Title: Relationship between defoliation intensities and the productive potential in pastures of quicuiu grass, annual ryegrass and black oats

 

Abstract: This work was based on the hypothesis that the intensification of pasture based animal production requires a de-intensification of the proportion of harvested forage favoring productive aspects of the forage plant and that the ecological mechanisms of tiller size/density compensation can act antagonistically on the LAI among species of forage grasses. The objective of this work was to evaluate the relationships between the pasture structure created by defoliation strategies by means of the proportion of defoliation at heights based on maximum management targets, as well as to determine the productive capacity of the pastures by determining the rate of accumulation in one warm perennial grass and two cool season annuals grasses submitted to cut and / or grazing in intermittent and continuous stocking methods. Two experiments were carried out: experiment 1 consisted of three trials and evaluated the effects of lenient (L, 20%), moderate (M, 40-50%), severe (S, 60%) and extremely severe (ES) defoliation intensities on leaf area index (LAI), forage accumulation rate (FAR), mean accumulation rate (FARm), height at maximum average rate of accumulation (HFARmmax), and tiller population density (TPD) contribution and average leaf area per tiller (La) in the LAI increase along the regrowth in pastures kept under intermittent stocking. Trial I was carried out in the summer of 2014 with kikuyu grass (Pennisetum clandestinum Hochst ex Chiov) being grazed at 40, 50, 60 and 70% from a pre-grazing height of 25 cm according to a experimental design in randomized blocks with three replicates; Trial II was performed in winter and spring of 2014 with annual ryegrass (Lolium multiflorum Lam. Cv. Common) being defoliated by mechanical cutting at 20, 40, 60 and 80% of the initial stipulated height of 20 cm in a completely randomized design with four replicates, and trial III in black oats pastures was composed of the combinations between three severities performed by cuts of 40, 60 and 80% of the initial height of 25 cm and two doses of nitrogen (N) 50 kg of N.ha-1 and 150 kg of N.ha-1 in a completely randomized design in factorial arrangement (3x2) with three replicates. Experiment 2 was conducted in two trials with the objective of evaluating the tiller size/density relationships mechanisms in two forage species and to test if variations in LAI, Af and TPD could explain variations in the productive potential index (PPI) in pastures submitted to different cutting heights simulating continuous stocking. Trials I and II of experiment 2 were conducted in a completely randomized design. Trial I was constituted of four strategies of management of quicuiu grass (7.5; 15; 22.5 and 30 cm) in the summer and fall of 2014 with three replicates of pastures grazed by cattle. In the second trial, annual ryegrass was evaluated in the winter and spring of 2015 submitted to cuts management, where the treatments corresponded to heights of 6, 12, 18, 24 and 30 cm with four replications. In the experiment 1 in both trials FAR was higher with L and M management, which ranged from 135 to 150 kg of MS.ha-1 .day-1 compared to the S and SM managements (50 to 100 kg of MS.ha-1 .day-1 ). Defoliated pastures S and ES showed HFARmmax greater than the L and M defoliated pastures. Larger increases in Tam are favored more by increases in La than in TPD. In experiment 2, Kikuyu grass showed the same LAI (6.5) at heights of 7.5; 15 and 22.5 where the plant adjusted the LAI by increments in La and TPD, allowing the plant to be managed in severe defoliation in comparison to annual ryegrass pastures when submitted to continuous stocking. The annual ryegrass in experiment 2 and all grass species of experiment 1 had an inverse relationship between height and PPI. In conclusion, severe defoliation reduces the productive capacity of pastures in both stocking methods.

 

Keywords: Leaf Area Index; Average leaf area; Tiller population density; Defoliation severity; Selfthinning; Sward productivity index.

 

Author: Clovis David Medeiros Martins

Leader: André Fischer Sbrissia

Thesis (Doctors in Animal Science)

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Title: Productive aspects and population stability in perennial grasses with different growth strategy grown as monocultures or mixture.

 

Abstract: Pastures are multifunctional ecosystems and their benefits could be enhanced when species with contrasting characteristics are grown mixed. In this way, it is necessary that populations of the different species persist in order to maximize ecosystem services, although, generally, the species most likely to capture the limiting resource will exclude those that are less competitive. Thus, this thesis aimed to test the central hypothesis that perennial grasses of different functional types can coexist and compose stable and productive mixed swards in a fertile environment with frequent and lenient defoliation. Three species with different size/shapes and contrasting growth strategies (Arrhenatherum elatius SCS314 Santa Vitória, Dactylis glomerata Ambar and Festuca arundinacea Quantum II) were cultivated for three years in monocultures and in a mixture of them. After establishment of plant communities (first year), all grasses were fertilized to maintain high levels of soil fertility and managed by frequent and lenient defoliation (defoliation when the pastures intercepted a maximum of 95% of incident light and cut down to 50% of its corresponding heights). Populations of A. elatius, D. glomerata and F. arundinacea were stable both, in monocultures and mixed swards, so that the four pastures had the same population stability index throughout the year (PSI = 1.06; P = 0.9738 ). Tiller dynamics of each species was similar when grown in monoculture or mixed and, in general, the highest mortality and birth tiller rates occurred in A. elatius and the lowest in F. arundinacea. Therefore, the proportion of species in the mixture was the same throughout the experimental period. The mixture showed the same production of the most productive monocultures, even with 68.1% of its post-cut biomass being composed by D. glomerata, the species with lower production in monoculture. Although transgressive overyielding was not observed, the mixture and D. glomerata showed the greatest productive stability. Arrhenatherum elatius and F. arundinacea presented overyieldings and, even representing the lower proportion of the mixture swards, were responsible for the overyieldings of the mixture. For the three species the overyieldings were more influenced by the production of leaves. The results presented here indicate the possibility of using perennial grasses with contrasting growth strategies to form stable and productive mixtures while maximizing leaf production when managed intensively.

 

Keywords: Complementarity, botanical composition, intercrop, monoculture, overyielding, tiller dynamic

 

Author: Paulo Gonçalves Duchini

Leader: André Fischer Sbrissia

Thesis (Doctors in Animal Science)