No-till seeded winter wheat: influence of date of nitrogen application on the seasonal pattern of crop growth and water use

Non-Peer ReviewedAn experiment was carried out to determine the influence of fertilizer N timing on the early season crop development and water use (ET) of no-till seeded winter wheat (Triticum aestivum L.). Ammonium nitrate N was surface broadcast either as early as possible (early), split between 2/3 early and 1/3 at the beginning of stem elongation (split), and 3 weeks after early (late), at rates of 0, 67, 134, and 202 kg N ha-1. Early and split-N application increased the early season plant development over Iate-N as recorded by tiller number and leaf area production. The development and maintenance of a larger leaf area with N fertilization in 1987 resulted in increased grain yields. However, high evaporative demand prior to anthesis in 1988 resulted in the 'collapse' of early season leaf and tiller responses. A positive correlation (r=0.82*) was recorded between leaf stomatal conductance (gl) and leaf relative water content, illustrating the importance of tissue water content in maintaining high photosynthetic activity. While added N increased pre-anthesis gl over the unfertilized check, the opposite response was recorded during the post-anthesis grain filling period. Increasing fertilizer N rate increased seasonal ET at 2 of the 8 trials by increasing post-anthesis ET over the unfertilized check. High pre-anthesis evaporative demand reduced season long ET to 159 mm in 1988, 59 % of the 218 mm recorded in 1987. Soil water contributed 16 % of total ET in 1987 and 30 % in 1988. The bulk of this soil water was taken up pre-anthesis, with 98 % of post-anthesis ET coming from rainfall

No-till seeded winter wheat: influence or date of nitrogen application on the grain yield, grain protein, and yield components

Non-Peer ReviewedAn experiment was carried out to determine the influence of date of nitrogen (N) fertilizer application on the grain yield, quality, and water use efficiency (WUE) for dry matter and grain yield production of no-till seeded winter wheat. Ammonium nitrate N was surface broadcast either as early as possible in the spring (early), split between 2/3 early and 113 at the beginning of stem elongation (split), and 3 weeks after early (late), at rates of 0,34,67,101,134,167, and 202 kg N ha-1. Grain yields ranged from 0.25 to 2.5 t ha-1. High pre-anthesis evaporative demand in 1988 reduced mean grain yield to 0.89 t ha-1 (42 % of 1987 yields). While 3 of the 8 trials showed a positive response to N rate, date of N application had no effect on harvest yield and yield components. Grain protein yield and protein concentration were better indicators of N response under these high stress conditions with 6 and 7, respectively, of the 8 trials showing a positive response to N rate. Added N increased water use efficiency of dry matter and grain yield in 5 and 3 of the trials, respectively. Increases in WUE were a reflection of grain and dry matter yield responses to added N and not differences in season long ET. The threshold ET required for zero dry matter and grain yield was 46 and 77 mm, respectively. Forward step-wise regression identified pre-anthesis evaporative demand as the only environmental or soil water parameter influencing harvest dry matter and grain yield response. Dependence of crop response on pre-anthesis evaporation indicates that yield was a function of the atmospheric demand for water in this experiment. Kernels per spike was the yield component that best represented grain yield, explaining 82 % of the variation recorded. High evaporative demand during stem elongation reduced the survival of early established tillers and increased the role of kernels per spike, the other pre-anthesis determined yield component, in grain yield formation. Only with the unfertilized check, where pre-anthesis production was reduced due to N deficiencies, did kernel weight have any significant influence in determining grain yield

Influence of nitrogen rate, form, and placement on the establishment of no-till winter wheat seedlings

Non-Peer Reviewe

Influence of climate and cultivar on grain protein concentration of wheat and rye

Non-Peer Reviewe

Data compression in the presence of observational error correlations

Numerical weather prediction (NWP) models are moving towards km-scale (and smaller) resolutions in order to forecast high-impact weather. As the resolution of NWP models increase the need for high-resolution observations to constrain these models also increases. A major hurdle to the assimilation of dense observations in NWP is the presence of non-negligible observation error correlations (OECs). Despite the difficulty in estimating these error correlations, progress is being made, with centres around the world now explicitly accounting for OECs in a variety of observation types. This paper explores how to make efficient use of this potentially dramatic increase in the amount of data available for assimilation. In an idealised framework it is illustrated that as the length-scales of the OECs increase the scales that the analysis is most sensitive to the observations become smaller. This implies that a denser network of observations is more beneficial with increasing OEC length-scales. However, the computational and storage burden associated with such a dense network may not be feasible. To reduce the amount of data, a compression technique based on retaining the maximum information content of the observations can be used. When the OEC length-scales are large (in comparison to the prior error correlations), the data compression will select observations of the smaller scales for assimilation whilst throwing out the larger scale information. In this case it is shown that there is a discrepancy between the observations with the maximum information and those that minimise the analysis error variances. Experiments are performed using the Ensemble Kalman Filter and the Lorenz-1996 model, comparing different forms of data reduction. It is found that as the OEC length-scales increase the assimilation becomes more sensitive to the choice of data reduction technique

