SEASONAL NITROGEN BUDGETS OF MATURE CITRUS TREES ON A SANDY ENTISOL     

Kelly Morgan  Johan Scholberg  Thomas Obreza  Thomas Wheaton 《Journal of plant nutrition》2013,36(13):2009-2023

Approximately 30% of Florida citrus is grown on well-drained Entisols with low nutrient-holding capacity, which are prone to high nitrogen (N) leaching losses. However, increasing application frequency of N-fertilizer via multiple fertigations does not increase crop yield, whereas in agronomic crops, such an approach typically enhances N uptake efficiency. We assessed seasonal tree N tissue concentration dynamics as affected by N rate for mature fourteen-year-old ‘Hamlin’ orange (Citrus sinensis L. Osbeck) trees on either Carrizo citrange (C. sinsensis L. Osbeck X Poncirus trifoliata L. Raf.) or Swingle citrumelo (C. paradisi Macf. X P. trifoliata L. Raf.) rootstocks. Nitrogen was applied as ammonium nitrate in six split fertigation applications with N target values of 179 and 269 kg ha^?1yr^?1. Leaf, twig, and branch bark tissue N concentrations decreased through the spring to minima in May and June. This time period corresponds to a period of high N demand associated with both vegetative and reproductive growth. Tissue N concentrations increased from late spring minimums to fall and winter maximum concentrations. Reduction in branch bark and wood tissue N concentrations may have been due to a redistribution of N to leaf, twig, and fruit tissues in response to low N supply. The majority of the spring N should be supplied prior to May.  相似文献   

Employee Perception of a Mandated Helmet Policy at Vail Resorts     

Christopher B. Davis  Mark R. Brownson  Brent J. Levy  Morgan A. Valley  Bruce Evans  Steven R. Lowenstein 《The Forestry Chronicle》2013,24(4):402-406

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Prevalence and significant geospatial clusters of bovine tuberculosis infection at livestock–wildlife interface ecosystem in Eastern Tanzania     

Richard Simon Mwakapuja  Zachariah Ephraim Makondo  Joseph Malakalinga  Ward Bryssinckx  Robinson Hammerthon Mdegela  Irmgard Moser  Rudovick Reuben Kazwala  Manfred Tanner 《Tropical animal health and production》2013,45(5):1223-1230

Bovine tuberculosis (BTB) is an important neglected zoonosis that affects livestock, wildlife and human. A study to determine prevalence and geospatial clusters for BTB was conducted from June 2010 to March 2012 at livestock–wildlife interface areas (LWIA). A total of 1,288 cattle located in vicinity of Mikumi-Selous ecosystem Tanzania were tested. Single Intradermal Comparative Tuberculin Test and spatial scan statistic analysis were applied to establish the status of the disease and identify significant spatial BTB clusters. Overall individual prevalence was 3.7 % (n?=?1,288) (95 % CI?=?2.8–4.9) and 7.8 % (95 % CI?=?6.4–9.4) with cut-off of >4 and >2 mm, respectively. Villages with at least one reactor were 55.8 % (n?=?43). Reactivity was significantly higher in Mvomero and Kilosa districts compared with Kilombero and Ulanga districts (χ ²?=?15.9; P?<?0.001). Significant spatial BTB clusters were revealed at 11 villages. BTB clustering was significant in Kilosa and Mvomero districts compared with Kilombero and Ulanga districts. There was overlap and aggregation of BTB clusters covering south and south-east of Kilosa district bordering Mikumi National Park (MNP) and Mvomero. Generally, clustering occurred around major rivers. The current study provides useful information on the dynamics and epidemiological status of BTB around the wildlife–livestock–human interface, it reveals that the wildlife are at risk of BTB from infected livestock. The study revealed hotspots for BTB that can be applied to guide implementation of participatory intervention at LWIA and control strategies in marginalised pastoralist communities. This study calls for similar studies in other Tanzania’s LWIA for efficient intervention of BTB countrywide.  相似文献   

