Growth of Megathyrsus maximuscv. Mombaça as affected by grazing strategies and environmental seasonality. I. Tillering dynamics and population stability

In rotationally grazed pastures, the canopy light environment can be modulated through both grazing frequency and severity, and the magnitude of sward responses may differ according to forage species and its ability to use available resources. We hypothesised that the tall, tufted, fast-growing, tussock-forming species Mombaça guineagrass (Megathyrsus maximus (Jacq.) B.K.Simon & S.W.L.Jacobs cv. Mombaça) can modulate its tillering dynamics and change its persistence pathway according to grazing strategy and the availability of growth factors. Treatments corresponded to all combinations of two levels of pre-grazing canopy light interception during regrowth (95% and maximum) and two post-grazing heights (30 and 50 cm), and were allocated to experimental units according to a randomised complete block design with four replications. Measurements were performed throughout contrasting climatic conditions during four seasons from January 2001 to February 2002. A quite stable tiller population density presented regardless of the range of grazing frequency and severity used in the study. However, tiller appearance and death were strongly influenced (P < 0.001) by season of the year, with highest rates recorded during the two summers and lowest during autumn–winter. There was no conclusive evidence that the persistence pathway of Mombaça guineagrass changes within the grazing management strategies studied.