Regrowth of brachiariagrasses as related to stubble characteristics under N fertilization and irrigation

Seasonal and annual changes in stubble characteristics can affect the regrowth of warm-season perennial grasses. Understanding these changes and their effects on forage accumulation rate (FAR) can improve defoliation management. Our objective was to describe and relate variations in stubble characteristics with FAR during regrowth of four palisadegrasses [Brachiaria brizantha (Hochst. Ex A. Rich.) Stapf. syn. Urochloa brizantha (Hochst. ex A. Rich.) R.D. Webster], genotypes Marandu, Xaraes, Arapoty, and Capipora, and one signalgrass [Brachiaria decumbens (Stapf.) syn. Urochloa decumbens (Stapf.) R.D. Webster] cultivar Basilisk, in southeastern Brazil. Plots were harvested at 15-cm stubble height every 28 d during the warm season and 42 d during the cool season of years 2005-2006 and 2007-2008. Stubble mass was similar to 1,070 kg DM ha(-1) greater in the cool than warm season, whereas FAR was less in the cool season. Arapoty and Basilisk showed generally less FAR (similar to 45 kg d(-1)) and stubble leaf, stem, dead material, and total mass during the warm season than more productive grasses Capipora and Xaraes (similar to 63 kg d(-1)). Leaf and canopy photosynthesis varied over seasons and years, but they were similar among grasses despite differences in stubble characteristics and FAR. Marandu accumulated more leaf in the stubble than other grasses, resulting in greater residual leaf area index, but it did not increase FAR. Under less favorable growth conditions, grasses increased stubble herbage mass (SHM). More productive grasses generally present greater SHM and leaf mass, indicating that stubble characteristics play an important role in the regrowth of brachiariagrasses.