bluuebunny/crossref_metadata_2025 huggingface dataset:
Sedimentological characterization of the quaternary deposits in the region between Marília and Presidente Prudente, São Paulo State, Brazil
Authors: Sallun Alethéa Ernandes Martins , Suguio Kenitiro
Published: April 2009

Sedimentologic characterization and provenance studies of quaternary colluvial deposits (9±1 to 980±100 ky B.P. - dated by luminescence) were based on textural and mineralogical analyses. These deposits occur extensively between Marília and Presidente Prudente (São Paulo State, Brazil), superimposed on the Bauru Group sedimentary rocks or the Serra Geral Formation basaltic rocks, both of Cretaceous age. They are distributed irregularly throughout the study area and are studied by sedimentologic and morphologic methods. These deposits are composed of very fine to coarse-grained unconsolidated sands, mostly constituted by quartzose monocrystalline grains reddened by iron oxide and hydroxide impregnation. Analyses of grain sizes indicated that total granulometric distributions are richer in the clay fraction than in the sedimentary rocks located. Non-micaceous transparent heavy minerals studied microscopically in fine-grained as well as in very fine-grained sands showed that zircon, tourmaline, staurolite and rutile are present in all the samples. Differences in grain sizes among the colluvial deposits and the Bauru Group sedimentary rocks are attributable to pedogenetic processes.
Molecular genetics of medullary thyroid carcinoma: the quest for novel therapeutic targets
Authors: Cerrato Aniello , De Falco Valentina , Santoro Massimo
Published: April 2009

Medullary thyroid carcinoma (MTC) is a rare tumour arising from neural crest-derived parafollicular C-cells. Metastatic MTC patients are incurable because the cancer does not respond to radiotherapy or chemotherapy. The REarranged during Transfection (RET) proto-oncogene plays a key role in the development of MTC. However, one-half of the sporadic MTC do not carry RET mutations. Mice models and early evidence obtained in human samples suggest that other genes, including those encoding components of the RB1 (retinoblastoma) and TP53 tumour-suppressor pathways, may be involved in MTC formation. Here, we review the data on the involvement of genes acting in the RET and RB1/TP53 pathways in MTC. Understanding genetic lesions that occur in MTC is a prerequisite to identifying molecular therapeutic targets in MTC and in improving the efficacy of RET-targeted therapies.
Statistical methods to correct for observation error in a density‐independent population model
Authors: Buonaccorsi John P. , Staudenmayer John
Published: April 2009

The problem of observation error in assessing the dynamics of populations over time has received increasing attention of late. Of particular interest has been a density‐independent dynamic model, which allows a trend and is commonly employed in population viability analysis (PVA). Most of the recent work in this area has focused on assessing the impact of the observation error and on finding corrected estimators, primarily under normal models with the observation errors assumed to have a constant variance. This paper provides a comprehensive overview of statistical methods for this problem and evaluates them through simulations. This includes the development and assessment of simple and practical ways to obtain standard errors and confidence intervals for the basic parameters in the model and functions of them, such as the intrinsic rate of increase or the probability of eventual extinction. We allow for unequally spaced data and possibly changing observation error variances, and we also discuss how to employ standard errors that often accompany the estimated abundances. Both likelihood techniques under normality and methods allowing non‐normal observation errors are discussed, and we describe how the various likelihood‐based techniques can be implement using standard mixed‐model software, such as PROC MIXED in SAS. The projection technique we use to handle functions of the basic parameters is also valuable when there is no observation error. The methods are motivated and illustrated using data for grizzly bears, Whooping Cranes, California Condors, and Puerto Rican Parrots. We present a simulation experiment to evaluate the performance of the some of the methods.
Vegetation mediated the impacts of postglacial climate change on fire regimes in the south‐central Brooks Range, Alaska
Authors: Higuera Philip E. , Brubaker Linda B. , Anderson Patricia M. , Hu Feng Sheng , Brown Thomas A.
Published: April 2009

We examined direct and indirect impacts of millennial‐scale climate change on fire regimes in the south‐central Brooks Range, Alaska, USA, using four lake sediment records and existing paleoclimate interpretations. New techniques were introduced to identify charcoal peaks semi‐objectively and to detect statistical differences between fire regimes. Peaks in charcoal accumulation rates provided estimates of fire return intervals (FRIs), which were compared among vegetation zones identified by fossil pollen and stomata. Climatic warming between ca. 15 000–9000 yr BP (calendar years before Common Era [CE] 1950) coincided with shifts in vegetation from herb tundra to shrub tundra to deciduous woodlands, all novel species assemblages relative to modern vegetation. Two sites cover this period and show decreased FRIs with the transition from herb toBetula‐dominated shrub tundra ca. 13 300–14 300 yr BP (FRImean= 144 yr; 95% CI = 120–169 yr), when climate warmed but remained cooler than present. Although warming would have favored shorter FRIs in the shrub tundra, the shift to more continuous, flammable fuels relative to herb tundra was probably a more important cause of increased burning. Similarly, a vegetation shift toPopulus‐dominated deciduous woodlands overrode the influence of warmer‐ and drier‐than‐present summers, resulting in lower fire activity from ca. 10 300–8250 yr BP (FRImean= 251 yr; 95% CI = 156–347 yr). Three sites record the mid‐to‐late Holocene, when climatic cooling and moistening allowedPicea glaucaforest–tundra andP. marianaboreal forests to establish ca. 8000 and 5500 yr BP, respectively. FRIs in forest–tundra were either similar to or shorter than those in the deciduous woodlands (FRImeanrange = 131–238 yr). The addition ofP. marianaca. 5500 yr BP increased landscape flammability, overrode the effects of climatic cooling and moistening and resulted in lower FRIs (FRImean= 145 yr; 95% CI = 130–163). Overall, shifts in fire regimes were strongly linked to changes in vegetation, which were responding to millennial‐scale climate change. We conclude that shifts in vegetation can amplify or override the direct influence of climate change on fire regimes, when vegetation shifts significantly modify landscape flammability. Our findings emphasize the importance of biophysical feedbacks between climate, fire, and vegetation in determining the response of ecosystems to past, and by inference, future climate change.
Scaling the effects of moose browsing on forage distribution, from the geometry of plant canopies to landscapes
Authors: Jager Nathan R. De , Pastor John , Hodgson Angela L.
Published: April 2009

