was to use the regional data as an input for two new assessment tools to evaluate their potential and sensitivity for detecting differences (aggradation or degradation) in management systems. The soil management assessment framework (SMAF) and the agro-ecosystem performance assessment tool (AEPAT) were used to score individual soil properties at each location relative to expected conditions based on inherent soil-forming factors and to compute index values that provide an overall assessment of the agronomic and environmental impact of the CON and ALT practices. SMAF index values were positively correlated with grain yield (an agronomic function) and total organic matter (an agronomic and environmental function). They were negatively correlated with soil nitrate concentration at harvest (an indicator of environmental function). There was general agreement between the two assessment tools when used to compare management practices. Users can measure a small number of soil properties and use one of these tools to easily assess the effectiveness of soil management practices. A higher score in either tool identifies more environmentally and agronomically sustainable management. Temporal variability in measured indicators makes dynamic assessments of management practices essential. Water-filled pore space, aggregate stability, particulate organic matter, and microbial biomass were sensitive to management and should be included in studies aimed at improving soil management. Reductions in both tillage and fallow combined with crop rotation has resulted in improved soil function (e.g., nutrient cycling, organic C content, and productivity) throughout the Great Plains.
An economic comparison of alternative and traditional cropping systems in the northern Great Plains, USA
Authors: DeVuyst Eric A. , Foissey Thomas , Kegode George O.
Published: February 2006

Current production practices in the Red River Valley of North Dakota and Minnesota involve use of extensive tillage and/or herbicides to control weeds. Given the erosion potential, environmental concerns associated with herbicides, and herbicide-resistant weeds, alternative cropping systems that mitigate these problems need to be assessed economically. Furthermore, the role that government commodity programs play in the adoption of more ecologically friendly cropping systems needs to be determined. We evaluated 8 years of yield data (1994–2001) from field plots near Fargo, North Dakota, to compare the economics of two alternative cropping systems, reduced-input (RI) and no-till (NT), to a conventional tillage (CT) cropping system. The RI system relies on a more diverse rotation of soybean (SB), spring wheat (SW), sweet clover (SC) and rye, and uses fewer herbicide and fertilizer inputs than CT or NT. Both NT and CT systems rotate SB and SW. We found that CT returns averaged over $47 ha−1more than NT during the study period. Because SC yield data were not available, the economic competitiveness of RI was calculated using break-even yields and returns for SC. Historical SC yields in Cass County, North Dakota were not statistically different from the break-even yields. However, when government program payments were considered, break-even returns for SC increased by about $15 and $18 ha−1and break-even yields by 0.44 and 0.52 MT ha−1for RI to compare with NT and CT, respectively. These results indicate that CT management offers greater economic return than either RI or NT and that government program payments impede adoption of more environmentally friendly cropping systems in the northern Great Plains.
Cropping system influences on soil chemical properties and soil quality in the Great Plains
Authors: Mikha M.M. , Vigil M.F. , Liebig M.A. , Bowman R.A. , McConkey B. , Deibert E.J. , Pikul J.L.
Published: February 2006

Soil management and cropping systems have long-term effects on agronomic and environmental functions. This study examined the influence of contrasting management practices on selected soil chemical properties in eight long-term cropping system studies throughout the Great Plains and the western Corn Belt. For each study, soil organic C (SOC), total N (TN), particulate organic matter (POM), inorganic N, electrical conductivity (EC), and soil pH were evaluated at 0–7.5, 7.5–15, and 15–30 cm within conventional (CON) and alternative (ALT) cropping systems for 4 years (1999–2002). Treatment effects were primarily limited to the surface 7.5 cm of soil. No-tillage (NT) and/or elimination of fallow in ALT cropping systems resulted in significantly (P<0.05) greater SOC and TN at 0–7.5 cm within five of the eight study sites [Akron, Colorado (CO); Bushland, Texas (TX); Fargo, North Dakota (ND); Mandan, ND; and Swift Current, Saskatchewan (SK), Canada]. The same pattern was observed with POM, where POM was significantly (P<0.05) greater at four of the eight study sites [Bushland, TX, Mandan, ND, Sidney, Montana (MT), and Swift Current, SK]. No consistent pattern was observed with soil EC and pH due to management, although soil EC explained almost 60% of the variability in soil NO3-N at 0–7.5 cm across all locations and sampling times. In general, chemical soil properties measured in this study consistently exhibited values more conducive to crop production and environmental quality in ALT cropping systems relative to CON cropping systems.
Seed germination and seedling emergence of three Artemisia species (Asteraceae) inhabiting desert sand dunes in China
Authors: Tobe Kazuo , Zhang Liping , Omasa Kenji
Published: February 2006

