206 research outputs found
Irrigation management for double-cropped fresh-market tomatoes on a high-water-table soil
Two tomato (Lycopersicon esculentum, Mill.)
experiments were conducted for two years on a southeastern
Coastal Plain soil that has a high, fluctuating water
table. In one experiment, two methods for managing
microirrigation were compared to a treatment that received
only rainfall by measuring marketable fruit yields for
spring and fall cropping seasons. Irrigation increased yields
for both seasons in the second year because of low rainfall.
Measurements among seven shallow wells on the site
showed no consistent differences for either water table
depth or gradient between adjacent wells. Two cultivars
were evaluated in the second year, primarily because frost
severely damaged the tomato plants about three weeks
after transplanting. In the second experiment, two
excessively irrigated treatments were evaluated in an effort
to induce a "soft-fruit" storage and shipping problem
experienced by many growers in this region. Although
extremely large quantities of irrigation water were applied,
these symptoms were not observed in this study. There
were no differences in fruit yield between the two water
management treatments in either spring or fall. Fruit
quality measurements showed no significant differences.
The 'Sunny' cultivar performed better than 'Walter' during
the fall season for the extremely wet soil condition. A
double-crop, microirrigation management system has
higher input costs but provides increased profitability for
fresh-market tomato production, particularly where
markets are available for both spring and fall crops
Correction of cone index for soil water content differences in a coastal plain soil
Soil penetration resistance (cone index) varies with water content. The field variation of water
content could mask treatment differences. The correction of cone index data to a single water
content would help prevent this. We used equations from TableCurve software and from the
literature to correct cone indices for differences in soil water contents. Data were taken from two
field experiments where cotton (Gossypium hirsutum L.) was grown using conventional and
conservation tillage without irrigation, and beans (Phaseolus vulgaris L.) were grown using
conventional tillage with microirrigation. Boundary conditions based on hard, dry and soft. wet
soils were imposed on the equations. Equations fit the data with coefficients of determination
ranging from 0.55 to 0.92 and error mean squares from 1.37 to 6.35. After correction, cone index
dependence on water content was reduced. A single-equation correction did not always fit the data
across all treatments. Separate corrections, based on treatment, might be required. When corrections
required multiple equations, differences may be real or may be a manifestation of the
correction differences. In this case, the correction may not be feasible (unless some future work
can coordinate different equations and assure a uniform correction)
A comparison of pressure chamber, leaf-press, and canopy temperature for four species under humid conditions
Numerous techniques are currently available for measurement of
plant water status in field environments, including pressure chambers and indices based upon
infrared-determined canopy temperatures. The Campbell-Brewster (J-14) leaf press has been
promoted as a compact alternative to the pressure chamber for plant water potential determination.
In-depth comparisons of the J-14 (?J) with the pressure chamber (?x) or with canopy
temperatures (Tc) and crop water stress index (CWSI) have been limited, and an evaluation of
the technique in a humid environment was needed. All three J-14 end points [exudation from
cut (?Jc) or uncut leaf edges (?Ju) or darkening of interveinal areas (?Jd)] were highly correlated
among themselves for the four species studied. Correlations of J-14 end points with other stress
indicators from unstable diurnal periods were poor. None of the water status indicators correlated
well with leaf diffusive resistance. Our data showed a species-related reliability of the J-14. The
J-14 produced r2 values above 0.7 for soybean [Glycine max. (L.) Merr.] for all but comparisons
with CWSI or Tc, minus air temperature (?T), and for corn (Zea mays L.) for ?x only. The J-14
did not perform well for tomato (Lypersician esculentum Mill.) or rapeseed (Brassica napes L.), and
is probably best regarded only as a relative indication of plant water status in the absence of
calibration with other techniques. Failure of ?x or J-14 to correlate well with CWSI underscores
difficulty with CWSI measurement under humid conditions
Comparison of Campbell-leaf press with standard plant water stress measurements for four species
The Campbell-Brewster (J-14) leaf press is a compact
alternative to the pressure chamber for plant water
potential determination. Data comparing the J-14
with the pressure chamber (?x) or with canopy
temperatures (Tc) and crop water stress index (CWSI)
are limited. All three J-14 end points (exudation
from cut or uncut leaf edges or darkening of
interveinal areas) were highly correlated among
themselves for the four species studied.
Correlations of J-14 end points with other stress
indicators from unstable diurnal periods were poor.
Our data shoved a species-related reliability of the
J-14. The J-14 produced r2 values above 0.7 for
soybean for all but comparisons with CWSI or Tc
minus air temperature (?T), and for corn for ?x
only. The J-14 did not perform well for tomato or
rapeseed. Failure of J-14 or ?x, to correlate well
with CWSI suggests difficulty with CWSI measurement
under humid southeastern conditions
Experiences with microirrigation for agronomic crops in the southeastern USA
Microirrigation offers several advantages over sprinkler irrigation in humid areas, including
ease of automation; lower water pressure and flow rate; improved management of water and
nutrients; and easy seasonal start-up, especially for subsurface placement. Microirrigation
system cost could be reduced and made more profitable for agronomic crops by using wider
spacing and subsurface placement of microirrigation laterals. Results are reviewed from five
experiments involving microirrigation of agronomic crops (corn, soybean, and cotton) and
including 14 site-years of data. Agronomic crops can be effectively and efficiently irrigated
in the southeastern Coastal Plain with microirrigation systems. In three experiments involving
nine site-years of data, both normal (0.76 - 1.0 m) and wide (1.5 - 2.0 m) lateral spacings
were used to irrigate corn and cotton; yields were equal except in one year when corn yield
was reduced by about 10% for the wide spacing. With corn, there was no yield difference
between surface and subsurface placement of laterals at the normal spacing (every row).
Other data indicate that wider spacing of laterals in subsurface installations produces cotton
lint yields similar to those for the same spacing in surface placements. Consequently, it
appears that surface or subsurface placement of laterals at wider spacings (alternate furrow,
1.5 - 2.0 m) has significant potential for profitable irrigation of agronomic crops such as corn,
cotton, and soybean in the southeastern USA
Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET
The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR
Relationship of edge localized mode burst times with divertor flux loop signal phase in JET
A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM
Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background
The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generically polarized gravitational waves. We find no evidence for a background of any polarization, and place the first direct bounds on the contributions of vector and scalar polarizations to the stochastic background. Under log-uniform priors for the energy in each polarization, we limit the energy densities of tensor, vector, and scalar modes at 95% credibility to Ω0T<5.58×10-8, Ω0V<6.35×10-8, and Ω0S<1.08×10-7 at a reference frequency f0=25 Hz. © 2018 American Physical Society
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