Componentes da biomassa e características estruturais em capim-aruana sob diferentes frequências e intensidades de desfolhação

Abstract

Resumo -O objetivo deste trabalho foi avaliar o efeito de frequências e intensidades de desfolhação sobre os componentes da biomassa e a estrutura do dossel em capim-aruana (Panicum maximum 'Aruana IZ-5'), pastejado sob lotação rotativa com ovinos. Avaliaram-se duas frequências de desfolhação (FD), com níveis de interceptação de 85 e 95% da radiação fotossinteticamente ativa (Irfa) incidente no topo do dossel, e duas intensidades de desfolhação (ID), com índices de área foliar residual (IAFr) de 1,0 e 1,8. Utilizou-se o delineamento inteiramente casualizado, com arranjo fatorial 2x2. Os componentes da biomassa e as características estruturais nas condições de pré-pastejo foram afetados principalmente pela FD, com a redução da biomassa de colmos verdes e de forragem morta, e, ainda, pela elevação da altura da primeira lígula viva. Pastos manejados com menor FD proporcionaram menor relação lâmina foliar/colmo, com média de 1,65, e os pastos com maior FD apresentaram média de lâmina foliar/colmo de 2,40. Os componentes da biomassa residual foram afetados pela ID, com maior biomassa de forragem verde residual em pastos manejados com IAFr de 1,8. Os pastos manejados com 95% de Irfa e IAFr de 1,8 apresentaram biomassa de colmo verde residual e biomassa de forragem morta residual superiores aos dos demais manejos. Para pastejo por ovinos, o capim-aruana deve ser manejado com frequência de 85% de Irfa e intensidade de desfolhação correspondente a IAFr de 1,0.Termos para indexação: Panicum maximum, altura do dossel, índice de área foliar residual, intercepção da radiação fotossinteticamente ativa. Biomass components and structural features in Guinea grass under different frequencies and intensities of defoliationAbstract -The objective of this work was to evaluate the effect of frequencies and intensities of defoliation on the biomass components and on the canopy structure of Guinea grass (Panicum maximum 'Aruana IZ-5') pasture under intermittent sheep stocking. Two defoliation frequencies (DF), with 85 and 95% interception levels of the photosynthetically active radiation (Ipar) incident on the top of the canopy, and two defoliation intensities (DI), with residual leaf area index (LAIr) of 1.0 and 1.8 were evaluated. A completely randomized design was carried out, in a 2x2 factorial arrangement. Biomass components and the structural features in the pre-grazing conditions were affected mainly by DF, with the reduction of green biomass of culms and of dead forage, and were also affected by the increase in the height of the first alive ligule. Pastures managed with lower DF provided lower leaf blade/culm ratio, with 1.65 average, while pastures managed with greater DF showed 2.40 mean leaf blade/culm ratio. Components of the residual biomass were affected by the DI, with a greater residual green forage biomass in pastures managed with LAIr of 1.8. Swards grazed at 95% Ipar and 1.8 LAIr showed residual green biomass of culms and residual dead forage biomass superior to those of the other managements. For grazing by sheep, '...

Herbage accumulation dynamics in digit grass subjected to defoliation frequencies

“…Because the defoliations were performed to the same post-cutting residual height of 10 cm, the plants took longer to reach greater heights, which led to longer cutting intervals. This behavior has also been described in the Marandu (DIFANTE et al, 2011), Mulato (SILVEIRA et al, 2013, Tanzania (EUCLIDES et al, 2014), Mombaça (EUCLIDES et al, 2015), and Aruana (SILVA et al, 2015a) grasses. These results reinforce the impossibility of using fixed and pre-determined rest days for the management of pastures, including digit grass.…”

Root dry matter mass and distribution of Florico grass under different grazing strategies

“…Variations in RDM and PD of the root density of Florico grass, managed using four different pasture strategies, were consistent with the management strategy applied to the shoots because of the close relationship between the aerial and the underground components of pasture growth, where the root is the source of energy and the shoot is a drain on the organic reserves (Rodrigues et al, 2007;Silva et al, 2015). To establish a relationship between the effects occurring in the aerial part of the plant and the root system, variables such as pre-grazing pasture height, accumulation of forage mass, and the LAI were analyzed.…”

“…In this context, it is difficult to design pasture management strategies that increase the intensity and/ or frequency of grazing without reducing the root dry matter mass reserve (Rodrigues et al, 2007;Sarmento et al, 2008;Kaiser et al, 2009). The effective depth of the root system of Florico grass under grazing was found to be 35 cm by Cunha et al (2010), whereas Camargo Filho (2007) showed that 85% of the roots were found at a depth of 40 cm.…”

Structural characteristics and chemical composition of andropogon grass pasture managed under different defoliation intensities and rest periods

“…After counting, the material contained inside estimate the forage biomass production; the samples were cut at the height established for the intensities of 15 and 30 cm (adapted from HERLING et al, 1998), the material was packed in properly identified plastic bags and sent to the laboratory and the plots were uniformed to start a new evaluation cycle. The material was separated into leaf, stem (true stem + sheath) and dead material (SILVA et al, 2015), the fractions were placed in identified paper bags and then weighed and dried in a forced circulation air oven at 55°C to constant weight and then weighed again. Thus, leaf dry biomass (LDB), stem dry biomass (SDB), dead forage biomass (DFB) and total dry forage biomass (TDFB) were estimated.…”

“…The leaf/stem ratio (L/S) was determined by dividing LDB by SDB (PINTO et al, 1994). Samples, which were pre-dried in an oven, were ground in 1-milliliter Willey sieves for analysis of DM content (%natural matter) and, based on DM, crude protein (CP), mineral matter (MM), according to AOAC procedures (2010); neutral detergent fiber (NDF), according to the methodology of Van Soest et al (1991) and acid detergent fiber (ADF) and acid detergent lignin (ADL), according to the methodology of Van Soest et al (1963). The collected data were tabulated and grouped according to the cycles during the rainy season.…”