Landscape heterogeneity influences large herbivores by altering their feeding rates, but as herbivores attempt to maximize feeding rates they also create spatial heterogeneity by altering plant growth. Herbivore feeding rates thus provide a quantitative link between the causes and consequences of spatial heterogeneity in herbivore‐dominated ecosystems.

The fractal geometry of plant canopies determines both the density and mass of twigs available to foraging herbivores. These properties determine a threshold distance between plants (d*) that distinguishes the mechanisms regulating herbivore intake rates. When d* is greater than the actual distance between plants (d), intake is regulated by the rate of food processing in the mouth. But when d* < d, intake is regulated by the rate at which the herbivore encounters new plants. Alterations to plant geometry due to past browsing could change the rate at which herbivores encounter and process bites of plant tissue, modify d* relative to d, and thus change intake rates and the distribution of mechanisms regulating it across landscapes.

We measured changes in the geometry of aspen (Populus tremuloides) and balsam fir (Abies balsamea) saplings along gradients of moose browsing from 2001 to 2005 at Isle Royale National Park, Michigan, USA. For aspen saplings, fractal dimension of bite density, bite mass, and forage biomass responded quadratically to increasing moose browsing and were greatest at ∼3–4 g·m−2·yr−1 consumption. For balsam fir, in contrast, these same measures declined steadily with increasing moose browsing.

The different responses of plant canopies to increased browsing altered d* around plants. In summer, d* ≥ d for aspen saplings at all prior consumption levels. Food processing therefore regulated summer moose feeding rates across our landscapes. In winter, changes in bite mass due to past browsing were sufficient to cause d* < d for aspen and balsam fir. Therefore, travel velocity and food processing jointly regulated intake rate during winter. Browsing‐induced changes in the small‐scale geometry of plant canopies can determine intake rate at larger spatial scales by changing d* relative to d and, hence, which mechanisms determine intake rate, essentially altering how herbivores sense the distribution of their food resources.
Assessing the relative importance of disturbance, herbivory, diversity, and propagule pressure in exotic plant invasion
Authors: Eschtruth Anne K. , Battles John J.
Published: April 2009

The current rate of invasive species introductions is unprecedented, and the dramatic impacts of exotic invasive plants on community and ecosystem properties have been well documented. Despite the pressing management implications, the mechanisms that control exotic plant invasion remain poorly understood. Several factors, such as disturbance, propagule pressure, species diversity, and herbivory, are widely believed to play a critical role in exotic plant invasions. However, few studies have examined the relative importance of these factors, and little is known about how propagule pressure interacts with various mechanisms of ecological resistance to determine invasion success.

We quantified the relative importance of canopy disturbance, propagule pressure, species diversity, and herbivory in determining exotic plant invasion in 10 eastern hemlock forests in Pennsylvania and New Jersey (USA). Use of a maximum‐likelihood estimation framework and information theoretics allowed us to quantify the strength of evidence for alternative models of the influence of these factors on changes in exotic plant abundance. In addition, we developed models to determine the importance of interactions between ecosystem properties and propagule pressure. These analyses were conducted for three abundant, aggressive exotic species that represent a range of life histories: Alliaria petiolata, Berberis thunbergii, and Microstegium vimineum.

Of the four hypothesized determinants of exotic plant invasion considered in this study, canopy disturbance and propagule pressure appear to be the most important predictors of A. petiolata, B. thunbergii, and M. vimineum invasion. Herbivory was also found to be important in contributing to the invasion of some species. In addition, we found compelling evidence of an important interaction between propagule pressure and canopy disturbance. This is the first study to demonstrate the dominant role of the interaction between canopy disturbance and propagule pressure in determining forest invasibility relative to other potential controlling factors. The importance of the disturbance–propagule supply interaction, and its nonlinear functional form, has profound implications for the management of exotic plant species populations. Improving our ability to predict exotic plant invasions will require enhanced understanding of the interaction between propagule pressure and ecological resistance mechanisms.
Maternal influences on reproduction in two populations of Columbian ground squirrels
Authors: Skibiel Amy L. , Dobson F. Stephen , Murie Jan O.
Published: April 2009

