881 research outputs found
Estimates of Potentially Mineralizable Soil Nitrogen Based on Short-term Incubations
Nitrogen mineralization potentials were determined for a
large number of soils by a method involving determination of
N mineralized after several consecutive incubations at 35C
under optimum soil water conditions. The determination of N
mineralization potential, No, based on the first-order equation,
log (No — Nt) = log No — kt/2.303, is laborious and usually
requires incubation periods of 8 weeks or more. From the
present study, involving soils from major agricultural areas
throughout the United States, it was demonstrated that No
could be estimated reliably from the amounts of N mineralized
during 2-week incubations following preliminary incubations of
1 to 2 weeks. From the above first-order equation, No = Nt /
(1-10–kt/2.303). Hence, for a 2-week incubation (t = 2), No =
9.77Nt (Nt = N mineralized in 2 weeks and k is the rate constant,
weeks-1). Estimates of No from short-term incubations
were similar to those derived after extensive periods of incubation.
Preincubation of soils is required in order to decompose
plant residues and for other possible reasons noted. Estimates
of No from preliminary incubations are meaningless. The implications
of No as a basis for predicting amounts of soil N mineralized
under fluctuating temperature and soil water conditions
are discussed
Residual Nitrate and Mineralizable Soil Nitrogen in Relation to Nitrogen Uptake by Irrigated Sugarbeets
Previously reported studies on N fertilization of sugarbeets
(Beta vulgaris L.) in southern Idaho revealed considerable
variation among sites in amounts of residual
soil NO? and N mineralized during short-term laboratory
incubations. Consequently, the amount of N fertilizer
needed to achieve near-maximum yields of sucrose differed
markedly. The purpose of this study was to determine
the feasibility of estimating amounts of N mineralized
in the root zone during the season, taking into
account site variations in temperature and soil water
regimes. Residual soil NO?--N and mineralizable N to
approximate rooting depth were estimated for 21 field
sites in 1971 and six sites in 1972. The relative contributions
of these two N sources to total N uptake by the
crop, in the absence of applied fertilizer N, were then
assessed. Estimates of N mineralized in the upper 45-
cm soil layer for each successive month, ?N, over a 6-
month period were derived using the expression, ?N/
?t kWN (k = fraction of N mineralized during each
month, ?t, adjusted for average air temperature; and W
the estimated soil water content expressed as a fraction
of the available water storage capacity). Resulting
estimates of the fraction of potentially mineralizable N
converted to (NO?- + NH?+)-N between 1 April and
30 September ranged from 0.15 to 0.22 (mean ± S.D. =
0.18 ± 0.02) in 1971 and 1972. On the average, mature
sugarbeets recovered about 73% of the estimated N mineralized
(6 months) plus residual NO?--N. The relative
contributions of these two sources of soil derived N, respectively,
were approximately 66 and 75%, as estimated
from multiple regression analyses
Residual Nitrate and Mineralizable Soil Nitrogen in Relation to Nitrogen Uptake by Irrigated Sugarbeets
Previously reported studies on N fertilization of sugarbeets
(Beta vulgaris L.) in southern Idaho revealed considerable
variation among sites in amounts of residual
soil NO? and N mineralized during short-term laboratory
incubations. Consequently, the amount of N fertilizer
needed to achieve near-maximum yields of sucrose differed
markedly. The purpose of this study was to determine
the feasibility of estimating amounts of N mineralized
in the root zone during the season, taking into
account site variations in temperature and soil water
regimes. Residual soil NO?--N and mineralizable N to
approximate rooting depth were estimated for 21 field
sites in 1971 and six sites in 1972. The relative contributions
of these two N sources to total N uptake by the
crop, in the absence of applied fertilizer N, were then
assessed. Estimates of N mineralized in the upper 45-
cm soil layer for each successive month, ?N, over a 6-
month period were derived using the expression, ?N/
?t kWN (k = fraction of N mineralized during each
month, ?t, adjusted for average air temperature; and W
the estimated soil water content expressed as a fraction
of the available water storage capacity). Resulting
estimates of the fraction of potentially mineralizable N
converted to (NO?- + NH?+)-N between 1 April and
30 September ranged from 0.15 to 0.22 (mean ± S.D. =
0.18 ± 0.02) in 1971 and 1972. On the average, mature
sugarbeets recovered about 73% of the estimated N mineralized
(6 months) plus residual NO?--N. The relative
contributions of these two sources of soil derived N, respectively,
were approximately 66 and 75%, as estimated
from multiple regression analyses
Rapid assembly and rejuvenation of a large silicic magmatic system : insights from mineral diffusive profiles in the Kidnappers and Rocky Hill deposits, New Zealand.
