468 research outputs found
Changes in phosphorus status of 'Cripps' Pink' apple trees after application of mulches
The effect of four different mulches on fruit quality was quantified, either
directly via mineral nutrient contributions or indirectly, by increasing nutrient uptake
efficiency in the soil. We hypothesised that fruit nutrient levels would increase more
when an organic mulch, containing nutrients, was applied to the soil, with smaller/no
increases when an inorganic mulch was applied to the tree row.
In this paper, we concentrate on changes in fruit phosphorus (P) concentrations
after application of five treatments: a clean cultivated control, an inorganic woven
geotextile fabric, and organic mulches â compost, wood chips and a vermi-castings/
wood chips combination. The trial was conducted on a commercial farm, Lourensford
Estate, South Africa, from October 2008 to April 2012 â on an adjacent light, sandy and
heavier, sandy-silt soil.
Mineral nutrient analyses of the soil, leaves, mulches and fruit were performed.
Yield and fruit size were determined. Soil temperatures and soil water status were
recorded hourly during the last two seasons. P concentrations did increase chronologically
from the soil, then into leaves and then into the fruit after application of
mulches that provided additional P to the soil. Sporadic increases in both leaves and
fruit occurred, but could not always be related to treatment effects. The significant
consistent increase of P levels of the vermi-castings treatment in the heavy soil is likely
to be a combination of reduced irrigation volumes, as well as a treatment effect.
All mulches resulted in the well-established buffering of soil temperatures, soil water content and percentage soil carbon. Based on results from this study, it is not
feasible to apply mulches for the sole purpose to increase P levels in the soil, leaves or
fruit of established trees â although increases were noticed from time to time. In
addition to water and temperature modifying effects of mulches that would differ
between soil textures and depend on the mulch source, increases in P concentrations
may result. As yield efficiency is still the primary factor determining income per hectare
for the producer, the decrease in yield that resulted from mulching under these
conditions, will still outweigh any positive contributions of mulches. It is therefore of
utmost importance to first adjust irrigation volumes to a mulch treatment before the
advantageous properties of mulching will be of value.Stellenbosch University and
HortgroScience.http://www.actahort.orgam201
Impact of asymptomatic plasmodium falciparum infection on the risk of subsequent matic malaria in a longitudinal cohort in Kenya
Background: Asymptomatic Plasmodium falciparum infections are common in sub-Saharan Africa, but their effect on subsequent symptomaticity is incompletely understood. Methods: In a 29-month cohort of 268 people in Western Kenya, we investigated the association between asymptomatic P. falciparum and subsequent symptomatic malaria with frailty Cox models. Results: Compared to being uninfected, asymptomatic infections were associated with an increased 1-month likelihood of symptomatic malaria [adjusted Hazard Ratio (aHR):2.61, 95%CI:2.05â3.33], and this association was modified by sex, with females [aHR:3.71, 95%CI:2.62â5.24] at higher risk for symptomaticity than males [aHR:1.76, 95%CI:1.24â2.50]. This increased symptomatic malaria risk was observed for asymptomatic infections of all densities and in people of all ages. Long-term risk was attenuated but still present in children under 5 [29-month aHR:1.38, 95%CI:1.05â1.81]. Conclusions: In this high-transmission setting, asymptomatic P. falciparum can be quickly followed by symptoms and may be targeted to reduce the incidence of symptomatic illness
The role of analytical chemistry in exposure science: Focus on the aquatic environment
Exposure science, in its broadest sense, studies the interactions between stressors (chemical, biological, and physical agents) and receptors (e.g. humans and other living organisms, and non-living items like buildings), together with the associated pathways and processes potentially leading to negative effects on human health and the environment. The aquatic environment may contain thousands of compounds, many of them still unknown, that can pose a risk to ecosystems and human health. Due to the unquestionable importance of the aquatic environment, one of the main challenges in the field of exposure science is the comprehensive characterization and evaluation of complex environmental mixtures beyond the classical/priority contaminants to new emerging contaminants.