In this study, we examined influences of maternal traits on offspring birth mass, growth rate, and weaning mass for two populations of Columbian ground squirrels (Spermophilus columbianus). We tested relationships between maternal body condition, structural size, change in mass (during gestation, during lactation, and during the entire reproductive period), timing of reproduction, and litter size on offspring traits using path analyses. To assess whether maternal investment in offspring traits extended beyond the period of direct maternal care, we examined associations between offspring traits and overwinter survival of pups. In general, females in better condition raised pups that were heavier at weaning and that had faster growth rates during lactation. Litter size had a negative effect on mass and growth rate, and only litter size had a significant effect on birth mass. For both populations, the average weaning mass of pups within a litter had a positive effect on the number of pups that survived to yearling age. In a population for which birth masses and growth rates were available, pups with faster growth rates survived better to yearling age, whereas birth mass had no effect on the number of surviving offspring in litters. We found substantial maternal influences on offspring growth and size, and evidence that these influences may extend beyond the juvenile period and constitute influences on fitness. The key to arriving at these conclusions was to take the number of offspring into account before testing for maternal effects.
Induction of dna strand breaks by genotoxicants in the algaChlamydomonas reinhardtii
Authors: David Rhiannon M. , Winter Matthew J. , Chipman J. Kevin
Published: April 2009

The use of unicellular algae in ecotoxicity testing is well established, particularly regarding whole-organism and population-level end points such as lethality and population growth. Conflicting information exists, however, on the potential for genetic toxicity to be incorporated into the safety studies in this test organism. In the present study, DNA strand breaks (Comet assay) and ethoxyresorufin-O-deethylase (EROD) activity were used as indicators of genetic toxicity and cytochrome P450 1A baseline xenobiotic metabolism, respectively, in the unicellular green alga Chlamydomonas reinhardtii. DNA strand breaks were quantified following exposure to the direct-acting genotoxic agents 4-nitroquinoline-1-oxide (NQO) and the N-hydroxy metabolite of 2-acetylamino-fluorene (N-OH-2-AAF) and the indirect-acting genotoxin chrysoidine. Following compound exposure, chrysoidine and N-OH-2-AAF produced statistically significant increases in DNA strand breaks at both 0.1 and 10 μM and 0.05 and 5 μM, respectively (p < 0.05 and p < 0.01). Different light sources were also found to influence DNA strand breaks, the minimum response being observed using a source that omits the ultraviolet range. Compared to many mammalian cells, both DNA damage responses and EROD activity were relatively weak. EROD activity was 0.03 pmol/min/106 cells in control cells, and the maximum level of DNA strand breaks observed was 14.1% at a 5 nM concentration of NQO. The responses exhibited were not enhanced by the use of a cell wall-free mutant strain. In conclusion, C. reinhardtii responded, albeit weakly, to selected direct- and indirect-acting genotoxicants and also exhibited measurable EROD activity.
Hydraulic Characteristics of Depositional Seals as Affected by Exchangeable Cations, Clay Mineralogy, and Polyacrylamide
Authors: Bhardwaj A. K. , McLaughlin R. A. , Shainberg I. , Levy G. J.
Published: April 2009

Depositional seals, formed when turbid waters infiltrate into soils, lead to a reduction in the hydraulic conductivity (HC) of soils and increased runoff. In this study, the effect of anionic polyacrylamide (PAM) on the HC and flocculation of depositional seals made of three clay minerals (montmorillonite, illite, and kaolinite), saturated with either Na or Ca, was investigated. A silt loam soil was packed in columns and leached with 5 g L−1 suspensions of the reference clays. Deposition of the clay particles on the soil surface formed seals. In the PAM treatment, dry granules of linear PAM were spread on the soil surface before the suspension application. Calcium seals were more permeable than Na seals in all the clay types, up to 26 times greater for montmorillonite. The HC of the seals for the clay minerals was in the order kaolinite (2.8–3.5 mm h−1) > illite (0.6–3.0 mm h−1) > montmorillonite (0.09–1.0 mm h−1). The addition of PAM generally enhanced clay flocculation, with the magnitude of the enhancement depending on the type of the exchangeable cation. The Na‐saturated seals in the three clay types had significantly higher initial HC with the PAM treatment. This increase, however, was transient except in Na‐illite. The impact of PAM on the degree of clay flocculation and floc density partially explained the effects of PAM on the HC of the depositional seals. An increase in clay flocculation or a decrease in floc density caused by PAM resulted in an increase in depositional seal HC.
Phenol Accumulation in a Young Humic Fraction following Anaerobic Decomposition of Rice Crop Residues
Authors: Olk D.C. , Jimenez R.R. , Moscoso E. , Gapas P.
Published: April 2009

