Morphogenesis of Basal and Aerial Tillers of Elephantgrass Subjected to Strategies of Rotational Stocking Managements.

Growth and senescence are influenced by combinations between defoliation frequency and severity, which could have different impacts on basal and aerial tillers. The objective of this experiment was to evaluate the effect of contrasting defoliation strategies on leaf elongation (LER) and senescence rates (SER) of basal and aerial tillers of elephantgrass (Pennisetum purpureum cv. Napier) under rotational stocking from January to April 2011, in Piracicaba, SP, Brazil (22º43’ S, 47º25’ W and 580m). Treatments corresponded to a 2x2 factorial arrangement between two pre-grazing (95% and maximum canopy light interception - LI_95% and LI_max) and two post-grazing conditions (stubble height of 35 and 45 cm), and were assigned to experimental units (850m² paddocks) according to a complete randomized block design, with four replications. Measurements were carried out every grazing cycle throughout the entire regrowth period, which was divided up into thirds (initial (1), intermediate (2) and final (3)). On each paddock, 30 tillers were tagged (six tussocks and five tillers per tussock) and monitored every five days. The LER for basal tillers linearly increased along the regrowth period and was larger than aerial tillers, which remained constant throughout all regrowth phases. Swards managed under LI_95% showed greater values of leaf elongation in phase 1 compared to LI_Max. Basal tillers had greater SER than aerial tillers (2.23 and 1.83 cm/tiller.day^-1, P<0.05). Swards under LI_95% had similar SER during phases 1 and 2, whereas greater values were observed in phase 3. Swards under LI_Max had a linear increase in SER along the regrowth period. Differences between frequencies were observed only in phase 2. Basal tillers showed larger growth potential than aerial tillers, with defoliation frequency being a key feature in determining morphogenetic responses. The LI_95% is an adequate management target for maintaining leafness and productivity of elephantgrass under rotation stocking management.