Predicting cumulative risk of bovine respiratory disease complex (BRDC) using feedlot arrival data and daily morbidity and mortality counts     

Abram H. Babcock  Brad J. White  David G. Renter  Suzanne R. Dubnicka  H. Morgan Scott 《Canadian journal of veterinary research》2013,77(1):33-44

Although bovine respiratory disease complex (BRDC) is common in post-weaning cattle, BRDC prediction models are seldom analyzed. The objectives of this study were to assess the ability to predict cumulative cohort-level BRDC morbidity using on-arrival risk factors and to evaluate whether or not adding BRDC risk classification and daily BRDC morbidity and mortality data to the models enhanced their predictive ability. Retrospective cohort-level and individual animal health data were used to create mixed negative binomial regression (MNBR) models for predicting cumulative risk of BRDC morbidity. Logistic regression models were used to illustrate that the percentage of correctly (within |5%| of actual) classified cohorts increased across days, but the effect of day was modified by arrival weight, arrival month, and feedlot. Cattle arriving in April had the highest (77%) number of lots correctly classified at arrival and cattle arriving in December had the lowest (28%). Classification accuracy at arrival varied according to initial weight, ranging from 17% (< 182 kg) to 91% (> 409 kg). Predictive accuracy of the models improved from 64% at arrival to 74% at 8 days on feed (DOF) when risk code was known compared to 56% accuracy at arrival and 69% at 8 DOF when risk classification was not known. The results of this study demonstrate how the predictive ability of models can be improved by utilizing more refined data on the prior history of cohorts, thus making these models more useful to operators of commercial feedlots.  相似文献   

Climate Change and North American Rangelands: Trends,Projections, and Implications     

H. Wayne Polley  David D. Briske  Jack A. Morgan  Klaus Wolter  Derek W. Bailey  Joel R. Brown 《Strength and Conditioning Journal》2013,66(5):493-511

The amplified “greenhouse effect” associated with increasing concentrations of greenhouse gases has increased atmospheric temperature by 1°C since industrialization (around 1750), and it is anticipated to cause an additional 2°C increase by mid-century. Increased biospheric warming is also projected to modify the amount and distribution of annual precipitation and increase the occurrence of both drought and heat waves. The ecological consequences of climate change will vary substantially among ecoregions because of regional differences in antecedent environmental conditions; the rate and magnitude of change in the primary climate change drivers, including elevated carbon dioxide (CO₂), warming and precipitation modification; and nonadditive effects among climate drivers. Elevated atmospheric CO₂ will directly stimulate plant growth and reduce negative effects of drying in a warmer climate by increasing plant water use efficiency; however, the CO₂ effect is mediated by environmental conditions, especially soil water availability. Warming and drying are anticipated to reduce soil water availability, net primary productivity, and other ecosystem processes in the southern Great Plains, the Southwest, and northern Mexico, but warmer and generally wetter conditions will likely enhance these processes in the northern Plains and southern Canada. The Northwest will warm considerably, but annual precipitation is projected to change little despite a large decrease in summer precipitation. Reduced winter snowpack and earlier snowmelt will affect hydrology and riparian systems in the Northwest. Specific consequences of climate change will be numerous and varied and include modifications to forage quantity and quality and livestock production systems, soil C content, fire regimes, livestock metabolism, and plant community composition and species distributions, including range contraction and expansion of invasive species. Recent trends and model projections indicate continued directional change and increasing variability in climate that will substantially affect the provision of ecosystem services on North American rangelands.  相似文献   

A standardized behavior test for potential guide dog puppies: Methods and association with subsequent success in guide dog training     

Lucy Asher  Simon Blythe  Rena Roberts  Lisa Toothill  Peter J. Craigon  Katy M. Evans  Martin J. Green  Gary C.W. England 《Journal of Veterinary Behavior: Clinical Applications and Research》2013,8(6):431-438