Soil phenols have been implicated as inhibitors of soil N cycling within many agroecosystems, including irrigated lowland rice (Oryza sativa L.). To quantify the effects of crop management on temporal patterns of phenol accumulation in lowland rice soils, we measured phenol concentrations in two humic fractions at two crop growth stages in each growing season during a 4‐yr field study at the International Rice Research Institute (Philippines). Samples were collected from two double‐crop rotations (continuous rice and rice–maize [Zea mays L.]) with two N fertilizer rates (0 and nonlimiting), and with either aerobic or anaerobic decomposition of incorporated crop residues. Phenols were determined by tetramethylammonium hydroxide thermochemolysis. Compared with the other field treatments, anaerobic decomposition of crop residues with continuous rice and nonlimiting rates of N fertilizer promoted a gradual increase in the relative enrichment of phenols in the mobile humic acid fraction during the 4 yr. The level of enrichment varied among phenol compounds, developing the fastest and becoming most pronounced with the smaller molecules of molecular weight 168 or less. Anaerobic decomposition had less effect on phenol enrichment for continuous rice cropping without N fertilizer. No phenol enrichment was found with anaerobic decomposition of rice residues in the rice–maize rotation. Our results are consistent with previous findings of inhibited mineralization of humic N with anaerobic decomposition, continuous rice, and nonlimiting rates of N fertilizer. Rotation of maize with rice or other techniques to ensure aerobic decomposition of crop residues may help mitigate or prevent phenol accumulation.
Continental United States Atmospheric Wet Calcium Deposition and Soil Inorganic Carbon Stocks
Authors: Goddard Megan A. , Mikhailova Elena A. , Post Christopher J. , Schlautman Mark A. , Galbraith John M.
Published: April 2009

Organic and inorganic soil C pools are major components of the global C budget, yet they are still poorly estimated and understood. This study ranked atmospheric wet Ca2+ deposition from 1994 to 2003 within the continental United States by soil order using spatial analysis of Ca2+ wet deposition data and a state soil geographic database. The total average annual atmospheric wet deposition (AAAWD) of Ca2+ within the continental United States was 8.6 × 108 kg, which would be equivalent to the theoretical formation of 2.6 × 108 kg C as soil inorganic C (SIC), barring losses from erosion and deep leaching. The soil orders receiving the highest area‐normalized total AAAWD of Ca2+ were: (i) Alfisols (172 kg km−2 Ca2+), (ii) Mollisols (170 kg km−2 Ca2+), (iii) Histosols (168 kg km−2 Ca2+), and (iv) Vertisols (157 kg km−2 Ca2+). Barring losses from erosion and leaching, these Ca2+ wet deposition fluxes would equate to the theoretical formation of the following amounts of area‐normalized total C equivalents in the pedon: (i) Alfisols, 52 kg C km−2; (ii) Mollisols, 51 kg C km−2; (iii) Histosols, 50 kg C km−2; and (iv) Vertisols, 47 kg C km−2 The sequestration of SIC has been shown to be important in soil orders of nonarid regions, particularly in Mollisols and Alfisols.
Crop Nitrogen Uptake and Soil Phenols Accumulation under Continuous Rice Cropping in Arkansas
Authors: Olk D.C. , Anders M.M. , Filley T.R. , Isbell C.
Published: April 2009

Soil C stocks in the Grand Prairie region of eastern Arkansas have declined under the prevalent 2‐yr rotation of rice (Orzya sativa L.)–soybean [Glycine max (L.) Merr.]. Continuous rice cropping could promote soil C sequestration, but in previous work continuous rice averaged 19% less grain yield than rice following soybean, apparently due to N deficiency. To further study N cycling, microplots were imbedded during the rice phase of a crop rotation field study in 2002 and 2004. Urea labeled with 15N was applied preflood, when all N fertilizer is conventionally applied. Crop biomass was often smaller with continuous rice than with rice following soybean (sampled both years) and rice following corn (Zea mays L.) (sampled only in 2004), although the difference varied by growth stage. Crop uptake of native 14N, presumably mineralized from soil organic matter, was inhibited with continuous rice in both years. This trend was clearest at harvest (P = 0.02), when continuous rice averaged 40 kg 14N ha−1 less uptake than rice in the two rotations. Fertilizer 15N averaged only 30% of total crop N and its uptake differed among cropping treatments only in 2002. At harvest, soil C with continuous rice cropping was enriched by 42% with syringyl phenols and by 83% with cinnamic phenols compared with the rotations. These enrichments appear unrelated to estimated input rates of lignin‐derived phenols. Results support the hypothesis that continuous rice cropping promotes the binding of soil N by lignin‐derived phenols, thereby inhibiting N mineralization and late‐season crop growth. Similar observations were reported for tropical rice production, suggesting that the responsible soil processes might be common in continuous rice cropping.
Soil Organic Carbon Stocks of Rio Grande do Sul, Brazil
Authors: Tornquist Carlos G. , Giasson Elvio , Mielniczuk Joao , Cerri Carlos Eduardo Pellegrino , Bernoux Martial
Published: April 2009

Robust and accurate regional estimates of C storage in soils are currently an important research topic because of ongoing debate about human‐induced changes in the terrestrial C cycle. Widely available geoprocessing tools were applied to estimate native soil organic C (SOC) stocks of Rio Grande do Sul state in southern Brazil to a depth of 30 cm from previously sampled soil pedons under undisturbed vegetation. The study used a statewide comprehensive soil survey comprising a small‐scale soil map, a climate map, and a soil pedon database. Soil organic C stocks under native vegetation were calculated with two different approaches: the Tier 1 method of the Intergovernmental Panel on Climate Change (IPCC) and a refined method based on actual field measurements derived from soil profile data. Highest SOC stocks occurred in Neossolos Quartzarênico hidromórfico (Aquents), Organossolos Tiomórficos (Hemists), Latossolos Brunos (Udox), and Vertissolos Ebânicos (Uderts) soil classes. Before human use of soils, most C was stored in the Latossolos Vermelhos (Udox) and Neossolos Regolíticos (Orthents), which occupy a large area of Rio Grande do Sul. Generally, IPCC default reference SOC stocks compared well with SOC stocks calculated from soil pedons. The total SOC stock of Rio Grande do Sul was estimated at 1510.3 Tg C (5.8 kg C m−2) by the IPPC method and 1597.5 ± 363.9 Tg C (7.4 ± 1.9 kg C m−2) calculated from soil pedons. The SOC digital map and SOC database developed in this study provide crucial background information for state‐level contemporary assessment of C stocks and soil C sequestration programs and initiatives.
Spiking Improved Solution Phosphorus‐31 Nuclear Magnetic Resonance Identification of Soil Phosphorus Compounds
Authors: Doolette A.L. , Smernik R.J. , Dougherty W.J.
Published: April 2009

