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| Author(s): |
Larissa Fernanda Garcia Carvalho
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: | 2023-08-04 |
| Examining board members: |
Sila Carneiro da Silva;
Rodrigo Amorim Barbosa;
André Fischer Sbrissia
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| Advisor: | Sila Carneiro da Silva |
| Abstract | |
Forage grass species can be grouped into functional groups (e.g. contrasting strategies of growth and perennation) which combined to form mixed pastures may result in reduced intraannual variation and increased herbage production, maximizing the productive potential of pastoral grazing systems. However, information regarding tropical pastures is almost nonexistent, since the large majority of the research has been conducted using forage plants from sub-tropical and temperate climate. The hypothesis of this study was that perennial tropical forage grasses that explore contrasting and complementary niches (e.g. resource conservation vs resource capture plants) may be used to compose stable, persistent and productive mixtures when cultivated in fertile environments and subjected to frequent and nonsevere defoliations. The objective was to evaluate population persistence, herbage production and productive stability of three perennial tropical forage grass species of contrasting growth strategies cultivated as monocultures and in association under a common intermittent defoliation regime. The experiment was carried out in Piracicaba, São Paulo, Brazil, from January 2020 to March 2022. Treatments corresponded to three perennial tropical forage grass species, Andropogon gayanus cv. Planaltina (andropogon grass), Panicum maximum cv. Massai (massai grass), and Brachiaria brizantha cv. BRS Piatã (piata grass) cultivated in monoculture and in association (the three grass species in equal proportions based on the number of viable seeds), and were allocated to experimental units (12 x 15 m paddocks) according to a complete randomized block design, with four replications. Defoliation management was common to all treatments and corresponded to a pre-cutting height of 35 cm and post-cutting of 17.5 cm. Piatã and massai grass showed the greatest rates of tiller appearance and death (turnover) during late spring and summer and smallest during autumn/winter/early spring. Andropogon grass showed rates of tiller appearance relatively stable throughout seasons of the year and smaller tiller death rate (greater survival rate) during autumn/winter/early spring. In the association, all forage grasses showed high tiller turnover during late spring and summer and low during autumn/winter/early spring, although with different timings for the transition from one strategy to another, which resulted in small seasonal fluctuations modulated by competition for light, as a temporal complementarity ensuring small variations in species populations. As consequence, population stability in the association was greater than in monocultures, and it was characterized by a smaller variation in tiller population density and tillering throughout the year. Plant population in the association was younger and with lesser variation in tiller age categories. There was no difference in tiller death and survival rate of plants when cultivated as monocultures or in association, with the greatest rates of tiller survival for all species recorded during autumn/winter/early spring, ensuring population stability during this season of the year. The botanical composition of the association remained relatively stable during the entire experimental period, with predominance of massai grass, followed by piatã grass and then andropogon grass (overall average of 70, 20 and 10%, respectively). Besides the differences in sward hergabe mass among grass species, net herbage accumulation rate and total forage yield were similar for the monocultures and the association. There was no variation in intra-annual herbage production neither overyielding for the association. Among the species comprising the association, piatã grass showed overyielding of leaves during summer and andropogon grass showed underyielding of stems during autumn/winter/early spring. The association allowed conditions for coexistence, with botanical composition relative stable throughout the year and between years, and herbage production and productive stability (intra-annual variation) similar to the monocultures. (AU) | |
| FAPESP's process: | 19/27582-6 - Association of perennial tropical forage grasses: potential of herbage production and stability and dynamics of tiller population |
| Grantee: | Larissa Fernanda Garcia |
| Support Opportunities: | Scholarships in Brazil - Doctorate |