An early understanding of behavioral suitability for guiding work in domestic dogs (Canis familiaris) would be useful for organizations which train dogs as mobility aids, such as the Guide Dogs for the Blind Association. We explored the potential for a standardized test of behavior in young dogs to reflect subsequent success in guide dog training. Five hundred eighty-seven potential guide dogs were exposed to a series of eight stimuli at 6-8 weeks of age. The responses of dogs were scored on a 7-point scale according to either responsiveness to human assessor or to environmental stimuli, on stimuli comprising following when called; retrieve; gentle restraint; noise; stroking; a moving toy squirrel; encouragement to go through a tunnel; and encouragement to go over a ramp. Five of these stimuli showed some association with success in guide dog training, and three of these stimuli could be usefully combined in a logistic regression model of success in training. There is potential for this test to be used to predict suitability for guiding work but adjustments to the scoring protocol are recommended.  相似文献   

1-Naphthaleneacetic acid and 6-benzyladenine thinning of a common slender spindle ‘Jonagold’/M.9 apple orchard. I: Dose effects and spray distribution in the crowns     

M. Stopar  G. Leskošek  A. Simončič 《The Journal of Horticultural Science and Biotechnology》2013,88(6):122-126

Summary

To find the most appropriate rates of application of plant growth regulator (PGR) thinning-agents for a common slender spindle apple (Malus × domestica Borkh.) orchard, different volumes of dilute 1-naphthaleneacetic acid (NAA) and 6-benzyladenine (BA) were sprayed ha^?1. Mature ‘Jonagold’/M.9 trees, 3.0 – 3.5 m high and 1.2 – 1.5 m wide, planted in a single row system with 3,030 trees ha^?1, were used. Significant thinning was observed in the case of dilute sprays of NAA at 10 mg l^?1, or BA at 100 mg l^?1, to run-off, using 2,000 l ha^?1 or 1,500 l ha^?1; while 1,000 l ha^?1 did not result in sufficient thinning. Thinning using smaller volumes (250, 500, or 750 l ha^?1) was also significant if the concentration of PGR thinner was proportionally higher (i.e., based on the 1,500 l ha^?1 application rate of more dilute sprays of NAA at 10 mg l^?1 or BA at 100 mg l^?1). Spray distribution measurements in the crowns showed better spray deposits when higher water volumes (i.e., more dilute PGR solutions) were sprayed at all positions (bottom, middle, or top) of the canopy. At 2,000 l ha^?1, 54 – 72% coverage of the leaf area was observed; but, at 250 l ha^?1, coverage was only 10 – 21%. The lower 30% of the canopy was covered poorly when smaller volumes of water (250, 500, or 1,000 l ha^?1) were applied. When 1,500 l ha^?1 was sprayed, good coverage of the lower and upper surfaces of the leaves occurred, and no differences in canopy positions were measured. It was concluded that 1,500 l ha^?1 (i.e., dilute PGR) spraying was the most appropriate volume to use when calculating the dose of NAA or BA to be applied ha^?1 to common (3.0 – 3.5 m-high) mature slender spindle apple orchards on M.9 rootstock. This study was part of the ISAFRUIT Smartfruit Project, aimed at improving existing methods for apple crop regulation with more precise use of PGR thinning agents and with minimum impact on the environment.  相似文献   

Plant architecture, its diversity and manipulation in agronomic conditions, in relation with pest and pathogen attacks     

E. Costes  P. E. Lauri  S. Simon  B. Andrieu 《European journal of plant pathology / European Foundation for Plant Pathology》2013,135(3):455-470