The timescales over which magmas in large silicic systems are reactivated, assembled and stored remains a fundamental question in volcanology. To address this question, we study timescales from Fe–Mg interdiffusion in orthopyroxenes and Ti diffusion in quartz from the caldera-forming 1200 km3 Kidnappers and 200 km3 Rocky Hill eruptions from the Mangakino volcanic centre (Taupo Volcanic Zone, New Zealand). The two eruptions came from the same source area, have indistinguishable 40Ar/39Ar ages (∼1.0 Ma) and zircon U–Pb age spectra, but their respective deposits are separated by a short period of erosion. Compositions of pumice, glass and mineral species in the collective eruption deposits define multiple melt dominant bodies but indicate that these shared a common magmatic mush zone. Diffusion timescales from both eruptions are used to build on chemical and textural crystal signatures and interpret both the crystal growth histories and the timing of magma accumulation. Fe–Mg interdiffusion profiles in orthopyroxenes imply that the three melt-dominant bodies, established through extraction of melt and crystals from the common source, were generated within 600 years and with peak accumulation rates within 100 years of each eruption. In addition, a less-evolved melt interacted with the Kidnappers magma, beginning ∼30 years prior to and peaking within 3 years of the eruption. This interaction did not directly trigger the eruption, but may have primed the magmatic system. Orthopyroxene crystals with the same zoning patterns from the Kidnappers and Rocky Hill pumices yield consistently different diffusion timescales, suggesting a time break between the eruptions of ∼20 years (from core–rim zones) to ∼10 years (outer rim zones). Diffusion of Ti in quartz reveals similarly short timescales and magmatic residence times of <30 years, suggesting quartz is only recording the last period of crystallization within the final eruptible melt. Accumulation of the eruptible magma for these two, closely successive eruptions was accomplished over centuries to decades, in contrast to the gestation time of the magmatic system of ∼200 kyr, as indicated by zircon age patterns. The magmatic system was able to recover after the Kidnappers eruption in only ∼10–20 years to accumulate enough eruptible melt and crystals for a second ∼200 km3 eruption. Our data support concepts of large silicic systems being stored as long-lived crystal mushes, with eruptible melts generated over extraordinarily short timescales prior to eruption
Nitrate Determination by a Modified Conway Microdiffusion Method
The proposed modified Conway microdiffusion
method provides for consecutive determinations
of NH?- and NO?-N in a given
aliquot of soil extract. Analyses of primary
nitrate standards showed essentially complete
recovery in the range of 1 to 20 ppm NO?-N
(4 to 80 µg N/aliquot). Results for (NH? +
NO?)-N and NO?-N in soil extracts are comparable
to those obtained, respectively, by
macrodistillation with Devarda's alloy and by
the phenoldisulfonic acid colorimetric method.
The method is rapid and suitable for routine
analyses of soil extracts, the equipment is
inexpensive, and no interferences are apparent
Measuring Atmospheric Neutrino Oscillations with Neutrino Telescopes
Neutrino telescopes with large detection volumes can demonstrate that the
current indications of neutrino oscillation are correct or if a better
description can be achieved with non-standard alternatives. Observations of
contained muons produced by atmospheric neutrinos can better constrain the
allowed region for oscillations or determine the relevant parameters of
non-standard models. We analyze the possibility of neutrino telescopes
measuring atmospheric neutrino oscillations. We suggest adjustments to improve
this potential. An addition of four densely-instrumented strings to the AMANDA
II detector makes observations feasible. Such a configuration is competitive
with current and proposed experiments.Comment: 36 pages, 21 figures, revte
A CRISPR/Cas9-based genome-editing system for yam (Dioscorea spp.)
Open Access Journal; Published online: 22 Nov 202
Untangling the complexities of processing and analysis for untargeted LC-MS data using open-source tools
Untargeted metabolomics is a powerful tool for measuring and understanding complex biological chemistries. However, employment, bioinformatics and downstream analysis of mass spectrometry (MS) data can be daunting for inexperienced users. Numerous open-source and free-to-use data processing and analysis tools exist for various untargeted MS approaches, including liquid chromatography (LC), but choosing the ‘correct’ pipeline isn’t straight-forward. This tutorial, in conjunction with a user-friendly online guide presents a workflow for connecting these tools to process, analyse and annotate various untargeted MS datasets. The workflow is intended to guide exploratory analysis in order to inform decision-making regarding costly and time-consuming downstream targeted MS approaches. We provide practical advice concerning experimental design, organisation of data and downstream analysis, and offer details on sharing and storing valuable MS data for posterity. The workflow is editable and modular, allowing flexibility for updated/changing methodologies and increased clarity and detail as user participation becomes more common. Hence, the authors welcome contributions and improvements to the workflow via the online repository. We believe that this workflow will streamline and condense complex mass-spectrometry approaches into easier, more manageable, analyses thereby generating opportunities for researchers previously discouraged by inaccessible and overly complicated software
Observation of hard scattering in photoproduction events with a large rapidity gap at HERA
Events with a large rapidity gap and total transverse energy greater than 5
GeV have been observed in quasi-real photoproduction at HERA with the ZEUS
detector. The distribution of these events as a function of the
centre of mass energy is consistent with diffractive scattering. For total
transverse energies above 12 GeV, the hadronic final states show predominantly
a two-jet structure with each jet having a transverse energy greater than 4
GeV. For the two-jet events, little energy flow is found outside the jets. This
observation is consistent with the hard scattering of a quasi-real photon with
a colourless object in the proton.Comment: 19 pages, latex, 4 figures appended as uuencoded fil
- …