Sistemas agroflorestais com erva-mate, no município de Áurea, RS.

Edição especial de Erva-mate

Nutritive value and in vitro methane production of two perennial grasses under different stocking rates in periurban areas of West-Africa

Background. In sub-Saharan Africa, pasture is the most used practice in ruminant production, and grazing areas characteristics varied in different environment. To improve ruminants’ performances, the quality of forages represents one of the most important factors to keep under control. Objective. To quantify the effects of grazing stocking rate on the nutrient composition, energy content and in vitro fermentation characteristics including volatile fatty acids (VFA) and methane production (CH4) of two local perennial grasses Dactyloctenium aegyptium L. and Leptochloa caerulescens L. Methodology. The forage samples were collected in three locations (Zinvié, Gakpé, Adounko) characterized by different stocking rate (low, medium and high). Their chemical composition, energy content and in vitro fermentation characteristics, including CH4 production, were determined. Results. D. aegyptium showed the highest crude protein, energy content, organic matter degradability and VFA production (p<0.01) when collected in Zinvié, whereas the highest (p<0.01) structural carbohydrates (NDF) content was detected in Gakpé area and the highest CH4 production was recorded from the sample collected in Adounko (p<0.01). Contrariwise, L. caerulescens showed the highest level of crude protein and degradability (p<0.01) when collected in Zinvié, whereas it proved the highest NDF content and the lowest lignin values (p<0.01) when collected in Adounko. The highest CH4 level was obtained from the sample collected in area of Gakpé (p<0.01). Higher (p<0.01) in vitro VFA production were recorded in samples collected in Adounko and Gakpé than in the Zinvié. Implications. The results obtained in this study highlight the significant influence of urbanization and herd concentration, as well as of other environmental conditions, on the nutritional value and potential environmental impact of the studied perennial grasses. Conclusion. Samples from high grazing stocking rate locations produced more in vitro methane. Further in vivo studies are needed to confirm these results

The Cauchy problem on a characteristic cone for the Einstein equations in arbitrary dimensions

We derive explicit formulae for a set of constraints for the Einstein equations on a null hypersurface, in arbitrary dimensions. We solve these constraints and show that they provide necessary and sufficient conditions so that a spacetime solution of the Cauchy problem on a characteristic cone for the hyperbolic system of the reduced Einstein equations in wave-map gauge also satisfies the full Einstein equations. We prove a geometric uniqueness theorem for this Cauchy problem in the vacuum case.Comment: 83 pages, 1 figur

Local and Global Analytic Solutions for a Class of Characteristic Problems of the Einstein Vacuum Equations in the "Double Null Foliation Gauge"

The main goal of this work consists in showing that the analytic solutions for a class of characteristic problems for the Einstein vacuum equations have an existence region larger than the one provided by the Cauchy-Kowalevski theorem due to the intrinsic hyperbolicity of the Einstein equations. To prove this result we first describe a geometric way of writing the vacuum Einstein equations for the characteristic problems we are considering, in a gauge characterized by the introduction of a double null cone foliation of the spacetime. Then we prove that the existence region for the analytic solutions can be extended to a larger region which depends only on the validity of the apriori estimates for the Weyl equations, associated to the "Bel-Robinson norms". In particular if the initial data are sufficiently small we show that the analytic solution is global. Before showing how to extend the existence region we describe the same result in the case of the Burger equation, which, even if much simpler, nevertheless requires analogous logical steps required for the general proof. Due to length of this work, in this paper we mainly concentrate on the definition of the gauge we use and on writing in a "geometric" way the Einstein equations, then we show how the Cauchy-Kowalevski theorem is adapted to the characteristic problem for the Einstein equations and we describe how the existence region can be extended in the case of the Burger equation. Finally we describe the structure of the extension proof in the case of the Einstein equations. The technical parts of this last result is the content of a second paper.Comment: 68 page

Effets des rhizobactéries PGPR sur le rendement et les teneurs en macroéléments du maïs sur sol ferralitique non dégradé au Sud-Bénin

L&#8217;objectif de l&#8217;&#233;tude est d&#8217;&#233;valuer les effets de 15 rhizobact&#233;ries promotrices de croissance v&#233;g&#233;tative (PGPR en Anglais) sur le rendement et l&#8217;&#233;tat nutritionnel des plants de ma&#239;s sur sol ferralitique non d&#233;grad&#233; du Sud-B&#233;nin. Les semences de ma&#239;s ont &#233;t&#233; inocul&#233;es avec des concentrations microbiennes d&#8217;environ 108 UFC/ml. Les teneurs en azote, en phosphore et en potassium d&#8217;&#233;chantillons de plants de ma&#239;s ont &#233;t&#233; d&#233;termin&#233;es. Les valeurs de rendement du ma&#239;s ont &#233;t&#233; soumises &#224; une analyse de la variance &#224; deux facteurs. Les rhizobact&#233;ries Pseudomonas fluorescens ont induit le rendement de ma&#239;s le plus &#233;lev&#233;, d&#233;passant de 41,46% le rendement de ma&#239;s obtenu avec l&#8217;inoculation de P. putida et de 118,05% le rendement de ma&#239;s obtenu au niveau des plants non inocul&#233;s. Les rendements de ma&#239;s induits par P. putida et Azospirillium lipoferum sont sup&#233;rieurs respectivement de 54,17% et de 26,39% au rendement obtenu au niveau des plants non inocul&#233;s. Les r&#233;sultats obtenus augurent de la possibilit&#233; d&#8217;utiliser les rhizobact&#233;ries PGPR comme des engrais biologiques pour une production durable de ma&#239;s. Au Sud du B&#233;nin, o&#249; la pression d&#233;mographique est forte et la baisse de la fertilit&#233; des sols croissante, l&#8217;utilisation de m&#233;thodes biologiques pour accro&#238;tre les r&#233;coltes est une solution incontournable.Mots cl&#233;s: Rhyzobact&#233;ries, Rendement, Ma&#239;s, Sol ferralitique, B&#233;ni

Theorems on existence and global dynamics for the Einstein equations

This article is a guide to theorems on existence and global dynamics of solutions of the Einstein equations. It draws attention to open questions in the field. The local-in-time Cauchy problem, which is relatively well understood, is surveyed. Global results for solutions with various types of symmetry are discussed. A selection of results from Newtonian theory and special relativity that offer useful comparisons is presented. Treatments of global results in the case of small data and results on constructing spacetimes with prescribed singularity structure or late-time asymptotics are given. A conjectural picture of the asymptotic behaviour of general cosmological solutions of the Einstein equations is built up. Some miscellaneous topics connected with the main theme are collected in a separate section.Comment: Submitted to Living Reviews in Relativity, major update of Living Rev. Rel. 5 (2002)

Pesquisa participativa visando ao desenvolvimento de alternativas para melhoria dos sistemas agroflorestais na regiao do Alto Uruguai Gaúcho.

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