899 research outputs found
Long-term response of corn to limited irrigation and crop rotations
Dwindling water supplies for irrigation are prompting alternative management choices by irrigators. Limited irrigation, where less water is applied than full crop demand, may be a viable approach. Application of limited irrigation to corn was examined in this research. Corn was grown in crop rotations with dryland, limited irrigation, or full irrigation management from 1985 to 1999. Crop rotations included corn following corn (continuous corn), corn following wheat, followed by soybean (wheat-corn-soybean), and corn following soybean (corn-soybean). Full irrigation was managed to meet crop evapotranspiration requirements (ETc). Limited irrigation was managed with a seasonal target of no more than 150 mm applied. Precipitation patterns influenced the outcomes of measured parameters. Dryland yields had the most variation, while fully irrigated yields varied the least. Limited irrigation yields were 80% to 90% of fully irrigated yields, but the limited irrigation plots received about half the applied water. Grain yields were significantly different among irrigation treatments. Yields were not significantly different among rotation treatments for all years and water treatments. For soil water parameters, more statistical differences were detected among the water management treatments than among the crop rotation treatments. Economic projections of these management practices showed that full irrigation produced the most income if water was available. Limited irrigation increased income significantly from dryland management
Field scale limited irrigation scenarios for water policy strategies
ABSTRACT. Approaches to reducing irrigation inputs to crops have been studied for the past 50 to 60 years in research settings. Fewer efforts have been made to document limited irrigation responses over a number of seasons on commercial fields. This study compared farm−based irrigation management (FARM) with best management practices (BMP), late initiation of irrigation (LATE), and a restricted allocation (ALLOC). These irrigation management strategies each occupied 1/8 of a center pivot system in southwest Nebraska in continuous corn production, on four cooperating farms, which were replicated at the same sites for 3 to 6 years. Irrigation variables were achieved by irrigating or not irrigating, or by speeding up or slowing down the center pivot. When the grain yields and irrigation amounts were normalized each year using the FARM treatment as the basis, on average for three of four locations, the BMP treatment yielded equal to the FARM treatment, the LATE treatment yielded 93 % of the FARM treatment and the ALLOC yielded 84 % of the FARM treatment. At the same time, it took 76 % and 57 % of the water for the LATE and ALLOC treatments, respectively, to achieve these yields. The adjusted gross returns (yield price – irrigation treatment costs) of the irrigation treatments were analyzed for each location. When the gross returns were normalized using the FARM treatment as the basis, FARM and BMP returns were equal across combinations of high and low input commodity prices and pumping costs. The LATE treatment gross return was 95 % of FARM return. The gross return for the ALLOC treatment was 85 % to 91 % of the FARM treatment. The higher the water costs, the lower the difference between the highest and lowest returning water treatments. Relationships between evapotranspiratio
Nitrate Leaching in Irrigated Corn and Soybean in a Semi-Arid Climate
Nitrate-nitrogen leached from the root zone of land in intensive corn production is a major groundwater contaminant in some of the intensively irrigated regions of the western Cornbelt, including central and western Nebraska. To obtain a clearer understanding of the amount and timing of nitrate leaching losses from irrigated crops, 14 monolithic percolation lysimeters were installed in 1989-1990 in sprinkler irrigated plots at the University of Nebraska’s West Central Research and Extension Center near North Platte, Nebraska. The lysimeters were used to provide a direct measure of leachate depth from continuous corn and a corn-soybean rotation. Both cropping systems were sprinkler irrigated and used current best management practices (BMPs) in the region for water and nitrogen management. Leachate was collected from 1990 through 1998 and analyzed for nitrate-N concentration. Results for the period 1993- 1998 are reported here. In the semi-arid climate of West-Central Nebraska, the interaction of rainfall patterns with the period of active uptake of water by crops played a major role in defining leaching patterns. Careful irrigation scheduling did not eliminate leaching during the growing season. There was no significant difference in drainage depth between continuous corn and the corn-soybean rotation. The average drainage depth among the lysimeters was 218 mm yr-1. This was more than expected, and in part resulted from above normal precipitation during several years of the study. No water quality benefit was found for the corn-soybean rotation as compared to continuous corn. Nitrate-N concentration in the leachate from continuous corn averaged 24 mg L-1, while that from the corn-soybean rotation averaged 42 mg L-1. Total yearly nitrate leaching loss averaged 52 kg ha-1 for continuous corn and 91 kg ha-1 for the rotation. This represents the equivalent of 27% and 105% of the amount of N fertilizer applied over the six years of study. In calculating N fertilizer needs for corn in Nebraska, the recommended legume N credit of 50 kg ha-1 for a preceding crop of soybean may be too low under irrigated production
Chemical Genetic Control of Protein Levels: Selective in Vivo Targeted Degradation