Artemisia ordosica,A. arenariaandA. sphaerocephalaare semi-shrubs inhabiting desert sand dunes in China and often used to rehabilitate desertified areas. Improvement of dune rehabilitation success by sowing requires better understanding of the processes involved in the control of seed germination and seedling emergence in these species. Thus, (1) effects of temperature, light and osmotica (polyethylene glycol-6000) on seed germination, and (2) effects of seed burial depth in sand and irrigation regime on seedling emergence, were studied under controlled conditions. Seeds of the three species required light for germination, and the light fluence needed for germination was dependent on temperature. Seedling emergence of the three species was maximal (70–94%) for seeds sown at a depth of 2.5 mm, and decreased with increasing seed burial depth when the pots were initially and subsequently treated with 16 mm and 3 mm irrigation at 1-d intervals. However, when the pots were initially and subsequently treated with 8 mm and 3 mm irrigation at 2-d intervals, seedling emergence was almost completely suppressed due to water deficiency in sand. It is suggested that the probability of seed germination and seedling emergence of the three species in the field is very limited, because the light requirement restricts seed germination to shallow sand layers where water is lost rapidly due to evaporation. Temperature appeared to have secondary effects on seed germination, by modifying the light sensitivity of seeds.
Effects of a butenolide present in smoke on light-mediated germination of Australian Asteraceae
Authors: Merritt D.J. , Kristiansen M. , Flematti G.R. , Turner S.R. , Ghisalberti E.L. , Trengove R.D. , Dixon K.W.
Published: February 2006

This study investigated the effects of 3-methyl-2H-furo[2,3-c]pyran-2-one, a germination active butenolide present in plant-derived smoke, gibberellic acid and smoke water on seeds of AustralianAsteraceaeexposed to different light regimes. Seeds of all species required light, with maximum germination occurring under white light, or light dominated by 640 nm. Compared to untreated seeds, butenolide increased germination ofAngianthus tomentosus,Gnephosis tenuissima,Myriocephalus guerinae,Podolepis canescensandRhodanthe citrinaat suboptimal light wavelengths and in the dark to a level equal to, or greater than, smoke water. Germination ofErymophyllum glossanthusandGnephosis aciculariswas not promoted by butenolide or smoke water under any light regime. The action of gibberellic acid was compared to that of butenolide for three species (Angianthus tomentosus,Myriocephalus guerinaeandPodolepis canescens), and both compounds were found to stimulate germination. This study provides evidence that butenolide can act in a similar fashion as gibberellic acid in promoting seed germination of light-sensitive seeds. The ecological significance of these findings is discussed.
Sensitivity to ethylene as a major component in the germination of seeds of Stylosanthes humilis
Authors: Ribeiro Dimas Mendes , Barros Raimundo Santos
Published: February 2006

Physiological dormancy of scarified seeds of Townsville stylo (Stylosanthes humilisH.B.K.) is broken by ethylene. When the biosynthesis of this gas was impaired by 2-aminoethoxyvinylglycine (AVG) plus Co2+, the response to ethylene at very low concentrations was appreciable in non-dormant seeds and nil in the dormant ones. Complete inhibition of germination of non-dormant seeds occurred only when they were treated with AVG plus Co2+under an ethylene-free atmosphere, a condition in which no trace of the gas in the atmosphere of Erlenmeyer flasks could be detected. Injection of ethylene into that system triggered germination of both dormant and non-dormant seeds, demonstrating a requirement for the gas. Non-dormant seeds were at least 50-fold more sensitive to ethylene than the dormant ones. Perception of ethylene occurred within a very short time (at most 15 min), since exposure of both dormant and non-dormant seeds to the gas, at a steeply declining concentration, sufficed to cause substantial germination.
The role of fluctuations in soil water content on the regulation of dormancy changes in buried seeds of Polygonum aviculare L.
Authors: Batlla Diego , Benech-Arnold Roberto Luis
Published: February 2006

