3,726 research outputs found
Recuperação de pastagens degradadas para sistemas intensivos de produção de bovinos.
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Alfalfa Response to Phosphorus Sources Associated with the Application of Liming and Gypsum-Shoot Numbers
Alfalfa (Medicago sativa L.) was grown in a Typic Mapluolox soil with triple superphosphate (TS), Gafsa phosphate (GP) and GP with gypsum (GP + G). Three rates of phosphorus application were used 50, 100 and 200 mg P dm-3, before and after liming. Alfalfa was harvested three times. Basal and axillary shoot numbers in alfalfa increased with increasing phosphorus rates. Shoots were produced in higher number with GP in comparison with TS. GP + G resulted in higher basal shoot number than GP. However, there was no gypsum effect on axillary shoot numbers. Liming before or after TS, GP and GP + G application had similar responses on shoot numbers
Nitrogen dynamics in the intact grasses Poa trivialis and Panicum maximum receiving contrastaing suplies of nitrogen.
Correlação do solo e fertilização de pastagens em sistemas intensivos de produção de leite.
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Correção do solo e fertilização de pastagens em sistemas intensivos de produção de leite
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Adaptation of the C4 grass Panicum maximum to defoliation is related to plasticity of N uptake, mobilisation and allocation patterns.
Dry mass production and persistence of Panicum maximum pastures depends on nitrogen supply. Defoliation influences N uptake and allocation patterns yet its effects on plasticity of N dynamics in P. maximum have not been investigated. Stable isotopes of N (15N) were used in order to test the hypothesis that defoliation in terms of proportion of the leaf area removed effects N mobilisation, uptake and allocation patterns in P. maximum. The plants were initially cut weekly to a height of either 0.15 m or 0.30 m for seven weeks. Eight weeks after the first defoliation, all plants were defoliated for a final time to remove 0, 25, 50, 75 or 100 % of the area of each individual leaf blade of the main tiller. Root N uptake was reduced when all leaf area was removed, but more lenient defoliation improved N uptake due to a positive effect on specific N uptake. Young leaves, side tillers and roots were the main sinks for N from root uptake. Roots of P. maximum became a net source of N for mobilisation immediately after severe defoliation. Root uptake was the main source of N for new growth in P. maximum plants. Allocation pattern of mobilised N was different from that of N derived from root uptake. It was concluded that adaptation of P. maximum to defoliation is related to plasticity of N uptake, mobilisation and allocation, but changes in N dynamics did not offset negative impacts of complete defoliation of the plants
Características morfogenéticas e taxa de acúmulo de forragem do Capim-Mombaça submetido a três intervalos de pastejo.
O objetivo deste trabalho foi avaliar características morfogenéticas e a taxa de acúmulo de forragem em pastos de capim-Mombaça submetidos a três intervalos de pastejo (28, 38 e 48 dias) entre outubro de 1995 e setembro de 1996. O delineamento experimentalfoi o de blocos completos ao acaso com arranjo em parcelas subdivididas no tempo. Foram avaliadas as taxas de alongamento e senescênciafoliar, a taxa de alongamento das hastes, a densidade populacional de perfilhos e a altura do pasto. Essas informações permitiram estimara taxa de acúmulo líquido de matéria seca. A taxa de alongamento de hastes e folhas seguiu comportamento estacional, sendo mais elevadanos meses de maior temperatura e precipitação. A taxa de senescência foliar foi maior com 48 dias de intervalo de pastejo e praticamentenula entre maio e setembro. O cultivar Mombaça deve ser pastejado com, aproximadamente, 28 dias no período de outubro a maio e 48dias entre maio e setembro. O manejo do capim-Mombaça não pode ser orientado apenas pelos valores de taxa de acúmulo de matériaseca, sendo necessários estudos sobre as perdas de pastejo e sobre os efeitos da presença das hastes na eficiência de pastejo, consumoe qualidade de forragem, a fim de se determinar melhor o manejo deste capim
Resposta de pastagens de capim-marandu em solo de cerrado à adubação com nitrogênio, em condições de sequeiro. ou sob irrigação
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GRB 970228 Within the EMBH Model
We consider the gamma-ray burst of 1997 February 28 (GRB 970228) within the
ElectroMagnetic Black Hole (EMBH) model. We first determine the value of the
two free parameters that characterize energetically the GRB phenomenon in the
EMBH model, that is to say the dyadosphere energy,
ergs, and the baryonic remnant mass in units of ,
. Having in this way estimated the
energy emitted during the beam-target phase, we evaluate the role of the
InterStellar Medium (ISM) number density (n) and of the ratio between the effective emitting area and the total surface area of the GRB
source, in reproducing the observed profiles of the GRB 970228 prompt emission
and X-ray (2-10 keV energy band) afterglow. The importance of the ISM
distribution three-dimensional treatment around the central black hole is also
stressed in this analysis.Comment: 4 pages, 1 figure, to appear in the Proceedings of the Los Alamos
"Gamma Ray Burst Symposium" in Santa Fe, New Mexico, September 8-12 2003 (AIP
Conf. Ser.), CHAPTER: GRB Connection to Supernova
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