Astrophysical thermonuclear functions

As theoretical knowledge and experimental verification of nuclear cross sections increases it becomes possible to refine analytic representations for nuclear reaction rates. In this paper mathematical/statistical techniques for deriving closed-form representations of thermonuclear functions are summarized and numerical results for them are given.The purpose of the paper is also to compare numerical results for approximate and closed-form representations of thermonuclear functions.Comment: 17 pages in LaTeX, 8 figures available on request from [email protected]

Infrared activity of hydrogen molecules trapped in Si

The rovibrational-translational states of a hydrogen molecule moving in a cage site in Si, when subjected to an electrical field arising from its surroundings, are investigated. The wave functions are expressed in terms of basis functions consisting of the eigenfunctions of the molecule confined to move in the cavity and rovibrational states of the free molecule. The energy levels, intensities of infrared and Raman transitions, effects of uniaxial stress, and a neighboring oxygen defect are found and compared with existing experimental data

Understanding and engineering beneficial plant–microbe interactions:Plant growth promotion in energy crops

Plant production systems globally must be optimized to produce stable high yields from limited land under changing and variable climates. Demands for food, animal feed, and feedstocks for bioenergy and biorefining applications, are increasing with population growth, urbanization and affluence. Low-input, sustainable, alternatives to petrochemical-derived fertilizers and pesticides are required to reduce input costs and maintain or increase yields, with potential biological solutions having an important role to play. In contrast to crops that have been bred for food, many bioenergy crops are largely undomesticated, and so there is an opportunity to harness beneficial plant–microbe relationships which may have been inadvertently lost through intensive crop breeding. Plant–microbe interactions span a wide range of relationships in which one or both of the organisms may have a beneficial, neutral or negative effect on the other partner. A relatively small number of beneficial plant–microbe interactions are well understood and already exploited; however, others remain understudied and represent an untapped reservoir for optimizing plant production. There may be near-term applications for bacterial strains as microbial biopesticides and biofertilizers to increase biomass yield from energy crops grown on land unsuitable for food production. Longer term aims involve the design of synthetic genetic circuits within and between the host and microbes to optimize plant production. A highly exciting prospect is that endosymbionts comprise a unique resource of reduced complexity microbial genomes with adaptive traits of great interest for a wide variety of applications

Entropy of chains placed on the square lattice

We obtain the entropy of flexible linear chains composed of M monomers placed on the square lattice using a transfer matrix approach. An excluded volume interaction is included by considering the chains to be self-and mutually avoiding, and a fraction rho of the sites are occupied by monomers. We solve the problem exactly on stripes of increasing width m and then extrapolate our results to the two-dimensional limit to infinity using finite-size scaling. The extrapolated results for several finite values of M and in the polymer limit M to infinity for the cases where all lattice sites are occupied (rho=1) and for the partially filled case rho<1 are compared with earlier results. These results are exact for dimers (M=2) and full occupation (\rho=1) and derived from series expansions, mean-field like approximations, and transfer matrix calculations for some other cases. For small values of M, as well as for the polymer limit M to infinity, rather precise estimates of the entropy are obtained.Comment: 6 pages, 7 figure

Quantum magneto-oscillations in a two-dimensional Fermi liquid

Quantum magneto-oscillations provide a powerfull tool for quantifying Fermi-liquid parameters of metals. In particular, the quasiparticle effective mass and spin susceptibility are extracted from the experiment using the Lifshitz-Kosevich formula, derived under the assumption that the properties of the system in a non-zero magnetic field are determined uniquely by the zero-field Fermi-liquid state. This assumption is valid in 3D but, generally speaking, erroneous in 2D where the Lifshitz-Kosevich formula may be applied only if the oscillations are strongly damped by thermal smearing and disorder. In this work, the effects of interactions and disorder on the amplitude of magneto-oscillations in 2D are studied. It is found that the effective mass diverges logarithmically with decreasing temperature signaling a deviation from the Fermi-liquid behavior. It is also shown that the quasiparticle lifetime due to inelastic interactions does not enter the oscillation amplitude, although these interactions do renormalize the effective mass. This result provides a generalization of the Fowler-Prange theorem formulated originally for the electron-phonon interaction.Comment: 4 pages, 1 figur