Title: Productive stability of mixtures of tropical grasses submitted to rotational grazing. 

 

Abstract: Recent studies have shown that the functional complementarity of cultivated species in grass mixtures in temperate regions generates environments with greater productive capacity, especially during a period of reduction in resource availability. From this premise it is possible to assume that the cultivated tropical climate grasses can appear as beneficial effects, with positive results on the production of wood for the joint construction of the regions. Thus, the objective of this study was to evaluate the stability of the strategies among the species submitted to management strategies, testing the following hypotheses: i) the mixtures between grasses attenuate the productive seasonality commonly observed in monocultures; ii) the productive capacity of mixtures composed of tropical climate grasses is directly related to the different forage canopy structures formed by these mixtures; iii) grazing management influences the productive capacity and stability of tropical grass mixtures. The experiment consisted of two mixtures of grasses (Mixture A: Panicum maximum BRS Zuri, Brachiaria brizantha cv. Xaraés and Brachiaria decumbens cv. Basilisk; Mixture B: Panicum maximum BRS Kenya, Brachiaria brizantha BRS Marandu and Brachiaria brizantha BRS Paiaguás) and one monoculture (Panicum maximum BRS Zuri). The experimental design was completely randomized with three replicates and five treatments (T1-T5), consisting of the following monoculture: monoculture managed with 80 cm of pre-grazing height and lowered to 50% of that height (T1), the mixture A was managed with 70 cm of pre-grazing height and lowered to 40% (T2) and 60% (T3) of that height, mixture B managed with 60 cm of pre-grazing height and lowered to 40% (T4) and 60 % (T5) of that height. The experimental period lasted 20 months, beginning in July 2017 and ending in February 2019. The forage mass, botanical composition and population density of tillers (DPP) were estimated by means of six 1- m² samples (1m × 1m) per picket. Forage accumulation was estimated by the difference in forage mass between pre-grazing of the current cycle (n) and post-grazing of the previous cycle (n-1). The means of grass mixtures and their respective management strategies were grouped and contrasted with the monoculture averages (T1 × [T2 + T3 + T4 + T5]), with the aid of the CONTRAST function of GLM (General Linear Model) procedure statistical package SAS (Statistical Analysis System, version 9.2). Subsequently, the means only of the grass mixtures and defoliation severity were grouped in factorial arrangement and the analysis of variance was performed through the PROC MIXED of the statistical package SAS. The averages were compared through the "LS MEANS", adopting the level of 10% of significance. From the first water season, the DPP of the mixtures was higher than that of the monoculture as well as the vegetal cover that, after the drought in 2018, was higher in the mixtures. The mixtures showed higher post-grazing LAI and higher root mass and distribution during the drought of 2018 when compared to monoculture, a fact probably responsible for the higher forage accumulation rate during this period and lower seasonality of forage production throughout the year. The mixtures with different structures presented similar productive capacities, regardless of whether they were defoliated at 40% or 60% of pre-grazing height, although more severe management resulted in lower soil cover by the forage canopy.

 

Keywords: Grass mixed; productive seasonality; tropical grasses; biodiverse pastoral environment; multifunctional pastures; biodiverse pastures.

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Author: Cauby de Medeiros Neto

Leader: André Fischer Sbrissia

Thesis (Doctors in Animal Science)

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Title: Grazing management strategies and their implications on the vegetation dynamics in a natural pasture with predominance of Andropogon lateralis Nees.

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Abstract: For conservation of native pasture is essential the use of management strategies that optimize the forage production without harming the plant species diversity. The objective of this study was to verify the effect of different grazing management strategies on the productive and ecological aspects of a native pasture with predominance of Andropogon lateralis Nees, commonly found in southern South America rangelands. The treatments were composed of four pre-grazing heights, 0.12, 0.20, 0.28 and 0.36 m, based on the predominant specie, and severity of 40% of pre-grazing height. The experimental design was in randomized blocks, with four replications. Ecological and productive aspects (Article 1), the vegetation dynamics (Article 2) and aspects related to the dominance and persistence of A. lateralis in natural pastures (Article 3) were verified during two consecutive years. Forage accumulation did not differ among management heights, due to adjustments in the plant community and functionality of the dominant specie. The increase in management height promoted greater dominance of A. lateralis and consequently reduction in richness and diversity of plants. A. lateralis presents resistance of clump and high phenotypic plasticity, which promotes its dominance and guarantees its persistence in natural pastures. In natural pastures with predominance of Andropogon lateralis Nees, it is important to maintain high grazing intensities that promote the reduction of its dominance. Canopy heights between 0.12 and 0.20 m of A. lateralis were adequate to grazing management because it maintains the accumulation of forage and favors the floristic diversity.

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Keywords: Management height; species diversity; clumps.

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Author: Pablo Giliard Zanella

Leader: André Fischer Sbrissia

Thesis (Doctors in Animal Science)