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| Author(s): |
Márcio André Stefanelli Lara
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 2011-04-15 |
| Examining board members: |
Carlos Guilherme Silveira Pedreira;
Luis Gustavo Barioni;
Durval Dourado Neto;
Flavia Lucila Tonani de Siqueira;
Cacilda Borges do Valle
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| Advisor: | Carlos Guilherme Silveira Pedreira |
| Abstract | |
In order to understand and describe forage growth knowledge is needed on their agronomical and physiological aspects as well as their responses to soil and climate. Developing tools that enable the rationalization of these relationships is important both under an academic (e.g., in studies of growth dynamics) and a practical (management and decision making in productions systems) standpoints. The objective of this study was to evaluate the agronomic, morphological and physiological responses of five genotypes of Brachiaria spp. and to develop growth models based on thermal sum (growing degree-days, GDD) and daylength (photothermal unit, PU) as well as to adapt the CROPGRO-Forage model, aiming at evaluating the potential of this resources in forage research and production. Four genotypes of Brachiaria brizantha (Hochst. ex A. Rich.) Stapf (Marandu, Xaraés, Arapoty, and Capiporã) and one of B. decumbens Stapf (Basilisk) were harvested at 15 and 7.5 cm over 11 cycles in one year. The experimental units (9 x 4 m plots) were irrigated and fertilized with the equivalent to 220 kg ha-1 yr-1 of N and K2O. The experimental design was a randomized complete block in split-plot with four replications. Total annual and seasonal forage yields were calculated. One mid-summer and one mid-winter regrowths were monitored weekly to describe stubble mass, tissue flow, forage accumulation rate and the rates of leaf photosynthesis, which were used to simulate canopy photosynthesis. Capiporã and Xaraés were more productive during the summer, but in winter there was no difference among genotypes in yield. Clipping at 7.5 cm yielded more forage for all genotypes and under this management, plants showed the highest growth rates at the tiller level, expressed as higher leaf appearance and elongation rates. There was also higher tiller turnover under these conditions. Despite the differences in forage yield among grasses rates of canopy photosynthesis were similar within the two clipping heights within each season, suggesting the operational of a compensatory mechanism between leaf area and photosynthesis per unit of leaf area. The accumulation models based on GDD and PU showed good fit to observed forage production. The PU model was effective in predicting the productivity of Brachiaria grasses. The adaptation of the CROPGRO-Forage model suggests it is an efficient tool to integrate physiological aspects of B. brizantha and can be used to simulate yield with good accuracy. (AU) | |