Title: Dynamics of forage accumulation and cattle selectivity in mixed pastures of kikuyugrass and tall fescue

 

Abstract: In regions with subtropical climate, such as southern Brazil, mixed canopies composed by warm-season and cool-season perennial grasses is an alternative to the current grassland-based animal production systems. However, little is known about the relations between canopy management and forage production in the pastures formed from this mixture. This research tested the hypothesis that the canopy height management and a strategic autumn grazing to 7 cm height alter the dynamics and stability of forage production of a mixture composed by kikuyugrass and tall fescue, perennial grasses with different physiological pathways (C4 and C3, respectively). Besides that, in a grasses mixed canopy, the animal can select any of the species of the mixture, in this sense, our hypothesis is that the animals select kikuyugrass in relation to tall fescue, during the summer period. The main goal of this research was to find a grazing management strategy for mixed pastures of kikuyugrass and tall fescue that allows better distribution of forage production throughout the year. Two experiments were carried out in a randomized complete block design, in a factorial arrangement (2×2), with three replicates. The first experiment was conducted during the first two years of the mixture implantation (October 2015 to October 2017). In this case, the factorial arrangement consisted of two canopy height managements (12 and 17 cm) associated or not with an autumn grazing to 7 cm height. The second experiment was conducted in January 2018 and January 2019, in which, the factorial arrangement was composed by two pre-grazing heights (15 and 20 cm) associated or not with a single spring grazing to a residue of 6 cm. In the first experiment, the autumn grazing to 7 cm increased the net forage accumulation rate of the mixture. However, this increase did not compensate the delay of 90 to 120 days to regrowth of 12 and 17 cm canopy heights. In the second year of evaluation (2017), tall fescue was the dominant species in all treatments. The kikuyugrass and tall fescue mixture showed productive potential in the first year of evaluation. However, the results suggest the need for suitable nitrogen fertilization for both species, in order to guarantee the kikuyugrass persistence in the mixture. In the second experiment, the hypothesis was confirmed, in which, grazing cattle select kikuyugrass in relation to tall fescue in the mixture, in the summer

 

Keywords: Canopy height, Perennial grass, Morphogenesis, Forage selection.

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Author: Angela Bernardon

Leader: André Fischer Sbrissia

Thesis (Doctors in Animal Science)