Full text
| |
| Author(s): |
André Fischer Sbrissia
Total Authors: 1
|
| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 2004-04-07 |
| Examining board members: |
Sila Carneiro da Silva;
Moacyr Corsi;
Anibal de Moraes;
Carlos Nabinger;
Carlos Guilherme Silveira Pedreira
|
| Advisor: | Sila Carneiro da Silva |
| Abstract | |
Brazil is a unique environment for developing efficient and sustainable pastoral systems of animal production. Advances in this area have been modest however, resulting in slow progress and revealing deficiencies of the current conceptual basis used for interpreting results from research, particularly those related to the dynamic and systemic characteristic of plant and animal responses to management in pastoral ecosystems. Against that background, the objective of this experiment was to study the morphogenesis, characteristics of individual tillers and tillering and herbage accumulation dynamics in Marandu grass swards continuously stocked by cattle. The experiment was carried out at Departamento de Zootecnia, USP/ESALQ, Piracicaba, SP, from November 2001 to December 2002. Treatments corresponded to four steady state sward conditions (10, 20, 30 and 40 cm sward surface height) and were allocated to experimental units according to a complete randomized block design with four replications. Morphogenetic traits and herbage accumulation dynamics were evaluated on 30 marked tillers per experimental unit. Measurements were performed every 3 or 4 days during the summer and at intervals no longer than 10 days during the winter and early spring. Characteristics of individual tillers were monitored on 60 tillers harvested in areas representative of the sward condition at the time of sampling. The following variables were recorded: tiller weight, volume, leaf area, leaf: stem ratio and leaf area: volume ratio. Tillering dynamics was evaluated within 30-cm diameter PVC rings anchored to the soil. Every 30 days, rates of tiller appearance, survival and death were determined and associations between them derived. The highest and the lowest phyllochron values were recorded for the 40 and 10 cm swards, respectively. There was a seasonal effect characterized by highest values during early spring and lowest values during late spring and summer. Short swards showed higher tiller population densities of small tillers than tall swards and vice-versa, indicating the existence of a tiller size/population density compensation mechanism. Tiller population stability analysis indicated that population density alone cannot be used as an index for characterizing pasture persistence and productivity. Linear coefficients of the Log x Log regression between tiller population density and mean tiller weight revealed no advantages for keeping Marandu grass pastures taller than 30 cm. Additionally, net herbage accumulation was maximized between 20-30 cm during the summer and 10-20 cm during periods of low rainfall and mild temperatures, indicating that Marandu grass has seasonal grazing management requirements. (AU) | |