Chemical characterization of soil organic P using31P nuclear magnetic resonance (NMR) spectroscopy relies on the correct assignment of resonances. We examined eight Australian soils and identified the main orthophosphate monoester peaks by spiking model organic P compounds (α‐ and β‐glycerophosphate, ethanolamine phosphate, phytate, scyllo‐inositol hexakisphosphate, and choline phosphate) into NaOH–ethylenediaminetetraacetic acid (EDTA) soil extracts. For five of the soils, the strongest monoester resonances were identified as being due to phytate, while for the other three soils, the strongest resonances were identified as being due to α‐ and β‐glycerophosphate. Importantly, the appearance of spectra dominated by phytate and those dominated by glycerophosphate were deceptively similar because the separation between the two strongest phytate resonances was very similar to the separation between the α‐ and β‐glycerophosphate resonances. We believe this may have resulted in the misidentification of these species in some previous studies. Identification of these species is hindered by the sensitivity of their chemical shifts to pH and electrolyte concentration. Our spiking methodology, in which we add only enough of the compound to approximately double the native concentration, overcomes this problem. We also investigated the alkaline hydrolysis of phospholipids as a likely source of α‐ and β‐glycerophosphate. We found that the rate of phospholipid hydrolysis was dependant on NaOH concentration and that the presence of glycerophosphate resonances in soil extracts probably results from the extraction and redissolution procedures rather than the presence of native glycerophosphate in the soils. We also identified an intermediate diester product that may have previously been misidentified as the phospholipid itself.
Complex Permittivity Model for Time Domain Reflectometry Soil Water Content Sensing: II. Calibration
Authors: Schwartz R.C. , Evett S.R. , Bell J.M.
Published: April 2009

Despite numerous applications of time domain reflectometry (TDR), serious difficulties in estimating accurate soil water contents under field conditions remain, especially in fine‐textured soils. A complex dielectric mixing model was calibrated for fine‐textured soils (24–45% clay) and its accuracy was evaluated and compared with empirical calibrations. The Ap and Bt horizons of two soils were packed into columns and adjusted to volumetric water contents (θ) ranging from air dry to near saturation. Travel time and bulk electrical conductivity (σ0) were measured using TDR at temperatures (T) of 8, 22, and 40°C and using three coaxial cables to obtain a range of input spectrum bandwidths (ωS). Apparent permittivities (Ka) were predicted using the complex permittivity model with measured θ, T, σ0, ωS, and soil bulk density, and fitted to measured Ka by optimizing specific surface area (As), the power‐law exponent (a), and an empirical polarization loss factor. Measured Ka was best approximated using the power‐law dielectric mixing model with a semiempirical effective frequency estimate and a = 0.68. Predicted As increased with increasing clay content, cation exchange capacity, and measured specific surface areas. The two‐parameter power‐law calibration removed temperature bias in θ estimates and reduced the RMSE in θ estimates by an average of 0.006 m3 m−3 compared with an empirical calibration. Empirical models predicted field θ with oscillations of up to 0.022 m3 m−3 in phase with soil temperatures resulting from permittivity temperature dependencies. In contrast, the calibrated dielectric mixing model removed or dampened in‐phase θ fluctuations to <0.004 m3 m−3, which permitted the detection of more subtle changes (<0.02 m3 m−3) in θ.
Fertilizer and Residue Quality Effects on Organic Matter Stabilization in Soil Aggregates
Authors: Fonte Steven J. , Yeboah Edward , Ofori Patrick , Quansah Gabriel W. , Vanlauwe Bernard , Six Johan
Published: April 2009

This study examined the influence of organic residue quality and N fertilizer on aggregate‐associated soil organic matter (SOM) in maize (Zea mays L.) cropping systems of southern Ghana. Six residue treatments of differing quality [Crotalaria juncea L., Leucaena leucocephala (Lam.) de Wit, maize stover, sawdust, cattle manure, and a control with no residues added] were applied at 4 Mg C ha−1 yr−1 both with and without fertilizer N additions (120 kg N ha−1 season−1). Soils (0–15 cm) were sampled 3 yr after study implementation and wet sieved into four aggregate size classes (8000–2000, 2000–250, 250–53, and <53 μm). Small macroaggregates (2000–250 μm) were further separated into coarse particulate organic matter (>250 μm), microaggregates within macroaggregates (53–250 μm), and macroaggregate‐occluded silt and clay (<53 μm). Nitrogen fertilizer additions reduced aggregate stability, as was evident from a 40% increase in the weight of the silt and clay fraction (P = 0.014) as well as a decrease in microaggregates across all residue types (P = 0.019). Fertilizer similarly affected C and N storage within these aggregate fractions, while the effects of residue quality were largely insignificant. Our results suggest that fertilizer effects on soil aggregation may have important implications for long‐term SOM dynamics.
Spatial and Temporal Distributions in Sandy Soils with Seepage Irrigation: I. Ammonium and Nitrate
Authors: Sato Shinjiro , Morgan Kelly T. , Ozores-Hampton Monica , Simonne Eric H.
Published: April 2009

