The Effect of Phosphorus Fertilization on Botanical Composition and Production in Temperate Pastures in Argentina

The objective of this paper is to evaluate floristic changes and above-ground primary production in native grasslands and old pastures dominated by tall fescue (Festuca arundinacea) that were fertilized with different levels of phosphorus. For this, aerial biomass was sequentially harvested from November 1998 to October 1999. Above-ground production of native grassland more than doubled (from 3000 to 7300 kg DM/ha) with the highest level of P through the increment of three naturalized species: the winter annual ryegrass (Lolium multiflorum) and two legumes: white clover (Trifolium repens) and lotus (Lotus corniculatus). In contrast, above-ground production of old fescue pastures remained unchanged while nutritive value improved as legumes and warm-season grasses increased where they were fertilized

Gradiente de pastoreo bovino desde la aguada según la permanencia animal en Digitaria eriantha diferida

3 sectors were defined with different intensity of disturbance in a paddock of Digitaria eriantha, by georeferenced positions of a cow. Fecal abundance into 9 squares sampling sites of 144 m2 and coverage of Digitaria and native winter species before and after grazing period, in 3 permanent transects 10 m long by sector, were registered. To summarize the information of vegetation, INTECO was applied and forage availability was estimated in 9 samples of 0.5 m2 by sector. Fecal concentration gradually decreased getting away from the watering point. Digitaria coverage and forage availability after grazing period decreased in the 3 sectors, while in winter species just did it in nearby "C" and medium "M". The forage condition established by INTECO decreased one category after grazing period for sectors "C" and "M", in "L" (far) show a greater impact due to the entry of external animals. The geoposition of grazing animals lets to define a grazing gradient, and the studied variables support this effect. The position of grazing animals allows to define a grazing gradient, and the studied variables support this effect. The identification of grazing gradient regard to the watering point is paramount to improve the design of paddocks and water distribution, to enhance the efficiency of forage harvest.Se delimitaron 3 sectores con distinta intensidad de disturbio en un potrero de Digitaria eriantha, mediante la localización georeferenciada de una vaca de cría. Se registraron las heces presentes en 9 cuadros de muestreo de 144 m2 y cobertura de digitaria e invernales forrajeras antes y después del periodo de pastoreo en 3 transectas fijas de 10 m de largo, por sector. Para sintetizar la información de la vegetación, se aplicó el INTECO y se estimó la disponibilidad forrajera de 9 muestras de 0,5 m2 por sector. La concentración de heces decreció gradualmente al alejarse de la aguada. Las coberturas de Digitaria y forrajimasa luego del periodo de pastoreo disminuyeron en los 3 sectores, mientras la de invernales sólo lo hizo en cercano “C” y medio “M”. La condición forrajera establecida por INTECO, disminuyó una categoría luego del pastoreo en los sectores “C” y “M”, en “L” (lejos) hubo un mayor impacto debido al ingreso de animales externos. La geoposición de animales en pastoreo permite definir un gradiente de pastoreo, y las variables estudiadas corroboran dicho efecto. La identificación del gradiente de pastoreo respecto a la aguada es de suma importancia para mejorar el diseño de potreros y aguadas, y optimizar la eficiencia de cosecha forrajera

Using bond-length dependent transferable force constants to predict vibrational entropies in Au-Cu, Au-Pd, and Cu-Pd alloys

A model is tested to rapidly evaluate the vibrational properties of alloys with site disorder. It is shown that length-dependent transferable force constants exist, and can be used to accurately predict the vibrational entropy of substitutionally ordered and disordered structures in Au-Cu, Au-Pd, and Cu-Pd. For each relevant force constant, a length- dependent function is determined and fitted to force constants obtained from first-principles pseudopotential calculations. We show that these transferable force constants can accurately predict vibrational entropies of L1$_{2}$-ordered and disordered phases in Cu$_{3}$Au, Au$_{3}$Pd, Pd$_{3}$Au, Cu$_{3}$Pd, and Pd$_{3}$Au. In addition, we calculate the vibrational entropy difference between L1$_{2}$-ordered and disordered phases of Au$_{3}$Cu and Cu$_{3}$Pt.Comment: 9 pages, 6 figures, 3 table

Dynamic of a non homogeneously coarse grained system

To study materials phenomena simultaneously at various length scales, descriptions in which matter can be coarse grained to arbitrary levels, are necessary. Attempts to do this in the static regime (i.e. zero temperature) have already been developed. In this letter, we present an approach that leads to a dynamics for such coarse-grained models. This allows us to obtain temperature-dependent and transport properties. Renormalization group theory is used to create new local potentials model between nodes, within the approximation of local thermodynamical equilibrium. Assuming that these potentials give an averaged description of node dynamics, we calculate thermal and mechanical properties. If this method can be sufficiently generalized it may form the basis of a Molecular Dynamics method with time and spatial coarse-graining.Comment: 4 pages, 4 figure

The Effect of Lattice Vibrations on Substitutional Alloy Thermodynamics

A longstanding limitation of first-principles calculations of substitutional alloy phase diagrams is the difficulty to account for lattice vibrations. A survey of the theoretical and experimental literature seeking to quantify the impact of lattice vibrations on phase stability indicates that this effect can be substantial. Typical vibrational entropy differences between phases are of the order of 0.1 to 0.2 k_B/atom, which is comparable to the typical values of configurational entropy differences in binary alloys (at most 0.693 k_B/atom). This paper describes the basic formalism underlying ab initio phase diagram calculations, along with the generalization required to account for lattice vibrations. We overview the various techniques allowing the theoretical calculation and the experimental determination of phonon dispersion curves and related thermodynamic quantities, such as vibrational entropy or free energy. A clear picture of the origin of vibrational entropy differences between phases in an alloy system is presented that goes beyond the traditional bond counting and volume change arguments. Vibrational entropy change can be attributed to the changes in chemical bond stiffness associated with the changes in bond length that take place during a phase transformation. This so-called ``bond stiffness vs. bond length'' interpretation both summarizes the key phenomenon driving vibrational entropy changes and provides a practical tool to model them.Comment: Submitted to Reviews of Modern Physics 44 pages, 6 figure

Meta-analysis of the detection of plant pigment concentrations using hyperspectral remotely sensed data

Passive optical hyperspectral remote sensing of plant pigments offers potential for understanding plant ecophysiological processes across a range of spatial scales. Following a number of decades of research in this field, this paper undertakes a systematic meta-analysis of 85 articles to determine whether passive optical hyperspectral remote sensing techniques are sufficiently well developed to quantify individual plant pigments, which operational solutions are available for wider plant science and the areas which now require greater focus. The findings indicate that predictive relationships are strong for all pigments at the leaf scale but these decrease and become more variable across pigment types at the canopy and landscape scales. At leaf scale it is clear that specific sets of optimal wavelengths can be recommended for operational methodologies: total chlorophyll and chlorophyll a quantification is based on reflectance in the green (550–560nm) and red edge (680–750nm) regions; chlorophyll b on the red, (630–660nm), red edge (670–710nm) and the near-infrared (800–810nm); carotenoids on the 500–580nm region; and anthocyanins on the green (550–560nm), red edge (700–710nm) and near-infrared (780–790nm). For total chlorophyll the optimal wavelengths are valid across canopy and landscape scales and there is some evidence that the same applies for chlorophyll a