This study aimed to contribute to the understanding of the morphogenesis and structure of signal grass (<i>Brachiaria decumbens</i> Stapf.) pastures, and how they are affected by the environment and cattle defoliation. A diagrammatic model was adopted to identify and relate the major morphogenetic and structural characteristics at different levels of organisation of the sward: phytomer, tiller, plant and population. The morphogenetic characteristics studied were leaf elongation rate (LER) and internode elongation rate (IER) at the phytomer and tiller level, leaf senescence rate (LSR) and leaf appearance rate (LAR) at the tiller level, and tiller birth rate (TBR) and tiller death rate (TDR) at the plant and population level. The structural characteristics analysed were length of phytomer components (blade, sheath and internode), number of phytomers per tiller, total length and number of live blades per tiller, number and size-age distributions of tillers per plant, and number and size distribution of plants and tillers per area. Experiments to analyse the effects of temperature, nitrogen application, season and defoliation intensity on sward structural and morphogenetic variables were performed under controlled and field conditions, and using destructive and non-destructive measurements. An initial experiment under controlled environments showed highest LAR, LER and IER values at 30°C, and strong mutual regulations between morphogenetic and structural characteristics at the phytomer and tiller levels. The effects of cattle grazing and nitrogen fertilisation on the dynamics of signal grass morphology, and the patterns of defoliation were monitored during one year in long established pastures in Santa Cruz, Bolivia. Plant population demography were mainly defined by the season: high number of seedlings and new vegetative tillers at the beginning of summer; new vegetative tillers, plant fragmentation, and flowering during summer (wet season); and low tiller and plant densities with low proportions of live leaf towards the following winter. Defoliation affected only the phytomer level of organisation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:642264 |
| Date | January 2001 |
| Creators | Busqué, Juan |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/27624 |
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