Plant architectural traits have been reported to impact pest and disease, i.e., attackers, incidence on several crops and to potentially provide alternative, although partial, solutions to limit chemical applications. In this paper, we introduce the major concepts of plant architecture analysis that can be used for investigating plant interactions with attacker development. We briefly review how primary growth, branching and reiteration allow the plant to develop its 3D structure which properties may allow it (or not) to escape or survive to attacks. Different scales are considered: (i) the organs, in which nature, shape and position may influence pest and pathogen attack and development; (ii) the individual plant form, especially the spatial distribution of leaves in space which determines the within-plant micro-climate and the shoot distribution, topological connections which influence the within-plant propagation of attackers; and (iii) the plant population, in which density and spatial arrangement affect the micro-climate gradients within the canopy and may lead to different risks of propagation from plant to plant. At the individual scale, we show how growth, branching and flowering traits combine to confer to every plant species an intrinsic architectural model. However, these traits vary quantitatively between genotypes within the species. In addition, we analyze how they can be modulated throughout plant ontogeny and by environmental conditions, here considered lato sensu, i.e. including climatic conditions and manipulations by humans. Examples from different plant species with various architectural types, in particular for wheat and apple, are provided to draw a comprehensive view of possible plant protection strategies which could benefit from plant architectural traits, their genetic variability as well as their plasticity to environmental conditions and agronomic manipulations. Associations between species and/or genotypes having different susceptibility and form could also open new solutions to improve the tolerance to pest and disease at whole population scale.  相似文献   

Community patterns of soil bacteria and nematodes in relation to geographic distance     

Fernando Monroy  Wim H. van der Putten  Etienne Yergeau  Simon R. Mortimer  Henk Duyts  T. Martijn Bezemer 《Soil biology & biochemistry》2012

Ecosystems consist of aboveground and belowground subsystems and the structure of their communities is known to change with distance. However, most of this knowledge originates from visible, aboveground components, whereas relatively little is known about how soil community structure varies with distance and if this variability depends on the group of organisms considered. In the present study, we analyzed 30 grasslands from three neighboring chalk hill ridges in southern UK to determine the effect of geographic distance (1–198 km) on the similarity of bacterial communities and of nematode communities in the soil. We found that for both groups, community similarity decayed with distance and that this spatial pattern was not related to changes either in plant community composition or soil chemistry. Site history may have contributed to the observed pattern in the case of nematodes, since the distance effect depended on the presence of different nematode taxa at one of the hill ridges. On the other hand, site-related differences in bacterial community composition alone could not explain the spatial turnover, suggesting that other factors, such as biotic gradients and local dispersal processes that we did not include in our analysis, may be involved in the observed pattern. We conclude that, independently of the variety of causal factors that may be involved, the decay in similarity with geographic distance is a characteristic feature of both communities of soil bacteria and nematodes.  相似文献   

Exploitation of glucose catabolic gene fusions to investigate in situ expression during Pseudomonas–plant interactions     

Olivia Rice  Simon H. Miller  John P. Morrissey  Fergal O’Gara 《Biology and Fertility of Soils》2012,48(2):235-238

Successful exploitation of bacterial inoculants in agriculture requires that the inoculant can colonize the crop rhizosphere and then express the gene(s) of interest. This study focuses on two glucose-metabolizing genes that are associated with the inorganic phosphate solubilization phenotype of Pseudomonas fluorescens: gcd, which encodes glucose dehydrogenase, and pqqB, which encodes a cofactor required for Gcd activity. Tn5-lux-gene fusions were created to assess the expression of these genes in situ on roots of two maize hybrids, DK315 and PR37Y15. Expression was compared to in vitro levels in the presence of root exudates and different carbon sources. Although root exudates from both varieties triggered similar levels of expression in in vitro cultures, there was a marked difference in situ, where significantly higher expression levels of both genes were observed on DK315 roots. This correlates with a higher level of rhizosphere colonization by the inoculant on this hybrid (over PR37Y15) and illustrates the importance of monitoring both colonization and expression levels in tandem. In addition to demonstrating expression of these important genes in the rhizosphere, this study also illustrates that variation can exist between cultivars or varieties and demonstrates a methodology to monitor the expression of genes of interest in the rhizosphere of the selected crop variety on which the inoculant is to be applied.  相似文献