Tomato (Lycopersicon esculentum Mill.) in southwest Florida is typically grown on fumigated, raised beds with polyethylene mulch under seepage irrigation. An average grower's N rate currently exceeds the University of Florida's Institute of Food and Agricultural Sciences (UF‐IFAS) recommendation (224 kg N ha−1 maximum). Excess nutrients are subject to runoff and leaching, which raises environmental concerns in Florida watersheds. A field study was conducted to elucidate N spatial distribution in tomato beds during the 2006 spring and winter growing seasons with 224 and 358 kg N ha−1 rates. Ammonium N was highest for both seasons during 0 to 1 wk after planting (WAP) at the 0‐ to 10‐cm depth in the fertilizer band, but rarely moved vertically. Lateral movement of NH4+–N was observed through 7 WAP, however, probably due to diffusion. Nitrate N at 0 to 10 cm in the band peaked during 3 to 4 WAP, indicating about 3 wk of nitrification in the spring; however, this process was shortened to 1 to 2 wk in the winter, probably due to greater bacterial activity with warmer temperatures in the beginning of the winter than the spring (average 8°C in the first 3 wk). Both lateral and vertical movements of NO3−–N were observed in the spring, even at the 20‐ to 30‐cm depth. A rise and subsequent fall of the water table level during 5 to 8 WAP particularly enhanced NO3−–N downward movement, which was attributed to greater diffusivity of NO3−–N than NH4+–N. Minimizing water table fluctuations and applying a reduced N rate are critical to reduce NO3−–N leaching loss.
Controversies in the Definition of “Iso” Soil Temperature Regimes
Authors: Tejedor M. , Jiménez C. , Rodríguez M. , Neris J.
Published: April 2009

The term iso in soil temperature regimes has been used in Soil Taxonomy to distinguish between tropical and temperate zones. It defines regimes with temperature differences of less than 6°C between summer (June, July, and August) and winter (December, January, and February). In the northern hemisphere, however, these months are not necessarily the warmest and coldest months. The island of Tenerife, which lies between 28 and 29° N near the Tropic of Cancer, is a transition point between the temperate and tropical regions. The trade winds, affecting mainly the northern side of the island, are the main reason for the presence of a tropical zone featuring iso, isomesic, and isothermic temperature regimes. In this zone, the warmest and coldest months are displaced by 2 to 3 mo compared with the months indicated in Soil Taxonomy. We examined the characteristics of “iso” regimes and a number of other possible methods for determining isotivity: the warmest and coldest months, astronomical summer and winter, and the equinoxes. We concluded that the soil temperature regime of the zone most influenced by the trade winds—a zone with rainforest vegetation and where tropical characteristics are most in evidence—would not lose its “iso” character under any of the methods. We suggest using the warmest and coldest months instead of summer and winter for the purposes of defining “iso” status. To facilitate estimations, we also suggest that the temperature of the equinox days be used. Changing the limit from 6 to 5°C would not affect the tropical soils of the island of Tenerife.
Soil Organic Carbon and Carbon Dioxide Emission from an Organically Amended Hawaiian Tropical Soil
Authors: Abbas Farhat , Fares Ali
Published: April 2009

Application of organic manure (OM) to arable lands improves soil tilth. The objectives of this study were to: (i) simulate the effect of OM application rates (0, 168, 336, and 672 kg total N ha−1) and types (chicken [Gallus domesticus] and dairy manures) on soil organic C (SOC) and CO2 emissions from a Hawaiian highly weathered tropical soil; and (ii) correlate SOC, CO2 emissions, and two major soil properties: bulk density (ρb) and saturated hydraulic conductivity (Ksat). Measurements of SOC and ρb were conducted on samples collected from the top 10 cm of soil tilled before and after manure application, cultivated with sweet corn (‘Super Sweet 10,’ Zea mays L. ssp. mays), and drip irrigated for two consecutive growing seasons. The Ksat values were calculated from infiltration data measured with a tension infiltrometer. The Rothamsted C turnover model was used to simulate SOC and CO2 emissions. The simulated and measured SOC agreed reasonably during model calibration (r2 = 0.93) and validation (r2 = 0.90). Results revealed that SOC, CO2 emissions, and Ksat increased while ρb decreased with increasing OM rates. There was no significant effect of OM type. There was a highly significant (P < 0.01) correlation between the measured and simulated SOC and between the measured SOC and the simulated CO2 emissions. The Ksat values significantly correlated (P < 0.05) with the measured and simulated SOC and the simulated CO2 emissions. A significant inverse relationship between ρb and Ksat was observed. We concluded that, in addition to improving soil aggregation, decreasing ρb, and increasing Ksat, OM application to this tropical soil increases SOC pools that contribute to atmospheric CO2 following tillage and other agricultural practices.
Cation Exchange Selectivity Coefficient Values on Smectite and Mixed‐Layer Illite/Smectite Minerals
Authors: Tournassat Christophe , Gailhanou Hélène , Crouzet Catherine , Braibant Gilles , Gautier Anne , Gaucher Eric C.
Published: April 2009

