Title: Tillering dynamics in kikuyu and tall fescue grass swards cultivated in association.

 

Abstract: In regions of subtropical climate the use of warm and cool season perennial grasses may be an alternative to maintain forage production practically during all the year. However, when grown in association, the management practices should favor the persistence of the species in the system. Therefore, the objective of this work was to test the hypothesis that grazing management strategies modulate the population dynamics in kikuyu and tall fescue pastures cultivated in association. Four treatments were implemented in a randomized complete block design, in a factorial scheme (2 x 2), with three replications. The treatments were composed by two pre- grazing heights: 15 and 20 cm (factor A) and two strategies of spring management: grazing or not the pasture to a residue of 6 cm (factor B) applied only once in the mid November. The severity of defoliation used was the removal of 40% of the initial height (residues of 9 and 12 cm, for treatments of 15 and 20 cm, respectively). In order to quantify tiller population density (TPD), leaf area index (LAI), forage mass and average weight per tiller (TW), forage samples were collected at 3 points in a 0.24 m2 quadrat. The tillering demography was obtained by counting, in a monthly basis, the number of new and dead tillers in rings with an area of 0.0314 m², through which the tiller appearance and mortality rates were calculated, as well as the stability index (SI) of the pasture. The lowering of pastures in the spring favored the recovery of the kikuyu grass in summer, with increases in forage mass and LAI, whereas for the tall fescue, there was an increase in TPD during the winter in the spring lowered grasses. Pastures managed with 15 cm show a larger tiller population independent of the spring management of pasture. The tall fescue presented a reduced tillering pattern during the summer, with the emission of new tillers in the winter period, and was characterized by longer-lived tillers, whereas kikuyu grass presented a higher rate of appearance of tillers during the summer, but with shorter-lived ones. These two distinct patterns of tillering led to transient population instability in mid-March and another following frost events, which was quickly circumvented by the winter population recovery of tall fescue. Spring hard grazing increased kikuyu grass population in the summer, without compromising the tillering of the tall fescue in the following winter. Spring hard grazing of the pastures proved to be an effective tool to favor the persistence of a mixture composed by tall fescue and kikuyu grass swards.

 

Keywords: Production stability; Forage grasses; Spring management.

 

Author: Fábio Luís Winter

Leader: André Fischer Sbrissia

Dissertation (Masters in Vegetal Production)

​

​

​

​

Title: Flow of tissues in canine grass profiles (Andropogon lateralis Ness) submitted to different heights of management.

 

Abstract: Areas with natural grasslands are part of a region located under a vast territorial extension that includes much of southern Brazil, Argentina, Paraguay and Uruguay. In spite of its ecosystemic importance and territorial representativeness, in the last years there has been a systematic reduction in the area occupied with this vegetation, replaced mainly by agricultural and forestry crops. Most natural grassland areas are not adequately managed, which reduces the productive potential of the plant. Thus, this study aimed to evaluate the morphogenic and structural characteristics of tillers of the Andropogon lateralis Nees species. subjected to different heights of management. The central hypothesis of this study is that management heights do not affect the tissue flow of this species. The experiment was conducted in an area of the Experimental Station of Agricultural Research and Rural Extension Company of Santa Catarina (Epagri), in Lages, during two evaluation periods: i) from February to April 2017; ii) from December 2017 to February 2018. The experimental area consists of a natural pasture with a predominance of cane grass, comprising 10.500m², divided into 12 paddocks of 875m² each. The treatments corresponded to four management heights based on A. laretalis, (pre-grazing heights of 12, 20, 28 and 36 cm), with three repetitions. The grazing management was carried out under intermittent stocking with beef cattle in order to reduce the height of the pasture in 40% of the pre-grazing height (residue heights: 7.2, 12, 16.8 and 21.6 cm, respectively). The experimental design was a randomized block design. In order to evaluate the morphogenic characteristics, the tagged tillers technique was used, which consists of the identification and evaluation of 20 tillers in each experimental unit, with measurements throughout the entire period of data collection. Leaf elongation (LER), senescence (LSR) rates, phyllochron (Phy) and tiller population density (TPD) presented different values between the evaluation periods. Thus, in the first period, only the phyllochron varied according to the treatments (P = 0.0008), with the highest values observed in the grasses managed with 28 cm, smaller in the 12 cm and intermediate in the 20 or 36 cm. In the second evaluation period, the LER and LSR were larger and equivalent to each other in the pastures managed with 28 and 36 cm (P = 0.0095 and P = 0.0084, respectively), the TPD was high and equivalent in a larger height range, 20-36 cm (P = 0.0316) and Phy was not affected by treatments (P> 0.05). Thus, it is concluded that in fields with predominance of Andropogon lateralis in low fertility soils, the management height modulates the morphogenic characteristics and, therefore, affect the productive characteristics of this pasture.

​

Keywords: Natural grassland; Morphogenesis; Pasture management; Plant growth.

​

Author: Lorena Karine Gomes Noronha

Leader: André Fischer Sbrissia

Dissertation (Masters in Vegetal Production)