Title: Morphogenesis and dynamics of forage accumulation in perennial winter pastures cultivated pure or in mixture. 

 

Abstract: This thesis tested the central hypothesis that perennial winter grasses with different growth strategies cultivated in a mixture and managed with frequent and lenient defoliation and in fertile habitat can coexist and present forage production similar to the monoculture of the most productive species. The objective of this work was to evaluate the morphogenesis and structural characteristics and the dynamics of forage accumulation in pure and mixed winter perennial grasses. Three winter perennial grasses with different forms/sizes and competitive abilities were used: Arrhenatherum elatius L. cv. SCS314 Santa Vitória, Dactylis glomerata L. cv. Ambar and Festuca arundinacea Schreb. The experiment was conducted in a completely randomized design with four treatments (corresponding to the pure cultivation of the three species and the mixture of the them) and three replications. The pastures received the same management of fertilization and cut (defoliated when they reached a maximum of 95% of interception of the incident light and the severity of 50% of the pre-cut height, which corresponded to 20 cm and 10 cm of average canopy height, respectively). Between 2014 and 2016, the morphogenetic and structural characteristics of the pastures were evaluated through the marked tillers technique, tiller population density and leaf area index pre and post cutting by means of destructive sampling. From data obtained via tissue flow and tiller population density was estimated forage accumulation rate. Morphogenesis data were submitted to two multivariate methods: factorial and cluster analysis. Three factors were generated by the factorial analysis, in which the first one showed a positive association of A. elatius with species characterized by a higher rate of tissue turnover and inversely for F. arundinacea. In the second factor D. glomerata presented positive relation characteristics of species with growth strategy based on competition for resources. In the third factor, plants cultivated in mixture, independent of the species, showed negative correlation with final leaf length. It was possible by the analysis of clusters and the construction of a dendrogram, to verify that each species belongs to different groups, correlating the variables with the competitive ability of each one. A. elatius and D. glomerata, so-called competitor and resource-users, had a smaller euclidean distance between them and a greater distance from the group constituting F. arundinacea, a resource conserving plants. We observed that there were not, for any species and variable analyzed, differences related to the form of cultivation (pure or in association). Pastures of the mixture showed accumulation of forage similar to the most productive monocultures (A. elatius and F. arundinacea). The dynamics of forage accumulation of each species occurred by different routes, according to the competitive ability of each species. The species A. elatius and D. glomerata invest in leaf elongation while F. arundinacea in low leaf senescence. In pastures of the mixture, the species D glomerata presented the highest proportion in the forage accumulation and in the population density of tiller. We conclude that perennial winter species cultivated in fertile environments, intensively managed and with different competitive abilities, when cultivated pure or in association, do not present morphogenic and structural differences. The forage yields of the mixture were similar to the most productive monocultures.

 

Keywords: Biodiverse environments; Growth strategy; Leaf elongation; Leaf senescence; Tissue flow.

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Author: Joilson Roda Echeverria

Leader: André Fischer Sbrissia

Thesis (Doctors in Animal Science)

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Title: Dynamics of tillering and forage accumulation in pastures of Pennisetum clandestinum and Fescue arundinacea cultivated in association.

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Abstract: The objective of this work was to evaluate tillering dynamics, populational stability and forage accumulation in pastures of Pennisetum clandestinum and Festuca arundinacea grown in association under different grazing management strategies. The experiment was conducted at Centro de Ciências Agrovetrinárias of the Santa Catarina State University, Lages, SC, Brazil. The treatments consisted of five grazing management conditions (7; 12; 17; 12/7 and 17/7), and in three of them, the pastures were maintained at 7, 12 and 17cm canopy heights throughout the whole experimental period. The other treatments, 12/7 and 17/7, refer to combinations of heights of 12 and 17 cm with a strategic grazing down to 7 cm in autumn, exclusively in the month of May. After the strategic reduction, they were allowed to return to their original heights (12 and 17 cm) which were maintained until the following autumn, where the same procedure was performed again. The experimental design was in randomized complete blocks with three replicates. Tillering dynamics was evaluated in PVC circles of 20 cm diameter fixed to the ground by means of metal clips. In addition, the rates of emergence and survival of tillers and the relationships between them were evaluated. Forage accumulation was evaluated through the use of exclusion cages technique. The botanical composition was obtained from samples of forage mass estimates collected with the aid of metallic frames with a surface area of 0.24 m2 . The Kikuiu grass presented a pattern of tiller renewal mostly in summer, however, the number of tillers per generation and the longevity of them decreased as the canopy height increased. The tall fescue plants presented a pattern of winter renewal, in addition, the number of tillers per generation and the longevity of the same were similar in the treatment conditions of 12, 17, 12/7 and 17/7. During the year 2016, the pastures presented transient instability during the autumn. In the year 2017, population increases were observed during the winter season in all management conditions. Forage accumulation was similar among all treatment in both evaluation years. During the year of 2016, the greatest accumulation of forage was recorded during the winter/spring season and in 2017, the greatest accumulations of forage were observed during the summer and winter/spring seasons. The Festuca arundinacea cv. Rizomat coexists with Pennisetum clandestinum at management heights ranging from 7 to 17 cm. The autumn grazing down does not alter the forage accumulation in pastures of Pennisetum clandestinum and Festuca arundinacea cv. Rizomat grown in association managed at heights between 12 and 17 cm.

 

Keywords: Coexistence between plants; Botanical composition; Population demography; Perennials grasses C3 and C4.

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Author: Tiagoo Miqueloto

Leader: André Fischer Sbrissia

Thesis (Doctors in Animal Science)