Forage Legumes in Tropical Regions: Recent Advances and Future Challenges

Nitrogen input in tropical pastures increases forage and animal productivity. Forage legumes can fix atmospheric nitrogen and are the most economical way to add this nutrient to the soil. Our objective was to report the benefits of forage legumes in tropical pastures and possible strategies to implement different forage legumes. In tropical conditions, such as in Brazil, the use of forage legumes is still scarce. Even with low legume adoption on tropical pastures, forage legumes can provide ecosystem services. Increased animal productivity is the first ecosystem service provided by these legumes, mainly due to the addition of nitrogen that is typically the most limiting nutrient on tropical soils and yet the most important driver of plant growth and development. Legumes also provide an opportunity to increase nitrogen cycling in grassland, reducing grassland degradation. Pastures that include legumes have greater litter quality than grass monocultures, increasing soil organic matter at a faster rate. Legumes improve diet nutritive value and animal performance, resulting in reduced enteric methane emissions per unit of animal product. Additionally, legumes are generally associated with lower nitrous oxide emissions than N-fertilized grass swards and reduce the carbon footprint from the system due to nitrogen manufacture, transport, storage, and application. However, the greatest challenge in tropical pastures is to increase the adoption of forage legumes. It is necessary to understand the role of different legumes in the pasture environment. Some legumes have high herbage accumulation and biological nitrogen fixation potential, but they have low canopy stability; nonetheless, they could be used on short-lived pastures as well as integrated crop-livestock systems. When the objective is to achieve grass-legume stability in mixed pastures, it is necessary to use clonal propagation legumes and provide appropriate defoliation management to minimize light competition among plant communities

Factors affecting pre-failure instability of sand under plane-strain conditions

Experimental data obtained from a plane-strain appara- tus are presented in this paper to show that a pre-failure instability in the form of a rapid and sustained increase in strain rate can occur for both contractive and dilative sand under fully drained conditions. However, this type of instability is different from the runaway type of instability observed under undrained conditions, and has therefore been called conditional instability. Despite the differences, the conditions for both types of instability are the same for contractive sand. There are also other factors that affect the pre-failure instability of sand ob- served in the laboratory. These include the stress ratio, void ratio, sand state, load control mode and reduction rate of the effective confining stress. In this paper, these factors are discussed and analysed using experimental data obtained from undrained instability (or creep) tests and constant shear drained (CSD) tests carried out under plane-strain conditions

Épocas de semeadura de mamona no Rio Grande do Sul.

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Measuring the vertical age structure of the Galactic disc using asteroseismology and SAGA

The existence of a vertical age gradient in the Milky Way disc has been indirectly known for long. Here, we measure it directly for the first time with seismic ages, using red giants observed by Kepler. We use Stroemgren photometry to gauge the selection function of asteroseismic targets, and derive colour and magnitude limits where giants with measured oscillations are representative of the underlying population in the field. Limits in the 2MASS system are also derived. We lay out a method to assess and correct for target selection effects independent of Galaxy models. We find that low mass, i.e. old red giants dominate at increasing Galactic heights, whereas closer to the Galactic plane they exhibit a wide range of ages and metallicities. Parametrizing this as a vertical gradient returns approximately 4 Gyr/kpc for the disc we probe, although with a large dispersion of ages at all heights. The ages of stars show a smooth distribution over the last 10 Gyr, consistent with a mostly quiescent evolution for the Milky Way disc since a redshift of about 2. We also find a flat age-metallicity relation for disc stars. Finally, we show how to use secondary clump stars to estimate the present-day intrinsic metallicity spread, and suggest using their number count as a new proxy for tracing the ageing of the disc. This work highlights the power of asteroseismology for Galactic studies; however, we also emphasize the need for better constraints on stellar mass-loss, which is a major source of systematic age uncertainties in red giant stars.Comment: MNRAS, accepted. SAGA website and data at http://www.mso.anu.edu.au/saga/data_access.htm

Produção de mamona na serra do sudeste, RS

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Fundamental stellar parameters of benchmark stars from CHARA interferometry. I. Metal-poor stars

