Components of herbage accumulation in elephant grass cvar Napier subjected to strategies of intermittent stocking management

Abstract

SUMMARYHerbage accumulation is determined by the tissue turnover of individual plants and by the regulation patterns of the number of individuals in a plant population, which function in conjunction to enable swards to adapt to variations in growth and management conditions. Based on the hypothesis that intermittent grazing strategies change the proportion of basal and aerial tillers and, consequently, sward herbage accumulation, the objective of the current experiment was to evaluate the components of herbage accumulation in elephant grass cvar Napier (Pennisetum purpureum Schum. cvar Napier) from January 2011 to April 2012. The treatments corresponded to combinations of two post-grazing (post-grazing heights of 35 and 45 cm) and two pre-grazing conditions (0·95 and maximum canopy light interception during regrowth – LI0·95 and LIMax) and were allocated to experimental units (850 m2 paddocks) according to a 2×2 factorial arrangement in a complete randomized block design with four replications. The following response variables were evaluated: the population density of basal tillers (TPDb) and the population density of aerial tillers (TPDa), the number of aerial tillers per supporting unit (A/B+VC), growth rates of the leaf (LGR) and stem (SGR), leaf senescence rate, net leaf accumulation rate (LAR), and the contributions of basal and aerial tillers to sward growth and senescence. The swards managed with the LI0·95 target had greater TPDb than those managed with the LIMax target, but no difference was recorded between the LI pre-grazing targets for TPDa. The larger A/B+VC ratio recorded for the swards managed with the LIMax target resulted in a higher contribution of aerial tillers to the growth and senescence of swards. This growth strategy resulted in a higher SGR and lower LGR and LAR for the swards managed with the LIMax target relative to those managed with the LI0·95 target. The post-grazing height targets affected only LGR during winter and the second summer and SGR on average for the experiment, with higher values recorded for the swards managed at 35 cm. The LI pre-grazing targets played a central role in defining the compensatory mechanisms responsible for the competitive ability of the plants, which were primarily expressed in the variation of the proportion of basal and aerial tillers in the tiller population and interfered with the components of herbage accumulation and total herbage yield of the swards.