Canopy Height and N Rate Affect the Composition of Leaf Area Index and Herbage Accumulation of Continuously Stocked Mulato II Brachiariagrass.

In grazed pastures leaf is the main component harvested by the animals and may affect leaf category contribution to LAI. Canopy height and N may affect the LAI composition and HA. The objective of this study was to quantify the effects of three canopy heights (10, 25, and 40 cm) maintained by continuous stocking and two N rates (50 and 250 kg N ha^–1 yr^–1) on the HA and leaf category composition of LAI of Mulato II brachiariagrass hybrid (Convert HD364) during two summer growing seasons in Piracicaba-SP, Brazil. Herbage samples were separated into expanding (EL), youngest fully expanded (YL), and mature leaves (ML) and used to calculate the contribution of leaf categories on LAI. There was a linear increase in HA and LAI with increased canopy height (HA from 8560 to 13600 kg DM ha^–1 yr^–1; LAI from 2.3 to 5.5). The relative contribution of EL and YL to the LAI increased with the reduction in canopy height. Greater N rate increased HA by 137% (6620 vs. 15660 kg DM ha^–1 yr^–1), and LAI by 28% (3.4 vs. 4.7). The contribution of leaf categories was not affected by N rate (P > 0.05). Although canopies kept at 10 cm showed greater proportion of younger leaves (EL and YL) in the LAI - which are those with greater photosynthetic rates - the HA was greater in taller canopies.Taller canopies associated with more N favors greater HA of continuously stocked Mulato II pastures.