Sodium‐K, Na‐Ca, Na‐Mg, and Na‐Sr exchange isotherms were performed at a total Cl concentration of about 0.005 mol L−1 on the fine fraction (<2 μm) of MX80 montmorillonite, mixed‐layer illite smectite minerals (IS), and clayey stones from European underground research laboratories. The derived selectivity coefficients for Na‐K, Na‐Ca, Na‐Mg, and Na‐Sr were found to vary very significantly as a function of the exchanger composition. A model was built to reproduce the data, taking into account the change of selectivity coefficient as a function of the exchanger composition of smectite. Model parameters were fitted using data from the present study and data from the literature obtained on smectite minerals. The addition of parameters for cation–anion pairs was found to improve the fitting results. The model was then successfully tested to reproduce published cation‐exchange features on natural clayey materials and soils suspended in fresh or saline water. Finally, it is shown that the simple combination of this smectite exchange model with a previously published illite exchange model is quite successful although perfectible in reproducing exchange data on IS.
Effects of L-carnitine and iron diet supplementations on growth performance, carcass characteristics and blood metabolites in fattening pigs
Authors: PIETRUSZKA A. , JACYNO E. , KOLODZIEJ A.
Published: April 2009

The aim of this study was to evaluate the effect of dietary L-carnitine supplementation either with or without extra Fe supplementation from Fe-amino acid (Fe-AA) complex on body weight gain, feed conversion, carcass characteristics and blood metabolite concentrations in fattening pigs. The study was carried out with 75 fatteners (30.100 kg body weight), divided into three groups, of 25 pigs each. The control group was given a basal diet that contained 85 mg/kg of Fe from premix. A L-carnitine group was given a basal diet supplemented with 100 mg/kg of L-carnitine, and a L-carnitine+Fe group was given a basal diet supplemented with 100 mg/kg of L-carnitine and 60 mg/kg of Fe from a Fe-AA complex. The supplement of L-carnitine to the diets did not have any effects on the growth performance and carcass traits. The L-carnitine supplement decreased the concentration of triglycerides (p.0.05), cholesterol (p .0.05) and low-density lipoproteins (p .0.01) in the blood serum of pigs, while it increased (p.0.01) the concentration of high-density lipoproteins. The combination of L-carnitine+Fe increased the growth performance of growing pigs (p .0.05) and the lean percentage and fatless ham weight in carcass and also increased (p .0.05) the Fe content in the blood serum and the longissimus dorsi muscle of pigs. The results suggest the more effective outcomes can be reached when L-carnitine+Fe rather than only L-carnitine is used in diets.;
Third sector organizations in rural development: a transaction cost perspective
Authors: VALENTINOV V.
Published: April 2009

In many parts of the world, rural development is supported by third sector organizations, such as nongovernmental organizations, farmer associations, and cooperatives. This essay develops a transaction cost explanation of these organizations role in rural areas. Since the traditional transaction cost theory is concerned with the choice of governance mechanisms within the for-profit sector, this essay adopts an alternative conceptualization of the notion of transaction cost by building on the theory of the division of labor. This theory regards transaction cost as a constraint on the division of labor causing the replacement of exchange with self-sufficiency. The proposed transaction cost explanation of rural third sector organizations consists of two arguments: 1) third sector organizations embody partial reliance on self-sufficiency; and 2) rural areas exhibit rurality-specific transaction cost acting as a constraint on the division of labor and thus creating a niche for third sector organizations. The essay concludes with suggesting a research program on developing an economic theory of the rural third sector.;
Metal concentrations in oats (Avena sativa L.) grown on acid sulphate soils
Authors: FÄLTMARSCH R. , ÖSTERHOLM P. , GREGER M.
Published: April 2009

The aim of the study was to investigate the impact of soil chemistry on the concentrations of Co, Ni, Zn, Mn, Cu and Fe in oats (Avena sativa L. cv. Fiia) grown on Finnish acid sulphate (AS) soils with varying geochemical characteristics. Twenty two soil profiles, which were sampled to a depth of 1 m (five 20 cm section splits), and 26 composite oat grain samples were collected on a total of five fields. The concentrations of Co, Ni, Zn and Mn in the grains were correlated with the NH4Ac-EDTA-extractable concentrations in the soils. However, as these four chalcophilic metals are in general easily lost to drains and not retained as a large pool in the soil in easily-extractable form, also the concentrations in the oats were not in general elevated as compared with average values on other soils. On one of the fields, however, the Co and Ni concentrations in the soil, and thus also in the oats, were clearly elevated. Copper and Fe displayed no correlation between the soil and oat concentrations, indicating that the plant-uptake mechanisms are much more important than variations in geochemistry. It was suggested that the NH4Ac-EDTA solution was not efficient in extracting Fe and Cu, which shows that these metals are bound in relatively immobile oxyhydroxides.;
Real-Time Research: An Experiment in the Design of Scholarship
Authors: Zimmerman Eric , Squire Kurt , Steinkuehler Constance , Dikkers Seann
Published: April 2009

