Defoliation Strategies in Pastures Submitted to Intermittent Stocking Method: Underlying Mechanisms Buffering Forage Accumulation over a Range of Grazing Heights

Abstract

For continuously stocked pastures, net forage accumulation is thought to be relatively unaffected across a rather large range of canopy‐based management targets. It is not known whether this is also characteristic of intermittently stocked canopies, and if so, the underlying mechanisms have not been well delineated. We hypothesized that initiation of grazing when canopy heights are shorter than heights corresponding to the critical leaf area index, associated with a moderate intensity of defoliation, do not reduce forage accumulation in pastures under intermittent stocking. Therefore, kikuyugrass (Pennisetum clandestinum Hochst. Ex Chiov) pastures were grazed at four pregrazing heights (10, 15, 20, and 25 cm) with the same proportion of defoliation (50% reduction in pregrazing height; i.e., postgrazing heights of 5, 7.5, 10, and 12.5 cm, respectively) from December 2011 to May 2013. As the canopy height increased, there was an inverse relationship between tiller weight and number; however, heavier tillers presented greater rates of leaf elongation. Pastures grazed at 15 to 25 cm had the same forage accumulation. The same homeostatic mechanisms that keep a constant forage accumulation in different heights when pastures are subjected to continuous stocking also allowed for a similar forage accumulation in pastures under intermittent stocking at different grazing heights.