The role of advanced analytical chemistry to identify and quantify potential chemical risks, that might cause adverse effects to the aquatic environment, is essential. In this paper, we present the strategies and tools that analytical chemistry has nowadays, focused on chromatography hyphenated to (high-resolution) mass spectrometry because of its relevance in this field. Key issues, such as the application of effect direct analysis to reduce the complexity of the sample, the investigation of the huge number of transformation/degradation products that may be present in the aquatic environment, the analysis of urban wastewater as a source of valuable information on our lifestyle and substances we consumed and/or are exposed to, or the monitoring of drinking water, are discussed in this article. The trends and perspectives for the next few years are also highlighted, when it is expected that new developments and tools will allow a better knowledge of chemical composition in the aquatic environment. This will help regulatory authorities to protect water bodies and to advance towards improved regulations that enable practical and efficient abatements for environmental and public health protection
Optimising the use of bio-loggers for movement ecology research
1.The paradigmâchanging opportunities of bioâlogging sensors for ecological research, especially movement ecology, are vast, but the crucial questions of how best to match the most appropriate sensors and sensor combinations to specific biological questions, and how to analyse complex bioâlogging data, are mostly ignored.
2.Here, we fill this gap by reviewing how to optimise the use of bioâlogging techniques to answer questions in movement ecology and synthesise this into an Integrated Bioâlogging Framework (IBF).
3.We highlight that multiâsensor approaches are a new frontier in bioâlogging, whilst identifying current limitations and avenues for future development in sensor technology.
4.We focus on the importance of efficient data exploration, and more advanced multiâdimensional visualisation methods, combined with appropriate archiving and sharing approaches, to tackle the big data issues presented by bioâlogging. We also discuss the challenges and opportunities in matching the peculiarities of specific sensor data to the statistical models used, highlighting at the same time the large advances which will be required in the latter to properly analyse bioâlogging data.
5.Taking advantage of the bioâlogging revolution will require a large improvement in the theoretical and mathematical foundations of movement ecology, to include the rich set of highâfrequency multivariate data, which greatly expand the fundamentally limited and coarse data that could be collected using locationâonly technology such as GPS. Equally important will be the establishment of multiâdisciplinary collaborations to catalyse the opportunities offered by current and future bioâlogging technology. If this is achieved, clear potential exists for developing a vastly improved mechanistic understanding of animal movements and their roles in ecological processes, and for building realistic predictive models
Tidal Evolution of Close Binary Asteroid Systems
We provide a generalized discussion of tidal evolution to arbitrary order in
the expansion of the gravitational potential between two spherical bodies of
any mass ratio. To accurately reproduce the tidal evolution of a system at
separations less than five times the radius of the larger primary component,
the tidal potential due to the presence of a smaller secondary component is
expanded in terms of Legendre polynomials to arbitrary order rather than
truncated at leading order as is typically done in studies of well-separated
system like the Earth and Moon. The equations of tidal evolution including
tidal torques, the changes in spin rates of the components, and the change in
semimajor axis (orbital separation) are then derived for binary asteroid
systems with circular and equatorial mutual orbits. Accounting for higher-order
terms in the tidal potential serves to speed up the tidal evolution of the
system leading to underestimates in the time rates of change of the spin rates,
semimajor axis, and mean motion in the mutual orbit if such corrections are
ignored. Special attention is given to the effect of close orbits on the
calculation of material properties of the components, in terms of the rigidity
and tidal dissipation function, based on the tidal evolution of the system. It
is found that accurate determinations of the physical parameters of the system,
e.g., densities, sizes, and current separation, are typically more important
than accounting for higher-order terms in the potential when calculating
material properties. In the scope of the long-term tidal evolution of the
semimajor axis and the component spin rates, correcting for close orbits is a
small effect, but for an instantaneous rate of change in spin rate, semimajor
axis, or mean motion, the close-orbit correction can be on the order of tens of
percent.Comment: 40 pages, 2 tables, 8 figure
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