Benchmark stars are crucial as validating standards for current as well as future large stellar surveys of the Milky Way. However, the number of suitable metal-poor benchmarks is currently limited. We aim to construct a new set of metal-poor benchmarks, based on reliable interferometric effective temperature ($T_\text{eff}$) determinations and a homogeneous analysis with a desired precision of $1\%$ in $T_\text{eff}$. We observed ten late-type metal-poor dwarf and giants: HD2665, HD6755, HD6833, HD103095, HD122563, HD127243, HD140283, HD175305, HD221170, and HD224930. Only three of the ten stars (HD103095, HD122563, and HD140283) have previously been used as benchmarks. For the observations, we used the high angular resolution optical interferometric instrument PAVO at the CHARA array. We modelled angular diameters using 3D limb darkening models and determined $T_\text{eff}$ directly from the Stefan-Boltzmann relation, with an iterative procedure to interpolate over tables of bolometric corrections. Surface gravities ($\log(g)$) were estimated from comparisons to Dartmouth stellar evolution model tracks. We collected spectroscopic observations from the ELODIE and FIES spectrographs and estimated metallicities ($\mathrm{[Fe/H]}$) from a 1D non-LTE abundance analysis of unblended lines of neutral and singly ionized iron. We inferred $T_\text{eff}$ to better than $1\%$ for five of the stars (HD103095, HD122563, HD127243, HD140283, and HD224930). The $T_\text{eff}$ of the other five stars are reliable to between $2-3\%$; the higher uncertainty on the $T_\text{eff}$ for those stars is mainly due to their having a larger uncertainty in the bolometric fluxes. We also determined $\log(g)$ and $\mathrm{[Fe/H]}$ with median uncertainties of $0.03\,\mathrm{dex}$ and $0.09\,\mathrm{dex}$, respectively. These ten stars can, therefore, be adopted as a new, reliable set of metal-poor benchmarks.Comment: 13 pages, 7 figures, 8 tables + 10 online tables, abstract shortened to meet arXiv requirements, accepted in A&

Biological Control of Fenusa pusilla (Hymenoptera: Tenthredinidae) in the Northeastern United States: A Thirty-four Year Perspective on Efficacy

Parasitoid releases against the birch leafminer Fenusa pusilla (Lepeletier) (Hymenoptera: Tenthredinidae) in eastern North America began in 1974, with releases in eastern Canada, followed by others in the Middle Atlantic States and New England. Of 4 parasitoids released, only 1, the ichneumonid Lathrolestes nigricollis (Thompson), established and spread widely. Studies of its preliminary impacts were made in several locations in the 1980s and 1990s, but full impact of the parasitoid on host density was not yet achieved in that period. Here we report results of surveys in 7 states (MA, CT, RI, NY, PA, NJ, DE) in 2007 documenting the current birch leaf miner levels (as % of leaves mined in spring) and parasitism. Survey results show that the pest has declined dramatically to barely detectable levels in 5 states (MA, CT, RI, NY, PA) but that in southern NJ, the pest remains abundant (ca 50% leaves mined) despite significant parasitism levels. Survey results, in context with previous evaluations made when populations were still declining, show that the project has been completely successful in much of the northeastern USA, but that there is a southern limit to efficacy in mid-New Jersey. Possible reasons for lack of control in this area, in contrast to high levels of control elsewhere, are discussed

Ages and fundamental properties of Kepler exoplanet host stars from asteroseismology

We present a study of 33 {\it Kepler} planet-candidate host stars for which asteroseismic observations have sufficiently high signal-to-noise ratio to allow extraction of individual pulsation frequencies. We implement a new Bayesian scheme that is flexible in its input to process individual oscillation frequencies, combinations of them, and average asteroseismic parameters, and derive robust fundamental properties for these targets. Applying this scheme to grids of evolutionary models yields stellar properties with median statistical uncertainties of 1.2\% (radius), 1.7\% (density), 3.3\% (mass), 4.4\% (distance), and 14\% (age), making this the exoplanet host-star sample with the most precise and uniformly determined fundamental parameters to date. We assess the systematics from changes in the solar abundances and mixing-length parameter, showing that they are smaller than the statistical errors. We also determine the stellar properties with three other fitting algorithms and explore the systematics arising from using different evolution and pulsation codes, resulting in 1\% in density and radius, and 2\% and 7\% in mass and age, respectively. We confirm previous findings of the initial helium abundance being a source of systematics comparable to our statistical uncertainties, and discuss future prospects for constraining this parameter by combining asteroseismology and data from space missions. Finally we compare our derived properties with those obtained using the global average asteroseismic observables along with effective temperature and metallicity, finding an excellent level of agreement. Owing to selection effects, our results show that the majority of the high signal-to-noise ratio asteroseismic {\it Kepler} host stars are older than the Sun.Comment: 25 pages, 17 figures, MNRAS accepte