Características estruturais e produção de forragem em pastos de capim-mombaça submetidos a períodos de descanso

Abstract

Resumo -Este trabalho teve como objetivo avaliar as características estruturais, morfológicas e produtivas em pastos de capim-mombaça sob lotação rotacionada com três períodos de descanso, definidos conforme o número de novas folhas expandidas por perfilho: 2,5, 3,5 e 4,5 folhas. O delineamento experimental foi inteiramente casualizado com seis repetições, num total de 18 piquetes. Foram avaliadas as características: biomassa total, taxa de crescimento cultural, altura do dossel, relação folha/colmo, índice de área foliar, interceptação da radiação, taxa de aparecimento e alongamento foliares, taxa de alongamento do colmo, densidade de perfilhos e coeficiente de extinção. As maiores taxas de acúmulo de forragem foram observadas em piquetes submetidos a período de descanso correspondente ao aparecimento de 2,5 folhas por perfilho. A menor biomassa de forragem por ciclo de pastejo deste tratamento foi compensada pelo maior número de ciclos observados. O índice de área foliar foi proporcional ao período de descanso, mas a interceptação da radiação ultrapassou o valor de 95% ao final do período de descanso em todos os tratamentos. O prolongamento do período de descanso resultou em comprometimento da estrutura do pasto, sinalizado por baixos valores da relação folha/colmo. O período de descanso em capim-mombaça não deve ultrapassar o tempo necessário para o aparecimento de três folhas por perfilho.Termos para indexação: acúmulo de forragem, índice de área foliar, interceptação da radiação, morfogênese, relação folha/colmo. Structural characteristics and forage production of Panicum maximum cv. Mombaça pasture according to rest periodsAbstract -The objective of this work was to evaluate structural, morphological and productive traits of Panicum Maximum cv. Mombaça pasture under rotational stocking. Three rest periods defined in terms of 2.5, 3.5 and 4.5 leaves per tiller were studied. Experimental design was completely randomized with six replicates (paddocks) per treatment. Experimental variables assessed were: forage biomass, biomass accumulation rate, plant height, leaf-stem ratio, leaf area index, interception of photosynthetically active radiation (PAR), leaf appearance and elongation rates, stem elongation rate, tiller density population and extinction coeficient. Forage biomass per grazing cycle, leaf area index and plant height varied directly while tiller population, crop growth rate and leafstem ratio varied inversely with length of the rest period. Though leaf area index and forage biomass related directly with the duration of the rest period, interception of PAR exceeded the value of 95% by the end of rest period, regardless of experimental treatment. Rest period prolongation jeopardizes the pasture structure, which could be verified by low values of leaf/stem ratio. Rest period in Panicum maximum cv. Mombaça should not be longer than the time for the appearance of three leaves per tiller.

Forage production of elephant grass under intermittent stocking

“…Increasing light interception from 90 to 95% also increased the accumulation rates. This result is in agreement with several studies, which show higher average growth rate of the pasture when the incident light interception is around 95% (Mello & Pedreira, 2004;Cândido et al, 2005;Carnevalli et al, 2006;Barbosa et al, 2007;Gomide et al, 2007).…”

“…The smaller production of green forage mass by the cultivar BRS Kurumi was offset by its lower rest period (Table 3), which confers a higher number of grazing cycles (Table 4) and resulted in higher forage production of this cultivar during the rainy season. Gomide et al (2007), working with different rest periods, based on the number of green leaves per tiller in Mombaça grass, also observed that the greater number of cycles with shorter rest periods (appearance of 2.5 leaves per tiller) offsets the lower production of pre-grazing forage mass. Furthermore, the authors reported higher forage accumulation rates and a better leaf/stem ratio for this shorter rest period.…”

“…The cultivar BRS Kurumi was an exception, since no difference was observed between the residues of 30 and 50 cm, at 95% LI. This can be explained by changes in canopy structure attributed to stem elongation (Gomide et al, 2007) and leaf angle (Mello & Pedreira, 2004) in response to different combinations of frequency and intensity of grazing, altering light penetration in the canopy and, consequently, light interception.…”

Canopy characteristics, animal behavior and forage intake by goats grazing on Tanzania-grass pasture with different heights

“…The positive association between sward height and LI is well described for temperate grasses, and it has also been verified for tropical grasses, such as mombaça-grass (CARNEVALLI et al, 2006) and Tanzania-grass (BARBOSA et al, 2007). These latter observed that the conditions of 90, 95 and 100% of LI were achieved with canopy heights around 60, 70 and 85 cm, respectively, whereas Gomide et al (2007), when evaluating heights up to 117.2 cm of mombaça-grass pasture, have obtained maximum LI of 96.4%, similar to observed in this study at 90 cm of canopy height, i.e., under experimental conditions, it was achieved higher LI at heights lower than reported by other authors.…”

“…Furthermore, the canopy structure, especially in tropical forage, exerts direct effect on the process of ingestion and consumption of forage, by affecting the forage intake by the animal. In this way, the canopy characteristics, such as height, leaf density, leaf stem -1 ratio and proportion of dead material interfere with the consumption because alter the bite size, bite rate, and grazing time (GONÇALVES et al, 2009;PALHANO et al, 2007;REGO et al, 2006).…”