Herbage production and grazing losses in Panicum maximum cv. Mombaca under four grazing managements

Grazing management is a key element determining herbage production and grazing efficiency. This study measured herbage accumulation and grazing efficiency in Mombaca grass pastures (Panicum maximum cv. Mombaca) subjected to intermittent defoliation managements. Treatments were combinations of 2 rest periods (grazing at either 95 or 100% canopy light interception LI) and 2 grazing intensities (30 and 50 cm post-grazing height), and were allocated to 2000 m(2) plots according to a complete randomised block design, in a 2 x 2 factorial arrangement, with 4 replications. Response variables measured from January 2001 to February 2002 were: sward height, herbage mass and morphological composition pre- and post-grazing, and losses due to grazing. Effective values for the 95 and 100% LI targets were 95.5 and 98.5%, respectively, and corresponded with 90 and 115 cm sward height, throughout the experiment, indicating that this could be a satisfactory parameter for monitoring grazing on farms. The apparently small difference in pre-grazing targets was large enough to cause changes in dry matter accumulation and composition of the herbage mass. The 95/30 treatment resulted in lowest pre-grazing herbage mass, shortest rest period (22-24 days in spring-summer and 95 days in autumn-winter) but highest total herbage accumulation (26 890 +/- s.e.m. 2506 kg/ha DM). It also resulted in high proportion of live leaf (71%) and low proportion of live stem (15%) pre-grazing. Averaged over the 30 and 50 ern treatments, there was no difference in total herbage accumulation (22 780 +/- 1772 kg/ha DM) and total herbage disappearance (20 160 +/- 1170 kg/ha DM) for the LI treatments. However, grazing losses were higher for the 100% (5860 +/- 550 kg/ha DM) than 95% LI treatments (4060 +/- 550 kg/ha DM). Consequently, the amount of herbage effectively harvested and grazing efficiency were higher for the 95% than 100% LI treatments. The 95/30 treatment resulted in highest total herbage accumulation (26 890 +/- 2506 kg/ha DM) and grazing efficiency (87%).