Genetic loss of function analysis is a powerful method for the study of protein function. However, some cell biological questions are difficult to address using traditional genetic strategies often due to the lack of appropriate genetic model systems. Here, we present a general strategy for the design and syntheses of molecules capable of inducing the degradation of selected proteins in vivo via the ubiquitin−proteasome pathway. Western blot and fluorometric analyses indicated the loss of two different targets: green fluorescent protein (GFP) fused with FK506 binding protein (FKBP12) and GFP fused with the androgen receptor (AR), after treatment with PROteolysis TArgeting Chimeric moleculeS (PROTACS) incorporating a FKBP12 ligand and dihydrotestosterone, respectively. These are the first in vivo examples of direct small molecule-induced recruitment of target proteins to the proteasome for degradation upon addition to cultured cells. Moreover, PROTAC-mediated protein degradation offers a general strategy to create “chemical knockouts,” thus opening new possibilities for the control of protein function
Measurement of the cross-section ratio sigma_{psi(2S)}/sigma_{J/psi(1S)} in deep inelastic exclusive ep scattering at HERA
The exclusive deep inelastic electroproduction of and
at an centre-of-mass energy of 317 GeV has been studied with the ZEUS
detector at HERA in the kinematic range GeV,
GeV and GeV, where is the photon virtuality, is the
photon-proton centre-of-mass energy and is the squared four-momentum
transfer at the proton vertex. The data for GeV were taken in
the HERA I running period and correspond to an integrated luminosity of 114
pb. The data for GeV are from both HERA I and HERA II
periods and correspond to an integrated luminosity of 468 pb. The decay
modes analysed were and for the
and for the . The cross-section ratio
has been measured as a function of
and . The results are compared to predictions of QCD-inspired
models of exclusive vector-meson production.Comment: 24 pages, 8 figure
Combined QCD and electroweak analysis of HERA data
A simultaneous fit of parton distribution functions (PDFs) and electroweak
parameters to HERA data on deep inelastic scattering is presented. The input
data are the neutral current and charged current inclusive cross sections which
were previously used in the QCD analysis leading to the HERAPDF2.0 PDFs. In
addition, the polarisation of the electron beam was taken into account for the
ZEUS data recorded between 2004 and 2007. Results on the vector and
axial-vector couplings of the Z boson to u- and d-type quarks, on the value of
the electroweak mixing angle and the mass of the W boson are presented. The
values obtained for the electroweak parameters are in agreement with Standard
Model predictions.Comment: 32 pages, 10 figures, accepted by Phys. Rev. D. Small corrections
from proofing process and small change to Fig. 12 and Table
Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering: Determined by the OLYMPUS Experiment
The OLYMPUS collaboration reports on a precision measurement of the
positron-proton to electron-proton elastic cross section ratio, ,
a direct measure of the contribution of hard two-photon exchange to the elastic
cross section. In the OLYMPUS measurement, 2.01~GeV electron and positron beams
were directed through a hydrogen gas target internal to the DORIS storage ring
at DESY. A toroidal magnetic spectrometer instrumented with drift chambers and
time-of-flight scintillators detected elastically scattered leptons in
coincidence with recoiling protons over a scattering angle range of to . The relative luminosity between the two beam species
was monitored using tracking telescopes of interleaved GEM and MWPC detectors
at , as well as symmetric M{\o}ller/Bhabha calorimeters at
. A total integrated luminosity of 4.5~fb was collected. In
the extraction of , radiative effects were taken into account
using a Monte Carlo generator to simulate the convolutions of internal
bremsstrahlung with experiment-specific conditions such as detector acceptance
and reconstruction efficiency. The resulting values of , presented
here for a wide range of virtual photon polarization ,
are smaller than some hadronic two-photon exchange calculations predict, but
are in reasonable agreement with a subtracted dispersion model and a
phenomenological fit to the form factor data.Comment: 5 pages, 3 figures, 2 table
Limits on the effective quark radius from inclusive scattering at HERA
The high-precision HERA data allows searches up to TeV scales for Beyond the
Standard Model contributions to electron-quark scattering. Combined
measurements of the inclusive deep inelastic cross sections in neutral and
charged current scattering corresponding to a luminosity of around 1
fb have been used in this analysis. A new approach to the beyond the
Standard Model analysis of the inclusive data is presented; simultaneous
fits of parton distribution functions together with contributions of "new
physics" processes were performed. Results are presented considering a finite
radius of quarks within the quark form-factor model. The resulting 95% C.L.
upper limit on the effective quark radius is cm.Comment: 10 pages, 4 figures, accepted by Phys. Lett.
Search for a narrow baryonic state decaying to and in deep inelastic scattering at HERA
A search for a narrow baryonic state in the and
system has been performed in collisions at HERA with the ZEUS detector
using an integrated luminosity of 358 pb taken in 2003-2007. The search
was performed with deep inelastic scattering events at an centre-of-mass
energy of 318 GeV for exchanged photon virtuality, , between 20 and 100
. Contrary to evidence presented for such a state around 1.52
GeV in a previous ZEUS analysis using a sample of 121 pb taken in
1996-2000, no resonance peak was found in the invariant-mass
distribution in the range 1.45-1.7 GeV. Upper limits on the production cross
section are set.Comment: 16 pages, 4 figures, accepted by Phys. Lett. B. Minor changes from
journal reviewing process, including a small correction to figure
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