This article reports on an unconventional collaborative event called Real-Time Research, a project that brought 25 participants together from radically divergent fields for a playful and somewhat improvisational investigation of what it means to do games and learning research. Real-Time Research took the form of a two-part workshop session at the ‘Games, Learning & Society’ (GLS) conference during the summer of 2008, in which attendees collaboratively designed and then conducted five research experiments that took place over the course of the two-day conference. The article reports on the results of those studies and the processes that generated them.
Conceptualizing Identity in Youth Media Arts Organizations: A Comparative Case Study
Authors: Halverson Erica Rosenfeld , Lowenhaupt Rebecca , Gibbons Damiana , Bass Michelle
Published: April 2009

In this article the authors explore the relationship between concepts of identity and the purpose, process, and products of youth media arts organizations. Since the explicit mission of these organizations is to work with adolescents to explore and represent identities, the authors develop our understanding of how organizations conceptualize identity development and how these concepts shape the digital film-making process and products. In a comparative case study of In Progress (St Paul, Minnesota) and Reel Works Teen Filmmaking (New York City), organizational leaders were interviewed, and a semiotic analysis conducted of the organizations' websites and other public, printed materials. The authors analyzed the films as products of these organizations' production processes to understand how these organizations define identity and what these definitions mean for how they do their work with youth. They found two distinct conceptualizations of identity: identity as community building, and identity as individualization. Unpacking these different conceptions helps us to understand how youth media arts organizations shape the identity development process and what is made possible for participating youth. This work can also lead us to more sophisticated models of adolescent identity development, particularly for non-mainstream communities who have often been saddled with dominant cultural models that do not quite fit.
‘Get Some Secured Credit Cards Homey’: Hip Hop Discourse, Financial Literacy and the Design of Digital Media Learning Environments
Authors: Devane Ben
Published: April 2009

In the midst of the worst economic crisis since the Great Depression, there exists a deficit of compelling financial education curricula in urban schools that serve financially vulnerable working-class students. Part of a design-based research investigation aimed at creating culturally-relevant financial literacy learning environments, this study is a Discourse analysis of a discussion of personal finance on a web-based fan forum dedicated to hip hop music and culture. In this analysis the author claims that the discourse strategies and participant roles present in this discussion are an example of the organic production of what has been called a borderlands Discourse that bridges school-based knowledge of financial literacy with the youth culture of hip hop. The analysis presented here highlights the complex and overlapping ways that discursive hybridity in both representational practices and textual performances of identity figure importantly in the financial literacy practices of community participants. The author further contends that the understandings that emerge from this analysis can help design researchers attempt to ‘engineer’ the values, identities and modes of interaction of hip hop discourse communities into academically-oriented learning environments.
The Simulation Cycle: Combining Games, Simulations, Engineering and Science Using StarLogo TNG
Authors: Klopfer Eric , Scheintaub Hal , Huang Wendy , Wendel Daniel , Roque Ricarose
Published: April 2009

StarLogo The Next Generation ( TNG) enables secondary school students and teachers to model decentralized systems through agent-based programming. TNG's inclusion of a three-dimensional graphical environment provides the capacity to create games and simulation models with a first-person perspective. The authors theorize that student learning of complex systems and simulations can be motivated and improved by transforming simulation models of complex systems phenomena (specifically this study examines systems including epidemics and Newtonian motion) into games. Through this transformation students interact with the model in new ways and increase their learning of both specific content knowledge and general processes such as inquiry, problem solving and creative thinking. During this study several methods for connecting the simulations to game dynamics were tried, ranging from student-created games, to altering existing games, to students playing premade games. This article presents the results of research data from two years of curriculum development and piloting in northern Massachusetts science classrooms to demonstrate the successes and challenges of integrating simulations and games. This article also explores the results of these interventions in terms of ease of implementation, student motivation and student learning.
Remembering Math: The Design of Digital Learning Objects to Spark Professional Learning
Authors: Halverson Richard , Wolfenstein Moses , Williams Caroline C. , Rockman Charles
Published: April 2009

This article describes how the design of digital learning objects can spark professional learning. The challenge was to build learning objects that would help experienced special education teachers, who had been teaching in math classes, to demonstrate their proficiency in middle and secondary school mathematics on the PRAXIS examination. While the learning sciences have focused on questions of learning new knowledge, the context of how adults recover information they had once studied has received less theoretical attention. The authors' thesis is that a central aspect for helping students to remember content they once learned is to uncover areas of ‘conceptual breakdown’ in ordinary math problems. Their theory is that the phenomenon of conceptual breakdown is different for remembering knowledge than for learning new knowledge. Remembering math involves reassembling misplaced, broken or fragmented conceptual knowledge once learned in school. The design of learning objects allows us to determine which aspects of PRAXIS-type questions highlight conceptual breakdown, and leads us to build learning objects that would help learners reassemble prior concepts to improve capacity to solve similar problems. This article reports on a design-based research investigation to build, implement and assess a series of math learning objects for adult learners. Twelve web-based learning objects were built over the course of 2 years, and tested with 59 adult learners. The authors discuss how the collaborative design process was structured to elicit the breakdown points present in typical math problems; describe an assessment process that produced pre- and post-learning results; and comment on how the design process illustrated their theory of adult math learning recovery and on the prospects for designing learning objects for adult learners.