Universidade Federal de Viçosa

About: Universidade Federal de Viçosa is a education organization based out in Viçosa, Brazil. It is known for research contribution in the topics: Population & Dry matter. The organization has 16012 authors who have published 26711 publications receiving 353416 citations.

Simulating the surface waters of the Amazon River basin: impacts of new river geomorphic and flow parameterizations

Abstract: This paper describes the impacts of new river geomorphic and flow parameterizations on the simulated surface waters dynamics of the Amazon River basin. Three major improvements to a hydrologic model are presented: (1) the river flow velocity equation is expanded to be dependent on river sinuosity and friction in addition to gradient forces; (2) equations defining the morphological characteristics of the river, such as river height, width and bankfull volume, are derived from 31 622 measurements of river morphology and applied within the model; (3) 1 km resolution topographic data from the Shuttle Radar Topography Mission (SRTM) are used to provide physically based fractional flooding of grid cells from a statistical representation of sub-grid-scale floodplain morphology. The discharge and floodplain inundation of the Amazon River is simulated for the period 1968–1998, validated against observations, and compared with results from a previous version of the model. These modifications result in considerable improvement in the simulations of the hydrological features of the Amazon River system. The major impact is that the average wet-season flooded area on the Amazon mainstem for the period 1983–1988 is now within 5% of satellite-derived estimates of flooded area, whereas the previous model overestimates the flooded area by about 80%. The improvements are a consequence of the new empirical river geomorphologic functions and the SRTM topography. The new formulation of the flow velocity equation results in increased river velocity on the mainstem and major tributaries and a better correlation between the mean monthly simulated and observed discharge. Copyright © 2007 John Wiley & Sons, Ltd.

Cost and mitigation of insecticide resistance in the maize weevil, Sitophilus zeamais

Abstract: . A common assumption in models of insecticide resistance evolution is the association between resistance and fitness costs in the absence of insecticides. There is empirical evidence of such associations, but their physiological basis (and mitigation) is little investigated. Pyrethroid-resistant populations of the maize weevil Sitophilus zeamais (Coleoptera: Curculionidae) offer this opportunity. Pyrethroid resistance in this species was initially observed in five Brazilian states by 1995, but the phenomenon apparently decreased and did not spread to other regions, probably due to the occurrence of a fitness disadvantage in resistant individuals in the absence of insecticides. The present investigation aims to verify whether differences in respiration rate and fat body morphology are related to differences in rate of development in Brazilian populations of S. zeamais resistant to insecticides, and thereby provide evidence for the existence (or not) of a physiological fitness cost acting against insecticide resistance in maize weevils. This may occur due to a possible energy trade-off between insecticide resistance and other physiological processes associated with development and reproduction. To achieve this, studies of the rate of development, respiration and fat body cytomorphology are carried out in one insecticide-susceptible (from Sete Lagoas) and two resistant populations (from Jacarezinho and Juiz de Fora) of S. zeamais. The resistant population from Jacarezinho shows that higher body mass is associated with higher energy reserves (larger trophocyte area) for development and reproduction, as well as for insecticide resistance. However, the resistant population from Juiz de Fora does not appear to have large enough energy allocation for insecticide-resistance expression and development and/or reproductive performance, suggesting a trade-off between resistance and other life history traits.

Carbono orgânico e estabilidade de agregados de um Latossolo Vermelho sob diferentes manejos

Abstract: O objetivo deste trabalho foi verificar a influencia de diferentes manejos no carbono orgânico e na estabilidade de agregados em um Latossolo Vermelho. Os seguintes tratamentos foram avaliados: PDs - plantio direto, por quatro anos, com a sucessao milho (silagem)/soja; PDg - plantio direto, por quatro anos, com a sucessao milho/milho/milho/soja; PDtf - tres anos continuos, com tifton (feno), e no quarto ano, soja sob plantio direto; SC - sistema convencional com soja, nos ultimos quatro anos; e MN - mata nativa. A estabilidade de agregados foi expressa pelos indices: diâmetro medio ponderado, diâmetro medio geometrico, porcentagem de agregados maiores que 2,0 mm estaveis em agua e indice de estabilidade de agregados. Em todos os tratamentos, houve diminuicao da estabilidade de agregados com o aumento da profundidade. Os tratamentos cultivados tiveram seus indices de agregacao reduzidos em relacao a mata nativa. O sistema convencional apresentou os menores indices de agregacao. O uso da graminea perene tifton foi o tratamento que promoveu a melhor recuperacao da estabilidade de agregados em agua. Correlacoes significativas e positivas foram obtidas entre carbono orgânico total e os indices de estabilidade estudados.