It has been hypothesized that fluctuations in soil water content may affect the dormancy status of weed seed banks under field conditions. In this paper, we present results showing that fluctuations in soil water content affect the dormancy status of buried seeds ofPolygonum aviculareL. stored at dormancy-releasing temperatures. Effects of fluctuations in soil water content on the dormancy status ofP. aviculareseeds were evaluated by comparing changes in the range of temperatures and water potentials permissive for germination, and in the sensitivity to fluctuating temperatures, between seeds subjected to a moist soil regime (MS) or to a fluctuating soil water content regime (FS). In comparison to the dormancy release pattern observed for seeds subjected to MS, seeds subjected to FS generally showed an increase in their dormancy level after periods of storage under dry soil conditions, and a decrease in their dormancy level after periods of storage under moist soil conditions. These effects were more pronounced during early stages of the storage period, producing larger changes in the thermal and water potential range for seed germination than in the sensitivity of seeds to fluctuating temperatures. Seeds subjected to FS generally exhibited a lower mean low-limit temperature, lower mean thermal time and hydrotime requirements for germination, and a higher proportion of the seed population with the capacity to germinatein situ, than seeds subjected to MS. The results obtained suggested that fluctuations in soil water content could be an additional factor affecting dormancy and weed emergence patterns under field conditions.
Seed dormancy in the early diverging eudicot Trochodendron aralioides (Trochodendraceae)
Authors: Baskin Jerry M. , Baskin Carol C. , Chien Ching-Te , Chen Shun-Ying
Published: February 2006

The embryo length/seed length (E/S) ratio of the early diverging eudicotTrochodendron aralioidesis 0.34. Embryos in fresh seeds were 0.36±0.01 mm long, and they increased in length by about 250% (in 20 d) before radicle emergence (germination) occurred, demonstrating that the embryo is underdeveloped at seed maturity. Seeds germinated to 95–100% at 20/10, 25/15 and 30/15°C in light in ≤4 weeks, without any pretreatment, but no seeds germinated in darkness. Thus, seeds ofT. aralioideshave morphological dormancy (MD), which is considered to be the primitive condition in seed plants, and MD probably has existed in the genusTrochodendronsince its origin in the early Tertiary.
Unifying perspectives of some mechanisms basic to desiccation tolerance across life forms
Authors: Berjak Patricia
Published: February 2006

Desiccation-tolerant organisms, or life-cycle stages of particular taxa, occur among animals, higher and lower plants, terrestrial micro-algae, lichens and bacteria. Recent investigations have revealed that a number of mechanisms conferring desiccation tolerance appear to be common to the diversity of life forms able to survive extreme dehydration. In particular, parallel processes involving late embryogenic abundant (LEA) or LEA-like proteins, accumulation of sugars, aspects of active oxygen species (AOS) and non-enzymic and enzymic antioxidants have been the recent focus of attention, some across a diversity of organisms. The present contribution considers advances made from the study of these processes, particularly in enhancing current understanding of the composition of, and protection afforded by, the glassy state in desiccated organisms. Strong evidence that proteins, particularly LEAs, are implicated in glass formation is reviewed, and behaviour of such proteins upon dehydration is discussed in this context. The question of the ability of cells to survive complete water removal is considered in the context that it is unlikely, and that the basis of the deterioration of very dry seeds results from abstraction of water necessary to maintain the integrity of the intracellular glassy state. Finally, the revelation that desiccated seeds deteriorate with time, even under extremely good genebanking conditions, is discussed.