Bruno Pedreira, Embrapa Agrossilvipastoral, Sinop, Brazil, Carlos G. Pedreira, Dept. Zootecnia, ESALQ - Univ. de Sao Paulo, Piracicaba, SP, Brazil, Marcio Lara, Animal Science, Federal University of Lavras, Lavras, Brazil and Renata Nave, Ohio State University, Columbus, OH
Advanced ranchers in Brazil are increasingly turning to fine-tuning in grazing of tropical forages, which may improve not only pasture productivity and nutritive value, but also persistence. The objective of this research was to describe organic reserve dynamics by studying total non-structural carbohydrate (TNC) and nitrogen reserves in shoots and roots of ‘Xaraes’ palisadegrass (Brachiaria brizanthacv. Xaraes), under intermittent grazing, during two growing seasons. Pastures were submitted to grazing strategies defined either by pre-graze light interception (LI) by the canopy (“target grazing”, at 95% LI or “delayed grazing”, approaching 100% LI for initiation of grazing) or fixed rest periods (28-d). Root and shoot samples were collected at the beginning (spring) and end (late summer) of the growing season and analyzed for N and TNC concentrations. Delayed grazed (DG) reduced plant density on pastures, due to longer rest periods which restricted light incidence at the base of the plants. As a consequence of longer rest periods and stem elongation, DG decreased residual LAI, and consequently reduced LI in summer. DG and 28-d resulted in higher post-graze forage mass, while TG, with shorter rest-periods, resulted in low forage mass and accumulation. Higher proportions of leaf were found in spring (13%) than in summer (8.9%) forage, while stem percentage was lower in spring (37.5%) and increased in summer (41.5%). All grazing strategies reduced stubble N from the first (12.5 g kg-1) to the second year (7.7 g kg-1). Target grazing resulted in higher TNC pool (238 g m-2), followed by delayed grazing (136 g m-2), and 28-d being similar to both (199 g m-2). The results suggest a negative effect of longer regrowth periods of the delayed and 28-d strategies. Target grazing seems to be the most indicated strategy for intensive management of ‘Xaraes’ palisadegrass pastures.